Franco De Michieli

Adipokines in NASH: Postprandial lipid metabolism as a link between adiponectin and liver disease†

Circulating levels of four adipokines (adiponectin, TNF‐α, leptin, and resistin) and the postprandial lipid and adiponectin responses to an oral fat load were assessed in 25 non‐obese, non‐diabetic patients with biopsy‐proven nonalcoholic steatohepatitis (NASH) and correlated with metabolic indices and liver histology. Circulating adiponectin was lower in NASH compared with controls (5,476 ± 344 vs. 11,548 ± 836 ng/mL; P = .00001) and on multiple regression analysis correlated negatively with liver steatosis, necroinflammation (OR = 5.0; P = .009), and fibrosis (OR = 8.0; P = .003).The magnitude of postprandial lipemia was significantly higher in NASH than in controls and was related to fasting adiponectin (β = −0.78; P = .00003). Controls showed a significant increase in serum adiponectin in response to the fat load, whereas patients with NASH showed a slight decrease. Postprandial free fatty acids response correlated inversely with adiponectin response in both groups and independently predicted the severity of liver steatosis in NASH (β = 0.51; P = .031). In conclusion, hypoadiponectinemia is present before overt diabetes and obesity appear and correlates with the severity of liver histology in NASH. Impaired postprandial lipid metabolism may be an additional mechanism linking hypoadiponectinemia and NASH and posing a higher cardiovascular risk to these subjects. The mechanism(s) underlying these differences are unknown, but the type of dietary fat seems to play a role. These findings may have important pathogenetic and therapeutic implications in both liver and metabolic disease. (HEPATOLOGY 2005.)

Hypoadiponectinemia Predicts the Severity of Hepatic Fibrosis and Pancreatic Beta-Cell Dysfunction in Nondiabetic Nonobese Patients with Nonalcoholic Steatohepatitis

OBJECTIVES:The relationships between the adipokines tumor necrosis factor (TNF)-α and adiponectin and the parameters of glucose homeostasis and severity of liver disease were assessed in nonobese nondiabetic subjects with nonalcoholic steatohepatitis (NASH).METHODS:A frequently sampled intravenous glucose tolerance test, serum cytokine measurement, and 7-day alimentary record were performed in 20 biopsy-proven NASH patients and 45 age-, sex-, and BMI-matched controls (30 insulin sensitive and 15 insulin resistant).RESULTS:Patients with NASH had impaired pancreatic β-cell function compared with both insulin-sensitive (adaptation index, AI: 97.7 ± 17.7 vs 307.4 ± 24.1 min−2 mmol−1 L; p = 0.00001) and insulin-resistant (adaptation index, AI: 97.7 ± 17.7 vs 201.4 ± 41.1 min−2 mmol−1 L; p = 0.001) controls. Serum adiponectin levels were also significantly lower in the NASH group than in the two control groups and correlated with adaptation index and with the severity of hepatic steatosis, necroinflammation, and fibrosis. When NASH patients were grouped according to the severity of histological liver damage, adiponectin was the only variable discriminating patients with higher necroinflammatory grade and fibrosis score from those with milder lesions.CONCLUSIONS:β-cell secretory impairment is present in nonobese patients with NASH before glucose intolerance appears and may contribute to their increased risk for developing diabetes. Hypoadiponectinemia is a feature of NASH and may have a pathogenetic role in β-cell dysfunction and in hepatic necroinflammation and fibrosis, independently of insulin resistance, visceral fat accumulation, TNF-α axis activity, and dietary habits. Our findings provide further rationale for therapeutic approaches aimed at increasing adiponectin levels together with restoring β-cell function and insulin sensitivity.

Adiponectin gene polymorphisms modulate acute adiponectin response to dietary fat: Possible pathogenetic role in NASH

Factors underlying the independent association of nonalcoholic steatohepatitis (NASH) with increased cardiovascular risk are unknown. Adiponectin polymorphisms predict cardiometabolic risk in the general population. This association is not always mediated by low fasting adiponectin levels, adipose tissue accumulation, or traditional risk factors. Adiponectin modulates lipid metabolism and liver injury in nonalcoholic fatty liver disease (NAFLD) even in the absence of obesity, dyslipidemia, and diabetes. We hypothesized adiponectin polymorphisms may predispose to NAFLD and may increase cardiovascular risk by modulating circulating lipoprotein and adiponectin response postprandially. The prevalence of adiponectin single‐nucleotide polymorphisms (SNPs) 45GT and 276GT was assessed in 70 nonobese, nondiabetic, normolipidemic NAFLD patients and 70 healthy matched controls; the impact of the adiponectin SNPs was subsequently correlated to liver histology and postprandial adiponectin and lipoprotein responses to oral fat load in a subgroup of 30 biopsy‐proven patients with NASH and 30 controls. The 45TT and 276GT/TT genotypes were more prevalent in NAFLD patients than in controls and independently predicted the severity of liver disease in NASH. In both patients and controls, these genotypes exhibited a blunted postprandial adiponectin response and higher postprandial triglycerides (Tg), free fatty acids (FFA), oxidized LDL (oxLDL), and VLDL levels than their counterparts, despite comparable fasting adipokines, lipids, dietary habits, adiposity, and insulin resistance. They were also independently associated, together with dietary polyunsaturated fatty acid intake, with postprandial adiponectin response. IAUC adiponectin independently predicted postprandial Tg, FFA, oxLDL, and intestinal and hepatic VLDL subfraction responses in NASH. Conclusion: The at‐risk adiponectin SNPs 45TT and 276GT are significantly more prevalent in NAFLD than in the general population; they are associated with severity of liver disease, with blunted postprandial adiponectin response, and with an atherogenic postprandial lipoprotein profile in NASH independently of fasting adipokine and lipid levels. (HEPATOLOGY 2008.)

Nonalcoholic steatohepatitis versus steatosis: Adipose tissue insulin resistance and dysfunctional response to fat ingestion predict liver injury and altered glucose and lipoprotein metabolism

Nonalcoholic fatty liver disease (NAFLD) ranges from simple steatosis (SS) to nonalcoholic steatohepatitis (NASH). Though liver‐related risk seems confined to NASH, it is currently unclear whether NASH has a higher risk of cardiovascular disease (CVD) and diabetes than SS as a result of the coexistence of obesity and other cardiometabolic confounders. Adipose tissue is an emerging modulator of liver disease in NAFLD and of cardiometabolic disease in the general population. We evaluated in SS and NASH (1) glucose homeostasis and cardiovascular risk profile and (2) the effect of adipose tissue dysfunction, assessed in fasting conditions and postprandially, on liver injury, glucose and lipoprotein metabolism, and markers of early atherosclerosis. Forty nonobese, nondiabetic, normolipidemic biopsy‐proven NAFLD patients (20 with SS and 20 with NASH) and 40 healthy subjects, matched for overall/abdominal adiposity and metabolic syndrome, underwent an oral fat load test, with measurement of plasma triglyceride‐rich lipoproteins, oxidized low‐density lipoproteins, adipokines, and cytokeratin‐18 fragments, and an oral glucose tolerance test with minimal model analysis to yield glucose homeostasis parameters. Circulating endothelial adhesion molecules were measured, and adipose tissue insulin resistance (adipose IR) index and visceral adiposity index were calculated. Despite similar fasting values, compared to SS, NASH showed a more atherogenic postprandial lipoprotein profile, an altered adipokine response (i.e., higher resistin increase and an adiponectin fall), and hepatocyte apoptosis activation after fat ingestion. Adipose IR index, endothelial adhesion molecules, and hepatic insulin resistance progressively increased across NAFLD stages. NASH, but not SS, showed an impaired pancreatic β‐cell function. On multiple regression analysis, adipose IR index and postprandial adiponectin independently predicted liver histology and altered cardiometabolic parameters. Conclusion: Adipose tissue dysfunction, including a maladaptive adipokine response to fat ingestion, modulates liver injury and cardiometabolic risk in NAFLD. (HEPATOLOGY 2012;56:933–942)

Prolonged saturated fat–induced, glucose-dependent insulinotropic polypeptide elevation is associated with adipokine imbalance and liver injury in nonalcoholic steatohepatitis: dysregulated enteroadipocyte axis as a novel feature of fatty liver

BACKGROUND Genetic and acquired mechanisms underlying the association of nonalcoholic fatty liver disease (NAFLD) with diabetes are unknown. Glucose-dependent insulinotropic polypeptide (GIP) was recently linked to adipocyte metabolism and obesity-related metabolic disorders, including NAFLD, induced by an excess of saturated fatty acids (SFAs), but its role in vivo, as well as underlying mechanisms, is unknown. We hypothesized that altered GIP secretion may contribute to the pathogenesis of NAFLD. OBJECTIVE We assessed GIP response to SFA ingestion and its effect on glucose and lipid metabolism and on liver injury in patients with nonalcoholic steatohepatitis (NASH). DESIGN Thirty-two nonobese, nondiabetic patients with NASH and 32 healthy controls matched for age, body mass index, and sex underwent a 7-d dietary record, an oral-glucose-tolerance test (OGTT), and a high-fat-load test. OGTT-derived indexes of glucose homeostasis were calculated; circulating lipoproteins, total antioxidant status, GIP, adiponectin, resistin, and cytokeratin-18 fragments (markers of hepatocyte apoptosis) after a high-fat meal were assessed. All subjects were genotyped for transcription factor 7-like 2 (TCF7L2) polymorphism. RESULTS Patients with NASH exhibited a prolonged GIP elevation after fat ingestion. GIP response correlated directly with hepatic steatosis, postprandial resistin, and free fatty acid (FFA) increase and inversely with beta cell function and incretin effect. Dietary polyunsaturated:saturated fatty acid ratio and TCF7L2 polymorphism independently predicted postprandial GIP response. Cytokeratin-18 fragments increased significantly postprandially in both groups but more consistently in patients with NASH; their increase was predicted by postprandial adiponectin and FFA responses. CONCLUSIONS GIP response to SFA ingestion is prolonged in nondiabetic patients with NASH and is correlated with liver disease, an unfavorable dynamic adipokine profile, and beta cell dysfunction, which provides a rationale for GIP antagonism in these subjects.

Sterol Regulatory Element-Binding Factor 2 (SREBF-2) Predicts 7-Year NAFLD Incidence and Severity of Liver Disease and Lipoprotein and Glucose Dysmetabolism

We prospectively assessed the impact of a sterol regulatory element-binding factor-2 (SREBF-2) polymorphism on the risk of developing nonalcoholic fatty liver disease (NAFLD) and on liver histology and lipoprotein and glucose metabolism in biopsy-proven NAFLD. In a population-based study, we followed 175 nonobese, nondiabetic participants without NAFLD or metabolic syndrome at baseline, characterized for the SREBF-2 rs133291 C/T polymorphism, dietary habits, physical activity, adipokines, C-reactive protein (CRP), and endothelial adhesion molecules. A comparable cohort of NAFLD patients underwent liver biopsy, an oral glucose tolerance test with minimal model analysis to yield glucose homeostasis parameters, and an oral fat tolerance test with measurement of plasma lipoproteins, adipokines, and cytokeratin-18 fragments. After 7 years, 27% of subjects developed NAFLD and 5% developed diabetes. SREBF-2 predicted incident NAFLD and diabetes and CRP and endothelial adhesion molecule changes. In biopsy-proven NAFLD patients, SREBF-2 predicted nonalcoholic steatohepatitis (odds ratio 2.92 [95% CI 2.08–4.18], P = 0.002) and the severity of tissue insulin resistance, β-cell dysfunction, and oral fat intolerance (characterized by higher postprandial lipemia, cholesterol enrichment of triglyceride-rich lipoproteins and oxidized LDLs, HDL cholesterol fall, adipokine imbalance, and postprandial apoptosis activation). An SREBF-2 polymorphism predisposes individuals to NAFLD and associated cardiometabolic abnormalities and affects liver histology and glucose and lipid metabolism in biopsy-proven NAFLD.

Comparison of the metabolic effects of mixed meal and standard oral glucose tolerance test on glucose, insulin and C-peptide response in healthy, impaired glucose tolerance, mild and severe non-insulin-dependent diabetic subjects

Dietary constituents other than glucose can influence insulin secretion in non-insulin-dependent diabetes mellitus and administration of a standard mixed meal has been proposed as a more physiological test in regard to human diet for evaluating the patient both at the time of diagnosis and during follow-up. This study was carried out to compare the effects of a standard meal and the oral glucose tolerance test on glucose, insulin and C-peptide plasma levels in four groups of subjects: healthy controls, subjects with impaired glucose tolerance, patients with mild non-insulin-dependent diabetes, and non-insulin-dependent diabetic patients with secondary failure to oral agents. Plasma glucose values were significantly higher after the oral glucose tolerance test than after the mixed meal in all four groups of subjects. Plasma insulin and C-peptide values were similar during the two tests in all groups of subjects except in non-insulin-dependent diabetics with secondary failure (flattened curves). Insulin and C-peptide responses per unit rise in blood glucose were significantly higher after the oral glucose tolerance test than after the mixed meal both in mild non-insulin-dependent diabetics (P<0.05 andP<0.05) and in non-insulin-dependent diabetics in secondary failure (P<0.01 andP<0.05). There was significant correlation between oral glucose tolerance test and mixed meal glucose incremental areas (r=0.511,P<0.001). The diagnostic relevance of the test was evaluated by comparing the 120 min plasma glucose levels following mixed meal and oral glucose tolerance test: there was a significant correlation between the values in the two tests (r=0.956,P<0.001); the differences among the four groups were statistically significant and there was a partial overlap between healthy controls and impaired glucose tolerance patients: 93±3 versus 111±7 mg/dl for controls; 107±3 versus 161±5 mg/dl for impaired glucose tolerance patients; 204±11 versus 284±12 mg/dl for mild non-insulin-dependent diabetics; 309±9 versus 440±17 mg/dl for NID diabetics in secondary failure. The sensitivity of the test was 73% and specificity 100%. The mixed meal is proposed for clinical practice as a more physiological test than the standard oral glucose tolerance test for further characterization and longitudinal evaluation of patients with impaired glucose tolerance or non-insulin-dependent diabetes mellitus.

Impact of sterol regulatory element-binding factor-1c polymorphism on incidence of nonalcoholic fatty liver disease and on the severity of liver disease and of glucose and lipid dysmetabolism

BACKGROUND Genetic factors that predispose individuals to nonalcoholic fatty liver disease (NAFLD) and associated diabetes and cardiovascular disease are unclear. The transcription factor sterol regulatory element-binding protein-1c (SREBP-1c) modulates lipogenesis and insulin sensitivity and was experimentally connected to NAFLD. OBJECTIVE We assessed the impact of a common SREBF-1c polymorphism on the incidence and severity of NAFLD and on associated glucose and lipoprotein dysmetabolism. DESIGN We followed up 212 randomly selected, nonobese, nondiabetic, insulin-sensitive participants in a population-based study without NAFLD or metabolic syndrome at baseline who were characterized for the common SREBF-1c gene rs11868035 A/G polymorphism, dietary habits, physical activity, adipokine profile, C-reactive protein (CRP), and circulating markers of endothelial dysfunction. A comparable cohort of NAFLD patients underwent a liver biopsy, an oral-glucose-tolerance test with minimal model analysis of glucose homeostasis variables, and an oral-fat-tolerance test with measurement of plasma lipoproteins, adipokines, and cytokeratin-18 fragments. RESULTS SREBF-1c predicted the 7-y incidence of NAFLD (OR: 1.71; 95% CI: 1.15, 2.53) and diabetes and the 7-y elevation in CRP and endothelial dysfunction markers. In biopsy-proven NAFLD patients, the SREBF-1c A allele conferred increased risk of severe steatosis and nonalcoholic steatohepatitis; more-severe hepatic, muscle, and adipose tissue insulin resistance; and pancreatic β cell dysfunction. SREBF-1c A allele carriers also had an impaired oral fat tolerance with a postprandial accumulation of large triglyceride-rich lipoproteins and oxidized LDLs, lower HDL cholesterol and adiponectin concentrations, and cytokeratin-18 fragment elevation. CONCLUSION SREBF-1c polymorphism is associated with increased risk of developing NAFLD with more severe liver histology and derangement in glucose and lipoprotein metabolism, which contribute to the presentation and natural history of NAFLD.

Fatty Liver and Chronic Kidney Disease: Novel Mechanistic Insights and Therapeutic Opportunities.

Chronic kidney disease (CKD) is a risk factor for end-stage renal disease (ESRD) and cardiovascular disease (CVD). ESRD or CVD develop in a substantial proportion of patients with CKD receiving standard-of-care therapy, and mortality in CKD remains unchanged. These data suggest that key pathogenetic mechanisms underlying CKD progression go unaffected by current treatments. Growing evidence suggests that nonalcoholic fatty liver disease (NAFLD) and CKD share common pathogenetic mechanisms and potential therapeutic targets. Common nutritional conditions predisposing to both NAFLD and CKD include excessive fructose intake and vitamin D deficiency. Modulation of nuclear transcription factors regulating key pathways of lipid metabolism, inflammation, and fibrosis, including peroxisome proliferator–activated receptors and farnesoid X receptor, is advancing to stage III clinical development. The relevance of epigenetic regulation in the pathogenesis of NAFLD and CKD is also emerging, and modulation of microRNA21 is a promising therapeutic target. Although single antioxidant supplementation has yielded variable results, modulation of key effectors of redox regulation and molecular sensors of intracellular energy, nutrient, or oxygen status show promising preclinical results. Other emerging therapeutic approaches target key mediators of inflammation, such as chemokines; fibrogenesis, such as galectin-3; or gut dysfunction through gut microbiota manipulation and incretin-based therapies. Furthermore, NAFLD per se affects CKD through lipoprotein metabolism and hepatokine secretion, and conversely, targeting the renal tubule by sodium–glucose cotransporter 2 inhibitors can improve both CKD and NAFLD. Implications for the treatment of NAFLD and CKD are discussed in light of this new therapeutic armamentarium.

Association of liver disease with postprandial large intestinal triglyceride-rich lipoprotein accumulation and pro/antioxidant imbalance in normolipidemic non-alcoholic steatohepatitis

Background. Dietary fat excess and antioxidant deficiency, altered lipid metabolism, and increased lipoperoxidation have been associated with non-alcoholic steatohepatitis (NASH), but the relative importance of each of these factors is unclear. Aims. To assess acute intestinal and hepatic very-low-density lipoprotein (VLDL) subfraction metabolism, lipid peroxidation, and pro/antioxidant imbalance after a fat load in NASH. Methods. Dietary habits, circulating adipokines, fasting and postprandial lipids, intestinal and hepatic VLDL, oxidized low-density lipoproteins (oxLDL), and total antioxidant status (TAS) were correlated to postprandial liver enzymes and to liver histology in 28 non-obese non-diabetic normolipidemic patients with NASH and 28 healthy controls. Results. Despite similar fasting profiles, NASH had more pronounced intestinal and hepatic VLDL1 accumulation, LDL lipid peroxidation and TAS fall postprandially. Postprandial intestinal VLDL1 independently predicted oxLDL and TAS responses in NASH. In NASH, hepatic steatosis was independently associated with postprandial intestinal VLDL1 and TAS; necroinflammation with postprandial serum gamma-glutamyltransferase, oxLDL and TAS responses; and fibrosis with adiponectin and postprandial TAS and oxLDL responses. Conclusions. Postprandial intestinal VLDL1 accumulation is associated with a pro-oxidant imbalance in normolipidemic non-diabetic NASH, and both correlate with the severity of liver disease. Modulating postprandial lipoprotein metabolism may be beneficial in NASH, even if normolipidemic.