Nowadays, acne vulgaris therapies are often unsuccessful. One of the responsible factors for the formation of comedones and inflammatory lesions could be the peroxidation of squalene, a hydrocarbon representing one of the major components of human sebum. This peroxidation is increased by solar irradiation. The purpose of this work was to set up an in vivo method for the extraction and quantification of squalene from acne skin and to correlate the results with biophysical skin parameters such as sebum amount, protein content and TEWL. Healthy volunteers were used as control. The results obtained demonstrated that acne-prone skin had a major quantity of squalene, and, in the stratum corneum area, its peroxide form is present. Moreover, Spearman\'s rank correlation showed a positive correlation between sebum content and peroxide squalene and between porphyrin intensity and peroxide squalene.

We combined quantum mechanics/molecular mechanics calculations with molecular dynamics simulations to study the addition of O2 to the pentadienyl radical of arachidonic acid (AA) catalyzed by the Leu597Val and Leu597Ala mutants of rabbit 15-lipoxygenase (15-rLO). In the Leu597Val mutant, the addition of O2 to C15 of AA is the predominant path, although it reduces the C15/C11 product ratio by almost ten times with respect to the wildtype enzyme. The S stereochemistry is kept. Mutation to Ala causes just the opposite effect: regiospecificity favoring addition to C15 is somewhat sharper than that in the wildtype, but the stereochemistry is R. This is because the extra space created by the mutation to Ala is big enough for AA to move so that it can adopt an alternative binding mode, and this opens new feasible paths for the attack of O2 . So, we showed that the Leu597Ala mutant of 15r-LO works as an aspirin-acetylated cyclooxygenase-2, which makes 15-(R)- hydroperoxyeicosatetraenoic acid.

15-Lipoxygenases (15-LOs) catalyse the peroxidation reaction of arachidonic acid (AA) in mammals with remarkable regio- and stereospecificity. This positional-specific peroxidation is of paramount importance because it determines the nature and biological functions of the final metabolites generated by each LO as a result of the oxidative metabolism of AA. Although several hypotheses have been formulated concerning the regio- and stereospecificity of LOs, the molecular basis of such behaviour is still unclear. Herein, we combined quantum mechanics/molecular mechanics calculations with molecular dynamics simulations of the complete rabbit 15-LO/AA solvated model to examine the most accepted hypotheses for the regio- and stereospecificity of LOs. We have found that the clue to explain this specificity is the oxygen-targeting hypothesis through steric shielding of specific residues (mainly Leu597, Gln548 and Phe175, as well as the AA tail itself). Our deductions are based primarily on the analysis of the energy barrier heights from the oxygen addition reaction profiles.