Introduction
Nonalcoholic fatty liver disease (NAFLD) refers to a wide range of diseases, from hepatic steatosis to cirrhosis, without involving excessive alcohol consumption, the use of steatogenic medications, or genetic disorders.
According to the recommendations for diagnosing and treating nonalcoholic fatty liver (NAFL) published by the American Association for the Study of Liver Diseases (AASLD), it is characterized by hepatic steatosis, inflammation, and ballooning degeneration in the hepatocytes.
Non-alcoholic steatohepatitis (NASH) is characterized by diffuse fatty infiltration in the liver, inflammation in the hepatocytes, ballooning hepatocyte injury, and hepatocellular carcinoma with the presence or absence of fibrosis. NASH can result in hepatocellular carcinoma (HCC), cirrhosis, and liver failure, while NAFL is benign and has a low risk of progressing to these conditions.
What Is Non-alcoholic Fatty Liver Disease (NAFLD)?
Non-alcoholic fatty liver disease (NAFLD) refers to a group of disorders in which excess fat accumulates in the liver of people who consume little to no alcohol. The most common type of NAFLD is fatty liver. Fat builds up in the liver cells of people with fatty livers. However, having fat in the liver is abnormal but does not harm the liver.
Nonalcoholic steatohepatitis (NASH), a more dangerous disorder, may be present in a few percent of individuals with NAFLD. Fat accumulation in NASH is linked to varying degrees of scarring and inflammation of the liver cells. NASH is a potentially dangerous illness that raises the risk of cirrhosis and severe liver damage.
Cirrhosis develops when the liver experiences significant injury with the replacement of liver cells by scar tissue, making the liver unable to function properly. Cirrhosis patients may eventually need a liver transplant, which is a surgical procedure in which the damaged liver is removed and replaced with a new liver.
What Are Carotenoids?
Carotenoids are fat-soluble pigments that provide yellow, red, and orange pigments to fruits and vegetables. Although there are over 600 carotenoids, approximately 40 are taken in human diets. Blood and tissues have been found to contain fourteen of these carotenoids. Since they can only be produced by plants and microbes, fruits and vegetables are their main sources.
The most researched carotenoids are lutein, zeaxanthin, β-cryptoxanthin, α-carotene, lycopene, and β-carotene. Carotenoids can be further classified as non-provitamin A carotenoids (lutein, lycopene, and zeaxanthin) and provitamin A carotenoids (β-cryptoxanthin, β-carotene, and α-carotene).
These chemicals play a significant role in human physiology because of their exceptional biological activities, including their effects on inflammation and oxidative stress. Carotenoids are strong antioxidants that protect cells from oxidative damage caused by reactive oxygen species (ROS).
What Is the Role of Carotenoids in Non-Alcohol Fatty Liver Disease?
The underlying cause of non-alcoholic fatty liver disease (NAFLD) is significantly influenced by obesity and metabolic problems associated with excessive fat intake. According to epidemiological research, healthy and effective therapies for reducing obesity-mediated insulin resistance and nonalcoholic fatty liver disease (NAFLD) include dietary changes with a lower caloric intake, weight loss, and increased physical activity.
As a result, numerous natural dietary ingredients have been researched for NAFLD prevention and therapy. Carotenoids are mostly found in fruits and vegetables. The most researched carotenoids are β-carotene and lycopene. The precise mechanisms underlying the preventive effects of carotenoids in nonalcoholic fatty liver disease have shown evidence that carotenoids may function through various mechanisms, including anti-inflammatory and antioxidant activity.
What Are the Common Carotenoids?
The most common carotenoids are,
Lycopene:
It is responsible for the red color of tomatoes and watermelons. It falls under the category of non-provitamin A carotenoid since it lacks vitamin A action. Lycopene, a fat-soluble hydrocarbon, contains 40 carbon and 56 hydrogen atoms. It is mostly found in fatty tissues such as the adrenal glands, liver, and testis. It has also been detected in other human tissues, including the lung, ciliary body, cervix, and retinal pigment epithelium. The primary protective function of lycopene is its antioxidant activity, which inactivates ROS and quenches free radicals.
β-carotene:
The most common carotenoid in dark green and yellow-orange fruits and vegetables is β-carotene. The most prevalent carotenoid in the liver is also β-carotene. β-carotene is the most active provitamin A carotenoid due to its partial conversion to vitamin A. β-carotene is a powerful antioxidant that scavenges free radicals and quenches singlet oxygen physically.
Green leafy vegetables, red palm oil, carrots, pumpkins, apricots, mangoes, sweet potatoes, and mature squashes are the main sources of β-carotene in the human diet. Because of its strong antioxidant properties, β-carotene has been investigated as a preventive factor in non-alcoholic fatty liver disease.
Astaxanthin, lutein, β-cryptoxanthin, and fucoxanthin are among the other carotenoids that have a protective impact on NAFLD.
Astaxanthin:
Astaxanthin exhibits antioxidant and hypolipidemic properties. Astaxanthin was found to reduce plasma total cholesterol and triglyceride levels and inhibit the formation of hepatic steatosis.
Lutein:
The activity of NF-κB DNA binding was decreased in the lutein group. These lutein antioxidant benefits may protect against NAFLD.
β-cryptoxanthin:
β-cryptoxanthin decreased steatosis by modifying the expression of genes linked to inflammatory responses, cell death, macrophage and other leukocyte infiltration and activation, T cell count, and free radical scavenging.
Fucoxanthin:
In obese premenopausal women with nonalcoholic fatty liver disease (NAFLD), fucoxanthin supplementation improved liver function tests and decreased body weight and fat content.
Conclusion
NAFLD has emerged as one of the most significant chronic liver diseases. Its clinical significance is further increased by its association with obesity, insulin resistance, metabolic syndrome, type 2 diabetes mellitus, and the development of cirrhosis and hepatocellular carcinoma. The process of NAFLD pathogenesis is quite complex and may involve multiple mechanisms. Understanding the pathogenic pathways may help to develop new preventive and treatment approaches.
