Depletion of total antioxidant capacity in type 2 diabetes

The purpose of the study was to examine the relationship between antioxidant depletion, glycemic control, and development of chronic complications in a controlled population of type 2 diabetic patients. Fifty age-matched type 2 diabetic patients receiving sulfonylureas but not insulin treatment were screened and assigned to two groups based on the presence or absence of proteinuria. A third group of normal subjects without diabetes were also enrolled in the study. All subjects in the three groups were Egyptians who were matched for body weight, and the two diabetic groups were also age-matched. Plasma glucose and fructosamine levels were higher in the two groups of diabetic patients versus the control group, but lipid peroxide levels were higher only in the patients with proteinuria. Compared with the control group, the total antioxidant capacity was depleted in the two diabetic groups, but the depletion was more severe in patients with proteinuria. Thus, the mean Trolox equivalent antioxidant capacity (TEAC) of the control group was 2.7+/-0.45, versus 1.7+/-0.5 (P < .001) in the patients without proteinuria. Furthermore, the TEAC measured in patients with proteinuria, who also had more diabetic complications, was lower (1.4+/-0.5, P < .001) than the TEAC in patients without urinary protein. In conclusion, a depletion of the total antioxidant capacity is associated with a higher incidence of diabetic complications.

Metabolic changes in the normal and hypoxic neonatal myocardium

Hypoxia is characterized by inadequate oxygen delivery to the myocardium with a resulting imbalance between oxygen demand and energy supply. Several adaptive mechanisms occur to preserve myocardial survival during hypoxia. These include both short- and long-term mechanisms, which serve to achieve a new balance between myocardial oxygen demand and energy production. Short-term adaptation includes downregulation of myocardial function along with upregulation of energy production via anaerobic glycolysis following an increase in glucose uptake and glycogen breakdown. Long-term adaptation includes genetic reprogramming of key glycolytic enzymes. Thus, the initial decline in high-energy phosphates following hypoxia is accompanied by a decrease in myocardial contractility and myocardial energy requirements are subsequently met by ATP supplied from anaerobic glycolysis. Thus, a downregulation in cardiac function and/or enhanced energy production via anaerobic glycolysis are the major mechanisms promoting myocardial survival during hypoxia. In contrast to the aforementioned metabolic changes occurring in adult myocardium, the effects of chronic hypoxia on neonatal myocardial metabolism remain undefined. Studies from our laboratory using a novel neonatal piglet model of chronic hypoxia have shown a shift in cardiac myocyte substrate utilization towards the newborn state with a preference for glucose utilization. We have also shown, using this same model, that chronically hypoxic neonatal hearts were more tolerant to ischemia than non-hypoxic hearts. This ischemic tolerance is likely due to adaptive metabolic changes in the chronically hypoxic hearts, such as increased anaerobic glycolysis and glycogen breakdown.

Regulation of glucose utilization by inhibition of mitochondrial fatty acid uptake in cardiac cells

In order to investigate the mechanism by which fatty acid oxidation inhibitors regulate cardiac metabolism, the effects of 2-tetradecylglycidic acid (2-TDGA), and 2-bromopalmitic acid (2-BPA) on the oxidation of [1-14C]palmitate, [1-14C]octanoate and [U-14C]glucose were studied in isolated rat myocytes. Fifty per cent inhibition of palmitate oxidation was achieved at 20 microM 2-TDGA and 60 microM 2-BPA. Octanoate oxidation was also inhibited by 2-BPA. In contrast to their effect on palmitate oxidation, fatty acid inhibitors significantly stimulated the oxidation of glucose in a concentration-dependent manner. Moreover, the oxidation of [2-14C]pyruvate was increased two-fold by these compounds. The rate of uptake of [U-14C]-2-deoxyglucose was also stimulated two-fold by these inhibitors. These studies suggest that the stimulation of glucose utilization via the inhibition of fatty acid oxidation may be mediated through the stimulation of both glucose transport and the oxidation of pyruvate by the pyruvate dehydrogenase complex.

On the rate-limiting step in the beta-oxidation of polyunsaturated fatty acids in the heart

This study was conducted to determine if the activity of 2,4-dienoyl-CoA reductase limits the rate of cardiac beta-oxidation of highly unsaturated fatty acids. Although growth hormone treatment of hypophysectomized rats caused a 3-fold increase in the activity of 2,4-dienoyl-CoA reductase, beta-oxidation of docosahexaenoate in cardiomyocytes was not stimulated by this treatment. Since cardiomyocytes oxidized oleic acid more rapidly than docosahexaenoic acid, the utilization of energy did not limit beta-oxidation. Respiration measurements with coupled rat heart mitochondria revealed that the rates of beta-oxidation with palmitoyl-CoA and palmitoylcarnitine as substrates were virtually identical but were 3- to 4-fold higher than the rates obtained with either docosahexaenoyl-CoA or docosahexaenoylcarnitine. Although the activity of carnitine palmitoyltransferase I (CPT I) was 5 times higher with palmitoyl-CoA as substrate than with docosahexaenoyl-CoA, this reaction is only one of several that may limit the beta-oxidation of docosahexaenoic acid. Surprisingly, an incremental inhibition of CPT I resulted in a parallel inhibition of respiration supported by either palmitoyl-CoA or docosahexaenoyl-CoA. This observation agrees with the notion that CPT I may also be a regulatory enzyme in cardiac fatty acid oxidation. It is concluded that the reduction of double bonds by 2,4-dienoyl-CoA reductase does not restrict the cardiac beta-oxidation of highly unsaturated fatty acid, like docosahexaenoic acid.

Myocardial tolerance to mechanical actuation is affected by biomaterial characteristics

Direct mechanical ventricular actuation (DMVA) uses a pressure regulated heart cup, fabricated from silicone rubber (SR) for mechanical massage of the heart. Because DMVA has demonstrated potential for long-term circulatory support, investigations are currently exploring the use of more durable materials for fabricating DMVA heart cups. This study assessed the acute effects of heart cups fabricated from SR versus polyurethane (PU) on the myocardium. Dogs (n - 18) received DMVA for 4 hr of ventricular fibrillation (VF) using either SR (n = 10) or PU (n = 8) cups. Microspheres were used to determine perfusion during sinus rhythm (control) and at 2 and 4 hr of support. After support, myocardial biopsies were assayed for high energy phosphate content. Results demonstrated that PU cups required relatively frequent adjustments in drive line parameters that were likely due to material softening during PU cup support. Both PU and SR cups achieved similar hemodynamics during 4 hr of support. Myocardial perfusion, however, demonstrated a marked hyperemia at 4 hr of PU versus SR cup support. Regional high energy phosphate content was significantly decreased in hearts supported by PU versus SR cups. These results suggest that the relatively compliant characteristics of SR materials are important for achieving effective DMVA support without injuring the myocardium.

Pulsatile versus nonpulsatile reperfusion improves cerebral blood flow after cardiac arrest

Cardiopulmonary bypass using nonpulsatile flow (NF) is currently advocated for treating refractory cardiac arrest. Although the heart can be revived using cardiopulmonary bypass support, the brain must recover if such therapy is to be considered successful. Previous studies have demonstrated that pulsatile flow (PF) reperfusion can improve neurologic outcome compared with NF reperfusion after cardiac arrest. The purpose of this study was to assess cerebral perfusion and oxygen consumption during either PF or NF reperfusion after cardiac arrest. Dogs (n = 22) underwent a 15-minute cardiac arrest followed by 1 hour of either PF or NF reperfusion. Microsphere techniques were used to assess cerebral perfusion and oxygen consumption at 3, 15, and 60 minutes of reperfusion. Mean arteriovenous gradients and total brain flows were similar in both groups. However, cerebral oxygen consumption was significantly improved at 3 minutes of reperfusion with PF versus NF (1.8 +/- 0.3 versus 0.9 +/- 0.3 mL O2.dL-1.min-1, respectively; p < 0.05). These results were coincident with improved gray-to-white flow ratios at 3 minutes of PF versus NF reperfusion (5.2 +/- 1.0 versus 2.0 +/- 0.3, respectively; p < 0.05). There were no statistically significant differences in brain perfusion variables by 15 minutes of reperfusion. However, a relative hyperemia was exhibited at 15 minutes of NF versus PF reperfusion, which suggests nutrient flow was insufficient during early NF versus PF reperfusion. In conclusion, PF reperfusion can better restore cerebral blood flow and oxygen consumption than can NF reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective inhibition of hepatic peroxisomal fatty acid beta-oxidation by enoximone

Although beta-oxidation of fatty acids occurs in both peroxisomes and mitochondria, beta-oxidizing enzymes in these organelles have distinct differences in their specifity and sensitivity to inhibitors. In this study, the effects of the phosphodiesterase inhibitor enoximone on hepatic peroxisomal and mitochondrial beta-oxidation were investigated. In liver homogenates from control rats, cyanide-insensitive peroxisomal beta-oxidation of palmitoyl-CoA was inhibited progressively by increasing concentrations of enoximone. Similar results were obtained in liver homogenates from rats pretreated with the known peroxisomal proliferator diethylhexylphthalate. In contrast, mitochondrial beta-oxidation of palmitoyl-CoA was not inhibited by enoximone. These data show that enoximone selectively inhibits basal as well as induced peroxisomal, but not mitochondrial, beta-oxidation of the CoA thioester of long-chain fatty acids. The availability of specific inhibitors of peroxisomal beta-oxidation should prove useful in elucidating regulatory mechanisms operative in this pathway in normal as well as in proliferated peroxisomes.

Stimulation of fatty acid oxidation in myocytes by phosphodiesterase inhibitors and adenosine analogues

The effect of various phosphodiesterase inhibitors, and adenosine analogues on palmitate oxidation, were studied in isolated rat myocytes. Enoximone, milrinone, and dipyridamole, at a concentration of 250 microM, stimulated palmitate oxidation by 78%, 40%, and 43%, respectively. The specific A1-agonist, N6-cyclopentyladenosine, increased palmitate oxidation by 56%, at a concentration of 250 microM. Moreover, the nucleoside transport inhibitor, S-(P-Nitrobenzyl-)6-thioinosine, increased palmitate oxidation by 40%, at a concentration of 100 microM. These data suggest that the stimulation of palmitate oxidation by enoximone and adenosine analogues may be mediated via the inhibition of the uptake and/or the oxidation of glucose in myocytes.