Plasma level of nociceptin, the endogenous agonist of orphanin FQ/ORL1 receptor was found to be significantly elevated in Wilson disease patients (13.98±2.44pg/ml, p<0.001, n=20) compared to age-matched healthy controls (9.18±1.63pg/ml, n=25). Wilson disease is an autosomal recessive disorder of copper metabolism caused by mutation of the gene ATP7B leading to toxic copper accumulation in the liver and other organs such as brain, kidney and cornea. Measurements were performed by 125I-radioimmunoassay. Neither sex differences nor correlation between plasma nociceptin levels and liver function test results were found. It is suggested that elevated plasma nociceptin level found in Wilson disease patients is due to inhibition of nociceptin-inactivating Zn-metallopeptidases (aminopeptidase N (APN) and endopeptidase 24.15) by the toxic copper deposits in liver and/or brain.
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