A Novel Inhibitor of β-Glucuronidase: l-Aspartic Acid

Abstract

Infants who consume casein hydrolysate formula have been shown to have lower neonatal jaundice levels than infants who consume routine formula or breast milk. Because casein hydrolysate has been shown to contain a ␤-glucuronidase inhibitor, one possible mechanism to explain this finding is blockage of the enterohepatic circulation of bilirubin by a component of the formula. The aim of this research was to identify the source of the ␤-glucuronidase inhibition in hydrolyzed casein. A ␤-glucuronidase inhibition assay and measurements of physical and kinetic parameters were used to analyze the components of hydrolyzed casein and infant formulas. Kinetic studies used purified ␤-glucuronidase. The L-aspartic acid in hydrolyzed casein accounts for the majority of the ␤-glucuronidase inhibition present. Kinetic studies indicate a competitive inhibition mechanism. L-Aspartic acid is a newly identified competitive inhibitor of ␤-glucuronidase. NaAC, sodium acetate/acetic acid buffer, pH 4.5 SAB, sodium acetate/acetic acid buffer, pH 5.0 AMP, 100 mM 2-amino-2-methyl-1-propanol buffer containing 0.2% (wt/vol) sodium lauryl sulfate at pH 11.0 NRTU, Nutramigen ready-to-use formula EHC, enzymatically hydrolyzed casein NLFS, Nutramigen lipid-free supernatant PLFS, Phenyl-Free, lipid-free supernatant In 1992, the new finding that all neonatal formulas are not equal in their effect on neonatal jaundice was first reported. Infants who consumed a casein hydrolysate formula had lower levels of jaundice than infants who received routine (whey or casein predominant) infant formulas (1). This finding was subsequently confirmed in an independent study (2). A potential mechanism has been proposed and a causative factor has been identified that might explain this phenomenon. The enterohepatic circulation of bilirubin could be interrupted by a ␤-glu inhibitor present in enzymatically hydrolyzed casein (3). Bilirubin, arising mainly from the degradation of heme, undergoes hepatic conjugation with glucuronic acid and excretion as bilirubin glucuronides via bile into the intestine. Intestinal ␤-glu can cleave the glucuronide linkage to produce unconjugated bilirubin, which can be absorbed by the intestine back into the blood circulation (4). Inhibition of ␤-glu can block this enterohepatic circulation of bilirubin, thus facilitating fecal excretion and lower serum bilirubin concentration (5). Inhibitors of ␤-glu have also been suggested to have anticarcinogenic properties because they will increase clearance of glucuronidated carcinogens (6).Because neonatal jaundice is the most common cause for hospital readmission of neonates (7), any potential new therapeutic considerations are of interest. Identification of any ␤-glu inhibitor that is currently acknowledged to be a safe dietary element would be of considerable appeal. In this paper, data are presented which demonstrate that L-aspartic acid (L-asp) is one component of hydrolyzed casein infant formula that is inhibitory to ␤-glu. L-asp has not previously been identified as a ␤-glu inhibitor...

Therapeutic significance of β-glucuronidase activity and its inhibitors: A review

“…L-aspartic acid (10, Fig. 3) in casein hydrolysate formulas was identified as the active bGLU inhibitor responsible for the lower levels of neonatal jaundice observed in newborns receiving such formulae [127]. At 100 mM, the natural amino acid showed~86% inhibition of bGLU that is, 100-fold more potent than D-isomer.…”

Inhibitory Effect of Heat-Treated 3-(3^|^prime;,4^|^prime;-dihydroxyphenyl)-L-alanine (DOPA) on ^|^beta;-glucuronidase Activity

“…Infants who consume casein hydrolysate formula have been shown to have a lower level of neonatal jaundice than infants who consume routine formula or breast milk. l-Aspartic acid, one component of hydrolyzed casein, was identified as a β-glucuronidase inhibitor (Kreamer et al, 2001).…”

Carbazole‐Linked 1,2,3‐Triazoles: In Vitro β‐Glucuronidase Inhibitory Potential, Kinetics, and Molecular Docking Studies

“…Moreover, along with its role in tumour development, upregulation of the enzyme is also observed in different types of other physiological disorders for instance tuberculosis, leprosy, arthritis, renal infections and urinary tract ailments . Owing to its direct involvement in the propagation of cancers and physiological disorders, development of β‐glucuronidase inhibitors may serve to treat such ailments and related diseases …”