Molecular modeling and inhibition of phospholipase A2 by polyhydroxy phenolic compounds.

Phospholipases A(2) are enzymes responsible for the hydrolysis of membrane phospholipids that release arachidonic acid, which serves as substrate for pro-inflammatory mediators, such as prostaglandins and leucotriens. The design of specific inhibitors for PLA(2) might help in the development of new anti-inflammatory drugs. Polyhydroxy phenolic compounds, such as flavonoids, vitamin E, rosmarinic acid and aristolochic acid, are able to inhibit PLA(2) from different sources. Herein, we have studied the kinetic behavior and the capacity of inhibiting edema formation induced by PLA(2) of five different polyhydroxy phenolic compounds (two phenolic derivatives and three acetophenone hydroxylated derivatives) extracted from the venom of Crotalus adamanteus. The results showed that compounds 1,3-dihydroxy benzene, 1,3,5-trihydroxy benzene and 2,4,6-trihydroxy acetophenone were the most efficient in the inhibition of the enzymatic activity and edema induction by PLA(2). It was also verified that the number of hydroxyls in each molecule is not a limiting factor for the inhibition capacity of these compounds. Molecular modeling studies indicated that the most active compounds are linked to the amino acid Asp 49 and that they destabilize the coordination of the calcium atom, which is essential to the catalytic activity. The study of potential surfaces showed that there are conditions in which the potential values must be adequate for enzyme complex formation with polyhydroxy phenolic compounds. When the potential over the hydroxyl surfaces is very high, formation of stable complexes does not occur and the enzyme does not act intensely. These results might be helpful in the design of a drug that specifically inhibits PLA(2).

Synthesis and evaluation of nitrostyrene derivative compounds, new snake venom phospholipase A2 inhibitors.

Several nitrostyrene derivatives were synthesized and their inhibitive activities on phospholipase A(2) (PLA(2)) from Bothrops jararacussu venom were evaluated. Some compounds were very efficient as inhibition agents against edema-inducing, enzymatic and myotoxic activities. Data revealed that the size of the substitute and substitution position in the nitrostyrene moiety had important influence on the inhibition capacities. The enzymatic kinetic studies show that the nitrostyrene derivatives compounds inhibit PLA(2) in a non-competitive manner. The electronic, molecular and topologic parameters were calculated using ab initio quantum calculations (density functional theory-DFT) and analyzed by chemometric methods (principal component analysis (PCA) and hierarchical cluster analysis (HCA)) in order to build models able to establish relationships between the electronic features and the structure-activity presented by the target compound. Compounds with the nitro group in the ortho, meta and para position (compounds 2-4) on the aromatic ring were more efficient in the inhibition of PLA(2) activity in all tests. These results indicate that the influence of the nitro group in the aromatic ring is, in fact, important. In addition, quantum chemistry calculations show that compounds with a higher capacity of inhibiting PLA(2) present lower values of highest occupied molecular orbital (HOMO) energy and polarizability, suggesting the formation of a charge-transferring complex between the nitrostyrene compounds and PLA(2).