Tissue distribution and biotransformation of zopolrestat, an aldose reductase inhibitor, in rats

Zopolrestat (Alond) is a new drug that is being evaluated as an aldose reductase inhibitor for the treatment of diabetic complications. 14C-labeled zopolrestat was orally administered to rats for a tissue distribution study and a bile duct cannulation metabolism study. Tissue samples from the distribution study were analyzed by complete oxidation and liquid scintillation counting. Urine and bile samples from the bile duct cannulation study were analyzed by microbore HPLC, with simultaneous radioactivity monitoring and atmospheric pressure ionization tandem mass spectrometry. The mass balance in the distribution study demonstrated that the greatest exposure (AUC0-infinity) occurred in the liver, followed by the ileum and large intestine. The time of maximal plasma concentrations for nearly all tissues was 4 hr after the dose, and the half-life of radioactivity in most tissues (8-10 hr) was similar to the half-life in plasma. For the bile duct-cannulated rat study, most of the radioactivity was recovered in the bile, indicating that biliary excretion is a major route of elimination of zopolrestat and its metabolites in rats. Numerous oxidative metabolites, as well as phase II conjugates, were identified in the bile and urine samples. Acyl glucuronides of zopolrestat and unchanged drug accounted for >85% of biliary radioactivity, whereas unchanged drug and degradation products of glutathione conjugates were identified as the major urinary metabolites.     

Tolerance and pharmacokinetics of single-dose atorvastatin, a potent inhibitor of HMG-CoA reductase, in healthy subjects

Tolerance and pharmacokinetics after single-dose administration of atorvastatin, an investigational inhibitor of HMG-CoA reductase, were examined in 22 healthy volunteers in a three-period, partially-blinded study. Participants received capsule and solution doses of atorvastatin (0.5 to 120 mg) and placebo at weekly intervals. Atorvastatin was well tolerated at doses as high as 80 mg. The adverse event profile was similar after administration of atorvastatin capsules and placebo. Atorvastatin solution was slightly less well tolerated. The most common side effect after administration of capsules and solution was headache, followed by sporadic reports of diarrhea, flatulence, and nausea. At the 120-mg solution dose, one participant experienced mild, transient restlessness, euphoria, and mental confusion that were considered to be dose-limiting side effects. Mean concentrations of atorvastatin, maximum concentration (Cmax), and area under the concentration-time curve from time 0 to the time of the last detectable concentration (AUCo-tldc) increased with increasing dose. Plasma elimination half-life (t1/2) ranged from 14.7 to 57.6 hours. The bioavailability of atorvastatin capsules was similar to that of solution. These results suggest that atorvastatin is well tolerated after single doses as high as 80 mg, and may require administration only once daily.     

Single- and multiple-dose pharmacokinetics of riluzole in white subjects

Riluzole is a novel neuroprotective agent that has been developed for the treatment of amyotrophic lateral sclerosis. A series of studies was undertaken to establish its pharmacokinetics on single- and multiple-dose administration in young white male volunteers. The mean absolute oral bioavailability of riluzole (50-mg tablet) was approximately 60%. Maximum plasma concentration (Cmax) and area under the concentration-time curve (AUC) values were linearly related to dose for the range studied. Cmax occurred at 1.0 hour to 1.5 hours after administration. Plasma elimination half-life appeared to be independent of dose. After repeated administration of 100 mg riluzole for 10 days, some intraindividual variability in bioavailability was seen. A high-fat meal significantly reduced the rate (tmax = 2 hours compared with 0.8 hours; Cmax = 216 ng.mL-1 compared to 387 ng.mL-1) and extent of absorption (AUC = 1,047 ng.hr.mL-1 versus 1,269 ng.hr.mL-1). With multiple-dose administration, riluzole showed dose-related absorption, although the terminal plasma half-life was prolonged slightly. Steady-state plasma concentrations were achieved within 5 days. Steady-state trough plasma concentrations were significantly higher with a 75-mg dose twice daily than with a 50-mg dose three times daily, although AUC values did not differ.     

Molecular modeling studies of the binding modes of aldose reductase inhibitors at the active site of human aldose reductase

Molecular modeling studies using the CHARMM method have been conducted to study the binding modes of aldose reductase inhibitors at the active site of aldose reductase. The energy minimized structures of aldose reductase with six structurally diverse inhibitors (spirofluorene-9,5'-imidazolidine-2',4'-dione (1), 9-fluoreneacetic acid (2), AL1576 (3), 2,7-difluoro-9-fluoreneacetic acid (4), FK366 (5), and Epalrestat (9)) indicate that the side chains of Tyr48, His110, and Trp111 can form numerous hydrogen bonds with either the carboxylate or the hydantoin group of the inhibitors while the side chains of Trp20, Trp111, and Phe122 are positioned to form aromatic-aromatic interactions. Of the three residues (Tyr 48, His 110, and Trp 111) that can form hydrogen bonds with the ionized portion of aldose reductase inhibitors, protonated His110 appears to play an important role in directing charged inhibitors to bind at the active site through charge interaction. Based on the binding mode of the inhibitors and their observed inhibitory activities, pharmacophore requirements for aldose reductase inhibitors are discussed.     

Time- and dose-dependent pharmacokinetics of L-754,394, an HIV protease inhibitor, in rats, dogs and monkeys

L-754,394 is a potent and specific inhibitor of the HIV-1 encoded protease that is essential for the maturation of the infectious virus. The drug exhibited dose-dependent kinetics in all species studied (rat, dog and monkey); the apparent clearance decreased when the dose was increased. However, the dose-dependency cannot be explained by Michaelis-Menten kinetics. L-754,394 in plasma declined log-linearly with time, but with an apparent half-life that increased with dose. The apparent terminal half-life of L-754,394 in rats increased from 20 min at 0.5 mg/kg i.v. to 118 min at 10 mg/kg i.v. Furthermore, L-754,394 exhibited time-dependent pharmacokinetics. After chronic i.v. doses for 7 days (1 mg/kg/dose/day), the apparent clearance of L-754,394 in rats decreased from 87 ml/min/kg after the first dose to 25 ml/min/kg after the last dose. Similar results were observed in dogs and monkeys. In vitro spectral studies indicated that approximately 40 to 60% of the content of cytochrome P-450 was inactivated when L-754,394 (10 microM) was incubated with rat, dog and monkey liver microsomes in the presence of NADPH. Little or no inactivation of cytochrome P-450 was observed when either NADPH or L-754,394 was omitted. In addition, L-754,394 selectively inhibited CYP 2C11-dependent testosterone 2 alpha- and 16 alpha-hydroxylase activity and CYP 3A1/2-dependent testosterone 6 beta-hydroxylase activity, but not CYP 2D1/2-dependent bufuralol 1'-hydroxylase activity nor CYP 1A2-dependent phenacetin O-deethylase activity in rat liver microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modification of aldose reductase by S-nitrosoglutathione

Kinetic and structural changes in recombinant human aldose reductase (AR) due to modification by S-nitrosoglutathione (GSNO) were investigated. Incubation of the enzyme with 10-50 microM GSNO led to a time- and concentration-dependent inactivation of the enzyme, with a second-order rate constant of 0.087 +/- 0.009 M-1 min-1. However, upon exhaustive modification, 30-40% of the enzyme activity was retained. The non-inactivated enzyme displayed a 2-3-fold change in Km for NADPH and Km fordl-glyceraldehyde, whereas the Km for the lipid peroxidation product, 4-hydroxy-2-trans nonenal (HNE), was comparable to that of the untreated enzyme. The residual activity of the enzyme after GSNO treatment was less sensitive to inhibition by the active site inhibitor sorbinil or to activation by sulfate. Significantly higher catalytic activity was retained when the enzyme was modified in the presence of NADPH, suggesting relatively low reactivity of the E-NADPH complex with GSNO. The modification site was identified using site-directed mutants in which each of the solvent-exposed cysteines of the enzyme was replaced individually by serine. The mutant C298S was insensitive to GSNO, whereas the sensitivity of the mutants C303S and C80S was comparable to that of the wild-type enzyme. Electrospray ionization mass spectroscopy of the GSNO-modified enzyme revealed a major modified species (70% of the protein) with a molecular mass that was 306 Da higher than that of the untreated enzyme, which is consistent with the addition of a single glutathione molecule to the enzyme. The remaining 30% of the protein displayed a molecular mass that was not significantly different from that of the native enzyme. No nitrosated forms of the enzyme were observed. These results suggest that inactivation of AR by GSNO is due to the selective formation of a single mixed disulfide between glutathione and Cys-298 located at the NADP(H)-binding site of the enzyme.     

Single- and multiple-dose mibefradil pharmacokinetics in normal and hypertensive subjects

OBJECTIVE: To determine the safest method of hepatic vascular clamping associated with the least ischemia-reperfusion injury of the liver during liver surgery. SETTING: University laboratories. SUBJECTS: Sixty-five adult male Wistar rats. METHODS: The hilar area of the left lateral and median lobes of rat liver was clamped for 10 minutes (group 1), 15 minutes (group 2), or 20 minutes (group 3) followed by 5 minutes of reperfusion. The procedure was repeated for a total period of ischemia of 60 minutes in each group. Control rats underwent laparotomy without vascular clamping. In addition to histological examination, we determined calpain mu activity, a marker of liver injury, by Western blotting using specific antibodies against the intermediate (activated) and proactivated forms of calpain mu. Measurements were performed at the end of ischemia and after 2 hours of reperfusion. We also determined the degradation of talin, an intracellular substrate of calpain mu, by Western blotting. RESULTS: The level of adenosine triphosphate and energy charge at 2 hours after reperfusion did not change after ischemia-reperfusion irrespective of the duration of ischemic cycle. After 60 minutes of intermittent ischemia followed by 2 hours of reperfusion, cell membrane bleb formation, calpain mu activation, and talin degradation were detected in groups 2 and 3 but not in group 1. CONCLUSION: The safest method of hepatic vascular clamping that produces a minimum or no ischemia-reperfusion injury is 60 minutes of 6 cycles of 10-minute vascular clamping interrupted by 5 minutes of reperfusion.     

Characterization of the human aldose reductase gene promoter

The promoter region of the human aldose reductase gene has been identified upstream of the translation start ATG codon. The promoter contains a TATA box, a CCAAT promoter element, and three Sp1 protein binding consensus sequences upstream of the capsite. A 640-base pair insert spanning +31 to -609 directs expression of the reporter gene chloramphenicol acetyltransferase in an orientation-specific manner in transfected Hep G2 cells. The promoter activity remained constant with deletions from base pairs -609 to -186. The TATA and the CCAAT consensus sequences show significant promoter activity, whereas the three Sp1 binding consensus sequences, individually, have no significant promoter activity. A GA-rich region (-186 to -146) contains two CGGAAA/G motifs, which show promoter activity and interaction with Hep G2 nuclear extract and GA-binding proteins (GABP alpha and GABP beta 1) as shown by mobility shift assays and DNase I footprinting. Similar cis-elements in herpes simplex virus type 1 interact with rat liver GABP and the viral VP16 protein to mediate the induction of immediate early viral genes. A GC-rich region (-87 to -31) is identified by mobility shift assay, and a consensus sequence of an androgen response element is present at -396 to -382. The human aldose reductase promoter, thus, has regulatory response elements that may be important during early development and puberty. These regulatory elements may play a significant role in the development of certain diabetic complications.     

An aldose reductase inhibitor and aminoguanidine prevent vascular endothelial growth factor expression in rats with long-term galactosemia

OBJECTIVE: To study the effects of an aldose reductase inhibitor (ARI-509, Wyeth-Ayerst, Princeton, NJ) and aminoguanidine (AMG), agents that have been reported to prevent or delay diabetic retinopathy, on retinal vascular abnormalities and the immunocytochemical expression in the retina of vascular endothelial growth factor (VEGF) in rats maintained for up to 2 years on a 50% galactose diet. METHODS: Albino rats were placed on a control diet, a diet containing 50% galactose, or the 50% galactose diet containing either ARI-509 or AMG. Treatment with ARI-509 or AMG was initiated at the beginning of the experiment or after 12 months of galactose feeding. After 22 to 24 months, the rats were killed and the retinal vasculature from half of one eye was isolated by trypsin-elastase digestion for semiquantitative evaluation of retinal vascular lesions. The other half of the retina was prepared for immunocytochemistry and stained for the presence of VEGF, factor VIII, vimentin, and glial fibrillary acidic protein. Red blood cells, sciatic nerves, and a portion of the retina from the second eye were assayed for glucose, galactose, fructose, sorbitol, galactitol, and myo-inositol. Red blood cells were also assayed for galactosylated hemoglobin. RESULTS: Galactose-fed animals developed a vascular retinopathy characterized by severe cellular loss in the retinal capillaries and intensification of periodic acid-Schiff staining of the vascular basement membranes. Some animals also displayed dilation and hypercellularity of vessels in the posterior retina. These changes were substantially reduced in animals receiving ARI-509 from the beginning of the galactose diet, but were unaffected in all of the other treatment groups. None of the rats receiving ARI-509 or AMG treatment, whether initiated from the onset or after 12 months of galactosemia, demonstrated VEGF immunoreactivity. With the exception of the animals receiving ARI-509 from the beginning of the experiment, all of the galactose-fed animals developed dense cataracts within 6 weeks of the beginning of the galactose diet. Galactitol levels in animals receiving ARI-509 were 86% to 93% lower in red blood cells, retina, and sciatic nerve than those in the other galactose-fed groups. CONCLUSIONS: Although ARI-509 and AMG have different abilities to delay or prevent the diabetic-like retinopathy in galactosemic rats, even when substantial retinal microvascular acellularity occurs, both drugs prevent the immunocytochemical expression of VEGF. These results suggest that factors other than hypoxia may be responsible for VEGF expression in the retina, and that aldose reductase inhibitors and AMG have potential roles in preventing such expression and, thus, perhaps preventing retinal neovascularization.     

Effects of an aldose reductase inhibitor, SNK-860, on the histopathological changes of retinal tissues in a streptozotocin-induced diabetic rat model

The efficacy of two protocols for the prevention of relapse using Mitomycin-C and alpha-Interferon in 56 patients with surface bladder carcinoma (stages Ta-T1) treated with TUR was compared in a prospective study. Relapse percentages and rates, related to the tumours' presentation characteristics (single, multiple, primary, recurrent), as well as their systemic and local toxicity, were evaluated. The study of statistical significance is made using the squared-chi test, and it is completed with a Fisher's test for groups containing few elements for accuracy. The results show no statistical differences (log rank p = 0.313) between the two groups of endovesical therapy, both confirming to be effective as adjuvant therapy to TUR in surface bladder tumours.     

Noncovalent enzyme-substrate interactions in the catalytic mechanism of yeast aldose reductase

Cases of Burkitt's lymphoma (BL) from north-western Iran were investigated for the usage and somatic mutational pattern of their immunoglobulin variable region genes. Potentially functional V(H) genes were amplified from 6/12 of the tumour masses and all of these were derived from the V(H)3 family, with 4/6 being derived from the most commonly used V(H)3 family member, V3-23. All of the tumour sequences were mutated from their germline counterparts, to varying degrees, with a mean level of 5.8%, indicating that the cell of origin had encountered the germinal centre. Intraclonal sequence heterogeneity was also evident in 4/6 of the lymphomas, showing that the tumour cells had undergone further somatic mutation following neoplastic transformation. Analysis of the five potentially functional mutated V(H) sequences showed a significant clustering of replacement mutations in the complementarity-determining region 2, consistent with a role for antigen in selection of tumour cell sequences. The pattern of extensive somatic mutation, and intraclonal variation, in these mainly EBV+ve tumours, was similar to that previously reported in V(H) sequences of EBV+ve endemic BL (eBL) and EBV-ve sporadic BL (sBL), with the mean level of somatic mutation lying between those reported for eBL (7.7%) and sBL (4.0%). However, VH gene bias and the distribution of mutations in the Iranian cases showed features which differed from those reported for endemic or sporadic BL.     

Synthesis and aldose reductase inhibitory activity of benzoyl-amino acid derivatives

Discoid lupus erythematosus (DLE) is an uncommon disease in childhood. We present two patients initially diagnosed as impetigo and photosensitive eczema with impetigo, respectively, who failed to respond to topical and systemic antistaphylococcal agents and in whom a diagnosis of discoid lupus erythematosus subsequently became apparent.     

Structural and kinetic determinants of aldehyde reduction by aldose reductase

Aldose reductase (AR) is a member of the aldo-keto reductase superfamily. Due to its ability to catalyze the formation of sorbitol from glucose during hyperglycemic and hypertonic stress, the aldose-reducing property of AR has been accepted as its main physiological and pathological function. Nonetheless, AR is a poor catalyst for glucose reduction and displays active-site properties unexpected of a carbohydrate-binding protein. We, therefore, examined the catalytic properties of AR with a series of naturally occurring aldehydes, compatible in their hydrophobicity to the large apolar active site of the enzyme. Our results show that recombinant human AR is an efficient catalyst for the reduction of medium- to long-chain unbranched saturated and unsaturated aldehydes. The enzyme displayed selective preference for saturated aldehydes, such as hexanal, and unsaturated aldehydes, such as trans-2-octenal and nonenal as well as their 4-hydroxy derivatives. Short-chain aldehydes such as propanal and acrolein were reduced less efficiently. Branched derivatives of acrolein or its glutathione conjugate (GS-propanal) were, however, reduced with high efficiency. In the absence of NADPH, the alpha, beta unsaturated aldehydes caused covalent modification of the enzyme. On the basis of electrospray mass spectrometric analysis of the wild-type and site-directed mutants of AR (in which the solvent exposed cysteines were individually replaced with serine), the site of modification was identified to be the active-site residue, Cys 298. The unsaturated aldehydes, however, did not modify the enzyme bound to NADPH and did not inactivate the enzyme during catalysis. Modeling studies indicate that the large hydrophobic active site of AR can accommodate a large number of aldehydes without changes in the structure of the binding site or movement of side chains. High hydrophobicity due to long alkyl chains or apolar substituents appears to stabilize the interaction of the aldehyde substrates with the enzyme. Apparently, such hydrophobic interactions provide substrate selectivity and catalytic efficiency of the order achievable by hydrogen bonding. Since several of the aldehydes reduced by AR are either environmental and pharmacological pollutants or products of lipid peroxidation, the present studies provide the basis of future investigations on the role of AR in regulating aldehyde metabolism particularly under pathological states associated with oxidative stress and/or aldehyde toxicity.     

The absence of synergism between the effects of an aldose reductase inhibitor, epalrestat, and a vasodilator, cilostazol, on the nerve conduction slowing and the myelinated fiber atrophy in streptozotocin-induced diabetic rats

The preventive effects of combined or separate treatment for 10 weeks with an aldose reductase inhibitor, epalrestat (50 mg/kg/day), and a vasodilator, cilostazol (30 mg/kg/day), on nerve conduction deficits and morphometric alterations were examined in streptozotocin-induced diabetic rats. The average motor nerve conduction velocities (MNCV) in the tail nerve of the untreated diabetic (DM) group, the group treated with epalrestat (ES), the group treated with cilostazol (CZ), the group with both agents together (ES&CZ), and the normal control group were 34.7, 37.7, 39.3, 39.0 and 42.1 m/s, respectively. All treatments partially but significantly prevented a reduction in MNCV. The MNCV in the ES&CZ group was almost the same as in the CZ group. In a morphometric study of the sural nerve, the DM group showed a reduction in the average diameter of myelinated fiber and in occupancy (percentage of the fascicular area occupied by myelinated fibers), and a shift in the diameter-frequency histogram to smaller diameters. Only the CZ group showed evidence of a partial but significant preventive effect on the decrease in occupancy. In the CS and ES&CZ groups, there was a significant tendency away from the shift of histograms to smaller diameters. The ES&CZ group did not show any fewer morphometric changes than the CZ group. Thus, there was no synergism between the effects of epalrestat and cilostazol on the development of experimental diabetic neuropathy. This finding may provide a useful clue to the mechanisms of action of ES and CZ in diabetic neuropathy.     

Bioavailability and pharmacokinetics of intravenously and orally administered allopurinol in healthy beagles

OBJECTIVES: To determine bioavailability and pharmacokinetic parameters for allopurinol and its active metabolite, oxypurinol. ANIMALS: 6 healthy, reproductively intact female Beagles, 4.9 to 5.2 years old, and weighing 9.5 to 11.5 kg. PROCEDURE: In the first part of the study, allopurinol was administered IV at a dosage of 10 mg/kg of body weight to 3 dogs and 5 mg/kg to 3 dogs; the sequence was then reversed. In the second part of the study, allopurinol was administered orally at a dosage of 15 mg/kg to 3 dogs and 7.5 mg/kg to 3 dogs; the sequence was then reversed. In the third part of the study, allopurinol was administered IV (10 mg/kg), orally (15 mg/kg) with food, and orally (15 mg/kg) without food. Plasma samples were obtained at timed intervals, and concentrations of allopurinol and oxypurinol were determined. RESULTS: Maximal plasma allopurinol concentration and area under plasma allopurinol and oxypurinol concentration-time curves were 2 times greater when dogs were given 10 mg of allopurinol/kg IV, compared with 5 mg/kg, and when dogs were given 15 mg of allopurinol/kg orally, compared with 7.5 mg/kg. Allopurinol elimination half-life, time to reach maximal plasma oxypurinol concentration, and oxypurinol elimination half-life were significantly greater when dogs received 10 mg of allopurinol/kg IV, compared with 5 mg/kg, and when dogs received 15 mg of allopurinol/kg orally, compared with 7.5 mg/kg. CONCLUSIONS: Elimination of allopurinol is dependent on nonlinear enzyme kinetics. The bioavailability of allopurinol, and pharmacokinetic parameters of allopurinol and oxypurinol after oral administration of allopurinol, are not affected by administration with food. CLINICAL RELEVANCE: A dose threshold exists beyond which additional allopurinol would not substantially further inhibit xanthine oxidase activity. Oral administration of > 15 mg of allopurinol/kg to dogs would not be expected to result in greater reduction of plasma and urine uric acid concentrations. Also, allopurinol may be administered to dogs for dissolution or prevention of urate uroliths without regard to time of feeding.     

Bioavailability and pharmacokinetics of beta-methyldigoxin after multiple oral and intravenous doses

To obtain true half lives, glycoside elimination from six healthy subjects was studied for 14 days after multiple intravenous doses or oral administration of a daily maintenance dose of beta-methyldigoxin 0.3 mg. After oral or intravenous administration of beta-methyldigoxin ceased, the plasma concentrations declined from the 14th to the 16th days with a half life of 1.7 days. From the 16th to the 20th day a change from a shorter to a longer half life of 2.8 and 2.9 days was observed. Similar half lives were found in urine: after the last dose the initial slope from the 14th to the 16th day had a half life of 1.8 days, and the terminal slope had one of 3.2 days. The results indicate release of the glycoside from slowly equilibrating tissues.