Drug Conjugation in Gunn Rats: Reduced UDP-Glucuronosyl Transferase and UDP-Glucosyl Transferase Activities with Increased Glycine-N-Acyltransferase Activity

Marniemi, Jukka; Vainio, H; Parkki, Max G.

doi:10.1159/000136943

“…4MU has been studied extensively as a model substrate for both metabolism and transport studies (11-13, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][46][47][48]. Some investigators have failed to detect 4MUS as a metabolite of 4MU and assumed that 4MUG was the only metabolite.…”

Section: Discussionmentioning

confidence: 99%

“…Besides glucuronidation, 4MU is also known to form a sulfate conjugate (4MUS) in most animal species (19)(20)(21)(22)(23). The substrate has been used extensively as a model substrate for the examination of UDP-glucuronosyltransferase activities in both the liver (24)(25)(26) and the intestine (27,28). The conjugates are found to undergo rapid hydrolysis to yield the aglycone (11-13, 29).…”

mentioning

confidence: 99%

“…The conjugates are found to undergo rapid hydrolysis to yield the aglycone (11-13, 29). Because of these properties, 4MU, 4MUS and 4MUG have served as substrates for UDP-glucuronosyltransferase (24)(25)(26), sulfatase (30-38) and p-glucuronidase activities (11). Works of Kauffman and colleagues (1 1-13) have suggested rapid desulfation of 4MUS to 4MU in the rat liver, the activities of which were found to be evenly distributed in rat and human liver microdissected tissue; sulfation and glucuronidation activities were found to be only slightly more concentrated in the periportal and perihepatic venous regions, respectively.…”

mentioning

confidence: 99%

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Futile cycling between 4-methylumbelliferone and its conjugates in perfused rat liver

Ratna¹

1993

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Futile cycling between 4-methylumbelliferone and its sulfate and glucuronide conjugates was examined in the single-pass perfused rat liver preparation. The steady-state hepatic extraction ratio of 4-methylumbelliferone was found to be high (0.97) at a low input concentration of 0.005 mumol/L (tracer), with a net 4-methylumbelliferyl sulfate/4-methylumbelliferyl glucuronide ratio of about 5:1; at 63 mumol/L the steady-state extraction ratio had remained constant despite a shift from net sulfation to net glucuronidation. At higher input 4-methylumbelliferone concentrations, saturation was evidenced by a decreased steady-state extraction ratio and reduced net sulfation and net glucuronidation. Because 4-methylumbelliferyl sulfate and 4-methylumbelliferyl glucuronide deconjugation would result in an intracellular accumulation of 4-methylumbelliferone, the phenomenon was monitored with a shift in tracer [3H]4-methylumbelliferone metabolism from sulfation to glucuronidation with increased intracellular 4-methylumbelliferone concentration. When 4-methylumbelliferyl sulfate (0 to 890 mumol/L) or 4-methylumbelliferyl glucuronide (0 to 460 mumol/L) was delivered simultaneously with tracer [3H]4-methylumbelliferone to the rat liver, notable desulfation of 4-methylumbelliferyl sulfate (18% to 38% rate in) but little deglucuronidation of 4-methylumbelliferyl glucuronide (1.2% to 2.1% rate in) was observed. With 4-methylumbelliferyl sulfate, 4-methylumbelliferone and 4-methylumbelliferyl glucuronide were readily found as metabolites, whereas with 4-methylumbelliferyl glucuronide, levels of the metabolites, 4-methylumbelliferone and 4-methylumbelliferyl sulfate, were much reduced. 4-Methylumbelliferyl sulfate and not 4-methylumbelliferyl glucuronide shifted tracer [3H]4-methylumbelliferone metabolism from [3H]4-methylumbelliferyl sulfate to [3H]4-methylumbelliferyl glucuronide formation in a concentration-dependent fashion. The steady-state extraction ratio for 4-methylumbelliferyl sulfate (0.1 to 0.3) was comparatively higher than that for 4-methylumbelliferyl glucuronide (0.05), and it was found to increase with concentration, an observation explained by the nonlinear protein binding of 4-methylumbelliferyl sulfate. Biliary excretion rates for 4-methylumbelliferone and 4-methylumbelliferyl sulfate were proportional to their input or net formation rates, regardless of whether 4-methylumbelliferone, 4-methylumbelliferyl glucuronide or 4-methylumbelliferyl sulfate was administered. By contrast, the excretion rate of 4-methylumbelliferyl glucuronide when administered was only 1/25 the excretion of 4-methylumbelliferyl glucuronide formed from 4-methylumbelliferone and 4-methylumbelliferyl sulfate. The extent of choleresis paralleled the excretion patterns of preformed and formed 4-methylumbelliferyl glucuronide; bile flow was normal with 4-methylumbelliferyl glucuronide administration and was markedly enhanced with increased 4-methylumbelliferone or 4-methylumbelliferyl sulfate administration. The data suggest the presence of a tr...

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“…Besides glucuronidation, 4MU is also known to form a sulfate conjugate (4MUS) in most animal species (19)(20)(21)(22)(23). The substrate has been used extensively as a model substrate for the examination of UDP-glucuronosyltransferase activities in both the liver (24)(25)(26) and the intestine (27,28). The conjugates are found to undergo rapid hydrolysis to yield the aglycone (11-13, 29).…”

mentioning

confidence: 99%

“…The conjugates are found to undergo rapid hydrolysis to yield the aglycone (11-13, 29). Because of these properties, 4MU, 4MUS and 4MUG have served as substrates for UDP-glucuronosyltransferase (24)(25)(26), sulfatase (30-38) and p-glucuronidase activities (11). Works of Kauffman and colleagues (1 1-13) have suggested rapid desulfation of 4MUS to 4MU in the rat liver, the activities of which were found to be evenly distributed in rat and human liver microdissected tissue; sulfation and glucuronidation activities were found to be only slightly more concentrated in the periportal and perihepatic venous regions, respectively.…”

mentioning

confidence: 99%

Futile cycling between 4-methylumbelliferone and its conjugates in perfused rat liver

Ratna

¹

,

Chiba

²

,

Bandyopadhyay

³

et al. 1993

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Futile cycling between 4-methylumbelliferone and its sulfate and glucuronide conjugates was examined in the single-pass perfused rat liver preparation. The steady-state hepatic extraction ratio of 4-methylumbelliferone was found to be high (0.97) at a low input concentration of 0.005 mumol/L (tracer), with a net 4-methylumbelliferyl sulfate/4-methylumbelliferyl glucuronide ratio of about 5:1; at 63 mumol/L the steady-state extraction ratio had remained constant despite a shift from net sulfation to net glucuronidation. At higher input 4-methylumbelliferone concentrations, saturation was evidenced by a decreased steady-state extraction ratio and reduced net sulfation and net glucuronidation. Because 4-methylumbelliferyl sulfate and 4-methylumbelliferyl glucuronide deconjugation would result in an intracellular accumulation of 4-methylumbelliferone, the phenomenon was monitored with a shift in tracer [3H]4-methylumbelliferone metabolism from sulfation to glucuronidation with increased intracellular 4-methylumbelliferone concentration. When 4-methylumbelliferyl sulfate (0 to 890 mumol/L) or 4-methylumbelliferyl glucuronide (0 to 460 mumol/L) was delivered simultaneously with tracer [3H]4-methylumbelliferone to the rat liver, notable desulfation of 4-methylumbelliferyl sulfate (18% to 38% rate in) but little deglucuronidation of 4-methylumbelliferyl glucuronide (1.2% to 2.1% rate in) was observed. With 4-methylumbelliferyl sulfate, 4-methylumbelliferone and 4-methylumbelliferyl glucuronide were readily found as metabolites, whereas with 4-methylumbelliferyl glucuronide, levels of the metabolites, 4-methylumbelliferone and 4-methylumbelliferyl sulfate, were much reduced. 4-Methylumbelliferyl sulfate and not 4-methylumbelliferyl glucuronide shifted tracer [3H]4-methylumbelliferone metabolism from [3H]4-methylumbelliferyl sulfate to [3H]4-methylumbelliferyl glucuronide formation in a concentration-dependent fashion. The steady-state extraction ratio for 4-methylumbelliferyl sulfate (0.1 to 0.3) was comparatively higher than that for 4-methylumbelliferyl glucuronide (0.05), and it was found to increase with concentration, an observation explained by the nonlinear protein binding of 4-methylumbelliferyl sulfate. Biliary excretion rates for 4-methylumbelliferone and 4-methylumbelliferyl sulfate were proportional to their input or net formation rates, regardless of whether 4-methylumbelliferone, 4-methylumbelliferyl glucuronide or 4-methylumbelliferyl sulfate was administered. By contrast, the excretion rate of 4-methylumbelliferyl glucuronide when administered was only 1/25 the excretion of 4-methylumbelliferyl glucuronide formed from 4-methylumbelliferone and 4-methylumbelliferyl sulfate. The extent of choleresis paralleled the excretion patterns of preformed and formed 4-methylumbelliferyl glucuronide; bile flow was normal with 4-methylumbelliferyl glucuronide administration and was markedly enhanced with increased 4-methylumbelliferone or 4-methylumbelliferyl sulfate administration. The data suggest the presence of a tr...

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