Clinical Review

Prevention of Type 2 Diabetes: Evidence and Strategies


 

References

In the IDPP study, both lifestyle changes and metformin reduced significantly and similarly the incidence of diabetes in adults with IGT, with no observed added benefit from combining both interventions [26]. It has not been clear, however, how much of this effect of metformin is a result of pharmacologic properties masking hyperglycemia or a true protective and preventive effect. In a washout study in which 1274 DPP participants who did not progress to diabetes underwent an OGTT after 1 to 2 weeks of discontinuing metformin or placebo, the incidence of diabetes was still reduced by 25% in the metformin group, after the washout period, compared to a 31% risk reduction in the primary DPP analysis, suggesting a partially sustained rather than temporary effect of metformin [41]. In the DPPOS long-term follow-up study, metformin (850 mg twice daily as tolerated) was continued in the group initially assigned to metformin in addition to lifestyle counseling [32]. Although the progression to diabetes was similar in all groups during the 5.7-year follow-up period, the cumulative incidence of diabetes at 10 years was still reduced in the metformin group by 18% when compared to control group. Furthermore, the weight loss associated with metformin was also interestingly sustained at 10 years. A meta-analysis echoed this beneficial effect of metformin observed in the DPP trial, reporting a relative risk reduction of new-onset diabetes of 40% with the use of metformin [42].

In summary, metformin has been shown to be effective in preventing diabetes in patients at risk, especially persons with younger age, higher BMI, and history of gestational diabetes and in native Asian Indians. The protective effect of metformin seems to be sustained over the long term in follow-up studies.

Thiazolidinediones

Thiazolidinediones (TZDs) are antidiabetic agents that have been evaluated in diabetes prevention trials. TZDs are peroxisome proliferator-activated gamma receptor (PPAR-γ) agonists that work by augmenting conversion of preadipocytes to adipocytes, which in turn increase adiponectin levels, promoting insulin sensitivity [43]. In addition to their antihyperglycemic properties, TZDs are thought to have a direct protective effect on beta cells, potentially translating into prevention and delay of diabetes [44].

The first study to demonstrate diabetes prevention with a TZD was the TRIPOD study (Troglitazone in Prevention of Diabetes), in which 266 Hispanic women with a history of gestational diabetes were randomly assigned to troglitazone or placebo [45]. Troglitazone use was significantly associated with reduction of progression to diabetes at 1.5-year follow-up when compared to placebo (relative risk reduction of 55%), with a decrease of endogenous insulin requirement at 3 months of therapy and sustained benefit after discontinuation of the TZD, suggesting an effect on beta cell preservation.

Moreover, troglitazone was an investigational drug in the DPP trial from 1996 to 1998, at which time it was discontinued because of associated fatal liver failure in a DPP participant. In the DPP trial, troglitazone was asso-ciated with a remarkable 75% decrease in progression to diabetes at 1 year. Troglitazone was withdrawn from the US market in 2000 because of its association with severe hepatotoxicity.

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