Jun Koshimura

Effect of metformin on adipose tissue resistin expression in db/db mice

Resistin, a novel adipose-derived protein, has been proposed to cause insulin-resistant states in obesity. To evaluate whether an insulin-sensitizing drug, metformin, regulates adipose tissue resistin expression, murine models of obesity and diabetes, db/db mice, were treated with metformin (metformin group), insulin (insulin group), and vehicle (control group) for 4 weeks, followed by analyzing resistin protein expression in their adipose tissues. Unexpectedly, resistin protein expression was increased by 66% in the metformin group relative to the control group, while it did not differ between the insulin and control groups. Hyperinsulinemia was improved in the metformin group, while the insulin group exhibited severe hyperinsulinemia, similar to the control group. Furthermore, in comparison between obese mice (db/db mice) and age-matched lean controls, resistin protein expression was reduced by 58% in the obese mice with severe hyperinsulinemia. These data collectively suggest that resistin expression may be suppressed by hyperinsulinemia and that metformin may upregulate resistin expression via the improvement of hyperinsulinemia in obesity.

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.

Effects of Protein Meals on the Urinary Excretion of Various Plasma Proteins in Healthy Subjects

To examine whether hemodynamic changes in response to acute protein loadings with different protein sources cause increases in urinary excretion of plasma proteins in healthy subjects, urinary excretions of various plasma proteins with various molecular radii and isoelectric points, namely albumin (Alb), IgG, IgG4, ceruloplasmin (CRL), and α2-macroglobulin (A2), were measured in healthy subjects after ingestion of a beef meal or of a tuna fish meal. Significant increases in urinary excretions of the negatively charged IgG4 and CRL and of the neutrally charged IgG were found in parallel with enhanced creatinine clearances after each protein ingestion. These renal responses returned to basal levels 9 h after the test. This finding suggests that in healthy subjects, the increase in glomerular filtration rate after acute protein loading caused selective enhancement of urinary excretions of plasma proteins with a molecular radius of approximately 55 Å (the radius of IgG, IgG4, and CRL), irrespective of the charge barrier of the glomerulus. The increases in these three plasma proteins may be induced by leakage via the shunt pathway in the glomerulus, as proposed earlier (see text). In contrast, increases in urinary excretions of A2 and Alb were not found. The former finding may be explained by the possibility that A2 would not pass through this pathway, since the molecular radius of A2 (88 Å) is larger than that of IgG, although the latter finding may be partially explained by preferential renal tubular reabsorption of Alb.

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.

Effects of Long-Term Pravastatin Treatment on Serum and Urinary Monocyte Chemoattractant Protein-1 Levels and Renal Function in Type 2 Diabetic Patients with Normoalbuminuria

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.