A multicenter phase II prospective clinical trial of glucocorticoid for patients with untreated IgG4-related disease.

OBJECTIVE: Although glucocorticoids are effective for patients with IgG4-related disease, the treatment has not yet been standardized. Therefore, the treatment strategy should be established. PATIENTS AND METHODS: Patients who fulfilled the comprehensive diagnostic criteria for definite IgG4-related disease were started on prednisolone (0.6 mg/kg body weight) with the dose reduced every two weeks. The subsequent maintenance dose and need for prednisolone were determined for individual patients. The primary endpoint was the complete remission (CR) rate at one year. Secondary endpoints included overall response rate (ORR), the maintenance dose, the relapse rate, and adverse events. RESULTS: This study enrolled 61 patients. After clinicopathological review, three patients were excluded, and one, 13, and 44 patients were diagnosed with probable, possible, and definite IgG4-related disease, respectively. Of the 44 patients with definite IgG4-RD, 29 (65.9%) achieved CR, and the ORR was 93.2%. No patient was refractory to primary treatment. The most frequent adverse events were glucose intolerance. Six patients relapsed. CONCLUSIONS: Glucocorticoid treatment is usually effective for patients with IgG4-RD, and we should examine the possibility of other disorders when a patient is glucocorticoid refractory. Some patients are misdiagnosed, making central clinicopathological review of diagnosis very important in conducting clinical studies.

Induction of DNA strand breaks is critical to predict the cytotoxicity of gemtuzumab ozogamicin against leukemic cells.

Gemtuzumab ozogamicin (GO) consists of the CD33 antibody linked to calicheamicin. The binding of GO to the CD33 antigen on leukemic cells results in internalization followed by the release of calicheamicin, thereby inducing DNA strand breaks. We hypothesized that the induction of DNA strand breaks would be a surrogate marker of GO cytotoxcity. Here, two GO-resistant variants (HL/GO-CSA [225-fold], HL/GO [200-fold]) were established by serially incubating human leukemia HL-60 cells with GO with or without a P-glycoprotein (P-gp) inhibitor, cyclosporine A, respectively. The CD33 positivity was reduced in both variants. The HL/GO-CSA cells showed an increased multidrug resistance protein-1 (MRP1) transcript, and an MRP1 inhibitor partially reversed GO resistance. The HL/GO cells had neither P-gp nor MRP1 overexpression. Microarray analysis and Western blotting indicated elevated levels of DNA repair-associated proteins in both variants. Two other leukemic subclones, showing either P-gp or MRP1 overexpression, were also GO-resistant. Using single cell gel electrophoresis analysis, it was determined that GO-induced DNA strand breaks increased dose-dependently in HL-60 cells, whereas the number of breaks was reduced in the GO-resistant cell lines. The induction of DNA strand breaks was correlated with GO sensitivity among these cell lines. The CD33 positivity and the expression levels of transporters were not proportional to drug sensitivity. Using primary leukemic cells, the induction of DNA strand breaks appeared to be associated with GO sensitivity. Thus, GO-induced DNA strand breaks as the final output of the mechanism of action would be critical to predict GO cytotoxicity.

Marked upregulation of Survivin and Aurora-B kinase is associated with disease progression in the myelodysplastic syndromes.

BACKGROUND: Myelodysplastic syndromes are a heterogeneous group of clonal hematopoietic stem cell disorders characterized by ineffective hematopoiesis. Survivin is a member of the inhibitor of apoptosis family and suppresses apoptosis. Survivin also functions as a subunit of the chromosomal passenger complex for regulating mitosis with Aurora-B. Survivin and Aurora-B play an important role in maintaining genome stability. The aim of this study was to determine the role of Survivin and Aurora-B kinase in disease progression and prognosis of myelodysplastic syndromes. DESIGN AND METHODS: We evaluated the expression levels of these two genes in CD34(+) cells prepared from 64 patients with myelodysplastic syndrome or leukemic blasts from 50 patients with de novo acute myeloid leukemia using quantitative real-time PCR. RESULTS: Survivin and Aurora-B expression levels were highly correlated with the type of myelodysplastic syndrome, were much higher in refractory anemia with excess blasts-1, refractory anemia with excess blasts-2, and secondary acute myeloid leukemia following myelodysplastic syndrome than in normal control, and increased during disease progression. There was a significant correlation between these expression levels and the International Prognostic Scoring System. Interestingly, these levels were remarkably higher in patients with secondary acute myeloid leukemia following myelodysplastic syndromes than in those with de novo acute myeloid leukemia. CONCLUSIONS: This is the first report showing that high levels of Survivin and Aurora-B kinase expression in CD34(+) cells are distinctive molecular features of high-risk myelodysplastic syndromes and secondary acute myeloid leukemia following myelodysplastic syndrome. Marked upregulation of Survivin and Aurora-B kinase may contribute to genetic instability and disease progression of myelodysplastic syndromes. Our data may explain why patients with high-risk myelodysplastic syndromes frequently show complex chromosomal abnormality.

Von Hippel-Lindau-coupled and transcription-coupled nucleotide excision repair-dependent degradation of RNA polymerase II in response to trabectedin.

PURPOSE: Ecteinascidin 743 (Et743; trabectedin, Yondelis) has recently been approved in Europe for the treatment of soft tissue sarcomas and is undergoing clinical trials for other solid tumors. Et743 selectively targets cells proficient for TC-NER, which sets it apart from other DNA alkylating agents. In the present study, we examined the effects of Et743 on RNA Pol II. EXPERIMENTAL DESIGN AND RESULTS: We report that Et743 induces the rapid and massive degradation of transcribing Pol II in various cancer cell lines and normal fibroblasts. Pol II degradation was abrogated by the proteasome inhibitor MG132 and was dependent on TC-NER. Cockayne syndrome (CS) cells and xeroderma pigmentosum (XP) cells (XPD, XPA, XPG, and XPF) were defective in Pol II degradation, whereas XPC cells whose defect is limited to global genome NER in nontranscribing regions were proficient for Pol II degradation. Complementation of the CSB and XPD cells restored Pol II degradation. We also show that cells defective for the VHL complex were defective in Pol II degradation and that complementation of those cells restores Pol II degradation. Moreover, VHL deficiency rendered cells resistant to Et743-induced cell death, a similar effect to that of TC-NER deficiency. CONCLUSION: These results suggest that both TC-NER-induced and VHL-mediated Pol II degradation play a role in cell killing by Et743.

Multiple inflammatory cytokine-productive ThyL-6 cell line established from a patient with thymic carcinoma.

Thymic epithelial cells can produce many kinds of cytokines, and interleukin (IL)-6-producing thymic carcinoma cases have been reported. However, a cytokine-producing human thymic tumor cell line has not previously been established. In this paper, we report a novel, multiple inflammatory cytokine-productive cell line that was established from a patient with thymic carcinoma. This cell line, designated ThyL-6, positively expressed epithelial membrane antigen, cytokeratins, vimentin intermediate filament and CD5, although hematological markers were not present in the cells. Cytokine antibody array analysis showed that the cells secreted several cytokines including IL-1alpha, IL-6, IL-8, RANTES, soluble TNFalpha-receptor 1, VEGF and CTLA into the culture medium. The addition of ThyL-6-cultured supernatant supported the growth of human myeloma ILKM-3 cells, which require the presence of IL-6 in the culture medium for the maintenance of cell growth, suggesting that the secreted IL-6 from ThyL-6 cells was biologically active. Chromosome analysis demonstrated that ThyL-6 cells had complex karyotype anomalies, including der(16)t(1;16); the latter has been recognized in thymic squamous cell carcinoma and thymic sarcomatoid carcinoma cases, as well as in several other kinds of malignancies. Heterotransplantation of the cells into nude mice showed tumorigenesis with neutrophil infiltration and liquefactive necrosis. These findings suggest that ThyL-6 cells will provide us with a new experimental tool for investigating not only the pathogenesis, biological behavior, chromo-somal analysis and therapeutic reagents of human thymic carcinoma, but also for studying cytokine-chemokine network systems.

[Physiology and dynamics of uric acid in hyperuricemia].

Gout is a type of inflammatory arthritis that is triggered by the crystallization of monosodium urate (MSU) within the joints and is often associated with hyperuricemia. Further understanding the physiology and dynamics of uric acid in human is required to make sure the disease mechanism of both gout and hyperuricemia in clinic. The amount of urate in the body consists urate pool, and which depends on the balance between dietary intake, synthesis, and excretion. Uric acid is a weak acid that exists largely as MSU, the ionized form, in urate pool at physiologic pH. But the solubility of MSU is influenced of pH, temperature and protein of blood and tissue.

Novel E-ring camptothecin keto analogues (S38809 and S39625) are stable, potent, and selective topoisomerase I inhibitors without being substrates of drug efflux transporters.

Camptothecin (CPT) analogues are powerful anticancer agents but are chemically unstable due to their alpha-hydroxylactone six-membered E-ring structure, which is essential for trapping topoisomerase I (Top1)-DNA cleavage complexes. To stabilize the E-ring, CPT keto analogues with a five-membered E-ring lacking the oxygen of the lactone ring (S38809 and S39625) have been synthesized. S39625 has been selected for advanced preclinical development based on its promising activity in tumor models. Here, we show that both keto analogues are active against purified Top1 and selective against Top1 in yeast and human cancer cells. The keto analogues show improved cytotoxicity toward colon, breast, and prostate cancer cells and leukemia cells compared with CPT. The drug-induced Top1-DNA cleavage complexes induced by the keto analogues show remarkable persistence both with purified Top1 and in cells following 1-h drug treatments. Moreover, we find that S39625 is not a substrate for either the ABCB1 (multidrug resistance-1/P-glycoprotein) or ABCG2 (mitoxantrone resistance/breast cancer resistance protein) drug efflux transporters, which sets S39625 apart from the clinically used CPT analogues topotecan or SN-38 (active metabolite of irinotecan). Finally, we show that nanomolar concentrations of S38809 or S39625 induce intense and persistent histone gamma-H2AX. The chemical stability of the keto analogues and the ability of S39625 to produce high levels of persistent Top1-DNA cleavage complex and its potent antiproliferative activity against human cancer cell lines make S39625 a promising new anticancer drug candidate. Histone gamma-H2AX could be used as a biomarker for the upcoming clinical trials of S39625.

Combined low-dose cytarabine, melphalan and mitoxantrone for older patients with acute myeloid leukemia or high-risk myelodysplastic syndrome.

BACKGROUND: Low-dose cytarabine (ara-C) has been used to treat older patients with acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome (MDS), but has resulted in complete remission for <20% of cases. A pilot study of the efficacy of a combination chemotherapy using low-dose ara-C, melphalan (Mel), and mitoxantrone (Mit) was conducted. PATIENTS AND METHODS: The treatment comprised ara-C (10 mg/m2) twice daily, melphalan (2 mg/body) every other day, and mitoxantrone (3 mg/m2) every 3 days. The treatment was discontinued if the nuclear cell count was <15,000/microl with <20% blast count in the bone marrow. The primary end-points were initial response and tolerability. RESULTS: The study comprised 9 patients with AML or high-risk MDS (median age, 75 years). Complete remission was achieved in 3 patients. All the patients displayed grade 4 neutropenia and thrombocytopenia. One patient died from sepsis. CONCLUSION: The present regimen was more effective and displayed similar safety, compared with low-dose ara-C alone.

Development of acute lymphoblastic leukemia with IgH-EPOR in a patient with secondary erythrocytosis.

We report the first patient to develop ALL with a fusion gene of the erythropoietin receptor (EPOR) with immunoglobulin heavy chain (IgH) 22 years after a diagnosis of secondary erythrocytosis with unknown etiology. The IgH-EPOR rearrangement is known to induce increased expression of EPOR, and activates EPO-associated signal pathways by exogenous EPO stimulation, resulting in the increased proliferation and survival of IgH-EPOR-positive leukemic cells. Interestingly, this case may provide supporting the possibility that IgH-EPOR-positive ALL has a growth advantage under sustained high concentrations of EPO.

Prognostic effect of peripheral blood cell counts in advanced diffuse large B-cell lymphoma treated with R-CHOP-like chemotherapy: A single institution analysis.

The primary objective of the present study was to correlate blood cell counts (lymphocyte, monocyte and platelet counts) with early disease relapse following the attainment of complete remission (CR) by the rituximab, cyclophosphamide, doxorubicin, vincristine and prednisolone (R-CHOP)-like regimen in patients with advanced diffuse large B-cell lymphoma (DLBCL). In total, 30 patients were evaluated, with a median follow-up period of 43 months. All the participating patients attained CR. In total, eight patients experienced relapse within two years of the diagnosis, and the three-year overall survival rate was recorded as 77%. The peripheral counts for lymphocytes, monocytes and platelets, and the lymphocyte-monocyte ratio, all of which have been reported to be prognostic in DLBCL, were assessed. None of these parameters were correlated with the incidence of early relapse or with the prognosis. The lymphocyte count was higher in the patients with durable remission than in those who relapsed, however, no significant differences were identified. Thus, the present study concluded that early disease relapse was not predicted by peripheral blood cell counts in advanced DLBCL that reached CR using the R-CHOP-like regimen.

Inhibition of repair of carboplatin-induced DNA damage by 9-beta-D-arabinofuranosyl-2-fluoroadenine in quiescent human lymphocytes.

Previous studies including ours have demonstrated that DNA repair is one of the important targets of fludarabine. The aim of this study is to clarify a mechanistic interaction of carboplatin and F-ara-A, from the perspective of F-ara-A-mediated inhibition of DNA repair initiated by carboplatin. Using human quiescent lymphocytes, we focused on DNA repair, since these cells provide a model of dormant cells. To evaluate the carboplatin-induced DNA incision and its repair, we used the alkaline comet assay. When lymphocytes were incubated with carboplatin, a dose-dependent increase in the tail-moment was observed. Then, tail-moment decreased in proportion to the incubation period in fresh media and recovered to the control level at 4 h. DNA rejoining was completely inhibited by F-ara-A at 10 microM through 0 to 6 h after washing out of these drugs and this F-ara-A-induced inhibition was concentration-dependent. Cellular damage after drug exposure was evaluated with the induction of apoptosis as well as cytotoxic effect. Exposure to carboplatin alone did not induce any apparent cellular damage in quiescent lymphocytes. In contrast, a more than additive induction of apoptosis as well as an enhancement of cytotoxic action was observed in cells treated with a combination of carboplatin and F-ara-A. In the CEM cell line, there was no enhancement of the cytotoxic action of these drugs, despite the clear demonstration of an inhibitory effect on DNA repair. These results indicate that chemotherapy with carboplatin opened a new target for F-ara-A by initiating DNA repair in quiescent cells.

Utility of PCR amplification and DNA microarray hybridization of 16S rDNA for rapid diagnosis of bacteremia associated with hematological diseases.

OBJECTIVES: The rapid diagnosis of bacteremia is crucial for patient management including the choice of antimicrobial therapy, especially in cases of hematological disease, because neutropenia occurs frequently during antineoplastic chemotherapy or disease progression. We describe a rapid detection and identification system that uses universal PCR primers to amplify a variable region of bacterial 16S ribosomal DNA (rDNA), followed by DNA microarray hybridization. METHODS: Probes for 72 microorganisms including most causal clinical pathogens were spotted onto a microarray plate. The DNA microarray and conventional methods of identification were applied to 335 cultures from patients with hematological diseases. RESULTS: Forty-one samples (12.2%) tested positive by conventional blood culture test in a few days, while 40 cases (11.9%) were identified by the new method within 24 h. The sensitivity and specificity of this new method were 93% and 99%, respectively, compared with conventional blood culture testing. CONCLUSIONS: PCR combined with a DNA microarray is useful for the management of febrile patients with hematological diseases.

Variation of urate transport in the nephrons in subtypes of hyperuricemia.

BACKGROUND: Hyperuricemia cases (HU) can be classified into four subgroups by combining the two main causes of hyperuricemia, i.e. urate underexcretion and overproduction. These subgroups are as follows: underexcretion-type cases (UE); overproduction-type cases (OP); combined-type cases, and normal-type cases. Since urinary urate excretion (Uua) and urate clearance differ significantly between UE and OP, urate transport in the nephrons and the intratubular urate contents might also differ. Such differences might help clarify the pathophysiology of urate underexcretion in subgroups of hyperuricemia, and thus reveal its underlying mechanisms. METHODS: Urate transport coefficients in each subtype of HU were determined employing the previously reported benzbromarone-loading urate clearance tests. The subtype cases of HU were plotted on a graph of urate transport coefficients versus Uua as coordinates. The characteristic features in the distribution of subtype cases on graphs were analyzed in relation to Uua. RESULTS: The mean (±standard error) tubular secretion rate (TSR) in the UE (48.7 ± 1.7 ml/min) was significantly lower and the postsecretory urate reabsorption rate (R2) in the UE (0.904 ± 0.004) was significantly higher than those in the normal controls (78.0 ± 2.1 ml/min and 0.877 ± 0.003) or the OP (61.1 ± 3.2 ml/min and 0.861 ± 0.009). Decrements of TSR and increments of R2 in the UE were largest in the subtypes of the HU, in terms of case numbers and the deviation rate of the group. Conversely, decrements of TSR and increments of R2 were smallest in the OP. A significant correlation was identified between TSR and Uua (r = 0.345, p < 0.0001), and a significant negative correlation was also found between R2 and Uua (r = -0.393, p < 0.0001). CONCLUSION: IN THE UE, HYPERURICEMIA IS INDUCED MAINLY BY URATE UNDEREXCRETION, WHICH RESULTS FROM THE COMBINATION OF TWO MAIN CAUSES IN URATE TRANSPORTERS OF THE NEPHRON: significantly lower TSR and significantly higher R2. Neither of these was observed in OP. Differences in urate transporters in subtypes of the HU might be important not only for understanding the pathophysiology and mechanisms of urate underexcretion and hyperuricemia, but also for providing a strategic therapy for hyperuricemia.

Detectable Wilms' tumor-1 transcription at treatment completion is associated with poor prognosis of acute myeloid leukemia: a single institution's experience.

BACKGROUND/AIM: The present retrospective study was conducted to measure Wilms' tumor-1 (WT1) mRNA levels in the peripheral blood of patients with acute myeloid leukemia (AML) in order to examine any association with the clinical outcomes. PATIENTS AND METHODS: A total of 58 AML patients were evaluated retrospectively in our institution. WT1 transcripts were determined by real-time reverse transcriptase-polymerase chain reaction in peripheral blood samples. RESULTS: WT1 levels at diagnosis did not vary according to response of induction treatments, and the levels were comparable between the patients with durable remission and the patients with relapse of disease. WT1 levels at the completion of the treatment were higher in the group with relapse of disease than in the group with sustained remission. Detectable WT1 transcripts after the completion of chemotherapy courses were associated with poor prognoses. CONCLUSION: WT1 mRNA levels at treatment completion may predict for prognosis of AML.

A high serum uric acid level is associated with poor prognosis in patients with acute myeloid leukemia.

Uric acid in serum (S-UA) is produced by the breakdown of the cellular nucleic acids of leukemia cells, and may be a marker of disease aggressiveness. S-UA levels were examined for association with clinical outcomes in patients with acute myeloid leukemia (AML). Fifty-six patients with AML admitted to our Institution were evaluated retrospectively. The median S-UA level at diagnosis was 5.0 mg/dl (range 2-13.8 mg/dl). The S-UA levels did not correlate with peripheral lactate dehydrogenase, peripheral white blood cell counts, or peripheral blast counts, and were not proportional to bone marrow blast counts or marrow cellularity. The S-UA levels in the patients who achieved complete remission were slightly lower than those in those who did not. S-UA levels less than, or equal to the median (5.0 mg/dl) were significantly associated with better prognoses, compared with S-UA levels greater than 5.0 mg/dl. Thus, the S-UA level may predict the prognosis of AML, and is a versatile and cost-effective test for such a purpose.

Early relapse is associated with high serum soluble interleukin-2 receptor after the sixth cycle of R-CHOP chemotherapy in patients with advanced diffuse large B-cell lymphoma.

The clinical significance of serum soluble interleukin-2 receptor (sIL2R) levels was retrospectively assessed in patients with advanced diffuse large B-cell lymphoma (DLBCL). Twenty-one patients, who were newly-diagnosed with advanced DLBCL (stage III and IV) between 2006 and 2009, were evaluated. The median follow-up period was 37 months. All patients received 6-8 cycles of chemotherapy with rituximab in combination with doxorubicin, cyclophosphamide, vincristine, and prednisolone (CHOP)-like regimens and attained complete remission. Although all patients reached complete remission, six patients experienced disease relapse within 1 year after treatment completion. The overall survival was significantly poorer in patients with relapse than in patients with durable remission. The sIL2R levels after the sixth cycle of treatment were significantly higher in the relapse group than in the non-relapse group. Thus, the present study suggests sIL2R levels to be a valuable predictor for the prognosis of patients with advanced DLBCL.

Wilms' tumor-1 transcript in peripheral blood helps diagnose acute myeloid leukemia and myelodysplastic syndrome in patients with pancytopenia.

BACKGROUND/AIM: Pancytopenia is caused by acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), aplastic anemia (AA), or by non-hematological diseases. Because Wilms' tumor-1 (WT1) is overexpressed in patients with AML and MDS, its expression level may be helpful for diagnosing these hematological malignancies. PATIENTS AND METHODS: We retrospectively investigated the WT1 transcripts in peripheral blood (PB) from 47 patients with decreased blood cell counts. RESULTS: The final diagnoses included AML, MDS, AA, drug poisoning, and non-hematological diseases. PB WT1 mRNA was overexpressed in AML and MDS, whereas the patients with other diseases mostly tested negatively for the transcript. The patients with MDS with higher marrow blast counts had higher PB WT1 mRNA levels. The sensitivity of the PB WT1 transcript in detecting AML and MDS was 78%, and the specificity was 90%. CONCLUSION: The WT1 mRNA level in PB may help diagnose AML and MDS in patients with pancytopenia.

Successful Administration of Recombinant Human Soluble Thrombomodulin α (Recomodulin) for Disseminated Intravascular Coagulation during Induction Chemotherapy in an Elderly Patient with Acute Monoblastic Leukemia Involving the t(9;11)(p22;q23) MLL/AF9 Translocation.

Patients with acute myelogenous leukemia complicate with disseminated intravascular coagulation (DIC), not only at the time of the initially leukemia diagnosis, but also during induction chemotherapy. In Japan, recently, a recombinant human soluble thrombomodulin alpha (Recomodulin) has been introduced as a new type of anti-DIC agent for clinical use in patients with hematological cancer or infectious disease. We describe a 67-year-old female case in which 25,600 units of Recomodulin for 6 days were successfully administered for both initially complicating and therapy-induced DIC without any troubles of bleeding in an acute monoblastic leukemia (AML-M5a) patient with the MLL gene translocation. Furthermore, the levels of DIC biomarkers recovered rapidly after the Recomodulin treatment. Our case suggests that DIC control using Recomodulin is one of the crucial support-therapies during remission induction chemotherapy in patients with acute leukemia of which type tends to complicate extramedullary or extranodal infiltration having potential to onset DIC.

Synergistic effects of combination with fludarabine and carboplatin depend on fludarabine-mediated inhibition of enhanced nucleotide excision repair in leukemia.

Overcoming drug resistance remains a major obstacle to curing relapsed or refractory lymphoma and obtaining a beneficial long-term prognosis for patients, despite the introduction of several salvage regimens to date. Our ultimate purpose is to establish a standard second-line salvage chemotherapy regimen for curing relapsed/refractory lymphoma. In this basic pre-clinical study, we evaluated a combination regimen consisting of 9-ß-D: -arabinofuranosyl-2-fluoroadenine (F-araA) and carboplatin that targeted nucleotide excision repair (NER) of DNA in five representative leukemia lineages in vitro. Isobologram analysis demonstrated that simultaneous exposure to these two drugs produced synergistic interactions in U937 and K562 cells, in which lines showed enhanced NER activity by the measurement of UV or drug-induced DNA strand break (comet assay), or quantitation of ERCC1 mRNA (RT-PCR), a key enzyme for NER. Histone γH2AX formation was synergistically induced, but no such formation was observed after exposure to either agent alone in K562 cells. In summary, we synergistically inhibited the NER activity of leukemia cells by treating them with a combination of F-araA and carboplatin, suggesting that this combinatory regimen could be used as a novel salvage therapy for refractory or drug-resistant lymphoma.

Quantitative estimation of urate transport in nephrons in relation to urinary excretion employing benzbromarone-loading urate clearance tests in cases of hyperuricemia.

BACKGROUND: A four-component system for urate transport in nephrons has been proposed and widely investigated by various investigators studying the mechanisms underlying urinary urate excretion. However, quantitative determinations of urate transport have not been clearly elucidated yet. METHODS: The equation C(ua) = {C(cr)(1 - R(1)) + TSR}(1 - R(2)) was designed to approximate mathematically urate transport in nephrons, where R(1) = urate reabsorption ratio; R(2) = urate postsecretory reabsorption ratio; TSR = tubular secretion rate; C(ua) = urate clearance, and C(cr) = creatinine clearance. To investigate relationships between the three unknown variables (R(1), R(2), and TSR), this equation was expressed as contour lines of one unknown on a graph of the other two unknowns. Points at regular intervals on each contour line for the equation were projected onto a coordinate axis and the high-density regions corresponding to high-density intervals of a coordinate were investigated for three graph types. For benzbromarone (BBR)-loading C(ua) tests, C(ua) was determined before and after oral administration of 100 mg of BBR and C(ua)BBR(∞) was calculated from the ratio of C(ua)BBR(100)/C(ua). RESULTS: Before BBR administration, points satisfying the equation on the contour line for R(1) = 0.99 were highly dense in the region R(2) = 0.87-0.92 on all three graphs, corresponding to a TSR of 40-60 ml/min in hyperuricemia cases (HU). After BBR administration, the dense region was shifted in the direction of reductions in both R(1) and R(2), but TSR was unchanged. Under the condition that R(1) = 1 and R(2) = 0, urate tubular secretion (UTS) was considered equivalent to calculated urinary urate excretion (U(ex)) in a model of intratubular urate flow with excess BBR; C(ua)BBR(∞) = TSR was deduced from the equation at R(1) = 1 and R(2) = 0. In addition, TSR of the point under the condition that R(1) = 1 and R(2) = 0 on the graph agreed with TSR for the dense region at excess BBR. TSR was thus considered approximately equivalent to C(ua)BBR(∞), which could be determined from a BBR-loading C(ua) test. Approximate values for urate glomerular filtration, urate reabsorption, UTS, urate postsecretory reabsorption (UR(2)), and U(ex) were calculated as 9,610; 9,510; 4,490; 4,150, and 440 µg/min for HU and 6,890; 6,820; 4,060; 3,610, and 520 µg/min for normal controls (NC), respectively. The most marked change in HU was the decrease in TSR (32.0%) compared to that in NC, but UTS did not decrease. Calculated intratubular urate contents were reduced more by higher UR(2) in HU than in NC. This enhanced difference resulted in a 15.4% decrease in U(ex) for HU. CONCLUSION: Increased UR(2) may represent the main cause of urate underexcretion in HU.