Can combined oral therapy improve muscular fitness?

Combined thiazolidinedione–metformin treatment synergistically improves insulin signalling to insulin receptor substrate-1-dependent phosphatidylinositol 3-kinase, atypical protein kinase C and protein kinase B/Akt in human diabetic muscle
Original source: Diabetologia Volume 52, Number 1
Authors: N. Temofonte, M. P. Sajan, S. Nimal, T. Pastoor, C. Fumero, L. Casaubon, J. L. Powe, M. L. Standaert1, and R. V. Farese (corresponding author)
Publication date: January, 2009
DOI (digital document ID): DOI: 10.1007/s00125-008-1180-z
Requires subscription? Yes
Publicly-available abstract: Yes

Synopsis:
Impaired insulin responses in Type 2 diabetes can make it difficult for glucose to get to muscles, where they are needed. It is believed that this is because certain insulin-activated protein enzymes (atypical protein kinase C (aPKC) and protein kinase B (PKB/Akt)) are not as thoroughly activated as they should be. Both metformin and thiazolidinediones (a class of oral diabetes-management drugs that includes rosiglitazone (Avandia) and pioglitazone (Actos)) improve this deficiency. The investigators wanted to know if adding both drugs together would create an even greater improvement.

Combined metformin-thiazolidinedione therapy was administered to Type 2 test ubjects for 5-6 weeks and the results measured. The investigators observed improved glucose movement and improved insulin-induced activity of four muscle signalling factors (insulin receptors plus two protein kinases). Despite this improved activity, the levels of aPKC in muscle tissues were not improved.

Because of the improvement in the four signalling factors, the investigators consider this test successful.

Reliability:
The number of patients tested was not available in the abstract, nor was any CONSORT statement, so it's difficult to tell whether the sample size was large enough to counteract small-sample skew. Several of the investigators are associated with a Veteran's Administration (VA) center. VA patients often get the worst possible levels of care, so it is hard to tell how far along the subjects' T2 had progressed, or how well it had been treated before the test. That we are looking at combined therapy and it is being called "therapeutically useful" even though depressed muscular aPKC levels were not affected by the treatment suggests that this is the sort of experiment that would be funded by a drug manufacturer, with an eye towards pushing more expensive drugs (such as Avandamet, a combination of Avandia and metformin) on the T2 public.

Practical Applications:
Improved muscular uptake of glucose could improve physical performance, and with it, positive incentives toward exercise. This could result in T2 patients being more interested in exercising, and thereby, improving both physical fitness and insulin sensitivity.

This synopsis was based on the abstract only.

Are adverse effects of some diabetes drugs related to their suppression of sex hormones?

Are the adverse effects of glitazones linked to induced testosterone deficiency?
Original source: Cardiovascular Diabetology 2008, 7:30
Authors: M. Carruthers (corresponding author), T. R. Trinick, E. Jankowska, and A.M. Traish
Publication date: 15 October 2008
DOI (digital document ID): 10.1186/1475-2840-7-30
Requires subscription? No
Publicly-available abstract: Yes

Synopsis:
The authors pose a theory that the various adverse effects of diabetes drugs in the class called "glitazones" -- including rosiglitazone (RGZ -- brand name Avandia) and pioglitazone (PGZ -- brand name Actos) -- may be related to a separate known action of these drugs -- their suppression of sex hormones. These side effects include heart disease, swelling, weight gain, and anemia.

Glitazones act on sex hormones by reducing the levels to which they are released and by making the body less sensitive to them. These sex hormones are responsible for directing new cell growth to become blood vessels, skin, muscle, and other types of structural cells, rather than fat cells. This might give further weight to an existing theory of how obesity might cause diabetes (called "Ungar's theory of the 'Lipocentric Pathway to Hyperglycemia'"(1)). The authors note evidence that low testosterone levels in men can cause a number of the same side effects that are being observed in diabetes patients treated with glitazones; furthermore, that diabetes and/or cardiovascular disease are often seen to develop where testosterone production has been suppressed in order to treat prostate cancer. Much of this can be tied to the abdominal weight gain related to low testosterone levels. Treatment with testosterone in these cases has been shown to reduce the side effects and lower the statistical occurrence of cardiovascular disease among patients showing a number of these metabolic symptoms.

The authors note a number of known effects of rosiglitazone and troglitazone (Resulin, which has been removed from the US market) on sex hormones and on the development and maturation of new body tissues.

The authors suggest that this hypothesis might be tested by double-blind, placebo-controlled clinical studies examining the endocrine profiles, and levels of sex hormones, in people with Type 2 diabetes both before and while/after being treated with a glitazone. Additionally, studies on treating diabetic men with testosterone might show us whether this might counteract (or at least lessen) the adverse effects of glitazones. They also suggest further research into exactly how glitazones inhibit sex hormones.

Reliability:
The authors are associated with a number of universities and medical research institutes throughout the world. The hypothesis was published in a peer-reviewed journal. The authors are posing a theory, rather than a statement of fact, and suggesting ways that others could determine whether or not their theory is correct.

Practical Applications:
If the theory is correct, and if administering testosterone to men can completely counteract the adverse effects of Avandia and similar medications, that would make Avandia a relatively safer choice to treat Type 2 diabetes than it is now.

For further reading:
(1) Roger H. Unger, MD Reinventing type 2 diabetes: pathogenesis, treatment, and prevention. Journal of the American Medical Association (JAMA), 2008;299(10):1185-1187.
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First 150 words available free.

"Evidence-Based Medicine", Patient Pages, Journal of the American Medical Association (JAMA)

This synopsis was based on the entire article.