Citrate shows protective effects on cardiovascular and renal function in ischemia-induced acute kidney injury

Effects of Extracellular Calcium Concentration on Hepatic Ischemia-Reperfusion Injury in a Rat Model

OBJECTIVES

Hypocalcemia is frequently identified during liver transplant. However, supplementation of extracellular calcium could induce increased intracellular calcium concentration, as a potential factor for injury to the liver graft. We evaluated the effects of regulating extracellular calcium concentrations on hepatic ischemia-reperfusion injury.

MATERIALS AND METHODS

We randomly divided 24 Sprague-Dawley rats into 3 groups: group C received normal saline (n = 8), group L received citrate to induce hypocalcemia (n = 8), and group L-Co received citrate followed by calcium gluconate to ameliorate hypocalcemia (n = 8). Liver enzyme levels and extracellular calcium were measured before surgery, 1 hour after ischemia, and 2 hours after reperfusion. The primary outcome was liver enzyme levels measured 2 hours after reperfusion. In addition, we evaluated intracellular calcium levels, lactate dehydrogenase activity, and histopathological results in liver tissue.

RESULTS

Three groups demonstrated significant differences in extracellular calcium concentrations, but intracellular calcium concentrations in liver tissue were not significantly different. Group L showed significantly lower mean arterial pressure than other groups at 1 hour after ischemia (93.6 ± 20.8 vs 69.4 ± 14.2 vs 86.6 ± 10.4 mmHg; P = .02, for group C vs L vs L-Co, respectively). At 2 hours after reperfusion, group L showed significantly higher liver enzymes than other groups (aspartate aminotransferase 443.0 ± 353.2 vs 952.3 ± 94.8 vs 502.4 ± 327.3 U/L, P = .01; and alanine aminotransferase 407.9 ± 406.5 vs 860.6 ± 210.9 vs 333.9 ± 304.2 U/L, P = .02; for group C vs L vs L-Co, respectively). However, no significant difference was shown in lactate dehydrogenase and histological liver injury grade.

CONCLUSIONS

Administering calcium to rats with hypocalcemia did not increase intracellular calcium accumulation but instead resulted in less hepatic injury compared with rats with low extracellular calcium concentrations in this rat model study.

Utilizing pathophysiological concepts of ischemia-reperfusion injury to design renoprotective strategies and therapeutic interventions for normothermic ex vivo kidney perfusion

Normothermic machine perfusion (NMP) has emerged as a promising tool for the preservation, viability assessment, and repair of deceased-donor kidneys prior to transplantation. These kidneys inevitably experience a period of ischemia during donation, which leads to ischemia-reperfusion injury when NMP is subsequently commenced. Ischemia-reperfusion injury has a major impact on the renal vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis. With an increased understanding of the underlying pathophysiological mechanisms, renoprotective strategies and therapeutic interventions can be devised to minimize additional injury during normothermic reperfusion, ensure the safe implementation of NMP, and improve kidney quality. This review discusses the pathophysiological alterations in the vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis of deceased-donor kidneys and delineates renoprotective strategies and therapeutic interventions to mitigate renal injury and improve kidney quality during NMP.

A systematic review of metabolomic findings in adult and pediatric renal disease

Chronic kidney disease (CKD) affects over 0.5 billion people worldwide across their lifetimes. Despite a growingly ageing world population, an increase in all-age prevalence of kidney disease persists. Adult-onset forms of kidney disease often result from lifestyle-modifiable metabolic illnesses such as type 2 diabetes. Pediatric and adolescent forms of renal disease are primarily caused by morphological abnormalities of the kidney, as well as immunological, infectious and inherited metabolic disorders. Alterations in energy metabolism are observed in CKD of varying causes, albeit the molecular mechanisms underlying pathology are unclear. A systematic indexing of metabolites identified in plasma and urine of patients with kidney disease alongside disease enrichment analysis uncovered inborn errors of metabolism as a framework that links features of adult and pediatric kidney disease. The relationship of genetics and metabolism in kidney disease could be classified into three distinct landscapes: (i) Normal genotypes that develop renal damage because of lifestyle and / or comorbidities; (ii) Heterozygous genetic variants and polymorphisms that result in unique metabotypes that may predispose to the development of kidney disease via synergistic heterozygosity, and (iii) Homozygous genetic variants that cause renal impairment by perturbing metabolism, as found in children with monogenic inborn errors of metabolism. Interest in the identification of early biomarkers of onset and progression of CKD has grown steadily in the last years, though it has not translated into clinical routine yet. This systematic review indexes findings of differential concentration of metabolites and energy pathway dysregulation in kidney disease and appraises their potential use as biomarkers.

The citrate transporter SLC13A5 as a therapeutic target for kidney disease: evidence from Mendelian randomization to inform drug development

BACKGROUND

Solute carrier family 13 member 5 (SLC13A5) is a Na+-coupled citrate co-transporter that mediates entry of extracellular citrate into the cytosol. SLC13A5 inhibition has been proposed as a target for reducing progression of kidney disease. The aim of this study was to leverage the Mendelian randomization paradigm to gain insight into the effects of SLC13A5 inhibition in humans, towards prioritizing and informing clinical development efforts.

METHODS

The primary Mendelian randomization analyses investigated the effect of SLC13A5 inhibition on measures of kidney function, including creatinine and cystatin C-based measures of estimated glomerular filtration rate (creatinine-eGFR and cystatin C-eGFR), blood urea nitrogen (BUN), urine albumin-creatinine ratio (uACR), and risk of chronic kidney disease and microalbuminuria. Secondary analyses included a paired plasma and urine metabolome-wide association study, investigation of secondary traits related to SLC13A5 biology, a phenome-wide association study (PheWAS), and a proteome-wide association study. All analyses were compared to the effect of genetically predicted plasma citrate levels using variants selected from across the genome, and statistical sensitivity analyses robust to the inclusion of pleiotropic variants were also performed. Data were obtained from large-scale genetic consortia and biobanks, with sample sizes ranging from 5023 to 1,320,016 individuals.

RESULTS

We found evidence of associations between genetically proxied SLC13A5 inhibition and higher creatinine-eGFR (p = 0.002), cystatin C-eGFR (p = 0.005), and lower BUN (p = 3 × 10-4). Statistical sensitivity analyses robust to the inclusion of pleiotropic variants suggested that these effects may be a consequence of higher plasma citrate levels. There was no strong evidence of associations of genetically proxied SLC13A5 inhibition with uACR or risk of CKD or microalbuminuria. Secondary analyses identified evidence of associations with higher plasma calcium levels (p = 6 × 10-13) and lower fasting glucose (p = 0.02). PheWAS did not identify any safety concerns.

CONCLUSIONS

This Mendelian randomization analysis provides human-centric insight to guide clinical development of an SLC13A5 inhibitor. We identify plasma calcium and citrate as biologically plausible biomarkers of target engagement, and plasma citrate as a potential biomarker of mechanism of action. Our human genetic evidence corroborates evidence from various animal models to support effects of SLC13A5 inhibition on improving kidney function.

Machine learning approach for assessment of arsenic levels using physicochemical properties of water, soil, elevation, and land cover

Groundwater is an essential resource; around 2.5 billion people depend on it for drinking and irrigation. Groundwater arsenic contamination is due to natural and anthropogenic sources. The World Health Organization (WHO) has proposed a guideline value for arsenic concentration in groundwater samples of 10[Formula: see text]g/L. Continuous consumption of arsenic-contaminated water causes various carcinogenic and non-carcinogenic health risks. In this paper, we introduce a geospatial-based machine learning method for classifying arsenic concentration levels as high (1) or low (0) using physicochemical properties of water, soil type, land use land cover, digital elevation, subsoil sand, silt, clay, and organic content of the region. The groundwater samples were collected from multiple sites along the river Ganga's banks of Varanasi district in Uttar Pradesh, India. The dataset was subjected to descriptive statistics and spatial analysis for all parameters. This study assesses the various contributing parameters responsible for the occurrence of arsenic in the study area based on the Pearson correlation feature selection method. The performance of machine learning models, i.e., Extreme Gradient Boosting (XGBoost), Gradient Boosting Machine (GBM), Decision Tree, Random Forest, Naïve Bayes, and Deep Neural Network (DNN), were compared to validate the parameters responsible for the dissolution of arsenic in groundwater aquifers. Among all the models, the DNN algorithm outclasses other classifiers as it has a high accuracy of 92.30%, a sensitivity of 100%, and a specificity of 75%. Policymakers can utilize the accuracy of the DNN model to approximate individuals prone to arsenic poisoning and formulate mitigation strategies based on spatial maps.

The effect of citrate in cardiovascular system and clot circuit in critically ill patients requiring continuous renal replacement therapy

We aimed to evaluate the impact of citrate on hemodynamic responses and secondary outcomes, including the filter life span, metabolic complications, and levels of inflammatory cytokines, in critically ill patients who required CRRT compared with those who underwent the heparin-free method. This prospective, multicenter, open-label randomized trial compared regional citrate anticoagulation (RCA) with a heparin-free protocol in severe acute kidney injury (AKI) patients who received continuous venovenous hemodiafiltration (CVVHDF) in the postdilution mode. We measured hemodynamic changes using the FloTrac Sensor/EV1000™ Clinical Platform at certain time points after starting CRRT (0, 6, 12, 24, 48, and 72 h.). The levels of inflammatory cytokines (IL-1β, IL-6, IL-8, IL-10 and TNF-ɑ) were measured on days 1 and 3. Forty-one patients were recruited and randomized into the heparin (n = 20) and citrate groups (n = 21). The cardiac performances were not significantly different between the 2 groups at any time point. The inflammatory cytokines declined similarly in both treatment arms. The maximum filter survival time was insignificantly longer in the RCA group than in the heparin-free group (44.64 ± 26.56 h. vs p = 0.693 in citrate and heparin free group). No serious side effects were observed for either treatment arm, even in the group of liver dysfunction patients. RCA did not affect hemodynamic changes during CRRT. Inflammatory cytokines decreased similarly in both treatment arms.The filter life span was longer in the citrate group. RCA is a valid alternative to traditional anticoagulation and results in stable hemodynamic parameters.

Spot Urinary Citrate Normograms in Children

Citrate in the urine inhibits nephrolithiasis, and oral citrate solutions are used to prevent stones forming. The present study aimed to estimate the normograms of the urinary levels of citrate, creatinine, and their ratio in spot urine samples collected from 237 healthy children, aged from 1 month to 14 years. The findings showed the mean, standard deviation, median, and 5th and 95th percentiles of the values and compared them among age groups and between the sexes by using analysis of variance and independent t-tests. Our findings indicate that the ratio of spot urinary citrate to creatinine was higher for children younger than 18 months of age, possibly related to the consumption of dairy protein as their main meal. The 5th percentiles (lower cut off) for spot urinary citrate-to-creatinine ratio, were 915 mg/g for children aged under 18 months, 109 mg/g and 126 mg/g for older boys and girls.

Involvement of Tricarboxylic Acid Cycle Metabolites in Kidney Diseases

Mitochondria are complex organelles that orchestrate several functions in the cell. The primary function recognized is energy production; however, other functions involve the communication with the rest of the cell through reactive oxygen species (ROS), calcium influx, mitochondrial DNA (mtDNA), adenosine triphosphate (ATP) levels, cytochrome c release, and also through tricarboxylic acid (TCA) metabolites. Kidney function highly depends on mitochondria; hence mitochondrial dysfunction is associated with kidney diseases. In addition to oxidative phosphorylation impairment, other mitochondrial abnormalities have been described in kidney diseases, such as induction of mitophagy, intrinsic pathway of apoptosis, and releasing molecules to communicate to the rest of the cell. The TCA cycle is a metabolic pathway whose primary function is to generate electrons to feed the electron transport system (ETS) to drives energy production. However, TCA cycle metabolites can also release from mitochondria or produced in the cytosol to exert different functions and modify cell behavior. Here we review the involvement of some of the functions of TCA metabolites in kidney diseases.

miR‑212 promotes renal interstitial fibrosis by inhibiting hypoxia‑inducible factor 1‑α inhibitor

Renal interstitial fibrosis is one of the common causes, and a major pathological basis for the development of various types of chronic progressive renal to end-stage renal diseases. Therefore, it is important to clarify the underlying mechanisms of disease progression in order to develop effective strategies for the treatment and prevention of these pathologies. The aim of the present study was to investigate the association between microRNA (miR)-212 expression and the development of renal interstitial fibrosis, as well as analyzing the role of miR-212 in the disease. The expression of miR-212 was significantly increased in the peripheral blood of patients with renal interstitial fibrosis and in the kidney tissues of unilateral ureteral obstruction (UUO) mice. Angiotensin (Ang) II, TGF-β1 and hypoxia were found to increase the expression of miR-212 and α smooth muscle actin (α-SMA) in NRK49F cells. Ang II stimulation induced the expression of miR-212 and α-SMA in NRK49F cells, while transfection of miR-212 mimics further upregulated the expression of α-SMA. miR-212 was also revealed to target hypoxia-inducible factor 1α inhibitor (HIF1AN) and to upregulate the expression of hypoxia-inducible factor 1α, α-SMA, connective tissue growth factor, collagen α-1(I) chain and collagen α-1(III) chain, whereas HIF1AN overexpression reversed the regulatory effects of miR-212. In UUO mice, miR-212 overexpression promoted the progression of renal interstitial fibrosis, whereas inhibiting miR-212 resulted in the opposite effect. These results indicated that high expression of miR-212 was closely associated with the occurrence of renal interstitial fibrosis, and that miR-212 may promote its development by targeting HIF1AN.

Proximal Tubular Oxidative Metabolism in Acute Kidney Injury and the Transition to CKD

The proximal tubule relies on oxidative mitochondrial metabolism to meet its energy needs and has limited capacity for glycolysis, which makes it uniquely susceptible to damage during AKI, especially after ischemia and anoxia. Under these conditions, mitochondrial ATP production is initially decreased by several mechanisms, including fatty acid-induced uncoupling and inhibition of respiration related to changes in the shape and volume of mitochondria. Glycolysis is initially insufficient as a source of ATP to protect the cells and mitochondrial function, but supplementation of tricarboxylic acid cycle intermediates augments anaerobic ATP production, and improves recovery of mitochondrial oxidative metabolism. Incomplete recovery is characterized by defects of respiratory enzymes and lipid metabolism. During the transition to CKD, tubular cells atrophy but maintain high expression of glycolytic enzymes, and there is decreased fatty acid oxidation. These metabolic changes may be amenable to a number of therapeutic interventions.

Mineral Content of the Pulp and Peel of Various Citrus Fruit Cultivars

The aim of the study was to compare the mineral content between the peel and the pulp of citrus fruits and to determine which citrus fruit, among orange (Citrus sinensis), pomelo (Citrus maxima), mandarin (Citrus reticulata Blanco), lemon (Citrus limon), key lime (Citrus aurantifolia), and red, yellow, or green grapefruit (Citrus paradisi), is the richest in minerals. The research material consisted of fresh citrus fruits belonging to the genus Citrus L in the family Rutaceae. The fruits were purchased at a supermarket at one time. To prepare laboratory samples, each fruit was cut in half, and one half was homogenized, treating the sample as a whole (peel + flesh), while the other half was peeled and the pulp (F) and peel (P) were homogenized separately. To determine the content of minerals (Na⁺, K⁺, Ca⁺², Mg⁺², Fe⁺², Zn⁺², Cu⁺², Mn⁺², and Se⁺²), the samples were mineralized and analyzed using an Analytik Jena PlasmaQuant PQ 9000 inductively coupled plasma optical emission spectrometer. The content of macro- and micronutrients in the peel of most of the fruits far exceeded their quantity in the pulp. Oranges and pomelos are the fruits richest in iron and copper, so they could be recommended in cases such as hemoglobin production disorders resulting from a deficiency of these elements. Oranges can additionally enrich the body with potassium, phosphorus, and manganese, while lime can be a source of calcium, zinc, sodium, and especially potassium. It should also be noted that all citrus fruits are a very valuable source of potassium, which is needed to ensure the water and electrolyte balance.

Protective Effect of Citric Acid Against Hepatic Ischemia Reperfusion Injury in Sprague-Dawley Rats

OBJECTIVE

Hepatic ischemia reperfusion (I/R) injury is regarded as a serious concern in clinical practice. Citric acid reduces oxidative stress and inflammation during hypoxia and reoxygenation. Our objective was to investigate the protective effect of citric acid against hepatic I/R injury in rats.

METHODS

We fed Sprague-Dawley rats either citric acid (100 mg/kg/d) or saline. One week later, ischemia was induced by clamping the rats' common hepatic artery and portal vein for 30 minutes. The rats were randomly divided into 3 major groups that were treated as follows: 1. the sham operated group; 2. the I/R group; and 3. the I/R-citric acid group.

RESULTS

Compared to the sham group, the I/R group had higher expression of aspartate aminotransferase and alanine aminotransferase and lower expression of catalase, superoxide dismutase, glutathione peroxidase, antioxidant, nitric oxide, and albumin. Compared to the I/R group, the I/R-citric acid group had higher expression of catalase, superoxide dismutase, antioxidants, and nitric oxide, and lower expression of aspartate aminotransferase and alanine aminotransferase.

CONCLUSIONS

These results suggest that citric acid therapy has significant therapeutic potential in ischemic liver injury.

TGF-β1 modifies histone acetylation and acetyl-coenzyme A metabolism in renal myofibroblasts

Histone acetylation is an important modulator of gene expression in fibrosis. This study examined the effect of the pre-eminent fibrogenic cytokine TGF-b1 on histone 3 (H3) acetylation and its regulatory kinetics in renal myofibroblasts. Fibroblasts propagated from rat kidneys after ureteric obstruction were treated with recombinant TGF-b1 or vehicle for 48 hours. TGF-b1 -induced myofibroblast activation was accompanied by a net decrease in total H3 acetylation, although changes in individual marks were variable. This was paralleled by a generalised reduction in histone acetyltransferases (HAT), and divergent changes in histone deacetylase (HDAC) enzymes at both transcript and protein levels. Globally this was manifest in a reduction in total HAT activity and increase in HDAC activity. TGF-b1 induced a shift in cellular metabolism from oxidative respiration to aerobic glycolysis resulting in reduced acetyl-CoA. The reduction in total H3 acetylation could be rescued by providing exogenous citrate or alternative sources of acetyl-CoA, without ameliorating changes in HAT/HDAC activity. In conclusion, TGF-b1 produces a metabolic reprogramming in renal fibroblasts, with less H3 acetylation through reduced acetylation, increased deacetylation and changes in carbon availability. Our results suggest that acetyl-CoA availability predominates over HAT and HDAC activity as a key determinant of H3 acetylation in response to TGF-b1.

In silico model of the dilutional effects of conventional component therapy versus whole blood in the management of massively bleeding adult trauma patients

BACKGROUND

There are multiple approaches to the blood product and fluid resuscitation of a bleeding trauma patient. An in silico model of different trauma resuscitation strategies was constructed to predict their effects on the volumes of the different body fluid compartments and on several important hemostatic factors.

STUDY DESIGN AND METHODS

This multicompartment dynamic deterministic model comprised four interconnected modules (hemostatic, resuscitation, body fluid compartment, and dilutional coagulopathy). The model was divided into five resuscitation phases with simulations using six different resuscitation strategies: whole blood (WB) only, conventional component therapy (CCT) only or 10 units of WB followed by CCT, with either 1 L of crystalloid or 1.5 units of WB or red blood cells in the prehospital phase.

RESULTS

At the end of the simulations using 1 L of crystalloid fluids in the prehospital resuscitation phase, the use of WB led to a 1.4 g/dL higher hemoglobin concentration, 32 mg/dL higher fibrinogen concentration, and 0.9 L lower total extracellular fluid volume compared to CCT. Prehospital blood product transfusion in place of crystalloid resulted in higher hemoglobin and fibrinogen concentrations and a lower international normalized ratio throughout the resuscitation regardless of the resuscitation strategy used. Throughout both the prehospital crystalloid and prehospital blood product transfusion simulations, the hemoglobin and fibrinogen concentrations and platelet counts were higher, and the international normalized ratio was lower, when WB was used compared to CCT.

CONCLUSIONS

This model predicted improved hemostatic factor levels and a smaller total extracellular fluid volume volume when WB was transfused instead of CCT to bleeding trauma patients.

Resveratrol Does Not Protect from Ischemia-Induced Acute Kidney Injury in an in Vivo Rat Model

BACKGROUND/AIMS

The natural polyphenol resveratrol (RSV) has been shown to ameliorate ischemia/reperfusion (I/R)-induced damage. Therefore, a rat model of I/R-induced AKI equipped with intensive monitoring was utilized to examine direct renal protection by RSV in vivo.

METHODS

AKI was induced by bilateral renal clamping (45 min) followed by reperfusion (3 h). Solvent-free RSV was continuously infused intravenously (0.056 and 0.28 mg/kg) in a total volume of 7 ml/kg/h starting from 30 min before renal clamping. At a mean arterial blood pressure below 70 mmHg for more than 5 min, bolus injections of 0.5 ml 0.9% NaCl solution were administered repetitively (max. 5 ml/kg/h).

RESULTS

No differences could be found between normoxic control groups with/without RSV. Bilateral renal clamping and subsequent reperfusion caused a progressive rise in creatinine, cystatin C, and CK, a decrease in cellular ATP content and diuresis. Infusion of RSV increased sirtuin 1 expression after ischemia/reperfusion and was associated with decreased blood pressure during ischemia and early reperfusion accompanied by an increased requirement of bolus injections as well as with increased expression of TNFα.

CONCLUSION

RSV did not exert protective effects on I/R-induced AKI in the present short-term in vivo rat model. The lack of protection is potentially connected to aggravation of blood pressure instability.