A Study on the Mechanism of Spin Clearance in In vivo ESR Measurement

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[ィイD114ィエD1C] carbamoyl-PROXYL and [ィイD114ィエD1C] methoxycarbonyl-PROXYL ([ィイD114ィエD1C] MC-PROXYL) were synthesized using liquid ammonia and [ィイD114ィエD1C] acetone as starting materials. The autoradiography of rats using these probes clearly demonstrated that [ィイD114ィエD1C] MC-PROXYL quickly distributed to brain through blood-brain-barrier whereas [ィイD114ィエD1C]carbamoyl-PROXYL did not. [ィイD114ィエD1C]MC-PROXYL distributed more to liver. Three-dimensional ESR images of the brain of rats taken with MC-PROXYL and carbamoyl-PROXYL suggested that MC-PROXYL is useful to make an image of rat brain. Radio protective effect of these spin probes was measured. MC-PROXYL injected to C3H mice (10 weeks old, male) at a dose of 600 mg/kg prolonged the survival of mice or even rescued (20% of total) the mice irradiated with γ-ray at 8.7 Gy. This finding suggests that MC-PROXYL may interact with free radicals generated by X-irradiation and lose the stable spin of the MC-PROXYL, which may be one of the mechanisms of spin clearance observed in in vivo ESR measurements.