Cholesterol Linked With Type 2 Diabetes
The study was based at Canada's Vancouver Child and Family Research Institute at the University of British Columbia, and is published online in Nature Medicine.
Type 2 diabetes is defined by two things. One is insulin resistance, and the other is reduced insulin production. The second is caused by reduction in insulin release by "beta cells" in the pancreas. Why this happens is poorly understood; however, it has been suggested that the build up of toxic lipids in the cells could be a reason.
Using mice, scientists showed that pancreatic beta cells, responsible for insulin release, begin to malfunction when their cholesterol levels build up.
They examined the role of a molecular transporter called "ATP-binding cassette transporter A1" (ABCA1). ABCA1 is important for "cholesterol homeostasis" which regulates cholesterol levels in cells. It also affects insulin secretion in pancreatic beta cells.
The scientists used genetically engineered mice and switched off their ABCA1 genes.
They found that these mice had normal insulin sensitivity, but lower levels of insulin secretion and significantly impaired glucose tolerance, displaying one of the classic symptoms of type 2 diabetes. They effectively became diabetic.
When they examined the pancreas of the mice, isolated and tested the cells "in vitro", they found the cholesterol homeostasis was different to normal as was the secretion of insulin. They also found a significant accumulation of cholesterol in the beta cells.
Cholesterol plays a number of roles in the human body, and one of these is to keep cell membranes healthy so they allow the right chemicals to pass in and out of the cells. However, the levels of cholesterol have to be regulated precisely.
In the case of the beta cells, if the cholesterol levels accumulate, they interfere with the secretion of insulin. This is the one of the possible explanations, say the scientists on this study.
However, there are competing theories. One is that amylin, one of the peptide hormones produced by the beta cells and secreted at the same time as insulin, builds up and interferes with insulin release.
According to Dr Michael Hayden, in whose lab the study was conducted, more studies will be done this year to see if cholesterol regulation problems also occur in humans with type 2 diabetes.
The Canadian Diabetes Association estimates that more than 2 million Canadians have diabetes, of which 1.8 million have type 2. And the figures are rising.
In 2000 the World Health Organization (WHO) estimated that over 177 million people had diabetes worldwide and they say by 2025 the figure will be 300 million.
If you have type 2 diabetes it means that glucose builds up in your blood instead of being metabolised and used for energy.
If you keep your blood glucose levels under control, that is within the target range set by your doctor, there is no reason why you should not live a long and healthy life.
According to the Canadian Diabetes Association you can do this by: eating healthy meals and snacks, taking regular exercise, and taking the diabetes medication (including insulin) that your doctor prescribes.
"Beta-cell ABCA1 influences insulin secretion, glucose homeostasis and response to thiazolidinedione treatment."
Liam R Brunham, Janine K Kruit, Terry D Pape, Jenelle M Timmins, Anne Q Reuwer, Zainisha Vasanji, Brad J Marsh, Brian Rodrigues, James D Johnson, John S Parks, C Bruce Verchere and Michael R Hayden
Nature Medicine Published online: 18 February 2007
Click here for Abstract.
Click here for Canadian Diabetes Association.
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