Effects of the Use of Non-Calcium Phosphate Binders in the Control and Outcome of Vascular Calcifications: A Review of Clinical Trials on CKD Patients

Phosphate Absorption and Hyperphosphatemia Management in Kidney Disease: A Physiology-Based Review

Phosphate absorption occurs in the gastrointestinal tract through paracellular absorption and transcellular transport. The paracellular pathway does not saturate and has a significantly higher absorption capacity than does the transcellular pathway. Evidence indicates that this pathway is the primary mechanism of intestinal phosphate absorption, particularly with Western diets containing high amounts of phosphorus. Elevated serum phosphorus concentrations are associated with cardiovascular morbidity and mortality but serum phosphorus concentrations > 5.5 mg/dL are highly prevalent despite best efforts with dietary phosphate restriction, dialysis, and the use of phosphate binders. The efficacy of phosphate binders may be inherently limited because the mechanism of action does not target any phosphate absorption pathway. Thus, therapeutic innovations are needed to address the limitations of phosphate binders. Novel therapies leveraging new mechanistic understandings of phosphate absorption and the primacy of the paracellular pathway may improve phosphate control. Phosphate absorption inhibitors that target the pathway are a novel therapeutic class. Tenapanor is an investigational first-in-class nonbinder phosphate absorption inhibitor that inhibits the sodium-hydrogen exchanger isoform 3 to reduce paracellular permeability specific to phosphate. Phosphate absorption inhibitors may represent a new mechanistic approach to phosphate management with the potential to improve clinical outcomes.

MicroRNA-103a regulates the calcification of vascular smooth muscle cells by targeting runt-related transcription factor 2 in high phosphorus conditions

Vascular calcification, such as atherosclerosis, is a serious complication of chronic kidney disease that is characterized by tunica media calcification, and has gained increasing attention from researchers. The commonly observed association between vascular calcification and osteoporosis suggests a link between bone and vascular disorders. As microRNAs (miRNAs) have a wide range of gene regulation functions, such as cell proliferation, apoptosis, stress and transdifferentiation, the current study aimed to determine whether miRNAs play a vital role in the calcification and osteoblastic differentiation of rat thoracic aorta vascular smooth muscle cells (VSMCs). Gene expression analysis was performed on seven miRNAs (miR-29a, -30b, -103a, -125b, -133a, -143 and -211) that maybe potentially involved in the differentiation of smooth muscle cells into osteoblastic cells. The results showed that the levels of miR-29a, -30b, -103a, -125b and -143 were markedly reduced in the VSMC calcification model, particularly miR-103a, whereas runt-related transcription factor 2 (RUNX2) expression was increased. Furthermore, it was found that the expression of RUNX2 was significantly decreased following the upregulation of miR-103a, and that the expression of RUNX2 was significantly increased by downregulating miR-103a in VSMCs. Therefore, it was concluded that miR-103a plays a notable role in the transdifferentiation of the VSMCs in high phosphorus-induced calcification by targeting the regulation of RUNX2, and may therefore constitute a new target for the diagnosis and treatment of vascular calcification.

Associations of plasma fibroblast growth factor 23 and other markers of chronic kidney disease-Mineral and bone disorder with all-cause mortality in South African patients on maintenance dialysis: A 3-year prospective cohort study

INTRODUCTION

Few studies have linked high levels of plasma C-terminal fibroblast growth factor 23 (FGF23) with poor clinical outcomes in patients on maintenance haemodialysis (MHD), while the association between intact FGF23 and mortality in this group of patients remains inconclusive. Therefore, the aim of this study was to evaluate the association between plasma levels of intact FGF23 and mortality in dialysis patients.

METHODS

A prospective multicenter study involving patients undergoing dialysis at three dialysis centers in Johannesburg was undertaken between 1st October 2014 and 31st December 2017.

RESULTS

The study comprised 165 chronic dialysis patients (111 blacks, 54 whites) with a mean age of 46.6 ±14.2 years. During a three year follow up period, there were 46 deaths (1.03 per 100 person-years). The median plasma FGF 23 level was 382 pg/ml (interquartile range [IQR], 145-2977). In adjusted multivariable analyses, there was a non-statistically significant increase in the risk of mortality with higher quartiles of FGF 23 levels: the adjusted hazard ratios (HR) for the second, third and fourth quantiles were HR 3.20 (95% CI, 0.99-10.35; P = 0.052), HR 2.43(95% CI,0.65-9.09; P = 0.19), and HR 2.09 (95% CI, 0.66-7.32; P = 0.25),respectively. Corrected serum calcium 2.38-2.5 mmol/l [HR 2.98 (95% CI, 1.07-8.29; P = 0.04] and > 2.50 mmol/l [HR 5.50 (95% CI, 1.84-16.48; P = 0.002] were independently associated with increased risk of death. Likewise, patients with intact parathyroid hormone > 600 pg/ml had a 3.46-fold higher risk of death (HR 3.46, 95% CI, 1.22-9.82 P = 0.019). These findings persisted in time -dependent analyses.

CONCLUSION

Higher levels of intact FGF 23 appear not to be independently associated with all-cause mortality in our dialysis patients, while hypercalcaemia and severe hyperparathyroidism were found to be independent predictors of mortality in this cohort of patients.

Menaquinone-4 modulates the expression levels of calcification-associated factors to inhibit calcification of rat aortic vascular smooth muscle cells in a dose-dependent manner

Vascular calcification (VC) caused by chronic kidney disease (CKD)-mineral and bone disorder is a common complication of CKD. Recent studies have demonstrated that menaquinone-4 (MK-4) is negativly associated with VC in patients with CKD. Furthermore, we have previously shown that runt-related transcription factor 2 (Runx2) is important in the phenotypic transformation process of rat vascular smooth muscle cells (VSMCs), which is the key step for the development of VC. The present study investigated the influence of MK-4 on the phenotypic transformation process of rat VSMCs in order to illustrate its role in the process of VC. Calcification assays were perfomed to access the calcified degree of rat VSMCs. Additionally, the genes and proteins related to phenotypic transformation were measured by reverse transcription-polymerase chain reaction and western blotting methods. It was revealed that calcium deposition in the cells was evidently increased with an addition of β-glycerophosphate (β-GP) and could be completely prevented by co-incubation with MK-4 in a dose-dependent manner. Furthermore, the expression of Runx2 in the β-GP-induced VSMCs was inhibited by MK-4. It was also revealed that the expression of SMAD1 and bone morphogenetic protein (BMP)-2 were decreased in the β-GP-induced VSMCs treated with MK-4 in a dose-dependent manner; however, the expression of SMAD7 was increased in the β-GP-induced VSMCs treated with MK-4 in a dose-dependent manner. These observations suggest that MK-4 reduces mineralization by regulating the BMP-2 signaling pathway in order to attenuate the expression of Runx2.

Extracellular acidosis suppresses calcification of vascular smooth muscle cells by inhibiting calcium influx via L-type calcium channels

Vascular calcification such as arteriosclerosis, which is characterized by a calcification of the tunica media, is a severe complication of chronic kidney disease (CKD), contributing to the high prevalence of cardiovascular morbidity and mortality in patients with CKD. An essential step during the development of arteriosclerosis is the transdifferentiation/calcification of vascular smooth muscle cells (VSMCs), resembling osteogenesis. Metabolic acidosis, a common clinical manifestation in CKD, is known to decrease vascular calcification. To understand the underlying regulatory mechanisms of acidosis, we investigated whether the acidosis-decreased VSMC calcification involves altered signaling of the LTCC/Ca²⁺/Runx2 pathway. Vascular calcifications, calcium content, runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), L-type calcium channel (LTCC) β₃ subunits, and calcium influx were measured in vivo or in vitro. Calcified nodules and calcium content increased either in aorta sections of vascular calcified rats or in VSMCs induced by β-GP. The expression of Runx2 and ALP activity markedly rose, accompanied by the increasing expression of LTCC β₃ subunits and calcium influx. However, acidosis supplementation successfully attenuated VC and VSMC calcification and inhibited Runx2, ALP, LTCC β₃ subunits, and calcium influx. In conclusion, acidosis significantly attenuated vascular calcification in association with downregulation of the LTCC/Ca²⁺/Runx2 pathway.

Efficacy of Ablation Therapy for Secondary Hyperparathyroidism by Ultrasound Guided Percutaneous Thermoablation

The objective of this study was to explore the value of ultrasound-guided percutaneous microwave thermoablation to treat secondary hyperparathyroidism (SHPT). One hundred and thirty-eight parathyroid glands from 56 patients with SHPT were ablated in this study. All the parathyroid glands were evaluated by real-time contrast-enhanced ultrasound before, during and after ablation. Changes in serum parathyroid hormone (sPTH) levels were measured before treatment and at 1 h, 1 wk, 1 mo and 6 mo after thermoablation treatment. All 56 cases had a 1-mo follow-up, and 34 cases had a 6-mo follow-up. The sPTH level of the 54 cases 1 mo after ablation was significantly lower than that before (p < 0.05). In the 34 cases that had a 6-mo follow-up, the sPTH levels were also significantly lower at 6 mo after ablation than before (p < 0.05). Bone pain in patients improved post-operatively (p < 0.05), but itchiness and insomnia did not improve (p > 0.05). Ultrasound-guided percutaneous microwave thermoablation is a feasible and effective non-surgical alternative treatment for SHPT patients.