GDF10 is a negative regulator of vascular calcification.

Cardiovascular mortality is particularly high and increasing in patients with chronic kidney disease, with vascular calcification (VC) as a major pathophysiologic feature. VC is a highly regulated biological process similar to bone formation involving osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs). We have previously demonstrated that loss of T-cell death-associated gene 51 (TDAG51) expression leads to an attenuation of medial VC. We now show a significant induction of circulating levels of growth differentiation factor 10 (GDF10) in TDAG51-/- mice, which was of interest due to its established role as an inhibitor of osteoblast differentiation. The objective of this study was to examine the role of GDF10 in the osteogenic transdifferentiation of VSMCs. Using primary mouse and human VSMCs, as well as ex vivo aortic ring cultures, we demonstrated that treatment with recombinant human (rh) GDF10 mitigated phosphate-mediated hydroxyapatite (HA) mineral deposition. Furthermore, ex vivo aortic rings from GDF10-/- mice exhibited increased HA deposition compared to C57BL/6J controls. To explain our observations, we identified that rhGDF10 treatment reduced protein expression of runt-related transcription factor 2, a key driver of osteogenic transdifferentiation of VSMCs and VC. In support of these findings, in vivo treatment with rhGDF10 attenuated VD3-induced VC. Furthermore, we demonstrated an increase in circulating GDF10 in patients with chronic kidney disease with clinically defined severe VC, as assessed by coronary artery calcium score. Thus, our studies identify GDF10 as a novel inhibitor of mineral deposition and as such, may represent a potential novel biomarker and therapeutic target for the detection and management of VC.

Vitamin D Status and Treatment in ESKD: Links to Improved CKD-MBD Laboratory Parameters in a Real-World Setting.

INTRODUCTION: Vitamin D insufficiency is common in patients who receive hemodialysis, yet there is no clear guidance regarding surveillance or treatment. We hypothesized that increasing 25(OH)D3 levels is associated with lower phosphate, parathyroid hormone (PTH), and alkaline phosphatase (ALP). METHODS: Baseline 25(OH)D3 level was measured in all patients receiving in-center hemodialysis in June 2017. Laboratory parameters were measured every 6 (phosphate, calcium) or 12 weeks (25(OH)D3, PTH, ALP) until February 2021. In September 2018, a treatment algorithm of 50,000 IU weekly until sufficient followed by 50,000 IU monthly was suggested. Generalized linear mixed regression models including linear spline effects, a log link function, and random effects were used to examine the impact of increasing 25(OH)D3 levels on calcium, phosphate, ALP, and PTH. RESULTS: Of 697 participants, 15% and 57% had vitamin D deficiency (25(OH)D3 <25 nmol/L) and insufficiency (between 25 and 74 nmol/L). Incorporating up to 7,272 observations, increasing 25(OH)D3 was associated with significantly decreasing PTH for 25(OH)D3 levels between 25 and 75 nmol/L regardless of vitamin D treatment. In an interaction model, the negative slope between 25(OH)D3 and PTH remained significant beyond 75 nmol/L in the absence of calcitriol. Increasing 25(OH)D3 was associated with significantly decreasing phosphate for 25(OH)D3 levels between 25 and 75 nmol/L regardless of vitamin D treatment and below 25 nmol/L in values of untreated patients. Calcium increased across the spectrum of 25(OH)D3 regardless of vitamin D treatment. Overall, 0.2% of 25(OH)D3 levels exceeded 250 nmol/L and 2.1% of calcium levels exceeded the normal range. CONCLUSIONS: Vitamin D treatment in a real-world setting was safe and associated with lower PTH levels. Whether improved biochemical markers translate to a reduction in clinical endpoints warrants further study.

Inhibit progression of coronary artery calcification with vitamin K in hemodialysis patients (the iPACK-HD study): a randomized, placebo-controlled multi-center, pilot trial.

BACKGROUND: Vitamin K activates matrix Gla protein (MGP), a key inhibitor of vascular calcification. There is a high prevalence of sub-clinical vitamin K deficiency in patients with end-stage kidney disease. METHODS: A parallel randomized placebo-controlled pilot trial was designed to determine whether 10 mg of phylloquinone thrice weekly versus placebo modifies coronary artery calcification progression over 12 months in patients requiring hemodialysis with a coronary artery calcium score (CAC) ≥30 Agatston Units (ClinicalTrials.gov identifier NCT01528800). The primary outcome was feasibility (recruitment rate, compliance with study medication, study completion and adherence overall to study protocol). CAC score was used to assess calcification at baseline and 12 months. Secondary objectives were to explore the impact of phylloquinone on vitamin K-related biomarkers (phylloquinone, dephospho-uncarboxylated MGP and the Gla-osteocalcin to Glu-osteocalcin ratio) and events of clinical interest. RESULTS: A total of 86 patients with a CAC score ≥30 Agatston Units were randomized to either 10 mg of phylloquinone or a matching placebo three times per week. In all, 69 participants (80%) completed the trial. Recruitment rate (4.4 participants/month) and medication compliance (96%) met pre-defined feasibility criteria of ≥4.17 and ≥90%, respectively. Patients randomized to phylloquinone for 12 months had significantly reduced levels of dephospho-uncarboxylated MGP (86% reduction) and increased levels of phylloquinone and Gla-osteocalcin to Glu-osteocalcin ratio compared with placebo. There was no difference in the absolute or relative progression of coronary artery calcification between groups. CONCLUSION: We demonstrated that phylloquinone treatment improves vitamin K status and that a fully powered randomized trial may be feasible.

Acute kidney injury is associated with subtle but quantifiable neurocognitive impairments.

BACKGROUND: Acute kidney injury (AKI) is associated with long-term morbidity and mortality. The effects of AKI on neurocognitive functioning remain unknown. Our objective was to quantify neurocognitive impairment after an episode of AKI. METHODS: Survivors of AKI were compared with age-matched controls, as well as a convenience sample of patients matched for cardiovascular risk factors with normal kidney function (active control group). Patients with AKI completed two assessments, while the active control group completed one assessment. The assessment included a standardized test: the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), and a robotic assessment: Kinarm. RESULTS: The cohort consisted of 21 patients with AKI, 16 of whom completed both assessments, and 21 active control patients. The majority of patients with AKI had Kidney Disease: Improving Global Outcomes Stage 3 AKI (86%), 57% received dialysis and 43% recovered to ≤25% of their baseline serum creatinine by their first assessment. Compared with the RBANS, which detected little impairment, the Kinarm categorized patients as impaired in visuomotor (10/21, 48%), attention (10/20, 50%) and executive tasks (11/21, 52%) compared with healthy controls. Additionally, patients with AKI performed significantly worse in attention and visuomotor domains when compared with the active controls. Neurocognitive performance was generally not impacted by the need for dialysis or whether kidney function recovered. CONCLUSIONS: Robotic technology identified quantifiable neurocognitive impairment in survivors of AKI. Deficits were noted particularly in attention, visuomotor and executive domains. Further investigation into the downstream health consequences of these neurocognitive impairments is warranted.

A Scoping Review of Alternative Anticoagulation Strategies for Hemodialysis Patients with a Mechanical Heart Valve.

INTRODUCTION: Patients with end-stage renal disease (ESRD) have high rates of cardiac valvulopathy but can develop contraindications for vitamin K antagonist (VKA) therapy. We explored the evidence for alternative anticoagulation strategies in patients with ESRD with a contraindication for VKA therapy. METHODS: A scoping review was completed, searching MEDLINE, Embase, Cochrane Central Register of Controlled Trials, Web of Science, and Conference abstracts from inception to March 30, 2021. The study population was patients with ESRD who were on VKA therapy and developed a contraindication to VKA therapy use. All data regarding studies, patient characteristics, anticoagulation strategy, and clinical outcomes were summarized. RESULTS: Twenty-three articles met inclusion criteria. These articles included 57 patients. Contraindications to VKA therapy included calcific uremic arteriolopathy (CUA) (n = 55) and warfarin-induced skin necrosis (n = 2). All studies were either case reports or case series. There were 10 anticoagulation strategies identified. Continuation of VKA therapy was associated with increased death and decreased rates of CUA resolution (80.0% and 10.0%, respectively), compared to apixaban (24.0% and 70.8%), subcutaneous (SC) low-molecular-weight heparin (LMWH) (14.3%, 85.7%), and SC unfractionated heparin (0.0%, 100.0%). While only 5 patient cases were reported with mechanical heart valves, SC LMWH use has been reported in this context with good outcomes. CONCLUSIONS: In patients with ESRD who develop a contraindication to VKA therapy, several alternative anticoagulation strategies have been reported with superior outcomes to VKA continuation. While outcomes appear superior to continuation of VKA therapy, more data are required before definitive recommendations can be made for the patient with ESRD and a mechanical heart valve.

Secreted Phosphoprotein 24 is a Biomarker of Mineral Metabolism.

The 24 kD form of secreted phosphoprotein (SPP-24), a cytokine-binding bone matrix protein with various truncated C-terminal products, is primarily synthesized by the liver. SPP-24 shares homology with fetuin-A, a potent vascular and soft tissue calcification inhibitor and SPP-24 is one component of calciprotein particles (CPPs), a circulating fetuin-mineral complex. The limited molecular evidence to date suggests that SPP-24 may also function as an inhibitor of bone formation and ectopic vascular calcification, potentially through bone morphogenic protein 2 (BMP-2) and Wnt-signaling mediated actions. The C-terminal products of SPP-24 bind to BMP-2 and attenuate BMP-2-induced bone formation. The aim of this study was to assess circulating SPP-24 in relation to kidney function and in concert with markers of mineral metabolism in humans. SPP-24 was measured in the serum of total of 192 subjects using ELISA-based measurements. Subjects were participants of one of two cohorts: (1) mGFR Cohort (n = 80) was participants of a study of measured GFR (mGFR) using inulin urinary clearance, recruited mostly from a chronic kidney disease clinic with low-range kidney function (eGFR 38.7 ± 25.0 mL/min/1.73 m2) and (2) CaMOS Cohort (n = 112) was a subset of randomly selected, community-dwelling participants of year 10 of the Canadian Multicentre Osteoporosis Study with eGFR in the normal range of 75.0 ± 15.9 mL/min/1.73 m2. In the combined cohort, the mean SPP-24 was 167.7 ± 101.1 ng/mL (range 33.4-633.6 ng/mL). The mean age was 66.5 ± 11.3, 57.1% female and mean eGFR (CKD-EPI) was 59.9 ± 27.0 mL/min/1.73 m2 (range 8-122 mL/min/1.73 m2). There was a strong inverse correlation between SPP-24 and eGFR (R = - 0.58, p < 0.001) that remained after adjustment for age. Following adjustment for age, eGFR, and sex, SPP-24 was significantly associated with phosphate (R = - 0.199), PTH (R = 0.298), and the Wnt-signaling inhibitor Dickkopf-related protein 1 (R = - 0.156). The results of this study indicate that SPP-24 is significantly altered by kidney function and is the first human data linking levels of SPP-24 to other biomarkers involved in mineral metabolism. Whether there is a role for circulating SPP-24 in bone formation and ectopic mineralization requires further study.

Circulating Levels of Dickkopf-Related Protein 1 Decrease as Measured GFR Declines and Are Associated with PTH Levels.

BACKGROUND: The Wnt/ß-catenin pathway has been implicated in the development of adynamic bone disease in early-stage chronic kidney disease (CKD). Dickkopf-related protein 1 (DKK1) and sclerostin are antagonists of the Wnt/ß-catenin pathway yet have not been widely used as clinical indicators of bone disease. This study characterized levels of DKK1, sclerostin, and other biomarkers of mineral metabolism in participants across a spectrum of inulin-measured glomerular filtration rate (GFR). METHODS: GFR was measured by urinary inulin clearance (mGFR) in 90 participants. Blood samples were obtained for measurement of circulating DKK1, sclerostin, fibroblast growth factor 23 (FGF-23), parathyroid hormone (PTH), calcium, phosphate, α-klotho, and vitamin D metabolites including 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3. Spearman correlations and linear regressions were used where appropriate to examine the associations between measured values. RESULTS: The median [IQR] age was 64 years [53.0-71.0], and the median [IQR] mGFR was 32.6 [21.7-60.6] mL/min. DKK1 decreased (r = 0.6, p < 0.001) and sclerostin increased (r = -0.4, p < 0.001) as kidney function declined, and both were associated with phosphate, PTH, FGF-23, and 1,25-dihydroxyvitamin D3 in the unadjusted analysis. After adjustment for age and mGFR, DKK1 remained significantly associated with PTH. CONCLUSION: The results of this study demonstrate opposing trends in Wnt/ß-catenin pathway inhibitors, DKK1 and sclerostin, as mGFR declines. Unlike sclerostin, DKK1 levels decreased significantly as mGFR declined and was independently associated with PTH. Future studies should determine whether measurement of Wnt signaling inhibitors may be useful in predicting bone histomorphometric findings and important clinical outcomes in patients with CKD.

Relationship of coronary artery calcification with renal function decline and mortality in predialysis chronic kidney disease patients.

BACKGROUND: Patients with chronic kidney disease (CKD) have higher levels of coronary artery calcification (CAC) compared with the general population. The role of CAC in renal function decline is not well understood. METHODS: In this prospective cohort study of Stages 3-5 CKD patients with CAC scores kidney function decline, development of end-stage kidney disease (ESKD) and all-cause mortality were determined at 5 and 10 years. Baseline variables included markers of CKD and chronic kidney disease mineral and bone disorder (CKD-MBD), demographics and comorbidities. Multivariable analyses identified predictors of outcomes, and survival curves demonstrated the association of CAC score with ESKD and mortality. RESULTS: One hundred and seventy-eight patients were enrolled between 2005 and 2007. Independent predictors of ESKD at 5 years were estimated glomerular filtration rate (eGFR) and urine albumin-creatinine ratio (UACR); at 10 years, eGFR was no longer a predictor, but CAC was now significant. Those who developed ESKD at the fastest rate either had the highest CAC score (≥400 AU) or were youngest and had the lowest calcidiol, and highest serum phosphate, UACR and percentage change in CAC per year. Predictors of eGFR decline over 5 years were UACR, parathyroid hormone and CAC score. Predictors of mortality at 5 years were age, diabetes and eGFR and at 10 years also included CAC score. CONCLUSIONS: In Stages 3-5 CKD patients, CAC is an independent predictor of both ESKD and mortality at 10 years. Those who developed ESKD at the fastest rate either had the highest CAC score or the worst CKD-MBD derangements.

Calcitriol Accelerates Vascular Calcification Irrespective of Vitamin K Status in a Rat Model of Chronic Kidney Disease with Hyperphosphatemia and Secondary Hyperparathyroidism.

Patients with chronic kidney disease (CKD) have a markedly increased risk for developing cardiovascular disease. Nontraditional risk factors, such as increased phosphate retention, increased serum fibroblast growth factor 23 (FGF-23), and deficiencies in vitamins D and K metabolism, likely play key roles in the development of vascular calcification during CKD progression. Calcitriol [1,25-(OH)2-D3] is a key transcriptional regulator of matrix Gla protein, a vitamin K-dependent protein that inhibits vascular calcification. We hypothesized that calcitriol treatment would inhibit the development of vascular calcification and this inhibition would be dependent on vitamin K status in a rat model of CKD. Rats were treated with dietary adenine (0.25%) to induce CKD, with either 0, 20, or 80 ng/kg of calcitriol with low or high dietary vitamin K1 (0.2 or 100 mg/kg) for 7 weeks. Calcitriol at both lower (20 ng/kg) and moderate (80 ng/kg) doses increased the severity of vascular calcification, and contrary to our hypothesis this was not significantly improved by high dietary vitamin K1. Calcitriol had a dose-dependent effect on: 1) lowering serum parathyroid hormone, 2) increasing serum calcium, and 3) increasing serum FGF-23. Calcitriol treatment significantly increased aortic expression of the calcification genes Runx2 and Pit-1 These data also implicate impaired vitamin D catabolism in CKD, which may contribute to the development of calcitriol toxicity and increased vascular calcification. The present findings demonstrate that in an adenine-induced rat model of CKD calcitriol treatment at doses as low as 20 ng/kg can increase the severity of vascular calcification regardless of vitamin K status.

Vitamin K Metabolism in a Rat Model of Chronic Kidney Disease.

BACKGROUND: Patients with chronic kidney disease (CKD) have very high levels of uncarboxylated, inactive, extra-hepatic vitamin K-dependent proteins measured in circulation, putting them at risk for complications of vitamin K deficiency. The major form of vitamin K found in the liver is phylloquinone (K1). Menaquinone-4 (MK-4) is the form of vitamin K that is preferentially found in extra-hepatic tissues. METHODS: In the present study, we assessed tissue concentrations of K1 and MK-4 and the expression of vitamin K-related genes in a rat model of adenine-induced CKD. RESULTS: It was found that rats with both mild and severe CKD had significantly lower amounts of K1 measured in liver, spleen and heart and higher levels of MK-4 measured in kidney cortex and medulla. All animals treated with high dietary K1 had an increase in tissue levels of both K1 and MK-4; however, the relative increase in K1 differed suggesting that the conversion of K1 to MK-4 may be a regulated/limiting process in some tissues. There was a decrease in the thoracic aorta expression of vitamin K recycling (Vkor) and utilization (Ggcx) enzymes, and a decrease in the kidney level of vitamin K1 to MK-4 bioconversion enzyme Ubiad1 in CKD. CONCLUSION: Taken together, these findings suggest that CKD impacts vitamin K metabolism, and this occurs early in the disease course. Our findings that vitamin K metabolism is altered in the presence of CKD provides further support that sub-clinical vitamin K deficiency may represent a modifiable risk factor for vascular and bone health in this population.

Phosphate-Containing Prescription Medications Contribute to the Daily Phosphate Intake in a Third of Hemodialysis Patients.

OBJECTIVES: Hyperphosphatemia is associated with all-cause mortality in hemodialysis (HD) patients and is managed by restricting dietary phosphate. Many patients are unable to adhere to the recommended dietary phosphate limit. We sought to quantify the additional phosphate burden from prescription medication in a hemodialysis population. DESIGN: Cross-sectional study. SUBJECTS: Adult patients on hemodialysis at a single center. SETTING: The Health Canada Drug Product Database was used to identify formulations of medications prescribed in an HD program that contain phosphate salts. The manufacturers of formulations containing a phosphate salt were contacted to request the phosphate content per tablet, and amounts were confirmed in select medications by the malachite green method. MAIN OUTCOME MEASUREMENTS: Prescription bottles of 101 HD patients were evaluated. Reported phosphate contents were used to determine patients' daily phosphate load from prescribed medications. RESULTS: A total 1,744 drug formulations of 124 different medications were reviewed. A total of 185 (11%) contained a phosphate salt. Central nervous system (CNS) and cardiovascular (CVS) medications accounted for 65% and 24% of phosphate-containing medications, respectively. Of HD patients, 30% were taking at least one medication that contained phosphate. The median phosphate burden from prescribed medications was 111 (67-168) mg per day. CONCLUSIONS: Knowledge about the phosphate content of commonly prescribed drugs within different classes should influence prescribing patterns. Particular consideration of which formulation of CVS and CNS drugs contain phosphate should be applied when prescribing. Phosphate-containing medications can meaningfully contribute to the daily phosphate load in HD patients; however, this burden will differ based on local dispensing patterns.

Magnesium Modifies the Impact of Calcitriol Treatment on Vascular Calcification in Experimental Chronic Kidney Disease.

Chronic kidney disease (CKD) patients are commonly treated with vitamin D analogs, such as calcitriol. Recent epidemiologic evidence revealed a significant interaction between vitamin D and magnesium, since an inverse relationship between vitamin D levels and mortality mainly occurs in patients with a high magnesium intake. The aim of the study was to assess the mechanisms involved by determining whether magnesium alone or combined with calcitriol treatments differentially impacts vascular calcification (VC) in male Sprague-Dawley rats with adenine-induced CKD. Treatment with moderate doses of calcitriol (80 µg/kg) suppressed parathyroid hormone to near or slightly below control levels. Given alone, this dose of calcitriol increased the prevalence of VC; however, when magnesium was given in combination, the severity of calcification was attenuated in the abdominal aorta (51% reduction), iliac (44%), and carotid arteries (46%) compared with CKD controls. The decreases in vascular calcium content were associated with a 20-50% increase in vascular magnesium. Calcitriol treatment alone significantly decreased TRPM7 protein (↓ to ∼11%), whereas the combination treatment increased both mRNA (1.7×) and protein (6.8×) expression compared with calcitriol alone. In summary, calcitriol increased VC in certain conditions, but magnesium prevented the reduction in TRPM7 and reduced the severity of VC, thereby increasing the bioavailable magnesium in the vascular microenvironment. These findings suggest that modifying the adverse effect profile of calcitriol with magnesium may be a plausible approach to benefiting the increasing number of CKD patients being prescribed calcitriol.

Sequence variation in vitamin K epoxide reductase gene is associated with survival and progressive coronary calcification in chronic kidney disease.

OBJECTIVE: Sequence variations in the gene(s) encoding vitamin K epoxide reductase complex subunit 1 (VKORC1), the enzyme target of warfarin, have been associated with increased cardiovascular disease in the general population. Coronary artery calcification (CAC) is a prevalent form of cardiovascular disease in chronic kidney disease. We tested the hypothesis that the VKORC1 rs8050894 CC genotype would be associated with mortality and progression of CAC ≤ 4 years. APPROACH AND RESULTS: This study is an observational, prospective study of 167 individuals with stages 3 to 5 chronic kidney disease. Survival ≤ 4 years was assessed in all participants, and CAC progression was measured in a subset of 86 patients. Participants with the CG/GG genotype of VKORC1 had higher baseline CAC scores (median score, 112 versus 299; P=0.036). Of those 86 patients who had a 4-year CAC score, those with the CG/GG genotype had an increased risk of progressive CAC (adjusted for age, diabetes mellitus, estimated glomerular filtration rate, and hypertension) compared with those with the CC genotype. Four-year mortality risk was 4 times higher for individuals with the CG/GG genotypes compared with individuals with the CC genotype (odds ratio, 3.8; 95% confidence interval, 1.2-12.5; P=0.02), adjusted for age, sex, diabetes mellitus, estimated glomerular filtration rate, baseline CAC, and hypertension. CONCLUSIONS: Patients with the CG/GG genotype of VKORC1 had a higher risk of CAC progression and a poorer survival. These data provide new perspectives on the potential extrahepatic role of VKORC1 in individuals with chronic kidney disease.

Prevention of dialysis catheter malfunction with recombinant tissue plasminogen activator.

BACKGROUND: The effectiveness of various solutions instilled into the central venous catheter lumens after each hemodialysis session (catheter locking solutions) to decrease the risk of catheter malfunction and bacteremia in patients undergoing hemodialysis is unknown. METHODS: We randomly assigned 225 patients undergoing long-term hemodialysis in whom a central venous catheter had been newly inserted to a catheter-locking regimen of heparin (5000 U per milliliter) three times per week or recombinant tissue plasminogen activator (rt-PA) (1 mg in each lumen) substituted for heparin at the midweek session (with heparin used in the other two sessions). The primary outcome was catheter malfunction, and the secondary outcome was catheter-related bacteremia. The treatment period was 6 months; treatment assignments were concealed from the patients, investigators, and trial personnel. RESULTS: A catheter malfunction occurred in 40 of the 115 patients assigned to heparin only (34.8%) and 22 of the 110 patients assigned to rt-PA (20.0%)--an increase in the risk of catheter malfunction by a factor of almost 2 among patients treated with heparin only as compared with those treated with rt-PA once weekly (hazard ratio, 1.91; 95% confidence interval [CI], 1.13 to 3.22; P = 0.02). Catheter-related bacteremia occurred in 15 patients (13.0%) assigned to heparin only, as compared with 5 (4.5%) assigned to rt-PA (corresponding to 1.37 and 0.40 episodes per 1000 patient-days in the heparin and rt-PA groups, respectively; P = 0.02). The risk of bacteremia from any cause was higher in the heparin group than in the rt-PA group by a factor of 3 (hazard ratio, 3.30; 95% CI, 1.18 to 9.22; P = 0.02). The risk of adverse events, including bleeding, was similar in the two groups. CONCLUSIONS: The use of rt-PA instead of heparin once weekly, as compared with the use of heparin three times a week, as a locking solution for central venous catheters significantly reduced the incidence of catheter malfunction and bacteremia. (Current Controlled Trials number, ISRCTN35253449.).

Calcification of the internal pudendal artery and development of erectile dysfunction in adenine-induced chronic kidney disease: a sentinel of systemic vascular changes.

INTRODUCTION: Chronic kidney disease (CKD), erectile dysfunction (ED), and cardiovascular disease share common vascular etiologies and risk factors. AIM: Using a rat model, this is the first study to characterize the consequences of CKD in the onset and development of ED associated with differential regional vascular calcification and circulatory changes. METHODS: Stable CKD was generated at 3 weeks in male Sprague-Dawley rats given dietary adenine and progressed until 7 weeks. Mineral content and morphometry were assessed in the internal pudendal arteries (IPAs), thoracic aorta, and carotid artery. Endothelial function was determined via changes in serum von Willebrand factor (VWF) and endothelium-dependent relaxation of the thoracic aorta. RESULTS: In severe CKD rats, calcium and phosphate content in all arteries increased, and pulse wave velocity was elevated. Distal IPA segments, in particular, were the first to calcify, but penile tissue per se did not. CKD rats had endothelial dysfunction, as indicated by a decrease in acetylcholine-mediated relaxation (∼40%) and an increase in serum VWF (∼40%), as well as increased lumen diameter (20%) of the distal IPA. Erectile function, assessed using a centrally acting dopaminergic agent, was significantly impaired by 7 weeks (∼40%). CONCLUSIONS: In CKD, the distal IPA appears to be more susceptible to vascular dysfunction and calcification. Additionally, the onset of ED may be an important sentinel of impending systemic vascular disease. To confirm this concept, future experimental and clinical studies will need to examine a range of vessel types and the use of supplementary methods to assess erectile function.

Phosphate: an old bone molecule but new cardiovascular risk factor.

Phosphate handling in the body is complex and involves hormones produced by the bone, the parathyroid gland and the kidneys. Phosphate is mostly found in hydroxyapatite. however recent evidence suggests that phosphate is also a signalling molecule associated with bone formation. Phosphate balance requires careful regulation of gut and kidney phosphate transporters, SLC34 transporter family, but phosphate signalling in osteoblasts and vascular smooth muscle cells is likely mediated by the SLC20 transporter family (PiT1 and PiT2). If not properly regulated, phosphate imblanace could lead to mineral disorders as well as vascular calcification. In chronic kidney disease-mineral bone disorder, hyperphosphataemia has been consistently associated with extra-osseous calcification and cardiovascular disease. This review focuses on the physiological mechanisms involved in phosphate balance and cell signalling (i.e. osteoblasts and vascular smooth muscle cells) as well as pathological consequences of hyperphosphataemia. Finally, conventional as well as new and experimental therapeutics in the treatment of hyperphosphataemia are explored.

Inorganic phosphate additives in meals and adaptations to 5-days of dietary inorganic phosphate loading alter acute calcium homeostasis in two randomized cross-over studies in healthy adults.

Diets containing inorganic phosphate additives are unbalanced with respect to calcium and these diets have been linked to the development of altered bone metabolism. Using 2 randomized cross-over studies in healthy humans, we (1) characterized the hormonal and urinary response to 2 meals with the same reported phosphorus amount (562-572 mg), where one was manufactured with inorganic phosphate additives and a comparatively lower Ca:P molar ratio (0.26 vs 0.48), and (2) assessed how acute homeostatic mechanisms adapt following 5-d exposure to recommended dietary phosphorus amount (~700 mg P/d) compared to a diet enriched with inorganic phosphate additives (~1100 mg P/d). Participants were then challenged with 500 mg of oral phosphorus in the form of inorganic phosphate after an overnight fast following each diet condition. Measurements included serum calcium, phosphate, PTH, and fibroblast growth factor 23 , vitamin D metabolites, and urine calcium and phosphate excretion. Following the meal containing inorganic phosphate additives with a low Ca:P ratio, serum phosphate was higher and more phosphate was excreted in the urine compared to the low additive meal. Although the Ca:P and calcium content was lower in the high additive meal, the same amount of calcium was excreted into the urine. Subsequently, increasing only dietary phosphate through additives resulted in lower 24-h excretion of calcium. The oral phosphate challenge promoted urinary calcium excretion, despite no consumption of calcium, which was attenuated when pre-acclimated to a high phosphate diet. These data suggest that ingestion of inorganic phosphate promotes calcium excretion, but homeostatic mechanisms may exist to reduce calcium excretion that are responsive to dietary intake of phosphate. Future studies are required to evaluate potential implication of diets enriched with inorganic phosphate additives on bone health.

Serum total testosterone is associated with phosphate and calcium excretion in response to oral phosphate loading in healthy middle-aged males.

Androgen receptors are expressed in the kidney and serum testosterone is negatively associated with serum phosphate in males, suggesting a role of testosterone in renal phosphate handling. In this cross-sectional study, we examined the association of serum total and free testosterone with acute phosphate and calcium excretion in males in response to an oral phosphate challenge. Thirty-five healthy adult males with normal baseline testosterone levels consumed a 500 mg phosphorus drink and the urinary excretion of minerals, as well as levels of relevant circulating parameters, were assessed at baseline and hourly for 4 h. Serum total testosterone was positively associated with overall phosphate excretion (r = 0.35, p = 0.04) and calcium excretion (r = 0.44, p = 0.00) in response to the challenge. Serum free testosterone was positively associated with post-challenge calcium excretion (r = 0.34, p = 0.048), but significance was not reached for phosphate excretion (r = 0.31, p = 0.07). Serum total and free testosterone were not associated with parathyroid hormone, fibroblast growth factor-23, or vitamin D-key factors implicated in phosphate and calcium regulation. Overall, higher serum total testosterone levels in healthy middle-aged males are associated with a greater capacity to acutely excrete phosphate and calcium after a single oral phosphate challenge, suggesting potential ramifications of testosterone deficiency related to mineral homeostasis.