Anyone who has ever had a sick child knows that one of the surest signs that he or she is recovering is a return of appetite. From a biological perspective, this is an attempt by the body to make up for any losses that took place during the illness. The major mediator of this effect is one set of a group of chemicals known as cytokines.
Cytokines are glycoproteins that behave like hormones and neurotransmitters, serving as chemical messengers between cells. There are many families of cytokines, including leptin, that we have met before. In recent years most of the attention of researchers has been directed not at the cytokines themselves, but at their receptors, whose activity is far more subtle.
Cytokine receptors are involved in the regulation of cell growth and repair and have important roles in immune responses. Apart from their role in feeding behavior, cytokines have roles in fatigue, fever, sleep, pain and stress. Some key cytokines: interleukin (IL)-1, IL-6 and IL-8 are dysregulated in fibromyalgia.
At a meeting of the 6th International Congress of Neuroendocrinology in Pittsburgh last month, researchers from the Centre National de la Recherche Scientifique (CNRS) at the Pasteur Institute and the University of Lille, France, presented evidence that The cytokine interleukin-7 (IL-7) is not only involved in immune function, but also prevents obesity-prone mice from getting fat. This is the converse of those cytokines that cause weight gain. IL-7 interacts with the regions of the hypothalamus involved in appetite control. This is yet another piece of evidence indicating that the immune and neuroendocrine systems are closely inter-linked.
This is not really a surprise. One of the big problems I people with many chronic illness, particularly cancer, is that they tend to lose appetite and weight. Sometimes they lose a great deal of weight even while maintaining a decent diet. The anorexia of cancer is caused by many factors working on the signaling pathways in the hypothalamus that modulate energy homeostasis. Research has shown that cytokines are major mediators of weight and appetite loss in cancer patients, by working on two systems known as melanocortin and neuropeptide-Y. It also seems likely that the weight loss that happens with stress, depression and chronic inflammation are all mediated by specific cytokines. These same cytokines increase the risk of developing heart disease. A recent study from Ireland has shown that treatment with an SSRI antidepressant reduces measures of systemic inflammation.
It may be that this new insight into the relationship between inflammation and weight will offer up some more solutions for the problems of obesity, but we are going to need to be alert to the possibility that anything that modulates cytokines may increase the risk of vascular disease.
The more that we learn, the more that we understand about the miraculous checks and balances that keep us healthy.
Technorati tags: Cytokines Leptin Cancer cachexia Weight control Inflammation
Comments