Quantitative liquid chromatography-tandem mass spectrometric analysis of 11dH-TXB2 and creatinine in urine
Platelets circulate in an inactive form in the body until they contact with defective areas of endothelial cells or encounter a clotting cascade [1]. Activated platelets release and express bioactive substances and acquire the ability to bind plasma fibrinogen. Abnormal activation of platelets is involved in atherosclerosis and thrombosis [2,3]. When platelets are stimulated and activated, phospholipase A2 is activated at the same time, which then cleaves membrane phospholipids and frees arachidonic acid (AA) [4]. The latter catalyzes thromboxane A2 (TXA2) via thromboxane synthetase [5], which is induced by the cyclooxygenase COX-1 to produce prostaglandins G2 and H2 [6]. TXA2 is highly unstable, with a half-life of only 30 s, and it is rapidly hydrolyzed to relatively stable thromboxane B2 (TXB2), which is then converted in the liver to 11-dehydrothromboxane B2 (11dH-TXB2), which has a longer half-life and is excreted in the urine [7]. Dehydrothromboxane B2 is the final stable metabolite of thromboxane A2, which is derived only from arachidonic acid metabolism and can represent thromboxane A2 level in the body [8]. Specifically, by inhibiting the action of COX-1, the most important enzyme in the process of arachidonic acid metabolism, aspirin inhibits the production of thromboxane A2, that is, the concentration of TXA2 affects the effect of aspirin on platelet aggregation. However, the half-life of TXA2 (including the metabolic intermediate TXB2) is too short to be accurately measured, so the detection of its metabolic end product 11dH-TXB2 can very accurately reflect the sensitivity of the body to aspirin [7]. The concentration of 11dH-TXB2 in the serum correlates well with the concentration of 11dH-TXB2 in the urine, so the determination of 11dH-TXB2 in the urine can more effectively reflect the production of TXA2 in vivo [8]. The 11dH-TXB2 concentration needs to be corrected with the urinary creatinine concentration to rule out the effects of the urine concentration and renal function, so random urine samples can be used for testing [6]. Aspirin can acetylate serine at the key site of cyclooxygenase and thus irreversibly inhibits the activity of COX-1, reduces the synthesis of TXA2, and blocks the production of TXA2 and its induced platelet aggregation. Low-dose aspirin (30–75 mg/day) can effectively inhibit 95% of COX-1 activity [7]. Since the production of TXA2 in serum is largely dependent on platelet COX-1 (a therapeutic target of aspirin), 11dH-TXB2 can be used as a monitor for aspirin-induced platelet inhibition [3]. Creatinine is a metabolic byproduct of muscle metabolism that is primarily excreted via glomerular filtration, and its level is indicative of renal function [9]. The 24-h creatinine clearance can also be used to determine the integrity of the sample or to correct the urine sample concentration with the creatinine ratio [10]. Currently, creatinine detection methods include the Jaffe method, enzymolysis spectrophotometry, HPLC, capillary electrophoresis, capillary zone electrophoresis, gas chromatography tandem mass spectrometry (GC-MS) and liquid chromatography tandem mass spectrometry (LC-MS/MS) [11]. At present, there is no method for the simultaneous detection of 11dH-TXB2 and creatinine. When both analytes are needed, separate tests must be performed, increasing the workload and sample volume requirements. Thus, developing a method that enables the concurrent quantification of 11dH-TXB2 and creatinine in a single assay remains a critical challenge. The aim of this study was to provide a method for the simultaneous detection of 11dH-TXB2 and creatinine and to alleviate the problem that 11dH-TXB2 and creatinine cannot be simultaneously detected. By developing a standardized quantitative approach for measuring 11dHTXB2 and creatinine in human urine, this study aims to provide reliable concentration data, thereby facilitating further clinical research and methodology optimization.