In our study on rats exposed to heated and unheated palm oil for 90 days, we found that consumption of unheated palm oil and HPO can cause damage to liver tissue. The criteria for this damage were the accumulation of fat in hepatocytes, a higher degree of heterochromatin and dark nuclei destruction of nucleoli, non-alcoholic steatohepatitis (NASH), cholestasis, and ductular reaction.
Micro-and macrovesicular steatosis are the two types of liver steatosis. In the macrovesicular type, a large or small drop of fat is placed in the cytoplasm of the liver cells and pushes the nucleus to the side. In the microvesicular type, small fat droplets accumulate in the cytoplasm, and the nucleus remains central. In NAFLD, steatosis can be of both types and is usually seen in the acinar zone 3, but in severe steatosis, it can be seen in other areas as well. NASH is a symptom of severe hepatic steatosis[17].
Symptoms of NASH include hepatocyte injury (ballooning and the presence of Mallory bodies), lobular inflammation typically localized in acinar zone 3 (polymorph neutrophils), and fibrosis. Having more than 5% hepatic steatosis, liver cell damage and inflammation is a sign of NAFLD disease[18]. In the present study, the signs of liver damage mentioned above were observed in unheated palm oil and were more intense in heated palm oil. Balloon liver cells were swollen and their cytoplasm became small and pale. [19]. These cells usually have Mallory bodies, which are associated with inflammation and the possibility of necrosis[20]. Mallory Denk bodies are observed in response to cellular stress in NASH disease[21]. Symptoms of mild inflammation include infiltration of neutrophils and eosinophils inside the liver lobule and around damaged cells. Scattered microgranulomas, Kupffer cells, lipogranulomas, and fat droplets are also seen in NASH[22]. The results of a study by Afolabi et al. showed that palm oil causes histopathological abnormalities such as inflammation in the liver of fish, which is consistent with the results of our study[23]. While Kamsiah Jaarin and colleagues stated that fresh palm oil does not harm heart tissue, heated palm oil causes necrosis of heart tissue[24]. The results of another study that contradicted the results of the present study showed that palm oil significantly reduced pro-inflammatory cytokines. and anti-apoptotic proteins in the liver of rats fed a hypercholesterolemic diet showed that this conflict may be due to hypercholesterolemia in rats or the doses of palm oil consumed[25].
Fibrosis around the sinuses and hepatocytes is caused by the deposition of collagen and other matrix fibers in fatty liver diseases. The formation of fibrosis in NASH is due to the activation of liver stellate cells, fibroblasts, Kupffer cells, and inflammatory cells migrating to the liver lobules[26]. Recent research has emphasized the importance of NAFLD diagnosis, the possibility of its progression to liver fibrosis, and the issue of public health, requiring doctors to be more sensitive to this disease[27]. Ductular reaction (DR) occurs in NAFLD, biliary diseases, and in the port area to compensate for the decreased function of the bile ducts[28]. DR that occurs in the liver of NASH patients has a direct relationship with the severity of inflammation and fibrosis, which shows the importance of ductal reactions in the progression of NASH [29],[30]. Sanhong Yu et al showed that the histological characteristics of the bile ducts can be useful in the diagnosis of lobular inflammation, cholestasis and ductal reaction[31]. Bile acids are synthesized from cholesterol in hepatocytes[32]. Cholestasis is the retention or reduction of bile secretion due to hepatocyte dysfunction or obstruction of the excretion path[33]. Clinical manifestations of cholestatic and fatty liver are the result of a complex interaction between hepatocytes and cholangiocytes, stellate cells, and pro-inflammatory cells, in which lipotoxicity of fatty acids causes cellular stress[34][35]. Histological studies have shown the presence of bile in the canaliculi and symptoms, such as closure of the bile ducts, expansion of the port area, and proliferation of the bile ducts[36].
The National Institute of Diabetes, Digestive and Kidney Diseases(NIDDK), which supports clinical studies of non-alcoholic steatohepatitis, has developed a histological scoring system based on the presence of histological lesions, including zone 3 macrosteatosis, ballooning of hepatocytes, and lobular inflammation, which is necessary for the diagnosis of non-alcoholic steatohepatitis. Lifestyle and overweight can cause NAFLD [37]. The progression of the disease leads to fibrosis and cirrhosis of the liver, and patients are exposed to liver damage compensation and death. This disease does not have a definite cure, and currently, the best treatment options include diet changes, physical activity, and weight loss [38].