Protein Tyrosine Phosphatase 1B Inhibitory Activity of Amentoflavone and Its Cellular Effect on Tyrosine Phosphorylation of Insulin Receptors

Abstract

Insulin binding to the insulin receptor (IR) results in autophosphorylation on specific tyrosine residues, which in turn further activates the receptor tyrosine kinase and provides binding sites for the recruitment and subsequent phosphorylation of signaling proteins such as insulin receptor substrate (IRS) 1-4.2,3) Phosphorylated IRS activate several signaling cascades that mediate the biological effects of insulin including glucose uptake and glycogen synthesis. 2,3)Protein tyrosine phosphatases (PTPs) catalyze the dephosphorylation of tyrosyl-phosphorylated proteins and are believed important negative regulators of insulin signaling. 2,3)Although several PTPs such as PTP-a, leukocyte antigen-related tyrosine phosphatase (LAR), and SH2-domain-containing phosphotyrosine phosphatase (SHP2) have been implicated in the regulation of insulin signaling, there is substantial evidence supporting PTP1B as the critical PTP controlling the insulin signaling pathway.2,3) PTP1B can interact with and dephosphorylate activated IR as well as IRS proteins.2,3) Its overexpression has been shown to inhibit the IR signaling cascade and increased expression of PTP1B occurs in insulin-resistant states. 4) Furthermore, recent genetic evidence has shown that PTP1B gene variants are associated with changes in insulin sensitivity. 5) As with the insulin signaling pathway, the leptin signaling pathway can be attenuated by PTPs and there is compelling evidence that PTP1B is also involved in this process.2,3) Therefore, it has been suggested that compounds that reduce PTP1B activity or expression levels could not only be used for the treatment of type 2 diabetes but also obesity. Although there have been a number of reports on the design and development of synthetic PTP1B inhibitors, 2,6) there are only a few reports on PTP1B inhibitors derived from plants. 7) In our continuing search for PTP1B inhibitors derived from plants, a MeOH extract of whole plants of Selaginella tamariscina (Selaginellaceae), which have been used to treat infectious diseases and malignant tumors, 8) was found to inhibit PTP1B activity (Ͼ70% inhibition at 30 mg/ml). Further fractionation of the MeOH extract as guided by in vitro PTP1B inhibitory assay afforded an active biflavonoid, amentoflavone (Fig. 1). Although amentoflavone has been reported to possess various pharmacological activities such as antioxidant, 9) anti-HIV, 10) anti-phospholipase Cg1, 11) and vasorelaxant effects, 12) there has been no study with regard to its inhibitory activity against PTP1B. In this study, we investigated the inhibitory effect of amentoflavone on PTP1B and confirmed its cellular effect on IR phosphorylation. MATERIALS AND METHODS Plant MaterialWhole plants of S. tamariscina were purchased from a local market in Daejeon, Korea. A voucher specimen (No. 005-041) has been deposited in our laboratory, KRIBB.Extraction and Isolation Dried whole plants of S. tamariscina (1 kg) were extracted with MeOH (3 l) at 50°C. The MeOH extract (50.5 g) was suspended in H 2 O and partitioned wit...

Antihyperglycemic activity of Selaginella tamariscina (Beauv.) Spring

“…Our recent studies demonstrated that the flavonoids are the prominent active biochemical compound of Selaginella tamariscina. Amentoflavone is one of the main flavonoids from Selaginella tamariscina and it has been reported that amentoflavone is a non-competitive inhibitor of PTP1B (Na et al, 2007), which can interact with and dephosphorylate activated IR as well as IRS proteins (Johnson et al, 2002;Asante-Appiah and Kennedy, 2003). Its overexpression has been shown to inhibit the IR signaling cascade and increased expression of PTP1B occurs in insulin-resistant states (Ahmad et al, 1997).…”

Natural products possessing protein tyrosine phosphatase 1B (PTP1B) inhibitory activity found in the last decades

“…Phaseollin 107 was synthesized by Mohamed et al in 1987 [64] (Figure 4). From the MeOH extract of plant Selaginella tamariscina, used to treat infectious disease and malignant tumors, amentoflavone 115 was obtained and characterized as a noncompetitive PTP1B inhibitor (IC 50 value of 7.3±0.5 μmol/L and K i value of 5.2 μmol/L) [65] . Treatment with 115 of 32D cells overexpressing the IR resulted in a dose-dependent increase in tyrosine phosphorylation of IR, possibly through inhibition of PTP1B to enhance insulin-induced intracellular signaling.…”

Prenylated Flavonoids with PTP1B Inhibitory Activity from the Root Bark of Erythrina mildbraedii

“…[6][7][8][9][10][11][12][13][14][15][16] Previously, we found that an EtOAcsoluble extract of the root bark of Erythrina mildbraedii exhibited inhibitory effect on PTP1B activity and demonstrated that prenylated flavonoids are principles of this extract. 14) Further study on the EtOAc-soluble extract of E. mildbraedii led to the isolation of three new (1-3) and three known (4-6) prenylated flavonoids.…”