Conversion of white fat to brown is associated with muscle atrophy and weight loss in cancer patients.
|Scooped by Graham Player Ph.D.|
Cachexia is a wasting disorder of fat and muscle tissue that results in severe weight loss, loss of appetite, altered taste, and weakness, as seen in people suffering from some chronic disease states such as cancer, HIV and others. About 50% of cancer patients suffer from cachexia, which impairs their quality of life, limits their cancer therapy and decreases their survival.
Cancer cachexia may not be able to be reversed by normal nutritional support and can lead to progressive functional impairment. It is the result of an interaction between the tumor, the person’s metabolism and the involvement of pro-inflammatory cytokines, which are protein molecules that signal cells to produce an inflammatory reaction.
Now a study published in Cell Metabolism has found a link that implicates the browning of white fat to cancer cachexia. One of the study authors, Erwin Wagner, comments that “the transformation of white fat into brown fat, currently one of the most researched subjects because of its potential effects on obesity and diabetes, has very severe consequences” when it comes to cancer.
The researchers, led by Michele Petruzzelli of the Spanish National Cancer Research Center, found that the browning of white fat was linked to higher expression of uncoupling protein 1 (UCP1), which increased lipid metabolism and promoted energy expenditure in mice.
You may wonder what brown fat is. So here is a brief introduction for you. We have two types of fat in our body – white fat and brown fat.
In healthy, non-overweight people, white fat represents up to 20% of body weight in men and 25% in women. White fat is the main form of fat in the body that we are familiar with. It is where excess calories are stored which can later be used as energy when needed, and it also acts as a thermal insulator, helping to maintain our body temperature. It also produces the hormone leptin (the "satiety hormone") which regulates the storage of fat in the body. Leptin also plays a role in other physiological processes. White fat cells have receptors for insulin, growth hormones, norepinephrine, and glucocorticoids.
Brown fat fulfils a different purpose, and is made up of several small fat droplets, together with a large number of iron-containing mitochondria which are the cell’s heat-burning engine. Brown fat's main function is to generate body heat. Fatter people have less brown fat than thinner people. It gets its color due to its high iron content and its many tiny blood vessels to support a higher oxygen consumption. It is mainly found in the upper part of the back, and the front and back of the neck. The purpose of brown fat is to burn calories (rather than store calories) in order to generate heat.
Brown fat is believed to be more like muscle than like white fat. When activated, brown fat burns white fat, and may be able to burn several hundred calories per day. So the browning of white fat in people with cancer could indeed lead to cachexia.
Here is an article published by the American Physiological Society on the subject of the Mechanisms of Cancer Cachexia for anybody interested - http://physrev.physiology.org/content/89/2/381
As cachexia often begins long before it is obvious on physical exam, it is important to address this complication in people with cancer as soon as possible after a diagnosis.