Cytotoxicity, zinc protection, and stress protein induction in rat proximal tubule cells exposed to cadmium chloride in primary cell culture

GSH and Zinc Supplementation Attenuate Cadmium-Induced Cellular Stress and Stimulation of Choline Uptake in Cultured Neonatal Rat Choroid Plexus Epithelia

Choroid plexus (CP) sequesters cadmium and other metals, protecting the brain from these neurotoxins. These metals can induce cellular stress and modulate homeostatic functions of CP, such as solute transport. We previously showed in primary cultured neonatal rat CP epithelial cells (CPECs) that cadmium induced cellular stress and stimulated choline uptake at the apical membrane, which interfaces with cerebrospinal fluid in situ. Here, in CPECs, we characterized the roles of glutathione (GSH) and Zinc supplementation in the adaptive stress response to cadmium. Cadmium increased GSH and decreased the reduced GSH-to-oxidized GSH (GSSG) ratio. Heat shock protein-70 (Hsp70), heme oxygenase (HO-1), and metallothionein (Mt-1) were induced along with the catalytic and modifier subunits of glutamate cysteine ligase (GCL), the rate-limiting enzyme in GSH synthesis. Inhibition of GCL by l-buthionine sulfoximine (BSO) enhanced stress protein induction and stimulation of choline uptake by cadmium. Zinc alone did not induce Hsp70, HO-1, or GCL subunits, or modulate choline uptake. Zinc supplementation during cadmium exposure attenuated stress protein induction and stimulation of choline uptake; this effect persisted despite inhibition of GSH synthesis. These data indicated up-regulation of GSH synthesis promotes adaptation to cadmium-induced cellular stress in CP, but Zinc may confer cytoprotection independent of GSH.

Synergistic effects of toxic elements on heat shock proteins

Heat shock proteins show remarkable variations in their expression levels under a variety of toxic conditions. A research span expanded over five decades has revealed their molecular characterization, gene regulation, expression patterns, vast similarity in diverse groups, and broad range of functional capabilities. Their functions include protection and tolerance against cytotoxic conditions through their molecular chaperoning activity, maintaining cytoskeleton stability, and assisting in cell signaling. However, their role as biomarkers for monitoring the environmental risk assessment is controversial due to a number of conflicting, validating, and nonvalidating reports. The current knowledge regarding the interpretation of HSPs expression levels has been discussed in the present review. The candidature of heat shock proteins as biomarkers of toxicity is thus far unreliable due to synergistic effects of toxicants and other environmental factors. The adoption of heat shock proteins as "suit of biomarkers in a set of organisms" requires further investigation.

Transport pathways for cadmium in the intestine and kidney proximal tubule: focus on the interaction with essential metals

Cadmium (Cd) is a toxic metal with a propensity to accumulate in the proximal tubules cells (PTC) of the kidney where it can lead to tubular dysfunction and eventually renal failure. Although Cd(2+)-induced nephrotoxicity has been well described there is still uncertainty about how this metal gains entry into these cells to induce toxicity. As a non-essential metal, specific transport proteins for Cd are unlikely to exist. Rather transport proteins/channels used by essential metals (iron, zinc, calcium) are thought to be responsible. When these dietary essential metals are in short supply and deficiencies develop, Cd absorption and toxicity are enhanced. This is primarily due to increased expression of essential metal transport proteins such as divalent metal transporter 1 (DMT1) which can transport Cd in the intestine and enhance toxicity in the kidney. The zinc/bicarbonate sympoters ZIP8 and 14 are expressed at the apical membrane of enterocytes and PTC, and can transport Cd into cells. TRPV5 and 6 are major transporters for calcium in intestine and kidney and may be involved in Cd transport in these locations. Cd in the circulation is bound to proteins such as metallothioneins (MT) which are readily filtered. Two multiligand receptors, megalin and cubulin, reabsorb filtered proteins including albumin and MT by the process of receptor-mediated endocytosis. This review summarises the transport pathways for Cd in the intestine and kidney proximal tubule focusing in particular at how Cd uses essential metal transport processes to gain entry to the circulation and the kidney.

Macro- and micronutrients in African-Americans with heart failure

An emerging body of evidence suggests secondary hyperparathyroidism (SHPT) may be an important covariant of congestive heart failure (CHF), especially in African-Americans (AA) where hypovitaminosis D is prevalent given that melanin, a natural sunscreen, mandates prolonged exposure of skin to sunlight and where a housebound lifestyle imposed by symptomatic CHF limits outdoor activities and hence sunlight exposure. In addition to the role of hypovitaminosis D in contributing to SHPT is the increased urinary and fecal losses of macronutrients Ca(2+) and Mg(2+) associated with the aldosteronism of CHF and their heightened urinary losses with furosemide treatment of CHF. Thus, a precarious Ca(2+) balance seen with reduced serum 25(OH)D is further compromised when AA develop CHF with circulating RAAS activation and are then treated with a loop diuretic. SHPT accounts for a paradoxical Ca(2+) overloading of diverse tissues and the induction of oxidative stress at these sites which spills over to the systemic circulation. In addition to SHPT, hypozincemia and hyposelenemia have been found in AA with compensated and decompensated heart failure and where an insufficiency of these micronutrients may have its origins in inadequate dietary intake, altered rates of absorption or excretion and/or tissue redistribution, and treatment with an ACE inhibitor or AT(1) receptor antagonist. Zn and Se deficiencies, which compromise the activity of several endogenous antioxidant defenses, could prove contributory to the severity of heart failure and its progressive nature. These findings call into question the need for nutriceutical treatment of heart failure and which is complementary to today's pharmaceuticals, especially in AA.

Zinc protects renal function during cadmium intoxication in the rat

This study investigates the effect in the rat of chronic CdCl2 intoxication (500 microg Cd2+/kg, daily i.p. injection for 5 days) on renal function and the changes in tight junction proteins claudin-2, claudin-3, and claudin-5 present in rat kidney. We also studied the effect of coadministration of ZnCl2 (500 microg Zn2+/kg) during chronic CdCl2 intoxication. Our results indicate that 1) most of the filtered Cd2+ is reabsorbed within the kidney; 2) chronic Cd2+ intoxication can induce a change in renal handling of ions without altering glomerular filtration rate; 3) a delayed nephropathy, showing Fanconi-like features, appears more than 5 days after the end of CdCl2 exposure; 4) epithelial integrity is altered by chronic Cd2+ intoxication affecting the expression and localization of claudin tight junction proteins; and 5) cotreatment with Zn2+ protects against the renal toxic effects of Cd2+, preventing altered claudin expression and inhibiting apoptosis. In conclusion, these results show that Cd2+ toxicity and cellular toxic mechanisms are complex, probably affecting both membrane transporters and tight junction proteins. Finally, Zn2+ supplementation may provide a basis for future treatments.

Ultrastructural alterations of the hepatopancreas in Porcellio scaber under stress

Cellular ultrastructure varies in accordance with physiological processes, also reflecting responses to environmental stress factors. Ultrastructural changes of the hepatopancreatic cells in the terrestrial isopod Porcellio scaber exposed to sublethal concentrations of zinc or cadmium in their food were identified by transmission electron microscopy. The exclusive structural characteristic of the hepatopancreas of animals exposed to metal-dosed food was grain-like electrondense deposits (EDD) observed in the intercellular spaces and in vesicles of B cells. In addition, hepatopancreatic cells of metal-exposed animals displayed non-specific, stress-indicating alterations such as cellular disintegration, the reduction of energetic reserves (lipid droplets, glycogen), electron dense cytoplasm, ultrastructural alterations of granular endoplasmic reticulum (GER), the Golgi complex and mitochondria.

Molecular chaperones in the kidney

The normal milieu of the kidney includes hypoxia, large osmotic fluxes, and an enormous amount of fluid/solute reabsorption. Renal adaptation to these conditions requires a host of molecular chaperones that stabilize protein conformation, target nascent proteins to their final intracellular destination, and prevent protein aggregation. Under physiologic or pharmacologic stress, inducible molecular chaperones provide additional mechanisms for repairing or degrading non-native proteins and for inhibiting stress-induced apoptosis. In contrast to intracellular chaperones, chaperones present on the cell surface regulate the immune system and have cytokine-like effects. A diverse range of chaperones and chaperone functions provide the renal cell with an armamentarium of responses to improve the chances of survival.

Mechanisms of nephrotoxicity from metal combinations: a review

The common environmental pollutants arsenic, lead, and cadmium are each known to induce chronic renal disease and the molecular mechanisms of such toxic events are being clarified. Nephrotoxicity of these metals is due to the fact that urinary elimination is a main route of excretion, and the proximal tubules are especially sensitive due to their high reabsorptive activity. Renal pathological effects of these metals vary with the chemical form of the metal, the dose, and whether the exposure is acute or chronic in nature. The few isolated studies of combined metal exposures indicate that these pathological effects may be altered due to unknown interactions of these metals within the kidney. Biological factors within the cell such as metal binding proteins and inclusion bodies may also influence metal-metal interactions. Further research is needed to specify the parameters or criteria by which metal interactions is to be assessed for unique biological response patterns to aid in the risk assessment analysis of environmental and occupational metal exposures.