Systemic photoprotection in solar urticaria with α-melanocyte-stimulating hormone analogue [Nle4-D-Phe7]-α-MSH.
BACKGROUND
Solar urticaria is a rare photosensitivity disorder demonstrating a range of action spectra, which can inflict a very large impact on life quality despite available treatments. Melanin broadly reduces skin penetration by ultraviolet-visible wavelengths, thus increased melanization may protect in solar urticaria.


OBJECTIVE
To examine quantitatively for impact of the potent α-melanocyte stimulating hormone analogue afamelanotide ([Nle(4)-D-Phe(7)]-α-MSH, Scenesse(®); Clinuvel Pharmaceuticals Ltd, Melbourne, Vic., Australia) on the solar urticaria response and skin melanization.


METHODS
Five patients with solar urticaria received a single dose of 16 mg subcutaneous afamelanotide implant in winter time. Melanin density was assessed spectrophotometrically from day 0 to day 60. Detailed monochromated light testing to geometric dose series (increment ) of wavelengths 300-600 nm was performed at 0, 30 and 60 days, with assessment of weal and flare area and minimum urticarial dose (MUD). Data were analysed by repeated-measures anova.


RESULTS
Mean melanin density increased by day 7, peaked at day 15 and remained elevated at day 60 (P=0·03, 0·01, 0·02 vs. baseline, respectively). Baseline phototesting revealed action spectra of 320-400 (n=1), 320-500 (n=2), 300-600 (n=1) and 370-500 nm (n=1), and on afamelanotide mean rises in MUD of 1-12 and 1-3 dose increments were seen at the individual wavelengths tested, at 30 and 60 days, respectively. A significant fall in weal area occurred across responding wavelengths from 300 to 600 nm at 60 days postimplant (P=0·049 vs. baseline), accompanied by greater than twofold overall increase in MUD (P=0·058 vs. baseline).


CONCLUSIONS
Melanization following afamelanotide is accompanied by reduction in solar urticaria response across a broad spectrum of wavelengths. Further study is warranted to assess clinical benefit under ambient conditions in summer.
Haylett
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Dermatological Sciences, Inflammation Sciences Research Group, School of Translational Medicine, University of Manchester, Manchester Academic Health Sciences Centre, Salford Royal NHS Foundation Trust, Manchester M6 8HD, UK.
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Brownrigg
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Taylor
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Rhodes
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D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D004305:Dose-Response Relationship, Drug; D004343:Drug Implants; D005260:Female; D006728:Hormones / Q000008:administration & dosage / Q000627:therapeutic use*; D006801:Humans; D007279:Injections, Subcutaneous; D008297:Male; D008543:Melanins / Q000378:metabolism; D008875:Middle Aged; D012867:Skin / Q000187:drug effects / Q000473:pathology; D012880:Skin Pigmentation / Q000187:drug effects* / Q000528:radiation effects; D013473:Sunscreening Agents / Q000008:administration & dosage*; D014466:Ultraviolet Rays / Q000009:adverse effects*; D014581:Urticaria / Q000188:drug therapy* / Q000378:metabolism; D055815:Young Adult; D000521:alpha-MSH / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use
D004343:Drug Implants; D006728:Hormones; D008543:Melanins; D013473:Sunscreening Agents; D000521:alpha-MSH; C534526:afamelanotide