Loop diuretics inhibit kynurenic acid production and kynurenine aminotransferases activity in rat kidneys.

BACKGROUND: Loop diuretics became a cornerstone in the therapy of hypervolemia in patients with chronic kidney disease or heart failure. Apart from the influence on water and electrolyte balance, these drugs were shown to inhibit tissue fibrosis and renin-angiotensin-system activity. The kynurenine (KYN) pathway products are suggested to be uremic toxins. Kynurenic acid (KYNA) is synthesized by kynurenine aminotransferases (KATs) in the brain and periphery. The cardiovascular and renal effects of KYNA are well documented. However, high KYNA levels have been correlated with the rate of kidney damage and its complications. Our study aimed to assess the effect of loop diuretics, ethacrynic acid, furosemide, and torasemide on KYNA synthesis and KATs activity in rat kidneys in vitro. METHODS: Quantitative analyses of KYNA were performed using fluorimetric HPLC detection. Additionally, molecular docking studies determined the possible interactions of investigated compounds with an active site of KAT I and KAT II. RESULTS: All studied drugs inhibited KYNA production in rat kidneys in vitro at 0.5-1.0 mmol/l concentrations. Only ethacrynic acid at 1.0 mmol/l concentration significantly lowered KAT I and KAT II activity in kidney homogenates, whereas other drugs were ineffective. Molecular docking results indicated the common binding site for each of the studied loop diuretics and KYNA. They suggested possible residues involved in their binding to the active site of both KAT I and KAT II model. CONCLUSIONS: Our study reveals that loop diuretics may decrease KYNA synthesis in rat kidneys in vitro. The presented results warrant further research in the context of KYN pathway activity regulation by loop diuretics.

Paraneoplastic Syndrome After Kidney Transplantation: Frequency, Risk Factors, Differences to Paraneoplastic Occurrence of Glomerulonephritis in the Native Kidney, and Implications on Long-Term Kidney Graft Function.

Posttransplant malignancies are an important complication of solid organ transplantation. Kidney transplant recipients are at particularly high risk of cancer development. The most relevant risk factors of carcinogenesis are the use of immunosuppressive agents and oncogenic viral infections. Additionally, immune dysregulation caused by these factors may predispose to various types of organ damage. Paraneoplastic glomerular diseases are one of the most interesting and understudied cancer manifestations. The appropriate diagnosis of paraneoplastic glomerular damage can be challenging in kidney transplant recipients, due to factors inherent to concomitant medication and common comorbidities. Recent advances in the field of molecular and clinical nephrology led to a significant improvement in our understanding of glomerular diseases and their more targeted treatment. On the other hand, introduction of novel anticancer drugs tremendously increased patients' survival, at the cost of kidney-related side effects. Our review aims to provide insights into diagnosis and treatment of paraneoplastic glomerular diseases, with a special attention to kidney transplant recipients.

The potential association between influenza vaccination and lower incidence of renal cell carcinoma.

It is well-established that kidney cancer or renal cell carcinoma (RCC) occurs more commonly in chronic kidney disease (CKD) than in the general population, although the underlying mechanisms are incompletely understood. Beyond hereditary RCC syndromes; smoking, obesity and hypertension are widely known risk factors for RCC, irrespective of CKD. Kidney-specific factors such as episodes of acute kidney injury, nephrolithiasis and cyst formation have also been shown to be associated with RCC development. One potential and less explored factor is the role of viruses in the development of kidney cancer. In this issue of Clinical Kidney Journal, Lin et al. raise the interesting hypothesis that influenza vaccination may be associated with lower incidence of RCC in adults with CKD. We discuss potential mechanisms underlying this interesting observation in the context of immune dysregulation in CKD.

Effects of Fenofibrate and Gemfibrozil on Kynurenic Acid Production in Rat Kidneys In Vitro: Old Drugs, New Properties.

Kidney dysfunction significantly increases the cardiovascular risk, even in cases of minor functional declines. Hypertriglyceridemia is the most common lipid abnormality reported in patients with kidney disorders. PPAR-α (peroxisome proliferator-activated receptor-α) agonists called fibrates are the main agents used to lower triglyceride levels. Kynurenic acid (KYNA) is a tryptophan (Trp) derivative directly formed from L-kynurenine (L-KYN) by kynurenine aminotransferases (KATs). KYNA is classified as a uremic toxin, the level of which is correlated with kidney function impairments and lipid abnormalities. The aim of this study was to analyze the effect of the most commonly used triglyceride-lowering drugs, fenofibrate and gemfibrozil, on KYNA production and KAT activity in rat kidneys in vitro. The influence of fenofibrate and gemfibrozil on KYNA formation and KAT activity was tested in rat kidney homogenates in vitro. Fenofibrate and gemfibrozil at 100 µM-1 mM significantly inhibited KYNA synthesis in rat kidney homogenates. Both fibrates directly affected the KAT I and KAT II isoenzyme activities in a dose-dependent manner at similar concentrations. The presented results reveal the novel mechanism of action of fibrates in the kidneys and suggest their potential role in kidney function protection beyond the well-known anti-hyperlipidemic effect.

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.

Binge-like mephedrone treatment induces memory impairment concomitant with brain kynurenic acid reduction in mice.

While mephedrone (4-methylmethcathinone), a synthetic cathinone derivative, is widely abused by adolescents and young adults, the knowledge about its long-term effects on memory processes is limited. Kynurenic acid (KYNA) is a neuroactive metabolite of the kynurenine pathway of tryptophan degradation. KYNA is considered an important endogenous modulator influencing physiological and pathological processes, including learning and memory processes. The aim of this study was to determine whether (A) binge-like mephedrone administration (10.0 and 30.0 mg/kg, intraperitoneally, in 4 doses separated by 2 h) induces memory impairments, assessed 2, 8 and 15 days after mephedrone cessation in the passive avoidance test in mice, and whether (B) KYNA is involved in these memory processes. To clarify the role of KYNA in the mephedrone effects, its production in the murine brain in vivo, and in cortical slices in vitro, as well as the activities of kynurenine aminotransferases (KATs) I and II were assessed. Furthermore, cell line experiments were conducted to investigate the effects of mephedrone on normal human brain cells. Our results showed memory impairments 8 and 15 days after binge-like mephedrone administration. At the same time, reduction in the KYNA level in the murine brain was noted. In vitro studies showed no effect of mephedrone on the production of KYNA in cortical slices or on the activity of the KAT I and II enzymes. Finally, exposure of normal cells to mephedrone in vitro resulted in a modest reduction of cell viability and proliferation.

Anticoagulant-related nephropathy: Focus on novel agents. A review.

Anticoagulant-related nephropathy (ARN) is a novel and not well-studied cause of acute kidney injury (AKI). The prevalence of ARN varies significantly between studies and is estimated at 20% in patients treated with warfarin. Patients with ARN have a significantly higher mortality risk and an increased risk of chronic kidney disease (CKD). Unexplained AKI with hematuria are clinical manifestations of ARN. In most cases, ARN is diagnosed within the first 2 months of anticoagulant therapy, but later ARN occurrence is possible. Among the studied anticoagulants, most data concern warfarin toxicity, whereas cases of ARN caused by direct oral anticoagulants (DOACs) have also been presented. Tubular obstruction by red blood cell casts or hemoglobin and iron tubular toxicity are the postulated mechanisms of ARN. On the molecular level, the inhibition of thrombin and protease-activated receptor-1 (PAR-1), leading to endothelial susceptibility to damage or abnormal protein C endothelial signaling, is suggested to contribute to ARN. Older age, impaired kidney function, hypertension, and diabetes mellitus are the main risk factors for ARN, but their significance may differ between anticoagulants. From therapeutic options, the withdrawal of the anticoagulant and the administration of its antidote, as well as corticosteroids or N-acetylcysteine, are proposed. Since the number of patients with kidney diseases on anticoagulants increases, and DOACs are starting to be more useful in this group of patients, we aim to summarize the pathogenesis, clinical picture and possible ways of treatment of DOAC-induced ARN.

Kynurenine pathway in kidney diseases.

Kidney diseases have become one of the most common health care problems. Due to a growing number of advanced aged patients with concomitant disorders the prevalence of these diseases will increase over the coming decades. Despite available laboratory tests, accurate and rapid diagnosis of renal dysfunction has yet to be realized, and prognosis is uncertain. Moreover, data on diagnostic and prognostic markers in kidney diseases are lacking. The kynurenine (KYN) pathway is one of the routes of tryptophan (Trp) degradation, with biologically active substances presenting ambiguous properties. The KYN pathway is known to be highly dependent on immunological system activity. As the kidneys are one of the main organs involved in the formation, degradation and excretion of Trp end products, pathologies involving the kidneys result in KYN pathway activity disturbances. This review aims to summarize changes in the KYN pathway observed in the most common kidney disease, chronic kidney disease (CKD), with a special focus on diabetic kidney disease, acute kidney injury (AKI), glomerulonephritis and kidney graft function monitoring. Additionally, the importance of KYN pathway activity in kidney cancer pathogenesis is discussed, as are available pharmacological agents affecting KYN pathway activity in the kidney. Despite limited clinical data, the KYN pathway appears to be a promising target in the diagnosis and prognosis of kidney diseases. Modulation of KYN pathway activity by pharmacological agents should be considered in the treatment of kidney diseases.

Hemodialysis Effect on the Composition of the Eye Fluid of Cataract Patients.

Numerous reports have proven that dialysis patients experience disturbances in the levels of elements in biological fluids. Disturbances in the homeostasis of essential elements or the appearance of highly toxic elements are serious problems also in clinical ophthalmology. The purpose of this study was to investigate the influence of hemodialysis (HD) on the elemental composition of anterior chamber aqueous humor (AH) in patients undergoing cataract surgery. The study involved 22 patients. The control group enrolled 16 patients (age 75.68 ± 9.67, female 54.55%, male 45.45%) with cataract and normal kidney function (control), and the second group included six patients (age 70.33 ± 12.74, female 33.33%, male 66.67%) with cataract undergoing HD treatment. The elements quantification was established using an inductively coupled plasma optical emission spectrometer (ICP-MS). In the eye fluid of dialysis patients, there were increased levels of manganese (Mn) and mercury (Hg) and decreased levels of vanadium (V) and zinc (Zn). In addition, a statistically significant increase in the Hg/Zn and Hg/selenium (Se) ratios and a lowering of the iron (Fe)/Mn ratio were observed in the studied group in comparison to the control. The obtained results indicated the need for Zn and Se supplementation in order to eliminate the hazards caused by Hg toxicity. A lower level of V in the eye fluid of dialysis patients may have a positive effect on maintaining a calcium and phosphorus homeostasis. Our study gives a deep insight into changes of elements concentrations in AH induced by HD.

Arginase Gene Polymorphism Increases Risk of Diabetic Retinopathy in Type 2 Diabetes Mellitus Patients.

Studies have demonstrated that polymorphic variants of arginase 1 gene (ARG1) are involved in human diseases, such as coronary heart disease, hypertension, and diabetes. Our study aimed to investigate the association between ARG1 rs2781666 single nucleotide polymorphism (SNP) and diabetic retinopathy (DR) in type 2 diabetes (T2DM) patients. Polymorphism was genotyped in 740 T2DM patients and 400 healthy individuals. A significant difference in the genotype distribution was observed between the patients and the controls. The T allele and TT genotype were associated with an increased risk of T2DM (OR 1.4, 95% CI 1.14-1.72, p = 0.001 and OR 2.16, 95% CI 1.23-3.80, p = 0.007, respectively). When the T2DM subjects were stratified into DR+ and DR- subgroups, the T allele and TT genotype frequencies were significantly higher in the DR+ group compared to the DR- group, demonstrating OR 1.68 (1.33-2.12), p < 0.0001 and OR 2.39 (1.36-4.18), p = 0.002, respectively. Logistic regression analysis was applied to determine the interaction between the ARG1 genotypes and other risk factors. Only ARG1 rs2781666 SNP was a significant risk predictor of DR (p = 0.003). In conclusion, this is the first report discussing the effect of ARG1 polymorphism on the microvascular complications that are associated with diabetes. Our findings demonstrate that ARG1 rs2781666 SNP is significantly associated with an increased susceptibility to DR in T2DM patients.

Haemochromatosis in a kidney transplant recipient: a case report.

BACKGROUND: Iron overload is inevitably related to chronic kidney disease (CKD) treatment. Haemochromatosis leads to multiorgan damage and is associated with increased mortality. Primary haemochromatosis is the most common autosomal recessive disease in white populations. In most cases, the classic form of hereditary haemochromatosis is caused by mutations, mainly C282Y and H63D, in the haemochromatosis gene (HFE). Secondary haemochromatosis can be triggered by iron administration and blood transfusions. Haemochromatosis is rarely reported in kidney transplant recipients. Atypical factors may evoke haemochromatosis in patients without HFE mutations or other standard risk factors. CASE PRESENTATION: In the current study, we present a patient who started to have haemochromatosis symptoms after kidney transplantation. A 37-year-old man after kidney transplantation from a deceased donor was admitted to the hospital due to high serum ferritin levels and impaired graft function. The patient's past medical history included arterial hypertension, embolization of both renal arteries and necrosis of the left femoral head. Glomerulonephritis was suspected as a cause of CKD; however, severe kidney failure was diagnosed, kidney biopsy was not performed, and the patient started intermittent haemodialysis. While on dialysis to treat anaemia, the patient had received erythropoietin and iron intravenously, and the maximal serum ferritin level was 2115 ng/ml. After kidney transplantation, ferritin levels started to increase rapidly, with a maximum level of 9468 ng/ml one and a half years after surgery. His genetic study showed HFE C282Y heterozygosity. Symptoms of haemochromatosis, such as skin hyperpigmentation, elevated activity of aminotransferases, impaired glucose tolerance and heart failure, were observed. Therapeutic phlebotomy was started, and 36 procedures were performed. After treatment, graft function significantly improved, most haemochromatosis symptoms resolved, and the serum ferritin level significantly decreased. CONCLUSIONS: Haemochromatosis can occur in heterozygotic HFE patients after kidney transplantation. Iron administration, infections, type of immunosuppression and liver dysfunction should be considered potential triggers of haemochromatosis in this group of patients.

Guillain-Barre syndrome: a typical paraneoplastic syndrome in a kidney transplant recipient with allograft renal cell carcinoma: a case report and review of the literature.

BACKGROUND: Guillain-Barré syndrome (GBS) is an autoimmune polyneuropathy affecting the peripheral nervous system. This neurological disorder has been previously reported in bone marrow transplant recipients but is uncommon after kidney transplantation. Viral infections and calcineurin inhibitors are the main triggers of GBS in renal transplant recipients. CASE PRESENTATION: In this report, we present a case of a 47-year-old male patient 12 years after his second kidney transplantation who developed GBS due to papillary renal cell carcinoma. Infectious and drug-related origins of GBS were excluded. Despite intensive treatment, graftectomy was performed, after which neurological symptoms resolved. CONCLUSIONS: In kidney transplant recipients, paraneoplastic aetiology should be considered in the differential diagnosis of GBS.

Correction to: Long-term vigabatrin treatment modifies pentylenetetrazole-induced seizures in mice: focused on GABA brain concentration.

The article Long-term vigabatrin treatment modifies pentylenetetrazole-induced seizures in mice: focused on GABA brain concentration.

Long-term vigabatrin treatment modifies pentylenetetrazole-induced seizures in mice: focused on GABA brain concentration.

BACKGROUND: The goal of our study was to examine the long-term effect of vigabatrin (VGB), a γ-aminobutyric acid aminotransferase (GABA-AT) inhibitor on clonazepam (CLO), ethosuximide (ETX) and valproate (VPA) anticonvulsive activity against pentylenetetrazole (PTZ)-induced seizures in mice. METHODS: VGB was administered for 3 and 7 days. Convulsions were evoked by PTZ at its CD97 (99 mg/kg). The influence of CLO, ETX and VPA alone or in combination with VGB on motor performance and long-term memory was analyzed. γ-aminobutyric acid (GABA) concentration in mice brain and plasma as well as glutamate decarboxylase (GAD) activity was measured. RESULTS: After 3 days of treatment, VGB in doses up to 500 mg/kg increased PTZ-induced seizure threshold, whereas after 7 days VGB (at the dose of 125 mg/kg) inhibited clonic seizures in experimental mice. 7 days of VGB administration did not change the protective effect of CLO, ETX and VPA against PTZ-induced seizures. 7 days of VGB treatment at a subthreshold dose of 75 mg/kg decreased TD50 of ETX and CLO in the chimney test, but did not affect TD50 value for VPA. 7 days of VGB administration in combination with AEDs did not affect long-term memory in mice. VGB after 3 days or 7 days of administration increased brain GABA concentration. GAD activity was decreased after 3 and 7 days of VGB administration. CONCLUSIONS: The presented results confirm anticonvulsive activity of VGB through GABA metabolism alteration and suggest care when combining VGB with ETX or CLO in the therapy.

Kynurenic acid selectively reduces heart rate in spontaneously hypertensive rats.

We found previously that intravenous kynurenic acid (KYNA), a native broad spectrum glutamate antagonist, increases renal blood flow and induces natriuresis in anesthetized spontaneously hypertensive rats (SHR). Since such changes may affect systemic circulation and can potentially find therapeutic application, in this study we examined long term influence of orally administered KYNA on systemic and renal hemodynamics and renal excretion in conscious SHR. KYNA was administered in drinking water at a dose of 25 mg/kg/day for 3 weeks. Heart rate (HR), systolic (SBP), and mean arterial pressure (MAP) were measured through telemetry. The records were taken at the beginning of the study (control, day 0), and then on day 7, 14, and 21 of treatment. Diuresis (V), total solute excretion (UosmV), and sodium excretion (UNaV) were determined on days 0, 7, and 14. KYNA consistently decreased HR, from 319 ± 8 to 291 ± 5, 299 ± 9 and 284 ± 6 beats/min on day 7, 14, and 21, respectively, (- 9, - 6, and - 11%; p < 0.01-0.0001); HR was stable in the solvent group. SBP, MAP, V, and UNaV were not affected by KYNA, whereas UosmV increased modestly. Chronic oral administration of KYNA to conscious SHR decreased HR without affecting MAP. Since tachycardia is an independent risk factor for cardiovascular disorders, and most drugs used to decrease HR have strong inotropic negative or hypotensive effect, such selective action seems of therapeutic potential. Moreover, food supplementation with KYNA can be considered in the prevention of heart diseases.

Influence of salbutamol on the anticonvulsant potency of the antiepileptic drugs in the maximal electroshock-induced seizures in mice.

BACKGROUND: ß2-Adrenergic receptor agonists are widely used agents in the treatment of asthma or preterm labor. Since prevalence of asthma was shown to be higher in patients with epilepsy and modulation of noradrenergic system activity may modify epilepsy course, the aim of the present study was to examine the effect of salbutamol (SALB), one of the most commonly used ß2-adrenergic receptor agonist on the anticonvulsant potency of four classical antiepileptic drugs (AEDs): valproate (VPA), carbamazepine (CBZ), phenytoin (DPH) and phenobarbital (PB) in mice subjected to the maximal electroshock (MES)-induced seizures. METHODS: Seizures were caused by a current delivered through ear-clip electrodes. The influence of AEDs and SALB on animals' motor coordination and memory processes was also evaluated. RESULTS: Single SALB injection did not change, whereas 7 days SALB administration decreased seizure threshold in the MES-induced seizures in mice. Moreover, SALB injected ip for 1 day and for 7 days lowered the antiepileptic activity of PB in the MES-induced seizures in mice, but did not change the effect of other analyzed AEDs: VPA, CBZ or DPH. Butoxamine, a selective ß2-adrenergic receptor antagonist, reversed SALB influence on the activity of PB. SALB given alone or in combination with the tested AEDs did not affect animals' motor performance and memory after both single and 7 days administration. CONCLUSIONS: Presented results show that SALB may decrease the antiepileptic efficacy of PB. A special caution is advised to patients with epilepsy receiving ß2-adrenergic receptors agonists in the pharmacotherapy of pulmonary and obstetrical disorders.

Blebbistatin reveals beneficial effects on the cystometric parameters in an animal model of detrusor overactivity.

The aims of the study were to determine the effectiveness of blebbistatin (BLEB) on detrusor overactivity (DO) in an animal model induced by retinyl acetate (RA) and, because of potential urothelial permeability, to evaluate the degenerative impact of BLEB on the urothelium. Three days after RA instillation into the urinary bladder, BLEB was administered into the bladder and immediately after cystometric assessment was performed. Furthermore, Evans Blue extravasation into bladder tissue and urothelium thickness were measured. Sixty female Wistar rats were used and randomly assigned to one of four groups (n = 15 in each group): (1) control, (2) RA, (3) BLEB, and (4) RA + BLEB. RA administration induced changes in cystometric parameters reflecting DO, as previously reported. Treatment with BLEB did not significantly alter cystometric parameters in rats which did not receive RA. Administration of BLEB to rats pretreated with RA reversed changes in cystometric parameters induced by RA in basal pressure, threshold pressure, detrusor overactivity index, amplitude of nonvoiding contractions, frequency of nonvoiding contractions, voided volume, volume threshold, intercontraction interval, bladder compliance, and volume threshold to elicit nonvoiding contractions. There were no significant differences in Evans Blue extravasation into bladder tissue or urothelium thickness between the groups. The current research provides new data on the possible utility of blebbistatin in the pharmacotherapy of DO, which is an important feature of overactive bladder (OAB). Further studies in human patients with DO/OAB are warranted to confirm these preclinical results.