Determination of Phytate in Urine by High-Performance Liquid Chromatography?Mass Spectrometry

Hexasodium fytate exposure-response correlations in a randomized, placebo-controlled study of patients on dialysis with cardiovascular calcification

Background: Patients receiving dialysis have high cardiovascular risk in part due to extensive vascular calcification. In the CaLIPSO study, infusion of hexasodium fytate (SNF472), the hexasodium salt of inositol hexaphosphate, for 52 weeks thrice weekly during hemodialysis significantly reduced progression of coronary artery calcification (CAC). This report examines pharmacokinetic/pharmacodynamic (PK/PD) and exposure-efficacy in CaLIPSO. Methods: We measured hexasodium fytate plasma concentrations (PK) by validated liquid chromatography-mass spectroscopy, and hydroxyapatite crystallization in plasma (PD) by validated spectrophotometry. Analyses included patients evaluable for PK, PD, and CAC change (per-protocol analysis). We developed a simple Emax model for maximum concentration (Cmax) and PD effect, and linear and non-linear Emax models for exposure-efficacy among individual average Cmax and absolute and percent changes in CAC score from baseline to week 52. Results: Among evaluable patients receiving placebo (n = 15), 300 mg (n = 20), or 600 mg (n = 20), average Cmax across visits was not quantifiable (<0.76 μM), 15 μM, and 46 μM, respectively. These results suggest a more-than-proportional increase, without accumulation, with a Cmax ratio of approximately 3 for the doses administered. Average inhibition of hydroxyapatite crystallization was 15%, 61%, and 75%, respectively, and similar across visits. Simple Emax models described 80% maximal effect at exposures >21.9 µM and a plateau in exposure-efficacy above the third quartile of Cmax (≥32 µM). Conclusion: Hexasodium fytate has exposure-dependent effects on hydroxyapatite crystallization and progression of cardiovascular calcification. Simple Emax models show robust relations among exposure, inhibition of hydroxyapatite crystallization, and change in CAC volume. Clinical Trial Registration: https://www.clinicaltrials.gov; identifier NCT02966028.

A novel fluorescent nanosensor based on small-sized conjugated polyelectrolyte dots for ultrasensitive detection of phytic acid

A novel nanosensor is developed for selective and highly sensitive detection of phytic acid (PA) based on small-sized conjugated polyelectrolyte dots (Pdots) fabricated from a new conjugated polymer (P1) by a modified reprecipitation method. P1 featuring a π-delocalized backbone bearing meta-substituted pyridyl groups can be endowed with enhanced flexibility and hence is beneficial for the synthesis of ultrasmall Pdots (i.e. Pdot-1, ∼3.8 nm in average diameter) as well as for the binding of Fe³⁺, thus leading to the obvious fluorescence quenching of Pdot-1 (∼444 nm) in the presence of Fe³⁺ via an electron transfer (ET) process. In addition, phytic acid with six phosphate groups exhibits strong chelating ability. When phytic acid is added, phytic acid readily binds to Fe³⁺ and the fluorescence of Pdot-1 around 444 nm can be recovered, rendering the supersensitive and selective sensing of PA. Under the optimum conditions, this ultra-small Pdot-based nanoprobe favors the fluorescent determination of PA with the detection limit as low as 10 nM. Particularly, Pdot-1 with bright blue fluorescence exhibits low cytotoxicity. Furthermore, the small-sized and biocompatible Pdot-1 can be applied to the sensitive fluorescence assay for PA in cell extracts and the efficient imaging of PA in live cells.

Validation of an LC-MS bioanalytical method for quantification of phytate levels in rat, dog and human plasma

Myo-inositol hexakisphosphate (phytate, IP6) is a naturally occuring compound whose determination in biological matrices is chanllenging. Several benefitial properties have been attributed to IP6 in parallel with the development of suitable analytical methodologies for its analytical determination in urine and some tissues. However, there is a lack of appropriate tools for its determination in plasma samples. In this paper, a direct, sensitive and selective bioanalytical method for the determination of IP6 based on LC-MS is presented. It is the first method published to quantify IP6 in plasma matrices directly through its molecular weight, being consequently a highly specific methodology. The method has been validated in rat, dog and human plasma, according to the acceptance criteria laid down in the FDA guidance Bioanalytical Method Validation. Accuracy and precision were not greater than 15% at medium and high concentrations and not greater than 20% at the LLOQ concentration. The mean absolute recovery obtained ranged from 78.74 to 102.44%, 62.10 to 87.21% and 61.61 to 86.99% for rat, dog and human plasma respectively. The LLOQ was 500ngmL(-1) due to the presence of endogenous IP6 in blank plasma samples and the limit of detection was within the range 30-80ngmL(-1).

The kinetic properties of a human PPIP5K reveal that its kinase activities are protected against the consequences of a deteriorating cellular bioenergetic environment

We obtained detailed kinetic characteristics--stoichiometry, reaction rates, substrate affinities and equilibrium conditions--of human PPIP5K2 (diphosphoinositol pentakisphosphate kinase 2). This enzyme synthesizes 'high-energy' PP-InsPs (diphosphoinositol polyphosphates) by metabolizing InsP₆ (inositol hexakisphosphate) and 5-InsP₇ (5-diphosphoinositol 1,2,3,4,6-pentakisphosphate) to 1-InsP₇ (1-diphosphoinositol 2,3,4,5,6-pentakisphosphate) and InsP₈ (1,5-bis-diphosphoinositol 2,3,4,6-tetrakisphosphate), respectively. These data increase our insight into the PPIP5K2 reaction mechanism and clarify the interface between PPIP5K catalytic activities and cellular bioenergetic status. For example, stochiometric analysis uncovered non-productive, substrate-stimulated ATPase activity (thus, approximately 2 and 1.2 ATP molecules are utilized to synthesize each molecule of 1-InsP₇ and InsP₈, respectively). Impaired ATPase activity of a PPIP5K2-K248A mutant increased atomic-level insight into the enzyme's reaction mechanism. We found PPIP5K2 to be fully reversible as an ATP-synthase in vitro, but our new data contradict previous perceptions that significant 'reversibility' occurs in vivo. PPIP5K2 was insensitive to physiological changes in either [AMP] or [ATP]/[ADP] ratios. Those data, together with adenine nucleotide kinetics (ATP Km=20-40 μM), reveal how insulated PPIP5K2 is from cellular bioenergetic challenges. Finally, the specificity constants for PPIP5K2 revise upwards by one-to-two orders of magnitude the inherent catalytic activities of this enzyme, and we show its equilibrium point favours 80-90% depletion of InsP₆/₅-InsP₇.