Resistin serum levels are associated with insulin resistance, disease severity, clinical complications, and prognosis in patients with chronic liver diseases

Metabolic syndrome and estimates of cardiovascular disease in cirrhotic patients

OBJECTIVE

The expected survival rate in patients with liver cirrhosis has increased in recent years, putting them into a clinical scenario in which cardiovascular disease and metabolic syndrome could be common causes of morbidity and mortality. This study aimed to analyze the prevalence of metabolic syndrome and other risk factors and estimate the risk of cardiovascular disease in patients with liver cirrhosis.

METHODS

We conducted a cross-sectional study assessing the patients' lifestyle, and their anthropometric and biochemical data. Their metabolic syndrome and estimates of their risk of cardiovascular disease were calculated, comparing patients with and without liver cirrhosis.

RESULTS

The study included 355 patients (99 cirrhotic and 256 non-cirrhotic patients). There were no differences between them in the prevalence of metabolic syndrome (39.4% vs. 45.7%, P = 0.340). In patients with liver cirrhosis, the mean values of criteria for metabolic syndrome increased as the model end-stage liver disease (MELD) score increased (P = 0.01). The mean value of a 10-year risk for cardiovascular disease was lower in the cirrhotic patients (3.4 +/- 3.5% vs. 5.8 +/- 6.8%, P = 0.001).

CONCLUSION

Metabolic syndrome is prevalent in patients with liver cirrhosis, but their estimated risk for cardiovascular disease is lower than in non-cirrhotics. The MELD score is a good marker for assessing the severity of the metabolic syndrome in this group.

The role of adipokines in liver fibrosis

Liver fibrosis is a dynamic process consisting of the chronic activation of the wound healing reaction in response to reiterated liver damage, leading to the excessive deposition of fibrillar extracellular matrix into the liver and eventually, if the cause of injury is not removed, to liver cirrhosis. The term "adipokines" identifies a group of polypeptide molecules secreted primarily by adipose tissue, which exert local, peripheral and/or central actions. Additionally to their well-established role in controlling adipose tissue physiology, adipokines have been shown to be involved in different obesity-related diseases, such as hypertension, atherosclerosis and type 2 diabetes. Accumulating data demonstrate that obesity and insulin resistance are associated with a more severe and faster progression of the fibrogenic process in different chronic liver diseases. Therefore, numerous recent studies have analyzed the role played by adipokines in the hepatic wound healing process, identifying novel roles as modulators of liver pathophysiology. This review summarizes the more significant and recent findings concerning the role played by adipocyte-derived molecules, such as leptin, adiponectin and resistin, in the liver fibrogenic process. The actions of different adipokines on the biology of liver resident cells, as well as their effects in different animal models of liver injury are discussed. The variations in the circulating levels and in the intrahepatic expression of these molecules occurring in patients with different chronic liver diseases will be also analyzed.

Resistin does not down-regulate the transcription of insulin receptor promoter

OBJECTIVE

To detect the effect of resistin on the transcription of insulin receptor promoter.

METHODS

Luciferase reporter gene was fused downstream of human insulin receptor promoter and the enzymatic activity of luciferase was determined in the presence or absence of resistin. The resistin expressed with plasmid was stained with antibody against Myc tag which was in frame fused with resistin coding sequence, and then imaged with confocal microscopy.

RESULTS

The treatment of pIRP-LUC transfected cells with recombinant resistin did not result in significant difference in the enzymatic activity of luciferase compared to the untreated cells. Cell staining showed that green fluorescence could be observed in the cytoplasm, but not in the nucleus.

CONCLUSION

The results suggest that the endogenous resistin may functionally locate in the cytoplasm, but does not enter the nucleus and not down-regulate the transcription of insulin receptor promoter.

Hepatitis C virus infection: molecular pathways to metabolic syndrome

Chronic infection with hepatitis C virus (HCV) can induce insulin resistance (IR) in a genotype-dependent fashion, thus contributing to steatosis, progression of fibrosis and resistance to interferon therapy. The molecular mechanisms in genotype 1 patients that lead to metabolic syndrome are still ambiguous. Based on our current understanding, HCV proteins associate with mitochondria and endoplasmic reticulum and promote oxidative stress. The latter mediates signals involving the p38 mitogen-activated protein kinase and activates nuclear factor kappa B. This transcription factor plays a key role in the expression of cytokines, tumor necrosis factor alpha (TNF-alpha), interleukin 6, interleukin 8, tumor growth factor beta, and Fas ligand. TNF-alpha inhibits the function of insulin receptor substrates and decreases the expression of the glucose transporter and lipoprotein lipase in peripheral tissues, which is responsible for the promotion of insulin resistance. Furthermore, reduced adiponectin levels, loss of adiponectin receptors, and decreased anti-inflammatory peroxisome proliferator-activated receptor alpha in the liver of HCV patients may contribute to reduced fatty acid oxidation, inflammation, and eventually lipotoxicity. This chain of events may be initiated by HCV-associated IR and provides a direction for future research in the areas of therapeutic intervention.

Pitavastatin improves serum resistin levels in patients with hypercholesterolemia

AIM

Resistin in serum is associated with high risk in patients with atherosclerosis. This clinical study aimed to investigate whether pitavastatin can regulate the serum level of resistin, together with levels of other inflammatory cytokines and adipocytokines.

METHODS

Forty two outpatients (mean age 65.2 +/- 12.6 yr, M/F: 21/21) with hypercholesterolemia were administered 2 mg of pitavastatin and serum levels of resistin, together with serum levels of adiponectin, leptin, TNF-alpha and hsCRP, were measured before, and 12 weeks after enrollment.

RESULTS

There was no significant gender-related difference in initial serum resistin levels. Pitavastatin significantly decreased LDL-cholesterol after 12 weeks. Initial levels of resistin showed a significant correlation with those of hsCRP (r=0.38, p=0.013), but not TNF-alpha or HOMA-R. Serum resistin, but not adiponectin and leptin, levels were significantly decreased, dropping from 17.1 +/- 9.9 ng/ dL to 15.2+/-10.0 (p=0.001) after 12 weeks of administration. The patient group with a baseline hsCRP > or = 0.1 at enrollment (n=17) had decreased levels of both resistin and hsCRP (p=0.011 and p=0.022, respectively).

CONCLUSION

This study showed the pleiotropic effect of pitavastatin on the serum resistin concentration, suggesting that it may assist in the prevention of atherosclerosis.

Influence of insulin resistance and adipokines in the grade of steatosis of nonalcoholic fatty liver disease

The objective of this work was to study the influence of insulin resistance and adipokines on the grade of steatosis in patients with NAFLD (nonalcoholic fatty liver disease) diagnosed by liver biopsy. A sample of 24 NAFLD patients was analyzed in a cross-sectional study. All patients with a two-week weight-stabilization period before recruitment were enrolled. A liver biopsy was realized. Weight, basal glucose, insulin, insulin resistance (HOMA), total cholesterol, LDL-cholesterol, HDL-cholesterol, triglycerides, and adipokines blood levels were measured. A nutritional evaluation (dietary intake, indirect calorimetry, and bioimpedance) was performed. The mean age was 41.6 +/- 8.7 years and the mean body mass index (BMI) 29.4 +/- 4.7. Twelve patients had a low grade of steatosis (grade 1 of the Brunt classification) and 12 patients had a high grade of steatosis (grade 2 or 3). Only HOMA was higher in patients with a high grade of steatosis (1.4 +/- 0.5 vs. 2.8 +/- 1.7 units; P < 0.05). Anthropometric data and dietary intake were similar for both groups. Blood levels of adiponectin were higher in patients with a low grade of steatosis (37.7 +/- 22.5 vs. 24.2 +/- 33 ng mL(-1); P < 0.05). Blood levels of resistin were higher in patients with a high grade of steatosis (2.36 +/- 0.6 vs. 2.8 +/- 0.6 mg mL(-1); P < 0.05), without differences in TNF-alpha or leptin levels. In logistic regression analysis, the HOMA-IR remained in the model, with an odds ratio to develop high grade of steatosis of 7.8 (95% CI: 1.8-75) with each 1 unit of HOMA-IR adjusted by age, sex, BMI, and dietary intake. This study demonstrates that insulin resistance determined with the HOMA model is associated with a high grade of steatosis in patients with NAFLD.

Roles of adipokines in liver injury and fibrosis

Adipose tissue is now recognized as the largest endocrine organ in the body, secreting over 100 proteins termed adipokines that influence energy homeostasis, lipid physiology, inflammation, immune function and wound healing. Some of these proteins, such as TNFalpha, have important proinflammatory effects, but during hepatic injury are principally secreted at a local level within the liver. Their role in liver injury and fibrosis is beyond the scope of this review. However, circulating adipose-derived proteins such as leptin, adiponectin and resistin have important systemic effects, including the modulation of injury and fibrosis. The activities of these adipokines in the pathogenesis of liver injury and fibrosis will be the topic of this review.

The effect of infliximab on circulating levels of leptin, adiponectin and resistin in patients with inflammatory bowel disease

BACKGROUND

Tumour necrosis factor alpha is a critical mediator of inflammation-related altered metabolism in inflammatory bowel disease (IBD), possibly through its interaction with adipokines, which play an important role in IBD. Infliximab is a well established antitumour necrosis factor alpha treatment in IBD.

AIM AND METHODS

We studied serum levels of leptin, adiponectin and resistin in 20 IBD patients before and after infliximab treatment using commercially available enzyme-linked immunosorbent assays. The results were correlated with alterations of disease activity, BMI and C-reactive protein.

RESULTS

Infliximab induced clinical response or remission in 18 out of 20 treated IBD patients. Mean serum-leptin levels were 4.6+/-0.5 and 5.1+/-0.5 ng/ml (P=0.41), mean serum-adiponectin levels were 10513.9+/-1216.9 and 9653.5+/-1031.5 ng/ml (P=0.36) and mean serum-resistin levels were 26.3+/-4.1 and 13.9+/-1.4 ng/ml (P=0.004), before and after infliximab treatment, respectively. No significant correlation between the changes of BMI, C-reactive protein or the clinical indices of activity and alterations of the examined adipokines was found.

CONCLUSIONS

Serum levels of leptin and adiponectin had no significant alterations, whereas serum-resistin levels are significantly decreased after infliximab therapy in IBD patients, suggesting a possible proinflammatory status for resistin in IBD and a role as a marker of successful therapy.

Resistin down-regulates insulin receptor expression, and modulates cell viability in rodent pancreatic beta-cells

The adipokine resistin is known to induce insulin resistance in rodent tissues. Increases in adipose tissue mass are known to have a negative effect on pancreatic beta-cell function, although the mechanisms are poorly understood. This study investigated the effects of resistin on insulin secretion, insulin receptor expression and cell viability in pancreatic beta-cells. BTC-6 or BRIN-BD11 cells were treated for 24h with resistin, and insulin receptor expression, insulin secretion and cell viability were measured. Incubation with 40ng/ml resistin caused significant decreases in insulin receptor mRNA and protein expression, but did not affect insulin secretion. At low concentrations, resistin caused significant increases in cell viability. These data implicate resistin as a factor that may regulate beta-cell function/viability, and suggests a potential mechanism by which increased adiposity causes beta-cell dysfunction.

Insulin resistance in liver cirrhosis is not associated with circulating retinol-binding protein 4

OBJECTIVE

Retinol-binding protein 4 (RBP4) has been identified as a novel adipokine mediating systemic insulin resistance, and elevated serum RBP4 indicates overt or impending insulin resistance in lean, obese, and type 2 diabetic subjects. As insulin resistance is present in nearly all patients with liver cirrhosis, we evaluated RBP4 in patients with chronic liver disease (CLD).

RESEARCH DESIGN AND METHODS

Serum RBP4 was measured in 111 CLD patients. Ninety-nine age- and sex-matched healthy blood donors served as control subjects. RBP4 gene expression was also quantified in normal and cirrhotic rat liver.

RESULTS

In CLD patients, serum RBP4 was significantly reduced compared with healthy control subjects and closely correlated with the stage of liver cirrhosis. CLD patients without cirrhosis showed normal RBP4 concentrations, which correlated with serum glucose and insulin secretion and inversely correlated with insulin sensitivity. In patients with Child A-C liver cirrhosis, however, RBP4 was not correlated with glucose metabolism or other adipokines, such as adiponectin or resistin, but closely linked to the hepatic biosynthetic capacity, fibrotic changes in liver histology, or clinical complications such as portal hypertension. In an animal model of experimental cirrhosis, hepatic RBP4 gene expression decreased in cirrhotic liver.

CONCLUSIONS

RBP4 appears, unlike in obesity or type 2 diabetes, not to be a relevant systemic factor in the pathogenesis of insulin resistance in liver cirrhosis. Liver function has a tremendous impact on RBP4 levels, and future studies will need to take liver function into account when examining serum RBP4 levels.

Fatty liver and the metabolic syndrome

PURPOSE OF REVIEW

Nonalcoholic fatty liver disease and its subset nonalcoholic steatohepatitis represent the liver manifestations of insulin resistance. This review briefly summarizes advances in our understanding of the pathogenesis of nonalcoholic fatty liver disease and its prevalence, natural history and treatment.

RECENT FINDINGS

The recognition of the role the renin-angiotensin system in promoting insulin resistance is worth noting because of available drugs. Endoplasmic reticulum stress has also become a recent target of investigation because endoplasmic reticulum stress is common in obesity, diabetes and various forms of liver disease including nonalcoholic fatty liver disease. Endoplasmic reticulum stress may be responsible for activation of c-Jun kinase, a process that may cause the hepatocellular injury in nonalcoholic steatohepatitis. Progress has also been made in estimating the prevalence of nonalcoholic fatty liver disease in adults and children. Patients enrolled in the Dallas Heart Study were found to have a 33% prevalence of nonalcoholic fatty liver disease and children dying of accidental deaths in San Diego were found to have a 13% prevalence of nonalcoholic fatty liver disease. Because about 10% of people with nonalcoholic fatty liver disease are at risk for progressive fibrosis, the burden of this disease is now quite substantial.

SUMMARY

Incremental progress in understanding nonalcoholic fatty liver disease and nonalcoholic steatohepatitis promises to lead to new therapeutic options for this common disease.