GC-MS-based metabolic profiling of essential oils from Citrus paradisi, Lawsonia inermis, and Ruta graveolens and assessment of their acetylcholinesterase inhibitory potential

Introduction: Plant-derived essential oils (EOs) are rich sources of bioactive compounds, some of which exhibit acetylcholinesterase (AChE) inhibitory activity and may offer therapeutic potential for the management of Alzheimer’s disease (AD). This study aimed to evaluate the chemical composition and AChE inhibitory potential of essential oils extracted from Citrus paradisi (grapefruit), Lawsonia inermis (henna), and Ruta graveolens (sadab).

Methods: Essential oils were obtained by hydrodistillation and analyzed using gas chromatography–mass spectrometry (GC–MS) to identify their chemical constituents. AChE inhibitory activity was determined using Ellman’s colorimetric assay, and IC₅₀ values were calculated to assess inhibitory potency.

Results: A total of 63 metabolites were identified across the three essential oils, accounting for approximately 90% of their total composition. Grapefruit EO was predominantly composed of limonene (89.94%), henna EO was rich in phytol (41.42%) and limonene (23.02%), while sadab EO was characterized by 1-hexadecanol acetate (26.39%) and phytol (20.54%). Grapefruit EO exhibited the strongest AChE inhibitory activity (IC₅₀ = 12.62 ± 0.48 μg/mL), followed by henna EO (IC₅₀ = 43.90 ± 0.97 μg/mL), whereas sadab EO showed negligible inhibition.

Discussion: The notable AChE inhibitory activity observed in grapefruit and henna essential oils is likely attributable to their high terpenoid content. These findings suggest that selected plant-derived essential oils may represent promising natural candidates for the prevention or management of neurodegenerative disorders such as Alzheimer’s disease.

1 Introduction

Alzheimer’s disease (AD) is a complex, progressive neurodegenerative condition marked by the deterioration of cholinergic neurons. It leads to a significant reduction in acetylcholine (ACh) levels and subsequent cognitive decline, memory impairment, and behavioral disturbances (Chen et al., 2021; Moore et al., 2021). Central to its pathophysiology are neurofibrillary tangles, amyloid plaques, oxidative stress, and heightened acetylcholinesterase (AChE) activity. As AChE is responsible for the hydrolysis of ACh, pharmacological inhibition of this enzyme remains a primary strategy in symptomatic AD treatment. Despite the clinical use of synthetic AChE inhibitors such as donepezil, rivastigmine, and galantamine, their therapeutic efficacy is often compromised by side effects and limited long-term effectiveness (Amawi et al., 2024; Ayaz et al., 2017; Sá et al., 2012).

This limitation has prompted a surge in interest towards plant-based compounds, particularly essential oils (EOs), which are natural, volatile mixtures rich in terpenoids, phenolics, and other bioactive constituents (Arjmand and Dastan, 2020; Dhifi et al., 2016). Their lipophilic nature facilitates passage through the blood-brain barrier, making them viable candidates for central nervous system (CNS) interventions. Numerous studies have demonstrated that EOs from aromatic plants exhibiting notable AChE-inhibitory effects, attributable to constituents (Ashmawy et al., 2024; Dhapola et al., 2024; Hung et al., 2022). Additionally, oxidative stress has been identified as a key contributor to AD pathogenesis, along with other chronic conditions (Dhapola et al., 2024; Juszczyk et al., 2021). This dual role of EOs as antioxidants and anticholinesterase agents enhances their therapeutic appeal in neurodegenerative disease contexts (Konfo et al., 2023; Salim et al., 2025).

Many studies reported the increased use of medicinal plants by population as part of primary healthcare, reflecting their importance in traditional medicine systems and ethnopharmacology (Al-Yateem et al., 2023; Patrício et al., 2022; Tuasha et al., 2023). Moreover, essential oils, beyond medicinal use, are employed in food preservation, cosmetics, and perfumery due to their broad-spectrum bioactivities (Butnariu, 2021; Mounira, 2024). For instance, the genus Curcuma is renowned for its phytochemical richness, particularly in curcuminoids, flavonoids, and EOs such as ar-turmerone, caryophyllene oxide, and limonene, which demonstrate antioxidant and neuroprotective properties (Alolga et al., 2022; Peng et al., 2022).

The current study aims to evaluate phytochemical composition and bioactivity, contributing to the discovery of new plant-based neuroprotective agents. Citrus species, particularly Citrus paradisi (grapefruit), represent a significant botanical source of bioactive EOs. The Citrus genus is lauded for its antioxidant, anti-inflammatory, antimicrobial, and anticholinesterase activities, largely attributed to its rich profile of flavonoids, coumarins, carotenoids, and terpenes such as limonene. These bioactive compounds are concentrated in the fruit peels, making them a valuable by-product in EO production (Saini et al., 2022; Wedamulla et al., 2022). Grapefruit EO has demonstrated notable AChE inhibition, with compounds like nootkatone and auraptene yielding inhibition rates between 17% and 24% at low concentrations (Lim, 2012). Studies suggested grapefruit phenolics enhance antioxidant defences in brain tissue and reduce neuroinflammation via suppression of IL-6 and TNF-α cytokines (Deng et al., 2020; Tan and Ismail, 2020).

Beyond neuroprotection, grapefruit EOs have cardioprotective, antihypertensive, antimicrobial, and metabolic regulatory effects (Osaili et al., 2023). Citrus EOs are widely used across industries for their antimicrobial, antidiabetic, and insecticidal properties, further underscoring the economic and therapeutic potential of valorizing Citrus peel waste, especially in Citrus-rich regions (Brah et al., 2023; Reddy et al., 2019).

Lawsonia inermis, or henna, is traditionally used for cosmetic purposes but also possesses a rich phytochemical repertoire with medicinal value. Indigenous to Africa and Asia and widely cultivated in tropical regions, henna leaves contain phenolic compounds such as lawsone, gallic acid, quercetin, and tannins, which have been linked to antioxidant, anti-inflammatory, and antimicrobial activities (Elaguel et al., 2019).

Henna EO has also demonstrated hypotensive, analgesic, antipyretic, antibacterial, and immunomodulatory effects. Traditionally, it has been used in treating wounds, gastrointestinal issues, fever, anemia, and tumors (Singh et al., 2015). With only a fraction of the world’s 250,000 to 500,000 plant species having been pharmacologically investigated, henna stands out as a valuable yet underexplored candidate for neuropharmacological applications. This study thus seeks to evaluate the chemical makeup and cholinesterase-inhibitory potential of UAE-derived henna EO, offering insights into its possible role as a neuroprotective agent.

Ruta graveolens, known as “sadab” in the UAE, is another aromatic plant of growing interest for neurodegenerative applications. A member of the Rutaceae family, sadab is a hardy evergreen shrub historically utilized in Ayurveda, Unani, and homeopathy for its sedative, antispasmodic, emmenagogic, and antimicrobial properties (Ainiwaer et al., 2023; Raghav et al., 2006; Shahrajabian, 2024). The plant is distributed across the Mediterranean, Europe, Africa, and Asia, and has been traditionally employed for treating insomnia, headaches, gastrointestinal disorders, and urinary problems (Ainiwaer et al., 2023).

Recent studies support the broader pharmacological potential of sadab, citing anti-diabetic, antiulcer, anti-inflammatory, and neuroprotective activities (França Orlanda and Nascimento, 2015). Yet, despite earlier phytochemical work in other regions (França Orlanda and Nascimento, 2015; Reddy and Al-Rajab, 2016), UAE-specific studies remain scarce.

Given this context, the present study was designed to extract and characterize essential oils from medicinal plants cultivated in the UAE, specifically grapefruit, henna, and sadab. Their cholinesterase-inhibitory activity was evaluated to assess their potential as natural anti-Alzheimer agents. This research not only contributes to the ethnopharmacological validation of traditional remedies but also addresses the urgent global need for effective, safe, and affordable neuroprotective therapeutics. Our study addresses the lack of sufficient research on essential oils in the UAE by providing new insights into the chemical composition and bioactivity of locally available plants. While essential oils have been widely studied in other regions, there is limited scientific data on their pharmacological properties and potential health benefits within the UAE context. By focusing on species commonly found or used in the region, our research contributes valuable evidence to support the safe and effective use of these natural products in local traditional medicine and potential pharmaceutical applications.

2 Materials and methods

2.1 Plant material

The grapefruit peels, henna leaves, and sadab leaves used in this study were sourced from local markets in Dubai, United Arab Emirates. These plants, long used in traditional herbal medicine, are now partially industrialized and readily available in commercial outlets. Species identification was confirmed through morphological comparison and verification against authenticated reference data to ensure botanical accuracy. A voucher specimen of each plant species has been collected and deposited in the Dubai Medical University Herbarium with the following voucher numbers: DMU-P-CP-101 grapefruit peels, DMU-P-LI-102 henna leaves, and DMU-P-RG-103 sadab leaves.

2.2 Extraction of essential oils

During the extraction process, 250 g of the dried plant material were accurately weighed and ground into a fine powder using a mechanical grinder. The resulting powder was transferred into a 5-L round-bottom flask in preparation for distillation. An appropriate volume of distilled water (2 L) was added to the flask, and the essential oil was extracted through hydrodistillation using a Clevenger-type apparatus. The mixture was heated continuously for approximately 4 hours, allowing the volatile components to evaporate and condense for collection.

To enhance the separation and yield of the essential oils from the aqueous layer, diethyl ether was employed following the distillation process. The ether layer containing the essential oils was then subjected to drying using a Termovap sample concentrator and anhydrous sodium sulfate to remove residual moisture, yielding a purified organic extract.

The final essential oil extract was transferred into airtight glass vials and stored at low temperatures (typically 4 C) to preserve its chemical integrity for subsequent analytical and bioactivity assays.

2.3 Gas chromatography–mass spectrometry (GC–MS) analysis

The essential oils (EOs) extracted from the three plant species were analyzed through metabolic profiling using gas chromatography–mass spectrometry (GC–MS). The analysis was carried out on a Shimadzu GC/MS-QP 2010 system (Kyoto, Japan), coupled with a Thermo-Finnigan SSQ 7000 quadrupole mass spectrometer (Bremen, Germany). A non-polar DB-5MS fused silica capillary column (30 m × 0.25 mm i. d., 0.25 µm film thickness; Agilent Technologies, Santa Clara, CA, United States) was employed for compound separation. The GC oven was programmed to start at 45 C (held for 120 s), then increase at a rate of 0.08 C/s until reaching 300 C, where it was held constant for 300 s. The injector and detector temperatures were maintained at 250 C and 280 C, respectively. Essential oil samples were diluted to a 1% (v/v) concentration in n-hexane, and 1 µL of each was injected automatically using a 1:15 split ratio. Helium was used as the carrier gas at a constant flow rate of 0.02 mL/s. The mass spectrometer operated in electron impact ionization mode at 70 eV, with the ion source temperature set at 200 C. Mass spectra were collected across a scan range of 35–500 m/z to support compound identification and characterization. Essential oil compositions were identified based on mass spectral data and calculated retention indices (RIs), determined using a homologous series of standard n-alkanes (C8–C28) analyzed under identical chromatographic conditions. The n-alkane standards, each at a concentration of 1,000 μg/mL in hexane, were obtained from Sigma-Aldrich (St. Louis, MO, United States) and stored at 2 C–8 C. Retention indices for compounds eluting beyond C28 were extrapolated using the linear regression of the retention times of the C8–C28 standard n-alkane series. Compound identification was based on mass spectral similarity with entries in the NIST and Wiley libraries and supported by retention index comparison with literature values. Pure analytical standards were not used except for n-alkane calibration.

2.4 Evaluation of antiacetylcholinesterase activity

Acetylcholinesterase (AChE) activity was evaluated using a modified 96-well microplate assay based on Ellman’s method (Beniaich et al., 2023). This highly sensitive technique measures thiocholine production resulting from the hydrolysis of acetylthiocholine, which continuously reacts with 5,5-dithiobis (2-nitrobenzoic acid) to form a measurable chromophore. Three buffer solutions were prepared as follows: Solution A consisted of 50 mM Tris/HCl, pH 8; Solution B contained 50 mM Tris/HCl, pH 8 with 0.1% bovine serum albumin (fraction V); and Solution C comprised 50 mM Tris/HCl, pH 8 with 0.1 M NaCl and 0.02 M MgCl₂·6H₂O. To each well of a 96-well microplate, 25 µL of acetylthiocholine iodide (15 µM), 125 µL of 5,5-dithiobis (2-nitrobenzoic acid) in Solution C (3 µM DTNB or Ellman’s reagent), 50 µL of Solution B, and 25 µL of the test compound - dissolved in methanol (MeOH) and diluted in Solution A to final concentrations of 0.5, 1, 2, 3.9, 7.8, 15.6, … , 500, and 1,000 μg/mL - were added. Each essential oil sample was first dissolved in methanol (MeOH) to prepare a stock solution, then serially diluted in Tris-HCl buffer (Solution A) to obtain final assay concentrations ranging from 0.5 to 1,000 μg/mL. From these, 25 µL was added per well. The final concentrations present in the wells were used to construct dose–response curves and calculate IC₅₀ values. At each dilution step, samples were visually inspected to confirm the absence of precipitation or phase separation. Even at the highest concentration (1,000 μg/mL), the EO solutions remained homogeneous when prepared in MeOH and diluted in Tris-HCl buffer and were mixed thoroughly before addition to the wells. The initial absorbance was recorded at 405 nm for 30 s using a Microplate TS-800 reader (BioTek, Winooski, United States). Subsequently, 25 µL of acetylcholinesterase (AChE) enzyme solution (0.22 U/mL) was added to each well, and the absorbance was measured again at 300-s intervals over a total period of 30 min (i.e., six readings per well), during incubation at room temperature (25 C ± 1 C).

IC₅₀ values were calculated using non-linear regression based on a four-parameter logistic (4 PL) model. Dose–response curves were generated from three independent experiments, each performed in triplicate, and results are expressed as mean ± standard deviation (SD). The percentage of AChE inhibition was determined by comparing the reaction rates of the test samples to those of the negative control, which consisted of 10% methanol in Solution A and was considered to represent 100% enzymatic activity. Donepezil was used as positive control at concentrations ranging from 0.5 to 1,000 μg/mL. All experiments were conducted in triplicate (n = 3), and results were expressed as mean ± standard deviation.

3 Results

3.1 Chemical composition of essential oils

Essential oils (EOs) have been successfully extracted by hydrodistillation from grapefruit peel, henna leaves, and sadab leaves. All three EOs were yellow, hydrophobic, and possessed characteristic scents. The essential oil yields obtained via hydrodistillation were 1.2% for grapefruit peel, 0.25% for henna leaves, and 0.4% for sadab leaves, calculated relative to the dry weight of the plant material. These yields are in agreement with those reported in previous studies.

Gas chromatography–mass spectrometry (GC-MS) identified a total of 63 compounds across the three EOs (Table 1; Figure 1). In grapefruit EO, limonene was the major component (89.94%), accompanied by minor constituents such as β-myrcene, α-pinene, and caryophyllene. Henna EO showed a more complex profile, with phytol (41.42%) and limonene (23.02%) as the predominant compounds, along with β-bisabolol, hexahydrofarnesyl acetone, and several long-chain hydrocarbons. Sadab EO contained 1-hexadecanol acetate (26.39%), phytol (20.54%), and hexahydrofarnesyl acetone (3.34%) as its primary constituents, along with other fatty acid derivatives and alkanes.

Table 1

Table 1. Chemical composition of essential oils based on GC/MS analysis.

Figure 1

Figure 1. Heatmap illustrating the relative concentrations (%) of identified chemical compounds across three essential oils: grapefruit, henna, and sadab. Rows represent individual volatile and semi-volatile compounds detected by GC–MS analysis while columns correspond to the different essential oil samples. Color intensity (white to dark blue) reflects increasing compound abundance, with numerical values shown within each cell indicating the measured concentration. The heatmap highlights both qualitative and quantitative differences in chemical profiles among the oils, demonstrating distinct compositional patterns as well as compounds uniquely present or enriched in specific essential oils.

3.2 Acetylcholinesterase inhibitory activity

The anti-acetylcholinesterase (AChE) activity of the EOs was assessed via Ellman’s colorimetric assay across a concentration gradient (0.5–1,000 μg/mL). Grapefruit EO exhibited the strongest inhibitory effect, with an IC₅₀ value of 12.62 ± 0.48 μg/mL. Henna EO showed moderate inhibition (IC₅₀ = 43.90 ± 0.97 μg/mL), while sadab EO showed negligible activity, with no measurable IC₅₀.

Among the active constituents, limonene (89.94% in grapefruit EO) and phytol (41.42% in henna EO) are likely key contributors to the observed inhibition. The dose-dependent inhibition curves are presented in Table 2 and Figure 2. Grapefruit EO’s inhibitory activity closely approached that of the positive control (standard AChE inhibitor), while henna EO displayed partial inhibition across the tested range. No significant inhibition was observed for sadab EO, even at the highest concentrations. Although sadab EO was tested across the full concentration range, measurable inhibition was only detected at 50 μg/mL (13.7%) and 500 μg/mL (42.7%). At intermediate concentrations (62.5–250 μg/mL), inhibition remained negligible and below the sensitivity threshold of the assay, indicating a non-linear and inconsistent response.

Table 2

Table 2. Acetylcholinesterase inhibitory activity (%) of plant extracts at various concentrations (µg/mL).

Figure 2

Figure 2. This figure illustrates the acetylcholinesterase (AChE) inhibitory activity of selected plant essential oils (grapefruit, henna, and sadab) compared with a reference AChE inhibitor (ACE standard). Percentage enzyme inhibition is plotted as a function of sample concentration (µg/mL). Data demonstrate a concentration-dependent increase in AChE inhibition for all samples, with the ACE standard showing the highest inhibitory potency across the tested range, followed by grapefruit and henna oils, while sadab exhibits comparatively weaker activity. The figure highlights differential inhibitory profiles among the essential oils, reflecting variations in their bioactive chemical compositions.

4 Discussion

The findings of this study provide new insights into the chemical and biological properties of essential oils (EOs) extracted from grapefruit peels, henna leaves, and sadab leaves, with a specific focus on their potential as natural acetylcholinesterase (AChE) inhibitors. Among the three oils, grapefruit EO exhibited the strongest anti-AChE activity, as evidenced by its low IC₅₀ value (12.62 μg/mL). This potent effect is primarily attributed to its high concentration of limonene, a monoterpene known for its ability to bind the catalytic site of AChE and modulate cholinergic neurotransmission (Eddin et al., 2021; Piccialli et al., 2021). The results align with previous reports on the neuroprotective effects of citrus-derived terpenes, reinforcing the potential of grapefruit EO as a candidate for managing Alzheimer’s disease (AD) symptoms (Matsuzaki and Ohizumi, 2021).

In comparison, henna EO demonstrated moderate but notable AChE inhibitory activity. Although its IC₅₀ value was higher than that of grapefruit, the oil still showed biologically meaningful inhibition, likely due to the synergistic actions of phytol and limonene. Both compounds are associated with antioxidant, anti-inflammatory, and neuroprotective properties (Eddin et al., 2023; Sathya et al., 2022). Phytol, in particular, has been implicated in the modulation of oxidative stress and cholinergic signaling pathways relevant to AD pathogenesis (Sharifi-Rad et al., 2022). Moreover, henna EO displayed a chemically diverse profile, suggesting the possibility of multitarget pharmacological effects beyond cholinesterase inhibition. This complexity may offer broader therapeutic potential, especially in multifactorial neurodegenerative conditions.

In contrast, sadab EO exhibited negligible AChE inhibitory activity. Despite the presence of phytol and hexahydrofarnesyl acetone, its chemical profile was dominated by long-chain alkanes and esters, which are generally less reactive and lack the polar functional groups necessary for effective enzyme binding (K et al., 2023; de Oliveira et al., 2019). The poor inhibitory performance of sadab EO supports the view that the presence of phytochemicals alone is not sufficient to guarantee bioactivity. Rather, the structural characteristics of individual constituents, such as molecular size, hydrophobicity, and hydrogen-bonding capacity, play a crucial role in determining their interaction with the AChE active site (de Oliveira et al., 2019; Gyebi et al., 2024; Kamli et al., 2022).

The potent AChE inhibitory activity observed in grapefruit and henna EOs is largely attributed to the high abundance of limonene and phytol, respectively. Although experimental inhibition was quantified, the precise molecular interaction between these compounds and AChE is crucial to understand their pharmacological relevance.

AChE possesses a deep active-site gorge that includes two key regions: the catalytic triad (Ser203, Glu334, His447 in human AChE) and the peripheral anionic site (PAS), which modulates substrate access. Molecular docking studies from previous reports suggest that limonene, a small nonpolar monoterpene, binds primarily through hydrophobic interactions and van der Waals forces within the gorge, potentially near the PAS, altering substrate entry (Kamli et al., 2022).

In contrast, phytol, a larger diterpenoid alcohol, is thought to anchor near the catalytic triad and interact via hydrophobic contacts and occasional H-bonding with Trp86 or Tyr337, residues involved in ligand stabilization (Arya et al., 2021; Sathya et al., 2022). Its flexible aliphatic chain allows it to conform to the AChE cavity, partially occluding the active site and thereby reducing substrate hydrolysis.

These mechanistic insights, though derived from existing computational studies, align with the experimental results obtained in this study. Incorporating future molecular docking of UAE-derived limonene and phytol variants could further confirm these interactions and guide structural optimization for enhanced inhibitory activity.

Although sadab EO contains 20.54% phytol, a component that demonstrated moderate AChE inhibition in henna EO, the oil exhibited negligible overall activity. This apparent contradiction may be explained by the chemical context of sadab EO, where active compounds are embedded within a matrix dominated by large, nonpolar, and biologically inert molecules. The high proportion of long-chain esters and saturated hydrocarbons, such as 1-hexadecanol acetate and squalene, likely impedes enzyme access by introducing steric hindrance and reducing solubility or dispersion of the active constituents (de Oliveira et al., 2019; Sathya et al., 2022).

In henna EO, phytol co-exists with limonene (23.02%), a potent AChE inhibitor known to facilitate synergistic or additive effects. In contrast, the absence of such co-activators in sadab may explain its failure to produce a typical sigmoidal dose–response curve. Inhibition was only observed at high concentrations (≥500 μg/mL), and no measurable IC₅₀ could be determined, reflecting incomplete and inconsistent inhibition. This suggests that phytol’s bioactivity is not only concentration-dependent but highly sensitive to formulation context, chemical synergy, and delivery environment (de Oliveira et al., 2019; Sathya et al., 2022).

In summary, the comparative analysis highlights grapefruit EO as the most promising cholinesterase inhibitor among the three, followed by henna with moderate potential, while sadab showed minimal activity. These findings contribute to the growing body of evidence supporting the use of EOs as natural AChE inhibitors and underscore the importance of chemical composition and molecular features in predicting bioactivity. Future investigations should focus on isolating and characterizing the most active constituents of the essential oils through bioassay-guided fractionation. Molecular docking and mechanistic studies will help elucidate the interactions between these compounds and the AChE enzyme, while in vivo efficacy studies, pharmacokinetic profiling, and safety assessments are critical to validate their therapeutic potential. Additionally, delivery strategies such as encapsulation or nanoformulation may enhance the bioavailability and stability of these components, facilitating their integration into clinical applications.

5 Conclusion

This study demonstrated the varying chemical compositions and acetylcholinesterase (AChE) inhibitory activities of essential oils (EOs) derived from grapefruit, henna, and sadab leaves. GC-MS analysis revealed that grapefruit EO was highly enriched in limonene (89.94%), while henna EO contained substantial amounts of phytol (41.42%) and limonene (23.02%). These terpenoid compounds are well-documented for their neuroprotective properties, and their presence likely contributes to the observed bioactivity.

The biological assays confirmed that grapefruit EO exhibited the most potent AChE inhibition, with an IC₅₀ value of 12.62 ± 0.48 μg/mL, suggesting high potential as a natural source of cholinesterase-inhibiting agents. Henna EO also demonstrated moderate AChE inhibitory activity (IC₅₀ = 43.90 ± 0.97 μg/mL), further supporting the therapeutic potential of plant-derived compounds in neurodegenerative disease contexts. Conversely, sadab EO showed negligible AChE inhibition despite containing compounds such as phytol and hexahydrofarnesyl acetone, highlighting the importance of both concentration and molecular structure in determining enzyme inhibition efficacy.

These results provide promising evidence for the development of natural anti-AChE agents derived from grapefruit and henna essential oils. Given the growing interest in alternative and complementary therapies for Alzheimer’s disease, these oils offer a multifaceted pharmacological profile that may extend beyond enzyme inhibition to include anti-inflammatory and antioxidant effects.

Further investigations should focus on isolating and characterizing the most active constituents through bioassay-guided fractionation. In addition, molecular docking and mechanistic studies would clarify the interactions between these compounds and the AChE enzyme. In vivo studies, pharmacokinetics, and safety profiling will be critical next steps to validate their suitability for therapeutic development. Delivery approaches such as nanoencapsulation may also enhance the bioavailability and stability of these essential oil components. Future studies should also explore the antioxidant and anti-inflammatory properties of these essential oils, which are often mechanistically linked to neuroprotection and may further support their use as multi-target agents in Alzheimer’s disease management.

In summary, grapefruit and henna essential oils represent promising plant-based candidates for the development of neuroprotective agents aimed at mitigating the progression or symptoms of Alzheimer’s disease.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

Author contributions

RA: Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review and editing. NA: Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Project administration, Software, Validation, Writing – review and editing.

Funding

The author(s) declared that financial support was received for this work and/or its publication. This research is supported in part by Research Fund 2024-2025 from Rochester Institute of Technology, Dubai.

Acknowledgements

The authors would like to thank the reviewers for their constructive feedback that contributed to the enhancement of this study.

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

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References

Ainiwaer, P., Li, Z., Zang, D., Jiang, L., Zou, G., and Aisa, H. A. (2023). ruta graveolens: boost melanogenic effects and protection against oxidative damage in melanocytes. Antioxidants 12, 1580. doi:10.3390/antiox12081580

PubMed Abstract | CrossRef Full Text | Google Scholar

Al-Yateem, N., Lajam, A. M. A., Othman, M. M. G., Ahmed, M. A. A., Ibrahim, S., Halimi, A., et al. (2023). The impact of cultural healthcare practices on children’s health in the United Arab Emirates: a qualitative study of traditional remedies and implications. Front. Public Health 11, 1266742. doi:10.3389/fpubh.2023.1266742

PubMed Abstract | CrossRef Full Text | Google Scholar

Alolga, R. N., Wang, F., Zhang, X., Li, J., Tran, L.-S. P., and Yin, X. (2022). Bioactive compounds from the zingiberaceae family with known antioxidant activities for possible therapeutic uses. Antioxidants 11, 1281. doi:10.3390/antiox11071281

PubMed Abstract | CrossRef Full Text | Google Scholar

Amawi, R. M., Al-Hussaeni, K., Keeriath, J. J., and Ashmawy, N. S. (2024). A machine learning approach to evaluating the impact of natural oils on Alzheimer’s disease progression. Appl. Sci. 14, 6395. doi:10.3390/app14156395

CrossRef Full Text | Google Scholar

Arjmand, Z., and Dastan, D. (2020). Chemical characterization and biological activity of essential oils from the aerial part and root of ferula haussknechtii. Flavour Fragr. J. 35, 114–123. doi:10.1002/ffj.3544

CrossRef Full Text | Google Scholar

Arya, A., Chahal, R., Rao, R., Rahman, M. H., Kaushik, D., Akhtar, M. F., et al. (2021). Acetylcholinesterase inhibitory potential of various sesquiterpene analogues for Alzheimer’s disease therapy. Biomolecules 11, 350. doi:10.3390/biom11030350

PubMed Abstract | CrossRef Full Text | Google Scholar

Ashmawy, N. S., Nilofar, N., Zengin, G., and Eldahshan, O. A. (2024). Metabolic profiling and enzyme inhibitory activity of the essential oil of citrus aurantium fruit peel. BMC Complement. Med. Ther. 24, 262. doi:10.1186/s12906-024-04505-2

PubMed Abstract | CrossRef Full Text | Google Scholar

Ayaz, M., Sadiq, A., Junaid, M., Ullah, F., Subhan, F., and Ahmed, J. (2017). Neuroprotective and anti-aging potentials of essential oils from aromatic and medicinal plants. Front. Aging Neurosci. 9, 168. doi:10.3389/fnagi.2017.00168

PubMed Abstract | CrossRef Full Text | Google Scholar

Beniaich, G., Zouirech, O., Allali, A., Bouslamti, M., Maliki, I., El Moussaoui, A., et al. (2023). Chemical characterization, antioxidant, insecticidal and anti-cholinesterase activity of essential oils extracted from cinnamomum verum L. Separations 10, 348. doi:10.3390/separations10060348

CrossRef Full Text | Google Scholar

Brah, A. S. A. A. F., Armah, F. A., Obuah, C., Akwetey, S. A., and Adokoh, C. K. (2023). Toxicity and therapeutic applications of citrus essential oils (CEOs): a review. Int. J. Food Prop. 26, 301–326. doi:10.1080/10942912.2022.2158864

CrossRef Full Text | Google Scholar

Butnariu, M. (2021). “Plants as source of essential oils and perfumery applications,” in Bioprospecting of plant biodiversity for industrial molecules, 261–292.

Google Scholar

Chen, X., Drew, J., Berney, W., and Lei, W. (2021). Neuroprotective natural products for Alzheimer’s disease. Cells 10, 1309. doi:10.3390/cells10061309

PubMed Abstract | CrossRef Full Text | Google Scholar

de Oliveira, M. S., da Cruz, J. N., Gomes Silva, S., da Costa, W. A., de Sousa, S. H. B., Bezerra, F. W. F., et al. (2019). Phytochemical profile, antioxidant activity, inhibition of acetylcholinesterase and interaction mechanism of the major components of the piper divaricatum essential oil obtained by supercritical CO₂. J. Supercrit. Fluids 145, 74–84. doi:10.1016/j.supflu.2018.12.003

CrossRef Full Text | Google Scholar

Deng, W., Liu, K., Cao, S., Sun, J., Zhong, B., and Chun, J. (2020). Chemical composition, antimicrobial, antioxidant, and antiproliferative properties of grapefruit essential oil prepared by molecular distillation. Molecules 25, 217. doi:10.3390/molecules25010217

PubMed Abstract | CrossRef Full Text | Google Scholar

Dhapola, R., Beura, S. K., Sharma, P., Singh, S. K., and HariKrishnaReddy, D. (2024). Oxidative stress in Alzheimer’s disease: current knowledge of signaling pathways and therapeutics. Mol. Biol. Rep. 51, 48. doi:10.1007/s11033-023-09021-z

PubMed Abstract | CrossRef Full Text | Google Scholar

Dhifi, W., Bellili, S., Jazi, S., Bahloul, N., and Mnif, W. (2016). Essential oils’ chemical characterization and investigation of some biological activities: a critical review. Medicines 3, 25. doi:10.3390/medicines3040025

PubMed Abstract | CrossRef Full Text | Google Scholar

Eddin, L. B., Jha, N. K., Meeran, M. F. N., Kesari, K. K., Beiram, R., and Ojha, S. (2021). Neuroprotective potential of limonene and limonene-containing natural products. Molecules 26, 4535. doi:10.3390/molecules26154535

PubMed Abstract | CrossRef Full Text | Google Scholar

Eddin, L. B., Azimullah, S., Jha, N. K., Nagoor Meeran, M. F., Beiram, R., and Ojha, S. (2023). Limonene, a monoterpene, mitigates rotenone-induced dopaminergic neurodegeneration by modulating neuroinflammation, hippo signaling and apoptosis in rats. Int. J. Mol. Sci. 24, 5222. doi:10.3390/ijms24065222

PubMed Abstract | CrossRef Full Text | Google Scholar

Elaguel, A., Kallel, I., Gargouri, B., Ben Amor, I., Hadrich, B., Ben Messaoud, E., et al. (2019). lawsonia inermis essential oil: extraction optimization by RSM, antioxidant activity, lipid peroxidation and antiproliferative effects. Lipids Health Dis. 18, 196. doi:10.1186/s12944-019-1141-1

PubMed Abstract | CrossRef Full Text | Google Scholar

França Orlanda, J. F., and Nascimento, A. R. (2015). Chemical composition and antibacterial activity of ruta graveolens L. (rutaceae) volatile oils from são luís. Maranhão, Braz. S Afr. J. Bot. 99, 103–106. doi:10.1016/j.sajb.2015.03.198

CrossRef Full Text | Google Scholar

Gyebi, G. A., Ogunyemi, O. M., Ibrahim, I. M., Ogunro, O. B., Afolabi, S. O., Ojo, R. J., et al. (2024). Identification of potential inhibitors of cholinergic and β-secretase enzymes from phytochemicals derived from gongronema latifolium benth leaf: an integrated computational analysis. Mol. Divers 28, 1305–1322. doi:10.1007/s11030-023-10658-y

PubMed Abstract | CrossRef Full Text | Google Scholar

Hung, N. H., Quan, P. M., Satyal, P., Dai, D. N., Hoa, V. V., Huy, N. G., et al. (2022). Acetylcholinesterase inhibitory activities of essential oils from Vietnamese traditional medicinal plants. Molecules 27, 7092. doi:10.3390/molecules27207092

PubMed Abstract | CrossRef Full Text | Google Scholar

Juszczyk, G., Mikulska, J., Kasperek, K., Pietrzak, D., Mrozek, W., and Herbet, M. (2021). Chronic stress and oxidative stress as common factors of the pathogenesis of depression and Alzheimer’s disease: the role of antioxidants in prevention and treatment. Antioxidants 10, 1439. doi:10.3390/antiox10091439

PubMed Abstract | CrossRef Full Text | Google Scholar

K, P., Prasanth, D. S. N. B. K., Shadakshara, M. K. R., Ahmad, S. F., Seemaladinne, R., Rudrapal, M., et al. (2023). Citronellal as a promising candidate for Alzheimer’s disease treatment: a comprehensive study on in silico and in vivo anti-acetylcholine esterase activity. Metabolites 13, 1133. doi:10.3390/metabo13111133

PubMed Abstract | CrossRef Full Text | Google Scholar

Kamli, M. R., Sharaf, A. A. M., Sabir, J. S. M., and Rather, I. A. (2022). Phytochemical screening of rosmarinus officinalis L. as a potential anticholinesterase and antioxidant medicinal plant for cognitive decline disorders. Plants 11, 514. doi:10.3390/plants11040514

PubMed Abstract | CrossRef Full Text | Google Scholar

Konfo, T. R. C., Djouhou, F. M. C., Koudoro, Y. A., Dahouenon-Ahoussi, E., Avlessi, F., Sohounhloue, C. K. D., et al. (2023). Essential oils as natural antioxidants for the control of food preservation. Food Chem. Adv. 2, 100312. doi:10.1016/j.focha.2023.100312

CrossRef Full Text | Google Scholar

Lim, T. K. (2012). “citrus x aurantium grapefruit group,” in edible medicinal and non-medicinal plants: volume 4, fruits (Dordrecht: Springer Netherlands), 755–785.

CrossRef Full Text | Google Scholar

Matsuzaki, K., and Ohizumi, Y. (2021). Beneficial effects of citrus-derived polymethoxylated flavones for central nervous system disorders. Nutrients 13, 145. doi:10.3390/nu13010145

PubMed Abstract | CrossRef Full Text | Google Scholar

Moore, M. M., Díaz-Santos, M., and Vossel, K. (2021). Alzheimer’s association 2021 facts and figures report. Alzheimer’s association 17 (3), 327–406.

Google Scholar

Mounira, G. M. (2024). “Essential oils and their bioactive molecules: recent advances and new applications,” in Essential oils—recent advances, new perspectives and applications.

Google Scholar

Osaili, T. M., Dhanasekaran, D. K., Zeb, F., Faris, M. E., Naja, F., Radwan, H., et al. (2023). A status review on health-promoting properties and global regulation of essential oils. Molecules 28, 1809. doi:10.3390/molecules28041809

PubMed Abstract | CrossRef Full Text | Google Scholar

Patrício, K. P., Minato, A. C. S., Brolio, A. F., Lopes, M. A., Barros, G. R., Moraes, V., et al. (2022). Medicinal plant use in primary health care: an integrative review. Cien Saude Colet. 27, 677–686. doi:10.1590/1413-81232022272.46312020

PubMed Abstract | CrossRef Full Text | Google Scholar

Peng, W., Li, P., Ling, R., Wang, Z., Feng, X., Liu, J., et al. (2022). Diversity of volatile compounds in ten varieties of zingiberaceae. Molecules 27, 565. doi:10.3390/molecules27020565

PubMed Abstract | CrossRef Full Text | Google Scholar

Piccialli, I., Tedeschi, V., Caputo, L., Amato, G., De Martino, L., De Feo, V., et al. (2021). The antioxidant activity of limonene counteracts neurotoxicity triggered by Aβ1-42 oligomers in primary cortical neurons. Antioxidants 10, 937. doi:10.3390/antiox10060937

PubMed Abstract | CrossRef Full Text | Google Scholar

Raghav, S. K., Gupta, B., Agrawal, C., Goswami, K., and Das, H. R. (2006). Anti-inflammatory effect of ruta graveolens L. in murine macrophage cells. J. Ethnopharmacol. 104, 234–239. doi:10.1016/j.jep.2005.09.008

PubMed Abstract | CrossRef Full Text | Google Scholar

Reddy, D. N., and Al-Rajab, A. J. (2016). Chemical composition, antibacterial and antifungal activities of ruta graveolens L. volatile oils. Cogent Chem. 2, 1220055. doi:10.1080/23312009.2016.1220055

CrossRef Full Text | Google Scholar

Reddy, D. N. (2019). “Essential oils extracted from medicinal plants and their applications,” in Natural bio-active compounds: volume 1: production and applications. Editors M. S. Akhtar, M. K. Swamy, and U. R. Sinniah (Singapore: Springer), 237–283.

CrossRef Full Text | Google Scholar

Sá, C., Cardoso, K., Freitas, R., and Feitosa, C. (2012). Effect of oral treatment with essential oil of citrus sinensis (L) osbeck in the retention of spatial memory in rats evaluated in the morris water maze. Rev. Ciênc Farm Basic Appl. 33, 211–215.

Google Scholar

Saini, R. K., Ranjit, A., Sharma, K., Prasad, P., Shang, X., Gowda, K. G. M., et al. (2022). Bioactive compounds of citrus fruits: a review of composition and health benefits of carotenoids, flavonoids, limonoids, and terpenes. Antioxidants 11, 239. doi:10.3390/antiox11020239

PubMed Abstract | CrossRef Full Text | Google Scholar

Salim, A., Arasteh, A. A., Sahrish, R., Labash, D., El-Keblawy, A. A., Gad, H. A., et al. (2025). Comparative metabolic profiling and biological evaluation of essential oils from conocarpus species: antidiabetic, antioxidant, and antimicrobial potential. Plants 14, 464. doi:10.3390/plants14030464

PubMed Abstract | CrossRef Full Text | Google Scholar

Sathya, S., Gowri, M. B., Kaliannan, T., Sethuraman, V., Kandasamy, R., and Devi, K. P. (2022). Phytol-loaded PLGA nanoparticles ameliorate scopolamine-induced cognitive dysfunction by attenuating cholinesterase activity, oxidative stress and apoptosis in wistar rat. Nutr. Neurosci. 25, 485–501. doi:10.1080/1028415X.2020.1764290

PubMed Abstract | CrossRef Full Text | Google Scholar

Shahrajabian, M. H. (2024). A candidate for health promotion, disease prevention and treatment: common rue (ruta graveolens L.), an important medicinal plant in traditional medicine. Curr. Rev. Clin. Exp. Pharmacol. 19, 2–11. doi:10.2174/2772432817666220510143902

PubMed Abstract | CrossRef Full Text | Google Scholar

Sharifi-Rad, J., Rapposelli, S., Sestito, S., Herrera-Bravo, J., Arancibia-Diaz, A., Salazar, L. A., et al. (2022). Multi-target mechanisms of phytochemicals in Alzheimer’s disease: effects on oxidative stress, neuroinflammation and protein aggregation. J. Pers. Med. 12, 1515. doi:10.3390/jpm12091515

PubMed Abstract | CrossRef Full Text | Google Scholar

Singh, D. K., Luqman, S., and Mathur, A. K. (2015). lawsonia inermis L.—A commercially important primaeval dyeing and medicinal plant with diverse pharmacological activity: a review. Ind. Crops Prod. 65, 269–286. doi:10.1016/j.indcrop.2014.11.025

CrossRef Full Text | Google Scholar

Tan, S. J., and Ismail, I. S. (2020). Potency of selected berries, grapes, and citrus fruit as neuroprotective agents. Evid. Based Complement. Altern. Med. 2020, 3582947. doi:10.1155/2020/3582947

PubMed Abstract | CrossRef Full Text | Google Scholar

Tuasha, N., Fekadu, S., and Deyno, S. (2023). Prevalence of herbal and traditional medicine in Ethiopia: a systematic review and meta-analysis of 20-year studies. Syst. Rev. 12, 232. doi:10.1186/s13643-023-02398-9

PubMed Abstract | CrossRef Full Text | Google Scholar

Wedamulla, N. E., Fan, M., Choi, Y. J., and Kim, E. K. (2022). Citrus peel as a renewable bioresource: transforming waste to food additives. J. Funct. Foods 95, 105163. doi:10.1016/j.jff.2022.105163

CrossRef Full Text | Google Scholar