Protective effects of AMP-activated protein kinase in the cardiovascular system

Anti-atherosclerotic action of Ger-Gen-Chyn-Lian-Tang and AMPK-dependent lipid lowering effect in hepatocytes

ETHNOPHARMACOLOGICAL RELEVANCE

The Ger-Gen-Chyn-Lian-Tang (GGCLT), an officially standardized mixture of Chinese herbal medicines, consists of Puerariae Radix, Scutellariae Radix, Coptidis Rhizoma and Glycyrrhizae Radix in a ratio of 8:3:3:2. In this study, we evaluated the benefits of GGCLT in atherosclerotic progression.

METHODS

The major constituents of GGCLT were analyzed by HPLC. ApoE-/- mice taken 0.15% cholesterol diet were orally given vehicle or GGCLT (2 g/kg/day) for 12 weeks. Serum levels of lipid and glucose were analyzed, and atherosclerosis was examined by histological analyses. Cultures of vascular smooth muscle cells, hepatocytes and bone marrow-derived macrophages were used to investigate the action mechanisms of GGCLT.

RESULTS

Our quantitation results indicated that GGCLT contains puerarin, daidzin, daidzein, baicalin, baicalein, wogonin, palmatine, coptisine, berberine and glycyrrhizin. GGCLT decreased serum levels of total cholesterol and LDL, but not TG and HDL in ApoE-/- mice. In parallel, GGCLT treatment reduced atherosclerotic lesions and collagen expression in atheroma plaques. In vascular smooth muscle cells, GGCLT could reduce cell migration, but failed to affect cell viability and proliferation. In hepatocytes, GGCLT can reduce lipid accumulation, and this action was accompanied by the activation of AMPK, upregulation of PPARs, and downregulation of FAS. Pharmacological approach indicated that the latter two events contributing to the anti-lipogenesis is resulting from AMPK pathway, and the lipid lowering effect of GGCLT in hepatocytes is mediated by AMPK and PPARα pathways. Meanwhile, two of the major components of GGCLT, berberine and puerarin, also activated AMPK and decreased lipid accumulation in hepatocytes with berberine of higher efficacy. Besides in hepatocytes, AMPK signaling was also activated by GGCLT in vascular smooth muscle cells and macrophages.

CONCLUSIONS

These results demonstrate the anti-atherosclerotic action of Chinese medicine mixture GGCLT in ApoE-/- atherosclerotic mouse model. Mechanistic study suggests that activation of AMPK and PPARα in hepatocytes leading to a decrease of lipid formation contributes to the beneficial action of GGCLT in atherosclerosis treatment.

Regulation of NAD(P)H oxidases by AMPK in cardiovascular systems

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are ubiquitously produced in cardiovascular systems. Under physiological conditions, ROS/RNS function as signaling molecules that are essential in maintaining cardiovascular function. Aberrant concentrations of ROS/RNS have been demonstrated in cardiovascular diseases owing to increased production or decreased scavenging, which have been considered common pathways for the initiation and progression of cardiovascular diseases such as atherosclerosis, hypertension, (re)stenosis, and congestive heart failure. NAD(P)H oxidases are primary sources of ROS and can be induced or activated by all known cardiovascular risk factors. Stresses, hormones, vasoactive agents, and cytokines via different signaling cascades control the expression and activity of these enzymes and of their regulatory subunits. But the molecular mechanisms by which NAD(P)H oxidase is regulated in cardiovascular systems remain poorly characterized. Investigations by us and others suggest that adenosine monophosphate-activated protein kinase (AMPK), as an energy sensor and modulator, is highly sensitive to ROS/RNS. We have also obtained convincing evidence that AMPK is a physiological suppressor of NAD(P)H oxidase in multiple cardiovascular cell systems. In this review, we summarize our current understanding of how AMPK functions as a physiological repressor of NAD(P)H oxidase.