To explore the effect and related regulatory mechanism of hawthorn leaf flavonoids (FHL) on cardiac function in rats with acute myocardial infarction (AMI).

Sixty SPF male Sprague-Dawley rats (9-week-old, weighing 300-350 g) were used in this study. Ten rats were assigned to sham operation group, and the remaining 50 rats were used to establish the AMI model with coronary artery ligation method, AMI was successfully established in 36 rats. AMI rats were randomly divided into AMI group and FHL low-, medium-, and high-dose groups (n=9 for each group). Rats received intraperitoneal injection (10 ml·kg^-1·day^-1) with physiological saline and FHL solution with concentrations of 0.3, 0.6, and 1.2 mg/ml, respectively for 4 consecutive weeks. Echocardiography was performed at the end of experiments. Left ventricular end diastolic diameter (LVEDD), left ventricular end diastolic anterior wall thickness (LAWD), left ventricular ejection fraction (LVEF) and left ventricular end diastolic pressure (LVEDP) were measured. Then the rats were sacrificed under deep anesthesia, and the left ventricular anterior wall tissue was used for pathological examinations by hematoxylin-eosin (HE) staining. Other myocardial tissue was used for in situ terminal transferase labeling (TUNEL) staining, and the apoptosis rate of cardiomyocytes was calculated. The myocardial cell apoptosis rate, the mRNA, and protein expressions of phosphatidylinositol 3β-kinase (PI3K), protein kinase B (Akt), glycogen synthetase kinase-3 (GSK3β), cyclin D1 and the protein expressions of p-Akt and p-GSK3β were detected by real-time fluorescent quantitative PCR (RT-qPCR) and Western blot respectively.

Compared with sham operation group, the LVEDD and LVEDP of the rats in AMI group and FHL low-, medium-and high-dose groups were increased, and the LAWD and LVEF were reduced (all P<0.05). Compared with AMI group, LVEDD and LVEDP were reduced, and LAWD and LVEF were increased in FHL low-, medium-and high-dose groups (allP<0.05). LVEDD and LVEDP decreased, and LAWD and LVEF increased in proportion to the increase of FHL dose (allP<0.05). LVEDD and LAWD values were similar between FHL low-dose and medium-dose groups (bothP>0.05). HE staining results evidenced necrotic myocardial tissue, together with disordered arrangement of myocardial fibers, and a large number of inflammatory cells infiltrated in the myocardial tissue in AMI group. The myocardial damage of rats in FHL low-, medium-, and high-dose groups was less than that of AMI group. The myocardial fibers were arranged neatly, but there were still partial breaks and a small amount of inflammatory cell infiltration in the myocardial tissue and there were scattered islands of normal myocardial tissue in the infarct area of these groups. Among them, myocardial damage was the least in FHL high-dose group. The results of TUNEL staining showed that compared with AMI group, the apoptosis rate of myocardial cells was significantly reduced in FHL low-, medium-, and high-dose groups (allP<0.001), but was still higher than that in sham operation group (allP<0.001). Myocardial cell apoptosis rate decreased in proportion with increasing FHL dose (P<0.05). The RT-qPCR results showed that compared with AMI group, the expression levels of PI3K and cyclin D1 mRNA were significantly upregulated in the myocardial tissue of rats in FHL low-, medium-, and high-dose groups, but still lower than those in sham operation group (allP<0.05), and PI3K and cyclin D1 mRNA expression levels increased with the increase dose of FHL (P<0.05). Western blot results showed that compared with AMI group, the expression levels of PI3K, p-Akt, p-GSK3β, and cyclin D1 were significantly upregulated in the myocardial tissue of rats in FHL low-, medium-, and high-dose groups, but still lower than those in sham operation group (allP<0.05), and the protein expression levels of PI3K, p-Akt, p-GSK3β, and cyclin D1 increased in proportion with the increase dose of FHL (allP<0.05).

FHL can effectively improve cardiac function in rats with AMI, and the beneficial effects may be partly mediated through activating PI3K/GSK3β/cyclin D1 signaling pathway.

Myocardial infarction; Heart function; Hawthorn leaves total flavonoids