Cytokines, including tumor necrosis factor‐α (TNFα) and interleukin‐6 (IL‐6), have been implicated in the pathogenesis of multiple sclerosis (MS). The production and release of these cytokines are regulated in part by specific purinergic (adenosine) cell surface receptors. To determine the extent to which the adenosine A1 receptor influenced cytokine expression in peripheral blood mononuclear cells (PBMCs) from MS and control patients, we measured plasma adenosine and TNFα levels, A1 receptor messenger RNA (mRNA) and protein amounts, and the effects of activation of A1 receptors on TNFα and IL‐6 production by PBMCs. Plasma levels of TNFα were significantly higher and adenosine levels were significantly lower in MS patients compared with control subjects. Levels of TNFα and IL‐6 in mitogen‐stimulated PBMC culture supernatants from MS patients or control patients were similar. Conversely, treatment of PBMCs with the adenosine A1 receptor agonist R‐phenylisopropyladenosine (R‐PIA) (1 μM) significantly inhibited mitogen‐stimulated production of TNFα but not IL‐6 in control subjects and significantly inhibited production of IL‐6 but not TNFα in MS patients. The effects of R‐PIA were selectively blocked by the A1 receptor antagonist 8‐cyclopentyl‐1,3‐dipropylxanthine (DPCPX). A1 receptor protein levels were decreased significantly in PBMCs from MS patients. Taken together, these results suggest that decreased levels of adenosine and its A1 receptor modulate TNFα and IL‐6 levels and may contribute to the pathogenesis of MS. Ann Neurol 1999;45:633–639
Adenosine levels increase in brain during cerebral ischemia, and adenosine has receptor-mediated neuroprotective effects. This study was performed to test the hypothesis that nitrobenzylthioinosine (NBMPR), a selective and potent inhibitor of one adenosine transporter subtype termed ENT1, or es, can protect against ischemic neuronal injury by enhancing adenosine levels and potentiating adenosine receptor-mediated effects, including attenuation of the cellular production and release of tumor necrosis factor-␣ (TNF-␣). In rats, the phosphorylated prodrug form of NBMPR, NBMPR-phosphate, or saline was administered by intracerebroventricular injection 30 min before forebrain ischemia. Seven days following the ischemic episode, rats were killed, and neuronal damage in the CA1 region of the hippocampus was assessed. The number of pyramidal neurons was significantly ( p Ͻ 0.001) greater in the NBMPR-P treatment group. A trend toward protection was still evident at 28 days postreperfusion. Adenosine increased significantly during ischemia to levels eight-to 85-fold above basal. NBMPR-P treatment did not cause statistically significant increases in ischemic adenosine levels; however, this treatment tended to increase adenosine levels in all brain regions at 7 min postreperfusion. Ischemiainduced expression of TNF-␣ was not altered by NBMPR-P treatment, and the nonselective adenosine receptor antagonist 8-( p-sulfophenyl)theophylline did not abolish the neuroprotective effects of NBMPR-P treatment. These data indicate that NBMPR can protect CA1 pyramidal neurons from ischemic death without statistically significant effects on adenosine levels or adenosine receptor-mediated inhibition of the proinflammatory cytokine TNF-␣. Key Words: Cerebral ischemia-Nucleoside transport-Nitrobenzylthioinosine -Tumor necrosis factor-␣-Adenosine.
SummaryNitrobenzylthioinosine (NBMPR) can potentiate the actions of adenosine through inhibition of adenosine influx mediated by the equilibrative nucleoside transporter subtype 1 (ENTl). As adenosine can decrease ischemic neuronal injury, we tested the hypothesis that peripheral administration of the pro-drug NBMPR-phosphate (NBMPR-P) can increase brain adenosine levels and reduce ischemia-induced loss of hippocampal CA1 neurons. Pre-ischemic, but not post-ischemic, peripheral administration of NBMPR-P significantly (P = 0.03) increased neuronal survival. Mechanistically, NBMPR-induced neuroprotection was associated with significant (P = 0.03) increases in adenosine levels relative to saline-treated controls. Hypothermia was tested for but did not account for the beneficial effects of NBMPR. Together, these data suggest that selective inhibition of ENTl adenosine transporters can increase post-ischemic levels of adenosine and reduce ischemic neuronal death.
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