Adipokines and cytokines in non-alcoholic fatty liver disease

Abnormal serum alanine aminotransferase levels are associated with impaired insulin sensitivity in young women with polycystic ovary syndrome

BACKGROUND AND AIM

Non-alcoholic fatty liver disease (NAFLD) and polycystic ovary syndrome (PCOS) are both associated with insulin resistance.We assessed whether NAFLD is associated with impaired insulin sensitivity in PCOS women independently of age and total adiposity.

SUBJECTS AND METHODS

We enrolled 14 young PCOS women with NAFLD, 14 women with PCOS alone and 14 healthy controls, who were matched for age, body mass index, and total body fat (by bio-impedance analyzer). NAFLD was diagnosed by the surrogate measure of abnormal serum alanine aminotransferase (ALT) concentrations (defined as ALT>19 U/l) after excluding other secondary causes of liver disease (alcohol, virus, and medications). Insulin sensitivity was measured by euglycemic hyperinsulinemic clamp.

RESULTS

Insulin sensitivity was markedly decreased (p<0.001) in PCOS women with abnormal ALT levels, whereas it was similar between PCOS women with normal ALT levels andmatched healthy controls (8.3+/-2.5 vs 12.1+/-1.7 vs 13.2+/-1.8 mg/min x kg of fat-free mass, respectively). PCOS women with abnormal ALT levels also had higher plasma triglycerides and lower HDLcholesterol concentrations than those with PCOS alone. There was a strong inverse association between serum ALT levels and insulin sensitivity in the whole group of PCOS women (r=-0.59, p=0.0013).

CONCLUSIONS

Abnormal serum ALT levels, as surrogate measure of NAFLD, are closely associated with impaired insulin sensitivity in young PCOS women in a manner that is independent from the contribution of age and total adiposity. Early recognition of NAFLD by radiological imaging tests in this group of young patients is warranted.

Adipokine serum levels are related to liver histology in severely obese patients undergoing bariatric surgery

BACKGROUND

Leptin, adiponectin, and resistin are adipokines linked to the development of insulin resistance, which plays a central role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). We aimed to define adipokine serum levels in severely obese patients undergoing bariatric surgery and to correlate these with anthropometric and metabolic variables, liver function tests, and histopathological parameters of NAFLD and nonalcoholic steatohepatitis (NASH).

METHODS

Surgical liver biopsies were obtained from 50 bariatric patients with no history of liver disease or significant alcohol consumption. Serum leptin, adiponectin, and resistin levels were measured, and histology was assessed using Brunt's and Kleiner's scoring systems.

RESULTS

Waist/hip ratio was significantly higher in men (p = 0.0001), and leptin (p = 0.036) and adiponectin (p = 0.0001) serum levels were higher in women. Forty-one of 50 patients (82%) had histological NAFLD, including 10 (20%) with NASH. Nine patients (18%) had normal liver histology (obese control subgroup). In NAFLD patients, serum adiponectin was negatively correlated with activity grade and fibrosis stage, resistin was negatively correlated with steatosis grade (p = 0.033), while leptin was not related to histology. Leptin/adiponectin ratio showed positive association with stage (p = 0.044). In the subgroup of NASH patients, adiponectin was negatively correlated only with stage (p = 0.01), while there was no correlation between leptin, resistin, or leptin/adiponectin and histology.

CONCLUSIONS

Serum adiponectin and resistin levels are related to liver histology in bariatric patients and may be indicative of the histological severity of NAFLD and the extent of hepatic steatosis, respectively. Serum leptin levels are not informative of underlying liver histology in severely obese patients.

Kupffer cells in non-alcoholic fatty liver disease: the emerging view

Non-alcoholic fatty liver disease (NAFLD) has become the most common liver disorder of our times. Simple steatosis, a seemingly innocent manifestation of NAFLD, may progress into steatohepatitis and cirrhosis, but this process is not well understood. Since NAFLD is associated with obesity and insulin resistance, mechanisms that link lipid metabolism to inflammation offer insights into the pathogenesis. An important parallel between obesity-related pathology of adipose tissue and liver pertains to the emerging role of macrophages and evidence is growing that Kupffer cells critically contribute to progression of NAFLD. Toll-like receptors, in particular TLR4, represent a major conduit for danger recognition linked to Kupffer cell activation and this process may be perturbed at multiple steps in NAFLD. Steatosis may interfere with sinusoid microcirculation and hepatocellular clearance of microbial and host-derived danger signals, enhancing responsiveness of Kupffer cells. Altered lipid homeostasis in NAFLD may unfavourably affect TLR4 receptor complex assembly and sorting, interfere with signalling flux redistribution, promote amplification loops, and impair negative regulation including alternative activation of Kupffer cells. These events are further promoted by altered adipokine secretion and reactive oxygen species production. Specific targeting of these interactions may provide more effective strategies in the treatment of NAFLD.

Abnormal serum alanine aminotransferase levels are associated with impaired insulin sensitivity in young women with polycystic ovary syndrome

BACKGROUND AND AIM

Non-alcoholic fatty liver disease (NAFLD) and polycystic ovary syndrome (PCOS) are both associated with insulin resistance.We assessed whether NAFLD is associated with impaired insulin sensitivity in PCOS women independently of age and total adiposity.

SUBJECTS AND METHODS

We enrolled 14 young PCOS women with NAFLD, 14 women with PCOS alone and 14 healthy controls, who were matched for age, body mass index, and total body fat (by bio-impedance analyzer). NAFLD was diagnosed by the surrogate measure of abnormal serum alanine aminotransferase (ALT) concentrations (defined as ALT>19 U/l) after excluding other secondary causes of liver disease (alcohol, virus, and medications). Insulin sensitivity was measured by euglycemic hyperinsulinemic clamp.

RESULTS

Insulin sensitivity was markedly decreased (p<0.001) in PCOS women with abnormal ALT levels, whereas it was similar between PCOS women with normal ALT levels andmatched healthy controls (8.3+/-2.5 vs 12.1+/-1.7 vs 13.2+/-1.8 mg/min x kg of fat-free mass, respectively). PCOS women with abnormal ALT levels also had higher plasma triglycerides and lower HDLcholesterol concentrations than those with PCOS alone. There was a strong inverse association between serum ALT levels and insulin sensitivity in the whole group of PCOS women (r=-0.59, p=0.0013).

CONCLUSIONS

Abnormal serum ALT levels, as surrogate measure of NAFLD, are closely associated with impaired insulin sensitivity in young PCOS women in a manner that is independent from the contribution of age and total adiposity. Early recognition of NAFLD by radiological imaging tests in this group of young patients is warranted.

Adipokines in nonalcoholic steatohepatitis: from pathogenesis to implications in diagnosis and therapy

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome and can vary from benign steatosis to end-stage liver disease. The pathogenesis of non-alcoholic steatohepatitis (NASH) is currently thought to involve a multiple-hit process with the first hit being the accumulation of liver fat which is followed by the development of necroinflammation and fibrosis. There is mounting evidence that cytokines secreted from adipose tissue, namely, adipokines, are implicated in the pathogenesis and progression of NAFLD. In the current review, we explore the role of these adipokines, particularly leptin, adiponectin, resistin, tumor necrosis factor-a, and interleukin-6 in NASH, as elucidated in experimental models and clinical practice. We also comment on their potential use as noninvasive markers for differentiating simple fatty liver from NASH as well as on their potential future therapeutic role in patients with NASH.

Patients with nonalcoholic fatty liver disease display increased serum resistin levels and decreased adiponectin levels

AIM

Resistin and adiponectin are recently discovered protein hormones, which are produced and secreted by adipocytes. Nonalcoholic fatty liver disease (NAFLD) is a metabolic syndrome, which is associated with obesity. The aim of this study was to evaluate the changes of serum adiponectin and resistin in patients with NAFLD and to determine the relationship between serum adipokine levels and clinicopathologic parameters of NAFLD.

METHODS

Forty-three patients with NAFLD and 43 controls were enrolled in this pair-matched study. Body weight, height, body mass index, abdominal wall fat thickness, waist circumference, hip circumference, and the percentage of body fat were measured. Additionally, serum lipid, glucose, alanine aminotransferase, aspartate aminotransferase, adiponectin, and resistin were determined in all individuals. Serum adiponectin and resistin levels were determined using ELISA kits.

RESULTS

Serum adiponectin levels were significantly lower in patients with NAFLD compared to the control group (control: 2.01+/-1.10 mg/l vs. NAFLD: 1.38+/-0.65 mg/l, P<0.01). Serum resistin levels were significantly elevated in patients with NAFLD compared to the control group (control: 4.70+/-3.30 ng/ml vs. NAFLD: 9.20+/-7.20 ng/ml, P<0.05). Serum adiponectin concentration was negatively correlated with the waist circumference (rho=-0.425), body mass index (rho=-0.329), percentage of body fat (rho=-0.256), abdominal wall fat thickness (rho=-0.226), and fasting blood glucose concentration (rho=-0.242), but was positively correlated with HDL (rho=0.226). Serum resistin concentration was positively correlated with waist circumference (rho=0.237). No correlation was found between resistin levels and blood pressure, fasting blood glucose concentration, triglyceride, total cholesterol, and HDL.

CONCLUSION

NAFLD patients had lower adiponectin levels and higher resistin levels. A positive correlation was found between resistin and waist circumference, whereas a negative correlation was found between adiponectin and waist circumference, body mass index, percentage of body fat, abdominal wall fat thickness, and fasting blood glucose concentration. These data suggested that hypoadiponectinemia and hyperresistinemia might be involved in the development of NAFLD.

Expression of cytokine signaling genes in morbidly obese patients with non-alcoholic steatohepatitis and hepatic fibrosis

BACKGROUND

White adipose tissue (WAT) from visceral adiposity plays an important role in the pathogenesis of non-alcoholic steatohepatitis (NASH). Development of NASH and its progression to fibrosis is partially due to cytokines and adipokines produced by WAT. The aim of this study was to assess the association of hepatic fibrosis and NASH by evaluating the intrinsic differences in the inflammatory cytokine signaling in the visceral adipose tissue obtained from morbidly obese patients.

METHODS

We used targeted microarrays representing human genes involved in the inflammatory and fibrogenic reactions to profile visceral adipose samples of 15 well-matched NASH patients with and without fibrosis. Additionally, visceral adipose samples were subjected to real-time polymerase chain reaction profiling of 84 inflammations related genes.

RESULTS

Eight genes (CCL2, CCL4, CCL18, CCR1, IL10RB, IL15RA, and LTB) were differentially expressed in NASH with fibrosis. Additionally, an overlapping but distinct list of the differentially expressed genes were found in NASH with type II diabetes (DM; IL8, BLR1, IL2RA, CD40LG, IL1RN, IL15RA, and CCL4) as compared to NASH without DM.

CONCLUSIONS

Inflammatory cytokines are differentially expressed in the adipose tissue of NASH with fibrosis, as well in NASH with DM. These findings point at the interaction of adipose inflammatory cytokines, DM, hepatic fibrosis in NASH, and its progression to cirrhosis and end-stage liver disease.

Adipocytokines and liver disease

Adipose tissue is a massive source of bioactive substances known as adipocytokines, including tumor necrosis factor (TNF)-alpha, resistin, leptin, and adiponectin. Recent advances in medical research view obesity as a chronic low-grade inflammatory state. Hypertrophied adipocytes in obesity release chemokines that induce macrophage accumulation in adipose tissue. Accumulated macrophages in obese adipose tissue produce proinflammatory cytokines and nitric oxide, and these inflammatory changes induce adipocytokine dysregulation. The latter is characterized by a decrease in insulinsensitizing and anti-inflammatory adipocytokines, and an increase in proinflammatory adipocytokines. Adipocytokine dysregulation induces obesity-related metabolic disorders, the so-called metabolic syndrome. Metabolic syndrome is a cluster of metabolic abnormalities, including diabetes mellitus, hypertension, hyperlipidemia, and nonalcoholic steatohepatitis (NASH). Recent studies have revealed that obesity is an independent risk factor for chronic liver diseases, such as NASH, alcoholic liver disease, chronic hepatitis C, and hepatocellular carcinoma. A common mechanism underlying these hepatic clinical states is thought to be adipocytokine dysregulation. In this review, we discuss the association of adipocytokines, especially leptin, adiponectin, TNF-alpha, and resistin, with liver diseases.

Orlistat for overweight subjects with nonalcoholic steatohepatitis: A randomized, prospective trial

The aim of this study was to determine if orlistat, an inhibitor of fat absorption, combined with caloric restriction in overweight subjects with nonalcoholic steatohepatitis results in weight loss and improved liver histology. Fifty overweight subjects (body mass index = >or=27) with biopsy proven nonalcoholic steatohepatitis were randomized to receive a 1,400 Kcal/day diet plus vitamin E (800 IU) daily with or without orlistat (120 mg three times a day) for 36 weeks. Liver biopsies were repeated at week 36. Twenty-three subjects in the orlistat/diet/vitamin E group and 18 in the diet/vitamin E group completed the study. The mean age was 47 +/- 9.0 (standard deviation) years and mean body mass index was 36.4 +/- 6.3 kg/m(2). Four subjects were diabetic. The orlistat group lost a mean of 8.3% body weight compared to 6.0% in the diet plus vitamin E group (not significant). Both groups also had similarly improved serum aminotransferases, hepatic steatosis, necroinflammation, ballooning, and nonalcoholic fatty liver disease activity scores. Stratified according to weight loss instead of treatment group, a loss of >or=5% body weight (n = 24) compared to <5% body weight (n = 17) correlated with improvement in insulin sensitivity (P = 0.001) and steatosis (P = 0.015). Comparing subjects who lost >or=9% of body weight (n = 16), to those that did not (n = 25), improved insulin sensitivity (P < 0.001), adiponectin (P = 0.03), steatosis (P = 0.005), ballooning (P = 0.04), inflammation (P = 0.045), and nonalcoholic fatty liver disease activity score (P = 0.009) were seen. Increases in adiponectin strongly correlated with improved ballooning and nonalcoholic fatty liver disease activity score (P = 0.03). Orlistat did not enhance weight loss or improve liver enzymes, measures of insulin resistance, and histopathology. However, subjects who lost >or=5% of body weight over 9 months improved insulin resistance and steatosis, and those subjects who lost >or=9% also achieved improved hepatic histologic changes.

Insulin resistance, inflammation, and non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), the major cause of abnormal liver function in the western world, is often associated with obesity and diabetes. In obese individuals, fat accumulation in the abdominal region affects both lipid and glucose metabolism, and a liver loaded with fat is insulin resistant. Insulin resistance (IR) is often associated with chronic low-grade inflammation, and numerous mediators released from immune cells and adipocytes contribute to development of IR. Recent results showing an important role for these mediators in NAFLD are providing us with a better understanding of this highly prevalent disease with implications for novel therapy development. This review highlights new aspects in development of liver steatosis and the relevance of various cytokines and adipocytokines in NAFLD.

Resveratrol inhibits nonalcoholic fatty liver disease in rats

BACKGROUND

The prevalence of nonalcoholic fatty liver disease (NAFLD) is high. NAFLD is linked to obesity, diabetes mellitus, and hypertriglyceridemia. Approximately 20% of patients with NAFLD will eventually develop cirrhosis. Our purpose was to investigate whether resveratrol decreased hepatic steatosis in an animal model of steatosis, and whether this therapeutic approach resulted in a decrease in tumor necrosis factor alpha (TNF-alpha) production, lipid peroxidation and oxidative stress.

METHODS

Male Wistar CRL: Wi (Han) (225 g) rats were randomized into three groups. A control group (n = 12) was given free access to regular dry rat chow for 4 weeks. The steatosis (n = 12) and resveratrol (n = 12) groups were given free access to feed (a high carbohydrate-fat free modified diet) and water 4 days per week, and fasted for the remaining 3 days for 4 weeks. Rats in the resveratrol group were given resveratrol 10 mg daily by the oral route. All rats were killed at 4 weeks and assessed for fatty infiltration and bacterial translocation. Levels of TNF-alpha in serum, hepatic malondialdehyde (MDA), oxidative stress (superoxide dismutase, glutathione peroxidase, catalase and nitric oxide synthase) and biochemical parameters were measured.

RESULTS

Fat deposition was decreased in the resveratrol group as compared to the steatosis group (Grade 1 vs Grade 3, P < 0.05). TNF-alpha and MDA levels were significantly increased in the steatosis group (TNF-alpha; 33.4 +/- 5.2 vs 26.24 +/- 3.47 pg/ml and MDA; 9.08 +/- 0.8 vs 3.17 +/- 1.45 muM respectively, P < 0.05). This was accompanied by increased superoxide dismutase, glutathione peroxidase and catalase and decreased nitric oxide synthase in the liver of resveratrol group significantly (P < 0.05 vs steatosis group). Bacterial translocation was not found in any of the groups. Glucose levels were decreased in the group of rats given resveratrol (P < 0.05).

CONCLUSION

Resveratrol decreased NAFLD severity in rats. This effect was mediated, at least in part, by TNF-alpha inhibition and antioxidant activities.

Resveratrol inhibits nonalcoholic fatty liver disease in rats

BACKGROUND

The prevalence of nonalcoholic fatty liver disease (NAFLD) is high. NAFLD is linked to obesity, diabetes mellitus, and hypertriglyceridemia. Approximately 20% of patients with NAFLD will eventually develop cirrhosis. Our purpose was to investigate whether resveratrol decreased hepatic steatosis in an animal model of steatosis, and whether this therapeutic approach resulted in a decrease in tumor necrosis factor alpha (TNF-alpha) production, lipid peroxidation and oxidative stress.

METHODS

Male Wistar CRL: Wi (Han) (225 g) rats were randomized into three groups. A control group (n = 12) was given free access to regular dry rat chow for 4 weeks. The steatosis (n = 12) and resveratrol (n = 12) groups were given free access to feed (a high carbohydrate-fat free modified diet) and water 4 days per week, and fasted for the remaining 3 days for 4 weeks. Rats in the resveratrol group were given resveratrol 10 mg daily by the oral route. All rats were killed at 4 weeks and assessed for fatty infiltration and bacterial translocation. Levels of TNF-alpha in serum, hepatic malondialdehyde (MDA), oxidative stress (superoxide dismutase, glutathione peroxidase, catalase and nitric oxide synthase) and biochemical parameters were measured.

RESULTS

Fat deposition was decreased in the resveratrol group as compared to the steatosis group (Grade 1 vs Grade 3, P < 0.05). TNF-alpha and MDA levels were significantly increased in the steatosis group (TNF-alpha; 33.4 +/- 5.2 vs 26.24 +/- 3.47 pg/ml and MDA; 9.08 +/- 0.8 vs 3.17 +/- 1.45 muM respectively, P < 0.05). This was accompanied by increased superoxide dismutase, glutathione peroxidase and catalase and decreased nitric oxide synthase in the liver of resveratrol group significantly (P < 0.05 vs steatosis group). Bacterial translocation was not found in any of the groups. Glucose levels were decreased in the group of rats given resveratrol (P < 0.05).

CONCLUSION

Resveratrol decreased NAFLD severity in rats. This effect was mediated, at least in part, by TNF-alpha inhibition and antioxidant activities.

Molecular mechanisms and therapeutic targets in steatosis and steatohepatitis

Steatosis of the liver may arise from a variety of conditions, but the molecular basis for lipid droplet formation is poorly understood. Although a certain amount of lipid storage may even be hepatoprotective, prolonged lipid storage can result in an activation of inflammatory reactions and loss of metabolic competency. Apart from drug-induced steatosis, certain metabolic disorders associated with obesity, insulin resistance, and hyperlipidemia give also rise to nonalcoholic fatty liver diseases (NAFLD). It is noteworthy that advanced stages of nonalcoholic hepatic steatosis and steatohepatitis (NASH) result ultimately in fibrosis and cirrhosis. In this regard, the lipid droplets (LDs) have been discovered to be metabolically highly active structures that play major roles in lipid transport, sorting, and signaling cascades. In particular, LDs maintain a dynamic communication with the endoplasmic reticulum (ER) and the plasma membrane via sphingolipid-enriched domains of the plasma membrane-the lipid rafts. These microdomains frequently harbor receptor tyrosine kinases and other signaling molecules and connect extracellular events with intracellular signaling cascades. Here, we review recent knowledge on the molecular mechanisms of drug and metabolically induced hepatic steatosis and its progression to steatohepatitis (NASH). The contribution of cytokines and other signaling molecules, as well as activity of nuclear receptors, lipids, transcription factors, and endocrine mediators toward cellular dysfunction and progression of steatotic liver disease to NASH is specifically addressed, as is the cross-talk of different cell types in the pathogenesis of NAFLD. Furthermore, we provide an overview of recent therapeutic approaches in NASH therapy and discuss new as well as putative targets for pharmacological interventions.

Hepatic steatosis: a mediator of the metabolic syndrome. Lessons from animal models

Epidemiological studies in humans, as well as experimental studies in animal models, have shown an association between visceral obesity and dyslipidemia, insulin resistance, and type 2 diabetes mellitus. Recently, attention has been focused on the excessive accumulation of triglycerides (TG) in the liver as part of this syndrome. In this review, important principles of the pathophysiological involvement of the liver in the metabolic syndrome obtained in rodent models are summarized. We focus on non-alcoholic causes of steatosis, because the animal experiments we refer to did not include alcohol as an experimental condition. In general, there is continuous cycling and redistribution of non-oxidized fatty acids between different organs. The amount of TG in an intrinsically normal liver is not fixed but can readily be increased by nutritional, metabolic, and endocrine interactions involving TG/free fatty acid (FFA) partitioning and TG/FFA metabolism. Several lines of evidence indicate that hepatic TG accumulation is also a causative factor involved in hepatic insulin resistance. Complex interactions between endocrine, metabolic, and transcriptional pathways are involved in TG-induced hepatic insulin resistance. Therefore, the liver participates passively and actively in the metabolic derangements of the metabolic syndrome. We speculate that similar mechanisms may also be involved in human pathophysiology.