Targeting of the kynurenic acid across the blood-brain barrier by core-shell nanoparticles

Neuroprotection effects of kynurenic acid-loaded micelles for the Parkinson's disease models

Anti-glutamatergic agents may have neuroprotective effects against excitotoxicity that is known to be involved in the pathogenesis of Parkinson's disease (PD). One of these agents is kynurenic acid (KYNA), a tryptophan metabolite, which is an endogenous N-methyl-D-aspartic acid (NMDA) receptor antagonist. However, its pharmacological properties of poor water solubility and limited blood-brain barrier (BBB) permeability rules out its systemic administration in disorders affecting the central nervous system. Our aim in the present study was to investigate the neuroprotective effects of KYNA-loaded micelles (KYNA-MICs) against PD in vitro and in vivo. Lipid-based micelles (MICs) in conjunction with KYNA drug delivery have the potential to enhance the penetration of therapeutic drugs into a diseased brain without BBB obstacles. KYNA-MICs were characterized by particle size (105.8 ± 12.1 nm), loading efficiency (78.3 ± 4.23%), and in vitro drug release (approximately 30% at 24 h). The in vitro experiments showed that KYNA-MICs effectively reduced 2-fold protein aggregation. The in vivo studies revealed that KYNA was successfully delivered by 5-fold increase in neurotoxin-induced PD brains. The results showed significant enhancement of KYNA delivery into brain. We also found that the KYNA-MICs exhibited several therapeutic effects. The KYNA-MICs reduced protein aggregation of an in vitro PD model, ameliorated motor functions, and prevented loss of the striatal neurons in a PD animal model. The beneficial effects of KYNA-MICs are probably explained by the anti-excitotoxic activity of the treatment's complex. As the KYNA-MICs did not induce any appreciable side-effects at the protective dose applied to a chronic PD mouse model, our results demonstrate that KYNA provides neuroprotection and attenuates PD pathology.

Lipid-Based Nanocarriers for Delivery of Neuroprotective Kynurenic Acid: Preparation, Characterization, and BBB Transport

Encapsulation possibilities of an extensively investigated neuroprotective drug (kynurenic acid, KYNA) are studied via lipid-based nanocarriers to increase the blood-brain barrier (BBB) specific permeability. The outcomes of various preparation conditions such as stirring and sonication time, concentration of the lipid carriers and the drug, and the drug-to-lipid ratio are examined. Considering the experimentally determined encapsulation efficiency, hydrodynamic diameter, and ζ-potential values, the initial lipid and drug concentration as well as the stirring and sonication time of the preparation were optimized. The average hydrodynamic diameter of the prepared asolectin-(LIP) and water-soluble lipopolymer (WSLP)-based liposomes was found to be ca. 25 and 60 nm under physiological conditions. The physicochemical characterization of the colloidal carriers proves that the preparation of the drug-loaded liposomes was a successful process, and secondary interactions were indicated between the drug molecule and the polymer residues around the WSLP membrane. Dissolution profiles of the active molecule under physiological conditions were registered, and the release of the unformulated and encapsulated drug is very similar. In addition to this outcome, the in vitro polar brain lipid extract (porcine)-based permeability test proved the achievement of two- or fourfold higher BBB specific penetration and lipid membrane retention for KYNA in the liposomal carriers relative to the unformatted drug.

Oral supplementation of solvent-free kynurenic acid/cyclodextrin nanosponges complexes increased its bioavailability

Many nutraceuticals present problems due to their poor water solubility or stability, which prevents the final bioactivity achievement. For that reason, the oral administration of KYNA complexed with HPβ-CD and βNS-CDI nanosponges was evaluated in mice. The solvent-free technology was used to prepare the complexes in a complete comparison between kneading in ball milling and classical inclusion complex preparation. The solvent-free ones showed higher strength and efficiency with ball milling, considerably reducing time. A 50 mg KYNA/kg/day dosage was orally administered in formulations showing a higher bioavailability when the nutraceutical was complexed with βNS-CDI compared to HPβ-CD and free KYNA, respectively. Several antioxidant statuses demonstrated a higher global antioxidant level perfectly related to bioavailability. Finally, the formulation of KYNA reduced the temporal oxidative stress damage in the kidney and liver, making βNS-CDI the best formulation. These results suggest an important future application of cyclodextrin-based nanosponges for the oral delivery of nutraceuticals and their stabilization.

Nanoparticles as Powerful Tools for Crossing the Blood-brain Barrier

The blood-brain barrier (BBB) is considered an important protective barrier in the central nervous system (CNS). The barrier is mainly formed by endothelial cells (ECs) interconnected by various junctions such as tight junctions (TJs), gap junctions, and adherent junctions. They collectively constitute an intensive barrier to the transit of different substances into the brain, selectively permitting small molecules to pass through by passive movement but holding off large ones such as peptides and proteins to cross the brain. Hence some molecules selectively transfer across the BBB by active routes via transcytosis. The BBB also forms a barrier against neurotoxins as well as pathogenic agents. Although various CNS disorders like Alzheimer's disease (AD) and Parkinson's disease (PD) could hamper the integrity of the border. Nevertheless, the BBB acts as a barrier for CNS disorders treatment because it prevents the drugs from reaching their target in the CNS. In recent years, different strategies, including osmotic disruption of BBB or chemical modification of drugs, have been used to transfer the chemotherapeutic agents into brain substances. Nowadays, nanoparticles (NPs) have been used as an effective and non-invasive tool for drug delivery and diagnosis of CNS disorders. In this review, we discuss the structural characteristic of BBB, safe passageways to cross the BBB, and the relation of barrier lesions with different CNS disorders. In the end, we explore the progress in drug delivery, diagnosis, imaging, and treatment of CNS disorders using nanoparticles.

A Review of the Health Benefits of Food Enriched with Kynurenic Acid

Kynurenic acid (KYNA), a metabolite of tryptophan, is an endogenous substance produced intracellularly by various human cells. In addition, KYNA can be synthesized by the gut microbiome and delivered in food. However, its content in food is very low and the total alimentary supply with food accounts for only 1-3% of daily KYNA excretion. The only known exception is chestnut honey, which has a higher KYNA content than other foods by at least two orders of magnitude. KYNA is readily absorbed from the gastrointestinal tract; it is not metabolized and is excreted mainly in urine. It possesses well-defined molecular targets, which allows the study and elucidation of KYNA's role in various pathological conditions. Following a period of fascination with KYNA's importance for the central nervous system, research into its role in the peripheral system has been expanding rapidly in recent years, bringing some exciting discoveries. KYNA does not penetrate from the peripheral circulation into the brain; hence, the following review summarizes knowledge on the peripheral consequences of KYNA administration, presents data on KYNA content in food products, in the context of its daily supply in diets, and systematizes the available pharmacokinetic data. Finally, it provides an analysis of the rationale behind enriching foods with KYNA for health-promoting effects.

Progress, Opportunities, and Challenges of Magneto-Plasmonic Nanoparticles under Remote Magnetic and Light Stimulation for Brain-Tissue and Cellular Regeneration

Finding curable therapies for neurodegenerative disease (ND) is still a worldwide medical and clinical challenge. Recently, investigations have been made into the development of novel therapeutic techniques, and examples include the remote stimulation of nanocarriers to deliver neuroprotective drugs, genes, growth factors, and antibodies using a magnetic field and/or low-power lights. Among these potential nanocarriers, magneto-plasmonic nanoparticles possess obvious advantages, such as the functional restoration of ND models, due to their unique nanostructure and physiochemical properties. In this review, we provide an overview of the latest advances in magneto-plasmonic nanoparticles, and the associated therapeutic approaches to repair and restore brain tissues. We have reviewed their potential as smart nanocarriers, including their unique responsivity under remote magnetic and light stimulation for the controlled and sustained drug delivery for reversing neurodegenerations, as well as the utilization of brain organoids in studying the interaction between NPs and neuronal tissue. This review aims to provide a comprehensive summary of the current progress, opportunities, and challenges of using these smart nanocarriers for programmable therapeutics to treat ND, and predict the mechanism and future directions.

Memory Enhancement with Kynurenic Acid and Its Mechanisms in Neurotransmission

Kynurenic acid (KYNA) is an endogenous tryptophan (Trp) metabolite known to possess neuroprotective property. KYNA plays critical roles in nociception, neurodegeneration, and neuroinflammation. A lower level of KYNA is observed in patients with neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases or psychiatric disorders such as depression and autism spectrum disorders, whereas a higher level of KYNA is associated with the pathogenesis of schizophrenia. Little is known about the optimal concentration for neuroprotection and the threshold for neurotoxicity. In this study the effects of KYNA on memory functions were investigated by passive avoidance test in mice. Six different doses of KYNA were administered intracerebroventricularly to previously trained CFLP mice and they were observed for 24 h. High doses of KYNA (i.e., 20–40 μg/2 μL) significantly decreased the avoidance latency, whereas a low dose of KYNA (0.5 μg/2 μL) significantly elevated it compared with controls, suggesting that the low dose of KYNA enhanced memory function. Furthermore, six different receptor blockers were applied to reveal the mechanisms underlying the memory enhancement induced by KYNA. The series of tests revealed the possible involvement of the serotonergic, dopaminergic, α and β adrenergic, and opiate systems in the nootropic effect. This study confirmed that a low dose of KYNA improved a memory component of cognitive domain, which was mediated by, at least in part, four systems of neurotransmission in an animal model of learning and memory.

Evaluation of noble metal nanostructure-serum albumin interactions in 2D and 3D systems: Thermodynamics and possible mechanisms

In this review, we clearly highlight the importance of the detailed study of the interactions between noble metal colloids (nanoparticles (NPs) and nanoclusters (NCs)) with serum albumins (SAs) due to their rapidly growing presence in biomedical research. Besides the changes in the structure and optical property of SA, we demonstrate that the characteristic localized surface plasmon resonance (LSPR) feature of the colloidal noble metal NPs and the size- and structure-dependent photoluminescence (PL) property of the sub-nanometer sized NCs are also altered differently because of the interactions between them. Namely, for plasmonic NPs - SA interactions the PL quenching of SA (mainly static) is identified, while the SA cause PL enhancement of the ultra-small NCs after complexation. This review summarizes that the thermodynamic nature and the possible mechanisms of the binding processes are dependent partly on the size, morphology, and type of the noble metals, while the chemical structure as well as the charge of the stabilizing ligands have the most dominant effect on the change in optical features. In addition to the thermodynamic data and proposed binding mechanisms provided by three-dimensional spectroscopic techniques, the quantitative and real-time data of "quasi" two-dimensional sensor apparatus should also be considered to provide a comprehensive evaluation on many aspects of the particle/cluster - SA interactions.

Potential of Nanocarrier-Based Drug Delivery Systems for Brain Targeting: A Current Review of Literature

The advent of nanotechnologies such as nanocarriers and nanotherapeutics has changed the treatment strategy and developed a more efficacious novel drug delivery system. Various drug delivery systems are focused on drug-targeting of brain cells. However, the manifestation of the brain barrier is the main hurdle for the effective delivery of chemotherapeutics, ultimately causing treatment failure of various drugs. To solve this problem, various nanocarrier-based drug delivery system has been developed for brain targeting. This review outlines nanocarrier-based composites for different brain diseases and highlights nanocarriers for drug targeting towards brain cells. It also summarizes the latest developments in nanocarrier-based delivery systems containing liposomal systems, dendrimers, polymeric micelles, polymeric nanocarriers, quantum dots (QDs), and gold nanoparticles. Besides, the optimal properties of nanocarriers and therapeutic implications for brain targeting have been extensively studied. Finally, the potential applications and research opportunities for nanocarriers in brain targeting are discussed.

The Kynurenine Pathway as a Potential Target for Neuropathic Pain Therapy Design: From Basic Research to Clinical Perspectives

Accumulating evidence suggests the key role of the kynurenine pathway (KP) of the tryptophan metabolism in the pathogenesis of several diseases. Despite extensive research aimed at clarifying the mechanisms underlying the development and maintenance of neuropathic pain, the roles of KP metabolites in this process are still not fully known. Although the function of the peripheral KP has been known for several years, it has only recently been acknowledged that its metabolites within the central nervous system have remarkable consequences related to physiology and behavior. Both the products and metabolites of the KP are involved in the pathogenesis of pain conditions. Apart from the neuroactive properties of kynurenines, the KP regulates several neurotransmitter systems in direct or indirect ways. Some neuroactive metabolites are known to have neuroprotective properties (kynurenic acid, nicotinamide adenine dinucleotide cofactor), while others are toxic (3-hydroxykynurenine, quinolinic acid). Numerous animal models show that modulation of the KP may turn out to be a viable target for the treatment of diseases. Importantly, some compounds that affect KP enzymes are currently described to possess analgesic properties. Additionally, kynurenine metabolites may be useful for assessing response to therapy or as biomarkers in therapeutic monitoring. The following review describes the molecular site of action and changes in the levels of metabolites of the kynurenine pathway in the pathogenesis of various conditions, with a particular emphasis on their involvement in neuropathy. Moreover, the potential clinical implications of KP modulation in chronic pain therapy as well as the directions of new research initiatives are discussed.

Recent advances in the design of inorganic and nano-clay particles for the treatment of brain disorders

Inorganic materials, in particular nanoclays and silica nanoparticles, have attracted enormous attention due to their versatile and tuneable properties, making them ideal candidates for a wide range of biomedical applications, such as drug delivery. This review aims at overviewing recent developments of inorganic nanoparticles (like porous or mesoporous silica particles) and different nano-clay materials (like montmorillonite, laponites or halloysite nanotubes) employed for overcoming the blood brain barrier (BBB) in the treatment and therapy of major brain diseases such as Alzheimer's, Parkinson's, glioma or amyotrophic lateral sclerosis. Recent strategies of crossing the BBB through invasive and not invasive administration routes by using different types of nanoparticles compared to nano-clays and inorganic particles are overviewed.

A physicochemical, thermodynamical, structural and computational evaluation of kynurenic acid/cyclodextrin complexes

In this work, the interaction between Kynurenic acid (KYNA) and several natural and modified cyclodextrins (CDs) is carried out. Among all the CD tested, HPβ-CD showed the strongest complexation constant (K_F), with a value of 270.94 ± 29.80 M^-1. Between natural (α- and β-) CDs, the complex of KYNA with β-CD was the most efficient. The inclusion complex of KYNA with CDs showed a strong influence of pH and temperature. The K_F value decreased at high pH values, when the pK_a was passed. Moreover, an increase of the temperature caused a decrease in the K_F values. The thermodynamic parameters of the complexation (ΔH°, ΔS° and ΔG°) were studied with negative entropy, enthalpy and spontaneity of the process at 25 °C. Moreover, the inclusion complex was also characterized using FTIR and TGA. Finally, molecular docking calculations provided different interactions and their influence in the complexation constant.

SZR-104, a Novel Kynurenic Acid Analogue with High Permeability through the Blood-Brain Barrier

By being an antagonist of glutamate and other receptors, kynurenic acid serves as an endogenous neuroprotectant in several pathologies of the brain. Unfortunately, systemic administration of kynurenic acid is hindered by its low permeability through the blood–brain barrier. One possibility to overcome this problem is to use analogues with similar biological activity as kynurenic acid, but with an increased permeability through the blood–brain barrier. We synthesized six novel aminoalkylated amide derivatives of kynurenic acid, among which SZR-104 (N-(2-(dimethylamino)ethyl)-3-(morpholinomethyl)-4-hydroxyquinoline-2-carboxamide) proved to have the highest permeability through an in vitro blood–brain barrier model. In addition, permeability of SZR-104 was significantly higher than that of kynurenic acid, xanthurenic acid and 39B, a quinolone derivative/xanthurenic acid analogue. Since peripherally administered SZR-104 is able to inhibit epileptiform activity in the brain, we conclude that SZR-104 is a promising kynurenic acid analogue with good penetrability into the central nervous system.

Evaluation of solubility enhancement, antioxidant activity, and cytotoxicity studies of kynurenic acid loaded cyclodextrin nanosponge

Kynurenic acid demonstrates antioxidant, neuroprotective and free radical scavenging properties. However, low aqueous solubility of kynurenic acid limits its therapeutic activity. In the present study, cyclodextrin nanosponges were used to improve the solubility and therapeutic activity of kynurenic acid. The formation of kynurenic acid loaded nanosponge was confirmed by different characterization techniques. The solubility of kynurenic acid was significantly increased with nanosponge (111.1 μg/ml) compared to free kynurenic acid (16.4 μg/ml) and β-cyclodextrin (28.6 μg/ml). High drug loading (19.06%) and encapsulation efficiency (95.31%) were achieved with NS. The particle size and zeta potential of kynurenic acid loaded nanosponge was around 255.8 nm and -23 mV respectively. Moreover, higher solubilization of kynurenic acid loaded nanosponge produced better antioxidant activity compared to free kynurenic acid. The kynurenic acid loaded nanosponge and blank nanosponge were found nontoxic in the cytotoxicity assay. Thus, these studies demonstrated that nanosponges can be used as a carrier for the delivery of kynurenic acid.

Systematic Review on the Involvement of the Kynurenine Pathway in Stroke: Pre-clinical and Clinical Evidence

Background: Stroke is the second leading cause of death after ischemic heart disease and the third leading cause of disability-adjusted life-years lost worldwide. There is a great need for developing more effective strategies to treat stroke and its resulting impairments. Among several neuroprotective strategies tested so far, the kynurenine pathway (KP) seems to be promising, but the evidence is still sparse.

Methods: Here, we performed a systematic review of preclinical and clinical studies evaluating the involvement of KP in stroke. We searched for the keywords: (“kynurenine” or “kynurenic acid” or “quinolinic acid”) AND (“ischemia” or “stroke” or “occlusion) in the electronic databases PubMed, Scopus, and Embase. A total of 1,130 papers was initially retrieved.

Results: After careful screening, forty-five studies were included in this systematic review, being 39 pre-clinical and six clinical studies. Despite different experimental models of cerebral ischemia, the results are concordant in implicating the KP in the pathophysiology of stroke. Preclinical evidence also suggests that treatment with kynurenine and KMO inhibitors decrease infarct size and improve behavioral and cognitive outcomes. Few studies have investigated the KP in human stroke, and results are consistent with the experimental findings that the KP is activated after stroke.

Conclusion: Well-designed preclinical studies addressing the expression of KP enzymes and metabolites in specific cell types and their potential effects at cellular levels alongside more clinical studies are warranted to confirm the translational potential of this pathway as a pharmacological target for stroke and related complications.

Are the neuroprotective effects of exercise training systemically mediated?

To date there is no cure available for dementia, and the field calls for novel therapeutic targets. A rapidly growing body of literature suggests that regular endurance training and high cardiorespiratory fitness attenuate cognitive impairment and reduce dementia risk. Such benefits have recently been linked to systemic neurotrophic factors induced by exercise. These circulating biomolecules may cross the blood-brain barrier and potentially protect against neurodegenerative disorders such as Alzheimer's disease. Identifying exercise-induced systemic neurotrophic factors with beneficial effects on the brain may lead to novel molecular targets for maintaining cognitive function and preventing neurodegeneration. Here we review the recent literature on potential systemic mediators of neuroprotection induced by exercise. We focus on the body of translational research in the field, integrating knowledge from the molecular level, animal models, clinical and epidemiological studies. Taken together, the current literature provides initial evidence that exercise-induced, blood-borne biomolecules, such as BDNF and FNDC5/irisin, may be powerful agents mediating the benefits of exercise on cognitive function and may form the basis for new therapeutic strategies to better prevent and treat dementia.

Blood-Brain Delivery Methods Using Nanotechnology

Pathologies of the brain, of which brain cancer, Alzheimer's disease, Parkinson's disease, stroke, and multiple sclerosis, are some of the most prevalent, and that presently are poorly treated due to the difficulties associated with drug development, administration, and targeting to the brain. The existence of the blood-brain barrier, a selective permeability system which acts as a local gateway against circulating foreign substances, represents the key challenge for the delivery of therapeutic agents to the brain. However, the development of nanotechnology-based approaches for brain delivery, such as nanoparticles, liposomes, dendrimers, micelles, and carbon nanotubes, might be the solution for improved brain therapies.

Synthetic Polymer Nanoparticles Functionalized with Different Ligands for Receptor-mediated Transcytosis across Blood-Brain Barrier

Polymeric nanoparticles have been investigated as biocompatible and promising nano-carriers to deliver drugs across the blood-brain barrier (BBB). However, most of the polymeric nanoparticles cannot be observed without attaching them with fluorescent dyes. Generally complex synthesis process is required to attach fluorescent dye tracing molecules with drug carrier nanoparticles. In this paper, we synthesized a novel fluorescent polymer based on poly [Triphenylamine-4-vinyl-(P-methoxy-benzene)] (TEB). This polymer was prepared from TEB polymer through coprecipitation. Furthermore, three types of ligands, transferrin (TfR), lactoferrin (LfR) and lipoprotein (LRP), were covalently attached on the nanoparticle surface to improve the BBB transport efficiency. All of prepared TEB-based nanoparticles were biocompatible, exhibited excellent fluorescence properties and could be observed in vivo. The transcellular transportation of these TEB-based nanoparticles across the BBB was evaluated by observing the fluorescent intensity. The translocation study was performed in an in vitro BBB model that were constructed based on mouse cerebral endothelial cells (bEnd.3). The results showed that ligand-coated TEB nanoparticles can be transported across BBB with high efficiencies (up to 29.02%). This is the first time that the fluorescent TEB nanoparticles were applied as nano-carriers for transport across the BBB. Such fluorescent polymeric nanoparticles have the potential applications in brain imaging or drug delivery.

Kynurenine 3-Monooxygenase Gene Associated With Nicotine Initiation and Addiction: Analysis of Novel Regulatory Features at 5' and 3'-Regions

Tobacco smoking is widespread behavior in Qatar and worldwide and is considered one of the major preventable causes of ill health and death. Nicotine is part of tobacco smoke that causes numerous health risks and is incredibly addictive; it binds to the α7 nicotinic acetylcholine receptor (α7nAChR) in the brain. Recent studies showed α7nAChR involvement in the initiation and addiction of smoking. Kynurenic acid (KA), a significant tryptophan metabolite, is an antagonist of α7nAChR. Inhibition of kynurenine 3-monooxygenase enzyme encoded by KMO enhances the KA levels. Modulating KMO gene expression could be a useful tactic for the treatment of tobacco initiation and dependence. Since KMO regulation is still poorly understood, we aimed to investigate the 5' and 3'-regulatory factors of KMO gene to advance our knowledge to modulate KMO gene expression. In this study, bioinformatics methods were used to identify the regulatory sequences associated with expression of KMO. The displayed differential expression of KMO mRNA in the same tissue and different tissues suggested the specific usage of the KMO multiple alternative promoters. Eleven KMO alternative promoters identified at 5'-regulatory region contain TATA-Box, lack CpG Island (CGI) and showed dinucleotide base-stacking energy values specific to transcription factor binding sites (TFBSs). The structural features of regulatory sequences can influence the transcription process and cell type-specific expression. The uncharacterized LOC105373233 locus coding for non-coding RNA (ncRNA) located on the reverse strand in a convergent manner at the 3'-side of KMO locus. The two genes likely expressed by a promoter that lacks TATA-Box harbor CGI and two TFBSs linked to the bidirectional transcription, the NRF1, and ZNF14 motifs. We identified two types of microRNA (miR) in the uncharacterized LOC105373233 ncRNA, which are like hsa-miR-5096 and hsa-miR-1285-3p and can target the miR recognition element (MRE) in the KMO mRNA. Pairwise sequence alignment identified 52 nucleotides sequence hosting MRE in the KMO 3' UTR untranslated region complementary to the ncRNA LOC105373233 sequence. We speculate that the identified miRs can modulate the KMO expression and together with alternative promoters at the 5'-regulatory region of KMO might contribute to the development of novel diagnostic and therapeutic algorithm for tobacco smoking.

The activation of the kynurenine pathway in a rat model with renovascular hypertension

Hypertension is a serious condition that can lead to many health problems. The mechanisms underlying this process are still not fully understood. The kynurenine pathway may be involved in the occurrence and progression of hypertension. The purpose of this study was to examine the activity of peripheral kynurenine pathway in rats with renovascular hypertension in Goldblatt 2K1C model. Hypertension was induced in the experimental groups by constricting the renal artery of the left kidney of the rats. Determination of tryptophan (Trp) and kynurenine pathway metabolites was assessed by high-performance liquid chromatography in plasma and tissues obtained at 4, 8, and 16 weeks after the surgical intervention or sham surgery. Levels of Ang II were evaluated using commercial immuno-enzymatic ELISA kits. Surgical treatment led to increased values of mean blood pressure and systolic blood pressure, whereas Trp concentrations were decreased in experimental animals compared to appropriate controls. Simultaneously, the considerable increment of kynurenine pathway components and a significant increase in the activity of tryptophan 2,3-dioxygenase were observed in rats with developed hypertension in comparison with controls. There were no differences between Ang II levels in controls and experimental groups. The inverse relationship was between plasma Trp and both SBP and Ang II values, and Trp independently affected Ang II concentrations in hypertensive rats. In contrast, tryptophan 2,3-dioxygenase activity and plasma kynurenine metabolites positively correlated with blood pressure values as well as with Ang II levels in these animals. Moreover, kynurenine was independently connected with MBP. Renovascular hypertension influences kynurenine pathway and leads to an imbalance in Trp and its metabolite levels. Tryptophan 2,3-dioxygenase and part of the kynurenine metabolites in plasma and tissues positively correlated with blood pressure values and Ang II levels. Although the mechanisms underlying this phenomenon are unclear, our experiment showed a link between renovascular hypertension and activation of kynurenine pathway. Impact statement As hypertension is a major health problem, our research has focused on the connection between the kynurenine pathway and hypertension. We assessed the levels of the main metabolites of dietary tryptophan and analyzed its levels in terms of high blood pressure. The results of our work indicated that in the renovascular rat's model of hypertension, an alteration of the kynurenine pathway occurred. According to our knowledge, this is the first study that has investigated in a comprehensive manner the alteration of the kynurenine pathway under the condition of elevated blood pressure. On the one hand, the work supports a better understanding of pathophysiological basics of the occurrence of hypertension, and on the other hand it provides potential opportunities to treat this disease.

Passage of Magnetic Tat-Conjugated Fe3O4@SiO2 Nanoparticles Across In Vitro Blood-Brain Barrier

Delivery of diagnostic or therapeutic agents across the blood-brain barrier (BBB) remains a major challenge of brain disease treatment. Magnetic nanoparticles are actively being developed as drug carriers due to magnetic targeting and subsequently reduced off-target effects. In this paper, we developed a magnetic SiO2@Fe3O4 nanoparticle-based carrier bound to cell-penetrating peptide Tat (SiO2@Fe3O4-Tat) and studied its fates in accessing BBB. SiO2@Fe3O4-Tat nanoparticles (NPs) exhibited suitable magnetism and good biocompatibility. NPs adding to the apical chamber of in vitro BBB model were found in the U251 glioma cells co-cultured at the bottom of the Transwell, indicating that particles passed through the barrier and taken up by glioma cells. Moreover, the synergistic effects of Tat and magnetic field could promote the efficient cellular internalization and the permeability across the barrier. Besides, functionalization with Tat peptide allowed particles to locate into the nucleus of U251 cells than the non-conjugated NPs. These results suggest that SiO2@Fe3O4-Tat NPs could penetrate the BBB through the transcytosis of brain endothelial cells and magnetically mediated dragging. Therefore, SiO2@Fe3O4-Tat NPs could be exploited as a potential drug delivery system for chemotherapy and gene therapy of brain disease.