Sevelamer restores bone volume and improves bone microarchitecture and strength in aged ovariectomized rats

Phosphate and bone fracture risk in chronic kidney disease patients

In chronic kidney disease (CKD), phosphate homoeostasis plays a central role in the development of mineral and bone disorder (MBD) together with decreased serum calcium and elevated serum parathyroid hormone, fibroblast growth factor 23 and sclerostin levels. Today there are only a few data exploring the direct role of abnormal phosphate homoeostasis and hyperphosphataemia in the development of CKD-MBD. On the other hand, several studies have looked at the link between hyperphosphataemia and cardiovascular morbidity and mortality in CKD, but there is a lack of evidence to indicate that lowering phosphate levels improves cardiovascular outcomes in this population. Furthermore, the impact of liberalizing phosphate targets on CKD-MBD progression and bone fracture is currently not known. In this review we discuss the central role of phosphate in the pathogenesis of CKD-MBD and how it may be associated with fracture risk, both in hyper- and hypophosphataemia.

The beneficial effect of icaritin on osteoporotic bone is dependent on the treatment initiation timing in adult ovariectomized rats

BACKGROUND

Epimedium-derived flavonoids (EFs) have a potential to treat established osteoporosis in postmenopausal women. However, one of the main disadvantages of the compound is the high volume and dosage during long-term administration period. Meanwhile, the beneficial effect of EFs on osteoporotic bone depends greatly on the intervention timing. Whether icaritin (ICT), an active molecular compound from EFs, can exert beneficial effect on osteoporotic bone and whether the beneficial effect is also dependent on the intervention timing remain unknown.

OBJECTIVE

The objective of this study was to evaluate the effect of the early and late ICT treatment on bone turnover markers, trabecular architecture, bone remodeling, biomechanics, colony formation of bone marrow stromal cells and osteoblast, adipocyte and osteoclast-related gene expression in adult ovariectomized rats.

METHODS

Eighty 9-month-old female rats (n=8/group) were sham-operated (Sham) or ovariectomized (OVX). The OVX rats were subjected to ICT treatment initiation at 1 month (early treatment) and 3 months (late treatment) post-operation, respectively. The vehicle-treated Sham and OVX rats starting at month 1 and month 3 post-operation served as the corresponding controls (Sham and OVX controls) for early and late ICT treatment, respectively. Those Sham and OVX rats sacrificed immediately before early and late ICT treatment served as the pretreatment baseline controls. Both ICT and vehicle treatments lasted for 2 months. The bone turnover markers, trabecular architecture, bone remodeling and bone biomechanical properties were analyzed with biochemistry, microCT, histomorphometry and mechanical testing, respectively. The population of bone marrow stromal cells (BMSCs) and osteoblasts were evaluated with colony formation assays, respectively. The expression levels of osteoblast, adipocyte and osteoclast-related genes in bone marrow were assessed by real-time polymerase chain reaction (PCR), respectively.

RESULTS

At the tissue level, early ICT treatment remarkably restored the trabecular bone mass, trabecular architecture and bone biomechanical properties towards pretreatment Sham levels, and significantly increased bone formation from pretreatment OVX level and markedly inhibited bone resorption towards pretreatment Sham level, whereas late ICT treatment failed to have any effect. At the cellular and molecular level, early ICT treatment significantly increased the number of osteoblastic colonies and the level of osteoblast-related gene expression compared to pretreatment OVX levels and remarkably decreased adipocyte and osteoclast-related gene expression towards pretreatment Sham levels. Late ICT treatment failed to have beneficial effect on any of these parameters.

CONCLUSION

ICT can exert anabolic and anti-resorptive effect on osteoporotic bone. The beneficial effect of ICT treatment is dependent on the intervention timing in established osteoporosis induced by estrogen depletion.

Potential beneficial role of sevelamer hydrochloride in diabetic retinopathy

Patients with chronic kidney disease (CKD) experience co-morbid illnesses, including cardiovascular disease and retinopathy. Sevelamer hydrochloride (Renagel®); a non-calcium phosphate binder reduces coronary artery and aortic calcification as compared to calcium containing phosphate binders and additionally effects inflammatory biomarkers such as C-reactive protein (CRP), and lowers LDL cholesterol in patients with CKD. Since retinopathy is proven to be associated with increased coronary calcification, shared pathophysiological processes may contribute to both microvascular and macrovascular disease. We here suggest three different mechanisms of possible sevelamer's influence on the retinopathy: (1) by direct effect on the microvasculature through lowering CRP and LDL, involved in endothelial dysfunction and atherogenesis, (2) indirectly by attenuation of vascular calcification of aorta and carotid internal artery, it reduces ischaemia and improves circulation in the opthalmic artery and hence postponing retinopathy, (3) through hypertension by reducing atherosclerosis and calcification of carotid arteries, sevelamer decreases stiffness and intima-media wall thickness, therefore lowering blood pressure, which is well known to increase progression of diabetic retinopathy. So far no studies have yet been published on the direct influence of sevelamer on the retinopathy which we believe has good theoretical background. With its combined macrovascular and microvascular effect, sevelamer could potentially postpone and/or decrease retinopathy in diabetic patients with hypertension, and that are on hemodialysis or even predialysis patients.

Npt2b deletion attenuates hyperphosphatemia associated with CKD

The incidence of cardiovascular events and mortality strongly correlates with serum phosphate in individuals with CKD. The Npt2b transporter contributes to maintaining phosphate homeostasis in the setting of normal renal function, but its role in CKD-associated hyperphosphatemia is not well understood. Here, we used adenine to induce uremia in both Npt2b-deficient and wild-type mice. Compared with wild-type uremic mice, Npt2b-deficient uremic mice had significantly lower levels of serum phosphate and attenuation of FGF23. Treating Npt2b-deficient mice with the phosphate binder sevelamer carbonate further reduced serum phosphate levels. Uremic mice exhibited high turnover renal osteodystrophy; treatment with sevelamer significantly decreased the number of osteoclasts and the rate of mineral apposition in Npt2b-deficient mice, but sevelamer did not affect bone formation and rate of mineral apposition in wild-type mice. Taken together, these data suggest that targeting Npt2b in addition to using dietary phosphorus binders may be a therapeutic approach to modulate serum phosphate in CKD.

Ten-year experience with sevelamer and calcium salts as phosphate binders

Most patients with chronic kidney disease experience abnormalities in serum calcium, phosphorus, parathyroid hormone, and vitamin D metabolism. These can lead to vascular calcification (VC), which has been associated with increased risk for cardiovascular disease and mortality. Although hyperphosphatemia is believed to be a risk factor for mortality and VC, no randomized trial was ever designed to demonstrate that lowering phosphate reduces mortality. Nonetheless, binders have been used extensively, and the preponderance of evidence shows that sevelamer slows the development of VC whereas calcium salts do not. Four studies have demonstrated a slower progression of VC with sevelamer than with calcium-containing binders, although a fifth study showed nonsuperiority. Conversely, the results on mortality with sevelamer have been variable, and data on calcium-based binders are nonexistent. Improved survival with sevelamer was demonstrated in a small randomized clinical trial, whereas a larger randomized trial failed to show a benefit. In addition, preclinical models of renal failure and preliminary clinical data on hemodialysis patients suggest a potential benefit for bone with sevelamer. Meanwhile, several randomized and observational studies suggested no improvement in bone density and fracture rate, and a few noted an increase in total and cardiovascular mortality in the general population given calcium supplements. Although additional studies are needed, there are at least indications that sevelamer may improve vascular and bone health and, perhaps, mortality in hemodialysis patients, whereas data on calcium-based binders are lacking.

Sevelamer and the bone-vascular axis in chronic kidney disease: bone turnover, inflammation, and calcification regulation

Hyperphosphatemia is a central characteristic feature of chronic kidney disease-mineral and bone disorder (CKD-MBD). Phosphorus excess is an independent cardiovascular risk factor for morbidity and mortality in patients with advanced CKD. Over the past 40 years, hyperphosphatemia has been a central therapeutic issue in advanced CKD. Mainstays of hyperphosphatemia treatment are reduction of dietary phosphorus, use of phosphate binders, and optimized phosphorus removal via dialysis. Currently, several phosphate binders are approved for use (aluminum, calcium, lanthanum, sevelamer); all share a common functionality in that they bind phosphorus and reduce the amount absorbed in the gastrointestinal lumen. Over the last decade, nephrologists have debated the relative tolerability and efficacy of these agents, especially the potential for vascular calcification and cardiovascular risk reduction. Recent research has focused on the question of whether a metal-free, calcium-free, and non-absorbed binder, such as sevelamer, offers advantages over other binder types. Most notable may be the potential benefit of reducing calcium load. In addition, sevelamer has several additional pleiotropic effects that may extend its basic indication, some of which may help attenuate vascular calcification. These include effects on bone turnover and the link between abnormal vascular processes and bone metabolism (the so-called 'bone-vascular axis'), as well as lipid metabolism, and systemic inflammatory mediators such as fetuin-A. We review the evidence for these pleiotropic effects, and suggest these may help in some way to improve the substantial disease burden in the CKD-MBD population.

Functional polymers as therapeutic agents: concept to market place

Biologically active synthetic polymers have received considerable scientific interest and attention in recent years for their potential as promising novel therapeutic agents to treat human diseases. Although a significant amount of research has been carried out involving polymer-linked drugs as targeted and sustained release drug delivery systems and prodrugs, examples on bioactive polymers that exhibit intrinsic therapeutic properties are relatively less. Several appealing characteristics of synthetic polymers including high molecular weight, molecular architecture, and controlled polydispersity can all be utilized to discover a new generation of therapies. For example, high molecular weight bioactive polymers can be restricted to gastrointestinal tract, where they can selectively recognize, bind, and remove target disease causing substances from the body. The appealing features of GI tract restriction and stability in biological environment render these polymeric drugs to be devoid of systemic toxicity that are generally associated with small molecule systemic drugs. The present article highlights recent developments in the rational design and synthesis of appropriate functional polymers that have resulted in a number of promising polymer based therapies and biomaterials, including some marketed products.

Epimedium-derived flavonoids promote osteoblastogenesis and suppress adipogenesis in bone marrow stromal cells while exerting an anabolic effect on osteoporotic bone

BACKGROUND

Epimedium-derived flavonoids (EFs) have been reported to prevent bone loss in ovariectomized (OVX) rats and late postmenopausal women but the underlying mechanism of the anabolic effect is unknown.

OBJECTIVE

This study aimed to investigate the effect of EFs on osteoporotic bone using histomorphometry and on osteoblastogenesis/adipogenesis of bone marrow stromal cells (BMSCs).

METHODS

11-month-old female Wistar rats were divided into Sham, OVX, Sham+soluble vehicle (Sham+SV), OVX+SV and OVX+EFs (10 mg/kg/day) groups. 3 months after surgery, rats from the first two groups were euthanized to verify the establishment of OVX-induced osteoporosis. Other groups were orally treated with either daily SV or EFs for 4 months. At sacrifice, serum was analyzed for the levels of osteocalcin and TRACP 5b, BMD in the proximal femur was measured by pQCT. Static and dynamic bone histomorphometry was performed in proximal tibiae with microCT and undecalcified sections, respectively. The effect of EF treatment on differentiation of rat BMSCs was assessed by colony formation assays and gene expression analysis, respectively. Gene expression, ALP activity and adipocyte numbers were determined in differentiating human BMSCs after exposure to conditioned serum from SV- or EFs-treated OVX rats.

RESULTS

The serum level of osteocalcin was higher and TRACP 5b was lower in EFs versus SV-treated OVX rats. BMD, BV/TV, Tb.N and Conn.D in EFs-treated OVX rats were significantly greater than those of SV-treated OVX rats. Bone histomorphometric parameters OS/BS, MAR, and BFR/BS were significantly higher in EFs versus SV-treated OVX rats. EFs significantly increased osteogenesis and decreased adipogenesis of BMSCs, as evidenced by CFU-ALP and CFU-Adipo assays, respectively. The mRNA level of Runx2 and bone sailoprotein was significantly higher while PPARgamma2 was significantly lower in BMSCs from EFs-treated versus SV-treated OVX rats. ALP activity and Runx2 mRNA was significantly higher while adipocyte number and PPARgamma2 mRNA was significantly lower in human BMSCs after exposure to conditioned serum from EFs versus SV-treated OVX rats.

CONCLUSION

EFs exerted anabolic effect on osteoporotic bone by concomitantly promoting osteogenic and suppressing adipogenic differentiation of BMSCs.