Asteraceae Plants as Sources of Compounds Against Leishmaniasis and Chagas Disease

Leishmaniasis and Chagas disease cause great impact on social and economic aspects of people living in developing countries. The treatments for these diseases are based on the same regimen for over 40 years, thus, there is an urgent need for the development of new drugs. In this scenario, Asteraceae plants (a family widely used in folk medicine worldwide) are emerging as an interesting source for new trypanocidal and leishmanicidal compounds. Herein, we provide a non-exhaustive review about the activity of plant-derived products from Asteraceae with inhibitory action toward Leishmania spp. and T. cruzi. Special attention was given to those studies aiming the isolation (or identification) of the bioactive compounds. Ferulic acid, rosmarinic acid, and ursolic acid (Baccharis uncinella DC.) were efficient to treat experimental leishmaniasis; while deoxymikanolide (Mikania micrantha) and (+)-15-hydroxy-labd-7-en-17-al (Aristeguietia glutinosa Lam.) showed in vivo anti-T. cruzi action. It is also important to highlight that several plant-derived products (compounds, essential oils) from Artemisia plants have shown high inhibitory potential against Leishmania spp., such as artemisinin and its derivatives. In summary, these compounds may help the development of new effective agents against these neglected diseases.


INTRODUCTION
Protozoa are unicellular eukaryotes that cause some of the most common diseases in humans and domestic animals. These parasites have a range of habitats within their hosts, living in various parts of the body during their life cycle (Ullah et al., 2017). The Trypanosomatidae family includes several human-infective protozoans, such as Leishmania spp., and Trypanosoma cruzi, and they cause Leishmaniasis and Chagas disease, respectively. They affect mainly people living in developing countries, causing great disruption in their quality of life. These diseases are considered neglected diseases by the World Health Organization (WHO, 2013).
Leishmaniasis is considered one of the most significant neglected tropical diseases (Feasey et al., 2010). It is endemic in 98 countries with 350 million people at risk of getting the disease. The mortality rate is 70.000 cases/per year worldwide. Leishmaniasis has an incidence of 0.5 million cases of the visceral form and 1.5-2.0 million cases of cutaneous form (Blum et al., 2004;Reithinger et al., 2007a,b;WHO, 2016). Currently, therapeutic approaches for controlling leishmaniasis comprises only five drugs: the pentavalent antimonial, amphotericin B and its liposomal formulation AmBisome, miltefosine, paromomycin, and pentamidine. These drugs are associated with serious problems such as toxicity and emergence of drug-resistant strains (Tiwari and Dubey, 2018;. Chagas disease (or American trypanosomiasis) is the main cause of heart failure by an infection in Latin America, where the morbidity and mortality associated with this disease is superior to other neglected ones (malaria, schistosomiasis, and leishmaniasis; Martins-Melo et al., 2016). About 10 million infection cases and 14.000 deaths are recorded per year (Coura, 2015). Benznidazole (BNZ), which was developed over 40 years ago, is the first-line drug for the treatment of Chagas disease (Davanço et al., 2016). BNZ shows good efficacy in the acute phase of the disease (80-90% cure), however its greatest restriction is the limited cure efficacy in the chronic phase, which is considered far of the ideal (8-20%) (Bern, 2015). In addition, treatment with BNZ presents other problems, such as high administered doses, long term treatment and high incidence of adverse reactions, which are probably related to the generation of reactive metabolites produced from the metabolism of BNZ (Palmeiro-Roldan et al., 2014;Bermudez et al., 2016).
Since pharmaceutical companies neglect these diseases, there is an urgent demand to accelerate the development of more effective drugs against them. Plants are emerging as interesting sources of new trypanocidal and leishmanicidal compounds. They hold the promise for improvements in the field of drug development, and the ethnomedicinal knowledge plays an essential role in this process (Bermudez et al., 2016). For example, several plants from the Asteraceae family have provided some lead molecules against Leishmania spp. and T. cruzi (Sülsen et al., 2008;Beer et al., 2016;García et al., 2017;Kimani et al., 2017;Laurella et al., 2017). Indeed, Asteraceae plants play important ethnopharmacological role worldwide making them attractive candidates for drug development (Ali et al., 2017;Carvalho et al., 2018;Fattori et al., 2018;Naß and Efferth, 2018).
This paper provides a non-exhaustive overview on the contribution of Asteraceae family for the development of leishmanicidal and trypanocidal drugs. The search for papers was done between January and December of 2018, in PUBMED and Google Scholar databases. Special emphasis was given to those studies about the isolation of bioactive compounds and/or their in vivo evaluation. The ethnomedicinal uses of the plants listed in this work are summarized in Table 1. In addition, the structures of the most promising compounds (those that presented Selective index ≥ 5) that are available at PubChem (https://pubchem.ncbi. nlm.nih.gov/) are shown in Figures 1, 2. PELLITORINE AND 8,9-Z-DEHYDROPELLITORINE FROM Achillea ptarmica L. ARE ACTIVE AGAINST TRYPANOSOMATIDS Extracts and isolated compounds of Achillea ptarmica L. flowers were tested against amastigote forms of L. donovani and T.
In addition, other report showed that the hydroalcoholic extract of A. conyzoides aerial parts inhibited promastigotes and trypomastigotes forms of L. amazonensis and T. cruzi (IC50 values of 107 and 104.7 µg/mL, respectively), as well as the infective abilities of L. amazonensis and T. cruzi (Teixeira et al., 2014). However, the extract showed toxicity against J774.G8 macrophages.
Hispidulin is a flavonoid isolated from the aerial parts of A. tenuifolia that showed action against epimastigotes (IC50 = 46.7 µM; SI> 3.6) and trypomastigotes (IC50 = 62.3 µM; SI> 2.7) forms of T. cruzi; and it was high activity against L. mexicana promastigotes (IC50 = 6.0 µM; SI > 27.8). The toxicity was evaluated using lymphoid cells (Sülsen et al., 2007). This compound was also isolated from the aerial parts of Baccharis uncinella showing action against T. cruzi . Although hispidulin has shown promising activity  against these trypanosomatids, there are no reports about its in vivo action.
Two sesquiterpene lactones were obtained from the aerial parts of A. tenuifolia (psilostachyin and peruvin) with anti-T. cruzi action (both with an IC50 of 2 µg/mL against epimastigotes forms). The authors also demonstrated the in vivo action of psilostachyin [the most active against trypomastigote forms; with an IC50 of 0.76 µg/mL and SI of 33.8 (tested using T lymphocytes)]. In addition, psilostachyin and peruvin also showed even higher activity against L. mexicana promastigotes with an IC50 values of 0.12 µg/mL (SI = 214.2) and 0.39 µg/mL (SI = 89.7), respectively. In the experimental model of Chagas disease, the treatment with psilostachyin (or benznidazole) started 5 days post-infection; and it was performed by intraperitoneal route for 5 days (1 mg/kg of body weight/day). All psilostachyin-treated animals survived, while the mice in the other groups (untreated mice or animals treated with benznidazole) died after 35 days (Sülsen et al., 2008). However, other study reported that psilostachyin was not efficient in an acute model of T. cruzi infection. These different results may be explained by the differences in the treatment schedule in each study (Da Silva et al., 2013).
The anti-T. cruzi activity of the sesquiterpene lactone psilostachyin C isolated from A. scabra was also reported (Sülsen et al., 2011). In this study, the authors showed that psilostachyin C inhibited all forms of T. cruzi with low IC50 values (epimastigotes: 0.6 µg/mL; trypomastigotes: 3.5 µg/mL; and amastigotes: 0.9 µg/mL) and high SI values (145.83, 97.22, and 25, respectively; when tested against murine peritoneal macrophages). The action of psilostachyin C on T. cruzi epimastigotes was associated with the induction of multivesicular bodies and vacuolization. Moreover, psilostachyin C also showed in vitro activity against the promastigote forms of L. mexicana (IC50 = 1.2 µg/mL; SI = 72.92) and L. amazonensis (IC50 = 1.5 µg/mL; SI = 58.33). Due the higher anti-T. cruzi properties of psilostachyin C, the in vivo effects were evaluated in a murine model of Chagas disease. The administration of psilostachyin C (1 mg/kg/day during 5 days) to animals with 5 days of T. cruzi infection resulted in the reduction of parasitaemia and increased survival, a result similar to benznidazole (Sülsen et al., 2011).
Later, the mechanisms involved in the anti-T. cruzi actions of both psilostachyin (from A. tenuifolia) and psilostachyin C (from A. scabra) were evaluated by a range of in vitro assays. The study revealed that despite their chemical similarities and the fact that both compounds activated the apoptosis pathways, the effects of each compound are associated with different targets on epimastigotes forms: psilostachyin interact with hemin and psilostachyin C with sterol synthesis. In addition, the treatment with psilostachyin resulted in a 5-fold increase in the levels of reactive oxygen species (ROS), while psilostachyin C lead to a 1.5 increase in ROS quantities (Sülsen et al., 2016). These results may be associated to the ultrastructural alterations induced by psilostachyin that included mitochondrial swelling and kinetoplast abnormality (Sülsen et al., 2010).
Other compound from the Ambrosia plants with promising action against trypanosomatids is cumanin, a sesquiterpene lactone isolated from A. elatior. Cumanin showed leishmanicidal (IC50 of 19 µM against promastigote forms of L. braziliensis and L. amazonensis) and anti-T. cruzi activities (IC50 of 8, 12, and 180 µM against amastigote, epimastigote and trypomastigote forms, respectively). The in vivo action of cumanin was also demonstrated in an experimental model of Chagas disease induced by intraperitoneal injection of the RA strain. Cumanin was administrated (1 mg/kg of body weight/day by intraperitoneal route) for 5 days after the 5th day of parasite infection. The treatment with cumanin resulted in the survival of the T. cruzi-infected mice and in the reduction of parasitemia, effects similar to those found in the treatment with benznidazole. Moreover, this work also highlighted that cordilin was also active against T. cruzi (epimastigotes and trypomastigotes; Sülsen et al., 2013).
The genus Artemisia is composed by plants used for different ethnomedicinal practices (Bora and Sharma, 2011;Olennikov et al., 2018) and some Artemisia-derived compounds are promising anti-protozoa agents (Emami et al., 2012). In addition, a recent review showed the application of Artemisia plants and their constituents against Trypanosomiasis (Naß and Efferth, 2018). Since several papers evaluated the leishmanicidal effects of the Artemisia genus, in this section we reviewed studies where in vivo assays were employed along with the identification of the active(s) compound(s). In this sense, besides the studies discussed in this section, anti-Leishmania properties were also reported for extracts of Artemisia absinthium L. (Azizi et al., 2016), Artemisia dracunculus L. (Mirzaei et al., 2016;Rezaei et al., 2017), and Artemisia seiberi L. (Esavand Heydari et al., 2013).
Essential oils (EO) from some Artemisia plants have been pointed as interesting leishmanicidal agents (Abad et al., 2012), such as those obtained from Artemisia ludoviciana Nutt. (Baldemir et al., 2018) and Artemisia abyssinica Sch.Bip. ex A.Rich. (Tariku et al., 2010). For some of them, the in vivo properties were demonstrated; as an example the EO from Artemisia absinthium L. has inhibitory effects toward L. amazonensis . A. absinthium EO was also evaluated against L. amazonensis in a murine model of experimental cutaneous leishmaniasis. The treatment with this oil (30 mg/kg by intralesional route) was able to reduce the lesion size and parasite burden, even when compared with mice treated with glucantime .
The EO from A. absinthium was also reported as active against L. aethiopica and L. donovani (Tariku et al., 2011). All these good results lead to the development of a new formulation of A. absinthium EO using nanocochleates. Although the formulation exhibited lower efficacy against the amastigote form of L. amazonensis, the animals that received 4 administrations with this nanoformulation (30 mg/kg by intralesional route) for 4 days exhibited smaller lesion size than the untreated mice or those treated with EO itself. The results were similar to those obtained with Glucantime R treatment (Tamargo et al., 2017).
The EOs from Artemisia campestris (L.) and Artemisia herbaalba (Asso.) were tested against promastigote forms of L. infantum showing IC50 values of 44 and 68 µg/mL, respectively. The CC50 values obtained on peritoneal macrophages from BALB/c treated with A. campestris and A. herba-alba were 124.4 and 160 µg/mL, respectively, corresponding to a SI value of 2.82 for A. campestris and 2.35 for A. herba-alba. These oils showed different chemical compositions: A. campestris EO was mostly composed by monoterpene hydrocarbons (87%) and its major compound was β-pinene (32.95%); while A. herba-alba had high content of oxygenated monoterpenes (85.79%) and its major compound was camphor (36.82%). However, besides these chemical differences, the mechanisms of action of both EOs were related to apoptosis induction and cell cycle arrest (Aloui et al., 2016).
The EO obtained from leaves of Artemisia annua Pall. has also be shown as a potential alternative agent against Leishmaniasis. This EO has IC50 values of 14.63 µg/mL against promastigotes and 7.3 µg/mL against L. donovani amastigotes, without provoking toxic effects in RAW 264.7 macrophages (when tested up to 200 µg/mL). This EO induced parasite apoptosis and its intra-peritoneal administration (200 mg/kg) was effective in the treatment of experimental L. donovaniinfected BALB/c mice. The major compounds of this oil were camphor (52.06%) and β-caryophyllene (10.95%) .
Another report showed that n-hexane fraction from leaves and seeds of A. annua were active against L. donovani promastigotes (IC50 of 14.4 and 14.615 µg/mL, respectively) and amastigotes forms (IC50 of 6.6 and 5.05 µg/mL, respectively) and these effects were also related to apoptosis induction. The major compounds found in the leaves hexanic fraction were α-amyrinyl acetate and β-amyrine; while the seed fraction showed cetin and nonacosane (EINECS 211-126-2). Both fractions were composed by derivatives of artemisinin (Islamuddin et al., 2012).
Artemisinin is a sesquiterpene lactone isolated from A. annua. Artemisinin and its derivatives were shown to inhibit L. donovani, L. infantum, and L. major (through the induction of parasite apoptosis; Sen et al., 2007Sen et al., , 2010Cortes et al., 2015;Ghaffarifar et al., 2015). Due its lipophilic character, some leishmanicidal formulations containing artemisinin were already evaluated in models in vitro and in vivo, as examples: poly lactic co-glycolic acid nanoparticles (Want et al., 2014(Want et al., , 2017 and nanoliposomes (Want et al., 2017).
Later, it was demonstrated the in vivo action of the n-hexane fractions from leaves and seeds of A. annua in a murine model of visceral leishmaniasis caused by L. donovani. The authors reported that besides inducing direct inhibition of parasite growth, these extracts also activated the Th1 response with generation of immunological memory . The efficacy of A. annua powder leaves was also confirmed in humans, where patients received capsules containing its powder (total of 30 g) for over 20 days. Although this study only evaluated two patients, it is important to highlight that both were healed after the treatment and without any adverse effects or manifestations of the disease even up to 24 months after the cure (Mesa et al., 2017).
These in vitro results encouraged the evaluation of the leishmanicidal properties of the fraction containing oleanolic and ursolic acids obtained from leaves of B. uncinella in a model of Tegumentar Leishmaniasis induced by L. amazonensis. Mice treated with this triterpenic fraction (at 1.0 or 5.0 mg/kg) showed lower levels of parasitism in the skin and decreased lesion size than untreated animals. These effects were similar to those observed for amphotericin B-treated mice. In both fractiontreated groups were also observed high amounts of interleukin-12 and interferon gamma (Yamamoto et al., 2014).
Later, it was reported that ursolic acid showed more potent action against L. amazonensis promastigotes than oleanolic acid. The effects of ursolic acid toward promastigotes were associated with activation of programmed cell death in a pathway dependent of mitochondria activity but not related to caspase 3/7. Only ursolic acid was able to eradicate the amastigotes by increasing the release of nitric oxide by peritoneal macrophages. The efficacy of ursolic acid was also proven in vivo using BALB/c mice infected L. amazonensis (Yamamoto et al., 2015). However, oleanolic acid has been highlighted in other works as an important lead molecule for development of drugs for treatment of leishmaniosis (Sifaoui et al., 2014(Sifaoui et al., , 2017Ghosh et al., 2016;Melo et al., 2016;Pertino et al., 2017).
Recently, the ursolic acid obtained from leaves of B. uncinella was also shown as a potent agent against experimental visceral leishmaniasis caused by L. infantum. The intraperitoneal injection of ursolic acid (1.0 or 2.0 mg/kg) reduced the parasites load in spleen and liver, induced the proliferation of splenic mononuclear cells and the production of IFN-γ and nitric oxide (Jesus et al., 2017). Additionally, a nanostructured lipid carrier system coated with N-octyl-chitosan surface for improve the delivery of ursolic acid was developed for treatment of visceral leishmaniosis induced by L. donovani. The oral treatment with this preparation was more effective than free ursolic acid treatment and reduced the parasite load in the spleen (Das et al., 2017).
Regarding B. dracunculifolia (the most important source of the Brazilian green propolis), the extract from leaves showed anti-T. cruzi effects and five active compounds were obtained; among them, isosakuranetin and baccharis oxide showed the best inhibitory potentials with IC50 values of 247.6 and 249.8 µM, respectively. Other compounds [aromadendrin-4'-methylether, ferulic acid, and 3-prenyl-4-(dihydrocinnamoyloxy)-cinnamic acid] were classified as moderated inhibitors. The authors did not evaluated the toxicity of these compounds (Da Silva Filho et al., 2014). On the other hand, the most active anti-L. donovani agents obtained from B. dracunculifolia were ursolic acid (IC50 = 3.7 µg/mL) and hautriwaic acid lactone (IC50 = 7.0 µg/mL; Da Silva Filho et al., 2014). Further, the EO from leaves of B. dracunculifolia showed action against the promastigote forms of L. donovani (IC50: 42 µM). This oil had (E)-nerolidol (33.51%) and spathulenol (16.24%) as major compounds. The oil was not toxic to Vero cells at the tested concentrations (Parreira et al., 2010).

COMPOUNDS ISOLATED FROM Calea PLANTS ARE ACTIVE AGAINST TRYPANOSOMATIDS
In relation to plants belonging to the Calea genus, antitrypanosomatids compounds have been isolated from two species: Calea pinnatifida (R.Br.) Less. and Calea uniflora Less. This last species is a plant with ethnomedicinal importance in the state of Santa Catarina (Brazil), however there are few scientific studies about its pharmacological properties . Two p-hydroxyacetophenone derivatives [2-senecioyl-4-(hydroxyethyl)-phenol and 2senecioyl-4-(pentadecanoyloxyethyl)-phenol] obtained from dichloromethane extract of C. uniflora reduced the viability of T. cruzi trypomastigotes by 70 and 71%, respctively (at a 500 µg/mL dose) (do Nascimento et al., 2004). Similarly, two chromanones [uniflorol-A and uniflorol-B] from this extract inhibited 88.9% of L. major promastigotes growth at a concentration of 100 µg/mL (Do Nascimento et al., 2007). The authors did not report the toxicity of these compounds above discussed.
Other compounds with promising inhibitory action toward T. cruzi amastigotes were isolated from dichloromethane and ethyl acetate fractions of C. uniflora leaves. Among them, ethyl caffeate showed the best activity with an IC50 of 18.27 µg/mL (SI = 12.95), while the mixture of butein and orobol (1:1) showed an IC50 of 26.53 µg/mL (SI = 3.61). The toxicity of these compounds was evaluated using THP-1 cells. The author also investigated the inhibitory action of the compounds isolated from C. uniflora leaves against L. amazonensis amastigotes, however no promising results were found (Lima et al., 2016).

SESQUITERPENES ISOLATED FROM Mikania SPECIES ARE ACTIVE AGAINST T. cruzi
The genus Mikania has been pointed as a source of bioactive compounds, based on this, the extracts of four species (Mikania micrantha Kunth, Mikania parodii Cabrera, Mikania periplocifolia Hook. & Arn, and Mikania cordifolia (L.f.) Willd.) were evaluated against T. cruzi and L. braziliensis. The organic extracts (prepared with dichloromethane/methanol solution; 1:1) of the four Mikania species exhibited inhibitory activity against both pathogens, however the M. micrantha extract was the most active, inhibiting by 77.6 and 84.9% the growth of epimastigotes and promastigotes of T. cruzi and L. braziliensis, respectively (Laurella et al., 2012).
Later, sesquiterpene lactones with inhibitory action against T. cruzi and L. braziliensis were obtained from dichloromethane extracts of M. micrantha and Mikania variifolia Hieron.

JACARANONE FROM Pentacalia desiderabilis IS ACTIVE AGAINST TRYPANOSOMATIDS
Jacaranone is a compound extracted from leaves of Pentacalia desiderabilis (Vell.) Cuatrec that showed inhibitory action against L. chagasi, L. braziliensis, and L. amazonensis with low IC50 values (ranging from 11.86 to 17.22 µg/mL); it was also active against T. cruzi trypomastigotes (IC50 = 13 µg/mL). However, this compound did not show activity against the amastigote forms of L. chagasi and T. cruzi. The cytotoxicity studies using MK2 cells suggested that jacaranone is not a promising compound for treatment of leishmaniosis and Chagas disease (Morais et al., 2012).
P. carolinensis EO also showed activity against both amastigote (IC50 = 6.2 µg/mL) and promastigote (IC50 = 24.7 µg/mL) forms of L. amazonensis, while cytotoxicity assay revealed a CC50 value of 28.3 µg/mL against peritoneal macrophage from BALB/c (SI =5). The intralesional application of this EO (30 mg/kg) resulted in the reduction of parasite burden and lesion size in mice, even when compared with those animals treated with Glucantime R . The major component in this EO was selin-11-en-4α-ol (about 51%), however, the authors did not tested it .
The in vivo effects of uvedalin and enhydrin was evaluated in a model of T. cruzi infection in mice. Both compounds were administrated by intraperitoneal injections (1 mg/kg of body weight/day) on the 7th day post-infection and the treatment was performed for 5 consecutive days. The animals treated with uvedalin or enhydrin exhibited lower levels of parasitaemia, and these effects were similar to those obtained with benznidazole (positive control). Mice treated with these sesquiterpene lactones also showed higher survival ratios and reduced weight loss when compared to untreated animals (Ulloa et al., 2017).

SESQUITERPENE LACTONES FROM Tanacetum parthenium ARE ACTIVE AGAINST TRYPANOSOMATIDS
Two sesquiterpene lactones with activity against trypanosomatids were isolated from Tanacetum parthenium (L.) Sch.Bip.: guaianolide and parthenolide. Guaianolide was obtained from the hydroalcoholic extract of the aerial parts of T. parthenium, and it showed an IC50 value of 2.6 µg/mL toward promastigote forms of L. amazonensis. It was also active against the amastigote form, reducing their survival to 10% when compared to untreated cells. The cytotoxicity analysis, carried out with J774G8 cells, revealed that this compound displayed a high selectivity toward the parasite (SI = 385). The effects of guaianolide on promastigotes were associated to severe morphological alterations including changes in size, shape and number of flagellum (Da Silva et al., 2010).
Guaianolide was also effective against all forms of T. cruzi with IC50 values of 5.7 ± 0.7, 18.1 ± 0.8, 66.6 ± 1.3 µM for trypomastigote (SI = 16.4), epimastigote and amastigote (SI = 1.40) forms. The ultrastructural modifications induced by guaianolide involved the reduction of cell size for trypomastigotes and epimastigotes; and decrease in mitochondrial membrane potential in epimastigotes. Further, guaianolide also exhibited synergistic effect with benznidazole against the epimastigote forms and additive effects against the trypomastigote forms (Cogo et al., 2012).
Similarly, parthenolide was also isolated from the aerial parts of T. parthenium and exhibited activity against L. amazonensis (Tiuman et al., 2005) and T. cruzi (Izumi et al., 2008). When concerning the anti-L. amazonensis activity, parthenolide showed IC50 values of 0.37 µg/mL and 0.81 µg/mL toward promastigote and amastigote forms, without inducing toxic effects against J774G8 macrophages and sheep erythrocytes. The leishmanicidal activity was associated to an increase in the lysosomes size and in the exocytose in the region of the flagellar pocket (Tiuman et al., 2005). New insights on the action mechanism of parthenolide against amastigote forms of L. amazonensis were provided by the work of Tiuman et al. (2014). This research showed that parthenolide effect was associated with the appearance of autophagic vacuole, loss of membrane integrity, and mitochondrial dysfunction. In addition, parthenolide did not induce genotoxic effects in mice, as evaluated by micronucleus test (Tiuman et al., 2014).
In relation to anti-T. cruzi action, parthenolide showed an IC50 of 0.5 µg/mL against epimastigote forms and reduced the internalization of trypomastigotes forms of T. cruzi in LLMCK2 cells (51 and 96% when the cells were treated at 2 and 4 µg/mL, respectively). The compound also exhibited low toxicity against LLMCK2 cells with a SI of 6.4. Parthenolide induced severe alterations on the parasite, that included increase in the number of nucleus, vacuoles and reservosomes, mitochondrion swelling and the distortion of internal membranes (Izumi et al., 2008). The combinatory effects of parthenolide and benznidazole toward T. cruzi were also evaluated. This combination was synergistic against epimastigotes, while an additive effect was observed against trypomastigote forms (Pelizzaro-Rocha et al., 2010).
Another plant from this genus with ethnopharmacological relevance is Vernonia scorpioides (Lam.) Pers. From this plant was extracted lupeol, that served as starting material for a semisynthetic approach in order to obtain antileishmanial and antitrypanosomal compounds. Among the derivatives, the best activity was observed for lup-20(29)-ene-diol with an IC50 of 12.4 µg/mL against T. cruzi amastigotes and a CC50 of 161.5 µg/mL toward THP-1 cells (SI = 12.94); this compound did not show antileishmanial action (Machado et al., 2018).
In turn, M. recutita EO showed an IC50 value of 10.8 and 10.4 µg/mL toward L. amazonensis and L. infantum promastigotes. Following, a bio-guided fractionation of the EO constituents resulted in the identification of α-bisabolol as a major compound. α-Bisabolol showed higher IC50 values for promastigotes (16.0 and 9.5 µg/mL for L. amazonensis and L. infantum, respectively). The efficacy of α-bisabolol on amastigotes of both studied species was also assessed, and IC50 values of 5.9 µg/mL (L. amazonensis) and 4.8 µg/mL (L. infantum) were obtained. The cytotoxic evaluation of α-bisabolol was performed using J774A.1 macrophages and revealed SI values of 5.4 and 6.6 for L. amazonensis and L. infantum, respectively. The SI value for L. amazonensis was lower than that reported by Colares et al. (2013). The action of αbisabolol is associated to a damage in the parasite membrane, phosphatidylserine externalization, and to a decrease in the mitochondrial membrane potential and total ATP levels (Hajaji et al., 2018). Similar results were obtained by Corpas-López et al. (2016a) that showed that α-bisabolol induced apoptosis in L. infantum, which is related to mitochondrial dysfunction and oxidative stress (Corpas-López et al., 2016a).
Moreover, α-bisabolol was evaluated in a murine model of visceral leishmaniasis induced by L. infantum. The daily oral treatment with α-bisabolol (at 50, 200, or 1,000 mg/kg doses) started 28 days after L. infantum infection and continued for 14 days. The best results were seen for animals treated with α-bisabolol at 200 mg/kg, where the reduction on parasite levels on spleen and liver were 71.60 and 89.22%, respectively. These results were even better than those observed for mice treated with meglumine antimoniate or the combination of meglumine antimoniate and α-bisabolol (Corpas-López et al., 2015). α-Bisabolol (in topical or oral treatment) was also shown to be effective in the treatment of cutaneous infection induced by L. tropica in hamsters (Corpas-López et al., 2016b). Recently, α-bisabolol was useful for the treatment of naturally acquired canine leishmaniasis. In this elegant work, the dogs received oral doses of α-bisabolol (30 mg/kg) during two series of 30 days, with 30 days of interval. The results showed that α-bisabolol-treated dogs showed lower levels of parasite load (in bone marrow, lymph node and peripheral blood) than the dogs treated with meglumine antimoniate. α-Bisabolol treatment also increased the expression of IFN-γ (Corpas-López et al., 2018).

CONCLUSION
Taken together, all these studies show that Asteraceae plants are interesting sources of compounds with inhibitory activity toward trypanosomatids. These compounds have the potential to improve the development of new effective agents against these neglected protozoan diseases. It is important to note that several of these compounds need to be evaluated with in vivo models. Furthermore, these papers provided scientific bases for the use of several plants with ethnopharmacological relevance in different countries.

AUTHOR CONTRIBUTIONS
RM and RS performed data collection and writing of the manuscript with support from LdS, TH, and AA. TH and MB contributed with the final version of the manuscript and with the important intellectual content of the study. LdS conceived the present study and design and implementation of the research and critical review of the manuscript regarding the important intellectual content of the study. AA contributed with the design of the research, data collection and supervised the work of RM and RS.