Hiroki Fujita

Vanderbilt University, Nashville, MI, United States

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Publications (27)85.26 Total impact

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    ABSTRACT: Dipeptidyl peptidase-4 (DPP-4) inhibitor is a new class of anti-diabetic drug which exerts its glucose-lowering action by suppressing the degradation of a gut incretin hormone glucagon-like peptide-1 (GLP-1). To elucidate whether treatment with stronger DPP-4 inhibitor on top of angiotensin II type 1 receptor blocker (ARB) provides greater renal protective effects, we performed a crossover study with two DPP-4 inhibitors, sitagliptin and alogliptin, in twelve type 2 diabetic patients with incipient nephropathy taking ARBs. This study consisted of three treatment periods: sitagliptin 50 mg/day for 4 weeks (first period), alogliptin 25 mg/day for 4 weeks (second period), and sitagliptin 50 mg/day for 4 weeks (third period). Significant changes in body mass index, blood pressure, serum lipids, serum creatinine, estimated glomerular filtration rate, and HbA1c were not observed among the three treatment periods. Reduced urinary levels of albumin and an oxidative stress marker 8-hydroxy-2'-deoxyguanosine (8-OHdG), increased urinary cAMP levels, and elevated plasma levels of stromal cell-derived factor-1α (SDF-1α) which is a physiological substrate of DPP-4 were observed after the switch from sitagliptin to a stronger DPP-4 inhibitor alogliptin. Given a large body of evidence indicating anti-oxidative action of cAMP and up-regulation of cellular cAMP production by SDF-1α, the present results suggest that more powerful DPP-4 inhibition on top of angiotensin II type 1 receptor blockade would offer additional protection against early-stage diabetic nephropathy beyond that attributed to glycemic control, via reduction of renal oxidative stress by SDF-1α-cAMP pathway activation.
    Endocrine Journal 11/2013; · 2.02 Impact Factor
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    ABSTRACT: Glucagon-like peptide-1 (GLP-1) is a gut incretin hormone that has an antioxidative protective effect on various tissues. Here, we determined whether GLP-1 has a role in the pathogenesis of diabetic nephropathy using nephropathy-resistant C57BL/6-Akita and nephropathy-prone KK/Ta-Akita mice. By in situ hybridization, we found the GLP-1 receptor (GLP-1R) expressed in glomerular capillary and vascular walls, but not in tubuli, in the mouse kidney. Next, we generated C57BL/6-Akita Glp1r knockout mice. These mice exhibited higher urinary albumin levels and more advanced mesangial expansion than wild-type C57BL/6-Akita mice, despite comparable levels of hyperglycemia. Increased glomerular superoxide, upregulated renal NAD(P)H oxidase, and reduced renal cAMP and protein kinase A (PKA) activity were noted in the Glp1r knockout C57BL/6-Akita mice. Treatment with the GLP-1R agonist liraglutide suppressed the progression of nephropathy in KK/Ta-Akita mice, as demonstrated by reduced albuminuria and mesangial expansion, decreased levels of glomerular superoxide and renal NAD(P)H oxidase, and elevated renal cAMP and PKA activity. These effects were abolished by an adenylate cyclase inhibitor SQ22536 and a selective PKA inhibitor H-89. Thus, GLP-1 has a crucial role in protection against increased renal oxidative stress under chronic hyperglycemia, by inhibition of NAD(P)H oxidase, a major source of superoxide, and by cAMP-PKA pathway activation.Kidney International advance online publication, 23 October 2013; doi:10.1038/ki.2013.427.
    Kidney International 10/2013; · 8.52 Impact Factor
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    ABSTRACT: BACKGROUND: Renal scintigraphy using 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) is widely used for the assessment of renal function in humans. However, the application of this method to animal models of renal disease is currently limited, especially in rodents. Here, we have applied 99mTc-MAG3 renal scintigraphy to a mouse model of unilateral ureteral obstruction (UUO) and evaluated its utility in studying obstructive renal disease. METHODS: UUO mice were generated by complete ligation of the left ureter. Sham-operated mice were used as a control. Renal function was investigated on days 0, 1, 3, and 6 post-surgery using dynamic planar imaging of 99mTc-MAG3 activity following retro-orbital injection. Time-activity curves (TACs) were produced for individual kidneys and renal function was assessed by 1) the slope of initial 99mTc-MAG3 uptake (SIU), which is related to renal perfusion; 2) peak activity; and 3) the time-to-peak (TTP). The parameters of tubular excretion were not evaluated in this study as 99mTc-MAG3 is not excreted from UUO kidneys. RESULTS: Compared to sham-operated mice, SIU was remarkably (>60%) reduced in UUO kidneys at day 1 post surgery and the TACs plateaued, indicating that 99mTc-MAG3 is not excreted in these kidneys. The plateau activity in UUO kidneys was relatively low (~40% of sham kidney's peak activity) as early as day1 post surgery, demonstrating that uptake of 99mTc-MAG3 is rapidly reduced in UUO kidneys. The time to plateau in UUO kidneys exceeded 200 sec, suggesting that 99mTc-MAG3 is slowly up-taken in these kidneys. These changes advanced as the disease progressed. SIU, peak activity and TTPs were minimally changed in contra-lateral kidneys during the study period. CONCLUSIONS: Our data demonstrate that renal uptake of 99mTc-MAG3 is remarkably and rapidly reduced in UUO kidneys, while the changes are minimal in contra-lateral kidneys. The parametric analysis of TACs suggested that renal perfusion as well as tubular uptake is reduced in UUO kidneys. This imaging technique should allow non-invasive assessments of UUO renal injury and enable a more rapid interrogation of novel therapeutic agents and protocols.
    BMC Nephrology 12/2012; 13(1):168. · 1.52 Impact Factor
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    ABSTRACT: Superoxide dismutase (SOD) is a major defender against excessive superoxide generated under hyperglycemia. We have recently reported that renal SOD1 (cytosolic CuZn-SOD) and SOD3 (extracellular CuZn-SOD) isoenzymes are remarkably down-regulated in KK/Ta-Ins2(Akita) diabetic mice, which exhibit progressive diabetic nephropathy (DN), but not in DN-resistant C57BL/6- Ins2(Akita) (C57BL/6-Akita) diabetic mice. To determine the role of SOD1 and SOD3 in DN, we generated C57BL/6-Akita diabetic mice with deficiency of SOD1 and/or SOD3 and investigated their renal phenotype at the age of 20 weeks. Increased glomerular superoxide levels were observed in SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita mice but not in SOD1(+/+)SOD3(-/-) C57BL/6-Akita mice. The SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita mice exhibited higher glomerular filtration rate, increased urinary albumin levels, and advanced mesangial expansion as compared with SOD1(+/+)SOD3(+/+) C57BL/6-Akita mice, yet the severity of DN did not differ between the SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita groups. Increased renal mRNA expression of transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF), reduced glomerular nitric oxide (NO), and increased renal prostaglandin E2 (PGE2) production were noted in the SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita mice. This finding indicates that such renal changes in fibrogenic cytokines, NO, and PGE2, possibly caused by superoxide excess, would contribute to the development of overt albuminuria by promoting mesangial expansion, endothelial dysfunction, and glomerular hyperfiltration. The present results demonstrate that deficiency of SOD1, but not SOD3, increases renal superoxide in the setting of diabetes and causes overt renal injury in nephropathy-resistant diabetic mice, and that SOD3 deficiency does not provide additive effects on the severity of DN in SOD1-deficient C57BL/6-Akita mice.
    Metabolism: clinical and experimental 05/2012; · 3.61 Impact Factor
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    ABSTRACT: Mice with endothelial nitric oxide synthase (eNOS) deletions have defined the crucial role of eNOS in vascular development, homeostasis, and pathology. However, cell specific eNOS function has not been determined, although an important role of eNOS has been suggested in multiple cell types. Here, we have generated a floxed eNOS allele in which exons 9-12, encoding the sites essential to eNOS activity, are flanked with loxP sites. Mice homozygous for the floxed allele showed normal eNOS protein levels and no overt phenotype. Conversely, homozygous mice with Cre-deleted alleles displayed truncated eNOS protein, lack of vascular NO production, and exhibited similar phenotype to eNOS knockout mice, including hypertension, low heart rate, and focal renal scarring. These findings demonstrate that the floxed allele is normal and it can be converted to a non-functional eNOS allele through Cre recombination. This mouse will allow time- and cell-specific eNOS deletion. genesis 50:685-692, 2012. © 2012 Wiley Periodicals, Inc.
    genesis 03/2012; 50(9):685-92. · 2.04 Impact Factor
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    ABSTRACT: Renal superoxide excess, which is induced by an imbalance of the superoxide-producing enzyme NAD(P)H oxidase and the superoxide-scavenging enzyme superoxide dismutase (SOD) under hyperglycemia, increases oxidative stress and contributes to the development of diabetic nephropathy. In this study, we treated non-obese and hypoinsulinemic C57BL/6-Ins2(Akita) (C57BL/6-Akita) diabetic mice with telmisartan (5 mg kg(-1) per day), an angiotensin II type 1 receptor blocker, or amlodipine (5 mg kg(-1) per day), a calcium channel blocker, for 4 weeks and compared the effects of these two anti-hypertensive drugs on renal NAD(P)H oxidase, SOD and transcription factor Nrf2 (NF-E2-related factor 2), which is known to upregulate several antioxidant enzymes including SOD. Vehicle-treated C57BL/6-Akita mice exhibited higher renal NAD(P)H oxidase and lower renal SOD activity with increased levels of renal superoxide than the C57BL/6-wild-type non-diabetic mice. Interestingly, telmisartan treatment not only reduced NAD(P)H oxidase activity but also enhanced SOD activity in C57BL/6-Akita mouse kidneys, leading to a reduction of renal superoxide levels. Furthermore, telmisartan-treated C57BL/6-Akita mice increased the renal protein expression of SOD and Nrf2. In parallel with the reduction of renal superoxide levels, a reduction of urinary albumin levels and a normalization of elevated glomerular filtration rate were observed in telmisartan-treated C57BL/6-Akita mice. In contrast, treatment with amlodipine failed to modulate renal NAD(P)H oxidase, SOD and Nrf2. Finally, treatment of C57BL/6-Akita mice with apocynin, an NAD(P)H oxidase inhibitor, also increased the renal protein expression of SOD and Nrf2. Collectively, our data suggest that NAD(P)H oxidase negatively regulates renal SOD, possibly by downregulation of Nrf2, and that telmisartan could upregulate renal SOD by the suppression of NAD(P)H oxidase and subsequent upregulation of Nrf2, leading to the amelioration of renal oxidative stress and diabetic renal changes.
    Hypertension Research 11/2011; 35(2):213-20. · 2.94 Impact Factor
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    ABSTRACT: Growing evidence indicates that oxidative stress induced by excessive superoxide has a central role in the pathogenesis of diabetic nephropathy (DN). Telmisartan, one of the currently available angiotensin II type 1 receptor blockers (ARBs), has been shown to exert a more powerful proteinuria (albuminuria) reduction in patients with DN, but whether the prominent renoprotective effect of telmisartan is mediated through enhancing antioxidant defense capacity and reducing oxidative stress has not been fully elucidated. The present study first revealed that the serum activity of superoxide dismutase (SOD) responsible for superoxide removal is reduced in the DN stage of microalbuminuria, but not in normoalbuminuria in type 2 diabetic patients. We next examined the alteration of SOD and oxidative stress following an 8-week treatment with telmisartan (40 mg per day) in 12 type 2 diabetic patients with microalbuminuria. Interestingly, the telmisartan treatment not only reduced the circulating levels of two oxidative stress markers, 8-hydroxy-2'-deoxyguanosine (8-OHdG) and nitrotyrosine (NT), but also enhanced serum SOD activity. Notably, a significant correlation was observed between the increase in serum SOD activity and the reduction in albuminuria. We further compared the anti-oxidative effect of telmisartan with that of losartan, another member of the ARB class, by implementing an 8-week interval crossover treatment with these ARBs in another 12 microalbuminuric type 2 diabetic patients. The patients showed higher serum SOD activity, and lower circulating levels of 8-OHdG and NT, during treatment with telmisartan than with losartan. These results suggest that telmisartan has a more potent antioxidative effect through its ability to enhance SOD activity in type 2 diabetic patients with microalbuminuria.
    Hypertension Research 08/2011; 34(12):1302-8. · 2.94 Impact Factor
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    ABSTRACT: Aims/Introduction: To clarify clinical characteristics related to optimal glycemic control achieved after adding once-daily pre-dinner biphasic insulin aspart 70/30 (BIAsp 30) in Japanese type 2 diabetic (T2D) patients with oral antidiabetic drug (OAD) failure. Materials and Methods: Under this regimen, we evaluated changes in HbA1c levels and daily self-monitoring blood glucose (BG) profiles, as well as the incidences of hypoglycemia and retinopathy progression. The patients adjusted BIAsp 30 dosages themselves every 3-4 days according to a pre-determined algorithm to achieve fasting BG levels of 101-120 mg/dL. HbA1c levels were expressed as Japan Diabetes Society values. Results: Of 29 enrolled patients, 22 (HbA1c levels, 8.5 ± 1.5% [mean ± SD]) and 20 patients completed the 16- and 24-week follow-up, respectively. At 16 weeks 68.2 and 45.5%, and at 24 weeks 80.0 and 35% of patients had achieved HbA1c levels of <7.0 and <6.5%, respectively. The patients who had achieved optimal glycemic control, including daytime postprandial BG profiles after treatment, had lower post-breakfast BG excursions at baseline, shorter diabetes durations and younger age. No severe hypoglycemic episodes were recorded. Progression of retinopathy was observed in 3 of the 29 enrolled patients. Conclusions: Lower post-breakfast BG excursions, shorter diabetes duration and younger age in Japanese T2D patients with OAD failure might warrant optimal glycemic control with safety after adding once-daily pre-dinner BIAsp 30 initiating regimen. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.00062.x, 2010).
    Journal of diabetes investigation. 01/2011; 2(1):63-70.
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    ABSTRACT: Superoxide excess plays a central role in tissue damage that results from diabetes, but the mechanisms of superoxide overproduction in diabetic nephropathy (DN) are incompletely understood. In the present study, we investigated the enzyme superoxide dismutase (SOD), a major defender against superoxide, in the kidneys during the development of murine DN. We assessed SOD activity and the expression of SOD isoforms in the kidneys of two diabetic mouse models (C57BL/6-Akita and KK/Ta-Akita) that exhibit comparable levels of hyperglycemia but different susceptibility to DN. We observed down-regulation of cytosolic CuZn-SOD (SOD1) and extracellular CuZn-SOD (SOD3), but not mitochondrial Mn-SOD (SOD2), in the kidney of KK/Ta-Akita mice which exhibit progressive DN. In contrast, we did not detect a change in renal SOD expression in DN-resistant C57BL/6-Akita mice. Consistent with these findings, there was a significant reduction in total SOD activity in the kidney of KK/Ta-Akita mice compared with C57BL/6-Akita mice. Finally, treatment of KK/Ta-Akita mice with a SOD mimetic, tempol, ameliorated the nephropathic changes in KK/Ta-Akita mice without altering the level of hyperglycemia. Collectively, these results indicate that down-regulation of renal SOD1 and SOD3 may play a key role in the pathogenesis of DN.
    Journal of the American Society of Nephrology 07/2009; 20(6):1303-13. · 9.47 Impact Factor
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    ABSTRACT: Clinical management and therapeutic intervention from the earlier stage of diabetic nephropathy (DN) is of major importance to prevent the progression of DN to end stage renal disease. At present, the measurement of albuminuria is used as a standardized non-invasive test for the diagnosis of early DN. Diabetic kidney disease, however, is not detected by this test in some cases. Hence, efforts have been made to find better diagnostic biomarkers of DN. These investigations have identified several proteins that can be used as diagnostic biomarkers of DN, including urinary immunoglobulin G, transferrin, ceruloplasmin and serum cystatin-C. Further, recent proteomics approaches have isolated potential biomarkers of DN. This review summarizes the diagnostic biomarkers developed over the last decade, and comments on their impacts in the diagnosis and management of this disease.
    Expert Opinion on Medical Diagnostics 02/2008; 2(2):161-9.
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    ABSTRACT: Previous studies have shown that Prostaglandin E(2) (PGE(2)) inhibits glucose-stimulated insulin secretion. However, the role of cyclooxygenase (COX)-1 vs. COX-2 derived PGE(2) production in glucose-stimulated insulin secretion remains poorly understood. Here we investigated the expression of COX-1 and COX-2 in pancreatic islets and the effect of selective inhibition of COX-1 and COX-2 on glucose-stimulated insulin secretion using C57BL/6 (B6) mice. Although immunofluorescence histochemistry showed the constitutive expression of both COX-1 and COX-2 in B6 mouse pancreatic islets, insulin secretion and hyperglycemia after glucose loading were ameliorated in B6 mice treated with selective COX-2 inhibitor (SC58236) for 18 weeks. Interestingly, incubation with selective COX-2 inhibitor for 24h led to a reduction in PGE(2) production in pancreatic islets isolated from B6 mice. In addition, selective COX-2 inhibition enhanced insulin secretion from the isolated islets. These results collectively suggest that selective inhibition of COX-2 enhances glucose-stimulated insulin secretion through a reduction in PGE(2) production in pancreatic islets.
    Biochemical and Biophysical Research Communications 12/2007; 363(1):37-43. · 2.28 Impact Factor
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    ABSTRACT: The minimental state examination (MMSE) is a widely used, standardized method to assess cognitive function including movement-related disorders with high reliability. We studied the relationship between MMSE scores and the ability to take oral medications correctly (ingestion compliance) in 70 elderly inpatients (mean age 71.3+/-7.0 years). Patients with abnormal glucose tolerance as determined by an HbA(1c) level of 5.8% or greater including diabetes showed a trend of lower MMSE scores compared with patients with normal glucose tolerance, and the scores were negatively correlated with HbA1c, age, and systolic blood pressure (P<0.05). Self-management in taking oral medications was very difficult in 4 patients whose MMSE scores were 21 points or less. Thus ingestion supervisions by nurses were required in these patients. Furthermore, 9 of 12 noncompliant patients had MMSE scores ranging from 22 to 26 points. We instructed these patients to take medications in a one-dose package as a useful tool to improve compliance. The MMSE score was 27 or higher in 44 of 54 compliant patients, and 10 patients had scores ranging from 21 to 26. The sensitivity and specificity for noncompliance at an MMSE score cut-off point of 26 were 75.0% and 81.5%, respectively. In conclusion, it is necessary to coordinate ingestion methods matched to each patient according to their abilities to comply with medication schedules. They should be preevaluated with the MMSE to improve ingestion compliance. The MMSE is a recommended test in hospitalized elderly patients for the assessment of the ability to take medications safely.
    Yakugaku zasshi journal of the Pharmaceutical Society of Japan 10/2007; 127(10):1731-8. · 0.31 Impact Factor
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    ABSTRACT: To explore the renoprotective and anti-inflammatory effects of pravastatin, we analyzed the changes in renal function and urinary monocyte chemoattractant protein-1 (MCP-1) level as a renal tubulointerstitial inflammatory biomarker and serum MCP-1 level as a systemic inflammatory biomarker following the introduction of treatment with 10 mg/day of pravastatin in 10 hyperlipidemic type 2 diabetic patients with normoalbuminuria. Twelve months of the pravastatin treatment did not affect urinary levels of albumin, transferrin, N-acetylglucosaminidase, or MCP-1 in the hyperlipidemic diabetic patients, whereas the treatment significantly reduced serum levels of MCP-1 in the patients. The pravastatin treatment effectively lowered low-density lipoprotein cholesterol (LDL-C) levels in the hyperlipidemic diabetic patients to levels nearly to those in 11 non-hyperlipidemic type 2 diabetic patients with normoalbuminuria. Interestingly, serum MCP-1 levels were significantly lower in the hyperlipidemic patients treated with pravastatin than in the non-hyperlipidemic patients. No significant correlation was observed between serum LDL-C and MCP-1 levels in all the data in the hyperlipidemic patients before and after the pravastatin treatment and in the non-hyperlipidemic patients. These results collectively indicate that pravastatin may ameliorate systemic vascular inflammation rather than local renal inflammation in hyperlipidemic type 2 diabetic patients with normoalbuminuria, independent of its cholesterol-lowering effects.
    Renal Failure 02/2007; 29(7):791-6. · 0.78 Impact Factor
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    ABSTRACT: Adiponectin is an adipose-derived protein which has anti-inflammatory and anti-atherogenic properties in addition to insulin-sensitizing effects. To date, the role of adiponectin in the pathogenesis of diabetic nephropathy remains unclear. The aim of the present study was to explore the relationship between adiponectin and renal tubular injury in diabetic nephropathy. We determined serum and urinary adiponectin levels in type 2 diabetic patients with normoalbuminuria (n = 19), microalbuminuria (n = 18), and overt diabetic nephropathy (n = 16), and then analyzed the correlations between serum and urinary adiponectin, urinary N-acetylglucosaminidase (NAG) as a clinical marker of renal tubular injury, urinary monocyte chemoattractant protein-1 (MCP-1) as an inflammatory marker in renal tubulointerstitium, and clinical markers of renal disease. Notably, serum and urinary adiponectin levels were significantly increased in patients with overt diabetic nephropathy compared to those with normoalbuminuria and microalbuminuria. In univariate linear regression analysis, serum adiponectin levels were positively correlated with serum creatinine (r = 0.648, P<0.0001), urinary albumin (r = 0.583, P<0.0001), urinary NAG (r = 0.406, P<0.01), urinary MCP-1 (r = 0.514, P<0.0001), and urinary adiponectin (r = 0.691, P<0.0001) levels in all diabetic patients. Urinary adiponectin levels were also positively correlated with serum creatinine (r = 0.729, P<0.0001), urinary albumin (r = 0.799, P<0.0001), urinary NAG (r = 0.701, P<0.0001), and urinary MCP-1 (r = 0.801, P<0.0001) levels in all diabetic patients. Multiple linear regression analysis showed that serum creatinine and urinary adiponectin levels were independently associated with serum adiponectin levels (r(2) = 0.522), and that serum creatinine, urinary NAG, urinary MCP-1, and serum adiponectin levels were independent determinants of urinary adiponectin levels (r(2) = 0.851). These results collectively indicate that renal insufficiency and tubular injury possibly play a contributory role in increases in serum and urinary adiponectin levels in overt diabetic nephropathy. We presume that an increase in circulating adiponectin in overt diabetic nephropathy might be a physiological response to mitigate renal tubular injury and to prevent the further progression of diabetic nephropathy through its anti-inflammatory and anti-atherogenic effects.
    Endocrine Journal 12/2006; 53(6):745-52. · 2.02 Impact Factor
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    ABSTRACT: Differential susceptibility to diabetic nephropathy has been observed in humans, but it has not been well defined in inbred strains of mice. The present studies characterized the severity of diabetic nephropathy in six inbred mouse strains including C57BL/6J, DBA/2J, FVB/NJ, MRL/MpJ, A/J, and KK/HlJ mice. Diabetes mellitus was induced using low-dose streptozotocin injection. Progression of renal injury was evaluated by serial measurements of urinary albumin excretion, glomerular filtration rate (GFR), and terminal assessment of renal morphology over 25 weeks. Despite comparable levels of hyperglycemia, urinary albumin excretion and renal histopathological changes were dramatically different among strains. DBA/2J and KK/HlJ mice developed significantly more albuminuria than C57BL/6J, MRL/MpJ, and A/J mice. Severe glomerular mesangial expansion, nodular glomerulosclerosis, and arteriolar hyalinosis were observed in diabetic DBA/2J and KK/HlJ mice. Glomerular hyperfiltration was observed in all diabetic strains studied except A/J. The significant decline in GFR was not evident over the 25-week period of study, but diabetic DBA/2J mice exhibited a tendency for GFR to decline. Taken together, these results indicate that differential susceptibility to diabetic nephropathy exists in inbred mice. DBA/2J and KK/HlJ mice are more prone to diabetic nephropathy, whereas the most widely used C57BL/6J mice are relatively resistant to development of diabetic nephropathy.
    Diabetes 10/2005; 54(9):2628-37. · 8.47 Impact Factor
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    ABSTRACT: Decreased circulating levels of adiponectin, a novel adipose-derived adipocytokine, in obesity possibly contribute to the development of insulin resistance which is a major factor in the pathogenesis of type 2 diabetes. The present study was conducted to examine whether circulating and adipose tissue adiponectin levels are modulated by chronic treatment with metformin and intensive treatment with insulin in murine models of obesity and type 2 diabetes, db/db mice with a C57BL/KsJ genetic background. Nine-week-old male db/db mice were treated with metformin, insulin, and vehicle for 4 weeks. Expectedly, metformin treatment led to inhibition of weight gain and improvement of hyperinsulinemia. Insulin treatment lowered fasting blood glucose levels to normal values, although it sustained hyperinsulinemic state. However, after 4 weeks of treatment, serum adiponectin levels were not significantly elevated in either metformin-treated or insulin-treated db/db mouse group (14.2 +/- 0.7 and 16.7 +/- 1.0 microg/ml, respectively) compared to vehicle-treated group (14.9 +/- 0.6 microg/ml). Similarly, adipose tissue adiponectin levels determined by Western blot analysis were not increased in either metformin-treated or insulin-treated group relative to vehicle-treated group. Recent studies have shown that adiponectin possibly has the same physiological effects on lipid and glucose metabolism that metformin has. Therefore, an elevation in blood concentration of metformin following the treatment might lead to suppression in adiponectin synthesis in adipose tissue, independent of inhibition in weight gain and improvement in hyperinsulinemia by metformin treatment. The present results indicate that adiponectin is not involved in the mechanism by which metformin treatment enhances insulin sensitivity. Moreover, our results suggest that adiponectin synthesis in adipose tissue may be suppressed under hyperinsulinemic state sustained by insulin treatment, even though hyperglycemia is markedly reduced. We conclude that antidiabetic treatment with metformin and insulin does not affect circulating and adipose tissue adiponectin levels.
    Endocrine Journal 09/2005; 52(4):427-33. · 2.02 Impact Factor
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    ABSTRACT: The aim of this study was to elucidate what kind of plasma proteins would change their urinary excretions when the glomerular filtration rate (GFR) was increased. We measured urinary excretions of three plasma proteins with different molecular radii (MR) and isoelectric points (pI): albumin, orosomucoid (OM) and transferrin (Tf), after acute protein loading in healthy subjects. Urinary excretion of OM with more anioic charge and smaller MR than albumin, and Tf with more cationic charge and slightly larger molecular weight than albumin, significantly increased in parallel with increased creatinine clearances after acute protein loading. These renal responses returned to basal levels 9 h after protein ingestion. In contrast, increases in urinary excretion of albumin were not observed. Because these findings could not be explained by changes in either size or charge selectivity of shunt pores in the glomerular capillary wall, it is suggested that urinary excretion of albumin may have a special property that distinguishes it from other plasma proteins and may be a less sensitive marker to reflect changes in renal hemodynamics than the other plasma proteins.
    Nephron Clinical Practice 02/2005; 100(2):c33-7. · 1.65 Impact Factor
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    ABSTRACT: Increased urinary excretions of several plasma proteins with different molecular radii <55 A and different isoelectric points (pI), such as IgG, ceruloplasmin, transferrin, and orosomucoid, have been independently reported to precede the development of microalbuminuria in diabetic patients. We examined whether increases in urinary excretions of these proteins would be in parallel in the same patient. Urinary excretion rates of proteins mentioned above in timed overnight urine samples were evaluated in 61 normoalbuminuric type 2 diabetic patients (group D) aged 40-60 years and in 17 age-matched control subjects (group C). The excretion rates of these proteins were significantly higher in group D than in group C. These exhibited a strong linear correlation with each other and had a weak correlation with the excretion rate of N-acethylglucosaminidase. The excretion rate of alpha2-macroglobulin with large molecular radii of 88 A was not different between groups C and D, nor did they have any correlations with the excretion rates of the other proteins. Creatinine clearance and blood pressure levels in group D were significantly higher than those in group C. In normoalbuminuric diabetic patients, excretion rates of plasma proteins with molecular radii <55 A increased in parallel with each other. In view of our previous finding that urinary excretions of these plasma proteins selectively increased in parallel with enhanced glomerular filtration rate after acute protein loading, the present finding may be explained by renal hemodynamic changes, such as increased intraglomerular hydraulic pressure.
    Diabetes Care 05/2004; 27(5):1176-81. · 8.57 Impact Factor
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    ABSTRACT: Adiponectin, a novel adipose-derived adipocytokine, has beneficial effects not only on improvement of insulin sensitivity but also on mitigation of vascular damage. To evaluate whether adiponectin is implicated in the pathogenesis of diabetic nephropathy characterized by microvascular damage, we examined urinary and serum adiponectin levels in type 2 diabetic patients with different stages of nephropathy. We first confirmed adiponectin is excreted into urine through Western blot analysis, followed by measurements of urinary and serum adiponectin levels by radioimmunoassay. Interestingly, urinary adiponectin excretion levels were markedly increased in patient group with overt nephropathy relative to the groups without nephropathy and with incipient nephropathy. Surprisingly, serum adiponectin levels were also elevated in patient group with overt nephropathy. Increased urinary adiponectin excretion may result from elevations in circulating adiponectin levels and enhanced filtration of circulating adiponectin through the damaged kidney. Furthermore, adiponectin synthesis in adipose tissue and its secretion into circulating blood may be enhanced to mitigate microvascular damage in the advanced stage of diabetic nephropathy.
    Biochemical and Biophysical Research Communications 04/2004; 316(1):165-9. · 2.28 Impact Factor
  • Endocrine Journal 01/2004; 50(6):831-2. · 2.02 Impact Factor

Publication Stats

491 Citations
85.26 Total Impact Points


  • 2008–2012
    • Vanderbilt University
      • • Department of Neurology
      • • Division of Nephrology and Hypertension
      Nashville, MI, United States
  • 2003–2011
    • Akita University
      • Department of Endocrinology, Diabetes and Geriatric Medicine
      Akita-shi, Akita-ken, Japan
  • 2002–2009
    • Akita University Hospital
      Akita, Akita, Japan