The effects of visible and blue light exposure on growth and melanogenesis of ocular melanoma cell lines

Abstract Purpose Cumulative ultraviolet (UV) exposure is important in skin and conjunctival melanomas and melanogenesis. UV light does not reach the inner posterior eye, but visible light radiates the retina, underlying retinal pigmented epithelium (RPE) and the choroid. The effects of visible light on the choroidal microenvironment and potential roles in choroidal melanoma progression are unknown. We examined human ocular melanoma cells for responses to white or blue light exposure, specifically, cell viability and cytotoxicity, and melanin production. Methods Ocular melanoma cells were grown in RPMI/L‐glutamine/sodium pyruvate (Choroidal: MP38 and MP46 (RPMI + 20% FBS), 92.1 (RPMI + 10% FBS); conjunctival: CM2005.1 (RPMI + 10% FBS)). Cells were grown in 96 well black plates (8000/well; n = 5 per cell line; triplicate) for 18 hrs, then fresh medium (1% FBS) for 16 hr. Cells were exposed to: (1) white light (λ: 400–700 nm), 32,000 lux (direct sunlight) for 4 hr (short‐term), or 4 hr/day × 4 days (16 hr, cumulative); or (2) blue light (λ: 460 nm): 3100 lux for 4 hr (short‐term) or 16 hr/day X 2 days (32 hrs, cumulative). Unexposed control cells were grown in parallel. Viability and cytotoxicity of light‐exposed and control cells were measured with alamarBlue and LDH assays, respectively. Intracellular melanin was assessed after cumulative white or blue light exposure. Results Short‐term and cumulative white light reduced viability (alamarBlue) by 5–15% (92.1, MP46 and CM2005.1 cells, but not MP38) and 10–25% (92.1, MP38, MP46 and CM2005.1 cells), respectively. Short‐term blue light did not affect viability of any cell lines; cumulative blue light exposure reduced viability by 10% in MP38 cells only. No significant change in cell cytotoxicity (LDH) or intracellular melanins was noted after white or blue light exposure for any cell lines. Conclusions Melanoma cells showed no light‐induced cytotoxicity (measured by LDH leak), although viability (measured by alamarBlue) was reduced after cumulative light exposure, suggesting reduced cell numbers rather than cell death. Although melanoma cell lines showed variable intracellular melanins, levels were unchanged with light exposure, despite cells expressing melanogenesis‐related proteins.