Modulation of the hepatic antioxidant defense system by air polluants from urban areas

This study describes the changes induced by organic extracts from airborne particuiate matter in some enzymes related to the antioxidant defense system as well as in peroxisomal acyl CoA oxidase activity in rat liver. After 48 h of i.p. injection (40 mg/kg b.wt.) the hepatic GSH content decreased by about 30 per cent, which was accompanied by a parallel increase in glutathione-S-transferase activity. In contrast the activity of glutathione peroxidase was significantly decreased (p < 0.05).Peroxisomal acyl CoA-oxidase was enhanced by about 40 per cent with a parallel increase of liver catalase (27 per cent), the peroxisomal H2O2-destroying enzyme. With the only exception hepatic lipid peroxidation, that remains unchanged, all the effects showed a dose-dependent response with respect to the content of polycyclic aromatic hydrocarbons in the organic airborne extracts. However, the content of other chemical pollutants such as plasticizers, pestcides and other organic compounds must be taken into account. These results suggest that organic extracts from Santiago airborne particles might induce a prooxidant state. According to this view the increase in GSTs and catalase activity may be considered as a protective response against the damage induced by airborne pollutants.

GPI biosynthesis in mammalian cells: CoA-dependent acylation of GlcN-PI

We have used microsomes prepared from murine lymphoma cell lines to investigate the individual reactions by glycosylphosphatidylinositol (GPI) is synthesized in mammalian cells. Previously, GTP was found to specifically stimulate the second reaction in the pathway, the deacetylation of GlcNAc-PI to GlcN-PI. An additional GPI precursor was detected in incubations with GTP and was found to be GlcN-PI(acyl), the glycolipid proposed to be the third intermediate in mammalian GPI biosynthesis. Investigation into the factors that affect the formation of GlcN-PI(acyl) revealed that, in the presence of GTP, the addition of either CoA or palmitoyl-CoA to the incubation greatly enhanced the amount of this product made. CoA stimulation of this reaction persisted even when ATP was depleted and no formation of acyl-CoA was possible, indicating that the free CoA rather than an acyl-CoA is the actual effector of GlcN-PI acylation. Therefore, we propose that the third reaction in mammalian GPI biosynthesis is catalyzed by a CoA-dependent transacylase rather than an acyl-CoA acyltransferase