Comparative effects of pioglitazone, glibenclamide, and voglibose on urinary endothelin-1 and albumin excretion in diabetes patients

Urinary endothelin (ET)-1 excretion is present in non-insulin dependent diabetes (NIDDM) patients with microalbuminuria, and an increase in circulating ET-1 precedes the microalbuminuric phase of renal injury related to diabetes. The aim of the present study was to determine whether various drugs alter urinary ET-1 levels and urinary albumin excretion (UAE) in NIDDM patients with microalbuminuria. Forty-five NIDDM patients with microalbuminuria were randomly assigned to three groups: those treated with pioglitazone at 30 mg/day (n=15), those treated with glibenclamide at 5 mg/day (n=15), and those treated with voglibose at 0.6 mg/day (n=15). Patients received these drugs for 3 months. UAE, urinary ET-1, and plasma ET-1 levels were measured in these patients before and after treatment. Before treatment, UAE, urinary ET-1, and plasma ET-1 levels differed little among the three groups. UAE in the 45 NIDDM patients (156.2+/-42.8 microg/min) was greater than that in 30 healthy controls (8.2+/-2.6 microg/min) (P<.001). Urinary ET-1 levels in the NIDDM patients (8.7+/-1.3 ng/g urinary creatinine (UC)) were significantly higher than that in the controls (2.4+/-0.2 ng/g UC) (P<.01). Plasma ET-1 levels, however, in the NIDDM patients (1.3+/-0.4 pg/ml) did not differ significantly from the levels in healthy controls (1.0+/-0.6 pg/ml). Pioglitazone but no glibenclamide or voglibose reduced UAE from 142.8+/-42.2 to 48. 4+/-18.2 microg/min (P<.01) and urinary ET-1 levels from 8.6+/-1.3 to 3.4+/-0.5 ng/g UC (P<.01). These data suggest pioglitazone to be effective in reducing UAE and urinary ET-1 concentrations in NIDDM patients with microalbuminuria.

Effects of angiotensin-converting enzyme inhibitor, angiotensin II receptor antagonist and calcium antagonist on urinary podocytes in patients with IgA nephropathy

The urinary podocyte is postulated to be a marker for estimation of the severity of active glomerular injury and a predictor of disease progression in children with glomerulonephritis. Non-dihydropyridine calcium antagonist, including verapamil, reduce proteinuria to an extent similar to that of the angiotensin-converting enzyme inhibitor (ACEI), including trandolapril, but to a greater extent than other antihypertensives. Angiotensin (Ang) II receptor antagonists, including candesartan cilexetil, show potent and long-term preventive effects against the progression of renal injury. The aim of the present study is to assess whether verapamil, trandolapril and candesartan cilexetil affect proteinuria and urinary podocytes in patients with IgA nephropathy. Thirty-two normotensive patients aged 18-54 years with biopsy-proven IgA nephropathy, nonnephrotic proteinuria (1-3 g/day), and normal renal function (creatinine clearance >80 ml/min) were studied. Twenty patients with diffuse mesangial proliferative glomerulonephritis (non-IgA PGN) and 20 healthy controls were also included in this study. The number of urinary podocytes in patients with advanced IgA nephropathy (n = 16) was significantly higher than that in patients with the disease in the mild stage (n = 16) (p < 0.01) or in patients with non-IgA PGN (p < 0.01). Urinary podocytes were not detected in healthy controls. The 32 patients with IgA nephropathy were randomly divided into four treatment groups: those treated with verapamil (120 mg/day, n = 8); those treated with trandolapril (2 mg/day, n = 8); those treated with candesartan cilexetil (8 mg/day, n = 8), and those given a placebo (n = 8). Treatment continued for 3 months. Antiproteinuric response in the trandolapril group was similar to that in the candesartan cilexetil group (-38 vs. -40%). The action of trandolapril or candesartan cilexetil was greater than that of verapamil (p < 0.01). Reduction in the number of urinary podocytes from baseline was significantly greater in patients treated with trandolapril or candesartan cilexetil than in patients treated with verapamil (p < 0.01). However, there was no difference between patients treated with trandolapril and those treated with candesartan cilexetil. Proteinuria and urinary podocytes were unaffected in the placebo group. These data suggest that urinary podocytes may be a marker of disease activity in adult patients with IgA nephropathy and that trandolapril and candesartan cilexetil are more effective than verapamil in reducing the number of podocytes.

Hemoperfusion with polymyxin B-immobilized fiber attenuates the increased plasma levels of thrombomodulin and von Willebrand factor from patients with septic shock

AIMS

The present study assessed whether plasma levels of thrombomodulin and von Willebrand factor (vWF) are altered in patients with septic shock and whether treatment with polymyxin B-immobilized fiber (PMX-F) affects these levels.

METHODS

Twenty-four patients with septic shock and 20 normal healthy controls were included in this study. Plasma levels of thrombomodulin and vWF were measured by enzyme immunoassay (EIA). The treatments with direct hemoperfusion using PMX-F column on patients with septic shock were repeated twice for 2 h each. Healthy controls were not subjected to hemoperfusion.

RESULTS

13 of 24 patients with septic shock survived (survival rate was 54.2%). Levels of blood endotoxin decreased significantly from 41.2 +/- 4.8 pg/ml at baseline to 13.2 +/- 3.6 pg/ml after direct hemoperfusion. Systolic blood pressure increased significantly from 82 +/- 6 mm Hg at baseline to 118 +/- 12 mm Hg after treatment. The patients with septic shock demonstrated significantly increased plasma levels of thrombomodulin (p < 0.001) and vWF (p < 0.001) compared with those in healthy controls. These increased levels of plasma thrombomodulin and vWF in patients with septic shock decreased significantly after treatment with PMX-F (p < 0.01).

CONCLUSION

These data suggest that plasma thrombomodulin and vWF may be related to septic shock and that PMX-F is effective in reducing these factors in patients with septic shock.

Identification of human cytochrome P450 isoforms involved in the 7-hydroxylation of chlorpromazine by human liver microsomes

Studies to identify the cytochrome P450 (CYP) isoform(s) involved in chlorpromazine 7-hydroxylation were performed using human liver microsomes and cDNA-expressed human CYPs. The kinetics of chlorpromazine 7-hydroxylation in human liver microsomes showed a simple Michaelis-Menten behavior. The apparent Km and Vmax values were 3.4+/-1.0 microM and 200.5+/-83.7 pmol/min/mg, respectively. The chlorpromazine 7-hydroxylase activity in human liver microsomes showed good correlations with desipramine 2-hydroxylase activity (r = 0.763, p < 0.05), a marker activity for CYP2D6, and phenacetin O-deethylase activity (r = 0.638, p < 0.05), a marker activity for CYP1A2. Quinidine (an inhibitor of CYP2D6) completely inhibited while alpha-naphthoflavone (an inhibitor of CYP1A2) marginally inhibited the chlorpromazine 7-hydroxylase activity in a human liver microsomal sample showing high CYP2D6 activity. On the other hand, alpha-naphthoflavone inhibited the chlorpromazine 7-hydroxylase activity to 55-65% of control in a human liver microsomal sample showing low CYP2D6 activity. Among eleven cDNA-expressed CYPs studied, CYP2D6 and CYP1A2 exhibited significant activity for the chlorpromazine 7-hydroxylation. The Km values for the chlorpromazine 7-hydroxylation of both cDNA-expressed CYP2D6 and CYP1A2 were in agreement with the Km values of human liver microsomes. These results suggest that chlorpromazine 7-hydroxylation is catalyzed mainly by CYP2D6 and partially by CYP1A2.

Effect of the antiplatelet drug dilazep dihydrochloride on urinary podocytes in patients in the early stage of diabetic nephropathy

OBJECTIVE

To determine whether the antiplatelet drug dilazep dihydrochloride affects the number of urinary podocytes in diabetic patients with microalbuminuria.

RESEARCH DESIGN AND METHODS

Fifty patients with type 2 diabetes and microalbuminuria (30 men and 20 women, mean age 48.6 years) and 30 age-matched control subjects (18 men and 12 women, mean age 49.2 years) were included in the study. No patients showed serum creatinine levels in excess of 2.0 mg/dl. Urinary podocytes were examined by immunofluorescence microscopy with monoclonal antibodies against podocalyxin.

RESULTS

Urinary podocytes were detected in 18 of the 50 microalbuminuric diabetic patients (mean, 1.3 cells/ml). Urinary podocytes were not detected in the remaining 32 patients or in the 30 healthy control subjects. Diabetic patients positive for urinary podocytes were divided into 2 treatment groups: a dilazep dihydrochloride treatment group (300 mg/day; n = 9, group A) and a placebo group (n = 9, group B). Treatments were continued for 6 months. In group A, microalbuminuria decreased significantly from 146 +/- 42 to 86 +/- 28 microg/min (P < 0.01) and urinary podocytes also decreased from 1.3 +/- 0.8 to 0.4 +/- 0.2 cells/ml (P < 0.01). However, in group B, microalbuminuria and urinary podocytes changed little over the study period.

CONCLUSIONS

Podocyte injury may occur in patients with early diabetic nephropathy, and dilazep dihydrochloride may be useful for preventing glomerular injury.

Urinary podocytes for the assessment of disease activity in lupus nephritis

BACKGROUND

Detection of podocytes in the urine indicates that severe injury of podocytes occurred in the glomerulus in children.

METHODS

The pathological significance of podocytes in the urine was determined in patients with lupus nephritis. Podocytes were detected by immunofluorescence using a monoclonal antibody against podocalyxin present on the surface of podocytes. Subjects who participated in the present study were of the following types: patients with systemic lupus erythematosus with stable renal function (group A, n = 8; WHO classes IlIa, b, IVb, and IVc at the time of biopsy); patients with clinically active lupus nephritis (group B, n = 8; WHO classes IVb and IVc); and healthy control subjects (group C, n = 10).

RESULTS

Podocytes were absent in the urine of subjects in groups A and C. However, podocytes were present in the urine of group B subjects. Patients in group B were examined monthly for urinary podocytes and were treated with methylprednisolone followed by prednisolone. Urinary podocytes were absent in all patients in group B after treatment.

CONCLUSIONS

These data indicate that urinary podocytes may be markers of the severity of lupus nephritis and that steroid therapy may be effective for podocyte injury in lupus nephritis.

Role of human cytochrome P450 3A4 in metabolism of medroxyprogesterone acetate

Medroxyprogesterone acetate (MPA) is a drug commonly used in endocrine therapy for advanced or recurrent breast cancer and endometrial cancer. The drug is extensively metabolized in the intestinal mucosa and in the liver. Cytochrome P450s (CYPs) involved in the metabolism of MPA were identified by using human liver microsomes and recombinant human CYPs. In this study, the overall metabolism of MPA was determined as the disappearance of the parent drug from an incubation mixture. The disappearance of MPA in human liver microsomes varied 2.6-fold among the 18 samples studied. The disappearance of MPA in the same panel of 18 human liver microsomes was significantly correlated with triazolam alpha-hydroxylase activity, a marker activity of CYP3A (r = 0.764; P < 0.001). Ketoconazole, an inhibitor of CYP3A4, potently inhibited the disappearance of MPA in 18 human liver microsomes. Anti-CYP3A antibody also inhibited 86% of the disappearance of MPA in human liver microsomes. Although sulfaphenazole (an inhibitor of CYP2C9) and S-mephenytoin (an inhibitor of CYP2C19) partially inhibited the disappearance of MPA, no effect of the anti-CYP2C antibody was observed. The disappearance of MPA did not correlate with either the activity metabolized via CYP2C9 (diclofenac 4'-hydroxylase activity) or the activity metabolized via CYP2C19 (S-mephenytoin 4'-hydroxylase activity). Among the 12 recombinant human CYPs (CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2D6, CYP2E1, CYP3A4, and CYP3A5) studied, only CYP3A4 showed metabolic activity of MPA. These results suggest that CYP3A4 is mainly involved in the overall metabolism of MPA in human liver microsomes.

Characterization and tRNA recognition of mammalian mitochondrial seryl-tRNA synthetase

Animal mitochondrial protein synthesis systems contain two serine tRNAs (tRNAs(Ser)) corresponding to the codons AGY and UCN, each possessing an unusual secondary structure; the former lacks the entire D arm, and the latter has a slightly different cloverleaf structure. To elucidate whether these two tRNAs(Ser) can be recognized by the single animal mitochondrial seryl-tRNA synthetase (mt SerRS), we purified mt SerRS from bovine liver 2400-fold and showed that it can aminoacylate both of them. Specific interaction between mt SerRS and either of the tRNAs(Ser) was also observed in a gel retardation assay. cDNA cloning of bovine mt SerRS revealed that the deduced amino acid sequence of the enzyme contains 518 amino acid residues. The cDNAs of human and mouse mt SerRS were obtained by reverse transcription-polymerase chain reaction and expressed sequence tag data base searches. Elaborate inspection of primary sequences of mammalian mt SerRSs revealed diversity in the N-terminal domain responsible for tRNA recognition, indicating that the recognition mechanism of mammalian mt SerRS differs considerably from that of its prokaryotic counterpart. In addition, the human mt SerRS gene was found to be located on chromosome 19q13.1, to which the autosomal deafness locus DFNA4 is mapped.

Enantioselectivity of bunitrolol 4-hydroxylation is reversed by the change of an amino acid residue from valine to methionine at position 374 of cytochrome P450-2D6

The enantioselectivity of 4-hydroxylation of bunitrolol (BTL), a beta-adrenoceptor blocking drug, was studied in microsomes from human liver, human hepatoma (Hep G2) cells expressing CYP2D6, and lymphoblastoid cells expressing CYP2D6. Kinetics in human liver microsomes showed that the Vmax value for (+)-BTL was 2.1-fold that of (-)-BTL, and that the Km value for (+)-BTL was lower than that for the (-)-antipode, resulting in the intrinsic clearance (Vmax/Km) of (+)-BTL being 2.1-fold over its (-)-antipode. CYP2D6 (CYP2D6-met) expressed in Hep G2 cells had a methionine residue at position 373 of the amino acid sequence and a rat-type N-terminal peptide (MELLNGTGLWSM) instead of the human-type (MGLEALVPLAVIV), and showed enantioselectivity of [(+)-BTL < (-)-BTL] for the rate of BTL 4-hydroxylation. In contrast, enantioselectivity [(+)-BTL > (-)-BTL] for Hep G2-CYP2D6 (CYP2D6-val) with a human-type N-terminal peptide that had a valine residue at 374, which corresponds to the methionine of the CYP2D6-met variant, was the same as that for human liver microsomes. We further confirmed that CYP2D6-met and CYP2D6-val expressed in human lymphoblastoid cells, both of which have methionine and valine, respectively, at position 374 and a human-type N-terminal peptide, exhibited the same enantioselectivities as those obtained from CYP2D6-met and CYP2D6-val expressed in the Hep G2 cell system. These results indicate that the amino acid at 374 of CYP2D6 is one of the key factors influencing the enantioselectivity of BTL 4-hydroxylation.

Species difference in enantioselectivity for the oxidation of propranolol by cytochrome P450 2D enzymes

We examined and compared enantioselectivity in the oxidation of propranolol (PL) by liver microsomes from humans and Japanese monkeys (Macaca fuscata). PL was oxidized at the naphthalene ring to 4-hydroxypropranolol, 5-hydroxypropranolol and side chain N-desisopropylpropranolol by human liver microsomes with enantioselectivity of [R(+)>S(-)] in PL oxidation rates at substrate concentrations of 10 microM and 1 mM. In contrast, reversed enantioselectivity [R(+)<S(-)] in PL 5-hydroxylation and N-desalkylation rates at the same substrate concentrations was observed in monkey liver microsomes, although the selectivity was the same for PL 4-hydroxylation between the two species. All oxidation reactions of the PL enantiomers in human liver microsomes showed biphasic kinetics, i.e. the reactions could be expressed as the summation of a low-K(m) phase and a high-K(m) phase. Inhibition studies using antibodies and characterization of CYP2D6 enzymes expressed in insect cells or human lymphoblastoid cells indicated that the enantioselectivity of PL oxidation, especially the ring 4- and 5-hydroxylations reflected the properties of CYP2D6 in human liver microsomes. In monkey liver microsomes, all of the oxidation reactions of S(-)-PL showed biphasic kinetics, whereas ring 4- and 5-hydroxylations were monophasic and side chain N-desisopropylation was biphasic for R(+)-PL. Similarly, from the results of inhibition studies using antibodies and inhibitors of cytochrome P450 (P450), it appears that the reversed selectivity [R(+)<S(-)] of PL oxidation rates is catalyzed by CYP2D enzyme(s) in monkey liver at low substrate concentrations. These results indicate that different properties of P450s belonging to the 2D subfamily cause the reversed enantioselectivity between human and monkey liver microsomes.

Human T-cell receptor BV6 gene polymorphism in relation to expression level and CD4/CD8 skewness

Using 50 samples of umbilical cord blood lymphocytes from Japanese donors, we analysed two human T-cell receptor beta variable (TCRBV) genes, BV6S4 and BV6S5, for their polymorphism, usage frequencies and CD4/CD8 skewness. They showed contrasting CD4/CD8 skewness, BV6S4 to CD8+ T cells and BV6S5 to CD4+ T cells. Genotyping of the BV6S4 alleles (A1, A2 and A3) revealed two of the six possible BV6S4 genotypes, A1/A2 and A2/A2. Among the two BV6S4 genotypes, no significant difference was detected in usage frequency or CD4/CD8 skewness. On the other hand, genotyping of the BV6S5 alleles (A1 and A2) revealed all three possible BV6S5 genotypes, A1/A1, A1/A2 and A2/A2, and the gene usage frequency was high, in the order A1/A1 > A1/A2 > A2/A2. These results indicate that the amino acid substitutions in BV6S5 (S36R and G70E) are in some way associated with the expression level of this gene. In the analysis of CD4/CD8 skewness, the three BV6S5 genotypes had similar skewness, indicating that A1 alleles are expressed more frequently than A2 alleles in both CD4+ and CD8+ T-cell populations. Although BV6S5 exhibits marked skewness to CD4+ T cells, our results indicate that the higher expression of A1 alleles is not associated with the increased ratio of CD4+ T cells.

Regulation of cellular functions by nucleoside diphosphate kinases in mammals

The role of nucleoside diphosphate (NDP) kinases in cell growth, differentiation, and tumor metastasis in relation to signal transduction was investigated. The essential role of NDP kinase in cell growth was validated by coupling between reduced NDP kinase levels, induced by antisense oligonucleotides, and the suppression of proliferative activity of a cultured cell line. In addition, because NDP kinase levels are often enhanced with development and differentiation, as has been demonstrated in postmitotic cells and tissues, such as the heart and brain, we further examined this possibility using the bone tissue (osteoblasts) and a cultured cell line PC12D. The enhanced NDP kinase accumulation was demonstrated in the matured osteoblasts in vivo and in vitro by immunohistochemistry. In PC12D cells, neurite outgrowth took place in NDP kinase beta-transfected clones without differentiation inducers, which was accompanied by prolongation of doubling time. Neurite outgrowth, triggered by nerve growth factor and a cyclic AMP analog, was down-regulated upon forced expression of inactive mutant NDP kinase by virtue of a dominant negative effect. NDP kinase alpha-transfected rat mammary adenocarcinoma cells (MTLn3) and nm23-H2-transfected human oral squamous cell carcinoma cells (LMF4) manifested reduced metastatic potential and were associated with an altered sensitivity to environmental factors, such as motility and growth factors. NDP kinase alpha, compared to NDP kinase beta, was involved in a wide variety of the cellular phenomena examined. Taken together, NDP kinase isoforms appear to elicit both their own respective and common effects. They may have an ability to lead cells to both proliferative and differentiated states by modulating responsiveness to environmental factors, but their fate seems to depend on their surrounding milieu.

Effect of plasma exchange on serum tissue inhibitor of metalloproteinase 1 and cytokine concentrations in patients with fulminant hepatitis

AIMS

The present study assessed whether the serum concentrations of tissue inhibitor of metalloproteinase 1 (TIMP-1) and cytokines are altered in patients with fulminant hepatitis and whether plasma exchange affects these concentrations.

METHODS

Fifteen patients with fulminant hepatitis, 14 patients with severe acute hepatitis, and 20 healthy controls were included in this study. The serum levels of tumor necrosis factor alpha (TNF-alpha), interleukin 1beta (IL-1beta), interleukin 6 (IL-6), transforming growth factor beta (TGF-beta), and TIMP-1 were determined in all patients upon hospital admission and before and after a single course of plasma exchange in the patients with fulminant hepatitis.

RESULTS

Ten out of the 15 patients with fulminant hepatitis and all patients with severe acute hepatitis survived. Serum TNF-alpha, IL-6, TGF-beta, and TIMP-1 levels in patients with fulminant hepatitis were significantly higher than the levels in patients with severe acute hepatitis (p < 0.01). IL-1beta was not detectable in either group. Plasma exchange reduced the increased serum concentrations of TNF-alpha, IL-6, TGF-beta, and TIMP-1 in patients with fulminant hepatitis (p < 0.01).

CONCLUSIONS

These data suggest that increased serum levels of TIMP-1 and cytokines may reflect severe hepatic inflammation and that plasma exchange is an effective therapy to reduce these levels.

The urinary podocyte as a marker for the differential diagnosis of idiopathic focal glomerulosclerosis and minimal-change nephrotic syndrome

BACKGROUND/AIMS

Detection of podocytes in the urine sediment of children indicates that severe podocyte injury occurred in the glomerulus. Focal glomerulosclerosis (FGS) and minimal-change nephrotic syndrome (MCNS) are kidney diseases characterized by massive proteinuria. The aim of the present study was to determine whether urinary podocytes can be detected in patients with idiopathic FGS or MCNS and whether immunosuppression therapy alters these cells.

METHODS

Twenty patients with MCNS (nephrotic stage, n = 12; remission stage, n = 8), 15 patients with FGS and 20 healthy controls were included in the present study. Urinary podocytes were stained by immunofluorescence. All patients with MCNS at the nephrotic stage received prednisolone for 6 months, and all patients with FGS received some form of immunosuppression therapy including prednisolone, cyclophosphamide or mizoribine for 12 months.

RESULTS

The 12 nephrotic-stage MCNS patients achieved remission after treatment. Seven of the 15 FGS patients also achieved remission, but the other 8 remained in the nephrotic stage. Urinary podocytes were not detected in any patient with MCNS nor were they detected in healthy controls. Urinary podocytes were detected in all FGS patients (mean, 4.2 cells/ml) before treatment and the number of cells decreased in the 7 patients who achieved remission. The number of podocytes was unchanged in the other 8 patients even after treatment.

CONCLUSION

Urinary podocytes may be a useful diagnostic indicator for differentiation between FGS and MCNS. These cells may also mark disease progression in cases of FGS.

Prediction of in vivo interaction between triazolam and erythromycin based on in vitro studies using human liver microsomes and recombinant human CYP3A4

PURPOSE

To quantitatively predict the in vivo interaction between triazolam and erythromycin, which involves mechanism-based inhibition of CYP3A4, from in vitro studies using human liver microsomes (HLM) and recombinant human CYP3A4 (REC).

METHODS

HLM or REC was preincubated with erythromycin in the presence of NADPH and then triazolam was added. alpha- and 4-hydroxy (OH) triazolam were quantified after a 3 min incubation and the kinetic parameters for enzyme inactivation (k(inact) and K('app)) were obtained. Drug-drug interaction in vivo was predicted based on a physiologically-based pharmacokinetic (PBPK) model, using triazolam and erythromycin pharmacokinetic parameters obtained from the literature and kinetic parameters for the enzyme inactivation obtained in the in vitro studies.

RESULTS

Whichever enzyme was used, triazolam metabolism was not inhibited without preincubation, even if the erythromycin concentration was increased. The degree of inhibition depended on preincubation time and erythromycin concentration. The values obtained for k(inact) and K('app) were 0.062 min(-1) and 15.9 microM (alpha-OH, HLM), 0.055 min(-1) and 17.4 microM (4-OH, HLM), 0.173 min(-1) and 19.1 microM (alpha-OH, REC), and 0.097 min(-1) and 18.9 microM (4-OH, REC). Based on the kinetic parameters obtained using HLM and REC, the AUCpo of triazolam was predicted to increase 2.0- and 2.6-fold, respectively, following oral administration of erythromycin (333 mg t.i.d. for 3 days), which agreed well with the reported data.

CONCLUSIONS

In vivo interaction between triazolam and erythromycin was successfully predicted from in vitro data based on a PBPK model involving a mechanism-based inhibition of CYP3A4.

Prediction of in vivo drug-drug interactions between tolbutamide and various sulfonamides in humans based on in vitro experiments

Drug-drug interactions between tolbutamide and sulfonamides have extensively been reported. We attempted to predict the in vivo interaction between tolbutamide and sulfonamides from the in vitro metabolic inhibition studies. The inhibition constant (K(i)) was derived from the inhibitory effects of eight sulfonamides (sulfaphenazole, sulfadiazine, sulfamethizole, sulfisoxazole, sulfamethoxazole, sulfapyridine, sulfadimethoxine, and sulfamonomethoxine) on tolbutamide metabolism. We found that the inhibitory effect of sulfaphenazole was greatest among the eight sulfonamides examined. Furthermore, the contribution of each P450 enzyme to tolbutamide metabolism was investigated by using recombinant P450 enzymes. Although cytochrome P450 (CYP) 2C8, 2C9, and 2C19 metabolized tolbutamide, the main enzyme involved was CYP2C9. The K(i) values of several sulfonamides were comparable between human liver microsomes and recombinant CYP2C9. The maximum unbound plasma concentration of sulfonamides in the portal vein was calculated from literature data on the pharmacokinetics of sulfonamides. Using the K(i) values obtained from in vitro inhibition studies, the degree of increase in tolbutamide area under the plasma concentration-time curve (AUC) was predicted. About 4.8- and 1.6-fold increases in tolbutamide AUC were predicted by coadministration of sulfaphenazole and sulfamethizole, respectively, which agreed well with the reported increases in humans. Furthermore, the increase in tolbutamide AUC by coadministration of sulfadiazine, sulfisoxazole, and sulfamethizole was predicted to be 1.5- to 2. 6-fold, although the corresponding in vivo effects have not been reported. It is concluded that some of these sulfonamides have to be carefully coadministered with CYP2C9 substrates such as tolbutamide although coadministration of sulfaphenazole needs the greatest care.

Inhibitory effects of amiodarone and its N-deethylated metabolite on human cytochrome P450 activities: prediction of in vivo drug interactions

AIMS

To predict the drug interactions of amiodarone and other drugs, the inhibitory effects and inactivation potential for human cytochrome P450 (CYP) enzymes by amiodarone and its N-dealkylated metabolite, desethylamiodarone were examined.

METHODS

The inhibition or inactivation potency of amiodarone and desethylamiodarone for human CYP activities were investigated using microsomes from B-lymphoblastoid cell lines expressing CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4. The in vivo drug interactions of amiodarone and desethylamiodarone were predicted in vitro using the 1+Iu/Ki values.

RESULTS

Amiodarone weakly inhibited CYP2C9, CYP2D6, and CYP3A4-mediated activities with Ki values of 45.1-271.6 microm. Desethylamiodarone competitively inhibited the catalytic activities of CYP2D6 (Ki=4.5 microm ) and noncompetitively inhibited CYP2A6 (Ki=13.5 microm ), CYP2B6 (Ki=5.4 microm ), and CYP3A4 (Ki=12.1 microm ). The catalytic activities of CYP1A1 (Ki=1.5 microm, alpha=5.7), CYP1A2 (Ki=18.8 microm, alpha=2.6), CYP2C9 (Ki=2.3 microm, alpha=5.9), and CYP2C19 (Ki=15.7 microm, alpha=4.5) were inhibited by desethylamiodarone with mixed type. The 1+Iu/Ki values of desethylamiodarone were higher than those of amiodarone. Amiodarone inactivated CYP3A4, while desethylamiodarone inactivated CYP1A1, CYP1A2, CYP2B6, and CYP2D6.

CONCLUSIONS

The interactions between amiodarone and other drugs might occur via the inhibition of CYP activities by its N-dealkylated metabolite, desethylamiodarone, rather than by amiodarone itself. In addition, the inactivation of CYPs by desethylamiodarone as well as by amiodarone would also contribute to the drug interactions.

Polymyxin b-immobilized fiber reduces increased plasma endothelin-1 concentrations in hemodialysis patients with sepsis

We studied whether plasma endothelin (ET)-1 concentrations are altered in patients with septic shock who are undergoing hemodialysis and whether polymyxin B-immobilized fiber (PMX-F) treatment affects on these concentrations. Fifteen hemodialysis patients with septic shock treated with PMX-F (group A), 10 such patients who received conventional treatments (group B), 20 hemodialysis patients without septic shock (group C) and 20 healthy controls (group D) were included in this study. Plasma ET1 levels were measured by radioimmunoassay and endotoxin levels were determined by endospecy test. The survival rate in group A (67%) was higher than that in group B (30%). Blood endotoxin levels decreased significantly from 36.4+/-8.2 pg/mL to 10.6+/-3.8 pg/mL (p < 0.01) after PMX-F treatment in group A. The pretreatment plasma ET-1 levels in patients in group A (58.6+/-9.8 pg/mL) and group B (56.8+/-7.8 pg/mL) were significantly higher than those in group C (p < 0.01) and group D (p < 0.001). Plasma ET-1 levels in group C (11.2+/-3.2 pg/mL) were higher than those in group D (2.6+/-0.6 pg/mL) (p < 0.01). Plasma ET-1 levels following hemodialysis (10.9+/-3.0 pg/mL) were not altered significantly compared with those before hemodialysis. Plasma ET-1 levels decreased significantly in group A after PMX-F treatment (11.4+/-3.6 pg/mL) (p < 0.01); the levels in group B were not altered after conventional treatment. Our data suggest that ET-1 may be associated with septic shock in patients undergoing hemodialysis and that PMX-F is effective in reducing plasma ET-1 levels in these patients.

Inhibition of human cytochrome P450 enzymes by 1,4-dihydropyridine calcium antagonists: prediction of in vivo drug-drug interactions

OBJECTIVE

1,4-Dihydropyridine calcium antagonists such as nifedipine are potent vasodilators. It is now commonly agreed that the oxidation of 1,4-dihydropyridine into pyridine, which is one of the main metabolic pathways, is catalysed by the cytochrome P450 (CYP) 3A4 isoform. In the present study, the inhibitory effects of 13 kinds of 1,4-dihydropyridine calcium antagonists clinically used in Japan on human CYP-isoform-dependent reactions were investigated to predict the drug interactions using microsomes from human B-lymphoblast cells expressing CYP.

RESULTS

The specific activities for human CYP isoforms included 7-ethoxyresorfin O-deethylation (CYP1A1), phenacetin O-deethylation (CYP1A2), coumarin 7-hydroxylation (CYP2A6), 7-benzyloxyresorufin O-dealkylation (CYP2B6), S-warfarin 7-hydroxylation (CYP2C9), S-mephenytoin 4'-hydroxylaion (CYP2C19), bufuralol 1'-hydroxylation (CYP2D6), chlorzoxazone 6-hydroxylation (CYP2E1), and testosterone 6beta-hydroxylation (CYP3A4). Benidipine and amlodipine competitively inhibited the CYP1A1 activity. Nifedipine, nisoldipine and aranidipine competitively inhibited the CYP1A2 activity. No 1,4-dihydropyridie calcium antagonists used in this study inhibited the CYP2A6 activity. Barnidipine and amlodipine inhibited the CYP2B6 activity. Nicardipine, benidipine, manidipine and barnidipine competitively inhibited the CYP2C9 and CYP2D6 activities. Inhibition extent of the CYP2E1 activity by nifedipine and aranidipine were weak. Nicardipine, benidipine and barnidipine inhibited the CYP2C19 and CYP3A4 activities. Among the human CYP isoforms investigated, the inhibitory effects of 1,4-dihydropyridine calcium antagonists were potent on human CYP1A2, CYP2B6, CYP2C9, CYP2C19 and CYP2D6 as well as CYP3A4. Furthermore, the isoform selectivity of inhibition by 1,4-dihydropyridine calcium antagonists was clarified.

CONCLUSIONS

In consideration of the Ki values obtained in the in vitro inhibition study and the concentration of 1,4-dihydropyridine calcium antagonists in human liver, the possibility of in vivo drug interactions of nicardipine and other drugs which are mainly metabolised by CYP2C9 and/or CYP3A4 was suggested. The inhibition of human CYP isoforms by 1,4-dihydropyridine calcium antagonists except nicardipine might be clinically insignificant.

Solitary subependymal giant cell astrocytoma: case report

In this report, we describe a case of subependymal giant cell astrocytoma in a patient lacking clinical symptoms of tuberous sclerosis. The absence of any features of tuberous sclerosis initially dissuaded us from including subependymal giant cell astrocytoma in our differential diagnosis.