Computational Studies Applied to Linalool and Citronellal Derivatives Against Alzheimer's and Parkinson's Disorders: A Review with Experimental Approach

Potential roles of inhalation aromatherapy on stress-induced depression by inhibiting inflammation in the peripheral olfactory system

According to principles of Traditional Chinese Medicine, the nose is the passage for exogenous evil to invade the body, while essential or volatile oils extracted from herbs have the effects of dispelling melancholy, repelling foulness, and resuscitation with aromatics. Inhalation aromatherapy can target the brain and has a potential therapeutic effect on mood disorders. However, in particular, the mechanism of the effect of inhalation aromatherapy on the olfactory mucosa (OM) of the nasal cavity at the peripheral level, the first step in olfactory detection, where olfactory sensory neurons (OSNs) relay information to brain for signal processing, remains unclear. Here, we examined the roles of inhalation aromatherapy with compound essential oils derived from Bergamot, Peppermint and Rosa rugose on chronic unpredictable mild stress (CUMS)-induced depression and explored potential therapeutic targets in the peripheral OM. We found that inhalation aromatherapy effectively ameliorated CUMS-induced depression and olfactory dysfunction in rats. Strikingly, inhalation aromatherapy improved pathological changes, significantly reduced apoptosis levels, and promoted olfactory neurogenesis in the OM, which may contribute to the beneficial effects on the olfactory function of depressed rats. Further, inhalation aromatherapy significantly may reverse inflammation levels in the OM through Sirt1/FKBP5/GR/NF-κB signaling pathway, and prevented neuroinflammation in other parts of the olfactory system such as the hippocampus and prefrontal cortex, which may play a role in the olfactory impairments in rats with depression. Collectively, we have demonstrated that inhalation aromatherapy could efficiently prevent the local inflammatory responses in the OM of CUMS depression model rats. These findings provide new insights into the treatment of depression with aromatherapy, as well as new concept for the identification of novel antidepressant strategies.

The effectiveness of Melissa officinalis L. essential oil inhalation on anxiety and symptom burden of hemodialysis patients: a randomized trial study

BACKGROUND

Hemodialysis patients suffer from physical and mental symptoms for which aromatherapy might be useful. This study aimed to determine the effectiveness of Melissa officinalis L. (Lemon Balm) essential oil inhalation on anxiety and the burden of symptoms in hemodialysis patients.

METHODS

This study is a randomized clinical trial with a pretest-posttest design. Sixty-eight hemodialysis patients were randomly divided into intervention (who underwent Melissa officinalis L. inhalation aromatherapy 3 times a week for one month) and control (who inhaled refined sweet almond oil) groups. The intervention in both groups was conducted during the hemodialysis session. The data were collected using the state-trait anxiety inventory and Dialysis Symptom Index. Data were analyzed through SPSS-25, using Mann-Whitney, Wilcoxon, t-tests and MANOVA.

RESULTS

Before the intervention, both groups were similar in terms of anxiety and symptoms burden (P > 0.05). However, after the intervention, a significant difference was found between the groups in terms of state and trait anxiety, and severity of constipation, nausea, vomit, diarrhea, swelling in legs, muscle cramps and shortness, worry, nervousness and anxiety, and trouble staying asleep. Moreover, after the intervention, a significant difference was observed between the groups regarding the prevalence of symptoms burden such as feeling anxious and having a dry mouth (P < 0.05).

CONCLUSION

Melissa officinalis L. essential oil inhalation aromatherapy reduced the symptoms burden and anxiety in hemodialysis patients. Given the effectiveness of aromatherapy in hemodialysis patients, it is suggested that healthcare workers should use this complementary and integrative health to reduce the anxiety and symptoms burden in hemodialysis patients.

TRIAL REGISTRATION RCT REGISTRY

Iranian Registry of Clinical Trials (IRCT) number: IRCT20191021045178N3; Registration date 27/04/2021.

Impact of plant monoterpenes on insect pest management and insect-associated microbes

The fight against insect pests primarily relies on the utilization of synthetic insecticides. However, improper application of these chemicals can lead to detrimental effects on both the environment and human health, as well as foster the development of insect resistance. Consequently, novel strategies must be implemented to address the challenges stemming from the prolonged use of synthetic insecticides in agricultural and public health environments. Certain strategies involve the combination of crop protectants, which not only enhance insecticidal effectiveness but also reduce application rates. Plant-based natural products emerge as promising alternatives for insect management. Monoterpenes, which are abundant plant compounds produced through the activation of various enzymes, have attracted significant attention for their effectiveness in insect control. Notably, they are prolific in fragrance-producing plants. This review explores the plant defense, insecticidal, and antimicrobial characteristics of monoterpenes against insect pests, shedding light on their potential modes of action and possibilities for commercialization. Emphasizing their role as targeted and environmentally safer, the review highlights the practical viability of monoterpenes within integrated pest management programs.

Anticonvulsant activity of Tetrahydrolinalool: behavioral, electrophysiological, and molecular docking approaches

Tetrahydrolinalool (THL) is an acyclic monoterpene alcohol, produced during linalol metabolism and also a constituent of essential oils. As described in the literature, many monoterpenes present anticonvulsant properties, and thus we became interested in evaluating the anticonvulsant activity of Tetrahydrolinalool using in mice model as well as in silico approaches. Our results demonstrated that THL increased latency to seizure onset and also reduced the mortality, in picrotoxin induced seizure tests. The results may be related to GABAergic regulation, which was also suggested in seizure testing induced by 3-mercapto-propionic acid. In the strychnine-induced seizure testing, none of the groups pretreated with THL modulated the parameters indicative of anticonvulsant effect. The electrophysiological results revealed that THL treatment reduces seizures induced by pentylenetetrazole. The in silico molecular docking studies showed that the interaction between THL and a GABAA receptor model formed a stable complex, in comparison to the crystaligraphic structure of diazepam, a structurally related ligand. In conclusion, all the evidences showed that THL presents effective anticonvulsant activity related to the GABAergic pathway, being a candidate for treatment of epileptic syndromes.

Therapeutic potential of the linalool against cadmium-induced testicular tissue damage

Cadmium (Cd) is a heavy metal that has harmful effects and is one of the contaminants found in the environment. Cd exposure causes important pathophysiological processes, such as reproductive toxicity. Linalool (Lnl) is a monoterpene, a component of essential oils known to be produced synthetically. Additionally, Lnl has many important beneficial effects, such as anti-inflammatory and antioxidant effects. The objective of this study is to determine whether Lnl has a healing impact in opposition to testicular tissue damage due to Cd exposure. In the study, 28 male rats were divided at random into four equal groups (n = 7). No treatment was applied to the control group. CdCl2 was applied intraperitoneally to the Cd group at a dose of 3 mg/kg for the first 7 days of the trial. For the Cd + Lnl group, 3 mg/kg CdCl2 was applied intraperitoneally for the first 7 days of the trial, and 100 mg/kg/day Lnl was applied. Upon completion of all applications, the rats were sacrificed and blood samples and testicular tissue were taken. Cd exposure caused histopathological changes, oxidative stress, inflammation, and an increase in apoptotic cells in testicular tissue. However, Cd altered endocrine hormones in the hypothalamic-pituitary-gonad axis. However, Lnl application against Cd exposure was able to regulate the negativity caused by Cd in both testicular tissue and endocrine hormone levels. In conclusion, Lnl may be a potential therapeutic strategy against Cd-induced reproductive toxicity. We believe that Lnl has a high potential for further studies to determine its detailed mechanisms of action and cellular signaling pathways.

Linalool, a Fragrance Compound in Plants, Protects Dopaminergic Neurons and Improves Motor Function and Skeletal Muscle Strength in Experimental Models of Parkinson's Disease

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the gradual loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc), resulting in reduced dopamine levels in the striatum and eventual onset of motor symptoms. Linalool (3,7-dimethyl-1,6-octadien-3-ol) is a monoterpene in aromatic plants exhibiting antioxidant, antidepressant, and anti-anxiety properties. The objective of this study is to evaluate the neuroprotective impacts of linalool on dopaminergic SH-SY5Y cells, primary mesencephalic and cortical neurons treated with 1-methyl-4-phenylpyridinium ion (MPP+), as well as in PD-like mice induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Cell viability, α-tubulin staining, western blotting, immunohistochemistry and behavioral experiments were performed. In MPP+-treated SH-SY5Y cells, linalool increased cell viability, reduced neurite retraction, enhanced antioxidant defense by downregulation of apoptosis signaling (B-cell lymphoma 2 (Bcl-2), cleaved caspase-3 and poly ADP-ribose polymerase (PARP)) and phagocyte NADPH oxidase (gp91phox), as well as upregulation of neurotrophic signaling (brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF)) and nuclear factor-erythroid 2 related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway. In MPP+-treated primary mesencephalic neurons, linalool enhanced the expressions of tyrosine hydroxylase (TH), Sirtuin 1 (SirT1), and parkin. In MPP+-treated primary cortical neurons, linalool upregulated protein expression of SirT1, γ-Aminobutyric acid type A-α1 (GABAA-α1), and γ-Aminobutyric acid type B (GABAB). In PD-like mice, linalool attenuated the loss of dopamine neurons in SNpc. Linalool improved the motor and nonmotor behavioral deficits and muscle strength of PD-like mice. These findings suggest that linalool potentially protects dopaminergic neurons and improves the impairment symptoms of PD.