Metabolomic analysis shows dysregulation in amino acid and NAD+ metabolism in palmitate treated hepatocytes and plasma of non-alcoholic fatty liver disease spectrum

Comprehensive metabolomics study identifies SN-38 organ specific toxicity in mice

SN-38 (7-ethyl-10-hydroxycamptothecin), the active metabolite of irinotecan, is a crucial anticancer agent frequently studied in drug delivery systems. Irinotecan (CPT-11) is used to treat various solid tumors but is associated with adverse effects such as nausea, vomiting, diarrhea, and steatohepatitis. However, the precise biochemical pathways underlying these side effects remain unclear. To explore SN-38's toxic mechanisms and provide insights for clinical applications of SN-38 delivery systems, we performed untargeted metabolomics to assess metabolic changes in the lungs, heart, stomach, blood, spleen, intestine, liver, and kidneys of SN-38-exposed male mice. Mice were divided into two groups: SN-38 (20 mg/kg/day intraperitoneal) and control (blank solvent). Gas chromatography-mass spectrometry (GC-MS) identified significant metabolic disturbances in all tissues. Specifically, 24, 15, 12, 21, 35, 26, 18, and 28 differential metabolites were detected in the lungs, heart, stomach, blood, spleen, intestine, liver, and kidneys, respectively. KEGG pathway enrichment revealed significant changes in metabolic pathways across these organs, particularly in purine, pyrimidine, amino acid, and glyceric acid metabolism, implicating disruptions in protein synthesis, cellular homeostasis, energy metabolism, and antioxidant defenses. This study is the first to characterize SN-38's multi-organ toxicity using metabolomics.

Knockout of Trpc6 attenuates T2DM-induced liver injury and inflammation by inhibiting CN-NFAT2-NLRP3 signalling in mice

Diabetic liver disease is a common complication of diabetes mellitus that poses significant harm to patients. Transient receptor potential cation channel 6 (TRPC6) is a non-selective cation channel with calcium permeability, playing a key role in signalling pathways associated with liver disease progression. This study aimed to investigate the effects of Trpc6 knockout on liver injury and its regulation of the calcineurin (CN)-nuclear factor of activated T cells 2 (NFAT2) signalling pathway in mice with type 2 diabetes mellitus (T2DM). Serum aspartate aminotransferase and alanine aminotransferase levels were measured to assess liver function, while haematoxylin and eosin staining, periodic acid-Schiff staining, and Masson staining were used to evaluate pathological injury. Nile Red and Oil Red O staining were performed to assess hepatic lipid deposition. Western blotting, quantitative real-time polymerase chain reaction, and immunohistochemistry were used to analyse fibrosis- and inflammation-related markers in mouse liver tissues. The results showed that Trpc6 knockout had no significant effect on hepatic lipid deposition, CD36 expression, or phosphorylated phospholipase C levels in the liver tissues of mice with T2DM. However, Trpc6 knockout significantly inhibited NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome activation, thereby alleviating liver injury and fibrosis in mice with T2DM. Further findings indicated that Trpc6 knockout markedly reduced CN and NFAT2 expression in T2DM liver tissues and resisted intracellular calcium overload in liver cells in vitro. This study suggests that Trpc6 knockout attenuates T2DM-induced hepatic inflammation and fibrosis by inhibiting hepatocyte calcium overload and suppressing the CN-NFAT2-NLRP3 signalling pathway.

Role of Kynurenine and Its Derivatives in Liver Diseases: Recent Advances and Future Clinical Perspectives

Liver health is integral to overall human well-being and the pathogenesis of various diseases. In recent years, kynurenine and its derivatives have gradually been recognized for their involvement in various pathophysiological processes, especially in the regulation of liver diseases, such as acute liver injury, non-alcoholic fatty liver disease, cirrhosis, and liver cancer. Kynurenine and its derivatives are derived from tryptophan, which is broken down by the enzymes indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO), converting the essential amino acid tryptophan into kynurenine (KYN) and other downstream metabolites, such as kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK), xanthurenic acid (XA), and quinolinic acid (QA). In liver diseases, kynurenine and its derivatives can promote the activity of the transcription factor aryl hydrocarbon receptor (AhR), suppress T cell activity for immune modulation, inhibit the activation of inflammatory signaling pathways, such as NF-κB for anti-inflammatory effects, and inhibit the activation of hepatic stellate cells to slow down fibrosis progression. Additionally, kynurenine and other downstream metabolites can influence the progression of liver diseases by modulating the gut microbiota. Therefore, in this review, we summarize and explore the mechanisms by which kynurenine and its derivatives regulate liver diseases to help develop new diagnostic or prognostic biomarkers and effective therapies targeting the kynurenine pathway for liver disease treatment.

Palmitic acid causes hepatocyte inflammation by suppressing the BMAL1-NAD+-SIRT2 axis

Palmitic acid is the most abundant saturated fatty acid in circulation and causes hepatocyte toxicity and inflammation. As saturated fatty acid can also disrupt the circadian rhythm, the present work evaluated the connection between clock genes and NAD+ dependent Sirtuins in protecting hepatocytes from lipid-induced damage. Hepatocytes (immortal cells PH5CH8, hepatoma cells HepG2) treated with higher doses of palmitic acid (400-600μM) showed typical features of steatosis accompanied with growth inhibition and increased level of inflammatory markers (IL-6 IL-8, IL-1α and IL-1β) together with decline in NAD+ levels. Palmitic acid treated hepatocytes showed significant decline in not only the protein levels of SIRT2 but also its activity as revealed by the acetylation status of its downstream targets (Tubulin and NF-ƙB). Additionally, the circadian expression of both SIRT2 and BMAL1 was inhibited in presence of palmitic acid in only the non-cancerous hepatocytes, PH5CH8 cells. Clinical specimens obtained from subjects with NASH-associated fibrosis, ranging from absent (F0) to cirrhosis (F4), showed a significant decline in levels of SIRT2 and BMAL1, especially in the cirrhotic liver. Ectopic expression of BMAL1 or activating SIRT2 by supplementation with nicotinamide riboside (precursor of NAD+) dampened the palmitic acid induced lipoinflammation and lipotoxicity more effectively in PH5CH8 cells as compared to HepG2 cells. Mechanistically, palmitic acid caused transcriptional suppression of SIRT2 by disrupting the chromatin occupancy of BMAL1 at its promoter site. Overall, the work suggested that SIRT2 is a clock-controlled gene that is transcriptionally regulated by BMAL1. In conclusion the activation of the BMAL1-NAD+-SIRT2 axis shows hepatoprotective effects by preventing lipotoxicity and dampening inflammation.

Molecular mechanism and therapeutic significance of essential amino acids in metabolically associated fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), also known as metabolically associated fatty liver disease (MAFLD), is a systemic metabolic disease characterized by lipid accumulation in the liver, lipid toxicity, insulin resistance, intestinal dysbiosis, and inflammation that can progress from simple steatosis to nonalcoholic steatohepatitis (NASH) and even cirrhosis or cancer. It is the most prevalent illness threatening world health. Currently, there are almost no approved drug interventions for MAFLD, mainly dietary changes and exercise to control weight and regulate metabolic disorders. Meanwhile, the metabolic pathway involved in amino acid metabolism also influences the onset and development of MAFLD in the body, and most amino acid metabolism takes place in the liver. Essential amino acids are those amino acids that must be supplemented from outside the diet and that cannot be synthesized in the body or cannot be synthesized at a rate sufficient to meet the body's needs, including leucine, isoleucine, valine (collectively known as branched-chain amino acids), tryptophan, phenylalanine (which are aromatic amino acids), histidine, methionine, threonine and lysine. The metabolic balance of the body is closely linked to these essential amino acids, and essential amino acids are closely linked to the pathophysiological process of MAFLD. In this paper, we will focus on the metabolism of essential amino acids in the body and further explore the therapeutic strategies for MAFLD based on the studies conducted in recent years.

Palmitoylation-driven PHF2 ubiquitination remodels lipid metabolism through the SREBP1c axis in hepatocellular carcinoma

Palmitic acid (PA) is the most common fatty acid in humans and mediates palmitoylation through its conversion into palmitoyl coenzyme A. Although palmitoylation affects many proteins, its pathophysiological functions are only partially understood. Here we demonstrate that PA acts as a molecular checkpoint of lipid reprogramming in HepG2 and Hep3B cells. The zinc finger DHHC-type palmitoyltransferase 23 (ZDHHC23) mediates the palmitoylation of plant homeodomain finger protein 2 (PHF2), subsequently enhancing ubiquitin-dependent degradation of PHF2. This study also reveals that PHF2 functions as a tumor suppressor by acting as an E3 ubiquitin ligase of sterol regulatory element-binding protein 1c (SREBP1c), a master transcription factor of lipogenesis. PHF2 directly destabilizes SREBP1c and reduces SREBP1c-dependent lipogenesis. Notably, SREBP1c increases free fatty acids in hepatocellular carcinoma (HCC) cells, and the consequent PA induction triggers the PHF2/SREBP1c axis. Since PA seems central to activating this axis, we suggest that levels of dietary PA should be carefully monitored in patients with HCC.

Roles of gut microbes in metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) is the most common chronic liver disease. Gut dysbiosis is considered a significant contributing factor in disease development. Increased intestinal permeability can be induced by gut dysbiosis, followed by the entry of lipopolysaccharide into circulation to reach peripheral tissue and result in chronic inflammation. We reviewed how microbial metabolites push host physiology toward MAFLD, including short-chain fatty acids (SCFAs), bile acids, and tryptophan metabolites. The effects of SCFAs are generally reported as anti-inflammatory and can improve intestinal barrier function and restore gut microbiota. Gut microbes can influence intestinal barrier function through SCFAs produced by fermentative bacteria, especially butyrate and propionate producers. This is achieved through the activation of free fatty acid sensing receptors. Bile is directly involved in lipid absorption. Gut microbes can alter bile acid composition by bile salt hydrolase-producing bacteria and bacterial hydroxysteroid dehydrogenase-producing bacteria. These bile acids can affect host physiology by activating farnesoid X receptor Takeda G protein-coupled receptor 5. Gut microbes can also induce MAFLD-associated symptoms by producing tryptophan metabolites kynurenine, serotonin, and indole-3-propionate. A summary of bacterial genera involved in SCFAs production, bile acid transformation, and tryptophan metabolism is provided. Many bacteria have demonstrated efficacy in alleviating MAFLD in animal models and are potential therapeutic candidates for MAFLD.

Mass spectrometry-based untargeted metabolomics study of non-obese individuals with non-alcoholic fatty liver disease

OBJECTIVES

Non-alcoholic fatty liver disease (NAFLD) is a disease characterized by the accumulation of excessive fat in the liver, which can lead to fibrosis and has an increasing prevalence. NAFLD requires non-invasive diagnostic biomarkers. While typically observed in overweight individuals, it can also occur in non-obese/non-overweight individuals. Comparative studies on non-obese NAFLD patients are scarce. This study aimed to conduct a using liquid chromatography-high resolution mass spectrometry (LC-MS/MS)-based metabolic profiling of non-obese NAFLD patients and healthy controls.

MATERIALS AND METHODS

The patient group consisted of 27 individuals with NAFLD, while the healthy control group included 39 individuals. Both groups were between 18 and 40 years old, had a BMI of less than 25 and had alcohol consumption less than 20 g/week for men and 10 g/week for women. Serum samples were collected and analyzed using LC-MS/MS. The data were analyzed using the TidyMass and MetaboAnalyst.

RESULTS

The LC-MS/MS analyses detected significant changes in D-amino acid metabolism, vitamin B6 metabolism, apoptosis, mTOR signaling pathway, lysine degradation, and phenylalanine metabolism pathways in non-obese NAFLD patients. Significant changes were also observed in the metabolites D-pantothenic acid, hypoxanthine, citric acid, citramalic acid, L-phenylalanine, glutamine, and histamine-trifluoromethyl-toluidide, β-hydroxymyristic acid, DL-Lactic acid, and 3-methyl-2-oxopentanoic. Overall, the study provides valuable insights into the metabolic changes associated with non-obese NAFLD patients and can contribute to the development of non-invasive diagnostic biomarkers for NAFLD.

CONCLUSIONS

This study sheds light on the metabolic changes in non-obese NAFLD patients. Further research is needed to better understand the metabolic changes associated with NAFLD and to develop effective treatment options.

Therapeutic application of natural products: NAD+ metabolism as potential target

BACKGROUND

Nicotinamide adenine dinucleotide (NAD⁺) metabolism is involved in the entire physiopathological process and is critical to human health. Long-term imbalance in NAD⁺ homeostasis is associated with various diseases, including non-alcoholic fatty liver disease, diabetes mellitus, cardiovascular diseases, neurodegenerative disorders, aging, and cancer, making it a potential target for effective therapeutic strategies. Currently, several natural products that target NAD⁺ metabolism have been widely reported to have significant therapeutic effects, but systematic summaries are lacking.

PURPOSE

To summarize the latest findings on the prevention and treatment of various diseases through the regulation of NAD⁺ metabolism by various natural products in vivo and in vitro models, and evaluate the toxicities of the natural products.

METHODS

PubMed, Web of Science, and ScienceDirect were searched using the keywords "natural products sources," "toxicology," "NAD⁺ clinical trials," and "NAD⁺," and/or paired with "natural products" and "diseases" for studies published within the last decade until January 2023.

RESULTS

We found that the natural products mainly include phenols (curcumin, cyclocurcumin, 4-hydroxybenzyl alcohol, salvianolic acid B, pterostilbene, EGCG), flavonoids (pinostrobin, apigenin, acacetin, tilianin, kaempferol, quercetin, isoliquiritigenin, luteolin, silybin, hydroxysafflor yellow A, scutellarin), glycosides (salidroside), quinones (emodin, embelin, β-LAPachone, shikonin), terpenoids (notoginsenoside R1, ginsenoside F2, ginsenoside Rd, ginsenoside Rb1, ginsenoside Rg3, thymoquinone, genipin), pyrazines (tetramethylpyrazine), alkaloids (evodiamine, berberine), and phenylpropanoids (ferulic acid). These natural products have antioxidant, energy-producing, anti-inflammatory, anti-apoptotic and anti-aging effects, which mainly influence the NAMPT/NAD⁺/SIRT, AMPK/SIRT1/PGC-1α, Nrf2/HO-1, PKCs/PARPs/NF-κB, and AMPK/Nrf2/mTOR signaling pathways, thereby regulating NAD⁺ metabolism to prevent and treat various diseases. These natural products have been shown to be safe, tolerable and have fewer adverse effects in various in vivo and in vitro studies and clinical trials.

CONCLUSION

We evaluated the toxic effects of natural products and summarized the available clinical trials on NAD⁺ metabolism, as well as the recent advances in the therapeutic application of natural products targeting NAD⁺ metabolism, with the aim to provide new insights into the treatment of multiple disorders.