Mahmood S. Mozaffari

Why is taurine cytoprotective

The concept that taurine exhibits cytoprotective activity was introduced in 1981. Although several studies at the time had supported the notion that taurine was capable of modulating Ca2+movement, most of those studies focused on the transporter affected by taurine. It was only after taurine was found to prevent Ca2+-induced cellular necrosis that its cytoprotective activity was recognized1. Since that date, numerous reports have documented that high levels of extracellular taurine render cells resistant to an array of damaging stimuli, including ischemia-reperfusion, hyperglycemia, reactive oxygen species, heat shock, toxic xenobiotics, cellular excitotoxicity and osmotic derangements. The ability of taurine to counteract these toxic stimuli has been attributed to four actions of taurine: (1) osmoregulation, (2) anti-oxidant/membrane stabilizing activity, (3) conjugation and (4) regulation of [Ca2+]i. Indeed, osmotic stress, oxidative stress and Ca2+overload are major causes of cellular necrosis and apoptosis. Nonetheless, cell death is a complex phenomenon, involving interactions between these and several other factors. For example, oxidative stress can damage membranes leading to changes in [Ca21. Conversely, high [Ca2+]ican cause enhanced free radical generation by the mitochondria. It is also known that osmotic stress affects the activity of ion transporters that regulate [Ca2+]i. Despite these and other interactions, it is clear that taurine affects each of the four factors individually. Thus, the aim of this review is to discuss the importance of each factor in the cytoprotective actions of taurine.

Role of oxidative stress in diabetes-mediated vascular dysfunction: unifying hypothesis of diabetes revisited.

Oxidative stress is recognized as a key participant in the development of diabetic complications in the vasculature. One of the seminal studies advancing the role of oxidative stress in vascular endothelial cells proposed that oxidative stress-mediated diversion of glycolytic intermediates into pathological pathways was a key underlying element in the development of diabetic complications. It is widely recognized that flux through glycolysis slows during diabetes. However, several bottlenecks develop in the glycolytic pathway, including glucose transport, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase and pyruvate kinase. Of these limiting steps in glycolysis, glyceraldehyde-3-phosphate dehydrogenase is most sensitive to oxidative stress, leading to the hypothesis that glyceraldehyde-3-phosphate inactivation by ribosylation underlies the diversion of glycolytic intermediates into pathological pathways. However, recent studies question the mechanism underlying the effect of reactive oxygen species on key enzymes of the glycolytic pathway. The present review critiques the major premises of the hypothesis and concludes that further study of the role of oxidative stress in the development of diabetes-mediated vasculature dysfunction is warranted.

Medicine in the early twenty-first century: paradigm and anticipation - EPMA position paper 2016.

Background Challenges of “standardisation” and “individualisation” have always been characteristic for medical services. In terms of individualisation, the best possible individual care is the ethical imperative of medicine, and it is a good right of any patient to receive it. However, in terms of standardisation, all the available treatments are based on guideline recommendations derived from large multicentre trials with many thousands of patients involved. In the most optimal way, the standardisation and individualisation should go hand-in-hand, in order to identify the right patient treating him/her with the right medication and the right dose at the right time point! Further, in paradigm and anticipation, there is a big discrepancy between “disease care” and “health care” which dramatically impacts ethical and economical aspects of medical services. Several approaches have been suggested in ancient and modern medicine to conduct medical services in a possibly optimal way. What is the difference amongst all of them and how big is the potential beyond corresponding approach to satisfy the needs of the individual, the patient, professional groups involved and society at large? On behalf of the “European Association for Predictive, Preventive and Personalised Medicine,” the dedicated EPMA working group provides a deep analysis in the issue followed by the expert recommendations considering the multifaceted aspects of both “disease care” and “health care” practices including ethics and economy, life quality of individuals and patients, interests of professional groups involved, benefits of subpopulations, health care system(s) and society as a whole.

Tyrosine kinase inhibitor, genistein, reduces renal inflammation and injury in streptozotocin-induced diabetic mice.

Tyrosine kinase inhibition is known to reduce diabetes-induced end-organ damage but the mechanisms remain elusive. We hypothesized that inhibition of tyrosine kinase reduces renal inflammation and injury in streptozotocin-induced diabetes. Male C57BL/6 mice were given daily injections of streptozotocin (45 mg/kg/day, i.p. for 5 days); control animals received the vehicle (citrate buffer). Thereafter, streptozotocin-treated mice were treated with genistein (10 mg/kg, i.p three times a week for 10 weeks, n=8-10/group) or the vehicle (5% DMSO). The streptozotocin-treated mice displayed significant elevation in blood glucose level and decrease in plasma insulin level compared to their vehicle-treated controls. Treatment with genistein reduced blood glucose level (~15%; p<0.05) without a significant effect on plasma insulin level; however, blood glucose remained significantly higher than the control group. The development of diabetes was associated with significant increases in total protein, albumin, nephrin and collagen excretions compared to their controls. In addition, the diabetic mice displayed increased urinary MCP-1 excretion in association with increased renal ICAM-1 expression and apoptotic cells. Furthermore, renal gp91 expression levels and urinary Thio-Barbituric Acid Reactive Substances (TBARs) excretion, indices of oxidative stress, were also elevated in diabetic mice. These changes were associated with increased renal phospho-tyrosine expression and renal phospho-ERK/ERK ratio. Importantly, treatment with genistein reduced all these parameters towards control values. Collectively, the results suggest that the reno-protective effect of genistein likely relates to reduced renal inflammation, oxidative stress and apoptosis in diabetic mice.

Endoplasmic reticulum stress response and inflammatory cytokines in type 2 diabetic nephropathy: role of indoleamine 2,3-dioxygenase and programmed death-1.

We tested the hypotheses that a) type 2 diabetes increases endoplasmic reticulum (ER) stress response, production of pro-inflammatory cytokines and kidney cell death and b) downregulations of renal indoleamine 2,3-dioxygenase (IDO) and programmed death-1 (PD-1) contribute to exacerbated inflammation and tissue injury. The growth arrest and DNA damage-inducible protein 153 (GADD153; a marker of ER stress response), inflammatory cytokines and cell death were determined in the context of assessment of IDO and PD-1 in an animal model of type 2 diabetic nephropathy (i.e., db/db mouse). Peripheral blood of 4-month-old db/db mice manifested significantly greater percents of interleukin (IL)-17 and IL-23 positive cells in association with greater percents of cells that were positive for PD-1 or GADD153. Compared to kidneys of db/m controls, renal cells prepared from kidneys of db/db mice displayed a) increased percent of cells that were positive for IL-17, IL-23, PD-1 and GADD153, b) decreased JC-1 aggregates but increased JC-1 monomers suggestive of disruption of mitochondrial membrane potential and c) increased apoptotic and necrotic cell death. Immunohistochemical analyses also revealed increased staining of renal tissue of db/db mice for IL-17, IL23, GADD153, Annexin V, caspase 3, PD-1 and IDO compared to db/m kidneys; these changes were generally more prominent in the glomeruli. In conclusion, type 2 diabetes upregulates systemic and local ER stress response and pro-inflammatory mechanisms thereby contributing to renal injury. However, the accompanying upregulations of PD-1 and IDO likely reflect activation of compensatory mechanisms to curtail inflammation and cell injury.

Effects of chronic taurine treatment on reactivity of the rat aorta

Summary. The effects of chronic taurine treatment on the reactivity of the aorta form male Wistar-Kyoto rats were investigated. Contractile responses to norepinephrine (NE) and potassium chloride (KCl) were attenuated in aortic rings from taurine-treated rats as compared to controls both in the absence and presence of endothelium. However, the degree of attenuation was greater in endothelium-intact tissues contracted with NE. Acetylcholine (Ach)-induced relaxation responses were augmented in endothelium-intact vessels from rats supplemented with taurine compared to the responses observed in control preparations. Relaxation responses of the aortae from control and taurine-treated rats to sodium nitroprusside (SNP) were not different from each other. Our results suggest that taurine treatment attenuates vascular contractility nonspecifically and this effect is partly mediated via the endothelium.

Effect of β-alanine treatment on mitochondrial taurine level and 5-taurinomethyluridine content

BackgroundThe β-amino acid, taurine, is a nutritional requirement in some species. In these species, the depletion of intracellular stores of taurine leads to the development of severe organ dysfunction. The basis underlying these defects is poorly understood, although there is some suggestion that oxidative stress may contribute to the abnormalities. Recent studies indicate that taurine is required for normal mitochondrial protein synthesis and normal electron transport chain activity; it is known that defects in these events can lead to severe mitochondrial oxidative stress. The present study examines the effect of taurine deficiency on the first step of mitochondrial protein synthesis regulation by taurine, namely, the formation of taurinomethyluridine containing tRNA.MethodsIsolated rat cardiomyocytes were rendered taurine deficient by incubation with medium containing the taurine transport inhibitor, β-alanine. The time course of cellular and mitochondrial taurine depletion was measured. The primer extension method was employed to evaluate the effect of β-alanine treatment on taurinomethyluridine content of tRNALeu. The protein levels of ND6 were also determined by Western blot analysis.Resultsβ-alanine caused a time-dependent decrease in cellular taurine content, which were reduced in half after 48 hrs of incubation. The amount of taurine in the mitochondria was considerably less than that in the cytosol and was unaffected by β-alanine treatment. Approximately 70% of the tRNALeu in the untreated cell lacked taurinomethyluridine and these levels were unchanged following β-alanine treatment. Protein content of ND6, however, was significantly reduced after 48 hours incubation with β-alanine.ConclusionsThe taurine levels of the cytosol and the mitochondria are not directly coupled. The β-alanine-mediated reduction in taurine levels is too small to affect taurinomethyluridine levels. Nonetheless, it interferes with mitochondrial protein synthesis, as exemplified by a decrease in ND6 protein content. Thus, β-alanine does not cause alterations in mitochondrial protein synthesis through the lowering of taurine levels.

Effect of glyburide on myocardial metabolism and function.

Exposure of perfused rat hearts to the second-generation sulfonylurea glyburide led to a dramatic increase in glycolytic flux and lactate production. Maximal response in the absence of insulin occurred at a concentration of 2.8 microM and resulted in a 45 percent increase in the glucose utilization rate. When insulin was included in the buffer, glyburide response was significantly increased. Similarly, glyburide potentiated the metabolic effects of insulin. Since glyburide did not promote glycogenolysis, the increase in glycolysis was caused solely by the rise in glucose utilization. The classic cross-over plot for glycolytic intermediates and transport showed that glyburide stimulates glycolysis by activating the rate-limiting enzyme phosphofructokinase and promoting glucose transport. Glycolytic intermediate data also suggested that the sulfonylurea promotes oxidation of pyruvate via the citric acid cycle. Since the drug does not alter oxygen consumption, the contribution of glucose to overall adenosine triphosphate production rises while that of fatty acids falls. These metabolic changes aid the heart in resisting an ischemic insult.

Mitochondrial complex I and NAD(P)H oxidase are major sources of exacerbated oxidative stress in pressure-overloaded ischemic-reperfused hearts.

We tested the hypothesis that pressure overload exacerbates oxidative stress associated with augmented mitochondrial permeability transition (MPT) pore opening and cell death in ischemic-reperfused hearts. Pressure overload decreased the level of reduced glutathione but increased nitrotyrosine and 8-hydroxydeoxyguanosine levels in ischemic-reperfused hearts. The activity of catalase, but not superoxide dismutase (SOD), was lower in ischemic-reperfused hearts perfused at higher pressure. Mitochondria from ischemic-reperfused hearts subjected to higher perfusion pressure displayed significantly greater [3H]-2-deoxyglucose-6-P entrapment suggestive of greater MPT pore opening and consistent with greater necrosis and apoptosis. Tempol (SOD mimetic) reduced infarct size in both groups but it remained greater in the higher pressure group. By contrast, uric acid (peroxynitrite scavenger) markedly reduced infarct size at higher pressure, effectively eliminating the differential between the two groups. Inhibition of xanthine oxidase, with allopurinol, reduced infarct size but did not eliminate the differential between the two groups. However, amobarbital (inhibitor of mitochondrial complex I) or apocynin [inhibitor of NAD(P)H oxidase] reduced infarct size at both pressures and also abrogated the differential between the two groups. Consistent with the effect of apocynin, pressure-overloaded hearts displayed significantly higher NAD(P)H oxidase activity. Furthermore, pressure-overloaded hearts displayed increased nitric oxide synthase activity which, along with increased propensity to superoxide generation, may underlie uric acid-induced cardioprotection. In conclusion, increased oxidative and nitrosative stress, coupled with lack of augmented SOD and catalase activities, contributes importantly to the exacerbating impact of pressure overload on MPT pore opening and cell death in ischemic-reperfused hearts.

DNA damage and expression of checkpoint genes p21WAF1/CIP1 and 14-3-3 σ in taurine-deficient cardiomyocytes

Abstract Objective : Taurine depletion is associated with development of cardiomyopathy. Further, oxidative stress is advanced as a critical factor mediating the effect of taurine deficiency on target organs. However, the molecular mechanism(s) linking taurine deficiency with the development of cardiomyopathy remains elusive. Since transition between apoptotic degeneration and cell proliferation in stress conditions is regulated at cell cycle checkpoints, we determined the expression of two such genes, namely p21 WAF1/CIP1 and 14-3-3 σ as well as p53 that are responsible for oxidative stress and DNA damage. We also carried out quantitative determination of DNA damage. Methods : Cardiomyocytes from β-alanine-induced taurine-depleted (TD) rats were used for this investigation. Single- and double-stranded DNA damage was quantified using comet assay analysis. Western blot and two-dimensional polyacrylamide gel electrophoresis with immunoblotting analysis were applied for protein analysis. Results : Comet assay analysis indicated that the extent of double-stranded DNA damage was greater in TD than in control cardiomyocytes. Whereas only traces of both p53 and p21 WAF1/CIP1 and no detectable expression of 14-3-3 σ were found in cardiomyocytes of control animals, the TD cardiomyocytes expressed all three genes. Conclusions : DNA damage and the consequent up-regulation of checkpoint proteins observed in TD cardiomyocytes indicate the involvement of cell cycle control mechanisms in the effect of taurine deficiency on cardiomyocytes. Single- and double-stranded DNA damage and the consequent arrest of cell proliferation in both G 1 and G 2 phases of the cell cycle induced by checkpoint proteins may trigger the cardiomyopathy that is associated with taurine deficiency.