Plasma Free Tryptophan Levels Research Articles

Abstract 1168: Impact of some common organics on cellular glycolysis and the differential survival of lung fibroblast and lung carcinoma cell lines

Abstract Tumor growth and abnormal cell survival were shown to be associated with a number of cellular metabolic abnormalities revealed by impaired oral glucose tolerance, depressed lipoprotein lipase activity leading to hypertriglyceridemia, and changes in amino acid profile as evidenced by increased plasma free tryptophan levels in patients with breast, lung, colon, stomach, and other cancers from various origins. The above findings seem to relate to or indicate a shift to non-oxidative metabolic pathways in cancer. In contrast to normal cells, cancer cells may lose the ability to utilize aerobic respiration due to either defective mitochondria or hypoxia within the tumor microenvironments. Glucose was shown to be the major energy source in cancer cells where it utilizes aerobic /anaerobic glycolysis with the resultant lactic acid formation. The role of energetic modulations and use of glycolytic inhibitors on cancer/normal cell survival is not clearly established in the literature. Therefore, the purpose of this study was to evaluate six potential glycolytic inhibitors namely, sodium ascorbate, oxalic acid, oxaloacetic acid, sodium citrate, fructose diphosphate (FDP) and sodium bicarbonate at mM concentrations on growing A549 (lung cancer) and MRC-5 (normal; human lung fibroblast) cell lines with the objective of determining their influence on cell survival. Exposed and non-exposed cells were tested with phase-contrast micro-scanning, survival/death and metabolic activity trends through MTT-assays, as well as death end-point determinations by testing re-growth on complete media and T4 cellometer counts. Results showed that oxalic acid and oxaloacetic acid both influenced the pH of the medium and resulted in differential massive cell debris within the exposure period. Sodium ascorbate, sodium citrate, sodium bicarbonate and FDP did not cause pH changes; however, they caused detectable cell disfigurement and loss of metabolic activity and survival/ death end points with the resultant death of the A549 cell line. MRC-5 cells were differentially unaffected by exposure to sodium ascorbate, sodium citrate, sodium bicarbonate, FDP and oxaloacxetic acid, underwent complete recovery and remained both attached and healthy for 6 weeks upon subculture when transferred to a new complete medium. Oxalic acid did not show differential modulation with the consequent loss of survival and death of the MRC-5 cell line. Phase contrast findings as well as the cell counts confirmed the findings of other tests. These studies show the potential for exploiting cellular metabolic differences in cancer control. Citation Format: Ibrahim O. Farah, Veshell L. Lewis, Zikri Arslan. Impact of some common organics on cellular glycolysis and the differential survival of lung fibroblast and lung carcinoma cell lines. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1168. doi:10.1158/1538-7445.AM2015-1168

Lack of Effects on Core Obsessive-Compulsive Symptoms of Tryptophan Depletion During Symptom Provocation in Remitted Obsessive-Compulsive Disorder Patients

Pharmacological evidence support that enhancement of serotonin (5-HT) neurotransmission is critical for treatment efficacy in obsessive-compulsive disorder (OCD). Surprisingly, acute tryptophan depletion (ATD), a procedure known to reduce 5-HT neurotransmission, carried out in remitted OCD patients on selective serotonin reuptake inhibitors (SSRIs) failed to worsen obsessive-compulsive (OC) symptoms. We hypothesized that the putative symptom exacerbation resulting from ATD would only be observed during symptom provocation but not at rest. Double-blind placebo-controlled ATD study conducted in 16 OCD patients with stable improvement under either SSRI (n = 8) or specialized cognitive behavior therapy alone (n = 8), coupled with gradual symptom provocation, performed 5 hours after drink ingestion. Acute tryptophan depletion markedly reduced total and free plasma tryptophan levels but did not significantly increase obsessions or compulsions at rest or following symptom provocation. However, subjective distress in response to triggering situations was significantly higher during ATD; significant mood lowering was also present during ATD. These results are consistent with the view that relapses in OC core symptoms in remitted OCD patients may not depend solely on short-term changes in presynaptic 5-HT availability. In contrast to its apparent lack of effect on core OC symptoms, ATD affected the patient's mood and distress level resulting from provocation.

Tumor-induced changes in host metabolism: a possible role for free tryptophan as a marker of neoplastic disease.

Tumor growth is associated with a number of metabolic abnormalities. Glucose metabolism is deranged as frequently revealed by an impaired oral glucose tolerance test. Lipoprotein lipase activity is depressed, resulting in hypertrigliceridemia after an exogenous lipid load. Also protein metabolism is deranged in cancer patients, as revealed by changes of plasma amino acid profile. Our previous studies on plasma amino acids have shown that increased plasma free tryptophan levels are a frequent finding in cancer patients. To sustain a possible role for free tryptophan as a marker of neoplastic disease, we measured its plasma concentrations in 241 patients with cancer. Plasma free tryptophan concentrations were found to be significantly elevated with respect to healthy controls in patients with breast, lung, colon, stomach, and cancer from various origin. The sensitivity of this marker in predicting the presence of the tumor was highest for stomach and lung cancer patients. High plasma free tryptophan concentrations seem to be directly related to the presence of the tumor, since in breast cancer patients they returned to within normal range after eradicative surgery.

Effects of rapid tryptophan depletion on brain 5-HT(2) receptors: a PET study.

The mechanism by which rapid tryptophan depletion (RTD) paradigm induces depressive relapse in recently remitted patients with depression is unknown. To determine the effects of RTD on brain 5-HT(2) receptors using positron emission tomography (PET) and (18)F-labelled setoperone. Ten healthy women under went two PET scans. Each scan was done 5 h after the ingestion of either a balanced or a tryptophan-deficient amino acid mixture, and the two test sessions were separated by at least 5 days. The RTD decreased plasma free tryptophan levels significantly but it had no significant effects on mood. Subjects showed a significant decrease in brain 5-HT(2) receptor binding in various cortical regions following the RTD session. When taken with the evidence that antidepressant treatment is associated with a decrease in brain 5-HT(2) receptors, these findings suggest that a decrease in 5-HT(2) binding following RTD might be an adaptive response that provides protection against depressive symptoms.

Effect of kynurenine on tryptophan-albumin binding in human plasma.

Increased plasma free tryptophan levels have been reported in cancer patients and causally associated to the presence of anorexia. The pathogenesis of this occurrence is yet to be completely understood. Kynurenine is a metabolite of tryptophan, and has been reported increased in plasma during tumor growth. Because of the similarities between tryptophan and kynurenine we speculate that their rise in the presence of a tumor might be causally related. To test this hypothesis, we performed a series of in-vitro studies, showing that kynurenine supplementation reduces the amount of tryptophan bound to albumin, and thus, by competition, increases free tryptophan levels. The likely clinical consequences of these findings are discussed.

Changes in the Albumin Binding of Tryptophan During Postoperative Recovery: A Possible Link With Central Fatigue?

Tryptophan is the precursor of the neurotransmitter 5-hydroxytryptamine (5-HT), known to be involved in sleep and fatigue. In the blood, tryptophan binds to albumin, and that which does not, free tryptophan, competes with branched chain amino acids (BCAA) for entry into the brain. The plasma concentrations of albumin, free tryptophan, total tryptophan, and BCAA were measured before and after major surgery in nine elderly and nine coronary artery bypass graft (CABG) patients. In both the elderly and the CABG patients plasma free tryptophan concentrations were increased after surgery, compared with baseline levels; the plasma free tryptophan/BCAA concentration ratio was also increased significantly after surgery. Plasma albumin concentrations were decreased significantly after surgery in both the elderly and the CABG patients. Plasma BCAA concentrations were not affected by surgery in either group. The effect of exercising to exhaustion on 5-HT and tryptophan were investigated in Nagase analbuminemic rats (NAR). The intrasynaptosomal concentration of tryptophan, 5-hydroxytryptophan, and 5-HT was increased by fatigue after exercise. In addition, running time to exhaustion was shortened in NAR. These data suggest that free tryptophan uptake and 5-HT synthesis were enhanced in the nerve terminal. A decrease in plasma albumin may account for the increase in plasma-free tryptophan levels. An increase in plasma free tryptophan, resulting in an enhanced plasma concentration ratio of free tryptophan/BCAA, may lead to a higher 5-HT concentration in some parts of the brain and, consequently, to central fatigue. It is suggested that provision of BCAA as a dietary supplement may counteract the increase in plasma free tryptophan and thus improve the status of some patients after major surgery.

Determination of the Lumped Constant for the α‐Methyltryptophan Method of Estimating the Rate of Serotonin Synthesis

The lumped constant (LC) for the alpha-methyl-L-tryptophan method to convert the brain's uptake of labeled alpha-methyl-L-tryptophan into the regional rate of serotonin synthesis was estimated. The method involved independently estimating the unidirectional uptake constant of the tracer (alpha-[14C]methyl-L-tryptophan) to the tissue and the tracee (tryptophan) (with the addition of a radioactive compound) and calculating their ratio. The LC was estimated from logarithmically transformed data. Similar experiments were performed using rats treated with the drug probenecid, which blocks the efflux of 5-hydroxyindoleacetic acid (a metabolite of serotonin) from the brain. The experiments using probenecid, corrected for the difference in the levels of plasma free tryptophan (increased in probenecid-treated rats) relative to control experiments, gave an average LC for the rat brain of 0.46 +/- 0.14 (mean +/- SD). This value was not significantly different from the one obtained in controls (0.43 +/- 0.13). In addition, the LC was also calculated using unidirectional uptake constants in the probenecid-treated rats for alpha-methyl-L-tryptophan and L-tryptophan. This LC value was 0.39 +/- 0.10. There was no significant difference between these three LC values. Thus, an average +/- SD LC of 0.42 +/- 0.07 for 28 brain structures investigated in this study was obtained. Statistically the LC obtained in different structures had a variability that could be accounted for by errors in measurements alone. In other words, dispersion in the LC values could be fully accounted for by chance alone. Data confirmed that the LC value did not change when the rate of serotonin synthesis was increased by probenecid treatment. We also showed that the rate of 5-hydroxyindoleacetic acid accumulation in probenecid-treated rats was 58 pmol g-1 min-1 (rat brain), which is about twice as much as reported by others for a normal rat. This difference could also be accounted for by the increase in the plasma level of free tryptophan in probenecid-treated rats.

The early cancer anorexia paradigm: changes in plasma free tryptophan and feeding indexes.

Tumor growth is accompanied by an anorexia mediated by humoral factors that appear to influence appetitive mechanisms in the brain. Because tumor resection is followed by resumption of normal food intake, the circulating anorexigenic substance(s) are produced either by the neoplastic tissue or by the host in response to the tumor. Increased levels of plasma free tryptophan and plasma ammonia have been proposed to mediate cancer anorexia. With animal models, it is often difficult to ascertain whether changes in food intake depend upon metabolic changes or the progressively increasing tumor mass per se. The feeding patterns and biochemical changes that occur during tumor growth were evaluated in 96 male Fischer rats that were inoculated with 10(6) methylcholanthrene sarcoma cells or saline (controls). Rats were placed into metabolic cages equipped with an Automated Computerized Rat Eater Meter to continuously determine meal size and meal number. Plasma free tryptophan and ammonia were evaluated 6, 10, 16, 18, 22, and 26 days after tumor inoculation. Anorexia developed by day 17-18, when food intake started to decrease via a decrease in meal size but not meal number and reached 60% of control by day 26. However, long before anorexia developed, free tryptophan was significantly higher 6 days after tumor inoculation, and the greatest increase occurred after 18 days. Ammonia did not differ from control at any time. Data confirm tumor-associated increases in plasma free tryptophan that occurred before the manifestation of anorexia and support a possible role of brain serotonin in cancer anorexia.

Plasma and CSF tryptophan in cancer anorexia

Eighteen untreated cancer patients and ten sex- and age-matched healthy volunteers were studied. In all patients eating behavior was investigated by means of a specific questionnaire from which the presence of anorexia and anorexia-related symptoms was assessed. To investigate the role of tryptophan in cancer anorexia, fasting plasma and CSF levels of tryptophan and other neutral amino acids were assayed in patients and controls. Cancer patients showed abnormally high plasma free tryptophan levels. In case of patients with cancer anorexia a significant rise of the ratio in plasma between free and tryptophan/large neutral amino acids, competing with tryptophan for its brain entry, was observed. This increase was correlated to a consistent rise of CSF tryptophan levels suggesting a specific role of the serotoninergic system in the pathogenesis of cancer anorexia.

Effect of the tumor on plasma free tryptophan levels in cancer patients : C. Cangiano, A. Cascino, F. Ceci, A. Avella, M. Muscaritoli, F. Rossi Fanelli. Lab. of Clin. Nutr., III Dept. of Intern. Med., Univ. of Rome “La Sapienza”, Rome, IT

Effect of the tumor on plasma free tryptophan levels in cancer patients : C. Cangiano, A. Cascino, F. Ceci, A. Avella, M. Muscaritoli, F. Rossi Fanelli. Lab. of Clin. Nutr., III Dept. of Intern. Med., Univ. of Rome “La Sapienza”, Rome, IT

Influence of tryptophan availability on selection of alcohol and water by men.

To study the effects of tryptophan on alcohol selection the tryptophan levels in subjects were altered through the administration of amino acid mixtures. Male social drinkers (N = 45) with no psychiatric or medical problems were divided into three groups and consumed a drink that contained, respectively, a nutritionally balanced amino acid mixture, a tryptophan-supplemented mixture, or a tryptophan-free mixture. After a waiting period of 5 hours, blood samples were taken and subjects participated in an ad-lib taste rating of six--one nonalcoholic and five alcoholic--beverages. Water was also made available to subjects. Although there was a marked effect on total and free plasma tryptophan levels showing a dramatic increase in the case of the tryptophan-supplemented group and a decrease in the tryptophan-free group, altered tryptophan levels did not influence the amount of alcohol subjects ingested. Tryptophan supplementation was found to decrease water intake significantly by an unknown mechanism without affecting alcohol selection.

Ventricular Size and CSF Transmitter Metabolite Concentrations in Severe Endogenous Depression

The relationship between neurotransmitter metabolite concentrations and measurements of ventricular size on CAT scans and pneumoencephalographs was investigated in 15 patients with severe affective disorder. An association was identified between reduced levels of plasma free tryptophan and ventricular enlargement, and also between raised ventricular CSF levels of 5 HIAA and ventricular enlargement.

Lowering of plasma free tryptophan in normal and portacaval shunt dogs

The purpose of this study was to develop a method which would produce immediate and sustained lowering of plasma free tryptophan. Glucose, insulin, and mixtures of the two in different concentrations were infused into dogs over a period of 6 hr. Blood was sampled during the course of the infusion for assay of plasma free and total tryptophan, free fatty acids, glucose, and insulin. The infusate found to produce the most significant and sustained reduction in plasma free tryptophan in normal dogs was a mixture of 25% glucose and insulin. The lowering ranged from 26 to 47% during the course of the infusion. When the same infusion mixture was administered to dogs with established portacaval shunts, and elevated plasma free tryptophan concentrations (3.3 ± 0.3 μg/ml compared to normal dogs which had 1.9 ± 0.1 μg/ml), there was a 35% reduction to normal levels (2.0–2.2 μg/ml). A glucose-insulin mixture has, therefore, been found which, upon infusion into dogs, significantly lowers plasma free tryptophan levels. The effect of such an infusion on the plasma levels of free tryptophan, and the clinical course of patients with hepatic encephalopathy remains to be determined.

Blood serotonin and free tryptophan concentration in autistic children.

In 37 autistic children and 67 normal control subjects, determinations of plasma free and total tryptophan and blood serotonin levels were made simultaneously in order to establish a relationship between these parameters and the clinical rating scales: Children's Psychiatric Rating Scale (CPRS-1), Werry-Weiss-Peters Activity Scale (WWPAS), and Developmental Quotient (DQ). The plasma free tryptophan level was significantly higher in autistic children than in normal control subjects. There tended to be a significant positive correlation between the plasma free tryptophan level and CPRS-1 or WWPAS score and a negative correlation between the plasma free tryptophan level and DQ. The blood serotonin level was significantly higher in autistic children than in normal control subjects. No correlation was established, however, between the blood serotonin level and CPRS-1, WWPAS score or DQ, and hence the clinical symptoms. Nor was there a correlation between blood serotonin and free tryptophan levels in these children. These results suggest that autistic children have some defect in tryptophan-serotonin metabolism in the brain, which is responsible for the clinical manifestations and behavioral abnormalities of infantile autism.

Changes in brain amines associated with cancer anorexia

Analysis of indole amine metabolism within acute (Walker 256 carcinosarcoma) and chronic (methycholanthrene-induced sarcoma) animal models of cancer anorexia demonstrated elevated levels of plasma free tryptophan, whole brain tryptophan, serotonin and 5-hydroxyindoleacetic acid in anorectic tumor-bearing rats. Whole brain levels of catecholamines were not changed within either tumor line. Regional central nervous system determination of tryptophan metabolism in rats bearing Walker 256 tumors revealed elevated tryptophan in the hypothalamus, corpus striatum, mesencephalon, diencephalon, cerebellum and cortex, increased serotonin in the diencephalon and cerebellum and elevated 5-hydroxyindoleacetic acid in the diencephalon, hippocampus, pons-medulla, cerebellum and cortex. Although tryptophan was significantly increased only in the corpus striatum and diencephalon of the more chronic methycholanthrene tumor model, serotonin concentration was elevated in the corpus stiratum, diencephalon, hippocampus, pons-medulla, cerebellum and cortex, while levels of 5-hydroxyindoleacetic acid were significantly increased in all these areas as well as in the mesencephalon. Since similar changes in indole activity were not observed in pair-fed control rats, it is concluded that the elevated serotonin and 5-hydroxyindoleacetic acid levels in tumor-bearing rats did not result from undernutrition alone. Assay of regional catecholamines revealed few food-relevant changes, with norepinephrine being elevated in the corpus striatum and decreased in the pons-medulla of tumor-bearing rats. Therefore, these experiments suggest that the increased serotonin metabolism observed in tumor-bearing rats may be involved in the etiology of the anorexia of cancer.

Relationship between plasma and brain tryptophan in pigs during experimental hepatic coma before and after hemodialysis with selective membranes.

Experimental acute liver ischemia in pigs induces an increment in plasma free tryptophan with decreased total tryptophan. Brain tryptophan is elevated in all brain areas. A slight, but significant increase of brain serotonin is demonstrated in the striatum only, while 5-HIAA (5-hydroxyindoleacetic acid) is significantly lower in the hypothalamus. Other brain areas do not show significant changes in serotonin and 5-HIAA levels. Neither the high plasma free tryptophan levels, nor the decreased sum of neutral competitive amino acids are consistent with such an elevation of brain tryptophan. Hemodialysis was carried out with two different kinds of membranes: cuprophan (with an efficient removal of molecules up to molecular weight 1300) and AN 69 polyacrylonitrile (efficient removal up to 15,000). Ammonia and aminoacid clearance are similar for both membranes. After AN 69, plasmatic free tryptophan and brain tryptophan are lower than after liver devascularization, but still higher than normal. Serotonin significantly increases in the cortex, midbrain and hypothalamus without concomitant rise of 5-HIAA levels. After cuprophan hemodialysis, plasma total tryptophan is lower than in normal and even comatose animals, whereas free tryptophan is normal. Intracerebral tryptophan is similar to AN 69 dialysed animals, but in the hypothalamus it is similar to nondialysed animals. Brain serotonin levels are not modified. 5-HIAA decreases in the hypothalamus. This finding suggests that middle molecules (which are not cleared out with cuprophan hemodialysis) are involved in the intracerebral transfer of tryptophan and the metabolism of serotonin, mainly in the hypothalamus.

Total and free serum tryptophan levels and brain 5-hydroxytryptamine metabolism in arthritic rats

In rats suffering from experimentally induced arthritis produced by Freund's adjuvant, there is a marked decrease in total serum tryptophan levels and a marked increase in plasma-free tryptophan levels at both 15 and 21 days after the administration of the adjuvant. Tryptophan, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid levels are increased in the brain and the spinal cord at 15 days. However, 21 days after administration of the adjuvant these levels returned to normal values in the brain, but remained increased in the spinal cord. These results are in agreement with investigations suggesting the possible involvement of the raphe-spinal system in response to pain stimuli but are contrary to the observation that there is a large decrease in plasma-free tryptophan levels in arthritic human patients. These opposite results still question the hypothesis of a relationship between changes in plasma-free tryptophan levels and the severity of pain.

A longitudinal study of tryptophan involvement in hepatic coma

Previous cross-sectional studies have demonstrated that hepatic coma is associated with abnormally high levels of plasma free tryptophan. Establishment of a more definitive relationship between this biochemical abnormality and hepatic coma requires an evaluation of biochemical changes in individual patients as they undergo alterations in the function of their central nervous systems. The present report is an evaluation of tryptophan and substances believed to influence its entry into the brain in six patients whose clinical status progressed from hepatic coma to complete recovery. Consistent significant decreases in plasma free tryptophan and free fatty acids were demonstrated to occur as the patients recovered. No consistent changes, however, were found in the plasma levels of the amino acids which have been reported to compete with tryptophan for transport across the blood-brain barrier, except for leucine which was significantly decreased in all six patients upon recovery from coma. Assay of lumbar cerebrospinal fluid for both tryptophan and the serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA), showed no consistent changes as the patients recovered from hepatic coma.

A study of proposed determinants of brain tryptophan concentration in rats after portocaval anastomosis or sham operation.

AbstractLiver dysfunction was produced in rats by surgical portocaval anastomosis (PCA), and the time‐course of changes in brain tryptophan and 5‐HT metabolism studied in relation to plasma changes possibly influencing brain tryptophan concentration.Brain tryptophan and 5‐hydroxyindolylacetic acid (5‐HIAA) levels were increased greatly and maximally on the day after PCA and remained high. 5‐HT changes were less marked but had a similar time‐course. Plasma total tryptophan was little changed but plasma free tryptophan was raised. The latter change showed a similar time‐course to that of brain tryptophan but was not large enough to account completely for it. Sham operation was followed by significant but transient increases in plasma free tryptophan, brain tryptophan and 5‐HIAA but these were much smaller than after PCA.Brain tryptophan did not correlate with plasma total tryptophan either in control or PCA rats but it correlated significantly with plasma free tryptophan in both groups. However brain levels were much higher in PCA rats than in controls with similar plasma free tryptophan levels at all times from the first day after operation. The increase of brain tryptophan in anastomosed rats not accounted for by plasma free tryptophan was explained neither by insulin changes nor by an increase of the insulin/glucagon ratio nor by changes in plasma concentrations of those amino acids which compete with tryptophan for entry into brain. The results therefore indicate an unknown influence on brain tryptophan concentration in PCA rats. As tyrosine changes in brain and plasma after PCA were very similar to those of tryptophan this influence may not be specific to tryptophan. Results suggest that under the conditions used brain tryptophan concentrations of both PCA and control rats are more influenced by changes of plasma free tryptophan concentration than by changes of plasma concentrations of competing amino acids.

Tryptophan and depressive illness

Plasma free tryptophan is significantly decreased in monopolar, depressed patients. No evidence was found to suggest that poor nutritional history prior to hospital admission was responsible for these low levels. Factors known to influence tryptophan-albumin binding in plasma, e.g. concentration of plasma proteins, albumin and non-esterified fatty acids, did not account for the low levels of free tryptophan in depressed patients. A significant decrease in plasma free tryptophan levels was found in perimenopausal but not in pre- or post-menopausal female controls. This mirrors the decrease in circulating oestrogens. Although exogenously administered oestrogens do not have any therapeutic efficacy in relieving mild residual depressive symptoms of lithium treated patients, they increased the levels of plasma free tryptophan. Clofibrate also displaces tryptophan from plasma protein binding sites in both depressed patients and controls. Utilization of the increased levels of plasma free tryptophan is reduced in depressed patients. A situation therefore exists in depressed patients where the plasma free tryptophan is not only reduced but also leaves the plasma less readily than in control subjects.