Whole blood glutathione peroxidase activity in melanoma patients

Hypoxia-Induced Changes in L-Cysteine Metabolism and Antioxidative Processes in Melanoma Cells

This study was performed on human primary (WM115) and metastatic (WM266-4) melanoma cell lines developed from the same individual. The expression of proteins involved in L-cysteine metabolism (sulfurtransferases, and cystathionine β-synthase) and antioxidative processes (thioredoxin, thioredoxin reductase-1, glutathione peroxidase, superoxide dismutase 1) as well as the level of sufane sulfur, and cell proliferation under hypoxic conditions were investigated. Hypoxia in WM115 and WM266-4 cells was confirmed by induced expression of carbonic anhydrase IX and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 4 by the RT-PCR and Western blot methods. It was shown that, under hypoxic conditions the inhibition of WM115 and WM266-4 melanoma cell proliferation was associated with decreased expression of thioredoxin reductase-1 and cystathionine β-synthase. These two enzymes may be important therapeutic targets in the treatment of melanoma. Interestingly, it was also found that in normoxia the expression and activity of 3-mercaptopyruvate sulfurtransferase in metastatic WM266-4 melanoma cells was significantly higher than in primary melanoma WM115 cells.

Regulation of Tyrosinase Enzyme Activity by Glutathione Peroxidase Mimics

Hydrogen peroxide plays a crucial role in the melanogenesis process by regulating the activity of the key melanin-forming enzyme tyrosinase, responsible for the browning of fruits, vegetables, and seafood. Therefore, a molecule with dual activities, both efficient tyrosinase inhibition and strong hydrogen peroxide degrading ability, may act as a promising antibrowning agent. Herein, we report highly efficient selone-based mushroom tyrosinase inhibitors 2 and 3 with remarkable glutathione peroxidase (GPx) enzyme-like activity. The presence of benzimidazole moiety enhances the tyrosinase inhibition efficiency of selone 2 (IC₅₀ = 0.4 μM) by almost 600 times higher than imidazole-based selone 1 (IC₅₀ = 238 μM). Interestingly, the addition of another aromatic ring to the benzimidazole moiety has led to the development of an efficient lipid-soluble tyrosinase inhibitor 3 (IC₅₀ = 2.4 μM). The selenium center and the -NH group of 2 and 3 are extremely crucial to exhibit high GPx-like activity and tyrosinase inhibition potency. The hydrophobic moiety of the inhibitors (2 and 3) further assists them in tightly binding at the active site of the enzyme and facilitates the C═Se group to strongly coordinate with the copper ions. Inhibitor 2 exhibited excellent antibrowning and polyphenol oxidase inhibition properties in banana and apple juice extracts.

NRF2 and Key Transcriptional Targets in Melanoma Redox Manipulation

Melanocytes are dendritic, pigment-producing cells located in the skin and are responsible for its protection against the deleterious effects of solar ultraviolet radiation (UVR), which include DNA damage and elevated reactive oxygen species (ROS). They do so by synthesizing photoprotective melanin pigments and distributing them to adjacent skin cells (e.g., keratinocytes). However, melanocytes encounter a large burden of oxidative stress during this process, due to both exogenous and endogenous sources. Therefore, melanocytes employ numerous antioxidant defenses to protect themselves; these are largely regulated by the master stress response transcription factor, nuclear factor erythroid 2-related factor 2 (NRF2). Key effector transcriptional targets of NRF2 include the components of the glutathione and thioredoxin antioxidant systems. Despite these defenses, melanocyte DNA often is subject to mutations that result in the dysregulation of the proliferative mitogen-activated protein kinase (MAPK) pathway and the cell cycle. Following tumor initiation, endogenous antioxidant systems are co-opted, a consequence of elevated oxidative stress caused by metabolic reprogramming, to establish an altered redox homeostasis. This altered redox homeostasis contributes to tumor progression and metastasis, while also complicating the application of exogenous antioxidant treatments. Further understanding of melanocyte redox homeostasis, in the presence or absence of disease, would contribute to the development of novel therapies to aid in the prevention and treatment of melanomas and other skin diseases.

Study of tobacco habits and alterations in enzymatic antioxidant system in oral cancer

AIM AND OBJECTIVE

Tobacco is a major etiological factor for oral cancer development, accounting 30-40% of all cancer cases in India. Tobacco consumption generates free radicals and causes oxidative damages. In order to counteract these lethal effects, normal living cells have multiple antioxidant defense systems in a cascade manner. Thus, it seems that studying biological parameters, like antioxidant enzyme system, may be helpful in risk assessment and early diagnosis of oral cancer. Therefore, we analyzed erythrocytic and tissue antioxidant enzyme activities in terms of glutathione-S-transferase (GST), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and plasma thiol levels.

MATERIALS AND METHODS

Study included healthy controls with no habit of tobacco (NHT, n = 25), controls with habit of tobacco (WHT, n = 31) and oral cancer patients (n = 52). All the parameters were analyzed with highly sensitive and specific spectrophotometric methods.

RESULTS

Erythrocytic SOD and plasma thiol levels were significantly lower (p = 0.03), while GPx and CAT levels were higher (p = 0.017) in WHT as compared to NHT. No significant changes in GST and GR levels were observed between NHT and WHT. GST, GR, SOD and CAT activities were significantly higher (p = 0.05, p < 0.001, p = 0.003 and p < 0.001, respectively) while GPx and thiol levels were lower (p = 0.035 and p < 0.001, respectively) in oral cancer as compared to WHT. Odds ratio for erythrocytic GR, SOD, CAT and plasma thiol showed significantly higher risk of oral cancer development in WHT. Mean levels of SOD and CAT were increased, while GPx and thiol were decreased with the increase in habit duration in oral cancer. GST, GR and SOD activities were significantly higher (p = 0.0001, p = 0.005 and p = 0.005, respectively), while, CAT and thiol levels were lower (p = 0.0001 and p = 0.015, respectively) in malignant tissues as compared to adjacent normal tissues.

CONCLUSION

The data revealed that evaluation of antioxidant enzyme activities and thiol levels in WHT can be helpful to identify individuals at a higher risk of oral cancer development

Chemopreventive efficacy of selenium against N-nitrosodiethylamine-induced hepatoma in albino rats

The chemopreventive/chemotherapeutic effect of sodium selenite on tricarboxylic acid cycle key enzymes was investigated against hepatoma induced by environmental carcinogen N-nitrosodiethylamine. Decreased activities of TCA cycle key enzymes such as isocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and alpha-ketoglutarate dehydrogenase (alpha-KGDH) in hepatoma and surrounding tissues of hepatoma-bearing rats were observed. Upon selenium supplementation the above biochemical changes were reverted in a dose- and duration-dependent manner. This study further confirms the chemopreventive/chemotherapeutic effect of sodium selenite which is found to be more effective in the initiation phase of carcinogenesis.