Adiponectin is a protein found to have associations with metabolic processes. Initial studies suggest that this protein is associated with processes such as regulation of glucose level and breaking down of fatty acids.
Adiponectin is produced by adipose tissue*, along with co-members in the group of proteins called adipokines. Latest medical reports linked adiponectin with health and disease. How significant is that linkage is yet to be known.
*Adipose tissue is composed of fat cells.
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Preliminary research assumed that low levels of adiponectin may be an indication of a dysfunctional adipose tissue. What is clear, however, is the strong linkage and association shown between the protein and some major types of diseases.
It has been found that people with cancer, heart disease, NAFLD, diabetes, lipid abnormalities, inflammation and cardiovascular diseases have low adiponectin levels. A causal relationship between these diseases and adiponectin also remains to be discovered.
Increasing Adiponectin Levels
Increasing adiponectin levels is possible in both humans and animals. It was shown that animals, particularly those with atherosclerosis, obesity and diabetes, benefit from adiponectin injections.
In humans, weight loss and thiazolidinediones treatments are some of the ways to increase the concentration of adiponectin. Diet changes can also help.
- Omega-3 supplements – Omega-3 polyunsaturated fatty acids increase adiponectin in people with coronary artery disease.
- Increase of fiber intake – Fiber and fish oil support healthy levels of adiponectin.
- Increase in consumption of spices – Several spices can help people lose weight. An example is curcumin which is also believed to have the ability to up-regulate adiponectin.
- Cutting the amount of monounsaturated fats; replace with saturated fats
Manufacturers of adiponectin supplements claim more benefits from increasing adiponectin levels. These are improved insulin function, faster burning of calories, decreased appetite and increased muscle efficiency.
Adiponectin, aside from acid oxidation and glucose regulation functions, perform several roles. It is secreted only by adipose tissue, although it is produced by the placenta among pregnant women. Effects of adiponectin in bodily processes include:
- Among patients, there is an inverse relationship between the body mass index (BMI) and adiponectin. The higher the adiponectin level is the lower is the BMI. No such correlation has been found among healthy adults.
- Caloric limitations in animals and humans result to increased adiponectin levels. This has been noted most especially on people with suffering from anorexia nervosa. In a research, it has been found that the increase is caused mainly by adipose tissue that is located in bone marrow.
- In combination with the protein leptin, adiponectin counteracts insulin resistance. The combination however causes synergistic effects.
- Scientists found that adiponectin acts on the brain and they think that this is the method by which it reduces a person’s weight.
Adiponectin has the highest concentration among all proteins in the blood. About 0.01% is adiponectin, suggesting that there are many other plasma proteins in far lower concentrations in the blood. The concentration of adiponectin is 2 – 30 milligrams per liter of blood.
Among adults, females have higher concentrations than males. Diabetics have lower concentrations. As mentioned earlier, weight reduction increases adiponectin concentrations.
The half-life of adiponectin in humans is 2.5 hours.
The basic structure of adiponectin is a 247 amino acid protein. It has four domains: a carboxyterminal globular domain, a collagenous domain, a nonconserved variable region and an amino terminal signal sequence.
Adiponectin is a self-associating chemical. The implication is an adiponectin molecule likes to connect with other adiponectin molecules and that it likes more to associate with larger molecules.
The image you can see is a combination of three adiponectin molecules – a homotrimer. Trimers like associating with other trimers, thus it is not rare to find hexamers and dodecamers of the adiponectin molecules. The more complex an adiponectin molecule is the higher is its weight. It is interesting to note that these different versions of the adiponectin molecules perform different biological functions.
The adiponectin forms that regulate glucose have “heavy” molecular weight. They are also the ones that have been detected in people with lower risk of diabetes and those with coronary artery disease. It is not clear whether the presence of “heavy” adiponectin is beneficial to people with these conditions.
Adiponectin and AMPK
Research is continuously unraveling the functions of adiponectin. One area being explored is its relation to AMPK (AMP-activated protein kinase). One study found that in muscle cells, adiponectin is able to activate AMPK using two mechanisms. One of these is the pathway that promotes LKB1 cystolic localization. The other pathway involves stimulation of release of the Ca2+ ion.
In another study, the effect of adiponectin on fatty acid oxidation and insulin sensitivity has been noted. This study suggests that it is through the activation of the AMPK that adiponectin is able to do these functions.
The research also noted that it is the AMPK molecules located in peripheral that are activated by adiponectin.
The researchers concluded that adiponectin, through AMPK activation, decreases energy expenditure and stimulates appetite.
The appetite-stimulating effect found in this study contradicts the claim of adiponectin supplements makers who said that the protein can reduce appetite.
In yet another study, the researcher noted that adipocytes (also called adipokines) release cytokines. The study claimed that cytokines modulate AMPK. Adipocytes are the substances that regulate the balance of energy in the entire body. Along with adiponectin, the research mentioned resistin and leptin as examples of adipocytes that perform this “balancing” function.
This study shared more information about the AMPK-adiponectin connection. It delved also on the idea that adiponectin also works on the AMPK that is in liver.
The study also shared information on the differences adiponectin has compared to the other two proteins. According to this research, the major functions that adiponectin performs are functions that resistin opposes.
With regard to leptin, the research noted the protein’s ability to activate muscular AMPK, but it also said that leptin inhibits a kinase in the hypothalamus of mice, concomitant with food intake repression.