The effect of serum BDNF levels on central serotonin transporter availability in obese versus non-obese adults: A [11C]DASB positron emission tomography study

•PET study examining in-vivo 5-HTT BP and serum BDNF in obese and non-obese adults.•BDNF has opposing effects on 5-HTT BP in NAcc in obese and non-obese.•BDNF and hippocampal 5-HTT BP are negatively correlated in 5-HTTLPR L/L homozygotes.•No considerable intergroup differences regarding BDNF levels and 5-HTT BP.•Findings indicate possible involvement of BDNF in pathogenesis of obesity.

BackgroundSerotonin (5-HT) and its neurotrophic support system, specifically brain-derived neurotrophic factor (BDNF), are thought to modulate energy homeostasis and susceptibility to obesity. Moreover, a polymorphism (5-HTTLPR) in the serotonin reuptake transporter (5-HTT) gene impairs its transcription, thereby altering serotonergic tone and potentially contributing to such susceptibility. This study aims to investigate the effect of BDNF, biallelic 5-HTTLPR, and central in-vivo 5-HTT availability in highly obese versus non-obese subjects using positron emission tomography (PET) and 5-HTT selective [11C]DASB.MethodsThirty-eight subjects, 24 obese, otherwise mentally and physically healthy, and 14 non-obese healthy controls were included in this study. Parametric images of binding potential were generated from PET data. Central 5-HTT availability, 5-HTTLPR genotype, and serum BDNF concentrations were analyzed, first in a volume of interest, then in a voxel-wise manner.ResultsOverall, our results showed an absence of a linear correlation between BDNF, in-vivo central 5-HTT availability, and body mass index (BMI). 5-HTTLPR genotyping revealed BDNF and hippocampal 5-HTT availability to be negatively correlated (r = −0.57, p = 0.007) in long allelic homozygotes. However, obese subjects exhibited opposing effects of BDNF levels on 5-HTT availability in the nucleus accumbens (NAcc) relative to our non-obese controls.ConclusionsOur data did not confirm an overall correlation between serum BDNF, in-vivo central 5-HTT availability, 5-HTTLPR, and BMI. However, there is evidence that serotonergic tone linked to BDNF, specifically in the NAcc, is involved in the pathophysiology of obesity, although this needs further exploration over a wide range of reward-related eating behaviors.