Urinary excretion of Tamm-Horsfall protein and epidermal growth factor in chronic nephropathy

Unveiling the Hidden Power of Uromodulin: A Promising Potential Biomarker for Kidney Diseases

Uromodulin, also known as Tamm-Horsfall protein, represents the predominant urinary protein in healthy individuals. Over the years, studies have revealed compelling associations between urinary and serum concentrations of uromodulin and various parameters, encompassing kidney function, graft survival, cardiovascular disease, glucose metabolism, and overall mortality. Consequently, there has been a growing interest in uromodulin as a novel and effective biomarker with potential applications in diverse clinical settings. Reduced urinary uromodulin levels have been linked to an elevated risk of acute kidney injury (AKI) following cardiac surgery. In the context of chronic kidney disease (CKD) of different etiologies, urinary uromodulin levels tend to decrease significantly and are strongly correlated with variations in estimated glomerular filtration rate. The presence of uromodulin in the serum, attributable to basolateral epithelial cell leakage in the thick ascending limb, has been observed. This serum uromodulin level is closely associated with kidney function and histological severity, suggesting its potential as a biomarker capable of reflecting disease severity across a spectrum of kidney disorders. The UMOD gene has emerged as a prominent locus linked to kidney function parameters and CKD risk within the general population. Extensive research in multiple disciplines has underscored the biological significance of the top UMOD gene variants, which have also been associated with hypertension and kidney stones, thus highlighting the diverse and significant impact of uromodulin on kidney-related conditions. UMOD gene mutations are implicated in uromodulin-associated kidney disease, while polymorphisms in the UMOD gene show a significant association with CKD. In conclusion, uromodulin holds great promise as an informative biomarker, providing valuable insights into kidney function and disease progression in various clinical scenarios. The identification of UMOD gene variants further strengthens its relevance as a potential target for better understanding kidney-related pathologies and devising novel therapeutic strategies. Future investigations into the roles of uromodulin and regulatory mechanisms are likely to yield even more profound implications for kidney disease diagnosis, risk assessment, and management.

Associations of plasma uromodulin and genetic variants with blood pressure responses to dietary salt interventions

Uromodulin, also named Tamm Horsfall protein, have been associated with renal function and sodium homeostasis regulation. The authors sought to examine the effects of salt intake on plasma and urinary uromodulin levels and the association of its genetic variants with salt sensitivity in Chinese adults. Eighty patients from our natural population cohort were maintained sequentially either on a usual diet for 3 days, a low-salt diet (3.0 g) for 7 days, and a high-salt diet (18.0 g) for an additional 7 days. In addition, the authors studied 514 patients of the Baoji Salt-Sensitive Study, recruited from 124 families who received the same salt intake intervention, and investigated the association of genetic variations in uromodulin gene with salt sensitivity. Plasma uromodulin levels were significantly lower on a high-salt diet than on a baseline diet (28.3 ± 4.5 vs. 54.9 ± 8.8 ng/ml). Daily urinary excretions of uromodulin were significantly decreased on a high-salt diet than on a low-salt diet (28.7 ± 6.7 vs. 157.2 ± 21.7 ng/ml). SNPs rs7193058 and rs4997081 were associated with the diastolic blood pressure (DBP), mean arterial pressure (MAP) responses to the high-salt diet. In addition, several SNPs in the uromodulin gene were significantly associated with pulse pressure (PP) response to the low-salt intervention. This study shows that dietary salt intake affects plasma and urinary uromodulin levels and that uromodulin may play a role in the pathophysiological process of salt sensitivity in the Chinese populations.

Protein Profiling of Urine from Dogs with Renal Disease Using ProteinChip Analysis

Measurement of total urinary proteins in individuals that tested positive by urinary dipstick is a typical method for assessing the presence of potentially serious renal disorders. In the absence of such overt proteinuria, however, measurement of specific urinary proteins may be useful in the diagnosis of nephropathies and may provide greater insight into the pathogenesis. The urine of 28 dogs (16 with renal disease and 12 healthy) was evaluated to determine whether specific low—molecular-weight proteins or the pattern of protein excretion could also be used as a marker of tubular dysfunction in dogs. Specific proteins were assessed by immunological methods, whereas protein profiles were determined by surface-enhanced laser desorption/ionization time–of-flight mass spectrometry (MS). In particular, changes in the excretion of retinol-binding protein (RBP) and Tamm-Horsfall protein (THP) appear to be of clinical relevance in the diagnosis of canine kidney diseases. The pattern of urinary protein and peptides revealed specific changes in abundance in dogs with renal disease at molecular masses (kD) of 11.58, 12.41, 12.60, 14.58, 20.95 (RBP), 27.85, and 65.69 (albumin). In conclusion, comparable proteins as in humans might be used as urinary markers for proximal (RBP) and distal (THP) tubular dysfunction in dogs. Surface-enhanced laser desorption/ionization time-of-flight MS is a promising tool for the study of kidney physiology and pathophysiology and might aid in the discovery of new biomarkers of renal disease.

The serum uromodulin level is associated with kidney function

BACKGROUND

In chronic kidney diseases of various etiologies, the urinary excretion of uromodulin is usually decreased in parallel with the glomerular filtration rate. This study aimed to investigate whether serum uromodulin is associated with kidney function.

METHODS

Within the framework of the Seniorlabor study, a subset of subjectively healthy individuals 60 years of age and older were included in the study. Serum uromodulin was measured with ELISA. The relationship between serum uromodulin and different stages of kidney function (i.e., cystatin C-based 2012-CKD-EPI eGFRCysC>90 mL/min/1.73 m2, 60-89 mL/min/1.73 m2, 45-59 mL/min/1.73 m2, and <45 mL/min/1.73 m2) was investigated. Furthermore, the relationship between serum uromodulin and other markers of kidney function (i.e., creatinine, cystatin C, and urea) was assessed.

RESULTS

In total, 289 participants (140 males/149 females; mean age 71±7 years) were included in the study. There were significant differences in serum uromodulin among the four groups according to different kidney function stages (p<0.001). Serum uromodulin displayed inverse relationships with creatinine (r=-0.39), cystatin C (r=-0.42), and urea (r=-0.30) and, correspondingly, a positive relationship with eGFRCysC (r=0.38, p<0.001 for all). These associations remained intact when fitting a regression model that incorporated age, gender, body mass index, and current smoking status as covariates.

CONCLUSIONS

Serum uromodulin behaves in a manner opposite that of the different conventional renal retention markers by displaying lower concentrations with decreasing kidney function. As uromodulin is produced by the cells of the thick ascending limb of the loop of Henle, lower uromodulin serum levels may reflect a reduction in number or function of these cells in chronic kidney disease.

A discovery-phase urine proteomics investigation in type 1 diabetes

Diabetes is a chronic metabolic disease which can lead to serious health problems particularly in and to the development of cardiovascular and renal complications. The aim of this study is to possibly identify distinctive molecular features in urine samples which might correlate to the progression and complications of type 1 diabetes. Diabetic patients with normo- and micro-albuminuria have been analyzed and compared to a group of control subjects. Urine proteins of control and type 1 diabetes subjects were investigated in their proteome profiles, using high-resolution two-dimensional gel electrophoresis separation and protein identifications by MALDI-TOF-MS and LC-MS/MS analysis. Proteomics analysis highlighted differential expression of several proteins between control and type 1 diabetes subjects. In particular, five proteins were found to be down-regulated and four proteins up-regulated. Lower protein representations in diabetic subjects were associated with Tamm-Horsfall urinary glycoprotein, apolipoprotein A-I, apolipoprotein E, α2-thiol proteinase inhibitor, and human complement regulatory protein CD59, while higher protein representations were found for α-1-microglobulin, zinc-α2 glycoprotein, α-1B glycoprotein, and retinol-binding protein 4. These differences were maintained comparing control subjects with type 1 diabetes normo-albuminuric and micro-albuminuric subjects. Furthermore, these proteins are correlated to glycosylated hemoglobin and microalbuminuria, confirming their role in diabetic pathology. This study gives new insights on potential molecular mechanisms associated with the complications of type 1 diabetic disease providing evidences of urine proteins potentially exploitable as putative prognostic biomarkers.

Uromodulin in renal transplant recipients: elevated urinary levels and bimodal association with graft failure

BACKGROUND

Urinary uromodulin (UMOD) predicts renal prognosis in native kidneys, but data are conflicting. We investigated its prognostic impact for graft failure (GF) in renal transplant recipients (RTR; n = 600).

METHODS

UMOD concentration was measured cross-sectionally in RTR at 6.0 years [2.6-11.4] post-transplant, in matched patients with native chronic kidney disease (CKD) and healthy subjects. In 59 cases, RTR allograft biopsies were reviewed.

RESULTS

During a follow-up of 5.3 years [4.5-5.7], GF had occurred in 7% of RTR. Median UMOD excretion (mg/24 h) was 20.4 in RTR, 11.6 in CKD and 5.7 in controls (p < 0.001). There was a curvilinear association between UMOD excretion and baseline renal function (p < 0.003) and death-censored GF, with 5.5, 11.5 and 4.0% of the cases in subsequent UMOD excretion tertiles, respectively (p = 0.002). On multivariate Cox regression analysis, hazard ratios for GF for the 1st and 3rd tertiles were 0.37 (p = 0.01) and 0.21 (p = 0.001), respectively. Interstitial fibrosis and tubular atrophy were more severe in the middle tertile (p = 0.007).

CONCLUSIONS

Urinary UMOD is elevated in RTR and associated with graft function, morphology and outcome in a bimodal fashion. Dissection of the disparate mechanisms of GF prediction by urinary UMOD might provide new clues for its alleged pathogenetic significance in progressive renal function loss.

Genome-wide association study of blood pressure extremes identifies variant near UMOD associated with hypertension

Hypertension is a heritable and major contributor to the global burden of disease. The sum of rare and common genetic variants robustly identified so far explain only 1%–2% of the population variation in BP and hypertension. This suggests the existence of more undiscovered common variants. We conducted a genome-wide association study in 1,621 hypertensive cases and 1,699 controls and follow-up validation analyses in 19,845 cases and 16,541 controls using an extreme case-control design. We identified a locus on chromosome 16 in the 5′ region of Uromodulin (UMOD; rs13333226, combined P value of 3.6×10⁻¹¹). The minor G allele is associated with a lower risk of hypertension (OR [95%CI]: 0.87 [0.84–0.91]), reduced urinary uromodulin excretion, better renal function; and each copy of the G allele is associated with a 7.7% reduction in risk of CVD events after adjusting for age, sex, BMI, and smoking status (H.R. = 0.923, 95% CI 0.860–0.991; p = 0.027). In a subset of 13,446 individuals with estimated glomerular filtration rate (eGFR) measurements, we show that rs13333226 is independently associated with hypertension (unadjusted for eGFR: 0.89 [0.83–0.96], p = 0.004; after eGFR adjustment: 0.89 [0.83–0.96], p = 0.003). In clinical functional studies, we also consistently show the minor G allele is associated with lower urinary uromodulin excretion. The exclusive expression of uromodulin in the thick portion of the ascending limb of Henle suggests a putative role of this variant in hypertension through an effect on sodium homeostasis. The newly discovered UMOD locus for hypertension has the potential to give new insights into the role of uromodulin in BP regulation and to identify novel drugable targets for reducing cardiovascular risk.

Hypertension is the leading contributor to global mortality with a global prevalence of 26.4% in 2000, projected to increase to 29.2% by 2025. While 50%–60% of population variation in blood pressure can be attributable to additive genetic factors, all the genetic variants robustly identified so far explain only 1%–2% of the population variance indicating the presence of additional undiscovered risk variants. Using an extreme case-control strategy, we have discovered a SNP in the promoter region of the uromodulin gene (UMOD) to be associated with hypertension (minor allele protective against hypertension). We then validated this association using large-scale population and case-control studies, where similar extreme criteria for selection of cases and controls have been used (21,466 cases and 18,240 controls). As the locus was related to uromodulin, a protein exclusively expressed in the kidneys, we show that the association is independent of renal dysfunction. We also show preliminary evidence that the SNP allele which is protective against hypertension is also protective against cardiovascular events in 26,654 Swedish subjects followed-up for 12 years. The newly discovered UMOD locus for hypertension has the potential to give unique insights into the role of uromodulin in BP regulation and to identify novel drugable targets.

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.

Evidence for a role of uromodulin in chronic kidney disease progression

BACKGROUND

Uromodulin (also known as Tamm-Horsfall protein) is the most abundant urinary protein in healthy individuals and exhibits diverse functions including prevention of ascending urinary tract infections by binding type I-fimbriated Escherichia coli. Although uromodulin is targeted to the apical membrane of thick ascending limb (TAL) cells and secreted into the lumen, detectable levels are also found in venous blood. Uromodulin has been shown to interact with and activate specific components of the immune system, and thus, may act as a signalling molecule for renal tubular damage.

METHODS

In order to investigate the potential involvement of uromodulin in chronic kidney disease (CKD), we quantified uromodulin in paired urine and serum from 14 healthy volunteers and 77 CKD patients. Clinical parameters such as estimated GFR (eGFR), proteinuria and urinary N-acetyl-beta-D-glucosaminidase (NAG) were measured. Mean infiltration and atrophy score were assessed in patient biopsies. Additionally, tumour necrosis factor-alpha, interleukin-6 (IL-6), IL-8 and IL-1 beta were measured in serum samples.

RESULTS

eGFR correlated positively with urinary uromodulin and negatively with serum uromodulin. Patients with abnormally low urinary uromodulin showed a broader range of serum uromodulin. Patients with both very low urinary and serum uromodulin had the highest tubular atrophy scores. There was a positive correlation of serum uromodulin with all cytokines measured. Additionally, in in vitro experiments, uromodulin caused a dose-dependent increase in pro-inflammatory cytokine release from whole blood.

CONCLUSIONS

Our data suggest that TAL damage, or damage distal to the TAL, results in an elevated interstitial uromodulin, which stimulates an inflammatory response. Persistent chronic TAL damage reduces TAL cell numbers and attenuates urinary and serum uromodulin concentrations. The combined analysis of serum and urinary uromodulin provides new insights into the role of uromodulin in CKD and suggest that uromodulin may be an active player in CKD progression.

The human urinary proteome reveals high similarity between kidney aging and chronic kidney disease

Aging induces morphological changes of the kidney and reduces renal function. We analyzed the low molecular weight urinary proteome of 324 healthy individuals from 2-73 years of age to gain insight on human renal aging. We observed age-related modification of secretion of 325 out of over 5000 urinary peptides. The majority of these changes were associated with renal development before and during puberty, while 49 peptides were related to aging in adults. We therefore focussed the remainder of the study on these 49 peptides. The majority of these 49 peptides were also markers of chronic kidney disease, suggesting high similarity between aging and chronic kidney disease. Blinded evaluation of samples from healthy volunteers and diabetic nephropathy patients confirmed both the correlation of biomarkers with aging and with renal disease. Identification of a number of these aging-related peptides led us to hypothesize that reduced proteolytic activity is involved in human renal aging. Finally, among the 324 supposedly healthy individuals, some had urinary aging-related peptide excretion patterns typical of an individual significantly older than their actual age. In conclusion, these aging-related biomarkers may allow noninvasive detection of renal lesions in healthy persons and show high resemblance between human aging and chronic kidney disease. This similarity has to be taken into account when searching for biomarkers of renal disease.

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.

Urine profiling by SELDI-TOF/MS: monitoring of the critical steps in sample collection, handling and analysis

The topic of this study is the impact of several pre-analytical and analytical variables on proteomic profiling of human urine by surface enhanced laser desorption/ionization time of flight-mass spectrometry (SELDI-TOF-MS) in healthy subjects. Urine storage at room temperature caused a progressive degradation of proteins, which was prevented by the addition of protease inhibitors only up to 2 h from the collection. The timing of collection over the day had only a minor impact on protein profile, although influencing the intensity of peaks. Repeated freeze/thaw cycles (up to five) did not affect either the number or the intensity of the peaks. A comparison of the protein profile from eight different healthy individuals showed fairly consistent inter-subject similarities, along with between-subject differences, which were markedly dependent on the sex and the type of ProteinChip array used. The addition of a variety of denaturing agents improved the quality of the spectra with all the chips tested (CM10, Q10 and H50), but not with the copper-coated IMAC-30 chip. Finally, SPA matrix allowed to achieve a better performance of SELDI-TOF/MS spectrum, as compared with CHCA, regardless of the ProteinChip array used and even in the low m/z range (2500-10,000). In conclusion, we suggest that a careful choice of a number of pre-analytical and analytical conditions is required to accomplish and define a unifying protocol for the analysis of human urine by SELDI-TOF/MS, in physiological and in pathological states.

Impact of diabetic nephropathy and angiotensin II receptor blockade on urinary polypeptide patterns

BACKGROUND

New insights into the pathogenesis and treatment of diabetic renal disease may emerge from recent advances in proteomics using high-throughput mass spectrometry (MS) of urine.

METHODS

Using a combination of online capillary electrophoresis (CE) and MS we evaluated urinary polypeptide patterns in four groups of type 2 diabetic patients matched for age, gender, and diabetes duration, including 20 normoalbuminuric patients with and 20 without diabetic retinopathy, 20 microalbuminuric patients with diabetic retinopathy, and 18 macroalbuminuric patients with diabetic retinopathy. Furthermore, changes in urinary polypeptide patterns during treatment with the angiotensin II receptor blocker (ARB) candesartan were evaluated in the macroalbuminuric patients in a randomized double-blinded, cross-over trial where each patient received treatment with placebo, candesartan 8, 16, and 32 mg daily each for 2 months.

RESULTS

Overall, 4551 different polypeptides were found in the samples. Urinary polypeptide patterns were comparable in normo- (with and without diabetic retinopathy) and microalbuminuric patients, whereas distinct differences were found in macroalbuminuric patients. Differences in urinary polypeptide patterns between normo- and macroalbuminuric patients permitted the establishment of a "diabetic renal damage" pattern consisting of 113 polypeptides. Eleven of these polypeptides had been sequenced and identified. Candesartan treatment in macroalbuminuric patients significantly changed 15 of the 113 polypeptides in the diabetic renal damage pattern toward levels in normoalbuminuric patients. Change in the diabetic renal damage pattern was not candesartan dose-dependent but individual changes correlated with changes in urinary albumin excretion at each dose level.

CONCLUSION

CE-MS serves as a fast and sensitive tool for identification of biomarkers and urinary polypeptide patterns specific for macroalbuminuric type 2 diabetic patients and may be used to explore and monitor renoprotective effects of ARB.

Tamm-Horsfall protein in patients with kidney damage and diabetes

Tamm-Horsfall protein (THP) is a glycoprotein present abundantly in human urine. It is localized in the thick ascending limb of the loop of Henle (TAL) and the early distal convoluted tubule (DCT). The rate of urinary excretion of THP has been studied in various diabetic groups. It has been postulated that urinary THP may be a useful marker for renal damage. The aim of this study was to compare directly the immunogold localization of THP in diabetic and control kidney tissue specimens with or without kidney damage. Immunogold labeling was performed on archival tissue samples of 34 diabetic and 18 control human kidneys at the light microscope level. Slides were ranked as having a high, moderate or low degree of reaction. The majority of diabetic samples had a slightly lower degree of THP, while patients with known renal dysfunction had lowest THP. Previous studies have found a decreased excretion of urinary THP in diabetics. Our results show that decreased gold labeling is associated with known renal damage and may indicate damage to the thick ascending limb of the loop of Henle and the early distal convoluted tubule, irrespective of presence or absence of diabetes.

Biologic markers for the early detection of acute kidney injury

PURPOSE OF REVIEW

This review discusses the current status of several biomarkers as potential diagnostic tools in patients with acute kidney disease.

RECENT FINDINGS

Although the term "acute renal failure" has generally been used to describe acute kidney dysfunction that runs the spectrum from mild prerenal azotemia with no renal pathologic changes and no functional failure to severe oliguric renal dysfunction associated with tubular necrosis with failure of function, this spectrum is better described by the term "acute kidney injury." The mortality rate of hospitalized patients with severe acute kidney disease has not decreased significantly over the past 50 years despite advances in supportive care. The absence of sensitive and specific biomarkers for detecting injury early, grading the severity of the injury, and monitoring the response to therapy has impaired progress in the field and has had a very detrimental effect on the design and outcome of clinical trials in acute kidney disease. As a result of reliance on serum creatinine as a marker for injury and diagnosis, the institution of therapy is markedly delayed.

SUMMARY

The search for new biomarkers for acute kidney injury is evolving rapidly with advancement in modern technologies. With better biomarkers we will have the ability to detect injury earlier, identify subclinical injury, provide prognostic information on the course of renal impairment, identify the nephron segments most affected, provide a rationale for segmentation of patients for clinical studies, guide timing of therapy, assess response to therapy, and screen patients at risk for renal injury.

Uromodulin storage diseases: Clinical aspects and mechanisms

The recent discovery of mutations in the uromodulin gene ( UMOD ) in patients with medullary cystic kidney disease type 2 (MCKD2), familial juvenile hyperuricemic nephropathy (FJHN), and glomerulocystic kidney disease (GCKD) provides the opportunity for a revision of pathogenic aspects and puts forth the basis for a renewed classification. This review focuses on clinical, pathological, and cell biology advances in UMOD -related pathological states, including a review of the associated clinical conditions described to date in the literature. Overall, 31 UMOD mutations associated with MCKD2 and FJHN (205 patients) and 1 mutation associated with GCKD (3 patients) have been described, with a cluster at exons 4 and 5. Most are missense mutations causing a cysteine change in uromodulin sequence. No differences in clinical symptoms between carriers of cysteine versus polar residue changes have been observed; clinical phenotypes invariably are linked to classic MCKD2/FJHN. A common motif among all reports is that many overlapping symptoms between MCKD2 and FJHN are present, and a separation between these 2 entities seems unwarranted or redundant. Cell experiments with mutant variants indicated a delay in intracellular maturation and export dynamics, with consequent uromodulin storage within the endoplasmic reticulum (ER). Patchy uromodulin deposits in tubule cells were found by means of immunohistochemistry, and electron microscopy showed dense fibrillar material in the ER. Mass spectrometry showed only unmodified uromodulin in urine of patients with UMOD mutations. Lack of uromodulin function(s) is associated with impairments in tubular function, particularly the urine-concentrating process, determining water depletion and hyperuricemia. Intracellular uromodulin trapping within the ER probably has a major role in determining tubulointerstitial fibrosis and renal failure. We propose the definition of uromodulin storage diseases for conditions with proven UMOD mutations.

Urinary Excretion Rate of Tamm-Horsfall Protein Is Related to Salt Intake in Humans

BACKGROUND/AIMS

Increased salt intake and enhanced salt sensitivity are implicated in the pathogenesis of hypertension. The aim of the present study was to investigate whether the urinary excretion rate of Tamm-Horsfall protein (THP) is dependent on salt intake in healthy, genetically hypertension-prone individuals.

METHODS

Thirty unrelated subjects (13 men and 17 women, mean age 48.1 +/- 6.7 years) with at least one first-degree relative with primary hypertension were studied. After a baseline investigation, the study subjects were put on a low-salt diet (10 mmol of sodium and 70 mmol of potassium per day) for 1 week. During the second week, sodium chloride capsules (230 mmol/day) were added to the diet to achieve a high-salt intake of 240 mmol/day. Urine samples (24-hour and overnight collections) were collected before the baseline investigation and at the end of the high- and low-salt diet weeks. The salt sensitivity was calculated as the difference between the blood pressure during high salt intake and the blood pressure during low salt intake.

RESULTS

A low salt intake induced a decrease in the urinary excretion rate of THP during the night (11.7 microg/min) compared with baseline (19.5 microg/min; p < 0.05) and high salt intake (23.1 microg/min; p < 0.01). Furthermore, a greater response in blood pressure to a high salt intake, i.e. high salt sensitivity, was associated with increased excretion of THP in urine during the change to high salt intake (r = 0.38, p < 0.05).

CONCLUSION

We were able to confirm that urinary excretion of THP is dependent on sodium intake. Patients with a high salt sensitivity, i.e. an exaggerated blood pressure response to high salt intake, responded to the high salt intake with an even greater increase in the urinary excretion rate of THP. The mechanism underlying this response is still unknown, but it might indicate that distal nephron function in healthy, genetically hypertension-prone individuals is altered.

Effects of chronic renal disease on the transport of vitamin A in plasma and urine of dogs

OBJECTIVE

To determine plasma and urine concentrations of retinol, retinyl esters, retinol-binding protein (RBP), and Tamm-Horsfall protein (THP) in dogs with chronic renal disease (CRD).

ANIMALS

17 dogs with naturally developing CRD and 21 healthy control dogs.

PROCEDURE

A diagnosis of CRD was established on the basis of clinical signs, plasma concentrations of creatinine and urea, and results of urinalysis. Concentrations of retinol and retinyl esters were measured by use of reverse-phase high-performance liquid chromatography. Concentrations of RBP and THP were measured by use of sensitive ELISA systems.

RESULTS

Dogs with CRD had higher plasma concentrations of retinol, which were not paralleled by differences in plasma concentrations of RBP. Calculated ratio of urinary total vitamin A (sum of concentrations of retinol and retinyl esters to creatinine concentration) and ratio of the concentration of urinary retinyl esters to creatinine concentration did not differ between groups. However, we detected a significantly higher retinol-to-creatinine ratio in the urine of dogs with CRD, which was paralleled by a higher urinary RBP-to-creatinine ratio. Thus, in dogs with CRD, the estimated fractional clearance of total vitamin A, retinol, and RBP was increased. Furthermore, dogs with CRD had a reduced urinary THP-to-creatinine ratio.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of this study documented that CRD affects the concentrations of retinol in plasma and urine of dogs. Analysis of the data indicates that measurement of urinary RBP and urinary THP concentrations provides valuable information that can be helpful in follow-up monitoring of dogs with CRD.

Isolation of mouse THP gene promoter and demonstration of its kidney-specific activity in transgenic mice

Tamm-Horsfall protein (THP), the most abundant urinary protein synthesized by the kidney epithelial cells, is believed to play important and diverse roles in the urinary system, including renal water balance, immunosuppression, urinary stone formation, and inhibition of bacterial adhesion. In the present study, we describe the isolation of a 9.3-kb, 5'-region of the mouse THP gene and show the highly conserved nature of its proximal 589-bp, 5'-flanking sequence with that in rats, cattle, and humans. We also demonstrate using the transgenic mouse approach that a 3.0-kb, proximal 5'-flanking sequence is sufficient to drive the kidney-specific expression of a heterologous reporter gene. Within the kidney, transgene expression was confined to the renal tubules that endogenously expressed the THP protein, which suggests specific transgene activity in the thick ascending limb of the loop of Henle and early distal convoluted tubules. Our results establish the kidney- and nephron-segment-specific expression of the mouse THP gene. The availability of the mouse THP gene promoter that functions in vivo should facilitate additional studies of the molecular mechanisms of kidney-specific gene regulation and should provide new molecular tools for better understanding renal physiology and disease through nephron-specific gene targeting.

Tamm-Horsfall protein excretion to predict the onset of renal insufficiency

OBJECTIVE

Immunosuppressive therapy after liver transplantation may be a risk for kidney dysfunction. This work was designed to determine whether Tamm-Horsfall Protein (THP) could be considered as a marker for nephrotoxicity.

DESIGN AND METHODS

THP was determined by an ELISA method in serial 24-h urine from liver transplant patients. Fourteen patients suffered renal insufficiency (LTr(1)) and 20 showed no acute renal damage (LTr(2)) after liver transplantation.

RESULTS

No clear association could be seen between daily THP excretion and plasma creatinine levels by comparing serial samples collected at the same time. Nevertheless, significant differences were observed in pretransplant THP excretion between both groups of patients. The results (Median/Interquartile Range) were:

CONTROLS

113.2/84.9 to 146.8 mg/24 h (n = 30); LTr(1): 36.9/18.3 to 54.5 mg/24 h (p<<0.001 with respect to C and LTr(2)); LTr(2): 90.8/61.5 to 139.7 mg/24 h.

CONCLUSIONS

The higher pretransplant synthesis and/or secretion of THP seem to have a protective role on the kidney during and after liver transplantation.

Evaluation of urinary Tamm-Horsfall protein in post-menopausal diabetic women

Tamm-Horsfall protein (THP), a glycoprotein produced in the thick ascending limb (TAL) and the early distal convoluted tubule (DCT), is normally excreted in large amounts in urine. Urinary THP may be a useful marker for renal damage. The goal of this research project was to determine the THP excretion in control and diabetic post-menopausal women. Twenty-four hour urine samples were collected from 19 controls and 19 diabetic patients (11 non-insulin dependent diabetic mellitus (non-IDDM) patients, and 8 insulin dependent diabetic mellitus (IDDM) patients). Polyacrylamide gel electrophoresis (PAGE), Western blotting, and enzyme linked immunosorbent assay (ELISA) methods were used. It was determined that urinary THP concentrations were significantly decreased in patients with IDDM compared to patients with non-IDDM and controls. In conclusion, laboratory quantitation of urinary THP may be a useful indicator of cellular abnormalities such as reduced protein (THP) synthesis of the cells of the TAL and early DCT in some IDDM patients.