Adiponectin, a hormone produced in adipose tissue in humans and animals, has a beneficial effect on health only when it is present in blood levels at normal concentrations. An elevated level in the blood can be found especially in people who are overweight and in obese patients. They have an increased risk of developing metabolic disease.
What is adiponectin?
Adiponectin has the gene names GBP-28, AdipoQ, and Acrp30 and is one of the adipokines (fat tissue hormones). The body produces it with the help of the gene APMI on chromosome 3q27. Adiponectin is always produced when the fat cells are only slightly filled. The tissue hormone, which is made up of 247 amino acids, has a collagen-like structure and is responsible for regulating sugar and fat metabolism. Certain diseases, such as chronic insulin dysregulation, which is associated with permanently elevated insulin levels, ensure that less adiponectin is produced in adipose tissue. Adiponectin administration can be used to accelerate the breakdown of adipose tissue – a method that could be helpful to weight loss patients in the future. In individuals with normal adiponectin levels, its share of the total proteins present in the blood serum is only 0.01 percent. Adiponectin concentration in blood is determined using the ELISA method.
Function, effects, and roles
Adiponectin, along with leptin, insulin, and other hormones, regulates glucose metabolism. It alters the action of insulin on fat cells. Therefore, it is also called an immune modulator. If the adiponectin content in the blood is low, the effect of insulin is also weakened. Since overweight people and insulin-resistant patients have low adiponectin levels, their risk of developing type 2 diabetes is significantly higher than that of people with normal weight. Adiponectin acts at the receptors AdipoR1 and AdipoR2. AdipoR1 is located in skeletal muscle, and AdipoR2 is located in liver tissue. In people with normal blood serum adiponectin levels, the hormone increases sensitivity to insulin and counteracts insulin resistance. It is secreted more when insulin levels rise briefly and promotes fat storage in fat cells. As an antagonist of pro-inflammatory hormones produced in abdominal adipose tissue, adiponectin has an anti-inflammatory (anti-inflammatory) effect. Therefore, individuals with normal adiponectin levels also have a low risk of developing atherosclerosis. However, in people with obesity who also suffer from coronary heart disease, too low a level causes even greater damage to the vascular system. Animal studies have shown that animals with too low a concentration of adiponectin in their blood die more frequently from blood poisoning than animals with normal adiponectin blood levels. Additional administration of the tissue hormone, on the other hand, drastically reduced this risk. It also inhibits new sugar (glucose) formation in the liver, stimulates fatty acid oxidation in the liver, stimulates glucose uptake into muscle, and causes insulin formation.
Formation, occurrence, properties, and optimal levels
Adiponectin is formed in the adipocytes (fat cells) of the body. However, their production is stimulated only when the adiponectin concentration in the blood serum is too low. Adiponectin, like the other hormone leptin produced in adipose tissue, has an effect on glucose and lipid metabolism. If it is present in sufficient quantities in the blood, it inhibits inflammatory processes in the body, such as those affecting blood vessel walls and cell membranes. People with normal adiponectin levels have a lower risk of developing type 2 diabetes. Scientists now believe that in the future, doctors will be able to use adiponectin blood levels to determine whether or not a patient is at increased risk of developing diabetes. Researchers also found that patients with a genetic variant of the hormone have a significantly higher risk of developing diabetes mellitus than those with “normal” adiponectin. Recent clinical trials have succeeded in increasing blood levels of adiponectin with the administration of certain drugs. Another way to normalize blood levels, according to medical experts, is to reduce obesity and change the diet.
Diseases and disorders
An abnormally low level of adiponectin in the blood causes the body to make inadequate use of the fatty acids stored in the adipose tissue. People with obesity not only have persistently (too) low adiponectin blood levels, but at the same time they also have elevated leptin levels. Leptin is the other hormone produced in adipose tissue. It normally ensures inhibition of appetite. However, since obesity blocks this positive effect of leptin, insulin resistance develops. The excessive leptin concentration leads to oxidative stress and therefore to increased inflammatory parameters. People with this dysfunction live with a greater risk of later developing type 2 diabetes, hardening of the arteries (atherosclerosis), coronary heart disease and heart attack. Too high triglyceride levels and too low HDL cholesterol levels can be detected in their blood. Total cholesterol levels are also elevated to a greater or lesser extent. To counteract this, physicians recommend significantly reducing weight (and thus above all fatty tissue). Lots of exercise in fresh air reduces resistance to insulin in people with diabetes via the adiponectin content. However, excessive adiponectin levels in the blood can increase the risk of dementia in female patients. Excessive adiponectin secretion may also promote the development of liver cirrhosis.
