Vinay Choubey

PGC-1{alpha} and PGC-1{beta} regulate mitochondrial density in neurons.

Recent studies indicate that regulation of cellular oxidative capacity through enhancing mitochondrial biogenesis may be beneficial for neuronal recovery and survival in human neurodegenerative disorders. The peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) has been shown to be a master regulator of mitochondrial biogenesis and cellular energy metabolism in muscle and liver. The aim of our study was to establish whether PGC-1α and PGC-1β control mitochondrial density also in neurons and if these coactivators could be up-regulated by deacetylation. The results demonstrate that PGC-1α and PGC-1β control mitochondrial capacity in an additive and independent manner. This effect was observed in all studied subtypes of neurons, in cortical, midbrain, and cerebellar granule neurons. We also observed that endogenous neuronal PGC-1α but not PGC-1β could be activated through its repressor domain by suppressing it. Results demonstrate also that overexpression of SIRT1 deacetylase or suppression of GCN5 acetyltransferase activates transcriptional activity of PGC-1α in neurons and increases mitochondrial density. These effects were mediated exclusively via PGC-1α, since overexpression of SIRT1 or suppression of GCN5 was ineffective where PGC-1α was suppressed by short hairpin RNA. Moreover, the results demonstrate that overexpression of PGC-1β or PGC-1α or activation of the latter by SIRT1 protected neurons from mutant α-synuclein- or mutant huntingtin-induced mitochondrial loss. These evidences demonstrate that activation or overexpression of the PGC-1 family of coactivators could be used to compensate for neuronal mitochondrial loss and suggest that therapeutic agents activating PGC-1 would be valuable for treating neurodegenerative diseases in which mitochondrial dysfunction and oxidative damage play an important pathogenic role.

Apoptosis in liver during malaria: role of oxidative stress and implication of mitochondrial pathway

Hepatic dysfunction is a common clinical complication in malaria, although its pathogenesis remains largely unknown. Using a variety of in vivo and ex vivo approaches, we have shown for the first time that malarial infection induces hepatic apoptosis through augmentation of oxidative stress. Apoptosis in hepatocyte has been confirmed by terminal deoxynucleotidyl transferase (TdT)‐mediated dUTP‐biotin‐nickend labeling assay (TUNEL) and caspase‐3 activation. Gene expression analysis using RT‐PCR indicates the significant down‐regulation of Bcl‐2 and up‐regulation of Bax expression in liver of malaria infected mice suggesting the involvement of mitochondrial pathway of apoptosis. The levels of Fas expression and caspase‐8 activity in infected liver were same as that of uninfected control mice indicating death receptor (Fas) pathway did not contribute to liver apoptosis during malarial infection. Moreover, evidence has been presented by confocal microscopy to show the translocation of Bax from cytosol to mitochondria in apoptotic hepatocyte, resulting in opening of permeability transition pores, which in turn decreases mitochondrial membrane potential and induces cytochrome c release into cytosol. Malarial infection induces the generation of hydroxyl radical (·OH) in liver, which may be responsible for the induction of oxidative stress and apoptosis as administration of ·OH specific antioxidant as well as spin trap, alpha‐phenyl‐tert‐butyl‐nitrone in malaria‐infected mice significantly inhibits the development of oxidative stress as well as induction of apoptosis. Thus, results suggest the implication of oxidative stress induced‐mitochondrial pathway of apoptosis in the pathophysiology of hepatic dysfunction in malaria.—Guha, M., Kumar, S., Choubey, V., Maity, P., Bandyopadhyay, U. Apoptosis in liver during malaria: Role of oxidative stress and implication of mitochondrial pathway. FASEB J. 20, E439–E449 (2006)

Melatonin inhibits free radical‐mediated mitochondrial‐dependent hepatocyte apoptosis and liver damage induced during malarial infection

Abstract:u2002 We showed earlier that malarial infection significantly induces liver apoptosis mediated by oxidative stress mechanisms. Thus, a nontoxic antioxidant–antiapoptotic molecule may be beneficial for hepatoprotection. Melatonin remarkably prevents hepatocyte apoptosis in mice induced during malaria as indicated by caspase 3 and TUNEL assays as well as transmission electron microscopy (TEM) of the liver tissue. The mitochondrial apoptotic pathway, which plays a critical role in liver cell death during malarial infection, was almost completely suppressed by melatonin as it corrects both the overexpression of Bax and down‐regulation of bcl‐2 as revealed by semiquantitative RT‐PCR. Fluorometric studies using JC‐1 documented that melatonin also restores mitochondrial transmembrane potential (ΔΨm) in malaria‐infected mice liver. The antiapoptotic effect of melatonin is associated with its antioxidant role because melatonin protects liver from oxidative stress induced during malaria by scavenging the hydroxyl radicals, preventing the depletion of reduced glutathione, inhibiting lipid peroxidation and protein carbonyl formation. The effective antioxidant dose of melatonin to protect liver from oxidative stress during malaria is 20 times lower than that of known antioxidants, vitamin C and vitamin E. Apoptosis of hepatocytes during malarial infection is well correlated with dysfunction of the liver while melatonin offers hepatoprotective effects as indicated by different liver function tests. Thus, melatonin may well be effective in combating oxidative stress‐induced apoptosis and liver damage during malaria infection.

Inhibition of Plasmodium falciparum choline kinase by hexadecyltrimethylammonium bromide: a possible antimalarial mechanism.

ABSTRACT Choline kinase is the first enzyme in the Kennedy pathway (CDP-choline pathway) for the biosynthesis of the most essential phospholipid, phosphatidylcholine, in Plasmodium falciparum. In addition, choline kinase also plays a pivotal role in trapping essential polar head group choline inside the malaria parasite. Recently, Plasmodium falciparum choline kinase (PfCK) has been cloned, overexpressed, and purified. However, the function of this enzyme in parasite growth and survival has not been evaluated owing to the lack of a suitable inhibitor. Purified recombinant PfCK enabled us to identify an inhibitor of PfCK, hexadecyltrimethylammonium bromide (HDTAB), which has a very close structural resemblance to hexadecylphosphocholine (miltefosin), the well-known antiproliferative and antileishmanial drug. HDTAB inhibited PfCK in a dose-dependent manner and offered very potent antimalarial activity in vitro against Plasmodium falciparum. Moreover, HDTAB exhibited profound antimalarial activity in vivo against the rodent malaria parasite Plasmodium yoelii (N-67 strain). Interestingly, parasites at the trophozoite and schizont stages were found to be particularly sensitive to HDTAB. The stage-specific antimalarial effect of HDTAB correlated well with the expression pattern of PfCK in P. falciparum, which was observed by reverse transcription-PCR and immunofluorescence microscopy. Furthermore, the antimalarial activity of HDTAB paralleled the decrease in phosphatidylcholine content, which was found to correlate with the decreased phosphocholine generation. These results suggest that inhibition of choline kinase by HDTAB leads to decreased phosphocholine, which in turn causes a decrease in phosphatidylcholine biosynthesis, resulting in death of the parasite.

Lansoprazole Protects and Heals Gastric Mucosa from Non-steroidal Anti-inflammatory Drug (NSAID)-induced Gastropathy by Inhibiting Mitochondrial as Well as Fas-mediated Death Pathways with Concurrent Induction of Mucosal Cell Renewal

We have investigated the mechanism of antiapoptotic and cell renewal effects of lansoprazole, a proton pump inhibitor, to protect and heal gastric mucosal injury in vivo induced by indomethacin, a non-steroidal anti-inflammatory drug (NSAID). Lansoprazole prevents indomethacin-induced gastric damage by blocking activation of mitochondrial and Fas pathways of apoptosis. Lansoprazole prevents indomethacin-induced up-regulation of proapoptotic Bax and Bak and down-regulation of antiapoptotic Bcl-2 and BclxL to maintain the normal proapoptotic/antiapoptotic ratio and thereby arrests indomethacin-induced mitochondrial translocation of Bax and collapse of mitochondrial membrane potential followed by cytochrome c release and caspase-9 activation. Lansoprazole also inhibits indomethacin-induced Fas-mediated mucosal cell death by down-regulating Fas or FasL expression and inhibiting caspase-8 activation. Lansoprazole favors mucosal cell renewal simultaneously by stimulating gene expression of prosurvival proliferating cell nuclear antigen, survivin, epidermal growth factor, and basic fibroblast growth factor. The up-regulation of Flt-1 further indicates that lansoprazole activates vascular epidermal growth factor-mediated controlled angiogenesis to repair gastric mucosa. Lansoprazole also stimulates the healing of already formed ulcers induced by indomethacin. Time course study of healing indicates that it switches off the mitochondrial death pathway completely but not the Fas pathway. However, lansoprazole heals mucosal lesions almost completely after overcoming the persisting Fas pathway, probably by favoring the prosurvival genes expression. This study thus provides the detailed mechanism of antiapoptotic and prosurvival effects of lansoprazole for offering gastroprotection against indomethacin-induced gastropathy.

Antiplasmodial Activity of [(Aryl)arylsulfanylmethyl]Pyridine

ABSTRACT A series of [(aryl)arylsufanylmethyl]pyridines (AASMP) have been synthesized. These compounds inhibited hemozoin formation, formed complexes (KD = 12 to 20 μM) with free heme (ferriprotoporphyrin IX) at a pH close to the pH of the parasite food vacuole, and exhibited antimalarial activity in vitro. The inhibition of hemozoin formation may develop oxidative stress in Plasmodium falciparum due to the accumulation of free heme. Interestingly, AASMP developed oxidative stress in the parasite, as evident from the decreased level of glutathione and increased formation of lipid peroxide, H2O2, and hydroxyl radical (·OH) in P. falciparum. AASMP also caused mitochondrial dysfunction by decreasing mitochondrial potential (ΔΨm) in malaria parasite, as measured by both flow cytometry and fluorescence microscopy. Furthermore, the generation of ·OH may be mainly responsible for the antimalarial effect of AASMP since ·OH scavengers such as mannitol, as well as spin trap α-phenyl-n-tertbutylnitrone, significantly protected P. falciparum from AASMP-mediated growth inhibition. Cytotoxicity testing of the active compounds showed selective activity against malaria parasite with selectivity indices greater than 100. AASMP also exhibited profound antimalarial activity in vivo against chloroquine resistant P. yoelii. Thus, AASMP represents a novel class of antimalarial.