[A study of the role of heme oxygenase-1 expression in ventilator induced lung injury and its mechanism in rats].

OBJECTIVE: To observe the changes in heme oxygenase-1 (HO-1) expression in lung tissue with ventilator induced lung injury (VILI) in rats, and to explore the mechanism of preventive effect of HO-1 inducer hemin on VILI.

METHODS: Fifty-six male Sprague-Dawley (SD) rats were randomly divided into control group (group C), VILI model group (group M), hemin group 1, 2, 3, 4 (group H1, H2, H3, H4, with intraperitoneal injection of hemin 40, 80, 120, 160 micromol/kg, respectively, 24 hours before model was reproduced), and suppressor Z group (intraperitoneal injection of ZnPP 10 micromol/kg 24 hours before reproduction of the model). After 4 hours of ventilation, all rats, except those of group C, were sacrificed, and bronchoalveolar lavage fluid (BALF) was collected. Total protein, the contents of tumor necrosis factor-alpha (TNF-alpha) and interleukin-10 (IL-10) in BALF were measured. The lung tissue specimen was collected, the wet-to-dry weight ratio (W/D), the level of lactate dehydrogenase (LDH), superoxide dismutase (SOD), malondialdehyde (MDA) and HO-1 protein expression were determined. Lung pathological changes were observed with microscope.

RESULTS: In group M, rat lung tissue was seriously damaged, and total protein in BALF, TNF-alpha, IL-10, W/D of lung, MDA and LDH activity, as well as HO-1 protein expression were markedly higher than those in group C, denoting that VILI model was successfully reproduced. Compared with group M, the total protein in BALF (g/L) in group H1, H2, H3 was gradually reduced (0.74+/-0.06, 0.73+/-0.07, 0.70+/-0.07 vs. 0.84+/-0.08, all P<0.01) with an increase in hemin dose. W/D of lung was reduced (4.93+/-0.27, 4.91+/-0.24, 4.87+/-0.23 vs. 5.53+/-0.48, all P<0.01). The activity of SOD (U/mg) was higher (85+/-9, 82+/-15, 93+/-11 vs. 55+/-12, all P<0.01), and the content of MDA (nmol/mg) was decreased (15+/-3, 15+/-3, 13+/-2 vs. 18+/-4, P<0.05 or P<0.01). The content of IL-10 (pg/L) in BALF was higher (0.42+/-0.06, 0.46+/-0.06, 0.47+/-0.05 vs. 0.36+/-0.07), and the content of TNF-alpha (pg/L) was decreased (0.18+/-0.07, 0.14+/-0.03, 0.10+/-0.07 vs. 0.23+/-0.06), but only the difference between group H2, H3 and group M was statistically significant (all P<0.01). The activity of LDH (U/g) was decreased (11 353+/-1 317, 11 516+/-1 613, 9 631+/-1 520 vs. 12 361+/-1 841), but only the difference between group H3 and group M was statistically significant (P<0.01). HO-1 expression [absorbance (A) value] was increased compared with that of group M (0.164+/-0.010, 0.190+/-0.149, 0.205+/- 0.018 vs. 0.122+/-0.016, all P<0.01), and the degree of lung injury was reduced with increase in dosage. With the further increase of hemin dose, lung injury in group H4 was more serious than that of group H1, H2 and H3. With ZnPP to inhibit HO-1 expression, the protective effect of HO-1 disappeared.

CONCLUSION: A moderate expression of HO-1 as induced by hemin can alleviate VILI, and the best dose of hemin is 120 micromol/kg. Its protective effect on lung tissue may possibly be attributed by its anti-inflammatory effect and anti-oxidative stress.