The effect of rat strain, diet composition and feeding period on the development of a nutritional model of non-alcoholic fatty liver disease in rats

Ex Vivo Demonstration of a Novel Dual-Frequency Ultrasound Method for Quantitative Measurements of Liver Fat Content

OBJECTIVE

The rise in metabolic dysfunction-associated steatotic liver disease prevalence, closely linked with metabolic syndromes and obesity, demands accurate, cost-effective diagnostic methods for early-stage fat quantification in the liver. Here we demonstrate a novel dual-frequency ultrasound method that enables the quantitative measurement of liver fat fraction ex vivo and its correlation with actual fat content.

METHODS

A total of 24 Wistar rats were divided into four different groups, where three groups were given a high-fat diet for 2, 4, and 6 wk, and the last group was given a control diet for 6 wk. Livers were imaged with ultrasound ex vivo in a water bath with a dual-frequency ultrasound transducer and experimental imaging protocol implemented on the Verasonics Vantage research ultrasound scanner. Ultrasound data were post-processed to estimate the non-linear bulk elasticity parameter and the liver samples were analyzed with respect to fat fraction and triglycerides.

RESULTS

Rats given a high-fat diet had increased mean levels of liver fat compared with the control group. More importantly, correlation between the ultrasound-based estimation of the non-linear bulk elasticity parameter and fat fraction and triglycerides on an individual level was found to be strong (R2 = 0.81, p = 5.8 × 10-9 and R2 = 0.72, p = 3.6 × 10-7, respectively).

CONCLUSION

This study demonstrates the potential of the novel dual-frequency ultrasound method for the quantitative measurement of liver fat fraction in excised rat livers, showing great promise for this method to become clinically relevant in the diagnosis and follow-up of patients with fatty liver disease.

Liquorice root extract and isoliquiritigenin attenuate high-fat diet-induced hepatic steatosis and damage in rats by regulating AMPK

Objective: This study compared the ability of Liquorice roots aqueous extract (LRE) and its ingredient, isoliquiritigenin (ISL), in alleviating high-fat diet (HFD)-induced hepatic steatosis and examined if this effect involves activation of AMPK.Materials and methods: Control or HFD-fed rats were treated with the vehicle, LRE (200 mg/kg), or ISL (30 mg/kg) for 8 weeks orally.Results: ISL and LRE reduced HFD-induced hyperglycaemia, improved liver structure, lowered serum and hepatic lipids, and attenuated hepatic oxidative stress and inflammation. In the control and HFD-fed rats, ISL and LRE significantly stimulated the muscular and hepatic mRNA and protein levels of AMPK, improved oral glucose tolerance, reduced hepatic mRNA levels of SREBP1/2, and upregulated hepatic levels of PPARα and Bcl2. These effects were comparable for ISL and LRE and were prevented by co-administration of compound C, an AMPK inhibitor.Discussion and conclusion: ISL and LRE provide an effective theory to alleviate hepatic steatosis through activating AMPK.

Utility of Human Relevant Preclinical Animal Models in Navigating NAFLD to MAFLD Paradigm

Fatty liver disease is an emerging contributor to disease burden worldwide. The past decades of work established the heterogeneous nature of non-alcoholic fatty liver disease (NAFLD) etiology and systemic contributions to the pathogenesis of the disease. This called for the proposal of a redefinition in 2020 to that of metabolic dysfunction-associated fatty liver disease (MAFLD) to better reflect the current understanding of the disease. To date, several clinical cohort studies comparing NAFLD and MAFLD hint at the relevancy of the new nomenclature in enriching for patients with more severe hepatic injury and extrahepatic comorbidities. However, the underlying systemic pathogenesis is still not fully understood. Preclinical animal models have been imperative in elucidating key biological mechanisms in various contexts, including intrahepatic disease progression, interorgan crosstalk and systemic dysregulation. Furthermore, they are integral in developing novel therapeutics against MAFLD. However, substantial contextual variabilities exist across different models due to the lack of standardization in several aspects. As such, it is crucial to understand the strengths and weaknesses of existing models to better align them to the human condition. In this review, we consolidate the implications arising from the change in nomenclature and summarize MAFLD pathogenesis. Subsequently, we provide an updated evaluation of existing MAFLD preclinical models in alignment with the new definitions and perspectives to improve their translational relevance.

Multi-Tissue Time-Domain NMR Metabolomics Investigation of Time-Restricted Feeding in Male and Female Nile Grass Rats

Metabolic disease resulting from overnutrition is prevalent and rapidly increasing in incidence in modern society. Time restricted feeding (TRF) dietary regimens have recently shown promise in attenuating some of the negative metabolic effects associated with chronic nutrient stress. The purpose of this study is to utilize a multi-tissue metabolomics approach using nuclear magnetic resonance (NMR) spectroscopy to investigate TRF and sex-specific effects of high-fat diet in a diurnal Nile grass rat model. Animals followed a six-week dietary protocol on one of four diets: chow ad libitum, high-fat ad libitum (HF-AD), high-fat early TRF (HF-AM), or high-fat late TRF (HF-PM), and their liver, heart, and white adipose tissues were harvested at the end of the study and were analyzed by NMR. Time-domain complete reduction to amplitude–frequency table (CRAFT) was used to semi-automate and systematically quantify metabolites in liver, heart, and adipose tissues while minimizing operator bias. Metabolite profiling and statistical analysis revealed lipid remodeling in all three tissues and ectopic accumulation of cardiac and hepatic lipids for HF-AD feeding compared to a standard chow diet. Animals on TRF high-fat diet had lower lipid levels in the heart and liver compared to the ad libitum group; however, no significant differences were noted for adipose tissue. Regardless of diet, females exhibited greater amounts of hepatic lipids compared to males, while no consistent differences were shown in adipose and heart. In conclusion, this study demonstrates the feasibility of performing systematic and time-efficient multi-tissue NMR metabolomics to elucidate metabolites involved in the crosstalk between different metabolic tissues and provides a more holistic approach to better understand the etiology of metabolic disease and the effects of TRF on metabolic profiles.

Low molecular weight NGF mimetic GK-2 normalizes the parameters of glucose and lipid metabolism and exhibits a hepatoprotective effect on a prediabetes model in obese Wistar rats

Signs of metabolic syndrome and prediabetes preceding type 2 diabetes are modelled in an experiment using a high-fat diet (HFD). The aim of this work was to study the effect of a low molecular weight systemically active nerve growth factor mimetic, compound GK-2 (hexamethylenediamide bis(N-monosuccinyl-L-glutamyl-L-lysine)), on indicators of abdominal obesity, basal blood glucose level, glucose tolerance, cholesterol and triglyceride blood levels, as well as the morphological structure of the liver in male Wistar rats fed a HFD. Rats were divided into three groups: one of them received standard food (control) and two others were fed a HFD containing 45% fat, 35% carbohydrates and 20% protein, with a total caloric value of 516 kcal/100 g, over 12 weeks. Starting from the 9th week, for the next 4 weeks, one of the HFD groups was treated orally with saline whilst the other group was treated orally with GK-2 at a dose of 5 mg/kg. GK-2 was found to reduce the basal glycemia level and improve glucose tolerance, as well as to reduce the blood level of cholesterol by 30% and that of triglycerides by 28% in comparison with the saline-treated HFD animals. GK-2 reduced the degree of abdominal obesity to the level of the healthy animals and eliminated morphological abnormalities in the liver caused by the HFD. The results of the study determine the feasibility of further GK-2 research as a potential agent for prediabetes treatment.

Maternal high-fat diet consumption programs male offspring to mitigate complications in liver regeneration

In the last decades, obesity and nonalcoholic fatty liver disease (NAFLD) have become increasingly prevalent in wide world. Fatty liver can be detrimental to liver regeneration (LR) and offspring of obese dams (HFD-O) are susceptible to NAFLD development. Here we evaluated LR capacity in HFD-O after partial hepatectomy (PHx). HFD-O re-exposed or not to HFD in later life were evaluated for metabolic parameters, inflammation, proliferation, tissue repair markers and survival rate after PHx. Increasing adiposity and fatty liver were observed in HFD-O. Despite lower IL-6 levels, Ki67 labeling, cells in S phase and Ciclin D1/PCNA protein content, a lower impact on survival rate was found after PHx, even when re-exposed to HFD. However, no difference was observed between offspring of control dams (SC-O) and HFD-O after surgery. Although LR impairment is dependent of steatosis development, offspring of obese dams are programmed to be protected from the damage promoted by HFD.

Investigation of Thiol/Disulfide Balance in Obese Rats with Non-Alcoholic Fatty Liver Disease

PURPOSE

Due to the increasing prevalence of obesity worldwide, non-alcoholic fatty liver disease (NAFLD) has reached epidemic dimensions over time. NAFLD is the most common cause of childhood chronic liver disease. There is a relationship between NAFLD and oxidative stress. This study aims to investigate the changes in thiol/disulfide homeostasis parameters to determine the oxidant/antioxidant balance in obese rats with diet-induced NAFLD and healthy rats.

METHODS

Twelve Wistar albino rats were used in this study. Experimentally produced NAFLD obese rats (n=6) and healthy rats were compared. Experimental NAFLD model was created with a special fatty liver diet (Altromin® C1063, Fatty Liver Diet, Exclusivet, Lage, Germany). The biochemical and histopathological features of the groups, as well as serum thiol/disulfide homeostasis parameters, were analyzed and compared.

RESULTS

In the experimentally induced NAFLD rat model, they gained more weight than the control group. Steatosis (at least grade 2) occurred in all rats fed with special fatty liver diet for 12 weeks. Histopathologically, no high-grade inflammation was observed in rats with experimental NAFLD after feeding a diet for 12 weeks. Results revealed that aspartate transaminase and alanine transaminase levels were high, albumin levels were low, oxidant stress parameters increased, and antioxidant thiol groups decreased.

CONCLUSION

Experimental NAFLD is characterized by increased oxidant stress accompanying fatty tissue in the liver. Analysis of thiol/disulfide homeostasis parameters in NAFLD can be used in further studies to develop effective treatment options.

Modeling Diet-Induced NAFLD and NASH in Rats: A Comprehensive Review

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, characterized by hepatic steatosis without any alcohol abuse. As the prevalence of NAFLD is rapidly increasing worldwide, important research activity is being dedicated to deciphering the underlying molecular mechanisms in order to define new therapeutic targets. To investigate these pathways and validate preclinical study, reliable, simple and reproducible tools are needed. For that purpose, animal models, more precisely, diet-induced NAFLD and nonalcoholic steatohepatitis (NASH) models, were developed to mimic the human disease. In this review, we focus on rat models, especially in the current investigation of the establishment of the dietary model of NAFLD and NASH in this species, compiling the different dietary compositions and their impact on histological outcomes and metabolic injuries, as well as external factors influencing the course of liver pathogenesis.

Diet-induced obesity in animal models: points to consider and influence on metabolic markers

Overweight and obesity are a worldwide public health problem. Obesity prevalence has increased considerably, which indicates the need for more studies to better understand these diseases and related complications. Diet induced-obesity (DIO) animal models can reproduce human overweight and obesity, and there are many protocols used to lead to excess fat deposition. So, the purpose of this review was to identify the key points for the induction of obesity through diet, as well as identifying which are the necessary endpoints to be achieved when inducing fat gain. For this, we reviewed the literature in the last 6 years, looking for original articles that aimed to induce obesity through the diet. All articles evaluated should have a control group, in order to verify the results found, and had worked with Sprague-Dawley and Wistar rats, or with C57BL-/-6 mice strain. Articles that induced obesity by other methods, such as genetic manipulation, surgery, or drugs were excluded, since our main objective was to identify key points for the induction of obesity through diet. Articles in humans, in cell culture, in non-rodent animals, as well as review articles, articles that did not have obesity induction and book chapters were also excluded. Body weight and fat gain, as well as determinants related to inflammation, hormonal concentration, blood glycemia, lipid profile, and liver health, must be evaluated together to better determination of the development of obesity. In addition, to select the best model in each circumstance, it should be considered that each breed and sex respond differently to diet-induced obesity. The composition of the diet and calorie overconsumption are also relevant to the development of obesity. Finally, it is important that a non-obese control group is included in the experimental design.

Mitochondrial oxidative injury: a key player in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become the most prevalent liver disease worldwide. NAFLD is tightly linked to the metabolic syndrome, insulin resistance, and oxidative stress. Globally, its inflammatory form, nonalcoholic steatohepatitis (NASH), has become the main cause of liver-related morbidity and mortality, mainly due to liver cirrhosis and primary liver cancer. One hallmark of NASH is the presence of changes in mitochondrial morphology and function that are accompanied by a blocked flow of electrons in the respiratory chain, which increases formation of mitochondrial reactive oxygen species in a self-perpetuating vicious cycle. Consequences are oxidation of DNA bases and mitochondrial DNA depletion that are coupled with genetic and acquired mitochondrial DNA mutations, all impairing the resynthesis of respiratory chain polypeptides. In general, several maladaptations of pathways that usually maintain energy homeostasis occur with the early and late excess metabolic stress in NAFLD and NASH. We discuss the interplay between hepatocyte mitochondrial stress and inflammatory responses, focusing primarily on events initiated and maintained by mitochondrial free radical-induced damage in NAFLD. Importantly, mitochondrial oxidative stress and dysfunction are modulated by key pharmacological targets that are related to excess production of reactive oxygen species, mitochondrial turnover and the mitochondrial unfolded protein response, mitophagy, and mitochondrial biogenesis. However, the efficacy of such interventions depends on NAFLD/NASH disease stage.

Quercetin administration post-weaning attenuates high-fructose, high-cholesterol diet-induced hepatic steatosis in growing, female, Sprague Dawley rat pups

BACKGROUND

Fructose and cholesterol-rich diets have been implicated in the upsurge of metabolic syndrome (MetS). Phytochemicals are being explored as alternatives for the prevention and management of MetS. Thirty-six 21-day-old, female Sprague Dawley rats fed a high-fructose, high-cholesterol diet post-weaning were used to investigate the prophylactic potential of quercetin. Group 1 was given standard rat chow (SRC); Group 2: SRC and quercetin (75 mg kg-1 daily); Group 3: SRC and fenofibrate (100 mg kg-1 daily); Group 4 was given a high cholesterol diet (HCD) (2% added dietary cholesterol in SRC), 20% fructose drinking solution (FS); Group 5 was given HCD, 20% FS and quercetin (75 mg kg-1 daily); Group 6: HCD, 20% FS and fenofibrate (100 mg kg-1 daily). Rats were fed ad libitum for 8 weeks, euthanized, and blood and liver samples were collected.

RESULTS

The HCD and FS significantly increased (P < 0.05) absolute and relative liver masses and serum cholesterol. Fasting blood glucose, serum triglycerides, alanine transaminase, creatinine, and urea were not significantly different (P > 0.05) between groups. The HCD and FS significantly increased liver lipid yield compared to the SRC and rats receiving SRC with fenofibrate (P < 0.05). Quercetin or fenofibrate together with HCD and FS attenuated the diet-induced increase in liver lipids by approximately 50%, although this was not statistically significant. Liver macro- and micro-steatosis scores were significantly increased (P < 0.05) in rats receiving HCD and FS. Quercetin or fenofibrate administration together with HCD and FS significantly decreased (P < 0.05) liver macro-steatosis scores.

CONCLUSION

The prophylactic effect of quercetin on fructose and cholesterol diet-induced liver lipid accumulation may be exploited in the fight against non-alcoholic fatty liver disease (NAFLD). © 2019 Society of Chemical Industry.

Lipid metabolism in adipose tissue and liver from diet-induced obese rats: a comparison between Wistar and Sprague-Dawley strains

Some researchers have proposed important variations in adipose tissue among different strains of rats and mice in response to a high-caloric (hc) diet, but data concerning the mechanisms underlying these differences are scarce. The aim of the present research was to characterize different aspects of triacylglycerol (TG) metabolism and clock genes between Sprague-Dawley and Wistar rats. For this purpose, 16 male Sprague-Dawley and 16 male Wistar rats were divided into four experimental groups (n = 8) and fed either a normal-caloric (nc) diet or a hc diet for 6 weeks. After sacrifice, liver and epididymal, perirenal, mesenteric, and subcutaneous adipose tissue depots were dissected, weighed and immediately frozen. Liver TG content was quantified, RNA extracted for gene expression analysis and fatty acid synthase enzyme activity measured. Two-way ANOVA and Student's t test were used to perform the statistical analyses. Under hc feeding conditions, Wistar rats were more prone to fat accumulation in adipose tissue, especially in the epididymal fat depot, due to their increased lipogenesis and fatty acid uptake. By contrast, both strains of rats showed similarly fatty livers after hc feeding. Peripheral clock machinery seems to be a potential explanatory mechanism for Wistar and Sprague-Dawley strain differences. In conclusion, Wistar strain seems to be the best choice as animal model in dietary-induced obesity studies.

Neonatal overfeeding in mice aggravates the development of methionine and choline-deficient diet-induced steatohepatitis in adulthood

Overfeeding in early life is associated with obesity and insulin resistance in adulthood. In the present study, a well-characterized mouse model was used to investigate whether neonatal overfeeding increases susceptibility to the development of non-alcoholic steatohepatitis (NASH) following feeding with a methionine and choline- deficient (MCD) diet. Neonatal overfeeding was induced by adjusting litters to 3 pups per dam (small litter size, SL) in contrast to 10 pups per dam as control (normal litter size, NL). At 11 weeks of age, mice were fed with standard (S) or a methionine and choline-deficient (MCD) diet for 4 weeks. Glucose tolerance tests, tissue staining with haematoxylin and eosin, oil-red O and immunohistochemistry for F4/80, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting were performed. Compared with NL mice, SL mice exhibited higher body weight gain from 2 weeks of age throughout adulthood, and more profound glucose intolerance as adults. Sterol regulatory element-binding protein 1c and fatty acid synthase mRNA expression levels in liver were upregulated in SL mice at 3 weeks of age. MCD diet induced typical NASH, especially in SL-MCD mice, evidenced by marked fat accumulation, macrovescular steatosis, ballooned hepatocytes, inflammatory cells infiltration and tumour necrosis factor-α mRNA upregulation in the liver, as well as increased alanine aminotransferase and aspartate aminotransferase levels in the serum. There were no significant differences in liver fibrosis in all groups. Overfeeding during early life exhibited effect with administration of MCD diet in inducing adverse effects on the metabolic function and in promoting the progression of NASH in mice, possibly mediated through dysregulated lipid metabolism in hepatocytes and aggravated hepatic inflammation.

Does Simple Steatosis Affect Liver Regeneration after Partial Hepatectomy in Rats?

AIM

The aim of our study was to assess whether simple steatosis impairs liver regeneration after partial hepatectomy (PHx) in rats.

METHODS

Male Sprague-Dawley rats were fed a standard diet (ST-1, 10% kcal fat) and high-fat diet (HFD, 71% kcal fat) for 6 weeks. Then the rats were submitted to 2/3 PHx and animals were sacrificed 24, 48 or 72 h after PHx. Serum biochemistry, respiration of mitochondria in liver homogenate, hepatic oxidative stress markers, selected cytokines and DNA content were measured, and histopathological samples were prepared. Liver regeneration was evaluated by incorporation of bromodeoxyuridine (BrdU) to hepatocyte DNA.

RESULTS

HFD induced simple microvesicular liver steatosis. PHx caused elevation of serum markers of liver injury in both groups; however, an increase in these parameters was delayed in HFD group. Hepatic content of reduced glutathione was significantly increased in both groups after PHx. There were no significant changes in activities of respiratory complexes I and II (state 3). Relative and absolute liver weights, total DNA content, and DNA synthesis exerted very similar changes in both ST-1 and HFD groups after PHx.

CONCLUSION

PHx-induced regeneration of the rat liver with simple steatosis was not significantly affected when compared to the lean liver.

The effect of D-galactosamine on lean and steatotic rat hepatocytes in primary culture

The aim of our work was to compare the effect of D-galactosamine (GalN) on primary cultures of lean and steatotic rat hepatocytes isolated from intact and fatty liver, respectively. GalN caused more severe injury to steatotic hepatocytes than to lean cells as documented by lactate dehydrogenase leakage. Necrotic mode of cell death strongly prevails over apoptosis since we did not observe any significant increase in activities of caspase 3, 8 and 9 in any group of hepatocytes treated with GalN. Reactive oxygen species (ROS) formation and lipid peroxidation were elevated in a dose-dependent manner by GalN and were significantly more pronounced in fatty hepatocytes. A decrease in the percentage of hepatocytes with energized mitochondria was observed from 30 mM and 10 mM GalN in lean and steatotic hepatocytes, respectively. Our results undoubtedly indicate that steatotic hepatocytes exert higher sensitivity to the toxic effect of GalN. This sensitivity may be caused by more intensive GalN-induced ROS production and lipid peroxidation and by higher susceptibility of mitochondria to loss of mitochondrial membrane potential in steatotic hepatocytes. In our experimental arrangement, apoptosis does not seem to participate considerably on hepatotoxic action of GalN in either group of hepatocytes.

Mouse models of metabolic liver injury

Metabolic liver injury is one of the fastest growing health problems worldwide. Alcoholic and non-alcoholic fatty livers have been shown to be associated with progression to end-stage liver diseases, as well as to liver cancers, in humans. More importantly, there are no validated therapies for these disorders, therefore intensive research is required in this area. This review of standard operation procedures focuses on the experimental models of fatty liver disease in the mouse. Firstly, use of these experimental models might improve understanding of underlying mechanisms, and secondly this might help to test potential therapeutic options. This article includes, besides a short historic background, an insight into the pathobiochemical mechanisms and detailed experimental procedures as well as the practical implementation of these models.

Melatonin reduces hepatic mitochondrial dysfunction in diabetic obese rats

Hepatic mitochondrial dysfunction is thought to play a role in the development of liver steatosis and insulin resistance, which are both common characteristics of obesity and type 2 diabetes mellitus (T2DM). It was hypothesized that the antioxidant properties of melatonin could potentially improve the impaired functions of hepatic mitochondria in diabetic obese animals. Male Zucker diabetic fatty (ZDF) rats and lean littermates (ZL) were given either melatonin (10 mg/kg BW/day) orally for 6 wk (M-ZDF and M-ZL) or vehicle as control groups (C-ZDF and C-ZL). Hepatic function was evaluated by measurement of serum alanine transaminase and aspartate transaminase levels, liver histopathology and electron microscopy, and hepatic mitochondrial functions. Several impaired functions of hepatic mitochondria were observed in C-ZDF in comparison with C-ZL rats. Melatonin treatment to ZDF rats decreases serum levels of ALT (P < 0.001), alleviates liver steatosis and vacuolation, and also mitigates diabetic-induced mitochondrial abnormalities, glycogen, and lipid accumulation. Melatonin improves mitochondrial dysfunction in M-ZDF rats by increasing activities of mitochondrial citrate synthase (P < 0.001) and complex IV of electron transfer chain (P < 0.05) and enhances state 3 respiration (P < 0.001), respiratory control index (RCR) (P < 0.01), and phosphorylation coefficient (ADP/O ratio) (P < 0.05). Also melatonin augments ATP production (P < 0.05) and diminishes uncoupling protein 2 levels (P < 0.001). These results demonstrate that chronic oral melatonin reduces liver steatosis and mitochondria dysfunction in ZDF rats. Therefore, it may be beneficial in the treatment of diabesity.

Characteristics of nonalcoholic fatty liver disease induced in wistar rats following four different diets

BACKGROUND/OBJECTIVES

The prevalence of nonalcoholic fatty liver disease (NAFLD) has increased worldwide in parallel with overnutrition characterized by high-fat and high-carbohydrate intake. Our objective was to establish, in 16 weeks, a model of NAFLD in Wistar pathogen-free rats following four dietary types.

MATERIALS/METHODS

Forty (6 weeks old) healthy Wistar male rats, weighing an average of 150 g were randomly divided into four groups of ten and assigned a diet with the same quantity (15 g/rat/day), but with different composition. The moderate-fat (MF) group was fed a moderate-fat diet (31.5% fat and 50% carbohydrates), the high-fat (HF) group was fed a fat-rich diet (51% fat), the high-sucrose (HS) group and the high-fructose (HFr) group were fed a carbohydrate-rich diet (61%). The carbohydrate contents of the HS group was composed of 60.3% sucrose while that of the HFr group was composed of 59.3% fructose.

RESULTS

At week 16, the HF group had the highest percentage of cells enriched in fat (40%) and the highest weight and liver weight (P < 0.05). The HFr group showed significantly higher levels of serum triglycerides, alanine aminotransferase and adiponectin at week 16 as compared to week 1 (P < 0.05).

CONCLUSIONS

The 15 g/rat/day diet composed of 51% fat or 61% carbohydrates enriched mainly in fructose may induce characteristics of NAFLD in rats.

Physical exercise antagonizes clinical and anatomical features characterizing Lieber-DeCarli diet-induced obesity and related metabolic disorders

BACKGROUND & AIMS

Lieber-DeCarli diet has been used to induce obesity and non-alcoholic steatohepatitis (NASH). As scarce anatomical and clinical-related information on this diet model exists and being exercise an advised strategy to counteract metabolic diseases, we aimed to analyze the preventive (voluntary physical activity - VPA) and therapeutic (endurance training - ET) effect of exercise on clinical/anatomical features of rats fed with Lieber-DeCarli diet.

METHODS

In the beginning of the protocol, Sprague-Dawley rats were divided into standard-diet sedentary (SS, n = 20), standard-diet VPA (SVPA, n = 10), high-fat diet sedentary (HS, n = 20) and high-fat diet VPA (HVPA, n = 10) groups. After 9-weeks, half (n = 10) of SS and HS groups were engaged in an ET program (8 wks/5 d/wk/60 min/day). At this time, a blood sample was collected for biochemical analysis. At the end of protocol (17-weeks) anatomic measures were assessed. Heart, liver, femur and visceral fat were weighted and blood was collected again. Liver section was used for histopathological examination.

RESULTS

At 17-weeks, high-fat diet increased visceral adiposity (HS vs. SS), which was counteracted by both exercises. However, ET was the only intervention able to diminished obesity-related measures and the histological features of NASH. Moreover, blood analysis at 9 weeks showed that high-fat diet increased ALT, AST, cholesterol and HDL while VLDL and TG levels were decreased (HS vs. SS). Notably, although these parameters were counteracted after 9-weeks of VPA, they were transitory and not observed after 17-weeks.

CONCLUSIONS

ET used as a therapeutic tool mitigated the clinical/anatomical-related features induced by Liber-DeCarli diet, thus possibly contributing to control obesity and metabolic disorders.

Protein carbonylation associated to high-fat, high-sucrose diet and its metabolic effects

The present research draws a map of the characteristic carbonylation of proteins in rats fed high-caloric diets with the aim of providing a new insight of the pathogenesis of metabolic diseases derived from the high consumption of fat and refined carbohydrates. Protein carbonylation was analyzed in plasma, liver and skeletal muscle of Sprague-Dawley rats fed a high-fat, high-sucrose (HFHS) diet by a proteomics approach based on carbonyl-specific fluorescence-labeling, gel electrophoresis and mass spectrometry. Oxidized proteins along with specific sites of oxidative damage were identified and discussed to illustrate the consequences of protein oxidation. The results indicated that long-term HFHS consumption increased protein oxidation in plasma and liver; meanwhile, protein carbonyls from skeletal muscle did not change. The increment of carbonylation by HFHS diet was singularly selective on specific target proteins: albumin from plasma and liver, and hepatic proteins such as mitochondrial carbamoyl-phosphate synthase (ammonia), mitochondrial aldehyde dehydrogenase, argininosuccinate synthetase, regucalcin, mitochondrial adenosine triphosphate synthase subunit beta, actin cytoplasmic 1 and mitochondrial glutamate dehydrogenase 1. The possible consequences that these specific protein carbonylations have on the excessive weight gain, insulin resistance and nonalcoholic fatty liver disease resulting from HFHS diet consumption are discussed.

The effect of tert-butyl hydroperoxide-induced oxidative stress on lean and steatotic rat hepatocytes in vitro

Oxidative stress and mitochondrial dysfunction play an important role in the pathogenesis of nonalcoholic fatty liver disease and toxic liver injury. The present study was designed to evaluate the effect of exogenous inducer of oxidative stress (tert-butyl hydroperoxide, tBHP) on nonfatty and steatotic hepatocytes isolated from the liver of rats fed by standard and high-fat diet, respectively. In control steatotic hepatocytes, we found higher generation of ROS, increased lipoperoxidation, an altered redox state of glutathione, and decreased ADP-stimulated respiration using NADH-linked substrates, as compared to intact lean hepatocytes. Fatty hepatocytes exposed to tBHP exert more severe damage, lower reduced glutathione to total glutathione ratio, and higher formation of ROS and production of malondialdehyde and are more susceptible to tBHP-induced decrease in mitochondrial membrane potential. Respiratory control ratio of complex I was significantly reduced by tBHP in both lean and steatotic hepatocytes, but reduction in NADH-dependent state 3 respiration was more severe in fatty cells. In summary, our results collectively indicate that steatotic rat hepatocytes occur under conditions of enhanced oxidative stress and are more sensitive to the exogenous source of oxidative injury. This confirms the hypothesis of steatosis being the first hit sensitizing hepatocytes to further damage.

Ameliorative potential of Tamarindus indica on high fat diet induced nonalcoholic fatty liver disease in rats

Nonalcoholic fatty liver disease (NAFLD), the prevalence of which is rising globally with current upsurge in obesity, is one of the most frequent causes of chronic liver diseases. The present study evaluated the ameliorative effect of extract of Tamarindus indica seed coat (ETS) on high fat diet (HFD) induced NAFLD, after daily administration at 45, 90, and 180 mg/kg body weight dose levels for a period of 6 weeks, in albino Wistar rats. Treatment with ETS at all tested dose levels significantly attenuated the pathological alterations associated with HFD induced NAFLD viz. hepatomegaly, elevated hepatic lipid and lipid peroxides, serum alanine aminotransferase, and free fatty acid levels as well as micro-/macrohepatic steatosis. Moreover, extract treatment markedly reduced body weight and adiposity along with an improvement in insulin resistance index. The study findings, therefore suggested the therapeutic potential of ETS against NAFLD, acting in part through antiobesity, insulin sensitizing, and antioxidant mechanisms.

Impairment of mitochondrial function of rat hepatocytes by high fat diet and oxidative stress

Fatty liver disease associated with obesity is an important medical problem and the mechanisms for lipid accumulation in hepatocytes are not fully elucidated yet. Recent findings indicate that mitochondria play an important role in this process. Our data on hepatocytes in which mitochondria are in contact with other cytosolic structures important for their function, extend observations obtained on isolated mitochondria and confirm inhibition of Complex I activity in hepatocytes isolated from rats fed by high fat diet (HFD) compared with controls fed by standard diet (STD). Furthermore we have found that HFD-hepatocytes are more sensitive to the peroxidative stress because under these conditions also Complex II activity is disturbed. Therefore in HFD animals decrease of Complex I activity cannot be compensated by Complex II substrates as in STD hepatocytes. Our data thus indicates that combination of HFD and peroxidative stress potentiates HFD damaging effect of mitochondria because both branches of the respiratory chain (NADH- and flavoprotein-dependent) are disturbed.

Ping-tang Recipe () improves insulin resistance and attenuates hepatic steatosis in high-fat diet-induced obese rats

OBJECTIVE

To investigate the therapeutic effects of Ping-tang Recipe (, PTR) on high-fat diet (HFD)-induced insulin resistance and non-alcoholic fatty liver disease (NAFLD), and to elucidate the underlying mechanisms.

METHODS

Forty male SD rats were included in the study. Ten rats were fed on normal diet as normal control, and thirty rats were fed on HFD for 8 weeks to induce obesity, followed with low dose (0.42 g/kg) or high dose (0.84 g/kg) of PTR or vehicle for 8 weeks with 10 animals for each group. Glucose metabolism and insulin sensitivity were evaluated by oral glucose tolerance test and insulin tolerance test. Hepatic steatosis was measured by immunohistochemistry. Liver lipid metabolic genes were analyzed by quantitative real-time polymerase chain reaction, while AMP-activated protein kinase (AMPK) expression was examined by Western blot.

RESULTS

Rats fed on HFD developed abdominal obesity, insulin resistance and NAFLD. PTR treatment reduced visceral fat (peri-epididymal and peri-renal) accumulation, improved glucose metabolism, and attenuated hepatic steatosis. The expressions of the key lipolytic regulating genes, including peroxisome proliferators-activated receptor γ co-activator 1α (PGC-1α), peroxisome proliferator-activated receptor γ (PRAR-γ) and α (PRAR-α), were up-regulated (P<0.05 or P<0.01), while the expressions of lipogenic genes such as sterol regulatory element-binding protein 1c (SREBP-1c), fatty acid synthase (FAS) and liver fatty acid-binding protein (L-FABP) were down-regulated (P<0.05 or P<0.01). In addition, PTR activated AMPK and promoted acetyl-CoA carboxylase phosphorylation in the liver.

CONCLUSIONS

PTR improves insulin resistance and reverse hepatic steatosis in the rat model of HFD-induced obesity through promotion of lipolysis and reduction of lipogenesis, which involves the AMPK signaling pathway, thus representing a new therapeutic intervention for obesity related insulin resistance and NAFLD.

Susceptibility of rat non-alcoholic fatty liver to the acute toxic effect of acetaminophen

BACKGROUND AND AIM

Acetaminophen overdose is the most frequent cause of acute liver failure. Non-alcoholic fatty liver disease is the most common chronic condition of the liver. The aim was to assess whether non-alcoholic steatosis sensitizes rat liver to acute toxic effect of acetaminophen.

METHODS

Male Sprague-Dawley rats were fed a standard diet (ST-1, 10% kcal fat) and high-fat gelled diet (HFGD, 71% kcal fat) for 6 weeks and then acetaminophen was applied in a single dose (1 g/kg body weight). Animals were killed 24, 48 and 72 h after acetaminophen administration. Serum biochemistry, activities of mitochondrial complexes, hepatic malondialdehyde, reduced and oxidized glutathione, triacylglycerol and cholesterol contents, and concentrations of serum and liver cytokines (TNF-α, TGF-β1) were measured and histopathological samples were prepared.

RESULTS

The degree of liver inflammation and hepatocellular necrosis were significantly higher in HFGD fed animals after acetaminophen administration. Serum markers of liver injury were elevated only in acetaminophen treated HFGD fed animals. Concentration of hepatic reduced glutathione and ratio of reduced/oxidized glutathione were decreased in both ST-1 and HFGD groups at 24 h after acetaminophen application. Mild oxidative stress induced by acetaminophen was confirmed by measurement of malondialdehyde. Liver content of TNF-α was not significantly altered, but hepatic TGF-β1 was elevated in acetaminophen treated HFGD rats. We did not observe acetaminophen-induced changes in activities of respiratory complexes I, II, and IV and activity of caspase-3.

CONCLUSION

Liver from rats fed HFGD is more susceptible to acute toxic effect of acetaminophen, compared to non-steatotic liver.

Liver mitochondrial respiratory function and coenzyme Q content in rats on a hypercholesterolemic diet treated with atorvastatin

Statins, inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, are effective drugs in the treatment of hypercholesterolemia, however, their undesirable actions are not fully known. We investigated the effects of atorvastatin on the oxidative phosphorylation and membrane fluidity in liver mitochondria, and also on the coenzyme Q (CoQ) content in the mitochondria, liver tissue, and plasma of rats on a standard (C) and hypercholesterolemic (HCh) diet. Atorvastatin was administered at either low (10 mg kg(-1)) or high dose (80 mg kg(-1)) for four weeks. The high dose of the drug decreased the concentrations of total cholesterol and triacylglycerols in the plasma and liver of rats on a HCh diet. Administration of atorvastatin was associated with decreased oxygen uptake (state 3), and oxidative phosphorylation rate in the mitochondria of both C and HCh rats. Further, the drug influenced mitochondrial membrane fluidity and dose-dependently reduced concentrations of oxidized and reduced forms of CoQ in the mitochondria. Our findings point to an association between in vivo administration of atorvastatin and impaired bioenergetics in the liver mitochondria of rats, regardless of diet, in conjunction with simultaneous depletion of oxidized and reduced CoQ forms from the mitochondria. This fact may play a significant role in the development of statin-induced hepatopathy.

Steatotic rat hepatocytes in primary culture are more susceptible to the acute toxic effect of acetaminophen

Acetaminophen (APAP) overdose is the most common cause of acute liver failure in humans. Non-alcoholic fatty liver disease is the most frequent chronic liver disease in developed countries. The aim of our work was to compare the effect of APAP on intact rat hepatocytes and hepatocytes isolated from steatotic liver in primary cultures. Male Wistar rats were fed with standard diet (10 % energy from fat) and high-fat diet (71 % energy from fat) for 6 weeks and then hepatocytes were isolated. After cell attachment, APAP (1; 2.5; 3.75 and 5 mM) was added to culture media (William's E medium) and hepatocytes were cultured for up to 24 hours. APAP caused more severe dose-dependent damage of steatotic hepatocytes as documented by increased release of lactate dehydrogenase (LDH) and LDH leakage, decreased activity of cellular dehydrogenases (WST-1 test) and reduced albumin production. Intact steatotic hepatocytes contained lower amount of reduced glutathione (GSH). Treatment with APAP (1 and 2.5 mmol/l) caused more pronounced decrease in GSH in steatotic hepatocytes. ROS (reactive oxygen species) formation after 24-hour incubation was significantly higher in fatty hepatocytes using APAP at concentration of 3.75 and 5 mmol/l. Interleukin 6 (IL-6) production was elevated in 2.5 mM APAP-treated nonsteatotic and steatotic hepatocyte cultures at 8 hours, compared to appropriate controls. In conclusions, our results indicate that steatotic hepatocytes exert higher sensitivity to the toxic action of APAP. This sensitivity may be caused by lower content of GSH in intact steatotic hepatocytes and by more pronounced APAP-induced decrease in intracellular concentration of GSH.

Prenatal dexamethasone exposure potentiates diet-induced hepatosteatosis and decreases plasma IGF-I in a sex-specific fashion

The clinical use of synthetic glucocorticoids in preterm infants to promote lung development has received considerable attention due to the potential for increased risk of developing metabolic disease in adulthood after such treatment. In this study, we examined the hypothesis that exposure to the synthetic glucocorticoid, dexamethasone (DEX), during late gestation in the rat results in the development of nonalcoholic fatty liver disease in adult offspring. Pregnant Sprague Dawley dams were treated with 0.4 mg/kg DEX beginning on gestational d 18 until parturition (gestational d 23). At postnatal d 21, offspring were weaned onto either a standard chow or high-fat (60% fat-derived calories) diet. In adulthood (postnatal d 60-65), hepatic tissue was harvested and examined for pathology. Liver steatosis, or fat accumulation, was found to be more severe in the DEX-exposed female offspring that were weaned onto the high-fat diet. This finding corresponded with decreased plasma IGF-I concentrations, as well as decreased hypothalamic expression of GHRH mRNA. Morphological measurements on body and long bone length further implicate a GH signaling deficit after fetal DEX exposure. Collectively, these data indicate suppression of GH axis function in the female DEX/high-fat cohort but not in the male offspring. Because deficits in the GH signaling can be linked to the development of nonalcoholic fatty liver disease, our results suggest that the prominent liver injury noted in female offspring exposed to DEX during late gestation may stem from abnormal development of the GH axis at the hypothalamic level.

Is rat liver affected by non-alcoholic steatosis more susceptible to the acute toxic effect of thioacetamide?

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic condition of the liver in the western world. There is only little evidence about altered sensitivity of steatotic liver to acute toxic injury. The aim of this project was to test whether hepatic steatosis sensitizes rat liver to acute toxic injury induced by thioacetamide (TAA). Male Sprague-Dawley rats were fed ad libitum a standard pelleted diet (ST-1, 10% energy fat) and high-fat gelled diet (HFGD, 71% energy fat) for 6 weeks and then TAA was applied intraperitoneally in one dose of 100 mg/kg. Animals were sacrificed in 24-, 48- and 72-h interval after TAA administration. We assessed the serum biochemistry, the hepatic reduced glutathione, thiobarbituric acid reactive substances, cytokine concentration, the respiration of isolated liver mitochondria and histopathological samples (H+E, Sudan III, bromodeoxyuridine [BrdU] incorporation). Activities of alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase and concentration of serum bilirubin were significantly higher in HFGD groups after application of TAA, compared to ST-1. There were no differences in activities of respiratory complexes I and II. Serum tumour necrosis factor alpha at 24 and 48 h, liver tissue interleukin-6 at 72 h and transforming growth factor β1 at 24 and 48 h were elevated in TAA-administrated rats fed with HFGD, but not ST-1. TAA-induced centrilobular necrosis and subsequent regenerative response of the liver were higher in HFGD-fed rats in comparison with ST-1. Liver affected by NAFLD, compared to non-steatotic liver, is more sensitive to toxic effect of TAA.