Two novel vitamin D receptor modulators with similar structures exhibit different hypercalcemic effects in 5/6 nephrectomized uremic rats

Endothelial Cell Dysfunction and Increased Cardiovascular Risk in Patients With Chronic Kidney Disease

The endothelium is considered to be the gatekeeper of the vessel wall, maintaining and regulating vascular integrity. In patients with chronic kidney disease, protective endothelial cell functions are impaired due to the proinflammatory, prothrombotic and uremic environment caused by the decline in kidney function, adding to the increase in cardiovascular complications in this vulnerable patient population. In this review, we discuss endothelial cell functioning in healthy conditions and the contribution of endothelial cell dysfunction to cardiovascular disease. Further, we summarize the phenotypic changes of the endothelium in chronic kidney disease patients and the relation of endothelial cell dysfunction to cardiovascular risk in chronic kidney disease. We also review the mechanisms that underlie endothelial changes in chronic kidney disease and consider potential pharmacological interventions that can ameliorate endothelial health.

Most exposed: the endothelium in chronic kidney disease

Accumulating evidence indicates that the pathological changes of the endothelium may contribute to the development of cardiovascular complications in chronic kidney disease (CKD). Non-traditional risk factors related to CKD are associated with the incidence of cardiovascular disease, but their role in uraemic endothelial dysfunction has often been disregarded. In this context, soluble α-Klotho and vitamin D are of importance to maintain endothelial integrity, but their concentrations decline in CKD, thereby contributing to the dysfunction of the endothelial lining. These hormonal disturbances are accompanied by an increment of circulating fibroblast growth factor-23 and phosphate, both exacerbating endothelial toxicities. Furthermore, impaired renal function leads to an increment of inflammatory mediators, reactive oxygen species and uraemic toxins that further aggravate the endothelial abnormalities and in turn also inhibit the regeneration of disrupted endothelial lining. Here, we highlight the distinct endothelial alterations mediated by the abovementioned non-traditional risk factors as demonstrated in experimental studies and connect these to pathological changes in CKD patients, which are driven by endothelial disturbances, other than atherosclerosis. In addition, we describe therapeutic strategies that may promote restoration of endothelial abnormalities by modulating imbalanced mineral homoeostasis and attenuate the impact of uraemic retention molecules, inflammatory mediators and reactive oxygen species. A clinical perspective on endothelial dysfunction in CKD may translate into reduced structural and functional abnormalities of the vessel wall in CKD, and ultimately improved cardiovascular disease.

Endothelial Dysfunction in Chronic Kidney Disease, from Biology to Clinical Outcomes: A 2020 Update

The vascular endothelium is a dynamic, functionally complex organ, modulating multiple biological processes, including vascular tone and permeability, inflammatory responses, thrombosis, and angiogenesis. Endothelial dysfunction is a threat to the integrity of the vascular system, and it is pivotal in the pathogenesis of atherosclerosis and cardiovascular disease. Reduced nitric oxide (NO) bioavailability is a hallmark of chronic kidney disease (CKD), with this disturbance being almost universal in patients who reach the most advanced phase of CKD, end-stage kidney disease (ESKD). Low NO bioavailability in CKD depends on several mechanisms affecting the expression and the activity of endothelial NO synthase (eNOS). Accumulation of endogenous inhibitors of eNOS, inflammation and oxidative stress, advanced glycosylation products (AGEs), bone mineral balance disorders encompassing hyperphosphatemia, high levels of the phosphaturic hormone fibroblast growth factor 23 (FGF23), and low levels of the active form of vitamin D (1,25 vitamin D) and the anti-ageing vasculoprotective factor Klotho all impinge upon NO bioavailability and are critical to endothelial dysfunction in CKD. Wide-ranging multivariate interventions are needed to counter endothelial dysfunction in CKD, an alteration triggering arterial disease and cardiovascular complications in this high-risk population.

Combined treatment with benzo[a]pyrene and 1α,25-dihydroxyvitamin D3 induces expression of plasminogen activator inhibitor 1 in monocyte/macrophage-derived cells

Benzo[a]pyrene (BaP) is an environmental pollutant found in cigarette smoke and is implicated as a causative agent of tobacco-related diseases, such as arteriosclerosis. In contrast, vitamin D signaling, which is principally mediated by conversion of vitamin D to the active form, 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃], decreases cardiovascular disease risk. However, combined treatment with BaP and 1,25(OH)₂D₃ enhances BaP toxicity, including BaP-DNA adduct formation. We further investigated the cross-talk between BaP and 1,25(OH)₂D₃ signaling pathways, and found that combined treatment with these compounds induces mRNA and protein expression of plasminogen activator inhibitor 1 (PAI-1) in monocyte/macrophage-derived THP-1 and U937 cells. Protein synthesis inhibitor treatment did not inhibit induction of the PAI-1 gene (SERPINE1) in these cells. BaP plus 1,25(OH)₂D₃ induced differentiation markers, inhibited cellular proliferation, and induced apoptosis and oxidative stress in these cells. Reactive oxygen species scavenger treatment suppressed apoptosis but not SERPINE1 induction in cells treated with BaP plus 1,25(OH)₂D₃. Thus, combined treatment with BaP and 1,25(OH)₂D₃ induced SERPINE1 mRNA expression in these cells through a mechanism that does not require de novo protein synthesis or reactive oxygen species production. These findings suggest that induction of the proinflammatory factor PAI-1 plays a role in BaP toxicity. Interestingly, PAI-1 knockdown decreased expression of the cell surface antigen CD14, a monocytic differentiation marker, in THP-1 cells treated with BaP plus 1,25(OH)₂D₃. PAI-1 induction may also be related to a function of monocytes/macrophages in response to xenobiotic and vitamin D signaling.

Preclinical studies of VS-505: a non-absorbable highly effective phosphate binder

BACKGROUND AND PURPOSE

Phosphate imbalance is often present in chronic kidney disease (CKD), and it contributes to a higher cardiovascular mortality rate. A phosphate binder is typically part of a treatment strategy for controlling phosphate imbalance. However, safety concerns and low compliance are two well-recognized disadvantages of on-market phosphate binders. This report describes the preclinical studies of VS-505, a non-absorbable, calcium- and aluminum-free, plant-derived polymer currently being evaluated in haemodialysis patients in Australia.

EXPERIMENTAL APPROACH

Normal Sprague Dawley (SD) rats or uraemic SD rats induced by 5/6 nephrectomy fed a high-phosphate diet were treated with VS-505 or sevelamer (0.05-10% in food) for 5 and 28 days respectively.

KEY RESULTS

Urinary and serum phosphate levels were significantly elevated in untreated rats, and were decreased by VS-505 and sevelamer. VS-505 increased faecal phosphate levels in a dose-dependent manner. High-phosphate diet also caused an increase in serum FGF-23 and parathyroid hormone in nephrectomized (NX) rats, effects prevented by VS-505 or sevelamer. Significant aortic calcification was observed in NX rats treated with 5% sevelamer, whereas VS-505 at all doses tested did not show effects. VS-505 had no effects on small intestine histomorphology and intestinal sodium-dependent phosphate cotransporter gene expression. In vitro characterizations showed that VS-505 has a relatively high density and low expansion volume when exposed to simulated gastric fluid.

CONCLUSIONS AND IMPLICATIONS

VS-505 is a safe and effective phosphate binder and may offer the advantage of having a reduced pill burden and minimal GI side effects for CKD patients.

Vitamin D receptor agonist VS-105 improves cardiac function in the presence of enalapril in 5/6 nephrectomized rats

Vitamin D receptor (VDR) agonists (VDRAs) are commonly used to manage hyperparathyroidism secondary to chronic kidney disease (CKD). Patients with CKD experience extremely high risks of cardiovascular morbidity and mortality. Clinical observations show that VDRA therapy may be associated with cardio-renal protective and survival benefits in patients with CKD. The 5/6 nephrectomized (NX) Sprague-Dawley rat with established uremia exhibits elevated serum parathyroid hormone (PTH), hypertension, and abnormal cardiac function. Treatment of 5/6 NX rats with VS-105, a novel VDRA (0.05 and 0.5 μg/kg po by gavage), once daily for 8 wk in the presence or absence of enalapril (30 mg/kg po via drinking water) effectively suppressed serum PTH without raising serum calcium. VS-105 alone reduced systolic blood pressure (from 174 ± 6 to 145 ± 9 mmHg, P < 0.05) as effectively as enalapril (from 174 ± 6 to 144 ± 7 mmHg, P < 0.05). VS-105 improved cardiac functional parameters such as E/A ratio, ejection fraction, and fractional shortening with or without enalapril. Enalapril or VS-105 alone significantly reduced left ventricular hypertrophy (LVH); VS-105 plus enalapril did not further reduce LVH. VS-105 significantly reduced both cardiac and renal fibrosis. The lack of hypercalcemic toxicity of VS-105 is due to its lack of effects on stimulating intestinal calcium transport and inducing the expression of intestinal calcium transporter genes such as Calb3 and TRPV6. These studies demonstrate that VS-105 is a novel VDRA that may provide cardiovascular benefits via VDR activation. Clinical studies are required to confirm the cardiovascular benefits of VS-105 in CKD.

VS-501: A NOVEL, NON-ABSORBED, CALCIUM- AND ALUMINUM-FREE, HIGHLY EFFECTIVE PHOSPHATE BINDER DERIVED FROM NATURAL PLANT POLYMER

Inadequate control of serum phosphate in chronic kidney disease can lead to pathologies of clinical importance. Effectiveness of on-market phosphate binders is limited by safety concerns and low compliance due to high pill size/burden and gastrointestinal discomfort. VS-501 is a non-absorbed, calcium- and aluminum-free, chemically-modified, plant-derived polymer. In vitro studies show that VS-501 has a high density and a low swell volume when exposed to simulated gastric fluid (vs. sevelamer). When male Sprague Dawley (SD) rats on normal diet were treated with VS-501 or sevelamer, serum phosphate was not significantly altered, but urinary phosphate levels decreased by >90%. VS-501 had no effect on serum calcium (Ca) or urinary Ca, while 3% sevelamer significantly increased serum and urine Ca. In 5/6 nephrectomized (NX) uremic SD rats on high-phosphate diet, increasing dietary phosphate led to an increase in serum and urine phosphate, which was prevented in rats treated with VS-501 or sevelamer (0.2-5% in food). High phosphate diet also increased serum FGF-23 and parathyroid hormone in 5/6 NX rats, which was prevented by VS-501 or sevelamer. VS-501 or sevelamer increased fecal phosphate in a dose-dependent manner. More aortic calcification was observed in 5/6 NX rats treated with 5% sevelamer, while VS-501 and sevelamer did not show significant effects on cardiac parameters, fibrosis, intestine histology and intestinal sodium-dependent phosphate cotransporter gene expression. These results suggest that VS-501 is effective in binding phosphate with no effects on calcium homeostasis, and may have improved pill burden and gastrointestinal side effects.

Synthesis of VS-105: A novel and potent vitamin D receptor agonist with reduced hypercalcemic effects

We have synthesized a novel vitamin D receptor agonist VS-105 ((1R,3R)-5-((E)-2-((3αS,7αS)-1-((R)-1-((S)-3-hydroxy-2,3-dimethylbutoxy)ethyl)-7α-methyldihydro-1H-inden-4(2H,5H,6H,7H,7αH)-ylidene)ethylidene)-2-methylenecyclohexane-1,3-diol). Preparation of a-ring phenylphosphine oxide 11, followed by Wittig-Horner coupling of 11 with the protected 25-hydroxy Grundmann's ketone 22 generated the precursor 12. Deprotection of the TBDMS groups of 12 produced the target compound VS-105. The biological profiles of VS-105 were evaluated using in vitro assays (VDR receptor binding, VDR reporter gene and HL-60 differentiation) in comparison to calcitriol (the endogenous hormone) or paricalcitol. Furthermore, the PTH suppressing potency and hypercalcemic side effects of VS-105 were evaluated in the 5/6 nephrectomized uremic rats in comparison to paricalcitol. Combining various changes at 20-epi, 22-oxa, 24-methyl, and 2-methylene yielded VS-105 that not only is highly potent in inducing functional responses in vitro, but also effectively suppresses PTH in a dose range that does not affect serum calcium in the 5/6 nephrectomized uremic rats.