Production of Malonaldehyde From Squalene, a Major Skin Surface Lipid, During Uv‐irradiation

Abstract

Malonaldehyde (MA), a product of lipid peroxidation, is known to have a number of toxicological effects. Among skin surface components, squalene has been suggested as a significant source of MA following UV exposure. Irradiation of squalene coated on the inside surface of glass tubes served as a simple model to examine skin surface photochemistry. Malonaldehyde produced during UV-irradiation was reacted with methyl hydrazine to form N-methylpyrazole, which was then measured by gas chromatographic analysis. Ultraviolet A-irradiation produced low levels of MA from squalene, with a maximum of 1.0 nmol MA/mumol squalene near 6 h. Malonaldehyde production varied with the energy of irradiation, with levels of 176 nmol/mg squalene and 9 nmol/mg squalene produced after 3 h of irradiation with UVB and UVA, respectively. The thiobarbituric acid (TBA) assay for lipid peroxidation showed large overestimations of MA levels under all irradiation conditions tested. The TBA assay predicted the highest levels of MA with UVC but we did not detect any MA with our assay.

Ion-trap tandem mass spectrometric analysis of squalene monohydroperoxide isomers in sunlight-exposed human skin

“…The presence of six double bonds allows SQ to undergo photooxidation, yielding squalene monohydroperoxide (SQ-OOH) as the primary oxidation product (10). We and other researchers reported that using LC-CL, or the rather insensitive LC-UV detection method at 210 nm, SQ-OOH levels increased markedly in skin surface lipids from human forehead after exposure to sunlight (11) or UV A and B (12)(13)(14). These studies (7,8,(10)(11)(12)(13)(14) suggested that SQ-OOH accumulation could be involved in inflammatory skin disorders such as skin cancer, cutaneous autoimmune disease, and skin aging.…”

Tubifex: A Sensitive Model for UV-B-Induced Phototoxicity

“…The oxidation of essential fatty acids may disturb the "ne structure of biological membranes and thus a!ect the permeability/functions of the membranes. Ultimately, these processes may cause irreversible damage to the cell and may initiate/promote the pathogenesis of certain injury and disease states (Dennis and Shibamoto, 1989;Ames et al, 1982). Thus an increased amount of TBA-RS may be considered one of the markers of radiation-induced toxicity to cells (Kappus, 1985).…”

Squalene Chemistry and Biology

“…Transfarnesal and short chain reactive aldehydes, in particular formaldehyde and malonyl dialdehyde complete the wide range of by-products generated by oxidative degradation of squalene. (De Luca et al 1996;Dennis and Shibamoto 1989;Yeo and Shibamoto 1992;Wei and Shibamoto 2007). It has been demonstrated that in physiological conditions, UVA induces oxidative degradation of squalene at a much higher extent than UVB (Ryu et al 2009).…”

“…Several in vitro studies indicate that squalene oxidation can be initiated by light exposure and both UVA and UVB radiations. Squalene is very efficient in scavenging singlet oxygen, which is generated upon excitation of photosensitizing molecules, which enhance the yield and the kinetics of oxidation by-products formation (Ohsawa et al 1984;Dennis and Shibamoto 1989;Kohno et al 1995;Matsuo et al 1983;Ryu et al 2009). Breakdown products of oxidized squalene expand the chemical variety of the oxidation by-products.…”

“…Altogether the SSL participate to the barrier function of skin in many respects. In particular, squalene covers several functions that range from the immunomodulatory, to the regulation of the skin microflora, to contrasting UV damages and skin ageing (Picardo et al 1991a;Dennis and Shibamoto 1989;Chiba et al 1999). As soon as the SG becomes fully active and excretes sebum, Proprionibacterium acnes ( P. acnes) finds the favorable conditions for the colonization of the pilosebaceous follicle.…”