No abstract

Systemic lupus erythematosus is an immunologically mediated autoimmune disease which has been reported to be aggravated by certain environmental agents such as ultraviolet irradiation (UV). To further investigate this interaction, we examined the consequences of UV exposure on the autoimmune process of several strains of autoimmune mice. Strains of age- and sex-matched, 3- to 4-month old, autoimmune (MRL-lpr/lpr, (NZB X NZW)F1, BXSB) and nonautoimmune (BALB/c, B10.A) mice were shaved and exposed to an acute (2 h daily X 7 days) and a chronic (3 h/weekly X 4 weeks) dose of UV (FS40 lamps, 2 mJ/cm2/s). UV-induced changes in survival, autoantibody production, splenic B-cell activity, and target organ pathology were examined. After an acute UV exposure there were (10/15) deaths in the UV BXSB males and (4/15) in the UV BXSB females, compared to (1/15) in the non-UV BXSB male group and (0/15) in the non-UV BXSB females. No deaths occurred in the other UV autoimmune or nonautoimmune groups. Likewise, chronic UV resulted in increased UV BXSB male mortality (13/15) compared to UV BXSB females (2/15) and non-UV BXSB males and females. No deaths occurred in the other autoimmune (MRL-lpr/lpr, (NZB X NZW)F1) or nonautoimmune (BALB/c, B10.A) strains, after chronic UV exposure. Equivalent doses of Mylar-filtered FS40 UV (UVB deleted) resulted in no deaths in the UV BXSB male group. Acute and chronic UV also resulted in a significant increase in serum single-stranded DNA antibody production, splenic polyclonal B-cell activity, and renal glomerular inflammatory changes in the UV BXSB male mice. Thus, UV resulted in premature death and accelerated autoimmunity in UV BXSB males and may serve as a useful model for phototoxicity in autoimmunity.

Abstract— Irradiation of mice with unfiltered FS40 sunlamps renders them susceptible to challenge with highly antigenic UV‐induced skin tumors. Dose‐response studies demonstrated that the susceptibility of mice to tumor challenge was directly proportional to the total dose of UV radiation, and was independent of the manner in which the dose was administered. A fractionated dose was no more effective than the same total dose given as a single treatment in inducing susceptibility to tumor challenge. The effects of even suboptimal doses of UV radiation persisted for as long as 6 months after the UV treatment.

Certain hexavalent chromium [Cr(VI)] compounds are human lung carcinogens. Although much is known about Cr-induced DNA damage, very little is known about mechanisms of Cr(VI) mutagenesis and the role that DNA repair plays in this process. Our goal was to investigate the role of excision repair (ER) pathways in Cr(VI)-mediated mutagenesis in mammalian cells. Repair-proficient Chinese hamster ovary cells (AA8), nucleotide excision repair (NER)-deficient (UV-5) and base excision repair (BER)-inhibited cells were treated with Cr(VI) and monitored for forward mutation frequency at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus. BER was inhibited using methoxyamine hydrochloride (Mx), which binds to apurinic/apyrimidinic sites generated during BER. Notably, we found that both NER-deficient (UV-5 and UV-41) and BER-inhibited (AA8 + Mx) cells displayed attenuated Cr(VI) mutagenesis. To determine whether this was unique to Cr(VI), we included the alkylating agent, methylmethane sulfonate (MMS) and ultraviolet (UV) radiation (260 nm) in our studies. Similar to Cr(VI), UV-5 cells exhibited a marked attenuation of MMS mutagenesis, but were hypermutagenic following UV exposure. Moreover, UV-5 cells expressing human xeroderma pigmentosum complementation group D displayed similar sensitivity to Cr(VI) and MMS-induced mutagenesis as AA8 controls, indicating that the genetic loss of NER was responsible for attenuated mutagenesis. Interestingly, Cr(VI)-induced clastogenesis was also attenuated in NER-deficient and BER-inhibited cells. Taken together, our results suggest that NER and BER are required for Cr(VI) and MMS-induced genomic instability. We postulate that, in the absence of ER, DNA damage is channeled into an error-free system of DNA repair or damage tolerance.