Anthony M. Freedman

Magnesium-deficiency elevates circulating levels of inflammatory cytokines and endothelin

SummaryWe have developed two rodent models of diet-induced magnesium-deficiency in which histologically defined cardiac lesions can be induced within two to three weeks. During the development of these lesions, the magnesium-deficient animals exhibit circulating cytokine levels which are indicative of a generalized inflammatory state. Dramatic elevations of the macrophage-derived cytokines, IL-1, IL-6, and TNF-α together with signigicantly elevated levels of the endothelial cell-derived cytokine, endothelin, were detected in the plasma of these animals. We believe that the pathophysiological effects caused by the action of these cytokines may play a role in the promotion of cardiovascular pathology associated with magnesium deficiency.

Protective effects of sulfhydryl-containing angiotensin converting enzyme inhibitors against free radical injury in endothelial cells

The effects of SH-containing (captopril, epi-captopril, and the free-SH form of zofenopril) and non-SH-containing (enalaprilat and lisinopril) angiotension converting enzyme (ACE) inhibitors on free radical injury in cultured endothelial cells were studied. When cultured endothelial cells were exposed to a superoxide and hydroxyl radical generating system (dihydroxyfumarate + Fe3(+)-ADP) for 30 min, lipid peroxidation [malondialdehyde (MDA) formation] occurred, and cellular viability (trypan blue exclusion) decreased to 41%; concomitantly, plasma membrane blebbing, assessed by scanning electron microscopy, occurred in 65% of the cells. Preincubation of the cells with each of the SH-agents before free radical addition resulted in an equipotent concentration-dependent (10-200 microM) inhibition (15-60%) of MDA formation; both losses in cellular viability and percent blebbed cells were reduced significantly (P less than 0.05) by concentrations as low as 10 microM of each SH-agent. However, neither of the non-SH agents up to 200 microM produced any major effect. When the effects on hydroxyl radical formation in the system were assessed by ESR spin-trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), concentrations of 10 and 50 microM of the SH-agents reduced the intensity of the DMPO-OH adducts 20 and 50% respectively. Similar results were observed when the hydroxyl radical was generated from the Fenton-reagents (Fe2+ + H2O2), suggesting direct hydroxyl radical scavenging. Thus, these results demonstrate that the SH-containing ACE agents are capable of protecting the endothelial cells against free radical induced lipid peroxidation and cell injury; the mechanism may be due to direct hydroxyl radical scavenging.

Magnesium deficiency-induced cardiomyopathy: Protection by vitamin E

Syrian male hamsters weighing 80-100g were placed on either a magnesium deficient diet (MgD) or an identical diet supplemented with 100 mmols/Kg MgCl. Animals from each group received vitamin E 10, 15, and 25mg three-week slow release pellets, as subcutaneous implants. The animals were sacrificed after 14 days and their hearts isolated for morphological analysis. H&E stained sections were examined by a computer image analysis system for a morphometric determination of the severity of myocardial injury. Vitamin E significantly (p less than 0.01) reduced both the numerical density and the area fraction of MgD lesions. These data indicate possible free radical participation in the mechanism of injury.

Propranolol reduces anoxia/reoxygenation-mediated injury of adult myocytes through an anti-radical mechanism☆

The effects of propranolol (PRO) and atenolol (ATE) on adult canine myocytes exposed to 30 min anoxia (A:95% N2/5% CO2) and subsequent reoxygenation (R:95% O2/5% CO2) for up to 20 min was investigated. In some studies, comparison of effects were made with that of superoxide dismutase (SOD). Although anoxia alone produced only minimal injury, reoxygenation in the absence of the beta-blockers or SOD was associated with significant losses of cellular viability, elevated release of cellular lactate dehydrogenase, and increased formation of lipid peroxidation products. Myocytes exposed to A/R in the presence of d,1-PRO (20, 200 microM) were afforded substantial, concentration-dependent protection during 20 min reoxygenation. Significant protection was also observed in the presence of 2 microM d-PRO (non-active beta-blocker), but only after a longer preincubation period (2 h). SOD (10 micrograms/ml) provided equi-potent protection to that of 200 microM d,1-PRO. By contrast, the more water-soluble beta-blocker, ATE (200 microM), offered only minor protection. Electron Spin Resonance spin trapping studies using alpha-phenyl-tert-butylnitrone (PBN) were also performed with A/R myocytes in the presence or absence of drug treatment. Short-term (10 min) exposure to d,1-PRO (200 microM) prior to A/R, or to SOD, resulted in a 71-84% reduction in total PBN lipid radical adduct formation (alkoxyl; alpha H = 2.0-2.5 G, alpha N = 13.5-13.75 G); long-term exposure (2 h) to 2 microM d-PRO resulted in a 51% reduction. These data suggest that the superoxide anion was an initiator of events leading to subsequent lipid radical formation and that the anti-peroxidative properties of PRO appear to be independent of beta-receptor blockade.

Oxygen radical-mediated injury of myocytes-protection by propranolol

UIe effects of propranolol and atenolol on free radical mediated injury in myocytes were examined. Freshly isolated adult canine myocytes were incubated with a superoxide generating (from dihydroxyfumarate) and Fe-catalyzed free radical system. Exposure of the myocytes to free radicals for 20 min resulted in more than a 5-fold increase in thiobarbituric acid reactant (peroxide) formation and elevated levels of lactate dehydrogenase (LDH) activity released into the media compared to controls. Ultrastructurally, severe sarcolemmal damage, mitochondrial and myofibril derangements were evident. At 40 min, cellular viability (trypan blue exclusion) in the samples exposed to free radicals decreased to about one-third of controls; concomitantly, major losses in total cellular phospholipids occurred. When the cells were pretreated with 200 microM propranolol before the addition of free radicals, both peroxide formation and increased LDH release were inhibited; in agreement, complete ultrastructural preservation was observed. In addition, the subsequent losses in cellular viability and phospholipids were prevented. For comparison, the more water soluble beta-blocker, atenolol at 200 microM was shown ineffective in providing significant protection against the induced injury. The results suggest that propranolol may provide antiperoxidative protection to myocytes when elevated levels of free radicals are present.

Propanolol preserves ultrastructure in adult cardiocytes exposed to anoxia/reoxygenation: A morphometric analysis

The protective effect of d,l-propranolol was studied using freshly isolated canine ventricular cardiocytes (1.5 x 10(6)/mL) exposed to 30 min anoxia (95% N2/5% CO2) and 0, 3, 20, and 45 min of reoxygenation (95% O2/5% CO2). In addition to preventing lipid peroxide formation, propranolol maintained cellular viability, and minimized ultrastructural alterations. In the absence of propranolol, the outer mitochondria become swollen and rounded up within the first few minutes of reoxygenation. The perinuclear mitochondrial area increased only slightly. We observed that the cellular injury process proceeded differentially from the exterior to the interior, with a mitochondrial area increase and outer membrane rupture. Sarcolemmal damage was also observed with prevalent blebbing and membrane loss. The Z-lines became wider and more diffuse with reoxygenation. Injury to the nuclear double membrane was observed. Incubation with propranolol showed significant protection during postanoxia reoxygenation. In contrast, the more water soluble beta-blocker atenolol only exhibited slight protection. In addition, d-propranolol (the non beta-blocking isomer) and the antioxidant enzymes, SOD and catalase, showed significant protection. These data support previous findings concerning the antioxidant properties of propranolol which appear to be independent of beta-receptor blockade.