Cell-Penetrating Delivery of Nitric Oxide by Biocompatible Dinitrosyl Iron Complex and Its Dermato-Physiological Implications

Modulating Nitric Oxide: Implications for Cytotoxicity and Cytoprotection

Despite the significant progress in the fields of biology, physiology, molecular medicine, and pharmacology; the designation of the properties of nitrogen monoxide in the regulation of life-supporting functions of the organism; and numerous works devoted to this molecule, there are still many open questions in this field. It is widely accepted that nitric oxide (•NO) is a unique molecule that, despite its extremely simple structure, has a wide range of functions in the body, including the cardiovascular system, the central nervous system (CNS), reproduction, the endocrine system, respiration, digestion, etc. Here, we systematize the properties of •NO, contributing in conditions of physiological norms, as well as in various pathological processes, to the mechanisms of cytoprotection and cytodestruction. Current experimental and clinical studies are contradictory in describing the role of •NO in the pathogenesis of many diseases of the cardiovascular system and CNS. We describe the mechanisms of cytoprotective action of •NO associated with the regulation of the expression of antiapoptotic and chaperone proteins and the regulation of mitochondrial function. The most prominent mechanisms of cytodestruction-the initiation of nitrosative and oxidative stresses, the production of reactive oxygen and nitrogen species, and participation in apoptosis and mitosis. The role of •NO in the formation of endothelial and mitochondrial dysfunction is also considered. Moreover, we focus on the various ways of pharmacological modulation in the nitroxidergic system that allow for a decrease in the cytodestructive mechanisms of •NO and increase cytoprotective ones.

Mechanistic and Kinetic Insights into Cellular Uptake of Biomimetic Dinitrosyl Iron Complexes and Intracellular Delivery of NO for Activation of Cytoprotective HO-1

Dinitrosyl iron unit (DNIU), [Fe(NO)2], is a natural metallocofactor for biological storage, delivery, and metabolism of nitric oxide (NO). In the attempt to gain a biomimetic insight into the natural DNIU under biological system, in this study, synthetic dinitrosyl iron complexes (DNICs) [(NO)2Fe(μ-SCH2CH2COOH)2Fe(NO)2] (DNIC-COOH) and [(NO)2Fe(μ-SCH2CH2COOCH3)2Fe(NO)2] (DNIC-COOMe) were employed to investigate the structure-reactivity relationship of mechanism and kinetics for cellular uptake of DNICs, intracellular delivery of NO, and activation of cytoprotective heme oxygenase (HO)-1. After rapid cellular uptake of dinuclear DNIC-COOMe through a thiol-mediated pathway (tmax = 0.5 h), intracellular assembly of mononuclear DNIC [(NO)2Fe(SR)(SCys)]n-/[(NO)2Fe(SR)(SCys-protein)]n- occurred, followed by O2-induced release of free NO (tmax = 1-2 h) or direct transfer of NO to soluble guanylate cyclase, which triggered the downstream HO-1. In contrast, steady kinetics for cellular uptake of DNIC-COOH via endocytosis (tmax = 2-8 h) and for intracellular release of NO (tmax = 4-6 h) reflected on the elevated activation of cytoprotective HO-1 (∼50-150-fold change at t = 3-10 h) and on the improved survival of DNIC-COOH-primed mesenchymal stem cell (MSC)/human corneal endothelial cell (HCEC) under stressed conditions. Consequently, this study unravels the bridging thiolate ligands in dinuclear DNIC-COOH/DNIC-COOMe as a switch to control the mechanism, kinetics, and efficacy for cellular uptake of DNICs, intracellular delivery of NO, and activation of cytoprotective HO-1, which poses an implication on enhanced survival of postengrafted MSC for advancing the MSC-based regenerative medicine.

Schwann cells acquire a repair phenotype after assembling into spheroids and show enhanced in vivo therapeutic potential for promoting peripheral nerve repair

The prognosis for postinjury peripheral nerve regeneration remains suboptimal. Although transplantation of exogenous Schwann cells (SCs) has been considered a promising treatment to promote nerve repair, this strategy has been hampered in practice by the limited availability of SC sources and an insufficient postengraftment cell retention rate. In this study, to address these challenges, SCs were aggregated into spheroids before being delivered to an injured rat sciatic nerve. We found that the three-dimensional aggregation of SCs induced their acquisition of a repair phenotype, as indicated by enhanced levels of c-Jun expression/activation and decreased expression of myelin sheath protein. Furthermore, our in vitro results demonstrated the superior potential of the SC spheroid-derived secretome in promoting neurite outgrowth of dorsal root ganglion neurons, enhancing the proliferation and migration of endogenous SCs, and recruiting macrophages. Moreover, transplantation of SC spheroids into rats after sciatic nerve transection effectively increased the postinjury nerve structure restoration and motor functional recovery rates, demonstrating the therapeutic potential of SC spheroids. In summary, transplantation of preassembled SC spheroids may hold great potential for enhancing the cell delivery efficiency and the resultant therapeutic outcome, thereby improving SC-based transplantation approaches for promoting peripheral nerve regeneration.

The Transplantation of 3-Dimensional Spheroids of Adipose-Derived Stem Cells Promotes Achilles Tendon Healing in Rabbits by Enhancing the Proliferation of Tenocytes and Suppressing M1 Macrophages

BACKGROUND

Tendons have limited regenerative potential, so healing of ruptured tendon tissue requires a prolonged period, and the prognosis is suboptimal. Although stem cell transplantation-based approaches show promise for accelerating tendon repair, the resultant therapeutic efficacy remains unsatisfactory.

HYPOTHESIS

The transplantation of stem cells preassembled as 3-dimensional spheroids achieves a superior therapeutic outcome compared with the transplantation of single-cell suspensions.

STUDY DESIGN

Controlled laboratory study.

METHODS

Adipose-derived stem cells (ADSCs) were assembled as spheroids using a methylcellulose hydrogel system. The secretome of ADSC suspensions or spheroids was collected and utilized to treat tenocytes and macrophages to evaluate their therapeutic potential and investigate the mechanisms underlying their effects. RNA sequencing was performed to investigate the global difference in gene expression between ADSC suspensions and spheroids in an in vitro inflammatory microenvironment. For the in vivo experiment, rabbits that underwent Achilles tendon transection, followed by stump suturing, were randomly assigned to 1 of 3 groups: intratendinous injection of saline, rabbit ADSCs as conventional single-cell suspensions, or preassembled ADSC spheroids. The tendons were harvested for biomechanical testing and histological analysis at 4 weeks postoperatively.

RESULTS

Our in vitro results demonstrated that the secretome of ADSCs assembled as spheroids exhibited enhanced modulatory activity in (1) tenocyte proliferation (P = .015) and migration (P = .001) by activating extracellular signal-regulated kinase (ERK) signaling and (2) the suppression of the secretion of interleukin-6 (P = .005) and interleukin-1α (P = .042) by M1 macrophages via the COX-2/PGE2/EP4 signaling axis. Gene expression profiling of cells exposed to an inflammatory milieu revealed significantly enriched terms that were associated with the immune response, cytokines, and tissue remodeling in preassembled ADSC spheroids. Ex vivo fluorescence imaging revealed that the engraftment efficiency of ADSCs in the form of spheroids was higher than that of ADSCs in single-cell suspensions (P = .003). Furthermore, the transplantation of ADSC spheroids showed superior therapeutic effects in promoting the healing of sutured stumps, as evidenced by improvements in the tensile strength (P = .019) and fiber alignment (P < .001) of the repaired tendons.

CONCLUSION

The assembly of ADSCs as spheroids significantly advanced their potential to harness tenocytes and macrophages. As a proof of concept, this study clearly demonstrates the effectiveness of using ADSC spheroids to promote tendon regeneration.

CLINICAL RELEVANCE

The present study lays a foundation for future clinical applications of stem cell spheroid-based therapy for the management of tendon injuries.

The neddylation inhibitor MLN4924 inhibits proliferation and triggers apoptosis of oral cancer cells but not for normal cells

Increased neddylation benefits the survival of several types of cancer cells. The inhibition of neddylation has the potential to exert anticancer effects but is rarely assessed in oral cancer cells. This study aimed to investigate the antiproliferation potential of a neddylation inhibitor MLN4924 (pevonedistat) for oral cancer cells. MLN4924 inhibited the cell viability of oral cancer cells more than that of normal oral cells (HGF-1) with 100% viability, that is, IC50 values of oral cancer cells (CAL 27, OC-2, and Ca9-22) are 1.8, 1.4, and 1.9 μM. MLN4924 caused apoptotic changes such as the subG1 accumulation, activation of annexin V, pancaspase, and caspases 3/8/9 of oral cancer cells at a greater rate than in normal oral cells. MLN4924 induced greater oxidative stress in oral cancer cells compared to normal cells by upregulating reactive oxygen species and mitochondrial superoxide and depleting the mitochondrial membrane potential and glutathione. In oral cancer cells, preferential inductions also occurred for DNA damage (γH2AX and 8-oxo-2'-deoxyguanosine). Therefore, this investigation demonstrates that MLN4924 is a potential anti-oral-cancer agent showing preferential inhibition of apoptosis and promotion of DNA damage with fewer cytotoxic effects on normal cells.

Conjugation of bone grafts with NO-delivery dinitrosyl iron complexes promotes synergistic osteogenesis and angiogenesis in rat calvaria bone defects

Craniofacial/jawbone deformities remain a significant clinical challenge in restoring facial/dental functions and esthetics. Despite the reported therapeutics for clinical bone tissue regeneration, the bioavailability issue of autografts and limited regeneration efficacy of xenografts/synthetic bone substitutes, however, inspire continued efforts towards functional conjugation and improvement of bioactive bone graft materials. Regarding the potential of nitric oxide (NO) in tissue engineering, herein, functional conjugation of NO-delivery dinitrosyl iron complex (DNIC) and osteoconductive bone graft materials was performed to optimize the spatiotemporal control over the delivery of NO and to activate synergistic osteogenesis and angiogenesis in rat calvaria bone defects. Among three types of biomimetic DNICs, [Fe2(μ-SCH2CH2COOH)2(NO)4] (DNIC-COOH) features a steady kinetics for cellular uptake by MC3T3-E1 osteoblast cells followed by intracellular assembly of protein-bound DNICs and release of NO. This steady kinetics for intracellular delivery of NO by DNIC-COOH rationalizes its biocompatibility and wide-spectrum cell proliferation effects on MC3T3-E1 osteoblast cells and human umbilical vein endothelial cells (HUVECs). Moreover, the bridging [SCH2CH2COOH]- thiolate ligands in DNIC-COOH facilitate its chemisorption to deproteinized bovine bone mineral (DBBM) and physisorption onto TCP (β-tricalcium phosphate), respectively, which provides a mechanism to control the kinetics for the local release of loaded DNIC-COOH. Using rats with calvaria bone defects as an in vivo model, DNIC-DBBM/DNIC-TCP promotes the osteogenic and angiogenic activity ascribed to functional conjugation of osteoconductive bone graft materials and NO-delivery DNIC-COOH. Of importance, the therapeutic efficacy of DNIC-DBBM/DNIC-TCP on enhanced compact bone formation after treatment for 4 and 12 weeks supports the potential for clinical application to regenerative medicine.

Neuroprotective Effect of NO-Delivery Dinitrosyl Iron Complexes (DNICs) on Amyloid Pathology in the Alzheimer's Disease Cell Model

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive impairment, memory loss, and behavioral deficits. β-amyloid1-42 (Aβ1-42) aggregation is a significant cause of the pathogenesis in AD. Despite the numerous types of research, the current treatment efficacy remains insufficient. Hence, a novel therapeutic strategy is required. Nitric oxide (NO) is a multifunctional gaseous molecule. NO displays a neuroprotective role in the central nervous system by inhibiting the Aβ aggregation and rescuing memory and learning deficit through the NO signaling pathway. Targeting the NO pathway might be a therapeutic option; however, NO has a limited half-life under the biological system. To address this issue, a biomimetic dinitrosyl iron complex [(NO)2Fe(μ-SCH2CH2COOH)2Fe(NO)2] (DNIC-COOH) that could stably deliver NO was explored in the current study. To determine whether DNIC-COOH exerts anti-AD efficacy, DNIC-COOH was added to neuron-like cells and primary cortical neurons along with Aβ1-42. This study found that DNIC-COOH protected neuronal cells from Aβ-induced cytotoxicity, potentiated neuronal functions, and facilitated Aβ1-42 degradation through the NO-sGC-cGMP-AKT-GSK3β-CREB/MMP-9 pathway.

Beneficial Effects of Dinitrosyl Iron Complexes on Wound Healing Compared to Commercial Nitric Oxide Plasma Generator

Nitric oxide (NO) is a gaseous molecule which plays a key role in wound healing. Previously, we identified the optimal conditions for wound healing strategies using NO donors and an air plasma generator. The aim of this study was to compare the wound healing effects of binuclear dinitrosyl iron complexes with glutathione (B-DNIC-GSH) and NO-containing gas flow (NO-CGF) at their optimal NO doses (0.04 mmol for B-DNIC-GSH and 1.0 mmol for NO-CGF per 1 cm²) in a rat full-thickness wound model over a 3-week period. Excised wound tissues were studied by light and transmission electron microscopy and immunohistochemical, morphometrical and statistical methods. Both treatments had an identical stimulating impact on wound healing, which indicated a higher dosage effectiveness of B-DNIC-GSH compared to the NO-CGF. B-DNIC-GSH spray application reduced inflammation and promoted fibroblast proliferation, angiogenesis and the growth of granulation tissue during the first 4 days after injury. However, prolonged NO spray effects were mild compared to NO-CGF. Future studies should determine the optimal B-DNIC-GSH solution course for a more effective wound healing stimulation.

Genomic capacities for Reactive Oxygen Species metabolism across marine phytoplankton

Marine phytoplankton produce and scavenge Reactive Oxygen Species, to support cellular processes, while limiting damaging reactions. Some prokaryotic picophytoplankton have, however, lost all genes encoding scavenging of hydrogen peroxide. Such losses of metabolic function can only apply to Reactive Oxygen Species which potentially traverse the cell membrane outwards, before provoking damaging intracellular reactions. We hypothesized that cell radius influences which elements of Reactive Oxygen Species metabolism are partially or fully dispensable from a cell. We therefore investigated genomes and transcriptomes from diverse marine eukaryotic phytoplankton, ranging from 0.4 to 44 μm radius, to analyze the genomic allocations encoding enzymes metabolizing Reactive Oxygen Species. Superoxide has high reactivity, short lifetimes and limited membrane permeability. Genes encoding superoxide scavenging are ubiquitous across phytoplankton, but the fractional gene allocation decreased with increasing cell radius, consistent with a nearly fixed set of core genes for scavenging superoxide pools. Hydrogen peroxide has lower reactivity, longer intracellular and extracellular lifetimes and readily crosses cell membranes. Genomic allocations to both hydrogen peroxide production and scavenging decrease with increasing cell radius. Nitric Oxide has low reactivity, long intracellular and extracellular lifetimes and readily crosses cell membranes. Neither Nitric Oxide production nor scavenging genomic allocations changed with increasing cell radius. Many taxa, however, lack the genomic capacity for nitric oxide production or scavenging. The probability of presence of capacity to produce nitric oxide decreases with increasing cell size, and is influenced by flagella and colony formation. In contrast, the probability of presence of capacity to scavenge nitric oxide increases with increasing cell size, and is again influenced by flagella and colony formation.

CXCR4-targeted nitric oxide nanoparticles deliver PD-L1 siRNA for immunotherapy against glioblastoma

While immunotherapy has emerged as a promising strategy to treat glioblastoma multiforme (GBM), the limited availability of immunotherapeutic agents in tumors due to the presence of the blood-brain barrier (BBB) and immunosuppressive tumor microenvironment dampens efficacy. Nitric oxide (NO) plays a role in modulating both the BBB and tumor vessels and could thus be delivered to disrupt the BBB and improve the delivery of immunotherapeutics into GBM tumors. Herein, we report an immunotherapeutic approach that utilizes CXCR4-targeted lipid‑calcium-phosphate nanoparticles with NO donors (LCP-NO NPs). The delivery of NO resulted in enhanced BBB permeability and thus improved gene delivery across the BBB. CXCR4-targeted LCP-NO NPs delivered siRNA against the immune checkpoint ligand PD-L1 to GBM tumors, silenced PD-L1 expression, increased cytotoxic T cell infiltration and activation in GBM tumors, and suppressed GBM progression. Thus, the codelivery of NO and PD-L1 siRNA by these CXCR4-targeted NPs may serve as a potential immunotherapy for GBM.

Cationic dinitrosyl iron complexes with thiourea exhibit selective toxicity to brain tumor cells in vitro

The cytotoxic activity of a series of dinitrosyl iron complexes (DNICs) with thioureas against cells of different origin has been studied in this work. The cytotoxicity of the studied DNICs proved to be substantially different depending on the structure of the complexes and cell line. Complexes with thiourea and 1,3-dimethylthiourea were found to induce notable cell death in different cell lines of both cancerous and non-cancerous origin, while the N-ethylthiourea-bearing complex induced cell death in cells derived from brain tumors. The studied DNICs effectively release NO while decomposing in solutions, as follows from the electrochemical analysis. It was found that the cytotoxic effects of the studied DNICs did not correlate with their NO-donating ability, hence suggesting that their cytotoxic activity is, in a big part, defined by the long-lived nitrosyl iron-sulfur intermediates formed during the decomposition of the complexes. The structures of the products formed upon hydrolytic decomposition of all studied DNICs have been studied by electrospray ionization mass spectrometry. Stable high-molecular cluster ions containing NO groups namely [Fe₄S₃(NO)₇]^- (Roussin's "black salt" anion), [Fe₄S₃(NO)⁵]^-, [Fe₄S₄(NO)₄]^-, [Fe₄S₃(NO)₄]^- and [Fe₄S₃(NO)₆]^- have been detected in the solution of the N-ethylthiourea-bearing complex. The mechanism of Roussin's "black salt" anion formation in a solution of DNIC with N'-ethylthiourea was studied using density functional theory. This moved us near understanding the reasons for the formation of biologically active intermediates upon the decomposition of the complex with N'-ethylthiourea, which are apparently responsible for the unique antiglioma activity of the complex.

Strontium Peroxide-Loaded Composite Scaffolds Capable of Generating Oxygen and Modulating Behaviors of Osteoblasts and Osteoclasts

The reconstruction of bone defects remains challenging. The utilization of bone autografts, although quite promising, is limited by several drawbacks, especially substantial donor site complications. Recently, strontium (Sr), a bioactive trace element with excellent osteoinductive, osteoconductive, and pro-angiogenic properties, has emerged as a potential therapeutic agent for bone repair. Herein, a strontium peroxide (SrO₂)-loaded poly(lactic-co-glycolic acid) (PLGA)-gelatin scaffold system was developed as an implantable bone substitute. Gelatin sponges serve as porous osteoconductive scaffolds, while PLGA not only reinforces the mechanical strength of the gelatin but also controls the rate of water infiltration. The encapsulated SrO₂ can release Sr²⁺ in a sustained manner upon exposure to water, thus effectively stimulating the proliferation of osteoblasts and suppressing the formation of osteoclasts. Moreover, SrO₂ can generate hydrogen peroxide and subsequent oxygen molecules to increase local oxygen tension, an essential niche factor for osteogenesis. Collectively, the developed SrO₂-loaded composite scaffold shows promise as a multifunctional bioactive bone graft for bone tissue engineering.

Magnetic Responsive Release of Nitric Oxide from an MOF-Derived Fe3O4@PLGA Microsphere for the Treatment of Bacteria-Infected Cutaneous Wound

Nitric oxide (NO) is an essential endogenous signaling molecule regulating multifaceted physiological functions in the (cardio)vascular, neuronal, and immune systems. Due to the short half-life and location-/concentration-dependent physiological function of NO, translational application of NO as a novel therapeutic approach, however, awaits a strategy for spatiotemporal control on the delivery of NO. Inspired by the magnetic hyperthermia and magneto-triggered drug release featured by Fe₃O₄ conjugates, in this study, we aim to develop a magnetic responsive NO-release material (MagNORM) featuring dual NO-release phases, namely, burst and steady release, for the selective activation of NO-related physiology and treatment of bacteria-infected cutaneous wound. After conjugation of NO-delivery [Fe(μ-S-thioglycerol)(NO)₂]₂ with a metal-organic framework (MOF)-derived porous Fe₃O₄@C, encapsulation of obtained conjugates within the thermo-responsive poly(lactic-co-glycolic acid) (PLGA) microsphere completes the assembly of MagNORM. Through continuous/pulsatile/no application of the alternating magnetic field (AMF) to MagNORM, moreover, burst/intermittent/slow release of NO from MagNORM demonstrates the AMF as an ON/OFF switch for temporal control on the delivery of NO. Under continuous application of the AMF, in particular, burst release of NO from MagNORM triggers an effective anti-bacterial activity against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). In addition to the magneto-triggered bactericidal effect of MagNORM against E. coli-infected cutaneous wound in mice, of importance, steady release of NO from MagNORM without the AMF promotes the subsequent collagen formation and wound healing in mice.

Enhanced Oral NO Delivery through Bioinorganic Engineering of Acid-Sensitive Prodrug into a Transformer-like DNIC@MOF Microrod

Nitric oxide (NO) is an endogenous gasotransmitter regulating alternative physiological processes in the cardiovascular system. To achieve translational application of NO, continued efforts are made on the development of orally active NO prodrugs for long-term treatment of chronic cardiovascular diseases. Herein, immobilization of NO-delivery [Fe₂(μ-SCH₂CH₂COOH)₂(NO)₄] (DNIC-2) onto MIL-88B, a metal-organic framework (MOF) consisting of biocompatible Fe³⁺ and 1,4-benzenedicarboxylate (BDC), was performed to prepare a DNIC@MOF microrod for enhanced oral delivery of NO. In simulated gastric fluid, protonation of the BDC linker in DNIC@MOF initiates its transformation into a DNIC@tMOF microrod, which consisted of DNIC-2 well dispersed and confined within the BDC-based framework. Moreover, subsequent deprotonation of the BDC-based framework in DNIC@tMOF under simulated intestinal conditions promotes the release of DNIC-2 and NO. Of importance, this discovery of transformer-like DNIC@MOF provides a parallel insight into its stepwise transformation into DNIC@tMOF in the stomach followed by subsequent conversion into molecular DNIC-2 in the small intestine and release of NO in the bloodstream of mice. In comparison with acid-sensitive DNIC-2, oral administration of DNIC@MOF results in a 2.2-fold increase in the oral bioavailability of NO to 65.7% in mice and an effective reduction of systolic blood pressure (SBP) to a ΔSBP of 60.9 ± 4.7 mmHg in spontaneously hypertensive rats for 12 h.