Thiazolidinedione therapy: the benefits of aggressive and early use in type 2 diabetes

Beta-cell preservation: a potential role for thiazolidinediones to improve clinical care in Type 2 diabetes

Type 2 diabetes is caused by progressively increasing insulin resistance coupled with deteriorating beta-cell function, and there is a growing body of evidence to suggest that both of these defects precede hyperglycaemia by many years. Several studies have demonstrated the importance of maintaining beta-cell function in patients with Type 2 diabetes. This review explores parameters used to indicate beta-cell dysfunction, in Type 2 diabetes and in individuals with a predisposition to the disease. A genetic element undoubtedly underlies beta-cell dysfunction; however, a number of modifiable components are also associated with beta-cell deterioration, such as chronic hyperglycaemia and elevated free fatty acids. There is also evidence for a link between pro-inflammatory cytokines and impairment of insulin-signalling pathways in the beta-cell, and the potential role of islet amyloid deposition in beta-cell deterioration continues to be a subject for debate. The thiazolidinediones are a class of agents that have demonstrated clinical improvements in indices of beta-cell dysfunction and have the potential to improve beta-cell function. Data are accumulating to show that this therapeutic group offers a number of advantages over traditionally employed oral agents, and these data demonstrate the growing importance of thiazolidinediones in Type 2 diabetes management.

Effect of rosiglitazone on serum liver biochemistries in diabetic patients with normal and elevated baseline liver enzymes

OBJECTIVES

Thiazolidinediones (TZD) are recommended to be used cautiously in diabetics with mild elevations in liver enzymes and not to be used in those with alanine aminotransferase>2.5 upper limit normal (ULN). However, studies are not adequate that evaluated the risk of TZD hepatotoxicity in diabetics with elevated liver enzymes. We conducted a study to test if diabetics with elevated liver enzymes have increased risk for hepatotoxicity from rosiglitazone (only TZD available on our formulary).

METHODS

This study consisted of two cohorts of patients prescribed rosiglitazone since January 2000. Cohort 1: 210 diabetics with elevated baseline liver enzymes (aspartate aminotransferase (AST)>40 IU/L and/or alanine aminotransferase (ALT)>35 IU/L) who received rosiglitazone, and cohort 2:628 diabetics with normal liver enzymes who received rosiglitazone. Elevations in liver biochemistries over a 12-month period after initiating rosiglitazone were characterized into mild to moderate or severe elevations and into "Hy's rule" based on published criteria.

RESULTS

Compared to cohort 2, patients in cohort 1 did not have higher incidence of mild to moderate (10% vs 6.6%, p=0.2) or severe elevations (0.9% vs 0.6%, p=0.9) in liver biochemistries. Similarly, the incidence of liver biochemistry abnormalities meeting the Hy's Rule was statistically not different between the two cohorts (0% vs 0.3%, p=0.9). The frequency of discontinuing rosiglitazone therapy during the follow-up was similar between cohorts 1 and 2 (8.6% vs 8.1%, p=1.0).

CONCLUSIONS

These results suggest that diabetics with elevated baseline liver enzymes do not have a higher risk of hepatotoxicity from rosiglitazone than those with normal enzymes.

Effets cardiovasculaires de la rosiglitazone

PROVEN EFFICACY

Since their launch on the French market in 2002, thiazolidinediones ("glitazones") prescribing conditions and therapeutic indications have progressively widened, although remaining strictly defined by the marketing licence. Clinical efficacy on glycemic control (HbA1c and glycemia), as well as beneficial metabolic effects (on lipids, insulinresistance and beta-cellular function) are now well established. Their side effects, generally minor or mild, are also well known. The problem of cardiovascular adverse events, although of a low incidence, should be known and recognized, notably fluid retention (and oedema) and risk of heart failure, more frequent in diabetic than in non diabetic patients. Clinicians must know and take into account the particular risk factors, clinical and diagnosis characteristics, possible pathophysiological mechanisms and their main preventive measures. POTENTIAL BENEFICIAL EFFECTS: On the other hand, numerous experimental and/or preliminary data in type 2 diabetic patients, including favourable effects on the various pathophysiological mechanisms involved in atherosclerosis and effects on cardiovascular risk factors or markers, justifies further large prospective long term clinical studies to assess glitazone effects on cardiovascular morbidity and mortality in type 2 diabetic patients at high cardiovascular risk. Several controlled studies are currently ongoing with rosiglitazone (ADOPT, BARI-2D, DREAM, RECORD, etc.), their results within the next coming Years will answer the questions on the anticipated benefits of rosiglitazone in terms of cardiovascular prevention and/or protection in type 2 diabetic patients.

Cœur, Diabète et Glitazones

Beneficial metabolic effects of rosiglitazone are now well established and its adverse events, generally minor or mild well known too. Following a brief review of these metabolic effects and main adverse events, we mainly describe fluid retention (and edema) and the heart failure risk, their risk factors, clinical and diagnosis characteristics, possible pathophysiological mechanisms and the main preventive measures are reviewed. Numerous experimental data and/or preliminary studies in type 2 diabetic patients, including effects on cardiovascular risk factors or markers, justify to conduct a large prospective long term clinical program to assess rosiglitazone effects on cardiovascular morbidity and mortality in type 2 diabetic patients at high cardiovascular risk, these studies are briefly described.