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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 (TNFα). 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 TNFα. The homeostatic role of albumin was also investigated in a mouse model of TNFα-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 β-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 TNFα 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 TNFα damage were associated with the restoration of a breakpoint between isocitrate and α-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 TNFα. 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., (© 2023 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.)

Besides its oncotic power, albumin exerts pleiotropic actions, including binding, transport, and detoxification of endogenous and exogenous molecules, antioxidant activity, and modulation of immune and inflammatory responses. In particular, recent studies have demonstrated that albumin reduces leukocyte cytokine production. Here, we investigated whether albumin also has the ability to protect tissues from the damaging actions of these inflammatory mediators. We circumscribed our investigation to tumor necrosis factor (TNF) α, which exemplifies the connection between immunity and tissue injury. In vivo experiments in analbuminemic mice showed that these mice exhibit a more pronounced response to a model of TNFα-mediated liver injury induced by the administration of lipopolysaccharide (LPS) and D-galactosamine (D-gal). A tissue protective action against LPS/D-gal liver injury was also observed during the administration of human albumin to humanized mice expressing the human genes for albumin and neonatal Fc receptor (hAlb +/+ /hFcRn +/+ ) with preestablished carbon tetrachloride (CCl 4 )-induced early cirrhosis. The cytoprotective actions of albumin against TNFα-induced injury were confirmed ex vivo, in precision-cut liver slices, and in vitro, in primary hepatocytes in culture. Albumin protective actions were independent of its scavenging properties and were reproduced by recombinant human albumin expressed in Oryza sativa. Albumin cytoprotection against TNFα injury was related to inhibition of lysosomal cathepsin B leakage accompanied by reductions in mitochondrial cytochrome c release and caspase-3 activity. These data provide evidence that in addition to reducing cytokines, the albumin molecule also has the ability to protect tissues against inflammatory injury., (© 2021 Federation of American Societies for Experimental Biology.)

Specialized proresolving mediators (SPMs) biosynthesized from docosahexaenoic acids (DHAs) including resolvins (Rvs), protectins, and maresins are potent endogenous autacoids that actively resolve inflammation, protect organs, and stimulate tissue regeneration. Our hypothesis was that failure of resolution programs may lead to unremitting inflammation in obesity, contributing to the development of metabolic comorbidities in this condition. Obese individuals with persistent low-grade systemic inflammation showed reduced leukocyte production of the DHA-derived monohydroxy fatty acid 17-hydroxy-DHA (HDHA) and unbalanced formation of SPMs (in particular D-series Rvs) accompanied by enhanced production of proinflammatory lipid mediators such as leukotriene B 4 . Mechanistic studies attributed this impairment to reduced 15-lipoxygenase (LOX) activity rather than altered DHA cellular uptake. Moreover, leukocytes from obese individuals exhibited decreased 5-LOX levels and reduced 5-LOX Ser271 phosphorylation and distinct intracellular 5-LOX redistribution. However, 15-LOX appears to be the most critical factor for the deficient production of SPMs by obese leukocytes because the formation of D-series Rvs was completely rescued by incubation with the intermediate precursor 17-HDHA. These data provide proof of concept that administration of intermediate precursors of SPM biosynthesis ( e.g. , 17-HDHA) could be more efficient in overriding impaired formation of these proresolving lipid mediators in conditions characterized by dysfunctional LOX activity, such as obesity.-López-Vicario, C., Titos, E., Walker, M. E., Alcaraz-Quiles, J., Casulleras, M., Durán-Güell, M., Flores-Costa, R., Pérez-Romero, N., Forné, M., Dalli, J., Clària, J. Leukocytes from obese individuals exhibit an impaired SPM signature.

Endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) are hallmarks of nonalcoholic fatty liver disease (NAFLD), which is the hepatic manifestation of the metabolic syndrome associated with obesity. The specialized proresolving lipid mediator maresin 1 (MaR1) preserves tissue homeostasis by exerting cytoprotective actions, dampening inflammation, and expediting its timely resolution. Here, we explored whether MaR1 protects liver cells from lipotoxic and hypoxia-induced ER stress. Mice were rendered obese by high-fat diet feeding, and experiments were performed in primary hepatocytes, Kupffer cells, and precision-cut liver slices (PCLSs). Palmitate-induced lipotoxicity increased ER stress and altered autophagy in hepatocytes, effects that were prevented by MaR1. MaR1 protected hepatocytes against lipotoxicity-induced apoptosis by activating the UPR prosurvival mechanisms and preventing the excessive up-regulation of proapoptotic pathways. Protective MaR1 effects were also seen in hepatocytes challenged with hypoxia and TNF-α-induced cell death. High-throughput microRNA (miRNA) sequencing revealed that MaR1 actions were associated with specific miRNA signatures targeting both protein folding and apoptosis. MaR1 also prevented lipotoxic-triggered ER stress and hypoxia-induced inflammation in PCLSs and enhanced Kupffer cell phagocytic capacity. Together, these findings describe the ability of MaR1 to oppose ER stress in liver cells under conditions frequently encountered in NAFLD.-Rius, B., Duran-Güell, M., Flores-Costa, R., López-Vicario, C., Lopategi, A., Alcaraz-Quiles, J., Casulleras, M., Lozano, J. J., Titos, E., Clària, J. The specialized proresolving lipid mediator maresin 1 protects hepatocytes from lipotoxic and hypoxia-induced endoplasmic reticulum stress., (© FASEB.)