High-fat Western diet alters crystalline silica-induced airway epithelium ion transport but not airway smooth muscle reactivity

Abstract

Objectives: Silicosis is an irreversible occupational lung disease resulting from crystalline silica inhalation. Previously, we discovered that Western diet (HFWD)-consumption increases susceptibility to silica-induced pulmonary inflammation and fibrosis. This study investigated the potential of HFWD to alter silica-induced effects on airway epithelial ion transport and smooth muscle reactivity.

Methods: Six-week-old male F344 rats were fed a HFWD or standard rat chow (STD) and exposed to silica (Min-U-Sil 5^®, 15 mg/m³, 6 h/day, 5 days/week, for 39 d) or filtered air. Experimental endpoints were measured at 0, 4, and 8 weeks post-exposure. Transepithelial potential difference (V_t), short-circuit current (I_SC) and transepithelial resistance (R_t) were measured in tracheal segments and ion transport inhibitors [amiloride, Na⁺ channel blocker; NPPB; Cl- channel blocker; ouabain, Na⁺, K⁺-pump blocker] identified changes in ion transport pathways. Changes in airway smooth muscle reactivity to methacholine (MCh) were investigated in the isolated perfused trachea preparation.

Results: Silica reduced basal I_SC at 4 weeks and HFWD reduced the I_SC response to amiloride at 0 week compared to air control. HFWD + silica exposure induced changes in ion transport 0 and 4 weeks after treatment compared to silica or HFWD treatments alone. No effects on airway smooth muscle reactivity to MCh were observed.

Keywords: Airway hyperreactivity; Epithelium; Ion transport; Obesity; Silica; Western diet.

Fig. 1

Experimental design for HFWD-induction of MetDys, silica-inhalation exposure and endpoint experiments. Schematic describes the design for single endpoint experiments using separate cohorts of animals (n = 8 for each group). Reproduced from Thompson et al. [14] with modifications

Fig. 2

Effects silica-inhalation, HFWD-consumption, and combined exposure on body weight in animals used for A IPT and B Ussing experiments. HFWD-consumption significantly increased animal body weight at all time points compared to STD control groups regardless of silica exposure; silica-inhalation had no significant effect on body weight. P < 0.05. * Indicates significance compared to STD + AIR group. ⁺ Indicates significance compared to STD + SIL group. For IPT experiments n = 8, 8, and 5–8 at 0, 4, and 8 weeks, respectively. For Ussing experiment n = 6–8, 8, and 8 at 0, 4, and 8 weeks, respectively

Fig. 3

Effects of silica-inhalation, HFWD-consumption, and combined exposure on bioelectric responses to ion transport inhibitors. Shown are basal and inhibitor-induced epithelial I_SC responses at A 0, B 4, and C 8 weeks post-exposure. Basal and agent-induced epithelial R_t responses at D 0, E 4, and F 8 weeks. Silica reduced basal I_SC at 4 weeks (B). HFWD reduced I_SC responses to amiloride at 0 week (A). HFWD + SIL increased basal I_SC and I_SC responses to amiloride at both 0 week (A) and 4 weeks (B). Solid lines indicate significant differences between different exposure groups at a given time point. P < 0.05. n = 6–8, 7–8, 3–8 at 0, 4, and 8 weeks, respectively

Fig. 4

Effects of silica-inhalation, HFWD-consumption, and combined exposure on V_t. There was no effect of silica, HFWD or combined HFWD + SIL exposure on basal V_t. P < 0.05. n = 6–8, 7–8, 3–8 at 0, 4, and 8 weeks, respectively

Fig. 5

Effect of silica-inhalation, HFWD-consumption, and combined exposure on airway reactivity to applied MCh in the isolated perfused trachea preparation. Concentration–response curves for extraluminally applied MCh at A 0, B 4, C 8 weeks and for intraluminally applied MCh at D 0, E 4, and F 8 weeks post-silica exposure. n = 5–6, 4–6, 5–7 at 0, 4, and 8 weeks, respectively

Fig. 6

Effect of silica-inhalation, HFWD-consumption, and combined exposure on normalized responses to MCh. Graphs depict percent maximum responses to extraluminally applied MCh at A 0, B 4, and C 8 weeks; intraluminally applied MCh at D 0, E 4, and F 8 weeks; and intraluminal response expressed as a percentage of the extraluminal maximal contractile response to MCh at G 0, H 4, and I 8 weeks post exposure to silica. n = 5–6, 4–6, 5–7 at 0, 4, and 8 weeks, respectively