Antidiabetic Activities of Korean Red Pine (Pinus densiflora) Inner Bark Extracts

Abstract

This study was carried out to investigate the potential of Korean red pine (Pinus densiflora) inner bark extracts as an antidiabetic agent. The ethyl acetate soluble fraction of the bark extracts was chromatographed on a Sephadex LH-20 column to yield five compounds, which structures were elucidated by NMR spectroscopy. The isolated compounds were (+)-catehin, (-)-epicatechin, taxifolin, taxifolin-3'-O-${\beta}$-D-(+)-glucose and $\tilde{n}$-courmaric acid. The antidiabetic activity of the different fractions, including the crude extracts and isolated compounds, was evaluated by ${\beta}$-cells insulin secretion and glucose uptake in skeletal muscle cells. The insulin secretion was 128% for taxifolin at $25{\mu}g/mL$. However, the other samples had no effect on this test. For the glucose uptake activity assay, $1{\mu}M$ insulin and 2 mM metformin were used as controls. Both the crude extract and taxifolin showed relatively low activity values, but the other samples yielded glucose uptake values over 260%. ${\rho}$-courmaric acid showed the highest uptake (270%). The results confirmed that Korean red pine extracts may be used as a hypoglycemic agent.

Fig. 1. Chemical structures of isolated compounds.

Fig. 2. Effects of crude on the viability of HIT-T15 cells.

Fig. 3. Effects of EtOAc soluble fraction on the viability of HIT-T15 cells.

Fig. 5. Effects of (+)-catechin on the viability of HIT-T15 cells.

Fig. 6. Effects of (-)-epicatechin on the viability of HIT-T15 cells.

Fig. 10. Insulin secretion of HIT-T15 treated with the crude.

Fig. 12. Insulin secretion of HIT-T15 treated with the H₂O soluble fraction.

Fig. 14. Insulin secretion of HIT-T15 treated with (-)-epicatechin.

Fig. 16. Insulin secretion of HIT-T15 treated with taxifolin-3′-O-β-D-(+)-glucose.

Fig. 11. Insulin secretion of HIT-T15 treated with the EtOAc soluble fraction.

Fig. 13. Insulin secretion of HIT-T15 treated with (+)-catechin.

Fig. 15. Insulin secretion of HIT-T15 treated with taxifolin.

Fig. 17. Insulin secretion of HIT-T15 treated with ρ-coumaric acid.

Fig. 18. Effects of crude on the viability of L6 cells.

Fig. 19. Effects of EtOAc soluble fraction on the viability of L6 cells.

Fig. 20. Effects of H₂O soluble fraction on the viability of L6 cells.

Fig. 21. Effects of (+)-catechin on the viability of L6 cells.

Fig. 26. Glucose uptake activities of the crude.

Fig. 28. Glucose uptake activities of the H₂O soluble fraction.

Fig. 30. Glucose uptake activities of (-)-epicatechin.

Fig. 32. Glucose uptake activities of taxifolin-3′-O-β-D-(+)-glucose.

Fig. 27. Glucose uptake activities of the EtOAc soluble fraction.

Fig. 29. Glucose uptake activities of (+)-catechin.

Fig. 31. Glucose uptake activities of taxifolin.

Fig. 33. Glucose uptake activities of ρ-coumaric acid.

Fig. 4. Effects of H₂O soluble fraction on the viability of HIT -T15 cells.

Fig. 7. Effects of taxifolin on the viability of HIT-T15 cells.

Fig. 8. Effects of taxifolin-3′-O-β-D-(+)-glucose on the viability of HIT-T15 cells.

Fig. 9. Effects of ρ-coumaric acid on the viability of HIT-T15 cells.

Fig. 22. Effects of (-)-epicatechin on the viability of L6 cells.

Fig. 23. Effects of taxifolin on the viability of L6 cells.

Fig. 24. Effects of taxifolin-3′-O-β-D-(+)-glucose on the viability of L6 cells.

Fig. 25. Effects of ρ-coumaric acid on the viability of L6 cells.

Table 1. Weight of each fraction of Korean red pine inner bark extracts

Table 2. Weight of the isolated compounds