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Biomedical subjects

A Frantz

Publications and source records attributed to A Frantz.

At least 19 recordsLinked to original sources
PubMed2006

Ecological specialization correlates with genotypic differentiation in sympatric host-populations of the pea aphid.

The pea aphid, Acyrthosiphon pisum, encompasses distinct host races specialized on various Fabaceae species, but the extent of genetic divergence associated with ecological specialization varies greatly depending on plant and geographic origins of aphid populations. Here, we studied the genetic structure of French sympatric pea aphid populations collected on perennial (pea and faba bean) and annual (alfalfa and red clover) hosts using 14 microsatellite loci. Classical and Bayesian population genetics analyses consistently identified genetic clusters mostly related to plant origin: the pea/faba bean cluster was highly divergent from the red clover and the alfalfa ones, indicating they represent different stages along the continuum of genetic differentiation. Some genotypes were assigned to a cluster differing from the one expected from their plant origin while others exhibited intermediate genetic characteristics. These results suggest incomplete barriers to gene flow. However, this limited gene flow seems insufficient to prevent ecological specialization and genetic differentiation in sympatry.

Animals↗
PubMed1999

Metabolic changes of the human donor cornea during organ-culture.

PURPOSE: To study metabolic changes of the human cornea during organ-culture. Morphological changes have been extensively studied, whereas changes in human corneal metabolism have not been investigated yet. MATERIAL AND METHODS: 106 human corneas were stored for 1, 7, 15, 18, 21 and 28 days in a closed-system under standard eyebank conditions. After storage, glucose, lactate, ATP, ADP and AMP concentrations were determined in each cornea. RESULTS: Glucose concentration decreased during the first two weeks with a minimum on day 15. ATP and ADP concentrations increased during the same period of time, but had their minimum later, on day 18. Lactate increased during the culture period up to day 21 and decreased thereafter. CONCLUSION: From these data we conclude that the human cornea recovers during organ-culture, especially during the first two weeks. The changes occurring after a fortnight might be related to the artificial culture conditions. Nevertheless, the metabolic status is better than in post-mortem corneas. The changes may be partly avoided by changing the medium after at least two weeks of organ-culture.

Adenine Nucleotides↗
PubMed1998

Boron-11 NMR of borocaptate: relaxation and in vivo detection in melanoma-bearing mice.

Longitudinal and transverse relaxation rates for the 11B resonances in sodium borocaptate (BSH) at varying concentrations were measured in undiluted horse serum in a 4.7 Tesla field. The results could be fit by a model that assumes fast exchange of the BSH molecule between a free and a bound state, using values of 0.77+/-0.7 MHz for the 11B quadrupole coupling constant and (6.3+/-0.9) x 10(-9) s for the rotational correlation time in the bound state. These results were used as a basis for assessing the requirements and limitations of quantitative determination of BSH concentrations in vivo, using 11B NMR. Surface coil 11B NMR spectroscopy was performed on a total of 14 mice injected with BSH. Some of the animals (n=9) had implanted M2R melanoma tumors grown to various sizes in the rear thigh, in which case the surface coil was placed against the tumor, whereas for the other animals (without tumor), the coil was placed against the rear thigh muscle. NMR spectra were acquired under fully relaxed conditions. The spectra were quantitated by peak integration; apparent absolute BSH concentrations were derived by comparison with spectra from a phantom with known BSH concentration, using extrapolation of the time-domain data to zero preacquisition delay. The results indicate significantly higher 11B BSH signal intensities in tumors, compared with muscle tissue, whereas the uptake and clearance kinetics were similar.

Algorithms↗
PubMed1998

A sensitive assay for the quantification of glucose and lactate in the human cornea using a modified bioluminescence technique.

BACKGROUND: Quantification of glucose and lactate concentrations in human corneal extracts has been performed using spectrophotometry. We employed a bioluminescence technique to obtain a more sensitive assay for glucose and lactate and to reduce the volume of the test sample. MATERIALS AND METHODS: The NAD(P)H bioluminescence assay (Boehringer Mannheim, Germany) was modified for glucose and lactate. Standard curves were established using a standard solution with 0.004 mM and 0.01 mM concentrations of glucose and lactate, respectively. RESULTS: Linear standard curves ranging from 0 to 200 pmol for glucose and from 0 to 250 pmol for lactate were established. The sample volume was reduced from 100 microliters to 25 microliters compared with spectrophotometry. DISCUSSION: The modified bioluminescence technique provides a highly sensitive quantification of glucose and lactate in the human cornea and thus reveals more details of the overall metabolic status of the tissue.

Aged↗
PubMed1998

[Correlation between glucose and lactate concentrations in the human cornea and in organ culture medium].

BACKGROUND: Metabolic changes of the human donor cornea during organ-culture are not at all reflected by the endothelium. Therefore metabolic investigations have become of increasing interest. It was the aim of this study to determine the correlation between glucose and lactate in storage medium and within the cornea itself and to find thereby an additional parameter for glucose metabolism during organ-culture. METHODS: Glucose and lactate were examined in 166 organ-culture medium samples as well as in 106 human corneas by enzymatical optical methods. Investigations were carried out after 1, 7, 15, 21 and 28 days of organ-culture. RESULTS: Glucose consumption was highest during the first two weeks of organ-culture. Glucose concentrations showed a good linear correlation between medium samples and the cornea (r = 0.923). The correlation coefficient for lactate was worse (r = 0.733). CONCLUSION: Glucose and lactate levels in the organ-culture medium can be used as a marker for glucose metabolism in the cornea.

Blood Glucose↗
PubMed1998

Changes in human donor corneas preserved for longer than 4 weeks.

PURPOSE: Corneas are usually stored for a maximum of approximately 30 days in European cornea banks. Although attempts are being made to prolong culture periods, data on their success are extremely limited to date. The following study was carried out to describe the capacities and limits of the established system. METHODS: Thirty-seven human corneas were stored for < or = 12 weeks under standard eye bank conditions [modified minimal essential medium (MEM), 31 degrees C, closed system]. Twenty-one fresh human corneas served as control. Both the adenylate nucleotides and the glucose and lactate concentrations were measured in the tissue (all cellular layers) by using the bioluminescence technique. The endothelial-cell densities also were determined. RESULTS: Endothelial-cell densities decreased from 2,963.4 +/- 58.7 cells/mm2 (fresh) to 2,649 cell/mm2 after 4 weeks and to 2,087 cells/mm2 after 6 weeks. Storage for periods >6 weeks led to total endothelial necrosis. Biochemical studies showed improving values during the first 4 weeks and acceptable conditions for < or = 6 weeks. CONCLUSION: From these data, we conclude that long-term organ culture in a closed system is limited to approximately 6 weeks and thereby confirm the clinical results of Früh and Böhnke.

Adenine Nucleotides↗
PubMed1997

[Energy metabolism of the human cornea in various culture systems].

BACKGROUND: There are two well known systems to culture human corneas prior to transplantation. First, corneal storage at 4 degrees C especially in Optisol medium. Second, organ-culture at physiological temperatures in a modified minimal essential medium (MEM). In the cold storage system the number of endothelial cells after storage might be overestimated because the damaged cells are not able to leave the monolayer. It has been supposed that the lack in energy recruitment is the main reason for that, but has not been proven yet. It was the purpose of this study to describe the energy status of the human cornea after storage in both systems. MATERIALS AND METHODS: 32 human corneas were investigated. They were stored for 7 days in Optisol, and for 7 days in MEM plus 1 day in MEM supplemented with 5% dextran 500 and 12 days in modified MEM plus 1 day in MEM supplemented with 5% dextran 500. The endothelial cell density (ECD) as well as the hydration were determined. Glucose, lactate, ATP, ADP and AMP were measured to reflect the energy status. RESULTS: Hydration was comparable in all three groups. ECD was slightly higher in Optisol stored corneas, although the amount of damaged cells was much higher. Optisol stored corneas showed a severe anaerobic situation, especially lacate concentrations were increased. In contrast ATP and ADP concentrations were twice as high in MEM than in Optisol stored corneas. DISCUSSION: The severe anaerobic situation in Optisol stored corneas leads to a lack in energy recruitment. This reduces the ability of cell function (mitosis) and the function of the monolayer (migration, elimination). Whether these changes are reversible after transplantation has to be determined in future.

Adenine Nucleotides↗
PubMed1997

Light-dependent oxygen consumption in bacteriochlorophyll-serine-treated melanoma tumors: on-line determination using a tissue-inserted oxygen microsensor.

Successful application of anticancer therapy, and especially photodynamic therapy (PDT) mediated by type II (PDTII) processes, depends on the oxygen content within the tumor before, during and after treatment. The high consumption of oxygen during type II PDT imposes constraints on therapy strategies. Although rates of oxygen consumption and repletion during PDTII were suggested by theoretical studies, direct measurements have not been reported. Application of a novel oxygen sensor allowed continuous and direct in situ measurements (up to a depth of 8-9 mm from the tumor surface and for several hours) of temporal variations in the oxygen partial pressure (pO2) during PDT. Highly pigmented M2R mouse melanoma tumors implanted in CD1 nude mice were treated with bacteriochlorophyll-serine (Bchl-Ser; a new photodynamic reagent) and were subjected to fractionated illumination (700 < lambda < 900 nm) at a fluence rate of 12 mW cm-2. This illumination led to total oxygen depletion with an average consumption rate of 7.2 microM(O2) s-1. Spontaneous reoxygenation (at an average rate of 2.5 microM(O2)/s) was observed during the following dark period. These rates are in good agreement with theoretical considerations (Foster et al., Radiat. Res. 126, 296, 1991 and Henning et al., Radiat. Res. 142, 221, 1995). The observed patterns of oxygen consumption and recovery during prolonged periods of light/dark cycles were interpreted in terms of vasculature damage and sensitizer clearance. The presented data support the previously suggested advantages of fractionated illumination for type II photodynamic processes.

Animals↗
PubMed1996

Employment of bioluminescence for the quantification of adenosine phosphates in the human cornea.

BACKGROUND: Quantification of adenosine phosphates in human corneal extracts has been performed using spectrophotometry. We employed the bioluminescence technique to obtain a more sensitive assay for adenosine phosphates and to reduce the volume of the test sample. METHODS: The bioluminescence assay for ATP, already known from sterility control, was modified and expanded. Standard curves were established using a standard solution with equimolar concentrations of ATP, ADP and AMP. To monitor the method, adenosine phosphates were measured in 35 human corneal extracts using both spectrophometry and bioluminescence. RESULTS: Linear standard curves ranging from 1 to 45 pmol were established. The two methods yielded comparable results despite the use of a basic dilution of 1:100 for the new technique. CONCLUSION: Bioluminescence provides a highly sensitive quantification of adenosine phosphates in the human cornea and facilitates an extremely detailed evaluation of the metabolic status of the cornea.

Adenine Nucleotides↗
PubMed1996

[Establishing human, conjunctival fibroblast cultures as a test system for evaluating ophthalmic drugs].

BACKGROUND: Chronic inflammation of the anterior eye segment caused by severe burns has to be treated by several drugs. Often it is very difficult to recognize the relationship between drug and side effects. Although the results were usually satisfying, proliferation of the conjunctival tissue was observed. Therefore the question was raised whether these proliferations might have been a side effect of the drugs. To answer this question, we established cultures of human conjunctival fibroblasts for ocular toxicity testing of drugs used in the therapy of severe eye burns. MATERIALS AND METHODS: Conjunctival fibroblasts from young donors were cultured under standard conditions (37 degrees C, 5% C02, 95% RH) in Medium 199 supplemented with 20% FCS without antibiotics. At the time of inoculation the following drugs were added: aprotinin, prednisolone, chloramphenicol and methylhydroxypropylcellulose. Cell growth was observed and growth kinetics were estimated by hemocytometer over a period of 7 days. RESULTS: The investigations of prednisolone showed the well-known dose-dependent anti-proliferative effect. The application of methylhydroxypropylcellulose resulted in decreased cell growth and in total cell detachment. Experiments with aprotinin and chloramphenicol showed no effects on the growth behaviour. The application of a drug mixture lead to similar results as in experiments with prednisolone. DISCUSSION: The presented cell-culture system is able to reproduce specific effects, especially the toxicity of ophthalmic drugs but a complex interaction of an inflammatory reaction, e.g. after severe eye burns, cannot be simulated. The network of reactions and the interaction of many substances playing an important role during this process are too complex.

Adult↗
PubMed1994

The cardiac care step-down unit at home.

Clinical pathways have proven to be the key to shortening hospital stays for cardiac patients, allowing them to move out of the hospital and back home sooner. These pathways have truly facilitated the paradigm shift from institutional to home care.

Cardiac Surgical Procedures↗