Oleic acid-induced perilipin 5 expression and lipid droplets formation are regulated by the PI3K/PPARα pathway in HepG2 cells.

Perilipin 5 (Plin5), a member of the PAT (Perilipin, ADRP, and Tip47) protein family, has been implicated in the regulation of cellular neutral lipid accumulation in nonalcoholic fatty liver diseases. However, the underlying regulatory mechanisms of Plin5 are not clear. The goal of the present study was to explore the mechanism of oleic acid (OA)-induced Plin5 expression in HepG2 cells. We found that the expression of Plin5 was increased during OA-induced lipid droplets formation in a dose- and time-dependent manner. During this process of OA-stimulated lipid droplets formation, peroxisome proliferator-activated receptor alpha (PPARα) was also upregulated. When PPARα activation was blocked by GW6471, OA-induced Plin5 expression and lipid droplets formation were effectively ablated. We further found that the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 was able to downregulate both PPARα and Plin5 expression and lipid droplets formation. Thus, we concluded that PI3K may, at least in part, act upstream of PPARα to regulate Plin5 expression and lipid droplets formation in HepG2 cells.

Pycnogenol® Induces Browning of White Adipose Tissue through the PKA Signaling Pathway in Apolipoprotein E-Deficient Mice.

Beige adipocytes in white adipose tissue (WAT) have received considerable recognition because of their potential protective effect against obesity. Pycnogenol (PYC), extracted from French maritime pine bark, has anti-inflammatory and antioxidant properties and can improve lipid profiles. However, the effect of PYC on obesity has never been explored. In this study, we investigated the effects of PYC on obesity and WAT browning in apolipoprotein E- (ApoE-) deficient mice. The results showed that PYC treatment clearly reversed body weight and the mass of eWAT gain resulting from a high-cholesterol and high-fat diet (HCD), but no difference in food intake. The morphology results showed that the size of the adipocytes in the PYC-treated mice was obviously smaller than that in the HCD-fed mice. Next, we found that PYC upregulated the expression of genes related to lipolysis (ATGL and HSL), while it decreased the mRNA level of PLIN1. PYC significantly increased the expression of UCP1 and other genes related to beige adipogenesis. Additionally, PYC increased the expression of proteins related to the protein kinase A (PKA) signaling pathway. The findings suggested that PYC decreased obesity by promoting lipolysis and WAT browning. Thus, PYC may be a novel therapeutic target for obesity.

Pycnogenol protects against diet-induced hepatic steatosis in apolipoprotein-E-deficient mice.

PycnogenolR (PYC), a combination of active flavonoids derived from French maritime pine bark, is a natural antioxidant that has various pharmacological activities. Here, we investigated the beneficial effect of PYC on diet-induced hepatic steatosis. Apolipoprotein E (ApoE)-deficient male mice were administered PYC at oral doses of 30 or 100 mg·kg-1·day-1 for 2 wk in advance and were then fed a high-cholesterol and -fat diet (HCD) for 8 wk. Biochemical, immunohistochemical, and gene expression analyses were conducted to explore the effect of PYC on lipid metabolism in ApoE-deficient mice on a HCD. Short-term treatment with HCD in ApoE-deficient mice induced hepatic injuries, such as lipid metabolism disorder and hepatic histopathological changes. We found that PYC reduced body weight and the increase of serum lipids that had been caused by HCD. Supplementation of PYC significantly reduced lipid deposition in the liver, as shown by the lowered hepatic lipid content and histopathological lesions. We subsequently detected genes related to lipid metabolism and inflammatory cytokines. The study showed that PYC markedly suppressed the expression of genes related to hepatic lipogenesis, fatty acid uptake, and lipid storage while increasing the lipolytic gene, which thus reduced hepatic lipid content. Furthermore, PYC mainly reduced the expression of inflammatory cytokines and the infiltration of inflammatory cells, which were resistant to the development of hepatic steatosis. These results demonstrate that PYC protects against the occurrence and development of hepatic steatosis and may provide a new prophylactic approach for nonalcoholic fatty liver disease (NAFLD).

Pycnogenol Reduces Toll-Like Receptor 4 Signaling Pathway-Mediated Atherosclerosis Formation in Apolipoprotein E-Deficient Mice.

Pycnogenol (PYC) is an extract from French maritime pine bark. Its antioxidative and anti-inflammatory effects have been shown to be beneficial for atherosclerosis. Here, we tested whether PYC could suppress high cholesterol and fat diet (HCD)-induced atherosclerosis formation in apolipoprotein E (apoE)-deficient mice. In our study, PYC suppressed oxidized low-density lipoprotein (ox-LDL)-induced lipid accumulation in peritoneal macrophages. Apolipoprotein E-deficient mice were orally administered PYC or a control solvent for ten weeks, and these mice were fed a standard diet or high cholesterol and fat diet during the latter eight weeks. Pycnogenol markedly decreased the size of atherosclerotic lesions induced by high cholesterol and fat diet compared with the nontreated controls. In addition, TLR4 expression in aortic sinus was stimulated by high cholesterol and fat diet feeding and was significantly reduced by PYC. A mechanistic analysis indicated that lipopolysaccharide (LPS) significantly increased expression of fatty acid binding protein (aP2) and macrophage scavenger receptor class A (SR-A), which were blocked by a JNK inhibitor. Furthermore, PYC inhibited the lipopolysaccharide-induced upregulation of aP2 and scavenger receptor class A via the JNK pathway. In conclusion, PYC administration effectively attenuates atherosclerosis through the TLR4-JNK pathway. Our results suggest that PYC could be a potential prophylaxis or treatment for atherosclerosis in humans.