Composition of volatile oil and acetylcholinesterase inhibitory activity from the leaves of Macaranga pachyphylla

Abstract

The genus Macaranga belongs to the Euphorbiaceae family and includes approximately 300 species of trees and shrubs found primarily in tropical Asia, Africa, and the Pacific Islands. Medicinally, Macaranga species have traditionally been used to treat various ailments, including fever, wounds, diarrhea, gastrointestinal disorders, skin infections, inflammation, or respiratory issues [1]. Phytochemically, Macaranga species are abundant in bioactive compounds such as flavonoids, stilbenes, tannins, phenolic acids, and triterpenoids [2, 3], whereas pharmacological studies have shown that Macaranga extracts exhibit antioxidant, anti-inflammatory, antimicrobial, cytotoxic, and antidiabetic activities [4, 5], making them promising candidates for drug development.

Macaranga pachyphylla Mull. Arg. is a small tree species that can grow up to approximately 13 m in height. Locally, it is known as ‘asang rabata’ and ‘sedaman kubal’ in parts of Borneo. This species is usually found at elevations ranging from about 500 to 1700 m above sea level. Its distribution spans Peninsular Malaysia, Sumatra, Java, and Borneo [6].

The leaves of M. pachyphylla were collected from Fraser Hill, Pahang in December 2023 and identified by Shamsul Khamis from UKM. The voucher specimen (SA-11/62) was deposited at the Herbarium Universiti Kebangsaan Malaysia Bangi (Herbarium UKMB).

The essential oil was obtained by hydrodistillation (4 h) from the fresh leaves (300 g) using a Clevenger-type apparatus. The oil yield (v/w) was 0.15 based on the fresh weight.

The chemical composition of the isolated oil was analyzed by GC-FID and GC-MS under conditions analogous to those published before [7]. For identification of essential oil components, co-injection with the standards was used, along with correspondence of retention indices and mass spectra with respect to those occurring in the literature [8].

Bioactivity. Acetylcholinesterase (AChE) inhibitory activity of the essential oil was measured according to the reported spectrophotometric method with minor modifications [9]. Electrophorus electricus (electric eel) AChE was used whereas acetylthiocholine iodide was employed as substrates of the reaction. DTNB acid was used for measurement of acetylcholinesterase activity. Galantamine was used as a positive control [10].

The chemical composition of the essential oil from M. pachyphylla is presented in Table 1, where all the compounds are arranged in order of their elution time. A total of 39 components were identified, accounting for 98.2% of the total oil.

The major components were identified as (E)-β-ocimene (19.8%), β-caryophyllene (9.2%), (3Z)-hexenyl acetate (8.5%), benzaldehyde (5.5%), and (3Z)-hexenol (5.0%). Notably, (E)-β-ocimene was also reported as the dominant compound in several other Macaranga species, such as M. bancana (9.0%), M. gigantea (32.5%), M. hosei (45.4%), M. indistincta (45.5%), M. lamellata (23.1%), and M. pearsonii (33.4%) [11]. Comparative analysis with previous studies indicates that other key components commonly found in Macaranga essential oils such as cis-3-hexenyl acetate, myrcene, trans-β-bergamotene, α-copaene, and benzaldehyde were also present in M. pachyphylla. It suggests a conserved chemotaxonomic trait within the genus, potentially linked to ecological adaptation strategies. Furthermore, the major compounds found in the essential oil of M. barteri in Nigeria (eremophilene, 6-epi-shyobunol, and methyl salicylate) [12], different than the pattern in Asia for the genus Macaranga, seem to support the ecological adaptation. Meanwhile, the essential oil exhibited inhibitory activity against AChE, achieving 69.5% inhibition at a concentration of 1000 μg/mL. For comparison, galantamine (positive control) showed 92.3% inhibition under the same assay conditions. This is a significant finding, suggesting the potential neuroprotective or cognitive-enhancing properties of the oil. Hence, it highlights the potential of M. pachyphylla as a source of bioactive natural products, warranting further investigation into its individual components and possible synergistic interactions [13, 14].