The tyrosine kinase inhibitor genistein directly inhibits GABAA receptors

Therapeutic efficacy of Genistein in activation of neuronal AC/cAMP/CREB/PKA and mitochondrial ETC-Complex pathways in experimental model of autism: Evidence from CSF, blood plasma and brain analysis

Autism is a complex neurodevelopmental condition characterized by repetitive behaviors, impaired social communication, and various associated conditions such as depression and anxiety. Its multifactorial etiology includes genetic, environmental, dietary, and gastrointestinal contributions. Pathologically, Autism is linked to mitochondrial dysfunction, oxidative stress, neuroinflammation, and neurotransmitter imbalances involving GABA, glutamate, dopamine, and oxytocin. Propionic acid (PRPA) is a short-chain fatty acid produced by gut bacteria, influencing central nervous system functions. Elevated PRPA levels can exacerbate Autism-related symptoms by disrupting metabolic processes and crossing the blood-brain barrier. Our research investigates the neuroprotective potential of Genistein (GNT), an isoflavone compound with known benefits in neuropsychiatric and neurodegenerative disorders, through modulation of the AC/cAMP/CREB/PKA signaling pathway and mitochondrial ETC complex (I-IV) function. In silico analyses revealed GNT's high affinity for these targets. Subsequent in vitro and in vivo experiments using a PRPA-induced rat model of autism demonstrated that GNT (40 and 80 mg/kg., orally) significantly improves locomotion, neuromuscular coordination, and cognitive functions in PRPA-treated rodents. Behavioral assessments showed reduced immobility in the forced swim test, enhanced Morris water maze performance, and restored regular locomotor activity. On a molecular level, GNT restored levels of key signaling molecules (AC, cAMP, CREB, PKA) and mitochondrial complexes (I-V), disrupted by PRPA exposure. Additionally, GNT reduced neuroinflammation and apoptosis, normalized neurotransmitter levels, and improved the complete blood count profile. Histopathological analyses confirmed that GNT ameliorated PRPA-induced brain injuries, restored normal brain morphology, reduced demyelination, and promoted neurogenesis. The study supports GNT's potential in autism treatment by modulating neural pathways, reducing inflammation, and restoring neurotransmitter balance.

Insulin signaling pathway assessment by enhancing antioxidant activity due to morin using in vitro rat skeletal muscle L6 myotubes cells

BACKGROUND

Plant-derived phytochemicals such as flavonoids have been explored to be powerful antioxidants that protect against oxidative stress-related diseases. In the present study, Morin, a flavonoid compound was studied for its antioxidant and antidiabetic properties in relation to oxidative stress in insulin resistant models conducted in rat skeletal muscle L6 cell line model.

METHODS

Evaluation of antioxidant property of morin was assayed using in vitro methods such as cell viability by MTT assay, estimation of SOD and CAT activity and NO scavenging activity. The anti-oxidative nature of morin on L6 cell line was conducted by the DCF-DA fluorescent activity. Glucose uptake in morin treated L6 myotubes are accessed by 2-NBDG assay in the presence or absence of IRTK and PI3K inhibitors. Further glycogen content estimation due to the morin treatment in L6 myotubes was performed. Antioxidant and insulin signaling pathway gene expression was examined over RT-PCR analysis.

RESULTS

Morin has a negligible cytotoxic effect at doses of 20, 40, 60, 80, and 100 µM concentration according to cell viability assay. Morin revealed that the levels of the antioxidant enzymes SOD and CAT in L6 myotubes had increased. When the cells were subjected to the nitro blue tetrazolium assay, morin lowered reactive oxygen species (ROS) formation at 60 µM concentration displaying 39% ROS generation in oxidative stress condition. Lesser NO activity and a drop in green fluorescence emission in the DCFDA assay, demonstrating its anti-oxidative nature by reducing ROS formation in vitro. Glucose uptake by the L6 myotube cells using 2-NBDG, and with IRTK and PI3K inhibitors (genistein and wortmannin) showed a significant increase in glucose uptake by the cells which shows the up regulated GLUT-4 movement from intracellular pool to the plasma membrane. Morin (60 µM) significantly enhanced the expression of antioxidant genes GPx, GST and GCS as well as insulin signalling genes IRTK, IRS-1, PI3K, GLUT-4, GSK-3β and GS in L6 myotubes treated cells.

CONCLUSION

Morin has the ability to act as an anti-oxidant by lowering ROS levels and demonstrating insulin mimetic activity by reversing insulin resistance associated with oxidative stress.

Modulation of recombinant human alpha 1 glycine receptor by flavonoids and gingerols

The inhibitory glycine receptor (GlyR) is a principal mediator of fast synaptic inhibition in mammalian spinal cord, brainstem, and higher brain centres. Flavonoids are secondary plant metabolites that exhibit many beneficial physiological effects, including modulatory action on neuronal receptors. Using whole-cell current recordings from recombinant human α1 GlyRs, expressed in HEK293 cells, we compared the flavonols kaempferol and quercetin, the flavanone naringenin, the flavones apigenin and nobiletin, the isoflavone genistein, and two gingerols, 6-gingerol and 8-gingerol for their modulation of receptor currents. All compounds were inhibitors of the GlyR with IC₅₀ values ranging between 9.3 ± 2.6 µM (kaempferol) and 46.7 ± 6.5 µM (genistein), following a mixed mode of inhibition. Co-application of two inhibitors revealed distinct binding sites for flavonoids and gingerols. Pore-lining mutants T258A and T258S were strongly inhibited by quercetin and naringenin, but not by 6-gingerol, confirming the existence of distinct binding sites for flavonoids and gingerols. Apigenin, kaempferol, nobiletin, naringenin and 6-gingerol showed biphasic action, potentiating glycine-induced currents at low concentration of both, modulator and glycine, and inhibiting at higher concentrations. Identification of distinct modulatory sites for flavonoids and related compounds may present pharmacological target sites and aid the discovery of novel glycinergic drugs.

Flavonoids as positive allosteric modulators of α7 nicotinic receptors

The use of positive allosteric modulators (PAM) of α7 nicotinic receptors is a promising therapy for neurodegenerative, inflammatory and cognitive disorders. Flavonoids are polyphenolic compounds showing neuroprotective, anti-inflammatory and pro-cognitive actions. Besides their well-known antioxidant activity, flavonoids trigger intracellular pathways and interact with receptors, including α7. To reveal how the beneficial actions of flavonoids are linked to α7 function, we evaluated the effects of three representative flavonoids -genistein, quercetin and the neoflavonoid 5,7-dihydroxy-4-phenylcoumarin- on whole-cell and single-channel currents. All flavonoids increase the maximal currents elicited by acetylcholine with minimal effects on desensitization and do not reactivate desensitized receptors, a behaviour consistent with type I PAMs. At the single-channel level, they increase the duration of the open state and produce activation in long-duration episodes with a rank order of efficacy of genistein > quercetin ≥ neoflavonoid. By using mutant and chimeric α7 receptors, we demonstrated that flavonoids share transmembrane structural determinants with other PAMs. The α7-PAM activity of flavonoids results in decreased cell levels of reactive oxygen species. Thus, allosteric potentiation of α7 may be an additional mechanism underlying neuroprotective actions of flavonoids, which may be used as scaffolds for designing new therapeutic agents.

Genistein alleviates anxiety-like behaviors in post-traumatic stress disorder model through enhancing serotonergic transmission in the amygdala

Post-traumatic stress disorder (PTSD) is a chronic psychiatric disorder, characterized by intense fear, and increased arousal and avoidance of traumatic events. The current available treatments for PTSD have limited therapeutic value. Genistein, a natural isoflavone, modulates a variety of cell functions. In this study, we tested anti-anxiety activity and underlying mechanisms of genistein in a PTSD rat model. The rats were trained to associate a tone with foot shock delivery on day 0, then fear conditioning was performed on day 7, 14 and 21. Genistein (2-8mg/kg) was injected intraperitoneally daily for 7 days. The anti-anxiety effects of genistein were measured by contextual freezing behavior and elevated plus maze. By the end of the experiments, the amygdala was extracted and subject to neurochemistry analysis. Genistein alleviated contextual freezing behavior and improved performance in elevated plus maze dose-dependently in PTSD rats. Furthermore, in these rats, genistein enhanced serotonergic transmission in the amygdala, including upregulation of tryptophan hydroxylase, serotonin, and phosphorylated (p)-CaMKII and p-CREB, as well. Genistein exerts anti-anxiety effects on a PTSD model probably through enhancing serotonergic system and CaMKII/CREB signaling pathway in the amygdala.

Phytoestrogens in Botanical Dietary Supplements: Implications for Cancer

Phytoestrogens are plant constituents that possess either estrogenic or antiestrogenic activity. Although their activities are weak as compared with human endogenous estrogens, the consumption of phytoestrogens may have clinically significant consequences. A number of botanicals, or the compounds contained therein, have been identified as putative estrogenic agents, but consensus in the biomedical community has been hampered by conflicting data from various in vitro and in vivo models of estrogenic activity. Phytoestrogens may serve as chemopreventive agents while at the same time being capable of promoting growth in estrogen receptor positive cancer cell lines. Furthermore, they may exert their estrogenic influence through receptor-dependent and/or receptor-independent mechanisms. These findings have led to speculation that phytoestrogen intake might be ill advised for patients at an increased risk for hormone-dependent cancers, cancer patients, or cancer survivors. This article will attempt to sort out discrepancies between various experimental models and establish whether certain herbs possess estrogenic activity. The review will focus on 5 popular botanical dietary supplements: Trifolium pratense (red clover), Cimicifuga racemosa (black cohosh), Humulus lupulus (hops), Angelica sinensis (dong quai), and Glycyrrhiza glabra (licorice). It will address their mechanisms of action, clinical evidence bases, and implications for use in cancer.

Comparative study of dietary soy phytoestrogens genistein and equol effects on growth parameters and ovarian development in farmed female beluga sturgeon, Huso huso

Oocyte maturation in fish is a hormonally regulated process. In the light of long-term oocyte maturation in beluga, the aim of this research was to study the estrogenic effects of different concentrations of soy dietary genistein (GE) and equol (EQ) on the growth performance and ovary development in farmed female Huso huso. Fish were fed with concentrations 0 (control), 0.2, 0.4, 0.8 and 1.6 g of EQ and GE per kg of isoproteic (CP 45 %) and isoenergetic (19.5 MJ/kg) diets during a year. Blood samples and ovary biopsies were collected from each fish seasonally. The main results of the present experimentation are that growth performance was not affected significantly both in GE and EQ (P > 0.05). EQ at concentration 0.4 g/kg had more estrogenic effects than other concentrations of EQ and GE in beluga so that 64 % of fish were matured sexually. Some reproductive indices such as oocyte diameter, testosterone (T) and 17β-estradiol (E₂) increased significantly at EQ 0.4 g/kg at the end of experiment (P < 0.05), while 17α-hydroxy progesterone level (17α-OHP) showed no significant changes at all concentrations. Biochemical indices such as calcium, phosphorous and cholesterol increased at GE concentrations, but decreased at EQ concentrations similarly at the end of experiment. There was a negative relationship between plasma phosphorous and alkaline phosphatase enzyme levels. Based on results, EQ at concentration 0.4 g/kg improved oocyte development more than the other concentrations of GE and EQ, and therefore, it can be used as an additive to diets for inducing ovary development in this species.

Inflammation-induced shift in spinal GABA(A) signaling is associated with a tyrosine kinase-dependent increase in GABA(A) current density in nociceptive afferents

To account for benzodiazepine-induced spinal analgesia observed in association with an inflammation-induced shift in the influence of the GABA(A) receptor antagonist gabazine on nociceptive threshold, the present study was designed to determine whether persistent inflammation is associated with the upregulation of high-affinity GABA(A) receptors in primary afferents. The cell bodies of afferents innervating the glabrous skin of the rat hind paw were retrogradely labeled, acutely dissociated, and studied before and after the induction of persistent inflammation. A time-dependent increase in GABA(A) current density was observed that was more than twofold by 72 h after the initiation of inflammation. This increase in current density included both high- and low-affinity currents and was restricted to neurons in which GABA increased intracellular Ca(2+). No increases in GABA(A) receptor subunit mRNA or protein were detected in whole ganglia. In contrast, the increased current density was completely reversed by 20-min preincubation with the tyrosine kinase inhibitor genistein and partially reversed with the Src kinase inhibitor PP2. Genistein reversal was partially blocked by the dynamin inhibitor peptide P4. Changes in nociceptive threshold following spinal administration of genistein and muscimol to inflamed rats indicated that the pronociceptive actions of muscimol observed in the presence of inflammation were reversed by genistein. These results suggest that persistent changes in relative levels of tyrosine kinase activity following inflammation provide not only a sensitive way to dynamically regulate spinal nociceptive signaling but a viable target for the development of novel therapeutic interventions for the treatment of inflammatory pain.

Genistein directly inhibits native and recombinant NMDA receptors

The protein tyrosine kinase (PTK) inhibitor genistein has been widely used to examine potential effects of tyrosine phosphorylation on neurotransmitter function. We report here that genistein inhibits N-methyl-d-aspartate (NMDA) receptors through a direct effect. Whole-cell NMDA-activated current was recorded in native receptors from mouse hippocampal slice culture and rat recombinant NR1aNR2A and NR1aNR2B receptors transiently expressed in HEK293 cells. Extracellular application of genistein and NMDA reversibly inhibited NMDA-activated current. The inhibition of NMDA-activated current by genistein applied externally was not affected when genistein was also pre-equilibrated in the intracellular solution. Daidzein, an analog of genistein that does not block PTK, also inhibited NMDA-activated current. Coapplication of lavendustin A, a specific inhibitor of PTK, had no effect on the NMDA response. Moreover, genistein-induced inhibition of NMDA-activated current displayed concentration- and voltage-dependence. Our results demonstrate that genistein has a direct inhibitory effect on NMDA receptors that is not mediated via inhibition of tyrosine kinase. Thus, other PTK inhibitors may be more suitable for studying involvement of PTKs in NMDA receptor-mediated events.

Impact of neonatal exposure to the ERalpha agonist PPT, bisphenol-A or phytoestrogens on hypothalamic kisspeptin fiber density in male and female rats

Neonatal exposure to endocrine disrupting compounds (EDCs) can impair reproductive physiology, but the specific mechanisms by which this occurs remain largely unknown. Growing evidence suggests that kisspeptin (KISS) neurons play a significant role in the regulation of pubertal onset and ovulation, therefore disruption of KISS signaling could be a mechanism by which EDCs impair reproductive maturation and function. We have previously demonstrated that neonatal exposure to phytoestrogens decreases KISS fiber density in the anterior hypothalamus of female rats, an effect which was associated with early persistent estrus and the impaired activation gonadotropin releasing hormone (GnRH) neurons. The goals of the present study were to (1) determine if an ERalpha selective agonist (PPT) or bisphenol-A (BPA) could produce similar effects on hypothalamic KISS content in female rats and (2) to determine if male KISS fiber density was also vulnerable to disruption by EDCs. We first examined the effects of neonatal exposure to PPT, a low (50 microg/kg bw) BPA dose, and a high (50 mg/kg bw) BPA dose on KISS immunoreactivity (-ir) in the anterior ventral periventricular (AVPV) and arcuate (ARC) nuclei of adult female rats, using estradiol benzoate (EB) and a sesame oil vehicle as controls. AVPV KISS-ir, following ovariectomy (OVX) and hormone priming, was significantly lower in the EB and PPT groups but not the BPA groups. ARC KISS-ir levels were significantly diminished in the EB and high dose BPA groups, and there was a nonsignificant trend for lower KISS-ir in the PPT group. We next examined effects of neonatal exposure to a low (50 microg/kg bw) dose of BPA and the phytoestrogens genistein (GEN) and equol (EQ) on KISS-ir in the AVPV and ARC of adult male rats, using OVX females as an additional control group. None of the compounds affected KISS-ir in the male hypothalamus. Our results suggest that the organization of hypothalamic KISS fibers may be vulnerable to disruption by EDC exposure and that females might be more sensitive than males.

Quercetin subunit specifically reduces GlyR-mediated current in rat hippocampal neurons

Quercetin is a substance of low molecular weight found in vascular plants with a wide range of biological activities including antioxidative and anti-inflammatory activities. In the present study, the effects of quercetin on native glycine receptors (GlyRs) in cultured rat hippocampal neurons were investigated using a whole-cell patch-clamp technique. Quercetin reversibly and concentration-dependently depressed glycine-induced current (I(Gly)), with an IC50 of 10.7+/-0.24 microM and a Hill coefficient of 1.08+/-0.12. Quercetin depressed maximum I(Gly) and significantly changed the EC50 for glycine and the Hill coefficient. Kinetic analysis indicated that quercetin accelerated the rates of desensitization. Interestingly, after the end of glycine with quercetin coapplication, a transient rebound occurred. The quercetin effects also displayed voltage-dependence, being greater at positive membrane potentials. These effects suggested that quercetin may act as an open channel blocker. Furthermore, in the sequential application protocol, quercetin inhibited the peak amplitude of I(Gly) to a macroscopic degree while slowing GlyR desensitization. These effects implied that quercetin has a depressant effect independent of GlyR channel's opening, which maybe caused by an allosteric mechanism. Strikingly, quercetin inhibited the amplitude of recombinant-induced current mediated by alpha2-, alpha2beta-, alpha3- and alpha3beta-GlyRs but had no effects on alpha1- and alpha1beta-GlyRs that were expressed in HEK293T cells. We also investigated the effects of quercetin on I(Gly) in spinal neurons during development in vitro. The extent of blockade by quercetin on I(Gly) was slighter in spinal neurons than in hippocampal neurons in a development-dependent manner. Taken together, our results suggest that quercetin has possible effects in information processing within a neuronal network by inhibition of I(Gly) and may be useful as a pharmacological probe for identifying the subunit types of GlyRs.

Genistein and daidzein induce neurotoxicity at high concentrations in primary rat neuronal cultures

It is known that estrogen can protect neurons from excitotoxicity. Since isoflavones possess estrogen-like activity, it is of interest to determine whether isoflavones can also protect neurons from glutamate-induced neuronal injury. Morphological observation and lactate dehydrogenase (LDH) release assay were used to estimate the cellular damage. It is surprising that, contrary to estrogen, isoflavones, specifically genistein and daidzein, are toxic to primary neuronal culture at high concentration. Treatment of neurons with 50 microM genistein and daidzein for 24 h increased LDH release by 90% and 67%, respectively, indicating a significant cellular damage. Under the same conditions, estrogen such as 17beta-estradiol did not show any effect on primary culture of brain cells. At 100 microM, both genistein and daidzein increased LDH release by 2.6- and 3-fold, respectively with a 30-min incubation. Furthermore, both genistein and daidzein at 50 microM increased the intracellular calcium level, [Ca(2+)](i), significantly. To determine their mode of action, genistein and daidzein were tested on glutamate and GABA(A)receptor binding. Both genistein and daidzein were found to have little effect on glutamate receptor binding, while the binding of [(3)H]muscimol to GABA(A) receptors was markedly inhibited. However, 17beta-estradiol did not affect GABA(A) receptor binding suggesting that the toxic effect of genistein and daidzein could be due to their inhibition of the GABA(A) receptor resulting in further enhancement of excitation by glutamate and leading to cellular damage.

ERK/MAPK pathway regulates GABAA receptors

The GABAA receptor is a ligand-gated ion channel whose function and activity can be regulated by ligand binding or alternatively may be influenced indirectly through the phosphorylation of specific subunits that comprise the GABAA receptor pentamer. With respect to phosphorylation, most studies have focused on either beta or gamma subunits, whereas the role of the alpha subunit as a relevant target of signaling kinases is largely unknown. Interestingly, we found a putative phosphorylation site for extracellular-signal regulated kinase (ERK), a key effector of the MAPK pathway, in almost all known alpha subunits of the GABAA receptor, including the ubiquitously expressed alpha1 subunit. To determine whether this putative ERK phosphorylation site was functionally relevant, we evaluated if ERK inhibition (through pharmacological inhibition of its upstream kinase, MEK) altered GABA-gated currents. Using HEK293 cells stably transfected with the alpha1beta2gamma2 form of the GABAA receptor, we found that UO126 reduced basal ERK phosphorylation and resulted in an enhancement of GABA-induced peak current amplitudes. Further, the enhancement of GABA-gated currents required an intact intracellular environment as it was robust in perforated patch recordings (which preserves the intracellular milieu), but absent in conventional whole-cell recordings (which dialyzes the cytosolic contents), supporting the involvement of an intracellular signaling pathway. Finally, mutation of the ERK phosphorylation site (T375-->A) prevented the UO126-induced enhancement of GABA-gated currents. Collectively, our results implicate the MAPK pathway as a negative modulator of GABAA receptor function, whose influence on GABA-gated currents may be mediated by phosphorylation of the alpha subunit.

Response to genistein: Assaying the activation status and chemotaxis efficacy of isolated neutrophils

Neutrophil (PMN) activation and chemotaxis toward inflammatory stimuli play critical roles in host defense and tissue inflammation. To determine the molecular mechanisms that regulate PMN function, many studies currently employ in vitro PMN activation and transmigration assays using freshly isolated peripheral PMN or PMN isolated from bone marrow. However, due to the highly sensitive nature of PMN, cell activation or priming can occur during isolation, which demands assay(s) that ensure the consistency of isolated PMN prior to using them in subsequent experiments. Here, we introduce a simple screening assay based on the observation that in transmigration assays, isolated PMN differentially respond to the tyrosine kinase inhibitor genistein and this is related to their activation status. As shown, we observed that isolated PMN for which early migration is enhanced by genistein have an overall high transmigration efficacy and that over 80% of applied PMN migrate across collagen-coated filters in a 2 h time period. Conversely, the inhibitory/non-enhancement effect of genistein is accompanied by a poor PMN transmigration, with less than 25% of applied PMN transmigrating across. Further analysis of PMN spontaneous adhesion, degranulation and cell surface CD11b/CD18 expression suggests that reduced migration of PMN is associated with PMN activation/priming that happens, in most cases, during the in vitro cell isolation procedure regardless of the blood donor. Thus, based on these observations, we developed a "genistein assay" to directly predict PMN status after each isolation. From our experience, this assay has not only revealed new insights into the mechanisms of PMN activation and assisted in functional assays, but it has also provided a method that can be mastered by both inexperienced and experienced researchers to assay isolated PMN and thus avoid using inconsistent cells (e.g. pre-activated PMN) in their experiments.

Neuroprotective effects of soy phytoestrogens in the rat brain

Soy extracts are widely used as an alternative to hormone replacement therapy for the treatment of menopausal symptoms. Soy phytoestrogens, such as genistein, may act on the nervous system, affecting mood, cognitive function and behavior. In addition, several studies suggest that soy phytoestrogens are neuroprotective. The hypothesis of the present study was that soy extracts may exert neuroprotection and that this effect is mediated by phytoestrogens such as genistein. To test this hypothesis we assessed whether an acute administration of soy extract or genistein in vivo affects hippocampal neuronal loss induced by the systemic administration of kainic acid to adult Wistar female rats. One week after ovariectomy, animals received one intraperitoneal injection of soy extract (0.2, 1, 2 or 20 mg/kg), one injection of genistein (0.1, 1 or 10 mg/kg) or one injection of vehicle. Thirty minutes later, all animals received one intraperitoneal injection of kainic acid (7 mg/kg) or vehicle. One week after the injections, all animals were fixed by perfusion and the number of Nissl-stained neurons in the hilus of the dentate gyrus was estimated by the optical disector method. Administration of soy extract, even at high doses, did not induce neuronal loss and did not increase neuronal degeneration after kainic acid injury. On the contrary, soy extract at doses ranging from 1 to 20 mg/kg prevented neuronal loss induced by kainic acid. Genistein showed neuroprotective effects only at high dose (10 mg/kg), suggesting that other components in the soy extract are involved in the neuroprotective effect.

Alpha7 neuronal nicotinic acetylcholine receptors are negatively regulated by tyrosine phosphorylation and Src-family kinases

Nicotine, a component of tobacco, is highly addictive but possesses beneficial properties such as cognitive improvements and memory maintenance. Involved in these processes is the neuronal nicotinic acetylcholine receptor (nAChR) alpha7, whose activation triggers depolarization, intracellular signaling cascades, and synaptic plasticity underlying addiction and cognition. It is therefore important to investigate intracellular mechanisms by which a cell regulates alpha7 nAChR activity. We have examined the role of phosphorylation by combining molecular biology, biochemistry, and electrophysiology in SH-SY5Y neuroblastoma cells, Xenopus oocytes, rat hippocampal interneurons, and neurons from the supraoptic nucleus, and we found tyrosine phosphorylation of alpha7 nAChRs. Tyrosine kinase inhibition by genistein decreased alpha7 nAChR phosphorylation but strongly increased acetylcholine-evoked currents, whereas tyrosine phosphatase inhibition by pervanadate produced opposite effects. Src-family kinases (SFKs) directly interacted with the cytoplasmic loop of alpha7 nAChRs and phosphorylated the receptors at the plasma membrane. SFK inhibition by PP2 [4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine] or SU6656 (2,3-dihydro-N,N-dimethyl-2-oxo-3-[(4,5,6,7-tetrahydro-1H-indol-2-yl)methylene]-1H-indole-5-sulfonamide) increased alpha7 nAChR-mediated responses, whereas expression of active Src reduced alpha7 nAChR activity. Mutant alpha7 nAChRs lacking cytoplasmic loop tyrosine residues because of alanine replacement of Tyr-386 and Tyr-442 were more active than wild-type receptors and insensitive to kinase or phosphatase inhibition. Because the amount of surface alpha7 receptors was not affected by kinase or phosphatase inhibitors, these data show that functional properties of alpha7 nAChRs depend on the tyrosine phosphorylation status of the receptor and are the result of a balance between SFKs and tyrosine phosphatases. These findings reveal novel regulatory mechanisms that may help to understand nicotinic receptor-dependent plasticity, addiction, and pathology.

Soy isoflavones and cognitive function

There is growing interest in the physiological functions of soy isoflavones, especially in whether they affect cognitive function and have beneficial effects on neurodegenerative diseases. Here we review the recent evidence from clinical and experimental studies supporting a role for soy isoflavones in cognitive function. Soy isoflavones may mimic the actions and functions of estrogens on brain, and they have been shown to have positive effects on the cognitive function in females; however, studies on their effects on spatial memory have not provided consistent results in males. Although data from humans, cultures, and animal models are currently insufficient for elucidating the metabolism of soy isoflavone actions on cognitive function and the nervous system, we suggest two putative pathways; (1) an estrogen receptor-mediated pathway and (2) via the inhibition of tyrosine kinase, in particular by genistein, which is one of the soy isoflavones. Although soy isoflavones appear to have a positive effect on brain function, further research is needed to determine not only the efficacy but also the safety of soy isoflavones on the nervous system and cognitive function.

Lateral hypothalamic signaling mechanisms underlying feeding stimulation: differential contributions of Src family tyrosine kinases to feeding triggered either by NMDA injection or by food deprivation

In rats, feeding can be triggered experimentally using many approaches. Included among these are (1) food deprivation and (2) acute microinjection of the neurotransmitter l-glutamate (Glu) or its receptor agonist NMDA into the lateral hypothalamic area (LHA). Under both paradigms, the NMDA receptor (NMDA-R) within the LHA appears critically involved in transferring signals encoded by Glu to stimulate feeding. However, the intracellular mechanisms underlying this signal transfer are unknown. Because protein-tyrosine kinases (PTKs) participate in NMDA-R signaling mechanisms, we determined PTK involvement in LHA mechanisms underlying both types of feeding stimulation through food intake and biochemical measurements. LHA injections of PTK inhibitors significantly suppressed feeding elicited by LHA NMDA injection (up to 69%) but only mildly suppressed deprivation feeding (24%), suggesting that PTKs may be less critical for signals underlying this feeding behavior. Conversely, food deprivation but not NMDA injection produced marked increases in apparent activity for Src PTKs and in the expression of Pyk2, an Src-activating PTK. When considered together, the behavioral and biochemical results demonstrate that, although it is easier to suppress NMDA-elicited feeding by PTK inhibitors, food deprivation readily drives PTK activity in vivo. The latter result may reflect greater PTK recruitment by neurotransmitter receptors, distinct from the NMDA-R, that are activated during deprivation-elicited but not NMDA-elicited feeding. These results also demonstrate how the use of only one feeding stimulation paradigm may fail to reveal the true contributions of signaling molecules to pathways underlying feeding behavior in vivo.

Dietary soy supplements produce opposite effects on anxiety in intact male and female rats in the elevated plus-maze

The effects of 2 popular, commercially available soy phytoestrogen supplements on anxiety in male, diestrus female, and proestrus female rats were examined with an elevated plus-maze. Both of the soy supplements were anxiolytic in proestrus females but anxiogenic in males as determined by time spent in the open arms. No effect of diet was seen in the diestrus females. The observed changes in anxiety were not because of altered levels of gonadal hormones, as serum estrogen and progesterone levels were unaffected by diet in the females. The results suggest that the soy supplements have sex- and cycle-specific effects on anxiety.

The dietary flavonoids apigenin and (-)-epigallocatechin gallate enhance the positive modulation by diazepam of the activation by GABA of recombinant GABA(A) receptors

The dietary flavonoids apigenin, genistein and (-)-epigallocatechin gallate (EGCG) inhibited the activation by GABA (40 microM) of recombinant human alpha1beta2gamma2L GABA(A) receptors expressed in Xenopus laevis oocytes with IC(50) values of 8, 30 and 15 microM, respectively. Apigenin and genistein also acted as GABA antagonists at flumazenil-insensitive alpha1beta2 GABA(A) receptors, indicating that they were not acting as negative modulators through flumazenil-sensitive benzodiazepine sites on GABA(A) receptors. In addition to these GABA(A) antagonist effects, a novel second order modulatory action was found for apigenin and EGCG on the first order enhancement of GABA responses by diazepam. Apigenin (1 microM) and EGCG (0.1 microM) enhanced the modulatory action of diazepam (3 microM) on the activation by GABA (5 microM) of recombinant human alpha1beta2gamma2L GABA(A) receptors by up to 22% and 52%, respectively. This was not found with genistein, nor was it observed with enhancement by allopregnanolone or pentobarbitone.

Flumazenil-independent positive modulation of γ-aminobutyric acid action by 6-methylflavone at human recombinant α1β2γ2L and α1β2 GABAA receptors

In view of the ability of flavones to displace radiolabelled benzodiazepines from brain tissue and the interesting behavioural profile of these compounds, the present study investigated the activity of 6-methylflavone at ionotropic gamma-aminobutyric acid (GABA) receptors expressed in Xenopus laevis oocytes. 6-Methylflavone (1-100 microM) was found to be a positive allosteric modulator at alpha1beta2gamma2L and alpha1beta2 GABAA receptors with no significant difference between the enhancement seen at either receptor subtype. At 100 microM, 6-methylflavone enhanced the response to 5 microM GABA by 183+/-20% at alpha1beta2gamma2L GABAA receptors. The methyl substituent was important since the parent flavone was significantly weaker as a positive modulator (103+/-24% enhancement of 5 microM GABA by 100 microM flavone). This enhancement is not mediated via high-affinity benzodiazepine sites as it was not inhibited by the classical benzodiazepine antagonist flumazenil under conditions where flumazenil inhibits the potentiation of the GABA response to diazepam. 6-Methylflavone (60 microM) did not significantly affect the GABA dose-response curve at rho1 GABAC receptors. 6-Methylflavone acts as a positive modulator of recombinant GABAA receptors at sites independent of flumazenil-sensitive benzodiazepine sites.

Genistein directly blocks glycine receptors of rat neurons freshly isolated from the ventral tegmental area

The effects of tyrosine kinase inhibitors on the glycine-induced current (I(Gly)) were studied in rat neurons freshly isolated from the ventral tegmental area (VTA). Genistein reversibly and concentration-dependently depressed I(Gly), with an IC(50) of 13 microM. Preincubation with genistein had no effect on I(Gly), indicating that genistein is effective only when glycine is bound to the receptor and channels are most likely open. Genistein depressed maximum I(Gly) without significantly changing the EC(50) for glycine. Genistein-induced inhibition of I(Gly) was sensitive to membrane voltage, being greater at positive membrane potentials. A kinetic analysis indicated that genistein lengthens the time constant of I(Gly) activation, but has no effect on deactivation or desensitization. When genistein was rapidly washed out, a transient rebound current probably reflected a faster dissociation of genistein, with respect to glycine. Results of competition experiments suggest that genistein acts on the same region of the glycine receptor as picrotoxin. Daidzein, an analog of genistein that does not act on protein kinases, also inhibited I(Gly). Co-application of lavendustin A, a specific inhibitor of tyrosine kinase, had no effect on I(Gly). Our results extend to neurons isolated from the VTA, the previous finding that genistein directly inhibits glycine receptors of hypothalamic brain slices.

Phytoestrogens as modulators of steroid action in target cells

Although numerous reports exist on the potential beneficial role of nutritional phytoestrogens in human health, their molecular mechanism in target cells is still not completely understood. Phytoestrogens promote estrogen and antiestrogen effects by interacting with numerous molecules, carrier proteins, enzymes and membrane and nuclear receptors, directly or indirectly involved in the transfer of estrogen signals. The hypothesis that the ER beta subtype plays a key role in antiproliferative effect of phytoestrogens, especially in breast cancer, is examined here. This review focus on the effects of phytoestrogens in developmental processes such as those linked to reproductive function, tumorigenesis and angiogenesis.

Tyrosine kinases enhance the function of glycine receptors in rat hippocampal neurons and human alpha(1)beta glycine receptors

Glycine receptors (GlyRs) are transmitter-gated channels that mediate fast inhibitory neurotransmission in the spinal cord and brain. The GlyR beta subunit contains a putative tyrosine phosphorylation site whose functional role has not been determined. To examine if protein tyrosine kinases (PTKs) regulate the function of GlyRs, we analysed whole-cell currents activated by applications of glycine to CA1 hippocampal neurons and spinal neurons. The role of a putative site for tyrosine phosphorylation at position 413 of the beta subunit was examined using site-directed mutagenesis and expression of recombinant (alpha(1)beta(Y413F)) receptors in human embryonic kidney (HEK 293) cells. Lavendustin A, an inhibitor of PTKs, depressed glycine-evoked currents (I(Gly)) in CA1 neurons and spinal neurons by 31 % and 40 %, respectively. In contrast, the intracellular application of the exogenous tyrosine kinase, cSrc, enhanced I(Gly) in CA1 neurons by 56 %. cSrc also accelerated GlyR desensitization and increased the potency of glycine 2-fold (control EC(50) = 143 microM; cSrc EC(50) = 74 microM). Exogenous cSrc, applied intracellularly, upregulated heteromeric alpha(1)beta receptors but not homomeric alpha(1) receptors. Substitution mutation of the tyrosine to phenylalanine at position beta-413 prevented this enhancement. Furthermore, a selective inhibitor of the Src family kinases, PP2, down-regulated wild-type alpha(1)beta but not alpha(1)beta(Y413F) receptors. Together, these findings indicate that GlyR function is upregulated by PTKs and this modulation is dependent on the tyrosine-413 residue of the beta subunit.

Effects of dietary phytoestrogens in vivo and in vitro in rainbow trout and Siberian sturgeon: interests and limits of the in vitro studies of interspecies differences

A study of the effects of dietary genistein on trout and sturgeon in vivo showed that sturgeon was sensitive to 20 ppm of genistein, whereas trout was not. To analyze the origin of this interspecies difference in sensitivity, a cell culture technique was developed with hepatocytes from sturgeon and compared to results obtained with hepatocytes from trout in the same system. The hepatocyte culture proved to be useful as bioassay for estrogenicity. Vitellogenin (VTG), assayed by a specific enzyme-linked immunosorbent assay, was used as a biomarker of the estrogenic activity. 17 beta-Estradiol, its glucuronide and sulfate derivatives, and estradiol analogues (ethynylestradiol and diethylstilbestrol) were tested. Nonestrogenic compounds such as androgens, progesterone, and cortisol were tested as negative controls. VTG production was monitored at doses ranging from 1 nM to 10 microM estradiol. Phytoestrogens, from the isoflavone family, were tested individually at increasing doses exhibiting dose response curves for concentrations from 500 nM to 10 microM. With tamoxifen, an antagonist of estrogen receptors, the estrogenic effect was partially reduced. The effect was the same with ICI182,780 in sturgeon, whereas the effect was the opposite in trout. The estrogenic potency of the isoflavones ranged differently between the two species in the following order: biochanin A < daidzein = formononetin < genistein < equol in trout and biochanin A < genistein < daidzein < formononetin < equol in sturgeon. Further, in sturgeon, formononetin was the most potent phytoestrogen in vitro, whereas its activity was weakest in vivo. These data suggest that one must reconsider the relevance of heterologous estrogenic tests and of homologous in vitro tests for estrogenic potency of chemicals.

The correlation between dietary soy phytoestrogens and neuropathic pain behavior in rats after partial denervation

Soy diets suppress the development of neuropathic pain behavior in rats undergoing partial sciatic nerve ligation (PSL) injury. Phytoestrogens, plant isoflavones and lignans, abundantly found in soy products, have powerful estrogenic properties. Because, in some preparations, steroid estrogens were found to exert antinociception, we examined whether the analgesic effect of dietary soy is mediated by phytoestrogens. Male Wistar rats were fed five different diets containing 8-180 microg of phytoestrogens per gram. These diets were administered 2 wk before and 2 wk after PSL injury. Levels of tactile allodynia and mechanical and heat hyperalgesia of these rats were determined on Days 3, 8, and 14 after PSL injury. Plasma levels of two major phytoestrogens (genistein and daidzein) and two daidzein metabolites (equol and dihydrodaidzein) were assessed on Day 14 postoperatively. We found that the plasma concentration of these phytoestrogens and the levels of allodynia and hyperalgesia varied highly among dietary groups. Average plasma concentrations of phytoestrogens were associated with reduced levels of tactile allodynia and mechanical hyperalgesia, but not with reduced heat allodynia. Low and high plasma phytoestrogen levels were not analgesic in these tests. This report is the first to show that, at certain plasma concentrations, phytoestrogens reduce neuropathic pain in rats.

IMPLICATIONS

Dietary soy suppresses neuropathic pain in rats after partial sciatic nerve ligation. Some of the pain-suppression properties of soy can be attributed to phytoestrogens, isoflavones abundantly found in soy products. Average, but not low or high, plasma levels of phytoestrogens are associated with analgesia.

Effects of lifelong dietary exposure to genistein or nonylphenol on amphetamine-stimulated striatal dopamine release in male and female rats

Estrogen modulates baseline and amphetamine-stimulated dopamine (DA) release in the adult female rat striatum. The isoflavone found in soybeans, genistein, is a phytoestrogen and may have comparable effects on striatal DA levels. Similarly, the industrial intermediate and potential endocrine disrupter, para-nonylphenol, has estrogen-like effects. Here, Sprague-Dawley rats were continuously exposed to phytoestrogen-free diets containing 0, 100, or 500 ppm genistein (Experiment 1) or 0 or 200, or 750 ppm nonylphenol (Experiment 2) beginning at conception and continuing throughout. To eliminate estrous cycle influences on DA levels, females were ovariectomized at adulthood. As adults, striatal levels of DA and its metabolites [3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA)] were measured in unanesthetized male and female rats via cerebral microdialysis before and for 200 min after an intraperitoneal injection of 2 mg/kg D-amphetamine. Although baseline 5-hydroxyindoleacetic acid (5-HIAA) levels indicated an isolated effect in genistein-treated females, there were no meaningful differences among treatment groups in baseline levels of DA, DOPAC, or HVA. However, dietary exposure to 500 ppm genistein significantly potentiated amphetamine-stimulated DA release in males and a similar trend was apparent, but not statistically significant, in females. Dietary exposure to 200 or 750 ppm nonylphenol had no significant effects in males or females. These results suggest that dietary genistein exposure may act similarly to estradiol in augmenting amphetamine-stimulated DA release.

Functional analysis of GABA(A) receptors in nucleus tractus solitarius neurons from neonatal rats

To gain insight into specific GABA(A) receptor configurations functionally expressed in the nucleus tractus solitarius (NTS), we conducted several physiological and pharmacological assessments. NTS neurons were characterized in thin brain slices from 1-14 day old rats using whole-cell patch clamp recordings. GABA(A-) receptor-mediated currents were detected in all neurons tested, with an average EC(50) of 22.2 microM. GABA currents were consistently stimulated by diazepam (EC(50)=63 nM), zolpidem (EC(50)=85 nM), loreclezole (EC(50)=10.1 microM) and the neurosteroid 5alpha-pregnan-3alpha-hydroxy-20-one (3alpha-OH-DHP). In contrast, GABA-gated currents of the NTS were inhibited by the divalent cation Zn(2+) (IC(50)=33.6 microM) picrotoxin (IC(50)=2.4 microM) and blockade of endogenous protein tyrosine kinase. GABA-activated currents were insensitive to furosemide (10-1000 microM) in all NTS neurons tested. Collectively, the data suggest that in neonatal rats, the predominant alpha subunit isoform present in GABA(A) receptors of the NTS appears to be the alpha1 and/or alpha2 subunit. beta2 and/or beta3 subunits are the major beta isoform, while the predominant gamma subunit is likely gamma2. Our data suggest the contribution to NTS GABA currents by alpha3-alpha6, beta1, gamma1 and delta subunits, if present, is minor by comparison.

Regulation of ion channels by protein tyrosine phosphorylation

Ion channels are regulated by protein phosphorylation and dephosphorylation of serine, threonine, and tyrosine residues. Evidence for the latter process, tyrosine phosphorylation, has increased substantially since this topic was last reviewed. In this review, we present a comprehensive summary and synthesis of the literature regarding the mechanism and function of ion channel regulation by protein tyrosine kinases and phosphatases. Coverage includes the majority of voltage-gated, ligand-gated, and second messenger-gated channels as well as several types of channels that have not yet been cloned, including store-operated Ca2+ channels, nonselective cation channels, and epithelial Na+ and Cl- channels. Additionally, we discuss the critical roles that channel-associated scaffolding proteins may play in localizing protein tyrosine kinases and phosphatases to the vicinity of ion channels.

Effect of genistein-enriched diets on the endocrine process of gametogenesis and on reproduction efficiency of the rainbow trout Oncorhynchus mykiss

Three practical diets were formulated to contain 0, 500, or 1000 ppm genistein. The three diets were distributed for 1 year to groups of rainbow trout undergoing their first gametogenesis and until spawning. Growth performance of rainbow trout was not affected by dietary treatments. Plasma cholesterol levels were equivalent between groups. In males, a slight but constant induction of vitellogenin (VTG) synthesis and a decrease in testosterone levels were observed. A slight decrease in plasma levels of betaFSH and betaLH was noticed at the end of spermatogenesis in the male fish fed a diet with 500 ppm (genistein) (from 2.16 +/- 0.39 to 1.47 +/- 0.23 for betaFSH and from 0.44 +/- 0.09 to 0.31 +/- 0.09 for betaLH). There was a significantly reduced 17alpha,20beta(OH)(2)-progesterone (from 10.93 +/- 0.88 in control to 5.46 +/- 0.92 in males and from 251.22 +/- 21.40 to 183.22 +/- 13.48 in females). Testicular development was accelerated in genistein-fed fish, and sperm motility and concentration were decreased in a dose-dependent manner at spawning. In females, a significant increase in plasma VTG occurred only at the beginning and at the end of oogenesis. Testosterone levels were decreased at the beginning of oogenesis. Both betaFSH and betaLH were decreased by genistein (from 6.38 +/- 1.55 to 3.44 +/- 0.82 for betaFSH and from 15.18 +/- 3.00 to 6.93 +/- 0.99 for betaLH in females), whereas spawning was delayed only in females fed the diet with 500 ppm of genistein. Gamete quality was impaired only in this group, as underlined by a lower percentage of ovulating females (from 100 to 79% at the end of the trial), a lower fertilization rate, and a lower viability of fry. These results may be explained by the agonistic/antagonistic effect of genistein on estrogen function related to the tissue ratio between endogenous estrogens/genistein.

Direct inhibition of glycine receptors by genistein, a tyrosine kinase inhibitor

Genistein, a tyrosine kinase inhibitor, has been widely used to examine potential effects of protein tyrosine kinase (PTK)-mediated regulation of receptor/channel function. Alteration of ion channel function in the presence of genistein has typically led to the conclusion that PTK regulates the activity of the channel under investigation. In the present report, we have assessed the possibility that genistein directly inhibits the glycine receptor, independent of effects on protein tyrosine kinase. Coapplication of genistein with glycine reversibly inhibited the strychnine-sensitive, glycine-activated current recorded from hypothalamic neurons. The time course of genistein action was rapid (within ms). Equilibration of genistein in the intracellular solution did not affect the ability of extracellularly applied genistein to inhibit the glycine response. Glycine concentration-response profiles generated in the absence and presence of genistein indicated the block was due to non-competitive antagonism. The genistein effect also displayed voltage-dependence. Daidzein, an analog of genistein that does not block protein kinases, also inhibited glycine-activated current. Coapplication of lavendustin A, a specific inhibitor of PTK, had no effect on the glycine response. Our results demonstrate that the tyrosine kinase inhibitor genistein has a direct inhibitory effect on glycine receptors that is not mediated via inhibition of PTK.

Biphasic, opposing modulation of cloned neuronal alpha1E Ca channels by distinct signaling pathways coupled to M2 muscarinic acetylcholine receptors

Neuronal alpha1E subunits are thought to form R-type Ca channels. When expressed in human embryonic kidney cells with M2 muscarinic acetylcholine receptors, Ca channels encoded by rabbit alpha1E exhibit striking biphasic modulation. Receptor activation first produces rapid inhibition of current amplitude and activation rate. However, in the continued presence of agonist, alpha1E currents subsequently increase. Kinetic slowing persists during this secondary stimulation phase. After receptor deactivation, kinetic slowing is quickly relieved, and current amplitude over-recovers before returning toward control levels. These features indicate that inhibition and stimulation of alpha1E are separate processes, with stimulation superimposed on inhibition. Pertussis toxin eliminates inhibition without affecting stimulation, demonstrating that inhibition and stimulation involve distinct signaling pathways. Neither inhibition nor stimulation is altered by coexpression of Ca channel beta2a or beta3 subunits. Stimulation is abolished by staurosporine and reduced by intracellular 5'-adenylylimidodiphosphate, suggesting that phosphorylation is required. However, stimulation does not seem to involve cAMP-dependent protein kinase, protein kinase C, cGMP-dependent protein kinase, tyrosine kinases, or phosphoinositide 3-kinases. Stimulation does not require a Ca signal, because it is not specifically altered by varying intracellular Ca buffering or by substituting Ba as the charge carrier. In contrast to those formed by alpha1E, Ca channels formed by alpha1A or alpha1B display only inhibition and no stimulation during prolonged activation of M2 receptors. The dual modulation of alpha1E may confer unique physiological properties on native R-type Ca channels. As one possibility, R-type channels may continue to mediate Ca influx during steady inhibition of N-type and P/Q-type channels by muscarinic or other receptors.