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Effects of lithium on blood-brain barrier transport of the neurotransmitter precursors choline, tyrosine and tryptophan
604
Brain Research, 193 (I 980) 604 607 ~'~ Elsevier/North-Holland Biomedical Press
Effects of lithium on blood-brain barrier transport of the neurotransmitter precursors choline, tyrosine and tryptophan
BARBARA E. EHRLICH, JARED M. DIAMOND, LEON D. BRAUN, EAIN M. CORNFORD and WILLIAM H. OLDENDORF Department of Physiology, UCLA School of Medicine, Los Angeles, Calif. 90024 and (L.D.B., E.M.C. and W.H.O.) Department of Neurology and (W.H.O.) Department of Psychiatry, UCLA School ~f Medicine and V.A. Brentwood Medical Center, Los Angeles, Calif. 90073 (U.S.A.)
(Accepted March 6tb, 1980) Key words: lithium -- blood brain barrier - - choline - - tyrosine - - tryptophan
Interest in effects of low (
605 depends on blood flow and thus defines the brain volume which the test substance could have entered. BUIs are calculated from the ratio12: [-tissue 14C/tissue 3H BUI = [
mix 14C/mix aH
tissue n3rnln/tissue a H ]
ml-X llamIn/mix
~
× 100
Because the BUI varies with the reference substance utilized and because we used two different reference compounds, brain extractions (E °/oo) were also calculated to normalize the data: E ~ = 0.85 × BUI for water reference, 0.045 × BUI for thiourea referencelL Four conditions were compared: (a) chronic Li + treatment; (b) chronic Na ÷ treatment; (c) 'acute Li ÷ treatment' (i.v. injection of 0.75 rnl isotonic LiC1 15 min before decapitation); and (d) 'acute Na + treatment' (i.v. injection of 0.75 ml isotonic NaC1 15 min before decapitation). After decapitation blood samples were obtained to measure plasma concentrations of Li + by a Varian atomic absorption spectrophotometer 4, and Na + and K + by a flame photometer, IL model 143. Student's t-test was used to determine statistical significance of the results. All radiochemicals were obtained from New England Nuclear (Boston, Mass.), and were of the highest spec. act. available (tyrosine: 522 mCi/mmol; tryptophan: 49.4 mCi/mmol; choline: 69.5 Ci/mmol). Average plasma [Li ÷] was 0.92 mM (range 0.67-1.2 mM) for chronic Li+-treated rats, 0.65 mM (range 0.57-0.75 mM) for acute Li+-treated rats at time of decapitation. Plasma Na-- or K ÷ levels did not differ among the 4 groups of rats. Differences in body weight between Li+-treated and Na+-treated groups were not statistically significant before (230 4- 20 vs 233 4- 16 g) or after (1280 4- 34 vs 299 4- 25 g) two weeks of treatment. BUIs for tyrosine and tryptophan were not affected by chronic Li + administration nor by the acute Li + load (Table 1). Values obtained for all 4 conditions were comparable to previously published values 11. Choline uptake across the BBB was reduced 20 ~ by chronic Li + treatment: BUI dropped from 153 4- 16 (n -- 6) in control rats to 125 4- 10 (n - 6) in chronic Li +treated rats (P < 0.005). Again, control values for brain extraction of choline agree with previously reported valuesL This result parallels Li+'s effect in the erythrocyte (RBC) where an irreversible reduction in choline transport of up to 9 0 ~ was measured 8. Na + or Li + injection 15 rain prior to decapitation did not reduce the choline E from control values (Table I). BUIs in acutely treated rats are lower than in chronically treated rats because different reference substances were used. Tyrosine and tryptophan, the precursors for the neurotransmitter dopamine and serotonin respectively, are both transported into brain by the same carrier mechanism 11, which exhibits properties of the L-system for neutral amino acids 1. Since the Lsystem is independent of Na ÷ (see ref. 1), and since many biological effects of Li + involve Na + (or K+)-dependent processes, the lack of effect of acute or chronic Li ÷ on the BU! of tyrosine and tryptophan is understandable.
606 TA BLE 1 Effeets (~['chronic and acute lithium treatment on brain uptake o f tyrosine, tryptophan, and choline in rats
BU 1 is the brain uptake index; E ~ is the normalized per cent brain extraction (see text for details); high BU! or E ~ means large transport from blood to brain across the blood-brain barrier. Concentration of test compound injected is value in parentheses. Values are the mean and S. D. Only the asterisked value was significantly different (P < 0.005) from control values (chronic Na ~).
Tyrosine (4 I~M) Tryptophan (30/~M) Choline (0.2/~M)
BUI E% n BUI E% n BUI E% n
Chronic Na ~
Chronic Li ~
Acute Na ~
Acute Li'
42 i 50 3 30 ~ 36 6 153 z 6.9 ~ 6
41 48 3 36 43 3 124 5.6 6
43 ! 4 51 3 36 ~ 2 42 3 9.2 ~1 2.6 7.8 i 2.2 3
44 L 1 52 3 35_-t~ 5 41 3 8.7 ..~ 1.0 7.4 ± 0.9 3
3 6 16 0.07
t 4 3:5 5 10' + 0.5
in contrast, chronic Li ~ does reduce BBB uptake of choline, the precursor of acetylcholine. Similarly, Li + alters choline t r a n s p o r t in h u m a n R B C 7,8, rat synaptosomes 6, and frog a r a c h n o i d (Ehrlich, Wright a n d D i a m o n d , in preparation). I n RBC as in BBB, there is a greater effect of chronic Li + t r e a t m e n t for several weeks than of acute Li + ; indeed we could n o t detect any effect of acute Li ÷ on BBB choline uptake. Using longer (5 vs 2 weeks) chronic Li + t r e a t m e n t a n d m u c h larger doses of Li* (50 m m o l Li+/kg diet) t h a n we did, McCall et al 9. measured a larger (57 vs 20 ~ ) reduction in choline BUI. These a u t h o r s also reported higher brain choline levels after a d m i n i s t r a t i o n of both choline a n d Li ~ to rats t h a n after a d m i n i s t r a t i o n of either a l o n O 0. These a n d our findings, together with previous evidence for a role of neurotransmitters in the etiology of manic-depressive illness, suggest that one mechanism of Li F therapy could involve effect on brain choline. This work was supported by N I H G r a n t s 14772 a n d M H 31272 and by the Veterans A d m i n i s t r a t i o n . B.E.E. is a Bank of A m e r i c a - G i a n n i n i F o u n d a t i o n Scholar.
1 Christensen, H. N., Biological Transport, W. A. Benjamin, Reading, Mass., 1975. 2 Cornford, E. M., Braun, L. D. and Oldendorf, W. H., Carrier mediated blood-brain barrier transport of choline and certain choline analogs, J. Neurochem., 30 (1978) 299-308. 3 Davis, J. M. and Fann, W. E., Lithium, Ann. Rev. PharmacoL, 1l (1971) 285-302. 4 Ehrlich, B. E. and Diamond, J. M., An ultramicro method for analysis of lithium and other biologically important cations, Biochim. biophys. Acta ( A m s t . ) , 543 (1978) 264-268. 5 Ehrlich, B. E. and Diamond, J. M., Lithium, membranes, and manic-depressive illness, J. membrane Biol., in press. 6 Jope, R. S., Effects of lithium treatment in vitro and in vivo on acetylcholine metabolism in rat brain, J. Neurochem., 33 (1979) 487-495. 7 Jope, R. S., Jenden, D. J., Ehrlich, B. E. and Diamond, J. M., Choline accumulates in erythrocytes during lithium therapy, New Engl. J. Med., 299 (1978) 833. 8 Lee, G., Lingsch, C., Lyte, P. T. and Martin, K.., Lithium treatment strongly inhibits choline transport in human erythrocytes, Brit. J. olin. Pharmacol., 1 (1974) 365-370.
607 9 McCall, A. L., Millington, W. R., Botticelli, L. J. and Wurtman, R. J., Lithium treatment effects on choline transport at the blood-brain harrier, Neurosci. Abstr. 1978. 10 Millington, W. R., McCall, A. L. and Wurtman, R. J., Lithium and brain choline levels, New Eng. J. Med., 300 (1979) 196-197. 11 Oldendorf, W. H., Brain uptake of radiolabeled amino acids, amines, and hexoses after arterial injection, Arner. J. Physiol., 221 (1971) 1629-1639. 12 Oldendorf, W. H. and Braun, L. D., [aH]Tryptamine and [all]water as diffusible internal standards for measuring brain extraction of radio-labeled substances following carotid injection, Brain Research, 113 (1976) 219.
Brain Research, 193 (I 980) 604 607 ~'~ Elsevier/North-Holland Biomedical Press
Effects of lithium on blood-brain barrier transport of the neurotransmitter precursors choline, tyrosine and tryptophan
BARBARA E. EHRLICH, JARED M. DIAMOND, LEON D. BRAUN, EAIN M. CORNFORD and WILLIAM H. OLDENDORF Department of Physiology, UCLA School of Medicine, Los Angeles, Calif. 90024 and (L.D.B., E.M.C. and W.H.O.) Department of Neurology and (W.H.O.) Department of Psychiatry, UCLA School ~f Medicine and V.A. Brentwood Medical Center, Los Angeles, Calif. 90073 (U.S.A.)
(Accepted March 6tb, 1980) Key words: lithium -- blood brain barrier - - choline - - tyrosine - - tryptophan
Interest in effects of low (
605 depends on blood flow and thus defines the brain volume which the test substance could have entered. BUIs are calculated from the ratio12: [-tissue 14C/tissue 3H BUI = [
mix 14C/mix aH
tissue n3rnln/tissue a H ]
ml-X llamIn/mix
~
× 100
Because the BUI varies with the reference substance utilized and because we used two different reference compounds, brain extractions (E °/oo) were also calculated to normalize the data: E ~ = 0.85 × BUI for water reference, 0.045 × BUI for thiourea referencelL Four conditions were compared: (a) chronic Li + treatment; (b) chronic Na ÷ treatment; (c) 'acute Li ÷ treatment' (i.v. injection of 0.75 rnl isotonic LiC1 15 min before decapitation); and (d) 'acute Na + treatment' (i.v. injection of 0.75 ml isotonic NaC1 15 min before decapitation). After decapitation blood samples were obtained to measure plasma concentrations of Li + by a Varian atomic absorption spectrophotometer 4, and Na + and K + by a flame photometer, IL model 143. Student's t-test was used to determine statistical significance of the results. All radiochemicals were obtained from New England Nuclear (Boston, Mass.), and were of the highest spec. act. available (tyrosine: 522 mCi/mmol; tryptophan: 49.4 mCi/mmol; choline: 69.5 Ci/mmol). Average plasma [Li ÷] was 0.92 mM (range 0.67-1.2 mM) for chronic Li+-treated rats, 0.65 mM (range 0.57-0.75 mM) for acute Li+-treated rats at time of decapitation. Plasma Na-- or K ÷ levels did not differ among the 4 groups of rats. Differences in body weight between Li+-treated and Na+-treated groups were not statistically significant before (230 4- 20 vs 233 4- 16 g) or after (1280 4- 34 vs 299 4- 25 g) two weeks of treatment. BUIs for tyrosine and tryptophan were not affected by chronic Li + administration nor by the acute Li + load (Table 1). Values obtained for all 4 conditions were comparable to previously published values 11. Choline uptake across the BBB was reduced 20 ~ by chronic Li + treatment: BUI dropped from 153 4- 16 (n -- 6) in control rats to 125 4- 10 (n - 6) in chronic Li +treated rats (P < 0.005). Again, control values for brain extraction of choline agree with previously reported valuesL This result parallels Li+'s effect in the erythrocyte (RBC) where an irreversible reduction in choline transport of up to 9 0 ~ was measured 8. Na + or Li + injection 15 rain prior to decapitation did not reduce the choline E from control values (Table I). BUIs in acutely treated rats are lower than in chronically treated rats because different reference substances were used. Tyrosine and tryptophan, the precursors for the neurotransmitter dopamine and serotonin respectively, are both transported into brain by the same carrier mechanism 11, which exhibits properties of the L-system for neutral amino acids 1. Since the Lsystem is independent of Na ÷ (see ref. 1), and since many biological effects of Li + involve Na + (or K+)-dependent processes, the lack of effect of acute or chronic Li ÷ on the BU! of tyrosine and tryptophan is understandable.
606 TA BLE 1 Effeets (~['chronic and acute lithium treatment on brain uptake o f tyrosine, tryptophan, and choline in rats
BU 1 is the brain uptake index; E ~ is the normalized per cent brain extraction (see text for details); high BU! or E ~ means large transport from blood to brain across the blood-brain barrier. Concentration of test compound injected is value in parentheses. Values are the mean and S. D. Only the asterisked value was significantly different (P < 0.005) from control values (chronic Na ~).
Tyrosine (4 I~M) Tryptophan (30/~M) Choline (0.2/~M)
BUI E% n BUI E% n BUI E% n
Chronic Na ~
Chronic Li ~
Acute Na ~
Acute Li'
42 i 50 3 30 ~ 36 6 153 z 6.9 ~ 6
41 48 3 36 43 3 124 5.6 6
43 ! 4 51 3 36 ~ 2 42 3 9.2 ~1 2.6 7.8 i 2.2 3
44 L 1 52 3 35_-t~ 5 41 3 8.7 ..~ 1.0 7.4 ± 0.9 3
3 6 16 0.07
t 4 3:5 5 10' + 0.5
in contrast, chronic Li ~ does reduce BBB uptake of choline, the precursor of acetylcholine. Similarly, Li + alters choline t r a n s p o r t in h u m a n R B C 7,8, rat synaptosomes 6, and frog a r a c h n o i d (Ehrlich, Wright a n d D i a m o n d , in preparation). I n RBC as in BBB, there is a greater effect of chronic Li + t r e a t m e n t for several weeks than of acute Li + ; indeed we could n o t detect any effect of acute Li ÷ on BBB choline uptake. Using longer (5 vs 2 weeks) chronic Li + t r e a t m e n t a n d m u c h larger doses of Li* (50 m m o l Li+/kg diet) t h a n we did, McCall et al 9. measured a larger (57 vs 20 ~ ) reduction in choline BUI. These a u t h o r s also reported higher brain choline levels after a d m i n i s t r a t i o n of both choline a n d Li ~ to rats t h a n after a d m i n i s t r a t i o n of either a l o n O 0. These a n d our findings, together with previous evidence for a role of neurotransmitters in the etiology of manic-depressive illness, suggest that one mechanism of Li F therapy could involve effect on brain choline. This work was supported by N I H G r a n t s 14772 a n d M H 31272 and by the Veterans A d m i n i s t r a t i o n . B.E.E. is a Bank of A m e r i c a - G i a n n i n i F o u n d a t i o n Scholar.
1 Christensen, H. N., Biological Transport, W. A. Benjamin, Reading, Mass., 1975. 2 Cornford, E. M., Braun, L. D. and Oldendorf, W. H., Carrier mediated blood-brain barrier transport of choline and certain choline analogs, J. Neurochem., 30 (1978) 299-308. 3 Davis, J. M. and Fann, W. E., Lithium, Ann. Rev. PharmacoL, 1l (1971) 285-302. 4 Ehrlich, B. E. and Diamond, J. M., An ultramicro method for analysis of lithium and other biologically important cations, Biochim. biophys. Acta ( A m s t . ) , 543 (1978) 264-268. 5 Ehrlich, B. E. and Diamond, J. M., Lithium, membranes, and manic-depressive illness, J. membrane Biol., in press. 6 Jope, R. S., Effects of lithium treatment in vitro and in vivo on acetylcholine metabolism in rat brain, J. Neurochem., 33 (1979) 487-495. 7 Jope, R. S., Jenden, D. J., Ehrlich, B. E. and Diamond, J. M., Choline accumulates in erythrocytes during lithium therapy, New Engl. J. Med., 299 (1978) 833. 8 Lee, G., Lingsch, C., Lyte, P. T. and Martin, K.., Lithium treatment strongly inhibits choline transport in human erythrocytes, Brit. J. olin. Pharmacol., 1 (1974) 365-370.
607 9 McCall, A. L., Millington, W. R., Botticelli, L. J. and Wurtman, R. J., Lithium treatment effects on choline transport at the blood-brain harrier, Neurosci. Abstr. 1978. 10 Millington, W. R., McCall, A. L. and Wurtman, R. J., Lithium and brain choline levels, New Eng. J. Med., 300 (1979) 196-197. 11 Oldendorf, W. H., Brain uptake of radiolabeled amino acids, amines, and hexoses after arterial injection, Arner. J. Physiol., 221 (1971) 1629-1639. 12 Oldendorf, W. H. and Braun, L. D., [aH]Tryptamine and [all]water as diffusible internal standards for measuring brain extraction of radio-labeled substances following carotid injection, Brain Research, 113 (1976) 219.