Measurement of kynurenine pathway metabolites by tandem mass spectrometry

Objectives

Recent studies have shown that derangements in kynurenine pathway metabolite levels are associated with various pathologies such as neurodegenerative diseases, schizophrenia, depression, bipolar disorder, rheumatoid arthritis, and cancer. Therefore, reliable, accurate, fast, and multiplex measurement methods for kynurenines have become increasingly important. This study aimed to validate a new mass spectrometric method for analyzing tryptophan metabolites.

Methods

A tandem mass spectrometric method, including protein precipitation and evaporation steps, was developed to measure serum levels of tryptophan, kynurenine, kynurenic acid, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid. Samples were separated using a Phenomenex Luna C18 reversed-phase column. The kynurenine pathway metabolites were detected by tandem mass spectrometry. The developed method was validated according to Clinical & Laboratory Standards Institute (CLSI) guidelines and applied to hemodialysis samples.

Results

The developed method was linear at the concentrations of 48.8 - 25,000, 0.98 - 500, 1.2-5000, 1.2-5000, and 0.98-250 ng/mL for tryptophan, kynurenic acid, kynurenine, 3-hydroxyanthranilic acid, and 3-hydroxykynurenine, respectively. The imprecisions were less than 12 %. The median serum concentrations of tryptophan, kynurenine, kynurenic acid, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid were 10530, 1100, 218, 17.6, and 25.4 ng/mL in pre-dialysis blood samples, respectively. They were 4560, 664, 135, 7.4, and 12.8 ng/mL in post-dialysis blood samples, respectively.

Conclusions

A fast, simple, cost-effective, accurate, robust, and validated tandem mass spectrometric method was developed, and the method was successfully used for the quantitation of kynurenine pathway metabolite concentrations in hemodialysis patients.

From fundamentals in calibration to modern methodologies: A tutorial for small molecules quantification in liquid chromatography-mass spectrometry bioanalysis

Over the last two decades, liquid chromatography coupled to mass-spectrometry (LC‒MS) has become the gold standard to perform qualitative and quantitative analyses of small molecules. When quantitative analysis is developed, an analyst usually refers to international guidelines for analytical method validation. In this context, the design of calibration curves plays a key role in providing accurate results. During recent years and along with instrumental advances, strategies to build calibration curves have dramatically evolved, introducing innovative approaches to improve quantitative precision and throughput. For example, when a labeled standard is available to be spiked directly into the study sample, the concentration of the unlabeled analog can be easily determined using the isotopic pattern deconvolution or the internal calibration approach, eliminating the need for multipoint calibration curves. This tutorial aims to synthetize the advances in LC‒MS quantitative analysis for small molecules in complex matrices, going from fundamental aspects in calibration to modern methodologies and applications. Different work schemes for calibration depending on the sample characteristics (analyte and matrix nature) are distinguished and discussed. Finally, this tutorial outlines the importance of having international guidelines for analytical method validation that agree with the advances in calibration strategies and analytical instrumentation.

The Origin-Adjusted Approach for Reliable Quantification of Endogenous Analytes in Mass Spectrometric Bioanalysis

The reliably accurate and precise quantification of biomarkers is a priceless objective in the drug development and diagnostic arenas. To employ a technique that brings such reliability and furthermore involves a simpler, faster, and inexpensive regime would only underline the potential importance of the concept and technique. To the existing established approaches for biomarker quantification in bioanalytical LC-MS, surrogate matrix (SUR-M) and surrogate analyte (SUR-A), in this Letter we present an approach that fulfills the aforementioned advantages. The concept builds on the historic method of standard addition (SA), in which one source of biological matrix is spiked with analyte to form a calibration curve. With the SA curve back-calculated, the heart of this procedure is the subsequent adjustment of the intercept to zero, the origin, and using only the slope of the curve for interpolation giving calculated sample concentrations. In SA, the concentration axis intercept indicates the endogenous analyte concentration, and our zeroing of this is equivalent to removing the endogenous level. This key shift of the calculated line to the origin unveils our novel origin-adjusted (OA) approach. It enables use akin to a regular xenobiotic method, with no need to ultimately account for the endogenous analyte level in the control matrix used for calibrants. We present a comparison of OA against the control approach of SUR-M in a representative application for kynurenine and tryptophan in human plasma by LC-MS. A numerical performance analysis performed is demonstrative of equivalence between the two approaches for both analytes.

Internal calibration as an emerging approach for endogenous analyte quantification: Application to steroids

The use of mass spectrometry methods with triple quadrupole instruments is well established for quantification. However, the preparation of calibration curves can be time-consuming and prone to analytical errors. In this study, an innovative internal calibration (IC) approach using a one-standard calibration with a stable isotope-labeled (SIL) standard version of the endogenous compound was developed. To ensure optimal quantitative performance, the following parameters were evaluated: the stability of the analyte-to-SIL response factor (RF), the chemical and isotopic purities of the SIL, and the instrumental reproducibility. Using six clinically important endogenous steroids and their respective SIL standards, we demonstrated that RFs obtained on different LC-MS platforms were consistent. The quantitative performance of the proposed approach was determined using quality control samples prepared in depleted serum, and showed both satisfactory precision (1.3%-12.4%) and trueness (77.5%-107.0%, with only 3 values outside ±30%). The developed method was then applied to human serum samples, and the results were similar to those obtained with the conventional quantification approach based on external calibration: the Passing-Bablok regression showed a proportional bias of 6.8% and a mean difference of -5.9% between the two methodologies. Finally, we showed that the naturally occurring isotopes of the SIL can be used to provide additional calibration points and increase the accuracy for analytes with low concentrations.

A validated surrogate analyte LC-MS/MS assay for quantification of endogenous cortisol in human whole blood

Cortisol is a steroid hormone that is frequently measured as a marker of stress, inflammation, and immune function. While commonly analyzed in saliva, hair, blood plasma and urine, a recent trend towards whole blood-based at-home collection devices has emerged, which necessitates development of more sensitive assays for cortisol in whole blood. To support the implementation of a patient-centric sampling approach in a drug development program, a fit-for-purpose surrogate analyte-based liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for cortisol in whole blood was developed using ¹³C₃-cortisol as a surrogate analyte and cortisol-d6 as the internal standard. The surrogate analyte approach was chosen due to a lack of available cortisol-free whole blood and the absence of appropriately representative surrogate matrices. Samples were prepared using supported liquid extraction, and the LC-MS/MS analysis consisted of a 4.00 min analytical run. The method demonstrated linearity between 0.500 and 500 ng/mL of ¹³C₃-cortisol, and accuracy, precision and robustness were all acceptable per current regulatory guidance for bioanalytical method validation of chromatographic assays for cortisol- and ¹³C₃-cortisol-based quality control (QC) samples when quantified against a ¹³C₃-cortisol calibration curve. The acceptable robustness of cortisol-based QCs when quantified against a ¹³C₃-cortisol-based calibration curve also suggests parallelism between the analytes. These results indicate a viable surrogate analyte method, that is fit-for-purpose to analyze whole blood cortisol levels using a surrogate analyte LC-MS/MS approach. Evaluation of patient samples showed very promising comparability between whole blood and plasma cortisol concentrations, suggesting that whole blood could be used in place of or in addition to a plasma-based sampling protocol in clinical trials analyzing cortisol. Overall, this method presents a novel tool that is a first step in supporting the trend towards sample miniaturization and at-home sample collection, and may be readily used in clinical and diagnostic settings.

Indoleamine and tryptophan 2,3-dioxygenases as important future therapeutic targets

Conversion of tryptophan to N-formylkynurenine is the first and rate-limiting step of the tryptophan metabolic pathway (i.e., the kynurenine pathway). This conversion is catalyzed by three enzyme isoforms: indoleamine 2,3-dioxygenase 1 (IDO1), indoleamine 2,3-dioxygenase 2 (IDO2), and tryptophan 2,3-dioxygenase (TDO). As this pathway generates numerous metabolites that are involved in various pathological conditions, IDOs and TDO represent important targets for therapeutic intervention. This pathway has especially drawn attention due to its importance in tumor resistance. Over the last decade, a large number of IDO and TDO inhibitors have been developed, many of which have entered clinical trials. Here, detailed structural comparisons of these three enzymes (with emphasis on their active sites), their involvement in cellular signaling, and their role(s) in pathological conditions are discussed. Furthermore, the most important recent inhibitors described in papers and patents and involved in clinical trials are reviewed, with a focus on both selective and multiple inhibitors. A short overview of the biochemical and cellular assays used for inhibitory potency evaluation is also presented. This review summarizes recent advances on IDO and TDO as potential drug targets, and provides the key features and perspectives for further research and development of potent inhibitors of the kynurenine pathway.

A validated surrogate analyte UPLC-MS/MS assay for quantitation of TUDCA, TCDCA, UDCA and CDCA in rat plasma: Application in a pharmacokinetic study of cultured bear bile powder

Bear bile is a valuable medicinal material used in traditional Chinese medicine for over 2000 years. However, developing a substitute has become necessary because of protection measures for this endangered species. The ingredients of in vitro cultured bear bile powder (CBBP) include tauroursodeoxycholic acid (TUDCA), taurochenodeoxycholic acid (TCDCA), ursodeoxycholic acid (UDCA) and chenodeoxycholic acid (CDCA, and it has pharmacological properties that are similar to those of natural bear bile powder (NBBP). In this study, the pharmacokinetic parameters of both CBBP and NBBP were measured in rats with a new surrogate analyte LC-MS method using stable isotopes as surrogate analytes (D4-TUDCA, D4-TCDCA, D4-UDCA and D4-CDCA) with response factors validated in authentic matrix (plasma) for simultaneously monitoring the authentic analytes (TUDCA, TCDCA, UDCA and CDCA). The method validation was satisfactory for the linear regression (r, 0.9975-0.9994), precision (RSD intra-day, 0.72-9.35%; inter-day, 3.82-9.02%), accuracy (RE, -12.42-5.67%) and matrix effect (95.53-99.80%), along with analyte recovery (95.90-98.82%) and stability (89.48-101.81%) of surrogate analytes, and precision (RSD intra-day, 1.06- 11.51%; inter-day, 2.23- 11.38%), accuracy (RE, -7.40-10.76%) and stability (87.37-111.70%) of authentic analytes. We successfully applied this method to evaluate the pharmacokinetics of CBBP and NBBP in rats, which revealed the critical in vivo properties of both bear bile preparations.

Effects of combined exercise training on the inflammatory profile of older cancer patients treated with systemic therapy

Cancer-related fatigue (CRF) is a major issue in older cancer patients as it is associated with functional decline and a lower quality of life, and an increased inflammatory activity during cancer therapy is suspected to play a key role in CRF etiology. Combined aerobic and resistance exercise training is known to reduce CRF, and this could be mediated by a protective effect against this increased inflammatory activity. Hence, the main objective was to measure the effect of a 12-week combined exercise training on the inflammatory profile of older cancer patients undergoing systemic therapy. A secondary objective was to verify if there was an association between inflammatory profile and CRF.

Methods

Twenty older non-metastatic cancer patients initiating chemotherapy and/or hormone therapy were randomly assigned to 12 weeks of supervised, combined exercise or a control group (static stretching). Primary outcomes were the inflammatory profile, Indoleamine 2,3-deoxygenase activity (KYN/TRP ratio), and CRF (FACIT-F questionnaire). Control outcomes were the fasting nutritional and hormonal blood profiles, body composition (iDXA), physical activity habits (PASE questionnaire), nutritional habits (3-day log), and treatment-related variables.

Results

No worsening of the inflammatory profile was observed in both arms of the study after the intervention. No significant change in CRF was observed, although there was a trend for a reduction in the experimental group (p ​= ​0.10). Significant correlations were found at both timepoints between the KYN/TRP ratio and the delay with the previous treatment received (p ​≤ ​0.03).

Conclusion

These results suggest that exercise might have elicited a positive effect on CRF, which was not mediated by the modulation of the pro-inflammatory cytokine profile. However, the decrease in IL-6/IL-10 ratio in the exercise group might reflect a possible anti-inflammatory effect of exercise. Moreover, exploratory analyses suggest that an acute effect of chemotherapy treatments influenced the inflammatory profile measurements, which could explain the absence of change in the fasting inflammatory profile.

Metabolic Profiling of Human Plasma and Urine, Targeting Tryptophan, Tyrosine and Branched Chain Amino Acid Pathways

Tryptophan and tyrosine metabolism has a major effect on human health, and disorders have been associated with the development of several pathologies. Recently, gut microbial metabolism was found to be important for maintaining correct physiology. Here, we describe the development and validation of a UHPLC-ESI-MS/MS method for targeted quantification of 39 metabolites related to tryptophan and tyrosine metabolism, branched chain amino acids and gut-derived metabolites in human plasma and urine. Extraction from plasma was optimised using 96-well plates, shown to be effective in removing phospholipids. Urine was filtered and diluted ten-fold. Metabolites were separated with reverse phase chromatography and detected using triple quadrupole MS. Linear ranges (from ppb to ppm) and correlation coefficients (r² > 0.990) were established for both matrices independently and the method was shown to be linear for all tested metabolites. At medium spiked concentration, recovery was over 80% in both matrices, while analytical precision was excellent (CV < 15%). Matrix effects were minimal and retention time stability was excellent. The applicability of the methods was tested on biological samples, and metabolite concentrations were found to be in agreement with available data. The method allows the analysis of up to 96 samples per day and was demonstrated to be stable for up to three weeks from acquisition.

Kynurenine Pathway Metabolites as Biomarkers for Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) currently lacks a robust and well-defined biomarker that can 1) assess the progression of the disease, 2) predict and/or delineate the various clinical subtypes, and 3) evaluate or predict a patient's response to treatments. The kynurenine Pathway (KP) of tryptophan degradation represent a promising candidate as it is involved with several neuropathological features present in ALS including neuroinflammation, excitotoxicity, oxidative stress, immune system activation and dysregulation of energy metabolism. Some of the KP metabolites (KPMs) can cross the blood brain barrier, and many studies have shown their levels are dysregulated in major neurodegenerative diseases including ALS. The KPMs can be easily analyzed in body fluids and tissue and as they are small molecules, and are stable. KPMs have a Janus face action, they can be either or both neurotoxic and/or neuroprotective depending of their levels. This mini review examines and presents evidence supporting the use of KPMs as a relevant set of biomarkers for ALS, and highlights the criteria required to achieve a valid biomarker set for ALS.

Phase I Study of the Indoleamine 2,3-Dioxygenase 1 (IDO1) Inhibitor Navoximod (GDC-0919) Administered with PD-L1 Inhibitor (Atezolizumab) in Advanced Solid Tumors

PURPOSE

IDO1 induces immune suppression in T cells through l-tryptophan (Trp) depletion and kynurenine (Kyn) accumulation in the local tumor microenvironment, suppressing effector T cells and hyperactivating regulatory T cells (Treg). Navoximod is an investigational small-molecule inhibitor of IDO1. This phase I study evaluated safety, tolerability, pharmacokinetics, and pharmacodynamics of navoximod in combination with atezolizumab, a PD-L1 inhibitor, in patients with advanced cancer.

PATIENTS AND METHODS

The study consisted of a 3+3 dose-escalation stage (n = 66) and a tumor-specific expansion stage (n = 92). Navoximod was given orally every 12 hours continuously for 21 consecutive days of each cycle with the exception of cycle 1, where navoximod administration started on day -1 to characterize pharmacokinetics. Atezolizumab was administered by intravenous infusion 1,200 mg every 3 weeks on day 1 of each cycle.

RESULTS

Patients (n = 157) received navoximod at 6 dose levels (50-1,000 mg) in combination with atezolizumab. The maximum administered dose was 1,000 mg twice daily; the MTD was not reached. Navoximod demonstrated a linear pharmacokinetic profile, and plasma Kyn generally decreased with increasing doses of navoximod. The most common treatment-related AEs were fatigue (22%), rash (22%), and chromaturia (20%). Activity was observed at all dose levels in various tumor types (melanoma, pancreatic, prostate, ovarian, head and neck squamous cell carcinoma, cervical, neural sheath, non-small cell lung cancer, triple-negative breast cancer, renal cell carcinoma, urothelial bladder cancer): 6 (9%) dose-escalation patients achieved partial response, and 10 (11%) expansion patients achieved partial response or complete response.

CONCLUSIONS

The combination of navoximod and atezolizumab demonstrated acceptable safety, tolerability, and pharmacokinetics for patients with advanced cancer. Although activity was observed, there was no clear evidence of benefit from adding navoximod to atezolizumab.