Metal ion-assisted self-assembly of complexes for controlled and sustained release of minocycline for biomedical applications

Reviewing particulate delivery systems loaded with repurposed tetracyclines - From micro to nanoparticles

Tetracyclines (TCs) are a class of broad-spectrum antibacterial agents recognized for their multifaceted properties, including anti-inflammatory, angiogenic and osteogenic effects. This versatility positions them as suitable candidates for drug repurposing, benefitting from well-characterized safety and pharmacological profiles. In the attempt to explore both their antibacterial and pleiotropic effects locally, innovative therapeutic strategies were set on engineering tetracycline-loaded micro and nanoparticles to tackle a vast number of clinical applications. Moreover, the conjoined drug carrier can function as an active component of the therapeutic approach, reducing off-target effects and accumulation, synergizing to an improvement of the therapeutic efficacy. In this comprehensive review we will critically evaluate recent advances involving the use of tetracyclines loaded onto micro- or nanoparticles, intended for biomedical applications, and discuss emerging approaches and current limitations associated with these drug carriers. Owing to their distinctive physical, chemical, and biological properties, these novel carriers have the potential to become a platform technology in personalized regenerative medicine and other therapeutic applications.

Advances in the prevention and treatment of Alzheimer's disease based on oral bacteria

With the global population undergoing demographic shift towards aging, the prevalence of Alzheimer's disease (AD), a prominent neurodegenerative disorder that primarily afflicts individuals aged 65 and above, has increased across various geographical regions. This phenomenon is accompanied by a concomitant decline in immune functionality and oral hygiene capacity among the elderly, precipitating compromised oral functionality and an augmented burden of dental plaque. Accordingly, oral afflictions, including dental caries and periodontal disease, manifest with frequency among the geriatric population worldwide. Recent scientific investigations have unveiled the potential role of oral bacteria in instigating both local and systemic chronic inflammation, thereby delineating a putative nexus between oral health and the genesis and progression of AD. They further proposed the oral microbiome as a potentially modifiable risk factor in AD development, although the precise pathological mechanisms and degree of association have yet to be fully elucidated. This review summarizes current research on the relationship between oral bacteria and AD, describing the epidemiological and pathological mechanisms that may potentially link them. The purpose is to enrich early diagnostic approaches by incorporating emerging biomarkers, offering novel insights for clinicians in the early detection of AD. Additionally, it explores the potential of vaccination strategies and guidance for clinical pharmacotherapy. It proposes the development of maintenance measures specifically targeting oral health in older adults and advocates for guiding elderly patients in adopting healthy lifestyle habits, ultimately aiming to indirectly mitigate the progression of AD while promoting oral health in the elderly.

Unveiling the Osteogenic Potential of Tetracyclines: A Comparative Study in Human Mesenchymal Stem Cells

Tetracyclines (TCs) are a class of broad-spectrum antibiotics with diverse pharmacotherapeutic properties due to their various functional groups being attached to a common core structure. Beyond their antibacterial activity, TCs trigger pleiotropic effects on eukaryotic cells, including anti-inflammatory and potentially osteogenic capabilities. Consequently, TCs hold promise for repurposing in various clinical applications, including bone-related conditions. This study presents the first comprehensive comparison of the in vitro osteogenic potential of four TCs-tetracycline, doxycycline, minocycline, and sarecycline, within human mesenchymal stem cells. Cultures were characterized for metabolic activity, cell morphology and cytoskeleton organization, osteogenic gene expression, alkaline phosphatase (ALP) activity, and the activation of relevant signaling pathways. TCs stimulated actin remodeling processes, inducing morphological shifts consistent with osteogenic differentiation. Osteogenic gene expression and ALP activity supported the osteoinduction by TCs, demonstrating significant increases in ALP levels and the upregulation of RUNX2, SP7, and SPARC genes. Minocycline and sarecycline exhibited the most potent osteogenic induction, comparable to conventional osteogenic inducers. Signaling pathway analysis revealed that tetracycline and doxycycline activate the Wnt pathway, while minocycline and sarecycline upregulated Hedgehog signaling. Overall, the present findings suggest that TCs promote osteogenic differentiation through distinct pathways, making them promising candidates for targeted therapy in specific bone-related disorders.

Antibacterial-Anti-Inflammatory-Bone Restoration Procedure Achieved by MIN-Loaded PLGA Microsphere for Efficient Treatment of Periodontitis

The main development process of periodontitis involves periodontal pathogenic bacteria as the initiating factor causing the onset of destructive inflammation, which in turn stimulates the destruction of periodontal tissue. It is difficult to achieve the eradication of periodontitis due to the complex interaction among antibacterial, anti-inflammatory, and bone restoration. Herein, we propose an antibacterial-anti-inflammatory-bone restoration procedural treatment strategy with minocycline (MIN) for the efficient treatment of periodontitis. In brief, MIN was prepared into PLGA microspheres with tunable release behavior using different species of PLGA, respectively. The optimally selected PLGA microspheres (LA:GA with 50:50, 10 kDa, and carboxyl group) had a drug loading of 16.91%, an in vitro release of approximately 30 days, which also had a particle size of approximately 11.8 µm with a smooth appearance and a rounded morphology. The DSC and XRD results showed that the MIN was completely encapsulated in the microspheres as an amorphous state. Cytotoxicity tests demonstrated the safety and biocompatibility of the microspheres (cell viabilities at a concentration of 1-200 μg/mL were greater than 97%), and in vitro bacterial inhibition tests showed that the selected microspheres could achieve effective bacterial inhibition at the initial stage after administration. The favorable anti-inflammatory (low TNF-α and IL-10 levels) and bone restoration effects (BV/TV: 71.8869%; BMD: 0.9782 g/cm³; TB.Th: 0.1366 mm; Tb.N: 6.9318 mm^-1; Tb.Sp: 0.0735 mm) were achieved in a SD rat periodontitis model after administering once a week for four weeks. The MIN-loaded PLGA microspheres were proved to be an efficient and safe treatment for periodontitis by procedural antibacterial, anti-inflammatory, and bone restoration.

A multiple controlled-release hydrophilicity minocycline hydrochloride delivery system for the efficient treatment of periodontitis

The complexity of periodontitis, including the complex formation mechanisms and the complex periodontium physiological environment, as well as the complex association with multiple complications, often results in poor therapy effects. Herein, we aimed to design a nanosystem with a controlled release of minocycline hydrochloride (MH) and good retention to effectively treat periodontitis by inhibiting inflammation and repairing the alveolar bone. Firstly, insoluble ion-pairing (IIP) complexes were constructed to improve the encapsulation efficiency of hydrophilic MH in PLGA nanoparticles. Then, a nanogenerator was constructed and combined with a double emulsion method to encapsulate the complexes into PLGA nanoparticles (MH-NPs). The average particle size of MH-NPs was about 100 nm as observed by AFM and TEM, and the drug loading and encapsulation efficiency were 9.59% and 95.58%, respectively. Finally, a multifunctional system (MH-NPs-in-gels) was prepared by dispersing MH-NPs into thermosensitive gels, which could continue to release drug for 21 days in vitro. And the release mechanism showed that this controlled release behavior for MH was influenced by the insoluble ion-pairing complex, PLGA nanoparticles, and gels. In addition, the periodontitis rat model was established to investigate the pharmacodynamic effects. After 4 weeks of treatment, changes in the alveolar bone were assessed by Micro-CT (BV/TV: 70.88%; BMD: 0.97 g/cm³; TB.Th: 0.14 mm; Tb.N: 6.39 mm^-1; Tb.Sp: 0.07 mm). The mechanism of MH-NPs-in-gels in vivo was clarified by the analysis of pharmacodynamic results, which showed that insoluble ion-pairing complexes with the aid of PLGA nanoparticles and gels achieved significant anti-inflammatory effects and bone repair capabilities. In conclusion, the multiple controlled-release hydrophilicity MH delivery system would have good prospects for the effective treatment of periodontitis.

Delivery of active minocycline hydrochloride by local sustained-release system of complex and thermoresponsive hydrogel for dogs

ABSTRACT The objective of this study was to develop a novel subgingival sustained-release system for local delivery of bioactive minocycline hydrochloride for periodontal disease treatment in dogs. The system incorporated the Minocycline hydrochloride-Calcium-Dextran sulfate sodium into a thermoresponsive Pluronic F127 hydrogel. Minocycline hydrochloride was sustained release from the system for up to 10 days and the release kinetics fit the power law model. The release medium had a significant statistical difference in antimicrobial activity to Aggregatibacter actinomycetemcomitans. The results showed the system was a promising subgingival sustained-release minocycline hydrochloride delivery system for periodontal disease treatment in dogs.

The potential use of tetracyclines in neurodegenerative diseases and the role of nano-based drug delivery systems

Neurodegenerative diseases are still a challenge for effective treatments. The high cost of approved drugs, severity of side effects, injection site pain, and restrictions on drug delivery to the Central Nervous System (CNS) can overshadow the management of these diseases. Due to the chronic and progressive evolution of neurodegenerative disorders and since there is still no cure for them, new therapeutic strategies such as the combination of several drugs or the use of existing drugs with new therapeutic applications are valuable strategies. Tetracyclines are traditionally classified as antibiotics. However, in this class of drugs, doxycycline and minocycline exhibit also anti-inflammatory effects by inhibiting microglia/macrophages. Hence, they have been studied as potential agents for the treatment of neurodegenerative diseases. The results of in vitro and in vivo studies confirm the effective role of these two drugs as anti-inflammatory agents in experimentally induced models of neurodegenerative diseases. In clinical studies, satisfactory results have been obtained in Multiple sclerosis (MS) but not yet in other disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), or Amyotrophic lateral sclerosis (ALS). In recent years, researchers have developed and evaluated nanoparticulate drug delivery systems to improve the clinical efficacy of these two tetracyclines for their potential application in neurodegenerative diseases. This study reviews the neuroprotective roles of minocycline and doxycycline in four of the main neurodegenerative disorders: AD, PD, ALS and MS. Moreover, the potential applications of nanoparticulate delivery systems developed for both tetracyclines are also reviewed.

Single subcutaneous injection of the minocycline nanocomposite-loaded thermosensitive hydrogel for the effective attenuation of experimental autoimmune uveitis

Autoimmune uveitis induces a serious pathological and inflammatory response in the retina/choroid and results in vision impairment and blindness. Here, we report a minocycline (Mino) nanocomposite-loaded hydrogel offering a high drug payload and sustained drug release for the effective control of ocular inflammation via a single subcutaneous injection. In the presence of divalent cations (i.e., Ca²⁺), Mino was found to co-assemble with a phosphorylated peptide (i.e., NapGFFpY) via electrostatic interaction and consequently generating Mino nanocomposite. The drug entrapment efficiency (EE) of the Mino nanocomposite varied from 29.93±0.76% to 67.90±6.57%, depending on different component concentrations. After incorporation into 30 wt% poly (D,L-lactide)-b-poly (ethylene glycol)-b-poly (D,L-lactide) (PDLLA-PEG-PDLLA) thermosensitive hydrogel, the resulting Mino nanocomposite-loaded hydrogel provided a sustained drug release over 21 days. In the experimental autoimmune uveitis (EAU) rat model, a single subcutaneous injection of the Mino nanocomposite-loaded hydrogel effectively alleviated ocular inflammation in a dose-dependent manner. As indicated by optical coherence tomography (OCT) and electroretinogram (ERG) measurements, the Mino nanocomposite-loaded hydrogel treatment not only remarkably reduced destruction of the retina by EAU, but also greatly rescued retinal functions. Moreover, the proposed Mino nanocomposite-loaded hydrogel exerted its therapeutic effect on EAU primarily through a significant reduction of the influx of leukocytes and Th17 cells as well as suppression of microglia activation and apoptosis in the retina. Overall, the proposed Mino nanocomposite-loaded hydrogel might be a promising strategy for the clinical management of EAU.

Therapeutic targets and nanomaterial-based therapies for mitigation of secondary injury after spinal cord injury

Spinal cord injury (SCI) and the resulting neurological trauma commonly result in complete or incomplete neurological dysfunction and there are few effective treatments for primary SCI. However, the following secondary SCI, including the changes of microvasculature, inflammatory response and oxidative stress around the injury site, may provide promising therapeutic targets. The advances of nanomaterials hold promise for delivering therapeutics to alleviate secondary SCI and promote functional recovery. In this review, we highlight recent achievements of nanomaterial-based therapy, specifically targeting blood-spinal cord barrier disruption, mitigation of the inflammatory response and lightening of oxidative stress after spinal cord injury.

Antimicrobial Properties of Strontium Functionalized Titanium Surfaces for Oral Applications, A Systematic Review

The aim of this systematic review was to assess the current scientific evidence of the antimicrobial potential of strontium (Sr) when used to functionalize titanium (Ti) for oral applications. Out of an initial list of 1081 potentially relevant publications identified in three electronic databases (MEDLINE via PubMed, Scopus, and Cochrane) up to 1 February 2021, nine publications based on in vitro studies met the inclusion criteria. The antimicrobial potential of Sr was investigated on different types of functionalized Ti substrates, employing different application methods. Nine studies reported on the early, i.e., 6–24 h, and two studies on the late, i.e., 7–28 days, antimicrobial effect of Sr, primarily against Staphylococcus aureus (S. aureus) and/or Escherichia coli (E. coli). Sr-modified samples demonstrated relevant early antimicrobial potential against S. aureus in three studies; only one of which presented statistical significance values, while the other two presented only the percentage of antimicrobial rate and biofilm inhibition. A relevant late biofilm inhibition potential against S. aureus of 40% and 10%—after 7 and 14 days, respectively—was reported in one study. Combining Sr with other metal ions, i.e., silver (Ag), zinc (Zn), and fluorine (F), demonstrated a significant antimicrobial effect and biofilm inhibition against both S. aureus and E. coli. Sr ion release within the first 24 h was generally low, i.e., below 50 µg/L and 0.6 ppm; however, sustained Sr ion release for up to 30 days, while maintaining up to 90% of its original content, was also demonstrated. Thus, in most studies included herein, Sr-functionalized Ti showed a limited immediate (i.e., 24 h) antimicrobial effect, likely due to a low Sr ion release; however, with an adequate Sr ion release, a relevant antimicrobial effect, as well as a biofilm inhibition potential against S. aureus—but not E. coli—was observed at both early and late timepoints. Future studies should assess the antimicrobial potential of Ti functionalized with Sr against multispecies biofilms associated with peri-implantitis.

Hydrogels as delivery systems for spinal cord injury regeneration

Spinal cord injury is extremely debilitating, both at physiological and psychological levels, changing completely the patient's lifestyle. The introduction of biomaterials has opened a new window to develop a therapeutic approach to induce regeneration after injury due to similarities with extracellular matrix. Particularly, hydrogels have the ability to support axonal growth and endogenous regeneration. Moreover, they can also act as potential matrixes in which to load and deliver therapeutic agents at injury site. In this review, we highlight some important characteristics to be considered when designing hydrogels as delivery systems (DS), such as rheology, mesh size, swelling, degradation, gelation temperature and surface charge. Additionally, affinity-based release systems, incorporation of nanoparticles, or ion-mediated interactions are also pondered. Overall, hydrogel DS aim to promote a sustained, controlled and prolonged release at injury site, allowing a targeted oriented action of the therapeutic agent that will be used.

Antibacterial Collagen Composite Membranes Containing Minocycline

Collagen membranes have been used as bioresorbable barrier membranes in guided tissue/bone regeneration. However, the collagen membranes currently used in clinics lack an active antibacterial function, although infection at surgical sites presents a realistic challenge for guided tissue/bone regeneration. In this study, we successfully prepared novel and advanced collagen composite membranes from collagen and complexes of heparin and chelates of minocycline and Ca²⁺ ions. These membranes were characterized for chemical structures, morphology, elemental compositions and tensile strength. In vitro release studies were conducted to evaluate the release kinetics of minocycline from these membranes. Agar disk diffusion assays were used to assess their sustained antibacterial capability against model pathogenic bacteria Staphylococcus aureus. The chemical and physical characterization confirmed the successful synthesis of minocycline-loaded collagen composite membranes, namely NCCM-1 and NCCM-2. Both membranes had weaker tensile strength as compared with commercial collagen membranes. They achieved sustained release of minocycline for at least 4 weeks in simulated body fluid (pH 7.4) at 37°C. Moreover, both membranes demonstrated potent sustained antibacterial effects against Staphylococcus aureus. These results suggested that the advanced collagen composite membranes containing minocycline can be exploited as novel guided tissue regeneration membranes or wound dressing by providing additional antibacterial functions.

In Vitro Evaluation of Antimicrobial Activity of Minocycline Formulations for Topical Application in Periodontal Therapy

Periodontal therapy using antimicrobials that are topically applied requires slow or controlled release devices. The in vitro antimicrobial activity of biodegradable polymer formulations that contain a new minocycline lipid complex (P-MLC) was evaluated. The new P-MLC formulations that contained 11.5% minocycline were compared with pure minocycline or an existing commercial formulation, which included determination of minimal inhibitory concentration (MIC) values against two oral bacteria and activity on six-species periodontal biofilm. Moreover, the flow of gingival crevicular fluid (GCF) was modeled up to 42 d and the obtained eluates were tested both for MIC values and inhibiting biofilm formation. In general, MICs of the P-MLC formulations were slightly increased as compared with pure minocycline. Biofilm formation was clearly inhibited by all tested formulations containing minocycline with no clear difference between them. In 3.5 d old biofilms, all formulations with 250 µg/mL minocycline decreased bacterial counts by 3 log10 and metabolic activity with no difference to pure antimicrobials. Eluates of experimental formulations showed superiority in antimicrobial activity. Eluates of one experimental formulation (P₅₀₃-MLC) still inhibited biofilm formation at 28 d, with a reduction by 1.87 log10 colony forming units (CFU) vs. the untreated control. The new experimental formulations can easily be instilled in periodontal pockets and represent alternatives in local antimicrobials, and thus warrant further testing.

Co-delivery of minocycline and paclitaxel from injectable hydrogel for treatment of spinal cord injury

Spinal cord injury (SCI) induces pathological and inflammatory responses that create an inhibitory environment at the site of trauma, resulting in axonal degeneration and functional disability. Combination therapies targeting multiple aspects of the injury, will likely be more effective than single therapies to facilitate tissue regeneration after SCI. In this study, we designed a dual-delivery system consisting of a neuroprotective drug, minocycline hydrochloride (MH), and a neuroregenerative drug, paclitaxel (PTX), to enhance tissue regeneration in a rat hemisection model of SCI. For this purpose, PTX-encapsulated poly (lactic-co-glycolic acid) PLGA microspheres along with MH were incorporated into the alginate hydrogel. A prolonged and sustained release of MH and PTX from the alginate hydrogel was obtained over eight weeks. The obtained hydrogels loaded with a combination of both drugs or each of them alone, along with the blank hydrogel (devoid of any drugs) were injected into the lesion site after SCI (at the acute phase). Histological assessments showed that the dual-drug treatment reduced inflammation after seven days. Moreover, a decrease in the scar tissue, as well as an increase in neuronal regeneration was observed after 28 days in rats treated with dual-drug delivery system. Over time, a fast and sustained functional improvement was achieved in animals that received dual-drug treatment compared with other experimental groups. This study provides a novel dual-drug delivery system that can be developed to test for a variety of SCI models or neurological disorders.

Self-Assembly of DNA-Minocycline Complexes by Metal Ions with Controlled Drug Release

Here we reported a study of metal ions-assisted assembly of DNA-minocycline (MC) complexes and their potential application for controlling MC release. In the presence of divalent cations of magnesium or calcium ions (M²⁺), MC, a zwitterionic tetracycline analogue, was found to bind to phosphate groups of nucleic acids via an electrostatic bridge of phosphate (DNA)-M²⁺-MC. We investigated multiple parameters for affecting the formation of DNA-Mg²⁺-MC complex, including metal ion concentrations, base composition, DNA length, and single- versus double-stranded DNA. For different nitrogen bases, single-stranded poly(A)₂₀ and poly(T)₂₀ showed a higher MC entrapment efficiency of DNA-Mg²⁺-MC complex than poly(C)₂₀ and poly(G)₂₀. Single-stranded DNA was also found to form a more stable DNA-Mg²⁺-MC complex than double-stranded DNA. Between different divalent metal ions, we observed that the formation of DNA-Ca²⁺-MC complex was more stable and efficient than the formation of DNA-Mg²⁺-MC complex. Toward drug release, we used agarose gel to encapsulate DNA-Mg²⁺-MC complexes and monitored MC release. Some DNA-Mg²⁺-MC complexes could prolong MC release from agarose gel to more than 10 days as compared with the quick release of free MC from agarose gel in less than 1 day. The released MC from DNA-Mg²⁺-MC complexes retained the anti-inflammatory bioactivity to inhibit nitric oxide production from pro-inflammatory macrophages. The reported study of metal ion-assisted DNA-MC assembly not only increased our understanding of biochemical interactions between tetracycline molecules and nucleic acids but also contributed to the development of a highly tunable drug delivery system to mediate MC release for clinical applications.

Recent advances in nanotherapeutic strategies for spinal cord injury repair

Spinal cord injury (SCI) is a devastating and complicated condition with no cure available. The initial mechanical trauma is followed by a secondary injury characterized by inflammatory cell infiltration and inhibitory glial scar formation. Due to the limitations posed by the blood-spinal cord barrier, systemic delivery of therapeutics is challenging. Recent development of various nanoscale strategies provides exciting and promising new means of treating SCI by crossing the blood-spinal cord barrier and delivering therapeutics. As such, we discuss different nanomaterial fabrication methods and provide an overview of recent studies where nanomaterials were developed to modulate inflammatory signals, target inhibitory factors in the lesion, and promote axonal regeneration after SCI. We also review emerging areas of research such as optogenetics, immunotherapy and CRISPR-mediated genome editing where nanomaterials can provide synergistic effects in developing novel SCI therapy regimens, as well as current efforts and barriers to clinical translation of nanomaterials.

A hydrogel engineered to deliver minocycline locally to the injured cervical spinal cord protects respiratory neural circuitry and preserves diaphragm function

We tested a biomaterial-based approach to preserve the critical phrenic motor circuitry that controls diaphragm function by locally delivering minocycline hydrochloride (MH) following cervical spinal cord injury (SCI). MH is a clinically-available antibiotic and anti-inflammatory drug that targets a broad range of secondary injury mechanisms via its anti-inflammatory, anti-oxidant and anti-apoptotic properties. However, MH is only neuroprotective at high concentrations that cannot be achieved by systemic administration, which limits its clinical efficacy. We have developed a hydrogel-based MH delivery system that can be injected into the intrathecal space for local delivery of high concentrations of MH, without damaging spinal cord tissue. Implantation of MH hydrogel after unilateral level-C4/5 contusion SCI robustly preserved diaphragm function, as assessed by in vivo recordings of compound muscle action potential (CMAP) and electromyography (EMG) amplitudes. MH hydrogel also decreased lesion size and degeneration of cervical motor neuron somata, demonstrating its central neuroprotective effects within the injured cervical spinal cord. Furthermore, MH hydrogel significantly preserved diaphragm innervation by the axons of phrenic motor neurons (PhMNs), as assessed by both detailed neuromuscular junction (NMJ) morphological analysis and retrograde PhMN labeling from the diaphragm using cholera toxin B (CTB). In conclusion, our findings demonstrate that local MH hydrogel delivery to the injured cervical spinal cord is effective in preserving respiratory function after SCI by protecting the important neural circuitry that controls diaphragm activation.

Sustained Release of Minocycline From Minocycline-Calcium-Dextran Sulfate Complex Microparticles for Periodontitis Treatment

It is important to address the periodontitis-associated bacteria in the residual subgingival plaque after scaling and root planing to successfully treat periodontitis. In this study, we explored the possibility of exploiting the ion pairing/complexation of minocycline, Ca²⁺, and sulfate/sulfonate-bearing biopolymers to develop an intrapocket delivery system of minocycline as an adjunct to scaling and root planing. Minocycline-calcium-dextran sulfate complex microparticles were synthesized from minocycline, CaCl₂, and dextran sulfate. They were characterized using Fourier-transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. An in vitro release study was conducted to evaluate the release kinetics of minocycline from these microparticles. Agar disk diffusion assays and biofilm-grown bacteria assays were used to assess antibacterial capability. High loading efficiency (96.98% ± 0.12%) and high loading content (44.69% ± 0.03%) for minocycline were observed for these complex microparticles. Mino-Ca-DS microparticles achieved sustained release of minocycline for at least 9 days at pH 7.4 and 18 days at pH 6.4 in phosphate-buffered saline, respectively. They also demonstrated potent antimicrobial effects against Streptococcus mutans and Aggregatibacter actinomycetemcomitans in agar disk diffusion and biofilm assays. These results suggested that the ion pairing/complexation of minocycline, Ca²⁺, and sulfonate/sulfate-bearing biopolymers can be exploited to develop complex microparticles as local delivery systems for periodontitis treatment.

Outlook on the Application of Metal-Liganded Bioactives for Stimuli-Responsive Release

Direct metal-liganded bioactive coordination complexes are known to be sensitive to stimuli such as pH, light, ion activation, or redox cues. This results in the controlled release of the bioactive(s). Compared to other drug delivery strategies based on metal complexation, this type of coordination negates a multi-step drug loading methodology and offers customized physiochemical properties through judicious choice of modulating ancillary ligands. Bioactive release depends on simple dissociative kinetics. Nonetheless, there are challenges encountered when translating the pure coordination chemistry into the biological and physiological landscape. The stability of the metal-bioactive complex in the biological milieu may be compromised, disrupting the stimuli-responsive release mechanism, with premature release of the bioactive. Research has therefore progressed to the incorporation of metal-liganded bioactives with established drug delivery strategies to overcome these limitations. This review will highlight and critically assess current research interventions in order to predict the direction that pharmaceutical scientists could pursue to arrive at tailored and effective metal-liganded bioactive carriers for stimuli-responsive drug release.

Activated Microglia Targeting Dendrimer-Minocycline Conjugate as Therapeutics for Neuroinflammation

Brain-related disorders have outmatched cancer and cardiovascular diseases worldwide as the leading cause of morbidity and mortality. The lack of effective therapies and the relatively dry central nervous system (CNS) drug pipeline pose formidable challenge. Superior, targeted delivery of current clinically approved drugs may offer significant potential. Minocycline has shown promise for the treatment of neurological diseases owing to its ability to penetrate the blood-brain barrier (BBB) and potency. Despite its potential in the clinic and in preclinical models, the high doses needed to affect a positive therapeutic response have led to side effects. Targeted delivery of minocycline to the injured site and injured cells in the brain can be highly beneficial. Systemically administered hydroxyl poly(amidoamine) (PAMAM) generation-6 (G6) dendrimers have a longer blood circulation time and have been shown to cross the impaired BBB. We have successfully prepared and characterized the in vitro efficacy and in vivo targeting ability of hydroxyl-G6 PAMAM dendrimer-9-amino-minocycline conjugate (D-mino). Minocycline is a challenging drug to carry out chemical transformations due to its inherent instability. We used a combination of a highly efficient and mild copper catalyzed azide-alkyne click reaction (CuAAC) along with microwave energy to conjugate 9-amino-minocycline (mino) to the dendrimer surface via enzyme responsive linkages. D-mino was further evaluated for anti-inflammatory and antioxidant activity in lipopolysaccharides-activated murine microglial cells. D-mino conjugates enhanced the intracellular availability of the drug due to their rapid uptake, suppressed inflammatory cytokine tumor necrosis factor α (TNF-α) production, and reduced oxidative stress by suppressing nitric oxide production, all significantly better than the free drug. Fluorescently labeled dendrimer conjugate (Cy5-D-mino) was systematically administered (intravenous, 55 mg/kg) on postnatal day 1 to rabbit kits with a clinically relevant phenotype of cerebral palsy. The in vivo imaging study indicates that Cy5-D-mino crossed the impaired blood-brain barrier and co-localized with activated microglia at the periventricular white matter areas, including the corpus callosum and the angle of the lateral ventricle, with significant implications for positive therapeutic outcomes. The enhanced efficacy of D-mino, when combined with the inherent neuroinflammation-targeting capability of the PAMAM dendrimers, may provide new opportunities for targeted drug delivery to treat neurological disorders.

Local delivery of minocycline from metal ion-assisted self-assembled complexes promotes neuroprotection and functional recovery after spinal cord injury

Many mechanisms contribute to the secondary injury cascades following traumatic spinal cord injury (SCI). However, most current treatment strategies only target one or a few elements in the injury cascades, and have been largely unsuccessful in clinical trials. Minocycline hydrochloride (MH) is a clinically available antibiotic and anti-inflammatory drug that has been shown to target a broad range of secondary injury mechanisms via its anti-inflammatory, anti-oxidant, and anti-apoptotic properties. However, MH is only neuroprotective at high concentrations. The inability to translate the high doses of MH used in experimental animals to tolerable doses in human patients limits its clinical efficacy. In addition, the duration of MH treatment is limited because long-term systemic administration of high doses of MH has been shown to cause liver toxicity and even death. We have developed a drug delivery system in the form of hydrogel loaded with polysaccharide-MH complexes self-assembled by metal ions for controlled release of MH. This drug delivery system can be injected into the intrathecal space for local delivery of MH with sufficient dose and duration, without causing any additional tissue damage. We show that local delivery of MH at a dose that is lower than the standard human dose (3 mg/kg) was more effective in reducing secondary injury and promoting locomotor functional recovery than systemic injection of MH with the highest dose and duration reported in experimental animal SCI (90-135 mg/kg).

Hemocompatible, antioxidative and antibacterial polypropylene prepared by attaching silver nanoparticles capped with TPGS

Synthesis of Ag NPs by TPGS and the excellent hemocompatibility, anti-oxidative and antibacterial properties of the deposition of Ag NPs onto PP grafted with NIPAAm and APMA.

Stability and controlled antibiotic release from thin films embedded with antibiotic loaded mesoporous silica nanoparticles

Thin films incorporated with gentamicin loaded mesoporous silica nanoparticles exhibit excellent stability and controlled release profile of the encapsulated antibiotic.