Summary
Endothelial dysfunction is involved in radiation responses in many normal tissues,
including intestine. Endothelium-directed interventions ameliorate intestinal radiation
injury (radiation enteropathy) in animal models, and anecdotal reports also suggest
a beneficial effect of heparin. This study assessed low molecular weight heparin as
an intestinal radiation response modifier. Rats underwent localized small bowel irradiation.
Groups of rats were treated with saline, nadroparin (3 mg/kg/d), or a nonanticoagulant
heparin (SR80258, 3 mg/kg/d), from 3 days before to 2 weeks after irradiation. The
intestinal radiation response was assessed 2 weeks and 6 weeks after irradiation using
quantitative histology; morphometry, and cellular and molecular endpoints. Compared
to vehicle-treated controls, nadroparin sig-nificantly exacerbated structural radiation
injury, neutrophil infiltration, and TGFβ and collagen I immunoreactivity levels 2
weeks after irradiation. SR80258 was associated with increased TGFβ levels, but the
other parameters did not reach statistical significance. At 6 weeks, structural, cellular,
and molecular injury was similar in the three experimental groups. Heparin, in contrast
to antiplatelet agents and direct thrombin inhibitors, does not ameliorate, but exacerbates
acute intestinal radiation toxicity. These data underscore the importance of heparin
as an inhibitor of physiological anti-inflammatory mechanisms during tissue injury,
as well as the non-anticoagulant effects of heparin. Moreover, these data may have
implications for the use of heparin during radiation therapy.
Keywords
Endothelium - intestine - radiation injuries - heparin