Study of mechanism of interaction of truncated isoniazid-nicotinamide adenine dinucleotide adduct against multiple enzymes of Mycobacterium tuberculosis by a computational approach

Objective/Background: Isoniazid [INH] is one of the effective antituberculosis [TB] drugs used for TB treatment. However, most of the drug-resistant Mycobacterium tuberculosis [MTB] clinical strains are resistant to INH, a first-line antituberculous drug. Certain metabolic enzymes such as adenosylhomocysteinase [Rv3248c], universal stress protein [Rv2623], nicotinamide adenine dinucleotide [reduced]-dependent enoyl-acyl carrier protein reductase [Rv1484], oxidoreductase [Rv2971], dihydrofolate reductase [Rv2763c], pyrroline- 5-carboxylate dehydrogenase [Rv1187] have been identified to bind INH-nicotinamide adenine dinucleotide [INH-NAD] and INH-nicotinamide adenine dinucleotide phosphate adducts coupled to Sepharose resin. These enzymes are reported to be involved in many important biochemical processes of MTB, including cysteine and methionine metabolism, mycobacterial growth regulation, mycolic acid biosynthesis, detoxification of toxic metabolites, folate biosynthesis, etc. The truncated INH-nicotinamide adenine dinucleotide [oxidized] adduct, 4-isonicotinoylnicotinamide, isolated from urine samples of human TB patients treated with INH therapy is proposed to have antimycobacterial activity

Methods: To understand the mechanism of interaction of the truncated INH-NAD adduct, binding energy studies were carried out on the aforementioned six enzymes with known three-dimensional structures using AutoDock4.2

Results: In silico docking analysis of these MTB enzymes with the truncated INH-NAD adduct showed favorable binding interactions with docking energies ranging from -5.29 to -7.07 kcal/mol

Conclusion: Thus, in silico docking study revealed that the INH-NAD adduct, which is generated in vivo after INH activation, may undergo spontaneous hydrolysis to form the truncated INH-NAD adduct and further binds and inhibits multiple enzymes of MTB, in addition to InhA, confirming that INH is an effective anti-TB drug acting at multiple enzymes. Further analysis of amino acid residues in the active site of INH-NAD-binding proteins showed the probable presence of catalytic triad in four enzymes possibly involved in INH binding to the enzyme

Pleomorphic adenoma of the minor salivary gland of the cheek

Pleomorphic adenoma is the most common tumour of the salivary gland. While the majority arises from the parotid gland, only a small percentage arises from the minor salivary glands. The cheek, however, is a rarely affected site with respect to pleomorphic adenomas of the minor salivary glands. Herein, we report a case of pleomorphic adenoma of the cheek, which presented with intraoral swelling, and conclude that complete surgical excision can be a curative treatment for this benign tumour.