Biomedical subjects

H Kamp

Publications and source records attributed to H Kamp.

9 recordsLinked to original sources

PubMed2006

Effect of 5alpha-dihydrotestosterone and testosterone on apoptosis in human dermal papilla cells.

Pathogenetic mechanisms in androgenetic alopecia are not yet fully understood; however, it is commonly accepted that androgens like testosterone (T) and 5alpha-dihydrotestosterone (5alpha-DHT) inhibit hair follicle activity with early induction of the catagen. Thus, we investigated the influence of T and 5alpha-DHT on proliferation, cell death and bcl-2/bax expression in cultured dermal papilla cells (DPC) from nonbalding scalp regions of healthy volunteers. T and 5alpha-DHT induced apoptosis in DPC in a dose-dependent and time-related manner; in addition a necrotic effect due to T at 10(-5) M was found. Interestingly, bcl-2 protein expression was decreased in T- and 5alpha-DHT-treated cells, leading to an increase in the bax/bcl-2 ratio. In addition, T and 5alpha-DHT induced proteolytic cleavage of caspase 8 and inhibited proliferation of DPC at 10(-5) M. High concentrations of T and 5alpha-DHT were needed to induce apoptotic effects in DPC. These data suggest that DPC from nonbalding scalp regions do have the capacity to undergo apoptosis, but need a high androgen stimulus. The present study provides an interesting new pathogenetic approach in androgenetic alopecia.

Apoptosis↗

PubMed2005

Antifungal effect of 5-aminolevulinic acid PDT in Trichophyton rubrum.

In the present investigation, we have shown for the first time that the onychomycosis-inducing dermatophyte Trichophyton rubrum was able to metabolize 5-aminolevulinic acid (ALA) to protoporphyrin IX (PpIX) in liquid culture medium. We have established and optimized the culture conditions and could show the typical PpIX-induced red fluorescence which was evaluated qualitatively by Wood's light examination and fluorescent microscopic analysis. The optimum concentration of ALA was in the range of 1-10 mmol l(-1). If used in higher concentrations, ALA leads to a significantly reduced growth rate and absence of PpIX formation due to highly acidic conditions. The first observation of red fluorescence was detected between 10 and 14 days poststimulation with ALA, increasing thereafter. Fluorescent microscopic examinations demonstrated that formation of PpIX was restricted to selected parts of the fungal mycelium. Repeated application of ALA in order to achieve the highest formation of PpIX in T. rubrum failed, probably due to the sustained low pH values. ALA treatment and irradiation of T. rubrum clearly demonstrated the growth-inhibiting effect of ALA PDT, either leading to reduced numbers of colonies or reduced diameters of single fungal colonies. Summarizing our results, ALA PDT might be a promising approach in the reduction of T. rubrum colonization in onychomycosis.

Aminolevulinic Acid↗

PubMed2003

Regulation of PDGF and PDGF receptor in cultured dermal papilla cells and follicular keratinocytes of the human hair follicle.

Platelet-derived growth factor (PDGF) is a potent mitogenic factor for many cell types and has been shown to be important in follicular development and vasculogenesis. In this study, we examined the expression pattern of both PDGF factors and their corresponding receptors in mesenchyme-derived dermal papilla cells (DPCs) and epithelial follicular keratinocytes (FKs). Both types of PDGF receptors are expressed in FKs, whereas DPCs only express PDGF receptor beta on the protein level, a finding also seen in whole organ cultures. By examining the expression of PDGF ligands, we were able to show that cultured FKs synthesize both PDGF-A and PDGF-B, whereas, DPCs only express PDGF-A. As immunomodulatory cytokines were shown to affect hair growth, we investigated the effects of IL-1beta, IL-4, TNF-alpha, TGF-beta and IFN-gamma on the expression levels of PDGF factors in cultured DPCs and FKs. Interestingly, we could show a significant down-regulatory effect by catagen-inducing cytokines like IL-1beta or IFN-gamma, suggesting a possible involvement of PDGF signaling in the induction of catagen. The question concerning the latter hypothesis remains to be elucidated in further studies on whole organ cultures.

Autocrine Communication↗

PubMed1995

Prototype theory and compositionality.

Osherson and Smith (1981, Cognition, 11, 237-262) discuss a number of problems which arise for a prototype-based account of the meanings of simple and complex concepts. Assuming that concept combination in such a theory is to be analyzed in terms of fuzzy logic, they show that some complex concepts inevitably get assigned the wrong meanings. In the present paper we argue that many of the problems O&S discovered are due to difficulties that are intrinsic to fuzzy set theory, and that most of them disappear when fuzzy logic is replaced by supervaluation theory. However, even after this replacement one of O&S's central problems remains: the theory still predicts that the degree to which an object is an instance of, say, "stripped apple" must be less than or equal to both the degree to which it is an instance of "striped" and the degree to which it is an instance of "apple", but this constraint conflicts with and the degree to which it is an instance of "apple", but this constraint conflicts with O&S's experimental results. The second part of the paper explores ways of solving this and related problems. This leads us to suggest a number of distinctions and principles concerning how prototypicality and other mechanisms interact and which seem important for semantics generally. Prominent among these are (i) the distinction between on the one hand the logical and semantic properties of concepts and on the other the linguistic that between concepts for which the extension is determined by their prototype and concepts for which extension and prototypicality are independent.

Attention↗

PubMed1973