Influence of Supraphysiologic Biomaterial Stiffness on Ventricular Mechanics and Myocardial Infarct Reinforcement.

Injectable intramyocardial biomaterials have promise to limit adverse ventricular remodeling through mechanical and biologic mechanisms. While some success has been observed by injecting materials to regenerate new tissue, optimal biomaterial stiffness to thicken and stiffen infarcted myocardium to limit adverse remodeling has not been determined. In this work, we present an in-vivo study of the impact of biomaterial stiffness over a wide range of stiffness moduli on ventricular mechanics. We utilized injectable methacrylated polyethylene glycol (PEG) hydrogels fabricated at 3 different mechanical moduli: 5 kPa (low), 25 kPa (medium/myocardium), and 250 kPa (high/supraphysiologic). We demonstrate that the supraphysiological high stiffness favorably alters post-infarct ventricular mechanics and prevents negative tissue remodeling. Lower stiffness materials do not alter mechanics and thus to be effective, must instead target biological reparative mechanisms. These results may influence rationale design criteria for biomaterials developed for infarct reinforcement therapy. STATEMENT OF SIGNIFICANCE: Acellular biomaterials for cardiac application can provide benefit via mechanical and biological mechanisms post myocardial infarction. We study the role of biomaterial mechanical characteristics on ventricular mechanics in myocardial infarcts. Previous studies have not measured the influence of injected biomaterials on ventricular mechanics, and consequently rational design criteria is unknown. By utilizing an in-vivo assessment of ventricular mechanics, we demonstrate that low stiffness biomaterial do not alter pathologic ventricular mechanics. Thus, to be effective, low stiffness biomaterials must target biological reparative mechanisms. Physiologic and supra-physiologic biomaterials favorably alter post-infarct mechanics and prevents adverse ventricular remodeling.

Metabolites of Synthetic Cannabinoid 5F-MDMB-PINACA Retain Affinity, Act as High Efficacy Agonists and Exhibit Atypical Pharmacodynamic Properties at CB1 Receptors.

Synthetic cannabinoid receptor agonists (SCRAs) are a large group of abused psychoactive compounds that elicit numerous toxic effects not observed with cannabis, including death. Abuse of third-generation SCRA 5F-MDMB-PINACA (also known as 5F-ADB) has been associated with over 40 fatalities. This SCRA is metabolized to several active phase I metabolites, including excessively high post-mortem serum concentrations of an ester hydrolysis metabolite, 5F-MDMB-PINACA-M7 (M7). Although high serum concentrations of M7 (and other active metabolites) have been suggested to contribute to 5F-MDMB-PINACA toxicity, the affinity of M7 for CB1 receptors is unknown and more complete pharmacodynamic characterization of 5F-MDMB-PINACA and its active metabolites is needed. Competition binding and G-protein modulation studies presented here confirm reports that 5F-MDMB-PINACA and a second N-5-hydroxypentyl metabolite (M2) exhibit nM affinity and act as high efficacy agonists at CB1 receptors. Also as previously published, M7 exhibits high efficacy at CB1 receptors; however, demonstrated here for the first time, M7 retains only low µΜ affinity. Empirically derived Kb values indicate rimonabant differentially antagonizes G-protein activation produced by 5F-MDMB-PINACA, relative to Δ9-THC (THC) or its metabolites. Chronic administration of 5F-MDMB-PINACA and metabolites results in CB1 down-regulation, but only 5F-MDMB-PINACA produces desensitization. Although low CB1 affinity/potency of M7 precluded in vivo studies, both M2 and THC produce locomotor suppression and CB1-mediated dose-dependent hypothermia and analgesia in mice. Collectively, these data confirm and extend previous studies suggesting that 5F-MDMB-PINACA is metabolized to active compounds exhibiting atypical pharmacodynamic properties at CB1 receptors, that may accumulate with parent drug to produce severe toxicity.

Effects of Laboratory Housing Conditions on Core Temperature and Locomotor Activity in Mice.

Drug developers worldwide assess compound safety and efficacy using measures that include mouse core temperature and locomotor activity. Subtle differences in animal housing conditions between institutions can alter these values, impacting scientific rigor and reproducibility. In these studies, adult male NIH Swiss mice were surgically implanted with radiotelemetry probes that simultaneously monitored core temperature and locomotor activity across various housing conditions. In the first study, ambient temperature was varied between 20 °C and 28°C in groups of singly housed mice. Additional studies held the mice at a constant ambient temperature and examined the effects of cage density (housing animals singly or in groups of 3 or 6), bedding change and provision of nesting material, and the availability of a running wheel on core temperature and locomotor activity. Mice overwhelmingly maintained species-typical core temperatures across all ambient temperatures, across all housing conditions, when bedding was fresh or old, and with or without the provision of cotton squares as nesting material. However, engaging in wheel running and the combination of fresh bedding and cotton squares transiently increased core temperatures beyond the species-typical range. Similarly, the circadian distribution of locomotor activity was significantly disrupted by placing animals in cages with fresh bedding or nesting material, or by performing both of these manipulations concurrently during the light period. These findings suggest that standard husbandry practices and common housing conditions may transiently affect core temperature in adult mice. Furthermore, these practices may have profound and relatively long-lasting effects on motor activity and the regulation of circadian rhythms.

The synthetic cathinone 3,4-methylenedioxypyrovalerone increases impulsive action in rats.

A previous study from our laboratory has shown that the selective catecholamine reuptake inhibitor 3,4-methylenedioxypyrovalerone (MDPV) persistently alters impulsive choice as measured by delay discounting. To further understand the proimpulsive effects of MDPV, we examined its capacity to modulate a different impulsive measure - impulsive action - using a differential reinforcement of low rates of responding task with an inter-response time of 20 s. Three groups of male, Sprague-Dawley rats (n = 6) were first tested in daily sessions to understand the acute effects of cocaine (1.0-30.0 mg/kg), MDPV (0.1-3.0 mg/kg), or saline (1.0 ml/kg) on impulsive action. Both cocaine and MDPV increased impulsive action, most notably by decreasing timing error responses and response efficiency, but MDPV was more effective than cocaine. Additionally, MDPV suppressed operant responding in two of six animals at the highest dose tested. Next, the same animals received 10 postsession injections, once every other day, of either 30.0 mg/kg cocaine, 3.0 mg/kg MDPV, or 1.0 ml/kg saline based on their treatment group. An acute dose-effect redetermination was completed following the repeated administration studies, and once again MDPV and cocaine demonstrated proimpulsive effects. Interestingly, timing error responses were decreased in both MDPV and cocaine groups after an acute saline injection, potentially indicating persistent impulsive changes following the repeated administration phase of the experiment. These studies indicate that MDPV increases impulsive action acutely and that this increase may be potentiated following a series of repeated administrations.

Repeated administration of synthetic cathinone 3,4-methylenedioxypyrovalerone persistently increases impulsive choice in rats.

3,4-Methylenedioxypyrovalerone (MDPV) is a selective catecholamine reuptake inhibitor abused for its psychostimulant properties. This study examined if MDPV administration alters impulsive choice measured by delay discounting in rats. Three groups of rats were tested in daily delay discounting sessions to determine the effects of acute cocaine (1.0-30.0 mg/kg), MDPV (0.1-3.0 mg/kg), or saline on mean adjusted delay (MAD). Dose-dependent decreases in MAD were elicited only by acute MDPV, which also suppressed operant responding at the highest dose. Next, rats received post-session injections (30.0 mg/kg cocaine, 3.0 mg/kg MDPV, or saline) every other day for a total of 10 injections. MAD increased during saline treatment, did not change during cocaine treatment, and was reduced during MDPV treatment. In dose-effect re-determinations, no acute drug effects on MAD were observed, but compared to the initial dose-effect determination, MDPV suppressed operant responding in more animals, with zero animals completing trials at the highest dose. All saline and MDPV-treated subjects were sacrificed, and striatal and cortical dopamine levels were quantified by HPLC. These studies indicate that administration of MDPV may increase impulsive choice acutely and persistently. These proimpulsive effects are possibly mediated by increases in striatal dopamine turnover.

In Utero Exposure to Norbuprenorphine, a Major Metabolite of Buprenorphine, Induces Fetal Opioid Dependence and Leads to Neonatal Opioid Withdrawal Syndrome.

Buprenorphine is the preferred treatment of opioid use disorder during pregnancy but can cause fetal opioid dependence and neonatal opioid withdrawal syndrome (NOWS). Notably, withdrawal severity is independent of maternal buprenorphine dose, suggesting that interindividual variance in pharmacokinetics may influence risk and severity of NOWS. Using a rat model of NOWS, we tested the hypothesis that clinically relevant doses of the active metabolite norbuprenorphine (NorBUP) can induce in utero opioid dependence, manifested as naltrexone-precipitated withdrawal signs in the neonate. Pregnant Long-Evans rats were implanted with 14-day osmotic minipumps containing vehicle, morphine (positive control), or NorBUP (0.3-10 mg/kg per day) on gestation day 9. By 12 hours post-delivery, an intraperitoneal injection of the opioid antagonist naltrexone (1 or 10 mg/kg) or saline was administered to pups. Precipitated withdrawal signs were graded by raters blinded to treatment conditions. In a separate group, NorBUP concentrations in maternal and fetal blood and brain on gestation day 20 were determined by liquid chromatography-tandem mass spectrometry. Steady-state maternal blood concentrations of NorBUP in dams infused with 1 or 3 mg/kg per day were comparable to values reported in pregnant humans treated with buprenorphine (1.0 and 9.6 ng/ml, respectively), suggesting a clinically relevant dosing regimen. At these doses, NorBUP increased withdrawal severity in the neonate as shown by an evaluation of 10 withdrawal indicators. These findings support the possibility that NorBUP contributes to fetal opioid dependence and NOWS following maternal buprenorphine treatment during pregnancy.

Encapsulated oligodendrocyte precursor cell fate is dependent on PDGF-AA release kinetics in a 3D microparticle-hydrogel drug delivery system.

Biomaterial drug delivery systems (DDS) can be used to regulate growth factor release and combat the limited intrinsic regeneration capabilities of central nervous system (CNS) tissue following injury and disease. Of particular interest are systems that aid in oligodendrocyte regeneration, as oligodendrocytes generate myelin which surrounds neuronal axons and helps transmit signals throughout the CNS. Oligodendrocyte precursor cells (OPCs) are found in small numbers in the adult CNS, but are unable to effectively differentiate following CNS injury. Delivery of signaling molecules can initiate a favorable OPC response, such as proliferation or differentiation. Here, we investigate the delivery of one such molecule, platelet derived growth factor-AA (PDGF-AA), from poly(lactic-co-glycolic) acid microparticles to OPCs in a 3D polyethylene glycol-based hydrogel. The goal of this DDS was to better understand the relationship between PDGF-AA release kinetics and OPC fate. The system approximates native brain tissue stiffness, while incorporating PDGF-AA under seven different delivery scenarios. Within this DDS, supply of PDGF-AA followed by PDGF-AA withdrawal caused OPCs to upregulate gene expression of myelin basic protein (MBP) by factors of 1.6-9.2, whereas continuous supply of PDGF-AA caused OPCs to remain proliferative. At the protein expression level, we observed an upregulation in O1, a marker for mature oligodendrocytes. Together, these results show that burst release followed by withdrawal of PDGF-AA from a hydrogel DDS stimulates survival, proliferation, and differentiation of OPCs in vitro. Our results could inform the development of improved neural regeneration strategies that incorporate delivery of PDGF-AA to the injured CNS. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2402-2411, 2018.

Effects of orally self-administered bath salt constituent 3,4-methylenedioxypyrovalerone (MDPV) in mice.

Synthetic cathinones in bath salts products are psychostimulant drugs of abuse, and 3,4-methylenedioxypyrovalerone (MDPV) is a common constituent of these products. Oral MDPV has been show to stimulate locomotor activity but reinforcing, locomotor and appetitive stimulus effects of oral MDPV are unknown. Choice procedures evaluated preference for 0.03, 0.10, 0.30, and 1.00mg/mL MDPV solutions versus 0.10mg/mL quinine solution or water. To verify that oral MDPV produced pharmacological effects, locomotor activity was monitored during and after consumption of water, quinine, or MDPV solutions. Conditioned place preference (CPP) tested the apparent appetitive effects of a preferred concentration of oral MDPV with locomotor stimulant effects (0.30mg/mL), using water as a control, and compared with results from intraperitoneally-administered MDPV. Consumption of MDPV solutions (0.03-1.00mg/mL) was low when the alternative fluid was water, but a history of MDPV consumption increased MDPV choice. When paired with a quinine control solution, MDPV solutions (0.03-0.30mg/mL) were almost exclusively preferred, and treatment with the catecholamine synthesis inhibitor αMPT decreased MDPV choice. Consumption of MDPV concentrations (0.1-1.0mg/mL) stimulated locomotor activity. Chronic (10day) access to 0.30mg/mL MDPV resulted in escalated consumption, but locomotor effects did not systematically change across the access period. Finally, consumption of 0.30mg/mL MDPV elicited CPP with a magnitude similar to the preference observed following intraperitoneal administration of MDPV. Consistent with human abuse patterns, oral MDPV has reinforcing effects in the mouse which are most likely related to its psychostimulant-like pharmacological profile.

Oligodendrocyte Precursor Cell Viability, Proliferation, and Morphology is Dependent on Mesh Size and Storage Modulus in 3D Poly(ethylene glycol)-Based Hydrogels.

Oligodendrocytes in the central nervous system (CNS) are responsible for generating myelin, an electrically insulating layer around neuronal axons. When myelin is damaged, neurons are incapable of sustaining normal communications, which can manifest in patients as pain and loss of mobility and vision. A plethora of research has used biomaterials to promote neuronal regeneration, but despite the wide implications of a disrupted myelin sheath, very little is known about how biomaterial environments impact proliferation of oligodendrocyte precursor cells (OPCs) or their differentiation into myelinating oligodendrocytes. This work investigates how the storage modulus and mesh size of a polyethylene glycol (PEG)-based hydrogel, varied via two different mechanisms, directly affect the proliferation of two OPC lines encapsulated and cultured in 3D. Viability and proliferation of both OPC lines was dependent on hydrogel swelling and stiffness, where the concentration of ATP increased more in the more compliant gels. OPCs multiplied in the 3D hydrogels, creating significantly larger spheroids in the less cross-linked conditions. Stiffer, more highly cross-linked materials lead to greater expression of PDGFRα, an OPC receptor, indicating that fewer cells were committed to the oligodendrocyte lineage or had dedifferentiated in compliant materials. Laminin incorporation in the 3D matrix was found to have little effect on viability or proliferation. These findings provide valuable information on how mesh size and stiffness affect OPCs where more compliant materials favor proliferation of OPCs with less commitment to a mature oligodendrocyte lineage. Such information will be useful in the development of translational biomaterials to stimulate oligodendrocyte maturation for neural regeneration.

Engineering Biomaterials to Influence Oligodendroglial Growth, Maturation, and Myelin Production.

Millions of people suffer from damage or disease to the nervous system that results in a loss of myelin, such as through a spinal cord injury or multiple sclerosis. Diminished myelin levels lead to further cell death in which unmyelinated neurons die. In the central nervous system, a loss of myelin is especially detrimental because of its poor ability to regenerate. Cell therapies such as stem or precursor cell injection have been investigated as stem cells are able to grow and differentiate into the damaged cells; however, stem cell injection alone has been unsuccessful in many areas of neural regeneration. Therefore, researchers have begun exploring combined therapies with biomaterials that promote cell growth and differentiation while localizing cells in the injured area. The regrowth of myelinating oligodendrocytes from neural stem cells through a biomaterials approach may prove to be a beneficial strategy following the onset of demyelination. This article reviews recent advancements in biomaterial strategies for the differentiation of neural stem cells into oligodendrocytes, and presents new data indicating appropriate properties for oligodendrocyte precursor cell growth. In some cases, an increase in oligodendrocyte differentiation alongside neurons is further highlighted for functional improvements where the biomaterial was then tested for increased myelination both in vitro and in vivo.