Varied protocols of cadmium exposure produce different effects on nitric oxide production in macrophages

Involvements of H2O2 and metallothionein in NO-mediated tomato tolerance to copper toxicity

Both H(2)O(2) and NO are involved in multiple physiological responses in plants. Metallothionein (MT) can bind heavy metal ions and reduce metal toxicity. Copper toxicity has become a major problem with increasing agricultural and environmental pollution. Here, we investigated the possible roles of ROS, NO and metallothionein in tomato plant responses to copper toxicity. We found that Cu(2+) stress caused the rapid release of H(2)O(2) and chlorotic leaves, and it stunted root growth and development. Cu treatment also caused an increase in NOS enzyme activity and NO release in roots and leaves. Application of the NO donor SNP efficiently alleviated the copper toxicity effect, as shown by increases in chlorophyll content and the biomass of fresh/dry leaves. SNP treatment also induced the transcription and increased activities of anti-oxidant enzymes, including catalase, peroxidase, superoxide dismutase and ascorbate peroxidase, and led to reduced H(2)O(2) accumulation in the leaves. Special inhibitors or scavengers of NO synthesis diminished the ameliorating effect of NO on copper toxicity. NO application induced MT transcription and accumulation in leaves. Furthermore, the antisense-MT transgenic tomato was more sensitive to copper stress, and this effect could not be efficiently reversed by NO treatment. From these data, we propose that NO induces tomato tolerance to copper toxicity through antioxidant enzyme activity and metallothionein accumulation, and that metallothionein acts downstream of NO signaling.

Lipid metabolism in liver of rat exposed to cadmium

We investigated the effect of exposition to cadmium (Cd, 15ppm for 8 weeks) through drinking water on liver lipid metabolism in adult male Wistar rats. As compared to metal non-exposed (control) rats, the serum triglycerides, cholesterol and LDL+VLDL cholesterol concentrations increased. This was associated to a decrease of lipoprotein lipase activity in post heparinic plasma. The VLDL secretion from liver was not modified. Cd treatment increased triglycerides and decreased esterified cholesterol contents in liver. The high triglyceride mass was related to the increased glycerol-3-phosphate acyltransferase mRNA expression. In addition, the liver fatty acids synthesis increased, as determined by an increment of fatty acid synthetase and isocitrate dehydrogenase activities, and [(14)C]-acetate incorporation into saponifiable lipid fraction. The relative percentage of palmitic acid (16:0) and total saturated fatty acids were increased compared with control. Hepatic glucose-6-phosphate dehydrogenase, malic dehydrogenase and cholesteryl ester hydrolase activities were unchanged. In liver, the Cd treatment decreased triglyceride and cholesterol in mitochondria, also increased triglyceride in cytosol, and cholesterol and phospholipid contents in nuclei, compared with control. In addition, an increase of nuclei phosphatidylcholine synthesis was observed. Cd exposure alters directly or indirectly the serum lipid content and liver lipid metabolism.

Effect of quercetin on metallothionein, nitric oxide synthases and cyclooxygenase-2 expression on experimental chronic cadmium nephrotoxicity in rats

Inflammation can play a key role in Cd-induced dysfunctions. Quercetin is a potent oxygen free radical scavenger and a metal chelator. Our aim was to study the effect of quercetin on Cd-induced kidney damage and metallothionein expression. The study was performed in Wistar rats that were administered during 9 weeks with either cadmium (1.2 mg Cd/kg/day, s.c.), quercetin (50 mg/kg/day, i.p.) or cadmium + quercetin. Renal toxicity was evaluated by measuring blood urea nitrogen concentration and urinary excretion of enzymes marker of tubular damage. Endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) renal expression were assessed by Western blot. Renal expression of metallothionein 1 and 2 (MT-1, MT-2) and eNOS mRNA was assessed by Northern blot. Our data demonstrated that Cd-induced renal toxicity was markedly reduced in rats that also received quercetin. MT-1 and MT-2 mRNA levels in kidney were substantially increased during treatment with Cd, being even higher when the animals received Cd and quercetin. Renal eNOS expression was significantly higher in rats receiving Cd and quercetin than in animals receiving Cd alone or in control rats. In the group that received Cd, COX-2 and iNOS expression was markedly higher than in control rats. In the group Cd+quercetin, no changes in COX-2 and iNOS expression were observed compared with the control group. Our results demonstrate that quercetin treatment prevents Cd-induced overexpression of iNOS and COX-2, and increases MT expression. These effects can explain the protection by quercetin of Cd-induced nephrotoxicity.

Alterations in the lipid content of pituitary gland and serum prolactin and growth hormone in cadmium treated rats

The present study was undertaken to assess whether chronic exposition to cadmium (Cd, 0.133 mM per liter for 2 months) through drinking water may affect the lipid contents in the pituitary anterior lobe (PAL) of adult male Wistar rats. As compared to metal non-exposed controls, PALs exposed to cadmium showed an increase in total phospholipid contents, which was associated to an increase of the incorporation of [1-14C]-methyl choline into phosphatidylcholine and of [U-14C]-glucose into total phospholipids. The incorporation of [1-14C]-methyl choline into sphingomyelin was not changed. Incorporation of [1-14C]-acetate into total fatty acids also increased but incorporation of [1-14C]-acetate into cholesterol did not change. The activity of phospholipase D decreased both in PALs from Cd exposed rats and in PAL dispersed cells treated with Cd in the culture medium from Cd non-exposed rats. In PALS from Cd exposed rats, a decrease of serum prolactin and growth hormone concentrations was determined. The results shown that cadmium modifies the lipid contents of pituitary gland and directly or indirectly the levels of prolactin and growth hormone in serum.