Natural endoperoxides as promising anti-leishmanials

BACKGROUND

The discovery of artemisinin, an endoperoxide, encouraged the scientific community to explore endoperoxides as potential anti-parasitic molecules. Although artemisinin derivatives are rapidly evolving as potent anti-malarials, their potential as anti-leishmanials is emerging gradually. The treatment of leishmaniasis, a group of neglected tropical diseases is handicapped by lack of effective vaccines, drug toxicities and drug resistance. The weak antioxidant defense mechanism of the Leishmania parasites due to lack of catalase and a selenium dependent glutathione peroxidase system makes them vulnerable to oxidative stress, and this has been successful exploited by endoperoxides.

PURPOSE

The study aimed to review the available literature on the anti-leishmanial efficacy of natural endoperoxides with a view to achieve insights into their mode of actions.

METHODS

We reviewed more around 110 research and review articles restricted to the English language, sourced from electronic bibliographic databases including PubMed, Google, Web of Science, Google scholar etc. RESULTS: Natural endoperoxides could potentially augment the anti-leishmanial drug library, with artemisinin and ascaridole emerging as potential anti-leishmanial agents. Due to higher reactivity of the cyclic peroxide moiety, and exploiting the compromised antioxidant defense of Leishmania, endoperoxides like artemisinin and ascaridole potentiate their leishmanicidal efficacy by creating a redox imbalance. Furthermore, these molecules minimally impair oxidative phosphorylation; instead inhibit glycolytic functions, culminating in depolarization of the mitochondrial membrane and depletion of ATP. Additionally, the carbon-centered free radicals generated from endoperoxides, participate in chain reactions that can generate even more reactive organic radicals that are toxic to macromolecules, including lipids, proteins and DNA, leading to cell cycle arrest and apoptosis of Leishmania parasites. However, the precise target(s) of the toxic free radicals remains open-ended.

CONCLUSION

In this overview, the spectrum of natural endoperoxide molecules as major anti-leishmanials and their mechanism of action has been delineated. In view of the substantial evidence that natural endoperoxides (e.g., artemisinin, ascaridole) exert a noxious effect on different species of Leishmania, identification and characterization of other natural endoperoxides is a promising therapeutic option worthy of further pharmacological consideration.

Ascaridole exerts the leishmanicidal activity by inhibiting parasite glycolysis

BACKGROUND

The global burden of leishmaniasis is exacerbated by the limited repertoire of drugs, resulting in an urgent need to develop new therapeutic alternatives. Endoperoxides like ascaridole have emerged as promising anti-parasitic candidates, and its effectiveness was established in an animal model of cutaneous leishmaniasis (CL). However, its impact on Leishmania donovani parasites, causative of visceral leishmaniasis (VL) remains to be established.

PURPOSE

This study aimed to delineate the underlying mechanisms contributing towards the leishmanicidal effect of ascaridole in terms of its impact on the cellular redox status and metabolic bioenergetics of L. donovani parasites.

METHODOLOGY

The anti-promastigote activity of ascaridole was established by a cell viability assay in L. donovani [MHOM/IN/1983/AG83] and anti-amastigote activity by microscopy and ddPCR (droplet digital polymerase chain reaction). The cellular redox status, mitochondrial membrane potential (MMP), annexin V positivity and cell cycle arrest was evaluated by flow cytometry, while cellular and mitochondrial bioenergetics was assessed using Agilent XFp Analyzer, and the levels of ATP was measured by chemiluminescence.

RESULTS

Ascaridole demonstrated strong anti-promastigote and anti-amastigote activities in l. donovani, IC₅₀ (half maximal Inhibitory concentration) being 2.47 ± 0.18 µM and 2.00±0.34 µM respectively, while in J774.A1 and murine peritoneal macrophages, the CC₅₀ (half maximal cytotoxic concentration) was 41.47 ± 4.89 µM and 37.58 ± 5.75 µM respectively. Ascaridole disrupted the redox homeostasis via an enhanced generation of reactive oxygen species (ROS), lipid peroxidation and concomitant depletion of thiols. However, it failed to increase the generation of mitochondrial superoxide, which minimally impacted on mitochondrial respiration and was corroborated by energy metabolism studies. Instead, ascaridole inhibited glycolysis of promastigotes, caused a loss in MMP, which translated into ATP depletion. In promastigotes, ascaridole enhanced annexin-V positivity and caused a cell cycle arrest at sub- G₀/G₁ phase.

CONCLUSION

In summary, ascaridole displays its leishmanicidal activity possibly due to its ability to auto-generate free radicals following cleavage of its endoperoxide bridge that led to disruption of the redox homeostasis, inhibition of glycolysis and culminated in an apoptotic like cell death.

Evaluation of Chilean Boldo Essential Oil as a Natural Insecticide Against Chrysomya megacephala (Diptera: Calliphoridae)

Chrysomya megacephala (Fabricius, 1794) is a vector of enteric bacteria, protozoa, helminths, and viruses. These Diptera can also be responsible for secondary myiasis in several animal species. Therefore, it is easy to understand the relevance of studies focusing on C. megacephala dissemination control. The employment of essential oils as natural insecticides must be considered as a promising alternative for the replacement of synthetic insecticides. In this context, the essential oil obtained from Chilean boldo leaves should be highlighted. The aim of the present work was to assess the insecticidal activity of Chilean boldo essential oil against C. megacephala blowflies in different life stages (larva, pupa, and adult). The essential oils were extracted from commercial samples of Chilean boldo leaves by hydrodistillation and were mixed to produce a pool that was employed in the study. Gas chromatographic techniques were used to enable the identification and quantification of the pool's components. Larvae, pupae, and adult insects of C. megacephala were exposed (topical application) to different concentrations of this essential oil pool. After that, the larvicidal, pupicidal, and insecticidal actions of the oil were tested. Its toxicity might be associated with compounds such as eucalyptol, linalool, α-pinene, limonene, and ascaridole, either acting alone or by synergic effects. Interestingly, the pupae appeared to be stronger than the larvae and adult insects, needing higher doses of essential oil to be killed. The oil's toxic effects could be useful to control C. megacephala dissemination in all of its development phases.

Combinations of ascaridole, carvacrol, and caryophyllene oxide against Leishmania

To date there are no vaccines against Leishmania and chemotherapy remains the mainstay for the control of leishmaniasis. The drugs currently used for leishmaniasis therapy are significantly toxic, expensive, and result in a growing frequency of refractory infections. In this study, we evaluated the effect of combinations of the main components of essential oil from Chenopodium ambrosioides (ascaridole, carvacrol, and caryophyllene oxide) against Leishmaniaamazonensis. Anti-leishmanial effects of combinations of pure compounds were evaluated in vitro and the fractional inhibitory concentration (FIC) indices were calculated. BALB/c mice infected with L. amazonensis were treated with different concentrations of ascaridole-carvacrol combinations by intralesional doses every 4 days. Disease progression and parasite burden in infected tissues were determined. In vitro experiments showed a synergistic effect of the combination of ascaridole-carvacrol against promastigotes of Leishmania with a FIC index of 0.171, while indifferent activities were observed for ascaridole-caryophyllene oxide (FIC index=3.613) and carvacrol-caryophyllene oxide (FIC index=2.356) combinations. The fixed ratio method showed that a 1:4 ascaridole-carvacrol ratio produced a better anti-protozoal activity on promastigotes, lower cytotoxicity, and synergistic activity on intracellular amastigotes (FIC index=0.416). Significant differences (p<0.05) in lesion size and parasite burden were demonstrated in BALB/c mice experimentally infected and treated with the ascaridole-carvacrol combinations compared with control animals. Carvacrol showed significant higher anti-radical activity in the DPPH assay compared with caryophyllene oxide. Electron spin resonance spectroscopy in combination with spin trapping suggested the presence of carbon-centered radicals after activation of ascaridole by Fe(2+). The intensity of the signals is preferably decreased upon addition of carvacrol. The ascaridole-carvacrol combination could represent a future alternative to monotherapeutic anti-leishmanial agents.

Antileishmanial activity of essential oil from Chenopodium ambrosioides and its main components against experimental cutaneous leishmaniasis in BALB/c mice

Chenopodium ambrosioides have been used during centuries by native people to treat parasitic diseases.

AIMS OF THE STUDY

To compare the in vivo anti-leishmanial activity of the essential oil (EO) from C. ambrosioides and its major components (ascaridole, carvacrol and caryophyllene oxide).

MATERIALS AND METHODS

Anti-leishmanial effect was evaluated in BALB/c mice infected with Leishmania amazonensis and treated with the EO, main compounds and artificial mix of pure components by intralesional route at 30 mg/kg every 4 days during 14 days. Diseases progression and parasite burden in infected tissues were determined.

RESULTS

EO prevented lesion development compared (p<0.05) with untreated animals and treated with vehicle. In addition, the efficacy of EO was also statistically superior (p<0.05) compared with the glucantime-treated animals. No potential effects were observed with pure components treatment. Mix of pure compounds cause death of animals after 3 days of treatment.

CONCLUSIONS

Our results demonstrate the superiority of EO against experimental cutaneous leishmaniasis caused by L. amazonensis.