Protective effect of sildenafil (Viagra) in transient spinal cord ischemia

Modulation of the ASK1-MKK3/6-p38/MAPK signalling pathway mediates sildenafil protection against chemical hypoxia caused by malonate

BACKGROUND AND PURPOSE

PD5 inhibitors have recently been reported to exert beneficial effects against ischaemia-reperfusion injury in several organs. However, there are few studies regarding their neuroprotective effects in brain ischaemia. The present study was designed to assess the effects of sildenafil against chemical hypoxia induced by malonate. Intrastriatal injection of malonate produces energy depletion and striatal lesions similar to that seen in cerebral ischaemia through mechanisms that involve generation of reactive oxygen species (ROS).

EXPERIMENTAL APPROACH

Volume lesion was analysed by cytochrome oxidase histochemistry. Generation of reactive species was determined by in situ visualization of superoxide production and nitrotyrosine measurement. Protein levels were determined by Western blot after subcellular fractionation.

KEY RESULTS

Sildenafil, given 30 min before malonate, significantly decreased the lesion volume in the rat. This protective effect cannot be attributed to any effect on ROS production but to the inhibition of downstream pathways. Thus, malonate induced the activation of apoptosis signal-regulating kinase-1 (ASK1) and two MAPK kinases, MKK3/6 and MKK7, which lead to an increased phosphorylation of JNK and p38 MAPK, effects that were blocked by sildenafil. Selective inhibitors of p38 and JNK (SB203580 or SP600125, respectively) were used in combination with malonate in order to evaluate the plausible implication of these pathways in the protection afforded by sildenafil. While inhibition of p38 provided a significant protection against malonate-induced neurotoxicity, inhibition of JNK did not.

CONCLUSIONS AND IMPLICATIONS

Sildenafil protects against the chemical hypoxia induced by malonate through the regulation of the ASK1-MKK3/6-p38/MAPK signalling pathway.

Neuroprotective effects of sildenafil in experimental spinal cord injury in rabbits

Neuroprotective agents such as methylprednisolone and sildenafil may limit damage after spinal cord injury. We evaluated the effects of methylprednisolone and sildenafil on biochemical and histologic changes after spinal cord injury in a rabbit model. Female New Zealand rabbits (32 rabbits) were allocated to 4 equal groups: laminectomy only (sham control) or laminectomy and spinal trauma with no other treatment (trauma control) or treatment with either methylprednisolone or sildenafil. Gelsolin and caspase-3 levels in cerebrospinal fluid and plasma were determined, and spinal cord histology was evaluated at 24 hours after trauma. There were no differences in mean cerebrospinal fluid or plasma levels of caspase-3 between the groups or within the groups from 0 to 24 hours after injury. From 0 to 24 hours after trauma, mean cerebrospinal fluid gelsolin levels significantly increased in the sildenafil group and decreased in the sham control and the trauma control groups. Mean plasma gelsolin level was significantly higher at 8 and 24 hours after trauma in the sildenafil than other groups. Histologic examination indicated that general structural integrity was better in the methylprednisolone in comparison with the trauma control group. General structural integrity, leptomeninges, white and grey matter hematomas, and necrosis were significantly improved in the sildenafil compared with the trauma control group. Caspase-3 levels in the cerebrospinal fluid and blood were not increased but gelsolin levels were decreased after spinal cord injury in trauma control rabbits. Sildenafil caused an increase in gelsolin levels and may be more effective than methylprednisolone at decreasing secondary damage to the spinal cord. 

PDE5 inhibition against acute renal ischemia reperfusion injury in rats: does vardenafil offer protection?

PURPOSE

To evaluate the effect of vardenafil on renal function after renal ischemia-reperfusion (IR) injury (IRI) in a rat model.

MATERIALS AND METHODS

Seventy-one Wistar rats were divided into 7 groups including (1) a vehicle-treated group, (2) a vehicle pretreated-IR group, (3-6) vardenafil pretreated-IR groups in doses of 0.02, 0.2, 2 and 20 μg/kg, respectively, (7) a group of IR followed by treatment with 2 μg/kg of vardenafil. Vardenafil or vehicle solution was administered one hour before unilateral nephrectomy and the induction of 45 min of ischemia on the contralateral kidney by clamping of renal pedicle. Four hours of reperfusion were allowed after renal ischemia. Studied parameters were serum creatinine, fractional excretion of sodium (FENa), and histological evaluation of renal specimens. In addition, renal tissue cGMP levels, ERK1/2 phosphorylation as well as renal function by renal scintigraphy were also evaluated.

RESULTS

Administration of vardenafil before the induction of ischemia resulted in a significant reduction in creatinine and FENa levels as well as in less histological lesions observed in treated kidneys in comparison with the vehicle-treated group. The underlying mechanism of cytoprotection was cGMP depended and involved the phosphorylation of ERK proteins. Renal scintigraphy confirmed that PDE5 inhibition attenuates renal IRI.

CONCLUSIONS

Vardenafil attenuates renal IRI. Based on similar results from relevant studies on other PDE-5 inhibitors in renal and cardiac IRI, it can be assumed that all PDE-5 inhibitors share a common mechanism of cytoprotection.

Sildenafil improves epicenter vascular perfusion but not hindlimb functional recovery after contusive spinal cord injury in mice

Nitric oxide (NO) is an important regulator of vasodilation and angiogenesis in the central nervous system (CNS). Signaling initiated by the membrane receptor CD47 antagonizes vasodilation and angiogenesis by inhibiting synthesis of cyclic guanosine monophosphate (cGMP). We recently found that deletion of CD47 led to significant functional locomotor improvements, enhanced angiogenesis, and increased epicenter microvascular perfusion in mice after moderate contusive spinal cord injury (SCI). We tested the hypothesis that improving NO/cGMP signaling within the spinal cord immediately after injury would increase microvascular perfusion, angiogenesis, and functional recovery, with an acute, 7-day administration of the cGMP phosphodiesterase 5 (PDE5) inhibitor sildenafil. PDE5 expression is localized within spinal cord microvascular endothelial cells and smooth muscle cells. While PDE5 antagonism has been shown to increase angiogenesis in a rat embolic stroke model, sildenafil had no significant effect on angiogenesis at 7 days post-injury after murine contusive SCI. Sildenafil treatment increased cGMP concentrations within the spinal cord and improved epicenter microvascular perfusion. Basso Mouse Scale (BMS) and Treadscan analyses revealed that sildenafil treatment had no functional consequence on hindlimb locomotor recovery. These data support the hypothesis that acutely improving microvascular perfusion within the injury epicenter by itself is an insufficient strategy for improving functional deficits following contusive SCI.

Effect of erythropoietin therapy on the progression of cisplatin induced renal injury in rats

Cisplatin is one of the most important chemotherapeutic agents useful in the treatment of a variety of solid tumors; however, it has several side effects such as nephrotoxicity. In the present study, the effect of rhEPO on acute kidney injury induced by i.p. injection of rats with 9.0 mg/kg cisplatin was studied. It was observed that EPO treated group showed a significantly lower rate in the extent and severity of the histological signs of kidney injury than untreated one. This is attributed to (i) a decrease in the elevated oxidative and nitrosative stress markers, (ii) reduction of the expression of VEGF, HO-1 and iNOS as well as (iii) improvement of Bcl2 immunoreaction in most tubular cells. Thus, EPO may be one of the futures therapeutic possibilities to overcome the side effects of anti-cancer drugs induced acute renal injury through various mechanisms including down regulation of vascular endothelial growth factor (VEGF), hemeoxygenase-1 (HO-1) and inducible nitric oxide synthase (iNOS) expressions in addition to stimulation of tubular cell regeneration.

Effects of sildenafil and tadalafil on ischemia/reperfusion injury in fetal rat brain

OBJECTIVE

The aim of the present study was to evaluate the effects of phosphodiesterase type 5 (PDE5) inhibitory drugs, sildenafil and tadalafil, in ischemia/reperfusion (I/R)-induced oxidative injury in fetal rat brain.

METHODS

Timed pregnant adult Wistar rats were randomly assigned to the following groups (n = 6 for each group): saline + none I/R (1), saline + I/R (2), sildenafil + none I/R (3); sildenafil + I/R (4), tadalafil + none I/R (5) and tadalafil + I/R (6). Fetal ischemia was induced by clamping the utero-ovarian artery bilaterally. Fetuses were delivered and 268 fetal rats were decapitated. Malondialdehyde (MDA) levels and, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were assessed in fetal brain tissue homogenates by spectrophotometric methods.

RESULTS

In saline + I/R group, MDA levels were increased and, SOD and GSH-Px activities were decreased significantly comparing with saline + none I/R group. Both tadalafil and sildenafil treatment decreased the MDA levels significantly in ischemia/reperfusion groups, whereas this effect was significantly more potent with tadalafil. SOD levels were significantly decreased in all groups after I/R. Tadalafil seems to be more effective than sildenafil by means of increasing GSH-Px activity significantly after I/R.

CONCLUSION

Our results indicate some beneficial effects of PDE5 inhibitory drugs, especially tadalafil, on oxidative I/R injury in fetal rat brains.

Protective effects of tadalafil on experimental spinal cord injury in rats

Tadalafil is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). Nitric oxide (NO) functions as a retrograde neurotransmitter in the spinal cord, and postsynaptic structures respond to NO by producing cGMP. The concentrations of cGMP in the spinal cord are controlled by the actions of PDE. The aim of the study was to evaluate and compare the effects of the use of both methylprednisolone and tadalafil on serum and tissue concentrations of NO, malondialdehyde (MDA) levels, superoxide dismutase (SOD) activity, and tissue glutathione peroxidase (GSH-Px) activity in rats with spinal cord injury (SCI). SCI was induced in Wistar albino rats by dropping a 10 g rod from a 5.0 cm height at T8-10. The 28 rats were randomly divided into four equal groups: tadalafil, methylprednisolone, non-treatment and sham groups. Rats were neurologically tested at 24 hours after trauma. At the end of the experiment, blood samples were collected and spinal cord tissue samples were harvested for biochemical evaluation. The tissue level of NO was increased in the tadalafil group compared with the non-treatment and methylprednisolone groups (p<0.05). The tissue levels of SOD and GSH-Px did not differ between the groups. Serum levels of NO were higher in the tadalafil group than in the non-treatment group (p<0.05). The increase in serum SOD levels was greater in the tadalafil group than the methylprednisolone group. Serum MDA levels in the tadalafil and methylprednisolone groups tended to be lower than in the non-treatment group (p>0.05). Tissue MDA levels in the tadalafil and methylprednisolone groups tended to be lower than in the non-treatment group and sham groups (p>0.05). Although there was no difference in neurological outcome scores between the tadalafil, methylprednisolone and non-treatment groups (p>0.05), the animals in the tadalafil and methylprednisolone groups tended to have better scores than the non-treatment group. Thus, tadalafil appears to be beneficial in reducing the effects of injury to the spinal cord by increasing tissue levels of NO and serum activity of SOD.

Pretreatment of sildenafil attenuates ischemia-reperfusion renal injury in rats

Sildenafil was the first selective inhibitor of phosphodiesterase-5 (PDE5) to be widely used for treating erectile dysfunction. Many recent studies have investigated the cardioprotective role of sildenafil in animal models. We evaluated the protective effects of sildenafil in experimental renal ischemia-reperfusion (IR) injury in two studies. In study 1, male Sprague-Dawley rats were divided into four groups: sham, sildenafil-treated sham, vehicle-treated IR, and sildenafil-treated IR groups. In study 2, we divided the rats into two groups: sildenafil-treated IR rats and PD98059 (ERK inhibitor)+sildenafil-treated IR rats. Functional parameters of the kidney were evaluated at the molecular and structural levels. Blood urea nitrogen (BUN) and serum creatinine levels were lower in sildenafil-treated IR rats than in vehicle-treated IR rats. The expression of inducible (iNOS) and endothelial nitric oxide synthase (eNOS) proteins in sildenafil-treated IR rats was significantly higher than in vehicle-treated IR rats. Pretreatment with sildenafil in IR rats increased ERK phosphorylation and reduced the renal Bax/Bcl-2 ratio, renal caspase-3 activity, and terminal dUTP nick end-labeling-positive apoptotic cells. In contrast, PD98059 treatment increased BUN and serum creatinine levels and attenuated the sildenafil-induced expression of pERK, iNOS, eNOS, and Bcl-2. PD98059 also increased caspase-3 activity but did not decrease the sildenafil-induced accumulation of cGMP. In conclusion, this study suggests that sildenafil has antiapoptotic effects in experimental IR renal injury via ERK phosphorylation, induction of iNOS and eNOS production, and a decrease in the Bax/Bcl-2 ratio.

Sildenafil attenuates renal injury in an experimental model of rat cisplatin-induced nephrotoxicity

Sildenafil is the first commercially available selective inhibitor of phosphodiesterase-5 (PDE5) and is widely used for the treatment of erectile dysfunction. In recent years, investigations of the role of sildenafil in cardioprotection in animal models have received considerable interest. We evaluated whether sildenafil can attenuate cisplatin-induced nephrotoxicity in a rat experimental model. Male Sprague-Dawley rats were divided into five groups: control rats, sildenafil-control rats, cisplatin-injected rats (5 mg kg(-1) IP, single dose), sildenafil-treated cisplatin-injected rats (0.4 mg kg(-1), daily), and sildenafil+NG-nitro-l-arginine methyl ester hydrochloride (l-NAME)-treated rats. The molecular, functional, and structural parameters of the kidney were measured. At 96 h after cisplatin injection, serum levels of creatinine were lower in rats treated with both sildenafil+cisplatin compared with rats treated with cisplatin alone, and renal iNOS and eNOS expression was significantly higher in sildenafil+cisplatin-treated rats compared with rats treated with cisplatin alone (all P<0.05). Renal Bax gene and protein expression was significantly higher in cisplatin-treated rats compared with control rats, and sildenafil treatment significantly reduced the levels of Bax and increased the renal Bax/Bcl-2 ratio (P<0.05). Sildenafil treatment also reduced renal caspase-3 activation and TUNEL-positive apoptotic cells. These data suggest that sildenafil attenuates experimental cisplatin-induced nephrotoxicity by preventing apoptosis.