Abstract
A specific ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method has been developed for the simultaneous determination of six Uncaria alkaloids in mouse blood with midazolam as the internal standard (IS). Only 20 μL blood was needed for sample preparation, and the protein was precipitated with acetonitrile. The UPLC BEH C18 column (2.1 mm × 100 mm, 1.7 μm) was used for chromatographic separation. The mobile phase consisted of 0.1% formic acid and acetonitrile with gradient elution within 5.5 min. Multiple reaction monitoring (MRM) and the positive electrospray ionization model were used for quantitative analysis. The accuracy of the UPLC-MS/MS method ranged from 86.5% to 110.4%. The precision for intraday and interday was ≤15% each. The mean recovery and the matrix effects were found to be 64.4-86.8% and 94.1-109.4%, respectively. The calibration curves in blood were linear in the range of 1-1000 ng/mL with a favorable correlation coefficient (r2) of 0.995. The pharmacokinetic results showed that six Uncaria alkaloids metabolized rapidly in mice with a half-life between 0.6 h and 4.4 h. The bioavailability of corynoxeine, isocorynoxeine, rhynchophylline, isorhynchophylline, hirsutine, and hirsuteine was 27.3%, 32.7%, 49.4%, 29.5%, 68.9%, and 51.0%, respectively, which showed satisfactory oral absorption of each alkaloid.
Highlights
Uncaria is a dry hooked branch of Rubiaceae, and it is a traditional Chinese medicine
No interfering endogenous substances were found at the retention time of the analytes and internal standard (IS)
In the optimization of mass spectrometry detection methodologies, we examined the sensitivity of the positive and negative electrodes
Summary
Uncaria is a dry hooked branch of Rubiaceae, and it is a traditional Chinese medicine. It has been included in the Chinese Pharmacopoeia; for example, Uncaria rhynchophylla. The alkaloid content in Hook Vine varies greatly due to the variety, geographical environment, rain, and harvest season. Even if it is the same medicinal material, the alkaloid content varies greatly because of the different parts (the part of the hooked stem branches are the most). Close to a hundred alkaloids have been identified in Hook Vine, among which the main indole alkaloids include rhynchophylline, isorhynchophylline, corynoxeine, and isocorynoxeine, and the main nonoxidized indole alkaloids include hirsutine and hirsuteine. Modern pharmacological studies have shown that Uncaria alkaloids have antihypertensive, vasodilating, neuroprotective, antidepressant, antiarrhythmic, antiepileptic, and antitumor activities [1, 2]
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