Customized flexible platform - starting point for the development of wearable sensor for the direct electrochemical detection of kynurenic acid in biological samples.

Kynurenic acid (KA) is an active metabolite of tryptophan with notable biological effects, such as antioxidant, neuroprotective, and anti-inflammatory properties. It often undergoes changes of the concentration in biological fluids in chronic diseases. Thus, detecting KA is of great importance for diagnosing inflammatory and neurodegenerative conditions, monitoring disease progression, and assessing responses to pharmacological treatment. This study aimed to design a tailored, flexible platform for sensitive and direct electrochemical detection of KA in biological fluids. Carbon-based electrodes were custom-printed in the lab using specialized inks and flexible substrates. The working electrodes were further functionalized with graphene oxide and subsequently electrochemically reduced to increase the sensitivity toward the analyte. An optimized differential pulse voltammetry protocol was developed for KA detection. The elaborated platform was firstly characterized and then evaluated regarding the analytical performances. It showed a good limit of detection (3 nM and demonstrated the capability to detect KA across a broad concentration range (0.01-500 µM). Finally, the elaborated flexible platform, was succesfully applied for KA determination in serum and saliva samples, in comparison with an optimized HPLC-UV method. The developed platform is the first example of in-lab printed flexible platform reported in literature so far for KA detection. It is also the first study reported in the literature of detection of KA in raw saliva collected from 10 subjects. The sensitivity towards the target analyte, coupled with the adaptability and portability, showcases the potential of this platform for thus illustrating great potential for further development of wearable sensors and biomedical applications.

Exploring the effect of prolonged fasting on kynurenine pathway metabolites and stress markers in healthy male individuals.

BACKGROUND/OBJECTIVES: Prolonged fasting triggers a stress response within the human body. Our objective was to investigate the impact of prolonged fasting, in conjunction with stress, on kynurenine pathway metabolites. SUBJECTS/METHODS: Healthy males were divided into fasting group (zero-calorie-restriction) for 6 days (FAST, n = 14), and control group (CON, n = 10). Blood and saliva samples were collected at baseline, Day 2, Day 4, Day 6 during fasting period, and 1 week after resuming regular diet. Plasma levels of kynurenine pathway metabolites were measured using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS). Plasma and salivary samples were analyzed for stress markers. RESULTS: A pronounced activation of the kynurenine pathway in individuals on FAST trial was revealed. Concentrations of picolinic acid (PIC), kynurenic acid (KYNA) and 3-hydroxykynurenine (3-HK) were significantly increased, with peak levels observed on Day 6 (P < 0.0001). Conversely, concentrations of tryptophan (TRP) and quinolinic acid (QUIN) decreased (P < 0.0001), while kynurenine (KYN) and nicotinamide (NAM) levels remained stable. Cortisol and noradrenaline concentrations remained unchanged. However, adrenaline levels significantly increased on Day 4 within FAST compared to CON (P = 0.005). Notably, all deviations in kynurenine pathway metabolite levels returned to baseline values upon resuming regular diet following the 6-day fasting regimen, even when weight and BMI parameters were not restored. CONCLUSIONS: Extended fasting over 6 days induces the kynurenine pathway and has minimal effects on stress markers. Restoration of metabolite concentrations upon regular feeding implies rapid adaptation of the kynurenine pathway synthetic enzymes to maintain homeostasis when faced with perturbations.

The Safety and Tolerability of Topically Delivered Kynurenic Acid in Humans. A Phase 1 Randomized Double-Blind Clinical Trial.

Scarring is a consequence of biological tissue repair following trauma. Currently, there are no generally agreed ways to prevent scarring. Recently, kynurenic acid has shown to be a potent modulator of extracellular matrix deposition and remodeling. Kynurenic acid can reduce matrix deposition and other fundamental characteristics of fibrosis in vitro and in vivo. Specifically, kynurenic acid has shown to increase matrix metalloproteinase-1 activity and subsequently reduce collagen deposition in a rabbit ear scar model. In the present study kynurenic acid cream in different concentrations was topically applied on healthy skin on volunteers to assess skin reactions and skin sensitivity in both acute and chronic application settings. Skin reactions were assessed, and concentrations for kynurenic acid were assessed both form serum and urine. Results showed to acute or delayed skin reactions. Kynurenic acid was not detectable in blood at any time point, and only trace elements of kynurenic acid were found in urine. This study supports safety and tolerability of topically administered FS2 when using a liposomal, compounding base carrier.

Tryptophan and its metabolites in patients with oral squamous cell carcinoma: preliminary study.

PURPOSE: It has been showed that tryptophan (TRP) degradation has been linked to modulation of cancer cell proliferation. The aim of our study was to estimate the concentration of TRP and its derivatives, such as anthranilic (AA) and kynurenic acid (KYNA) in plasma, saliva, squamous cell carcinoma (SCC) tissues and healthy oral mucosa in patients with oral SCC. MATERIAL AND METHODS: The study was performed on plasma, non-stimulated, mixed saliva and squamous cell carcinoma tissues and healthy oral mucosa in patients with oral SCC. The concentration of TRP and its metabolites were determined by high-performance liquid chromatography (HPLC). RESULTS: In plasma the concentration of TRP was 33.73 +/- 2.52 microM, of KYNA was 26.97 +/- 5.35 nM and of AA was 32.40 +/- 2.30 nM. In saliva the concentration of TRP was 3.81 +/- 0.62 microM, of KYNA was 8.06 +/- 1.86 nM and of AA was 20.41 +/- 10.77 nM. In cancer tissues the levels of TRP (30.21 +/- 5.88 microM), KYNA (15.85 +/- 1 .82 nM) and AA (265.32 +/- 1 51.45 nM) were higher in respect to the concentration of TRP (13.28 +/- 0.62 microM), KYNA (12.75 +/- 2.28 nM) and AA (31.68 +/- 8.89 nM) in normal tissues. The increase in the content of TRP, KYNA and AA in cancer tissues reached 127.48 +/- 5.95%, 24.31 +/- 4.35% and 737.50 +/- 206.96%, respectively. CONCLUSIONS: Our study has demonstrated the change of TPR metabolism, which is reflected by the increase TRP, AA and KYNA concentrations in patients with oral squamous cell carcinoma. We can suppose that these substances may be one of many factors responsible for cancer development.