Paradoxical influence of combined effect of Semax and ammonium molybdate on learning and memory in rats

The combined effect of Semax with water solutions of plumbum diacetate (10^–7 M) and ammonium molybdate (10^–5 M) on the two-way active avoidance learning in rats in the shuttle chamber was studied. It was established that both salts of heavy metals oppress the learning and memory; plumbum diacetate caused larger oppression. Semax slowed down the development of the conditioned response but counteracted the negative influence on this process from the side of both metals. The effect of Semax on the development of the avoidance reaction in the presence of ammonium molybdate, which oppressed the avoidance by itself, paradoxically intensified. During the combined effect of the peptide and ammonium molybdate, the development of the conditioned reaction occurred much faster than against the background of Semax without the combination with molybdenum. In total, data obtained indicate a counteraction of Semax to neurotoxic effect of plumbum and molybdenum salts. Since oxidative stress is the main mechanism of neurotoxic effect of heavy metals, the indicated positive effect of Semax can, in our opinion, confirm the presence of antioxidant properties in the spectrum of the peptide pharmacological activity.     

Nootropic and analgesic effects of Semax following different routes of administration

Heptapeptide Semax (MEHFPGP) is the fragment of ACTH(4-10) analogue with prolonged neurotropic activity. The aim of the present work was to study the Semax effects on learning capability and pain sensitivity in white rats following intraperitoneal and intranasal administration in different doses. Semax nootropic effects were studied in the test of acquisition of passive avoidance task. Pain sensitivity was estimated in Randall-Selitto paw-withdrawal test. It was shown that Semax exerts nootropic and analgesic activities following intraperitoneal administration. Analysis of dependence of these effects on dose resulted in different dose-response curves. Following intranasal administration, Semax was more potent in learning improvement compared to intraperitoneal administration. The peptide failed to affect the animal pain sensitivity following intranasal administration as opposed to intraperitoneal administration. The data obtained suggest different mechanisms and brain structures involved in realization of the nootropic and analgesic effects of Semax.     

Long-lasting behavioral effects of chronic neonatal treatment with ACTH (4-10) analogue semax in white rat pups

It is well known that ACTH/MSH-like peptides (melanocortins) have neurotrophic and neuroprotective effects on the central and peripheral nervous systems in the early postnatal life. The aim of present work was to study consequences of the ACTH (4-10) analogue Semax influence on the developing brain. The work was carried out in white rat pups. The peptide (0.05 mg/kg, i/p) was injected daily on the 8th-21st postnatal days. Delayed long-lasting effects of such treatment on animal behavior were revealed. At the age of four to eight weeks, Semax-treated rats displayed elevated exploratory activity, decreased anxiety level and improved passive avoidance conditioning. The results suggest that neonatal Semax administration modulates the development of the central nervous system.     

Semax,An ACTH(4-10) Analogue with Nootropic Properties,Activates Dopaminergic and Serotoninergic Brain Systems in Rodents

Corticotrophin (ACTH) and its analogues, particularly Semax (Met-Glu-His-Phe-Pro-Gly-Pro), demonstrate nootropic activity. Close functional and anatomical links have been established between melanocortinergic and monoaminergic brain systems. The aim of present work was to investigate the effects of Semax on neurochemical parameters of dopaminergic- and serotonergic systems in rodents. The tissue content of 5-hydroxyindoleacetic acid (5-HIAA) in the striatum was significantly increased (+25%) 2 h after Semax administration. The extracellular striatal level of 5-HIAA gradually increased up to 180% within 1–4 h after Semax (0.15 mg/kg, ip) administration. This peptide alone failed to alter the tissue and extracellular concentrations of dopamine and its metabolites. Semax injected 20 min prior d-amphetamine dramatically enhanced the effects of the latter on the extracellular level of dopamine and on the locomotor activity of animals. Our results reveal the positive modulatory effect of Semax on the striatal serotonergic system and the ability of Semax to enhance both the striatal release of dopamine and locomotor behavior elicited by d-amphetamine. Special issue dedicated to Dr. Simo S. Oja.     

Effects of chronic Semax administration on exploratory activity and emotional reaction in white rats

Effects of chronic intranasal administration of ACTH(4-10) analog Semax (MEHFPGP) on exploratory activity, anxiety level, and depression-like behaviour were studied in white rats. The peptide was injected daily in dose 0.05 mg/kg during 10 or 14 days. It was shown that chronic Semax administration at 1-2 weeks induced anxiolytic and antidepressant effects but did not influenced the exploratory activity in non-stressogenic environment. The Semax effects may be the results of activation of the brain serotoninergic system as well as increased BDNF expression in the rat hippocampus.     

Synacton and individual activity of synthetic and natural corticotropins

Short endogenous peptides represent one of the most important constituents of the mammalian body's general regulatory system. Some synthesized analogs and modified natural peptides (eg, corticotropins) also show high biological activity. Nevertheless, the mechanism of action of regulatory peptides remains unclear. To explain the effects of peptides of intermolecular processes, the hypothesis that a synactonal mechanism underlies the action of regulatory peptides, exemplified by the heptapeptide Semax, has been proposed. Thus, in the total pool of Semax metabolites, which includes the cleavage products of the parental molecule, we can distinguish the functional core, represented by the major metabolic products—peptides HFPGP and PGP. These peptides have their own binding sites with similar although differing characteristics. Together with Semax, they constitute a single complex of bioregulators acting in a certain sequence and in interaction, ie, synacton. It can be assumed that the diverse clinically significant effects of the drug Semax are determined by its synacton. Specific interactions between some tritium‐labeled peptides (basic constituents of the Semax synacton) and plasma membranes of neurons have been characterized. Only a few peptides of the Semax synacton showed competitive activity for the Semax binding sites. Fragments comprising 5 amino acid residues (EHFPG and HFPGP) showed the highest competitive activity. We also characterized the processes of specific ligand‐receptor interactions of some tritium‐labeled corticotropins ([³H‐Pro]MEHFPGP, [³H‐Pro]HFPGP, and [³H‐Pro]PGP) by applying mathematical discriminative models (Scatchard, Hill, Bjerrum, and Lineweaver‐Burk plots). So the intermolecular interactions of these peptides with plasma membranes of neuronal brain targets are probably not limited by specific binding at orthosteric sites. The effect of peptides that act in the synacton considerably extends the regulatory potential of the initial molecule.     

Kinetics of semax penetration into the brain and blood of rats after its intranasal administration

The radioactive petide analogue Semax corresponding to the ACTH(4–10) sequence (Met-Glu-His-Phe-Pro-Gly-Pro) with a specific radioactivity of 56 Ci/mmol labeled with tritium at the C-terminal Pro was prepared. The labeled peptide was used for studying the kinetics of Semax penetration into rat brain and blood after its intranasal administration (50 μg/kg, 20 μl of solution) to nonbred white rats of body mass 200–250 g. It was demonstrated that 0.093% of the total introduced radioactivity per gram can be found in the rat brain 2 min after the administration, 80% of this radioactivity belonged to Semax, and the rest, to its metabolites. The peptide undergoes rapid enzymatic degradation, with the tripeptide Pro-Gly-Pro prevailing in biological samples relative to the total content of Semax and its metabolites.     

Kinetics of Semax penetration into the brain and blood of rats after its intranasal administration

The radioactive peptide analogue Semax corresponding to the ACTH(4-10) sequence (Met-Glu-His-Phe-Pro-Gly-Pro) with a molar radioactivity of 56 Ci/mmol labeled with tritium at the C-terminal Pro was prepared. The labeled peptide was used for studying the kinetics of Semax penetration into rat brain and blood after its intranasal administration (50 microg/kg, 20 microl of solution) to nonbred white rats of body mass 200-250 g. It was demonstrated that 0.093% of the total introduced radioactivity per gram can be found in the rat brain 2 min after the administration, 80% of this radioactivity belonged to Semax, and the rest, to its metabolites. The peptide undergoes rapid enzymatic degradation, with the tripeptide Pro-Gly-Pro prevailing in biological samples relative to the total content of Semax and its metabolites.     

Effect of peptide Semax and its C-terminal fragment PGP on Vegfa gene expression during incomplete global cerebral ischemia in rats

Vascular endothelial growth factor (VEGF-A) is hypoxia-inducible signal glycoprotein. VEGF-A induces vascular endothelial cell proliferation, which leads to the reconstitution of the vascular network in brain regions damaged by ischemia. However, this protein is also involved in the processes of inflammation and edema in early stages of ischemia. The synthetic peptide Semax has neuroprotective and anti-inflammatory properties and is actively used in the treatment of cerebral ischemia. We have previously shown that Semax reduces vascular injury and activates the mRNA synthesis of neurotrophins and their receptors during global cerebral ischemia in rats. In this work, we studied the effect of Semax and its C-terminal Pro-Gly-Pro tripeptide on Vegfa mRNA expression in different regions of the rat brain after 0.5, 1, 2, 4, 8, 12 and 24 h, which is the irreversible occlusion of the common carotid arteries. It was shown that ischemia increases the levels of Vegfa mRNA in rat brains (4 h after occlusion in cerebellum, cerebral cortex, and hippocampus; 8 h after occlusion in the cortex and hippocampus; and 24 h after occlusion in the cortex). Treatment with Semax reduces the levels of Vegfa mRNA in the frontal cortex (4, 8 and 12 h after occlusion) and the hippocampus (2 and 4 h after occlusion). The effect of PGP on the Vegfa gene expression was almost negligible. It was shown that Semax prevents the activating effect of hypoxia on the expression of the Vegfa gene at early stages of global cerebral ischemia. In turn, an increase in the level of Vegfa mRNA in the hippocampus 24 h after occlusion and Semax administration apparently reflects the neuroprotective properties of the drug.     

In vitro oxidation of ascorbic acid and its prevention by GSH

The interaction of glutathione (GSH) with ascorbic acid and dehydroascorbic acid was examined in in-vitro experiments in order to examine the role of GSH in protecting against the autoxidation of ascorbic acid and in regenerating ascorbic acid by reaction with dehydroascorbic acid. If a buffered solution (pH 7.4) containing 1.0 mM ascorbic acid was incubated at 37 degrees C, there was a rapid loss of ascorbic acid in the presence of oxygen. When GSH was added to this solution, ascorbic acid did not disappear. Maximum protection against ascorbic acid autoxidation was achieved with as little as 0.1 mM GSH. Cupric ions (0.01 mM) greatly accelerated the rate of autoxidation of ascorbic acid, an effect that was inhibited by 0.1 mM GSH. Other experiments showed that GSH complexes with cupric ions, resulting in in a lowering of the amount of GSH in solution as measured in GSH standard curves. These results suggest that the inhibition of ascorbic acid autoxidation by GSH involves complexation with cupric ions that catalyze the reaction. When ascorbic acid was allowed to autoxidize at 37 degrees C the subsequent addition of GSH (up to 10 mM) did not lead to the regeneration of ascorbic acid. This failure to detect a direct reaction between GSH and the dehydroascorbic acid formed by oxidation of ascorbic acid under this condition was presumably due to the rapid hydrolysis of dehydroascorbic acid. When conditions were chosen, i.e., low temperature, that promote stability of dehydroascorbic acid, the direct reaction between GSH and dehydroascorbic acid to form ascorbic acid was readily detected. The marked instability of dehydroascorbic acid at 37 degrees C raises questions regarding the efficiency of the redox couple between GSH and dehydroascorbic acid in maintaining the concentration of ascorbic acid in mammalian cells exposed to an oxidative challenge.     

Effect of exogenous ascorbic acid intake on biosynthesis of ascorbic acid in mice

The effect of exogenous ascorbic acid intake on biosynthesis of ascorbic acid in mice has been studied. After the mice were on diets containing added ascorbic acid for two months, the activities of ascorbic acid synthesizing enzymes in the mouse liver homogenates were measured using L-gulono-gamma-lactone as a substrate. Exogenous ascorbic acid intake (0.5, 1 or 5% in the diet) was able to increase the concentration of ascorbic acid in the blood and to decrease the activities of ascorbic acid synthesizing enzymes in mouse liver. The results suggest that ascorbic acid synthesis was controlled by local regulatory mechanism or by the concentration of ascorbic acid in the hepatic portal blood. Ingestion of dietary erythorbic acid, a stereoisomer of ascorbic acid, had no effect on the activities of ascorbic acid synthesizing enzymes.     

Influence of semax on the emotional state of white rats in the norm and against the background of cholecystokinin-tetrapeptide action

The effects of the adrenocorticotropic hormone (ACTH(4–10)) analog, Semax (MEHFPGP), on the level of anxiety and depression in white rats have been studied in the normal state and against the back-ground of cholecystokinin-tetrapeptide (CCK-4) action. Semax was injected intranasally in doses of 50 and 500 μg/kg 15 min before the testing. CCK-4 was administered intraperitoneally in a dose of 400 μg/kg 40 min before the testing. The level of anxiety was estimated in the elevated plus-maze test, and the degree of depression, in the forced swimming test. Semax administration did not influence the emotional state of animals in the normal state. The CCK-4 injection led to an increase in anxiety and depression in rats. Semax normalized the animal behavior disturbed by the CCK-4 administration, which attests to its anxiolytic and antidepressant effects at elevated levels of anxiety and depression.     

Neuroprotective effects of semax in MPTP-induced disturbances of brain dopamine system

Effects of an ACTH (4-10) analogue Semax (MEHFPGP) on behaviour of white rats with MPTP-induced disturbances of brain DA-system have been studied. It was shown that MPTP administration (25 mg/kg) reduced motor activity and auhmented the anxiety level in rats. Semax administration (daily intranasal 0.2 mg/kg) attenuated behaviour disturbances induced by neurotoxin. The observed protective action of Semax in rats with MFTP-induced DA system disturbances may be due to both its modulating influence on the brain DA system and peptide neuroprotective effects.     

The comparison of gastroprotective properties of Semax and its metabolites

Semax (MEHFPGP) was shown to increase gastric mucosal homeostasis to the action of such ulcerogenic factors as ethanol and stress. In the case of the stress model of ulcer formation, Semax and its two metabolites—HFPGP and FPGP—at the wide range of doses (0.06–3.7 μmol/kg) have demonstrated protective antiulcerogenic properties. In the case of ethanol model of ulcer formation, only Semax in two used doses (0.06 and 0.37 μmol/kg) reported reliable protective antiulcerogenic property. It was supposed that Semax’s gastroprotective activity directed to peripheral mechanisms of ulcerogenesis did not depend on its metabolites’ activities. On the contrary, Semax’s gastroprotective activity directed to the central mechanisms of ulcerogenesis might be also caused by gastroprotective activities of HFPGP and FPGP metabolites.     

The Protective Effect of Semax in a Model of Stress-Induced Impairment of Memory and Behavior in White Rats

The effect of acute restrained stress on cognitive functions and anxiety-like behavior in white rats has been studied; furthermore, the influence of the fragment ACTH(4–10) analog Semax on the stress effects was evaluated. It was shown that stress exposure leads to impaired retention of previously acquired food-motivated maze task as well as reduced anxiety-like behavior in the elevated plus maze in rats. Preliminary intraperitonial administration of Semax (0.1 mg/kg) attenuates cognitive impairment caused by acute restrained stress, but it does not affect stress-induced changes in anxiety.     

The binding of Semax, ACTH 4-10 heptapeptide, to plasma membranes of the rat forebrain basal nuclei and its biodegradation

The binding characteristics of the peptide Semax (Met-Glu-His-Phe-Pro-Gly-Pro) to plasma membranes of basal nuclei of the rat forebrain and the dynamics of its degradation during its incubation with these membranes were studied. Binding of the homogeneously labeled [G-3H]Semax was shown to be time-dependent, specific, and reversible. Specific binding of the heptapeptide depended on calcium ions and was characterized by the dissociation constant of the ligand-receptor complex Kd = 2.41 +/- 1.02 x 10(-9) M and by the concentration of binding sites Bmax = 33.5 +/- 7.9 x 10(-15) mol/mg of protein. A method of studying Semax biodegradation in the presence of plasma membranes of rat brain was developed. It is based on the use of the peptide homogeneously labeled with tritium and on an HPLC analysis with UV detection at 220 and 254 nm of the peptide fragments formed. The half-life of Semax in the presence of the plasma membranes was demonstrated to be longer than 1 h. Dipeptidylaminopeptidases are considered to be the main enzymes responsible for its biodegradation; they successively cleave Semax to the HFPGP pentapeptide and the PGP tripeptide. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 3; see also http://www.maik.ru.     

Gene c-Fos expression in brain of rats resistant and predisposed to emotional stress after intraperitoneal injection of the ACTH(4-10)analog--semax

The effect of the ACTH(4-10) analog Semax on immediate early gene c-Fos expression was studied in Wistar rats with high and low resistance to emotional stress under the usual conditions and during psychoemotional loading. Fos-immunoreactive cells in the were counted automatically with the help of a computer. It was shown that under the usual conditions the intraperitoneal Semax injection induced immediate early gene c-Fos expression in the lateral septal region in rats predisposed to emotional stress and in the paraventricular hypothalamus in rats of both groups. Preliminary Semax injection decreased the stress-induced c-Fos expression in the paraventricular hypothalamus and medial septum in rats predisposed to emotional stress and tended to reduce the number of stress-induced c-Fos-immunopositive cells in the lateral septum and basolateral amygdala in both groups of animals. The obtained data suggest that Semax differently affects the immediate early c-Fos gene expression in the brain of rats resistant and predisposed to emotional stress and this effect reflects the antistressor properties of the regulatory peptide.     

The Binding of Semax, ACTH 4–10 Heptapeptide, to Plasma Membranes of the Rat Forebrain Basal Nuclei and Its Biodegradation

The binding characteristics of the peptide Semax (Met-Glu-His-Phe-Pro-Gly-Pro) to plasma membranes of basal nuclei of the rat forebrain and the dynamics of its degradation during its incubation with these membranes were studied. Binding of the homogeneously labeled [G-³H]Semax was shown to be time-dependent, specific, and reversible. Specific binding of the heptapeptide depended on calcium ions and was characterized by the dissociation constant of the ligand–receptor complex K _d 2.41 ± 1.02 × 10^–9 M and by the concentration of binding sites B _max 33.5 ± 7.9 × 10^–15 mol/mg of protein. A method of studying Semax biodegradation in the presence of plasma membranes of rat brain was developed. It is based on the use of the peptide homogeneously labeled with tritium and on an HPLC analysis with UV detection at 220 and 254 nm of the peptide fragments formed. The half-life of Semax in the presence of the plasma membranes was demonstrated to be longer than 1 h. Dipeptidylaminopeptidases are considered to be the main enzymes responsible for its biodegradation; they successively cleave Semax to the HFPGP pentapeptide and the PGP tripeptide.