Adenosine deaminase inhibitor in cardioplegia enhanced function preservation of the hypothermically stored rat heart

The effect of adenosine deaminase inhibition on the A1 adenosinergic and M2 muscarinergic control of contractility in eu- and hyperthyroid guinea pig atria

The A1 adenosine and M2 muscarinic receptors exert protective (including energy consumption limiting) effects in the heart. We investigated the influence of adenosine deaminase (ADA) inhibition on a representative energy consumption limiting function, the direct negative inotropic effect elicited by the A1 adenosinergic and M2 muscarinergic systems, in eu- and hyperthyroid atria. Furthermore, we compared the change in the interstitial adenosine level caused by ADA inhibition and nucleoside transport blockade, two well-established processes to stimulate the cell surface A1 adenosine receptors, in both thyroid states. A classical isolated organ technique was applied supplemented with the receptorial responsiveness method (RRM), a concentration estimating procedure. Via measuring the contractile force, the direct negative inotropic capacity of N(6)-cyclopentyladenosine, a selective A1 receptor agonist, and methacholine, a muscarinic receptor agonist, was determined on the left atria isolated from 8-day solvent- and thyroxine-treated guinea pigs in the presence and absence of 2'-deoxycoformycin, a selective ADA inhibitor, and NBTI, a selective nucleoside transporter inhibitor. We found that ADA inhibition (but not nucleoside transport blockade) increased the signal amplification of the A1 adenosinergic (but not M2 muscarinergic) system. This action of ADA inhibition developed in both thyroid states, but it was greater in hyperthyroidism. Nevertheless, ADA inhibition produced a smaller rise in the interstitial adenosine concentration than nucleoside transport blockade did in both thyroid states. Our results indicate that ADA inhibition, besides increasing the interstitial adenosine level, intensifies the atrial A1 adenosinergic function in another (thyroid hormone-sensitive) way, suggesting a new mechanism of action of ADA inhibition.

Effect of adenosine monophosphate deaminase-1 C34T allele on the requirement for donor inotropic support and on the incidence of early graft dysfunction after cardiac transplantation

The C34T T allele of the adenosine monophosphate deaminase-1 (AMPD1) gene has been associated with improved outcome in patients with cardiac dysfunction. We hypothesized that possession of this allele by donor hearts plays a role in the outcome of cardiac transplantation; 262 cardiac donors and 190 of their recipients were studied. AMPD1 C34T genotype was determined using 5' exonuclease chemistry. Requirement for inotropic agents before organ donation, 1-year post-transplantation survival, cause of death, and factors known to affect survival after transplantation were also studied. Multiple regression models for factors affecting survival were constructed. A significant yearly increase in frequency of the T allele in donors was noted (0.06 to 0.18 from 1994 to 1999). Donors with the CT or TT genotype required less inotropic support than those with the CC genotype (mean number of inotropes per donor with CT or TT genotype 0.27 compared with 0.47 per donor with CC genotype, n = 206, p = 0.03). Recipients of T-allele-carrying organs showed worse 1-year survival after transplantation (59% vs 79%, p <0.001). Excess deaths in these patients was due to early graft dysfunction (odds ratio for early graft dysfunction 6.6, 95% confidence interval 2 to 21.6, p = 0.0001). Multivariate analysis showed donor AMPD1 genotype, recipient age, and pretransplantation anemia to independently affect 1-year post-transplantation survival (adjusted hazard ratios 3.7, 1.06, and 2.6, respectively). In conclusion, possession of the AMPD1 T allele is associated with decreased inotropic requirements before heart donation. The incidence of early graft dysfunction, however, was significantly higher in recipients who received AMPD1 T-allele-possessing organs resulting in worse 1-year survival.

Photo-irradiation improved functional preservation of the isolated rat heart

BACKGROUND AND OBJECTIVE

Photo-irradiation causes a variety of effects in different cells and tissues. We hypothesized that photo-irradiation may improve cardiac preservation based on these observations.

STUDY DESIGN/MATERIALS AND METHODS

For pre-storage treatment (Pre), the heart in an anesthetized open-chest rat was irradiated using an Argon-dye laser with a wavelength of 660 nm at a fluence of 16.8 J/cm2 or sham-operated. The heart was excised, perfused with Krebs-Henseleit Buffer, cardioplegically arrested, and stored by immersion at 0 degree C for 18 hrs. Functional recovery was evaluated by working reperfusion for 30 min. For post-storage treatment (Post), the isolated hearts were stored for 18 hrs at 0 degree C; laser irradiation at a fluence of 36 J/cm2 was administered during working reperfusion. Hearts which did not receive irradiation during reperfusion served as control. Furthermore, isolated cardiomyocytes were used to study laser effect on cellular ATP content, catalase activity, and nitric oxide (NO) release.

RESULTS

Both Pre and Post groups showed significant improvement in recovery of aortic flow, cardiac output, and work compared to the corresponding control groups (P < 0.05). Combined Pre/Post laser treatment did not improve function. Investigation using isolated rat cardiomyocytes found that both end-storage ATP and end-reperfusion catalase activity in the laser-treated group were significantly higher than those in the untreated cells (P < 0.05). NO release increased by 15% in the laser group after 18 hrs of 37 degrees C incubation.

CONCLUSION

Photo-irradiation improves functional recovery of the cold-stored rat heart possibly via conservation of ATP and antioxidant enzyme activity.

cGMP-stimulated cyclic nucleotide phosphodiesterase regulates the basal calcium current in human atrial myocytes

EHNA (Erythro-9-[2-hydroxy-3-nonyl]adenine) is a wellknown inhibitor of adenosine deaminase. Recently, EHNA was shown to block the activity of purified soluble cGMPstimulated phosphodiesterase (PDE2) from frog, human, and porcine heart with an apparent Ki value of approximately 1 microM and with negligible effects on Ca2+/calmodulin PDE (PDE1), cGMP-inhibited PDE (PDE3), and low Km cAMP-specific PDE (PDE4) (Méry, P.F., C. Pavoine, F. Pecker, and R. Fischmeister. 1995. Mol. Pharmacol. 48:121-130; Podzuweit, T., P. Nennstiel, and A. Muller. 1995. Cell. Signalling. 7:733- 738). To investigate the role of PDE2 in the regulation of cardiac L-type Ca2+ current (ICa), we have examined the effect of EHNA on ICa in freshly isolated human atrial myocytes. Extracellular application of 0.1-10 microM EHNA induced an increase in the amplitude of basal ICa ( approximately 80% at 1 microM) without modification of the current-voltage or inactivation curves. The maximal stimulatory effect of EHNA on ICa was comparable in amplitude with the maximal effect of isoprenaline (1 microM), and the two effects were not additive. The effect of EHNA was not a result of adenosine deaminase inhibition, since 2'-deoxycoformycin (1-30 microM), another adenosine deaminase inhibitor with no effect on PDE2, or adenosine (1-10 microM) did not increase ICa. In the absence of intracellular GTP, the substrate of guanylyl cyclase, EHNA did not increase ICa. However, under similar conditions, intracellular perfusion with 0.5 microM cGMP produced an 80% increase in ICa. As opposed to human cardiomyocytes, EHNA (1-10 microM) did not modify ICa in isolated rat ventricular and atrial myocytes. We conclude that basal ICa is controlled by PDE2 activity in human atrial myocytes. Both PDE2 and PDE3 may contribute to keep the cyclic nucleotides concentrations at minimum in the absence of adenylyl and/or guanylyl cyclase stimulation.

Acadesine and lipopolysaccharide-evoked pulmonary dysfunction after resuscitation from traumatic shock

BACKGROUND

We have reported that the purine precursor acadesine (AICAR) improved the microcirculation, repleted adenosine triphosphate, and attenuated local and lung neutrophil infiltration after intestinal reperfusion and that it quickly improved systemic hemodynamics after resuscitation from hemorrhagic shock. This study evaluated the therapeutic potential of AICAR after fluid resuscitated trauma.

METHODS

Anesthetized (fentanyl) mongrel pigs were subjected to tissue injury plus hemorrhage and randomized to receive resuscitation fluids comprised of shed blood plus either lactated Ringer's solution (LR) or AICAR (1 or 10 mg/kg bolus + 0.5 mg/kg/min x 30 min). Thereafter either LR or AICAR (1 or 10 mg/kg) was administered at 12-hour intervals for 72 hours. In a smaller series (n = 7) a single bolus (0.5 mg/kg) of the adenosine deaminase inhibitor deoxycoformycin was administered at the time of resuscitation. After 72 hours, and endotoxin challenge (0.5 microgram/kg, lipopolysaccharide [LPS]) was administered.

RESULTS

At 1 mg/kg (n = 9), AICAR had no obvious effect versus LR (n = 31). At 10 mg/kg AICAR (n = 11), the fluid required to stabilize hemodynamics after trauma was higher (66 +/- 5 versus 52 +/- 3 ml/kg/hr, p = 0.014), but there were fewer deaths 3 days after trauma versus LR (0 of 11 versus 4 of 31, p = 0.210), fewer deaths within 5 hours after LPS administration (3 of 11 versus 16 of 27, p = 0.074), and a longer survival time after LPS administration (4.5 +/- 0.3 versus 3.9 +/- 0.2 hr, p = 0.054). Deoxycoformycin had similar salutary effects on survival after LPS administration. LPS increased protein permeability of pulmonary capillaries, increased peak inspiratory pressures on constant tidal volume, increased dead space ventilation, and caused progressive arterial desaturation on 0.65 FiO2 (all p < 0.05). This pulmonary dysfunction was associated with a compensatory increase in cardiac output, decrease in systemic vascular resistance, increase in O2 consumption, and rise in plasma cortisol level (all p < 0.05). All these changes were blunted or eliminated with 10 mg/kg AICAR. Hematocrit and systemic pressures were maintained relatively constant after LPS administration with fluid resuscitation, but less was required with AICAR versus LR (40 +/- 8 versus 83 +/- 14 ml/kg/hr, p = 0.023). AICAR caused a concentration-related reduction in CD18 expression on LPS-stimulated neutrophils in vitro, but there was no effect versus LR on circulating leukocyte counts in vivo and no effect of AICAR on LPS-stimulated production of tumor necrosis factor in vitro or in vivo.

CONCLUSIONS

1. AICAR reduced the pulmonary dysfunction associated with posttrauma endotoxemia but had no effect on circulating leukocytes, so its mechanism could be related to an adenosine-mediated improvement in peripheral perfusion or O2 use. 2. AICAR is a generic compound that is safe and apparently efficacious in human beings, so AICAR prophylaxis could be cost-effectively administered to trauma patients.