Hypoxic cellular deterioration and its prevention by the amino acid taurine in a transplantation model with renal tubular cells (LLC-PK1)

Ameliorative effect of taurine against diabetes and renal-associated disorders (Review)

To develop novel therapeutic methods for both diabetic and renal disorders, scientists had initially focused on elucidating the molecular mechanisms of taurine in established cell lines and mouse models. Although a large amount of data have been revealed, taurine has been confirmed to be the next step of novel promising therapeutic interventions against diabetic disorders. Taurine appears to ameliorate diabetes 1-related complications in various organs through its antioxidant, anti-inflammatory and anti-hormonal actions. In type 2 diabetes, taurine has been positively implicated in glucose homeostasis, exerting potent hypoglycemic, anti-obesity, hypotensive and hypolipidemic effects. Of particular interest is that taurine provides protection against renal dysfunction, including hypertension and proteinuria, specific glomerular and tubular disorders, acute and chronic renal conditions, and diabetic nephropathy. The ameliorative effects of taurine against renal disorders are based on its osmoregulatory properties, its association with signaling pathways and its association with the renin-angiotensin-aldosterone system (RAAS). Further clinical studies are required to ensure the importance of research findings.

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.

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.

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.

Developmental changes in organic osmolytes in prenatal and postnatal rat tissues

At high osmotic pressures, mammalian kidney medulla, heart, lens, and brain utilize organic osmolytes to regulate cell volume. However the types and proportions of these solutes vary among tissues in patterns and for non-osmotic roles not fully elucidated. To clarify these, we analyzed osmolyte-type solute contents in rat tissues at 7 and 2 days prenatal and at 0, 7, 14, 21 (weaning), 35 (juvenile) and 77 (adult) days postnatal. Placentas were dominated by betaine, taurine, and creatine, which decreased between the prenatal times. Fetuses were dominated by glutamate and taurine, which increased between the times. In cerebrum, hindbrain and diencephalon, taurine dominated at early stages, but dropped after postnatal day 7, while myo-inositol, glutamine, creatine and glutamate increased after birth, with the latter two dominating in adults. In olfactory bulb, taurine content declined gradually with age and was equal to glutamate in adults. In all brain regions, glycerophosphorylcholine (GPC) reached a peak in juveniles. In postnatal renal medulla, urea, sodium, GPC, betaine, and taurine increased sharply at day 21. Thereafter, most increased, but taurine decreased. In heart, taurine dominated, and increased with age along with creatine and glutamine, while glutamate decreased after postnatal day 7. In lens, taurine dominated and declined in adults. These patterns are discussed in light of hypotheses on non-osmotic and pathological roles of these solutes.

The mechanisms of taurine mediated protection against cell damage induced by hypoxia and reoxygenation

Taurine administered during hypoxia markedly reduced the cell damage due to O2 deficiency and reoxygenation. Different mechanisms are responsible for the improved survival of the renal cell cultures. Taurine markedly reduces the osmoregulatory deterioration during hypoxia and reoxygenation. Calcium homeostasis was markedly improved. Ca2+ efflux during hypoxia as well as Ca2+ overload during reoxygenation was significantly reduced by the amino acid. The effect of taurine was partly comparable to the effect induced by Ca2+ channel blockers. One of the effects mainly responsible for cellular protection seems to be the taurine-induced acceleration of cellular growth processes in spite of hypoxia and reoxygenation. The spectrum of cytoprotective effects of taurine predisposes this substance to be a physiological protective agent responsible for cellular homeostasis or enantiostasis.

Protective effect of taurine on hypoxia and reoxygenation-induced damage of human colon cells (HT 29)

In this experimental model, taurine administered during hypoxia markedly reduced the cell damage due to O2 deficiency, and the beneficial effect outlasted the period of reoxygenation. The mechanisms for the improved survival rates are postulated to be a reduced osmoregulatory disturbance of cellular integrity, improved Ca2+ homeostasis and induction of accelerated cellular growth processes. In our simplified cell culture model the UW solution seems to be the most appropriate solution for the cold (hypoxic) preservation of human colon cells. We conclude, that within this experimental model and under these experimental conditions, taurine supplementation of the conventionally used preservation solutions improved the solutions markedly. Considering our previous studies, taurine seems to be a potent endogenous protective agent against cellular deterioration due to hypoxia and reoxygenation.