Continuous intravenous infusion of ATP in humans yields large expansions of erythrocyte ATP pools but extracellular ATP pools are elevated only at the start followed by rapid declines

Abstract

The pharmacokinetics of adenosine 5′-triphosphate (ATP) was investigated in a clinical trial that included 15 patients with advanced malignancies (solid tumors). ATP was administered by continuous intravenous infusions of 8 h once weekly for 8 weeks. Three values of blood ATP levels were determined. These were total blood (erythrocyte) and blood plasma (extracellular) ATP pools along with the initial rate of release of ATP into the blood plasma. We found that values related to erythrocyte ATP pools showed great variability (diversity) among individuals (standard deviation of about 30-40 % of mean at baseline). It was discovered that erythrocyte baseline ATP pool sizes are unique to each individual and that they fall within a narrow range in each individual. At the end of an 8 h continuous intravenous infusion of ATP, intracellular erythrocyte ATP pools were increased in the range of 40-60 % and extracellular ATP declined from elevated levels achieved at the beginning and middle of the infusion, to baseline levels. The ability of erythrocytes to sequester exogenously administered ATP to this degree, after its initial conversion to adenosine in the blood plasma is unexpected, considering that some of the adenosine is likely to have been degraded by in vivo catabolic activities or taken up by organs. The data suggest that administration of ATP by short-term intravenous infusions, of up to 4 h, may be a favorable way for elevating extracellular ATP pools. A large fraction of the total exogenously administered ATP is sequestered into the intracellular compartments of the erythrocytes after an 8 h intravenous infusion. Erythrocytes loaded with ATP are known to release their ATP pools by the application of previously established agents or conditions applied locally or globally to circulating erythrocytes. Rapid degradation of intravenously administered ATP to adenosine and subsequent accumulation of ATP inside erythrocytes indicate the existence of very effective mechanisms for uptake of adenosine from blood plasma. These in vivo studies offer an understanding as to how both adenosine and ATP can act as purinergic transmission signals. ATP levels in blood are always accompanied by adenosine formed by catabolism of ATP. The continuous uptake of adenosine enables both to act in transmission of sometimes opposite functions.

The ATP Receptors P2X7 and P2X4 Modulate High Glucose and Palmitate-Induced Inflammatory Responses in Endothelial Cells

“…Exposure of HUVECs to high glucose and palmitate increased transcript levels ( Fig 1A ; 24 h) of P2X7 (3.3±0.4-fold; p = 0.002) and P2X4 (3.6±0.2-fold; p = 0.002) as well as their protein levels ( Fig 1B ; 48 h), which were increased by 1.46±0.1-fold ( p = 0.008) and 1.49±0.08-fold ( p = 0.0006), respectively. The protein bands for P2X4 [ 29 ] and P2X7 (~75 kDa; data not shown) were validated with pre-adsorption of the antibodies with the respective control antigens. We next tested if high glucose and palmitate could affect levels of eATP in the HUVECs and indeed, we observed a significant increase in the relative luminescence, which is proportional to the amount of ATP.…”

“…HUVECs were seeded to achieve a confluence of 70–80% on the day of transfection. Transient transfection with P2X4 and P2X7-specific siRNA was performed as previously described [ 29 ]. In brief, siRNA at a final concentration of 10 nM/L was incubated with Lipofectamine RNAiMAX reagent in OPTI-MEM to form complexes.…”

Validation of a LC/MSMS method for simultaneous quantification of 9 nucleotides in biological matrices

“…ATP can also be sequestered in erythrocytes which could explain the increasing of ATP concentration in red blood cells after venous stasis. Upon signals (chemical, mechanical, or physiological), ATP can be released but several stimuli are needed to induce deformability of erythrocytes inducing the release of ATP and that may explain why the results did not show an increase in the plasmatic concentration of ATP [27,28]. As ATP is quickly degraded in ADP by ATPase, this could also explain the increasing in ADP concentration in erythrocytes after the stasis.…”

<p>ATP-loaded biomimetic nanoparticles as controlled release system for extracellular drugs in cancer applications</p>

“…[10][11][12] Recently, Rapaport et al reported that the administration of ATP by continuous infusion for 8 hours did not increase the extracellular ATP concentration, a finding that could be due to the fact that ATP is rapidly metabolized by multiple ecto-ATPases, since erythrocytes can sequester large amounts of the nucleotide for a later release. 13 This type of administration represents a disadvantage for the application of ATP in patients with cancer because it is not possible to raise the concentration of extracellular ATP required to generate the anticarcinogenic effect. Therefore, administering ATP as coated nanoparticles could be a reasonable alternative to prevent its rapid metabolism.…”