Inflammation, metabolic dysregulation, and pulmonary function among obese urban adolescents with asthma

Abstract

Rationale: Insulin resistance and low high-density lipoprotein (HDL) are associated with pulmonary morbidity, including asthma, but the underlying mechanisms are not well elucidated.

Objectives: To investigate whether systemic inflammation underlies the association of metabolic abnormalities with pulmonary function among urban adolescents.

Methods: Th-cell responses and monocyte subsets, and their association with serum homeostatic model assessment of insulin resistance (HOMA-IR) and HDL, and pulmonary function were quantified in 168 adolescents, including 42 obese subjects with asthma, 42 normal-weight subjects with asthma, 40 obese subjects without asthma, and 44 healthy control subjects. Th-cell responses (Th1 [CD4(+)IFNγ(+)] and Th2 [CD4(+)IL4(+)] cells) to stimulation with phytohemagglutinin, leptin, and dust mite, and classical (CD14(+)CD16(-)), resident (CD14(+)CD16(+)), and patrolling (CD14dimCD16(+)) monocytes, and their C-C chemokine receptor type-2 (CCR2) expression were quantified by flow cytometry.

Measurements and main results: Th1/Th2 ratio to all three stimuli was higher in obese subjects with asthma than normal-weight subjects with asthma and directly correlated with HOMA-IR. Classical monocytes inversely associated with Th1/Th2 ratio to phytohemagglutinin (r = -0.43; P = 0.01) and directly with Asthma Control Test score (β = 1.09; P = 0.04), while patrolling monocytes correlated with Composite Asthma Severity Index score (β = 1.11; P = 0.04) only among obese subjects with asthma. HDL was inversely associated with patrolling monocytes and directly associated with CCR2 expression on resident monocytes. CCR2 expression on patrolling monocytes predicted residual volume (RV), RV/TLC ratio, and FRC, after adjusting for HDL, but not after adjusting for body mass index. Association of Th1/Th2 ratio with RV, FRC, and inspiratory capacity was attenuated after adjusting for HOMA-IR.

Conclusions: Th1 polarization and monocyte activation among obese subjects with asthma correlates with metabolic abnormalities. Association of monocyte activation with pulmonary function is mediated by body mass index, whereas that of Th1 polarization is mediated by insulin resistance.

Keywords: asthma; inflammation; metabolic dysregulation; obesity; pulmonary function.

Figure 1.

Between study group comparison of Th-cell responses. Proportion of CD4⁺IFNγ⁺ T cells (A–C), CD4⁺IL-4⁺ T cells (D–F), and their ratio (G–I) were quantified to determine Th-cell responses to phytohemagglutinin (PHA), leptin, and Dermatophagoides farinae (Df), respectively. The proportions of Th cells were log10 transformed before comparison among study groups. The middle bar represents the mean values and the side bars represent the 25th and 75th percentile. HC = healthy control subjects; NwA = normal-weight subjects with asthma; OA = obese subjects with asthma; Ob = obese subjects without asthma. The asterisks denote statistically significant between-group differences (*P < 0.05, **P < 0.01, ***P < 0.001).

Figure 2.

Between study group comparison of monocyte activation. Monocyte activation was defined by comparing the proportion of (A) classical, (B) patrolling, and (C) resident monocytes in each study group. The middle bar represents the mean values and the side bars represent the 25th and 75th percentile. HC = healthy control subjects; NwA = normal-weight subjects with asthma; OA = obese subjects with asthma; Ob = obese subjects without asthma. The asterisks denote statistically significant between-group differences (*P < 0.05, **P < 0.01, ***P < 0.001).

Figure 3.

Association of monocyte activation with systemic Th-cell responses among obese subjects with asthma compared with obese subjects without asthma. Association of Th-cell response to phytohemagglutinin (PHA) with (A) classical monocytes and (B) patrolling monocytes was compared between obese subjects with asthma and obese subjects without asthma.