Size and charge selectivity of the glomerular filter in patients with insulin-dependent diabetes mellitus: urinary immunoglobulins and glycosaminoglycans

Significance of urinary glycosaminoglycans/proteoglycans in the evaluation of type 1 and type 2 diabetes complications

Because of the high incidence of kidney disease in diabetic patients, the early diagnosis of renal impairment is a key point for intervention and management. Although urinary albumin excretion currently represents the accepted standard to assess both diabetic nephropathy and cardiovascular risk, it has some limitations as structural changes in the glomerular basement membrane may occur before the onset of microalbuminuria. It is therefore important to identify urinary markers that may provide greater sensitivity, earlier detection, and greater predictive power for diabetes complications. In this respect, urinary glycosaminoglycans/proteoglycans (GAGs/PGs) have been long associated with several kidney diseases as well as diabetic nephropathies as their levels increase more readily than albuminuria. In particular, heparan sulfate, a key component of the glomerular basement membrane responsible for its charge-dependent permeability, is excreted into urine at higher concentrations during the early kidney remodeling events caused by the altered glucose metabolism in diabetes. Over the past few years, also urinary trypsin inhibitor has been linked to a chronic inflammatory condition in both type 1 and 2 diabetes. The underlying mechanisms of such increase are not completely known since either a systemic inflammatory condition or a more localized early renal impairment could play a role. Nevertheless, the association with other inflammatory markers and a detailed urinary trypsin inhibitor structural characterization in diabetes remain to be elucidated. This review will discuss a great deal of information on the association between urinary GAGs/PGs and type 1 and 2 diabetes, with particular emphasis on renal involvement, and their potential as markers useful in screening, diagnosis and follow up to be associated with the current standard tests.

Risk factors for development and progression of nonproliferative retinopathy in normoalbuminuric patients with type 1 diabetes

BACKGROUND

The aim of this study was to evaluate risk factors for development and progression of nonproliferative retinopathy (NPR) in normoalbuminuric patients with type 1 diabetes mellitus (T1DM).

METHODS

A total of 223 T1DM with normal renal function and normoalbuminuria were included in this study and followed for 48 months. Photodocumented retinopathy status was made according to the EURODIAB protocol. Urinary albumin excretion rate (UAE) was measured from at least two 24-h urine samples. Possible risk factors for development or progression of NPR were examined in backward stepwise Cox's multiple regression analysis.

RESULTS

The majority of patients (70%) had no retinopathy while 67 (30%) had NPR at baseline. Patients with NPR were older, had longer duration of diabetes, higher systolic blood pressure, BMI, resting heart rate, UAE and lower estimated glomerular filtration rate (p ≤ 0.04 for all). After 48 months 24 patients (10.7%) developed NPR or progressed to proliferative retinopathy. Systolic blood pressure (HR 1.03, CI 1.01-1.05, p=0.02), UAE (HR 1.14, CI 1.07-1.21, p<0.001), and resting heart rate (HR 1.05, CI 1.01-1.09, p=0.006) were significantly associated with development or progression of NPR.

CONCLUSIONS

Our results suggest that retinopathy is present and may progress in T1DM even when coexisting renal disease is excluded. Normoalbuminuric T1DM requires close monitoring for the early detection of retinopathy, especially if they have a higher UAE, systolic blood pressure and resting heart rate.

Association between urinary IgG and relative risk for factors affecting proteinuria in type 2 diabetic patients

Abnormal glomerular permeability is the primary step towards the glomerulosclerosis. The progression rate of glomerulosclerosis is proportionate to abundance and severity of lesions created at incipient stage, which is reflected as proteinuria even though eGFR remains in the normal range. Therefore, there is a current need to find out the association between relative risks for the factors leading to proteinuria. The relations could be more informative, if it is with respect to the macromolecules like "IgG" excretion in urine. Type 2 diabetic patients were selected for this study with eGFR > 75 ml/min/1.73 m(2) and grouped into four quartiles based on UIgGCR. The markers of key factors affecting progression of proteinuria were estimated through biochemical tests. The impact of these markers on proteinuria was accessed by applying multinomial logistic regression. The adjusted odds ratio for the UGAGCR was 1.186 (95 % CI: 1.061-1.327) P < 0.003 in highest quartiles of UIgGCR, followed by odds ratio for markers of collagen catabolism 1.051 (95 % CI: 1.025-1.079) P < 0.001, and USACR 1.044 (95 % CI: 1.013-1.077) P < 0.006 respectively. The marker of glycation, i.e., glycated hemoglobin showed the highest odds ratio 5.449 (95 % CI: 1.132-26.236) P < 0.035. In addition, odds for the systolic blood pressure was observed 1.387 (95 % CI: 1.124-1.712) P < 0.002. The higher odds inform and could help to discriminate the diabetic patients with fast progressive diabetic nephropathy. The study describes critical relationship between the urinary excretion of IgG and factors leading to proteinuria in type 2 diabetic patients.

Urinary markers of glomerular injury in diabetic nephropathy

Diabetic nephropathy, the leading cause of renal failure worldwide, affects approximately one-third of all people with diabetes. Microalbuminuria is considered the first sign and the best predictor of progression to renal failure and cardiovascular events. However, albuminuria has several limitations. Therefore, earlier, more sensitive and specific biomarkers with greater predictability are needed. The aim of this paper is to discuss the current literature on biomarkers of glomerular injury that have been implicated in diabetic kidney disease.

Elevated urinary excretion of immunoglobulins in nonproteinuric patients with type 1 diabetes

Increased albuminuria is a hallmark of early diabetic nephropathy, whereas the role of immunoglobulins (Igs), such as IgG (its 1-4 subtypes), IgA, and IgM, different in charge and size, has not been examined in early nephropathy in the past due to lack of a sensitive and reliable method. Our study group consisted of subjects with type 1 diabetes (T1D) and normoalbuminuria (n = 78), microalbuminuria (n = 78), and of 75 healthy subjects (HS). A Luminex-based immunoassay (1,000 time more sensitive than nephelometry-based method) was validated for the urine matrix and used for the measurements of IgG1-4, IgA, and IgM in our study groups. The Luminex-based assay detected Igs in 87% of HS subjects and in 100% of T1D subjects. Recovery of known amounts of Igs added to urine was 92-118%. In the normoalbuminuria group, urinary concentrations of albumin, IgG2, IgA, and IgM were significantly higher than in HS, whereas in the microalbuminuria, further elevation of IgG2, IgG4, and IgA was the most pronounced. In all three groups, fractional excretion of Igs was at least 100 times lower than that of albumin. Fractional excretion of IgG2 was the highest among all Igs. We validated a sensitive method for measuring Igs in urine using Luminex. We found that elevated concentrations of Igs, particularly in IgG2 and IgA, is present in subjects with T1D and no proteinuria. Elevation of those particular Ig subtypes suggests a contribution of novel mechanisms in early diabetic nephropathy, different from charge and size barrier impairment.

Increased Urine IgM and IgG(2) Levels, Indicating Decreased Glomerular Size Selectivity, Are Not Affected by Dalteparin Therapy in Patients with Type 2 Diabetes

Fifty-four type 2 diabetic patients with neuroischemic foot ulcers were randomised to treatment with 5000 IU of dalteparin, (n = 28), or physiological saline, (n = 26), once daily until ulcer healing or for a maximum of 6 months. Thirty-three patients had normo-, 15 micro-, and 6 macroalbuminuria. The urinary levels of IgM and IgG₂ were elevated in 47 and 50 patients, respectively. Elevated urinary levels of IgM and IgG₂ indicate decreased glomerular size selectivity. Urine IgM levels were associated with IGF-1/IGFBP-1 and IGFBP-1 levels. Dalteparin treatment increased urinary levels of glycosaminoglycans (P < 0.001) and serum IGFBP-1 (P < 0.05) while no significant effects were seen in any of the other studied parameters. In conclusion, dalteparin therapy in patients with type 2 diabetes had no effects on urinary levels of albumin, IgM, or IgG₂ despite significantly increased glycosaminoglycans in urine. Elevated urinary levels of IgM and IgG₂ might be more sensitive markers of renal disease than albuminuria in patients with type 2 diabetes and antihypertensive therapy.

Tamm-Horsfall protein gene is associated with distal tubular dysfunction in patients with type 1 diabetes

OBJECTIVE

The first changes in the diabetic kidney are glycogen deposits in the epithelial cells of the thick ascending limb of Henle, which leads to decreased production of Tamm-Horsfall protein (THP). The production of THP is also influenced by nitric oxide (NO). The aims of this study were to investigate whether low excretion of THP, a sign of distal tubular dysfunction, in patients with type 1 diabetes was associated with polymorphisms in the THP gene and the endothelial NO synthase (eNOS) gene.

MATERIAL AND METHODS

Urine was collected from 301 patients with type 1 diabetes, 164 with normoalbuminuria, 91 with microalbuminuria and 46 with macroalbuminuria. Urinary THP concentration below median (3.12 mg/l) was defined as tubular dysfunction. Representative polymorphisms were analysed in the THP and eNOS genes.

RESULTS

Patients with tubular dysfunction had longer diabetes duration and higher blood pressure than patients without tubular dysfunction. Tubular dysfunction was common in patients with macroalbuminuria (70% of patients) and it was associated with the AA+AT genotypes of rs12444268 in the THP gene [odds ratio (OR) 1.8, 95% confidence interval (CI) 1.1-2.8], and the GG genotype of rs1799983 in the eNOS gene (OR 1.6, 95% CI 1.03-2.6). When adjusting for other associated factors, diabetes duration, glycosylated haemoglobin (HbA(1c)), mean arterial pressure and albuminuria, the THP rs12444268 and macroalbuminuria were independently associated with tubular dysfunction.

CONCLUSION

Distal tubular dysfunction was associated with the THP gene and macroalbuminuria in patients with type 1 diabetes.

Urinary biomarkers involved in type 2 diabetes: a review

Diabetes mellitus is one of the most challenging health concerns of the 21st century. With at least 30% of the diabetic population remaining undiagnosed, effective and early diagnosis is of critical concern. Development of a diagnostic test, more convenient and reliable than those currently used, would therefore be highly beneficial. Urine as a diagnostic medium allows for non-invasive detection of biomarkers, including some associated with type 2 diabetes and its complications. This review provides a synopsis of those urinary biomarkers that potentially may provide a basis for the development of improved diagnostic tests. Three main pathways for the sourcing of potential makers are identified: kidney damage, oxidative stress and low-grade inflammation including atherosclerosis/vascular damage. This review briefly presents each pathway and some of the most relevant urinary biomarkers that may be used to monitor the development or progression of diabetes and its complications. In particular, biomarkers of renal dysfunction such as transferrin, type IV collagen and N-acetyl-beta-D-glucosaminidase might prove to be more sensitive than urinary albumin, the current gold standard, in the detection of incipient nephropathy and risk assessment of cardiovascular disease. Inflammatory markers including orosomucoid, tumour necrosis factor-alpha, transforming growth factor-beta, vascular endothelial growth factor and monocyte chemoattractant protein-1, as well as oxidative stress markers such as 8-hydroxy-2'deoxyguanosine may also be useful biomarkers for diagnosis or monitoring of diabetic complications, particularly kidney disease. However, the sensitivity of these markers compared with albumin requires further investigation.

Non enzymatic glycosylation of IgG and their urinary excretion in patients with diabetic nephropathy

Diabetic nephropathy is a major cause of end stage renal disease. Increased excretion of albumin has widely been recognized as an early manifestation of diabetic nephropathy particularly in subjects with diabetes mellitus. However, certain other proteins besides albumin may be excreted in high amount during early phase of diabetic nephropathy. The serum and urinary IgG, Glycosylated hemoglobin, fructosamine and glycosylated IgG were evaluated in the present study. Thirty-two patients of Type 2 Diabetes without any complications, thirty-one patients of Type 2 Diabetes with nephropathy, twenty-six patients of non-diabetic nephropathy and forty normal healthy individuals were enrolled in this study. Subjects were grouped based on their serum creatinine level. Serum IgG, glycosylation of IgG and urinary IgG excretion were increased significantly in diabetic patients compared to healthy controls, which were further increased significantly in chronic renal failure patients with respect to the clinical stage of nephropathy. A positive correlation was observed between glycosylation of IgG and IgG excretion (R(2)=0.5995, 0.7114 respectively) in diabetic patients without any complications and diabetic nephropathy patients only, suggesting a significant role of IgG glycosylation in the vascular clearances of IgG during diabetic nephropathy.

Decreased urinary concentration of Tamm-Horsfall protein is associated with development of renal failure and cardiovascular death within 20 years in type 1 but not in type 2 diabetic patients

OBJECTIVE

The first changes in the diabetic kidney are glycogen deposits in the epithelial cells of the thick ascending limb of Henle. These cells produce Tamm-Horsfall protein (THP). Is low excretion of THP associated with the development of renal insufficiency or cardiovascular disease?

MATERIAL AND METHODS

Urine samples were collected at baseline in patients with type 1 (n = 131) and type 2 (n = 108) diabetes who were followed for a mean of 14 years (range 1-20 years) and 4.5 years (range 1-15 years), respectively.

RESULTS

Twenty percent of type 1 and 54% of type 2 diabetic patients died and 24% and 29%, respectively developed uraemia. A decreased urinary concentration of THP (u-THP) was associated with an eight-fold increased risk of renal failure and cardiovascular death in type 1 but not in type 2 diabetic patients, irrespective of the degree of albuminuria and glycosylated haemoglobin and blood pressure levels. There were no differences in the degrees of albuminuria, serum creatinine or u-THP between the two types of diabetic patients at baseline. Low u-THP occurred in 8% and 9% of normoalbuminuric type 1 and type 2 diabetic patients, respectively.

CONCLUSION

A decreased u-THP was associated with an eight-fold increased risk of cardiovascular death and uraemia in type 1 but not in type 2 diabetic patients.

Size and charge selectivity of the glomerular filter in early experimental diabetes in rats

Microalbuminuria is an early sign of diabetic nephropathy. The aim of the present study was to investigate whether the changes of the glomerular filtration barrier in early experimental diabetes are due to size- or charge-selective alterations. Wistar rats, made diabetic by streptozotocin (STZ) and having their blood glucose maintained at ∼20 mM for 3 or 9 wk, were compared with age-matched controls. Glomerular clearances of native albumin (Cl-HSA) and neutralized albumin (Cl-nHSA) were assessed using a renal uptake technique. Glomerular filtration rate and renal plasma flow were assessed using51Cr-EDTA and [125I]iodohippurate, respectively. In a separate set of animals, diabetic for 9 wk, and in controls, glomerular sieving coefficients (θ) for neutral FITC-Ficoll (molecular radius: 15–90 Å) were assessed using size exclusion chromatography. At 3 wk of diabetes, Cl-HSA and Cl-nHSA remained unchanged, indicating no alteration in either size or charge selectivity. By contrast, at 9 wk of diabetes, there was a twofold increase of Cl-HSA, whereas Cl-nHSA remained largely unchanged, at first suggesting a glomerular charge defect. However, according to a two-pore model, the number of large pores, assessed from both Ficoll and Cl-HSA, increased twofold. In addition, a small reduction in proximal tubular reabsorption was observed at 3 wk, which was further reduced at 9 wk. In conclusion, no functional changes were observed in the glomerular filtration barrier at 3 wk of STZ-induced diabetes, whereas at 9 wk there was a decrease in size selectivity due to an increased number of large glomerular pores.

Early changes in glomerular size selectivity in young adults with type 1 diabetes and retinopathy. Results from the Diabetes Incidence Study in Sweden

OBJECTIVE

To investigate the relationship between early-onset retinopathy and urinary markers of renal dysfunction.

RESEARCH DESIGN AND METHODS

The Diabetes Incidence Study in Sweden (DISS) aims to register all new cases of diabetes in young adults (15-34 years). In 1987-1988, 806 patients were reported and later invited to participate in a follow-up study focusing on microvascular complications after approximately 10 years of diabetes. In the present study, 149 patients with type 1 diabetes, completed eye examination, and urine sampling were included.

RESULTS

The patients with retinopathy (n=58, 39%) had higher HbA(1c) (P<.001) and urinary IgG2/creatinine (P<.05) and IgG2/IgG4 ratios (P<.05). Patients with maculopathy had the highest levels. No significant differences in urinary albumin/creatinine, glycosaminoglycans (GAGs)/creatinine, Tamm-Horsfall protein (THP)/creatinine, and IgG4/creatinine ratios were found. Women had higher urinary albumin/creatinine (P<.01) and urinary IgG2/creatinine ratios (P<.01) than men.

CONCLUSIONS

Young adults with type 1 diabetes and early-onset retinopathy had higher IgG2/creatinine and IgG2/IgG4 ratios than patients without retinopathy indicating that retinopathy is associated with a change in glomerular size selectivity. This was found in association with normal urinary albumin and THP excretion and may be suspected to reflect early general vascular changes.

Functional and molecular alterations of the glomerular barrier in long-term diabetes in mice

AIMS/HYPOTHESIS

Despite the fact that diabetic nephropathy is an increasingly common disorder that may lead to uraemia, the underlying mechanisms are still poorly understood and there is no specific therapy. To clarify whether long-term diabetes alters glomerular size- or charge-selectivity or both, we studied non-obese diabetic mice for up to 40 weeks.

MATERIALS AND METHODS

During the study period, spot urine was collected and blood pressure measured. At weeks 10 and 40, the right kidney was isolated and perfused at 8 degrees C to inhibit tubular function, allowing for analysis of glomerular selectivity with albumin and Ficoll clearance. The left kidney was removed for further investigation using electron microscopy and molecular biology. Real-time PCR with low-density arrays was done to evaluate renal cortex mRNA expression of proteoglycans and other components in the glomerular barrier. After 40 weeks of diabetes, kidneys showed morphological changes typical of diabetic complications.

RESULTS

At 40 weeks, the fractional clearance for negatively charged albumin was three times higher in the diabetic animals (0.0160) than in controls (0.0051, p<0.001), while fractional clearance for neutral Ficoll 35.5 A with a Stokes Einstein radius similar to that of albumin was unaffected. In addition, protein and mRNA levels for versican and decorin were downregulated after 40 weeks of diabetes.

CONCLUSIONS/INTERPRETATION

We conclude that glomerular charge- but not size-selectivity was impaired in the diabetic animals with proteinuria. Also, glomerular components such as versican, decorin and fibromodulin were found to be downregulated after 40 weeks of diabetes.

Measurement of urinary glycosaminoglycans in dogs

OBJECTIVES

To measure urine concentrations of sulfated glycosaminoglycans (GAGs), determine optimal storage conditions for urine samples, establish a reference range, and determine whether there is correlation between 24-hour total urine GAG excretion and the GAG-to-creatinine ratio (GCR).

ANIMALS

14 healthy adult dogs.

PROCEDURE

Single urine sample GAG concentrations and GCRs were measured in samples collected from 14 healthy dogs at the start of the 24-hour collection period. Twenty-four-hour total urine GAG excretions were determined from urine collected during a 24-hour period in the same 14 dogs. Total sulfated GAG concentrations were also measured in urine from these dogs after the urine had been stored at 4 degrees C and -20 degrees C for 1, 7, and 30 days.

RESULTS

Urine GAG concentrations were not significantly different from baseline values after urine was stored at 4 degrees C for up to 1 day and -20 degrees C for up to 30 days. Neither single urine sample GAG concentration (R2, 0.422) nor GCR (R2, 0.084) was an adequate predictor of 24-hour total urine GAG excretion.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of this study provide data that can be used to establish a reference range for 24-hour total urine GAG excretion in dogs and adequate conditions for sample storage. Contrary to findings in humans, there was no significant linear correlation between 24-hour total urine GAG excretion and single urine sample GCR in dogs, limiting clinical use of the single urine sample test.

Ficoll and dextran vs. globular proteins as probes for testing glomerular permselectivity: effects of molecular size, shape, charge, and deformability

Polydisperse mixtures of dextran or Ficoll have been frequently used as molecular probes for studies of glomerular permselectivity because they are largely inert and not processed (reabsorbed) by the proximal tubules. However, dextrans are linear, flexible molecules, which apparently are hyperpermeable across the glomerular barrier. By contrast, the Ficoll molecule is almost spherical. Still, there is ample evidence that Ficoll fractional clearances (sieving coefficients) across the glomerular capillary wall (GCW) are markedly higher than those for neutral globular proteins of an equivalent in vitro Stokes-Einstein (SE) radius. Physical data, obtained by "crowding" experiments or measurements of intrinsic viscosity, suggest that the Ficoll molecule exhibits a rather open, deformable structure and thus deviates from an ideally hard sphere. This is also indicated from the relationship between (log) in vitro SE radius and (log) molecular weight (MW). Whereas globular proteins seem to behave in a way similar to hydrated hard spheres, polydisperse dextran and Ficoll exhibit in vitro SE radii that are much larger than those for compact spherical molecules of equivalent MW. For dextran, this can be partially explained by a high-molecular-size asymmetry. However, for Ficoll the explanation may be that the Ficoll molecule is more flexible (deformable) than are globular proteins. An increased compressibility of Ficoll and an increased deformability and size asymmetry for dextran may be the explanation for the fact that the permeability of the GCW is significantly higher when assessed using polysaccharides such as Ficoll or dextran compared with that obtained using globular proteins as molecular size probes. We suggest that molecular deformability, besides molecular size, shape, and charge, plays a crucial role in determining the glomerular permeability to molecules of different species.

Pore size and charge selectivity of the glomerular membrane at the time of diagnosis of diabetes

The urinary albumin excretion rate is increased at the time of diagnosis of diabetes. We investigated whether this is caused by change in pore size or charge selectivity in the glomerular basement membrane. Urine excretion of immunoglobulins (IgG2, IgG4), glycosaminoglycans (GAG), and albumin was analyzed during the first 20 days after diagnosis of diabetes in children aged 4-15 years; 36 diabetic and 24 age-matched apparently healthy children were included. The excretion of albumin was significantly increased on day 1 in the diabetic children. Between day 1 and 20 the excretion of IgG2 and IgG4 decreased significantly from normal to a level below normal. GAG excretion was not affected. The GAG/creatinine index (GAGCI) was normal. IgG2CI was significantly below normal on days 4-20. IgG4CI was below normal on days 2-20. The albumin creatinine index decreased significantly from day 1 to normal levels on day 4-20. A charge selectivity index, expressed as the ratio between the neutrally charged IgG2 and the negatively charged IgG4, was significantly below the normal level on days 16 and 20. In conclusion, an increased albumin excretion rate in urine did not seem to be caused by a change in charge selectivity. Other explanations such as change in the small pore radius or tubular reabsorption are suggested.

Increased glomerular permeability in patients with nephropathia epidemica caused by Puumala hantavirus

BACKGROUND

Nephropathia epidemica (NE) is the Scandinavian type of haemorrhagic fever with renal syndrome. Usually heavy transient proteinuria is present at the onset of the disease.

METHODS

We investigated glomerular permeability in eight patients with acute NE and in eight healthy controls. Six patients were followed for 1 year. The glomerular filtration rate (GFR) was determined by inulin clearance and effective renal plasma flow (ERPF) by para-aminohippurate clearance.

RESULTS

GFR and ERPF were significantly reduced in NE patients during the acute phase compared with those in controls (P<0.001 and P<0.001, respectively). The filtration fraction (FF) was thus high, 0.37. The fractional clearances of albumin, IgG, and IgG(4) were markedly increased. As a sign of tubular dysfunction, increased urinary excretion of alpha(1)-microglobulin was observed in all patients. After 1 year, the GFR of the patients no longer differed from that of the controls. ERPF was lower and FF higher than those in controls (P=0.014 and P=0.009, respectively). The fractional clearances of albumin, IgG, and IgG(4) remained increased. The high-molecular fractional dextran clearances in the patients were significantly increased compared with controls during the acute phase. Computed analysis of glomerular membrane-pore structure showed that the "shunt-flow" was increased in the patients during the acute phase compared with the controls. There was a positive correlation between the FF and the shunt (r=0.768, P=0.026). In addition, fractional clearances of albumin and IgG correlated significantly with the shunt (r=0.810, P=0.015 and r=0.762, P=0.028, respectively).

CONCLUSIONS

Renal involvement in the acute phase of NE is characterized by a markedly decreased GFR and ERPF. Increased glomerular permeability is associated with impairment of both the size- and charge-selectivity properties of the glomerular filter.