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As obesity and
diabetes form twin epidemics in the United States, scientists are peeling back
layers of understanding on the underlying mechanisms in both conditions. When
leptin was discovered in the mid-1990s, it was heralded as an obesity fighter
because it turns off your appetite and can cause you to burn more calories. The
promises of leptin waned, however, and proved to work in far more complex ways
than previously understood. Little did researchers know at the time that in the
mid- to late 2000s leptin would emerge as a potential agent in preventing and
treating insulin resistance, a condition that can lead to diabetes. Leptin works
in the organ that produces insulin and may act as a remote control of the cells
that release insulin.
Leptin
Leptin is a protein
hormone that your fat cells release while you are sleeping. Leptin binds to
receptors in your brain, and that process diminishes your appetite after you
eat. That's why it's often called the "satisfaction" hormone. Leptin is also an
energy regulator. It senses when you have too many stored calories and can make
your body rev up its calorie-burning mechanisms. Much of the research
surrounding leptin concerns the possibility of it contributing to new obesity
treatments, but after being discovered in 1994, scientists have learned that
leptin is far more complex.
Insulin Resistance
Your pancreas's beta
cells secrete insulin -- a hormone -- in response to your eating. One of its
major functions is to transport glucose from the foods you eat into your cells.
Insulin resistance happens when cells, whether in muscles, tissue, fat or the
liver, don't respond properly to insulin. As a result, glucose builds up in your
bloodstream instead of going into your cells. This malfunction can wreak havoc
on your organs, including your pancreas, which strives to keep up with your
body's need for insulin. Over time, insulin resistance can become prediabetes
and ultimately type 2 diabetes as blood sugar levels increase. Losing weight and
getting more physical activity are the most important factors under your control
to help reverse insulin resistance, but leptin therapy may also one day
help.
Leptin and Insulin
Secretion
Harvard University's
Joslin Diabetes Center researchers say that in addition to the brain, leptin
receptors are located throughout the body, including the pancreas. Through
animal research, they learned that leptin plays a key role in modulating the
cells that release insulin. Their research involved mice genetically programmed
to have no leptin receptors in the pancreas. When these mice were fed high-fat
diets, they naturally became obese and insulin resistant. The researchers
determined that the combination of lack of pancreatic leptin, obesity and
insulin resistance affected the growth and functioning of beta cells. This
dysfunction led to poor blood sugar. More research should uncover precisely how
leptin and insulin talk to each other in the pancreas and lead the way to drugs
that can manipulate both proteins to treat diabetes.
Prevention Research
An earlier study by
National Institutes of Health researchers showed that leptin therapy improved
insulin responsiveness by decreasing the amount of blood sugar the livers of
mice produced, and at the same time, it decreased their blood lipids and
enhanced the burning off of fatty acids. Excess lipids, like triglycerides and
cholesterol, are common in the Western diet and are thought to play a role in
both obesity and the development of insulin resistance. High-fat feeding, says a
University of Pittsburgh researcher, causes problems in the uptake of blood
sugar, fatty acid metabolism and insulin signaling. In an experimental study
with rats, John Joseph Dube determined that leptin therapy could indeed prevent
some forms of insulin resistance.
References
- "Harvard Gazette"; Obesity: Reviving the Promise of Leptin; Nancy Fliesler; January 6, 2009
- "Annual Reviews of Nutrition"; Leptin: Much More than a Satiety Signal; Ruth Harris; July 2000
- National Diabetes Information Clearinghouse; Insulin Resistance and Pre-diabetes; October 2008
- Joslin Diabetes Center; Joslin Researchers Uncover Potential Role of Leptin in Diabetes; October 1, 2007
- "Endocrinology"; Leptin Improves Insulin Resistance and Hyperglycemia in a Mouse Model of Type 2 Diabetes; Yuka Toyoshima et al.; September 2005
- University of Pittsburgh; Leptin and Insulin Sensitivity; John Joseph Dube; 2005
http://www.livestrong.com/article/456824-leptin-insulin-resistance/
