Single inhalation exposure to polyamide micro and nanoplastic particles impairs vascular dilation without generating pulmonary inflammation in virgin female Sprague Dawley rats

Abstract

Background: Exposure to micro- and nanoplastic particles (MNPs) in humans is being identified in both the indoor and outdoor environment. Detection of these materials in the air has made inhalation exposure to MNPs a major cause for concern. One type of plastic polymer found in indoor and outdoor settings is polyamide, often referred to as nylon. Inhalation of combustion-derived, metallic, and carbonaceous aerosols generate pulmonary inflammation, cardiovascular dysfunction, and systemic inflammation. Additionally, due to the additives present in plastics, MNPs may act as endocrine disruptors. Currently there is limited knowledge on potential health effects caused by polyamide or general MNP inhalation.

Objective: The purpose of this study is to assess the toxicological consequences of a single inhalation exposure of female rats to polyamide MNP during estrus by means of aerosolization of MNP.

Methods: Bulk polyamide powder (i.e., nylon) served as a representative MNP. Polyamide aerosolization was characterized using particle sizers, cascade impactors, and aerosol samplers. Multiple-Path Particle Dosimetry (MPPD) modeling was used to evaluate pulmonary deposition of MNPs. Pulmonary inflammation was assessed by bronchoalveolar lavage (BAL) cell content and H&E-stained tissue sections. Mean arterial pressure (MAP), wire myography of the aorta and uterine artery, and pressure myography of the radial artery was used to assess cardiovascular function. Systemic inflammation and endocrine disruption were quantified by measurement of proinflammatory cytokines and reproductive hormones.

Results: Our aerosolization exposure platform was found to generate particles within the micro- and nano-size ranges (thereby constituting MNPs). Inhaled particles were predicted to deposit in all regions of the lung; no overt pulmonary inflammation was observed. Conversely, increased blood pressure and impaired dilation in the uterine vasculature was noted while aortic vascular reactivity was unaffected. Inhalation of MNPs resulted in systemic inflammation as measured by increased plasma levels of IL-6. Decreased levels of 17β-estradiol were also observed suggesting that MNPs have endocrine disrupting activity.

Conclusions: These data demonstrate aerosolization of MNPs in our inhalation exposure platform. Inhaled MNP aerosols were found to alter inflammatory, cardiovascular, and endocrine activity. These novel findings will contribute to a better understanding of inhaled plastic particle toxicity.

Keywords: Cardiovascular; Endocrine disruption; Inflammation; Inhalation; Microplastic; Nanoplastic; Nylon; Particle; Polyamide.

Fig. 1

General schematic of the rodent whole-body inhalation platform used for experimentation

Fig. 2

Real-time size characterization of the whole-body inhalation facility shows the presence of nanoscale particles (A), and microparticles (B). Time-integrated characterization of the overall particle size fractionation during exposure was quantified using a Harvard Compact Cascade Impactor (C). Data are presented as mean ± SEM.

Fig. 3

Representative images of H&E-stained sections at 20x, 100x, and 200x magnification from naïve female rat controls (n = 9) or polyamide exposed rats (n = 8) are above. Low magnification morphological appearance of the conducting airways can be seen at 20x magnification (A and D). The proximal bronchioles (red arrows) and the distal bronchioles (black arrows) are shown at a 100x magnification (B and E). Representative images of the alveolar region are shown at 200x magnification (C and F)

Fig. 4

Vascular reactivity in the abdominal aorta and uterine artery was assessed by establishing concentration response curves with the endothelial-dependent vasodilator methacholine (A and D), the endothelial-independent vasodilator sodium nitroprusside (B and E), and the vasoconstrictor phenylephrine (C and F). Significance was assessed by comparing overall reactivity via a four-parameter nonlinear regression analysis. Data are presented as mean ± SEM, n = 9–11, *Significantly different (p < 0.05) from filtered air controls

Fig. 5

Vascular reactivity in the radial artery was assessed by establishing drug response curves with the endothelial-dependent vasodilator, methacholine (A), the endothelial independent-vasodilator, sodium nitroprusside (B), and the vasoconstrictor, phenylephrine (C). Significance was assessed by comparing overall reactivity via a four-parameter nonlinear regression analysis. Data are presented as mean ± SEM, n = 7–9, *Significantly different (p < 0.05) from filtered air controls

Fig. 6

Enzyme-linked immunosorbent assays for IL-6 (A), CRP (B), and MCP-1 (C) were carried out for assessment of systemic inflammation. Samples with analyte levels below the level of quantification and above the level of detection were assigned the value LOQ/2. Significance was assessed by comparing outcomes with a two-tailed t-test assuming equal variance between groups. Data are presented as mean ± SEM, n = 7–9, *Significantly different (p < 0.05) from filtered air controls; ^TTrending difference (p ≤ 0.10) from filtered air controls

Fig. 7

Enzyme-linked immunosorbent assays for 17β-estradiol (A) and progesterone (B). Samples with analyte levels below the level of quantification and above the level of detection were assigned the value LOQ/2. Significance was assessed by comparing outcomes with a two-tailed t-test assuming equal variance between groups. Data are presented as mean ± SEM, n = 7–9, *Significantly different (p < 0.05) from filtered air controls