Targeted neurotransmitter metabolomics profiling of oleanolic acid in the treatment of spontaneously hypertensive rats

Abstract

Essential hypertension (EH) is a prevalent chronic medical condition and a major risk factor for cardiovascular morbidity and mortality. Neurotransmitters are involved in the physiological process of blood pressure regulation in the body. Studies have shown that oleanolic acid (OA) can effectively regulate neurotransmitter-related metabolic disorders caused by EH, but the mechanism is still unclear. Here, we studied the neurotransmitter metabolic profiles in five brain regions by targeted metabolomics approaches in spontaneously hypertensive rats (SHRs) treated with OA and vehicle. Samples from five brain regions (hippocampus, striatum, hypothalamus, temporal lobe, and frontal lobe) were collected from the control group, the spontaneously hypertensive rat (SHR) group, and the OA group. Targeted metabolomics based on UPLC-Q-Exactive-MS was employed to characterize the dramatically changed neurotransmitters in the brain regions of SHRs treated with OA and vehicle. The expressions of the key enzymes involved in the neurotransmitter metabolism were detected by the reverse transcription-polymerase chain reaction (RT-PCR). The metabolomic profiles of SHRs pre-protected by OA were significantly different from those of unprotected SHRs. A total of 18 neurotransmitters could be confirmed as significantly altered metabolites, which were involved in tyrosine and glutamate metabolism as well as other pathways. The results showing seven key enzymes in neurotransmitter metabolism further validated the changes in the metabolic pathways. OA could effectively restore tyrosine metabolism in the striatum and hypothalamus, glutamate metabolism in the hippocampus, striatum and temporal lobe, cholinergic metabolism in the striatum, and histidine metabolism in the hypothalamus due to its inhibition of inflammatory reactions, structural damage of the neuronal cells, and increase in sedative activity. This study indicated that brain region-targeted metabolomics can provide a powerful tool to further investigate the possible mechanism of OA in EH.

Fig. 1. Systolic blood pressure and diastolic blood pressure before and after 1–4 weeks of intervention (*P < 0.05, **P < 0.01 compared to the SHR group).

Fig. 2. 2D-PCA scores map (PC1 versus PC2) of the LC/MS data derived from all the brain regions of the control, SHR, and OA groups (n = 6 per group).

Fig. 3. 2D cross-validated OPLS-DA score plot of the LC/MS data derived from (A) hippocampus, (B) striatum, (C) hypothalamus, (D) temporal lobe, and (E) frontal lobe obtained from the SHR and OA group brain tissues (n = 6 per group). The OPLS-DA score plots show a clear discrimination between the SHR and OA groups in all five brain regions. Each dot represents an individual sample.

Fig. 4. Validated model plots of the LC/MS data derived from the SHR group and the OA group: (A) hippocampus, (B) striatum, (C) hypothalamus, (D) temporal lobe, and (E) frontal lobe.

Fig. 5. Potential biomarkers discovered by VIP values in the five brain regions: (A) hippocampus, (B) striatum, (C) hypothalamus, (D) temporal lobe, and (E) frontal lobe.

Fig. 6. The relative expression levels of DDC, COMT, MAO, GAD67, DβH, TH, and ACHE in the five brain regions of rats treated with OA (P < 0.05, **P < 0.01 compared to the model group).