Mechanism of D-amphetamine inhibition of protein synthesis

Interplay Between Amphetamine and Activity Level in Gene Networks of the Mouse Striatum

The psychostimulant amphetamine can be prescribed to ameliorate the symptoms of narcolepsy, attention-deficit hyperactivity disorder and to facilitate weight loss. This stimulant can also have negative effects including toxicity and addiction risk. The impact of amphetamine on gene networks is partially understood and this study addresses this gap in consideration of the physical activity. The striata of mice exposed to either amphetamine or saline treatment were compared in a mouse line selected for home cage physical overactivity, a phenotype that can be mitigated with amphetamine, and in a contemporary control line using RNA-seq. Genes presenting opposite expression patterns between treatments across lines included a pseudogene of coiled-coil-helix-coiled-coil-helix domain containing 2 gene (Chchd2), ribonuclease P RNA component H1 (Rpph1), short stature homeobox 2 (Shox2), transient receptor potential melastatin 6 (Trpm6), and tumor necrosis factor receptor superfamily, member 9 (Tnfrsf9). Genes presenting consistent treatment patterns across lines, albeit at different levels of significance included cholecystokinin (Cck), vasoactive intestinal polypeptide (Vip), arginine vasopressin (Avp), oxytocin/neurophysin (Oxt), thyrotropin releasing hormone (Trh), neurotensin (Nts), angiotensinogen (Agt), galanin (Gal), prolactin receptor (Prlr), and calcitonin receptor (Calcr). Potassium inwardly rectifying channel, subfamily J, member 6 (Kcnj6), and retinoic acid-related (RAR)-related orphan receptor alpha (Rora) were similarly differentially expressed between treatments across lines. Functional categories enriched among the genes presenting line-dependent amphetamine effect included genes coding for neuropeptides and associated with memory and neuroplasticity and synaptic signaling, energy, and redox processes. A line-dependent association between amphetamine exposure and the synaptic signaling genes neurogranin (Nrgn) and synaptic membrane exocytosis 1(Rims1) was highlighted in the gene networks. Our findings advance the understanding of molecular players and networks affected by amphetamine in support of the development of activity-targeted therapies that may capitalize on the benefits of this psychostimulant.

Neurotoxic Doses of Chronic Methamphetamine Trigger Retrotransposition of the Identifier Element in Rat Dorsal Dentate Gyrus

Short interspersed elements (SINEs) are typically silenced by DNA hypermethylation in somatic cells, but can retrotranspose in proliferating cells during adult neurogenesis. Hypomethylation caused by disease pathology or genotoxic stress leads to genomic instability of SINEs. The goal of the present investigation was to determine whether neurotoxic doses of binge or chronic methamphetamine (METH) trigger retrotransposition of the identifier (ID) element, a member of the rat SINE family, in the dentate gyrus genomic DNA. Adult male Sprague-Dawley rats were treated with saline or high doses of binge or chronic METH and sacrificed at three different time points thereafter. DNA methylation analysis, immunohistochemistry and next-generation sequencing (NGS) were performed on the dorsal dentate gyrus samples. Binge METH triggered hypomethylation, while chronic METH triggered hypermethylation of the CpG-2 site. Both METH regimens were associated with increased intensities in poly(A)-binding protein 1 (PABP1, a SINE regulatory protein)-like immunohistochemical staining in the dentate gyrus. The amplification of several ID element sequences was significantly higher in the chronic METH group than in the control group a week after METH, and they mapped to genes coding for proteins regulating cell growth and proliferation, transcription, protein function as well as for a variety of transporters. The results suggest that chronic METH induces ID element retrotransposition in the dorsal dentate gyrus and may affect hippocampal neurogenesis.

Morphometric and neurosecretory changes in supraoptic neurons after D-amphetamine treatment

Several morphological and immunochemical characteristics of the neurosecretory neurons of the supraoptic nucleus (SON) have been studied of rats treated for 1 month with D-amphetamine sulfate (AMP) (8 mg/kg weight, daily). An increase of SON volume (11%) has been observed as a consequence of the growth of the dorsoventral axis. Neurosecretory neurons increased their nucleolar area (11.4%), their nuclear area (8.3%), and their cytoplasmatic area (18.3%). Vasopressin immunoreaction did not show any differences between treated and control animals, but oxytocin immunostaining displayed an important increase (23.7%) in the neuronal cytoplasm of the treated rats. The SON hypertrophy of the AMP-treated rats corresponded to the hypertrophy/hyperfunction of its oxytocinergic neurons, and could be considered as a new mechanism of the action of the AMP. The results are discussed in relation to the plastic features of the SON and its central (neuronal) and peripheral (hormonal) function.

Effects of amphetamine on protein synthesis and energy metabolism in mouse brain: role of drug-induced hyperthermia

Changes in brain protein synthesis activity, and in brain levels of glucose, glycogen, and several high-energy phosphate metabolites, were evaluated under conditions of amphetamine-induced hyperthermia in mice. Protein synthesis showed a striking dependence on rectal temperature (TR), falling abruptly at TR above 40 degrees C. A similar result was obtained following direct heating of the animals. Protein synthesis activity in liver showed the same temperature dependence observed for brain. Increased synthesis of a protein with characteristics of the major mammalian stress protein, hsp 70, was demonstrated in both brain and liver following amphetamine administration. Brain protein synthesis showed significant recovery within 2 h after amphetamine administration whereas that of liver remained below 30% of control activity, suggesting significant temporal and quantitative differences in the response of individual tissues to elevated temperatures. Brain glycogen levels after amphetamine administration were significantly lower under conditions of ambient temperature which resulted in more severe drug-induced hyperthermia but did not correlate as strikingly as protein synthesis with the temperatures of individual animals. Brain glycogen also fell in animals whose temperatures were increased by brief exposure at high ambient temperature. Brain glucose levels did not consistently change with hyperthermia. Slight decreases in high-energy phosphates with increasing TR were likely the result of fixation artifact. These results demonstrate the fundamental role of hyperthermia in the reduction of protein synthesis in brain and other tissues by amphetamine, and suggest that temperature also constitutes a significant source of variability in the effects of this drug on brain energy metabolism, in particular glycogenolysis.

Inhibition of rat brain and liver protein synthesis by amphetamine

Dose-dependent, amphetamine-induced reductions in protein synthesis were determined in vivo by measuring [3H]lysine incorporation into trichloroacetic acid precipitated protein in homogenates prepared from different regions of the brain or liver. Low-to-moderate doses of amphetamine (1-5 mg/kg) decreased striatal protein synthesis whereas higher doses (10 mg/kg) reduced it in the cerebral cortices, cerebellum, and remaining portions of the cerebrum, as well as in the striatum and liver. Reductions in regional brain protein synthesis occur following amphetamine treatment in relatively low doses known to change various aspects of physiology and behavior.

Inhibition of aminoacyl-tRNA synthetases by p-chloroamphetamine and its role in protein synthesis inhibition

p-Chloroamphetamine inhibited to some degree all amino acid-dependent pyrophosphate-exchange activities which could be detected in a rabbit reticulocyte extract. A detailed kinetic analysis of the reaction catalyzed by reticulocyte leucyl-tRNA synthetase demonstrated that the inhibitor affected only amino acid binding. Less rigorous studies of other synthetases from both rabbit reticulocyte and Escherichia coli could be similarly interpreted, suggesting that this compound interacts in a common manner with these several enzymes. The contribution of such effects to the inhibition of protein synthesis by the drug was investigated using cell-free translation systems in which rates of amino acid incorporation were limited to varying degrees by the synthesis and availability of aminoacyl-tRNA. In a wheat germ system programmed with globin mRNA, in which levels of amino acids and aminoacyl-tRNAs were shown to limit the rate of protein synthesis, the inhibition produced by p-chloroamphetamine could be partially reversed by increasing the concentration of the limiting amino acid. In a reticulocyte lysate, in which amino acid concentrations were not limiting, inhibition failed to show an amino acid-reversible component. Thus, while the inhibition of aminoacyl-tRNA synthetases by amphetamines can be shown in some cases to play a role in the effects of these compounds on in vitro protein synthesis, other sites of interference with initiation and/or elongation reactions may predominate, depending on the construction of the system under study.

Influence of drugs on macromolecular synthesis during cell synchronization

A cell culture system has been used to examine the effect of various pharmacologic agents on DNA synthesis with the hope of utilizing this system for the evaluation of drugs at the cellular level. Glucocorticoids have been shown to have a differential effect on growth dependent on the cell type studied. For this reason steroidal anti-inflammatory agents were chosen to study in our culture system. Aspirin, a non-steroidal anti-inflammatory agent, was also studied for a comparison with glucocorticoids. The CNS stimulants, caffeine and amphetamines, were studied for their effects on non-target cells in culture and compared with the response of target cells. Doxorubicin, an anti-neoplastic agent, has been shown to depress growth in a variety of cells. This drug was also studied in our culture system. We have found that steroidal anti-inflammatory drugs induced a dose-dependent stimulation of DNA synthesis in normal human fibroblasts that was also age-dependent, while decreasing DNA synthesis in SV40 virus transformed cells. Aspirin (25 micrograms/ml) exhibited a similar response. Human fibroblasts were found to be responsive to the CNS stimulants, exhibiting a dose-dependent decrease in DNA synthesis when exposed to caffeine. Amphetamine (200 microM) depressed DNA synthesis in normal fibroblasts and increased it in SV40 virus transformed cells. All cells studied exhibited a depression of DNA synthesis when treated with doxorubicin (0.1 microgram/ml).

The regulation of protein synthesis in heart muscle under normal conditions and in the adriamycin-cardiomyopathy

The regulation of cardiac protein synthesis, in particular messenger-RNA (mRNA) and polyribosome metabolism, has been investigated in normal rat heart muscle and in the adriamycin-cardiomyopathy by using newly developed methods for the isolation, characterization and in-vitro translation of cardiac polyribosomes and mRNA. The obtained data allow the following conclusions: 1. Normal heart muscle has a high content of polyribosomes (865 micrograms/g) and of mRNA (20-60 micrograms/g), and thus a high rate of protein synthesis. 2. The level of cardiac polyribosomes and mRNA is strictly age-dependent and much higher in young animals (2-3 x). This corresponds to a higher cardiac protein synthesis rate in young animals with a growing heart muscle, and shows that the protein-synthetic reserves of heart muscle decrease sharply with age. 3. Withdrawal of food for 1-3 days results in a pronounced decrease (-50% to -70%) of cardiac polyribosomes and mRNA, demonstrating that the cardiac protein synthesis reacts very sensitively to conditions of starving. 4. The cardiac polyribosomes and mRNA are unevenly distributed in the myocyte. The bulk of these substances is present in the cardiac microsomes, and much less is found in nuclei, myofibrils, mitochondria and in the post-microsomal fraction (=cell-sap) of the cardiac muscle. This shows that the major intracellular site of cardiac protein synthesis is the microsomal fraction of the myocyte. 5. A pool of untranslated mRNA was demonstrated to be present in the cell-sap of the myocyte. This mRNA is to some extent translatable in-vitro and appears to represent mRNA sub-pools with two functions: a) mRNA which is partially broken down or in the process of being broken down, and b) intact mRNA which could have a "reserve-function", e.g., by being utilized to increase cardiac protein synthesis under certain conditions. 6. A method of quantitating small amounts of cardiac mRNA (25-50 ng) has been developed which makes it possible to estimate the mRNA content of cardiac biopsies. 7. These methods were utilized to study the relevance of changes in RNA- and protein synthesis in the development of the adriamycin-cardiomyopathy. It appears that severe decreases in cardiac mRNA and polyribosome levels are a key factor in the pathogenesis of the adriamycin-cardiomyopathy. These decreases are probably caused by the direct binding of adriamycin to cardiac DNA and lead themselves to a persisting decrease in cardiac protein synthesis which in view of the short half-lives of the cardiac contractile proteins (5-12 days) causes a gradual loss of cardiac structure and function.

Comparison of the effect of intravenous administration of d-lysergic acid diethylamide on free and membrane-bound polysomes in the rabbit brain

The intravenous administration of LSD to young adult rabbits resulted in the disaggregation of both free and membrane-bound classes of brain polysomes. Based on the analysis of LSD dosage and the time course of the LSD-induced brain polysome shift, it was found that free polysomes were more sensitive to the drug than the membrane-bound polysome fraction. LSD-induced hyperthermia may be involved in the disaggregation of free and membrane-bound polysomes, since a correlation was found between the extent of LSD-induced hyperthermia and the degree of brain polysome shift. Prevention of LSD-induced hyperthermia by maintaining the animal at 4 degrees C blocked the disaggregation of both polysome classes. Induction of hyperthermia by elevation of ambient temperature also resulted in a shift in free and membrane-bound polysomes. In all cases the disaggregation of polysomes to monosomes was not caused by RNase activation. During polysome disaggregation, polyadenylated mRNA associated with both free and membrane-bound polysomes was not degraded but was relocalized from polysomes to monosomes.

Polysome-dependent in vitro translation system capable of peptide chain reinitiation

A sensitive in vitro translation system has been developed which makes use of cellular polysomes as the source of mRNA and ribosomes. The soluble factors are derived from the preincubated S-30 fraction by centrifugation through a discontinuous sucrose gradient. Of the four fractions tested, fraction 1 (topmost fraction in the gradient) and fraction 2 (fraction sedimenting in 0.5 M sucrose) were stimulatory. These two fractions together yield the highest activity, corresponding to about 125 times the background incorporation. The polysome-directed system exhibits optimal activity in the range 1.8-2 mM Mg2+ and 125-175 mM KCl. The polysome-directed in vitro products exhibit a complexity comparable to the in vivo products resolved on the two-dimensional polyacrylamide gels of O'Farrell [O'Farrell, P. (1975) J. Biol. Chem. 250, 4007-4021]. The system is capable of active chain reinitiation as indicated by partial inhibition by 7-methylguanosine 5'-monophosphate and pactomycin and N-terminal end analysis of in vitro products. This system can also translate polysomes from diverse tissues such as mouse liver, rat liver, and rat brain. The levels and also the authenticity of translation of rat liver albumin and mouse liver carbamoyl phosphate synthetase I were tested by immunoprecipitation with monospecific antibodies. The results show that the major as well as the minor translation products are synthesized in this system at levels comparable to the physiological levels.

Fate of mRNA following disaggregation of brain polysomes after administration of (+)-lysergic acid diethylamide in vivo

Intravenous injection of (+)-lysergic acid diethylamide into young rabbits induced a transient brain-specific disaggregation of polysomes to monosomes. Investigation of the fate of mRNA revealed that brain poly(A+)mRNA was conserved. In particular, mRNA coding for brain-specific S100 protein was not degraded, nor was it released into free ribonucleoprotein particles. Following the (+)-lysergic acid diethylamide-induced disaggregation of polysomes, mRNA shifted from polysomes and accumulated on monosomes. Formation of a blocked monosome complex, which contained intact mRNA and 40-S plus 60-S ribosomal subunits but lacked nascent peptide chains, suggested that (+)-lysergic acid diethylamide inhibited brain protein synthesis at a specific stage of late initiation or early elongation.

Protein synthesis in rat brain in hypoxia, anoxia and hypoglycemia

The effect of cerebral hypoxia on protein synthesis was investigated by exposing rats to 5% O2, and examining polypeptide synthesis and size distribution profiles of ribosomes. The findings were compared with the results from cerebral anoxia (decapitation) and hypoglycemia. In cerebral hypoxia there was suppression of polypeptide synthesis, though to a lesser extent than in cerebral anoxia, while no effect was detected in hypoglycemia. Among 4 different ribosomal fractions used for polypeptide synthesis, the microsome was the most sensitive for hypoxia and anoxia, and the polyribosome after short centrifugation was the least sensitive. The size distribution profiles of 3 different ribosomes revealed an increase in the size of the monomere-dimer complex and a decrease of the polysome peak both in cerebral hypoxia and anoxia. Comparison of the energy state and the extent of lactic acidosis in cerebral hypoxia, anoxia and hypoglycemia available in the literature and the functional and structural state of polyribosomes in the present investigation suggests that intracellular acidosis may be the main cause of the suppression of polypeptide synthesis and disaggregation of polyribosomes in hypoxia, and the depletion of energy reserve may be the main cause in anoxia-ischemia.

Structure-activity relationships among the halogenated amphetamines

p-Chloroamphetamine and various analogs influence brain serotonin neurons through multiple actions. Comparison of these compounds has permitted the distinction between short-term and long-term depletion of serotonin and among inhibition of tryptophan hydroxylation, release of serotonin, inhibition of serotonin reuptake, and inhibition of monoamine oxidase as mechanisms involved in the actions of these agents on serotonin neurons.