Visceral fat: a key mediator of steatohepatitis in metabolic liver disease

Adipose tissue inflammation and liver pathology in human obesity

The increase in circulating inflammatory factors found in obese subjects and the recent discovery of macrophage infiltration in white adipose tissue (WAT) have opened up new fields of investigation, allowing a reevaluation of the pathophysiology of human obesity. The so-called 'low-grade' inflammatory state, which characterizes this complex disease, is revealed by the moderate, but chronic, systemic rise of a growing panel of molecules with proinflammatory functions. The qualitative and quantitative alterations in the production of these molecules (free fatty acids, cytokines) by the different WAT cell types, particularly in the omental fat depot, are considered new factors with the potential to modify local WAT biology and to contribute, via the portal system, to liver alteration. The aim of this review is to present the most upto-date knowledge regarding the relationships between inflammatory processes in WAT and non-alcoholic liver disease in human obesity.

Young adult obese subjects with and without insulin resistance: what is the role of chronic inflammation and how to weigh it non-invasively?

BACKGROUND

Obesity is a leading risk factor for metabolic syndrome whose further expression is non-alcoholic fatty liver disease. Metabolic syndrome is associated with a proinflammatory state that contributes to insulin resistance. Finally, a "metabolically benign obesity" that is not accompanied by insulin resistance has recently been postulated to exist.

AIM

To find whether any inflammation markers were independently associated with the presence of insulin resistance, evaluating specific anthropometric, ultrasonographic and laboratory parameters in a population of young adult obese subjects.

METHODS

Of forty two young individuals, divided into two groups (with or without insulin resistance), were studied serum C-reactive protein and fibrinogen as indexes of chronic pro-inflammatory status. Body mass index, waist circumference and metabolic syndrome presence were assessed as part of the metabolic evaluation. Ultrasonography weighted visceral and subcutaneous abdominal fat thickness, spleen size as longitudinal diameter and liver hyperechogenicity.

RESULTS AND DISCUSSION

Serum C-reactive protein and fibrinogen as well as spleen longitudinal diameter were significantly increased in the obese young with insulin resistance compared to non-insulin resistance group. Insulin resistance was significantly associated with hepatic steatosis score at sonography (r = 0.33, P = 0.03), spleen longitudinal diameter (r = 0.35, P = 0.02) and C-reactive protein (r = 0.38, P = 0.01), but not with body mass index, visceral or subcutaneous abdominal adipose tissue, waist circumference and fibrinogen (P = 0.18, 0.46, 0.33, 0.37 and 0.4, respectively). Steatosis score at sonography was well associated with spleen volume (rho = 0.40, P = 0.01) and C-reactive protein levels (rho = 0.49, P = 0.002). Metabolic syndrome was much more frequent in obese patients with insulin resistance. These findings show that in young adults the only abdominal adiposity without insulin resistance, plays a scarce role in determining hepatic steatosis as well as metabolic syndrome.

CONCLUSION

Increases in spleen size and CRP levels represent a reliable tool in diagnosing insulin resistance.

Current status of therapy in nonalcoholic Fatty liver disease

The obesity epidemic has now spread worldwide. With increase in weight, there is an increase in dysregulated energy metabolism ultimately leading to dysfunction of multiple organ systems recognized as the metabolic syndrome. Nonalcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease worldwide, and is thought to be the hepatic manifestation of metabolic syndrome. It is a nondiscriminating disease affecting both children and adults and no socioeconomic class is spared. There is a well-defined increase in both liver-related and all-cause mortality. Current projections foresee a continued worsening in prevalence, especially with the increased rate of childhood obesity. Prevention would be the ultimate goal, but with continued trends in obesity, therapeutic options are needed to manage this chronic liver disease and prevent its complications of cirrhosis and even hepatocellular carcinoma. Therapies will need to be affordable, tolerable, and safe to be useful on such a large scale. This article will discuss some of the basic understanding of NAFLD, as well as review the currently tested therapies, some novel therapies, and potential future therapeutic options.

The trials and tribulations of the treatment of nonalcoholic fatty-liver disease

PURPOSE OF REVIEW

To review published clinical trials, with a focus on those of randomized design, of the management of nonalcoholic fatty-liver disease (NAFLD), an increasing complication of the obesity epidemic.

RECENT FINDINGS

There is increasing recognition that cardiovascular risk issues are associated with NAFLD. Clinical trials of management of NAFLD have focused mainly on hepatic complications. The weight of data point to greatest biochemical and histological benefit with weight-loss measures and thiazolidinediones, but further trials are needed to characterize the benefits and risks of the latter agents. There is currently insufficient trial data to recommend other strategies for treating NAFLD. There is an emerging need for early multiple factor risk intervention, emphasizing cardiometabolic risk and weight management, in addition to minimizing risk of hepatic complications.

SUMMARY

Given the strong association of NAFLD with the metabolic syndrome, early recognition, assessment and management of NAFLD is essential. The management emphasizes weight reduction and attention to cardiometabolic risk factors, similar to recommendations for management of the metabolic syndrome. Future research, guided by increasing knowledge of the pathogenetic factors driving the condition, should clarify the role of other therapies for reducing hepatic and cardiovascular morbidity associated with NAFLD.

Effect of dietary monosodium glutamate on trans fat-induced nonalcoholic fatty liver disease

The effects of dietary monosodium glutamate (MSG) on trans-fatty acid (TFA)-induced nonalcoholic fatty liver disease (NAFLD) are addressed in an animal model. We used Affymetrix microarray analysis to investigate hepatic gene expression and the contribution of visceral white adipose tissue (WAT) to diet-induced NAFLD. Trans-fat feeding increased serum leptin, FFA, HDL-cholesterol (HDL-C), and total cholesterol (T-CHOL) levels, while robustly elevating the expression of genes involved in hepatic lipogenesis, including the transcription factor sterol-regulatory element binding protein 1c. Histological examination revealed hepatic macrosteatosis in TFA-fed animals. Conversely, dietary MSG at doses similar to human average daily intake caused hepatic microsteatosis and the expression of beta-oxidative genes. Serum triglyceride, FFA, and insulin levels were elevated in MSG-treated animals. The abdominal cavities of TFA- or MSG-treated animals had increased WAT deposition compared with controls. Microarray analysis of WAT gene expression revealed increased lipid biosynthetic gene expression, together with a 50% decrease in the key transcription factor Ppargc1a. A combination of TFA+MSG resulted in the highest levels of serum HDL-C, T-CHOL, and leptin. Microarray analysis of TFA+MSG-treated livers showed elevated expression of markers of hepatic inflammation, lipid storage, cell damage, and cell cycle impairment. TFA+MSG mice also had a high degree of WAT deposition and lipogenic gene expression. Levels of Ppargc1a were further reduced to 25% by TFA+MSG treatment. MSG exacerbates TFA-induced NAFLD.

Disease-specific mechanisms of fibrosis: hepatitis C virus and nonalcoholic steatohepatitis

Our mechanistic understanding of liver fibrosis has increased dramatically in recent years for all liver diseases and for hepatitis C and nonalcoholic steatohepatitis (NASH) in particular. Hepatitis C causes liver injury and fibrosis through direct cytopathic means, direct and indirect interactions with hepatic stellate cells, and activation of the immune system. Steatosis and insulin resistance, which are intrinsic deficits in NASH, are also of great importance in hepatitis C and may be induced by viral or host metabolic factors. For NASH, the key mediators of damage include oxidative stress, fat compartmentalization, visceral fat, apoptosis, and adipokine derangement. This article explores in depth the disease-specific mechanisms of fibrosis in hepatitis C and NASH, with a focus on recent developments.