The effect of polyethylene glycol recombinant human growth hormone on growth and glucose metabolism in hypophysectomized rats
To study the effect of polyethylene glycol recombinant human growth hormone on growth and glucose metabolism in hypophysectomized rats, and compare the effect of treatment between recombinant human growth hormone (rhGH) and polyethylene glycol rhGH (PEG-rhGH). Hypophysectomy was performed in juvenile rats to build the animal model of GH deficiency. The hypophysectomized animals were randomly assigned into three groups and treated with saline (negative control, n=20), rhGH (n=20) and PEG-rhGH (n=20). A sham operation was performed to set up the normal control (n=20). Body weight, body length and tail length were recorded every 2days for a 14-day treatment and bone growth was measured at the end of therapy. Glucose infusion rate (GIR) determined by euglycemic hyperinsulinemic clamp was used to evaluate insulin sensitivity after GH treatment. We also examined plasma glucose and serum insulin levels Compared with the negative control, the body weight, body length, tail length and bone growth increased significantly in hypophesectomized rats treated by GH (P<0.01). Although the weight gain in the first 10days was higher in the PEG-rhGH group than in the rhGH group (P<0.05), the growth promoting effect was similar between rhGH and PEG-rhGH (P>0.05). Neither rhGH nor PEG-rhGH impaired glucose tolerance of rats after hypophesectomy. Compared with negative controls, according to decreased serum insulin, reduced insulin expression in pancreatic cells and increased GIR in the clamp, both rhGH and PEG-rhGH groups had improved insulin sensitivity within 14 days (P<0.01). However, with prolonged treatment, the GIR in the rhGH-treated rats decreased significantly (P<0.05); while PEG-rhGH did not interfere with GIR, even after a doubled dose (P>0.05). PEG-rhGH had the same linear growth promoting efficacy as unmodified rhGH. The short-term GH replacement could improve insulin sensitivity in hypophysectomized rats, especially after PEGylation.
[Show abstract] [Hide abstract] ABSTRACT: Delivery of proteins/peptides in gastrointestinal (GI) tract via peroral/oral route involves tremendous challenges due to unfavorable environmental conditions like harsh pH, presence of proteolytic enzymes and absorption barriers. Detailed research is being conducted at academic and industrial level to diminish these troubles and various products are under clinical trials. Several approaches have been established to optimize oral delivery of proteins and peptides and can be broadly categorized into chemical and physical strategies. Chemical strategies include site specific mutagenesis, proteinylation, glycosylation, PEGylation and prodrug approaches, whereas physical strategies comprise of formulation based approaches including application of absorption enhancers and metabolism modifiers along with delivering them via colloidal carrier systems such as nanoparticles, liposomes, microparticles, micro- and nano-emulsions. This review stands to accomplish the diverse aspects of oral delivery of proteins/peptides and summarizes the key concepts involved in targeting the biodrugs to specific sites of GI tract such as, intestine and colon. Furthermore some light has also been shed on the current industrial practices followed in developing oral formulations of such bioactives.
- "Mono-PEGylation of bovine lactoferrin, an anticancer iron-binding glycoprotein, enhanced its resistance towards proteolytic degradation in the GI fluid and increased its oral absorption (10-folds) in comparison to unmodified lactoferrin  . A PEGylated version of human growth hormone represented similar activity, in terms of growth, as unmodified form but enhanced the sensitivity of insulin in hypophysectomized rats when tested with respect to glucose metabolism . Youn et al. developed a Lys 18 -amine specific PEGylated derivative of salmon calcitonin for oral administration and results suggested that PEGylated protein has enhanced resistance against pancreatic peptidases and brush-border peptidases along with reduced systemic clearance. "
- [Show abstract] [Hide abstract] ABSTRACT: To explore the mechanism and effect of maternal high-fat diet before and during pregnancy on bone growth of neonatal offspring rats. Forty female Sprague-Dawley rats were divided into high-fat diet and control groups (n=20) that were fed with 35% high-fat diet and standard chow, respectively. After 8 weeks, 8 female rats from each group were sacrificed for liver pathological examinations and the other female rats were mated with male rats and fed continuously with 35% high-fat diet and standard chow throughout gestation, respectively. The body lengths (from apex nasi to end of tail) of the offspring rats from both groups were measured within 24 hours after birth. Enzyme-linked immunosorbent assay was used to detect serum insulin-like growth factor (IFG-I) levels. Liver pathological changes were observed under a light microscope. The expression of insulin receptor substrate 1 (IRS-1) and phosphorylation IRS-1 (Phospho-IRS-1) in tibia and femur samples were detected by immunohistochemistry. The expression of mitogen-activated protein kinase (MAPK) and phosphorylation MAPK (Phospho-MAPK), phosphatidylinositol 3-kinase (PI3K) and phosphorylation PI3K (Phospho-PI3K), protein kinase B (AKT1) and phosphorylation AKT1 (Phospho-AKT1) in tibia and femur samples were detected by Western blot. The offspring rats from the high-fat diet group showed a significant shorter body length compared with those from the control group (P<0.05). The level of serum IGF-I in offspring rats from the high-fat diet group decreased by 20.1% in comparison to those from the control group, but there was no significant difference between the two groups (P>0.05). Fatty degeneration was found in livers of both high-fat diet-fed maternal rats and their offspring rats under a light microscope. There were no significant differences in IRS-1 and Phospho-IRS-1 expression in chondrocytes of tibia and femur samples between the offspring rats of the two groups (P>0.05). The protein expression of MAPK in chondrocytes of tibia and femur samples of offspring rats from the high-fat diet group was higher than that from the control group (P<0.05). There were no significant differences of PI3K and AKT1/Phospho-AKT1 between the offspring rats of the two groups (P>0.05). A maternal high-fat diet before and during pregnancy may affect the bone growth of offspring rats in utero, which is possibly associated with the decreased IGF-I level. However, further study on the exact mechanism of IGF-I on the bone growth is needed.