Effects of EOS789, a novel pan-phosphate transporter inhibitor, on phosphate metabolism : Comparison with a conventional phosphate binder

BACKGROUND

Inorganic phosphate (Pi) binders are the only pharmacologic treatment approved for hyperphosphatemia. However, Pi binders induce the expression of intestinal Pi transporters and have limited effects on the inhibition of Pi transport. EOS789, a novel pan-Pi transporter inhibitor, reportedly has potent efficacy in treating hyperphosphatemia. We investigated the properties of EOS789 with comparison to a conventional Pi binder.

METHODS

Protein and mRNA expression levels of Pi transporters were measured in intestinal and kidney tissues from male Wistar rats fed diets supplemented with EOS789 or lanthanum carbonate (LC). 32Pi permeability was measured in intestinal tissues from normal rats using a chamber.

RESULTS

Increased protein levels of NaPi-2b, an intestinal Pi transporter, and luminal Pi removal were observed in rats treated with LC but not in rats treated with EOS789. EOS789 but not LC suppressed intestinal protein levels of the Pi transporter Pit-1 and sodium/hydrogen exchanger isoform 3. 32Pi flux experiments using small intestine tissues from rats demonstrated that EOS789 may affect transcellular Pi transport in addition to paracellular Pi transport.

CONCLUSION

EOS789 has differing regulatory effects on Pi metabolism compared to LC. The properties of EOS789 may compensate for the limitations of LC therapy. The combined or selective use of EOS789 and conventional Pi binders may allow tighter control of hyperphosphatemia. J. Med. Invest. 70 : 260-270, February, 2023.

EOS789, pan-phosphate transporter inhibitor, ameliorates the progression of kidney injury in anti-GBM-induced glomerulonephritis rats

Hyperphosphatemia associated with chronic kidney disease (CKD) not only dysregulates mineral metabolism and bone diseases, but also strongly contributes to the progression of kidney disease itself. We have identified a novel drug for hyperphosphatemia, EOS789, that interacts with several sodium-dependent phosphate transporters (NaPi-IIb, PiT-1, and PiT-2) known to contribute to intestinal phosphate absorption. In this study, we investigated whether EOS789 could ameliorate kidney disease progression in glomerulonephritis rats. Anti-glomerular basement membrane (GBM) nephritis was induced in rats by intravenously administering two types of anti-rat GBM antibodies. We evaluated the effect of EOS789 administered in food admixture on hyperphosphatemia and kidney disease progression. In an anti-GBM nephritis rats, which exhibit a significant increase in serum phosphate and a decline in renal function, EOS789 dose-dependently improved hyperphosphatemia and EOS789 at 0.3% food admixture significantly ameliorated kidney dysfunction as shown in the decline of serum creatinine and BUN. Renal histopathology analysis showed that EOS789 significantly decreased crescent formation in glomeruli. To elucidate the mechanism underlying glomerular disease progression, human mesangial cells were used. High phosphate concentration in media significantly increased the expression of Collagen 1A1, 3A1, and αSMA mRNA in human mesangial cells and EOS789 dose-dependently suppressed these fibrotic markers. These results indicate that EOS789 prevented glomerular crescent formation caused by mesangial fibrosis by ameliorating hyperphosphatemia. In conclusion, EOS789 would not only be useful against hyperphosphatemia but may also have the potential to relieve mesangial proliferative glomerulonephritis with crescent formation.

Evidence of an intestinal phosphate transporter alternative to type IIb sodium-dependent phosphate transporter in rats with chronic kidney disease

Background

Phosphate is absorbed in the small intestine via passive flow and active transport.NaPi-IIb, a type II sodium-dependent phosphate transporter, is considered to mediate active phosphate transport in rodents. To study the regulation of intestinal phosphate transport in chronic kidney disease (CKD), we analyzed the expression levels of NaPi-IIb, pituitary-specific transcription factor 1 (PiT-1) and PiT-2 and the kinetics of intestinal phosphate transport using two CKD models.

Methods

CKD was induced in rats via adenine orThy1 antibody injection. Phosphate uptake by intestinal brush border membrane vesicles (BBMV) and the messenger RNA (mRNA) expression of NaPi-IIb, PiT-1 and PiT-2 were analyzed. The protein expression level of NaPi-IIb was measured by mass spectrometry (e.g. liquid chromatography tandem mass spectrometry).

Results

In normal rats, phosphate uptake into BBMV consisted of a single saturable component and its Michaelis constant (K_m) was comparable to that of NaPi-IIb. The maximum velocity (V_max) correlated with mRNA and protein levels of NaPi-IIb. In the CKD models, intestinal phosphate uptake consisted of two saturable components. The V_max of the higher-affinity transport, which is thought to be responsible for NaPi-IIb, significantly decreased and the decrease correlated with reduced NaPi-IIb expression. The K_m of the lower-affinity transport was comparable to that of PiT-1 and -2. PiT-1 mRNA expression was much higher than that of PiT-2, suggesting that PiT-1 was mostly responsible for phosphate transport.

Conclusions

This study suggests that the contribution of NaPi-IIb to intestinal phosphate absorption dramatically decreases in rats with CKD and that a low-affinity alternative to NaPi-IIb, in particular PiT-1, is upregulated in a compensatory manner in CKD.

Significant Species Differences in Intestinal Phosphate Absorption between Dogs, Rats, and Monkeys

A treatment for hyperphosphatemia would be expected to reduce mortality rates for CKD and dialysis patients. Although rodent studies have suggested sodium-dependent phosphate transporter type IIb (NaPi-IIb) as a potential target for hyperphosphatemia, NaPi-IIb selective inhibitors failed to achieve efficacy in human clinical trials. In this study, we analyzed phosphate metabolism in rats, dogs, and monkeys to confirm the species differences. Factors related to phosphate metabolism were measured and intestinal phosphate absorption rate was calculated from fecal excretion in each species. Phosphate uptake by intestinal brush border membrane vesicles (BBMV) and the mRNA expression of NaPi-IIb, PiT-1, and PiT-2 were analyzed. In addition, alkaline phosphatase (ALP) activity was evaluated. The intestinal phosphate absorption rate, including phosphate uptake by BBMV and NaPi-IIb expression, was the highest in dogs. Notably, urinary phosphate excretion was the lowest in monkeys, and their intestinal phosphate absorption rate was by far the lowest. Dogs and rats showed positive correlations between V_max/K_m of phosphate uptake in BBMV and NaPi-IIb expression. Although phosphate uptake was observed in the BBMV of monkeys, NaPi-IIb expression was not detected and ALP activity was low. This study revealed significant species differences in intestinal phosphate absorption. NaPi-IIb contributes to intestinal phosphate uptake in rats and dogs. However, in monkeys, phosphate is poorly absorbed due to the slight degradation of organic phosphate in the intestine.

EOS789, a novel pan-phosphate transporter inhibitor, is effective for the treatment of chronic kidney disease-mineral bone disorder

Chronic kidney disease is characterized as impaired renal function along with the imbalance and dysregulation of mineral metabolism; recognized as chronic kidney disease-mineral and bone disorder. Hyperphosphatemia, characterized by altered phosphate homeostasis along with elevated fibroblast growth factor-23 and intact parathyroid hormone, is such an alteration of mineral metabolism. We discovered a novel inhibitor, EOS789, that interacts with several sodium-dependent phosphate transporters (NaPi-IIb, PiT-1, and PiT-2) known to contribute to intestinal phosphate absorption. This inhibitor dose-dependently increased the fecal phosphorus excretion rate and inversely decreased the urinary phosphorus excretion rate in normal rats, suggesting inhibition of intestinal phosphorus absorption. In rats with adenine-induced hyperphosphatemia, EOS789 markedly decreased the serum phosphate, fibroblast growth factor-23, and intact parathyroid hormone below values found in normal control rats. Notably, this pan-phosphate transporter inhibitor exhibited a more potent effect on serum phosphate than a NaPi-IIb-selective inhibitor in rats with hyperphosphatemia indicating that PiT-1 and PiT-2 play important roles in intestinal phosphate absorption. Moreover, in a long-term study, EOS789 sustained the suppression of serum phosphorus in parallel with fibroblast growth factor-23 and intact parathyroid hormone and ameliorated ectopic calcification of the thoracic aorta. Additionally, EOS789 treatment also ameliorated kidney deterioration in rats with progressive kidney injury, probably due to the strict phosphate control. Thus, EOS789 has potent efficacy against hyperphosphatemia and its complications and could provide a significant benefit to patients who are ineffectively treated with phosphate binders.

Effect of Npt2b deletion on intestinal and renal inorganic phosphate (Pi) handling

BACKGROUND

Hyperphosphatemia is common in chronic kidney disease and is associated with morbidity and mortality. The intestinal Na⁺-dependent phosphate transporter Npt2b is thought to be an important molecular target for the prevention of hyperphosphatemia. The role of Npt2b in the net absorption of inorganic phosphate (Pi), however, is controversial.

METHODS

In the present study, we made tamoxifen-inducible Npt2b conditional knockout (CKO) mice to analyze systemic Pi metabolism, including intestinal Pi absorption.

RESULTS

Although the Na⁺-dependent Pi transport in brush-border membrane vesicle uptake levels was significantly decreased in the distal intestine of Npt2b CKO mice compared with control mice, plasma Pi and fecal Pi excretion levels were not significantly different. Data obtained using the intestinal loop technique showed that Pi uptake in Npt2b CKO mice was not affected at a Pi concentration of 4 mM, which is considered the typical luminal Pi concentration after meals in mice. Claudin, which may be involved in paracellular pathways, as well as claudin-2, 12, and 15 protein levels were significantly decreased in the Npt2b CKO mice. Thus, Npt2b deficiency did not affect Pi absorption within the range of Pi concentrations that normally occurs after meals.

CONCLUSION

These findings indicate that abnormal Pi metabolism may also be involved in tight junction molecules such as Cldns that are affected by Npt2b deficiency.

Increased serum resistin levels in patients with type 2 diabetes are not linked with markers of insulin resistance and adiposity

The role of resistin in human biology remains uncertain. We measured serum resistin levels in Japanese patients with (n=111) and without (n=98) type 2 diabetes mellitus and investigated the significance of this hormone in the pathophysiology of diabetes. The levels of serum adiponectin and leptin were also measured. Resistin levels were increased significantly in patients with type 2 diabetes compared with non-diabetic subjects (24.7+/-2.6 vs. 15.0+/-1.2 ng/ml, p=0.0013). However, there was no correlation in either patient group between serum resistin levels and markers of insulin resistance, obesity or hyperlipidaemia. These results were in direct contrast to the data of leptin or adiponectin, both of which were closely related to these clinical markers of diabetes. Multivariate regression analysis on the combined data of the two groups demonstrated that the presence of diabetes and HDL cholesterol levels were significant predictors of serum resistin levels (diabetes: beta=0.159, p=0.035; HDL: beta=-0.172, p=0.039). No correlation was observed between C-reactive protein and resistin adjusted for BMI. Taken together, these findings demonstrate that serum resistin levels are increased in patients with type 2 diabetes, but this increase is not linked to markers of insulin resistance or adiposity. Further studies are necessary to elucidate the significance of serum resistin concentration in human pathophysiology.

Sign and speech: amodal commonality in left hemisphere dominance for comprehension of sentences

The neural basis of functional lateralization in language processing is a fundamental issue in systems neuroscience. We used functional MRI (fMRI) to examine hemispheric dominance during the processing of signed and spoken sentences. By using tasks involving comprehension of sentences (Sc) and sentential non-word detection (Sn), we compared different groups and stimulus conditions. Under the sign condition with sentence stimuli in Japanese Sign Language (JSL), we tested two groups of subjects: Deaf signers (Deaf) of JSL, and hearing bilinguals (children of Deaf adults, CODA) of JSL and Japanese (JPN). Under the speech condition, we tested hearing monolinguals (Mono) of JPN with auditory JPN stimuli alone (AUD), or with an audiovisual presentation of JPN and JSL stimuli (A&V). We found that the overall bilateral activation patterns under the four experimental conditions of Deaf, CODA, AUD and A&V were almost identical, despite differences in stimuli (JSL and JPN) and groups (Deaf, CODA and Mono). Moreover, consistently left-dominant activations involving frontal and temporo-parietal regions were observed across all four conditions. Furthermore, irrespective of the modalities of sign and speech, the main effects of task (Sc-Sn) were found primarily in the left regions: the ventral part of the inferior frontal gyrus (F3t/F3O), the precentral sulcus, the superior frontal gyrus, the middle temporal gyrus, the angular gyrus and the inferior parietal gyrus. Among these regions, only the left F3t/F3O showed no main effects of modality condition. These results demonstrate amodal commonality in the functional dominance of the left cortical regions for comprehension of sentences, as well as the essential and universal role of the left F3t/F3O in processing linguistic information from both signed and spoken sentences.

[Use of normal human hepatocytes in a hybrid organ system]

Using the bioreactor model developed by J. Gerlach, we examined the potential of normal human hepatocytes for application in bioartificial liver devices. From normal human donor livers 1.5 x 10(8) hepatocytes were isolated. Hepatocytes were perfused in a woven multi-compartment capillary system in serum-free culture medium containing ammoniachloride over a period of 2 weeks. These cells demonstrated a well differentiated ultrastructure with formation of junctional complexes and bile canaliculi between adjacent cells. During reactor run, a constant albumin synthesis with levels above 11 mg/ml and maintenance of urea production and lignocaine metabolism (MEGX-test) were detected. These initial results indicate that normal human hepatocytes express typical morphology and ultrastructure and are able to keep differentiated functions in suitable perfusion models. Combination of the distinct human liver cell populations might enable promotion of further specific functions (clotting factors) and induction of liver cell proliferation.