My name is Henning Grønbæk. I'm a professor and consultant, in hepatology at Aarhus University Hospital in Denmark. I have worked in the field of non-alcoholic fatty liver disease for more than 15 years describing the first patients with NASH in Denmark back in 2003 and I have had a key interest in the pathogenesis, biomarkers, and treatments and have performed both experimental and clinical NASH studies. As previously taught in this course, NAFLD comprise a spectrum from simple steatosis, which may progress to steatohepatisis (NASH) with inflammation, ballooning of hepatocytes, fibrosis, and subsequent risk of progression to liver cirrhosis and also liver cancer, hepatocellular carcinoma. In this presentation, I will take you through the current concept of the pathophysiology of simple steatosis to inflammation, fibrosis, and cirrhosis. Professor Cristae from Newcastle, England proposed the two-hit hypothesis back in 1998. The first hit was characterized by the accumulation of lipids in the liver associated with simple steatosis. The second hit was caused by oxidative stress, lipid peroxidation, and increases in tumor necrosis factor production causing inflammation. He also proposed that other mechanisms were involved as significant risk factors were associated with steatosis. These risk factors included obesity, the metabolic syndrome, age, and genetics, and all contributing to the progression from simple steatosis to NASH with inflammation, fibrosis, and cirrhosis. In the early days, patients classified as cryptogenic cirrhosis, most likely had NASH cirrhosis. Finally, there is an increased risk of ACC development. However, this simple two-hit model has been challenged, and in 2010, professor Tilg and co-workers proposed a multiple-hit hypothesis comprising both developments of simple steatosis and its transitions from simple steatosis to NASH. In the multiple-hit hypothesis, a close interaction with adipose tissue is described with increased adipose tissue, excretion of free fatty acids, increased TNF, and IL6 production along with reduced levels of adiponectin and increased leptin levels. These mediators, through their receptors, induced lipogenesis with increased triglyceride production and hepatic steatosis. An increased intake of calories, especially for carbohydrates but also fat, further contributes to fat accumulation. However, the microbiome and gut derived metabolites, including gut hormones seem to be involved in the pathogenesis as well. During the last decade, further information derived from both experimental and clinical studies have provided further knowledge in the complex pathophysiology and pathogenesis or NAFLD to NASH progression. I will try to take you through these different steps as a deep understanding of the pathogenesis which may provide new knowledge for the discovery of biomarkers, as well as treatment targets and potential new drugs. For the development of steatosis, going from a healthy liver to the accumulation of fat in simple steatosis, a number of different hits are of importance. As mentioned, increased intake of calories, especially sucrose and also dietary fat is important along with adipose tissue dysfunction. In the adipose tissue, there is an increased lipolysis with the release of free fatty acids to enter the circulation and the liver. In the liver we see increased liver de novo lipogenesis with lipid accumulation and a decrease in VLDL secretion accompanied by increased hepatic insulin resistance. In addition, that seem to be important contributions in the pathogenesis by genetics and also dysbiosis of the microbiome, including toxic metabolites. The pathogenesis is presented more simplified in this figure of adipose tissue, development of liver steatosis and then the progression to active steatohepatitis with inflammation. In this context, I would like to draw your attention to the important role of the macrophages or Kupffer cells as part of the inflammatory process, stimulating stellate cells that are involved in fibrosis formation. But first, I will take you to the association between fatty liver disease and the metabolic syndrome. Professor Julia McCosine from Bolonia was the first to describe the association between NAFLD and metabolic syndrome back in 1998. He investigated 46 patients with NAFLD characterized by elevated levels of liver enzymes, and steatosis determined by ultrasound and compared these to 92 healthy subjects. He showed that NAFLD patients had higher blood glucose and insulin levels and increased insulin resistance as determined by the HOMA index. As shown here, the odds ratio for fasting and glucose-induced hyperinsulinemia and triglyceride levels were around three and for insulin resistance, the odds ratio was 15. He concluded that NAFLD is associated with insulin resistance and hyperinsulinemia and even in lean subjects. He continued his research in this area and performed a hyperinsulinemic clamp study to investigate insulin resistance in patients with NAFLD, type 2 diabetes and healthy controls. He observed type 2 diabetic patients and NAFLD patients had the same metabolic aberrations regarding glucose disposal during the clamp and elevated free fatty acid levels before and after the clamp and significantly different from the healthy subjects. He concluded that NAFLD patients are characterized by the same clinical and biochemical abnormalities as patients with type 2 diabetes. And he suggested that NAFLD should be considered an additional feature of the metabolic syndrome. As previously mentioned, genes seem to play a significant role on NAFLD pathogenesis and we start to have some data to support this. During recent years, the number of gene variants have been associated with both fat accumulation and also progression to steatohepatitis and fibrosis. The best described and investigated gene variant is the PNPLA3 gene, which is associated with both steatosis, steatohepatitis, and fibrosis. Numerous variants are also described on genes encoding the transmembrane 6 superfamily 2 and lately also irisin encoding gene. Both are linked to hepatic steatosis. A normal area of interest is the epigenetic changes the methylations and influenced by the environment, for example, specific dietary consumptions, and so on. But much more work is needed in this area. [ MUSIC ].
