Age-correlated DNA damage in human muscle tissue

This investigation represents the largest study so far published on human DNA damage and aging. The subject of this investigation is damage, determined as DNA alterations which give rise to complete molecular breaks in the course of treatment of purified DNA solutions with single-strand-specific nucleases. The DNA is derived from milligram samples of human muscle of individuals mostly undergoing surgical treatment. Care has been taken to bring the muscle samples, once shut off from blood circulation to liquid nitrogen temperatures within few seconds. The DNA is prepared by a procedure keeping breaks by handling and by DNAase attack as low as possible, however pushing DNA purity, especially with respect to protein as high as possible. Highly purified DNA treated in this way has some sites which are susceptible to single-strand (ss) specific DNAase splitting (ss-events). Three different deoxyribonucleases have been used: Nuclease S1, Nuclease BAL31 and Pea Endo-Nuclease. They give very similar results, i.e. splitting of the DNA so as to yield DNA pieces of given distribution. The lengths of these double-strand (ds) pieces have been determined from their electron microscopical pictures, either by following the image contours with a magnetostrictive stylo of the projected photo on a pad, by following the contours with a mileage ruler, or by integrating the silver grains on the photo. The molecular weight averages of the ds DNA threads between two ss-events for each individual have been determined from 20 to 200 molecules. The 470 individuals contributing their data were from age groups from 1 to 91 years. The molecular weights show a considerable scatter with an average molecular weight of the DNA ds pieces between two ss-events of 43.93 MDa and a standard deviation of 17.99 MDa. Among the single-strand breaks (ssb) that split the DNA into such pieces is a fraction, the number of which increases in a highly significant fashion with the age of the donor. From this derives the fact that the average molecular weight of the DNA strand pieces between two ssb decreases with age. It is remarkable that the standard deviation of the molecular weights of such pieces increases with age significantly, too. On the basis of additional information mainly supplied by the DNA donor himself or by his parents the 470 members of the main group M where grouped according to their life-style, into: (1) abstinent people, essentially non-smokers and refraining from use of licit or illicit drugs, sub-group N.(ABSTRACT TRUNCATED AT 400 WORDS)