Protective effects of selectin ligands/inhibitor (SKK-60060) against retinal ischemia-reperfusion injury

Effect of intravitreal injection of ranibizumab on retinal ganglion cells and microvessels in the early stage of diabetic retinopathy in rats with streptozotocin-induced diabetes

The aim of the present study was to investigate the effect of intravitreal injection of ranibizumab on retinal ganglion cells and microvessels at the early stage of diabetic retinopathy (DR) in rats with streptozotocin-induced diabetes mellitus (DM). DM was induced by a single intraperitoneal injection of 60 mg/kg body weight streptozotocin. A total of 80 diabetic rats were randomly assigned to four treatment groups (n=20 in each group) and were treated with an oculus dexter intravitreal injection of ranibizumab. Groups A and B were injected with ranibizumab two and four weeks after DM-induction, respectively, while groups a and b (controls) were injected with phosphate-buffered saline at the same time points. In addition, 20 normal rats were assigned to group N (blank control; without intraocular injection). Vitreous humors were isolated for vascular endothelial growth factor (VEGF)-A ELISA and retinas were obtained for hematoxylin and eosin staining, periodic acid-Schiff staining and fluorescence imaging techniques at six and eight weeks after the onset of DM. At six and eight weeks, a significantly increased in retinal ganglion cells (RGCs) was observed in group A compared with group a (P<0.01), and in group B compared with group b (P<0.01). In addition, there was a significant difference in the RGC level between groups A and B at six weeks after DM induction (P<0.01), but not at eight weeks (P>0.05). VEGF-A concentrations in rat vitreous humors were significantly lower in groups A and B compared with groups a and b at six and eight weeks after DM induction (P<0.01). Furthermore, the ratio of endotheliocytes to pericytes in groups A and B was significantly lower compared with groups a and b at six and eight weeks (P<0.05). Furthermore, it was also demonstrated that type IV collagen-positive strands were not present in group A during the eight-week observation period, which was significantly different from groups a, b and B (P<0.01). In conclusion, intravitreal injection of ranibizumab at a very early stage of DR in streptozotocin-induced DM rats slowed the progression of DR by reducing vascular regression or damage and maintaining RGC numbers, as well as reducing VEGF-A concentrations.

Aldose reductase inhibitor fidarestat attenuates leukocyte-endothelial interactions in experimental diabetic rat retina in vivo

PURPOSE

Dysregulation of the polyol pathway has been implicated as a major cause of diabetic retinopathy. The aldose reductase inhibitor fidarestat was recently reported to prevent retinal oxidative stress and overexpression of vascular endothelial growth factor (VEGF) protein in diabetic rats. In this study, we investigated the effect of fidarestat on leukocyte-endothelial cell interactions in an in vivo experimental model for diabetic retina.

MATERIALS AND METHODS

Diabetes was induced in six-week-old male Long-Evans rats by intraperitoneal injection of streptozotocin (STZ) (75 mg/kg). The rats were divided into four experimental groups: non-diabetic control rats, untreated diabetic rats, and diabetic rats treated with a low (4 mg/kg/day) or high (16 mg/kg/day) oral dose of fidarestat. After four weeks of treatment, accumulated leukocytes in the retina were counted in vivo by acridine orange digital fluorography. Intercellular adhesion molecule-1 (ICAM-1) and VEGF-164 mRNA levels in the retina were analyzed using the quantitative reverse transcription-polymerase chain reaction. ICAM-1 protein expression in the retina was investigated by immunohistochemistry.

RESULTS

Fidarestat treatment significantly decreased concentrations of sorbitol and fructose in the retinas of STZ-induced diabetic rats. Leukocyte accumulation in the retinas of fidarestat-treated rats was significantly less than in the untreated diabetic group (P < 0.01). Fidarestat treatment significantly reduced the expression ICAM-1 mRNA, but not VEGF-164 mRNA, in the retina of diabetic rats. Immunohistochemical study also revealed the suppressive effect of fidarestat on expression of ICAM-1.

CONCLUSIONS

Oral administration of fidarestat attenuated leukocyte accumulation in the retina of STZ induced-diabetic rats, suggesting that fidarestat may have a therapeutic role in preventing the progression of diabetic retinopathy.

Pitavastatin attenuates leukocyte-endothelial interactions induced by ischemia-reperfusion injury in the rat retina

PURPOSE

Statins (3-hydroxy-methylglutaryl coenzyme A reductase inhibitors) have been shown to lower serum cholesterol levels in clinical use. Moreover, it has been reported that statins exert pleiotropic and beneficial effects on vascular endothelium. Therefore, we investigated the effects of pitavastatin, a new statin, on leukocyte accumulation during ischemia-reperfusion injury.

MATERIALS AND METHODS

Transient retinal ischemia was induced in Long-Evans rats for 60 min by temporal ligation of the optic nerve. Pitavastatin (0.12, 0.35, or 1.1 mg/kg) was administered 5 min prior to the induction of retinal ischemia. Leukocyte-endothelial interactions in the post-ischemic retina were evaluated in vivo with acridine orange digital fluorography. The number of rolling leukocytes, number of accumulated leukocytes, and diameters of the major retinal artery and vein were evaluated. Intercellular adhesion molecule-1 (ICAM-1) mRNA expression in the retina was semiquantitatively studied using the RT-PCR method.

RESULTS

Pitavastatin-treated rats at doses of 0.35 and 1.1 mg/kg showed mild arterial narrowing (p < 0.01) and venous dilation (p < 0.01) compared with vehicle-treated (ischemic) rats. In rats treated with 0.35 mg/kg pitavastatin, the number of rolling leukocytes was significantly reduced by 35.5% (p < 0.01) 12 hr after reperfusion compared with that of vehicle-treated rats. With treatment at a dose of 0.35 mg/kg pitavastatin, the number of accumulated leukocytes was reduced to 68.7% (p < 0.01) 24 hr after reperfusion. Moreover, pitavastatin treatment significantly reduced ICAM-1 mRNA expression in the retina during ischemia-reperfusion injury.

CONCLUSIONS

Pitavastatin effectively attenuated ischemia-induced leukocyte-endothelial interactions in the rat retina.

Pitavastatin prevents NMDA-induced retinal ganglion cell death by suppressing leukocyte recruitment

Excitotoxicity is a major cause of retinal ganglion cell (RGC) death during ischemic diseases such as vessel occlusion and diabetic retinopathy. However, the underlying mechanisms are not well understood. Statins, inhibitors of the HMG-CoA reductase, have neuroprotective effects in addition to their original role in lowering cholesterol. We hypothesize that pitavastatin, a recently introduced potent statin, is protective against N-methyl-d-aspartic acid (NMDA)-induced RGC death. Pitavastatin, administered by gavage, abolished NMDA-induced loss of RGCs. To elucidate the mechanisms underlying the neuroprotective effect of pitavastatin, we investigated its impact on inflammation. NMDA increased the expression of interleukin-1beta and TNF-alpha, and endothelial adhesion molecules, including ICAM-1, and induced leukocyte accumulation in the retinal vessels. Pitavastatin significantly reduced NMDA-induced leukocyte accumulation and up-regulation of endothelial adhesion molecules, whereas cytokine expression was unaffected. Systemic blockade of ICAM-1 in wild-type mice or absence of CD18 in gene-deficient (CD18(-/-)) mice significantly suppressed NMDA-induced leukocyte accumulation and RGC death. These findings suggest a novel and causative role for inflammatory leukocyte recruitment in NMDA-induced excitotoxicity. Furthermore, we show the novel neuroprotective effect of statins against excitotoxicity-induced RGC death. Statins or other anti-inflammatory agents may thus have therapeutic benefits in excitotoxicity-associated neuronal diseases through blockade of leukocyte recruitment.

Insulin enhances leukocyte-endothelial cell adhesion in the retinal microcirculation through surface expression of intercellular adhesion molecule-1

The purpose of this study was to evaluate the effects of insulin on leukocyte-endothelial cell adhesion in the retinal microcirculation in vitro and in vivo. Human retinal endothelial cells (HRECs) were cultured in medium with or without insulin, and neutrophils allowed to adhere. Adherent neutrophils were quantified by measuring myeloperoxidase activity. Surface expression of endothelial adhesion molecules were studied with the use of an enzyme immunoassay. Insulin at concentrations of 50 and 100 microU/ml significantly increased neutrophil adhesion to HRECs compared with the control cells (P < 0.01, respectively). Surface expression of intercellular adhesion molecule-1 (ICAM-1) significantly increased when HRECs were exposed to 100 microU/ml insulin, as compared with the control cells (P < 0.05). Anti-ICAM-1 antibody significantly inhibited neutrophils adhesion to HRECs (P < 0.0001). Brown-Norway rats received subcutaneous injection of 0.2 U per 100 g body weight insulin three times. Control rats received the same amount of phosphate-buffered saline. Leukocyte entrapment in the retina was evaluated using acridine orange leukocyte fluorography. The number of leukocytes trapped in the retina of insulin-treated rats was significantly elevated compared with that in the control animals (P < 0.0001). These results suggested that insulin enhances leukostasis in retinal microcirculation. Hyperinsulinemia may be a risk factor of retinal microcirculatory disturbances.

Protective effect of polyethylene glycol-superoxide dismutase on leukocyte dynamics in rat retinal microcirculation under lipid hydroperoxide-induced oxidative stress

The levels of lipid hydroperoxide (LHPs) in vitreous are elevated in a variety of retinal disorders. Recently, we have shown that increased levels of LHPs in the vitreous enhanced leukocyte-endothelium interaction in the retina, which should contribute to the initial disturbance of the retinal microcirculation. Based upon the previous work, the purpose of the present study was to investigate the effect of polyethylene glycol-superoxide dismutase (PEG-SOD), one of the important enzyme antioxidants, on leukocyte-endothelial interaction in the retinal microcirculation under LHP-induced oxidative stress. Male Brown-Norway rats weighing approximately 250 g were used. LHP(18:2) was made from linoleic acid (LA) with lipoxygenase and 10 microg of LHP dissolved in 5 microl of sodium borate buffer (SBB, 0.02 m) was slowly injected into the vitreous using a 33-gauge needle. PEG-SOD (5000 units/kg) was given intravenously 5 min before LHP injection. At 2, 4, 6, 12, 24 and 48 hr after the vitreous injections, we evaluated the number of rolling leukocytes along the major retinal veins and the number of leukocytes that accumulated in the retinal microvasculature with acridine orange digital fluorography. In LHP-treated rats, leukocyte rolling along the major retinal veins was maximal at 6 hr after LHP injection. The number of rolling leukocytes in the PEG-SOD-treated rats was decreased to 5.5% of those in the LHP-treated rats at 6 hr after LHP injection (P<0.01). No rolling leukocytes were observed in either control or vehicle-treated eyes. The number of accumulated leukocytes in LHP-treated eyes started to increase at 12 hr, and peaked at 24 hr which was significantly higher than in both control and vehicle-treated eyes (P<0.01). The number of accumulated leukocytes in the PEG-SOD-treated rats was reduced by 88.0% at 24 hr (P<0.01). Intravenous injection of PEG-SOD significantly inhibited the leukocyte rolling and its accumulation under LHP-induced oxidative stress. These results suggest that PEG-SOD might attenuate various retinal microcirculatory disorders associated with LHP.

The relationship between soluble L-selectin and the development of diabetic retinopathy

Diabetic retinopathy is a leading cause of adult vision loss and blindness. Earlier studies have shown that polymorphonuclear neutrophils play an important role in the pathogenesis of diabetic vascular complications. Stimulation of these cells is associated with the desquamation of L-selectin. The aim of the study was to evaluate the relationship between the serum concentration of L-selectin and the development of retinopathy in Type 2 diabetic patients. The study comprised 51 Type 2 diabetic patients, aged 65.2 +/- 7.5 years, with a diabetes duration of 10.1 +/- 8.9 years and HbA1c of 8.2 +/- 1.4. The study subjects were divided into two groups: Group A diabetic patients with retinopathy (n = 28) and Group B diabetic patients without retinopathy (n = 23). Twenty age- and sex-matched nondiabetic healthy subjects were enrolled as the control group. Patients with any inflammatory disease were excluded. Retinopathy was assessed by centrally graded retinal photographs. The serum concentration of sL-selectin was estimated using an ELISA test. We observed significantly higher serum concentrations of sL-selectin in Type 2 diabetic patients with retinopathy than in healthy subjects (36.5 +/- 18.1 vs. 11.4 +/- 7.5 ng/ml, p < 0.001). There was also a significant difference between Group A and Group B (36.5 +/- 18.1 vs. 24.2 +/- 13.5 ng/ml, p < 0.05) as well as between Group B and the controls (24.2 +/- 13.5 vs. 11.4 +/- 7.5 ng/ml, p < 0.01) with regard to sL-selectin levels. sL-selectin was significantly correlated with HbA1c (r = 0.93, p < 0.001) and with diabetes duration (r = 0.44, p < 0.001). These results suggest that there was a strong relationship between sL-selectin and diabetic retinopathy. The strong correlation between sL-selectin and HbA1c levels supports the concept that the sL-selectin level is increased with poor glycemic control, which may affect endothelial cell activity and cause subsequent microvascular complications.

Suppressive effects of selectin inhibitor SKK-60060 on the leucocyte infiltration during endotoxin induced uveitis

BACKGROUND

It is well known that selectin is involved in the development of endotoxin induced uveitis (EIU), and has a major role in leucocyte infiltration. Recently, a novel selectin inhibitor (SKK-60060) that can block P and L selectins in vitro has been developed. This study was designed to investigate the anti-inflammatory effects of SKK-60060 on the inflammatory reaction during EIU in rats by studying leucocyte-endothelium interactions.

METHODS

EIU was induced in Lewis rats by footpad injection of lipopolysaccharide (LPS). SKK-60060 was administered 15 minutes before LPS injection, and its suppressive effects on inflammatory leucocyte behaviour were evaluated in vivo with acridine orange digital fluorography; the diameters of retinal arteries and veins were also measured. After these studies, aqueous humour was collected to evaluate leucocyte infiltration and protein leakage.

RESULTS

After LPS injection, rolling leucocytes were observed in major retinal veins, followed by leucocyte infiltration into the vitreous cavity. Following treatment with SKK-60060, leucocyte rolling was significantly inhibited in the retinal veins (p <0.01), and subsequent leucocyte infiltration into the vitreous cavity was also significantly suppressed (p <0.01). Retinal vasodilation was also substantially suppressed in SKK-60060 treated rats (p <0.01). Similarly, leucocyte infiltration and protein leakage into the aqueous humour were reduced significantly by SKK-60060 (p <0.01).

CONCLUSIONS

SKK-60060 treatment significantly inhibited the inflammatory reaction induced by LPS. Its inhibitory effects on P and L-selectin resulted in suppression of leucocyte infiltration and the subsequent inflammatory reaction caused by accumulated leucocytes. The current findings suggest that SKK-60060 may be useful in the management of uveitis.

Therapeutic potential of monoclonal antibodies in myocardial reperfusion injury

While reperfusion therapy in myocardial infarction is associated with better short- and long-term outcomes, it paradoxically results in reperfusion injury mediated by interactions between leukocytes, endothelial cells, platelets, and the myocardium. Several surface receptors, adhesion molecules, and ligands have been shown to be important in the pathogenesis of myocardial reperfusion injury, and therapeutic strategies employing the use of monoclonal antibodies have been attempted against many of them. These have included monoclonal antibodies against activated complement 5 (C5a) to inhibit leukotaxis, monoclonal antibodies against P-selectin, P-selectin glycoprotein ligand (PSGL)-1, L-selectin and E-selectin to inhibit leukocyte rolling, and monoclonal antibodies against the Mac-1 (CD11b/CD18) receptor and intercellular adhesion molecule (ICAM)-1 to block firm adhesion of leukocytes to endothelial cells. In addition, although initially developed as an antiplatelet agent, the glycoprotein IIb/IIIa receptor antagonist abciximab shows significant ability to diminish or prevent reperfusion injury, presumably through its ability to block the Mac-1 receptor on leukocytes. Finally, monoclonal antibodies have also been tested against several cytokines and adhesion molecules implicated in so-called subacute endothelial activation, including interleukin-8 and vascular cell adhesion molecule (VCAM)-1. Studies in animals evaluating the use of monoclonal antibodies in reperfusion injury against various potential targets have largely been successful; however, studies in humans have been disappointing, underscoring the pitfalls of using animal models for the study of complex diseases. Based upon current knowledge, it is becoming clear that a successful strategy against reperfusion injury will require targeting several pathways at once, rather than attempting to block one final common pathway. In addition, inhibition of subacute endothelial activation through inhibition of transcription factors, namely nuclear factor (NF)-kappa B, may be a prerequisite to significantly reducing the extent of myocardial damage in this condition. The future of monoclonal antibodies in the overall strategy remains unclear. Newer small molecule inhibitors are also under development, and the eventual role of gene therapy remains to be elucidated.