P-Aminobenzoic Acid As an Alternative Chemical Biopsy Agent for Human Hepatic UDP-glucose

p-Aminobenzoic acid (PABA) was evaluated for noninvasive sampling of UDP-glucose in the liver. Six healthy subjects ingested 550 mg PABA during a breakfast meal. Urine was collected 0-2 and 2-4 h after PABA ingestion. N-acetyl PABA glucuronide (NAPG) was identified with 522 ± 212 μmol recovered in the 2-4 h urines. One of the subjects ingested 2 g of 98% [U-H]glucose alongside PABA and the NAPG was analyzed for positional H-enrichment by H NMR following derivatization to 5-O-acetyl monoacetone glucuronolactone. In conclusion, PABA is an effective agent for the chemical biopsy of hepatic UDP-glucose in humans.