Therapeutic effects of troglitazone in experimental chronic pancreatitis in mice

Abstract

Peroxisome proliferator-activated receptor (PPAR)-gamma controls growth, differentiation, and inflammation. PPAR-gamma agonists exert anti-inflammatory effects in vitro and inhibit the activation of pancreas stellate cells, implicated in the formation and progression of fibrosis. We determined the influence of troglitazone, a ligand for PPAR-gamma, on pancreatic damage and fibrosis in experimental chronic pancreatitis. Mice received six hourly intraperitoneal injections with 50 microg/kg of cerulein or saline, three times a week for 6 weeks. One week after the last injection all mice were sacrificed. Untreated mice were compared with mice treated with troglitazone either during weeks 1 to 6 or weeks 4 to 6. All mice that received cerulein injections displayed histopathological signs of chronic pancreatitis at week 7. Troglitazone treatment improved all markers for severity of pancreatitis. Moreover, early and postponed troglitazone treatments were equally effective in diminishing intrapancreatic fibrosis as quantified by Sirius red staining, hydroxyproline content, and laminin staining as well as the increased number of pancreatic stellate cells and pancreas levels of transforming growth factor-beta. Thus, troglitazone attenuated pancreatic damage and inflammation in experimental chronic pancreatitis and remained beneficial in a therapeutic setting when given after initial damage had been established.

Figure 1

Experimental design. Five groups of mice (n = 10 each) were studied. All mice received six hourly intraperitoneal injections, three times a week for 6 weeks; groups A and B received saline injections (no induction of pancreatitis), groups C, D, and E received cerulein injections (50 μg/kg; induction of pancreatitis). Groups A and C received normal chow throughout the entire 7-week study period. Groups B and D received chow mixed with troglitazone (TGZ) 0.2% for a total of 6 weeks (weeks 1 to 6). Group E received normal chow during the first 3 weeks (weeks 1 to 3) and chow mixed with 0.2% TGZ for the next 3 weeks (weeks 4 to 6). All groups received normal chow in the final (seventh) week, after which mice were killed. Arrows indicate six intraperitoneal injections with saline or cerulein.

Figure 2

Troglitazone treatment reduces pancreatic damage. Representative H&E-stained pancreas histology slides from a total of 10 mice per group. For the description of groups A to E see Figure 1. For data derived from scoring H&E-stained pancreas specimens see Table 1. H& E staining. Original magnifications: ×10; ×40 (insets).

Figure 3

Troglitazone treatment reduces pancreatic collagen content. Representative Sirius red-stained pancreas sections from a total of 10 mice per group used to quantify tissue collagen content. For the description of groups A to E see Figure 1. For data derived from image analysis of Sirius red-stained specimens see Table 2. H& E staining. Original magnifications: ×10; ×40 (insets).

Figure 4

Troglitazone treatment reduces MPO content. Pancreas MPO activity is expressed as a percentage of group A. Open bars represent saline-injected mice (without pancreatitis); filled bars represent cerulein-injected mice (with pancreatitis). Data are mean ± SE of 10 mice per group. For the description of groups A to E see Figure 1. #, P < 0.05 versus A and B; *, P < 0.05 versus C.

Figure 5

Troglitazone treatment reduces loss in pancreas acinar cell content. Open bars represent saline-injected mice (without pancreatitis); filled bars represent cerulein-injected mice (with pancreatitis). Data are mean ± SE of 10 mice per group. For the description of groups A to E see Figure 1. #, P < 0.05 versus A and B; *, P < 0.05 versus C.

Figure 6

Troglitazone reduces pancreatic active TGF-β1 levels during experimental chronic pancreatitis. Open bars represent saline-injected mice (without pancreatitis); filled bars represent cerulein-injected mice (with pancreatitis). Data are mean ± SE of 10 mice per group and are expressed as pg/mg protein. For the description of groups A to E see Figure 1. #, P < 0.05 versus A and B; *, P < 0.05 versus C.

Figure 7

Troglitazone reduces plasma IL-6 and soluble TNFR-1 during experimental chronic pancreatitis. Open bars represent saline-injected mice (without pancreatitis); filled bars represent cerulein-injected mice (with pancreatitis). Data are mean ± SE of 10 mice per group. For the description of groups A to E see Figure 1. #, P < 0.05 versus A and B; *, P < 0.05 versus C.