A potentiometric titration study of the interaction of heparin with metal cations.
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ABSTRACT:
SUBMITTER: Grant D
PROVIDER: S-EPMC1132812 | biostudies-other | 1992 Jul
REPOSITORIES: biostudies-other
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Project description:Measurement of the decrease in pH that accompanies the addition of Zn2+ to heparin in solution provided an indirect method of examining cation-polyanion interaction. Construction of plots analogous to isothermal saturation binding plots revealed the existence, for defined conditions of interaction, of a [heparin]-independent direct proportionality between the fraction of the maximal pH change occurring and the [Zn2+]/[heparin disaccharide] ratio. This accords with results from polarimetric examination of Ca(2+)- and Cu(2+)-heparin interactions. It suggests that, under the conditions used, cation-heparin interaction may result in the formation of a complex that exists in a colloid-like phase, between which and the aqueous phase, exchange of cations does not follow simple solution-phase reversible equilibrium thermodynamic behaviour. The results suggest that the putative Zn(2+)-containing complex is less stable in the presence of NaCl than is the corresponding Ca(2+)-containing complex. Addition of Zn2+ to low concentrations of heparins is accompanied by the usual decrease in pH, followed by a removal of H+ from solution as the [Zn2+]/[heparin disaccharide] ratio increases, suggesting dissolution of the putative complex. This reversal of the initial pH change was not seen for most other cation-heparin interactions under the conditions studied.
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Project description:BackgroundBleeding complications are common in cardiac surgery. Perioperative handling of heparin and protamine may influence the haemostasis. We hypothesized that heparin and protamine dosing based on individual titration curves would improve haemostasis in comparison to standard dosing.Subjects and methodsSixty patients scheduled for first time elective coronary artery bypass grafting or valve surgery were included in a prospective randomized study. The patients were randomized to heparin and protamine dosing with Hepcon HMS Plus device or to standard weight and activated clotting time (ACT) based dosing. Blood samples were collected before and 10 minutes, 2 hours and 4 hours after cardiopulmonary bypass. Primary endpoint was endogenous thrombin potential in plasma 2 hours after surgery as assessed by calibrated automated thrombography. Secondary endpoints included total heparin and protamine doses, whole blood clot formation (thromboelastometry) and post-operative bleeding volume and transfusions. Heparin effect was assessed by measuring anti-Xa activity.ResultsEndogenous thrombin potential and clot formation deteriorated in both groups after surgery without statistically significant intergroup difference. There were no significant differences between the groups in total heparin and protamine doses, heparin effect, or postoperative bleeding and transfusions at any time point. Significant inverse correlations between anti-Xa activity and endogenous thrombin potential were observed 10 min (r = -0.43, p = 0.001), 2 hours (r = -0.66, p<0.001) and 4 hours after surgery (r = -0.58, p<0.001).ConclusionIn conclusion, the results suggest that perioperative heparin and protamine dosing based on individual titration curves does not improve haemostasis after cardiac surgery. Postoperative thrombin generation capacity correlates to residual heparin effect.Trial registrationwww.isrctn.com ISRCTN14201041.
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Project description:A very simple and inexpensive method to detect oversulfated chondroitin sulfate (OSCS) or other high-charge density polyanionic structures as contaminants in heparin products using potentiometric polyanion sensors is described. In the potentiometric measurement, a greater change in the phase boundary equilibrium potential of polymeric membranes formulated with tridodecylmethylammonium (TDMA) anion exchange sites is observed for the contaminated heparin than for the untainted heparin due to the higher charge density of OSCS or other impurities compared to that of porcine heparin. Detection of 0.5 wt % OSCS impurity is readily achieved using only 1 mg/mL of final polyion concentration. Even lower detection limits for OSCS contamination may be possible if higher final concentrations of heparin preparations can be employed in the test procedure.
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Project description:The goal of this study was to determine the effects of commonly used nuclease treatments and their divalent metal cation cofactors on Pol I occupancy during NET-seq. Other groups have previously used micrococcal nuclease (MNase) + CaCl2 and deoxyribonuclease I (DNase I) + MnCl2 in NET-seq protocols probing for Pol II occupancy. However, the effect of these treatments on polymerase occupancy has not been fully explored. Therefore, we tested the impact of these treatments (CaCl2, CaCl2 + MNase, MnCl2, and MnCl2 + DNase I) on Pol I occupancy in vivo. We found that the exposure of Pol I to either CaCl2 or MnCl2 caused a significant reduction in occupancy on the rDNA template. Nuclease treatment (with either MNase or DNase I) did not cause an additional significant effect on Pol I occupancy in vivo beyond that of either CaCl2 or MnCl2. Finally, we found that MnCl2 treatment caused a more significant reduction in Pol I occupancy as compared to CaCl2, suggesting that perhaps MnCl2 stimulates the intrinsic cleavage activity of Pol I more robustly vs. CaCl2 in vivo. Altogether, these findings indicate that the inclusion of these treatments (especially that of divalent metal cations) in NET-seq protocols for Pol I cause a significant change in the polymerase occupancy.
2022-10-27 | GSE216460 | GEO
Project description:Quantification of oversulfated chondroitin sulfate (OSCS) in biomedical heparin preparations is achieved using a recently described potentiometric polyanion sensor-based approach operated in a kinetic mode of analysis. This is accomplished by adjusting the concentration of the test sample to a range where the OSCS level is low enough for the sensor not to achieve a full and rapid equilibrium phase boundary potential change at the membrane/sample interface upon exposure to the heparin sample. Using this method, the OSCS wt% determined within heparin samples containing OSCS are shown to be in good agreement with those determined by an accepted NMR method.
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Project description:The study aims to develop simple, sensitive, and selective methods for detecting methylphenidate in its bulk, dosage form and human urine. Sensing materials include β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), and 4-tertbutylcalix[8]arene as ionophores or electroactive materials have been used for construction of sensors 1, 2, and 3, respectively; Potassium tetrakis (4-chlorophenyl)borate (KTpClPB) as an ion additive was used and dioctyl phthalate as a plasticizer. The sensors displayed a fast, stable response over a wide concentration range of methylphenidate (8 × 10-6 M to 1 × 10-3 M) with 10-6 M detection limit over the pH range of 4-8. The developed sensors displayed a Near-Nernstian cationic response for methylphenidate at 59.5, 51.37, and 56.5 mV/decade for sensors β-CD, γ-CD, or 4-tertbutylcalix[8]arene respectively. Validation of the proposed sensors is supported by high accuracy, precision, stability, fast response, and long lifetimes, as well as selectivity for methylphenidate in the presence of different species. Sensitive and practical sensors for the determination of methylphenidate in bulk, in pharmaceutical forms and urine were developed and validated for routine laboratory use. The results were comparable to those obtained by HPLC method.
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Project description:This review is focused on the structural and physicochemical aspects of metal cation coordination to G-Quadruplexes (GQ) and their effects on GQ stability and conformation. G-quadruplex structures are non-canonical secondary structures formed by both DNA and RNA. G-quadruplexes regulate a wide range of important biochemical processes. Besides the sequence requirements, the coordination of monovalent cations in the GQ is essential for its formation and determines the stability and polymorphism of GQ structures. The nature, location, and dynamics of the cation coordination and their impact on the overall GQ stability are dependent on several factors such as the ionic radii, hydration energy, and the bonding strength to the O6 of guanines. The intracellular monovalent cation concentration and the localized ion concentrations determine the formation of GQs and can potentially dictate their regulatory roles. A wide range of biochemical and biophysical studies on an array of GQ enabling sequences have generated at a minimum the knowledge base that allows us to often predict the stability of GQs in the presence of the physiologically relevant metal ions, however, prediction of conformation of such GQs is still out of the realm.
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Project description:Tau aggregates into paired helical filaments within neurons, a pathological hallmark of Alzheimer's disease. Heparin promotes tau aggregation and recently has been shown to be involved in the cellular uptake of tau aggregates. Although the tau-heparin interaction has been extensively studied, little is known about the glycan determinants of this interaction. Here, we used surface plasmon resonance (SPR) and NMR spectroscopy to characterize the interaction between two tau fragments, K18 and K19, and several polysaccharides, including heparin, heparin oligosaccharides, chemically modified heparin, and related glycans. Using a heparin-immobilized chip, SPR revealed that tau K18 and K19 bind heparin with a KD of 0.2 and 70 μM, respectively. In SPR competition experiments, N-desulfation and 2-O-desulfation had no effect on heparin binding to K18, whereas 6-O-desulfation severely reduced binding, suggesting a critical role for 6-O-sulfation in the tau-heparin interaction. The tau-heparin interaction became stronger with longer-chain heparin oligosaccharides. As expected for an electrostatics-driven interaction, a moderate amount of salt (0.3 M NaCl) abolished binding. NMR showed the largest chemical-shift perturbation (CSP) in R2 in tau K18, which was absent in K19, revealing differential binding sites in K18 and K19 to heparin. Dermatan sulfate binding produced minimal CSP, whereas dermatan disulfate, with the additional 6-O-sulfo group, induced much larger CSP. 2-O-desulfated heparin induced much larger CSP in K18 than 6-O-desulfated heparin. Our data demonstrate a crucial role for the 6-O-sulfo group in the tau-heparin interaction, which to our knowledge has not been reported before.
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