Adiponectin is a hormone created and secreted into the bloodstream by adipocytes. It is a protein consisting of 244 amino acids and is similar in structure to the cytokine tumor necrosis factor-alpha (TNF-a).
Adiponectin plays a role in several physiological functions:
- Glucose regulation
- Fatty acid catabolism
- Blood vessel dilation (vasodilatation)
- Renal filtration support
- Anti-inflammation
- Tumor suppression
Energy Metabolism
Adiponectin stimulates the oxidation of fatty acids in the mitochondria for more efficient cellular energy generation. It also contributes to the ability of insulin to induce glucose mobilization into cells. Reduced plasma levels of adiponectin may be observed with the insulin-resistance associated with type 2 diabetes mellitus.
Vasodilating Properties
Adiponectin has a relaxing effect on the smooth muscle of blood vessels. It does this by directly stimulating the cells that line vessels (endothelial tissue) to produce a substance called nitric oxide (NO). NO is a cellular messenger that signals smooth muscle to release its contractions and relax temporarily. Relaxed vessels dilate and allow more blood to flow at lower pressure. This may be crucial in situations of impaired heart function like congestive heart failure (CHF) and coronary artery occlusion.
Renal Support
Adiponectin lends a protective effect to renal function. It does this by directly supporting cells involved in the physical filtration of impurities from the blood. As levels of this hormone decrease, kidney function deteriorates and may be the reason obese patients develop the initial signs of renal disease.
Physiology and Use in Prediction of Disease
Adiponectin is created by adipocytes that do not contain much fat. As the cells sequester fat from the diet, these cells produce less of the hormone. Those experiencing anorexia or fasting conditions like uncontrolled type-1 diabetes mellitus may exhibit elevated levels of adiponectin, while obese folks generally have reduced amounts. Though adiponectin research is ongoing, guidelines for use as a biomarker are emerging. Average levels of this hormone in US subjects range 7-8.5 ug/ml. Reduced plasma levels are often associated with, and predictive of development of type-2 diabetes, heart disease, and renal insufficiency.
Tentative Measurement Predictions
While still experimental, some sources recommend the following guidelines:
- >10 ug/ml low risk heart disease and diabetes
- 7-10 ug/ml normal risk
- 4-7 ug/ml high risk
- <4 ug/ml very high risk
Supplemental Resources
Dong, F. and J. Ren (2009). "Adiponectin improves cardiomyocyte contractile function in db/db diabetic obese mice." Obesity (Silver Spring) 17(2): 262-8.
Otani, K., J. Kitayama, et al. (2009). "Adiponectin suppresses tumorigenesis in Apc(Min)(/+) mice." Cancer Lett.
Pena, A. S., D. P. Belobrajdic, et al. (2009). "Adiponectin relates to smooth muscle function and folate in obese children." Int J Pediatr Obes: 1-7.
Sowers, J. R. (2008). "Endocrine functions of adipose tissue: focus on adiponectin." Clin Cornerstone 9(1): 32-40.
Tanianskii, D. A., E. M. Firova, et al. (2008). "[Adiponectin: lowering in metabolic syndrome and independent relation to hypertriglyceridemia]." Kardiologiia48(12): 20-5.
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