Investigation of high-throughput ultrafiltration for the determination of an unbound compound in human plasma using liquid chromatography and tandem mass spectrometry with electrospray ionization

A developed and validated centrifugal ultrafiltration coupled with high performance liquid chromatography-tandem mass spectrometry method for rapid quantification of unbound lenvatinib in human plasma

In clinical practice, the determination of unbound drug concentration is very important for dose adjustment and toxicity prediction because only the unbound fraction can achieve a pharmacological effect. A fast, sensitive and accurate analytical method of centrifugal ultrafiltration coupled with high performance liquid chromatography-tandem mass spectrometry method was developed and applied to allow the quantification of unbound lenvatinib concentration. The application of linear regression analysis was used to examine the effects of centrifugal force, centrifugal time, and protein content on ultrafiltrate volume (Vu). The results indicated that the centrifugal force and centrifugal time have an influence on Vu that is significantly positive (P < 0.05). This developed method with good linearity (r2 = 0.9996), good accuracy (bias % ≤ 2.24 %), good precision (CV % ≤ 7.10 %), and good recovery (95.46 %-106.46 %) was suitable for routine clinical practice and studies. Particularly, the ultrafiltration membrane had no non-specific binding to lenvatinib. The unbound fractions can be separated in just 15 min. This method was applied to quantify clinical samples and to determine the plasma protein binding and unbound fraction of lenvatinib. This study provides a more effective and promising method for determination of unbound lenvatinib. It could be beneficial to measure the unbound concentration of lenvatinib in personalized medicine and therapeutic drug monitoring in routine clinical practice.

A more accurate indicator to evaluate oxidative stress in rat plasma with osteoporosis

Background: oxidative stress is linked to various human diseases which developed into the idea of "disrupted redox signaling". Osteoporosis (OP) is a chronic skeletal disorder characterized by low bone mineral density and deterioration of bone microarchitecture among which estrogen deficiency is the main cause. Lack of estrogen leads to the imbalance between oxidation and anti-oxidation in patients, and oxidative stress is an important link in the pathogenesis of OP. The ratio of the reduced to the oxidized thiols can characterize the redox status. However, few methods have been reported for the simultaneous determination of reduced forms and their oxidized forms of thiols in plasma. Methods: we developed a hollow fiber centrifugal ultrafiltration (HFCF-UF) method for sample preparation and validated a high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method to determine two reduced forms of thiols-homocysteine (Hcy), cysteine (Cys) levels and their respective oxidized compounds, homocystine (HHcy) and cystine (Cyss) in rat plasma simultaneously for the first time. Thirty-six female rats were randomly divided into three groups: normal control (NC), oxidative stress (ovariectomy, OVX) and ovariectomy with hydrogen-rich saline administration (OVX + HRS). Results: the validation parameters for the methodological results were within the acceptance criteria. There were both significant differences of Hcy/HHcy (Hcy reduced/oxidized) and Cys/Cyss (Cys reduced/oxidized) in rat plasma between three groups with both p < 0.05 and meanwhile, the p values of malondialdehyde, superoxide dismutase and glutathione peroxidase were all less than 0.01. The value of both Hcy/HHcy and Cys/Cyss were significantly decreased with the change of Micro-CT scan result of femoral neck in OVX group (both the trabecular thickness and trabecular number significantly decreased with a significant increase of trabecular separation) which demonstrate OP occurs. The change of Hcy/HHcy is more obvious and prominent than Cys/Cyss. Conclusions: the Hcy/HHcy and Cys/Cyss could be suitable biomarkers for oxidative stress and especially Hcy/HHcy is more sensitive. The developed method is simple and accurate. It can be easily applied in clinical research to further evaluate the oxidative stress indicator for disease risk factors.

Analysis of free concentrations of lamotrigine and active oxcarbazepine metabolite in clinical patients by hollow-fiber centrifugal ultrafiltration

Aim: To establish a simple and accurate method to explore the correlation between free and total concentrations of lamotrigine (LTG) and the active oxcarbazepine metabolite monohydroxy derivative (MHD) (10,11-dihydro-10-hydroxycarbamazepine) in clinical patients. Materials & methods: Serum samples were prepared by hollow-fiber centrifugal ultrafiltration and then injected into UPLC for analysis. Results: Absolute recovery was as high as approximately 90.1-98.6% with excellent precision (relative standard deviation <6.7%). Analysis time was reduced to 5 min. There were significant individual differences in the protein binding rates of both LTG and MHD that were probably due to the use of different clinical patients. Conclusion: Free concentrations of LTG and MHD cannot be estimated by total concentration in specific clinical patients. Free drug monitoring of LTG and MHD in clinical therapeutic drug monitoring is important and essential.

Relationship Between the Free and Total Methotrexate Plasma Concentration in Children and Application to Predict the Toxicity of HD-MTX

High-dose methotrexate (HD-MTX) can be highly effective as well as extremely toxic. Many drug molecules can bind to plasma proteins to different extents in vivo, whereas only the free drug can reach the site of action to exert a pharmacological effect and cause toxicity. However, free MTX concentrations in plasma have not been reported. Traditional analyses of free drugs are both cumbersome and inaccurate. We collected 92 plasma samples from 52 children diagnosed with ALL or NHL or other lymphomas that were treated with HD-MTX. The hollow fiber centrifugal ultrafiltration (HFCF-UF) was used to prepare plasma samples for analysis of the free MTX concentration. Protein precipitation was employed to measure the total MTX concentration. The HFCF-UF is a simple method involving a step of ordinary centrifugation; the validation parameters for the methodological results were satisfactory and fell within the acceptance criteria. A linearity coefficient r² of 0.910 was obtained for the correlation between the free and total MTX plasma concentrations in 92 plasma samples. However, the free and total MTX concentrations was only weakly correlated in 16 clinical plasma specimens with total MTX concentrations >2 μmol L⁻¹ (r² = 0.760). Both the free and total MTX concentrations at 42 h were negatively correlated with the creatinine clearance (CCr) level (P = 0.023, r = −0.236 for total MTX and P = 0.020, r = −0.241for free MTX, respectively). The free MTX concentration could not be accurately estimated from the total MTX concentration for patients with high MTX levels which are conditions under which toxic reactions are more likely to occur. High plasma MTX levels could become a predictor of the occurrence of MTX nephrotoxicity to draw people's attention. The proposed HFCF-UF method is a simple and accurate way to evaluate efficacy and toxicity in clinical therapeutic drug monitoring.

In vitro metabolism, reaction phenotyping, enzyme kinetics, CYP inhibition and induction potential of ataluren

Ataluren promotes ribosomal readthrough of premature termination codons in mRNA which result from nonsense mutations. In vitro studies were performed to characterize the metabolism and enzyme kinetics of ataluren and its interaction potential with CYP enzymes. Incubation of [¹⁴C]‐ataluren with human liver microsomes indicated that the major metabolic pathway for ataluren is via direct glucuronidation and that the drug is not metabolized via cytochrome P450 (CYP). Glucuronidation was also observed in the incubation in human intestinal and kidney microsomes, but not in human pulmonary microsomes. UGT1A9 was found to be the major uridine diphosphate glucuronosyltransferase (UGT) responsible for ataluren glucuronidation in the liver and kidney microsomes. Enzyme kinetic analysis of the formation of ataluren acyl glucuronide, performed in human liver, kidney, and intestinal microsomes and recombinant human UGT1A9, found that increasing bovine serum albumin (BSA) levels enhanced the glucuronidation Michaelis‐Menten constant (K_m) and ataluren protein binding but had a minimal effect on maximum velocity (V_max) of glucuronidation. Due to the decreased unbound Michaelis‐Menten constant (K_m,u), the ataluren unbound intrinsic clearance (CL_int,u) increased for all experimental systems and BSA concentrations. Human kidney microsomes were about 3.7‐fold more active than human liver microsomes, in terms of CL_int,u/mg protein, indicating that the kidney is also a key organ for the metabolism and disposition of ataluren in humans. Ataluren showed no or little potential to inhibit or induce most of the CYP enzymes.

Ultrafiltration Method for Plasma Protein Binding Studies and Its Limitations

Plasma protein binding plays a critical role in drug therapy, being a key part in the characterization of any compound. Among other methods, this process is largely studied by ultrafiltration based on its advantages. However, the method also has some limitations that could negatively influence the experimental results. The aim of this study was to underline key aspects regarding the limitations of the ultrafiltration method, and the potential ways to overcome them. The main limitations are given by the non-specific binding of the substances, the effect of the volume ratio obtained, and the need of a rigorous control of the experimental conditions, especially pH and temperature. This review presents a variety of methods that can hypothetically reduce the limitations, and concludes that ultrafiltration remains a reliable method for the study of protein binding. However, the methodology of the study should be carefully chosen.

Practical approaches to evaluating and optimizing brain exposure in early drug discovery

Developing drugs for CNS related diseases continues to be one of the most challenging endeavors in drug discovery. This is at least in part related to the existence of the Blood Brain Barrier (BBB), a complex multicellular organization that provides selective access to required nutrients and hormones, while removing waste and restricting exposure to potential harmful toxins, pathogens, and xenobiotics. Consequently, designing and selecting molecules that can overcame this protection system are unique and critical aspects of the CNS drug discovery. Here we review modern CNS pharmacokinetic concepts and methods suitable for early drug discovery, and medicinal chemistry strategies towards molecules with optimal CNS exposure.

Liquid chromatography-tandem mass spectrometry for the simultaneous quantitation of ceftriaxone, metronidazole and hydroxymetronidazole in plasma from seriously ill, severely malnourished children

We have developed and validated a novel, sensitive, selective and reproducible reversed-phase high-performance liquid chromatography method coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS/MS) for the simultaneous quantitation of ceftriaxone (CEF), metronidazole (MET) and hydroxymetronidazole (MET-OH) from only 50 µL of human plasma, and unbound CEF from 25 µL plasma ultra-filtrate to evaluate the effect of protein binding. Cefuroxime axetil (CEFU) was used as an internal standard (IS). The analytes were extracted by a protein precipitation procedure with acetonitrile and separated on a reversed-phase Polaris 5 C18-Analytical column using a mobile phase composed of acetonitrile containing 0.1% (v/v) formic acid and 10 mM aqueous ammonium formate pH 2.5, delivered at a flow-rate of 300 µL/min. Multiple reaction monitoring was performed in the positive ion mode using the transitions m/z555.1→ m/z396.0 (CEF), m/z172.2→ m/z 128.2 (MET), m/z188.0→ m/z125.9 (MET-OH) and m/z528.1→ m/z 364.0 (CEFU) to quantify the drugs. Calibration curves in spiked plasma and ultra-filtrate were linear ( r ² ≥ 0.9948) from 0.4-300 µg/mL for CEF, 0.05-50 µg/mL for MET and 0.02 - 30 µg/mL for MET-OH. The intra- and inter- assay precisions were less than 9% and the mean extraction recoveries were 94.0% (CEF), 98.2% (MET), 99.6% (MET-OH) and 104.6% (CEF in ultra-filtrate); the recoveries for the IS were 93.8% (in plasma) and 97.6% (in ultra-filtrate). The validated method was successfully applied to a pharmacokinetic study of CEF, MET and MET-OH in hospitalized children with complicated severe acute malnutrition following an oral administration of MET and intravenous administration of CEF over the course of 72 hours.

Determination of total and unbound docetaxel in plasma by ultrafiltration and UPLC-MS/MS: application to pharmacokinetic studies

A sensitive and specific liquid chromatographic/tandem mass spectrometric (LC-MS/MS) method was developed and validated for quantifying total and unbound docetaxel drug concentrations in plasma. Calibration curves for unbound and total docetaxel were linear over the respective ranges of 0.108~10.8 and 0.54~216 ng/mL. The intra- and interday assay accuracy and precision did not exceed 15%. The methods were validated to show the standard range linearity, sensitivity, selectivity, accuracy, precision, and stability of docetaxel in the matrices tested. In addition, this method is fast and simple with a short run time of 4.5 min and a small plasma sample volume (500 µL). The validated method was successfully applied to a pharmacokinetic study of a docetaxel micelle formulation in rat plasma after intravenous administration at a dose of 10 mg/kg. Docetaxel micelles slowly released their drug payload, and protein-bound, unbound, and micellar drug pools existed simultaneously. These various forms in plasma pools were also measured in the study. We confirmed that most of the docetaxel in plasma was micelle-associated (96.52% at 24 h and 83.14% at 72 h) after micellar docetaxel administration, as a result of sequestration of the drug in long-circulating micelles.

Liquid chromatography-tandem mass spectrometry for the simultaneous quantitation of ceftriaxone, metronidazole and hydroxymetronidazole in plasma from seriously ill, severely malnourished children

We have developed and validated a novel, sensitive, selective and reproducible reversed-phase high-performance liquid chromatography method coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS/MS) for the simultaneous quantitation of ceftriaxone (CEF), metronidazole (MET) and hydroxymetronidazole (MET-OH) from only 50 µL of human plasma, and unbound CEF from 25 µL plasma ultra-filtrate to evaluate the effect of protein binding. Cefuroxime axetil (CEFU) was used as an internal standard (IS). The analytes were extracted by a protein precipitation procedure with acetonitrile and separated on a reversed-phase Polaris 5 C18-Analytical column using a mobile phase composed of acetonitrile containing 0.1% (v/v) formic acid and 10 mM aqueous ammonium formate pH 2.5, delivered at a flow-rate of 300 µL/min. Multiple reaction monitoring was performed in the positive ion mode using the transitions m/z555.1→ m/z396.0 (CEF), m/z172.2→ m/z 128.2 (MET), m/z188.0→ m/z125.9 (MET-OH) and m/z528.1→ m/z 364.0 (CEFU) to quantify the drugs. Calibration curves in spiked plasma and ultra-filtrate were linear ( r 2 ≥ 0.9948) from 0.4-300 µg/mL for CEF, 0.05-50 µg/mL for MET and 0.02 - 30 µg/mL for MET-OH. The intra- and inter- assay precisions were less than 9% and the mean extraction recoveries were 94.0% (CEF), 98.2% (MET), 99.6% (MET-OH) and 104.6% (CEF in ultra-filtrate); the recoveries for the IS were 93.8% (in plasma) and 97.6% (in ultra-filtrate). The validated method was successfully applied to a pharmacokinetic study of CEF, MET and MET-OH in hospitalized children with complicated severe acute malnutrition following an oral administration of MET and intravenous administration of CEF over the course of 72 hours.

The Influence of Plasma Albumin Concentration on the Analysis Methodology of Free Valproic Acid by Ultrafiltration and Its Application to Therapeutic Drug Monitoring

BACKGROUND

Free drug analysis is increasingly becoming popular in therapeutic drug monitoring (TDM). Centrifugal ultrafiltration (CF-UF) is the primary method to separate free drug from that of bound drug. However, the volume ratio of ultrafiltrate to sample solution (Vu/Vs) affects the accuracy of CF-UF, which highly depends on the different plasma conditions. Plasma protein concentrations in patients are different from those observed in healthy subjects, and there are also significant differences among patients with different diseases. Only very few studies have reported on the effect of protein concentration on the analysis methodology of free drug by CF-UF.

METHODS

In this study, valproic acid was used as the representative drug, and plasma samples with different albumin concentrations were analyzed by CF-UF and hollow fiber centrifugal ultrafiltration (HFCF-UF).

RESULTS

There was no significant difference of free drug concentrations by HFCF-UF and CF-UF when plasma albumin concentrations ranged 40-60 g/L. However, at low albumin concentrations (<40 g/L), a considerable difference was detected, and the difference was increased with the decrease of plasma albumin concentration. When the albumin concentration was as low as 10 g/L, the free drug concentration was 17.3 mcg/mL by CF-UF, whereas it was 10.2 mcg/mL by HFCF-UF.

CONCLUSIONS

The accuracy of free drug measurement by CF-UF was albumin concentration dependent. However, such an effect was not observed when samples were prepared by HFCF-UF, which was more suitable for TDM of plasma samples from different patients. Therefore, this method could be readily applied to the measurement of free valproic acid plasma concentrations for TDM in patients.

Pretreatment of plasma samples by a novel hollow fiber centrifugal ultrafiltration technique for the determination of plasma protein binding of three coumarins using acetone as protein binding releasing agent

A novel and practical sample pretreatment method based on hollow fiber centrifugal ultrafiltration (HFCF-UF) was developed to determine plasma protein binding by using HPLC. The samples for analyzing unbound and total concentrations could be prepared in parallel simultaneously by the same device. It only required centrifugation for a short time and the filtrate could be injected directly for HPLC analysis without further treatment. Coumarins were selected as the model drugs. Acetone was chosen as the releasing agent to free the binding drug from the drug-protein complex for the total drug concentration determination. Non-specific bindings (NSBs) between the analytes and hollow fiber membrane materials were investigated. The type and volume of protein binding releaser were optimized. Additionally, centrifugal speed and centrifugal time were considered. Under the optimized conditions, the absolute recovery rates of the unbound and total concentrations were in the range of 97.5-100.9% for the three analytes. The limits of detection were in the range of 0.0135-0.0667μgmL(-1). In vitro plasma protein binding of the three coumarins was determined at three concentrations using the validated method and the relative standard deviations (RSDs) were less than 3.4%. Compared with traditional method, the HFCF-UF method is simple to run, no specialized equipment requirement and is a more accurate plasma pretreatment procedure with almost excellent drug-protein binding equilibrium. Therefore, this method can be applied to determine the plasma protein binding in clinical practice. It also provides a reliable alternative for accurate monitoring of unbound or total drug concentration in therapeutic drug monitoring (TDM).

Interpreting physicochemical experimental data sets

With the wealth of experimental physicochemical data available to chemoinformaticians from the literature, commercial, and company databases an increasing challenge is the interpretation of such datasets. Subtle differences in experimental methodology used to generate these datasets can give rise to variations in physicochemical property values. Such methodology nuances will be apparent to an expert experimentalist but not necessarily to the data analyst and modeller. This paper describes the differences between common methodologies for measuring the four most important physicochemical properties namely aqueous solubility, octan-1-ol/water distribution coefficient, pK(a) and plasma protein binding highlighting key factors that can lead to systematic differences. Insight is given into how to identify datasets suitable for combining.

Determination of the free and total concentrations of vancomycin by two-dimensional liquid chromatography and its application in elderly patients

A robust two-dimensional liquid chromatography (2D-LC) method for determining the free and total concentrations of vancomycin in plasma was developed and validated. The 2D-LC system, which exhibited a strong capacity for inhibiting interference, comprised a unique RP1-IEX-RP2 column system and an "Assistant Flow" configuration. Ultrafiltration technology was employed to separate free vancomycin from the protein-bound fraction in human plasma. The influence of ultrafiltration conditions on the free vancomycin concentration was evaluated. The calibration curve was linear over the 0.195-49.92μg/ml range for the free and total vancomycin concentrations. The within- and between-run precision ranges were 1.5-3.9% and 2.0-4.7% for the total concentration, 1.4-3.3% and 2.4-4.0% for the free concentration, respectively. Ultrafiltration was susceptible to variations in the experimental conditions, including the centrifugation time, the centrifugal force, and the nominal molecular weight limit of the ultrafiltration membrane. A total of 101 serum samples from 84 elderly patients were analyzed by this method. The free vancomycin concentration was 5.88±3.75μg/ml (range: 0.240-16.79μg/ml), the total concentration was 12.36±5.36μg/ml (range: 2.16-27.14μg/ml), and the unbound fraction was 45.6±18.8% (range: 11.1-96.9%). There was a poor correlation between the free and total vancomycin concentrations (R(2)=0.596, p<0.05). This method appears to be sensitive, precise, selective, and suitable for use in protein-binding studies of vancomycin.

Accuracy of the analysis of free vancomycin concentration by ultrafiltration in various disease states

The different ultrafiltrate volume results in different unbound vancomycin fractions as determined by centrifugal ultrafiltration and hollow fiber centrifugal ultrafiltration.

The bioanalytical challenge of determining unbound concentration and protein binding for drugs

Knowledge regarding unbound concentrations is of vital importance when exploring the PK and PD of a drug. The accurate and reproducible determination of plasma protein binding and unbound concentrations for a compound/drug is a serious challenge for the bioanalytical laboratory. When the drug is in equilibrium with the binding protein(s), this equilibrium will shift when physiological conditions are not met. Furthermore, the true unbound fraction/concentration is unknown, and there are numerous publications in the scientific literature reporting and discussing data that have been produced without sufficient control of the parameters influencing the equilibrium. In this Review, different parameters affecting the equilibrium and analysis are discussed, together with suggestions on how to control these parameters in order to produce as trustworthy results for unbound concentrations/fractions as possible.

Effect of volume ratio of ultrafiltrate to sample solution on the analysis of free drug and measurement of free carbamazepine in clinical drug monitoring

Traditional ultrafiltration (UF) usually has a large volume ratio of ultrafiltrate to sample solution, and this ratio cannot be well controlled. It can break the balance of protein-binding equilibrium and exert an influence on the analysis of free drug. In the present study, we evaluated the influence of volume ratio of ultrafiltrate to sample solution on the analysis of free drug in human plasma. We used carbamazepine as a model drug and studied the effect of different centrifugation times on ultrafitrate volume and the related effects on unbound carbamazepine measurement. Moreover, we compared the hollow fiber centrifugal ultrafiltration (HFCF-UF) with traditional UF. Our results showed that the ultrafiltrate volume was changed from 40 to 400 μL with the increase of centrifugation time for the traditional UF, and the related changes in unbound concentration were significant. The rate of protein binding (BP) was changed from 40% to 70%. In contrast, a tiny and invariant ultrafiltrate yield (40 μL) was obtained using the HFCF-UF method, and the BP rate was around 72%. In addition, with the HFCF-UF method, the volume ratio of ultrafiltrate to sample solution could be also well controlled by the inner diameters of both the glass tube and hollow fiber. The HFCF-UF method was a more accurate plasma pretreatment procedure, by which the in vivo balance of protein-binding equilibrium was hardly broken. Therefore, this method was successfully employed to quantify the free fraction of carbamazepine in clinical samples.

Screening of chemicals for human bioaccumulative potential with a physiologically based toxicokinetic model

Human bioaccumulative potential is an important element in the risk assessment of chemicals. Due to the high number of synthetic chemicals, there exists the need to develop prioritisation strategies. The purpose of this study was to develop a predictive tool for human bioaccumulation risk assessment that incorporates not only the chemical properties of the compounds, but also the processes that tend to decrease the concentration of the compound such as metabolisation. We used a generic physiologically based toxicokinetic model that based on in vitro human liver metabolism data, minimal renal excretion and a constant exposure was able to assess the bioaccumulative potential of a chemical. The approach has been analysed using literature data on well-known bioaccumulative compounds and liver metabolism data from the ECVAM database and a subset of the ToxCast phase I chemical library-in total 94 compounds covering pharmaceuticals, plant protection products and industrial chemicals. Our results provide further evidence that partitioning properties do not allow for a reliable screening criteria for human chemical hazard. Our model, based on a 100% intestinal absorption assumption, suggests that metabolic clearance, plasma protein-binding properties and renal excretion are the main factors in determining whether bioaccumulation will occur and its amount. It is essential that in vitro metabolic clearance tests with metabolic competent cell lines as well as plasma protein-binding assays be performed for suspected bioaccumulative compounds.

Alternative (non-animal) methods for cosmetics testing: current status and future prospects-2010

The 7th amendment to the EU Cosmetics Directive prohibits to put animal-tested cosmetics on the market in Europe after 2013. In that context, the European Commission invited stakeholder bodies (industry, non-governmental organisations, EU Member States, and the Commission's Scientific Committee on Consumer Safety) to identify scientific experts in five toxicological areas, i.e. toxicokinetics, repeated dose toxicity, carcinogenicity, skin sensitisation, and reproductive toxicity for which the Directive foresees that the 2013 deadline could be further extended in case alternative and validated methods would not be available in time. The selected experts were asked to analyse the status and prospects of alternative methods and to provide a scientifically sound estimate of the time necessary to achieve full replacement of animal testing. In summary, the experts confirmed that it will take at least another 7-9 years for the replacement of the current in vivo animal tests used for the safety assessment of cosmetic ingredients for skin sensitisation. However, the experts were also of the opinion that alternative methods may be able to give hazard information, i.e. to differentiate between sensitisers and non-sensitisers, ahead of 2017. This would, however, not provide the complete picture of what is a safe exposure because the relative potency of a sensitiser would not be known. For toxicokinetics, the timeframe was 5-7 years to develop the models still lacking to predict lung absorption and renal/biliary excretion, and even longer to integrate the methods to fully replace the animal toxicokinetic models. For the systemic toxicological endpoints of repeated dose toxicity, carcinogenicity and reproductive toxicity, the time horizon for full replacement could not be estimated.

Semi-automated protein binding methodology using equilibrium dialysis and a novel mixed-matrix cassette approach

A semi-automated protein binding assay using equilibrium dialysis (ED) and a novel mixed-matrix methodology has been developed. This method decreases mass spectrometer run time and reduces the likelihood of experimental artifacts. In this cassette-based approach, a single matrix is prepared following dialysis by mixing dialyzed plasma and buffer containing different test compounds from the same dialysis plate. This approach differs from the traditional mixed-matrix method where fresh plasma and fresh buffer are mixed with opposing dialyzed samples. This new mixed-matrix methodology is compatible with various high-throughput ED and ultrafiltration devices, many liquid handling systems, and can be used for plasma, serum, albumin, alpha-1 acid glycoprotein, microsomal, and fine tissue homogenate binding studies. The utility of the method can be further enhanced by varying the number of replicates, concentrations, and matrices with simple modifications. Using 29 structurally diverse marketed drugs with a wide range of protein binding values reported in the literature, we have shown the new procedure reduces the total number of samples by nearly half compared to traditional methods, eliminates the need for standard curves, and increases the uniformity of the sample matrix for LC/MS/MS analysis.

Evaluation of serum protein binding by using in vitro pharmacological activity for the effective pharmacokinetics profiling in drug discovery

The establishment of a new index for the profile of serum protein binding was analyzed theoretically. The in vitro pharmacological activity ratio of the inhibition constant in the absence of serum protein to that in its presence (activity ratio), which represents the extent of specific binding to serum protein, was suggested as the new index. To clarify the usefulness of the activity ratio, theoretical analysis by the activity ratio for 3% human serum albumin was examined in comparison with conventional methods of equilibrium dialysis. In-house very late antigen-4 antagonists were used as model compounds, whose pharmacokinetics were strongly influenced by serum protein binding. Although the theoretical and actual unbound fractions were similar, the latter tended to be slightly lower than the former. This small difference was considered to correspond to nonspecific binding. These results suggested that the specific and nonspecific binding could be discriminated by comparing the activity ratio data with those of conventional methods. Moreover, the activity ratio was suggested to be useful in profiling the influence of protein binding on pharmacokinetics. In conclusion, it was considered that the activity ratio could avoid the risk of misleading interpretation by nonspecific binding in pharmacokinetics/pharmacological activity. Moreover, the activity ratio was considered to be valuable as one of the useful parameters in pharmacokinetics profiling and as a tool of rational drug design for drug discovery.

A novel method for the separation and determination of non-encapsulated pyrene in plasma and its application in pharmacokinetic studies of pyrene-loaded MPEG-PLA based nanoparticles

During the pharmacokinetic processes of nanoparticles, encapsulated drugs and non-encapsulated (free and protein-bound) drugs are the drug forms existing in plasma. It is necessary and important to measure the bioavailable drug concentration, namely, the non-encapsulated drug concentration, in pharmacokinetic studies of nanoparticles. A new method using liquid-liquid extraction was first developed and validated for the separate determination of non-encapsulated drugs in plasma. The method was based on the significant difference of extractability between non-encapsulated and encapsulated drugs, and used n-heptane as an extractant. Satisfactory results were obtained with a good linear relationship in the range of 1-80 ng ml(-1) (r = 0.9999) and good reproducibility with coefficients of variation (CVs) less than 10% of intra- and inter-day evaluation results, and the accuracy of intra- and inter-day evaluation results ranged from 92.4% to 109.2%. The extraction recovery was stable in the range 68.6%-75.6%. The developed method had been proven to be an ideal method with high specificity and sensitivity, and the method is simple and rapid. The method described herein has been successfully applied for pharmacokinetic studies in female Wistar rats after the administration of a 5 mg equivalent pyrene kg(-1) dose of pyrene-loaded nanoparticles. The results showed that the non-encapsulated drug had a different pharmacokinetic behavior compared with that of the total drug.