Transepithelial Effect of Probiotics in a Novel Model of Gut Lumen to Nerve Signaling

Recent studies have shown that the gut microbiome changes brain function, behavior, and psychiatric and neurological disorders. The Gut-Brain Axis (GBA) provides a neuronal pathway to explain this. But exactly how do commensal bacteria signal through the epithelial layer of the large intestine to activate GBA nerve afferents? An in vitro model is described. We differentiated two human cell lines: Caco2Bbe1 into mature epithelium on 0.4-micron filters and then SH-SY5Y into mature neurons in 24-well plates. These were co-cultured by placing the epithelium-laden filters 1 mm above the neurons. Twenty-four hours later they were tri-cultured by apical addition of 10⁷Lactobacillus rhamnosus or Lactobacillus fermentum which settled on the epithelium. Alone, the Caco2bbe1 cells stimulated neurite outgrowth in underlying SH-SY5Y. Beyond this, the lactobacilli were well tolerated and stimulated further neurite outgrowth by 24 h post-treatment, though not passing through the filters. The results provide face validity for a first-of-kind model of transepithelial intestinal lumen-to nerve signaling. The model displays the tight junctional barrier characteristics found in the large intestine while at the same time translating stimulatory signals from the bacteria through epithelial cells to attracted neurons. The model is easy to set-up with components widely available.

Transepithelial Anti-Neuroblastoma Response to Kale among Four Vegetable Juices Using In Vitro Model Co-Culture System

Juicing vegetables is thought to be an anticancer treatment. Support exists for a rank order of anticancer greens (kale > dandelion > lettuce > spinach) based on degrees of bioavailability of different phytochemicals, also offset by some noxious molecules (i.e., calcium-oxalate). We developed a new in vitro transepithelial anti-neuroblastoma model system. The juices were diluted as predicted once in the small intestine. They were applied to apical Caco-2Bbe1 cells atop dividing SH-SY5Y neuroblastoma cells, and changes in transepithelial electrical resistance (TEER) and cell growth were considered with juice spectroscopies. Studied first in monoculture, kale and dandelion were the most cytostatic juices on SH-SY5Ys, lettuce showed no effect, and high (4.2%) spinach was cytotoxic. In co-culture, high (4.2%) kale was quickest (three days) to inhibit neuroblastoma growth. By five days, dandelion and kale were equally robust. Lettuce showed small anti-proliferative effects at five days and spinach remained cytotoxic. Spinach’s cytotoxicity corresponded with major infrared bands indicative of oxalate. Kale juice uniquely induced reactive oxygen species and S-phase cell cycle arrest in SH-SY5Y. The superiority of kale and dandelion was also apparent on the epithelium, because raising TEER levels is considered healthy. Kale’s unique features corresponded with a major fluorescent peak that co-eluted with kaempferol during high performance liquid chromatography. Because the anticancer rank order was upheld, the model appears validated for screening anticancer juices.

Human Cells Grown With or Without Substitutes for Fetal Bovine Serum

Safety concerns over cell-derived pharmaceutical products being manufactured in supplements of fetal bovine serum (FBS) have ignited pleas to replace FBS. Herein, four newly marketed alternatives to FBS were compared: a xeno-free product called Cell-Ess®, a human platelet lysate marketed as GroPro®, and two mixtures of adult bovine serum varying in their proportions of neonatal growth factors, called Liporo® and FetalGro®. An endothelial cell line (C2BBe1) and a neuronal cell line (SHSY5Y) near confluency in media with 10% FBS were selectively scraped and taken through a 25-day step-wise algorithm to replace FBS, and another human endothelial cell line (HRA-19) was studied to replicate C2BBe1. Cells were stained, counted, and compared for viability, migration, and spheroids. The C2BBe1 and HRA-19 cell lines failed to proliferate in 10% Cell-Ess® but grew in 10% GroPro® or 10% FetalGro® reasonably well compared to reference 10% FBS. With SH-SY5Y, only FetalGro® approached FBS's efficacy. These were all inferior to 11 different branded lots of FBS (positive controls), but five days into switching just amongst the FBS brands, 4 of 11 supported less proliferation than reference FBS in endothelial HRA-19 (p < 0.004). Moreover, neurospheres were enriched in two branded lots of FBS and FetalGro® (each p < 0.004), neurospheres being an unwanted phenotype for any neuronal cell application. Because platelet-derived GroPro® stood out amongst the non-FBS growth supplements to allow proliferation without inducing spheroids, it seems the best (mindful that the cells still grew slower in it compared to FBS). While no perfect replacement was found amongst the alternatives to FBS, the algorithm for switching should be useful in future testing of new alternatives to FBS as the need arises to switch from FBS and expand pharmaceutical products with safety for human use.

Agmatine: clinical applications after 100 years in translation

Agmatine (decarboxylated arginine) has been known as a natural product for over 100 years, but its biosynthesis in humans was left unexplored owing to long-standing controversy. Only recently has the demonstration of agmatine biosynthesis in mammals revived research, indicating its exceptional modulatory action at multiple molecular targets, including neurotransmitter systems, nitric oxide (NO) synthesis and polyamine metabolism, thus providing bases for broad therapeutic applications. This timely review, a concerted effort by 16 independent research groups, draws attention to the substantial preclinical and initial clinical evidence, and highlights challenges and opportunities, for the use of agmatine in treating a spectrum of complex diseases with unmet therapeutic needs, including diabetes mellitus, neurotrauma and neurodegenerative diseases, opioid addiction, mood disorders, cognitive disorders and cancer.

Putative agmatinase inhibitor for hypoxic-ischemic new born brain damage

Agmatine is an endogenous brain metabolite, decarboxylated arginine, which has neuroprotective properties when injected intraperitoneally (i.p.) into rat pups following hypoxic-ischemia. A previous screen for compounds based on rat brain lysates containing agmatinase with assistance from computational chemistry, led to piperazine-1-carboxamidine as a putative agmatinase inhibitor. Herein, the neuroprotective properties of piperazine-1-carboxamidine are described both in vitro and in vivo. Organotypic entorhinal-hippocampal slices were firstly prepared from 7-day-old rat pups and exposed in vitro to atmospheric oxygen depletion for 3 h. Upon reoxygenation, the slices were treated with piperazine-1-carboxamidine or agmatine (50 μg/ml agents), or saline, and 15 h later propidium iodine was used to stain. Piperazine-1-carboxamidine or agmatine produced substantial in vitro protection compared to post-reoxygenated saline-treated controls. An in vivo model involved surgical right carotid ligation followed by exposure to hypoxic-ischemia (8 % oxygen) for 2.5 h. Piperazine-1-carboxamidine at 50 mg/kg i.p. was given 15 min post-reoxygenation and continued twice daily for 3 days. Cortical agmatine levels were elevated (+28.5 %) following piperazine-1-carboxamidine treatment with no change in arginine or its other major metabolites. Histologic staining with anti-Neun monoclonal antibody also revealed neuroprotection of CA1-3 layers of the hippocampus. Until endpoint at 22 days of age, no adverse events were observed in treated pups' body weights, rectal temperatures, or prompted ambulation. Piperazine-1-carboxamidine therefore appears to be a neuroprotective agent of a new category, agmatinase inhibitor.

Pro-inflammatory biomakers in depression: treatment with venlafaxine

High levels of pro-inflammatory biomarkers have been reported in depression. In the present study, five pro-inflammatory biomarkers were measured in the blood of patients with major depressive disorder (MDD). Biomarker levels were compared to age- and sex-matched healthy subjects. Patients with MDD had significantly higher baseline levels of tumour necrosis factor-alpha (TNFalpha, P=0.04), interleukin-1beta (IL1beta, P=0.03), and monocyte chemotactic protein-1 (MCP-1; P=0.02) compared to controls. There were no differences between groups in levels of cell determinant-40 ligand (CD40L) and C-reactive protein (CRP). A subset of the MDD patients consented to undergo treatment with venlafaxine (an SNRI: at lower doses a selective serotonin reuptake inhibitor; at higher doses also a norepinephrine reuptake inhibitor) for 8 weeks. By week 8, all treatment completers had responded therapeutically. However, levels of TNFalpha, IL1beta, and MCP-1 remained elevated. A concave quadratic equation described the associations between plasma venlafaxine concentrations and IL1beta (P=0.03), TNFalpha (P=0.09), and MCP-1 (P=0.02), suggesting that these biomarkers may have become selectively lowered in the serotonergic dose range of venlafaxine. This is the first report of venlafaxine's possible effect on pro-inflammatory biomarkers.

IRAS, a candidate for I1-imidazoline receptor, mediates inhibitory effect of agmatine on cellular morphine dependence

Agmatine, an endogenous ligand for the I1-imidazoline receptor, has previously been shown to prevent morphine dependence in rats and mice. To investigate the role of imidazoline receptor antisera-selected protein (IRAS), a strong candidate for I1R, in morphine dependence, two CHO cell lines were created, in which mu opioid receptor (MOR) was stably expressed alone (CHO-mu) or MOR and IRAS were stably co-expressed (CHO-mu/IRAS). After 48 h administration of morphine (10 microM), naloxone induced a cAMP overshoot in both cell lines, suggesting cellular morphine dependence had been produced. Agmatine (0.1-2.5 microM) concentration-dependently inhibited the naloxone-precipitated cAMP overshoot when co-pretreated with morphine in CHO-mu/IRAS, but not in CHO-mu. Agmatine at 5-100 microM also inhibited the cAMP overshoot in CHO/mu and CHO-mu/IRAS. Efaroxan, an I1R-preferential antagonist, completely blocked the effect of agmatine on the cAMP overshoot at 0.1-2.5 microM in CHO-mu/IRAS, while partially reversing the effects of agmatine at 5-100 microM. L-type calcium channel blocker nifedipine entirely mimicked the effects of agmatine at high concentrations on forskolin-stimulated cAMP formation in CHO-mu and naloxone-precipitated cAMP overshoot in morphine-pretreated CHO-mu. Therefore, IRAS, in the co-transfected CHO-mu/IRAS cell line, appears necessary for low concentrations of agmatine to cause attenuation of cellular morphine dependence. An additional effect of agmatine at higher concentrations seems to relate to both transfected IRAS and some naive elements in CHO cells, and L-type voltage-gated calcium channels are not ruled out. This study suggests that IRAS mediates agmatine's high affinity effects on cellular morphine dependence and may play a role in opioid dependence.

Imidazoline receptors associated with noradrenergic terminals in the rostral ventrolateral medulla mediate the hypotensive responses of moxonidine but not clonidine

We determined whether the cardiovascular actions of central anti-hypertensive agents clonidine and moxonidine are dependent on noradrenergic or serotonergic innervation of the rostral ventrolateral medulla (RVLM) in conscious rabbits. 6-Hydroxydopamine (6-OHDA) or 5,6-dihydroxytriptamine (5,6-DHT) was injected into the RVLM to deplete noradrenergic and serotonergic terminals respectively. One, 2 and 4 weeks later, responses to fourth ventricular (4V) clonidine (0.65 microg/kg) and moxonidine (0.44 microg/kg) were examined. Destruction of noradrenergic pathways in the RVLM by 6-OHDA reduced the hypotensive response to 4V moxonidine to 62%, 47% and 60% of that observed in vehicle treated rabbits at weeks 1, 2 and 4 respectively. The moxonidine induced bradycardia was similarly attenuated (to 46% of vehicle). Conversely, 6-OHDA had no effect on the hypotensive or bradycardic effects of 4V clonidine. Efaroxan (I(1)-imidazoline receptor/alpha(2)-adrenoceptor antagonist; 3.5, 11, 35 microg/kg) and 2-methoxyidazoxan (alpha(2)-adrenoceptor antagonist; 0.3, 0.9, 3 microg/kg) equally reversed the hypotension to 4V clonidine, suggesting a mainly alpha(2)-adrenoceptor mechanism. Efaroxan preferentially reversed responses to moxonidine in both vehicle and 5,6-DHT groups and in the 1st week after 6-OHDA, suggesting a mechanism involving mainly I(1)-imidazoline receptors. This selectivity was subsequently lost in the 2nd and 4th weeks when the remaining hypotension was mainly mediated by alpha(2)-adrenoceptors. Depletion of serotonergic terminals did not alter the responses to either agonist nor did it change the relative effectiveness of the antagonists. Western blots of RVLM tissues probed with imidazoline and alpha(2)-adrenoceptor antisera showed a pattern of bands close to that reported in other species. The main effect of 6-OHDA was an 18% lower level of the 42 kDa imidazoline protein (P<0.05). We conclude that the hypotensive and bradycardic actions of moxonidine but not clonidine are mediated through imidazoline receptors and are dependent on intact noradrenergic pathways within the RVLM. Furthermore, the noradrenergic innervation may be associated with a 42 kDa imidazoline receptor protein.

Effect of agmatine against cell death induced by NMDA and glutamate in neurons and PC12 cells

AIMS

Agmatine is an endogenous guanido amine and has been shown to be neuroprotective in vitro and in vivo. The aims of this study are to investigate whether agmatine is protective against cell death induced by different agents in cultured neurons and PC12 cells.

METHODS

Cell death in neurons, cultured from neonatal rat cortex, was induced by incubating with (a) NMDA (100 microM) for 10 min, (b) staurosporine (protein kinase inhibitor, 100 nM) for 24 h, and (c) calcimycin (calcium ionophore, 100 nM) for 24 h in the presence and absence of agmatine (1 micro M to 1 mM). Cell death in PC12 cells was induced by exposure to glutamate (10 mM), staurosporine (100 nM), and calcimycin (100 nM). The activity of lactate dehydrogenase (LDH) in the medium was measured as the marker of cell death and normalized to cellular LDH activity.

RESULTS

Agmatine significantly reduced the medium LDH in NMDA-treated neurons but failed to reduce the release of LDH induced by staurosporin or calcimycin. In PC12 cells, agmatine significantly reduced LDH release induced by glutamate exposure, but not by staurosporine or calcimycin. Agmatine itself neither increased LDH release nor directly inhibited the enzyme activity.

CONCLUSION

We conclude that agmatine protects against NMDA excitotoxicity in neurons and PC12 cells but not the cell death induced by protein kinase blockade or increase in cellular calcium.

Effect of postmortem delay on imidazoline receptor-binding proteins in human and mouse brain

Immunoreactive proteins of 45-kD and 29/30-kD doublet bands are candidate imidazoline receptor binding proteins (IRBP) based on associations with I(1) or I(2) binding sites, respectively. It was reported that the density of cortical membrane 29/30-kD I(2) protein is diminished whereas a 45-kD I(1) protein is increased in depressed suicide victims versus controls. IRBP immunoreactive bands of similar size have been suggested to be breakdown products of the 170-kD protein known as IRAS (putative full-length I(1) receptor). This study compares nonpathologic human brains collected and frozen after postmortem delays of 13.4 hours +/- 1.7 (SEM) with brains of longer postmortem delays (26.1 hours +/- 1.2). The fresher human brains possessed more full-length IRAS (P = 0.05). In another study, the postmortem decay of IRBP bands in mouse brain was shown to be linear over time. The results are relevant to previous studies of IRBP bands in postmortem brains of depressed suicide victims.

Structure-activity analysis of guanidine group in agmatine for brain agmatinase

To identify a selective inhibitor of mammalian agmatinase, screening was performed on four analogues of agmatine with modifications directly to the guanidine group, six analogues with modifications to the carbon-amine chain, and one analogue with modifications at both ends of the molecule. Control compounds were aminoguanidine and 7-nitroindazole, known inhibitors of the three isoforms (i, e, n) of nitric oxide synthase (NOS), and arcaine, a known inhibitor of the glutamate NMDA receptor. These compounds were compared for inhibition of rat agmatinase and arginine decarboxylase (ADC) activities. Results were studied by ab initio Hartee-Fock descriptors based on optimized geometries and van der Waals radii. Linear correlations were obtained using various geometric and electronic descriptors of the carbon (C), nitrogen (N), and hydrogen (H) atoms in the guanidine moiety. The best fit equation for percent activity remaining of rat agmatinase was = 0.3225 D + 72.76 D1916 + 64.97 D1920 - 192.58 H21 - 253.09 (r = 0.89), where D is the calculated dipole moment, D1916 and D1920 are the N19-N16 and N19-N20 distances, respectively, and H21 is the charge on H21. This agmatinase equation is distinct from the equations fit for ADC, the three NOS isoforms, and inhibition of NMDA receptor binding.

Intracellular effect of imidazoline receptor on alpha(2A)-noradrenergic receptor

Imidazoline-1 receptors (I(1)R) and alpha(2)-noradrenergic receptors (alpha(2)AR) are known to coexist in many cell types and bind many of the same imidazoline ligands. Herein, the possibility of an interaction between these receptors was explored using a cloned cDNA that encodes a protein with I(1)R-like binding properties, designated imidazoline receptor antisera-selected (IRAS). Chinese hamster ovary (CHO) sublines permanently expressing the human subtype alpha(2A)AR cDNA were transiently cotransfected with the human IRAS cDNA (pIRAS). Saturation radioligand binding experiments on membranes isolated from the various sublines allowed distinction between I(1)R and alpha(2A)AR. Transfection of pIRAS into either subline led to a rise in membrane I(1)R-binding sites. Immunoblotting revealed that IRAS was enriched in membranes more than in cytosolic fractions. Transfection of pIRAS in CHO cells harboring the alpha(2A)AR cDNA resulted in a twofold increase in alpha(2A)AR binding sites with no change in alpha(2A)AR binding affinity, compared with controls. Immunoblotting also revealed increased expression of membranous alpha(2A)AR by IRAS. Thus, pIRAS transfection led to I(1) binding sites and to an increase in alpha(2A)AR binding sites in CHO cells expressing the human alpha(2A)AR. Although the mechanism is unclear, this increase in binding sites may explain previous imidazoline drug effects suggestive of interactions between these two receptors.

Regulation of inducible nitric oxide synthase and agmatine synthesis in macrophages and astrocytes

Agmatine is a novel endogenous guanido amine synthesized from arginine by arginine decarboxylase. Among several biologic effects, the ability of agmatine to protect against ischemic injury and chronic neuropathic pain is particularly interesting. Because inflammation is a common contributor to these conditions, we sought to determine if agmatine acts by decreasing the production of proinflammatory molecules such as nitric oxide and if agmatine synthesis is regulated by inflammatory stimuli. We tested whether agmatine affects astroglial and macrophage (RAW 264.7 cell line) nitric oxide synthase-2 (NOS-2) expression. NOS-2 was induced in these cells by incubation with lipopolysaccharide (LPS) plus three cytokines for astrocytes and LPS alone for RAW 264.7 cells in the presence and absence of varying concentrations of agmatine. NOS-2 activity was assessed after 24 hours by nitrite accumulation in the culture media. Agmatine dose-dependently inhibited nitrite accumulation, and shorter incubation with agmatine (1 and 4 hours) also caused significant reduction. Agmatine decreased the expression of NOS-2 activity and NOS-2 protein as determined by immunoblot analysis. Incubation of astrocytes and RAW 264.7 cells with LPS/cytokines for 2 hours resulted in an increase in arginine decarboxylase (ADC) activity, whereas longer-term incubation (12-17 hours) lowered ADC activity. Agmatine levels in these cells are increased after 6-hour incubation with LPS/cytokines. These results show that agmatine inhibits the production of nitric oxide by decreasing the activity of NOS-2 in macrophages and astroglial cells by decreasing the levels of NOS-2 protein. These findings provide a molecular basis for the neuroprotective and anti-inflammatory actions of agmatine.

Atypical [(3)H]clonidine binding sites in human caudate and platelets on cryostat-cut sections

Pharmacological characterization is described for a human imidazoline binding site (I-site) labeled by [(3)H]clonidine using standard autoradiographic method. Under conditions that mask alpha(2)-adrenergic sites, only a single high affinity site was observed in human caudate and blood platelet sections. Affinity constants (K(i)) were highly correlated between the two tissues (r = 0.90, P = 0.0003). This site is dissimilar to classical I(1) and I(2) sites, even though both tissues possess abundant I(1) and I(2) sites by filtration binding methods. It is suggested that the isotonic buffer conditions inherent to the procedure alter drug affinities to the classical I(1) site.

Expression of human arginine decarboxylase, the biosynthetic enzyme for agmatine

Agmatine, an amine formed by decarboxylation of L-arginine by arginine decarboxylase (ADC), has been recently discovered in mammalian brain and other tissues. While the cloning and sequencing of ADC from plant and bacteria have been reported extensively, the structure of mammalian enzyme is not known. Using homology screening approach, we have identified a human cDNA clone that exhibits ADC activity when expressed in COS-7 cells. The cDNA and deduced amino acid sequence of this human ADC clone is distinct from ADC of other forms. Human ADC is a 460-amino acid protein that shows about 48% identity to mammalian ornithine decarboxylase (ODC) but has no ODC activity. While naive COS-7 cells do not make agmatine, these cells are able to produce agmatine, as measured by HPLC, when transfected with ADC cDNA. Northern blot analysis using the cDNA probe indicated the expression of ADC message in selective human brain regions and other human tissues.

Cell Signaling by Imidazoline-1 Receptor Candidate, IRAS, and the Nischarin Homologue

IRAS transfection into Chinese hamster ovary (CHO) or pheochromocytoma (PC-12) cell lines leads to the appearance of nonadrenergic binding sites for radiolabeled-clonidine. Nischarin is the mouse homologue of IRAS. IRAS seems to be a cytosolic protein that is anchored to the intracellular side of plasma membranes by a POX domain. Previous studies of IRAS-transfected HEK293 cells, and Nischarin-transfected 3T3 cells have shown this protein can intrinsically mediate cell growth and differentiation independent of imidazoline drugs through binding to insulin receptor substrates (HEK293 cells) and fibronectin receptors (3T3 cells). Herein, a growth-arrested PC-12 cell line stably transfected with IRAS is shown to express lower basal and nerve growth factor-stimulated levels of the activated form of extracellular receptor kinase than found in a vector-only transfected control cell line treated similarly. These findings suggest that IRAS is a membrane-associated mediator of receptor signaling.

Relationship between Platelet Imidazoline Receptor-Binding Peptides and Candidate Imidazoline-1 Receptor, IRAS

A candidate human imidazoline-1 receptor, designated imidazoline receptor antisera-selected (IRAS) protein, was cloned based on immunoreactivity with antiserum against a purified imidazoline receptor binding peptide (IRBP antiserum). Human IRAS is 167 kD in size, different from 33- to 85-kD IRBP bands previously linked to the human platelet I(1) receptor. To explore the possible relationship between IRAS and these smaller proteins, seven different epitope-specific antisera against IRAS were raised in rabbits for comparison with IRBP antiserum. Focus was on antiserum(227-241), corresponding to amino acids No. 227 to 241 in IRAS, because this antiserum was found uniquely able to immunoprecipitate non-denatured 85-kD and 170-kD forms of IRAS from a human megakaryoblastoma cell line (MEG01), a model of platelet-producing cells. Human platelets lacked the 170-kD form of IRAS, but 33-kD and 85-kD bands were detectable and seemed to be possible fragments of full-length IRAS. The intensity of the 85-kD band detected by antiserum(227-241) was significantly correlated (r = 0.62, P = 0.04) with the intensity of the 33-kD band across 11 human platelet samples. A positive correlation between the intensities of the 33-kD and 85-kD bands is consistent with both being fragments of IRAS.

Relevance of Imidazoline Receptors and Agmatine to Psychiatry: A Decade of Progress

The cardiovascular relevance of imidazoline receptors (IR) has received tremendous attention since their discovery in 1984. However, evidence also has accumulated for the relevance of IR and an endogenous ligand, agmatine, to psychiatric disease. Emphasis has been placed on altered levels of the I(1)-imidazoline site on human platelets and in human postmortem brain tissue from depressed patients. Attempts at exploring the molecular nature of the I(1) protein have led to the cloning of a protein, IRAS. Based on transfection studies, IRAS seems to be involved in neuronal plasticity events. The I(2) site also appears linked to psychiatric research since some of these sites are localized to a specific domain on monoamine oxidases. Different peptides have been identified by means of an imidazoline-receptor-binding-protein (IRBP) antiserum, and these peptides, some of which appear to be fragments derived from IRAS, undergo changes in platelets and brain commensurate with altered mood states of the subject, notably depressive symptomatology. The search for an endogenous ligand for imidazoline receptor(s) also has led to agmatine, a decarboxylated derivative of arginine. Research on agmatine has mushroomed over the past several years and its measurement in the blood and brain has opened new research opportunities. This novel neurotransmitter interacts with a variety of receptors and has been implicated in mediation of stress responses, analgesia, drug addiction and withdrawal, convulsions, and neuroprotection. Given that IR and agmatine appear involved in a multitude of neurophysiologic and pathologic functions, the potential for new drug development is intriguing.

Agmatine Crosses the Blood-Brain Barrier

The question of whether agmatine crosses the blood-brain barrier has not been directly addressed, even though peripheral injection of this compound has produced behavioral responses in drug withdrawal, antidepressant, and anti-anxiety paradigms. Two models were used in this investigation. In the first, mice were injected intraperitoneally (i.p.) with agmatine (10, 50, or 300 mg/kg body weight) or arginine (600 mg/kg). After 1 or 3 hours, the animals were killed under gas anesthesia by perfusing their brains with ice-cold saline, and whole-brain agmatine was measured by HPLC. In parallel studies, a rhesus monkey was injected under gas anesthesia either intravenously (i.v.) with agmatine (30 mg/kg) or arginine (150 mg/kg), or intracerebroventricularly (i.c.v.) with agmatine (0.3 mg/kg i.c.v.). At varying times thereafter, cisterna magna cerebrospinal fluid (CSF) and blood plasma were collected and analyzed for agmatine levels. A rise in mouse brain agmatine was apparent after doses of 50 and 300 mg/kg i.p. Monkey CSF agmatine peaked in parallel with plasma agmatine 15 minutes following intravenous (i.v.) agmatine injection and at one sixth the level of the plasma peak. Monkey CSF agmatine peaked 43 minutes after i.v. arginine injection. The ventricular injection of agmatine resulted in a threefold sustained rise in blood plasma agmatine for at least 24 hours after injection. Therefore, agmatine and its precursor, arginine, cross the blood-brain barrier. CSF agmatine may be newly synthesized from peripherally injected arginine.

IRAS Splice Variants

The human I(1)-imidazoline receptor candidate gene, iras, has previously been cloned and mapped to locus 3p21.1-9 (also known as Nischarin; accession No. AC006208). By comparison to a database of expressed sequence tags (ESTs), three alternatively spliced transcripts have been deduced. A map of 21 exons was constructed for the medium-length transcript (IRAS-M) containing 5,232 base pairs (bp) and encoding 1,504 amino acids (aas). Introns 13B and 13C are inserted into the two alternative transcripts, forming IRAS-S and IRAS-L mRNA (short and long isoforms). Northern blots confirmed the existence of these mRNA isoforms. In most brain regions the order of mRNA abundance was IRAS-M > IRAS-L > IRAS-S mRNA. Although aas 1 through 510 are theoretically identical, truncated proteins could be derived from IRAS-S (2,678 bp transcript yields 515 aas) and IRAS-L (9,457 bp transcript yields 583 aas). Because exon-16 of the iras gene has been proposed to encode the functional domains of imidazoline and a-5 integrin binding, only IRAS-M is expected to possess I(1) receptor properties. Subtype-selective cDNA expression constructs were therefore generated and used to transfect CHO cells. High-affinity I(1) binding was endowed by IRAS-M and IRAS-L, but not by IRAS-S transfection.

Is Agmatine an Endogenous Factor Against Stress?

Agmatine is an endogenous amine synthesized from the decarboxylation of arginine. A proposed intracellular role of agmatine is to balance the production of polyamines (a promitotic process) and nitric oxide (an inflammatory process). Agmatine is also released from neurons upon depolarization. We previously reported that agmatine concentrations are increased in rat pups' brains shortly after hypoxic-ischemia and in the plasma of depressed patients. Herein, male rats (270-290 g) were divided into four groups receiving different degrees of known stress: 2-hour restraint at 21 degrees C, 4-hour restraint at 21 degrees C, 4-hour restraint at 4 degrees C, and control rats only handled at 21 degrees C. Cortex, cerebellum, medulla, hippocampus, hypothalamus, and blood plasma samples were collected for determination of endogenous agmatine levels. No changes in agmatine levels were detected after 2-hour and 4-hour restraint at room temperature, but concentrations of agmatine were increased in all brain regions except cerebellum after 4-hour restraint in the cold. Plasma agmatine levels (ng/mL) were 6.8 +/- 0.6 in controls versus 58.1 +/- 12.8 in the 4-hour restraint-plus-cold group. Cortical agmatine levels (ng/g wet tissue) were 15.3 +/- 2.4 in controls versus 57.4 +/- 19.6 in the 4-hour restraint-plus-cold group. Therefore, endogenous agmatine was increased in response to cold-restraint stress, possibly as a neuroprotective agent.

Association Between I2 Binding Sites and Monoamine Oxidase-B Activity in Platelets

An I(2) imidazoline binding site on monoamine oxidase-B (MAO-B) is known to be encoded by a noncatalytic part of the enzyme, different from that which recognizes mechanism-based inhibitors. Herein, the relationship between I(2)-imidazoline binding sites and MAO-B activity has been assessed using a semi-purified source of MAO-B: platelet mitochondrial membranes. A positive correlation between I(2) sites and MAO-B activity was observed (r = 0.61, P = 0.0016) among 24 human subjects. Nevertheless, the variance in MAO-B activity cannot be completely accounted for in relation to I(2) sites. Therefore, I(2) density and MAO-B activity are only weakly correlated in platelets.

IRAS Is an Anti-Apoptotic Protein

Active cell death, also known as apoptosis, has been implicated in the pathophysiology of diseases such as cancer, heart failure and neurodegenerative disorders. We report the anti-apoptotic function of IRAS, which was previously shown to bind imidazoline ligands. The amino acid sequence of human IRAS (hIRAS) is unrelated to known proteins, except for rat IRAS and a mouse homologue named nischarin, which binds the alpha5 integrin subunit of the fibronectin receptor. When stably transfected into PC12 cells, hIRAS localizes to the cytosol as a 167 kDa immunoreactive protein. Clonal PC12 cell lines expressing hIRAS displayed normal serum growth responses. However, hIRAS expression led to prolonged cell survival against known apoptotic stimuli: serum starvation or thapsigargin or staurosporine treatments. The apoptotic population of hIRAS-expressing cells was significantly reduced, and this protection was achieved by a decrease in caspase-3 activity, phosphatidylserine translocation, and nuclear fragmentation. Similar protective effect was obtained in COS7 cells transiently transfected with hIRAS. A partial activation of the PI3 kinase pathway is possibly implicated in the anti-apoptotic effect of IRAS. Thus, IRAS appears to represent a previously unknown anti-apoptotic protein involved in the regulation of cell survival.

Differential expression of alpha2-adrenoceptor vs. imidazoline binding sites in postmortem orbitofrontal cortex and amygdala of depressed subjects

Clonidine is a well established antihypertensive agent that is also used effectively to treat a variety of psychiatric disorders. Clonidine is a prototypic imidazoline compound that acts as an alpha(2)-adrenergic agonist but possesses nearly equivalent affinity for non-adrenergic imidazoline binding sites (I-sites). Receptor autoradiography of [(3)H]-clonidine binding presented herein compares densities of alpha(2)-adrenoceptors and I-sites (under a noradrenergic-mask) in Brodmann's area 47 of the left orbitofrontal cortex (OFC) and in six amygdaloid nuclei of subjects with major depression (n=12) vs. controls with no psychiatric history (n=11). Postmortem diagnoses were made from psychiatric interviews with next-of-kin. [(3)H]-Clonidine binding to alpha(2)-adrenoceptors in each of six OFC layers was lower, although not reaching statistical significance in any one layer by multivariate analysis, in depressives vs. control subjects. Binding to I-sites was conversely higher in depressives compared to control OFC layers, but did not reach statistical significance alone. However, the ratios of alpha(2)-adrenoceptor : I-sites in all six layers of OFC of depressed subjects were nearly half that of control subjects (P<0.008). In amygdalas from a different group of depressed patients there were no changes in alpha(2)-adrenoceptors or I-sites, or their ratios, compared with controls. The results support previous western blot data indicating a cortex-selective shift away from alpha(2)AR towards I-site preponderance in depressed patients.

Non-adrenergic exploratory behavior induced by moxonidine at mildly hypotensive doses

Moxonidine is a centrally-active imidazoline compound with preferential affinity for imidazoline receptors (IR) over alpha(2)-adrenoceptors (alpha(2)AR). Clinically, moxonidine has proven advantageous for treating hypertension over pure alpha(2)-adrenergic agonists (i.e., guanabenz) due to its lowered incidence of sedative side effects. The present experiments reveal divergent behavioral effects of low doses of moxonidine and guanabenz in C57Bl/6 mice in an exploratory arena. Low-dose moxonidine (0.05 mg kg(-1) i.p.) elicited an increase in novel object contacts (+36%) and more movement into central space (+56%; P<0.01) compared to saline-injected controls; whereas guanabenz induced only dose-responsive sedative-like behaviors in the same paradigm. Yet, the two agonists were indistinguishable in terms of blood pressure changes over a similar dose range (0.025-0.1 mg kg(-1) i.p.) in consciously free-moving mice (Delta mean+/-S.E.M.=-12.3+/-3.2 mm Hg for moxonidine versus -13.5+/-1.9 mm Hg for guanabenz). As expected of alpha(2)AR involvement, the sedative-like effects of guanabenz were completely blocked by pretreatment with the non-imidazoline alpha(2)AR-antagonist, SKF86466 (0.5 or 1.0 mg kg(-1) i.p.). However, the pro-exploratory effects of low doses of moxonidine (0.05 or 0.1 mg kg(-1)) were not antagonized by SKF86466. These results suggest that moxonidine acts preferentially through a non-adrenergic mechanism, possibly IR-mediated, to elicit pro-exploratory behavior.

Agmatine suppresses nitric oxide production and attenuates hypoxic-ischemic brain injury in neonatal rats

Nitric oxide and excitatory amino acids contribute to hypoxic-ischemic brain injury. Agmatine, an endogenous neurotransmitter or neuromodulator, is an inhibitor of nitric oxide synthase and an antagonist of N-methyl-D-aspartate receptors. Does agmatine reduce brain injury in the rat pup hypoxic-ischemic model? Seven-day old rat pups had right carotid arteries ligated followed by 2.5 h of hypoxia (8% oxygen). Agmatine or vehicle was administered by i.p. injection at 5 min after reoxygenation and once daily thereafter for 3 d. Brain damage was evaluated by weight deficit of the right hemisphere at 22 d after hypoxia by a blinded observer. Agmatine treatments significantly reduced weight loss in the right hemisphere from -30.5 +/- 3.6% in vehicle-treated pups (n = 22) to -15.6 +/- 4.4% in the group treated with 50 mg/kg (n = 18, p < 0.05) and to -15.0 +/- 3.7% in the group treated with 100 mg/kg (n = 18, p < 0.05), but the group treated with 150 mg/kg showed no reduction. Other pups received agmatine or vehicle at 5 min after reoxygenation, and brain biochemistry was assessed. Levels of endogenous brain agmatine rose 2- to 3-fold owing to hypoxic-ischemic (3 h), whereas pups treated with agmatine (100 mg/kg) showed 50-fold higher brain agmatine levels (3 h). Agmatine (100 mg/kg) blocked a hypoxia-induced increase in brain nitric oxide metabolites at 6 h (vehicle-treated, +60.2 +/- 15.2%; agmatine-treated, +4.2 +/- 8.4%; p < 0.05). Agmatine thus reduces brain injury in the neonatal rat hypoxic-ischemic model, probably by blunting the rise in nitric oxide metabolites normally seen after hypoxia.

Insulin receptor substrate 4 associates with the protein IRAS

The insulin receptor substrates (IRSs) are key components in signaling from the insulin receptor, and consequently any proteins that interact with them are expected to participate in insulin signaling. In this study we have searched for proteins that interact with IRS-4 by identifying the proteins that coimmunoprecipitated with IRS-4 from human embryonic kidney 293 cells by microsequencing through mass spectrometry. A group of proteins was found. These included phosphatidylinositol 3-kinase, a protein previously identified as an IRS-4 interactor, and several proteins for which there was no previous evidence of IRS-4 association. One of these proteins, named IRAS, that had been found earlier in another context was examined in detail. The results from the overexpression of IRAS, where its amount was about the same as that of IRS-4, indicated that IRAS associated directly with IRS-4 and showed that the increased complexation of IRS-4 with IRAS did not alter the insulin-stimulated tyrosine phosphorylation of IRS-4 or the association of IRS-4 with phosphatidylinositol 3-kinase or Grb2. On the other hand, overexpression of IRAS enhanced IRS-4-dependent insulin stimulation of the extracellularly regulated kinase. The domains of IRAS and IRS-4 responsible for the association of these two proteins were identified, and it was shown that IRAS also associates with IRS-1, IRS-2, and IRS-3.

Down-regulation of platelet imidazoline-1-binding sites after bupropion treatment

An elevation of I1 (imidazoline-1)-binding sites on platelets may be a state marker for depression. Herein, platelet I1 sites were compared in two groups of unipolar depressed patients given different regimens of bupropion treatment: Regimen 1 (n = 13 titrated up to 300 mg/d by week 4 and held constant until week 6); Regimen 2 (n = 15 titrated up to 300 mg/d by week 2, to 450 mg/d by week 6, and held constant until week 8). Platelet I1 sites were quantified by p-[125I]iodoclonidine binding (0.5-15 nM) and displaced by moxonidine under a saturating concentration of norepinephrine to mask alpha2-adrenoceptors. I1 B max values were confirmed to be high at pretreatment in depressed patients (n = 28) compared to healthy control subjects (n = 18; p = 0.02). Highest B max values at pretreatment were found in patients who responded worst to treatment. More than two-thirds of patients recovered from depression (69 and 80% in Regimens 1 and 2, respectively) after treatment. Dose and/or time of exposure to bupropion were relevant variables since (1). only Regimen 2 led to platelet I1 down-regulation and (2). the extent of down-regulation correlated with plasma concentrations of bupropion. The data suggest a dissociation exists between I1 down-regulation and therapeutic response, or else platelet I1 down-regulation lags behind clinical antidepressant response before becoming measurable.

Imidazoline receptors: possible involvement in the pathophysiology and treatment of depression

Imidazoline receptors (IR), a novel family of non-adrenergic receptors, are present in brain, especially the limbic system, and platelets among other organs. Their functions include central mediation of blood pressure control and possibly modulation of affective symptomatology. Studies of unipolar depressed patients have revealed consistent up-regulation of the I(1) subtype on the platelet. Treatment with cyclic antidepressants is accompanied by down-regulation in responders. Treatment with the non-cyclic bupropion produced similar findings. Studies of human post-mortem brain show changes in depressed subjects but the protein fragments assessed are of different molecular weights than in the platelet. Plasma agmatine is believed to be a putative endogenous ligand for I receptors. Thus, IR may be useful state markers of affective disorders. Copyright 2001 John Wiley & Sons, Ltd.

Autoradiographic comparison of [3H]-clonidine binding to non-adrenergic sites and alpha(2)-adrenergic receptors in human brain

Clonidine is a partial agonist at brain alpha(2)-adrenoceptors (alpha(2)AR), but also has high affinity (K(D) = 51 nM) in homogenate binding assays for non-adrenergic imidazoline-binding sites (I-sites; imidazoline receptors). Herein, an autoradiographic comparison of [3H]-clonidine binding to I-sites and alpha(2)AR in sections of human brain is reported. For I-sites, the adrenergic component of 50 nM [3H]-clonidine binding was masked with either 60 microM norepinephrine (NE; alpha(2)AR agonist) or 12.5 microM methoxy-idazoxan (MIDX; selective alpha(2)AR antagonist), whereas the remaining non-adrenergic sites were studied by displacement with 20 microM cirazoline. Levels of [3H]-clonidine binding to alpha(2)AR and I-sites, determined in adjacent tissue sections, were positively correlated across 27 brain regions (p = 0.0003; r(2) = 0.385). The principal olivary nucleus and the rostral portion of the ventrolateral medulla had highest ratios of I-sites: alpha(2)AR (>4:1). Quantitative transepts drawn across hippocampal images revealed alpha(2)AR enrichments in the CA-1 and inner molecular layers of the dentate gyrus-areas not enriched in I-sites. Competition curves were generated for I-sites in caudate sections using 10 ligands known to distinguish between I(1) and I(2) subtypes. The rank-order of affinities were cirazoline > harmane > BDF6143 > idazoxan = tizanidine (affinities of agmatine, efaroxan, moxonidine, NE, and oxymetazoline were too low to be reliable). Only the endogenous I-site ligand, harmane, had a monophasic displacement curve at the non-adrenergic sites (Ki = 521 +/- 12 nM).

IN CONCLUSION

1) the distribution of non-adrenergic [3H]-clonidine binding sites in human brain sections was correlated with, but distinct from alpha(2)AR; and 2) the affinities of these sites was distinct from alpha(1)AR, alpha(2)AR, I(1) or I(2) sites as previously defined in membrane binding assays. The properties of this non-adrenergic [3H]-clonidine binding site are consistent with I-sites previously labeled by [3H]-cirazoline in rat brain.

Imidazoline receptor proteins are decreased in the hippocampus of individuals with major depression

BACKGROUND

A downregulation of I(2)-imidazoline binding sites has been reported in frontal cortices of depressed suicide victims, according to I(2)-radioligand binding and confirmed by Western blotting. We now report Western blots of imidazoline receptor proteins in hippocampi of subjects with and without depression at the time of death.

METHODS

Postmortem diagnoses were obtained from 17 cases of Axis I major depressive disorder and 17 cases without Axis I psychopathology. No psychotropic compounds were found in body fluids. Hippocampi were removed, sectioned, and assessed histologically. Throughout the analysis, each major depressive disorder sample was paired with a sample from a psychiatrically healthy subject based on equivalent life spans and postmortem delays. The antiserum was identical to that used in previous studies that reported a downregulation of cortical 29/30-kd imidazoline receptor-binding proteins in depression.

RESULTS

A triad of imidazoline receptor-binding protein bands (40-50 kd) was detected in the human hippocampus. Subjects with major depressive disorder had significantly less intensity in each imidazoline receptor-binding proteins band compared with control subjects (p =. 01 for overall bands).

CONCLUSIONS

The present results can be aligned with previous reports of downregulation of I(2)-radioligand binding sites in both cortices and platelets of depressed patients.

Imidazoline and alpha(2a)-adrenoceptor binding sites in postmenopausal women before and after estrogen replacement therapy

BACKGROUND

Platelet alpha(2A)-adrenoceptors (alpha(2A)AR) and imidazoline binding sites (subtype I(1)) have been proposed as peripheral markers of brain stem receptors that mediate sympathetic outflow and are reported to be elevated in major depression.

METHODS

In our study, p[(125)I]-iodoclonidine was used to assess platelet alpha(2A)AR and I(1) binding sites in healthy postmenopausal women (n = 34) compared with healthy women of reproductive age (n = 26). Receptor determinations were repeated in 19 postmenopausal women following 59-60 days of estrogen replacement therapy (ERT; 0.1 mg estradiol transdermal patches).

RESULTS

I(1) binding sites were twofold higher in platelets of postmenopausal women compared with women of reproduction age but were down-regulated (normalized) after 59-60 days of ERT. All other binding parameters, including platelet alpha(2A)AR density, were not different between groups nor were they changed after ERT. Platelet I(1) densities after 59-60 days of ERT were positively correlated with plasma luteinizing hormone concentrations.

CONCLUSIONS

It is suggested that increased imidazoline binding sites might be associated with mood and behavioral changes in postmenopausal women.

Elevated P-selectin on platelets in depression: response to bupropion

Increased platelet activation has been suggested as a possible reason for the increased vulnerability of depressed patients to ischemic heart disease (IHD). Translocation of P-selectin, an integral alpha-granule membrane protein, to the platelet surface is a measure of platelet activation. Herein, western blots of platelet plasma membranes containing P-selectin were quantified in patients with major depression (n=19; mean age=39 +/- 2 years) and healthy comparison subjects (n=17; mean age=36 +/- 2 years). None evidenced clinical signs of IHD, and only two patients had a lifestyle IHD risk factor (smoking). Blood was obtained from all 19 depressed patients before treatment, and 15 returned after 6-8 weeks of open-label bupropion treatment. Bupropion was chosen as the antidepressant because it did not elevate plasma norepinephrine or serotonin, endogenous agonists that can induce platelet degranulation. Western blotting revealed more P-selectin immunoreactivity (75 kD band) in depressed patients compared to healthy controls (P=0.003). After bupropion treatment, P-selectin remained high in depressed patients. beta3-Integrin, a reference plasma membrane protein that does not translocate during activation, was of equivalent density in depressed patients and healthy control subjects, and was unchanged after treatment with bupropion. P-Selectin failed to correlate with severity of illness based on the Hamilton Depression scale, or with the post-treatment plasma concentration of bupropion. The results suggest an elevation in P-selectin on platelet plasma membranes might be a trait marker for depression.

Imidazoline receptor antisera-selected (IRAS) cDNA: cloning and characterization

The imidazoline-1 receptor (IR1) is considered a novel target for drug discovery. Toward cloning an IR1, a truncated cDNA clone was isolated from a human hippocampal lambda gt11 cDNA expression library by relying on the selectivity of two antisera directed against candidate IR proteins. Amplification reactions were performed to extend the 5' and 3' ends of this cDNA, followed by end-to-end PCR and conventional cloning. The resultant 5131-basepair molecule, designated imidazoline receptor-antisera-selected (IRAS) cDNA, was shown to encode a 1504-amino acid protein (IRAS-1). No relation exists between the amino acid sequence of IRAS-1 and proteins known to bind imidazolines (e.g., it is not an alpha2-adrenoceptor or monoamine oxidase subtype). However, certain sequences within IRAS-1 are consistent with signaling motifs found in cytokine receptors, as previously suggested for an IR1. An acidic region in IRAS-1 having an amino acid sequence nearly identical to that of ryanodine receptors led to the demonstration that ruthenium red, a dye that binds the acidic region in ryanodine receptors, also stained IRAS-1 as a 167-kD band on SDS gels and inhibited radioligand binding of native I1 sites in untransfected PC-12 cells (a source of authentic I1 binding sites). Two epitope-selective antisera were also generated against IRAS-1, and both reacted with the same 167-kD band on Western blots. In a host-cell-specific manner, transfection of IRAS cDNA into Chinese hamster ovary cells led to high-affinity I1 binding sites by criteria of nanomolar affinity for moxonidine and rilmenidine. Thus, IRAS-1 is the first protein discovered with characteristics of an IR1.

Effect of bupropion on immunodensity of putative imidazoline receptors on platelets of depressed patients

A substantial number of studies have demonstrated increased imidazoline receptors (I1 binding sites) on platelets of depressed patients and downregulation following antidepressant treatments. Herein, imidazoline receptor binding protein (IRBP) antiserum was used to quantify imidazoline receptors on platelets of depressed patients before and after treatment with the atypical aminoketone antidepressant, bupropion. Western blots revealed an increase in IRBP-immunodensity (p = 0.01, two-tailed) in a 33 kDa protein band in untreated depressed patients (n = 21) as compared with controls (n = 17). This band has been positively correlated with I1 binding sites on platelets. Following 6 weeks' treatment with bupropion, IRBP-immunodensity was downregulated in depressed patients (p = 0.03, paired t-test); predominantly in responders (p = 0.005). Patients non-responsive to bupropion (n = 5) were significantly different from responders (p = 0.05) by exhibiting no elevation in IRBP-immunodensity at pre-treatment and no downregulation of the 33 kDa band after treatment. IRBP-immunodensity was negatively correlated (r = -0.79, p = 0.01) with plasma concentrations of bupropion and its metabolites at week-4 of BUP treatment. Thus, a 33-kDa IRBP on platelet plasma membranes is elevated in depression and normalized in responders to bupropion.

Plasma agmatine and platelet imidazoline receptors in depression

Plasma agmatine concentrations are elevated significantly in depressed patients compared to healthy controls. Treatment with the antidepressant bupropion normalized plasma agmatine levels. Correlational evidence is presented that a change in plasma agmatine levels may lead to similar changes in platelet I1 imidazoline receptors.

Imidazoline receptor antisera-selected cDNA clone and mRNA distribution

A novel cDNA, designated Imidazoline Receptor Antisera-Selected cDNA-1 (iras-1), encodes a 167-kD protein. Two of its predicted peptides (42-43 kD) are immunologically consistent with a previously reported 1(1)-imidazoline binding protein. In the present study, two forms of iras mRNA (6.0 and 9.5 kb) were quantified across fresh rat tissues. Highest levels were found in brain (almost exclusively 6.0 kb in size), followed by liver and lung (9.5 > or = 6.0 kb iras mRNA), kidney (6.0 > 9.5 kb), heart (6.0 kb), spleen (6.0 > or = 9.5 kb), testes (6.0 > 9.5 kb), and skeletal muscle (6.0 > 9.5 kb). A correlation exists (p = 0.71, p = 0.05) between total (6.0 + 9.5 kb) iras mRNA and I1 BMAX values across rat tissues, corrected for housekeeping gene expression. Thus, total iras mRNA appears to be roughly proportional to the density of I1-imidazoline binding sites.

Characterization of a partial cDNA clone detected by imidazoline receptor-selective antisera

A cDNA clone has been isolated from a human hippocampal cDNA expression library by relying on the selectivity of two antisera that are specific for imidazoline binding proteins. A 1789 bp cDNA clone was sequenced and shown to contain a single open-reading frame that predicts a 66 kDa polypeptide, but it is truncated based on its lack of a stop codon and poly-A+ tail. Two regions of homology exist for the predicted amino acid sequence in common with chromogranin-A and B proteins, a zinc finger protein, and the ryanodine receptor. Northern blot analyses of poly-A+ mRNA from 36 human tissues indicated two differentially expressed transcripts of 6.0 and 9.5 kb. The 6.0 kb mRNA form was enriched in brain and endocrine tissues as compared to other tissues, but not in strict concordance with I1-imidazoline binding sites. The highest overall amounts of the combined transcripts were found in pituitary. In situ hybridization histochemistry revealed an enrichment of the message in neuronal cell bodies of the rat hippocampus and cerebellar cortex. This clone has some of the properties expected of an imidazoline receptor.

Alpha 2-adrenoceptors and I1-imidazoline binding sites: relationship with catecholamines in women of reproductive age

A comparison is presented between plasma catecholamine concentrations and platelet [125I]-p-iodoclonidine binding sites in 16 healthy women. Blood samples were obtained at six regularly spaced intervals over two consecutive menstrual cycles from healthy women with regular menstrual periods. Although no cycle-related changes were observed per se, there were significant correlations between the platelet binding sites and plasma norepinephrine and epinephrine concentrations. The densities of platelet alpha 2-adrenoceptors were negatively correlated in an exponential fashion (r2 = 0.694, P = 0.009) with plasma epinephrine concentrations, implying agonist-induced downregulation. On the other hand, platelet I1-imidazoline binding sites were positively correlated with plasma concentrations of norepinephrine in a linear fashion (r2 = 0.326, P = 0.021). This is the first indication that I1 binding sites might be upregulated by a physiological factor. Furthermore, the data suggest that elevations in plasma norepinephrine might explain reports of upregulated I1 binding sites in depressed patients.

Co-detection by two imidazoline receptor protein antisera of a novel 85 kilodalton protein

Imidazoline receptors (I-receptors) are considered as potential therapeutic targets for a spectrum of stress-induced illnesses. Yet, I-receptors remain poorly defined at the molecular level. In this study, candidate imidazoline receptor proteins were compared using two imidazoline receptor-selective antisera of diverse origins. One antiserum was derived from affinity-purified imidazoline-binding protein. The second antiserum was produced as an anti-idiotypic antiserum, from purified IgG selective for imidazolines. Despite such diverse origins, both antisera co-identified an 85 kDa band on western blots from a variety of tissues. The integrity of the 85 kDa band was dependent on protection by eight different protease inhibitors. Other proteolytic breakdown products (obtained after homogenization with only one protease inhibitor) were comparable in size to previously reported smaller immunoreactive bands. The full-size 85 kDa band was also enriched in plasma membrane fractions and abundant in rat PC12 cells and brain regions known to be abundant in I1 binding sites. Furthermore, the immunodensity of the 85 kDa band, against anti-idiotypic antiserum, was linearly correlated with reported I1 site radioligand Bmax values (r2 = 0.8736, P = 0.0002) across nine rat tissues. Therefore, a possible candidate for the full-length imidazoline receptor(s) appears to be an 85 kDa protein.

Imidazoline receptor proteins are regulated in platelet-precursor MEG-01 cells by agonists and antagonists

The I1-imidazoline receptor is a novel brainstem modulator of sympathetic outflow that is elevated on platelets and in brains of depressed patients. A positive correlation has been reported (accompanying manuscript) between plasma norepinephrine (NE) concentrations and the densities (Bmax) of platelet I1 binding sites (I1 sites). I1-candidate proteins of 33 kDa and 85 kDa are now identified on Western blots probed with anti-imidazoline receptor antiserum (IRBP antiserum), that correlate with Bmax values for I1 sites. Furthermore, a human megakaryoblastoma cell line (MEG-01) has been used to study the regulation of these proteins on megakaryocytic cells, while bovine adrenal chromaffin cells provide a standard I1 cell type for comparison. Both the 33 kDa and 85 kDa IRBP-immunoreactive bands were enriched in plasma membrane fractions. IRBP antiserum did not cross-react with I2 imidazoline binding sites located on platelet mitochondrial membranes. The 85 kDa band was enhanced under conditions lacking fetal bovine serum (FBS) from the culture medium 6 h prior to harvesting. Conversely, 33 kDa protein was enhanced on MEG-01 cells grown in the presence of 10% FBS; suggesting that a precursor (85 kDa) and product (33 kDa) relationship might be induced by serum. The 85 kDa band was robustly up-regulated in response to imidazoline receptor-sensitive ligands; moxonidine, idazoxan and agmatine (10 microM each for 6 h). NE also up-regulated the 85 kDa IRBP-immunoreactive protein on MEG-01 membranes, but to a lesser extent. Idazoxan, an imidazoline alpha 2-antagonist, off-set its induction of 85 kDa protein by reducing the 33 kDa band. Yohimbine, a non-imidazoline alpha 2-antagonist, was ineffective alone, or in combination with moxonidine (up to 40 microM), but yohimbine blocked NE's induction of the 85 kDa band. Therefore, a rise in either plasma NE and/or endogenous I-site ligands (i.e. agmatine) could explain an elevation of imidazoline receptors observed in depression.

Plasma MHPG response to yohimbine treatment in women with hypoactive sexual desire

The use of yohimbine to treat impotence has suggested that decreased male sexual desire may relate to decreased activity of central noradrenergic neurons. Previous trials of yohimbine to treat female sexual problems are not available. Yohimbine is an alpha 2-adrenergic antagonist that stimulates norepinephrine (NE) release. In the present study, plasma concentrations of 3-methoxy-4-hydroxyphenylglycol (MHPG), the major central nervous system metabolite of NE, were measured in 9 women diagnosed with hypoactive sexual desire. Daily logs of mood and sexual activity, and trimonthly MHPG blood drawings, were obtained over an initial baseline menstrual cycle followed by two subsequent treatment cycles (yohimbine or placebo), in randomized order. Blood samples were obtained at 9:00 a.m. during (a) the early follicular phase of each cycle (24 hr after the onset of each cycle), (b) the ovulatory phase (i.e., within 1 day of an oral temperature rise), and (c) the midluteal phase (i.e., 20-25 days into each cycle). Comparisons were made with a group of 7 healthy female controls. Women with hypoactive sexual desire had slightly lower plasma MHPG values than controls at baseline, although there was only a trend toward significance during the early follicular phase (p = .09). Yohimbine (5.4 mg orally, 3 times daily, beginning at menses) caused a sustained rise in plasma MHPG of similar magnitude to that reported in men. However, in terms of improved sexual desire, yohimbine had no obvious therapeutic effect. Thus, plasma MHPG and the alpha 2-adrenergic response to yohimbine appeared within normal ranges in women with hypoactive sexual desire, with no therapeutic response to yohimbine.

Chronic imipramine treatment downregulates IR1-imidazoline receptors in rat brainstem

One subtype of imidazoline receptors (IR1) is similar to alpha 2-adrenoceptors (alpha 2 AR) based on their high affinity for clonidine and related imidazoline compounds. On the other hand, IR1 possess low affinity for norepinephrine (NE) and other catecholamines. Imidazoline receptors have also been found to be over-expressed in plasma membranes from platelets and brain tissues of depressed patients. Over-expression of IR1 in platelet membranes of depressed patients became normalized after various antidepressant treatment to the patients. Herein, the prototypic antidepressant, imipramine (IMI), has been studied in regard to its treatment effects on [125I]p-iodoclonidine binding to both alpha 2 AR and IR1 in rat brainstem membranes. No effects of chronic IMI treatment were found on brainstem alpha 2 AR binding sites (Bmax and/or KD parameters unchanged) after 25 days of daily injections (i.p. IMI 20 mg/kg/day). However, IMI induced a decrease in the density (Bmax measured under NE mask) of brainstem IR1 sites, with no change in KD. Downregulation of IR1 sites was dose-dependent (minimal effective dose of i.p. IMI was 10 mg/kg/day) and time-dependent (> 16 days of treatment). These results implicate brainstem IR1 in the chronic effects of antidepressants.

The imidazoline receptor in control of blood pressure by clonidine and allied drugs

Clonidine, moxonidine, and rilmenidine are centrally acting antihypertensive agents that lower arterial pressure by inhibiting the tonic activity of sympathoexcitatory neurons in the rostral ventrolateral medulla. Competing hypotheses have been put forward by different investigators to explain the sympathoinhibition evoked by "imidazoline drugs": either via central actions at alpha 2-adrenergic receptors or novel I1-imidazoline receptors. These different perspectives are presented in the accompanying reviews.

Determination of agmatine in brain and plasma using high-performance liquid chromatography with fluorescence detection

Decarboxylated arginine, agmatine, is a neurotransmitter candidate for imidazoline receptors. A method is described to measure agmatine in rat brain and human plasma by isocratic high-performance liquid chromatography (HPLC) with fluorescence detection and o-phthalaldehyde derivatization. Quantitation is based on the method of additions of internal agmatine spikes. This assay has sensitivity in the low picomole range and a detection limit of 100 fmol. The correlation coefficient for the agmatine standard curve was 0.999+/-0.001 S.D., and intra- and inter-assay C.V.s were less than 8%. The accuracy of our isocratic method compared favorably with a gradient HPLC protocol, originally developed for bacterial agmatine, which we modified for use with tissues. Agmatine concentrations in rat brain were proportioned similarly to the regional distribution of imidazoline-1 receptors. These methods can be used as reliable research tools in various biological samples.