Stachytarpheta cayennensis extract inhibits promastigote and amastigote growth in Leishmania amazonensis via parasite arginase inhibition

ETHNOPHARMACOLOGY RELEVANCE

Stachytarpheta cayennensis is a plant that is traditionally used to treat tegumentary leishmaniasis and as an anti-inflammatory agent.

AIM OF THE STUDY

This study aimed to evaluate the action of S. cayennensis extracts on the Leishmania (Leishmania) amazonensis arginase enzyme.

MATERIALS AND METHODS

S. cayennensis was collected from the Brazilian Amazon region. Aqueous extracts were fractionated with n-butanol. The leishmanicidal effects of the n-butanolic fraction (BUF) were evaluated in L. (L.) amazonensis promastigotes and amastigotes. BUF was tested against recombinant arginase from both L. (L.) amazonensis and macrophage arginase. Promastigote cultures and infected macrophage cultures were supplemented with L-ornithine to verify arginase inhibition. NMR analysis was used to identify the major components of BUF.

RESULTS

BUF showed an EC₅₀ of 51 and 32µg/mL against promastigotes and amastigotes of L. (L.) amazonensis, respectively. BUF contains a mixture of verbascoside and isoverbascoside (7:3 ratio) and is a potent L. (L.) amazonensis arginase inhibitor (IC₅₀=1.2µg/mL), while macrophage arginase was weakly inhibited (IC₅₀>1000µg/mL). The inhibition of arginase by BUF in promastigotes and amastigotes could be demonstrated by culture media supplementation with L-ornithine, a product of the hydrolysis of L-arginine by arginase.

CONCLUSIONS

Leishmanicidal effects of the S. cayennensis BUF fraction on L. (L.) amazonensis are associated with selective parasite arginase inhibition.

Sedative and anxiolytic effects of the extracts of the leaves of Stachytarpheta cayennensis in mice

The leaves are used ethnomedicinally in Nigeria and other parts of the world for insomnia and anxiety among other uses. The investigations sought scientific evidence for the ethnomedicinal use of the leaves for the management of insomnia and anxiety as well as the neural mechanisms for the activities. The sedative and anxiolytic effects of the extracts of the leaves of Stachytarpheta cayennensis were examined in this study. The methanolic extract (5-50 mg/kg, i.p.) as well as the ethylacetate (10-50 mg/kg, i.p.), butanol and aqueous fractions (5-50 mg/kg, i.p.) of the extract were examined. Sedation was assessed as reduced novelty-induced rearing (NIR), reduced spontaneous locomotor activity (SLA) and increased pentobarbitone-induced sleeping time (PIST) in mice. The anti-anxiety effect (methanol 2.5-5.0; butanol 5.0; aqueous 20.0; ethylacetate 25.0 mg/kg, i.p.) was assessed using an elevated plus maze. LD50 was calculated for the extract and the fractions after the intraperitoneal route of administration using the Locke method. The methanolic extract, the butanol and the aqueous fractions inhibited rearing and spontaneous locomotion but prolonged pentobarbitone induced sleep. The ethylacetate fraction however increased both rearing and locomotion and decreased pentobarbitone sleeping time. The butanol and aqueous fractions, but not the methanol extract showed indices of open arm avoidance consistent with anti-anxiety effect. Naltrexone (2.5 mg/kg, i.p.) reversed the inhibition of rearing, locomotion and prolongation of pentobarbitone sleep due to the aqueous fraction of the extract. Flumazenil (2mg/kg, i.p.) abolished the effects of both methanolic extract and the butanol fraction on rearing, locomotion, pentobarbitone sleep and anxiety model. The methanolic extract, the butanol and aqueous fractions possess sedative activity while the ethylacetate fraction possesses stimulant property. The anxiolytic effect was found in both the aqueous fraction and the butanol fraction but not in the main methanol extract and also not in the ethylacetate fraction. Flumazenil, blocked the effect of the leaves of Stachytarpheta cayennensis on rearing, locomotion and elevated plus maze suggesting that GABA receptors are involved in the observed sedative and anxiolytic activities. This study also found opioid receptors involved in the sedative activity of the leaves of Stachytarpheta cayennensis. The rationale for the ethnomedicinal use of the leaves for the management of insomnia and anxiety were confirmed scientifically in this study.

In vivo antimalarial activity of ethanolic leaf extract of Stachytarpheta cayennensis

OBJECTIVE

To evaluate the in vivo antiplasmodial activity of the ethanol leaf extract of Stachytarpheta cayennensis in the treatment of various ailment in Niger Delta region of Nigeria, in Plasmodium berghei infected mice.

MATERIALS AND METHODS

The ethanolic leaf extract of Stachytarpheta cayennensis (90-270 mg/kg/day) was screened for blood schizonticidal activity against chloroquine sensitive Plasmodium berghei berghei in mice. The schizonticidal effect during early and established infections was investigated.

RESULT

Stachytarpheta cayennensis (90-270 mg/kg/day) exhibited significant (P< 0.05) blood schizonticidal activity both in 4-day early infection test and in established infection with a considerable mean survival time comparable to that of the standard drug, chloroquine, 5 mg/kg/day.

CONCLUSION

The leaf extract possesses significant (P< 0.05) antiplasmodial activity which confirms it's use in folkloric medicine in the treatment of malaria.