A high-fat and cholesterol diet causes fatty liver in guinea pigs. The role of iron and oxidative damage

Novel high molecular weight polymerized hemoglobin in a non-obese model of cardiovascular and metabolic dysfunction

The widespread adoption of high-calorie, high-fat, high-sucrose diets (HFHSD) has become a global health concern, particularly due to their association with cardiovascular diseases and metabolic disorders. These comorbidities increase susceptibility to severe outcomes from viral infections and trauma, with trauma-related incidents significantly contributing to global mortality rates. This context underscores the critical need for a reliable blood supply. Recent research has focused on high molecular weight (MW) polymerized human hemoglobin (PolyhHb) as a promising alternative to red blood cells (RBCs), showing encouraging outcomes in previous studies. Given the overlap of metabolic disorders and trauma-related health issues, it is crucial to assess the potential toxicity of PolyhHb transfusions, particularly in models that represent these vulnerable populations. This study evaluated the effects of PolyhHb exchange transfusion in guinea pigs that had developed metabolic disorders due to a 12-week HFHSD regimen. The guinea pigs, underwent a 20 % blood volume exchange transfusion with either PolyhHb or the lower molecular weight polymerized bovine hemoglobin, Oxyglobin. Results revealed that both PolyhHb and Oxyglobin transfusions led to liver damage, with a more pronounced effect observed in HFHSD-fed animals. Additionally, markers of cardiac dysfunction indicated signs of cardiac injury in both the HFHSD and normal diet groups following the Oxyglobin transfusion. This study highlights how pre-existing metabolic disorders can exacerbate the potential side effects of hemoglobin-based oxygen carriers (HBOCs). Importantly, the newer generation of high MW PolyhHb showed lower cardiac toxicity compared to the earlier generation low MW PolyhHb, known as Oxyglobin, even in models with pre-existing endothelial and metabolic challenges.

An overview of the cholesterol metabolism and its proinflammatory role in the development of MASLD

Cholesterol is an essential lipid molecule in mammalian cells. It is not only involved in the formation of cell membranes but also serves as a raw material for the synthesis of bile acids, vitamin D, and steroid hormones. Additionally, it acts as a covalent modifier of proteins and plays a crucial role in numerous life processes. Generally, the metabolic processes of cholesterol absorption, synthesis, conversion, and efflux are strictly regulated. Excessive accumulation of cholesterol in the body is a risk factor for metabolic diseases such as cardiovascular disease, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease (MASLD). In this review, we first provide an overview of the discovery of cholesterol and the fundamental process of cholesterol metabolism. We then summarize the relationship between dietary cholesterol intake and the risk of developing MASLD, and also the animal models of MASLD specifically established with a cholesterol-containing diet. In the end, the role of cholesterol-induced inflammation in the initiation and development of MASLD is discussed.

Helicobacter pylori components increase the severity of metabolic syndrome and its hepatic manifestations induced by a high fat diet

The metabolic syndrome, often accompanied by hepatic manifestations, is a high-risk factor for developing cardiovascular disease. Patients with metabolic dysfunction associated with steatohepatic disease (MASDL) are at significant risk of developing coronary artery disease. Atherosclerosis is a systemic inflammatory disorder in which several factors, including dietary or infectious factors, can cause an inflammatory response. Helicobacter pylori (HP) bacteria have been implicated in the progression of proatherogenic vascular endothelial lesions, moreover, our previous study in an experimental in vivo model of Cavia porcellus showed that HP components and high-fat substances acted synergistically in promoting vascular endothelial inflammation, leading to an early onset of a proatherogenic environment. In the present study, our goal was to determine the contribution of HP components to the development of hepatic manifestations of metabolic syndrome in an experimental model. Our results showed that HP infection in animals exposed to a high-fat diet increased oxidative stress and lipid peroxidation, followed by endothelial lipid deposition, impaired endothelial apoptosis, cell lysis, and increased vascular stiffness. Finally, histopathological analysis of liver tissue showed signs of MASLD development in HP-infected animals fed a high-fat diet.

The Hypolipidemic Effect of Hawthorn Leaf Flavonoids through Modulating Lipid Metabolism and Gut Microbiota in Hyperlipidemic Rats

Objective. The purpose of this study was to explore the potential mechanisms of the lipid-regulating effects and the effect on modulating the gut microbiota of hawthorn leaf flavonoids (HLF) in the high-fat diet-induced hyperlipidemic rats. Methods. The hypolipidemic effect of HLF was investigated in the high-fat diet-induced hyperlipidemic rats. The action targets of HLF in the treatment of hyperlipidemia were predicted by network pharmacology and KEGG enrichment bubble diagram, which were verified by the test of western blotting. Meanwhile, we used 16S rRNA sequencing to evaluate the effects of HLF on the microbes. Results. The results of animal experiments showed that HLF could reduce the body weight and regulate the levels of serum lipid in high-fat diet (HFD) rats. Meanwhile, for the related targets of cholesterol metabolism, HLF could significantly upregulate the expression of LDLR, NR1H3, and ABCG5/ABCG8; reduce the expression of PCSK9; and increase the level of CYP7A1 in the intestinal tissue, whereas cholesterol biosynthetic protein expressions including HMGCR and SCAP were lowered by HLF. In addition, HLF increased the activities of plasma SOD, CAT, and GSH-Px and decreased the levels of Casp 1, NLRP3, IL-1β, IL-18, and TNF-α, improving the degree of hepatocyte steatosis and inflammatory infiltration of rats. Notably, HLF significantly regulated the relative abundance of major bacteria such as g_Lactobacillus, g_Anaerostipes, g_[Eubacterium]_hallii_group, g_Fusicatenibacter, g_Akkermansia, and g_Collinsella. Synchronously, we found that HLF could regulate the disorder of plasma HEPC and TFR levels caused by HFD. Conclusion. This study demonstrates that HLF can regulate metabolic hyperlipidemia syndromes and modulate the relative abundance of major bacteria, which illustrated that it might be associated with the modulation of gut microbiota composition and metabolites.

Mineral metabolism and ferroptosis in non-alcoholic fatty liver diseases

Nonalcoholic fatty liver disease (NAFLD) has become the most prevalent chronic liver disease worldwide. Minerals including iron, copper, zinc, and selenium, fulfil an essential role in various biochemical processes. Moreover, the identification of ferroptosis and cuproptosis further underscores the importance of intracellular mineral homeostasis. However, perturbation of minerals has been frequently reported in patients with NAFLD and related diseases. Interestingly, studies have attempted to establish an association between mineral disorders and NAFLD pathological features, including oxidative stress, mitochondrial dysfunction, inflammatory response, and fibrogenesis. In this review, we aim to provide an overview of the current understanding of mineral metabolism (i.e., absorption, utilization, and transport) and mineral interactions in the pathogenesis of NAFLD. More importantly, this review highlights potential therapeutic strategies, challenges, future directions for targeting mineral metabolism in the treatment of NAFLD.

Helicobacter pylori Infection Acts Synergistically with a High-Fat Diet in the Development of a Proinflammatory and Potentially Proatherogenic Endothelial Cell Environment in an Experimental Model

Classic atherosclerosis risk factors do not explain all cases of chronic heart disease. There is significant evidence that gut microbiota may influence the development of atherosclerosis. The widespread prevalence of chronic Helicobacter pylori (H. pylori, HP) infections suggests that HP can be the source of components that stimulate local and systemic inflammatory responses. Elevated production of reactive oxygen species during HP infection leads to cholesterol oxidation, which drives atherogenesis. The aim of this study is to explore the link between persistent HP infection and a high-fat diet in the development of proinflammatory conditions that are potentially proatherogenic. An in vivo model of Caviae porcellus infected with HP and exposed to an experimental diet was investigated for the occurrence of a proinflammatory and proatherogenic endothelial environment. Vascular endothelial primary cells exposed to HP components were tested in vitro for oxidative stress, cell activation and apoptosis. The infiltration of inflammatory cells into the vascular endothelium of animals infected with HP and exposed to a high-fat diet was observed in conjunction with an increased level of inflammatory markers systemically. The arteries of such animals were the least elastic, suggesting the role of HP in arterial stiffness. Soluble HP components induced transformation of macrophages to foam cells in vitro and influenced the endothelial life span, which was correlated with Collagen I upregulation. These preliminary results support the hypothesis that HP antigens act synergistically with a high-fat diet in the development of proatherogenic conditions.

High fat high sucrose diet-induced dyslipidemia in guinea pigs

Easy access to high-calorie and fat-dense fast food has resulted in unhealthy dietary and lifestyle changes worldwide, which affects both developed and developing economies. This predisposes populations to a considerable number of metabolic and inflammatory conditions, such as diabetes, nonalcoholic fatty liver disease (NAFLD), and cardiovascular disease (CVD). Guinea pigs have been proposed as a model to study high-fat diet-induced metabolic disease due to their similar antioxidant metabolism and lipid profile to humans, and their susceptibility to atherosclerosis and endothelial disease. This study aims to evaluate cardiovascular and metabolic disorders induced by high-fat high-sucrose diet (HFHSD) in guinea pigs. Two to three-week-old male guinea pigs were fed a normal diet (ND) or HFHSD for 12 wk. Guinea pigs fed a HFHSD developed glucose intolerance, dyslipidemia, and liver, cardiac, and kidney damage. However, hypertension, dysautonomia, endothelial disease, and obesity were absent in these HFHSD guinea pigs. Taken together, these results show that guinea pigs fed a HFHSD are a nonobese model of metabolic disorders, resulting in important cardiac damage. Moreover, our findings suggest that NAFLD may be an important risk factor for diet-induced CVD.NEW & NOTEWORTHY In this study, we show a new animal model for diet-induced disease metabolic disorders without obesity in guinea pigs. Moreover, results suggest a strong relation between liver disease and increased cardiovascular risks.

The development of nonalcoholic steatohepatitis is subjected to breeder dependent variation in guinea pigs

Variability in disease development due to differences in strains and breeders constitutes a substantial challenge in preclinical research. However, the impact of the breeder on non-alcoholic steatohepatitis (NASH) is not yet fully elucidated. This retrospective study investigates NASH development in guinea pigs from Charles River or Envigo fed a high fat diet (20% fat, 15% sucrose, 0.35% cholesterol) for 16 or 24/25 weeks. Charles River animals displayed more severe NASH, with higher steatosis (p < 0.05 at week 16), inflammation (p < 0.05 at both week), fibrosis (p < 0.05 at week 16) and disease activity (p < 0.05 at both weeks). Accordingly, alanine and aspartate aminotransferase were increased at week 24/25 (p < 0.01). Hepatic expression of inflammatory (Ccl2, Cxcl8) and fibrotic (Pdgf, Serpine1, Col1a1) genes was also increased (p < 0.05). Differences were observed in healthy chow (4% fat, 0% sucrose, 0% cholesterol) fed animals: Envigo animals displayed higher relative liver weights (p < 0.01 at both weeks), liver cholesterol (p < 0.0001 at week 24/25) and aspartate aminotransferase (p < 0.05 at week 16), but lower levels of alkaline phosphatase (p < 0.0001 at week 24/25). These findings accentuates the importance of the breeder and its effect on NASH development and severity. Consequently, this may affect reproducibility, study comparison and limit the potential of developing novel therapies.

Molecular mechanisms of hepatic lipid accumulation in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is currently the world's most common liver disease, estimated to affect up to one-fourth of the population. Hallmarked by hepatic steatosis, NAFLD is associated with a multitude of detrimental effects and increased mortality. This narrative review investigates the molecular mechanisms of hepatic steatosis in NAFLD, focusing on the four major pathways contributing to lipid homeostasis in the liver. Hepatic steatosis is a consequence of lipid acquisition exceeding lipid disposal, i.e., the uptake of fatty acids and de novo lipogenesis surpassing fatty acid oxidation and export. In NAFLD, hepatic uptake and de novo lipogenesis are increased, while a compensatory enhancement of fatty acid oxidation is insufficient in normalizing lipid levels and may even promote cellular damage and disease progression by inducing oxidative stress, especially with compromised mitochondrial function and increased oxidation in peroxisomes and cytochromes. While lipid export initially increases, it plateaus and may even decrease with disease progression, sustaining the accumulation of lipids. Fueled by lipo-apoptosis, hepatic steatosis leads to systemic metabolic disarray that adversely affects multiple organs, placing abnormal lipid metabolism associated with NAFLD in close relation to many of the current life-style-related diseases.

Liraglutide Decreases Hepatic Inflammation and Injury in Advanced Lean Non-Alcoholic Steatohepatitis

Although commonly associated with obesity, non-alcoholic fatty liver disease (NAFLD) is also present in the lean population representing a unique disease phenotype. Affecting 25% of the world's population, NAFLD is associated with increased mortality especially when progressed to non-alcoholic steatohepatitis (NASH). However, no approved pharmacological treatments exist. Current research focuses mainly on NASH associated with obesity, leaving the effectiveness of promising treatments in lean NASH virtually unknown. This study therefore aimed to evaluate the effect of liraglutide (glucagon-like peptide 1 analogue) and dietary intervention, alone and in combination, in guinea pigs with non-obese NASH. After 20 weeks of high-fat feeding (20% fat, 15% sucrose, 0.35% cholesterol), 40 female guinea pigs were block-randomized based on weight into four groups receiving one of four treatments for 4 weeks: continued high-fat diet (HF, control), high-fat diet and liraglutide treatment (HFL), chow diet (4% fat, 0% sucrose, 0% cholesterol; HFC) or chow diet and liraglutide treatment (HFCL). High-fat feeding induced NASH with severe fibrosis. Liraglutide decreased inflammation (p < 0.05) and hepatocyte ballooning (p < 0.05), while increasing hepatic α-tocopherol (p = 0.0154). Dietary intervention did not improve liver histopathology significantly, but decreased liver weight (p = 0.004), plasma total cholesterol (p = 0.0175), LDL-cholesterol (p = 0.0063), VLDL-cholesterol (p = 0.0034), hepatic cholesterol (p < 0.0001) and increased hepatic vitamin C (p = 0.0099). Combined liraglutide and dietary intervention induced a rapid weight loss, necessitating periodical liraglutide dose adjustment/discontinuation, limiting the strength of the findings from this group. Collectively, this pre-clinical study supports the beneficial effect of liraglutide on NASH and extends this notion to lean NASH.

A potential high risk for fatty liver disease was found in mice generated after assisted reproductive techniques

Abnormal gametogenesis and embryonic development may lead to poor health status of the offspring. The operations involved in the assisted reproductive technologies (ARTs) occur during the key stage of gametogenesis and early embryonic development. To assess the potential risk of abnormal lipid metabolism in the liver of adult ARTs offspring, two ARTs mice models derived from preimplantation genetic diagnosis (PGD group) and in vitro cultured embryos without biopsy (IVEM group) were constructed. And control mice were from in vivo naturally conceived (Normal group). The results showed that ARTs offspring had increased body weight and body fat content comparing to normal group. An increasing volume and amount of lipid droplets as well as lipid droplet fusion were found in the hepatocytes of ARTs mice, and a significantly increased liver TG content was also shown in the ARTs mice, which due to the increased TG synthesis and decreased TG transport in the liver. All the results indicated that the manipulations involved in ARTs might play an important role in the lipid accumulation of adult offspring. By analyzing the DNA methylation profiles of 7.5dpc embryos, we proposed that methylation deregulation of the genes related to liver development in ARTs embryos might contribute to the abnormal phenotype in the offspring. The study demonstrated that ARTs procedures have adverse effect on liver development which resulted in abnormal lipid metabolism and induced the potential high risk of fatty liver in adulthood.

Hepcidin: Homeostasis and Diseases Related to Iron Metabolism

Iron is an essential metal for cell survival that is regulated by the peptide hormone hepcidin. However, its influence on certain diseases is directly related to iron metabolism or secondary to underlying diseases. Genetic alterations influence the serum hepcidin concentration, which can lead to an iron overload in tissues, as observed in haemochromatosis, in which serum hepcidin or defective hepcidin synthesis is observed. Another genetic imbalance of iron is iron-refractory anaemia, in which serum concentrations of hepcidin are increased, precluding the flow and efflux of extra- and intracellular iron. During the pathogenesis of certain diseases, the resulting oxidative stress, as well as the increase in inflammatory cytokines, influences the transcription of the HAMP gene to generate a secondary anaemia due to the increase in the serum concentration of hepcidin. To date, there is no available drug to inhibit or enhance hepcidin transcription, mostly due to the cytotoxicity described in the in vitro models. The proposed therapeutic targets are still in the early stages of clinical trials. Some candidates are promising, such as heparin derivatives and minihepcidins. This review describes the main pathways of systemic and genetic regulation of hepcidin, as well as its influence on the disorders related to iron metabolism.

The Potential of Non-Provitamin A Carotenoids for the Prevention and Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is an obesity-associated spectrum of comorbidities defined by the presence of metabolic dysfunction, oxidative stress, inflammation, and fibrosis in the liver. If left untreated, NAFLD can progress to cirrhosis, liver failure, or hepatocellular carcinoma. NAFLD is recognized as the most common liver disease in the United States, affecting around 30% of the population. Identification of dietary components capable of reducing or preventing NAFLD is therefore essential to battle this condition. Dietary carotenoids including astaxanthin, lycopene, lutein, and zeaxanthin have been demonstrated to be potent antioxidants as well as to exhibit anti-inflammatory effects. Many studies report the protective effect(s) of these carotenoids against different conditions such as atherosclerosis, diabetic complications, age-related macular degeneration, and liver diseases. In this review, we will focus on the effects of these carotenoids in the prevention or reduction of NAFLD as seen in epidemiological observations and clinical trials, as well as the suggested mechanism of action derived from animal and cell studies.

High-fat but not sucrose intake is essential for induction of dyslipidemia and non-alcoholic steatohepatitis in guinea pigs

Background

Non-alcoholic fatty liver disease (NAFLD) and dyslipidemia are closely related. Diet plays an important role in the progression of these diseases, but the role of specific dietary components is not completely understood. Therefore, we investigated the role of dietary sucrose and fat/cholesterol on the development of dyslipidemia and NAFLD.

Methods

Seventy female guinea pigs were block-randomized (based on weight) into five groups and fed a normal chow diet (control: 4 % fat), a very high-sucrose diet (vHS: 4 % fat, 25 % sucrose), a high-fat diet (HF: 20 % fat, 0.35 % cholesterol), a high-fat/high-sucrose diet (HFHS: 20 % fat, 15 % sucrose, 0.35 % cholesterol) or a high-fat/very high-sucrose diet (HFvHS: 20 % fat, 25 % sucrose, 0.35 % cholesterol) for 16 and 25 weeks.

Results

All three high-fat diets induced dyslipidemia with increased concentrations of plasma cholesterol (p < 0.0001), LDL-C (p < 0.0001) and VLDL-C (p < 0.05) compared to control and vHS. Contrary to this, plasma triglycerides were increased in control and vHS compared to high-fat fed animals (p < 0.01), while circulating levels of free fatty acids were even between groups. Histological evaluation of liver sections revealed non-alcoholic steatohepatitis (NASH) with progressive inflammation and bridging fibrosis in high-fat fed animals. Accordingly, hepatic triglycerides (p < 0.05) and cholesterol (p < 0.0001) was increased alongside elevated levels of alanine and aspartate aminotransferase (p < 0.01) compared to control and vHS.

Conclusion

Collectively, our results suggest that intake of fat and cholesterol, but not sucrose, are the main factors driving the development and progression of dyslipidemia and NAFLD/NASH.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0110-1) contains supplementary material, which is available to authorized users.

A comprehensive approach to formulation of seaweed-enriched meat products: From technological development to assessment of healthy properties

Meat consumption is influenced by various kinds of factors, among them health implications. Different strategies can be effective in developing meat-based functional foods. These basically entail reducing the presence of compounds with negative health implications and enhancing the presence of beneficial compounds. This article reviews a comprehensive model for the development of meat-based functional foods based on a presentation of the research achieved in terms of the design and development of qualitatively and quantitatively modified meat products (frankfurters, patties and restructured steaks). These were reformulated to incorporate nutrients associated with three different seaweeds (wakame-Undaria pinnatifida; nori-Porphyra umbilicalis; and sea spaghetti-Himanthalia elongata) as sources of bioactive substances, while simultaneously reducing sodium and fat and improving fatty acid profiles. Those seaweeds were chosen, because in terms of composition and health implications, abundance on Spanish coasts, relatively widespread consumption, and suitability in terms of flavour and colour they are better suited than others for use as ingredients in new products. It also discusses the consequences of the use of this type of meat-based functional foods (combination of pork meat and 5% of each seaweed with or without hypercholesterolaemic agent included in the diets) on growing animals (Wistar male rats), and their effects on different aspects of lipoprotein metabolism, oxidative stress and liver structure. This article, then, reports a comprehensive approach to the production of seaweed-enriched meat products, considering aspects of technological development aimed at achieving the functional effect.

Vascular Damage in Patients with Nonalcoholic Fatty Liver Disease: Possible Role of Iron and Ferritin

Non Alcoholic Fatty Liver Disease (NAFLD) is the most common chronic liver disease in Western countries. Recent data indicated that NAFLD is a risk factor by itself contributing to the development of cardiovascular disease independently of classical known risk factors. Hyperferritinemia and mild increased iron stores are frequently observed in patients with NAFLD and several mechanisms have been proposed to explain the role of iron, through oxidative stress and interaction with insulin metabolism, in the development of vascular damage. Moreover, iron depletion has been shown to decrease atherogenesis in experimental models and in humans. This review presents the recent evidence on epidemiology, pathogenesis, and the possible explanation of the role of iron and ferritin in the development of cardiovascular damage in patients with NAFLD, and discusses the possible interplay between metabolic disorders associated with NAFLD and iron in the development of cardiovascular disease.

Normal weight dyslipidemia: Is it all about the liver?

OBJECTIVE

The liver coordinates lipid metabolism and may play a vital role in the development of dyslipidemia, even in the absence of obesity. Normal weight dyslipidemia (NWD) and patients with nonalcoholic fatty liver disease (NAFLD) who do not have obesity constitute a unique subset of individuals characterized by dyslipidemia and metabolic deterioration. This review examined the available literature on the role of the liver in dyslipidemia and the metabolic characteristics of patients with NAFLD who do not have obesity.

METHODS

PubMed was searched using the following keywords: nonobese, dyslipidemia, NAFLD, NWD, liver, and metabolically obese/unhealthy normal weight. Additionally, article bibliographies were screened, and relevant citations were retrieved. Studies were excluded if they had not measured relevant biomarkers of dyslipidemia.

RESULTS

NWD and NAFLD without obesity share a similar abnormal metabolic profile. When compared with patients with NAFLD who have obesity, the metabolic abnormalities of NAFLD without obesity are similar or less severe. Furthermore, hepatic lesions develop independent of obesity, and the extent of dyslipidemia seems comparable.

CONCLUSIONS

NAFLD may impair hepatic lipid handling, causing faulty lipid homeostasis, and serves as a likely starting point for initiation and propagation of dyslipidemia along with associated comorbidities in patients without obesity.

Diet-induced dyslipidemia leads to nonalcoholic fatty liver disease and oxidative stress in guinea pigs

Chronic dyslipidemia imposed by a high-fat and high-caloric dietary regime leads to debilitating disorders such as obesity, nonalcoholic fatty liver disease (NAFLD), and insulin resistance. As disease rates surge, so does the need for high validity animal models to effectively study the causal relationship between diet and disease progression. The dyslipidemic guinea pig displays a high similarity with the human lipoprotein profile and may in this aspect be superior to other rodent models. This study investigated the effects of 2 long-term Westernized diets (0.35% cholesterol, 18.5% vegetable oil and either 15% or 20% sucrose) compared with isocaloric standard chow in adult guinea pigs. Biochemical markers confirmed dyslipidemia in agreement with dietary regimens; however, both high-fat groups displayed a decreased tissue fat percentage compared with controls. Macroscopic appearance, histopathologic evaluation, and plasma markers of liver function confirmed NAFLD in high-fat groups, supported by liver redox imbalance and markers suggesting hepatic endothelial dysfunction. Plasma markers indicated endothelial dysfunction in response to a high-fat diet, although atherosclerotic lesions were not evident. Evaluation of glucose tolerance showed no indication of insulin resistance. The 5% increase in sucrose between the 2 high-fat diets did not lead to significant differences between groups. In conclusion, we find the dyslipidemic guinea pig to be a valid model of diet imposed dyslipidemia, particularly with regards to hepatic steatosis and endothelial dysfunction. Furthermore, the absence of obesity supports the present study setup as targeting NAFLD in nonobese individuals.

Ergothioneine, an adaptive antioxidant for the protection of injured tissues? A hypothesis

Ergothioneine (ET) is a diet-derived, thiolated derivative of histidine with antioxidant properties. Although ET is produced only by certain fungi and bacteria, it can be found at high concentrations in certain human and animal tissues and is absorbed through a specific, high affinity transporter (OCTN1). In liver, heart, joint and intestinal injury, elevated ET concentrations have been observed in injured tissues. The physiological role of ET remains unclear. We thus review current literature to generate a specific hypothesis: that the accumulation of ET in vivo is an adaptive mechanism, involving the regulated uptake and concentration of an exogenous natural compound to minimize oxidative damage.

Liver ergothioneine accumulation in a guinea pig model of non-alcoholic fatty liver disease. A possible mechanism of defence?

L-ergothioneine (ET), a putative antioxidant compound acquired by animals through dietary sources, has been suggested to accumulate in certain cells and tissues in the body that are predisposed to high oxidative stress. In the present study, we identified an elevation of ET in the liver of a guinea pig model of non-alcoholic fatty liver disease (NAFLD), elucidated a possible mechanism for the increased uptake and investigated the possible role for this accumulation. This increase in liver ET levels correlated with cholesterol accumulation and disease severity. We identified an increase in the transcriptional factor, RUNX1, which has been shown to upregulate the expression of the ET-specific transporter OCTN1, and could consequently lead to the observable elevation in ET. An increase was also seen in heat shock protein 70 (HSP70) which seemingly corresponds to ET elevation. No significant increase was observed in oxidative damage markers, F2-isoprostanes, and protein carbonyls, which could possibly be attributed to the increase in liver ET through direct antioxidant action, induction of HSP70, or by chelation of Fe(2+), preventing redox chemistry. The data suggest a novel mechanism by which the guinea pig fatty liver accumulates ET via upregulation of its transporter, as a possible stress response by the damaged liver to further suppress oxidative damage and delay tissue injury. Similar events may happen in other animal models of disease, and researchers should be aware of the possibility.

Does vitamin C deficiency promote fatty liver disease development?

Obesity and the subsequent reprogramming of the white adipose tissue are linked to human disease-complexes including metabolic syndrome and concurrent non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). The dietary imposed dyslipidemia promotes redox imbalance by the generation of excess levels of reactive oxygen species and induces adipocyte dysfunction and reprogramming, leading to a low grade systemic inflammation and ectopic lipid deposition, e.g., in the liver, hereby promoting a vicious circle in which dietary factors initiate a metabolic change that further exacerbates the negative consequences of an adverse life-style. Large epidemiological studies and findings from controlled in vivo animal studies have provided evidence supporting an association between poor vitamin C (VitC) status and propagation of life-style associated diseases. In addition, overweight per se has been shown to result in reduced plasma VitC, and the distribution of body fat in obesity has been shown to have an inverse relationship with VitC plasma levels. Recently, a number of epidemiological studies have indicated a VitC intake below the recommended daily allowance (RDA) in NAFLD-patients, suggesting an association between dietary habits, disease and VitC deficiency. In the general population, VitC deficiency (defined as a plasma concentration below 23 μM) affects around 10% of adults, however, this prevalence is increased by an adverse life-style, deficiency potentially playing a broader role in disease progression in specific subgroups. This review discusses the currently available data from human surveys and experimental models in search of a putative role of VitC deficiency in the development of NAFLD and NASH.