Nardostachys jatamansi DC Extract Alleviates Insulin Resistance and Regulates Glucose Metabolism in C57BL/KsJ-db/db Mice Through the AMP-Activated Protein Kinase Signaling Pathway

This study investigated whether Nardostachys jatamansi DC extract (NJE) improved insulin sensitivity and suppressed hepatic glucose production in an animal model of type 2 diabetes. C57BL/KsJ-db/db mice were divided into three dietary groups: regular diet (control), NJE, and rosiglitazone. After 6 weeks of feeding, blood glucose, glycosylated hemoglobin, and plasma insulin levels were significantly lower in NJE than in diabetic control group mice. The oral glucose tolerance test also revealed a positive effect of NJE on increasing insulin sensitivity. The homeostatic index of insulin resistance was significantly lower in NJE than in diabetic control group mice. NJE markedly lowered the plasma lipid concentration compared to diabetic control group mice. In the skeletal muscle, the expression of phosphorylated AMP-activated protein kinase, pAkt substrate of 160 kDa, and plasma membrane glucose transporter type 4 increased more in NJE compared to diabetic control group mice. NJE also decreased the expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase in the liver. These findings demonstrate that NJE alleviates hyperglycemia by improving insulin sensitivity and inhibiting gluconeogenesis in the liver.

Aristolone in Nardostachys jatamansi DC. induces mesenteric vasodilation and ameliorates hypertension via activation of the KATP channel and PDK1-Akt-eNOS pathway

BACKGROUND

Nardostachys jatamansi DC. is a common medicinal herb used to treat cardiovascular diseases, particularly hypertension. Previously, our lab characterized the chemical compounds of N. jatamansi. However, the bioactive compounds of N. jatamansi and their mechanisms of action on blood pressure and blood vessels are unknown.

PURPOSE

The vasorelaxant effects of the methanolic extract (MeOH ext.) of the roots and rhizomes of N. jatamansi, its main compounds, and their underlying mode of action, were investigated.

METHODS

The main compounds of N. jatamansi were isolated and identified using UHPLC-TOF MS. The antihypertensive effect of N. jatamansi extracts and (-)-aristolone were determined using spontaneously hypertensive rats. The extracts, fractions, and compounds were also evaluated for their vasorelaxant effects on U46619 contractile responses in isolated thoracic aortic and mesenteric arterial rings. The endothelial-dependent relaxation, as well as the regulatory pathways and targets of (-)-aristolone, were studied in-vitro and ex-vivo. Molecular docking and biophysical characterization (Surface plasmon resonance) studies were utilized to investigate the molecular interaction between (-)-aristolone and the target protein.

RESULTS

MeOH ext. (200 mg/kg) reduces the systolic and diastolic blood pressure in spontaneously hypertensive rats. MeOH ext. and its ethyl acetate fraction (EtOAc Fr.), but not the H₂O fraction, had a significant relaxing effect on the thoracic aorta. (-)-aristolone and kanshone H from EtOAc Fr. induced vasorelaxation of the thoracic aorta and mesenteric artery. In human umbilical vein endothelial cells, (-)-aristolone treatment upregulated phosphorylation of Akt (T308) and eNOS. Molecular docking and surface plasmon resonance experiments revealed an interaction between (-)-aristolone and phosphoinositide-dependent protein kinase 1 (PDK1), an upstream protein kinase that phosphorylates Akt at T308. Treatment with PDK1 inhibitor PHT-427 and eNOS inhibitor L-NAME consistently inhibited (-)-aristolone-induced vasorelaxation. In addition, K_ATP channel inhibitor glibenclamide dramatically inhibited the vasorelaxant effects of (-)-aristolone and kanshone H in the endothelium-denuded thoracic aorta. Finally, (-)-aristolone lowers hypertensive rats' systolic and diastolic blood pressure.

CONCLUSIONS

The extracts of N. jatamansi promote vasorelaxation and alleviate hypertension. The essential chemicals responsible for producing vasorelaxation effects are (-)-aristolone and kanshone H, which activate the PDK1-Akt-eNOS-NO relaxing pathway and stimulate the opening of the K_ATP channel. These findings point to N. jatamansi and aristolone as possible antihypertensive agents.