Hospital-based case control study and animal study on the relationship between nonylphenol exposure and depression

The aim of this work is to explore the association between chronic exposure to nonylphenol (NP), a representative environmental endocrine disruptor (EED), and the risk of depression and its potential mechanism.

A hospital-based case control study was conducted from August to December 2018. Forty-one patients with confirmed depression and 47 healthy volunteers were recruited. In vitro, 20 rats were randomly divided into the control group (corn oil) and NP exposure group (n=10 per group), which were gavaged at a dose of 4 mg/kg w/day for 180 days.

The depressed patient group had higher Zung Self-Rating Depression Scale (SDS) (P<0.001) and Self-Rating Anxiety Scale (SAS) (P<0.001) scores than the healthy group. The serum NP level (P=0.009) in the depressed group was higher than that in the healthy group, and the BDNF level (P=0.001) was lower. The serum levels of monoamine neurotransmitters dopamine (DA) (P=0.070), epinephrine (E) (P=0.001), and noradrenaline (NE) (P=0.000) were lower than those in the healthy group. In the sucrose preference test, the sucrose preference time for the exposure group of rats was lower than that of the control group (P<0.001). In the forced swim test, a longer resting time was measured for the exposure group of rats as compared to the control group (P<0.05). The level of NP (P<0.001) in the brain tissue of the NP exposure group was higher than that in the control group, and the serum level of brain-derived neurotrophic factor (BDNF) (P=0.004) was lower. Histopathological examination of the brain biopsies illustrated that the neuronal cells and nuclei in the hippocampus of the exposed group exhibited slight shrinkage.

Chronic exposure to NP at environmental doses will result in the accumulation of NP in the brain and blood, and induction of depression, which might be associated with the alterations in the expression levels of BDNF and monoamine neurotransmitters.