In vivo and in vitro evaluation of the use of a newly developed melatonin loaded emulsion combined with UV filters as a protective agent against skin irradiation.

Background: Melatonin has attracted attention because of their high antioxidant and anticarcinogenic activity. Otherwise, the use of sunscreens is recommended for patients after chemotherapy and radiotherapy treatments or to prevent UV radiation-induced skin damages that may result in pre-cancerous and cancerous skin lesions.

Objective: To evaluate the beneficial influence of melatonin in topical sunscreen emulsions combined with three common ultraviolet filters.

Methods: After the formulation characterization in terms of rheology, stability studies were performed. Release studies let us to evaluate its mechanism of delivery and ex vivo permeation study through human skin, the amount of melatonin retained. The antioxidant activity assay was also carried out, and finally the in vivo photoprotective effect in rats was tested as transepidermal water loss and erythema formation.

Results: The rheological behaviour of formulations was pseudoplastic fluid, all emulsions had good physical stability. Release studies showed a trend of enhancement in melatonin release from emulsions incorporating UV filters and followed a Weibull model. Melatonin permeation was higher from the emulsion containing melatonin combined with a mixture of three ultraviolet filters (MMIX) formulation. Equally this formulation exhibited the highest radical scavenging activity. Finally the photoprotective assay showed that only skin areas treated with this formulation were statistically equivalent to the unirradiated control area.

Conclusion: MMIX formulation would be a promising formulation for preventing the undesirable adverse effects of UV skin irradiation because melatonin not only acts as a potent antioxidant itself, but also is capable of activating an endogenous enzymatic protective system against oxidative stress.