Central to understanding the photochemical function(s) of melanosomes is the determination of their absorption properties and an understanding of how the absorption varies with the molecular composition of melanin. Herein, the absorption coefficients for melanosomes containing predominantly eumelanin, a polymeric pigment derived from the molecular precursors 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), are reported for λ = 244 nm. The absorption coefficient varies with the DHICA/DHI ratio, determined from chemical degradation analyses. With increasing DHICA content, the absorption coefficient of the melanosome increases. This observation is consistent with reported extinction coefficients, which reveal that at 244 nm, the extinction coefficient of DHICA is a factor of ∼2.1 greater than that of DHI. The melanosome absorption coefficients are compared to predicted values based on a linear combination of the absorption of the constituent monomers. SECTION Biophysical Chemistry Eumelanin is a commonly occurring pigment derived from the molecular precursors 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA).1-4 Even though the molecular structure of eumelanin remains elusive, exquisite analytical techniques have been developed that enable determination of the relative contributions of these two precursors to the overall pigment. 2,5Studies of eumelanins from different tissues exhibit a wide range of DHICA/DHI ratios. [5][6][7][8] However, how such changes in the molecular composition affect the eumelanic UV absorption coefficient has not been examined for natural systems.

Because sunlight is essential for human survival, we have developed complex mechanisms for detecting and responding to light stimuli. The eyes and skin are major organs for sensing light and express several light-sensitive opsin receptors. These opsins mediate cellular responses to spectrally-distinct wavelengths of visible and ultraviolet light. How the eyes mediate visual phototransduction is well studied, but less is known about how the skin detects light. Both human and murine skin express a wide array of opsins, with one of the most highly expressed being the functionally elusive opsin 3 (OPN3). In this review we explore light reception, opsin expression and signaling in skin cells; and compile data elucidating potential functions for human OPN3 in skin, with emphasis on recent studies investigating OPN3 regulation of melanin within epidermal melanocytes.

A severe case of COVID-19 was observed in an otherwise healthy 28-year-old man who had taken oxandrolone 40 mg/day as an anabolic steroid. The patient had been taking oxandrolone for enhanced bodybuilding 30 days prior to presenting to an outpatient clinic with COVID-19 symptoms. The patient reported that his symptoms have rapidly worsened over the course of 4 days prior to presenting at the clinic. As part of an experimental antiandrogen treatment for hyperandrogenic men suffering from COVID-19, he was administered a single 600 mg dose of the novel antiandrogen proxalutamide. Twenty-four hours after administration of this dose, marked improvement of symptoms and markers of disease severity were observed. To our knowledge, this is the first case that potentially links anabolic steroid use to COVID-19 disease severity.