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Aetiology and Laboratory Diagnosis
Published in Raimo E Suhonen, Rodney P R Dawber, David H Ellis, Fungal Infections of the Skin, Hair and Nails, 2020
Raimo E Suhonen, Rodney P R Dawber, David H Ellis
Dermatophytosis of the scalp, glabrous skin and nails is caused by a closely related group of fungi known as dermatophytes which have the ability to utilise keratin as a nutrient source, i.e. they have a unique enzymatic capacity (keratinase). The disease process in dermatophytosis is unique for two reasons: first, no living tissue is invaded — the keratinised stratum corneum, hair or nail is simply colonised. However, the presence of the fungus and its metabolic products typically induces an inflammatory response in the host. The type and severity of the host response are often related to the species and strain of dermatophyte causing the infection. Second, the dermatophytes are the only fungi that have evolved a dependency on human or animal infection for the survival and dissemination of their species. In fact, the common anthropophilic species (Table 1.1) are primarily parasitic on humans. They are unable to colonise other animals and have no other environmental sources. Geophilic species normally inhabit the soil where they are believed to decompose keratinaceous debris. Some species may cause infections in animals and humans following contact with soil. Zoophilic species are primarily parasitic on animals and infections may be transmitted to humans following contact with the animal host (Table 1.1). Zoophilic infections usually evoke a strong host response on the skin where contact with the infective animal has occurred, i.e. arms, legs, body or face.
Topical Formulations for Onychomycosis: A Review
Published in Andreia Ascenso, Sandra Simões, Helena Ribeiro, Carrier-Mediated Dermal Delivery, 2017
Barbara S. Gregorí Valdes, Carolina de Carvalho Moore Vilela, Andreia Ascenso, Joao Moura Bordado, Helena Ribeiro
Keratinolytic enzymes hydrolyze the keratin matrix of the nail plate, altering its barrier properties and facilitating permeation. Studies have shown that keratinase enzyme markedly enhances nail permeation [61]. This enzyme affects the surface of human nail, causing corneocytes to detach and lift off the plate corroding the surface.
Dermatophytosis
Published in Rebecca A. Cox, Immunology of the Fungal Diseases, 2020
The major cell wall constituents of dermatophytes are chitin and glucan in addition to the glycopeptides which are the major antigens. The chemical structures of glycopeptides from several dermatophytes have been analyzed in a number of studies (reviewed in Reference 90). The dermatophytes, like other fungi, have a very complicated antigenic makeup. “Trichophytin” is a name used for antigenic extracts of dermatophytes (usually Trichophyton sp.), and such preparations appear to contain a variety of antigens. Using crossed-immunoelectrophoresis, Christiansen and Svejgaard91 analyzed the antigenic structure of several of these organisms and found 35 antigens in T. rubrum, 26 in T. mentagrophytes, and 25 in E. floccosum. Most of the antigens appear to be different between the species, except for two that T. rubrum shares with the others. Since only about 17% of the dry weight of the fungi could be solubilized by their extraction procedure (homogenization in distilled water), these authors consider the numbers of antigens they found to be a minimum of those possibly present. Moser and Pollack92 carried out an immunochemical analysis on ethylene glycol extracts of T. mentagrophytes, T. rubrum, and M. canis and found that only a glycopeptide fraction containing mannopeptides has reactivity in delayed-hypersensitivity skin tests. Barker et al.93 found that extracts of T. mentagrophytes containing carbohydrates or peptides are associated with immediate or delayed skin tests, respectively. Grappel and Blank94 provided evidence from experiments using T. mentagrophytes infections in guinea pigs that the keratinases may be important antigens. They detected strong delayed-hyper-sensitivity reactivity to keratinases (particularly keratinase II) in guinea pigs that had been sensitized by a previous cutaneous infection. In addition, they detected antibodies in immunized guinea pigs which could inhibit the proteolytic activity of the keratinase.
Cinnamon (Cinnamomum zeylanicum) as an antidote or a protective agent against natural or chemical toxicities: a review
Published in Drug and Chemical Toxicology, 2018
Mahyar Dorri, Shirin Hashemitabar, Hossein Hosseinzadeh
AFB1 is an aflatoxin produced by Aspergillus flavus and A. parasiticus (Koehler et al.1975, Sun et al.2015). Cinnamaldehyde (CIN), a natural extract from Cinnamomum spp. has indicated a protective effect towards AFB1 and AFG1 via inhibiting spore germination and oxidative stress changes in A. flavus (Abd El-Aziz et al.2015, Sun et al.2015). In another work, it was revealed that cinnamon essential oil may alter the structure of cells and denaturation of the fungal growth enzymes. Cinnamon essential oil leads to the interference with the amino acid participating in germination (Abd El-Aziz et al.2015). Also another research showed that cinnamon extract has fungistatic and fungicidal activities, although the fungistatic activity of cinnamon is more potent than its fungicidal activity. The fungistatic effect of cinnamon is due to its elastase and keratinase activity inhibition. Elastase and keratinase are two extracellular enzymes affiliated with their virulence factor in A. fumigatus and Trichophyton rubrum. Aflatoxin biosynthesis is mediated mostly by oxygenases enzymes. Hence antiaflatoxigenic effect of essential oils is due to its antioxidant properties (Manso et al.2014, Kosegarten et al.2017).
In vitro and ex vivo biofilms of dermatophytes: a new panorama for the study of antifungal drugs
Published in Biofouling, 2020
Débora de Souza Collares Maia Castelo-Branco, Lara de Aguiar, Géssica dos Santos Araújo, Raissa Geovanna Pereira Lopes, Jamile de Alencar Sales, Waldemiro Aquino Pereira-Neto, Adriana de Queiroz Pinheiro, Germana Costa Paixão, Rossana de Aguiar Cordeiro, José Júlio Costa Sidrim, Raimunda Sâmia Nogueira Brilhante, Marcos Fábio Gadelha Rocha
The main pathogenic attribute of dermatophytes is their ability to degrade keratin as a nutritional source, which, in turn, has an important role in dermatophyte survivability (Gnat et al. 2018, 2020). Gnat et al. (2019), for instance, demonstrated that the keratinase activity of Trichophyton verrucosum is substrate-induced, evidencing the influence that the surrounding environment exerts on dermatophyte pathogenesis. This fact may partly explain why the biomass of biofilms grown ex vivo did not reduce after exposure to antifungal drugs, as opposed to what was observed for biofilms grown in vitro.
A novel technique to evaluate nail softening effects of different urea formulations
Published in Pharmaceutical Development and Technology, 2021
Hiep X. Nguyen, Yujin Kim, Tejas D. Kekatpure, Emily Lesica, Ajay K. Banga
In vivo nail permeation has been predicted and calculated from the results of in vitro studies using various tissue models such as avulsed human cadaver nail plates, nail clippings from healthy volunteers, and bovine hoof membranes (Mertin and Lippold 1997). Generally, the human tissues are scarce in the supply quantity as well as small in the dimension. Alternatively, animal hoof membranes have been reported to possess analogous properties to human nails (the content of keratin and release of soluble protein on incubation with keratinase) (Vignardet et al. 1999). Thus, animal hooves have been preferably alternative options to assess the permeability of topical products in vitro (Monti et al. 2005; Täuber and Müller-Goymann 2015). The results from these in vitro studies would be used to predict the behavior of the product in vivo. Nogueiras-Nieto et al. observed the similarity of the distribution of pore diameters between hoof membranes and human nails (approximately 10 µm) (Nogueiras-Nieto et al. 2011). Monti et al. employed finely sliced bovine hooves to investigate the use of ciclopirox in the treatment of onychomycosis. The authors have validated bovine hoof membranes as a reliable alternative to human nails in vitro. The membranes had the adaptability to fit conventional diffusion cells, sufficiently large dimensions, regular and flat shape, the similarity in resistance and thickness to human nail (Monti et al. 2005). Moreover, the ability to reduce the hoof membranes’ thickness allowed rapid hydration of the membranes, significantly increasing the drug transungual flux and shortening the experiment duration. The variation among the membranes was found to be low, thus, the membrane-generated data was reliable and the number of tests required was small (Monti et al. 2011).