Hydrogen Sulfide Promotes Osteogenesis by Modulating Macrophage Polarization

Endogenous sulfur dioxide deficiency impairs bone regeneration through abolishing S-sulfenylating p38 at cysteine 211

Bone defects result in substantial medical expenses and a diminished quality of life for patients. Macrophage polarization is crucial in the bone regeneration process mediated by bone marrow-derived mesenchymal stem cells (BMSCs). macrophage-derived sulfur dioxide (SO2), the fourth endogenous gas signaling molecule, following hydrogen sulfide (H2S), has been shown to regulate macrophage chemotaxis and inflammatory responses. Nevertheless, the specific regulatory effects and mechanisms of macrophage-derived SO2 on bone regeneration are not yet fully understood. This study reveals for the first time that the absence of macrophage-derived SO2 promotes M1 macrophage polarization, whereas the administration of exogenous SO2 donors inhibits M1 polarization. The deficiency of macrophage-derived SO2 results in impaired osteogenic differentiation of BMSCs, whereas the administration of SO2 donors enhances this differentiation process. Further investigations have elucidated that p38α MAPK (p38) is crucial in mediating SO2's effects on M1 macrophage polarization and BMSCs osteogenic differentiation. Mechanistically, SO2 induces S-sulfenylation of p38 in macrophages, an effect that can be reversed by the thiol reductant dithiothreitol. Additionally, the C211S mutation in p38 abrogates the SO2-induced S-sulfenylation of p38, thereby preventing the inhibition of p38 activation and subsequently disrupting the regulation of M1 macrophage polarization and BMSCs osteogenic differentiation. In a model of mouse calvarial bone defects, we consistently observed that inhibiting SO2 production using the SO2-generating enzyme inhibitor HDX impaired bone regeneration capacity in mice, whereas the administration of an SO2 donor enhanced this capacity. In summary, macrophage-derived SO2 S-sulfenylates p38 at cysteine 211, thereby suppressing p38 activation, which inhibits M1 polarization and subsequently maintains the osteogenic differentiation of BMSCs. This study is the first to elucidate the role and mechanism of SO2 in sustaining osteogenesis, offering a novel strategy for addressing bone defect-related disorders.

Design and Development of ZnO/BMP-2 Sustained-Release Hydrogel for Enhanced Bone Tissue Repair

Bone infections caused by microbial invasion often lead to tissue damage and functional impairment. Although bone implants are a primary clinical approach to reduce recurrence and promote healing, the growing challenge of antimicrobial resistance necessitates innovative postoperative therapies to improve patient outcomes. In this study, a CG@ZnO/BMP-2 hydrogel with rapid antibacterial and bone regeneration capabilities was developed via a self-assembly technique. This approach leverages the chelation interaction between CG and ZnO, as well as the strong hydrogen bonding between CG and BMP-2. The resulting CG@ZnO/BMP-2 hydrogel exhibited a honeycomb-like structure with excellent swelling, water retention, and biodegradability. Antibacterial assays revealed that, under UV irradiation, the hydrogel achieved antibacterial rates of 85.4% against Escherichia coli and 87.3% against Staphylococcus aureus. The incorporation of ZnO conferred sustained antibacterial activity to the hydrogel. In vitro osteogenesis studies demonstrated that BMSCs gradually differentiated into osteoblasts over time, indicating robust osteogenic potential. Collectively, the CG@ZnO/BMP-2 hydrogel demonstrated a combination of effective antibacterial performance and accelerated bone-inducing functionality. This composite hydrogel holds significant promise for applications in bone infection treatment and bone tissue repair, especially for enhancing bone healing and minimizing postoperative infection recurrence.

S-propargyl-cysteine attenuates temporomandibular joint osteoarthritis by regulating macrophage polarization via Inhibition of JAK/STAT signaling

BACKGROUND

Temporomandibular joint osteoarthritis (TMJ-OA) is a disease characterized by cartilage degradation and synovial inflammation, with limited effective treatment currently. Synovial macrophage polarization is pivotal in TMJ-OA progression, making it a promising therapeutic aspect. This study investigated the effects of S-propargyl-cysteine (SPRC), an endogenous H2S donor, on macrophage polarization and its therapeutic potential in alleviating TMJ-OA.

METHODS

A MIA-induced TMJ-OA rat model and LPS-stimulated RAW264.7 macrophages were employed to evaluate the effects of SPRC in vivo and in vitro. TMJ bone and cartilage were analyzed via micro-CT and histological methods, while macrophage polarization markers expression were assessed via RT-qPCR, western blot, and immunofluorescence. RNA sequencing was performed on macrophages, and the JAK2/STAT3 signaling pathway was validated using the JAK2-specific inhibitor AG490. The direct effects of SPRC on rat primary condylar chondrocytes were examined by evaluating ECM synthesis and degradation. Co-culture experiments further assessed macrophage-chondrocyte interactions.

RESULTS

SPRC significantly alleviated cartilage and bone damage in the TMJ-OA rat model, as demonstrated by improved bone volume and cartilage structure. SPRC reduced pro-inflammatory M1 macrophage infiltration and enhanced anti-inflammatory M2 macrophage polarization. SPRC effectively inhibited the JAK2/STAT3, leading to reduction of inflammatory markers, including TNF-α, IL-6, and iNOS. Co-culture experiments revealed that SPRC-treated macrophage-conditioned medium improved chondrocyte metabolic activity and restored ECM integrity.

CONCLUSIONS

SPRC-modulated macrophage polarization alleviates TMJ-OA via JAK/STAT downregulation, thereby reducing synovial inflammation and cartilage degradation. These findings position SPRC as a promising therapeutic candidate for TMJ-OA and provide insights into novel strategies targeting macrophage polarization and synovium-cartilage crosstalk.

An Enhanced Osseointegration of Titanium Implants by H2S Sustained-Release Coating via Promoting Osteogenesis and Inhibiting Osteoclastogenesis

The surfaces of titanium implants lack the ability of promoting osteogenesis and inhibiting osteoclastogenesis, which primarily contributes to their inadequate integration with surrounding bone tissue in osteoporotic environments. Developing a bioactive coating for the materials is regarded as a promising approach to address the challenge. In this study, a hydrogen sulfide (H2S) sustained-release coating is fabricated on the surfaces of titanium implants. The coating consists of bovine serum albumin nanoparticles encapsulating the H2S donor morpholin-4-ium(4-methoxyphenyl)-morpholin-4-ylsulfanylidenesulfido-λ5-phosphane (GYY4137), which is prepared with the participation of dopamine self-polymerization. The release rate of H2S could be precisely controlled by adjusting the crosslinking degree of the nanoparticles. The coating proves to have excellent biocompatibility and satisfactory hemocompatibility. In vitro, the coating could significantly promote the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and inhibit the osteoclastic differentiation of mouse monocytic macrophage leukemia cells (RAW264.7 cells). In vivo, this work successfully verifies the conclusion obtained in vitro experiments. The coating restores the bone homeostasis imbalance surrounding the functionalized titanium implants in the femurs of osteoporotic rats, thereby accelerating new bone formation and enhancing the osseointegration capability of the implants. This work provides a practical strategy for the development of titanium implants suitable for osteoporosis patients.

A microenvironment-adaptive GelMA-ODex@RRHD hydrogel for responsive release of H2S in promoted chronic diabetic wound repair

Chronic diabetic wounds present significant treatment challenges due to their complex microenvironment, often leading to suboptimal healing outcomes. Hydrogen sulfide (H2S), a crucial gaseous signaling molecule, has shown great potential in modulating inflammation, oxidative stress and extracellular matrix remodeling, which are essential for effective wound healing. However, conventional H2S delivery systems lack the adaptability required to meet the dynamic demands of different healing stages, thereby limiting their therapeutic efficacy. To address this, we developed an injectable, ROS-responsive H2S donor system integrated within a gelatin methacryloyl (GelMA) hydrogel matrix, forming a double-network hydrogel (GelMA-ODex@RRHD). The injectability of this hydrogel allows for minimally invasive application, conforming closely to wound contours and ensuring uniform distribution. The incorporation of oxidatively modified dextran derivatives (ODex) not only preserves biocompatibility but also enables the chemical attachment of ROS-responsive H2S donors. The GelMA-ODex@RRHD hydrogel releases H2S in response to oxidative stress, optimizing the environment for cell growth, modulating macrophage polarization and supporting vascular regeneration. This innovative material effectively suppresses inflammation during the initial phase, promotes tissue regeneration in the proliferative phase and facilitates controlled matrix remodeling in later stages, ultimately enhancing wound closure and functional recovery. The H2S released by GelMA-ODex@RRHD not only expedited the process of wound healing but also improved the biomechanical characteristics of newborn skin in diabetic mice, particularly in terms of stiffness and elasticity. This enhancement resulted in the skin quality being more similar to normal skin during the wound healing process. By aligning therapeutic delivery with the natural healing process, this approach offers a promising pathway toward more effective and personalized treatments for chronic diabetic wounds.

"Three birds, one stone" strategy of NIR-responsive CO/H2S dual-gas Nanogenerator for efficient treatment of osteoporosis

Osteoporosis (OP), the most prevalent bone degenerative disease, has become a significant public health challenge globally. Current therapies primarily target inhibiting osteoclast activity or stimulating osteoblast activation, but their effectiveness remains suboptimal. This paper introduced a "three birds, one stone" therapeutic approach for osteoporosis, employing upconversion nanoparticles (UCNPs) to create a dual-gas storage nanoplatform (UZPA-CP) targeting bone tissues, capable of concurrently generating carbon monoxide (CO) and hydrogen sulfide (H2S). Through the precise modulation of 808 nm near-infrared (NIR) light, the platform could effectively control the release of CO and H2S in the OP microenvironment, and realize the effective combination of promoting osteogenesis, inhibiting osteoclast activity, and improving the immune microenvironment to achieve the therapeutic effect of OP. High-throughput sequencing results further confirmed the remarkable effectiveness of the nanoplatform in inhibiting apoptosis, modulating inflammatory response, inhibiting osteoclast differentiation and regulating multiple immune signaling pathways. The gas storage nanoplatform not only optimized the OP microenvironment with the assistance of NIR, but also restored the balance between osteoblasts and osteoclasts. This comprehensive therapeutic strategy focused on improving the bone microenvironment, promoting osteogenesis and inhibiting osteoclast activity provides an ideal new solution for the treatment of metabolic bone diseases.

Functional Amino Acids in the Regulation of Bone and Its Diseases

Bone as a vigorous tissue is constantly undergoing bone remodeling. The homeostasis of bone remodeling requires combined efforts of multifarious bone cells. Amino acids (AA), known as essential components of life support, are closely related to the regulation of bone homeostasis. In recent years, the concept of functional amino acids (FAAs) has been proposed, which is defined as AA that regulate key metabolic pathways to improve health, survival, growth, development, lactation, and reproduction of organisms, to highlight their outstanding contributions in the body. In the hope of exploring new therapeutic strategies, this review focus on summarizing recent progress in the vital role of FAAs in bone homeostasis maintaining and potential implications of FAAs in bone-related diseases, and discussing related mechanisms. The results showed that FAAs are closely related to bone metabolism and therapeutic strategy targeting FAAs metabolism is one of the future trends for bone disorders, while the explorations about possible impact of FAAs-based diets are still limited.

Effect of Sodium Thiosulfate Pre-Treatment on Renal Ischemia-Reperfusion Injury in Kidney Transplantation

We recently reported in a rat model of kidney transplantation that the addition of sodium thiosulfate (STS) to organ preservation solution improved renal graft quality and prolonged recipient survival. The present study investigates whether STS pre-treatment would produce a similar effect. In vitro, rat kidney epithelial cells were treated with 150 μM STS before and/or during exposure to hypoxia followed by reoxygenation. In vivo, donor rats were treated with PBS or 2.4 mg/kg STS 30 min before donor kidneys were procured and stored in UW or UW+150 μM STS solution at 4 °C for 24 h. Renal grafts were then transplanted into bilaterally nephrectomised recipient rats which were then sacrificed on post-operative day 3. STS pre-treatment significantly reduced cell death compared to untreated and other treated cells in vitro (p < 0.05), which corresponded with our in vivo result (p < 0.05). However, no significant differences were observed in other parameters of tissue injury. Our results suggest that STS pre-treatment may improve renal graft function after transplantation.

Unveiling the Potential of Sulfur-Containing Gas Signaling Molecules in Acute Lung Injury: A Promising Therapeutic Avenue

Acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS), are pulmonary conditions that cause significant morbidity and mortality. The common etiologies of these conditions include pneumonia, pulmonary contusion, fat embolism, smoke inhalation, sepsis, shock, and acute pancreatitis. Inflammation, oxidative stress, apoptosis, and autophagy are key pathophysiological mechanisms underlying ALI. Hydrogen sulfide (H2S) and sulfur dioxide (SO2) are sulfur-containing gas signaling molecules that can mitigate these pathogenic processes by modulating various signaling pathways, such as toll-like receptor 4 (TLR4)/nod-like receptor protein 3 (NLRP3), extracellular signal-regulating protein kinase 1/2 (ERK1/2), mitogen-activated protein kinase (MAPK), phosphatidyl inositol 3 kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR), and nuclear factor kappa B (NF-κB), thereby conferring protection against ALI. Given the limited clinical effectiveness of prevailing ALI treatments, investigation of the modulation of sulfur-containing gas signaling molecules (H2S and SO2) in ALI is imperative. This article presents an overview of the regulatory pathways of sulfur-containing gas signaling molecules in ALI animal models induced by various stimuli, such as lipopolysaccharide, gas inhalation, oleic acid, and ischemia-reperfusion. Furthermore, this study explored the therapeutic prospects of diverse H2S and SO2 donors for ALI, stemming from diverse etiologies. The aim of the present study was to establish a theoretical framework, in order to promote the new treatment of ALI.

Harnessing anti-inflammatory pathways and macrophage nano delivery to treat inflammatory and fibrotic disorders

Targeting specific organs and cell types using nanotechnology and sophisticated delivery methods has been at the forefront of applicative biomedical sciences lately. Macrophages are an appealing target for immunomodulation by nanodelivery as they are heavily involved in various aspects of many diseases and are highly plastic in their nature. Their continuum of functional "polarization" states has been a research focus for many years yielding a profound understanding of various aspects of these cells. The ability of monocyte-derived macrophages to metamorphose from pro-inflammatory to reparative and consequently to pro-resolving effectors has raised significant interest in its therapeutic potential. Here, we briefly survey macrophages' ontogeny and various polarization phenotypes, highlighting their function in the inflammation-resolution shift. We review their inducing mediators, signaling pathways, and biological programs with emphasis on the nucleic acid sensing-IFN-I axis. We also portray the polarization spectrum of macrophages and the characteristics of their transition between different subtypes. Finally, we highlighted different current drug delivery methods for targeting macrophages with emphasis on nanotargeting that might lead to breakthroughs in the treatment of wound healing, bone regeneration, autoimmune, and fibrotic diseases.

Recent advances in the mechanism of hydrogen sulfide in wound healing in diabetes

Wound healing difficulties in diabetes continue to be a clinical challenge, posing a considerable burden to patients and society. Recently, exploration of the mechanism of wound healing and associated treatment options in diabetes has become topical. Of note, the positive role of hydrogen sulfide in promoting wound healing has been demonstrated in recent studies. Hydrogen sulfide is a confirmed gas transmitter in mammals, playing an essential role in pathology and physiology. This review describes the mechanism underlying the role of hydrogen sulfide in the promotion of diabetic wound healing and the potential for hydrogen sulfide supplementation as a therapeutic application.

Development of europium(III) complex fluorescent probe for hydrogen sulfide detection and its application in water samples

Hydrogen sulfide (H2 S) is a crucial endogenous signaling component in organisms that is involved in redox homeostasis and numerous biological processes. Modern medical research has confirmed that hydrogen sulfide plays an important role in the pathogenesis of many diseases. Herein, a fluorescent probe Eu(ttbd)3 abt based on europium(III) complex was designed and synthesized for the detection of H2 S. Eu(ttbd)3 abt exhibited significant quenching for H2 S at long emission wavelength (625 nm), with rapid detection ability (less than 2 min), high sensitivity [limit of detection (LOD) = 0.41 μM], and massive Stokes shift (300 nm). Additionally, this probe showed superior selectivity for H2 S despite the presence of other possible interference species such as biothiols. Furthermore, the probe Eu(ttbd)3 abt was successfully applied to detect H2 S in water samples.

Study of hydrogen sulfide biosynthesis in synovial tissue from diabetes-associated osteoarthritis and its influence on macrophage phenotype and abundance

Type 2 diabetes (DB) is an independent risk factor for osteoarthritis (OA). However, the mechanisms underlying the connection between both diseases remain unclear. Synovial macrophages from OA patients with DB present a marked pro-inflammatory phenotype. Since hydrogen sulphide (H₂S) has been previously described to be involved in macrophage polarization, in this study we examined H₂S biosynthesis in synovial tissue from OA patients with DB, observing a reduction of H₂S-synthetizing enzymes in this subset of individuals. To elucidate these findings, we detected that differentiated TPH-1 cells to macrophages exposed to high levels of glucose presented a lower expression of H₂S-synthetizing enzymes and an increased inflammatory response to LPS, showing upregulated expression of markers associated with M1 phenotype (i.e., CD11c, CD86, iNOS, and IL-6) and reduced levels of those related to M2 fate (CD206 and CD163). The co-treatment of the cells with a slow-releasing H₂S donor, GYY-4137, attenuated the expression of M1 markers, but failed to modulate the levels of M2 indicators. GYY-4137 also reduced HIF-1α expression and upregulated the protein levels of HO-1, suggesting their involvement in the anti-inflammatory effects of H₂S induction. In addition, we observed that intraarticular administration of H₂S donor attenuated synovial abundance of CD68⁺ cells, mainly macrophages, in an in vivo model of OA. Taken together, the findings of this study seem to reinforce the key role of H₂S in the M1-like polarization of synovial macrophages associated to OA and specifically its metabolic phenotype, opening new therapeutic perspectives in the management of this pathology.

S-sulfhydration of SIRT3 combats BMSC senescence and ameliorates osteoporosis via stabilizing heterochromatic and mitochondrial homeostasis

Senescence of bone marrow mesenchymal stem cells (BMSCs) is one of the leading causes of osteoporosis. SIRT3, an essential NAD-dependent histone deacetylase, is highly correlated with BMSC senescence-mediated bone degradation and mitochondrial/heterochromatic disturbance. S-sulfhydration of cysteine residues favorably enhances SIRT3 activity by forming persulfides. Nevertheless, the underlying molecular mechanism of SIRT3 S-sulfhydration on mitochondrial/heterochromatic homeostasis involved in BMSC senescence remains unknown. Here, we demonstrated that CBS and CSE, endogenous hydrogen sulfide synthases, are downregulated with BMSC senescence. Exogenous H₂S donor NaHS-mediated SIRT3 augmentation rescued the senescent phenotypes of BMSCs. Conversely, SIRT3 deletion accelerated oxidative stress-induced BMSC senescence through mitochondrial dysfunction and the detachment of the heterochromatic protein H3K9me3 from the nuclear envelope protein Lamin B1. H₂S-mediated SIRT3 S-sulfhydration modification rescued the disorganized heterochromatin and fragmented mitochondria induced by the S-sulfhydration inhibitor dithiothreitol, thus leading to elevated osteogenic capacity and preventing BMSC senescence. The antisenescence effect of S-sulfhydration modification on BMSCs was abolished when the CXXC sites of the SIRT3 zinc finger motif were mutated. In vivo, aged mice-derived BMSCs pretreated with NaHS were orthotopically transplanted to the ovariectomy-induced osteoporotic mice, and we proved that SIRT3 ameliorates bone loss by inhibiting BMSC senescence. Overall, our study for the first time indicates a novel role of SIRT3 S-sulfhydration in stabilizing heterochromatin and mitochondrial homeostasis in counteracting BMSC senescence, providing a potential target for the treatment of degenerative bone diseases.

From Gasotransmitter to Immunomodulator: The Emerging Role of Hydrogen Sulfide in Macrophage Biology

Hydrogen sulfide (H2S) has been increasingly recognized as a crucial inflammatory mediator in immune cells, particularly macrophages, due to its direct and indirect effects on cellular signaling, redox homeostasis, and energy metabolism. The intricate regulation of endogenous H2S production and metabolism involves the coordination of transsulfuration pathway (TSP) enzymes and sulfide oxidizing enzymes, with TSP's role at the intersection of the methionine pathway and glutathione synthesis reactions. Additionally, H2S oxidation mediated by sulfide quinone oxidoreductase (SQR) in mammalian cells may partially control cellular concentrations of this gasotransmitter to induce signaling. H2S is hypothesized to signal through the posttranslational modification known as persulfidation, with recent research highlighting the significance of reactive polysulfides, a derivative of sulfide metabolism. Overall, sulfides have been identified as having promising therapeutic potential to alleviate proinflammatory macrophage phenotypes, which are linked to the exacerbation of disease outcomes in various inflammatory conditions. H2S is now acknowledged to have a significant influence on cellular energy metabolism by affecting the redox environment, gene expression, and transcription factor activity, resulting in changes to both mitochondrial and cytosolic energy metabolism processes. This review covers recent discoveries pertaining to the involvement of H2S in macrophage cellular energy metabolism and redox regulation, and the potential implications for the inflammatory response of these cells in the broader framework of inflammatory diseases.