Exogenous administration of unacylated ghrelin attenuates hepatic steatosis in high-fat diet-fed rats by modulating glucose homeostasis, lipogenesis, oxidative stress, and endoplasmic reticulum stress

Protective effects of ghrelin on pancreas in fructose diet and streptozotocin-induced diabetic rats

Ghrelin, which is widely expressed in central and peripheral tissues, has several metabolic effects. It has been suggested that these effects may include anti-inflammatory, anti-oxidant, and anti-apoptotic effects. Therefore, we aimed to investigate the effects of ghrelin administered to diabetic rats on DNA repair and apoptosis mechanisms, and differences in oxidative stress (OS) and pancreatic hormone levels in the pancreas. Twenty-one rats were randomly divided into three groups: control, type 2 diabetes mellitus (T2DM), and T2DM treated with ghrelin (T2DM + ghrelin). We examined PCNA and PARP-1 to evaluate the effect of ghrelin on DNA repair, caspase-3 and caspase-9 to evaluate its effect on apoptosis, and insulin and glucagon to evaluate its role in regulating glucose homeostasis by immunohistochemistry in diabetic rats. Malondialdehyde, glutathione, and protein carbonyl levels, as well as catalase, glutathione-S-transferase, and superoxide dismutase (SOD) activities, were measured spectrophotometrically to detect the ghrelin effect on OS. Homeostasis model assessment for insulin resistance (HOMA-IR) and pancreatic insulin levels were assessed by ELISA method. Ghrelin may be a potential regulator of apoptosis as it significantly reduced the number of caspase-3 and caspase-9 immunopositive cells (p < 0.0001). In addition, ghrelin treatment reduced OS by decreasing glutathione (p < 0.001), malondialdehyde, and protein carbonyl, as well as the activity of SOD (p < 0.05) in diabetic rats. The results suggest that ghrelin is a potential apoptotic regulator and may be considered as a therapeutic agent due to its significant ability to suppress OS in T2DM.

Alterations in Glutathione Redox Homeostasis in Metabolic Dysfunction-Associated Fatty Liver Disease: A Systematic Review

Low molecular weight (LMW) thiols, particularly glutathione, play pathogenic roles in various multiorgan diseases. The liver is central for the production and systemic distribution of LMW thiols; thus, it is particularly susceptible to the imbalance of redox status that may determine increased oxidative stress and trigger the liver damage observed in metabolic dysfunction-associated steatotic liver disease (MASLD) models and humans. Indeed, increased LMW thiols at the cellular and extracellular levels may be associated with the severity of MASLD. Here, we present a systematic literature review of recent studies assessing the levels of LMW thiols in MASLD in in vivo and in vitro models and human subjects. Based on the PRISMA 2020 criteria, a search was conducted using PubMed and Scopus by applying inclusion/exclusion filters. The initial search returned 1012 documents, from which 165 eligible studies were selected, further described, and qualitatively analysed. Of these studies, most focused on animal and cellular models, while a minority used human fluids. The analysis of these studies revealed heterogeneity in the methods of sample processing and measurement of LMW thiol levels, which hinder cut-off values for diagnostic use. Standardisation of the analysis and measure of LMW thiol is necessary to facilitate future studies.

Intestinal perfusion of unacylated ghrelin alleviated metabolically associated fatty liver disease in rats via a central glucagon-like peptide-1 pathway

Unacylated ghrelin (UAG), the unacylated form of ghrelin, accounts for 80%-90% of its circulation. Accumulated studies have pointed out that UAG may be used to treat metabolic disorders. This study aimed to investigate the effect of intestinal perfusion of UAG on metabolically associated fatty liver disease (MAFLD) induced by a high-fat diet and its possible mechanisms. Neuronal retrograde tracking combined with immunofluorescence, central administration of a glucagon-like peptide-1 receptor (GLP-1R) antagonist, and hepatic vagotomy was performed to reveal its possible mechanism involving a central glucagon-like peptide-1 (GLP-1) pathway. The results showed that intestinal perfusion of UAG significantly reduced serum lipids, aminotransferases, and food intake in MAFLD rats. Steatosis and lipid accumulation in the liver were significantly alleviated, and lipid metabolism-related enzymes in the liver were regulated. UAG upregulated the expression of GLP-1 receptor (GLP-1R) in the paraventricular nucleus (PVN) and GLP-1 in the nucleus tractus solitarii (NTS), as well as activated GLP-1 neurons in the NTS. Furthermore, GLP-1 fibers projected from NTS to PVN were activated by the intestinal perfusion of UAG. However, hepatic vagotomy and GLP-1R antagonists delivered into PVN before intestinal perfusion of UAG partially attenuated its alleviation of MAFLD. In conclusion, intestinal perfusion of UAG showed a therapeutic effect on MAFLD, which might be related to its activation of the GLP-1 neuronal pathway from NTS to PVN. The present results provide a new strategy for the treatment of MAFLD.NEW & NOTEWORTHY Intestinal perfusion of UAG, the unacylated form of ghrelin, has shown promising potential for treating MAFLD. This study unveils a potential mechanism involving the central GLP-1 pathway, with UAG upregulating GLP-1R expression and activating GLP-1 neurons in specific brain regions. These findings propose a novel therapeutic strategy for MAFLD treatment through UAG and its modulation of the GLP-1 neuronal pathway.

Molecular and cellular mechanisms underlying the hepatoprotective role of ghrelin against NAFLD progression

The underlying mechanisms for the development and progression of nonalcoholic fatty liver disease (NAFLD) are complex and multifactorial. Within the last years, experimental and clinical evidences support the role of ghrelin in the development of NAFLD. Ghrelin is a gut hormone that plays a major role in the short-term regulation of appetite and long-term regulation of adiposity. The liver constitutes a target for ghrelin, where this gut-derived peptide triggers intracellular pathways regulating lipid metabolism, inflammation, and fibrosis. Interestingly, circulating ghrelin levels are altered in patients with metabolic diseases, such as obesity, type 2 diabetes, and metabolic syndrome, which, in turn, are well-known risk factors for the pathogenesis of NAFLD. This review summarizes the molecular and cellular mechanisms involved in the hepatoprotective action of ghrelin, including the reduction of hepatocyte lipotoxicity via autophagy and fatty acid β-oxidation, mitochondrial dysfunction, endoplasmic reticulum stress and programmed cell death, the reversibility of the proinflammatory phenotype in Kupffer cells, and the inactivation of hepatic stellate cells. Together, the metabolic and inflammatory pathways regulated by ghrelin in the liver support its potential as a therapeutic target to prevent NAFLD in patients with metabolic disorders.

NAFLD and nutraceuticals: a review of completed phase III and IV clinical trials

Background

Nonalcoholic Fatty Liver Disease (NAFLD) has become a significant public health concern, affecting approximately one-fourth of the population. Despite its prevalence, no FDA-approved drug treatments specifically target NAFLD.

Aim

To provide a review of clinical trials investigating the use of herbal remedies and dietary supplements in NAFLD management, utilizing the ClinicalTrials.gov database.

Methods

This review evaluates the current evidence by examining completed phase III and IV clinical trials registered on ClinicalTrials.gov. An exhaustive search was performed on April 17, 2023, using the terms "Nonalcoholic Fatty Liver Disease" and "NAFLD." Two independent reviewers appraised eligible trials based on pre-defined inclusion and exclusion criteria.

Results

An initial search yielded 1,226 clinical trials, with 12 meeting the inclusion criteria after filtration. The majority of trials focused on Omega-3 fatty acids (20.0%) and vitamin D (26.7%), followed by caffeine, chlorogenic acid, ginger, phosphatidylcholine, Trigonella Foenum-graecum seed extract, vitamin C, and vitamin E (each 6.7%). Most studies were Phase 3 (75.0%) and used a parallel assignment model (91.7%). Quadruple masking was the most prevalent technique (58.3%), and Iran was the leading country in terms of trial locations (25.0%). These interventions constitute two herbal interventions and nine supplement interventions.

Conclusion

This reveals a diverse range of nutraceuticals, with Omega-3 fatty acids and vitamin D being predominant in the management of NAFLD. The global distribution of trials highlights the widespread interest in these therapeutics. However, more rigorous, large-scale trials are needed to establish safety, efficacy, and optimal dosages.

Role of the Ghrelin System in Colitis and Hepatitis as Risk Factors for Inflammatory-Related Cancers

It is not known exactly what leads to the development of colorectal cancer (CRC) and hepatocellular carcinoma (HCC), but there are specific risk factors that increase the probability of their occurrence. The unclear pathogenesis, too-late diagnosis, poor prognosis as a result of high recurrence and metastasis rates, and repeatedly ineffective therapy of both cancers continue to challenge both basic science and practical medicine. The ghrelin system, which is comprised of ghrelin and alternative peptides (e.g., obestatin), growth hormone secretagogue receptors (GHS-Rs), and ghrelin-O-acyl-transferase (GOAT), plays an important role in the physiology and pathology of the gastrointestinal (GI) tract. It promotes various physiological effects, including energy metabolism and amelioration of inflammation. The ghrelin system plays a role in the pathogenesis of inflammatory bowel diseases (IBDs), which are well known risk factors for the development of CRC, as well as inflammatory liver diseases which can trigger the development of HCC. Colitis-associated cancer serves as a prototype of inflammation-associated cancers. Little is known about the role of the ghrelin system in the mechanisms of transformation of chronic inflammation to low- and high-grade dysplasia, and, finally, to CRC. HCC is also associated with chronic inflammation and fibrosis arising from different etiologies, including alcoholic and nonalcoholic fatty liver diseases (NAFLD), and/or hepatitis B (HBV) and hepatitis C virus (HCV) infections. However, the exact role of ghrelin in the progression of the chronic inflammatory lesions into HCC is still unknown. The aim of this review is to summarize findings on the role of the ghrelin system in inflammatory bowel and liver diseases in order to better understand the impact of this system on the development of inflammatory-related cancers, namely CRC and HCC.