The conjugative metabolism of 4-methylumbelliferone and deconjugation to the parent drug examined by isolated perfused liver and in vitro liver homogenate of rats.

Miyauchi, Seiji; Sugiyama, Yuichi; Iga, Tatsuji; Hanano, Manabu

doi:10.1248/cpb.37.475

Cited by 14 publications

(20 citation statements)

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“…Although the production of SN-38 from SN-38G was highest for the liver, ␤-glucuronidase is normally located in the microsomal and lysosomal fractions, representing sites that are relatively inaccessible to polar conjugates in intact hepatocytes (Miyauchi et al, 1989). Homogenization of tissue results in the mechanical lysis of cells and release of these enzymes.…”

Section: Discussionmentioning

confidence: 99%

The Importance of Tumor Glucuronidase in the Activation of Irinotecan in a Mouse Xenograft Model

Dodds

Tobin²,

Stewart³

et al. 2002

J Pharmacol Exp Ther

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The anticancer drug irinotecan (CPT-11) is activated to the potent topoisomerase I inhibitor, , by esterases. SN-38 is in turn conjugated to the inactive SN-38 glucuronide (SN-38G). The reverse reaction is mediated by ␤-glucuronidases. Hence, production of SN-38 may occur through either pathway. In this study we conducted in vitro studies to examine these two reactions in neuroblastoma xenograft tumors (NB1691) and compared the rates of SN-38 production with those observed in the liver and plasma of the host SCID (severe-combined immunodeficient) mice. The rate of formation of SN-38 from CPT-11 by esterases slowed considerably during a 60-min incubation, consistent with the known deacylation-limited nature of this reaction. For xenograft tumor tissue, K m and V max values of 1.6 M and 4.4 pmol/ min/mg of protein, respectively, were observed. By comparison, these parameters were estimated to be 6.9 M and 9.4 pmol/min/mg for mouse liver and 2.1 M and 40.0 pmol/ min/mg for mouse plasma, respectively. The formation of SN-38 from SN-38G was very pronounced in both liver and xenograft tumor tissue, in which it was nonsaturable (0.125-50 M) and time-independent (0 -60 min). The derived values of V max /K m were 0.65 l/min/mg for the tumor and 2.12 l/min/mg for the liver preparations. Microdialysate experiments revealed the concentrations of SN-38G and CPT-11 in tumor to be comparable. At equal substrate concentrations, production of SN-38 from SN-38G in tumor extracts was comparable with that from CPT-11. Therefore, reactivation of SN-38 in the tumor by ␤-glucuronidases may represent an important route of tumor drug activation for CPT-11.

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Section: Discussionmentioning

confidence: 99%

The Importance of Tumor Glucuronidase in the Activation of Irinotecan in a Mouse Xenograft Model

Dodds

Tobin²,

Stewart³

et al. 2002

J Pharmacol Exp Ther

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“…3 The 4MU so formed serves as a substrate for either resulfation or glucuronidation. 4,7,8 Sulfation, being the high-affinity, low-capacity pathway, predominates at lower 4MU concentrations. 8 The futile cycle has been shown to alter the net disappearance of 4MU, 4MUS, and 4-methylumbelliferyl glucuronide (4MUG) in rat liver perfusion studies when either 4MU or 4MUS was given.…”

mentioning

confidence: 99%

“…With 4MUS given to the perfused rat liver, sulfation of 4MU, the formed metabolite, was attenuated in the presence of 2,6-dichloro-4-nitrophenol (DCNP), a sulfation inhibitor, and when sulfate ion was substituted by chloride ion. 4MU sulfation, being a highaffinity system, was reduced most effectively at the lowest 4MUS concentration (15 mol/L) used, evidenced by the increased (24%) net hepatic extraction ratio of 4MUS and reduced utilization (72%) of infused tracer 35 Some sulfate conjugates, e.g., p-nitrocatechol sulfate, estrone sulfate 1,2 , and 4-methylumbelliferyl sulfate (4MUS), [3][4][5][6][7][8] are known to undergo desulfation and participate in futile cycling with their parent compounds. 4MUS is a typical example because it undergoes extensive desulfation to form 4-methylumbelliferone (4MU), mostly by arylsulfatase C, although arylsulfatase A and B are also found to mediate desulfation of 4MUS in vitro.…”

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confidence: 99%

Carrier-mediated entry of 4-methylumbelliferyl sulfate: Characterization by the multiple-indicator dilution technique in perfused rat liver

Chiba¹,

Schwab²,

Goresky³

et al. 1998

Hepatology

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The hepatocellular entry of 4-methylumbelliferyl sulfate (4MUS) a highly ionized and highly bound anion capable of futile cycling, was examined in the single-pass albumin-free perfused rat liver preparation. Desulfation of 4MUS to 4-methylumbelliferone (4MU) was verified in vitro to be a low-affinity, high-capacity process (Km = 731 micromol/L; Vmax = 414 nmol min(-1) g(-1) liver). With 4MUS given to the perfused rat liver, sulfation of 4MU, the formed metabolite, was attenuated in the presence of 2,6-dichloro-4-nitrophenol (DCNP), a sulfation inhibitor, and when sulfate ion was substituted by chloride ion. 4MU sulfation, being a high-affinity system, was reduced most effectively at the lowest 4MUS concentration (15 micromol/L) used, evidenced by the increased (24%) net hepatic extraction ratio of 4MUS and reduced utilization (72%) of infused tracer 35SO4(2-) by 4MU for 4MU35S formation. Single-pass multiple indicator dilution (MID) studies were thus conducted under identical conditions (DCNP and absence of inorganic sulfate), with injection of [3H]4MUS and a set of noneliminated vascular and cellular reference indicators into the portal vein (prograde) or hepatic vein (retrograde), against varying background bulk concentrations of 4MUS (5 to 900 micromol/L). The steady-state removal rate of 4MUS and formation rates of 4MU and its glucuronide conjugate (4MUG) were not altered with perfusion flow direction, suggesting the presence of even or parallel distributions of 4MUS desulfation and 4MU glucuronidation activities. When the outflow dilution profile of [3H]4MUS was evaluated with the barrier-limited model of Goresky, a slight red cell carriage effect was found for 4MUS. The permeability surface area product for cellular entry for prograde showed a dramatic concentration-dependent decrease (from 0.13 to 0.01 mL sec(-1) g(-1), or 7.4 to 0.56 times the blood perfusate flow rate) and was resolved as saturable and nonsaturable components, while data for retrograde were more scattered, varying from 2.8 to 1 times the blood perfusate flow rate. Efflux (coefficient = 0.0096 +/- 0.0024 and 0.0088 +/- 0.0062 mL sec(-1) g(-1), respectively) was relatively insensitive to concentration and flow direction. The same was observed for the removal capacity for metabolism and excretion (sequestration coefficient: for prograde, 0.0056 +/- 0.0017 mL sec(-1) g(-1); for retrograde, 0.0056 +/- 0.003 mL sec(-1) g(-1)). The decrease in the apparent partition coefficient (ratio of 4MUS concentration estimated in tissue to unbound plasma concentration) and the increase in relative throughput component with concentration further substantiate the claim on the presence of concentrative processes at the sinusoidal membrane.

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“…Most sulfate conjugates undergo biliary excretion. However, 4-methylumbelliferyl sulfate (4MUS) suffers desulfation mediated via evenly distributed arylsulfatases (6,7) to refurnish the aglycone (6,8,9). …”

mentioning

confidence: 99%

“…Sulfate conjugates also exhibit a higher plasma protein binding to albumin than their parent compounds (8)(9)(10)(11)(12). The protein binding of 4MUS became saturated prior to the saturation of desulfation enzymes, a condition that contributed to an increase, then decrease in the extraction ratio of 4MUS with increasing concentration (13).…”

mentioning

confidence: 99%

Transport, Binding, and Futile Cycling of Sulfate Conjugates in Liver

Pang

Goresky

Schwab

et al. 1993

Drug Metabolism and Pharmacokinetics

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Sulfate conjugates are an important class of polar compounds which are highly ionized at physiological pH. The liver is the most important sulfation organ for most substrates. When formation and processing of sulfate conjugates are viewed as distributed-in-space phenomena, that drug and sulfate conjugate cell entry and removal occur along the direction of flow such that a concentration gradient is created from the inlet to the outlet of the liver, the differential handling of the formed vs. preformed sulfate conjugate becomes apparent. From single-pass prograde (P, entry via portal vein) and retrograde (R, entry via hepatic vein) single pass perfusion studies, formation of sulfate conjugates from acetaminophen (1), harmol (2), gentisamide (3), salicylamide (4) and 4-methylumbelliferone (4MU) (5) was found to occur in the periportal (zone 1) of the rat liver. The anterior sulfation activities modulate the substrate flux and metabolic rates with downstream enzymes. Most sulfate conjugates undergo biliary excretion. However, 4-methylumbelliferyl sulfate (4MUS) suffers desulfation mediated via evenly distributed arylsulfatases (6,7) to refurnish the aglycone (6,8,9).Without specific carriers on the liver cell, cellular entry of sulfate conjugates is anticipated to be poor. Sulfate conjugates also exhibit a higher plasma protein binding to albumin than their parent compounds (8-12). The protein binding of 4MUS became saturated prior to the saturation of desulfation enzymes, a condition that contributed to an increase, then decrease in the extraction ratio of 4MUS with increasing concentration (13). With use of the multiple indicator dilution (MID) technique, a technique that entails injection of a MID dose containing 51Cr-labeled red blood cells (vascular marker), 125I-albumin and [14C]sucrose (interstitial space marker), D2O (cellular space marker) and labeled sulfate conjugate, mechanisms of

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The conjugative metabolism of 4-methylumbelliferone and deconjugation to the parent drug examined by isolated perfused liver and in vitro liver homogenate of rats.

Cited by 14 publications

References 0 publications

The Importance of Tumor Glucuronidase in the Activation of Irinotecan in a Mouse Xenograft Model

The Importance of Tumor Glucuronidase in the Activation of Irinotecan in a Mouse Xenograft Model

Carrier-mediated entry of 4-methylumbelliferyl sulfate: Characterization by the multiple-indicator dilution technique in perfused rat liver

Transport, Binding, and Futile Cycling of Sulfate Conjugates in Liver

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