Potential effect of the medicinal plants Calotropis procera. Ficus elastica and Zingiber officinale against Schistosoma mansoni in mice

Abstract

Context. Calotropis procera (Ait.) R. Br. (Asclepiadaceae), Ficus elastica Roxb. (Moraceae) and Zingiber officinale Roscoe (Zingiberaceae) have been traditionally used to treat many diseases.

Objective: The antischistosomal activity of these plant extracts was evaluated against Schistosoma mansoni.

Materials and methods: Male mice exposed to 80 ± 10 cercariae per mouse were divided into two batches. The first was divided into five groups: (I) infected untreated, while groups from (II–V) were treated orally (500 mg/kg for three consecutive days) by aqueous stem latex and flowers of C. procera, latex of F. elastica and ether extract of Z. officinale, respectively. The second batch was divided into four comparable groups (except Z. officinale-treated group) similarly treated as the first batch in addition to the antacid ranitidine (30 mg/kg) 1 h before extract administration. Safety, worm recovery, tissues egg load and oogram pattern were assessed.

Results. Calotropis procera latex and flower extracts are toxic (50–70% mortality) even in a small dose (250 mg/kg) before washing off their toxic rubber. Zingiber officinale extract insignificantly decrease (7.26%) S. mansoni worms. When toxic rubber was washed off and ranitidine was used, C. procera (stem latex and flowers) and F. elastica extracts revealed significant S. mansoni worm reductions by 45.31, 53.7 and 16.71%, respectively. Moreover, C. procera extracts produced significant reductions in tissue egg load (∼34–38.5%) and positively affected oogram pattern.

Conclusion: The present study may be useful to supplement information with regard to C. procera and F. elastica antischistosomal activity and provide a basis for further experimental trials.

• Asclepiadaceae
• moraceae
• oogram pattern
• tissue egg load
• worm burden
• zingiberaceae

Introduction

Schistosomiasis is a chronic and debilitating disease, caused by trematode flatworms of the genus Schistosoma that exacerbates poverty (Davis, 2009; King & Dangerfield-Cha, 2008). Although close to 800 million individuals are at risk of contracting the disease and over 200 million people are thought to be infected, schistosomiasis is often neglected (Utzinger et al., 2009). The global burden of schistosomiasis has been estimated at 1.7–4.5 million disability-adjusted life years, but even the higher estimate might be an underestimation of the true burden (King et al., 2005; King & Dangerfield-Cha, 2008). Praziquantel (PZQ) is the only widely used drug for treatment and control of this parasitemia. Although no clinically relevant resistance to PZQ has been described to date, development of drug-resistance remains a growing threat, particularly in view of the mounting PZQ pressure (Melman et al., 2009). The growing need for the development of novel and inexpensive drugs against schistosomiasis has led the scientific community to intensify the search for extracts and pure compounds obtained from plants exhibiting potential schistosomicidal properties (Adamu et al., 2006; Perrett et al., 1995). The promising results obtained from plants, encourage the screening of more plants for their antischistosomal activity to come up with natural products that are more effective schistosomicides, especially in rural communities where these plants abound. Therefore, it seems important to screen and evaluate the potency of some local plants that are active on parasitic organisms.

Calotropis procera (Ait.) R. Br. (Asclepiadaceae), a wild growing tropical plant, commonly known as Arka in India, is widely distributed in Asia, Africa, South America and abundant in northeast Brazil. It is a common xerophytic plant throughout Egypt particularly in the southern extreme arid sections of the deserts and Nile regions. Calotropis procera is one of the latex-producing plants, which usually secrete milk-like fluid from a network of laticifer cells, in which subcellular organelles intensively synthesize proteins and secondary metabolites (Lopes et al., 2009). The biological importance of latex fluids is still unclear and knowledge of their physiological role is still limited (Ramos et al., 2007). Nevertheless, strong proteolytic activity was attributed to the abundant endogenous enzymes such as cysteine proteinases (EC 3.4.22.16) and chitinases (EC 3.2.1.14) that present in C. procera fluids (Freitas et al., 2007).

Calotropis procera has been used in Indian folk medicine for the treatment of various ailments such as rheumatism, aches, gastrointestinal disorders, leprosy, ulcers, piles and tumors (Kumar & Arya, 2006). The plant has also antimicrobial (Malik & Chaughati, 1979), antioxidant (Roy et al., 2005), anticancer (Ayoub & Kingston, 1981) and anthelmintic activities (Al-Qarawi et al., 2001; Iqbal et al., 2005). Experimentally, an ethanol extract of C. procera flowers was reported to have antipyretic, analgesic (Mascolo et al., 1988), anticancerogenic (Smit et al., 1995), antimalarial (Sharma & Sharma, 1999, 2001) and hepatoprotective (Qureshi et al., 2007) activities. The milky white latex of this plant has been reported to exhibit potent anti-inflammatory and analgesic, and weak antipyretic activities in various experimental models (Dewan et al., 2000; Kumar & Basu, 1994; Kumar & Arya, 2006). It has also been demonstrated to possess antioxidant, antihyperglycemic and hepatoprotective properties (Padhy et al., 2007; Roy et al., 2005).

Ficus elastica Roxb. (Moraceae) is a tropical evergreen tree. It is found in the Egyptian main gardens like Orman garden in Cairo and Antoniades garden in Alexandria and in many streets as used for decoration. Its constituents of coumarins, triterpenes, steroids, flavonoids and tannins as well as alkaloids characterize the plant (Mbosso et al., 2012). Practitioners of herbal medicine in West Africa use the plant for the treatment of muscle and joint pain. Sackeyfio and Lugeleka (1986) reported anti-inflammatory activity of F. elastica aqueous extract against carrageenin-induced edema and adjuvant-induced arthritis in rats.

Ginger [Zingiber officinale Roscoe (Zingiberaceae)] has been used as a spice for over thousand years (Bartley & Jacobs, 2000). Ginger is said to be a native of China and India and is currently grown commercially in the warm, moist, areas of the Mediterranean (Egypt), tropical and subtropical areas of Africa, Southeast Asia, Latin America and Australia. Toxic activities or effects were recorded in the plant latex and the proteins in it such as ficin (Konno et al., 2004). On the other hand, the plant roots contain polyphenol compounds (6-gingerol and shogaols), which possess a high antioxidant activity (Stoilova et al., 2007). In addition, ginger was reported to be a detoxifying agent against alcohol abuse (Shati & Elsaid, 2009) and bromobenzene intoxication (El-Sharaky et al., 2009). Matsuda et al. (2009) and Habib et al. (2008) reported its antidiabetic, antihyperlipidimic and hepatic anticancer effect. Moreover, its efficacy as a molluscicide against Biomphalaria alexandrina, the snail intermediate host of S. mansoni was reported by Omran et al. (2007).

Despite the favorable ethnopharmacological properties of these plant extracts, its potential activity against S. mansoni has not been previously explored. These extracts showed promising in vitro S. mansoni worm killing (an investigation by the same authors under publication). Therefore, the present study was designed to evaluate the in vivo antischistosomal activity of the extracts of C. procera stem latex and flowers, F. elastica and Z. officinale using parasitological criteria of cure (worm recovery, tissues egg load and oogram pattern), and their safety by assessing acute oral toxicity.

Materials and methods

Chemicals

Acetic anhydride, potassium hydroxide (KOH) and chloroform (BDH, England), sulphuric acid (H₂SO₄) and Dragendorff’s reagent (solution of potassium bismuth iodide), methanol and acetone (Sigma-Aldrich, St. Louis, MO), ferric chloride (FeCl₃), hydrochloric acid (HCl) and ether (Merck, Darmstadt, Germany).

Plant collections

Calotropis procera was collected in spring (March 2009) from desert fields close to Cairo city, Egypt. Ficus elastica were collected (April 2009) from Egyptian botanical gardens, while Z. officinale rhizomes were purchased (April 2009) from the local markets. The plants were authenticated by Wafaa M. Amer, Professor of Taxonomy, Department of Botany, Faculty of Science, Cairo University, Giza, Egypt. Voucher specimens (Reg. No. C-II, F1 and G-2, respectively) were kept in the herbarium, Medicinal Chemistry Department, Theodor Bilharz Research Institute (TBRI), Giza, Egypt.

Plants extraction

Calotropis procera stem latex and flowers extraction

The latex of C. procera was collected from the stem near the buds of the plant and was dried on glass plates under the shade at room temperature for at least 15 days, then scratched from the glass plates and with the help of a mortar it was ground to small granules, and extracted with water. The extract was then concentrated to dryness in a vacuum rotary evaporator and stored at 4 °C until used. About 100 g of powdered C. procera flowers was mixed with 1000 ml of distilled water in a 2-liter flask and boiled for 1.5 h. Following cooling to 40 °C, the “brew” was filtered using Whatman No. 1 filter paper. The filtrate was then concentrated to dryness in a vacuum rotary evaporator, washed with chloroform to extract and purify lipids and was stored at 4 °C until used.

Ficus elastica extraction

The latex of F. elastica was collected from the stems of the plant, dried as described for stem latex of C. procera and extracted with water. The resulting water extract was filtered using Whatman No. 1 filter paper and concentrated to dryness under vacuum using a rotary evaporator, then the extract stored at 4 °C for subsequent experiments.

Removal of toxic rubber

The toxic rubber materials of C. procera and F. elastica dry latex were washed out by extraction with aqueous methanol (85%). Then, the extract was filtrated and dried under vacuum. The dry residue obtained was washed again with boiled acetone. The clean, rubber-free acetone-insoluble portion was used in all subsequent experiments. This procedure eliminates acetone-soluble molecules while retaining almost all proteins.

Zingiber officinale extraction

The dried powdered rhizomes (500  g) were extracted using ether. The extracts were concentrated under reduced pressure using a rotary evaporator at temperature not >50 °C and were kept at 4 °C until used for phytochemical and pharmacological studies.

Phytochemical screening

The different extracts were subjected to qualitative phytochemical screening using the standard procedures for the identification of the phytoconstituents. All extracts were tested for tannins, flavonoids, saponins, sterols, terpenes and alkaloids (Harborne, 1998; Siddiqui et al., 2009).

Animals and infection

Male Swiss albino mice (CD-1 strain) obtained from Schistosome Biological Supply Center (SBSC) at TBRI, Giza, Egypt and weighing 18–20 g were used in this study. The animals were maintained on a standard commercial pellet diet and were kept in air-conditioned animal house at 20–22 °C. All experimental procedures described below were carried out in accordance with the guidelines of institutional animal ethics committee. Mice were infected with 80 ± 10 S. mansoni cercariae per mouse (provided by SBSC of TBRI) according to the method described by Liang et al. (1987).

Acute toxicity study

Adult normal male mice were used to study acute oral toxicity (Bruce, 1985) of test plant extracts. For each plant extract, mice were divided equally into five groups, each of 6 mice and were given the extract at increasing oral doses of 100, 200, 400, 800 and 1600 mg/kg, respectively. Animals were observed individually after dosing at least once during the first 30 min, periodically during the first 24  h, with special attention given during the first 4  h. In addition, the general behavior of animals, signs of discomfort or any nervous manifestations were observed for further up to 14 days following treatment.

Animal groups

Before removal of toxic rubber

Schistosoma mansoni-infected mice were classified into three groups; one of them was left without treatment as respective control. While the other two groups were given C. procera stem latex and flower extracts orally in a dose of 250 mg/kg (the lowest test dose survived animals to the time of sacrifice) divided equally on five consecutive days as a suspension with gum acacia in normal saline.

After removal of rubber

A group of S. mansoni-infected mice was divided equally into two batches. The first batch was divided into five groups. The first one was left without treatment as respective untreated control, while groups from the second to the fifth were given extracts of stem latex and of flower (C. procera), F. elastica and Z. officinale orally in a dose of 1500 mg/kg divided equally on three consecutive days. The second batch of mice was divided into four groups. The first one was left without treatment as untreated control. While groups from the second to the fourth were given extracts of stem latex and of flower (C. procera) and F. elastica orally in a dose of 1500 mg/kg divided equally on three consecutive days after 1 h of the antacid ranitidine (30 mg/kg) administration. Animals of all infected groups were treated with plant extracts 7 weeks after infection and were killed by rapid decapitation 9-weeks post-infection.

Assessment of parasitological criteria

To recover mature and immature worms for subsequent counting and determination of sex, hepatic and mesenteric vessels of animals were perfused according to Duvall and DeWitt (1967). The number of ova per gram of liver or intestinal tissues (tissue egg load) was counted according to the method of Kamel et al. (1977), in which a piece of small intestinal or hepatic tissue was weighed before digestion in 5% KOH. The percentage of different egg developmental stages (oogram pattern) was studied according to the method of Pellegrino et al. (1962), in which eggs at different stages of maturity were identified (from I to IV) according to the size of the embryo and were counted. In addition, mature eggs containing fully developed miracidium and dead eggs (granular, dark and semitransparent) were also counted in three fragments of small intestine and the mean number of each stage was calculated.

Statistical analysis

Results are expressed as mean ± SEM. Differences between means in different groups were analyzed statistically for significance using Student’s t-test and p value of 0.05 or less was considered significant.

Results and discussion

Phytochemical screening studies

Preliminary phytochemical screening of the tested extracts revealed the presence of low concentrations of tannins, sterols, terpenes (C. procera flowers) and alkaloids in Z. officinale. In addition, moderate and high concentrations of tannins, flavonoids, saponins and terpenes were identified in Z. officinale. On the other hand, none of these secondary six metabolites was found in the stem latex of C. procera and F. elastica (Table 1). The concentrations of the most active compounds were recorded to be present in the water (C. procera flowers) and Z. officinale ether extracts. These results are in agreement with those of Atta et al. (2010) and Murti et al. (2010).

Table 1. Phytochemical screening of selected plant extracts.

	C. procera stem latex	C. procera flowers	F. elastica stem latex	Zingiber officinale
Tannins	−	+	−	++
Flavonoids	−	++	−	+++
Saponins	−	−	−	++
Sterols	−	+	−	+
Terpenes	−	+	−	++
Alkaloids	−	−	−	+

− = not present.

+ = present in low concentration.

++ = present in moderately high concentration.

+++ = present in high concentration.

Safety and in vivo efficacy against S. mansoni

Oral administration of water extracts of stem latex and flowers of C. procera in a total dose of 250 mg/kg produced percentage mortality of 50–70% (data not shown) without any significant change in the parasitological parameters assessed (Table 2). In this regard, El-Badwi et al. (1998) reported that the whole latex of C. procera has been described as a rich source of toxic compounds. Also, Konno et al. (2004) suggested that plant latex and the proteins in it such as papain, ficin and bromelain, all possess toxic activities or effects.

Table 2. Effect of C. procera stem latex and flower extracts oral administration (50 mg/kg for five consecutive days) on worm burden, egg count and the percentage of egg developmental stages (oogram pattern) in S. mansoni-infected mice 2-week post-treatment.

Animal groups	Total worms	Hepatic ova count × 10^3	Intestinal ova count × 10^3	% Total immature ova	% Mature ova	% Dead ova
Infected untreated (n = 5)	27.40 ± 1.21	14.81 ± 1.12	19.25 ± 1.35	54.96 ± 4.19	36.71 ± 4.05	8.33 ± 0.62
C. procera stem latex (n = 6)	24.67 ± 1.50	13.34 ± 1.81	18.03 ± 1.32	52.72 ± 0.94	38.82 ± 1.47	8.47 ± 1.11
C. procera flower (n = 6)	24.17 ± 1.25	13.04 ± 1.14	17.40 ± 1.40	52.69 ± 1.68	38.85 ± 1.16	8.47 ± 0.76

Values are expressed as means ± SEM.

n = Number of mice.

When the latex was washed off, it lost toxicity, hence, upon oral administration of water extracts of stem latex and flowers of C. procera. F. elastica and ether extract of Z. officinale at any dose level up to the highest dose tested (1600 mg/kg) did not reveal symptoms of morbidity or mortality. These results showed that, at single dose, there are no adverse effects of plant extracts used indicating that the medium lethal dose (LD₅₀) should be >1600 mg/kg and the tested plants are safe for use (Table 3). Therefore, 500 mg/kg body weight was used as a therapeutic dose. Although a numerical decrease (7.26–17.71%) in total number of worms was recorded (Table 4), yet no statistically significant changes were recorded in the total number of worms, tissue egg load and % egg developmental stages after the oral administration of plant extracts. Concerning Z. officinale, results are in agreement with those of Sanderson et al. (2002) who reported that neither oral nor subcutaneous administration of 150 mg/kg of ethyl acetate extract of ginger produced any significant reduction in S. mansoni worm numbers compared with untreated controls. Conversely, Mostafa et al. (2011) reported that worm burden and the egg density in liver and faeces of mice treated with ginger were fewer than in non-treated ones.

Table 3. Acute toxicity of the test plant extracts administered orally to mice.

Treatments	Dose (mg/kg)	D/T	Mortality latency (h)	Toxic symptoms
Control	–	0/6	–	None
C. procera stem latex	100, 200, 400, 800 and 1600	0/6 per dose × 5 doses (i.e. 0/30)	–	None
C. procera flower		0/6 per dose × 5 doses (i.e. 0/30)	–	None
Ficus elastica		0/6 per dose × 5 doses (i.e. 0/30)	–	None
Zingiber officinale		0/6 per dose × 5 doses (i.e. 0/30)	–	Hypoactivity

D/T = dead/treated mice; none = no toxic symptoms during the observation period; mortality latency = time to death (in days) after oral administration. Mice in each group were carefully examined for any signs of toxic (behavioral changes and mortality) for 14 days. Control group received drug vehicles.

Table 4. Effect of C. procera stem latex and flower, Ficus elastica and Zingiber officinale extracts oral administration (500 mg/kg for three consecutive days) on worm burden, ova count and the percentage of egg developmental stages (oogram pattern) in S. mansoni-infected mice 2-week post-treatment.

Animal groups	Total worms	Hepatic ova count × 10^3	Intestinal ova count × 10^3	% Total immature ova	% Mature ova	% Dead ova
Infected untreated (n = 7)	19.14 ± 1.45	16.47 ± 1.27	24.10 ± 1.95	53.14 ± 2.06	36.86 ± 2.30	10.00 ± 0.49
C. procera stem latex (n = 8)	17.25 ± 1.36 (9.87)	14.97 ± 1.46	21.84 ± 1.71	52.50 ± 1.93	38.13 ± 2.02	9.38 ± 0.75
C. procera flower (n = 8)	17.75 ± 0.77 (7.26)	15.19 ± 0.92	22.10 ± 0.86	54.38 ± 2.19	36.63 ± 1.83	9.00 ± 0.42
Ficus elastica (decora) (n = 8)	15.75 ± 1.25 (17.71)	13.13 ± 0.80	17.64 ± 1.70	55.25 ± 1.26	36.25 ± 1.31	8.50 ± 0.50
Zingiber officinale (ginger) (n = 8)	17.75 ± 0.82 (7.26)	16.75 ± 0.51	22.11 ± 2.68	55.00 ± 1.81	35.63 ± 1.39	9.38 ± 0.86

Values are expressed as means ± SEM.

n = Number of mice.

Numbers between parentheses indicate percentage reduction from infected control.

The laticifer fluid of C. procera and F. elastica is rich in proteins (cysteine proteases in particular) and there is evidence that they are involved in the pharmacological properties of the latex (Freitas et al., 2007; Konno et al., 2004). The cysteine proteases found in the latices and extracts of laticiferous plant fruits all have a neutral pH optimum of ∼7, with a range, for example in the case of ficin, in which some activity is retained from pH 4–8.5 (Robbins, 1930). The author added that fruit derived, secreted cysteine proteases cannot work effectively at lower or higher pH (although some intracellular cysteine proteases have lower optimal pHs), hence an expected antitrematodal activity has been considered a remote possibility in the trematode model flatworms of S. mansoni. Huet et al. (2006) reported that the effect of acidity on cysteine proteases is irreversible. In view of the above-mentioned information, results from this work did not reveal any activity against S. mansoni when the C. procera latex and flowers as well as the latex of F. elastica were given orally. However, when acid secretion was temporarily blocked by giving the antacid ranitidine 1 h before the plant extracts (Table 5), a significant reduction in total worm burden has been observed that was highest with C. procera flowers (p < 0.001; 53.7%) followed by C. procera stem latex (p < 0.001; 45.31%). Meanwhile, F. elastica latex showed less significant worm reduction (p < 0.05; 16.71%). With C. procera stem or flower extracts, both worm sex was more or less equally insulted with evident uncoupling that reached almost 50% of the total number of worms (Table 5). Several studies showed the anthelmintic activity of C. procera latex and flowers against Haemonchus contortus, the gastrointestinal nematodes of sheep (Al-Qarawi et al., 2001; Iqbal et al., 2005). Meanwhile, the parasiticidal activity of latex of some other species of Ficus was attributed to the presence of ficin (Pistelli et al., 2000).

Table 5. Effect of C. procera stem latex and flower and Ficus elastica extracts oral administration (500 mg/kg for 3 days + ranitidine 30 mg/kg for 3 days) on total males, females and worm burden in S. mansoni-infected mice 2-week post-treatment.

Animal groups	Total males	Total females	Total couples	Total worms
Infected untreated (n = 8)	13.63 ± 0.75	11.75 ± 0.45	10.75 ± 0.67	25.38 ± 1.12
C. procera stem latex + ranitidine (n = 8)	7.50 ± 0.91***	6.38 ± 0.32***	5.50 ± 0.42***	13.88 ± 0.90*** (45.31)
C. procera flower + ranitidine (n = 8)	6.50 ± 0.89***	5.25 ± 0.77***	5.13 ± 0.79***	11.75 ± 1.42*** (53.70)
Ficus elastica + ranitidine (n = 8)	11.29 ± 0.57*	9.86 ± 0.77	9.71 ± 0.78	21.14 ± 1.16* (16.71)

Values are expressed as means ± SEM.

n = Number of mice.

Numbers between parentheses indicate percentage reduction from infected control.

*p < 0.05, ***p < 0.001 (significant difference compared with infected control group).

In the present study, data revealed significant reduction (p < 0.05) in both the hepatic (38.3%) and intestinal (37.6%) tissue egg loads upon administration of C. procera flower extract post-ranitidine. Meanwhile, this reduction was noticed only in the intestinal tissue egg load (34.9%) in C. procera stem latex-treated group in comparison with infected untreated control (Figure 1). These findings were accompanied with significant decrease in the percentage of total immature eggs (p < 0.001; 35.9% for C. procera stem latex and 27.3% for flowers) and a significant increase in the percentage of both mature (p < 0.01; 30.3% for C. procera stem latex and 25.9% for flowers) and dead eggs (p < 0.001; 88.8% for C. procera stem latex and p < 0.01; 53.3% for flowers) compared with the infected untreated control (Figure 2). These results are in consistence with Pellegrino et al. (1962) who stated that if viable ova of all developmental stages are still present after specific chemotherapy in experimental schistosomiasis, the drug is considered inactive. They also added that a dose level of the drug was considered to have a definite action against S. mansoni when the oogram showed an increase (from ∼35% to 50% or more) in mature ova with the absence of one or more of the immature stages of ova. On the other hand, F. elastica showed insignificant changes in tissue egg load and percentage egg developmental stages (Figure 2). In this context, Seif el-Din et al. (2006) and Ebeid et al. (2007) recorded that administration of the antioxidants β-carotene or N-acetylcysteine (NAC) produced significant reduction in S. mansoni worm burden accompanied with significant increase in the percentage of dead ova and a decrease in the percentage of mature ova stages. Moreover, Seif el-Din et al. (2011) reported that treatment with NAC alone increased the percentage of dead ova and enhanced the decrease in total number of worms and tissue egg loads when used in addition to the anti-malarial drug artemether. Accordingly, the antischistosomal effects of C. procera and F. elastica could be attributed to their anthelmintic activity (Al-Qarawi et al., 2001; Iqbal et al., 2005; Pistelli et al., 2000), antioxidative and anti-inflammatory properties of the phytochemical constituents and that of the cysteine proteases of these extracts (Kumar & Arya, 2006; Roy et al., 2005; Sackeyfio & Lugeleka, 1986).

Figure 1. Effect of C. procera stem latex and flower and Ficus elastica extracts oral administration (500 mg/kg for 3 days + ranitidine 30 mg/kg for 3 days) on hepatic and intestinal tissue egg loads in S. mansoni-infected mice 2-week post-treatment. Values are expressed as means ± SEM. *p < 0.05 (significant difference compared with infected control group).

Figure 2. Effect of C. procera stem latex and flower and Ficus elastica extracts oral administration (500 mg/kg for 3 days + ranitidine 30 mg/kg for 3 days) on the percentage of egg developmental stages (oogram pattern) in S. mansoni-infected mice 2-week post-treatment. Values are expressed as means ± SEM. **p < 0.01, ***p < 0.001 (significant difference compared with infected control group).

Conclusions

The stem latex and flowers of C. procera were found toxic before rubber removal even in low doses. The ether extract of Z. officinale has no antischistosomal activity, while results of the C. procera stem latex and flowers and latex of F. elastica (after washing off toxic rubber materials) clearly demonstrate promising antischistosomal activity when used 1 h after administration of the antacid ranitidine. These effects could be due to an antischistosomal, antioxidant or anti-inflammatory activity of their content of cysteine proteases, tannins, flavonoids, sterols and terpenes. However, further detailed studies are required to identify their chemical nature and the possibility that further fractionation may lead to a proper lead antischistosomal of natural origin.

Declaration of interest

There are no conflicts of interest. The authors alone are responsible for the content and writing of the article.

This work is part of the research project [Development of new compounds with effect on schistosomiasis (bilharzia); 2009–2012] funded by the Swedish Research Council [Swedish-MENA Research Links (SRL-MENA)], Contract No. (348-2008-6102), Swedish PI Prof. Olov Sterner, Chemistry Department, Lund University, Sweden and Egyptian PI Prof. Sanaa Botros, Pharmacology Department, Theodor Bilharz Research Institute, Giza, Egypt.

Acknowledgements

The authors would like to thank Dr. Wafaa M. Amer, Professor of Taxonomy, Department of Botany, Faculty of Science, Cairo University, Giza, Egypt for plant authentication.