Current Enzyme Inhibition - Volume 10, Issue 2, 2014

Poly(ADP-ribosyl)ation is one of the most pertinent post translational modifications involved in regulation of chromatin structure, cell cycle progression, tissue development and differentiation and other vital biological phenomena. The enzymes that catalyze the synthesis and degradation of poly(ADP) ribose polymers are PARP and PARG, respectively. The role of PARP has been implicated in development of various diseases since a long time and hence it has evolved as an important pharmacological target but a plethora of drawbacks associated with PARP inhibitors compelled the shift of focus towards PARG. Recently PARG has evolved as an alternative target to overcome the hurdles being faced in the treatment of various conditions like multiple organ failure, ischemic organ damage, diabetic nephropathy, neurodegenerative diseases and cancer. The review provides a compendium on PARG, its mode of action, inhibitors, and its therapeutic applications and also discusses the reasons due to which PARG inhibitors have not been able to reach the clinical trials. PARG inhibitors, though far from success, definitely appear as alluring topics for further research as PARG emerges out as an eminent pharmacological target in making which can shape the future of medicines to provide better therapy with reduced side effects and more efficiency.

Natural proteinaceous protease inhibitors inhibit through nonproductive binding to proteases and steric blockage of active sites. These complexes are among the most structurally complementary protein-protein interactions. To see if complementarity is correlated to activity, we scored the shape complementarity in 15 serine protease-inhibitor complexes through in silico docking and compared the scores against their reported inhibition constants (Ki). A statistically significant, moderate and positive correlation was observed between shape complementarity and Ki (R = 0.58; P = 0.023). We also analyzed other physicochemical factors involved in serine protease-inhibitor interactions for correlation, but no other factor was correlated to Ki. However, significant correlations were observed between hydrogen bonds and interface areas (R = 0.762; P = 0.0004); and between hydrophobic interactions and free energies of solvation (R = -0.634; P = 0.011).

Despite the explosion in structural biologythe multi-dimensional complexity of the structure determination process of biomolecules like proteins significantly poses hindrances to drug development and study of interaction of ligands to the target. Since virtual screening has come up as a potential tool in the process of drug discovery the availability of macromolecular structures has limitations. Moreover, when more than one 3D structure is available it becomes all the more important to select the right structure for the study as the protein stability plays an important role in structure based drug design (SBDD). This study was carried out to find the most stable structure among the seven (2NMZ, 3FX5, 3BVB, 3IXO, 1KZK, 1ODW and 3HBO) structures HIV-1 Protease available in the protein data bank. The structure analysis of chain A of these PDB entries using in-silico approaches such as ANOLEA assessment server; Ramachandran plot analysis and Swiss model structure assessment server were performed. The structure assessment analysis revealed that there is a major difference among these PDB entries based on their energy and structural analysis. The PDB ID 2NMZ with a resolution of 0.97Åwas found to be the most stable and reliable structure for structure based drug designing.

Tuberculosis (TB) remains to be one of the major public health concerns worldwide. The continuing emergence of Mtb strains resistant to known drugs makes the campaign for successful TB control and treatment very difficult to accomplish. It is therefore imperative to search for newer chemical entities that could inhibit the growing number of putative drug targets for the development of more efficient anti-tubercular drugs. One such ideal target is the 7, 8- diaminopelargonic acid aminotransferase enzyme (BioA). This enzyme is mainly involved in the bacterium’s lipid biosynthesis and metabolism machinery, and is considered as a very promising target due to the fact that humans lack this enzyme. In this study, structure-based pharmacophore screening, molecular docking, and ADMET evaluation of compounds obtained from the InterBioScreen Synthetic Compounds (IBS SC) were performed against the MtbBioA enzyme. Five compounds from the library showed more favorable binding energies as compared to the enzyme’s known inhibitor, amiclenomycin (ACM). Moreover, a pyridazinyladamantane 2-carboxylic acid and two sulfone derivatives have indicated good ADMET properties. These compounds are predicted to possess desirable properties of a lead and should be the subject of subsequent structural optimization and experimental bioactivity evaluations.

Lipase inhibitors have a high pharmacological interest because they could help in the therapy of diseases in which lipases play an important role such as obesity. Extracts from two Algerian spontaneous plants: Oudneya africana and Pulicaria crispa, were screened for potential lipase inhibitory activity. The enzymatic inhibition produced by these plants extracts is described here for the first time. Additionally, the antioxidant activity of extracts was investigated using 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities, 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical cation scavenging activities and phosphomolybdenum complex. The results have shown that ethyl acetate fraction of Pulicaria crispa extract obtained by 70% (v/v) aqueous acetone was the best extract based on its lipase inhibitory activity (IC50 1.33±0.03mg/ml). The extracts of Oudneya africana and Pulicaria crispa showed a pronounced scavenging activity on DPPH, ABTS radicals and had a potent reductive ability on phosphomolybdate assay.

Lipase inhibitors are drugs used to reduce the activity of lipase found in the intestine. These inhibitors are used for the treatment of obesity and cardiovascular diseases. The purpose of this work was to explore in vitro the enzymatic and antioxidant activities of secondary metabolites extracts such as, phenolic compounds, flavonoids and tannins obtained with various extraction solvent systems: methanol/water, acetone/water and methanol/acetone/water from the aerial parts of five medicinal Algerian plants: Thymus algeriensis, Zygophyllum album, Thymus sepyllum, Marrubium vulgare L and Echium vulgare L. The lipase inhibition by these extracts described here has been for the first time. The results have shown a potent inhibitor, activity of lipase in acetone/water extraction mixture with ethyl acetate and butanol fractions from Thymus sepyllum and in methanol/acetone/water extraction mixture with ethyl acetate fraction from Marrubium vulgare L. The evaluation of antioxidant capacity was achieved by three chemical tests DPPH, Phosphomolybdenum and ABTS showing that our extracts possess potential antioxidant activities compared to standards.

Eighty four endophytic fungi were isolated from Ocimum sanctum. Secondary metabolites extracted from these endophytic fungi were tested for the inhibitors of enzymes responsible for the glycaemic index and polyol pathway. Six isolates were positive for both α-glucosidase and α-amylase inhibitors. Secondary metabolites from four endophytic fungal isolates inhibited aldose reductase enzyme extracted from rat lens. Crude extracts of fungal isolates POST075 and POST083 were found to be the most potent α-glucosidase inhibitors among the active isolates with IC50 values of 29.51 and 31.26 μg/mL respectively. Whereas, ethyl acetate extracts of fungal isolates POST034 and POST075 showed highest inhibition for pancreatic α-amylase enzyme in-vtiro with an IC50 value of 27.34 and 40.73 μg/mL respectively. The IC50 value for α-amylase enzyme inhibitors of POST034 and POST075 was very close to IC50 value of standard drug acarbose (25.7 μg/mL) tested under similar conditions. Crude extract of endophytic fungal isolate POST047 was found to be an effective aldose reductase inhibitor with an IC50 value of 29 μg/mL when compared to the IC50 value of standard drug quercetin that has an IC50 value of 15 μg/mL under similar condition. Fungal isolates with best inhibition activity were identified as Alternaria tenuissima (POST34), Trichoderma sp. (POST047), Diaporthe sp (POST075) and Colletotrichum gloesporioides (POST083) by the rDNA molecular method.

Colchicine is a toxic alkaloid known for its therapeutic applications. In addition to the inhibition of microtubule polymerization, colchicine has been reported to inhibit many key enzymes. Here we provide evidence for colchicine binding and inhibiting ζ-crystallin purified from camel eye lens. Indeed, we demonstrated the molecular interaction between colchicine and ζ-crystallin using fluorescence quenching. Moreover, colchicines inhibited ζ-crystallin activity with respect to two different substrates 9,10-phenanthrenequinone (PQ) and 1,2-Naphthoquinone (NQ) as well as NADPH as coenzyme. The inhibition was time-independent but concentration-dependent with an IC50 value of 1.52 ± 0.055 μM. NADPH was able to protect 38% of enzyme activity against colchicine whereas ζ-crystallin substrates protected only 12-16%. Kinetic analysis revealed that colchicine-induced inhibition of ζ-crystallin activity was non-competitive and uncompetitive with respect to PQ/NQ and NADPH, respectively. In addition, the kinetic analyses along with the protection assay clearly suggest that the binding of colchicine to ζ-crystallin occurs at or close to NADPH binding site. Our data reveal for the first time the inhibitory effect of colchicine on the oxidoreductase activity of camel lens ζ-crystallin illustrating the diversity of colchicine-targeted enzymes. Finally, our findings are of great importance in therapy since ζ-crystallin is known to play a key role in the detoxification processes. Therefore, a particular attention should be taken during colchicine-based therapies to avoid kidney injury and cataract formation.

Dextransucrase isolated from Weissella cibaria JAG8 was subjected to active site mapping analysis by using lysine specific inhibitor viz. pyridoxal-5’-phosphate (PLP) and 2,4,6-trinitrobenzenesulphonic acid (TNBS) gave 98.5% and 98.7% inhibition in enzyme activity at 25 mM concentration respectively. The -NH2 lysine derivative of enzymeinhibitor complex with PLP and TNBS gave absorbance maxima at 325 and 369 nm, respectively. PLP modified dextransucrase on reduction with sodium borohydride led to the formation of N-phosphopyridoxyl lysine complex showed fluorescence maxima at 397 nm indicating that one or more lysine residues present near or at the active site and are essential for enzyme activity. Sucrose, provided protection to the enzyme against inactivation by PLP. The enzyme inactivation caused by cysteine specific inhibitors, DTNB (10 mM) and iodoacetic acid (25 mM) was 98.7% and 98.9%, respectively. Enzyme-inhibitor complexes with DTNB (thio-nitrobenzoate) and iodoacetic acid (thio-acetate) were confirmed by appearance of absorbance maxima at 406 and 323 nm, respectively. These results showed that one or more cysteine residues present near or at the active site and are essential for enzyme activity. Essential cysteine residue at the active site is reported for the first time in dextransucrase.