Glomerular hyperfiltration in non-proteinuric and non-hypertensive Japanese type 2 diabetic patients

Update on Pathogenesis of Glomerular Hyperfiltration in Early Diabetic Kidney Disease

In the existing stages of diabetic kidney disease (DKD), the first stage of DKD is called the preclinical stage, characterized by glomerular hyperfiltration, an abnormally elevated glomerular filtration rate. Glomerular hyperfiltration is an independent risk factor for accelerated deterioration of renal function and progression of nephropathy, which is associated with a high risk for metabolic and cardiovascular disease. It is imperative to understand hyperfiltration and identify potential treatments to delay DKD progress. This paper summarizes the current mechanisms of hyperfiltration in early DKD. We pay close attention to the effect of glucose reabsorption mediated by sodium-glucose cotransporters and renal growth on hyperfiltration in DKD patients, as well as the mechanisms of nitric oxide and adenosine actions on renal afferent arterioles via tubuloglomerular feedback. Furthermore, we also focus on the contribution of the atrial natriuretic peptide, cyclooxygenase, renin-angiotensin-aldosterone system, and endothelin on hyperfiltration. Proposing potential treatments based on these mechanisms may offer new therapeutic opportunities to reduce the renal burden in this population.

Glucose control, diabetic retinopathy, and hemodialysis induction in subjects with normo-microalbuminuric type 2 diabetic patients with normal renal function followed for 15 years

AIMS

A high urinary albumin excretion (UAE) and low glomerular filtration rate (GFR) are risk factors for progressive renal function loss in type 2 diabetic patients. In addition, diabetic retinopathy (DR) is also a risk factor for progressive renal function decline in microalbuminuric type 2 diabetic patients. We aimed to elucidate the factors, including DR, associated with a more severe situation of diabetic nephropathy, i.e., hemodialysis (HD) induction in normo- and microalbuminuric type 2 diabetic patients without renal dysfunction.

METHODS

Normo- and microalbuminuric type 2 diabetic patients with normal renal function whose GFRs had been measured by iohexol injection in 1995-1997 and had been followed for over 5 years were analyzed (n = 199). HbA1c levels was divided into HbA1c ≥ 7.0 (n = 146) and <7.0 (n = 53) groups. The UAE levels were classified as normoalbuminuria (NA, n = 114) and microalbuminuria (MA, n = 85). Seventy-two patients had DR, and 96 had hypertension. Patients were followed up for 15.7 ± 6.0 years and frequency of and duration to the HD induction were evaluated.

RESULTS

During the study period, 8 patients received HD induction. There were no remarkable differences in the rates of HD induction between patients with and without HbA1c ≥7.0, microalbuminuria, DR or hypertension. A Kaplan-Meier analysis revealed that HbA1c ≥7.0 (p = 0.037) and DR (p = 0.037) were associated with a significantly higher risk of HD induction than HbA1c <7.0 and no DR, respectively while albuminuria grade and hypertension were not associated with the risk of HD induction. There was significant negative correlation between HbA1c and annual decline rate of eGFR and annual decline rate of eGFR in the patients with prepro-proliferative DR (PDR) was significantly higher than that in the patients without DR. In the multivariate analysis, HbA1c and PDR showed significant relationships with the annual decline rate of eGFR.

CONCLUSIONS

It was reasonable that poorer glycemic control affected HD induction for 16 years follow-up. However, DR, especially PDR, should also be considered a substantial risk factor for HD induction although microalbuminuria and hypertension did not predict it at the early stage of diabetic nephropathy in type 2 diabetic patients with normal renal function.

Metabolic Risk Factors Associated With Chronic Kidney Disease in a Middle-Aged and Elderly Taiwanese Population: A Cross-Sectional Study

Background: This study aimed to quantify the proportion of participants with chronic kidney disease (CKD) and associated metabolic risk factors in a middle-aged and elderly population in Guishan District, Taoyuan City, Taiwan. Methods: This cross-sectional study enrolled residents aged 50-90 years living in one community. All participants received a standardized personal interview, including a structured questionnaire, anthropometric measurements, and blood samples collected for laboratory testing. CKD was defined as the presence of kidney damage (urine albumin-creatinine ratio ≥30 mg/g) or estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2. Multiple logistic regression models were used to evaluate the risk factors associated with CKD. Results: A total of 400 participants were enrolled. The overall proportion of participants with CKD was 20.5% (95% confidence interval [CI]: 16.54-24.46%). The proportions of participants with CKD among those aged 50-64, 65-74, and 75 years and over were 17.7, 18.8, and 35.7%, respectively (p = 0.01). Multiple logistic regression model revealed that elevated blood pressure (odds ratio [OR] = 2.23, 95% CI: 1.16-4.30), hyperglycemia (OR = 2.87, 95% CI: 1.64-5.00), hyperuricemia (OR = 1.38, 95% CI: 1.14-1.69), and metabolic syndrome (OR = 2.30, 95% CI: 1.31-4.06) were significantly associated with CKD. Conclusions: The prevalence of CKD in the study population was high. Hypertension, hyperglycemia, hyperuricemia, and metabolic syndrome are significantly associated with CKD in a middle-aged and elderly population in Taiwan.

Arteriolar hyalinosis is related to rapid GFR decline and long-standing GFR changes observed on renal biopsies in normo-microalbuminuric type 2 diabetic patients

AIMS

Whether or not renal structural changes, especially arteriolar hyalinosis, are related to the rate of renal functional decline and increase in urinary albumin excretion (UAE) at the early stage of diabetic nephropathy in patients with type 2 diabetes is still unknown. Our previous study determined that arteriolar hyalinosis is an independent risk factor for low GFR. We sought to determine whether arteriolar hyalinosis is also a risk factor for rapidly progressive decline in GFR.

METHODS

We evaluated 22 type 2 diabetic patients with normo- or microalbuminuria who took part in the previous study, to clarify which renal histological factors were associated with changes in UAE and the glomerular filtration rate (GFR) during 11.0 ± 3.0 years of follow-up. Light and electron microscopy-based morphometric analyses were performed to quantitatively evaluate the glomerular and interstitial structural changes.

RESULTS

In all 22 patients, the GFR was significantly decreased from baseline to follow-up, while the UAE did not change markedly between the 2 periods. After 11 ± 3 years of follow-up, the GFR was significantly lower in the rapid decliner group (annual rate of GFR decline ≥3.0%) than in the non-rapid decliner group (p = 0.017). The index of arteriolar hyalinosis (IAH) at baseline in the rapid decliners was significantly larger than in the non-rapid decliners (p = 0.015). The IAH showed a significant negative correlation with the GFR at follow-up (r = 0.50, p = 0.018) and the annual rate in the GFR decline (r = 0.47, p = 0.027) and significant positive correlations with UAE at follow-up (r = 0.46, p = 0.034) and the annual rate in the UAE increase (r = 0.57, p = 0.005). The GFR at follow-up in patients with IAH ≥2.0 was significantly decreased from baseline (p = 0.042) and significantly lower than that of the patients with IAH <2.0 (p = 0.026), which did not decrease significantly from baseline. The frequency of rapid decliners was larger in the IAH ≥2.0 than in the IAH <2.0 patients (p = 0.037).

CONCLUSIONS

Aggravated arteriolar hyalinosis was a risk factor for a rapid GFR decline. This finding might reflect initial changes in early diabetic nephropathy.

Synergistic Impact of Diabetes and Hypertension on the Progression and Distribution of Glomerular Histopathological Lesions

BACKGROUND

Diabetes and hypertension share renal histopathological features, such as arterial lesions and glomerular hypertrophy, that have not been investigated in relation to the blood pressure status of diabetic subjects. The severity of glomerular lesions varies across locations of the renal cortex, which may be further affected by diabetes and/or hypertension.

METHODS

Histopathological lesions in different parts of the renal cortex of autopsy kidneys were evaluated and analyzed based on medical histories of diabetes and hypertension.

RESULTS

This study included a total of 82 Japanese autopsies composed of normotensive nondiabetics (n = 31), hypertensive nondiabetics (n = 28), normotensive diabetics (n = 14), and hypertensive diabetics (n = 9). There were no differences in age, sex, renal function, or body size among groups. In both the superficial and juxtamedullary cortices, increased glomerular volume (GV) was significantly associated with either diabetes or hypertension. In addition, diabetes and hypertension showed a significant interaction with GV regardless of the cortical location. Values for global glomerulosclerosis (GGS) and arteriolar hyalinosis (AH) were associated with diabetes but not with hypertension. Only values for GGS consistently showed cortical surface superiority. The zonal distribution of AH, GV, or other diabetic glomerular lesions differed among the lesions depending on the presence or absence of hypertension.

CONCLUSIONS

These results imply that diabetes and hypertension synergistically enhance glomerular hypertrophy across all layers of the human renal cortex. The process is closely associated with the severity of GGS and AH predominantly associated with diabetes.

Serial renal biopsies in normo- and microalbuminuric patients with type 2 diabetes demonstrate that loss of renal function is associated with a reduction in glomerular filtration surface secondary to mesangial expansion

AIMS

The aim of the present study was to explore the relationship between changes in renal structure in patients with type 2 diabetes at an early stage of diabetic nephropathy using serial renal biopsies, and change in renal function.

METHODS

The study population comprised 10 patients with type 2 diabetes with normo- or microalbuminuria at baseline. Light and electron microscopy-based morphometric analyses were performed to quantitatively evaluate glomerular and interstitial structural changes. Urinary albumin excretion (UAE) and glomerular filtration rate (GFR) were measured annually. A second renal biopsy was performed after a mean of 6.1 ± 2.4 years of follow-up.

RESULTS

UAE, GFR, blood pressure and severity of diabetic retinopathy (DR) did not change between the baseline and follow-up. The annual decrease in the surface density of the peripheral glomerular basement membrane (GBM) (Sv[PGBM/glom]) was correlated with the rate of loss of GFR during the six-year follow-up period. The annual change in the Sv(PGBM/glom) was negatively correlated with the change in mesangial volume fraction.

CONCLUSIONS

Decreases in the GFR in patients with type 2 diabetes with normo- or microalbuminuria at baseline were associated with a decreased glomerular filtration surface, as a result of mesangial expansion during a mean six years of observation. These findings confirm ongoing pathological progression of glomerulopathy despite no significant change in albuminuria or retinopathy status.

A Mendelian Randomization-Based Approach to Identify Early and Sensitive Diagnostic Biomarkers of Disease

BACKGROUND

Identifying markers of chronic kidney disease (CKD) that occur early in the disease process and are specific to loss of kidney function rather than other underlying causes of disease may allow earlier, more accurate identification of patients who will develop CKD. We therefore sought to identify diagnostic blood markers of early CKD that are caused by loss of kidney function by using an innovative “reverse Mendelian randomization” (MR) approach.

METHODS

We applied this technique to genetic and biomarker data from 4147 participants in the Outcome Reduction with Initial Glargine Intervention (ORIGIN) trial, all with known type 2 diabetes, impaired fasting glucose, or impaired glucose tolerance. Two-sample MR was conducted using variants associated with creatinine-based eGFR (eGFRcrea) from the CKDGen Consortium (n = 133814) to estimate the effect of genetically decreased eGFRcrea on 238 serum biomarkers.

RESULTS

With reverse MR, trefoil factor 3 (TFF3) was identified as a protein that is increased owing to decreased eGFRcrea (β = 1.86 SD per SD decrease eGFRcrea; 95% CI, 0.95–2.76; P = 8.0 × 10−5). Reverse MR findings were consistent with epidemiological associations for incident CKD in ORIGIN (OR = 1.28 per SD increase in TFF3; 95% CI, 1.18–1.38; P = 4.58 × 10−10). Addition of TFF3 significantly improved discrimination for incident CKD relative to eGFRcrea alone (net reclassification improvement = 0.211; P = 9.56 × 10−12) and in models including additional risk factors.

CONCLUSIONS

Our results suggest TFF3 is a valuable diagnostic marker for early CKD in dysglycemic populations and acts as a proof of concept for the application of this novel MR technique to identify diagnostic biomarkers for other chronic diseases.

ClinicalTrials.gov Identifier

NCT00069784

Different association between renal hyperfiltration and mortality by sex

AIM

Renal hyperfiltration (RHF) is a marker of early kidney injury that was recently shown to be a novel marker of mortality. However, it has no clear definition. In this study, we suggested an age- and sex-adjusted RHF definition and explored the association between RHF and mortality by sex.

METHODS

We analyzed data from individuals receiving routine health examinations from 1995 to 2009. RHF was defined as an estimated glomerular filtration rate over the 95th percentile matched for age and sex.

RESULTS

A total of 114 966 individuals were included. During the 75-month of observation period, 2559 (2.2%) participants died. Among those, 71.4% were men. Because sex and RHF had a significant interaction for mortality (P for interaction < 0.001), we performed survival analysis according to sex. RHF was related to lower body weight and a higher proportion of cigarette smoking in men, whereas these relationships were not found in women. In the Kaplan-Meier curve, RHF was associated with higher mortality rate than non-RHF in both sexes, but this relationship was more prominent in men. In the multivariate analysis, RHF remained as an independent risk factor for all-cause mortality even after adjustment for confounding in men (hazard ratio, 1.34; 95% confidence interval, 1.12-1.59; P = 0.001). In women, RHF was not associated with increased mortality.

CONCLUSIONS

We demonstrated that RHF was a significant risk factor for mortality in men but not in women. The mechanisms and clinical implications of these different associations according to sex require a further clarification.

Arteriolar Hyalinosis Predicts Increase in Albuminuria and GFR Decline in Normo- and Microalbuminuric Japanese Patients With Type 2 Diabetes

OBJECTIVE

This study investigated the association between renal histology, as assessed by morphometric analysis using light (LM) and electron (EM) microscopy, and changes in urinary albumin excretion (UAE) and glomerular filtration rate (GFR) in Japanese people with type 2 diabetes in the early stages of diabetic nephropathy.

RESEARCH DESIGN AND METHODS

We performed percutaneous renal biopsies in 29 patients with type 2 diabetes (22 men, mean ± SD age 49 ± 10 years and GFR 119 ± 27 mL/min/1.73 m², with 15 normoalbuminuric [UAE <20 μg/min] and 14 microalbuminuric [UAE 20-200 μg/min]) to clarify which histological factors were associated with changes in UAE and GFR during 8.0 ± 3.5 years' follow-up. Glomerular structural changes including mesangial volume fraction [Vv(Mes/glom)] were estimated using EM, whereas the index of arteriolar hyalinosis (IAH) score was assessed by LM. Patients underwent annual measurement of GFR using iohexol injection with simultaneous urine collections for UAE.

RESULTS

Vv(Mes/glom) was negatively correlated with baseline and follow-up GFR but not with UAE. The IAH score was positively correlated with UAE and negatively correlated with GFR at follow-up, but it was not correlated with either UAE or GFR at baseline. GFR at follow-up was significantly decreased from baseline in patients with IAH scores ≥2.0 and significantly lower than in patients with IAH scores <2.0. Patients with IAH scores <2.0 showed no significant change in GFR during follow-up.

CONCLUSIONS

Arteriolar hyalinosis is an additional histological predictor for albuminuria increase and GFR decline in normo- and microalbuminuric Japanese people with type 2 diabetes.

Glomerular Hyperfiltration in Diabetes: Mechanisms, Clinical Significance, and Treatment

An absolute, supraphysiologic elevation in GFR is observed early in the natural history in 10%-67% and 6%-73% of patients with type 1 and type 2 diabetes, respectively. Moreover, at the single-nephron level, diabetes-related renal hemodynamic alterations-as an adaptation to reduction in functional nephron mass and/or in response to prevailing metabolic and (neuro)hormonal stimuli-increase glomerular hydraulic pressure and transcapillary convective flux of ultrafiltrate and macromolecules. This phenomenon, known as glomerular hyperfiltration, classically has been hypothesized to predispose to irreversible nephron damage, thereby contributing to initiation and progression of kidney disease in diabetes. However, dedicated studies with appropriate diagnostic measures and clinically relevant end points are warranted to confirm this assumption. In this review, we summarize the hitherto proposed mechanisms involved in diabetic hyperfiltration, focusing on ultrastructural, vascular, and tubular factors. Furthermore, we review available evidence on the clinical significance of hyperfiltration in diabetes and discuss currently available and emerging interventions that may attenuate this renal hemodynamic abnormality. The revived interest in glomerular hyperfiltration as a prognostic and pathophysiologic factor in diabetes may lead to improved and timely detection of (progressive) kidney disease, and could provide new therapeutic opportunities in alleviating the renal burden in this population.

Type 2 diabetic patients with diabetic retinopathy and concomitant microalbuminuria showed typical diabetic glomerulosclerosis and progressive renal dysfunction

AIMS

To determine whether or not diabetic retinopathy (DR) in type 2 diabetic patients can predict the renal functional decline.

METHODS

We examined 32 normo-microalbuminuric type 2 diabetic patients by renal biopsy (23 men, age 49±10yrs) divided into two groups according to the presence (n=19) or absence (n=13) of DR. Electron microscopic morphometry including mesangial fractional volume [Vv(Mes/glom)] were performed and light microscopic tissues were categorized as: C1, normal/near normal renal structure; C2, typical diabetic glomerulopathy; C3, atypical injury patterns. Patients were followed up for 7.1±3.8years, and glomerular filtration rate (GFR) and urinary albumin excretion (UAE) measurements were taken annually.

RESULTS

Vv(Mes/glom) was larger in DR+ than that in DR-. Vv(Mes/glom) positively correlated with the UAE if patients had DR. The patients with DR had a significant higher rate of C2 pattern compared to those in DR-. Among patients with DR and C2, GFR in microalbuminuria (n=7) decreased while GFR in normoalbuminuria (n=5) did not change during the observation.

CONCLUSIONS

Type 2 diabetic patients with DR and C2 showed progressive renal dysfunction after they had microalbuminuria. DR and albuminuria should be considered to determine renal function decline in type 2 diabetic patients.

Correlation of high urinary Smad1 level with glomerular hyperfiltration in type 2 diabetes mellitus

The aim of this study was to assess the relationship between urinary Smad1 and glomerular hyperfiltration (GHF) in type 2 diabetes mellitus (T2DM), and to explore the factors related to the urinary Smad1 in T2DM. The reference value of the estimated glomerular filtration rate (eGFR) was determined in 248 healthy individuals. 30 patients with GHF, 58 patients with norm-GFR T2DM, and 24 healthy patients who served as controls were recruited. Urinary Smad1, fasting plasma glucose (FPG), fasting serum C-Peptide (C-P), hemoglobin A1C (HbA1c), cystatin C, and other chemistry laboratory parameters of T2DM participants and controls were measured. Patients with GHF had higher levels of urinary Smad1 than the control group, and those with norm-GFR. For T2DM patients with body mass index, age, and gender adjustments, urinary Smad1 was positively correlated with FPG, HbA1C, and eGFR, but negatively correlated with fasting serum C-P. Multivariate linear regression analysis demonstrated that eGFR, HbA1C, and fasting serum C-P were independently associated with urinary Smad1. High levels of urinary Smad1 were found in GHF patients with T2DM, which may be another potential mechanism of GHF in relation to diabetic nephropathy.

Prevalence of and factors associated with chronic kidney disease (CKD) in Japanese subjects without notable chronic diseases, undergoing an annual health checkup

BACKGROUND

The prevalence of chronic kidney disease (CKD) is increasing dramatically. The aim of the present study is to explore the prevalence of and the factors associated with CKD in subjects without notable chronic disease.

METHODS

In a cross-sectional study, we analyzed the annual health checkup data of 39,211 residents (11,636 males and 27,575 females) aged 40-74 years (58.6 ± 8.6 years) without notable chronic diseases, who underwent a health checkup at the Public Health Centers of Osaka city. CKD was defined as those with an estimated glomerular filtration rate (eGFR) less than 60 ml/min/1.73 m2 and/or urinary protein of (+) or more.

RESULTS

The overall prevalence of CKD was 20.5%, and increased remarkably with age. Multivariate logistic regression analysis demonstrated that male gender (OR: 0.83, p<0.0001), age of 50-59 years (2.92, p<0.0001), age of 60-74 years (4.92, p<0.0001), the presence of diabetes (0.80, p=0.0307), dyslipidemia (1.21, p=0.0138), obesity (1.23, p<0.0001), hyperuricemia (2.63, p<0.0001) and a history of cardiovascular disease (1.26, p=0.0135) were significant factors that were independently associated with CKD.

CONCLUSIONS

In urban subjects without notable chronic disease, the prevalence of CKD was 20.5%. Several metabolic abnormalities, i.e., dyslipidemia and hyperuricemia, were significantly associated with CKD.

Changes of the tubular markers in type 2 diabetes mellitus with glomerular hyperfiltration

AIM

To assess whether glomerular hyperfiltration (GHF) could result in renal tubular damage in type 2 diabetes mellitus (T2DM) patients.

METHODS

Reference value of estimated glomerular filtration rate (eGFR) was determined in 248 healthy individuals based on serum CysC levels. GHF was defined as an eGFR exceeding the sex-specific 97.5th percentile in non-diabetic individuals. In the present study, 30 with GHF, 58 with norm-GFR T2DM, and 24 healthy controls were recruited. Tubular markers, such as urinary N-acetyl-β-D-glucosaminidase (NAG) and kidney injury molecule 1 (KIM-1), as well as serum and urinary neutrophil gelatinase-associated lipocalin (NGAL), were measured and compared. The correlation of these markers with eGFR was analyzed in the GHF group.

RESULTS

The GHF group had higher urinary NGAL and KIM-1 levels but lower serum NGAL level than the norm-GFR and control groups. Slightly decreased serum NGAL and increased urinary NGAL levels were also noted in the norm-GFR group compared with those of the controls. There was no statistical difference in the urinary NAG values among the three groups. Correlation analysis showed that eGFR was positively related to fasting blood glucose (FBG), HbA1c, urinary NGAL, and KIM-1, but negatively with serum NGAL in the GHF group.

CONCLUSION

Higher urinary tubular damage markers were found in T2DM patients with GHF than the norm-GFR and control groups, probably a direct proof that GHF is a deleterious factor for diabetic nephropathy.

Which anthropometric parameter is best related with urinary albumin excretion and creatinine clearance in type 2 diabetes: body mass index, waist circumference, waist-to-hip ratio, or conicity index?

OBJECTIVE

We analyzed the relationships between body mass index (BMI), waist circumference (WC), waist-to-hip ratio, and conicity index and 24-hour urinary albumin excretion rate (UAER) and creatinine clearance.

DESIGN

Cross-sectional study.

SETTING

Patients presenting to a state hospital.

PATIENTS

Study involved patients with type 2 diabetes.

METHODS

Study participants underwent medical history examination, measurement of office blood pressure (BP), measurement of anthropometric factors and calculations (including BMI, WC, waist-to-hip ratio, and conicity index), physical examination, biochemical analysis, and 24-hour urine specimen collection to determine creatinine clearance and UAER.

RESULTS

In all, 202 patients with type 2 diabetes (male/female: 91/111, aged: 58.4 ± 10.1 years) were included. It was found that 24-hour UAER correlated with WC (rho: +0.176, P = .012), serum albumin (rho: -0.324, P < .0001), and systolic BP (rho: +0.153, P = .029), whereas creatinine clearance correlated with age (rho: -0.152, P = .031), BMI (rho: +0.191, P = .007), albumin level (rho: +0.365, P < .0001), and uric acid level (rho: -0.369, P < .0001). The stepwise linear regression analysis revealed that WC (P = .012), glycosylated hemoglobin (P = .018), and systolic BP (P = .043) were found to be independently related to logarithmically converted 24-hour UAER, whereas creatinine clearance was found to be related to duration of diabetes (P = .001), BMI (P = .008), presence of peripheral arterial disease (P = .021), fasting serum glucose level (P = .003), and uric acid level (P < .0001). However, after correction for body surface area, BMI was no longer associated with creatinine clearance.

CONCLUSION

Among the anthropometric parameters, only an increase in WC was found to be independently related to 24-hour UAER. Although BMI was associated with creatinine clearance, this association was lost after creatinine clearance was corrected for body surface area.

Low serum creatinine is associated with type 2 diabetes in morbidly obese women and men: a cross-sectional study

BACKGROUND

Low skeletal muscle mass is associated with insulin resistance and metabolic syndrome. Serum creatinine may serve as a surrogate marker of muscle mass, and a possible relationship between low serum creatinine and type 2 diabetes has recently been demonstrated. We aimed to validate this finding in a population of Caucasian morbidly obese subjects.

METHODS

Cross-sectional study of 1,017 consecutive morbidly obese patients with an estimated glomerular filtration rate >60 ml/min/1.73 m2. Logistic regression (univariate and multiple) was used to assess the association between serum creatinine and prevalent type 2 diabetes, including statistically testing for the possibility of non-linearity in the relationship by implementation of Generalized Additive Models (GAM) and piecewise linear regression. Possible confounding variables such as age, family history of diabetes, waist-to-hip ratio, hypertension, current smoking, serum magnesium, albuminuria and insulin resistance (log HOMA-IR) were adjusted for in three separate multiple logistic regression models.

RESULTS

The unadjusted GAM analysis suggested a piecewise linear relationship between serum creatinine and diabetes. Each 1 mumol/l increase in serum creatinine was associated with 6% (95% CI; 3%-8%) and 7% (95% CI; 2%-13%) lower odds of diabetes below serum creatinine levels of 69 and 72 mumol/l in women and men, respectively. Above these breakpoints the serum creatinine concentrations did not reduce the odds further. Adjustments for non-modifiable and modifiable risk factors left the piecewise effect for both women and men largely unchanged. In the fully adjusted model, which includes serum magnesium, albuminuria and log HOMA-IR, the piecewise effect for men was statistically non-significant, but it remained present for women. Patients with creatinine levels below median had approximately 50% (women) and 75% (men) increased odds of diabetes.

CONCLUSIONS

Low serum creatinine is a predictor of type 2 diabetes in Caucasian morbidly obese patients, independent of age, gender, family history of diabetes, anthropometric measures, hypertension, and current smoking. Longitudinal studies of both obese and non-obese populations are needed to investigate whether serum creatinine may be causally linked with type 2 diabetes, and if so, precisely how they are linked.

Determinants of decline in glomerular filtration rate in nonproteinuric subjects with or without diabetes and hypertension

BACKGROUND AND OBJECTIVES

This study investigated whether the slope of estimated GFR is different between nonproteinuric subjects with and without diabetes, and what clinical factors are associated with the GFR slope.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

An observational cohort study was performed in 923 subjects, and the predictive value of baseline variables on the GFR slope was investigated.

RESULTS

On the basis of the median 3-yr follow-up and 7 measurements of GFR, GFR slope (%/yr, median and interquartile range) was significantly larger in subjects with diabetes (-2.39 (-4.86 to 0.15), n=729) than in those without diabetes (-1.02 (-4.28 to 1.37), n=194), and this difference remained significant with or without presence of hypertension. After adjustments for confounding factors, predictors of GFR decline were found to be baseline high values of glycosylated hemoglobin A1C(HbA1C), GFR, systolic blood pressure, and low plasma total protein in subjects with diabetes, whereas only the latter two were significant in subjects without diabetes. In subjects with diabetes, the high GFR was accounted for by high HbA1C at baseline, and the predictors of GFR decline differed between those with and without hypertension, or with high and low baseline GFR. Any combination of the predictors showed increased risk for GFR decline.

CONCLUSIONS

GFR slope is substantially affected by multiple factors at various stages. The degree of chronic hyperglycemia is likely to play a crucial role in elevating GFR and accelerating the decline in patients with type 2 diabetes even from the normoalbuminuric stage.

Renal structure as an indicator for development of albuminuria in normo- and microalbuminuric type 2 diabetic patients

Baseline glomerular structure in microalbuminuric (MA) and proteinuric Caucasian type 2 diabetic patients predicted progressive glomerular filtration rate decline while baseline urinary albumin excretion (UAE) did not. Little is known about whether or not renal structure at the early stages of diabetic nephropathy (DN) in type 2 diabetic patients can predict further functional development of DN. Baseline renal structure and function and follow-up data of renal function were examined in 17 type 2 diabetic patients (11 men, 45+/-7 (mean+/-S.D.) years old) with known diabetes duration 11+/-8 years without definable renal disease other than DN. Six patients showed normoalbuminuria (NA), 11 microalbuminuria (MA), and were followed up for 6.4+/-1.8 years after the baseline renal biopsy. Light and electron microscopic morphometric analyses provided quantitative glomerular and tubulointerstitial structural changes. No statistically significant difference was observed in hemoglobin A1c (HbA1c) values or mean blood pressure (MBP) between baseline and follow-up, even though the number of patients placed on antihypertensive drugs increased from 3 to 7. Follow-up UAE was not significantly different from the baseline UAE although 13 of 17 cases showed an increase. Baseline UAE did not correlate with the follow-up UAE or morphometric measures. Glomerular basement membrane width and volume fraction of the mesangium and mesangial matrix positively correlated with follow-up UAE. In NA and MA Japanese type 2 diabetic patients, baseline renal structural measures are more reliable indicators for the development of UAE than baseline UAE.

Detailed glomerular ultrastructure in Japanese type 2 diabetic patients by the quick-freezing and deep-etching method

Mesangial expansion and glomerular basement membrane (GBM) thickening did not correlate with urinary albumin excretion (UAE) in type 2 diabetic patients in our previous studies; therefore, it was necessary to elucidate more detailed ultrastructural changes in the early stages of diabetic nephropathy (DN) in type 2 diabetic patients. The quick-freezing and deep-etching (QF-DE) method allows us to examine three-dimensional ultrastructures of human renal glomeruli in vivo at high resolution. The QF-DE method was applied to six type 2 diabetic patients without definable renal diseases other than DN. Four patients were normoalbuminuric (NA) and the other two were microalbuminuria (MA). Three control specimens were the normal parts from nephrectomies due to renal cell carcinomas. Electron microscopic morphometric analyses provided quantitative glomerular structural changes. Replica membranes were prepared by the QF-DE method, and diameters of mesh structures at the GBM and mesangial matrix (MM) were measured on electron micrographs as previously described. By the QF-DE method, both the GBM middle layer and MM were composed of polygonal meshwork structures. The mesh pores of the GBM and MM were more enlarged and irregular in shape in NA diabetic patients than those of the controls, and these ultrastructural changes became more obvious in MA patients. The mesh diameters of the GBM and MM in the diabetic patients were also larger than those of the controls. Such a mesh diameter of the GBM was well correlated with the amount of UAE, while the mesh diameter of MM showed a slight correlation with UAE. Although there were small number of subjects in the present study, the detailed ultrastructural changes in NA and MA type 2 diabetic patients, which had not been disclosed by conventional electron microscopy, were revealed by the QF-DE method. Increased mesh diameters of GBM might be related with the increase of UAE.

Glomerular hyperfiltration: a new marker of metabolic risk

Chronic kidney disease coexists with metabolic syndrome and this relationship may be apparent before overt manifestations of cardiovascular disease. To investigate early stages of the natural history of associations between renal function and metabolic syndrome, we phenotyped 1572 young (mean age=18.4 years), apparently healthy men for metabolic risk factors and estimated their creatinine clearance based on the Cockcroft-Gault equation. High metabolic risk (clustering of at least three metabolic risk factors) was revealed in 8.7% (137) of the subjects and was associated with a 6.9-fold increase in the odds of glomerular hyperfiltration (95% confidence interval (CI): 3.9-11.5) when compared to reference (from none to two metabolic risk factors). Overweight, elevated blood pressure, and low high-density lipoprotein (HDL) cholesterol increased the multivariate-adjusted odds ratio of glomerular hyperfiltration to 6.6 (95% CI: 3.8-11.6), 1.8 (95% CI: 1.0-3.0), and 2.5 (95% CI: 1.5-4.3), respectively. Systolic and diastolic blood pressures clustered together with leptin in the factor analysis and this blood pressure-adiposity component correlated with estimated creatinine clearance (r=0.329, P<0.0001) and explained on its own 10.2% of the variance in the estimated renal function. Our data reveal the silent epidemics of metabolic risk among young, apparently healthy men. Furthermore, the results indicate that high metabolic risk is associated with glomerular hyperfiltration before overt manifestations of cardiovascular disease.

Glomerular hyperfiltration predicts the development of microalbuminuria in stage 1 hypertension: the HARVEST

Factors related to the development of microalbuminuria in hypertension are not well known. We did a prospective study to investigate whether glomerular hyperfiltration precedes the development of microalbuminuria in hypertension. We assessed 502 never-treated subjects screened for stage 1 hypertension without microalbuminuria at baseline and followed up for 7.8 years. Creatinine clearance was measured at entry. Urinary albumin and ambulatory blood pressure were measured at entry and during the follow-up until subjects developed sustained hypertension needing antihypertensive treatment. Subjects with hyperfiltration (creatinine clearance >150 ml/min/1.73 m2, top quintile of the distribution) were younger and heavier than the rest of the group and had a greater follow-up increase in urinary albumin than subjects with normal filtration (P<0.001). In multivariable linear regression, creatinine clearance adjusted for confounders was a strong independent predictor of final urinary albumin (P<0.001). In multivariable Cox regression, patients with hyperfiltration had an adjusted hazard ratio for the development of microalbuminuria based on at least one positive measurement of 4.0 (95% confidence interval (CI), 2.1-7.4, P<0.001) and an adjusted hazard ratio for the development of microalbuminuria based on two consecutive positive measurements of 4.4 (95% CI, 2.1-9.2, P<0.001), as compared with patients with normal filtration. Age, female gender, and 24 h systolic blood pressure were other significant predictors of microalbuminuria. In conclusion, stage 1 hypertensive subjects with glomerular hyperfiltration are at increased risk of developing microalbuminuria. Early intervention with medical therapy may be beneficial in these subjects even if their blood pressure falls below normal limits during follow-up.