This chapter focuses on deglucuronidation by
beta-glucuronidase in
inflammation. We investigated whether
glucuronides were converted to free parent compounds by
beta-glucuronidase released from human-stimulated neutrophils in
inflammation.
Beta-glucuronidase activity was assayed using 4-methylumbelliferyl-glucuronide and
methanol extracts of rat plasma containing
luteolin monoglucuronide as a substrate. The released
4-methylumbelliferone, a fluorescent molecule, was quantitated on a microplate fluorometer. Deglucuronidation of
luteolin monoglucuronide was examined by high-performance liquid chromatography (HPLC) analysis. The
beta-glucuronidase activity in mouse plasma after iv injection of
lipopolysaccharide (LPS) increased with time, as did the levels of
inflammation marker, tumor necrosis factor-alpha, and soluble
intercellular adhesion molecule-1. Four kinds of human cell (neutrophils, human umbilical vein endothelial cells, IMR-90, and Caco-2) possess
beta-glucuronidase activity. Among these, Caco-2 cells showed the highest level of
beta-glucuronidase activity. Supernatants obtained from neutrophils stimulated with
cytochalasin B and
ionomycin showed higher levels of
beta-glucuronidase activity than those of nonstimulated neutrophils. HPLC analyses also showed that supernatants obtained from stimulated neutrophils hydrolyzed
luteolin monoglucuronide to free
luteolin. As reported previously (Shimoi et al., 1998), two main peaks (free
luteolin and
luteolin monoglucuronide) were observed in plasma of rats administered with
luteolin. In LPS-treated rats, the peak of
luteolin monoglucuronide decreased to about half and the ratio of
luteolin to
luteolin monoglucuronide increased. These results suggest that
beta-glucuronidase released from neutrophils or certain injured cells may hydrolyze
glucuronide conjugates to free aglycones at the site of
inflammation.