Natural products from Zanthoxylum heitzii with potent activity against the malaria parasite.

BACKGROUND: Zanthoxylum heitzii (Rutaceae) (olon) is used in traditional medicine in Central and West Africa to treat malaria. To identify novel compounds with anti-parasitic activity and validate medicinal usage, extracts and compounds isolated from this tree were tested against the erythrocytic stages of the human malaria parasite Plasmodium falciparum and for inhibition of transmission in rodent malaria parasite Plasmodium berghei. RESULTS: Hexane bark extract showed activity against P. falciparum (IC50 0.050 µg/ml), while leaf and seed extracts were inactive. Fractionation of the hexane bark extract led to the identification of three active constituents; dihydronitidine, pellitorine and heitziquinone. Dihydronitidine was the most active compound with an IC50 value of 0.0089 µg/ml (25 nM). This compound was slow acting, requiring 50 % longer exposure time than standard anti-malarials to reach full efficacy. Heitziquinone and pellitorine were less potent, with IC50 values of 3.55 µg/ml and 1.96 µg/ml, but were fast-acting. Plasmodium berghei ookinete conversion was also inhibited by the hexane extract (IC50 1.75 µg/ml), dihydronitidine (0.59 µg/ml) and heitziquinone (6.2 µg/ml). Water extracts of Z. heitzii bark contain only low levels of dihydronitidine and show modest anti-parasitic activity. CONCLUSIONS: Three compounds with anti-parasitic activity were identified in Z. heitzii bark extract. The alkaloid dihydronitidine is the most effective of these, accounting for the bulk of activity in both erythrocytic and transmission-blocking assays. These compounds may present good leads for development of novel anti-malarials and add to the understanding of the chemical basis of the anti-parasitic activity in these classes of natural product.

A new benzophenanthridine alkaloid and other bioactive constituents from the stem bark of Zanthoxylum heitzii.

Heitziquinone (7), a new benzophenanthridine alkaloid, together with five known compounds; isoarnottianamide (5), rhoifoline B (6), isobauerenol (8), 6-hydroxypellitorine (9) and sylvamide (10), were isolated as minor compounds from the hexane extract of stem bark from Zanthoxylum heitzii. Four previously reported compounds (1-4) were found, as well. Compounds 5 and 7 were both found to exist as 4:1 mixtures of two atropisomers. The structures were elucidated by 1D and 2D NMR spectroscopy and by mass spectrometry. Compounds 5-10 were identified for the first time in this species, and they are all rare natural compounds. Pellitorine (4), one of the main compounds from the hexane bark extract, was found to be responsible for the brine shrimp larvae toxicity (LC50 37 µM, 8 µg/ml) of the crude extract (LC50 24 µg/ml). Low cytotoxicity against a macrophage cell line was observed.

Identification of chemical constituents of Zanthoxylum heitzii stem bark and their insecticidal activity against the malaria mosquito Anopheles gambiae.

BACKGROUND: Zanthoxylum heitzii bark extracts have insecticidal properties and have been reported to be used against malaria in Western Africa. Previously, it has been shown that a hexane extract of the bark is toxic to adult females of the mosquito Anopheles gambiae, a malaria vector. As part of our project on the control of malaria vectors using plant extracts, the phytochemistry of Z. heitzii bark hexane extract has been investigated with the aim to identify the major components with adulticidal and larvicidal effects on An. gambiae. METHODS: Z. heitzii stem bark was extracted with hexane, and the extract was fractionated to isolate major components from the bark, identified by NMR spectroscopy. Isolated compounds were tested for toxicity towards adult female An. gambiae mosquitoes and for larvicidal effects towards An. gambiae. RESULTS: The alkaloid dihydronitidine, the sesquiterpenoid caryophyllene oxide, the amide pellitorine and the lignan sesamin were identified as the major constituents in Z. heitzii bark. Pellitorine was toxic to both adult insects (LD50 50 ng/mg insect) and larvae (LD50 13 µg/ml). None of the other compounds were toxic to adults, but caryophyllene oxide and sesamin exhibited moderate larvicidal effects (LD50 > 150 µg/ml). A mixture of the four compounds in the same ratio as in the hexane extract showed higher toxicity (LD50 34 ng/mg insect) towards adult insects than the pure compounds. CONCLUSION: The toxicity of Z. heitzii bark hexane extract to An. gambiae is mostly due to pellitorine, although interactions between pellitorine and other, inactive constituents may enhance the activity of the extract.

Insecticidal activities of bark, leaf and seed extracts of Zanthoxylum heitzii against the African malaria vector Anopheles gambiae.

The olon tree, Zanthoxylum heitzii (syn. Fagara heitzii) is commonly found in the central-west African forests. In the Republic of Congo (Congo-Brazzaville) its bark is anecdotally reported to provide human protection against fleas. Here we assess the insecticidal activities of Z. heitzii stem bark, seed and leaf extracts against Anopheles gambiae s.s, the main malaria vector in Africa. Extracts were obtained by Accelerated Solvent Extraction (ASE) using solvents of different polarity and by classical Soxhlet extraction using hexane as solvent. The insecticidal effects of the crude extracts were evaluated using topical applications of insecticides on mosquitoes of a susceptible reference strain (Kisumu [Kis]), a strain homozygous for the L1014F kdr mutation (kdrKis), and a strain homozygous for the G119S Ace1R allele (AcerKis). The insecticidal activities were measured using LD50 and LD95 and active extracts were characterized by NMR spectroscopy and HPLC chromatography. Results show that the ASE hexane stem bark extract was the most effective compound against An. gambiae (LD50 = 102 ng/mg female), but was not as effective as common synthetic insecticides. Overall, there was no significant difference between the responses of the three mosquito strains to Z. heitzii extracts, indicating no cross resistance with conventional pesticides.