Long term model for evaluation of myocardial metabolic recovery following global ischemia

Potential Clinical Benefits of D-ribose in Ischemic Cardiovascular Disease

Cardiovascular disease still remains the leading cause of deaths worldwide. Atherosclerosis, the most common type of cardiovascular disease, has continued to progress due to many factors, genetics, and lifestyles. All cells require adequate adenosine triphosphate (ATP) levels to maintain their integrity and function. Myocardial ischemia commonly found in atherosclerosis can produce lower levels of ATP, which affects not only cellular energy, but also alters normal function. D-ribose, a naturally occurring pentose carbohydrate, has been shown to increase cellular energy levels and improve function following ischemia in pre-clinical studies and have demonstrated potential benefits in clinical evaluations. This review paper presents an overview of ischemic cardiovascular disease and the potential role that D-ribose could play in improving myocardial energy levels and function in the area of ischemic cardiovascular diseases.

Proof of concept and feasibility studies examining the influence of combination ribose, adenine and allopurinol treatment on stroke outcome in the rat

Background

Cerebral ischaemia results in a rapid and profound depletion of adenosine triphosphate (ATP), the energy currency of the cell. This depletion leads to disruption of cellular homeostasis and cell death. Early replenishment of ATP levels might therefore have a neuroprotective effect in the injured brain. We have previously shown that the ATP precursors, D-ribose and adenine (RibAde), restored the reduced ATP levels in rat brain slices to values similar to those measured in the intact rodent brain. The aim of this study was to assess whether RibAde, either alone or in combination with the xanthine oxidase inhibitor allopurinol (RibAdeAll; to further increase the availability of ATP precursors), could improve outcome in an in vivo rodent model of transient cerebral ischaemia.

Methods

After 60 min occlusion of the middle cerebral artery, and upon reperfusion, rats were administered saline, RibAde, or RibAdeAll for 6 h. Baseline lesion volume was determined by diffusion-weighted MRI prior to reperfusion and final infarct volume determined by T2-weighted MRI at Day 7. Neurological function was assessed at Days 1, 3 and 7.

Results

Ischaemic lesion volume decreased between Days 1 and 7: a 50% reduction was observed for the RibAdeAll group, 38% for the RibAde group and 18% in the animals that received saline. Reductions in lesion size in treatment groups were accompanied by a trend for faster functional recovery.

Conclusion

These data support the potential use of ribose, adenine and allopurinol in the treatment of cerebral ischaemic injury, especially since all compounds have been used in man.

Modulation of intracellular ATP determines adenosine release and functional outcome in response to metabolic stress in rat hippocampal slices and cerebellar granule cells

Cerebral ischaemia rapidly depletes cellular ATP. Whilst this deprives brain tissue of a valuable energy source, the concomitant production of adenosine mitigates the damaging effects of energy failure by suppressing neuronal activity. However, the production of adenosine and other metabolites, and their loss across the blood-brain barrier, deprives the brain of substrates for the purine salvage pathway, the primary means by which the brain makes ATP. Because of this, cerebral ATP levels remain depressed after brain injury. To test whether manipulating cellular ATP levels in brain tissue could affect functional neuronal outcomes in response to oxygen/glucose deprivation (OGD), we examined the effects of creatine and d-ribose and adenine (RibAde). In hippocampal slices creatine delayed ATP breakdown, reduced adenosine release, retarded both the depression of synaptic transmission and the anoxic depolarization caused by OGD, and improved the recovery of transmission. In contrast, RibAde increased cellular ATP, caused increased OGD-induced adenosine release and accelerated the depression of synaptic transmission, but did not improve functional recovery. However, RibAde improved the viability of cerebellar granule cells when administered after OGD. Our data indicate that RibAde may be effective in promoting recovery of brain tissue after injury, potentially via enhancement of salvage-mediated ATP production.

Using fructose-1,6-diphosphate during hypothermic rabbit-heart preservation: a high-energy phosphate study

BACKGROUND

In this study, we evaluated the effects of fructose-1,6-diphosphate (FDP) on high-energy phosphate metabolism during 18-hour hypothermic rabbit-heart preservation.

METHODS

Under general anesthesia and artificial ventilation, hearts from 42 adult New Zealand white rabbits were harvested, flushed, and preserved in St. Thomas solution at 4(o)C for 18 hours. In the study group (n = 15), FDP (5 mmol/liter) was added to the St. Thomas solution, whereas in the control group (n = 17), fructose (5 mmol/liter) was added. Another 10 hearts did not undergo hypothermic storage, but were used as the normal group for high-energy phosphate concentration comparison.

RESULTS

After 18 hours of hypothermic preservation, myocardial high-energy phosphate content decreased in both preservation groups. In the study group, left ventricular adenosine triphosphate (ATP) content was 33% of that in the normal hearts, but in the control group, ATP decreased to 14% of normal. Adenosine diphosphate (ADP) content, energy charge, and ATP-to-ADP ratio showed similar decreases. The high-energy phosphate profile (content in the atria and ventricles and the ratio of ATP to ADP to AMP) was maintained in the study group but not in the control group. High-energy phosphate metabolites such as inosine monophosphate (IMP), inosine, and hypoxanthine increased in both preservation groups, but the increase was more prominent in the control group.

CONCLUSION

Adding FDP to St. Thomas solution attenuated the depletion of high-energy phosphate concentration in the preserved hearts. This difference was especially prominent in the left and right ventricles. The protective effect of FDP during hypothermic heart preservation deserves further study.

Pre-conditioning activates adenosine utilization in a cost-effective way during myocardial ischaemia

During pre-conditioning the interstitial concentration of adenosine, in contrast to lactate, presents a die-away curve-pattern for every successive episode of ischaemia. This die-away pattern might not necessarily be attributed to diminished adenosine production. The present study was undertaken to investigate whether pre-conditioning alters the metabolic turnover of adenosine as observed by the lactate production during ischaemia. Interstitial levels of metabolites in pre-conditioned (n=21) and non-preconditioned (n=21) porcine hearts were monitored with microdialysis probes inserted in both ischaemic and non-ischaemic tissue in an open chest heart model. Three subgroups perturbated with either plain microdialysis buffer (control), buffer containing adenosine (375 microM), or buffer containing deoxyadenosine (375 microM) were studied. All animals were subjected to 90 min of equilibrium microdialysis before 40 min of regional myocardial ischaemia and 120 min of reperfusion. Pre-conditioning consisted of four repetitive episodes of 10 min of ischaemia and 20 min of reperfusion. Significantly higher levels of inosine and lactate were found in the ischaemic tissue of the pre-conditioned subgroup receiving adenosine (P < 0.05) compared with the other two subgroups receiving deoxyadenosine and plain buffer, respectively. This difference was only valid for pre-conditioned ischaemic myocardium, and hence equal amounts of inosine and lactate were produced in the non-preconditioned ischaemic myocardium regardless of the presence of adenosine or deoxyadenosine. In the non-ischaemic myocardium baseline levels of metabolites were measured in all subgroups. Pre-conditioning favoured degradation of exogenous adenosine to inosine successively ending up in enhanced lactate production. This was probably because of the involvement of the hexose monophosphate pathway in the pre-conditioned ischaemic myocardium. This route may therefore be supplementary in energy metabolism as a metabolic flow can be started by adenosine ending up in lactate without initial adenosine 5'-triphosphate (ATP) investment. Utilization of adenosine in this way may also explain the successive die-away pattern of adenosine seen in consecutive pre-conditioning cycles.

Effects of ribose on exercise-induced ischaemia in stable coronary artery disease

There is no established treatment specifically aimed at protecting or restoring cardiac energy metabolism, which is greatly impaired by ischaemia. Even after reperfusion, myocardial content of ATP remains low for more than 72 h. Long-term post-ischaemic dysfunction and irreversibility of ischaemic damage have been associated with low ATP content. Evidence that the pentose sugar ribose stimulates ATP synthesis and improves cardiac function led us to test the possibility that ribose increases tolerance to myocardial ischaemia in patients with coronary artery disease (CAD). 20 men with documented severe CAD underwent two symptom-limited treadmill exercise tests on 2 consecutive days; we postulated that the ischaemia induced might bring about changes in ATP metabolism lasting for several days. Patients whose baseline tests showed reproducibility were randomly allocated 3 days of treatment with placebo or ribose 60 g daily in four doses by mouth. Exercise testing was repeated after treatment on day 5. At that time mean (95% confidence interval) treadmill walking time until 1 mm ST-segment depression was significantly greater in the ribose than in the placebo group (276 [220-331] vs 223 [188-259] s; p = 0.002). The groups did not differ significantly in time to moderate angina. In the ribose-treated group the changes from baseline to day 5 in both time to ST depression and time to moderate angina were significant (p less than 0.005), but these changes were not significant in the placebo group. In patients with CAD, administration of ribose by mouth for 3 days improved the heart's tolerance to ischaemia. The presumed effects on cardiac energy metabolism offer new possibilities for adjunctive medical treatment of myocardial ischaemia.