Olfactory stimulation modulates the blood glucose level in rats

Impaired olfactory system in metabolic imbalance-related neuropathology

Olfactory dysfunction, influenced by factors such as aging and environmental stress, is linked to various neurological disorders. The olfactory bulb's connections to brain areas like the hypothalamus, piriform cortex, entorhinal cortex, and limbic system make olfactory dysfunction a contributor to a range of neuropathological conditions. Recent research has underscored that olfactory deficits are prevalent in individuals with both metabolic syndrome and dementia. These systemic metabolic alterations correlate with olfactory impairments, potentially affecting brain regions associated with the olfactory bulb. In cases of metabolic syndrome, phenomena such as insulin resistance and disrupted glucose metabolism may result in compromised olfactory function, leading to multiple neurological issues. This review synthesizes key findings on the interplay between metabolic-induced olfactory dysfunction and neuropathology. It emphasizes the critical role of olfactory assessment in diagnosing and managing neurological diseases related to metabolic syndrome.

Parallel evolution of fish bi-modal breathing and expansion of olfactory receptor (OR) genes: toward a universal ORs nomenclature

Olfactory receptors (ORs) play a key role in the prime sensorial perception, being highly relevant for intra/interspecific interactions. ORs are a subgroup of G-protein coupled receptors that exhibit highly complex subgenomes in vertebrates. However, OR repertoires remain poorly studied in fish lineages, precluding finely retracing their origin, evolution, and diversification, especially in the most basal groups. Here, we conduct an exhaustive gene screening upon 43 high-quality fish genomes exhibiting varied gene repertoires (2-583 genes). While the early vertebrates performed gas exchange through gills, we hypothesize that the emergence of new breathing structures (swim bladder and paired lungs) in early osteichthyans may be associated with expansions in the ORs gene families sensitive to airborne molecules. Additionally, we verify that the OR repertoire of moderns actinopterygians has not increased as expected following a whole genome duplication, likely due to regulatory mechanisms compensating the gene load excess. Finally, we identify 25 distinct OR families, allowing us to propose an updated universal nomenclature for the fish ORs.

Olfactory Stimulation by Fennel (Foeniculum vulgare Mill.) Essential Oil Improves Lipid Metabolism and Metabolic Disorders in High Fat-Induced Obese Rats

In this study, odor components were analyzed using gas chromatography/mass spectrometry (GC/MS) and solid-phase microextraction (SPME), and odor-active compounds (OACs) were identified using GC-olfactometry (GC-O). Among the volatile compounds identified through GC-O, p-anisaldehyde, limonene, estragole, anethole, and trans-anethole elicit the fennel odor. In particular, trans-anethole showed the highest odor intensity and content. Changes in body weight during the experimental period showed decreasing values of fennel essential oil (FEO)-inhaled groups, with both body fat and visceral fat showing decreased levels. An improvement in the body’s lipid metabolism was observed, as indicated by the increased levels of cholesterol and triglycerides and decreased levels of insulin in the FEO-inhaled groups compared to group H. Furthermore, the reduction in systolic blood pressure and pulse through the inhalation of FEO was confirmed. Our results indicated that FEO inhalation affected certain lipid metabolisms and cardiovascular health, which are obesity-related dysfunction indicators. Accordingly, this study can provide basic research data for further research as to protective applications of FEO, as well as their volatile profiles.

Olfactory Dysfunction: A Complication of Diabetes or a Factor That Complicates Glucose Metabolism? A Narrative Review

The present narrative review presents emerging data regarding the association between diabetes mellitus and olfactory dysfunction and discusses the role of olfactory dysfunction in glucose metabolism. We searched relevant published articles in PubMed and Google Scholar until October 2021. Main key words included “olfactory dysfunction”, “diabetes mellitus”, and “glucose metabolism”. Olfactory dysfunction has been associated with diabetes mellitus. Furthermore, it has been proposed to be a diabetic complication, given that it has been linked with microvascular complications, such as diabetic peripheral neuropathy. Interestingly, it has been suggested that olfactory dysfunction is a manifestation of central neuropathy in diabetes, a hypothesis based on the observation that diabetes, olfactory dysfunction, and cognitive decline often coexist. However, evidence is limited and inconsistent. More importantly, olfactory and endocrine systems are closely linked, and olfactory dysfunction plays a significant role in glucose metabolism and obesity. Indeed, food behaviour and energy balance are influenced by olfaction status.

Inhalation of Patchouli (Pogostemon Cablin Benth.) Essential Oil Improved Metabolic Parameters in Obesity-Induced Sprague Dawley Rats

This study investigated effects of patchouli essential oil (PEO) inhalation on metabolic parameters. First, to characterize aromatic compounds in PEO, solid-phase microextraction-gas chromatography/mass spectrometric detection was employed in which 19 aromatic compounds were identified. In GC-olfactometry analysis, linalool, α-patchoulene, and β-patchoulene were found to be the constituents exhibiting the highest similarity to the aromatic compounds in patchouli. In an animal experiment using Sprague Darley rats, groups with PEO inhalation had a reduced food intake compared to the control group. Additionally, body weight was lower in the obesity-induced animal model exposed to PEO inhalation than the group without PEO. However, we found no significant difference in organ weights between groups. In our serum analysis, high-density lipoprotein cholesterol was significantly higher in the PEO inhalation groups, while low-density lipoprotein cholesterol content was highest in the positive control group, suggesting that inhalation of the aromatic compounds present in patchouli may improve cholesterol profile. In addition, leptin levels were reduced in the groups treated with PEO inhalation, which explains the differences in food intake and body weight gains. Last, animal groups exposed to PEO inhalation showed a relatively lower systolic blood pressure which suggests that inhalation of PEO (or aromatic compounds therein) may assist in regulating blood pressure. Collectively, our data demonstrate that the inhalation of PEO influenced certain markers related to metabolic diseases, hence provide basic data for future research as to preventive/therapeutic applications of PEO as well as their aromatic constituents.