Jimmy Toussaint

Physicochemical characterization of a novel graphene-based magnetic resonance imaging contrast agent.

We report the synthesis and characterization of a novel carbon nanostructure-based magnetic resonance imaging contrast agent (MRI CA); graphene nanoplatelets intercalated with manganese (Mn2+) ions, functionalized with dextran (GNP-Dex); and the in vitro assessment of its essential preclinical physicochemical properties: osmolality, viscosity, partition coefficient, protein binding, thermostability, histamine release, and relaxivity. The results indicate that, at concentrations between 0.1 and 100.0 mg/mL, the GNP-Dex formulations are hydrophilic, highly soluble, and stable in deionized water, as well as iso-osmolar (upon addition of mannitol) and iso-viscous to blood. At potential steady-state equilibrium concentrations in blood (0.1–10.0 mg/mL), the thermostability, protein-binding, and histamine-release studies indicate that the GNP-Dex formulations are thermally stable (with no Mn2+ ion dissociation), do not allow non-specific protein adsorption, and elicit negligible allergic response. The r1 relaxivity of GNP-Dex was 92 mM−1s−1 (per-Mn2+ ion, 22 MHz proton Larmor frequency); ~20- to 30-fold greater than that of clinical gadolinium (Gd3+)- and Mn2+-based MRI CAs. The results open avenues for preclinical in vivo safety and efficacy studies with GNP-Dex toward its development as a clinical MRI CA.

Dose ranging, expanded acute toxicity and safety pharmacology studies for intravenously administered functionalized graphene nanoparticle formulations.

Graphene nanoparticle dispersions show immense potential as multifunctional agents for in vivo biomedical applications. Herein, we follow regulatory guidelines for pharmaceuticals that recommend safety pharmacology assessment at least 10-100 times higher than the projected therapeutic dose, and present comprehensive single dose response, expanded acute toxicology, toxicokinetics, and respiratory/cardiovascular safety pharmacology results for intravenously administered dextran-coated graphene oxide nanoplatelet (GNP-Dex) formulations to rats at doses between 1 and 500 mg/kg. Our results indicate that the maximum tolerable dose (MTD) of GNP-Dex is between 50 mg/kg ≤ MTD < 125 mg/kg, blood half-life < 30 min, and majority of nanoparticles excreted within 24 h through feces. Histopathology changes were noted at ≥250 mg/kg in the heart, liver, lung, spleen, and kidney; we found no changes in the brain and no GNP-Dex related effects in the cardiovascular parameters or hematological factors (blood, lipid, and metabolic panels) at doses < 125 mg/kg. The results open avenues for pivotal preclinical single and repeat dose safety studies following good laboratory practices (GLP) as required by regulatory agencies for investigational new drug (IND) application.

Towards An Advanced Graphene-Based Magnetic Resonance Imaging Contrast Agent: Sub-acute Toxicity and Efficacy Studies in Small Animals.

Current clinical Gd3+-based T1 magnetic resonance imaging (MRI) contrast agents (CAs) are suboptimal or unsuitable, especially at higher magnetic fields (>1.5 Tesla) for advanced MRI applications such as blood pool, cellular and molecular imaging. Herein, towards the goal of developing a safe and more efficacious high field T1 MRI CA for these applications, we report the sub-acute toxicity and contrast enhancing capabilities of a novel nanoparticle MRI CA comprising of manganese (Mn2+) intercalated graphene nanoparticles functionalized with dextran (hereafter, Mangradex) in rodents. Sub-acute toxicology performed on rats intravenously injected with Mangradex at 1, 50 or 100 mg/kg dosages 3 times per week for three weeks indicated that dosages ≤50 mg/kg could serve as potential diagnostic doses. Whole body 7 Tesla MRI performed on mice injected with Mangradex at a potential diagnostic dose (25 mg/kg or 455 nanomoles Mn2+/kg; ~2 orders of magnitude lower than the paramagnetic ion concentration in a typical clinical dose) showed persistent (up to at least 2 hours) contrast enhancement in the vascular branches (Mn2+ concentration in blood at steady state = 300 ppb, per voxel = 45 femtomoles). The results lay the foundations for further development of Mangradex as a vascular and cellular/ molecular MRI probe.

Early versus Delayed Excision and Grafting of Full-thickness Burns in a Porcine Model: A Randomized Study

Background: The standard of care for full-thickness burns is tangential excision followed by skin autografting; however, the timing of excision and grafting is subject to debate. The authors compared early (2 days) versus delayed (14 days) excision and grafting in a porcine full-thickness burn model. Methods: Full-thickness burns (n = 12) were created on the backs of two anesthetized pigs and assigned randomly to no excision, tangential excision followed by skin autografting 2 days after injury, or tangential excision followed by skin autografting 14 days after injury. Digital images and full-thickness biopsy specimens were taken at 16, 21, 28, and 42 days after injury to determine percentage reepithelialization and scar depth. Results: At day 16, all burns that were excised early were completely reepithelialized, whereas only eight of 11 nonexcised burns (72.7 percent) were reepithelialized (p = 0.02). By day 21, all burns were completely reepithelialized. Scar thickness was greatest at 42 days in nonexcised burns (7.5 ± 2.1 mm); scars were thinner after early excision than after late excision (2.2 ± 1.8 mm versus 4.0 ± 1.1 mm; p < 0.001, analysis of variance). Wounds treated with early or late tangential excision followed by skin autografting were flat and minimally contracted, whereas all nonexcised burns were red, contracted, and slightly raised. Scar contraction at 28 and 42 days was greatest in nonexcised control wounds compared with early and late excised wounds. Conclusions: Both early and late excision followed by autografting reduce scarring in a full-thickness porcine burn model. However, early excision (2 days after injury) reduces scar thickness to a greater extent than later (after 14 days) excision.

The evaluation and management of thermal injuries: 2014 update

Burns are among the most common injuries presenting to the emergency department. While burns, especially large ones, may be associated with significant morbidity and mortality, most are minor and can be managed by emergency practitioners and discharged home with close follow-up. In contrast, patients with large burns require aggressive management of their airway, breathing and circulation in order to reduce mortality and morbidity. While early endotracheal intubation of patients with actual or impending airway compromise and aggressive fluid resuscitation have been emphasized, it appears that the pendulum may have swung a bit too far towards the extreme. The current review will briefly cover the epidemiology, pathogenesis and diagnosis of burn injuries with greater emphasis on airway and fluid management. We will also discuss the local management of the burn wound, which is all that is required for most burn patients in the emergency department.

The effects of topical nitric oxide on healing of partial thickness porcine burns

BACKGROUND Nitric oxide is a wound mediator that promotes wound healing. We hypothesized that topical application of nitric oxide would speed reepithelialization, enhance angiogenesis, and reduce scar thickness in a partial thickness porcine burn model. METHODS While under general anesthesia, 20 partial thickness burns were created on the backs of four female Yorkshire swine using a 2.5cm×2.5cm×7.5cm, 150-g aluminum bar, preheated to 80°C and applied for 20s. The necrotic epidermis was removed and the burns were randomized to low, medium, and high concentrations of a novel nitric-oxide (NO) releasing drug or its ointment vehicle applied 3 times weekly for 28 days. Full thickness punch biopsies were performed at 8, 11, 14 and 28 days after injury to determine percentage wound reepithelialization and scar thickness using H&E staining and blood vessel density using CD31 staining. RESULTS At day 11, the percentages (SD) wound reepithelialization were: control, 26.3 (34.6); low NO, 23.9 (36.9); medium NO, 43.3 (42.9); and high NO, 59.9 (43.6); ANOVA, P=0.02. The number of CD31 stained blood vessels at days 8 and 11 were greater in wounds treated with high dose NO vs. controls (48.1 vs. 22.9 [P<0.001] and 44.0 vs. 33.5 [P=0.05] per 1mm2 respectively). Scar thicknesses (SD) in mm at day 28 by treatment allocation were: control, 4.8 (1.2); low NO, 4.7 (1.2); medium NO, 4.3 (1.2); and high NO, 4.1 (1.0); P=0.22. CONCLUSIONS Treatment of partial thickness porcine burns with high concentrations of topical NO resulted in earlier reepithelization and increased angiogenesis but not reduced scar thickness compared with its control vehicle in a partial thickness porcine burn model.

Effects of burn location and investigator on burn depth in a porcine model

INTRODUCTION In order to be useful, animal models should be reproducible and consistent regardless of sampling bias, investigator creating burn, and burn location. We determined the variability in burn depth based on biopsy location, burn location and investigator in a porcine model of partial thickness burns. METHODS 24 partial thickness burns (2.5 cm by 2.5 cm each) were created on the backs of 2 anesthetized pigs by 2 investigators (one experienced, one inexperienced) using a previously validated model. In one of the pigs, the necrotic epidermis covering each burn was removed. Five full thickness 4mm punch biopsies were obtained 1h after injury from the four corners and center of the burns and stained with Hematoxylin and Eosin and Massons trichrome for determination of burn depth by a board certified dermatopathologist blinded to burn location and investigator. Comparisons of burn depth by biopsy location, burn location and investigator were performed with t-tests and ANOVA as appropriate. RESULTS The mean (SD) depth of injury to blood vessels (the main determinant of burn progression) in debrided and non-debrided pigs pooled together was 1.8 (0.3)mm, which included 75% of the dermal depth. Non-debrided burns were 0.24 mm deeper than debrided burns (P<0.001). Burn depth increased marginally from cephalic to caudal in non-debrided burns, but showed no statistical differences for these locations, in debrided burns. Additionally, there were also no statistical differences in burn depths from midline to lateral in either of these burn types. Burn depth was similar for both investigators and among biopsy locations. CONCLUSIONS Burn depth was greater for caudal locations in non-debrided burns and overall non-debrided burns were deeper than debrided burns. However, burn depth did not differ based on investigator, biopsy site, and medial-lateral location.

Topical antibiotic ointment versus silver-containing foam dressing for second-degree burns in swine.

OBJECTIVES Second-degree burns are very common but their management is controversial. These burns may be treated with either topical antimicrobial agents or advanced occlusive dressings; however, there is no established treatment comparator for preclinical studies. This study was designed to determine which of two commonly used comparator therapies (a silver-containing advanced dressing or a topical antibiotic ointment) resulted in faster reepithelialization and less scarring. The hypothesis was that second-degree burns treated with a topical antimicrobial ointment would heal faster and with less scarring than those treated with a silver-containing occlusive foam dressing in a porcine model. METHODS Deep partial-thickness burns were created on the flanks of three anesthetized female domestic pigs (20 to 25 kg) using a 150-g aluminum bar preheated in 80°C water bath and applied to the skin for 20 seconds using a force of 2 kg. The burn eschars were excised 48 hours later with an electric dermatome set at a depth of 0.75 mm. The wound beds were treated with a thin layer of triple-antibiotic petrolatum-based ointment (changed three times weekly) or a silver-containing foam dressing (changed once weekly). Full-thickness punch biopsies were obtained at 9, 11, 14, 16, 18, and 21 days for determination of percentage complete wound reepithelialization and at 28 days for measurement of scar depth. RESULTS At all dressing changes the wounds treated with the topical antibiotic appeared moist, while those treated with the silver-based dressings appeared dry. At day 21 all wounds treated with the ointment were completely reepithelialized, while only 55% of those treated with the silver dressing were reepithelialized (p < 0.001). Scar depth at day 28 was also significantly less in wounds treated with the topical antibiotic ointment (4.3 mm vs. 5.1 mm, difference = 0.7 mm; 95% confidence interval [CI] = 0.1 to 1.4 mm). There was less scar contraction in wounds treated with the topical antibiotic compared with the silver-based dressing (mean ± SD = 25.0% ± 14.6% vs. 38.9% ± 16.9%, difference = 13.9%; 95% CI = 5.7% to 22.0%). CONCLUSIONS In this model of excised deep partial-thickness burns, a triple-antibiotic ointment enhanced reepithelialization and reduced scar depth and contraction compared with a silver-based foam dressing. This triple-antibiotic ointment should be considered as a control for studies evaluating novel topical burn therapies.

The effects of platelet rich plasma on healing of full thickness burns in swine

INTRODUCTION Platelet rich plasma (PRP) is rich in growth factors and has been shown to improve healing in a variety of wounds. We determined the effects of PRP on healing and scarring in full thickness porcine burns with and without tangential excision and grafting (TEG). METHODS Standardized full thickness 5cm by 5cm burns were created on each of the backs and flanks of 10 anesthetized female pigs (25kg) using a validated model. The burns were created with a heating device that emits heat at a temperature of 400°C for a period of 30s. The burns were randomized to one of six treatments: no TEG or PRP, no TEG+PRP, early (day 2) TEG and no PRP, early TEG+PRP, late (day 14) TEG and no PRP, and late TEG+PRP. Tangential excision was performed down to viable tissue and autografts were 0.2mm thick. When used, a thin layer of autologous PRP was applied below the graft. All wounds were then treated with a topical antibiotic ointment 3 times weekly for 42 days. Digital images and full thickness biopsies were taken at 9, 11, 14, 18, 21, 28, 35 and 42days after injury to determine percentage reepithelialization, scar depth, and scar contraction. Tissue sections were stained with H&E and viewed by a dermatopathologist masked to treatment assignment. RESULTS There was no reduction in platelet and white blood cell concentrations in PRP and blood samples for the first 14days after-full thickness burns. A total of 120 burns were created on 10 animals evenly distributed between the six treatment groups. Burns undergoing early TEG reepithelialized fastest and with the thinnest scars followed by late TEG. Burns that did not undergo TEG had the slowest reepithelialization and greatest amount of scarring. Application of PRP had no additional effects on reepithelialization, scar depth, or scar contraction in any of the treatment groups. CONCLUSIONS Addition of PRP had similar effects on reepithelialization and scarring of full thickness porcine burns as standard topical antibiotic ointment regardless of whether the burns underwent excision or grafting or the timing of excision and grafting.