Quantification of triiodothyronine and thyroxine in rat serum using liquid chromatography tandem mass spectrometry

Chiral LC-MS/MS method for the discrimination of triiodothyronine enantiomers on a crown ether-based chiral stationary phase

Considering the greater pharmaceutical and clinical interest of triiodothyronine (T3 ) thyroid hormone, an effective D/L-T3 enantiomer separation was performed on a crown ether-based chiral stationary phase by LC-MS/MS. In optimal analytical condition and selected reaction monitoring mode, the two enantiomers of T3 were baseline separated within 10 min. The limit of detection and limit of quantitation were found to be 0.05 and 0.10 ng/μl; 0.20 and 0.50 ng/μl for D- and L-T3 , respectively. During validation, this method proved to be feasible, accurate as well as enantioselective and sensitive for the resolution of T3 enantiomers. For commercial D- and L-T3 chemicals, the enantiomeric impurities as the other enantiomer were 0.11% and 4.61%. On the other hand, the impurity as D-T3 for commercial pharmaceutical products (liothyronine sodium tablets, two suppliers) was 0.68% and 6.57%.

An optimized radioimmunoassay for quantification of total serum thyroxine (T4) in fetal, neonatal, and pregnant rats

Identifying xenobiotics that interrupt the thyroid axis has significant public health implications, given that thyroid hormones are required for brain development. As such, some developmental and reproductive toxicology (DART) studies now require or recommend serum total thyroxine (T4) measurements in pregnant, lactating, and developing rats. However, serum T4 concentrations are normally low in the fetus and pup which makes quantification difficult. These challenges can be circumvented by technologies like mass spectrometry, but these approaches are expensive and not always widely available. To demonstrate the feasibility of measuring T4 using a commercially available assay, we examine technical replicates of rat serum samples measured both by liquid chromatography mass spectrometry (LC/MS/MS) and radioimmunoassay (RIA). These samples were obtained from rats on gestational day 20 (dams and fetuses) or postnatal day 5 (pups), following maternal exposure to the goitrogen propylthiouracil (0-3 ppm) to incrementally decrease T4. We show that with assay modification, it is possible to measure serum T4 using low sample volumes (25-50 μL) by an RIA, including in the GD20 fetus exposed to propylthiouracil. This proof-of-concept study demonstrates the technical feasibility of measuring serum T4 in DART studies.

Therapeutic drug monitoring of caffeine and its primary metabolites in plasma using LC-ESI-MS/MS for apnea of prematurity treatment: Evaluation of ultrapure water as a surrogate matrix

The growing evidence has endorsed the view that therapeutic drug monitoring (TDM) of caffeine for apnea of prematurity is helpful for dose tailoring when the therapeutic response is lacking or toxicity is suspected. However, the plasma without caffeine is difficult to obtain. Therefore, a method was developed and validated to measure caffeine and its three primary metabolites (paraxanthine, theobromine, and theophylline) using LC-ESI-MS/MS in human plasma and several surrogate matrices. The chromatographic separation of analytes was finally achieved on a Waters Symmetry C18 (4.6 × 75 mm, 3.5 μm) column. Several strategies were successfully applied to overcome the matrix effects: 1) appropriate dilution for sample cleanup; 2) a starting lower proportion of organic phase; 3) multiple individual stable-labeled isotopic internal standards. The parallelism between the authentic matrix and surrogate matrices was convincing. The recovery of the analytes in both human plasma and rat plasma was acceptable over the linear range (0.500 to 50.0 μg/mL for caffeine, and 0.0100 to 1.00 μg/mL for three metabolites). The method was successfully applied in 118 samples from 74 preterm infants with apnea of prematurity. The rat plasma or ultrapure water as surrogate matrix is worthy of being recommended for routine TDM of caffeine.

Determining nonesterified and total docosahexaenoic acid and eicosapenaenoic acid concentrations by LC-MS/MS in the plasma of patients with schizophrenia

Background: Nonesterified, total docosahexaenoic acid (DHA) and eicosapenaenoic acid (EPA) plasma levels were evaluated in patients with schizophrenia on different medications compared with healthy individuals using validated LC-MS/MS methods. Methods: Samples for nonesterified DHA and EPA assay were extracted in n-hexane-dichloromethane-isopropyl alcohol (2:1:0.1, V/V/V) and hydrolyzed at 90°C for 2 h before total DHA and EPA determination. Methods were validated in surrogate matrix and plasma. Results: These methods generated similar recovery for plasma (>89%) and surrogate matrix (>87%) and negligible matrix effects. Linearity, lower limit of quantification, accuracy, precision and stability were also validated. Conclusions: This study successfully determined DHA and EPA plasma levels in patients with schizophrenia and healthy individuals using validated LC-MS/MS methods. Therefore, nonesterified DHA and total EPA levels could be used as schizophrenia biomarkers.

Development and validation of an ultraperformance liquid chromatography-tandem mass spectrometry method for quantitation of total 3,3',5-triiodo-L-thyronine and 3,3',5,5'-tetraiodo-L-thyronine in rodent serum

Many environmental chemicals are known to disrupt thyroid function. Measurement of thyroid hormones in animal studies provides useful information to understand the effects of environmental chemicals on thyroid hormone metabolism. We report an efficient method, utilizing a protein precipitation followed by ultraperformance liquid chromatography-tandem mass spectrometry analysis, to quantitate total 3,3',5-triiodo-L-thyronine (triiodothyronine, T3) and total 3,3',5,5'-tetraiodo-L-thyronine (thyroxine, T4) in rodent serum. The use of synthetic serum for calibration standards eliminated the interferences from endogenous total T3 and T4 and allowed the experimental lower limits of quantitation (LOQ) to be set at the required concentration (T3, 20 ng/dL; T4, 0.5 μg/dL) to allow quantitation of endogenous concentrations. The method was linear (r>0.99; range 20.0-600 ng/dL T3, 0.500-15 μg/dL T4) with good assay recoveries (90.4-107%) for both analytes. Intra- and inter-day accuracy, estimated as percent relative error, were ≤ ±7.6% and intra- and inter-day precision, estimated as the relative standard deviation, were ≤ 5.3% for both analytes. The method may easily be adapted to a well-plate format thereby further improving the efficiency. Total T3 and T4 concentrations were stable in male and female rat and mouse serum when stored in the freezer (~ -70 °C) for up to 62 d with determined values within 92.8-111% of day 0 for both analytes. The method can be extended to quantitate total T3 and T4 concentrations in humans or other species with minimal optimization.