Photosensitization of Human Diploid Cell Cultures by Intracellular Flavins and Protection by Antioxidants

Abstract

Abstract— The damaging effects of near ultraviolet and visible light on WI‐38 human diploid lung fibroblasts were investigated. WI‐38 cells in culture were killed by light doses ranging from 2 to 10 × 103 W/m2 h. There was an inverse correlation between culture age, i.e. population doubling level and photosensitivity. However, this effect could not be related to capacity for DNA synthesis and cell division. Flavins were clearly implicated as endogenous photosensitizers, and antioxidants such as d, l‐α‐tocopherol (vitamin E), BHT and ascorbic acid were found to afford the cells protection from light damage. Furthermore, products of lipid peroxidation could be detected in cell homogenates irradiated in the presence of ribofiavin.

Activation of flavin-containing oxidases underlies light-induced production of H 2 O 2 in mammalian cells

“…Previous studies have shown that irradiation of mammalian cells with violet or blue light induced H 2 O 2 production and DNA damage (1)(2)(3)(4)(5)(6)(7)(8)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Catalase and other antioxidants prevented this damage, indicating that H 2 O 2 production was a critical, early step in the process.…”

“…Less recognized or understood is that toxicity can be induced by visible light. Specifically, violet (400-450 nm) and blue (450-490 nm) light are known to cause mutations and even death of cultured mammalian cells at irradiation doses of 2-6 J/cm 2 (1)(2)(3)(4)(5)(6)(7)(8), which is equivalent to 5-10 min of direct sunlight (9). Although most human cells are protected from sunlight by physical barriers (skin, hair, clothing), clinical pathologies resulting from intense sources of violet-blue light have been reported, e.g., solar retinopathy (10,11) and erythropoietic protoporphyria (12,13).…”

Photodamage to hepatocytes by visible light

“…WI-38 human fibroblasts show a gradual decline m growth rate with exposure to visible light [6] with younger cells bemg more susceptrble to photokilling and with partial protection observed by DL-o-tocopherol or vitamin E. Visible lightabsorbing chromophores and vitamin E are largely associated with the inner mltochondnal membrane. A previous study made on the effect of visible light exposure to isolated mrtochondna has indicated a flavin-photosenatized mitration process and oxygendependent damage to energy coupling, flavm dehydrogenases and quinones, but not to hemoproteins of the inner membrane.…”

Potential for Genetic Damage from Multivitamin Solutions Exposed to Phototherapy Illumination

“…Such concerns seem justified in view of DNA modifying activity of phototherapy (9), a property shared with many chemical carcinogens and teratogens (1). The photodynamic damage of intracellular DNA has been well characterized and is enhanced by, but not dependent upon, the presence of exogenous photosensitizing agents (3,7,10,11). Such enhancement takes on clinical significance when it is realized that many low birth-weight infants receiving phototherapy are simultaneously administered parenteral hyperalimentation solutions containing photosensitizers, i.e., multivitamins, amino acids, etc.…”