Simple and sensitive HPLC-UV method for determination of bexarotene in rat plasma

Nanoscale insights into the local structural rearrangements of amyloid-β induced by bexarotene

A better understanding of the abnormal protein aggregation and the effect of anti-aggregation agents on the fibrillation pathways and the secondary structure of aggregates can determine strategies for the early treatment of dementia. Herein, we present a combination of experimental and theoretical studies providing new insights into the influence of the anti-aggregation drug bexarotene on the secondary structure of individual amyloid-β aggregates and its primary aggregation. The molecular rearrangements and the spatial distribution of β-sheets within individual aggregates were monitored at the nanoscale with infrared nanospectroscopy. We observed that bexarotene limits the parallel β-sheets formation, known to be highly abundant in fibrils at later phases of the amyloid-β aggregation composed of in-register cross-β structure. Moreover, we applied molecular dynamics to provide molecular-level insights into the investigated system. Both theoretical and experimental results revealed that bexarotene slows down the protein aggregation process via steric effects, largely prohibiting the antiparallel to parallel β-sheet rearrangement. We also found that bexarotene interacts not only via the single hydrogen bond formation with the peptide backbone but also with the amino acid side residue via a hydrophobic effect. The studied model of the drug-amyloid-β interaction contributes to a better understanding of the inhibition mechanism of the amyloid-β aggregation by the small molecule drugs. However, our nanoscale findings need to meet in vivo research requiring different analytical approaches.

A highly sensitive and rapid LC-MS/MS method for quantification of bexarotene in mouse plasma and brain tissue: Application to mice pharmacokinetic study

Emerging evidence has suggested that bexarotene, a nearly 20-year-old skin cancer drug, may be a potential drug candidate to treat Alzheimer's disease (AD) and other neurodegenerative disorders. As described in this study, a highly sensitive and rapid method, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) to determine bexarotene in mouse plasma and brain tissue, was established and validated for the first time. Single-step protein precipitation utilizing methanol solution (containing 0.05 % acetic acid) as precipitation agent was employed to prepare the samples of plasma and brain tissue. Chromatographic separation in gradient elution mode was conducted via an Agilent ZORBAX SB-C18 column (50 mm × 4.6 mm, 5 µm) employing methanol-ammonium acetate buffer (5 mM, pH adjusted to 4.6 with acetic acid) as mobile phase which flowed at 0.45 mL/min. The total run time was 6 min for each sample. Detection through mass spectrometric technique was operated by selected reaction monitoring (SRM) in negative electrospray ionization mode. The method was linear within the range of 10.0-15000 ng/mL for plasma and 10.0-600 ng/mL for brain tissue homogenate with the lower limit of quantification of 10.0 ng/ml. The plasma or tissue homogenate was only required 20 μL. The intra- and inter-day precision were less than 13.8 %, and the RE was between -7.4 % and 3.4 %. The method was applied to investigate the plasma pharmacokinetics and brain distribution of bexarotene in mice after being intragastrically administered with bexarotene at the dosage of 100 mg/kg. The results showed that both brain and plasma concentrations of bexarotene peaked at 1.0 h. Bexarotene was rapidly eliminated with a half-life of 2.0 h.

A Simple Bioanalytical Method for Simultaneous Estimation of Amlodipine and Celecoxib in Rat Plasma by High Performance Liquid Chromatography

A simple, precise, rapid and accurate UFLC method has been developed with due validation for the simultaneous estimation of Amlodipine besylate and Celecoxib in rat plasma. The separation has been taken place by C18 Eclipse plus column at 1ml/min flow rate. The mobile phase comprises of 20 mM sodium acetate buffer of pH 4.5 adjusted with glacial acetic acid and methanol (30:70% v/v). The effluents were monitored at 228 nm with a total run time of 15min. The retention time of Amlodipine besylate and celecoxib were found to be 7.69 min and 10.69 min respectively. The extraction of drugs have been achieved by protein precipitation technique with methanol as a solvent. The detection concentration was linear over 60-420 ng/ml for Amlodipine besylate and 600-4200 ng/ml for Celecoxib. Regression equation of Amlodipine besylate and Celecoxib were found to be y = 30.996x + 520.29 & y = 39.722x + 23706 with regression coefficient 0.9944 & 0.9941 respectively using unweighted and weighted linear regression with a weighting factor of 1/x0, 1/x, 1/✓x and 1/x2. The percentage recoveries were found to be 88.52±1.276 to 93.06±2.872 for Amlodipine & 89.40±0.728 to 94.05±0.221 for Celecoxib. This liquid chromatography method was extensively validated for linearity, accuracy precision, and stability studies.

A novel nucleoside rescue metabolic pathway may be responsible for therapeutic effect of orally administered cordycepin

Although adenosine and its analogues have been assessed in the past as potential drug candidates due to the important role of adenosine in physiology, only little is known about their absorption following oral administration. In this work, we have studied the oral absorption and disposition pathways of cordycepin, an adenosine analogue. In vitro biopharmaceutical properties and in vivo oral absorption and disposition of cordycepin were assessed in rats. Despite the fact that numerous studies showed efficacy following oral dosing of cordycepin, we found that intact cordycepin was not absorbed following oral administration to rats. However, 3′-deoxyinosine, a metabolite of cordycepin previously considered to be inactive, was absorbed into the systemic blood circulation. Further investigation was performed to study the conversion of 3′-deoxyinosine to cordycepin 5′-triphosphate in vitro using macrophage-like RAW264.7 cells. It demonstrated that cordycepin 5′-triphosphate, the active metabolite of cordycepin, can be formed not only from cordycepin, but also from 3′-deoxyinosine. The novel nucleoside rescue metabolic pathway proposed in this study could be responsible for therapeutic effects of adenosine and other analogues of adenosine following oral administration. These findings may have importance in understanding the physiology and pathophysiology associated with adenosine, as well as drug discovery and development utilising adenosine analogues.

A Bioanalytical Method for Eliglustat Quantification in Rat Plasma

A simple and sensitive bioanalytical HPLC-UV method has been developed and validated for quantification of eliglustat in rat plasma. The liquid-liquid extraction method was found to be more efficient compared to protein precipitation technique. Chromatographic separation of eliglustat was achieved using Kromasil C18 column with a mobile phase consisting of a mixture of methanol and ammonium acetate (pH 3.2) in a ratio of 60:40. Detection wavelength was set at 282 nm. The developed method was specific, accurate, precise with good recovery and stability profile. The calibration curve constructed over a range of 0.3-10 μg/mL was linear (R2 > 0.997). Accuracy in intra and inter-day assay were found to be 96.27-107.35% and 96.80-106.57%, respectively. The corresponding precision (%CV) values were within 4.31-10.90% and 4.82-9.97%, respectively. Till date, no method is available for bioanalysis of eliglustat in any type of biological matrix. This is the first time to report a bioanalytical method for this molecule. The developed bioanalytical method was applied to quantitate eliglustat in the plasma samples of a single dose oral pharmacokinetic study in Sprague Dawley rat.

Optimization and validation of extraction and quantification methods of antimalarial triterpenic esters in Keetia leucantha plant and plasma

The aim of this study is to develop validated methods for the extraction and quantification of antimalarial triterpene esters from Keetia leucantha and from plasma samples. These compounds, showing in vitro and in vivo antiplasmodial activities, were optimally extracted from Keetia leucantha twigs using ultrasounds with dichloromethane and from plasma using protein precipitation with acetonitrile. We then developed and validated HPLC-UV quantification methods, which proved to be selective, accurate, linear, true and precise, both in plant and plasma samples for the eight triterpenic esters in mixture. Based on the total error concept as decision criteria, the validated dosage ranges of the triterpene esters mixture were set between 14.68 and 73.37 μg/mL in plants and 15.90 and 106.01 μg/mL in plasma injected solutions, corresponding to 7.95 and 53.01 μg/mL in plasma. These reliable methods were used to determine effectively triterpene esters content in collected samples, that seems highly variable in plant extracts, and will be helpful to further investigate pharmacokinetics parameters of these interesting bioactive compounds.

Quantitative Prediction of Oral Bioavailability of a Lipophilic Antineoplastic Drug Bexarotene Administered in Lipidic Formulation Using a Combined In Vitro Lipolysis/Microsomal Metabolism Approach

For performance assessment of the lipid-based drug delivery systems (LBDDSs), in vitro lipolysis is commonly applied because traditional dissolution tests do not reflect the complicated in vivo micellar formation and solubilization processes. Much of previous research on in vitro lipolysis has mostly focused on rank-ordering formulations for their predicted performances. In this study, we have incorporated in vitro lipolysis with microsomal stability to quantitatively predict the oral bioavailability of a lipophilic antineoplastic drug bexarotene (BEX) administered in LBDDS. Two types of LBDDS were applied: lipid solution and lipid suspension. The predicted oral bioavailability values of BEX from linking in vitro lipolysis with microsomal stability for lipid solution and lipid suspension were 34.2 ± 1.6% and 36.2 ± 2.6%, respectively, whereas the in vivo oral bioavailability of BEX was tested as 31.5 ± 13.4% and 31.4 ± 5.2%, respectively. The predicted oral bioavailability corresponded well with the oral bioavailability for both formulations, demonstrating that the combination of in vitro lipolysis and microsomal stability can quantitatively predict oral bioavailability of BEX. In vivo intestinal lymphatic uptake was also assessed for the formulations and resulted in <1% of the dose, which confirmed that liver microsomal stability was necessary for correct prediction of the bioavailability.

Lipophilic activated ester prodrug approach for drug delivery to the intestinal lymphatic system

The intestinal lymphatic system plays an important role in the pathophysiology of multiple diseases including lymphomas, cancer metastasis, autoimmune diseases, and human immunodeficiency virus (HIV) infection. It is thus an important compartment for delivery of drugs in order to treat diseases associated with the lymphatic system. Lipophilic prodrug approaches have been used in the past to take advantage of the intestinal lymphatic transport processes to deliver drugs to the intestinal lymphatics. Most of the approaches previously adopted were based on very bulky prodrug moieties such as those mimicking triglycerides (TG). We now report a study in which a lipophilic prodrug approach was used to efficiently deliver bexarotene (BEX) and retinoic acid (RA) to the intestinal lymphatic system using activated ester prodrugs. A range of carboxylic ester prodrugs of BEX were designed and synthesised and all of the esters showed improved association with chylomicrons, which indicated an improved potential for delivery to the intestinal lymphatic system. The conversion rate of the prodrugs to BEX was the main determinant in delivery of BEX to the intestinal lymphatics, and activated ester prodrugs were prepared to enhance the conversion rate. As a result, an 4-(hydroxymethyl)-1,3-dioxol-2-one ester prodrug of BEX was able to increase the exposure of the mesenteric lymph nodes (MLNs) to BEX 17-fold compared to when BEX itself was administered. The activated ester prodrug approach was also applied to another drug, RA, where the exposure of the MLNs was increased 2.4-fold through the application of a similar cyclic activated prodrug. Synergism between BEX and RA was also demonstrated in vitro by cell growth inhibition assays using lymphoma cell lines. In conclusion, the activated ester prodrug approach results in efficient delivery of drugs to the intestinal lymphatic system, which could benefit patients affected by a large number of pathological conditions.