Effect of lovastatin on the development of polycystic kidney disease in the Han:SPRD rat

Murine models of polycystic kidney disease: molecular and therapeutic insights

Numerous murine (mouse and rat) models of polycystic kidney disease (PKD) have been described in which the mutant phenotype results from a spontaneous mutation or engineering via chemical mutagenesis, transgenic technologies, or gene-specific targeting in mouse orthologs of human PKD genes. These murine phenotypes closely resemble human PKD, with common abnormalities observed in tubular epithelia, the interstitial compartment, and the extracellular matrix of cystic kidneys. In both human and murine PKD, genetic background appears to modulate the renal cystic phenotype. In murine models, these putative modifying effects have been dissected into discrete factors called quantitative trait loci and genetically mapped. Several lines of experimental evidence support the hypothesis that PKD genes and their modifiers may define pathways involved in cystogenesis and PKD progression. Among the various pathway abnormalities described in murine PKD, recent provocative data indicate that structural and/or functional defects in the primary apical cilia of tubular epithelia may play a key role in PKD pathogenesis. This review describes the most widely studied murine models; highlights the data regarding specific gene defects and genetic modifiers; summarizes the data from these models that have advanced our understanding of PKD pathogenesis; and examines the effect of various therapeutic interventions in murine PKD.

Dietary conjugated linoleic acid reduces PGE2 release and interstitial injury in rat polycystic kidney disease

BACKGROUND

Conjugated linoleic acid (CLA) describes positional isomers of linoleic acid (LA). Experimental health benefits of CLA include amelioration of malignancy and inflammatory disease and reduction of adiposity. The Han:SPRD-cy rat model of polycystic kidney disease (PKD) features prominent renal interstitial inflammation and fibrosis that is amenable to dietary modification. We studied CLA supplementation in the modification of inflammatory outcomes in the Han:SPRD-cy rat.

METHODS

Male offspring of Han:SPRD-cy heterozygotes were fed diets, using corn oil or corn oil with a CLA enriched oil (1% of diet by weight as CLA). After 8 weeks, measurements included renal function and morphometry, ex vivo release of renal prostaglandin E2 (PGE2), and renal and hepatic tissue fatty acid profiles.

RESULTS

Urine creatinine was significantly higher in PKD animals fed CLA (P = 0.004), but differences in serum creatinine and creatinine clearance did not quite reach significance in PKD animals. CLA feeding reduced interstitial inflammation (P < 0.001), fibrosis (P = 0.03), and renal PGE2 release (P = 0.02). Cystic change and oxidized low-density lipoprotein (LDL) staining did not change significantly. CLA feeding produced increased renal and hepatic CLA isomers. Hepatic, but not renal, LA proportion was reduced on the CLA diet. The renal proportion of the PGE2 precursor, arachidonic acid (AA), was not changed by diet, but hepatic AA proportion increased significantly with CLA feeding (P= 0.009).

CONCLUSION

CLA reduces renal production of PGE2, without reduced availability of the precursor fatty acid, AA. Short-term feeding of CLA to Han:SPRD-cy rats also has significant renal anti-inflammatory and antifibrotic effects. As inflammation and fibrosis are important components of the progression of chronic renal injury, CLA may be a useful agent in dietary amelioration of renal disease.

Bcl-xL overexpression protects from apoptosis induced by HMG-CoA reductase inhibitors in murine tubular cells

BACKGROUND

Hyperplasia is attributed to enhanced tubular cell proliferation with unbalanced cell death. The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors induce apoptosis in a variety of cell lines, including proximal tubular cells. However, the mechanisms by which statins induce apoptosis in tubular cells have not been fully addressed.

METHODS

Apoptosis induced by simvastatin was measured in murine tubular cells with and without overexpressing Bcl-xL. Expression of genes implicated in cell death was studied by Northern and Western blot.

RESULTS

The treatment of proliferating murine tubular cells (MCT) with simvastatin induced apoptosis in a time- and dose-dependent manner (0.1 to 1 micromol/L). Apoptosis was correlated with Bcl-xL mRNA and protein down-regulation. By contrast, the treatment with simvastatin did not modify the expression of the proapoptotic protein Bax. Simvastatin treatment was associated with cytochrome C release from the mitochondria to the cytosol. We also observed the presence of active caspase 9 and 3 during apoptosis induced by simvastatin. These effects were reversed by mevalonate, farnesylpyrophosphate (FPP), and geranylgeranylpyrophosphate (GGPP), suggesting the involvement of protein prenylation. Simvastatin appears to alter the balance between cell-life and death-promoting genes, as reflected by the decreased Bcl-xL/Bax ratio. Supporting this hypothesis, overexpression of Bcl-xL reduced the amount of apoptosis induced by simvastatin by 80% when compared with control vector-expressing cells. The overexpression of Bcl-xL also prevented the activation of caspase 9 and 3.

CONCLUSION

Our results indicate that down-regulation of Bcl-xL expression mediates apoptosis induced by statins in tubular cells. These results may be relevant to the treatment of disorders characterized by altered tubular proliferation.

Renal activation of extracellular signal-regulated kinase in rats with autosomal-dominant polycystic kidney disease

BACKGROUND

Abnormal proliferation of renal tubule epithelial cells is a central factor in the biogenesis and sustained expansion of cysts in autosomal-dominant polycystic kidney disease (ADPKD). Recent evidence from in vitro studies of human cyst wall epithelial cells has implicated a role for the mitogen-activated protein (MAP) kinase pathway in this aberrant proliferation. To determine the extent to which this signaling pathway is involved in cyst pathogenesis in vivo, we measured the expression of select components of the MAP kinase cascade in Han:SPRD rats with ADPKD at an early stage of the disease.

METHODS

Kidneys of 8-week-old normal Han:SPRD rats (+/+) or rats heterozygous (Cy/+) for ADPKD were examined by Western blot analysis and immunohistochemistry to determine the expression of extracellular-regulated kinase (ERK), phosphorylated ERK (P-ERK), Raf-1 (MAPKKK), phosphorylated Raf-1 (P-Raf-1), B-Raf, Rap-1 and phosphorylated protein kinase A (P-PKA).

RESULTS

P-ERK was expressed to a greater extent in Cy/+ kidneys (3.74 +/- 1.07 fold) than in normal kidneys, whereas ERK abundance was not different. P-Raf-1 levels were higher in Cy/+ than in +/+ kidneys (1.53 +/- 0.08 fold) consistent with upstream stimulation of receptor tyrosine kinase. B-Raf and Raf-1 abundances were greater in Cy/+ than in +/+ (1.74 +/- 0.25 and 1.27 +/- 0.08 fold, respectively). In Cy/+, immunohistochemistry showed increased P-ERK and B-Raf expression in the abnormal mural epithelial cells within cysts. These findings, together with the detection of P-PKA and the small G protein, Rap-1, in cyst epithelial cells, implicate a potential role for cyclic adenosine monophosphate (AMP) in the activation of ERK in ADPKD cells.

CONCLUSIONS

We conclude that the MAP kinase pathway is activated to the level of ERK in the abnormal mural epithelial cells lining cysts in animals with a dominantly inherited type of polycystic kidney disease. We suggest that cAMP, acting through PKA, Rap-1 and B-Raf, may contribute to the activation of ERK in a way that complements receptor tyrosine kinase-mediated agonists in the promotion of cyst enlargement.

Detrimental effects of a high fat diet in early renal injury are ameliorated by fish oil in Han:SPRD-cy rats

Dietary fish oils containing (n-3) fatty acids can modulate renal inflammatory injury. We previously demonstrated that a high fat (HF) diet worsens early renal disease progression in the Han:SPRD-cy rat model of polycystic kidney disease (PKD). Therefore, using HF (20 g/100 g diet) and low fat (LF; 5 g/100 g diet) diets, we compared the effects of menhaden oil (MO), soybean oil (SO) and cottonseed oil (CO) on renal function and histology in male Han:SPRD-cy rats fed the diets for 6 wk in the early stages of renal disease. Overall, rats fed HF compared with those fed LF diets had larger kidneys, more renal fibrosis and lower creatinine clearance (main effects of fat level). Rats fed MO rather than CO and SO diets had significantly lower kidney weights, kidney water content, cyst volumes and serum cholesterol and triglyceride concentrations (main effects of fat type). Rats fed MO diets also had less renal fibrosis than those fed CO diets, but the least fibrosis was in rats fed SO diets. Analysis of simple effects (due to interactions between fat level and type) revealed that HF diets increased renal inflammation in rats fed CO diets, but reduced inflammation was present in those fed SO and MO diets; HF diets also increased compared with LF diets serum urea nitrogen concentrations in rats fed the MO and CO diets, but not the SO diet. These results confirm that high dietary fat worsens early disease progression in this model of renal disease, and further demonstrate that diets with oils containing (n-3) fatty acids ameliorate some of the detrimental effects of a high fat diet.

Dietary flax oil reduces renal injury, oxidized LDL content, and tissue n-6/n-3 FA ratio in experimental polycystic kidney disease

As whole flaxseed is beneficial in the treatment of experimental renal disease, we undertook a study to determine whether previously documented benefits of whole flaxseed could be reproduced with dietary low-lignan flax oil (FO), a rich source of alpha-linolenic acid, in experimental polycystic kidney disease. Male offspring of Han:SPRD-cy heterozygous rats were fed a synthetic diet containing FO or corn oil (CO) for 8 wk from the time of weaning. Renal inflammation, fibrosis, proliferation, cystic change, and oxidized-LDL were assessed morphometrically. Hepatic and renal lipid composition was assessed using GC. FO feeding produced hepatic and renal enrichment of n-3 PUFA and an increase in C18:>C18 PUFA ratios (18-carbon PUFA compared to longer-chain PUFA), with a reduction in proportion of hepatic long-chain PUFA. The FO-based diet was associated with lower mean cystic change by 29.7% (P = 0.018), fibrosis by 21.7% (P = 0.017), macrophage infiltration by 31.5% (P < 0.0001), epithelial proliferation by 18.7% (P = 0.0035), and ox-LDL detection by 31.4% (P < 0.0001) in Han:SPRD-cy heterozygotes. Serum creatinine was significantly lower in FO-fed diseased animals. A small hypocholesterolemic effect was noted in all animals fed FO. FO feeding moderates renal injury, modifies the profile of substrates available for elongation to eicosanoid precursors, and inhibits the elongation of C18 PUFA in this model. The consumption of FO-based products may prove a more practical way of obtaining health benefit than attempts to increase dietary content of unrefined seed.

The effects of antihypertensive agents on the survival rate of polycystic kidney disease in Han:SPRD rats

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disorder in humans. Hypertension is one of the major complications, and its control might affect the renal survival and disease mortality. Suitable antihypertensive agents have been discussed based on clinical and animal studies, but no definitive conclusion has been reached. Generally, therefore, all antihypertensives are indiscriminately treated as if providing the same level of blood pressure control. In this study, the blood pressure control of two antihypertensives was investigated using a rat model of ADPKD in humans. Twenty-four male Hannover-Sprague Dawley (Han:SPRD) rats were divided into three groups: a group receiving amlodipine (6 mg/day), a group receiving benazepril (6 mg/day) and an untreated control group. Blood pressure, body weight, and urinary protein excretion were regularly measured up to week 52. Amlodipine and benazepril significantly decreased blood pressure and urinary protein excretion to the same degree. Moreover, a remarkably prolonged survival rate was observed in both groups (at week 52, the survival rate was 25% in controls, 50% in the amlodipine group, and 50% in the benazepril group). Examination at autopsy revealed that enlarged cysts were prevalent in the renal tissue of both experimental all three groups, suggesting that the cystic disease had reached the end-stage in all the animals. In conclusion, both amlodipine and benazepril significantly improved blood pressure control, urinary protein excretion, and survival rate, possibly due to their enhancement of renal survival.

Effect of simvastatin on renal function in autosomal dominant polycystic kidney disease

BACKGROUND

In animal models, HMG-CoA reductase inhibitors were able to improve renal function and endothelium-dependent vascular reactivity. In various experimental renal diseases, including autosomal dominant polycystic kidney disease (ADPKD), HMG-CoA reductase inhibitors improved the rate of decline in renal function. We studied the effect of simvastatin on ADPKD patients.

METHODS

In a double-blind cross-over study, 10 normocholesterolaemic ADPKD patients were treated in random order for 4 weeks with 40 mg simvastatin or placebo daily. After each treatment period, we investigated the effect of simvastatin on renal blood flow and endothelium-dependent vascular reactivity. These periods were separated by a 4-week wash-out period.

RESULTS

After treatment with simvastatin, glomerular filtration rate (GFR) significantly increased from 124+/-4 ml/min to 132+/-6 ml/min (P<0.05). Simultaneously, effective renal plasma flow (ERPF) increased significantly from 494+/-30 ml/min to 619+/-67 ml/min after simvastatin treatment (P<0.05). These renal effects were accompanied by a significantly enhanced vasodilator response to acetylcholine in the forearm after simvastatin treatment. Total serum cholesterol levels were significantly reduced after treatment with simvastatin, from 4.24+/-0.32 to 3.17+/-0.22 mmol/l (P<0.001).

CONCLUSION

We concluded that simvastatin treatment can ameliorate renal function in ADPKD patients, by increasing renal plasma flow, possibly via improvement of endothelial function. Long-term clinical trials with HMG-CoA reductase inhibitors are needed to confirm these results and to establish a chronic inhibiting effect of HMG-CoA reductase inhibitors on the progression towards end-stage renal disease in ADPKD patients.

Treatment prospects for autosomal-dominant polycystic kidney disease

An increased understanding of the molecular genetic and cellular pathophysiologic mechanisms responsible for the development of autosomal-dominant polycystic kidney disease (ADPKD), made possible by the advances in molecular biology and genetics of the last three decades, has laid the foundation for the development of effective therapies. As the concept that a polycystic kidney is a neoplasm in disguise is becoming increasingly accepted, the development of therapies for ADPKD may benefit greatly from the expanding body of information on cancer chemoprevention and chemosuppression. This review summarizes the observations that already have been made and discusses therapies for PKD that deserve investigation.

A possible role for metalloproteinases in renal cyst development

The expansion of cysts in polycystic kidneys bears several similarities to the invasion of the extracellular matrix by benign tumors. We therefore hypothesized that cyst-lining epithelial cells produce extracellular matrix-degrading metalloproteinases and that the inhibition of these enzymes may represent a potential target for therapeutic intervention. Using in situ hybridization, we first analyzed the expression of membrane-type metalloproteinase 1 (MMP-14), an essential matrix metalloproteinase, of its inhibitor TIMP-2, and of the cytokine transforming growth factor (TGF)-beta2 in the (cy/+) rat model of autosomal-dominant polycystic kidney disease. Upregulated MMP-14 mRNA was predominantly located in cyst-lining epithelia and distal tubules, whereas TIMP-2 mRNA was confined almost exclusively to fibroblasts. TGF-beta2, a cytokine known to regulate the expression of matrix metalloproteinases and their inhibitors, was also expressed by cyst wall epithelia. We then treated (cy/+) rats with the metalloproteinase inhibitor batimastat for a period of 8 wk. The treatment with the metalloproteinase inhibitor batimastat resulted in a significant reduction of cyst number and kidney weight. Our study suggests that metalloproteinase inhibitors represent a new therapeutic tool against polycystic kidney disease, which should be applicable independently of the background of the disease.

Endotoxin and nanobacteria in polycystic kidney disease

BACKGROUND

Microbes have been suspected as provocateurs of polycystic kidney disease (PKD), but attempts to isolate viable organisms have failed. Bacterial endotoxin is the most often reported microbial product found in PKD fluids. We assessed potential microbial origins of endotoxin in cyst fluids from 13 PKD patients and urines of PKD and control individuals.

METHODS

Fluids were probed for endotoxin and nanobacteria, a new bacterium, by the differential Limulus Amebocyte Lysate assay (dLAL), genus-specific antilipopolysaccharide (LPS) antibodies, monoclonal antibodies to nanobacteria, and hyperimmune serum to Bartonella henselae (HS-Bh). Selected specimens were also assessed by transmission electron microscopy (TEM) and nanobacterial culture methods.

RESULTS

LPS or its antigenic metabolites were found in more than 75% of cyst fluids tested. Nanobacteria were cultured from 11 of 13 PKD kidneys, visualized in 8 of 8 kidneys by TEM, and immunodetected in all 13 PKD kidneys. By immunodetection, nanobacterial antigens were found in urine from 7 of 7 PKD males, 1 of 7 PKD females, 3 of 10 normal males, and 1 of 10 normal females. "Nanobacterium sanguineum" was dLAL positive and cross-reactive with antichlamydial LPS and HS-Bh. Some cyst fluids were also positive for LPS antigens from Escherichia coli, Bacteroides fragilis and/or Chlamydia, and HS-Bh, as were liver cyst fluids from one patient. Tetracycline and citrate inhibited nanobacterial growth in vitro.

CONCLUSION

Nanobacteria or its antigens were present in PKD kidney, liver, and urine. The identification of candidate microbial pathogens is the first step in ascertaining their contribution, if any, to human disease.

Effect of probucol in a murine model of slowly progressive polycystic kidney disease

Epithelial proliferation, extracellular matrix remodeling, and interstitial inflammation are central elements in the pathogenesis of slowly progressive polycystic kidney disorders. Probucol, an antioxidant that lowers plasma cholesterol, has been shown to decrease smooth muscle cell proliferation and macrophage accumulation in blood vessels and to prevent restenosis after coronary angioplasty. We determined in 30-day-old male BDF1-pcy hybrid mice (derived from mating DBA/2FG-pcy and C57BL/6FG-pcy) the effect of probucol administered in the diet (1%) for 200 days on kidney weight relative to body weight (KW/BW), cyst expansion, renal interstitial fibrosis, and serum urea nitrogen (SUN) concentration. Animals were fed a moderately high-protein diet (HPD, 36%) to accentuate the development of renal cysts and to promote interstitial fibrosis. Probucol decreased serum cholesterol from 68 to 16 mg/dL but had no effect on food intake or body weight. Probucol decreased relative kidney size from 4.16% +/- 0.55% to 2.64% +/- 0.12% KW/BW (P < 0.01), SUN from 30.5 +/- 1.8 to 25.9 +/- 1.0 mg/dL (P < 0.05), cystic index from 2.45 +/- 0.11 to 1.36 +/- 0.10 (P < 0.01), and fibrosis index from 2.40 +/- 0.11 to 1.82 +/- 0.08 (P < 0.01). We conclude that probucol ameliorates the progressive deterioration in renal function and structure in pcy mice ingesting a relatively high level of dietary protein.

Modification of polycystic kidney disease and fatty acid status by soy protein diet

Modification of polycystic kidney disease and fatty acid status by soy protein diet.

BACKGROUND

Previous studies have demonstrated that soy protein can slow progression of renal injury in the Han:SPRD-cy rat. We undertook a study to establish whether this benefit was independent of any nutritional deprivation, and whether or not it was associated with changes in polyunsaturated fatty acid status that have been previously linked to the anti-inflammatory or antineoplastic potential of soy diets.

METHODS

Male Han:SPRD-cy rats were pair fed a 20% casein or 20% soy protein diet for six weeks from weaning. Tissue was harvested for analysis of cystic change, cell proliferation, macrophage infiltration, and fibrosis. Renal and hepatic tissues were also harvested for lipid analysis using gas chromatography.

RESULTS

Animals thrived on both diets. Soy protein feeding was associated with reduced cystic change (4.3 vs. 7.0 mL/kg, P < 0.0001), epithelial cell proliferation (15.7 vs. 21.0 cells/mm epithelium, P < 0.0001), macrophage infiltration (25.3 vs. 43.5 cells/high-power field, P < 0.0001), and fibrosis (0.6 vs. 1.07 mL/kg, P < 0.0001). The soy diet prevented a significant elevation in serum creatinine in diseased versus normal animals. Soy feeding was associated with higher renal and hepatic linoleic acid content and higher hepatic alpha-linolenic acid, but lower hepatic arachidonic acid content.

CONCLUSIONS

Isocaloric soy protein feeding ameliorates both epithelial and interstitial changes in the Han:SPRD-cy rat independent of a hypocholesterolemic effect. The histologic benefit is associated with changes in polyunsaturated fatty acid metabolism that may influence both inflammatory and proliferative pathways.

Recent advances in statins and the kidney

BACKGROUND

Experimental and clinical studies have suggested a correlation between the progression of renal disease and dyslipidemia. Indeed, apolipoprotein B-containing lipoproteins have been demonstrated to be an independent risk factor for the progression of renal disease in humans. Interventional strategies in experimental models of renal disease have clearly demonstrated a beneficial effect on renal structure and function in a variety of models of renal disease. Investigations into the mechanisms whereby reduction of lipids by lipid-lowering agents benefits renal disease have suggested that the 3-hydroxy-3-methylglutaryl coenzyme reductase inhibitors, the so-called statin class of lipid-lowering agents, may have additional effects on the biology of inflammation that are germane to the progression of renal disease.

METHODS

Both in vivo and in vitro studies that investigated secondary mechanisms of statin effects are reviewed. In addition, new studies that investigated the effects on novel cellular mechanisms are presented.

RESULTS

Lipid-lowering agents appear to have biologically important effects in modulating a variety of intracellular signaling systems involved in cell proliferation, inflammatory responses that involve macrophage adhesion, recruitment, and maturation. In addition, the effects on fibrogenesis have been recently defined. These latter effects may influence not only the development of glomerulosclerosis, but also interstitial fibrosis. These potentially major effects of lipid-lowering agents appear to be related to the effects on intracellular synthesis of nonsterol isoprenoids, which are involved in prenylation of critical small molecular weight proteins involved in cell signal transduction.

CONCLUSIONS

In addition to the beneficial effects of the reduction in serum lipids, statins and other lipid-lowering agents may influence important intracellular pathways that are involved in the inflammatory and fibrogenic responses, which are common components of many forms of progressive renal injury.

Effect of lipid-lowering strategies on tubular cell biology

BACKGROUND

Interstitial fibrosis and the development of renal cysts are crucial phenomena in renal disease progression. While 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors has been shown to reduce the progression of several experimental nephropathies, the mechanism of their potential protective effect remaines unclear.

METHODS

The antiproliferative, apoptotic, and fibrinolytic effects of HMG-CoA reductase inhibitors were assessed in primary cultured rat (rPTCs) and mouse proximal tubule cells (mPTCs), in isolated rat proximal tubules, and in vivo in 5/6 nephrectomized rats (Nx).

RESULTS

In vitro, lovastatin inhibited rPTC proliferation in a manner selectively prevented by mevalonate, farnesyl-, or geranylgeranyl-pyrophosphate (FPP or GGPP). Lovastatin reduced membrane-bound p21ras and fetal calf serum-induced c-fos and c-jun protein expression. Gel shift assay showed that lovastatin reduced activated protein-1 (AP-1) binding activity. In vivo, lovastatin inhibited tubular cell proliferation after Nx, as measured by proliferative cell nuclear antigen staining. Lovastatin-treated mPTCs displayed nucleus cleavage and DNA ladder formation, which were prevented by GGPP. Like C3 exoenzyme, lovastatin induced actin filament disruption, which preceded evidence of apoptosis. Lovastatin increased tissue-type plasminogen activator (PA) and decreased PA inhibitor activities and antigens; these effects were prevented by mevalonate and GGPP but not FPP, and were reproduced by C3 exoenzyme in a manner insensitive to GGPP.

CONCLUSIONS

HMG-CoA reductase inhibitors decreased proliferation, increased apoptosis, and enhanced fibrinolytic activity of renal tubular cells via modulation of different isoprenylated proteins. These effects could participate to reduce the progression of renal diseases.

In vitro effects of simvastatin on tubulointerstitial cells in a human model of cyclosporin nephrotoxicity

To investigate the possibility that 3-hydroxy-3-methylglutaryl CoA (HMGCoA) reductase inhibitors ameliorate renal disease via direct effects on the tubulointerstitium, primary cultures of human proximal tubule cells (PTC) and renal cortical fibroblasts (CF) were exposed for 24 h to simvastatin (0.1-10 micromol/l) under basal conditions and in the presence of 1,000 ng/ml of cyclosporin (CsA), which we have previously shown to promote in vitro interstitial matrix accumulation at least partially via activation of local cytokine networks. Simvastatin, in micromolar concentrations, engendered cholesterol-independent inhibition of CF and PTC thymidine incorporation and cholesterol-dependent suppression of PTC apical Na+/H+ exchange (NHE) (ethylisopropylamiloride-sensitive apical 22Na+ uptake). Similarly, CF secretion of insulin-like growth factor-I (IGF-I) and IGF binding protein-3 were depressed, whereas CF collagen synthesis ([3H]proline incorporation) and PTC secretion of the fibrogenic cytokines, transforming growth factor-beta1, and platelet-derived growth factor were unaffected. A lower concentration (0.1 micromol/l) of simvastatin did not affect any of the above parameters under basal conditions but completely prevented CsA-stimulated CF collagen synthesis (control, 6.6 +/- 0.6; CsA, 8.3 +/- 0.6; CsA+simvastatin, 6.2 +/- 0.5%; P < 0.05) and IGF-I secretion (89.5 +/- 16.6, 204.7 +/- 57.0, and 94.6 +/- 22.3 ng. mg protein-1. day-1, respectively; P < 0.05). The results suggest that simvastatin exerts direct cholesterol-dependent and -independent effects on the human kidney tubulointerstitium. HMGCoA reductase inhibitors may ameliorate interstitial fibrosis complicating CsA therapy via direct actions on human renal cortical fibroblasts.

Flaxseed ameliorates interstitial nephritis in rat polycystic kidney disease

BACKGROUND

Flaxseed has demonstrated useful antiinflammatory properties in a number of animal models and human diseases. We undertook a study to determine if flaxseed would also modify clinical course and renal pathology in the Han:SPRD-cy rat.

METHODS

Male Han:SPRD-cy rats were pair fed a 10% flaxseed of control rat chow diet for eight weeks from weaning. Tissue was harvested for analysis of cystic change, apoptosis, cell proliferation, and fibrosis. Tissue was also harvested for lipid analysis using gas chromatography.

RESULTS

Animals thrived on both diets. Flaxseed-fed animals had lower serum creatinine (69 vs. 81 mumol/liter, P = 0.02), less cystic change (1.78 vs. 2.03 ml/kg, P = 0.02), less renal fibrosis (0.60 vs. 0.93 ml/kg, P = 0.0009), and less macrophage infiltration (13.8 vs. 16.7 cells/high-power video field) of the renal interstitium than controls. The groups did not differ in renal tubular epithelial cell apoptosis and proliferation. Lipid analysis revealed significant renal enrichment of 18 and 20 carbon omega 3 polyunsaturated fatty acids (total omega 6:omega 3 ratio 3.6 vs. 9.1, P < 0.0001).

CONCLUSIONS

Flaxseed ameliorates Han:SPRD-cy rat polycystic kidney disease through moderation of the associated chronic interstitial nephritis. The diet alters renal content of polyunsaturated fatty acids in a manner that may promote the formation of less inflammatory classes of renal prostanoids.

Dietary soy protein effects on inherited polycystic kidney disease are influenced by gender and protein level

The effects of dietary soy protein compared to casein were examined in male and female CD1-pcy/pcy (pcy) mice with polycystic kidney disease. Animals 10 wk of age were fed purified diets containing either soy protein isolate or casein given at a level of 17.4 or 6% protein. After 13 wk on the diets, body weights and serum concentrations of albumin and protein indicated that protein nutrition was adequate on all diets. Overall, animals fed soy protein versus casein had 28% lower (P = 0.0037) relative kidney weights (g/100 g body wt), 37% lower (P = 0.0089) cyst scores (% cyst area x relative kidney weight), and 25% less (P = 0.0144) kidney water (g). Dietary protein reduction resulted in 30% lower (P = 0.0010) relative kidney weights, 25% lower (P = 0.0327) cyst scores, and 35% less (P = 0.0001) kidney water. Analysis of interactions between main effects revealed that the effects of soy protein on kidney size were significant only in females, and that effects of soy protein on cyst score were significant only in animals on the low protein diets. In addition, differences in kidney weights and cyst score due to protein reduction were significant in animals fed soy protein, but not in those fed casein as the protein source. These results show that both dietary protein source and level significantly affect polycystic kidney disease in pcy animals, with the effects of dietary soy protein being most pronounced in female animals fed the low protein diets and the effects of protein reduction being most pronounced in animals fed soy protein-based diets.

Soy protein modification of rat polycystic kidney disease

We undertook a study to determine whether soy protein feeding would ameliorate renal injury in the Han:SPRD-cy rat model of polycystic kidney disease (PKD). Male offspring of Han:SPRD-cy heterozygotes received isocaloric diets based on 20% casein or 20% heat-treated soy protein at weaning ad libitum for 8 wk. Soy-fed animals demonstrated lower serum creatinine (66 vs. 125 mumol/l; P = 0.002), lower urinary ammonium excretion (0.080 vs. 0.173 mmol/kg; P = 0.01), reduced renal cysts (0.98 vs. 4.92 ml/kg body wt, P < 0.0001), renal fibrosis (0.79 vs. 1.4 ml/kg; P = 0.016), macrophage infiltration, renal tubular cell proliferation, and apoptosis. Proton nuclear magnetic resonance (1H-NMR) studies of urine demonstrated that soy diet was associated with increased losses of citric acid cycle organic anions. 1H-NMR of perchloric acid-extracted tissue found that levels of succinate were not depleted in soy-fed animals, despite increased urinary losses. Soy-fed animals had marked elevation of tissue betaine (P < 0.001), with reduced taurine and cholines, compared with casein-fed animals (P < 0.001). Soy feeding dramatically reduces both tubular and interstitial pathology in the Han:SPRD-cy rat model of PKD, through mechanisms that remain to be determined.

New insights into polycystic kidney disease and its treatment

Major advances in the understanding of the genetics and pathogenesis of autosomal dominant polycystic kidney disease have occurred within the past year. The proteins encoded by the PKD1 and PKD2 genes, polycystin 1 and polycystin 2, are membrane proteins, capable of interacting physically in vitro, and are likely components of a complex signalling pathway. The majority of PKD1 and PKD2 mutations so far identified are unique inactivating mutations dispersed over the entire genes. Immunohistochemical studies have shown that polycystin 1 and polycystin 2 are developmentally regulated and are overexpressed in polycystic kidneys. The cysts probably result from clonal expansions of single cells. The demonstration of loss of heterozygosity for PKD1 and the absence of immunoreactive polycystin 1 in approximately 20% of the cysts supports a two-hit tumor suppressor gene model of cystogenesis. Regardless of the nature of the initial pathogenic mechanism, the cysts in autosomal dominant polycystic kidney disease are accompanied by partial dedifferentiation of the epithelial cells, disregulation of epithelial cell proliferation, expression of a secretory phenotype, and disarray of cell matrix interactions which leads to interstitial inflammation and matrix accumulation. Recent observations in animal models of inherited polycystic kidney disease have implicated oxidative stress in its pathogenesis. These downstream pathogenetic events have been targeted for intervention, and an increasing number of studies have demonstrated that the course of polycystic kidney disease in rodents can be altered by environmental and pharmacological interventions. Nevertheless, these experimental observations cannot be extrapolated to human autosomal dominant polycystic kidney disease. The recent generation of mice with PKD1 or PKD2 targeted mutations will help to bridge this gap.

Lovastatin-induced inhibition of renal epithelial tubular cell proliferation involves a p21ras activated, AP-1-dependent pathway

Proliferation of tubular epithelial cells underlies the development of cystic lesions and the subsequent impairment of renal function after renal mass reduction. The effect of HMG CoA reductase inhibitors (HRI) on cell proliferation was investigated in rat renal proximal tubular epithelial cells in primary culture. Treatment of renal tubular epithelial cells with three different HRI reduced fetal calf serum (FCS)-induced [3H]-thymidine incorporation (IC50 values were 0.7 microM, 1.7 microM, and 1.6 microM for simvastatin, lovastatin, and compactin, respectively), and lovastatin blocked BrdUrd incorporation, as assessed by immunocytochemical studies. The proliferative effect of epidermal growth factor (EGF) was similarly abolished by lovastatin. The effect of lovastatin (1 microM) was prevented by 100 microM mevalonate, 5 microM farnesyl-pyrophosphate and 5 microM geranylgeranyl-pyrophosphate (in percent of control value, 31% vs. 102%, 60%, and 82%, respectively) while cholesterol and other products of the mevalonate pathway were inactive. Immunoblot analysis showed that lovastatin decreased membrane-bound p21ras and inhibited FCS-induced c-fos and c-jun protein expression. Furthermore, electrophoretic mobility shift assay demonstrated the functional impairement of AP-1 DNA binding activity in lovastatin-treated cells. In conclusion, these results demonstrate that HRI are antiproliferative in epithelial tubule cells and that this effect is exerted, at least in part, via inhibition of the p21ras-activated and AP-1 dependent mitogenic cascade.

HMG-CoA reductase inhibitors induce apoptosis in mouse proximal tubular cells in primary culture

Renal cyst formation in polycystic diseases or after nephron reduction is attributed to enhanced tubular cell proliferation with unbalanced cell death. The induction of tubular cell death could be effective to reduce renal cyst formation. In this study, we examined the effects of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors on apoptosis in mouse proximal tubular (MPT) cells in primary culture. After treatment with HMG-CoA reductase inhibitors, the extracted DNA was analyzed by gel-electrophoresis under ultraviolet light. Apoptosis was evaluated quantitatively by estimating the ratio of fragmented DNA over intact DNA. For morphologic studies, cells were stained with Hoechst 33,258. DNA ladder pattern of 200 kDa typical of apoptosis and significant increase in DNA fragmentation were seen after 24 hours of treatment with lovastatin, a HMG-CoA reductase inhibitor. Staining with the Hoechst dye revealed cleavage of nucleus into pieces under the same condition. Geranylgeranylpyrophosphate (20 microM) and mevalonate (500 microM) completely reversed the effect of lovastatin, while farnesylpyrophosphate (20 microM) partially reversed it. Other products of HMG-CoA pathway such as cholesterol, ubiquinone, dolichol, and isopentenyladenine had no effect. Perillic acid and alpha-hydoxyfarnesylphosphonic acid, isoprenylation inhibitors, induced apoptosis of the cells. A treatment with lovastatin caused actin filament disruption. Cytochalasin D, an inhibitor of actin polymerization, induced apoptosis. Interleukin-1 beta-converting enzyme inhibitor II, a protease inhibitor, had no effect on the apoptosis induced by either HRI or cytochalasin D. The present study suggests that in mouse proximal tubules, HMG-CoA reductase inhibitors induce apoptosis via inhibition of isoprenoid production, and disruption of actin filaments may play a role in the apoptosis induction.

The effect of paclitaxel on the progression of polycystic kidney disease in rodents

Woo et al (Nature 368:750-753) reported that parenteral administration of paclitaxel arrested the striking renal enlargement and prolonged life in C57BL/6J-cpk/cpk mice with a rapidly progressive form of polycystic kidney disease (PKD). In the current study, we sought to determine whether paclitaxel could alter the progression of other forms of hereditary PKD in rodents. Paclitaxel was administered by intraperitoneal injection to C57BL/6J-cpk/cpk mice and Han:SPRD-Cy/Cy rats with rapidly progressive PKD and to DBA/2FG-pcy/pcy mice and Han:SPRD-Cy/+ rats with slowly progressive PKD. Paclitaxel (150 micrograms/wk) prolonged the survival of cpk/cpk mice from 24.5 days to more than 65 days and decreased kidney weight relative to body weight from 16.5% at 21 days of age to 8.2% at more than 65 days of age. Mortality attributable to paclitaxel was 12%. By contrast, the administration of paclitaxel (0.1 to 15 mg/kg/wk) to 7- to 10-day-old Han:SPRD-Cy/Cy rats with rapidly progressive PKD had no effect on the course of the disease; moreover, paclitaxel caused severe side effects and premature death in all the Cy/Cy animals. Heterozygous male Cy/+ rats develop slowly progressive renal enlargement and azotemia. Paclitaxel, administered at 7, 15, or 27 mg/kg/wk to male Cy/+ rats from 4 until 10 weeks of age, reduced body weight gain, had an inconsistent effect on kidney weight relative to body weight, and had no effect on the serum urea nitrogen concentration. Mortality associated with the 7, 15, and 27 mg/kg/wk doses of paclitaxel was 0%, 15.4%, and 28.5%, respectively. DBA/2FG-pcy/pcy mice of either sex developed slowly progressive renal enlargement and azotemia. The administration of paclitaxel (100 to 150 micrograms/wk) from 2 to 10 weeks of age to DBA/2FG-pcy/pcy mice with cystic disease had no effect on the increase in kidney weight or on the level of serum urea nitrogen in comparison to untreated cystic animals. Mortality associated with 100- and 150-micrograms/wk doses of paclitaxel was 0% and 20%, respectively. We conclude that paclitaxel diminished the rate of renal enlargement and increased the life span of cpk/cpk mice but not Cy/Cy rats with rapidly progressive forms of PKD. Paclitaxel had no apparent benefit in Cy/+ rats nor pcy/pcy mice with slowly progressive PKD. On the basis of these studies in rodents, it appears that paclitaxel has limited potential usefulness as a therapeutic agent in the treatment of PKD.

The etiology, pathogenesis, and treatment of autosomal dominant polycystic kidney disease: recent advances

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in at least three different genes: PKD1, PKD2, and PKD3. ADPKD1 is an inherited disorder that has led to the discovery of a novel protein, polycystin. Polycystin, a 460 kd protein with a host of domains implicating a potential role in cell-cell and cell-matrix regulation, is encoded by a 52 kb gene with a 14 kb mRNA. The PKD2 protein is also large (110 kd) and is thought to interact with polycystin. ADPKD1 is caused by mutated DNA that encodes an abnormal form of polycystin. Polycystin appears to have a normal role in the differentiation of epithelial cells, and when defective, these cells fail to maturate fully. These incompletely differentiated cells proliferate abnormally and express altered amounts of otherwise normal electrolyte transport proteins that result in excessive secretion of solute and fluid into the cysts. The proliferation of the cells and the associated apoptosis, and the secretion of the fluid into the cysts created by the enlarging tubule segments appear to be regulated by growth factors, hormones, and cytokines that can alter the extent to which the disease is clinically expressed among individuals. The formation of the cysts is associated with complex changes in the extracellular matrix of the kidneys and other organs that may be directly or indirectly tied to mutated polycystin. The summation of these pathogenetic elements leads to renal interstitial infiltration, with monocytes, macrophages, and fibroblasts culminating in fibrosis and progressive loss of renal function. The modem understanding of cyst pathogenesis opens opportunities to develop treatments that may diminish or halt altogether the progression of this disease.

Modification of disease progression in rats with inherited polycystic kidney disease

The most common inherited form of human polycystic kidney disease (PKD), autosomal dominant PKD (ADPKD), is a leading cause of chronic renal failure, but has a variable clinical presentation, with end-stage renal disease occurring in only 25% to 75%. Several findings are consistent with the idea that factors in addition to the primary mutation can affect the progression of cystic change and chronic renal failure in PKD. Epithelial cell proliferation is a central element in the pathogenesis of renal cysts. We postulated that the superimposition of a growth-promoting stimulus might promote more intense proliferation of cystic epithelial cells in inherited cystic disease. To study this, we subjected Han:SPRD rats, with a form of ADPKD that resembles human ADPKD, from 4 until 10 weeks of age to diets designed to promote tubule cell growth. The diets included supplemental NH4Cl (280 mmol/L in drinking water), limited dietary K+ (0.016% of diet; control diet was 1.1% K+), and increased dietary protein (50%; control diet was 23% protein). Treatments designed to promote cell growth caused more aggressive PKD in males and females, worsened azotemia in males, and resulted in azotemia in females (which normally develop PKD but not azotemia at the ages studied). NH4Cl, K+ restriction, and increased dietary protein each caused greater kidney enlargement in males (kidney weight/body weight ratios increased by 35%, 78%, and 105%, respectively) and worsened azotemia in males (serum urea nitrogen values increased by 63%, 514%, and 224%, respectively); in contrast, decreased dietary protein (4%) caused less severe PKD in males (kidney weight/body weight ratios decreased by 43%) and lessened azotemia in males (serum urea nitrogen values decreased by 49%). Similarly, NH4Cl and K+ restriction caused greater kidney enlargement in females (kidney weight/body weight ratios increased by 206% and 203%, respectively) and caused azotemia in females (serum urea nitrogen values increased by 177% and 430%, respectively). On the basis of these results, we conclude that growth-promoting stimuli can alter the expression of hereditary renal cystic disease. These findings demonstrate that the progression of hereditary renal cystic disease can be altered by factors in addition to the primary genetic defect.