Overexpression of spermidine/spermine N1-acetyltransferase elevates the threshold to pentylenetetrazol-induced seizure activity in transgenic mice

Activation of polyamine catabolism in transgenic mice through an overexpression of spermidine/spermine N(1)-acetyltransferase (SSAT) results in a massive overaccumulation of the diamine putrescine in most tissues including brain. Putrescine pool in transgenic animals was strikingly expanded in every six brain regions analyzed at present. Pons (23-fold), cerebellum (37-fold), cerebrum (34-fold), and hippocampus (16-fold) showed the greatest increases in putrescine levels. Moreover, the molar ratio of putrescine to spermidine was increased in the different brain regions of the transgenic animals on an average of nearly 40-fold. Upon an exposure of the animals to pentylenetetrazol (PTZ) infusions, a compound known to induce epilepsy-like seizure activity, the SSAT transgenic mice showed significantly elevated seizure threshold to both clonic and tonic convulsions in comparison with their syngenic littermates. This difference, however, disappeared when the animals were treated with ifenprodil prior to PTZ infusions. The latter compound acts as an antagonist of N-methyl-D-aspartate receptor by binding to the polyamine site of the receptor. Overexpression of SSAT likewise appeared to protect the transgenic animals from PTZ-induced neuron loss in the hippocampus. As putrescine is known to serve as a precursor to gamma-aminobutyric acid (GABA), we carried out (1)H NMR analyses the results of which revealed that the levels of the inhibitory amino acid GABA and its excitatory counterpart glutamate were indistinguishable in syngenic and transgenic animals in all brain regions analyzed. The present results suggest that the frequently observed enhanced accumulation of putrescine in response to brain insults belongs to neuroprotective measures rather than being a cause of the subsequent injury.     

Overexpression of spermidine/spermine N-acetyltransferase in transgenic mice protects the animals from kainate-induced toxicity

We recently generated a transgenic mouse line with activated polyamine catabolism through overexpression of spermidine/spermine N1-acetyltransferase (SSAT). A detailed analysis of brain polyamine concentrations indicated that all brain regions of these animals showed distinct signs of activated polyamine catabolism, e.g. overaccumulation of putrescine (three- to 17-fold), appearance of N1-acetylspermidine and decreases in spermidine concentrations. In situ hybridization analyses revealed a marked overexpression of SSAT-specific mRNA all over the brain tissue of the transgenic animals. The transgenic animals appeared to tolerate subcutaneous injections of high-dose kainate substantially better as their overall mortality was less than 50% of that of their syngenic littermates. We used the expression of glial fibrillary acidic protein (GFAP) as a marker of brain injury in response to kainate. In situ hybridization analysis with GFAP oligonucleotide up to 7 days after the administration of sublethal kainate doses showed reduced GFAP expression in transgenic animals in comparison with their non-transgenic littermates. This difference was especially striking in the cerebral cortex of the transgenic mice where the exposure to kainate hardly induced GFAP expression. The treatment with kainate likewise resulted in loss of the hippocampal (CA3) neurons in non-transgenic but not transgenic animals. These results support our earlier findings indicating that elevated concentrations of brain putrescine, irrespective whether derived from an overexpression of ornithine decarboxylase, or as shown here, from an overexpression of SSAT, play in all likelihood a neuroprotective role in brain injury.     

Effects of felbamate on brain polyamine changes following transient cerebral ischemia in the Mongolian gerbil

We sought to determine whether treatment with felbamate was capable to reduce the accumulation of putrescine induced by transient forebrain ischemia in the Mongolian gerbil. Gerbils underwent 10 min ligation of common carotid arteries followed by recirculation. Immediately after the release of the arterial occlusion, felbamate (75 and 150 mg kg(-1) i.p.) was administered. Putrescine and polyamine levels were measured in hippocampus and striatum at 1, 8, 24 and 48 h after recirculation. Putrescine levels appeared enhanced already 8 h after the release of the arterial occlusion and kept increasing up to 48 h in the hippocampus and striatum. No significant changes in spermidine levels during recirculation were detected. Conversely, spermine appeared to decrease in the hippocampus while it did not show changes in the striatum. Felbamate significantly reduced the ischemia induced changes in putrescine brain content only at the dose of 150 mg kg(-1) i.p.     

Effect of modulators of the polyamine site on the development of seizures induced by systemic and intracerebral administration of N-methyl-D-aspartate in albino mice

Systemic intraperitoneal administration of polyamine agonist IEM-1460 containing the Me₃N⁺ group with a stable positive charge preventing permeation of this substance through the blood-brain barrier and polyamine antagonist arcaine had no effect on the development of seizures caused by intracerebral injection of N-methyl-D-aspartate in mice. Intraperitoneal injection of IEM-40 potentiated, while arcaine decreased the severity of seizures induced by intraperitoneal treatment with N-methyl-D-aspartate. This effect was related to modulation of the permeability of the blood-brain barrier for N-methyl-D-aspartate probably due to modulating effects of IEM-40 and arcaine on the polyamine site of N-methyl-D-aspartate receptors in the blood-brain barrier. __________ Translated From byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 143, No. 5, Pp. 557–559, May, 2007     

葡聚糖-寡胺纳米粒基因载体的制备及表征

 目的制备聚阳离子纳米粒非病毒基因载体:葡聚糖-寡胺化合物。方法以葡聚糖、过碘酸钠、精胺等为反应物,经多步化学合成制备了该载体;并以红外光谱测定仪、激光纳米粒度测定仪、透射电子显微镜对其进行了理化表征;以绿色荧光蛋白基因为报告基因考察所制备载体的基因转染效能。结果葡聚糖与寡胺间以共价键连接成稳定的纳米粒基因载体,载体平均粒径为9.0 nm,Zeta电位为+31.1 mV、形状为类圆形;载体具有较高的基因转染率。结论实验结果表明,文中方法可以合成出优良的聚阳离子纳米粒非病毒基因载体。     

人精脒/精胺N1乙酰基转移酶基因的克隆、表达和纯化

目的构建人精脒/精胺N1乙酰基转移酶基因的原核表达载体,诱导该质粒在大肠杆菌中表达并纯化其表达的重组蛋白。方法从大肠癌组织中提取总RNA,采用RT-PCR法扩增人SSAT基因的cDNA片段,经TA克隆及亚克隆方法构建原核表达载体pTriEx-4-SSAT。将重组表达质粒转化入E.coli JM109 (DE3)中,经IPTG诱导表达,SDS-PAGE电泳和Western blot鉴定表达蛋白,并通过6His-tag,利用亲和层析法纯化表达的融合蛋白。结果酶切鉴定和DNA测序显示,人SSAT的cDNA片段成功插入表达载体pTriEx-4中,而且方向正确,SDS-PAGE电泳显示表达出20?kD的外源蛋白。Western blot检测结果显示,表达出的蛋白为6His-tag的融合蛋白,而且用Ni-NTA亲和层析法纯化了该重组蛋白。结论成功构建、表达和纯化了重组SSAT蛋白,为制备其抗体及研究该基因与结直肠肿瘤的关系提供了有力的工具。     

Spermine induces cell death in cultured human embryonic cerebral cortical neurons through N-methyl-D-aspartate receptor activation

The polyamines putrescine, spermidine, and spermine play important roles in cell proliferation, differentiation, and modulation of ion channel receptors. However, the function of increased concentrations of these compounds in brain injury and disease is unclear, in that they have been proposed as being both neuroprotective and neurotoxic. The effects of spermine and putrescine were studied in human primary cerebral cortical cultures containing both neurons and glia. No toxic effects were induced at 8 days in vitro (DIV) by either of the two polyamines at concentrations ranging from 0.3 microM to 2 mM. However, when the oxidative metabolism of spermine that generates toxic byproducts was induced by the presence of fetal calf serum, spermine caused cellular death with an LC(50) of approximately 50 microM. At 14 DIV, the coapplication of spermine 2 mM and glutamate 5 mM induced neuron cell death, but the effect of applying both components separately was null. Both spermine and glutamate were toxic to older neurons (26-42 DIV cultures), and here the coapplication of glutamate was found always to intensify the effect of spermine. Spermine showed greater toxicity than glutamate in neurons. Another effect observed is that glutamate, but not spermine, induced astrocyte swelling. Spermine toxicity was inhibited by both MK801 and ifenprodil, indicating a mechanism involving N-methyl-D-aspartate (NMDA) receptor activation. Moreover, a strong spermine modulation of the NMDA receptor was demonstrated by the inhibition of glutamate toxicity by ifenprodil. Putrescine induced minor effects also as a neurotoxic agent. In conclusion, neuronal death by spermine can be induced by its toxic byproducts as well as through NMDA receptor action. The present results confirm the potentially harmful role of the polyamines in excitotoxicity-related human disorders.     

Role of Mg block of the inward rectifier K current in cardiac repolarization reserve: A quantitative simulation

Different K⁺ currents serve as “repolarization reserve” or a redundant repolarizing mechanism that protects against excessive prolongation of the cardiac action potential and therefore arrhythmia. Impairment of the inward rectifier K⁺ current (I_K1) has been implicated in the pathogenesis of cardiac arrhythmias. The characteristics of I_K1 reflect the kinetics of channel block by intracellular cations, primarily spermine (a polyamine) and Mg²⁺, whose cellular levels may vary under various pathological conditions. However, the relevance of endogenous I_K1 blockers to the repolarization reserve is still not fully understood in detail. Here we used a mathematical model of a cardiac ventricular myocyte which quantitatively reproduces the dynamics of I_K1 block to examine the effects of the intracellular spermine and Mg²⁺ concentrations, through modifying I_K1, on the action potential repolarization. Our simulation indicated that an I_K1 transient caused by relief of Mg²⁺ block flows during early phase 3. Increases in the intracellular spermine/Mg²⁺ concentration, or decreases in the intracellular Mg²⁺ concentration, to levels outside their normal ranges prolonged action potential duration by decreasing the I_K1 transient. Moreover, reducing both the rapidly activating delayed rectifier current (I_Kr) and the I_K1 transient caused a marked retardation of repolarization and early afterdepolarization because they overlap in the voltage range at which they flow. Our results indicate that the I_K1 transient caused by relief of Mg²⁺ block is an important repolarizing current, especially when I_Kr is reduced, and that abnormal intracellular free spermine/Mg²⁺ concentrations may be a missing risk factor for malignant arrhythmias in I_Kr-related acquired (drug-induced) and congenital long QT syndromes.     

人精胺/精眯N 1-乙酰基转移酶单克隆抗体的制备及鉴定

 目的制备鼠抗人精胺/精眯N1鄄乙酰基转移酶（SSAT）单克隆抗体,分析该抗体的效价、抗原特异性及其在Western blot和免疫组织化学等分析技术中的可用性。方法在BL21（DE3）中原核表达带6伊His 标签的SSAT 重组蛋白,并用Ni鄄NTA 树脂亲和层析纯化。用SSAT 重组蛋白免疫Balb/C 小鼠,通过杂交瘤技术制备抗SSAT 单克隆抗体,所得抗体的特异性及效价用ELISA、Western blot及免疫组织化学技术检测。结果成功建立了稳定分泌鼠抗人SSAT的单克隆抗体杂交瘤细胞株,该单克隆抗体可用于ELISA、Western blot、免疫组织化学、免疫荧光等分析技术。结论成功制备SSAT 单克隆抗体,为SSAT 相关的分子和病理研究奠定了基础。     

Cerebral Ischemia Enhances Polyamine Oxidation: Identification of Enzymatically Formed 3-Aminopropanal as an Endogenous Mediator of Neuronal and Glial Cell Death

To elucidate endogenous mechanisms underlying cerebral damage during ischemia, brain polyamine oxidase activity was measured in rats subjected to permanent occlusion of the middle cerebral artery. Brain polyamine oxidase activity was increased significantly within 2 h after the onset of ischemia in brain homogenates (15.8 ± 0.9 nmol/h/mg protein) as compared with homogenates prepared from the normally perfused contralateral side (7.4 ± 0.5 nmol/h/mg protein) (P <0.05). The major catabolic products of polyamine oxidase are putrescine and 3-aminopropanal. Although 3-aminopropanal is a potent cytotoxin, essential information was previously lacking on whether 3-aminopropanal is produced during cerebral ischemia. We now report that 3-aminopropanal accumulates in the ischemic brain within 2 h after permanent forebrain ischemia in rats. Cytotoxic levels of 3-aminopropanal are achieved before the onset of significant cerebral cell damage, and increase in a time-dependent manner with spreading neuronal and glial cell death. Glial cell cultures exposed to 3-aminopropanal undergo apoptosis (LD₅₀ = 160 μM), whereas neurons are killed by necrotic mechanisms (LD₅₀ = 90 μM). The tetrapeptide caspase 1 inhibitor (Ac-YVAD-CMK) prevents 3-aminopropanal–mediated apoptosis in glial cells. Finally, treatment of rats with two structurally distinct inhibitors of polyamine oxidase (aminoguanidine and chloroquine) attenuates brain polyamine oxidase activity, prevents the production of 3-aminopropanal, and significantly protects against the development of ischemic brain damage in vivo. Considered together, these results indicate that polyamine oxidase–derived 3-aminopropanal is a mediator of the brain damaging sequelae of cerebral ischemia, which can be therapeutically modulated.