An angiotensin I-converting enzyme insertion/deletion polymorphism is associated with Pakistani asthmatic cases and controls

Altered renin-angiotensin system gene expression in airways of antigen-challenged mice: ACE2 downregulation and unexpected increase in angiotensin 1-7

OBJECTIVE

Evidence suggest that the renin-angiotensin system (RAS) is activated in people with asthma, although its pathophysiological role is unclear. Angiotensin-converting enzyme 2 (ACE2) is the major enzyme that converts angiotensin II to angiotensin 1-7 (Ang-1-7), and is also known as a receptor of SARS-CoV-2. The current study was conducted to identify the change in RAS-related gene expression in airways of a murine asthma model.

METHODS

The ovalbumin (OA)-sensitized mice were repeatedly challenged with aerosolized OA to induce asthmatic reaction. Twenty-four hours after the last antigen challenge, the main bronchial smooth muscle (BSM) tissues were isolated.

RESULTS

The KEGG pathway analysis of differentially expressed genes in our published microarray data revealed a significant change in the RAS pathway in the antigen-challenged mice. Quantitative RT-PCR analyses showed significant increases in the angiotensin II-generating enzymes (Klk1, Klk1b3 and Klk1b8) and a significant decrease in Ace2. Surprisingly, ELISA analyses revealed a significant increase in Ang-1-7 levels in bronchoalveolar lavage (BAL) fluids of the antigen-challenged animals, while no significant change in angiotensin II was observed. Application of Ang-1-7 to the isolated BSMs had no effect on their isometrical tension.

CONCLUSION

The expression of Ace2 was downregulated in the BSMs of OA-challenged mice, while Klk1, Klk1b3 and Klk1b8 were upregulated. Despite the downregulation of ACE2, the level of its enzymatic product, Ang-1-7, was increased in the inflamed airways, suggesting the existence of an unknown ACE2-independent pathway for Ang-1-7 production. The functional role of Ang-1-7 in the airways remains unclear.

Genetically high angiotensin-converting enzyme concentrations causally increase asthma risk: A meta-analysis using Mendelian randomization

Objectives

This meta-analysis aimed to test the association of angiotensin-converting enzyme (ACE) gene I/D polymorphism with asthma risk and circulating ACE changes.

Methods

Public literature retrieval, publication selection, and information extraction were completed independently by two investigators. Effect-size values are expressed as odds ratios (ORs) or standardized mean differences (SMDs) with a 95% confidence interval (95% CI).

Results

Nineteen studies (2,888 patients and 9,549 controls) fulfilled the eligibility criteria. Overall investigations demonstrated that ACE gene I/D polymorphism was significantly associated with asthma risk under allelic (OR, 95% CI: 1.26, 1.08 to 1.48), homozygous genotypic (1.50, 1.09 to 2.06), and recessive (1.53, 1.24 to 1.89) models with moderate heterogeneity (I2 statistic: 64% to 79%). Subsidiary investigations recorded that race, matched status, asthma diagnosis, sample size, and age possibly accounted for the existence of significant heterogeneity. Relative to carriers with the II genotype, those with the DD genotype, ID genotype, and the combination of DD and ID genotypes had significantly higher concentrations of circulating ACE (WMD: 3.13, 2.07, and 2.83 U/L, respectively, p < 0.05). Adoption of Mendelian randomization analyses revealed that one unit increment in circulating ACE concentrations was found to be significantly associated with a 1.14-fold increased risk of asthma (95% CI: 1.02 to 4.24).

Conclusion

We provided strong meta-analytical evidence supporting the causal implication of high circulating ACE concentrations in the development of asthma.