DNA Repair as a Causal Factor in Chronic Diseases in the Population

Lawrence Grossman, Genevieve M. Matanoski, Even R. Farmer, Mohammad Hedayati, Sagacity Ray, Bruce J. Trock, Joan Hanfalt, George C. Roush, Marianne Berwick, and Jennifer Hu
The Johns Hopkins University School of Hygiene and Public Health
The Johns Hopkins University School of Medicine
Baltimore, MD 21205
and Georgetown University Medical Center
Washington, DC 20007
and New York University Medical Center
New York, NY 10010

These molecular epidemiology studies examine the DNA repair changes (DRC) of affected subjects with a number of chronic diseases and their controls. These include case-control studies of (i) basal cell carcinoma (BC:C) skin cancer patients, ii) Black Foot disease (BFD) amongst Taiwanese peasants exposed to arsenic in their drinking water as well as (iii) breast cancer patients in which a plasmid host cell reactivation assay (or DNA Repair Capacity -DRC) is used to monitor human populations. In this essay a damaged expression vector plasmid is transfected into peripheral blood T-lymphocytes from the subjects. The host cellular repair enzymes repair the damage in the plasmid and 40 hours later the plasmid encoded reporter (cat) chloramphenicol acetyl transferase is measured.

An age related decline in this DNA repair capacity, amounting to approximately -0.61 pent per year (p = 0.0001) occurred in the controls from 20 - 60 years of age. There was a corresponding age-related increase in post-UV mutability (measured as mutations introduced into a transfected plasmid of +0.6% per year (p=.001) in lymphoblastoid cells lines from normal donors of the same age. Reduced DNA repair capacity was a particularly important risk factor for young basal cell carcinoma cases and for those individuals with a family history of skin cancer. A family history of BCC is a harbinger of reduced DNA repair amongst both cases and their controls. Young basal cell carcinoma cases repair their DNA damage poorly when compared to controls. As the basal cell carcinoma patient aged, however, the differences between the cases and controls gradually disappeared. The normal decline in DNA with increasing age may account for the increasing risk of skin cancer which begins in middle age. Patients with reduced DNA repair capacity and overexpose to sunlight had an estimated risk of basal cell carcinoma more than 5-fold greater than the control group. Such a risk was even greater (10-fold) in female subjects. This gender orientation may be explained by the responsiveness of DNA repair to some hormones. It was found that the lower the DRC was, the greater number of skin tumors in individuals (p < 0.05) after adjustment for age. Further, family history of skin cancers was more likely reported in those cases with multiple BCCs. These findings are consistent with the fact that genetically determined low DRC tends to be associated wide multipliciy of skin tumors as seen in XP patients. The persistence of photochemical damage because of reduced repair,results in point mutations in the p53 and allelic loss of the nevoid basal cell carcinoma gene (Gorlin's syndrome ) located on chromosome 9q. These studies were extended to a population of peasants in Taiwan with '`Black foot" disease. The distribution of BCC is abnormally high - unusual in that BCC is rarely found in oriental or black subjects. The cases had been exposed to high levels of arsenic in their drinking water at one time which was reflected in significantly reduced levels of DRC for sunlight exposure. Thus, reduced DRC is a susceptibility factor in BCC, a finding consistent with our earlier studies. How arsenic affects DNA repair is currently under study.

Cryopreserved lymphocytes from two breast cancer case control studies involving 39 breast cancer cases and 61controls conducted at New York University and Georgetown were used for DNA repair measurements. The data show that the mean DNA repair activity was consistly lower in the breast cancer cases (13.1-13.86% in a combined analysis 0f the two institutions, (p < O.O6) based on weighted mean of the data from the two 1ocations. Hence, DNA repair capacity is lower on breast cancer cases than in controls. DRC deficiency appears to be a susceptibility factor in breast cancer. DRC in lymphocytes may be employed as a biomarker for human breast cancer risk. Future studies with a larger sample size will focus on the regulation of DRC by oxidant/antioxidant balance, aging, family history for the diseases and estrogen use.

This work was supported by a grant from the National Institutes of Health ( Merit Award GM-22846) to L.G.