Curtisia dentata ( Cornaceae ) leaf extracts and isolated compounds inhibit motility of parasitic and free-living nematodes

SHAI, L.J., BIZIMENYERA, E.S., BAGLA, A.V., McGAW, L.J. & ELOFF, J.N. 2009. Curtisia dentata (Cornaceae) leaf extracts and isolated compounds inhibit motility of parasitic and free-living nematodes. Ondesterpoort Journal of Veterinary Research, 76:249–256 Haemonchus contortus and Trichostrongylus colubriformis are among the most important parasitic nematodes of small ruminants. Caenorhabditis elegans, a free-living nematode, is used as a model for evaluating anthelmintic activity of a variety of test substances. Extracts of several medicinal plants are useful in vitro and in vivo against nematode development. Extracts of Curtisia dentata, a South African medicinal plant, and compounds isolated from leaves of this plant were investigated for anthelmintic activity against T. colubriformis, H. contortus and C. elegans. The acetone and dichloromethane extracts were active against all nematodes at concentrations as low as 160 μg/ml. Betulinic acid and lupeol were active against the parasitic nematodes only at the high concentrations of 1 000 and 200 μg/ml, respectively. All compounds were effective against C. elegans with active concentrations as low as 8 μg/ml. Betulinic acid was less active than lupeol and ursolic acid against C. elegans. The acetone and dichloromethane extracts were also active against C. elegans with a concentration of 0.31 mg/ml resulting in almost 80 % inhibition of larval motility. The use of free-living nematodes may provide information on the activity of potential anthelmintics against parasitic nematodes. Extracts of various medicinal plant species may provide solutions to ill-health of small ruminants caused by parasitic nematodes in poor communities of southern Africa.

The usual mode of control of these parasitic diseases relies on the repeated and strategic use of proprietary anthelmintic drugs.However, these drugs are often so highly priced that they are not accessible to subsistence and small-scale livestock farmers in developing countries (Hounzangbe-Adote et al. 2005).Extensive use of drugs by commercial farmers has created anthelmintic resistance that has become cosmopolitan.The emergence of resistance of gastrointestinal nematodes to conventional anthelmintics and resulting economic and production losses emphasize the need to search for alternative methods of worm control (Prichard 1990;Wol sten holme, Fairweather, Prichard, Von Samson-Himmelstjerna & Sangster 2004;Jabbar, Iqbal, Kerboeuf, Muhammad, Khan & Afaq 2006).
One of the alternative methods of worm control is the use of medicinal plants.In many parts of the developing world, small-scale and subsistence farmers rely on traditional methods of deworming that include the administration of remedies derived from plants (Hammond, Fielding & Bishop 1997;Danø & Bøgh 1999).The scientific evidence of the efficacy and safety to support widespread use of plant-based remedies as anthelmintics is still scanty (Hammond et al. 1997).Extracts of several African plant species are active against parasitic and free-living nematodes (Hammond et al. 1997;Enwerem, Okogun, Wambebe, Okorie & Akah 2001;Bizimenyera, Githiori, Eloff & Swan 2006).Extracts of Artemisia sp. have shown activity against Haemonchus sp.(Idris, Adam & Tartour 1982;Iqbal, Lateef, Ashraf & Jabbar 2004) and Trichostrongylus species (Sharma 1993).Furthermore, Hördegen, Hertzberg, Heilmann, Langhans & Maurer (2003) demonstrated anthelmintic activity of ethanolic extracts of several plant species in an in vivo sheep model.Some compounds and plant extracts that possess anthelmintic activity also have antifungal efficacy.In 1993, Padmaja, Thankamany & Hisham reported that extracts of the root bark of Uvaria hookeri and Uvaria narum, together with the isolated aceto genins, have antifungal, antibacterial and anthel mintic activities.Benzimidazole carbamates, a class of anthelmintics used in human and veterinary medicine have antifungal activity (Murray, Hudson & Yassa 1992;Katiyar, Gordon, McLaughlin & Edlind 1994).Polyphenols isolated from the leaves of Piper betle had both antifungal and anthelmintic activity (Evans, Bowers & Funk 1984).The extracts of C. dentata leaves showed antifungal activity against Candida albicans and several other fungal species (Shai 2007;Shai, McGaw, Masoko & Eloff 2008).We investigated anthelmintic activity in C. dentata extracts and compounds isolated from the leaves of the plant to discover potential correlations with known antifungal activity.
Curtisia dentata is traditionally used in humans for stomach ailments and diarrhoea, as a blood strengthener and an aphrodisiac (Hutchings, Scott, Lewis & Cunningham 1996;Pujol 2000).It is also used in the treatment of heartwater in cattle in the Eastern Cape Province (Dold & Cocks 2001) and as a pimple treatment (Grierson & Afolayan 1999).The anthelmintic activity of C. dentata extracts has not been reported in available literature.Betulinic acid is one of the compounds isolated from C. dentata leaves (Shai 2007).Betulinic acid is active against Caenorhabditis elegans, a free-living nematode, at a concentration of 500 μg/mℓ after 7 days of incubation (Enwerem et al. 2001).The dichloromethane and acetone extracts of C. dentata leaves, containing high concentrations of betulinic acid, were selected for investigation of their anthelmintic activity against the parasitic nematodes T. colubriformis and H. contortus, and the free-living C. elegans.Betulinic acid and two other compounds isolated from the leaves of C. dentata, ursolic acid and lupeol, were also tested for anthelmintic activity.This study was aimed at investigating whether the extracts of the leaves of C. dentata and compounds from it, which have shown antifungal activity (Shai 2007), also have anthelmintic activity.

Plant extracts and compounds
Plant leaves were collected from the Lowveld National Botanical Garden in Nelspruit, South Africa in woven sacks and dried at room temperature prior to powdering in a laboratory mill.A herbarium specimen, Shai 002, was deposited in the medicinal plant herbarium at the University of Pretoria (Depart ment of Paraclinical Sciences).Powdered leaves (837 g) of C. dentata were serially extracted with hexane, dichloromethane, acetone and methanol, and compounds were isolated from the dichloromethane extract as previously described (Shai 2007).Aliquots of the dichloromethane and acetone extracts were dissolved in DMSO to a concentration of 100 mg/mℓ.Stock solutions of 2 mg/mℓ of the isolated compounds betulinic acid, lupeol and ursolic acid were also prepared in DMSO.Preliminary tests confirmed that the final concentration of DMSO used in the assays was not toxic to the nematodes.

Caenorhabditis elegans
Caenorhabditis elegans was maintained in sterile Petri-dishes on Nematode Growth (NG) agar (composition per litre: 3 g NaCl, 2.5 g peptone, 17 g agar, 5 mg cholesterol, 0.246 g MgSO 4 .7H 2 O, 0.147 g CaCl 2 .2H 2 O, 2.7 g KH 2 PO 4 , and 0.9 g K 2 HPO 4 ) seeded with Escherichia coli (Brenner 1974) .The nematodes were incubated at 20 °C in the dark for 6 days prior to the anthelmintic assay which was performed using the method of Rasoanaivo & Rat simamanga-Urverg (1993) modified by McGaw, Jäger & Van Staden (2000).Several plates were washed with 1 mℓ M9 buffer (composition per litre: 6 g Na 2 HPO 4 , 3 g KH 2 PO 4 , 5 g NaCl and 0.25 g MgSO 4 .7H 2 O) to obtain a solution of approximately 100 nematodes per 10 μℓ.Into 24-well plates, 2 mℓ of plant extracts or compounds dissolved in a small amount of DMSO and made up to the final concentration in M9 buffer were added.The final concentration of DMSO did not exceed 1 %, which was not toxic to the nematodes.Nematodes (10 μℓ) were added into the wells and plates were incubated for 2 h, and then 7 days in the dark.Non-motile or paralysed larvae were considered dead.The number of dead and viable larvae were counted after each incubation period and the percentage of dead larvae was calculated.Levamisole 5 and 10 μg/mℓ (Sig ma) was used as a positive control while untreated larvae were used as negative controls.

Recovery and preparation of eggs of parasitic nematodes
Faecal pellets were collected from lambs that were infected with either T. colubriformis or H. contortus, using sterilized harnesses and collecting bags.The eggs were prepared according to a modified version (Bizimenyera et al. 2006) of the World Association for the Advancement of Veterinary Parasitology (WAAVP) guidelines for detection of resistance in nematodes of veterinary importance (Coles, Bauer, Borgesteede, Geerts, Klei, Taylor & Waller 1992).

Anthelmintic activity against third stage larvae
The eggs (1 mℓ) were added into Petri dishes in the presence of 50 μℓ of a suspension of E. coli (ATCC 9637) for the development of nematode larvae (Hubert & Kerboeuf 1992) and 10 μℓ (50 μg/mℓ stock solution) of amphotericin B (Sigma®) to control fungal growth.The dishes were incubated for 5 days to allow the larvae to develop to the third stage (L3).The L3 larvae were frozen at -20 °C until needed.For the anthelmintic assay, the larvae were washed off the base of the dish with M9 buffer and treated with various concentrations of compounds and extracts of C. dentata in wells of a 24-well plate and incubated for 48 h.Motile and non-motile larvae were counted to obtain the percentage inhibition of motility.

Inhibition of motility of adult parasitic nematodes
The acetone and dichloromethane extracts of C. dentata inhibited motility of T. colubriformis at a concentration range of 0.16-2.5 mg/mℓ.The lowest lethal concentration of both the acetone and dichloromethane extracts, 0.16 mg/mℓ, led to over 60 % of larvae being paralysed.The lowest tested concentration of both extracts, 0.08 mg/mℓ, resulted in less than 10 % of non-motile larvae.The inhibition of larval motility percentages by acetone extracts was very similar to that induced by the dichloromethane extracts (Fig. 1).The average survival in untreated controls was 99 %.
The dichloromethane extract was active against H. contortus at a concentration range of 0.63 to 2.5 mg/mℓ.About 20 % average inhibition of motility of larvae resulted from a concentration of 0.63 mg/mℓ.The acetone extract was active at a concentration range of 0.31 to 2.5 mg/mℓ.Over 70 % of the larvae were not motile after 48 h of incubation in the presence of 0.31 mg/mℓ of the acetone extract.At this concentration (0.31 mg/mℓ) the percentage of nonmotile larvae resulting from the acetone extract was significantly higher than that resulting from the dichloromethane extract.Concentrations of 2.5 mg/mℓ and 1.25 mg/mℓ of both acetone and dichloromethane resulted in 100 % inhibition of larval motility after 48 h of incubation.Concentrations of both 0.16 and 0.08 mg/mℓ of both extracts only managed to inhibit motility of less than 10 % of the larvae (Fig. 2).The average survival in untreated controls was 99 %.
Two compounds isolated from C. dentata leaves, namely, betulinic acid and lupeol were tested to evaluate their ability to paralyse T. colubriformis and H. contortus larvae.Unfortunately, ursolic acid was not isolated in sufficient quantities to test for anti-parasitic activity.Lupeol and betulinic acid were tested at a concentration range of 0.32-1 000 μg/mℓ.Both compounds inhibited larval motility only at high concentrations (Fig. 3 and 4).Low concentrations did not result in appreciable numbers of motionless larvae.The average survival in untreated control of both species was 99 %.Lupeol and betulinic acid are poorly soluble in aqueous media.Upon mixing with water during dilution, precipitation resulted in a milky suspension, possibly making these compounds unavailable to act on the test nematode larvae.Modifications of their structures may result in more soluble derivatives of these lupane triterpenes.
The extracts showed more activity against the larvae than the isolated compounds.It would seem that, apart from lupeol and betulinic acid, other components in the extract contribute to the activity against larval motility.This emanates from the fact that betulinic acid and lupeol were, by themselves, not very active against the tested parasitic nematodes.The compounds failed to exert 100 % inhibition of larval motility at all concentrations tested.
The compounds and extracts did not affect egg hatching of H. contortus and T. colubriformis (results not shown).In the controls the number of unhatched eggs was comparable to eggs treated with plant extracts and compounds.It was observed that at high concentrations (16.7, 8.3, 4.17 and 2.1 mg/ mℓ) of plant extracts no eggs or larvae were present, suggesting that lysis occurred.In concentrations where the numbers of motile larvae were low the eggs still hatched prior to paralysis.

Inhibition of motility of free-living nematodes
In vitro anthelmintic activity assay methods using C. elegans as the test organism provide a cheap, simple and rapid system in which broad-spectrum anthelmintic activity of plant extracts and pure compounds can be evaluated, keeping in mind the limitations of using a free-living nematode as a model for anti-parasitic activity (Eloff & McGaw 2006).Furthermore, it has been reported that most registered deworming drugs have demonstrated activity against C. elegans, supporting the use of C. elegans as a model for testing compounds and plant extracts against parasitic nematodes (Simpkin & Coles 1981).
Three compounds isolated from the dichloromethane extract of C. dentata, namely, lupeol, betulinic acid and ursolic acid, together with the acetone and dichloromethane extracts were assessed for ability to inhibit the motility of the free-living nematode, C. elegans.After 2 h of incubation, the highest concen-trations of isolated compounds (200 μg/mℓ) inhibited up to 90 % of larval motility.Concentrations ranging from 0.16 to 40 μg/mℓ resulted in about 20 % inhibition of larval motility after 2 h of incubation at 25 °C (Fig. 5).The highest concentrations of extracts (2.5 mg/mℓ) resulted in about 35 % inhibition of larval motility whereas lower concentrations ranging from 1.25 to 0.08 mg/mℓ resulted in less than 20 % inhibition of larval motility (Fig. 6).In the untreated control 4 % motionless larvae were observed after 2 h of incubation.In the levamisole-treated (10 μg/mℓ) controls average inhibition of larval motility was 25 %.
After 7 days of incubation the highest concentrations of all tested compounds resulted in 100 % inhibition of larval motility.Lupeol was the most active of the isolated compounds.A concentration of 40 μg/mℓ of lupeol produced over 80 % inhibition of larval motility while betulinic acid led to 40 % inhibition.Ursolic acid, though less active than lupeol, produced higher inhibition of motility than betulinic acid at most concentrations tested (Fig. 7).All the compounds led to 100 % paralysis of larvae at 200 μg/mℓ.En werem et al. (2001) reported that 500 μg/mℓ of betulinic acid caused 100 % paralysis of C. elegans larvae after 7 days in treatment.In the untreated controls approximately 85 % motility was observed.In 5 and 10 μg/ mℓ levamisole-treated controls 65 % and 48 % motility were observed respectively.
Both the acetone and dichloromethane extracts of C. dentata leaves were similar in their inhibition of larval motility after 7 days of incubation, displaying a concentration-dependent effect.Concentrations rang ing from 2.5 to 0.63 mg/mℓ of each extract led to over 80 % inhibition of larval motility after 7 days of incubation.At 0.31 mg/mℓ, both extracts led to over 60 % inhibition of larval motility while lower concentrations were less effective (Fig. 8).
Several extracts of different medicinal plants show anthelmintic activity (Raj, 1975;Enwerem et al. 2001;Ademola, Fagbemi & Idowu 2004).Hounzang be-Adote et al. (2005) tested the in vitro effects of four tropical plants for activity against parasitic nematodes.They reported that concentrations of between 300 and 2 400 μg/mℓ of ethanolic extracts of Zanthoxylum zanthoxyloides, Carica papaya, Mo rinda lucida and Newbouldia laevis were active against H. contortus.Bizimenyera et al. (2006) reported that extracts of Peltophorum africanum had in vitro activity against egg hatching and larval development of T. colubriformis.The ED 50 values reported were 0.619 mg/mℓ for leaf extract, 0.383 mg/ mℓ for bark extract and 0.280 mg/mℓ for extract of the roots (Bizimenyera et al. 2006).In this study in vitro activity of extracts of C. dentata leaves was demonstrated against parasitic and free-living nematodes in a concentration-dependent manner.These results indicate that the leaves of C. dentata may be useful to treat helminthosis in South African folk medicine.
Despite the indication that some plant extracts are active against several nematodes, the exact mechanism remains unclear.Some compounds such as palasonin, the active principle of Butea frondosa inhibit glucose uptake and accelerate glycogen depletion in target nematodes (Kumar, Mishra, Tandan & Tripathi 1995).The mechanism of action of many anthelmintic plant extracts may involve inhibition of energy metabolism (Dahanukar, Kulkarni & Rege 2000).
In this study, betulinic acid induced paralysis of the tested nematodes, C. elegans, H. contortus and T. colubriformis at concentrations between 1 000 and 200 μg/mℓ.Against C. elegans, betulinic acid induced 100 % paralysis at a concentration of 200 μg/ mℓ.These results confirm the study by Enwerem et al. (2001) in which it was reported that betulinic acid isolated from Berlina grandiflora had strong activity against C. elegans at concentrations of 100 and 500 μg/mℓ.The mechanism involved in the activity of betulinic acid against parasitic and free-living nematodes is yet to be described.Furthermore, its activity against parasitic nematodes in vivo and in vitro has not been previously demonstrated.As far as the available literature is concerned, this appears to be the first report of the effects of betulinic acid against the parasitic nematodes, T. colubriformis and H. contortus.Investigations of the in vivo activity of both the extracts of C. dentata and the isolated compounds may conclusively indicate their potential as anthelmintics.There was no obvious correlation between anthelmintic activity and anti-Candida activity of both extracts and isolated compounds.The calculated R 2 value was 0.0132.The use of free-living nematodes may provide information on the activity of potential anthelmintics against parasitic nematodes.Extracts of various medicinal plant species may provide solutions to illhealth of small ruminants caused by parasitic nematodes in poor communities of southern Africa.
FIG. 1 Percentage of dead T. colubriformis larvae after 48 h of incubation in the presence of varying concentrations of the acetone (ACN) and dichloromethane (DCM) extracts of C. dentata leaves The results are means (with standard deviations) of two independent experiments performed in triplicate.The estimated LC 50 value was 0.15 mg/mℓ for both extracts