Exploring the neuroregenerative potential of tacrolimus

The Effects of Growth Hormone on Nerve Regeneration and Alloimmunity in Vascularized Composite Allotransplantation

BACKGROUND

Poor outcomes in functional recovery after upper extremity transplantation are largely attributable to denervation-induced muscle atrophy that occurs during the prolonged period of nerve regeneration. Growth hormone (GH) has well-established trophic effects on neurons, myocytes, and Schwann cells, and represents a promising therapeutic approach to address this challenge. This study sought to confirm the positive effects of GH treatment on nerve regeneration and functional recovery and to evaluate the effects of GH treatment on the immune response in the setting of vascularized composite allotransplantation.

METHODS

Rats underwent orthotopic forelimb transplantation across a full major histocompatibility complex mismatch and received either porcine-derived growth hormone or no treatment ( n = 18 per group). Functional recovery was measured using electrically stimulated grip strength testing. Animals were monitored for clinical and subclinical signs of rejection.

RESULTS

Neuromuscular junction reinnervation and grip strength were improved in GH-treated animals ( P = 0.005, P = 0.08, respectively). No statistically significant differences were seen in muscle atrophy, degree of myelination, axon diameter, or axon counts between groups. The rates of clinical and histologic rejection did not differ significantly between groups.

CONCLUSIONS

The findings alleviate concern for increased risk of transplant rejection during GH therapy and support the translation of GH as a therapeutic method to promote improved functional recovery in upper extremity transplantation.

CLINICAL RELEVANCE STATEMENT

The authors' findings suggest that growth hormone is a promising therapeutic option to improve motor functional recovery in upper extremity transplantation without increased risk of rejection.

Nanoparticle-hydrogel composite as dual-drug delivery system for the potential application of corneal graft rejection

Immune rejection remains the major cause of corneal graft failure. Immunosuppressants (such as rapamycin; RAPA) adjunctive to antibiotics (such as levofloxacin hydrochloride; Lev) are a clinical mainstay after corneal grafts but suffer from poor ocular bioavailability associated with severe side effects. In this study, we fabricated a Lev@RAPA micelle loaded cationic peptide-based hydrogel (NapFFKK) as a dual-drug delivery system by integrating RAPA micelles with Lev into a cationic NapFFKK hydrogel to potentially reduced the risk of corneal graft rejection. The properties of the resulting hydrogels were characterized using transmission electronmicroscopy and rheometer. Lev@RAPA micelles loaded NapFFKK hydrogel provided sustained in vitro drug release without compromising their inherent pharmacological activities. Topical instillation of Lev@RAPA micelles loaded NapFFKK hydrogel resulted in the great ocular tolerance and extended precorneal retention over 60min, thus significantly enhancing the ocular bioavailability of both Lev and RAPA. Overall, such dual-drug delivery system might be a promising formulation for the suppression of corneal graft failure.

Electrospun aligned tacrolimus-loaded polycaprolactone biomaterials for peripheral nerve repair

Background: Efficacious repair of peripheral nerve injury is an unmet clinical need. The implantation of biomaterials containing neurotrophic drugs at the injury site could promote nerve regeneration and improve outcomes for patients. Materials & methods: Random and aligned electrospun poly-ε-caprolactone scaffolds containing encapsulated tacrolimus were fabricated, and the gene expression profile of Schwann cells (SCs) cultured on the surface was elucidated. On aligned fibers, the morphology of SCs and primary rat neurons was investigated. Results: Both scaffold types exhibited sustained release of drug, and the gene expression of SCs was modulated by both nanofibrous topography and the presence of tacrolimus. Aligned fibers promoted the alignment of SCs and orientated outgrowth from neurons. Conclusion: Electrospun PCL scaffolds with tacrolimus hold promise for the repair of peripheral nerve injury.

The Effect of Local Purified Exosome Product, Stem Cells, and Tacrolimus on Neurite Extension

PURPOSE

The combination of cellular and noncellular treatments has been postulated to improve nerve regeneration through a processed nerve allograft. This study aimed to evaluate the isolated effect of treatment with purified exosome product (PEP), mesenchymal stem cells (MSCs), and tacrolimus (FK506) alone and in combination when applied in decellularized allografts.

METHODS

A three-dimensional in vitro-compartmented cell culture system was used to evaluate the length of regenerating neurites from the neonatal dorsal root ganglion into the adjacent peripheral nerve graft. Decellularized nerve allografts were treated with undifferentiated MSCs, 5% PEP, 100 ng/mL FK506, PEP and FK506 combined, or MSCs and FK506 combined (N = 9/group) and compared with untreated nerve autografts (positive control) and nerve allografts (negative control). Neurite extension was measured to quantify nerve regeneration after 48 hours, and stem cell viability was evaluated.

RESULTS

Stem cell viability was confirmed in all MSC-treated nerve grafts. Treatments with PEP, PEP + FK506, and MSCs + FK506 combined were found to be superior to untreated allografts and not significantly different from autografts. Combined PEP and FK506 treatment resulted in the greatest neurite extension. Treatment with FK506 and MSCs was significantly superior to MSC alone. The combined treatment groups were not found to be statistically different.

CONCLUSIONS

Although all treatments improved neurite outgrowth, treatments with PEP, PEP + FK506, and MSCs + FK506 combined had superior neurite growth compared with untreated allografts and were not found to be significantly different from autografts, the current gold standard.

CLINICAL RELEVANCE

Purified exosome product, a cell-free exosome product, is a promising adjunct to enhance nerve allograft regeneration, with possible future avenues for clinical translation.

Nerve Wrap for Local Delivery of FK506/Tacrolimus Accelerates Nerve Regeneration

Peripheral nerve injuries (PNIs) occur frequently and can lead to devastating and permanent sensory and motor function disabilities. Systemic tacrolimus (FK506) administration has been shown to hasten recovery and improve functional outcomes after PNI repair. Unfortunately, high systemic levels of FK506 can result in adverse side effects. The localized administration of FK506 could provide the neuroregenerative benefits of FK506 while avoiding systemic, off-target side effects. This study investigates the utility of a novel FK506-impregnated polyester urethane urea (PEUU) nerve wrap to treat PNI in a previously validated rat infraorbital nerve (ION) transection and repair model. ION function was assessed by microelectrode recordings of trigeminal ganglion cells responding to controlled vibrissae deflections in ION-transected and -repaired animals, with and without the nerve wrap. Peristimulus time histograms (PSTHs) having 1 ms bins were constructed from spike times of individual single units. Responses to stimulus onsets (ON responses) were calculated during a 20 ms period beginning 1 ms after deflection onset; this epoch captures the initial, transient phase of the whisker-evoked response. Compared to no-wrap controls, rats with PEUU-FK506 wraps functionally recovered earlier, displaying larger response magnitudes. With nerve wrap treatment, FK506 blood levels up to six weeks were measured nearly at the limit of quantification (LOQ ≥ 2.0 ng/mL); whereas the drug concentrations within the ION and muscle were much higher, demonstrating the local delivery of FK506 to treat PNI. An immunohistological assessment of ION showed increased myelin expression for animals assigned to neurorrhaphy with PEUU-FK506 treatment compared to untreated or systemic-FK506-treated animals, suggesting that improved PNI outcomes using PEUU-FK506 is mediated by the modulation of Schwann cell activity.

Neuroprotective Action of Tacrolimus before and after Onset of Neonatal Hypoxic-Ischaemic Brain Injury in Rats

(1) Background: Neonatal brain injury can lead to permanent neurodevelopmental impairments. Notably, suppressing inflammatory pathways may reduce damage. To determine the role of neuroinflammation in the progression of neonatal brain injury, we investigated the effect of treating neonatal rat pups with the immunosuppressant tacrolimus at two time points: before and after hypoxic-ischaemic (HI)-induced injury. (2) Methods: To induce HI injury, postnatal day (PND) 10 rat pups underwent single carotid artery ligation followed by hypoxia (8% oxygen, 90 min). Pups received daily tacrolimus (or a vehicle) starting either 3 days before HI on PND 7 (pre-HI), or 12 h after HI (post-HI). Four doses were tested: 0.025, 0.05, 0.1 or 0.25 mg/kg/day. Pups were euthanised at PND 17 or PND 50. (3) Results: All tacrolimus doses administered pre-HI significantly reduced brain infarct size and neuronal loss, increased the number of resting microglia and reduced cellular apoptosis (p < 0.05 compared to control). In contrast, only the highest dose of tacrolimus administered post-HI (0.25 mg/kg/day) reduced brain infarct size (p < 0.05). All doses of tacrolimus reduced pup weight compared to the controls. (4) Conclusions: Tacrolimus administration 3 days pre-HI was neuroprotective, likely mediated through neuroinflammatory and cell death pathways. Tacrolimus post-HI may have limited capacity to reduce brain injury, with higher doses increasing rat pup mortality. This work highlights the benefits of targeting neuroinflammation during the acute injurious period. More specific targeting of neuroinflammation, e.g., via T-cells, warrants further investigation.

Long-term normalization of calcineurin activity in model mice rescues Pin1 and attenuates Alzheimer's phenotypes without blocking peripheral T cell IL-2 response

BACKGROUND

Current treatments for Alzheimer's disease (AD) have largely failed to yield significant therapeutic benefits. Novel approaches are desperately needed to help address this immense public health issue. Data suggests that early intervention at the first stages of mild cognitive impairment may have a greater chance for success. The calcineurin (CN)-Pin1 signaling cascade can be selectively targeted with tacrolimus (FK506), a highly specific, FDA-approved CN inhibitor used safely for > 20 years in solid organ transplant recipients. AD prevalence was significantly reduced in solid organ recipients treated with FK506.

METHODS

Time release pellets were used to deliver constant FK506 dosage to APP/PS1 mice without deleterious manipulation or handling. Immunofluorescence, histology, molecular biology, and behavior were used to evaluate changes in AD pathology.

RESULTS

FK506 can be safely and consistently delivered into juvenile APP/PS1 mice via time-release pellets to levels roughly seen in transplant patients, leading to the normalization of CN activity and reduction or elimination of AD pathologies including synapse loss, neuroinflammation, and cognitive impairment. Pin1 activity and function were rescued despite the continuing presence of high levels of transgenic Aβ42. Indicators of neuroinflammation including Iba1 positivity and IL-6 production were also reduced to normal levels. Peripheral blood mononuclear cells (PBMC) obtained during treatment or splenocytes isolated at euthanasia activated normally after mitogens.

CONCLUSIONS

Low-dose, constant FK506 can normalize CNS CN and Pin1 activity, suppress neuroinflammation, and attenuate AD-associated pathology without blocking peripheral IL-2 responses making repurposed FK506 a viable option for early, therapeutic intervention in AD.

Glutamatergic neurotransmission: A potential pharmacotherapeutic target for the treatment of cognitive disorders

In the mammalian brain, glutamate is regarded to be the primary excitatory neurotransmitter due to its widespread distribution and wide range of metabolic functions. Glutamate plays key roles in regulating neurogenesis, synaptogenesis, neurite outgrowth, and neuron survival in the brain. Ionotropic and metabotropic glutamate receptors, neurotransmitters, neurotensin, neurosteroids, and others co-ordinately formulate a complex glutamatergic network in the brain that maintains optimal excitatory neurotransmission. Cognitive activities are potentially synchronized by the glutamatergic activities in the brain via restoring synaptic plasticity. Dysfunctional glutamate receptors and other glutamatergic components are responsible for the aberrant glutamatergic activity in the brain that cause cognitive impairments, loss of synaptic plasticity, and neuronal damage. Thus, controlling the brain's glutamatergic transmission and modifying glutamate receptor function could be a potential therapeutic strategy for cognitive disorders. Certain drugs that regulate glutamate receptor activities have shown therapeutic promise in improving cognitive functions in preclinical and clinical studies. However, several issues regarding precise functional information of glutamatergic activity are yet to be comprehensively understood. The present article discusses the scope of developing glutamatergic systems as prospective pharmacotherapeutic targets to treat cognitive disorders. Special attention has been given to recent developments, challenges, and future prospects.

Localization of drug biodistribution in a 3D-bioengineered subcutaneous neovascularized microenvironment

Local immunomodulation has shown the potential to control the immune response in a site-specific manner for wound healing, cancer, allergy, and cell transplantation, thus abrogating adverse effects associated with systemic administration of immunotherapeutics. Localized immunomodulation requires confining the biodistribution of immunotherapeutics on-site for maximal immune control and minimal systemic drug exposure. To this end, we developed a 3D-printed subcutaneous implant termed 'NICHE', consisting of a bioengineered vascularized microenvironment enabled by sustained drug delivery on-site. The NICHE was designed as a platform technology for investigating local immunomodulation in the context of cell therapeutics and cancer vaccines. Here we studied the ability of the NICHE to localize the PK and biodistribution of different model immunomodulatory agents in vivo. For this, we first performed a mechanistic evaluation of the microenvironment generated within and surrounding the NICHE, with emphasis on the parameters related to molecular transport. Second, we longitudinally studied the biodistribution of ovalbumin, cytotoxic T lymphocyte-associated antigen-4-Ig (CTLA4Ig), and IgG delivered locally via NICHE over 30 days. Third, we used our findings to develop a physiologically-based pharmacokinetic (PBPK) model. Despite dense and mature vascularization within and surrounding the NICHE, we showed sustained orders of magnitude higher molecular drug concentrations within its microenvironment as compared to systemic circulation and major organs. Further, the PBPK model was able to recapitulate the biodistribution of the 3 molecules with high accuracy (r ​> ​0.98). Overall, the NICHE and the PBPK model represent an adaptable platform for the investigation of local immunomodulation strategies for a wide range of biomedical applications.

Murine glial progenitor cells transplantation and synthetic PreImplantation Factor (sPIF) reduces inflammation and early motor impairment in ALS mice

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuronal disorder characterized by neuronal degeneration and currently no effective cure is available to stop or delay the disease from progression. Transplantation of murine glial-restricted precursors (mGRPs) is an attractive strategy to modulate ALS development and advancements such as the use of immune modulators could potentially extend graft survival and function. Using a well-established ALS transgenic mouse model (SOD1^G93A), we tested mGRPs in combination with the immune modulators synthetic PreImplantation Factor (sPIF), Tacrolimus (Tac), and Costimulatory Blockade (CB). We report that transplantation of mGRPs into the cisterna magna did not result in increased mice survival. The addition of immunomodulatory regimes again did not increase mice lifespan but improved motor functions and sPIF was superior compared to other immune modulators. Immune modulators did not affect mGRPs engraftment significantly but reduced pro-inflammatory cytokine production. Finally, sPIF and CB reduced the number of microglial cells and prevented neuronal number loss. Given the safety profile and a neuroprotective potential of sPIF, we envision its clinical application in near future.

Two Decades of Hand Transplantation: A Systematic Review of Outcomes

ABSTRACT

Hand transplantation for upper extremity amputation provides a unique treatment that restores form and function, which may not be achieved by traditional reconstruction and prosthetics. However, despite enhancing quality of life, hand transplantation remains controversial, because of immunological complications, transplant rejection, and medication effects. This systematic literature review sought to collect information on current experiences and outcomes of hand transplants to determine the efficacy and utility of hand transplants. The databases PubMed, Scopus, and Embase were analyzed with combinations of "hand" or "upper extremity" or "arm" and "transplant" or "allograft," with information collected on recipient characteristics, details of transplant, immunological outcomes, functional outcomes, and complications. Functional outcomes, as measured by Disabilities of Arm, Shoulder and Hand score, were compared between patient groups using Wilcoxon signed-rank test or 1-way analysis of variance test and post hoc Tukey test. Within the 108 articles that fulfilled inclusion and exclusion criteria, there were 96 patients with 148 hand transplants. There were 57 patients who experienced acute rejection and 5 patients with chronic rejection. Disabilities of the Arm, Shoulder and Hand scores significantly decreased after hand transplantation and were significantly lower for distal transplants compared with proximal transplants. There were 3 patients with concurrent face transplantation and 2 patients with simultaneous leg transplants. Sixteen patients experienced amputation of the hand transplant, and there were 5 deaths. This study found that hand transplantation provides significant restoration of function and form, especially for proximal transplants. Reduction in complications, such as rejection and amputation, can be achieved by decreasing medication cost and patient education.

Tacrolimus Combined with Corticosteroids Improved the Outcome of CIDP Patients with Autoantibodies Against Paranodal Proteins

PURPOSE

To investigate the response of tacrolimus to chronic inflammatory demyelinating polyneuropathy (CIDP) with autoantibodies against paranodal proteins, including neurofascin-155 (NF155), contactin-1 (CNTN1) and contactin-associated protein 1 (Caspr1).

METHODS

We retrospectively reviewed all CIDP patients who carried anti-NF155, CNTN1 and Caspr1 antibodies and were treated with tacrolimus at Tongji hospital from Jan 2018 to Apr 2021.

RESULTS

There were 58 patients with CIDP and only 9 patients had autoantibodies against paranodal proteins (17.2%). Five of the 9 patients received tacrolimus treatment with an initial dose of 2-3 mg once daily. One patient with anti-CNTN1 antibody started tacrolimus and corticosteroid treatment, at the first episode and eventually achieved full clinical remission without relapse. Four patients with anti-NF155 or -Caspr1 antibodies experienced relapse during corticosteroids tapering. Then, they were given oral tacrolimus and presented with clinical improvement. During follow-up, only one patient developed worsening weakness due to unreasonable tacrolimus discontinuation. Moreover, 3 patients were successfully withdrawn from corticosteroids and 2 patients took corticosteroids at low maintenance dose (10mg/d) after tacrolimus treatment. No severe adverse events were observed in all the patients.

CONCLUSION

Patients with autoantibodies against paranodal proteins had a better long-term outcome after adding tacrolimus. Combination therapy with corticosteroids and tacrolimus may be an effective therapeutic regimen.

Immunosuppressive Drugs

Immunosuppressant is a class of medicines that inhibit or decrease the intensity of the immune response in the body. Most of these medications are used to allow the body less likely to resist a transplanted organ. In solid organ transplantation, immunosuppressive agents are needed for the activation of early-stage immunosuppression, the management of late-stage immunosuppression or for the maintenance of organ rejection. The emergence of novel agents and improvements in immunosuppression regimens after transplantation are significant factors leading to this progress. However, these drugs also increase the risk of infection, cancers and specific adverse side effects specific to each agent in patients particularly in pregnant women and fertility issues. Corona virus disease being hot topic of debate is has given positive outcome to immunosuppressive drugs however need more attention in future. Transplant centers across the world utilize multiple immunosuppression protocols; nevertheless, each patient can require an individually formulated immunosuppression regimen to manage the advantages and possible damage of treatment thus eliminating the likelihood of their primary disease recurrence.

Functional and immunological peculiarities of peripheral nerve allografts

This review addresses the accumulating evidence that live (not decellularized) allogeneic peripheral nerves are functionally and immunologically peculiar in comparison with many other transplanted allogeneic tissues. This is relevant because live peripheral nerve allografts are very effective at promoting recovery after segmental peripheral nerve injury via axonal regeneration and axon fusion. Understanding the immunological peculiarities of peripheral nerve allografts may also be of interest to the field of transplantation in general. Three topics are addressed: The first discusses peripheral nerve injury and the potential utility of peripheral nerve allografts for bridging segmental peripheral nerve defects via axon fusion and axon regeneration. The second reviews evidence that peripheral nerve allografts elicit a more gradual and less severe host immune response allowing for prolonged survival and function of allogeneic peripheral nerve cells and structures. Lastly, potential mechanisms that may account for the immunological differences of peripheral nerve allografts are discussed.

Mesenchymal stem cells and local tacrolimus delivery synergistically enhance neurite extension

BACKGROUND

The aim of this study was to investigate the combined effect of mesenchymal stem cells (MSC) and local delivery of tacrolimus (FK506) on nerve regeneration when applied to nerve autografts and decellularized allografts.

METHODS

A three-dimensional in vitro compartmented cell culture system consisting of a neonatal dorsal root ganglion adjacent to a nerve graft was used to evaluate the regenerating neurites into the peripheral nerve scaffold. Nerve autografts and allografts were treated with (i) undifferentiated MSCs, (ii) FK506 (100 ng/mL) or (iii) both (N = 9/group). After 48 hours, neurite extension was measured to quantify nerve regeneration and stem cell viability was evaluated.

RESULTS

Stem cell viability was confirmed in all MSC-treated grafts. Neurite extension was superior in autografts treated with FK506, and MSCs and FK506 combined (p < 0.001 and p = 0.0001, respectively), and autografts treated with MSCs (p = 0.12) were comparable to untreated autografts. In allografts, FK506 treatment and combined treatment were superior to controls (p < 0.001 and p = 0.0001, respectively), and treatment with MSCs (p = 0.09) was comparable to controls. All autograft groups were superior compared to their respective allograft treatment group (p < 0.05) in neurite extension.

CONCLUSIONS

Alone, either MSC or FK506 treatment improved neurite outgrowth, and combined they further enhanced neurite extension in both autografts and allografts.

Enhanced Nerve Regeneration by Exosomes Secreted by Adipose-Derived Stem Cells with or without FK506 Stimulation

Exosomes secreted by adipose-derived stem cells (ADSC-exo) reportedly improve nerve regeneration after peripheral nerve injury. Herein, we investigated whether pretreatment of ADSCs with FK506, an immunosuppressive drug that enhances nerve regeneration, could secret exosomes (ADSC-F-exo) that further augment nerve regeneration. Designed exosomes were topically applied to injured nerve in a mouse model of sciatic nerve crush injury to assess the nerve regeneration efficacy. Outcomes were determined by histomorphometric analysis of semi-thin nerve sections stained with toluidine blue, mouse neurogenesis PCR array, and neurotrophin expression in distal nerve segments. Isobaric tags for relative and absolute quantitation (iTRAQ) were used to profile potential exosomal proteins facilitating nerve regeneration. We observed that locally applied ADSC-exo and ADSC-F-exo significantly enhanced nerve regeneration after nerve crush injury. Pretreatment of ADSCs with FK506 failed to produce exosomes possessing more potent molecules for enhanced nerve regeneration. Proteomic analysis revealed that of 192 exosomal proteins detected in both ADSC-exo and ADSC-F-exo, histone deacetylases (HDACs), amyloid-beta A4 protein (APP), and integrin beta-1 (ITGB1) might be involved in enhancing nerve regeneration.

Effect of Tacrolimus on Peripheral Nerve Regeneration in Allograft Transplantation: A Light and Electron Microscopic Study

OBJECTIVES

Peripheral nerve injuries are common in Europe; however, the treatment techniques may lead to disabilities. This study aimed to evaluate the effect of tacrolimus use on the capacity of the epineural sheath graft to improve its regeneration quality in rat sciatic nerves as a treatment option for nerve injuries.

MATERIALS AND METHODS

In the experimental process, 30 male Sprague Dawley were used as recipients and 10 Wistar rats were used as donors. Under anesthesia, all rats were operated on to resect the sciatic nerve. The nerve tissue of Wistar rats was used as allograft. In the autograft group, the resected nerve was reversed and sutured, resulting in an epineural sheath graft. For the allograft groups, rats were randomly divided into 2 groups as the tacrolimus-treated group and the nontreated group after allograft transplant. Tacrolimus was administered intramuscularly at 0.1 mg/kg daily for 12 weeks. After the treatment period, rats were killed and evaluated histomorphologically with light and electron microscopy.

RESULTS

Histological examination showed no remarkable differences between different regions of the sciatic nerves (distal, middle, and proximal). The axonal density was decreased in the allograft groups compared with the autograft group (P < .001). Results showed that the number of mast cells was increased in the allograft group without tacrolimus treatment (P < .05). Similarly, there was a mild increase in mast cell count in the tacrolimus-treated allograft group.

CONCLUSIONS

Our results showed that tacrolimus use in rats with implanted epineural nerve sheath supported recovery in terms of morphological and physiological regeneration of the nerve.

Combined local delivery of tacrolimus and stem cells in hydrogel for enhancing peripheral nerve regeneration

The application of scaffold-based stem cell transplantation to enhance peripheral nerve regeneration has great potential. Recently, the neuroregenerative potential of tacrolimus (a U.S. Food and Drug Administration-approved immunosuppressant) has been explored. In this study, a fibrin gel-based drug delivery system for sustained and localized tacrolimus release was combined with rat adipose-derived mesenchymal stem cells (MSC) to investigate cell viability in vitro. Tacrolimus was encapsulated in poly(lactic-co-glycolic) acid (PLGA) microspheres and suspended in fibrin hydrogel, using concentrations of 0.01 and 100 ng/ml. Drug release over time was measured. MSCs were cultured in drug-released media collected at various days to mimic systemic exposure. MSCs were combined with (i) hydrogel only, (ii) empty PLGA microspheres in the hydrogel, (iii) 0.01, and (iv) 100 ng/ml of tacrolimus PLGA microspheres in the hydrogel. Stem cell presence and viability were evaluated. A sustained release of 100 ng/ml tacrolimus microspheres was observed for up to 35 days. Stem cell presence was confirmed and cell viability was observed up to 7 days, with no significant differences between groups. This study suggests that combined delivery of 100 ng/ml tacrolimus and MSCs in fibrin hydrogel does not result in cytotoxic effects and could be used to enhance peripheral nerve regeneration.

The interaction of stem cells and vascularity in peripheral nerve regeneration

The degree of nerve regeneration after peripheral nerve injury can be altered by the microenvironment at the site of injury. Stem cells and vascularity are postulated to be a part of a complex pathway that enhances peripheral nerve regeneration; however, their interaction remains unexplored. This review aims to summarize current knowledge on this interaction, including various mechanisms through which trophic factors are promoted by stem cells and angiogenesis. Angiogenesis after nerve injury is stimulated by hypoxia, mediated by vascular endothelial growth factor, resulting in the growth of pre-existing vessels into new areas. Modulation of distinct signaling pathways in stem cells can promote angiogenesis by the secretion of various angiogenic factors. Simultaneously, the importance of stem cells in peripheral nerve regeneration relies on their ability to promote myelin formation and their capacity to be influenced by the microenvironment to differentiate into Schwann-like cells. Stem cells can be acquired through various sources that correlate to their differentiation potential, including embryonic stem cells, neural stem cells, and mesenchymal stem cells. Each source of stem cells serves its particular differentiation potential and properties associated with the promotion of revascularization and nerve regeneration. Exosomes are a subtype of extracellular vesicles released from cell types and play an important role in cell-to-cell communication. Exosomes hold promise for future transplantation applications, as these vesicles contain fewer membrane-bound proteins, resulting in lower immunogenicity. This review presents pre-clinical and clinical studies that focus on selecting the ideal type of stem cell and optimizing stem cell delivery methods for potential translation to clinical practice. Future studies integrating stem cell-based therapies with the promotion of angiogenesis may elucidate the synergistic pathways and ultimately enhance nerve regeneration.

Proof that the high molecular weight immunophilin FKBP52 mediates the in vivo neuroregenerative effect of the macrolide FK506

The immunosuppressant drug FK506 (or tacrolimus) is a macrolide that binds selectively to immunophilins belonging to the FK506-binding protein (FKBP) subfamily, which are abundantly expressed proteins in neurons of the peripheral and central nervous systems. Interestingly, it has been reported that FK506 increases neurite outgrowth in cell cultures, implying a potential impact in putative treatments of neurodegenerative disorders and injuries of the nervous system. Nonetheless, the mechanism of action of this compound is poorly understood and remains to be elucidated, with the only certainty that its neurotrophic effect is independent of its primary immunosuppressant activity. In this study it is demonstrated that FK506 shows efficient neurotrophic action in vitro and profound effects on the recovery of locomotor activity, behavioural features, and erectile function of mice that underwent surgical spinal cord injury. The recovery of the locomotor activity was studied in knock-out mice for either immunophilin, FKBP51 or FKBP52. The experimental evidence demonstrates that the neurotrophic actions of FK506 are the consequence of its binding to FKBP52, whereas FK506 interaction with the close-related partner immunophilin FKBP51 antagonises the function of FKBP52. Importantly, our study also demonstrates that other immunophilins do not replace FKBP52. It is concluded that the final biological response is the resulting outcome of the drug binding to both immunophilins, FKBP51 and FKBP52, the latter being the one that commands the dominant neurotrophic action in vivo.

Role of tacrolimus in return of hand function after brachial plexus injury in a lung transplantation patient

We report a patient who has been on tacrolimus for bilateral lung transplantation and presented with a brachial plexus injury (BPI), with unusual improvement of lower trunk innervated hand function. The lower trunk injury with resultant left hand paralysis had developed after his sternotomy 18 months ago. He has been treated with tacrolimus as part of his immunosuppression protocol since the surgery, without severe side effects. Physical examination at 18 months demonstrated unusual excellent grip pattern and full opposition of his thumb with slight claw deformity of his ulnar two digits. While the neurotoxic effects of tacrolimus are more emphasised, the neuroregenerative properties have been recently explored. The recovery in this patient is unique and unusual after BPI and is most likely as a result of the low dose tacrolimus treatment.