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Biomedical subjects

A Fahr

Publications and source records attributed to A Fahr.

63 records · Page 4Linked to original sources
PubMed1981

Transmembranous incorporation of photoelectrically active bacteriorhodopsin in planar lipid bilayers.

Various methods to incorporate bacteriorhodopsin in black lipid membranes are reported. Both purple membrane patches and monomeric bacteriorhodopsin were used as starting material. The incorporation of bacteriorhodopsin into planar lipid bilayers was achieved by the following methods. (i) Purple membrane patches were transferred from water to solutions of lipids in n-alkanes. Black membranes were formed from such organic suspensions. (ii) Lipid layers containing solvent and purple membranes were spread on an air/water interface. These layers were used to form planar bilayers. (iii) Vesicles containing purple membranes or monomeric bacteriorhodopsin were spread on an air/water interface and, from the resulting layer, bilayers were formed. On illumination, steady-state photocurrents were observed in all three cases, indicating that these methods lead to functional transmembranous integration of the protein in the planar black lipid membrane. The influence of an applied electric field on the pumping process was studied on membranes formed by using method i. At approximately 200 mV, the photocurrent tends to zero. Furthermore, it was possible to make planar lipid bilayers photoelectrically active by adding vesicles containing monomeric bacteriorhodopsin to the bathing solution. Because, in this case, only transient photocurrents were observed, it can be concluded that the vesicles are attached to but not fused with the black lipid membrane.

Bacteriorhodopsins↗
PubMedDate not supplied

Combined transductional and transcriptional targeting of melanoma cells by artificial virus-like particles.

BACKGROUND: Artificial virus-like particles (AVPs) represent a novel type of liposomal vector resembling retroviral envelopes. AVPs are serum-resistant and non-toxic and can be endowed with a peptide ligand as a targeting device. The vitronectin receptor, alphavbeta3-integrin, is commonly upregulated on malignant melanoma cells. In the present study we investigated whether AVPs carrying cyclic peptides with an RGD integrin binding motif (RGD-AVPs) are suitable for the specific and efficient transduction of human melanoma cells. METHODS: Plasmid DNA was complexed with low molecular weight non-linear polyethyleneimine and packaged into anionic liposomes. Transduction efficiencies were determined after transient transfection of different cell lines in serum-free medium using green fluorescent protein or luciferase reporter genes. RESULTS: We demonstrated that RGD-AVPs transduced human melanoma cells with high efficiencies of > 60%. Efficient transduction was clearly dependent on the presence of the cyclic RGD ligand and was selective for melanoma cells. The specificity of the vector system could be further enhanced by using the melanocyte-specific tyrosinase promoter to drive transgene expression. CONCLUSION: Our findings suggest that the AVP technology is a useful approach for generating highly efficient and specific non-viral vectors for melanoma targeting, in particular in a setting of combined transductional and transcriptional targeting.

Amino Acid Sequence↗
PubMedDate not supplied

A new colloidal lipidic system for gene therapy.

A novel type of liposomal vector for gene therapy is described (Artificial Virus Particles; AVPs). This vector is based on the composition of retroviral envelopes, serum-resistant and non-toxic and smaller than 200 nm in size. The DNA is condensed using low molecular weight branched PEI. Equipment of these particles with a cyclic RGD peptide ligand as targeting device renders them selective for tumor endothelial and melanoma cells expressing high levels of alphavbeta3-integrins, and allows for an efficient delivery of the enclosed genetic material. The specificity of the vector system for melanoma cells could be further improved by using a melanocyte-specific tyrosinase promoter to drive transgene expression.

Cell Separation↗
PubMedDate not supplied

Treatment of alopecia areata in the DEBR model using Cyclosporin A lipid vesicles.

Alopecia areata (AA) is a chronic cutaneous disease with a suspected autoimmune origin. We evaluated the efficacy of 0.5% Cyclosporin A (CyA) in a topically applied liposomal formulation as a potential treatment for AA using the Dundee Experimental Bald Rat (DEBR) model. The vehicle consisted of liposomes (75% phosphatidylcholine, 5% lysophosphatidylcholine, 5% sterol, natural oils) of 10% wt. in ethanol with and without 2% wt. terpenes (d-limonene: citral: cineole, 10:45:45) as a penetration enhancer (PE). Fifteen DEBR were allocated to 3 groups of 5. Groups I, II and III received CyA vesicles with PE, CyA vesicles without PE, and CyA in ethanol respectively. All rats were treated twice a day for 6 weeks within a 4 cm2 area on one bald flank with CyA while the contralateral flank received an equivalent control formulation. Rats in group I exhibited visible hair regrowth on the drug treated site after one week of drug application. Group II rats had visible hair regrowth by the end of the second week. The hair growth was progressive and reached a maximum density at the site of application after six weeks in both groups. Histological examination revealed a reduced inflammatory infiltrate and improved hair follicle morphology within the drug treated area as compared to the contralateral vehicle treated skin. Group III rats showed neither visible signs of hair growth nor reduction of hair follicle inflammation. The results of this proof of concept preliminary study suggest that CyA vesicle formulations with and without PE have promising potential as a topical treatment for AA in humans.

Administration, Cutaneous↗
PubMedDate not supplied

Mechanisms of hepatic transport of cyclosporin A: an explanation for its cholestatic action?

The hepatic transport of the immunosuppressive Cyclosporin A (CyA) was studied using liposomal phospholipid membranes, freshly isolated rat hepatocytes and bile canalicular plasma membrane vesicles from rat liver. The Na(+)-dependent, saturable uptake of the bile acid 3H-taurocholate into isolated rat liver cells was apparently competitively inhibited by CyA. However, the uptake of CyA into the cells was neither saturable, nor temperature-dependent nor Na(+)-dependent, nor could it be inhibited by bile salts or CyA-derivatives, indicating passive diffusion. In steady state depolarization fluorescence studies, CyA caused a concentration-dependent decrease of anisotropy, indicating a membrane fluidizing effect. Ion flux experiments demonstrated that CyA dramatically increases the permeability of Na+ and Ca2+ across phospholipid membranes in a dose- and time-dependent manner, suggesting a iontophoretic activity that might have a direct impact on cellular ion homeostasis and regulation of bile acid uptake. Photoaffinity labeling with a [3H]-labeled photolabile CyA-derivative resulted in the predominant incorporation of radioactivity into a membrane polypeptide with an apparent molecular weight of 160,000 and a minor labeling of polypeptides with molecular weights of 85,000-90,000. In contrast, use of a photolabile bile acid resulted in the labeling of a membrane polypeptide with an apparent molecular weight of 110,000, representing the bile canalicular bile acid carrier. The photoaffinity labeling as well as CyA transport by canalicular membrane vesicles were inhibited by CyA and the p-glycoprotein substrates daunomycin and PSC-833, but not by taurocholate, indicating that CyA is excreted by p-glycoprotein. CyA uptake by bile canalicular membrane vesicles was ATP-dependent and could not be inhibited by taurocholate. CyA caused a decrease in the maximum amount of bile salt accumulated by the vesicles with time. However, initial rates of [3H]-taurocholate uptake within the first 2.5 min remained unchanged at increasing CyA concentrations. In summary, the data indicate that CyA does not directly interact with the hepatic bile acid transport systems. Its cholestatic action may rather be the result of alterations in membrane fluidity, intracellular effects and an interaction with p-glycoprotein.

Affinity Labels↗