John R. Mahoney

Enhanced high energy phosphate recovery with ribose infusion after global myocardial ischemia in a canine model

High energy phosphate levels are depressed following global ischemia and require several days to completely recover. Short-term methods to enhance ATP recovery have included infusion of ATP precursors, inhibition of enzymes that catabolize AMP, and membrane transport stabilization. Several precursors have been used to augment adenine nucleotide synthesis including adenosine, inosine, adenine, and ribose. Because of the short-term nature of previous experiments, recovery had been incomplete and the effects in the intact animal unknown. The purpose of this study was to determine the effects of ribose infusion in a long-term model of global ischemia and attempt to identify the precursor which limits myocardial ATP regeneration in the intact animal. Global myocardial ischemia (20 min, 37 degrees C) was produced in dogs on cardiopulmonary bypass. With reperfusion either ribose (80 mM) in normal saline or normal saline alone was infused at 1 ml/min into the right atrium and the animals were followed for 24 hr. Ventricular biopsies were obtained through an indwelling ventricular cannula prior to ischemia, at the end of ischemia, and 4 and 24 hr postischemia and analyzed for adenine nucleotides and creatine phosphate levels. Radiolabeled microspheres were used to measure myocardial and renal blood flows and no significant difference was found between ribose-treated control groups. In both groups, myocardial ATP levels fell by at least 50% at the end of ischemia. No significant ATP recovery occurred after 24 hr in the control dogs, but in the ribose-treated animals, ATP levels rebounded to 85% of control by 24 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraerythrocytic plasmodial calcium metabolism

Abstract Both prokaryotes and eukaryotes require Ca ++ for a variety of cellular functions. Intraerythrocytic plasmodia, however, exist within a cell ordinarily impermeable to external Ca ++ . Our investigations of Ca ++ homeostasis in murine Plasmodium berghei reveal that (1) infected erythrocytes contain 10 – 15 times as much Ca ++ as do uninfected red cells, (2) these large amounts of Ca ++ are located almost exclusively within the parasite, and (3) the parasite obtains at least a portion of this Ca ++ through causing increased permeability of the host cell membrane to external Ca ++ .

Chloroquine resistant malaria: Association with enhanced plasmodial protease activity

Abstract Chloroquine resistant Plasmodium berghei has several unusual features including (i) lack of malaria “pigment”, (ii) more efficient host catabolism of heme from infected erythrocytes, and (iii) relatively inefficient uptake of external chloroquine by infected red cells. The malaria pigment produced by chloroquine sensitive P. berghei is probably incompletely catabolized hemoglobin, the heme group of which is unavailable for subsequent catabolism by the hosts reticuloendothelial system. This pigment has been suggested by others as the site of high affinity chloroquine binding. We hypothesized that all three characteristics of chloroquine resistant infections might be explained by enhanced proteolytic digestion of host cell hemoglobin. In confirmation, we report that chloroquine resistant P. berghei has 700–800% greater protease activity than the chloroquine sensitive form. This greatly elevated protease activity may explain the aforementioned characteristics of chloroquine resistant P. berghei and may help elucidate the basis of chloroquine resistance in human P. falciparum .

A comparison of different carbohydrates as substrates for the isolated working heart

Ribose has been shown to greatly enhance ATP recovery in situations such as postischemia when total adenine nucleotides have been depleted by catabolism. In addition, metabolic studies have reported that both five carbon sugars and alcohols (ribose and xylitol) can support energy metabolism presumably after conversion to substrates for glycolysis. Because of the importance of these two aspects of energy metabolism to myocardial function, we compared the ability of ribose and xylitol with glucose and pyruvate as exclusive substrates for the isolated working rat heart. Our studies revealed, however, that the utilization of ribose or xylitol as substrates by the myocardium is not sufficiently rapid to rely on these as exclusive oxidizable substrates. In fact, ribose or xylitol are no more effective than substrate-free medium in this regard. Myocardial glycogen was depleted in these groups and after a lag period consumption of oxygen also decreased. In contrast to the postischemic situation the total adenine nucleotide levels were preserved during ribose, xylitol or substrate-free perfusion. Consequently, the energy charge in these hearts fell significantly. In hearts perfused with ribose, xylitol or no substrate, the rate pressure product and the stroke volume rapidly declined after an initial brief stable period corresponding to glycogen depletion. Glycogen levels were 6% of the average control value in ribose- and xylitol-perfused hearts and were undetectable in substrate-free perfused hearts. In contrast, either glucose or pyruvate supported steady levels of ATP and myocardial oxygen consumption; maintained the energy charge; and supported the stroke volume, rate pressure product, and cardiac work. In glucose-perfused hearts the glycogen was reduced to 21% of control values, while in pyruvate-perfused hearts the average glycogen levels were 76% of control. Thus, although the heart is able to metabolize ribose and xylitol through the hexose monophosphate pathway, the rate of utilization through glycolysis and presumably the TCA cycle is not sufficient for these compounds to serve as exclusive substrates for the isolated working heart.

High molecular weight forms of deferoxamine: novel therapeutic agents for treatment of iron-mediated tissue injury.

The iron chelator, deferoxamine (Desferal®), is presently used clinically for the treatment of acute and chronic iron toxicity. The chelator is an effective inhibitor of iron-catalyzed reactions leading to the formation of both oxygen and lipid-derived radicals. Deferoxamine (DFO) has been incorporated in a number of studies involving oxygen and lipid radical mediated reactions leading to tissue injury and has proven efficacious in ameliorating reperfusion injury.