Abstract
Tyrosine and phenolic ring de-iodination of thyroid hormones (TH) is crucial for regulating their physiological activity. Furthermore, reactions such as de-carboxylation to thyronamines (TAM) and de-amination to thyroacetic acids (TAc) produce TH metabolites (THM) with distinct biological properties. This needs to be considered when studying effects of TH and THM. The accurate and precise quantitative analysis of TH and THM in cell culture supernatants and cell lysates are key procedures required for studying the in vitro metabolism of TH. We report here the development of a liquid-liquid extraction/isotope dilution-liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS) method for the quantification of 9 thyronines (TN) and 6 TAM in human hepatocellular carcinoma Hep G2 cell lysate extracts. In addition, we adapted the method to quantify TH, TAM and TAc, in cell lysates of FBS-depleted rat thyroid epithelium PCCL3 cells. The methods for both cell lines were validated by rigorous assessment of linearity, limits of quantification and detection (LLOQ and LLOD respectively), intra- and inter-day accuracy, precision, process efficiency (PE), matrix effect (ME) and relative recovery (RE). Calibration curves covering 11 concentrations (based on 400 μl of lysate) were linear in the range 0.016–50 nM and 0.010–50 nM for Hep G2 and PCCL3 cells respectively. The lower limits of quantification were in the range 0.031 to 1 nM. We applied the PCCL3 version of the LC-MS/MS method to the analysis of lysed cell extracts from PCCL3 cells that had been incubated with 3-iodo-L-thyronine (T1), 3-iodothyronamine (3-T1AM) and 3-iodothyroacetic acid (3-T1Ac). Over the course of 30 minutes incubation 3-T1AM was de-iodinated to 4-[4-(2-aminoethylphenoxy)]phenol (thyronamine, T0AM) and de-aminated to 3-T1Ac respectively, whilst T1 underwent de-iodination to T0. This data indicates avid metabolism of these mono-iodinated compounds and the utility of LC-MS/MS to quantify such cellular metabolism.
Highlights
The thyroid hormone (TH) 3,5,3’-triiodo-L-thyronine (T3) regulates a variety of processes that ensure proper development, growth and metabolism
We recently reported a preliminary adaption of the above method to analyse a limited number of TN (T4, T3 and rT3) in Madin-Darby canine kidney 1 cell lysate extracts as part of a study on molecular characterization of monocarboxylate transporters involved in cellular thyroid hormones (TH) uptake and efflux [13]
Representative chromatograms for TAM and TN in Hep G2 and for TAM, TN and thyroacetic acids (TAc) in PCCL3 cell lysate extracts are displayed in Figs 2 and 3 respectively
Summary
The thyroid hormone (TH) 3,5,3’-triiodo-L-thyronine (T3) regulates a variety of processes that ensure proper development, growth and metabolism. TH metabolites (THM, see Fig 1.) include thyronamines (TAM), resulting from TH de-carboxylation, and thyroacetic acids (TAc) resulting from the deamination of TAM. Some of these THM are endogenous and possess biological activity [4,5,6,7]. The mechanisms of action of TH and THM in cell culture systems in vitro are of high scientific interest; uptake, release and intracellular metabolism affect their bioavailability or may lead to the formation of products with their own distinct biological activity in the experimental system. The development of a validated and convenient analytical method for TH, TAM and TAc in cell extracts in vitro is of major importance
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