Anti-parkinsonian agents procyclidine and ethopropazine alleviate thermal hyperalgesia in neuropathic rats

Ultra-high throughput-based screening for the discovery of antiplatelet drugs affecting receptor dependent calcium signaling dynamics

Distinct platelet activation patterns are elicited by the tyrosine kinase-linked collagen receptor glycoprotein VI (GPVI) and the G-protein coupled protease-activated receptors (PAR1/4) for thrombin. This is reflected in the different platelet Ca2+ responses induced by the GPVI agonist collagen-related peptide (CRP) and the PAR1/4 agonist thrombin. Using a 96 well-plate assay with human Calcium-6-loaded platelets and a panel of 22 pharmacological inhibitors, we assessed the cytosolic Ca2+ signaling domains of these receptors and developed an automated Ca2+ curve algorithm. The algorithm was used to evaluate an ultra-high throughput (UHT) based screening of 16,635 chemically diverse small molecules with orally active physicochemical properties for effects on platelets stimulated with CRP or thrombin. Stringent agonist-specific selection criteria resulted in the identification of 151 drug-like molecules, of which three hit compounds were further characterized. The dibenzyl formamide derivative ANO61 selectively modulated thrombin-induced Ca2+ responses, whereas the aromatic sulfonyl imidazole AF299 and the phenothiazine ethopropazine affected CRP-induced responses. Platelet functional assays confirmed selectivity of these hits. Ethopropazine retained its inhibitory potential in the presence of plasma, and suppressed collagen-dependent thrombus buildup at arterial shear rate. In conclusion, targeting of platelet Ca2+ signaling dynamics in a screening campaign has the potential of identifying novel platelet-inhibiting molecules.

Pretreatment of rhesus monkeys with transdermal patches containing physostigmine and procyclidine: implications of the delivery system for the potential application against VX nerve agent intoxication in humans

Physostigmine (Phs) is a reversible inhibitor of acetylcholinesterase (AChE) that penetrates the blood-brain barrier (BBB) and could be used to protect the central nervous system (CNS) against the effects of nerve agents. For prophylactic effectiveness, long, steady, and adequate inhibition of AChE activity by Phs is needed to broadly protect against the CNS effects of nerve agents. Here, we evaluated the efficacy of transdermal patches containing Phs and procyclidine (PC) as prophylactic agents. Patches (25 cm²) containing 4.4 mg Phs and 17.8 mg PC had a protective ratio of approximately 78.6-fold in rhesus monkeys challenged with VX nerve agent and given an antidote. Physiologically based pharmacokinetic model in conjunction with an indirect pharmacodynamic (PBPK/PD) was developed for Phs and scaled to rhesus monkeys. The model was able to reproduce the concentration profile and inhibitory effect on AChE of Phs in monkeys, as evidenced by correlation coefficients of 0.994 and 0.992 for 25 cm² and 49 cm² patches, respectively (i.e., kinetic data), and 0.989 and 0.968 for 25 cm² and 49 cm² patches, respectively (i.e., dynamic data). By extending the monkey PBPK/ PD model to humans, the effective human dose was predicted to be five applications of a 25 cm² patch (i.e., 22 mg Phs), and two applications of a 49 cm² patch (i.e., 17.4 mg Phs). Therefore, given that patch application of Phs in rhesus monkeys has a prolonged effect (namely, AChE inhibition of 19.6% for the 25 cm² patch and 23.0% for the 49 cm² patch) for up to 216 h, patch formulation of Phs may provide similar protection against nerve agent intoxication in humans.

CuH-Catalyzed Enantioselective Ketone Allylation with 1,3-Dienes: Scope, Mechanism, and Applications

Chiral tertiary alcohols are important building blocks for the synthesis of pharmaceutical agents and biologically active natural products. The addition of carbon nucleophiles to ketones is the most common approach to tertiary alcohol synthesis but traditionally relies on stoichiometric organometallic reagents that are difficult to prepare, sensitive, and uneconomical. We describe a mild and efficient method for the copper-catalyzed allylation of ketones using widely available 1,3-dienes as allylmetal surrogates. Homoallylic alcohols bearing a wide range of functional groups are obtained in high yield and with good regio-, diastereo-, and enantioselectivity. Mechanistic investigations using density functional theory (DFT) implicate the in situ formation of a rapidly equilibrating mixture of isomeric copper(I) allyl complexes, from which Curtin-Hammett kinetics determine the major isomer of the product. A stereochemical model is provided to explain the high diastereo- and enantioselectivity of this process. Finally, this method was applied to the preparation of an important drug, ( R)-procyclidine, and a key intermediate in the synthesis of several pharmaceuticals.

Drug repositioning in head and neck squamous cell carcinoma: An integrated pathway analysis based on connectivity map and differential gene expression

The severe damage to health and social burden caused by head and neck squamous cell carcinoma (HNSCC) generated an urgent need to develop novel anti-cancer therapy. Currently, drug repositioning has risen in responses to the proper time as an efficient approach to invention of new anti-cancer therapies. In the present study, we aimed to screen candidate drugs for HNSCC by integrating HNSCC-related pathways from differentially expressed genes (DEGs) and drug-affected pathways from connectivity map (CMAP). We also endeavored to unveil the molecular mechanism of HNSCC through creating drug-target network and protein-to-protein (PPI) network of component DEGs in key overlapping pathways. As a result, a total of 401 DEGs were obtained from TCGA and GTEx mRNA-seq data. Taking the intersection part of 27 HNSCC-related Kyoto Encyclopedia of Genes and Genomes pathways and 33 drug-affected pathways, we retained 22 candidate drugs corresponding to two key pathways (cell cycle and p53 signaling pathways) of the five overlapping pathways. Two of the hub genes (PCNA and CCND1) identified from the PPI network of component DEGs in cell cycle and p53 signaling pathways were defined as the critical targets of candidate drugs with increased protein expression in HNSCC tissues, which was reported by the human protein atlas (HPA) database and cBioPortal. Finally, we validated via molecular docking analysis that two drugs with unknown effects in HNSCC: MG-262 and bepridil might perturb the development of HNSCC through targeting PCNA. These candidate drugs possessed broad application prospect as medication for HNSCC.

In vitro efficacies of clinically available drugs against growth and viability of an Acanthamoeba castellanii keratitis isolate belonging to the T4 genotype

The effects of clinically available drugs targeting muscarinic cholinergic, adrenergic, dopaminergic, and serotonergic receptors; intracellular calcium levels and/or the function of calcium-dependent biochemical pathways; ion channels; and cellular pumps were tested against a keratitis isolate of Acanthamoeba castellanii belonging to the T4 genotype. In vitro growth inhibition (amoebistatic) assays were performed by incubating A. castellanii with various concentrations of drugs in the growth medium for 48 h at 30°C. To determine amoebicidal effects, amoebae were incubated with drugs in phosphate-buffered saline for 24 h, and viability was determined using trypan blue exclusion staining. For controls, amoebae were incubated with the solvent alone. Of the eight drugs tested, amlodipine, prochlorperazine, and loperamide showed potent amoebicidal effects, as no viable trophozoites were observed (>95% kill rate), while amiodarone, procyclidine, digoxin, and apomorphine exhibited up to 50% amoebicidal effects. In contrast, haloperidol did not affect viability, but all the drugs tested inhibited A. castellanii growth. Importantly, amlodipine, prochlorperazine, and loperamide showed compelling cysticidal effects. The cysticidal effects were irreversible, as cysts treated with the aforementioned drugs did not reemerge as viable amoebae upon inoculation in the growth medium. Except for apomorphine and haloperidol, all the tested drugs blocked trophozoite differentiation into cysts in encystation assays. Given the limited availability of effective drugs to treat amoebal infections, the clinically available drugs tested in this study represent potential agents for managing keratitis and granulomatous amoebic encephalitis caused by Acanthamoeba spp. and possibly against other meningoencephalitis-causing amoebae, such as Balamuthia mandrillaris and Naegleria fowleri.

Dorsal root ganglion application of muscimol prevents hyperalgesia and stimulates myelin protein expression after sciatic nerve injury in rats

BACKGROUND

Peripheral nerve injuries may result in debilitating pain that is poorly responsive to conventional treatment. Neuropathic pain induced by peripheral nerve injury is caused, in part, by ectopic discharges from the injury site or the dorsal root ganglia (DRG) resulting in enhanced central input and central hyperexcitability. A heterogeneous family of γ-aminobutyric acid (GABA)(A) channels is important in quieting neuronal excitability. We have recently reported that in vivo modulation of GABAergic neurons in DRG can alter the course of neuropathic pain development after peripheral nerve injury. It seems that direct application of a potent GABA(A) agonist, muscimol, to the ipsilateral DRG prevents the development of hyperalgesia in rats subjected to a sciatic nerve crush injury. In addition to potentially curtailing hyperexcitability, GABAergic stimulation upregulated expression of peripheral myelin protein 22 (PMP22), a key component of the basal lamina. PMP22 expression correlates with peripheral myelin formation and nerve regeneration.

METHODS

Because of the importance of PMP22 for the formation and stability of myelin, and the fact that PMP22 expression could be GABAergically modulated, we examined whether direct DRG application of muscimol can restore PMP22 protein expression and the integrity of nerve fibers after crush injury of a sciatic nerve.

RESULTS

Using adult female rats and a crush injury model, we found that GABAergic modulation in the ipsilateral DRG restores PMP22 protein expression in the distal segment of the sciatic nerve and improves myelin stability in the basal membrane of nerve fibers, thus giving the morphological appearance of lessened nerve injury or faster nerve fiber regeneration. Both the enhanced PMP22 protein expression and morphological improvements coincide with the abolishment of thermal and mechanical hypersensitivity.

CONCLUSIONS

The DRG could be a promising therapeutic target in nerve regeneration and pain alleviation after crush injury of a myelinated peripheral nerve.

Selective T-type calcium channel blockade alleviates hyperalgesia in ob/ob mice

OBJECTIVE

Morbid obesity may be accompanied by diabetes and painful diabetic neuropathy, a poorly understood condition that is manifested by mechanical or thermal allodynia and hyperalgesia. Recent studies have highlighted the importance of T-type calcium channels (T-channels) in peripheral nociception; therefore, our goal was to examine the function of these channels in the pathophysiology and development of painful diabetic neuropathy.

RESEARCH DESIGN AND METHODS

In vivo testing of mechanical and thermal sensation, morphometric peripheral nerve studies, and electrophysiological and biochemical measurements were used to characterize the role of T-channels and the development of painful diabetic neuropathy in leptin-deficient (ob/ob) mice.

RESULTS

We found that ob/ob mice developed significant mechanical and thermal hypersensitivity early in life that coincided with hyperglycemia and was readily reversed with insulin therapy. These disturbances were accompanied by significant biophysical and biochemical modulation of T-channels in dorsal root ganglion neurons as measured by a large increase in the amplitude of T-currents and the expression of mRNA. The most prevalent subtype, alpha1H (Ca(v)3.2), was most strongly affected. Moreover, (3beta,5alpha,17beta)-17-hydroxyestrane-3-carbonitrile (ECN), a novel neuroactive steroid and selective T-channel antagonist, provided dose-dependent alleviation of neuropathic thermal and mechanical hypersensitivity in diabetic ob/ob mice.

CONCLUSIONS

Our results indicate that pharmacological antagonism of T-channels is potentially an important novel therapeutic approach for the management of painful diabetic neuropathy.

Differential effects of endogenous cysteine analogs on peripheral thermal nociception in intact rats

Previous in vivo studies indicate that locally injected redox-modulating agents can sensitize polymodal peripheral skin nociceptors resulting in acute changes in pain perception. Since endogenous thiol-modifying redox agents are normally present in the interstitial tissue, and could be found in higher concentration in certain conditions (e.g., tissue injury, inflammation, and ischemia), we designed this study to evaluate the peripheral nociceptive effects of locally injected endogenous-reducing cysteine analogs, L-cysteine, D-cysteine and D,L-homocysteine and endogenous-oxidizing cysteine analogs, L-cystine, D-cystine and D,L-homocystine using the acute model of thermal peripheral nociception in intact rats. We found that the reducing cysteine analogs induced potent dose- and time-dependent hyperalgesia and conversely the oxidizing cysteine analogs induced potent dose- and time-dependent analgesia. In the presence of 3betaOH, a novel neuroactive steroid and potent voltage-dependent blocker of T-type Ca2+ channels, the hyperalgesic effects of the reducing agents were diminished, whereas the analgesic effects of the oxidizing agents were enhanced strongly suggesting that the observed nociceptive effects were, at least in part, mediated via the peripheral T channels. Our findings imply that changes in the redox states of the peripheral nociceptors (favoring either reduced or oxidized forms of cysteine molecules) may function as a local intrinsic mechanism in controlling peripheral pain perception.

5alpha-reduced neuroactive steroids alleviate thermal and mechanical hyperalgesia in rats with neuropathic pain

5alpha-reduced neuroactive steroids with selective modulatory action in vitro on T or combined modulatory action on T and GABA(A) currents present in peripheral sensory neurons have been shown to induce potent peripheral analgesia in vivo in intact animals. Although the role of T and GABA(A) currents in pathophysiology of neuropathic pain (NPP) is not established, it appears that blockade of T currents and/or potentiation of GABA(A) currents could be beneficial in the management of NPP. To study the potential usefulness of 5alpha-reduced neuroactive steroids in alleviating NPP, we selected two newly synthesized steroids-ECN and CDNC24-with a selective blocking effect on T currents and a selective potentiating effect on GABA(A) currents, respectively, and commercial analogs-alphaxalone and 3alpha5alphaP-with the effects on both ion channels. We used a sciatic nerve ligation model to induce thermal and mechanical hyperalgesia in adult rats and tested peripheral thermal and mechanical nociception following local injection of neuroactive steroids into the peripheral receptive fields of a ligated hind paw. We found that 5alpha-reduced neuroactive steroids alleviate thermal and mechanical hyperalgesia in NPP rats. ECN and CDNC24 were more selective in alleviating thermal nociception in NPP than in sham animals when compared to 3alpha5alphaP and alphaxalone although the anti-nociceptive effect induced by 3alpha5alphaP and alphaxalone was more profound. CDNC24 was most selective since it had very minimal anti-nociceptive effect in sham animals but a very profound anti-nociceptive effect in NPP animals suggesting that, under pathological conditions, peripheral GABA(A) receptors might be an attractive therapeutic target.

New evidence that both T-type calcium channels and GABAA channels are responsible for the potent peripheral analgesic effects of 5α-reduced neuroactive steroids

Neurosteroids are potent blockers of neuronal low-voltage activated (T-type) Ca(2+) channels and potentiators of GABA(A) ligand-gated channels, but their effects in peripheral pain pathways have not been studied previously. To investigate potential analgesic effects and the ion channels involved, we tested the ability of locally injected 5alpha-reduced neurosteroids to modulate peripheral thermal nociception to radiant heat in adult rats in vivo and to modulate GABA(A) and T-type Ca(2+) channels in vitro. The steroid anesthetic alphaxalone (ALPX), the endogenous neurosteroid allopregnanolone (3alpha5alphaP), and a related compound ((3alpha,5alpha,17beta)-3-hydroxyandrostane-17-carbonitrile, (ACN)), induced potent, dose-dependent, enantioselective anti-nociception in vivo and modulation of both T-type Ca(2+) currents and GABA(A)-mediated currents in vitro. Analgesic effects of ALPX were incompletely antagonized by co-injections of the GABA(A) receptor antagonist bicuculline. The neurosteroid analogue ((3alpha,5alpha)-3-hydroxy-13,24-cyclo-18,21-dinorchol-22-en-24-ol (CDNC24), a compound with GABAergic but not T-type activity, was not analgesic. However, (3beta,5alpha,17beta)-17-hydroxyestrane-3-carbonitrile (ECN)), which has effects on T-type channels but not on GABA(A) receptors, also induced potent enantioselective peripheral anti-nociception. ECN increased pain thresholds less than ALPX, 3alpha5alphaP and ACN. However, when an ineffective dose of CDNC24 was combined with ECN, anti-nociceptive activity was greatly enhanced, and this effect was bicuculline-sensitive. These results strongly suggest that GABA(A) channels do not contribute to baseline pain transmission, but they can enhance anti-nociception mediated by blockade of T-type Ca(2+) channels. In conclusion, we demonstrate that potent peripheral analgesia induced by 5alpha-reduced neurosteroid is mediated in part by effects on T-type Ca(2+) channels. Our results also reveal a role of GABA-gated ion channels in peripheral nociceptive signaling.

Redox modulation of peripheral T-type Ca2+ channels in vivo: alteration of nerve injury-induced thermal hyperalgesia

We reported recently that redox agents, including the endogenous amino acid L-cysteine, modulate T-type Ca2+ currents in primary sensory neurons in vitro, and alter mechanical and thermal nociception in peripheral nociceptors in vivo in intact animals [Neuron 31 (2001) 75]. Here, we studied the effects of locally applied redox agents (L-cysteine and 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB) on thermal hyperalgesia in animals with neuropathic pain due to chronic constrictive injury (CCI) of the sciatic nerve. We found that, following injection into the peripheral receptive fields, the endogenous reducing agent L-cysteine increased thermal hyperalgesia in a dose-dependent manner in rats with CCI of the sciatic nerve as well as in sham-operated rats. However, the magnitude of the increase was smaller and duration of effect was shorter in rats with CCI of the sciatic nerve compared to sham-operated animals. DTNB, an exogenous oxidizing agent, induced dose-dependent alleviation of thermal hyperalgesia in rats with CCI of the sciatic nerve and caused analgesia in sham-operated rats. DTNB completely blocked L-cysteine-induced thermal hyperalgesia in both animal groups. Mibefradil, a potent and preferential T-type Ca2+ channel blocker, abolished L-cysteine-induced increase in thermal hyperalgesia in both animal groups suggesting the involvement of T-type Ca2+ channels in peripheral nociception. These results indicate for the first time that redox modulation of T-type Ca2+ channels in rat peripheral nociceptors is operational in pain states caused by peripheral axonal injury. Since thermal hyperalgesia is a common symptom of axonal injury, locally applied oxidizing agents could be used as a novel treatment to ameliorate neuropathic pain.

5beta-reduced neuroactive steroids are novel voltage-dependent blockers of T-type Ca2+ channels in rat sensory neurons in vitro and potent peripheral analgesics in vivo

T-type Ca(2+) channels are believed to play an important role in pain perception, and anesthetic steroids such as alphaxalone and allopregnanolone, which have a 5alpha-configuration at the steroid A, B ring fusion, are known to inhibit T-type Ca(2+) channels and cause analgesia in a thermal nociceptive model (Soc Neurosci Abstr 29:657.9, 2003). To define further the structure-activity relationships for steroid analgesia, we synthesized and examined a series of 5beta-reduced steroids for their ability to induce thermal antinociception in rats when injected locally into the peripheral receptive fields of the nociceptors and studied their effects on T-type Ca(2+) channel function in vitro. We found that most of the steroids completely blocked T-type Ca(2+) currents in vitro with IC(50) values at a holding potential of -90 mV ranging from 2.8 to 40 microM. T current blockade exhibited mild voltage-dependence, suggesting that 5beta-reduced neuroactive steroids stabilize inactive states of the channel. For the most potent steroids, we found that other voltage-gated currents were not significantly affected at concentrations that produce nearly maximal blockade of T currents. All tested compounds induced dose-dependent analgesia in thermal nociceptive testing; the most potent effect (ED(50), 30 ng/100 microl) obtained with a compound [(3beta,5beta,17beta)-3-hydroxyandrostane-17-carbonitrile] that was also the most effective blocker of T currents. Compared with previously studied 5alpha-reduced steroids, these 5beta-reduced steroids are more efficacious blockers of neuronal T-type Ca(2+) channels and are potentially useful as new experimental reagents for understanding the role of neuronal T-type Ca(2+) channels in peripheral pain pathways.

Potent analgesic effects of anticonvulsants on peripheral thermal nociception in rats

1. Anticonvulsant agents are commonly used to treat neuropathic pain conditions because of their effects on voltage- and ligand-gated channels in central pain pathways. However, their interaction with ion channels in peripheral pain pathways is poorly understood. Therefore, we studied the potential analgesic effects of commonly used anticonvulsant agents in peripheral nociception. 2. We injected anticonvulsants intradermally into peripheral receptive fields of sensory neurons in the hindpaws of adult rats, and studied pain perception using the model of acute thermal nociception. Commonly used anticonvulsants such as voltage-gated Na+ channel blockers, phenytoin and carbamazepine, and voltage-gated Ca2+ channel blockers, gabapentin and ethosuximide, induced dose-dependent analgesia in the injected paw, with ED50 values of 0.30, 0.32 and 8, 410 microg per 100 microl, respectively. 3. Thermal nociceptive responses were not affected in the contralateral, noninjected paws, indicating a lack of systemic effects with doses of anticonvulsants that elicited local analgesia. 4. Hill slope coefficients for the tested anticonvulsants indicate that the dose-response curve was less steep for gabapentin than for phenytoin, carbamazepine and ethosuximide. 5. Our data strongly suggest that cellular targets like voltage-gated Na+ and Ca2+ channels, similar to those that mediate the effects of anticonvulsant agents in the CNS, may exist in the peripheral nerve endings of rat sensory neurons. Thus, peripherally applied anticonvulsants that block voltage-gated Na+ and Ca2+ channels may be useful analgesics.