[Tetrahydrobiopterin improves left ventricular diastolic function possibly through upregulating phosphorylated...

Objective: To investigate whether tetrahydrobiopterin (BH₄) could improve left ventricular diastolic function through phosphoinositide-3 kinase/protein kinase B (PI₃K/Akt) signaling pathway in hypertensive mice. Methods: Ten-week-old male C57BL/6 mice were used to establish the deoxycorticosterone acetate (DOCA)-salt hypertensive model, age matched Sham mice serve as the controls. Mice were divided into four groups: Sham(n=20), Sham+ BH₄ (n=20), DOCA (n=22), and DOCA+ BH₄ (n=22). On the 14 days after surgery, mice in Sham+ BH₄ and DOCA+ BH₄ groups received BH₄ (0.1 ml/10 g) supplement for 7 days, while mice in Sham and DOCA groups were given equal volume of normal saline.The blood pressure measurements were performed 7 days later.Hemodynamic and echocardiographic parameters were used to assess left ventricular functions.High performance liquid chromatography (HPLC) analysis was used to measure cardiac biopterins BH₄ and BH₂.The phosphorylated phospholamban (p-PLB) was detected by immunohistochemical staining. PI₃K, Akt and phosphorylated Akt were assayed with Western blot analysis. Results: (1) The systolic and diastolic blood pressure of DOCA group were significantly higher than control group (P<0.05). Compared with DOCA group, the systolic blood pressure was lower in DOCA+ BH₄ mice (P=0.027). Diastolic blood pressure was similar between the groups. (2) Compared with Sham group, the left ventricular diastolic function indexes such as mitral annulus velocity (E') and E'/A'ratio were significantly lower, while the E/ E'ratio was significantly higher(P<0.05)in DOCA mice. The E/ E'ratio of DOCA+ BH₄ group was significantly lower than that of DOCA group (P<0.05). Compared with Sham group, the left ventricular end-diastolic pressure (LVEDP), left ventricular end-diastolic pressure volumetric coefficient (EDPVR) and left ventricular relaxation time constant Tau index were significantly higher in DOCA mice (P=0.002, 0.011 and 0.016, respectively). The EDPVR and Tau index were significantly lower in DOCA+ BH₄ group than in DOCA group (P<0.05). (3) Compared with Sham group, the myocardial contents of BH₄ and BH₂ were significantly lower in DOCA mice (P<0.05). The BH₄ levels and BH₄/BH₂ ratio were significantly higher in Sham+ BH₄ and DOCA+ BH₄ groups than in the DOCA group (P<0.05), but the BH₂ levels were similar between groups. (4) The cGMP content, SOD activity and NO content in the left ventricular myocardial tissue were significantly lower (P<0.05), while the MDA content was significantly higher in DOCA mice than in Sham mice.The NO content and SOD activity in DOCA+ BH₄ groups were significantly higher than in the DOCA group (P<0.05). (5) Compared with DOCA group, the expression of p-PLB was significantly higher in Sham mice and lower in DOCA+ BH₄ mice (P<0.05). (6) The expression of PI₃K, Akt and p-Akt (Ser473 and Thr308) in DOCA mice were significantly lower than in Sham group (P<0.05). The expression of PI₃K, Akt and p-Akt (Ser473) was significantly higher in DOCA+ BH₄ group than in DOCA group (P<0.05). p-Akt (Thr308) expression was similar between DOCA + BH₄ group and DOCA group (all P>0.05). Conclusion: Our results suggest that BH₄ could improve left ventricular diastolic function in hypertensive mice, this effect might be mediated by reducing the oxidative stress in ventricular myocardium through modlating the expression of Akt and PLB phosphorylation.