Production of superoxide and hydrogen peroxide from specific mitochondrial sites under different bioenergetic conditions.

Mitochondrial production of superoxide and hydrogen peroxide is potentially important in cell signaling and disease. Eleven distinct mitochondrial sites that differ markedly in capacity are known to leak electrons to oxygen to produce O2̇̄ and/or H2O2 We discuss their contributions to O2̇̄/H2O2 production under native conditions in mitochondria oxidizing different substrates and in conditions mimicking physical exercise and the changes in their capacities after caloric restriction. We review the use of S1QELs and S3QELs, suppressors of mitochondrial O2̇̄/H2O2 generation that do not inhibit oxidative phosphorylation, as tools to characterize the contributions of specific sites in situ and in vivo.

Suppression of superoxide/hydrogen peroxide production at mitochondrial site IQ decreases fat accumulation, improves glucose tolerance and normalizes fasting insulin concentration in mice fed a high-fat diet.

We developed S1QEL1.719, a novel bioavailable S1QEL (suppressor of site IQ electron leak). S1QEL1.719 prevented superoxide/hydrogen peroxide production at site IQ of mitochondrial complex I in vitro. The free concentration giving half-maximal suppression (IC50) was 52 nM. Even at 50-fold higher concentrations S1QEL1.719 did not inhibit superoxide/hydrogen peroxide production from other sites. The IC50 for inhibition of complex I electron flow was 500-fold higher than the IC50 for suppression of superoxide/hydrogen peroxide production from site IQ. S1QEL1.719 was used to test the metabolic effects of suppressing superoxide/hydrogen peroxide production from site IQin vivo. C57BL/6J male mice fed a high-fat chow for one, two or eight weeks had increased body fat, decreased glucose tolerance, and increased fasting insulin concentrations, classic symptoms of metabolic syndrome. Daily prophylactic or therapeutic oral treatment of high-fat-fed animals with S1QEL1.719 decreased fat accumulation, strongly protected against decreased glucose tolerance and prevented or reversed the increase in fasting insulin level. Free exposures in plasma and liver at Cmax were 1-4 fold the IC50 for suppression of superoxide/hydrogen peroxide production at site IQ and substantially below levels that inhibit electron flow through complex I. These results show that the production of superoxide/hydrogen peroxide from mitochondrial site IQin vivo is necessary for the induction and maintenance of glucose intolerance caused by a high-fat diet in mice. They raise the possibility that oral administration of S1QELs may be beneficial in metabolic syndrome.

Effect of bFGF on HLA-DR expression of human bone marrow-derived mesenchymal stem cells.

There has been a steady rise in the therapeutic applications of bone marrow mesenchymal stem cells (BM-MSCs) because of their unique properties of multilineage differentiation and immune modulation as well as the ease in isolation. However, up-regulation of surface HLA-DR levels when maintaining MSCs in culture under the influence of mitotic factors such as Basic fibroblast growth factor (bFGF) is an area of concern when considering them for the purpose of clinical applications. Thus, we investigated the association of bFGF supplemented to the culture media and the surface expression levels of HLA-DR in BM-MSCs in order to optimize the yield, while keeping HLA-DR levels under permissible levels. Human BM-MSCs were culture expanded in the absence of bFGF and in the presence of 1 ng/ml or 2 ng/ml bFGF. The HLA-DR profile of the cultures was analyzed at the end of each passage. On comparing the percent HLA-DR+ cell population at different concentrations as well as absence of bFGF, significant differences were not observed in the HLA-DR expression levels of the MSC cultures which had reached complete confluence. However, variations in HLA-DR expressions levels were seen which could be traced to the age of cells in culture with values drastically reduced to below 4% on maintaining MSCs typically two to three days beyond achieving full confluence. On the basis of the findings from this study, no significant correlation could be established on the effect of bFGF in modulating HLA-DR surface expression of BM-MSCs. Instead, the data are suggestive of the reasoning that the duration for which BM-MSCs are maintained in culture directly influences their phenotypic characteristics in terms of HLA-DR expression levels, with lowest levels achieved on their prolonged maintenance in culture.