Retinal Degeneration Induced by N-Methyl-N-Nitrosourea and Detection of 7-Methyldeoxyguanosine in the Rat Retina

Abstract

Retinal degeneration induced by a single parenteral dose (40 mg) of N-methyl-N-nitrosourea (MNU) was studied in rats and rabbits. Sequential observations showed that severe pathological changes, that is, complete or widespread destruction of the photoreceptor layer and the outer nuclear layer of the retina, occurred in both animals by 72 hr after the administration of MNU. At week 5, at the end stage of the retinal degeneration induced by MNU, thin remnants remained with the inner nuclear layer in direct contact with the pigment epithelium. An additional immunohistochemistry study using antibodies against 7-methyldeoxyguanosine (7-mdGua), revealed the presence of high levels of 7-mdGua DNA adducts in the nuclei of the outer nuclear layer cells. This finding suggests that the alkylation of the outer nuclear layer by MNU was the direct cause of the retinal degeneration seen in these animals.

Keywords

Alkylation rabbit photoreceptor layer outer nuclear layer

References

1. Abbott PJ and Saffhill R (1979). DNA synthesis with methylated poly(dC-dG) templates. Evidence for a competitive nature to miscoding by O6-methylgua® nine. Biochim. Biophys. Acta 562: 51–61.

2. Asamoto M , Mikheev AM , Jidug YZ , Wild CP , Hall J , and Montesano R (1991). Immunohistochemical detection of DNA alkylation adducts in rat and hamster liver after treatment with dimethylnitrosamine. Exp. Pathol 41: 71–78.

3. Degan P , Montesano R , and Wild CP (1988). Antibodies against 7-methyldeoxyguanosine: Its detection in rat peripheral blood lymphocyte DNA and potential applications to molecular epidemiology. Cancer Res 48: 5065–5070.

4. Herrold KM (1976). Pigmentary degeneration of the retina induced by N-methyl-N-nitrosourea. Arch. Ophthal 78: 650–653.

5. Heywood R and Gopinath C (1990). Morphological assessment of visual dysfunction. Toxicol. Pathol 18: 204–217.

6. International Agency for Research on Cancer (IARC) (1978). N-nitroso-N-methylurea. IARC monographs on the evaluation of the carcinogenic risk of chemicals to humans. Some N-nitroso Compounds. Vol. 17, IARC, Lyon, France, pp. 227–255.

7. Ishikawa T and Sakurai J (1985). Retinal injury induced by N-methyl-N-nitrosourea (MNU). Trans. Societatis Patholog. Jappon LXXIV: 475 (in Japanese).

8. Ludlum DB (1970). The properties of 7-methylgua-nine-containing templates for ribonucleic acid polymerase. J. Biol. Chem 245: 477–482.

9. Meier-Ruge W (1972). Drug induced retinopathy. CRC Crit. Rev. Toxicol 1:325–360.

10.

10. Saffhill R , Margison GP , and O'Connor PJ (1985). Mechanisms of carcinogenesis induced by alkylating agents. Biochim. Biophys. Acta 82: 111–145.

11.

11. Scherer E , Benthem JV , Terheggen PMAB , Vermeulen E , Winterwerp HHK , and Engelse LD (1988). Immunocytochemical analysis of DNA adducts in single cells: A new tool for experimental carcinogenesis, chemotherapy and molecular epidemiology. IARC Sci. Publ 89: 286–291.