Genetic polymorphisms in ataxin-3 and liver cirrhosis risk related to aflatoxin B1

Mitochondria, mitophagy, and the role of deubiquitinases as novel therapeutic targets in liver pathology

Liver diseases such as nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH), fibrosis, and hepatocellular carcinoma (HCC) have increased over the past few decades due to the absence or ineffective therapeutics. Recently, it has been shown that inappropriate regulation of hepatic mitophagy is linked to the pathogenesis of the above-mentioned liver diseases. As mitophagy maintains cellular homeostasis by removing damaged and nonfunctional mitochondria from the cell, the proper function of the molecules involved are of utmost importance. Thereby, mitochondrial E3 ubiquitin ligases as well as several deubiquitinases (DUBs) appear to play a unique role for the degradation of mitochondrial proteins and for proper execution of the mitophagy process by either adding or removing ubiquitin chains from target proteins. Therefore, these enzymes could be considered as valuable liver disease biomarkers and also as novel targets for therapy. In this review, we focus on the role of different DUBs on mitophagy and their contribution to NAFLD, NASH, alcohol-related liver disease, and especially HCC.

The metabolism and biotransformation of AFB1: Key enzymes and pathways

Aflatoxins B₁ (AFB₁) is a hepatoxic compound produced by Aspergillus flavus and Aspergillus parasiticus, seriously threatening food safety and the health of humans and animals. Understanding the metabolism of AFB₁ is important for developing detoxification and intervention strategies. In this review, we summarize the AFB₁ metabolic fates in humans and animals and the key enzymes that metabolize AFB₁, including cytochrome P450s (CYP450s) for AFB₁ bioactivation, glutathione-S-transferases (GSTs) and aflatoxin-aldehyde reductases (AFARs) in detoxification. Furthermore, AFB₁ metabolism in microbes is also summarized. Microorganisms specifically and efficiently transform AFB₁ into less or non-toxic products in an environmental-friendly approach which could be the most desirable detoxification strategy in the future. This review provides a wholistic insight into the metabolism and biotransformation of AFB₁ in various organisms, which also benefits the development of protective strategies in humans and animals.

Research progress on the protection and detoxification of phytochemicals against aflatoxin B1-Induced liver toxicity

Aflatoxin B₁ (AFB₁) is a potent hepatotoxic toxin, which can cause hepatitis, cirrhosis, and liver immunological damage. It has been involved in the etiology of human hepatocellular carcinoma. AFB₁ can cause oxidative stress in the body's metabolism process, and then cause cytotoxicity, such as apoptosis and DNA damage. Scientific research has discovered that phytochemicals can induce the detoxification pathway of AFB₁ through its biotransformation, thereby reducing the damage of AFB₁ to the human body. In clinical treatment, certain phytochemicals have been effectively used in the treatment of liver injury due to the advantages of multiple targets, multiple pathways, low toxicity and side effects. Therefore, the article summarizes the toxic mechanism of AFB₁-induced hepatoxicity, and the related research progress of phytochemicals for preventing and treating its cytotoxicity and genotoxicity. We also look forward to the existing problems and application prospects of phytochemicals in the pharmaceutical industry, in order to provide theoretical reference for the prevention and treatment of AFB₁ poisoning in future research work.

Aflatoxins as a risk factor for liver cirrhosis: a systematic review and meta-analysis

Background

Liver cirrhosis is characterized by fibrosis and nodule formation in the liver, due to a chronic injury, and subsequent alteration of the normal architecture of the liver. Even though there is a huge effort to elucidate the possible etiologic factors of liver cirrhosis, a significant number of cases are cryptogenic, especially in Sub Saharan Africa, where there is a high burden of aflatoxin exposure. Aflatoxins are known to cause hepatocellular carcinoma, which share similar etiologic factors with liver cirrhosis. This study aimed to assess the association between aflatoxin exposure and the risk of liver cirrhosis.

Methods

Relevant studies were identified through systematic searches conducted in Ovid MEDLINE, PubMed and Google Scholar. Also, by searching the references of retrieved articles. The abstracts and full text were screened for eligibility and the risk of bias was assessed for each study using Joanna Briggs Institute (JBI) critical appraisal checklist for observational studies. The extracted data from included studies using Microsoft Excel were exported to Stata software version 15.0 for analyses. The overall pooled estimation of outcomes was calculated using a random-effects model of DerSimonian–Laird method at a 95% confidence level. The heterogeneity of studies was determined using I2 statistics. The presence of publication bias between studies was evaluated using the Begg’s and Egger’s tests and funnel plot. The protocol of this systematic review and meta-analysis was registered in the Prospero database with reference number ID: CRD42019148481.

Results

A total of 5 studies published between the years 2005 and 2018 that met the pre-defined inclusion and exclusion criteria were included. The meta-analysis showed that a significant increase in the risk of liver cirrhosis is associated with aflatoxin exposure (unadjusted pooled odds ratio (OR) = 3.35, 95% CI: 2.74–4.10, p = 0.000; I² = 88.3%, p = 0.000; adjusted OR = 2.5, 95% CI: 1.84–3.39, p = 0.000; I² = 0%, p = 0.429).

Conclusions

The present meta-analysis suggests that aflatoxin exposure is associated with a higher risk of liver cirrhosis.

Aflatoxin B1 induces S phase arrest by upregulating the expression of p21 via MYC, PLK1 and PLD1

Aflatoxin B1 (AFB1), a member of the aflatoxin family, is a common contaminant in foods and feeds, and AFB1 exposure is associated with various clinical conditions. Thus far, research on the toxicity of AFB1 has mainly focused on its induction of liver cancer, but little research has been reported on renal toxicity, especially with regards to the underlying molecular mechanisms. In this study, we found that AFB1 treatment significantly induced kidney damage and reduced kidney weight. The human kidney cell line HEK293T was used to further study the molecular mechanism of the toxicity of AFB1 to kidney cells. We found that AFB1 significantly and dose-dependently induced S phase arrest and upregulated p21 mRNA and protein expression. Upstream of p21, three negative regulators, PLK1, MYC, and PLD1, were significantly downregulated under AFB1 treatment. Consistently, p21 was upregulated, and PLK1, MYC and PLD1 were downregulated in mouse kidney after AFB1 treatment. Interestingly, AFB1 also decreased the physical interaction between PLK1 and MYC and weakened the stability of the MYC protein. Importantly, overexpression of PLK1, MYC and PLD1 significantly blocked the upregulation of p21 and attenuated the S phase arrest caused by AFB1. In summary, AFB1 markedly induces kidney damage and strongly induces S phase arrest by upregulating the expression of p21 via PLK1, PLD1 and MYC, which represents a noval mechanism of the renal toxicity of AFB1.