Importance of the source of hyaluronidase preparations in determining protective effect on ischemic heart muscle in acute myocardial infarction

Identification and characterization of a bacterial hyaluronidase and its production in recombinant form

Hyaluronidases (Hyals) are broadly used in medical applications to facilitate the dispersion and/or absorption of fluids or medications. This study reports the isolation, cloning, and industrial-scale recombinant production, purification and full characterization, including X-ray structure determination at 1.45 Å, of an extracellular Hyal from the nonpathogenic bacterium Streptomyces koganeiensis. The recombinant S. koganeiensis Hyal (rHyal_Sk) has a novel bacterial catalytic domain with high enzymatic activity, compared with commercially available Hyals, and is more thermostable and presents higher proteolytic resistance, with activity over a broad pH range. Moreover, rHyal_Sk exhibits remarkable substrate specificity for hyaluronic acid (HA) and poses no risk of animal cross-infection.

Proteases from actinomycetes interfere in solid media plate assays of hyaluronidase activity

Four hundred and fifteen actinomycete strains were screened for hyaluronidase activity in two plate assays media. In the first one, using hyaluronic acid as substrate and bovine serum albumin (BSA) to help precipitation of the nondegraded substrate, only strain 594 and hyaluronidase control were positive. In the second assay, plates with hyaluronic acid, but not BSA, gave the same results. For plates containing only BSA, proteinase activity was detected in strain 594. When hyaluronic acid was treated with pronase, the only clear zones, in the second assay without BSA, were those around hyaluronidase controls. Protease activity, commonly found in actinomycetes, was detected only in strain 594, among the 415 studied, when tested in hyaluronidase assay using hyaluronate plus BSA. This may be due to the composition of the growth medium, since media with different composition gave different results for protease activity in each of the 15 strains analyzed. These data suggest that proteases can affect an accurate detection of hyaluronidase in media containing proteins, not only from hyaluronate preparations, but also from other medium ingredients. Thus, for a correct interpretation of the method, they must be excluded. Commercial Hyaluronidase used as controls must be also tested for the presence of protease contamination.

Limitation of myocardial infarct size by metabolic interventions that reduce accumulation of fatty acid metabolites in ischemic myocardium

The effects on myocardial damage of metabolic interventions by nicotinic acid, oxfenicine, or a combination of the two were assessed in open-chest dogs exposed to coronary artery occlusion for 6 hours. The accumulation of metabolites of free fatty acids (FFAs) was studied in tissue samples of the left ventricle taken 60 minutes after coronary occlusion in separate animals. The percentage of the hypoperfused zone that evolved to infarction was 96 +/- 3% (mean +/- SEM) in control dogs, 74 +/- 4% in dogs treated with nicotinic acid (p less than 0.05 vs control dogs), 72 +/- 2% in dogs treated with oxfenicine (p less than 0.05 vs control dogs), and 54 +/- 5% in dogs with combined nicotinic acid and oxfenicine (p less than 0.05 vs control dogs, p less than 0.05 vs nicotinic acid and oxfenicine). Arterial FFA concentration was markedly reduced in dogs treated with nicotinic acid and those treated with combination nicotinic acid and oxfenicine. The accumulation of long-chain acyl carnitine was substantially reduced in the ischemic myocardium after nicotinic acid, oxfenicine, and a combination of the two, whereas the lowering of long-chain acyl CoA was less pronounced. Thus, nicotinic acid and oxfenicine, which depress myocardial FFA metabolism by different mechanisms, both reduce myocardial infarct size and their effects are additive.

Does infarct size influence loss of embolised 15-micrometer microspheres from ischaemic myocardium?

The relationship between myocardial infarct size and loss of 15-micron microspheres from ischaemic tissue was investigated in anaesthetized cats. Radioactive microspheres were injected in the left atrium before and 5 h after left anterior descending coronary artery occlusion. Left ventricular hypoperfused zone (HZ) averaged 36.6% and infarct size (IS) 31.6%. Thus, 86% of HZ evolved into necrosis. Preocclusion blood flow was lower in ischaemic (1.62 ml/min per g) compared with non-ischaemic myocardium (2.09, p = 0.002), indicating 22% microsphere loss. In ischaemic subendocardium, oedema (3.7%) could account for the apparent loss. In ischaemic subepicardium, oedema was less pronounced and 18% physical sphere loss occurred. Subepicardial loss increased in proportion to IS and IS/HZ ratio (r2 = 0.71; p less than 0.005). Non-entrapment of 15-micron spheres in coronary circulation averaged 0.6%, and preocclusion spheres appeared in coronary sinus blood throughout the ischaemic period. In systemic circulation, non-entrapment during injection of preocclusion spheres was 7.8%, but only 1.8% 5 h later. Release of postocclusion spheres took place during KCl injection. Thus, myocardial ischaemia is associated with alterations in microvascular function allowing release of entrapped 15-micron spheres. Also, the magnitude of microsphere loss per gram tissue is related to infarct size.

Comparative effects of propranolol, timolol and metoprolol on myocardial infarct size after experimental coronary artery occlusion

The effects of equiblocking doses of three beta-adrenergic blocking agents, propranolol, timolol and metoprolol, on myocardial infarct size were evaluated in 28 dogs after acute experimental coronary artery occlusion. Heart rate, arterial pressure and arterial free fatty acid concentration were measured in an attempt to evaluate their effects on the extent of myocardial injury. The zone at risk of infarction in each dog 1 minute after left anterior coronary artery occlusion was assessed by injecting highly radioactive albumin microspheres into the left atrium, and the hypoperfused zone was determined by autoradiography. After 15 minutes, the dogs were randomized into four groups: control dogs (n = 7), propranolol-treated dogs (1.2 mg/kg intravenously, n = 7), timolol-treated dogs (0.2 mg/kg intravenously, n = 7) and metoprolol-treated dogs (1.2 mg/kg intravenously, n = 7). After 6 hours, the dogs were killed. The left ventricle was sliced and stained with triphenyl-tetrazolium chloride for measurement on infarct size. The same slices were then autoradiographed for measurement of the hypoperfused zone. The percent of hypoperfused zone that evolved to infarction (the ratio of infarct size to hypoperfused zone) was 90.4 +/- 1.9% in the control group, 72.4 +/- 2.4% in the propranolol-treated dogs (p less than 0.05 versus control group); 57.9 +/- 4.4% in the timolol-treated dogs (p less than 0.01 versus control group; p less than 0.05 versus propranolol) and 54.4 +/- 3.7% in the metoprolol-treated dogs (p less than 0.01 versus control group; p less than 0.05 versus propranolol). Thus, propranolol, timolol and metoprolol reduced myocardial infarct size in dogs by 20, 36 and 40%, respectively, after experimental coronary artery occlusion. Metoprolol and timolol protected the ischemic myocardium more effectively than did propranolol.

Heparin inhibits bovine testicular hyaluronidase activity in myocardium of dogs with coronary artery occlusion

Bovine testicular hyaluronidase (BTH) reduces experimental myocardial infarct size and ameliorates electrocardiographic signs of ischemia. This study was done to determine if heparin, an in vitro inhibitor of hyaluronidase activity, blocks the action of BTH in the myocardium of dogs after coronary artery occlusion. BTH was administered intravenously as 5,000 NF units/kg at 0.5 and 2.5 hours after coronary occlusion. Heparin was administered intravenously as a 150-unit/kg loading dose, followed by 10 units/kg per hour i.v., beginning 15 minutes before coronary occlusion. The area of myocardial ischemia at risk was assessed by a radiolabeled microsphere technique; the area that developed necrosis was assessed by a histochemical technique. In vivo activity of BTH was assessed by a colorimetric analysis of the BTH substrate, i.e., hyaluronic acid (HA), extracted from myocardial tissue. For biochemical analysis of HA, the heart was divided into anterior myocardium, which included ischemic tissue and posterior nonischemic myocardium. The myocardial HA content of dogs treated with BTH plus heparin (anterior, 3.44 +/- 0.40 micrograms HA/mg protein; posterior, 3.69 +/- 0.33 micrograms HA/mg protein) was not significantly different from control (anterior, 3.61 +/- 0.29 micrograms HA/mg protein; posterior, 3.55 +/- 0.23 micrograms HA/mg protein). In contrast, BTH lowered myocardial HA content (anterior, 2.16 +/- 0.21 micrograms HA/mg protein; posterior, 2.08 +/- 0.14 micrograms HA/mg protein) compared with either BTH plus heparin or control groups in both anterior myocardium (p = 0.006) and posterior myocardium (p = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of lidocaine and droxicainide on myocardial necrosis: a comparative study

Lidocaine has been shown to protect ischemic myocardium, but the degree of its effectiveness is not yet well established. Therefore, in this study, the effects of this drug on ultimate infarct size were examined quantitatively. Another member of the same class of drugs, droxicainide (ALS1249), DL-N-(2-hydroxyethyl)-pipecolinyl-2,6-dimethylanilide hydrochloride, is a new antiarrhythmic agent that has shown a good therapeutic index in the initial experimental studies. Accordingly, the effects of this drug on ultimate infarct size were examined and compared with those of lidocaine. Coronary artery occlusion was performed on 29 dogs. One minute later, technetium-99m labeled microspheres were injected into the left atrium for assessment of the hypoperfused zone (the zone at risk of infarction). Fifteen minutes after occlusion, the dogs were randomized into three groups: 9 dogs served as a control group, 10 were given lidocaine and 10 were given the same dosage of droxicainide. Six hours after occlusion, the dogs were sacrificed and the hearts cut into 3 mm thick slices and incubated in triphenyltetrazolium chloride to delineate the area of myocardial damage. Autoradiography of the same slices provided images of the areas of myocardial hypoperfusion. Thereafter, in each dog, the percent of hypoperfused area that evolved to necrosis was calculated. In control dogs, it was 85.6 +/- 2.0%; in lidocaine-treated dogs, 68.1 +/- 4.1% (p less than 0.01), a reduction of 20%; and in droxicainide-treated dogs, 50.1 +/- 5.3%, a reduction of 41% (p less than 0.001 versus control and p less than 0.005 versus lidocaine).