Association of transforming growth factor β (TGF-β) immunoreactivity with specific histopathologic lesions in subacute and chronic experimental radiation enteropathy

Abstract

Irradiated intestine consistently exhibits increased immunoreactivity of transforming growth factor β-1 (TGF-β1). It is not known whether this increase occurs secondary to mucosal barrier disruption (consequential injury) or to injury in late-responding tissue compartments (primary radiation enteropathy). This study therefore assessed the association between TGF-β immunoreactivity and specific consequential and primary histopathologic alterations. A small bowel loop was fixed inside the scrotum in male rats and subsequently exposed to either 18 daily fractions of 2.8 Gy or nine daily fractions of 5.6 Gy orthovoltage X-radiation. Radiation-induced intestinal complications were recorded and groups of animals were euthanized 2 and 26 weeks post-irradiation. Radiation injury was assessed with a histopathologic radiation injury score (RIS). Total TGF-β was detected immunohistochemically and measured with interactive computerized image analysis. The image analysis technique yielded highly reproducible quantitation data. The 2.8-Gy group maintained mucosal integrity and had fewer intestinal complications, lower RIS and lower TGF-β levels than the 5.6-Gy group. There was highly significant correlation between TGF-β immunoreactivity and radiation injury at both observation times ( P < 0.001 and P < 0.0001). At 2 weeks, TGF-β immunoreactivity correlated with mucosal ulceration ( P = 0.002), epithelial atypia ( P = 0.005), and serosal thickening ( P = 0.0004). At 26 weeks, TGF-β levels correlated significantly with six of seven histopathologic parameters, most strikingly with vascular sclerosis ( P = 0.0003). We conclude that mucosal barrier breakdown is closely associated with increased TGF-β immunoreactivity in consequential radiation enteropathy. The highly significant correlation between TGF-β expression levels and alterations in late-responding tissue compartments also suggest a role for TGF-β in primary radiation enteropathy.