DNA damage and repair in immunologically active cells

Aberrant processing of oxidative DNA damage in systemic lupus erythematosus

Defective DNA damage processing has been reported in systemic lupus erythematosus (SLE). Vitamin C may modulate formation/removal of the oxidative DNA lesion 8-oxo-2'-deoxyguanosine (8-oxodG). Baseline levels of 8-oxodG measured in SLE serum, urine and PBMC DNA did not differ significantly from healthy subjects. In contrast to healthy subjects, no significant decrease in PBMC 8-oxodG or increase in urinary 8-oxodG was noted in vitamin C supplemented SLE patients. A significant, although attenuated, increase in serum 8-oxodG was detected in SLE patients, compared to healthy subjects. These data support putative abnormalities in the repair/processing of 8-oxodG in SLE.

Increased oxidative stress and decreased antioxidant defenses in mucosa of inflammatory bowel disease

Inflammatory bowel disease (IBD) is characterized by chronic intestinal inflammation whose cellular components are capable of oxidative respiratory bursts that may result in tissue injury. Mucosal biopsies were analyzed for protein carbonyl content (POPs), DNA oxidation products [8-hydroxy-2'-deoxyguanosine (8-OHdG)], reactive oxygen intermediates (ROIs), trace metals (copper, zinc, and iron) and superoxide dismutase (Cu-Zn SOD). In Crohn's disease biopsies, there was an increase in ROIs, POPs, 8-OHdG, and iron, while decreased copper and Cu-Zn SOD activity were found in inflamed tissues compared to controls. For ulcerative colitis, there was an increase in ROIs, POPs, and iron in inflamed tissue compared to controls, while decreased zinc and copper were observed. An imbalance in the formation of reactive oxygen species and antioxidant micronutrients may be important in the pathogenesis and/or perpetuation of the tissue injury in IBD and may provide a rationale for therapeutic modulation with antioxidants.

Oxidative DNA damage and cellular sensitivity to oxidative stress in human autoimmune diseases

OBJECTIVES

To estimate the extent of genomic DNA damage and killing of lymphocytes by reactive oxygen intermediates in autoimmune diseases.

METHODS

8-Oxo-7-hydrodeoxyguanosine (8-oxodG), a promutagenic DNA lesion induced by reactive oxygen intermediates, was measured by high performance liquid chromatography, coupled with electrochemical detection, in hydrolysates of DNA which had been extracted from lymphocyte and polymorphonuclear leucocyte fractions of human blood. In addition, human primary blood lymphocytes stimulated by concanavalin A were assayed for cytotoxicity induced by hydrogen peroxide on day 0, by assessing cell proliferation during seven days of culture.

RESULTS

Constitutive 8-oxodG was detectable (mean (2 SEM) moles 8-oxodG/10(6) moles deoxyguanosine) in DNA isolated from normal human blood lymphocytes (68 (8), n = 26) and polymorphonuclear leucocytes (118 (24), n = 24). Lymphocyte DNA from donors with the following inflammatory autoimmune diseases contained significantly higher levels of 8-oxodG than that from healthy donors: rheumatoid arthritis (98 (16)), systemic lupus erythematosus (137 (28)), vasculitis (100 (32)), and Behçet's disease (92 (19)). Lymphocyte 8-oxodG levels in non-autoimmune controls and patients with scleroderma were not significantly different from those of healthy controls. The levels of 8-oxodG were significantly higher in the DNA from normal polymorphonuclear leucocytes than in paired DNA samples from normal lymphocytes, but there were no differences between levels of 8-oxodG in polymorphonuclear leucocytes from normal subjects and the patients studied. Levels of 8-oxodG did not correlate with disease duration, disease severity, or age. Lymphocytes from patients with systemic lupus erythematosus and rheumatoid arthritis, but not those with scleroderma, also showed cellular hypersensitivity to the toxic effects of hydrogen peroxide.

CONCLUSION

There was increased genomic DNA damage, and increased susceptibility to cytotoxic killing by hydrogen peroxide, in lymphocytes from patients with certain autoimmune diseases. These results might be explained by defective repair of DNA damage or by increased production of reactive oxygen intermediates in inflammation. Although more direct studies are needed, the evidence available favours the former explanation.

Interference of deoxyadenosine with transmembrane signaling events in human T lymphocytes

Deoxyadenosine (dAdo) has been recognized as the toxic metabolite in the immunodeficiency disease associated with adenosine deaminase (ADA) deficiency. Under ADA deficient conditions, dAdo accumulates intracellularly as deoxyadenosine triphosphate (dATP) which by interference with ribonucleotide reductase, prevents DNA synthesis. Recently, we and others have demonstrated that in cells rendered ADA deficient by treatment with deoxycoformycin, dAdo affects T-cell activation events which precede DNA synthesis, such as interleukin 2 receptor (IL-2R) expression and IL-2 production. Here we have analyzed interference of dAdo with the early events of T-cell activation. It is shown that dAdo affects the mitogen induced phosphatidyl inositol turnover. Furthermore dAdo interferes with increase of intracellular calcium. Deoxycytidine, although capable of preventing intracellular accumulation of dATP, cannot reverse the functional consequences of dAdo treatment. The ability of a cell to increase its cytoplasmic free Ca2+, as induced by ionomycin, is not affected by dAdo. The exact target for this novel effect of dAdo is at the present unknown.

Increased sensitivity of lymphocytes from patients with systemic autoimmune diseases to DNA alkylation by the methylating carcinogen N-methyl-N-nitrosourea

Lymphocytes from patients with various diseases associated with autoimmunity showed both impaired capacity to repair O6-methylguanine (a powerful, promutagenic, directly miscoding base lesion) and increased sensitivity to the cytocidal effects of cellular methylation by N-methyl-N-nitrosourea (MNU) compared with normal controls and patients with other disorders. Defective repair of O6-methylguanine was significantly associated with arthritis and myositis in the group with systemic lupus erythematosus (SLE), and increased sensitivity to the toxic action of MNU was associated with the presence of immune complexes and the administration of steroids to patients with Behçet's syndrome. The results indicate that lymphocytes from patients with the autoimmune diseases studied are more susceptible to DNA damage with possible relevance to aetiopathogenesis.

Ciamexone, a highly selective immunomodulator--a tool for autoimmune diseases?

Both organ-specific diseases such as insulin dependent diabetes mellitus as well as non organ-specific disorders such as rheumatoid arthritis are thought to be autoimmune in origin. Both T-cell and B-cell mediated immune responses are involved in these diseases. More or less specific immunosuppressants are therefore widely used drugs in the treatment of autoimmune diseases which, however, suppress the immune reactions not only against autoantigens but also against foreign antigens. Cyclosporine (Cyclosporin A) has been a tremendous step forward in a more specific direction but it creates problems in the long term treatment of autoimmune diseases due to the impairment of immune reactions against foreign antigens as well as to compound specific side effects. Ciamexone, a new highly selective immunomodulator, might be an interesting new approach in the treatment of autoimmune diseases. The compound has had effect in different experimental autoimmune situations such as the diabetic BB-rat and experimentally-induced arthritis in mice or rats. The compound does not show antiproliferative activity on T-lymphocytes or B-lymphocytes. The immune response against foreign antigens, e.g. foreign major histocompatibility complex, viral or fungal antigens is not impaired. On the other hand, however, Ciamexone suppresses the antibody production in different animal systems. It is likely that Ciamexone exhibits its immunosuppressive property via the induction of regulating mechanisms. Due to its remarkably good tolerance, Ciamexone has been used in first pilot trials in different human autoimmune situations such as rheumatoid arthritis and insulin dependent diabetes mellitus.(ABSTRACT TRUNCATED AT 250 WORDS)

UV-induced unscheduled DNA synthesis in fibroblasts of aging inbred rats

Because of the suggested relationship between the lifespan of an organism and the amount of unscheduled DNA synthesis (UDS) occurring in its cells after treatment with genotoxic agents, we initiated a lifespan study of this step of the nucleotide excision repair pathway in female Wistar (WAG/Rij) rats. Skin fibroblasts were isolated at 2 time points, separated by a 9-month interval, from rats of various ages. The isolated cells were cultured for 1 passage, irradiated with ultraviolet light (UV) and analyzed by autoradiography for their capacity to perform UDS. The results of the two cross-sectional series of determinations were identical: small variations among individual animals and a slight, but statistically significant age-related decrease in the initial rate but not in the end level of UV-induced UDS. The small variation among individual inbred rats as compared with the large variation reported for UDS in human populations suggests that the latter is largely due to genetic differences. The lack of a more pronounced age-related decrease along with the small individual variation suggests that the activity of the DNA nucleotide excision repair pathway is not an important single determinant of individual longevity in inbred rats of the same strain and sex.