On-pump inhibition of es-ENT1 nucleoside transporter and adenosine deaminase during aortic crossclamping entraps intracellular adenosine and protects against reperfusion injury: role of adenosine A1 receptor

Multiple Drug Transporters Contribute to the Placental Transfer of Emtricitabine

Emtricitabine (FTC) is a first-line antiviral drug recommended for the treatment of AIDS during pregnancy. We hypothesized that transporters located in the placenta contribute to FTC transfer across the blood-placenta barrier. BeWo cells, cell models with stable or transient expression of transporter genes, primary human trophoblast cells (PHTCs), and small interfering RNAs (siRNAs) were applied to demonstrate which transporters were involved. FTC accumulation in BeWo cells was reduced markedly by inhibitors of equilibrative nucleoside transporters (ENTs), concentrative nucleoside transporters (CNTs), organic cation transporters (OCTs), and organic cation/carnitine transporter 1 (OCTN1) and increased by inhibitors of breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs). ENT1, CNT1, OCTN1, MRP1/2/3, and BCRP, but not ENT2, CNT3, OCTN2, or multidrug resistance protein 1 (MDR1), were found to transport FTC. FTC accumulation in PHTCs was decreased significantly by inhibitors of ENTs and OCTN1. These results suggest that ENT1, CNT1, and OCTN1 probably contribute to FTC uptake from maternal circulation to trophoblasts and that ENT1, CNT1, and MRP1 are likely involved in FTC transport between trophoblasts and fetal blood, whereas BCRP and MRP1/2/3 facilitate FTC transport from trophoblasts to maternal circulation. Coexistence of tenofovir or efavirenz with FTC in the cell medium did not influence FTC accumulation in BeWo cells or PHTCs.

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.

Dual effects of tumor necrosis factor alpha on myocardial injury following prolonged hypoperfusion of the heart

OBJECTIVE

To examine the dose response of TNFα in an ex vivo rat model of myocardial ischemia reperfusion.

METHODS AND RESULTS

Seventy-two rat hearts were mounted on Langendorff apparatus and perfused with oxygenated Krebs-Henseleit solutions. Ischemia was induced by reducing the perfusate flow rate. During reperfusion, incremental doses of recombinant TNFα were infused as a part of perfusate. TNFα was blocked with monoclonal TNFα antibody. Myocardial function was measured by dP/dT and relaxation time (IVRT). Cellular injury was assessed by released myoglobin and tissue concentration of malondialdehyde activity of the heart homogenates. Baseline +dP/dT was 1645 ± 125 mmHg/sec, -dP/dT was 945 ± 73 mmHg/sec and IVRT was 65 ± 5 msec. At the conclusion of reperfusion period, lower doses of TNFα increased +dP/dT and lowered IVRT. In contrast, the higher doses of TNFα decreased +dP/dT and prolonged IVRT. Pretreating the hearts with monoclonal TNFα antibody completely abolished the effects of TNFα on myocardial contractility and relaxation comparable to ischemia controls.

CONCLUSION

Low dose TNFα improved myocardial function and decreased resultant cellular injury while high dose TNFα decreased myocardial function and increased myocardial injury following ischemia and reperfusion.

Hot shot induction and reperfusion with a specific blocker of the es-ENT1 nucleoside transporter before and after hypothermic cardioplegia abolishes myocardial stunning in acutely ischemic hearts despite metabolic derangement: hot shot drug delivery before hypothermic cardioplegia

OBJECTIVE

Simultaneous inhibition of the cardiac equilibrative-p-nitrobenzylthioinosine (NBMPR)-sensitive (es) type of the equilibrative nucleoside transport 1 (ENT1) nucleoside transporter, with NBMPR, and adenosine deaminase, with erythro-9-[2-hydroxy-3-nonyl]adenine (EHNA), prevents release of myocardial purines and attenuates myocardial stunning and fibrillation in canine models of warm ischemia and reperfusion. It is not known whether prolonged administration of hypothermic cardioplegia influences purine release and EHNA/NBMPR-mediated cardioprotection in acutely ischemic hearts.

METHODS

Anesthetized dogs (n = 46), which underwent normothermic aortic crossclamping for 20 minutes on-pump, were divided to determine (1) purine release with induction of intermittent antegrade or continuous retrograde hypothermic cardioplegia and reperfusion, (2) the effects of postischemic treatment with 100 μM EHNA and 25 μM NBMPR on purine release and global functional recovery, and (3) whether a hot shot and reperfusion with EHNA/NBMPR inhibits purine release and attenuates ventricular dysfunction of ischemic hearts. Myocardial biopsies and coronary sinus effluents were obtained and analyzed using high-performance liquid chromatography.

RESULTS

Warm ischemia depleted myocardial adenosine triphosphate and elevated purines (ie, inosine > adenosine) as markers of ischemia. Induction of intermittent antegrade or continuous retrograde hypothermic (4°C) cardioplegia releases purines until the heart becomes cold (<20°C). During reperfusion, the levels of hypoxanthine and xanthine (free radical substrates) were >90% of purines in coronary sinus effluent. Reperfusion with EHNA/NBMPR abolished ventricular dysfunction in acutely ischemic hearts with and without a hot shot and hypothermic cardioplegic arrest.

CONCLUSIONS

Induction of hypothermic cardioplegia releases purines from ischemic hearts until they become cold, whereas reperfusion induces massive purine release and myocardial stunning. Inhibition of cardiac es-ENT1 nucleoside transporter abolishes postischemic reperfusion injury in warm and cold cardiac surgery.

Basolateral uptake of nucleosides by Sertoli cells is mediated primarily by equilibrative nucleoside transporter 1

The blood-testis barrier (BTB) prevents the entry of many xenobiotic compounds into seminiferous tubules thereby protecting developing germ cells. Understanding drug transport across the BTB may improve drug delivery into the testis. Members of one class of drug, nucleoside reverse transcriptase inhibitors (NRTIs), do penetrate the BTB, presumably through interaction with physiologic nucleoside transporters. By investigating the mechanism of nucleoside transport, it may be possible to design other drugs to bypass the BTB in a similar manner. We present a novel ex vivo technique to study transport at the BTB that employs isolated, intact seminiferous tubules. Using this system, we found that over 80% of total uptake by seminiferous tubules of the model nucleoside uridine could be inhibited by 100 nM nitrobenzylmercaptopurine riboside (NBMPR, 6-S-[(4-nitrophenyl)methyl]-6-thioinosine), a concentration that selectively inhibits equilibrative nucleoside transporter 1 (ENT1) activity. In primary cultured rat Sertoli cells, 100 nM NBMPR inhibited all transepithelial transport and basolateral uptake of uridine. Immunohistochemical staining showed ENT1 to be located on the basolateral membrane of human and rat Sertoli cells, whereas ENT2 was located on the apical membrane of Sertoli cells. Transepithelial transport of uridine by rat Sertoli cells was partially inhibited by the NRTIs zidovudine, didanosine, and tenofovir disoproxil fumarate, consistent with an interaction between these drugs and ENT transporters. These data indicate that ENT1 is the primary route for basolateral nucleoside uptake into Sertoli cells and a possible mechanism for nucleosides and nucleoside-based drugs to undergo transepithelial transport.

Myocardial protection in beating heart cardiac surgery: I: pre- or postconditioning with inhibition of es-ENT1 nucleoside transporter and adenosine deaminase attenuates post-MI reperfusion-mediated ventricular fibrillation and regional contractile dysfunction

OBJECTIVE

To determine the role of the p-nitrobenzylthioinosine-sensitive equilibrative nucleoside transporter 1 (es-ENT1) in postmyocardial infarction reperfusion injury-mediated ventricular fibrillation and regional dysfunction. We used erythro-9 (2-hydroxy-3-nonyl)-adenine and p-nitrobenzylthioinosine to inhibit both adenosine deamination and transport in a canine model of off pump acute myocardial infarction.

METHODS

Anesthetized adult dogs (n = 37), instrumented to monitor the percentage of systolic segmental shortening and wall thickening using sonomicrometry, underwent 90 minutes of left anterior descending coronary artery occlusion and 120 minutes of reperfusion. Myocardial coronary blood flow, adenosine triphosphate pool, infarct size, and the incident of ventricular fibrillation and cardioversion were also measured. The dogs received an intravenous infusion of the vehicle (control) or 100 μM of erythro-9 (2-hydroxy-3-nonyl)-adenine and 25 μM p-nitrobenzylthioinosine before ischemia (preconditioning group) or just before reperfusion (postconditioning group).

RESULTS

In the control group, adenosine triphosphate depletion was associated with the accumulation of more inosine than adenosine during ischemia and washed out during reperfusion. Myocardial adenosine and inosine were the major nucleosides in the pre- and postconditioning groups during ischemia and remained detectable during reperfusion. In both groups, recovery of systolic segmental shortening and wall thickening and a reduction in the incidence of ventricular fibrillation (P < .05 vs the control group) coincided with retention of myocardial nucleosides. The infarct size in the 3 groups was not significantly different, independent of myocardial blood flow during ischemia.

CONCLUSIONS

Preconditioning or postconditioning with erythro-9 (2-hydroxy-3-nonyl)-adenine/p-nitrobenzylthioinosine significantly reduced the incidence of ventricular fibrillation and cardioversion and attenuated regional contractile dysfunction mediated by postmyocardial infarction reperfusion injury. It is concluded that p-nitrobenzylthioinosine-sensitive equilibrative nucleoside transporter 1 played a major role in these events.