Abstract:
Alstonia boonei (AB) and Alstonia congensis (AC), belonging to the family Apocynaceae are different but
closely related species, indigenous to Africa. The two plants possess varied biological activities including
antimalarial, antihypertensive and antidiarrhoeal. However, the apparent similarities between the two species
could lead to misidentification and inappropriate medicinal utilisation, necessitating the need to establish
diagnostic characters for each species for proper identification. This study, was therefore, aimed at evaluating
molecular, pharmacognostic, antispasmodic and antidiarrhoeal profiles of the two plants for their
pharmacopoeial standardisation.
Deoxyribonucleic acid was isolated from nine accessions of AB and AC leaves (ABL and ACL) collected
from southwestern Nigeria and amplified, using Internal Transcribed Spacer (ITS) region.
Micromorphological diagnostic characters of leaves and stem-barks were studied by light microscopy.
Physico-chemical and elemental analysis of the powdered samples were determined using incineration method
and Atomic Absorption Spectroscopy, respectively. Aqueous extraction of plant samples was done, extracts
were concentrated in vacuo and freeze dried. The freeze-dried extracts were partitioned successively into
dichloromethane (DCM), ethyl acetate and aqueous fractions. Antispasmodic activities of the extracts and
fractions were evaluated on high-potassium induced and spontaneous contractions on isolated rat ileum. The
AB and AC stem-barks (ABSb, ACSb) extracts and their dichloromethane fractions (DCM-ABSb, DCM ACSb) showing high antispasmodic activity were evaluated for in vivo antidiarrhoeal activities in mice (22-
25 g b.w). Loperamide (5mg/kg) was used as standard. Compounds were isolated from the most active fraction
(DCM-ABSb) using chromatographic techniques (Column, TLC). Structures of the isolated compounds were
elucidated using spectroscopic techniques (NMR and MS) and their antispasmodic activities evaluated. Data
were analysed using descriptive statistics, unweighted pair group method with arithmetic mean and one-way
ANOVA and Tukey’s multiple comparison at α0.05.
The amplification of the ITS region discriminated between the two Alstonia species. The adaxial epidermal
cells of both species were polygonal, straight anticlinal walls and leaves were hypostomatic. The vascular
bundle of ABL mid-rib was arc-shaped, while that of ACL was V-shaped. Moisture content values of stem bark of AB (6.4±0.06%) was significantly different from that of AC (7.2±0.4%), while the values were not
significantly different for the leaves. Elemental analysis revealed that calcium was the most abundant mineral
in the leaves of AB (68.2±3.2 mg/g) and AC (65.7 ±1.0 mg/g). The stem-bark extracts of AB and AC were
antispasmodic with IC50 of 0.03±0.2, 0.12±0.01 mg/mL and 1.15±0.1, 1.05±0.8 mg/mL on high-potassium
induced and spontaneous contractions, respectively. The DCM-ABSb fraction exhibited significant
antispasmodic activity (IC50: 0.02±0.05, 0.31±0.02 mg/mL) on high-potassium induced and spontaneous
contractions, respectively. The DCM-ABSb (200 mg/kg b.w.) showed significant antidiarrhoeal activity
(87.3%) comparable to Loperamide (87.5%). The isolated compounds from DCM-ABSb were β-amyrin and
boonein with only boonein exhibiting antispasmodic activities on both high-potassium induced (IC50:
0.09±0.01 µg/mL) and spontaneous (0.29±0.05 µg/mL) contractions.
Alstonia boonei and Alstonia congensis were identified as two distinct species. The diagnostic indices of the
two plants provided pharmacopoeial standards for their identification. The isolated boonein could serve as a
template for the development of antidiarrhoeal drugs
