1 Introduction

Leishmaniasis is caused by parasites belonging to the Trypanosomatidae family and Leishmania genus. There are three main forms of leishmaniasis—visceral, cutaneous and mucocutaneous [1]. Most cases of cutaneous leishmaniasis occur in Afghanistan, Algeria, Brazil, Colombia, Islamic Republic of Iran, Pakistan, Peru, Saudi Arabia and Syrian Arab Republic [1].

Leishmaniasis treatment is performed with pentavalent antimonials (sodium stibogluconate and meglumine antimoniate), amphotericin B and pentamidine. However, the use of these agents is questionable due to the variability in their efficacy among Leishmania species, high cost, need for parenteral administration, and high toxicity [2, 3]. The search for alternative therapies is very important, and medicinal plants are a source of bioactive molecules [4].

Annona species are used in traditional medicine to treat leishmaniasis. In vitro, antileishmanial studies of extracts validated the popular use [5,6,7]. Some studies about antileishmanial activity of Annona attribute its activity to alkaloids [8, 9] and acetogenins [10].

Several alkaloids were active against Leishmania, among these are coronaridine (Fig. 1a), 18-methoxycoronaridine (Fig. 1b) [11], O-methylarmepavine (Fig. 1c) [10], liriodenine (Fig. 1d) [12]. Moreover, acetogenins annonacinone (Fig. 1e) and corossolone (Fig. 1f) were also promising as leishmanicide [10].

Fig. 1
figure 1

Compounds isolated from species of Annona. Legend: (a) Coronaridine, (b) 18-Methoxycoronaridine, (c) O-methylarmepavine, (d) Liriodenine, (e) Corossolone, (f) Annonacinone

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Previous studies on species of the genus Annona present biological investigations on promastigote and amastigote forms of Leishmania, for example, from seeds of A. squamosa a trihydroxylated acetogenin with two tetrahydrofuran rings and α, β-unsaturated lactonic ring of 37 carbon atoms endowed with antihelmintic and antiprotozoal properties was isolated. This substance showed leishmanicidal action against promastigotes and amastigotes of L. chagasi [10]. The volatile oil of A. foetida was active against promastigotes of four different species of Leishmania, having been more active in L. guyanensis (IC50: 4.1 μg/mL) [9].

The alkaloids fraction from leaves of A. coriacea revealed activity against promastigotes of L. chagasi, with an IC50 of 41.6 μg/mL. In amastigote forms, they caused death to 27.2% of the parasites, at a concentration of 20 μg/mL [8]. The alkaloid fraction of A. foetida, showed activity against the promastigotes of L. braziliensis and L. guyanensis [12].

In this context, to validate the popular use on leishmaniasis, the analysis of several studies of Annona species was performed, focused on their antileishmanial activity.

2 Materials and methods

A survey was performed with the selection of scientific articles available at CAPES, PUBMED and GOOGLE SCHOLAR DATABASE; the year of publication was not limited. The search was carried out in January 2020 and only articles in Portuguese, English and Spanish, which presented leishmanicidal activity (inhibitory concentration 50%—IC50) were considered. The following exclusion criteria were adopted: articles in other languages, those that did not address the proposed theme, in duplicate, and articles that could not be accessed in full.

For the search, descriptors related to the theme were used in an associated way: Leishmania and Annona. The preliminary result included 1796 papers for screening (CAPES = 21, PUBMED = 15 and GOOGLE SCHOLAR DATABASE = 1760), using as criterion articles with titles that fit the theme, summary compatible with this study proposal, and the exclusion of duplicate occurrences. Four articles from CAPES and twelve from PUBMED were eliminated due to duplication. Regarding GOOGLE SCHOLAR DATABASE, most of the eliminated articles had inappropriate title or duplication (1757). When the title and abstract were analyzed, 14 papers were included. Figure 2 shows the screening identification procedure included for analysis.

Fig. 2
figure 2

Flowchart of article eligibility

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Two reviewers selected, independently, studies based on their title and abstract, those considered potentially relevant were obtained for complete analysis. Any discrepancies were solved by consensus and a third reviewer was consulted to ensure compliance with the inclusion criteria. At the end, 13 articles were selected for discussion and inclusion in this analysis (Fig. 2).

Regarding data analysis, it was done in two stages: in the first, a table with the following data was used: plant material, type of extract, fractions and isolated substances, IC50 and the cytotoxic concentration (CC50). The results are summarized in tables and anti-Leishmania activity was assessed using the following criteria: IC50 ≤ 100 μg/mL active, IC50 between 101 and 200 μg/mL moderately active and IC50 ≥ 200 μg/mL inactive [13]. Cytotoxicity results were assessed by the following criteria: CC50 ≤ 100 μg/mL cytotoxic, CC50 between 101 and 500 μg/mL moderately cytotoxic, and CC50 ≥ 500 μg/mL non-cytotoxic [13].

3 Results

In order to identify whether Annona extracts presented antileishmanial activity, an extensive literature review was done, and the results are highlighted in Table 1. Studies about antileishmanial activity for these species are scarce, with only their anti-promastigote activity being evaluated (Table 1).

Table 1 Antileishmanial activity of Annona species
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The ethanol extracts obtained from root barks, stem barks, and stem wood of A. crassiflora were active against promastigotes of L. donovani (IC50: 3.7 ± 0.3 µg/mL, 12.4 ± 0.3 µg/mL, and 8.3 ± 0.8 µg/mL, respectively; Table 1) [14]. The total alkaloids obtained from the ethanol extract of A. crassiflora leaves were active against L. chagasi (IC50: 24.9 ± 0.8; Table 1) [8]. The essential oil of A. foetida was active against promastigotes of L. guyanensis (IC50: 4.1 ± 0.1 µg/mL), L. braziliensis (IC50: 9.9 ± 1.2 µg/mL), L. amazonensis (IC50: 16.2 ± 1.9 µg/mL), and L. chagasi (IC50: 27.2 ± 6.2 µg/mL), however, it was cytotoxic in peritoneal macrophages BALB/c (PMBC; CC50: 5.67; Table 1) [9]. The hexane extract from of A. foetida was active against promastigotes of L. guyanensis (IC50: 42.7 ± 5.4 µg/mL). The dichloromethane extract was active against promastigotes of L. guyanensis (IC50: 2.7 ± 0.4 µg/mL) and L. amazonensis (IC50: 23.0 ± 0.6 µg/mL). The dichloromethane extract fractionation yielded the alkaloid fraction. However, this fraction showed lower activity against promastigotes of L. guyanensis (IC50: 10.3 ± 0.9 µg/mL) and L. amazonensis (IC50: 18.3 ± 2.5 µg/mL). Nevertheless, the methanol extract of A. foetida was active against L. guyanensis (IC50: 23.6 ± 3.1 µg/mL) and L. amazonensis (IC50: 40.4 ± 3.2 µg/mL), and fractionation contributed to the activity (L. guyanensis IC50: 9.1 ± 0.8 µg/mL and L. amazonensis IC50: 24.3 ± 1.9 µg/mL; Table 1) [12].

The antileishmanial activity of alkaloids and acetogenins isolated from A. foetida were evaluated. The alkaloid liriodenine was more promising against L. guyanensis (IC50: 21,0.5 ± 0.4 µg/mL and 55.92 ± 3.55 µg/mL) [9, 15] and PH8- L. amazonensis (IC50: 1.43 ± 0.58 µg/mL). Liriodenine showed high toxicity for BALB/c mice peritoneal macrophages (CC50: 19.11 ± 1.06 µg/mL) and low selectivity in L. guyanensis (SI: 0.34; Table 1) [15].

Different extracts obtained from Annona mucosa were tested on L. donovani, L. amazonensis, and L. braziliensis. Most of the extracts showed activity against promastigotes of L. amazonensis (PH8, IC50: 9.3–46.5 µg/mL), although it was not observed significant reduction in the rate of macrophages infection by amastigotes (30%). When cytotoxicity and anti-promastigote activity are related, a low selectivity index is observed (SI: 0.9–6; Table 1) [15].

From Annona mucosa, the alkaloids oxoaporphine, atherospermidina and liriodenine were isolated. Liriodenine was active against promastigotes of L. amazonensis (IC50: 1.43 ± 0.58 µg/mL) and amastigotes forms of L. amazonensis [15]. High selectivity was observed (SI: 13.36), especially for liriodenine (SI: 13.37; Table 1).

The anti-promastigote activity of A. muricata was extensively evaluated, yielding inactive (hexane and methanol extracts from pericarp: IC50 > 1000 µg/mL), moderately active (hexane and methanol extracts from leaves: IC50 > 100 µg/mL), and active extracts (hexane and methanol extracts from stem and ethyl acetate extracts from pericarp, leaves, and stem: IC50 ≤ 100 µg/mL). Fractionation of A. muricata extracts led to the isolation of acetogenins, which were more active than the extracts against promastigotes (Table 1) [10, 16].

Scoparone, corossolone, and annonacinone isolated from A. muricata were active against promastigotes of L. donovanni, L. mexicana, and L. major [10, 16]. Annonacinone displayed the major activity against those three Leishmania species (IC50: 6.72–8.00 µg/mL) [16]. Annonacinone (IC50: 37.6 µg/mL) and corossolone (IC50: 25.9 µg/mL) showed less activity against promastigotes of L. chagasi. These substances were also tested against amastigotes of L. chagasi, being annonacinone (IC50: 13.5 µg/mL) more active than corossolone (IC50: 28.7 µg/mL). Annonacinone also presented higher selectivity (CC50: 59.5 µg/mL; SI: 4.4) than corossolone (CC50: 54 µg/mL; SI: 1.9; Table 1) [10].

Scoparone presented lower activity than others acetogenins against promastigotes of L. donovanni (IC50: 27.51 ± 0.97 µg/mL), but presented activity similar to the others compounds against L. mexicana (IC50: 9.11 ± 0.25 µg/mL) and L. major (IC50: 14.37 ± 0.98 µg/mL; Table 1) [16].

The alkaloid O-methylarmepavine and the acetogenin C37 trihydroxy adjacent bistetrahydrofuran were isolated from A. squamosa. Both O-methylarmepavine and trihydroxy adjacent bistetrahydrofuran showed similar inhibitory effects against promastigotes (IC50: 23.3 and 26.4 µg/mL) and amastigotes of L. chagasi (IC50: 25.4 and 25.3 µg/mL). However, this acetogenins showed higher cytotoxicity in RAW 264.7 cells (CC50: 43.5 µg/mL) than the alkaloid (CC50: 79.7 µg/mL; Table 1) [16].

The hydroalcoholic leaf extract of A. glabra was active against L. amazonensis promastigotes (IC50: 37.8 ± 0.1 µg/mL) [17]. The extracts obtained from the leaves and branches of A. senegalensis also showed activity against another strain of Leishmania (L. donovani; IC50 10.8 µg/mL and 27.8 µg/mL respectively) [18]. However, the two samples were moderately cytotoxic for human T-cell of acute leukemia (JURKAT; CC50: 273.49 µg/mL and 127.95 µg/mL respectively) [18] and the leaf extract showed best selectivity index (SI: 25.3; Table 1).

The methanol and aqueous extracts from A. purpurea bark and seed were evaluated against L. donovani promastigotes. The methanol extract from the seed showed better activity (IC50: 28.57 ± 1.78 µg/mL) but was cytotoxic in nasopharyngeal cells. (KB; CC50: 7.81 ± 1.45; IS: 0.27). However, the aqueous seed extract presented the best selectivity index (IC50: 179.9 ± 4.1 µg/mL; CC50: 96.7 ± 3.9 µg/mL; SI: 0.53; Table 1) [19]. The fraction E2 obtained from the hydroalcoholic leaf extract of A. purpurea was active against L. panamensis (IC50: 0.961) and moderately cytotoxic in human monocyte cells, presenting a high selectivity index (U937; CC50: 124.02 µg/mL; SI: 129.05; Table 1) [20].

The extract from A. cornifolia was moderately active in L. amazonensis (IC50: 175 µg/mL) and cytotoxic in African green monkey kidney cells (VERO; CC50: 34.33 µg/mL; SI: 0.196; Table 1) [21]. Other extracts from branches and leaves of A. muricata were active against promastigotes of L. amazonensis, L. braziliensis and L. donovani (Table 1) [22].

The ethyl acetate extracts from both the branch and the leaves showed better results in the 3 Leishmania species (branch: IC50: 63.2 µg/mL; leaves: 25 µg/mL; Table 1) [22].

4 Discussion

Different species belonging to the Annona genus have popular use for leishmaniasis or wounds treatment [7, 10, 12]. However, there is the following question: this activity is related to the presence of acetogenins, or their alkaloids, or it is related to the synergism between these metabolites.

Previous study demonstrated annomontine alkaloid was the most active against L. amazonensis [12]. Alkaloids can interfere with tubulin polymerization or stabilize the DNA topoisomerase complex [23]. The biological activity of liriodenine can be attributed to the intercalation between neighboring base pairs of the DNA double helix [24, 25].

The oxo function induces cytotoxicity on precursor incorporation into DNA [25, 26]. Indeed, acetogenins binds to complex I of the mitochondrial electron transport chain [27, 28]. In addition, it inhibits ubiquinone-bound NADH oxidase [29,30,31]. Due to the differences in mechanisms of action, it is believed that there may be synergy to leishmanicide activity.

In the present review, although acetogenins were very active against promastigotes of different species of Leishmania, with an IC50 of less than 30 µg/mL [10, 16] corosolone and annonacinona were still active against the amastigote form [10]. In contrast, structural changes seem to interfere in the antileishmanial activity of alkaloids and this activity may be more pronounced depending on the parasite species [10, 12, 15].

If only antiparasitic activity is considered, this may suggest that acetogenins are more promising than alkaloids as leishmanicide. However, you must consider the toxicological aspects and the selectivity index (SI).

Unfortunately, most of the acetogenins isolated from Annona lack cytotoxicity studies, and preliminary results suggest that corossolone (SI = 2.08) and annonacinone (SI = 1.58) have a selectivity index of less than 10 [10]. However, additional genotoxicity, mutagenicity and in vivo studies need to be carried out to determine the safety of its use as a leishmanicide.

Another issue that needs to be analyzed is whether the fractionation contributes to antileishmanial activity. In the case of A. muricata, fractionation contributed significantly to biological activity, it also seems to contribute to selectivity [7, 22].

Nevertheless, for A. crassiflora, some extracts showed better antileishmanial potential than isolated substances [8, 14]. For A. foetida, alkaloid fractions appear to be promising for leishmaniasis treatment (Table 1) [12].

The fractionation of A. purpurea extract contributed to antileishmanial activity and high selectivity index, with the E2 fraction being a strong candidate for anti-leishmania drug, since this showed better anti-leishmania activity (IC50: 0.961 µg/mL), moderate cytotoxicity, resulting in a selectivity index > 10 among the extracts, fractions and isolated substances evaluated from Annona species (IS: 129.05) [20].

5 Conclusion

Annona species are promising for the treatment of leishmaniasis, bearing in mind the importance of extract fractionation and alkaloids or acetogenins isolation, since many alkaloids and acetogenins have antiparasitic activity, which can be important tools against parasites drug resistant.