Essential fatty acid deficiency ameliorates acute renal dysfunction in the rat after the administration of the aminonucleoside of puromycin

Vitamin D Receptor/Vitamin D Response Element Directly Modulate Nestin Transcription to Ameliorate PAN-Induced Podocyte Morphological Changes

BACKGROUND

The change of podocyte morphology is a pathologic feature of chronic kidney disease. Several studies have suggested that vitamin D plays a role in the protection of podocytes, but the underlying mechanism remains unclear.

METHODS

The effects of paricalcitol on podocyte injury were tested in a puromycin aminonucleoside (PAN)-induced rat model and cultured mouse podocytes. Proteinuria, podocyte foot process (FP) effacement, and the expression of nestin and vitamin D receptor (VDR) were evaluated. VDR-siRNA or plasmids containing VDR-shRNA were transfected into podocytes to silence VDR expression. Chromatin immunoprecipitation (ChIP) and luciferase reporter assays were performed to verify the connection between VDR and nestin gene expression.

RESULTS

Paricalcitol significantly alleviated proteinuria and podocyte FP effacement in PAN-induced nephrosis, which was accompanied by increased VDR expression in the glomeruli. Paricalcitol also inhibited PAN-induced nestin overexpression in the glomeruli. In an in vivo study, PAN significantly inhibited VDR protein expression, stimulated nestin protein expression, and resulted in nestin filament derangement in mouse podocytes, while paricalcitol treatment abolished these effects. In contrast, downregulation of VDR resulted in derangement and overexpression of nestin. ChIP assays demonstrated the presence of a vitamin D response element (VDRE) in the nestin promoter, and paricalcitol enhanced the binding of VDR to VDRE. Furthermore, luciferase reporter assays of the nestin promoter fragment showed that paricalcitol effectively repressed nestin reporter gene expression after PAN treatment, and mutation of VDRE abolished this effect.

CONCLUSIONS

Paricalcitol directly regulates nestin transcription through the interaction of VDR/VDRE, thereby preventing morphological changes of podocytes in PAN nephropathy.

Upregulation of nestin protects podocytes from apoptosis induced by puromycin aminonucleoside

BACKGROUND

Nestin is an intermediate filament protein widely used as a marker of stem cells or progenitor cells. Nestin is also highly expressed in the glomerular podocyte, a type of terminally differentiated epithelial cell. Little is known about the significance of nestin in podocytes.

METHODS

Puromycin aminonucleoside (PAN) was injected into the rats to produce a PAN nephrosis model. Transmission electronic microscopy and terminal dUTP nick end-labeling assay were used to examine the podocyte foot process (FP) effacement and apoptosis, respectively. A mouse podocyte cell line was cultured and incubated with PAN. Immunoblot was used to examine the level of nestin expression both in vivo and in vitro. Enhanced green fluorescence protein-tagged plasmids containing nestin shRNA were transfected into the cultured podocytes to silence nestin expression. F-actin arrangement within cultured podocytes was investigated by immunofluorescence, while the apoptosis rate was examined by both Hoechst stain and flow cytometry.

RESULTS

In the PAN-induced rat nephrosis model, podocyte nestin expression was increased in the absence of apparent podocyte apoptosis, even though the FP was significantly effaced. In the cultured mouse podocytes, PAN upregulated nestin expression in a time-dependent manner within 24 h of treatment. Notably, no significant apoptosis occurred, however knocking down nestin expression resulted in a remarkable derangement of actin cytoskeleton and an increase in apoptosis in the cultured podocytes 24 h after being incubated with PAN.

CONCLUSIONS

Upregulation of nestin expression during PAN nephrosis could protect podocytes from apoptosis and that this process is mediated by maintaining the regular arrangement of actin cytoskeleton.

Differential efficiency of simvastatin and lipoic acid treatments on Bothrops jararaca envenomation-induced acute kidney injury in mice

Snake bite accidents by Bothrops genus is an important public health issue in Brazil and one of its most serious complications is the acute kidney injury (AKI). Here we evaluated the effects of Bothrops jararaca venom (vBj) and the treatments with lipoic acid (LA) and simvastatin (SA) on renal function, aminopeptidase (AP) activities and renal redox status. Primordial events for establishment of AKI by vBj were hyperuricemia, hypercreatinemia, urinary hyperosmolality, renal oxidative stress and reduction of hematocrit and protein content in the membrane of renal cortex and medulla and in the plasma. In the renal cortex and medulla the changes caused by vBj in soluble and membrane-bound AP activities had a similar pattern. The beneficial effects of LA and SA on envenomed mice were similar on the hyperuricemia, renal oxidative stress and reduction of hematocrit. LA mitigated the hypercreatinemia, but exacerbated the urinary urea and creatinine, whereas SA mitigated the decrease of plasma urea, urinary hyperosmolality and hypercreatinuria induced by vBj. The beneficial effects of LA and especially of SA on renal effects of vBj open a new perspective for clinical investigations of these drugs as coadjuvant agents in the serotherapy of Bothrops envenomation.

Chronic nephropathies of cocaine and heroin abuse: a critical review

Renal disease in cocaine and heroin users is associated with the nephrotic syndrome, acute glomerulonephritis, amyloidosis, interstitial nephritis, and rhabdomyolysis. The pathophysiologic basis of cocaine-related renal injury involves renal hemodynamic changes, glomerular matrix synthesis and degradation, and oxidative stress and induction of renal atherogenesis. Heroin is the most commonly abused opiate in the United States. Previous studies identified a spectrum of renal diseases in heroin users. The predominant renal lesion in black heroin users is focal segmental glomerulosclerosis and in white heroin users is membranoproliferative glomerulonephritis. Although the prevalence of heroin use in the United States has increased, the incidence of "heroin nephropathy" has declined. Because reports of heroin nephropathy predated the surveillance of hepatitis C virus and HIV, the varied findings might be related to the spectrum of viral illnesses that are encountered in injection drug users. Socioeconomic conditions, cultural and behavioral practices, or differences in genetic susceptibilities may be more associated with the development of nephropathy in heroin users than the drug's pharmacologic properties. Administration of cocaine in animal models results in nonspecific glomerular, interstitial, and tubular cell lesions, but there is no animal model of heroin-associated renal disease. The heterogeneity of responses that are associated with heroin is not consistent with a single or simple notion of nephropathogenesis. There are no well-designed, prospective, epidemiologic studies to assess the incidence and the prevalence of renal disease in populations of opiate users and to establish the validity of a syndrome such as heroin nephropathy. It is concluded although there is a paucity of evidence to support a heroin-associated nephropathy, the evidence from in vitro cellular and animal studies to support the existence of cocaine-induced renal changes is more convincing.

Partial depletion of macrophages by ED7 reduces renal injury in Adriamycin nephropathy

BACKGROUND

Because macrophages are considered to be possible effectors of disease in Adriamycin (ADR) nephrosis, we hypothesized that depletion of macrophages might protect against the initiation of renal injury. In the present study, a monoclonal antibody (ED7) directed against CD11b/CD18 integrin, which is expressed by macrophages, was used to investigate the pathogenetic effects of macrophages in ADR nephropathy.

METHODS

Male Wistar rats were treated with ED7 antibody, starting 1 day prior to ADR (7.5 mg/kg) treatment, or 7 days post-ADR when overt proteinuria was established.

RESULTS

Circulating ED7-positive cells were reduced by approximately 30% in rats with ADR nephrosis by the ED7 antibody, while the number of macrophages in the renal cortex of ADR rats was reduced by nearly 50% with the ED7 treatment, whether administered before or after ADR. Creatinine clearance was significantly ameliorated by ED7 when commenced pre-ADR (P < 0.05), but not when commenced post-ADR (P = NS) in comparison to untreated ADR rats. However, proteinuria was not alleviated by either ED7 treatment. Morphometric analysis showed less glomerular sclerosis when ED7 was commenced pre-ADR compared with ADR alone (P < 0.01), but not when commenced post-ADR (P = NS). Tubular atrophy was reduced by ED7 when it was commenced pre-ADR (tubular cell height and tubular diameter: P < 0.01 and P < 0.001, respectively), as was interstitial expansion (P < 0.01) compared with ADR alone. Cortical macrophage infiltration was reduced by 50% compared with ADR alone by the ED7 commenced before or after ADR. The number of cortical CD4+ T cells fell with ED7 starting pre-ADR, but not with the ED7 treatment commencing after ADR.

CONCLUSION

Partial macrophage depletion starting before but not after ADR protected both renal function and structure in this model of chronic proteinuric renal disease.

Effect of zelandopam, a dopamine D1-like receptor agonist, in puromycin aminonucleoside nephrosis rats

The present experiment was designed to investigate the role of peripheral dopamine D1-like receptors and to evaluate the prophylactic effect of zelandopam, a dopamine D1-like receptor agonist, on puromycin aminonucleoside (PA)-induced nephrosis in rats. Rats were divided into six groups (n=10 per group): 0.9% saline-injected rats (control); PA-injected rats (PAN); PA-injected rats treated with the selective dopamine D1-like receptor agonist zelandopam (30, 100, 300 mg/kg p.o. twice a day); PA-injected rats treated with prednisolone (1 mg/kg p.o. once a day). Nephrosis was induced in rats with a single intravenous injection of PA at a dose of 50 mg/kg. The effects of zelandopam and prednisolone in PA nephrosis rats were evaluated before injection of PA and at 7 and 14 days after injection. PA-induced nephrosis was characterized by an increase in urinary protein excretion (proteinuria) and plasma total cholesterol. Zelandopam dose-dependently attenuated the increase in proteinuria and total cholesterol. Prednisolone significantly attenuated the increase in proteinuria and total cholesterol and resulted in a significant decrease in body weight. The present study demonstrates for the first time that zelandopam, a selective dopamine D1-like receptor agonist, is effective in blunting the development of PA-induced nephrosis, and that the effects of zelandopam are dose dependent.

Retinoids as a potential treatment for experimental puromycin-induced nephrosis

1 Puromycin aminonucleoside (PAN)-induced nephrosis is a model of human minimal change disease. In rats, PAN induces nephrotic-range proteinuria, renal epithelial cell (podocyte) damage, infiltration of mononuclear leukocytes, and apoptosis of several renal cell types. 2 Retinoic acid (RA) modulates a wide range of biological processes, such as inflammation and apoptosis. Since renal damage by PAN is characterized by inflammatory infiltration and epithelial cell death, the effect of treatment with all-trans RA (tRA) was examined in the PAN nephrosis model and in the cultured differentiated podocyte. 3 Treatment with tRA 4 days after PAN injection did not inhibit the proteinuria peak but reversed it significantly. However, treatment with tRA both before and 2 days after the injection of PAN protected the glomerular epithelial cells, diminishing the cellular edema and diffuseness of the foot process effacement. Preservation of the podocyte architecture correlated with the inhibition of proteinuria. The anti-inflammatory effect of tRA was evidenced by the inhibition of PAN-induced interstitial mononuclear cell infiltration and the decreased renal expression of two molecules involved in monocyte infiltration: fibronectin and monocyte chemoattractant protein-1. TUNEL assays showed that tRA inhibited the PAN-induced apoptosis of cultured differentiated mouse podocytes. 4 We conclude that tRA treatment may prevent proteinuria by protecting the podocytes from injury and diminishing the interstitial mononuclear infiltrate in the model of PAN nephrosis. Retinoids are a potential new treatment for kidney diseases characterized by proteinuria and mononuclear cell infiltration.

Lipid abnormalities and renal disease: is dyslipidemia a predictor of progression of renal disease?

Dyslipidemia is a cardiovascular disease (CVD) risk factor that is associated with enhanced atherosclerosis and plaque instability. Renal insufficiency is associated with abnormalities in lipoprotein metabolism in both the early and the advanced stages of chronic renal failure. These include alterations in apolipoprotein A (apo A)- and B- containing lipoproteins, high-density lipoproteins, and triglycerides. In animal models, these alterations in lipid metabolism and action lead to macrophage activation and infiltration in the kidney with resultant tubulointerstitial and endothelial cell injury. Limited data in humans suggest that, in addition to contributing to CVD, dyslipidemia may be a risk factor for the progression of renal disease. The effects of dyslipidemia on the kidney are mainly observed in those with other risk factors for renal disease progression such as hypertension, diabetes, and proteinuria. Renal disease is a strong risk factor for CVD and African Americans have high rates of renal disease. Therefore, examining the effects of dyslipidemia on the development or progression or renal disease will be an important question for the Jackson Heart Study and is the topic of this review.

Fatty acids exacerbate tubulointerstitial injury in protein-overload proteinuria

The role of the albumin-carried fatty acids in the induction of tubulointerstitial injury was studied in protein-overload proteinuria. Rats were injected with fatty acid-carrying BSA [FA(+)BSA], fatty acid-depleted BSA [FA(-)BSA], or saline. Macrophage infiltration was measured by immunohistochemical staining, apoptotic cells were detected by in situ end labeling, and proliferating cells were identified by in situ hybridization for histone mRNA. Macrophage infiltration was significantly greater in the FA(+)BSA group than in the FA(-)BSA and saline groups. The infiltrate was largely restricted to the outer cortex. Apoptosis was greater in the FA(+)BSA group than in the FA(-)BSA and saline groups. Compared with the saline group, apoptosis was significantly increased in the FA(+)BSA group but not in the FA(-)BSA group. Cortical cells proliferated significantly more in the FA(+)BSA and FA(-)BSA groups than in the saline group. FA(+)BSA is therefore a more potent inducer of macrophage infiltration and cell death than FA(-)BSA. The fatty acids carried on albumin may be the chief instigators of tubulointerstitial injury in protein-overload proteinuria.

Long-term caffeine consumption exacerbates renal failure in obese, diabetic, ZSF1 (fa-fa(cp)) rats

BACKGROUND

Our preliminary studies indicate that chronic caffeine consumption has adverse renal effects in nephropathy associated with high blood pressure and insulin resistance. The purpose of this study was to investigate the effects of early (beginning at 8 weeks of age) and long-term (30 weeks) caffeine treatment (0.1% solution) on renal function and structure in obese, diabetic ZSF1 rats.

METHODS

Metabolic and renal function measurements were performed at six-week intervals and in a subset of animals (N = 6 per group) heart rate (HR) and mean arterial blood pressure (MABP) were monitored by a radiotelemetric technique. At the end of the study acute, measurements of renal hemodynamics and excretory function were conducted in anesthetized animals.

RESULTS

Caffeine produced a very mild increase (4 to 5%) of MABP and HR, but greatly augmented proteinuria (P < 0.001), reduced creatinine clearance (P < 0.05) and had a mixed effect on metabolic status in obese ZSF1 rats. Caffeine significantly reduced body weight, glycosuria, fasting glucose and insulin levels and improved glucose tolerance, had no effect on elevated plasma triglycerides levels and significantly increased plasma cholesterol level (P < 0.001). Acute measurements of renal function revealed increased renal vascular resistance (95.1 +/- 11 vs. 50.7 +/- 2.4 mm Hg/mL/min/g kidney, P < 0.01) and decreased inulin clearance (0.37 +/- 0.11 vs. 0.97 +/- 0.13 mL/min/g kidney, P < 0.002) in caffeine-treated versus control animals, respectively. Caffeine potentiated the development of more severe tubulointerstitial changes (P < 0.05) and increased focal glomerulosclerosis (14.7 +/- 1.7 vs. 6.5 +/- 0.9%, caffeine vs. control, P < 0.002).

CONCLUSION

The present study provides the first evidence that caffeine (despite improving insulin sensitivity) exacerbates renal failure in obese, diabetic ZSF1 rats. Further mechanistic studies of adverse renal effects of caffeine in chronic renal failure associated with metabolic syndrome are warranted.

Role of immunocompetent cells in nonimmune renal diseases

Renal infiltration with macrophages and monocytes is a well-recognized feature of not only immune, but also nonimmune kidney disease. This review focuses on the investigations that have shown accumulation of immunocompetent cells in experimental models of acute and chronic ischemia, protein overload, hypercholesterolemia, renal ablation, obstructive uropathy, polycystic kidney disease, diabetes, aging, murine hypertension, and nephrotoxicity. We examine the mechanisms of infiltration of immunocompetent cells and their participation in the self-perpetuating cycle of activation of the angiotensin system, generation of reactive oxygen species, and further recruitment of monocytes and lymphocytes. We also discuss the possibility of antigen-dependent and antigen-independent mechanisms of immune cell activation in these animal models. Finally, we review the recent studies in which suppression of cellular immunity with mycophenolate mofetil has proven beneficial in attenuating or preventing the progression of renal functional and histologic damage in experimental conditions of nonimmune nature.

Neutral lipid from proteinuric rat urine is a novel inhibitor of the red blood cell calcium pump

Proteinuria may be associated with hypertension and progression of renal insufficiency, which in turn may accompany abnormalities in cell calcium homeostasis. Therefore, urine from rats made proteinuric by puromycin aminoglycoside administration was analyzed, in a search for factors affecting cellular calcium transport. Proteinuric urine was fractionated by thin-layer chromatography and HPLC, and the effects of the fractions on the plasma membrane calcium pump in human red blood cells were assessed. Proteinuric urine contained a powerful specific inhibitor of the calcium pump that had little or no effect on the Na+/K+- or Mg2+-ATPases. The inhibitor was characterized as a neutral lipid, migrating as a single band, that inhibited 45Ca2+ efflux. To confirm the presence of an inhibitor in other proteinuric states, the urine from two patients with proteinuria was examined and subjected to chromatography as in the rat studies. These thin-layer chromatographic fractions contained a very strong inhibitor of the red blood cell calcium pump, suggesting that this substance may have relevance for the pathogenesis of proteinuric renal disease in human patients. Rat proximal tubule cells in tissue culture, when challenged with lipid-replete albumin, secreted an inhibitor of the calcium pump that migrated in the same chromatographic band as the urine factor. Therefore, the processing of fatty acids borne by albumin into endocytosing proximal tubular epithelium results in the synthesis and release of a previously unknown lipid modulator of the calcium pump, an effect that may predispose kidney tissue toward elevations in cytosolic calcium levels in target cells.

Gene expression of 5-lipoxygenase and LTA4 hydrolase in renal tissue of nephrotic syndrome patients

Leukotrienes (LT) of the 5-lipoxygenase pathway constitute a class of potent biological lipid mediators of inflammation implicated in the pathogenesis of different models of experimental glomerulonephritis. The key enzyme, 5-lipoxygenase (5-LO), catalyses oxygenation of arachidonic acid to generate the primary leukotriene LTA4. This LT, in turn, serves as a substrate for either LTA4 hydrolase, to form the potent chemoattractant LTB4, or LTC4 synthase, to produce the powerful vasoconstrictor LTC4. To investigate the potential role of LT in the pathogenesis of human glomerulonephritis with nephrotic syndrome, we examined the gene expression of 5-LO and LTA4 hydrolase in renal tissue of 21 adult patients with nephrotic syndrome and 11 controls. The patients consisted of 11 cases of membranous nephropathy (MN), seven focal and segmental glomerulosclerosis (FSGS), two non-IgA mesangial glomerulonephritis and one minimal change disease. Total RNA purified from renal tissue was reverse transcribed into cDNA and amplified with specific primers in a polymerase chain reaction (RT-PCR). Eight patients' renal tissue, four MN and four FSGS, co-expressed 5-LO and LTA4 hydrolase. In situ hybridization analysis revealed 5-LO expression and distribution limited to the interstitial cells surrounding the peritubular capillaries. Comparative clinical and immunohistological data showed that these eight patients had impaired renal function and interstitial changes that significantly correlated with 5-LO expression. These findings suggest that leukotrienes may play an important role in the pathogenesis of MN and FSGS. These results are also relevant to elucidating the pathophysiologic mechanisms which underlie progression to renal failure in these diseases.

MR imaging of intrarenal macrophage infiltration in an experimental model of nephrotic syndrome

The objective of this study was to use MR imaging to detect macrophage infiltration of the kidney after injection of ultrasmall superparamagnetic iron oxide (USPIO) particles in a rat model of experimental nephropathy. Ninety micromol of USPIO were injected intravenously in 10 rats with nephropathy secondary to intravenous injection of 5 mg of puromycin aminonucleoside (PAN), and in 10 control rats. The signal intensity was measured in each kidney compartment before and 24 h after injection of the contrast agent. FLASH sequences were performed on a spectrometer operating at 4.7 T. MR findings were compared with histological data. Twenty-four hours after injection of USPIO, a significant decrease (P < 0.0001) was observed in signal intensity in each kidney compartment in the PAN group. There was no variation in the control group. In the diseased kidneys, histological data revealed the presence of macrophages with iron oxide particles within their cytoplasm and lysosomes. Using USPIO, MR imaging can evidence infiltration of the rat kidney by macrophages.

Metal-catalyzed oxidation of extracellular matrix increases macrophage nitric oxide generation

BACKGROUND

Oxygen radicals are believed to play a significant role in glomerular disease. In part this may be due to oxidation of lipids, but protein oxidation may play a contributory role as well. We have demonstrated that the mesangial extracellular matrix is susceptible to metal-catalyzed oxidation and that this increases scavenger receptor-mediated adhesion of macrophages, cells which appear to be important participants in glomerular injury via their secretory products. As other scavenger receptor ligands can increase macrophage nitric oxide generation, we examined whether oxidation of matrix could increase the activity of macrophage inducible nitric oxide synthase (iNOS).

METHODS

Extracellular matrix was oxidized using a metal-catalyzed oxidation system. Matrix oxidation was measured using carbonyl analysis, and iNOS activity in macrophages seeded onto the matrix was measured by nitrite determination and Western and Northern analyses for iNOS.

RESULTS

Macrophages exposed to oxidized matrix demonstrated a significant enhancement of iNOS activity. This enhancement could be antagonized by cotreatment of matrix with the radical spin trap N-tert-butyl-a-phenylnitrone, resulting in a corresponding decrease in protein carbonyl content, a measure of protein oxidation. Seeding macrophages onto oxidized matrix and adding the scavenger receptor ligand polyinosinic acid further augmented iNOS activity, suggesting that additional scavenger receptors were available to bind ligand and that further augmentation of iNOS activity did not require an additional change in cell shape. Western blot analysis revealed an increase in iNOS protein expression as a consequence of interaction with the oxidized matrix, but there was no difference in iNOS mRNA expression by Northern analysis suggesting a post-transcriptional mechanism for enhanced iNOS activity.

CONCLUSION

These data demonstrate that oxidation of extracellular matrix enhances macrophage nitric oxide generation, and suggest a previously undescribed role for extracellular matrix modification in the regulation of cellular function and possibly the mediation of glomerular injury.

Thrombospondin 1 precedes and predicts the development of tubulointerstitial fibrosis in glomerular disease in the rat

Tubulointerstitial fibrosis is one of the most important histologic features that predicts progression in kidney disease. Thrombospondin 1 is an extracellular matrix protein that can activate latent TGF-beta, a cytokine implicated in the pathogenesis of tubulointerstitial fibrosis. We examined the expression of thrombospondin 1 in several animal models of glomerulonephritis (anti-Thy1 model, aminonucleoside nephrosis, passive Heymann nephritis) that are associated with tubulointerstitial disease. Thrombospondin 1 mRNA and protein were transiently increased in tubular cells, myofibroblasts and some macrophages in areas of tubulointerstitial injury. Thrombospondin 1 expression always preceded the development of tubulointerstitial fibrosis, and correlated quantitatively and spatially with the later development of interstitial fibrosis. Thrombospondin 1 expression predicted the severity of tubulointerstitial fibrosis better than the degree of macrophage or myofibroblast accumulation. Thrombospondin 1 expression was associated with increased expression and activation of TGF-beta1 and decreased expression of LAP-TGF-beta in areas of tubulointerstitial injury. We conclude that thrombospondin 1 is an early marker predicting the development of tubulointerstitial kidney disease. De novo expression of thrombospondin 1 is associated and colocalized with increased expression of TGF-beta1 and decreased expression of LAP-TGF-beta during the development of tubulointerstitial disease in vivo. These data are consistent with the possibility that thrombospondin 1 may be an endogenous activator of TGF-beta.

Role of complement in acute tubulointerstitial injury of rats with aminonucleoside nephrosis

The present work was designed to elucidate the in vivo role of complement in the proteinuria-associated tubulointerstitial injury. Rats were intravenously injected with puromycin aminonucleoside, and massive proteinuria was observed within 5 days. Prominent tubulointerstitial injury characterized by proximal tubular degeneration, tubular dilatation, and leukocyte infiltration were observed 7 days after injection. C3 and C5b-9 were observed in the luminal side of proximal tubular cells. Renal function, assessed by inulin and para-aminohippurate clearance, was significantly decreased. To-assess the role of complement in this model, rats were injected with either cobra venom factor or soluble recombinant human complement receptor type 1 starting at day 3. These manipulations significantly improved tubulointerstitial pathology and para-aminohippurate clearance without affecting the degree of proteinuria. Deposition of C3 and C5b-9 was not detected in the kidney of rats depleted of complement by cobra venom factor. In rats treated with soluble complement receptor, C3 was still detected in the tubules, but deposition of C5b-9 was not observed. Soluble complement receptor was detected at the site of C3 deposition and in the urine. These data strongly suggest that complement plays a pivotal role in proteinuria-associated tubulointerstitial injury and that systemic complement depletion or inhibition of complement in the tubular lumen may diminish the tubulointerstitial damage.

Semiautomatic quantitation of macrophages in human renal biopsy specimens in proteinuric states

AIMS

To develop and validate a rapid and economical semiautomated approach to the measurement of immunostainable tissue components which is applicable to routine diagnostic practice. To apply this approach to the measurement of macrophages in renal biopsy specimens in nephrotic states, as protein in the renal tubules may induce macrophage infiltration, and the morphology of macrophages in tissue sections does not lend itself to cell counting.

METHODS

Macrophages were identified by immunostaining with a pan-macrophage marker, followed by digital image capture and analysis using a macro procedure written for the freeware image analysis program NIH-Image.

RESULTS

The method was rapid, robust and accurate to within the limits imposed by sampling error inherent in the use of small needle biopsy specimens. Very few macrophages are found in normal kidney (mean volume fraction (+/- 95% confidence limits) 0.04% (0.02%)) but infiltration of macrophages was detected in minimal change nephropathy (0.29% (0.12%)) and in membranous glomerulonephritis (0.42% (0.11%)). A statistically significant correlation was found between macrophage volume fraction and weight of proteinuria in minimal change nephropathy but not in membranous glomerulonephritis. Correlations were found in both diseases between macrophage volume fraction and serum creatinine at time of biopsy.

CONCLUSIONS

The equipment is inexpensive and measurement takes less than one minute per biopsy specimen. The results indicate that macrophage infiltration is part of the pathological process in minimal change nephropathy and membranous glomerulonephritis. The correlation with creatinine at time of biopsy suggests that renal impairment in minimal change nephropathy may result from infiltration by immunologically active cells and not merely from haemodynamic changes in nephrons. However, the correlation is not close, indicating that the relation between macrophage infiltration and disease severity is not a simple one.

Tubulointerstitial responses in the progression of glomerular diseases: albuminuria modulates alpha v beta 5 integrin

Proteinuria represents one of the most unfavorable prognostic factors in the progression of nephropathies. Several lines of evidence support a role for proteinuria per se in the development of interstitial fibrosis, albeit the molecular mechanisms are still unknown. We investigated the potential role of integrins expressed on tubular cells in regulating the synthesis and organization of interstitial matrix or as mediators of tubulointerstitial damage in conditions mimicking the nephrotic milieu. Under basal conditions, cultured tubular cells highly expressed alpha 3 beta 1 and, at focal contacts, alpha v beta 3. In contrast, alpha v beta 5 was weakly and diffusely distributed all over the plasma membrane. Cultures on a variety of matrix substrates (fibronectin, laminin, collagen types I and IV, vitronectin, von Willebrand factor, fibrinogen) did not induce any phenotypic change in integrin expression by tubular cells. Conversely, the addition of albumin resulted in a highly increased membrane expression of beta 5, which was organized in typical focal contacts and was related to the dose of albumin added. Immunofluorescence, flow cytometry, immunoprecipitation and RT-PCR experiments argue for a complex mechanism that includes increased post-transcriptionally regulated protein synthesis, accelerated conversion of precursors to mature forms, and increased surface delivery to discrete adhesive structures. Up-regulation of the beta 5 chain in tubular cells was confirmed in 9 out of 11 kidney biopsies from proteinuric glomerulonephritides including membranous and focal sclerosing glomerulonephritis, while it was not expressed in nonproteinuric kidneys including five biopsy specimens. This is the first report indicating that proteinuria up-regulates the surface expression and distribution of a specific integrin chain on tubular cells. These observations suggest the participation of integrins in a hitherto unexplored mechanism of tubulo-interstitial responses to glomerular injury.

Morphine-induced macrophage activity modulates mesangial cell proliferation and matrix synthesis

Glomerular mesangial injury is the predominant renal lesion in patients with heroin addition. We studied the effect of morphine (an active metabolite of heroin)activated macrophages on mesangial cell (MC) proliferation and matrix synthesis. We prepared conditioned media containing either vehicle along (CSP), macrophage secretory products (MSP) and secretory products of morphine treated macrophages (M-MSP), M-MSP increased (P < 0.01) the proliferation of MC when compared with MSP alone. M-MSP increased synthesis of laminin by MC at concentrations of 10 to 50% when compared with cells treated with MSP alone (at 50% concentration, MSP, 126 +/- 19 vs. M-MSP, 312 +/- 14 ng/mg protein, P < 0.001). M-MSP also increased the synthesis of collagen type IV by MC. This effect of M-MSP was attenuated (P < 0.05) by anti-TGF-beta antibodies. Since M-MSP also increased mRNA expression for TGF-beta by MC, it appears that the effected of M-MSP on MC may be mediated through the generation of TGF-beta.

The possible roles of hyperlipidemia and mononuclear cells in glomeruli in puromycin aminonucleoside nephrosis in rats

The possibility that hyperlipidemia and an increase of mononuclear cells in the glomeruli could participate in the pathogenesis of minimal change glomerulopathy was evaluated in puromycin aminonucleoside (PAN) nephrosis in rats. Significant increases in intraglomerular CD4-, IL-2-receptor (R)- and ED-1-positive cells were found in PAN rats. Urinary protein excretion and mononuclear cells in the glomeruli of 1% cholesterol diet-fed rats significantly increased, compared with standard diet feeding. Moreover, administration of a subnephrogenic dose of PAN in cholesterol diet-fed rats substantially increased urinary protein excretion and mononuclear cells in the glomeruli. Additionally, antihyperlipidemia agents and immunosuppressive agents prevented urinary protein excretion and increases of CD4-, IL-2R- and ED-1-positive cells in the glomeruli of PAN nephrotic rats. Monoclonal antibodies directed against these cells also prevented urinary protein excretion. These results suggest that CD4-, IL-2R- and ED-1-positive cells and hyperlipidemia are involved in the progression, but not the pathogenesis, of PAN.

Tubulointerstitial lesions in young Zucker rats

Zucker (Z) rats spontaneously develop proteinuria and focal glomerulosclerosis (FGS), but little is known about tubulointerstitial (TI) changes in the early stages of their disease. Thirteen male Z rats (9 obese, 4 lean) were examined at 75 (n = 6) and 120 (n = 7) days of age. Twenty-four-hour urinary protein excretion (UPr), percent of glomeruli with FGS, proportion of cortex and outer stripe occupied by vimentin (V)-positive (+) tubules (a marker of tubular damage) and the number of OX4+ (Ia+), OX42+(monocyte/macrophage), OX19+(pan T cell), OX8+(T cytotoxic cell), and OX22+(B cell) cells in both normal areas and around V+ tubules were assessed at each age. Mean UPr was 34.2 +/- 18.5 mg/day at 75 days and 183.6 +/- 129.9 mg/day at 120 days. FGS was only observed in 1% to 3% of glomeruli in five 120-day-old obese rats. All rats showed varying degrees of focal TI injury histologically. V+ tubules were observed in 12 rats, and the proportion of cortex and outer stripe occupied by V+ tubules varied from 0.1% to 7.7%. The extent of TI damage was greater at 120 days (3.7% +/- 2.9%) than at 75 days (0.5% +/- 0.5%). There was a 2- to 12-fold increase in the number of OX4+, OX42+, OX19+, and OX8+ cells in areas around V+ tubules, with OX4+ and OX42+ cells predominating.(ABSTRACT TRUNCATED AT 250 WORDS)

Tubulointerstitial lesions in human membranous glomerulonephritis: relationship to proteinuria

Recent studies in experimental glomerular disease suggest that proteinuria may be involved in the pathogenesis of accompanying tubulointerstitial (TI) lesions. To investigate whether there is a relationship between proteinuria and TI damage in membranous glomerulonephritis, 78 biopsy specimens with no or mild vascular disease and 10% or less obsolete glomeruli were examined and evaluated quantitatively. Extent of TI damage was represented by the TI index (TII) obtained for each biopsy specimen by dividing the morphometrically measured area of cortical damage by the total cortical area and multiplying the result by 1,000. The TII increased with stage of glomerular disease, but only the difference between stages 3 and 1 was significant (P < 0.016). The TII showed significant individual correlation with 24-hour urinary protein (r = 0.435, P < 0.0001), serum albumin (r = -0.327, P = 0.0045), and percent of glomeruli with visceral epithelial cell protein absorption droplets (r = 0.419, P = 0.0001), but not with age, serum creatinine, or percent obsolete glomeruli. With multivariate analysis TII correlated significantly with urinary protein (r = 0.286, P = 0.0146) and percent glomeruli with visceral epithelial cell protein droplets (r = 0.304, P = 0.0058). The results are consistent with the hypothesis that proteinuria is involved in the development of TI injury in glomerular disease.

Passive dual immunization against tumour necrosis factor-alpha (TNF-alpha) and IL-1 beta maximally ameliorates acute aminonucleoside nephrosis

Rats receiving a single dose (10 mg/100 g) of aminonucleoside of puromycin (PAN) develop heavy proteinuria and acute interstitial nephritis (AIN). Whole isolated glomeruli from rats injected with PAN secreted both TNF-alpha and IL-1 beta cytokines. TNF-alpha secretion was first and maximally detected on day 3, whereas IL-beta activity was found on day 7, when rats were heavily proteinuric and AIN developed. In vivo treatment with either anti-TNF-alpha or anti-IL-1 beta antibodies produced a drastic and simultaneous reduction in both levels of proteinuria and intensity of interstitial cell infiltrate. These effects improved when both antibodies were administered together. Our studies demonstrate the effectiveness of immunosuppressive therapy against these two cytokines in rats with PAN-induced nephrosis.

Fish oil feeding modulates leukotriene production in murine lupus nephritis

Diets enriched with fish oil (FO) ameliorate kidney disease in the MRL-lpr/lpr murine model of lupus nephritis. Although the mechanisms of this effect are not known, FO is rich in the polyunsaturated fatty acid eicosapentaenoic acid (EPA) which may have profound effects on eicosanoid metabolism. In MRL-lpr/lpr mice, FO feeding reduces renal production of cyclooxygenase metabolites. However, EPA may also affect the metabolism of arachidonate by the 5-lipoxygenase (5-LO) pathway and enhanced production of 5-LO metabolites has been implicated in the pathogenesis of kidney disease in MRL-lpr/lpr mice. We therefore investigated the effects of FO feeding on production of 5-LO metabolites in 20 week old MRL-lpr/lpr mice. After 8 weeks of dietary supplementation with FO, both renal hemodynamic function and glomerular histology were improved compared to safflower oil (SO) controls. Amelioration of kidney disease was associated with alterations in the pattern of leukotriene production by macrophages and kidneys from FO fed mice. There was a significant decrease in the production of leukotriene B4 (LTB4) and tetraene peptidoleukotrienes by peritoneal macrophages isolated from mice given FO compared to control animals. Similarly, dietary supplementation with FO decreased renal production of LTB4. Reduced production of tetraene leukotrienes was accompanied by a modest increase in the production of pentaene leukotrienes by macrophages from FO fed mice. We speculate that this modulation of leukotriene production by FO feeding may have beneficial effects on renal disease in autoimmune nephritis.

Fish oil supplementation and essential fatty acid deficiency reduce nitric oxide synthesis by rat macrophages

Both fish oil-derived omega-3 polyunsaturated fatty acid (omega 3 PUFA) supplementation and essential fatty acid (EFA) deficiency have been shown to exert anti-inflammatory effects and, hence, to ameliorate immune-mediated glomerulonephritis. The mechanisms underlying these effects include alterations in the production of eicosanoids, cytokines (that is, tumor necrosis factor, TNF-alpha) and reactive oxygen species by blood borne cells. Because, in addition to these mediators nitric oxide (NO) is also implicated in glomerular injury, we have examined if both diets affected macrophage NO production as well. Rats were fed a standard chow, an omega 3 PUFA-supplemented diet, or an EFA-deficient diet for six weeks before resident peritoneal macrophages were isolated. These cells were exposed to lipopolysaccharide (LPS) and the NO metabolite, nitrite (NO2-), was measured in the medium using the Griess reagent. Release of NO2- was enhanced by LPS in a dose-dependent manner. With 10 ng/ml LPS challenge, NO2- release was reduced by 37% and 57% by omega 3 PUFA supplementation and EFA deficiency, respectively. NO2- returned to control levels two weeks after the end of diet. Macrophage production of TNF-alpha responded in a similar manner. Diet-induced reduction of NO2- release was neither attributable to a reduction of inducible NO synthase mRNA levels as shown by Northern blot analysis, nor to an increased competition of NO synthase and arginase for the substrate (L-arginine). Indeed, arginase activity of macrophages was even slightly reduced by both omega 3 PUFA-supplemented diet and EFA-deficient diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Tubular catabolism of albumin is associated with the release of an inflammatory lipid

Proteinuria and tubulointerstitial inflammation (TII) correlate with progression to renal failure in human glomerulonephritis. Various forms of experimental nephrotic syndrome are associated with TII. To study the genesis of TII, we utilized the model of albumin overload. Rats received intraperitoneal bovine serum albumin (BSA) for 1 to 14 days, developing heavy proteinuria. A predominantly macrophage interstitial infiltrate was present at days 3, 7 and 14. The urine of the rats contained a factor chemotactic for macrophages which partitioned into the organic phase with ethyl acetate extraction. TLC and HPLC characteristics were those of a novel, non-polar lipid. Supernatant from the culture of proximal tubule (PT) segments after in vivo or in vitro exposure to high concentrations of lipid-replete BSA showed chemotactic activity with similar chromatographic characteristics. PT cultured with delipidated BSA produced little activity. Thus, the generation of this inflammatory factor occurs as a consequence of tubular metabolism of albumin-borne fatty acids and may contribute to the development of proteinuria-associated TII.

Effects of human immunodeficiency virus sera and macrophage supernatants on mesangial cell proliferation and matrix synthesis

Patients with human immunodeficiency virus (HIV) infection are prone to the development of focal segmental glomerulosclerosis, a lesion in which increased mesangial cell proliferation and matrix synthesis may play a role. We undertook the present study to determine whether HIV sera may affect mesangial cell proliferation and matrix synthesis either directly or indirectly via effects on macrophage supernatants. Pooled HIV sera was found to significantly enhance (P < 0.01) mesangial cell proliferation in a concentration-related manner. Mesangial cell proliferation was significantly suppressed by two medications commonly utilized in HIV-infected patients, azidothymidine and trimethoprim/sulfamethoxazole, and was not significantly altered by lipopolysaccharide, suggesting that these medications as well as recurrent infection are unlikely to account for the proliferative effect of HIV sera. Supernatants from HIV sera-treated macrophages were found to significantly enhance (P < 0.01) mesangial cell incorporation of [3H]proline, a marker for synthesis of the matrix component collagen, compared to supernatants from control sera-treated macrophages. These results suggest that HIV sera may directly enhance mesangial cell proliferation and may indirectly increase mesangial cell matrix synthesis by altering macrophage secretory products. These effects may play a role in the development of glomerulosclerosis in patients with HIV infection.

Collagen studies in newborn rat kidneys with incomplete ureteric obstruction

Collagen studies in newborn rats with incomplete ureteric obstruction were performed to describe and quantify changes in collagen deposition resulting from urinary tract obstruction at an early developmental age. Incomplete ureteric obstruction was created in three-day-old rats by placing the left ureter in a tunnel formed by the psoas muscle, and sham-operated controls underwent a laparotomy. The rats were sacrificed at 10, 17, 24 or 31 days. Collagen types I, III, IV, and V were localized by indirect immunofluorescence microscopy, the total collagen content of the kidney was quantitated using hydroxyproline analysis, and collagen types I and III were quantitated using cyanogen bromide (CNBr) peptide analysis. Increased immunofluorescent staining for all of the collagens was found in the diffusely widened medullary interstitium of the obstructed kidney, and more focally in the cortical interstitium. Collagen types I, III and V, but not collagen type IV, were also found in bands in the interstitium at the junction of the cortex with the medulla. Increased staining for collagen type IV was found in thickened and tortuous tubular basement membranes (TBM) of the obstructed kidneys. The total collagen content of the obstructed kidney was significantly increased compared to the amounts in both the contralateral kidneys and in the kidneys from sham-operated controls at 24 and 31 days of age (P < 0.01 in each case, Wilcoxon matched pairs rank sum test and Mann Whitney U-test, respectively). The amount of collagen in the kidneys correlated with the degree of hydronephrosis (Spearman correlation test, r = 0.78, P < 0.02). CNBr peptide analysis demonstrated that over 50% of the collagen in the normal neonatal rat kidney was collagen type I and approximately 25% was collagen type III. In the obstructed kidneys most of the collagen was also collagen type I and collagen type III, although the proportion of total collagen comprised by these collagen types was decreased compared with the controls. The amount of collagen type III in the contralateral kidneys was reduced compared to that in the controls. Thus, the neonatal renal response to obstruction resulted in increased amounts of a range of collagens in the interstitium and TBM, and the extent of this response was partially related to the degree of hydronephrosis.

Mechanisms of proteinuria in noninflammatory glomerular diseases

Neither the initiating factors nor the proximate causes of injury that produce proteinuria in nephrotic syndrome have been clearly defined. Immune mechanisms have been postulated in minimal-change nephrotic syndrome (MCNS), focal segmental glomerular sclerosis (FSGS), and glomerular sclerosis associated with human immunodeficiency virus (HIV) infection. Circulating factors have been proposed in MCNS and FSGS, although no specific mediator has been identified. Prompt remission of proteinuria following steroid treatment and the presence of altered immune responsiveness in patients with MCNS have been used to support the participation of an immune mechanism in the pathogenesis of MCNS. Both FSGS and HIV-related nephropathy are usually steroid-resistant. Immune mechanisms are postulated in FSGS because of early recurrence after transplantation, and in HIV-related nephropathy because of the numerous associated immune abnormalities. Experimental models of nephrotic syndrome based on neutralization of glomerular charge, toxic injury to podocytes, injection of antibodies to glomerular components, or abnormalities in transgenic mice have been used to define mechanisms of glomerular injury. This review summarizes physiologic and immunologic abnormalities in MCNS, FSGS, and HIV-associated nephropathy and in several experimental models of nephrotic syndrome, and outlines the immunologic mechanisms and cellular reactions that may be responsible for glomerular dysfunction in these entities.

Macrophage supernatants have both stimulatory and suppressive effects on mesangial cell proliferation

Macrophages may modulate mesangial expansion following renal injury via secretory products. We undertook the present study to determine the effects of macrophage supernatants on mesangial cell proliferation. Macrophage supernatants collected in serum-free media after 24 hours caused significantly enhanced mesangial cell proliferation in long-term culture at concentrations up to 50% but caused suppression at higher concentrations (control, 122,000 +/- 14,000 cells/well; 50% supernatant, 188,000 +/- 15,100 cells/well, P < 0.02 compared to control, n = 4; 80% supernatant, 52,000 +/- 3,500 cells/well, P < 0.01 compared to control, n = 4). In short-term culture [3H]thymidine incorporation, a measure of DNA synthesis, was significantly enhanced compared to control at supernatant concentrations up to 30% (30% supernatant, 4,120 +/- 310 cpm/well; control, 3,210 +/- 97 cpm/well, P < 0.5, n = 4), but uptake was reduced at high concentration (80% supernatant, 2,900 +/- 74 cpm/well; control, 3,210 +/- 97 cpm/well, P < 0.05, n = 4). When macrophage supernatants were collected after 48 hours incubation and incubated with mesangial cells, mesangial cell thymidine uptake was significantly suppressed compared to control (48-hour supernatant, 4,060 +/- 260 cpm/well; control, 5,890 +/- 270 cpm/well, P < 0.01, n = 4) and compared to 24-hour supernatants, which enhanced uptake (24-hour supernatant, 8,080 +/- 340 cpm/well; control, 5,890 +/- 270 cpm/well, P < 0.01, n = 4). Our results suggest that macrophage supernatants can directly enhance mesangial cell proliferation in vitro in both short-term and long-term culture, though this effect is lost at high concentrations of supernatant. These data lend support to the potential role of the macrophage in mediating mesangial expansion following renal injury.

Mesangial cell proliferation is directly enhanced by sera from patients with renal insufficiency

We undertook the present study to determine whether there is a direct effect of sera from patients with renal insufficiency on mesangial cell proliferation. Growth-arrested mesangial cells were incubated with sera from patients with varying degrees of renal insufficiency and then pulsed with [3H]thymidine. Thymidine uptake was progressively greater with more advanced renal failure and was linearly correlated with (creatinine)-1. This data suggests that serum from patients with loss of renal function contains mitogens capable of directly enhancing mesangial cell proliferation.

Renal extracellular matrix accumulation in acute puromycin aminonucleoside nephrosis in rats

Progressive renal fibrosis is considered to be the final common pathway leading to chronic renal insufficiency. In this study, the authors examined some of the cellular and molecular mechanisms regulating the renal accumulation of extracellular matrix (ECM) proteins using rats with puromycin amino-nucleoside (PAN) nephrosis as an acute model system. Puromycin aminonucleoside rats developed reversible nephrotic syndrome accompanied by an interstitial infiltrate of monocytes. The number of interstitial fibroblasts expressing ST4 antigen did not increase. During the first 4 days, steady-state mRNA levels for all genes examined remained at or below control levels. At 1 week, nephrotic syndrome and interstitial inflammation were established, and a period of renal cell proliferation occurred, identified by increased histone mRNA levels and localized by tritiated thymine autoradiography to tubular epithelial cells and occasional interstitial cells. Transforming growth factor-beta (TGF-beta) steady-state mRNA levels were increased eightfold, but returned to control levels by 3 weeks. At week 1, there was a 10- to 20-fold increase in kidney steady-state mRNA levels for genes encoding interstitial matrix proteins collagen I and fibronectin and basement membrane collagen IV. By in situ hybridization, alpha 1(I) procollagen mRNA was localized to interstitial cells. Immunofluorescence microscopy demonstrated focal accumulation of ECM proteins in the tubulointerstitial compartment at 2 and 3 weeks, but by 6 weeks, kidney immunohistology was normal again. Steady-state mRNA levels for the matrix degrading metalloproteinase stromelysin remained at control values, whereas the levels for interstitial collagenase were normal at week 1 and increased twofold to threefold at 2 and 3 weeks. Steady-state mRNA levels for the tissue inhibitor of metalloproteinases (TIMP) increased fivefold at 1 week and returned to baseline values over the next 2 weeks. The results of this study suggest that tubulointerstitial ECM accumulation occurs in rats with acute PAN nephrosis because of the activation of genes encoding several matrix proteins and inhibition of matrix degradation mediated by TIMP. These events are reversed during the phase of recovery from nephrotic syndrome. Increased mRNA levels for TGF-beta, possibly originating from inflammatory interstitial monocytes, are likely to be one of the mediators of the molecular events observed.

Glomerular macrophages and the mesangial proliferative response in the experimental nephrotic syndrome

Mesangial cell proliferation, which is a harbinger of glomerulosclerosis, occurs in both immune and nonimmune glomerulopathies. The proximity of infiltrating glomerular macrophages to the contractile mesangial cells during acute puromycin aminonucleoside (PA) nephrosis suggests the possibility of a paracrine effect on mesangial cell growth. To test this, three maneuvers to either raise or lower the glomerular macrophage number during acute PA nephrosis (2 weeks after PA) were employed: 1) an essential fatty acid-deficient (EFAD) diet; 2) a cholesterol-supplemented diet (CSD); and 3) a single dose (600 rad) whole-body X-irradiation (XI) given to CSD-fed PA rats. Both the glomerular macrophage number and proliferation within the mesangium were evaluated immunohistochemically with ED-1, a mouse monoclonal anti-rat macrophage label, and 19A2, a mouse monoclonal anti-proliferating cell nuclear antigen (PCNA)/cyclin antibody, respectively. Immunohistochemical detection of 5'-bromo-2'-deoxyuridine (BrdU) incorporation confirmed that proliferation was occurring within the mesangial zones. The EFAD diet significantly reduced both the glomerular macrophage and PCNA/cyclin-positive cell number at 2 weeks after PA with a positive correlation (r = 0.89, P < 0.05). The CSD maneuver significantly increased both the glomerular macrophage and PCNA/cyclin cell number with a strong degree of correlation (r = 0.95, P < 0.01). X-irradiation administered to CSD-fed PA rats significantly lowered both the glomerular macrophage and PCNA/cyclin-positive cell number at 2 weeks. In all groups, the glomerular tufts did not express muscle actin using HHF 35, a specific immunolabel, suggesting that the proliferation in this model is not related to direct mesangial cell injury. This study shows that maneuvers that modulate the glomerular macrophage number are also associated with corresponding changes in the number of proliferating cells within the mesangium, suggesting a paracrine growth stimulation by the infiltrating macrophage during acute PA nephrosis. The infiltrating glomerular macrophage may be an effector mechanism for the propagation of initial glomerular injury to glomerulosclerosis by augmenting mesangial cell proliferation early in the course of this nonimmune progressive glomerulopathy.

Tubulointerstitial changes as a major determinant in the progression of renal damage

Tubulointerstitial injury is an invariant finding in the chronically diseased kidney, irrespective of the type of disease or the compartment in which the disease originates. Such histologic changes are functionally significant in that scores for such damage, rather than glomerular injury, correlate with decline of renal function. This review summarizes (1) clinical evidence attesting to tubulointerstitial changes as an index of functional impairment, (2) mechanisms by which tubulointerstitial injury impairs renal function, and (3) interactions of pathologic processes in the vascular, glomerular, tubular, and interstitial compartments that culminate in tubulointerstitial injury. This report concludes with a review of interstitial fibrosis, a pathologic process regarded as an irreversible outcome from tubulointerstitial injury.

Pathogenesis of interstitial fibrosis in chronic purine aminonucleoside nephrosis

A cellular and molecular approach was used to gain new insight into the pathogenesis of interstitial fibrosis in chronic purine aminonucleoside nephrosis (PAN) nephrosis. Thirty experimental rats (PAN rats) were given 15 mg/100 g body wt of i.p. PAN at time 0, followed by 4.3 mg/100 g body wt i.p. on days 20, 27 and 34; 25 control rats received i.p. saline at the same time intervals. All rats had a right unilateral nephrectomy within the first four days. Groups of control and PAN rats were killed at 21, 37, 52, 72 and 91 days. Renal sections were studied by immunofluorescence to quantitate interstitial macrophages, T lymphocytes and fibroblasts, and to characterize the deposition of the extracellular matrix (ECM) proteins (collagens I, III and IV, fibronectin and laminin) and the tissue inhibitor of the metalloproteinases (TIMP). Steady state concentrations of mRNA from the whole kidney for these ECM proteins, the metalloproteinases, TIMP, and transforming growth factor beta (TGF-beta 1) were quantitated by Northern blot analysis. Significant increases in the number of interstitial macrophages and T lymphocytes were found in the PAN rat groups compared to that in controls. All ECM proteins examined were quantitatively increased in the tubulo-interstitium of PAN rats. The pattern of distribution of some ECM proteins was also modified in experimental animals. TIMP was increased in the interstitium of PAN rats; at later times, TIMP was most prominent in sclerotic regions of the glomeruli and in tubular protein droplets. Northern blot analysis revealed increased steady-state mRNA levels for components of each of the ECM proteins, no change for the metalloproteinases--stromelysin or collagenase--and a marked increase for TIMP and TGF-beta 1 in PAN animals. The results of this study suggest that the diffuse interstitial fibrosis found in chronic PAN nephrosis results from both increased production of ECM proteins and decreased matrix degradation.

Omega-3 polyunsaturated fatty acids: a potential new treatment of immune renal disease

Omega-3 polyunsaturated fatty acids are among new treatments being tested for efficacy in immune renal disease. The principal omega-3 polyunsaturated fatty acids are eicosapentaenoic acid and docosahexaenoic acid. They are derived from alpha-linolenic acid, which is found mainly in marine lipids. Eicosapentaenoic acid and docosahexaenoic acid undergo biologic transformation into trienoic eicosanoids that alter inflammatory mediators and vascular reactivity, both of which are important in the pathogenesis of certain glomerular immune diseases. Investigators have shown that proteinuria was prevented and survival was prolonged in autoimmune models of nephritis after dietary supplementation with fish oil. Furthermore, vascular damage may be modified by the influence of eicosapentaenoic acid and docosahexaenoic acid on blood rheology, aggregation of platelets, and plasma lipids. In short-term clinical studies, omega-3 polyunsaturated fatty acids seem to diminish cyclosporine-induced nephrotoxicity and the attendant complication of hypertension, to inhibit inflammatory and atherogenic mechanisms in lupus nephritis, and to preserve renal function and reduce proteinuria in IgA nephropathy. Long-term clinical trials for testing fish oil in these three clinical conditions are under way to confirm or refute these apparent beneficial therapeutic results.

A relationship between proteinuria and acute tubulointerstitial disease in rats with experimental nephrotic syndrome

The relationship between tubulointerstitial nephritis and proteinuria was characterized in experimental nephrosis in rats. In one group, proteinuria induced by aminonucleoside of puromycin (PAN) was reduced by using an 8% protein diet and adding the angiotensin I-converting enzyme (ACE) inhibitor enalapril to the drinking water. Two control groups were injected with saline and PAN, respectively, and fed a 27% protein diet. The first group had significantly reduced albuminuria and a definite attenuation of tubular cell injury. There was a strong positive correlation between the number of interstitial macrophages and albuminuria. The beneficial effect was reproduced by dietary-protein restriction alone, whereas ACE inhibition alone had an insignificant effect on the degree of proteinuria. Depletion of circulating T lymphocytes in one group of nephrotic rats eliminated interstitial lymphocytes but did not affect interstitial macrophage influx. Inhibition of the in situ proliferation of resident interstitial macrophages by unilateral kidney irradiation failed to change the intensity of the macrophage infiltration. Treatment of rats with sodium maleate produced proximal tubular cell toxicity but interstitial inflammation did not develop, suggesting that the latter is not a nonspecific response to tubular injury. These studies demonstrate a strong relationship between tubulointerstitial nephritis and the severity of proteinuria in experimental nephrosis.