Anti-inflammatory effects of a polyphenol-rich spearmint extract

A rat paw edema model showed that this extract has similar anti-inflammatory properties to indomethacin and superior effects to rosmarinic acid alone

A study published in The FASEB Journal has assessed the anti-inflammatory effects of a polyphenol-rich spearmint extract containing rosmarinic acid using a rat paw edema model.

Four groups of male Wistar rats received intraperitoneal administration of either a proprietary spearmint extract containing 15% rosmarinic acid at doses of 10, 30 or 100mg/kg; rosmarinic acid standard at doses of 15 or 50mg/kg; Indomethacin, an anti-inflammatory agent, at 10 mg/kg; or saline alone as a vehicle control.

15 minutes later, subplantar injections of carrageenan (100μl,) were administered to induce paw edema in all animals with the exception of four animals in the saline control group who received a saline subplantar injection (saline-saline group).

Paw volumes were assessed by the volume displacement method immediately after carrageenan injection (baseline) and three and six hours later. Paw edema was expressed as mean percent change of paw volume compared to baseline.

Results

As expected for the rats in the saline-carrageenan group, paw volume increased by 36% and 46% respectively at three and six hours post-injection and was significantly higher than the saline-saline group at the same time points.

Rats treated with spearmint extract demonstrated limited inflammation with paw volume increases of 9%, 11% and -8% at six hours post-injection for the 10, 30 and 100mg/kg spearmint groups respectively. This was significantly lower than the saline-carrageenan group.

In addition, the increase in paw volume in rats treated with 100mg/kg spearmint extract at three hours was significantly lower than that in the saline-carrageenan group.

Similarly, rats treated with the anti-inflammatory agent had limited inflammation compared to the saline-carrageenan group at three and six hours post-injection, with increases in paw volumes of 6% and 3% from baseline.

Animals treated with 15 and 50mg/kg rosmarinic acid showed increased paw volumes of 20% and 7% at three hours, and 10% and 5% respectively at six hours compared to baseline. These volumes were also significantly lower than the saline-carrageenan group at both time points.

Conclusion

When comparing the attenuation in inflammation following spearmint extract treatment to the anti-inflammatory agent, the spearmint extract group performed equally well at attenuating local inflammation.

Furthermore, when comparing the 15 mg/kg rosmarinic acid group with the spearmint extract group that contained an equivalent amount of rosmarinic acid (100mg/kg group), the animals receiving the spearmint extract injections exhibited significantly less inflammation than the rosmarinic acid standard group at both the three and six hour time points, indicating that additional actives in the spearmint extract have an effect on the inflammation response.

In conclusion, these data show that this polyphenol-rich spearmint extract has similar anti-inflammatory properties to indomethacin and superior effects to rosmarinic acid alone, indicating a potential synergy between the constituents present in the spearmint extract.

The study is supported by Kemin Industries. More information can be found here.

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