Decrease in plasma tryptophan after a tryptophan-free amino acid solution. A comparison between cirrhotic and control subjects

Pergamon Press

Life Sciences, Vol. 42, pp. 1551-1556 Printed in the U.S.A.

DECREASE

Egidio Daniele (4)

IN PLASMA

A. Moja Castoldi

TRYPTOPHAN AFTER TRYPTOPHAN-FREE MIXTURES IN MAN

AMINO ACID

(1), David M. Stoff (2), Gian Luigi Gessa (3), (4), Roberto Assereto (4) and Odoardo Tofanetti

(1) Chair of Psychobiology, Medical School, University of Modena, 41100 Modena, Italy: (2) Department of Psychiatry, Medical College Pennsylvania, Philadelphia, Pa., of USA: (3) Department of Neurosciences, University of Cagliari, Italy: (4) Research Department, Boehringer Biochemia Robin, Milan, Italy. (Receivedin final form February 22, 1988) Summary

healthy subjects, fasting 12 hours, ingested increasing amounts of a mixture containing a fixed proportion of seven essential amino acids (L-isoleucine 11.5%, L-leucine 18.0%, L-methionine L-lysine 13.1%, 18.08, L-phenylalanine 18.0%, L-valine 13.1%) L-threonine 8.2%, and lacking tryptophan. The diets produced a rapid fall in plasma tryptophan which was proportional to the total amount of the amino acids the highest dose administered (36.6 g) ingested. Following plasma tryptophan fell to a minimum of about 35% the initial remained markedly level and reduced at 6 hours after treatment. The mechanism of this decrease and its potential clinical relevance are discussed. Male

studies have shown that the acute administration of Previous an amino acid mixture containing all the essential amino acids, except causes the rapid fall in plasma free and total tryptophan, tryptophan in rats (1). This effect was associated with a parallel depletion in brain tryptophan, serotonin 5-hydroxyindole and acid acetic content Therefore, it has been suggested that (2). tryptophan-free amino acid mixtures might represent a simple, specific and non-toxic method to deplete brain serotonin, and a too1 for clarifying the physiological role of this amine possible in the CNS (2). that the acute administration of Accordingly, it was shown devoid of tryptophan resulted in enhanced amino acid mixtures sexual activity (3) and decreased REM sleep in rats (4). In humans, such diets increased stage 4 sleep (5) and produced a rapid lowering of mood (6). In these studies, mixtures of very composition were used. For example, Moja et amino acid different volunteers 12.2 g of a mixture to healthy al. (5) administered whereas Young et al. (6) administered containing 7 amino acids, 100 g of a mixture containing 15 amino acids. 0024-3205188$3.00 + .OO Copyright (c) 1988 Pergamon Press plc

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work the present we have administered In to healthy volunteers increasing amounts of a mixture containing a fixed proportion of 7 essential amino acids but devoid of tryptophan. that the decrease in total plasma tryptophan is The results show dose-related to the total amount of amino acids ingested. Materials

and Methods

The study involved Subjects. 5 male who had no medical problems, no dietary and -were freepsychiatric disorders partecipating in this investigation, informed consent form.

subjects (19-51 years old) restriction, no historv of of any medications. Before all the subjects signed an

Fasting and four amino acid mixtures Experimental treatments. treatments, According to a previous were used as experimental frota .our -Laboratory report (5), a first tryptophan-free-mixture (lT-) contained: L-isoleucine, 1.4 g: L-leucine, 2.2 g: L-lysine, 2.2 g: L-phenylalanine, 2.2 g; L-threonine, 1.6 g; L-methionine, for a total of 12.2 g. A second 1.0 g and L-valine, 1.6 g, contained a double amount of the mixture tryptophan-free (2T-) amino acids (L-isoleucine, 2.8 g: L-leucine, 4.4 g; L-lysine, same 4.4 g; L-phenylalanine, 4.4 g; L-threonine, 3.2 g; L-methionine, for a total of 24.4 g. A third 2.0 g and L-valine, 3.2 g) contained a triple amount of the mixture tryptophan-free (3T-) amino acids (L-isoleucine, 4.2 g: L-leucine, 6.6 g; L-lysine, same 6.6 g; L-threonine, 6.6 g; L-phenylalanine, 4.8 g; L-methionine for a total of 36.6 g. The fourth 3.0 g and L-valine, 4.8 9) (lT+) contained the same amount of amino acids as lT- plus mixture for a total of 12.7 g. The composition of the 0.5 g L-tryptophan fourth mixture was selected according to the daily ideal intake of proposed by Rose (7) for adult humans. In essential amino acids all the mixtures, amino acids were mixed with 25 g sucrose, 0.2 g monopalmitate, 0.6 g citric acid, 0.4 g natural flavors on sucrose were invited to and 200 mL water. The subjects maltodextrine suspension in as short a time as possible because of swallow the impalatable taste. No serious intestinal distress the somewhat occurred. received subject all the five experimental Procedures. Each treatments (Fasting, lT-, 2T-, 3T-, lT+) in different days. Experimental units were randomly assigned to the treatments with treatment. During the interval between each at least a 7-day experimental the subjects arrived at the Laboratory at 9:00 days, a.m. after an overnight fast. A blood sample was taken for measurement of total plasma tryptophan (base-line levels) and then acid mixtures were ingested (during the fast-day, the amino received just 200 mL plain water). Blood samples were subjects after the collected at 20, 60, 120, 210 and 360 minutes of the mixtures: in fasting subjects, blood samples administration collected at 20, 60, 210 and 360 minutes after ingestion of were water. Plasma tryptophan measurement. total plasma tryptophan withdrawal, Krstulovic et al. (8). Design assuming

and the

Immediately was measured

after each blood by HPLC method of

analysis. A randomized block design was used, data repeated measures subjects as blocks. A two-way

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Plasma TryptophanDecrease

was performed taking into account the block analysis of variance effect. time-point, multiple comparisons were performed At each using the method of Scheffe' (9). Results Concentrations of total plasma treatments are presented in Table 1.

TABLE -Changes in total plasma administration of different amino acid mixture.

tryptophan

after different

1

tryptophan amounts of

_______________________________________________.__ Minutes after treatment 0 20 60 120 Treatment

induced by the a tryptophan-free ______ 210

13.6k0.8 Fasting 14.721.0 14.721.1 15.020.8 lT+ 15.7fl.l 18.821.6 26.622.0 21.6k1.3 16.3+1.5 lT16.020.6 14.820.3 12.710.6 11.4k0.8 11.7k0.9 2T17.6k1.3 16.021.3 14.8+1.0 10.6+0.7 8.7k0.5 3T17.4k0.9 16.3k0.9 14.121.4 10.221.9 5.820.3 __________________________________________.____________

360 13.2k0.6 15.1k0.9 13.7k0.8 11.1+1.0 7.4k0.5

fasting Subjects 12 hours received the amino acid mixtures orally at time 0. Each value is the mean (mcq/mL)+s.e. of five subjects. lT- = amino acid mixture devoid of tryptophan (see Methods): 3T- = the same mixture as lT- but twice and thrice 2T- and its amount, respectively: lT+ = the same composition of lT- but containing tryptophan. analysis indicated Statistical highly significant difference among treatments (~=21.66; ::f.=4,16; p=0.0001) and among times of observation (F=87.27; d.f.=4,64: p=0.0001). There was also a significant time x treatment interaction (F=22.03; that means that treatments did non generate d.f.=16,64; p=0.0001) parallel slopes of time courses. Multiple comparisons gave the following results: I) no significant difference was observed across mean basal tryptophan levels at time 0 (immediately before treatment): II) 20 and 60 min after lT+ mixture induced a significant (pX0.05) treatments, the increase of plasma tryptophan with respect to fasting and Tmixtures: levels after the T- mixtures and fast were not significantly different: 210 min, the 3T- and the 2TIII) at mixtures induced a decrease of plasma tryptophan that was significantly different as compared with each other treatment: the decrease after the 3T- was also significantly more marked than same after the 2T-; at the time, there was no significant difference between fast and the lT+ but there was a significant difference between the lT+ and the lT-; IV) at 360 min, there was a significant difference between the 3T- and each other treatment alid between the 2T- and the lT-.

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dose-response effect The apparent from Figure 1, in which

of the T- mixtures is immediately the data of Table 1 are plotted.

Inspection of this Figure suggests that the decrease of plasma tryptophan began in the first hour after the administration decrease was maximum at 120 min after the lTof the diets. The and at 210 min after the 2T- and the 3T- mixtures. 6 hours diet after administration of the 2Tand the 3T- mixtures, the the levels of plasma tryptophan were still markedly low as compared with basal values or after fast. increase of plasma tryptophan The the firs t hour and disappeared about compared wiith basal values.

after the lT+ diet began in completely after 210 min as

30 i-t fasting -lT+ -1 T+.2T‘-3T-

25

20

15

10

5

I 0

I 60

I 120

I 180

I 240

I 300

I 360

Minutes Figure 1. Time course of changes in total plasma tryptophan concentrations induced by the ingestion of an amino acid mixture containing tryptophan (lT+) and increasing amounts of tryptophan free mixtures (lT-, 2T-, 3T-). The points values of five subjects as reported in represent the mean Table 1. Discussion administration of the amino acid mixture expected, the As increase of total tryptophan caused an plasma containing reached a maximal concentration after 60 minutes. tryptophan that This increase expected because the diet provided was new elicited insulin secretion that has been reported tryptophan and

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to

elevate

blood

tryptophan

Plasma Tryptophan Decrease

1555

(10).

and to basal level, our results Compared to fast levels in humans the administration of tryptophan-free showed also that mixtures decreased total plasma tryptophan following a amino acid the decrease being proportional to the total dose-response curve, acids. In particular, the smallest administered amino amount of (12.2 g) and the highest dose used (36.6 g) induced a maximum 29% and 66% respectively of pre-treatment values. In decrease of young et al. (6) showed a decline in agreement with these data, plasma tryptophan of 76% after a 100 g tryptophan-free diet. total These authors reported the value of plasma tryptophan only after 5 preliminary this as the hours stating that evidence suggested moment of minimum level of plasma tryptophan after the ingestion our data show that the maximum decline of the 100 g diet. Because reached in plasma tryptophan is 120 minutes after the administration of the 12.2 g diet and 210 minutes after the administration of the 36.6 g diet, it is possible that the time to reach the minimum level is proportional to the amount necessary used. inhibitor that the protein synthesis It has been shown decrease of blood tryptophan after a cicloheximide blocks the tryptophan-free diet (11). On the basis of these data, Gessa et that decline in blood tryptophan 11) hypothesized the al. (1, may be due to removal of tryptophan-free diet the after a tryptophan by the liver to allow protein synthesis from endogenous amino acid supplement. data are consistent with this the Our hypothesis because, on its basis, one would expect a dose-response endogenous tryptophan incorporation of into new proteins after increasing doses of essential amino acids. This appears to be true even if evidence that protein synthesis in liver is there is decreased after a diet. Both Wunner tryptophan-free et al. (12) and Sidransky et al. (13) have in fact reported that incorporation of amino acids by microsomal preparations from the liver of fasted then rodents previously acutely fed a tryptophan-devoid diet is and that this is associated a low rate of low with polysome formation. administration of thryptophan has been studied for its The effects on a variety of behaviors including sleep, depression, pain, aggression and appetite reduction (see review in 14). The rationale for these behavioral studies was the demonstration that tryptophan intake increased blood tryptophan and, therefore, brain tryptophan serotonin levels in laboratory animals (see review and in report 15). The that the acute administration of a mixture produced in tryptophan-free rats a decrease of serum and of brain tryptophan tryptophan and serotonin (2) made it possible to behavioral changes related to a specific and study non-toxic technique to reduce brain serotonin (2, 14). The acute administration of devoid of mixtures tryptophan was shown to induce modifications in sexual bT;;yior (3, 16), sleep (4, 5), mood behavioLzi 17) and food intake . In all these studies, modifications were interpreted as caused by the reduction of serotoninergic activity due to decreased the availability of blood tryptophan and, therefore, brain tryptophan. In the present paper we showed that increasing amount of tryptophan-free mixtures induced a dose-response decrease of blood tryptophan. These data might imply the possibility to modulate the

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behavioral changes reported after according to dose-response curves.

Vol. 42, No. 16, 1988

tryptophan-free

mixtures

Acknowledgements We thank Dr. A. Petroccione

for help

in statistical

analysis.

References 1.

2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

15.

16. 17.

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