One-week in vivo sustained release of a peptide formulated into in situ forming implants

In-situ forming PLGA implants: Towards less toxic solvents

In-situ forming poly(lactic-co-glycolic acid) (PLGA) implants offer a great potential for controlled drug delivery for a variety of applications, e.g. periodontitis treatment. The polymer is dissolved in a water-miscible solvent. The drug is dissolved or dispersed in this solution. Upon contact with aqueous body fluids, the solvent diffuses into the surrounding tissue and water penetrates into the formulation. Consequently, PLGA precipitates, trapping the drug. Often, N-methyl-2-pyrrolidine (NMP) is used as a water-miscible solvent. However, parenteral administration of NMP raises toxicity concerns. The aim of this study was to identify less toxic alternative solvent systems for in-situ forming PLGA implants. Various blends of polyethylene glycol 400 (PEG 400), triethyl citrate (TEC) and ethanol were used to prepare liquid formulations containing PLGA, ibuprofen (as an anti-inflammatory drug) and/or chlorhexidine dihydrochloride (as an antiseptic agent). Implant formation and drug release kinetics were monitored upon exposure to phosphate buffer pH 6.8 at 37 °C. Furthermore, the syringeability of the liquids, antimicrobial activity of the implants, and dynamic changes in the latter's wet mass and pH of the release medium were studied. Importantly, 85:10:5 and 60:30:10 PEG 400:TEC:ethanol blends provided good syringeability and allowed for rapid implant formation. The latter controlled ibuprofen and chlorhexidine release over several weeks and assured efficient antimicrobial activity. Interestingly, fundamental differences were observed concerning the underlying release mechanisms of the two drugs: Ibuprofen was dissolved in the solvent mixtures and partially leached out together with the solvents during implant formation, resulting in relatively pronounced burst effects. In contrast, chlorhexidine dihydrochloride was dispersed in the liquids in the form of tiny particles, which were effectively trapped by precipitating PLGA during implant formation, leading to initial lag-phases for drug release.

3D printed PLGA implants: How the filling density affects drug release

Different types of ibuprofen-loaded, poly (D,L lactic-co-glycolic acid) (PLGA)-based implants were prepared by 3D printing (Droplet Deposition Modeling). The theoretical filling density of the mesh-shaped implants was varied from 10 to 100%. Drug release was measured in agarose gels and in well agitated phosphate buffer pH 7.4. The key properties of the implants (and dynamic changes thereof upon exposure to the release media) were monitored using gravimetric measurements, optical microscopy, Differential Scanning Calorimetry, Gel Permeation Chromatography, and Scanning Electron Microscopy. Interestingly, drug release was similar for implants with 10 and 30% filling density, irrespective of the experimental set-up. In contrast, implants with 100% filling density showed slower release kinetics, and the shape of the release curve was altered in agarose gels. These observations could be explained by the existence (or absence) of a continuous aqueous phase between the polymeric filaments and the "orchestrating role" of substantial system swelling for the control of drug release. At lower filling densities, it is sufficient for the drug to be released from a single filament. In contrast, at high filling densities, the ensemble of filaments acts as a much larger (more or less homogeneous) polymeric matrix, and the average diffusion pathway to be overcome by the drug is much longer. Agarose gel (mimicking living tissue) hinders substantial PLGA swelling and delays the onset of the final rapid drug release phase. This improved mechanistic understanding of the control of drug release from PLGA-based 3D printed implants can help to facilitate the optimization of this type of advanced drug delivery systems.

TREM-1 Modulation Strategies for Sepsis

The triggering receptor expressed on myeloid cells-1 (TREM-1) is a pattern recognition receptor, which can be upregulated in inflammatory diseases as an amplifier of immune responses. Once activated, TREM-1 induces the production and release of pro-inflammatory cytokines and chemokines, in addition to increasing its own expression and circulating levels of the cleaved soluble extracellular portion of TREM-1 (sTREM-1). This amplification of the inflammatory response by TREM-1 has now been considered as a critical contributor to the dysregulated immune responses in sepsis. Studies have shown that in septic patients there is an elevated expression of TREM-1 on immune cells and increased circulating levels of sTREM-1, associated with increased mortality. As a result, a considerable effort has been made towards identifying endogenous ligands of TREM-1 and developing TREM-1 inhibitory peptides to attenuate the exacerbated inflammatory response in sepsis. TREM-1 modulation has proven a promising strategy for the development of therapeutic agents to treat sepsis. Therefore, this review encompasses the ligands investigated as activators of TREM-1 thus far and highlights the development and efficacy of novel inhibitors for the treatment of sepsis and septic shock.

How agarose gels surrounding PLGA implants limit swelling and slow down drug release

The aim of this study was to better understand to which extent and in which way the presence of an agarose gel (mimicking living tissue) around a PLGA [poly(lactic-co-glycolic acid)] implant affects the resulting drug release kinetics. Ibuprofen-loaded implants were prepared by hot melt extrusion. Drug release was measured upon exposure to phosphate buffer pH 7.4 in Eppendorf tubes, as well as upon inclusion into an agarose gel which was exposed to phosphate buffer pH 7.4 in an Eppendorf tube or in a transwell plate. Dynamic changes in the implants' dry & wet mass and dimensions were monitored gravimetrically and by optical macroscopy. Implant erosion and polymer degradation were observed by SEM and GPC. Different pH indicators were used to measure pH changes in the bulk fluids, gels and within the implants during drug release. Ibuprofen release was bi-phasic in all cases: A zero order release phase (~20% of the dose) was followed by a more rapid, final drug release phase. Interestingly, the presence of the hydrogel delayed the onset of the 2nd release phase. This could be attributed to the sterical hindrance of implant swelling: After a certain lag time, the degrading PLGA matrix becomes sufficiently hydrophilic and mechanically instable to allow for the penetration of substantial amounts of water into the system. This fundamentally changes the conditions for drug release: The latter becomes much more mobile and is more rapidly released. A gel surrounding the implant mechanically hinders system swelling and, thus, slows down drug release. These observations also strengthen the hypothesis of the "orchestrating" role of PLGA swelling for the control of drug release and can help developing more realistic in vitro release set-ups.

Drug release from in situ forming implants and advances in release testing

In situ forming implants, defined as liquid formulations that generate solid or semisolid depots following administration, have shown a range of advantages in drug delivery. This drug delivery strategy allows localized delivery, sustained drug release over periods of days to months, and is a less invasive option compared to traditional solid implants which typically require surgical implantation. Unfortunately, there are a number of quality control challenges in terms of drug release testing of these delivery systems which is likely to have contributed to the relatively few commercially available in situ forming implant products. This article reviews current marketed in situ forming implant products, FDA guidance on in vitro release testing, and formulation and environmental parameters influencing drug release from in situ forming implants. Formulation considerations for development of biological agents loaded in situ forming implants are also discussed. The advantages and limitations of typically used in vitro release testing methods are summarized. Difficulties in the development of in vitro-in vivo correlations (IVIVCs) for in situ forming implant are discussed. The knowledge presented will be helpful for the development of in situ forming implants, as well as for the development of appropriate in vitro testing methods and IVIVCs.

Long-lasting in situ forming Implant loaded with Bupivacaine: Investigation on the Polymeric and Non-polymeric Carrier and Solvent Effect

INTRODUCTION

Typically, in situ forming implants utilize Poly (lactide-co-glycolide) (PLGA) as a carrier and N-methyl-2-pyrrolidone (NMP) as a solvent. However, it is essential to develop different carriers to release various drugs in a controlled and sustained manner with economic and safety considerations.

OBJECTIVE

The present study aims to evaluate the in-vitro release of Bupivacaine HCl from in situ forming systems as post-operative local anesthesia.

METHODS

We used Sucrose acetate isobutyrate (SAIB), PLGA 50:50, and a mixture of them as carriers to compare the release behavior. Besides, the effect of PLGA molecular weight (RG 502H, RG 503H, and RG 504H), solvent type, and solvent concentration on the drug release profile was evaluated. The formulations were characterized by investigating their in-vitro drug release, rheological properties, solubility, and DSC, in addition to their morphological properties. Furthermore, the Korsmeyer-Peppas and Weibull models were applied to the experimental data. The results revealed that a mixture of SAIB and PLGA compared to using them solely can extend the Bupivacaine HCl release from 3 days to two weeks.

RESULTS

The DSC results demonstrated the compatibility of the mixture by showing a single Tg. The formulation with NMP had a higher burst release and final release in comparison with other solvents by 30% and 96%, respectively. Increasing the solvent concentration from 12% to 32% raised the drug release significantly, which confirmed the larger porosity in the morphology results. From the Korsmeyer-Peppas model, the mechanism of drug release is predicted to be non-Fickian diffusion.

Triggering receptor expressed on myeloid cells-1 (TREM-1) as a therapeutic target in infectious and noninfectious disease: a critical review

The triggering receptor expressed on myeloid cells-1 (TREM-1) is an innate immune receptor found in the surface of several immune and non-immune cells. Since its first description in 2000, this molecule and its soluble form (sTREM-1) have been implicated in many diseases with infectious and noninfectious origins. As an amplifier of inflammation, the membrane-associated TREM-1 (mTREM-1) isoform induces the production of pro-inflammatory mediators, thus contributing to the pathogenesis of diseases such as sepsis, arthritis, colitis and infections. In this context, many studies have used molecules capable of inhibiting TREM-1 activity as anti-inflammatory drugs. In this regard, a few peptides have been showing promising results in the amelioration of detrimental immune responses. Some commercially available drugs, including corticosteroids and antibiotics, with known anti-inflammatory effects, have also shown activity in TREM-1 signaling. Therefore, considering the potential of this receptor as a therapeutic target, the present review encompasses the main compounds explored so far in TREM-1 modulation, highlighting and critically discussing its effects and major drawbacks of such approaches.

The characteristics and pivotal roles of triggering receptor expressed on myeloid cells-1 in autoimmune diseases

Triggering receptor expressed on myeloid cells-1 (TREM-1) engagement can directly trigger inflammation or amplify an inflammatory response by synergizing with TLRs or NLRs. Autoimmune diseases are a family of chronic systemic inflammatory disorders. The pivotal role of TREM-1 in inflammation makes it important to explore its immunological effects in autoimmune diseases. In this review, we summarize the structural and functional characteristics of TREM-1. Particularly, we discuss recent findings on TREM-1 pathway regulation in various autoimmune diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), inflammatory bowel disease (IBD), type 1 diabetes (T1D), and psoriasis. This receptor may potentially be manipulated to alter the inflammatory response to chronic inflammation and possible therapies are explored in this review.

In-situ forming PLGA implants for intraocular dexamethasone delivery

Different types of in-situ forming implants based on poly(lactic-co-glycolic acid) (PLGA) and N-methyl-pyrrolidone (NMP) were prepared for controlled ocular delivery of dexamethasone. The impact of the volume of the release medium, initial drug content, polymer molecular weight and PLGA concentration on the resulting drug release kinetics were studied and explained based on a thorough physico-chemical characterization of the systems. This included for instance the monitoring of dynamic changes in the implants' wet and dry mass, morphology, PLGA polymer molecular weight, pH of the surrounding bulk fluid and water/NMP contents upon exposure to phosphate buffer pH 7.4. Importantly, the systems can be expected to be rather robust with respect to variations in the vitreous humor volumes encountered in vivo. Interestingly, limited drug solubility effects within the implants as well as in the surrounding aqueous medium play an important role for the control of drug release at a drug loading of only 7.5%. Furthermore, the polymer molecular weight and PLGA concentration in the liquid formulations are decisive for how the polymer precipitates during solvent exchange and for the swelling behavior of the systems. These features determine the resulting inner system structure and the conditions for mass transport. Consequently, they affect the degradation and drug release of the in-situ formed implants.

Effects of Porphyromonas gingivalis LPS and LR12 peptide on TREM-1 expression by monocytes

Periodontal disease involves the activation of host immune response, acting not only as defender of periodontal tissues against bacterial aggression but also as mediator of tissue destruction. Triggering receptor expressed on myeloid cells 1 (TREM-1) is an immune receptor that synergizes with Toll-like receptors in amplifying the inflammatory response mediated by microbial molecules.

AIM

To investigate the role of P. gingivalis lipopolysaccharide (LPS) and the effect of LR12, a TREM-1 inhibitory peptide, on the expression of membrane-bound and soluble form of TREM-1 on human primary monocytes, as well as the production of proinflammatory cytokines.

MATERIAL AND METHODS

Cells were stimulated with 1 μg/ml of LPS with or without LR12. PCR, flow cytometry and ELISA were used to determine TREM-1 expressions and cytokines release by monocytes.

RESULTS

P. gingivalis LPS can induce a significant increase in TREM-1 expression (mRNA, membrane-bound and soluble form, p < 0.001) as well as cytokines (IL-1β, TNFα) and chemokines (IL-8) production by monocytes. This monocytes' activation was partly prevented by LR12.

CONCLUSIONS

TREM-1 inhibitors such as LR12 could be interesting for the modulation of the excessive inflammatory response that occurs during periodontal disease.