Debrisoquine hydroxylation in Parkinson’s disease Steiger MJ, Lledo P, Quinn NP, Marsden CD, Turner P, Jenner PG. Debrisoquine hydroxylation in Parkinson’s disease. Acta Neurol Scand 1992: 86: 159-164.
M. J. Steiger’, P. Lledo’, N. P. Quinn’, C. D. Marsden P. Turner’, P. G. Jenner
’,
’
Debrisoquine (DBQ) metabolism was studied in 80 Parkinson’s disease (PD) patients, 26 of whom had young onset Parkinson’s disease (YOPD), and in 143 controls. There was no significant difference between the proportion of poor metabolisers of DBQ among YOPD patients compared either to other parkinsonians, or to controls. Nor was there a significant correlation between the age of disease onset and DBQ metabolic ratio (MR). The results do not support the suggestion that impairment of DBQ metabolism (and hence cytochrome P450) is a primary defect in YOPD. However, in comparison with controls, MR values were modestly but significantly higher in P D patients, even in those not treated with drugs known to affect DBQ metabolism.
The concept that Parkinson’s disease (PD) might be caused by an environmental toxin received strong support following the discovery of MPTP induced parkinsonism (1-3). If a toxin contributes to PD, there are several ways in which it might selectively affect a minority of people. First, those individuals developing PD might have been exposed to the toxin whilst those free of the disease had no such exposure. Second, individuals developing PD may have had a greater acute or chronic exposure to the toxin. Third, everyone in the population might be exposed to similar amounts of toxin, but may metabolise it in different ways in a manner which is genetically determined. The end product of any difference in metabolism would depend on whether the metabolite is more, or less, toxic than the parent compound. These notions have therefore stimulated a search not only for toxic compounds in the environment, but also some index of differential susceptibility to the toxic effects of such agents. One possibility relates to the heterogeneity of hepatic microsomal oxidative metabolism and in particular of a cytochrome P450 isozyme (P450DII6) (4) which hydroxylates debrisoquine to 4hydroxydebrisoquine (4-OH DBQ) (5,6) and whose activity is genetically determined. Thus, homozygotes for the recessive poor metaboliser gene on chromosome 22 (7) excrete only small quantities of 4-OH DBQ. In addition to genetic factors, exposure to inducers or inhibitors of cytochrome P450 may
Departments of Clinical Neurology, Institute of Neurology, National Hospital for Neurology & Neurosurgery, Clinical Pharmacology, St. Bartholomew’s Hospital, Parkinson’s Disease Society Experimental Research Laboratory, Pharmacology Group, Biomedical Sciences Division, King’s College, London, England
Key words: Parkinson’s disease; debrisoquine metabolism; environmental toxins Dr M.J. Steiger, Department of Neurology, Royal Free Hospital, Pond St., Hampstead, London NW3, England
I
Accepted for publication December 17, 1991
also interfere with the formation of 4-OH debrisoquine (8, 9) (Table 1). Finally, it has also been established that MPTP is oxidised in the liver by the same P450 isozyme, and that it is a competitive inhibitor of the enzyme (10). In 1985 Barbeau et al. (1 1) reported that significantly more parkinsonian than control subjects had partially or totally defective 4-hydroxylation of debrisoquine. However, later work by the same group revealed that direct actions of some antiparkinsonian drugs on cytochrome P450 activity had not been taken into account (12). Nevertheless they maintained that “patients with a very early age of onset (younger than 40 years) (YOPD) all had some impairment of debrisoquine hydroxylation”. Table 1. Commonly used drugs that interfere with the metabolism of debrisoquine AnticholinergicdAntihistamines Amitriptyline Apomorphine Chlorpromazine Fluphenazine Haloperidol lmipramine Metoclopramide Metoprolol Oxprenolol Pindolol PropranoIoI Quinidine TimoIoI
159
Steiger et al. Subsequent studies by other groups have given negative or inconsistent results (13-20). We have therefore examined DBQ hydroxylation in a large group of PD patients, including 26 with YOPD, and a group of healthy controls.
DBQ in the sample a modified version of the method described by Lennard et al. (22) was employed consisting of gas chromatography using a thermionic specific detector. The metabolic ratio (MR) was calculated using the formula (6):
% of dose excreted Material and methods
as unchanged drug
Eighty patients with clinical PD were studied. They were divided into 2 groups (Table 2). Group A comprised 54 patients (of whom 16 had YOPD) who were either drug naive, or were not taking drugs known to interfere with DBQ metabolism. Group B comprised 26 patients (10 of whom had YOPD) who were taking drugs known to affect DBQ metabolism (Table 2). The control group comprised 143 healthy volunteers, none of whom were on drugs known to affect DBQ metabolism. This control population was not age matched to the patient group. However, age does not appear to affect the rate of DBQ metabolism (21). Assessment of DBQ hydroxylation
All subjects were instructed to empty their bladder at 11 pm, then take the equivalent of 10 mg oral debrisoquine base (debrisoquine sulphate 12.8 mgDeclinax 10 mg, Roche), and collect their urine over the next 8 hours. The total volume of urine was measured to within 5 mls, and an aliquot stored at - 20°C until analysed. To measure DBQ and 4-OH Table 2. Details of patients and controls and their debrisoquine metabolic ratio (MR) log,,MR
Controls Group A Group A YOPD Group A minus YOPD Group B Group B YOPD Group B minus YOPD Group A&B All YOPD Group A&B minus YOPD
=
% of dose excreted
in the urine.
as metabolite (4-OH DBQ) Patients were classified as poor or extensive metabolisers according to the criteria proposed by Evans et al. (23). Poor metabolisers were defined by a M R > 12.6 (log,,MR> 1.1) Results
Nine of the 54 (16.7%) patients either untreated or not taking drugs known to interfere with DBQ metabolism (group A) were poor metabolisers, including 1 of 16 (6.3 %)with YOPD (Table 2). This compares with 5 of 26 (19.2%) patients on drugs known to interfere with DBQ metabolism (group B), including 3 of 10 (30%) with YOPD. Among the controls, 13 of 143 (9.1%) were poor metabolisers. These percentages of poor metabolisers were similar across the 3 groups (A,B, and controls) (chi-square = 3.52, p = 0.17). There was no significant excess of poor metabolisers in the YOPD patients in group A or group B compared with controls (chi-square = 4.8, p = 0.09). values Mean log,,MR (SD)
No. (%)with log,oMR> 1.1
No. of subjects
Age (range) (SD) years
143 54 16
23.7 (18-41) (4.6) 54.1 (35-74) (10.0) 43.5 (35-561 (5.8)
-0.22 (0.87) 0.11 (1.20)” -0.14 (0.89Ib
13 (9.1%) 9(16.7%) 1(6.3%)
38
58.9 (43-741 (8.4)
0.22 (1.32)”
8 (14.8%)
26 10
58.3 (35-84) (13.2) 45.7 (40-55) (6.6)
0.34 (1.30Id 0.57 (1.30Ie
5 (19.2%) 3 130.0%)
16
66.9 (54-84) (8.5)
0.19 (1.21V
2 (12.5%)
80 26 54
55.7 (35-84) (1 1.51 44.0 (35-55) (5.7) 61.3 (43-84) (9.1)
0.19 (1.2018 0.13 ( l . l O ) d 0.20 (1.30)”
14 (17.5%) 4 ( 15.4%) 10(18.5%)
p=0.05 compared with controls. p1.1
> 12.0 1-12.6 >1
> 1.08
O
M. J. Steiger’, P. Lledo’, N. P. Quinn’, C. D. Marsden P. Turner’, P. G. Jenner
’,
’
Debrisoquine (DBQ) metabolism was studied in 80 Parkinson’s disease (PD) patients, 26 of whom had young onset Parkinson’s disease (YOPD), and in 143 controls. There was no significant difference between the proportion of poor metabolisers of DBQ among YOPD patients compared either to other parkinsonians, or to controls. Nor was there a significant correlation between the age of disease onset and DBQ metabolic ratio (MR). The results do not support the suggestion that impairment of DBQ metabolism (and hence cytochrome P450) is a primary defect in YOPD. However, in comparison with controls, MR values were modestly but significantly higher in P D patients, even in those not treated with drugs known to affect DBQ metabolism.
The concept that Parkinson’s disease (PD) might be caused by an environmental toxin received strong support following the discovery of MPTP induced parkinsonism (1-3). If a toxin contributes to PD, there are several ways in which it might selectively affect a minority of people. First, those individuals developing PD might have been exposed to the toxin whilst those free of the disease had no such exposure. Second, individuals developing PD may have had a greater acute or chronic exposure to the toxin. Third, everyone in the population might be exposed to similar amounts of toxin, but may metabolise it in different ways in a manner which is genetically determined. The end product of any difference in metabolism would depend on whether the metabolite is more, or less, toxic than the parent compound. These notions have therefore stimulated a search not only for toxic compounds in the environment, but also some index of differential susceptibility to the toxic effects of such agents. One possibility relates to the heterogeneity of hepatic microsomal oxidative metabolism and in particular of a cytochrome P450 isozyme (P450DII6) (4) which hydroxylates debrisoquine to 4hydroxydebrisoquine (4-OH DBQ) (5,6) and whose activity is genetically determined. Thus, homozygotes for the recessive poor metaboliser gene on chromosome 22 (7) excrete only small quantities of 4-OH DBQ. In addition to genetic factors, exposure to inducers or inhibitors of cytochrome P450 may
Departments of Clinical Neurology, Institute of Neurology, National Hospital for Neurology & Neurosurgery, Clinical Pharmacology, St. Bartholomew’s Hospital, Parkinson’s Disease Society Experimental Research Laboratory, Pharmacology Group, Biomedical Sciences Division, King’s College, London, England
Key words: Parkinson’s disease; debrisoquine metabolism; environmental toxins Dr M.J. Steiger, Department of Neurology, Royal Free Hospital, Pond St., Hampstead, London NW3, England
I
Accepted for publication December 17, 1991
also interfere with the formation of 4-OH debrisoquine (8, 9) (Table 1). Finally, it has also been established that MPTP is oxidised in the liver by the same P450 isozyme, and that it is a competitive inhibitor of the enzyme (10). In 1985 Barbeau et al. (1 1) reported that significantly more parkinsonian than control subjects had partially or totally defective 4-hydroxylation of debrisoquine. However, later work by the same group revealed that direct actions of some antiparkinsonian drugs on cytochrome P450 activity had not been taken into account (12). Nevertheless they maintained that “patients with a very early age of onset (younger than 40 years) (YOPD) all had some impairment of debrisoquine hydroxylation”. Table 1. Commonly used drugs that interfere with the metabolism of debrisoquine AnticholinergicdAntihistamines Amitriptyline Apomorphine Chlorpromazine Fluphenazine Haloperidol lmipramine Metoclopramide Metoprolol Oxprenolol Pindolol PropranoIoI Quinidine TimoIoI
159
Steiger et al. Subsequent studies by other groups have given negative or inconsistent results (13-20). We have therefore examined DBQ hydroxylation in a large group of PD patients, including 26 with YOPD, and a group of healthy controls.
DBQ in the sample a modified version of the method described by Lennard et al. (22) was employed consisting of gas chromatography using a thermionic specific detector. The metabolic ratio (MR) was calculated using the formula (6):
% of dose excreted Material and methods
as unchanged drug
Eighty patients with clinical PD were studied. They were divided into 2 groups (Table 2). Group A comprised 54 patients (of whom 16 had YOPD) who were either drug naive, or were not taking drugs known to interfere with DBQ metabolism. Group B comprised 26 patients (10 of whom had YOPD) who were taking drugs known to affect DBQ metabolism (Table 2). The control group comprised 143 healthy volunteers, none of whom were on drugs known to affect DBQ metabolism. This control population was not age matched to the patient group. However, age does not appear to affect the rate of DBQ metabolism (21). Assessment of DBQ hydroxylation
All subjects were instructed to empty their bladder at 11 pm, then take the equivalent of 10 mg oral debrisoquine base (debrisoquine sulphate 12.8 mgDeclinax 10 mg, Roche), and collect their urine over the next 8 hours. The total volume of urine was measured to within 5 mls, and an aliquot stored at - 20°C until analysed. To measure DBQ and 4-OH Table 2. Details of patients and controls and their debrisoquine metabolic ratio (MR) log,,MR
Controls Group A Group A YOPD Group A minus YOPD Group B Group B YOPD Group B minus YOPD Group A&B All YOPD Group A&B minus YOPD
=
% of dose excreted
in the urine.
as metabolite (4-OH DBQ) Patients were classified as poor or extensive metabolisers according to the criteria proposed by Evans et al. (23). Poor metabolisers were defined by a M R > 12.6 (log,,MR> 1.1) Results
Nine of the 54 (16.7%) patients either untreated or not taking drugs known to interfere with DBQ metabolism (group A) were poor metabolisers, including 1 of 16 (6.3 %)with YOPD (Table 2). This compares with 5 of 26 (19.2%) patients on drugs known to interfere with DBQ metabolism (group B), including 3 of 10 (30%) with YOPD. Among the controls, 13 of 143 (9.1%) were poor metabolisers. These percentages of poor metabolisers were similar across the 3 groups (A,B, and controls) (chi-square = 3.52, p = 0.17). There was no significant excess of poor metabolisers in the YOPD patients in group A or group B compared with controls (chi-square = 4.8, p = 0.09). values Mean log,,MR (SD)
No. (%)with log,oMR> 1.1
No. of subjects
Age (range) (SD) years
143 54 16
23.7 (18-41) (4.6) 54.1 (35-74) (10.0) 43.5 (35-561 (5.8)
-0.22 (0.87) 0.11 (1.20)” -0.14 (0.89Ib
13 (9.1%) 9(16.7%) 1(6.3%)
38
58.9 (43-741 (8.4)
0.22 (1.32)”
8 (14.8%)
26 10
58.3 (35-84) (13.2) 45.7 (40-55) (6.6)
0.34 (1.30Id 0.57 (1.30Ie
5 (19.2%) 3 130.0%)
16
66.9 (54-84) (8.5)
0.19 (1.21V
2 (12.5%)
80 26 54
55.7 (35-84) (1 1.51 44.0 (35-55) (5.7) 61.3 (43-84) (9.1)
0.19 (1.2018 0.13 ( l . l O ) d 0.20 (1.30)”
14 (17.5%) 4 ( 15.4%) 10(18.5%)
p=0.05 compared with controls. p1.1
> 12.0 1-12.6 >1
> 1.08
O
