Taurine reduces renal ischemia/reperfusion injury in the rat

Sulfur-Containing Amino Acids, Hydrogen Sulfide, and Sulfur Compounds on Kidney Health and Disease

Hydrogen sulfide (H₂S) plays a decisive role in kidney health and disease. H₂S can ben synthesized via enzymatic and non-enzymatic pathways, as well as gut microbial origins. Kidney disease can originate in early life induced by various maternal insults throughout the process, namely renal programming. Sulfur-containing amino acids and sulfate are essential in normal pregnancy and fetal development. Dysregulated H₂S signaling behind renal programming is linked to deficient nitric oxide, oxidative stress, the aberrant renin-angiotensin-aldosterone system, and gut microbiota dysbiosis. In animal models of renal programming, treatment with sulfur-containing amino acids, N-acetylcysteine, H₂S donors, and organosulfur compounds during gestation and lactation could improve offspring's renal outcomes. In this review, we summarize current knowledge regarding sulfide/sulfate implicated in pregnancy and kidney development, current evidence supporting the interactions between H₂S signaling and underlying mechanisms of renal programming, and recent advances in the beneficial actions of sulfide-related interventions on the prevention of kidney disease. Modifying H₂S signaling is the novel therapeutic and preventive approach to reduce the global burden of kidney disease; however, more work is required to translate this into clinical practice.

Versatile Triad Alliance: Bile Acid, Taurine and Microbiota

Taurine is the most abundant free amino acid in the body, and is mainly derived from the diet, but can also be produced endogenously from cysteine. It plays multiple essential roles in the body, including development, energy production, osmoregulation, prevention of oxidative stress, and inflammation. Taurine is also crucial as a molecule used to conjugate bile acids (BAs). In the gastrointestinal tract, BAs deconjugation by enteric bacteria results in high levels of unconjugated BAs and free taurine. Depending on conjugation status and other bacterial modifications, BAs constitute a pool of related but highly diverse molecules, each with different properties concerning solubility and toxicity, capacity to activate or inhibit receptors of BAs, and direct and indirect impact on microbiota and the host, whereas free taurine has a largely protective impact on the host, serves as a source of energy for microbiota, regulates bacterial colonization and defends from pathogens. Several remarkable examples of the interaction between taurine and gut microbiota have recently been described. This review will introduce the necessary background information and lay out the latest discoveries in the interaction of the co-reliant triad of BAs, taurine, and microbiota.

Metabolomics Analysis of the Renal Cortex in Rats With Acute Kidney Injury Induced by Sepsis

Sepsis-induced acute kidney injury (AKI) can increase the mortality of critically ill patients and the incidence of chronic kidney disease in critically ill survivors. The main goal was to investigate the possible link between metabolic changes and sepsis-induced AKI development. The experimental animal model of sepsis-induced AKI was established by intraperitoneal injection of lipopolysaccharide in rats. Non-targeted metabolic screening of the renal cortex in the control and sepsis-induced AKI groups was carried out based on gas chromatography coupled with quadrupole time-of-flight mass spectrometry (GC-TOFMS) technology. The data between the two groups were analyzed by combining univariate and multivariate statistical methods, and the metabolites associated with AKI in rats with sepsis were screened. By examining the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, altered metabolic pathways associated with acute renal injury in sepsis were identified. The cross validated scores plot of orthogonal partial least squares discriminant analysis (OPLS-DA) showed a distinct separation trend between the model and control groups in the profile of renal cortex metabolites, indicating a significant change in endogenous metabolites in the rat renal cortex. Further analysis and screening showed that 26 different metabolites were identified in the renal cortex between the two groups, mainly involving taurine and hypotaurine metabolism, pantothenic acid and CoA biosynthesis, phenylalanine metabolism, and other metabolic pathways. The metabolic disorders of taurine, pantothenic acid, and phenylalanine in the renal cortex are related to the development of acute renal injury in sepsis. Correcting these metabolic disorders is expected to prevent and treat sepsis-induced AKI.

Protective effects of taurine against renal ischemia/reperfusion injury in rats by inhibition of gelatinases, MMP-2 and MMP-9, and p38 mitogen-activated protein kinase signaling

Dysregulated expression of matrix metalloproteinases (MMPs) is closely associated with the pathogenesis of renal ischemia/reperfusion injury (I/R). The production of excessive reactive oxygen species (ROS) causes tissue damage. Increased ROS production causes activation of p38 mitogen-activated protein kinase (MAPK) signaling, which participates in gene regulation of MMPs, especially MMP-2 and MMP-9 (gelatinases). Taurine (2-aminoethanesulfonic acid) in mammalian cells functions in bile acid conjugation, maintenance of calcium homeostasis, osmoregulation, membrane stabilization, and antioxidation, antiinflammatory, and antiapoptotic action. We investigated the effects of taurine and the possible role of p38 MAPK signaling on regulation of MMP-2 and MMP-9 in a renal I/R injury model in rats. Rats were divided into three groups: sham, I/R, and I/R + taurine treated. After a right nephrectomy, I/R was induced by clamping the left renal pedicle for 1 h followed by 6 h reperfusion. Taurine was administered 45 min prior to induction of ischemia. Renal function was assessed by serum creatinine and blood urea nitrogen (BUN) levels. Tubule injury and structural changes were evaluated by light microscopy. Malondialdehyde (MDA) levels were analyzed by high performance liquid chromatography (HPLC). Superoxide dismutase (SOD) activity levels were measured using a colorimetric kit. mRNA expression of MMP-2 and MMP-9 was determined by real-time polymerase chain reaction. MMP-2 and MMP-9 activities were measured using a fluorimetric kit. Phosphorylated p38 (p-p38) and total p38 MAPK protein expressions were evaluated by western blot. Taurine pretreatment significantly attenuated renal dysfunction and histologic damage, such as renal tubule dilation and loss of brush borders. The pretreatment also decreased the MDA level and attenuated the reduction of SOD activity in the kidney during I/R. Taurine pretreatment also decreased significantly both MMP-2 and MMP-9 mRNA expression and MMP-9 activity induced by I/R. In addition, the activity of p38 MAPK signaling was down-regulated significantly by taurine administration. Inhibition of MMP-2 and MMP-9 expression and MMP-9 activity caused by taurine may be associated with suppression of p38 MAPK activation during I/R induced renal injury in rats. Therefore, taurine administration may prove to be a strategy for attenuating renal I/R injury.

Nuclear Magnetic Resonance Metabolomic Profiling of Mouse Kidney, Urine and Serum Following Renal Ischemia/Reperfusion Injury

Background

Ischemia/reperfusion (I/R) is the most common cause of acute kidney injury (AKI). Its pathophysiology remains unclear. Metabolomics is dedicated to identify metabolites involved in (patho)physiological changes of integrated living systems. Here, we performed ¹H-Nuclear Magnetic Resonance metabolomics using urine, serum and kidney samples from a mouse model of renal I/R.

Methods

Renal 30-min ischemia was induced in 12-week-old C57BL/6J male mice by bilaterally clamping vascular pedicles, and was followed by 6, 24 or 48-hour reperfusion (n = 12/group). Sham-operated mice were used as controls. Statistical discriminant analyses, i.e. principal component analysis and orthogonal projections to latent structures (OPLS-DA), were performed on urine, serum and kidney lysates at each time-point. Multivariate receiver operating characteristic (ROC) curves were drawn, and sensitivity and specificity were calculated from ROC confusion matrix (with averaged class probabilities across 100 cross-validations).

Results

Urine OPLS-DA analysis showed a net separation between I/R and sham groups, with significant variations in levels of taurine, di- and tri-methylamine, creatine and lactate. Such changes were observed as early as 6 hours post reperfusion. Major metabolome modifications occurred at 24h post reperfusion. At this time-point, correlation coefficients between urine spectra and conventional AKI biomarkers, i.e. serum creatinine and urea levels, reached 0.94 and 0.95, respectively. The area under ROC curve at 6h, 24h and 48h post surgery were 0.73, 0.98 and 0.97, respectively. Similar discriminations were found in kidney samples, with changes in levels of lactate, fatty acids, choline and taurine. By contrast, serum OPLS-DA analysis could not discriminate sham-operated from I/R-exposed animals.

Conclusions

Our study demonstrates that renal I/R in mouse causes early and sustained metabolomic changes in urine and kidney composition. The most implicated pathways at 6h and 24h post reperfusion include gluconeogenesis, taurine and hypotaurine metabolism, whereas protein biosynthesis, glycolysis, and galactose and arginine metabolism are key at 48h post reperfusion.

Role of Cystathionine Gamma-Lyase in Immediate Renal Impairment and Inflammatory Response in Acute Ischemic Kidney Injury

Hydrogen sulfide (H₂S) is known to act protectively during renal ischemia/reperfusion injury (IRI). However, the role of the endogenous H₂S in acute kidney injury (AKI) is largely unclear. Here, we analyzed the role of cystathionine gamma-lyase (CTH) in acute renal IRI using CTH-deficient (Cth^−/−) mice whose renal H₂S levels were approximately 50% of control (wild-type) mice. Although levels of serum creatinine and renal expression of AKI marker proteins were equivalent between Cth^−/− and control mice, histological analysis revealed that IRI caused less renal tubular damage in Cth^−/− mice. Flow cytometric analysis revealed that renal population of infiltrated granulocytes/macrophages was equivalent in these mice. However, renal expression levels of certain inflammatory cytokines/adhesion molecules believed to play a role in IRI were found to be lower after IRI only in Cth^−/− mice. Our results indicate that the systemic CTH loss does not deteriorate but rather ameliorates the immediate AKI outcome probably due to reduced inflammatory responses in the kidney. The renal expression of CTH and other H₂S-producing enzymes was markedly suppressed after IRI, which could be an integrated adaptive response for renal cell protection.

Comparison of Aerobic Preservation by Venous Systemic Oxygen Persufflation or Oxygenated Machine Perfusion of Warm-Ischemia-Damaged Porcine Kidneys

Background/Aim: The global shortage of donor organs for transplantation has necessitated the expansion of the organ pool through increased use of organs from less ideal donors. Venous systemic oxygen persufflation (VSOP) and oxygenated machine perfusion (OMP) have previously demonstrated beneficial results compared to cold storage (CS) in the preservation of warm-ischemia-damaged kidney grafts. The aim of this study was to compare the efficacy of VSOP and OMP for the preservation of warm-ischemia-damaged porcine kidneys using the recently introduced Ecosol preservation solution compared to CS using Ecosol or histidine-tryptophan-ketoglutarate solution (HTK). Materials and Methods: Kidneys from German Landrace pigs (n = 5/group) were retrieved and washed out with either Ecosol or HTK after 45 min of clamping of the renal pedicle. As controls, kidneys without warm ischemia, cold stored for 24 h in HTK, were employed. Following 24 h of preservation by VSOP, OMP, CS-Ecosol, or CS-HTK, renal function and damage were assessed during 1 h using the isolated perfused porcine kidney model. Results: During reperfusion, urine production was significantly higher in the VSOP and OMP groups than in the CS-HTK group; however, only VSOP could demonstrate lower urine protein concentrations and fractional excretion of sodium, which did not differ from the non-warm-ischemia-damaged control group. VSOP, CS-Ecosol, and controls showed better maintenance of the acid-base balance than CS-HTK. Reduced lipid peroxidation, as reflected in postreperfusion tissue thiobarbituric acid-reactive substance levels, was observed in the VSOP group compared to the OMP group, and the VSOP and CS-Ecosol groups had concentrations similar to the controls. The ratio of reduced to oxidized glutathione was higher in the VSOP, OMP, and CS-Ecosol groups than in the CS-HTK group and controls, with a higher ratio in the VSOP than in the OMP group. Conclusion: VSOP was associated with mitigation of oxidative stress in comparison to OMP and CS. Preservation of warm-ischemia-damaged porcine kidneys by VSOP was improved compared to OMP and CS, and was comparable to preservation of non-warm-ischemia-damaged cold-stored kidneys.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Taurine and the renal system

Taurine participates in a number of different physiologic and biologic processes in the kidney, often reflected by urinary excretion patterns. The kidney is key to aspects of taurine body pool size and homeostasis. This review will examine the renal-taurine interactions relative to ion reabsorption; renal blood flow and renal vascular endothelial function; antioxidant properties, especially in the glomerulus; and the role of taurine in ischemia and reperfusion injury. In addition, taurine plays a role in the renal cell cycle and apoptosis, and functions as an osmolyte during the stress response. The role of the kidney in adaptation to variations in dietary taurine intake and the regulation of taurine body pool size are described. Finally, the protective function of taurine against several kidney diseases is reviewed.

Taurine prevents myocardial ischemia/reperfusion-induced oxidative stress and apoptosis in prolonged hypothermic rat heart preservation

Taurine (2-aminoethanesulfonic acid) is a potent antioxidant and inhibits cell apoptosis in ischemic reperfusion injury. In this study we evaluated whether addition of taurine to St. Thomas' cardioplegic solution enhances its myocardial protective effects in prolonged hypothermic heart preservation in rats. Hearts isolated from male Sprague-Dawley rats were mounted on a Langendorff apparatus to estimate baseline cardiac function, then arrested and stored in St. Thomas' cardioplegic solution, with taurine (10 mM; taurine group, n = 8) or without taurine (control group, n = 8), for 6 h at 4 degrees C. After storage, the hearts were reperfused and heart rate (HR), coronary flow (CF), left ventricular developed pressure (LVP), and positive maximum left ventricular developing pressure (max LV dp/dt) were measured. The LV tissue was examined immunohistochemically for determining DNA oxidative stress and cell apoptosis. Compared with control groups, recovery of LVP (P < 0.001), max LV dp/dt (P < 0.001), and coronary flow (P < 0.001) were significantly enhanced, whereas glutamic oxaloacetic transaminase (P < 0.01), lactate dehydrogenase (P < 0.05), creatine phosphate kinase (P < 0.01), 8-hydroxy-2'-deoxyguanosine index (P < 0.01), caspase-3 mRNA expression (P < 0.05), and percentage of TUNEL-positive cardiomyocytes (P < 0.05) were reduced in the taurine group. Addition of taurine to St. Thomas' cardioplegic solution improved cardiac function recovery for prolonged hypothermic rat heart preservation by suppressing DNA oxidative stress and cell apoptosis.

Accelerated NaCl-induced hypertension in taurine-deficient rat: Role of renal function

Taurine modulates blood pressure and renal function. As the kidney plays a pivotal role in long-term control of arterial pressure, we tested the hypothesis that taurine-deficient rats display maladaptive renal and blood pressure responses to uninephrectomy. Control and taurine-deficient (i.e., beta-alanine-treated) rats with either one or two remaining kidneys were fed diets containing basal or high (8%) NaCl diet. Urine osmolality was greater in the taurine-deficient than controls fed a normal NaCl diet; proteinuria and blood pressure were unaffected by uninephrectomy. Following 6 weeks on an 8% NaCl diet, the uninephrectomized (UNX) animals developed significant hypertension, which was more severe in the taurine-deficient group; baroreflex function was unaffected. However, the UNX taurine-deficient rats displayed impaired ability to dispose of an acute isotonic saline volume load before a switchover to a high NaCl diet. Nonetheless, a more protracted exposure (i.e., 14 weeks) to dietary NaCl excess eliminated the blood pressure differential between the two groups; at this stage, renal excretory responses to an acute saline volume load or to atrial natriuretic peptide were similar in the two groups. Nonetheless, hypertensive taurine-deficient rats displayed greater proteinuria, although both groups excreted proteins of similar molecular weights ( approximately 15-66 kDa). Further, taurine-deficient kidney specimens displayed periarterial mononuclear cell infiltrates with strong immunoreactivity to the histiocyte marker CD68, suggestive of increased phagocytic activity. In conclusion, taurine deficiency modulates renal adaptation to combined uninephrectomy and dietary NaCl excess, resulting in an accelerated development of hypertension.

Taurine inhibits ischemia/reperfusion-induced compartment syndrome in rabbits

AIM

To investigate effects of taurine on ischemia/reperfusion (I/R)-induced compartment syndrome in rabbit hind limbs.

METHODS

Rabbits underwent femoral artery occlusion after ligation of branches from terminal aorta to femoral artery. After a 7-h ischemia, reperfusion was established with the use of heparinized polyethylene shunts. Rabbits received taurine (1g/kg) or normal saline (control) by iv infusion 10 min before shunt placement. During reperfusion, anterior compartment pressure (ACP) was monitored continuously in the left lower extremity. Gastrocnemius muscle triphenyltetrazolium chloride (TTC) level, taurine content and myeloperoxidase activity were assayed. Oxidative stress was induced in the in vitro gastrocnemius muscle slices by free radical generating systems (FRGS), and the malondialdehyde content was measured in presence or absence of taurine.

RESULTS

After 7 h of ischemia, none of the parameters that we measured were different from those before ischemia, except that TTC reduction decreased by 80%. In the control group, after 2 h of reperfusion, ACP increased 4.5-fold, and gastrocnemius muscle taurine content was reduced by 33%. In taurine-treated animals, at 2h reperfusion, the mean arterial blood pressure and heart rate were increased, by 6% and 10%. ACP decreased by 39%, muscle edema decreased by 16%, TTC reduction increased by 150%, and lactate dehydrogenase decreased by 36% compared to control group. Plasma and muscle taurine content increased by 70% and 88%, respectively. In the taurine-treated group, at 2 h reperfusion, plasma malondialdehyde and conjugated diene content were decreased by 38% and 23%, respectively, and muscle malondialdehyde and conjugated diene content decreased by 22% and 30%, respectively compared to the control group. At 2 h reperfusion, myeloperoxidase activity was increased 3.5-fold in control animals. In the in vitro study, taurine decreased malondialdehyde content in muscle slices incubated with hypochlorous acid in a dose-dependent manner, but there was no change when incubated with hydrogen peroxide and xanthine oxidase.

CONCLUSION

Treatment with taurine inhibited I/R-induced compartment syndrome by at least in part attenuating oxidative stress injury induced by I/R, suggesting clinical application of taurine might be a new strategy for the prevention and treatment of compartment syndrome.