Protective effects of glycyrrhizin against β₂-adrenergic receptor agonist-induced receptor internalization and cell apoptosis

Biol Pharm Bull. 2011;34(5):609-17. doi: 10.1248/bpb.34.609.

Abstract

It has been reported that treatment with β₂ adrenergic receptor (β₂AR) agonist bronchodilators may result in airway β₂ARs internalization and cardiac muscle cells apoptosis. This could lead to the loss of pharmacological effect of β₂AR agonists and increase adverse cardiovascular events in asthma patients receiving β₂AR agonist therapy. Glycyrrhizin, the major bioactive component of licorice root extract, has been reported to exhibit protective effect on respiratory system. Here, we investigate the effects of glycyrrhizin against β₂AR agonist salbutamol-induced receptor internalization and cell apoptosis. In our study, the live cell confocal imaging and fixed-cell enzyme-linked immunosorbent assay (ELISA) assay revealed that glycyrrhizin significantly inhibited salbutamol-induced surface β₂AR internalization. The underlying mechanisms were then identified to be that glycyrrhizin could reduce the association of β₂ARs with β-arrestins and clathrin heavy chain as well as the level of G protein-coupled receptor kinase (GRK) mediated phosphorylation of β₂ARs. The inhibition of receptor internalization by glycyrrhizin further lead to stabilization of the β₂AR mRNA and protein expression, thus amplified the transmembrane signaling via the β₂ARs. We also proved that glycyrrhizin could profoundly attenuate salbutamol-induced early cellular apoptosis by regulating the expressions of B-cell lymphoma 2 (Bcl-2) family genes. Taken together, our results suggest that glycyrrhizin exhibits protective effects against β₂AR agonist-induced receptor internalization and cell apoptosis. These findings might have practical implications for future strategies of combined application of glycyrrhizin with β₂AR receptor agonists to improve the efficacy of bronchodilators in patients with asthma and chronic obstructive pulmonary disease (COPD).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenergic beta-Agonists / pharmacology*
  • Albuterol / antagonists & inhibitors
  • Albuterol / pharmacology
  • Apoptosis / drug effects*
  • Arrestins / metabolism
  • Base Sequence
  • Cell Line
  • Clathrin / metabolism
  • Cyclic AMP / metabolism
  • DNA Primers
  • Endocytosis / drug effects*
  • Glycyrrhizic Acid / pharmacology*
  • Humans
  • RNA, Messenger / genetics
  • Receptors, Adrenergic, beta-2 / drug effects*
  • Receptors, Adrenergic, beta-2 / genetics
  • Receptors, Adrenergic, beta-2 / metabolism
  • beta-Arrestins

Substances

  • Adrenergic beta-Agonists
  • Arrestins
  • Clathrin
  • DNA Primers
  • RNA, Messenger
  • Receptors, Adrenergic, beta-2
  • beta-Arrestins
  • Glycyrrhizic Acid
  • Cyclic AMP
  • Albuterol