Role of trace elements in hepatic encephalopathy: zinc and manganese.

Apart from increased blood ammonia, alterations in various other substances have been implicated in the pathogenesis of hepatic encephalopathy (HE). The role of trace elements like zinc and manganese has been described recently. Zinc is an essential trace element and functions as an antioxidant. Low zinc concentrations have been reported in patients with cirrhosis of the liver, particularly those with HE. Patients with fulminant hepatic failure and subacute hepatic failure have also been shown to have low serum zinc levels. In animal experiments, zinc supplementation leads to a reduction in blood ammonia. Zinc deficiency also leads to alteration of neurotransmitters like gamma aminobutyric acid and norepinephrine. Zinc supplementation has been tried in HE. It may have a role in mild chronic HE, though further trials are necessary. Increased serum manganese levels have been shown in acute and chronic hepatitis, cirrhosis and congenital disorders like Alagille's syndrome. High manganese content has been reported in the globus pallidus in animals as well as brain tissues of patients dying of HE. Miners with chronic manganese exposure have encephalopathy and extra-pyramidal features similar to HE. It has been postulated that manganese impairs neuronal oxidative metabolism. The role of manganese in the pathogenesis of HE and the possibility of its chelation as treatment need further study.