Clinlca Chimica dcta, 205 (1992) 145-147 © 1992 Elsevier Science Publishers B.V. All rights reserved 0009-8981/92/$05.00
145
CCA 05197
Letter to the Editor
More on monoamine oxidase activity in whole blood (Received 17 Octo~r 1991; accepted 23 October 1991)
Dear Editor, In the human brain, monoamine oxidase (MAd; amine oxygen oxidoreduetase (deaminating), EC 1.4.3.4) catalyzes the oxidative deamination of nourotransmitters, including serotonin and dopamine. The two M A d forms A and B, show different substrate and inhibitor specificities (for review see Ref. 1). It has been shown that human platelet MAd (P-MAd) activity is exclusively of the B-type. Although serotonin is a poor substrate for P-MAd, its activity has been used for many years as a reflection of the size of serotoninergic systems in the brain. It has been suggested that low P-MAd activity may predispose individuals to psychiatric disorders [2]. Recently, P-MAd activity has also been measured in neuro-degenerative disorders e.g. Parkinson's disease [3], in which a deficient nigrostriatal dopamine system exists. MAO-B activity is usually measured in platelets prepared from platelet rich plasma (PRP), by means of centrifugation. Results in patients may be discrepant, however, although similar methods have been used. The discrepancies can probably be explained to an extent by critical steps in the isolation procedure for platelets. A high density platelet fraction (containing a higher MAd activity) may be missed, when blood is centrifuged to prepare PRP. Damage to the relatively fragile platelets has been reported during centrifugation of PRP. Finally, plasma protein may be absorbed on the platelet pellet, decreasing the M A d results, if these are expressed as activity per mg platelet protein [4]. van Kempen et al. [5] described a manual spectrofluorimetric assay of whole blood (WB) MAd, thus avoiding the above-mentioned problems, with kynuramine as a substrate. These authors showed, that WB-MAO is due almost exclusively (>95%) to P-MAd activity. For various reasons we considered it worth scrutinizing this assay. Venous morning EDTA-blood (ethylenediaminetetra-acetic acid) samples were collected from apparently healthy volunteers and from patients in the neurological department. Within 1 h after drawing the blood, platelets were counted on a Coulter Counter "1"660.We measured [5] the M A d activity (in units/10E9 platelets) in fresh samples within 3 h. The amount of 4-hydroxyquinoline, formed by the action of
146
MAO, was quantitated by means o f a Kontron SFM 23 spectrofluorimeter. One unit of MAO activity is defined as #tool 4-hydroxyquinoline released per h (37°C). The imprecision study of the method was done with fresh blood samples and with specimens frozen at -70°C. The within-batch C.V. percentages were better than 2.6 (range 193-389 units/10E9 platelets of MAO). The between-day imprecision was performed with multiple portions of two blood samples, which were frozen at -70°C. The C.V. percentages were 4.8 and 5.2 at 112 and 202 units/10E9 platelets, respectively, as determined on 20 days within 3 months. The imprecision, determined for duplicate measurements for automatic platelet counts, was C.V. = 1.9%. Subsequently, an experiment was done to investigate changes in MAO activity, if blood specimens were stored at -70°C. Individual portions of blood, sampled from randomly selected patients and volunteers, were frozen immediately at -70°C. A decrease (6%, range 0-16%) in the mean MAO activity was observed in 28 samples, stored for 1-3 h. This decrease was greater (9%, range 1-19%), when samples (n = 53) were stored for 2-4 months. Although these figures were statistically not significant, fresh material is to be preferred, especially in a longitudinal study. In addition, we obtained an estimate of normal variations in WB-MAO activity over time. Blood from seven healthy volunteers was drawn on 6 days, with an inter-
>
~'400 •
145
CCA 05197
Letter to the Editor
More on monoamine oxidase activity in whole blood (Received 17 Octo~r 1991; accepted 23 October 1991)
Dear Editor, In the human brain, monoamine oxidase (MAd; amine oxygen oxidoreduetase (deaminating), EC 1.4.3.4) catalyzes the oxidative deamination of nourotransmitters, including serotonin and dopamine. The two M A d forms A and B, show different substrate and inhibitor specificities (for review see Ref. 1). It has been shown that human platelet MAd (P-MAd) activity is exclusively of the B-type. Although serotonin is a poor substrate for P-MAd, its activity has been used for many years as a reflection of the size of serotoninergic systems in the brain. It has been suggested that low P-MAd activity may predispose individuals to psychiatric disorders [2]. Recently, P-MAd activity has also been measured in neuro-degenerative disorders e.g. Parkinson's disease [3], in which a deficient nigrostriatal dopamine system exists. MAO-B activity is usually measured in platelets prepared from platelet rich plasma (PRP), by means of centrifugation. Results in patients may be discrepant, however, although similar methods have been used. The discrepancies can probably be explained to an extent by critical steps in the isolation procedure for platelets. A high density platelet fraction (containing a higher MAd activity) may be missed, when blood is centrifuged to prepare PRP. Damage to the relatively fragile platelets has been reported during centrifugation of PRP. Finally, plasma protein may be absorbed on the platelet pellet, decreasing the M A d results, if these are expressed as activity per mg platelet protein [4]. van Kempen et al. [5] described a manual spectrofluorimetric assay of whole blood (WB) MAd, thus avoiding the above-mentioned problems, with kynuramine as a substrate. These authors showed, that WB-MAO is due almost exclusively (>95%) to P-MAd activity. For various reasons we considered it worth scrutinizing this assay. Venous morning EDTA-blood (ethylenediaminetetra-acetic acid) samples were collected from apparently healthy volunteers and from patients in the neurological department. Within 1 h after drawing the blood, platelets were counted on a Coulter Counter "1"660.We measured [5] the M A d activity (in units/10E9 platelets) in fresh samples within 3 h. The amount of 4-hydroxyquinoline, formed by the action of
146
MAO, was quantitated by means o f a Kontron SFM 23 spectrofluorimeter. One unit of MAO activity is defined as #tool 4-hydroxyquinoline released per h (37°C). The imprecision study of the method was done with fresh blood samples and with specimens frozen at -70°C. The within-batch C.V. percentages were better than 2.6 (range 193-389 units/10E9 platelets of MAO). The between-day imprecision was performed with multiple portions of two blood samples, which were frozen at -70°C. The C.V. percentages were 4.8 and 5.2 at 112 and 202 units/10E9 platelets, respectively, as determined on 20 days within 3 months. The imprecision, determined for duplicate measurements for automatic platelet counts, was C.V. = 1.9%. Subsequently, an experiment was done to investigate changes in MAO activity, if blood specimens were stored at -70°C. Individual portions of blood, sampled from randomly selected patients and volunteers, were frozen immediately at -70°C. A decrease (6%, range 0-16%) in the mean MAO activity was observed in 28 samples, stored for 1-3 h. This decrease was greater (9%, range 1-19%), when samples (n = 53) were stored for 2-4 months. Although these figures were statistically not significant, fresh material is to be preferred, especially in a longitudinal study. In addition, we obtained an estimate of normal variations in WB-MAO activity over time. Blood from seven healthy volunteers was drawn on 6 days, with an inter-
>
~'400 •
