A possible neuroprotective action of a vinylic telluride against Mn-induced neurotoxicity

Manganese accumulation in the CNS and associated pathologies

Manganese (Mn) is an essential metal for life. It is a key constituent of clue enzymes in the central nervous system, contributing to antioxidant defenses, energetic metabolism, ammonia detoxification, among other important functions. Until now, Mn transport mechanisms are partially understood; however, it is known that it shares some mechanisms of transport with iron. CNS is susceptible to Mn toxicity because it possesses mechanisms that allow Mn entry and favor its accumulation. Cases of occupational Mn exposure have been extensively reported in the literature; however, there are other ways of exposure, such as long-term parental nutrition and liver failure. Manganism and hepatic encephalopathy are the most common pathologies associated with the effects of Mn exposure. Both pathologies are associated with motor and psychiatric disturbances, related in turn to mechanisms of damage such as oxidative stress and neurotransmitters alterations, the dopaminergic system being one of the most affected. Although manganism and Parkinson's disease share some characteristics, they differ in many aspects that are discussed here. The mechanisms for Mn transport and its participation in manganism and hepatic encephalopathy are also considered in this review. It is necessary to find an effective therapeutic strategy to decrease Mn levels in exposed individuals and to treat Mn long term effects. In the case of patients with chronic liver failure it would be worthwhile to test a low-Mn diet in order to ameliorate symptoms of hepatic encephalopathy possibly related to Mn accumulation.

Hepatoprotective activity of a vinylic telluride against acute exposure to acetaminophen

Acetaminophen (APAP) hepatotoxicity has been related with several cases of cirrhosis, hepatitis and suicides attempts. Notably, oxidative stress plays a central role in the hepatic damage caused by APAP and antioxidants have been tested as alternative treatment against APAP toxicity. In the present study, we observed the hepatoprotector activity of the diethyl-2-phenyl-2-tellurophenyl vinylphosphonate (DPTVP), an organotellurium compound with low toxicity and high antioxidant potential. When the dose of 200 mg/kg of APAP was used, we observed that all used doses of DPTVP were able to restore the -SH levels that were depleted by APAP. Furthermore, the increase in thiobarbituric acid reactive substances levels and in the seric alanine aminotransferase (ALT) activity and the histopathological alterations caused by APAP were restored to control levels by DPTVP (30, 50 and 100 μmol/kg). On the other hand, when the 300 mg/kg dose of APAP was used, DPTVP restored the non-proteic -SH levels and repaired the normal liver morphology of the intoxicated mice only at 50 μmol/kg. Our in vitro results point out to a scavenging activity of DPTVP against several reactive species, action that is attributed to its chemical structure. Taken together, our results demonstrate that the pharmacological action of DPTVP as a hepatoprotector is probably due to its scavenging activity related to its chemical structure.

Prolactin is a peripheral marker of manganese neurotoxicity

Excessive exposure to Mn induces neurotoxicity, referred to as manganism. Exposure assessment relies on Mn blood and urine analyses, both of which show poor correlation to exposure. Accordingly, there is a critical need for better surrogate biomarkers of Mn exposure. The aim of this study was to examine the relationship between Mn exposure and early indicators of neurotoxicity, with particular emphasis on peripheral biomarkers. Male Wistar rats (180-200g) were injected intraperitoneally with 4 or 8 doses of Mn (10mg/kg). Mn exposure was evaluated by analysis of Mn levels in brain and blood along with biochemical end-points (see below).

RESULTS

Brain Mn levels were significantly increased both after 4 and 8 doses of Mn compared with controls (p<0.001). Blood levels failed to reflect a dose-dependent increase in brain Mn, with only the 8-dose-treated group showing significant differences (p<0.001). Brain glutathione (GSH) levels were significantly decreased in the 8-dose-treated animals (p<0.001). A significant and dose-dependent increase in prolactin levels was found for both treated groups (p<0.001) compared to controls. In addition, a decrease in motor activity was observed in the 8-dose-treated group compared to controls.

CONCLUSIONS

(1) The present study demonstrates that peripheral blood level is a poor indicator of Mn brain accumulation and exposure; (2) Mn reduces GSH brain levels, likely reflecting oxidative stress; (3) Mn increases blood prolactin levels, indicating changes in the integrity of the dopaminergic system. Taken together these results suggest that peripheral prolactin levels may serve as reliable predictive biomarkers of Mn neurotoxicity.