Differential effects of cyclosporine A on ornithine decarboxylase activity induced by ultraviolet-B and PUVA in mouse skin

The effect of plaque retention on cyclosporine-induced gingival overgrowth in rats

The purpose of this study was to examine the role of plaque retention on cyclosporine A (CsA)-induced gingival overgrowth. Forty-five male Sprague-Dawley rats, 15 for each of three CsA dosage conditions, were unilaterally ligated around the first mandibular molar (plaque retention). The silk ligature was left in place for 6 weeks. Contralateral first molars served as unligated controls. The daily dosage of CsA, administered by gastric feeding, was 0, 3, or 10 mg/kg body weight. Stone models from biweekly impressions of the molar sites were used to investigate development of gingival overgrowth. Rats were sacrificed at 6 weeks for histopathological and histometric examination of the molar sites. Gingival overgrowth was significantly increased in sites with higher CsA dosage, longer treatment duration, and ligation. Gingival overgrowth was enhanced in ligated sites regardless of CsA dosage. However, the odds ratio of ligated over unligated sites for gingival overgrowth increased with increasing CsA dosage. The histopathological and histometric examination revealed significantly increased gingival volume in ligated sites in CsA-treated animals. The tissue enlargement included both the epithelium and the connective tissue; however, the epithelium to connective tissue ratio remained unaltered. Within limitations of the study, we suggest that plaque retention magnifies CsA-induced gingival overgrowth; thus, dental plaque appears to be a cofactor in the development of CsA-induced gingival overgrowth.

Effects of cyclosporin and ultraviolet radiation on growth and ornithine decarboxylase activity in cultured human epidermal keratinocytes

Both cyclosporin (CyA) and ultraviolet radiation are effective in the treatment of psoriasis, but their precise mechanisms of action are uncertain. We investigated their effects on ornithine decarboxylase (ODC) activity, ODC gene expression, and cellular proliferation stimulated by epidermal growth factor (EGF), in cultured normal human epidermal keratinocytes. CyA (5 micrograms/ml) inhibited ODC activity, ODC mRNA level, and cell growth induced by 50 ng/ml EGF. Ultraviolet B (10 mJ/cm2) irradiation suppressed the induction of ODC, ODC mRNA, and cell proliferation stimulated by EGF, but ultraviolet A (0-15 J/cm2) irradiation inhibited neither EGF-stimulated ODC activity nor cell proliferation. These findings indicate that reduction of ODC activity in CyA- or ultraviolet B-treated human keratinocytes may contribute to the antiproliferative mechanism of these agents. These results also suggest that the regulation of ODC activity by ultraviolet B and A irradiation may be mediated by different signal transduction pathways.

Effects of colchicine on the induction of ornithine decarboxylase and its gene expression by the phorbol ester tumour promoter

The activity and gene expression of ornithine decarboxylase (ODC, an indicator of tumour promotion) were induced by the phorbol ester tumour promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), in mouse skin. In the present study, the effect of colchicine, a microtubule-disrupting agent, on ODC activity and its gene expression were investigated. On administration of colchicine (100 micrograms) intraperitoneally 1.5 h before TPA treatment, ODC activity and ODC mRNA levels stimulated by TPA were suppressed to about 52 and 64%, respectively. These results suggest the involvement of a microtubule or colchicine-sensitive substrate in the signal transduction system for gene expression.

Effects of ultraviolet-B and PUVA on ornithine decarboxylase activity, DNA synthesis, and protein kinase C activity in mouse skin

Ultraviolet-B and PUVA share several biological events with phorbol ester tumor promoters. The effects of ultraviolet-B irradiation and topical PUVA treatment on ornithine decarboxylase activity, DNA synthesis, and protein kinase C activity, which are known to be induced or activated by phorbol ester tumor promoter, were investigated in hairless mouse skin. Ornithine decarboxylase activity was remarkably enhanced by ultraviolet-B and PUVA. Although PUVA did not affect DNA synthesis significantly, ultraviolet-B stimulated epidermal DNA synthesis approximately 5-fold over control values at 48 h. However, unexpectedly, neither cytosolic nor membrane-bound protein kinase C activity showed any change during the 2 h after either treatment. These results suggest that the protein kinase C system is not involved in the initial signal transduction system of ultraviolet-B or PUVA, unlike the case with phorbol ester tumor promoter.

Effects of butylated hydroxyanisole on ornithine decarboxylase activity induced by ultraviolet-B and PUVA in mouse skin

The effects of butylated hydroxyanisole (BHA), a representative phenolic antioxidant, on the activity of ornithine decarboxylase (ODC, an indicator of tumor promotion and epidermal hyperproliferation) induced by ultraviolet-B (UVB) or PUVA in mouse skin were investigated. By topical application of BHA (55 mumol), PUVA-induced ODC activity was suppressed by about 60% at both 12 h and 24 h after treatment. In contrast, BHA failed to suppress UVB-induced ODC activity in mouse skin. These results suggest that the induction of ODC activity by UVB or PUVA is mediated by different pathways.