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At least 469 records · Page 26Linked to original sources
PubMedDate not supplied

Evaluation of diabetic retinopathy by fluorophotometry. European concerted action on ocular fluorometry.

BACKGROUND: Fluorophotometric variables (permeability of the blood-retinal barrier (BRB) and blood-aqueous barrier (BAB), corneal autofluorescence, and lenticular light transmittance) are reported to correlate with the severity of diabetic retinopathy. This preliminary multicenter study was performed to measure these variables simultaneously in patients with type 2 diabetes mellitus and to assess which of these variables could be of help in evaluating diabetic retinopathy. METHODS: Eighty-two patients with type 2 diabetes and diabetic retinopathy were recruited in seven European university clinics. Each patient was investigated three times, at intervals of about one year. The investigations included fluorophotometric determination of corneal autofluorescence, lenticular light transmittance, and permeability of the BRB and BAB. Retinopathy was classified into four grades, using a simplified evaluation system based on the Modified Airlie House retinopathy classification and applied to color fundus slides of standard fields 1 and 2. RESULTS: Multiregression analyses revealed that only corneal autofluorescence and BRB permeability were correlated with the severity of diabetic retinopathy (P < 0.05). Corneal autofluorescence and BRB permeability as single variables were found to be indicative of severe nonproliferative retinopathy and proliferative retinopathy (sensitivity 100% and 86%, respectively, and specificity 65% and 85%, respectively). Combination of both variables increased specificity to 92%. CONCLUSIONS: This preliminary multicenter study shows that fluorophotometric variables can be measured simultaneously and reliably in patients with diabetes and that corneal autofluorescence and BRB permeability (individually or in combination) could be of help in detecting severe non-proliferative retinopathy and proliferative retinopathy.

Blood-Aqueous Barrier↗
PubMedDate not supplied

Development of a time-resolved fluorometry based immunoassay for the determination of canine haptoglobin in various body fluids.

A time-resolved immunofluorometric assay (TR-IFMA) was developed for the determination of haptoglobin (Hp) in canine serum. Haptoglobin was purified from canine acute phase serum by ammonium sulphate precipitation followed by gel filtration. This isolated dog Hp was used as the standard to calibrate the assay. Intra- and inter-assay coefficients of variation of the assay were, respectively, 5.7% and 16.6% at 0.51 mg/mL, 2.4% and 10.6% at 2.1 mg/mL and 10.5% and 11.9% at 32.5 mg/mL. The dilution of serum samples with high Hp concentrations resulted in linear regression equations with R2 of 0.99 and 0.97. A high correlation was found in serum Hp measurements by TR-IFMA and a commercial assay based on peroxidase activity of haemoglobin bound to haptoglobin (R2 = 0.96). The limit of detection for the TR-IFMA method was 0.002 microg/mL. The addition of fresh haemolysate to serum samples did not affect the haptoglobin concentration (P = 0.694). Statistical differences (P < 0.003) were found between healthy dogs and dogs with different pathological processes. In whole blood, Hp concentrations were much lower than in serum but closely related (R2 = 0.84) whereas saliva Hp concentrations were poorly related with serum concentrations (R2 = 0.53). However, the concentration of Hp in saliva was significantly (P < 0.039) higher in dogs with pathological processes compared to healthy dogs. The assay sensitivity was adequate to also be applied to whole blood and saliva specimens.

Animals↗
PubMed1996

Ranking of P-glycoprotein substrates and inhibitors by a calcein-AM fluorometry screening assay.

In order to compare the capacities of a variety of compounds to interfere with P-glycoprotein (Pgp) function, a novel assay was set up to work on a large screening scale. The model assay measures the capacity of parental sensitive (Par) and multidrug-resistant (MDR) cells to efflux a small fixed amount of acetoxymethyl calcein (calcein-AM) after their pretreatment with concentration ranges of known Pgp modulators. This microplate cytometry-based assay was performed with two different pairs of cell lines, the human lymphocytic leukemia CEM cells and the murine monocytic leukemia P388 cells. For a given Pgp-expressing MDR cell line, a Pgp modulator EC50 was defined as the concentration required to restore half of the calcein retention shown by similarly treated Par cells. With both MDR-P388 and MDR-CEM cells, EC50 comparisons ranked five reference Pgp modulators as follows: SDZ 280-446 > SDZ PSC 833 > cyclosporin A > verapamil > vinblastine. Further use of the MDR-CEM cells could rank 15 Pgp modulators for their capacity to interfere with calcein-AM efflux as follows: SDZ 280-446 1.9 x > SDZ PSC 833 8.3 x > cyclosporin A 3.8 x > amiodarone 1.1 x > quinacrine 1.6 x > verapamil 1.4 x > quinidine 1.1 x > vinblastine 11 x > vincristine 2 x > chloroquine > beta-lumicolchicine > or = gamma-lumicolchicine > or = colchicine > etoposide > or = doxorubicin. This calcein-AM assay should open the way for ranking large numbers of novel structures for their potential Pgp modulator properties, particularly for an efficient screening of Pgp function antagonists, but it does not allow defining whether their inhibition may be competitive or not.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1975

A pulse fluorometry study of lipoamide dehydrogenase. Evidence for non-equivalent FAD centers.

The time dependence of the fluorescence of tryptophanyl and flavin residues in lipoamide dehydrogenase has been investigated with single-photon decay spectroscopy. When the two FAD molecules in the enzyme were directly excited the decay could only be analyzed in a sum of two exponentials with equal amplitudes. This phenomenon was observed at 4 degrees C (tau-1 = 0.8 ns, tau-2 = 4.7 ns) and at 20 degrees C (tau-1 = 0.8 ns, tau-2 = 3.4 ns) irrespective of the emission and excitation wavelengths. This result reveals a difference in the nature of the two FAD centers. By excitation at 290 nm the fluorescence decay curves of tryptophan and FAD were obtained. The decays are analyzed in terms of energy transfer from tryptophanyl to flavin residues. The results, which are in good agreement with those obtained previously with static fluorescence methods, show that one of the two tryptophanyl residues within the subunit transfers its excitation energy to the flavin located at a distance of 1.5 nm.

Animals↗
PubMed1980

Pulse-fluorometry study on actin and heavy meromyosin using F-actin labelled with N-(1-pyrene)maleimide.

The single-photoelectron counting technique was used for measurement of the fluorescence decay kinetics of N-(1-pyrene)maleimide conjugated to the fast reactive cysteine of actin. The fluorescence decay curve of the labelled G-actin could not be described by a single-exponential function but by a double-exponential function. Polymerization of actin was accompanied by significant changes in the decay parameters of the two decay components. We found that the ionic strength, which plays an important role in the G-F equilibrium, scarcely affected these parameters provided that the labelled actin exists in the monomeric state. Thus it is suggested that the conformational change of actin protomer occurs at the time of association. When heavy meromyosin was added to the labelled F-actin, the decay parameter changed monotonically on increasing saturation of binding of heavy meromyosin and it levelled-off around a ratio of heavy meromyosin:actin of 0.5 mol/mol. Decay parameters under the influence of heavy meromyosin had values intermediate between those observed for the labelled G-actin and for the labelled F-actin. Therefore, it is suggested that binding of heavy meromyosin to F-actin alters the conformation of actin protomer towards that similar to G-actin.

Actins↗
PubMed1993

Comparison of Nucleic Acid Hybridization and Fluorometry for Measurement of the Relationship between RNA/DNA Ratio and Growth Rate in a Marine Bacterium.

Continuous culture of Pseudomonas stutzeri Zobell, a marine denitrifying bacterium, was used to determine the relationship between growth rate and nucleic acid content. The trend of decreasing RNA content with decreasing growth rate, well known for enteric organisms, was found to occur in P. stutzeri Zobell as well, even at very long generation times such as those thought to occur in the oligotrophic ocean. When assayed by ethidium bromide fluorescence, the total RNA/DNA ratio was linear for generation times between 6 and 60 h. We also developed a 200-bp nucleic acid probe (with species-specific potential) for a portion of the 23S rRNA gene of P. stutzeri Zobell, which was used to quantify rRNA and rDNA by hybridization in the same continuous cultures. The rRNA/rDNA ratio also exhibited a decrease with decreasing growth rate, but the relationship, although significant, was not simply linear. The sensitivity and accuracy of the two methods are compared, and the potential for species specificity in future hybridizations is discussed.

Journal Article↗