sorbinil and quercitrin

Aldose reductase (alditol:NADP+ 1-oxidoreductase, EC 1.1.1.21) has been partially purified from human erythrocytes by DEAE-cellulose (DE-52) column chromatography. This enzyme is activated severalfold upon incubation with 10 microM each glucose 6-phosphate, NADPH, and glucose. The activation of the enzyme was confirmed by following the oxidation of NADPH as well as the formation of sorbitol with glucose as substrate. The activated form of aldose reductase exhibited monophasic kinetics with both glyceraldehyde and glucose (Km of glucose = 0.68 mM and Km of glyceraldehyde = 0.096 mM), whereas the native (unactivated) enzyme exhibited biphasic kinetics (Km of glucose = 9.0 and 0.9 mM and Km of glyceraldehyde = 1.1 and 0.14 mM). The unactivated enzyme was strongly inhibited by aldose reductase inhibitors such as sorbinil, alrestatin, and quercetrin, and by phosphorylated intermediates such as ADP, glycerate 3-phosphate, glycerate 1,3-bisphosphate, and glycerate 2,3-trisphosphate. The activated form of the enzyme was less susceptible to inhibition by aldose reductase inhibitors and phosphorylated intermediates.

Topics: Aldehyde Reductase; Diabetes Mellitus; Enzyme Activation; Erythrocytes; Glucose; Glyceraldehyde; Humans; Imidazoles; Imidazolidines; Isoquinolines; Kinetics; NADP; Quercetin; Sorbitol; Sugar Alcohol Dehydrogenases

The tricyclic ring structure of several of the aldose reductase inhibitors indicates that they could be detected by optical spectroscopy in certain ocular tissues. Four of these compounds (Quercetin, Quercitrin, AY22-284, and Sorbinil) were investigated with respect to their UV absorption, fluorescence, and phosphorescence characteristics. All absorb in the UV wavelength and have measurable fluorescence (room temperature) and phosphorescence characteristics (77 K). The phosphorescence characteristics were utilized to monitor for the presence of Quercetin, Quercitrin, and AY22-284 in rat, rabbit, and human lenses incubated with each of the inhibitors. Following IP injection, rat and rabbit lenses were removed and subjected to phosphorescence spectroscopy for these three reagents. AY22-284 gave the sharpest and clearest phosphorescence spectra with emission wavelengths well removed from intrinsic lens phosphorescence. It can be detected in the extracted ocular lens within 30 minutes after in vivo IP administration, as well as in vitro lens incubations. The spectral data correlate well with aldose reductase inhibitor levels in such lenses as measured by a biochemical technique. Similar data were obtained with Quercitrin. Sorbinil was best monitored by fluorescence spectroscopy and could be detected in the lens following in vivo administration, as well as in vitro lens incubations.

Topics: Aldehyde Reductase; Animals; Imidazoles; Imidazolidines; In Vitro Techniques; Isoquinolines; Lens, Crystalline; Quercetin; Rabbits; Rats; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Sugar Alcohol Dehydrogenases

The susceptibility of human lens aldose reductase (HLAR), human placental aldose reductase (HPAR), and rat lens aldose reductase (RLAR) to inhibition by 10 structurally diverse inhibitors is compared. Significant differences in the susceptibility of these enzymes was observed; however, no trends could be predicted. In general, HPAR appeared to be less susceptible to inhibition than either HLAR or RLAR, with the susceptibility of HLAR being more similar to RLAR than to HPAR. These findings indicate that the evaluation of aldose reductase inhibitors for potential clinical use may require the use of human aldose reductase from the appropriate target tissue.

Topics: Aldehyde Reductase; Animals; Cataract; Chromones; Female; Humans; Imidazoles; Imidazolidines; Isoquinolines; Lens, Crystalline; Placenta; Pregnancy; Quercetin; Rats; Sugar Alcohol Dehydrogenases; Sugar Alcohols