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

A functional tacrolimus-releasing nerve wrap for enhancing nerve regeneration following surgical nerve repair

JOURNAL/nrgr/04.03/01300535-202501000-00036/figure1/v/2024-05-14T021156Z/r/image-tiff Axonal regeneration following surgical nerve repair is slow and often incomplete, resulting in poor functional recovery which sometimes contributes to lifelong disability. Currently, there are no FDA-approved therapies available to promote nerve regeneration. Tacrolimus accelerates axonal regeneration, but systemic side effects presently outweigh its potential benefits for peripheral nerve surgery. The authors describe herein a biodegradable polyurethane-based drug delivery system for the sustained local release of tacrolimus at the nerve repair site, with suitable properties for scalable production and clinical application, aiming to promote nerve regeneration and functional recovery with minimal systemic drug exposure. Tacrolimus is encapsulated into co-axially electrospun polycarbonate-urethane nanofibers to generate an implantable nerve wrap that releases therapeutic doses of bioactive tacrolimus over 31 days. Size and drug loading are adjustable for applications in small and large caliber nerves, and the wrap degrades within 120 days into biocompatible byproducts. Tacrolimus released from the nerve wrap promotes axon elongation in vitro and accelerates nerve regeneration and functional recovery in preclinical nerve repair models while off-target systemic drug exposure is reduced by 80% compared with systemic delivery. Given its surgical suitability and preclinical efficacy and safety, this system may provide a readily translatable approach to support axonal regeneration and recovery in patients undergoing nerve surgery.

Simultaneous determination of HD56, a novel prodrug, and its active metabolite in cynomolgus monkey plasma using LC-MS/MS for elucidating its pharmacokinetic profile

An LC-MS/MS method was developed and validated for the simultaneous determination of the carboxylic acid ester precursor HD56 and the active product HD561 in cynomolgus monkey plasma. Then, the pharmacokinetic characteristics of both compounds following single and multiple i.g. administrations in cynomolgus monkeys were elucidated. In the method, chromatographic separation was achieved with a C18 reversed-phase column and the target quantification was carried out by an electrospray ionization (ESI) source coupled with triple quadrupole mess detector in positive ionization mode with multiple reaction monitoring (MRM) approach. Using the quantification method, the in vitro stability of HD56 in plasma and HD56 pharmacokinetic behavior after i.g. administration in cynomolgus monkey were investigated. It was approved that HD56 did convert into HD561 post-administration. The overall systemic exposure of HD561 post-conversion from HD56 accounted for only about 17% of HD56. After repeated administration at the same dose, there was no significant difference in exposure levels of both HD56 and HD561. However, after multiple dosing, the exposure of HD56 tended to decrease while that of HD561 tended to increase, resulting in a 30% in the exposure ratio. Remarkably, with a carboxylesterase (CES) activity profile akin to humans, the observed in vivo pharmacokinetic profile in cynomolgus monkeys holds promise for predicting HD56/HD561 PK profiles in humans.

Reaching New Heights: A Comprehensive Study of Hand Transplantations in Korea after Institutionalization of Hand Transplantation Law

PURPOSE

With the revision of the Organ and Transplantation Act in 2018, the hand has become legal as an area of transplantable organs in Korea. In January 2021, the first hand allotransplantation since legalization was successfully performed, and we have performed a total of three successful hand transplantation since then. By comparing and incorporating our experiences, this study aimed to provide a comprehensive reconstructive solution for hand amputation in Korea.

MATERIALS AND METHODS

Recipients were selected through a structured preoperative evaluation, and hand transplantations were performed at the distal forearm level. Postoperatively, patients were treated with three-drug immunosuppressive regimen, and functional outcomes were monitored.

RESULTS

The hand transplantations were performed without intraoperative complications. All patients had partial skin necrosis and underwent additional surgical procedures in 2 months after transplantation. After additional operations, no further severe complications were observed. Also, patients developed acute rejection within 3 months of surgery, but all resolved within 2 weeks after steroid pulse therapy. Motor and sensory function improved dramatically, and patients were very satisfied with the appearance and function of their transplanted hands.

CONCLUSION

Hand transplantation is a viable reconstructive option, and patients have shown positive functional and psychological outcomes. Although this study has limitations, such as the small number of patients and short follow-up period, we should focus on continued recovery of hand function, and be careful not to develop side effects from immunosuppressive drugs. Through the present study, we will continue to strive for a bright future regarding hand transplantation in Korea.

A New Graph Autoencoder-Based Consensus-Guided Model for scRNA-seq Cell Type Detection

Single-cell RNA sequencing (scRNA-seq) technology is famous for providing a microscopic view to help capture cellular heterogeneity. This characteristic has advanced the field of genomics by enabling the delicate differentiation of cell types. However, the properties of single-cell datasets, such as high dropout events, noise, and high dimensionality, are still a research challenge in the single-cell field. To utilize single-cell data more efficiently and to better explore the heterogeneity among cells, a new graph autoencoder (GAE)-based consensus-guided model (scGAC) is proposed in this article. The data are preprocessed into multiple top-level feature datasets. Then, feature learning is performed by using GAEs to generate new feature matrices, followed by similarity learning based on distance fusion methods. The learned similarity matrices are fed back to the GAEs to guide their feature learning process. Finally, the abovementioned steps are iterated continuously to integrate the final consistent similarity matrix and perform other related downstream analyses. The scGAC model can accurately identify critical features and effectively preserve the internal structure of the data. This can further improve the accuracy of cell type identification.

Advancing Nerve Regeneration: Translational Perspectives of Tacrolimus (FK506)

Peripheral nerve injuries have far-reaching implications for individuals and society, leading to functional impairments, prolonged rehabilitation, and substantial socioeconomic burdens. Tacrolimus, a potent immunosuppressive drug known for its neuroregenerative properties, has emerged in experimental studies as a promising candidate to accelerate nerve fiber regeneration. This review investigates the therapeutic potential of tacrolimus by exploring the postulated mechanisms of action in relation to biological barriers to nerve injury recovery. By mapping both the preclinical and clinical evidence, the benefits and drawbacks of systemic tacrolimus administration and novel delivery systems for localized tacrolimus delivery after nerve injury are elucidated. Through synthesizing the current evidence, identifying practical barriers for clinical translation, and discussing potential strategies to overcome the translational gap, this review provides insights into the translational perspectives of tacrolimus as an adjunct therapy for nerve regeneration.

The Role of Sensory Innervation in Homeostatic and Injury-Induced Corneal Epithelial Renewal

The cornea is the window through which we see the world. Corneal clarity is required for vision, and blindness occurs when the cornea becomes opaque. The cornea is covered by unique transparent epithelial cells that serve as an outermost cellular barrier bordering between the cornea and the external environment. Corneal sensory nerves protect the cornea from injury by triggering tearing and blink reflexes, and are also thought to regulate corneal epithelial renewal via unknown mechanism(s). When protective corneal sensory innervation is absent due to infection, trauma, intracranial tumors, surgery, or congenital causes, permanent blindness results from repetitive epithelial microtraumas and failure to heal. The condition is termed neurotrophic keratopathy (NK), with an incidence of 5:10,000 people worldwide. In this report, we review the currently available therapeutic solutions for NK and discuss the progress in our understanding of how the sensory nerves induce corneal epithelial renewal.

Adult spinal cord tissue transplantation combined with local tacrolimus sustained-release collagen hydrogel promotes complete spinal cord injury repair

The strategy of replacing a completely damaged spinal cord with allogenic adult spinal cord tissues (aSCs) can potentially repair complete spinal cord injury (SCI) in combination with immunosuppressive drugs, such as tacrolimus (Tac), which suppress transplant rejection and improve graft survival. However, daily systemic administration of immunosuppressive agents may cause harsh side effects. Herein, a localized, sustained Tac-release collagen hydrogel (Col/Tac) was developed to maximize the immune regulatory efficacy but minimize the side effects of Tac after aSC transplantation in complete SCI recipients. Thoracic aSCs of rat donors were transplanted into the complete thoracic spinal cord transection rat recipients, after which Col/Tac hydrogel was implanted. The Tac-encapsulated collagen hydrogel exhibited suitable mechanical properties and long-term sustained Tac release behaviour. After Col/Tac hydrogel implantation in SCI rats with aSC transplantation, the recipients' survival rate significantly improved and the side effects on tissues were reduced compared with those with conventional Tac medication. Moreover, treatment with the Col/Tac hydrogel exhibited similarly reduced immune rejection levels by regulating immune responses and promoted neurogenesis compared to daily Tac injections, and thus improved functional restoration. Localized delivery of immunosuppressive agents by the Col/Tac hydrogel may be a promising strategy for overcoming immune rejection of transplants, with significant potential for clinical application in the future.

Mitochondrial-nuclear communication by FKBP51 shuttling

The HSP90-binding immunophilin FKBP51 is a soluble protein that shows high homology and structural similarity with FKBP52. Both immunophilins are functionally divergent and often show antagonistic actions. They were first described in steroid receptor complexes, their exchange in the complex being the earliest known event in steroid receptor activation upon ligand binding. In addition to steroid-related events, several pleiotropic actions of FKBP51 have emerged during the last years, ranging from cell differentiation and apoptosis to metabolic and psychiatric disorders. On the other hand, mitochondria play vital cellular roles in maintaining energy homeostasis, responding to stress conditions, and affecting cell cycle regulation, calcium signaling, redox homeostasis, and so forth. This is achieved by proteins that are encoded in both the nuclear genome and mitochondrial genes. This implies active nuclear-mitochondrial communication to maintain cell homeostasis. Such communication involves factors that regulate nuclear and mitochondrial gene expression affecting the synthesis and recruitment of mitochondrial and nonmitochondrial proteins, and/or changes in the functional state of the mitochondria itself, which enable mitochondria to recover from stress. FKBP51 has emerged as a serious candidate to participate in these regulatory roles since it has been unexpectedly found in mitochondria showing antiapoptotic effects. Such localization involves the tetratricopeptide repeats domains of the immunophilin and not its intrinsic enzymatic activity of peptidylprolyl-isomerase. Importantly, FKBP51 abandons the mitochondria and accumulates in the nucleus upon cell differentiation or during the onset of stress. Nuclear FKBP51 enhances the enzymatic activity of telomerase. The mitochondrial-nuclear trafficking is reversible, and certain situations such as viral infections promote the opposite trafficking, that is, FKBP51 abandons the nucleus and accumulates in mitochondria. In this article, we review the latest findings related to the mitochondrial-nuclear communication mediated by FKBP51 and speculate about the possible implications of this phenomenon.

The Scaffold Immunophilin FKBP51 Is a Phosphoprotein That Undergoes Dynamic Mitochondrial-Nuclear Shuttling

The immunophilin FKBP51 forms heterocomplexes with molecular chaperones, protein-kinases, protein-phosphatases, autophagy-related factors, and transcription factors. Like most scaffold proteins, FKBP51 can use a simple tethering mechanism to favor the efficiency of interactions with partner molecules, but it can also exert more complex allosteric controls over client factors, the immunophilin itself being a putative regulation target. One of the simplest strategies for regulating pathways and subcellular localization of proteins is phosphorylation. In this study, it is shown that scaffold immunophilin FKBP51 is resolved by resolutive electrophoresis in various phosphorylated isoforms. This was evidenced by their reactivity with specific anti-phosphoamino acid antibodies and their fade-out by treatment with alkaline phosphatase. Interestingly, stress situations such as exposure to oxidants or in vivo fasting favors FKBP51 translocation from mitochondria to the nucleus. While fasting involves phosphothreonine residues, oxidative stress involves tyrosine residues. Molecular modeling predicts the existence of potential targets located at the FK1 domain of the immunophilin. Thus, oxidative stress favors FKBP51 dephosphorylation and protein degradation by the proteasome, whereas FK506 binding protects the persistence of the post-translational modification in tyrosine, leading to FKBP51 stability under oxidative conditions. Therefore, FKBP51 is revealed as a phosphoprotein that undergoes differential phosphorylations according to the stimulus.

Sustained Release of Tacrolimus From a Topical Drug Delivery System Promotes Corneal Reinnervation

Purpose

Corneal nerve fibers provide sensation and maintain the epithelial renewal process. Insufficient corneal innervation can cause neurotrophic keratopathy. Here, topically delivered tacrolimus is evaluated for its therapeutic potential to promote corneal reinnervation in rats.

Methods

A compartmentalized neuronal cell culture was used to determine the effect of locally delivered tacrolimus on sensory axon regeneration in vitro. The regenerating axons but not the cell bodies were exposed to tacrolimus (50 ng/mL), nerve growth factor (50 ng/mL), or a vehicle control. Axon area and length were measured after 48 hours. Then, a biodegradable nanofiber drug delivery system was fabricated via electrospinning of a tacrolimus-loaded polycarbonate–urethane polymer. Biocompatibility, degradation, drug biodistribution, and therapeutic effectiveness were tested in a rat model of neurotrophic keratopathy induced by stereotactic trigeminal nerve ablation.

Results

Sensory neurons whose axons were exposed to tacrolimus regenerated significantly more and longer axons compared to vehicle-treated cultures. Trigeminal nerve ablation in rats reliably induced corneal denervation. Four weeks after denervation, rats that had received tacrolimus topically showed similar limbal innervation but a significantly higher nerve fiber density in the center of the cornea compared to the non-treated control. Topically applied tacrolimus was detectable in the ipsilateral vitreal body, the plasma, and the ipsilateral trigeminal ganglion but not in their contralateral counterparts and vital organs after 4 weeks of topical release.

Conclusions

Locally delivered tacrolimus promotes axonal regeneration in vitro and corneal reinnervation in vivo with minimal systemic drug exposure.

Translational Relevance

Topically applied tacrolimus may provide a readily translatable approach to promote corneal reinnervation.

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.

Tacrolimus-Induced Neurotrophic Differentiation of Adipose-Derived Stem Cells as Novel Therapeutic Method for Peripheral Nerve Injury

Peripheral nerve injuries (PNIs) are frequent traumatic injuries across the globe. Severe PNIs result in irreversible loss of axons and myelin sheaths and disability of motor and sensory function. Schwann cells can secrete neurotrophic factors and myelinate the injured axons to repair PNIs. However, Schwann cells are hard to harvest and expand in vitro, which limit their clinical use. Adipose-derived stem cells (ADSCs) are easily accessible and have the potential to acquire neurotrophic phenotype under the induction of an established protocol. It has been noticed that Tacrolimus/FK506 promotes peripheral nerve regeneration, despite the mechanism of its pro-neurogenic capacity remains undefined. Herein, we investigated the neurotrophic capacity of ADSCs under the stimulation of tacrolimus. ADSCs were cultured in the induction medium for 18 days to differentiate along the glial lineage and were subjected to FK506 stimulation for the last 3 days. We discovered that FK506 greatly enhanced the neurotrophic phenotype of ADSCs which potentiated the nerve regeneration in a crush injury model. This work explored the novel application of FK506 synergized with ADSCs and thus shed promising light on the treatment of severe PNIs.

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.

Biosynthesis of Nonimmunosuppressive ProlylFK506 Analogues with Neurite Outgrowth and Synaptogenic Activity

Separating the immunosuppressive activity of FK506 (1) from its neurotrophic activity is required to develop FK506 analogues as drugs for the treatment of neuronal diseases. Two new FK506 analogues, 9-deoxo-36,37-dihydro-prolylFK506 (2) and 9-deoxo-31-O-demethyl-36,37-dihydro-prolylFK506 (3) containing a proline moiety instead of the pipecolate ring at C-1 and modifications at the C-9/C-31 and C-36-C-37 positions, respectively, were biosynthesized, and their biological activities were evaluated. The proline substitution in 9-deoxo-36,37-dihydroFK506 and 9-deoxo-31-O-demethyl-36,37-dihydroFK506 reduced immunosuppressive activity by more than 120-fold, as previously observed. Compared with FK506 (1), 2 and 3 exhibited ∼1.2 × 105- and 2.2 × 105-fold reductions in immunosuppressive activity, respectively, whereas they retained almost identical neurite outgrowth activity. Furthermore, these compounds significantly increased the strength of synaptic transmission, confirming that replacement of the pipecolate ring with a proline is critical to reduce the strong immunosuppressive activity of FK506 (1) while enhancing its neurotrophic activity.