Role of sympathetic nervous system in rat model of chronic visceral pain.

BACKGROUND: Changes in central pain modulation have been implicated in generalized pain syndromes such as irritable bowel syndrome (IBS). We have previously demonstrated that reduced descending inhibition unveils a role of sympathoneuronal outflow in decreasing peripheral sensory thresholds, resulting in stress-induced hyperalgesia. We investigated whether sympathetic nervous system (SNS) exacerbation of pain sensation when central pain inhibition is reduced is relevant to chronic pain disorders using a rat colon irritation (CI) model of chronic visceral hypersensitivity with hallmarks of IBS. METHODS: Rats were treated to a series of colorectal balloon distensions (CRD) as neonates resulting in visceral and somatic hypersensitivity and altered stool function that persists into adulthood. The visceral sensitivity was assessed by recording electromyographic (EMG) responses to CRD. Somatic sensitivity was assessed by paw withdrawal thresholds to radiant heat. The effects on the hypersensitivity of (i) inhibiting sympathoneuronal outflow with pharmacological and surgical interventions and (ii) enhancing the outflow with water avoidance stress (WAS) were tested. KEY RESULTS: The alpha2-adrenergic agonist, clonidine, and the alpha1-adrenergic antagonist, prazosin, reduced the visceral hypersensitivity and WAS enhanced the pain. Chemical sympathectomy with guanethidine and surgical sympathectomy resulted in a loss of the chronic visceral hypersensitivity. CONCLUSIONS & INFERENCES: The results support a role of the SNS in driving the chronic visceral and somatic hypersensitivity seen in CI rats. The findings further suggest that treatments that decrease sympathetic outflow or block activation of adrenergic receptors on sensory nerves could be beneficial in the treatment of generalized pain syndromes.

Transient allodynia pain models in mice for early assessment of analgesic activity.

BACKGROUND AND PURPOSE: The most common preclinical models of neuropathic pain involve surgical ligation of sensory nerves, which is especially difficult in mice. Transient models of chemically sensitized allodynia are potentially useful for rapidly characterizing the analgesic profile of compounds and conducting mechanistic studies. EXPERIMENTAL APPROACH: Increasing doses of NMDA, sulprostone (an EP1/EP3 prostaglandin receptor agonist) or phenylephrine (an alpha (1) adrenoceptor agonist) were injected intrathecally (i.t.) or i.p., and animals were subsequently assessed for allodynia. The effects of receptor antagonists and analgesic compounds on allodynia were also assessed. KEY RESULTS: A comparison of total body doses that cause allodynia following spinal or systemic administration indicated that NMDA induces allodynia in the spinal cord while sulprostone and phenylephrine act through a peripheral mechanism. Inhibition of the allodynia with receptor antagonists indicated that each agent induces allodynia by a distinct mechanism. The three models were benchmarked using compounds known to be active in neuropathic pain patients and nerve injury animal models, including gabapentin, amitriptyline and clonidine. CONCLUSIONS AND IMPLICATIONS: These transient allodynia models are a useful addition to the toolbox of preclinical pain models. They are simple, rapid and reproducible, and will be especially useful for characterizing the pain phenotype of knockout mice.

alpha(2)-Adrenoceptor agonists inhibit vitreal glutamate and aspartate accumulation and preserve retinal function after transient ischemia.

Recent studies have suggested that alpha(2)-adrenergic agonists prevent neuronal cell death in a number of animal models, although the mechanism of alpha(2)-neuroprotection remains unclear. In a retinal ischemia model, the alpha(2)-specific agonist brimonidine (1 mg/kg i.p.) preserves approximately 80% of the electroretinogram (ERG) b-wave. The protective effect of brimonidine is completely blocked by coadministration of the alpha(2)- antagonist rauwolscine. Brimonidine treatment preserves the ERG b-wave if animals are treated 1 or 3 h before ischemia, but has no effect if it is injected during ischemia. The 3-h pretreatment effect is blocked by i.v. injection of rauwolscine 2 h later (1 h before ischemia). A comparison of vitreous humor glutamate levels between untreated and brimonidine-treated eyes shows that 1) after ischemia, glutamate levels rise 2- to 3-fold in the untreated animals, and 2) glutamate levels in the brimonidine-treated animals are comparable to the nonischemic controls. Hence, the mechanism for brimonidine-mediated protection in the retinal ischemia model requires activation of the alpha(2)-adrenergic receptors immediately before and during ischemia. These data suggest that activation of the alpha(2)-adrenergic receptor may reduce ischemic retinal injury by preventing the accumulation of extracellular glutamate and aspartate.

Woodchuck hepatitis virus posttranscriptional regulatory element enhances expression of transgenes delivered by retroviral vectors.

The expression of genes delivered by retroviral vectors is often inefficient, a potential obstacle for their widespread use in human gene therapy. Here, we explored the possibility that the posttranscriptional regulatory element of woodchuck hepatitis virus (WPRE) might help resolve this problem. Insertion of the WPRE in the 3' untranslated region of coding sequences carried by either oncoretroviral or lentiviral vectors substantially increased their levels of expression in a transgene-, promoter- and vector-independent manner. The WPRE thus increased either luciferase or green fluorescent protein production five- to eightfold, and effects of a comparable magnitude were observed with either the immediate-early cytomegalovirus or the herpesvirus thymidine kinase promoter and with both human immunodeficiency virus- and murine leukemia virus-based vectors. The WPRE exerted this influence only when placed in the sense orientation, consistent with its predicted posttranscriptional mechanism of action. These results demonstrate that the WPRE significantly improves the performance of retroviral vectors and emphasize that posttranscriptional regulation of gene expression should be taken into account in the design of gene delivery systems.

The hepatitis B virus post-transcriptional regulatory element contains two conserved RNA stem-loops which are required for function.

Human Hepatitis B Virus (HBV) RNAs contain a cis -acting sequence, the post-transcriptional regulatory element (HPRE), which facilitates the cytoplasmic localization of intronless transcripts. Our previous studies have shown that the HPRE is composed of at least two independent sub-elements, HPREalpha and HPREbeta, which co-activate a reporter for RNA export in a greater than additive manner. Utilizing deletion, mutation and co-variational analyses, we have identified three regions important for full HPRE activity. The three separate regions of the HPRE function can function independently in a dose-dependent manner when multimerized. Two of these regions contain stem loops, HSLalpha and HSLbeta1, which are necessary for full HPRE function. These structures are conserved throughout the mammalian Hepadnaviruses. Disruption of either stem-loop structure by mutagenesis decreases HPRE function while compensatory mutations restore activity. The location of the stem-loops in the genome reveal that they are present in all of the HBV transcripts. HSLalpha and HSLbeta1 are likely to contain the binding sites for the cellular factor(s) which mediates HPRE function.

A single amino-acid substitution in the EP2 prostaglandin receptor confers responsiveness to prostacyclin analogs.

A high degree of homology between the four Gs-coupled prostaglandin (PG) receptors [EP2, EP4, prostacyclin (IP), PGD2 (DP)] and the four Gq/Gi-coupled receptors [EP1, EP3, PGF2alpha (FP), thromboxane A2 (TP)] suggests that prostaglandin receptors evolved functionally from an ancestral EP receptor before the development of distinct binding epitopes. If so, ligand selectivity should be determined by a limited number of amino acids. EP2 receptor transmembrane domain residues that are similar to those in the EP4 receptor but differ from those in the IP receptor were mutated to the corresponding IP receptor residue. Activation of the mutant receptors by PGE2 (EP2 ligand), iloprost (stable prostacyclin analog), and PGE1 (EP2/IP ligand) was determined using a cAMP-dependent reporter gene assay. A Leu304-to-tyrosine substitution in the seventh transmembrane domain enhanced iloprost potency approximately 100-fold. A glycine substitution at Ser120 in the third transmembrane domain had no effect on drug potency but improved the response of the Tyr304 mutant. The potency of the natural prostaglandins PGF2alpha and PGD2 was not enhanced by the mutations. In contrast, the potency of all prostaglandins was reduced 10- to 100-fold when arginine 302, which is thought to be a counterion for the prostaglandin carboxylic acid, was mutated. Thus, a single amino acid change resulted in a selective gain of function for iloprost, which is consistent with the proposed phylogeny of the prostaglandin receptors.

Leptomycin B inhibits equine infectious anemia virus Rev and feline immunodeficiency virus rev function but not the function of the hepatitis B virus posttranscriptional regulatory element.

Human immunodeficiency virus type 1 Rev export depends upon the presence of the nuclear export signal (NES), a leucine-rich stretch of hydrophobic amino acids. Recently, the nuclear NES-binding receptor has been identified as CRM1 or exportin 1. Rev export has been shown to be CRM1 dependent. The function of the atypical NES-containing Rev-like proteins of equine infectious anemia virus (EIAV) and feline immunodeficiency virus (FIV) is inhibited by leptomycin B, a drug that specifically blocks NES-CRM1 interactions. These data suggest that the function of atypical NES-containing proteins is CRM1 dependent. In contrast to the inhibition of EIAV Rev and FIV Rev, the cytoplasmic accumulation of hepatitis B virus (HBV) posttranscriptional regulatory element (PRE)-containing and Mason-Pfizer monkey virus (MPMV) constitutive transport element (CTE)-containing RNAs is not inhibited by leptomycin B treatment. We conclude that the HBV PRE, like the MPMV CTE, functions independently of an NES receptor-exportin 1 interaction.

Woodchuck hepatitis virus contains a tripartite posttranscriptional regulatory element.

The hepatitis B virus posttranscriptional regulatory element (HBVPRE) is a cis-acting RNA element that partially overlaps with enhancer I and is required for the cytoplasmic accumulation of HBV surface RNAs. We find that the closely related woodchuck hepatitis virus (WHV), which has been shown to lack a functional enhancer I, also contains a posttranscriptional regulatory element (WPRE). Deletion analysis suggests that the WPRE consists of three independent subelements. Comparison of the bipartite HBVPRE and tripartite WPRE activities reveals that the tripartite WPRE is two to three times more active than the bipartite HBVPRE. Mutation of a single WPRE subelement decreases WPRE activity to the level of the HBVPRE. Bipartite and tripartite chimeras of the WPRE and HBVPRE possess activities which suggest that elements containing three subelements are posttranscriptionally stronger than those containing two. These data demonstrate that the posttranscriptional regulatory element is conserved within the mammalian hepadnaviruses and that its strength is determined by the number of subelements within the RNA.

The hepatitis B virus posttranscriptional regulatory element is composed of two subelements.

The RNAs of the hepatitis B virus (HBV) contain a cis-acting regulatory element which facilitates the cytoplasmic localization of unspliced transcripts (J. Huang and T. J. Liang, Mol. Cell. Biol. 13:7476-7486, 1993, and Z. M. Huang and T. S. Yen, J. Virl. 68:3193-3199, 1994). Such localization is presumed to be mediated by cellular factors which interact with the element. The HBV posttranscriptional regulatory element (HBVPRE) can efficiently activate an RNA export reporter system in an orientation-dependent and position-independent manner. Deletion analysis reveals that the HBVPRE consists of two subelements which function synergistically. A synergistic effect was also observed when the 5' (PREalpha) or 3' (PREbeta) subelements were duplicated. The bipartite structure of the HBVPRE is reminiscent of reports that the high-affinity binding sites of the Rev-like proteins must be duplicated to function efficiently (M. Grone, E. Hoffmann, S. Berchtold, B.R. Cullen, and R. Grassmann, Virology 204:144-152, 1994; X. Huang, T.J. Hope, B.L. Bond, D. McDonald, K. Grahl, and T. G. Parslow, J. Virol. 65:2131-2134, 1991; and D. McDonald, T. J. Hope, and T. G. Parslow, J. Virol. 66:7232-7238, 1992).

Molecular characterization and ocular hypotensive properties of the prostanoid EP2 receptor.

The cloning of the genes that encode for prostaglandin (PG) receptors has resolved much of the complexity and controversy in this area by confirming the classification proposed by Coleman, et al. Two issues that remained unresolved were (1) the inability of the EP2 agonist butaprost to interact with the cloned putative EP2 receptor and (2) molecular biological confirmation of a fourth PGE2-sensitive receptor, which was pharmacologically designated EP4. In order to provide clarification, we attempted to clone further PGE2-sensitive receptors. By using a cDNA probe that encodes for the human EP3A receptor, a cDNA clone that encoded for a novel PGE2-sensitive receptor was obtained by screening a human placenta library. This cDNA clone was transfected into COS-7 cells for pharmacological studies. The cDNA clone obtained from human placenta had only about 30% amino acid identity with cDNAs for other PG receptors, including those that encode for the previously proposed murine and human EP2 receptors. Radioligand binding studies on the novel EP receptor expressed in COS-7 cells revealed that selective EP2 agonists such as butaprost, AH 13205, AY 23626 and 19(R)-OH PGE2 all competed with 3H-PGE2 for its binding sites, whereas selective agonists for other PG receptor subtypes had minimal or no effect. This receptor was coupled to adenylate cyclase and EP2 agonists caused dose-related increases in cAMP. It appears that the cDNA described herein encodes for the pharmacologically defined EP2 receptor. Ocular studies revealed that AH 13205 decreased intraocular pressure in normal and ocular hypertensive monkeys by a mechanism that does not appear to involve inhibition of aqueous humor secretion.

Cloning of a novel human prostaglandin receptor with characteristics of the pharmacologically defined EP2 subtype.

A cDNA that when expressed has the binding and functional characteristics of the pharmacologically defined EP2 prostaglandin (PG) receptor [Cardiovasc. Drug Rev. 11:165-179 (1993)] has been cloned from a human placenta library. This clone, known as Hup-4, encodes a protein of 358 amino acids that has only approximately 30% overall identity with other PG receptors, including mouse and human clones that have been designated as EP2 receptors [J. Biol. Chem. 268:7759-7762 (1993); Biochem. Biophys. Res. Commun. 197:263-270 (1993)]. In COS-7 cells transfected with Hup-4, PGE2 stimulated the formation of cAMP with an EC50 of approximately 50 nM. The EP2-selective agonists AH13205 and butaprost were also active, with EC50 values in the range of 2-6 microM. The order of potency of PGs for competition with binding of [3H]PGE2 to membranes prepared from COS-7 cells transfected with Hup-4 was PGE2 > or = PGE1 > 16,16-dimethyl-PGE2 > or = 11-deoxy-PGE1 > butaprost > AH13205 > 19(R)-OH-PGE2. Natural PGs and analogues that are selective for the FP (PGF2a), DP (PGD2), EP1 (sulprostone), EP3 (MB 28767), and EP4 (1-OH-PGE1) receptors were inactive or competed poorly with the binding of [3H]PGE2 (< 50% displacement of specific binding at 10 microM). Northern blot analysis showed the presence of a Hup-4 message of approximately 3.1 kilobases in mRNA from human lung and placenta. Reverse transcription-polymerase chain reaction studies also indicated that Hup-4 is probably expressed in human uterus and in HL-60 (human promyelocytic leukemia) cells. Our findings suggest that Hup-4 encodes the pharmacologically defined EP2 receptor, whereas the mouse and human cDNAs previously classified as EP2 may represent another EP receptor subtype or the recently defined EP4 subtype [Prostaglandins 47:151-168 (1994)].

Molecular cloning and expression of human EP3 receptors: evidence of three variants with differing carboxyl termini.

1. The polymerase chain reaction (PCR) was used in combination with plaque hybridization analysis to clone four variants of the EP3 prostaglandin receptor from a human small intestine cDNA library. 2. Three of these variants, i.e. the EP3A, EP3E and EP3D, share the same primary amino acid sequence except for their carboxyl termini, which diverge from one another at the same point, approximately 10 amino acids away from the end of the seventh membrane spanning domain of the receptor. The fourth variant (EP3A1) has a nucleotide coding sequence identical to EP3A but has a completely different 3' untranslated sequence. 3. The carboxyl termini of the three isoforms differ most obviously in length with the EP3A being the longest (41 amino acids) and the EP3E being the shortest (16 amino acids). They also differ in content with the EP3A containing 9 serine and threonines in its carboxyl terminus and the EP3E none. 4. Transient expression in eukaryotic cells showed that the human EP3 receptor variants had similar but not identical radioligand binding properties and differed in their functional coupling to second messenger pathways. Up to 3 pmol mg-1 protein of [3H]-prostaglandin E2 binding could be obtained with more than 95% specific binding. Using a reporter gene assay, as a measure of intracellular cyclic AMP levels, the EP3A coupled more efficiently to the inhibition of adenylyl cyclase than did the EP3E. 5. PCR was used to confirm the presence of mRNAs encoding the four human EP3 receptor variants in tissues of the human small intestine, heart and pancreas. These findings indicate that the EP3 receptor variants identified here are likely to be expressed in tissues. The differences in the carboxyl termini at the protein level, and in the 3' untranslated regions at the mRNA level, could be profound in terms of the regulation and functional coupling of these receptor isoforms.