Morphologic changes of peritoneum and expression of VEGF in encapsulated peritoneal sclerosis rat models

Simple sclerosis consisted of a thin layer of submesothelial sclerotic tissue in peritoneal dialysis patients. Encapsulated peritoneal sclerosis (EPS) was characterized by thick sclerotic tissue involving vascular alterations in peritoneal dialysis patients. The objective of the present study is to evaluate serial morphologic changes and expressions of angiogenic factors [i.e., vascular endothelial growth factor (VEGF), angiopietin-1 (Ang-1), and angiopoietin-2 (Ang-2)] in EPS rat models.

Twenty-four rats were given a daily intraperitoneal injection of chlorhexidine gluconate and ethanol dissolved in saline (CH). Nine rats were injected with CH and anti-VEGF neutralizing antibody simultaneously. Quantitative blood vessel evaluation was performed by staining for GS1-lectin. The mRNA expression of VEGF, Ang-1, Ang-2, and their receptors was evaluated by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Immunohistochemical staining was performed in peritoneal vessels using anti-VEGF, Ang-1, and Ang-2 antibodies. Hematopoietic stem cells were detected using anti-CD34 antibody.

The vessel area, diameter, and length gradually increased until day 21, and then decreased. VEGF and Ang-2 mRNA expressions gradually increased until day 35. In contrast, Ang-1 peaked at day 21 and then decreased significantly. VEGF blockade improved the experimental EPS. In immunohistochemistry, the vessels stained by VEGF and Ang-2 were detected in subfibrous layer. CD34-positive cells were markedly stained at day 21.

Neoangiogenesis was observed in a rat model of experimental EPS. VEGF and angiopoietin/Tie system play an important role in the neoangiogenesis in this model. An analysis using this experimental rat model may elucidate the development of EPS in peritoneal dialysis patients.