Tamm Horsfall glycoprotein in diabetes mellitus: abnormal chemical composition and colloid stability

The glycobiology of uropathogenic E. coli infection: the sweet and bitter role of sugars in urinary tract immunity

Urinary tract infections (UTI) are among the most prevalent infectious diseases and the most common cause of nosocomial infections, worldwide. Uropathogenic E. coli (UPEC) are responsible for approximately 80% of all UTI, which most commonly affect the bladder. UPEC colonize the urinary tract by ascension of the urethra, followed by cell invasion, and proliferation inside and outside urothelial cells, thereby causing symptomatic infections and quiescent intracellular reservoirs that may lead to recurrence. Sugars, or glycans, are key molecules for host–pathogen interactions, and UTI are no exception. Surface glycans regulate many of the events associated with UPEC adhesion and infection, as well as induction of the host immune response. While the bacterial protein FimH binds mannose‐containing host glycoproteins to initiate infection and UPEC‐secreted polysaccharides block immune mechanisms to favour intracellular replication, host glycans on the urothelial surface and on secreted glycoproteins prevent or limit infection by inhibiting UPEC adhesion. Given the importance of glycans during UTI, here we review the glycobiology of UPEC infection to highlight fundamental sugar‐mediated processes of immunological interest for their potential clinical applications. Interdisciplinary approaches incorporating glycomics and infection biology may help to develop novel non‐antibiotic‐based therapeutic strategies for bacterial infections as the spread of antimicrobial‐resistant uropathogens is currently threatening modern healthcare systems.

Design of drug-like hepsin inhibitors against prostate cancer and kidney stones

Hepsin, a transmembrane serine protease abundant in renal endothelial cells, is a promising therapeutic target against several cancers, particularly prostate cancer. It is involved in the release and polymerization of uromodulin in the urine, which plays a role in kidney stone formation. In this work, we design new potential hepsin inhibitors for high activity, improved specificity towards hepsin, and promising ADMET properties. The ligands were developed in silico through a novel hierarchical pipeline. This pipeline explicitly accounts for off-target binding to the related serine proteases matriptase and HGFA (human hepatocyte growth factor activator). We completed the pipeline incorporating ADMET properties of the candidate inhibitors into custom multi-objective optimization functions. The ligands designed show excellent prospects for targeting hepsin via the blood stream and the urine and thus enable key experimental studies. The computational pipeline proposed is remarkably cost-efficient and can be easily adapted for designing inhibitors against new drug targets.

Tamm-Horsfall glycoprotein engages human Siglec-9 to modulate neutrophil activation in the urinary tract

Urinary tract infections (UTI) are a major problem in human medicine for which better understanding of native immune defenses may reveal new pathways for therapeutic intervention. Tamm-Horsfall glycoprotein (THP), the most abundant urinary protein, interacts with bacteria including uropathogenic E. coli (UPEC) as well host immune cells. In addition to its well-studied functions to antagonize bacterial colonization, we hypothesize that THP serves a critical host defense function through innate immune modulation. Using isolated human neutrophils, we found that THP binds neutrophils and that this interaction reduces reactive oxygen species generation, chemotaxis, and killing of UPEC. We discovered that THP engages the inhibitory neutrophil receptor sialic acid-binding Ig-like lectin-9 (Siglec-9), and mouse functional ortholog Siglec-E, in a manner dependent on sialic acid on its N-glycan moieties. THP-null mice have significantly more neutrophils present in the urine compared to WT mice, both with and without the presence of inflammatory stimuli. These data support THP as an important negative regulator of neutrophil activation in the urinary tract, with dual functions to counteract bacterial colonization and suppress excessive inflammation within the urinary tract.

Serum uromodulin is associated with impaired glucose metabolism

Uromodulin is the most abundant urine protein under physiological conditions. It has recently been described as a serum and plasma marker for kidney disease. Whether uromodulin is associated with impaired glucose metabolism is unknown.We therefore measured serum uromodulin and glucose traits in a cohort of 529 consecutively recruited patients.Serum uromodulin was significantly and inversely correlated with fasting plasma glucose (r = -0.161; P < 0.001), with plasma glucose 2 hours after an oral 75 g glucose challenge (r = -0.158; P = 0.001), and with HbA1c (r = -0.103; P = 0.018). A total of 146 (27.6%) of our patients had type 2 diabetes mellitus (T2DM). Analysis of covariance confirmed that T2DM was an independent determinant of serum uromodulin (F = 5.5, P = 0.020) after multivariate adjustment including hypertension and glomerular filtration rate. Prospectively, uromodulin was lowest in patients with T2DM at baseline, higher in initially nondiabetic subjects who developed diabetes during follow-up (FU) and highest among nondiabetic patients (147.7 ± 69.9 vs 164 ± 67 vs 179.9 ± 82.2 ng/mL, Ptrend < 0.001). Similar results were seen with respect to prediabetes (168.0 ± 81.2 vs 172.8 ± 66.3 vs 188.2 ± 74.0 ng/mL, P = 0.011).We conclude that serum uromodulin is significantly associated with impaired glucose metabolism and the development of prediabetes and diabetes.

Streptozocin-induced diabetic mouse model of urinary tract infection

Diabetics have a higher incidence of urinary tract infection (UTI), are infected with a broader range of uropathogens, and more commonly develop serious UTI sequelae than nondiabetics. To better study UTI in the diabetic host, we created and characterized a murine model of diabetic UTI using the pancreatic islet beta-cell toxin streptozocin in C3H/HeN, C3H/HeJ, and C57BL/6 mouse backgrounds. Intraperitoneal injections of streptozocin were used to initiate diabetes in healthy mouse backgrounds, as defined by consecutive blood glucose levels of >250 mg/dl. UTIs caused by uropathogenic Escherichia coli (UTI89), Klebsiella pneumoniae (TOP52 1721), and Enterococcus faecalis (0852) were studied, and diabetic mice were found to be considerably more susceptible to infection. All three uropathogens produced significantly higher bladder and kidney titers than buffer-treated controls. Uropathogens did not have as large an advantage in the Toll-like receptor 4-defective C3H/HeJ diabetic mouse, arguing that the dramatic increase in colonization seen in C3H/HeN diabetic mice may partially be due to diabetic-induced defects in innate immunity. Competition experiments demonstrated that E. coli had a significant advantage over K. pneumoniae in the bladders of healthy mice and less of an advantage in diabetic bladders. In the kidneys, K. pneumoniae outcompeted E. coli in healthy mice but in diabetic mice E. coli outcompeted K. pneumoniae and caused severe pyelonephritis. Diabetic kidneys contained renal tubules laden with communities of E. coli UTI89 bacteria within an extracellular-matrix material. Diabetic mice also had glucosuria, which may enhance bacterial replication in the urinary tract. These data support that this murine diabetic UTI model is consistent with known characteristics of human diabetic UTI and can provide a powerful tool for dissecting this infection in the multifactorial setting of diabetes.

Tamm-Horsfall protein is a critical renal defense factor protecting against calcium oxalate crystal formation

BACKGROUND

The tubular fluid of the mammalian kidney is often supersaturated with mineral salts, but crystallization rarely occurs under normal conditions. The unique ability of the kidney to avoid harmful crystal formation has long been attributed to the inhibitory activity of the urinary macromolecules, although few in vivo studies have been carried out to examine this hypothesis. Here we examined the role of Tamm-Horsfall protein (THP), the principal urinary protein, in urinary defense against renal calcium crystal formation, using a THP knockout model that we recently developed.

METHODS

Wild-type and THP knockout mice were examined for the spontaneous formation of renal calcium crystals using von Kossa staining. The susceptibility of these mice to experimentally induced renal crystal formation was evaluated by administering mice with ethylene glycol, a precursor of oxalate, and vitamin D(3), which increases calcium absorption. Renal calcium crystals were visualized by von Kossa stain, dark field microscopy with polarized light and scanning electron microscopy.

RESULTS

Inactivating the THP gene in mouse embryonic stem cells results in spontaneous formation of calcium crystals in adult kidneys. Excessive intake of calcium and oxalate, precursors of the most common type of human renal stones, dramatically increases both the frequency and the severity of renal calcium crystal formation in THP-deficient, but not in wild-type mice. Under high calcium/oxalate conditions, the absence of THP triggers a marked, adaptive induction in renal epithelial cells of osteopontin (OPN), a potent inhibitor of bone mineralization and vascular calcification. Thus, OPN may serve as an inducible inhibitor of calcium crystallization, whereas THP can serve as a constitutive and apparently more effective inhibitor.

CONCLUSION

These results provide the first in vivo evidence that THP is a critical urinary defense factor and suggest that its deficiency could be an important contributing factor in human nephrolithiasis, a condition afflicting tens of millions of people in the world annually.

Ablation of the Tamm-Horsfall protein gene increases susceptibility of mice to bladder colonization by type 1-fimbriated Escherichia coli

The adhesion of uropathogenic Escherichia coli to the urothelial surface of the bladder is a prerequisite for the establishment of bladder infections. This adhesion process relies on E. coli adhesins and their cognate urothelial receptors, and it also is influenced by an intricate array of defense mechanisms of the urinary system. In this study, we examined the in vivo role of Tamm-Horsfall protein (THP), the most abundant urinary protein, in innate urinary defense. We genetically ablated the mouse THP gene and found that THP deficiency predisposes mice to bladder infections by type 1-fimbriated E. coli. Inoculation of too few type 1-fimbriated E. coli to colonize wild-type mice caused significant bladder colonization in THP-knockout mice. In contrast, THP deficiency did not enhance the ability of P-fimbriated E. coli to colonize the bladder. Our results provide the first in vivo evidence indicating that under physiological conditions, the mannosylated THP can serve as an effective soluble "receptor," binding to the type 1-fimbriated E. coli and competitively inhibiting them from adhering to the uroplakin Ia receptors present on the urothelial surface. These results suggest that potential THP defects, either quantitative or qualitative, could predispose the urinary bladder to bacterial infections. The generation of THP-deficient mice established the role of THP as a first line of urinary defense and should help elucidate other potential functions of this major protein in urinary tract physiology and diseases.

Adherence of type 1-fimbriated Escherichia coli to uroepithelial cells: more in diabetic women than in control subjects

OBJECTIVE

Women with diabetes have bacteriuria more often than women without diabetes. Because Escherichia coli adhere better to vaginal cells of nondiabetic patients with recurrent urinary tract infections (UTIs) than to those obtained from healthy control subjects, it was hypothesized that E. coli adhere more to the uroepithelial cells of diabetic women, either because of substances excreted in the urine (e.g., albumin, glucose, and Tamm Horsfall protein) or because of a difference in the uroepithelial cells.

RESEARCH DESIGN AND METHODS

A T24 bladder cell line and uroepithelial cells of 25 diabetic women and 19 control subjects were incubated with three different E. coli strains.

RESULTS

The mean numbers of type 1-fimbriated E. coli that adhered to diabetic and control cells were 12.9 and 6.1 (P = 0.001), respectively, whereas those of P-fimbriated E. coli were 8.8 and 8.1 (P = 0.8), and those of nonfimbriated E. coli were 2.7 and 3.4 (P = 0.4). The addition of various substances did not influence the adherence of E. coli to a T24 bladder cell line.

CONCLUSIONS

Type 1-fimbriated E. coli adhere more to diabetic than to control uroepithelial cells.

Pathogenesis of bacteriuria in women with diabetes mellitus

Women with diabetes mellitus (DM) have asymptomatic bacteriuria (ASB) and symptomatic urinary tract infections (UTIs) more often than women without DM. The increased prevalence of bacteriuria in diabetic patients can be the result of differences in the host responses between diabetic and nondiabetic patients, or a difference in the infecting bacterium itself. We have shown that the increased prevalence of ASB in diabetic women is not the result of a difference in bacteria, because the same number of virulence factors was found in the infecting Escherichia coli (most common causative microorganism of ASB) in our diabetic women with ASB, as listed in the literature for nondiabetic patients with ASB. We found that bacterial growth in vitro was increased after the addition of different glucose concentrations, as found in urine of poorly controlled patients. However, we could not confirm that glucosuria was a risk factor for ASB in vivo. In addition, we demonstrated that women with both DM and ASB have lower urinary cytokine and leukocyte concentrations than women without DM but with ASB. Finally, we found that E. coli expressing type 1 fimbriae (the virulence factor that plays an important role in the pathogenesis of UTIs) adhere better to uroepithelial cells of women with DM compared with the cells of women without DM.

The sugar moiety of Tamm-Horsfall protein is affected by the carbohydrate-deficient glycoprotein type I syndrome. A case study

As the sugar moiety of Tamm-Horsfall protein (THP) is affected by many pathological conditions, the aim of this study was to examine the influence of carbohydrate-deficient glycoprotein syndrome (CDG) on THP glycans. THP was isolated from urine of one patient with CDG type I and N-glycan profiling, analysis of monosaccharide content, determination of THP reactivity with specific lectins and with anti-THP antibodies were performed. THP of the CDG patient showed markedly lower amounts of all monosaccharides. Diminished amounts of lactosamine-type chains, galactose and alpha2,3 linked sialic acid were expressed in lower reactivity with PHA-L, DSA and MAA, respectively. These modifications were reflected in altered proportions of tetrasialylated and disialylated oligosaccharide chains. THP of the CDG patient reacted slightly more with anti-THP antibodies. Our results indicate that the CDG type I affects the THP sugar moiety and slightly enhances the THP immunoreactivity.

Composition of the sugar moiety of Tamm-Horsfall protein in patients with urinary diseases

The sugar moiety of Tamm-Horsfall protein (THP) is altered by pathological conditions. The aim of this study was to investigate the composition of THP glycans in urinary diseases. THP was isolated from the urine of patients with urinary tract infection (group A), glomerulonephritis or interstitial nephritis (group B), and Bartter's syndrome (BS) (group C). Monosaccharides, N-glycan profile, THP reactivity with specific lectins and some other proteins were analyzed. THP of patients from groups A, B, and C showed lower amounts of N-acetylgalactosamine (P<0.05, P<0.005, and P<0.05, respectively) than controls; this was reflected in lower reactivity with Phaseolus vulgaris lectin (P<0.005, P<0.05, and P<0.005). Reduced amounts of N-acetylglucosamine were noticed in groups A (P<0. 05) and B (P<0.05). In group A lower amounts of galactose and alpha2, 6-linked sialic acid, as determined by reactivity with Datura stramonium lectin (P<0.005) and Sambucus nigra lectin (P<0.005), were observed. In patients with BS there was a shift from tetrasialylated glycans towards less-sialylated chains. We found also that THP of all patients binds more strongly to IgG(1) (P<0.005, for all patient groups). Our results indicate that the urinary diseases examined affect the THP sugar moiety and the binding of THP to IgG(1).

A study of Tamm-Horsfall protein excretion in hypertensive patients and type 1 diabetic patients

OBJECTIVE

The study was performed in order to evaluate to what extent hypertension or diabetes mellitus may affect the urinary excretion rate of Tamm-Horsfall protein.

MATERIALS AND METHOD

The urinary excretion rates of albumin and Tamm-Horsfall protein, a measure of glomerular and distal tubular function, respectively were measured in patients with essential hypertension (n = 17) and in type 1 diabetes with (n = 20) or without nephropathy (n = 8) and in apparently healthy subjects (n = 10).

RESULTS

Mean 24-h ambulatory blood pressure measurements showed higher blood pressure levels in the hypertensive (167/ 106 mmHg, p < 0.001) than in the diabetic patients with (136/84 mmHg) and without nephropathy (121/74 mmHg) and in healthy subjects (122/76 mmHg). Day and night ratios of systolic and diastolic blood pressure levels were not different among the four groups. Urinary albumin excretion rate was increased in patients with hypertension (30.8 x/ 3.4 microg/min; geometric mean x/tolerance factor; p < 0.001) and diabetes with nephropathy (462 x/ 3.5 microg/min; p < 0.001) compared with diabetic patients without nephropathy and healthy subjects (4.6 x/ 1.9 and 3.7 x/ 1.5 microg/min, respectively). The Tamm-Horsfall protein excretion rate was decreased in patients with diabetic nephropathy (11.6 x/ 3.5 microg/min) compared to patients with hypertension (36.3 x/2.1 1g/min; p < 0.01), diabetes without nephropathy (39.2 x/ 2.0 microg/min; p < 0.05) and healthy subjects (63.0 x/ 1.4 microg/min; p < 0.001), whereas no differences were found among the latter three groups.

CONCLUSION

These data indicate that high blood pressure may be associated with albuminuria, while a decrease in excretion rate of Tamm-Horsfall protein may be associated with diabetic nephropathy. These associations need to be studied in a larger population.

Isoelectric focusing of Tamm-Horsfall glycoproteins: a simple tool for recognizing recurrent calcium oxalate renal stone formers

Tamm-Horsfall glycoproteins (THPs) from healthy probands and a majority of recurrent calcium oxalate renal stone formers reveal different physicochemical properties when analyzed using isoelectric focusing (IEF). The pI values of THPs from healthy probands are approximately 3.5 while THPs from recurrent renal stone formers have pI values of between 4.5 and 6. The two groups of THPs exhibit completely different protein patterns. The differences in IEF analysis allow differentiation between THPs from healthy probands and recurrent calcium oxalate stone formers and may possibly be used as a simple diagnostic method for the recognition of recurrent calcium oxalate renal stone formers.

A simple diagnostic method for the differentiation of Tamm-Horsfall glycoproteins from healthy probands and those from recurrent calcium oxalate renal stone formers

Tamm-Horsfall glycoproteins (THPs)* from healthy probands, and those from a majority of recurrent calcium oxalate renal stone formers, reveal different properties when analyzed using isoelectric focusing. The pl-values of THPs from healthy probands are approximately 3.5 while THPs from recurrent renal stone formers have pl-values between 4.5 and 6. The two groups of THPs exhibit completely different protein patterns in IEF. This proves the structural difference of these THPs. The differences in IEF analysis allow the differentiation between THPs from healthy probands and those from recurrent calcium oxalate stone formers. These differences could possibly be used as a simple diagnostic method for the recognition of recurrent calcium oxalate renal stone formers.

Tamm-Horsfall glycoprotein in streptozotocin diabetic rats: a study of kidney in situ hybridization, immunohistochemistry, and urinary excretion

Tamm-Horsfall glycoprotein, present only in the kidney thick ascending limb of Henle's loop, was studied here in streptozotocin diabetic rats. Tamm-Horsfall glycoprotein mRNA in situ hybridization was performed on snap-frozen left kidneys; the right kidneys were perfusion-fixed with 4% paraformaldehyde and embedded either in paraffin, for Tamm-Horsfall glycoprotein immunohistochemistry, or in Epon for stereologic measurements. The length of the thick ascending limb of Henle's loop and the amount of glycogen were measured and the ultrastructure of the cells was evaluated. Urinary excretion of Tamm-Horsfall glycoprotein, calcium, magnesium and albumin was measured. After 10 and 50 days' duration of diabetes, kidney weight increased 20 and 41%, respectively and the length of the thick ascending limb of Henle's loop increased 28 and 56%, respectively, compared with controls. Substantial glycogen accumulations were present in the thick ascending limb of Henle's loop, and electron microscopy revealed a significant decrease in organelles and basolateral membranes. After 10 and 50 days' duration of diabetes, in situ hybridization of Tamm-Horsfall glycoprotein mRNA revealed a fourfold decrease, and the immunostaining for Tamm-Horsfall glycoprotein showed a threefold decrease as measured by densitometry. However, urinary Tamm-Horsfall glycoprotein excretion rate was increased fivefold and urinary concentration about twofold. Urinary calcium excretion increased three-fold and magnesium twofold, but urinary albumin excretion was not significantly increased. The increased amount of Tamm-Horsfall glycoprotein, calcium and magnesium in the urine in diabetes occurs here concomitant with severe cellular damage in the thick ascending limb of Henle's loop.

Urinary excretion rate of NC1 and Tamm-Horsfall protein in the microalbuminuric type I diabetic patient

Fifty-six type I diabetic patients with microalbuminuria (albumin excretion rate 20-200 micrograms/min) were characterized as to sex, age, duration of diabetes, smoking habits, blood pressure, glomerular filtration rate, urinary NC1 (the carboxy-terminal domain of collagen IV), and Tamm-Horsfall protein excretion rate. Albumin excretion rate was considered a sign of glomerular damage, NC1 excretion rate a measure of renal basement membrane turnover, and Tamm-Horsfall protein excretion rate a marker for distal tubular function. There were no differences between males and females and between smokers and nonsmokers with respect to blood pressure, body-mass index, albumin excretion rate, glomerular filtration rate, excretion rate of NC1, and Tamm-Horsfall protein. As a group, the patients with microalbuminuria had normal glomerular filtration rate, excretion rate of NC1, and Tamm-Horsfall protein. The latter was influenced by glycosylated hemoglobin (HbA1c) levels, especially so in patients with an albumin excretion rate less than the median value of 53.0 micrograms/min (r = -0.61, p < 0.01). Furthermore, both excretion rate of NC1 and Tamm-Horsfall protein were increased in patients with high glomerular filtration rate > or = 130 mL min-1 1.73 m-2). There was no association between glomerular filtration rate and HbA1c levels. As glomerular filtration rate is related to kidney size, these observations suggest that patients with a high glomerular filtration rate have an increased mass and turnover of tubular basement membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Marked reduction of Tamm-Horsfall protein synthesis in hyperprostaglandin E-syndrome

Hyperprostaglandin E-syndrome (HPS), a recently described variant of Bartter's syndrome (BS), resembles BS in a number of symptoms but is distinct from BS in others. Similar to BS, HPS is characterized by congenital hypokalemic alkalosis, hypertrophy of the juxtaglomerular apparatus, hyperreninemia, secondary hyperaldosteronism, normal blood pressure and renal diabetes insipidus. Other than BS, HPS is constantly associated with chronic hypercalciuria and nephrocalcinosis as well as both renal and systemic PGE2 overproduction. Correction of most of the symptoms in HPS is achieved by permanent inhibition of prostaglandin synthesis with indomethacin. Among the causes leading to HPS, a selective damage of the distal tubule in HPS has been suggested. Therefore, synthesis of Tamm-Horsfall protein (THP), a glycoprotein exclusively produced in the thick ascending limb of the loop of Henle, was measured by ELISA in the urine of seven infant HPS patients (aged 3 to 8 years). Patients were investigated both under constant indomethacin treatment and after a one week period without indomethacin. Nine healthy children (aged 5 months to 10 years) served as controls. In controls mean daily THP excretion was 54.2 +/- 13.9 (median 46.0) mg/24 hr/1.73 m2 whereas in HPS, THP levels were strongly diminished. During withdrawal of indomethacin treatment, mean THP level was 12.7 +/- 10.1 (median 7.2) mg/24 hr/1.73 m2 and 10.3 +/- 10.1 (median 3.5) mg/24 hr/1.73 m2 under indomethacin treatment, respectively. THP excretion values both without indomethacin and under indomethacin treatment were significantly different from controls (P < or = 0.005); however, there was no significant difference between the THP levels during or after cessation of indomethacin treatment. Creatinine clearance in HPS patients was 75.1 +/- 15.9 (median 76.2) ml/min/1.73 m2 without indomethacin and 81.9 +/- 15.1 (median 83.0) ml/min/1.73 m2 under indomethacin treatment. Control values were not obtained. Comparative measurements of THP excretion in six classical BS-patients (aged 3 months to 17 years) revealed normal THP values in two individuals and intermediate levels in the others: the mean level of six BS patients was 30.8 +/- 13.5 (median 25.0) mg/24 hr/1.73 m2 and was thus significantly higher than in HPS both with and without indomethacin treatment (P < or = 0.05). Immunohistochemistry in renal biopsies of three of the HPS patients showed a strong reduction of cortical tubular THP immunoreactivity in two cases and a less pronounced reduction in the third. In situ hybridization using a THP-riboprobe in these three biopsies revealed significantly reduced or absent THP-mRNA levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Tubular secretion of Tamm-Horsfall protein in type 1 (insulin-dependent) diabetes mellitus using a simplified enzyme linked immunoassay

The relationship between glomerular and tubular dysfunction and metabolic control in type 1 diabetes was studied. To that end the urinary excretion rates of albumin and Tamm-Horsfall protein as well as HbA1c levels were measured in 58 patients with different degrees of diabetic nephropathy and in 76 apparently healthy subjects matched for sex and age. The urinary Tamm-Horsfall protein levels were measured by a simplified enzyme linked immunoassay. The intra- and interassay variations were 8.9% and 13.6%, respectively. The intraindividual variation was 41% and the sensitivity of the assay was 4 micrograms/l. The Tamm-Horsfall protein excretion rate was 42.1 x/2.0 micrograms/min (geometric mean x/tolerance factor) in the diabetic patients compared to 34 x/1.9 micrograms/min in the control subjects (NS). The diabetic patients had higher albumin excretion rate (38.5 x/7.3 micrograms/min) than the control subjects (4.7 x/2.3 micrograms/min; P less than 0.001). By using multivariate analysis of variance, HbA1c level was found to be the only independent variable associated with Tamm-Horsfall protein excretion rate in diabetic patients (r = -0.28; P = 0.04), while no relationship was found between Tamm-Horsfall protein excretion rate and age, age at onset and duration of diabetes, gender, serum creatinine, diuresis, urinary albumin excretion rate, systolic and diastolic blood pressure levels and antihypertensive treatment. The urinary albumin excretion rate was associated with diastolic blood pressure (r = 0.34; P = 0.02) but not with HbA1c levels when testing the above variables by multivariate analysis of variance. In conclusion, these results may indicate a lack of relationship between glomerular and tubular dysfunction. The former was influenced only by diastolic blood pressure levels and the latter only by the degree of metabolic control. However, the correlations were weak and do not provide any insight into what is actually responsible for glomerular and tubular dysfunction.