Xenobiotica the fate of foreign compounds in biological systems
ISSN: 0049-8254 (Print) 1366-5928 (Online) Journal homepage: http://www.tandfonline.com/loi/ixen20
Stereoselective Disposition of Fenfluramine Enantiomers in the Rat A. Jori, P. De Ponte & S. Caccia To cite this article: A. Jori, P. De Ponte & S. Caccia (1978) Stereoselective Disposition of Fenfluramine Enantiomers in the Rat, Xenobiotica, 8:9, 583-588 To link to this article: http://dx.doi.org/10.3109/00498257809061258
Published online: 30 Sep 2009.
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Date: 09 November 2015, At: 04:23
XENOBIOTICA,
1978, VOL. 8,
NO.
9, 583-588
Stereoselective Disposition of Fenfluramine Enantiomers in the Rat A. JORI, P. DE PONTE, and S. CACCIA Istituto di Ricerche Farmacologiche Milan, Italy
"
Mario Negri
"
Via Eritrea, 62-201 57
Downloaded by [University of Otago] at 04:23 09 November 2015
(Received 25 October 1977) 1. Rats were treated with d-, I- or dl-fenfluramine. The two optical isomers and their metabolites were determined in plasma, red blood cells and brain areas such as striatum and brainstem. 2. In all cases, the levels of d-fenfluramine were higher than those of the I-enantiomer, while levels of the metabolite norfenfluramine were lower for the d- than the I-form. 3 . When metabolism of fenfluramine was inhibited by pre-treatment with S K F 525-A, the concentrations of the enantiomers no longer differed.
Introduction Analytical methods used for pharmacokinetic studies frequently do not distinguish between enantiomers when a drug is given as the racemic form. Yet it is known not only that optical isomers may have different biochemical (Taylor & Snyder, 1971) and pharmacological (Taylor & Snyder, 1970; Benington et al., 1973) effects, but that they may also undergo stereoselective metabolism (Goldstein & Anagnoste, 1965; Furner et al., 1969; Keberle, Hoffman & Bernhard, 1962); hence the need to measure the enantiomers in biological fluids and tissues as separate chemical entities. T h e two optical isomers (d- and Z-forms) of fenfluramine, a well known anorectic agent, have characteristic individual pharmacological properties. For instance, the d-form is more effective than the I in decreasing food intake (Le Douarec, Schmitt & Laubie, 1966), but the I-form is more effective than the d in increasing the levels of homovanillic acid in the striatum (Jori et al., 1973). Previous studies have investigated the absorption, distribution and metabolism of fenfluramine (Bruce & Maynard, 1968; Beckett & Brookes, 1967; Campbell, 1970), but no attempts were made to distinguish the optical isomers. This work was undertaken to examine the levels of d- and I-fenfluramine in blood and brain of rats after administration of the racemic compound, taking advantage of the recent development in these laboratories of a new g.1.c. method (Caccia & Jori, 1977) which allows resolution and quantitative determination of the optical isomers of fenfluramine and of its main metabolite, norf enfluramine. Materials and methods Female Charles River rats (180 g 10) received intraperitoneally or intravenously d-, I- or dl-fenfluramine hydrochloride (7.5 and 15 mg/kg). I n one experiment rats were given an inhibitor of liver microsomal enzymes, S K F 525-A (50 mg/kg intraperitoneally), 45 min before and after 3 h after fenfluramine.
584
A. J o ~ et i al.
Downloaded by [University of Otago] at 04:23 09 November 2015
The animals were killed at various times after fenfluramine administration. Brains were immediately removed and the dissected areas were stored at - 20" until assay of fenfluramine. Plasma and red cells were separated by centrifugation and stored at - 20". Fenfluramine and norfenfluramine enantiomers were extracted from biological samples, resolved as N pentafluoropropionyl-I-proline derivates and chromatographed as previously described in more detail (Caccia & Jori, 1977).
Results Table 1 summarizes the plasma levels of d- and Z-fenfluramine and d- and I-norfenfluramine at different times after intraperitoneal administration of racemic fenfluramine (15 mg/kg). Concentrations of d-fenfluramine and of it metabolite d-norfenfluramine, and of Z-fenfluramine and I-norfenfluramine after administration of the single corresponding optical isomer of fenfluramine at the dose of 7.5 mg/kg are also reported. I n both experimental situations, the I-isomer of fenfluramine disappears more rapidly from plasma than the d-isomer. This may be explained by the fact that the levels of norfenfluramine, the major metabolite of fenfluramine, are higher for the Z than for the d-form. Table 2 shows the drug levels in the striatum, a brain area considered of importance for the pharmacological effects of fenfluramine and in brain-stem. I n this case too, administration of racemic fenfluramine results in considerably higher striatum levels of the d-form than the Z-form, particularly after 5 and 8 hours. Concomitantly there is more I than d-norfenfluramine. I t also appears that sometimes there is more norfenfluramine and less fenfluramine when the isomer is given alone than when the racemic compound is Table 1. Plasma concentrations of d- and I-fenfluramine and d- and I-norfenfluramine after intraperitoneal administration of fenfluramine racemate or its enantiomers ~ _ _ _ _ _ _ -.
~
_ _ _ _ _ ~
Plasma concentrations (pglml) of metabolites Time after treatment (h)
d-Fenfluramine
I-Fenfluramine d-Norfenfluramine I-Norfenfluramine
__-
dl-Fenfluramine administered? 1 0.50 +_ 0.03 2 0.35 f0.02 5 0.24 f0.04 8 0.24 i0.01
0.36 k 0.02* 0.21 f.0*02* 0.1 1 ri:0.02* 0-11 ri:0.03"
0.04 k 0.00 0.05 f0.00 0.06 f.0.01 0.04 k 0.02
0.09 f0.00* 0.11 & o.oo* 0.13 k 0.01* 0.1 1 k 0.04"
d- or 1-Fenflurammeadministeredf 1 0.52 & 0.16 2 0.31 k 0.04 5 0.18 k 0.01 8 0.09 f 0.04
0.38 f0.06' 0.21 Ifr 0.02* 0.11 k0.01* 0 4 4 f0.08*
0.04 f0.00 0.06 k 0.00 0.08 k 0.00 0.10 0.00
0 4 9 f0.00* 0.1 3 0.02" 0.17f0.01* 0.22 ri- 0.04"
*
Values are means k S.E.M. for 6 rats.
* Significant differences between d and I , P < 0.01 by Student's paired t test.
? The values for metabolite concentrations were obtained from rats treated with dlfenfluramine (15 mg/kg intraperitoneally). $. The values for d-fenfluramine and d-norfenfluramine were obtained from rats treated with d-fenfluramine (7.5 mg/kg intraperitoneally) ; I-fenfluramine and Z-norfenfluramine from rats treated with l-fenfluramine (7.5 mg/kg intraperitoneally).
15.3k1.2 12.4f1.0 8.5 f0.3 6.6 f0.6
16.0f1.8 11.2 f0.8 6.0 k 0.8 4-3 f0.3
16.9f1.5 13.6 f 0 . 1 5.4 t 0.7 4.6f1.0
13,6f2.3 12.7fl.1 6.4 f0.6 6.1 f0.7
13.721.3 8.8+1.0* 4.0 k 0.4* 2.0 f0.5"
Striatum
1.4f0.1 2.2 f0.1 3.5 f0.2 4.0 f0.2
1.7f0.1 2.0f0.2 2.8 f0.3 3.2 f0.5
Striatum
1.7k0.1 2.1 f0.2 2.8 k 0.3 3.4 f0.2
1.3fO.3 1.8f0.1 2.40 f0.3 2.7 k 0.2
Brain-stem
d-nor fenfluramhe
4*0f0.5* 5.Of 0.2* 8.1 k 0.9* 7-1 f0.7*
3.0f0.5 4.4+0.8* 5.6 f0.8* 6.5 f 1.0*
Striatum
3.6f0.6* 4.9 +_ 0+4* 7.1 f0.5* 6.4 k 1*0*
2.9f0.4 5.5fO.3* 5.4 k 0.1 * 5.7 k 0*4*
Brain-stem
I-Norfenfluramine
Student's paired t test. f The values for d-fenfluramine, 1-fenfluramine,d-norfenfluramine and 1-norfenfluraminewere obtained from rats treated intraperitoneally with racemic fenfluramine (15 mg/kg). 1The value for d-fenfluramine and d-norfenfluramine, or for I-fenfluramine and I-norfenfluramine were obtained from rats treated intraperitoneally with d-fenfluramine or I-fenfluramine respectively at a dose of 7.5 mg/kg.
12-6f0.4* 9.5 f0.7* 3.4 +_ 0.3*
ISSN: 0049-8254 (Print) 1366-5928 (Online) Journal homepage: http://www.tandfonline.com/loi/ixen20
Stereoselective Disposition of Fenfluramine Enantiomers in the Rat A. Jori, P. De Ponte & S. Caccia To cite this article: A. Jori, P. De Ponte & S. Caccia (1978) Stereoselective Disposition of Fenfluramine Enantiomers in the Rat, Xenobiotica, 8:9, 583-588 To link to this article: http://dx.doi.org/10.3109/00498257809061258
Published online: 30 Sep 2009.
Submit your article to this journal
Article views: 6
View related articles
Citing articles: 1 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ixen20 Download by: [University of Otago]
Date: 09 November 2015, At: 04:23
XENOBIOTICA,
1978, VOL. 8,
NO.
9, 583-588
Stereoselective Disposition of Fenfluramine Enantiomers in the Rat A. JORI, P. DE PONTE, and S. CACCIA Istituto di Ricerche Farmacologiche Milan, Italy
"
Mario Negri
"
Via Eritrea, 62-201 57
Downloaded by [University of Otago] at 04:23 09 November 2015
(Received 25 October 1977) 1. Rats were treated with d-, I- or dl-fenfluramine. The two optical isomers and their metabolites were determined in plasma, red blood cells and brain areas such as striatum and brainstem. 2. In all cases, the levels of d-fenfluramine were higher than those of the I-enantiomer, while levels of the metabolite norfenfluramine were lower for the d- than the I-form. 3 . When metabolism of fenfluramine was inhibited by pre-treatment with S K F 525-A, the concentrations of the enantiomers no longer differed.
Introduction Analytical methods used for pharmacokinetic studies frequently do not distinguish between enantiomers when a drug is given as the racemic form. Yet it is known not only that optical isomers may have different biochemical (Taylor & Snyder, 1971) and pharmacological (Taylor & Snyder, 1970; Benington et al., 1973) effects, but that they may also undergo stereoselective metabolism (Goldstein & Anagnoste, 1965; Furner et al., 1969; Keberle, Hoffman & Bernhard, 1962); hence the need to measure the enantiomers in biological fluids and tissues as separate chemical entities. T h e two optical isomers (d- and Z-forms) of fenfluramine, a well known anorectic agent, have characteristic individual pharmacological properties. For instance, the d-form is more effective than the I in decreasing food intake (Le Douarec, Schmitt & Laubie, 1966), but the I-form is more effective than the d in increasing the levels of homovanillic acid in the striatum (Jori et al., 1973). Previous studies have investigated the absorption, distribution and metabolism of fenfluramine (Bruce & Maynard, 1968; Beckett & Brookes, 1967; Campbell, 1970), but no attempts were made to distinguish the optical isomers. This work was undertaken to examine the levels of d- and I-fenfluramine in blood and brain of rats after administration of the racemic compound, taking advantage of the recent development in these laboratories of a new g.1.c. method (Caccia & Jori, 1977) which allows resolution and quantitative determination of the optical isomers of fenfluramine and of its main metabolite, norf enfluramine. Materials and methods Female Charles River rats (180 g 10) received intraperitoneally or intravenously d-, I- or dl-fenfluramine hydrochloride (7.5 and 15 mg/kg). I n one experiment rats were given an inhibitor of liver microsomal enzymes, S K F 525-A (50 mg/kg intraperitoneally), 45 min before and after 3 h after fenfluramine.
584
A. J o ~ et i al.
Downloaded by [University of Otago] at 04:23 09 November 2015
The animals were killed at various times after fenfluramine administration. Brains were immediately removed and the dissected areas were stored at - 20" until assay of fenfluramine. Plasma and red cells were separated by centrifugation and stored at - 20". Fenfluramine and norfenfluramine enantiomers were extracted from biological samples, resolved as N pentafluoropropionyl-I-proline derivates and chromatographed as previously described in more detail (Caccia & Jori, 1977).
Results Table 1 summarizes the plasma levels of d- and Z-fenfluramine and d- and I-norfenfluramine at different times after intraperitoneal administration of racemic fenfluramine (15 mg/kg). Concentrations of d-fenfluramine and of it metabolite d-norfenfluramine, and of Z-fenfluramine and I-norfenfluramine after administration of the single corresponding optical isomer of fenfluramine at the dose of 7.5 mg/kg are also reported. I n both experimental situations, the I-isomer of fenfluramine disappears more rapidly from plasma than the d-isomer. This may be explained by the fact that the levels of norfenfluramine, the major metabolite of fenfluramine, are higher for the Z than for the d-form. Table 2 shows the drug levels in the striatum, a brain area considered of importance for the pharmacological effects of fenfluramine and in brain-stem. I n this case too, administration of racemic fenfluramine results in considerably higher striatum levels of the d-form than the Z-form, particularly after 5 and 8 hours. Concomitantly there is more I than d-norfenfluramine. I t also appears that sometimes there is more norfenfluramine and less fenfluramine when the isomer is given alone than when the racemic compound is Table 1. Plasma concentrations of d- and I-fenfluramine and d- and I-norfenfluramine after intraperitoneal administration of fenfluramine racemate or its enantiomers ~ _ _ _ _ _ _ -.
~
_ _ _ _ _ ~
Plasma concentrations (pglml) of metabolites Time after treatment (h)
d-Fenfluramine
I-Fenfluramine d-Norfenfluramine I-Norfenfluramine
__-
dl-Fenfluramine administered? 1 0.50 +_ 0.03 2 0.35 f0.02 5 0.24 f0.04 8 0.24 i0.01
0.36 k 0.02* 0.21 f.0*02* 0.1 1 ri:0.02* 0-11 ri:0.03"
0.04 k 0.00 0.05 f0.00 0.06 f.0.01 0.04 k 0.02
0.09 f0.00* 0.11 & o.oo* 0.13 k 0.01* 0.1 1 k 0.04"
d- or 1-Fenflurammeadministeredf 1 0.52 & 0.16 2 0.31 k 0.04 5 0.18 k 0.01 8 0.09 f 0.04
0.38 f0.06' 0.21 Ifr 0.02* 0.11 k0.01* 0 4 4 f0.08*
0.04 f0.00 0.06 k 0.00 0.08 k 0.00 0.10 0.00
0 4 9 f0.00* 0.1 3 0.02" 0.17f0.01* 0.22 ri- 0.04"
*
Values are means k S.E.M. for 6 rats.
* Significant differences between d and I , P < 0.01 by Student's paired t test.
? The values for metabolite concentrations were obtained from rats treated with dlfenfluramine (15 mg/kg intraperitoneally). $. The values for d-fenfluramine and d-norfenfluramine were obtained from rats treated with d-fenfluramine (7.5 mg/kg intraperitoneally) ; I-fenfluramine and Z-norfenfluramine from rats treated with l-fenfluramine (7.5 mg/kg intraperitoneally).
15.3k1.2 12.4f1.0 8.5 f0.3 6.6 f0.6
16.0f1.8 11.2 f0.8 6.0 k 0.8 4-3 f0.3
16.9f1.5 13.6 f 0 . 1 5.4 t 0.7 4.6f1.0
13,6f2.3 12.7fl.1 6.4 f0.6 6.1 f0.7
13.721.3 8.8+1.0* 4.0 k 0.4* 2.0 f0.5"
Striatum
1.4f0.1 2.2 f0.1 3.5 f0.2 4.0 f0.2
1.7f0.1 2.0f0.2 2.8 f0.3 3.2 f0.5
Striatum
1.7k0.1 2.1 f0.2 2.8 k 0.3 3.4 f0.2
1.3fO.3 1.8f0.1 2.40 f0.3 2.7 k 0.2
Brain-stem
d-nor fenfluramhe
4*0f0.5* 5.Of 0.2* 8.1 k 0.9* 7-1 f0.7*
3.0f0.5 4.4+0.8* 5.6 f0.8* 6.5 f 1.0*
Striatum
3.6f0.6* 4.9 +_ 0+4* 7.1 f0.5* 6.4 k 1*0*
2.9f0.4 5.5fO.3* 5.4 k 0.1 * 5.7 k 0*4*
Brain-stem
I-Norfenfluramine
Student's paired t test. f The values for d-fenfluramine, 1-fenfluramine,d-norfenfluramine and 1-norfenfluraminewere obtained from rats treated intraperitoneally with racemic fenfluramine (15 mg/kg). 1The value for d-fenfluramine and d-norfenfluramine, or for I-fenfluramine and I-norfenfluramine were obtained from rats treated intraperitoneally with d-fenfluramine or I-fenfluramine respectively at a dose of 7.5 mg/kg.
12-6f0.4* 9.5 f0.7* 3.4 +_ 0.3*
