I.T. Mak

Models of Injury of Cardiovascular Membranes by Amphiphiles and Free Radicals

Current evidence from ultrastructural, biochemical and electrophysiological studies suggest that membrane damage is an early event in ischemic myocardial injury (1–3). Previous investigations (4–8) suggest that sarcolemmal, microsomal and lysosomal structural and functional integrity may be compromised by any one or combinations of mechanisms that may be active during ischemia. During ischemia, cellular membranes may be subjected to perturbations by accumulated lipid metabolites, elevated levels of free radicals and activated lipolytic enzymes. We have investigated the molecular nature of several injurious processes in vitro in an effort to determine the potential sequence of events leading to ischemic membrane damage. Incubation of highly purified hepatic lysosomes at acid pH results in loss of lysosomal latency and leakage of lysosomal lipases. When the sarcolemmal (SL) membranes from canine myocytes were incubated with the soluble lysosomal enzymes, the membrane phospholipids were differentially hydrolyzed. In the presence of a .02− driven (derived from dihydroxyfumarate) iron catalyzed-free radical generating system, the SL membrane fluidity was altered. The peroxidation of the SL membrane was accompanied by a selective loss of phospholipids and the membrane-bound Na,K-ATPase was also inactivated.

Combination ART-Induced Oxidative/Nitrosative Stress, Neurogenic Inflammation and Cardiac Dysfunction in HIV-1 Transgenic (Tg) Rats: Protection by Mg

Chronic effects of a combination antiretroviral therapy (cART = tenofovir/emtricitatine + atazanavir/ritonavir) on systemic and cardiac oxidative stress/injury in HIV-1 transgenic (Tg) rats and protection by Mg-supplementation were assessed. cART (low doses) elicited no significant effects in normal rats, but induced time-dependent oxidative/nitrosative stresses: 2.64-fold increased plasma 8-isoprostane, 2.0-fold higher RBC oxidized glutathione (GSSG), 3.2-fold increased plasma 3-nitrotyrosine (NT), and 3-fold elevated basal neutrophil superoxide activity in Tg rats. Increased NT staining occurred within cART-treated HIV-Tg hearts, and significant decreases in cardiac systolic and diastolic contractile function occurred at 12 and 18 weeks. HIV-1 expression alone caused modest levels of oxidative stress and cardiac dysfunction. Significantly, cART caused up to 24% decreases in circulating Mg in HIV-1-Tg rats, associated with elevated renal NT staining, increased creatinine and urea levels, and elevated plasma substance P levels. Strikingly, Mg-supplementation (6-fold) suppressed all oxidative/nitrosative stress indices in the blood, heart and kidney and substantially attenuated contractile dysfunction (>75%) of cART-treated Tg rats. In conclusion, cART caused significant renal and cardiac oxidative/nitrosative stress/injury in Tg-rats, leading to renal Mg wasting and hypomagnesemia, triggering substance P-dependent neurogenic inflammation and cardiac dysfunction. These events were effectively attenuated by Mg-supplementation likely due to its substance P-suppressing and Mg’s intrinsic anti-peroxidative/anti-calcium properties.

Hypomagnesemia in diabetes patients: comparison of serum and intracellular measurement of responses to magnesium supplementation and its role in inflammation.

Purpose In this clinical trial, we assessed the efficacy of magnesium (Mg) supplementation in hypomagnesemic type 2 diabetes patients in restoring serum and intracellular Mg levels. The study had two coprimary end points: the change in serum and intracellular Mg level between baseline and after 3 months of supplementation. We compared the efficacy with regard to lowering hemoglobin A1c (HbA1c), C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), and 8-isoprostane as secondary end points. Patients and methods In an open-label trial, 47 hypomagnesemic type 2 diabetes patients were administered 336 mg Mg daily. At baseline and after 3 months, serum, cellular Mg, and inflammation biomarkers were measured. For intracellular Mg levels, sublingual epithelial cells were analyzed by analytical scanning electron microscopy using computerized elemental X-ray analysis. Blood samples were analyzed for Mg, creatinine, HbA1c, and CRP. Systemic inflammatory markers including TNF-α and the oxidative stress marker 8-isoprostane were determined using enzyme-linked immunosorbent assay. Results Mg supplementation significantly increased the intracellular and serum levels. Statistically clinical improvement in HbA1c and CRP levels was not observed, but significant decreases in TNF-α as well as in 8-isoprostane were found. Conclusion A feasible clinical method for the assessment of intracellular Mg was demonstrated in tissue samples obtained noninvasively, providing evidence for potential clinical translation of this method to routinely determine intracellular Mg concentration.