Normal mitotic reactivity of fibroblasts and mesothelial cells in thrombocytopenic rat

Increased transforming growth factor beta (TGF-beta) immunoreactivity is independently associated with chronic injury in both consequential and primary radiation enteropathy

PURPOSE

Radiation enteropathy is characterized by sustained increase in transforming growth factor beta (TGF-beta) immunoreactivity and connective tissue mast cell (CTMC) hyperplasia that may be responsible for progressive fibrosis and lead to clinical complications. We examined to what extent these chronic molecular and cellular phenomena are associated with acute mucosal breakdown (consequential injury) and/or direct (primary) radiation injury in late-responding compartments.

METHODS AND MATERIALS

Rat small intestine was exposed to 50.4 Gy x-irradiation given either over 18 days (2.8 Gy daily or 5.6 Gy every other day) or 9 days (2.8 Gy twice daily or 5.6 Gy daily). Intestinal complications were recorded and groups of animals were euthanized at 2 and 26 weeks to assess subacute and chronic injury. Histopathologic changes were assessed with a radiation injury scoring system (RIS), total TGF-beta immunoreactivity was quantified with computerized image analysis, and CTMC hyperplasia was assessed in toluidine blue-stained sections.

RESULTS

TGF-beta immunoreactivity and CTMC hyperplasia colocalized in areas of injury and were highly significantly correlated. Increased fraction size and decreased overall treatment time were associated with increased RIS (p < 0.01 and p < 0.00001), increased TGF-beta immunoreactivity (p = 0.01 andp < 0.001), and degree of CTMC hyperplasia (p = 0.01 and p < 0.001). Postradiation CTMC numbers increased across treatment groups from 2 to 26 weeks (p < 0.01). TGF-beta immunoreactivity was independently associated with chronic intestinal wall fibrosis (p = 0.003).

CONCLUSION

This in vivo study supports in vitro evidence linking increased TGF-beta immunoreactivity and mast cell hyperplasia and strongly suggests their involvement in the molecular pathogenesis of both primary and consequential radiation enteropathy.

Tumor-bearing depresses distant mast-cell-mediated mitogenesis

A methylcholanthrene-induced sarcoma grafted subcutaneously in rats was used in early transplantation generations. Tumor-bearing rats showed weight loss compatible with cachexia. Healthy rats of the same age served as controls. In tumor-bearing rats the basal mesenteric proliferation was unaffected whereas the strictly mast-cell-mediated hyperproliferative reaction in the mesentery was significantly reduced after intraperitoneal injection of the mast-cell-secretagogue compound 48/80, as judged from specific DNA activity and mitosis counting. However, in mesentery and peritoneal lavage the number of mast cells, their histamine-releasing capacity, and their content of histamine, 5-hydroxytryptamine and heparin were unaffected by tumor-burden. The findings suggest the presence of a tumor-associated systemic factor of unknown nature which interferes with the biochemical events leading to the mast-cell-dependent mitogenesis. Since this mitogenic reaction may normally compensate for injury at the cellular level it is questioned whether the decreased mast-cell-dependent proliferation in tumor-bearing is a component of cachexia.

Further studies on the delayed mast-cell-mediated mitogenesis in diabetic rat

We have investigated whether the delayed augmented mast-cell-dependent mitogenesis that we recently demonstrated in the true mesentery of diabetic rats may occur also in a tissue which is essentially different both functionally and structurally. Cutaneous proliferation in insulin-deficient rats following a single intradermal injection of compound 48/80 was assessed by the specific DNA activity and mitotic index, on days 7 and 28 after giving streptozotocin. The proliferation variables, which ran parallel, indicated that mast-cell secretion was not followed by proliferation on day 7, whereas there was markedly augmented proliferation on day 28. Mitosis counting showed that cell production following mast-cell secretion was significantly increased not only in the entire cutis but also in epithelial structures (epidermis and epidermal appendages). These findings are closely similar to the delayed augmentation of mast-cell-dependent mesenteric mitogenesis in diabetic rats. It is concluded that there may be a general pattern of delay in the appearance of augmented mast-cell-mediated mitogenesis in rats with chemically induced diabetes. It is questioned whether or not this delayed mitogenesis may be connected with the postponed proliferation in a variety of tissues and organs (such as arteries, eyes, and kidneys) that occurs in experimental and clinical diabetes.

Intradermal mast-cell secretion causing cutaneous mitogenesis

This study demonstrated that mast-cell secretion elicited by intradermal injection of compound 48/80 initiated cell proliferation in rat skin. The mast-cell secretion was confirmed by microscopical demonstration of degranulation of mast cells, and by quantifying histamine release, whereas the proliferation was assessed by measuring DNA-synthesis and the frequency of mitosis. The results, which fully support our previous findings in the true mesentery, indicate that the common type of mast cell, when appropriately activated, is capable of playing a role in governing cell proliferation in diverse tissues.

The effect of insulin on delayed augmented mast-cell mediated mitogenesis in diabetic rats

Delayed augmented mitogenic reactivity follows mast-cell secretion in mesentery and skin in streptozotocin-diabetic rats with 4-week insulin-deficiency (Norrby 1982; Norrby et al. 1982; Norrby 1983). In such rats the basal proliferation is essentially unchanged in the mesentery and skin, whereas it is significantly increased in the small gut and significantly decreased in the kidney. On treating rats with 4-week-old diabetes with very-long-acting insulin for over 3 days (16 U/kg X 2 daily) the basal proliferation of the small gut and the kidney apparently became normal, the body weight increased, and the blood glucose concentration dropped substantially and progressively. However, insulin-treatment did not affect the mast-cell-dependent mitogenesis in the mesentery following intraperitoneal injection of the mast-cell secretagogue compound 48/80, as judged by specific DNA activity and mitosis counting. We conclude that some metabolic or cellular feature of diabetes which is not restored by 3-day insulin treatment, and not insulin deficiency itself, is the cause of the delayed increased mitogenic reactivity that follows mast-cell secretion in diabetic rat.