Topical application of acidified nitrite to the nail renders it antifungal and causes nitrosation of cysteine groups in the nail plate.

BACKGROUND: Topical treatment of nail diseases is hampered by the nail plate barrier, consisting of dense cross-linked keratin fibres held together by cysteine-rich proteins and disulphide bonds, which prevents penetration of antifungal agents to the focus of fungal infection. Acidified nitrite is an effective treatment for tinea pedis. It releases nitric oxide (NO) and other NO-related species. NO can react with thiol (-SH) groups to form nitrosothiols (-SNO). OBJECTIVES: To determine whether acidified nitrite can penetrate the nail barrier and cure onychomycosis, and to determine whether nitrosospecies can bind to the nail plate. METHODS: Nails were treated with a mixture of citric acid and sodium nitrite in a molar ratio of 0.54 at either low dose (0.75%/0.5%) or high dose (13.5%/9%). Immunohistochemistry, ultraviolet-visible absorbance spectroscopy and serial chemical reduction of nitrosospecies followed by chemiluminescent detection of NO were used to measure nitrosospecies. Acidified nitrite-treated nails and the nitrosothiols S-nitrosopenicillamine (SNAP) and S-nitrosoglutathione (GSNO) were added to Trichophyton rubrum and T. mentagrophytes cultures in liquid Sabouraud medium and growth measured 3 days later. Thirteen patients with positive mycological cultures for Trichophyton or Fusarium species were treated with topical acidified nitrite for 16 weeks. Repeat mycological examination was performed during this treatment time. RESULTS: S-nitrothiols were formed in the nail following a single treatment of low- or high-dose sodium nitrite and citric acid. Repeated exposure to high-dose acidified nitrite led to additional formation of N-nitrosated species. S-nitrosothiol formation caused the nail to become antifungal to T. rubrum and T. mentagrophytes. Antifungal activity was Cu(2+) sensitive. The nitrosothiols SNAP and GSNO were also found to be antifungal. Topical acidified nitrite treatment of patients with onychomycosis resulted in > 90% becoming culture negative for T. rubrum. CONCLUSIONS: Acidified nitrite cream results in the formation of S-nitrosocysteine throughout the treated nail. Acidified nitrite treatment makes a nail antifungal. S-nitrosothiols, formed by nitrosation of nail sulphur residues, are the active component. Acidified nitrite exploits the nature of the nail barrier and utilizes it as a means of delivery of NO/nitrosothiol-mediated antifungal activity. Thus the principal obstacle to therapy in the nail becomes an effective delivery mechanism.

Selenium protects primary human keratinocytes from apoptosis induced by exposure to ultraviolet radiation.

The generation of reactive oxygen species has been implicated in ultraviolet radiation (UVR)-induced skin damage. In mice, increasing dietary selenium intake protects skin from UVR-induced DNA damage and photocarcinogenesis. We sought to determine whether selenium supplementation could protect keratinocytes from apoptosis resulting from exposure to broadband (TL20W/12) UVR. Unirradiated cultures contained 6.5 +/- 1% apoptotic cells; the maximum percentage of apoptotic cells (34 +/- 5%) was seen 16 h after UVR of 600 J/m(2). Under these conditions cell death from necrosis was 15 +/- 2.5% of the total cells. A 24-h preincubation with sodium selenite (10 nm(-1) microm) or selenomethionine (50 nm(-1) microm) protected cultured human keratinocytes from UVR-induced apoptosis. In primary keratinocytes the greatest reduction in apoptosis was found with 100 nm of either selenium compound (71% reduction in the numbers of total apoptotic cells; P < 0.01). Supplementation with 100-200 nm selenite or selenomethionine prevented UVR-induced apoptosis, but did not decrease the levels of UVR-induced p53, as measured by Western blotting. Collectively, this data suggests that selenium prevents UVR-induced cell death by inhibiting p53-independent cell death pathways.