Cellular and molecular toxicology of lead. III Effect of lead on heme synthesis

Protective effect of curcumin against heavy metals-induced liver damage

Occupational or environmental exposures to heavy metals produce several adverse health effects. The common mechanism determining their toxicity and carcinogenicity is the generation of oxidative stress that leads to hepatic damage. In addition, oxidative stress induced by metal exposure leads to the activation of the nuclear factor (erythroid-derived 2)-like 2/Kelch-like ECH-associated protein 1/antioxidant response elements (Nrf2/Keap1/ARE) pathway. Since antioxidant and chelating agents are generally used for the treatment of heavy metals poisoning, this review is focused on the protective role of curcumin against liver injury induced by heavy metals. Curcumin has shown, in clinical and preclinical studies, numerous biological activities including therapeutic efficacy against various human diseases and anti-hepatotoxic effects against environmental or occupational toxins. Curcumin reduces the hepatotoxicity induced by arsenic, cadmium, chromium, copper, lead and mercury, prevents histological injury, lipid peroxidation and glutathione (GSH) depletion, maintains the liver antioxidant enzyme status and protects against mitochondrial dysfunction. The preventive effect of curcumin on the noxious effects induced by heavy metals has been attributed to its scavenging and chelating properties, and/or to the ability to induce the Nrf2/Keap1/ARE pathway. However, additional research is needed in order to propose curcumin as a potential protective agent against liver damage induced by heavy metals.

Subchronic toxic effects of tributyltin (TBT) and inorganic lead (PbII) in rats

This study evaluated the toxic effects of two doses of inorganic lead (PbII) and tributyltin (TBT), separately and together in different exposure times (30 and 60 days) in rats. After exposure, liver, kidney, brain and blood were sampled for histopathological, hematological and enzymatic analysis. The number of peritoneal cells and lipopolysaccharide (LPS)-induced neutrophil migration after exposure was also analyzed. The liver presented necrotic areas in all exposed individuals while hematological and enzymatic parameters showed no changes. TBT, but not PbII, reduced the number of resident peritoneal macrophages. The combination of both toxicants abolished TBT effects at lower doses and even increased the number of macrophages at higher doses. The neutrophil migration was increased by lead and lead associated with TBT. These results confirm the potential hepatotoxicity of these compounds and they may have antagonistic effects on the immune cells when administered alone. The combination of toxicants induced an increased inflammatory response suggesting that lead effects may prevail over TBT reduction on macrophage number.

Effects of lead treatment on intracellular iron and copper concentrations in cultured astroglia

Astroglia are implicated in the pathogenesis of lead (Pb) neurotoxicity in two capacities: as a lead sink that sequesters lead and as a target for direct cellular damage. A proposed cellular mechanism of Pb neurotoxicity is the alteration of metal concentrations, particularly the intracellular accumulation of Cu2+. We measured Pb uptake and the effects of Pb acetate on intracellular trace metal concentrations in astroglial cultures prepared from 0- to 4-day-old rat cerebral hemispheres. Mature Sprague Dawley and immature Wistar rat astroglia in culture took up lead from the medium. This finding replicates in vitro the finding reported by others that astroglia in the brain take up Pb. Intracellular Cu and Fe concentrations (micrograms per 2 x 10(6) cells) were increased fourfold or more by treatment with 100 microM Pb for 3 days in the cultures of immature astroglia. Cu levels were also increased twofold or more in mature astroglia treated for 1-3 days with 100 microM Pb. The significance of this finding is that Cu is a potent inhibitor of Na+, K+-ATPase, an enzyme by which astroglia are thought to remove K+ from the extracellular fluid in the brain. Thus, this finding supports the hypothesis that elevated [Cu], and perhaps [Fe], is a subcellular mechanism of neurotoxicity.

Toxicology investigations with cell culture systems

This review concerns some of the cell culture systems that are most frequently used in toxicology investigations. In particular, it sets out to evaluate the effectiveness of these cell culture systems in assessing the toxic potential of chemicals. Metabolic studies and general and specific toxicology investigations are highlighted. Specific toxicology investigations relate to the effects of the tests substances on the highly specialized functions typical of the cell systems chosen. The general toxicology investigations include most of the other studies where differentiated or undifferentiated cells have been used to evaluate the effects of the tested substances on common basic biochemical processes essential for life. Lastly, we have attempted to focus attention on the most promising applications of cell cultures in toxicology studies for the near future and to identify those areas where further research is needed. Because of the several excellent reviews that already exist, we have decided not to consider cell cultures utilized in screening potential mutagens and carcinogens. We have also excluded investigations of drug therapeutic effects and action mechanisms of drugs.

Cellular and molecular toxicology of lead. I. Effect of lead on cultured cell proliferation

Growth studies were done on a cultured rat liver cell line (RLC-GAI) grown in a chemically defined medium in the presence of lead nitrate. Lead reversibly inhibited the growth of these cells even after 6 d of exposure to the heavy metal. To compare lead sensitivity in various cell lines, GI50 and LD50 values were determined in the RLC-GAI cells as well as two glioma cell lines (B82 and C(6)) and a neuroblastoma cell line (N18). The LD50 values paralleled but were consistently lower than the GI50 values. Since lead is known to affect heme synthesis, hemin was added to test the possibilty of preventing the growth-inhibitory effect of the lead. The growth capacity of lead-treated cells did not change with the addition of hemin. It is thought that differentiated cultured cell lines such as these could be useful in examining the molecular mechanism of lead toxicity.