Koji Kuboki

Long-term effect of epalrestat, an aldose reductase inhibitor, on the development of incipient diabetic nephropathy in Type 2 diabetic patients.

The aim of the present study was to elucidate the long-term effect of epalrestat, an aldose reductase inhibitor (ARI), on renal function in patients with type 2 diabetes mellitus showing microalbuminuria. Patients were allocated to two groups (cases and controls) matched for age, BMI, and the extent of urinary albumin excretion (UAE). Thirty-five type 2 diabetic patients presenting microalbuminuria were included in this study: cases were treated with epalrestat (150 mg/day) for 5 years. No significant changes were found in blood pressure, HbA1c, and total cholesterol in either group during the observation period. In the control group, UAE increased significantly (P<.01) from 82+/-12 mg/g Cr at the baseline to 301+/-111 mg/g Cr at the end of the study, while UAE remained unchanged, 81+/-15 mg/g Cr at the baseline and 87+/-19 mg/g Cr at the end of the study, in the epalrestat-treated group. Reciprocal creatinine measured by an enzyme assay decreased significantly (P<.01) in both groups; however, the reduction rate in the epalrestat-treated group was significantly (P<.05) smaller than that in the control group. These results suggest the potential usefulness of ARIs in preventing the progression of incipient diabetic nephropathy in patients with type 2 diabetes mellitus.

Role of protein kinase C-angiotensin II pathway for extracellular matrix production in cultured human mesangial cells exposed to high glucose levels.

The intrarenal renin-angiotensin system has been implicated in the pathogenesis of diabetic nephropathy. This study investigates the mechanisms for glucose-induced increase in angiotensin II (AII) production by human mesangial cells (MCs) in relation to protein kinase C (PKC). We also examine whether locally produced AII mediates extracellular matrix protein production in high-glucose conditions. Human MCs were cultured in 5 or 33 mmol/l glucose for 8 days, and were incubated with or without 5 mmol/l GFX, a PKC inhibitor, 0.1 micromol/l candesartan cilexetil (CC), a specific type 1 AII receptor antagonist, for another 24 h. In addition, MCs grown in 5 mmol/l glucose were incubated with 0.1 micromol/l phorbol-12,13-dibutyrate (PDBu) for 24 h. AII, TGF-beta1, fibronectin and type IV collagen in the culture media were measured by ELISA. The amount of AII secreted from MCs exposed to high-glucose levels was significantly greater (P<0.01) than that in normal glucose levels. The increase in AII production was completely prevented by GFX. The addition of PDBu mimicked the effect of glucose on AII production. The glucose-induced increases in the production of TGF-beta1, fibronectin and type IV collagen were partially, but significantly restored (P<0.01) by CC, while GFX totally abolished these effects of glucose. These results suggest that elevated glucose levels stimulate AII production via mechanisms dependent on glucose-induced PKC activation in human MCs, and that locally produced AII partly mediates the increase in mesangial matrix synthesis in high-glucose conditions.

High glucose levels enhance TGF-β1–thrombospondin-1 pathway in cultured human mesangial cells via mechanisms dependent on glucose-induced PKC activation

We have previously demonstrated that thrombospondin-1 (TSP-1) promotes activation of latent TGF-beta1 in cultured human mesangial cells (MCs) [Nephron 79 (1998) 38.]. This study was performed to clarify the relationship between protein kinase C (PKC) activity and activation of TGF-beta1 and TSP-1 production in cultured human MCs exposed to high glucose levels. MCs grown in 33 mmol/l glucose demonstrated a significant (P< .01) increase in activation of TGF-beta1 compared with those in 5 mmol/l glucose, which were evaluated by both an ELISA and a bioassay. High glucose-induced increase in active TGF-beta1 was completely inhibited by coincubation with 5 micromol/l GFX, a PKC inhibitor, and was mimicked by the addition of 0.1 micromol/l phorbol 12,13-dibutyrate (PDBu). On the other hand, increased TSP-1 production from MCs stimulated by 0.1 nmol/l recombinant TGF-beta1 and 0.1 micromol/l PDBu were significantly (P< .01) reduced by the addition of 10 nmol/l latency-associated peptide (LAP), a specific inhibitor of TGF-beta1 activity. The amount of TSP-1 secreted from MCs increased by a high ambient glucose. The glucose-induced increase in TSP-1 production was markedly attenuated by the treatment with GFX and LAP, while those agents did not affect TSP-1 production in low-glucose concentrations. Taken together, our results suggest that glucose-induced activation of TGF-beta1 is dependent on PKC activity, leading to a sequential increase in TSP-1 synthesis in cultured human MCs. Thus, we propose that high glucose conditions induce an increase in PKC-TGF-beta1 activity-TSP-1 pathway, and that glucose-induced increase in TSP-1 may synergistically facilitate TGF-beta1 activation in an autocrine manner in MCs.

A Case of Severe Acute Necrotizing Pancreatitis after Administration of Sitagliptin

A 55-year-old Japanese man with a 3-year history of type 2 diabetes mellitus was admitted to our hospital for upper abdominal pain. Control of diabetes mellitus was good with voglibose and metformin, with sitagliptin added to this regimen 8 months prior. His pancreatic enzyme levels were elevated, and abdominal computed tomography (CT) showed diffuse pancreatic swelling with fluid accumulation and ascites of CT grade 3. The patient was diagnosed with severe acute pancreatitis. There were no obvious causes for pancreatitis except the recently administered sitagliptin. Since incretin-related drugs entered the market, the number of incretin-related drugs prescriptions rapidly increased and so did the incidence of pancreatitis. There are several reports suggesting the correlation between incretin-related drugs and pancreatitis, such as a report based on data obtained from the United States Food and Drug Administration (FDA) which revealed a significant correlation between the administration of exenatide or sitagliptin and pancreatitis. However, there also is a report that denied the evidence for such in a large cohort study. The relation between incretin based drugs and pancreatitis is still controversial.

Relationship between urinary excretion of fibronectin degradation products and proteinuria in diabetic patients, and their suppression after continuous subcutaneous heparin infusion

To explore the possibility that the excretion of urinary fibronectin degradation products (U-FnDP) can be an indicator of the progression of diabetic nephropathy, U-FnDP and urinary protein(U-P) were determined in 64 diabetic patients and 11 healthy volunteers. Moreover, to determine whether continuous subcutaneous heparin infusion (CSHI) reduces elevated U-FnDP and U-P in diabetic patients with persistent proteinuria, heparin sodium was administered as a bolus subcutaneous injection of 5000 IU, followed by subcutaneous infusion of 250 IU/kg per 24 h heparin sodium for 7 days. U-FnDP excretion rate elevated proportionally to the degree of U-P. CSHI reduced significantly elevated U-FnDP from 172.68 +/- 15.79 to 100.04 +/- 14.93 micrograms/24 h (P < 0.01) and U-P from 1.76 +/- 0.13 to 1.20 +/- 0.12 g/24 h (P < 0.01). No significant changes in blood pressure and diurnal mean plasma glucose levels were found. APTT was prolonged with a decrease of AT-III activity during the treatment. These findings suggest that U-FnDP can be one of the indicators which reflects the degree of progression of diabetic nephropathy, and that CSHI may be useful for the normalization of elevated U-FnDP and reduction in U-P in diabetic nephropathy.

Increased intraglomerular thrombin formation in diabetic microangiopathy

Estimations of soluble fibrin monomer complexes (SFMC) in plasma are a convenient index of thrombin activation. Renal venous-arterial differences in plasma SFMC concentrations were determined in 16 randomly chosen diabetic patients by sampling directly and simultaneously from the renal artery and vein according to the method of Seldinger. In all subjects, SFMC concentrations were higher in the renal vein than in the renal artery, indicating that the kidney is an important source of SFMC. Venous-arterial differences were markedly elevated in patients with severe renal and retinal microangiopathy coupled with hypertension. The hypothesis is advanced that elevated plasma SFMC levels lead to abnormal fibrin deposits in lesioned glomeruli and retinal vessels. It is postulated that plasma SFMC may be a useful parameter for the assessment of diabetic vascular complications.

Transforming Growth Factor-Beta-1 Latency-Associated Peptide and Soluble Betaglycan Prevent a Glucose-Induced Increase in Fibronectin Production in Cultured Human Mesangial Cells

This study was performed to investigate the effects of transforming growth factor-β1 (TGF-β1) latency-associated peptide (LAP) and betaglycan on TGF-β1 activity, and on the glucose-induced overproduction of fibronectin in cultured human mesangial cells (MCs). We found that recombinant LAP and recombinant soluble betaglycan decrease the active form of TGF-β1, measured by ELISA, in a dose-dependent manner in a cell-free system. The effective dosages of LAP and soluble betaglycan for a 50% reduction were approximately 20- and 75-fold of the TGF-β1 concentration, respectively. The active form of TGF-β1 in the media secreted from MCs was significantly (p < 0.01) reduced by the addition of 10 nmol/l LAP and 10 nmol/l soluble betaglycan with no significant change in total (active + latent) TGF-β1. Recombinant LAP and soluble betaglycan also inhibited a recombinant TGF-β1-stimulated increase in fibronectin production in MCs. Furthermore, the glucose-induced increase in fibronectin secreted from MCs was significantly (p < 0.01) suppressed by concomitant incubation with LAP or soluble betaglycan, while these agents had no effect on fibronectin production under physiological glucose concentrations. These results indicate that recombinant LAP and soluble betaglycan suppress the glucose-induced overproduction of fibronectin presumably via inhibition of TGF-β1 activity in MCs. Further in vivo studies are needed to define the possible beneficial effects of these agents in diabetic nephropathy.