Cardiovascular responses of the taurine-depleted rat to vasoactive agents

Summary. The objective of this study was to assess the effect of taurine-depletion on cardiovascular responses of rat to vasoactive agents. Male Wistar-Kyoto (WKY) rats were given either tap water (control) or 3% β-alanine (taurine-depleted) for three weeks. Thereafter, mean arterial pressure (MAP) and heart rate of the freely moving animal were measured in response to vasoactive agents. Administration of phenylephine (5–40 μg/kg/min; i.v.) resulted in a similar and significant increase in MAP but a reduction in heart rate in both control and taurine-depleted groups. On the other hand, administration of sodium nitroprusside (15–300 μg/kg/min; i.v.) elicited a similar and significant reduction in MAP but increased heart rate in both groups. Lack of a differential response to phenylephrine and sodium nitroprusside between the two groups suggests that baroreflex regulation of cardiovascular function is not adversely affected by taurine-depletion. Administration of angiotensin II (0.1–3.0 μg/kg/min; i.v.) resulted in a dose-related increase in the pressor response and a decrease in heart rate in both groups. However, angiotensin II-induced pressor response was reduced in the taurine-depleted compared to the control rats (p < 0.05); heart rate was similarly reduced in both groups. Acute exposure to β-alanine (3 g/kg; i.v., 30-minutes) did not alter angiotensin II-induced hemodynamic responses. Similarly, incubation of aortic rings with β-alanine (40 mM, 30 minutes) did not affect the contractile responses to angiotensin II. The results suggest that β-alanine, per se, does not affect angiotensin II-induced responses in rat. However, β-alanine-induced taurine depletion is associated with a reduction in the pressor response to angiotensin II without impairing baroreflex function. Received December 17, 1999/Accepted January 12, 2000     

Studies of aminochrome toxicity in a mouse derived neuronal cell line: is this toxicity mediated via glutamate transmission?

Summary. Aminochrome was found to be toxic in a mouse-derived neuronal cell line (CNh). The effect was concentration dependent (10–150 μM). The issue whether aminochrome toxicity involves glutamate transmission was studied with several glutamate receptors antagonists. Incubation of the cells with aminochrome (150 μM) in the presence of 100 μM of the AMPA an-tagonist, NBQX resulted in an increase of cell survival, from 52 to 73%. However, this protective effect did not seem to be related to activation of ionotropic glutamate receptors since incubation of CNh cells with 200 μM of glutamate resulted in only 10% decrease of cell survival. However, NBQX was found to inhibit in vitro the autoxidation process. One hundred μM AP-5 did not have any effect on aminochrome toxicity. The toxic effect of aminochrome on CNh cells seems to be dependent of extracellular activation since addition of dicoumarol, a specific inhibitor of DT-diaphorase, did not affect that toxicity, which can be explained perhaps by a lack of a transport system for aminochrome into the CNh cells. Received July 28, 1999, Accepted December 6, 1999     

Mangroves of Oman during the late Holocene; climatic implications and impact on human settlements

Pollen and micropalaeontological analyses carried out on mangrove swamp sediments of Suwayh, Oman (22°05.589'N, 50°40.033'E) reveal environmental changes linked both to climate (monsoon) and geomorphological (sea-level) variations during the Late Holocene. A Rhizophora mangrove developed at Suwayh around 6000 years B. P. under climate conditions marked by an increased tropical influence as compared to the modern situation, with dominant summer rains. The later extension of Prosopis cineraria at Suwayh provides evidence for a different rainfall pattern, with a winter rainy season. Pollen and micropalaeontological composition shows three episodes influenced by the sea water at Suwayh. The most important corresponded to the mangrove episode centred ca 6000 B. P. This was followed by two episodes of slight seawater incursion at ca. 5100 and 4500 B. P. responsible for the formation of a brackish laagon. Comparison based on ¹⁴C measurements on shell recovered from both the sedimentary sequence of Suwayh and the nearby archaeological sites demonstrates that close relations existed between man and mangroves during the Neolithic and the Early Bronze Age. Received October 31, 2001 / Accepted January 24, 2002 Correspondence to: Anne-Marie Lézine     

The renal type H+/peptide symporter PEPT2: structure-affinity relationships

Summary. The H⁺/peptide cotransporter PEPT2 is expressed in a variety of organs including kidney, lung, brain, mammary gland, and eye. PEPT2 substrates are di- and tripeptides as well as peptidomimetics, such as β-lactam antibiotics. Due to the presence of PEPT2 at the bronchial epithelium, the aerosolic administration of peptide-like drugs might play a major role in future treatment of various pulmonary and systemic diseases. Moreover, PEPT2 has a significant influence on the in vivo disposition and half-life time of peptide-like drugs within the body, particularly in kidney and brain. PEPT2 is known to have similar but not identical structural requirements for substrate recognition and transport compared to PEPT1, its intestinal counterpart. In this review we compiled available affinity constants of 352 compounds, measured at different mammalian tissues and expression systems and compare the data whenever possible with those of PEPT1.     

Interaction between the actions of taurine and angiotensin II

Summary. The amino acid, taurine, is an important nutrient found in very high concentration in excitable tissue. Cellular depletion of taurine has been linked to developmental defects, retinal damage, immundeficiency, impaired cellular growth and the development of a cardiomyopathy. These findings have encouraged the use of taurine in infant formula, nutritional supplements and energy promoting drinks. Nonetheless, the use of taurine as a drug to treat specific diseases has been limited. One disease that responds favorably to taurine therapy is congestive heart failure. In this review, we discuss three mechanisms that might underlie the beneficial effect of taurine in heart failure. First, taurine promotes natriuresis and diuresis, presumably through its osmoregulatory activity in the kidney, its modulation of atrial natriuretic factor secretion and its putative regulation of vasopressin release. However, it remains to be determined whether taurine treatment promotes salt and water excretion in humans with heart failure. Second, taurine mediates a modest positive inotropic effect by regulating [Na⁺]_i and Na⁺/Ca²⁺ exchanger flux. Although this effect of taurine has not been examined in human tissue, it is significant that it bypasses the major calcium transport defects found in the failing human heart. Third, taurine attenuates the actions of angiotensin II on Ca²⁺ transport, protein synthesis and angiotensin II signaling. Through this mechanism taurine would be expected to minimize many of the adverse actions of angiotensin II, including the induction of cardiac hypertrophy, volume overload and myocardial remodeling. Since the ACE inhibitors are the mainstay in the treatment of congestive heart failure, this action of taurine is probably very important. Received November 10, 1998, Accepted May 19, 1999     

Alterations in neutrophil (PMN) free intracellular alpha-keto acid profiles and immune functions induced by L-alanyl-L-glutamine, arginine or taurine

Summary. The objective of this study was to determine the dose as well as duration of exposure-dependent effects of L-alanyl-L-glutamine, arginine or taurine on polymorphonuclear neutrophil (PMN) free α-keto acid profiles and, in a parallel study, on PMN immune functions. Exogenous L-alanyl-L-glutamine significantly increased PMN α-ketoglutarate, pyruvate PMN superoxide anion (O₂⁻) generation, hydrogen peroxide (H₂O₂) formation and released myeloperoxidase (MPO) activity. Arginine also led to significant increases in α-ketoglutarate, pyruvate, MPO release and H₂O₂ generation. Formation of O₂⁻ on the other hand was decreased by arginine. Incubation with taurine resulted in lower intracellular pyruvate and α-ketobutyrate levels, decreased O₂⁻ and H₂O₂ formation and a concomitant significantly increased MPO activity. We therefore believe that considerable changes in PMN free-α-keto-acid profiles, induced for example by L-alanyl-L-glutamine, arginine or taurine, may be one of the determinants in cell nutrition that considerably modulates the immunological competence of PMN.     

Cloning and heterologous expression of a rape cDNA encoding UDP-glucose:sinapate glucosyltransferase

A cDNA encoding a UDP-glucose:sinapate glucosyltransferase (SGT) that catalyzes the formation of 1-O-sinapoylglucose, was isolated from cDNA libraries constructed from immature seeds and young seedlings of rape (Brassica napus L.). The open reading frame encoded a protein of 497 amino acids with a calculated molecular mass of 55,970 Da and an isoelectric point of 6.36. The enzyme, functionally expressed in Escherichia coli, exhibited broad substrate specificity, glucosylating sinapate, cinnamate, ferulate, 4-coumarate and caffeate. Indole-3-acetate, 4-hydroxybenzoate and salicylate were not conjugated. The amino acid sequence of the SGT exhibited a distinct sequence identity to putative indole-3-acetate glucosyltransferases from Arabidopsis thaliana and a limonoid glucosyltransferase from Citrus unshiu, indicating that SGT belongs to a distinct subgroup of glucosyltransferases that catalyze the formation of 1-O-acylglucosides (β-acetal esters). Received: 14 July 2000 / Accepted: 8 August 2000     

Kinetic and proteomic analyses of <Emphasis Type="Italic">S</Emphasis>-nitrosoglutathione-treated hexokinase A: consequences for cancer energy metabolism

Summary. Mammalian hexokinase (HXK) is found at the outer mitochondrial membrane, exposed to mitochondrial oxygen- and nitrogen-radicals. Given the important role of this enzyme in metabolic pathways and diseases, the effect of S-nitrosoglutathione (GSNO) on HXK A structure and activity was studied. To focus on the catalytic domain, yeast HXK A was used because it has a significant homology to the mammalian domain that contains both the regulatory and catalytic sites. Biologically relevant [GSNO]/[HXK] caused a significant decrease in V_max with glucose (but not with fructose), along with oxidation of 5 Met and nitration of 4 Tyr. Preincubation of HXK with glucose abrogated the effect of GSNO whereas fructose was ineffective. These results are interpreted by considering the tight binding of glucose to the enzyme as opposed to that of fructose. The segment comprised from amino acids 304 to 306 contained the most modifications. Given that this sequence is highly conserved in HXK from various species, a decline in activity is expected when a high-affinity substrate is presented. Considering that changes in primary structure are envisioned at high [GSNO]/[HXK] ratios, like those present under normal conditions, it could be hypothesized that the high concentration of hexokinase present in fast growing tumors may serve not only to sustain high glycolysis rates, but also to minimize protein damage that might result in activity decline, compromising energy metabolism.     

Reactivity and oxidative potential of fructose and glucose in enkephalin-sugar model systems

Summary. The reactions of Leu- and Met-enkephalin (Tyr-Gly-Gly-Phe-Leu/Met) with fructose resulted in the parallel formation of Heyns compounds (N-peptidyl-d-mannosamine and -d-glucosamine) and sugar-peptide generated imidazolidinone diastereomers. Glucose showed higher level of reactivity than fructose with respect to the extent of glycated product formation. The presence of fructose in the incubation mixtures makes Met residue more susceptible to oxidation than glucose. Authors’ address: Dr. Štefica Horvat, Division of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, POB 180, 10002 Zagreb, Croatia     

Effects of endogenous glutamate on extracellular concentrations of taurine in striatum and nucleus accumbens of the awake rat: Involvement of NMDA and AMPA/kainate receptors

Summary. Using microdialysis, the effects of endogenous glutamate on extracellular concentrations of taurine in striatum and nucleus accumbens of the awake rat were investigated. The glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC) was used to increase the extracellular concentration of glutamate. PDC (1, 2 and 4 mM) produced a dose-related increase of extracellular concentrations of glutamate and taurine in striatum and nucleus accumbens. Increases of extracellular taurine were significantly correlated with increases of extracellular glutamate, but not with PDC doses, which suggests that endogenous glutamate produced the observed increases of extracellular taurine in striatum and nucleus accumbens. The role of ionotropic glutamate receptors on the increases of taurine was also studied. In striatum, perfusion of the antagonists of NMDA and AMPA/kainate glutamate receptors attenuated the increases of extracellular taurine. AMPA/kainate, but not NMDA receptors, also reduced the increases of extracellular taurine in nucleus accumbens. These results suggest that glutamate-taurine interactions exist in striatum and nucleus accumbens of the awake rat. Received March 5, 1999/Accepted September 22, 1999     

Felinine stability in the presence of selected urine compounds

Summary. The stability of felinine, an amino acid present in feline urine, was investigated. Synthetic felinine was unstable in the urine of a selection of mammals. Felinine was found to stable in feline urine in which urea had been degraded. Synthetic felinine was found to react specifically with urea and did not react with urea analogues such as biuret or thiourea or other nucleophilic compounds such as ammonia which is more nucleophilic or acetamide and water which are less nucleophilic than urea. The reaction of urea and felinine was independent of pH over the range of 3–10. Urea did not react with N-acetyl-felinine suggesting a felinine N-terminal interaction with urea. Mass spectral analysis of the reaction products showed the presence of carbamylated felinine and fragmentation ions derived from carbamyl-felinine. The physiological relevance of felinine carbamylation is yet to be determined.     

Identification of the site of glucocorticoid action on neutral amino acid transport in superficial nephrons of rat kidney

Summary. Glucocorticoid hormones enhance the reabsorptive capacity of filtered amino acids in rat kidney, as it was shown in previous in vivo clearance experiments. In the present study, the site of glucocorticoid action on neutral amino acid transport in superficial nephrons of rat kidney was investigated using in vivo micropuncture technique. Adult female Wistar rats were treated with dexamethasone (DEX), and fractional excretion of L-glutamine (L-Gln) and L-leucine (L-Leu) were determined and related to inulin after microinfusion into different nephron segments. DEX reduced fractional excretion of both neutral amino acids as a sign of enhanced reabsorptive capacity. The site of main DEX action on L-Leu reabsorption has been localized in the proximal straight tubule. However, in the case of L-Gln, the inhibition of γ-glutamyltranspeptidase (γ-GT) by administration of acivicin indicated the importance of this brush border enzyme in reduced L-Gln excretion. DEX enhanced γ-GT activity by tubular acidification. It can be presumed a DEX-inducible transport system for neutral amino acids mainly localized in proximal straight tubules of rat kidney. Received July 8, 1999     

The role of substance P in stress and anxiety responses

Summary. Substance P (SP) is one of the most abundant peptides in the central nervous system and has been implicated in a variety of physiological and pathophysiological processes including stress regulation, as well as affective and anxiety-related behaviour. Consistent with these functions, SP and its preferred neurokinin 1 (NK1) receptor has been found within brain areas known to be involved in the regulation of stress and anxiety responses. Aversive and stressful stimuli have been shown repeatedly to change SP brain tissue content, as well as NK1 receptor binding. More recently it has been demonstrated that emotional stressors increase SP efflux in specific limbic structures such as amygdala and septum and that the magnitude of this effect depends on the severity of the stressor. Depending on the brain area, an increase in intracerebral SP concentration (mimicked by SP microinjection) produces mainly anxiogenic-like responses in various behavioural tasks. Based on findings that SP transmission is stimulated under stressful or anxiety-provoking situations it was hypothesised that blockade of NK1 receptors may attenuate stress responses and exert anxiolytic-like effects. Preclinical and clinical studies have found evidence in favour of such an assumption. The status of this research is reviewed here.     

Effects of glucocorticoids on polyamine metabolism in liver and spleen of guinea pig during sensitization

Summary. Glucocorticoids are potent anti-inflammatory and immunosuppressive agents. As endogenous inhibitors of cytokine synthesis, glucocorticoids suppress immune activation and uncontrolled overproduction of cytokines, preventing tissue injury. Also, polyamine spermine is endogenous inhibitor of cytokine production (inhibiting IL-1, IL-6 and TNF synthesis). The idea of our work was to examine dexamethasone effects on the metabolism of polyamines, spermine, spermidine and putrescine and polyamine oxidase activity in liver and spleen during sensitization of guinea pigs. Sensitization was done by application of bovine serum albumin with addition of complete Freund’s adjuvant. Our results indicate that polyamine amounts and polyamine oxidase activity increase during immunogenesis in liver and spleen. Dexamethasone application to sensitized and unsensitized guinea pigs causes depletion of polyamines in liver and spleen. Dexamethasone decreases polyamine oxidase activity in liver and spleen of sensitized guinea pigs, increasing at the same time PAO activity in tissues of unsensitized animals.     

Chlorpromazine,clozapine and olanzapine inhibit anionic amino acid transport in cultured human fibroblasts

Summary. We report here that chlorpromazine, a first generation antipsychotic drug, inhibits anionic amino acid transport mediated by system X⁻ _AG (EAAT transporters) in cultured human fibroblasts. With 30 μM chlorpromazine, transport inhibition is detectable after 3 h of treatment, maximal after 48 h (>60%), and referable to a decrease in V_max. Chlorpromazine effect is not dependent upon changes of membrane potential and is selective for system X⁻ _AG since transport systems A and y⁺ are not affected. Among antipsychotic drugs, the inhibitory effect of chlorpromazine is shared by two dibenzodiazepines, clozapine and olanzapine, while other compounds, such as risperidon, zuclopentixol, sertindol and haloperidol, are not effective. Transport inhibition by clozapine and olanzapine, but not by chlorpromazine, is reversible, suggesting that the mechanisms involved are distinct. These results indicate that a subset of antipsychotic drugs inhibits EAAT transporters in non-nervous tissues and prompt further investigation on possible alterations of glutamate transport in peripheral tissues of schizophrenic patients.     

Galanin as a modulator of anxiety and depression and a therapeutic target for affective disease

Summary. Galanin is a 29 amino-acid (30 in humans) neuropeptide with a close functional relationship with neurotransmitter systems implicated in the pathophysiology and treatment of depression and anxiety disorders. In rodent models of depression-related behavior, treatment with galanin or compounds with agonist actions at galanin receptors has been shown to affect depression-related behaviors and the behavioral and neurochemical effects of antidepressants. Treatment with clinically efficacious antidepressants alters galanin and galanin receptor gene expression in rodents. Rodent anxiety-like behaviors appear to be modulated by galanin in a complex manner, with studies showing either increases, decreases and no effects of galanin treatments and galanin mutations on anxiety-like behavior in various tasks. One concept to emerge from this literature is that galanin recruitment during extreme behavioral and physiological provocations such as stress and opiate withdrawal may serve to attenuate negative emotional states caused by noradrenergic hyperactivation. The specific galanin receptor subtypes mediating the anxiety- and depression-related effects of galanin remains to be determined, with evidence supporting a possible contribution of GalR1, GalR2 and GalR3. While our understanding of the role of galanin as a modulator of emotion remains at an early stage, recent progress in this rapidly evolving field raise possibility of that galanin may represent a target for the development of novel antidepressant and anxiolytic drug treatments.     

Biochemistry of D-aspartate in mammalian cells

Summary. Recent investigations have shown that D-aspartate (D-Asp) plays an important physiological role(s) in the mammalian body. Here, several recent studies of free D-Asp metabolism in mammals, focusing on cellular localization in tissues, intracellular localization, biosynthesis, efflux, uptake and degradation are reviewed. D-Asp in mammalian tissues is present in specific cells, indicating the existence of specific molecular components that regulate D-Asp levels and localization in tissues. In the rat pheochromocytoma cell line (PC12) and its subclones, D-Asp is synthesized intracellularly, most likely by Asp racemase(s). Endogenous D-Asp apparently has two different intracellular localization patterns: cytoplasmic and vesicular. In PC12 cells, D-Asp release can occur through three distinct pathways: 1) spontaneous, continuous release of cytoplasmic D-Asp, which is not associated with a specific stimulus; 2) release of cytoplasmic D-Asp via a volume-sensitive organic anion channel that connects the cytoplasm and extracellular space; 3) exocytotic discharge of vesicular D-Asp. Under certain conditions, D-Asp can be released via a mechanism that involves the L-Glu transporter. D-Asp is thus apparently in dynamic flux at the cellular level to carry out its physiological function(s) in mammals.     

Microinjection of heme oxygenase genes rescues phytochrome-chromophore-deficient mutants of the moss Ceratodon purpureus

 In protonemal tip cells of the moss Ceratodon purpureus (Hedw.) Brid., phototropism and chlorophyll accumulation are regulated by the photoreceptor phytochrome. The mutant ptr116 lacks both responses as a result of a defect in the biosynthesis of phytochromobilin, the chromophore of phytochrome, at the point of biliverdin formation. The rescue of the phototropic response and of chlorophyll synthesis were tested by injecting different substances into tip cells of ptr116. Microinjection was first optimised with the use of fluorescent dyes and an expression plasmid containing a green fluorescent protein (GFP) gene. Injected phycocyanobilin, which substitutes for phytochromobilin, rescued both the phototropic response and light-induced chlorophyll accumulation in ptr116. The same results were obtained when expression plasmids with heme oxygenase genes of rat (HO-1) and Arabidopsis thaliana (L.) Heynh. (HY1) were injected. Heme oxygenase catalyses the conversion of heme into biliverdin. Whereas HY1 has a plastid target sequence and is presumably transferred to plastids, HO-1 is proposed to be cytosolic. The data show that ptr116 lacks heme oxygenase enzyme activity and indicate that heme oxygenases of various origin are active in Ceratodon bilin synthesis. In addition, it can be inferred from the data that the intracellular localisation of the expressed heme oxygenase is not important since the plastid enzyme can be replaced by a cytosolic one. Received: 8 March 1999 / Accepted: 30 July 1999