Neutralization of Intracellular pH Homeostasis to Inhibit Osteoclasts Based on a Spatiotemporally Selective Delivery System

Influences and strategies for bone regeneration based on microenvironment pH adjustment

Bone possesses remarkable endogenous regenerative capacity. Bone regeneration is typically divided into three stages: inflammation, bone formation, and bone remodeling, during which pH is a critical variable. The influence of pH on the bone regeneration process depends on three main factors: (1) the activity and differentiation of cells involved in bone regeneration are affected by pH; (2) protein activity is regulated by pH; and (3) extracellular calcium phosphate precipitates in a pH-dependent manner. The aim of this study is to review the mechanisms by which microenvironment pH affects bone regeneration and to explore specific sites and signaling pathways involved in pH regulation during the bone regeneration process. Therapeutic approaches aimed at enhancing bone regeneration via modulation of microenvironment pH are discussed, including pH adjustment via biological implant materials, pH-responsive material setting, and pH stabilization through anti-inflammatory therapy. Investigating the impact of microenvironment pH on bone regeneration is of considerable clinical importance, as it provides valuable insights for improving the success rates of bone implants and promoting bone healing. This review offers insights into regulatory mechanisms, establishes theoretical foundations, and presents new perspectives for current research on bone defect repair.

Bioengineered bacterial extracellular vesicles for targeted delivery of an osteoclastogenesis-inhibitory peptide to alleviate osteoporosis

Osteoporosis (OP) is a systemic skeletal disease commonly found in women after 55 years old and men after 65 years old. With the worldwide aging of population, its prevalence rate is increasing rapidly, bringing huge financial burdens to all countries. As a potential alternative to the conventional OP therapeutics with limited efficacies and side effects, a linear peptide FRATtide capable of binding with phosphorylated GSK3β has been discovered by us to inhibit osteoclastogenesis thus reduce bone loss. While its poor proteolytic stability and osteoclast targetability hinder its effective in vivo treatment. As such, bacterial extracellular vesicles secreted by the rationally recombinant probiotics Escherichia coli Nissle 1917 that express pre-osteoclast fusion protein DC-STAMP (BEV-DCS) are engineered and exploited as delivery vehicles. The BEV-DCS not only protect FRAT from enzymatic degradation but also enable its targeted intracellular delivery into pre-osteoclasts. On the ovariectomy mouse model, the FRAT encapsulated BEV-DCS (FRAT@BEV-DCS) exhibit remarkable bone targeting capacity and osteoporosis ameliorating efficacy without any obvious toxicity. These results reveal the great potential of FRAT@BEV-DCS as a novel therapeutic option for the effective and safe OP treatment.

K+-H+ coupling strategy for immune regulation and bone defect repair

Ion homeostasis is crucial for maintaining cell function. Potassium ion (K+) is one of the most important cations in the human body, and it plays key role in maintaining biological activities and cellular functions, including the intricate balance of ion homeostasis that underpins both physiological and pathological processes. This study explored a novel role of K+ ions in regulating immune cell function and promoting tissue repair, especially in macrophage-mediated environments after severe tissue injury. We designed and synthesized a platelet-liposome vesicles loaded KHCO3 (KHCO3@PLV) that precisely delivered potassium bicarbonate to the site of injury extracellular after intravenous injection; then, precise ultrasound-triggered K+ release regulated extracellular K+ concentrations in the local macrophage environment. These effects collectively validate the K+-H+ coupling strategy - a novel mechanism whereby extracellular K+ elevation induces intracellular pH modulation, subsequently activating the AMPK/Nrf2 axis to reprogram macrophage metabolism and facilitating tissue regeneration through resolution of chronic inflammation. The main conclusion of the study is that an elevated extracellular K+ environment, which is an innovative treatment, is a potentially effective strategy for regulating immune responses and promoting repair after severe tissue injury.

Nanocomposite hydrogels optimize the microenvironment by exterior/interior crosstalk for reprogramming osteoporotic homeostasis in bone defect healing

Discovering new tactics for healing bone defects becomes a worldwide challenge in osteoporosis patients. The disordered acidic microenvironment plays a pivotal role in driving the imbalance of bone homeostasis regulated by osteoblasts and osteoclasts. However, the scarcity of hydrogel materials developed to optimize local bone microenvironment has made osteoporotic defect healing more challenging. Herein, we present innovative nanocomposite hydrogels with precisely engineered microarchitectures designed to optimize the acidic microenvironment by facilitating crosstalk between exterior and interior spaces, aimed at enhancing the reconstruction of osteoporotic bone defects. The chlorogenic acid grafted chitosan as double-sided crosslinkers is specially designed to not only combine with acid-reversible Laponite® nanosheet via interfacial interactions but also integrate with gold nanorod (a typical photothermal agent) through catechol-Au bond. The supramolecular construction of nanocomposite hydrogels holds promise for achieving a highly continuous and homogeneous pore network microarchitecture. As expected, hydrogels display outstanding spatiotemporal local mild hyperthermia, which accelerates the neutralization reaction between OH- ions released from Laponite® and hydrogen ions (pH ∼ 4.0). The optimized microenvironment restores osteoclast/osteoblast homeostasis, resulting in the promotion of osteoblastogenesis and inhibition of osteoclastogenesis, thereby facilitating the healing of osteoporotic bone defects. This work is hoped to design versatile hydrogels for optimizing the microenvironment, displaying promising integrative substitute materials for clinically effective treatment of osteoporotic bone defects.

Nanomaterials-Based Drug Delivery Systems for Therapeutic Applications in Osteoporosis

The etiology of osteoporosis is rooted in the disruption of the intricate equilibrium between bone formation and bone resorption processes. Nevertheless, the conventional anti-osteoporotic medications and hormonal therapeutic regimens currently employed in clinical practice are associated with a multitude of adverse effects, thereby constraining their overall therapeutic efficacy and potential. Recently, nanomaterials have emerged as a promising alternative due to their minimal side effects, efficient drug delivery, and ability to enhance bone formation, aiding in restoring bone balance. This review delves into the fundamental principles of bone remodeling and the bone microenvironment, as well as current clinical treatment approaches for osteoporosis. It subsequently explores the research status of nanomaterial-based drug delivery systems for osteoporosis treatment, encompassing inorganic nanomaterials, organic nanomaterials, cell-mimicking carriers and exosomes mimics and emerging therapies targeting the osteoporosis microenvironment. Finally, the review discusses the potential of nanomedicine in treating osteoporosis and outlines the future trajectory of this burgeoning field. The aim is to provide a comprehensive reference for the application of nanomaterial-based drug delivery strategies in osteoporosis therapy, thereby fostering further advancements and innovations in this critical area of medical research.

Design of indomethacin novel small molecule hydrogels for concomitant release and permeability increases

With the expansion of gel research, organic small molecule gels are beginning to gain attention. Whether the small-molecule gel approach can be a new formulation strategy of solubilization and permeation promotion for poorly soluble drugs needs to be explored in this study. The model ingredient indomethacin (IND) as a nonsteroidal anti-flammatory drug shows limited therapeutic application mainly due to its low water solubility. Herein, the IND small molecule hydrogel was design to co-formed with a small molecule ligand by integrating theory-model-experiment techniques. Then, the formed IND small molecule hydrogels (i.e., IND-MEG hydrogel and IND-ARG hydrogel) with meglumine (MEG) or arginine (ARG) appeared typical 3-D network with good rheology. In comparison to crystalline IND, the solubilities of IND-MEG hydrogel and IND-ARG hydrogel exhibited 506.71-fold and 479.63-fold improvements, respectively. Meanwhile, both IND hydrogels performed significantly enhanced release rate and degree, and maintained supersaturation for a long time arising from the complexation reaction of IND and ligand, which was revealed by phase solubility and fluorescence quenching studies. Furthermore, the designed IND hydrogels significantly promoted IND membrane permeability compared to the commercial IND hydrogel, and enhanced the development potential of novel IND hydrogels for oral and transdermal applications. Therefore, this study provides a new formulation technique to increase the solubility/release and permeability of poorly water-soluble drugs by designing their small molecule hydrogel systems.

4-Hydroxyphenylacetic Acid, a microbial-derived metabolite of Polyphenols, inhibits osteoclastogenesis by inhibiting ROS production

Intracellular reactive oxygen species (ROS) accumulation is key to osteoclast differentiation. Plant-derived polyphenols that have reduced ROS production have been widely studied for the treatment of osteoporosis. However, these compounds are rarely absorbed in the small intestine and are instead converted to phenolic acids by the microbiota in the colon. These large quantities of low-molecular-weight phenolic acids can then be absorbed by the body. 4-Hydroxyphenylacetic acid (4-HPA) is an important metabolite of these polyphenols that is generated by the human intestinal microbiota. However, its potential mechanism is not fully understood. In this study, we aimed to elucidate the role of 4-HPA on osteoclastogenesis and treating osteoporosis. Our study showed that 4-HPA inhibited osteoclast differentiation and function and downregulated osteoclast-specific genes, including NFATc1, Atp6v0d2, MMP9, CTSK, Acp5, and c-Fos. As for further mechanism exploration, 4-HPA reduced ROS accumulation by regulating nuclear factor erythroid 2-related factor (Nrf2) and subsequently inhibited the nuclear factor kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. To evaluate the effect of 4-HPA on postmenopausal osteoporosis, an ovariectomized (OVX) mouse model was used. The Micro-CT and histomorphometry analyses showed that 4-HPA effectively prevents bone loss. Encouragingly, 4-HPA demonstrated efficacy in treating osteoporosis induced by OVX. In conclusion, our study revealed that 4-HPA, a polyphenol metabolite produced by intestinal microorganisms, also inhibits osteoclast formation and treats osteoporosis, which provides a new experimental basis and candidate drug for the treatment of osteoporosis.

Insight into Formation, Synchronized Release and Stability of Co-Amorphous Curcumin-Piperine by Integrating Experimental-Modeling Techniques

Intermolecular interactions between drug and co-former are crucial in the formation, release and physical stability of co-amorphous system. However, the interactions remain difficult to investigate with only experimental tools. In this study, intermolecular interactions of co-amorphous curcumin-piperine (i.e., CUR-PIP CM) during formation, dissolution and storage were explored by integrating experimental and modeling techniques. The formed CUR-PIP CM exhibited the strong hydrogen bond interaction between the phenolic OH group of CUR and the CO group of PIP as confirmed by FTIR, ss 13C NMR and molecular dynamics (MD) simulation. In comparison to crystalline CUR, crystalline PIP and their physical mixture, CUR-PIP CM performed significantly increased dissolution accompanied by the synchronized release of CUR and PIP, which arose from the greater interaction energy of H2O-CUR molecules and H2O-PIP molecules than CUR-PIP molecules, breaking the hydrogen bond between CUR and PIP molecules, and then causing a pair-wise solvation of CUR-PIP CM at the molecular level. Furthermore, the stronger intermolecular interaction between CUR and PIP was revealed by higher binding energy of CUR-PIP molecules, which contributed to the excellent physical stability of CUR-PIP CM over amorphous CUR or PIP. The study provides a unique insight into the formation, release and stability of co-amorphous system from MD perspective. Meanwhile, this integrated technique can be used as a practical methodology for the future design of co-amorphous formulations.

Bone-Targeted Supramolecular Nanoagonist Assembled by Accurate Ratiometric Herbal-Derived Therapeutics for Osteoporosis Reversal

Developing novel strategies for defeating osteoporosis has become a world-wide challenge with the aging of the population. In this work, novel supramolecular nanoagonists (NAs), constructed from alkaloids and phenolic acids, emerge as a carrier-free nanotherapy for efficacious osteoporosis treatment. These precision nanoagonists are formed through the self-assembly of berberine (BER) and chlorogenic acid (CGA), utilizing noncovalent electrostatic, π-π, and hydrophobic interactions. This assembly results in a 100% drug loading capacity and stable nanostructure. Furthermore, the resulting weights and proportions of CGA and BER within the NAs are meticulously controlled with strong consistency when the CGA/BER assembly feed ratio is altered from 1:1 to 1:4. As anticipated, our NAs themselves could passively target osteoporotic bone tissues following prolonged blood circulation, modulate Wnt signaling, regulate osteogenic differentiation, and ameliorate bone loss in ovariectomy-induced osteoporotic mice. We hope this work will open a new strategy to design efficient herbal-derived Wnt NAs for dealing with intractable osteoporosis.

Development of paste-like organic/inorganic artificial bones compatible with bone remodeling cycles, consisting of β-tricalcium phosphate, calcium sulfate hemihydrate, and poly(lactic-co-glycolic acid) particles

Schematic illustration of organic/inorganic hybrid cement with the simultaneous addition of CSH and PLGA particles.