A small dose of the immunosuppressive agent FK506 (tacrolimus) protects peripheral nerve from ischemic fiber degeneration

Local delivery of FK506 to injured peripheral nerve enhances axon regeneration after surgical nerve repair in rats

Administration of FK506, an FDA approved immunosuppressant, has been shown to enhance nerve regeneration following peripheral nerve injuries. However, the severe side effects of the systemically delivered FK506 has prevented clinicians from the routine use of the drug. In this study, we analyzed the effectiveness of our fibrin gel-based FK506 delivery system to promote axon regeneration in a rat peripheral nerve transection and immediate surgical repair model. In addition, biodistribution of FK506 from the local delivery system to the surrounding tissues was analyzed in vivo. Rats in the negative control groups either did not receive any delivery system treatment or received fibrin gel with empty microspheres. The experimental groups included rats treated with fibrin gel loaded with solubilized, particulate, and poly(lactic-co-glycolic) acid microspheres-encapsulated FK506. Rats in experimental groups receiving FK506 microspheres and the particulate FK506 regenerated the highest number of motor and sensory neurons. Histomorphometric analysis also demonstrated greater numbers of myelinated axons following particulate FK506 and FK506 microspheres treatment compared to the negative control groups. In biodistribution studies, FK506 was found at the nerve repair site, the sciatic nerve, and spinal cord, with little to no drug detection in other vital organs. Hence, the local application of FK506 via our delivery systems enhanced axon regeneration whilst avoiding the toxicity of systemic FK506. This local delivery strategy represents a new opportunity for clinicians to use for cases of peripheral nerve injuries. STATEMENT OF SIGNIFICANCE: This work for the first time investigated the influence of locally administered FK506 to the site of nerve injury and immediate repair directly on the number of motor and sensory neurons that regenerated their axons. Furthermore, using the immediate nerve repair model, we obtained valuable information about the biodistribution of FK506 within the nervous system following its release from the delivery system implanted at the site of nerve injury and repair. The strategy of local FK506 delivery holds a great promise in the clinical translation, as the localized delivery circumvents the main limitation of the systemic delivery of FK506, that of immunosuppression and toxicity.

Effects of α-MSH on ischemia/reperfusion injury in the rat sciatic nerve

Background:

Ischemia/reperfusion (I/R) causes the production of toxic free radicals and leads to pathological changes in nerve tissue. We investigated the effect of alpha-melanocyte stimulating hormone (α-MSH) in a rat model for sciatic nerve I/R and discuss the possible cytoprotective and antioxidant mechanism of α-MSH against ischemic fiber degeneration.

Methods:

Experiments were performed using 42 adult male Wistar rats. Rats were divided into six experimental groups: control group, ischemia group, I/R groups, and α-MSH treated groups. Ischemia was produced by clamping of the femoral vessels. Immediately after ischemia that lasted 3 h, 75 μg/kg of α-MSH was administered subcutaneously before reperfusion and the tissue malondialdehyde (MDA) level was evaluated as an indicator of lipid peroxidation in groups with different reperfusion periods.

Results:

The reperfusion injury did not begin in the first hour of reperfusion after 3 h of ischemia, and MDA levels increased on the first day of reperfusion. During the first day, blood MDA levels were decreased in the α-MSH group compared to the control group. The tissue from animals pre-treated with α-MSH showed fewer morphological alterations. Myelin breakdown was significantly diminished after treatment with α-MSH, and the ultrastructural features of axons showed remarkable improvement. Two-way analysis of variance was used for comparing three or more groups. When a significant difference existed, the post-hoc multiple-comparison test was applied to demonstrate the differences.

Conclusions:

The results confirm that pre-treatment with α-MSH after ischemia protected the peripheral nerves against I/R injury.

Stereological analysis of sciatic nerve in chickens following neonatal pinealectomy: an experimental study

Background

Although the injury to the peripheral nervous system is a common clinical problem, understanding of the role of melatonin in nerve degeneration and regeneration is incomplete.

Methods

The current study investigated the effects of neonatal pinealectomy on the sciatic nerve microarchitecture in the chicken. The chickens were divided into two equal groups: unpinealectomized controls and pinealectomized chickens. At the end of the study, biochemical examination of 10 sciatic nerve samples from both groups was performed and a quantitative stereological evaluation of 10 animals in each group was performed. The results were compared using Mann-Whitney test.

Results

In this study, the results of axon number and thickness of the myelin sheath of a nerve fiber in newly hatched pinealectomy group were higher than those in control group. Similarly, surgical pinealectomy group had significantly larger axonal cross-sectional area than the control group (p < 0.05). In addition, the average hydroxyproline content of the nerve tissue in neonatal pinealectomy group was higher than those found in control group. Our results suggest that melatonin may play a role on the morphologic features of the peripheral nerve tissue and that melatonin deficiency might be a pathophysiological mechanism in some degenerative diseases of peripheral nerves. The changes demonstrated by quantitative morphometric methods and biochemical analysis has been interpreted as a reflection of the effects of melatonin upon nerve tissue.

Conclusion

In the light of these results from present animal study, changes in sciatic nerve morphometry may be indicative of neuroprotective feature of melatonin, but this suggestion need to be validated in the human setting.

Neuroregenerative Effects of Preinjury FK-506 Administration

BACKGROUND

FK-506 is used in organ transplantation because it promotes neurite outgrowth in vitro and enhances neuroregeneration in peripheral nerve injury transection models. Immunosuppressive mechanisms of FK-506 are well defined, with demonstration of decreased neuroregenerative effects with delayed administration. The purpose of this study was to describe the effects of preinjury administration of FK-506 in rats with tibial nerve transection injury.

METHODS

Eight inbred male Lewis rats per group in three separate groups underwent tibial nerve transection with primary repair. Group I received placebo, group II received FK-506 treatment at 1 day before surgery, and group III received FK-506 preloading 3 days before surgery.

RESULTS

Histologic and histomorphometric results demonstrated the preload FK-506 group had superior results compared with the immediate FK-506 group. Both FK-506 groups were superior to the placebo group. The preload FK-506 demonstrated superior regeneration in mean total nerve fiber counts (p < 0.05), greater percentage neural tissue (p < 0.05), greater mean nerve fiber density (p < 0.05), and lower percentage of debris (p > 0.05). Mean nerve fiber widths were similar in the preload and immediate FK-506 groups but superior to the placebo group.

CONCLUSION

These data suggest that enhancement of FK-506's neuroregenerative effect is enhanced when administered before nerve injury such as when performing elective surgery.

Beneficial effects of melatonin on reperfusion injury in rat sciatic nerve

Studies have shown that ischemia-reperfusion (I/R) produces free radicals leading to lipid peroxidation and to damage of the nervous tissue. Melatonin, a main secretory product of the pineal gland, has free radical scavenging and antioxidant properties and has been shown to diminish I/R injury in many tissues. There are a limited number of studies related to the effects of melatonin on I/R injury in the peripheral nervous system. Therefore, in the present study, the protective effect of melatonin was investigated in rats subjected to 2 hr of sciatic nerve ischemia followed by 3 hr of reperfusion. Following reperfusion, nerve tissue samples were collected for quantitative assessment of malondialdehyde (MDA), an oxidative stress marker, and superoxide dismutase (SOD), a principal antioxidant enzyme. Samples were further evaluated at electron microscopic level to examine the neuropathological changes. I/R elevated the concentration of MDA significantly while there was a reduction at SOD levels. Melatonin treatment reversed the I/R-induced increase and decrease in MDA and SOD levels, respectively. Furthermore, melatonin salvaged the nerve fibers from ischemic degeneration. Histopathologic findings in the samples of melatonin-treated animals indicated less edema and less damage to the myelin sheaths and axons than those observed in the control samples. Our results suggest that administration of melatonin protects the sciatic nerve from I/R injury, which may be attributed to its antioxidant property.

Tacrolimus hydrate (FK506): therapeutic effects and selection of responders in the treatment of myasthenia gravis

Tacrolimus hydrate (FK506) reduces myasthenic symptoms due to its immunosuppressive properties. We studied the therapeutic effects of FK506 and noted improvement in 7 of 13 myasthenic patients on the clinical muscle test (myasthenia gravis, MG score). Two other patients with relapsing ocular symptoms improved. We also examined patient sensitivity to FK506, but could not predict such sensitivity before FK506 treatment in the present study.

Current and Future Strategies for Preventing and Managing Erectile Dysfunction Following Radical Prostatectomy

INTRODUCTION AND OBJECTIVES

As radical prostatectomy remains a commonly used procedure in the treatment of clinically localized prostate cancer, we critically analyzed current and future strategies for preventing and managing postoperative erectile dysfunction.

METHODS

Systematic literature review using Medline and CancerLit from January 1997 to June 2003. Abstracts published in the journals European Urology, The Journal of Urology and the International Journal of Impotence Research as official proceedings of internationally known scientific societies held in the same time period were also assessed.

RESULTS

Patient selection and surgical technique are the major determinants of postoperative erectile function. Apoptosis of corporeal smooth muscle cells plays a role in the development of cavernous veno-occlusive dysfunction following radical prostatectomy. Pharmacological prophylaxis and treatment of postoperative erectile dysfunction is effective and safe. The concepts of cavernous nerve reconstruction and neuroprotection have been associated to promising results.

CONCLUSIONS

In the hands of experienced surgeons, properly selected patients undergoing a nerve sparing radical prostatectomy should achieve unassisted or medically assisted erections postoperatively.

Immunophilin Ligands Promote Penile Neurogenesis and Erection Recovery After Cavernous Nerve Injury

PURPOSE

We investigated the long-term effect of immunophilin ligands on erection physiology and cavernous tissue histology using rat models of unilateral and bilateral cavernous nerve (CN) injury.

MATERIALS AND METHODS

Adult male Sprague-Dawley rats were administered the immunophilin ligand FK506 (5 mg/kg subcutaneously daily for 5 days), the nonimmunosuppressant FK506 derivative GPI1046 (3 to 3-pyridyl)-1-propyl(2 seconds)-1-(3,3-dimethyl-1,2-dioxopentyl)-2-pyrrolidine carboxylate) (40 mg/kg subcutaneously daily for 5 or 28 days) or saline immediately upon induction of 2 paradigms of cavernous nerve injury, namely focal transection of the CN unilaterally, and a combination of focal transection of the CN unilaterally and excision of a 5 mm segment of contralateral CN (BIL treated). At 28 days following CN injury electrical stimulation of the transected CN and penile erection monitoring were performed. Whole penes were removed and evaluated immunohistochemically for the nitric oxide generator neuronal nitric oxide synthase, the neuronal marker synaptophysin, the endothelial marker CD31 and the smooth muscle marker alpha-actin.

RESULTS

In unilaterally treated groups erection recovery was significantly greater in FK506 treated than in saline treated animals ((83.5% +/- 9.2% vs 24.3% +/- 8.1%, p <0.001) and similarly greater in GPI1046 treated animals than in the respective saline treated controls for this group (57.9% +/- 12.6% vs 23.8% +/- 7.0%, p <0.05). In BIL treated groups erection recovery for FK506 and GPI1046 treated rats exceeded saline treated values by approximately 70% (p <0.05) and 40% (p = 0.14), respectively. After 28 days of continuous treatment in BIL treated groups erection recovery for GPI1046 treated rats exceeded saline treated values by 140% (p <0.05). Neuronal and endothelial staining was preserved after immunophilin ligand treatment.

CONCLUSIONS

Immunophilin ligands exert neurotrophic effects on the penile innervation that preserve cavernous tissue structure and promote erectile function recovery in rats after extensive CN injury.

Protective effect of FK506 (tacrolimus) in pentylenetetrazol-induced kindling in mice

The repeated administration of otherwise subconvulsant dose of pentylenetetrazol (PTZ) is known to produce chemical kindling in animals. In our study, chronic administration of subconvulsant dose of PTZ (40 mg/kg) produced chemical kindling in mice. Pretreatment with L-arginine (50-100 mg/kg ip) potentiated the PTZ-induced kindling, whereas N(omega)-nitro-L-arginine methyl ester (L-NAME) (10-20 mg/kg ip) showed a protective effect. FK506, a potent neuroprotective agent, dose dependently (0.5-1 mg/kg po) decreased the kindling score. When given in combination, L-NAME potentiated the protective effect of lower dose of FK506 (0.5 mg/kg) on PTZ-induced kindling. L-Arginine (50-100 mg/kg) reversed the protective effect of FK506 (1 mg/kg) and L-NAME (20 mg/kg). Biochemical studies showed the potential role of free radical toxicity in the kindled mice, as there was an increased lipid peroxidation as indicated by elevated malondialdehyde (MDA) and nitrite levels and decrease in GSH and superoxide dismutase (SOD) levels. FK506 pretreatment significantly reversed the elevated MDA and nitrite levels, GSH and SOD depletion induced by PTZ treatment. In conclusion, the results of the present study suggest the possible neuroprotective action of FK506 against PTZ-induced kindling.

FK506 binding protein 12 is expressed in rat penile innervation and upregulated after cavernous nerve injury

To evaluate whether FK506 and other immunophilin ligands may have potential therapeutic efficacy for erectile function preservation after penile nerve injury, we demonstrated localizations of the immunophilin FK506 binding protein 12 (FKBP 12) in intact and injured rat penile nerves and correlated these findings with localizations of neuronal nitric oxide synthase (nNOS), which neuronally forms nitric oxide for mediation of penile erection, in response to systemically administered FK506. Adult male Sprague-Dawley rats were subjected to unilateral right cavernous nerve forceps crush injury and administered FK506 (1 mg/kg i.p.) or saline at the same time and daily up to 7 days. At 1, 3 and 7 days after injury, bilateral cavernous nerves and major pelvic ganglia were collected for nNOS immunohistochemistry, FKBP 12 immunohistochemistry, and FKBP 12 in situ hybridisation. Protein expressions of nNOS and FKBP 12 were observed in major pelvic ganglion, cavernous nerve and nerve terminals within the rat penis as well as mRNA expression of FKBP 12 observed in the rat major pelvic ganglion neuronal cell bodies to a minimal extent at baseline conditions. After cavernous nerve injury, nNOS immunoreactivity was observed to be slightly diminished in ipsilateral penile nerve structures at only one day following injury while both FKBP 12 protein and mRNA expressions were observed to be increased at each interval of study. FK506 treatment did not affect staining of intact or injured nerves. Our demonstration that FKBP 12 is localized to penile innervation in the rat and becomes upregulated following cavernous nerve crush injury, independent of FK506 treatment, suggests that this immunophilin mediates a neurotrophic mechanism. Whether FK506 affords neuroprotection that preserves penile erection through FKBP 12 upregulation is unclear.