Allopurinol and endothelial function: A systematic review with meta-analysis of randomized controlled trials

Oxidative stress and endothelial dysfunction are two inter-related conditions commonly seen in patients with cardiovascular risk factors. The enzyme, xanthine oxidase, is an important contributor to these phenomena but to a variable degree in different patient populations. This meta-analysis will summarize the effect of allopurinol, an established xanthine oxidase inhibitor, on endothelial function among patients with different comorbidities.

Medline Complete, PubMed, ProQuest, ClinicalKey, Wiley Online Library, and Cochrane Central Register of Controlled Trials were searched till July 29, 2017. Meta-analysis was planned for randomized controlled trials (RCTs) that investigated allopurinol effects on endothelial function. A random effect model was used to calculate the standardized mean difference (with 95% confidence intervals: CI) as an estimate of effect size. Heterogeneity was quantified by four types of information: Q statistics, I² statistic, Tau-squared (T² ), and Tau (T).

Thirty eligible studies were identified; 12 were included in the final analysis and subdivided among 3 patient's groups: patients with chronic heart failure (CHF; 197 patients), patients with chronic kidney disease (CKD; 183 patients), and patients with type 2 diabetes mellitus (DM; 170 patients). Allopurinol was found to have a statistically significant benefit on endothelial function in patients with CHF and CKD but not in type 2 DM. The standardized mean differences and CI in the three patient's groups were 0.776 (0.429, 1.122), 0.350 (0.009, 0.690), and 1.331 (-0.781, 3.444), respectively.

Allopurinol has an antioxidant property that might partially reverse endothelial dysfunction in patients with certain comorbidities. The importance of this property and the magnitude of the beneficial effect are likely to be related to the relative contribution of xanthine oxidase into the oxidative stress associated with different underlying pathologies.