Supression of hemin-mediated oxidation of low-density lipoprotein and subsequent endothelial reactions by hydrogen sulfide (H(2)S).

Heme-mediated oxidative modification of low-density lipoprotein (LDL) plays a crucial role in early atherogenesis. It has been shown that hydrogen sulfide (H(2)S) produced by vascular smooth muscle cells is present in plasma at a concentration of about 50 micromol/L. H(2)S is a strong reductant which can react with reactive oxygen species like superoxide anion and hydrogen peroxide. The current study investigated the effect of H(2)S on hemin-mediated oxidation of LDL and oxidized LDL (oxLDL)-induced endothelial reactions. H(2)S dose dependently delayed the accumulation of lipid peroxidation products-conjugated dienes, lipid hydroperoxides (LOOH), and thiobarbituric acid reactive substances-during hemin-mediated oxidation. Moreover, H(2)S decreased the LOOH content of both oxidized LDL and lipid extracts derived from soft atherosclerotic plaque, which was accompanied by reduced cytotoxicity. OxLDL-mediated induction of the oxidative stress responsive gene, heme oxygenase-1, was also abolished by H(2)S. Finally we have shown that H(2)S can directly protect endothelium against hydrogen peroxide and oxLDL-mediated endothelial cytotoxicity. These results demonstrate novel functions of H(2)S in preventing hemin-mediated oxidative modification of LDL, and consequent deleterious effects, suggesting a possible antiatherogenic action of H(2)S.

Effects of tocopherols and 2,2'-carboxyethyl hydroxychromans on phorbol-ester-stimulated neutrophils.

Tocopherol vitamers [e.g., alpha-, gamma- and delta-tocopherol (alpha-TOC, gamma-TOC and delta-TOC, respectively)] and their water-soluble 2,2'-carboxyethyl hydroxychroman metabolites (e.g., alpha-, gamma- and delta-CEHC) all possess antioxidant properties. As a consequence, and similarly to other natural antioxidants, vitamin E compounds may be useful in preventing inflammatory and oxidative-stress-mediated diseases. In this study, we investigated the concentration-dependent effect of tocopherols and water-soluble metabolites on a key event in oxidative stress, for example, the oxidative burst in neutrophils. It was found that not only alpha-TOC but also gamma-TOC and delta-TOC as well as alpha-, gamma- and delta-CEHC at physiological concentrations inhibit superoxide anion (O2(*-)) production in phorbol-ester-stimulated neutrophils. This effect was mediated by the inhibition of the translocation and activation of protein kinase C (PKC) enzyme, which is the key event in the phorbol-ester signaling. Importantly, CEHCs were stronger inhibitors of PKC as compared with the vitamer precursors, and the gamma forms of both tocopherol and CEHC showed the highest inhibitory activities. Tocopherols, but not CEHCs, directly inhibit the fully activated nicotine-adenine-dinucleotide phosphate (NADPH) oxidase. However, none of the test compounds was able to directly scavenge O2(*-) when tested in a cell-free system. In conclusion, vitamin E compounds can control the neutrophil oxidative burst through the negative modulation of PKC-related signaling and NADPH oxidase activity. As an original finding, we observed that CEHC metabolites might contribute to regulate PKC activity in these cells. These results may have important implications in the anti-inflammatory and antioxidant role of vitamin E compounds.