Cerebral ischemia-reperfusion injury (CIRI) is a secondary injury of ischemic stroke with higher morbidity, disability, and recurrence rates for adults worldwide. Severe CIRI can lead to irreversible ischemic nervous tissue damage in a short time (Yao et al., 2022; Deng et al., 2022). It is a great challenge to find effective therapeutic strategies for curing CIRI. To date, a large amount of chemical components or extracts of traditional Chinese medicines (TCMs) have been reported as an effect of improvement on CIRI. Thymus quinquecostatus Celak., a member of thymus genus in Lamiaceae family, has been used as a folk medicine for relieving exterior syndrome and alleviating pain in Northwest China (Shaanxi Revolutionary Committee Health Bureau commercial Bureau, 1971). In addition, it was reported to have good antioxidant activity in both its essential oils and ethanol extracts in our previous work. (He et al., 2020; Yan et al., 2021). Meanwhile, the polyphenol-rich fraction (PRF), a non-volatile ethanol extract, have been researched in our previous work (Fan et al., 2021). The primary chemical components were identified by HPLC-MS. The quality control of PRF was also established. In addition, PRF could significantly improve CIRI by activating Keap1/Nrf2/HO-1 signaling pathway. The anti-CIRI effect of PRF is closely associated with its abundant flavonoids and phenolic acids, the components absorbed into blood and brain as well as their PK-PD properties are still obscure, which hinders further application to prevent and improve CIRI.

Pharmacokinetic-pharmacodynamic (PK-PD) model is a useful tool for exploring dynamic changes of chemical components and evaluating the effects of drugs on pathological processes (Zhang et al., 2016; Zhu et al., 2023). In general, the PK indicative components are selected as the representative of TCMs or their prescription, which often can be absorbed into blood, quantified continuously, or show related effects (Yao et al., 2018). Similarly, the selection of PD indicators should be closely related to the drug effect with a certain dose-effect relationship and the characteristics of continuous quantification and repeatability. In addition, the fitting of PK-PD models for TCM is also difficult. At present, most studies on PK-PD binding models still rely on pharmacokinetic software, such as classical PK compartmental models (one and two compartments) combined with PD models such as Emax and Sigmoid Emax by indirect connection (Chen et al., 2022; Cheng et al., 2018;T. T. Liu et al., 2021; ). Therefore, it is necessary to develop and apply superior methods for the PK-PD research of TCMs. Artificial neural network (ANN), a modeling method based on the analysis of biological neural network systems, has the characteristics of high fault tolerance, generalization ability, intelligence, and autonomous learning, which has good advantages for dealing with nonlinear and complex models in TCM research (Othman et al., 2023; Grebner et al., 2021).

The classic PD index is usually a determined and limited biochemical measurement that is probably not relevant to the biological responses induced at the target organ directly (Yan et al., 2018). Metabolomics is a comprehensive tool for simultaneously monitoring and analyzing the changes of endogenous metabolites involved with a variety of metabolic pathway disorders (Wu et al., 2022). It has been widely used for the exploration of potential biomarkers, which further elucidated the regulatory effect of drugs (Morad et al., 2022; Qiu et al., 2023). Meanwhile, the identification of potential biomarkers is advantageous for early detection, proactive intervention, and subsequent innovative therapies against CIRI in clinical settings. Therefore, the combination of PK-PD correlation and metabolomics will give a better understanding of the mechanism of PRF anti-CIRI.

In the present study, the metabolism profile and PK-PD modeling studies were researched and accessed. Besides, the possible underlying mechanism of PRF in the prevention and reduction risk of CIRI rats was explored preliminarily. To sum up, this research provides a convincing foundation to develop PRF of T. quinquecostatus Celak. into therapeutic products in the maintenance of human health disorders.