Heparin therapy for ulcerative colitis? Effects and mechanisms.

Despite intensive medical treatment with steroids and immunosuppressants, acute colitis is still associated with a colectomy rate of up to 15%. Following the observation that a patient with severe steroid-resistant colitis went into remission when treated with heparin for a deep vein thrombosis, there have been a number of reports on the use of heparin in acute ulcerative colitis. Although small and uncontrolled, these studies consistently demonstrate the beneficial effects of heparin, with surprisingly few side-effects in a disease characterized by mucosal haemorrhage. The mechanisms by which heparin may ameliorate ulcerative colitis remain unclear. A simple anticoagulant effect may be responsible, but similar effects are not seen with warfarin. As a result of their intense negative charge, the glycosaminoglycans that constitute heparin have diverse biological effects. These include potent anti-inflammatory actions, in vitro and in vivo, and the potentiation of the activity of the peptide growth factors necessary for mucosal regeneration and repair. This review summarizes the clinical reports on heparin treatment for ulcerative colitis and explores the mechanisms by which this novel form of treatment may exert its effects.

Insulin-like growth factors and their binding proteins in human colonocytes: preferential degradation of insulin-like growth factor binding protein 2 in colonic cancers.

We have compared the expression of insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) in ten paired samples of normal and tumour colonic tissue with regard to both mRNA and protein. We have compared sensitivity of these tissues to IGF-I using primary cultures of epithelial cells of colonic mucosa, and we have examined the production of IGFs and IGFBPs by these cells. In the tissues, IGFBP-2 mRNA was expressed in all normal and cancer samples but other IGFBPs showed variable expression. mRNAs for IGF-I were expressed in all normal and cancer tissues but IGF-II mRNA was only detected in cancer tissue (3 out of 10). Immunostaining of sections of normal and cancer tissue was negative for IGF-I and IGF-II; IGFBP-2 was positive in 2 out of 10 cancer tissues and 7 out of 10 normal tissues; IGFBP-3 was positive in 7 out of 10 cancer tissues and 7 out of 10 normal tissues; and IGFBP-4 was positive in 5 out of 10 cancer tissues and 6 out of 10 normal tissues. In the cells in culture, cancer cells showed increased incorporation of [35S]methionine into protein and [3H]thymidine into DNA (P < 0.02) when treated with IGF-I. Western blotting of serum-free conditioned media from cells in culture showed that 8 out of 10 normal and 3 out of 10 cancer cultures produced a 32-kDa immunoreactive IGFBP-2. No IGFBP-3 was secreted by any culture but 24-kDa IGFBP-4 was found in 3 out of 10 normal and 5 out of 10 cancer tissues. Because of the discrepancy between mRNA and protein expression for IGFBP-2, degradation of native IGFBPs was assessed using tissue extracts. Colon cancer extracts were able to degrade exogenous IGFBP-2, IGFBP-3 and IGFBP-4, whereas normal tissue extracts were without effect on IGFBP-2. We conclude that IGFBPs are synthesized and secreted by cells of the colonic mucosa but that proteolysis of secreted IGFBP-2 occurs in colon cancer tissue. This selective degradation may confer a growth advantage.

Insulin-like growth factor binding proteins as mediators of IGF-I effects on colon cancer cell proliferation.

Human colon cancer cell lines COLO205, HT29 and SW620 are known to secrete insulin-like growth factor II (IGF-II) and its modulatory binding proteins (IGFBPs). We have characterised the sensitivity of these cell lines to exogenous IGF-I and have examined the effects of their autocrine IGFBPs on these responses. Cells cultured in serum-free medium were treated with 1-100 ng/ml IGF-I, or des(1,3)IGF-I, a truncated IGF-I with low affinity for IGFBPs. DNA synthesis was determined by 24 h incorporation of 3H-thymidine. Experiments were repeated in the presence of 24 h cell-conditioned media containing endogenous IGFBPs. In all 3 cell lines, cell-conditioned media reduced sensitivity to IGF-I but not to des(1,3)IGF-I suggesting that IGFBPs in the cell-conditioned media of colon cells inhibit IGF-I action. IGFBPs in the cell layer and 24 h cell-conditioned media were identified by Western ligand and antibody analyses. IGFBP-4 was secreted by all cell lines and IGFBP-2 from the COLO205 and SW620 cells lines but not the HT29 cells. No IGFBP-3 was secreted by any of the cell lines but IGFBP-3 was found in the cell layer in all of the cell lines. When endogenous secreted IGFBPs were removed, cell lines were consistently more sensitive to IGF-I than des(1,3)IGF-I suggesting that IGFBP-3 associated with the cell layer enhances responses to IGF-I. This is in contrast to the effects of the secreted IGFBPs. Differential modulating actions of IGFBPs may be important in regulating colon cell turnover.