Mitochondrial DNA (mtDNA) damage in semen as surrogate marker for nucleoside analogue toxicity

Mitochondrial damage is increasingly being linked to nucleoside toxicity, particularly lipoatrophy, peripheral neuropathy and lactic acidosis, yet there are currently no monitoring assays that can help in monitoring changes in mitochondrial DNA, or to use as a surrogate marker for the risk of future toxicity.

The most commonly affected tissues (muscle, fat, liver and peripheral nerve) are difficult and intrusive to sample, and blood is unsuitable as mitochondria are not present in red cells and low expression in leucocytes. Cellular mitochondrial division however occurs at a similar rate in semen to that of key affected tissue and spermatozoa contain relatively few mitochondria with a slower metabolic rate (and therefore highly consistent wild-type).

This prospective study presented by Dr Dush Mital from the Birmingham Heartlands Hospital, analysed semen mtDNA in an HIV-positive man before and during HAART. Semen mtDNA was isolated using Puregene DNA isolation kit and analysed by mass spectrophotometry.

An initial treatment with 3TC/delavirdine/indinavir was quickly modified to ddI/d4T/nevirapine/hydroxyurea due to toxicity. After 12 weeks this was changed again, to 3TC/ZDV/nevirapine. Analysis of mtDNA (the long PCR result was shown on an agarose gel after electrophoresis viewed with ultraviolet light) showed wild-type both at baseline pre-treatment and after 12 weeks. At week 24 additional bands showed wild-type and mutant deletions. No nucleoside-associated toxicities were reported in this subject at any point in this study.

Although there is not a comparable sample for mtDNA toxicity analysis in women, the technology and expertise for developing assays should this prove successful are at a similar level to that required for viral load or resistance assays. The researchers have since expanded this research with a larger group of patients, including naive and experienced patients with a well documented history, and a wider range of lipodystrophy symptoms, and will present data at the forthcoming 2nd Workshop on Lipodystrophy in Toronto in the Autumn.