Protective effects of heme oxygenase-1 against cyclophosphamide-induced haemorrhagic cystitis in rats

To investigate the expression profiles and protective roles of the inducible isoform of heme oxygenase-1 (HO-1) in cyclophosphamide (CYP)-induced cystitis, as the HO system is involved in heme degradation and plays an important role in cellular homeostasis but its characterization is still unknown in urinary tract diseases.

In female Sprague-Dawley rats CYP was administed intraperitoneally and the bladders excised at various time points. In separate experiments, hemin, an inducer of HO, was administered before CYP treatment, and bladders were harvested 24 h after CYP injection. The expressions of HO-1 and HO-2 were investigated by reverse-transcription polymerase chain reaction and immunohistochemistry. The effects of CYP with/without hemin pretreatment were evaluated by microscopic features, bladder wet weight, myeloperoxidase activity, nitric oxide (NO)-metabolite production, and expression levels of inflammation-related genes.

CYP injection resulted in severe cystitis with time-dependent increases both in bladder wet weight and HO-1 mRNA expression. Pretreatment with hemin enhanced the CYP-induced expression of HO-1 mRNA and protein further, but significantly ameliorated inflammatory changes and reduced the increases in bladder oedema and myeloperoxidase activity. NO-metabolite production and inducible NO synthase (iNOS) expression, induced by CYP, were down-regulated significantly by hemin pretreatment. By contrast, HO-2 was constitutively present in the urothelium and its expression was not influenced by CYP or by CYP plus hemin.

HO-1 expression is up-regulated in bladders with CYP-induced haemorrhagic cystitis, and this inducible enzyme plays cytoprotective roles in association with down-regulation of NO production and iNOS expression. Our results suggest that HO-1 induction might have therapeutic potential against inflammatory insults such as CYP-induced cystitis.