Dopamine receptor D2 confers colonization resistance via microbial metabolites

The gut microbiome has major roles in modulating host physiology. One such function is colonization resistance, or the ability of the microbial collective to protect the host against enteric pathogens1-3, including enterohaemorrhagic Escherichia coli (EHEC) serotype O157:H7, an attaching and effacing (AE) food-borne pathogen that causes severe gastroenteritis, enterocolitis, bloody diarrhea and acute renal failure4,5 (haemolytic uremic syndrome). Although gut microorganisms can provide colonization resistance by outcompeting some pathogens or modulating host defence provided by the gut barrier and intestinal immune cells6,7, this phenomenon remains poorly understood. Here, we show that activation of the neurotransmitter receptor dopamine receptor D2 (DRD2) in the intestinal epithelium by gut microbial metabolites produced upon dietary supplementation with the essential amino acid L-tryptophan protects the host against Citrobacter rodentium, a mouse AE pathogen that is widely used as a model for EHEC infection8,9. We further find that DRD2 activation by these tryptophan-derived metabolites decreases expression of a host actin regulatory protein involved in C. rodentium and EHEC attachment to the gut epithelium via formation of actin pedestals. Our results reveal a noncanonical colonization resistance pathway against AE pathogens that features an unconventional role for DRD2 outside the nervous system in controlling actin cytoskeletal organization in the gut epithelium. Our findings may inspire prophylactic and therapeutic approaches targeting DRD2 with dietary or pharmacological interventions to improve gut health and treat gastrointestinal infections, which afflict millions globally.

The Modulatory Activity of Tryptophan Displaying Nanodevices on Macrophage Activation for Preventing Acute Lung Injury

Macrophages play an important role in the initiation, progression and resolution of inflammation in many human diseases. Effective regulation of their activation and immune responses could be a promising therapeutic strategy to manage various inflammatory conditions. Nanodevices that naturally target macrophages are ideal agents to regulate immune responses of macrophages. Here we described a special tryptophan (Trp)-containing hexapeptide-coated gold nanoparticle hybrid, PW, which had unique immunomodulatory activities on macrophages. The Trp residues enabled PW higher affinity to cell membranes, and contributed to inducing mild pro-inflammatory responses of NF-κB/AP-1 activation. However, in the presence of TLR stimuli, PW exhibited potent anti-inflammatory activities through inhibiting multiple TLR signaling pathways. Mechanistically, PW was internalized primarily through micropinocytosis pathway into macrophages and attenuated the endosomal acidification process, and hence preferentially affected the endosomal TLR signaling. Interestingly, PW could induce the expression of the TLR negative regulator IRAK-M, which may also contribute to the observed TLR inhibitory activities. In two acute lung injury (ALI) mouse models, PW could effectively ameliorate lung inflammation and protect lung from injuries. This work demonstrated that nanodevices with thoughtful design could serve as novel immunomodulatory agents to manage the dysregulated inflammatory responses for treating many chronic and acute inflammatory conditions, such as ALI.

Oxytocin levels in response to pituitary provocation tests in healthy volunteers

OBJECTIVE

Oxytocin, secreted into circulation through the posterior pituitary, regulates lactation, weight, and socio-behavioral functioning. Oxytocin deficiency has been suggested in patients with hypopituitarism; however, diagnostic testing for oxytocin deficiency has not been developed. The aim of this study was to investigate known pituitary provocation tests to stimulate plasma oxytocin.

DESIGN

Sixty-five healthy volunteers underwent either the hypertonic saline or arginine infusion test, known to stimulate copeptin, or the oral macimorelin test, known to stimulate growth hormone. Plasma oxytocin was measured before and once plasma sodium level ≥ 150 mmol/L for the hypertonic saline, after 60 min for the arginine infusion, and after 45 min for the oral macimorelin test (expected peak of copeptin and growth hormone levels, respectively). Primary outcome was a change from basal to stimulated oxytocin levels using paired t-tests.

RESULTS

As expected, copeptin increased in response to hypertonic saline and arginine infusion (P < 0.001), and growth hormone increased to oral macimorelin (P < 0.001). Oxytocin increased in response to hypertonic saline infusion from 0.4 (0.2) to 0.6 pg/mL (0.3) (P = 0.003) but with a high variance. There was no change to arginine infusion (P = 0.4), and a trend to lower stimulated levels to oral macimorelin (P = 0.05).

CONCLUSION

Neither the arginine infusion nor the oral macimorelin test stimulates plasma oxytocin levels, whereas there was an increase with high variance upon hypertonic saline infusion. As a predictable rise in most participants is required for a reliable pituitary provocation test, none of the investigated pituitary provocation tests can be recommended diagnostically to identify patients with an oxytocin deficiency.

Dietary Tryptophan Supplementation Alters Fat and Glucose Metabolism in a Low-Birthweight Piglet Model

Low birthweight (LBW) is associated with metabolic complications, such as glucose and lipid metabolism disturbances in early life. The objective of this study was to assess: (1) the effect of dietary tryptophan (Trp) on glucose and fat metabolism in an LBW piglet model, and (2) the role peripheral 5-hydroxytryptamine type 3 (5HT3) receptors in regulating the feeding behavior in LBW piglets fed with Trp-supplemented diets. Seven-day-old piglets were assigned to 4 treatments: normal birthweight-0%Trp (NBW-T0), LBW-0%Trp (LBW-T0), LBW-0.4%Trp (LBW-T0.4), and LBW-0.8%Trp (LBW-T0.8) for 3 weeks. Compared to LBW-T0, the blood glucose was decreased in LBW-T0.8 at 60 min following the meal test, and the triglycerides were lower in LBW-T0.4 and LBW-T0.8. Relative to LBW-T0, LBW-T0.8 had a lower transcript and protein abundance of hepatic glucose transporter-2, a higher mRNA abundance of glucokinase, and a lower transcript of phosphoenolpyruvate carboxykinase. LBW-T0.4 tended to have a lower protein abundance of sodium-glucose co-transporter 1 in the jejunum. In comparison with LBW-T0, LBW-T0.4 and LBW-T0.8 had a lower transcript of hepatic acetyl-CoA carboxylase, and LBW-T0.4 had a higher transcript of 3-hydroxyacyl-CoA dehydrogenase. Blocking 5-HT3 receptors with ondansetron reduced the feed intake in all groups, with a transient effect on LBW-T0, but more persistent effect on LBW-T0.8 and NBW-T0. In conclusion, Trp supplementation reduced the hepatic lipogenesis and gluconeogenesis, but increased the glycolysis in LBW piglets. Peripheral serotonin is likely involved in the regulation of feeding behavior, particularly in LBW piglets fed diets supplemented with a higher dose of Trp.

Effects of Tyrosine and Tryptophan Supplements on the Vital Indicators in Mice Differently Prone to Diet-Induced Obesity

We studied the effects of the addition of large neutral amino acids, such as tyrosine (Tyr) and tryptophan (Trp), in mice DBA/2J and tetrahybrid mice DBCB receiving a high-fat, high-carbohydrate diet (HFCD) for 65 days. The locomotor activity, anxiety, muscle tone, mass of internal organs, liver morphology, adipokines, cytokines, and biochemical indices of animals were assessed. The Tyr supplementation potentiated increased anxiety in EPM and contributed to a muscle tone increase, a decrease in the AST/ALT ratio, and an increase in protein anabolism in both mice strains. Tyr contributed to a decrease in liver fatty degeneration and ALT reduction only in DBCB that were sensitive to the development of obesity. The addition of Trp caused an increase in muscle tone and potentiated an increase in anxiety with age in animals of both genotypes. Trp had toxic effects on the livers of mice, which was manifested in increased fatty degeneration in DBCB, edema, and the appearance of micronuclei in DBA/2J. The main identified effects of Tyr on mice are considered in the light of its modulating effect on the dopamine neurotransmitter metabolism, while for the Trp supplement, effects were presumably associated with the synthesis of its toxic metabolites by representatives of the intestinal microflora.

Thorough QT/QTc Study Evaluating the Effect of Macimorelin on Cardiac Safety Parameters in Healthy Participants

Macimorelin is an orally active growth hormone secretagogue indicated for the diagnosis of adult growth hormone deficiency. The primary objective of this study was to evaluate the effect of macimorelin on the baseline and placebo-corrected mean QT interval using Fridericia's formula (ΔΔQTcF). Secondary objectives were to determine QTcF for moxifloxacin; evaluate the effects of macimorelin on other cardiac intervals (PR, QRS, RR), heart rate, and electrocardiogram morphology parameters; characterize pharmacokinetics; and assess safety of macimorelin. The phase 1 thorough QT/QTc study, designed according to the International Council for Harmonisation E14 guideline, was a randomized, placebo-controlled, double-blind, 3-way complete crossover study comparing the effect of macimorelin 2.0 mg/kg with placebo and moxifloxacin 400 mg (positive control). Data were collected over a 3-month span from male (n=36) and female participants (n=24) aged 18 to 55 years with body mass index between 18.5 and 30.0 kg/m2 . Fifty-six participants received all 3 treatments. The ΔΔQTcF for macimorelin showed a prolongation with a maximum mean value of 9.61 milliseconds (2-sided 90% confidence interval, 7.81 milliseconds and 11.41 milliseconds) at 4 hours after dosing. The 2-sided 90% confidence interval of this value also exceeded the 10 millisecond threshold at 3 hours after dosing. Assay sensitivity was confirmed with moxifloxacin. Other electrocardiogram parameters evaluated were not influenced by macimorelin. Macimorelin did not raise other safety concerns and was well tolerated. In summary, a single supratherapeutic dose of macimorelin prolonged cardiac repolarization according to the regulatory guideline.

Ameliorative Effect of Dietary Tryptophan on Neurodegeneration and Inflammation in d-Galactose-Induced Aging Mice with the Potential Mechanism Relying on AMPK/SIRT1/PGC-1α Pathway and Gut Microbiota

Dietary tryptophan affects intestinal homeostasis and neurogenesis, whereas the underlying mechanism and the reciprocal interaction between tryptophan and gut microbiota in aging are unclear. This investigation was performed to determine the effect and mechanism of tryptophan on intestinal- and neuro- health in aging. In present study, the 0.4% tryptophan diet significantly ameliorated the oxidative stress and inflammation in the aging mice, potentially through the regulation of 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK) and nuclear factor κB (NF-κB) pathways. The 0.4% tryptophan diet increased the levels of indoles in colon contents, which indicated the potential contribution of tryptophan metabolites. Microbiome analysis revealed that the 0.4% tryptophan diet raised the relative abundance of Akkermansia in aging. The ameliorated effect of 0.4% tryptophan on neurodegeneration and neuroinflammation was summarized to potentially rely on the brain-derived neurotrophic factor- (BDNF) and NF-κB-related pathways. These findings provide the research evidence for the beneficial effect of tryptophan on aging.

Activation of 5-HT1A and 5-HT7 receptors enhanced a positively reinforced long-term memory

Memory is one of the most important capabilities of our mind since it determines our individuality. Memory formation involves different stages: acquisition, consolidation and retrieval. There are many studies about early stages, however little is known about memory retrieval. Retrieval is the use of learned information and represents a big problem in patients with memory deficits where the main issue is that they can learn but cannot remember. Previous findings have demonstrated that 5-hydroxytryptamine (5-HT) is a neurotransmitter involved in memory process. Hence, here we are exploring the role of 5-HT in memory retrieval by using its metabolic precursor l-tryptophan and several ligands at 5-HT1A and 5-HT7 receptors. Experimental protocol consisted of evaluating conditioned responses (%CR) after one week of interruption following autoshaping sessions for memory formation; a decrease of %CR was interpreted as memory decay. Systemic administration of: (1) l-tryptophan (50 and 100 mg/kg), (2) 5-HT1A receptor agonist 8-OH-DPAT (0.031 and 0.062 mg/kg), (3) the selective antagonist 5-HT1A receptor WAY 100635 (0.3 and 0.6 mg/kg), (4) the 5-HT7 receptor agonist, LP 211, in a dose-dependent manner (1, 2.5, 5.0 and 10.0 mg/kg) enhanced memory retrieval. Further, the 5-HT7 receptor antagonist, SB 269970 (10.0 mg/kg), had no effect. Finally, SB 269970 (10.0 mg/kg) significantly blocked memory retrieval enhancement produced by 10.0 mg/kg LP 211, but not that induced by 2.5 mg/kg LP 211.These results, taken together, suggest that activation of 5-HT1A and 5-HT7 receptors enhanced memory retrieval and these receptors may be therapeutic targets to improve long-term memory retrieval.

Effects of intragastric administration of L-tryptophan on the glycaemic response to a nutrient drink in men with type 2 diabetes - impacts on gastric emptying, glucoregulatory hormones and glucose absorption

BACKGROUND

The rate of gastric emptying and glucoregulatory hormones are key determinants of postprandial glycaemia. Intragastric administration of L-tryptophan slows gastric emptying and reduces the glycaemic response to a nutrient drink in lean individuals and those with obesity. We investigated whether tryptophan decreases postprandial glycaemia and slows gastric emptying in type 2 diabetes (T2D).

METHODS

Twelve men with T2D (age: 63 ± 2 years, HbA1c: 49.7 ± 2.5 mmol/mol, BMI: 30 ± 1 kg/m2) received, on three separate occasions, 3 g ('Trp-3') or 1.5 g ('Trp-1.5') tryptophan, or control (0.9% saline), intragastrically, in randomised, double-blind fashion, 30 min before a mixed-nutrient drink (500 kcal, 74 g carbohydrates), containing 3 g 3-O-methyl-D-glucose (3-OMG) to assess glucose absorption. Venous blood samples were obtained at baseline, after tryptophan, and for 2 h post-drink for measurements of plasma glucose, C-peptide, glucagon and 3-OMG. Gastric emptying of the drink was quantified using two-dimensional ultrasound.

RESULTS

Tryptophan alone stimulated C-peptide (P = 0.002) and glucagon (P = 0.04), but did not affect fasting glucose. In response to the drink, Trp-3 lowered plasma glucose from t = 15-30 min and from t = 30-45 min compared with control and Trp-1.5, respectively (both P < 0.05), with no differences in peak glucose between treatments. Gastric emptying tended to be slower after Trp-3, but not Trp-1.5, than control (P = 0.06). Plasma C-peptide, glucagon and 3-OMG increased on all days, with no major differences between treatments.

CONCLUSIONS

In people with T2D, intragastric administration of 3 g tryptophan modestly slows gastric emptying, associated with a delayed rise, but not an overall lowering of, postprandial glucose.

Pattern of postruminal administration of l-tryptophan affects blood serotonin in cattle

Serotonin (5-HT) has many important functions in both central and peripheral nervous systems. Although it has been demonstrated that manipulation of serotonin metabolism is possible in many species, there is limited information about l-tryptophan (TRP), a serotonin precursor, in cattle, and these provide conflicting results. Furthermore, there is no study evaluating how different patterns of intra-abomasal infusion of TRP impact circulating 5-HT. The objective of this study was to evaluate if intra-abomasal infusion patterns of TRP can affect circulating 5-HT and other metabolites from TRP metabolism in the plasma and serum and circulating glucose and insulin in cattle. Eight ruminally cannulated Holstein steers were used in a replicated 4 × 4 Latin square design. Each received intra-abomasal water infusion (control) or intra-abomasal TRP infusion (50 mg/kg BW) in 3 different patterns: a pulse infusion once a day (pulse once), pulse infusion twice a day (pulse twice), or continuous infusion (continuous). For continuous treatment, the TRP dose was diluted in tap water and infused by a peristaltic pump (300 mL/h). To equalize conditions, the other treatments had a water infusion (300 mL/h). The steers were fed every 2 h, and blood was collected from a jugular vein catheter every 4 h for 24 h after the initial infusion. Urine produced during the 24 h period was collected. Serum and plasma TRP, 5-HT and kynurenine, plasma glucose, and serum insulin concentrations were analyzed. Urine was analyzed for concentrations of 5-hydroxyindoleacetic acid. Both serum TRP and kynurenine were increased (P < 0.05) by all TRP infusion treatments, but concentrations in pulse dose treatments were greater than those in continuous infusion. Serum 5-HT increased (P < 0.05) with both pulse TRP infusion treatments; however, the continuous TRP infusion did not increase the serum 5-HT. Plasma 5-HT, glucose, and insulin had a tendency to increase with TRP pulse infusions. The urinary 5-hydroxyindoleacetic acid excretion was highest for pulse dose treatments. An acute supply of TRP in 1 or 2 daily doses increases serum 5-HT and increases circulating glucose and insulin in cattle. The TRP and kynurenine concentrations are similar in plasma and serum. However, the serum 5-HT concentration is more responsive to TRP administration than plasma.

Improving performance of finishing pigs with added valine, isoleucine, and tryptophan: validating a meta-analysis model

Based on results of a recent meta-analysis, we hypothesized that increased dietary Val, Ile, or Trp could correct possible amino acid interactions because of excess Leu in diets containing high levels of corn protein, namely dried distiller's grains with solubles (DDGS). A total of 1,200 pigs (PIC TR4 × (Fast LW × PIC L02); initially 33.6 ± 0.6 kg) were used in a 103-d study. The 6 dietary treatments were corn-soybean meal (SBM)-DDGS-based as follows: (1) high SBM and low level of l-Lys HCl (HSBM), (2) high l-Lys HCl and moderate Ile, Val, Trp (AA above NRC 2012 estimates; NC), (3) moderate l-Lys HCl and high Ile, Val, and Trp (PC), and PC with either increased (4) L-Val (PC+Val), (5) L-Ile (PC+Ile), or (6) L-Trp (PC+Trp). Pigs fed the NC diet were predicted to have the poorest average daily gain (ADG), the PC diet to be intermediate, and pigs fed the HSBM, PC+Val, PC+Ile, and PC+Trp have the same and highest predicted ADG. In the grower period (34 to 90 kg), ADG was greater (Ρ < 0.05) for the pigs fed HSBM and PC+Val diets than the NC with pigs fed other diets intermediate. Pigs fed HSBM were more (Ρ < 0.05) efficient (G:F) than the NC and PC with pigs fed other diets intermediate. In the finisher period (90 to 136 kg), ADG was greater (Ρ < 0.05) for pigs fed PC+Ile than that of the NC with pigs fed other diets intermediate. Pigs fed PC+Val had greater (Ρ < 0.05) average daily feed intake (ADFI) than the NC with pigs fed other diets intermediate. However, PC+Ile pigs were more (Ρ < 0.05) efficient than PC+Val with pigs fed other diets intermediate. Overall, ADG was greater (Ρ < 0.05) for pigs fed HSBM, PC+Val, and PC+Ile diets than the NC with pigs fed other diets intermediate. Pigs fed the PC+Val diet had greater (Ρ < 0.05) ADFI than the NC with pigs fed other diets intermediate. No differences were detected between treatments for overall G:F or other carcass characteristics. In conclusion, increasing Val or Ile in high l-Lys-HCl-DDGS-based diets improved growth performance compared with pigs fed diets containing high levels of l-Lys HCl without added Val and Ile. These results present evidence that the recently developed meta-analysis can predict the relative differences in overall ADG for pigs fed the NC, PC, PC+Val, and PC+Ile diets; however, the predicted G:F was less accurate. The data demonstrate that the negative effects of high Leu concentrations in corn-DDGS-based diets can be reversed by increasing the ratios of Val and Ile relative to Lys.

Involvement of kynurenine pathway in depressive-like behaviour induced by nandrolone decanoate in mice

Nandrolone decanoate (ND) belongs to the class II of anabolic-androgenic steroids (AAS), which is composed of 19-nor-testosterone-derivatives. AAS represent a group of synthetic testosterone that is used in clinical treatment. However, these drugs are widely abused among individuals as a means of promoting muscle growth or enhancing athletic performance. AAS in general and ND in particular have been associated with several behavioral disturbances, such as anxiety, aggressiveness and depression. A factor that contributes to the development of depression is the brain activation of indoleamine 2,3-dioxygenase (IDO), the rate-limiting enzyme of kynurenine pathway (KP). In the present study, we examined the involvement of KP in depressive phenotype induced by a ND treatment (10 mg/kg/day/s.c., for 28 days) that mimics human abuse system (e.g. supraphysiological doses) in C57B/6J mice. Our results showed that ND caused depressive like-behavior in the tail suspension test and anhedonic-like state measured in the sucrose preference test. ND administration decreased the levels of brain-derived neurotrophic factor and neurotrophin-3 and reduced Na⁺,K⁺-ATPase activity in the hippocampus, striatum and prefrontal cortex. We also found that ND elicited KP activation, as reflected by the increase of IDO activity and kynurenine levels in these brain regions. Moreover, ND decreased serotonin levels and increased 5-hydroxyindoleacetic acid levels in the brain. Treatment with IDO inhibitor 1-methyl-dl-trypthophan (1 mg/kg/i.p.) reversed the behavioral and neurochemical alterations induced by ND. These results indicate for the first time that KP plays a key role in depressive-like behavior and neurotoxicity induced by supraphysiologicaldoses of ND in mice.

Investigating the effects of incremental conditioning and supplemental dietary tryptophan on the voluntary activity and behaviour of mid-distance training sled dogs

Serotonin is a neurotransmitter synthesized by the amino acid tryptophan, that has the potential to impact the behaviour and activity of dogs. The objective of this study was to assess the effects of supplemental tryptophan and a 12-week incremental training regimen on the voluntary activity and behaviour of client-owned Siberian Huskies. Sixteen dogs were blocked for age, BW and sex and then randomly allocated to either the control or treatment group. Both groups were fed the same dry extruded diet; however, the treatment group were supplemented with tryptophan to achieve a tryptophan: large neutral amino acid ratio of 0.075:1. Once a week, a 5-minute video recording was taken immediately pre- and post- exercise to evaluate dogs' behaviours. Activity monitors were used to record voluntary activity on both training and rest days. Linear regression analysis was used to assess the relationship between training week and time spent performing each behaviour. Additionally, a repeated measure mixed model was used to test differences between diet groups and training week for both behavioural and activity count data. The time spent performing agonistic behaviours prior to exercise was negatively associated with week for treatment dogs (β = -0.32, 95% CI [-0.55, -0.10], P < 0.05) and no change was observed for control dogs (β = -0.13, 95% CI [-0.41, 0.15], P > 0.10). Treatment did not have any effect on activity levels (P > 0.10). For all dogs, locomotive behaviours decreased prior to exercise as weeks progressed (P < 0.05), while run day voluntary activity depended on the distance run that day (P < 0.05). These data suggest that sled dogs experience an exercise-induced reduction in voluntary locomotion in response to both single bouts and repetitive bouts of exercise. Additionally, tryptophan supplementation may decrease agonistic behaviours, without having any effect on voluntary activity.

Effects of intragastric tryptophan on acute changes in the plasma tryptophan/large neutral amino acids ratio and relationship with subsequent energy intake in lean and obese men

Circulating tryptophan/large neutral amino acids (tryptophan/LNAA) ratio, an indicator of brain serotonin levels, may be important in appetite regulation, together with gastrointestinal (gastric emptying, plasma cholecystokinin) mechanisms. We have compared effects of intragastric tryptophan ('Trp') on the plasma tryptophan/LNAA ratio in lean and obese men, and the associations of the tryptophan/LNAA ratio, gastric emptying and CCK concentrations with energy intake. Lean and obese male participants (n = 16 each) received 3 g Trp or volume-matched control intragastrically, 15 min before a mixed-nutrient drink (300 mL, 400 kcal) (t = 0 min) in randomised, double-blind fashion. Plasma amino acid (for calculation of the plasma tryptophan/LNAA ratio) and CCK concentrations were measured from t = -20-60 min. Gastric emptying was assessed from t = 0-60 min, and ad-libitum energy intake from a standardised buffet-style meal from t = 60-90 min. The increase in the plasma tryptophan/LNAA ratio was less in obese, than lean, participants (P < 0.05), and greater in lean participants who reduced their energy intake (by >0 kcal) after Trp compared with those who did not (by ≤0 kcal) (P < 0.05). Moreover, in participants who reduced their energy intake, the ratio was lower in obese, than in lean (P < 0.05). There was a trend for an inverse correlation between energy intake with the plasma tryptophan/LNAA ratio in lean (r = -0.4, P = 0.08), but not in obese, participants. There was no significant difference in gastric emptying or CCK between participants who reduced their energy intake and those who did not. In conclusion, the plasma tryptophan/LNAA ratio appears to be a determinant of the suppression of energy intake in response to tryptophan in normal-weight people, but not in those with obesity. The role of the plasma tryptophan/LNAA ratio to regulate energy intake, and potential changes in obesity, warrant evaluation in prospective studies.

Maternal Tryptophan Supplementation Protects Adult Rat Offspring against Hypertension Programmed by Maternal Chronic Kidney Disease: Implication of Tryptophan-Metabolizing Microbiome and Aryl Hydrocarbon Receptor

Hypertension and chronic kidney disease (CKD) can originate during early-life. Tryptophan metabolites generated by different pathways have both detrimental and beneficial effects. In CKD, uremic toxins from the tryptophan-generating metabolites are endogenous ligands of the aryl hydrocarbon receptor (AHR). The interplay between AHR, nitric oxide (NO), the renin–angiotensin system (RAS), and gut microbiota is involved in the development of hypertension. We examined whether tryptophan supplementation in pregnancy can prevent hypertension and kidney disease programmed by maternal CKD in adult offspring via the aforementioned mechanisms. Sprague–Dawley (SD) female rats received regular chow or chow supplemented with 0.5% adenine for 3 weeks to induce CKD before pregnancy. Pregnant controls or CKD rats received vehicle or tryptophan 200 mg/kg per day via oral gavage during pregnancy. Male offspring were divided into four groups (n = 8/group): control, CKD, tryptophan supplementation (Trp), and CKD plus tryptophan supplementation (CKDTrp). All rats were sacrificed at the age of 12 weeks. We found maternal CKD induced hypertension in adult offspring, which tryptophan supplementation prevented. Maternal CKD-induced hypertension is related to impaired NO bioavailability and non-classical RAS axis. Maternal CKD and tryptophan supplementation differentially shaped distinct gut microbiota profile in adult offspring. The protective effect of tryptophan supplementation against maternal CKD-induced programmed hypertension is relevant to alterations to several tryptophan-metabolizing microbes and AHR signaling pathway. Our findings support interplay among tryptophan-metabolizing microbiome, AHR, NO, and the RAS in hypertension of developmental origins. Furthermore, tryptophan supplementation in pregnancy could be a potential approach to prevent hypertension programmed by maternal CKD.

Randomized Double-Blind Controlled Trial on the Effect of Proteins with Different Tryptophan/Large Neutral Amino Acid Ratios on Sleep in Adolescents: The PROTMORPHEUS Study

Disturbed sleep is common in adolescents. Ingested nutrients help regulate the internal clock and influence sleep quality. The purpose of this clinical trial is to assess the effect of protein tryptophan (Trp)/large neutral amino acids (LNAAs) ratio on sleep and circadian rhythm. Ingested Trp is involved in the regulation of the sleep/wake cycle and improvement of sleep quality. Since Trp transport through the blood-brain barrier is competing with LNAAs, protein with higher Trp/LNAAs were expected to increase sleep efficiency. This randomized double-blind controlled trial will enroll two samples of male adolescents predisposed to sleep disturbances: elite rugby players (n = 24) and youths with obesity (n = 24). They will take part randomly in three sessions each held over a week. They will undergo a washout period, when dietary intake will be calibrated (three days), followed by an intervention period (three days), when their diet will be supplemented with three proteins with different Trp/LNAAs ratios. Physical, cognitive, dietary intake, appetite, and sleepiness evaluations will be made on the last day of each session. The primary outcome is sleep efficiency measured through in-home electroencephalogram recordings. Secondary outcomes include sleep staging, circadian phase, and sleep-, food intake-, metabolism-, and inflammation-related biochemical markers. A fuller understanding of the effect of protein Trp/LNAAs ratio on sleep could help in developing nutritional strategies addressing sleep disturbances.

Discovery of indoximod prodrugs and characterization of clinical candidate NLG802

A series of different prodrugs of indoximod, including estesrs and peptide amides were synthesized with the aim of improving its oral bioavailability in humans. The pharmacokinetics of prodrugs that were stable in buffers, plasma and simulated gastric and intestinal fluids was first assessed in rats after oral dosing in solution or in capsule formulation. Two prodrugs that produced the highest exposure to indoximod in rats were further tested in Cynomolgus monkeys, a species in which indoximod has oral bioavailability of 6-10% and an equivalent dose-dependent exposure profile as humans. NLG802 was selected as the clinical development candidate after increasing oral bioavailability (>5-fold), C_max (6.1-3.6 fold) and AUC (2.9-5.2 fold) in monkeys, compared to equivalent molar oral doses of indoximod. NLG802 is extensively absorbed and rapidly metabolized to indoximod in all species tested and shows a safe toxicological profile at the anticipated therapeutic doses. NLG802 markedly enhanced the anti-tumor responses of tumor-specific pmel-1 T cells in a melanoma tumor model. In conclusion, NLG802 is a prodrug of indoximod expected to increase clinical drug exposure to indoximod above the current achievable levels, thus increasing the possibility of therapeutic effects in a larger fraction of the target patient population.

Effects of Duodenal Infusion of Lauric Acid and L-Tryptophan, Alone and Combined, on Fasting Glucose, Insulin and Glucagon in Healthy Men

The fatty acid, lauric acid ('C12'), and the amino acid, tryptophan ('Trp'), when given intraduodenally at loads that individually do not affect energy intake, have recently been shown to stimulate plasma cholecystokinin, suppress ghrelin and reduce energy intake much more markedly when combined. Both fatty acids and amino acids stimulate insulin secretion by distinct mechanisms; fatty acids enhance glucose-stimulated insulin secretion, while amino acids may have a direct effect on pancreatic β cells. Therefore, it is possible that, by combining these nutrients, their effects to lower blood glucose may be enhanced. We have investigated the potential for the combination of C12 and Trp to have additive effects to reduce blood glucose. To address this question, plasma concentrations of glucose, insulin and glucagon were measured in 16 healthy, lean males during duodenal infusions of saline (control), C12 (0.3 kcal/min), Trp (0.1 kcal/min), or C12+Trp (0.4 kcal/min), for 90 min. Both C12 and C12+Trp moderately reduced plasma glucose compared with control (p < 0.05). C12+Trp, but not C12 or Trp, stimulated insulin and increased the insulin-to-glucose ratio (p < 0.05). There was no effect on plasma glucagon. In conclusion, combined intraduodenal administration of C12 and Trp reduced fasting glucose in healthy men, and this decrease was driven primarily by C12. The effects of these nutrients on postprandial blood glucose and elevated fasting blood glucose in type 2 diabetes warrant evaluation.

Combined Supplementation with Glycine and Tryptophan Reduces Purine-Induced Serum Uric Acid Elevation by Accelerating Urinary Uric Acid Excretion: A Randomized, Single-Blind, Placebo-Controlled, Crossover Study

The authors previously confirmed the serum uric acid-lowering effects of the combination of glycine and tryptophan in subjects with mild hyperuricemia. This study examined whether combined supplementation with glycine and tryptophan suppressed the elevation in serum uric acid levels caused by purine ingestion and accelerated urinary uric acid excretion in subjects with lower urate excretion using a randomized, single-blind, placebo-controlled, crossover clinical trial design. Healthy Japanese adult males with lower urate excretion ingested water containing purines in addition to dextrin (placebo), tryptophan, glycine, or a glycine and tryptophan mixture. The combined supplementation with glycine and tryptophan significantly reduced the elevated serum uric acid levels after purine ingestion. Glycine alone and in combination with tryptophan significantly increased urinary uric acid excretion and urate clearance compared with the effects of the placebo. Urinary pH increased by the ingestion of the mixture. These results suggested that the improved water solubility of uric acid due to increased urinary pH contributed to the increase of urinary uric acid excretion.

Dietary tryptophan supplementation induces a transient immune enhancement of gilthead seabream (Sparus aurata) juveniles fed fishmeal-free diets

European aquaculture is an industry with a high sustainability profile contributing to the supply of safe seafood. However, several diseases can affect farmed fish and it is imperative to find alternatives for chemotherapeutic treatments when disease outbreaks occur. Maintenance of health through nutrition is well-establish in modern animal farming, and amino acids (AA) are promising candidates as functional additives to improve fish health. Therefore, the goal of this research is to provide a better understanding of the influence of tryptophan supplementation on nutritional condition and immune mechanisms in fish. Triplicate groups of fish (13.3 ± 0.3g) previously fed with a fishmeal-based diet were either fed a control diet with an extreme formulation (0% fishmeal) but meeting the AA requirements (CTRL), or the SUP diet, formulated as the CTRL with an increase in tryptophan (TRP) content. After 2 and 13 weeks of feeding, head-kidney (HK), liver (L) and white skeletal muscle (WSM) were collected for gene expression, whereas plasma was suited for humoral immune parameters. A holistic approach using transcriptomic, humoral and zootechnical parameters was undertaken. The expression of 29-31 genes for WSM, L or HK confirms an effect due to the treatment across time. A two-way ANOVA analysis revealed that 15-24 genes varied significantly depending on the tissue, and the multivariate analysis by means of PLS-DA explained (R²) and predicted (Q²) with four components up to 93% and 78% of total variance, respectively. Component 1 (R² = 50.06%) represented the time effects, whereas components 2 (24.36%) and 3 (13.89%) grouped fish on the basis of dietary treatment, at early sampling. The HK results in particular suggest that fish fed SUP diet displayed an immunostimulated state at 2 weeks. No major differences were observed in plasma humoral parameters, despite an increase in antiprotease and peroxidase activities after 13 weeks regardless of dietary treatment. These results suggest that tryptophan supplementation may improve the seabream immune status after 2 weeks. Hence, the use of functional feeds is especially relevant during a short-term feeding period before a predictable stressful event or disease outbreak, considering that these putative advantageous effects seem to disappear after a 13 weeks feeding period.

Effects of dietary tryptophan levels on antioxidant status and immunity for juvenile blunt snout bream (Megalobrama amblycephala) involved in Nrf2 and TOR signaling pathway

Dietary administration of tryptophan has been proved improving growth performance of fish. An 8-week feeding trial was conducted to investigate the effects of dietary tryptophan level on antioxidant capacity and immune response through Nrf2 and TOR signaling pathway. The results showed that, 0.08% tryptophan level significantly increased plasma aspartate aminotransferase (AST), while immunoglobulin M (IgM) and alkaline phosphatase (ALP) were strikingly increased by 0.40% level. The level of plasma complement component 3 (C3), alanine aminotransferase (ALT) and albumin (ALB) were independent of tryptophan supplementation. Total superoxide dismutase (T-SOD), catalase (CAT), total antioxidant capacity (T-AOC) and glutathione (GSH) activity were increased with increasing dietary tryptophan level until 0.40% and then decreased, while the level of malondialdehyde (MDA) showed a reverse trend. 0.19% and 0.28% tryptophan level significantly improved the glutathione peroxidase 1 (GPx-1) activity. Compared with 0.08% dietary tryptophan level, 0.40% level significantly improved nuclear factor erythroid 2-related factor 2 (Nrf2), GPx, manganese superoxide dismutase (Mn-SOD), CAT and transforming growth factor-β (TGF-β) mRNA level, while Kelch-like ECH-associated protein 1 (Keap1) and interleukin 1β (IL-1β) mRNA level were significantly decreased. The relative expression of copper zinc superoxide dismutase (Cu/Zn-SOD), heme oxygenase-1 (HO-1), target of rapamycin (TOR), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K), protein kinase B (Akt) and interleukin 10 (IL-10) were significantly improved by 0.28% diet, while the mRNA level of tumor necrosis factor-α (TNF-α) and nuclear factor-kappa B (NF-κB) were increased by 0.08% diet. Interleukin 8 (IL-8) mRNA level was not significantly affected by dietary tryptophan. Based on MDA and T-SOD value, the optimal dietary tryptophan level of juvenile blunt snout bream was determined to be 0.33% (1.03% of dietary protein) and 0.36% (1.13% of dietary protein), respectively, using quadratic regression analysis.

Dietary tryptophan affects growth performance, digestive and absorptive enzyme activities, intestinal antioxidant capacity, and appetite and GH-IGF axis-related gene expression of hybrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂)

The 56-day feeding trial was carried out to investigate the effects of dietary tryptophan (Trp) on growth performance, digestive and absorptive enzyme activities, intestinal antioxidant capacity, and appetite and GH-IGF axis-related genes expression of hybrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂). A total of 864 hybrid catfish (21.82 ± 0.14 g) were fed six different experimental diets containing graded levels of Trp at 2.6, 3.1, 3.7, 4.2, 4.7, and 5.6 g kg^-1 diet. The results indicated that dietary Trp increased (P < 0.05) (1) final body weight, percent weight gain, specific growth rate, feed intake, feed efficiency, and protein efficiency ratio; (2) fish body protein, lipid and ash contents, protein, and ash production values; (3) stomach weight, stomach somatic index, liver weight, intestinal weight, length and somatic index, and relative gut length; and (4) activities of pepsin in the stomach; trypsin, chymotrypsin, lipase, and amylase in the pancreas and intestine; and γ-glutamyl transpeptidase, Na⁺, K⁺-ATPase, and alkaline phosphatase in the intestine. Dietary Trp decreased malondialdehyde content, increased antioxidant enzyme activities and glutathione content, but downregulated Keap1 mRNA expression, and upregulated the expression of NPY, ghrelin, GH, GHR, IGF1, IGF2, IGF1R, PIK3Ca, AKT1, TOR, 4EBP1, and S6K1 genes. These results indicated that Trp improved hybrid catfish growth performance, digestive and absorptive ability, antioxidant status, and appetite and GH-IGF axis-related gene expression. Based on the quadratic regression analysis of PWG, SGR, and FI, the dietary Trp requirement of hybrid catfish (21.82-39.64 g) was recommended between 3.96 and 4.08 g kg^-1 diet (9.4-9.7 g kg^-1 of dietary protein).

The Association of Aromatic Amino Acids with Incident Hip Fracture, aBMD, and Body Composition from the Cardiovascular Health Study

In 5187 persons from the Cardiovascular Health Study, there was no significant association of dietary intakes of aromatic amino acids (AAA) with areal BMD of the hip or body composition. However, those who had the lowest dietary intakes of AAA were at increased risk for incident hip fractures. Prior studies of the association of protein intake with osteoporosis are conflicting and have not directly examined the relationship of aromatic amino acids (AAA) with fractures, areal bone mineral density (aBMD), and body composition. We sought to determine the relationship of dietary intakes of AAA with osteoporosis parameters in elderly men and women. 5187 men and women aged ≥ 65 years from the Cardiovascular Health Study (CHS) with dietary intakes of AAA (tryptophan, phenylalanine, tyrosine) estimated by food frequency questionnaire (FFQ) were included. We examined the relationship between a one-time estimate of daily dietary AAA intake with risk of incident hip fractures over a median of 13.2 years of fracture follow-up. A subset (n = 1336) who had dual energy X-ray absorptiometry (DXA) performed were included in a cross-sectional analysis of the association of dietary AAA intake with aBMD of the total hip and measurements of body composition. In multivariable models adjusted for demographic and clinical variables, medication use, and diet, higher dietary AAA intake was not significantly associated with incident hip fractures. All hazard ratios (HR) were less than one (tryptophan, HR 0.14, 95% CI 0.01 to 1.89; phenylalanine, HR 0.60, 95% CI 0.23 to 1.55; tyrosine, HR 0.59, 95% CI 0.27 to 1.32), but confidence intervals were wide and included no difference. However, in post hoc analyses, the lowest quartile of intake for each AAA was associated with an increased risk for hip fracture compared to higher quartiles (p ≤ 0.047 for all). Dietary AAA intakes were not significantly associated with total hip aBMD or any measurements of body composition. Overall, there was no significant association of dietary AAA intake with hip fractures, aBMD of the hip, or body composition. However, there may be a subset of elderly individuals with low dietary intakes of AAA who are at increased for hip fractures.

Effects of intraduodenal administration of lauric acid and L-tryptophan, alone and combined, on gut hormones, pyloric pressures, and energy intake in healthy men

BACKGROUND

The fatty acid, lauric acid ('C12'), and the amino acid, L-tryptophan ('Trp'), modulate gastrointestinal functions including gut hormones and pyloric pressures, which are important for the regulation of energy intake, and both potently suppress energy intake.

OBJECTIVE

We hypothesized that the intraduodenal administration of C12 and Trp, at loads that do not affect energy intake individually, when combined will reduce energy intake, which is associated with greater modulation of gut hormones and pyloric pressures.

DESIGN

Sixteen healthy, lean males (age: 24 ± 1.5 y) received 90-min intraduodenal infusions of saline (control), C12 (0.3 kcal/min), Trp (0.1 kcal/min), or C12 + Trp (0.4 kcal/min), in a randomized, double-blind, cross-over study. Antropyloroduodenal pressures were measured continuously, and plasma cholecystokinin (CCK), ghrelin, and glucagon-like peptide-1 (GLP-1) concentrations, appetite perceptions, and gastrointestinal symptoms at 15-min intervals. Immediately after the infusions, energy intake from a standardized buffet meal was quantified.

RESULTS

C12 + Trp markedly reduced energy intake (kcal; control: 1,232 ± 72, C12: 1,180 ± 82, Trp: 1,269 ± 73, C12 + Trp: 1,056 ± 106), stimulated plasma CCK (AUC(area under the curve)0-90 min, pmol/L*min; control: 21 ± 8; C12: 129 ± 15; Trp: 97 ± 16; C12 + Trp: 229 ± 22) and GLP-1 (AUC0-90 min, pmol/L*min; control: 102 ± 41; C12: 522 ± 102; Trp: 198 ± 63; C12 + Trp: 545 ± 138), and suppressed ghrelin (AUC0-90 min, pg/mL*min; control: -3,433 ± 2,647; C12: -11,825 ± 3,521; Trp: -8,417 ± 3,734; C12 + Trp: -18,188 ± 4,165) concentrations, but did not stimulate tonic, or phasic, pyloric pressures, compared with the control (all P < 0.05), or have adverse effects. C12 and Trp each stimulated CCK (P < 0.05), but to a lesser degree than C12 + Trp, and did not suppress energy intake or ghrelin. C12, but not Trp, stimulated GLP-1 (P < 0.05) and phasic pyloric pressures (P < 0.05), compared with the control.

CONCLUSION

The combined intraduodenal administration of C12 and Trp, at loads that individually do not affect energy intake, substantially reduces energy intake, which is associated with a marked stimulation of CCK and suppression of ghrelin. The study was registered as a clinical trial at the Australian and New Zealand Clinical Trial Registry (www.anzctr.org.au,) as 12613000899741.

Serum Uric Acid-Lowering Effects of Combined Glycine and Tryptophan Treatments in Subjects with Mild Hyperuricemia: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study

We determined the serum uric acid-lowering effects of combined daily supplementation of glycine and tryptophan in patients with mild hyperuricemia using a randomized, double-blind, placebo-controlled, crossover clinical trial design. Japanese healthy adult males and females with mild hyperuricemia (fasting serum uric acid of 6.6–7.9 mg/dL) ingested a powder mixture containing 3.0 g of glycine and 0.2 g of tryptophan or a placebo powder once daily at bedtime for 6 weeks. Combined supplementation with glycine and tryptophan significantly decreased serum uric acid levels (from 7.1 mg/dL to 6.7 mg/dL, p = 0.004) before and after the trial. Serum uric acid concentrations significantly decreased in the subjects supplemented with the amino acid mixture compared with those in placebo-treated subjects (p = 0.028). In addition, the combination treatment with glycine and tryptophan decreased serum triglyceride levels (from 119 mg/dL to 86 mg/dL, p = 0.002). Increased solubility of uric acid caused by urinary pH were likely contributors to the serum uric acid-lowering effects of the amino acid mixture.

Imaging tryptophan uptake with positron emission tomography in glioblastoma patients treated with indoximod

INTRODUCTION

Glioblastoma (GBM) is the most frequent and aggressive primary tumor of the central nervous system, accounting for over 50% of all primary malignant gliomas arising in the adult brain. Even after surgical resection, adjuvant radiotherapy (RT) and temozolomide (TMZ) chemotherapy, as well as tumor-treating fields, the median survival is only 15-20 months. We have identified a pathogenic mechanism that contributes to the tumor-induced immunosuppression in the form of increased indoleamine 2,3 dioxygenase 1 (IDO1) expression; an enzyme that metabolizes the essential amino acid, tryptophan (Trp), into kynurenine (Kyn). However, real-time measurements of IDO1 activity has yet to become mainstream in clinical protocols for assessing IDO1 activity in GBM patients.

METHODS

Pre-treatment and on-treatment α-[11C]-methyl-L-Trp (AMT) positron emission tomography (PET) with co-registered MRI was performed on patients with recurrent GBM treated with the IDO1 pathway inhibitor indoximod (D1-MT) and TMZ.

RESULTS

Regional intratumoral variability of AMT within enhancing and non-enhancing tumor was noted at baseline. On treatment imaging revealed decreased regional uptake suggesting IDO1 pathway modulation with treatment.

CONCLUSIONS

Here, we have validated the ability to use PET of the Trp probe, AMT, for use in visualizing and quantifying intratumoral Trp uptake in GBM patients treated with an IDO1 pathway inhibitor. These data serve as rationale to utilize AMT-PET imaging in the future evaluation of GBM patients treated with IDO1 enzyme inhibitors.

Effect of dietary L-tryptophan on the survival, immune response and gut microbiota of the Chinese mitten crab, Eriocheir sinensis

This study investigated the influence of L-tryptophan (L-trp) on the survival, immune response and gut microbiota of the Chinese mitten crab, Eriocheir sinensis (with an average weight of 16.58 ± 2.20 g). After 30 days of feeding with diets supplemented with L-trp at 0.36%, 0.47%, 0.73% and 1.05% (groups 1, 2, 3 and 4, respectively), the survival rate and bacterial challenge (Aeromonas hydrophila) were evaluated, the activities of antioxidant and phosphatase enzymes in the serum were assessed, and the gut microbiota were measured via high-throughput Illumina sequencing. The results showed that the supplementation of L-trp significantly improved the survival rate of crabs (P < 0.05). After feeding for 7 days, it was observed that a high L-trp diet significantly increase the survival rate relative to a basal diet after a 96-h post-challenge with A. hydrophila (P < 0.05). The activity of CAT and AKP in the serum were increased by the addition of L-trp. The activity of CAT and AKP in the serum in group 4 were higher than those in group 1 (P < 0.05). Furthermore, we observed that adjunction of the L-trp can significantly increase the richness and diversity of the gut microbiota. The dominant phylum in the intestine of the Chinese mitten crab were Tenericutes, Proteobacteria, Firmicutes, Chloroflexi and Actinobacteria. The L-trp in the diets increased the richness of Proteobacteria, Firmicutes and Actinobacteria in the intestine significantly. These bacteria were all dominant bacteria and had a specific role in promoting the immunity of E. sinensis. Therefore, it could be inferred that L-trp supplementation is beneficial in the diet of E. sinensis. Based in these results, the dietary 0.47% or 0.73%L-trp supplemented is found to be optimum to improve E. sinensis survival.

Breast Cancer Chemo-immunotherapy through Liposomal Delivery of an Immunogenic Cell Death Stimulus Plus Interference in the IDO-1 Pathway

Immunotherapy provides the best approach to reduce the high mortality of metastatic breast cancer (BC). We demonstrate a chemo-immunotherapy approach, which utilizes a liposomal carrier to simultaneously trigger immunogenic cell death (ICD) as well as interfere in the regionally overexpressed immunosuppressive effect of indoleamine 2,3-dioxygenase (IDO-1) at the BC tumor site. The liposome was constructed by self-assembly of a phospholipid-conjugated prodrug, indoximod (IND), which inhibits the IDO-1 pathway, followed by the remote loading of the ICD-inducing chemo drug, doxorubicin (DOX). Intravenous injection of the encapsulated two-drug combination dramatically improved the pharmacokinetics and tumor drug concentrations of DOX and IND in an orthotopic 4T1 tumor model in syngeneic mice. Delivery of a threshold ICD stimulus resulted in the uptake of dying BC cells by dendritic cells, tumor antigen presentation and the activation/recruitment of naı̈ve T-cells. The subsequent activation of perforin- and IFN-γ releasing cytotoxic T-cells induced robust tumor cell killing at the primary as well as metastatic tumor sites. Immune phenotyping of the tumor tissues confirmed the recruitment of CD8⁺ cytotoxic T lymphocytes (CTLs), disappearance of Tregs, and an increase in CD8⁺/FOXP3⁺ T-cell ratios. Not only does the DOX/IND-Liposome provide a synergistic antitumor response that is superior to a DOX-only liposome, but it also demonstrated that the carrier could be effectively combined with PD-1 blocking antibodies to eradicate lung metastases. All considered, an innovative nano-enabled approach has been established to allow deliberate use of ICD to switch an immune deplete to an immune replete BC microenvironment, allowing further boosting of the response by coadministered IDO inhibitors or immune checkpoint blocking antibodies.

L-tryptophan administration and increase in cerebral serotonin levels: Systematic review

The amino acid tryptophan (2-Amino-3-(lH-indol-3-yl)-propanoic acid; Trp) is a precursor of the neurotransmitter serotonin (5-hydroxytryptamine; 5-HT) that performs various brain functions. The administration of Trp is used in experimental studies to manipulate the serotonergic system, however the dose of Trp required to raise brain 5-HT levels is controversial. The aim of this study was to systemically review the effect of the administration of different doses of Trp on cerebral 5-HT levels. Two independent authors conducted a systematic review in the electronic databases. Twenty-five studies were included in the present review. Trp was administered orally, intraperitoneally or subcutaneous in adult animals. The brain 5-HT levels elevated after Trp administration in different intensities, dependent of the brain region evaluated and the time of administration. Further studies are needed to assess the dose-response of Trp administration to brain 5-HT levels.

Mitigation of Oxidation in Therapeutic Antibody Formulations: a Biochemical Efficacy and Safety Evaluation of N-Acetyl-Tryptophan and L-Methionine

PURPOSE

Biotherapeutics can be susceptible to oxidation during manufacturing and storage. Free L-methionine is known to protect methionine residues in proteins from oxidation. Similarly, free tryptophan and other indole derivatives have been shown to protect tryptophan residues from oxidation. N-acetyl-DL-tryptophan was previously identified as a potentially superior antioxidant to tryptophan as it has a lower oxidation potential and produces less peroxide upon light exposure. This study sought to confirm the antioxidant efficacy and safety of N-acetyl-DL-tryptophan and L-methionine as formulation components for biotherapeutic drugs.

METHODS

Antibodies were subjected to AAPH and light exposure in the presence of N-acetyl-DL-tryptophan and L-methionine. Oxidation in relevant CDR and Fc residues was quantified by peptide map. In silico, in vitro, and in vivo studies were performed to evaluate the safety of N-acetyl-DL-tryptophan and L-methionine.

RESULTS

Peptide mapping demonstrated that N-acetyl-DL-tryptophan was effective at protecting tryptophans from AAPH stress, and that the combination of N-acetyl-DL-tryptophan and L-methionine protected both tryptophan and methionine from AAPH stress. The safety assessment suggested an acceptable safety profile for both excipients.

CONCLUSIONS

N-acetyl-tryptophan and L-methionine effectively reduce the oxidation of susceptible tryptophan and methionine residues in antibodies and are safe for use in parenteral biotherapeutic formulations.

The effect of graded concentrations of dietary tryptophan on canine behavior in response to the approach of a familiar or unfamiliar individual

Tryptophan (Trp) is an indispensable dietary amino acid that supports the modulation of mood and behavior in mammalian species through its role in the serotonergic pathway. This study assessed the behavior patterns of 36 healthy, female adult mixed-breed hound dogs fed a control diet (tryptophan = 0.18% as-fed) or 1 of several experimental diets with graded concentrations of tryptophan (0.05%, 0.1%, and 0.15% of the total diet) supplemented on top of the 0.18% basal level. At baseline, and every 8 weeks throughout the 24-week period, behavioral parameters were evaluated for each dog in response to the approach of an individual familiar to the dogs and another individual who was unfamiliar to the dogs. Differences in behavior scores (activity, P = 0.0197; distance, P = 0.0358; confidence, P < 0.0001; and ear position, P < 0.0001) between the unfamiliar and familiar individuals supported the efficacy of the behavioral ethogram used. No consistent and significant differences in behavior were observed, however, among dogs fed the control diet and those fed an experimental diet with any level of tryptophan supplementation. Future research should consider the tryptophan-to-large-neutral-amino-acid ratio and not just tryptophan concentrations, seek to understand the variation in tryptophan requirements among breeds, and look to utilize additional markers of serotonin status.

Low-Protein Diets Decrease Porcine Nitrogen Excretion but with Restrictive Effects on Amino Acid Utilization

Reducing dietary crude protein (CP) intake effectively decreases nitrogen excretion in growing-finishing pigs but at the expense of poor growth when dietary CP content is reduced by ≥3%. In this study, we investigated the main disadvantages of low-protein diets supplemented with lysine, methionine, threonine, and tryptophan in pigs. First, changes in the nitrogen balance in response to differences in dietary CP content (18%, 15%, and 13.5%) were investigated in barrows (40 kg). Then, barrows (40 kg) surgically fitted with catheters in the mesenteric vein, portal vein, hepatic vein, and carotid artery were used to investigate changes in amino acid (AA) metabolism in the portal-drained viscera and liver in response to differences in dietary CP content. The results showed that low-protein diets reduced fecal and urinary nitrogen excretion ( P < 0.05) meanwhile resulted in significant decreases in nitrogen retention ( P < 0.05). Moreover, a reduction in the dietary CP content from 18% to 13.5% resulted in decreases in the net portal fluxes of NH₃, glycine, and alanine as well as in the urea production in the liver ( P < 0.05), whereas their values as a percentage of nitrogen intake did not decline ( P > 0.05). The net portal fluxes of nonessential AA (NEAA) were reduced in the low-protein diet groups ( P < 0.05), while essential AA consumption in the liver increased ( P < 0.05). Thus, low-protein diets result in reductions in both nitrogen excretion and retention, and NEAA deficiency may be a major disadvantage of low-protein diets.

Macimorelin as a Diagnostic Test for Adult GH Deficiency

PURPOSE

The diagnosis of adult GH deficiency (AGHD) is challenging and often requires confirmation with a GH stimulation test (GHST). The insulin tolerance test (ITT) is considered the reference standard GHST but is labor intensive, can cause severe hypoglycemia, and is contraindicated for certain patients. Macimorelin, an orally active GH secretagogue, could be used to diagnose AGHD by measuring stimulated GH levels after an oral dose.

MATERIALS AND METHODS

The present multicenter, open-label, randomized, two-way crossover trial was designed to validate the efficacy and safety of single-dose oral macimorelin for AGHD diagnosis compared with the ITT. Subjects with high (n = 38), intermediate (n = 37), and low (n = 39) likelihood for AGHD and healthy, matched controls (n = 25) were included in the efficacy analysis.

RESULTS

After the first test, 99% of macimorelin tests and 82% of ITTs were evaluable. Using GH cutoff levels of 2.8 ng/mL for macimorelin and 5.1 ng/mL for ITTs, the negative agreement was 95.38% (95% CI, 87% to 99%), the positive agreement was 74.32% (95% CI, 63% to 84%), sensitivity was 87%, and specificity was 96%. On retesting, the reproducibility was 97% for macimorelin (n = 33). In post hoc analyses, a GH cutoff of 5.1 ng/mL for both tests resulted in 94% (95% CI, 85% to 98%) negative agreement, 82% (95% CI, 72% to 90%) positive agreement, 92% sensitivity, and 96% specificity. No serious adverse events were reported for macimorelin.

CONCLUSIONS

Oral macimorelin is a simple, well-tolerated, reproducible, and safe diagnostic test for AGHD with accuracy comparable to that of the ITT. A GH cutoff of 5.1 ng/mL for the macimorelin test provides an excellent balance between sensitivity and specificity.

Effect of Supplementation of a Whey Peptide Rich in Tryptophan-Tyrosine-Related Peptides on Cognitive Performance in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Study

Background: Previous epidemiological and clinical studies have shown that dairy products have beneficial effects on cognitive decline and dementia. Enzymatic digestion of whey protein produces a whey peptide rich in tryptophan-tyrosine-related peptides which improve cognitive performance in mice. We evaluated the effects of whey peptides on cognitive functions in healthy adults in a randomized, double-blind, placebo-controlled design. Methods: 101 healthy adults (45 to 64 years), with a self-awareness of cognitive decline received either whey peptide or placebo supplements for 12 weeks. Changes in cognitive function were assessed using neuropsychological tests at 6 and 12 weeks after the start of supplementation. Results: Verbal fluency test (VFT) score changes tended to be higher in the whey peptide group compared with the placebo at 12 weeks. Subgroup analysis classified by the degree of subjective fatigue showed that changes in the VFT as well as the Stroop and subjective memory function tests between baseline and 6 weeks of intervention were significantly better in subjects with high-level fatigue from the whey peptide group as compared to the placebo group.

CONCLUSIONS

Intake of whey peptide might improve cognitive function in healthy middle- and older-aged adults with high subjective fatigue levels. Further studies will elucidate the relationship among cognitive improvement, whey peptides, and psychological fatigue.

Effect of l-tryptophan and its metabolites on food passage from the crop in chicks

l-tryptophan (l-Trp), an essential amino acid, is well known as a precursor of 5-hydroxytryptamine (5-HT) and melatonin. In mammals, l-Trp itself has been reported to suppress gastric emptying in mammals. In addition, 5-HT and melatonin are found in the gastrointestinal tract and affect food passage from the digestive tract in mammals. While the function of these factors in mammals is documented, there is little knowledge on their function in the digestive tract of birds. Therefore, the purpose of the present study was to determine if l-Trp and its metabolites affect the crop emptying rate in chicks (Gallus gallus). We also investigated the effects of kynurenic acid (KYNA) and quinolinic acid (QA), which are metabolites of the kynurenine pathway for l-Trp. Oral administration of l-Trp significantly reduced the crop emptying rate in chicks. Among the metabolites, intraperitoneal injection of 5-HT and melatonin significantly reduced the crop emptying rate, whereas KYNA and QA had no effect. The present study suggests that l-Trp, 5-HT, and melatonin inhibit the movement of food in the digestive tract and thereby affect the utilization of nutrients in the diet of chicks.

Effects of Dietary Acute Tryptophan Depletion (ATD) on NPY Serum Levels in Healthy Adult Humans Whilst Controlling for Methionine Supply-A Pilot Study

Central nervous serotonin (5-HT) can influence behaviour and neuropsychiatric disorders. Evidence from animal models suggest that lowered levels of neuropeptide Y (NPY) may have similar effects, although it is currently unknown whether decreased central nervous 5-HT impact NPY concentrations. Given that the production of NPY is dependent on the essential amino acid methionine (MET), it is imperative to account for the presence of MET in such investigations. Hence, this study sought to examine the effects of acute tryptophan depletion (ATD; a dietary procedure that temporarily lowers central nervous 5-HT synthesis) on serum concentrations of NPY, whilst using the potential renal acid load indicator (PRAL) to control for levels of MET. In a double-blind repeated measures design, 24 adult humans randomly received an AA-load lacking in TRP (ATD) on one occasion, and a balanced control mixture with TRP (BAL) on a second occasion, both with a PRAL of nearly 47.3 mEq of MET. Blood samples were obtained at 90, 180, and 240 min after each of the AA challenges. ATD, and therefore, diminished substrate availability for brain 5-HT synthesis did not lead to significant changes in serum NPY concentrations over time, compared to BAL, under an acute acidotic stimulus.

Effects of Intragastric Administration of Tryptophan on the Blood Glucose Response to a Nutrient Drink and Energy Intake, in Lean and Obese Men

Tryptophan stimulates plasma cholecystokinin and pyloric pressures, both of which slow gastric emptying. Gastric emptying regulates postprandial blood glucose. Tryptophan has been reported to decrease energy intake. We investigated the effects of intragastric tryptophan on the glycaemic response to, and gastric emptying of, a mixed-nutrient drink, and subsequent energy intake. Lean and obese participants (n = 16 each) received intragastric infusions of 1.5 g ("Trp-1.5g") or 3.0 g ("Trp-3.0g") tryptophan, or control, and 15 min later consumed a mixed-nutrient drink (56 g carbohydrates). Gastric emptying (¹³C-acetate breath-test), blood glucose, plasma C-peptide, glucagon, cholecystokinin and tryptophan concentrations were measured (t = 0-60 min). Energy intake was assessed between t = 60-90 min. In lean individuals, Trp-3.0g, but not Trp-1.5g, slowed gastric emptying, reduced C-peptide_AUC and increased glucagon_AUC (all P < 0.05), but did not significantly decrease the blood glucose response to the drink, stimulate cholecystokinin or reduce mean energy intake, compared with control. In obese individuals, Trp-3.0g, but not Trp-1.5g, tended to slow gastric emptying (P = 0.091), did not affect C-peptide_AUC, increased glucagon_AUC (P < 0.001) and lowered blood glucose at t = 30 min (P < 0.05), and did not affect cholecystokinin or mean energy intake. In obese individuals, intragastrically administered tryptophan may reduce postprandial blood glucose by slowing gastric emptying; the lack of effect on mean energy intake requires further investigation.

Effects of l-tryptophan on the growth, intestinal enzyme activities and non-specific immune response of sea cucumber (Apostichopus japonicus Selenka) exposed to crowding stress

In order to reveal the effects of l-tryptophan (Trp) on the physiology and immune response of sea cucumber (Apostichopus japonicus Selenka) exposed to crowding stress, four density groups of sea cucumbers (i.e. 4, 8, 16 and 32 individuals per 40 L water, represented as L, ML, MH and H) were fed with diets containing 0, 1, 3 and 5% l-tryptophan respectively for 75 days. The results showed that the specific growth rates (SGR) of the sea cucumber fed with diet with 3% Trp (L, 2.1; ML, 1.76; MH, 1.2; H, 0.7) were significantly higher than those fed with basal diet without Trp supplementation (P < .05). Peak amylase activity occurred at H stress density at 3% dietary Trp. Trypsin activity was higher in diet 3% in ML and MH densities than the controls, which increased by 66.4% and 53.8%. However, the lipase activity first increased and then decreased from the stocking density L to H, with highest values of 3% Trp group showed the highest value than other groups. Compared to those fed with the basal diet, sea cucumber fed diets with Trp (3%) had significantly higher phagocytic activities (0.28 OD540/10⁶ cells, H) in coelomic fluid and respiratory burst activities (0.105 OD630/10⁶ cells, MH) (P < .05). The results suggested that Trp cannot improve superoxide dismutase (SOD) activity at L, ML and MH densities. The alkaline phosphatase activity (AKP) significantly decreased at H stress density. Under the experimental conditions, the present results confirmed that a diet supplemented with 3% Trp was able to enhance intestinal enzyme activities, non-specific immune response and higher growth performance of A. japonicus.

A Novel Concept of Amino Acid Supplementation to Improve the Growth of Young Malnourished Male Rats

BACKGROUNDS/AIMS

This study was aimed at understanding the relationship between plasma amino acids and protein malnutrition and at determining whether amino acid supplementation associated with malnutrition and growth improves linear growth in growing rats.

METHODS

Body length and plasma amino acids were measured in young male rats that were fed the following diet for 3 weeks, mimicking a low and imbalanced protein diets based on maize, a major staple consumed in developing countries: a 70% calorically restricted cornmeal-based diet (C), C + micronutrients (CM), CM + casein (CMC), CM + soy protein (CMS) or CMS + 0.3% lysine.

RESULTS

A correlation analysis of linear growth and plasma amino acids indicated that lysine, tryptophan, branched-chain amino acids, methionine, and phenylalanine significantly correlated with body length. Supplementation with these 5 amino acids (AA1) significantly improved the body length in rats compared to CMC treatment whereas, nitrogen-balanced amino acid supplemented controls (AA2) did not (CM +1.2 ± 0.2, CMC +2.7 ± 0.3, CMS +2.1 ± 0.3, AA1 +2.8 ± 0.2, and AA2 +2.5 ± 0.3 cm).

CONCLUSION

With securing proper amino acid balance, supplementing growth-related amino acids is more effective in improving linear growth in malnourished growing male rats. Analysis of the correlation between plasma amino acids and growth represents a powerful tool to determine candidate amino acids for supplementation to prevent malnutrition. This technology is adaptable to children in developing countries.

Local immune response of two mucosal surfaces of the European seabass, Dicentrarchus labrax, fed tryptophan- or methionine-supplemented diets

Immune responses relies on an adequate provision of multiple nutrients that sustain the synthesis of key effector molecules. These needs are depicted in the already reported increase of circulating free amino acids in fish under stressful conditions. Since aquaculture and the inherent fish welfare are an emergent call, the immunomodulatory effects of amino acids on gut- and skin-associated lymphoid tissues of the European seabass (Dicentrarchus labrax) were studied under unstressed conditions and after an inflammatory insult. To achieve this goal, fish were distributed in duplicate tanks (fifteen fish per tank) and were fed for 14 days with methionine or tryptophan-supplemented diets at 2× dietary requirement level (MET and TRP, respectively) or a control diet meeting the amino acids requirement levels (CTRL). Afterwards, samples of skin and posterior gut were collected from 6 fish per dietary treatment for the assessment of the immune status while the remaining animals were intraperitoneally-injected with inactivated Photobacterium damselae subsp. piscicida and subsequently sampled either 4 or 24 h post-injection. The immune status of both mucosal surfaces was poorly affected, although a tryptophan effect was denoted after bacterial inoculation, with several immune-related genes up-regulated in the gut at 4 h post-injection, which seems to suggest a neuroendocrine-immune systems interaction. In contrast, skin mucosal immunity was inhibited by tryptophan dietary supplementation. Regarding methionine, results were often statistically non-significant, though increasing trends were denoted in a few parameters. Overall, dietary methionine did not significantly affect neither gut nor skin immunity, whereas tryptophan supplementation seems to induce modulatory mechanisms that might be tissue-specific.

Comparison of plasma tryptophan-related metabolites in crossbred Piétrain and Duroc pigs

Besides being incorporated into proteins, Trp, an indispensable AA, is involved in numerous metabolic pathways. Previous data showed that Trp conversion into kynurenine (Kyn) and nicotinamide (Nam) differs among studies, and such differences cannot be explained by different dietary niacin supplies. We hypothesized that pig genotype influences Trp metabolism and thus the conversion of Trp into its metabolites. The objective of this study was to compare plasma appearance of Trp and related metabolites in 12 Duroc and 12 Piétrain crossbred postweaning pigs fed 2 contrasting dietary Trp levels. Within each genotype, 6 pigs were fed a basal (B-Trp: 17% and 15% standardized ileal digestible [SID] Trp:Lys for starter and prestarter diets) or supplemented (S-Trp: 24% and 23% SID Trp:Lys for starter and prestarter diets) Trp diet. Growth was monitored, and plasma fasted concentrations were measured over 4 wk, and then pigs were fitted with a jugular catheter for frequent blood samplings. After overnight fasting, 350 g of the experimental diets were offered to each pig, and plasma concentrations of Trp, Kyn, Nam, and 5-hydroxytryptamine (5-HT) were measured for 6 h. The activities of Trp-degrading enzymes were measured in different tissues collected after pig slaughtering. Plasma Trp fasted concentrations did not differ between B-Trp and S-Trp diets and increased from weaning to 2 and 4 wk after weaning for Piétrain but not for Duroc crossbred pigs (time × genotype, = 0.001). Plasma Kyn concentrations were greater 4 wk after weaning ( = 0.002) than at weaning and for Piétrain compared to Duroc genetics ( = 0.008). Plasma Nam concentrations were greater for pigs fed the S-Trp diet than for those fed the B-Trp diet ( = 0.0001) and for Duroc than for Piétrain genetic lines ( = 0.001); this difference tends to be greater at weaning than after ( = 0.055). Our data showed an increase in plasma concentrations of Trp, Kyn, Nam, and 5-HT according to time after a meal and to the dietary Trp content. However, postprandial plasma concentrations of Trp metabolites and enzyme activities were not significantly different between Duroc and Piétrain crossbred pigs. In conclusion, our results suggest that Nam endogenous synthesis capacity from Trp is greater in Duroc than in Piétrain crossbred pigs, but this was apparent only at weaning.

Non-invasive tryptophan fluorescence measurements as a novel method of grading cataract

Development of non-invasive treatments for cataract calls for a sensitive diagnostic assay. We conducted a study to test whether the ratio of folded tryptophan to non-tryptophan fluorescence emission (F-factor) may be used for grading cataracts in human lenses. The F-factor was measured on aspirated lens material from eyes undergoing femtosecond laser assisted cataract surgery (FLACS) and was compared to a preoperative optical grading of cataract using Scheimpflug imaging. The preoperative optical grading allocated the cataracts to 1 of 4 categories according to the density of the cataract. All cataracts were age-related. Lens material from 16 eyes of 14 patients was included in the study. Cataracts were preoperatively graded in categories 1, 2 and 3. No lenses were category 4. For nuclear cataracts mean values of F-factor were 52.9 (SD 12.2), 61.7 (SD 5.3) and 75.7 (SD 8.9) for categories 1, 2 and 3 respectively. Linear regression on F-factor as a function of preoperative grading category showed increasing values of F-factor with increasing preoperative grading category, R² = 0.515. Our experiment showed that preoperative optical grading of cataracts by Scheimpflug imaging may correlate to measures of tryptophan and non-tryptophan fluorescence in human lenses. Based on our results we find that measuring the ratio between tryptophan- and non-tryptophan fluorescence may be a future tool for grading cataracts, but further research is needed.

Therapeutic effects of an alpha-casozepine and L-tryptophan supplemented diet on fear and anxiety in the cat

Objectives This study assessed the anxiolytic effectiveness of a test diet (Royal Canin Feline Calm diet) supplemented with L-tryptophan and alpha-casozepine. Methods Subjects were 24 cats that were classified as mildly or markedly fearful based on the presence of a person in their home room. Three different protocols were used to assess anxiety: (1) evaluation of the response to a human in the cat's home room (home room test); (2) analysis of the response to placement in an empty test room (open-field test); and (3) analysis of the response to an unfamiliar human (human interaction test). All three protocols were first run at baseline, and the results were used to assign the animals to control and test diet groups that showed equivalent fear and anxiety. Both groups were retested on the three protocols after 2 weeks (test 1) and again after 4 weeks (test 2). Results The diet groups differed for two behavioral measures in the open-field test: inactivity duration and inactivity frequency. The control group showed statistically significant increases in inactivity duration between baseline and test 1 and baseline and test 2, while the group fed the test diet showed a marginally not significant decrease in inactivity duration between baseline and test 1 and a not significant decrease for test 2. There was also a significant increase in inactivity frequency between baseline and test 1 in the test diet group and marginally not significant decrease in the control group. There were no differences between groups in the approach of the cats toward people for the home room test and the human interaction test. Conclusions and relevance These results suggest that the test diet reduced the anxiety response to placement in an unfamiliar location, but that fear in the presence of an unfamiliar person was not counteracted by the diet.

Metabolomic changes demonstrate reduced bioavailability of tyrosine and altered metabolism of tryptophan via the kynurenine pathway with ingestion of medical foods in phenylketonuria

BACKGROUND

Deficiencies of the monoamine neurotransmitters, such as dopamine synthesized from Tyr and serotonin synthesized from Trp, are of concern in PKU. Our objective was to utilize metabolomics analysis to assess monoamine metabolites in subjects with PKU consuming amino acid medical foods (AA-MF) and glycomacropeptide medical foods (GMP-MF).

METHODS

Subjects with PKU consumed a low-Phe diet combined with AA-MF or GMP-MF for 3weeks each in a randomized, controlled, crossover study. Metabolomic analysis was conducted by Metabolon, Inc. on plasma (n=18) and urine (n=9) samples. Catecholamines and 6-sulfatoxymelatonin were measured in 24-h urine samples.

RESULTS

Intake of Tyr and Trp was ~50% higher with AA-MF, and AA-MF were consumed in larger quantities, less frequently during the day compared with GMP-MF. Performance on neuropsychological tests and concentrations of neurotransmitters derived from Tyr and Trp were not significantly different with AA-MF or GMP-MF. Plasma serotonin levels of gut origin were higher in subjects with variant compared with classical PKU, and with GMP-MF compared with AA-MF in subjects with variant PKU. Metabolomics analysis identified higher levels of microbiome-derived compounds synthesized from Tyr, such as phenol sulfate, and higher levels of compounds synthesized from Trp in the kynurenine pathway, such as quinolinic acid, with ingestion of AA-MF compared with GMP-MF.

CONCLUSIONS

The Tyr from AA-MF is less bioavailable due, in part, to greater degradation by intestinal microbes compared with the Tyr from prebiotic GMP-MF. Research is needed to understand how metabolism of Trp via the kynurenine pathway and changes in the intestinal microbiota affect health for individuals with PKU. This trial is registered at www.clinicaltrials.gov as NCT01428258.

Effect of L-Tryptophan Supplementation on Eosinophils and Eotaxin in Guinea Pigs

Eosinophilie Myalgia Syndrome is a hypereosinophilic disorder that appears to result from the ingestion of the dietary supplement L-tryptophan by susceptible individuals. It is unclear if this disease results from tryptophan, contaminants found in tryptophan, individual predisposition (such as immune status and allergies), or some combination of effects. To evaluate effects of L-tryptophan on eosinophil migration, guinea pigs were compared with or without supplemental tryptophan (0. g/kg/day), with or without immune sensitization, and with or without immune challenge. Eosinophil counts were obtained from bone marrow, blood, lung, and bronchial alveolar lavage fluid (BAL). Lung cells were obtained to measure eotaxin concentrations in supernates and lysates with or without antigen and calcium ionophore challenge using direct ELISA. Skin biopsies were taken from both non-injected and antigen injection sites. The tryptophan supplemented, antigen-sensitized/antigen-challenged guinea pigs showed a significant decrease in blood eosinophils, compared to control (cellulose) supplemented antigen-sensitized/antigen-challenged guinea pigs [(0.086 ± 0.023) × 106 vs (0.147 ± 0.021) × 106 eoslnophils/ml recovered, respectively] with a significant increase in BAL eosinophils [(0.052 ± 0.008) × 106 vs (0.033 ± 0.005) × 10s eosinophils/ml recovered, respectively]. Unchallenged lung cell lysates from tryptophan-supplemented guinea pigs contained significantly less eotaxin compared to cellulose-supplemented guinea pigs regardless of whether they were sensitized (0.006 ± 0.002 vs 0.027 ± 0.008 ng/106 cells, respectively). No differences were observed in skin biopsies between cellulose and tryptophan groups. These results suggest that L-tryptophan-supplemented guinea pigs have altered eotaxin regulation, a potential mechanism by which human overconsumption of tryptophan dietary supplements could lead to hypereosinophilic disorders in susceptible individuals.

Protective effects of high Tryptophan diet on aging-induced passive avoidance impairment and hippocampal apoptosis

In our previous work we have shown that L-Tryptophan (TrP) enriched diet prevents the age-induced decline of hippocampal Serotonin (5-HT) production. Considering that loss or reduction in 5-HT neurotransmission may contribute to age-related cognitive decline, here we have investigated the effect of such diet on passive avoidance (PA) behavior, cell death, pro- and anti- apoptotic molecules (BAX, Bcl-2 and Caspase-3) and an important transcription factor involved in synaptic plasticity and memory (CREB). The increase in 5-HT neurotransmission in the Hippocampus (Hp) of aged rats was induced by 1 month of high TrP administration. In the first phase of our study we found that high TrP diet improves PA behaviour of aged rats and this correlated with a decrease of TUNEL positive cells in all hippocampal regions tested (CA1, CA2, CA3, DG). Interestingly, the Hp of aged animals fed with high TrP diet showed a significant downregulation of proapoptotic proteins, caspase-3 and BAX, and an increase of antiapoptotic molecules Bcl-2 as indicated by Western Blot and immunohistochemical analyses. Also, high TrP diet partially rescued the age-induced inhibition of hippocampal CREB phosphorylation. Altogether, our data suggest that enhanced TrP intake, and in consequence a potential increase in 5-HT neurotransmission, might be beneficial in preventing age-related detrimental features by inhibition of hippocampal apoptosis.

Effect of L-Tryptophan and L-Leucine on Gut Hormone Secretion, Appetite Feelings and Gastric Emptying Rates in Lean and Non-Diabetic Obese Participants: A Randomized, Double-Blind, Parallel-Group Trial

Background/Objectives

Gut hormones such as cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) play a role as satiation factors. Strategies to enhance satiation peptide secretion could provide a therapeutic approach for obesity. Carbohydrates and lipids have been extensively investigated in relation to peptide release. In contrast, the role of proteins or amino acids is less clear. Our aim was to compare the effects of the amino acids L-tryptophan (L-trp) and L-leucine (L-leu) separately on gastric emptying and gut peptide secretion.

Participants/Methods

The study was conducted as a randomized (balanced), double-blind, parallel-group trial. A total of 10 lean and 10 non-diabetic obese participants were included. Participants received intragastric loads of L-trp (0.52 g and 1.56 g) and L-leu (1.56 g), dissolved in 300 mL tap water; 75 g glucose and 300 mL tap water served as control treatments.

Results

Results of the study are: i) L-trp at the higher dose stimulates CCK release (p = 0.0018), and induces a significant retardation in gastric emptying (p = 0.0033); ii) L-trp at the higher dose induced a small increase in GLP-1 secretion (p = 0.0257); iii) neither of the amino acids modulated subjective appetite feelings; and iv) the two amino acids did not alter insulin or glucose concentrations.

Conclusions

L-trp is a luminal regulator of CCK release with effects on gastric emptying, an effect that could be mediated by CCK. L-trp’s effect on GLP-1 secretion is only minor. At the doses given, the two amino acids did not affect subjective appetite feelings.

Trial Registration

ClinicalTrials.gov NCT02563847

Photosensitizer-conjugated tryptophan-containing peptide ligands as new dual-targeted theranostics for cancers

Here we report that new dual-targeted theranostic anti-cancer agents can be produced by simple conjugation of photosensitizers with tryptophan-containing peptide ligands via cyclic disulfide linkages. In the proof-of-concept study, photosensitizers conjugated with EGFR-targeting peptide GE11 (C-EGFR) were in close proximity with tryptophan residues in the conjugate, resulting in quenching of its fluorescence and singlet oxygen generation. C-EGFR specifically binds to target receptors on the cancer cell surface, after which it is internalized via receptor-mediated endocytosis. Intracellular cleavage of cyclic disulfide bonds allows separation of the photosensitizers from the tryptophan residue, after which they emit near-infrared (NIR) fluorescence and produce a phototoxic effect in the target cells. This strategy enabled us to accomplish simultaneous real-time NIR fluorescence imaging of EGFR-overexpressing cancer cells with high contrast and selective photodynamic therapy.

Efficacy of differently applied tyrosine and tryptophan for modulation of phenolic metabolism in Trachyspermum ammi (L.) sprague seedlings

Phenolics are pharmaceutically important molecules. Tyrosine and tryptophan are precursors of phenolic metabolism. It was aimed to investigate the potential of exogenously introduced precursors on the phenolic contents in Trachyspermum ammi (L.) Sprague seedlings. The seeds of two local varieties (Chakwal and Desi) were grown in completely randomized design in a growth chamber at 19 ± 2°C with two amino acids (tyrosine and tryptophan) applied (priming and supplementation in rooting medium) at two treatment levels (0, and 1%). Ten days old seedlings were harvested and subjected for growth (root and shoot length, fresh weight and dry weight) and phenolic estimation was done by HPLC method. Presence of seven phenolic acids including quercitin, chromatotropic acid, gallic acid, chlorogenic acid, sinnapic acid, trans 4 hydroxy 3 methoxy cinamic acid and P-courmeric acid was confirmed in both varieties with dissimilar fraction. Poor growth was observed by "Desi" under controlled conditions that were efficiently enhanced by tyrosine and tryptophan treatments. As precursors both amino acids differed for allosteric regulation of the pathway. That varied from application to application and variety to variety too for a pattern of phenolic accumulation. In conclusion, tyrosine and tryptophan application can be useful for farmers for improved growth of T. ammi and for pharmaceutical scientists to modulate metabolites of interest.