Characterisation of a functional polyamine site on rat mast cells: association with a NMDA receptor macrocomplex

Polyamines can modulate activation of N-methyl-d-aspartate (NMDA) receptors by binding to a specific polyamine site associated with a NMDA receptor macrocomplex. Polyamines induce histamine release from mast cells, although the mechanism had not been defined. We have examined whether spermine, a natural polyamine, and compound , regarded as a synthetic polyamine, activate mast cells by a polyamine site associated with a NMDA receptor macrocomplex. Spermine induced secretion of histamine from rat peritoneal mast cells and rat brain mast cells in a concentration-dependent manner. Rat peritoneal mast cells were used as a model system to explore the effects of NMDA antagonists on polyamine-induced histamine release. Ifenprodil, MK801 and arcaine inhibited histamine secretion from mast cells exposed to polyamines; the percentage inhibition was greater against spermine than compound . These data support the proposal that spermine (and possibly compound ) induce histamine release from mast cells by interacting with a specific polyamine site on a NMDA receptor complex.     

Polyamines regulate glycine interaction with the N-methyl-D-aspartate receptor

[3H]Glycine binding studies have been performed to further characterize polyamine interactions with the rat brain N-methyl-D-aspartate (NMDA) receptor. Strychnine-insensitive [3H]glycine binding to washed cortical membranes was enhanced by spermine, spermidine, and hirudonin. Spermine stimulation of binding was additive with that produced by the NMDA receptor agonist L-glutamate. A high concentration of the L-glutamate antagonist 2-amino-5-phosphonovaleric acid reduced, but did not eliminate, spermine effects. Saturation experiments indicated that L-glutamate and spermine enhancement of binding was due to an increase in [3H]glycine binding affinity. Kinetic studies showed that optimal concentrations of spermine and L-glutamate reduced [3H]glycine association and dissociation rates by approximately fivefold and 30-fold, respectively. In competition experiments, the presence of L-glutamate and spermine had differential effects on the affinities of compounds that act as either agonists or antagonists at the glycine site of the NMDA receptor. The affinities of the agonists glycine, D-serine, and D-alanine, were increased about fivefold, while antagonist (HA-966, 7-chlorokynurenic acid) inhibitory potencies were unchanged. These data support our previous results showing that the NMDA receptor possesses a novel polyamine recognition site and demonstrate that these compounds directly modulate glycine's interactions with the receptor complex.     

A comparison of thyroxine- and polyamine-mediated enhancement of rat facial nerve regeneration

Thyroid hormones and spermidine, a motor neuron trophic polyamine (PA), have been shown to enhance peripheral motor nerve regeneration; however, the mechanism by which these treatment modalities exert their effect is unknown. Similarities in treatment outcome suggest that these molecules may be working via a common mechanism. Such an explanation is plausible since thyroid hormone is a potent inducer of ornithine decarboxylase (ODC), which is the rate-limiting enzyme involved in polyamine synthesis. This study was designed to morphologically evaluate the effects of exogenous thyroxine and spermidine on the regeneration of the rat facial nerve. Myelinated fiber density, axonal size, and degree of myelination were assayed by light and electron microscopy 21 days following facial nerve crush. Strikingly, the two treatment modalities had identical effects on all parameters tested. Each significantly enhanced the density of myelinated axons in regenerating nerves relative to the vehicle control. In addition, relative to the control treatment, both thyroxine and spermidine significantly increased the cross-sectional area of regenerating axons (P < 0.05). Interestingly, neither of the drug treatments had any effect on remyelination at the position where this parameter was analyzed. The concurrent administration of both thyroxine and spermidine did not synergistically enhance motor neuron regeneration. These data support the hypothesis that thyroxine and spermidine enhance neural regeneration by a common mechanism.     

Inhibition of arterial thrombosis by polyamines in a canine coronary artery injury model

Polyamines are polycations present in all living organisms and have been shown to play an important role in various physiological functions. Previous studies have shown that various amines including polyamines inhibit platelet activation. Among the amines tested tetra-amine, spermine is the potent inhibitor of platelet aggregation. In spite of vast literature on the anti-aggregatory effect of amines, there are no definitive studies testing their efficacy in an in vivo thrombosis model. In the present study, we investigated if polyamines could inhibit in-vivo thrombosis. A partially occlusive thrombus was generated by application of electric current in canine coronary artery. In control animals, the artery was completely in 76+/-14 min after the current was discontinued. When 40 mg/kg (1.44 mM) spermine was given immediately after stopping the current blood flow remained patent for >240 min. At equimolar concentration, triamine, spermidine and diamine putrescine are also equally effective in preventing thrombus development. The anti thrombic effect of polyamines was not associated with increased bleeding tendency, as judged by the amount of blood adsorbed by a gauge pad placed in a surgical incision extending to the muscle tissue and by a standard template bleeding. These results indicate that apart from inhibiting in-vitro platelet aggregation polyamines can also inhibit in-vivo thrombus formation.     

Spermine-induced negative inotropic effect in isolated rat heart,is mediated through the release of ATP

Putrescine, spermidine and spermine are natural compounds found in up to millimolar concentrations in eukaryotic and prokaryotic cells. At physiologic pH, the polyamines are protonated (+2, +3 and +4 charges), their polycationic properties lead to the assumption that they could affect physiological systems by binding to anionic sites of the cellular membrane and/or by modulating ion channels. At the cardiovascular level, their effects are not completely understood. However, these compounds may be able to exert the induction of synthesis and release of cellular mediators. In an attempt to explore this possibility, we used the isolated and perfused rat heart, Langendorff, model in order to evaluate the inotropic effects of these polyamines, putrescine, spermidine and spermine. Dose-response curves (0.1-0.6 mM) for putrescine, spermidine and spermine were constructed; with the finding that spermine had the largest negative effect. The obtained effects were not blocked by nitric oxide synthesis inhibitors (L-NAME), H(1) and H(2) receptor antagonists (Brompheniramine and Cimetidine) or by Glibenclamide, an antagonist of ATP-sensitive K(+) channels. We found that spermine-induced and increased ATP concentration in cardiac effluents. Reactive Blue, a P(2y) purinoreceptor antagonist and Aminophylline, an unspecific adenosine receptor antagonist, blocked the spermine-induced effects. These results showed that ATP, at least in part, is responsible of the spermine cardiovascular effects. Adenosine was shown to also play an important role on those effects.     

Polyamine and nucleic acid metabolism in myocardial hypertrophy of the overloaded heart

The metabolism of polyamines and nucleic acids in the hearts of rats undergoing physical activity for 2 hours once daily for 5 days has been studied. The results show a significant rise of the specific radioactivity of the polyamines (spermine and spermidine); this phenomenon reaches its peak on the second day of muscular activity. Under the same experimental conditions, the enzymic activity of amine-oxidase was evaluated, and increased on the second day of exercise; after reaching the maximum level, it remained constant until the end of the experiment. The specific activity of RNA of all the sub-cellular fractions of the heart showed a progressive increase with the duration of muscular activity. Experiments carried out with the perfused heart showed that spermine, at the concentration of 0.3 mm, stimulated the incorporation of [³H]ribose into RNA. The results suggest that the polyamines may be involved in the mechanism of myocardial RNA synthesis.     

盐酸司维拉姆对糖尿病肾病患者血管钙化的疗效及机制

[目的]探讨盐酸司维拉姆对糖尿病肾病(DN)患者中短期抗血管钙化的疗效及相关作用机制.[方法]行维持性血液透析(MHD)且联用盐酸司维拉姆的34例DN患者为研究组;将同期入院行MHD的26例DN患者纳入对照组.两组均持续治疗12周后观察比较其入组时和治疗12周后血磷、血钙、钙磷乘积、甲状旁腺激素(iPTH)、脂代谢指标[低密度脂蛋白胆固醇(LDL-C)、高密度脂蛋白胆固醇(HDL-C)、总胆固醇(TC)、三酰甘油(TG)]、炎症指标[C反应蛋白(CRP)、白细胞介素-6(L-6)、肿瘤坏死因子-α(TNF-α)]变化情况,分析两组3年随访期内冠状动脉钙化(CAC)积分变化情况及3年生存率、CAC率、心血管事件病死率的差异.[结果]治疗后,研究组除血钙水平及HDL-C水平较入组时无差异(P＞0.05)外,血磷、钙磷乘积、iPTH、LDL-C、TC、TG、CRP、L-6、TNF-α等均较入组时显著降低(P＜0.05);对照组则较入组时无明显差异(P＞0.05).3年随访期内,研究组CAC积分及CAC率均显著低于对照组(P＜0.05);两组3年生存率和心血管事件病死率比较则差异无显著性(P＞0.05).[结论]盐酸司维拉姆治疗DN患者能有效改善其血管钙化情况,对降低CAC发生率、调节血脂水平、抑制炎症反应等具有积极影响.     

Agmatine Signaling: Odds and Threads

Agmatine is a metabolite of L‐arginine. It is formed by the decarboxylation of L‐arginine via arginine decarboxylase in bacteria, plants and mammals. It is becoming clear that it has multiple physiological functions as a potential transmitter. Agmatine binds to α₂‐adrenoceptors and to imidazoline binding sites. It blocks NMDA receptors and other ligand‐gated cation channels. It also inhibits nitric oxide synthase, induces release of peptide hormones and antizyme and plays a role during cell proliferation by interacting with the generation and transport of polyamines. Although the precise function of endogenously released agmatine is presently still unclear, this review will summarize several aspects concerning the biological function of agmatine.     

The effect of polyamines on the binding of anti-DNA antibodies from patients with SLE and normal human subjects

Antibodies to DNA (anti-DNA) are the serological hallmark of systemic lupus erythematosus (SLE). To elucidate specificity further, the effect of polyamines on the binding of anti-DNA antibodies from patients with lupus was tested by ELISA to calf thymus (CT) DNA; we also assessed the binding of plasmas of patients and normal human subjects (NHS) to Micrococcus luteus (MC) DNA. As these studies showed, spermine can dose-dependently inhibit SLE anti-DNA binding to CT DNA and can promote dissociation of preformed immune complexes. With MC DNA as antigen, spermine failed to inhibit the NHS anti-DNA binding. Studies using plasmas adsorbed to a CT DNA cellulose affinity indicated that SLE plasmas are mixtures of anti-DNA that differ in inhibition by spermine and binding to conserved and non-conserved determinants. Together, these studies demonstrate that spermine can influence the binding of anti-DNA autoantibodies and may contribute to the antigenicity of DNA.