Yassine Mallem

β-Adrenoceptor-mediated vascular relaxation in spontaneously hypertensive rats

Abstract Although the impairment of beta-adrenoceptor (β-AR)-induced vascular relaxation to isoprenaline has been extensively described, discrepancy persisted in the literature. In this work, we investigated β-AR-induced relaxation in spontaneously hypertensive and normotensive rats aorta. We attempted to determine β-AR subtypes involved in order to understand the conflicting data regarding the β-AR-induced vasodilation to isoprenaline. Aortic rings isolated from 12-week-old Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs) were placed in organ baths and constricted with phenylephrine (α 1 -AR agonist). Then, cumulative concentration–relaxation curves (CCRC) to AR agonists were constructed. In intact aortic rings from both strains, isoprenaline (a nonselective β-AR agonist) (0.001–10 μM) induced similar concentration-dependent relaxations. CCRC was shifted to the right and upward in the presence of nadolol (a nonspecific β 1 and β 2 -AR antagonist) (10 μM). After endothelium removal, the response to isoprenaline was partly inhibited in WKY rats, but was strongly inhibited in SHRs. In WKY rats, isoprenaline-induced endothelium-independent relaxation was not modified in the presence of nadolol but was inhibited in the presence of CGP 20712A (low-affinity-state β 1 -AR antagonist). In endothelium-denuded rings, SR 58611A (a preferential β 3 -AR agonist) (0.1–30 μM) produced a very small relaxation in both strains. In WKY rats, CGP 12177 (CGP) (0.1–30 μM) and cyanopindolol (0.01–3 μM) (partial β 3 -AR and low-affinity-state β 1 -AR agonists with β 1 -AR and β 2 -AR antagonistic properties) produced endothelium-independent relaxations. CGP-induced effect was significantly inhibited by CGP 20712A (10 μM) or bupranolol (10 μM) (low-affinity-state β 1 -AR antagonists). In SHRs, similarly to the impaired endothelium-independent relaxation to isoprenaline, endothelium-independent relaxations to CGP and cyanopindolol were greatly blunted. These relaxations were not modified in the presence of CGP 20712A. In endothelium-denuded rings pretreated with pertussis toxin, CGP-induced relaxation was not modified in WKY rats, but was partly restored in SHRs. In conclusion, these results showed, that in 12-week-old SHRs, the endothelium-independent component of the relaxation to isoprenaline was impaired, and this impairment could involve the low-affinity-state β 1 -AR. G i protein overexpression and/or overstimulation may be possible factors that contribute to this alteration in hypertension.

Separation and Biological Activities of Phospholipase A2 (Mb-PLA2) from the Venom of Montivipera bornmuelleri, a Lebanese Viper

Phospholipase A2 (PLA2), a common toxic component of snake venom, is responsible for a wide spectrum of biological and toxicological effects including bactericidal, anticoagulant, hemolytic, as well as neurotoxic and cardiotoxicity activities. In the present work, phospholipase A2 named (Mb-PLA2) was isolated from the venom of Montivipera bornmuelleri a Lebanese snake, by a two-step procedure consisting of gel filtration chromatography on Biogel P60 and reverse phase high pressure liquid chromatography (RP-HPLC) on a Restek Ultra II C18 column. The experimentally determined molecular weight of the Mb-PLA2 was 13650 Da, which was determined by electrospray ionization mass spectrometry and close to 14400 Da as judged by SDS-PAGE electrophoresis. The isolated Mb-PLA2 was evaluated for bactericidal activity against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Mb-PLA2 showed strong antibacterial activity against the Gram positive bacteria S. aureus, followed by the Gram negative bacteria, E. coli, and then P. aeruginosa. Moreover, the Mb-PLA2 exhibited hemolytic activity toward human erythrocyte, as well as an anticoagulant activity when evaluated on human plasma.

Protein Content Analysis and Antimicrobial Activity of the Crude Venom of Montivipera bornmuelleri; a Viper from Lebanon

Viperidae snakes venoms represent a source of efficient bioactive components that have already led to the development of several new drugs. In this work, we analyzed the protein content of the Montivipera bornmuelleri crude venom using LC-ESI-MS, sephadex G-75 gel filtration and SDS-PAGE and demonstrated the presence of proteins with molecular masses corresponding to metalloprotease III, serine-protease and PLA2 in three fractions collected after gel filtration. Equally, we examined the antimicrobial effect of the venom that showed an important potency, as bactericidal agent, based on MBC and MIC values obtained, against Staphylococcus aureus and Morganella morganii bacteria. However, no activity was registered against Enterococcus faecalis, being the most resistant bacteria, neither against Aspergillus flavus and Penicillium digitatum fungal. Furthermore, on eleven other bacterial strains and the Candida albicans fungus, the venom has shown an intermediate efficacy by slightly reducing the growth. Our data concerning the Montivipera bornmuelleri venom give evidence of a rich and complex content aiding the exploration of new bioactive molecules for biopharmaceuticals purposes.