Protective Role of the M-Sec-Tunneling Nanotube System in Podocytes

BACKGROUND

Podocyte dysfunction and loss are major determinants in the development of proteinuria. FSGS is one of the most common causes of proteinuria, but the mechanisms leading to podocyte injury or conferring protection against FSGS remain poorly understood. The cytosolic protein M-Sec has been involved in the formation of tunneling nanotubes (TNTs), membrane channels that transiently connect cells and allow intercellular organelle transfer. Whether podocytes express M-Sec is unknown and the potential relevance of the M-Sec-TNT system in FSGS has not been explored.

METHODS

We studied the role of the M-Sec-TNT system in cultured podocytes exposed to Adriamycin and in BALB/c M-Sec knockout mice. We also assessed M-Sec expression in both kidney biopsies from patients with FSGS and in experimental FSGS (Adriamycin-induced nephropathy).

RESULTS

Podocytes can form TNTs in a M-Sec-dependent manner. Consistent with the notion that the M-Sec-TNT system is cytoprotective, podocytes overexpressed M-Sec in both human and experimental FSGS. Moreover, M-Sec deletion resulted in podocyte injury, with mitochondrial abnormalities and development of progressive FSGS. In vitro, M-Sec deletion abolished TNT-mediated mitochondria transfer between podocytes and altered mitochondrial bioenergetics. Re-expression of M-Sec reestablishes TNT formation and mitochondria exchange, rescued mitochondrial function, and partially reverted podocyte injury.

CONCLUSIONS

These findings indicate that the M-Sec-TNT system plays an important protective role in the glomeruli by rescuing podocytes via mitochondrial horizontal transfer. M-Sec may represent a promising therapeutic target in FSGS, and evidence that podocytes can be rescued via TNT-mediated horizontal transfer may open new avenues of research.

Increased serum uric acid levels are associated to renal arteriolopathy and predict poor outcome in IgA nephropathy

BACKGROUND AND AIMS

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide and a leading cause of end stage renal disease (ESRD). In addition to classical progression factors, other atherosclerosis-related factors, including hyperuricemia (HU), have been associated to the renal progression of IgAN. Increased serum uric acid (SUA) levels are well known to be concomitant of cardiovascular and kidney diseases, and have been proposed to be implicated in the development of arteriolar damage (AD). The aim of the present study was to explore the correlation between SUA levels, renal damage and its implication for outcome in IgAN patients.

METHODS AND RESULTS

Clinical, laboratory and histologic data of 145 patients with biopsy proven IgAN were collected and retrospectively analyzed to determine the correlation between SUA levels, renal damage and the primary outcome (death or ESRD). Biopsy-proven AD was defined by the presence of arteriolar hyalinosis and/or intimal thickening. HU, defined as the highest SUA gender-specific tertile, was >7.7 mg/dl for males and >6.2 mg/dl for females. The prevalence of AD increased with the increase in the SUA level tertiles (p = 0.02). At logistic regression analysis SUA was independently related to the presence of AD (OR 1.75 [95%CI 1.10-2.93], p = 0.03). HU and AD had a synergic impact on progression of IgAN. Patients having both AD and HU, showed a reduced survival free from the primary outcome as compared to those having only one risk factor or neither (p = 0.01).

CONCLUSIONS

SUA levels are independently associated with AD and poor prognosis in patients with IgAN.

P0010INCREASED SERUM URIC ACID LEVELS ARE ASSOCIATED TO RENAL ARTERIOLOPATHY AND PREDICT POOR OUTCOME IN IGA NEPHROPATHY

Background and Aims

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide and a leading cause of End Stage Renal Disease (ESRD). In addition to the classical progression factors, including hypertension, proteinuria, and decreased renal function, other atherosclerosis-related factors, such as hypertriglyceridemia, have been reported to the renal progression of IgAN. Above all, many studies have indicated an association between hyperuricemia and progression of IgAN. Increased serum uric acid (SUA) levels are also well known to be associated with hypertension, endothelial dysfunction and development of cardiovascular and kidney diseases both in general population and high-risk patients. Previous studies suggested that uric acid induces proliferation of vascular smooth muscle cells, activates the renin–angiotensin–aldosterone system (RAAS) and also reduces the synthesis of nitric oxide. Furthermore, there is evidence that uric acid can promote the oxygenation of low-density lipoproteins (LDL) and increase the production of free oxygen radicals, increasing inflammation and oxidative stress.

In consequence of these processes, SUA might specifically promote atherosclerosis and arteriolar damage, possibly playing a major role in pathogenesis and progression of IgAN.

The aim of the present study was to explore the correlation between SUA levels, renal damage and its implication for renal outcome and all cause death in IgAN patients.

Method

The data for clinical features, laboratory and renal pathological examination were collected from 145 renal biopsy-proven IgAN patients and were retrospectively analyzed to determine the correlation between SUA levels, renal damage and overall outcome. Hyperuricemia (HU) was defined as the highest SUA gender-specific tertile. Biopsy-proven arteriolar damage was defined by the presence of arteriolar hyalinosis or intimal thickening. The primary outcome was death or ESRD.

Results

The mean baseline serum uric acid levels of the 42 female and 103 male patients at the time of kidney biopsy were 5.4 ±1.7 and 7.2 ±1.8 mg/dL, respectively. HU was >7.7 mg/dl for males and > 6.2 mg/dl for females.

Patients were stratified on the basis of baseline gender-specific SUA level tertiles. Clinical and histologic characteristics are described in table 1.

The higher the gender-specific SUA tertile, the greater the prevalence of arteriolar damage (p=0.02). No other histologic feature was significantly correlated with uric acid levels, therefore we analyzed laboratory and clinical characteristics on the basis of the presence/absence of biopsy-proven arteriolar damage (Table 2).

At logistic regression analyses SUA was associated with arteriolar damage at univariate (OR 1.45 CI [1.12-1.87], p=0.004) and multivariate analyses (OR 1.75 CI [1.10-2.93], p=0.03), recorded in Table 3.

Receiver Operating Curve (ROC) was performed and the sensitivity and specificity of SUA for predicting arteriolar damage were showed in Figure 1. The area under the ROC curve was 0.67 (IC95% 0.61 to 0.73) indicating that SUA is a fair test for detecting arteriolar damage.

Patients with arteriolar damage had a worst outcome compared to patients without it (Kaplan Maier survival analysis, log rank test p=0.002, Figure 2a). HU and arteriolar damage had a synergic impact on progression of IgAN. Patients having both arteriolar damage and HU, showed a reduced survival free from the primary outcome as compared to those having only one risk factor or neither (log rank test p=0.003, Figure 2b).

Conclusion

SUA levels are directly associated with arteriolar damage and poor prognosis in patients with IgAN. Our study suggests the presence of higher SUA levels in IgAN patients identifies a sub-population at increased risk of progressing to ESRD or death, for whom a particular surveillance is warranted, possibly because of the pathogenetic role of SUA on arteriolar damage.

Enhanced myostatin expression and signalling promote tubulointerstitial inflammation in diabetic nephropathy

Myostatin (MSTN), a family member of the transforming growth factor (TGF)-β super family, has been detected in the tubuli of pig kidney, but its role in the human kidney is not known. In this study we observed upregulation of MSTN mRNA (~8 to 10-fold increase) both in the glomeruli and tubulointerstitium in diabetic nephropathy (DN). In DN, immunoreactive MSTN was mainly localized in the tubuli and interstitium (∼4-8 fold increase), where it colocalized in CD45⁺ cells. MSTN was also upregulated in the glomeruli and the arterial vessels. Tubulointerstitial MSTN expression was directly related to interstitial fibrosis (r = 0.54, p < 0.01). In HK-2 tubular epithelial cells, both high (30 mmol) glucose and glycated albumin upregulated MSTN mRNA and its protein (p < 0.05-0.01). MSTN-treated HK-2 cells underwent decreased proliferation, together with NF-kB activation and CCL-2 and SMAD 2,3 overexpression. In addition, MSTN induced intracellular ROS release and upregulated NADPH oxidase, effects which were mediated by ERK activation. In conclusion, our data show that MSTN is expressed in the human kidney and overexpressed in DN, mainly in the tubulointerstitial compartment. Our results also show that MSTN is a strong inducer of proximal tubule activation and suggest that MSTN overexpression contributes to kidney interstitial fibrosis in DN.

Cellular Senescence Is Associated with Faster Progression of Focal Segmental Glomerulosclerosis

BACKGROUND

A current, albeit unproven, hypothesis is that an acceleration of cellular senescence is involved in impaired renal repair and progression of glomerular diseases. Focal segmental glomerulosclerosis (FSGS) is a glomerular disease with a substantial risk for progression to ESRD. However, if and to what extent cell senescence predicts a negative outcome in FSGS is still unknown.

METHODS

The hypothesis that cell senescence represents a proximate mechanism by which the kidney is damaged in FSGS (NOS phenotype) was investigated in 26 consecutive kidney biopsies from adult FSGS cases (eGFR 72 ± 4 mL/min, proteinuria 2.3 ± 0.6 g/day) who were incident for 2 years in a Northern Italian nephrology center and had a 6-year clinical follow-up.

RESULTS

Cell senescence (p16INK4A, SA-β-galactosidase [SA-β-Gal]) was upregulated by ∼3- to 4-fold in both glomerular and tubular cells in kidney biopsies of FSGS as compared to age-matched controls (p < 0.05-0.01). Tubular SA-β-Gal correlated with proteinuria and glomerulosclerosis, while only as a trend, tubular p16INK4A was directly associated with interstitial fibrosis. At univariate analysis, basal eGFR, proteinuria, and tubular expression of SA-β-Gal and p16INK4A were significantly directly related to the annual loss of eGFR. No correlation was observed between glomerular p16INK4A and eGFR loss. However, at multivariate analysis, eGFR, proteinuria, and tubular p16INK4A, but not SA-β-Gal, contributed significantly to the prediction of eGFR loss.

CONCLUSIONS

The results indicate that an elevated cell senescence rate, expressed by an upregulation of p16INK4A in tubules at the time of initial biopsy, represents an independent predictor of progression to ESRD in adult patients with FSGS.

Protective role of cannabinoid receptor type 2 in a mouse model of diabetic nephropathy

OBJECTIVE

The cannabinoid receptor type 2 (CB2) has protective effects in chronic degenerative diseases. Our aim was to assess the potential relevance of the CB2 receptor in both human and experimental diabetic nephropathy (DN).

RESEARCH DESIGN AND METHODS

CB2 expression was studied in kidney biopsies from patients with advanced DN, in early experimental diabetes, and in cultured podocytes. Levels of endocannabinoids and related enzymes were measured in the renal cortex from diabetic mice. To assess the functional role of CB2, streptozotocin-induced diabetic mice were treated for 14 weeks with AM1241, a selective CB2 agonist. In these animals, we studied albuminuria, renal function, expression of podocyte proteins (nephrin and zonula occludens-1), and markers of both fibrosis (fibronectin and transforming growth factor-β1) and inflammation (monocyte chemoattractant protein-1 [MCP-1], CC chemokine receptor 2 [CCR2], and monocyte markers). CB2 signaling was assessed in cultured podocytes.

RESULTS

Podocytes express the CB2 receptor both in vitro and in vivo. CB2 was downregulated in kidney biopsies from patients with advanced DN, and renal levels of the CB2 ligand 2-arachidonoylglycerol were reduced in diabetic mice, suggesting impaired CB2 regulation. In experimental diabetes, AM1241 ameliorated albuminuria, podocyte protein downregulation, and glomerular monocyte infiltration, without affecting early markers of fibrosis. In addition, AM1241 reduced CCR2 expression in both renal cortex and cultured podocytes, suggesting that CB2 activation may interfere with the deleterious effects of MCP-1 signaling.

CONCLUSIONS

The CB2 receptor is expressed by podocytes, and in experimental diabetes, CB2 activation ameliorates both albuminuria and podocyte protein loss, suggesting a protective effect of signaling through CB2 in DN.

Effect of the monocyte chemoattractant protein-1/CC chemokine receptor 2 system on nephrin expression in streptozotocin-treated mice and human cultured podocytes

OBJECTIVE

Monocyte chemoattractant protein-1 (MCP-1), a chemokine binding to the CC chemokine receptor 2 (CCR2) and promoting monocyte infiltration, has been implicated in the pathogenesis of diabetic nephropathy. To assess the potential relevance of the MCP-1/CCR2 system in the pathogenesis of diabetic proteinuria, we studied in vitro if MCP-1 binding to the CCR2 receptor modulates nephrin expression in cultured podocytes. Moreover, we investigated in vivo if glomerular CCR2 expression is altered in kidney biopsies from patients with diabetic nephropathy and whether lack of MCP-1 affects proteinuria and expression of nephrin in experimental diabetes.

RESEARCH DESIGN AND METHODS

Expression of nephrin was assessed in human podocytes exposed to rh-MCP-1 by immunofluorescence and real-time PCR. Glomerular CCR2 expression was studied in 10 kidney sections from patients with overt nephropathy and eight control subjects by immunohistochemistry. Both wild-type and MCP-1 knockout mice were made diabetic with streptozotocin. Ten weeks after the onset of diabetes, albuminuria and expression of nephrin, synaptopodin, and zonula occludens-1 were examined by immunofluorescence and immunoblotting.

RESULTS

In human podocytes, MCP-1 binding to the CCR2 receptor induced a significant reduction in nephrin both mRNA and protein expression via a Rho-dependent mechanism. The MCP-1 receptor, CCR2, was overexpressed in the glomerular podocytes of patients with overt nephropathy. In experimental diabetes, MCP-1 was overexpressed within the glomeruli and the absence of MCP-1 reduced both albuminuria and downregulation of nephrin and synaptopodin.

CONCLUSIONS

These findings suggest that the MCP-1/CCR2 system may be relevant in the pathogenesis of proteinuria in diabetes.

The monocyte chemoattractant protein-1/cognate CC chemokine receptor 2 system affects cell motility in cultured human podocytes

In crescentic glomerulonephritis (GN), monocyte chemoattractant protein-1 (MCP-1) is overexpressed within the glomeruli, and MCP-1 blockade has renoprotective effects. Adult podocytes are in a quiescent state, but acquisition of a migratory/proliferative phenotype has been described in crescentic GN and implicated in crescent formation. The cognate CC chemokine receptor 2 (CCR2), the MCP-1 receptor, is expressed by other cell types besides monocytes and has been implicated in both cell proliferation and migration. We investigated whether MCP-1 binding to CCR2 can induce a migratory/proliferative response in cultured podocytes. MCP-1 binding to CCR2 enhanced podocyte chemotaxis/haptotaxis in a concentration-dependent manner and had a modest effect on cell proliferation. Closure of a wounded podocyte monolayer was delayed by CCR2 blockade, and CCR2 was overexpressed at the wound edge, suggesting a role for CCR2 in driving podocyte migration. Immunohistochemical analysis of kidney biopsies from patients with crescentic GN demonstrated CCR2 expression in both podocytes and cellular crescents, confirming the clinical relevance of our in vitro findings. In conclusion, the MCP-1/CCR2 system is functionally active in podocytes and may be implicated in the migratory events triggered by podocyte injury in crescentic GN and other glomerular diseases.

RAGE‐ and TGF‐ β receptor‐mediated signals converge on STAT5 and p21wafto control cell‐cycle progression of mesangial cells: a possible role in the development and progression of diabetic nephropathy

The molecular events associated with acute and chronic exposure of mesangial cells (MC) to hyperglycemia were evaluated. We found that, unlike high glucose (HG) and Amadori adducts, advanced glycation end products (AGE) and transforming growth factor-beta (TGF-beta) induced p21waf expression and accumulation of MC in G0/G1. TGF-beta1 blockade inhibited AGE-mediated collagen production but only partially affected AGE-induced p21waf expression and cell-cycle events, indicating that AGE by binding to AGE receptor (RAGE) per se could control MC growth. Moreover, AGE and TGF-beta treatment led to the activation of the signal transduction and activators of transcription (STAT)5 and the formation of a STAT5/p21SIE2 complex. The role of STAT5 in AGE- and TGF-beta-mediated p21waf expression and growth arrest, but not collagen production, was confirmed by the expression of the dominant negative STAT5 (DeltaSTAT5) or the constitutively activated STAT5 (1*6-STAT5) constructs. Finally, in p21waf-/- fibroblasts both AGE and TGF-beta failed to inhibit cell-cycle progression. A potential in vivo role of these mechanisms was sustained by the increasing immunoreactivity for the activated STAT5 and p21(waf) in kidney biopsies from early to advanced stage of diabetic nephropathy. Our data indicate that AGE- and TGF-beta-mediated signals, by converging on STAT5 activation and p21waf expression, may regulate MC growth.

Nephrin expression is reduced in human diabetic nephropathy: evidence for a distinct role for glycated albumin and angiotensin II

We studied the distribution of nephrin in renal biopsies from 17 patients with diabetes and nephrotic syndrome (7 type 1 and 10 type 2 diabetes), 6 patients with diabetes and microalbuminuria (1 type 1 and 5 type 2 diabetes), and 10 normal subjects. Nephrin expression was semiquantitatively evaluated by measuring immunofluorescence intensity by digital image analysis. We found an extensive reduction of nephrin staining in both type 1 (67 +/- 9%; P < 0.001) and type 2 (65 +/- 10%; P < 0.001) diabetic patients with diabetes and nephrotic syndrome when compared with control subjects. The pattern of staining shifted from punctate/linear distribution to granular. In patients with microalbuminuria, the staining pattern of nephrin also showed granular distribution and reduction intensity of 69% in the patient with type 1 diabetes and of 62 +/- 4% (P < 0.001) in the patients with type 2 diabetes. In vitro studies on human cultured podocytes demonstrated that glycated albumin and angiotensin II reduced nephrin expression. Glycated albumin inhibited nephrin synthesis through the engagement of receptor for advanced glycation end products, whereas angiotensin II acted on cytoskeleton redistribution, inducing the shedding of nephrin. This study indicates that the alteration in nephrin expression is an early event in proteinuric patients with diabetes and suggests that glycated albumin and angiotensin II contribute to nephrin downregulation.

The long pentraxin PTX3 is synthesized in IgA glomerulonephritis and activates mesangial cells

The long pentraxin PTX3 has been recently involved in amplification of the inflammatory reactions and regulation of innate immunity. In the present study we evaluated the expression and role of PTX3 in glomerular inflammation. PTX3 expression was investigated in the IgA, type I membranoproliferative, and diffuse proliferative lupus glomerulonephritis, which are characterized by inflammatory and proliferative lesions mainly driven by resident mesangial cells, and in the membranous glomerulonephritis and the focal segmental glomerular sclerosis, where signs of glomerular inflammation are usually absent. We found an intense staining for PTX3 in the expanded mesangial areas of renal biopsies obtained from patients with IgA glomerulonephritis. The pattern of staining was on glomerular mesangial and endothelial cells. Scattered PTX3-positive cells were also detected in glomeruli of type I membranoproliferative glomerulonephritis. The concomitant expression of CD14 suggests an inflammatory origin of these cells. Normal renal tissue and biopsies from patients with the other glomerular nephropathies studied were mainly negative for PTX3 expression in glomeruli. However, PTX3-positive cells were detected in the interstitium of nephropathies showing inflammatory interstitial injury. In vitro, cultured human mesangial cells synthesized PTX3 when stimulated with TNF-alpha and IgA and exhibited specific binding for recombinant PTX3. Moreover, stimulation with exogenous PTX3 promoted mesangial cell contraction and synthesis of the proinflammatory lipid mediator platelet-activating factor. In conclusion, we provide the first evidence that mesangial cells may both produce and be a target for PTX3. The detection of this long pentraxin in the renal tissue of patients with glomerulonephritis suggests its potential role in the modulation of glomerular and tubular injury.

Nephrin redistribution on podocytes is a potential mechanism for proteinuria in patients with primary acquired nephrotic syndrome

We investigated the distribution of nephrin by immunofluorescence microscopy in renal biopsies of patients with nephrotic syndrome: 13 with membranous glomerulonephritis (GN), 10 with minimal change GN, and seven with focal segmental glomerulosclerosis. As control, six patients with IgA GN without nephrotic syndrome and 10 normal controls were studied. We found an extensive loss of staining for nephrin and a shift from a podocyte-staining pattern to a granular pattern in patients with nephrotic syndrome, irrespective of the primary disease. In membranous GN, nephrin was co-localized with IgG immune deposits. In the attempt to explain these results, we investigated in vitro whether stimuli acting on the cell cytoskeleton, known to be involved in the pathogenesis of GN, may induce redistribution of nephrin on the surface of human cultured podocytes. Aggregated but not disaggregated human IgG(4), plasmalemmal insertion of membrane attack complex of complement, tumor necrosis factor-alpha, and puromycin, induced the shedding of nephrin with a loss of surface expression. This phenomenon was abrogated by cytochalasin and sodium azide. These results suggest that the activation of cell cytoskeleton may modify surface expression of nephrin allowing a dislocation from plasma membrane to an extracellular site.

alpha 1-Antitrypsin (AAT) deficiency and ANCA-positive systemic vasculitis: genetic and clinical implications

A high incidence of alpha 1-antitrypsin (AAT) deficiency has been reported in patients with C-ANCA systemic vasculitis in association with antibodies against proteinase-3 (PR3). To clarify the role of AAT deficiency in the acute vasculitic process as well as in progression of the disease, we studied 84 patients with either C-ANCA or P-ANCA vasculitis with special reference to: (a) the AAT gene, (b) the phenotypic (Pi) variants and (c) the serum levels during both acute illness and remission. The PiZ gene was found in six patients (8% vs. 1.5% controls) irrespective of the type of autoantibodies (C-ANCA vs. P-ANCA). All PiZ patients displayed the ability to raise their AAT serum levels up to the normal range during acute illness. In contrast, 24 patients with the PiM phenotype presented low AAT serum levels during acute illness. In all these patients, the AAT levels returned to normal values during the remission. Low AAT levels were associated with low levels of C-reactive protein (PCR) (P < 0.001), with a less severe renal involvement or a minor risk of death, and, in one tested patient, with a novel point mutation (TCGA-->TCAA) at the enhancer-promoter region of the AAT gene. Low AAT serum levels did not correlate with either type/titre of autoantibody or distribution/severity of the vasculitis process. In the case-control study, high AAT levels emerged as a major determinant of progression towards end-stage renal failure [odds ratio 3 (95% CI 1.1-8.4)]. These results indicate: (a) a high incidence of the PiZ gene of AAT in systemic vasculitis irrespective of the type of autoantibodies; (b) a novel form of AAT deficiency associated with the normal PiM phenotype becoming manifest only during acute illness; (c) dysregulation of the acute-phase response affecting selectively AAT or both AAT and PCR; (d) correlation between low plasma levels of AAT and less severe renal involvement or risk of death.

IgA nephropathy associated with Takayasu's arteritis: report of a case and review of the literature

We report the case of a patient with Takayasu's arteritis, nephrotic syndrome, and pANCA. The kidney biopsy specimen showed the classic features of IgA nephropathy. The course of this patient supports the view that the glomerular and vasculitic involvements of Takayasu's arteritis may result from a common immunologic mechanism, and cases with urinary abnormalities should be carefully followed for the possible coexistence of glomerulonephritis.

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.

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.

Receptor antagonists of platelet-activating factor do not influence the development of passive Heymann nephritis

Heymann nephritis in the rat is a proteinuric condition caused by glomerular lesions similar to those found in human membranous nephritis. In the present study the effect of two different receptor antagonists of platelet-activating factor (PAF) on the course of passive Heymann nephritis was assessed. It was found that rats treated with either antagonist showed the same degree of proteinuria and the same glomerular immunopathological features as untreated rats. Furthermore, at sacrifice, 7 days after the initiation of the disease, the concentration of circulating PAF in treated as well as untreated rats was normal. These results indicate that PAF is not crucial in the pathogenesis of Heymann nephritis.

Effect of chlorpromazine on the development of experimental glomerulonephritis and Arthus reaction

Chlorpromazine blocks antibody-mediated redistribution of cell surface antigens in vitro and in vivo and inhibits the development of passive Heymann glomerulonephritis, a disease characterized by in situ formation of immune complexes (Camussi et al J Immunol 1986, 136:2127-2135). The aim of this study was to establish whether chlorpromazine exerts similar effects in other rat models characterized by in situ formation of immune complexes. In glomerulonephritis induced by antibodies reactive with an exogenous antigen "planted" in glomeruli pretreatment with chlorpromazine prevented formation of "humps" and exudative and proliferative lesions. Likewise, chlorpromazine prevented passive reverse Arthus reaction in the skin. In contrast, the drug was ineffective when these lesions were already established, and also failed to inhibit the fulminant course of nephrotoxic serum glomerulonephritis with an enhanced autologous phase. It is proposed that the antiinflammatory effect of chlorpromazine is due to its ability to block the recruitment of inflammatory cells and the release of inflammatory mediators.

Effect of amino acid ingestion on blood amino acid profile in patients with chronic renal failure

Arterial whole blood levels of amino acids (AA) were determined in patients with chronic renal failure (CRF) and in healthy volunteers before and for 75 min after the ingestion of an AA mixture simulating the AA content of an animal-protein meal. In CRF patients, total AA increased more than in control subjects as a consequence of an exaggerated rise in nonessential AA (+86%), mainly glutamine, proline, glutamate, serine, glycine, and alanine. Total essential AA in patients increased as much as in control subjects; however, threonine and phenylalanine showed greater increases while leucine had a smaller increase. As a consequence of the observed alterations, a striking unbalance in the postprandial pattern of arterial AA ensued in CRF patients. The flow of AA to all the organs is altered during the absorptive phase, which is crucial for body nitrogen-pool replenishment.

Heymann antibodies induce complement-dependent injury of rat glomerular visceral epithelial cells

The aim of this study was to investigate the in vitro role of the complement membrane attack complex (MAC) in the injury induced by nephritogenic anti-brush border vesicle (Fx1A) antibodies on rat glomerular visceral epithelial cells (GEC). Both sheep and rabbit anti-rat brush border vesicle IgG-induced complement-dependent lysis of cultured GEC. Fab fragments of sheep anti-rat brush border vesicles and polyclonal or monoclonal gp330 IgG were devoid of lytic activity. Shedding of cell-surface antigens induced by sheep or rabbit anti-rat brush border vesicle IgG protected GEC from subsequent exposure to lytic antibodies and complement, an effect that was not obtained with Fab fragments. When GEC were incubated with sheep or rabbit anti-rat brush border vesicle IgG in capping conditions, the C3 component was co-redistributed with Heymann immune complexes; in contrast, the MAC remained diffusely bound to the cell surface, indicating that it was not associated with the antigen-antibody complexes. The MAC was demonstrated on the surface of GEC by immunofluorescence staining with anti-MAC neoantigen and by electron microscopy of negatively stained membranes showing focal clusters of 110 A MAC lesions. When GEC were treated with sheep IgG or rabbit IgG plus C6-deficient sera, the cells were not lysed and MAC was not demonstrable on the surface; however, lytic activity was restored when C6-deficient sera were reconstituted with purified C6. The results are consistent with the interpretation that injury induced by Heymann antibodies on GEC is MAC-dependent.

Tumor necrosis factor/cachectin stimulates peritoneal macrophages, polymorphonuclear neutrophils, and vascular endothelial cells to synthesize and release platelet-activating factor

Murine tumor necrosis factor (mTNF) stimulates production of platelet-activating factor (PAF) by cultured rat peritoneal macrophages in amounts comparable to those formed during treatment with the calcium ionophore A23187 or phagocytosis of zymosan. The cell-associated PAF that was released into the medium was identical to synthetic PAF, as determined with physicochemical, chromatographic, and enzymatic assays. Furthermore, de novo synthesis of PAF by macrophages was demonstrated by the incorporation of radioactive precursors such as [3H]acetyl-coenzyme A or [3H]2-lyso-PAF. Macrophages incubated with mTNF for 4 h synthesized PAF only during the first h of treatment. At this time, the amount of cell-associated PAF was approximately equal to that released into the medium. The cell-associated PAF decreased afterwards, whereas that in the medium did not correspondingly increase, suggesting that some PAF was being degraded. The response of rat macrophages to different doses of mTNF and human TNF (hTNF) was examined. Maximal synthesis of PAF was obtained with 10 ng/ml of mTNF and 50 ng/ml of hTNF. This finding may be explained by a lower affinity of hTNF for TNF receptors of rat cells. The hTNF stimulated production of PAF by human vascular endothelial cells cultured from the umbilical cord vein. The time course of PAF synthesis was slower than that observed with macrophages, with maximal production between 4 and 6 h of treatment. Optimal synthesis of PAF was obtained with 10 ng/ml of hTNF. Only 20-30% of the PAF synthesized by endothelial cells was released into the medium, even after several hours of incubation. Synthesis of PAF in response to TNF was also detected in rat polymorphonuclear neutrophils, but not in human tumor cells and dermal fibroblasts. Therefore, production of PAF is a specialized response that is transient in macrophages continuously treated with TNF, and that appears to be controlled by unidentified regulatory mechanisms.

Heymann antibodies induce complement-dependent injury of rat glomerular visceral epithelial cells

The aim of this study was to investigate the in vitro role of the complement membrane attack complex (MAC) in the injury induced by nephritogenic anti-brush border vesicle (Fx1A) antibodies on rat glomerular visceral epithelial cells (GEC). Both sheep and rabbit anti-rat brush border vesicle IgG-induced complement-dependent lysis of cultured GEC. Fab fragments of sheep anti-rat brush border vesicles and polyclonal or monoclonal gp330 IgG were devoid of lytic activity. Shedding of cell-surface antigens induced by sheep or rabbit anti-rat brush border vesicle IgG protected GEC from subsequent exposure to lytic antibodies and complement, an effect that was not obtained with Fab fragments. When GEC were incubated with sheep or rabbit anti-rat brush border vesicle IgG in capping conditions, the C3 component was co-redistributed with Heymann immune complexes; in contrast, the MAC remained diffusely bound to the cell surface, indicating that it was not associated with the antigen-antibody complexes. The MAC was demonstrated on the surface of GEC by immunofluorescence staining with anti-MAC neoantigen and by electron microscopy of negatively stained membranes showing focal clusters of 110 A MAC lesions. When GEC were treated with sheep IgG or rabbit IgG plus C6-deficient sera, the cells were not lysed and MAC was not demonstrable on the surface; however, lytic activity was restored when C6-deficient sera were reconstituted with purified C6. The results are consistent with the interpretation that injury induced by Heymann antibodies on GEC is MAC-dependent.

Immune deposits and immune complex disease

Presence in tissues of immune deposits containing antigens, antibodies and complement is the hallmark of immune complex disease. In the Review the present concepts concerning the pathogenesis of inflammatory injury associated with immune deposits resulting from a local deposition of circulating immune complexes or formed 'in situ' are discussed.

Effects of hemodialysis on guanidinopropionic acid metabolism

Blood levels of guanidinopropionic acid (GPA), a putative uremic toxin, have been evaluated in 5 uremic patients before a dialytic session, at the end of it and during the following 68 h. GPA levels are markedly higher in uremic patients than in controls and are significantly reduced at the end of dialysis even if still higher than in controls. The clearance of GPA is similar to those of urea and creatinine, even if at the end of the dialysis session the percent decrease of GPA is significantly lower than that of urea. During the first 8 h after the end of dialysis GPA levels increase steeply; subsequently, the rate of accumulation of GPA in blood declines markedly remaining constant until the 68th hour. In conclusion GPA is markedly increased in blood of uremic patients and is significantly removed by dialysis. The evaluation of GPA increase per hour after the end of dialysis may provide an estimation of GPA production in uremic patients.