Extended Release of Bupivacaine from Temperature-responsive Hydrogels Provides Multi-day Analgesia for Postoperative Pain

OBJECTIVE

A local anesthetic that provides analgesia lasting at least three days could significantly improve postoperative pain management. This study evaluated the analgesic efficacy and safety of an extended-release formulation of bupivacaine based on the injectable hydrogel carrier poly(N-isopropylacrylamide-co-dimethylbutyrolactone acrylamide-co-Jeffamine M-1000 acrylamide) (PNDJ).

METHODS

The efficacy of PNDJ containing 4% bupivacaine (SBG004) given by peri-incisional subcutaneous injection (SBG004 SC) or wound filling instillation (SBG004 WF) was evaluated compared to saline, liposomal bupivacaine, bupivacaine collagen sponge, bupivacaine-meloxicam polyorthoester, and bupivacaine HCl in a porcine skin and muscle incision model. Mechanical allodynia was assessed by withdrawal from application of von Frey filaments, and local tolerance was evaluated by histology. Bupivacaine pharmacokinetics for SBG004 SC were measured in rabbits (16.5 mg bupivacaine/kg).

RESULTS

Animals demonstrated less mechanical allodynia at incisions receiving SBG004 SC for up to 96 hours postoperatively. Incisions treated with SBG004 SC tolerated more force without a withdrawal indicative of pain compared to saline for 96 hours, and compared to SBG004 WF and all active controls at 24, 48, and 72 hours except bupivacaine-meloxicam polyorthoester at 72 hours. By 49 days, SBG004 was histologically absent and was replaced with granulation tissue infiltrated with immune cells in some areas. In rabbits, Cmax was 41.6 ± 9.7 ng/mL with t1/2 82.0 ± 35.8 hours (mean ± SD).

CONCLUSIONS

Peri-incisional SBG004 SC provided extended release of bupivacaine sufficient to reduce sensation of incisional pain for 96 hours, in vivo bupivacaine delivery for at least 7 days, and a favorable local and systemic toxicity profile.

Local antimicrobial delivery from temperature-responsive hydrogels reduces incidence of intra-abdominal infection in rats

The objective of this study was to evaluate local antimicrobial delivery from temperature-responsive hydrogels for preventing infection in a rat model of intra-abdominal infection (IAI), and to determine whether delivery of tobramycin and vancomycin in combination is effective against IAI pathogens. Rats received intraperitoneal inoculation of E. coli, rat cecal contents, or cecal contents supplemented with E. coli, and received either no treatment, subcutaneous cefoxitin, or local delivery from hydrogels containing vancomycin, tobramycin, or both antimicrobials. Only the hydrogel with tobramycin and vancomycin significantly increased the infection free-rate compared to no treatment for all inocula (E. coli: 13/17, p < 0.0001; cecal contents: 11/17, p = 0.0013; cecal contents + E. coli: 15/19, p < 0.0001). Additionally, tobramycin and vancomycin displayed no synergy or antagonism against clinical isolates in vitro. Local delivery of tobramycin and vancomycin from temperature-responsive hydrogels provides broad coverage and high antimicrobial concentrations for several hours that may be effective for preventing IAIs.

PNJ scaffolds promote microenvironmental regulation of glioblastoma stem-like cell enrichment and radioresistance

Glioblastoma (GBM) brain tumors contain a subpopulation of self-renewing multipotent Glioblastoma stem-like cells (GSCs) that are believed to drive the near inevitable recurrence of GBM. We previously engineered temperature responsive scaffolds based on the polymer poly(N-isopropylacrylamide-co-Jeffamine M-1000 acrylamide) (PNJ) for the purpose of enriching GSCs in vitro from patient-derived samples. Here, we used PNJ scaffolds to study microenvironmental regulation of self-renewal and radiation response in patient-derived GSCs representing classical and proneural subtypes. GSC self-renewal was regulated by the composition of PNJ scaffolds and varied with cell type. PNJ scaffolds protected against radiation-induced cell death, particularly in conditions that also promoted GSC self-renewal. Additionally, cells cultured in PNJ scaffolds exhibited increased expression of the transcription factor HIF2α, which was not observed in neurosphere culture, providing a potential mechanistic basis for differences in radio-resistance. Differences in PNJ regulation of HIF2α in irradiated and untreated conditions also offered evidence of stem plasticity. These data show PNJ scaffolds provide a unique biomaterial for evaluating dynamic microenvironmental regulation of GSC self-renewal, radioresistance, and stem plasticity.

In vivo evaluation of temperature-responsive antimicrobial-loaded PNIPAAm hydrogels for prevention of surgical site infection

Surgical site infections (SSIs) are a persistent clinical challenge. Local antimicrobial delivery may reduce the risk of SSI by increasing drug concentrations and distribution in vulnerable surgical sites compared to what is achieved using systemic antimicrobial prophylaxis alone. In this work, we describe a comprehensive in vivo evaluation of the safety and efficacy of poly(N-isopropylacrylamide-co-dimethylbutyrolactone acrylamide-co-Jeffamine M-1000 acrylamide) [PNDJ], an injectable temperature-responsive hydrogel carrier for antimicrobial delivery in surgical sites. Biodistribution data indicate that PNDJ is primarily cleared via the liver and kidneys following drug delivery. Antimicrobial-loaded PNDJ was generally well-tolerated locally and systemically when applied in bone, muscle, articulating joints, and intraperitoneal space, although mild renal toxicity consistent with the released antimicrobials was identified at high doses in rats. Dosing of PNDJ at bone-implant interfaces did not affect normal tissue healing and function of orthopedic implants in a transcortical plug model in rabbits and in canine total hip arthroplasty. Finally, PNDJ was effective at preventing recurrence of implant-associated MSSA and MRSA osteomyelitis in rabbits, showing a trend toward outperforming commercially available antimicrobial-loaded bone cement and systemic antimicrobial administration. These studies indicate that antimicrobial-loaded PNDJ hydrogels are well-tolerated and could reduce incidence of SSI in a variety of surgical procedures.

PNIPAAm-co-Jeffamine® (PNJ) scaffolds as in vitro models for niche enrichment of glioblastoma stem-like cells

Glioblastoma (GBM) is the most common adult primary brain tumor, and the 5-year survival rate is less than 5%. GBM malignancy is driven in part by a population of GBM stem-like cells (GSCs) that exhibit indefinite self-renewal capacity, multipotent differentiation, expression of neural stem cell markers, and resistance to conventional treatments. GSCs are enriched in specialized niche microenvironments that regulate stem phenotypes and support GSC radioresistance. Therefore, identifying GSC-niche interactions that regulate stem phenotypes may present a unique target for disrupting the maintenance and persistence of this treatment resistant population. In this work, we engineered 3D scaffolds from temperature responsive poly(N-isopropylacrylamide-co-Jeffamine M-1000® acrylamide), or PNJ copolymers, as a platform for enriching stem-specific phenotypes in two molecularly distinct human patient-derived GSC cell lines. Notably, we observed that, compared to conventional neurosphere cultures, PNJ cultured GSCs maintained multipotency and exhibited enhanced self-renewal capacity. Concurrent increases in expression of proteins known to regulate self-renewal, invasion, and stem maintenance in GSCs (NESTIN, EGFR, CD44) suggest that PNJ scaffolds effectively enrich the GSC population. We further observed that PNJ cultured GSCs exhibited increased resistance to radiation treatment compared to GSCs cultured in standard neurosphere conditions. GSC radioresistance is supported in vivo by niche microenvironments, and this remains a significant barrier to effectively treating these highly tumorigenic cells. Taken in sum, these data indicate that the microenvironment created by synthetic PNJ scaffolds models niche enrichment of GSCs in patient-derived GBM cell lines, and presents tissue engineering opportunities for studying clinically important behaviors such as radioresistance in vitro.

Optical barcoding of PLGA for multispectral analysis of nanoparticle fate in vivo

Understanding of the mechanisms by which systemically administered nanoparticles achieve delivery across biological barriers remains incomplete, due in part to the challenge of tracking nanoparticle fate in the body. Here, we develop a new approach for "barcoding" nanoparticles composed of poly(lactic-co-glycolic acid) (PLGA) with bright, spectrally defined quantum dots (QDs) to enable direct, fluorescent detection of nanoparticle fate with subcellular resolution. We show that QD labeling does not affect major biophysical properties of nanoparticles or their interaction with cells and tissues. Live cell imaging enabled simultaneous visualization of the interaction of control and targeted nanoparticles with bEnd.3 cells in a flow chamber, providing direct evidence that surface modification of nanoparticles with the cell-penetrating peptide TAT increases their biophysical association with cell surfaces over very short time periods under convective current. We next developed this technique for quantitative biodistribution analysis in vivo. These studies demonstrate that nanoparticle surface modification with the cell penetrating peptide TAT facilitates brain-specific delivery that is restricted to brain vasculature. Although nanoparticle entry into the healthy brain parenchyma is minimal, with no evidence for movement of nanoparticles across the blood-brain barrier (BBB), we observed that nanoparticles are able to enter to the central nervous system (CNS) through regions of altered BBB permeability - for example, into circumventricular organs in the brain or leaky vasculature of late-stage intracranial tumors. In sum, these data demonstrate a new, multispectral approach for barcoding PLGA, which enables simultaneous, quantitative analysis of the fate of multiple nanoparticle formulations in vivo.

Hyaluronic acid-laminin hydrogels increase neural stem cell transplant retention and migratory response to SDF-1α

The chemokine SDF-1α plays a critical role in mediating stem cell response to injury and disease and has specifically been shown to mobilize neural progenitor/stem cells (NPSCs) towards sites of neural injury. Current neural transplant paradigms within the brain suffer from low rates of retention and engraftment after injury. Therefore, increasing transplant sensitivity to injury-induced SDF-1α represents a method for increasing neural transplant efficacy. Previously, we have reported on a hyaluronic acid-laminin based hydrogel (HA-Lm gel) that increases NPSC expression of SDF-1α receptor, CXCR4, and subsequently, NPSC chemotactic migration towards a source of SDF-1α in vitro. The study presented here investigates the capacity of the HA-Lm gel to promote NPSC response to exogenous SDF-1α in vivo. We observed the HA-Lm gel to significantly increase NPSC transplant retention and migration in response to SDF-1α in a manner critically dependent on signaling via the SDF-1α-CXCR4 axis. This work lays the foundation for development of a more effective cell therapy for neural injury, but also has broader implications in the fields of tissue engineering and regenerative medicine given the essential roles of SDF-1α across injury and disease states.

Enhancing neural stem cell response to SDF-1α gradients through hyaluronic acid-laminin hydrogels

Traumatic brain injury (TBI) initiates an expansive biochemical insult that is largely responsible for the long-term dysfunction associated with TBI; however, current clinical treatments fall short of addressing these underlying sequelae. Pre-clinical investigations have used stem cell transplantation with moderate success, but are plagued by staggeringly low survival and engraftment rates (2-4%). As such, providing cell transplants with the means to better dynamically respond to injury-related signals within the transplant microenvironment may afford improved transplantation survival and engraftment rates. The chemokine stromal cell-derived factor-1α (SDF-1α) is a potent chemotactic signal that is readily present after TBI. In this study, we sought to develop a transplantation vehicle to ultimately enhance the responsiveness of neural transplants to injury-induced SDF-1α. Specifically, we hypothesize that a hyaluronic acid (HA) and laminin (Lm) hydrogel would promote 1. upregulated expression of the SDF-1α receptor CXCR4 in neural progenitor/stem cells (NPSCs) and 2. enhanced NPSC migration in response to SDF-1α gradients. We demonstrated successful development of a HA-Lm hydrogel and utilized standard protein and cellular assays to probe NPSC CXCR4 expression and NPSC chemotactic migration. The findings demonstrated that NPSCs significantly increased CXCR4 expression after 48 h of culture on the HA-Lm gel in a manner critically dependent on both HA and laminin. Moreover, the HA-Lm hydrogel significantly increased NPSC chemotactic migration in response to SDF-1α at 48 h, an effect that was critically dependent on HA, laminin and the SDF-1α gradient. Therefore, this hydrogel serves to 1. prime NPSCs for the injury microenvironment and 2. provide the appropriate infrastructure to support migration into the surrounding tissue, equipping cells with the tools to more effectively respond to the injury microenvironment.

Temperature responsive hydrogels enable transient three-dimensional tumor cultures via rapid cell recovery

Recovery of live cells from three-dimensional (3D) culture would improve analysis of cell behaviors in tissue engineered microenvironments. In this work, we developed a temperature responsive hydrogel to enable transient 3D culture of human glioblastoma (GBM) cells. N-isopropylacrylamide was copolymerized with hydrophilic grafts and functionalized with the cell adhesion peptide RGD to yield the novel copolymer poly(N-isopropylacrylamide-co-Jeffamine(®) M-1000 acrylamide-co-hydroxyethylmethacrylate-RGD), or PNJ-RGD. This copolymer reversibly gels in aqueous solutions when heated under normal cell culture conditions (37°C). Moreover, these gels redissolve within 70 s when cooled to room temperature without the addition of any agents to degrade the synthetic scaffold, thereby enabling rapid recollection of viable cells after 3D culture. We tested the efficiency of cell recovery following extended 3D culture and were able to recover more than 50% of viable GBM cells after up to 7 days in culture. These data demonstrate the utility of physically crosslinked PNJ-RGD hydrogels as a platform for culture and recollection of cells in 3D.

Implications of vaccination and waning immunity

For infectious diseases where immunization can offer lifelong protection, a variety of simple models can be used to explain the utility of vaccination as a control method. However, for many diseases, immunity wanes over time and is subsequently enhanced (boosted) by asymptomatic encounters with the infection. The study of this type of epidemiological process requires a model formulation that can capture both the within-host dynamics of the pathogen and immune system as well as the associated population-level transmission dynamics. Here, we parametrize such a model for measles and show how vaccination can have a range of unexpected consequences as it reduces the natural boosting of immunity as well as reducing the number of naive susceptibles. In particular, we show that moderate waning times (40-80 years) and high levels of vaccination (greater than 70%) can induce large-scale oscillations with substantial numbers of symptomatic cases being generated at the peak. In addition, we predict that, after a long disease-free period, the introduction of infection will lead to far larger epidemics than that predicted by standard models. These results have clear implications for the long-term success of any vaccination campaign and highlight the need for a sound understanding of the immunological mechanisms of immunity and vaccination.

An in-host model of acute infection: measles as a case study

The epidemiology of acute infections is strongly influenced by the immune status of individuals. In-host models can provide quantitative predictions of immune status and can thus offer valuable insights into the factors that influence transmission between individuals and the effectiveness of vaccination protocols with respect to individual immunity. Here we develop an in-host model of measles infection. The model explicitly considers the effects of immune system memory and CD8 T-cells, which are key to measles clearance. The model is used to determine the effects of waning immunity through vaccination and infection, the effects of booster exposures or vaccines on the level of immunity, and the immune system characteristics that result in measles transmission (R(0)>1) even if an individual has no apparent clinical symptoms. We find that the level of immune system CD8 T-cells at the time of exposure to measles determines whether an individual will experience a measles infection or simply a boost in immunity. We also find that the infected cell dynamics are a good indicator of measles transmission and the degree of symptoms that will be experienced. Our results indicate that the degree of immunity in adults is independent of the source of exposure in early childhood, be it vaccine or natural infection.

Improving estimates of the basic reproductive ratio: using both the mean and the dispersal of transition times

In both within-host and epidemiological models of pathogen dynamics, the basic reproductive ratio, R0, is a powerful tool for gauging the risk associated with an emerging pathogen, or for estimating the magnitude of required control measures. Techniques for estimating R0, either from incidence data or in-host clinical measures, often rely on estimates of mean transition times, that is, the mean time before recovery, death or quarantine occurs. In many cases, however, either data or intuition may provide additional information about the dispersal of these transition times about the mean, even if the precise form of the underlying probability distribution remains unknown. For example, we may know that recovery typically occurs within a few days of the mean recovery time. In this paper we elucidate common situations in which R0 is sensitive to the dispersal of transition times about their respective means. We then provide simple correction factors that may be applied to improve estimates of R0 when not only the mean but also the standard deviation of transition times out of the infectious state can be estimated.

Temporal cortex synaptophysin mRNA is reduced in Alzheimer's disease and is negatively correlated with the severity of dementia

We measured synaptophysin mRNA in neocortical tissue from 7 prospectively assessed, pathologically verified normal individuals, 17 subjects with Alzheimer's disease (AD), and 13 subjects with a non-AD dementia. In temporal cortex (Brodmann area 21), synaptophysin mRNA was decreased in AD and non-AD dementia groups compared to controls. The loss was also present relative to polyadenylated mRNA content. Synaptophysin mRNA signal correlated negatively with the degree of dementia and negatively with the pathological severity of AD. In occipital cortex (Brodmann area 17) there were no differences between groups nor clinicopathological correlations. These data extend the evidence for a regional synaptic pathology in AD which affects synaptic protein gene expression by temporal cortex neurons.

Amyloid precursor protein mRNAs in Alzheimer's disease

Hybridization studies of mRNA link genetic with neurochemical and neuropathological approaches to Alzheimer's disease (AD). Here we review the distribution and abundance of amyloid precursor protein mRNAs in normal and AD-afflicted brains. The expression of apolipoprotein E and presenilin mRNAs are also discussed.

Effect of serotonin treatment on intestinal transport in the rabbit

The hormone serotonin (5-hydroxytryptamine) has been implicated as the cause of the diarrhea seen in many patients with the carcinoid syndrome. To determine whether serotonin is an intestinal secretagogue, the effect of serotonin on intestinal water and electrolyte transport was evaluated in the rabbit. Two weeks of daily subcutaneous injection of serotonin suspended in oil resulted in a blood serotonin level elevated to twice that of controls. Intestinal transport was studied in vivo by a perfusion technique. Serotonin treatment resulted in ileal secretion and decreased mid-jejunal absorption of water and electrolytes but did not effect water absorption in the proximal jejunum or colon. Intestinal absorption of D-glucose and the amino acid L-tryptophan and glucose-dependent water and electrolyte absorption were normal in serotonin-treated animals. Serotonin-induced ileal secretion was reversed by methysergide, a peripheral antagonist of serotonin action. No alterations in intestinal histology or permeability occurred in serotonin-treated animals. Serotonin-induced intestinal secretion was not associated with alterations in the activities of intestinal mucosal adenylate cyclase, cyclic nucleotide phosphodiesterase, or Na-K-ATPase.