Control of Spermidine and Spermine Levels in Rat Tissues by trans-4-Methylcyclohexylamine, a Spermidine-Synthase Inhibitor

Spermidine Affects Cardiac Function in Heart Failure Mice by Influencing the Gut Microbiota and Cardiac Galectin-3

Spermidine, which can be synthesized by the gut microbiota, can prevent cardiac hypertrophy and delay the progression to heart failure (HF). However, it is not clear whether the effect of spermidine on cardiac function is mediated by modulating the gut microbiota when HF occurs. Female HF Kunming mice induced by transverse aortic constriction were administered spermidine (HF+S group) or its antagonist (HF+SR group). Echocardiography, messenger ribonucleic acid (RNA) and protein expression of galectin-3 in the heart, cardiomyocyte apoptosis assays and gut microbiota analysis were detected. Left ventricular end-diastolic volume and diameter (LVVd and LVDd), and left ventricular end-systolic volume and diameter in the HF+SR group were significantly enlarged compared with those in the HF group (all P < 0.05). The HF+S group had a smaller LVDd and LVVd than the HF+SR group (5.01 ± 0.67 vs. 6.13 ± 0.45 mm, P = 0.033; 121.44 ± 38.74 vs. 189.94 ± 31.42 μL, P = 0.033). The messenger RNA and protein expression of galectin-3 and the number of apoptotic cardiomyocytes increased significantly in the HF+SR group compared to the HF group. Gut microbiota analysis showed that spermidine antagonists reduced the Firmicutes/Bacteroidetes ratio and changed the microbial community richness and diversity. In conclusion, spermidine can improve cardiac function in HF, and the regulation of gut microbiota and cardiac fibrosis may be a factor in the effect of spermidine on the improvement of cardiac function.

Chemoprevention of B-cell lymphomas by inhibition of the Myc target spermidine synthase

The oncogenic transcription factor c-Myc (Myc) is frequently overexpressed in human cancers. Myc is known to induce or repress a large set of genes involved in cell growth and proliferation, explaining the selection for mutations in cancer that deregulate Myc expression. Inhibition of ornithine decarboxylase, an enzyme of the polyamine biosynthetic pathway and a Myc target, has been shown to be chemopreventive. In the present study, we have dissected the role of another enzyme in the polyamine biosynthetic pathway, spermidine synthase (Srm), in Myc-induced cancer. We find that Srm is encoded by a Myc target gene containing perfect E-boxes and that it is induced by Myc in a direct manner. RNA interference against Srm shows that it is important for Myc-induced proliferation of mouse fibroblasts but to a lesser extent for transformation. Using the compound trans-4-methylcyclohexylamine, we show that Srm inhibition can delay the onset of B-cell lymphoma development in lambda-Myc transgenic mice. We therefore suggest that inhibition of Srm is an additional chemopreventive strategy that warrants further consideration.

Polyamines are essential in embryo implantation: expression and function of polyamine-related genes in mouse uterus during peri-implantation period

Polyamines are key regulators in cell growth and differentiation. It has been shown that ornithine decarboxylase (Odc) was essential for post-implantation embryo development, and overexpression of spermidine/spermine N1-acetyltransferase will lead to ovarian hypofunction and hypoplastic uteri. However, the expression and function of polyamine-related genes in mouse uterus during early pregnancy are still unknown. In this study we investigated the expression, regulation, and function of polyamine-related genes in mouse uterus during the peri-implantation period. Odc expression was strongly detected at implantation sites and stimulated by estrogen treatment. The expression of Odc antizyme 1 and spermidine/spermine N1-acetyltransferase was also highly shown at implantation sites and regulated by Odc or polyamine level in uterine cells. Embryo implantation was significantly inhibited by alpha-difluoromethylornithine, an Odc inhibitor. Moreover, the reduction of Odc activity caused by alpha-difluoromethylornithine treatment was compensated by the up-regulation of S-adenosylmethionine decarboxylase gene expression. Collectively, our results indicated that the coordinated expression of uterine polyamine-related genes may be important for embryo implantation.

Conformational selection in silico: loop latching motions and ligand binding in enzymes

Ligand binding frequently induces significant conformational changes in a protein receptor. Understanding and predicting such conformational changes represent an important challenge for computational biology, including applications to structure-based drug design. We describe an approach to this problem based on the assumption that the holo state is at least transiently populated in the absence of a ligand; this hypothesis has been referred to as "conformational selection." Here, we apply a method that tests this hypothesis on a challenging class of ligand-induced conformational changes, which we refer to as loop latching: the closing of a loop around an active site that sequesters the ligand from solvent. The method uses a combination of replica exchange molecular dynamics and a loop prediction algorithm to generate low-energy loop structures, and docking to select the conformation appropriate for binding a particular ligand. On a test set of six proteins, it yields loop structures including hololike conformations, generally below 2 A RMSD from the liganded structure, for loops that span up to 15 residues. Docking serves as a stringent test of the predictions. In five of the six cases, the predicted loop conformations improve the ranks of cognate ligands relative to using the apo structure, although the results remain, in most cases, significantly worse than using a holo structure. The poses of the cognate ligands are correct in four of the six test cases, while they are correct for five of the six using a holo structure.

Cellular and subcellular rat brain spermidine synthase expression patterns suggest region-specific roles for polyamines, including cerebellar pre-synaptic function

In the brain, the polyamines spermidine (Spd) and spermine (Spm) serve highly specific functions by interacting with various ion channel receptors intimately involved with synaptic signaling. Both, glial cells and neurons contain Spd/Spm, but release and uptake mechanisms could re-distribute polyamines between cell types. The cellular and subcellular localization of polyamine biosynthetic enzymes may therefore offer a more appropriate tool to identify local sources of enhanced Spd/Spm synthesis, which may be related with specific roles in neuronal circuits and synaptic function. A recently characterized antibody against Spd synthase was therefore used to screen the rat brain for compartment-specific peaks in enzyme expression. The resulting labeling pattern indicated a clearly heterogeneous expression predominantly localized to neurons and neuropil. The highest levels of Spd synthase expression were detected in the accumbens nucleus, taenia tecta, cerebellar cortex, cerebral cortical layer I, hippocampus, hypothalamus, mesencephalic raphe nuclei, central and lateral amygdala, and the circumventricular organs. Besides a diffuse labeling of the neuropil in several brain areas, the distinct labeling of mossy fiber terminals in the cerebellar cortex directly indicated a synaptic role for Spd synthesis. Electron microscopy revealed a preferential distribution of the immunosignal in synaptic vesicle containing areas. A pre-synaptic localization was also observed in parallel and climbing fiber terminals. Electrophysiological recordings in acute cerebellar slices revealed a Spd-induced block of evoked extracellular field potentials resulting from mossy fiber stimulation in a dose-dependent manner.

Assay for spermidine synthase activity by micellar electrokinetic chromatography with laser-induced fluorescence detection

An assay for spermidine synthase (SPDS) activity in rat liver has been developed using micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence (LIF) detection to enable the discovery of SPDS inhibitors. The assay was established by estimating the amount of spermidine (SPD) produced from the putrescine (PUT) present by SPDS. The SPD in an enzyme reaction mixture of homogenized rat liver could directly react with 7-fluoro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-F) as a fluorescence derivatization reagent. The NBD derivatives of SPD and PUT could be separated and detected by MEKC-LIF detection within 15 min. The IC(50) value measured for SPDS inhibitor, 4-methylcyclohexylamine, in rat liver by this assay was consistent with published data. Our SPDS assay using MEKC-LIF is simple and allows easy determination of SPDS activity in homogenized samples without troublesome procedures such as preparation of antibody or fluorescence-labeled substrate. The assay should be effective for discovering the SPDS inhibitors using biological samples.

Regulation of Polyamine and Cancer

This review describes my work in the field of polyamine research for the last 35 years. My research started with developing the improved synthesis of decarboxylated S-adenosylmethionine and then moved to the purification of spermidine synthase from rat prostate. I also took considerable efforts to find the synthetic procedure for various polyamines with high yield in order to prepare (15)N-labeled polyamines. On the basis of these methodological work, I searched for the inhibitor of spermidine synthase and found trans-4-methylcyclohexylamine (MCHA), the most effective one at the present time. I also developed a new analytical method for polyamines using stable isotope and ionspray ionization mass spectrometry (IS-MS). Based on these studies I examined the role of polyamines in liver regeneration and found that oral administration of MCHA effectively changed the concentration of polyamines and inhibited the hepatic growth. I also found the close relationship between the concentration ratio of spermidine to spermine and the extent of liver regeneration. These results may shed new light on the control of cell growth by polyamine in vivo.

Inhibition of putrescine aminopropyltransferase influences rat liver regeneration

A close relationship between rat liver regeneration and the concentration ratio of spermidine to spermine (spd:spm) was demonstrated by the oral administration of trans-4-methylcyclohexylamine (MCHA), a specific inhibitor of putrescine aminopropyltransferase. A decrease in recovery rate of remnant liver with MCHA, as a percentage index of remnant liver weight to body weight, correlated well with a decrease of the spd:spm value, with a correlation coefficient of 0.952 for the remnant livers on day 3 after partial hepatectomy. The decrease in recovery rate could be explained by a prolonged cell cycle based on the data of the proliferating cell nuclear antigen labelling index and mitotic cell index in both livers of day 2 and day 3 after partial hepatectomy. The results presented here will give a new aspect in the field of polyamine regulation to control cell growth in vivo.

Aminopropyltransferases: Function, Structure and Genetics

Aminopropyltransferases use decarboxylated S-adenosylmethionine as an aminopropyl donor and an amine acceptor to form polyamines. This review covers their structure, mechanism of action, inhibition, regulation and function. The best known aminopropyltransferases are spermidine synthase and spermine synthase but other members of this family including an N(1)-aminopropylagmatine synthase have been characterized. Spermidine synthase is an essential gene in eukaryotes and is very widely distributed. Key regions in the active site, which are very highly conserved, were identified by structural studies with spermidine synthase from Thermotoga maritima bound to S-adenosyl-1,8-diamino-3-thiooctane, a multisubstrate analog inhibitor. A general mechanism for catalysis by aminopropyltransferases can be proposed based on these studies. Spermine synthase is less widely distributed and is not essential for growth in yeast. However, Gy mice lacking spermine synthase have multiple symptoms including a profound growth retardation, sterility, deafness, neurological abnormalities and a propensity to sudden death, which can all be prevented by transgenic expression of spermine synthase. A large reduction in spermine synthase in human males due to a splice site variant causes Snyder-Robinson syndrome with mental retardation, hypotonia and skeletal abnormalities.