Guangdong University of Technology ES&T: Chloropolycyclic aromatic hydrocarbons induce THP-1 macrophage immunosuppression—characterized by disorders of amino acid metabolism

Chlorinated PAHs induce immunosuppression in THP-1 macrophages characterized by disrupted amino acid metabolism

First author: Li Xinyan

Corresponding author: Luan Tiangang

Author: Guangdong University of Technology

By Xinyan Li, Mei Ma, Bilin Zhao, Na Li, Ling Fang, Donghong Wang, Tiangang Luan*

Research highlights

In this study, high-throughput multi-target immunotoxicity detection and non-targeted metabolomics technology were integrated to jointly evaluate the immunotoxicity of chlorinated polycyclic aromatic hydrocarbons and explore the immune metabolism mechanism
.

This study demonstrated for the first time that chlorinated polycyclic aromatic hydrocarbons can induce immunotoxicity at a lower concentration (1 μM) without activating AhR, and discussed the role of macrophage metabolism in the induction of immune response by Cl-PAHs/PPAHs, which provided strong support
for the development of a new method for risk assessment of environmental chemicals based on immunometabolic mechanism.

Summary of results

Chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) are a new type of persistent organic pollutants with certain bioaccumulation and long-distance transport capabilities, the main sources of which are automobile exhaust emissions, waste incineration and electronic waste dismantling processes
.
Cl-PAHs have been reported to be widely present in a variety of environmental mediators and even biological samples, and the latest studies confirm the evidence of exposure in human blood, so it is urgent and necessary
to study the exposure risk and toxicity of Cl-PAHs.
Although toxicity studies of PAHs have been going on for many years, the health risk evaluation of their chlorinated products is still in its infancy, and currently mainly focuses on aromatic hydrocarbon receptor effects (AhR effects
).
It has been found that some Cl-PAHs with low aromatic ring number can cause a stronger AhR effect than parent polycyclic aromatic hydrocarbons (PPAHs), and have dioxin-like toxicity
.
Given that the immune system is a sensitive target for dioxin-like attack, it is suggested that chlorinated polycyclic aromatic hydrocarbons are potentially immunotoxic, but direct evidence
is lacking.
In this study, the immunotoxicity
of Cl-PAHs and corresponding PPAHs on THP-1 macrophages was evaluated using a high-content screening system and a self-developed high-throughput multi-target detection method based on THP-1 macrophage immune function.
It was found that Cl-PAHs exhibited significant immunosuppressive toxicity, while PPAHs showed different immune interferences
.
On this basis, through multiple correlation analysis of untargeted metabolomics and immunophenotypic results, it is found that abnormal amino acid metabolism is likely to be the cause
of induced immunotoxicity of Cl-PAHs and its parent compounds.

introduction

As the first barrier to exogenous chemical exposure, the immune system is vulnerable to attack by pollutants, thereby increasing disease susceptibility, and is a potentially sensitive target for pollutant toxicity risk assessment
.
Due to the complex mechanisms of immunotoxicity and multiple cross-over toxicity endpoints, it is often difficult to systematically assess the immunotoxicity
of environmental pollutants with scattered test results.
In response to this problem, we developed a series of high-throughput detection methods for the morphology and function of human macrophages (THP-1) based on high-content screening systems (2020, 10.
1021/acs.
est.
0c01152; 2022, 10.
1021/acsestwater.
1c00252)
。

Figure 1.
General workflow for detection of immunophenotypes by high-content screening systems

In recent years, studies have found that the metabolic process of immune cells is one of the key factors in regulating the
immune response.
Immune cells can help adapt to a dynamically changing microenvironment by flexibly regulating intracellular nutrient metabolism to meet the energy and intermediate metabolites
required during the immune response.
This view provides a new window into the mechanistic study of environmental toxicology, i.
e.
, pollutants may trigger immune dysfunction
by interfering with cellular metabolic processes.
Therefore, studying immunotoxicity from the perspective of metabolic abnormalities caused by pollutants may be an effective breakthrough in discovering new markers of immunotoxicity and exploring new toxicity mechanisms
.

In previous studies, we found that both 9-chloroanthracene (9Cl-Ant) and 2,7-dichlorofluorene (2,7-Fl) cause more intense dioxin-like toxicity (DNA damage and AhR effects) than their parent compounds anthracene and fluorene, suggesting potential immunotoxicity
。 Therefore, this study combined the detection of immune function by high-content screening system and the acquisition of metabolite information by non-targeted metabolomics, and elucidated the immunotoxicity mechanism of Cl-PAHs and corresponding PPAHs-exposed macrophages by establishing the correlation between immunophenotype and differential metabolite information, and identified potential biomarkers of immune metabolism
.

Graphic introduction

Figure 2.
Correlation analysis of immunophenotypes with significantly different metabolites

By correlating the results of metabolomics with immunophenotyping, we found that Cl-PAHs/PAHs activate macrophages' defense responses to stress and inflammation, manifested by abnormalities
in multiple amino acid synthesis and metabolic pathways.
Multiple Spearman correlation analysis was used to identify immunometabolic biomarkers, and the results showed that the decrease of plant sphingoglycine and the increase of glycerophosphocholine in the PPAHs group in the Cl-PAHs group may be the cause of cell adhesion and morphological changes, while the increase of L-kynurenine may be the cause of
phagocytosis inhibition.