We have shown previously that inhibition of sEH (soluble epoxide hydrolase) increased EETs (epoxyeicosatrienoic acids) levels and reduced renal injury in diabetic mice and these changes were associated with induction of HO (haem oxygenase)-1. The present study determines whether the inhibition of HO negates the renoprotective effect of sEH inhibition in diabetic SHR (spontaneously hypertensive rats). After 6 weeks of induction of diabetes with streptozotocin, SHR were divided into the following groups: untreated, treated with the sEH inhibitor t-AUCB { trans -4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid}, treated with the HO inhibitor SnMP (stannous mesoporphyrin), and treated with both inhibitors for 4 more weeks; non-diabetic SHR served as a control group. Induction of diabetes significantly increased renal sEH expression and decreased the renal EETs/DHETEs (dihydroxyeicosatrienoic acid) ratio without affecting HO-1 activity or expression in SHR. Inhibition of sEH with t-AUCB increased the renal EETs/DHETEs ratio and HO-1 activity in diabetic SHR; however, it did not significantly alter systolic blood pressure. Treatment of diabetic SHR with t-AUCB significantly reduced the elevation in urinary albumin and nephrin excretion, whereas co-administration of the HO inhibitor SnMP with t-AUCB prevented these changes. Immunohistochemical analysis revealed elevations in renal fibrosis as indicated by increased renal TGF-β (transforming growth factor β) levels and fibronectin expression in diabetic SHR and these changes were reduced with sEH inhibition. Co-administration of SnMP with t-AUCB prevented its ability to reduce renal fibrosis in diabetic SHR. In addition, SnMP treatment also prevented t-AUCB-induced decreases in renal macrophage infiltration, IL-17 expression and MCP-1 levels in diabetic SHR. These findings suggest that HO-1 induction is involved in the protective effect of sEH inhibition against diabetic renal injury.

RGC (retinal ganglion cell) death following ischaemic insult is the major cause of a number of vision-threatening diseases, including glaucoma. The aim of the present study was to evaluate the role of HO-1 (haem oxygenase-1) in the retina against IR (ischaemia/reperfusion) injury. Adenovirus-mediated HO-1 gene transfer (Adv-HO-1) was carried out by injection into the vitreous body to induce HO-1 overexpression. At 3 weeks after transfection, levels of HO-1 expression, as measured by Western blot analysis, immunohistochemical staining and activity assay, were drastically up-regulated. Transient retinal ischaemia was induced by raising the intraocular pressure to 150 mmHg for 60 min. Untreated IR caused a significant decrease in RGC numbers at 3 and 7 days after reperfusion (76.1 and 67.2% of control eyes with sham IR respectively; P <0.001). Eyes pretreated with Adv-HO-1 had less RGC loss on day 3 and 7 following reperfusion compared with control eyes injected with Adv-GFP (adenovirus containing a gene for green fluorescent protein; 94.3 and 88.2% respectively; P =0.007 and 0.001). SnP (tin protoporphyrin), an HO-1 inhibitor, counteracted the effects of Adv-HO-1. In conclusion, these findings provide evidence that augmentation of HO-1 enzyme overexpression by intravitreal injection is able to protect RGCs against IR-induced damage.

IR (ischaemia/reperfusion) injury of the intestine occurs commonly during abdominal surgery. We have previously shown that PDTC (pyrrolidine dithiocarbamate), an HO-1 (haem oxygenase-1) donor, improves intestinal microvascular perfusion. In the present study, we have investigated the effects of PDTC on the intestinal microcirculation following IR (ischaemia/reperfusion) injury of the intestine. Male Sprague–Dawley rats ( n =72) were randomly assigned to four groups ( n =18/group): (i) sham-operated group, who underwent laparotomy without induction of IR of the intestine; (ii) IR group, who were subjected to 30 min of superior mesenteric artery occlusion and 2 h of reperfusion; (iii) PDTC+IR group, who received PDTC prior to IR; and (iv) ZnPP group, who received the HO-1 inhibitor ZnPP (zinc protoporphyrin) followed by procedures as in group (iii). The ileum was evaluated for changes in tissue cytochrome c oxidase redox status, RBC (red blood cell) dynamics and leucocyte–endothelial interactions. The expression of HO-1 in the ileal tissue was examined at the end of the reperfusion. PDTC significantly improved the intestinal tissue oxygenation, mucosal perfusion index and RBC velocity compared with the IR and ZnPP groups. PDTC also decreased the leucocyte–endothelial interactions ( P <0.05 compared with the IR and ZnPP groups). PDTC induced the expression of HO-1, whereas ZnPP abolished this effect.

Reactive oxygen species produced at toxic levels are damaging species. When produced at sub-toxic levels, however, they are involved as second messengers in numerous signal transduction pathways. In addition to these findings, we can add the concept that iron (often viewed as the ‘villain’ in free radical biology) can also be considered as a signalling species. Iron is intimately involved in the regulation of its own storage, compartmentalization and turnover. During adult respiratory distress syndrome (ARDS) and sepsis, such regulation may be aberrant or altered in some predisposed way. Such changes may have profound implications for tissue damage, and for the modulation of the inflammatory response in these patients. The search for a genetic predisposition in patients that leads to the development of ARDS associated with abnormalities in iron turnover and signalling would seem to be an important and logical progression for studies into the disease. These may lead eventually to the design of effective treatment regimens that involve the control of iron.