Mitochondrial DNA Damage in Spermatozoa of Faroese Men Exposed to Organochlorines

Abstract

Mitochondria are essential for sperm function and fertility, serving such functions as cellular energy for motility, apoptosis during spermatogenesis and capacitation. Interest in mitochondria has increased in epidemiologic studies but there has been no focus on sperm so far. Few mechanisms have been explored why sperm counts have been declining over the last 40 years. We sought to demonstrate the relationship between mitochondrial DNA and sperm health. This pilot study used mitochondrial DNA damage and copy number to assess negative effects of exposure to organochlorines on sperm. Semen and serum samples from men (n=50) 22-44 years old who participated in Faroe Islands health studies were randomly selected from the first and third tertiles (n=25 for each tertile) of serum concentrations p,p’-DDE and PCB congeners 118, 138, 153, and 180 (adjusted for total lipids). Mitochondrial DNA damage was determined using QPCR that measures the decrease in DNA amplification due to the presence of DNA lesions that stalls the progression of DNA polymerase. Validated primers that amplify a long sequence were used to increase the probability that a DNA lesion will be present. The average mtDNA copy number of per sperm cell in each sample was measured using previously published primers. Amplification progress was followed using cyber green dye and amplification specificity was controlled by using temperature melting curves. Mitochondrial DNA content was calculated using the difference in cycle thresholds between nuclear and mitochondrial DNA. Multivariate adjusted Poisson models were used to estimate the relationship between organochlorine exposure and DNA damage. Age, abstinence time, smoking status, were all potential confounders controlled for in the adjusted analysis. Incidence rate ratios (IRRs) and 95% confidence intervals were calculated for each model. We expect to see an increase in mitochondrial DNA damage in sperm of men with higher exposures to p,p’-DDE and PCBs.