Transcription profiling of cadmium-exposed livers reveals alteration of lipid metabolism and predisposition to hepatic steatosis

Unraveling cadmium-driven liver inflammation with a focus on arachidonic acid metabolites and TLR4/ IκBα /NF-κB pathway

Epidemiological studies have demonstrated exposure to cadmium ion (Cd2+) is significantly associated with the incidence and aggravation of nonalcoholic fatty liver disease (NAFLD) to non-alcoholic steatohepatitis (NASH). Cd2+ exposure could alter lipid metabolism, and changed lipid metabolites are significantly associated with NASH. Arachidonic acid (ArA) is an omega-6 polyunsaturated fatty acid. Promotion of ArA synthesis and profile changes by Cd2+ exposure potentially to cause NAFLD. ArA metabolism pathway has been identified to enrich in Cd2+ exposure-facilitated NASH. ArA could be generation an impressive metabolic profile through mainly three pathways, including Cyclooxygenases (COX), Lipoxygenases (LOX) and Cytochrome P450 (CYP450) pathway. However, the functions of these metabolites and underlying mechanism in hepatic inflammation are still not clear. In present study, by integrative transcriptomics and metabolomics analysis, we identified that the fatty acid metabolic process and the pro-inflammatory NF-κB signaling pathway were enriched in Cd2+-regulated differentially expressed genes (DEGs) and Cd2+-altered differential metabolites, such as, fatty acid biosynthesis, degradation, and ArA metabolism. The metabolites levels of LOX pathway products 5-HETE and leukotriene C4 (LTC4), and COX catalytic product prostaglandin D2 (PGD2) were significantly elevated in Cd2+ exposed mouse livers. 5-HETE, LTC4, and PGD2 were significantly positive correlated with NF-κB signaling. In addition, the synthase of 20-Hydroxyeicosatetraenoic acid (20-HETE), CYP450 gene 4 family (CYP4A32), was also involved in NF-κB signaling network. Results from both in vitro and in vivo proved that Cd2+ exposure increased ArA metabolite to PGD2 and 20-HETE, and upregulated the mRNA level of their catalytic enzyme PGDS and CYP4A32. Cd2+-induced ArA metabolite to PGD2 and 20-HETE promoted activation of TLR4/IκBα/NF-κB signaling and pro-inflammatory of hepatocytes. Our study explores novel molecular mechanism of Cd2+ exposure-aggravated liver diseases and provides potential novel targets for in hepatic inflammatory treatments and prevention.

Cadmium exacerbates liver injury by remodeling ceramide metabolism: Multiomics and laboratory evidence

Cadmium (Cd) is a toxic heavy metal that primarily targets the liver. Cd exposure disrupts specific lipid metabolic pathways; however, the underlying mechanisms remain unclear. This study aimed to investigate the lipidomic characteristics of rat livers after Cd exposure as well as the potential mechanisms of Cd-induced liver injury. Our analysis of established Cd-exposed rat and cell models showed that Cd exposure resulted in liver lipid deposition and hepatocyte damage. Lipidomic detection, transcriptome sequencing, and experimental analyses revealed that Cd mainly affects the sphingolipid metabolic pathway and that the changes in ceramide metabolism are the most significant. In vitro experiments revealed that the inhibition of ceramide synthetase activity or activation of ceramide decomposing enzymes ameliorated the proapoptotic and pro-oxidative stress effects of Cd, thereby alleviating liver injury. In contrast, the exogenous addition of ceramide aggravated liver injury. In summary, Cd increased ceramide levels by remodeling ceramide synthesis and catabolism, thereby promoting hepatocyte apoptosis and oxidative stress and ultimately aggravating liver injury. Reducing ceramide levels can serve as a potential protective strategy to mitigate the liver toxicity of Cd. This study provides new evidence for understanding Cd-induced liver injury at the lipidomic level and insights into the health risks and toxicological mechanisms associated with Cd.

Sex, Nutrition, and NAFLD: Relevance of Environmental Pollution

Non-alcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease and represents an increasing public health issue given the limited treatment options and its association with several other metabolic and inflammatory disorders. The epidemic, still growing prevalence of NAFLD worldwide cannot be merely explained by changes in diet and lifestyle that occurred in the last few decades, nor from their association with genetic and epigenetic risk factors. It is conceivable that environmental pollutants, which act as endocrine and metabolic disruptors, may contribute to the spreading of this pathology due to their ability to enter the food chain and be ingested through contaminated food and water. Given the strict interplay between nutrients and the regulation of hepatic metabolism and reproductive functions in females, pollutant-induced metabolic dysfunctions may be of particular relevance for the female liver, dampening sex differences in NAFLD prevalence. Dietary intake of environmental pollutants can be particularly detrimental during gestation, when endocrine-disrupting chemicals may interfere with the programming of liver metabolism, accounting for the developmental origin of NAFLD in offspring. This review summarizes cause-effect evidence between environmental pollutants and increased incidence of NAFLD and emphasizes the need for further studies in this field.

Chronic exposure to low-dose cadmium facilitated nonalcoholic steatohepatitis in mice by suppressing fatty acid desaturation

Exposure to cadmium (Cd), a toxic metal, is epidemiologically linked to nonalcoholic steatohepatitis (NASH) in humans. However, the role of Cd in NASH remains to be fully elucidated. This study employed a novel murine NASH model to investigate the effects of chronic low-dose Cd on hepatic pathology and its underlying mechanisms. NASH is characterized by lipid accumulation, extensive cell death, and persistent inflammation in the liver. We found that treatment with Cd in drinking water (10 mg/L) for 6 or 12 weeks significantly boosted hepatic fat deposition, increased hepatocyte destruction, and amplified inflammatory responses in mice, confirming that low-dose Cd can facilitate NASH development in vivo. Mechanistically, chronic Cd exposure reshaped the hepatic transcriptional landscape, with PPAR-mediated fatty acid metabolic pathways being the most significantly altered. In particular, Cd repressed fatty acid desaturation, leading to the accumulation of saturated fatty acids whose lipotoxicity exacerbated cell death and, consequently, inflammatory activation. In summary, we validated the causal effects of chronic low-dose Cd on NASH in vivo and identified the fatty acid desaturation program as a novel target for Cd to instigate hepatopathological alterations.