Association between non-alcoholic fatty liver disease and subclinical coronary atherosclerosis: An observational cohort study

Is There an Association of Vascular Disease and Atherosclerosis in Children and Adolescents With Obesity and Non-alcoholic Fatty Liver Disease?

Carotid intima media thickness (cIMT) and brachial flow-mediated dilation (FMD) evaluated by ultrasound are non-invasive markers of atherosclerosis. Increased cIMT in adults has been correlated to early vascular damage. Several studies show similar correlations of elevated cIMT in children with obesity, hyperlipidemia, and metabolic syndrome. Additionally, several articles have correlated non-alcoholic fatty liver disease (NAFLD) with elevated cIMT, indicating early atherosclerosis. It is alarming that these vascular changes may be seen in children as young as 10 years of age. Children with NAFLD may also have an increased pulse wave velocity that correlates to increased arterial stiffness and increased left ventricular dimension, mass, and diastolic dysfunction. These articles are persuasive, indicating a correlation of Pediatric NAFLD and early vascular disease. However, study limitations include the use of elevated alanine aminotransferase (ALT) and echogenic changes on ultrasound that may have low accuracy to identify NAFLD. Ultrasound has low sensitivities and specificities for detection of NAFLD and therefore is not recommended for diagnosis. In comparison, studies that used liver biopsy or proton magnetic resonance spectroscopy to identify NAFLD did not find a correlation with elevated cIMT or reduction in FMD. Due to these conflicting findings, more studies looking at cIMT and FMD changes in children with NAFLD are needed with more accurate diagnostic methods for steatosis to identify if there truly is a correlation of increased liver steatosis to early atherosclerosis.

A low-protein diet eliminates the circadian rhythm of serum insulin and hepatic lipid metabolism in mice

Insulin is a key molecule that synchronizes peripheral clocks, such as that in the liver. Although we previously reported that mice fed a low-protein diet showed altered expression of lipid-related genes in the liver and induction of hepatic steatosis, it is unknown whether a low-protein diet impairs insulin secretion and modifies the hepatic circadian rhythm. Therefore, we investigated the effects of the intake of a low-protein diet on the circadian rhythm of insulin secretion and hepatic lipid metabolism in mice. Under 12-h light/12-h dark cycle, mice fed a low-protein diet for 7 days displayed enhanced food intake at the end of the light phase, although central and peripheral PER2 expression rhythm was maintained. Serum insulin levels in mice fed a low-protein diet remained low during the day, and the insulin secretion in OGTT was also markedly lower than in normal mice. In mice fed low-protein diet, hepatic TG accumulation was observed during the nighttime, with relatively high levels of ACC1 mRNA and total ACC proteins. Although there were no differences in the activity rhythm of hepatic mTOR between mice fed a normal or low-protein diet, hepatic IRS-2 expression in mice fed a low-protein diet remained low during the day, with no increase at the beginning of the light period. These results suggested that the low-protein diet eliminated the circadian rhythm of serum insulin and hepatic lipid metabolism in mice, providing insights into our understanding of the mechanisms of hepatic disorders of lipid metabolism.

Non-parenchymal hepatic cell lipotoxicity and the coordinated progression of non-alcoholic fatty liver disease and atherosclerosis

PURPOSE OF REVIEW

Non-alcoholic fatty liver disease (NAFLD) appears to be independently associated with the development of atherosclerosis. The biological mechanisms underlying this association are complex, and likely involve liver-resident cell types other than hepatocytes. Thus, we review recent evidence that non-parenchymal hepatic cell responses to lipid excess contribute to the pathogenesis of both NAFLD and atherosclerosis.

RECENT FINDINGS

Significant independent associations between NAFLD and atherosclerosis have been identified through cross-sectional studies and meta-analyses. Mechanistic studies in cell cultures and in rodent models suggest that liver-resident macrophages, activated hepatic stellate cells (HSC) and liver sinusoidal endothelial cells (LSEC) mount lipotoxic responses under NAFLD conditions which can contribute to the progression of both NAFLD and atherosclerosis.

SUMMARY

Non-parenchymal hepatic cell types exhibit some similarity in their responses to lipid excess, and in their pathogenic mechanisms, which likely contribute to the coordinated progression of NAFLD and atherosclerosis. In response to lipotoxic conditions, macrophages, Kupffer cells and HSC initiate robust inflammatory responses, whereas LSEC generate excess reactive oxygen species (ROS). The extent to which inflammatory cytokines and ROS produced by non-parenchymal cells contribute to the progression of both NAFLD and atherosclerosis warrants further investigation.