Mitochondria are the main source of reactive oxygen species (ROS), most of them deriving from the mitochondrial respiratory chain. Among the numerous enzymatic and non-enzymatic antioxidant systems present in mitochondria, mitochondrial glutathione (mGSH) emerges as the main line of defense for maintaining the appropriate mitochondrial redox environment. mGSH’s ability to act directly or as a co-factor in reactions catalyzed by other mitochondrial enzymes makes its presence essential to avoid or to repair oxidative modifications that can lead to mitochondrial dysfunction and subsequently to cell death. Since mitochondrial redox disorders play a central part in many diseases, harboring optimal levels of mGSH is vitally important. In this review, we will highlight the participation of mGSH as a contributor to disease progression in pathologies as diverse as Alzheimer’s disease, alcoholic and non-alcoholic steatohepatitis, or diabetic nephropathy. Furthermore, the involvement of mitochondrial ROS in the signaling of new prescribed drugs and in other pathologies (or in other unmet medical needs, such as gender differences or coronavirus disease of 2019 (COVID-19) treatment) is still being revealed; guaranteeing that research on mGSH will be an interesting topic for years to come.

GAS6 signaling through AXL receptor contributes to the progression of nonalcoholic steatohepatitis (NASH). Soluble AXL significantly increases both in NASH patients and mouse models. Experimental AXL inhibition by bemcentinib diminishes inflammation and fibrosis, supporting its therapeutic use in NASH.BACKGROUND AND AIMS: GAS6 signaling, through the TAM receptor tyrosine kinases AXL and MERTK, participates in chronic liver pathologies. Here, we addressed GAS6/TAM involvement in Non-Alcoholic SteatoHepatitis (NASH) development.METHODS: GAS6/TAM signaling was analyzed in cultured primary hepatocytes, hepatic stellate cells (HSC) and Kupffer cells (KCs). Axl -/-, Mertk -/and wild-type C57BL/6 mice were fed with Chow, High Fat Choline-Deficient Methionine-Restricted (HFD) or methionine-choline-deficient (MCD) diet. HSC activation, liver inflammation and cytokine/chemokine production were measured by qPCR, mRNA Array analysis, western blotting and ELISA. GAS6, soluble AXL (sAXL) and MERTK (sMERTK) levels were analyzed in control individuals, steatotic and NASH patients. RESULTS:In primary mouse cultures, GAS6 or MERTK activation protected primary hepatocytes against lipid toxicity via AKT/STAT-3 signaling, while bemcentinib (small molecule AXL inhibitor BGB324) blocked AXL-induced fibrogenesis in primary HSCs and cytokine production in LPS-treated KCs. Accordingly; bemcentinib diminished liver inflammation and fibrosis in MCD-and HFD-fed mice. Upregulation of AXL and ADAM10/ADAM17 metalloproteinases increased sAXL in HFD-fed mice. Transcriptome profiling revealed major reduction in fibroticand inflammatory-related genes in HFDfed mice after bemcentinib administration. HFD-fed Mertk -/mice exhibited enhanced NASH, while Axl -/mice were partially protected. In human serum, sAXL levels augmented even at initial stages, whereas GAS6 and sMERTK increased only in cirrhotic NASH patients. In agreement, sAXL increased in HFD-fed mice before fibrosis establishment, while bemcentinib prevented liver fibrosis/inflammation in early NASH.CONCLUSION: AXL signaling, increased in NASH patients, promotes fibrosis in HSCs and inflammation in KCs, while GAS6 protects cultured hepatocytes against lipotoxicity via MERTK. Bemcentinib, by blocking AXL signaling and increasing GAS6 levels, reduces experimental NASH, revealing AXL as an effective therapeutic target for clinical practice.

Inflammation is an adaptive response in pursuit of homeostasis reestablishment triggered by harmful conditions or stimuli, such as an infection or tissue damage. Liver diseases cause approximately 2 million deaths per year worldwide and hepatic inflammation is a common factor to all of them, being the main driver of hepatic tissue damage and causing progression from non-alcoholic fatty liver disease (NAFLD) to non-alcoholic steatohepatitis (NASH), cirrhosis and, ultimately, hepatocellular carcinoma (HCC). The metabolic sensor SIRT1, a class III histone deacetylase with strong expression in metabolic tissues such as the liver, and transcription factor NF-κB, a master regulator of inflammatory response, show an antagonistic relationship in controlling inflammation. For this reason, SIRT1 targeting is emerging as a potential strategy to improve different metabolic and/or inflammatory pathologies. In this review, we explore diverse upstream regulators and some natural/synthetic activators of SIRT1 as possible therapeutic treatment for liver diseases.

Evasive mechanisms triggered by the tyrosine kinase inhibitor sorafenib reduce its efficacy in hepatocellular carcinoma (HCC) treatment. Drug-resistant cancer cells frequently exhibit sphingolipid dysregulation, reducing chemotherapeutic cytotoxicity via the induction of ceramide-degrading enzymes. However, the role of ceramide in sorafenib therapy and resistance in HCC has not been clearly established. Our data reveals that ceramide-modifying enzymes, particularly glucosylceramide synthase (GCS), are upregulated during sorafenib treatment in hepatoma cells (HepG2 and Hep3B), and more importantly, in sorafenib-resistant cell lines. GCS silencing or pharmacological GCS inhibition sensitized hepatoma cells to sorafenib exposure. GCS inhibition, combined with sorafenib, triggered cytochrome c release and ATP depletion in sorafenib-treated hepatoma cells, leading to mitochondrial cell death after energetic collapse. Conversely, genetic GCS overexpression increased sorafenib resistance. Of interest, GCS inhibition improved sorafenib effectiveness in a xenograft mouse model, recovering drug sensitivity of sorafenib-resistant tumors in mice. In conclusion, our results reveal GCS induction as a mechanism of sorafenib resistance, suggesting that GCS targeting may be a novel strategy to increase sorafenib efficacy in HCC management, and point to target the mitochondria as the subcellular location where sorafenib therapy could be potentiated.

Natural killer T (NKT) cells exhibit a specific tissue distribution, displaying the liver the highest NKT/conventional T cell ratio. Upon antigen stimulation, NKT cells secrete Th1 cytokines, including interferon γ (IFNγ), and Th2 cytokines, including IL-4 that recruit and activate other innate immune cells to exacerbate inflammatory responses in the liver. Cysteine cathepsins control hepatic inflammation by regulating κB-dependent gene expression. However, the contribution of cysteine cathepsins other than Cathepsin S to NKT cell activation has remained largely unexplored. Here we report that cysteine cathepsins, cathepsin B (CTSB) and cathepsin S (CTSS), regulate different aspects of NKT cell activation. Inhibition of CTSB or CTSS reduced hepatic NKT cell expansion in a mouse model after LPS challenge. By contrast, only CTSS inhibition reduced IFNγ and IL-4 secretion after in vivo α-GalCer administration. Accordingly, in vitro studies reveal that only CTSS was able to control α-GalCer-dependent loading in antigen-presenting cells (APCs), probably due to altered endolysosomal protein degradation. In summary, our study discloses the participation of cysteine cathepsins, CTSB and CTSS, in the activation of NKT cells in vivo and in vitro.

Inflammation and oxidative stress play a key role in the pathophysiology of advanced chronic liver disease (ACLD) and portal hypertension (PH). Considering the current lack of effective treatments, we evaluated an anti-inflammatory and antioxidant nutraceutical rich in docosahexaenoic acid (DHA) as a possible therapy for ACLD. We investigated the effects of two-week DHA supplementation (500 mg/kg) on hepatic fatty acids, PH, oxidative stress, inflammation, and hepatic stellate cell (HSC) phenotype in rats with ACLD. Additionally, the effects of DHA were evaluated in murine macrophages and human HSC. In contrast to vehicle-treated animals, cirrhotic rats receiving DHA reestablished a healthy hepatic fatty acid profile, which was associated with an improvement in PH. The mechanisms underlying this hemodynamic improvement included a reduction in oxidative stress and inflammation, as well as a marked HSC deactivation, confirmed in human HSC. Experiments with cultured macrophages showed that treatment with DHA protects against pro-inflammatory insults. The present preclinical study demonstrates that a nutraceutical rich in DHA significantly improves PH in chronic liver disease mainly by suppressing inflammation and oxidative stress-driven HSC activation, encouraging its evaluation as a new treatment for PH and cirrhosis.

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