5-Hydroxytryptophan acts as a gap junction inhibitor to limit the spread of chemotherapy-induced cardiomyocyte injury and mitochondrial dysfunction.

Anthracycline chemotherapeutics like doxorubicin (DOX) are widely used against various cancers but are accompanied by severe cardiotoxic effects that can lead to heart failure. Through whole transcriptome sequencing and pathological tissue analysis in a murine model, our study has revealed that DOX impairs collagen expression in the early phase, causing extracellular matrix anomalies that weaken the mechanical integrity of the heart. This results in ventricular wall thinning and dilation, exacerbating cardiac dysfunction. In this work, we have identified 5-hydroxytryptophan (5-HTP) as a potent inhibitor of gap junction communication. This inhibition is key to limiting the spread of DOX-induced cardiotoxicity. Treatment with 5-HTP effectively countered the adverse effects of DOX on the heart, preserving ventricular structure and ejection fraction. Moreover, 5-HTP enhanced mitochondrial respiratory function, as shown by the O2k mitochondrial function assay, by improving mitochondrial complex activity and ATP production. Importantly, the cardioprotective benefits of 5-HTP did not interfere with DOX's ability to combat cancer. These findings shed light on the cardiotoxic mechanisms of DOX and suggest that 5-HTP could be a viable strategy to prevent heart damage during chemotherapy, offering a foundation for future clinical development. This research opens the door for 5-HTP to be considered a dual-purpose agent that can protect the heart without compromising the oncological efficacy of anthracycline chemotherapy.

The differential sensitivity of the hypothalamic-hypophysial-ovarian axis to 5-hydroxytryptophan alters the secretion of estradiol.

Serotonin [5-hydroxytryptamine (5-HT)] modulates ovarian function. The precursor of 5-HT, 5-hydroxytryptophan (5-HTP), has been used to treat depression. However, the effects of 5-HTP on ovarian and reproductive physiology remain unknown. In this research, we analysed the impact of 5-HTP on the monoaminergic system and its interactions with the reproductive axis and ovarian estradiol secretion when administered by distinct routes. Female rats 30 days of age were injected with 5-HTP i.p. (100 mg/kg), into the ovarian bursa (1.5 µg/40 µL) or into the median raphe nucleus (20 µg/2.5 µL) and were killed 60 or 120 min after injection. As controls, we used rats of the same age injected with vehicle (0.9% NaCl). Monoamine, gonadotrophin and steroid ovarian hormone concentrations were measured. The injection of 5-HTP either i.p. or directly into the ovarian bursa increased the concentrations of 5-HT and the metabolite 5-hydroxyindole-3-acetic acid in the ovary. For both routes of administration, the serum concentration of estradiol increased. After i.p. injection of 5-HTP, the concentrations of luteinizing hormone were decreased and follicle-stimulating hormone increased after 120 min. Micro-injection of 5-HTP into the median raphe nucleus increased the concentrations of 5-HT in the anterior hypothalamus and dopamine in the medial hypothalamus after 120 min. Our results suggest that the administration of 5-HTP either i.p. or directly into the ovarian bursa enhances ovarian estradiol secretion.

Serotonin alters the response to a glucose challenge in lactating cows.

Energy partitioning in lactating cows affects milk production, feed efficiency, and body reserves, with the latter having health implications for the transition into the following lactation. One molecule likely involved in the regulation of energy partitioning is serotonin. The objective of this experiment was to explore how increasing circulating serotonin, by intravenous infusion of the serotonin precursor 5-hydroxytryptophan (5-HTP), affects metabolic responses to a glucose challenge in midlactation cows as a means to manipulate energy partitioning. We intravenously infused Holstein cows with 5-HTP (1 mg/kg bodyweight dissolved in saline, n = 11) or saline alone as control (n = 9) over 1 h/day for 3 days. Cows were fasted overnight on day 2. On day 3, fasted cows were given an intravenous bolus of glucose (0.092 g/kg bodyweight). Blood samples were collected for the following 120 min for metabolic and hormonal analysis. Infusion of 5-HTP elevated circulating concentrations of serotonin and free fatty acids, reduced the concentration of insulin and amino acids, and did not affect the concentration of glucose and glucagon before the glucose challenge. Surrogate insulin sensitivity indices indicated improved insulin sensitivity in 5-HTP cows, but due to the unique metabolism of lactating ruminants, these index changes may instead reflect effects in insulin-independent glucose disposal, like milk synthesis. Challenging 5-HTP-treated cows with a glucose bolus reduced the insulin spike and blunted the decrease in free fatty acids, compared to saline cows, without changing glucose dynamics. Overall, these results suggest that serotonin stimulates insulin-independent glucose disposal, requiring less insulin to maintain normoglycemia.

5-Hydroxytryptophan inhibits ß-casein biosynthesis and promotes goat mammary epithelial cell apoptosis through the JAK2/STAT5a axis and the HTR7.

5-Hydroxytryptamine (5-HT) is an amine produced in both the mammary gland and the central nervous system. Tryptophan hydroxylase 1 (TPH1) catalyzes the conversion of 5-hydroxytryptophan (5-HTP) into l-tryptophan, which is then converted into 5-HT by monoamine-oxidase (MAO-A). In the mammary gland, 5-HT has been shown to have a variety of paracrine-autocrine actions, including suppressing lactation, controlling the destiny of mammary epithelial cells, and maintaining calcium homeostasis throughout the transition from pregnancy to lactation. To examine the effects of 5-HT on the composition of colostrum and milk, a total of 30 transition Guan Zhong dairy goats were intramuscularly injected with 5-HTP (1.0 mg/kg) every morning before feeding from 10 d before the projected parturition date to the day of parturition. The average number of days animals received injections was 8.2 ± 3.2 d. 5-HTP treatment increased serum 5-HT concentration from days 5 to 2 relative to parturition (P < 0.05), and decreased the casein concentration of colostrum (P < 0.05). In the in vitro experiment, mammary epithelial cells isolated from three individual goats' mammary glands were separately treated with 200 µM 5-HTP, 30 µM PCPA (the specific inhibitor of TPH1), or 200 µM 5-HTP + 50 µM SB269970 (the selective antagonist of 5-HTR7). The results showed that 200 µM 5-HTP inhibited the expression of ß-casein, downregulated the activity of the JAK2/ STAT5a signaling pathway, and promoted the apoptosis of goat mammary epithelial cells (GMECs) (P < 0.05). When GMECs were treated with 30 µM Four-chloro-dl-phenylalanine (PCPA), a specific inhibitor of 5-HT synthesis, the mRNA expression of STAT5a and the phosphorylated STAT5a protein level were upregulated. The 50 µM SB269970 treatment rescued the effects of 5-HTP on GMECs (P < 0.05). Taken together, the results indicated that 5-HTP exerted an inhibitory effect on ß-casein synthesis and a proapoptotic effect in GMECs via HTR7 and the JAK2/STAT5a axis.

5-Hydroxytryptamine (5-HT), which is produced in both the mammary gland and the central nervous system, is a recognized important regulator of mammary gland homeostasis. Casein is the major protein in the milk of mammals including cows, goats, and humans, and is a crucial source of high-quality amino acids for humans. In this study, prenatal intramuscular injection of 5-hydroxytryptophan (5-HTP), the precursor of 5-HT, not only increased the level of 5-HT in the serum of goats before delivery but also decreased the concentration of casein in colostrum. Furthermore, in goat mammary epithelial cells which are responsible for milk synthesis, it was found that 5-HTP blocked genes and signal pathways related to casein synthesis, and also promoted cell apoptosis. Additional results demonstrated that the type 7 5-HT receptor (HTR7) mediated the impacts of 5-HT, which provided a potential reliable target for improving milk quality.

Corylin ameliorates chronic ulcerative colitis via regulating the gut-brain axis and promoting 5-hydroxytryptophan production in the colon.

BACKGROUND: Chronic ulcerative colitis (UC) is a lifelong disease, patients with chronic UC have a high prevalence of common mental disorders. The increasing interest in the role of gut-brain axis is seen in inflammatory bowel diseases. PURPOSE: Corylin is a representative flavonoid compound isolated from the Psoraleae Fructus. This study aimed to identify the effects and mechanism of corylin on the inflammation interactions and 5-HT synthesis between the gut and brain in chronic UC. METHODS: Dextran sulfate sodium (DSS) induced chronic UC mouse model was established to assess the therapeutic effect of corylin on chronic UC symptoms. The expression of inflammatory cytokines was detected in the colon and brain. The expression of tight junction (TJ) proteins of intestinal mucosal barrier and blood-brain barrier (BBB) and the ionized calcium-binding adaptor molecule 1 (Iba1) in the hippocampus were determined by western blotting and immunofluorescence staining. In addition, several tryptophan (Trp) metabolites and related neurotransmitters in faeces, colon, serum, and brain were detected by UPLC-MS/MS. The interaction between corylin and 5-hydroxytryptophan decarboxylase (5-HTPDC) was performed by molecular docking and surface plasmon resonance (SPR). Finally, the changes of gut microbiota composition were analyzed by 16S rRNA sequencing. RESULTS: Corylin significantly alleviated colitis symptoms and inhibited inflammatory response in the colon and brain of DSS-induced chronic UC mice. The TJ proteins of intestinal mucosal barrier and BBB were improved and the expression of Iba1 in the hippocampus was normalized after corylin treatment. In addition, corylin treatment increased the expression of neurotransmitters in the brain, especially 5-hydroxytryptamine (5-HT) and 5-hydroxytryptophan (5-HTP), but the expression of 5-HT in the colon was inhibited. Further study firstly proved that corylin could bind to the 5-HTDPC, and then inhibit the expression of 5-HTDPC and VB6, resulting in the 5-HT reduction and 5-HTP accumulation in the colon. Moreover, the intake of corylin transformed the diversity and composition of intestinal microbiota, Bacteroides, Escherichia-Shigella, and Turicibacter were decreased but Dubosiella, Enterorhabdus, and Candidatus_Stoquefichus were increased. CONCLUSION: Corylin administration ameliorated DSS-induced colitis and inhibited intestinal inflammation and neuroinflammation via regulating the inflammation interactions across gut-brain axis and increasing 5-HTP generation in the colon.

The Effects of 5-HTP on Body Composition: An 8-Week Preliminary RCT.

The purpose of this investigation was to determine the effects of supplementing with 100 mg daily of 5-Hydroxytryptophan (5-HTP) on indices of body composition in exercise-trained men and women. Sixty-one subjects volunteered for this investigation. Forty-eight subjects were randomized into a treatment (n = 31, 12 male/19 female; 100 mg 5-HTP daily; CLEANMOOD™) or a placebo (n = 17, six male/11 female; maltodextrin). Body composition was assessed pre- and post-treatment after eight weeks via a multi-frequency bioelectrical impedance device (InBody® 270). Subjects were instructed to not change their training or eating habits; moreover, they were instructed to track their diet ∼2-3 days per week using a mobile app (MyFitnessPal). There were no changes in food intake (i.e. total energy intake or grams of macronutrients) between or within groups. Lean body mass, total body water, and % body fat did not change significantly in either group. Fat mass decreased significantly post versus pre in the 5-HTP group (p = 0.02) but did not change in the placebo group (p = 0.58). Moreover, changes in fat mass were significantly different between the 5-HTP and placebo group (p = 0.048). Based on the limited data from this investigation, daily supplementation with 100 mg of 5-HTP may affect body composition.

Role of 5-HT2A, 5-HT2C, 5-HT1A and TAAR1 Receptors in the Head Twitch Response Induced by 5-Hydroxytryptophan and Psilocybin: Translational Implications.

There is increasing interest in the therapeutic potential of psilocybin. In rodents, the serotonin precursor, 5-hydroxytryptophan (5-HTP) and psilocybin induce a characteristic 5-HT2A receptor (5-HT2AR)-mediated head twitch response (HTR), which is correlated with the human psychedelic trip. We examined the role of other serotonergic receptors and the trace amine -associated receptor 1 (TAAR1) in modulating 5-HTP- and psilocybin-induced HTR. Male C57BL/6J mice (11 weeks, ~30 g) were administered 5-HTP, 50-250 mg/kg i.p., 200 mg/kg i.p. after pretreatment with 5-HT/TAAR1 receptor modulators, psilocybin 0.1-25.6 mg/kg i.p. or 4.4 mg/kg i.p., immediately preceded by 5-HT/TAAR1 receptor modulators. HTR was assessed in a custom-built magnetometer. 5-HTP and psilocybin induced a dose-dependent increase in the frequency of HTR over 20 min with attenuation by the 5-HT2AR antagonist, M100907, and the 5-HT1AR agonist, 8-OH-DPAT. The 5-HT2CR antagonist, RS-102221, enhanced HTR at lower doses but reduced it at higher doses. The TAAR1 antagonist, EPPTB, reduced 5-HTP- but not psilocybin-induced HTR. We have confirmed the key role of 5-HT2AR in HTR, an inhibitory effect of 5-HT1AR, a bimodal contribution of 5-HT2CR and a role of TAAR1 in modulating HTR induced by 5-HTP. Compounds that modulate psychedelic-induced HTR have important potential in the emerging therapeutic use of these compounds.

Quinonoid dihydropteridine reductase, a tetrahydrobiopterin-recycling enzyme, contributes to 5-hydroxytryptamine-associated platelet aggregation in mice.

Quinonoid dihydropteridine reductase (QDPR) regenerates tetrahydrobiopterin (BH4), which is an essential cofactor for catecholamine and serotonin (5-hydroxytryptamine, 5-HT) biosynthesis. Serotonin is known as an important platelet agonist, but its role under BH4-synthesizing or recycling enzymes deficiency is unknown. In the present study, we evaluated the effect of Qdpr gene disruption on platelet aggregation using knockout (Qdpr-/-) mice. Platelet aggregation was monitored by light transmission aggregometry using adenosine diphosphate (ADP) and collagen as agonists. We also assessed how platelet aggregation was modified by 5-HT recovery through supplementation with 5-hydroxytryptophan (5-HTP), a 5-HT precursor, or by blocking the serotonin 5-HT2A receptor. Platelet aggregation in the Qdpr-/- mice was significantly suppressed in comparison with that in wild-type (Qdpr+/+) mice, particularly at the maintenance phase of aggregation. 5-HT storage was decreased in Qdpr-/- platelets, and 5-HTP supplementation recovered not only the intraplatelet 5-HT levels but also platelet aggregation. In addition, 5-HT signal blockade using sarpogrelate suppressed platelet aggregation in Qdpr+/+ mice, and platelets in Qdpr-/- mice were hardly affected. Our results indicate that QDPR deficiency suppresses platelet aggregation by impairing 5-HT biosynthesis in mice.

Hippocampal ischaemia from accidental 5-Hydroxytryptophan (5-HTP) overdose case report.

We report severe reversible hippocampal ischaemia following an accidental 5-Hydroxytryptophan (5-HTP) overdose. Serious consequences from 5-HTP overdose have not been reported. A 44-year-old previously well man ingested ten times the recommended dose of 5-HTP powder. After four hours he developed marked antegrade and retrograde amnesia, disorientation and confusion in the absence of loss of consciousness, seizure activity or features of serotonin toxicity. Magnetic resonance imaging (MRI) of the brain on day two revealed extensive symmetrical restricted diffusion bilaterally in the hippocampi, suggestive of ischaemia or seizure. Electroencephalogram was normal. Short and long-term memory improved sufficiently to return to work after two months. MRI at eleven months was normal. The most likely mechanism is drug-induced hippocampal ischaemia resulting from marked increase in 5-HTP.

ß-carboline-independent antidepressant-like effect of the standardized extract of the barks of Mimosa tenuiflora (Willd) Poir. occurs via 5-HT2A/2C receptors in mice.

BACKGROUND: Depression is a psychiatric disorder with limited therapy options. Psychedelics are new antidepressant candidates, being the ayahuasca one of the most promising ones. A synergistic combination of N,N-dimethyltryptamine (DMT) and ß-carbolines allows ayahuasca antidepressant properties. Another psychedelic and DMT-containing beverage is the jurema wine used religiously by indigenous people from Northeastern Brazil. AIMS: To evaluate the antidepressant-like effect of standardized extract of Mimosa tenuiflora (SEMT), associated or not with harmine (ß-carboline), in behavioral models of depression. METHODS: The SEMT was submitted to (+) ESI-IT-LC/MS analysis for DMT quantification. To assess the antidepressant-like effect of SEMT, the open field (OFT), tail suspension (TST), and forced swim (FST) tests were performed. To verify the participation of serotonergic systems, the 5-hydroxytryptophan (5-HTP)-induced head twitch test was performed. RESULTS: The content of DMT found in SEMT was 24.74 ± 0.8 mg/g. Yuremamine was also identified. SEMT presented an antidepressant-like effect in mice submitted to the TST and FST, independent from harmine, with no significant alterations on the OFT. The sub-dose interaction between SEMT and ketamine also produced an anti-immobility effect in the TST, with no changes in the OFT. SEMT potentiated the head twitch behavior induced by 5-HTP and ketanserin prevented its antidepressant-like effect in the TST (p < 0.05). CONCLUSIONS: SEMT presented a harmine-independent antidepressant-like effect in mice submitted to the TST and FST. This effect occurs possibly via activation of serotonergic systems, particularly the 5-HT2A/2C receptors.

L-5-hydroxytryptophan promotes antitumor immunity by inhibiting PD-L1 inducible expression.

BACKGROUND: The repression or downregulation of programmed death-ligand 1 (PD-L1) can release its inhibition of T cells and activate antitumor immune responses. Although PD-1 and PD-L1 antibodies are promising treatments for diverse tumor types, their inherent disadvantages and immune-related adverse events remain significant issues. The development of small molecule inhibitors targeting the interaction surface of PD-1 and PD-L1 has been reviving, yet many challenges remain. To address these issues, we aimed to find small molecules with durable efficacy and favorable biosafety that alter PD-L1 surface expression and can be developed into a promising alternative and complementary therapy for existing anti-PD-1/PD-L1 therapies. METHODS: Cell-based screen of 200 metabolic molecules using a high-throughput flow cytometry assay of PD-L1 surface expression was conducted, and L-5-hydroxytryptophan (L-5-HTP) was found to suppress PD-L1 expression induced by interferon gamma (IFN-γ). Inhibition of PD-L1 induction and antitumor effect of L-5-HTP were evaluated in two syngeneic mouse tumor models. Flow cytometry was performed to investigate the change in the tumor microenvironment caused by L-5-HTP treatment. RESULTS: We discovered that L-5-HTP suppressed IFN-γ-induced PD-L1 expression in tumor cells transcriptionally, and this effect was directly due to itself. Mechanistically, L-5-HTP inhibited IFN-γ-induced expression of RTK ligands and thus suppressed phosphorylation-mediated activation of RTK receptors and the downstream MEK/ERK/c-JUN signaling cascade, leading to decreased PD-L1 induction. In syngeneic mouse tumor models, treatment with 100 mg/kg L-5-HTP (intraperitoneal) inhibited PD-L1 expression and exhibited antitumor effect. L-5-HTP upregulated the ratio of granzyme B+ CD8+ activated cytotoxic T cells. An intact immune system and PD-L1 expression was critical for L-5-HTP to exert its antitumor effects. Furthermore, L-5-HTP acted synergistically with PD-1 antibody to improve anticancer effect. CONCLUSION: Our study illustrated L-5-HTP's inhibitory effect on PD-L1 induction stimulated by IFN-γ in tumor cells and also provided insight into repurposing L-5-HTP for use in tumor immunotherapy.

Acute treatment with 5-hydroxytryptophan increases social approach behaviour but does not activate serotonergic neurons in the dorsal raphe nucleus in juvenile male BALB/c mice: A model of human disorders with deficits of sociability.

BACKGROUND: The BALB/c mouse has been proposed as a model of human psychiatric disorders characterised by elevated anxiety and altered sociability. Juvenile BALB/c mice show decreased social exploratory behaviour, increased anxiety, and reduced brain serotonin synthesis compared to other strains including C57BL/6J mice. AIM: To determine whether supplementation of brain serotonin synthesis alters social behaviour and activation of serotonergic neurons across subregions of the dorsal raphe nucleus (DR) in BALB/c mice. METHODS: Juvenile male BALB/c mice were assigned to one of four treatment conditions: vehicle/vehicle, carbidopa (25 mg/kg)/vehicle, vehicle/5-HTP (10 mg/kg), carbidopa (25 mg/kg)/5-HTP (10 mg/kg). Social behaviour was measured using the three-chamber social approach test, followed by immunohistochemical staining for TPH2 and c-Fos to measure activation of serotonergic neurons across subregions of the DR. RESULTS: Mice treated with carbidopa/5-HTP spent more time in the social cage zone and covered more distance in the social approach test compared to other treatment groups. There was no difference between treatment groups in the activation of serotonergic neurons across subregions of the DR. However, the DRD was associated with increased social approach behaviour in carbidopa/5-HTP treated animals. CONCLUSIONS: Supplementation of serotonin synthesis can increase social approach behaviour in juvenile BALB/c mice. An increase in locomotor behaviour was also observed suggesting that increasing central serotonin synthesis may have led to a reduction in state anxiety, manifesting in increased exploratory behaviour. As no effect on serotonergic activation within the DR was found, alternative mechanisms are likely important for the effects of 5-HTP on social behaviour.

In vitro effects of 5-Hydroxy-L-tryptophan supplementation on primary bovine mammary epithelial cell gene expression under thermoneutral or heat shock conditions.

Serotonin (5-HT) is an autocrine-paracrine molecule within the mammary gland regulating homeostasis during lactation and triggering involution after milk stasis. Exposure of dairy cows to hyperthermia during the dry period alters mammary gland involution processes leading to reduced subsequent yields. Herein, primary bovine mammary epithelial cells (pBMEC) under thermoneutral (TN, 37 °C) or heat shock (HS, 41.5 °C) conditions were cultured with either 0, 50, 200, or 500 µM 5-Hydroxy-L-tryptophan (5-HTP; 5-HT precursor) for 8-, 12- or 24-h. Expression of 95 genes involved in 5-HT signaling, involution and tight junction regulation were evaluated using a Multiplex RT-qPCR BioMark Dynamic Array Circuit. Different sets of genes were impacted by 5-HTP or temperature, or by their interaction. All 5-HT signaling genes were downregulated after 8-h of HS and then upregulated after 12-h, relative to TN. After 24-h, apoptosis related gene, FASLG, was upregulated by all doses except TN-200 µM 5-HTP, and cell survival gene, FOXO3, was upregulated by HS-50, 200 and 500 µM 5-HTP, suggesting 5-HTP involvement in cell turnover under HS. Supplementing 5-HTP at various concentrations in vitro to pBMEC modulates the expression of genes that might aid in promoting epithelial cell turn-over during involution in dairy cattle under hyperthermia.

Tryptophan-enriched diet or 5-hydroxytryptophan supplementation given in a randomized controlled trial impacts social cognition on a neural and behavioral level.

Understanding of emotions and intentions are key processes in social cognition at which serotonin is an important neuromodulator. Its precursor is the essential amino acid tryptophan (TRP). Reduced TRP availability leads to weaker impulse control ability and higher aggression, while TRP supplementation promotes confidence. In a double-blind placebo-controlled fMRI study with 77 healthy adults, we investigated the influence of a 4 week TRP enriched diet and an acute 5-hydroxytryptophan (5-HTP) intake on two social-cognitive tasks, a moral evaluation and an emotion recognition task. With 5-HTP, immoral behavior without negative consequences was rated as more reprehensible. Additionally, during story reading, activation in insula and supramarginal gyrus was increased after TRP intake. No significant effects of TRP on emotion recognition were identified for the whole sample. Importantly, emotion recognition ability decreased with age which was for positive emotions compensated by TRP. Since the supramarginal gyrus is associated with empathy, pain and related information integration results could be interpreted as reflecting stricter evaluation of negative behavior due to better integration of information. Improved recognition of positive emotions with TRP in older participants supports the use of a TRP-rich diet to compensate for age related decline in social-cognitive processes.

Changes in Locomotor Activity and Oxidative Stress-Related Factors after the Administration of an Amino Acid Mixture by Generation and Age.

Amino acids, as nutrients, are expected to improve sleep disorders. This study aimed to evaluate the generation- and age-dependent sleep-improving effects of γ-aminobutyric acid (GABA) and 5-hydroxytryptophan (5-HTP) coadministration. The differentially expressed genes and generation-related behavior after the administration of a GABA/5-HTP mixture were measured in a Drosophila model, while age-related changes in gene expression and oxidative stress-related parameters were measured in a mouse model. The GABA/5-HTP-treated group showed significant behavioral changes compared to the other groups. Sequencing revealed that the GABA/5-HTP mixture influenced changes in nervous system-related genes, including those involved in the regulation of the expression of behavioral and synaptic genes. Additionally, total sleep time increased with age, and nighttime sleep time in the first- and third-generation flies was significantly different from that of the control groups. The GABA/5-HTP mixture induced significant changes in the expression of sleep-related receptors in both models. Furthermore, the GABA/5-HTP mixture reduced levels of ROS and ROS reaction products in an age-dependent manner. Therefore, the increase in behavioral changes caused by GABA/5-HTP mixture administration was effective in eliminating ROS activity across generations and ages.

L-DOPA and 5-HTP modulation of air-stepping in newborn rats.

KEY POINTS: In newborn rats, L-DOPA increases the occurrence of air-stepping activity without affecting movement characteristics. L-DOPA administration increases the spinal content of dopamine in a dose-dependent manner. Injection of 5-HTP increases the spinal serotonin content but does not trigger air-stepping. 5-HTP counteracts the pro-locomotor action of L-DOPA. Less dopamine and serotonin are synthesized when L-DOPA and 5-HTP are administered as a cocktail. ABSTRACT: The catecholamine precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), is a well-established pharmacological agent for promoting locomotor action in vertebrates, including triggering air-stepping activities in the neonatal rat. Serotonin is also a well-known neuromodulator of the rodent spinal locomotor networks. Here, using kinematic analysis, we compared locomotor-related activities expressed by newborn rats in response to varying doses of L-DOPA and the serotonin precursor 5-hydroxytryptophan (5-HTP) administered separately or in combination. L-DOPA alone triggered episodes of air-stepping in a dose-dependent manner (25-100 mg/kg), notably determining the duration of locomotor episodes, but without affecting step cycle frequency or amplitude. In contrast, 5-HTP (25-150 mg/kg) was ineffective in instigating air-stepping, but altered episode durations of L-DOPA-induced air-stepping, and decreased locomotor cycle frequency. High performance liquid chromatography revealed that L-DOPA, which was undetectable in control conditions, accumulated in a dose-dependent manner in the lumbar spinal cord 30 min after its administration. This was paralleled by an increase in dopamine levels, whereas the spinal content of noradrenaline and serotonin remained unaffected. In the same way, the spinal levels of serotonin increased in parallel with the dose of 5-HTP without affecting the levels of dopamine and noradrenaline. When both precursors are administrated, they counteract each other for the production of serotonin and dopamine. Our data thus indicate for the first time that both L-DOPA and 5-HTP exert opposing neuromodulatory actions on air-stepping behaviour in the developing rat, and we speculate that competition for the production of dopamine and serotonin occurs when they are administered as a cocktail.

Histological and transcriptomic analysis of adipose and muscle of dairy calves supplemented with 5-hydroxytryptophan.

In mammals, peripheral serotonin is involved in regulating energy balance. Herein, we characterized the transcriptomic profile and microstructure of adipose and muscle in pre-weaned calves with increased circulating serotonin. Holstein bull calves (21 ± 2 days old) were fed milk replacer supplemented with saline (CON, 8 mL/day n = 4) or 5-hydroxytryptophan (5-HTP, 90 mg/day, n = 4) for 10 consecutive days. Calves were euthanized on d10 to harvest adipose and muscle for RNA-Sequencing and histological analyses. Twenty-two genes were differentially expressed in adipose, and 33 in muscle. Notably, Interferon gamma inducible protein-47 was highly expressed and upregulated in muscle and adipose (avg. log FC = 6.5). Enriched pathways in adipose tissue revealed serotonin's participation in lipid metabolism and PPAR signaling. In muscle, enriched pathways were related to histone acetyltransferase binding, Jak-STAT signaling, PI3K-Akt signaling and cell proliferation. Supplementation of 5-HTP increased cell proliferation and total cell number in adipose and muscle. Adipocyte surface area was smaller and muscle fiber area was not different in the 5-HTP group. Manipulating the serotonin pathway, through oral supplementation of 5-HTP, influences signaling pathways and cellular processes in adipose and muscle related to endocrine and metabolic functions which might translate into improvements in calf growth and development.

Residual effects of abomasal 5-hydroxytryptophan administration on serotonin metabolism in cattle.

Studies of serotonin in animal husbandry has received growing interest. However, there is limited information about serotonin manipulation using 5-HTP administered postruminally and its residual effects in cattle. The objective of this study was to evaluate the effectiveness of 5-HTP infused into the abomasum for enhancing circulating serotonin in cattle. Four Holstein steers (487 ± 7.6 kg) fitted with ruminal cannulas were used in a 4 × 4 Latin Square design experiment. The treatments were intra-abomasal infusion of 5-HTP at 0, 0.25, 0.5, and 1 mg/kg BW. Blood was collected from the jugular vein of each steer at -60, -30, 0, 30, 60, 120, 240, and 480 min from 5-HTP infusion for basal and short term evaluation and, at 1, 2, 4, and 7 d after 5-HTP infusion for long term evaluation. Dry matter intake was not affected (P > 0.05) by intra-abomasal infusions. The half-life of 5-HTP was dose-independent (128 min). The serum 5-HTP, serotonin, and 5-hydroxyindoleacetic acid area under the curve increased (P < 0.05) linearly with an increased dose of 5-HTP. Serum 5-HTP reached peak concentration in approximately 30 min after dosing while serum and plasma serotonin peaked after 240 min postinfusion. Serotonin was greater than control for all 5-HTP doses 1 d and 2 d after infusion in serum and plasma, respectively. Intra-abomasal infusion of 5-HTP at doses up to 1 mg/ kg BW increases circulating serotonin for up 2 days.

Anorectic interaction and safety of 5-hydroxytryptophan/carbidopa plus phentermine or diethylpropion in rat.

Drug combinations are being studied as potential therapies to increase the efficacy or improve the safety profile of weight loss medications. This study was designed to determine the anorectic interaction and safety profile of 5-hydroxytryptophan (5-HTP)/carbidopa + diethylpropion and 5-HTP/carbidopa + phentermine combinations in rats. The anorectic effect of individual drugs or in combination was evaluated by the sweetened milk test. Isobologram and interaction index were employed to determine the anorectic interaction between 5-HTP/carbidopa and diethylpropion or phentermine. Plasma serotonin (5-HT) was measured by ELISA. Safety of repeated doses of both combinations in rats was evaluated using the tail sphygmomanometer, cardiac ultrasound, hematic biometry and blood chemistry. A single oral 5-HTP, diethylpropion or phentermine dose increased the anorectic effect, in a dose-dependent fashion, in 12 h-fasted rats. A dose of carbidopa at 30 mg/kg reduced the 5-HTP-induced plasmatic serotonin concentration and augmented the 5-HTP-induced anorectic effect. Isobologram and interaction index indicated a potentiation interaction between 5-HTP/30 mg/kg carbidopa + diethylpropion and 5-HTP/30 mg/kg carbidopa + phentermine. Chronic administration of experimental ED40 of 5-HTP/30 mg/kg carbidopa + phentermine, but not 5-HTP/30 mg/kg carbidopa + diethylpropion, increased the mitral valve leaflets area. Moreover, there were no other significant changes in cardiovascular, hematic or blood parameters. Both combinations induced around 20% body weight loss after 3 months of oral administration. Results suggest that 5-HTP/30 mg/kg carbidopa potentiates the anorectic effect of diethylpropion and phentermine with an acceptable safety profile, but further clinical studies are necessary to establish their therapeutic potential in the obesity treatment.

5-Hydroxytryptophan (5-HTP)-induced intracellular syndrome in mouse non-neural embryonic cells is associated with inhibited proliferation and cell death.

Biogenic monoamines are involved in the regulation of various processes in both neural and non-neural cells during development. The present study aimed to identify the regulatory effects of serotonin (5-HT) and its precursors (l-tryptophan and 5-hydroxytryptophan, 5-HTP) on proliferation and cell death in mouse embryonic stem cells (ESCs) and embryonic fibroblasts (MEFs and 3T3 cells). The concentration-dependent cell growth and viability of the ESCs, MEFs and 3T3 cells were analyzed after treatment with l-tryptophan, 5-HTP and 5-HT in the concentration range 10-6 - 10-2 M. Treating the cells with 5-HTP, but not l-tryptophan and 5-HT, induced reversible toxic effects. 5-HTP treatment (10-3 - 10-2 M) significantly inhibited cell proliferation through blocking of the S-phase of the cell cycle and increasing apoptotic and necrotic cell death. Moreover, 5-HTP treatment stimulated a reorganization of the actin and tubulin networks and upregulated the gene expression of enzymes involved in 5-HT synthesis and metabolism: aromatic amino acid decarboxylase (Aadc/Ddc), monoamine oxidase A (Maoa), and transglutaminase 2 (Tgm2). HPLC analysis found no changes in the intracellular and extracellular levels of 5-HT after 5-HTP treatment, but a significant increase of intracellular 5-HTP levels. However, inhibition of AADC with NSD-1015 or transglutaminase with cystamine prevented 5-HTP-induced cell growth impairment and attenuated the toxic effects of 5-HTP treatment. Our results suggest that 5-HTP can induce toxic effects through cell cycle arrest and cell death in embryonic stem and somatic cells by enhancing the levels of 5-HT-mediated protein modifications. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.