Understanding the relationship between PNPLA3, NAFLD and insulin resistance: do ethnic differences bring more questions or more answers?

Sarcopenia in Liver Disease: Current Evidence and Issues to Be sResolved

Sarcopenia is a common clinical symptom in aging and patients with wasting diseases, characterized by a decreased skeletal muscle mass. As a consequence of lifestyle change, the nonalcoholic fatty liver disease (NAFLD) presents a rising trend. In the past three decades, increasing evidence has proved that sarcopenia is related to NAFLD. In this chapter, we will summarize the emerging evidence of the predictive role of sarcopenia in NAFLD and review the diagnosis value, feasible mechanism, and therapy strategies of sarcopenia in NAFLD. Sarcopenia is a potential risk factor for NAFLD, and targeting sarcopenia can benefit NAFLD to some extent.

Composite prognostic models across the non-alcoholic fatty liver disease spectrum: Clinical application in developing countries

Heterogeneity in clinical presentation, histological severity, prognosis and therapeutic outcomes characteristic of non-alcoholic fatty liver disease (NAFLD) necessitates the development of scientifically sound classification schemes to assist clinicians in stratifying patients into meaningful prognostic subgroups. The need for replacement of invasive liver biopsies as the standard method whereby NAFLD is diagnosed, graded and staged with biomarkers of histological severity injury led to the development of composite prognostic models as potentially viable surrogate alternatives. In the present article, we review existing scoring systems used to (1) confirm the presence of undiagnosed hepatosteatosis; (2) distinguish between simple steatosis and NASH; and (3) predict advanced hepatic fibrosis, with particular emphasis on the role of NAFLD as an independent cardio-metabolic risk factor. In addition, the incorporation of functional genomic markers and application of emerging imaging technologies are discussed as a means to improve the diagnostic accuracy and predictive performance of promising composite models found to be most appropriate for widespread clinical adoption.

Non-alcoholic fatty liver disease, metabolic syndrome and patatin-like phospholipase domain-containing protein3 gene variants

BACKGROUND & AIMS

Non-alcoholic fatty liver disease was traditionally interpreted as a condition which may progress to liver-related complications. However, the increased mortality is primarily a result of cardiovascular diseases. It has been suggested that fatty liver can be considered as the hepatic consequence of the metabolic syndrome. The aim was to describe the different clinical presentations of non-alcoholic fatty liver disease on the basis of the patatin-like phospholipase domain-containing protein3 (PNPLA3) rs738409 gene variant.

METHODS

Fatty liver was defined by ultrasonographic Hamaguchi's criteria in 211 consecutive subjects with non-alcoholic fatty liver disease. The rs738409 polymorphism was determined by TaqMan assays. Metabolic syndrome was defined according to ATPIII modified criteria.

RESULTS

Prevalence of PNPLA3-148II, PNPLA3-148IM, and PNPLA3-148MM genotypes was 45.0%, 40.7%, and 14.3% respectively. Prevalence of metabolic syndrome progressively increased with the severity of liver steatosis (from 52.5% to 65.2%, and 82.3% respectively, p<0.01). The PNPLA3-148MM group had significantly lower mean serum triglycerides (p<0.001), Framingham cardiovascular risk score (p<0.01) and lower prevalence of metabolic syndrome (p<0.05) and its components. Age and HOMA-IR were positive independent predictors of metabolic syndrome, while a negative independent association was found between metabolic syndrome and the homozygotes PNPLA3 I148M variant.

CONCLUSIONS

We suggest a lower prevalence of MetS and reduced cardiovascular risk in NAFLD patients with PNPLA3MM genotype.

Role of patatin-like phospholipase domain-containing 3 on lipid-induced hepatic steatosis and insulin resistance in rats

Genome-wide array studies have associated the patatin-like phospholipase domain-containing 3 (PNPLA3) gene polymorphisms with hepatic steatosis. However, it is unclear whether PNPLA3 functions as a lipase or a lipogenic enzyme and whether PNPLA3 is involved in the pathogenesis of hepatic insulin resistance. To address these questions we treated high-fat-fed rats with specific antisense oligonucleotides to decrease hepatic and adipose pnpla3 expression. Reducing pnpla3 expression prevented hepatic steatosis, which could be attributed to decreased fatty acid esterification measured by the incorporation of [U-(13) C]-palmitate into hepatic triglyceride. While the precursors for phosphatidic acid (PA) (long-chain fatty acyl-CoAs and lysophosphatidic acid [LPA]) were not decreased, we did observe an ∼20% reduction in the hepatic PA content, ∼35% reduction in the PA/LPA ratio, and ∼60%-70% reduction in transacylation activity at the level of acyl-CoA:1-acylglycerol-sn-3-phosphate acyltransferase. These changes were associated with an ∼50% reduction in hepatic diacylglycerol (DAG) content, an ∼80% reduction in hepatic protein kinase Cε activation, and increased hepatic insulin sensitivity, as reflected by a 2-fold greater suppression of endogenous glucose production during the hyperinsulinemic-euglycemic clamp. Finally, in humans, hepatic PNPLA3 messenger RNA (mRNA) expression was strongly correlated with hepatic triglyceride and DAG content, supporting a potential lipogenic role of PNPLA3 in humans.

CONCLUSION

PNPLA3 may function primarily in a lipogenic capacity and inhibition of PNPLA3 may be a novel therapeutic approach for treatment of nonalcoholic fatty liver disease-associated hepatic insulin resistance.