Mahmoud Ahmed | UAE University (original) (raw)

Papers by Mahmoud Ahmed

Research paper thumbnail of Effect of human serum albumin on transplacental transfer of glyburide

Biochemical Pharmacology, 2006

M.S. Ahmed). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m ... more M.S. Ahmed). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c h e m p h a r m 0006-2952/$ -see front matter #

Research paper thumbnail of Methadone metabolism by human placenta

Biochemical Pharmacology, 2004

Methadone pharmacotherapy is considered the standard for treatment of the pregnant heroin/opioid ... more Methadone pharmacotherapy is considered the standard for treatment of the pregnant heroin/opioid addict. One of the factors affecting the transfer kinetics of opioids across human placenta and their levels in the fetal circulation is their metabolism by the tissue. The aim of this investigation is to identify the enzyme(s) responsible for the metabolism of methadone, determine the kinetics of the reaction and the metabolites formed utilizing placental tissue obtained from term healthy pregnancies. Microsomal fractions of trophoblast tissue homogenates had the highest activity in catalyzing the metabolism of methadone. The product formed was identified by HPLC-UV as 2ethylidine-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP). Inhibitors selective for cytochrome P450 (CYP) isozymes were used to identify the enzyme catalyzing the biotransformation of methadone. Aminoglutethimide and 4-hydroxyandrostenedione inhibited EDDP formation by 88 and 70%, respectively, suggesting that CYP19/aromatase is the enzyme catalyzing the reaction. This was confirmed by the effect of monoclonal antibodies raised against CYP19 that caused an 80% inhibition of the reaction. The apparent K m and V max values for the CYP19 catalyzed metabolism of methadone to EDDP were 424 AE 92 mM and 420 AE 89 pmol (mg protein) À1 min À1 , respectively. Kinetic analysis of a cDNA-expressed CYP19 for the metabolism of methadone to EDDP was identical to that by placental microsomes. Taken together, these data indicate that CYP19/aromatase is the major enzyme responsible for the metabolism of methadone to EDDP in term human placentas obtained from healthy pregnancies.

Research paper thumbnail of The effect of methadone and buprenorphine on human placental aromatase

Biochemical Pharmacology, 2006

Research paper thumbnail of The effect of opiates on the activity of human placental aromatase/CYP19

Biochemical Pharmacology, 2007

b i o c h e m i c a l p h a r m a c o l o g y 7 3 ( 2 0 0 7 ) 2 7 9 -2 8 6 Aromatase/CYP19 Estrog... more b i o c h e m i c a l p h a r m a c o l o g y 7 3 ( 2 0 0 7 ) 2 7 9 -2 8 6 Aromatase/CYP19 Estrogen formation Pregnancy a b s t r a c t Aromatase, cytochrome P450 19, is a key enzyme in the biosynthesis of estrogens by the human placenta. It is also the major placental enzyme that metabolizes the opiates L-acetylmethadol (LAAM), methadone, and buprenorphine (BUP). Methadone and BUP are used in treatment of the opiate addict and are competitive inhibitors of testosterone conversion to estradiol (E 2 ) and 16a-hydroxytestosterone (16-OHT) to estriol (E 3 ) by aromatase. The aim of this investigation is to determine the effect of 20 opiates, which can be administered to pregnant patients for therapeutic indications or abused, on E 2 and E 3 formation by placental aromatase. Data obtained indicated that the opiates increased, inhibited, or had no effect on aromatase activity. Their effect on E 3 formation was more pronounced than that on E 2 due to the lower affinity of 16-OHT than testosterone to aromatase. The K i values for the opiates that inhibited E 3 formation were sufentanil, 7 AE 1 mM; LAAM, 13 AE 8 mM; fentanyl, 25 AE 5 mM; oxycodone, 92 AE 22 mM; codeine, 218 AE 69 mM; (+)-pentazocine, 225 AE 73 mM. The agonists morphine, heroin, hydromorphone, oxymorphone, hydrocodone, propoxyphene, meperidine, levorphanol, dextrorphan, and (À)-pentazocine and the antagonists naloxone and naltrexone caused an increase in E 3 formation by 124-160% of control but had no effect on E 2 formation. Moreover, oxycodone and codeine did not inhibit E 2 formation and the IC 50 values for fentanyl, sufentanil, and (+)pentazocine were >1000 mM. It is unlikely that the acute administration of the opiates that inhibit estrogen formation would affect maternal and/or neonatal outcome. However, the effects of abusing any of them during the entire pregnancy are unclear at this time. # dinorLAAM, nor-and dinor-levo-a-acetylmethadol a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c h e m p h a r m

Research paper thumbnail of Transfer of metformin across the dually perfused human placental lobule

American Journal of Obstetrics and Gynecology, 2006

Research paper thumbnail of Transfer of methadone across the dually perfused preterm human placental lobule

American Journal of Obstetrics and Gynecology, 2008

The objective of the study was to determine the effect of gestational age and P-glycoprotein expr... more The objective of the study was to determine the effect of gestational age and P-glycoprotein expression on transplacental transfer of methadone. STUDY DESIGN: Dual perfusion of placental lobule was utilized. Methadone (200 ng/mL) and its [ 3 H]-isotope were cotransfused from the maternal-to-fetal circuit with the marker compound antipyrine (20 g/ mL) and its [ 14 C]-isotope. Concentration of the drugs in trophoblast tissue and both circuits was determined by liquid scintillation spectrometry.

Research paper thumbnail of N-Demethylation of levo-α-acetylmethadol by human placental aromatase

Biochemical Pharmacology, 2004

Levo-a-acetylmethadol (LAAM) is a methadone derivative used to treat the opiate addict. We previo... more Levo-a-acetylmethadol (LAAM) is a methadone derivative used to treat the opiate addict. We previously reported on the kinetics for transplacental transfer of LAAM and its levels in the fetal circuit using the technique of dual perfusion of the placental lobule. The aim of this investigation was to identify the enzyme responsible for the biotransformation of LAAM and norLAAM and the metabolites formed in the term human placenta. Placental microsomes exhibited higher activities than the mitochondrial and cytosolic fractions in metabolizing LAAM to norLAAM. None of these subcellular fractions catalyzed the formation of dinorLAAM from either LAAM or norLAAM as determined by HPLC/UV. Evidence obtained from the effects of cytochrome P450 (CYP) inhibitors on the demethylation of LAAM to norLAAM by placental microsomes suggested that CYP 19/aromatase is the major enzyme involved. Out of 10 monoclonal antibodies raised against various CYP isoforms, only that for aromatase caused over 80% inhibition of norLAAM formation. The biotransformation of LAAM to norLAAM exhibited monophasic kinetics with apparent K m and V max values of 105 AE 57 mM and 86:8 AE 15:6 pmol mg À1 protein min À1 , respectively. The kinetic profile determined for a cDNA-expressed CYP 19 metabolism of LAAM to norLAAM was similar to that determined for placental microsomes. Taken together, the above data indicate that CYP 19/ aromatase is the enzyme responsible for the N-demethylation of LAAM to norLAAM in term human placentas obtained from healthy pregnant women. #

Research paper thumbnail of Role of P-glycoprotein in transplacental transfer of methadone

Biochemical Pharmacology, 2005

Methadone is the therapeutic agent of choice for treatment of the pregnant opiate addict. However... more Methadone is the therapeutic agent of choice for treatment of the pregnant opiate addict. However, little is known on the factors affecting its concentration in the fetal circulation during pregnancy and how it might relate to neonatal outcome. Therefore, a better understanding of the function of placental metabolic enzymes and transporters should add to the knowledge of the role of the tissue in the disposition of methadone and its relation to neonatal outcome. We hypothesized that the expression and activity of the placental efflux transporter P-glycoprotein (P-gp) would affect the transfer of methadone to the fetal circulation. Data obtained utilizing dual perfusion of placental lobule and monolayers of Be-Wo cell line indicated that methadone is extruded by P-gp. Transfer of methadone to the fetal circuit was increased by 30% in the presence of the P-gp inhibitor GF120918 while the transfer of paclitaxel, a typical substrate of the glycoprotein, was increased by 50%. In the Be-Wo cell line, methadone and paclitaxel uptake was also increased in the presence of the P-gp inhibitor cyclosporin A. Moreover, the expression of P-gp in placental brush-border membranes varied between term placentas. Taken together, these data strongly suggest that the concentration of methadone in the fetal circulation is affected by the expression and activity of P-gp. It is reasonable to speculate that placental disposition of methadone affects its concentration in the fetal circulation. If true, this may also be directly related to the incidence and intensity of neonatal abstinence syndrome (NAS).

Research paper thumbnail of Identification of glyburide metabolites formed by hepatic and placental microsomes of humans and baboons

Biochemical Pharmacology, 2006

M.S. Ahmed). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m ... more M.S. Ahmed). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c h e m p h a r m 0006-2952/$ -see front matter #

Research paper thumbnail of Bidirectional transfer of methadone across human placenta

Biochemical Pharmacology, 2005

Methadone maintenance programs are considered the standard of care for the pregnant opiate addict... more Methadone maintenance programs are considered the standard of care for the pregnant opiate addict. However, data on changes in methadone pharmacokinetics (PK) during pregnancy are limited and do not include its disposition by the placenta due to obvious ethical and safety considerations. Accordingly, investigations in our laboratory are focusing on human placental disposition of opiates including methadone. Recently, we reported on methadone metabolism by placental aromatase and provide here data on its bidirectional transfer across the tissue utilizing the technique of dual perfusion of placental lobule. The concentrations of the opiate transfused into the term placental tissue were those reported for its in vivo levels in the maternal serum of women under treatment with the drug. Data obtained indicated that the opiate has no adverse effects on placental viability and functional parameters and that it is retained by the tissue. Also, methadone transfer and its clearance index in the fetal to maternal direction (0.97 AE 0.05) was significantly higher (P < 0.05) than in the maternal to fetal (0.83 AE 0.09). The observed asymmetry in methadone transfer could be explained by the unidirectional activity of the efflux transporter P glycoprotein (P-gp) that is highly expressed in variable amounts in trophoblast tissue. Therefore, placental disposition of methadone might be an important contributor to the regulation of its concentration in the fetal circulation and consequently may affect the incidence and intensity of neonatal abstinence syndrome for women treated with the drug during pregnancy. #

Research paper thumbnail of Effect of human serum albumin on transplacental transfer of glyburide

Biochemical Pharmacology, 2006

M.S. Ahmed). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m ... more M.S. Ahmed). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c h e m p h a r m 0006-2952/$ -see front matter #

Research paper thumbnail of Methadone metabolism by human placenta

Biochemical Pharmacology, 2004

Methadone pharmacotherapy is considered the standard for treatment of the pregnant heroin/opioid ... more Methadone pharmacotherapy is considered the standard for treatment of the pregnant heroin/opioid addict. One of the factors affecting the transfer kinetics of opioids across human placenta and their levels in the fetal circulation is their metabolism by the tissue. The aim of this investigation is to identify the enzyme(s) responsible for the metabolism of methadone, determine the kinetics of the reaction and the metabolites formed utilizing placental tissue obtained from term healthy pregnancies. Microsomal fractions of trophoblast tissue homogenates had the highest activity in catalyzing the metabolism of methadone. The product formed was identified by HPLC-UV as 2ethylidine-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP). Inhibitors selective for cytochrome P450 (CYP) isozymes were used to identify the enzyme catalyzing the biotransformation of methadone. Aminoglutethimide and 4-hydroxyandrostenedione inhibited EDDP formation by 88 and 70%, respectively, suggesting that CYP19/aromatase is the enzyme catalyzing the reaction. This was confirmed by the effect of monoclonal antibodies raised against CYP19 that caused an 80% inhibition of the reaction. The apparent K m and V max values for the CYP19 catalyzed metabolism of methadone to EDDP were 424 AE 92 mM and 420 AE 89 pmol (mg protein) À1 min À1 , respectively. Kinetic analysis of a cDNA-expressed CYP19 for the metabolism of methadone to EDDP was identical to that by placental microsomes. Taken together, these data indicate that CYP19/aromatase is the major enzyme responsible for the metabolism of methadone to EDDP in term human placentas obtained from healthy pregnancies.

Research paper thumbnail of The effect of methadone and buprenorphine on human placental aromatase

Biochemical Pharmacology, 2006

Research paper thumbnail of The effect of opiates on the activity of human placental aromatase/CYP19

Biochemical Pharmacology, 2007

b i o c h e m i c a l p h a r m a c o l o g y 7 3 ( 2 0 0 7 ) 2 7 9 -2 8 6 Aromatase/CYP19 Estrog... more b i o c h e m i c a l p h a r m a c o l o g y 7 3 ( 2 0 0 7 ) 2 7 9 -2 8 6 Aromatase/CYP19 Estrogen formation Pregnancy a b s t r a c t Aromatase, cytochrome P450 19, is a key enzyme in the biosynthesis of estrogens by the human placenta. It is also the major placental enzyme that metabolizes the opiates L-acetylmethadol (LAAM), methadone, and buprenorphine (BUP). Methadone and BUP are used in treatment of the opiate addict and are competitive inhibitors of testosterone conversion to estradiol (E 2 ) and 16a-hydroxytestosterone (16-OHT) to estriol (E 3 ) by aromatase. The aim of this investigation is to determine the effect of 20 opiates, which can be administered to pregnant patients for therapeutic indications or abused, on E 2 and E 3 formation by placental aromatase. Data obtained indicated that the opiates increased, inhibited, or had no effect on aromatase activity. Their effect on E 3 formation was more pronounced than that on E 2 due to the lower affinity of 16-OHT than testosterone to aromatase. The K i values for the opiates that inhibited E 3 formation were sufentanil, 7 AE 1 mM; LAAM, 13 AE 8 mM; fentanyl, 25 AE 5 mM; oxycodone, 92 AE 22 mM; codeine, 218 AE 69 mM; (+)-pentazocine, 225 AE 73 mM. The agonists morphine, heroin, hydromorphone, oxymorphone, hydrocodone, propoxyphene, meperidine, levorphanol, dextrorphan, and (À)-pentazocine and the antagonists naloxone and naltrexone caused an increase in E 3 formation by 124-160% of control but had no effect on E 2 formation. Moreover, oxycodone and codeine did not inhibit E 2 formation and the IC 50 values for fentanyl, sufentanil, and (+)pentazocine were >1000 mM. It is unlikely that the acute administration of the opiates that inhibit estrogen formation would affect maternal and/or neonatal outcome. However, the effects of abusing any of them during the entire pregnancy are unclear at this time. # dinorLAAM, nor-and dinor-levo-a-acetylmethadol a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c h e m p h a r m

Research paper thumbnail of Transfer of metformin across the dually perfused human placental lobule

American Journal of Obstetrics and Gynecology, 2006

Research paper thumbnail of Transfer of methadone across the dually perfused preterm human placental lobule

American Journal of Obstetrics and Gynecology, 2008

The objective of the study was to determine the effect of gestational age and P-glycoprotein expr... more The objective of the study was to determine the effect of gestational age and P-glycoprotein expression on transplacental transfer of methadone. STUDY DESIGN: Dual perfusion of placental lobule was utilized. Methadone (200 ng/mL) and its [ 3 H]-isotope were cotransfused from the maternal-to-fetal circuit with the marker compound antipyrine (20 g/ mL) and its [ 14 C]-isotope. Concentration of the drugs in trophoblast tissue and both circuits was determined by liquid scintillation spectrometry.

Research paper thumbnail of N-Demethylation of levo-α-acetylmethadol by human placental aromatase

Biochemical Pharmacology, 2004

Levo-a-acetylmethadol (LAAM) is a methadone derivative used to treat the opiate addict. We previo... more Levo-a-acetylmethadol (LAAM) is a methadone derivative used to treat the opiate addict. We previously reported on the kinetics for transplacental transfer of LAAM and its levels in the fetal circuit using the technique of dual perfusion of the placental lobule. The aim of this investigation was to identify the enzyme responsible for the biotransformation of LAAM and norLAAM and the metabolites formed in the term human placenta. Placental microsomes exhibited higher activities than the mitochondrial and cytosolic fractions in metabolizing LAAM to norLAAM. None of these subcellular fractions catalyzed the formation of dinorLAAM from either LAAM or norLAAM as determined by HPLC/UV. Evidence obtained from the effects of cytochrome P450 (CYP) inhibitors on the demethylation of LAAM to norLAAM by placental microsomes suggested that CYP 19/aromatase is the major enzyme involved. Out of 10 monoclonal antibodies raised against various CYP isoforms, only that for aromatase caused over 80% inhibition of norLAAM formation. The biotransformation of LAAM to norLAAM exhibited monophasic kinetics with apparent K m and V max values of 105 AE 57 mM and 86:8 AE 15:6 pmol mg À1 protein min À1 , respectively. The kinetic profile determined for a cDNA-expressed CYP 19 metabolism of LAAM to norLAAM was similar to that determined for placental microsomes. Taken together, the above data indicate that CYP 19/ aromatase is the enzyme responsible for the N-demethylation of LAAM to norLAAM in term human placentas obtained from healthy pregnant women. #

Research paper thumbnail of Role of P-glycoprotein in transplacental transfer of methadone

Biochemical Pharmacology, 2005

Methadone is the therapeutic agent of choice for treatment of the pregnant opiate addict. However... more Methadone is the therapeutic agent of choice for treatment of the pregnant opiate addict. However, little is known on the factors affecting its concentration in the fetal circulation during pregnancy and how it might relate to neonatal outcome. Therefore, a better understanding of the function of placental metabolic enzymes and transporters should add to the knowledge of the role of the tissue in the disposition of methadone and its relation to neonatal outcome. We hypothesized that the expression and activity of the placental efflux transporter P-glycoprotein (P-gp) would affect the transfer of methadone to the fetal circulation. Data obtained utilizing dual perfusion of placental lobule and monolayers of Be-Wo cell line indicated that methadone is extruded by P-gp. Transfer of methadone to the fetal circuit was increased by 30% in the presence of the P-gp inhibitor GF120918 while the transfer of paclitaxel, a typical substrate of the glycoprotein, was increased by 50%. In the Be-Wo cell line, methadone and paclitaxel uptake was also increased in the presence of the P-gp inhibitor cyclosporin A. Moreover, the expression of P-gp in placental brush-border membranes varied between term placentas. Taken together, these data strongly suggest that the concentration of methadone in the fetal circulation is affected by the expression and activity of P-gp. It is reasonable to speculate that placental disposition of methadone affects its concentration in the fetal circulation. If true, this may also be directly related to the incidence and intensity of neonatal abstinence syndrome (NAS).

Research paper thumbnail of Identification of glyburide metabolites formed by hepatic and placental microsomes of humans and baboons

Biochemical Pharmacology, 2006

M.S. Ahmed). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m ... more M.S. Ahmed). a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o c h e m p h a r m 0006-2952/$ -see front matter #

Research paper thumbnail of Bidirectional transfer of methadone across human placenta

Biochemical Pharmacology, 2005

Methadone maintenance programs are considered the standard of care for the pregnant opiate addict... more Methadone maintenance programs are considered the standard of care for the pregnant opiate addict. However, data on changes in methadone pharmacokinetics (PK) during pregnancy are limited and do not include its disposition by the placenta due to obvious ethical and safety considerations. Accordingly, investigations in our laboratory are focusing on human placental disposition of opiates including methadone. Recently, we reported on methadone metabolism by placental aromatase and provide here data on its bidirectional transfer across the tissue utilizing the technique of dual perfusion of placental lobule. The concentrations of the opiate transfused into the term placental tissue were those reported for its in vivo levels in the maternal serum of women under treatment with the drug. Data obtained indicated that the opiate has no adverse effects on placental viability and functional parameters and that it is retained by the tissue. Also, methadone transfer and its clearance index in the fetal to maternal direction (0.97 AE 0.05) was significantly higher (P < 0.05) than in the maternal to fetal (0.83 AE 0.09). The observed asymmetry in methadone transfer could be explained by the unidirectional activity of the efflux transporter P glycoprotein (P-gp) that is highly expressed in variable amounts in trophoblast tissue. Therefore, placental disposition of methadone might be an important contributor to the regulation of its concentration in the fetal circulation and consequently may affect the incidence and intensity of neonatal abstinence syndrome for women treated with the drug during pregnancy. #