Influence of Cyclooxygenase-2 Inhibitors on Kynurenic Acid Production in Rat Brain in Vitro

Small Intestinal Bacterial Overgrowth in Various Specialties of Medical Practice (Literature Review and Expert Council Resolution)

Aim: to discuss current views on the clinical significance, diagnostic opportunities, and therapeutic approaches in the treatment of small intestinal bacterial overgrowth (SIBO) as an important component in the gut microbiota function assessment, to assess the awareness of physicians and the opportunities in the diagnosis and treatment of this disease in patients in the Federal districts of the Russian Federation, as well as to present the proceedings of the Expert Council held on December 16, 2023 in Moscow.

Key points. SIBO is a common syndrome often associated with irritable bowel syndrome, liver cirrhosis, asthma, and congestive heart failure, being also a predictor of early death in the elderly. Today, in many regions of the Russian Federation, there are limitations for instrumental diagnosis of this disease — lack of awareness among doctors, unavailability of gas analyzers for diagnosing SIBO, lack of information about the need to diagnose SIBO in the standards of compulsory health insurance. Rifaximin is the first-line treatment due to the highest therapeutic efficacy. One of the ways to increase the efficacy of SIBO treatment is to include strain-specific probiotics in the treatment regimen. Saccharomyces boulardii CNCM I-745 is thought to be the most studied, promising probiotic. The review also presents statistical data on the issues in the diagnosis and treatment of SIBO in the regions of the Russian Federation.

Conclusion. Optimization of approaches to the diagnosis and treatment of SIBO, the development of domestic gas analyzers, increasing the awareness of physicians in all regions of the Russian Federation, as well as the development and optimization of clinical recommendations appear to be necessary measures to increase the effectiveness of medical care, the duration and quality of life of the Russian population. These goals can be achieved within the framework of Federal programs under the supervision of specialized reference centers of the Ministry of Health of the Russian Federation.

Novel Activity of Oral Hypoglycemic Agents Linked with Decreased Formation of Tryptophan Metabolite, Kynurenic Acid

Kynurenic acid is a tryptophan (Trp) metabolite formed along the kynurenine (KYN) pathway in the brain and in peripheral tissues. The disturbed formation of kynurenic acid, which targets glutamate-mediated neurotransmission, GPR35, and aryl hydrocarbon receptors of immune or redox status, was implicated in the development of neuropsychiatric and metabolic disorders among others. Kynurenic acid exerts neuroprotective and immunomodulatory effects, yet its high brain levels may negatively impact cognition. Changes in the Trp-KYN pathway are also linked with the pathogenesis of diabetes mellitus, which is an established risk factor for cardiovascular and neurological diseases or cognitive deficits. Here, the effects of metformin and glibenclamide on the brain synthesis of kynurenic acid were evaluated. Acute exposure of rat cortical slices in vitro to either of the drugs reduced kynurenic acid production de novo. Glibenclamide, but not metformin, inhibited the activity of kynurenic acid biosynthetic enzymes, kynurenine aminotransferases (KATs) I and II, in semi-purified cortical homogenates. The reduced availability of kynurenic acid may be regarded as an unwanted effect, possibly alleviating the neuroprotective action of oral hypoglycemic agents. On the other hand, considering that both compounds ameliorate the cognitive deficits in animal and human studies and that high brain kynurenic acid may hamper learning and memory, its diminished synthesis may improve cognition.

Roles of endothelial prostaglandin I2 in maintaining synchronous spontaneous Ca2+ transients in rectal capillary pericytes

In hollow visceral organs, capillary pericytes appear to drive spontaneous Ca2+ transients in the upstream arterioles. Here, mechanisms underlying the intercellular synchrony of pericyte Ca2+ transients were explored. Ca2+ dynamics in NG2 chondroitin sulphate proteoglycan (NG2)-expressing capillary pericytes were examined using rectal mucosa-submucosa preparations of NG2-GCaMP6 mice. Spontaneous Ca2+ transients arising from endoplasmic reticulum Ca2+ release were synchronously developed amongst capillary pericytes in a gap junction blocker (3 μM carbenoxolone)-sensitive manner and could spread into upstream vascular segments. Spontaneous Ca2+ transients were suppressed by the Ca2+ -activated Cl- channel (CaCC) blocker niflumic acid and their synchrony was diminished by a TMEM16A inhibitor (3 μM Ani9) in accordance with TMEM16A immunoreactivity in pericytes. In capillaries where cyclooxygenase (COX)-2 immunoreactivity was expressed in endothelium but not pericytes, non-selective COX inhibitors (1 μM indomethacin or 10 μM diclofenac) or COX-2 inhibitor (10 μM NS 398) disrupted the synchrony of spontaneous Ca2+ transients and raised the basal Ca2+ level. Subsequent prostaglandin I2 (PGI2 ; 100 nM) or the KATP channel opener levcromakalim restored the synchrony with a reduction in the Ca2+ level. PGI2 receptor antagonist (1 μM RO1138452) also disrupted the synchrony of spontaneous Ca2+ transients and increased the basal Ca2+ level. Subsequent levcromakalim restored the synchrony and reversed the Ca2+ rise. Thus, the synchrony of spontaneous Ca2+ transients in pericytes appears to be developed by the spread of spontaneous transient depolarisations arising from the opening of TMEM16A CaCCs. Endothelial PGI2 may play a role in maintaining the synchrony, presumably by stabilising the resting membrane potential in pericytes. KEY POINTS: Capillary pericytes in the rectal mucosa generate synchronous spontaneous Ca2+ transients that could spread into the upstream vascular segment. Spontaneous Ca2+ release from the endoplasmic reticulum (ER) triggers the opening of Ca2+ -activated Cl- channel TMEM16A and resultant depolarisations that spread amongst pericytes via gap junctions, establishing the synchrony of spontaneous Ca2+ transients in pericytes. Prostaglandin I2 (PGI2 ), which is constitutively produced by the endothelium depending on cyclooxygenase-2, appears to prevent premature ER Ca2+ releases in the pericytes allowing periodic, regenerative Ca2+ releases. Endothelial PGI2 may maintain the synchrony of pericyte activity by stabilising pericyte resting membrane potential by opening of KATP channels.

Comparative structural study of selective and non-selective NSAIDs against the enzyme cyclooxygenase-2 through real-time molecular dynamics linked to post-dynamics MM-GBSA and e-pharmacophores mapping

BACKGROUND

Inflammation-provoked disorders including cancer are arbitrated by cyclooxygenase-2 (COX-2). Celecoxib and niflumic acid are among the potent and selective inhibitors of this enzyme while aspirin (acetylsalicylic acid) and sodium salicylate are its non-selective and lesser potent inhibitors. Despite these proven studies, the comparative structural study of these selective and non-selective molecules at atomistic scale in complex state with COX-2 that may answer this differential inhibitory behavior has not been accomplished spotlighting the imperative need of additional research in this area. Thus, this study was framed to provide a strong explanation for the enigma of higher inhibitory activity of celecoxib-niflumic acid duo in comparison to aspirin and sodium salicylate towards COX-2.

METHODS

A contemporary approach including advanced molecular docking against COX2, molecular dynamics of receptor-ligand complexes, simulation-trajectory-backed MMGBSA for different time points, radius of gyration (Rg) calculations, and e-pharmacophores approach was employed to attain a rational conclusion.

RESULTS

Our findings demonstrated the higher binding affinity of celecoxib and niflumic acid over aspirin and sodium salicylate against COX-2. Although both selective and non-selective COX-2 inhibitors manifested nearly the same stability in the active site of this enzyme but the e-pharmocophoric features found in the case of selective inhibitors scored over non-selective ones. Thus, our findings excluded the differential stability to be the cause of stronger potency of selective inhibitors but attributed their potency to greater number of complementary features present in these inhibitors against the active site of inflammation engendering COX-2.

Transplantation-based screen identifies inducers of muscle progenitor cell engraftment across vertebrate species

Stem cell transplantation presents a potentially curative strategy for genetic disorders of skeletal muscle, but this approach is limited by the deleterious effects of cell expansion in vitro and consequent poor engraftment efficiency. In an effort to overcome this limitation, we sought to identify molecular signals that enhance the myogenic activity of cultured muscle progenitors. Here, we report the development and application of a cross-species small-molecule screening platform employing zebrafish and mice, which enables rapid, direct evaluation of the effects of chemical compounds on the engraftment of transplanted muscle precursor cells. Using this system, we screened a library of bioactive lipids to discriminate those that could increase myogenic engraftment in vivo in zebrafish and mice. This effort identified two lipids, lysophosphatidic acid and niflumic acid, both linked to the activation of intracellular calcium-ion flux, which showed conserved, dose-dependent, and synergistic effects in promoting muscle engraftment across these vertebrate species.

Kynurenines in the Pathogenesis of Peripheral Neuropathy During Leprosy and COVID-19

Inflammatory disorders are associated with the activation of tryptophan (TRYP) catabolism via the kynurenine pathway (KP). Several reports have demonstrated the role of KP in the immunopathophysiology of both leprosy and coronavirus disease 19 (COVID-19). The nervous system can be affected in infections caused by both Mycobacterium leprae and SARS-CoV-2, but the mechanisms involved in the peripheral neural damage induced by these infectious agents are not fully understood. In recent years KP has received greater attention due the importance of kynurenine metabolites in infectious diseases, immune dysfunction and nervous system disorders. In this review, we discuss how modulation of the KP may aid in controlling the damage to peripheral nerves and the effects of KP activation on neural damage during leprosy or COVID-19 individually and we speculate its role during co-infection.

Biosynthesis of gold nanoparticles for the treatment of osteoarthritis alone or in combination with Diacerein® in a rat model

Gold (Au) compounds were used as an effective therapeutic agent for various inflammatory diseases; however, the use of Au compounds becomes limited because of its association with several side effects. Hence, gold nanoparticles (AuNPs) were developed as a new option for the medical proposes. However, the safety evaluation of gold nanoparticles (AuNPs) in osteoarthritis (OA) treatment remains vague. This study aimed to biosynthesize, characterize and evaluate the therapeutic effects of biosynthesized AuNPs and/or Diacerein^® (DIA) in experimental OA. OA was induced by a single injection of monosodium iodoacetate (3 mg/joint) in the intra-articular knee of female rats. Normal rats (N-rats) and OA-rats were treated orally for 5 weeks as follow: untreated N-rats; untreated OA-rats; N-rats received DIA (50 mg/kg b.w); N-rats received AuNPs (30 μg/kg b.w.); N-rats received AuNPs plus DIA; OA-rats received DIA; OA-rats received AuNPs, and OA-rats received AuNPs plus DIA. Blood, knee cartilage, liver and kidney samples were collected for biochemical and histological analysis. The synthesized AuNPs were nearly spherical with average size of 20 nm and zeta potential of 33 mV. AuNPs and DIA induced a significant improvement in serum inflammatory cytokines, biochemical parameters, estrogen level, hepatic and renal oxidative markers, hepatic DNA fragmentation, genomic template stability and cartilage joint histology of OA-rats. AuNPs were more effective than DIA and the combined treatment was more effective than the single treatment. It could be concluded that AuNPs are promising for the treatment of OA alone or in combination with DIA.

Kynurenine Pathway of Tryptophan Metabolism in Neuropsychiatric Disorders: Pathophysiologic and Therapeutic Considerations

Under physiological conditions 95% of the ingested essential amino acid tryptophan is metabolized by the kynurenine pathway (KP) to yield the ubiquitous co-enzyme nicotinamide adenine dinucleotide, fulfilling cellular energy require-ments. Importantly, the intermediaries of KP exert crucial effects throughout the body, including the central nervous system. Besides, KP metabolites are implicated in diverse disease processes such as inflammation/immune disorders, endocrine/metabolic conditions, cancers and neuropsychiatric diseases. A burgeoning body of research indicates that the KP plays a pathogenic role in major psychiatric diseases like mood disorders and schizophrenia. Triggered by inflammatory processes, the balance between neurotoxic and neuroprotective branches of the KP is disturbed. In preclinical models these discrepancies result in behaviors reminiscent of depression and psychosis. In clinical samples, recent studies are discovering key kynurenine pathway abnormalities which incriminate it in the pathogenesis of the main psychiatric disorders. Harnessing this knowledge has the potential to find disease biomarkers helpful in identifying and prognosticating neuropsychiatric disorders. Concurrently, earnest research efforts directed towards manipulating the KP hold the promise of discovering novel pharmacological agents that have therapeutic value. In this manuscript, an in-depth appraisal of the extant literature is done to understand the working of KP as this applies to neuropsychiatric disorders. It is concluded that this pathway plays an overarching role in the development of major psychiatric disorders, the KP metabolites have the potential to serve as disease markers and new medications based on KP modulation can bring lasting cures for patients suffering from these intractable conditions.

The Role of Brain Cyclooxygenase-2 (Cox-2) Beyond Neuroinflammation: Neuronal Homeostasis in Memory and Anxiety

Cyclooxygenases are a group of heme-containing isozymes (namely Cox-1 and Cox-2) that catalyze the conversion of arachidonic acid to largely bioactive prostaglandins (PGs). Cox-1 is the ubiquitous housekeeping enzyme, and the mitogen-inducible Cox-2 is activated to cause inflammation. Interestingly, Cox-2 is constitutively expressed in the brain at the postsynaptic dendrites and excitatory terminals of the cortical and spinal cord neurons. Neuronal Cox-2 is activated in response to synaptic excitation to yield PGE₂, the predominant Cox-2 metabolite in the brain, which in turn stimulates the release of glutamate and neuronal firing in a retrograde fashion. Cox-2 is also engaged in the metabolism of new endocannabinoids from 2-arachidonoyl-glycerol to modulate their actions at presynaptic terminals. In addition to these interactions, the induction of neuronal Cox-2 is coupled to the trans-synaptic activation of the dopaminergic mesolimbic system and some serotoninergic receptors, which might contribute to the development of emotional behavior. Although much of the focus regarding the induction of Cox-2 in the brain has been centered on neuroinflammation-related neurodegenerative and psychiatric disorders, some evidence also suggests that Cox-2 release during neuronal signaling may be pivotal for the fine tuning of cortical networks to regulate behavior. This review compiles the evidence supporting the homeostatic role of neuronal Cox-2 in synaptic transmission and plasticity, since neuroinflammation is originally triggered by the induction of glial Cox-2 expression. The goal is to provide perspective on the roles of Cox-2 beyond neuroinflammation, such as those played in memory and anxiety, and whose evidence is still scant.

Dopamine and glutamate in schizophrenia: biology, symptoms and treatment

Glutamate and dopamine systems play distinct roles in terms of neuronal signalling, yet both have been proposed to contribute significantly to the pathophysiology of schizophrenia. In this paper we assess research that has implicated both systems in the aetiology of this disorder. We examine evidence from post-mortem, preclinical, pharmacological and in vivo neuroimaging studies. Pharmacological and preclinical studies implicate both systems, and in vivo imaging of the dopamine system has consistently identified elevated striatal dopamine synthesis and release capacity in schizophrenia. Imaging of the glutamate system and other aspects of research on the dopamine system have produced less consistent findings, potentially due to methodological limitations and the heterogeneity of the disorder. Converging evidence indicates that genetic and environmental risk factors for schizophrenia underlie disruption of glutamatergic and dopaminergic function. However, while genetic influences may directly underlie glutamatergic dysfunction, few genetic risk variants directly implicate the dopamine system, indicating that aberrant dopamine signalling is likely to be predominantly due to other factors. We discuss the neural circuits through which the two systems interact, and how their disruption may cause psychotic symptoms. We also discuss mechanisms through which existing treatments operate, and how recent research has highlighted opportunities for the development of novel pharmacological therapies. Finally, we consider outstanding questions for the field, including what remains unknown regarding the nature of glutamate and dopamine function in schizophrenia, and what needs to be achieved to make progress in developing new treatments.