GABA-containing compound gammapyrone protects against brain impairments in Alzheimer's disease model male rats and prevents mitochondrial dysfunction in cell culture

Neuroinflammation, oxidative stress, decreased glucose/energy metabolism, and disrupted neurotransmission are changes that occur early in sporadic Alzheimer's disease (AD), manifesting as mild cognitive impairment. Recently, the imbalanced function of the gamma-aminobutyric acid (GABA) system was identified as a critical factor in AD progression. Thus, maintaining balance among neurotransmitter systems, particularly the GABA system, can be considered a beneficial strategy to slow AD progression. The present study investigated the effects of the compound gammapyrone, a molecule containing three GABA moieties: "free" moiety attached to the position 4 of the 1,4-dihydropyridine (DHP) ring, and two "crypto" moieties as part of the DHP scaffold. The "free" and "crypto" GABA moieties are linked by a peptide bond (-CONH-), resulting in a peptide-mimicking structure. In a nontransgenic male rat AD model generated by intracerebroventricular (icv) streptozocin (STZ) administration, gammapyrone (0.1 and 0.5 mg/kg ip) mitigated the impairment of spatial learning and memory, prevented astroglial and microglial neuroinflammation, and normalized acetylcholine breakdown and GABA biosynthesis. In PC12 cells, gammapyrone protected against oxidative stress, mitochondrial dysfunction and apoptosis caused by the mitochondrial toxin di-2-ethylhexyl phthalate (DEHP). Gammapyrone did not bind to GABA-A and GABA-B receptors in vitro; therefore, we cannot attribute its neuroprotective action to a specific interaction with GABA receptors. Nevertheless, we suggest that the peptide-like regulatory mechanisms of gammapyrone or its allosteric modulatory properties are essential for the observed effects. Since, the icv STZ model resembles the early stages of AD, gammapyrone, and/or its congeners could be useful in the design of anti-dementia drugs.

Very low doses of muscimol and baclofen ameliorate cognitive deficits and regulate protein expression in the brain of a rat model of streptozocin-induced Alzheimer's disease

Recent studies devoted to neuroprotection have focused on the role of the gamma-aminobutyric acid (GABA) system in regulating neuroinflammatory processes which play a key role in the neurodegenerative processes observed in Alzheimer's disease (AD) by inducing glial cell overactivation and impairing neurotransmission. Data on the efficacy of classical GABA-A and GABA-B receptor agonists (muscimol and baclofen, respectively) in animal models of AD are not available. Moreover, no published studies have examined the ability of optimal doses of these compounds to prevent neuroinflammation, the alterations in neurotransmission and cognitive deficits. In the present study, we used a non-transgenic rat model of AD obtained by intracerebroventricular streptozocin (STZ) injection and assessed the effects of muscimol and baclofen at very low doses (0.01-0.05mg/kg) on spatial memory and the expression of cortical and hippocampal proteins related to neuroinflammation, namely proteins involved in astroglial functions (glial fibrillary acidic protein, GFAP), GABA synthesis (GABA synthesizing enzyme, glutamic acid decarboxylase 67, GAD67) and acetylcholine degradation (acetylcholine esterase). The presented study demonstrated that in a rat model of STZ-induced AD both muscimol and baclofen at the tested doses exerted memory-enhancing and anti-inflammatory effects, as well as normalization of acetylcholine esterase and GABA expression. We suggested that the function of very low doses of GABA receptor agonists differs from typical GABA-related inhibition and may be mediated by the allosteric sites of GABA receptors or other non-specific cell regulatory pathways.

Memory-enhancing and brain protein expression-stimulating effects of novel calcium antagonist in Alzheimer's disease transgenic female mice

The prevalence of Alzheimer's disease (AD) is higher in females than in males, and causes more severe cognitive, memory and behavioral impairments. Previously, in male transgenic (Tg) APPSweDI mice, we reported that the novel lipophilic 1,4-dihydropyridine (DHP) derivative AP-12 crossed the blood-brain barrier, blocked neuronal and vascular calcium channels, changed brain protein expression and improved behavior. In this study, we used female Tg APPSweDI mice to assess the effects of AP-12 on behavior, and brain protein expression, with a particular focus on those of the GABAergic system. The results showed that in female Tg mice, similar to male Tg mice, AP-12 improved spatial learning/memory performance in the water maze test and demonstrated anxiolytic effect in the elevated zero maze (after single administration of AP-12) and elevated plus maze (after chronic injections of AP-12). In addition, we demonstrated upregulated expression of glutamate decarboxylase 67 (GAD67) and vesicular GABA transporter (VGAT) in the cingulate cortex and hippocampus, pointing to the role of the GABAergic system as one of the neural networks dysregulated in AD. In both female and male mice, AP-12 did not change the expression of hippocampal Homer-1, a protein which is involved in synaptic plasticity. However, in cingulate cortex, the staining density of Homer-1 was significantly increased in female mice. Further, female mice (similar to male mice) did not show changes in brain AChE expression and in the amyloid beta load in the hippocampus and cingulate cortex. In conclusion, the memory enhancing, anxiolytic and protein expression effects of AP-12 did not show sex specificity in APPSweDI mice. Considering the ability of AP-12 to block brain calcium channels and improve memory by enhancing the GABAergic and synaptic plasticity processes, AP-12 is a promising compound which merits further pre-clinical studies to investigate its usefulness in the treatment of AD.

A Novel 1,4-Dihydropyridine Derivative Improves Spatial Learning and Memory and Modifies Brain Protein Expression in Wild Type and Transgenic APPSweDI Mice

Ca²⁺ blockers, particularly those capable of crossing the blood-brain barrier (BBB), have been suggested as a possible treatment or disease modifying agents for neurodegenerative disorders, e.g., Alzheimer’s disease. The present study investigated the effects of a novel 4-(N-dodecyl) pyridinium group-containing 1,4-dihydropyridine derivative (AP-12) on cognition and synaptic protein expression in the brain. Treatment of AP-12 was investigated in wild type C57BL/6J mice and transgenic Alzheimer’s disease model mice (Tg APP_SweDI) using behavioral tests and immunohistochemistry, as well as mass spectrometry to assess the blood-brain barrier (BBB) penetration. The data demonstrated the ability of AP-12 to cross the BBB, improve spatial learning and memory in both mice strains, induce anxiolytic action in transgenic mice, and increase expression of hippocampal and cortical proteins (GAD67, Homer-1) related to synaptic plasticity. The compound AP-12 can be seen as a prototype molecule for use in the design of novel drugs useful to halt progression of clinical symptoms (more specifically, anxiety and decline in memory) of neurodegenerative diseases, particularly Alzheimer’s disease.

Mildronate improves cognition and reduces amyloid-β pathology in transgenic Alzheimer's disease mice

Mildronate, a carnitine congener drug, previously has been shown to provide neuroprotection in an azidothymidine-induced mouse model of neurotoxicity and in a Parkinson's disease rat model. The aim of this study was to investigate the effects of mildronate treatment on cognition and pathology in Alzheimer's disease (AD) model mice (APP(SweDI)). Mildronate was administered i.p. daily at 50 or 100 mg/kg for 28 days. At the end of treatment, the animals were behaviorally and cognitively tested, and brains were assessed for AD-related pathology, inflammation, synaptic markers, and acetylcholinesterase (AChE). The data show that mildronate treatment significantly improved animal performance in water maze and social recognition tests, lowered amyloid-β deposition in the hippocampus, increased expression of the microglia marker Iba-1, and decreased AChE staining, although it did not alter expression of proteins involved in synaptic plasticity (GAP-43, synaptophysin, and GAD67). Taken together, these findings indicate mildronate's ability to improve cognition and reduce amyloid-β pathology in a mouse model of AD and its possible therapeutic utility as a disease-modifying drug in AD patients.

Lunasin-induced behavioural effects in mice: focus on the dopaminergic system

The present study for the first time is devoted to identify central effects of synthetic lunasin, a 43 amino acid peptide. A markedly expressed neuroleptic/cataleptic effect was observed at low (0.1-10 nmol/mouse) centrally administered doses in male C57Bl/6 mice. Lunasin considerably reduced the amphetamine hyperlocomotion but weakly apomorphine climbing behaviour. No influence on ketamine and bicuculline effects was observed. Binding assay studies demonstrated modest affinity of lunasin for the dopamine D₁ receptor (Ki=60 ± 15 μM). In a functional assay of cAMP accumulation on live cells lunasin antagonised apomorphine effect on D₁ receptor activation (pEC₅₀=6.1 ± 0.3), but had no effect in cells expressing D₂ receptors. The obtained data suggest that lunasin's action at least in part is provided via dopaminergic D1 receptor pathways. However, other non-identified mechanisms (probably intracellular) may play an important role in lunasin's central action. Nevertheless further studies of lunasin are promising, particularly taking into account a necessity for novel type of antipsychotic drugs.

Mildronate and its neuroregulatory mechanisms: targeting the mitochondria, neuroinflammation, and protein expression

This review for the first time summarizes the data obtained in the neuropharmacological studies of mildronate, a drug previously known as a cardioprotective agent. In different animal models of neurotoxicity and neurodegenerative diseases, we demonstrated its neuroprotecting activity. By the use of immunohistochemical methods and Western blot analysis, as well as some selected behavioral tests, the new mechanisms of mildronate have been demonstrated: a regulatory effect on mitochondrial processes and on the expression of nerve cell proteins, which are involved in cell survival, functioning, and inflammation processes. Particular attention is paid to the capability of mildronate to stimulate learning and memory and to the expression of neuronal proteins involved in synaptic plasticity and adult neurogenesis. These properties can be useful in neurological practice to protect and treat neurological disorders, particularly those associated with neurodegeneration and a decline in cognitive functions.

Search for stroke-protecting agents in endothelin-1-induced ischemic stroke model in rats

BACKGROUND AND OBJECTIVE

Ischemic stroke may initiate a reperfusion injury leading to brain damage cascades where inflammatory mechanisms play a major role. Therefore, the necessity for the novel stroke-protecting agents whose the mechanism of action is focused on their anti-inflammatory potency is still on the agenda for drug designers. Our previous studies demonstrated that cerebrocrast (a 1,4-dihydropyridine derivative) and mildronate (a representative of the aza-butyrobetaine class) possessed considerable anti-inflammatory and neuroprotective properties in different in vitro and in vivo model systems. The present study investigated their stroke-protecting ability in an endothelin-1 (ET-1)-induced ischemic stroke model in rats.

MATERIAL AND METHODS

Male Wistar rats were pretreated (for 7 days, per os) with cerebrocrast (0.1 mg/kg), mildronate (100 mg/kg), or their combination, followed by the intracerebral injection of ET-1. Functional and behavioral tests were carried out up to 14 days after the ET-1 injection. Ex vivo, the number of degenerated neurons and the infarction size in the cerebral cortical tissue were assessed histologically.

RESULTS

Cerebrocrast and mildronate effectively normalized ET-1-induced disturbances in neurological status, improved the muscle tone, and decreased the number of degenerated cortical cells. Both drugs also reduced the infarction size, and cerebrocrast showed at least a 2-fold higher activity than mildronate. The combination of both drugs did not cause a more pronounced effect in comparison with the action of drugs administered separately.

CONCLUSIONS

The 1,4-dihydropyridine and aza-butyrobetaine structures may serve for the design of novel stroke-protecting agents to prevent severe neurological poststroke consequences.

Comparative study of taurine and tauropyrone: GABA receptor binding, mitochondrial processes and behaviour

OBJECTIVES

Taurine, a sulfur-containing amino acid, has high hydrophilicity and is poorly absorbed. Tauropyrone, a taurine-containing 1,4-dihydropyridine derivative, is suggested to have greater activity than taurine owing to improved physicochemical properties that facilitate delivery of the compound to target cells. The aim of this study was to determine whether the 1,4-dihydropyridine moiety in tauropyrone improves the pharmacological efficacy of taurine in vitro and in vivo.

METHODS

The effects of taurine and tauropyrone, as well as of the 1,4-dihydropyridine moiety were compared in in-vitro experiments to determine the binding to GABA receptors and influence on mitochondrial processes (isolated rat liver mitochondria), and in in-vivo tests to assess the influence on behavioural effects caused by the GABA-A receptor ligands, bicuculline, diazepam and ethanol.

KEY FINDINGS

Unlike taurine, tauropyrone did not display binding activity for the GABA-A receptor, and only taurine (but not tauropyrone) at low doses (0.1, 1.0 and 10 mg/kg) antagonised the bicuculline-induced convulsion effect. Taurine and tauropyrone had no effect on diazepam myorelaxing action, and they both exerted a comparable 'anti-ethanol' effect (shortening of the ethanol-sleeping time). Taurine and tauropyrone did not influence processes of mitochondrial bioenergetics.

CONCLUSIONS

The action of tauropyrone at the level of the GABA-A receptor differs qualitatively from that of taurine, probably because of its 1,4-dihydropyridine moiety, which may hinder access to the GABA-A receptor GABA site. Tauropyrone does not show improved pharmacological efficacy in in-vitro and in-vivo studies in comparison with taurine.

Mildronate as a regulator of protein expression in a rat model of Parkinson's disease

BACKGROUND

Mildronate (3-[2,2,2-trimethylhydrazinium] propionate dihydrate) traditionally is a well-known cardioprotective drug. However, our recent studies convincingly demonstrated its neuroprotective properties. The aim of the present study was to evaluate the influence of mildronate on the expression of proteins that are involved in the differentiation and survival of the nigrostriatal dopaminergic neurons in the rat model of Parkinson's disease (PD). The following biomarkers were used: heat shock protein 70 (Hsp70, a molecular chaperone), glial cell line-derived nerve growth factor (GDNF, a growth factor promoting neuronal differentiation, regeneration, and survival), and neural cell adhesion molecule (NCAM).

MATERIAL AND METHODS

PD was modeled by 6-hydroxydopamine (6-OHDA) unilateral intrastriatal injection in rats. Mildronate was administered at doses of 10, 20, and 50 mg/kg for 2 weeks intraperitoneally before 6-OHDA injection. Rat brains were dissected on day 28 after discontinuation of mildronate injections. The expression of biomarkers was assessed immunohistochemically and by western blot assay.

RESULTS

6-OHDA decreased the expression of Hsp70 and GDNF in the lesioned striatum and substantia nigra, whereas in mildronate-pretreated (20 and 50 mg/kg) rats, the expression of Hsp70 and GDNF was close to the control group values. NCAM expression also was decreased by 6-OHDA in the striatum and it was totally protected by mildronate at a dose of 50 mg/kg. In contrast, in the substantia nigra, 6-OHDA increased the expression of NCAM, while mildronate pretreatment (20 and 50 mg/kg) reversed the 6-OHDA-induced overexpression of NCAM close to the control values.

CONCLUSION

The obtained data showed that mildronate was capable to regulate the expression of proteins that play a role in the homeostasis of neuro-glial processes.

Neuroprotective properties of mildronate, a mitochondria-targeted small molecule

Mildronate, a representative of the aza-butyrobetaine class of drugs with proven cardioprotective efficacy, was recently found to prevent dysfunction of complex I in rat liver mitochondria. The present study demonstrates that mildronate also acts as a neuroprotective agent. In a mouse model of azidothymidine (anti-HIV drug) neurotoxicity, mildronate reduced the azidothymidine-induced alterations in mouse brain tissue: it normalized the increase in caspase-3, cellular apoptosis susceptibility protein (CAS) and iNOS expression assessed by quantitative and semi-quantitative analysis. Mildronate also normalized the changes in cytochrome c oxidase (COX) expression, reduced the expression of glial fibrillary acidic protein (GFAP) and cellular infiltration. The present results show that the neuroprotective action of mildronate results at least partially from anti-neurodegenerative (anti-apoptotic) and anti-inflammatory mechanisms. It might be suggested that the molecular conformation of mildronate can facilitate its easy binding to mitochondria, and regulate the expression of different signal molecules, hence maintaining cellular signaling and survival.

The evolutionary history and tissue mapping of amino acid transporters belonging to solute carrier families SLC32, SLC36, and SLC38

Members of the solute carrier families (SLC) 32, 36, and 38, together also designated the beta-group of SLCs, are known to transport neutral amino acids. In this paper, we show that these three families were present before the split of the animal lineage and that they are likely to share a common decent. We also show that the APF transporters found in plants are most likely homologous to the mammalian beta-group, suggesting that this type of transporters arouse early in the evolution of eukaryotes. We performed detailed tissue expression analysis of all the members of the beta-group in rat and found several examples of highly specific expression patterns, with SLC38A7 being exclusively found in liver, SLC38A5 in blood, and SLC38A4 in muscle and liver. Moreover, we found that SLC38A10 is expressed in several endocrine organs. We also found that SLC38A1 is highly up regulated in the cortex from rats treated with diazepam and that SLC38A2 is significantly down regulated in the same tissue. In addition, we performed a detailed expression analysis of SLC38A1 and SLC38A6 in mouse brain using in situ hybridization, which showed that both these transporters are widely expressed in the brain.

Potato (Solanum tuberosum) juice exerts an anticonvulsant effect in mice through binding to GABA receptors

Naturally occurring benzodiazepines have been identified in regular food such as wheat and potato, but there is still no evidence that potato extracts can affect CNS responses in vivo. Here we found that undiluted potato juice and potato juice diluted with saline 1 : 2 administered 10 min intracisternally ( I. C.) and 30 min per os before bicuculline exerted significant anticonvulsant activity in the bicuculline-induced seizure threshold test in mice. In vitro, potato juice from different harvests at dilution series from 10 % to 0.000001 %, diluted 100,000-fold, displaced 50 % of gamma-aminobutyric acid (GABA) receptor ligand [ (3)H]GABA and diluted 40-fold displaced 50 % of [(3)H]flunitrazepam from binding sites in mice forebrain membranes. The low content of diazepam (0.04 +/- 0.01 mg/kg) determined by HPLC and mass spectrometry in the potato extracts could not sustain the anticonvulsant activity of potato juice in vivo; therefore we hypothesized that potato juice might contain GABA (A) receptor GABA-site active compounds. The findings of this study suggest that potato juice as well as potato taken as food may have the capacity of influencing brain GABA-ergic activity.

Protection of azidothymidine-induced cardiopathology in mice by mildronate, a mitochondria-targeted drug

Azidothymidine, a nucleoside-analogue reverse transcriptase inhibitor (NRTI), is a commonly used antiretroviral drug in AIDS treatment, however its use is limited by severe toxic side effects due to its influence on mitochondria that result in myopathy, particularly affecting the cardiac muscle. We suggest that effective protection of azidothymidine-induced cardiopathology can be expected from drugs that are capable of targeting mitochondria. Therefore the present study in mice was carried out with mildronate, a cardioprotective drug of the aza-butyrobetaine class, which previously has been shown to act as a highly potent protector of mitochondrial processes. In our study, saline (control), azidothymidine (50 mg/kg), mildronate (50, 100 and 200 mg/kg), and azidothymidine + mildronate (at the doses mentioned) were injected intraperitoneally daily in separate groups of mice for two weeks. At the termination of the experiment, mice were sacrificed, the hearts were removed and cardiac tissue was examined morphologically and immunohistochemically. It was found that azidothymidine, compared to control and mildronate groups, induced major morphologic changes in cardiac tissue, which were manifestated as degeneration and inflammation. These changes were prevented when mildronate was co-administered with azidothymidine. Mildronate also reduced the azidothymidine-induced expression of nuclear factor kappaBp65 (NF-kappaBp65). The obtained data demonstrate a high ability of mildronate of preventing azidothymidine-induced cardiopathologic changes, and suggest mildronate's indirect action on azidothymidine-caused oxidative stress reactions leading to mitochondrial dysfunction. This offers a rational combination of mildronate with azidothymidine or other anti-HIV drugs for beneficial application in AIDS therapy.

Study of the interaction of 1,4-dihydropyridine derivatives with glucocorticoid hormone receptors from the rat liver

Seventeen derivatives of 1,4-dihydropyridine (DHP) series were tested in vitro for their ability to inhibit [1,2,4-(3)H]-dexamethasone binding to glucocorticoid receptor from the rat liver cytosol. Depending on structural features and inhibiting activities, the compounds can be divided into three groups. The first group (nifedipine, foridone, J-6-163, OSI-4164 and OSI-7724) had the highest activity: they inhibited specific ligand-receptor binding by 70-80% at concentrations of 10(-5) M and 10(-4) M, with apparent IC(50)values of 1.5-6.0 muM. The second group (cerebrocrast, diethone, OSI-1211 and OSI-7265) was active at concentration of 10(-4) M, and their IC(50) values were 23-45 muM; compound OSI-5003 was almost inactive. Both groups are compounds with scarce water solubility, more or less lipophilic. The third group of compounds comprises ionogenic compounds (organic cations or anions with corresponding inorganic counterions): most of them are water-soluble (glutapyrone, carbatone, gammapyrone, OSI-2780, OSI-1580, OSI-2140) or liposome-forming (A-74). They lack the above-mentioned activity. Among the first two groups, compounds possessing more bulky substituents in positions 3 and 5 are less active. The aromatic ring in the position 4 is essential for the optimal activity. It seems that there is a bell-shaped dependence of activity upon lipophilicity. In general, the compounds of the first group are strong Ca-antagonists, while the second group includes moderate Ca-antagonists, but each group comprises also compounds which lack Ca antagonistic activity. All compounds of the third group lack Ca antagonistic properties.

Distinct effects of atypical 1,4-dihydropyridines on 1-methyl-4-phenylpyridinium-induced toxicity

Our previous data obtained from in vivo experiments demonstrated high neuroprotective effects of three novel atypical neuronal non-calcium antagonistic 1,4-dihydropyridine (DHP) derivatives cerebrocrast, glutapyrone and tauropyrone. The present studies were carried out in vitro to clarify, at least in part, their mechanism of action in primary culture of cerebellar granule cells by use of 1-methyl-4-phenylpyridinium (MPP+) as a neurotoxic agent which causes dramatic oxidative stress. Cerebrocrast (highly lipophilic, with a classical two-ring structure) dose-dependently (0.01-10.0 microM, EC50 = 13 nM) reduced MPP+-induced cell death. At the same time, the calcium antagonist nimodipine (reference drug) protected cell death at much higher concentrations (EC50 = 12.4 microM). Cerebrocrast decreased also the generation of reactive oxygen species and loss of mitochondrial membrane potential. In contrast, low lipophilic amino acid-containing DHPs glutapyrone and tauropyrone (glutamate- and taurine-containing, correspondingly) were without significant effects indicating their distinct mode of action in comparison to cerebrocrast. We have demonstrated for the first time an ability of atypical non-calcium antagonistic DHP cerebrocrast (which has classical DHP structure elements and high lipophilicity) to protect MPP+-induced deterioration of mitochondrial bioenergetics. One may suggest mitochondria as an essential intracellular target for the neuroprotective action of cerebrocrast and indicate its usefulness in the treatment of Parkinson's disease.

3,4-trans-4-Aryl-3-(1-pyridinio)-1,2,3,4-tetrahydropyridine-6-thiolates--new group of potential cardiotonic drugs

3,4-trans-4-Aryl-3-(1-pyridinio)-1,2,3,4-tetrahydropyridine-6-thiolates 6-11 were prepared by a Michael reaction of N-acetonylpyridinium chloride with 3-aryl-2-cyanothioacrylamides or by a one-pot three-carbon condensation of N-acetonylpyridinium chloride, aromatic aldehyde and 2-cyanothioacetamide, and their cardiotonic properties were studied. 3,4-trans-5-cyano-2-hydroxy-2-methyl-4-(3-nitrophenyl)-3-(1-pyridinio)-1,2,3,4-tetrahydropyridine-6-thiolate 8 was considered as a lead compound in this series since it in vitro experiments (spontaneously beating rat atria) showed a cardiotonic activity similar to that of milrinone 2, however compound 8 induced activity at lover concentrations and without influence on chronotropic action of the heart. Unlike milrinone 2, thiolate 8 in vivo experiments (anaesthetized rats) did not influence blood pressure and heart rate. The acute toxicity of compound 8 was more than 10 times lower than that of milrinone 2.

Opposite effects of gamma(1)- and gamma(2)-melanocyte stimulating hormone on regulation of the dopaminergic mesolimbic system in rats

By use of the brain microdialysis technique we show that administration of gamma(1)-melanocyte stimulating hormone (gamma(1)-MSH) into the ventral tegmental area of anaesthetized rats causes an increase in the release of extracellular dopamine and its metabolite 3,4-dihydroxyphenylacetic acid in the nucleus accumbens, while gamma(2)-MSH causes the opposite effect. Moreover, gamma(2)-MSH pre-treatment considerably reduced the gamma(1)-MSH-induced effects. Our findings suggest an opposing action of two gamma-MSH-activated pathways on the mesolimbic dopaminergic system, which could be important in the maintenance of a balanced psychoactivation state.

Anti-inflammatory effects of cerebrocrast in a model of rat paw edema and on mononuclear THP-1 cells

Cerebrocrast (IOS 1.1212; 4-[2-(difluoromethoxy)phenyl]-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylic acid di(2-propoxyethyl) diester) is a novel derivative of 1,4-dihydropyridine, which does not antagonize Ca(2+) influx in neuronal tissues. Since several classical dihydropyridines possess anti-inflammatory properties, we first studied the effects of cerebrocrast in a model of rat paw edema induced by carrageenan. Cerebrocrast had a preventative effect in this model of inflammation, with maximal activity (32-45% inhibition) in the 0.1-0.25 mg kg(-1) range. It was ineffective when added after the injection of carrageenan. Subsequent in vitro experiments showed that cerebrocrast in the micromolar range inhibited secretion of interleukin-1 beta, interleukin-6 and neurotoxic products by cells of the human monocytic THP-1 line while failing to affect secretion of tumor necrosis factor (TNF-alpha). It also lacked any direct neuroprotective effect against toxic secretions from stimulated THP-1 cells. The data obtained suggest that cerebrocrast may be useful not only in various inflammatory disorders of peripheral tissues, but also in treating neurodegenerative diseases, where inflammatory mechanisms in general and microglial activation, in particular, are thought to play an important role.

The MC4 receptor mediates alpha-MSH induced release of nucleus accumbens dopamine

Strong evidence suggests a functional link between the melanocortin and dopamine systems. alpha-Melanocyte stimulating hormone (alpha-MSH) induced grooming behaviour, which can be blocked by dopamine receptor antagonists, is associated with increased dopaminergic transmission in the striatal regions. Whether this effect is mediated specifically by melanocortin (MC) receptors has not previously been established. Using in vivo microdialysis on anesthesized rats we have shown that alpha- MSH administered into the ventral tegmental area induced a significant increase in dopamine and DOPAC levels in the nucleus accumbens. This increase was completely blocked by pre-treatment with the MC4 receptor selective antagonist HS131, indicating that the effects of alpha-MSH on dopamine transmission may be mediated by the MC4 receptor.

Hypericum extract and hyperforin: memory-enhancing properties in rodents

Effects of a Hypericum extract in therapeutic use and hyperforin sodium salt were evaluated in rat and mouse avoidance tests. In a conditioned avoidance response (CAR) test on the rat, oral daily administration of hyperforin (1.25 mg/kg/day) or of the extract (50 mg/kg/day) before the training sessions considerably improved learning ability from the second day onwards until the day 7. In addition, the memory of the learned responses acquired during 7 consecutive days of administration and training was largely retained even after 9 days without further treatment or training. The observations made using different doses indicate that these learning-facilitating and/or memory-consolidating effects by the agents follow inverse U-shaped dose-response curves in dose ranges lower than (for hyperforin) or equal to (for Hypericum extract) their effective dose in the behavioral despair test for antidepressants. In a passive avoidance response test on the mouse, a single oral dose (1.25 mg/kg) of hyperforin not only improved memory acquisition and consolidation, but also almost completely reversed scopolamine-induced amnesia. The single Hypericum extract dose tested (25 mg/kg) did not reveal any significant effects in the passive avoidance response (PAR) test on the mouse. These observations suggest that the Hypericum extract could be a novel type of antidepressant with memory enhancing properties, and indicate that hyperforin is involved in its cognitive effects. Pure hyperforin seems to be a more potent antidementia agent than an antidepressant.

The gamma(2)-MSH peptide mediates a central analgesic effect via a GABA-ergic mechanism that is independent from activation of melanocortin receptors

Using the latency for tail-flick after thermal stimulation we have assessed the effects of alpha-, gamma(1)- and gamma(2)-MSH on nociceptive threshold in the mice. Intracisternal injections of gamma(2)-MSH induced a distinct analgesia, while gamma(1)-MSH in the same doses gave only a minor analgesia. Intracisternal alpha-MSH instead gave a short-term hyperalgesia. The effect of gamma(2)-MSH was not blocked by any of the MC(4)/MC(3)receptor antagonist HS014, naloxone or by the prior intracisternal administrations of gamma(1)-MSH. However, the gamma(2)-MSH analgesic response was completely attenuated by treating animals with the GABA(A)antagonist bicuculline. The gamma(2)-MSH analgesic effect was moreover additive to the analgesia afforded by muscimol and ethanol, but not to that afforded by diazepam. In addition both gamma(1)- and gamma(2)-MSH induced moderate catalepsy, but could at the same time attenuate haloperidol induced catalepsia. We conclude that gamma(2)-MSH mediates a central analgesic effect via GABA-receptor dependent pathway that is distinct from melanocortic- and opioid-receptors. Moreover, the mechanism for gamma(2)-MSH's analgesic effect appears to be distinct from that causing moderate catalepsia by gamma-MSH's.

Behavioural responses of gamma-MSH peptides administered into the rat ventral tegmental area

The behavioural effects induced by alpha-, gamma1- and gamma2-MSH peptides (0.3 and 3 nmole per rat) injected into the left ventral tegmental area (VTA) of rats were compared. alpha- and gamma1-MSH caused grooming of comparable magnitude, and also additional vertical activity (rearing). By contrast gamma2-MSH caused a moderate but stable catalepsy, and practically no grooming. Moreover, intra-VTA pre-treatment with gamma2-MSH, 15 min prior to intra-VTA gamma1-MSH, markedly attenuated both the gamma1-induced grooming and vertical activities. The differences in the behavioural response of the MSH peptides indicate that they act differentially on MC receptors in the VTA.

"Atypical" neuromodulatory profile of glutapyrone, a representative of a novel 'class' of amino acid-containing dipeptide-mimicking 1,4-dihydropyridine (DHP) compounds: in vitro and in vivo studies

Glutapyrone, a disodium salt of 2-(2,6-dimethyl-3,5-diethoxycarbonyl-1,4-dihydropyridine-4-carboxamido)- glutaric acid, is a representative of a novel 'class' of amino acid-containing 1,4-dihydropyridine (DHP) compounds developed at the Latvian Institute of Organic Synthesis, Riga, Latvia. Conceptually, the glutapyrone molecule can be regarded as a dipeptide-mimicking structure formed by the "free" amino acid (glutamate) moiety and "crypto" (built into the DHP cycle) amino acid ("GABA") elements. Both of these amino acids are joined by the peptide bond. This compound unlike classical DHPs lacks calcium antagonistic or agonistic properties. Our previous studies revealed a profound and long-term anticonvulsant, stress-protective and neurodeficit-preventive activities of glutapyrone. In view of structural properties the role of glutamatergic mechanisms in the mediation of central effects of glutapyrone was considered. In the present study glutapyrone at the concentration range of 1 microM(-1) mM failed to effect both NMDA ([3H]TCP) and non-NMDA ([3H]KA and [3H]AMPA) receptor ligand binding in the rat cortical membranes in vitro. The compound markedly enhanced motor hyperactivity induced by the NMDA antagonist PCP and the dopamine releasing compound D-amphetamine in the rats. Glutapyrone displayed activity in a variety of animal models relevant for affective/depressive disorders in humans i.e. reserpine-induced ptosis and hypothermia, forced swimming test and open field test. These data indicate that the unusually "broad" pharmacological spectrum of glutapyrone might involve concomitant actions on multiple neurotransmitter systems, particularly, GABA-ergic and the catecholamines. It is discussed whether these functional properties are secondary to action on intracellular events, predominantly, G protein-related since glutapyrone appears to lack direct interactions with a number of receptors including ionotropic glutamate and GABA(A)/Bzd receptors.

Evaluation of behavioural effects of neural melanocortin receptor antagonists injected ICV and in VTA in rats

The natural melanocortic peptides are known to exert a variety of effects after central administration. Recently, we discovered the first potent and selective substances for the MC4 receptor, i.e. HS964 and HS014. We found HS964 to be an antagonist for the MC1, MC3, MC4 and MC5 receptors in vitro. HS014 is an antagonist for the MC3 and MC4 receptors and a partial antagonist for the MC1 and MC5 receptors. We injected alpha-MSH and these substances, both intracerebroventricular (ICV) and in the ventral tegmental area (VTA) in rats and scored several behavioural effects. The results show that alpha-MSH caused intensive grooming which was antagonized by pre-treatment of both HS014 and HS964. The data give further support to the hypothesis that it is the MC4 receptor which mediates grooming in rodents. The grooming effects of alpha-MSH were more pronounced after intra-VTA administration compared to the ICV administration. Both alpha-MSH, HS014 and HS964 caused an increase in vertical activity of the rats after intra-VTA administration but not after ICV administration. Horizontal activity was virtually not affected by the administration of the peptides. The data indicate that the neural MC3 and MC4 receptors are not likely to be an important mediators of locomotor activity in rats.

Modification of swelling-contraction-aggregation processes in rat muscle mitochondria by the 1,4-dihydropyridines, cerebrocrast and glutapyrone, themselves and in the presence of azidothymidine

The influence of the 1,4-dihydropyridines (DHPs), water-soluble glutapyrone available as sodium, potassium and ammonium salts of 2-(2,6-dimethyl-3,5-diethoxycarbonyl-1,4-DHP-4-carboxamide)glutaric acid, from one side, and a lipophylic cerebrocrast, 2-propoxyethyl 2,6-dimethyl-4-(2-difluoromethoxyphenyl)-1,4-DHP-3,5-dicarboxylate, from the other side, on partially damaged mitochondria of the Wistar rat hindlimb muscle was also studied. The following tests were made: (1) rates of endogenous respiration and substrate (succinate) oxidation and oxidative phosphorylation; (2) rates and amplitudes of high-amplitude swelling and contraction after the addition of ATP, ADP and succinate to the previously swollen mitochondria and (3) rate of reversible self-aggregation of mitochondria isolated in salt media after ATP-induced contraction without and in the presence of azidothymidine (AZT). Cerebrocrast (10-100 microM) partially normalized the endogenous respiration rate and slightly augmented the respiration rate after the addition of succinate and to lesser extent ADP. Cerebrocrast in a concentration-dependent manner (2.5-50 microM) increased (two-fold at 20-50 microM) the active contraction amplitude of swollen mitochondria, induced by single or repeated additions of ATP. The influence of cerebrocrast on the ADP- and succinate-induced contractions was less obvious. Unlike cerebrocrast glutapyrone caused a reduction of the ATP-induced contraction amplitude (two-fold at 0.5-5.0 mM), not impairing the mitochondrial contraction ability in response to ATP or succinate. Pre-exposure to 2.5 mM glutapyrone resulted in at least a 10-fold inhibition of the reversible aggregation rate in the presence of 99 and 198 microM AZT. The results suggest the usefulness of further study of cerebrocrast and glutapyrone in preventing AZT-induced and some other mitochondrial myopathies.

Major pharmacological distinction of the ACTH receptor from other melanocortin receptors

The mouse adrenocortical cell line Y1, that expresses ACTH receptors (MC2R), was used to probe the binding of ACTH and MSH peptides by using radio-labelled ACTH (1-39). The Y1 cells were found to bind [125I]-labelled ACTH (1-39) with high affinity (Kd approximately 130 pM). However, none of the melanocortin peptides NDP-MSH, alpha-MSH, beta-MSH or gamma 1-MSH could compete with the binding of the labelled ACTH(1-39). When other MC receptor subtype DNAs (MC1, MC3 and MC4) were transfected into the Y1 cells, characteristic binding of the [125I]NDP-MSH appeared for each of the receptor subtype, but no specific binding was present in non-transfected cells. This is the first report clearly demonstrating that the ACTH receptor binds only ACTH, but not other melanocortin peptides.

Thymopentin antagonizes stress-induced changes of GABA/benzodiazepine receptor complex

Intraperitoneal administration of thymopentin, a thymopentin II-derived pentapeptide, had no stable and evident effect in the two anxiety models (elevated plus-maze and licking-conflict test) studied. However, in the elevated plus-maze test thymopentin antagonized the behavioral effects of DMCM, a beta-carboline derivative with anxiogenic properties. Further, it was demonstrated that the licking-conflict test procedure itself produced a significant elevation of plasma corticosterone levels, increased the number of [3H]flunitrazepam and decreased the number of [3H]muscimol binding sites in rat hippocampus. The forced-swimming stress similarly to the licking-conflict test also caused an increase in hippocampal [3H]flunitrazepam binding sites. Although ineffective behaviorally in the tests for anxiety, thymopentin pretreatment effectively reversed the changes in corticosterone levels caused by the licking-conflict test. Moreover, it normalized the changed number of benzodiazepine and GABA receptors after stressful stimuli. It is well known that not all anxiolytic drugs (i.e. buspirone) are equally active in behavioral tests for anxiety. According to our data we propose that thymopentin has stress-protective activity. As in vivo and in vitro thymopentin did not change [3H]-flunitrazepam and [3H]muscimol binding, the direct effect of this peptide on the GABA-benzodiazepine-Cl- ionophore receptor complex is unlikely. The action of this peptide on GABA release and/or metabolism can be suggested.