Catalase and paraoxonase in hypertensive type 2 diabetes mellitus: correlation with glycemic control

OBJECTIVES: Type 2 diabetes mellitus (DM) is well recognized as being associated with increased prevalence of hypertension. Experimental and epidemiologic studies have shown that oxygen-free radicals are elevated because antioxidant enzyme activities are altered both in uncontrolled essential hypertension and DM itself. Recently paraoxonase (PON) has been recognized as an antioxidant enzyme that hydrolyzes lipid peroxides. The aim of this study is to evaluate simultaneously PON activities and antioxidant status in hypertensive type 2 DM cases and to establish any possible relationship between these parameters and duration of hypertension or diabetes, hemoglobin (Hb) A1c levels, and lipid parameters. DESIGN AND METHODS: Nineteen normotensive subjects with type 2 DM, 37 hypertensive (diastolic blood pressure 90 mm Hg or more) subjects with type 2 DM, and 25 normotensive control subjects with normal glucose tolerance were selected for this study. Superoxide dismutase (SOD), catalase, and basal-stimulated PON activities were measured by the methods of Sun et al.; Goth; and Eckerson, Wyte, and La Du, respectively; other lipid parameters were determined using an autoanalyzer. RESULTS: Catalase activities of either hypertensive patients with type 2 DM or type 2 DM patients without complication were found to be higher than controls (p<0.01), although no significant difference in SOD and basal-stimulated PON activities was observed between these groups. A significant elevation in catalase activity (p = 0.004) of patients with high HbA1c levels (>7.0%) (n = 37) compared with patients with low HbA1c levels (<7.0%) (n = 19) was detected. There was also a positive correlation between the catalase activities and fasting glucose levels and HbA1c concentrations in hypertensive patients with type 2 DM (r = 0.4567, p<0.05 and r = 0.3686, p<0.05, respectively). An increase in catalase activity of patients with B and/or AB phenotype compared with patients with A phenotype was also noted. CONCLUSION: Poor glycemic control in diabetes is strongly associated with an increase in free radicals and consequent diabetic complications. Uncontrolled glucose metabolism may also be the cause of alterations in antioxidant enzymes. Among these, catalase correlates best with poor glycemic control. The current data reveal that B allele carriers of PON are more susceptible to oxidant stress.