5-Methoxyindole-2-carboxylic acid (MICA) is a well-established reversible inhibitor of mitochondrial dihydrolipoamide dehydrogenase (DLDH). This chemical, as an indole derivative, has been shown to be neuroprotective against ischemic stroke injury when administered either before or after ischemic stroke in animal models. MICA has also been studied as a potential antidiabetic agent by numerous investigators, though the underlying mechanisms remain sketchy. To attempt to elucidate the mechanisms of its antidiabetic action, we tested the effect of MICA on ZSF1 rat, a widely used rodent model of type 2 diabetes. ZSF1 rats as well as its healthy controls were fed with control diet or MICA-containing diet (200 mg/kg/day) for 9 weeks. Unexpectedly, comparison of body weight changes and blood glucose levels at the end of the 9-week's feeding period indicated that MICA failed to show any anti-diabetic effect in the ZSF1 diabetic rats. The reasons for this failure were discussed.
To examine whether combining arsenic trioxide (ARS) and pamidronate (PAM), anticancer drugs that generate reactive oxygen species (ROS), enhanced targeting of redox sensitive growth signals, we studied cloning efficiency, protein tyrosine phosphatase (PTPase) activity, and epidermal growth factor receptor (EGFR) phosphorylation in DU-145 and PC-3 human prostate cancer cells in response to treatment with ARS and/or PAM for 24 h. IC50 concentrations in a clonogenic assay for ARS and PAM were 9 and 20 μM, respectively, in DU-145 cells; and 2 and 12 μM, in PC-3 cells. When combined, ARS and PAM demonstrated additive cytotoxicity in the DU-145 line (combination index [CI] of 1.10) and synergy for PC-3 cells (CI of 0.86). ARS (20 μM for 24 h) inhibited PTPase activity by 36 ± 7 %, p < 0.05 vs. untreated controls, in DU-145 cells; and by 58 ± 8%, p < 0.05, in the PC-3 line. PAM (20 μM for 24 h) decreased PTPase activity by 24 ± 9%, p = 0.06, and 8 ± 1%, p < 0.01, in DU-145 and PC-3 cells, respectively. Combining ARS and PAM significantly inhibited PTPase activity in both cell lines at lower concentrations of each drug. Pretreatment with N-acetyl-L-cysteine reversed ARS- and PAM-induced inhibition of PTPase activity. PTPase inhibition by ARS and/or PAM treatment in both DU-145 and PC-3 cells was associated with prolonged EGFR activation. These experiments demonstrate additive or synergistic cell killing by the ARS/PAM combination in DU-145 or PC-3 cells and suggest that enhanced antitumor activity may be related to alterations in receptor tyrosine kinase signaling that occur, in part, due to ROS-mediated PTPase inhibition.
Shifted NAD(H) redox status and enhanced reactive oxygen species (ROS) scavenging systems have been observed in cancers. However, how such redox shift is related to the ROS level in cancer cells is less clear. Based on collecting the intrinsic fluorescence of oxidized flavoproteins (Fp containing flavin adenine dinucleotide) and reduced nicotinamide adenine dinucleotide (NADH), optical redox imaging (ORI) provides a quantitative measure of the mitochondrial redox state by the optical redox ratio, Fp/(NADH+Fp), a surrogate marker of the NAD+-coupled redox state NAD+/NADH. Our study aims to explore the relationship between NAD(H) redox status and ROS by imaging NADH, Fp, and ROS levels using cultured breast cancer cell models. By manipulating either ROS levels via application of exogenous H2O2 or redox status via metabolic perturbation compounds, we found that: (1) oxidation of NAD(H) redox status correlates with ROS levels at lower H2O2 concentrations (up to ~700 μM), but not necessarily at higher concentrations; (2) an elevated ROS level diminishes NADH and reduces redox ratio plasticity; (3) either more oxidized or more reduced status can correlate to an increased ROS level; and (4) sometimes, a more oxidized status can correlate to a decreased ROS level depending on cell lines. These observations indicated that cellular NAD(H) redox state and ROS are intricately related but can also change separately. This study can benefit cancer research as both NAD(H) redox status and ROS have been implicated in cancer transformation and progression.
Dietary supplementation with omega-3 fatty acids, also known as n-3 fatty acids, has been widely considered cardiovascular protective in the general human population. This widely acclaimed status of omega-3 fatty acids as cardiovascular protective molecules has, however, been questioned by findings from multiple rigorously designed randomized controlled trials, recently reported in the New England Journal of Medicine. Although the anti-inflammatory and other beneficial effects of omega-3 fatty acids are substantiated by research in experimental models as well as findings from observational epidemiological studies, dietary supplementation with omega-3 fatty acids at the typical dosage of 1 g daily does not appear to be an effective strategy for either primary or secondary prevention of cardiovascular disease in humans.
Regulation of antioxidant gene expression is essential for controlling oxidative stress and maintaining physiological homeostasis. In this context, the nuclear factor E2-related factor 2 (Nrf2) has been identified as the chief regulator of the transcription of diverse antioxidant genes as well as many other cytoprotective genes. Nrf2 activity is subjected to the regulation at various levels including protein stability, transcription, and post-transcription. Among the various regulatory pathways, the Keap1-Cul3-Rbx1 axis is the most prominent regulator of Nrf2 activity. Being a tightly controlled transcriptional activator of antioxidant genes, Nrf2 signaling is intimately involved in health and disease. While Nrf2 is a protector against oxidative and electrophilic tissue injury, persistent activation of Nrf2 signaling may also contribute to disease pathophysiology, such as cancer progression.
