Imen Aissa

University of Sfax, Şafāqis, Şafāqis, Tunisia

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Publications (12)19.22 Total impact

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    ABSTRACT: Ascorbyl lipophilic derivatives (Asc-C2 to Asc-C18:1), were synthesized in a good yield using lipase from Staphylococcus xylosus produced in our laboratory and immobilized onto silica aerogel. Results showed that esterification had little effect on radical-scavenging capacity of purified ascorbyl esters using DPPH assay in ethanol. However, long chain fatty acids esters displayed higher protection of target-lipids from oxidation. Moreover, compared to ascorbic acid, synthesized derivatives exhibited an antibacterial effect. Furthermore, ascorbyl derivatives were evaluated, for the first time, for their antileishmanial effects against visceral (Leishmania infantum) and cutaneous parasites (Leishmania major). Among all the tested compounds, only Asc-C10, Asc-C12 and Asc-C18:1 exhibited antileishmanial activities. The interaction of ascorbyl esters with a phospholipid monolayer showed that only medium and unsaturated long chain (Asc-C10 to Asc-C18:1) derivative esters were found to interact efficiently with mimetic membrane of leishmania. These properties would make ascorbyl derivatives good candidates to be used in cosmetic and pharmaceutical lipophilic formulations.
    Journal of agricultural and food chemistry. 08/2014;
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    ABSTRACT: A new L-amino acid oxidase (LAAO) from Cerastes cerastes snake venom, named CC-LAAO, was purified to homogeneity using a combination of size-exclusion, ion-exchange and affinity chromatography. CC-LAAO is a homodimeric glycosylated flavoprotein with a molecular mass around 58 kDa under reducing conditions and about 115 kDa in its native form when analysed by SDS-PAGE and gel filtration chromatography, respectively. This enzyme displayed a Michaelis-Menten behavior with an optimal pH at 7.8. However, unlike known SV-LAAOs which display their maximum activity at 37 °C, CC-LAAO has an optimal temperature at 50 °C. Kinetic studies showed that the enzyme displayed high specificity towards hydrophobic L-amino acids. The best substrates were L-Phe, L-Met and L-Leu. CC-LAAO activity was inhibited by the substrate analog N-acetyl tryptophan. The N-terminal amino acid sequence of this protein was determined by automated Edman degradation. The CC-LAAO cDNA was cloned from the venom gland total RNA preparation. The cDNA sequence contained an open-reading frame (ORF) of 1551-bp, which encoded a protein of 516 amino acids comprising a signal peptide of 18 amino acids and 498-residues mature protein. CC-LAAO sequence and its tertiary model shared high similarity with other snake venom LAAOs.
    Toxicon : official journal of the International Society on Toxinology. 07/2014;
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    ABSTRACT: Recombinant DNA methods are being widely used to express proteins in both prokaryotic and eukaryotic cells for both fundamental and applied research purposes. Expressed protein must be well characterized to be sure that it retains the same properties as the native one, especially when expressed protein will be used in the pharmaceutical field. In this aim, interfacial and kinetic properties of native, untagged recombinant and tagged recombinant forms of a pancreatic lipase were compared using the monomolecular film technique. Turkey pancreatic lipase (TPL) was chosen as model. A kinetic study on the dependence of the stereoselectivity of these three forms on the surface pressure was performed using three dicaprin isomers spread in the form of monomolecular films at the air-water interface. The heterologous expression and the N-His-tag extension were found to modify the pressure preference and decrease the catalytic hydrolysis rate of three dicaprin isomers. Besides, the heterologous expression was found to change the TPL regioselectivity without affecting its stereospecificity contrary to the N-tag extension which retained that regioselectivity and changed the stereospecificity at high surface pressures. The study of parameters, termed Recombinant expression Effects on Catalysis (REC), N-Tag Effects on Catalysis (TEC), and N-Tag and Recombinant expression Effects on Catalysis (TREC) showed that the heterologous expression effects on the catalytic properties of the TPL were more deleterious than the presence of an N-terminal tag extension.
    PLoS ONE 01/2014; 9(8):e104221. · 3.53 Impact Factor
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    ABSTRACT: a b s t r a c t Preparation of dopamine derivatives was carried out as a response to the increasing demand for new lipophilized antioxidants in food, cosmetic and pharmaceutical industries. A large series of dopamine esters (DA-C 3 to DA-C 18:1) with increasing lipophilicity was synthesized using lipase from Candida antarctica (Novozyme 435) as a biocatalyst. The highest conversion yield (52.75%) was reached when caprylic acid (DA-C 8) was used as acyl donor. Synthesized compounds were purified and evaluated for their antioxidant activity using the DPPH and the ABTS tests. Results showed that esterification had little effect on radical-scavenging capacity. However, long chain fatty acid esters displayed higher protective effect of oil against oxidation at 70 • C as compared to the parent dopamine or to the BHT. The hemolytic activity of dopamine esters was studied. Middle chain length derivatives (DA-C 8 and DA-C 12) of dopamine and oleic acid derivative (DA-C 18:1) showed the highest hemolytic activity against human erythrocyte. The antimicrobial activities of dopamine esters were also evaluated using well diffusion and minimal inhibi-tion concentration methods. Among all the tested compounds, DA-C 8 and DA-C 12 exhibited the highest antibacterial activities. These results open up potential applications by using dopamine derivatives as antioxidants and antimicrobial compounds in cosmetic, food and pharmaceutical industries.
    Process Biochemistry. 08/2013; 48:1481-1487.
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    ABSTRACT: a b s t r a c t Preparation of dopamine derivatives was carried out as a response to the increasing demand for new lipophilized antioxidants in food, cosmetic and pharmaceutical industries. A large series of dopamine esters (DA-C 3 to DA-C 18:1) with increasing lipophilicity was synthesized using lipase from Candida antarctica (Novozyme 435) as a biocatalyst. The highest conversion yield (52.75%) was reached when caprylic acid (DA-C 8) was used as acyl donor. Synthesized compounds were purified and evaluated for their antioxidant activity using the DPPH and the ABTS tests. Results showed that esterification had little effect on radical-scavenging capacity. However, long chain fatty acid esters displayed higher protective effect of oil against oxidation at 70 • C as compared to the parent dopamine or to the BHT. The hemolytic activity of dopamine esters was studied. Middle chain length derivatives (DA-C 8 and DA-C 12) of dopamine and oleic acid derivative (DA-C 18:1) showed the highest hemolytic activity against human erythrocyte. The antimicrobial activities of dopamine esters were also evaluated using well diffusion and minimal inhibi-tion concentration methods. Among all the tested compounds, DA-C 8 and DA-C 12 exhibited the highest antibacterial activities. These results open up potential applications by using dopamine derivatives as antioxidants and antimicrobial compounds in cosmetic, food and pharmaceutical industries.
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    ABSTRACT: A lipolytic activity was located in the scorpion venom glands (telsons), from which a phospholipase A2 (Sm-PLVG) was purified. Like known phospholipases A2 from scorpion venom, which are 14-18 kDa proteins, the purified Scorpio maurus-Phospholipase from Venom Glands (Sm-PLVG) has a molecular mass of 17 kDa containing long and short chains linked by disulfide bridge. It has a specific activity of 5500 U/mg measured at 47°C and pH 8.5 using phosphatidylcholine as a substrate in presence of 8 mM NaTDC and 12 mM CaCl2. The NH2-terminal amino acid sequences of the purified Sm-PLVG showed similarities with those of long and short chains of some previously purified phospholipases from venom scorpions. Moreover, the Sm-PLVG exhibits hemolytic activity towards human, rabbit or rat erythrocytes. This hemolytic activity was related to its ability to interact with phospholipids' monolayer at high surface pressure. These properties are similar to those of phospholipases isolated from snake venoms.
    Toxicon 07/2013; · 2.92 Impact Factor
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    ABSTRACT: New tyrosyl ester derivative, a naturally occurring phenol with interesting biological properties, has been synthesized in good yield by a direct esterification of tyrosol (Ty) with p-hydroxyphenylacetic acid (p-HPA) using Candida antarctica lipase as a catalyst. The response surface methodology was used to modulate the effects of the enzyme amount (10–50 mg), the tert-butanol/hexane (v/v) ratio (0.16–0.84), the temperature (35–55 °C) and the reaction time (15–45 h) on the tyrosyl hydroxyphenylacetate (Ty-HPA) conversion yield. Under the optimal predicted conditions (enzyme amount: 10 mg, solvents volume ratio 0.16, reaction temperature; 45 °C and 34 h of incubation), a high conversion yield of 79.33 ± 4% was reached. The obtained ester was purified and characterized by NMR, LC/MS and FT-IR methods. ABTS free radical quenching potency demonstrated that the esterified tyrosol (Ty-HPA) was more effective than the natural separated antioxidants: Ty and p-HPA. Furthermore, when used at a non-cytotoxic concentration (100 μM), tyrosyl ester showed significant effectiveness in preventing iron-induced oxidative stress in blood cells compared to the two separated compounds. The antibacterial activity of Ty, p-HPA, mixed solution of Ty + p-HPA and Ty-HPA was performed by determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using a micro-well dilution method. Compared to the separated substrates, synthesized ester exhibits the most antibacterial effect mainly against Gram+ bacteria.
    Process Biochemistry. 12/2012; 47(12):2356–2364.
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    ABSTRACT: A lipolytic activity was located in the chicken uropygial glands, from which a carboxylesterase (CUE) was purified. Pure CUE has an apparent molecular mass of 50 kDa. The purified esterase displayed its maximal activity (200 U/mg) on short-chain triacylglycerols (tributyrin) at a temperature of 50°C. No significant lipolytic activity was found when medium chain (trioctanoin) or long chain (olive oil) triacylglycerols were used as substrates. The enzyme retained 75% of its maximal activity when incubated during 2h at 50°C. The NH(2)-terminal amino acid sequence showed similarities with the esterase purified recently from turkey pharyngeal tissue. Esterase activity remains stable after its incubation during 30 min in presence of organic solvents such as hexane or butanol. CUE is a serine enzyme since it was inactivated by phenylmethanesulphonyl fluoride (PMSF), a serine-specific inhibitor. The purified enzyme, which tolerates the presence of some organic solvent and a high temperature, can be used in non-aqueous synthesis reactions. Hence, the uropygial esterase immobilised onto CaCO(3) was tested to produce the isoamyl and the butyl acetate (flavour esters). Reactions were performed at 50°C in presence of hexane. High synthesis yields of 91 and 67.8% were obtained for isoamyl and butyl acetate, respectively.
    International journal of biological macromolecules 04/2012; 50(5):1238-44. · 2.37 Impact Factor
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    ABSTRACT: Preparation of tyrosyl lipophilic derivatives was carried out as a response to the food, cosmetic and pharmaceutical industries' increasing demand for new lipophilic antioxidants. A large series of tyrosyl esters (TyC₂ to TyC₁₈:₁) with increasing lipophilicity was synthesized in a good yield using lipase from Candida antarctica (Novozyme 435). Spectroscopic analyses of purified esters showed that the tyrosol was esterified on the primary hydroxyl group. Synthetized compounds were evaluated for either their antimicrobial activity, by both diffusion well and minimal inhibition concentration (MIC) methods, or their antileishmanial activity against Leishmania major and Leishmania infantum parasite species.Among all the tested compounds, our results showed that only TyC₈, TyC₁₀ and TyC₁₂ exhibited antibacterial and antileishmanial activities. When MIC and IC50 values were plotted against the acyl chain length of each tyrosyl derivative, TyC₁₀ showed a parabolic shape with a minimum value. This nonlinear dependency with the increase of the chain length indicates that biological activities are probably associated to the surfactant effectiveness of lipophilic derivatives. These results open up potential applications to use medium tyrosyl derivatives surfactants, antioxidants, antimicrobial and antileishmanial compounds in cosmetic, food and pharmaceutical industries.
    Lipids in Health and Disease 01/2012; 11:13. · 2.31 Impact Factor
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    ABSTRACT: Waxes are esters of long-chain fatty acids and long-chain alcohols. Their principal natural sources are animals (sperm whale oil) and vegetables (jojoba) which are expensive and not easily available. Wax esters synthesized by enzymatic transesterification, using palm stearin as raw material, can be considered as an alternative to natural ones. Palm stearin is a solid fraction obtained by fractionation of palm oil. Palm stearin was esterified with cetyl alcohol to produce a mixture of wax esters. A non-commercial immobilized lipase from Rhizopus oryzae was used as biocatalyst. Response surface methodology was employed to determine the effects of the temperature (30-50 °C), the enzyme concentration (33.34-300 IU/mL), the alcohol/palm stearin molar ratio (3-7 mol/mol) and the substrate concentration (0.06-0.34 g/mL) on the conversion yield of palm stearin. Under optimal conditions (temperature, 30 °C; enzyme concentration, 300 IU/mL; molar ratio 3 and substrate concentration 0.21 g/mL) a high conversion yield of 98.52% was reached within a reaction time of 2 h. Response surface methodology was successfully applied to determine the optimum operational conditions for synthesis of palm stearin based wax esters. This study may provide useful tools to develop economical and efficient processes for the synthesis of wax esters.
    BMC Biotechnology 06/2011; 11:68. · 2.17 Impact Factor
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    ABSTRACT: The ability of a noncommercial immobilized lipase from Staphylococcus xylosus (SXLi) to catalyze the transesterification of tyrosol and ethyl acetate was investigated. Response surface methodology was used to evaluate the effects of the temperature (40-60 degrees C), the enzyme amount (50-500 UI), and the ethyl acetate/hexane volume ratio (0.2-1) on the tyrosol acetylation conversion yield. Two independent replicates were carried out under the optimal conditions predicted by the model (reaction temperature 54 degrees C, enzyme amount 500 UI, and volume ratio ethyl acetate/hexane 0.2). The maximum conversion yield reached 95.36 +/- 3.6%, which agreed with the expected value (96.8 +/- 3.7%). The ester obtained was characterized by spectroscopic methods. Chemical acetylation of tyrosol was performed, and the products were separated using HPLC. Among the eluted products from HPLC, mono- and diacetylated derivatives were identified by positive mass spectrometry. Tyrosol and its monoacetylated derivative exert similar antiradicalar activity on 2,2-diphenyl-1-picrylhydrazyle.
    Journal of Agricultural and Food Chemistry 01/2008; 55(25):10298-305. · 2.91 Impact Factor
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    ABSTRACT: Lipase-catalyzed synthesis of eight fatty acid tyrosyl esters (TyC2 to TyC18:1) was investigated using non commercial lipases from Rhizopus oryzae and Staphylococcus xylosus immobilized onto CaCO3. The monomolecular film technique was used to compare the ability of the various synthesized tyrosyl fatty acid esters to form a stable monolayer at the air/water interface and their capacity to interact with a phospholipid monolayer. The measurements of surface pressure versus the molecular area shows that, in contrast to tyrosol esterified with short and medium chains (acetic (TyC2), propionic (TyC3), caprylic (TyC8) and capric (TyC10) acids), tyrosol esterified with long chains: lauric (TyC12), palmitic (TyC16), stearic (TyC18) and oleic (TyC18:1) acids are able to form a stable monolayer at the air/water interface. A direct correlation was observed between the length of the saturated acyl chain of the derivatives and their corresponding collapse pressures. The presence of unsaturation reduces the collapse pressure value. The interaction of tyrosyl esters with a phospholipid monolayer was studied and the critical surface pressure (πc) of each ester was determined. Only medium and long chain (TyC8 to TyC18:1) derivatives esters were found to interact efficiently with DiC12PC film.
    Journal of Molecular Catalysis B Enzymatic 83:125–130. · 2.82 Impact Factor