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

Polycystic Kidney Disease Diet: What is Known and What is Safe

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder characterized by kidney cyst formation and progressive kidney function loss. Dietary interventions such as caloric restriction, intermittent fasting, and ketogenic diet have recently emerged as potential strategies to induce metabolic reprogramming and slow ADPKD progression. We review the available evidence supporting the efficacy and safety of these interventions in ADPKD. Dietary interventions show promise in managing ADPKD by improving metabolic health and reducing oxidative stress. However, while preclinical studies have shown favorable outcomes, limited clinical evidence supports their effectiveness. In addition, the long-term consequences of these dietary interventions, including their effect on adverse events in patients with ADPKD, remain uncertain. To optimize ADPKD management, patients are advised to follow a dietary regimen that aims to achieve or maintain an ideal body weight and includes high fluid intake, low sodium, and limited concentrated sweets. Caloric restriction seems particularly beneficial for patients with overweight or obesity because it promotes weight loss and improves metabolic parameters. Supplementation with curcumin, ginkgolide B, saponins, vitamin E, niacinamide, or triptolide has demonstrated uncertain clinical benefit in patients with ADPKD. Notably, β -hydroxybutyrate supplements have shown promise in animal models; however, their safety and efficacy in ADPKD require further evaluation through well-designed clinical trials. Therefore, the use of these supplements is not currently recommended for patients with ADPKD. In summary, dietary interventions such as caloric restriction, intermittent fasting, and ketogenic diet hold promise in ADPKD management by enhancing metabolic health. However, extensive clinical research is necessary to establish their effectiveness and long-term effects. Adhering to personalized dietary guidelines, including weight management and specific nutritional restrictions, can contribute to optimal ADPKD management. Future research should prioritize well-designed clinical trials to determine the benefits and safety of dietary interventions and supplementation in ADPKD.

Nonpharmacological Management of Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease is a slowly progressive, lifelong disease characterized by continuous development and enlargement of kidney cysts. Thus, nonpharmacological interventions are crucial in disease management and have the potential for a large clinical impact as standalone interventions or in conjunction with pharmacological therapies. Current potential strategies regarding nonpharmacological management of autosomal dominant polycystic kidney disease include nonpharmacological management of blood pressure, calorie restriction, weight loss or weight management, enhanced hydration, limiting caffeine, dietary sodium restriction, protein restriction or altering the type of protein intake, phosphorus restriction, and reducing net acid load. This brief review discusses the available evidence, including cell culture, animal, epidemiological, and clinical studies, regarding the utility of such strategies in the nonpharmacological management of autosomal dominant polycystic kidney disease. We assert that lifestyle modification strategies should be a critical aspect of the treatment of autosomal dominant polycystic kidney disease, while further trial and mechanistic evidence continue to become available.

Diet and Polycystic Kidney Disease: Nutrients, Foods, Dietary Patterns, and Implications for Practice

Polycystic kidney disease (PKD) is a chronic, progressive hereditary condition characterized by abnormal development and growth of cysts in the kidneys and other organs. There is increasing interest in exploring whether dietary modifications may prevent or slow the disease course in people with PKD. Although vasopressin-receptor agonists have emerged as a novel drug treatment in advancing care for people with PKD, several recent landmark trials and clinical discoveries also have provided new insights into potential dietary-related therapeutic strategies. In this review, we summarize the current evidence pertaining to nutrients, foods, dietary patterns, cyst growth, and progression of PKD. We also describe existing evidence-based dietary care for people with PKD and outline the potential implications for advancing evidence-based dietary interventions. Semin Nephrol 43:x-xx © 2023 Elsevier Inc. All rights reserved.

Dietary Interventions in Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the progressive growth of renal cysts, leading to the loss of functional nephrons. Recommendations for individuals with ADPKD to maintain a healthy diet and lifestyle are largely similar to those for the general population. However, recent evidence from preclinical models suggests that more tightly specified dietary regimens, including caloric restriction, intermittent fasting, and ketogenic diets, hold promise to slow disease progression, and the results of ongoing human clinical trials are eagerly awaited. These dietary interventions directly influence nutrient signaling and substrate availability in the cystic kidney, while also conferring systemic metabolic benefits. The present review focuses on the importance of local and systemic metabolism in ADPKD and summarizes current evidence for dietary interventions to slow disease progression and improve quality of life.

Metabolic Reprogramming in Autosomal Dominant Polycystic Kidney Disease: Evidence and Therapeutic Potential

Autosomal dominant polycystic kidney disease is characterized by progressive development and enlargement of kidney cysts, leading to ESKD. Because the kidneys are under high metabolic demand, it is not surprising that mounting evidence suggests that a metabolic defect exists in in vitro and animal models of autosomal dominant polycystic kidney disease, which likely contributes to cystic epithelial proliferation and subsequent cyst growth. Alterations include defective glucose metabolism (reprogramming to favor aerobic glycolysis), dysregulated lipid and amino acid metabolism, impaired autophagy, and mitochondrial dysfunction. Limited evidence supports that cellular kidney metabolism is also dysregulated in humans with autosomal dominant polycystic kidney disease. There are notable overlapping features and pathways among metabolism, obesity, and/or autosomal dominant polycystic kidney disease. Both dietary and pharmacologic-based strategies targeting metabolic abnormalities are being considered as therapies to slow autosomal dominant polycystic kidney disease progression and are attractive, particularly given the slowly progressive nature of the disease. Dietary strategies include daily caloric restriction, intermittent fasting, time-restricted feeding, a ketogenic diet, and 2-deoxy-glucose as well as alterations to nutrient availability. Pharmacologic-based strategies include AMP-activated kinase activators, sodium glucose cotransporter-2 inhibitors, niacinamide, and thiazolidenediones. The results from initial clinical trials targeting metabolism are upcoming and anxiously awaited within the scientific and polycystic kidney disease communities. There continues to be a need for additional mechanistic studies to better understand the role of dysregulated metabolism in autosomal dominant polycystic kidney disease and for subsequent translation to clinical trials. Beyond single-intervention trials focused on metabolic reprograming in autosomal dominant polycystic kidney disease, great potential also exists by combining metabolic-focused therapeutic approaches with compounds targeting other signaling cascades altered in autosomal dominant polycystic kidney disease, such as tolvaptan.

The pathobiology of polycystic kidney disease from a metabolic viewpoint

Autosomal dominant polycystic kidney disease (ADPKD) affects an estimated 1 in 1,000 people and slowly progresses to end-stage renal disease (ESRD) in about half of these individuals. Tolvaptan, a vasopressin 2 receptor blocker, has been approved by regulatory authorities in many countries as a therapy to slow cyst growth, but additional treatments that target dysregulated signalling pathways in cystic kidney and liver are needed. Metabolic reprogramming is a prominent feature of cystic cells and a potentially important contributor to the pathophysiology of ADPKD. A number of pathways previously implicated in the pathogenesis of the disease, such as dysregulated mTOR and primary ciliary signalling, have roles in metabolic regulation and may exert their effects through this mechanism. Some of these pathways are amenable to manipulation through dietary modifications or drug therapies. Studies suggest that polycystin-1 and polycystin-2, which are encoded by PKD1 and PKD2, respectively (the genes that are mutated in >99% of patients with ADPKD), may in part affect cellular metabolism through direct effects on mitochondrial function. Mitochondrial dysfunction could alter the redox state and cellular levels of acetyl-CoA, resulting in altered histone acetylation, gene expression, cytoskeletal architecture and response to cellular stress, and in an immunological response that further promotes cyst growth and fibrosis.

Nutritional therapy in autosomal dominant polycystic kidney disease

CKD-related nutritional therapy (NT) is a crucial cornerstone of CKD patients' treatment, but the role of NT has not been clearly investigated in autosomal dominant polycystic kidney disease (ADPKD). Several clinical studies have focused on new pharmacological approaches to delay cystic disease progression, but there are no data on dietary interventions in ADPKD patients. The aim of this paper is to analyze the evidence from the literature on the impact of five nutritional aspects (water, sodium, phosphorus, protein intake, and net acid load) in CKD-related ADPKD extrapolating-where information is unavailable-from what occurs in CKD non-ADPKD patients Sodium intake restriction could be useful in decreasing the growth rate of cysts. Although further evidence is needed, restriction of phosphorus and protein intake restriction represent cornerstones of the dietary support of renal non-ADPKD patients and common sense can guide their use. It could be also helpful to limit animal protein, increasing fruit and vegetables intake together with a full correction of metabolic acidosis. Finally, fluid intake may be recommended in the early stages of the disease, although it is not to be prescribed in the presence of moderate to severe reduction of renal function.

Soy Protein and Chronic Kidney Disease: An Updated Review

Chronic kidney disease (CKD) is a serious universal problem that is the main risk for several diseases including cardiovascular disease. Dietary factors are important to prevent and control the kidney disease. Some evidence has shown that modifying the amount and the types of dietary protein exert a major effect on renal failure so limiting dietary protein and substituting animal protein with soy protein has suggested. However, there is a lot of controversy about it, especially in human. Thus, this paper will review the clinical trial studies conducted on the effects of soy protein intake on CKD in both animal and human and its effect mechanism.

Distinct effects of dietary flax compared to fish oil, soy protein compared to casein, and sex on the renal oxylipin profile in models of polycystic kidney disease

Oxylipins are bioactive lipids derived from polyunsaturated fatty acids (PUFA) that are important regulators of kidney function and health. Targeted lipidomic analyses of renal oxylipins from four studies of rodent models of renal disease were performed to investigate the differential effects of dietary flax compared to fish oil, soy protein compared to casein, and sex. Across all studies, dietary fish oil was more effective than flax oil in reducing n-6 PUFA derived oxylipins and elevating eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) derived oxylipins, whereas dietary flax oil resulted in higher α-linolenic acid (ALA) oxylipins. Dietary soy protein compared to casein resulted in higher linoleic acid (LA) derived oxylipins. Kidneys from females had higher levels of arachidonic acid (AA) oxylipins, but similar or lower levels of oxylipins from other PUFA. Modulation of the oxylipin profile by diet and sex may help elucidate their effects on renal physiology and health.

The Associations of Plant Protein Intake With All-Cause Mortality in CKD

BACKGROUND

Plant protein intake is associated with lower production of uremic toxins and lower serum phosphorus levels. Therefore, at a given total protein intake, a higher proportion of dietary protein from plant sources might be associated with lower mortality in chronic kidney disease.

STUDY DESIGN

Observational study.

SETTINGS & PARTICIPANTS

14,866 NHANES III participants 20 years or older without missing data for plant and animal protein intake and mortality.

PREDICTORS

Plant protein to total protein ratio and total plant protein intake. Patients were stratified by estimated glomerular filtration rate (eGFR)<60 or ≥60mL/min/1.73m(2).

OUTCOMES

All-cause mortality.

MEASUREMENTS

Plant and total protein intakes were estimated from 24-hour dietary recalls. Mortality was ascertained by probabilistic linkage with National Death Index records through December 31, 2000.

RESULTS

Mean values for plant protein intake and plant protein to total protein ratio were 24.6±13.2 (SD) g/d and 33.0% ± 14.0%, respectively. The prevalence of eGFRs<60mL/min/1.73m(2) was 4.9%. There were 2,163 deaths over an average follow-up of 8.4 years. Adjusted for demographics, smoking, alcohol use, comorbid conditions, body mass index, calorie and total protein intake, and physical inactivity, each 33% increase in plant protein to total protein ratio was not associated with mortality (HR, 0.88; 95% CI, 0.74-1.04) in the eGFR≥60mL/min/1.73m(2) subpopulation, but was associated with lower mortality risk (HR, 0.77; 95% CI, 0.61-0.96) in the eGFR<60mL/min/1.73m(2) subpopulation. In sensitivity analyses, results were similar in those with eGFR<60mL/min/1.73m(2) defined by serum cystatin C level.

LIMITATIONS

Whether results are related to plant protein itself or to other factors associated with more plant-based diets is difficult to establish.

CONCLUSIONS

A diet with a higher proportion of protein from plant sources is associated with lower mortality in those with eGFR<60mL/min/1.73m(2). Future studies are warranted to determine the causal role of plant protein intake in reducing mortality in those with eGFR<60mL/min/1.73m(2).

Interventions for preventing the progression of autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited disorder causing kidney disease. Current clinical management of ADPKD focuses primarily on symptom control and reducing associated complications, particularly hypertension. In recent years, improved understanding of molecular and cellular mechanisms involved in kidney cyst growth and disease progression has resulted in new pharmaceutical agents to target disease pathogenesis to prevent progressive disease.

OBJECTIVES

We aimed to evaluate the effects of interventions for preventing ADPKD progression on kidney function, kidney endpoints, kidney structure, patient-centred endpoints (such as cardiovascular events, sudden death, all-cause mortality, hospitalisations, BP control, quality of life, and kidney pain), as well as the general and specific adverse effects related to their use.

SEARCH METHODS

We searched the Cochrane Renal Group's Specialised Register to 6 June 2015 using relevant search terms.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing any interventions for preventing the progression of ADPKD with other interventions or placebo were considered for inclusion without language restriction.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study risks of bias and extracted data. We summarised treatment effects on clinical outcomes, kidney function and structure and adverse events using random effects meta-analysis. We assessed heterogeneity in estimated treatment effects using the Cochran Q test and I(2) statistic. Summary treatment estimates were calculated as a mean difference (MD) or standardised mean difference (SMD) for continuous outcomes and a risk ratio (RR) for dichotomous outcomes together with their 95% confidence intervals.

MAIN RESULTS

We included 30 studies (2039 participants) that investigated 11 pharmacological interventions (angiotensin-converting enzyme inhibitors (ACEi), angiotensin receptor blockers (ARBs), calcium channel blockers, beta blockers, vasopressin receptor 2 (V2R) antagonists, mammalian target of rapamycin (mTOR) inhibitors, somatostatin analogues, antiplatelet agents, eicosapentaenoic acids, statins and vitamin D compounds) in this review.ACEi significantly reduced diastolic blood pressure (9 studies, 278 participants: MD -4.96 mm Hg, 95% CI -8.88 to -1.04), but had uncertain effects on kidney volumes (MD -42.50 mL, 95% CI -115.68 to 30.67), GFR (MD -3.41 mL/min/1.73 m(2), 95% CI -15.83 to 9.01), and SCr (MD -0.02 mg/dL, 95% CI -0.14 to 0.09), in data largely restricted to children. ACEi did not show different effects on GFR (MD -8.19 mL/min/1.73 m(2), 95% CI -29.46 to 13.07) and albuminuria (SMD -0.19, 95% CI -1.77 to 1.39) when compared with beta-blockers, or SCr (MD 0.00 mg/dL, 95% CI -0.09 to 0.10) when compared with ARBs.Data for effects of V2R antagonists on kidney function and volumes compared to placebo were limited to narrative information within a single study while these agents increased thirst (1444 participants: RR 2.70, 95% CI 2.24 to 3.24) and dry mouth (1455 participants: RR 1.33, 95% CI 1.01 to 1.76).Compared with no treatment, mTOR inhibitors had uncertain effects on kidney function (2 studies, 115 participants: MD 4.45 mL/min/1.73 m(2), 95% CI -3.20 to 12.11) and kidney volume (MD -0.08 L, 95% CI -0.75 to 0.59) but in three studies (560 participants) caused angioedema (RR 13.39, 95% CI 2.56 to 70.00), oral ulceration (RR 6.77, 95% CI 4.42 to 10.38), infections (RR 1.14, 95% CI 1.04 to 1.25) and diarrhoea (RR 1.70, 95% CI 1.26 to 2.29).Somatostatin analogues (6 studies, 138 participants) slightly improved SCr (MD -0.43 mg/dL, 95% CI -0.86 to -0.01) and total kidney volume (MD -0.62 L, 95% CI -1.22 to -0.01) but had no definite effects on GFR (MD 9.50 mL/min, 95% CI -4.45 to 23.44) and caused diarrhoea (RR 3.72, 95% CI 1.43 to 9.68).Data for calcium channel blockers, eicosapentaenoic acids, statins, vitamin D compounds and antiplatelet agents were sparse and inconclusive.Random sequence generation was adequate in eight studies, and in almost half of the studies, blinding was not present or not specified. Most studies did not adequately report outcomes, which adversely affected our ability to assess this bias. The overall drop-out rate was over 10% in nine studies, and few were conducted using intention-to-treat analyses.

AUTHORS' CONCLUSIONS

Although several interventions are available for patients with ADPKD, at present there is little or no evidence that treatment improves patient outcomes in this population and is associated with frequent adverse effects. Additional large randomised studies focused on patient-centred outcomes are needed.

Evidence for a role of proteins, lipids, and phytochemicals in the prevention of polycystic kidney disease progression and severity

Polycystic kidney disease (PKD) is a heritable disease characterized by renal cysts and is a leading cause of end-stage renal disease. Dietary intervention offers a potentially efficacious, cost-effective, and safe therapeutic option for PKD. The aim of this article was to review studies investigating the effect of dietary components on PKD and potential mechanisms of action. Low-protein diets are commonly recommended for PKD patients, but inconsistent findings in human and animal PKD studies suggest that the type rather the amount of protein may be of greater importance. Dietary soy protein has been shown to have renal protective effects in various animal models of PKD. Other than dietary proteins, studies investigating the role of the amount and type of dietary lipids on PKD progression are increasing. The omega-3 polyunsaturated fatty acids can alter multiple steps in PKD pathogenesis. Phytoestrogens and phytochemicals are other dietary compounds shown to attenuate cyst pathogenesis in animal studies. A better understanding of the role of nutrition in PKD can contribute to the development of dietary recommendations and diet-based therapies to reduce PKD progression and severity.

Renal cyclooxygenase and lipoxygenase products are altered in polycystic kidneys and by dietary soy protein and fish oil treatment in the Han:SPRD-Cy rat

SCOPE

Dietary fish oil (FO) and soy protein (SP) are two interventions that slow disease progression in the Han:SPRD-Cy rat model of polycystic kidney disease (PKD). Inhibition of cyclooxygenase (COX)-derived eicosanoids also reduces disease progression, but the role of lipoxygenase (LOX) products in this disease is not known.

METHODS AND RESULTS

Since dietary FO and SP have been shown to alter eicosanoid formation via differing mechanisms, Han:SPRD-Cy rats were given diets containing either casein protein (CP) or SP, and soy oil (SO) or FO. Analysis of eicosanoids revealed that renal COX products were higher and LOX products were lower in diseased kidneys. SP feeding resulted in lower COX products, activity and COX1 protein and higher LOX products in the diseased kidneys in parallel with reduced renal cyst growth and fibrosis. By comparison, FO reduced both COX and LOX products produced from n-6 fatty acids and increased 3-series prostanoids in both normal and diseased cortex and medulla, but these differences did not parallel effects on disease.

CONCLUSION

Renal COX-derived eicosanoids are elevated and LOX products are reduced in this model of kidney disease. The effects of dietary SP, but not FO, on renal eicosanoids parallel the effects on disease.

Free fatty acid and triacylglycerol forms of CLA isomers are not incorporated equally in the liver but do not lead to differences in bone density and biomarkers of bone metabolism

Few studies have compared differences between conjugated linoleic acid (CLA) in triacylglycerol (TG) and free fatty acid (FFA) form. This study assessed differences in liver incorporation, mineral mass balance, bone density, and biomarkers of bone metabolism between FFA and TG CLA diets. Rats (n=36) were fed a control (CTRL) or 1% CLA diet in FFA or TG form (1:1 mixture c9, t11: t10, c12). Liver content of c9, t11 CLA from FFA was greater than TG form and CTRL (FFA: 0.05±0.01 vs. TG: 0.02±0.01 vs. CTRL: 0.001±0.001% total fatty acids, P<0.0001). Liver t10, c12 CLA did not differ among groups (P=0.11). No diet differences among groups for growth, bone biomarkers or mass nor mineral balance were found. These findings suggest that c9, t11 CLA in FFA form is preferentially incorporated in the liver but fatty acid forms of CLA do not affect bone or mineral outcomes.

Distinctive effects of plant protein sources on renal disease progression and associated cardiac hypertrophy in experimental kidney disease

SCOPE

Dietary soy protein reduces renal disease progression in a number of renal diseases, suggesting that plant compared with animal proteins may be renoprotective. The inclusion of other plant protein sources could enhance compliance of intervention diets, but the effects of other plant protein sources are not known.

METHODS AND RESULTS

Weanling Han:SPRD-cy rats with experimental polycystic kidney disease were given hemp-, pea- and soy protein-based diets compared with the standard AIN 93G diet with casein as the protein source. Kidneys from diseased rats given diets which contained soy or hemp protein compared with casein-based diets were less enlarged, had lower fluid content, smaller cyst volumes, less fibrosis, lower chemokine receptor 2 (CCR2) levels and normalized serum creatinine levels. Soy and hemp protein diets also normalized heart size, which was enlarged in diseased compared with normal rats consuming casein. Kidneys from diseased rats given pea protein compared with casein were more enlarged and had higher fluid content and cyst volumes, despite growing better and having lower serum creatinine and renal chemokine receptor 2 levels, and similar levels of renal fibrosis.

CONCLUSION

Not all plant proteins are equally protective in experimental kidney disease and associated cardiac hypertrophy.

Dietary soy protein benefit in experimental kidney disease is preserved after isoflavone depletion of diet

Soy diet ameliorates renal injury in the Han:SPRD-cy rat. The relative roles of protein, isoflavones and changes in polyunsaturated fatty acid (PUFA) status are not determined. We fed male Han:SPRD-cy heterozygotes casein (C), high isoflavone soy protein (HIS), alcohol-extracted low isoflavone soy protein (LIS) or mixed soy protein diet (MIS). LIS and MIS were associated with a small decrease in animal weight compared with HIS or C. Soy diets preserved normal renal function and reduced relative renal weight (10.9-14.6 g/kg, cf. 23.6, P < 0.001), scores for cystic change (0.168-0.239, cf. 0.386, P < 0.05), fibrosis (0.013-0.015, cf. 0.032, P < 0.05), tissue oxidized LDL content (0.012-0.021, cf. 0.048, P < 0.05), inflammation (8.5-12.9, cf. 31.2, P < 0.05) and epithelial cell proliferation (6.5-13.8, cf. 26.3, P < 0.05). In post hoc testing, LIS produced a greater reduction in relative renal weight, cystic change and epithelial proliferation, whereas HIS produced a significantly greater reduction in oxidized-LDL. Soy diets were associated with increased hepatic content of 18C PUFA (P < 0.001). LIS and HIS diets were associated with a small increase in body fat content (P < 0.001). Alcohol-extracted soy protein retains its major protective effects in this model with subtle differences attributable to isoflavones.

Relative efficacy of casein or soya protein combined with palm or safflower-seed oil on hyperuricaemia in rats

Diets that ameliorate the adverse effects of uric acid (UA) on renal damage deserve attention. The effects of casein or soya protein combined with palm or safflower-seed oil on various serum parameters and renal histology were investigated on hyperuricaemic rats. Male Wistar rats administered with oxonic acid and UA to induce hyperuricaemia were fed with casein or soya protein plus palm- or safflower-seed oil-supplemented diets. Normal rats and hyperuricaemic rats with or without allopurinol treatment (150 mg/l in drinking water) were fed with casein plus maize oil-supplemented diets. After 8 weeks, allopurinol treatment and soya protein plus safflower-seed oil-supplemented diet significantly decreased serum UA in hyperuricaemic rats (one-way ANOVA; P < 0.05). In addition, soya protein and casein attenuated hyperuricaemia-induced decreases in serum albumin and insulin, respectively (two-way ANOVA; P < 0.05). Safflower-seed oil significantly decreased serum TAG and UA, whereas palm oil significantly increased serum cholesterol, TAG, blood urea N and creatinine. However, soya protein significantly decreased renal NO and nitrotyrosine and palm oil significantly decreased renal nitrotyrosine, TNF-alpha and interferon-gamma and increased renal transforming growth factor-beta. Casein with safflower-seed oil significantly attenuated renal tubulointerstitial nephritis, crystals and fibrosis. Comparing casein v. soya protein combined with palm or safflower-seed oil, the results support that casein with safflower-seed oil may be effective in attenuating hyperuricaemia-associated renal damage, while soya protein with safflower-seed oil may be beneficial in lowering serum UA and TAG.

A rat model of chronic kidney disease-mineral bone disorder

Chronic Kidney Disease-Mineral Bone Disorder (CKD-MBD) is a newly defined syndrome encompassing patients with chronic kidney disease that have a triad of biochemical alterations in calcium, phosphorus and parathyroid hormone, vascular calcification, and bone abnormalities. Here we describe a novel Cy/+ rat model of slowly progressive kidney disease spontaneously developing the three components of CKD-MBD when fed a normal phosphorus diet. Since the renal disorder progressed 'naturally' we studied the effect of dietary manipulation during the course of the disease. Animals with early, but established, chronic kidney disease were fed a casein-based or a grain-based protein diet both of which had equivalent total phosphorus contents. The two different sources of dietary protein had profound effects on the progression of CKD-MBD, likely due to differences in intestinal bioavailability of phosphorus. Although both dietary treatments resulted in the same serum phosphorous levels, the casein-fed animals had increased urinary phosphorus excretion and elevated serum FGF23 compared to the grain-fed rats. This model should help identify early changes in the course of chronic kidney disease that may lead to CKD-MBD.

The effect of eicosapentaenoic acid on renal function and volume in patients with ADPKD

BACKGROUND

Soy protein ameliorates rat polycystic kidney disease with concomitant renal enrichment of omega3-polyunsaturated fatty acids. A study was conducted to examine the effects of eicosapentaenoic acids (EPA) on renal volume and function in patients with autosomal dominant polycystic kidney disease (ADPKD).

METHODS

Non-azotemic patients were randomized to either a control group (n = 20) or an EPA group (n = 21). EPA capsules (2.4 g/day) were administered in the EPA group for 2 years. Twenty-four hours of urine was collected for the creatinine clearance (Ccr) measurement every year. At baseline and 24 months, fatty acid compositions in erythrocytes were measured and computerized tomographies were obtained for calculation of renal volume by the modified ellipsoid and volumetric methods.

RESULTS

In the EPA group, the EPA concentration (1.80 +/- 0.99 versus 4.40 +/- 1.79 area%, P < 0.001) and the omega3/omega6 ratio in the erythrocyte increased, but docosahexaenoic acid (DHA) (6.76 +/- 1.19 versus 5.64 +/- 1.45 area%, P < 0.010) concentration decreased. Ccr decreased by 8.5 +/- 9.5 and 9.0 +/- 13.0 ml/min/1.73 m(2)/2 years in the control and EPA groups, respectively (NS). The increases in renal volume calculated by either method were not significantly different between the two groups.

CONCLUSIONS

A beneficial effect of EPA on renal function and kidney volume in ADPKD patients could not be confirmed in the present study. Administration of EPA with DHA supplementation and/or longer intervention might be necessary to demonstrate preventive effects of omega3-polyunsaturated fatty acids on progression of ADPKD.

Soybeans ameliolate diabetic nephropathy in rats

Diabetic nephropathy is one of the most frequent and serious complications of diabetes mellitus. Soybeans have been shown to reduce urinary albumin excretion and total cholesterol in non-diabetic patients with nephrotic syndrome. However, reports focusing specifically on diabetic nephropathy are scarce and the available results are inconsistent. It was reported that soybean consumption reduced urinary protein excretion in type 1 diabetic patients with diabetic nephropathy, whereas it was found to elicit an increase in urinary protein excretion when soybeans were consumed by type 2 diabetic patients. This study aims to investigate the effects of soybean in diabetic nephropathy, particularly the effects of consuming soybeans on the histopathology of diabetic nephropathy, using aquaporin (AQP) and osteopontin (OPN) expression as diagnostic markers. Male Sprague-Dawley rats were assigned to one of three groups: control, diabetic with red chow diet and diabetic with soybean diet. For histological examination, the expression of OPN and AQP, renal function and hemoglobin A1c were evaluated at the end of the study. Improvements in glomerular and tubulointerstitial lesions were demonstrated in the diabetic rat group given a soybean diet. OPN and AQP expression were suppressed in the kidney specimens of diabetic rats with the soybean diet. In conclusion, soybeans may prevent the weight loss and morphological disruption of the kidney associated with diabetes mellitus. Soybeans also may improve glycemic control. It seems likely that long-term control of blood glucose levels using a soybean diet could prevent the progression of diabetes mellitus, and therefore, nephropathy could be prevented.

Late dietary intervention limits benefits of soy protein or flax oil in experimental polycystic kidney disease

BACKGROUND/AIMS

Dietary soy protein and flax oil retard kidney disease progression when initiated in the early stages of disease in several experimental models, including the Han:SPRD-cy rat. However, individuals with kidney disease often do not become aware of their condition until injury to the kidney is extensive. The objective of this study was to determine whether initiating these interventions in established disease would alter further progression of renal injury.

METHODS

Two-month-old adult male Han:SPRD-cy rats were given either a flax oil diet (7% flax oil), a soy protein diet (20% soy protein) or a control diet (7% corn oil, 20% casein) for 4 months. Renal disease progression was assessed by examining morphological, immunohistochemical and biochemical parameters.

RESULTS

Compared to controls, there was 21-24% less staining of proliferating cells, 21-24% less oxidative damage and 13-15% less renal inflammation in kidneys from rats given dietary soy protein and flax oil. Renal cystic growth and fibrosis and serum creatinine levels were not altered by these dietary treatments.

CONCLUSIONS

Late intervention with dietary soy protein and flax oil reduces some disease-associated pathologies in established renal disease in Han:SPRD-cy rats. The potential benefits of the antioxidant and anti-inflammatory effects on ultimate renal disease outcome in the long term remains to be determined.

[A case report of a terminally ill patient who achieved good pain control by pharmaceutical intervention in home terminal care]

We provided consultations with pharmacists to a terminally ill patient with radicular pain at his home. Before pharmaceutical intervention, the patient's compliance had been poor and consequently he had not achieved stable pain. The pharmacists suggested changes in the pharmacological and physical regimen that satisfied both the patient and his family. These changes were instructed with the help of the patient's doctors, home-visiting nurses and family, and subsequently the patient's compliance improved. The patient achieved good pain control and maintained excellent quality of life up to the time of his death. By providing home consultations to a terminally ill patient, we have contributed to maintaining an acceptable quality of life for him by building a team that consisted of doctors, nurses and pharmacists.

Feeding flaxseed oil but not secoisolariciresinol diglucoside results in higher bone mass in healthy rats and rats with kidney disease

Flaxseed's oil and lignan, secoisolariciresinol diglucoside (SDG), are implicated in attainment of health and treatment of renal injury and osteoporosis. To test for these benefits, weanling Han:SPRD-cy rats (n=171) with or without kidney disease were randomized to diets made with either corn oil or flaxseed oil and with or without SDG for 12 weeks. In females, weight was lower with the SDG diet. In males fed flaxseed oil, lean mass was higher and fat % was lower. In both sexes, fat % was lower in diseased rats. Bone mineral content (BMC) and density were higher in rats fed flaxseed oil and lower in diseased rats, additionally; BMC was lower in SDG-supplemented females. The benefit of flaxseed oil on body composition is sex specific but the effect on bone mass is not. Lastly, reduced weight due to early rat kidney disease is not due to loss of lean body mass.

Are High-Protein, Vegetable-Based Diets Safe for Kidney Function? A Review of the Literature

In individuals with chronic kidney disease, high-protein diets have been shown to accelerate renal deterioration, whereas low-protein diets increase the risk of protein malnutrition. Vegetarian diets have been promoted as a way to halt progression of kidney disease while maintaining adequate nutrition. We review the literature to date comparing the effects of animal and vegetable protein on kidney function in health and disease. Diets with conventional amounts of protein, as well as high-protein diets, are reviewed. The literature shows that in short-term clinical trials, animal protein causes dynamic effects on renal function, whereas egg white, dairy, and soy do not. These differences are seen both in diets with conventional amounts of protein and those with high amounts of protein. The long-term effects of animal protein on normal kidney function are not known. Although data on persons with chronic kidney disease are limited, it appears that high intake of animal and vegetable proteins accelerates the underlying disease process not only in physiologic studies but also in short-term interventional trials. The long-term effects of high protein intake on chronic kidney disease are still poorly understood. Several mechanisms have been suggested to explain the different effects of animal and vegetable proteins on normal kidney function, including differences in postprandial circulating hormones, sites of protein metabolism, and interaction with accompanying micronutrients.

Dietary soya protein during pregnancy and lactation in rats with hereditary kidney disease attenuates disease progression in offspring

Dietary soya protein substitution for casein initiated at weaning slows disease progression in animal models of chronic renal disease. As there is increasing evidence that fetal programming can have a significant impact on kidney physiology and function in offspring, the objective of the current study was to determine whether exposure to soya protein in the diet earlier than weaning would have further benefits. Han:SPRD-cy (cy/+) breeder rats were fed a casein-based or soya protein-based diet 2 weeks prior to mating, throughout pregnancy and during lactation. Following this maternal period, 3-week-old pups were given either the same or the alternate diet for a 7-week weaning period. Dietary soya protein compared with casein in the maternal or weaning period both independently resulted in less renal inflammation (macrophage infiltration lower by 24% (P=0.0003) and 32% (P<0.001), respectively). When soya protein was given in both feeding periods, the effect was additive. Soya protein substitution for casein resulted in less oxidative damages as indicated by 28% lower oxidized-LDL staining (P=0.013) when present in the maternal period, or in the weaning period (by 56%, P<0.0001). Renal cell proliferation was reduced by 29-33% (P<0.05) in rats given soya protein whether the exposure was during the maternal or weaning period. Soya protein compared with casein in the maternal period also resulted in 33% (P=0.0013) less proteinuria, indicating superior renal function. Dietary soya protein during pregnancy and lactation represents a potential preventative approach in treating for those with congenital kidney diseases.

Effects of flaxseed derivatives in experimental polycystic kidney disease vary with animal gender

Flaxseed derivatives, including both oil and flax lignan, modify progression of renal injury in animal models, including Han:SPRD-cy polycystic kidney disease (PKD). Gender is a significant factor in the rates of progression of many forms of human renal disease, but the role of gender in the response to nutrition intervention in renal disease is unexplored. In this study, male and female Han:SPRD-cy rats or normal littermates were fed either corn oil (CO) or flax oil (FO) diets, with or without 20 mg/kg of the diet flax lignan secoisolaricinoresinol dyglycoside (SDG). Renal injury was assessed morphometrically and biochemically. Renal and hepatic PUFA composition was assessed by GC and renal PGE2 release by ELISA. FO preserved body weight in PKD males, with no effect in females. SDG reduced weight in both normal and PKD females. FO reduced proteinuria in both male and female PKD. FO reduced cystic change and renal inflammation in PKD males but reduced cystic change, fibrosis, renal inflammation, tissue lipid peroxides, and epithelial proliferation in PKD females. SDG reduced renal inflammation in all animals and lipid peroxides in PKD females. A strong interaction between SDG and FO was observed in renal FA composition of female kidneys only, suggesting increased conversion of C18 PUFA to C20 PUFA. FO reduced renal release of PGE2 in both genders. Gender influences the effects of flaxseed derivatives in Han:SPRD-cy rats. Gender-based responses to environmental factors, such as dietary lipid sources and micronutrients, may contribute to gender-based differences in disease progression rates.

Modulation of carbohydrate metabolism and peptide hormones by soybean isoflavones and probiotics in obesity and diabetes

Soybean and its isoflavones have been shown to have beneficial effects on carbohydrate and lipid metabolism and on renal function. Probiotics may potentiate the beneficial effects of isoflavones by converting the inactive isoflavone glycoside to aglycones, which are biologically active, thereby producing a synergistic effect. We therefore studied the effects of soybean isoflavones in the presence and absence of probiotics on glucose and triglyceride metabolism and the peptide hormones involved in their metabolism. Lean and obese SHR/N-cp rats were fed AIN-93 diets containing 0.1% soybean isoflavone mixture, 0.1% probiotics mixture or both. Plasma was analyzed for glucose, triglycerides, parameters of renal function and peptide hormones -- insulin, leptin, glucagon and ACTH -- that are involved in glucose and lipid metabolism. Isoflavones given alone lowered plasma glucose in both phenotypes while triglyceride was decreased only in lean animals. Isoflavones also lowered aspartate amino transferase and alanine amino transferase in both phenotypes. Isoflavones had significant effect on plasma insulin, leptin and glucagon in lean rats but not in obese rats. Thus, our data show that in lean animals, isoflavones have hypoglycemic and hypolipidemic effect, and the effect is mediated by changes in peptide hormones. When lipid levels are very high as in obese rats, isoflavones fail to lower plasma triglyceride levels. Probiotics do not appear to enhance the effect of isoflavones.

Recent advances in understanding the pathogenesis of polycystic kidney disease: therapeutic implications

Hereditary polycystic kidney disease (PKD) is a common cause of renal failure. Increasing knowledge is available regarding mechanisms of cyst development and progression, and renal functional deterioration in PKD. On the basis of this information and theories regarding the pathophysiology of these processes, studies to alter progression and potentially treat PKD have been reported. Cyst development and progression requires epithelial cell proliferation, transepithelial fluid secretion and extracellular matrix remodelling. Several interventions designed to inhibit cell proliferation or alter fluid secretion modify the progression of PKD in selected animal models. Renal functional deterioration appears to involve interstitial inflammation and fibrosis, and tubular apoptosis. Glucocorticoids with anti-inflammatory and antifibrotic properties slow the progression of cystic disease and renal functional deterioration in animal models of PKD. Other interventions, such as dietary modification and angiotensin antagonism, shown to be of benefit in non-PKD models of slowly progressive renal disease, are also of benefit in animal models of PKD. Caution should be used in extrapolating interventional studies in one animal model to another model and certainly to human disease, since examples exist in which treatments in one model of PKD have different effects in another model. Nonetheless, early attempts to determine whether potential treatments are tolerated and of potential benefit in patients with PKD are beginning to appear. Ultimately, treatment of PKD may involve efforts to identify patients at greatest risk for disease progression, thus allowing targeted therapy, use of surrogate markers for disease progression to assist assessment of therapeutic efficacy, and combination therapy to retard disease progression and renal functional deterioration in this common hereditary cause of chronic renal failure.

Isolated soy protein consumption reduces urinary albumin excretion and improves the serum lipid profile in men with type 2 diabetes mellitus and nephropathy

Soy protein was shown to exhibit several beneficial effects on renal function in nondiabetic patients with nephropathy, and to improve serum lipids. This study examined the effects of isolated soy protein consumption on urinary albumin excretion, serum lipids, plasma amino acids, and isoflavones in diabetic patients with nephropathy. Male patients (n = 14) with type 2 diabetes and nephropathy were followed in a crossover design for 7 mo. The study comprised two 8-wk intervention periods, placed between a 4-wk lead-in and two 4-wk washout periods. In the 2 intervention periods, 0.5 g/(kg. d) of the dietary protein was provided as either isolated soy protein (ISP) or casein, in random order. Blood and urine samples were collected at the beginning and end of each period. Data were analyzed by multiple linear regression for a repeated-measure design. ISP consumption led to changes of -9.5% in urinary albumin excretion (P < 0.0001), -0.45 in the total-to-HDL-cholesterol ratio (P < 0.05), -0.20 in the LDL-to-HDL cholesterol ratio (P < 0.05), and +4.3% in HDL cholesterol (P = 0.0040). Plasma arginine concentrations, the arginine-to-lysine ratio, and plasma isoflavone concentrations were higher after ISP consumption (P < 0.05). Urinary albumin excretion was negatively correlated with plasma total isoflavones (rho = -0.441), daidzein (rho = -0.326), and O-desmethylangolesin (rho = -0.389) (P < 0.05). The findings indicate that isolated soy protein consumption improves several markers that may be beneficial for type 2 diabetic patients with nephropathy.

Conjugated linoleic acid reduces parathyroid hormone in health and in polycystic kidney disease in rats

BACKGROUND

Feeding conjugated linoleic acid (CLA) is reported to reduce prostaglandin E(2) synthesis, which is required for parathyroid hormone (PTH) release.

OBJECTIVE

This study was undertaken to determine whether CLA would suppress hyperparathyroidism and the resulting high-turnover bone disease in a rat model of polycystic kidney disease (PKD).

DESIGN

Outcome measurements were conducted after 8 wk of feeding diets supplemented with and without CLA (1% of dietary fat) to Han:SPRD-cy male rats (n = 52). PTH, bone formation, and resorption were assessed in addition to femur bone mass with use of dual-energy X-ray absorptiometry.

RESULTS

CLA feeding resulted in attenuation of PTH concentrations in both PKD-affected and nonaffected rats (by 60%) but did not significantly alter bone formation and resorption.

CONCLUSION

Reduction in PTH may open possibilities for CLA as an adjunctive therapy in secondary hyperparathyroidism.

Dietary soy protein attenuates renal disease progression after 1 and 3 weeks in Han:SPRD-cy weanling rats

Compared with casein, dietary soy protein slows disease progression in animal models of chronic renal injury. To determine whether dietary soy protein feeding can alter early disease progression, male Han:SPRD-cy rats (n = 87) in a very early stage of chronic kidney disease were fed soy protein compared with casein-based diets for 1 or 3 wk. Kidneys were assessed for fibrosis, cyst growth, fatty acid composition and prostaglandin E(2) (PGE(2)) production. Soy protein feeding significantly reduced renal fibrosis by 22% (P = 0.0347) and 38% (P = 0.0102) after 1 and 3 wk of diet, and cyst growth was 34% lower after 3 wk (P < 0.0001). Kidney 18:2(n-6) levels were reduced in normal and diseased rats after as little as 1 wk of consuming the soy protein diet. Dietary soy protein also partially ameliorated the suppression of PGE(2) production observed in diseased kidneys. Compared with diseased kidneys from casein-fed rats, ex vivo PGE(2) release was 31-32% higher after 1 (P = 0.0281) and 3 (P = 0.0189) wk of dietary soy protein consumption. Hence, the first signs of a beneficial soy protein effect were observed after 1 wk of feeding, with further improvements evident after 3 wk. These data demonstrate that dietary soy protein compared with casein delays disease progression in an early stage of chronic kidney disease.

Dietary flaxseed meal reduces proteinuria and ameliorates nephropathy in an animal model of type II diabetes mellitus

BACKGROUND

Evidence is emerging that varying the type or source of dietary protein intake can have beneficial effects on chronic renal disease. Consumption of soybean and soy-based food products, as the source of plant protein, can retard the development and progression of chronic renal disease. We studied the obese spontaneously hypertensive/NIH-corpulent (SHR/N-cp) rat, a model of obesity and type II diabetes mellitus that consistently develops nephropathy resembling diabetic nephropathy. We specifically sought to determine whether changing the source of protein intake from animal protein, casein, to plant protein in the form of either soy protein concentrate or flaxseed protein in the diet has a different impact on renal function and nephropathy in this model.

METHODS

Male obese SHR/N-cp rats were randomly assigned to one of three diets containing either 20% casein, 20% soy protein concentrate, or 20% flaxseed meal. Except for the protein source, all three diets were identical and contained similar amounts of protein, fat, carbohydrates, minerals, and vitamins. All animals were maintained on these diets for 6 months. At the end of the study, blood sampling and 24-hour urine collections were performed for renal functional measurements, and the kidneys were harvested and examined for histologic evaluation.

RESULTS

All three groups had similar amounts of food intake and body weight gain and exhibited fasting hyperglycemia and hyperinsulinemia. Plasma glucose levels did not differ among the three groups, but plasma insulin concentration was significantly lower in rats fed flaxseed meal than those fed either casein or soy protein concentrate. Mean plasma creatinine, creatinine clearance, and urinary urea excretion also did not differ significantly between the three groups. By contrast, urinary protein excretion was significantly lower (P < 0.01) in rats fed flaxseed than in rats fed either casein or soy protein concentrate. Morphologic analysis of renal structural lesions showed that the percentage of abnormal glomeruli with mesangial expansion and the tubulointerstitial score (an index of severity of tubulointerstitial damage) were significantly reduced in rats fed flaxmeal compared to those fed casein or soy protein concentrate.

CONCLUSION

We conclude that dietary protein substitution with flaxseed meal reduces proteinuria and glomerular and tubulointerstitial lesions in obese SHR/N-cp rats and that flaxseed meal is more effective than soy protein in reducing proteinuria and renal histologic abnormalities in this model. The reduction in proteinuria and renal injury was independent of the amount of protein intake and glycemic control. Which dietary component(s) present in flaxseed meal is (are) responsible for the renal protective effect remains to be determined.

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.

Evidence that soyasaponin Bb retards disease progression in a murine model of polycystic kidney disease

BACKGROUND

We reported a lessened cyst growth in the pcy mouse model of polycystic kidney disease (PKD) when mice were fed a soy protein isolate (SPI)-based diet and hypothesized that the soyasaponins may be associated with this therapeutic effect. The effects of feeding a saponin-enriched alcohol extract (SEAE) from SPI, an isoflavone- and saponin-enriched soy supplement (Novasoy 400), or a 99.5% pure soyasaponin Bb powder on cyst growth are reported here.

METHODS

The therapeutic effects of the soyasaponins were studied in 60-day-old male pcy mice in two separate, 90-day feeding trials. In the first study, mice were fed either a casein-based (control) diet, a diet in which SPI replaced the casein or the control diet supplemented with SEAE. In the second study, mice were fed the control diet unsupplemented or supplemented with either a soyasaponin- and isoflavone-enriched soy product (Novasoy 400) or a 99.5% pure soyasaponin Bb powder.

RESULTS

In study 1, kidney weight, water content, and plasma creatinine and urea levels were markedly reduced in the SEAE-fed animals compared to tissues from the control group; likewise, mice fed the SPI-based diet showed a decreased plasma creatinine, but only a slightly reduced plasma urea. In study 2, kidney weight, water content, plasma creatinine and urea levels were significantly reduced in mice fed the soyasaponin Bb powder and the Novasoy-400 supplement, compared to controls.

CONCLUSION

Soyasaponin Bb can impede kidney enlargement and cyst growth in the pcy mouse model of PKD. Further studies are needed to determine its most effective dose and mechanism of action.

Altering dietary protein type and quantity reduces urinary albumin excretion without affecting plasma glucose concentrations in BKS.cg-m +Lepr db/+Lepr db (db/db) mice

Protein restriction is used conventionally in the prevention and treatment of diabetic nephropathy. Recently, the use of soy protein instead of animal protein has been postulated as a new preventive and treatment option. The aim of this study was to determine the qualitative and quantitative effects of dietary protein on biomarkers of diabetic nephropathy in a Type 2 diabetes mellitus mouse model (BKS.cg-m +Lepr(db)/+Lepr(db) mice). Diabetic (+Lepr(db)/+Lepr(db)) and control (m+/m+) mice (n = 24/group) consumed one of four different diets ad libitum [20% casein, 20% soy protein, 12% casein or 12% soy protein (energy-based percentages)] from 35 +/- 4 d of age until termination (184-217 d of age). Blood and urine were collected throughout the study to measure biomarkers of diabetes and diabetic nephropathy. Kidney tissue was collected at the end of the study for weight. In diabetic mice, a 20% casein diet increased urinary albumin excretion to macroalbuminuric levels, whereas a 20% soy protein diet led to no major changes in urinary albumin excretion. Low protein diets (12%), independently of protein type, decreased urinary albumin excretion to low microalbuminuric levels. There were no significant differences in plasma glucose concentrations. These findings show lower urinary albumin excretion when a soy protein diet or a low casein diet is fed, suggesting a delay in the progression of diabetic nephropathy.

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.

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.

Dietary phytoestrogens: a possible role in renal disease protection

There is growing evidence that dietary phytoestrogens have a beneficial role in chronic renal disease. This review summarizes the recent findings from dietary intervention studies performed in animals and humans suggesting that consumption of soy-based protein rich in isoflavones and flaxseed rich in lignans retards the development and progression of chronic renal disease. In several animal models of renal disease, both soy protein and flaxseed have been shown to limit or reduce proteinuria and renal pathological lesions associated with progressive renal failure. In studies of human subjects with different types of chronic renal disease, soy protein and flaxseed also appear to moderate proteinuria and preserve renal function. However, most of these clinical trials were of relatively short duration and involved a small number of patients. Furthermore, it is not clear whether the renal protective effects of soy protein and flaxseed are caused by the isoflavones (daidzein and genistein) and lignans (matairesinol and secoisolariciresinol) or some other component. The biochemistry, metabolism, and mechanisms of actions of isoflavones and lignans are discussed. Isoflavones and lignans appear to act through various mechanisms that modulate cell growth and proliferation, extracellular matrix synthesis, inflammation, and oxidative stress. Some of these actions have been shown in vitro, but studies of the mechanisms operative in vivo are lacking. The diversity of cellular actions of isoflavones and lignans supports their protective effects in a variety of experimental and human types of chronic renal disease. Further investigations are needed to evaluate their long-term effects on renal disease progression in patients with chronic renal failure.

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.

Calorie restriction in obesity: prevention of kidney disease in rodents

The incidence of end-stage renal disease (ESRD) has risen considerably in the past two decades. This trend is partly due to the alarming rise in the incidence of type 2 diabetes over the same period, which in turn might be linked to the staggering increase in overweight and obesity. If these trends continue, ESRD can be expected not only to cause suffering of ever growing numbers of patients, but also to become an increasing financial as well as logistical burden on the health care system. Therefore, it is imperative not only to gain a better understanding of the molecular, cellular and metabolic mechanisms involved in renal pathology, but also to uncover treatment modalities, including lifestyle changes, that can help prevent and/or slow the progression of kidney pathogenesis. Insights into both of these aspects are provided by animal models of obesity and diabetes. It has long been known that food restriction, more so than restriction of any particular dietary component, can greatly enhance longevity in laboratory rodents. These findings are being extended into a variety of other mammals, including nonhuman primates. These studies have indicated that caloric restriction in nonobese laboratory animals does not primarily affect specific disease processes but rather nonspecifically slows the aging process. In contrast, a growing body of evidence suggests that in genetically obese animals, food restriction can prevent or greatly delay the onset of specific degenerative lesions, in particular glomerulonephritis associated with obesity and diabetes.

Dietary betaine modifies hepatic metabolism but not renal injury in rat polycystic kidney disease

We undertook a morphometric and proton nuclear magnetic resonance ((1)H-NMR) study to test the hypothesis that 1% dietary betaine supplementation would ameliorate renal disease in the heterozygous Han:SPRD-cy rat, a model of polycystic kidney disease (PKD) and progressive chronic renal failure. After 8 wk of pair feeding, betaine had no effect on renal cystic change, renal interstitial fibrosis, serum creatinine, serum cholesterol, or serum triglycerides. (1)H-NMR spectroscopy of renal tissue revealed no change in renal osmolytes, including betaine, or renal content of other organic anions in response to diet. (1)H-NMR spectroscopy of hepatic tissue performed to explore the metabolic fate of ingested betaine revealed that heterozygous animals fed the control diet had elevated hepatic levels of gluconeogenic amino acids, increased beta-hydroxybutyrate, and increased levels of some citric acid cycle metabolites compared with animals without renal disease. Betaine supplementation eliminated these changes. Chronic renal failure in the Han:SPRD-cy rat is associated with disturbances of hepatic metabolism that can be corrected with betaine therapy, suggesting the presence of a reversible methylation defect in this form of chronic renal failure.

The pathogenesis of autosomal dominant polycystic kidney disease: an update

The identification of PKD1 and PKD2, the two major genes responsible for autosomal dominant polycystic kidney disease, are the seminal discoveries upon which much of the current investigation into the pathogenesis of this common heritable disease is based. A major mechanistic insight was achieved with the discovery that autosomal dominant polycystic kidney disease occurs by a two-hit mechanism requiring somatic inactivation of the normal allele in individual polarized epithelial cells. Most recent advances are focused on the function of the respective protein products, polycystin-1 and polycystin-2. Indirect evidence supports an interaction between polycystin-1 and -2, albeit it is unlikely that they work in concert in all tissues and at all times. They associate in yeast two hybrid and cotransfection assays and there is a striking similarity in the renal and pancreatic cystic phenotypes of Pkd2-/- and Pkd1del34/del34 mice. Also, the respective homologues of both proteins are expressed in the same sensory neuronal cells in the nematode and the human disease phenotypes remain completely overlapping with the major difference being in relative severity. Mounting evidence supports the hypothesis that polycystin-1 is a cell surface receptor. A close homologue in the sea urchin sperm mediates the acrosome reaction in response to contact with egg-jelly, the nematode homologue functions in mechano- or chemosensation, and the solution structure of the repeated extracellular polycystic kidney disease domains reveals a beta-sandwich fold commonly found in surface receptor molecules. Indirect evidence also supports the initial hypothesis that polycystin-2 is a calcium channel subunit. Several closely related homologues retain the calcium channel signature motif but differ in their predicted interaction domains, and one of these homologues has been shown to be a calcium regulated cation channel. Several important distinctions in polcystin-1 and -2 function have also been discovered. Polycystin-2 has a role in cardiac development that polcystin-1 does not. High level polycystin-2 expression in renal epithelial cells coincides with maturation and elongation of tubules and, unlike polycystin-1, persists into adulthood. In cells in tissue culture, polycystin-2 is expressed exclusively in the endoplasmic reticulum whilst the cellular expression of polycystin-1 remains unknown. Overall, the difficult task of understanding the autosomal dominant polycystic disease process is proceeding apace.