Poloxamer-188 as an adjunct to primary percutaneous transluminal coronary angioplasty for acute myocardial infarction

Highlights in poloxamer-based drug delivery systems as strategy at local application for vaginal infections

Infectious diseases related to the vagina include diseases caused by the imbalance of the vaginal flora and by sexually transmitted infections. Some of these present themselves as a public health problem due to the lack of efficient treatment that leads to their complete cure, and others due to the growing resistance to drugs used in therapy. In this sense, new treatment strategies are desirable, with vaginal administration rout being a great choice since can bypass first-pass metabolism and decrease drug interactions and adverse effects. However, it is worth highlighting limitations related to patient's discomfort at application time. Thereby, the use of poloxamer-based drug delivery systems is desirable due its stimuli-sensitive characteristic. Therefore, the present review reports a brief overview of poloxamer properties, biological behavior and advances in poloxamer applications in controlled drug release systems for infectious diseases related to the vagina treatment and prevention.

Cardiac Muscle Membrane Stabilization in Myocardial Reperfusion Injury

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In myocardial ischemia, the integrity of the cardiac sarcolemma is severely stressed in the critical earliest moments upon reperfusion. Bolstering sarcolemma integrity improves myocyte survival.

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This review focuses on cardiac sarcolemma stability and its role as a therapeutic target in ischemia-reperfusion injury.

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Synthetic block copolymers have been shown to interface with the muscle membrane to confer membrane stabilization during stress.

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Integrated multidisciplinary research teams, spanning cardiology, physiology, chemistry, and chemical engineering are essential to guide future mechanistic and translational studies of novel chemical-based membrane stabilizers for preserving viable heart muscle during ischemia-reperfusion injury in human patients.

The phospholipid bilayer membrane that surrounds each cell in the body represents the first and last line of defense for preserving overall cell viability. In several forms of cardiac and skeletal muscle disease, deficits in the integrity of the muscle membrane play a central role in disease pathogenesis. In Duchenne muscular dystrophy, an inherited and uniformly fatal disease of progressive muscle deterioration, muscle membrane instability is the primary cause of disease, including significant heart disease, for which there is no cure or highly effective treatment. Further, in multiple clinical forms of myocardial ischemia-reperfusion injury, the cardiac sarcolemma is damaged and this plays a key role in disease etiology. In this review, cardiac muscle membrane stability is addressed, with a focus on synthetic block copolymers as a unique chemical-based approach to stabilize damaged muscle membranes. Recent advances using clinically relevant small and large animal models of heart disease are discussed. In addition, mechanistic insights into the copolymer-muscle membrane interface, featuring atomistic, molecular, and physiological structure-function approaches are highlighted. Collectively, muscle membrane instability contributes significantly to morbidity and mortality in prominent acquired and inherited heart diseases. In this context, chemical-based muscle membrane stabilizers provide a novel therapeutic approach for a myriad of heart diseases wherein the integrity of the cardiac muscle membrane is at risk.

Impact of poloxamer 188 (Pluronic F-68) additive on cell mechanical properties, quantification by real-time deformability cytometry

Advances in cellular therapies have led to the development of new approaches for cell product purification and formulation, e.g., utilizing cell endogenous properties such as size and deformability as a basis for separation from potentially harmful undesirable by-products. However, commonly used additives such as Pluronic F-68 and other poloxamer macromolecules can change the mechanical properties of cells and consequently alter their processing. In this paper, we quantified the short-term effect of Pluronic F-68 on the mechanotype of three different cell types (Jurkat cells, red blood cells, and human embryonic kidney cells) using real-time deformability cytometry. The impact of the additive concentration was assessed in terms of cell size and deformability. We observed that cells respond progressively to the presence of Pluronic F-68 within first 3 h of incubation and become significantly stiffer (p-value < 0.001) in comparison to a serum-free control and a control containing serum. We also observed that the short-term response manifested as cell stiffening is true (p-value < 0.001) for the concentration reaching 1% (w/v) of the poloxamer additive in tested buffers. Additionally, using flow cytometry, we assessed that changes in cell deformability triggered by addition of Pluronic F-68 are not accompanied by size or viability alterations.

Differential effects of commercial-grade and purified poloxamer 188 on renal function

Poloxamer 188 (P188) is a non-ionic amphiphilic copolymer with hemorheologic, antithrombotic, anti-inflammatory, and cytoprotective properties. It potentially has clinical utility in diverse diseases, such as acute myocardial infarction, acute limb ischemia, shock, acute stroke, heart failure, and sickle cell crisis. P188 is available as an excipient-grade product, manufactured to National Formulary specifications, which we refer to as P188-NF. During synthesis of P188-NF, polymerization of its polyoxyethylene and polyoxypropylene components generates undesirable low molecular weight (LMW) substances, such as truncated polymers and glycols. In early clinical studies, P188-NF yielded unexpected renal dysfunction. Here, we explore the nature of the renal dysfunction associated with P188-NF and use a purified (more homogenous) form of P188-NF (P188-P) to show that removal of LMW substances is associated with substantially less renal dysfunction. In both a remnant-kidney animal model and in clinical studies, P188-P demonstrates a substantially improved renal safety profile.

Tc-99m SPECT sestamibi for the measurement of infarct size

There are a variety of approaches to assess the efficacy of reperfusion therapy, and myocardial protection, in acute myocardial infarction. This review summarizes the available evidence validating the use of technetium-99m sestamibi single-photon emission computed tomography (SPECT) for this purpose. Multiple lines of evidence have validated its clinical utility. SPECT sestamibi infarct size has been used as an endpoint in multiple randomized clinical trials. A smaller number of clinical trials have used both early and later imaging with SPECT sestamibi to assess myocardium at risk and myocardial salvage. SPECT sestamibi has a number of limitations which must be recognized. Nevertheless, SPECT sestamibi infarct size is a well-validated measurement with a long track record of performance as an endpoint in multicenter, randomized clinical trials.

Poloxamer 188 protects against ischemia-reperfusion injury in a murine hind-limb model

BACKGROUND

Ischemia-reperfusion injury can activate pathways generating reactive oxygen species, which can injure cells by creating holes in the cell membranes. Copolymer surfactants such as poloxamer 188 are capable of sealing defects in cell membranes. The authors postulated that a single-dose administration of poloxamer 188 would decrease skeletal myocyte injury and mortality following ischemia-reperfusion injury.

METHODS

Mice underwent normothermic hind-limb ischemia for 2 hours. Animals were treated with 150 microl of poloxamer 188 or dextran at three time points: (1) 10 minutes before ischemia; (2) 10 minutes before reperfusion; and (3) 2 or 4 hours after reperfusion. After 24 hours of reperfusion, tissues were analyzed for myocyte injury (histology) and metabolic dysfunction (muscle adenosine 5'-triphosphate). Additional groups of mice were followed for 7 days to assess mortality.

RESULTS

When poloxamer 188 treatment was administered 10 minutes before ischemia, injury was reduced by 84 percent, from 50 percent injury in the dextran group to 8 percent injury in the poloxamer 188 group (p < 0.001). When administered 10 minutes before reperfusion, poloxamer 188 animals demonstrated a 60 percent reduction in injury compared with dextran controls (12 percent versus 29 percent). Treatment at 2 hours, but not at 4 hours, postinjury prevented substantial myocyte injury. Preservation of muscle adenosine 5'-triphosphate paralleled the decrease in myocyte injury in poloxamer 188-treated animals. Poloxamer 188 treatment significantly reduced mortality following injury (10 minutes before, 75 percent versus 25 percent survival, p = 0.0077; 2 hours after, 50 percent versus 8 percent survival, p = 0.032).

CONCLUSION

Poloxamer 188 administered to animals decreased myocyte injury, preserved tissue adenosine 5'-triphosphate levels, and improved survival following hind-limb ischemia-reperfusion injury.

Endoscopic ultrasound-guided celiac plexus neurolysis using a reverse phase polymer

AIM: To assess the feasibility of endoscopic ultrasound (EUS)-guided celiac plexus neurolysis (CPN) using a poloxamer.

METHODS: In this prospective evaluation, six Yorkshire pigs underwent EUS-guided CPN. Three received an injection of 10 mL of 0.25% Lidocaine plus methylene blue (group 1) and three received an injection of 10 mL of 0.25% Lidocaine plus blue colored poloxamer (PS137-25) (group 2). Necropsy was performed immediately after the animals were sacrificed. The abdominal and pelvic cavities were examined for the presence of methylene blue and the blue colored poloxamer.

RESULTS: EUS-guided CPN was successfully performed in all 6 pigs without immediate complication. Methylene blue was identified throughout the peritoneal and retroperitoneal cavity in group 1. The blue colored poloxamer was found in the retroperitoneal cavity immediately adjacent to the aorta, in the exact location of the celiac plexus in group 2.

CONCLUSION: EUS-guided CPN using a reverse phase polymer in a non-survival porcine model was technically feasible. The presence of a poloxamer gel at the site of the celiac plexus at necropsy indicates a precise delivery of the neurolytic agent.

Limitation of myocardial infarct size in the clinical setting: current status and challenges in translating animal experiments into clinical therapy

This review takes a critical look at the current effectiveness of reperfusion therapy for acute myocardial infarction and at the potential for cardioprotective agents to improve it. Reperfusion alone limits the median value of infarct size to approximately 50% of the ischemic region. However, the range of infarct sizes is very wide, and one-fourth of these patients have more than 75% of the ischemic zone infarcted despite successful coronary reperfusion. Available studies suggest that mortality and morbidity is increased when more than 20% of the left ventricle is infarcted. Therefore, to be effective infarct size-limiting therapy would have to reduce infarction to or below this 20% target. To achieve this goal in the quartile of patients with the biggest infarcts the cardioprotective agent would have to be potent enough to reduce infarct size from its current value of 75% of the ischemic zone to 40% or less. While ischemic preconditioning and some pretreatment drugs might be potent enough to achieve this goal, few of the agents given at the clinically relevant time of at or just before reperfusion have exhibited such potency. Several cardioprotective agents have recently been evaluated in clinical trials but their results have been disappointing. Some of the poor clinical trial performance may stem from study designs which fail to identify those patients falling within the upper quartile of infarct sizes, presumably the only group that would be expected to actually benefit from a reduction in infarct size. Other possible causes could be that co-morbidities or drugs patients are taking may block the pathways involved in the anti-infarct effect or that the drugs simply do not protect even in animal models. Few agents have been thoroughly tested in clinically relevant animal models prior to their testing in man.

Safety Assessment of Poloxamers 101, 105, 108, 122, 123, 124, 181, 182, 183, 184, 185, 188, 212, 215, 217, 231, 234, 235, 237, 238, 282, 284, 288, 331, 333, 334, 335, 338, 401, 402, 403, and 407, Poloxamer 105 Benzoate, and Poloxamer 182 Dibenzoate as Used in Cosmetics

Poloxamers are polyoxyethlyene, polyoxypropylene block polymers. The impurities of commercial grade Poloxamer 188, as an example, include low-molecular-weight substances (aldehydes and both formic and acetic acids), as well as 1,4-dioxane and residual ethylene oxide and propylene oxide. Most Poloxamers function in cosmetics as surfactants, emulsifying agents, cleansing agents, and/or solubilizing agents, and are used in 141 cosmetic products at concentrations from 0.005% to 20%. Poloxamers injected intravenously in animals are rapidly excreted in the urine, with some accumulation in lung, liver, brain, and kidney tissue. In humans, the plasma concentration of Poloxamer 188 (given intravenously) reached a maximum at 1 h, then reached a steady state. Poloxamers generally were ineffective in wound healing, but were effective in reducing postsurgical adhesions in several test systems. Poloxamers can cause hypercholesterolemia and hypertriglyceridemia in animals, but overall, they are relatively nontoxic to animals, with LD50 values reported from 5 to 34.6 g/kg. Short-term intravenous doses up to 4 g/kg of Poloxamer 108 produced no change in body weights, but did result in diffuse hepatocellular vacuolization, renal tubular dilation in kidneys, and dose-dependent vacuolization of epithelial cells in the proximal convoluted tubules. A short-term inhalation toxicity study of Poloxamer 101 at 97 mg/m3 identified slight alveolitis after 2 weeks of exposure, which subsided in the 2-week postexposure observation period. A short-term dermal tox-icity study of Poloxamer 184 in rabbits at doses up to 1000 mg/kg produced slight erythema and slight intradermal inflammatory response on histological examination, but no dose-dependent body weight, hematology, blood chemistry, ororgan weight changes. A6-month feeding study in rats and dogs of Poloxamer 188 at exposures up to 5% in the diet produced no adverse effects. Likewise, Poloxamer 331 (tested up to 0.5 g/kg day-1), Poloxamer 235 (tested up to 1.0 g/kg day-1), and Poloxamer 338 (at 0.2 or 1.0 g/kg day-1) produced no adverse effects in dogs. Poloxamer 338 (at 5.0 g/kg day-1) produced slight transient diarrhea in dogs. Poloxamer 188 at levels up to 7.5% in diet given to rats in a 2-year feeding study produced diarrhea at 5% and 7.5% levels, a small decrease in growth at the 7.5% level, but no change in survival. Doses up to 0.5 mg/kg day-1 for 2 years using rats produced yellow discoloration of the serum, high serum alkaline phosphatase activity, and elevated serum glutamicpyruvic transaminase and glutamic-oxalacetic transaminase activities. Poloxamers are minimal ocular irritants, but are not dermal irritants or sensitizers in animals. Data on reproductive and developmental toxicity of Poloxamers were not found. An Ames test did not identify any mutagenic activity of Poloxamer 407, with or without metabolic activation. Several studies have suggested anti-carcinogenic effects of Poloxamers. Poloxamers appear to increase the sensitivity to anticancer drugs of multidrug-resistant cancer cells. In clinical testing, Poloxamer 188 increased the hydration of feces when used in combination with a bulk laxative treatment. Compared to controls, one study of angioplasty patients receiving Poloxamer 188 found a reduced myocardial infarct size and a reduced incidence of reinfarction, with no evidence of toxicity, but two other studies found no effect. Poloxamer 188 given to patients suffering from sickle cell disease had decreased pain and decreased hospitilization, compared to controls. Clinical tests of dermal irritation and sensitization were uniformly negative. The Cosmetic Ingredient Review (CIR) Expert Panel stressed that the cosmetic industry should continue to use the necessary purification procedures to keep the levels below established limits for ethylene oxide, propylene oxide, and 1,4-dioxane. The Panel did note the absence of reproductive and developmental toxicity data, but, based on molecular weight and solubility, there should be little skin penetration and any penetration of the skin should be slow. Also, the available data demonstrate that Poloxamers that are introduced into the body via routes other than dermal exposure have a rapid clearance from the body, suggesting that there would be no risk of reproductive and/or developmental toxicity. Overall, the available data do not suggest any concern about carcinogenesis. Although there are gaps in knowledge about product use, the overall information available on the types of products in which these ingredients are used, and at what concentration, indicates a pattern of use. Based on these safety test data and the information that the manufacturing process can be controlled to limit unwanted impurities, the Panel concluded that these Poloxamers are safe as used.

Structural and functional recovery of electropermeabilized skeletal muscle in-vivo after treatment with surfactant poloxamer 188

A critical requirement for cell survival after trauma is sealing of breaks in the cell membrane [M. Bier, S.M. Hammer, D.J. Canaday, R.C Lee, Kinetics of sealing for transient electropores in isolated mammalian skeletal muscle cells, Bioelectromagnetics 20 (1999) 194-201; R.C. Lee, D.C. Gaylor, D. Bhatt, D.A. Israel, Role of cell membrane rupture in the pathogenesis of electrical trauma, J. Surg. Res. 44 (1988) 709-719; R.C. Lee, J.F. Burke, E.G. Cravalho (Eds.), Electrical Trauma: The Pathophysiology, Manifestations, and Clinical Management, Cambridge University Press, 1992; B.I. Tropea, R.C. Lee, Thermal injury kinetics in electrical trauma, J. Biomech. Engr. 114 (1992) 241-250; F. Despa, D.P. Orgill, J. Newalder, R.C Lee, The relative thermal stability of tissue macromolecules and cellular structure in burn injury, Burns 31 (2005) 568-577; T.A. Block, J.N. Aarsvold, K.L. Matthews II, R.A. Mintzer, L.P. River, M. Capelli-Schellpfeffer, R.L. Wollman, S. Tripathi, C.T. Chen, R.C. Lee, The 1995 Lindberg Award. Nonthermally mediated muscle injury and necrosis in electrical trauma, J. Burn Care and Rehabil. 16 (1995) 581-588; K. Miyake, P.L. McNeil, Mechanical injury and repair of cells, Crit. Care Med. 31 (2003) S496-S501; R.C. Lee, L.P. River, F.S. Pan, R.L. Wollmann, Surfactant-induced sealing of electropermeabilized skeletal muscle membranes in vivo, Proc. Natl. Acad. Sci. 89 (1992) 4524-4528; J.D. Marks, C.Y. Pan, T. Bushell, W. Cromie, R.C. Lee, Amphiphilic, tri-block copolymers provide potent membrane-targeted neuroprotection, FASEB J. 15 (2001) 1107-1109; B. Greenebaum, K. Blossfield, J. Hannig, C.S. Carrillo, M.A. Beckett, R.R. Weichselbaum, R.C. Lee, Poloxamer 188 prevents acute necrosis of adult skeletal muscle cells following high-dose irradiation, Burns 30 (2004) 539-547; G. Serbest, J. Horwitz, K. Barbee, The effect of poloxamer-188 on neuronal cell recovery from mechanical injury, J. Neurotrauma 22 (2005) 119-132]. The triblock copolymer surfactant Poloxamer 188 (P188) is known to increase the cell survival after membrane electroporation [R.C. Lee, L.P. River, F.S. Pan, R.L. Wollmann, Surfactant-induced sealing of electropermeabilized skeletal muscle membranes in vivo, Proc. Natl. Acad. Sci. 89 (1992) 4524-4528; Z. Ababneh, H. Beloeil, C.B. Berde, G. Gambarota, S.E. Maier, R.V. Mulkern, Biexponential parametrization of T2 and diffusion decay curves in a rat muscle edema model: Decay curve components and water compartments, Magn. Reson. Med. 54 (2005) 524-531]. Here, we use a rat hind-limb model of electroporation injury to determine if the intravenous administration of P188 improves the recovery of the muscle function. Rat hind-limbs received a sequence of either 0, 3, 6, 9, or 12 electrical current pulses (2 A, 4 ms duration, 10 s duty cycle). Magnetic resonance imaging (MRI) analysis, muscle water content and compound muscle action potential (CMAP) amplitudes were compared. Electroporation injury manifested edema formation and depression of the CMAP amplitudes. P188 (one bolus of 1 mg/ml of blood) was administrated 30 or 60 min after injury. Animals receiving P188 exhibited reduced tissue edema (p<0.05) and increased CMAP amplitudes (p<0.03). By comparison, treatment with 10 kDa neutral dextran, which produces similar serum osmotic effects as P188, had no effect on post-electroporation recovery. Noteworthy, the present results suggest that a single intravenous dose of P188 is effective to restore the structural integrity of damaged tissues with intact circulation.

Effects of time, dose, and inversion time for acute myocardial infarct size measurements based on magnetic resonance imaging-delayed contrast enhancement

OBJECTIVES

This study sought to investigate the influence of time, dose, and inversion time (TI) and their interactions on myocardial infarct size measurements to establish the foundation for a standardized protocol for multicenter trials.

BACKGROUND

There is growing interest in using magnetic resonance imaging (MRI) infarct size measurements as an end point in clinical trials. However, no standardized protocol exists, and there are limited data concerning the effects of time, contrast agent dose, and TI.

METHODS

First, we determined the influence of postcontrast imaging time (5 to 40 min), contrast agent dose (0.1 vs. 0.2 mmol/kg), TI, and their interactions in an animal model (n = 14). Second, we tested whether the findings of the animal study apply to patients and are generalizable. Therefore, we retested the diagnostic window in a multicenter study. A total of 48 patients with first acute myocardial infarction (AMI) from three centers were imaged twice (5 and 30 min) after injection of 0.15 mmol/kg gadolinium diethylenetriamine-pentaacetate using an adjusted TI.

RESULTS

The animal study showed that the infarct size is independent of time and dose (p = 0.9 and p = 0.16, respectively) using an adjusted TI. Using a fixed TI, however, infarct size is a function of time and dose (p = 0.0001 and p = 0.01, respectively). The multicenter study showed that MRI 1 (16.9 +/- 12% of left ventricle) was not statistically different from MRI 2 (16.4 +/- 12% of left ventricle, p = NS) with no difference between sites (p = NS).

CONCLUSIONS

The AMI size can be measured with MRI using a contrast dose between 0.1 and 0.2 mmol/kg and a time window of 5 to 30 min after contrast administration, provided that the TI is adjusted.

Safety of purified poloxamer 188 in sickle cell disease: phase I study of a non-ionic surfactant in the management of acute chest syndrome

Acute chest syndrome (ACS) is the most common cause of death in patients with sickle cell anemia. Its management is primarily palliative. We performed a Phase I evaluation of purified poloxamer 188 (a non-ionic surfactant) in the management of ACS. Forty-three patients with sickle cell disease and ACS were treated with doses as high as 2960 mg/day by continuous intravenous (IV) infusion. The maximum tolerated dose has not been identified. No evidence of renal toxicity or other limiting adverse events were found. One adult patient died due to sepsis and adult respiratory distress syndrome, which were unrelated to treatment. Poloxamer 188 is safe to administer to patients with ACS, and preliminary data suggest that it may shorten its duration and the length of hospitalization in a dose related manner. Children appeared to benefit more than adults. The data and safety profile justify further studies with purified poloxamer 188 in the treatment of ACS.

Temporary vascular occlusion with poloxamer 407

There is a need for safe and reversible occlusions during percutaneous endovascular procedures. Poloxamer 407 is a non-ionic surfactant with rapid reversible sol-gel transition behaviour. The safety and efficacy of this polymer as a temporary embolic agent was investigated. First, dissolution time after gelation of poloxamer was determined in an in vitro model. Then, transient poloxamer occlusion of renal and pulmonary arteries of seven dogs was followed by serial angiograms. Macroscopic and pathological changes were studied 1 week later. This experiment was repeated in similar arteries in one pig, and in auricular arteries of two rabbits. Poloxamer dissolution after in vitro polymerization was completed within 1-20 h, depending on concentrations. In vivo poloxamer 22% injections led to complete occlusion, followed by full recanalization within 10-90 min without complication. The only biochemical effect of poloxamer occlusions was transient elevation of triglyceride levels. There were no pathological abnormalities at 1 week. Poloxamer 407 could be used as an embolic material for temporary occlusions.

Poloxamer 188 Volumetrically Decreases Neuronal Loss in the Rat in a Time-dependent Manner

OBJECTIVE

Excitotoxicity is a multistep process that results in either necrosis or apoptosis. It has been associated with neuronal death in trauma, ischemia, and neurodegeneration. The final step in necrotic cell death is the rupture of a cell's plasma membrane; repair of this membrane rupture is a potentially powerful technique of neuroprotection. Poloxamer 188 (P-188) is a synthetic surfactant that seals experimentally porated membranes. This study investigated the usefulness and time dependence of intrathecal P-188 in protecting neurons in an in vivo model of excitotoxicity in the rat.

METHODS

Twenty-eight Sprague-Dawley rats underwent striatal infusion of quinolinic acid to produce a spherical excitotoxic lesion. Each animal then received either vehicle or P-188 at 10 minutes, 4 hours, or both time points after surgery by direct cisterna magna injection. Animals were killed at 1 week, and brains were stained immunohistochemically for the neuronal marker Neu-N. Volumes of neuronal loss were calculated and compared between groups by analysis of variance.

RESULTS

All animals were found to have spherical, stereotyped lesions. The animals that received intrathecal poloxamer at the early injection time had statistically smaller lesions (8.16 +/- 6.12 mm(3); n = 5; P = 0.0015) than controls (18.25 +/- 11.42 mm(3); n = 11). Those animals that received poloxamer at both injection times also had statistically smaller lesions (10.57 +/- 9.00 mm(3); n = 7; P = 0.0095). The group that received poloxamer at the late injection time only did not have significantly decreased lesion size (14.86 +/- 7.95 mm(3); n = 5).

CONCLUSION

Intrathecal P-188 reduces neuronal loss after excitotoxic injury in the rat only when delivered immediately after the toxin. This observation confirms the potential of surfactant molecules as neuroprotectants but predicts that their usefulness is best realized by early and potentially ongoing treatment.

The quantification of infarct size

We sought to summarize the published evidence regarding the measurement of infarct size by serum markers, technetium-99m sestamibi single-photon emission computed tomography (SPECT) myocardial perfusion imaging, and magnetic resonance imaging. The measurement of infarct size is an attractive surrogate end point for the early assessment of new therapies for acute myocardial infarction. For each of these three approaches, we reviewed reports published in English providing the clinical validation for the measurement of infarct size and the relevant clinical trial experience. The measurement of infarct size by serum markers has multiple theoretical and practical limitations. The measurement of troponin is promising, but the available data validating this marker are limited. Sestamibi SPECT imaging has five separate lines of published evidence supporting its validity and has received extensive study in multicenter trials. Magnetic resonance imaging has great promise but has less clinical validation and no multicenter trial experience. Therefore, SPECT sestamibi imaging is currently the best available technique for the quantitation of infarct size to assess the incremental treatment benefit of new therapies in multicenter trials of acute myocardial infarction.

Biodistribution and safety studies of hDel-1 plasmid-based gene therapy in mouse and rabbit models

A plasmid encoding the human developmentally regulated endothelial locus-1 (hDel-1) protein formulated with poloxamer 188 is a potential gene therapy for peripheral arterial disease in man. As a prelude to clinical trials, the biodistribution and safety of this therapy were evaluated after intramuscular and intravenous administration in mice and rabbits. In mice, plasmid DNA persisted at the intramuscular injection site for at least 28 days, but was barely detectable in distal tissues by 24 h and essentially cleared by 28 days. By 24 h after intravenous administration, plasmid DNA was readily detected in blood, muscle, and lungs but sporadically and at low levels in other tissues. At 28 days, plasmid DNA was readily detectable only at the intravenous injection site (tail) after low- and high-dose administration, and sporadically in blood and muscle after high-dose administration. In rabbits, the highest intramuscular (4.2 mg kg(-1)) or intravenous (3.7 mg kg(-1)) dose caused no deaths; no treatment-related clinical signs; no changes in body weight, clinical pathology parameters, ophthalmology, ECG, or histopathology; and no detectable increase in antinuclear antibodies by 28 days. The results supported testing of hDel-1 plasmid-based gene therapy in phase I clinical trials.

The surfactant poloxamer-188 protects against glutamate toxicity in the rat brain

Membrane repair of damaged neurons by surfactant poloxamers has been noted in experimental spinal cord injury and in vitro excitotoxicity. We examined poloxamer-188 (P-188)-mediated neuroprotection in a rat model of glutamate toxicity. Quinolinate was infused into the striatum followed 10 min and 4 h later by P-188 administered either i.v. or intracisternally (i.c.), or by vehicle. Mean neuronal loss examined volumetrically 7 days later in control animals was 50% greater (P < 0.01) than after i.c. P-188 treatment; control lesion volumes were 38% greater than lesion volumes after i.v. P-188 treatment; however, that comparison did not reach significance. This robust protection against glutamate toxicity may predict P-188-mediated neuroprotection against a broad range of clinically relevant neural insults.

Synthesis and characterization of self-assembling block copolymers containing bioadhesive end groups

3,4-Dihydroxyphenyl-L-alanine (DOPA) is an unusual amino acid found in mussel adhesive proteins (MAPs) that is believed to lend adhesive characteristics to these proteins. In this paper, we describe a route for the conjugation of DOPA moieties to poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers. Hydroxyl end groups of PEO-PPO-PEO block copolymers were activated by N,N'-disuccinimidyl carbonate and then reacted with DOPA or its methyl ester with high coupling efficiencies from both aqueous and organic solvents. DOPA-modified PEO-PPO-PEO block copolymers were freely soluble in cold water, and dye partitioning and differential scanning calorimetry analysis of these solutions revealed that the copolymers aggregated into micelles at a characteristic temperature that was dependent on block copolymer composition and concentration in solution. Oscillatory rheometry demonstrated that above a block copolymer concentration of approximately 20 wt %, solutions of DOPA-modified PEO-PPO-PEO block copolymers exhibited sol-gel transitions upon heating. The gelation temperature could be tailored between approximately 23 and 46 degrees C by changing the composition, concentration, and molecular weight of the block copolymer. Rheological measurement of the bioadhesive interaction between DOPA-modified Pluronic and bovine submaxillary mucin indicated that DOPA-modified Pluronic was significantly more bioadhesive than unmodified Pluronic.

Infarct size measured by single photon emission computed tomographic imaging with (99m)Tc-sestamibi: A measure of the efficacy of therapy in acute myocardial infarction

BACKGROUND

Use of mortality as an end point in randomized trials of reperfusion therapy requires increasingly large sample sizes to test advances compared with existing therapy, which is already highly effective. There has been a growing interest in infarct size measurements by (99m)Tc-sestamibi SPECT (single photon emission computed tomographic) imaging as a surrogate end point.

METHODS AND RESULTS

We reviewed the reports published in English regarding infarct size measurements by (99m)Tc-sestamibi. Four separate lines of published evidence support the validity of SPECT imaging with (99m)Tc-sestamibi for determination of infarct size. This end point has been used in a total of 7 randomized trials-1 single center and 6 multicenter. The end point compares favorably with left ventricular function and infarct size measurements with the use of other radiopharmaceuticals. The most important limitation of this approach is the absence thus far of a randomized trial that has shown a corresponding decrease in mortality in association with a therapy that reduces infarct size.

CONCLUSIONS

SPECT imaging with (99m)Tc-sestamibi is the best available measurement tool for infarct size. It has already served as an end point in early pilot studies to evaluate potential efficacy and in dose-ranging studies. It has the potential to serve as a surrogate end point to uncover advantages of new therapies that may be equivalent to existing therapies with respect to early mortality.

Threshold values for preserved viability with a noninvasive measurement of collateral blood flow during acute myocardial infarction treated by direct coronary angioplasty

BACKGROUND

Quantitative measures of myocardial perfusion defect severity from acute (99m)Tc-sestamibi tomographic images (nadir) have correlated closely with collateral and residual antegrade blood flow during acute myocardial infarction. The purpose of this study was to determine whether a viability threshold could be identified from this measure in patients with acute myocardial infarction treated in a homogeneous manner with successful reperfusion therapy.

METHOD AND RESULTS

The study group consisted of 61 patients with acute myocardial infarction with a risk area of >6% LV treated with primary angioplasty between 120 and 240 minutes after symptom onset. All patients were injected with 20 to 30 mCi of (99m)Tc-sestamibi before primary angioplasty and imaged after the procedure. Acute myocardium at risk (MAR) and subsequent infarct size (IS) were quantified by a threshold program. Severity (nadir) from the acute image was the lowest ratio of minimal/maximum counts from 5 short-axis slices. Infarct location was anterior in 22 and inferior in 39 patients. MAR was 33+/-15% LV and IS was 13+/-15% LV: 23 patients had no infarction despite MAR similar to those with infarction. Receiver-operator characteristic curve analysis identified a nadir value of 0.26 as providing the best separation of patients with and without infarction (sensitivity, 74%; specificity, 74%). This nadir threshold varied by infarct location: anterior defect, 0.21; inferior defect, 0.31. The sensitivity and specificity for absent infarction for these values were anterior, 69% and 67%, and inferior, 88% and 84%, respectively.

CONCLUSIONS

In a time frame in which the presence of residual blood flow is important, the severity of the acute (99m)Tc-sestamibi defect can be used to predict whether infarction will develop despite successful reperfusion.

Effect of Poloxamer 188 on Collateral Blood Flow, Myocardial Infarct Size, and Left Ventricular Function in a Canine Model of Prolonged (3-Hour) Coronary Occlusion and Reperfusion

Poloxamer 188 is a surfactant with hemorheological, antithrombotic, and neutrophil-inhibitory properties. This agent has been demonstrated to reduce infarct size and to improve left ventricular function in animal models of myocardial infarction and reperfusion, and recently in a randomized trial of patients receiving thrombolytic therapy for acute myocardial infarction. In addition to reducing reperfusion injury, poloxamer 188 might be beneficial by increasing collateral blood flow. The purpose of this study was to determine the effect of poloxamer 188 on collateral blood flow, myocardial infarct size, and left ventricular function in a canine model of prolonged (3 hours) coronary occlusion and reperfusion. Closed-chest dogs (n = 21) underwent a 3-hour coronary occlusion and 3 hours of reperfusion. At 1 hour of occlusion, dogs received poloxamer 188, 75 mg/kg IV bolus, followed by 150 mg/kg/h IV for the final 2 hours of coronary occlusion and throughout reperfusion, or a saline placebo. Regional myocardial blood flow was measured using colored microspheres. Myocardial infarct size and area at risk were determined by postmortem histochemical staining. Compared with controls, poloxamer 188-treated dogs showed no significant increase in collateral blood flow during the final 2 hours of a 3-hour coronary artery occlusion. In addition, poloxamer 188 treatment had no beneficial effect on infarct size or left ventricular function in this model. Increased collateral blood flow is unlikely to be a beneficial mechanism of poloxamer 188 in myocardial infarction. These data also question the benefit of this agent to reduce reperfusion injury in the setting of more prolonged (3-hour) coronary occlusion.

Randomized, controlled trial of RheothRx (poloxamer 188) in patients with suspected acute myocardial infarction. RheothRx in Myocardial Infarction Study Group

BACKGROUND

Patients with acute myocardial infarction (AMI) who are not eligible for thrombolytic therapy or primary coronary angioplasty are distinguished by advanced age, complicated medical histories, relatively frequent use of prior revascularization procedures, and worse outcomes than their counterparts who are eligible for reperfusion therapy.

METHODS AND RESULTS

The purpose of this randomized, controlled trial was to determine whether RheothRx, a hemorheologic agent, reduced myocardial infarct size and improved left ventricular function in patients who had suspected AMI at the time of hospital admission and were not eligible for reperfusion therapy. Patients were randomly assigned to RheothRx (n = 97) or placebo (n = 99). Patients in the two groups were similar with respect to age, sex, medical history, and clinical presentation. Enzyme evidence of AMI was present in 69% of the treatment group and 70% of the placebo group. Infarct size measured before hospital discharge was similar in the two groups (14.1% +/- 18.5% vs 11.7% +/- 14.1%, p = 0.60), although left ventricular ejection fraction was lower in the treatment group (47 +/- 14 vs 52 +/- 11, p = 0.026). Hospital mortality rate was 11.3% and 7.1% in patients receiving RheothRx and patients receiving placebo, respectively (p = 0.30). There was a higher occurrence of acute renal dysfunction in the RheothRx group (12% vs 2%, p = 0.005). Because of changes in drug dosage necessitated by the occurrence of acute renal dysfunction, the trial was stopped.

CONCLUSIONS

In this study of patients who had suspected AMI and were not eligible for thrombolytic therapy, RheothRx did not decrease infarct size or favorably alter outcome. The need for effective treatment for this large patient population remains largely unmet.

Noninvasive prediction of residual blood flow within the risk area during acute myocardial infarction: a multicenter validation study of patients undergoing direct coronary angioplasty

BACKGROUND

In a previous study from a single center, radionuclide measures of collateral flow with technetium 99m sestamibi have been shown to be significantly associated with angiographic residual (antegrade and collateral) flow and independent predictors of final infarct size in acute myocardial infarction. This study examined whether the previously described radionuclide measures of blood flow to the infarct zone were reproducible with different laboratories and imaging systems.

METHODS AND RESULTS

Residual flow to the infarct zone was assessed by both invasive and noninvasive methods in 77 patients with first-time myocardial infarction (32 anterior, 45 nonanterior). All patients underwent acute coronary angiography before any intervention within 8 hours of the onset of chest pain (4.0 +/- 1.5 hours; range 1.2 to 7.9 hours). 99mTc sestamibi was injected intravenously before reperfusion therapy, and tomographic imaging was performed 1 to 6 hours after injection. A central core laboratory processed the acquired images from three centers, each with a unique camera and computer system. Three previously published methods based on the severity of the acute perfusion defect were used to measure residual flow to the infarct zone (nadir, severity index, area). Antegrade (Thrombolysis in Myocardial Infarction flow) and collateral flow before direct angioplasty were blindly graded on a four-point scale (0 to 3) from the acute angiogram. The simple sum of the two grades was defined as the angiographic flow index, representing residual flow to the jeopardized zone. All three noninvasive measures of residual flow were highly associated with the angiographic flow index in a linear fashion: severity index (p = 0.0006), area (p = 0.003), and nadir (minimum/maximum counts; p = 0.004). This association was independent of the laboratory where the data were acquired.

CONCLUSIONS

Despite different laboratories and camera systems, radionuclide measures of residual flow were highly associated with the angiographic flow index before reperfusion therapy. These results suggest that these measures are applicable on a broader scale for the noninvasive determination of collateral and antegrade flow in acute myocardial infarction.