Implications of hydrogen sulfide in liver pathophysiology: Mechanistic insights and therapeutic potential

Background

Over the last several decades, hydrogen sulfide (H₂S) has been found to exert multiple physiological functions in mammal systems. The endogenous production of H₂S is primarily mediated by cystathione β-synthase (CBS), cystathione γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (3-MST). These enzymes are widely expressed in the liver tissues and regulate hepatic functions by acting on various molecular targets.

Aim of Review

In the present review, we will highlight the recent advancements in the cellular events triggered by H₂S under liver diseases. The therapeutic effects of H₂S donors on hepatic diseases will also be discussed.

Key Scientific Concepts of Review

As a critical regulator of liver functions, H₂S is critically involved in the etiology of various liver disorders, such as nonalcoholic steatohepatitis (NASH), hepatic fibrosis, hepatic ischemia/reperfusion (IR) injury, and liver cancer. Targeting H₂S-producing enzymes may be a promising strategy for managing hepatic disorders.

Mitochondria in innate immune signaling

Mitochondria are functionally versatile organelles. In addition to their conventional role of meeting the cell's energy requirements, mitochondria also actively regulate innate immune responses against infectious and sterile insults. Components of mitochondria, when released or exposed in response to dysfunction or damage, can be directly recognized by receptors of the innate immune system and trigger an immune response. In addition, despite initiation that may be independent from mitochondria, numerous innate immune responses are still subject to mitochondrial regulation as discrete steps of their signaling cascades occur on mitochondria or require mitochondrial components. Finally, mitochondrial metabolites and the metabolic state of the mitochondria within an innate immune cell modulate the precise immune response and shape the direction and character of that cell's response to stimuli. Together, these pathways result in a nuanced and very specific regulation of innate immune responses by mitochondria.

Mitochondria in innate immune signaling

Mitochondria are functionally versatile organelles. In addition to their conventional role of meeting the cell's energy requirements, mitochondria also actively regulate innate immune responses against infectious and sterile insults. Components of mitochondria, when released or exposed in response to dysfunction or damage, can be directly recognized by receptors of the innate immune system and trigger an immune response. In addition, despite initiation that may be independent from mitochondria, numerous innate immune responses are still subject to mitochondrial regulation as discrete steps of their signaling cascades occur on mitochondria or require mitochondrial components. Finally, mitochondrial metabolites and the metabolic state of the mitochondria within an innate immune cell modulate the precise immune response and shape the direction and character of that cell's response to stimuli. Together, these pathways result in a nuanced and very specific regulation of innate immune responses by mitochondria.

Role of reactive oxygen species in male infertility: An updated review of literature

Objectives

To review the literature and provide an updated summary on the role of reactive oxygen species (ROS) in male infertility.

Methods

A review of PubMed, Cochrane review, and Web of Science databases for full-text English-language articles published between 1943 and 2017 was performed, focusing on the aetiology of ROS, physiological role of ROS on spermatic function, pathological role of ROS in infertility, evaluation of ROS, and role of antioxidants in oxidative stress.

Results

ROS play a role in spermatic function and fertilisation. The literature describes both a physiological and a pathological role of ROS in fertility. A delicate balance between ROS necessary for physiological activity and antioxidants to protect from cellular oxidative injury is essential for fertility.

Conclusion

Although elevated levels of ROS are implicated as a cause of infertility, there is no consensus on selecting patients to test for ROS, which test to perform, or if treatment for ROS can have a positive impact on infertility rates and pregnancy.

Vitamin C acts as a hepatoprotectant in carbofuran treated rat liver slices in vitro

The observations of liver slices when treated with different concentrations of carbofuran were as follows:-

1.

increased LPO

2.

decreased SOD, CAT, & protein content in all the treatments

The observations of liver slices when treated with different concentrations of carbofuran along with vitamin C were as follows:-

1.

the levels of LPO, SOD, CAT & total protein content reinstated towards normal level only in liver slices treated with low concentration

2.

at higher concentration of carbofuran treatment Vitamin C does not ameliorate the hepatic toxicity induced by carbofuran

The in vitro liver slice culture may prove to be a useful model for hepatotoxicological studies and Vitamin C, as a hepatoprotectant in mammalian system.

Carbamates, most commonly used pesticides in agricultural practices, have been reported to produce free radicals causing deleterious effects in animals. The present study was designed to assess the carbofuran induced oxidative stress in rat liver slices in vitro and also to evaluate protective role of vitamin C by incubating them in Krebs-Ringer HEPES Buffer (KRHB) containing incubation media (Williams medium E (WME) supplemented with glucose and antibiotics) with different concentrations of carbofuran. The results demonstrated that carbofuran caused significant increase in lipid peroxidation and inhibition in the activity of hepatic superoxide dismutase (SOD) in concentration dependent manner. The data with incubation medium reflected that carbofuran at lowest concentration caused an increase in SOD activity followed by its inhibition at higher concentration. Carbofuran treatment caused inhibition in the activity of catalase in liver slices and WME incubation medium. Pre-incubation of liver slices and the WME media with vitamin C restored the values of biochemical indices tested. The results indicated that carbofuran might induce oxidative stress in hepatocytes. The pretreatment with vitamin C may offer hepatoprotection from toxicity of pesticide at low concentration only.

Metadoxine Versus Placebo for the Treatment of Non-alcoholic Steatohepatitis: A Randomized Controlled Trial

OBJECTIVE AND DESIGN

The study aimed at assessing the therapeutic efficacy and safety of metadoxine versus placebo on the ultrasonographic and histological features of non-alcoholic steatohepatitis (NASH).

SUBJECTS

134 subjects with biopsy-confirmed NASH were randomized to receive metadoxine 500 mg two times daily (n = 75) or placebo (n = 59) added to the standard of care, over 16 weeks.

EFFICACY ENDPOINTS

Originally, the primary efficacy endpoint was the composite of: reduction in the steatosis by ≥1 grade, reduction in hepatic necro-inflammation by ≥1 grade and ALT normalization. Since >50% of patients refused the second biopsy, it was decided to analyze only the individual parameters.

RESULTS

There was no significant difference between the treatment and the placebo groups in either liver histology or ALT or AST. Overall, as expected both groups showed reduction in serum ALT and AST compared to baseline. Compared to placebo (9 out 54), patients on metadoxine (34 out of 75) had significantly higher rates of improvement in 1-point in steatosis grade on ultrasound (P-value <0.001). Safety and tolerability did not differ between treatments.

CONCLUSION

Metadoxine is not effective in improvement of liver histology or serum ALT or AST in patients with NASH. However, there was significant improvement of steatosis assessed by ultrasound. To properly estimate the effects on histology and transaminases, further studies of longer duration and at higher doses are needed.