The anti-oxidant effects are not the main mechanism for glutamine's protective effects on acute kidney injury in mice

The role of amino acids and protein administration in preventing cardiac surgery-associated acute kidney injury

Acute kidney injury (AKI) persists as one of the most common complications after cardiac surgery. Beyond being burdened by high morbidity and mortality rates, effective therapeutic options are still lacking. To date, the management of cardiac surgery-associated AKI (CSA-AKI) mainly focuses on preventive strategies, e.g. the implementation of standardized care bundles. Interestingly, recent experimental studies have suggested a potential nephroprotective role for both amino acids (AA) and proteins. As such, these compounds show multiple beneficial renal effects, spanning enhancement of renal blood flow, improved oxygenation, and recruitment of renal functional reserve. Moreover, clinical studies have investigated the therapeutic potential of single AA, AA combinations, and proteins. A recent large multicenter randomized controlled trial showed reduced AKI incidence in cardiac surgery patients receiving intravenous AA supplementation. However, these interventions have not yet demonstrated beneficial effects on major clinical outcomes, such as survival. Given the well-established AA safety profile and the underlying biological rationale supporting their use, this review summarizes the existing literature on the effects of various formulations and combinations of perioperative AA and protein on renal outcomes when administered in cardiac surgery patients.

Glutaminolysis is a Potential Therapeutic Target for Kidney Diseases

Metabolic reprogramming contributes to the progression and prognosis of various kidney diseases. Glutamine is the most abundant free amino acid in the body and participates in more metabolic processes than other amino acids. Altered glutamine metabolism is a prominent feature in different kidney diseases. Glutaminolysis converts glutamine into the TCA cycle metabolite, alpha-ketoglutarate, via a cascade of enzymatic reactions. This metabolic pathway plays pivotal roles in inflammation, maladaptive repair, cell survival and proliferation, redox homeostasis, and immune regulation. Given the crucial role of glutaminolysis in bioenergetics and anaplerotic fluxes in kidney pathogenesis, studies on this cascade could provide a better understanding of kidney diseases, thus inspiring the development of potential methods for targeted therapy. Emerging evidence has shown that targeting glutaminolysis is a promising therapeutic strategy for ameliorating kidney disease. In this narrative review, equation including keywords related to glutamine, glutaminolysis and kidney are subjected to an exhaustive search on Pubmed database, we identified all relevant articles published before 1 April, 2024. Afterwards, we summarize the regulation of glutaminolysis in major kidney diseases and its underlying molecular mechanisms. Furthermore, we highlight therapeutic strategies targeting glutaminolysis and their potential clinical applications.

The Preventive Role of Glutamine Supplementation in Cardiac Surgery-Associated Kidney Injury from Experimental Research to Clinical Practice: A Narrative Review

Acute kidney injury represents a significant threat in cardiac surgery regarding complications and costs. Novel preventive approaches are needed, as the therapeutic modalities are still limited. As experimental studies have demonstrated, glutamine, a conditionally essential amino acid, might have a protective role in this setting. Moreover, the levels of glutamine after the cardiopulmonary bypass are significantly lower. In clinical practice, various trials have investigated the effects of glutamine supplementation on cardiac surgery with encouraging results. However, these studies are heterogeneous regarding the selection criteria, timing, dose, outcomes studied, and way of glutamine administration. This narrative review aims to present the potential role of glutamine in cardiac surgery-associated acute kidney injury prevention, starting from the experimental studies and guidelines to the clinical practice and future directions.

Effect of Glutamine Administration After Cardiac Surgery on Kidney Damage in Patients at High Risk for Acute Kidney Injury: A Randomized Controlled Trial

BACKGROUND

Acute kidney injury (AKI) is a common complication after cardiac surgery and is associated with increased morbidity and mortality. However, no specific treatment options are available, emphasizing the need for preventive measures. The aim of this study was to clarify the effect of glutamine on [TIMP2]*[IGFBP7] levels at the end of the intervention period.

METHODS

In a randomized clinical, double-blind pilot study, 64 eligible cardiac surgery patients at high risk for AKI identified by high urinary [TIMP2]*[IGFBP7] were randomized, and body weight-adapted intravenous glutamine or saline-control was administered continuously for 12 hours postoperatively. The primary outcome was urinary [TIMP2]*[IGFBP7] at the end of the 12-hour study period. Secondary outcomes included kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) at 12 hours, overall AKI rates at 72 hours, free days through day 28 of mechanical ventilation and vasoactive medication, renal recovery at day 90, requirement of renal replacement therapy and mortality each at days 30, 60, and 90, length of intensive care unit (ICU) and hospital stay, and major adverse kidney events consisting of mortality, dialysis dependency, and persistent renal dysfunction (serum creatinine ≥2× compared to baseline value) at day 90 (major adverse kidney event; MAKE 90 ).

RESULTS

Sixty-four patients (mean age, 68.38 [standard deviation {SD} ± 10.48] years; 10 of 64 women) were enrolled and randomized. Patients received coronary artery bypass graft surgery (32/64), valve surgery (18/64), coronary artery bypass graft and valve surgery (6/64), or other procedures (8/64). Mean on-pump time was 68.38 (standard deviation ± 10.48) minutes. After glutamine administration, urinary [TIMP-2]*[IGFBP7] was significantly lower in the glutamine compared to the control group (primary end point, intervention: median, 0.18 [Q1, Q3; 0.09, 0.29], controls: median, 0.44 [Q1, Q3; 0.14, 0.79]; P = .01). In addition, [KIM-1] and [NGAL] were also significantly lower in the glutamine group. The overall AKI rate within 72 hours was not different among groups: (intervention 11/31 [35.5%] versus control 8/32 [25.0%]; P = .419; relative risk [RR], 0.86% [95% confidence interval {CI}, 0.62-1.20]). There were no differences regarding secondary end points.

CONCLUSIONS

Glutamine significantly decreased markers of kidney damage in cardiac surgery patients at high risk for AKI. Future trials have to be performed to investigate whether the administration of glutamine might be able to reduce the occurrence of AKI after cardiac surgery.

Glutamine prevents acute kidney injury by modulating oxidative stress and apoptosis in tubular epithelial cells

Acute kidney injury (AKI) represents a common complication in critically ill patients that is associated with increased morbidity and mortality. In a murine AKI model induced by ischemia/reperfusion injury (IRI), we show that glutamine significantly decreases kidney damage and improves kidney function. We demonstrate that glutamine causes transcriptomic and proteomic reprogramming in murine renal tubular epithelial cells (TECs), resulting in decreased epithelial apoptosis, decreased neutrophil recruitment, and improved mitochondrial functionality and respiration provoked by an ameliorated oxidative phosphorylation. We identify the proteins glutamine gamma glutamyltransferase 2 (Tgm2) and apoptosis signal-regulating kinase (Ask1) as the major targets of glutamine in apoptotic signaling. Furthermore, the direct modulation of the Tgm2-HSP70 signalosome and reduced Ask1 activation resulted in decreased JNK activation, leading to diminished mitochondrial intrinsic apoptosis in TECs. Glutamine administration attenuated kidney damage in vivo during AKI and TEC viability in vitro under inflammatory or hypoxic conditions.

Metabolomic Mechanisms of Radix Fici Hirtae against Carbon Tetrachloride-Induced Acute Liver Damage in Mice

Background

Radix Fici Hirtae (RFH), known as Cantonese ginseng, is an alternative folk medicine that is widely used to treat various diseases in southern China. The aim of this study was to investigate the effect and metabolic mechanisms of pretreatment with RFH on the serum metabolic profiles of carbon tetrachloride (CCl₄) induced acute liver injury in mice.

Methods

Mice fed with the water extract of RFH at a dose of 1.5 g/kg and 0.75 g/kg for consecutive 7 days, and then serum samples were taken for the metabolomic analysis. Furthermore, the bioinformatics and pathways analysis were measured.

Results

The UHPLC-Orbitrap/MS based-metabolomic analysis identified 20 differential metabolic markers in serum of CCl₄-induced liver injury mice compared to that of the normal controls, which were mainly related to the metabolism of amino acids and fatty acids. Furthermore, most of these biomarkers contributing to CCl₄ induction were ameliorated by RFH, and the bioinformatics and pathways analysis revealed that therapeutic actions of RFH were mainly involved in the regulation of the oxidative stress responses and energy homeostasis.

Conclusion

These findings provide potential metabolic mechanism for future study and allow for hypothesis generation about the hepatoprotective effects of Radix Fici Hirtae.

Analysis of microRNA Expression after Glutamine Intervention in Acute Renal Ischemia-Reperfusion Injury

Background

Ischemia-reperfusion acute kidney injury (I/R AKI) is a severe kidney disease with high mortality and morbidity. This study aimed to explore the protective mechanism of glutamine (GLN) against I/R AKI.

Methods

The I/R AKI rat model was established, and HE staining of kidney tissue and serum creatinine (SCr) and blood urea nitrogen (BUN) detection were performed. The miRNAs were sequenced by high throughput in rat kidney tissue samples. Differentially expressed miRNAs (DEmiRs) between the I/R group and I/R + GLN group were screened, and enrichment analysis for target genes of DEmiRs was performed. Meanwhile, human HK-2 cells were cultured, and an I/R model was established to verify the expression of DEmiRs.

Results

Compared with the I/R group, the SCr and BUN levels at each time point were lower in the I/R + GLN group. Vacuolar degeneration of renal tubules in the I/R + GLN group was significantly reduced. In the 104 DEmiRs, we selected miR-132-5p, miR-205, and miR-615 as key miRNAs. KEGG analysis showed that the Notch signaling pathway, PI3K-Akt signaling pathway, and cGMP signaling pathway were mainly related to the GLN against I/R. qRT-PCR verified the downregulation of miR-205 in the I/R group, compared to the sham and I/R + GLN group. The I/R model was established with HK-2 cells, and the expression of miR-132-5p and miR-205 was decreased.

Conclusion

GLN reduced I/R-induced AKI. There were significant differences between miRNAs expression in I/R after GLN treatment. The process of GLN against I/R-induced AKI may be related to the Notch and PI3K-Akt signaling pathway.

Beneficial effect of trimetazidine on folic acid-induced acute kidney injury in mice: Role of HIF-1α/HO-1

Acute kidney injury (AKI) is a complex syndrome associated with a decrease in renal function and a significant impact on patient outcomes. Injection of folic acid (FA) in mice is used for studying the pathogenesis of AKI. This study investigated the impact of trimetazidine (a metabolic modulator-antianginal drug; TMZ), against FA-induced AKI. AKI was induced by FA (250 mg/kg, ip) in mice. Two doses of TMZ were administered orally for 10 days. Administration of TMZ at a high dose (20 mg/kg) exhibited significant decreases in the renal somatic index (RSI), serum levels of lactate dehydrogenase (LDH), creatinine (Cr), blood urea nitrogen (1), and proteins level in urine. Moreover, TMZ significantly increased creatinine clearance (CCr), serum albumin, urine creatinine, and urine urea levels. This improvement in markers of kidney damage was associated with marked renal antioxidant effects (↓NO and ↓lipid peroxidation, normalized reduced glutathione (GSH) level and superoxide dismutase (SOD) activity, and increased HIF-1α/HO-1 level). Furthermore, TMZ significantly decreased FA-induced expression of MPO and inflammatory cytokine IL-18, TNF-α, and NF-κB p65 subunit. Renal apoptosis, along with apoptotic markers, were enhanced by FA injection and suppressed by TMZ administration (↓Caspase-3, ↓Bax, and ↑Bcl2 expression). Finally, TMZ amended FA-induced histopathological changes in kidneys. By mitigating functional alteration, oxidative stress, and preventing the development of inflammatory and apoptosis signals, TMZ provides dose-dependent defense against FA-induced AKI mainly via stimulation of hypoxia-inducible factor-1 alpha (HIF-1α)/heme oxygenase-1 (HO-1) pathway.

Integrated gut microbiota and fecal metabolomics reveal the renoprotective effect of Rehmanniae Radix Preparata and Corni Fructus on adenine-induced CKD rats

Rehmanniae Radix Preparata (RR) and Corni Fructus (CF), well-known traditional Chinese medicines (TCMs), were generally used together in the clinical practices to treat chronic kidney disease (CKD) with synergistic effects for thousands of years, but their combination mechanism remains largely unknown so far. Recent evidences have implicated intestinal flora as potential targets for the therapy of CKD. In this study, the CKD rat model was induced by adenine. The levels of proteinuria, serum creatine (SCr), blood urea nitrogen (BUN) and creatinine clearance (Ccr) were used to assess the cooperation effect of RR and CF. Furthermore, high-throughput 16S ribosomal RNA (rRNA) gene sequencing combined with fecal metabonomics based on UPLC-Q-TOF-MS/MS were applied to explore the variations of intestinal flora and their metabolic profiles. 16S rRNA gene sequencing data indicated that CKD rats treated with RR, CF and RC showed the differences in the composition of gut microbiota. The abundance of beneficial bacteria including Ruminococcaceae UCG-014, Ruminococcus 1, Prevotellaceae_NK3B31_group, Lachnospiraceae NK4A136 group and Lachnospiraceae UCG-001 were elevated in various degrees, while the opportunistic pathogen such as Desulfovibrio was markedly decreased after the treatment. Moreover, fecal metabolite profiles revealed 15 different metabolites associated with CKD. These metabolites were mainly involved in the related metabolic pathways such as amino acid metabolism, bile acids metabolism and glycerophospholipid metabolism. The results implied that gut flora and their metabolites might play a vital role in the progress of CKD, which provided a potential target for the development of novel drugs for the therapy of CKD.

Nicorandil mitigates folic acid-induced nephrotoxicity in mice: Role of iNOS and eNOS

Folic acid (FA)-induced acute kidney injury (AKI) is a commonly used model in experimental animals for studying renal injury. This study aimed to investigate the probable protecting impact of nicorandil against FA-induced renal dysfunction. A mouse model was executed by a single injection of FA (250 mg/kg). Nicorandil was orally administrated in two doses (50 and 100 mg/kg) for 10 days. Nicorandil repressed the progression of FA-induced AKI as evidenced by the improvement of histopathological alterations and the substantial decrease of serum levels of creatinine, urea, blood urea nitrogen, malondialdehyde (MDA), and urinary protein levels. Moreover, nicorandil resulted in a profound reduction in oxidative stress as manifested by decreased MDA and increased reduced glutathione and superoxide dismutase in renal tissue. Notably, nicorandil suppressed FA-induced inflammation; it reduced renal levels of nuclear factor-κB, tumor necrosis factor-α, and interleukin-6. Furthermore, nicorandil decreased renal levels of nitric oxide, inducible nitric oxide synthase, and increased endothelial nitric oxide synthase. Lastly, nicorandil efficiently decreased expression of the proapoptotic protein (Bax) and caspase 3. Nicorandil confers dose-dependent protection against FA-induced AKI by alleviating oxidative stress, inflammation besides modulating nitric oxide synthase and reducing apoptosis.

Nitrolipids in kidney physiology and disease

The kidneys are vital organs responsible for maintaining body fluid homeostasis within proper physiologic ranges. Kidney disease is an epidemic clinical problem causing significant morbidity and mortality, and current treatments are limited to renin-angiotensin system blockade or renal replacement therapy for the majority of affected individuals. There is a critical, unmet need for novel pharmacological agents to improve the outcome of patients with kidney disease. Nitro-oleic acid (NO2-OA) is an endogenously generated electrophilic compound with the capacity to modify thiols in proteins, altering their function. The most important targets appear to be the Keap1/Nrf2 and NF-κB pathways, which have widespread effects on antioxidant, detoxifying, and inflammatory responses in cells and tissues. Through these and potentially additional protective actions, NO2-OA may be capable of preserving or enhancing kidney function in acute and chronic kidney diseases.

Chitosan oligosaccharide affects antioxidant defense capacity and placental amino acids transport of sows

BACKGROUND

Chitosan oligosaccharide (COS) is widely consumed as a functional food due to its multiple health effects, but few studies about COS supplement on placental antioxidant and nutrition transport capacity were reported. Taken pregnant sow as a model, we aimed to investigate the effects of dietary COS supplementation during late gestation on placental amino acids transport and antioxidant defense capacity of sows. From day (d) 85 of gestation to parturition, sixteen pregnant sows were divided into a control group (basal diet without COS supplementation) and a COS group (30 mg COS/kg basal diet). Plasma sample of sow was collected on d 110 of gestation, and placenta tissue was obtained during parturition. Then plasma antioxidant enzyme's activities, the relative level of oxidant stress related genes, amino acids transport related genes and mTOR pathway molecules in placenta were determined.

RESULTS

Results showed that maternal dietary supplementation with COS increased (P < 0.05) plasma total SOD, caused a downtrend in plasma MDA (0.05 < P < 0.10) on d 110 of gestation. Interestingly, the mRNA expression of some antioxidant genes in the placenta were increased (P < 0.05) and pro-inflammatory cytokines were reduced (P < 0.05) by COS supplement, whereas no significant difference was observed in the activities of placental total SOD and CAT between two groups. Additionally, further study demonstrated that COS feeding stimulated mTOR signaling pathway, increased amino acids transporters expression in placenta.

CONCLUSIONS

These observations suggested that COS supplement in sow's diet during late gestation enhanced antioxidant defense capacity of sows, promoted placental amino acids transport, which may contribute to the health of sows and development of fetus during gestation.

Renoprotective approaches and strategies in acute kidney injury

Acute kidney injury (AKI) is a major renal disease associated with high mortality rate and increasing prevalence. Decades of research have suggested numerous chemical and biological agents with beneficial effects in AKI. In addition, cell therapy and molecular targeting have been explored for reducing kidney tissue damage and promoting kidney repair or recovery from AKI. Mechanistically, these approaches may mitigate oxidative stress, inflammation, cell death, and mitochondrial and other organellar damage, or activate cytoprotective mechanisms such as autophagy and pro-survival factors. However, none of these findings has been successfully translated into clinical treatment of AKI. In this review, we analyze these findings and propose experimental strategies for the identification of renoprotective agents or methods with clinical potential. Moreover, we propose the consideration of combination therapy by targeting multiple targets in AKI.

Modulation of cellular stress response via the erythropoietin/CD131 heteroreceptor complex in mouse mesenchymal-derived cells

Tissue-protective properties of erythropoietin (EPO) have let to the discovery of an alternative EPO signaling via an EPO-R/CD131 receptor complex which can now be specifically targeted through pharmaceutically designed short sequence peptides such as ARA290. However, little is still known about specific functions of alternative EPO signaling in defined cell populations. In this study, we investigated effects of signaling through EPO-R/CD131 complex on cellular stress responses and pro-inflammatory activation in different mesenchymal-derived phenotypes. We show that anti-apoptotic, anti-inflammatory effects of ARA290 and EPO coincide with the externalization of CD131 receptor component as an immediate response to cellular stress. In addition, alternative EPO signaling strongly modulated transcriptional, translational, or metabolic responses after stressor removal. Specifically, we saw that ARA290 was able to overcome a TNFα-mediated inhibition of transcription factor activation related to cell stress responses, most notably of serum response factor (SRF), heat shock transcription factor protein 1 (HSF1), and activator protein 1 (AP1). We conclude that alternative EPO signaling acts as a modulator of pro-inflammatory signaling pathways and likely plays a role in restoring tissue homeostasis. Key message: Erythropoietin (EPO) triggers an alternative pathway via heteroreceptor EPO/CD131. ARA290 peptide specifically binds EPO/CD131 but not the canonical EPO/EPO receptor. Oxidative stress and inflammation promote cell surface expression of CD131. ARA290 prevents tumor necrosis factor-mediated inhibition of stress-related genes. Alternative EPO signaling modulates inflammation and promotes tissue homeostasis.