Lysyl-tRNA synthetase produces diadenosine tetraphosphate to curb STING-dependent inflammation

Inflammation is an essential part of immunity against pathogens and tumors but can promote disease if not tightly regulated. Self and non-self-nucleic acids can trigger inflammation, through recognition by the cyclic GMP-AMP (cGAMP) synthetase (cGAS) and subsequent activation of the stimulator of interferon genes (STING) protein. Here, we show that RNA:DNA hybrids can be detected by cGAS and that the Lysyl-tRNA synthetase (LysRS) inhibits STING activation through two complementary mechanisms. First, LysRS interacts with RNA:DNA hybrids, delaying recognition by cGAS and impeding cGAMP production. Second, RNA:DNA hybrids stimulate LysRS-dependent production of diadenosine tetraphosphate (Ap4A) that in turn attenuates STING-dependent signaling. We propose a model whereby these mechanisms cooperate to buffer STING activation. Consequently, modulation of the LysRS-Ap4A axis in vitro or in vivo interferes with inflammatory responses. Thus, altogether, we establish LysRS and Ap4A as pharmacological targets to control STING signaling and treat inflammatory diseases.

Preclinical studies on the anti-migraine drug, sumatriptan

Sumatriptan is believed to constrict selectively the cranial vessels that are distended and inflamed during migraine. The action is mediated by activation of a 5-HT1 receptor subtype which has been shown in animals to be localized in cranial vessels. Further studies to elaborate sumatriptan's precise clinical mode of action have focused on the human meningeal circulation and should lead to a better understanding of the pathogenesis of migraine. Administering [14C]sumatriptan, drug-related material was shown to be well absorbed. Following absorption there was some first-pass metabolism resulting in oral bioavailabilities of 37, 58 and 23% in rat, dog and rabbit, respectively. In all species, circulating sumatriptan was cleared rapidly by metabolic and renal clearance with a half-life of 1-2 h. The indoleacetic acid metabolite is the primary metabolic product; however, rats, mice and rabbits also N-demethylate the methylaminosulphonylmethyl side-chain. The passage of sumatriptan and its metabolites across the blood-brain barrier appeared to be very limited, although some drug could be detected in the cerebrospinal fluid after administration of high intravenous doses. Safety studies in various animal species showed that sumatriptan produced few adverse pharmacodynamic effects when administered acutely, except at high doses, although it was less well tolerated in dogs. No findings of toxicological significance were observed in rats and dogs after chronic dosing for 1 year or more.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroleptic-induced catalepsy as a model of Parkinson's disease. I. Effect of dopaminergic agents

Catalepsy was observed in the rat following intrastriatal injections of the dopamine antagonists sulpiride or fluphenazine and after subcutaneous administration of fluphenazine. The neuroleptic-induced catalepsy was reversed by the classical anti-parkinsonian agent L-DOPA and by agents that function through dopamine systems such as d- and methamphetamine and the direct D2 receptor agonist quinpirole. The D1 agonist SKF 38393, and the D1/D2 agonist apomorphine, were ineffective in this model. These results support limited use of the rat catalepsy model for the screening of potential anti-parkinsonian compounds and indicate that this procedure can provide valuable information concerning striatal dopamine function.

Effects of classical and novel agents in a MPTP-induced reversible model of Parkinson's disease

A modified primate model of Parkinson's disease was developed to assess the effectiveness of various agents that act via dopamine, acetylcholine, serotonin or glutamate systems. Using a MPTP dosing regimen a reversible parkinsonian-like syndrome was produced in the marmoset. An obvious advantage of such a protocol is that it allows multiple drug studies to be undertaken in animals, without the need for prolonged anti-parkinsonian therapy to maintain their health. Results show that dopamine D2 agonists (bromocriptine, quinpirole, N,N-dipropyl,A,5,6-DTN, (+)3PPP and PHNO), anti-muscarinics (atropine, scopolamine and benztropine), in addition to L-DOPA and nomifensine, all reduced the bradykinesia induced by MPTP. The D1 agonist SKF-38393 and the partial dopamine agonist (-)3PPP were both ineffective. Finally, agents with potential therapeutic use in Parkinson's disease were also tested. However, a glutamate antagonist (MK801) and three serotonin antagonists (ritanserin, ketanserin and ICI 170,809) were all unable to alter the MPTP effects, at the doses used in our study.

D2 dopamine receptors in rat striatum are homogeneous as revealed by ligand-binding studies

D2 dopamine receptors in rat striatum have been analysed using the binding of [3H]domperidone. Competition experiments were performed with classical dopamine antagonists and antagonists reported by other workers to discriminate D2 dopamine receptor sub-classes. In all cases competition data conformed to a single binding site interaction so that there is no evidence for heterogeneity of the D2 dopamine receptor.

Neuropeptides and dopamine in the marmoset. Effect of treatment with 1-methyl-4-phenyl-1, 2, 3, 6 tetrahydropyridine (MPTP): an animal model for Parkinson's disease?

Neurochemical studies of post-mortem human parkinsonian brains have demonstrated specific alterations in neuropeptide concentrations within the substantia nigra and striatal structures. The drug, 1-methyl-4-phenyl-1, 2, 3, 6 tetrahydropyridine (MPTP) has been reported to act as a selective toxin to nigrostriatal dopamine neurons, and induces a parkinsonian-like syndrome in primates. In this study, marmosets developed features typical of Parkinson's disease following treatment with MPTP for four days. The effects of MPTP treatment on the concentrations of dopamine and neuropeptides were determined and changes compared with those reported for Parkinson's disease. It was found that within the substantia nigra, substance P concentrations doubled following treatment with MPTP; in contrast, concentrations of vasoactive intestinal peptide and neuropeptide Y were significantly reduced. No changes were observed in the concentrations of six other neuropeptides measured in this region, notably cholecystokinin. Despite marked depletion of dopamine within the caudate nucleus and putamen, concentrations of all neuropeptides within these structures remained unchanged with the exception of an isolated reduction of neuropeptide Y within the putamen. Somatostatin concentrations within the frontal cortex and hippocampus were significantly elevated in the marmosets treated with MPTP. These neuropeptide changes in the CNS contrast with those reported for Parkinson's disease. In view of the autonomic dysfunction associated with Parkinson's disease, peripheral concentrations of neuropeptides were determined. Significant depletion of neuropeptide Y was identified in the ureter, adrenal and cardiovascular tissue. Thus the neurochemical changes induced by MPTP may not be as selective as previously reported.

Failure of SKF 38393-A to relieve parkinsonian symptoms induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the marmoset

Chronic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced parkinsonian symptoms, predominantly bradykinesia and tremor, in marmosets. These symptoms were reduced by L-DOPA plus benserazide but the putative D1-receptor agonist SKF 38393-A did not affect tremor and increased the bradykinesia. Neither treatment affected behaviour in normal marmosets. It is suggested that D1-receptor agonists are unlikely to be effective in the treatment of Parkinson's disease.

Pharmacological evidence for the subclassification of central dopamine receptors in the rat

1 The relative potencies of dopamine receptor agonists in causing stereotypy in rats when injected into the olfactory tubercles, and contralateral rotation when injected unilaterally into the caudate nucleus of rats with lesions of the nigro-striatal dopamine pathway, were determined. The actions of some agonists in eliciting these responses following peripheral injection, and the relative potencies of dopamine receptor antagonists in inhibiting them were also determined. 2 Dopamine, apomorphine and 2-amino-5,6 and 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (A-5, 6 DTN, A-6, 7 DTN) and N,N dipropyl A-5, 6DTN induced both responses. In contrast, 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine HCl (SK & F 38393) whether injected intracerebrally or peripherally, induced contralateral rotation but not stereotypy. 3 Contralateral rotation and stereotypy induced by apomorphine or N,N dipropyl A-5, 6 DTN were inhibited by haloperidol, pimozide and fluphenazine but these drugs failed to inhibit rotation induced by SK & F 38393. Clozapine inhibited rotation induced by SK & F 38393, apomorphine or N,N dipropyl A-5,6 DTN but failed to inhibit stereotypy. Loxapine was more potent in inhibiting stereotypy than rotation,, whereas clothiapine inhibited rotation and stereotypy at similar doses irrespective of the agonist used to elicit the response. 4 Contralateral rotation induced by SK & F 38393 was not inhibited by yohimbine, prazosin, atropine, methysergide, mepyramine or propranolol. 5 The results provide evidence that contralateral rotation induced by dopamine receptor agonists is mediated by two different classes of dopamine receptors and that these receptors differ from those mediating the stereotypy response. 6 The receptors mediating these responses appear classifiable in terms of their sensitivity to the agonist actions of SK & F 38393 or apomorphine respectively. SK & F 38393-sensitive receptors are susceptible to blockade by clozapine but are not blocked by haloperidol, pimozide or fluphenazine. Apomorphine-sensitive receptors are susceptible to blockade by haloperidol, pimozide and fluphenazine but appear divisible into two sub-classes depending on whether or not they are blocked by clozapine and on their sensitivity to blockade by loxapine.

Alpha 2-adrenoceptors mediate clonidine-induced sedation in the rat

1 The central alpha-adrenoceptors responsible for mediating clonidine-induced sedation in rats have been characterized according to their sensitivity to alpha-adrenoceptor agonists and antagonists.2 Clonidine, injected intraperitoneally or intracerebroventricularly, caused dose-dependent sedation, both in terms of a reduction in the time that rats could remain on an accelerating rotarod and in terms of overt sedation assessed visually. Following intracerebroventricular injection, xylazine, naphazoline and methoxamine, but not phenylephrine, produced similar effects.3 The sedation caused by intraperitoneal injection of clonidine was antagonized by intracerebroventricularly injected phentolamine, yohimbine, piperoxan and tolazoline but not by labetalol, thymoxamine or prazosin.4 The relative potencies of the agonists in causing sedation and of the antagonists in inhibiting the sedative effect of clonidine clearly demonstrated that the central alpha-adrenoceptors mediating clonidine-induced sedation are the same as the peripheral presynaptic alpha(2)-adrenoceptors.5 All the alpha-adrenoceptor agonists caused hypothermia after intracerebroventricular injection, but their order of potency was different from that in producing sedation. The hypothermic effect of intraperitoneally injected clonidine was little affected by any of the antagonists administered intracerebroventricularly. No conclusions could be drawn concerning the type of receptor responsible for mediating hypothermia.