Isoniazid induces apoptosis: Role of oxidative stress and inhibition of nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2).

AIMS: Long-term treatment of Isoniazid (INH) in tuberculosis (TB) patients can lead to anti-tuberculosis drug-induced hepatotoxicity. To understand the mechanism of hepatotoxicity, an attempt has been made to elucidate the role of Nrf2, a transcription factor induced by oxidative stress, in INH induced apoptosis liver cancer cell lines. MATERIALS AND METHODS: Cytotoxicity was evaluated by MTT assay. Apoptosis and reactive oxygen species (ROS) generation was performed by flow cytometry. mRNA and protein expression of various genes involves in INH induced toxicity was evaluated via Real-time PCR and western blot analysis respectively. Differential protein expression was performed by two-dimensional gel electrophoresis followed by identification using MALDI TOF/TOF. KEY FINDINGS: INH induced ROS and apoptosis in HepG2 as well as THLE-2 cells. Nuclear damage was also observed by INH treatment in HepG2 cells. Expression of apoptotic (Cytochrome C and Caspase 9) and antioxidative (Keap1 and Nrf2) genes were observed to increase. INH induced PKCδ phosphorylation and released Nrf2 from its inhibitor Keap1 in the cytoplasm of HepG2 cells. However, over-expression of Nrf2 did not affect nuclear Nrf2 protein level as well as its downstream target NQO1. Nrf2 importer, Karyopherin ß1 level was observed to decrease in HepG2 as well as THLE-2 cells following INH treatment. SIGNIFICANCE: These findings suggest that INH prevented Nrf2 translocation into the nucleus by inhibiting its importer Karyopherin ß1. Therefore Nrf2 might not able to bind ARE sequences from inducing antioxidative response for protecting the cells undergoing apoptosis.

Isoniazid prevents Nrf2 translocation by inhibiting ERK1 phosphorylation and induces oxidative stress and apoptosis.

Isoniazid is used either alone or in combination with other drugs for the treatment of tuberculosis. It is also used for the prevention of tuberculosis. Chronic treatment of Isoniazid may cause severe liver damage leading to acute liver failure. The mechanism through which Isoniazid causes liver damage is investigated. Isoniazid treatment generates reactive oxygen species and induces apoptosis in Hep3B cells. It induces antioxidative and apoptotic genes leading to increase in mRNA expression and protein levels in Hep3B cells. Whole genome expression analysis of Hep3B cells treated with Isoniazid has resulted in differential expression of various genes playing prime role in regulation of apoptotic, antioxidative, DNA damage, cell signaling, cell proliferation and differentiation pathways. Isoniazid increased cytosolic Nrf2 protein level while decreased nuclear Nrf2 protein level. It also decreased ERK1 phosphorylation and treatment of Hep3B cells with ERK inhibitor followed by Isoniazid resulting in increased apoptosis in these cells. Two dimensional gel electrophoresis results have also shown differential expression of various protein species including heat shock proteins, proteins playing important role in oxidative stress, DNA damage, apoptosis, cell proliferation and differentiation. Results suggest that Isoniazid induces apoptosis through oxidative stress and also prevents Nrf2 translocation into the nucleus by reducing ERK1 phosphorylation thus preventing cytoprotective effect.

Protective association exhibited by the single nucleotide polymorphism (SNP) rs1052133 in the gene human 8-oxoguanine DNA glycosylase (hOGG1) with the risk of squamous cell carcinomas of the head & neck (SCCHN) among north Indians.

BACKGROUND & OBJECTIVES: Imbalances in compactly regulated DNA repair pathways in the form of single nucleotide polymorphisms (SNPs) within vital DNA repair genes may result in insufficient DNA repair and increase in DNA breaks thus rendering the human system vulnerable to the debilitatory effects of grave diseases like cancers. The present study involves investigation of association of the non-synonymous SNP rs1052133 (C8069G/Ser326Cys) located in the exonic region of the gene human 8-oxoguanine DNA glycosylase (hOGG1) with the risk of squamous cell carcinomas of the head and neck (SCCHN). METHODS: Case-control based genetic association study was performed among 575 (250 SCCHN cases and 325 normal healthy controls) sub-population cluster-matched (Indo-Europeans linguistic subgroup + Caucasoid morphological subtype) samples from the north Indian States of Uttar Pradesh and Uttarakhand using polymerase chain reaction followed by restriction fragment length polymorphism (PCR-RFLP) and DNA sequencing analysis. RESULTS: Our results demonstrated statistically significant protective association for the heterozygous CG [Odds Ratio (OR) 0.6587, 95% Confidence Interval (CI) 0.4615 to 0.9402, P=0.0238], homozygous mutant GG (OR 0.2570, 95% CI 0.1070 to 0.6175, P=0.0013) and combined mutant CG + GG (OR 0.6057, 95% CI 0.4272 to 0.8586, P=0.0059) genotypes. INTERPRETATION & CONCLUSIONS: The results indicate that the polymorphism rs1052133 is strongly associated with SCCHN susceptibility and the mutant (G) allele might be a protective factor for SCCHN among north Indian subpopulations.