Bence Jones proteins bind to a common peptide segment of Tamm-Horsfall glycoprotein to promote heterotypic aggregation

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.

[Nephropathy associated with monoclonal immunoglobulins: From clonal expansion B to renal toxicity of pathological immunoglobulins]

Germinal center regulation pathways are often involved in lymphomagenesis and myelomagenesis. Most of the lymphomas (and multiple myeloma) derive from post-germinal center B-cells that have undergone somatic hypermutation and class switch recombination. Hence, B-cell clonal expansion can be responsible for the presence of a monoclonal component (immunoglobulin) of variable titer which, owing to physicochemical properties, can provoke pathologically defined entities of diseases. These diseases can affect any functional part of the kidney, by multiple mechanisms, either well known or not. The presence of renal deposition is influenced by germinal gene involved, immunoglobulin primary structure, post-translational modifications and microenvironmental interactions. The two ways immunoglobulin can cause kidney toxicity are (i) an excess of production (overcoming catabolism power by proximal tubule epithelial cells) with an excess of free light chains within the distal tubules and a subsequent risk of precipitation due to local physicochemical properties; (ii) by structural characteristics that predispose immunoglobulin to a renal disease (whatever their titer). The purpose of this manuscript is to review literature concerning the pathophysiology of renal toxicities of clonal immunoglobulin, from molecular B-cell expansion mechanisms to immunoglobulin renal toxicity.

Light Chain Cast Nephropathy in Multiple Myeloma: Prevalence, Impact and Management Challenges

“Cast nephropathy” (CN) is a pathological feature of myeloma kidney, also seen to a lesser extent in the context of severe nephrotic syndrome from non-haematological diseases. The name relates to obstruction of distal tubules by “casts” of luminal proteins concentrated by intensive water reabsorption resulting from dehydration or high-dose diuretics. Filtered proteins form complexes with endogenous tubular Tamm-Horsfall glycoprotein. The resulting gel further slows or stops luminal flow upon complete obstruction of distal convoluted tubules and collecting ducts. Thus, a tubular obstructive form of acute kidney injury (AKI) is a common consequence of CN. The pathogenesis of CN will be reviewed in light of recent advances in the understanding of monoclonal disorders of B lymphocytes, leading to the release of immunoglobulin components (free light chains, FLC) into the bloodstream and their filtration across the glomerular basement membrane. Treatment aiming at reduction of the circulating burden of FLC may help recovery of renal function in a fraction of these patients, besides filling the void between the onset of AKI, histopathological diagnosis, and full response to pharmacologic treatment.

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Extratubular Polymerized Uromodulin Induces Leukocyte Recruitment and Inflammation In Vivo

Uromodulin (UMOD) is produced and secreted by tubular epithelial cells. Secreted UMOD polymerizes (pUMOD) in the tubular lumen, where it regulates salt transport and protects the kidney from bacteria and stone formation. Under various pathological conditions, pUMOD accumulates within the tubular lumen and reaches extratubular sites where it may interact with renal interstitial cells. Here, we investigated the potential of extratubular pUMOD to act as a damage associated molecular pattern (DAMP) molecule thereby creating local inflammation. We found that intrascrotal and intraperitoneal injection of pUMOD induced leukocyte recruitment in vivo and led to TNF-α secretion by F4/80 positive macrophages. Additionally, pUMOD directly affected vascular permeability and increased neutrophil extravasation independent of macrophage-released TNF-α. Interestingly, pUMOD displayed no chemotactic properties on neutrophils, did not directly activate β2 integrins and did not upregulate adhesion molecules on endothelial cells. In obstructed neonatal murine kidneys, we observed extratubular UMOD accumulation in the renal interstitium with tubular atrophy and leukocyte infiltrates. Finally, we found extratubular UMOD deposits associated with peritubular leukocyte infiltration in kidneys from patients with inflammatory kidney diseases. Taken together, we identified extratubular pUMOD as a strong inducer of leukocyte recruitment, underlining its critical role in mounting an inflammatory response in various kidneys pathologies.

Myeloma light chain cast nephropathy, a review

Multiple Myeloma is a plasma cell proliferative disorder that commonly involves the kidney. Renal impairment is a serious complication during the course of the disease that is associated with increased morbidity and mortality. Light chain cast nephropathy is the predominant pattern of renal injury in Multiple Myeloma. This review article focuses on the pathophysiology and diagnostic approach of myeloma cast nephropathy. The management of precipitating factors as well as anti-plasma cell treatment modalities in the context of renal impairment are also discussed.

Uromodulin: from physiology to rare and complex kidney disorders

Uromodulin (also known as Tamm-Horsfall protein) is exclusively produced in the kidney and is the most abundant protein in normal urine. The function of uromodulin remains elusive, but the available data suggest that this protein might regulate salt transport, protect against urinary tract infection and kidney stones, and have roles in kidney injury and innate immunity. Interest in uromodulin was boosted by genetic studies that reported involvement of the UMOD gene, which encodes uromodulin, in a spectrum of rare and common kidney diseases. Rare mutations in UMOD cause autosomal dominant tubulointerstitial kidney disease (ADTKD), which leads to chronic kidney disease (CKD). Moreover, genome-wide association studies have identified common variants in UMOD that are strongly associated with risk of CKD and also with hypertension and kidney stones in the general population. These findings have opened up a new field of kidney research. In this Review we summarize biochemical, physiological, genetic and pathological insights into the roles of uromodulin; the mechanisms by which UMOD mutations cause ADTKD, and the association of common UMOD variants with complex disorders.

Free immunoglobulin light chain (FLC) promotes murine colitis and colitis-associated colon carcinogenesis by activating the inflammasome

Numerous studies have demonstrated that free Ig light chain (FLC), a novel inflammation mediator, participates in many inflammatory diseases by activating mast cells and extending the survival of neutrophils. However, it remains unclear whether FLC is involved in colitis and colitis-associated colon carcinogenesis (CAC). In this study, we found a significant increase in FLC in murine models of DSS (Dextran Sulfate Sodium Salt)-induced colitis and CAC compared to controls. Peptide F991, a functional blocker of FLC, significantly attenuated colitis progression, which included abrogating the development of diarrhea and tumor burden, elevating survival rate, greatly reducing the infiltration of inflammatory cells (such as ROS⁺ active neutrophils), especially reducing tumorigenesis in CAC. Furthermore, we demonstrated that F991 inhibited the activation of the inflammasome by reducing the expression of cleaved caspase-1 and the maturation of IL-1β and IL-18. Altogether, our findings demonstrate that FLC can promote the pathogenesis of colitis and CAC and may be used as novel biomarker for the diagnosis of inflammatory bowel disease. Additionally, F991 may become a potential therapeutic option for colitis or colorectal cancer.

Calorimetric markers of Bence Jones and nonsecretory multiple myeloma serum proteome

The present work provides a thermodynamic description of blood serum from patients diagnosed with Bence Jones myeloma (BJMM) and nonsecretory myeloma (NSMM) by means of differential scanning calorimetry (DSC), serum protein electrophoresis, and free light chain assay. Specific alterations in the thermodynamic behavior of both BJMM and NSMM proteome have been revealed. On the basis of the transition temperature of the main transition in the calorimetric profiles and the shape similarity criterion, we defined BJMM and NSMM sets/subsets of thermograms with very similar thermodynamic features. We show that some of the BJMM and NSMM subsets correlate with previously defined secretory myeloma subsets (Todinova et al. Anal. Chem. 2011, 83, 7992). The established analogies strongly suggest that common molecular markers contribute to the calorimetric profiles of the different, secretory and nonsecretory, myeloma types; our data show robust evidence that these are ligands stabilizing the major serum proteins. We demonstrate that the DSC approach might be highly beneficial, especially for NSMM patients, since the characteristic modifications in the DSC profiles might serve as calorimetric markers when no monoclonal proteins can be detected in the bloodstream and the diagnosis heavily relies on invasive methods.

Myeloma-related kidney disease

Multiple myeloma is a malignant plasma cell disorder characterized by the overproduction of monoclonal proteins. The kidney is 1 of the major target organs of multiple myeloma. Most often, this is the result of the monoclonal proteins, which can injure the kidney via several mechanisms. In some cases, direct invasion by myeloma cells and/or bone marrow cells can also result in kidney injury. A kidney biopsy can help distinguish the various myeloma-related kidney diseases and aid in the treatment plan.

Novel renal replacement strategies for the elimination of serum free light chains in patients with kappa light chain nephropathy

Multiple myeloma (MM) is a malignancy with excessive production of monoclonal proteins. At disease presentation 30% of MM patients have significant renal impairment which may progress to renal failure requiring dialysis. Besides chemotherapy extracorporeal elimination procedures such as plasma exchange have been applied as adjuvant strategies to eliminate free light chains from circulating blood, however the efficacy was poor with older techniques. We report about a highly efficient method to eliminate serum free light chain (sFLC) using a newly designed protein leaking membrane in patients suffering from sFLC induced acute renal failure. The protein leaking membrane (HCO 1100) is characterized by increased pore size facilitating elimination of middle molecules such as sFLC kappa (22.5 kD). The HCO 1100 membrane was applied in a hemodialysis and hemodiafiltration mode and compared to standard procedures (high flux hemodialysis, hemodiafiltration and plasma exchange). Hemodiafiltration with the protein leaking membrane HCO 1100 was superior to all other extracorporeal replacement strategies in eliminating sFLC-kappa from circulating blood. A median blood reduction rate of 40.8% (range 13.9% - 66.4%) was achieved during hemodiafiltration. The corresponding peak clearance rate was 25 ml/min. Importantly, the poorest elimination rate was achieved by plasma exchange followed by standard high flux hemodialysis. Extracorporeal elimination strategies with the protein leaking membrane HCO 1100 may be a promising adjuvant treatment strategy for patients with sFLC nephropathy requiring dialysis. Hemodiafiltration and to lesser extend also hemodialysis with the HCO 1100 hemofilter are able to eliminate substantial amounts of sFLC kappa in MM patients.

Mechanisms of light chain injury along the tubular nephron

The tubular nephron is responsible for reabsorption and catabolism of filtered low molecular weight proteins that include Ig free light chains. In the setting of a plasma cell dyscrasia, significant amounts of free light chains, now monoclonal proteins, present to the tubular nephron for disposal. The result may be clinical renal dysfunction in the form of AKI, progressive CKD, and end-stage kidney disease. Here, I review the mechanisms involved in these processes that result in tubular injury, including proximal tubulopathy and cast nephropathy.

The pathogenesis of acute kidney impairment in patients with multiple myeloma

Acute kidney injury in myeloma, a serious complication associated with poor prognosis, is generally mediated by the toxic and inflammatory effects of monoclonal free light chains (FLCs) on kidney proximal tubule cells and by the formation of intratubular casts through interaction with Tamm-Horsfall proteins. Production of excessive quantities of FLCs is seen in most cases of FLC-associated kidney injury, although a direct relation between quantity and nephrotoxicity does not exist, indicating variable toxicity among light chain species. Toxic effects of FLCs include inhibition of transport functions, Fanconi syndrome, generation of reactive oxygen species, cytoskeletal abnormalities, and apoptosis and necrosis in proximal tubule cells. Excessive endocytosis of FLCs in proximal tubule cells also induces cell stress responses that result in stimulation of inflammatory pathways through activation of nuclear transcription factors κB and mitogen-activated protein kinases, induction of proinflammatory cytokines, and epithelial to mesenchymal transition. The mechanisms of nephrotoxicity of FLC described here explain the basis of acute kidney injury seen in patients with multiple myeloma and provide the rationale for eliminating or reducing the FLC burden in myeloma patients with renal involvement. The inflammatory pathways that are activated as a result of FLC toxicity also show clearly how severe chronic tubulointerstitial nephritis can occur in patients with myeloma kidney and identify several attractive opportunities for novel therapeutic interventions.

Predictors of positive immunofixation testing in patients with acute kidney injury

INTRODUCTION

Acute kidney injury may be the presenting manifestation of multiple myeloma, although optimal use of immunofixation testing in this setting is incompletely defined. The authors attempted to determine clinical and laboratory predictors of positive immunofixation testing in patients with acute kidney injury.

PATIENTS AND METHODS

The authors did a retrospective study of hospitalized patients with acute kidney injury who had immunofixation studies done. Various clinical and laboratory variables that may be predictive of the presence of multiple myeloma were evaluated and correlations with immunofixation test results determined.

RESULTS

One hundred twenty-eight patients were studied. Thirteen had a monoclonal paraprotein detected by immunofixation testing (positive result). Patients with positive testing had higher total, ionized and corrected calcium levels, although the median total calcium in immunofixation-positive patients was normal at 9.7 mg/dL. Patients with positive testing also had lower hemoglobin and platelet counts. An anion gap of <7 mmol/L and total protein-albumin gap >4 g/dL were also associated with positive results.

CONCLUSIONS

In patients with acute kidney injury, relatively higher total, ionized and corrected calcium levels and lower hemoglobin and platelet counts may predict the presence of a monoclonal paraprotein. An anion gap of <7 mmol/L and total protein-albumin gap >4 g/dL may also be predictors. The metabolic consequences of acute kidney injury may attenuate some of these abnormalities as well. These findings may help guide optimal use of immunofixation testing and hence help potentially identify patients who may have multiple myeloma.

Mechanism and prevention of acute kidney injury from cast nephropathy in a rodent model

A common renal complication of multiple myeloma is "myeloma kidney," a condition also known as cast nephropathy. The renal lesions (casts) are directly related to the production of monoclonal immunoglobulin free light chains (FLCs), which coprecipitate with Tamm-Horsfall glycoprotein (THP) in the lumen of the distal nephron, obstructing tubular fluid flow. Here, we report that analysis of the binding interaction between FLCs and THP demonstrates that the secondary structure and key amino acid residues on the complementarity-determining region 3 (CDR3) of FLCs are critically important determinants of the molecular interaction with THP. The findings permitted development of a cyclized competitor peptide that demonstrated strong inhibitory capability in the binding of FLCs to THP in vitro. When used in a rodent model of cast nephropathy, this cyclized peptide construct served as an effective inhibitor of intraluminal cast formation and prevented the functional manifestations of acute kidney injury in vivo. These experiments provide proof of concept that intraluminal cast formation is integrally involved in the pathogenesis of acute kidney injury from cast nephropathy. Further, the data support a clinically relevant approach to the management of renal failure in the setting of multiple myeloma.

Uromodulin in kidney injury: an instigator, bystander, or protector?

Uromodulin, also known as Tamm-Horsfall protein, is a glycoprotein expressed exclusively by renal tubular cells lining the thick ascending limb of the loop of Henle. Although the physiologic functions of this protein remain elusive, significant progress has been made during the last decade that highlights the importance of uromodulin in the pathophysiology of various diseases, such as medullary cystic kidney disease, urinary tract infections, and nephrolithiasis. Meanwhile, there is renewed interest in the role of uromodulin in kidney injury, both acute and chronic. In this article, we review the existing evidence that supports a role for uromodulin in acute kidney injury, chronic kidney disease, and renal inflammation. Contrary to the conventional view of uromodulin as an instigator in kidney injury, new data from uromodulin knockout mice show a protective role for this protein in acute kidney injury, possibly through downregulating interstitial inflammation. In chronic kidney disease, uromodulin excretion, when adjusted for kidney function, is increased; the significance of this is unclear. Although it has been suggested that uromodulin exacerbates progressive kidney injury, we propose that the elevation in uromodulin secretion is instead reactive to injury and reflects an increase of uromodulin in the renal parenchyma, where it slows the injury process.

The pathogenesis and diagnosis of acute kidney injury in multiple myeloma

Renal failure remains a principal cause of morbidity for patients with multiple myeloma. Once reversible factors such as hypercalcemia have been corrected, the most common cause of severe renal failure in these patients is a tubulointerstitial pathology that results from the very high circulating concentrations of monoclonal immunoglobulin free light chains. These endogenous proteins can result in isolated proximal tubule cell cytotoxicity, tubulointerstitial nephritis and cast nephropathy (myeloma kidney). Less frequently, high levels of free light chains can lead to immunoglobulin light chain amyloidosis and light chain deposition disease, although these conditions are usually associated with insidious progression of renal failure rather than acute kidney injury. Unless there is rapid intervention, progressive and irreversible damage occurs, particularly interstitial fibrosis and tubular atrophy. Despite advances in our understanding of the pathogenesis of these processes there has been a gap in translating these achievements into improved patient outcomes. The International Kidney and Monoclonal Gammopathy Research Group was formed to address this need. In this Review, we discuss the mechanisms of disease and diagnostic approaches to patients with acute kidney injury complicating multiple myeloma.

Recent advances in the pathogenesis and management of cast nephropathy (myeloma kidney)

Multiple myeloma is an incurable plasma cell malignancy that is often accompanied by renal failure; there are a number of potential causes of this, of which cast nephropathy is the most important. Renal failure is highly significant in myeloma, as patient survival can be stratified by the severity of the renal impairment. Consequently, there is an ongoing focus on the pathological basis of cast nephropathy and the optimal treatment regimens in this setting, including effective chemotherapy regimens to reduce light chain production and emerging extracorporeal techniques to remove circulating light chains. This paper bridges recent advances in the pathogenesis and management of cast nephropathy in multiple myeloma.

Online high-efficiency haemodiafiltration achieves higher serum free light chain removal than high-flux haemodialysis in multiple myeloma patients: preliminary quantitative study

BACKGROUND

Fast reduction of serum free light chain (FLC) levels correlate with renal recovery in cast nephropathy. Because convection has the capacity to remove proteins of higher molecular weights, we hypothesized that haemodiafiltration (HDF) would be superior to haemodialysis (HD) for FLC clearance.

METHODS

We retrospectively identified all renal replacement therapy (RRT) sessions performed in multiple myeloma patients with pre- and post-treatment FLC measurements during a 2-year period. Using kinetic modelling, we calculated reduction percentages corrected for net ultrafiltration, effective clearances, net mass removal and Kt/V for both kappa (κ) and lambda (λ) serum FLC.

RESULTS

We analysed 27 (10 HD and 17 HDF) RRT sessions realized in a total of six subjects. HDF resulted in higher FLC removal rates when compared to HD. Moreover, high-efficiency (i.e. substitution volume > 15 L/session) HDF demonstrated median efficient FLC clearances roughly twice superior to high-flux HD for both κ (59.0 versus 33.8 mL/min, respectively; P < 0.01) and λ (40.5 versus 19.7 mL/min, respectively; P = 0.02) FLC. In post-dilution HDF treatments, corrected FLC reduction percentages positively correlated with substitution volumes. Total plasma proteins increased during RRT in the HDF group.

CONCLUSIONS

This preliminary quantitative study demonstrates the superiority of high-efficiency HDF over high-flux HD for serum FLC removal in multiple myeloma patients on RRT. No negative impact on total plasma proteins was noted.

A phase I clinical trial of the histone deacetylase inhibitor belinostat in patients with advanced hematological neoplasia

PURPOSE

To determine the safety, dose-limiting toxicity and maximum tolerated dose (MTD) of the novel hydroxamate histone deacetylase inhibitor belinostat (PXD101) in patients with advanced hematological neoplasms.

PATIENTS AND METHODS

Sequential dose-escalating cohorts of three to six patients with hematological malignancies received belinostat administered as a 30-min i.v. infusion on days 1-5 of a 21-d cycle. Experience from a parallel dose-finding study in patients with solid tumors influenced the selection of the final dose.

RESULTS

Sixteen patients received belinostat at one of three dose levels: 600 mg/m(2)/d (three patients), 900 mg/m(2)/d (three patients) and 1000 mg/m(2)/d (10 patients), the dose determined to be the MTD in a phase I solid tumor study [Steele et al. (2008) Clin Cancer Res, 14, 804-10]. The most common treatment-related adverse events (all grades) were nausea (50%), vomiting (31%), fatigue (31%) and flushing (31%). No grade 3 or 4 hematological toxicity compared with baseline occurred except one case of grade 3 lymphopenia. There were two related grade 4 adverse events of renal failure observed. Both events occurred in patients with multiple myeloma and had similar characteristics, i.e. an acute episode of decrease in renal function (pre-existing nephropathy in one patient), with a metabolic profile and decrease in tumor burden consistent with tumor lysis syndrome. No other related grade 4 events were noted. The only related grade 3 events noticed in more than one patient were fatigue and neurological symptoms (one patient had status epilepticus in association with uremia and one patient had paresthesia), all other related grade 3 events occurred in single patients. No cardiac events were noted. No complete or partial remissions were noted in these heavily pre-treated (median of four prior regimens) patients. However, five patients, including two patients with diffuse large-cell lymphoma [including one patient with transformed chronic myelocytic leukaemia (CLL)], two patients with CLL and one patient with multiple myeloma, achieved disease stabilization in of two to nine treatment cycles.

CONCLUSIONS

Intravenous belinostat at 600, 900 and 1000 mg/m(2)/d is well tolerated by patients with hematological malignancies. The study was carried out in parallel to a similar dose-finding study in patients with solid tumors, in which the MTD was determined to be 1000 mg/m(2)/d days 1-5 in a 21-d cycle. This dose can also be recommended for phase II studies in patients with hematological neoplasms.

Tamm-Horsfall protein protects the kidney from ischemic injury by decreasing inflammation and altering TLR4 expression

Tamm-Horsfall protein (THP) is a glycoprotein with unclear functions expressed exclusively in thick ascending limbs (TAL) of the kidney. Its role in ischemic acute kidney injury is uncertain, with previous data suggesting a possible negative effect by enhancing cast formation and promoting inflammation. Using a recently characterized THP knockout mouse (THP-/-), we investigated the role of THP in renal ischemia-reperfusion injury (IRI). In wild-type mice (THP+/+), THP expression was increased by injury. THP-/- mice developed more functional and histological renal damage after IRI compared with THP+/+. THP-/- kidneys showed more inflammation and tubular necrosis. Cast formation correlated with the severity of injury and was independent of THP presence. THP absence was associated with a more necrotic, rather than apoptotic, phenotype of cell death. The outer medulla was predominantly affected, where significant interstitial neutrophil infiltration was detected in proximity to injured S3 proximal tubular segments and TAL. This coincided with an enhanced expression of the innate immunity receptor Toll-like receptor 4 (TLR4) in S3 segments of THP-/- compared with THP+/+ mice. Specifically, a basolateral S3 expression of TLR4 was more evident in THP-/- kidneys compared with a more apical distribution in THP+/+. Such basolateral location for TLR4 allows a greater interaction with proinflammatory ligands present in the interstitium during ischemia. In conclusion, we are showing a completely novel role for a very old protein in the setting of renal injury. Our data suggest that THP stabilizes the outer medulla in the face of injury by decreasing inflammation, possibly through an effect on TLR4.

Deposition-associated diseases related with a monoclonal compound

Up to 3% of adults over 50 years of age show a monoclonal peak values in blood or urine. Findings and prognosis will be distinct in view of the nature of this factor. In B-cell neoplasias (multiple myeloma, Waldeström macroglobulinaemia, chronic myeloid leukaemia and non-Hodgkin lymphoma) the clinical pattern is dominated by the systemic effects produced by the expansion of the malign clone; the monoclonal protein may result in hyperviscosity syndrome or renal damage. On the other hand, there are other less frequent processes called diseases associated to monoclonal components, where the main clinical manifestations and prognosis depend of the biological effects of the monoclonal protein. With reference to this last group, which is the objective of this revision, no bone lesions, anaemia or a greater tendency to infections usually occur when compared with the first group. Even so, there are some cases of interposition between both groups: for instance, type IgM immunoglobulin present in Waldeström macroglobulinaemia may have cold agglutinin activity, and in the case of multiple myeloma, the clone may secrete amyloidogenic light chains.

Does Tamm–Horsfall protein–uric acid binding play a significant role in urate homeostasis?

BACKGROUND

Mutations in Tamm-Horsfall protein (THP), also known as uromodulin, lead to a group of diseases known as the uromodulin storage disorders. Clinically, these diseases present with tubulo-interstitial damage, progressive renal dysfunction, hyperuricaemia, and gout. However, it remains unclear how a mutation in THP, a protein produced in the thick ascending limb, can cause hyperuricaemia when most of the uric acid transport is believed to occur in the proximal tubule. However, one study in humans suggests that uric acid could also be secreted in the distal tubule. Thus, an attractive hypothesis could be that THP would bind to uric acid in the distal tubule, and decrease its subsequent reabsorption in the distal nephron.

METHODS

We screened for uric acid binding to THP using four independent binding assays.

RESULTS

There was no evidence that uric acid could bind to THP.

CONCLUSION

THP-uric acid binding does not seem to play a significant role in the regulation of urate homeostasis.

Light-chain-mediated acute tubular interstitial nephritis: a poorly recognized pattern of renal disease in patients with plasma cell dyscrasia

CONTEXT

Acute renal failure may be the first clinical presentation in patients with plasma cell dyscrasia. Recognition of the unusual interstitial inflammatory lesion associated with monoclonal light chains and renal failure described herein is important to guide clinicians in requesting appropriate tests to confirm plasma cell dyscrasia and providing adequate treatment.

OBJECTIVE

To describe an unusual pattern of tubular interstitial nephritis in patients with underlying plasma cell dyscrasia characterized by an interstitial inflammatory reaction associated with deposition of light chains along tubular basement membranes.

DESIGN

Eight cases of light-chain-mediated acute tubular interstitial nephritis were identified from the archives of 4296 kidney biopsy specimens. In all cases, routine light microscopic examination, direct immunofluorescence, and electron microscopic examination were performed. Ultrastructural immunogold labeling was performed in specimens with inconclusive findings and in specimens from patients with no clinical history of plasma cell dyscrasia.

RESULTS

All patients presented with acute renal failure. Light microscopy revealed acute tubular interstitial nephritis. In some of the cases, direct immunofluorescence and electron microscopy failed to show definitive evidence of light-chain deposition along tubular basement membranes. Ultrastructural immunogold labeling aided the demonstration of monotypical light chains along some tubular basement membranes. No light chains were present in other renal compartments.

CONCLUSIONS

Accumulation of light chains along tubular basement membranes may induce an interstitial process that mimics acute tubular interstitial nephritis. Recognition of this unusual pattern of renal disease in patients with plasma cell dyscrasia requires ancillary diagnostic techniques.

Tamm-Horsfall protein: a multilayered defence molecule against urinary tract infection

Urinary tract infection (UTI) is the most common nonepidemic bacterial infection in humans, representing a constant danger for the host. Both innate and adaptive components of the immune system as well as stromal cells including bladder epithelium are involved in the prevention and clearance of UTI. However, the particular properties of the urogenital tract, which does not comprise typical physical barriers like a mucus or ciliated epithelium, necessitate soluble mediators with potent immunomodulatory capabilities. One candidate molecule capable of both mediating direct antimicrobial activity and alerting immune cells is the evolutionary conserved Tamm-Horsfall protein (THP). Tamm-Horsfall protein is exclusively produced by the kidney in the distal loop of Henle; however, its definite physiological function remains elusive. Mounting evidence indicates that beyond a mere direct antimicrobial activity, THP exerts potent immunoregulatory activity. Furthermore, the genetic ablation of the THP gene leads to severe infection and lethal pyelonephritis in an experimental model of UTI. Recent data are provided demonstrating that THP links the innate immune response with specific THP-directed cell-mediated immunity. In light of these novel findings we discuss the particular role of THP as a specialized defence molecule. We propose an integrated model of protective mechanisms against UTI where THP acts by two principle nonmutually exclusive mechanisms involving the capture of potentially dangerous microbes and the ability of this peculiar glycoprotein to induce robust protective immune responses against uropathogenic bacteria.

Tamm-Horsfall glycoprotein links innate immune cell activation with adaptive immunity via a Toll-like receptor-4-dependent mechanism

Tamm-Horsfall glycoprotein (THP) is expressed exclusively in the kidney and constitutes the most abundant protein in mammalian urine. A critical role for THP in antibacterial host defense and inflammatory disorders of the urogenital tract has been suggested. We demonstrate that THP activates myeloid DCs via Toll-like receptor-4 (TLR4) to acquire a fully mature DC phenotype. THP triggers typical TLR signaling, culminating in activation of NF-kappaB. Bone marrow-derived macrophages from TLR4- and MyD88-deficient mice were nonresponsive to THP in contrast to those from TLR2- and TLR9-deficient mice. In vivo THP-driven TNF-alpha production was evident in WT but not in Tlr4-/- mice. Importantly, generation of THP-specific Abs consistently detectable in urinary tract inflammation was completely blunted in Tlr4-/- mice. These data show that THP is a regulatory factor of innate and adaptive immunity and therefore could have significant impact on host immunity in the urinary tract.

Management of paraproteinemic renal disease

PURPOSE OF REVIEW

Paraproteinemic renal diseases comprise a group of renal disorders that are difficult to manage, in part because of subtleties in the clinical presentation and confusion regarding diagnosis and appropriate therapy. Often, nephrologists make the diagnosis of the underlying plasma cell dyscrasia following renal biopsy. This review seeks to provide a greater understanding of the mechanism of disease and recent approaches to the management of patients who have AL-amyloidosis, monoclonal light-chain and light and heavy-chain deposition disease [termed ML(H)CDD], and cast nephropathy. All three renal lesions are caused by deposition of immunoglobulin light chains. This review seeks to provide a greater understanding of the mechanism of disease and recent approaches to the management of these patients.

RECENT FINDINGS

The immunoglobulin light chain takes the center stage in the pathogenesis of AL-amyloidosis, ML(H)CDD and cast nephropathy. Modifications in the variable domain are responsible for the affinity of the light chain for a given segment of the nephron and the subsequent toxic manifestations. Therapy aimed at eradicating the offending clone of plasma cells that secrete the monoclonal light chain should be beneficial, but this hypothesis lacks confirmation. Four nonrandomized studies have now demonstrated clinical benefit, including return of renal function, of high-dose chemotherapy with autologous stem cell transplantation (HDT/SCT) in the treatment of patients who have AL-amyloidosis or ML(H)CDD.

SUMMARY

While randomized trials are lacking, the data support the clinical efficacy of more aggressive treatments designed to reduce the plasma cell clone responsible for these renal disorders.

Tamm-Horsfall glycoprotein: biology and clinical relevance

Tamm-Horsfall glycoprotein (THP) is the most abundant urinary protein in mammals. Urinary excretion occurs by proteolytic cleavage of the large ectodomain of the glycosyl phosphatidylinositol-anchored counterpart exposed at the luminal cell surface of the thick ascending limb of Henle's loop. We describe the physical-chemical structure of human THP and its biosynthesis and interaction with other proteins and leukocytes. The clinical relevance of THP reported here includes: (1) involvement in the pathogenesis of cast nephropathy, urolithiasis, and tubulointerstitial nephritis; (2) abnormalities in urinary excretion in renal diseases; and (3) the recent finding that familial juvenile hyperuricemic nephropathy and autosomal dominant medullary cystic kidney disease 2 arise from mutations of the THP gene. We critically examine the literature on the physiological role and mechanism(s) that promote urinary excretion of THP. Some lines of research deal with the in vitro immunoregulatory activity of THP, termed uromodulin when isolated from urine of pregnant women. However, an immunoregulatory function in vivo has not yet been established. In the most recent literature, there is renewed interest in the capacity of urinary THP to compete efficiently with urothelial cell receptors, such as uroplakins, in adhering to type 1 fimbriated Escherichia coli. This property supports the notion that abundant THP excretion in urine is promoted in the host by selective pressure to obtain an efficient defense against urinary tract infections caused by uropathogenic bacteria.

Analysis of an expanded width of albumin fraction by cellulose acetate membrane electrophoresis in IgA nephropathy urine before treatment

Cellulose acetate membrane electrophoresis with colloidal silver stain re-vealed that the width of the albumin fraction in IgA nephropathy (IgAN) urine before treatment was significantly expanded. This phenomenon was not shown in IgAN urine after treatment or in non-IgAN urine. There was a reverse correlation between the width of the albumin fraction and the albumin con-centration in IgAN urine. By immuno-fixation, Tamm-Horsfall protein (THP) was located in the same position as the albumin band in IgAN urine before treatment; however, in the urine of a healthy subject it was located in the same position as alpha(1)-globulin. By ELISA, the THP-albumin complex concentration in IgAN urine before treatment was significantly higher than in the other two diseases. The width of the albumin fraction and the sodium ion concentra-tion of the urine were significantly correlated. The THP/albumin ratio in IgAN urine before treatment was significantly higher than in the other two groups. This suggests that the characteristic expanded width of albumin found by immunofixation indicates a THP-albumin complex, and that the sodium concentration of urine is involved in the formation of this complex.

Urinary proteins and renal dysfunction in patients with multiple myeloma

Besides bone pain, pathologic fractures, anaemia, and recurrent infectious diseases, renal failure is one of the most serious complications in multiple myeloma patients. Its incidence is generally underestimated because of the low reliability of the parameters routinely used for the evaluation of renal dysfunction. Other laboratory tests in the literature are reported to be more suitable to better define the extension of the renal impairment, namely urinary proteins or creatinine clearance. We here report on the clinical implication of urinary parameters in defining the renal function in myeloma patients.

Mapping the binding domain of immunoglobulin light chains for Tamm-Horsfall protein

Cast nephropathy, or myeloma kidney, is a potentially reversible cause of chronic renal failure. In this condition, filtered light chains bind to a common site on Tamm-Horsfall protein (THP), which is produced by cells of the thick ascending limb of the loop of HENLE: Subsequent aggregation of these proteins produces casts that obstruct tubule fluid flow and results in renal failure. In the present study, we used the yeast two-hybrid system to determine the site of interaction of light chains with THP. The third complementarity-determining region (CDR3) of both kappa and lambda light chains interacted with THP. These findings were confirmed in a series of competition studies using a synthetic peptide that corresponded to the CDR3 region and purified THP and light chains. Variations in the CDR3 sequence of the light chain affected binding. Thus, the current studies increase our understanding of the process of cast formation and provide an opportunity to develop strategies that may inhibit this interaction and prevent the clinical manifestations of myeloma kidney.

Binding of nascent collagen by amyloidogenic light chains and amyloid fibrillogenesis in monolayers of human fibrocytes

Light (L) chain dimers expressed by multiple myeloma cells and collected as Bence-Jones proteins from the urine of human subjects were tested for their ability to form deposits in fibroblast monolayer cell cultures. Bence-Jones proteins from subjects with primary amyloidosis associated with L chains were shown to form fibrillar deposits by the in vitro assay introduced in this report. Filaments interspersed with nascent collagen could be detected after only 48 h. Deposition of L chains continued over a period of 72 h culminating in the appearance of dense fibrils with widths of 80-100 A and a variety of lengths. Formation of amyloid-like fibrils was accompanied by interference with the maturation of the collagen produced by the fibroblast cells. Fibrils composed of the Mcg lambda-type L chain were deposited between collagen fibers, thus expanding them laterally and leading to their partial disintegration. Mature collagen was completely missing from fibroblast monolayers exposed to the Sea lambda chain and the Jen kappa chain. Collagen with the characteristic striped pattern matured normally in control samples, such as those not dosed with amyloid precursors or those treated with a non-amyloidogenic Bence-Jones protein (e.g., the Hud lambda chain dimer). By immunochemical techniques using fluorescein- and gold-labeled anti-L chain antibodies, amyloidogenic L chains were shown to decorate the strands of nascent collagen. This observation suggests that amyloidogenic L chains are concentrated in the extracellular matrix by monovalent antigen-antibody type reactions. The capacity of the Mcg L chain dimer to bind collagen-derived sequences was tested by soaking crystals with a collagenase substrate, PZ-Pro-Leu-Gly-Pro-D-Arg. Difference Fourier analysis at 2.7 A resolution indicated that the PZ-peptide is a site-filling ligand. It could not be removed from the active site by perfusion of the crystal with ammonium sulfate crystallizing media. Similar experiments with the collagen-derived peptide (Pro-Pro-Gly)(5) showed substantial hysteresis effects extending from one end of the Mcg dimer to the other. After the ligand was withdrawn, the active site of the Mcg dimer could no longer bind the PZ-peptide. However, if the active site was first blocked by the PZ-peptide and subsequently exposed to the (Pro-Pro-Gly)(5) peptide, the difference Fourier map was indistinguishable from that obtained with the PZ-peptide alone. We concluded that amyloidogenic L chains such as the Mcg dimer could be concentrated in the perivascular space by binding to normal tissue constituents. These components include nascent collagen, which can be deterred from maturing as a result of this binding. Participation in such pathological activity is also self-destructive to the amyloidogenic L chains, which lose their binding capabilities for collagen-derived peptides and also become susceptible to irreversible conversion to amyloid fibrils. All of these events may be prevented by prior treatment of the amyloidogenic L chains with site-filling ligands. (c) 2000 John Wiley & Sons, Ltd.

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).

Alterations of the sugar moiety of Tamm-Horsfall protein in children with malignancies of lymphoid cells

The aim of this study was to examine whether the sugar moiety of Tamm-Horsfall protein (THP) is affected by pathological processes caused by acute lymphoblastic leukemia (ALL) or non-Hodgkin's lymphoma (NHL). The carbohydrate part of THP was studied by monosaccharide analysis, N-glycan profiling, and reactivity with specific lectins. Our results have shown that THP of ALL or NHL patients, in comparison with healthy subjects, have modified sugar chains. This is expressed in lower contents of N-acetylgalactosamine, alpha2,6-linked sialic acid and alpha1,6-linked fucose as well as in altered proportions of various N-glycans. We have shown that pathological processes also affect the carbohydrate unit of human immunoglobulin G (IgG) isolated from sera of ALL or NHL patients. As compared with healthy subjects, in IgG of the patient group, lower amounts of sialic acid and fucose were observed. These changes did not influence the biological properties of THP as judged by their unaltered ability to bind with interleukin-1alpha, alpha1-acid glycoprotein, serum albumin, transferrin, IgG1 and the light and heavy chains of IgG. Neither the in vivo alterations of IgG caused by ALL or NHL nor its in vitro modifications influence the interaction between IgG and THP.

Kappa light chain-associated Fanconi's syndrome: molecular analysis of monoclonal immunoglobulin light chains from patients with and without intracellular crystals

Plasma cell dyscrasias may be responsible for Fanconi's syndrome, due to the toxicity of a free monoclonal kappa light chain toward kidney proximal tubules. Eight cases of Fanconi's syndrome were analyzed. We compared the structures of VkappaI variability subgroup V domains from five cases of Fanconi's syndrome and one myeloma without renal involvement. Among Fanconi cases, four putative structures were obtained after molecular modeling by homology, and the other had previously been refined by X-ray crystallography. The complete sequences of one VkappaI, one VkappaIII and N-terminal sequences of two VkappaI light chains, from patients with different forms of Fanconi's syndrome, were compared with four previously studied sequences. All three kappa chains responsible for a 'classical' form with intralysosomal crystals and a low mass myeloma, were encoded by the LCO2/O12 germline gene and had an unusual non-polar residue exposed to the solvent in the CDR-L1 loop. Of both VkappaI light chains from patients with Fanconi's syndrome without intracellular crystals, one derived from LCO2/O12 and the other from LCO8/O18 gene. Another feature that could be related to non-crystallization was the absence of accessible side chains in the CDR-L3 loop which is known to be implicated in dimer formation.

Dietary salt regulates expression of Tamm-Horsfall glycoprotein in rats

BACKGROUND

Tamm-Horsfall glycoprotein (THP) is a unique protein that is produced exclusively by cells of the thick ascending limb of Henle's loop (TALH). This study examined whether dietary salt altered renal THP production.

METHODS

Male Sprague-Dawley rats were examined on days 1, 4, and 15 following placement in metabolic cages on diet that contained 0.3%, 1.0% or 8.0% NaCl. THP expression was quantified using Northern hybridization and Western blotting analysis.

RESULTS

An increase in dietary salt produced sustained increases in relative steady-state mRNA and protein levels of THP in the kidney. Addition of furosemide, but not chlorothiazide, to animals on the 8.0% NaCl diet further augmented steady-state mRNA levels of THP.

CONCLUSIONS

An increase in dietary salt and the loop diuretic, furosemide, increased expression of THP in the rat. The data support the involvement of this unique protein in the function of the TALH during changes in dietary salt. These findings also suggest that restriction of dietary salt may be beneficial in cast nephropathy in multiple myeloma and recurrent nephrolithiasis, two diseases in which THP can play an important pathogenetic role.

Tamm-Horsfall protein isolated from urine of pregnant and non-pregnant women has similar oligosaccharides

BACKGROUND

Differences in the immunosuppressive activity of Tamm-Horsfall protein and uromodulin claimed by many investigators are controversial. They have been ascribed to variations in the carbohydrate moiety.

METHODS

We isolated urinary glycoproteins from 18 non-pregnant (THP) and 12 pregnant (UM) women using the same method (adsorption on diatomaceous earth) and performed comparative studies including monocarbohydrate analysis and tests of reactivity with lectins, cytokines and serum proteins.

RESULTS

No significant differences in monocarbohydrate content or in the reactivity with specific lectins were found between the native urinary glycoproteins or between their proteolytic products. Also, in Sda+ and Sda- donors monitored throughout pregnancy and after delivery, no time-dependent differences in the sugar moiety were observed. We found that THP/UM from Sda+ donors reacted more strongly with PHA-L than THP/UM from Sda- donors, providing further evidence for carbohydrate variations between Sda+ and Sda- determinants. No differences between THP and UM in terms of their reactivity with recombitant human interleukin (rhIL) 1 alpha, recombinant human tumour necrosis factor (rhTNF) alpha and some serum proteins were found, indicating similar biological activity.

CONCLUSION

The results of our carbohydrate analysis together with previous data on amino acid analysis indicate that Tamm-Horsfall protein and uromodulin are identical or very similar glycoproteins.

Localization of a single binding site for immunoglobulin light chains on human Tamm-Horsfall glycoprotein

Cast nephropathy is a severe complication of multiple myeloma. Binding of filtered monoclonal light chains (LC) with Tamm-Horsfall glycoprotein (THP) triggers heterotypic aggregation of these two proteins to form casts in the distal nephron of the kidney. To localize the LC binding site on THP, human THP was deglycosylated and underwent limited trypsin digestion in the presence or absence of a nephrotoxic LC known to bind THP. A 29.6-kD band was protected from trypsin digestion by the addition of LC. NH2-terminal amino acid sequence and amino acid analyses revealed this band was located between the 6th and 287th amino acid residues of THP. Six peptides located within this 29.6-kD fragment were synthesized and used as potential inhibitors of binding or aggregation of five different nephrotoxic LCs with THP. Peptide AHWSGHCCL (from amino acid 225 to 233) completely inhibited binding and aggregation of these proteins. Optimal inhibition required a cystine residue in this peptide. Truncation experiments demonstrated the entire sequence was necessary for ideal inhibition and the histidine residue explained the effects of pH on binding. These studies provided a basis for further study of LC-THP interaction and a potential approach toward the prevention of cast nephropathy.

Differential glycosylation of Bence Jones protein and kidney impairment in patients with plasma cell dyscrasia

Although Bence Jones protein (BJP) is generally accepted to be critically involved in the pathogenic process of kidney impairment in patients with myeloma, patients with BJP do not always have kidney dysfunction. As proteins often undergo glycosylation and alter their molecular nature, it is expected that the heterogeneity in kidney dysfunction can be explained at least partly by the differential affinity to the kidneys of BJP dependent on its glycosylation. Accordingly, we analyzed the structures of carbohydrates of urine BJP biochemically to correlate the structure with kidney function. BJP was obtained from 16 patients with myeloma, 2 patients with light chain amyloidosis, a patient with plasma cell leukemia, and a patient with Waldenstrom's macroglobulinemia. All BJP had five forms of oligosaccharides: three forms of biantennary oligosaccharides and two forms of triantennaries. The three biantennaries correspond to previously reported oligosaccharides on only lambda-type BJP, whereas the triantennaries are novel oligosaccharides found on BJP. Among the five oligosaccharides, the triantennary oligosaccharide Gal(beta)1-4GlcNAc(beta)1-2Man(alpha)1-6 [Gal(beta)1-GlcNA(beta)1-4(Gal(beta)1-4GlcNAc(beta) 1-2)Man(alpha)1-3]Man(beta)1-4GlcNAc(beta)1-4GlcNAc showed a significant negative correlation with the serum creatinine level (p = 0.015 by Spearman's correlation test, R = 0.744). Thus determination of BJP glycosylation may be useful for the evaluation of kidney impairment in patients with BJP.

cDNA cloning of an abundant human lacrimal gland mRNA encoding a novel tear protein

An abundant 1.05 kb human lacrimal gland mRNA has been characterized by cDNA cloning. It encodes a predicted 180 residue, 20546 Da secreted protein, with a charge of +11 at ph 7 and 24.5% proline, designated as Basic Proline-rich Lacrimal Protein (BPLP), Southern blot analysis is consistent with a single BPLP gene. BPLP lacks any distinct repetitive structure, and is unrelated to the salivary proline-rich protein super-family. The pre-proprotein shows modest overall similarity to a superfamily comprising human PRPb, the mouse MSG proteins, and rat VCS-alpha 1, VCS-beta 1 and submandibular apomucin. BPLP also contains a domain with similarity to the Zp2 protein domain found in several otherwise unrelated proteins. Northern blot analysis indicated that the BPLP gene is also expressed at modest levels in the human submandibular gland, and in situ hybridization demonstrated expression of BPLP in the secretory endpieces of the human lacrimal gland. The BPLP cDNA clone defines a new human tear protein, and should provide a useful phenotypic marker of differentiation in in vitro studies of lacrimal gland function.