Evaluation of the relationship between a pharmaceutical compound's distribution coefficient, log D and adsorption loss to polypropylene in urine and CSF

Impact of introducing a new biological matrix into a validated bioanalytical method: Focus on matrix protein content

International guidance on bioanalytical method validation recommends the practice of partial validation when introducing a new matrix from the same species into a previously fully validated assay. Planning the partial validation protocol should include an evaluation of analyte chemistry, consideration of sample container materials, and a comparison of properties between the relevant biological matrices. Transition of a serum/plasma-validated bioanalytical method to analysis from a low-protein matrix, such as urine, cerebral spinal fluid, or oral fluid can result in inconsistent analyte recovery. The low recovery can potentially be mistaken for signal suppression or lack of drug stability and may be more pronounced in low-concentration or low-volume samples. In addition, adsorption and absorption interactions with containers may be exacerbated in low-protein matrices. Several possibilities exist for mitigating the impact of non-specific binding and low-protein matrices, including surfactants, bovine serum albumin, and β-cyclodextrin. Finally, higher matrix protein can facilitate analyte stability. Given all this, matrix protein content should not be overlooked when anticipating a partial bioanalytical method validation.

An LC-ESI-MS/MS method for determination of ondansetron in low-volume plasma and cerebrospinal fluid: Method development, validation, and clinical application

Ondansetron is used in clinical settings as an antiemetic drug. Although the animal studies showed its potential effectiveness also in treating neuropathic pain, the results from humans are inconclusive. The lack of efficacy of ondansetron in a subset of patients might be due to the overexpression of P-glycoprotein, which could result in low concentrations of ondansetron in the central nervous system (CNS). A surrogate of the CNS exposure might be drug concentration in the cerebrospinal fluid (CSF), especially in humans, as assessing the drug disposition directly in the patient's brain would be challenging. The study aimed to develop a sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to determine concentrations of ondansetron in human K3EDTA plasma and CSF. Ondansetron was extracted from biological matrices by liquid-liquid extraction. The quantification was performed on a Sciex QTRAP 6500+ mass spectrometer with labeled ondansetron as an internal standard. The calibration range was 0.25-350 ng/mL in plasma and 0.025-100 ng/mL in CSF; for both matrices, 25 µL of samples was required for the assays. The method was validated according to the FDA and EMA guidelines and showed acceptable results. A pilot study confirmed its suitability for clinical samples: after 4-16 mg of intravenous ondansetron, the determined concentrations in plasma were 1.22-235.90 ng/mL, while in CSF - 0.018-11.93 ng/mL. In conclusion, the developed method fulfilled all validation requirements and can be applied to pharmacokinetic studies assessing the CNS ondansetron exposure in humans. The method's advantages, such as a low volume of matrix and a wide calibration range, support its use in a study in which rich sampling and various drug doses are expected.

A Practical Perspective on the Evaluation of Small Molecule CNS Penetration in Drug Discovery

The separation of the brain from blood by the blood-brain barrier and the bloodcerebrospinal fluid (CSF) barrier poses unique challenges for the discovery and development of drugs targeting the central nervous system (CNS). This review will describe the role of transporters in CNS penetration and examine the relationship between unbound brain (Cu-brain) and unbound plasma (Cu-plasma) or CSF (CCSF) concentration. Published data demonstrate that the relationship between Cu-brain and Cu-plasma or CCSF can be affected by transporter status and passive permeability of a drug and CCSF may not be a reliable surrogate for CNS penetration. Indeed, CCSF usually over-estimates Cu-brain for efflux substrates and it provides no additional value over Cu-plasma as the surrogate of Cu-brain for highly permeable non-efflux substrates. A strategy described here for the evaluation of CNS penetration is to use in vitro permeability, P-glycoprotein (Pgp) and breast cancer resistance protein efflux assays and Cu-brain/Cu-plasma in preclinical species. Cu-plasma should be used as the surrogate of Cu-brain for highly permeable non-efflux substrates with no evidence of impaired distribution into the brain. When drug penetration into the brain is impaired, we recommend using (total brain concentration * unbound fraction in the brain) as Cu-brain in preclinical species or Cu-plasma/in vitro Pgp efflux ratio if Pgp is the major limiting mechanism for brain penetration.

LC-MS/MS quantification of 7α-hydroxy-4-cholesten-3-one (C4) in rat and monkey plasma

7α-hydroxy-4-cholesten-3-one (C4) is an oxidative enzymatic product of cholesterol metabolism via cholesterol 7α-hydroxylase, an enzyme also known as cholesterol 7-alpha-monooxygenase or cytochrome P450 7A1 (CYP7A1). C4 is a stable intermediate in the rate limiting pathway of bile acid biosynthesis. Previous studies showed that plasma C4 levels correlated with CYP7A1 enzymatic activity and could serve as a biomarker for bile acid synthesis. Here we developed and qualified a simple and robust high-throughput method using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) to quantify C4 in rat and monkey plasma. As C4 being an endogenous compound, this method used calibration standards in 50/50: acetonitrile/water (v/v). In order to mimic the incurred samples, quality control samples were prepared in the authentic plasma. Stable isotope labeled C4 (C4-d₇) was used as the internal standard. The sample volume for analysis was 20μL and the sample preparation method was protein precipitation with acetonitrile. The average endogenous C4 concentrations, from 10 different lots of rat and monkey plasma, were 53.0±16.5ng/mL and 6.8±5.6ng/mL, respectively. Based on these observed endogenous C4 levels, the calibration curve ranges were established at 1-200ng/mL and 0.5-100ng/mL for rat assay and monkey assay, respectively. The method was qualified with acceptable accuracy, precision, linearity, and specificity. Matrix effect, recovery, and plasma stability of bench-top, freeze-thaw, and long-term frozen storage were also evaluated. The method has been successfully applied to pre-clinical studies.

Lipidomic Evaluation of Feline Neurologic Disease after AAV Gene Therapy

GM1 gangliosidosis is a fatal lysosomal disorder, for which there is no effective treatment. Adeno-associated virus (AAV) gene therapy in GM1 cats has resulted in a greater than 6-fold increase in lifespan, with many cats remaining alive at >5.7 years of age, with minimal clinical signs. Glycolipids are the principal storage product in GM1 gangliosidosis whose pathogenic mechanism is not completely understood. Targeted lipidomics analysis was performed to better define disease mechanisms and identify markers of disease progression for upcoming clinical trials in humans. 36 sphingolipids and subspecies associated with ganglioside biosynthesis were tested in the cerebrospinal fluid of untreated GM1 cats at a humane endpoint (∼8 months), AAV-treated GM1 cats (∼5 years old), and normal adult controls. In untreated GM1 cats, significant alterations were noted in 16 sphingolipid species, including gangliosides (GM1 and GM3), lactosylceramides, ceramides, sphingomyelins, monohexosylceramides, and sulfatides. Variable degrees of correction in many lipid metabolites reflected the efficacy of AAV gene therapy. Sphingolipid levels were highly predictive of neurologic disease progression, with 11 metabolites having a coefficient of determination (R²) > 0.75. Also, a specific detergent additive significantly increased the recovery of certain lipid species in cerebrospinal fluid samples. This report demonstrates the methodology and utility of targeted lipidomics to examine the pathophysiology of lipid storage disorders.

A validated LC-MS/MS assay for quantification of 24(S)-hydroxycholesterol in plasma and cerebrospinal fluid

24(S)-hydroxycholesterol [24(S)-HC] is a cholesterol metabolite that is formed almost exclusively in the brain. The concentrations of 24(S)-HC in cerebrospinal fluid (CSF) and/or plasma might be a sensitive marker of altered cholesterol metabolism in the CNS. A highly sensitive 2D-LC-MS/MS assay was developed for the quantification of 24(S)-HC in human plasma and CSF. In the development of an assay for 24(S)-HC in CSF, significant nonspecific binding of 24(S)-HC was observed and resolved with the addition of 2.5% 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) into CSF samples. The sample preparation consists of liquid-liquid extraction with methyl-tert-butyl ether and derivatization with nicotinic acid. Good linearity was observed in a range from 1 to 200 ng/ml and from 0.025 to 5 ng/ml, for plasma and CSF, respectively. Acceptable precision and accuracy were obtained for concentrations over the calibration curve ranges. Stability of 24(S)-HC was reported under a variety of storage conditions. This method has been successfully applied to support a National Institutes of Health-sponsored clinical trial of HP-β-CD in Niemann-Pick type C1 patients, in which 24(S)-HC is used as a pharmacodynamic biomarker.