Autosomal dominant medullary cystic disease: a disorder with variable clinical pictures and exclusion of linkage with the NPH1 locus

BACKGROUND

The nephronophthisis-medullary cystic disease (NPH/MCD) complex represents a heterogeneous group of hereditary tubulointerstitial nephritis. The most common variant is juvenile recessive NPH, for which a gene locus (NPH1) has been mapped on chromosome 2q13. MCD is a less common dominant condition usually recognized later in life, which resembles NPH in many aspects, still presenting remarkable clinical differences. Nothing is known about the chromosome locus of MCD.

METHODS

Five MCD families were studied. Diagnosis was made by inference from family history, type of inheritance, clinical signs and histology. Multipoint linkage analysis was performed by markers D2S293, D2S340 and D2S160 spanning the entire NPH1 locus.

RESULTS

Diagnosis of MCD was made in 28 affected members (16 males; 12 females), belonging to five families. Histological diagnosis was available in 10 patients; clinical diagnosis in 11; seven deceased relatives had diagnosis of chronic nephritis. The age at diagnosis ranged from 8 to 65 years. Renal medullary cysts were found in a minority of patients. In family 1, the disease was associated with hyperuricaemia and gouty arthritis. Progression of renal disease presented intra- and extra-family variability with members of the same family showing mild elevation of creatinine or terminal renal failure. The NPH1 locus associated to recessive NPH was excluded from linkage to the dominant MCD.

CONCLUSIONS

MCD might be more common than previously assumed. Variability in clinical presentation and absence of histopathological hallmarks contribute to make the diagnosis uncommon. The most remarkable clinical difference with NPH is the age of onset in some kindreds and a delayed progression towards renal failure. The exclusion of linkage to the NPH1 locus suggests the existence of an MCD responsible locus, still to be mapped.

Nephronophthisis-medullary cystic disease: clinical and genetic aspects

Nephronophthisis (NPH)/medullary cystic disease (MCD) is an intriguing complex. NPH and MCD have been considered in the past to be the same entity, being histologically indistinguishable and showing a similar clinical behavior. In both entities, clinical onset and course are so insidious, and involve such a paucity of signs and symptoms, that diagnosis in the pre-azotemic stage is very uncommon. Extrarenal manifestations are often associated only to NPH. Nevertheless the two forms can be distinguished on the basis of inheritance and evolution. Indeed, in NPH, end-stage renal failure is encountered during early adolescence, while it occurs late in adulthood in MCD; more importantly, however, the mode of inheritance differs, being autosomal recessive in NPH and autosomal dominant in MCD. Since the beginning of the 1990s, studies on molecular genetics have led to the identification of a candidate gene for NPH on chromosome 2: in 60-70% of the NPH population a large homozygous deletion has been found. In NPH-associated retinal lesions (Senior Loken syndrome), no linkage with chromosome 2 gene loci have been identified. Studies on MCD-affected families have so far excluded an MCD gene on chromosome 2.

Cell-specific regulation of alpha1(III) and alpha2(V) collagen by TGF-beta1 in tubulointerstitial cell models

BACKGROUND

TGF-beta1 modulates the cellular expression of extracellular matrix (ECM) in several renal cell systems in vitro and is considered a determinant of ECM accumulation in tubulointerstitial fibrosis.

METHODS

We evaluated the effects of TGF-beta1 on collagen transcription, expression, and removal of the relevant collagens by rat tubuloepithelial cells (NRK 52E) and both rat and monkey interstitial fibroblasts (NRK 49F, CV1) in vitro.

RESULTS

TGF-beta1 upregulated the expression of alpha1(III) collagen by fibroblasts (+300%) without affecting its removal. In parallel, a threefold increment of COL3A1 mRNA was found. Experiments of cell transfection employing CV1 fibroblasts as the unique suitable model, and chimaeric constructs of COL3A1 and COL5A2 promoters fused to the luciferase reporter gene, demonstrated a twofold stimulation of a large 1436 COL3A1 promoter construct and negligible effects on shorter fragments, suggesting the presence of a positive responsive element in a region of COL3A1 promoter between -1375 and -579. TGF-beta1 did not influence COL5A2 mRNA and the relative promoter activity in renal fibroblasts. With NRK 52E cell line, TGF-beta1 induced comparable increment of both alpha1(III) collagen expression (+300%) and COL3A1 mRNA (+300%) without affecting the COL3A1 promoter activity of any constructs. TGF-beta1 also upregulated the expression of alpha2(V) collagen chain (+500%) and COL5A2 mRNA (+500%) with a stimulatory effect (+100%) on a 1177 bp fragment of COL5A2 promoter. In this case a relevant inhibitory effect of TGF-beta1, on removal of alpha2(V) by supernatants of NRK 52E was also observed, indicating a double regulatory role of the cytokine on both transcription and removal of this component of ECM.

CONCLUSION

Taken together these data indicate that TGF-beta1 is a potent stimulator of alpha1(III) collagen expression by renal fibroblast cell lines in vitro, the basic mechanism being stimulation of COL3A1 transcription. With renal epithelial cell lines, TGF-beta1 mainly upregulated the expression of type V collagen with the most relevant effect on stimulation of collagen transcription and inhibition of its removal. Tubular epithelial cells and renal fibroblasts should play distinct roles in renal fibrosis induced by TGF-beta1 in vivo.

Resolution of fibronectin and other uncharacterized proteins by two-dimensional polyacrylamide electrophoresis with thiourea

Several proteins, which are recognized components of serum, are not resolved by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) under standard conditions. One major example is fibronectin, which is detected in fairly high concentration (milligram range) by immunoassays, while undetectable in 2D-PAGE gels. Following several experiments with a combination of zwitterionic and chaotropic substances we obtained a good resolution of the protein in gels containing 0.5 M thiourea plus 8 M urea. By this technique, fibronectin was, for the first time, found to be microheterogeneous between pl values of 5.3 and 5.6. Besides fibronectin we detected three other families of uncharacterized proteins with Mr of 130000, 110000 and 34000 respectively, whose identity and function are currently under investigation.

Autosomal dominant polycystic kidney disease: clinical and genetic aspects

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited systemic disease caused by at least three different genes. The renal and extrarenal clinical manifestations, and the systemic complications due to cystic and non-cystic abnormalities in ADPKD patients have been widely investigated. Cellular and molecular aspects of cystogenetic mechanisms concern epithelial tubular cell proliferation, remodelling of extracellular matrix, fluid secretion and accumulation, and relations between cell proliferation and apoptosis. In vitro studies on cystogenesis suggest a key role of cell-to-cell or cell-to-matrix interactions. Surface proteins mediating cell-to-cell contact, such as E-cadherin (polycystin?), integrin interactions, growth factors, receptor expression, are involved in the process of differentiation of the cellular condition and of the extracellular matrix. Blocking any one of these complex mechanisms should influence the orientation and polarization of epithelial tubular cells and should mediate the inversion of fluid secretion which ends in renal cystogenesis. ADPKD comprises at least three phenotypically indistinguishable but genetically distinct entities, caused by mutations in three autosomal genes: PKD1 (chromosome 16p13.3) is present in about 85% of patients; PKD2 (chromosome 4q13q23) in 10%; PKD3 (unknown chromosome) in a few families. PCR-based mutation detection methods, automated DNA sequencing, and other "functional" methods are used to screen and analyse ADPKD patients. It is not yet known whether the mutations identified so far in PKD1 and PKD2 inactivate the genes or generate an aberrant product. The products of PKD1 and PKD2 genes have been called polycystin 1 and 2. Polycystins are members of a family of interactive proteins involved in complex adhesive cell-cell, cell-matrix, protein-protein, and protein-carbohydrate interactions in the extracellular compartment, and are involved in the same pathway (ion channel regulator? ion channel? pore?) where mutations in only one of the simple genes (PKD3 too?) may cause the ADPKD phenotype. Genotype-phenotype correlations, in terms of disease severity and/or progression to end-stage renal disease, probably depend on other factors, both genetic and environmental (for instance: DD genotype of the ACE gene in ADPKD hypertensive patients), that might influence the clinical course and progression of ADPKD. The hypothesis of the "two hits" has been proposed to explain at the molecular level the focal nature of cyst formation.

Lysyl oxidase expression and collagen cross-linking during chronic adriamycin nephropathy

Collagen cross-linking induced by lysyl oxidase has been implicated in liver and lung fibrosis. To define the role of this process in kidney fibrosis, we investigated the renal expression of lysyl oxidase and the content in collagen cross-links at various stages of chronic Adriamycin nephropathy in Sprague-Dawley rats. Lysyl oxidase expression was determined by RT-PCR; collagen pyridinium residues, indicating lysyl oxidase induced cross-links, were evaluated by HPLC. These parameters followed a synergic albeit asynchronous outcome: (a) lysyl oxidase mRNA levels in total kidney, glomeruli and medulla from Adriamycin-treated rats increased up to 3 times compared to controls between week 8 and 12, then returning within the normal range; (b) the pyridinium residue content did not show any significant difference between Adriamycin-treated and control rats, until diffuse interstitial fibrosis developed (16 weeks), showing at this time a 2- to 3-fold increment. Lysyl oxidase was expressed by several renal cell lines and in tubular-epithelial cells it was up-regulated in vitro by TGF beta-1, a recognized fibrogenetic factor in Adriamycin nephropathy. Our observations demonstrated that an increased expression of lysyl oxidase in the kidney precedes the development of diffuse fibrotic lesions and that, at this stage, collagenic structures contain highly cross-linked components, the final product of lysyl oxidase activity. The evidence of lysyl oxidase up-regulation in tubular epithelial cells by the same factor implicated in Adriamycin toxicity in the kidney suggests a common pathogenetic mechanism. Collagen cross-link formation by lysyl oxidase may be implicated in the pathogenesis of irreversible, fibrotic renal lesions.

Negative staining of proteins in polyacrylamide gels with methyl trichloroacetate

This paper describes a new, sensitive (in the nanogram range), and rapid (two-step) technique for the negative staining of proteins in polyacrylamide gels in the presence or absence of sodium dodecyl sulfate. After separation, gels are incubated with 8% methyl trichloroacetate ester in 38% isopropanol and then washed in water to produce a negative image of colorless proteins against an opaque background. The technique allows unmodified proteins to be recovered for biological studies or transblot for amino acid sequence. Finally, owing to the reversibility of the process, gels can be restained after rapid visualization. For these reasons, negative staining with methyl trichloroacetate should become the method of choice for rapid and sensitive staining of proteins prior to further processing, including stable staining with silver ions.

Effects of peritoneal effluents on mesothelial cells in culture: cell proliferation and extracellular matrix regulation

Peritoneal fibrosis in patients on peritoneal dialysis is the result of interstitial collagen accumulation within the peritoneal membrane and in mural spaces. Hypothetically, collagen expression by target cells may be regulated by specific endoperitoneal factors, though the existence of such factors has not yet been demonstrated. We evaluated the effects of cell-free peritoneal effluents obtained from six children undergoing peritoneal dialysis on several mesothelial cell functions in vitro. Human peritoneal mesothelial cells (MC) were obtained from the omental tissue of six uraemic children who were undergoing surgery for insertion of a peritoneal catheter. Cells at confluence were utilized to determine cytotoxicity (LDH release), viability (trypan blue), proliferation (3H-thymidine incorporation), collagen expression (3H-proline incorporation, SDS-Page) and mRNA (dot-blot). A preliminary series of experiments, was undertaken to define which of the successive fluid collections during a dialytic procedures induces the greatest changes; this revealed maximal effects of the effluent from the long stasis period. Exposure to peritoneal effluents obtained from four patients with acute peritonitis induced marked changes in cell morphology, stimulated by (3H)-thymidine incorporation into DNA by 300% and upregulated the expression and transcription of type III collagen (6-fold increment in COL3A1 mRNA). Qualitatively but not quantitatively comparable changes in cell proliferation (+100%) and collagen expression were induced by peritoneal effluents from patients without peritonitis. In an effort to reproduce the effect of peritoneal effluents in vitro, we exposed mesothelial cells to various cytokines putatively present in infected peritoneal effluents, namely IL-2, TGF beta and TNF alpha; in no case did we find stimulation of cell proliferation. Finally TGF beta but not TNF alpha or IL2 upregulated collagen synthesis by these cells. These findings demonstrate a direct influence of cell-free peritoneal effluents on mesothelial cell functions, including stimulation of interstitial collagen expression. All these changes were more evident upon exposure to effluents collected during acute peritonitis, which suggests a link between recurrent peritoneal infection and collagen deposition, the most typical precursor of peritoneal fibrosis.

Deposition of kappa and lambda light chains in amyloid filaments of dialysis-related amyloidosis

beta 2-Microglobulin (beta 2m) is considered to be the amyloidogenic precursor in dialysis-related amyloidosis, although the implication of other relevant cofactors in the pathogenesis of this disease has also been hypothesized. It is conceivable that substances found in amyloid deposits might represent something more than simple codeposition, possibly playing a pathogenic role in amyloidogenesis. Along these lines, a detailed analysis of the protein composition of amyloid fibrils purified from synovial material surgically obtained from nine patients on long-term dialysis was carried out. By the use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, several other protein components, in addition to beta 2m, were found. These were characterized by NH2 amino-terminal sequencing and immunoblotting. In fibrils obtained by water extraction, which fulfill the electron microscopy criteria of highly pure amyloid material, polyclonal kappa and lambda light chains were detected with a concentration of 15 micrograms/mL in the water extraction material; the beta 2m concentration was 200 micrograms/mL. Light microscopy immunohistochemistry was performed on samples from five patients. Amyloid deposits reacted with anti-beta 2m, and anti-light (kappa, lambda), chain antibodies. The immunoreaction of amyloid filaments to anti-beta 2m, anti-lambda, and anti-kappa light chain antibodies was also tested by electron microscopy by use of the immunogold staining procedure. Amyloid filaments were labeled by the three antibodies and showed a different intensity of immunostaining apparently related to their different aggregation pattern. These observations demonstrate that polyclonal immunoglobulin light chains (kappa and lambda) are not contaminants but, together with beta 2m, represent a major constituent of amyloid deposits in dialysis-related osteoarticular amyloidosis, thus indicating their possible role in amyloidogenesis.

A new biallelic DNA polymorphism of the human COL5A1 gene

A cDNA probe of the human COL5A1 gene detects a frequent biallelic PstI polymorphism. Allele A has a frequency of 54% whereas that of allele B is 46%. This restriction fragment length polymorphism provides a useful marker for linkage analysis in 9q34.3.

Activation of the intracellular glutathione system by oxydative stress during cardiopulmonary bypass and myocardial perfusion

The glutathione (GSH) system is the main defence of tissues against free radicals and red blood cells (RBC) are the most efficient sites for GSH redox cycle activation. Total GSH was assayed during cardiopulmonary bypass (CPB) in RBC and serum from the coronary sinus, peripheral arteries and veins in 18 children corrected of their cardiac defect. Our conclusions are: (1) RBC-GSH redox cycle is activated during heart ischaemia and reperfusion; (2) the activation of intracellular GSH system is preponderant compared with the extracellular one; (3) variations in intraerythrocytic total GSH during heart ischaemia and perfusion are detectable in peripheral veins and arteries, which can be the convenient sites for monitoring changes in the GSH cycle; and (4) increased total GSH levels are present in RBC before aortic crossclamping: at the beginning of mechanical ventilation in veins and, when CPB is started, also in arteries.

Purification of alpha-1-antitrypsin monomer by preparative electrophoresis

Alfa-1-antitrypsin (alpha 1AT) was purified by pseudoligand chromatography and preparative electrophoresis from the serum of a patient with alpha 1AT deficiency. The combination of the two techniques yielded a high grade batch of alpha 1AT monomer and this was successfully used to purify the protein from the serum of PiMIM1, PiMIM2, and PiZZ phenotype subjects. This procedure should facilitate structural studies of alpha 1AT variants susceptible to intracellular accumulation.

Cyclosporine enhances the synthesis of selected extracellular matrix proteins by renal cells "in culture". Different cell responses and phenotype characterization

Glomerulosclerosis and interstitial fibrosis are 2 major side effects of protracted therapy with CsA in heart transplant patients and in nonrenal immunologic diseases. To investigate whether there is any cause-effect correlation between CsA and the synthesis of extracellular matrix in the kidney, we determined the amount and composition of collagens produced by various renal cells "in culture" upon exposure to increasing levels of CsA. The cellular models we used included primary cultures of both human and rat mesangial cells (hMC, rMC), human and rat renal fibroblasts (hFib, rFib), and human tubular epithelia as well as cell lines of rat renal fibroblasts (NRK49F) and of tubular epithelia (NRK52E). In the case of primary cell cultures, CsA induced a marked increment of total collagen synthesis. This was highest for renal fibroblasts (+330% hFib, +110% rFib), followed by rMC (+170%), hMC (+100%), and human tubular epithelia (+130%). At the highest dosage of CsA (5 ng/ml), this corresponded to a net increment in collagen III synthesis by both hMC and hFib (+150% and +300%), while collagen I and collagen IV were unaffected. On hMC, CsA also induced a maximal increase in a component with 70 kDa molecular mass, which was produced only in a negligible amount by these cells in standard conditions. This low molecular mass collagen was tentatively characterized by cyanogen-bromide digestion and fingerprint analysis as a novel molecule showing a peptide composition without comparable features for any reported collagen map. NRK49F and NRK52E cell lines were not affected by CsA. Taken together, these observations demonstrate that CsA is able to induce the synthesis of specific collagens, mainly of collagen III and of a 70-kDa component, by various renal cells in cultures. Since the same cells are the renal site of production of extracellular matrix in pathological conditions, we hypothesize that this effect is a relevant one in the pathogenesis of glomerulosclerosis/interstitial fibrosis during protracted therapies with CsA.

Selective enhancement by cyclosporin A of collagen expression by mesangial cells 'in culture'

Extracellular matrix deposition in mesangial areas leading to glomerulosclerosis is the major side effect of protracted therapies with cyclosporin A. In order to define any direct correlation between a chronic therapy with the drug and glomerulosclerosis we studied the effects of cyclosporin A on extracellular matrix production by human mesangial cells in culture. By immunoprecipitation and sodium dodecyl sulfate polyacrylamide electrophoresis (SDS-PAGE) of [3H]proline-labeled mesangial cells it was found that cyclosporin A induced a dose-dependent increase in total collagen synthesis (+80%), corresponding to a net increment in collagen III (+120%) and in a component with 70 kDa molecular weight which was produced only in negligible amount by mesangial cells under standard conditions. This collagen was characterized by cyanogen bromide digestion and finger print analysis as a novel molecule, not sharing any peptide composition similarities with the already characterized collagens. These data indicate that cyclosporin A stimulates the synthesis by mesangial cells of selected collagens, mainly collagen III and a new low molecular weight component. This mechanism may be relevant in cyclosporin A induced glomerulosclerosis occurring during protracted therapies with the drug.

Protracted high-dose interferon gamma therapy for chronic experimental nephropathy

This study focused on the utility of interferon gamma (IFN gamma) as an anti-fibrotic drug in renal experimental fibrosis; the nephropathy was induced by two doses of Adriamycin (ADR) in 20 Sprague Dawley rats, 10 of which were randomly assigned to receive IFN gamma (45,000 UI) on alternate day for 16 weeks. At the end of the follow up, ADR rats treated with IFN gamma developed massive proteinuria, slight renal insufficiency, and presented diffuse glomerulosclerosis, tubulo interstitial infiltration and fibrosis. No difference was found in the composition of tubulo-interstitial infiltrates, mainly consisting in CD4+T lymphocytes with a minor component of CD8+T cells, in comparison with rats treated with ADR alone. These observations demonstrate the inefficacy of a protracted high-dose treatment with IFN gamma in chronic experimental nephropathy with interstitial fibrosis.

Intact renal albumin downregulates the extracellular matrix expression by mesangial cells and renal fibroblasts in vitro

Chronic Adriamycin (ADR) nephropathy is invariably associated with glomerulosclerosis and tubulointerstitial fibrosis. To investigate the hypothesis that severe albuminuria plays a role in the pathogenesis of both processes, we purified the protein from conditioned media of rats with advanced ADR nephropathy and tested the fibrogenic effect on renal fibroblasts and mesangial cells in vitro. Albumin was purified by pseudoligand chromatography and was identified on the basis of the NH2 amino terminus. Furthermore, it was differentiated from the urinary homologue, being more anionic and more fatted while maintaining a conserved peptide composition. The exposure of renal cells to renal albumin induced a dose-dependent reduction in collagen synthesis with a half-maximal decrease with 0.2 microgram/ml of albumin. With renal albumin levels of 0.4 microgram/ml the collagen incorporation of 3H-proline by mesangial cells and renal fibroblasts (primary cultures and cell lines) was reduced by 76, 81 and 45% respectively. A qualitative analysis by SDS-polyacrylamide electrophoresis and immunoprecipitation of radiolabelled collagens demonstrated a drastic and unselective decrease in all major collagens synthesized by mesangial cells and fibroblasts, including type I, III and V. Previous immunoprecipitation of the protein with anti-rat albumin antibodies completely reversed this phenomenon. Finally, albumin purified from urines of rats with ADR nephropathy downregulated the synthesis by renal cells of the same collagens but this effect was less evident compared to renal albumin. These findings demonstrate that renal albumin drastically reduces the synthesis of collagens by mesangial cells and renal fibroblasts, this effect being most evident on those components which constitute the extracellular matrix in glomerulosclerosis and interstitial fibrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracellular matrix formation by epithelial cells from human polycystic kidney cysts in culture

Cells from the cysts of patients with autosomal dominant polycystic kidney disease (PKD) were grown in vitro under standard conditions without the aid of collagen-pretreated surfaces, and both the synthesis and composition of the extracellular matrix were investigated. At confluence, PKD cells presented the typical features of epithelial cells, but showed a different collagen composition from fibroblasts. Compared with normal tubular epithelia (NTE), PKD monolayers produced an excess of extracellular matrix, which accounted for 30% of the total incorporation of [3H] proline, although this value was considerably lower (by a factor of 10) in the case of NTE. Immunohistochemical and electrophoretic techniques revealed a complex collagen composition in the extracellular matrix which included [alpha (III)]3 and collagen IV. However, part of the collagen components remained unidentified in spite of the fact that they exhibited a typical M(r) of alpha 1(I) and alpha 2(I) in the presence of urea. Immunoprecipitation with monospecific antibodies and Northern blotting with specific probes failed to recognize alpha 1(I) and alpha 2(I), but demonstrated their presence in fibroblasts. Purification and cyanogen bromide digestion demonstrated a strong interhomology in fingerprint peptide composition among the uncharacterized collagens synthesized by PKD cells, thus suggesting a common identity. These observations document a markedly augmented production of extracellular matrix by PKD cultured cells in vitro, and show the presence of collagens which do not share homologies with the major collagen molecules. A better characterization of extracellular matrix composition is central to any comprehension of the cytogenetic mechanisms in vivo.

Are the nail-patella syndrome and the autosomal Goltz-like syndrome the phenotypic expressions of different alleles at the COL5A1 locus?

The COL5A1 gene, which encodes the pro alpha 1(V) chain, was recently mapped to 9q34.3 in the same region as the nail-patella locus. This was taken as an indication that the nail-patella syndrome may be an inherited connective tissue disorder. We demonstrate COL5A1 heterozygous deletion and fibroblast under-expression of alpha 1(V) chains in a girl with an unbalanced translocation resulting in 9q32-->qter monosomy. The patient presents dysplastic nails, a sign typical of nail-patella syndrome, but normal patella. Moreover, she has skin and bone disorders similar to those found in the Goltz syndrome. We suggest that monosomy for the COL5A1 gene is responsible for these connective tissue disorders. Accordingly, the nail-patella syndrome could be attributable to mutations inside the COL5A1 gene rather than to a deletion of it.

Progression of chronic adriamycin nephropathy in leukopenic rats

In this study, we examined the progression of chronic Adriamycin (ADR) nephropathy in mild leukopenic rats and tried to define the possible relationship between tubulointerstitial lesions and proteinuria in this model. Chronic ADR nephropathy was induced by 2 doses of ADR (2 mg/kg) in 32 Sprague-Dawley rats. Eight of these were randomly assigned to cyclophosphamide treatment (50 mg/kg), given intravenously every week, to keep the blood leukocyte count constantly lower than 5,000/mm3. Serial parameters were followed for 16 weeks including clearance studies with iothalamate and p-aminohippurate and the analysis of urinary protein composition by: (a) an enzymatic assay for beta-glucosidase; (b) specific ELISA using antibodies against rat albumin and RBP, and finally (c) two-dimensional electrophoresis. ADR-treated rats rapidly (within 2 weeks) developed massive proteinuria which was in constant increment throughout the disease evolution in each single component (i.e., high and low molecular weight proteinuria, enzymuria) and developed renal insufficiency. At week 8, in ADR rats, glomerulosclerosis was mild whereas tubulointerstitial infiltrates predominated, characterized mainly by CD4+ T lymphocytes while CD8+ T lymphocytes were inconspicuous, and macrophages were only occasionally present. All such alterations had worsened after 16 weeks when the tubulointerstitial infiltration was associated with marked interstitial fibrosis and tubular atrophy. Leukopenia induced by cyclophosphamide was in all cases associated with a net amelioration of renal histopathology reducing tubulointerstitial infiltrates (by 40%) and glomerulosclerosis (33 +/- 5 vs. 52.2 +/- 7.5% sclerotic glomeruli) and also ameliorated glomerular filtration indexes (Cl 780 +/- 40 vs. 447 +/- 66 microliters/min/kg-1). In spite of these differences, albuminuria and urinary-retinol-binding protein were comparable at weeks 4, 8 and 16 in this group, while urinary beta-glucosidase was decreased at week 16 (p < 0.001) in cyclophosphamide-treated rats. No other qualitative changes in urinary proteins were detectable by 2-dimensional electrophoresis during the disease development. We concluded that chronic leukopenia prevents interstitial cellular infiltration by lymphocytes, interstitial fibrosis and slows down the decline of renal function typical of chronic ADR nephropathy. Glomerulosclerosis is also reduced in leukopenic rats without any appreciable changes in the urinary excretion of high molecular weight proteins deriving from the glomerulus. Finally, the improvement in tubulointerstitial alteration is associated with the reduction in urinary lysosomal enzymes. Tubulointerstitial alterations are implicated with a prominent role in the progression towards renal failure in chronic ADR glomerulopathy.

Mapping of the human COL5A1 gene to chromosome 9q34.3

A 353-bp region encoding for the NH2 terminus of the noncollagenic part of the alpha 1(V) chain was amplified by the polymerase chain reaction (PCR), subcloned and sequenced. The subcloned PCR product (pGC1) presented the same nucleotide sequence as the original fragment from the published sequence of COL5A1. In situ hybridization, using pGC1 as a probe, mapped the COL5A1 gene to chromosome 9q34.3. This assignment shows that COL5A1 is not synthetic with COL5A2, which is localized together with other collagen genes on chromosome 2.

Multiple mechanisms for doxorubicin cytotoxicity on glomerular epithelial cells 'in vitro'

This study was planned to define the metabolic pathways for free radical production by isolated glomeruli and glomerular epithelial cells in vitro after exposure to cytotoxic doses of doxorubicin. A net increment in glomerular superoxide anion (O2.) synthesis was observed at doxorubicin doses between 10 and 30 micrograms/ml, a drug level which also induced a parallel increment in uric acid synthesis. Since the synthesis of O2. with production of uric acid implies an activity of xanthine oxidase, a few experiments were performed with glomeruli which had been deprived of xanthine oxidase activity. In this case doxorubicin-inducible O2. and uric acid synthesis by glomeruli was practically nil. A similar stimulatory effect of O2. synthesis was induced by doxorubicin on glomerular epithelial cells and also in this case O2. synthesis was suppressed by pre-treating cells with deoxyconformicin, a selective inhibitor of adenosine deaminase. Finally, equimolar amounts of the drug were equally cytotoxic even when kept constantly outside the cell by a stable linkage with an agarose macroporous bed. In summary, these data demonstrate that O2. is generated by isolated glomeruli and glomerular epithelial cells 'in vitro' when exposed to cytotoxic amounts of doxorubicin and that purine degradation to uric acid furnish the metabolic pathways for glomerular O2. generation. However, doxorubicin is comparably cytotoxic on glomerular epithelial cells from outside cells thus suggesting that also a membrane perturbation may activate the series of events leading to cell injury.

Urinary excretion of brush border antigens and other proteins in children with vesico-ureteric reflux

This study was designed to evaluate the occurrence and the type of proteinuria in 82 children with vesico-ureteric reflux (VUR) with or without renal scars. The urinary excretion of the high molecular weight protein albumin was taken as an index of glomerular alterations and the excretion of retinol-binding protein (RBP), beta 2-microglobulin and brush border antigens (BBA) (measured by monoclonal antibody-based enzyme-linked immunosorbent assay) was taken as an index of tubular alterations. All such markers were increased in children with VUR and were related to the degree of renal function. Patients showing reduced creatinine clearance had very high levels of albuminuria, microproteinuria and BBA, with all these variables reciprocally correlated. In children with normal renal function however, only microproteins (not albumin or BBA) were slightly increased, thus indicating an isolated tubular defect without involvement of the proximal segment of the tubule. However, microprotein excretion did not correlate with the grade of scarring (99mtechnetium-dimercaptosuccinic acid scan), both RBP and beta 2-microglobulin excretion being normal in 75% of children with radioisotopic signs of renal lesions but increased in 17% of children without scars. Therefore, tubular proteinuria identifies different groups of children with VUR but is not related to renal scarring. Prospective studies will define the usefulness of proteinuria as a reliable indicator of renal outcome.

Modulation of proteinuria and renal xanthine oxidase activity by dietary proteins in acute adriamycin nephrosis in rats: lack of correlation with intra- and extracellular amino acids

Protein restriction ameliorates proteinuria in acute adriamycin (ADR) nephrosis and decreases the renal levels of xanthine oxidase (XO), a putative mediator of ADR nephrotoxicity. Hypothetically, the effect of protein restriction on renal XO levels may be due to variations in plasma and tissue proteic amino acids (AA). To elucidate this point, the levels of AA in plasma and in renal homogenates were determined in rats with ADR nephrosis and fed diets with different protein contents: (a) high (35%) casein; (b) standard (21%) casein; (c) low (9%) casein; (d) low casein plus a synthetic mixture of Val, Leu and Ile. The protein content of the diet determined certain marked variations in plasma AA: high levels of Val, Leu and Ile were found in rats fed on a high protein diet, while the same AA were low, in rats on low protein regimen. Supplementation of the low protein diet with a synthetic mixture of branched-chain AA (Val, Leu and Ile) normalized the plasma levels of these AA. In spite of these changes, tissue AA were similar in all groups, regardless of the protein contents of the diets. Furthermore, the levels of renal XO and proteinuria were unrelated to variations in plasma AA, since both parameters were low in protein-restricted and protein-restricted AA-supplemented rats while high in rats fed a high or normoproteic diet. These data demonstrate that low protein diets induce marked alterations in plasma AA composition which are similar in may respects to those found in protein malnutrition.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytotoxic effect of adriamycin and agarose-coupled adriamycin on glomerular epithelial cells: role of free radicals

It has been suggested that the generation of toxic radicals plays an important role in toxicity by Adriamycin (ADR) on cancer cell lines and in vivo. We have examined the role of free radicals in determining toxicity and resistance to ADR of rat glomerular epithelial cells in culture; this method provides a good model for analyzing the mechanisms responsible for ADR experimental nephrosis in rats. Three points were established: a) the intra- or extracellular site of ADR toxicity; b) the role of the superoxide anion and of the hydroxyl radical in determining intra- and -extracellular cytotoxicity; and c) the implication of oxido-reduction cycling as a potential route for ADR semiquinone transformation. Free ADR was found to induce the same inhibition of [3H]thymidine incorporation into DNA as ADR bound to an agarose macroporous bed which prevents the intracellular incorporation of the drug. Specific scavenging of free radical activity by the enzymes catalase and superoxide dismutase, the hydroxyl radical inhibitors dimethyl sulfoxide and dimethylthiourea (DMTU) and by chelation of intracellular free iron with deferoxamine produced only a partial restoration of [3H]thymidine incorporation into DNA, which was maximal for DMTU (30% of normal incorporation). DMTU treatment was unsuccessful in preventing the extracellular cytostatic effect of ADR. Finally, glomerular epithelial cell killing (51Cr-release method) by 5-iminodaunorubicin, an ADR analogue with a modified quinone function that prohibits oxido-reduction cycling, was higher than unmodified ADR. These results indicate that ADR may exert its cytotoxic effects on glomerular epithelial cells by interaction at the cell surface, whereas the intracellular compartment, principally DNA, does not seen to be the target of ADR effects. They also suggest that the free radicals are in part responsible for ADR intracellular cytotoxicity, but other mechanisms should also be hypothesized. Finally, the participation of the ADR semiquinone radical in oxido-reduction cycling seems not important for the induction of the cellular damage.

Puromycin aminonucleoside metabolism by glomeruli and glomerular epithelial cells in vitro

Two puromycin aminonucleoside (PAN) excretion products were purified by HPLC from urine of PAN-treated rats and characterized by nuclear magnetic resonance as N6-dimethyl-3'amino-3'deoxyadenosine (DA-Ado) and N6-methyl-3'amino-3'deoxyadenosine (MA-Ado), respectively, the former corresponding to unmodified PAN. DA-Ado was not a substrate for adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP) or xanthine oxidase (XO), while MA-Ado was consecutively converted into hypoxanthine by a mixture of ADA and PNP. A different rate of transformation of DA-Ado and MA-Ado into hypoxanthine by isolated glomeruli was observed and was higher for the monomethylated analogue by a factor of 3 (79% vs. 21%); this was ascribed to the rate-limiting level of a demethylase activity acting on DA-Ado. Furthermore, DA-Ado was not transformed by glomerular epithelial cells in culture, while a little amount of MA-Ado was converted into hypoxanthine after six hours of incubation. In spite of this different metabolic behavior, the same order of cytotoxicity on glomerular epithelial cells in culture was observed for MA-Ado, DA-Ado and commercial PAN. All these molecules induced a dose response inhibition of [3H]thymidine incorporation into DNA after exposure for two hours and a marked alteration of cell viability which was not inhibited by free radical scavengers and deferoxamine. This study provides the first evidence for a glomerular metabolism of PAN and its urinary metabolite MA-Ado involving their transformation via the purine cycle enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between cationic dyes and erythrocyte membranes in minimal change nephropathy: an electrophoretic approach

A study was undertaken to clarify the usefulness of two cationic dyes, alcian blue (AB) and ruthenium red (RR) in demonstrating the defect in cellular membranes noted in minimal change nephropathy (MCN). The binding of both dyes to RBC membranes purified from normal and nephrotic children was evaluated by electrophoretic titration curves. When examined separately, AB was found to precipitate spontaneously, producing macro-aggregates with no electrophoretic mobility at pH 5. This was presumed to be the result of hydrophobic interaction of the dye with itself. The same phenomenon was observed when this dye was incubated at 37 degrees C with RBC ghost's from normal children, when AB presented a sigmoidal curve with a net positive charge for pHs higher than 5.5 and lower than 5 and no electrophoretic mobility at pH 5. However, incubation of AB with RBC ghosts from children with MCN resulted in an improvement of the solubility of the dye which then migrated with a net positive charge along the whole gradient of pH from 3.5 to 9. The presence of zwitterionic neutral detergents such as CHAPS, but not of a charged substance such as protamine sulphate, inhibited precipitation at pH 5 when incubated with membranes from normal children, supporting the hydrophobic nature of the phenomenon. When RR was used instead of AB, it was fully protonated (i.e. did not precipitate) when analysed alone, but when incubated with normal RBC ghosts, it also revealed no electrophoretic mobility at pH 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary protein restriction on renal purines and purine-metabolizing enzymes in adriamycin nephrosis in rats: a mechanism for protection against acute proteinuria involving xanthine oxidase inhibition

1. A low protein diet prevents the development of proteinuria and glomerular damage in adriamycin experimental nephrosis without affecting renal haemodynamics. In this study the hypothesis was tested as to whether protein restriction is able to modulate the purine metabolic cycle and related enzymes such as xanthine oxidase, one of the putative effectors of adriamycin nephrotoxicity. 2. Renal activities of xanthine oxidase and purine nucleoside phosphorylase were markedly depressed in adriamycin-treated rats fed a 9% casein (low protein) diet compared with the group fed a 22% casein (normal protein) diet both 1 day after adriamycin administration and at the time of appearance of heavy proteinuria (day 15), whereas the activity of renal adenosine deaminase was unchanged. 3. The concentrations of the metabolic substrates of xanthine oxidase, i.e. hypoxanthine and xanthine, were constantly lower in renal homogenates of rats fed a low protein diet compared with those on a normal protein diet. In urine, uric acid, the product of hypoxanthine-xanthine transformation, was lower 1 day after adriamycin injection in protein-restricted rats compared with the group on a normal protein diet which showed a marked increase in its excretion. At the same time, the urinary efflux of adenosine 5'-monophosphate, which is the precursor nucleotide of the above-mentioned nucleosides and bases, was very high in rats fed a low protein diet, whereas it was absent in the group on a normal protein diet. 4. The progressive increment in proteinuria of glomerular origin (i.e. increased excretion of albumin and transferrin) typical of adriamycin-treated rats fed a normal protein diet was inhibited in the protein-restricted animals, which were normoproteinuric on day 10 and were only slightly proteinuric on day 15. 5. Like protein restriction, the pharmacological suppression of renal xanthine oxidase by dietary tungstate and the scavenging by dimethylthiourea of the putative free radical deriving from the action of xanthine oxidase, were associated with a similar (quantitative and qualitative) inhibition of glomerular proteinuria. 6. These data demonstrate that dietary protein restriction is associated with a block in purine metabolism within the kidney due to a marked reduction in the activities of two main enzymes of the cycle, i.e. purine nucleoside phosphorylase and xanthine oxidase, the latter being a putative effector of adriamycin nephrotoxicity. The partial reduction of proteinuria induced by a low protein diet is quantitatively and qualitatively comparable with the reduction induced by the specific block of renal xanthine oxidase or by the scavenging of OH.deriving from hypoxanthine and xanthine transformation.(ABSTRACT TRUNCATED AT 400 WORDS)

Purification of proteinase-free collagenase from commercial batches of the enzyme

A method is described for purifying a collagenase fraction from commercial batches of the enzyme, which is free of proteolytic effects. The method, which is based on preparative electrophoresis in discontinuous buffers followed by electroelution, enables the separation and purification of 6 collagenase fractions with a good recovery of the protein (approximately 80%). Proteinase activity was a peculiarity of the low molecular weight components whereas one high MW fraction (C2) had maximal collagenase activity but was free from aspecific proteolytic effects. Only this collagenase should be employed for molecular studies on the collagen composition of the basement membrane.

Urinary excretion of brush-border antigen and plasma proteins in early stages of diabetic nephropathy

In 109 patients with insulin-dependent diabetes mellitus (IDDM), we measured the urinary excretion of albumin, the low molecular weight proteins (LMWP) retinol-binding protein (RBP) and beta 2-microglobulin (beta 2m), and brush-border antigens (BBA) revealed by monoclonal antibodies. All such markers of kidney damage and/or dysfunction were higher in diabetic patients than in 44 controls. Increased urinary levels of BBA (p = 0.0001) were associated with higher values of albumin (p = 0.0002), RBP (p = 0.0005) and, to a lesser extent, of beta 2m (p = 0.1), different combinations of values above the reference limits being observed. Some 30 and 40% of patients with and without microalbuminuria, respectively, also exhibited signs of tubulopathy. Although under certain circumstances tubular defects may give rise to small increases in albuminuria, the most likely explanation for our findings is the coexistence of glomerular and tubular damage in some patients with IDDM. Neither the prognostic value nor the pathophysiological meaning of tubular damage and/or dysfunction can be assessed by the present study, owing to its cross-sectional design. Tubular markers thus deserve further studies to clarify whether in diabetic patients they indicate a more severe or diffuse kidney impairment.

Hypertension and renal selectivity properties in diabetic microalbuminuria

The renal selectivity properties towards albumin were evaluated in ten diabetic patients with arterial hypertension before and after the pharmacological normalisation of blood pressure, and were compared to 12 subjects with essential hypertension. While all patients of the control group were normoalbuminuric during hypertension, six of the diabetic group were microalbuminuric when hypertensive and became almost normoalbuminuric after blood pressure pharmacological control. All microalbuminuric diabetic patients presented altered properties of renal selectivity as epitomised by a non-preferential urinary excretion of glycosyl albumin (GA) (urinary GA/serum GA less than or equal to 1). At variance the selectivity properties were normal in normoalbuminuric diabetic patients and in essential hypertension. It was concluded that in diabetes mellitus arterial hypertension is associated with microalbuminuria when the renal properties of selectivity are altered, but does not implicate any proteinuric effect in those cases where the GBM function is preserved.

Low-protein diet and xanthine-metabolising enzymes in adriamycin nephrosis

Proteinuria and renal xanthine metabolising enzymes, xanthine oxidase and xanthine dehydrogenase, were evaluated in Adriamycin-treated rats fed standard (21% casein) and low-protein (6% casein) diets. In rats fed a standard diet Adriamycin was associated with increased activities in the kidney of xanthine oxidase and xanthine dehydrogenase and induced massive proteinuria. The pharmacological block of both enzymes by allopurinol and tungsten block of both enzymes by allopurinol and tungsten reduced proteinuria to one-third of the original levels. Rats fed a low-protein diet presented decreased levels of renal xanthine oxidase and xanthine dehydrogenase and were only slightly proteinuric. Finally, rats shifted from a low-protein diet to a normal one developed massive proteinuria in spite of normal or slightly decreased levels of renal xanthine oxidase and xanthine dehydrogenase. We conclude that a low-protein diet is effective in decreasing the levels of xanthine metabolising enzymes that are in part responsible for the renal damage due to Adriamycin. This is not however the unique mechanism by which the low-protein diet protects against the development of proteinuria in Adriamycin nephrosis; other factors must also be hypothesised.

Tubular epithelium culture from nephronophthisis-affected kidneys: a new approach to molecular disorders of tubular cells

Abnormalities of tubular membrane structure and composition have been proposed as the primary defect in nephronophthisis (NEF). In order to characterize the protein composition of tubular cells in NEF, in vitro methods were developed to culture and propagate tubular cells obtained from biopsy fragments. Accordingly, microdissected cortical slices (1 x 3 mm) were first digested with collagenase and DNAse and then grown in RPMI medium supplemented with 10% NU serum and conditioned serum deriving from 3T3 cultures. At confluence, cultured cells from NEF showed characteristics which were typical of normal tubules, i.e. presence of cytokeratin and positivity for succinic dehydrogenase and alkaline phosphatase stainings, and presented no morphological alterations compared to cultured cells from normal tubular epithelium. Moreover, no difference was observed for fibronectin, collagen IV and laminin stains. Analysis by two-dimensional electrophoresis of cellular extracts revealed several changes in protein composition of NEF, the main one being the decrease in NEF cells of a polypeptide with a molecular weight of 120 kD and a pI of 4.8; this polypeptide was a constant finding in normal kidneys. These observations demonstrated that human tubular epithelial cells can be successfully cultured from very small biopsy fragments, which represents a new approach to the study of molecular disorders involving tubular cells in inherited disease. Cultured cells from NEF maintain the same morphological, immunological and cytochemical characteristics as normal tubular cells, but present a few alterations in polypeptide composition which may have pathogenetic relevance. A more careful analysis of these alterations is needed to define the molecular disorder(s) involving the tubule in NEF.

Endogenous albumin as a marker of renal selectivity in steroid-unresponsive nephrotic syndrome

Albumin electrical charge, conformation and hydrophobicity taken as indexes of renal selectivity were evaluated in 8 children affected by steroid-unresponsive nephrotic syndrome associated with glomerulosclerosis or mesangial hypercellularity. These characteristics related to urinary albumin have already been reported to vary markedly in steroid-responsive nephrotic syndrome of minimal-change nephropathy giving rise to new pathogenetic possibilities in this disease. In the steroid-unresponsive nephrotic children albumin was found to be more microheterogenous and cationic in urine than in serum and at the same time it was conformationally altered. Regarding these characteristics, the selectivity properties of the renal filter are similar in steroid-unresponsive nephrotic syndrome, suggesting a pathogenetic connection between these two renal disorders.

Peroxidative damage of the erythrocyte membrane in children with nephrotic syndrome

The structural composition of erythrocyte ghosts was analysed in children affected by steroid-responsive (SRNS) and unresponsive nephrotic syndrome (SUNS). No variation of either intrinsic or extrinsic ghost proteins was found by discontinuous SDS-electrophoresis associated with a very sensitive double staining technique. By contrast, the composition of inner-layer phospholipids--phosphatidyl ethanolamine (PE) and phosphatidyl serine (PS)--was altered in SRNS with minor changes also involving phosphatidic acid, phosphatidyl inositol and lysophosphatidyl choline. Signs of peroxidative damage were present in both SRNS and SUNS ghosts and inside the cells; these included high levels of fluorescent amino-iminopropene derivates of PE and PS, increased intraerythrocytic amounts of malonyldialdehyde and decreased levels of reduced glutathione. Taken together these results support the concept that in SRNS and SUNS erythrocytes are target cells for peroxidative damage. In SRNS peroxidation of membrane lipids results in a marked alteration of the phospholipid composition of erythrocyte ghosts.

Preparative high performance chromatography of a major browning compound derived from lysine and glucose

A major browning compound derived from lysine and glucose was purified by high performance chromatography on a RP8 column after several extractions in methanol plus acetonitrile. This compound was separated by a main contaminant corresponding to unreacted lysine by extracting the aminoacid after its derivatization with ninhydrin.

Reaction of 2-amino-2-deoxy-D-glucose and lysine: isolation and characterization of 2,5-bis(tetrahydroxybutyl)pyrazine

The reaction of 2-amino-2-deoxy-D-glucose with lysine in water under simulated physiological conditions gave several browning products, with characteristic optical (lambda max 340 nm) and fluorescent properties (emission at 430 nm for excitation at 362 nm). The major product was isolated and characterized by mass spectrometry and n.m.r. spectroscopy as 2,5-bis(tetrahydroxybutyl)pyrazine derived by the condensation of two molecules of 2-amino-2-deoxy-D-glucose.

Hydrophobic interaction of alcian blue with soluble and erythrocyte membrane proteins

Alcian Blue (AB), a cationic dye widely employed for monitoring negative surface charge variations on red blood cell (RBC), platelet and glomerular membranes of patients with nephrotic syndromes, was found in fact to aggregate with itself and precipitate in the pH range 7.0-7.8, i.e., at the physiological pH values used for performing the binding assay between the dye and cell surfaces. This aggregation appears to be essentially hydrophobic as it is insensitive to urea but fully prevented in presence of 2% zwitterionic detergent. In addition, AB binds to most RBC membrane proteins solubilized by urea-detergent extraction, again suggesting hydrophobic interaction. AB also interacts with freely soluble proteins such as haemoglobin and myoglobin; such binding is disrupted by ethylurea and/or 2% zwitterionic detergent, typical inhibitors of hydrophobic liaisons. AB also strongly binds to myoglobin with all the negative charges blocked by esterification of the carboxyl groups, again ruling out direct interaction via surface negative charges. It is concluded that AB binding to the RBC surface can hardly monitor variations in surface charge due to sialic acid residues but, at best, variations in surface hydrophobicity.

Characterization of cationic albumin in minimal change nephropathy

The presence of isoalbumins with a less anionic charge than the normal protein (pI = 4.7) is the hallmark of proteinuria in minimal change nephropathy (MCN). Steroid-induced restoration of near normal levels of proteinuria is characterized by the appearance in urines of isoalbumins with a pI still more anionic than the normal. In our search for an explanation for the pI changes, we used preparative isoelectric focusing in granulated gels to split the microheterogeneous bands obtained from nine MCN-affected children into four fractions (A1, A2, A3, A4) with decreasing pI from 5.8 to 4.0 and we have determined their fatty acid content. The least anionic fraction, A1, was the most defatted, followed by A2, A3 and A4 in which fatty acid content progressively increased, A4 being the most fatted fraction. Accordingly, the mean content of fatty acids in urinary albumin in proteinuric children was lower than in both the remission phase and in normal children (2.17 +/- 0.03 vs. 20.91 +/- 0.38 and 20.94 +/- 0.39, respectively) and was lower by a factor of 4 compared to serum albumin in the same phase of the disease (2.17 +/- 0.03 vs. 8.59 +/- 1.64). Among medium and long-chain fatty acids, the ratio between serum and urinary albumin was the highest for linoleic acid (approximately 7), followed by that of oleic acid, palmitic acid and lauric acid. At variance in five other patients affected by non-MCN nephrotic syndrome this ratio was for practically all FAs about 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal selectivity properties towards endogenous albumin in minimal change nephropathy

It is well accepted that the molecular charge and conformation of serum proteins are major determinants of their glomerular filtration, but few studies characterizing the molecular features of circulating proteins in renal diseases are currently available. In 11 children affected by minimal change nephropathy (MCN) we determined the electrical charge and the fluorescence quantum yield of Tyrosine (Tyr) and Tryptophan (Trp) (taken as index of conformation) of serum and urinary albumin before and after steroid-induced remission of proteinuria. In all proteinuric children at the onset of the disease, urinary albumin was formed by one band with an isoelectric point (pI) of 4.7 (pI of the native protein), and by numerous other, less anionic bands with pIs between 4.8 and 5.5 accounting for about 50% of the total amount of this protein. The normalization of proteinuria which followed steroid therapy was characterized by the disappearance in urines of the less anionic fraction and by the appearance of numerous isoforms with a pI still more anionic (pI less than 4.7) than normal. At the same time, in the proteinuric phase, the fluorescence quantum yield of Trp of urinary albumin was markedly quenched, returning to near normal levels after steroid-induced remission of proteinuria. These data indicate that in MCN the charge-dependent renal selectivity properties are partially maintained and that the less anionic isoforms of albumin are a main component of urinary albumin. Together with the electrical charge, the conformation of albumin as a major determinant of its urinary excretion in MCN must also be considered.

Reactivity with diazonium salts of albumin from micro and macroalbuminuric diabetic patients

A recent theory of the pathogenesis of diabetic microalbuminuria points to an involvement of glycated albumin, which has been demonstrated as being able to fluetrate the renal filter. The chemical characterization of urinary albumin, initially performed on the electrical charge and conformation of the protein has now been extended to the affinity properties for specific chemical probes. In this context, urinary albumin from Albustix-negative diabetic patients was found to be highly reactive towards diazonium salts (a dye specific for pyrrole rings) while the same protein purified from macroproteinuric diabetics showed no difference in reactivity towards diazonium salts compared to serum or normal albumin. These data indicate that, beside being highly anionic and conformationally deranged, urinary albumin in conditions of normal renal selectivity contains pyrrole structures. The reasons for considering this reactivity as an indirect sign of rearranged structure are presented here.