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Intestinal permeability enhancement of levothyroxine sodium by straight chain fatty acids studied in MDCK epithelial cell line
Abstract
Levothyroxine sodium (T4), administered orally, is used for the treatment of hypothyroidism. T4 is a narrow therapeutic index drug with highly variable bioavailability (40-80%). The purpose of the present study was to increase the transepithelial transport of T4 using straight chain fatty acids across Madin-Darby Canine kidney (MDCK) cell line. Capric acid (C10), lauric acid (C12) and oleic acid (C18) were studied in molar ratios of 1:0.5, 1:1, 1:2 and 1:3 (T4:fatty acid). Transport of the hydrophilic marker, Lucifer yellow, was also studied. All three fatty acids proved to significantly increase T4 transport and the order of enhancement was to the effect of C12 approximately C18>C10. This Increase in transport was accompanied by reductions in transepithelial electrical resistance (TEER) values, which indicates an opening of tight junctions. Cytotoxic effects of the fatty acids were evaluated by TEER measurements, lactate dehydrogenase release, percent viability and propidium iodide staining of the cells. At the lower molar concentrations of 1:1, the fatty acids did not show any toxicity. However, C12 and C18 when added, to T4:fatty acid molar ratio of 1:2 and 1:3, respectively showed severe toxicity with irreversible damage to the cells. Hence, addition of fatty acids to T4 formulations at low concentrations can significantly improve intestinal permeability of T4 without any toxicity potentially leading to improved bioavailability.
... Other studies have found that long-chain PUFAs have a concentration-dependent effect on immune response [34]. Low concentration intake of long-chain n-3 fatty acids, such as fish oils, has been shown to enhance immune function, while high concentrations can reduce various immune functions, such as antigen-presentation, adhesion molecule expression, and Th1 and Th2 response [34]. ...
... Other studies have found that long-chain PUFAs have a concentration-dependent effect on immune response [34]. Low concentration intake of long-chain n-3 fatty acids, such as fish oils, has been shown to enhance immune function, while high concentrations can reduce various immune functions, such as antigen-presentation, adhesion molecule expression, and Th1 and Th2 response [34]. High concentrations of PUFA intake have even been shown to induce lymphocyte apoptosis [34]. ...
... Low concentration intake of long-chain n-3 fatty acids, such as fish oils, has been shown to enhance immune function, while high concentrations can reduce various immune functions, such as antigen-presentation, adhesion molecule expression, and Th1 and Th2 response [34]. High concentrations of PUFA intake have even been shown to induce lymphocyte apoptosis [34]. From this study, it is evident that further randomized control studies on dosing must be conducted in order to fully understand the therapeutic usage of LCFAs for the various ailments that they can mitigate. ...
The intestinal mucosal barrier plays a critical role in maintaining the integrity of the gastrointestinal (GI) tract and protecting the body from harmful toxins and pathogens. Nutrition additionally serves as a vital component in maintaining bodily homeostasis. Macronutrients, micronutrients, and specific dietary habits exert profound effects on the immune system. The complex interactions of the immune system reflect a multifaceted, integrated epithelial and immune cell-mediated regulatory system. While several factors can influence the intestinal mucosal barrier and its pro- and anti-inflammatory processes, such as myeloid cell, regulatory T cell (Treg), or intraepithelial lymphocyte populations, there is growing evidence that macronutrients play an essential role in regulating its function. Herein this is a review of the peer-reviewed literature pertaining to dietary effects on mucosal integrity, including intraepithelial lymphocyte populations and immune function. This review is intended to explore the underlying mechanisms by which macronutrients impact and modulate the mucosal immune system.
... It is a permeation enhancer that alters the lipid structural dynamics of the biological membranes. 18 OA is commonly used to promote the CPP of the amphiphilic lipids that induce the phase transition from the cubic to the hexagonal phase. 17,19,20 Finally, pluronics are biocompatible amphiphilic block copolymers that are available in different grades such as F127 and F108. ...
... As a fusogenic lipid, OA could induce permeability changes. 18 In Vitro Cytotoxicity Study. The results of the in vitro cytotoxicity study of FH solution, blank HEX, and OFH-HEX against HepG2 cell lines revealed a concentration-dependent cytotoxic effect (Figure 7). ...
The aim of this study was to investigate the feasibility of hexosomes (HEXs) as competent platforms for fluoxetine hydrochloride (FH) repurposing against HepG2 hepatocellular carcinoma. Different FH-loaded HEX formulations were prepared and optimized by the hot emulsification method. The HEX features such as particle size, ζ potential, and drug entrapment efficiency (EE%) can be tailored by tuning HEX components and fabrication conditions. The composition of the optimized FH hexosome (OFH-HEX) was composed of 3.1, 1.4, 0.5, 0.2, and 94.8% for glyceryl monooleate, oleic acid, pluronic F127, FH, and deionized water, respectively. The anionic OFH-HEX with a particle size of 145.5 ± 2.5 nm and drug EE% of 45.4 ± 1.2% was able to prolong the in vitro FH release, where only 19.5 ± 2.3% released in phosphate-buffered saline (PBS) pH 7.4 after 24 h. Contrarily, HEX rapidly released FH in acetate buffer pH 5.5 and achieved a 90.5 ± 4.7% release after 24 h. The obtained HEX showed an improved cellular internalization in a time-dependent manner and enhanced the cytotoxicity (2-fold higher than FH solution). The current study suggests the potential of FH-HEX as a possible anticancer agent against hepatocellular carcinoma.
... The studies on LCM in SEN have been focused on their chain length as compared to the medium chain monoglyceride (MCM) [2,6], while the commercially available LCMs also vary in the number of double bonds [7], which may also influence their functions in forming SEN with other excipients and activities on membrane permeability. Even though there are some publications discussing on the impact of long chain lipids with various degree of unsaturation on permeability enhancement including lymphatic transportation and tight junction opening, the studies are limited to long chain fatty acid (LCFA) [8,[10][11][12]. LCM, which has the larger hydrophilic head group and higher emulsifying capacity than LCFA [5], may not result in the similar effect to the reported LCFA. ...
... Lucifer yellow (LY, MW 457) is a commonly used paracellular transport marker to indicate the tight junction integrity [12,13]. The cumulative transport of LY across the monolayer obtained by DPBS was 0.11-0.95% ...
Unsaturated long chain monoglycerides (LCMs) used to formulate self-emulsified nanoemulsion (SEN) are varied in their degree of unsaturation which may influence their activities on membrane permeability. Therefore, this study highlights the impact of double bond in LCMs on the tight junctions of Madin-Darby Canine Kidney (MDCK) cell monolayer. Two LCMs, Glyceryl monooleate (one double bond) and Glyceryl monolinoleate (two double bonds) were formulated into SENs (SEN2 and SEN3, respectively) with Glyceryl tricaprylate and PEG-40 hydrogenated castor oil (1:1:2), and compared to the SEN (SEN1) consisted of only Glyceryl tricaprylate and PEG-40 hydrogenated castor oil (1:4). Lucifer Yellow (LY, MW 457) or Fluorescein isothiocyanate–Dextran4K (FD4, MW 3000-5000) was added to the aqueous phase of the SENs and tested for their transport across the cell monolayer. The cumulative transport of LY and FD4 achieved by SEN2 and SEN3 were significantly (p < 0.05) higher than those in phosphate buffer, 0.5% PEG-40 hydrogenated castor oil, and SEN1, indicating that the tight junctions were opened by the SENs containing LCMs. The cumulative transport of FD4 achieved by SEN3 was also 2-3 folds higher than SEN2 (p < 0.05). Therefore, LCM with two double bonds have greater potency of opening tight junction than LCM with a single double bond in SEN formulation.
... Capric acid (C10), lauric acid (C12) and oleic acid (C18) significantly increase levothyroxine sodium transport and the order of enhancement was C12%C18 > C10. This increase in transport and the reductions in transepithelial electrical resistance (TEER) values indicate opening of tight junctions to improve the paracellular permeability [13]. Sodium caprate induced increased permeability to polysucrose and opening of the tight junctions was visualized by transmission electron microscopy [11]. ...
... Lauric acid, myristic acid and linoleic acid, show the highest impact on absorption of caffeic acid in transport studies using Caco-2 cell monolayers. Capric acid, lauric acid and oleic acid are known to increase the permeability of polar drugs in other cell monolayers [13]. Lauric acid, myristic acid and capric acid are among the major fatty acids present in coconut oil. ...
Polyphenolic antioxidants are mainly absorbed through passive paracellular permeation regulated by tight junctions. Some fatty acids are known to modulate tight junctions. Fatty acids resulting from the digestion of edible oils may improve the absorption of polyphenolic antioxidants. Therefore, we explored the effect of three edible oils on the intestinal absorption of caffeic acid. Rats were fed with soybean oil and caffeic acid dissolved in distilled water. Caffeic acid contents in the plasma collected up to 1 hr were quantified. The experiment was repeated with coconut oil and olive oil. Component fatty acids of the oils were individually tested in vitro for their effect on permeability of caffeic acid using Caco-2 cell monolayers. Highest absorption of caffeic acid was observed in animals fed with coconut oil. In vitro transport percentages of caffeic acid in 2.5 mmol/L solutions of fatty acids were 22.01±0.12 (lauric), 15.30 ± 0.25 (myristic acid), 13.59 ± 0.35 (linoleic acid), 3.70 ± 0.09 (oleic acid) and 0.10–2.0 (all other fatty acids). Lauric acid and myristic acid are the two major fatty acids present in coconut oil. Therefore, these fatty acids may contribute to the higher absorption of caffeic acid in the presence of coconut oil.
... 9 It is a fusogenic lipid capable of inducing permeability changes by altering the lipid structural dynamics of biological membranes. 10 Being lipophilic in nature it could be solubilized easily in molten GMO and incorporated in its mesophase structure. The addition of OA in various concentrations causes phase transitions among inverse bicontinuous cubic phase, inverse hexagonal phase, and inverted micellar cubic phase. ...
... 46 Moreover, OA is reported to increase the paracellular absorption by penetrating the epithelial cell membrane and disrupting its barrier function. 47 Similar findings were observed by Pabla et al., 10 where modulation of cellular tight junctions by OA was proved by reductions in the transepithelial electrical resistance values. ...
This study aimed to explore the potential of tailoring the liquid crystalline structure for augmenting the oral absorption and biopharmaceutical performance of Rosuvastatin. Rosuvastatin-loaded liquid crystalline nanodispersions (LCNDs) were prepared via emulsification technique. The effect of incorporating oleic acid (OA) in various proportions in the lipid domain of the LCNDs was studied. The formulations were characterized for particle size, zeta potential, in-vitro release, ex-vivo intestinal permeation, in-vivo oral bioavailability and stability. All the prepared LCNDs possessed uniform nanometric size and negative zeta potential. Employing OA in the lipid domain enhanced rosuvastatin entrapment efficiency, and resulted in structural transition from cubic to hexagonal phase as proved by TEM. Increasing OA proportion up to a certain ratio prolonged the in vitro drug release rate, after which further increase in OA had no significant effect. The OA bearing hexagonal LCNDs provided a significant enhancement in the intestinal permeation compared to GMO cubical nanodispersion and demonstrated an outstanding in vivo performance by maintaining higher ROS plasma levels up to 8 hours and enhancing oral bioavailability compared to commercial tablet. They proved to be promising carriers for improved oral delivery of ROS with substantial bioavailability enhancing effects, and superiority compared to cubosomes and OA emulsion.
... In addition to the P app , in nanoparticulate oral drug delivery systems, the evaluation of the cell monolayer integrity before and after transport via the measurement of TEER using a voltohmmeter, as well as assessing the permeability of radiolabelled mannitol (by liquid scintillation counting) as an internal standard for paracellular integrity is a common procedure [68,96,97]. TEER values between 200 and 300 cm 2 measured before the study, is an indicative of formation of a cell monolayer with TJs [98]. Other parameters which can be helpful to include [99] are the %-transport efficiency (is the ratio between the concentration of the drug transported to the basolateral side and the initial concentration of the drug added to the apical side) and the %-absorption efficiency (is the ration between the concentration of the drug retained in the Caco-2 monolayer and the initial concentration of the drug added to the apical side). ...
... Another cell-based model frequently used for the permeability studies is MDCK (Madin-Darby canine kidney). In an appropriate culture medium, similar to Caco-2 cells, MDCK differentiate into columnar epithelial cells containing TJs [49,98]. About 23 years ago, this model was used to assess the membrane permeability of therapeutics. ...
... Circulating T 4 is also eliminated in the feces (15). Bioavailability of commercial thyroid hormone replacement drugs is dependent on drug formulation, recent ingestion of food, diet, and considerable individual patient variability (16,17). High fecal concentrations of T 4 might be explained if the housemate was routinely fed prior to medicating, had a diet low in fatty acids, or had abnormally poor intestinal absorption (16,17). ...
... Bioavailability of commercial thyroid hormone replacement drugs is dependent on drug formulation, recent ingestion of food, diet, and considerable individual patient variability (16,17). High fecal concentrations of T 4 might be explained if the housemate was routinely fed prior to medicating, had a diet low in fatty acids, or had abnormally poor intestinal absorption (16,17). It has been suggested that dogs are relatively resistant to thyrotoxicosis with doses upwards of 10 to 20 times the therapeutic dose required to induce clinical signs (18). ...
A 9-year-old golden retriever dog was evaluated for polyuria, polydipsia, weight loss, and elevated serum thyroxine. Targeted questioning revealed that the dog was coprophagic and routinely ingested the feces of a dog that was treated with twice-daily levothyroxine. Clinical signs resolved and serum thyroxine decreased to normal levels in the affected dog with prevention of coprophagy.
... A major advantage of these excipients is their incorporation into conventional oral dosage forms without the need for complex or expensive formulation techniques. (Dimple et al. 2010) IV. CONCLUSION Significant research work has been committed to the development of oral, rectal or nasal formulations of poorly absorbed drugs with absorption modifying agents. ...
Human skin acts as a barrier, thermo regulator and prevents excess water loss from internal organs. Various ways of transferring drugs have been developed by altering the barrier properties of the skin. Improvement of skin penetration, partitioning and solubility effects through hydration of the stratum corneum or the use of chemical enhancers acting on lipids and keratinized structures in the stratum corneum is a promising tool in potential clinical applications. Penetration enhancement is a new emerging technology that has the potential to increase the amount of trans-dermally administered drugs. Also drugs with short biological half-lives can be easily administered. Among the many advantages over other routes, three important ones are avoidance of hepatic metabolism, minimal adverse effects, and increased bioavailability. The stratum corneum prevents the loss of physiologically essential substances and consequently provides penetration resistance by acting as a protective barrier. This is the rate-limiting step for absorption of the drug percutaneously. In this review article, we summarize the various advances made in the field of access enhancers based on a literature survey of various research articles.
... Mokale and coworkers showed that ethyl cellulose nanoparticles loaded with Met HCl could be prepared by spray freeze drying as a way of preparing sustained release formulation [5]. Long-chain fatty acids, such as capric acid (C10:0), lauric acid (C12:0), and oleic acid (C18:1 (cis ∆9)), increase the transpeithelial transport possibly opening tight junctions [6]. In addition, fatty acid stearate could be used to prepare a controlled-release tablet of Met HCl [7]. ...
A gastroretentive in situ oral gel containing metformin hydrochloride (Met HCl) was prepared based on sodium alginate (Sod ALG), calcium carbonate, and hydroxyethylcellulose (HEC). The optimal composition of the formulation was explored based on the design of experiments (DoE). First, a 32 full factorial design was used for formulation E1 to determine proper composition of Sod ALG and calcium carbonate. Second, a circumscribed central composite design was employed to add HEC as a thickening agent (formulation E2). The dissolution rates at 15, 30, 60, 120, and 240 min were used as responses. Partial least squares regression analysis indicated the effect of each component in delaying the release of Met HCl in the oral gel formulation. The optimized formulation E2-08 consisting of 1.88% Sod ALG, 0.63% HEC, and 1.00% calcium carbonate and two more formulations, E2-10 and E2-12 conformed to USP monograph for extended release. Other physicochemical properties, including floating lag time and duration, viscosity, and pH, measured for each batch and FT-IR spectrometry analysis showed no unexpected interaction between Met HCl and excipients. The current study suggests the potential use of a gastroretentive in situ oral gel for Met HCl helping patient compliance. This study highlights that a systematic approach based on DoE allows the formulation optimization.
... 157 It has also been categorized as a BCS class 3 drug i.e. the API has permeability limited oral absorption. 136,[158][159][160] However, other reports indicate that the API has dissolution limited oral absorption. 156 Won et al. elucidated the pH solubility profile of levothyroxine and determined the solubility of the unionized form of the API (i.e. ...
Even though levothyroxine sodium pentahydrate tablets have been in the market since 1955, there continue to be recalls due to sub potency. We have comprehensively reviewed the factors affecting its stability in solid oral dosage forms. A compilation of marketed formulation compositions enabled the identification of the potential ‘problem excipients’. Two excipient properties, hygroscopicity and microenvironmental acidity, appeared to be responsible for inducing drug instability. In drug products, depending on the formulation composition and storage conditions, the pentahydrate can dehydrate to highly reactive levothyroxine sodium monohydrate, or undergo salt disproportionation to the free acid form of the drug. The USP assay method (HPLC based) is insensitive to these different physical forms of the drug. The influence of physical form of levothyroxine on its chemical stability is incompletely understood. The USP has five product-specific dissolution tests reflecting the complexity in its evaluation.
... 58 Both surfactants, G44 and BL4, contain lauric acid moieties that enhance intestinal permeability. 59 Meanwhile, the T max of SSuM was slightly delayed, indicating that continuous intestinal absorption of RVP occurred via supersaturated micelle formation. Therefore, we suggest that SSuM would be a promising candidate for the clinical development of the BCS II drug such as RVP. ...
Purpose
To enhance the oral bioavailability of revaprazan (RVP), a novel solid, supersaturable micelle (SSuM) was developed.
Methods
Surfactants and solid carriers were screened based on a solubility and a flowability test, respectively. Supersaturating agents, including Poloxamer 407 (P407), were screened. The SSuM was optimized using a Box-Behnken design with three independent variables, including Gelucire 44/14:Brij L4 (G44/BL4; X1) and the amounts of Florite PS-10 (FLO; X2) and Vivapur 105 (VP105; X3), and three response variables, ie, dissolution efficiency at 30 min (Y1), dissolution enhancing capacity (Y2), and Carr’s index (Y3). The solid state property was evaluated, and a dissolution test was conducted. RVP, Revanex®, solid micelle (P407-free from the composition of SSuM), and SSuM were orally administrated to rats (RVP 20 mg equivalent/kg) for in vivo pharmacokinetic study.
Results
G44 and BL4 showed great solubility, with a critical micelle concentration range of 119.2–333.0 μg/mL. P407 had an excellent supersaturating effect. FLO and VP105 were selected as solid carriers, with a critical solidifying ratio (g/mL) of 0.30 and 0.91, respectively. With optimized values of X1 (–0.41), X2 (0.31), and X3 (–0.78), RVP (200 mg)-containing SSuM consisting of G44 (253.8 mg), BL4 (106.2 mg), FLO (99.3 mg), VP105 (199.8 mg), and P407 (40 mg) was developed, resulting in Y1 (40.3%), Y2 (0.008), and Y3 (12.3%). RVP existed in an amorphous state in the optimized SSuM, and the SSuM formed a nanosized dispersion in the aqueous phase, with approximately 71.7% dissolution at 2 h. The optimized SSuM improved the relative bioavailability of RVP in rats by approximately 478%, 276%, and 161% compared to raw RVP, Revanex®, and solid micelle, respectively.
Conclusion
The optimized SSuM has great potential for the development of solidified formulations of poorly water-soluble drugs with improved oral absorption.
... Compared to expensive animal models with limited screening capabilities, the simple, reliable and highly reproducible intestinal cell models are widely used in studies on the interaction between food factors and intestines (Langerholc, Maragkoudakis, Wollgast, Gradisnik, & Cencic, 2011). At present, many cell lines such as Caco-2 (Sharma, Tripathi, Sharma, & Dixit, 2020), HT-29 (Meng, Zhang, & Lu, 2017), Intestinal epithelial cell (IEC)-6 (Xie et al., 2019) and Mardin-Darby canine kidney (MDCK) (Pabla, Akhlaghi, & Zia, 2010) were used to simulate intestine in vitro, among which the Caco-2 cell model is by far one of the most extensive studied and applied intestinal cell model. ...
Background
Food-intestine interaction study has always been a hot topic in food science and nutrition due to diverse physiological functions of intestine. Compared to expensive animal models with limited screening capabilities, the simple, reliable and highly reproducible intestinal cell models are widely used in food-intestine interaction study. There are many functional cell models used to simulate the intestine in vitro, among which the Caco-2 cell model is one of the most widely used and classical models. Recently years, the differentiated Caco-2 cell model has been greatly developed due to the development of various technologies, which not only overcomes the limitations of the traditional model, but also further broadens its application.
Scope and approach
This review aims to overview the current applications of the differentiated Caco-2 cell model as a specialized model of intestinal cells in vitro, as well as new approaches solving the existing challenges of utilization, which can guide its future trends in interaction between food factors and the intestine.
Key findings and conclusions: With high flexibility, high repeatability and low cost, the differentiated Caco-2 cell model has been applied to a variety of intestinal studies including intestinal absorption, intestinal transport, intestinal metabolism, intestinal barrier, intestinal immunity and intestinal adhesion. Furthermore, future study should break limitations of traditional models with the help of automation, biochemistry, molecular biology and cells co-culture, so as to make it more closer to the internal environment without sacrificing its simplicity and reliability, and more suitable for cost-effective large-scale analysis of food-intestine interaction.
... 25−30 In the case of unsaturated long-chain FFA, in vitro cell experiments showed increased membrane fluidity 31−33 and opened tight junctions. 26,34 These biopharmaceutical effects can further enhance drug absorption from surfactant formulations. ...
The scientific rational for selection of surfactant type during oral formulation development requires an in-depth understanding of the interplay between surfactant characteristics and biopharmaceutical factors. Currently, however, there is a lack of comprehensive knowledge of how surfactant properties, such as hydrophilic-lipophilic balance (HLB), digestibility and fatty acid (FA) chain length, translate into in vivo performance. In the present study, the relationship between surfactant properties, in vitro characteristics and in vivo bioavailability was systematically evaluated. An in vitro lipolysis model was used to study the digestibility of a variety of non-ionic surfactants. Eight surfactants and one surfactant mixture were selected for further analysis using the model poorly water-soluble drug nilotinib. In vitro lipolysis of all nilotinib formulations was performed followed by an in vivo pharmacokinetic evaluation in rats. The in vitro lipolysis studies showed that medium chain FA based surfactants were more readily digested compared to long chain surfactants. The in vivo study demonstrated that a Tween 20 formulation significantly enhanced the absolute bioavailability of nilotinib up to 5.2-fold relative to an aqueous suspension. In general, surfactants that were highly digestible in vitro tended to display higher bioavailability of nilotinib in vivo. The bioavailability may additionally be related to the FA chain length of digestible surfactants with an improved exposure in the case of medium chain FA based surfactants. There was no apparent relationship between the HLB value of surfactants and the in vivo bioavailability of nilotinib. The impact of this study’s findings suggests that when designing surfactant-based formulations to enhance oral bioavailability of the poorly water-soluble drug nilotinib, highly digestible, medium chain-based surfactants are preferred. Additionally, for low permeability drugs such as nilotinib, which is subject to efflux by intestinal P-glycoprotein, the biopharmaceutical effects of surfactants merit further consideration.
... However, Pabla et al. reported that the permeation enhancing effect of fatty acids increased with the increase in their chain length [5], which was opposite to the Tween®s. The difference between fatty acids and FAEs is that the latters have larger hydrophilic head groups making them able to self-assemble to form micelles at the concentration higher than their critical micelle concentration (CMC) [6]. ...
Although the cytotoxic and permeation enhancing activities of some fatty acid esters (FAEs) have been studied individually, there lacks systemic studies on how their molecular structures can affect these activities and how the activities would change when FAEs form micelles or nanoemulsion droplets. Therefore, this study aims to address these issues by investigating the cytotoxic and permeation enhancing effects of twenty-six FAEs in lipid droplets on MDCK cell monolayer. The effect of FAEs on the cytotoxicity and the transport of nanoemulsion droplets depends on how easy the FAE monomers can diffuse out of the droplets and perturbate into the cellular membrane, which determined by the critical structures of FAEs including hydrophilic head size, chain length, number of chains, and number of double bond(s) in the chain. The less the intermolecular attraction, the easier the monomer to diffuse out of the lipid droplets and the more interaction with the cell monolayer. Fatty acid monoester (FAME) with less intermolecular attraction than di- and tri-esters had more cytotoxic and higher permeation enhancing effects. Among the FAMEs, the cytotoxicity and permeation enhancing effects were in the order: medium-chain with small hydrophilic head (propylene glycol and glycol) > long-chain with two double bonds > medium-chain with large head (sorbitan, polyethylene glycol, sucrose, and PEGylated sorbitan) ≈ long-chain with single double bond > saturated long-chain, which are consistent with the intermolecular attraction force (low-high). However, the more kinks in the monomer’s tail caused by the double bond, the less the monomer can perturbate into the cell membrane, resulting in less cytotoxicity and permeation enhancement. In conclusion, the FAEs with less intermolecular attraction and straight chain have more cytotoxic and permeation enhancing effects when formulated in nanoemulsion.
... Eagle's minimum essential medium (EMEM) was purchased from ATCC® (Manassas, VA). 24 The completed culture medium (cMedium) was prepared from DMEM mixed with 10% FBS and 1% penicillin-streptomycin solution. ...
Literature review shows that various media have been used for in vitro transport study, but their impact on the monolayer integrity and permeability has been somehow neglected, and there is no systemic study on this subject. This study aims to investigate the impact of six commonly used media on MDCK cell viability and adherence, and the permeation of mannitol and propranolol. DMEM, cMedium (DMEM with serum), HBSS, HBSS- (without Ca2+/Mg2+), DPBS, and DPBS- (without Ca2+/Mg2+) exhibited no cytotoxicity. Cell detachment was observed in four media in the order of DPBS- ≈ HBSS- > DPBS > HBSS. HBSS-/DPBS- caused 70% TEER reduction and 4-fold higher apparent permeability (Papp) of mannitol than the other media. The addition of D-glucose in DPBS- decreased the Papp of mannitol. Cations and glucose negligibly influenced the Papp of Propranolol. The addition of HEPES in HBSS increased the Papp of both mannitol and propranolol for 2-3 folds without TEER reduction. In conclusion, the media compositions (Ca2+/Mg2+, glucose, vitamins, amino acids, and HEPES) can affect the monolayer integrity and permeability. DMEM and cMedium without HEPES are hence suggested as the media in transport study to avoid the potential impact on the monolayer integrity and permeability by the media.
... Lauric acid (C12) has been reported to cause significant increase in the absorption of various hydrophilic drugs compared to C8, C10 and C14 [19,20]. Pronounced effect on transepithelial transport of drugs have also been reported for lauric acid [21]. However, lauric acid is negatively charged. ...
The clopidogrel was successfully encapsulated in cationically modified lauric acid solid lipid nanoparticles for its targeted antithrombotic drug delivery. Cationic SLNs with mean particle size of 244nm and zeta potential of approximately +12.1 mV were produced by hot homogenization followed by ultrasonication on the addition of stearylamine. Characterizations of the prepared nanoparticles were done by DSC, X-ray diffraction and atomic force microscopy (AFM) to confirm the solid nature and also the homogeneous distribution of drug within the lipid matrix. In vitro release studies at pH 7.4 phosphate buffer and pH 1.2, 0.1N HCl showed a slow release in both the media. These nanoparticles were non cytotoxic and demonstrated the ability to open the tight junction on evaluation in caco-2 cell monolayer. This facilitated increased intestinal absorption of clopidogrel. The optimized SLN formulation has shown good blood compatibility and improved muco-adhessiveness. In vivo oral administration of the formulation significantly increased the bioavailability of clopidogrel. The relative bioavailability of clopidogrel was 2.8 fold higher than that obtained for drug suspension of similar concentration. Pharmacodynamics was demonstrated by evaluating the whole blood clotting time. Accelerated stability studies revealed that there was no significant change in mean particle size and potency with a projected shelf life of 13.25 months. © 2017 Society for Biomaterials and Artificial Organs - India. All rights reserved.
... A similar effect was also observed with capric, lauric, and oleic acids. These fatty acids increase hydrophilic transport and reduce transepithelial electrical resistance, indicating the opening of TJs [74]. Paracellular transport has been related, in several papers, to the transport of poorly absorbed drugs. ...
The intracellular delivery of nanomaterials and drugs has been attracting increasing research interest, mainly because of their important effects and functions in several organelles. Targeting specific organelles can help treat or decrease the symptoms of diabetes, cancer, infectious, and autoimmune diseases. Tuning biological and chemical properties enables the creation of functionalized nanomaterials with enhanced intracellular uptake, ability to escape premature lysosome degradation, and to reach a specific target. Here, we provide an update of recent advances in the intracellular delivery mechanisms that could help drugs reach their target more efficiently.
... One example being the recent report on the feasibility of combining safe permeation enhancers in a mucoadhesive particulate system for the oral delivery of peptide drugs was assessed for polyelectrolyte complex nanoparticles, prepared by ionic interaction of spermine with polyacrylic acid polymer, that efficiently improve the oral absorption of calcitonin [15]. There are several studies based on different models and methodologies that provide relevant information about different possible absorption enhancers, demonstrating their importance and potential as strategies to improve oral bioavailability in particular for protein drugs [24][25][26][27]. ...
... The saturated solubility of each individual microcapsule studied by taking specified amount in glass vial containing water which rotated on lab shaker for 24 hours. The sample were prepared and diluted further for analysing drug contained in it 7,8,9,11 . ...
The microencapsulation process is used for size reduction with enclosing polymer coat on active pharmaceutical ingredient. The microencapsulation process used in present study is solvent evaporation process which formulated prior as o/o emulsification process. The polymer for encapsulation was selected based on drug entrapment efficiency and concentration of polymer mix was selected in ratio 1:2, further ratio was adjusted in central composite design for application of DOE in which independent variables was drug release after 2 hours and permeability across bio membrane after 4 hours. Results are shown revealed significant rise in bioavailability of drug than pure API. Scanning electron microscopy referred the size of microcapsule were in range of 10 - 5000 𝜇m. They were spherical in shape with a rough surface and good solubility. Microcapsule were seen in SEM images are sphere with rough surfaces in all batches irrelevant of drug used. Drug encapsulation efficiencies of all the polymes were higher than 90%, which suggested that this method has potential to prepare microcapsules with efficient drug loading and increased bioavailability.
Keywords: Bioavailability Enhancement, Microencapsulation, Solvent Evaporation Technique, Design of Experiment (DOE), Quality by Design (QbD), Central Composite Design.
... So, in the present work chicken's small intestine was used for intestinal absorption studies of prepared tablets based on the assumption that membrane permeability of drugs is not species dependent since the composition of plasma membrane of intestinal epithelial cells is similar across the species. [9,10] ...
The present study is to formulate an anti-diabetic tablet containing permeation enhancer which enhances gastrointestinal absorption of poorly absorbable anti-diabetic drug. Metformin hydrochloride (HCl) is a BCS class III drug which has high solubility and poor intestinal absorption characteristic. The gastrointestinal absorption of metformin hydrochloride was enhanced using permeation enhancer like cyclodextrin. The permeation of drug was measured by everted sac technique using chicken intestine. The drug was absorbed through chicken intestine mainly by passive diffusion mechanism. The absorbed drug was determined by using U.V Visible Spectrophotometer at 234nm. After analyzing the results it was found that cyclodextrin enhance the absorption of metformin hydrochloride from chicken intestine. This cyclodextrin was used to reduce dose of metformin hydrochloride in tablet dosage form. For optimizing the dose of metformin hydrochloride, different batches of different permeation enhancer were used and tablets were prepared by direct compression method with different concentration of permeation enhancer and metformin hydrochloride. Metformin hydrochloride exhibits poor compressibility during compaction, often resulting in weak and unacceptable tablets with a high tendency to cap. The purpose was to develop directly compressible metformin hydrochloride by the spray-drying technique in the presence of polymer. This help in increase in the flow property of metformin HCL. The permeability of this drug was increased by the addition of cyclodextrin which acts as a permeation enhancer. This in turn results in better absorption enhancement.
... Mild histopathological changes coupled with granuloma size reduction wereboth indicative of liver protection. Oleic acid-induced activity enhancement may involve enhanced drug permeation as a result of membrane permeabilization and structural deformation of tight junctions [53] and/or promotion of the interaction with the tegument membrane due to fusogenic properties [36]. Indeed, fatty acids were reported to kill schistosomes by exposing antigens on tegumental surface to the host immune system, achieving significant improvement in clinical effects [54,55]. ...
Miltefosine (MFS) is an alkylphosphocholine used for the local treatment of cutaneous metastases of breast cancer and oral therapy of visceral leishmaniasis. Recently, the drug was reported in in vitro and preclinical studies to exert significant activity against different developmental stages of schistosomiasis mansoni, a widespread chronic neglected tropical disease (NTD). This justified MFS repurposing as a potential antischistosomal drug. However, five consecutive daily 20 mg/kg doses were needed for the treatment of schistosomiasis mansoni in mice. The present study aims at enhancing MFS efficacy to allow for a single 20mg/kg oral dose therapy using a nanotechnological approach based on lipid nanocapsules (LNCs) as oral nanovectors. MFS was incorporated in LNCs both as membrane-active structural alkylphospholipid component and active antischistosomal agent. MFS-LNC formulations showed high entrapment efficiency (EE%), good colloidal properties, sustained release pattern and physical stability. Further, LNCs generally decreased MFS-induced erythrocyte hemolytic activity used as surrogate indicator of membrane activity. While MFS-free LNCs exerted no antischistosomal effect, statistically significant enhancement was observed with all MFS-LNC formulations. A maximum effect was achieved with MFS-LNCs incorporating CTAB as positive charge imparting agent or oleic acid as membrane permeabilizer. Reduction of worm load, ameliorated liver pathology and extensive damage of the worm tegument provided evidence for formulation-related efficacy enhancement. Non-compartmental analysis of pharmacokinetic data obtained in rats indicated independence of antischistosomal activity on systemic drug exposure, suggesting possible gut uptake of the stable LNCs and targeting of the fluke tegument which was verified by SEM. The study findings put forward MFS-LNCs as unique oral nanovectors combining the bioactivity of MFS and biopharmaceutical advantages of LNCs, allowing targeting via the oral route. From a clinical point of view, data suggest MFS-LNCs as a potential single dose oral nanomedicine for enhanced therapy of schistosomiasis mansoni and possibly other diseases.
... Thus, the drug concentration increases during the digestion process, which improves the transport across nonstirred water layers and then the bio-membranes. In addition, fatty acids and monoglycerides produced during digestion increase the fluidity and permeability of membranes due to their surface activity, which is also an important factor in enhancing drug absorption [40]. Furthermore, lymphatic transport can also increase the oral bioavailability of lipophilic drugs [41]. ...
The aim of this study was to compare various formulations solid dispersion pellets (SDP), nanostructured lipid carriers (NLCs) and a self-microemulsifying drug delivery system (SMEDDS) generally accepted to be the most efficient drug delivery systems for BCS II drugs using fenofibrate (FNB) as a model drug. The size and morphology of NLCs and SMEDDS was characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Their release behaviors were investigated in medium with or without pancreatic lipase. The oral bioavailability of the various formulations was compared in beagle dogs using commercial Lipanthyl® capsules (micronized formulation) as a reference. The release of FNB from SDP was much faster than that from NLCs and SMEDDS in medium without lipase, whereas the release rate from NLCs and SMEDDS was increased after adding pancreatic lipase into the release medium. However, NLCs and SMEDDS increased the bioavailability of FNB to 705.11% and 809.10%, respectively, in comparison with Lipanthyl® capsules, although the relative bioavailability of FNB was only 366.05% after administration of SDPs. Thus, lipid-based drug delivery systems (such as NLCs and SMEDDS) may have more advantages than immediate release systems (such as SDPs and Lipanthyl® capsules).
... During nanocarrier optimization, absorption enhancers are widely used excipients to improve the bioavailability of poorly water soluble drugs. Disparate mechanisms of permeability enhancement were reported in literature, such as modifying barrier integrity by opening of tight junction [56,64,65], membrane fluidization, micellar solubilization [66], and the inhibition of efflux transporters such as P-gp [56,67]. However, a relationship was established between paracellular transport enhancement and cell viability, as surfactants may cause local irritations, membrane damage and cell damage [56]. ...
Nanomedicines are enjoying a widespread popularity realizing their intriguing potential to solve drug delivery obstacles. Assessment of major quality attributes of nanocarriers is a crucial process for approving their therapeutic outcomes. Disparate assessment methods were employed that recently encompassed cell line technique. Routinely, cell line model was viewed as an excellent platform for gene and vaccine delivery. However, its application in pharmaceutical assessment of nanocarriers was not so far overviewed. This review provides a meticulous look at cell culture implementations in evaluation of major quality attributes of nanocarriers, including oral permeability, cytotoxicity and efficiency of tumor targeting. Among others, cell culture technique strikes the right balance between predictability and throughput. It could circumvent drawbacks of in-vivo and in-vitro techniques while gathering privileges of both. Imperative pharmaceutical considerations demanded for proper application of this technique were emphasized. Furthermore, challenges encountered in assessment of versatile nanocarriers were highlighted with proposed solutions. Finally, future research perspectives in this theme issue were suggested.
... It has been reported that FAs can disrupt the lipid bilayer of the mucosal lining thereby increasing drug transport and bioavailability. Oleic acid (OA), in particular, has been reported as an effective CPE for drugs such as levothyroxine sodium via the intestinal route 34 , caffeine and diclofenac sodium (DS) via the transdermal route 35 and 5-fluorouracil via the buccal route 1 . Novel derivatives of OA will therefore be useful for further improving their permeation-enhancing potential and will contribute to the pool of permeation enhancers for enhancing drug permeability. ...
Abstract The aim of this study was to explore the potential of novel oleic acid (OA) derivatives as buccal permeation enhancers for the delivery of didanosine (ddI). The OA derivatives, i.e. ester derivative (OA1E), the dicarboxylic acid derivative (OA1A) and the bicephalous dianionic surfactant (OA1ANa) were synthesized and their effects were compared to the parent OA. OA, OA1E, OA1A and OA1ANa at 1% w/w all showed potential for enhancing the buccal permeability of ddI with enhancement ratio (ER) of 1.29, 1.33, 1.01 and 1.72, respectively. OA1ANa at 1% w/w demonstrated the highest flux (80.30 ± 10.37 µg cm(-2 )h), permeability coefficient (4.01 ± 0.57 × 10(-3) cm h(-1)) and ER (1.72). The highest flux for ddI (144.00 ± 53.54 µg cm(-2 )h) was reported with OA1ANa 2% w/w, which displayed an ER of 3.09 more than that with ddI alone. At equivalent concentrations, OA1ANa (ER = 3.09) had a significantly higher permeation-enhancing effect than its parent OA (ER = 1.54). Histomorphological studies confirmed that OA1ANa at all concentrations (0.5, 2.0 and 6.0% w/w) had no adverse effects on the mucosae. Morphological changes such as vacuoles formation and increased intercellular spaces were attributed to the buccal permeation-enhancing effect of OA1ANa. This study demonstrated the potential of novel OA derivatives as buccal permeation enhancers. OA1ANa at 2% w/w was also identified as the optimal novel OA derivative to widen the pool of fatty acid derivatives as chemical permeation enhancers for buccal drug delivery.
... To date, chitosan has been used as stabiliser in buparvaquone nanosuspensions [130]. In addition to chitosan and its derivatives, fatty acids could also enhance the permeation of drugs across the MDCK cell line [128, 131]. All these permeation enhancers could be used as excipients or stabilisers in the formulation of nanosus- pensions [132]. ...
A surprisingly large proportion of new chemical entities (NCE) are emerging from the drug discovery pipeline, and many active components extracted from herbal medicines are water insoluble, which represents a great challenge for their development. Nanosuspensions, which are submicron colloidal dispersions of pure drug particles that are stabilised by a small percentage of the excipients, could dramatically enhance the saturated solubility, dissolution rate and adhesion of drug particles to cell membranes. Nanosuspensions are the most suitable for drugs that require high dosing or have limited administrative volume. After 20 years of development, several oral products and one injectable product are commercially available. The aim of this review is to fill the gap between rational formulation designs and the in vivo performance of poorly water-soluble drug nanosuspensions. Specifically, this review will correlate characteristics of nanosuspension formulations, including drug property, particle size, crystallinity, stabiliser and surface property, with their transport, pharmacokinetics, bioactivity and toxicity after delivery by different administration routes. The elucidation of the mechanisms of targeted drug delivery, cellular transport and internalisation of nanosuspensions are also reviewed to interpret the in vivo performance of these nanosuspensions. Moreover, the recent application of nanosuspensions for poorly water-soluble herbal medicines is highlighted.
... OATP does not express in this cell line. These data provide therefore clear evidence on the fact that thyroid hormones cannot cross membranes by passive diffusion [32]. Our determined protonation microconstants and speciesspecific partition coefficients of thyroid hormones can explain several empirical data at the submolecular level such as the membrane processes of thyroid hormones. ...
A total of 30 species-specific partition coefficients of three thyroid hormones (thyroxine, liothyronine, reverse liothyronine) and their two biological precursors (monoiodotyrosine, diiodotyrosine) are presented. The molecules were studied using combined methods of microspeciation and lipophilicity. Microspeciation was carried out by (1)H NMR-pH and UV-pH titration techniques on the title compounds and their auxiliary derivatives of reduced complexity. Partition of some of the individual microspecies was mimicked by model compounds of the closest possible similarity, then correction factors were determined and introduced. Our data show that the iodinated aromatic ring system is the definitive structural element that fundamentally determines the lipophilicity of thyroid hormones, whereas the protonation state of the aliphatic part plays a role of secondary importance. On the other hand, the lipophilicity of the precursors is highly influenced by the protonation state due to the relative lack of overwhelmingly lipophilic moieties. The different logp values of the positional isomers liothyronine and reverse liothyronine represent the importance of steric and electronic factors in lipophilicity. Our investigations provided clear indication that overall partition, the best membrane transport - predicting physico-chemical parameter depends collectively on the site-specific basicity and species-specific partition coefficient. At physiological pH these biomolecules are strongly amphipathic due to the lipophilic aromatic rings and hydrophilic amino acid side chains which can well be the reason why thyroid hormones cannot cross membranes by passive diffusion and they are constituents of biological membranes. The lipophilicity profile of thyroid hormones and their precursors are calculated and depicted in terms of species-specific lipophilicities over the entire pH range.
... In line with the above considerations, solubility is not expected to be the limiting factor for LT4 absorption. Permeability data are not totally conclusive and suggest LT4 to be on the margin between high and low permeability drug [11,12,35]. So, it can be concluded that LT4 is on the borderline between BCS Class I and III drug. ...
The aim of this case study was to develop a drug-specific absorption model for levothyroxine (LT4) using mechanistic gastrointestinal simulation technology (GIST) implemented in the GastroPlus™ software package. The required input parameters were determined experimentally, in silico predicted and/or taken from the literature. The simulated plasma profile was similar and in a good agreement with the data observed in the in vivo bioequivalence study, indicating that the GIST model gave an accurate prediction of LT4 oral absorption. Additionally, plasma concentration-time profiles were simulated based on a set of experimental and virtual in vitro dissolution data in order to estimate the influence of different in vitro drug dissolution kinetics on the simulated plasma profiles and to identify biorelevant dissolution specification for LT4 immediate-release (IR) tablets. A set of experimental and virtual in vitro data was also used for correlation purposes. In vitro-in vivo correlation model based on the convolution approach was applied in order to assess the relationship between the in vitro and in vivo data. The obtained results suggest that dissolution specification of more than 85% LT4 dissolved in 60 min might be considered as biorelevant dissolution specification criteria for LT4 IR tablets.
To enhance the oral bioavailability of atorvastatin calcium (ATV), a novel solidified micelle (S-micelle) was developed. Two surfactants, Gelucire 48/16 (G48) and Tween 20 (T20), were employed for micelle formation, and two solid carriers (SC), Florite PS-10 (FLO) and Vivapur 105 (VP105), were selected as solid carriers. The S-micelle was optimized using a Box-Behnken design with three independent variables, including G48:T20 (X1, 1.8:1), SC:G48 + T20 (X2, 0.65:1), and FLO:VP105 (X3, 1.4:0.6), resulting in a droplet size (Y1) of 198.4 nm, dissolution efficiency at 15 min in the pH 1.2 medium (Y2) of 47.6%, Carr's index (Y3) of 16.9, and total quantity (Y4) of 562.5 mg. The optimized S-micelle resulted in good correlation showing percentage prediction values less than 10%. The optimized S-micelle formed a nanosized dispersion in the aqueous phase, with a higher dissolution rate than raw ATV and crushed Lipitor®. The optimized S-micelle improved the relative bioavailability of oral ATV (25 mg equivalent/kg) in rats by approximately 509% and 271% compared to raw ATV and crushed Lipitor®, respectively. In conclusion, the optimized S-micelle possesses great potential for the development of solidified formulations for improved oral absorption of poorly water-soluble drugs.
Improving the solubility and permeability of drugs via cocrystallization is an important theme in crystal engineering with practical applications for the discovery and development of high bioavailability medicines. The past decade has witnessed a surge of publications on pharmaceutical cocrystals/salts to improve the permeability of Biopharmaceutics Classification System (BCS) class IV drugs. In this review article, the reader is introduced to the fundamentals of drug permeability mechanisms and then examples of pharmaceutical cocrystals and salts designed to enhance drug diffusion and permeability are presented, in order to understand the different structural factors that modulate drug flux and transport across a semipermeable membrane. Broadly, two main phenomena can be summarized from the 50 or so examples: (1) The heterosynthons in hydrogen-bonded drug-coformer aggregates survive long enough in the experimental media such that the drug, which is present in high concentration due to supersaturation, exhibits higher flux across the semipermeable membrane. (2) The coformer or cocrystal is able to reduce the transepithelial electrical resistance (TEER) values of lipid monolayers, which impairs their tight junctions, and facilitates drug passage to improve its diffusion/permeability. The medicinal chemistry literature on high permeability drugs is recapitulated with the idea that these principles may be utilized in the de novo design of high permeability coformers for the synthesis of improved-performance pharmaceutical cocrystals. Enhancing drug solubility and permeability without changing its molecular structure in supramolecular complexes of pharmaceutical cocrystals and salts will address the poor bioavailability challenge for a majority of BCS class II and IV drugs.
Drug absorption is a complex process governed by a number of interrelated physicochemical, biopharmaceutical, and pharmacokinetic factors. In order to explore complex relationships among these factors, multivariate exploratory analysis was performed on the dataset of drugs with diverse bioperformance. The investigated dataset included subset of drugs for which bioequivalence between solid dosage form and oral solution has been reported, and subset of drugs described in the literature as low solubility/low permeability compounds. Discriminatory power of hierarchical clustering on principal components was somewhat higher when applied on the data subsets of drugs with similar bioperformance, while analysis of the integrated dataset indicated existence of two groups of drugs with the boundaries reflected in Peff value of approximately 2 × 10⁻⁴ cm/s and Fa and Fm values higher than 85% and 50%, respectively. Majority of the investigated drugs within the integrated dataset were grouped within their initial subset indicating that overall drug bioperformance is closely related to its physicochemical, biopharmaceutical and pharmacokinetic properties. Classification models constructed using the random forest (RF) and support vector machine with polynomial kernel function were able to predict food effect based on drug dose/solubility ratio (D/S), effective permeability (Peff), percent of dose metabolized (Fm), and elimination half-life (τ1/2). Although both models performed well during training and testing, only RF kept satisfying performance when applied on the external dataset (kappa value > 0.4). The results obtained indicate that data mining can be employed as useful tool in biopharmaceutical drug characterization which merits further investigation.
Recent work has highlighted the potential of puerarin (PU) as a valuable compound to treat Parkinson's disease (PD), but its poor water solubility and bioavailability have constrained its utility. In this study, we sought to develop nanoparticles (NPs) which could be used to encapsulate PU, thereby extending its in vivo half-life and improving its bioavailability and accumulation in the brain to treat the symptoms of PD. We prepared spherical NPs (88.36 ± 1.67 nm) from six-armed star-shaped poly(lactide-co-glycolide) (6-s-PLGA) NPs that were used to encapsulate PU (PU-NPs) with 89.52 ± 1.74% encapsulation efficiency, 42.97 ± 1.58% drug loading and a 48-h sustained drug release. NPs formation and drug loading were largely mediated by hydrophobic interactions, while changes in the external environment led these NPs to become increasingly hydrophilic, thereby leading to drug release. Relative to PU alone, PU-NPs exhibited significantly improved cellular internalization, permeation and neuroprotective effects. Based upon Förster resonance energy transfer (FRET) of NPs-administered zebrafish, we were able to determine that these NPs were rapidly absorbed into circulation whereupon they were able to access the brain. We further conducted oral PU-NPs administration to rats, revealing significant improvements in PU accumulation within the plasma and brain relative to rats administered free PU. In a MPTP-mediated murine model of PD, we found that PU-NPs treatment improved disease-associated behavioral deficits and depletion of dopamine and its metabolites. These findings indicated that PU-NPs represent a potentially viable approach to enhancing PU oral absorption, thus improving its delivery to the brain wherein it can aid in the treatment of PD.
Aim:
High-fat diet (HFD) intake has been associated with changes in intestinal microbiota composition, increased intestinal permeability, and onset of type 2 diabetes mellitus (T2DM). The aim of this work was twofold: 1) to investigate the structural and functional alterations of the tight junction (TJ)-mediated intestinal epithelial barrier of ileum and colon, that concentrate most of the microbiota, after exposure to a HFD for 15, 30 and 60 days, and 2) to assess the effect of in vitro exposure to free fatty acids (FFAs), one of the components of HFD, on paracellular barrier of colon-derived Caco-2 cells.
Methods/key findings:
HFD exposure induced progressive metabolic changes in male mice that culminated in prediabetes after 60d. Morphological analysis of ileum and colon mucosa showed no signs of epithelial rupture or local inflammation but changes in the junctional content/distribution and/or cellular content of TJ-associated proteins (claudins-1, -2, -3, and occludin) in intestinal epithelia were seen mainly after a prediabetes state has been established. This impairment in TJ structure was not associated with significant changes in intestinal permeability to FITC-dextran. Exposure of Caco-2 monolayers to palmitic or linoleic acids seems to induce a reinforcement of TJ structure while treatment with oleic acid had a more diverse effect on TJ protein distribution.
Significance:
TJ structure in distal intestinal epithelia can be specifically impaired by HFD intake at early stage of T2DM, but not by FFAs in vitro. Since the TJ change in ileum/colon was marginal, probably it does not contribute to the disease onset.
Background:
Bariatric surgery can lead to changes in the oral absorption of many drugs. Levothyroxine is a narrow therapeutic drug for hypothyroidism, a common condition among patients with obesity.
Objective:
The purpose of this work was to provide a mechanistic overview of levothyroxine absorption, and to thoroughly analyze the expected effects of bariatric surgery on oral levothyroxine therapy.
Methods:
We performed a systematic review of the relevant literature reporting the effects of bariatric surgery on oral levothyroxine absorption and postoperative thyroid function. A PubMed search for relevant keywords resulted in a total of 14 articles reporting levothyroxine status before versus after bariatric surgery.
Results:
Different mechanisms may support opposing trends as to levothyroxine dose adjustment postsurgery. On the one hand, based on impaired drug solubility/dissolution attributable to higher gastric pH as well as reduced gastric volume, compromised levothyroxine absorption is expected. On the other hand, the great weight loss, and altered set-point of thyroid hormone homeostasis with decreased thyroid-stimulating hormone after the surgery, may result in a decreased dose requirement.
Conclusions:
For patients after bariatric surgery, close monitoring of both the clinical presentation and plasma thyroid-stimulating hormone and T4 levels is strongly advised. Better understanding and awareness of the science presented in this article may help to avoid preventable complications and provide optimal patient care.
Background
The high molecular weight and increasing lipophilicity drug face many problems starting from the drug development to formulation and conduction of pharmacological, toxicological and pharmacokinetic studies to its biological application. To overcome this problem, a different formulation of nano-sized drugs was developed recently. The use of Solid lipid nanoparticles (SLNs) and Nanostructured lipid carriers (NLCs) offers new insight into the formulation of the poorly soluble drug.
Objective
The study aimed to investigate the literature with regard to the development of SLNs and NLCs for lipid-based nano drug delivery of poorly soluble drugs, with a view to identifying the factors influencing the optimization of the formulation of SLNs and NLCs and strategies to decrease the use of organic solvent during the preparation.
Results
This review highlights the simple and easily scaled-up novel lipid nanoparticles (SLNs and NLCs) and their factors to be considered in the formulation for the proper selection of excipients. Also, this review summarizes the research findings reported by the different researchers regarding the principle formulation components, different preparation techniques, characterization, and toxicology of lipid nanoparticles.
Conclusion
The SLNs/NLCs make this drug delivery system as one of the promising delivery systems, and safe colloidal lipid carriers for the delivery of poorly soluble drug and will be a solution to the formulation scientist for the solubility and permeability problem associated with the drugs to assure its good bioavailability.
Lipid nanocapsules (LNCs) have shown potential to increase the bioavailability and efficacy of orally administered drugs. However, their intestinal translocation to distal target sites and their implication in pharmacokinetic (PK)–pharmacodynamic (PD) relationships are yet to be elucidated. In this study, the effect of LNCs on the PD activity and pharmacokinetics of praziquantel (PZQ), the mainstay of schistosomiasis chemotherapy, was investigated.
Purpose
Lipid nanocapsules (LNCs) have shown potential to increase the bioavailability and efficacy of orally administered drugs. However, their intestinal translocation to distal target sites and their implication in pharmacokinetic (PK)–pharmacodynamic (PD) relationships are yet to be elucidated. In this study, the effect of LNCs on the PD activity and pharmacokinetics of praziquantel (PZQ), the mainstay of schistosomiasis chemotherapy, was investigated.
Materials and methods
The composition of LNCs was modified to increase PZQ payload and to enhance membrane permeability. PZQ–LNCs were characterized in vitro for colloidal properties, entrapment efficiency (EE%), and drug release. PD activity of the test formulations was assessed in Schistosoma mansoni-infected mice 7 days post-oral administration of a single 250 mg/kg oral dose. Pharmacokinetics of the test formulations and their stability in simulated gastrointestinal (GI) fluids were investigated to substantiate in vivo data.
Results
PZQ–LNCs exhibited good pharmaceutical attributes in terms of size (46–62 nm), polydispersity index (0.01–0.08), EE% (>95%), and sustained release profiles. Results indicated significant efficacy enhancement by reduction in worm burden, amelioration of liver pathology, and extensive damage to the fluke suckers and tegument. This was partly explained by PK data determined in rats. In addition, oral targeting of the worms was supported by the stability of PZQ–LNCs in simulated GI fluids and scanning electron microscopy (SEM) visualization of nanostructures on the tegument of worms recovered from mesenteric/hepatic veins. Cytotoxicity data indicated tolerability of PZQ–LNCs.
Conclusion
Data obtained provide evidence for the ability of oral LNCs to target distal post-absorption sites, leading to enhanced drug efficacy. From a practical standpoint, PZQ–LNCs could be suggested as a potential tolerable single lower dose oral nanomedicine for more effective PZQ mass chemotherapy.
BCS class III drugs suffer from a drawback of low permeability even though they have high aqueous solubility. The objective of current work was to screen the suitability of glyceryl monooleate (GMO)/Pluronic F127 cubic phase liquid crystals precursors for permeation enhancement and in turn the bioavailability of tenofovir disoproxil fumarate (TDF), a BCS class III drug. Spray-drying method was used for preparation of TDF loaded liquid crystal precursors (LCP) consisting of GMO/Pluronic F127 and lactose monohydrate with an ability to in situ transform into stable cubic phases upon hydration. The quality by design (QbD) approach (Factorial design) was used for batch optimization. Spherical TDF loaded LCP as revealed by scanning electron microscopy photographs when hydrated and analyzed by small angle X-ray scattering confirmed formation of cubic phase. Differential scanning calorimetry and X-ray diffraction studies confirmed the molecular dispersion of TDF in polymer matrix and also suggested the conversion of TDF from crystalline to amorphous form. In vitro TDF release from prepared LCP showed controlled drug release over a period of 10 h. Further ex vivo studies revealed permeation enhancing activity of prepared LCP, which was highest when tested in presence of digestive enzyme extract. Thus, formulation of stable liquid crystal powder precursor can serve as an alternative for designing oral delivery system for drugs with low permeability.
Active agents have been considered the main ingredients of any therapeutic product since the early ages of formulation technology. However, the importance of the inactive ingredients has been realized during the last three decades. With the development and manufacturing of more intelligent and multifunction excipients, new ways became available for formulation technologists to increase the beneficial effects of drugs on human body. Many modern active agents have internal characteristics that significantly decrease their potential and theoretical bioavailability; however, today we have the widest variety of inactive ingredients that we can utilize in order to change these properties. The careful and educated selection of excipients might significantly influence the effect of the drugs, including hastening or delaying their onset of action, increasing their bioavailability by changing their physicochemical characteristics, and increasing their stability. In this chapter, we focus primarily on the factors determining and influencing bioavailability as well as the selection of excipients for formulating new dosage forms with enhanced therapeutic efficacy, based on the physicochemical properties of drugs. We will provide some examples from the scientific literature to demonstrate the achievements in this multidisciplinary area.
A dual drug repurposing/nanotechnological approach was used to develop an alternative oral treatment for schistosomiasis mansoni using miltefosine (MFS), an anticancer alkylphosphocholine, and lipid nanocapsules (LNCs) as oral nanovectors. We demonstrated earlier that MFS possesses significant activity against different developmental stages of S. mansoni in the mouse model using 5 successive 20mg/kg/day oral doses. Moreover, an effective single dose (20mg/kg) oral treatment against the adult stage of S. mansoni in mice was developed using LNCs, particularly modified with CTAB, a positive charge imparting agent (MFS-LNC-CTAB(+)), or oleic acid as membrane permeabilizer (MFS-LNC-OA). Efficacy enhancement involved, at least in part, targeting of the worm tegument with MFS-LNCs as a new therapeutic entity. As the tegument surface charge and composition may differ in pre-patent stages of the parasite, it was of importance in the present study to assess the efficacy of a single oral dose of the two MFS-LNC formulations against invasive and immature stages for potential advantage relative to praziquantel. Results indicated potent schistosomicidal effects against both invasive and immature stages of S. mansoni in infected mice, efficacy being both formulation and developmental stage dependent. This was indicated by the significant reduction in the total worm burden of the invasive stage by 91.6% and 76.8% and the immature stage by 82.7% and 96.7% for MFS-LNC-CTAB+ and MFS-LNC-OA, respectively. Histopathological findings indicated amelioration of hepatic pathology with regression of the granulomatous inflammatory reaction and reduction in granulomas number and size, verifying marked improvement in architecture of hepatic lobules. From a clinical perspective, MFS-LNCs offer potential as an alternative single oral dose nanomedicine with a wide therapeutic profile for the mass chemotherapy of schistosomiasis mansoni.
Need for an oral replacement to parenteral delivery has led to renewed attentiveness in excipients like intestinal permeation enhancers which improve oral drug bioavailability. Delivery of a drug by oral route is predominantly restricted by pre-systemic degradation and poor penetration across the gut wall. The major challenge in the oral drug delivery is the development of novel dosage forms to endorse absorption of poorly permeable drugs across the intestinal epithelium. Fifty years ago research on oral absorption enhancers that increases gut permeability was first commenced yet clinical success yet to be achieved. Development has been troubled by lack of adequate reproducibility interest as well as perceived safety concerns. We reviewed some selected permeation enhancement techniques that are advantageous for increasing permeability of poorly permeable drugs.
The bonding behavior was determined for hydrophobically modified alkaline-treated gelatin on wet porcine intestinal surfaces. The modified gelatin films were obtained by reacting the amino groups of alkaline-treated gelatin with fatty acid chlorides of different alkyl chain lengths, namely, hexanoyl (Hx: C-6) chloride, decanoyl (Dec: C-10) chloride, and stearoyl (Ste: C-18) chloride. Three kinds of the films were prepared, 32HxAlGltn, 24DecAlGltn, and 26SteAlGltn that had substitution ratios of hydrophobic groups to the amino groups of 32HxAlGltn, 24DecAlGltn, and 26SteAlGltn of 32%, 24%, and 26%, respectively. The 32HxAlGltn film had the strongest bonding to porcine intestinal surfaces. A thick 32HxAlGltn film remained on the intestinal surface even after the bonded film was scraped off for the measurement of bonding strength. In addition, the burst strength increased with an increase in the substitution ratio of the Hx group. Thus, the HxAlGltn film with the higher Hx modification ratio has a potential as a sealant material to prevent agglutination of intestinal surfaces.
Transport of a drug across the biological membrane of the gastrointestinal tract has turned out to be a critical barrier against the success of any oral drug delivery technology. The unique advantages of the oral route, along with need for an oral substitute of invasive parenteral formulations and the reduction of intersubject variability in plasma profiles, has been an incentive for the use of excipients with absorption-enhancing properties to boost the bioavailability of poorly absorbed drugs. The development of such excipients is not a simple task, so understanding enhancement mechanisms in relation to physiology can facilitate the identification of structure-function relationships as well as the development of newer agents for customary applications. The literature is replete with reports of absorption promoters, the selection of which is influenced by the mechanisms, safety, pharmacological inertness, rapidity of action, reversibility of induced membrane alterations and excipient compatibility. Despite promising results in preliminary screenings, the development process is hindered by low reproducible efficacy and pharmacologically driven safety issues. In this review, we elaborate on the importance of permeation enhancers in oral drug delivery, their current status, and issues at the forefront of the development of formulations using absorption promoter technologies.
Although it is acknowledged that the main impediment of orally administered therapeutic agents is their extensive and changeable pre-systemic metabolism, low absorption and instability in harsh environment of gastrointestinal (GI) tract are also mainly influential factors, resulting into inadequate and erratic bioavailability. To overcome these shortcomings, nanotechnology has been offered new promising strategies to prevent and treat a wide variety of diseases by employing different oral drug-carrier structures capable to enhance therapeutic effects and minimize the toxicity of healthy organs or cells. This review, in general, elucidates some considerable features of in vitro oral drug delivery in three different parts. The first one summarizes the main challenges for oral drug delivery and available absorption mechanisms. The second part embodies an in-depth discussion on the role of intestinal absorption models used to predict permeability, cellular uptake or even toxicity of nanoparticles, resulting into the design of nanocarriers with optimum efficacy for oral delivery. The third section of the literature is devoted, more particularly, to nanocarriers developed for oral absorption in the past few years, including the behaviour of nanovehicles upon oral administration with respect to membrane permeability, retention properties and stability, as well as methods which may lengthen residence time in the GI environment or improve drug absorption.
Prediction of human intestinal absorption is a major goal in the design, optimization, and selection of drugs intended for oral delivery, in particular proteins, which possess intrinsic poor transport across intestinal epithelium. There are various techniques currently employed to evaluate the extension of protein absorption in the different phases of drug discovery and development. Screening protocols to evaluate protein absorption include a range of preclinical methodologies like in silico, in vitro, in situ, ex vivo and in vivo. It is the careful and critical use of these techniques that can help to identify drug candidates, which most probably will be well absorbed from the human intestinal tract. It is well recognized that the human intestinal permeability cannot be accurately predicted based on a single preclinical method. However, the present social and scientific concerns about the animal well care as well as the pharmaceutical industries need for rapid, cheap and reliable models predicting bioavailability give reasons for using methods providing an appropriate correlation between results of in vivo and in vitro drug absorption. The aim of this review is to describe and compare in silico, in vitro, in situ, ex vivo and in vivo methods used to predict human intestinal absorption, giving a special attention to the intestinal absorption of therapeutic peptides and proteins.
The aim of this study was to investigate the influence of experimental conditions on levothyroxine sodium release from two immediate-release tablet formulations which narrowly passed the standard requirements for bioequivalence studies. The in vivo study was conducted as randomised, single-dose, two-way cross-over pharmacokinetic study in 24 healthy subjects. The in vitro study was performed using various dissolution media, and obtained dissolution profiles were compared using the similarity factor value. Drug solubility in different media was also determined. The in vivo results showed narrowly passing bioequivalence. Considering that levothyroxine sodium is classified as Class III drug according to the Biopharmaceutics Classification System, drug bioavailability will be less sensitive to the variation in its dissolution characteristics and it can be assumed that the differences observed in vitro in some of investigated media probably do not have significant influence on the absorption process, as long as rapid and complete dissolution exists. The study results indicate that the current regulatory criteria for the value of similarity factor in comparative dissolution testing, as well as request for very rapid dissolution (more than 85% of drug dissolved in 15 min), are very restricted for immediate-release dosage forms containing highly soluble drug substance and need further investigation. The obtained results also add to the existing debate on the appropriateness of the current bioequivalence standards for levothyroxine sodium products.
Objective. - To develop a set of minimum clinical guidelines for use by primary care physicians in the evaluation and management of patients with hyperthyroidism and hypothyroidism. Participants. - Guidelines were developed by a nine-member ad hoc Standards of Care Committee of the American Thyroid Association (the authors of this article). The participants were selected by the committee chair and the president of the American Thyroid Association on the basis of their clinical experience. The committee members represented different geographic areas within the United States, in order to take into account different practice styles. Evidence. - Guidelines were developed on the basis of expert opinion of the participants, as well as on available published information. Consensus Process. - Input was obtained from all of the participants, each of whom wrote an initial section of the document. A complete draft document was then written by three participants (P.A.S., D.S.C., and E.G.L.) and resubmitted to the entire committee for revision. The revised document was then submitted to the entire membership of the American Thyroid Association for written comments, which were then reviewed (mainly by P.A.S., D.S.C., and E.G.L.). Many of the suggestions of the American Thyroid Association members were incorporated into the final draft, which was then approved by the Executive Council of the American Thyroid Association. The entire process, from initial drafts to final approval, took approximately 18 months. Conclusions. - A set of minimum clinical guidelines for the diagnosis and treatment of hyperthyroidism and hypothyroidism were developed by consensus of a group of experienced thyroidologists. The guidelines are intended to be used by physicians in their care of patients with thyroid disorders, with the expectation that more effective care can be provided, and at a cost savings.
The bioavailabilities of orally administered drugs depend to a great extent on their capability of being transported across the intestinal mucosa. In an attempt to develop an in vitro model for studying the intestinal transport of drugs, we used an intestinal epithelial cell line (Caco 2) derived from a human colon adenocarcinoma. A renal epithelial cell line (MDCK) was also used to determine the tissue specificity of drug transport. These cell lines, which were grown on filters, form a monolayer of well-polarized cells coupled by tight junctions and can be used for transcellular transport experiments. We studied the transport of nine antimicrobial agents with different physicochemical and pharmacokinetic characteristics using these epithelial cell monolayers to determine whether this model could be predictive of oral bioavailability. The transepithelial passage was assayed from the apical (AP) to the basolateral (BL) side and in the opposite direction (BL to AP) in both cell lines. Radioactively labeled mannitol was used to monitor the intactness of the cell monolayer during drug passage. The results indicated that all antimicrobial agents tested tended to behave in vitro generally according to their known in vivo absorptive characteristics. In addition, the use of epithelia from different tissues enabled us to divide the drugs into four groups according to their behaviors and suggested the existence of different transport mechanisms. In particular, two antibiotics, gentamicin and teicoplanin, showed no passage in either direction or cell line, in accordance with their very poor in vivo absorbances after oral administration. In contrast, rifapentine, rifampin, and nalidixic acid passed very efficiently at similar rates in both directions and cell lines in a concentration-dependent, nonsaturable manner, which is suggestive of passive diffusion down a concentration gradient. Of the remaining drugs, isoniazid and novobiocin sodium showed some differences in passage between the two cell lines and, given their ionized state at the pH that was used, may use the paracellular route. Finally, trimethoprim and D-cycloserine exhibited differences in passage both with respect to polarity and cell line; in particular, trimethoprim had a faster rate of passage only in Caco 2 cells and in the BL to AP direction, while D-cycloserine was exclusively transported by Caco 2 cells in the AP to BL direction. In both cases it is possible that active transport mechanisms are involved.
The transepithelial passage of the orally bioavailable antibacterial agent oxazolidin-2-one (OXa) and 10 derivatives has been studied with human intestinal (Caco-2) and canine renal (MDCK) cell lines grown on polycarbonate filters. The transepithelial passage was assayed in the apical-to-basolateral (AP-to-BL) direction and in the opposite direction (BL to AP) in both cell lines. The observed passage rates of OXa were similar in both directions in the two cell lines, suggesting passive diffusion. This was further confirmed by the fact that transport kinetics were linear as a function of initial concentration. The rates of AP-to-BL passage of OXa and seven of the derivatives in both cell lines were linearly related to lipophilicity, whether expressed as high-passage liquid chromatography retention time or as the logarithm of the n-octanol-water partition coefficient (log P). These data suggest that the lipophilicity of OXa is important for its observed bioavailability after oral administration. Interestingly, three of the derivatives exhibited a higher passage rate than predicted by lipophilicity. Further studies indicated that this transport was saturable, similar in the two directions, and not affected by energy depletion, suggesting the presence of an additional carrier-mediated facilitated-transport mechanism.
This review gives an overview of the current approaches to evaluate drug absorption potential in the different phases of drug discovery and development. Methods discussed include in silico models, artificial membranes as absorption models, in vitro models such as the Ussing chamber and Caco-2 monolayers, in situ rat intestinal perfusion and in vivo absorption studies. In silico models such as iDEA can help optimizing chemical synthesis since the fraction absorbed (Fa) can be predicted based on structural characteristics only. A more accurate prediction of Fa can be obtained by feeding the iDEA model with Caco-2 permeability data and solubility data at various pH's. Permeability experiments with artificial membranes such as the filter-IAM technology are high-throughput and offer the possibility to group compounds according to a low and a high permeability. Highly permeable compounds, however, need to be further evaluated in Caco-2 cells, since artificial membranes lack active transport systems and efflux mechanisms such as P-glycoprotein (PgP). Caco-2 and other "intestinal-like" cell lines (MDCK, TC-7, HT29-MTX, 2/4/A1) permit to perform mechanistic studies and identify drug-drug interactions at the level of PgP. The everted sac and Ussing chamber techniques are more advanced models in the sense that they can provide additional information with respect to intestinal metabolism. In situ rat intestinal perfusion is a reliable technique to investigate drug absorption potential in combination with intestinal metabolism, however, it is time consuming, and therefore not suited for screening purposes. Finally, in vivo absorption in animals can be estimated from bioavailability studies (ratio of the plasma AUC after oral and i.v. administration). The role of the liver in affecting bioavailability can be evaluated by portal vein sampling experiments in dogs.
This review examines reported methods for the enhancement of the oral absorption of polar drugs, including polar peptides and proteins. The microstructure of the intestinal brush border is described, and the interactions of various absorption enhancers with this microstructure are examined. For each absorption enhancer class, this review examines the physical properties of the enhancer, its interactions with model membranes, its absorption enhancing effects, and its potential toxicity. The enhancers reviewed are the bile salts, anionic detergents, non-ionic detergents, medium chain glycerides, salicylates, acyl amino acids, acylcarnitines, lysolecithin, ethylenediaminetetraacetic acid and particulate carriers.
In vitro absorption of carboxylfluorescein was performed with everted colonic segments of rats. Oleic acid solubilized by a nonionic surfactant HCO-60, but not HCO-60 alone, markedly enhanced the permeation of the otherwise poorly permeant carboxylfluorescein through the colonic mucosa. The effect produced by oleic acid was reduced to different extents by pretreating the mucosa with several SH reagents, with being the most effective. The inhibitory effect of was concentration dependent, with more than 5mM completely blocking the enhancement of transmucosal permeability by oleic acid. The in vitro effect of in the absorption experiments was also observed in situ. The inhibitory effect of HgCl2 and iodoacetamide were comparable to that of , whereas PCMPS, an impermeant SH blocker, had no effect on the enhanced permeation. Various other amino-group modifiers had also no effect on the enhancement. On the other hand, the inhibition was accompanied by a significant reduction in the level of non-protein thiols as well as protein SH groups. Diethyl maleate, which reduced only the non-protein SH level, had no pronounced effect on the oleic acid-induced permeability change. These results suggest that the intact SH group of membrane-associated protein is necessary for the enhanced permeation of carboxyfluorescein elicited by oleic acid.
Thyroid hormone has profound effects on the heart and cardiovascular system. This article describes the cellular mechanisms by which thyroid hormone acts at the level of the cardiac myocyte and the vascular smooth muscle cell to alter phenotype and physiology. Because it is well established that thyroid hormone, specifically T(3), acts on almost every cell and organ in the body, studies on the regulation of thyroid hormone transport into cardiac and vascular tissue have added clinical significance. The characteristic changes in cardiovascular hemodynamics and metabolism that accompany thyroid disease states can then be best understood at the cellular level.
This review examines reported methods for the enhancement of the oral absorption of polar drugs, including polar peptides and proteins. The microstructure of the intestinal brush border is described, and the interactions of various absorption enhancers with this microstructure are examined. For each absorption enhancer class, this review examines the physical properties of the enhancer, its interactions with model membranes, its absorption enhancing effects, and its potential toxicity. The enhancers reviewed are the bile salts, anionic detergents, non-ionic detergents, medium chain glycerides, salicylates, acyl amino acids, acylcarnitines, lysolecithin, ethylenediaminetetraacetic acid and particulate carriers.
The effects of a series of fatty acids on the rectal absorption of propranolol (PL) were examined in vitro, using macrogol 1500 base and rat rectal tissue. Lauric acid, at a fatty acid: PL molar ratio of 1:1, produced the largest increase in permeation rate (Js), penetration coefficient and partition coefficient of PL. PL flux was increased 2.5-fold in the presence of lauric acid compared to that without the fatty acid. However, the Js value of PL was decreased at increased molar ratios (e.g., 3:1) of lauric acid. The permeation rate of lauric acid across the rectal membrane was much larger than that of PL. Furthermore, the apparent partition coefficient of PL in an n-octanol/buffer system was significantly increased at a 1:1 molar ratio to lauric acid compared with that of PL alone. These results suggest that a complex-mediated mechanism facilitates PL transport, thereby partially contributing to the enhancement of PL rectal absorption. A similar mechanism is applicable to percutaneous drug absorption, as reported previously. Thus, a portion of PL, after first forming a complex with fatty acids, may rapidly permeate across rectal membranes.
The distribution of intestinal absorption of 131I-labeled thyroxine (T4*) was studied in 4 normal subjects after oral and i.v. T4*, given in separate experimental sessions. In addition to collection of time-activity curves for plasma T4* from the two sessions, distribution and transport of T4* through the gut was quantified by external imaging. Time-activity curves were obtained for the stomach, duodenum, and upper jejunoileum. A multicompartmental model for systemic T4, with three distribution compartments and a single exit route, was employed. Additional, gastrointestinal, compartments were introduced. The stomach data were fitted to a model with three compartments, two for transport and a small sink of gastric activity that does not interact with the absorptive sites. Transfer from the duodenum to the upper jejunoileum and from the upper to the lower jejunoileum was modeled from fits to the peak T4* activities in the images of the duodenum and upper jejunoileum. The rate of transfer from the lower jejunoileum into more distal intestinal sites was fixed, but the impact on the results of using various values for this parameter was analyzed. The model calculations of absorption (mean +/- SD for 3 of the subjects) are duodenum, 15 +/- 5%, upper jejunoileum, 29 +/- 14%, and lower jejunoileum, 24 +/- 11%. The fourth subject, whose global absorption was abnormally low for uncertain reasons, had 17% absorption from the duodenum, 9% from the upper jejunoileum and none from the lower jejunoileum. Model projections mimicking clinical gut abnormalities known to affect T4 absorption were compatible with the results of published studies.
Transport of 14C-labeled acetic, propionic (PA), butyric, valeric, heptanoic (HA), and octanoic (OA) acids across the Madin Darby canine kidney (MDCK) epithelial cell monolayer grown on a porous polycarbonate membrane was studied in Hanks' balanced salt solution (HBSS) at 37 degrees C in both apical-to-basolateral and basolateral-to-apical directions. At micromolar concentrations of solutes, metabolic decomposition was significant as evidenced by [14C]CO2 production during the OA transport. The apparent permeability (Pe) indicates that as lipophilicity increases, diffusion across the "unstirred" boundary layer becomes rate limiting. In support of this notion, transport of OA and HA was enhanced by agitation, showed an activation energy of 3.7 kcal/mol for OA, and resulted in identical Pe values for both transport directions. Analysis of Pe changes with varying alkyl chain length resulted in a delta G of -0.68 +/- 0.09 kcal/mol for -CH2-group transfer from an aqueous phase to the MDCK cells. When the intercellular tight junctions were opened by the divalent chelator EGTA in Ca2+/Mg2(+)-free HBSS, transport of the fluid-phase marker Lucifer yellow greatly increased because of paracellular leakage. PA transport also showed a significant increase, but OA transport was independent of EGTA. Although albumin also undergoes paracellular transport in the presence of EGTA and OA binds strongly to albumin, OA transport in EGTA solution was unchanged by albumin. These observations indicate that transmembrane transport is the major mechanism for lipophilic substances. The present study, together with earlier work on the transport of polar substances, shows that the MDCK cell monolayer is an excellent model of the transepithelial transport barrier.
Two strains of Madin Darby canine kidney (MDCK) cells were grown on a polycarbonate membrane with 3-micron pores without any extracellular matrix treatment. The membrane, 2.45 cm in diameter, which is part of a commercially obtained presterilized culture insert, provides two chambers when placed in a regular six-well culture plate. This device was found to be convenient for investigating transport of a few selected fluid-phase markers across the MDCK cell monolayer. Both the strain from the American Type Culture Collection (ATCC) and the so-called highly resistant strain I, at a serial passage between 65 and 70, showed a seeding concentration-dependent lag phase followed by a growth phase with a 21-hr doubling time. When seeded at 5 x 10(4) cells/cm2, cell confluence was achieved in 5 days in a modified Eagle's minimum essential medium (MEM) containing 10% fetal bovine serum under a 5% CO2 atmosphere. Similarly, transepithelial electrical resistance (TEER) also reached a plateau value in 5 days. Both light and electron microscopic examinations revealed well-defined junctional structures. Transport of the fluid-phase markers, sucrose, lucifer yellow CH (LY), inulin, and dextran across the MDCK cell monolayers was studied primarily at 37 degrees C following the apical-to-basolateral as well as the basolateral-to-apical direction. Large variations in the steady-state transport rate were observed for a given marker between the cell layer preparations. Thus, the present study proposes an "internal standard" procedure for meaningful comparisons of the transport rate. When normalized to the rate of sucrose, the rate ratio was 1.00:0.80:0.67:0.15 for sucrose:LY:inulin:dextran.(ABSTRACT TRUNCATED AT 250 WORDS)
Thyroxine replacement therapy for 21 adult patients with primary hypothyroidism was adjusted to the dosage at which each patient had a normal thyrotrophin (TSH) response to thyrotrophin releasing hormone (TRH). Clinical assessment and measurement of TSH (by sensitive immunoradiometric assay), free thyroxine (FT4) and free tri-iodothyronine (FT3) were made at this dosage and at higher and lower doses of thyroxine. Clinical observations, FT3 and FT4 assays were relatively insensitive to small alterations of thyroxine dosage, in contrast to which basal TSH measurements correlated well with TRH responsiveness and were sensitive to fine adjustments of thyroxine dosage.
The promoting effects of sodium salts of N-acyl-L-phenylalanines, p-substituted benzoic acids, saturated straight-chain fatty acids, saturated straight-chain α-bromofatty acids and N-acyl-N-methylglycines on the rectal absorption of sodium ampicillin (ABPC Na) were investigated in rats. The absorption-promoting effect of each carboxylic acid sodium salt was found to be parabolically correlated with its lipo-hydrophilic character (log P). The optimal log P value (log P0) of carboxylic acids exerting the maximum rectal absorption-promoting effect was in the range of 4.2-4.8. Among these carboxylic acids, sodium caprate was selected for examination of its rectal absorption-promoting action on four penicillins (ampicillin, sulbenicillin, piperacillin and mezlocillin) and eight cephalosporins (cephacetrile, ceftizoxime, cephalothin, cefazolin, cefmetazole, cefotiam, cefoperazone and cefpiramide). The extents of rectal absorption of the β-lactam antibiotics coadministered with sodium caprate were found to correlate well with the permeability of the drugs to cellulose membrane.
Because the exact site of thyroid hormone absorption in man is not known, we assessed the absorption of oral [125I]Na-L-T4 in patients with varying lengths of intact bowel and correlated this absorption with bowel length. Two normal subjects and five patients with surgical bowel resections, all of whom were euthyroid, were studied. Each received a tracer dose of [125I]Na-L-T4 orally, and serial samples of serum were assayed for radioactivity both with and without butanol extraction. The peak serum radioactivity in normal subjects occurred 2 h post ingestion and was 15% and 17% of the administered dose per liter serum and 11% and 13%/liter serum in butanol-extracted serum, respectively. In patients with shortened bowel, the peak radioactivity both in serum and butanol extracted serum was decreased, ranging from 2%-7% and 0%-5%/liter, respectively. There was no absorption of labeled T4 in the patient with a duodenum only. No consistent relationship was found between absorption and bowel length distal to the duodenum.
Sodium salts of medium chain fatty acids (MCFAs) enhance the absorption of hydrophilic drugs across the intestinal mucosa, but the mechanism behind the effect is largely unknown. In this study, the dose-dependent effects of the sodium salts of four MCFAs, C6 (caproate), C8 (caprylate), C10 (caprate) and C12 (laurate), on the permeability of the hydrophilic marker molecule [14C]mannitol were studied in monolayers of the human intestinal epithelial cell line, Caco-2, grown on permeable supports. C8, C10 and C12, but not C6, enhanced the permeability of [14C]mannitol in a dose-dependent manner. Comparison of the cellular effects of the MCFAs at concentrations that gave comparable (8.1- to 8.5-fold) absorption enhancement showed that: 1) C8 was active as absorption enhancer only when the tonicity of the medium was increased; 2) absorption enhancement mediated by C10 was related to a redistribution of the cytoskeleton and structural dilatations in the tight junctions; and 3) C12 was without effect on the cytoskeleton and cellular morphology. Studies on C10 under anisotonic conditions showed that deviations from isotonicity enhanced its effect. These results suggest that structurally similar MCFAs display dramatic differences in their mechanism of action. In addition, the effects of osmolality provide an explanation for the previously reported variability in the efficacy of MCFAs as absorption enhancers.
We report four female patients with nodular goiter (in two of the four due to Hashimoto's thyroiditis) and one male patient with frank hypothyroidism due to Hashimoto's thyroiditis in whom TSH-suppressive or replacement L-T4 therapy failed to suppress or, respectively, normalize serum TSH. As is typical in our country, our patients took L-T4 15-20 min before a light breakfast. Gastrointestinal or other diseases and drugs known to interfere with the intestinal absorption of L-T4 were not the cause of this failure. The gastrointestinal absorption test of L-T4 (1000 micrograms) was performed in four patients; in three patients it revealed peculiar abnormalities in that (i) the absorption peak was > 70% but occurred at 4 hr vs an average of 2 hr in 12 euthyroid controls (EC) and 3 hr in the 10 primary hypothyroid controls (HC); (ii) 50% of the maximal absorption occurred at 110 min vs 45 min in EC and 50 min in HC; (iii) the maximal increment in T4 absorption was between 90 and 120 min (+111%) vs between 30 and 60 min in EC (+312%) and HC (+354%). In sum, only the first part of the absorption curve of T4 was shifted to the right (in three of the four women) and this shift was more pronounced and extended to the second part of the curve in the fourth patient; in this last patient absorption peak was 44% at 180 min. Based on these results, we obtained full suppression or normalization of TSH by postponing breakfast for at least 60 min after T4 ingestion.(ABSTRACT TRUNCATED AT 250 WORDS)
To develop a set of minimum clinical guidelines for use by primary care physicians in the evaluation and management of patients with hyperthyroidism and hypothyroidism.
Guidelines were developed by a nine-member ad hoc Standards of Care Committee of the American Thyroid Association (the authors of this article). The participants were selected by the committee chair and the president of the American Thyroid Association on the basis of their clinical experience. The committee members represented different geographic areas within the United States, in order to take into account different practice styles.
Guidelines were developed on the basis of expert opinion of the participants, as well as on available published information.
Input was obtained from all of the participants, each of whom wrote an initial section of the document. A complete draft document was then written by three participants (P.A.S., D.S.C., and E.G.L.) and resubmitted to the entire committee for revision. The revised document was then submitted to the entire membership of the American Thyroid Association for written comments, which were then reviewed (mainly by P.A.S., D.S.C., and E.G.L.). Many of the suggestions of the American Thyroid Association members were incorporated into the final draft, which was then approved by the Executive Council of the American Thyroid Association. The entire process, from initial drafts to final approval, took approximately 18 months.
A set of minimum clinical guidelines for the diagnosis and treatment of hyperthyroidism and hypothyroidism were developed by consensus of a group of experienced thyroidologists. The guidelines are intended to be used by physicians in their care of patients with thyroid disorders, with the expectation that more effective care can be provided, and at a cost savings.
To the Editor.
—The article by Dr Singer and colleagues1 fails to discuss the treatment of congenital hypothyroidism diagnosed and treated in the newborn period. Because of almost universal screening for this condition, this omission is serious. Physicians treating hypothyroid newborns with the 4-μg/kg dose of levothyroxine recommended for children (on page 811 of the article) would be undertreating their patients. Such a dose is fine for a 6-year-old child with acquired disease, but not for a newborn in whom 8 to 10 μg/kg would be a more appropriate starting dose.
The mechanism of action of the absorption enhancers such as sodium caprate (C10) and decanoylcarnitine (DC) was examined. Both C10 and DC increased the epithelial permeability of fluorescein isothiocyanate dextran 4000 and decreased the transepithelial electrical resistance in Caco-2 cell monolayer. Irrespective of the presence or absence of mucosal calcium, C10 rapidly increased intracellular calcium levels dose-dependently. Compound 48/80, a phospholipase C inhibitor, prevented the increases of the intracellular calcium level and permeability of fluorescein isothiocyanate dextran 4000 by C10. Furthermore, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride, a strong calmodulin inhibitor, also significantly decreased the enhancing effect of C10. These results suggest that C10 releases calcium from intracellular stores via activation of phospholipase C in plasma membrane. The increase of the calcium levels was considered to induce the contraction of calmodulin-dependent actin microfilament, followed by dilatation of the paracellular route. Although DC also increased intracellular calcium levels, neither compound 48/80 nor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride decreased the enhancing effect of DC. The enhancing mechanisms were different for C10 and DC.
Enhanced flux of neutral solutes during transdermal iontophoresis is attributed largely to electroosmotic volume flow. In this study, the iontophoretic fluxes of tritiated water (3H2O) and 14C-labeled mannitol through hairless mouse skin (HMS) were determined. The following questions were addressed: (i) What is the variability of water flux during iontophoresis? (ii) To what extent is the iontophoretic flux of a neutral solute correlated with water flux? (iii) Does the intrinsic permeability of the skin to neutral solutes change following iontophoresis? (iv) What is the effect of low pH on electroosmotic volume flow? and (v) Does the skin remain permselective after removal of the stratum corneum? Transport of both water and mannitol reached steady-state levels during 10 hr of constant-current iontophoresis (0.36 mA/cm2). Anodal fluxes exceeded cathodal values. Cathodal mannitol flux was retarded, relative to passive transport, by net volume flow in the opposite direction, such that transport of this molecule increased significantly after the termination of current passage. Anodal equivalent volume flows for water and mannitol, respectively, were 2.7 (+/- 1.3) and 1.23 (+/- 0.59) microL/hr cm2, indicating that only approximately 50% of the water flux participated in the electroosmosis of mannitol. The passive permeability of water and mannitol after 10 hr of iontophoresis was, respectively, 6 and 30 times greater than the pretreatment values. At pH 7, the cationic permselectivity of HMS was marginal [the Na+ transport number (tNa+) was determined to be 0.46] and less than that reported for human skin.(ABSTRACT TRUNCATED AT 250 WORDS)
In an attempt to establish an in vitro/in situ correlation of intestinal permeability data, the permeability coefficients (Papp) for a series of model peptides, which were determined using an in situ perfused rat ileum model, were compared to the permeability coefficients (Pmono) determined using an in vitro cell culture model (Caco-2). The model peptides, which were all blocked on the N-terminal (acetyl, Ac) and the C-terminal (amide, NH2) ends, consisted of D-phenylalanine (F) residues (e.g., AcFNH2, AcFFNH2, AcFFFNH2). To alter the degree of hydrogen bonding potential, the nitrogens of the amide bonds were sequentially methylated [e.g., AcFF(Me)FNH2, AcF(Me)F(Me)FNH2, Ac(Me)F(Me)FNH2, Ac(Me)F(Me)F(Me)]. These peptides were shown not to be metabolized in the in situ perfused rat ileum system. The results of the transport experiments showed that there were poor correlations between the apparent permeability coefficients (Papp) determined in an in situ perfused rat ileum model and the octanol-water partition coefficients (r = 0.60) or the hydrogen bonding numbers (r = 0.63) of these peptides. However, good correlations were observed between the in situ Papp values for these peptides and their partition coefficients in heptane-ethylene glycol (r = 0.96) and the differences in their partition coefficients between octanol-water and isooctane-water (r = 0.86). These results suggest that lipophilicity may not be the major factor in determining the intestinal permeability of these peptides and that hydrogen bonding potential may be a major contributing factor. These results suggest that lipophilicity may not be the major factor in determining the intestinal permeability of these peptides and that hydrogen bonding potential may be a major contributing factor.(ABSTRACT TRUNCATED AT 250 WORDS)
The effects of the absorption enhancer sodium caprate on human intestinal epithelial cells were investigated using Caco-2 cell monolayers. The effects on epithelial integrity and drug transport are dependent on time and concentration and are decreased by Ca2+, most likely through the formation of Ca2+ soaps. Morphological data indicate that exposure to sodium caprate results in cytoskeletal changes and in structural alterations of the tight junctions in the form of dilatations, while the effects on the apical cell membranes are limited. We conclude that sodium caprate increases the absorption of drugs mainly by the paracellular route.
The effects of five different permeation enhancer systems on the transport properties of a peptidomimetic thrombin inhibitor. CRC 220, were investigated in monolayers of a human intestinal cell line (Caco-2).
The transepithelial transport rates and additionally the cytotoxic properties of these enhancers were characterized using the following tests: measurement of the transepithelial electrical resistance (TEER), the MTT-transformation, the protein content and the release of cytosolic lactate dehydrogenase (LDH), as well as FITC-phalloidin and propidium iodide staining.
All permeation enhancer systems showed concentration-dependent effects on cell permeability and toxicity. The most prominent effects on peptide transport were seen at the highest concentration (40 mM), yielding the rank order, NaTC > NaTC/Cholesterol > Solulan C24 > NaTC/Oleic acid > NaTC/PC18. Using the TEER after 120 min exposure as the most sensitive parameter describing cytotoxicity, the following order was obtained: Solulan C24 > NaTC > NaTC/PC18 = NaTC/Cholesterol > NaTC/Oleic acid > NaTC/PC. Generally, efficient enhancement of peptide transport was associated with a noticeable influence on cell viability under in-vitro conditions.
Taking into account permeation and cytotoxicity as a function of concentration, both NaTC at 15 mM and the mixed micellar system NaTC/oleic acid at 0.75 mM offer interesting enhancement properties, showing an 18-fold increase in CRC 220 transport rates. The effects on cell viability and cytotoxicity were comparatively low and of reversible nature.
Water-in-oil (w/o) microemulsions have been developed which, in addition to non-ionic medium-chain glycerides, incorporate ionic lipids, primarily medium-chain fatty acids, such as caprylic (C8) capric (C10) and lauric (C12) acids and their corresponding sodium salts. The absorption enhancing activity of w/o microemulsions incorporating these lipids was evaluated in the rat using Calcein (MW = 623) a water-soluble and poorly absorbed marker molecule.
Phase diagrams were constructed where C8/C10 or C12 fatty acids were treated as lipophilic surfactants and their sodium salts as hydrophilic ones. The anesthetised rat model was employed to evaluate Calcein absorption upon a single intraduodenal administration from a solution and the various w/o microemulsions.
A wide range of clear and transparent w/o microemulsions were obtained at ambient temperature either in liquid or solid form when a fixed blend of medium chain fatty acid/salt was titrated by a fixed ratio of the oil containing the oil-soluble mono- and diglycerides and deionized water or physiological saline. Upon intraduodenal administration in the anesthetised rat, the absorption of Calcein was improved from about 2% in aqueous solution up to about 37% in w/o microemulsions. Solid and liquid formulations were equally effective in improving bioavailability. The absorption enhancement activity of the fatty acids/salts followed the order C8 approximately C10 > C12. Absorption enhancement of Calcein was significantly reduced in the absence or presence of low levels of C8/C10 mono-/diglycerides.
These results further support the use of medium-chain glycerides and fatty acids/salts in microemulsion formulations to improve intestinal absorption of water-soluble compounds.
The mucus layer covering the surface of the gastrointestinal tract may act as a barrier to drug absorption. The aim of this investigation was to study the self-diffusion coefficients of model drugs with different physicochemical properties in gastrointestinal mucus. An in vitro method was used to determine the self-diffusion coefficients of radiolabeled model drugs in different diffusion media. Glucosamine, mannitol, glucuronic acid, glucose, metoprotol, antipyrine, propranolol, hydrocortisone, and testosterone, which display large differences in charge and octanol/water distribution ratios (K), were used as model drugs. The diffusion coefficients of model drugs were compared in phosphate buffer (PB), native pig intestinal mucus (PIM), and purified pig gastric much (PPGM). PIM was not purified and therefore contained all the original components of native mucus, whereas PPGM contained only high molecular weight mucin molecules. Charge had only minor effects on the diffusion coefficients of the model drugs. Lipophilicity, however, had a much larger effect, the largest decrease in diffusion coefficient, 58%, was observed for testosterone in PIM. A negative relationship between the diffusion coefficient and log K was observed in PIM, but no relationship was observed in PPGM and PB. In contrast, the diffusion coefficients for two larger molecules of comparable size, the lipophilic peptide cyclosporin and the hydrophilic peptide D-arginine vasopressin, were markedly reduced in PIM. In conclusion, the most important physicochemical characteristic influencing the diffusion coefficient of most drugs in gastrointestinal mucus appears to be lipophilicity, whereas molecular size appears to have more influence for larger peptide drugs.
The medium chain fatty acid sodium caprate (C10) is approved as an absorption enhancer but its mechanism of action has not been studied in humans. The aim of this study was to investigate the mechanism of action of C10 in human subjects after rectal administration.
Twelve healthy human subjects were randomised to receive ampicillin suppositories with (AM-C10) or without (AM) C10. Serum and urine samples were collected and analysed for ampicillin by HPLC. Rectal biopsies were taken before and 25 min (approximate time of maximum serum concentration, Cmax, for ampicillin) and 185 min (during the final part of the elimination phase) after rectal administration of the suppositories. The osmolality of the rectal fluid was also measured.
AM-C10 administration increased Cmax, area under the serum concentration-time curve (AUC) and urinary recovery of ampicillin 2.6-, 2.3- and 1.8-fold, respectively, compared to AM. Histological examination of the biopsies showed that AM-C10 exposure resulted in reversible mucosal damage that occurred at the same time as the Cmax for ampicillin while AM prolonged mucosal damage. A reversible increase in rectal fluid osmolality was observed with both treatments.
AM-C10-enhanced absorption of ampicillin coincides with non-specific damage to the rectal mucosa. C10 itself as well as the suppository base and the hyperosmolality of the rectal fluid contributed to this effect. However, the histological damage was reversible with AM-C10, suggesting that C10 also has a protective effect on the rectal mucosa.
In July 1995 we began noticing an unusually high rate of elevated TSH levels in patients with differentiated thyroid cancer treated with levothyroxine-specifically the brand Levothroid-becoming more obvious from September 1995. Faced with the possibility that these findings had some relationship to the drug taken, we carried out a prospective study, changing this brand of levothyroxine for another.
We studied 58 patients with differentiated thyroid carcinoma (50 women and eight men; aged 22-75 years) who were being treated with levothyroxine and who had previously had adequate TSH suppression. Their Levothroid tablets were changed to the same dose of Dexnon tablets, and their clinical and analytical response was evaluated 2 months later. The patients were divided into two groups according to their TSH level at the start of the study: group 1, 42 patients with TSH > 0.2 mU/l (not suppressed) and group 2, 16 patients with TSH < or = 0.2 mU/l (suppressed).
After 2 months with Dexnon the TSH levels in group 1 fell significantly (P < 0.0001) also decreasing in group (P < 0.09). The free T4 and free T3 rose significantly in both groups. After the change to Dexnon, 17 patients (40%) in group 1 had suppressed TSH and 26 (62%) had free T4 levels above the upper limit of normal vs none at baseline (P < 0.001). The group 2 patients maintained their inhibited TSH values after treatment with Dexnon, and the free T4 was above the upper limit of normal in 15 (94%) vs 3 (19%) at baseline (P < 0.001). The Levothroid tablets collected from the patients in both groups formed part of those which the manufacturer later withdraw from the market. These batches possessed the correct dosage, but they had been made from 'non-micronized' raw materials from another supplier.
The most probable cause of the inadequate TSH suppression in our patients was the reduction in bioavailability in certain batches of Levothroid, although we are unable to rule out the possibility that the results obtained after the changeover to Dexnon were due to its greater bioavailability. Simple changes in the manufacture of levothyroxine tablets may produce important variations in their bioavailability, having an adverse effect on the clinical control of the patients, and causing extra expense by the need for repeated patient visits and thyroid function tests.
Medium chain fatty acids (MCFAs) are used to enhance the permeability of mucosal tissues to hydrophilic drugs, but their mechanism of action is largely unknown. In this study, the absorption-enhancing effects of the sodium salts of two MCFAs, capric acid (C10) and lauric acid (C12), were studied in monolayers of human intestinal epithelial Caco-2 cells. Both MCFAs induced a rapid increase in epithelial permeability to the hydrophilic marker molecule sodium fluorescein. Inhibition of phospholipase C and inhibition or activation of various kinases and buffering of intracellular calcium indicated that the effects on epithelial permeability were mediated through phospholipase C-dependent inositol triphosphate/diacylglycerol pathways. Surprisingly, the inositol triphosphate and diacylglycerol pathways were found to have opposing effects on paracellular permeability. Exposure to the MCFAs also resulted in a concentration dependent reduction of cellular dehydrogenase activity and ATP levels. C10, but not C12, induced redistribution of the tight junction proteins ZO-1 and occludin. These results indicate that the two MCFAs have partially different and more complex mechanisms than previously recognized, which has important implications for their use in vivo.
The goal of this work was to investigate the use of MDCK (Madin-Darby canine kidney) cells as a possible tool for assessing the membrane permeability properties of early drug discovery compounds. Apparent permeability (Papp) values of 55 compounds with known human absorption values were determined using MDCK cell monolayers. For comparison, Papp values of the same compounds were also determined using Caco-2 cells, a well-characterized in vitro model of intestinal drug absorption. Monolayers were grown on 0. 4-microm Transwell-COL membrane culture inserts. MDCK cells were seeded at high density and cultured for 3 days, and Caco-2 cells were cultured under standard conditions for 21 to 25 days. Compounds were tested using 100 microM donor solutions in transport medium (pH 7.4) containing 1% DMSO. The Papp values in MDCK cells correlated well with those in Caco-2 cells (r2 = 0.79). Spearman's rank correlation coefficient for MDCK Papp and human absorption was 0.58 compared with 0.54 for Caco-2 Papp and human absorption. These results indicate that MDCK cells may be a useful tool for rapid membrane permeability screening.
Different absorption enhancing principles for a potent cyclopeptidic alpha(nu)beta(3)-antagonist (EMD 121974) were investigated in monolayers of a human intestinal cell line (Caco-2). Transepithelial transport was quantitated by reversed-phase high-performance liquid chromatography. Cytotoxic effects were characterized by determination of transepithelial electrical resistances (TEERs), propidium iodide (PI)-influx, FITC-phalloidin staining and the release of cytosolic lactate dehydrogenase (LDH). Medium chain fatty acids (MCFAs, NaC10, NaC12) and taurocholate (NaTC) were the most efficient enhancers of cyclopeptide and FITC-dextran 4400 permeability coefficients, displaying different time profiles of activity. Whereas NaTC (15 mM) showed almost a constant permeation enhancing effect from 20 min up to 120 min (ca. 12-fold), MCFA absorption enhancement was markedly dependent on incubation time (NaC10, 20 min: 1.2-fold, 120 min: 17-fold; NaC12, 20 min: 4.3-fold, 120 min: 13-fold). All cytotoxicity assays demonstrated that MCFAs were significantly more cytotoxic than NaTC. Ion pairing with hydrophobic amino acids and heptane sulfonate distinctly increased octanol-buffer partition coefficients of the cationic cyclopeptide but did not enhance its transepithelial permeability. Nanoparticles as well as beta-cyclodextrin neither affected integrity of the cells nor transport properties of the cyclopeptide. In summary, significant absorption enhancement was only observed with NaTC or MCFAs. Increase in permeability coefficients using NaTC occurred rapidly with acceptable cytotoxicities and merits further investigations.
Thyroid hormone has profound effects on the heart and peripheral vascular system. This is best demonstrated by the characteristic changes in cardiovascular hemodynamics that accompany both hyper- and hypothyroidism. These effects can be explained by the ability of thyroid hormone to regulate expression of specific cardiac genes as well as to alter systemic vascular resistance. Treatment of the underlying disease process predictably reverses these changes and restores normal cardiovascular physiology. Recent observations suggest therapeutic benefit of thyroid hormone when administered short term to patients who have undergone cardiac surgery and also when given to patients with varying degrees of heart failure. The rapidity of these effects suggests nonnuclear sites of action that may involve membrane ion channel function causing altered myocyte contractility and excitability. This in turn could explain the varied effects of thyroid hormone on cardiac rhythm disturbances and on vascular tone. Thus, the clinical signs and symptoms of thyroid disease are the result of both nuclear and nonnuclear actions of thyroid hormone on the heart and systemic vasculature.
The absorption enhancement by the sodium salts of several fatty acids was investigated in rat large intestine for model compounds having a wide range of molecular weight. Sodium caprylate (C8), sodium caprate (C10), sodium laurate (C12), which are categorized in medium-chain fatty acid, and sodium oleate (C18:1), long-chain unsaturated fatty acid, were employed as lipoidal adjuvants. Phenol red (MW=354.4), glycyrrhizin (822.9), fluorescein isothiocyanate-dextran-4 (FD-4, 4400), FD-10 (9400) and FD-40 (38900) were selected as model compounds for the assessment of the enhancing effect of the lipoidal adjuvants. The absorption of phenol red was promoted at the highest level, about 20 times higher by C12 and C18:1 than the control. The absorption rate - time profiles calculated by deconvolution method showed that C12 takes effect most rapidly and efficiently. In the case of glycyrrhizin, four adjuvants including C12 showed almost the same improvement of the absorption, about 30-40 times larger than the control. C8 and sodium citrate did not significantly enhance the absorption of those model compounds. For FD-4, FD-10 and FD-40, C10, C12 and C18:1 revealed almost the same enhancing effect and the absorption of FD-4, FD-10 and FD-40 was enhanced about 80 times, 1000-1800 times and about 200 times, respectively, larger than the control. The enhancement ratio, the ratio of AUC with adjuvant to AUC of control, suggests that these lipoidal adjuvants would improve most efficiently the absorption of the compound having the molecular weight of around 10000. Furthermore, C12 was suggested to be an effective adjuvant for the compounds with the wide range of molecular weight.
The advent of more efficient methods to synthesize and screen new chemical compounds is increasing the number of chemical leads identified in the drug discovery phase. Compounds with good biological activity may fail to become drugs due to insufficient oral absorption. Selection of drug development candidates with adequate absorption characteristics should increase the probability of success in the development phase. To assess the absorption potential of new chemical entities numerous in vitro and in vivo model systems have been used. Many laboratories rely on cell culture models of intestinal permeability such as, Caco-2, HT-29 and MDCK. To attempt to increase the throughput of permeability measurements, several physicochemical methods such as, immobilized artificial membrane (IAM) columns and parallel artificial membrane permeation assay (PAMPA) have been used. More recently, much attention has been given to the development of computational methods to predict drug absorption. However, it is clear that no single method will sufficient for studying drug absorption, but most likely a combination of systems will be needed. Higher throughput, less reliable methods could be used to discover 'loser' compounds, whereas lower throughput, more accurate methods could be used to optimize the absorption properties of lead compounds. Finally, accurate methods are needed to understand absorption mechanisms (efflux-limited absorption, carrier-mediated, intestinal metabolism) that may limit intestinal drug absorption. This information could be extremely valuable to medicinal chemists in the selection of favorable chemo-types. This review describes different techniques used for evaluating drug absorption and indicates their advantages and disadvantages.
Levothyroxine is the overwhelming choice of clinicians for the treatment of hypothyroidism and for the suppression of goitre and thyroid nodules in selected cases. The monitoring of serum levels of thyroid stimulating hormone is necessary for appropriate dosage adjustment of levothyroxine. Levothyroxine has a narrow therapeutic index: both underdosage (subclinical hypothyroidism) and excessive dosage (subclinical hyperthyroidism) are associated with adverse symptoms and pathophysiological effects and are to be avoided. The consequent necessity for careful titration of doses has had an impact on the issue of switchability, or bioequivalence, of the various marketed levothyroxine products. In this article, the basis for concern about currently accepted standards of the FDA for pharmacological bioequivalence are examined in the context of levothyroxine. The history and status of the recent request by the FDA for a new drug application for all levothyroxine products, and its impact on the market leader Synthroid, is also discussed.
At the present time, optimal therapy for hypothyroidism requires replacement of the deficiency in thyroid hormone with synthetic levothyroxine. Precise titration of this narrow therapeutic index drug is necessary to return the patient to a chemically and clinically euthyroid state. Seven levothyroxine formulations are Food and Drug Administration (FDA)-approved and four are available to the physician. Proper dosage is established based on thyrotropin (TSH) testing and clinical evaluation. Each levothyroxine preparation must comply with FDA standards for bioavailability but may vary with respect to its dissolution and absorption properties and are not interchangeable. This equivalence testing is done on normal volunteers and requires a suprapharmacologic dose of levothyroxine in order to make the determination of bioavailability. In this review we discuss the various methods to evaluate therapeutic efficacy and bioequivalence of levothyroxine preparations in the treatment of thyroid disease. These are relevant to the physician and patient because small differences in the efficacy can produce unwanted effects of either underreplacement or overreplacement.
Since its inception in 1995, the biopharmaceutical classification system (BCS) has become an increasingly important tool for regulation of drug products world-wide. Until now, application of the BCS has been partially hindered by the lack of a freely available and accurate database summarising solubility and permeability characteristics of drug substances. In this report, orally administered drugs on the Model list of Essential Medicines of the World Health Organization (WHO) are assigned BCS classifications on the basis of data available in the public domain. Of the 130 orally administered drugs on the WHO list, 61 could be classified with certainty. Twenty-one (84%) of these belong to class I (highly soluble, highly permeable), 10 (17%) to class II (poorly soluble, highly permeable), 24 (39%) to class III (highly soluble, poorly permeable) and 6 (10%) to class IV (poorly soluble, poorly permeable). A further 28 drugs could be provisionally assigned, while for 41 drugs insufficient or conflicting data precluded assignment to a specific BCS class. A total of 32 class I drugs (either certain or provisional classification) were identified. These drugs can be further considered for biowaiver status (drug product approval based on dissolution tests rather than bioequivalence studies in humans).