Simultaneous determination of unbound thyroid hormones in human plasma using high performance frontal analysis with electrochemical detection

Development and validation of a high-performance liquid chromatography method for levothyroxine sodium quantification in plasma for pre-clinical evaluation of long-acting drug delivery systems

Levothyroxine (LEVO) sodium is an FDA-approved drug that is used to treat underactive thyroid (hypothyroidism) and other conditions. It is generally used as a thyroid-stimulating hormone administered orally. However, this approach has some drawbacks such as this drug should be taken every day 30 min to 1 h prior to breakfast with an empty stomach, moreover, some food interactions must be monitored. Thus, alternative innovative approaches capable of providing sustained LEVO release should be developed. Our research was designed to establish a simple quantitative determination method for LEVO in rat plasma for pre-clinical evaluation of long acting formulations using a high-performance liquid chromatography method, to validate the analytical method according to ICH guidelines and to characterise its pharmacokinetic behavior in rats. After simple protein precipitation with acetonitrile, LEVO was eluted on a Xselect CSH™ C18 column (Waters, 3.0 × 150 mm) with a particle size of 3.5 μm using a mobile phase of water and acetonitrile at a ratio of 65 : 35% v/v, including 0.1% v/v of trifluoracetic acid. The calibration standards used for plasma ranged between 0.5-1000 ng mL^-1 with a correlation coefficient (r²) of ≥0.998. The limit of detection was 0.44 ng mL^-1 and the lower limit of quantitation was 1.33 ng mL^-1. The extraction recovery of LEVO in rat plasma samples by this method was between 80 and 85%. The method was selective, sensitive, accurate and precise for detecting and quantifying LEVO in a pharmacokinetic study carried out in rats for pre-clinical evaluation of long acting formulations. The validated HPLC method meets the ICH established requirements and therefore offers a wide range of potential applications in pre-clinical therapeutic drug monitoring, pharmacokinetics and toxicology.

Nano optical and electrochemical sensors and biosensors for detection of narrow therapeutic index drugs

For the first time, a comprehensive review is presented on the quantitative determination of narrow therapeutic index drugs (NTIDs) by nano optical and electrochemical sensors and biosensors. NTIDs have a narrow index between their effective doses and those at which they produce adverse toxic effects. Therefore, accurate determination of these drugs is very important for clinicians to provide a clear judgment about drug therapy for patients. Routine analytical techniques have limitations such as being expensive, laborious, and time-consuming, and need a skilled user and therefore  the nano/(bio)sensing technology leads to high interest.

HPLC method for levothyroxine quantification in long-acting drug delivery systems. Validation and evaluation of bovine serum albumin as levothyroxine stabilizer

Deficiency of thyroid hormones (hypothyroidism) is treated with oral levothyroxine (LEVO). However, the effectiveness of oral administration is highly dependent on the co-administration of food and other drugs. This factor, in combination with the chronic nature of this condition, mean that there are concerns with patient compliance. Development of long acting formulations to treat hypothyroidism could potentially solve this problem. However, LEVO instability in solution could be problematic. In order to develop long acting LEVO delivery systems in vitro drug release experiments should be carried out. However, short term LEVO stability in aqueous solution will prevent this. BSA was used as a stabiliser for LEVO; extending the stability of the drug in aqueous solutions from a few hours to 2 weeks. In order to achieve this, the required concentration of the protein was 0.1% w/v. Subsequently, an HPLC method capable of separating LEVO from the protein was developed and validated following ICH guidelines. The analysis was carried out using a reverse phase HPLC method on an Agilent 1220 Infinity II LC system. The column used to achieve separation was a Zorbax Eclipse plus C18 (95 Å pore size, 250 mm length x 4.6 mm internal diameter; 5 μm particle size). The mobile phase used was composed of acetonitrile and 0.1% trifluoroacetic acid at a ratio of 50:50% v/v. UV detection of LEVO sodium was carried out at 225 nm. The retention time for the drug was 6.6 minutes. The method showed a limit of detection of 0.03 μg/mL and a limit of quantification of 0.09 μg/mL. Finally, this method was used to evaluate the release from implants containing 20% w/w of LEVO. These devices were prepared using a solvent casting method with poly(caprolactone) and LEVO. These devices showed an initial burst release over the first 3 days. Subsequently, they were capable of providing a linear release rate over the following 25 days.

Isomeric discrimination and quantification of thyroid hormones, T3 and rT3, by the single ratio kinetic method using electrospray ionization mass spectrometry

The single ratio kinetic method is applied to the discrimination and quantification of the thyroid hormone isomers, 3,5,3'-triiodothyronine and 3,3',5'-triiodothyronine, in the gas phase, based on the kinetics of the competitive unimolecular dissociations of singly charged transition-metal ion-bound trimeric complexes [M(II)(A)(ref*)(2)-H](+) (M(II) = divalent transition-metal ion; A = T(3) or rT(3); ref* = reference ligand). The trimeric complex ions are generated using electrospray ionization mass spectrometry and the ions undergo collisional activation to realize isomeric discrimination from the branching ratio of the two fragment pathways that form the dimeric complexes [M(II)(A)(ref*)-H](+) and [M(II)(ref*)(2)-H](+). The ratio of the individual branching ratios for the two isomers R(iso) is found strongly dependent on the references and the metal ions. Various sets are tried by choosing the reference from amino acids, substituted amino acids, and dipeptides in combination with the central metal ion chosen from five transition-metal ions (Co(II), Cu(II), Mn(II), Ni(II), and Zn(II)) for the complexes in this experiment. The results are compared in terms of the isomeric discrimination for the T(3)/rT(3) pair. Calibration curves are constructed by relating the ratio of the branching ratios against the isomeric composition of their mixture to allow rapid quantitative isomer analysis of the sample pair. Furthermore, the instrument-dependence of this method is investigated by comparing the two sets of results, one obtained from a quadrupole ion trap mass spectrometer and the other from a quadrupole time-of-flight mass spectrometer.

Biantennary Glycans as Well as Genetic Variants of α1-Acid Glycoprotein Control the Enantioselectivity and Binding Affinity of Oxybutynin

PURPOSE

The purpose of this study was to investigate the role of biantennary branching glycans of alpha1-acid glycoprotein (AGP) and its genetic variants in the enantioselective binding of oxybutynin (OXY).

METHOD

Human native AGP was separated using imminodiacetate-copper (II) affinity chromatography into two fractions, the A variant and a mixture of the F1 and S variants (F1-S). These fractionated AGPs were further separated by concanavalin A affinity chromatography into two fractions, with and without biantenarry glycans. An on-line high-performance liquid chromatography (HPLC) system consisting of a high-performance frontal analysis column, an extraction column, and an analytical HPLC column was developed to determine the binding affinities of OXY enantiomers for respective AGP species.

RESULTS

The total binding affinity as well as the enantiomeric selectivity of OXY in the F1-S mixed variant was significantly higher than that for the A variant, indicating that the chiral recognition ability of native AGP for the OXY enantiomers highly depends on the F1-S mixed variant. Furthermore, not only the genetic variants but also bianntenary glycans of AGP affect the binding affinity of OXY and are also responsible for the enantioselectivity.

CONCLUSIONS

Both genetic variants and glycan structures significantly contribute to the enantioselectivity and the binding affinity of OXY.