Physical activity and telomere length in early stage breast cancer survivors
Measures
Primary outcome
Telomere length was determined using mean terminal restriction fragment (TRF) lengths as described by Lorenzini et al. [10] with minor modifications. Five hundred nanograms of purified DNA isolated from peripheral blood mononuclear cells (PBMCs) were digested to completion with HinfI and RsaI. Digested samples and size markers (32P-end-labeled 1 Kb Plus DNA ladder and HindIII-cut lambda DNA) were separated in a 0.5% agarose gel. Within the gel, DNA was denatured under alkaline conditions, neutralized, and then hybridized with a 32P-end-labeled oligonucleotide (CCCTAA)4 probe overnight at 55°C. Blots were washed to remove non-specifically bound probe, and visualized using a PhosPhorImager (Molecular Dynamics Sunnyvale, CA). Mean TRF length was calculated as:
Σ(ODi)/Σ(ODi/Li), (1)
where ODi is the total radioactivity above background in interval i and Li is the average length of i in base pairs (bp). The genomic DNA was verified to be of high molecular weight by electrophoresing the undigested DNA samples on 0.5% agarose gels that were subsequently stained with ethidium bromide to show that >99% of the DNA ran at limit-mobility.