An Emerging Cross-Species Marker for Organismal Health: Tryptophan-Kynurenine Pathway

Remission of HPV-Related Diseases by Antivirals for Herpesvirus: Clinical Cases and a Literature Review

Epidemiological studies have shown that HPV-related diseases are the most prevalent sexually transmitted infections. In this context, this report will present various clinical cases demonstrating the effectiveness of Acyclovir (ACV) or its prodrug Valaciclovir (VCV), both acyclic guanosine analogs commonly used for the treatment of HHV-1 and HHV-2, for the treatment of HPV-related diseases. The report shows the remission of five cases of penile condyloma and a case of remission in a woman affected by cervical and vaginal condylomas and a vulvar giant condyloma acuminate of Buschke and Lowenstein. The literature review shows that ACV is effective in treating skin warts when administered orally, topically, and intralesionally, suggesting its therapeutic potential in other diseases associated with HPV. ACV was also used successfully as an adjuvant therapy for juvenile and adult forms of laryngeal papillomatosis, also known as recurrent respiratory papillomatosis, prolonging the patient's symptom-free periods. Although the prevention of HPV infections is certainly achieved with the HPV vaccine, ACV and VCV have shown to be effective even against genotypes not included in the current vaccine and can be helpful for those problematic clinical cases involving unvaccinated individuals, immunocompromised patients, people who live with HIV, or non-responders to the vaccine. We and others concluded that randomized clinical trials are necessary to determine the efficacy of ACV and VCV for HPV-related diseases.

Determination of well-being-related markers in nails by liquid chromatography tandem mass spectrometry

Well-being is a multifactorial positive state that is highly influenced by some endogenous molecules that control happiness and euphoric feelings. These molecules, e.g., neurotransmitters, hormones and their derivatives, play a crucial role in metabolism and may be referred to as "well-being-related markers". The deregulation of well-being-related markers can lead to organism malfunctions and life-threatening states. In this research, we aimed to evaluate the potential of nails for the chronic production of several well-being-related markers. For this purpose, we developed an LCMS /MS-based method for the determination of 10 well-being-related markers, including melatonin, serotonin, cortisol, kynurenine and several precursors and metabolites. The method was optimized regarding different analytical steps: required sample amount, extraction time, number of required extractions, preconcentration, injection volume and MS conditions. Method validation was performed by two different approaches: (i) using surrogate nail matrix and (ii) using authentic nail samples by standard additions. The method was found to be linear in the expected endogenous range and sensitive enough to determine the low endogenous concentration levels in nails. Accuracy and precision were appropriate in both validation approaches. As proof of concept, the method was used (i) to correlate fingernail and toenail levels for all metabolites in 22 volunteers, (ii) to establish the endogenous concentration range of all metabolites in females (n = 50) and males (n = 34) and (iii) to correlate the metabolite levels with age. For some metabolites, the calculated ranges have been reported for the first time. In summary, the present strategy to evaluate well-being-related markers in nails may be a useful tool for the evaluation of the production of these important compounds with high potential for a wide range of clinical purposes.

Metabolic reprogramming: Unveiling the therapeutic potential of targeted therapies against kidney disease

As a high-metabolic-rate organ, the kidney exhibits metabolic reprogramming (MR) in various disease states. Given the >800 million cases of kidney disease worldwide in 2022, understanding the specific bioenergetic pathways involved and developing targeted interventions are vital needs. The reprogramming of metabolic pathways (glucose metabolism, amino acid metabolism, etc.) has been observed in kidney disease. Therapies targeting these specific pathways have proven to be an efficient approach for retarding kidney disease progression. In this review, we focus on potential pharmacological interventions targeting MR that have advanced through Phase III/IV clinical trials for the management of kidney disease and promising preclinical studies laying the groundwork for future clinical investigations.

Effect of the Probiotic Bacillus subtilis DE-CA9TM on Fecal Scores, Serum Oxidative Stress Markers and Fecal and Serum Metabolome in Healthy Dogs

BACKGROUND

There is increasing interest in the use of Bacillus species as probiotics since their spore-forming ability favors their survival in the acidic gastric environment over other probiotic species. The subsequent germination of B. subtilis to their vegetative form allows for their growth in the small intestine and may increase their beneficial effect on the host. B. subtilis strains have also previously been shown to have beneficial effects in humans and production animals, however, no reports are available so far on their use in companion animals.

STUDY DESIGN

The goal of this study was therefore to investigate the daily administration of 1 × 109 cfu DE-CA9TM orally per day versus placebo on health parameters, fecal scores, fecal microbiome, fecal metabolomics, as well as serum metabolomics and oxidative stress markers in ten healthy Beagle dogs in a parallel, randomized, prospective, placebo-controlled design over a period of 45 days.

RESULTS

DE-CA9TM decreased the oxidative status compared to controls for advanced oxidation protein products (AOPP), thiobarbituric acid reactive substances (TBARS) and reactive oxygen metabolites (d-ROMS), suggesting an antioxidant effect of the treatment. Fecal metabolomics revealed a significant reduction in metabolites associated with tryptophan metabolism in the DE-CA9TM-treated group. DE-CA9TM also significantly decreased phenylalanine and homocysteine and increased homoserine and threonine levels. Amino acid metabolism was also affected in the serum metabolome, with increased levels of urea and cadaverine, and reductions in N-acetylornithine in DE-CA9TM compared to controls. Similarly, changes in essential amino acids were observed, with a significant increase in tryptophan and lysine levels and a decrease in homocysteine. An increase in serum guanine and deoxyuridine was also detected, with a decrease in beta-alanine in the animals that ingested DE-CA9TM.

CONCLUSIONS

Data generated throughout this study suggest that the daily administration of 1 × 109 cfu of DE-CA9TM in healthy Beagle dogs is safe and does not affect markers of general health and fecal scores. Furthermore, DE-CA9TM administration had a potential positive effect on some serum markers of oxidative stress, and protein and lipid metabolism in serum and feces.

Identification and characterization of tryptophan-kynurenine pathway-related genes involving lamprey (Lampetra japonica) innate immunity

The tryptophan-kynurenine (TRP-KYN) pathway is involved in several biological functions, including immunosuppression, inflammatory response, and tumor suppression. Six TRP-KYN pathway-related genes, tryptophan 2,3-dioxygenase (TDO), indoleamine 2,3-dioxygenase 2 (IDO2), aminoadipate aminotransferase (AADAT), glutamate oxaloacetate transaminase 2 (GOT2), kynurenine monooxygenase (KMO), and kynureninase (KYNU) have been identified and cloned from the jawless vertebrate lamprey (Lampetra japonica) to gain insights into their evolution and characterization. Expression distribution showed that the key gene Lj-TDO was highly expressed in the oral gland. Real-time quantitative PCR showed that TRP-KYN pathway-related genes were significantly overexpressed after multi-stimulation. RNA interference showed that Lj-IDO2 knockdown regulated the expression of inflammatory factors. In conclusion, our study successfully clarified the ancestral features and functions of the TRP-KYN pathway, while providing valuable insights into the involvement of this pathway in the immune responses of a jawless vertebrate.

Phase-and disorder-specific differences in peripheral metabolites of the kynurenine pathway in major depression, bipolar affective disorder and schizophrenia

OBJECTIVES

Kynurenine, kynurenic and quinolinic acid are important metabolites in tryptophan metabolism. Due to an involvement in glutamatergic neurotransmission and immune response, previous studies have investigated this pathway in mental disorders such as major depressive disorder (MDD), bipolar disorder (BD) or schizophrenia (SCZ). Tryptophan and kynurenine have been shown to be decreased across disorders, hinting at the missing link how inflammation causes neurotoxicity and psychiatric symptoms. The main aim of our study was to investigate if individual catabolites could serve as diagnostic biomarkers for MDD, BD and SCZ.

METHODS

We measured plasma levels of tryptophan, kynurenine, kynurenic acid, quinolinic acid and ratio of quinolinic acid/kynurenic acid using mass spectrometry in n = 175 participants with acute episodes and after remission, compared with controls.

RESULTS

Decreased levels of all tryptophan catabolites were found in the whole patient group, driven by the difference between BD and HC. Manic and mixed phase BD individuals displayed significantly lower kynurenine and kynurenic acid levels. We could not find significant differences between disorders. Upon reaching remission, changes in catabolite levels partially normalised.

CONCLUSIONS

Our data suggests an involvement of the kynurenine pathway in mental disorders, especially BD but disqualifying those metabolites as biomarkers for differential diagnosis.

Exercise for Mental Well-Being: Exploring Neurobiological Advances and Intervention Effects in Depression

Depression is a common mental disorder in which patients often experience feelings of sadness, fatigue, loss of interest, and pleasure. Exercise is a widely used intervention for managing depression, but the specific molecular mechanisms underlying its antidepressant effect are unclear. In this narrative review, we aim to synthesize current knowledge on the molecular, neural, and physiological mechanisms through which exercise exerts its antidepressant effect and discuss the various exercise interventions used for managing depression. We conducted a narrative review of the literature on the topic of exercise and depression. Our review suggests that exercise impacts peripheral tryptophan metabolism, central inflammation, and brain-derived neurotrophic factors through the peroxisome proliferator-activated receptor γ activating factor 1α (PGC-1α) in skeletal muscles. The uncarboxylated osteocalcin facilitates "bone-brain crosstalk", and exercise corrects atypical expression of brain-gut peptides, modulates cytokine production and neurotransmitter release, and regulates inflammatory pathways and microRNA expression. Aerobic exercise is recommended at frequencies of 3 to 5 times per week with medium to high intensity. Here we highlight the significant potential of exercise therapy in managing depression, supported by the molecular, neural, and physiological mechanisms underlying its antidepressant effect. Understanding the molecular pathways and neural mechanisms involved in exercise's antidepressant effect opens new avenues for developing novel therapies for managing depression.

Tryptophan in Nutrition and Health 2.0

This editorial summarizes the eight articles that have been collected for the Special Issue entitled "Tryptophan in Nutrition and Health 2 [...].

Lipopolysaccharide Preconditioning Restricts Microglial Overactivation and Alleviates Inflammation-Induced Depressive-like Behavior in Mice

Overactive microglia and severe neuroinflammation play crucial roles in the development of major depressive disorder. Preconditioning with lipopolysaccharide (LPS) provides protection against severe neuroinflammation. However, administering high doses of LPS to mice triggers depressive symptoms. Therefore, the optimal dose of LPS preconditioning needs to be determined by further experiments. LPS preconditioning is an effective agent in anti-inflammation and neuroprotection, but the mechanism by which LPS preconditioning acts in depression remain unclear. This study finds that the anti-inflammation mechanism of low-dose LPS preconditioning is mainly dependent on G-protein-coupled receptor 84 (GPR84). We use low-dose LPS for preconditioning and re-challenged mice or BV2 microglia with high-dose LPS. In addition, RNA-seq is used to explore underlying changes with LPS preconditioning. Low-dose LPS preconditioning reduces the expression of pro-inflammatory mediators and inhibits microglial activation, as well as suppresses the depressive-like behavior when the mice are re-challenged with high-dose LPS. Further investigation reveals that the tolerance-like response in microglia is dependent on the GPR84. Here, we show that low-dose LPS preconditioning can exert anti-inflammation effects and alleviates inflammation-induced depressive-like behavior in mice. As a potential therapeutic target for depression, LPS preconditioning needs to be given further attention regarding its effectiveness and safety.

Kratom (M. speciosa) exposure during adolescence caused long-lasting cognitive behavioural deficits associated with perturbated brain metabolism pathways in adult rats

Kratom (M. speciosa Korth) is an herbal plant native to Southeast Asia. The leaves have been widely used to alleviate pain and opioid withdrawal symptoms. However, the increasing trend of recreational use of kratom among youth is concerning because substance abuse may render the adolescent brain more susceptible to neuropathological processes, causing dramatic consequences that persist into adulthood. Therefore, the present study aimed to investigate the long-term effects of mitragynine, the main alkaloid and lyophilized kratom decoction (LKD) exposure during adolescence on cognitive behaviours and brain metabolite profiles in adult rats. Adolescent male Sprague-Dawley rats were given mitragynine (3, 10 or 30mg/kg) or LKD orally for 15 consecutive days during postnatal days 31-45 (PND31-45). Behavioural testing was performed during adulthood (PND70-84) and the brains were subjected to metabolomic analysis. The results show that a high dose of mitragynine impaired long-term object recognition memory. Social behaviour and spatial learning were not affected, but both mitragynine and LKD impaired reference memory. Brain metabolomic study revealed several altered metabolic pathways that may be involved in the cognitive behavioural effects of LKD and mitragynine exposure. These pathways include arachidonic acid, taurine and hypotaurine, pantothenate and CoA biosynthesis, and tryptophan metabolism, while the N-isovalerylglycine was identified as the potential biomarker. In summary, adolescent kratom exposure can cause long-lasting cognitive behavioural deficits and alter brain metabolite profiles that are still evident in adulthood. This finding also indicates that the adolescent brain is vulnerable to the impact of early kratom use.

The influence of cyclooxygenase inhibitors on kynurenic acid production in rat kidney: a novel path for kidney protection?

BACKGROUND

Kidney diseases have become a global health problem, affecting about 15% of adults and being often under-recognized. Immunological system activation was shown to accelerate kidney damage even in inherited disorders. The kynurenine pathway is the main route of tryptophan degradation. A metabolite of kynurenine (KYN), kynurenic acid (KYNA), produced by kynurenine aminotransferases (KATs), was reported to affect fluid and electrolyte balance as a result of natriuresis induction. The accumulation of KYNA was shown in patients with impaired kidney function and its level was related to the degree of kidney damage. Cyclooxygenase (COX) inhibitors are well-known analgesics and most of them demonstrate an anti-inflammatory effect. Their main mechanism of action is prostaglandin synthesis blockade, which is also responsible for their nephrotoxic potential. Since the KYN pathway is known to remain under immunological system control, the purpose of this study was to analyze the effect of 9 COX inhibitors on KYNA production together with KATs' activity in rat kidneys in vitro.

METHODS

Experiments were carried out on kidney homogenates in the presence of L-KYN and the selected compound in 6 various concentrations.

RESULTS

Among the examined COX inhibitors only acetaminophen did not change KYNA production in rat kidneys in vitro. Additionally, acetaminophen did not affect the activity of KAT I and KAT II, whereas acetylsalicylic acid and ibuprofen inhibited only KAT II. The remaining COX inhibitors decreased the activity of both KATs in rat kidneys in vitro.

CONCLUSION

Our study provides novel mechanisms of COX inhibitors action in the kidney, with possible implications for the treatment of kidney diseases.

SLC6A4 DNA Methylation Levels and Serum Kynurenine/Tryptophan Ratio in Eating Disorders: A Possible Link with Psychopathological Traits?

Background: The incidence of eating disorders (EDs), serious mental and physical conditions characterized by a disturbance in eating or eating-related behaviors, has increased steadily. The present study aims to develop insights into the pathophysiology of EDs, spanning over biochemical, epigenetic, psychopathological, and clinical data. In particular, we focused our attention on the relationship between (i) DNA methylation profiles at promoter-associated CpG sites of the SCL6A4 gene, (ii) serum kynurenine/tryptophan levels and ratio (Kyn/Trp), and (iii) psychopathological traits in a cohort of ED patients. Among these, 45 patients were affected by restricting anorexia nervosa (AN0), 21 by purging AN (AN1), 21 by bulimia (BN), 31 by binge eating disorders (BED), 23 by unspecified feeding or eating disorders (UFED), and finally 14 by other specified eating disorders (OSFED) were compared to 34 healthy controls (CTRs). Results: Kyn level was higher in BED, UFED, and OSFED compared to CTRs (p ≤ 0.001). On the other hand, AN0, AN1, and BN patients showed significatively lower Kyn levels compared to the other three ED groups but were closed to CTRs. Trp was significantly higher in AN0, AN1, and BN in comparison to other ED groups. Moreover, AN1 and BN showed more relevant Trp levels than CTRs (p <0.001). BED patients showed a lower Trp as compared with CTRs (p ≤ 0.001). In addition, Kyn/Trp ratio was lower in the AN1 subtype but higher in BED, UFED, and OSFED patients than in CTRs (p ≤ 0.001). SCL6A4 DNA methylation level at CpG5 was lower in AN0 compared to BED (p = 0.021), and the CpG6 methylation was also significantly lower in AN0 in comparison to CTRs (p = 0.025). The mean methylation levels of the six CpGs analyzed were lower only in the AN0 subgroup compared to CTRs (p = 0.008). Relevant psychological trait EDI-3 subscales were correlated with biochemical and epigenetic data. Conclusions: These findings underline the complexity of psychological and pathophysiological components of EDs.

Microbiota of the gastrointestinal tract: Friend or foe?

The gut microbiota is currently considered an external organ of the human body that provides important mechanisms of metabolic regulation and protection. The gut microbiota encodes over 3 million genes, which is approximately 150 times more than the total number of genes present in the human genome. Changes in the qualitative and quantitative composition of the microbiome lead to disruption in the synthesis of key bacterial metabolites, changes in intestinal barrier function, and inflammation and can cause the development of a wide variety of diseases, such as diabetes, obesity, gastrointestinal disorders, cardiovascular issues, neurological disorders and oncological concerns. In this review, I consider issues related to the role of the microbiome in the regulation of intestinal barrier function, its influence on physiological and pathological processes occurring in the body, and potential new therapeutic strategies aimed at restoring the gut microbiome. Herewith, it is important to understand that the gut microbiota and human body should be considered as a single biological system, where change of one element will inevitably affect its other components. Thus, the study of the impact of the intestinal microbiota on health should be considered only taking into account numerous factors, the role of which has not yet been fully elucidated.

Comparative analysis of tryptophan and downstream metabolites of the kynurenine and serotonin pathways in patients with arterial hypertension and coronary artery disease

Aim    To compare serum concentrations of tryptophane (Trp) and its metabolites in subjects with no cardiovascular disease (CVD) and patients with СVD, including arterial hypertension (AH) and ischemic heart disease (IHD).Material and methods    This study included 131 participants; 58 participants (11 of them with documented peripheral atherosclerosis) were included into the AH group, 46 participants were included into the IHD group, and 27 participants with no signs of CVD were included into the control group. Plasma concentrations of Trp and its metabolites were measured by high-performance liquid chromatography in combination with a triple quadrupole analyzer.Results    Comparison of the three study groups revealed significant differences in concentrations of Trp (р=0.029), kynurenine (p<0.001), kynurenine/Trp ratio (p<0.001), quinolinic acid (р=0.007), kynurenic acid (р=0.003), serotonin (p<0.001), and 5‑hydroxyindoleacetic acid (5‑HIAA) (р=0.011). When the AH group was subdivided into subgroups without and with documented peripheral atherosclerosis, the intergroup differences remained for concentrations of kynurenine, kynurenine/Trp ratio, quinolinic acid, kynurenic acid, serotonin, and 5‑HIAA. Also, correlations were found between concentrations of Trp metabolites and laboratory and instrumental data, primarily inflammatory markers. Conclusion    Analysis of serum concentrations of Trp and its metabolites in CVD patients showed increases in kynurenine, kynurenine/Trp ratio, quinolinic acid, kynurenic acid, and 5‑HIAA along with decreases in concentrations of Trp and serotonin in the groups of AH, AH with documented peripheral atherosclerosis, and IHD.

Integrating Armchair, Bench, and Bedside Research for Behavioral Neurology and Neuropsychiatry: Editorial

"To learning much inclined, who went to see the Elephant (though all of them were blind) that each by observation might satisfy the mind" [...].

Mitochondrial Impairment: A Common Motif in Neuropsychiatric Presentation? The Link to the Tryptophan-Kynurenine Metabolic System

Nearly half a century has passed since the discovery of cytoplasmic inheritance of human chloramphenicol resistance. The inheritance was then revealed to take place maternally by mitochondrial DNA (mtDNA). Later, a number of mutations in mtDNA were identified as a cause of severe inheritable metabolic diseases with neurological manifestation, and the impairment of mitochondrial functions has been probed in the pathogenesis of a wide range of illnesses including neurodegenerative diseases. Recently, a growing number of preclinical studies have revealed that animal behaviors are influenced by the impairment of mitochondrial functions and possibly by the loss of mitochondrial stress resilience. Indeed, as high as 54% of patients with one of the most common primary mitochondrial diseases, mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome, present psychiatric symptoms including cognitive impairment, mood disorder, anxiety, and psychosis. Mitochondria are multifunctional organelles which produce cellular energy and play a major role in other cellular functions including homeostasis, cellular signaling, and gene expression, among others. Mitochondrial functions are observed to be compromised and to become less resilient under continuous stress. Meanwhile, stress and inflammation have been linked to the activation of the tryptophan (Trp)-kynurenine (KYN) metabolic system, which observably contributes to the development of pathological conditions including neurological and psychiatric disorders. This review discusses the functions of mitochondria and the Trp-KYN system, the interaction of the Trp-KYN system with mitochondria, and the current understanding of the involvement of mitochondria and the Trp-KYN system in preclinical and clinical studies of major neurological and psychiatric diseases.