HYDROLYSIS OF ESTER-TYPE DRUGS BY THE PURIFIED ESTERASE FROM HUMAN INTESTINAL MUCOSA Michiko INOUE, Masako MORIKAWA, Minoru TSUBOI, Takashi YAMADA and Mamoru SUGIURA* Department of Pharmacology, Tokyo College of Pharmacy, Horinouchi, Hachioji-shi, Tokyo 192-03, Japan *Department of Pharmacy, Gifu College of Pharmacy, Mitahorahigashi, Gifu-shi, Gifu 502, Japan Accepted July 5, 1978 Abstract-Esterase from human intestinal mucosa was purified 210 fold by solubilization with Triton X-100, chromatography on DEAF-cellulose, Sephadex G-100 and hydroxy lapatite, and isoelectric focusing. The purified esterase showed a single band by polyacrylamide gel electrophoresis. The molecular weight of the purified esterase was estimated to be about 55,000 by gel filtration on Sephadex G-150, and the isoelectric point was 5.02. The purified esterase was strongly inhibited by diethyl p-nitrophenyl phosphate (E-600) and diisopropyl fluorophosphate (DFP), and was not inhibited by eserine sulfate and p-chloromercuribenzoate. The purified esterase from human intestinal mucosa was found to be one of the carboxylesterases. The purified esterase hydrolyzed ester-type drugs, i.e., aspirin, clofibrate, indanyl carbenicillin and procaine, but did not hydrolyze amide-type drugs and choline-type drugs. Carboxylesterase hydrolyzing carboxyl esters, thiol esters and aromatic amides, are found in most animal tissues (1). brain (2-3). The esterases have been purified from human liver and There are however, only a few reports on intestinal esterases (4-5) and there are apparently few reports regarding these drug-metabolizing activities and detailed properties. We reported elsewhere that the intestinal estrase was present in the absorption site of the intestine, and the intestinal esterase differed characteristically from hepatic esterase (6). Furthermore, there was a difference in intestinal esterase activities among several species of animals (6). absorption. Human intestinal esterase hydrolyzes ester-type drugs to a large extent during Recently, a variety of estertype drugs is being used in many ways as prodrugs (7). Reported herein is the purification of esterase from human intestinal mucosa and examination of the enzyme properties. Crude Enzyme MATERIALS AND METHODS The small intestine (jejunum) from humans was obtained at autopsy 12 hr after death. It was excised, shown to be non-pathologic, frozen and kept at -40'C until use. The intestinal mucosa was collected by scraping and was homogenized in Tris-mannitol medium; Tris-HC1 buffer (ph 7.4) containing 0.278 M mannitol at O 'C. Assay of Esterase Activity Esterase and lipase activities were determined according to the methods described
previously using /3-naphthyl derivatives, phenyl acetate (PA), tributyrin and olive oil as substrates (8-9). The esterase activities using acetylsalicylic acid (aspirin), ethylchloro phenoxyisobutyrate (clofibrate, CPIB) and indanyl carbenicillin (I-CBPC) as substrates were determined according to the methods described previously (6). Procaine and procainamide hydrolyzing activity was assayed at 37'C for 30 min by incubating with 1 mm procaine, procainamide as substrates and the product formed was determined according to the method of Tobin et al. (10). Acetanilide and phenacetin-hydrolyzing activity was determined by measuring the formation of aniline by the method of Krisch (11). Lidocaine-hydrolyzing activity was determined according to the method of Keenagham (12). The esterase activities using atropine, acetylcholine, benzoylcholine and succinylcholine as substrates were deter mined according to the method of Augustinsson (13). One unit of enzyme activity was defined as the amount of product formed per min. Assay of Protein The protein content during the purification was determined according to the method of Lowry et al. (14) and U. V. absorbance at 280 nm. Disc Electrophoresis Disc electrophoresis was carried out according to the method of Davis (15) using 7.5 polyacrylamide gel at ph 9.4. Isoelectric Focusing Isoelectric focusing was carried out according to the method of Vesterberg and Sevensson (16) using 1 % carrier ampholyte, ph 4.0-6.0. After the electrophoresis, esterase activity, ph and protein content of the elution from the column were determined. Materials Diethylaminoethyl (DEAE)-cellulose was from Brown, hydroxylapatite was obtained from Seikagaku Kogyo, Tokyo, Japan, and Sephadex G-150 were obtained from Pharmacia, Uppsala, Sweden. All other chemicals were commercial products. RESULTS Purification of Esterase from Human Intestinal Mucosa Triton X-100 was added (0.1 /o final concentration) to the homogenate solution and the solubilization completed after 3 hr under magnetic stirring. After 20 min centrifugation at 10,000 rpm, the supernatant was dialyzed overnight against 2 liters of 10 mm Tris-HCI buffer, ph 7.3. The dialyzed enzyme solution was applied on a DEAE-cellulose column equilibrated with the same buffer as used for the dialysis. After the column was washed, esterase was eluted from the column with a linear NaCI gradient, 0-0.3 M. Fractions of 5 ml were collected at a flow rate of 24 ml per hour. Eesterase activity was eluted in one peak, as shown in Fig. 1. The active fractions were pooled and concentrated to 20 ml using a membrane filter. The concentrated enzyme was dialyzed for 24 hr against 10 mm Tris-HCI buffer, ph 7.3. The concentrated enzyme was applied to a Sephadex G-100 column (3.0 x 90 cm) equilibrated
FIG. 1. Chromatography of esterase from human intestinal mucosa on DEAE-cellulose DEAE-cellulose was equilibrated with 10 mm Tris-HCl buffer (ph 7.3). Elution was carried out by changing the concentration of NaCI, linearly from 0 to 0.3 M. Esterase activity ( ) was expressed in units/ml of fraction. The concen tration of protein ( -0-). Column size: 2 x 25 cm, flow rate: 24 ml/hr FIG. 2. Chromatography of esterase from human intestinal mucosa on hydroxy lapatite. Hydroxy apatite was eqilibrated with 1 mm phosphate buffer (ph 7.3). Elution was carried out changing the concentration of phosphate, linearly from 0 to 100 mm. Esterase activity ( ) was expressed in units/ml of fraction. The concentration of protein (-s-). with 10 mm Tris-HCl buffer, ph 7.3. Elution was performed with 10 mm Tris-HC1 buffer, ph 7.3, at a flow rate of 22 ml per hour. Fractions of 5 ml were collected. The active fractions were pooled and concentrated to 25 ml using a membrane filter. The concentrated enzyme was dialyzed overnight against 1 mm phosphate buffer, ph 7.3. The concentrated enzyme was applied to a hydroxylapatite column (1.3 x 15 cm) equilibrated with 1 mm phosphate buffer, ph 7.3 and elution was carried out as described in the legend to Fig. 2. Fractions of 5 ml were collected. The results are shown in Fig. 2.
The active fractions were pooled and concentrated to 15 ml using a membrane filter. The concentrated enzyme was dialyzed overnight against 10 mm Tris-HC1 buffer, ph 7.3. The enzyme solution was subjected to isoelectric focusing. Elution was carried out as described in the legend to Fig. 3. Fractions of 5 ml were collected. Esterase activity was eluted in one peak, as shown in Fig. 3. The isoelectric point of the esterase was estimated to be ph 5.02. The yield and specific activity of the esterase fraction at each step of purification are summarized in Table I. With 3-naphthyl acetate, the specific activity of the final material FIG. 3. Isoelectric focusing pattern of esterase from human intestinal mucosa. Electro phresis was performed with I % carrier ampholyte (ph 4-6) at a constant voltage of 700 V for 40 hr. Esterase activity ), ph ( -- ). FIG. 4. Disc electrophoresis of the esterase purified from human intestine. Electro phoresis was carried out at a constant current of 3 ma/column for 90 min using 7.5% polyacrylamide gel (ph 9.4). After the electrophresis, protein (A) and esterase (B) were stained with Amidoblack lob and Fast blue B, respectively. TABLE 1. Purification of Esterase from Human Intestinal Mucosa Esterase activities were measured using (3-naphthyl acetate as a substrate units:,u moles min, a) supernatant of the centrifugation at 10,000 rpm for 20 min.
FIG. 6. Lineweaver-Bark plot of purified FIG. 5. Determination of molecular weight of intestinal esterase by gel filtration on Sephadex G-150. 1: cytochrome C, 2: ovalbumin, 3: human intestinal esterase, 4: bovine serum albumin, 5: v-globulin, column size: 0.5 x 10 cm, buffer: 10 mm Tris-HC1 (7.3) containing 0.1 M NaCI. esterase from human intestinal mucosa. The enzyme activity was determined with,3-naphthyl acetate in various concentra tions, as a substrate. The optical density value at 540 nm was used instead of the reaction velocity. was increased approximately 210 fold over that of the initial crude enzyme preparation with recovery of 8.5 %. The polyacryl amide disc gel electrophoresis pattern of the final preparation is shown in Fig. 5. The purified esterase showed a single band with faint tailing in this electrophoresis. The molecular weight of the purified esterase was estimated to be 53,000-55,000 by gel filtration on Sephadex G-150 (17) as shown in Fig. 5. Enzymatic Properties of Esterase The Michaelis content of the purified esterase to ~3-naphthyl acetate was measured in the standard assay system and estimated to be 2.3 mm (Fig. 6). The esterase activity was then assayed at various ph and temperature. As shown in Fig. 7, the optimum ph of activity between 7.5 and 8.0 was found with j3-naphthyl acetate, and the maximum activity was observed at 40--C. The enzyme stability was determined at various ph and temperatures and results are shown in Fig. 8. The esterase was stable in the ph range of 6.0-9.0 during incubation at 37 C for 30 min, and the esterase was stable in the temperature below 40'C when the solution was incubated at ph 7.5 for 20 min. Influence of Chemicals on the Esterase Activity The effect of several chemicals on the purified esterase activity was examined. As shown in Table 2, the esterase was strongly inhibited by I /LM diethy p-nitrophenyl phosphate
(E-600) and diisopropyl fluorophosphate (DFP) and moderately inhibited by cystein, 2 mercaptoethanol, iodine and HgCl2. Eserine sulfate and p-chloromercuribenzoate (PCMB) had no effect on the esterase activity. Substrate Specificity of the Esterase The substrate specificities of the purified esterase are summarized in Table 3. Among the i3-naphthol-esters tested, the highest hydrolytic activity by the purified esterase was observed with naphthyl butyrate. Furthermore, the purified esterase hydrolyzed ester-type FIG. 7. Effect of ph (a) and temperature (b) on the activity of esterase from human intestinal mucosa. Tris-HCI buffer ( -) and Beronal-HCI buffer (...0...) at 37'C were used. In the experiment of the effect of temperature, the enzyme reaction was carried out at ph 7.5 with tris-hci buffer. FIG. 8. Effect of ph (a) and temperature (b) on the stability of esterase from human intestinal mucosa. The enzyme solution was incubated with buffer solution for 20 min and the remaining activity of esterase was assayed. Buffer solution used for the study of ph stability was Britton-Robinson. In the experiment of thermal stability, Tris-HCI buffer (ph 7.5) was used.
TABLE 2. Effect of various reagents and metal salts on activity of purified esterase from human intestinal mucosa 1) N-Bromosuccinimide. 2) p-chloromercuribenzoate. 3) Diethyl p-nitrophenyl phosphate. 4) Diisopropyl fluorophosphate. The concentrations of the reagent and metal salt used here were 10-4 M except at the asterisk. The enzyme activity was determined using 13-naphthyl acetate as substrate after the treatment by the reagent and metal salt with 50 mm Tris-HCl buffer (ph 7.5) at 37 C for 30 min. The remaining activity was expressed as a percentage of the control value. TABLE 3. Substrate specificities of esterase from human intestinal mucosa The rates of hydrolysis were expressed as the relative rate to that obtained using (3-naphthyl acetate. N.D.: Not detectable.
drugs such is aspirin, CE'IB, 1-CPC,an,, procaine to a lesser extent and did not hydrolyze olive oil,?-naphthyl o!cate, amide-tyke drugs such as procainatnide, and three cholines. DISCUSSION Esterase from human intestinal mucosa Was purified 210 fold with a recovery of 8.5 by solubilizati-nn with Triton X-100, chromatography on DEAF-cellulose, Sephadex G-100 and hydroxylapatite, and isoelectric focusing. The purified esterase showed a single band by polyacrylamide gel electrophoresis. The molecular weight of the purified esterase.vas estimated to be 53,000-55,000 by gel filtration on Sepphadex G-150. Junge et al. (2) reported that the molecular weight of hepatic esterase front humans was about :81,000-186,000 and the subunit weight was about 60,000. The esterase purified was similar to the rat intestinal esterase (5) in the enzyme activity and stability in various ph and temperatures. The purified csterase hydrolyzed short chain esters such as t3-naphthyl butyrate, and ester-type drugs such as aspirin, CPIB, I-CBPC and procaine, however long chain esters such as,.1-naphthyl oleate and olive oil, and amide-type drugs and choline-type drugs were not hydrolyzed by the esterase purified in this study. The hydrolysis rates of ester-type drugs are only about one-thousand those of the,3-naphthyl esters. But, considering the concentration in the intestine of ester-type drugs administered orally, the esterase purified from human intestinal mucosa may effectively hydrolyze those ester-type drugs. The purified esterase was inhibited by organophosphates such as DFP and E-600 but not by eserine sulfate and p-chloromercuribenzoate (PCMB). From these results, the esterase purified from human intestinal mucosa vas found to belong to carboxylesterase (B-esterase) (1). Intestinal esterase acts on ester-type drugs administerd orally at the beginning of ester type drug-metabolization. In particular, in ester-type drugs such as prodrugs, it has been confirmed that those pharmacological effects were influenced by the hydrolyzing activity of intestinal esterase. We consider that this study on human intestinal esterase provides some clues as to the action of ester-type drugs. REFERENCES 1) KRIscFI, K.: Carboxylic ester hydrolase. The Enzyme, Edited by BOYLR. P. 0., Vol. V, p. 43-85, Third edition, Academic Press, New York and London (1971) 2) JUNGE, WV., HMIANN, F,. AND,LRiscuu, K.: Human liver carboxyl esterase. Arehs Biochein. B; is. 165, 749-763 (1974) 3) HOJRING, N. AND SVENSA-MARK, 0,: Carboxylesterases of human brain extract. Biochem. Biophys. Acta 480', 5990--51-1 (1477) 4) MAKHOTRA, O.P. AND PIiI~.Ia, G.: Purification and physical properties of goat intestinal esterase. Ind. J. J'iocheeP. 3, 7-11 (1966) 5) RFRNANDEZ-Lo?'r.X, V., SERRFRO, C j., NEGRFL, R. AND AILHAUD, O.: Esterolytic activities of rat intestinal mucosa.. Europ. J. Biochem. 71, 259-270 (1976) 6) INOUE, M., MORIRAWA, M., Tsunni, N". AND SUGIURA,.: Species difference and characteri zation of intestinal esterase on the hydrolizing activity of ester-type drugs. Japan. J. Pharmacol. (in press) 7) SINLULA. A.A. AND YALROWSKY, S.H.: Rationale for design of biologically reversible drug
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