Methyl-accepting chemotaxis like Rv3499c (Mce4A) protein in Mycobacterium tuberculosis H37Rv mediates cholesterol-dependent survival.

Cholesterol, an essential cellular component in macrophages, is exploited for entry and long-term survival of Mycobacterium inside the host. Cholesterol-deficient macrophages can restrict the cholesterol-dependent entry of Mycobacterium. Rv3499c protein in Mycobacterium has high binding affinity for cholesterol. Rv3499c gene is a part of mce4 operon which is reported to act as cholesterol transport system in mycobacteria. Earlier we reported Rv3499c protein to localise on cell wall and facilitate entry of Mycobacterium inside macrophages. Here we performed fold recognition and multiple sequence alignment to find similarity with methyl-accepting chemotaxis protein (MCP). MCP allows detection of level of nutrient in the medium, which in this case is cholesterol. We showed Rv3499c protein expression is important for host cholesterol utilization by Mycobacterium for its survival. Infected female balb/c mice presented increased CFU of Rv3499c overexpressing M. tuberculosis H37Rv marked with early disease conditions and increased lung pathology. Thus, findings suggest specific domain of MCP of Rv3499c help in regulation of downstream PDIM synthesis pathways for ligand utilization by M. tuberculosis H37Rv.

PDIM and SL1 accumulation in Mycobacterium tuberculosis is associated with mce4A expression.

Lipid metabolism forms the heart and soul of Mycobacterium tuberculosis life cycle. Starting from macrophage invasion at cholesterol rich micro-domains to a sustainable survival for infection by utilizing cholesterol, Mycobacterium displays the nexus of metabolic pathways around host derived lipids. mce4 operon acts as cholesterol import system in M. tuberculosis and here we demonstrate role of mce4A gene of this operon in cholesterol catabolism. Here M. tuberculosis H37Rv overexpressing Rv3499c (mce4A) recombinant was used as a model to decipher the metabolic flux during intake and utilization of host lipids by mycobacteria. We analysed the impact of mce4A expression on carbon shift initiated during cholesterol utilization necessary for long term survival of mycobacterium. Through transcriptional analysis, upregulation in methylcitrate cycle (MCC) and methylmalonyl pathway (MMP) genes was observed in Rv3499c overexpressing recombinants of M. tuberculosis H37Rv. Up-regulation of methylmalonyl pathway associated enzyme encoding genes increased accumulation of virulence associated mycobacterial lipids phthiocerol dimycocerates (PDIM) and sulfolipid (SL1). We demonstrate that MCC and MMP associated enzyme encoding genes are upregulated upon mce4A overexpression and lead to enhanced accumulation of PDIM and SL1 which are responsible for pathogenicity of M. tuberculosis.

Neuroprotective and Antioxidant Activities of 4-Methylcoumarins: Development of Structure-Activity Relationships.

Coumarins are a major class of polyphenols that are abundantly present in many dietary plants and possess different biological activities. Neuroprotective effect of 28 variously substituted 4-methylcoumarins was evaluated in a cell model of oxidative stress-induced neurodegeneration, which measures viability in PC12 cells challenged with hydrogen peroxide by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The inhibitory activity of these compounds against intracellular reactive oxygen species (ROS) formation was also determined by 2',7'-dichlorofluorescein diacetate method in the same cells. Chemical redox-based assays including 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) tests were employed to explore structure-antioxidant activity relationships in a cell-free environment. The results demonstrated that 4-methylcoumarins containing ortho-dihydroxy or ortho-diacetoxy substituents on the benzenoid ring possess considerable neuroprotective effects. ortho-Dihydroxy compounds inhibited cytotoxicity (44.7-62.9%) and ROS formation (41.6-71.1%) at 50 µM and showed considerable antioxidant effects. We conclude that 4-methylcoumarins are promising neuroprotective and antioxidant scaffolds potentially usefull for management of neurodegenerative diseases.

Coumarin Derivatives as Adjuvants: From In Silico Physicochemical Characterization to In Vitro Evaluation against Gram Positive Bacteria.

AIMS: A series of acylated coumarin derivatives have been evaluated for their in silico ADMET properties and in vitro antibacterial activities. METHODS AND RESULTS: In silico analysis confirmed their physicochemical properties in conformation with various layout filters and further their ADMET properties were predicted. Antibacterial activities were evaluated by Resazurin based microbroth dilution assay against standard Gram positive bacteria: Staphylococcus aureus (MTCC No. 3160) and Bacillus cereus (MTCC No. 10085). When used alone, these derivatives showed higher MIC values. However, in combination with standard drugs they exhibited synergistic effects according to fractional inhibitory concentration index. The synergistic effect was further confirmed by time kill curves. Their cytotoxity was evaluated by haemolytic assay and they were found to be non-toxic upto a concentrations of 500 µg ml-1. CONCLUSION: The data support the potential use of acylated coumarin derivatives as next generation adjuvants as evaluated by their in silico ADMET analysis and in vitro antibacterial and cytotoxicity evaluation. Further research involving these combinations is warranted. SIGNIFICANCE AND IMPACT OF THE STUDY: This study suggests that acylated coumarin derivatives act as antibacterial adjuvants in combination with standard drugs and have potential to be used in pharmaceutical preparations.

4-Methylcoumarin derivatives with anti-inflammatory effects in activated microglial cells.

Inflammation contributes to the pathogenesis of neurodegenerative diseases and anti-inflammatory compounds may have a role in prevention or treatment of these pathologies. 4-Methylcoumarins are effective antioxidants with anti-inflammatory properties. In this study, the inhibitory effects of two 4-methylcoumarin derivatives, 7,8-dihydroxy-3-ethoxycarbonylmethyl-4-methylcoumarin (DHEMC) and 7,8-diacetoxy-3-ethoxycarbonylmethyl-4-methylcoumarin (DAEMC) were examined on the inflammatory processes induced by lipopolysaccharide (LPS) in activated primary rat microglial cultures. LPS-induced production of nitric oxide (NO, measured by Griess method) and other pro-inflammatory mediators, thromboxane (TX) B2 and prostaglandin (PG) E2 (both determined by radioimmunoassay (RIA)), as well as tumor necrosis factor (TNF)-α (determined by enzyme-linked immunosorbent assay (ELISA)) were inhibited in the presence of 100 µM DHEMC and DAEMC. DAEMC was able to significantly inhibit NO, TXB2 and TNF-α production also at 50 µM. Both compounds at 100 µM significantly lowered cyclooxygenase-2 (COX-2) protein expression in LPS-stimulated microglial cells measured by Western blot, but only DAEMC showed an inhibitory effect on inducible nitric oxide synthase (iNOS) protein expression at 100 µM. In conclusion, our findings show that 4-methylcoumarin derivatives can modulate inflammatory pathways in microglial cells, probably by acting at the protein expression level.

Protein acyltransferase function of purified calreticulin. Part 1: characterization of propionylation of protein utilizing propoxycoumarin as the propionyl group donor.

We have earlier reported that an endoplasmic reticulum luminal protein calreticulin (CR) mediated the acetylation of certain receptor proteins such as glutathione S-transferase (GST) by polyphenolic acetates, leading to irreversible inhibition. This function of calreticulin was termed calreticulin transacetylase. In this communication, we have demonstrated for the first time the ability of the purified recombinant calreticulin of a parasitic nematode Haemonchus contortus to transfer propionyl group from 7,8-Dipropoxy-4-methylcoumarin (DPMC) to recombinant Schistosoma japonicum glutathione S-transferase (rGST). Calreticulin transacetylase exhibited hyperbolic kinetics and yielded K(m) (140 microM) and V(max) (105 units) when the concentration of DPMC was varied keeping the concentration of rGST constant. rGST thus propionylated was found to positively interact with anti-acetyl lysine antibody. Also, the nanoscale LC-MS/MS analysis identified the propionylation sites on three lysine residues: Lys-11, -180 and -181 of rGST. These results highlight the transacylase function of calreticulin (CRTAase).

The role of calreticulin transacetylase in the activation of human platelet nitrite reductase by polyphenolic acetates.

Our earlier investigations demonstrated the remarkable activation of cytochrome P-450 reductase and nitric oxide synthase by 7,8-diacetoxy-4-methylcoumarin, a model polyphenolic acetate by way of acetylation, catalyzed by the Calreticulin. Protein acetyltransferase action of Calreticulin was hence termed Calreticulin transacetylase (CRTAase). Nitric oxide synthase and nitrite reductase are now considered as parts of nitric oxide cycle. The activation of platelets nitric oxide synthase by 7,8-diacetoxy-4-methylcoumarin has already been demonstrated by us. Also, there are reports that certain proteins such as cytochrome P-450 reductase and cytochrome P-450 are endowed with the nitrite reductase activity in mammalian cells. Keeping these facts in view, we turned our attention to probe whether 7,8-diacetoxy-4-methylcoumarin could alter the levels of nitric oxide independent of the action of nitric oxide synthase in the human platelets model. The incubation of 7,8-diacetoxy-4-methylcoumarin and nitrite with platelets caused significant elevation of nitric oxide and cyclic guanosine monophosphate levels possibly due to the activation of nitrite reductase. Several polyphenolic acetates were similarly found to activate the nitrite reductase in tune with their affinities as substrate to CRTAase. N-omega-Nitro-L-arginine methyl ester, the inhibitor of nitric oxide synthase, failed to reverse such an effect of 7,8-diacetoxy-4-methylcoumarin. Clotrimazole which is known to be an inhibitor of nitrite reductase, effectively abolished the 7,8-diacetoxy-4-methylcoumarin mediated enhancement of nitric oxide levels in platelets as well as the nitric oxide mediated effects; such as cyclic guanosine monophosphate levels as well as adenosine diphospate induced platelets aggregation due to nitrite.