Measurement of the Endogenous Adenosine Concentration in Humans In Vivo: Methodological Considerations

Abstract

The endogenous nucleoside adenosine has profound tissue protective effects in situations of ischaemia or inflammation. Animal studies have shown that various drugs can activate this protective mechanism by interfering with the metabolism of adenosine. Translation of this concept to the clinical arena is hampered by the difficulties encountered in measuring the adenosine concentration, due to the rapid cellular uptake and degradation of adenosine, which continues unabated after blood sampling, and due to the metabolically active endothelial barrier for adenosine. In the current paper, we critically discuss the various methods to measure the adenosine concentration in humans in vivo. For the measurement of circulating adenosine, we conclude that the use of a pharmacological blocker solution (containing inhibitors of the enzymes ecto-5'-nucleotidase, adenosine deaminase, and adenosine kinase, and of the equilibrative nucleoside transporter) and a purpose-built syringe which mixes the blood with this solution immediately at the tip of the needle, seems to be the most sensitive technique. However, for the measurement of adenosine concentrations in interstitial tissue, microdialysis is a suitable method, when used with an appropriate method to determine the recovery of adenosine across the semipermeable membrane to calculate the absolute adenosine concentration. Consistent use of these methods could help in the comparison of the various studies focussed on endogenous adenosine and could help to facilitate the use of drugs that modulate the adenosine concentration to protect tissues in the clinical arena.

A physiological model for interpretation of arterial spin labeling reactive hyperemia of calf muscles

“…Increased formation of adenosine during hypoxia results from the elevated activity of ecto 5’-nucleotidase converting muscle-released AMP into adenosine [28]. However, it is difficult to quantify the exact reaction rate and concentrations of AMP and adenosine because a wide range of values was reported, potentially because real-time interstitial measurements in vivo remain challenging [29]. Hence, we only roughly estimated the adenosine formation rate and described it as a simple 2-mode function in Eq (18).…”

Loss of equilibrative nucleoside transporter 1 in mice leads to progressive ectopic mineralization of spinal tissues resembling diffuse idiopathic skeletal hyperostosis in humans

“…Blood was collected by cardiac puncture into a syringe containing NaCl (118 mM), KCl (5 mM), EDTA (13.2 mM), 5-iodotubercidin (10 mM) to inhibit adenosine kinase, erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride (EHNA, 100 mM) to inhibit adenosine deaminase, and dilazep (10 mM) to inhibit adenosine transport. (39) Plasma was isolated by sedimentation at 3,000g for 10 minutes at 48C. Plasma was applied to a 10-kDa cutoff ultrafiltration column and sedimented at 14,000g for 15 minutes at 48C.…”

A metabolomic, geographic, and seasonal analysis of the contribution of pollen-derived adenosine to allergic sensitization

“…(Parent 1992; Brofeldt et al 1987) Therefore, the volume of dilution assumed for the various models are 1 l, 0.083 l, and 0.042 l for DD, P2, and EX respectively. At the peak of tree season the DD model calculates 4.0 nM adenosine, which is sub-physiological, (Ramakers et al 2008; Zhang et al 2011) but the validity of this model is questionable. The P2 and EX models show much higher concentrations due the higher pollen count due to much lower volumes of nasal fluid per unit time.…”

“…For comparison, the levels of adenosine in human plasma are typically measured at less than 200 nM, but can be in excess of 500 nM in people with sickle cell disease. (Ramakers et al 2008; Zhang et al 2011) Airway surface liquid is normally 150–200 nM adenosine (Zuo et al 2008) although recent evidence suggests that at the cell surface, where many of the regulatory enzymes and receptors are positioned, the concentration may be 5 to 10 times higher (Amarante et al 2014). …”