It has been estimated that approximately ¼ of the US population has the Insulin Resistant Syndrome (IRS). The notion that insulin resistance and compensatory hyperinsulinemia lead to a cluster of abnormalities that increase CVD risk was first introduced in 1988, and central to the changes identified was a dyslipidemia characterized by a high plasma triglyceride (TG) and low high-density lipoprotein cholesterol (HDL-C) concentration. The atherogenic lipoprotein pattern associated with the IRS has grown to include enhanced postprandial lipemia and smaller and denser low-density lipoprotein (LDL) particles. In addition to being associated with insulin resistance and compensatory hyperinsulinemia, these changes in lipoprotein metabolism have been identified as increasing CVD risk. The power of the dyslipidemia associated with the IRS is reinforced by reports that the plasma TG/HDL-C concentration ratio is as powerful a predictor of CVD, if not more so, than the more conventional total plasma cholesterol/LDL-C concentration ratio, and evidence from the Copenhagen Male Study of the interaction between the plasma TG and HDL-C concentrations, “conventional” CVD risk factors, and CVD events. Specifically, these latter investigators were able to show in a prospective study (11) that CVD events were substantially attenuated in: 1) smokers; 2) patients with high blood pressure; 3) individuals with a high LDL-C concentration; and 4) subjects who were sedentary; as long as they were in the lowest 1/3rd of the population with the lowest TG/HDL-C concentration ratio and presumably insulin sensitive. Conversely, if they were in the tertile with the highest plasma TG/HDL-C concentration ratio, and presumably insulin resistant, they had a significant increase in CVD events in the absence of the four conventional CVD risk factors evaluated.
An obvious alternative therapeutic approach to decreasing CVD risk in patients with the IRS would be to administer a thiazolidinedione (TZD) compound in an effort to directly treat the basic defect of the syndrome. However, based upon our own results with rosiglitazone (ROSI) in several different patient populations, improvements in insulin sensitivity were not associated with a significant improvement in dyslipidemia. For example, in a recent study (unpublished) of ROSI-treated patients with type 2 diabetes, neither plasma TG (358 to 347 mg/dL) nor HDL-C (40 to 42 mg/dL) concentrations improved, and both total (215 to 239 mg/dL and LDL-C (118-142mg/dL) concentrations actually increased. Since the patients in this study became more insulin sensitive with treatment, and had lower daylong plasma glucose, insulin, and free fatty acid concentrations, the reason for the lack of a beneficial effect of ROSI on lipoprotein metabolism is not clear. On the other hand, given evidence of the importance of dyslipidemia in increasing CVD risk in insulin resistant individuals, it seems reasonable to question the notion that TZD compounds provide the most beneficial approach to decreasing CVD risk in the dyslipidemic patient with the IRS.
With this background in mind, we propose to initiate a study in which insulin resistant individuals with the dyslipidemia characteristic of the IRS will be randomized to treatment with fenofibrate,ROSI, or weight loss and the effect of these three treatments on CVD risk factors compared. It is postulated that although insulin resistance will improve to a greater degree with ROSI treatment, the atherogenic lipoprotein profile known to link IRS and CVD will only significantly improve following treatment with fenofibrate and effects of weight loss can effect both of these. |
