Therapeutic role for bismuth compounds in TNBS-induced colitis in the rat.

The 2,4,6-trinitrobenzene sulfonic acid (TNBS) -induced model of chronic inflammation of the rat colon was used to determine the efficacy of bismuth subsalicylate (BSS), bismuth subcitrate (CBS), and 5-aminosalicylic acid (5-ASA) administered in enema form. A novel bismuth compound 1, 2-bis[2-(1,3-dithiobismolane)thio]ethane [Bi2(EDT)3] was also tested. On day 1 colitis was induced with 50 mg TNBS/50% ethanol in female Sprague-Dawley rats, while controls received a saline enema. On day 3, twice-daily treatment with enemas of either saline, BSS, CBS, Bi2(EDT)3, or 5-ASA were initiated in the colitis and control rats. All rats were killed on day 14, and the colons excised, weighed, rated macroscopically, and then fixed for hematoxylin and eosin staining. Blinded microscopic scoring was used to determine injury and healing in all groups. Colon mass and macroscopic scores were increased (P < 0.05) in the group of rats treated with TNBS (N = 16) compared to saline controls (N = 12). Colon mass and macroscopic scores in controls treated with BSS (N = 4), CBS (N = 4), Bi2(EDT)3 (N = 4), and 5-ASA (N = 4) alone did not differ from saline control animals. Macroscopic scoring showed a decrease (P < 0.05) in the degree of damage in the group of rats treated with TNBS plus BSS (N = 15), TNBS plus Bi2(EDT)3 (N = 10) and TNBS plus CBS (N = 4) compared to the group of rats treated with TNBS plus saline (N = 16). A decrease (P < 0.05) in injury and an increase (P < 0.05, Kruskal-Wallis) in healing was observed in the groups of rats treated with TNBS plus BSS, TNBS plus CBS, and TNBS plus 5-ASA compared to the group of rats treated with TNBS plus saline. It appeared that Bi2(EDT)3 was not protective against injury at the microscopic level but that the novel Bi2(EDT)3 has an effective healing capacity at the macroscopic level. We conclude that BSS and CBS decrease injury and/or promote healing as effectively as 5-ASA in this model.

Effect of pentoxifylline in rat and swine models of hepatic fibrosis: role of fibroproliferation in its mechanism.

Fibroproliferation was studied in two animal models of liver disease. Oral feeding of yellow phosphorus to pigs reproducibly results in fibrosis after 8 weeks of feeding, extensive fibrosis after 12 weeks and cirrhosis after 16 weeks of yellow phosphorus. Bile duct ligation was used to induce cirrhosis in the rat. Fibroproliferation was assessed as uptake of tritiated thymidine into fibroblasts which had been incubated with monocyte-conditioned medium obtained from monocytes of pigs treated with yellow phosphorus or bile duct-ligated rats and compared to the corresponding controls. Fibrosis was assessed by collagen content of liver sections obtained from the two animal models. The collagen content was determined by quantitation of Sirius red/Fast green-stained liver sections. In both animal models collagen content was significantly elevated at the conclusion of the treatment. Collagen content of liver sections of yellow phosphorus-treated animals were elevated (40 +/- 2.7, n = 15) compared to mineral oil-treated controls (23 +/- 1.2, n = 12) and collagen levels in the bile duct-ligated rat model liver sections were elevated (31.2 +/- 1.6, n = 6) compared to sham-operated controls (21.6 +/- 0.7, n = 6). The results of the fibroproliferation assay indicate that monocytes obtained from pigs treated with yellow phosphorus produce fibroproliferative factors during the development of fibrosis. This is in contrast to the bile duct-ligated rat model where no differences were observed in the production of fibroproliferative factors in the bile duct-ligated rats compared to sham operated controls suggesting that this may not be a key event in this model of fibrosis. Pentoxifylline treatment of the yellow phosphorus induced swine model of hepatic fibrosis has been associated with a marked improvement in fibrosis. In this study treatment of fibrotic pigs with pentoxifylline was associated with an improvement in liver function tests, a reduction of collagen content of liver sections, and reduction in fibroproliferation in pigs receiving yellow phosphorus treatment. Fibroproliferative factors were produced during the development of fibrosis in the swine model of fibrosis and their effect was blocked by pentoxifylline administered in vivo. This is in contrast to the bile duct-ligated rat model where pentoxifylline treatment was not associated with improvement in liver function tests or reduction of collagen content of liver sections and did not alter the fibroproliferative activity of monocyte-conditioned media. Taken together these results suggest that fibroproliferation and increased synthesis of collagen are key events in the yellow phosphorus-induced pig model of hepatic fibrosis and that the action of pentoxifylline in this animal model is likely to be related to its effects on fibroproliferation with a subsequent effect on collagen production. This is in contrast to the bile duct-ligated rat model where pentoxifylline does not prevent hepatic fibrosis.

Pentoxifylline prevents fibrosis in an animal model and inhibits platelet-derived growth factor-driven proliferation of fibroblasts.

Liver fibrosis is a complex process characterized by two major events: fibroproliferation and increased collagen synthesis. The exact role of cytokines in the pathogenesis of hepatic fibrosis remains to be established, but platelet-derived growth factor clearly stimulates proliferation of fibroblasts and increases collagen synthesis. In in vitro studies, pentoxifylline, a methylxanthine, significantly reduced platelet-derived growth factor-driven proliferation of fibroblasts. Platelet-derived growth factor has also been identified as a fibroproliferative factor produced spontaneously by monocytes obtained from patients with liver disease. Long-term administration of pentoxifylline (16 mg/kg orally, 5 days/wk for 12 wk) in an animal model of liver fibrosis prevented elevations in gamma-glutamyl transpeptidase and alkaline phosphatase levels and prevented the reduction in serum albumin level normally observed in this animal model of liver disease. The animal model used was a long-term, low-dose yellow phosphorus--induced model in pigs that reproducibly results in extensive fibrosis after 10 to 12 wk of treatment. Long-term administration of pentoxifylline also prevented the histological changes characteristic of fibrosis in this animal model. Collagen concentration was significantly elevated in liver sections obtained from animals receiving yellow phosphorus, compared with controls. Long-term pentoxifylline treatment resulted in significantly lower collagen concentrations in liver sections from animals receiving yellow phosphorus than in sections from animals receiving yellow phosphorus alone; this was supported by histological observation. Therefore administration of pentoxifylline prevented the biochemical and histological changes associated with an animal model of liver disease. Pentoxifylline will likely have an important therapeutic role in liver fibrosis.

Monocyte aryl hydrocarbon hydroxylase (AHH) activity mimics Kupffer cell and hepatocyte AHH activity in an animal model of liver disease.

We have previously reported that monocyte aryl hydrocarbon hydroxylase (AHH) activity is depressed in patients with liver disease and is decreased more in cirrhosis than in early stage liver disease. To determine if monocyte AHH activity reflects liver AHH activity, we studied an animal model of cirrhosis, i.e., yellow phosphorus induced cirrhosis in the pig. AHH activity was detectable in monocytes isolated from peripheral blood of normal pigs (0.32 +/- 0.13 nmol.mg-1 P.h-1, n = 11) and was comparable to the level of AHH activity in hepatic Kupffer cells isolated from wedge or needle biopsies of livers of normal pigs (0.38 +/- 0.21, n = 7). The AHH level in pig Kupffer cells was approximately 10% of the AHH level in hepatocytes and microsomes. To induce liver disease, pigs were administered yellow phosphorus (0.6 mg/kg) 5 days per week for 16 weeks. At 4 weeks of treatment, monocyte AHH activity was not different from control and liver histology was normal. Depression of monocyte AHH activity was evident at 8 weeks of treatment when liver fibrosis was seen histologically. At 12 weeks of treatment when histology revealed extensive liver fibrosis and collagen levels were elevated, the level of monocyte AHH activity was decreased 67% compared with controls. Similar changes were observed at 12 weeks in Kupffer cell AHH activity (86% decrease) and hepatocyte AHH activity (70% decrease) compared with controls. These results suggest that monocyte AHH activity reflects liver AHH activity and may be a good indicator of change in liver enzyme function in liver disease in the pig model of cirrhosis.