Calciphylaxis mimicking skin lesions of connective tissue diseases

Calciphylaxis is a rare condition found in patients with end-stage renal disease and secondary hyperparathyroidism. We describe two cases of prominent cutaneous manifestations of calciphylaxis in which skin lesions were refractory to topical treatments. We also include a brief description of calciphylaxis.

Salt-sensitive hypertension: lessons from animal models

The underlying etiology of salt-sensitive hypertension has been elusive, in part because the term represents a syndrome rather than a specific disease entity and in part because of the difficulty in completely defining the characteristics of the syndrome. The introduction of inbred models of salt-sensitive hypertension has facilitated understanding blood pressure response to dietary salt. Careful examination of one of these models, the Dahl/Rapp rat, has shown that the L-arginine:nitric acid (NO) pathway is integrally involved in production of hypertension in response to an increase in dietary salt. This review provides an overview of NO, salt sensitivity, and the role of NO in the pathogenesis of salt-sensitive hypertension.

Assessing staff attitudes towards information security in a European healthcare establishment

Information security is now recognized as an important consideration in modern healthcare establishments (HCEs), with a variety of guidelines and standards currently available to enable the environments to be properly protected. However, financial and operational constraints often exist which influence the practicality of these recommendations. This paper establishes that the staff culture of the organization is of particular importance in determining the level and types of security that will be accepted. This culture will be based upon staff awareness of and attitudes towards security and it is, therefore, important to have a clear idea of what these attitudes are. To this end, two surveys have been conducted within a reference environment to establish the attitudes of general users and technical staff, allowing the results to be fed back to HCE management to enable security policy to be appropriately defined. These results indicated that, although the establishment had participated in a European healthcare security initiative, staff attitudes and awareness were still weak in some areas.

In vitro AL-amyloid formation by rat and human mesangial cells

AA-amyloid has been produced experimentally in animal models, allowing the study of mechanisms involved in AA-amyloidogenesis, but those involved in renal AL-amyloidogenesis have not been adequately investigated due, in part, to lack of appropriate in vitro models. Rat and human mesangial cells were grown on a human extracellular matrix (Amgel) derived from normal tissues and on coverslips in the presence of 10 microliters of amyloid enhancing factor (AEF) per milliliter of media and 10 micrograms/ml monoclonal lambda light chains (LCs) obtained from two patients with AL-amyloidosis. Two additional lambda LCs derived from the urine of patients with myeloma and tubulointerstitial renal disease were used as controls. To verify amyloid deposition, light and electron microscopic examination, as well as Congo red and thioflavin T staining, were performed on samples incubated under different experimental conditions. Intracellular and extracellular amyloid was identified in samples incubated for 24 hours with human mesangial cells (for 48 hours with rat mesangial cells), amyloidogenic monoclonal LCs, and AEF. The amount of amyloid detected, which increased with longer incubation times, was found to be most abundant at 14 days. Amyloid was not present in cultures of mesangial cells incubated with amyloidogenic LCs alone or in the absence of mesangial cells. Likewise, incubation of mesangial cells with amyloidogenic LC or AEF separately or amyloidogenic LC in the presence of AEF but without mesangial cells did not result in amyloid formation. Amyloid was not seen when LCs obtained from the urine of patients with tubulointerstitial renal disease were incubated with AEF and mesangial cells. AL-amyloid production requires all three components--mesangial cells, amyloidogenic LCs, and AEF. In addition, amyloid was detected intracellular in mesangial cells, supporting the hypothesis that the production of AL-amyloid in the kidney requires intracellular processing by these cells. This system provides a unique experimental model to study renal AL-amyloidogenesis and a platform to explore mesangial cell-matrix interactions.

The SEISMED guidelines for host systems security

The increasing use of and reliance upon information technology within modern healthcare establishments underlines a need for adequate security controls to protect the confidentiality, integrity and availability of systems and data. Whilst the consideration of security is now generally accepted as part of the design and implementation of new systems, many systems are already in operation in which these needs have not been adequately addressed. This paper presents a summary of the recommendations arising from the AIM SEISMED (Secure Environment for Information Systems in MEDicine) project relating to the addition and enhancement of security in existing healthcare systems. The paper is based upon material originally presented at the SEISMED Workshop "Security and Legal Aspects of Advanced Health Telematics", Brussels, 11 July 1994. The content has been revised in light of the workshop discussion and the further development of the guidelines since that time.

Biochemical interaction between Tamm-Horsfall glycoprotein and Ig light chains in the pathogenesis of cast nephropathy

BACKGROUND

Cast nephropathy in multiple myeloma patients is caused by heterotypic aggregation of Tamm-Horsfall glycoprotein (THP) with monoclonal light chains (Bence Jones protein, BJP). Co-aggregation of these proteins is triggered by the binding of BJP to a specific peptide portion of THP. Defining those factors that alter the interaction between BJP and THP may help to understand further the pathogenesis of cast nephropathy and serve to decrease the morbidity and mortality of cast nephropathy. We hypothesized that pH, calcium, furosemide, and the carbohydrate moiety of THP all modulate the protein-protein interaction between BJP and THP.

EXPERIMENTAL DESIGN

Binding affinity and aggregation rate of human THP with two human nephrotoxic BJP were tested at pH 8.5, 7.4, and 5.0. The effects of calcium, furosemide, and free sialic acid were also evaluated. Binding and aggregation of BJP with THP purified from normal volunteers treated with oral colchicine were observed. The carbohydrate components of THP were also analyzed.

RESULTS

An acidic environment increased initial binding rate and produced a parallel increase in the aggregation rate of THP with BJP. Calcium and furosemide enhanced aggregation rates without interfering with binding. Colchicine treatment decreased the amount of sialic acid linked alpha(2-6) to galactose (NeuAc alpha 2-6Gal) and sialic acid linked alpha(2-3) to galactose (NeuAc alpha 2-3Gal) on THP and thereby decreased the aggregation rate with BJP without altering binding. Addition of free sialic acid did not alter binding but did decrease aggregation rates of the two proteins.

CONCLUSIONS

Environmental conditions modulate BJP-THP interactions and may be responsible for inducing case nephropathy in multiple myeloma. Modification of carbohydrate components of THP or use of oligosaccharides may decrease or prevent cast nephropathy.

Pathogenesis of glomerulosclerosis in light chain deposition disease. Role for transforming growth factor-beta

The glomerulopathy of monoclonal immunoglobulin light chain deposition disease is a progressive disorder characterized by accumulation of monoclonal light chains and matrix proteins in the mesangium. To define the role of light chains in this process, cultured rat mesangial cells were exposed to different light chains and human albumin. Two light chains were purified from the urine of patients who had biopsy-proven light chain deposition disease. These proteins inhibited mesangial cell proliferation and increased production of matrix proteins, including type IV collagen, laminin, and fibronectin. By immunocytochemistry and bioassay, transforming growth factor-beta (TGF-beta) production and activity increased when mesangial cells were exposed to these proteins. Furthermore, anti-TGF-beta antibody abolished the inhibition of cell proliferation and the increase of extracellular matrix protein production caused by these light chains. These findings were not observed in mesangial cells exposed to human albumin and two other light chains previously characterized to be tubulopathic. We concluded that the glomerulopathic light chains increased TGF-beta, which inhibited mesangial cell proliferation and increased matrix protein production. Together with overexpression of TGF-beta in affected glomeruli of light chain deposition disease, light chain-mediated stimulation of mesangial cells to produce TGF-beta appears to be a key pathological mechanism of this disease.

Development of security guidelines for existing healthcare systems

As modern healthcare establishments become increasingly dependent upon information systems it is vital to ensure that adequate security is present to safeguard the confidentiality and integrity of data and the availability of systems. Whilst this is now generally recognized in the design of new systems, many existing operational systems have been implemented without security in mind. This paper describes the need for a standardized approach in the protection of existing healthcare systems within Europe and presents an overview of a new set of information security guidelines that have been developed specifically for the medical community. The guidelines discussed have been produced as a deliverable of the Commission of European Communities (CEC) SEISMED (Secure Environment for Information Systems in Medicine) project, under the Advanced Informatics in Medicine (AIM) programme.

Cyclosporine inhibits the renal response to L-arginine in human kidney transplant recipients

To evaluate the association of cyclosporine (CsA)-related nephrotoxicity with nitric oxide (NO) and endothelin, the effects of L-arginine (LA) and branched-chain amino acid (BCAA) infusions on renal hemodynamics in 5 normal volunteers and 12 renal transplant recipients were assessed. In normal humans, LA, but not BCAA, reduced mean arterial pressure and renal vascular resistance while increasing RPF and urinary nitrate (NO3-) excretion. Group 1 included six transplant recipients not on CsA; Group 2 subjects (N = 6) were receiving CsA. In both groups, mean arterial pressure declined during the infusion of LA (116 +/- 4 to 109 +/- 4 mm Hg; P < 0.001) but not BCAA (116 +/- 3 to 115 +/- 3; P = not significant). In Group 1, LA increased RPF 33 +/- 13% (329 +/- 48 to 436 +/- 77 mL/min per 1.73 m2; P = 0.01) and GFR 37 +/- 16% (95 +/- 7 to 130 +/- 18 mL/min per 1.73 m2; P = 0.01); renal vascular resistance declined 27 +/- 6%. In Group 2, LA did not affect renal hemodynamics. No changes occurred with BCAA in either group. LA increased urinary NO3-excretion by 27 +/- 17% in Group 1 (P < 0.05), but only by 16 +/- 13% in Group 2 (P = not significant). Urinary endothelin excretion was higher in Group 2 subjects (10.1 +/- 1.3 versus 5.3 +/- 0.8 pg/mL of GFR, P < 0.01). LA-induced renal vasodilation is associated with the increased urinary excretion of NO3-.(ABSTRACT TRUNCATED AT 250 WORDS)

L-arginine and arginine analogs in progressive renal failure

This review summarizes the envolving role of L-arginine, the metabolic precursor of nitric oxide (NO), in disease states that produce progressive loss of kidney function. Hypertension and hypertensive nephrosclerosis manifested in the Dahl/Rapp salt-sensitive rat are exquisitely sensitive to oral L-arginine, which can completely prevent hypertension and subsequent renal damage in these rats. L-Arginine also has been shown to decrease glomerular sclerosis in the remnant kidney model and improve renal hemodynamics and function in animal models of diabetes mellitus. Finally, accumulation of inhibitors of NO production occurs in renal failure and may contribute to hypertension in these patients. Understanding the role of L-arginine and the L-arginine:NO pathway in diseases that produce progressive renal failure may provide new approaches to management.

Pathogenesis and treatment of myeloma kidney

The focus of therapy of cast nephropathy, or "myeloma kidney," has been chemotherapy to decrease production of the abnormal monoclonal immunoglobulin and immunoglobulin light chain, known as Bence Jones protein. Little attention has been given to understanding and disrupting the pathophysiologic mechanisms involved in production of intraluminal casts that obstruct and ultimately destroy renal function. Myeloma casts develop in the distal nephron when cast-forming light chains bind to a specific portion of Tamm-Horsfall glycoprotein, secreted by cells of the thick ascending limb of the loop of Henle, to form an insoluble protein complex. A variety of factors including tubule fluid flow rate and concentrations of calcium and sodium chloride in the distal nephron modify the interactions between these proteins and thus influence subsequent clinical renal failure. This review summarizes the latest developments in the pathogenesis and management of cast nephropathy.

Growth factors in monoclonal light-chain--related renal diseases

The immunomorphological expressions of monoclonal light-chain-related renal diseases (MLCRRD) are extremely varied but have a common pathogenetic feature: monoclonal light-chain deposition. The underlying cellular events involved in these processes are likely a reflection of interactions of a complex cascade of inciting and modulating factors. This study explored the potential role of growth factors in MLCRRD by examining the expression of insulin-like growth factor (IGF-I), fibroblast growth factor (FGF), transforming growth factor-beta (TGF-beta), and platelet-derived growth factor A chain (PDGF-A) and B chain (PDGF-B) in 36 cases of MLCRRD. All growth factors examined were expressed in tubules, primarily proximal, but to varying extent. Intensity of IGF-I and TGF-beta tubular staining correlated with tubular injury and interstitial fibrosis. Intensity of tubular staining with antibodies to FGF also correlated with interstitial fibrosis. Platelet-derived growth factor B chain was strongly detected in glomeruli and, in some cases, in vascular structures. Transforming growth factor-beta was detected only in glomeruli of three patients with nodular glomerulopathy associated with light-chain-deposition disease. Insulin-like growth factor, FGF, and PDGF-A were not detected in glomeruli or vessels in any of the cases. Proliferating cell nuclear antigen (PCNA) staining in tubules and glomeruli was markedly increased in light-chain-deposition disease and less but still significantly increased above control values in the other variants of MLCRRD. These results suggested: (1) a correlation between IGF-I and TGF-beta staining in the tubular interstitium and tubular damage; (2) a correlation between IGF-I, TGF-beta, and FGF staining in the tubular interstitium and interstitial fibrosis; (3) a likely important role for PDGF-B activation in certain glomerular alterations that occur in MLCRRD; (4) a role for TGF-beta in light-chain-deposition disease; and (5) the presence of a significant proliferation signal in all cases of MLCRRD but most notably in light-chain-deposition disease in glomerular and tubular compartments. A cascade of events related to growth factor activation appears to play a fundamental role in the pathophysiological processes governing MLCRRD.

Ultrastructural immunolabeling: a unique diagnostic tool in monoclonal light chain-related renal diseases

Ultrastructural labeling can play a key role in the evaluation of morphologic expressions of monoclonal light chain-related renal diseases in cases where light microscopy, electron microscopy, and immunofluorescence data, even when combined, are not definitive in conveying a diagnosis and, in other cases, in clarifying the findings by providing immunomorphologic correlation. The important role of ultrastructural labeling is highlighted by the fact that in some of these cases bone marrow aspirates and biopsy specimens obtained at the time of the evaluation of the renal specimens are often unable to establish unequivocally a diagnosis of plasma cell dyscrasia. This is in part because renal manifestations commonly precede overt diagnostic bone marrow alterations. Overt bone marrow findings and clinical manifestations may be preceded for as long as 16 years by the renal manifestations. Determination or confirmation of monoclonality and detection of early deposition of monotypical light chains before the finding of ultrastructural morphologic correlates (ie, subendothelial, punctate, granular, electron-dense material) represent unique attributes of this technique. The increased sensitivity of ultrastructural immunolabeling compared with other available diagnostic techniques and its exquisite immunomorphologic correlative capabilities result in a comprehensive evaluation. Sixteen monoclonal light chain-related renal disease cases with early, unusual, or equivocal immunomorphologic manifestations that may have not been characterized properly if ultrastructural labeling had not been performed are presented. The crucial role played by ultrastructural labeling in evaluating these cases and establishing an accurate diagnosis is illustrated and emphasized.

A generic methodology for health care data security

The aim is to outline the framework of a generic methodology for specifying countermeasures in health care environments. The method is specifically aimed at the enhancement of security in existing health care systems, and a key element is the use of predetermined 'profiles' by which these may be classified. Example scenarios are presented to illustrate how the concept could be applied in practice. The paper is based upon work that was initially carried out as part of the Commission of European Communities SEISMED (Secure Environment for Information Systems in MEDicine) project, the aim of which is to provide security recommendations for European health care establishments (HCEs).

Role of nitric oxide synthesis in salt-sensitive hypertension in Dahl/Rapp rats

Nitric oxide is a potent endogenous vasodilator that regulates arterial tone. A family of nitric oxide synthases uses L-arginine and L-homoarginine stereospecifically as substrates for nitric oxide production in vivo. By preventing expression of inducible but not constitutive nitric oxide synthases, glucocorticoids differentiate which enzyme in this family is the predominant source of nitric oxide generation in a given situation. We proposed that defective production of nitric oxide produces salt-sensitive hypertension in the Dahl/Rapp rat. Plasma concentrations of L-arginine, citrulline, and ornithine of salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats on 8% sodium chloride chow for 1 week did not differ. However, intravenous infusion of L-arginine and L-homoarginine, but not D-arginine, increased urinary excretion of nitrate, the degradation product of nitric oxide, and simultaneously lowered blood pressure in hypertensive SS/Jr rats. Oral L-arginine also prevented development of hypertension and increased urinary excretion of cyclic GMP and nitrate in these rats. Dexamethasone, in a dose that prevented hypotension from parenteral injection of lipopolysaccharide, completely prevented the increase in excretion of cyclic GMP and nitrate, and hypertension resulted despite concomitant treatment with L-arginine. These studies supported an important role of dexamethasone-suppressible nitric oxide synthesis in the prevention of salt-sensitive hypertension in the Dahl/Rapp rat.

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

Bence Jones proteins (BJPs) are the major pathogenic factor causing cast nephropathy ("myeloma kidney") by coaggregation with Tamm-Horsfall glycoprotein (THP). Understanding the interaction between these proteins is therefore important in developing treatment strategies to prevent renal failure from cast formation in multiple myeloma. We developed an enzyme-linked immunoassay to examine this phenomenon. Five different human BJPs (four kappa and one lambda immunoglobulin light chains) were used in this assay that demonstrated these proteins bound THP with different affinity. BJPs competed among themselves for binding to THP. The binding site was a peptide portion of THP since these proteins also bound deglycosylated THP. Also, one monoclonal antibody directed against a peptide segment of human THP prevented binding of THP to BJPs. By altering the conformation of THP, reducing agents decreased binding between these two proteins in concentration-dependent fashion. In turbidity studies, the monoclonal antibody that prevented binding and a reducing agent, dithiothreitol, decreased coaggregation. Deglycosylated THP did not coaggregate with BJPs. We concluded that ionic interaction between BJPs and a specific peptide binding site on THP promoted heterotypic coaggregation. The carbohydrate moiety of THP was also essential for coaggregation, perhaps by facilitating homotypic aggregation of THP.

Monoclonal immunoglobulin light chain-related renal diseases

The spectrum of renal lesions associated with deposition of monoclonal light chains is varied and extensive, yet the simultaneous occurrence of two or more of these lesions in the same patient is unusually recognized. In addition, patients may excrete large amounts of monoclonal light chains and have no clinically evident renal dysfunction. Thus, the type of renal lesion that occurs appears to depend on the physiochemical properties of the unique monoclonal light chain produced. The particular nephrotoxic properties responsible have not yet been identified but are currently under intensive examination. For example, various studies suggest that cast-forming Bence Jones proteins have isoelectric points above 5.1. Finally, along with these intrinsic properties, environmental factors combine to promulgate the lesion or prevent clinical expression of renal injury. Attention to the subtle morphological renal manifestations of MLCRRD is essential to diagnose these diseases early in the course. Characterization of the morphological pattern and degree of renal affectation is important because therapeutic modalities may vary accordingly. As understanding of the molecular events responsible for the renal alterations improves, additional therapeutic approaches may emerge to reverse renal failure in MLCRRD.

Renal involvement in plasma cell dyscrasias

Monoclonal light chain-related renal diseases represent a unique collection of renal disorders with monoclonal light chain deposition underlying the pathogenesis of these disorders. Yet, despite this common pathogenic mechanism, each renal lesion is unique. In addition, these syndromes are unusual in that, unlike many other renal disorders, they are potentially reversible causes of renal failure. This review focuses on the pathogenesis of three light chain-related renal diseases: AL amyloidosis, granular light chain deposition disease, and cast nephropathy ("myeloma kidney"). Management of these renal lesions in relation to the different pathophysiologic mechanisms is also discussed. Treatment should be designed to decrease production of nephrotoxic light chains and to prevent the binding interaction between these light chains and the various structures of the nephron.

Hypertensive nephrosclerosis in the Dahl/Rapp rat. Initial sites of injury and effect of dietary L-arginine supplementation

BACKGROUND

The Dahl/Rapp strains of salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rat were developed to examine pathogenetic mechanisms that produce hypertension in response to an increase in dietary salt. We have shown that providing SS/Jr rats with L-arginine, the metabolic precursor of nitric oxide, acutely prevented salt-sensitive hypertension, suggesting that SS/Jr rats developed hypertension because of inadequate nitric oxide production while on a high-salt diet.

EXPERIMENTAL DESIGN

Male 23-day SS/Jr and SR/Jr rats were placed on chow that contained 8% sodium chloride. One group of SS/Jr rats also received L-arginine, 1.25 g/liter, in their drinking water. These three groups were examined at weekly intervals for 4 weeks.

RESULTS

SS/Jr rats rapidly developed hypertension when placed on the high-salt chow. After 2 weeks on this diet, inulin clearance dramatically decreased, and albumin excretion rate increased. By the fourth week of study, SS/Jr rats on the high-salt diet had died or were dying. Coincident with the progressive decline in inulin clearance, renal morphologic analysis confirmed development of myointimal thickening, fibrinoid necrosis, and glomerulosclerosis. In contrast, over the 4 weeks of study, SS/Jr rats supplemented with oral L-arginine did not develop hypertension and any of the associated renal complications seen in age-matched SS/Jr rats on the high-salt diet. L-Arginine also corrected hypertension in SS/Jr rats exposed to the high-salt chow for 2 weeks before the inception of L-arginine. L-Arginine administration after 3 weeks on this chow, however, failed to reverse hypertension and the depressed inulin clearance and morphologic renal damage.

CONCLUSIONS

Along with previous work (Chen PY, Sanders PW, J Clin Invest 88:1559-67), these studies were consistent with the hypothesis that hypertension and hypertensive nephrosclerosis developed in SS/Jr rats because, while on a high-salt diet, substrate (L-arginine) became a rate-limiting factor in the synthesis of nitric oxide.

Pathobiology of cast nephropathy from human Bence Jones proteins

Renal failure is a common accompaniment of multiple myeloma and is usually due to cast nephropathy, or "myeloma kidney." To understand this lesion, four human Bence Jones proteins (BJP) were purified from the urine of volunteers who had either no evidence of renal dysfunction (BJP1) or renal failure from cast nephropathy (BJP2, BJP3, BJP4). When infused directly into the rat nephron in vivo, BJP2, BJP3, and BJP4 produced intraluminal obstruction by precipitating in the distal nephron; protein casts were never identified before the tip of the loop of Henle. Obstruction was related to the concentration of BJP in the perfusate. Addition of furosemide to the perfusate augmented obstruction in a concentration-dependent fashion. Pretreatment of rats with colchicine completely prevented obstruction and cast formation of perfused nephrons; beta-lumicolchicine did not prevent obstruction. Tamm-Horsfall glycoprotein purified from beta-lumicolchicine-treated and untreated rats coaggregated with BJP3 in vitro. Tamm-Horsfall glycoprotein from colchicine-treated rats did not contain sialic acid and did not aggregate with BJP3 in vitro. Thus, cast-forming human BJP coaggregated with Tamm-Horsfall glycoprotein and obstructed the rat distal nephron. Intranephronal obstruction was aggravated by decreasing extracellular fluid volume or adding furosemide. Finally, by decreasing secretion and altering the carbohydrate moiety of Tamm-Horsfall glycoprotein, colchicine prevented intraluminal cast formation and obstruction of the rat nephron.

L-arginine abrogates salt-sensitive hypertension in Dahl/Rapp rats

This study examined the contribution of nitric oxide (NO) to the susceptibility or resistance to the hypertensive effects of high sodium chloride (8.0% NaCl) intake in young Dahl/Rapp salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats. Using NG-monomethyl-L-arginine (L-NMMA) as a probe for NO production in vivo, we found that increasing dietary sodium chloride increased NO activity in salt-resistant rats, but not in salt-sensitive rats. Exogenous L-arginine, the substrate for NO synthesis, decreased blood pressure to normotensive levels in salt-sensitive rats made hypertensive for 2 wk from 8.0% NaCl chow. D-arginine had no effect on blood pressure of these rats and L-arginine did not change blood pressure of salt-resistant rats. Intraperitoneal injections of L-arginine and its precursor, L-citrulline, and oral L-arginine, but not D-arginine, prevented the increase in blood pressure in salt-sensitive rats on the high salt chow over 2 wk of observation. In contrast, L-arginine did not alter the development of hypertension in spontaneously hypertensive rats. Mean urinary cGMP levels were higher in salt-sensitive rats on oral L-arginine than salt-sensitive rats on D-arginine. Infusion of L-NMMA acutely decreased, whereas intravenous L-arginine rapidly increased, urinary cGMP in both groups. L-arginine and L-citrulline increased production of NO and prevented salt-sensitive hypertension in Dahl/Rapp rats.

Spectrum of glomerular and tubulointerstitial renal lesions associated with monotypical immunoglobulin light chain deposition

The purpose of this study was to characterize the spectrum of renal lesions associated with plasma cell dyscrasias from a population of patients who had renal disease identified by kidney biopsy. Thirty-six patients (2.6% of 1361 kidney specimens examined over 6 years) had evidence of monotypical light chain with or without concomitant heavy chain deposition. A variety of lesions was found, including (a) AL-amyloid and glomerular nonamyloid light chain deposition manifesting as nodular, membranoproliferative, mesangioproliferative, and "minimal-change" glomerulopathies; (b) fibrillary glomerulopathy; (c) tubulointerstitial lesions (cast nephropathy, acute tubular necrosis, and tubulointerstitial nephritis); and (d) vascular (arterioles and small and medium-sized arteries) lesions. AL-amyloid was the most common renal lesion (39%), nonamyloid deposition occurred second most commonly (33%), and cast nephropathy ("myeloma kidney") was third most frequent (14%). Clinical and laboratory manifestations of a plasma cell dyscrasia were frequently subtle. Immunoelectrophoresis of both serum and urine did not demonstrate a monotypical light chain or immunoglobulin in almost 35% of this population. Thus, the correct diagnosis was not considered in the majority of these patients before biopsy. Progressive deterioration of renal function was common with all of the lesions, except for proximal tubule injury, which tended to improve over the period of study. Renal biopsy with careful examination for monotypical light chain with or without associated heavy chain deposition using immunofluorescence or immunoelectron microscopy was crucial in identifying and characterizing the varied lesions associated with lymphoplasmacytic disorders.

Mechanisms of intranephronal proteinaceous cast formation by low molecular weight proteins

Proteinaceous cast formation in the distal nephron of the kidney from low molecular weight proteinuria is a significant, but poorly characterized, cause of renal failure. To study this phenomenon, we: (a) microperfused the loop segment (LS) of rats in vivo with artificial tubule fluid (ATF) containing four different low molecular weight proteins, 0.01-50 mg/ml, to detect alterations in LS function, and (b) examined the interaction between several proteins and Tamm-Horsfall glycoprotein (THP) in vitro with turbidity and dynamic light-scattering measurements. Perfusion of the LS for less than 2 min with cast-forming proteins (Bence Jones protein [BJP3] and myoglobin) decreased chloride absorption and elevated early distal tubule fluid (ED) [Cl-], compared with results obtained with control perfusions that used ATF alone. BJP3 decreased chloride absorption in a concentration-dependent fashion. Perfusion with non-cast-forming proteins (albumin and BJP1) enhanced chloride absorption and decreased ED [Cl-]. In vitro, proteins that had isoelectric points (pI) greater than 5.1 aggregated with THP. Aggregation was enhanced with increasing [NaCl] or [CaCl2]. Albumin (pI 4.8) and beta-lactoglobulin (pI 5.1) did not coprecipitate. The molecular size of THP alone increased when [NaCl] greater than 80 mM. Thus, cast-forming proteins aggregated with THP in vitro and caused in vivo LS dysfunction, which elevated ED [Cl-], facilitating aggregation. In contrast, non-cast-forming proteins either did not interact with THP or lowered ED [Cl-], which did not provide an environment for aggregation. Altered LS function and interaction of some proteins with THP were related to different physicochemical properties of the proteins and independently contributed to the formation of proteinaceous casts in the kidney.