Essential role for albumin in preserving liver cells from TNFα-induced mitochondrial injury

Cytokine-induced inflammation and mitochondrial oxidative stress are key drivers of liver tissue injury. Here, we describe experiments modeling hepatic inflammatory conditions in which plasma leakage leads to large amounts of albumin to reach the interstitium and parenchymal surfaces to explore whether this protein plays a role in preserving hepatocyte mitochondria against the damaging actions of the cytotoxic cytokine tumor necrosis factor alpha (TNF alpha). Hepatocytes and precision-cut liver slices were cultured in the absence or presence of albumin in the cell media and then exposed to mitochondrial injury with the cytokine TNF alpha. The homeostatic role of albumin was also investigated in a mouse model of TNF alpha-mediated liver injury induced by lipopolysaccharide and D-galactosamine (LPS/D-gal). Mitochondrial ultrastructure, oxygen consumption, ATP and reactive oxygen species (ROS) generation, fatty acid beta-oxidation (FAO), and metabolic fluxes were assessed by transmission electron microscopy (TEM), high-resolution respirometry, luminescence-fluorimetric-colorimetric assays and NADH/FADH(2) production from various substrates, respectively. TEM analysis revealed that in the absence of albumin, hepatocytes were more susceptible to the damaging actions of TNF alpha and showed more round-shaped mitochondria with less intact cristae than hepatocytes cultured with albumin. In the presence of albumin in the cell media, hepatocytes also showed reduced mitochondrial ROS generation and FAO. The mitochondria protective actions of albumin against TNF alpha damage were associated with the restoration of a breakpoint between isocitrate and alpha-ketoglutarate in the tricarboxylic acid cycle and the upregulation of the antioxidant activating transcription factor 3 (ATF3). The involvement of ATF3 and its downstream targets was confirmed in vivo in mice with LPS/D-gal-induced liver injury, which showed increased hepatic glutathione levels, indicating a reduction in oxidative stress after albumin administration. These findings reveal that the albumin molecule is required for the effective protection of liver cells from mitochondrial oxidative stress induced by TNF alpha. These findings emphasize the importance of maintaining the albumin levels in the interstitial fluid within the normal range to protect the tissues against inflammatory injury in patients with recurrent hypoalbuminemia.