Lack of effect of long-term glutathione administration on aflatoxin B1-induced hepatoma in male rats

Functional Characterization and Whole-Genome Analysis of an Aflatoxin-Degrading Rhodococcus pyridinivorans Strain

Simple Summary

The microbiological degradation of AFB₁ has been a promising approach to control AFB₁ contamination. Here, we characterize a Rhodococcus pyridinivorans strain that can efficiently degrade AFB₁. The AFB₁-degrading capacity of this bacterial strain was characterized, and the completed genome was sequenced and analyzed. Further proteomic analyses of this strain identified a total of 723 proteins in an extracellular component that showed the strongest capacity to degrade AFB₁ (degradation rate 83.7%). Multiple potential AFB₁-degrading enzymes, and enzymes that are reported to respond to AFB₁ treatment, have been identified accordingly. These findings provide a genomic, proteomic, and experimental approach for characterizing an efficient AFB₁-degrading bacterial strain with great potential for use in the remediation of AFB₁ contamination.

Abstract

Aflatoxin B₁ (AFB₁) is one of the most toxic, naturally occurring carcinogen compounds and is produced by specific strains of fungi. Crop contamination with AFB₁ can cause huge economic losses and serious health problems. Many studies have examined the microbiological degradation of AFB₁, especially the use of efficient AFB₁-degrading microorganisms, to control AFB₁ contamination. Here, we reported the identification of a new Rhodococcus pyridinivorans strain (4-4) that can efficiently degrade AFB₁ (degradation rate 84.9%). The extracellular component of this strain showed the strongest capacity to degrade AFB₁ (degradation rate 83.7%). The effects of proteinase K, SDS, temperature, pH, incubation time, and AFB₁ concentration on the AFB₁ degradation ability of the extracellular component were investigated. We sequenced the complete genome of this strain, encoding 5246 protein-coding genes and 169 RNA genes on a circular chromosome and two plasmids. Comparative genomic analysis revealed high homology with other Rhodococcus strains with high AFB₁-degradation ability. Further proteomic analyses of this strain identified a total of 723 proteins in the extracellular component, including multiple potential AFB₁-degrading enzymes, along with enzymes that are reported to response to AFB₁ treatment. Overall, the results demonstrate that R. pyridinivorans 4-4 would be an excellent candidate for the biodegradation and detoxification of AFB₁ contamination.

Glutathione treatment of hepatocellular carcinoma

This prospective study was undertaken to substantiate observations that glutathione (GSH) inhibits or reverses tumor growth in humans with hepatocellular carcinoma (HCC), a neoplasm with an extremely poor prognosis. Eight patients with biopsy-proven HCC not amenable to surgery were given 5 g of GSH daily from the time of diagnosis. Two patients withdrew shortly after receiving GSH due to intolerable side-effects. Of the six eligible patients, two had mildly advanced tumors and four moderately advanced tumors. At 1-2-month intervals the liver was CT and ultra-sound scanned to assess the growth status of the tumor (progression, stagnation or regression). All the patients, except a male with a fibrolamellar type of HCC, died within 1 year after diagnosis. Two women with moderately advanced tumors survived almost 1 year, tumor growth stopped or regressed and in one of the women an initially abnormal alfa-1-fetoprotein (AFP) returned to normal after GSH treatment. AFP remained normal throughout the treatment period in the other women. These observations indicate that GSH may have a sex-dependent effect on HCC. However, further studies involving more patients are required to pursue this hypothesis.

Effects of antioxidants on aflatoxin-induced hepatic tumors in rats

Female Wistar rats pretreated with Aflatoxin B1 (AFB) were administered reduced glutathione, butylated hydroxytoluene, methionine or ascorbic acid on a daily basis, p.o., for 8 months. None of the treatments produced a decrease in incidence or size of hepatic nodules. While there was some evidence that ascorbic acid reduced the incidence of cystic cholangioma, the ascorbic acid and methionine treatment groups also contained significantly fewer animals surviving to the 26-month sacrifice. The lack of effect of glutathione is not consistent with previous work showing a marked glutathione dependent regression of AFB-induced hepatocellular carcinoma.

Effect of glutathione and N-acetylcysteine on hepatocellular modifications induced by 2-acetylaminofluorene

The exposure of rats to a dietary regimen containing 2-acetylaminofluorene induces a sequence of hepatocellular alterations leading to the development of preneoplastic nodules. Groups of 2-acetylaminofluorene-treated rats were given glutathione or N-acetylcysteine to evaluate the effects of these different thiols on the sequence of events that originate transformed cells. It is well known that intracellular thiols protect biological macromolecules from scavenging free radicals and electrophilic compounds produced by the metabolism of chemical agents. Male Wistar rats were maintained on a feeding regimen containing 0.05% 2-acetylaminofluorene. The diet of 2 groups of 2-acetylaminofluorene-treated animals was supplemented with either 0.1% glutathione or N-acetylcysteine. The effects in the liver of the exogenously supplied thiols during 2-acetylaminofluorene treatment were assessed evaluating DNA damage, glutathione levels, activity of marker enzymes glucose-6-phosphatase, gamma-glutamyltranspeptidase, and glutathione-S-transferase, survival rates, and development of salivary gland tumors. Our results demonstrate that the mortality due to 2-acetylaminofluorene exposure was reduced or completely abolished by thiols and that the development of salivary gland tumors was inhibited. Exogenously supplied thiols significantly reduced DNA damage as assessed by alkaline elution. At the doses employed, glutathione and N-acetylcysteine induce early stimulation of glutathione-S-transferase, had little effect on the loss of glucose-6-phosphatase activity and scanty influence on the net increase in gamma-glutamyltranspeptidase activity.