In the general population, obesity has been associated with reduced mitochondrial size in skeletal muscle [30], reduced muscle mtDNA content and mitochondrial dysfunction [31]. Animal models of obesity also demonstrate mitochondrial dysfunction in the liver associated U0126 solubility dmso with steatosis [32]. We therefore postulate that pre-existing impairments in both liver and muscle mitochondrial function in those with higher BMIs are exacerbated by exposure to NRTIs, leading to an increased risk of LA and SHL. Female gender has been reported by others as being associated with the development of LA in retrospective studies [33], and has been

reported particularly in resource-limited settings [11], with associations with an elevated BMI [9,25] or higher body weight [28]. In a large multicentre, retrospective case–control study, female gender was significantly associated with LA even in multivariate analysis [5]. In another more recent

retrospective case–control study in South Africa, female gender and BMI were significant risk factors in multivariate analysis [34]. Although we found a significant association between female gender and the development of LA/SHL, this association was no longer significant after correction for BMI. We therefore feel that previously reported gender differences in the risk of development of LA/SHL may be attributable, at least in part, to differences between sexes in body habitus and fat content. We did not find any association Stem Cell Compound Library between PBMC mtDNA or RNA at baseline, or changes in mtDNA or RNA on treatment and the development of LA/SHL. One cross-sectional study demonstrated a reversible lower PBMC mtDNA content in treated HIV-infected subjects with hyperlactataemia compared with untreated HIV-infected individuals, but did not compare mtDNA content between treated HIV-infected subjects with and without hyperlactataemia [15]. LA/SHL is caused by mitochondrial dysfunction in tissues such as skeletal muscle Phosphoribosylglycinamide formyltransferase and the liver, and PBMC mtDNA content has previously been shown not to correlate well with muscle mtDNA content [19].

While we found subtle changes in mtDNA in both cases and controls with treatment, these changes were not statistically significant, despite the sample size, and therefore we feel routine monitoring of PBMC mtDNA has no value for prediction of the development of LA/SHL in the clinical setting. A potential limitation of our study is that serum lactate was not routinely measured in the INITIO trial, and so we may have underestimated the number of cases of LA/SHL. However, subjects continued to be monitored at regular intervals while on the study, and were followed up for a median of 192 weeks. Given that most cases of LA/SHL occurred within the first year of therapy and relatively few occurred afterwards, we feel that it is likely that we captured most incidences of LA/SHL.