Takashi Shimotomai

Association of monocyte chemoattractant protein-1 with renal tubular damage in diabetic nephropathy.

Monocyte chemoattractant protein-1 (MCP-1), is a chemokine that mediates renal interstitial inflammation, tubular atrophy, and interstitial fibrosis by recruiting monocytes/macrophages into renal tubulointerstitium. Recent studies have demonstrated that protein overload in renal tubular cells up-regulates MCP-1 gene and its protein expression. Therefore, we hypothesized that increased expression of MCP-1 in renal tubuli, probably triggered by an increase in the leakage of plasma protein from glomerular capillary to tubular fluid, may contribute to renal tubular damage and accelerate the progression of diabetic nephropathy. To test this hypothesis, we examined urinary excretion levels of MCP-1 and N-acetylglucosaminidase (NAG), a sensitive marker of renal tubular damage, in Japanese Type II diabetic patients with normoalbuminuria (n=29), microalbuminuria (n=25), and macroalbuminuria (n=18). The median urinary excretion level of MCP-1 in patients with macroalbuminuria (394.4 ng/g creatinine) was significantly elevated compared to the levels in patients with normoalbuminuria and microalbuminuria (159.6 and 193.9 ng/g creatinine, respectively). Furthermore, the urinary MCP-1 excretion level was positively correlated with urinary excretion levels of albumin (r=.816, P<.001) and NAG (r=.569, P<.001) in all subjects. These results suggest that MCP-1 is produced in renal tubular cells and released into urine in proportion to the degree of proteinuria (albuminuria), and that increased MCP-1 expression in renal tubuli contributes to renal tubular damage. Therefore, we conclude that heavy proteinuria itself may accelerate the progression of diabetic nephropathy by increasing the MCP-1 expression in renal tubuli.

Increased Urinary Excretion of Monocyte Chemoattractant Protein-1 in Proteinuric Renal Diseases

Monocyte chemoattractant protein-1 (MCP-1) is a chemokine that is produced mainly by tubular epithelial cells in kidney and contributes to renal interstitial inflammation and fibrosis. More recently, we have demonstrated that urinary MCP-1 excretion is increased in proportion to the degree of albuminuria (proteinuria) and positively correlated with urinary N-acetylglucosaminidase (NAG) levels in type 2 diabetic patients. Based on these findings, we have suggested that heavy proteinuria, itself, probably aggravates renal tubular damage and accelerates the disease progression in diabetic nephropathy by increasing the MCP-1 expression in renal tubuli. In the present study, to evaluate whether urinary MCP-1 excretion is increased in the proteinuric states not only in diabetic nephropathy but also in other renal diseases, we examined urinary MCP-1 levels in IgA nephropathy patients with macroalbuminuria (IgAN group; n = 6), and compared the results with the data obtained from type 2 diabetic patients with overt diabetic nephropathy (DN group; n = 23) and those without diabetic nephropathy (non-DN group; n = 27). Urinary MCP-1 excretion levels in non-DN, DN, IgAN groups were 157.2 (52.8–378.5), 346.1 (147.0–1276.7), and 274.4 (162.2–994.5) ng/g creatinine, median (range), respectively. Expectedly, urinary MCP-1 and NAG excretion levels in DN and IgAN groups were significantly elevated as compared with non-DN group. Therefore, we suggest that MCP-1 expression in renal tubuli is enhanced in proteinuric states, irrespective of the types of renal disease, and that increased MCP-1 expression probably contributes to renal tubular damage in proteinuric states.

Enhanced urinary adiponectin excretion in IgA-nephropathy patients with proteinuria.

Adiponectin is secreted specifically by adipose tissue. It was reported that the serum adiponectin level was markedly increased in patients with end-stage renal disease and was positively associated with abnormal renal function in type 2 diabetes. Recently, we found that urinary adiponectin level was significantly increased in type 2 diabetic patients with overt diabetic nephropathy, but not in those without nephropathy. The aim of the present study was to evaluate whether the urinary adiponectin level is increased not only in diabetic patients with macroalbuminuria but also in IgA-nephropathy patients with macroalbuminuria. We measured urinary adiponectin levels in 24 healthy control subjects, 12 IgA-nephropathy patients, and 19 type 2 diabetic nephropathy patients, and they were, in medians, 2.24 µg/g creatinine (ranges of 0.85 ~ 3.70), 59.2 µg/g creatinine (4.95 ~ 186), and 33.1 µg/g creatinine (4.69 ~ 114), respectively. In the two patient groups, urinary adiponectin levels were significantly higher than in control subjects (P < 0.01). Moreover, positive correlations between urinary adiponectin levels and albumin-to-creatinine ratios were observed in IgA-nephropathy (R2 = 0.53, P < 0.01) and diabetic nephropathy patients (R2 = 0.61, P < 0.01), but not in control subjects. Serum adiponectin levels were unchanged in these three groups. These findings suggested that the increase of urinary adiponectin levels partly results from enhanced filtration of circulating adiponectin through the changes of glomerular permselectivity and intraglomerular hydruric pressure. However, clinical implication of urinary adiponectin excretion in healthy control remains to be elucidated.

Increased urinary excretion of N-acetylglucosaminidase in subjects with impaired glucose tolerance.

N-acetylglucosaminidase (NAG) is a lysosomal enzyme produced by renal proximal tubular cells and has been widely used as a marker, which indicates a degree of renal tubular damage. An increase in urinary NAG excretion is thought to result from the renal tubular damage. The aim of this study was to evaluate whether even mild hyperglycemia causes an increase in urinary excretion of NAG, which is a renal tubular protein. We examined urinary NAG excretion in overnight urine in 22 Japanese men with impaired glucose tolerance (IGT) for more than two years (IGT group) and 41 healthy control subjects matched in age, gender, BMI and blood pressure (control group). Urinary NAG excretion levels of IGT group and control group were 2.89 (1.23–7.97) and 2.22 (0.60–4.93) U/g creatinine, median (range), respectively. The IGT group showed significantly higher urinary excretion of NAG compared to the control group (p<0.01). Several studies have indicated that plasma proteins filtered through the glomerular capillary may have intrinsic renal toxicity. Recently, we have reported that urinary excretion of plasma proteins (ceruloplasmin, IgG4 and IgG) with molecular radii of approximately 45–55 Å is increased in subjects with IGT compared to healthy control subjects with normal glucose tolerance. Considering the present result together with our recent finding, we suggest that increased urinary excretion of NAG in the mildly hyperglycemic subjects may be due to the adverse effects of the plasma proteins highly filtered through the glomerular capillary on tubular cells.

No association of glutathione S-transferase M1 gene polymorphism with diabetic nephropathy in Japanese type 2 diabetic patients.

Oxidative stress possibly contributes to the development of diabetic nephropathy. Therefore, the levels of endogenous antioxidants may be one of determinants of the susceptibility to diabetic nephropathy. Glutathione S-transferases (GSTs) can work as one of endogenous antioxidants to protect cells from oxidative stress. The M1 member of GST mu class (GSTM1) is polymorphic and only expressed in 55–60% of Caucasians because of the homozygous deletion of the gene (null genotype). Recent studies have provided evidence that the GSTM1 null genotype, i.e. lack of the GSTM1 activity, is associated with an increased susceptibility to lung cancer and colorectal cancer. The present study was conducted to determine whether the genetic polymorphism influences the development of diabetic nephropathy. We examined 105 patients with diabetic nephropathy and 69 patients without diabetic nephropathy in Japanese type 2 diabetic patients with proliferative diabetic retinopathy. GSTM1 genotyping was performed by polymerase chain reaction. The two patient groups were well matched with regard to age, body mass index and HbA1c. GSTM1 null genotype was observed in 48.6% of patients with nephropathy versus 55.1% of patients without nephropathy. The frequency of GSTM1 null genotype was not significantly higher in the patient group with nephropathy than in the patient group without nephropathy. This study is the first to investigate the association of GSTM1 gene polymorphism with the development of diabetic nephropathy. The present results suggest that GSTM1 null genotype does not contribute to the development of diabetic nephropathy in Japanese type 2 diabetic patients.

Effects of Chronic Intake of Vegetable Protein Added to Animal or Fish Protein on Renal Hemodynamics

Background/Aims: To examine whether chronic intake of vegetable protein added to animal protein diet affects renal hemodynamics or not, we studied effects of three kinds of diets containing various amounts of animal and vegetable protein with 1-week dietary program in each on renal hemodynamics. Methods: The crossover design of different amounts of vegetable protein added to the constant amount of animal protein was applied to two groups of 7 healthy individuals after the control dietary program. Renal function and 24 hours’ urinary albumin excretion rate (AER) were examined on every 7th day of three consecutive 1-week dietary programs. Results: Glomerular filtration rate (GFR; sodium thiosulphate clearance) and renal plasma flow (RPF) significantly decreased after decreasing the intake of animal protein by one third with keeping the amount of vegetable protein constant. The results when substituting vegetable protein for some of the animal protein in the diet without changing the total amount of protein were identical. The filtration fraction and AER did not change over the study periods regardless of dietary composition. Conclusion: The lack of an effect a 1-week intake of vegetable protein added to animal protein on GFR and RPF suggests that vegetable protein may be excluded from lists of restriction in low protein diet therapy in patients with renal insufficiency.

Urinary Excretion of Transferrin and Orosomucoid Are Increased after Acute Protein Loading in Healthy Subjects

Background/Aims: 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. Methods: 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. Results: 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. Conclusion: 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.

Efficacy and safety of patient‐directed titration of once‐daily pre‐dinner premixed biphasic insulin aspart 70/30 injection in Japanese type 2 diabetic patients with oral antidiabetic drug failure: STEP‐AKITA study

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.