Treadmill exercise preconditioning attenuates lung damage caused by systemic endotoxemia in type 1 diabetic rats

Abstract

Endotoxemia induces a series of inflammatory responses that may result in lung injury. However, heat shock protein72 (HSP72) has the potential to protect the lungs from damage. The objective of this study was to determine whether prior exercise conditioning could increase the expression of HSP72 in the lungs and attenuate lung damage in diabetic rats receiving lipopolysaccharide (LPS). Streptozotocin was used to induce diabetes in adult male Wistar rats. Rats were randomly assigned to sedentary or exercise groups. Rats in the exercise condition ran on a treadmill 5 days/week, 30-60 min/day, with an intensity of 1.0 mile/hour over a 3-week period. Rats received an intravenous infusion of LPS after 24 hrs from the last training session. Elevated lavage tumor necrosis factor-alpha (TNF- α ) level in response to LPS was more marked in diabetic rats. HSP72 expression in lungs was significantly increased after exercise conditioning, but less pronounced in diabetic rats. After administration of LPS, exercised rats displayed higher survival rate as well as decreased lavage TNF- α level and lung edema in comparison to sedentary rats. Our findings suggest that exercise conditioning could attenuate the occurrence of inflammatory responses and lung damage, thereby reducing mortality rate in diabetic rats during endotoxemia.

Figure 1

The changes of rats' body weight after STZ injection and 3-week exercise training. N: nondiabetic rats; NE: nondiabetic rats with exercise; S: STZ-induced diabetic rats; SE: STZ-induced diabetic rats with exercise (n = 8 per group). *P < 0.05, compared with the N group; **P < 0.05, compared with NE group, and ***P < 0.05, compared with the S group; (one-way repeat measurement ANOVA).

Figure 2

The colonic temperature (T _co⁡) of the animals in response to LPS challenge. NL: nondiabetic rats receiving LPS administration; SL: STZ-induced diabetic rats injected with LPS; SEL: STZ-induced diabetic rats with exercise injected with LPS (n = 8 per group).

Figure 3

The survival rate of rats with or without exercise after LPS administration (15 mg/kg, i.v.). NL: nondiabetic rats receiving LPS administration; SL: STZ-induced diabetic rats injected with LPS; SEL: STZ-induced diabetic rats with exercise injected with LPS (n = 8 per group). ^† P < 0.05, compared with the NL group; ^‡ P < 0.05, compared with the SL group (Kaplan-Meier test).

Figure 4

Levels of TNF-α, IL-6, and IL-10 in lavage fluid at 240 min after saline or LPS administration. NS: nondiabetic rats injected with saline; NL: nondiabetic rats injected with LPS; SS: STZ-induced diabetic rats injected with saline; SL: STZ-induced diabetic rats injected with LPS; SES: STZ-induced diabetic rats with exercise injected with saline; SEL: STZ-induced diabetic rats with exercise injected with LPS. Data are expressed as the mean ± SEM of eight rats per group. *P < 0.05, compared with the NS group; ^† P < 0.05, compared with the NL group; ***P < 0.05, compared with the SS group; ^‡ P < 0.05, compared with the SL group; ***P < 0.05, compared with the SES group (one-way ANOVA).

Figure 5

The lung wet/dry weight ratios and albumin content in lung lavage at 240 min after administration of saline or LPS. Albumin content in the brochoalveolar lavage fluid was calculated as [(mg of albumin)/(mL of lavage fluid)]/(g of dried lung weight). NS: nondiabetic rats injected with saline; NL: nondiabetic rats injected with LPS; SS: STZ-induced diabetic rats injected with saline; SL: STZ-induced diabetic rats injected with LPS; SES: STZ-induced diabetic rats with exercise injected with saline; SEL: STZ-induced diabetic rats with exercise injected with LPS. Data are expressed as the mean ± SEM of eight rats per group. *P < 0.05, compared with the NS group; ^† P < 0.05, compared with the NL group; ***P < 0.05, compared with the SS group; ^‡ P < 0.05, compared with the SL group; ****P < 0.05, compared with the SES group (one-way ANOVA).

Figure 6

Histological examination of right upper lobe taken after 240 min of saline or LPS administration. (a) NS: nondiabetic rats injected with saline; (b) NL: nondiabetic rats injected with LPS; (c) SS: STZ-induced diabetic rats injected with saline; (d) SL: STZ-induced diabetic rats injected with LPS; (e) SES: STZ-induced diabetic rats with exercise injected with saline; (f) SEL: STZ-induced diabetic rats with exercise injected with LPS. The interstitial spaces of alveoli became wider after LPS administration, due to polymorphonuclear cell infiltration and edematous changes of alveolar walls (b), (d). Scale bar: 10 μm.

Figure 7

The lung injury score in different groups after LPS administration. Data are expressed as mean ± S.E.M. *P < 0.05, compared with the NS group; ***P < 0.05, compared with the SS group; ****P < 0.05, compared with the SES group (one-way ANOVA).

Figure 8

The expression of HSP72 in lungs in the rats with or without exercise after saline or LPS administration. NS: nondiabetic rats injected with saline; NES: nondiabetic rats with exercise injected with saline; SS: STZ-induced diabetic rats injected with saline; SES: STZ-induced diabetic rats with exercise injected with saline; NL: nondiabetic rats injected with LPS; NEL: nondiabetic rats with exercise injected with LPS; SL: STZ-induced diabetic rats injected with LPS; SEL: STZ-induced diabetic rats with exercise injected with LPS. Data are expressed as the mean ± SEM of eight rats per group. Protein levels are expressed as a ratio to the NS group. Below each column is a representative Western blot of HSP72 protein. Data are expressed as the mean ± SEM of eight rats per group. *P < 0.05, compared with the N group; **P < 0.05, compared with NE group (one-way ANOVA).