Elsevier

Phytomedicine

Volume 13, Issue 8, 11 September 2006, Pages 558-563
Phytomedicine

In vitro antifungal and anti-elastase activity of some aliphatic aldehydes from Olea europaea L. fruit

https://doi.org/10.1016/j.phymed.2005.09.009Get rights and content

Abstract

Olea europaea preparations are traditionally employed in a variety of troubles, including skin infections. Olive extracts and some of their pure compounds have shown antimicrobial activity in vitro. The present study deals with the antifungal activity of some aliphatic aldehydes from olive fruit [hexanal, nonanal, (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal, (E)-2-nonenal] against Tricophyton mentagrophytes (6 strains), Microsporum canis (1 strains) and Candida spp. (7 strains). The capability of these substances to inhibit elastase, a virulence factor essential for the dermatophytes colonization, and their cytotoxicity on cultures of reconstructed human epidermis, are also described.

Aldehydes tested, inhibited the growth of T. mentagrophytes and M. canis in the range of concentration between <1.9 and 125 μg/ml; the unsaturated aldehydes showed the most broad spectrum of activity in that inhibited all strains tested. None of the aldehydes exhibited activity against Candida spp. strains. (E)-2-octenal and (E)-2-nonenal inhibited the elastase activity in a concentration-dependent manner; the anti-elastase activity suggests an additional target of the antimicrobial activity of these compounds. Aldehydes were devoid of cytotoxicity on cultures of human reconstructed epidermis.

The antifungal activity of the aldehydes from olive fruit here reported, substantiates the use of olive and olive oil in skin diseases and suggests that these natural compounds could be useful agents in the topical treatment of fungal cutaneous infections.

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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