Extracellular 2′,3′-cAMP Is a Source of Adenosine

Abstract

We discovered that renal injury releases 2,3-cAMP (positional isomer of 3,5-cAMP) into the interstitium. This finding motivated a novel hypothesis: renal injury leads to activation of an extracellular 2,3-cAMP-adenosine pathway (i.e. metabolism of extracellular 2,3-cAMP to 3-AMP and 2-AMP, which are metabolized to adenosine, a retaliatory metabolite). In isolated rat kidneys, arterial infusions of 2,3-cAMP (30 mol/ liter) increased the mean venous secretion of 3-AMP (3,400-fold), 2-AMP (26,000-fold), adenosine (53-fold), and inosine (adenosine metabolite, 30-fold). Renal injury with metabolic inhibitors increased the mean secretion of 2,3-cAMP (29-fold), 3-AMP (16-fold), 2-AMP (10-fold), adenosine (4.2-fold), and inosine (6.1-fold) while slightly increasing 5-AMP (2.4-fold). Arterial infusions of 2-AMP and 3-AMP increased secretion of adenosine and inosine similar to that achieved by 5-AMP. Renal artery infusions of 2,3-cAMP in vivo increased urinary excretion of 2-AMP, 3-AMP and adenosine, and infusions of 2-AMP and 3-AMP increased urinary excretion of adenosine as efficiently as 5-AMP. The implications are that 1) in intact organs, 2-AMP and 3-AMP are converted to adenosine as efficiently as 5-AMP (previously considered the most important adenosine precursor) and 2) because 2,3-cAMP opens mitochondrial permeability transition pores, a pro-apoptotic/pronecrotic process, conversion of 2,3-cAMP to adenosine by the extracellular 2,3-cAMP-adenosine pathway would protect tissues by reducing a pro-death factor (2,3-cAMP) while increasing a retaliatory metabolite (adenosine).Our past work supports the existence of a biochemical mechanism of adenosine biosynthesis that involves 3Ј,5Ј-cAMP and that contributes to the extracellular levels of adenosine, i.e. the extracellular 3Ј,5Ј-cAMP-adenosine pathway (Fig. 1, left side) (1-20). In this regard, we propose that the extracellular 3Ј,5Ј-cAMP-adenosine pathway involves four sequential steps that are spatially linked and occur on a quasi-solid surface (i.e. the membrane surface). The four sequential steps are: 1) receptormediated intracellular production of 3Ј,5Ј-cAMP; 2) active transport of 3Ј,5Ј-cAMP from the intracellular compartment to the cell surface; 3) extracellular metabolism of 3Ј,5Ј-cAMP to 5Ј-AMP; and 4) extracellular conversion of 5Ј-AMP to adenosine. Independent laboratories now confirm the existence of the extracellular 3Ј,5Ј-cAMP-adenosine pathway in pial microvessels (21) and more recently in skeletal muscle (22) and the gastrointestinal tract (23). Moreover, Müller et al. (24) report the existence of a 3Ј,5Ј-cAMP-adenosine pathway in which the sequential conversion of 3Ј,5Ј-cAMP to 5Ј-AMP and 5Ј-AMP to adenosine occurs on the outward facing membrane surface of lipid droplets within adipocytes.To study in more detail the role of 3Ј,5Ј-cAMP-adenosine pathway in the kidney, we recently developed a novel assay to measure 3Ј,5Ј-cAMP and other purines in the renal venous effluent from isolated, perfused kidneys (25). Unlike commercially available kits for 3Ј,5...

Screening of Biochemical and Molecular Mechanisms of Secondary Injury and Repair in the Brain after Experimental Blast-Induced Traumatic Brain Injury in Rats

“…This is consistent with the fact that we previously reported on axonal injury, rather than neuronal death, and argues against a major role for ischemia in the initial 24 h. Although 5¢-AMP (produced from ATP/ADP metabolism) is considered the major precursor for adenosine, recent studies suggest that adenosine may also derive from the metabolism of 2¢,3¢-cAMP to 3¢-AMP or 2-AMP, with subsequent metabolism to adenosine. 25 Our current study reveals that brain tissue levels of adenosine are strongly associated with 2¢-AMP, but not 5¢-AMP, consistent with 2¢-AMP as a source of adenosine in the injured brain. It has been shown that 934 KOCHANEK ET AL.…”

“…Brain samples placed in 1-propanol were analyzed for 3¢,5¢-cAMP (cyclic adenosine monophosphate), 2¢,3¢-cAMP, 5¢-AMP, 3¢-AMP, 2¢-AMP, adenosine, and inosine using our standard liquid chromatography/tandem mass spectrometry (LC-MS/MS) purine assay with selected reaction monitoring (SRM). 25 Brain samples placed in perchloric acid were analyzed for ATP and adenosine diphosphate (ADP), also using LC-MS/MS, but with modifications of our standard purine assay. For ATP and ADP, the high-performance liquid chromatography reversed-phase column was a Bonus-RP (1 · 50 mm; 3.5 lm; Agilent Technology, Lexington, MA), and the mobile phase consisted of two eluents.…”

The Guanosine-Adenosine Interaction Exists In Vivo

“…Renal vascular resistance (RVR) and mesenteric vascular resistance (MVR) were calculated by dividing the MABP by the RBF or MBF, respectively. In nine control rats and 12 guanosine-treated rats, urine collected before the infusions of adenosine was analyzed for guanosine, adenosine, and inosine using high-performance liquid chromatography-tandem mass spectrometry as previously described (Jackson et al, 2009). It was not possible to compare the urine levels of these purines in the presence of adenosine because urine volumes were severely reduced in those rats receiving guanosine plus adenosine.…”

Modulation of bladder function by luminal adenosine turnover and A1receptor activation

“…Adenosine, AMP, and inosine concentrations in the samples were determined using a triple quadrupole mass spectrometer (TSQ QuantumUltra, ThermoFisher Scientific, San Jose, CA) as previously described (26).…”