RNA Interference Protects Against 5-Lipoxygenase-Induced Cocarcinogen, Benzidine, Oxidation and Cytotoxicity in Human Tracheobronchial Epithelial Cells

5-Lipoxygenase Contributes to Benzo[a]pyrene-Induced Cytotoxicity and DNA Damage in Human Bronchial Epithelial Cells

Metabolic activation of indirect-acting carcinogens in target organs is a recognized mechanism of carcinogenesis. This study aimed to determine the role of benzo[a]pyrene (BaP) metabolism enzymes lipoxygenase (LOX), cytochrome P4501A1 (CYP1A1), and prostaglandin synthetase (PGS) in the cytotoxicity and DNA damage induced by BaP in the human tracheobronchial epithelial cells (HBECs) using RNA interference strategy and metabolic enzyme inhibitors. Our results showed that in three epithelial cell lines (HBE, HTR-8/SVneo, and HaCat), BaP significantly upregulated 5-LOX protein expression. 15-LOX-2 expression also increased with increasing BaP concentration, but the change was less pronounced than that of 5-LOX. BaP caused significant cytotoxicity, DNA strand breaks, and 8-hydroxy-2'-deoxyguanosine formation in HBE, which was inhibited by 5-LOXshRNA, a specific inhibitor of 5-LOX (AA861), the CYP1A1 inhibitor α-naphthoflavone, and the PGS inhibitor naproxen. The protective effects of 5-LOXshRNA were stronger than AA861, naproxen and α-naphthoflavone. We conclude that BaP may be activated more by 5-LOX than by CYP1A1 and PGS to produce cytotoxicity and DNA damage in HBE.

Emerging Roles of 5-Lipoxygenase Phosphorylation in Inflammation and Cell Death

5-Lipoxygenase (ALOX5) is an iron-containing and nonheme dioxygenase that catalyzes the peroxidation of polyunsaturated fatty acids such as arachidonic acid. ALOX5 is the rate-limiting enzyme for the biosynthesis of leukotrienes, a family of proinflammatory lipid mediators derived from arachidonic acid. ALOX5 also make great contributions to mediating lipid peroxidation. In recent years, it has been discovered that ALOX5 plays a central role in cell death including apoptosis, pyroptosis, and ferroptosis, a newly discovered type of cell death. According to the previous studies, ALOX5 can regulate cell death in two ways: one is inflammation and the other is lipid peroxidation. Meanwhile, it has been shown that ALOX5 activity is regulated by several factors including protein phosphorylation, ALOX5-interactng protein, redox state, and metal ions such as iron and calcium. In this review, we aim to summarize the knowledge on the emerging roles of ALOX5 protein phosphorylation in the regulation of cell death and inflammation in order to explore a potential target for human diseases.

Lipoxygenase Protein Expression and Its Effect on Oxidative Stress Caused by Benzidine in Normal Human Urothelial Cell Lines

Metabolic activation of indirect-acting carcinogens in the target organ is an effective mechanism of carcinogenesis. Lipoxygenase (LOX) can co-oxidize the bladder carcinogen benzidine (BZ). However, it is not entirely clear whether BZ is activated and which enzyme is involved in its activation in bladder epithelial cells. Our results showed that BZ induced 5-LOX protein expression but had no significant influence on the expression of 15-LOX-2, CYP1B1, and CYP2E1 in SV-40 immortalized human uroepithelial SV-HUC-1 cells. BZ induced oxidative stress in SV-HUC-1 cells by increasing reactive oxygen species (ROS) and malondialdehyde levels significantly in the 100 and 200 μmol/L-BZ-treated groups and decreased the level of the antioxidant reduced glutathione significantly at 200 μmol/L BZ. Concurrently, the activity of catalase was increased, while the activity of superoxide dismutase was increased at 50 μmol/L BZ but gradually decreased with increasing concentrations of BZ ( P < 0.05). However, the oxidative stress and damage in SV-HUC-1 cells caused by BZ were effectively inhibited by the 5-LOX-specific inhibitor AA861 at 10 μmol/L. Thus, 5-LOX is probably the major LOX isozyme to co-oxidize exogenous chemicals in SV-HUC-1 cells. AA861 has a protective effect on the oxidative stress and damage induced by BZ in SV-HUC-1 cells. We conclude that BZ can be activated by 5-LOX to produce ROS and oxidative stress, which may be associated with bladder cancer caused by BZ.