Comparison of Phosphate Binding Capacities of PA21, A Novel Phosphate Binder, with those of other Phosphate Binders in vitro and in vivo

The hollow core-shell ferric oxide entrapped chitosan microcapsules as phosphate binders for phosphorus removal in vitro

Patients in hyperphosphatemia are orally prescribed with phosphate binders to excrete the non-metabolic phosphorus. Aiming for the bio-compatibility and binding efficacy, the Fe-based phosphate binders of low toxicity have been explored and improved. Herein, the hollow core-shell microcapsules as Fe@CH (nano ferric oxide entrapped in the polymerized chitosan) were constructed via emulsion interface polymerization, to enhance the phosphate binding from -NH₂ group and iron complex, and limit iron leakage significantly. Via the double emulsion polymerization based on the primary Pickering emulsion stabilized by oleic acid-modified ferric oxide, Fe@CH performed as the rough polymerized-chitosan microcapsules entrapping well-distributed ferric oxide for the phosphate adsorption in vitro. At pH 3 and pH 5, Fe@CH bound phosphorus efficiently, with the capacity of 55 mg/g and 65 mg/g respectively, along with the excellent shell isolation from iron leakage and remarkable safety. Prospectively, the Fe@CH micro-sorbent is the proper candidate as the phosphate binder for hyperphosphatemia.

Great enhancement in phosphate uptake onto lanthanum carbonate grafted microfibrous composite under a low-voltage electrostatic field

Removal of phosphorus from water via cost-effective measures becomes important for water industry mainly due to eutrophication in waterbody. In our lab, a novel lanthanum carbonate-microfibrous composite (LC-MC) with good performance was previously synthesized for the removal of phosphorus. In this study, we further improved our technology by applying the electrostatic field (direct current, DC) to the adsorption system. It was showed that the applied DC can greatly improve the adsorption of phosphate in particular the adsorption capacity. Better removal was seen in the pH range of 5-9 at a higher temperature. The maximum adsorption capacity of 47.57 mg-PO₄^3- g^-1 was achieved, which was 1.4 times of that operated in the absence of applied DC. The adsorption equilibrium was established at the contact time of 240 min; the adsorption history was well described by the intraparticle surface diffusion model. The negative effect from oxygen-containing anions on the phosphate uptake followed the decreasing sequence of: humic acid > carbonate > nitrate > sulfate; on the other hand, the halogen anions had almost no influence on it. Finally, the mechanism study by XPS, XRD, and IR demonstrated that the ligand exchange played an important role in the electro-assisted phosphate uptake process.

Phosphate Binders and Nonphosphate Effects in the Gastrointestinal Tract

Phosphate binders are commonly prescribed in patients with end-stage kidney disease to prevent and treat hyperphosphatemia. These binders are usually associated with gastrointestinal distress, may bind molecules other than phosphate, and may alter the gut microbiota, altogether having systemic effects unrelated to phosphate control. Sevelamer is the most studied of the available binders for nonphosphate-related effects including binding to bile acids, endotoxins, gut microbiota-derived metabolites, and advanced glycation end products. Other binders (calcium- and noncalcium-based binders) may bind vitamins, such as vitamin K and folic acid. Moreover, the relatively new iron-based phosphate binders may alter the gut microbiota, as some of the iron or organic ligands may be used by the gastrointestinal bacteria. The objective of this narrative review is to provide the current evidence for the nonphosphate effects of phosphate binders on gastrointestinal function, nutrient and molecule binding, and the gut microbiome.

A comparison between the combined effect of calcium carbonate with sucroferric oxyhydroxide and other phosphate binders: an in vitro and in vivo experimental study

Background

Approximately 30% of patients on dialysis received combination therapy for their phosphate binder prescription; however, few studies for combined effects of phosphate binders are reported. For the purpose of evaluating the efficacy of combination therapy, we compared the efficacy of sucroferric oxyhydroxide (PA21) combined with calcium carbonate with that of lanthanum carbonate hydrate, sevelamer hydrochloride, and ferric citrate hydrate combined with calcium carbonate.

Methods

For in vitro studies, calcium carbonate and the other phosphate binders alone or in combination were stirred in phosphate solution at pH 2–8 for 2 h. After centrifuging the suspension, the phosphorus level in the supernatant was determined. For in vivo studies, rats were orally administered calcium carbonate and the other phosphate binders (except for sevelamer hydrochloride) alone or in combination, followed by oral administration of phosphate solution adjusted to pH 2 or 7. Serum samples were collected from the rats at predetermined timepoints and the serum phosphorus levels were determined and analyzed using a two-way analysis of variance.

Results

In the in vitro study, the measured phosphate-binding capacity of combining sevelamer hydrochloride, PA21, and lanthanum carbonate hydrate with calcium carbonate was approximately equal to or greater than the theoretical values under most conditions. Furthermore, these combined effects were insensitive to pH in that order. The measured phosphate-binding capacity of ferric citrate hydrate combined with calcium carbonate was smaller than the theoretical values, and the combination did not exhibit efficacy under any of the tested conditions. In the in vivo study, the combined effect of PA21 and calcium carbonate at both pH values and that of lanthanum carbonate hydrate and calcium carbonate at pH 2 were additive. In contrast, the combined effect of lanthanum carbonate hydrate and calcium carbonate at pH 7 and that of ferric citrate hydrate and calcium carbonate at pH 2 were antagonistic.

Conclusions

These results suggest that coadministration of PA21 and calcium carbonate showed good and relatively stable efficacy throughout the range of the gastrointestinal pH and that combining lanthanum carbonate hydrate and ferric citrate hydrate with calcium carbonate may not produce the expected efficacy under certain conditions.

[Pharmacological, pharmaceutical and clinical profiles of sucroferric oxyhydroxide (P-TOL® Chewable Tab. 250 mg, 500 mg), a therapeutic agent for hyperphosphatemia]

Sucroferric oxyhydroxide (P-TOL^® chewable tablets, 250 and 500 mg) is a phosphate binder for oral use; it is composed of polynuclear iron (III)-oxyhydroxide, sucrose, and starches, and is currently indicated for alleviating hyperphosphatemia in patients with chronic kidney disease (CKD) on dialysis. The results of non-clinical pharmacological studies have suggested that P-TOL consistently decreases serum phosphorus levels in the aqueous environment at pH levels similar to those in the gastrointestinal tract, thereby suppressing the progression of secondary hyperparathyroidism, aberrant calcification, and abnormal bone metabolism associated with hyperphosphatemia. Since the diameter of the P-TOL tablet exceeds 15 mm, it is manufactured with a doughnut-shape to minimize choking hazards. From the results of pharmaceutical studies, it was indicated that the P-TOL tablets promptly disintegrated in the gastrointestinal tract and excessive iron uptake from this product is unlikely to occur. In clinical studies, P-TOL (one tablet/dose, t.i.d.) decreased serum phosphorus levels during treatment Week 1 and allowed stable, long-term control of serum phosphorus levels. Furthermore, P-TOL was expected to reduce the tablet burden on patients and to improve medication adherence. The most common adverse reaction was diarrhea. However, in most cases, the symptoms were mild and oral administration of P-TOL could be continued. Although iron-related parameters tended to increase, iron uptake from this product was low, and the risk of iron overload was considered to be low. These findings confirm the efficacy and safety of P-TOL in CKD patients with hyperphosphatemia. Therefore, sucroferric oxyhydroxide therapy is a potentially useful treatment option for hyperphosphatemia.

Pharmacotherapy in chronic kidney disease hyperphosphatemia – effects on vascular calcification and bone health

Hyperphosphatemia (HP) in patients with chronic kidney disease (CKD) leads to complications such as renal osteodistrophy, cardiovascular calcification and hemodynamic abnormalities, all of them having a serious impact on the survival rate and quality of life. Also, HP is a key pathogenic factor in the development of secondary hyperparathyroidism (SHPT) in CKD. Having in regard the significance of controlling serum phosphorus levels (Pi), in this paper, the needs and obstacles to successful pharmacological management of HP in CKD are presented, with an overview of major classes of phosphate binders (PBs) and other drugs affecting Pi level, such as active vitamin D sterols and calcimimetics (CMs). In addition, their effects on progression of cardiovascular calcification and bone health are elaborated. In this regard, a PubMed search was carried out to capture all abstracts and articles relevant to the topic of CKD, HP and mineral metabolism, bone disorders and vascular/valvular calcification (VC), published from January 2007 to August 2017. The search was limited to English language, with the search terms including drug name AND hyperphosphatemia or cardiovascular calcification or bone disorder. Comparative studies, clinical studies/trials and meta-analyses related to different classes/representatives of PBs, vitamin D analogues and CMs were reviewed and research data related to their efficacy and safety compared. Keywords: chronic kidney disease, hyperphosphatemia, phosphate binders, active vitamin D sterols, calcimimetics, bone disorders, cardiovascular calcification

Chitosan-Fe (III) Complex as a Phosphate Chelator in Uraemic Rats: A Novel Treatment Option

Phosphate retention and hyperphosphataemia are associated with increased mortality in patients with chronic kidney disease (CKD). We tested the use of cross-linked iron chitosan III (CH-FeCl) as a potential phosphate chelator in rats with CKD. We evaluated 96 animals, divided equally into four groups (control, CKD, CH-FeCl and CKD/CH-FeCl), over 7 weeks. We induced CKD by feeding animals an adenine-enriched diet (0.75% in the first 4 weeks and 0.1% in the following 3 weeks). We administered 30 mg/kg daily of the test polymer, by gavage, from the third week until the end of the study. All animals received a diet supplemented with 1% phosphorus. Uraemia was confirmed by the increase in serum creatinine in week 4 (36.24 ± 18.56 versus 144.98 ± 22.1 μmol/L; p = 0.0001) and week 7 (41.55 ± 22.1 versus 83.98 ± 18.56 μmol/L; p = 0.001) in CKD animals. Rats from the CKD group treated with CH-FeCl had a 54.5% reduction in serum phosphate (6.10 ± 2.23 versus 2.78 ± 0.55 mmol/L) compared to a reduction of 25.6% in the untreated CKD group (4.75 ± 1.45 versus 3.52 ± 0.74 mmol/L, p = 0.021), between week 4 and week 7. At week 7, renal function in both CKD groups was similar (serum creatinine: 83.98 ± 18.56 versus 83.10 ± 23.87 μmol/L, p = 0.888); however, the CH-FeCl-treated rats had a reduction in phosphate overload measured by fractional phosphate excretion (FEPi) (0.71 ± 0.2 versus 0.4 ± 0.16, p = 0.006) compared to the untreated CKD group. Our study demonstrated that CH-FeCl had an efficient chelating action on phosphate.