Modification of the ultrafiltration technique to overcome solubility and non-specific binding challenges associated with the measurement of plasma protein binding of corticosteroids

Determination of 3- and 4-chloromethcathinone interactions with plasma proteins: study involving analytical and theoretical methods

PURPOSE

The purpose of this paper was to determine 3- and 4-chloromethcathinone (3- and 4-CMC) binding degree and possible binding interaction modes with human serum albumin (HSA) using analytical and theoretical methods.

METHODS

Experimental determination of 3- and 4-CMC binding degree with HSA was performed using gas chromatography-tandem mass spectrometry preceded by the equilibrium dialysis (ED) and ultrafiltration (UF). Nuclear magnetic resonance (NMR) spectroscopy was used to determine 3- and 4-CMC epitope-binding maps and possible binding sites in HSA. The molecular docking and molecular dynamics were employed to obtain detailed information about binding modes of 3- and 4-CMC enantiomers in HSA.

RESULTS

As follows from the presented data, the degree of binding of 3- and 4-CMC is at a similar level of approx. 80%. This indicates a relatively strong binding of CMC to plasma proteins. The model studies employing the NMR spectroscopy and molecular simulations indicate that both CMCs bind to HSA. The whole 3- and 4-CMC molecules are embedded in the binding sites, with aromatic moieties being in the closest contact with the HSA residues. Moreover, conducted experiments show that  Sudlow site II is the main binding center for 3- and 4-CMC and  Sudlow site I acts as the secondary binding site.

CONCLUSIONS

Although many studies describe pharmacological and toxicological properties of synthetic cathinones (SC), the data taking SCs binding in plasma into consideration are scarce. To our knowledge, this is the first report presenting comprehensive experimental and theoretical characterization of 3- and 4-CMC binding with plasma proteins.

Use of in vitro ADME methods to identify suitable analogs of homosalate and octisalate for use in a read-across safety assessment

Case studies are needed to demonstrate the use of human-relevant New Approach Methodologies in cosmetics ingredient safety assessments. For read-across assessments, it is crucial to compare the target chemical with the most appropriate analog; therefore, reliable analog selection should consider physicochemical properties, bioavailability, metabolism, as well as the bioactivity of potential analogs. To complement in vitro bioactivity assays, we evaluated the suitability of three potential analogs for the UV filters, homosalate and octisalate, according to their in vitro ADME properties. We describe how technical aspects of conducting assays for these highly lipophilic chemicals were addressed and interpreted. There were several properties that were common to all five chemicals: they all had similar stability in gastrointestinal fluids (in which no hydrolysis to salicylic occurred); were not substrates of the P-glycoprotein efflux transporter; were highly protein bound; and were hydrolyzed to salicylic acid (which was also a major metabolite). The main properties differentiating the chemicals were their permeability in Caco-2 cells, plasma stability, clearance in hepatic models, and the extent of hydrolysis to salicylic acid. Cyclohexyl salicylate, octisalate, and homosalate were identified suitable analogs for each other, whereas butyloctyl salicylate exhibited ADME properties that were markedly different, indicating it is unsuitable. Isoamyl salicylate can be a suitable analog with interpretation for octisalate. In conclusion, in vitro ADME properties of five chemicals were measured and used to pair target and potential analogs. This study demonstrates the importance of robust ADME data for the selection of analogs in a read-across safety assessment.

Preclinical pharmacokinetic exploration of a novel osteoporotic quinazolinone-benzopyran-indole hybrid (S019-0385) using LC-MS/MS

1. The current investigation was to develop and validate the LC-MS/MS method in order to analyse the various pharmacokinetic parameters of S019-0385. A sensitive, selective, and robust LC-MS/MS approach was established and validated for measuring S019-0385 in female mice plasma and tissue, using optimal multiple reaction monitoring (MRM) transition m/z 488.25/329.12 on positive mode. On a Waters Symmetry Shield C18 column, the analyte was separated using acetonitrile and deionised water with formic acid within 6 min at 0.7 mL/min. Linearity (R2 ≥ 0.99) was observed across 0.195-100 ng/mL concentration range using linear least-squares regression.2. Blood-to-plasma ratio and plasma protein drug binding (%) in mice and human was assessed and found to be less than 1 and >83%, respectively. Absolute bioavailability (%F) of S019-0385 in female Swiss mice was exhibited to be 6.90%. Percent dose excreted S019-0385 in unchanged form through urine and faecal was found to be less than 2% and 0.5%, respectively.3. Following oral administration at 5 mg/kg, the concentration of S019-0385 in tissue distribution was found to be in the order of C small intestine > C bone > C lung > C spleen > C kidney > C liver > C heart > C brain.

Plasma Protein Binding Determination for Unstable Ester Prodrugs: Remdesivir and Tenofovir Alafenamide

Remdesivir (RDV) and tenofovir alafenamide (TAF) are prodrugs designed to be converted to their respective active metabolites. Plasma protein binding (PPB) determination of these prodrugs is important for patients with possible alteration of free fraction of the drugs due to plasma protein changes in renal impairment, hepatic impairment, or pregnancy. However, the prodrugs' instability in human plasma presents a challenge for accurate PPB determination. In this research work, two approaches were used in the method development and qualification for PPB assessment of RDV and TAF. For RDV, dichlorvos was used to inhibit esterase activity to stabilize the prodrug in plasma during equilibrium dialysis (ED). The impact of dichlorvos on protein binding was evaluated and determined to be insignificant by comparing the unbound fraction (fu) determined by the ED method with dichlorvos present and the fu determined by an ultrafiltration method without dichlorvos. In contrast to RDV, TAF degradation in plasma is ∼3-fold slower, and TAF stability cannot be improved by dichlorvos. Fit-for-purpose acceptance criteria for the TAF PPB method were chosen, and an ED method was developed based on these criteria. These two methods were then qualified and applied for PPB determinations in clinical studies.

ADME characterization and PBK model development of 3 highly protein-bound UV filters through topical application

Estimating human exposure in the safety assessment of chemicals is crucial. Physiologically based kinetic (PBK) models which combine information on exposure, physiology, and chemical properties, describing the absorption, distribution, metabolism, and excretion (ADME) processes of a chemical, can be used to calculate internal exposure metrics such as maximum concentration and area under the concentration-time curve in plasma or tissues of a test chemical in next-generation risk assessment. This article demonstrates the development of PBK models for 3 UV filters, specifically octyl methoxycinnamate, octocrylene, and 4-methylbenzylidene camphor. The models were parameterized entirely based on data obtained from in vitro and/or in silico methods in a bottom-up modeling approach and then validated based on human dermal pharmacokinetic (PK) data. The 3 UV filters are "difficult to test" in in vitro test systems due to high lipophilicity, high binding affinity for proteins, and nonspecific binding, for example, toward plastic. This research work presents critical considerations in ADME data generation, interpretation, and parameterization to assure valid PBK model development to increase confidence in using PBK modeling to help make safety decisions in the absence of human PK data. The developed PBK models of the 3 chemicals successfully simulated the plasma concentration profiles of clinical PK data following dermal application, indicating the reliability of the ADME data generated and the parameters determined. The study also provides insights and lessons learned for characterizing ADME and developing PBK models for highly lipophilic and protein-bound chemicals in the future.

Small volume rapid equilibrium dialysis (RED) measures effects of interstitial parameters on the protein-bound fraction of topical drugs

The importance of plasma protein binding in the early stages of drug development is well recognized. Free and bound drug fractions in plasma are routinely determined with well-established methods. However, for physiological fluids with a small accessible volume and low protein concentrations, such as dermal interstitial fluid (dISF) validated methods are currently missing. Due to the low protein concentration and highly dynamic processes in the dermis, protein binding data obtained from plasma samples may underestimate in-vivo efficacy. This study aimed to validate a small volume rapid equilibrium dialysis (RED) for low protein samples, as a tool to examine drug-protein binding directly in the biological fluid at the site of action. The sample volume required for RED was successfully downscaled to 50 µl and plasma protein binding values of the four model drugs were consistent with previous studies with an average recovery of 88 ± 8% which makes all tested drugs suitable for small volume RED. Inter- and intra-batch variability showed sufficient reproducibility across RED plates. Small volume RED was successfully applied to assess the effects of interstitial parameters, including the evaluation of the major binding protein and the effects of binding protein concentration, drug concentration, and pH on the protein-bound drug fraction using 2% HSA and/or diluted human plasma as a surrogate for dISF.

Preclinical pharmacokinetics, biodistribution, excretion, and plasma protein binding study of 58Fe-labeled hemin by ICP-MS

BACKGROUND

Hemin, a stable form of heme iron, is a potential iron supplement for the treatment of iron deficiency. To date, the pharmacokinetics and in vivo ADME properties of hemin are to be elucidated.

METHODS

In this study, a rapid, sensitive, and validated inductively coupled plasma mass spectrometry (ICP-MS) method was used in combination with ⁵⁸Fe stable isotope labeling to systemically investigate the plasma pharmacokinetics, biodistribution, excretion, and plasma binding profiles of hemin in animals.

RESULTS

Results showed that the ICP-MS method is accurate and sensitive enough to quantitatively determine the in vivo disposition process of ⁵⁸Fe derived from ⁵⁸Fe-labeled hemin. Following intra-gastric administration, ⁵⁸Fe was rapidly absorbed in gastrointestinal tract, with C_max of 41.1 ± 23.1 ng/mL, T_max of 1.38 ± 0.48 h, and bioavailability of 1.12 ± 0.45 % in beagle dogs. Moreover, ⁵⁸Fe was distributed to various organs including stomach, small intestine, spleen, and liver, within a few hours after intra-gastric administration in rats. Excretion of ⁵⁸Fe in rats was predominantly via feces (76.3 ± 15.1 % of dosage), whereas minimally via urine (0.14 ± 0.08 % of dosage). Protein binding study revealed majority of ⁵⁸Fe in plasma was bound to proteins, with average binding rates of 81.0 % and 92.7 % in human and rat plasma, respectively.

CONCLUSION

In conclusion, the present study validated the work-flow of preclinical pharmacokinetic studies of iron-containing drug candidates with using ICP-MS and stable (trace) isotope labeling strategy. It also provided useful information to support the further development of hemin as a drug/nutrition supplement candidate.

Plasma Protein Binding Rate and Pharmacokinetics of Lekethromycin in Rats

Lekethromycin (LKMS), a novel macrolide lactone, is still unclear regarding its absorption. Thus, we conducted this study to investigate the characteristics of LKMS in rats. We chose the ultrafiltration method to measure the plasma protein binding rate of LKMS. As a result, LKMS was characterized by quick absorption, delayed elimination, and extensive distribution in rats following intramuscular (im) and subcutaneous (sc) administration. Moreover, LKMS has a high protein binding rate (78–91%) in rats at a concentration range of 10–800 ng/mL. LKMS bioavailability was found to be approximately 84–139% and 52–77% after im and sc administration, respectively; however, LKMS was found to have extremely poor bioavailability after oral administration (po) in rats. The pharmacokinetic parameters cannot be considered linearly correlated with the administered dose. Additionally, LKMS and its corresponding metabolites were shown to be metabolically stable in the liver microsomes of rats, dogs, pigs, and humans. Notably, only one phase I metabolite was identified during in vitro study, suggesting most of drug was not converted. Collectively, LKMS had quick absorption but poor absorption after oral administration, extensive tissue distribution, metabolic stability, and slow elimination in rats.

Preclinical pharmacokinetics, CYP phenotyping, and tissue distribution study of novel anti-breast cancer candidate S-011-1559

S-011-1559 is a tyrosine-derived novel benzoxazine CDRI molecule targeted to the estrogen-related receptor (ER-α/β) modulator in breast cancer. To explore the pharmacokinetics of S-011-1559, a selective and sensitive bioanalytical method using LC-MS/MS was established and validated in different biological matrices of female rats.Blood-to-plasma ratio and plasma protein binding (PPB) of S-011-1559 was found to be <1 and >97% in both rats and humans respectively. The human serum albumin (HSA) and alpha-1-acid glycoprotein (AAG) binding was found in the range of >68 to 45% and >14% respectively. Half-life and intrinsic clearance by microsomal stability study were found to be 28.83 min and 0.05 mL/min/mg in rats, 78.35 min and 0.036 mL/min/mg in humans respectively. The IC₅₀ value of S-011-1559 against CYP isoforms was revealed to moderately inhibit CYP2D6 by a reversible noncompetitive mechanism.Tissue distribution of S-011-1559 on single intravenous injection at 2mg/kg was found in the order of C lungs > C mammary gland > C spleen > C heart > C kidney > C liver > C brain.The data from the present study provides crucial information about S-011-1559 for further development as a novel potential drug candidate in modulating ER-α/β receptors of lung and breast neoplasia.

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.

In vitro methods for predicting the bioconcentration of xenobiotics in aquatic organisms

The accumulation of anthropogenic chemical substances in aquatic organisms is an immensely important issue from the point of view of environmental protection. In the context of the increasing number and variety of compounds that may potentially enter the environment, there is a need for efficient and reliable solutions to assess the risks. However, the classic approach of testing with fish or other animals is not sufficient. Due to very high costs, significant time and labour intensity, as well as ethical concerns, in vivo methods need to be replaced by new laboratory-based tools. So far, many models have been developed to estimate the bioconcentration potential of chemicals. However, most of them are not sufficiently reliable and their predictions are based on limited input data, often obtained with doubtful quality. The octanol-water partition coefficient is still often used as the main laboratory tool for estimating bioconcentration. However, according to current knowledge, this method can lead to very unreliable results, both for neutral species and, above all, for ionic compounds. It is therefore essential to start using new, more advanced and credible solutions on a large scale. Over the last years, many in vitro methods have been newly developed or improved, allowing for a much more adequate estimation of the bioconcentration potential. Therefore, the aim of this work was to review the most recent laboratory methods for assessing the bioconcentration potential and to evaluate their applicability in further research.

Pretreatment and non-specific binding in ultrafiltration device: Impact on protease inhibitor quantification

INTRODUCTION

Ultrafiltration (UF) is used to separate unbound drugs; however, non-specific binding (NSB) may be a limiting factor of this technique. Pretreatment of UF devices has been suggested to reduce NSB. Therefore, the pretreatment methodologies for UF devices were evaluated in order to test their effectiveness in reducing NSB of protease inhibitors (PIs).

METHODOLOGY

Two PIs (lopinavir-LPV and ritonavir-RTV) were tested. UF devices were pretreated with ultrapure water, Tween-20 or Tween-80. To evaluate the NSB, after UF devices being pretreated, ultrafiltrate solutions containing the analytes at two concentrations (low and high) were used. Samples were quantified by LC-MS/MS.

RESULTS

UF devices pretreated with Tween-5% had the lowest NSB for both analytes. NSB values varied between 7 and 11% at low concentration 16-34% at high LPV concentration, respectively. For RTV, NSB was approximately 6% for low concentration and 18% for high concentration. Failure to completely remove Tween in UF devices could results in an overestimation of NSB.

CONCLUSION

Pretreatment of UF device with Tween and subsequent removal proved to be effective in reducing NSB of PI.

Quantitative Assessment of Pulmonary Targeting of Inhaled Corticosteroids Using Ex Vivo Receptor Binding Studies

The goal of locally acting inhaled corticosteroids is to achieve distinct pulmonary effects with reduced systemic side effects. The present work using an ex vivo receptor binding model in rats was interested in assessing pulmonary targeting for several commercially available corticosteroids by monitoring receptor occupancies in the lung and systemic organs (liver, kidney, spleen, and brain) after intravenous (IV) injection or intratracheal (IT) instillation of a dry powder administration at a dose of 100 μg/kg. Pulmonary targeting, defined as the difference in cumulative receptor occupancies (AUC_E) between the lung and kidney after pulmonary delivery, differed across the investigated corticosteroids (ΔAUC_E range, 33 ± 46 to 143 ± 52% *h) with the highest degree found for corticosteroids with high systemic clearance and pronounced lipophilicity (presumably allowing a long pulmonary residence time). Additionally, this study demonstrated differences in the receptor occupancies across systemic organs. Using kidney receptor occupancies as the comparator, liver receptor occupancies were reduced (ΔAUC_E range: - 157 ± 43 to 178 ± 42% *h) after IV and IT administration for corticosteroids with high intrinsic clearance, while they were increased for corticosteroid prodrugs due to hepatic activation. Spleen receptor occupancies were increased after IT (ΔAUC_E range: 33 ± 35 to 135 ± 28% *h), but not after IV administration. This was especially true for slowly dissolving drugs. Reduced brain uptake was also observed for ciclesonide (CIC) and des-ciclesonide (desCIC), two compounds previously not investigated. In summary, ex vivo receptor binding studies represent a powerful tool to assess the fate of ICSs.

Development of Robust 17(R),18(S)-Epoxyeicosatetraenoic Acid (17,18-EEQ) Analogues as Potential Clinical Antiarrhythmic Agents

17(R),18(S)-Epoxyeicosatetraenoic acid (EEQ) is a cytochrome P450 metabolite of eicosapentaenoic acid (EPA) and a powerful negative chronotrope with low nanomolar activity in a neonatal rat cardiomyocyte (NRCM) arrhythmia model. Prior studies identified oxamide 2b as a soluble epoxide hydrolase (sEH) stable replacement but unsuitable for in vivo applications due to limited oral bioavailability and metabolic stability. These ADME limitations have been addressed in an improved generation of negative chronotropes, e.g., 4 and 16, which were evaluated as potential clinical candidates.

Development and validation of an assay for quantifying budesonide in dried blood spots collected from extremely low gestational age neonates

Budesonide is a potential therapeutic option for the prevention of bronchopulmonary dysplasia in mechanically ventilated premature neonates. The dose and concentrations of budesonide that drive effective prophylaxis are unknown, due in part to the difficulty in obtaining serial blood samples from this fragile population. Of primary concern is the limited total blood volume available for collection for the purposes of a pharmacokinetic study. Dried blood spots (DBS), which require the collection of <200 μL whole blood to fill an entire card, are an attractive low-blood volume alternative to traditional venipuncture sampling. We describe a simple and sensitive method for determining budesonide concentrations in DBS using an ultra-high-performance liquid chromatography - tandem mass spectrometry assay. Budesonide was liberated from a single 6 mm punch using a basified methyl tert-butyl ether extraction procedure. The assay was determined to be accurate and precise in the dynamic range of 1 to 50 ng/mL. The validated assay was then successfully applied to DBS collected as part of a multi-center, dose-escalation study of budesonide administered in surfactant via intra-tracheal instillation to premature neonates between 23 and 28 weeks gestational age. These findings show that DBS are a useful technique for collecting pharmacokinetic samples in premature neonates and other pediatric populations.

Effect of Ling-Gui-Zhu-Gan decoction major components on the plasma protein binding of metoprolol using UPLC analysis coupled with ultrafiltration

Using traditional Chinese medicine formula Ling-Gui-Zhu-Gan decoction (LGZGD) plus selective β1-adrenergic receptor inhibitor metoprolol to treat arrhythmia of coronary heart disease can significantly improve efficiency with no adverse reactions. However, the effect of major components of LGZGD on the plasma protein binding of metoprolol is unclear. Firstly, this study aimed to computationally predict the molecular interactions between metoprolol, the major components of LGZGD, and bovine serum albumin (BSA). Secondly, the plasma protein binding of metoprolol combined with major components of LGZGD was investigated by UPLC analysis coupled with ultrafiltration. The MOE (2008.10) software package was used to investigate the molecular interactions among metoprolol, the major components of LGZGD, and BSA. Using in vitro experiments, BSA was separately spiked with a mixtures of metoprolol and the major components of LGZGD. The results showed that metoprolol interacted with BSA mainly through arene-arene interactions, as did cinnamic acid and liquiritin. However, the energy scores of cinnamic acid and liquiritin were lower than that of metoprolol. There were no interactions between metoprolol and the major components of LGZGD. Further studies in vitro showed that the presence of the major components of LGZGD did not change the plasma protein binding of metoprolol. We adopted molecular docking to predict the drug-herb plasma protein binding interactions of metoprolol and then used ultrafiltration to verify the docking results. There were no drug-herb interactions between metoprolol and LGZGD in BSA, which indicated that this combination therapy might be safe and feasible.

Methods and Study Designs for Characterizing the Pharmacokinetics and Pharmacodynamics of Carrier-Mediated Agents

Major advances in carrier-mediated agents (CMAs), which include nanoparticles, nanosomes, and conjugates, have revolutionized drug delivery capabilities over the past decade. While providing numerous advantages, such as greater solubility, duration of exposure, and delivery to the site of action over their small molecule counterparts, there is substantial variability in systemic clearance and distribution, tumor delivery, and pharmacologic effects (efficacy and toxicity) of these agents. In this chapter, we focus on the analytical and phenotypic methods required to design a study that characterizes the pharmacokinetics (PK) and pharmacodynamics (PD) of all forms of these nanoparticle-based drug agents. These methods include separation of encapsulated and released drugs, ultrafiltration for measurement of non-protein bound active drug, microdialysis to measure intra-tumor drug concentrations, immunomagnetic separation and flow cytometry for sorting cell types, and evaluation of spatial distribution of drug forms relative to tissue architecture by mass spectrometry imaging and immunohistochemistry.

Effect of inhaled and systemic glucocorticoid treatment on CD4+ regulatory and effector T cells in a mouse model of allergic asthma

To achieve a better understanding of mechanisms underlying the anti-asthmatic action of inhaled and systemic glucocorticoids (GCs) and to provide more data regarding the risk of a negative effect of inhaled GCs on CD4⁺ T cells, a study was conducted on the effect of ciclesonide and methylprednisolone on CD4⁺ effector (Teff), regulatory (Treg) and resting (Trest) T cells within respiratory and extra-respiratory tissues in a mouse model of allergic asthma. The study indicated that one, and possibly a key mechanism, underlying the anti-asthmatic action of inhaled and systemic GCs is the prevention of the activation and clonal expansion of CD4⁺ Teff cells in the mediastinal lymph nodes (MLNs), which consequently prevents infiltration of the lungs with CD4⁺ Teff cells. The beneficial effects of GCs in asthma treatment were not mediated through increased recruitment of Treg cells into the MLNs and lungs and/or local generation of Treg cells. The results demonstrated that inhaled and systemic GCs induced comparable depletion of normal CD4⁺ Teff, Trest and Treg cells in the MLNs, head and neck lymph nodes and peripheral blood. Furthermore, inhaled, but not systemic GC therapy, led to the loss of these cells in the lungs. Thus, the study suggests that inhaled GC therapy may not be safer at all than systemic one with respect to the adverse effect on CD4⁺ T cells present within and outside the respiratory tract. Moreover, administration of inhaled GCs can produce negative effects on lung-residing CD4⁺ T cells.

Inhaled corticosteroids: potency, dose equivalence and therapeutic index

Glucocorticosteroids are a group of structurally related molecules that includes natural hormones and synthetic drugs with a wide range of anti-inflammatory potencies. For synthetic corticosteroid analogues it is commonly assumed that the therapeutic index cannot be improved by increasing their glucocorticoid receptor binding affinity. The validity of this assumption, particularly for inhaled corticosteroids, has not been fully explored. Inhaled corticosteroids exert their anti-inflammatory activity locally in the airways, and hence this can be dissociated from their potential to cause systemic adverse effects. The molecular structural features that increase glucocorticoid receptor binding affinity and selectivity drive topical anti-inflammatory activity. However, in addition, these structural modifications also result in physicochemical and pharmacokinetic changes that can enhance targeting to the airways and reduce systemic exposure. As a consequence, potency and therapeutic index can be correlated. However, this consideration is not reflected in asthma treatment guidelines that classify inhaled corticosteroid formulations as low-, mid- and high dose, and imbed a simple dose equivalence approach where potency is not considered to affect the therapeutic index. This article describes the relationship between potency and therapeutic index, and concludes that higher potency can potentially improve the therapeutic index. Therefore, both efficacy and safety should be considered when classifying inhaled corticosteroid regimens in terms of dose equivalence. The historical approach to dose equivalence in asthma treatment guidelines is not appropriate for the wider range of molecules, potencies and device/formulations now available. A more robust method is needed that incorporates pharmacological principles.

Simultaneous determination of azilsartan and chlorthalidone in rat and human plasma by liquid chromatography-electrospray tandem mass spectrometry

Azilsartan medoxomil (AZM), an ester prodrug of azilsartan (AZ), and chlorthalidone (CLT) have recently been approved as a combination therapy for the management of hypertension. This is the first report which described a selective and sensitive method for the simultaneous quantification of AZ and CLT in rat and human plasma using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). AZ and CLT were extracted from plasma by liquid-liquid extraction technique and separated on a C18 reverse phase column using ammonium acetate (10mM, pH 4)-mixture of methanol and acetonitrile (8:92, v/v) as a mobile phase at a flow rate of 0.7mL/min. Detection was performed by electrospray ionization (ESI) operated in negative multiple reaction monitoring (MRM) mode. The lower limit of quantitation (LLOQ) of this method was 1ng/mL and the calibration curves were linear (r(2)≥0.995) over the concentration range of 1-4000ng/mL for both the analytes. The intra- and inter-day precision and accuracy were well within the acceptable limits. The mean extraction recoveries were found to be about 80% and no matrix effect was observed. AZ and CLT were found to be stable under all relevant storage conditions. The method was successfully applied to the oral pharmacokinetic study of AZM and CLT in rats. Further, the sensitivity of the method enabled the determination of protein binding of AZ and CLT in human plasma.

Quantitative determination of free/bound atazanavir via high-throughput equilibrium dialysis and LC-MS/MS, and the application in ex vivo samples

Aim: The determination of drug–protein binding is important in the pharmaceutical development process because of the impact of protein binding on both the pharmacokinetics and pharmacodynamics of drugs. Equilibrium dialysis is the preferred method to measure the free drug fraction because it is considered to be more accurate. The throughput of equilibrium dialysis has recently been improved by implementing a 96-well format plate. Results/methodology: This manuscript illustrates the successful application of a 96-well rapid equilibrium dialysis (RED) device in the determination of atazanavir plasma–protein binding. Discussion/conclusion: This RED method of measuring free fraction was successfully validated and then applied to the analysis of clinical plasma samples taken from HIV-infected pregnant women administered atazanavir. Combined with LC-MS/MS detection, the 96-well format equilibrium dialysis device was suitable for measuring the free and bound concentration of pharmaceutical molecules in a high-throughput mode.

Protein binding of fentanyl and its metabolite nor-fentanyl in human plasma, albumin and α-1 acid glycoprotein

1.Fentanyl is a highly lipophilic opioid commonly used to treat cancer pain. Plasma protein binding (PPB) of fentanyl in human plasma is reported as 80-85%, however it is unclear whether fentanyl binds primarily to albumin (ALB) or α-1 acid glycoprotein (AAG) and no studies have been conducted on the metabolite, nor-fentanyl. Fentanyl is also known to bind to plasticware and ultrafiltration (UF) devices which impacts adversely on binding experiments. 2.PPB of fentanyl and nor-fentanyl to ALB and AAG in isotonic phosphate buffer solution and seeded human plasma was quantified. PPB was also performed in plasma samples obtained from cancer patients receiving transdermal fentanyl. The adsorption of fentanyl and nor-fentanyl to UF devices and plasticware commonly used in PPB studies was also assessed. 3.Fentanyl was shown to bind primarily to ALB as opposed to AAG, with nor-fentanyl exhibiting negligible binding to plasma proteins. Total PPB of fentanyl was 86-89% in seeded human plasma. PPB in 56 cancer patient samples was 95.1 ± 3.52% for fentanyl and 32.4 ± 21.9% for nor-fentanyl. 4.UF was shown to be a reliable and convenient method for PPB studies, thereby removing the need for complex testing for adsorption of the drug to plasticware during UF.

Determination of total and unbound concentrations of lopinavir in plasma using liquid chromatography-tandem mass spectrometry and ultrafiltration methods

Lopinavir is an HIV protease inhibitor with high protein binding (98-99%) in human plasma. This study was designed to develop an ultrafiltration method to measure the unbound concentrations of lopinavir overcoming the non-specific binding issue. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of total concentrations of lopinavir in plasma was developed and validated, and an adaptation was also optimized and validated for the determination of unbound concentrations. The chromatographic separation was performed with a C18 column (100 mm × 2.1mm i.d., 5 μm particle size) using a mobile phase containing deionized water with formic acid, and acetonitrile, with gradient elution at a flow-rate of 350 μL min(-1). Identification of the compounds was performed by multiple reaction monitoring, using electrospray ionization in positive ion mode. The method was validated over a clinical range of 0.01-1 μg/mL for human plasma ultrafiltrate and 0.1-15 μg/mL in human plasma. The inter and intra-assay accuracies and precisions were between 0.23% and 11.37% for total lopinavir concentrations, and between 3.50% and 13.30% for plasma ultrafiltrate (unbound concentration). The ultrafiltration method described allows an accurate separation of the unbound fraction of lopinavir, circumscribing the loss of drug by nonspecific binding (NSB), and the validated LC-MS/MS methodology proposed is suitable for the determination of total and unbound concentrations of lopinavir in clinical practice.

Measurement of plasma protein and lipoprotein binding of pyrethroids

INTRODUCTION

A simple, reliable procedure was developed to measure binding of pyrethroid insecticides to total proteins and lipoproteins of rat and human plasma.

METHODS

The extent of binding of (14)C-labeled deltamethrin (DLM), cis-permethrin (CIS) and trans-permethrin (TRANS) was quantified by a 3-step organic solvent extraction technique. Rat and human plasma samples, containing NaF to inhibit esterases, were spiked with a range of concentrations of each radiolabeled pyrethroid. Protein binding reached equilibrium within ~1h of incubation at 37°C. The samples were extracted in turn with: isooctane to collect the unbound fraction; 2-octanol to extract the lipoprotein-bound fraction; and acetonitrile to obtain the protein-bound fraction.

RESULTS

Absolute recoveries of DLM, CIS and TRANS ranged from 86 to 95%. Adherence of these very lipophilic chemicals to glass and plastic was minimized by using silanized glass vials and LoBind® plastic pipettes. The method's ability to distinguish lipoprotein from protein binding was confirmed by experiments with diazepam and cyclosporine, drugs that bind selectively to albumin and lipoproteins, respectively.

DISCUSSION

This procedure was effectively utilized for studies of the species-dependence of plasma protein and lipoprotein binding of three pyrethroids for inclusion in physiologically-based pharmacokinetic models of pyrethroids for use in health risk assessments of the insecticides in children and adults.

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.

[In vitro comparative study of plasma protein binding of 99mTc-DTPA used in renal scintigraphy]

The radiopharmaceutical (99m)Tc-DTPA (diethylene-triamine-pentaacetic acid) is a tracer widely used in renal scintigraphy to assess glomerular filtration rate. The estimation of protein binding is very important due to its impact on clinical parameters biodistribution since only the free fraction is filtered by the kidney. A number of laboratory techniques have been developed to study protein binding. Precipitation and ultrafiltration are the mostly used techniques in pharmacology for studies of the binding between proteins and small molecules. The aim of this work is to apply and compare those two analytical methods in (99m)Tc-DTPA protein binding determination in vitro before in vivo application. The results obtained by precipitation with trichloroacetic acid are not enough reproducible, while those obtained by ultrafiltration seem more consistent and reproducible.

A mass balance approach for calculation of recovery and binding enables the use of ultrafiltration as a rapid method for measurement of plasma protein binding for even highly lipophilic compounds

The aim of this study is to further validate the use of ultrafiltration (UF) as a method for determining plasma protein binding (PPB) by demonstrating that non-specific binding (NSB) is not a limitation, even for highly lipophilic compounds, because NSB sites on the apparatus are passivated in the presence of plasma. Mass balance theory was used to calculate recovery of 20 commercial and seven investigational compounds during ultrafiltration in the presence and absence of plasma. PPB was also measured using this mass balance approach for comparison to PPB determined by rapid equilibrium dialysis (RED) and as found in the literature. Compound recovery during UF was dramatically different in the presence and absence of plasma for compounds with high NSB in PBS only. A comparison of PPB calculated by ultrafiltration with literature values or calculated by RED gave concordant results. Discrepancies could be explained by changes in pH, insufficient time to equilibrium, or compound instability during RED, problems which were circumvented by ultrafiltration. Therefore, NSB, as measured by the traditional incubation of compound in PBS, need not be an issue when choosing UF as a PPB assay method. It is more appropriate to calculate compound recovery from the device in plasma as measured by mass balance to determine the suitability of the method for an individual compound. The speed with which UF can be conducted additionally avoids changes in pH or compound loss that can occur with other methods. The mass balance approach to UF is thus a preferred method for rapid determination of PPB.

Biopharmaceutical characterization of decursin and their derivatives for drug discovery

Angelica gigas Nakai and its components are known to have neuroprotective, antiplatelet, and anticancer activities. The present study evaluated the in vitro and in vivo biopharmaceutical characterization of Angelica gigas component substances, including decursin (the main substance), decursinol angelate (decursin isomer), JH714 (ether form of decursin) and epoxide decursin (epoxide form of decursin). Decursin, decursinol angelate and JH714 exhibited acceptable metabolic stability (>50%) in liver microsomes from human and higher bound fraction (>90%) in human plasma operating ultrafiltration. Decursin and decursinol angelate in CYP1A2 and CYP2C19 indicated less than 50% CYP activity, suggesting inhibition of the CYP isoforms using Vivid® CYP screening kit. JH714 only showed an apparent permeability coefficient of <10 × 10⁻⁶ cm/s in MDCK cells, suggesting that it is poorly absorbed. Blood brain barrier permeability was examined after oral administration to male Sprague-Dawley (SD) rats, and pharmacokinetic studies were performed after oral and intravenous administration of 10 mg/kg compounds. Decursin, decursinol angelate and JH714 showed ratios of compound concentration in brain with respect to plasma (Cbrain/Cplasma) of >1.5, suggesting good brain/plasma ratio at 0.5, 1, 3, and 5 h. In contrast, Cbrain/Cplasma was <0.5 for epoxide decursin. For all test compounds, >1.5% of the dose remained in GI tract after 8 h, and the excretion rate in urine was <0.5% which suggests that gastro intestinal tract may be major site of disposition following oral administration. Finally, these results may be useful for the design of dosage regimens of decursin and its derivatives.

Quantification of unbound prednisolone, prednisone, cortisol and cortisone in human plasma by ultrafiltration and direct injection into liquid chromatrography tandem mass spectrometry

BACKGROUND

The existing methods for quantitative analysis of free corticosteroids require high volume of plasma and laborious extraction processes. Development of ultrafiltration followed by the liquid chromatrography tandem mass spectrometry (LC-MS/MS) method that requires 300 microL of plasma, does not entail any offline extraction and achieves good sensitivity was described.

METHODS

Unbound corticosteroids were separated by the ultrafiltration of plasma using Microcon centrifugal filter devices (10,000 Dal nominal molecular weight limit). A 30 microL aliquot of the ultrafiltrate was directly injected into a two-dimensional high-performance liquid chromatography clean-up and separation system coupled with API-4000 mass spectrometer. The clean-up was performed on a Strata-X on-line extraction cartridge. A Zorbax-SB Phenyl, Rapid Resolution HT (2.1 x 100 mm) column was employed to chromatographically resolve cortisol and prednisolone from each other, from cortisone and prednisone as well as from interferences found in plasma from stable kidney transplant recipients.

RESULTS

Intra- and inter-run imprecision and inaccuracy within +/-15% were achieved during a three-batch validation for quality control samples at six concentrations in ultrafiltrate from charcoal-stripped plasma and three concentrations from normal plasma, over a 2000-fold dynamic range. The lower limit of quantification was 0.100 ng/mL for all four corticosteroids.

CONCLUSIONS

A highly selective, sensitive, simple and robust LC-MS/MS method was developed for the simultaneous quantification of free cortisol, cortisone, prednisolone and prednisone. The performance of the Strata-X on-line extraction cartridge was maintained for over 700 injections. The assay was successfully applied for the analysis of the analytes in over 500 plasma samples from stable kidney transplant recipients.

Correction for nonspecific binding to various components of ultrafiltration apparatus and impact on estimating in vivo rat clearance for a congeneric series of 5-ethyl, 5-n-alkyl barbituric acids

Accurately predicting in vivo metabolic clearance from in vitro liver microsomes or hepatocytes requires a good understanding of the factors contributing to the prediction. Although much work has concentrated on deriving scaling factors and optimizing the metabolic stability techniques for consistency and rigor, it is only relatively recently that the importance of binding to microsomes and hepatocytes has been appreciated. Ultrafiltration is often used to estimate binding to plasma proteins and microsomes, but the level of nonspecific binding (NSB) to the ultrafiltration apparatus has not been adequately described. We derive an equation to correct for NSB and demonstrate that this can significantly affect the estimate of binding to microsomes and improve the accuracy of scaling to in vivo clearance for a series of barbiturates.

Bovine serum albumin decreases Km values of human UDP-glucuronosyltransferases 1A9 and 2B7 and increases Vmax values of UGT1A9

The human UDP-glucuronosyltransferase (UGT) enzymes UGT1A9 and UGT2B7 play important roles in the hepatic glucuronidation of many drugs. The presence of bovine serum albumin (BSA) during in vitro assays was recently reported to lower the K(m) values of both these UGTs for their aglycone substrates without affecting the corresponding V(max) values. Nonetheless, using the specific substrates entacapone and zidovudine (AZT) for UGT1A9 and UGT2B7, respectively, and using an improved ultrafiltration method for measuring drug binding to BSA and to biological membranes, we found that the presence of BSA during the glucuronidation reaction leads to a large increase in the V(max) value of UGT1A9, in addition to lowering its K(m) value. On the other hand, in the case of UGT2B7, our results agree with the previously described effect of BSA, namely lowering the K(m) value without a large effect on the enzyme's V(max) value. The unexpected BSA effect on UGT1A9 was independent of the expression system because it was found in a recombinant enzyme that was expressed in baculovirus-infected insect cells as well as in the native enzyme in human liver microsomes. Moreover, the effect of BSA on the kinetics of 4-methylumbelliferone glucuronidation by recombinant UGT1A9 was similar to its effect on entacapone glucuronidation. Contrary to the aglycone substrates, the effect of BSA on the apparent K(m) of UGT1A9 for the cosubstrate UDP-α-D-glucuronic acid was nonsignificant. Our findings call for further investigations of the BSA effects on different UGTs and the inhibitors that it may remove.

Physiological and molecular characterization of aristolochic acid transport by the kidney

Consumption of herbal medicines derived from Aristolochia plants is associated with a progressive tubulointerstitial disease known as aristolochic acid (AA) nephropathy. The nephrotoxin produced naturally by these plants is AA-I, a nitrophenanthrene carboxylic acid that selectively targets the proximal tubule. This nephron segment is prone to toxic injury because of its role in secretory elimination of drugs and other xenobiotics. Here, we characterize the handling of AA-I by membrane transporters involved in renal organic anion transport. Uptake assays in heterologous expression systems identified murine organic anion transporters (mOat1, mOat2, and mOat3) as capable of mediating transport of AA-I. Kinetic analyses showed that all three transporters have an affinity for AA-I in the submicromolar range and thus are likely to operate at toxicologically relevant concentrations in vivo. Structure-activity relationships revealed that the carboxyl group is critical for high-affinity interaction of AA-I with mOat1, mOat2, and mOat3, whereas the nitro group is required only by mOat1. Furthermore, the 8-methoxy group, although essential for toxicity, was not requisite for transport. Mouse renal cortical slices avidly accumulated AA-I, achieving slice-to-medium concentration ratios >10. Uptake by slices was sensitive to known mOat1 and mOat3 substrates and the organic anion transport inhibitor probenecid, which also blocked the production of DNA adducts formed with reactive intracellular metabolites of AA-I. Taken together, these findings indicate that OAT family members mediate high-affinity transport of AA-I and may be involved in the site-selective toxicity and renal elimination of this nephrotoxin.

Analysis of biliary excretion of icariin in rats

Icariin is a bioactive herbal ingredient isolated from Epimedii Herba. This study evaluates the distribution of icariin in rats by microdialysis sampling and high-performance liquid chromatography with ultraviolet detection (HPLC-UV). Microdialysis probes were simultaneously placed in the jugular vein, brain striatum, and bile duct of each anesthetized rat for sampling after the administration of icariin (dose=10 or 20 mg/kg) via the femoral vein. The role of P-glycoprotein (P-gp) on icariin distribution was assessed by pretreatment with cyclosporine (CsA, dose=20 mg/kg). This study is the first report of the biliary excretion of icarin in rats, defined as the blood-to-bile distribution (k value), calculated by dividing the area under the concentration-time curve (AUC) of icariin in bile by that in blood (k=AUCbile/AUCblood). The k values were 19.0±5.9 and 18.8±3.8 at the doses of 10 and 20 mg/kg, respectively. The decreased biliary excretion of icariin due to pretreatment with CsA was evidenced by the reduced k values (18.8±3.8 vs 9.9±1.9, p=0.005). This work demonstrates that biliary excretion is the major elimination pathway for icariin disposition and that transporters, such as P-gp, might be related to icariin's biliary excretion.

Critical topics in ensuring data quality in bioanalytical LC–MS method development

The use of LC–MS for bioanalysis of pharmaceuticals is entering its third decade and may be considered to be a mature technology. In many respects this is true, considering the advances made in such areas as instrument performance, electronics, software and automation of use. However, there remain instrumental and noninstrumental areas that require significant attention to ensure data quality. Increasing regulatory focus on analytical method performance and unaddressed method issues require the bioanalyst to understand those areas that most greatly impact data quality. This review will focus on instrumental and noninstrumental areas that can influence data quality, including reference standard and internal standard quality and physicochemical properties, matrix effects, stability in matrix, sample preparation, LC and MS.

Identification and characterization of human UDP-glucuronosyltransferases responsible for the in vitro glucuronidation of daphnetin

Daphnetin has been developed as an oral medicine for treatment of coagulation disorders and rheumatoid arthritis in China, but its in vitro metabolism remains unknown. In the present study, the UDP-glucuronosyltransferase (UGT) conjugation pathways of daphnetin were characterized. Two metabolites, 7-O-monoglucuronide daphnetin (M-1) and 8-O-monoglucuronide daphnetin (M-2), were identified by liquid chromatography/mass spectrometry and NMR when daphnetin was incubated, respectively, with liver microsomes from human (HLM), rat (RLM), and minipig (PLM) and human intestinal microsomes (HIM) in the presence of UDP-glucuronic acid. Screening assays with 12 human recombinant UGTs demonstrated that the formations of M-1 and M-2 were almost exclusively catalyzed by UGT1A9 and UGT1A6, whereas M-1 was formed to a minor extent by UGT1A3, 1A4, 1A7, 1A8, and 1A10 at a high substrate concentration. Kinetics studies, chemical inhibition, and correlation analysis were used to demonstrate that human UGT1A9 and UGT1A6 were major isoforms involved in the daphnetin glucuronidations in HLM and HIM. By in vitro-in vivo extrapolation of the kinetic data measured in HLM, the hepatic clearance and the corresponding hepatic extraction ratio were estimated to be 19.3 ml/min/kg b.wt. and 0.93, respectively, suggesting that human clearance of daphnetin via the glucuronidation is extensive. Chemical inhibition of daphnetin glucuronidation in HLM, RLM, and PLM showed large species differences although the metabolites were formed similarly among the species. In conclusion, the UGT conjugation pathways of daphnetin were fully elucidated and its C-8 phenol group was more selectively catalyzed by UGTs than by the C-7 phenol.