Chronic low level lead (Pb) exposure is associated with decrements in renal function in humans, but the molecular mechanisms underlying toxicity are not understood. We investigated cytosolic ...Pb-binding proteins (PbBP) in kidney of environmentally-exposed humans to identify molecular targets of Pb and elucidate mechanisms of toxicity. This study is unique in that it localized PbBPs based on physiologic Pb that was bound in vivo. Two Pb-binding polypeptides were identified, thymosin
β
4 (T
β
4, 5 kDa) and acyl-CoA binding protein (ACBP, 9 kDa, also known as diazepam binding inhibitor, DBI). These polypeptides, which have not been previously recognized for their metal-binding capabilities, were shown to bind Pb with high affinity (
K
d≈14 nM) and to account for an estimated >35% of the total Pb in kidney cortex tissue. Both T
β
4 and ACBP (DBI) occur across animal species from invertebrates to mammals and in all major tissues, serving multiple possible functions (e.g. regulation of actin polymerization, calmodulin-dependent enzyme activity, acyl-CoA metabolism, GABA-A/benzodiazepine receptor modulation, steroidogenesis, etc.). Thus, these data provide the first evidence of specific molecular targets of Pb in kidney of environmentally-exposed humans, and they suggest that low-level Pb toxicity may occur via alteration of T
β
4 and ACBP (DBI) function in renal and other tissues, including the central nervous system.
The ability of chromium (Cr) salts to increase metallothionein (MT) levels in rat liver, kidney and pancreas, and its relationship with the presence of toxic effects are reported here. Rats were ...injected subcutaneously with 0, 10, 20, 30, 40, or 50 mg K
2Cr
2O
7/kg and sacrificed 24 h later. Total Cr accumulation followed a dose-dependent pattern, levels in kidney being higher than those in liver or pancreas, suggesting different tissue bioavailabilities and accumulation patterns. Cr(IV) administration resulted in a tissue-specific MT induction: pancreas and liver showed five- and 3.5-fold MT increases, respectively; no increase was observed in the kidney. A positive correlation was observed between zinc and MT concentrations in liver, and between total Cr and MT concentrations in pancreas. Serum α-amylase activity showed a dose-dependent increase starting from 20 mg/kg, whereas serum glucose levels increased at doses higher than 30 mg/kg. Serum aspartate aminotransferase and alanine aminotransferase activities were increased in a dose-dependent manner, from 20 and 30 mg/kg, respectively. Our results showed that treatment with Cr(VI) can induce MT synthesis in pancreas and suggests a subsequent binding of Cr to MT. Also, pancreas is a target organ for Cr toxicity, and the usefulness of α-amylase activity as a sensitive biomarker of Cr toxicity in human exposed populations merits further study.
