Taurine transporter gene expression in peripheral mononuclear blood cells of type 2 diabetic patients.

Taurine acts as antioxidant, cell osmolyte, modulator of glucose metabolism, and plays a role in the retinal function. It is 10(3)-fold more concentrated in the intracellular than in the extracellular milieu due to a specific taurine-Na-dependent transporter (TauT), which is upregulated by hypertonicity, low extracellular taurine, or oxidative stress and acutely downregulated 'in vitro' by high glucose concentrations. Aim of this study was to investigate whether TauT expression was modified in mononuclear peripheral blood cells (MPC) of type 2 diabetic patients with or without micro/macrovascular complications. Plasma taurine, as well as other sulphur-containing aminoacids (assayed by HPLC) and TauT gene expression (assayed by real-time PCR analysis) were measured in MPC of 45 controls and of 81 age-and-sex matched type 2 diabetic patients with or without micro/macrovascular complications. Median value (interquartile range) of plasma taurine was significantly lower in diabetic patients than in controls [28.7 (13.7) µmol/l vs. 46.5 (20.3) µmol/l; P<0.05], while median TauT expression, in arbitrary units, was significantly higher in diabetics than in controls [3.8 (3.9) vs. 1 (1.3); P<0.05) and was related to HbA1c only in controls (r=0.34; P<0.05). Patients with retinopathy (n=25) had lower TauT expression than those who were unaffected [3.1 (2.8) vs. 4.1 (3.4); P<0.05], while persistent micro/macroalbuminuria was associated with unchanged TauT expression. A trend toward reduction in TauT expression was observed in patients with macroangiopathy [n=27; 3.3 (2.5) vs. 4 [3.7]; P=NS]. In conclusion, TauT gene is overexpressed in MPC of type 2 diabetic patients, while presence of retinopathy is specifically associated with a drop in TauT overexpression, suggesting its possible involvement in this microangiopathic lesion.

Highly reactive oxygen species: detection, formation, and possible functions.

The so-called reactive oxygen species (ROS) are defined as oxygen-containing species that are more reactive than O(2) itself, which include hydrogen peroxide and superoxide. Although these are quite stable, they may be converted in the presence of transition metal ions, such as Fe(II), to the highly reactive oxygen species (hROS). hROS may exist as free hydroxyl radicals (HO·), as bound ("crypto") radicals or as Fe(IV)-oxo (ferryl) species and the somewhat less reactive, non-radical species, singlet oxygen. This review outlines the processes by which hROS may be formed, their damaging potential, and the evidence that they might have signaling functions. Since our understanding of the formation and actions of hROS depends on reliable procedures for their detection, particular attention is given to procedures for hROS detection and quantitation and their applicability to in vivo studies.

The detection of hydroxyl radicals in vivo.

Several indirect methods have been developed for the detection and quantification of highly reactive oxygen species (hROS), which may exist either as free hydroxyl radicals, bound "crypto" radicals or Fe(IV)-oxo species, in vivo. This review discusses the strengths and weaknesses associated with those most commonly used, which determine the hydroxylation of salicylate or phenylalanine. Chemical as well as biological arguments indicate that neither the hydroxylation of salicylate nor that of phenylalanine can guarantee an accurate hydroxyl radical quantitation in vivo. This is because not all hydroxylated product-species can be used for detection and the ratio of these species strongly depends on the chemical environment and on the reaction time. Furthermore, at least in the case of salicylate, the high concentrations of the chemical trap required (mM) are known to influence biological processes associated with oxidative stress. Two, newer, alternative methods described, the 4-hydroxy benzoic acid (4-HBA) and the terephthalate (TA) assays, do not have these drawbacks. In each case reaction with hROS leads to only one hydroxylated product. Thus, from a chemical viewpoint, they should provide a better hROS quantitation. Further work is needed to assess any possible biological effects of the required millimolar (4-HBA) and micromolar (TA) concentrations of the chemical traps.

Taurine in women with a history of gestational diabetes.

Taurine is the most abundant amino acid in the human body and seems to play an important role in increasing glucose-mediated insulin secretion, as well as in programming beta-cell maturation during the prenatal life in utero. To test the hypothesis that plasma taurine is related to glucose tolerance, insulin sensitivity and insulin secretion in subjects with history of beta-cell dysfunction such as women with history of gestational diabetes (GDM), we studied 72 non-diabetic women with history of GDM (n=43), impaired glucose tolerance (IGT; n=7), and normal glucose tolerance (NGT; n=22) as previously classified by a 100g-3h-OGTT performed between the 24th and the 28th gestational week. Insulin sensitivity (ISIogtt, calculated through Matsuda-DeFronzo index) and a proxy for insulin secretion (basal plasma C-peptide/fasting plasma glucose; CP/glucose) were measured during and after pregnancy. Plasma taurine was measured after a median period of 6 years (2-11 years) from index pregnancy, when glucose tolerance was retested by a 75 g-2h-OGTT. Plasma taurine was significantly lower in women who had experienced GDM and was unrelated to ISIogtt. Moreover, plasma taurine was inversely related to previous gestational area-under-curve of glucose and directly related to post-gestational CP/glucose, as well to CP/glucose measured during pregnancy (p<0.05 for both). The relative risk of altered glucose metabolism during previous pregnancies (IGT+GDM) was higher as plasma taurine decreased, even after adjusting for age, time-lag from pregnancy, body mass index and family history of diabetes (OR: 0.980; CI 95%: 0.963-0.999, p=0.003). In conclusion plasma taurine seems to be a fair marker of altered glucose metabolism during past pregnancies in women with antecedent GDM and appears to be inversely related to the previous as well as to the actual insulin secretion in these subjects.

Taurine Transporter Gene Expression in Mononuclear Blood Cells of Type 1 Diabetes Patients.

BACKGROUND: Taurine transporter gene expression (RNA-TauT) has a role in retinal cell function and is modulated in vitro and in vivo by hyperglycemia and/or oxidative stress. This study was aimed at testing whether RNA-TauT gene expression is modified in blood mononuclear peripheral cells (MPCs) of type 1 diabetic patients, is related to plasma markers of oxidative stress or endothelial dysfunction, or, finally, is related to presence of retinopathy. METHODS: RNA-TauT was measured in MPCs by real-time PCR-analysis in 35 type 1 diabetic patients and in 33 age- and sex-matched controls, additionally measuring plasma and cell taurine and markers of oxidative stress and endothelial dysfunction. RESULTS: RNA-TauT, expressed as 2(-ΔΔCt), was significantly higher in MPCs of type 1 diabetic patients than in controls [median (interquartile range): 1.32(0.31) versus 1.00(0.15); P = 0.01]. In diabetic patients RNA-TauT was related to HbA1c (r = 0.42; P = 0.01) and inversely to plasma homocysteine (r = -0.39; P = 0.02) being additionally significantly higher in MPCs of patients without retinopathy [(n = 22); 1.36(0.34)] compared to those with retinopathy [(n = 13); 1.16(0.20)], independently from HbA1c or diabetes duration. CONCLUSIONS: RNA-TauT gene expression is significantly upregulated in MPCs of type 1 diabetes patients and is related to HbA1c levels and inversely to plasma homocysteine. Finally, in diabetes patients, RNA-TauT upregulation seems to be blunted in patients with retinopathy independently of their metabolic control or longer diabetes duration.

The selective A2A receptor antagonist SCH 58261 reduces striatal transmitter outflow, turning behavior and ischemic brain damage induced by permanent focal ischemia in the rat.

Adenosine A(2A) receptor antagonists have been proved protective in different ischemia models. In this study we verified if the protective effect of the selective A(2A) antagonist, SCH 58261, could be attributed to the reduction of the excitatory amino acid outflow induced by cerebral focal ischemia. A vertical microdialysis probe was inserted into the striatum of male Wistar rats and, after 24 h, permanent right intraluminal middle cerebral artery occlusion (MCAo) was induced. Soon after waking, rats showed a definite contralateral turning behavior, which persisted up to 7 h after MCAo. During 4 h after MCAo, glutamate, aspartate, GABA, adenosine and taurine outflow increased. SCH 58261 (0.01 mg/kg, i.p.), administered 5 min after MCAo, suppressed turning behavior and significantly reduced the outflow of glutamate, aspartate, GABA and adenosine. At 24 h after MCAo, the rats showed severe sensorimotor deficit and damage in both the striatum and cortex. SCH 58261 significantly reduced cortical damage but did not protect against the sensorimotor deficit. The protective effect of SCH 58261 against turning behavior and increased outflow of excitatory amino acids in the first hours after MCAo suggests the potential utility of selective adenosine A(2A) antagonists when administered in the first hours after ischemia. Furthermore, this study, for the first time, proposes that turning behavior after permanent intraluminal MCAo, be used as a precocious index of neurological deficit and neuronal damage.

Taurine prevents streptozotocin impairment of hormone-stimulated glucose uptake in rat adipocytes.

Streptozotocin-treated rats were used as models of type 1 diabetes to study the effects of dietary taurine on insulin- and adrenergic-stimulated 2-deoxyglucose uptake by isolated adipocytes. In addition to the well-established impairment of basal and insulin-stimulated 2-deoxyglucose uptakes in adipocytes prepared from streptozotocin-diabetic rats, the alpha-(phenylephrine) and beta-(isoproterenol) adrenergic stimulations of glucose uptake were also abolished. The insulin stimulation of glucose uptake in adipocytes was selectively abolished by the phosphatidylinositol 3-kinase inhibitor wortmannin, whereas that by the adrenergic agonists, phenylephrine and isoproterenol, was inhibited by prazosin and propranolol, respectively. Dietary taurine, 4 weeks before and 4 weeks after streptozotocin administration, prevented the loss of both insulin and adrenergic agonist stimulations of 2-deoxyglucose uptake, without affecting hyperglycaemia. Because insulin and adrenergic activations of glucose transport by adipocytes are coupled to different signalling pathways, it is unlikely that these effects of taurine are related to these disparate postreceptor mechanisms.

Species-specific chemosignals evoke delayed excitation of the vomeronasal amygdala in freely-moving female rats.

Male rat chemosignals attract females and influence their reproductive status. Through the accessory olfactory bulb and its projection target, the posteromedial cortical nucleus of the amygdala (PMCo), species-specific chemosignals detected by the vomeronasal organ (VNO) may reach the hypothalamus. To test this hypothesis in vivo, behavioural activation and neurotransmitter release in the PMCo were simultaneously monitored in freely moving female oestrus rats exposed to either rat or mouse urinary stimuli, or to odorants. Plasma levels of the luteinizing hormone were subsequently monitored. All stimuli induced an immediate behavioural activation, but only species-specific chemosignals led to a delayed behavioural activation. This biphasic behavioural activation was accompanied by a VNO-mediated release of the excitatory amino acids, aspartate and glutamate, in the PMCo. The late behavioural and neurochemical activation was followed by an increase in the levels of circulating luteinizing hormone. In conclusion, these data show that only species-specific chemosignals induce a delayed behavioural activation and excitatory activation of the PMCo, which is dependent on an intact VNO.