The effect of chronic alcohol consumption on mitochondrial calcium handling in hepatocytes

Abstract

The damage to liver mitochondria is universally observed in both humans and animal models after excessive alcohol consumption. Acute alcohol treatment has been shown to stimulate calcium (Ca) release from internal stores in hepatocytes. The resultant increase in cytosolic Ca is expected to be accumulated by neighboring mitochondria, which could potentially lead to mitochondrial Ca overload and injury. Our data indicate that total and free mitochondrial matrix Ca levels are, indeed, elevated in hepatocytes isolated from alcohol-fed rats compared with their pair-fed control littermates. In permeabilized hepatocytes, the rates of mitochondrial Ca uptake were substantially increased after chronic alcohol feeding, whereas those of mitochondrial Ca efflux were decreased. The changes in mitochondrial Ca handling could be explained by an up-regulation of the mitochondrial Ca uniporter and loss of a cyclosporin A-sensitive Ca transport pathway. In intact cells, hormone-induced increases in mitochondrial Ca declined at slower rates leading to more prolonged elevations of matrix Ca in the alcohol-fed group compared with controls. Moreover, treatment with submaximal concentrations of Ca-mobilizing hormones markedly increased the levels of mitochondrial reactive oxygen species (ROS) in hepatocytes from alcohol-fed rats, but did not affect ROS levels in controls. The changes in mitochondrial Ca handling are expected to buffer and attenuate cytosolic Ca increases induced by acute alcohol exposure or hormone stimulation. However, these alterations in mitochondrial Ca handling may also lead to Ca overload during cytosolic Ca increases, which may stimulate the production of mitochondrial ROS, and thus contribute to alcohol-induced liver injury.

Alcohol and calcium make a potent cocktail

“…Although mitochondrial Ca 2+ was not directly measured in the current study, the authors have recently reported that several parameters of mitochondrial Ca 2+ signalling, as well as mitochondrial ROS formation, are increased in ALD (Wang et al . ). In the current work, the related measurement of aconitase activity furthermore confirms that chronic ethanol feeding results in increased mitochondrial ROS formation.…”

Chronic alcohol feeding potentiates hormone‐induced calcium signalling in hepatocytes

“…As we reported previously, there was also an alcohol‐dependent decrease in nuclear and mitochondrial encoded polypeptide subunits involved in the assembly of mitochondrial respiratory chain complexes I and IV, suggesting the onset of mitochondrial injury (see Wang et al . ). However, consistent with previous studies we observed no evidence for increased fibrosis using Sirius red staining as a readout.…”

“…We have also reported that mitochondrial Ca 2+ levels and mitochondrial ROS formation are elevated in hepatocytes from alcohol‐fed rats compared to control (Wang et al . ). Importantly, hormone challenge selectively increased mitochondrial ROS levels in the alcohol group, providing support for our hypothesis that the chronic alcohol‐dependent shift in Ca 2+ responses may increase oxidative damage and cell injury.…”

“…) and calcium‐induced ROS production is increased in alcohol‐fed rat hepatocytes (Wang et al . ). Additionally, the dysregulation of Ca 2+ signalling is emerging as a underlying factor in tumorigenic progression and metastasis (Stewart et al .…”

Mitochondrial fusion and Bid-mediated mitochondrial apoptosis are perturbed by alcohol with distinct dependence on its metabolism

“…Dysregulation of ΔΨ m or Ca 2+ transport could also cause a decrease in mitochondrial fusion. In hepatocytes isolated from EtOH-fed animals, Gaspers et al 41 reported higher levels and uptake of mitochondrial Ca 2+ , attributed to higher expression of VDAC (voltage-dependent anion channel) and MCU (mitochondrial Ca 2+ uniporter) proteins. However, in VL-17A or HepG2 cells, EtOH treatment did not change mitochondrial Ca 2+ uptake or ΔΨ m excluding the role of these factors in fusion inhibition.…”