Urinary IgG4 and Smad1 Are Specific Biomarkers for Renal Structural and Functional Changes in Early Stages of Diabetic Nephropathy.

Diabetic nephropathy (DN) is the major cause of end-stage kidney disease, but early biomarkers of DN risk are limited. Herein we examine urinary IgG4 and Smad1 as additional early DN biomarkers. We recruited 815 patients with type 2 diabetes; 554 patients fulfilled the criteria of an estimated glomerular filtration rate (eGFR) >60 mL/min and no macroalbuminuria at baseline, with follow-up for 5 years. Patients without macroalbuminuria were also recruited for renal biopsies. Urinary IgG4 and Smad1 were determined by enzyme-linked immunoassays using specific antibodies. The specificity, sensitivity, and reproducibility were confirmed for each assay. Increased urinary IgG4 was significantly associated with lower eGFR. The level of urinary IgG4 also significantly correlated with surface density of peripheral glomerular basement membrane (Sv PGBM/Glom), whereas Smad1 was associated with the degree of mesangial expansion-both classic pathological findings in DN. Baseline eGFR did not differ between any groups; however, increases in both urinary IgG4 and Smad1 levels at baseline significantly predicted later development of eGFR decline in patients without macroalbuminuria. These data suggest that urinary IgG4 and Smad1 at relatively early stages of DN reflect underlying DN lesions and are relevant to later clinical outcomes.

Neuropathological alteration of aquaporin 1 immunoreactive enteric neurons in the streptozotocin-induced diabetic rats.

Long-term diabetic patients exhibit major clinical gastrointestinal problems, such as diarrhea and constipation. In recent years, water channel protein, aquaporin 1 (AQP1) has been identified in the enteric nervous system (ENS). We have examined the pathological changes in AQP1 immunoreactive (IR) neurons in streptozotocin-induced (STZ) diabetic rats. Eight-week-old Wistar rats were injected with streptozotocin, and artificial diabetes was induced. Sixteen-week-old STZ rats were then examined with double immunofluorescence staining and ABC immunohistochemical staining. AQP1-IR neurons in STZ rats were significantly increased compared with control rats (p<0.01). The ratio of AQP1 vs. HuC/D in STZ rats was also clearly increased as compared with control rats (p<0.05). It was apparent that thick AQP1-IR fibers were frequently observed in the secondary and tertiary myenteric plexus of STZ rats. The AQP1-IR fibers of STZ rats conspicuously showed many swollen varicosities. These swollen varicose fibers were also observed in the longitudinal and circular muscle layers. Streptozotocin-induced diabetic rats showed pathological changes in AQP1-IR neurons of the ENS. The alteration of AQP1-IR neurons may be possible contribute to diabetic gastrointestinal dysfunction in streptozotocin-induced diabetic rats.

IGT with fasting hyperglycemia is more strongly associated with microalbuminuria than IGT without fasting hyperglycemia.

Previous studies have established that impaired glucose tolerance (IGT) patients with fasting hyperglycemia (IGT/FH: fasting plasma glucose (FPG) level 6.1-7.0 mmol/l and 2 h PG level of 7.8-11.1 mmol/l) exhibit higher insulin resistance than those with isolated IGT (FPG level <6.1 mmol/l and 2 h PG level of 7.8-11.1 mmol/l), but the association with microalbuminuria has not been determined. Here, we evaluate the prevalence of microalbuminuria in non-diabetic Japanese males 20-70 years of age. The subjects were classified into four groups based on the results of OGTT: normal glucose tolerance (NGT: n=71), impaired fasting glucose (IFG: n=24), isolated IGT (n=36), and IGT/FH (n=23). A urinary albumin-to-creatinine ratio (ACR) from 30 to 300 microg/mg creatinine was counted as microalbuminuria. The prevalence of microalbuminuria was higher in subjects with IGT/FH than in subjects with isolated IGT (26% versus 14%). Logistic regression analysis showed microalbuminuria to be more significantly associated with IGT/FH (OR=3.82, 95% CI 1.09-13.36) than with isolated IGT (OR=1.75, 95% CI 0.50-6.17). While insulin resistance (HOMA-IR) in isolated IGT was not significantly different from that in NGT, insulin resistance in IGT/FH was significantly higher (P<0.01). Regression analysis of ACR in IGT showed a significant correlation with insulin resistance (P=0.012). Accordingly, microalbuminuria is more strongly associated with IGT/FH than with isolated IGT, most likely due to the higher insulin resistance.

The role of the TSC-22 (-396) A/G variant in the development of diabetic nephropathy.

TSC-22 is a leucine zipper transcriptional factor and expression of the TSC-22 gene is highly induced by TGF-beta treatment. We estimated the frequency of the -396 A/G polymorphism of the TSC-22 gene with an Alu I-Restriction fragment length polymorphism (RFLP) method in 498 Japanese subjects with type 2 diabetes mellitus. We also determined the promoter activity. The diabetic patients with the AA genotype had a significantly higher incidence of the diabetic nephropathy (vs. the AG genotype, P<0.05, odds ratio: 1.95; 95% confidence intervals 1.14-3.33). There was no significant difference in the promoter activity between the fragments with -396A and -396G. These findings suggest that the TSC-22 gene (-396) A allele is associated with an increasing risk of the diabetic nephropathy.

Factors responsible for development from normal glucose tolerance to isolated postchallenge hyperglycemia.

OBJECTIVE: Isolated postchallenge hyperglycemia (IPH), defined as fasting plasma glucose (FPG) level <7.0 mmol/l and 2-h plasma glucose (PG) level >/=11.1 mmol/l, is a subtype of early-stage diabetes. This study evaluates the metabolic profiles of insulin secretion and insulin sensitivity in IPH to clarify the factors responsible for development of this form of type 2 diabetes. RESEARCH DESIGN AND METHODS: We conducted cross-sectional analysis of 231 Japanese men aged 20-70 years. The subjects were classified into the following three groups, based on the results of a 75-g oral glucose tolerance test (OGTT): 1) normal glucose tolerance (NGT), defined as FPG level <6.1 mmol/l and 2-h PG level <7.8 mmol/l (n = 89); 2) impaired glucose tolerance (IGT), defined as FPG level <7.0 mmol/l and 2-h PG level of 7.8-11.1 mmol/l (n = 94); and 3) IPH (n = 48). We compared the three groups for insulin secretion (insulinogenic index) and insulin sensitivity (index of insulin resistance using homeostasis model assessment [HOMA-IR]). RESULTS: The insulinogenic index in IPH was the lowest of the three groups (P < 0.001 versus NGT). The HOMA-IR in the IGT and IPH groups were significantly higher than in the NGT group (P < 0.001), but both were similar. By linear regression analysis, the insulinogenic index rather than fasting insulin or HOMA-IR was the more significant factor in the 2-h PG level in IGT and IPH. CONCLUSIONS: Subjects with IPH exhibited distinctly impaired early-phase insulin secretion and only mild insulin resistance, indicating that reduced insulin secretion is the primary determinant of deterioration from NGT to IGT and IPH in development of type 2 diabetes in these subjects.

Impaired beta-cell function and insulin sensitivity in Japanese subjects with normal glucose tolerance.

The development of type 2 diabetes mellitus is characterized by both impaired beta-cell function and increasing insulin resistance. To clarify the roles of them in developing type 2 diabetes, we evaluated insulin resistance by HOMA-IR and insulin secretion by HOMA beta-cell in 453 Japanese subjects whose fasting plasma glucose (FPG) and HbA(1c) levels were within normal range. HOMA beta-cell was found to decrease in the over 30 years groups, while HOMA-IR increased with body mass index (BMI). To analyze the reserve capacity of insulin secretion and insulin sensitivity, the 67 of them, who underwent a standard oral glucose tolerance test and were diagnosed with normal glucose tolerance (NGT), were divided into four degrees of BMI age-adjusted to 50 years. They were compared for insulinogenic index and ISI composite proposed by Matsuda and DeFronzo across the range of BMI. ISI composite was significantly less in the highest BMI group, while insulin secretion did not increase in the higher BMI groups. The subjects with higher BMI had remarkably lower insulinogenic indices than those with lower BMI. These data suggest that insulin secretory reserve is insufficient to compensate for increased insulin resistance in Japanese people with NGT at about 50 years of age.