Effects of solar radiation on mitochondrial activity and protoporphyrin IX synthesis

Abstract

The skin plays an important role in maintaining the body's homeostasis, offering an effective barrier against external agents, including solar radiation. Excessive exposure to the sun causes uncontrolled production of reactive chemical species, such as electronically excited states, free radicals and many other oxidizing species, disturbing redox signaling and homeostasis and culminating in increased damage to the structure and function of biomolecules. Current photo-protection strategies are inadequate, as they focus only on the range of solar radiation that causes cutaneous erythema, which is mainly the range of ultraviolet B (UVB, 280-320nm). Consequently, the measurement of photo-protection effectiveness is based mainly on the measurement of the relative increase in the UVB irradiation time that leads to erythema. These measures do not consider the free radicals produced in the skin, more than half of them result from the absorption of photons in the visible region (400-700nm). Photons in the UVA (320-400nm) and in the visible ranges of solar radiation penetrate deeper into the skin and are not properly filtered or scattered by current photoprotectors. As there is no efficient method to comprehensively assess sun damage and protection, we are proposing here to assess this by estimating the activity/viability of the skin's mitochondria. Photons in both the UV and visible ranges are absorbed by endogenous photosensitizing molecules, which are present in high concentrations in mitochondria (for example, flavins and cytochromes), giving rise to excited and reactive species and causing irreversible damage to this organelle. Damage to mitochondria of epithelial cells can lead to numerous consequences for skin tissue. On the other hand, there is no method currently available that can measure the activity of mitochondria in the skin of individuals exposed to the sun. Protoporphyrin IX (PPIX) is a natural photosensitizer and fluorophore, being biosynthesized in mitochondria from aminolevolinic acid (ALA). The speed of synthesis of PPIX, which can be assessed by simple fluorimetry equipment, seems to depend on mitochondrial function. In this project, we intend to understand how mitochondrial function and PPIX production are affected by the different wavelength ranges of sunlight. In 2D and 3D models of human keratinocytes, we will evaluate mitochondrial function and PPIX production, as induced by the external administration of methyl aminolevolinic acid (m-ALA, a lipophilic derivative of ALA). We expect to understand how the different wavelengths of sunlight affect the function and structure of mitochondria and how this correlates with the production of PPIX and cellular/molecular markers of autophagy. In addition to providing subsidies for an in-depth understanding of the effect of sunlight on the skin, this knowledge can lead to the development of a more robust method of quantifying photodamage/photoprotection, based on the production of PPIX induced by m-ALA. (AU)