Appetite-Enhancing Effects: The Influence of Concentrations of Benzylacetone and trans-Cinnamaldehyde and Their Inhalation Time, as Well as the Effect of Aroma, on Body Weight in Mice

Effects of Essential Oils and Fragrant Compounds on Appetite: A Systematic Review

Appetite dysregulation is one of the factors contributing to anorexia, bulimia nervosa, obesity, and diabetes. Essential oils or fragrant compounds have been proven to regulate food intake and energy expenditure; hence, this study aimed to summarize their effects on appetite and the underlying mechanisms. The PubMed and Web of Science databases were searched until July 2022. Only two of the 41 studies were performed clinically, and the remaining 39 used animal models. Oral administration was the most common route, and a dosage range of 100-2000 mg/kg for mice or 2-32 mg/kg for rats was applied, with a duration of 12 days to 4 weeks, followed by inhalation (10^-6-10^-3 mg/cage or 10^-9-10^-2 mg/cm³ within 1 h). Approximately 11 essential oil samples and 22 fragrant compounds were found to increase appetite, while 12 essential oils and seven compounds decreased appetite. These fragrant components can exert appetite-regulating effects via leptin resistance, the activity of sympathetic/parasympathetic nerves, or the mRNA expression of neuropeptide Y (NPY)/agouti-related protein (AgRP), cocaine- and amphetamine-regulated transcript (CART)/proopiomelanocortin (POMC) in the hypothalamus. Fragrance memory and cognitive processes may also play roles in appetite regulation. The findings of this study accentuate the potential of essential oils and fragrant compounds to regulate appetite and eating disorders.

Individual and Combined Inhalational Sedative Effects in Mice of Low Molecular Weight Aromatic Compounds Found in Agarwood Aroma

Agarwood is known to have a sedative effect and the less studied volatile aromatic constituents it contains may have contribution to the activity. In this study, two Kyara grade (highest-grade agarwood in Japan) samples were extracted using headspace-solid phase microextraction (HS-SPME) and analyzed through gas chromatography-mass spectrometry (GC-MS). Six low molecular weight aromatic compounds (LACs) and one structurally simple compound (diethylene glycol monoethyl ether) present in the aromas were individually evaluated for inhalational sedative activity in mice through open field test. Doses of 0.0001 g/L to 1 g/L were prepared for each compound and administered to mice (n = 6/dose/compound). Results revealed all compounds decreased spontaneous motor activity at almost all doses. Strongest sedative activity of each compound reduced total spontaneous motor activity by more than half against control, demonstrating their contribution to agarwood aroma and potential as independent sedating agents. Mixtures of compounds using their most effective dose were made and evaluated again for inhalational sedative effect. Interestingly, the combination of all compounds showed no significant effect and even caused stimulation in mice movements. This result suggests antagonistic-like interaction between the compounds, which is probably due to structural similarities. Consequently, it implies the other constituents present in agarwood, along with LACs, are also important to the overall sedative activity.

The Combination of Aquilaria sinensis (Lour.) Gilg and Aucklandia costus Falc. Volatile Oils Exerts Antidepressant Effects in a CUMS-Induced Rat Model by Regulating the HPA Axis and Levels of Neurotransmitters

The Aquilaria sinensis (Lour.) Gilg (CX)-Aucklandia costus Falc. (MX) herbal pair is frequently used in traditional Chinese medicine prescriptions for treating depression. The volatile oil from CX and MX has been shown to have good pharmacological activities on the central nervous system, but its curative effect and mechanism in the treatment of depression are unclear. Therefore, the antidepressant effect of the volatile oil from CX-MX (CMVO) was studied in chronic unpredictable mild stress (CUMS) rats. The suppressive effects of CMVO (25, 50, 100 μL/kg) against CUMS-induced depression-like behavior were evaluated using the forced swimming test (FST), open field test (OFT) and sucrose preference test (SPT). The results showed that CMVO exhibited an antidepressant effect, reversed the decreased sugar preference in the SPT and prolongation of immobility time in the FST induced by CUMS, increased the average speed, time to enter the central area, total moving distance, and enhanced the willingness of rats to explore the environment in the OFT. Inhalational administration of CMVO decreased levels of adrenocorticotropic hormone and corticosterone in serum and the expression of corticotropin-releasing hormone mRNA in the hypothalamus, which indicated regulation of over-activation of the hypothalamic-pituitary-adrenal (HPA) axis. In addition, CMVO restored levels of 5-hydroxytryptamine (5-HT), dopamine, norepinephrine and acetylcholine in the hippocampus. The RT-PCR and immunohistochemistry results showed that CMVO up-regulated the expression of 5-HT_1A mRNA. This study demonstrated the antidepressant effect of CMVO in CUMS rats, which was possibly mediated via modulation of monoamine and cholinergic neurotransmitters and regulation of the HPA axis.

Appetite-enhancing effects of nutmeg oil and structure-activity relationship of habituation to phenylpropanoids

Nutmeg (Myristica fragrans) is widely used to flavour sweet and savoury foods and has been used as a herbal medicine to enhance appetite in Asian countries. Nutmeg oil contains compounds such as myristicin and methyl eugenol. Previously, we found that inhalation of phenylpropanoid compounds increased appetite in mice. These volatile aroma compounds with appetite-enhancing effects have attracted the attention of healthcare professionals who care for older people with dementia because many of these older people have hypophagia, which leads to frailty and becoming bedridden. Thus, appetite-enhancing agents that are inexpensive and easy to administer are particularly desirable. In this study, we showed that the inhalation of nutmeg oil, myristicin and methyl eugenol produced appetite-enhancing effects in mice. Methyl eugenol alone has shown appetite-enhancing effects and locomotor-reducing effects at the same dose. In a previous study, benzylacetone produced those two effects at the same dose and also increased the body weight of mice significantly; methyl eugenol, however, did not because the mice experienced olfactory habituation after repeated inhalations of methyl eugenol. A structure-activity study showed that a carbonyl group on the aliphatic chain prevented habituation to aroma compounds, which is important information for identifying suitable phenylpropanoid compounds for long-term treatment of loss of appetite.

Chemical Constituents and Pharmacological Activity of Agarwood and Aquilaria Plants

Agarwood, a highly precious non-timber fragrant wood of Aquilaria spp. (Thymelaeaceae), has been widely used in traditional medicine, religious rites, and cultural activities. Due to the inflated demanding and depleted natural resources, the yields of agarwood collected from the wild are shrinking, and the price is constantly rising, which restricts agarwood scientific research and wide application. With the sustainable planting and management of agarwood applied, and especially the artificial-inducing methods being used in China and Southeast Asian countries, agarwood yields are increasing, and the price is becoming more reasonable. Under this condition, illuminating the scientific nature of traditional agarwood application and developing new products and drugs from agarwood have become vitally important. Recently, the phytochemical investigations have achieved fruitful results, and more than 300 compounds have been isolated, including numerous new compounds that might be the characteristic constituents with physiological action. However, no one has focused on the new compounds and presented a summary until now. Alongside phytochemical advances, bioactivity screening and pharmacological investigation have also made a certain progress. Therefore, this review discussed the new compounds isolated after 2010, and summarized the pharmacological progress on agarwood and Aquilaria plants.

Appetite-Enhancing Effects of Curry Oil

Inhalation of scent compounds with phenylpropanoidal structures, such as trans-cinnamaldehyde, is expected to increase the appetite. The scent of curry powder is well known for its appetite-enhancing effect on humans. In this work, we show that the appetite of mice after inhalation of curry powder essential oil or benzylacetone showed a similar increase. The components of curry oil, trans-cinnamaldehyde, trans-anethole, and eugenol, each showed appetite-enhancing effects; therefore, these three scent compounds may be the active compounds in curry powder oil.