metallothionein and Manganese-Poisoning

Juvenile (20-24-month-old) rhesus monkeys were exposed to airborne-manganese sulfate (MnSO(4)) 1.5 mg Mn/m(3) (6h/day, 5 days/week) for 15 or 33 days, or for 65 days followed by a 45 or 90 days post-exposure recovery period, or air. We assessed biochemical endpoints indicative of oxidative stress and excitotoxicity in the cerebellum, frontal cortex, caudate, globus pallidus, olfactory cortex, and putamen. Glutamine synthetase (GS), glutamate transporters (GLT-1 and GLAST) and tyrosine hydroxylase (TH) protein levels, metallothionein (MT), GLT-1, GLAST, TH and GS mRNA levels, and total glutathione (GSH) levels were determined for all brain regions. Exposure to Mn significantly decreased MT mRNA in the caudate (vs. air-exposed controls). This depression persisted at least 90 days post-exposure. In contrast, putamen MT mRNA levels were unaffected by Mn exposure. GLT-1 and GLAST were relatively unaffected by short term Mn exposure, except in the globus pallidus where exposure for 33 days led to decreased protein levels, which persisted after 45 days of recovery for both proteins and 90 days of recovery in the case of GLAST. Exposure to 1.5 mg Mn/m(3) caused a significant decrease in GSH levels in the caudate and increased GSH levels in the putamen of monkey exposed for 15 and 33 days with both effects persisting at least 90 days post-exposure. Finally, TH protein levels were significantly lowered in the globus pallidus of the monkeys exposed for 33 days but mRNA levels were significantly increased in this same region. Overall, the nonhuman primate brain responds to airborne Mn in a heterogeneous manner and most alterations in these biomarkers of neurotoxicity are reversible upon cessation of Mn exposure.

Topics: Amino Acid Transport System X-AG; Animals; Biomarkers; Blotting, Northern; Blotting, Western; Brain; Excitatory Amino Acid Transporter 2; Glutamate-Ammonia Ligase; Glutathione; Inhalation Exposure; Macaca mulatta; Male; Manganese; Manganese Poisoning; Metallothionein; Nerve Tissue Proteins; RNA, Messenger; Tyrosine 3-Monooxygenase

The purpose of this study was to evaluate biochemical markers of neurotoxicity following subchronic manganese sulfate (MnSO(4)) inhalation. Juvenile rhesus monkeys were exposed to MnSO(4) at 0, 0.06, 0.3, or 1.5 mg Mn/m(3) for 65 days. Glutamine synthetase (GS), glutamate transporters (glutamate transporter-1 [GLT-1] and glutamate/aspartate transporter [GLAST]) and tyrosine hydroxylase (TH) protein levels, metallothionein (MT), GLT-1, GLAST, TH and GS mRNA levels, and total glutathione (GSH) levels were assessed in known targets (caudate, globus pallidus, putamen) as well as the cerebellum, frontal cortex, and olfactory cortex. All MnSO(4)-exposed monkeys had decreased pallidal GS protein, decreased caudate GLT-1 mRNA, decreased pallidal GLAST protein, and increased olfactory cortical TH mRNA levels. Monkeys exposed to MnSO(4) at 0.06 or 0.3 mg Mn/m(3) had significantly increased pallidal mRNA levels for GLT-1, GLAST, and TH. Monkeys exposed to MnSO(4) at > or = 0.3 mg Mn/m(3) had several alterations including decreased frontal cortical MT mRNA, decreased caudate, globus pallidus, olfactory cortex, and cerebellum GLT-1 protein, decreased olfactory cortex and cerebellum GLAST protein, increased cerebellar GLAST mRNA, and decreased pallidal TH protein levels. Lastly, GSH levels were significantly increased in the frontal cortex and decreased in the caudate of monkeys exposed to the 1.5-mg Mn/m(3) compared to the controls. Overall, as in our previous studies, we observed that increased Mn concentrations due to airborne Mn exposure differentially affects biomarkers in each brain region (e.g., GSH was increased in the frontal cortex and decreased in the caudate despite two- to threefold increases in Mn concentrations in these regions).

Topics: Animals; Biomarkers; Blotting, Northern; Blotting, Western; Endpoint Determination; Excitatory Amino Acid Transporter 1; Excitatory Amino Acid Transporter 2; Glutamate-Ammonia Ligase; Glutathione; Inhalation Exposure; Macaca mulatta; Manganese; Manganese Poisoning; Metallothionein; Nerve Tissue Proteins; Oxidative Stress; RNA, Messenger; Tyrosine 3-Monooxygenase

Neonatal female and male rats were exposed to airborne manganese sulfate (MnSO4) during gestation and postnatal d 1-18. Three weeks postexposure, rats were killed and we assessed biochemical end points indicative of oxidative stress in five brain regions: cerebellum, hippocampus, hypothalamus, olfactory bulb, and striatum. Glutamine synthetase (GS) protein levels, metallothionein (MT) and GS mRNA levels, and total glutathione (GSH) levels were determined for all five regions. Overall, there was a statistically significant effect of manganese exposure on decreasing brain GS protein levels (p=0.0061), although only the highest dose of manganese (1 mg Mn/m3) caused a significant increase in GS messenger RNA (mRNA) in both the hypothalamus and olfactory bulb of male rats and a significant decrease in GS mRNA in the striatum of female rats. This highest dose of manganese had no effect on MT mRNA in either males or females; however, the lowest dose (0.05 mg Mn/m3) decreased MT mRNA in the hippocampus, hypothalamus, and striatum in males. The median dose (0.5 mg Mn/m3) led to decreased MT mRNA in the hippocampus and hypothalamus of the males and olfactory bulb of the females. Overall, manganese exposure did not affect total GSH levels, a finding that is contrary to those in our previous studies. Only the cerebellum of manganese-exposed young male rats showed a significant reduction (p<0.05) in total GSH levels compared to control levels. These data reveal that alterations in biomarkers of oxidative stress resulting from in utero and neonatal exposures of airborne manganese remain despite 3 wk of recovery; however, it is important to note that the doses of manganese utilized represent levels that are 100-fold to a 1000-fold higher than the inhalation reference concentration set by the US Environmental Protection Agency.

Topics: Administration, Inhalation; Animals; Animals, Newborn; Biomarkers; Brain; Cerebellum; Corpus Striatum; Female; Glutamate-Ammonia Ligase; Glutathione; Hippocampus; Hypothalamus; Male; Manganese Compounds; Manganese Poisoning; Metallothionein; Olfactory Bulb; Oxidative Stress; Pregnancy; Prenatal Exposure Delayed Effects; Rats; RNA, Messenger; Sulfates

The nature of hepatic metallothionein (MT) induction by several metals and its relationship to an inflammatory response was studied in chicks. Intraperitoneal (ip) injection of chromium (Cr), managanese, and iron (Fe) caused a much greater increase in hepatic MT (10.2-, 9.0-, and 6.8-fold) compared with cobalt and nickel (2.5- and 2.9-fold); thus not all transition metals are effective. Cr3+ caused markedly greater hepatic MT accumulation than Cr6+, suggesting that the ionic nature of the metal is an important factor. Small organic complexes of Fe (ferrous gluconate or lactate, 6.2-fold) caused significantly greater accumulation of hepatic MT than ferric dextran (1.4-fold), a large organic aggregate. In vitro data from chick hepatocytes and/or fibroblasts clearly indicated that Fe does not effect the induction of MT directly. The role of inflammation, as measured by recruitment of peritoneal exudate cells (PEC), was examined. Endotoxin (LPS), Sephadex (S), and Fe elicited significant elevations in PEC number at 24 h posttreatment (S), and Fe elicited significant elevations in PEC number at 24 h posttreatment (S = Fe greater than LPS much greater than control). The percentage of heterophils but not macrophages was significantly correlated with the accumulation and induction of hepatic MT. In a similar experiment with Cr, we demonstrated that Cr3+ but not Cr6+ stimulated MT messenger RNA accumulation and concomitant hetereophil infiltration at 3 h after injection. Our results indicate that the induction of hepatic MT by the parenteral administration of a number of metals is dependent on the chemical nature of the metal and is associated with an inflammatory response.

Topics: Animals; Cells, Cultured; Chick Embryo; Chickens; Chlorides; Chromium; Chromium Compounds; Cobalt; Ferric Compounds; Fibroblasts; Inflammation; Injections, Intraperitoneal; Kinetics; Liver; Male; Manganese Compounds; Manganese Poisoning; Metallothionein; Metals; Nickel