Chronic effects of dietary vitamin D deficiency without increased calcium supplementation on the progression of experimental polycystic kidney disease

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.

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.

Effect of Early and Delayed Commencement of Paricalcitol in Combination with Enalapril on the Progression of Experimental Polycystic Kidney Disease

Vitamin D secosteroids are intranuclear regulators of cellular growth and suppress the renin-angiotensin system. The aim of this study was to test the hypothesis that the vitamin D receptor agonist, paricalcitol (PC), either alone or with enalapril (E) (an angiotensin-converting enzyme inhibitor), reduces the progression of polycystic kidney disease. Preventative treatment of Lewis polycystic kidney (LPK) and Lewis control rats with PC (0.2 μg/kg i.p. 5 days/week) or vehicle from postnatal weeks 3 to 10 did not alter kidney enlargement. To evaluate the efficacy in established disease, LPK rats received either PC (0.8 μg/kg i.p; 3 days/week), vehicle, E (50 mg/L in water) or the combination of PC + E from weeks 10 to 20. In established disease, PC also did not alter the progression of kidney enlargement, kidney cyst growth or decline in renal function in LPK rats. Moreover, the higher dose of PC was associated with increased serum calcium and weight loss. However, in established disease, the combination of PC + E reduced systolic blood pressure and heart-body weight ratio compared to vehicle and E alone (p < 0.05). In conclusion, the combination of PC + E attenuated cardiovascular disease but caused hypercalcaemia and did not alter kidney cyst growth in LPK rats.

Interactions between FGF23 and Genotype in Autosomal Dominant Polycystic Kidney Disease

BACKGROUND

Higher serum intact fibroblast growth factor 23 (iFGF23) was associated with disease progression in participants with autosomal dominant polycystic kidney disease (ADPKD) in the HALT-PKD Studies. PKD mutation is also an important determinant of progression. We hypothesized that serum levels of iFGF23 and vitamin D metabolites (1,25-dihydroxyvitamin D [1,25(OH)₂D] and 25-hydroxyvitamin D [25[OH]D]) differ according to ADPKD mutation and differentially predict clinical end points according to genotype (significant interaction between genotype and mineral metabolites).

METHODS

A total of 864 individuals with ADPKD who participated in the HALT-PKD Study A or B and had measurements of mineral metabolites (1,25[OH]₂D, 25[OH]D, iFGF23) were categorized by PKD mutation (PKD1 truncating, PKD1 nontruncating, PKD2, or no mutation detected [NMD]). The association of the interactions of genotype × iFGF23, genotype × 1,25(OH)2D, and genotype × 25(OH)D with (1) annualized change in eGFR; (2) mean annualized percentage change in height-corrected total kidney volume (Study A only); and (3) time to a composite of 50% reduction in eGFR, ESKD, or death were evaluated using linear regression and Cox proportional hazards regression.

RESULTS

Median (interquartile range) iFGF23 differed (PKD1 truncating, 55.8 [40.7-76.8]; PKD1 nontruncating, 49.9 [37.7-71.0]; PKD2, 49.0 [33.8-70.5]; NMD, 50.3 [39.7-67.4] pg/ml; P=0.03) and mean±SD 1,25(OH)₂D differed (PKD1 truncating, 32.8±12.8; PKD1 nontruncating, 33.4±12.5; PKD2, 34.1±13.1; NMD, 38.0±14.6 pg/ml; P=0.02) according to PKD genotype. There was a significant interaction between iFGF23 and genotype (P=0.02) for the composite end point in fully adjusted models, but no significant interaction between 1,25(OH)₂D or 25(OH)D and genotype for clinical end points.

CONCLUSIONS

ADPKD genotype interacts significantly with FGF23 to influence clinical end points. Whereas the worst outcomes were in individuals with a PKD1-truncating or -nontruncating mutation and the highest iFGF23 tertile, risk of the composite end point differed according to iFGF23 the most in the PKD1-nontruncating and PKD2 groups.

Association of Vitamin D Levels With Kidney Volume in Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Vitamin D possesses renoprotective effects beyond mineral metabolism, potentially reducing arterial blood pressure and inflammation and vitamin D enzymes (CYP24A1 and CYP27B1) as well as vitamin D receptor (VDR) contribute to its homeostasis. In the present study, we aimed to determine vitamin D association with kidney volume, blood pressure parameters and inflammatory markers in ADPKD. This cross-sectional study, conducted from August 2011 through May 2016, evaluated 25(OH)D, 1,25(OH)2D and other hormonal/biochemical serum and urinary parameters, inflammatory markers and monocyte expression of VDR, CYP24A1, CYP27B1 in 74 ADPKD patients. The height-adjusted total kidney volume (htTKV) was determined by MRI and blood pressure (BP) measured through 24-h ambulatory BP monitoring (ABPM).Vitamin D insufficiency was present in 62% of patients and CYP24A1 was overexpressed in this group, raising a hypothesis of 25(OH)D increased catabolism. Serum 25(OH)D levels and VDR expression were negatively correlated with htTKV as was VDR with IL-6, IL-10, CRP, and NFκB. A multiple linear regression analysis with htTKV as dependent variable, including hypertension, CRP, eGFR, age, time since diagnosis, VDR, and 25(OH)D adjusted for season of the year showed that only the first three parameters were independent predictors of the former. There has been no association of serum 25(OH)D and VDR expression with ABPM parameters. Present findings suggested that low levels of serum 25(OH)D and VDR expression are associated with a higher kidney volume in ADPKD patients, but do not represent independent risk factors for htTKV.

Effect of dimethyl fumarate on renal disease progression in a genetic ortholog of nephronophthisis

Dimethyl fumarate is an FDA-approved oral immunomodulatory drug with anti-inflammatory properties that induces the upregulation of the anti-oxidant transcription factor, nuclear factor erythroid-derived factor 2. The aim of this study was to determine the efficacy of dimethyl fumarate on interstitial inflammation and renal cyst growth in a preclinical model of nephronophthisis. Four-week-old female Lewis polycystic kidney disease (a genetic ortholog of human nephronophthisis-9) rats received vehicle (V), 10 mg/kg (D10) or 30 mg/kg (D30) ( n = 8-9 each) dimethyl fumarate in drinking water for eight weeks. Age-matched Lewis control rats were also studied ( n = 4 each). Nuclear factor erythroid-derived factor 2 was quantified by whole-slide image analysis of kidney sections. Renal nuclear factor erythroid-derived factor 2 activation was partially reduced in vehicle-treated Lewis polycystic kidney disease rats compared to Lewis control (21.4 ± 1.7 vs. 27.0 ± 1.6%, mean ± SD; P < 0.01). Dimethyl fumarate upregulated nuclear factor erythroid-derived factor 2 in both Lewis Polycystic Kidney Disease (D10: 35.9 ± 3.8; D30: 33.6 ± 3.4%) and Lewis rats (D30: 34.4 ± 1.3%) compared to vehicle-treated rats ( P < 0.05). Dimethyl fumarate significantly reduced CD68+ cell accumulation in Lewis polycystic kidney disease rats (V: 31.7 ± 2.4; D10: 23.0 ± 1.1; D30: 21.5 ± 1.9; P < 0.05). In Lewis polycystic kidney disease rats, dimethyl fumarate did not alter the progression of kidney enlargement (V: 6.4 ± 1.6; D10: 6.9 ± 1.2; D30: 7.3 ± 1.3%) and the percentage cystic index (V: 59.1 ± 2.7; D10: 55.7 ± 3.5; D30: 58.4 ± 2.9%). Renal dysfunction, as determined by the serum creatinine (Lewis + V: 26 ± 4 vs. LPK + V: 60 ± 25 P < 0.01; LPK + D10: 47 ± 7; LPK + D30: 47 ± 9 µmol/L), and proteinuria were also unaffected by dimethyl fumarate treatment. In conclusion, the upregulation of nuclear factor erythroid-derived factor 2 by dimethyl fumarate reduced renal macrophage infiltration in nephronophthisis without adverse effects, suggesting that it could potentially be used in combination with other therapies that reduce the rate of renal cyst growth. Impact statement This is the first study to investigate the effects of dimethyl fumarate in a model of cystic kidney disease. The study assessed the therapeutic efficacy of dimethyl fumarate in upregulating renal nuclear factor erythroid-derived factor 2 expression, reducing macrophage accumulation and cyst progression in a Lewis polycystic kidney disease rat model. This study demonstrates that dimethyl fumarate significantly upregulated renal nuclear factor erythroid-derived factor 2 expression and attenuates renal macrophage infiltration, but had no effect on renal cyst progression, cardiac enlargement, and improving renal function.

Vitamin D deficiency causes inward hypertrophic remodeling and alters vascular reactivity of rat cerebral arterioles

Background and purpose

Vitamin D deficiency (VDD) is a global health problem, which can lead to several pathophysiological consequences including cardiovascular diseases. Its impact on the cerebrovascular system is not well understood. The goal of the present work was to examine the effects of VDD on the morphological, biomechanical and functional properties of cerebral arterioles.

Methods

Four-week-old male Wistar rats (n = 11 per group) were either fed with vitamin D deficient diet or received conventional rat chow with per os vitamin D supplementation. Cardiovascular parameters and hormone levels (testosterone, androstenedione, progesterone and 25-hydroxyvitamin D) were measured during the study. After 8 weeks of treatment anterior cerebral artery segments were prepared and their morphological, biomechanical and functional properties were examined using pressure microangiometry. Resorcin-fuchsin and smooth muscle actin staining were used to detect elastic fiber density and smooth muscle cell counts in the vessel wall, respectively. Sections were immunostained for eNOS and COX-2 as well.

Results

VDD markedly increased the wall thickness, the wall-to-lumen ratio and the wall cross-sectional area of arterioles as well as the number of smooth muscle cells in the tunica media. As a consequence, tangential wall stress was significantly lower in the VDD group. In addition, VDD increased the myogenic as well as the uridine 5’-triphosphate-induced tone and impaired bradykinin-induced relaxation. Decreased eNOS and increased COX-2 expression were also observed in the endothelium of VDD animals.

Conclusions

VDD causes inward hypertrophic remodeling due to vascular smooth muscle cell proliferation and enhances the vessel tone probably because of increased vasoconstrictor prostanoid levels in young adult rats. In addition, the decreased eNOS expression results in endothelial dysfunction. These morphological and functional alterations can potentially compromise the cerebral circulation and lead to cerebrovascular disorders in VDD.

A randomised Phase II/III study to evaluate the efficacy and safety of orally administered Oxalobacter formigenes to treat primary hyperoxaluria

Primary hyperoxaluria (PH) patients overproduce oxalate because of rare genetic errors in glyoxylate metabolism. Recurrent urolithiasis and/or progressive nephrocalcinosis are PH hallmarks and can lead to kidney damage, systemic oxalosis and death. Based on previous studies, we hypothesised that treatment with the oxalate-metabolizing bacterium Oxalobacter formigenes would mediate active elimination of oxalate from the plasma to the intestine of PH patients, thereby reducing urinary oxalate excretion (Uox). The efficacy and safety of O. formigenes (Oxabact™ OC3) were evaluated for 24 weeks in a randomised, placebo-controlled, double-blind study. The primary endpoint was reduction in Uox. Secondary endpoints included change in plasma oxalate (Pox) concentration, frequency of stone events, number of responders, and Uox in several subgroups. Additional post hoc analyses were conducted. Thirty-six patients were randomised; two patients withdrew from placebo treatment. Both OC3 and placebo groups demonstrated a decrease in Uox/urinary creatinine ratio, but the difference was not statistically significant. No differences were observed with respect to change in Pox concentration, stone events, responders’ number or safety measures. In patients with estimated glomerular filtration rate (eGFR) < 90 mL/min/1.73 m², Pox increased by 3.25 µmol/L in the placebo group and decreased by −1.7 µmol/L in the OC3 group (p = 0.13). After 24 weeks, eGFR had declined to a greater degree in the placebo than in the OC3 group: −8.00 ± 2.16 versus −2.71 ± 2.50; p = 0.01. OC3 treatment did not reduce urinary oxalate over 24 weeks of treatment compared with placebo in patients with PH. The treatment was well tolerated.

A randomised Phase I/II trial to evaluate the efficacy and safety of orally administered Oxalobacter formigenes to treat primary hyperoxaluria

BACKGROUND

Primary hyperoxaluria (PH) is a rare, genetic disorder which involves the overproduction of endogenous oxalate, leading to hyperoxaluria, recurrent urolithiasis and/or progressive nephrocalcinosis and eventually resulting in kidney failure and systemic oxalosis. The aim of this trial was to investigate whether treatment involving an oxalate-metabolising bacterium (Oxalobacter formigenes) could reduce urinary oxalate excretion in PH patients.

METHODS

The efficacy and safety of O. formigenes (Oxabact® OC5; OxThera AB, Stockholm, Sweden) was evaluated in a randomised, placebo-controlled, double-blind study for 8 weeks. The primary objective was reduction in urinary oxalate excretion (Uox). Secondary objectives included faecal O. formigenes count and decrease in plasma oxalate concentration (Pox).

RESULTS

Twenty-eight patients randomised 1:1 to the treatment group (OC5) or the placebo group completed the study. After 8 weeks of treatment, there was no significant difference in the change in Uox (mmol/24 h/1.73 m²) between the groups (OC5: +0.042, placebo: -0.140). Post-hoc analysis showed a statistically significant increase in Uox per urinary creatinine excretion in the OC5 group (OC5: +5.41, placebo: -15.96; p = 0.030). Change in Pox from baseline was not significantly different between groups (p = 0.438). The O. formigenes cell count was significantly increased in OC5-treated patients (p < 0.001) versus placebo. The treatment response to O. formigenes was related to individual stage of kidney deterioration, and Pox was directly correlated to kidney function, even for early-stage patients (chronic kidney disease stage 1). No safety issues were observed.

CONCLUSIONS

Treatment with OC5 did not significantly reduce Uox or Pox over 8 weeks of treatment. The treatment was well tolerated and successfully delivered to the gastrointestinal tract.

Effects of TORC1 Inhibition during the Early and Established Phases of Polycystic Kidney Disease

The disease-modifying effects of target of rapamycin complex 1 (TORC1) inhibitors during different stages of polycystic kidney disease (PKD) are not well defined. In this study, male Lewis Polycystic Kidney Disease (LPK) rats (a genetic ortholog of human NPHP9, phenotypically characterised by diffuse distal nephron cystic growth) and Lewis controls received either vehicle (V) or sirolimus (S, 0.2 mg/kg by intraperitoneal injection 5 days per week) during the early (postnatal weeks 3 to 10) or late stages of disease (weeks 10 to 20). In early-stage disease, sirolimus reduced kidney enlargement (by 63%), slowed the rate of increase in total kidney volume (TKV) in serial MRI by 78.2% (LPK+V: 132.3±59.7 vs. LPK+S: 28.8±12.0% per week) but only partly reduced the percentage renal cyst area (by 19%) and did not affect the decline in endogenous creatinine clearance (CrCl) in LPK rats. In late-stage disease, sirolimus reduced kidney enlargement (by 22%) and the rate of increase in TKV by 71.8% (LPK+V: 13.1±6.6 vs. LPK+S: 3.7±3.7% per week) but the percentage renal cyst area was unaltered, and the CrCl only marginally better. Sirolimus reduced renal TORC1 activation but not TORC2, NF-κB DNA binding activity, CCL2 or TNFα expression, and abnormalities in cilia ultrastructure, hypertension and cardiac disease were also not improved. Thus, the relative treatment efficacy of TORC1 inhibition on kidney enlargement was consistent at all disease stages, but the absolute effect was determined by the timing of drug initiation. Furthermore, cystic microarchitecture, renal function and cardiac disease remain abnormal with TORC1 inhibition, indicating that additional approaches to normalise cellular dedifferentiation, inflammation and hypertension are required to completely arrest the progression of PKDs.

Pyrrolidine dithiocarbamate reduces the progression of total kidney volume and cyst enlargement in experimental polycystic kidney disease

Heterocyclic dithiocarbamates have anti‐inflammatory and anti‐proliferative effects in rodent models of chronic kidney disease. In this study, we tested the hypothesis that pyrrolidine dithiocarbamate (PDTC) reduces the progression of polycystic kidney disease (PKD). Male Lewis polycystic kidney (LPK) rats (an ortholog of Nek8/NPHP9) received intraperitoneal injections of either saline vehicle or PDTC (40 mg/kg once or twice daily) from postnatal weeks 4 until 11. By serial magnetic resonance imaging at weeks 5 and 10, the relative within‐rat increase in total kidney volume and cyst volume were 1.3‐fold (P =0.01) and 1.4‐fold (P < 0.01) greater, respectively, in LPK + Vehicle compared to the LPK + PDTC(40 mg/kg twice daily) group. At week 11 in LPK rats, PDTC attenuated the increase in kidney weight to body weight ratio by 25% (P < 0.01) and proteinuria by 66% (P < 0.05 vs. LPK + Vehicle) but did not improve renal dysfunction. By quantitative whole‐slide image analysis, PDTC did not alter interstitial CD68+ cell accumulation, interstitial fibrosis, or renal cell proliferation in LPK rats at week 11. The phosphorylated form of the nuclear factor (NF)‐κB subunit, p105, was increased in cystic epithelial cells of LPK rats, but was not altered by PDTC. Moreover, PDTC did not significantly alter nuclear expression of the p50 subunit or NF‐κB (p65)‐DNA binding. Kidney enlargement in LPK rats was resistant to chronic treatment with a proteasome inhibitor, bortezomib. In conclusion, PDTC reduced renal cystic enlargement and proteinuria but lacked anti‐inflammatory effects in LPK rats.

Lewis polycystic kidney rats were treated with pyrrolidine dithiocarbamate (PDTC) from weeks 4 to 11. Quantitative analysis of serial magnetic resonance images indicated that over time, the change in total kidney volume was 1.3‐fold higher in PDTC‐treated than in vehicle‐treated rats. PDTC treatment also decreased kidney weight to body weight ratio, renal cystic volume, and proteinuria.