A Lower Olfactory Capacity Is Related to Higher Circulating Concentrations of Endocannabinoid 2-Arachidonoylglycerol and Higher Body Mass Index in Women

Abstract

The endocannabinoid (eCB) system can promote food intake by increasing odor detection in mice. The eCB system is over-active in human obesity. Our aim is to measure circulating eCB concentrations and olfactory capacity in a human sample that includes people with obesity and explore the possible interaction between olfaction, obesity and the eCB system. The study sample was made up of 161 females with five groups of body mass index sub-categories ranging from under-weight to morbidly obese. We assessed olfactory capacity with the "Sniffin´Sticks" test, which measures olfactory threshold-discrimination-identification (TDI) capacity. We measured plasma concentrations of the eCBs 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine or anandamide (AEA), and several eCB-related compounds, 2-acylglycerols and N-acylethanolamines. 2-AG and other 2-acylglycerols fasting plasma circulating plasma concentrations were higher in obese and morbidly obese subjects. AEA and other N-acylethanolamine circulating concentrations were lower in under-weight subjects. Olfactory TDI scores were lower in obese and morbidly obese subjects. Lower TDI scores were independently associated with higher 2-AG fasting plasma circulating concentrations, higher %body fat, and higher body mass index, after controlling for age, smoking, menstruation, and use of contraceptives. Our results show that obese subjects have a lower olfactory capacity than non-obese ones and that elevated fasting plasma circulating 2-AG concentrations in obesity are linked to a lower olfactory capacity. In agreement with previous studies we show that eCBs AEA and 2-AG, and their respective congeners have a distinct profile in relation to body mass index. The present report is the first study in humans in which olfactory capacity and circulating eCB concentrations have been measured in the same subjects.

Fig 1. Endocannabinoid and related compounds plasma concentrations.

Box plots of plasma concentrations of 2-arachidonoyl glycerol (A), anandamide (B), 2-linoleoylglycerol (C), docosahexaenoylethanolamide (D), 2-oleoylglycerol (E), oleoylethanolamide (F), linoleoylethanolamide (G), and palmitoylethanolamide (H) of subjects from each of the body mass index (BMI) sub-groups. The median is represented as a line within the box plot and the mean is represented as a + sign. Significant differences (p<0.05) of endocannabinoids and related compounds concentrations between BMI subgroups are represented by asterisks (*).

Fig 2. Olfactory scores.

Box plots of odor threshold-discrimination-identification (TDI) scores (A), odor threshold scores (B), odor discrimination scores (C), and odor identification scores (D) of subjects from each of the body mass index (BMI) sub-groups. The median is represented as a line within the box plot and the mean is represented as a + sign. Discontinuous line in (A) represents the TDI score of 30.3 that separates normosmia from hyposmia. Significant differences (p<0.05) of olfactory scores between BMI sub-groups are represented asterisks (*).