Acute impact of afamelanotide on UVR erythemal and melanogenic responses in healthy humans in vivo: an exploratory study.
Afamelanotide may reduce acute UVR-induced erythema, but the clinical significance of these findings is uncertain due to the small sample size and lack of long-term data.
Where it sits
this study against the rest of the afamelanotide corpusSummary and findings
This study measured the acute effects of afamelanotide on UVR-induced erythema and melanogenic responses in healthy humans. Participants received a 16 mg subcutaneous implant of afamelanotide and were assessed for changes in minimal erythema dose and melanin density after UV exposure. The study involved 9 participants aged 27-43 years with skin phototypes II-III.
Abstract
Afamelanotide, an analogue of α-melanocyte stimulating hormone, activates the melanocortin-1 receptor and has a range of protective properties as demonstrated largely in vitro. While afamelanotide is approved to treat a visible light-induced inflammatory dermatosis, erythropoetic protoporphyria, its acute effects in vivo are poorly characterised. We explored short-term effects of afamelanotide on the acute inflammatory response of UVR-induced erythema and on the melanogenic response, in healthy humans. Participants (n = 9, 5 M:4 F, 27-43y, phototypes II-III) had melanin density and skin lightness measured at six skin sites using spectrophotometry. A broadband UVB dose-series (7-80 mJ/cm<sup>2</sup> erythemally-weighted UVR, Philips TL12) was applied to buttock skin. After 24 h, minimal erythema dose (MED) was assessed, spectrophotometric measurements were taken of erythema at each dose site and two unexposed sites, and an unexposed site was biopsied. Afamelanotide was administered (16 mg subcutaneous implant) and after six days the same UVR dose-series applied to contralateral buttock skin, and measurements and biopsy repeated. Melanin was stained in biopsy sections (modified Warthin-Starry method) and quantified by image analysis. The UVR-erythema dose response (area-under-curve) decreased post-afamelanotide (mean 3.5 pre, 2.7 post, P = 0.018) with an apparent increase in MED (median 21 mJ/cm<sup>2</sup> pre, 29.9 post, not sign.). Melanin density (reflectance at 420 and 400 nm) increased (mean overall increase 2.4% to 2.9%, P = 0.001), while melanin staining was unaltered. The demonstrated protection against acute UVR-induced erythema shortly after afamelanotide application supports that anti-inflammatory effects observed in vitro may operate in vivo, warranting further investigation in acute UVR-induced inflammatory conditions.
Background
The paper investigates the acute effects of afamelanotide, an analogue of α-melanocyte stimulating hormone, on UVR-induced erythema and melanogenesis in humans. Prior research has shown protective properties of afamelanotide largely in vitro, but its in vivo effects remain poorly characterized. Understanding these effects is crucial as afamelanotide is already approved for treating erythropoietic protoporphyria, and this study aims to clarify its role in acute inflammatory responses.
Methods
This exploratory study involved 9 healthy participants (5 males, 4 females) aged 27-43 years with skin phototypes II-III. Participants received a 16 mg subcutaneous implant of afamelanotide, followed by a broadband UVB dose-series applied to their buttock skin after six days. Primary outcome measures included minimal erythema dose and melanin density, assessed through spectrophotometry and biopsy.
Results
The primary endpoint showed that the UVR-erythema area-under-curve decreased from mean 3.5 pre to 2.7 post afamelanotide, with a p-value of 0.018. The median minimal erythema dose increased from 21 mJ/cm² pre to 29.9 mJ/cm² post, which was not statistically significant. Additionally, melanin density increased from a mean of 2.4% to 2.9%, with a p-value of 0.001.
Interpretation
The findings suggest that afamelanotide may provide some protective effects against UVR-induced erythema, as indicated by the decrease in the area-under-curve for erythema. However, the increase in minimal erythema dose was not statistically significant, raising questions about the clinical relevance of this finding. The small sample size and lack of long-term follow-up limit the generalizability of the results, indicating that further research is needed to confirm these effects.
Key findings
- UVR-erythema area-under-curve decreased from mean 3.5 pre to 2.7 post afamelanotide, P=0.018.
- Median minimal erythema dose increased from 21 mJ/cm² pre to 29.9 mJ/cm² post, not significant.
- Melanin density increased from mean 2.4% to 2.9%, P=0.001.
Limitations
- small n=9 study
- short follow-up period of six days
- no long-term durability assessment
- lack of significant change in minimal erythema dose