Figure 4.

The ability to synthesize and maintain reduced glutathione decreases with age. (A) Representative Western blot probed for γ-glutamylcysteine ligase (GCL), GSH reductase (GR), and glyceraldehyde phosphate dehydrogenase in lung homogenate. Protein expression levels of both (B) GCL, the rate-limiting enzyme in glutathione synthesis, and (C) GR were quantified. GCL declines with age and is induced with cigarette smoke (CS) in young mice but not aged mice. GR expression is unchanged with age but is only induced by CS in the 2- and 8-month-old mice. Data represented as mean ± SEM with *P < 0.05, **P < 0.01 compared between air and CS; ^§P < 0.05, ^§§P < 0.01 compared with air-exposed young mice; n = 4–6.