Capsaicin-responsive NADH oxidase activities from urine of cancer patients

Trans-plasma membrane electron transport in mammals: functional significance in health and disease

Trans-plasma membrane electron transport (t-PMET) has been established since the 1960s, but it has only been subject to more intensive research in the last decade. The discovery and characterization at the molecular level of its novel components has increased our understanding of how t-PMET regulates distinct cellular functions. This review will give an update on t-PMET, with particular emphasis on how its malfunction relates to some diseases, such as cancer, abnormal cell death, cardiovascular diseases, aging, obesity, neurodegenerative diseases, pulmonary fibrosis, asthma, and genetically linked pathologies. Understanding these relationships may provide novel therapeutic approaches for pathologies associated with unbalanced redox state.

Cancer Site-Specific Isoforms of ENOX2 (tNOX), A Cancer-Specific Cell Surface Oxidase

Introduction

All neoplastic cells express one or more members of a unique family of tumor-associated cell surface ubiquinone (NADH) oxidase proteins with protein disulfide-thiol interchange activity (ENOX2 or tNOX proteins) that are characteristically blocked by quinone site inhibitors with anti-cancer activity.

Methods

Analyses using two-dimensional gel electrophoresis with detection on western blots using a pan ENOX2 recombinant antibody revealed unique ENOX2 isoforms or unique combinations of isoforms of differing molecular weights and/or isoelectric points in sera of patients with cancers of different cellular or tissue origins.

Results and Discussion

Isoform presence provides for broad-range cancer detection. The specific patterns and molecular weights of the isoforms present allows for identification of the cell type and/or tissue of origin of the neoplasm. ENOX2 isoform presence and relative amounts are largely independent of stage but may be proportional to tumor burden to provide indications of response to therapy and disease progression.

A Drug-Unresponsive and Protease-Resistant CNOX Protein from Human Sera

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and ammonium sulfate fractionation were employed in series to purify and concentrate a 12.5-kDa protein fragment with a periodic (24-min period) proteinase K-resistant and drug-unresponsive NADH oxidase (CNOX) activity from pooled sera from healthy volunteers. The activity was unresponsive to capsaicin to distinguish it from the previously isolated cancer-associated NOX form (tNOX). Polyclonal antisera generated to the CNOX fragment cross-reacted with 20.5- to 24-kDa proteins of human sera, human lymphocytes, and plasma membranes from Escherichia coli with the molecular weight depending on source and conditions of treatment with proteinase K.

Medicinal herbs: drugs or dietary supplements?

The process of evaluating medicinal herbs is complex, and there is a need to carefully define a research strategy that addresses a solution to safe and efficacious herbal products. Notwithstanding the immense value of distilling the pharmacological activity of an herb into a chemical suitable for drug development, another approach is to develop a standardized herbal extract that yields consistent pharmacological activity. However, it frequently is forgotten that even in an extract several active ingredients contribute to the pharmacological action. Sufficient evidence exists to suggest that extracts of medicinal herbs, once isolated in their pure state, can produce pharmacological effects that differ significantly from that of the whole herb. This article discusses a research-based strategy that may be suitable for validating, in part, the putative health benefits of medicinal herbs. Additionally, the body of scientific evidence that underpins the pharmacological activity of several herbs is reviewed briefly.

Cell-surface NAD(P)H-oxidase: relationship to trans-plasma membrane NADH-oxidoreductase and a potential source of circulating NADH-oxidase

The surface of mammalian cells faces an oxidizing environment that has the potential to damage proteins, lipids, and carbohydrates to which it is exposed. In contrast, the cytoplasm is reducing and its redox state is tightly regulated. Trans-plasma membrane oxidoreductases that shift electrons from cytosolic NADH to external electron acceptors such as oxygen are widely involved in cellular redox control. They reduce oxygen to water and may generate reactive oxygen species such as superoxide and hydrogen peroxide. In addition, external NAD(P)H-oxidases have been demonstrated on intact cells and as eluted proteins, but the relationship between trans-plasma membrane NADH-oxidoreductases and cell-surface NAD(P)H-oxidases is not known. To investigate further the relationship between plasma membrane NAD(P)H-oxidoreductases, and to gain insight into the physiological functions of these redox active membrane proteins, we have adapted a simple colorimetric assay for measuring the trans-plasma membrane NADH-oxidoreductase activity of viable cells to measure NAD(P)H-oxidase at the cell surface in real time. Using the cell-impermeable tetrazolium salt WST-1 in the presence of NADH or NADPH, but in the absence of an intermediate electron acceptor, we show that cell-surface NAD(P)H-oxidase is widely expressed on mammalian cells, being more abundant on rapidly proliferating cells than on resting neutrophils and spleen cells. The ratio of cofactor dependence of NAD(P)H-oxidase (NADH:NADPH) varied widely between different cells (0.7-5.2), suggesting a family of cell surface oxidases or that the activity of these enzymes may be modulated in various ways. Comparison of NAD(P)H-oxidase on the surface of viable cells with trans-membrane NADH-oxidoreductase, measured with WST-1 in the presence of 1-methoxy PMS, showed that cell-surface NAD(P)H-oxidase was differentially inhibited by the cell-impermeable thiol-blocking agent pCMBS, but was unaffected or stimulated by other thiol blocking agents. Capsaicin, which inhibits trans-plasma membrane NADH-oxidoreductase activity, stimulated surface NAD(P)H-oxidase. Metabolic inhibitors had little effect on surface NAD(P)H-oxidase activity but inhibited trans-plasma membrane activity. These results do not support the view the surface NAD(P)H-oxidase is a terminal oxidase for trans-plasma membrane NADH-oxidoreductase.