Inhibition of lipid peroxidation, protein glycation and elevation of membrane ion pump activity by taurine in RBC exposed to high glucose

Enhanced protection for interfacial lipid ozonolysis by sulfur-containing amino acids

Sulfur-containing amino acids have been proposed as drugs for lipid oxidation associated with diseases for a long time, but the molecular-level mechanism on the effectiveness of sulfur-containing amino acids against lipid oxidation remains elusive. In this work, with the interfacial sensitivity mass spectrometry method, oxidation of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG), a widely used model lipid, was significantly inhibited on hung droplet surface in presence of sulfur-containing amino acids, such as cysteine (Cys) and methionine (Met). Both the Cys and Met showed a self-sacrificing protection. The amino acids with -S-R tails (R referring to methyl or t-butyl group) showed more effective against POPG oxidation than those with -SH tails, and this process was not related to the conformations of amino acids. The low effectiveness of Cys during the interfacial chemistry was proved to arise from the formation of disulfide bond. This study extends the current understanding of chemistry of sulfur-containing amino acids and provides insights to aid the sulfur-containing amino acids against cell oxidation.

Oxidative stress, inflammation and hormesis: The role of dietary and lifestyle modifications on aging

Oxidative stress (OS) is primarily caused by the formation of free radicals and reactive oxygen species; it is considered as one of the prominent factors in slowing down and degrading cellular machinery of an individual, and it eventually leads to aging and age-related diseases by its continuous higher state. The relation between molecular damage and OS should be particularized to understand the beginning of destruction at the cellular levels, extending outwards to affect tissues, organs, and ultimately to the organism. Several OS biomarkers, which are established at the biomolecular level, are useful in investigating the disease susceptibility during aging. Slowing down the aging process is a matter of reducing the rate of oxidative damage to the cellular machinery over time. The breakdown of homeostasis, the mild overcompensation, the reestablishment of homeostasis, and the adaptive nature of the process are the essential features of hormesis, which incorporates several factors, including calorie restriction, nutrition and lifestyle modifications that play an important role in reducing the OS. In the current review, along with the concept and theories of aging (with emphasis on free radical theory), various manifestations of OS with special attention on mitochondrial dysfunction and age-related diseases have been discussed. To alleviate the OS, hormetic approaches including caloric restriction, exercise, and nutrition have also been discussed.

The effects of taurine supplementation on diabetes mellitus in humans: A systematic review and meta-analysis

•

The first meta-analysis to comprehensively evaluate the effects of taurine supplementation on diabetic patients.

•

Statistical significance in HbA1C, Fasting Blood Sugar, HOMA-IR after oral supplemental of taurine by diabetic patients than that of placebo.

•

Taurine is expected to be a new option for the management of diabetes.

Objective

The ameliorative effect of taurine on diabetes has received extensive attention in recent years. Despite promising data from animal studies, the efficacy of taurine supplementation in human studies has been inconsistent. We thus did a meta-analysis of randomized controlled trials to assess the effect of taurine supplement on glycemic indices, serum lipids, blood pressure, body composition in patients with diabetes.

Methods

We systematically searched PubMed, Embase, Cochrane, Web of Science, FDA.gov, and ClinicalTrials.gov for randomized controlled trials (published from inception to January 15, 2022; no language restrictions) about the effect of taurine supplement on diabetes. Values of Standardized Mean Differences (SMD) were determined for continuous outcomes.

Results

Of 2206 identified studies, 5 randomized controlled trials were eligible and were included in our analysis (N = 209 participants). Compared with the control group, taurine could significantly reduce HbA1c (SMD −0.41[95% CI: −0.74, −0.09], p = 0.01), Fasting Blood Sugar (SMD − 1.28[95% CI: −2.42, −0.14], p = 0.03) and HOMA-IR (SMD − 0.64[95% CI: −1.22, −0.06], p = 0.03). In addition, taurine also reduced Insulin (SMD −0.48 [95% CI: −0.99, 0.03], p = 0.06) and TG (SMD −0.26 [95% CI: −0.55, 0.02], p = 0.07), but did not reach statistical significance.

Conclusions

Taurine supplementation is beneficial in reducing glycemic indices, such as HbA1c, Fasting Blood Sugar, HOMA-IR in diabetic patients, but has no significant effect on serum lipids, blood pressure and body composition in diabetic patients. Taurine emerges as a new option for the management of patients with diabetes. Further studies are needed to understand the potential effect of taurine in diabetic patients.

Dysregulated Erythroid Mg2+ Efflux in Type 2 Diabetes

Hyperglycemia is associated with decreased Mg²⁺ content in red blood cells (RBC), but mechanisms remain unclear. We characterized the regulation of Mg²⁺ efflux by glucose in ex vivo human RBC. We observed that hemoglobin A_1C (HbA_1C) values correlated with Na⁺-dependent Mg²⁺ efflux (Na⁺/Mg²⁺ exchange) and inversely correlated with cellular Mg content. Treatment of cells with 50 mM D-glucose, but not with sorbitol, lowered total cellular Mg (2.2 ± 0.1 to 2.0 ± 0.1 mM, p < 0.01) and enhanced Na⁺/Mg²⁺ exchange activity [0.60 ± 0.09 to 1.12 ± 0.09 mmol/10¹³ cell × h (flux units, FU), p < 0.05]. In contrast, incubation with selective Src family kinase inhibitors PP2 or SU6656 reduced glucose-stimulated exchange activation (p < 0.01). Na⁺/Mg²⁺ exchange activity was also higher in RBC from individuals with type 2 diabetes (T2D, 1.19 ± 0.13 FU) than from non-diabetic individuals (0.58 ± 0.05 FU, p < 0.01). Increased Na⁺/Mg²⁺ exchange activity in RBC from T2D subjects was associated with lower intracellular Mg content. Similarly increased exchange activity was evident in RBC from the diabetic db/db mouse model as compared to its non-diabetic control (p < 0.03). Extracellular exposure of intact RBC from T2D subjects to recombinant peptidyl-N-glycosidase F (PNGase F) reduced Na⁺/Mg²⁺ exchange activity from 0.98 ± 0.14 to 0.59 ± 0.13 FU (p < 0.05) and increased baseline intracellular Mg content (1.8 ± 0.1 mM) to normal values (2.1 ± 0.1 mM, p < 0.05). These data suggest that the reduced RBC Mg content of T2D RBC reflects enhanced RBC Na⁺/Mg²⁺ exchange subject to regulation by Src family kinases and by the N-glycosylation state of one or more membrane proteins. The data extend our understanding of dysregulated RBC Mg²⁺ homeostasis in T2D.

Aedes aegypti Shows Increased Susceptibility to Zika Virus via Both In Vitro and In Vivo Models of Type II Diabetes

Chronic conditions like type II diabetes (T2DM) have long been known to exacerbate many infectious diseases. For many arboviruses, including Zika virus (ZIKV), severe outcomes, morbidity and mortality usually only occur in patients with such pre-existing conditions. However, the effects of T2DM and other pre-existing conditions on human blood (e.g., hypo/hyperinsulinemia, hyperglycemia and hyperlipidemia) that may impact infectivity of arboviruses for vectors is largely unexplored. We investigated whether the susceptibility of Aedes aegypti mosquitoes was affected when the mosquitoes fed on “diabetic” bloodmeals, such as bloodmeals composed of artificially glycosylated erythrocytes or those from viremic, diabetic mice (LEPRDB/DB). Increasing glycosylation of erythrocytes from hemoglobin A1c (HgbA1c) values of 5.5–5.9 to 6.2 increased the infection rate of a Galveston, Texas strain of Ae. aegypti to ZIKV strain PRVABC59 at a bloodmeal titer of 4.14 log10 FFU/mL from 0.0 to 40.9 and 42.9%, respectively. ZIKV was present in the blood of viremic LEPRDB/DB mice at similar levels as isogenic control C57BL/6J mice (3.3 log10 FFU/mL and 3.6 log10 FFU/mL, respectively. When mice sustained a higher ZIKV viremia of 4.6 log10 FFU/mL, LEPRDB/DB mice infected 36.3% of mosquitoes while control C57BL/6J mice with a viremia of 4.2 log10 FFU/mL infected only 4.1%. Additionally, when highly susceptible Ae. aegypti Rockefeller mosquitoes fed on homozygous LEPRDB/DB, heterozygous LEPRWT/DB, and control C57BL/6J mice with viremias of ≈ 4 log10 FFU/mL, 54%, 15%, and 33% were infected, respectively. In total, these data suggest that the prevalence of T2DM in a population may have a significant impact on ZIKV transmission and indicates the need for further investigation of the impacts of pre-existing metabolic conditions on arbovirus transmission.

Erythrocytes: Central Actors in Multiple Scenes of Atherosclerosis

The development and progression of atherosclerosis (ATH) involves lipid accumulation, oxidative stress and both vascular and blood cell dysfunction. Erythrocytes, the main circulating cells in the body, exert determinant roles in the gas transport between tissues. Erythrocytes have long been considered as simple bystanders in cardiovascular diseases, including ATH. This review highlights recent knowledge concerning the role of erythrocytes being more than just passive gas carriers, as potent contributors to atherosclerotic plaque progression. Erythrocyte physiology and ATH pathology is first described. Then, a specific chapter delineates the numerous links between erythrocytes and atherogenesis. In particular, we discuss the impact of extravasated erythrocytes in plaque iron homeostasis with potential pathological consequences. Hyperglycaemia is recognised as a significant aggravating contributor to the development of ATH. Then, a special focus is made on glycoxidative modifications of erythrocytes and their role in ATH. This chapter includes recent data proposing glycoxidised erythrocytes as putative contributors to enhanced atherothrombosis in diabetic patients.

Phytometabolomic analysis of boiled rhizome of Nymphaea nouchali (Burm. f.) using UPLC-Q-TOF-MSE, LC-QqQ-MS & GC-MS and evaluation of antihyperglycemic and antioxidant activities

Phytometabolomic analysis of Nymphaea nouchali (Burm. F.) boiled rhizome was carried out utilizing UPLC-Q-TOF-MS^E, LC-QqQ-MS and GC-MS techniques and evaluated for antihyperglycemic and antioxidative stress potentials. Metabolomic analysis revealed presence of multiple antidiabetic and antioxidant compounds. Boiled rhizome powder exhibited potent antihyperglycemic activity against sugar-induced postprandial hyperglycemia in rats plausibly due to the presence of intestinal α-glucosidase inhibitory and augmenting cellular glucose uptake activities. It also prevented hyperglycemia-induced hemoglobin and insulin glycation. Rhizome displayed potent reducing power, effectively scavenged various reactive oxygen species. It displayed antioxidative stress potential in assuaging H₂O₂ induced erythrocyte hemolysis and antioxidant activity by inhibiting membrane lipid peroxidation. Boiled rhizome was also found to preserve the loss of cellular antioxidants under H₂O₂ induced oxidative stress and disturbances caused to mitochondrial membrane potential. This is the first research reporting boiled N. nouchali rhizome as an ideal food material to manage the cause of hyperglycemia and resultant oxidative stress.

High Glucose Concentrations Affect Band 3 Protein in Human Erythrocytes

Hyperglycemia is considered a threat for cell homeostasis, as it is associated to oxidative stress (OS). As erythrocytes are continuously exposed to OS, this study was conceived to verify the impact of either diabetic conditions attested to by glycated hemoglobin (Hb) levels (>6.5% or higher) or treatment with high glucose (15-35 mM, for 24 h) on erythrocyte homeostasis. To this aim, anion exchange capability through the Band 3 protein (B3p) was monitored by the rate constant for SO₄^2- uptake. Thiobarbituric acid reactive species (TBARS), membrane sulfhydryl groups mostly belonging to B3p, glutathione reduced (GSH) levels, and B3p expression levels were also evaluated. The rate constant for SO₄^2- uptake (0.063 ± 0.001 min^-1, 16 min in healthy volunteers) was accelerated in erythrocytes from diabetic volunteers (0.113 ± 0.001 min^-1, 9 min) and after exposure to high glucose (0.129 ± 0.001in^-1, 7 min), but only in diabetic volunteers was there an increase in TBARS levels and oxidation of membrane sulfhydryl groups, and a decrease in both GSH and B3p expression levels was observed. A combined effect due to the glycated Hb and OS may explain what was observed in diabetic erythrocytes, while in in vitro hyperglycemia, early OS could explain B3p anion exchange capability alterations as proven by the use of melatonin. Finally, measurement of B3p anion exchange capability is a suitable tool to monitor the impact of hyperglycemia on erythrocytes homeostasis, being the first line of high glucose impact before Hb glycation. Melatonin may be useful to counteract hyperglycemia-induced OS at the B3p level.

Taurine attenuates Cr(VI)-induced cellular and DNA damage: an in vitro study using human erythrocytes and lymphocytes

Hexavalent chromium [(Cr(VI)] is widely used in several industries, but human exposure results in multiple organ toxicity. Enhanced generation of free radicals and reactive species is thought to play a key role in Cr(VI)-induced toxicity. We have examined the effect of taurine, a simple sulphur-containing amino acid and an antioxidant, on potassium dichromate [K₂Cr₂O₇, a Cr(VI) compound]-induced cytotoxicity and genotoxicity in human blood cells. Erythrocytes were treated with K₂Cr₂O₇, either alone or after incubation with different concentrations of taurine. Treatment of erythrocytes with K₂Cr₂O₇ alone led to marked increase in generation of reactive oxygen and nitrogen species, lipid and protein oxidation. This was accompanied by decrease in total sulfhydryl and glutathione content and lowered antioxidant power of the cells. This suggests that Cr(VI) induces oxidative stress in the cells. Incubation of erythrocytes with taurine prior to addition of K₂Cr₂O₇, resulted in a concentration-dependent decrease in the generation of reactive oxygen and nitrogen species, mitigation of oxidative stress and amelioration of antioxidant power of these cells. It also restored the activities of several metabolic, antioxidant and membrane-bound enzymes. Cr(VI)-induced damage to erythrocyte membrane and lymphocyte DNA was also significantly attenuated by prior administration of taurine. These results suggest that taurine can function as a chemoprotectant against Cr(VI)-induced oxidative injury and can be potentially used to mitigate the toxic effects of this transition metal ion.

Ameliorative effects of taurine against diabetes: a review

Diets in rats and humans have shown promising results. Taurine improved glucagon activity, promoted glycemic stability, modified glucose levels, successfully addressed hyperglycemia via advanced glycation end-product control, improved insulin secretion and had a beneficial effect on insulin resistance. Taurine treatment performed well against oxidative stress in brain, increased the secretion of required hormones and protected against neuropathy, retinopathy and nephropathy in diabetes compared with the control. Taurine has been observed to be effective in treatments against diabetic hepatotoxicity, vascular problems and heart injury in diabetes. Taurine was shown to be effective against oxidative stress. The mechanism of action of taurine cannot be explained by one pathway, as it has many effects. Several of the pathways are the advanced glycation end-product pathway, PI3-kinase/AKT pathway and mitochondrial apoptosis pathway. The worldwide threat of diabetes underscores the urgent need for novel therapeutic measures against this disorder. Taurine (2-aminoethane sulfonic acid) is a natural compound that has been studied in diabetes and diabetes-induced complications.

Prophylactic role of taurine and its derivatives against diabetes mellitus and its related complications

Taurine is a conditionally essential amino acid present in the body in free form. Mammalian taurine is synthesized in the pancreas via the cysteine sulfinic acid pathway. Anti-oxidation and anti-inflammation are two main properties through which it exerts its therapeutic effects. Many studies have shown its excellent therapeutic potential against diabetes mellitus and related complications like diabetic neuropathy, retinopathy, nephropathy, hematological dysfunctions, reproductive dysfunctions, liver and pancreas related complications etc. Not only taurine, a number of its derivatives have also been reported to be important in ameliorating diabetic complications. The present review has been aimed to describe the importance of taurine and its derivatives against diabetic metabolic syndrome and related complications.

Taurine mitigates nitrite-induced methemoglobin formation and oxidative damage in human erythrocytes

Nitrite is present as a noxious contaminant in drinking water and causes oxidative damage in various tissues of humans and animals. It is a well-known methemoglobin-forming agent that has been shown to damage blood cells. The protective effect of taurine, a semi-essential sulfur-containing amino acid, was studied on sodium nitrite (NaNO₂)-induced oxidative damage in human erythrocytes. Erythrocytes were incubated with NaNO₂, in the presence and absence of taurine, and changes in oxidative stress parameters determined. Pretreatment with taurine significantly ameliorated NaNO₂-induced oxidative damage to lipids, proteins, and plasma membrane. It also reduced the NaNO₂-induced increase in methemoglobin levels and ROS production. Taurine improved the antioxidant capacity of cells, restored the alterations in the activities of various metabolic enzymes, and prevented morphological changes in erythrocytes. Thus, taurine can be potentially used as a protective agent against the damaging effects of nitrite.

Cardiorenal protective effect of taurine against cyclophosphamide-induced toxicity in albino rats

Cyclophosphamide (CP) is a cytotoxic alkylating agent used in the treatment of malignant diseases and autoimmune disorders. Its clinical use is limited to its marked cardiorenal toxicity. The present study aimed to investigate the possible protective role of taurine (Tau; 200 mg·kg^-1 per day, i.p.) on CP-induced cardiorenal toxicity. CP (200 mg·kg^-1) was administered as a single intraperitoneal injection whereas; Tau was administered for 3 weeks on a daily basis. The results showed that CP produced an elevation in serum activities of creatine kinase, creatine kinase isoenzyme, lactate dehydrogenase, creatinine as well as blood urea nitrogen. CP also induced an elevation in the oxidative stress markers viz. elevation in the serum lipid peroxides level (measured as malondialdehyde; MDA) and reduction in reduced glutathione level and superoxide dismutase activity in both heart and renal tissue. On the other hand, administration of Tau attenuated the CP-evoked disturbances in the above mentioned parameters. In addition, CP exhibited electrocardiographic (ECG) changes, which were significantly reversed by Tau treatment. Finally, the histopathological examination emphasized the obtained results. In conclusion, Tau is suggested to be a potential candidate to ameliorate CP-induced cardiorenal toxicity that may be related to its antioxidant activity.

Effect of high glucose concentrations on human erythrocytes in vitro

Exposure to high glucose concentrations in vitro is often employed as a model for understanding erythrocyte modifications in diabetes. However, effects of such experiments may be affected by glucose consumption during prolonged incubation and changes of cellular parameters conditioned by impaired energy balance. The aim of this study was to compare alterations in various red cell parameters in this type of experiment to differentiate between those affected by glycoxidation and those affected by energy imbalance. Erythrocytes were incubated with 5, 45 or 100 mM glucose for up to 72 h. High glucose concentrations intensified lipid peroxidation and loss of activities of erythrocyte enzymes (glutathione S-transferase and glutathione reductase). On the other hand, hemolysis, eryptosis, calcium accumulation, loss of glutathione and increase in the GSSG/GSH ratio were attenuated by high glucose apparently due to maintenance of energy supply to the cells. Loss of plasma membrane Ca²⁺-ATPase activity and decrease in superoxide production were not affected by glucose concentration, being seemingly determined by processes independent of both glycoxidation and energy depletion. These results point to the necessity of careful interpretation of data obtained in experiments, in which erythrocytes are subject to treatment with high glucose concentrations in vitro.

•

Erythrocytes were incubated for up to 72 h in 5 mM, 45 mM and 100 mM glucose.

•

High glucose concentrations intensified lipid peroxidation.

•

High glucose attenuated hemolysis, eryptosis, Ca²⁺ accumulation and glutathione loss.

•

Glucose is a glycating agent but also energy source.

•

Results of exposure to high glucose should be interpreted with care.

Oxidative stress induced by cadmium in the plasma, erythrocytes and lymphocytes of rats: Attenuation by grape seed proanthocyanidins

The present study has been designed to investigate the ameliorative effect of grape seed proanthocyanidins (GSP) on cadmium (Cd)-induced oxidative damage in rat erythrocytes. Twenty four male Wistar rats were divided into four groups: control, GSP-treated group (100 mg kg(-1) body weight (BW)), Cd-treated group (cadmium chloride, 5 mg kg(-1) BW), and GSP + Cd-treated group in which GSP was orally pre-administered 90 min before Cd intoxication for 4 weeks. At the end of the experimental period, blood samples were collected by cardiac puncture and were processed for various biochemical estimations. The extent of oxidative damage in isolated rat erythrocyte membrane was assessed by measuring lipid peroxidation, enzymatic and non-enzymatic content, calcium ion (Ca(2+))/magnesium ion (Mg(2+))-ATPase and sodium ion (Na(+))/potassium ion (K(+))-ATPase activities, free iron, calcium, hydrogen peroxide (H2O2) concentration, and osmotic fragility. Our results unveiled that Cd intoxication significantly increased the erythrocyte lipid peroxidation markers and decreased the activity of enzymatic and non-enzymatic markers in erythrocytes. Conversely, GSP pretreatment significantly prevented the decrease in the activities of antioxidant enzymes and membrane-bound ATPases. GSP also restored the levels of iron, calcium, and H2O2 in Cd-treated rats. Conformational changes in erythrocytes of various groups were also determined using morphological and ultrastructural electron microscopic analysis. The findings of our study clearly revealed that GSP affords superior protection against Cd-induced reactive oxygen species generation, lipid peroxidation, and free radical generation in Cd-treated rats, which presumably reflects the ability of this flavonoid to protect erythrocytes and lymphocytes of rats from the toxic effects of Cd.

Protective Effects of Ferulic Acid on High Glucose-Induced Protein Glycation, Lipid Peroxidation, and Membrane Ion Pump Activity in Human Erythrocytes

Ferulic acid (FA) is the ubiquitous phytochemical phenolic derivative of cinnamic acid. Experimental studies in diabetic models demonstrate that FA possesses multiple mechanisms of action associated with anti-hyperglycemic activity. The mechanism by which FA prevents diabetes-associated vascular damages remains unknown. The aim of study was to investigate the protective effects of FA on protein glycation, lipid peroxidation, membrane ion pump activity, and phosphatidylserine exposure in high glucose-exposed human erythrocytes. Our results demonstrated that FA (10-100 μM) significantly reduced the levels of glycated hemoglobin (HbA1c) whereas 0.1-100 μM concentrations inhibited lipid peroxidation in erythrocytes exposed to 45 mM glucose. This was associated with increased glucose consumption. High glucose treatment also caused a significant reduction in Na⁺/K⁺-ATPase activity in the erythrocyte plasma membrane which could be reversed by FA. Furthermore, we found that FA (0.1-100 μM) prevented high glucose-induced phosphatidylserine exposure. These findings provide insights into a novel mechanism of FA for the prevention of vascular dysfunction associated with diabetes.

H2S donors attenuate diabetic nephropathy in rats: Modulation of oxidant status and polyol pathway

BACKGROUND

Sulfurous mineral water and its main active ingredient sodium hydrosulfide (NaHS) are major sources of H2S. The present study aimed to explore their protective effect on one of the serious long-term complications of diabetes; diabetic nephropathy.

METHODS

Sulfurous mineral water (as drinking water), NaHS (14 μmol/kg/day; ip), and gliclazide (10mg/kg; po) were administered daily for 6 weeks to streptozotocin (STZ)-diabetic rats.

RESULTS

STZ-induced diabetes was associated with body weight reduction, hyperglycemia, overproduction of glycated hemoglobin, as well as decline in serum insulin, C-peptide, and insulin like growth factor-I. Besides, diabetes impaired kidney functions and imposed oxidative and nitrosative stress as manifested by elevated contents of renal thiobarbituric acid reactive substances and nitric oxide, parallel to reduced glutathione content. These deleterious effects were antagonized by sulfurous water and to a better extent by NaHS. Activities of myeloperoxidase and sorbitol dehydrogenase were not altered by STZ or any of the treatments. However, STZ-induced diabetes was accompanied by an increment of aldose reductase which was only mitigated by gliclazide and NaHS. Histopathological examination of kidney sections corroborated the biochemical findings.

CONCLUSION

This study suggests a novel therapeutic approach for diabetic nephropathy using H2S donors.

An update on oxidative stress-mediated organ pathophysiology

Exposure to environmental pollutants and drugs can result in pathophysiological situations in the body. Research in this area is essential as the knowledge on cellular survival and death would help in designing effective therapeutic strategies that are needed for the maintenance of the normal physiological functions of the body. In this regard, naturally occurring bio-molecules can be considered as potential therapeutic targets as they are normally available in commonly consumed foodstuffs and are thought to have minimum side effects. This review article describes the detailed mechanisms of oxidative stress-mediated organ pathophysiology and the ultimate fate of the cells either to survive or to undergo necrotic or apoptotic death. The mechanisms underlying the beneficial role of a number of naturally occurring bioactive molecules in oxidative stress-mediated organ pathophysiology have also been included in the review. The review provides useful information about the recent progress in understanding the mechanism(s) of various types of organ pathophysiology, the complex cross-talk between these pathways, as well as their modulation in stressed conditions. Additionally, it suggests possible therapeutic applications of a number of naturally occurring bioactive molecules in conditions involving oxidative stress.

Impairment of calcium ATPases by high glucose and potential pharmacological protection

The review deals with impairment of Ca(2+)-ATPases by high glucose or its derivatives in vitro, as well as in human diabetes and experimental animal models. Acute increases in glucose level strongly correlate with oxidative stress. Dysfunction of Ca(2+)-ATPases in diabetic and in some cases even in nondiabetic conditions may result in nitration of and in irreversible modification of cysteine-674. Nonenyzmatic protein glycation might lead to alteration of Ca(2+)-ATPase structure and function contributing to Ca(2+) imbalance and thus may be involved in development of chronic complications of diabetes. The susceptibility to glycation is probably due to the relatively high percentage of lysine and arginine residues at the ATP binding and phosphorylation domains. Reversible glycation may develop into irreversible modifications (advanced glycation end products, AGEs). Sites of SERCA AGEs are depicted in this review. Finally, several mechanisms of prevention of Ca(2+)-pump glycation, and their advantages and disadvantages are discussed.

Mechanism of the protective action of taurine in toxin and drug induced organ pathophysiology and diabetic complications: a review

Taurine (2-aminoethanesulfonic acid), a conditionally essential amino acid, is found in large concentrations in all mammalian tissues and is particularly abundant in aquatic foods. Taurine exhibits membrane stabilizing, osmoregulatory and cytoprotective effects, antioxidative properties, regulates intracellular Ca(2+) concentration, modulates ion movement and neurotransmitters, reduce the levels of pro-inflammatory cytokines in various organs and controls blood pressure. Recently, emerging evidence from the literature shows the effectiveness of taurine as a protective agent against several environmental toxins and drug-induced multiple organ injuries as the outcome of hepatotoxicity, nephrotoxicity, neurotoxicity, testicular toxicity and cardiotoxicity in several animal models. Besides, taurine is also effective in combating diabetes and its associated complications, including cardiomyopathy, nephropathy, neuropathy, retinopathy and atherosclerosis. These beneficial effects appear to be due to the multiple actions of taurine on cellular functions. This review summarizes the mechanism of the prophylactic role of taurine against several environmental toxins and drug-induced organ pathophysiology and diabetes.

Taurine ameliorates alloxan-induced diabetic renal injury, oxidative stress-related signaling pathways and apoptosis in rats

Hyperglycemia-induced oxidative stress plays a vital role in the progression of diabetic nephropathy. The renoprotective nature of taurine has also been reported earlier; but little is known about the mechanism of this beneficial action. The present study has, therefore, been carried out to explore in detail the mechanism of the renoprotective effect of taurine under diabetic conditions. Diabetes was induced in rats by alloxan (single i.p. dose of 120 mg/kg body weight) administration. Taurine was administered orally for 3 weeks (1% w/v in drinking water) either from the day on which alloxan was injected or after the onset of diabetes. Alloxan-induced diabetic rats showed a significant increase in plasma glucose, enhanced the levels of renal damage markers, plasma creatinine, urea nitrogen and urinary albumin. Diabetic renal injury was associated with increased kidney weight to body weight ratio and glomerular hypertrophy. Moreover, it increased the productions of reactive oxygen species, enhanced lipid peroxidation and protein carbonylation in association with decreased intracellular antioxidant defense in the kidney tissue. In addition, hyperglycemia enhanced the levels of proinflammatory cytokins (TNF-α, IL-6, IL-1β) and Na(+)--K(+)-ATPase activity with a concomitant reduction in NO content and eNOS expression in diabetic kidney. Investigation of the oxidative stress-responsive signaling cascades showed the upregulation of PKCα, PKCβ, PKCε and MAPkinases in the renal tissue of the diabetic animals. However, taurine administration decreased the elevated blood glucose and proinflammatory cytokine levels, reduced renal oxidative stress (via decrease in xanthine oxidase activity, AGEs formation and inhibition of p47phox/CYP2E1 pathways), improved renal function and protected renal tissue from alloxan-induced apoptosis via the regulation of Bcl-2 family and caspase-9/3 proteins. Taurine supplementation in regular diet could, therefore, be beneficial to regulate diabetes-associated renal complications.

Taurine reduces nitrosative stress and nitric oxide synthase expression in high glucose-exposed human Schwann cells

The role of taurine in regulating glucose-induced nitrosative stress has been examined in human Schwann cells, a model for understanding the pathogenesis of diabetic neuropathy. Exposure to high glucose increased nitrated proteins (1.56 fold p<0.05), inducible nitric oxide synthase (iNOS) and neuronal NOS (nNOS) mRNA expression (1.55 fold and 2.2 fold respectively, p<0.05 both), phospho-p38 MAPK (1.32 fold, p<0.05) abundance and decreased Schwann cell growth (11±2%, p<0.05). Taurine supplementation prevented high-glucose induced iNOS and nNOS mRNA upregulation, reduced nitrated proteins and phospho-p38 MAPK (56±11% and 45±18% (p<0.05 both) respectively) and restored Schwann cell growth to control levels. High glucose and taurine treatment alone reduced phospho-p42/44 MAPK and phospho-AKT to below detectable levels. Treatment of human Schwann cells with donors of nitric oxide and peroxynitrite reduced taurine transporter (TauT) expression (by 35±5% and 29±7% respectively p<0.05 both) as well as the maximum velocity of taurine uptake (TauT Vmax). NOS inhibition prevented glucose-mediated TauT mRNA downregulation, and restored TauT Vmax. These data demonstrate an important role for taurine in the prevention of nitrosative stress in human Schwann cells, which may have important implications for the development and treatment of diabetic neuropathy.

The potential usefulness of taurine on diabetes mellitus and its complications

Taurine (2-aminoethanesulfonic acid) is a free amino acid found ubiquitously in millimolar concentrations in all mammalian tissues. Taurine exerts a variety of biological actions, including antioxidation, modulation of ion movement, osmoregulation, modulation of neurotransmitters, and conjugation of bile acids, which may maintain physiological homeostasis. Recently, data is accumulating that show the effectiveness of taurine against diabetes mellitus, insulin resistance and its complications, including retinopathy, nephropathy, neuropathy, atherosclerosis and cardiomyopathy, independent of hypoglycemic effect in several animal models. The useful effects appear due to the multiple actions of taurine on cellular functions. This review summarizes the beneficial effects of taurine supplementation on diabetes mellitus and the molecular mechanisms underlying its effectiveness.

Investigation of toxicological effects of Shuanghuanglian injection in Beagle dogs by metabonomic and traditional approaches

In this study, clinical biochemistry, hematology, histopathology and (1)H nuclear magnetic resonance spectroscopy-based metabonomic approaches were applied to investigate the toxicological effects of Shuanghuanglian (SHL) injection after intravenous administration (dosed at 4, 12 and 36 mL stock/kg) in Beagle dogs for 30 d. Decreases in red blood cells, hemoglobin, mean cell volume, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration were observed in the high-dose group. Elevated reticulocytes, total bilirubin and direct bilirubin were also observed in this group. Moreover, significant hemosiderosis and Prussian blue positivity were detected in the liver, spleen and kidney from high-dose group animals, and transmission electron microscopy examination revealed an appreciable number of acanthrocytes in the liver. These results collectively indicate that SHL injection has the potential to cause hemolytic anemia. Metabonomic analysis showed increases in serum lactate, choline and phosphocholine but a decrease in taurine in treated groups and these findings may underlie the toxicological mechanism of SHL injection. In summary, SHL injection shows hemolytic effects in Beagle dogs; moreover, serum choline and phosphocholine as well as lactate and taurine may be the biomarkers for hemolytic anemia induced by SHL injection.

Taurine supplementation increases skeletal muscle force production and protects muscle function during and after high-frequency in vitro stimulation

Recent studies report that depletion and repletion of muscle taurine (Tau) to endogenous levels affects skeletal muscle contractility in vitro. In this study, muscle Tau content was raised above endogenous levels by supplementing male Sprague-Dawley rats with 2.5% (wt/vol) Tau in drinking water for 2 wk, after which extensor digitorum longus (EDL) muscles were examined for in vitro contractile properties, fatigue resistance, and recovery from fatigue after two different high-frequency stimulation bouts. Tau supplementation increased muscle Tau content by approximately 40% and isometric twitch force by 19%, shifted the force-frequency relationship upward and to the left, increased specific force by 4.2%, and increased muscle calsequestrin protein content by 49%. Force at the end of a 10-s (100 Hz) continuous tetanic stimulation was 6% greater than controls, while force at the end of the 3-min intermittent high-frequency stimulation bout was significantly higher than controls, with a 12% greater area under the force curve. For 1 h after the 10-s continuous stimulation, tetanic force in Tau-supplemented muscles remained relatively stable while control muscle force gradually deteriorated. After the 3-min intermittent bout, tetanic force continued to slowly recover over the next 1 h, while control muscle force again began to decline. Tau supplementation attenuated F(2)-isoprostane production (a sensitive indicator of reactive oxygen species-induced lipid peroxidation) during the 3-min intermittent stimulation bout. Finally, Tau transporter protein expression was not altered by the Tau supplementation. Our results demonstrate that raising Tau content above endogenous levels increases twitch and subtetanic and specific force in rat fast-twitch skeletal muscle. Also, we demonstrate that raising Tau protects muscle function during high-frequency in vitro stimulation and the ensuing recovery period and helps reduce oxidative stress during prolonged stimulation.

Oxidative stress: Does it play a role in the genesis of early glycated proteins?

Glycation and oxidative stress are two important processes known to play a key role in complications of many pathophysiological processes. The two traditional factors found to modulate the early glycation of proteins are the prevailing concentration of glucose and half life of the protein. But evidences in the literature have documented an increased glycated protein levels in some non-diabetic pathological states. So it stands to reason that hyperglycemia, while clearly the culprit in diabetes, is not the complete answer to the etiology of increased early glycated products in non-diabetic conditions. A common denominator in all these above mentioned non-diabetic pathological conditions is oxidative stress. Collective evidences from the literature reveal that malondialdehyde, reduced glutathione, vitamin C, vitamin E and drugs with antioxidant properties mitigate the process of protein glycation. Taking all the above factors into account, we hypothesis that oxidative stress either via increasing reactive oxygen species or by depleting the antioxidants may modulate the genesis of early glycated proteins in vivo.

The effect of chronic diazepam administration on lipid peroxidation and Ca2+ -ATPase activity in rat liver

Chronic administration of diazepam (DZP) caused an increase in malondialdehyde (MDA) levels and a decrease in glutathione (GSH) content. DZP also markedly lowered Ca2+ATPase activity. Treatment with Se plus vitamin E reduced MDA levels and increased GSH content. Our results suggest that, increased lipid peroxidation together with alteration in Ca2+ -ATPase activity may play a role in DZP induced hepatic injury and Se plus vitamin E treatment may contribute to the attenuation of DZP induced hepatotoxicity.

Inhibition of high glucose-induced erythrocyte phosphatidylserine exposure by leupeptin and disaccharides

High glucose can lead to serious phosphatidylserine exposure of erythrocytes which may influence the protective effect of glucose on lyophilization of erythrocytes. In this study, caspase activation has not occurred during phosphatidylserine exposure of erythrocytes. However, leupeptin can efficiently inhibit phosphatidylserine exposure of erythrocytes induced by high glucose. With increase of the leupeptin concentrations, the percentages of cells with exposed phosphatidylserine were decreased steadily. In addition, trehalose and sucrose can significantly inhibit phosphatidylserine exposure and cell shrinkage of erythrocytes induced by high glucose through increasing tolerance to osmotic shock. When the disaccharide concentrations were more than 100 mM, the percentages of cells with exposed phosphatidylserine were similar to those of control cells. Moreover, addition of disaccharides in the glucose buffer can result in high osmotic pressure which may facilitate uptake of glucose and disaccharides into erythrocytes and higher cellular glucose and disaccharide concentrations can provide more protection for lyophilized erythrocytes. Although disaccharides can increase the osmotolerance and decrease the phosphatidylserine exposure of erythrocytes exposed to high glucose, whether disaccharides can prevent phosphatidylserine exposure of lyophilized erythrocytes still needs further researches.

Association between erythrocyte Na+K+-ATPase activity and some blood lipids in type 1 diabetic patients from Lagos, Nigeria

BACKGROUND

Altered levels of erythrocyte Na+K+-ATPase, atherogenic and anti-atherogenic lipid metabolites have been implicated in diabetic complications but their pattern of interactions remains poorly understood.This study evaluated this relationship in Nigerian patients with Type 1 diabetes mellitus.

METHODS

A total of 34 consented Type 1 diabetic patients and age -matched 27 non-diabetic controls were enrolled. Fasting plasma levels of total cholesterol, triglycerides and HDL-cholesterol were determined spectrophotometrically and LDL-cholesterol estimated using Friedewald formula. Total protein content and Na+K+-ATPase activity were also determined spectrophotometrically from ghost erythrocyte membrane prepared by osmotic lysis.

RESULTS

Results indicate significant (P < 0.05) reduction in Na+K+-ATPase activity in the Type 1 diabetic patients (0.38 +/- 0.08 vs. 0.59 +/- 0.07 microM Pi/mgprotein/h) compared to the control but with greater reduction in the diabetic subgroup with poor glycemic control (n = 20) and in whom cases of hypercholesterolemia (8.8%), hypertriglyceridemia (2.9%) and elevated LDL-cholesterol (5.9% each) were found. Correlation analyses further revealed significant (P < 0.05) inverse correlations [r = -(0.708-0.797] between all the atherogenic lipid metabolites measured and Na+K+-ATPase in this subgroup contrary to group with good glycemic control or non-diabetic subjects in which significant (P < 0.05) Na+K+-ATPase and HDL-C association were found (r = 0.427 - 0.489). The Na+K+-ATPase from the diabetic patients also exhibited increased sensitivity to digoxin and alterations in kinetic constants Vmax and Km determined by glycemic status of the patients.

CONCLUSION

It can be concluded that poor glycemic control evokes greater reduction in erythrocyte Na+K+-ATPase activity and promote enzyme-blood atherogenic lipid relationships in Type 1 diabetic Nigerian patients.

Nutritional regulation of proteases involved in fetal rat insulin secretion and islet cell proliferation

Epidemiological studies have indicated that malnutrition during early life may programme chronic degenerative disease in adulthood. In an animal model of fetal malnutrition, rats received an isoenergetic, low-protein (LP) diet during gestation. This reduced fetal β-cell proliferation and insulin secretion. Supplementation during gestation with taurine prevented these alterations. Since proteases are involved in secretion and proliferation, we investigated which proteases were associated with these alterations and their restoration in fetal LP islets. Insulin secretion and proliferation of fetal control and LP islets exposed to different protease modulators were measured. Lactacystin and calpain inhibitor I, but not isovaleryl-l-carnitine, raised insulin secretion in control islets, indicating that proteasome and cysteinyl cathepsin(s), but not μ-calpain, are involved in fetal insulin secretion. Insulin secretion from LP islets responded normally to lactacystin but was insensitive to calpain inhibitor I, indicating a loss of cysteinyl cathepsin activity. Taurine supplementation prevented this by restoring the response to calpain inhibitor I. Control islet cell proliferation was reduced by calpain inhibitor I and raised by isovaleryl-l-carnitine, indicating an involvement of calpain. Calpain activity appeared to be lost in LP islets and not restored by taurine. Most modifications in the mRNA expression of cysteinyl cathepsins, calpains and calpastatin due to maternal protein restriction were consistent with reduced protease activity and were restored by taurine. Thus, maternal protein restriction affected cysteinyl cathepsins and the calpain–calpastatin system. Taurine normalised fetal LP insulin secretion by protecting cysteinyl cathepsin(s), but the restoration of LP islet cell proliferation by taurine did not implicate calpains.

The oxidative damage of butenolide to isolated erythrocyte membranes

Butenolide (CAS No. 16275-44-8), a mycotoxin produced by several Fusarium species, has been shown to be a potential risk factor for animal and human health. This study was undertaken to investigate the potential oxidative damage of butenolide to biomembranes in vitro using the erythrocyte membrane model. Following exposure of isolated rat erythrocyte membranes to butenolide, the extent of oxidative damage was assessed by measuring lipid peroxidation, -SH groups content, Ca2+/Mg2+-ATPase and Na+/K+-ATPase activities, and conformational changes in membrane proteins. It was observed that butenolide resulted in a significant lipid peroxidation, revealed by a concentration-dependent increase in the level of thiobarbituric acid reactive substances (TBARS). Similarly, this toxin induced a concentration-dependent decrease in the content of membrane total -SH groups, as well as free -SH groups. Membrane-bound enzymes were also impaired by the toxin, demonstrated by the marked inhibition of the activities of Na+/K+-ATPase and Ca2+/Mg2+-ATPase. Conformational changes in membrane proteins were determined using electron paramagnetic resonance (EPR) spin labeling. Butenolide caused an increase in the ratio of weakly to strongly immobilized components (W/S ratio) in a manner of concentration-dependent, indicating conformational changes in membrane proteins occurred. In conclusion, these findings indicate that butenolide is capable of inducing significant oxidative damage to membrane lipids and proteins.

Low doses of vanadate and Trigonella synergistically regulate Na+/K + -ATPase activity and GLUT4 translocation in alloxan-diabetic rats

Oral administration of vanadate to diabetic animals have been shown to stabilize the glucose homeostasis and restore altered metabolic pathways. However, vanadate exerts these effects at relatively high doses with several toxic effects. Low doses of vanadate are relatively safe but unable to elicit any antidiabetic effects. The present study explored the prospect of using low doses of vanadate with Trigonella foenum graecum, seed powder (TSP), another antidiabetic agent, and to evaluate their antidiabetic effect in diabetic rats. Alloxan diabetic rats were treated with insulin, vanadate, TSP and low doses of vanadate with TSP for three weeks. The effect of these antidiabetic compounds was examined on general physiological parameters, Na(+)/K(+) ATPase activity, membrane lipid peroxidation and membrane fluidity in liver, kidney and heart tissues. Expression of glucose transporter (GLUT4) protein was also examined by immunoblotting method in experimental rat heart after three weeks of diabetes induction. Diabetic rats showed high blood glucose levels. Activity of Na(+)/K(+) ATPase decreased in diabetic liver and heart. However, kidney showed a significant increase in Na(+)/K(+) ATPase activity. Diabetic rats exhibited an increased level of lipid peroxidation and decreased membrane fluidity. GLUT4 distribution was also significantly lowered in heart of alloxan diabetic rats. Treatment of diabetic rats with insulin, TSP, vanadate and a combined therapy of lower dose of vanadate with TSP revived normoglycemia and restored the altered level of Na(+)/K(+) ATPase, lipid peroxidation and membrane fluidity and also induced the redistribution of GLUT4 transporter. TSP treatment alone is partially effective in restoring the above diabetes-induced alterations. Combined therapy of vanadate and TSP was the most effective in normalization of altered membrane linked functions and GLUT4 distribution without any harmful side effect.

Taurine modifies insulin signaling enzymes in the fructose-fed insulin resistant rats

OBJECTIVES

High fructose feeding induces insulin resistance and hyperinsulinemia in rats. The present study was proposed to elucidate the derangements in the insulin signaling pathway in high fructose-fed rats and whether taurine, a sulphur-containing amino acid could improve insulin action by modulating the signal transduction pathway.

METHODS

Male Wistar rats of body weight 170-190 g were divided into 4 groups of 6 rats each. Control rats received control diet and water ad libitum. Fructose fed animals received high fructose diet (> 60% of total calories) and water ad libitum. Fructose + taurine rats received fructose diet and 2% taurine solution ad libitum. Control + taurine rats received control diet and 2% taurine solution ad libitum. After the experimental period of 30 days, the effects of taurine on certain parameters on glucose metabolism were determined. The activities of protein tyrosine kinase (PTK) and protein tyrosine phosphatase (PTP) were assayed in liver.

RESULTS

The activities of the glycolytic enzymes were significantly lower while the activities of the gluconeogenic enzymes were higher in untreated fructose-fed rats as compared to control animals. Depletion of liver glycogen was observed in fructose-fed rats. Fructose-fed rats showed alterations in the activities of insulin signaling enzymes PTK and PTP. Taurine administration improved insulin sensitivity and controlled hyperglycemia and hyperinsulinemia in fructose-fed rats. Taurine treatment also restored the glucose metabolizing enzyme activities in fructose-fed rats.

CONCLUSIONS

Taurine supplementation might have a beneficial effect in overcoming insulin resistance and its associated abnormalities by modifying the post-receptor events of insulin action.

Taurine prevents fructose-diet induced collagen abnormalities in rat skin

OBJECTIVE

The aim of the study is to investigate the effect of taurine administration on the content and characteristics of skin collagen in high-fructose-fed rats.

RESEARCH DESIGN AND METHODS

Adult male Wistar rats were divided into four groups of six each: a control group (CON) and a taurine-supplemented control group (CON+TAU), a high fructose diet-fed group (FRU), and a taurine supplemented fructose diet-fed group (FRU+TAU). After 30 days, collagen was isolated from the skin, and its physicochemical properties were studied.

RESULTS

Fructose administration caused an accumulation of collagen and extensive cross-linking. This was evidenced by increases in glycation, fluorescence, and peroxidation in collagen samples. The physicochemical properties of collagen, like shrinkage temperature, aldehyde content, solubility pattern, and susceptibility to denaturing agents, were altered in the fructose-fed rats. The sodium dodecyl sulphate-polyacrylamide gel electrophoretic (SDS-PAGE) pattern of collagen from fructose-fed rats showed and elevated beta component of Type I collagen. Simultaneous administration of taurine alleviated these changes.

CONCLUSION

The positive influence of taurine on both collagen content and its properties suggests a potential mechanism for the ability of taurine to delay diabetic complications.

Peroxynitrite induced decrease in Na+, K+-ATPase activity is restored by taurine

AIM: Peroxynitrite (ONOO^-) is a powerful oxidant shown to damage membranes. In the present study, the effect of taurine on changes of liver plasma membrane Na⁺, K⁺-ATPase induced by ONOO^- was investigated.

METHODS: Liver plasma membrane was exposed to ONOO^- with or without taurine. Na⁺, K⁺-ATPase activity and lipid peroxidation as thiobarbituric acid reactive substances (TBARS) levels were measured.

RESULTS: Different concentrations of ONOO^- (100, 200, 500, and 1000 μmol/L) were found to decrease liver plasma membrane Na⁺, K⁺-ATPase activity significantly. The depletion of enzyme activity was not concentration dependent. Effects of different concentrations of taurine on liver plasma membrane Na⁺, K⁺-ATPase activity were also measured. Taurine did not cause any increase in enzyme activity. When plasma membranes were treated with 200 μmol/L ONOO^- with different concentrations of taurine, a restoring effect of taurine on enzyme activity was observed. TBARS levels were also measured and taurine was found to decrease the elevated values.

CONCLUSION: Taurine is observed to act as an antioxidant of ONOO^- to decrease lipid peroxidation and thus affect liver plasma membrane Na⁺, K⁺-ATPase by restoring its activity.

Hypoxia inducible factor pathways as targets for functional foods

The etiology of most chronic angiogenic diseases such as rheumatoid arthritis, atherosclerosis, diabetes complications, and cancer includes the presence of pockets of hypoxic cells growing behind aerobic cells and away from blood vessels. Hypoxic cells are the result of uncontrolled growth and insufficient vascularization and have undergone a shift from aerobic to anaerobic metabolism. Cells respond to hypoxia by stimulating the expression of hypoxia inducible factor (HIF), which is critical for survival under hypoxic conditions and in embryogenesis. HIF is a heterodimer consisting of the O2-regulated subunit, HIF-1alpha, and the constitutively expressed aryl hydrocarbon receptor nuclear translocator, HIF-1beta. Under hypoxic conditions, HIF-1alpha is stable, accumulates, and migrates to the nucleus where it binds to HIF-1beta to form the complex (HIF-1alpha + HIF-1beta). Transcription is initiated by the binding of the complex (HIF-1alpha + HIF-1beta) to hypoxia responsive elements (HREs). The complex [(HIF-1alpha + HIF-1beta) + HREs] stimulates the expression of genes involved in angiogenesis, anaerobic metabolism, vascular permeability, and inflammation. Experimental and clinical evidence show that these hypoxic cells are the most aggressive and difficult angiogenic disease cells to treat and are a major reason for antiangiogenic and conventional treatment failure. Hypoxia occurs in early stages of disease development (before metastasis), activates angiogenesis, and stimulates vascular remodeling. HIF-1alpha has also been identified under aerobic conditions in certain types of cancer. This review summarizes the role of hypoxia in some chronic degenerative angiogenic diseases and discusses potential functional foods to target the HIF-1alpha pathways under hypoxic and normoxic conditions. It is reported that dietary quinones, semiquinones, phenolics, vitamins, amino acids, isoprenoids, and vasoactive compounds can down-regulate the HIF-1 pathways and therefore the expression of several proangiogenic factors. Considering the lack of efficiency or the side effects of synthetic antiangiogenic drugs at clinical trials, down-regulation of hypoxia-induced angiogenesis by use of naturally occurring functional foods may provide an effective means of prevention.

Stimulation of glucose utilization and inhibition of protein glycation and AGE products by taurine

AIM

Pathological effects of the process of non-enzymatic glycation of proteins are reflected in chronic complications of diabetes mellitus. We investigated the antiglycating effect of taurine in high fructose fed rats in vivo and the inhibiting potency of taurine in the process of in vitro glycation. Additionally, we investigated whether taurine enhances glucose utilization in the rat diaphragm.

METHODS

Rats fed a high fructose diet (60% total calories) were provided 2% taurine solution for 30 days. The effects of taurine on plasma glucose, fructosamine, protein glycation and glycosylated haemoglobin in high fructose rats were determined. For in vitro glycation a mixture of 25 mm glucose and 25 mm fructose was used as glycating agent, bovine serum albumin as the model protein and taurine as the inhibitor. Incubations were carried out in a constant temperature bath at 37 degrees C for 3-30 days. Amadori products and advanced glycation end products (AGEs) formed were measured. In vitro utilization of glucose was carried out in the rat diaphragm in the presence and absence of insulin in which taurine was used as an additive.

RESULTS

The contents of glucose, glycated protein, glycosylated haemoglobin and fructosamine were significantly lowered by taurine treatment to high fructose rats. Taurine prevented in vitro glycation and the accumulation of AGEs. Furthermore, taurine enhanced glucose utilization in the rat diaphragm. This effect was additive to that of insulin and did not interfere with the action of insulin.

CONCLUSIONS

These results underline the potential use of taurine as a therapeutic supplement for the prevention of diabetic pathology.