Bone demineralisation in a large cohort of Wilson disease patients

Although recent epidemiological studies found a positive correlation between dietary vitamin C intake and bone mineral density, data on plasma levels of vitamin C or other antioxidants in osteoporotic subjects are scanty. The aim of this study was to evaluate whether antioxidant defenses are decreased in elderly osteoporotic women and, if this is the case, to understand whether osteoporosis is a condition characterized by increased oxidative stress. To answer these questions, plasma vitamins C, E, and A; uric acid; and the enzymatic activities of superoxide dismutase in plasma and erythrocytes and of glutathione peroxidase in plasma were measured in 75 subjects with osteoporosis and 75 controls. Dietary and endogenous antioxidants were consistently lower in osteoporotic than in control subjects. On the other hand, plasma levels of malondialdehyde, a byproduct of lipid peroxidation, did not differ between groups. Our results reveal that antioxidant defenses are markedly decreased in osteoporotic women. The mechanisms underlying antioxidant depletion and its relevance to the pathogenesis of osteoporosis deserve further investigation.

Wilson disease is caused by accumulation of Cu(2+) in cells, which results in liver cirrhosis and, occasionally, anemia. Here, we show that Cu(2+) triggers hepatocyte apoptosis through activation of acid sphingomyelinase (Asm) and release of ceramide. Genetic deficiency or pharmacological inhibition of Asm prevented Cu(2+)-induced hepatocyte apoptosis and protected rats, genetically prone to develop Wilson disease, from acute hepatocyte death, liver failure and early death. Cu(2+) induced the secretion of activated Asm from leukocytes, leading to ceramide release in and phosphatidylserine exposure on erythrocytes, events also prevented by inhibition of Asm. Phosphatidylserine exposure resulted in immediate clearance of affected erythrocytes from the blood in mice. Accordingly, individuals with Wilson disease showed elevated plasma levels of Asm, and displayed a constitutive increase of ceramide- and phosphatidylserine-positive erythrocytes. Our data suggest a previously unidentified mechanism for liver cirrhosis and anemia in Wilson disease.

Wilson disease (WD) is a rare hereditary condition that is caused by a genetic defect in the copper-transporting ATPase ATP7B that results in hepatic copper accumulation and lethal liver failure. The present study focuses on the structural mitochondrial alterations that precede clinical symptoms in the livers of rats lacking Atp7b, an animal model for WD. Liver mitochondria from these Atp7b–/– rats contained enlarged cristae and widened intermembrane spaces, which coincided with a massive mitochondrial accumulation of copper. These changes, however, preceded detectable deficits in oxidative phosphorylation and biochemical signs of oxidative damage, suggesting that the ultrastructural modifications were not the result of oxidative stress imposed by copper- dependent Fenton chemistry. In a cell-free system containing a reducing dithiol agent, isolated mitochondria exposed to copper underwent modifications that were closely related to those observed in vivo. In this cell-free system, copper induced thiol modifications of three abundant mitochondrial membrane proteins, and this correlated with reversible intramitochondrial membrane crosslinking, which was also observed in liver mitochondria from Atp7b–/– rats. In vivo, copper-chelating agents reversed mitochondrial accumulation of copper, as well as signs of intra-mitochondrial membrane crosslinking, thereby preserving the functional and structural integrity of mitochondria. Together, these findings suggest that the mitochondrion constitutes a pivotal target of copper in WD.