In vitro antifungal and anti-elastase activity of some aliphatic aldehydes from Olea europaea L. fruit
Introduction
Olea europaea L. (Oleaceae) preparations have been used widely in folk medicine in European Mediterranean area, Arabia peninsula, India and other tropical and subtropical regions, as diuretic, hypotensive, emollient and for urinary and bladder infections (Samova et al., 2003); they are also employed in the treatment of skin diseases (Elkhalifa, 2002).
In a recent open pilot study olive oil mixed with honey and beeswax showed to be effective, after topical application, in the treatment of skin fungal infections; clinical response was obtained in 86% of patients with Pityriasis versicolor, 78% of patients with Tinea cruris and in 75% of patients with Tinea corporis (Al-Waili, 2004). The same preparation resulted also effective in reducing the symptoms of diaper dermatitis and eradicated Candida albicans from 50% of culture-positive patients during a 7-day trial (Al-Waili, 2005).
Several investigations deal with the ability of O. europaea extracts or their pure components to inhibit or delay the growth of microorganisms. An olive leaf water extract was tested against bacteria and fungi: the extract killed almost all bacteria while dermatophytes were inhibited following a 3-day exposure and C. albicans was killed following a 24 h (Markin et al., 2003).
Oleuropein and hydroxytyrosol, secoiridoides contained in olive and olive oil, showed antimicrobial activity on ATCC and clinical isolated bacteria responsible for intestinal or respiratory tract infections in man. In particular, oleuropein inhibited the growth of Salmonella spp., Vibrio spp. and Staphylococcus aureus with minimum inhibitory concentration (MIC) between 62.5 and 125 μg/ml for ATCC strains and between 31.25 and 250 μg/ml for clinical isolates. Hydroxytyrosol, derived from oleuropein by enzymatic hydrolysis, showed a more broad spectrum and a higher potency in that inhibited also Haemophilus influenzae and Moraxella catharralis; its MIC values were between 0.24 and 7.85 μg/ml for ATCC strains and between 0.97 and 31.25 μg/ml for clinical isolates (Bisignano et al., 1999). Furthermore, oleuropein showed activity against several species of Mycoplasma (Furneri et al., 2002).
Noteworthy is the activity of some aldehydes, volatile flavor components of olive fruit and oil, against different fungal and bacterial strains. Kubo et al. (1995) described the antimicrobial activity of long chain saturated and unsaturated aldehydes from olive fruit against a broad spectrum of food-borne microfungal and bacteria strains; among the microorganisms tested, fungi were the most sensitive. This activity is of particular interest since most of plant secondary metabolites show in general more potent activity against Gram-positive bacteria than against fungi. More recently, Bisignano et al. (2001) described the activity of some of these compounds against a number of standard bacteria strains that may be causal agents of human infections. The results obtained pointed out that unsaturated aldehydes have a broad antimicrobial spectrum and show similar activity against Gram-positive and Gram-negative bacteria. It has been hypothesized that these phytochemicals act both on the plasmatic membrane, by perturbating its lipidic fraction, and on intracellular targets (Trombetta et al., 2002; Kubo et al., 2003).
Finally, α, β-unsaturated aldehydes for their antimicrobial properties are considered to be involved in the resistance of olive to microbe and insect attack (Kubo and Hanke, 1985).
The current study was focused on the antifungal activity of some aliphatic aldehydes from olive fruit against Tricophyton mentagrophytes and Microsporum canis, dermatophytes responsible for infection of keratinized tissue, and Candida spp. All microorganisms used, were also examined for their capability of producing elastase, a serine proteinase enzyme that hydrolytically degrades elastin. Elastase together with other proteolytic enzymes, enables microorganisms to invade and subsequently disseminate through the Stratum corneum (Muhsin et al., 1997); for this reason the aliphatic aldehydes were also tested for their ability to inhibit elastase activity. Finally, the cytotoxicity of tested substances on cultures of reconstructed human epidermis (RHE) was evaluated to assess their tolerability after topical application.
Section snippets
Substances
Hexanal (98%), nonanal (95%), (E)-2-hexenal (⩾98%), (E)-2-heptenal (97%), (E)-2-octenal (94%) and (E)-2-nonenal (97%) were obtained from Aldrich (Milan, Italy). Aldehydes were dissolved in dimethyl sulfoxide (DMSO). Sodium dodecyl sulfate (SDS), Phosphate buffer solution (PBS), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT), MCDB 153 medium, Elastin-Congo red, Elastin and Pancreatic Porcin Elastase type II were obtained from Sigma (St. Louis, MO, USA), phenylmethylsulfonyl
Antifungal activity
In our experiments the aldehydes investigated showed a different spectrum of antimicrobial activity (Table 1); in particular hexanal and nonanal inhibited the growth of T. mentagrophytes 7 (MIC 3.9 μg/ml and 15.6 μg/ml respectively) and T. mentagrophytes 61 (MIC 125 μg/ml and <1.9 μg/ml, respectively). Nonanal was also active against T. mentagrophytes 13 and M. canis 70 at the concentrations of <1.9 and of 3.9 μg/ml, respectively. The other aldehydes inhibited all the dermatophytes tested with MIC
Discussion
The present study was aimed to assess the antifungal activity of some aldehydes from O. europaea, namely hexanal and nonanal (saturated), (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal and (E)-2-nonenal (unsaturated).
The aldehydes from olive exhibited a significant antifungal activity against Tricophyton mentagrophytes and Microsporum canis strains. The unsaturated ones showed to be active against all dermatophytes tested with MIC starting from <1.9 μg/ml; particularly (E)-2-hexenal and
Acknowledgments
Dr. Lucia Battinelli was supported by the “Enrico and Enrica Sovena” Foundation (Italy).
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2022, Biomedicine and PharmacotherapyCitation Excerpt :E-2-heptanal (2) was found to be the least specific for the tested fungi, with MIC values below 1.9 µg/mL for T. mentagrophytes 7, 13, and 61. Shortening the aliphatic chain in (E)− 2-heptanal (2) by one carbon atom leads to the formation of compound 1, which exhibits antifungal activity against all tested microorganisms, with MIC values ranging from 15.6 to 62.5 µg/mL [56]. Saturated aldehydes, such as hexanal (5) and nonanal (6), show a narrow spectrum of action compared with those of unsaturated aldehydes (1–4).