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Biomedical subjects

W Schmehl

Publications and source records attributed to W Schmehl.

10 recordsLinked to original sources
PubMed1989

[Absorption and fluorescence spectrometry measurement of intraocular lenses].

Light absorption and fluorescence measurements can be used to detect accumulations of small molecules in intraocular lenses (IOLs). It was shown that HEMA IOLs can store and to some extent release a variety of drugs and fluorescein. PMMA and silicone IOLs, however, do not have this characteristic. UV-blocking IOLs absorb UV light completely. The absorption limit varies between 390 and 410 nm, depending on the make. Neither absorption nor fluorescence response were affected by exposure to UV light or heat.

Acebutolol↗
PubMed1989

[Natural fluorescence of nuclear cataract lenses and melanomas of the eye].

For various reasons, it is desirable to have an objective cataract classification system that does not depend on either the opinion of the physician or the patient. Since both highly molecular protein aggregates and chromophores are formed in cataractous lenses, which fluoresce under suitable stimulation, we have developed a fluorescence apparatus that illuminates the lens with five monochromatic wavelengths between 350 and 500 nm in situ. The fluorescence spectrum is recorded up to 100 ms with an optical multi-channel analyzer. This fluorescence method is non-invasive and does not harm the eye; it also uses the native fluorophore. The set of fluorescence spectra obtained by this method describes the condition of the cataractous lens both quantitatively and qualitatively. Because of the sensitivity of the method, it can also be used to assess the disease objectively in the early stages and to test and determine the effectiveness of anti-cataract drugs. Another use was discovered by using the fluorescence measurements for the diagnosis of malignant melanomas. With this equipment, melanomas in the eye and the surrounding area can be diagnosed both rapidly and precisely.

Cataract↗
PubMed1986

The importance of SH-containing substances for red blood cells in acute myeloic leukemia.

Electron spin resonance (ESR) spectra of lyophilized erythrocytes obtained from patients with acute myeloid leukemia (AML) show, in comparison to controls, a characteristic change especially in the low-field region of the spectrum concomitant with a reduction of the spin concentration. This effect can be simulated by addition of SH-containing substances (e.g. reduced glutathione or cysteine) to healthy erythrocytes. S-S containing compounds exhibit no effect. Since SH-containing substances can hardly permeate plasma membranes, the membrane surface seems to be defective in the case of "AML" erythrocytes. Furthermore, it can be concluded that the concentration of SH-containing substances, such as cysteine, is increased in the plasma of AML-patients, which could be confirmed by HPLC-measurements. In the case of a successful treatment of the patients with alexan, daunoblastin, and thioguanine the spin concentration increased again and the resulting ESR spectrum is very similar to the control spectrum. It should be pointed out, that the ascorbic acid concentration is very low in both plasma and erythrocytes of AML patients.

Ascorbic Acid↗
PubMed1986

[Significance of fluorescence spectra for the evaluation of lens opacities].

The fluorescence spectra of nucleus and cortex material from human lenses obtained as a result of extracapsular cataract extraction were observed. With advancing cataract formation the fluorescence spectra changed in a very characteristic way. The changes in ascorbic acid were compared with those caused by cataract development. Clinical application of corresponding measuring instruments would appear to make sense.

Adult↗
PubMed1986

Influence of metal ions on the transport of ascorbate across membranes.

The effect of Fe2+, Cu2+, Ca2+, and Mg2+ on the permeation of ascorbate across membranes of dipalmitoyllecithin (DPPC) vesicles was investigated. As in previous experiments, the spin label I (1,14) was used for monitoring this transport. While Mg2+ and Ca2+ exerted a small effect only, Fe2+ and Cu2+ increased considerably the reduction of the spin label. In the case of Fe2+, this is not only due to a higher permeation rate of ascorbate but is also caused by a permeation of Fe2+. As a matter of fact, the largest reduction of the spin label was obtained if Fe2+ alone was added to the spin labelled DPPC solution. The reduction of the spin label seems to depend on the redox potentials of the constituents.

Ascorbic Acid↗
PubMedDate not supplied

Interaction between spin labels and DPPC vesicles.

1H NMR studies on DPPC vesicles labeled with the spin labels (1,14) or (12,3) have shown that both of the spin labels influence the fatty acid side chains as well as the choline head groups. The spin label (12,3) affects, naturally, the head groups stronger than the spin label (1,14), while the reversed effect can be observed at the side chains. This effect progresses with time after vesicle preparation and is fully developed after about 24 h. Addition of Na-ascorbate, at this time, seems to reverse the effect indicating a stabilizing effect of the vitamin on the membrane. These results could be confirmed by ESR investigations according to which the high-field signal seems to be indicative for changes occurring at the side chains, while the low-field signal seems to reflect modifications of the head groups. Since the spin label (1,14) affects considerably the head groups at temperatures less than 6 degrees C, in which case the spectrum is very similar to that obtained with spin label (12,3) at 24 degrees C, one might conclude that there might be a phase transition in regard to the head groups.

1,2-Dipalmitoylphosphatidylcholine↗