Quantification of tea-derived catechins without the requirement for respective calibration curves by single reference liquid chromatography based on relative molar sensitivity

Plasma Gel Matrix as a Promising Carrier of Epigallocatechin Gallate for Regenerative Medicine

Plasma gel (PG) is a protein matrix prepared from platelet-poor plasma and can be utilized as a drug carrier for controlled release. We previously demonstrated its applicability as a carrier of polyphosphate. Epigallocatechin-3-gallate (EGCG) is the main flavonoid found in green tea and functions as a strong antioxidant. To explore the applicability of PG as an EGCG carrier, we examined the release of EGCG from the PG matrix using an in vitro system. Pooled platelet-poor plasma (PPP) was prepared from four healthy adult male donors, mixed with EGCG, and heated at 75 °C for 10 or 20 min to prepare the PG matrix. The PG-EGCG matrix was incubated in PBS at 37 °C, and the EGCG released into PBS was determined using spectrophotometry. The antioxidant capacity was determined based on the principle of the iodine decolorization reaction. EGCG precipitated and incorporated into the PG matrix during thermal preparation. Trypsin, used to simulate the in vivo degradation of PG, released EGCG from the PG matrix over time. The released EGCG maintained its antioxidant capacity during incubation. These results indicate that thermally prepared PG matrices can be utilized as a promising EGCG carrier in the fields of tissue engineering and regenerative medicine.

Development of a useful single-reference HPLC method for therapeutic drug monitoring of phenytoin and carbamazepine in human plasma

A single reference high-performance liquid chromatographic (SR-HPLC) method was developed and validated for the therapeutic drug monitoring (TDM) of phenytoin (PHT) and carbamazepine (CBZ) in plasma from patients. The analytical parameters evaluated were linearity, limit of quantification (LOQ), selectivity, accuracy, and stability according to the US Food and Drug Administration (FDA) guideline. The developed method shows good linearity (r2 > 0.999; LOQ-50 µg/mL), and LOQ values were 1.56 µg/mL for PHT and 0.40 µg/mL for CBZ at 254 nm. For the development of SR-HPLC method, we evaluated to improve the detection wavelength, stirred retention time, and stability for SR, and selected 5-(p-methylphenyl)-5-phenylhydantoin for PHT (relative molar sensitivity, RMS = 0.848) and 10-methoxyiminostilbene for CBZ (RMS = 0.263). The established differential definite quantities of PHT and CBZ in plasma samples were similar using the RMS and absolute calibration methods based on RSD < 5.10%. A preliminary application was performed using chemiluminescent immunoassay and SR-HPLC method, in which the detectable values of the correlation coefficient and the slope of the intercept were PHT: 0.964 and 0.992647, and CBZ: 0.969 and 1.072089, respectively. Based on these results, we propose that the SR-HPLC method with RMS would be offered to the useful and accurate TDM of various medicines in plasma/serum samples.

Study on the Synthesis of Methylated Reference and Their Application in the Quantity of Curcuminoids Using Single Reference Liquid Chromatography Based on Relative Molar Sensitivity

We report on the recommendation of the simple and versatility of methylated reference (MR) to improve applications in the single reference (SR)-LC based on relative molar sensitivity (RMS). Three curcuminoids (Curs) such as curcumin, demethoxycurcumin and bisdemethoxycurcumin in turmeric products were determined using authentic standards and methylated curcumin. In addition, high-speed countercurrent chromatography (HSCCC) purification is necessary to separate Curs for indicating the RMS. For HSCCC separation, a biphasic solvent system was used to obtain these fractions, which were then subjected to ¹H quantitative NMR to determine their contents in each test solution. Using these solutions, the RMS of Curs are calculated from slopes ratios of calibration curves (three ranges from 0-100 µmol/L, r² > 0.998). The averaged RMS of Curs were 8.92 (relative standard deviation (RSD), 1.17%), 8.97 (2.18%), and 9.61 (0.77%), respectively. Cur concentrations in turmeric products can be determined using RMS, peak area, and MR content added in these samples. This proposed method, which is based on chemical methylation and the SR-LC assay has been successfully applied for the simple and reliable estimation of Curs in turmeric products.