Behavioral Battery for Testing Candidate Analgesics in Mice. II. Effects of Endocannabinoid Catabolic Enzyme Inhibitors and ∆9-Tetrahydrocannabinol

Enhanced signaling of the endocannabinoid (eCB) system through inhibition of the catabolic enzymes monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH) has received increasing interest for development of candidate analgesics. This study compared effects of MAGL and FAAH inhibitors with effects of ∆9-tetrahydrocannabinol (THC) using a battery of pain-stimulated, pain-depressed, and pain-independent behaviors in male and female mice. Intraperitoneal injection of dilute lactic acid (IP acid) served as an acute visceral noxious stimulus to stimulate two behaviors (stretching, facial grimace) and depress two behaviors (rearing, nesting). Nesting and locomotion were also assessed in the absence of IP acid as pain-independent behaviors. THC and a spectrum of six eCB catabolic enzyme inhibitors ranging from MAGL- to FAAH-selective were assessed for effectiveness to alleviate pain-related behaviors at doses that did not alter pain-independent behaviors. The MAGL-selective inhibitor MJN110 produced the most effective antinociceptive profile, with 1.0 mg/kg alleviating IP acid effects on stretching, grimace, and nesting without altering pain-independent behaviors. MJN110 effects on IP acid-depressed nesting had a slow onset and long duration (40 minutes to 6 hours), were blocked by rimonabant, and tended to be greater in females. As inhibitors increased in FAAH selectivity, antinociceptive effectiveness decreased. PF3845, the most FAAH-selective inhibitor, produced no antinociception up to doses that disrupted locomotion. THC decreased IP acid-stimulated stretching and grimace at doses that did not alter pain-independent behaviors; however, it did not alleviate IP acid-induced depression of rearing or nesting. These results support further consideration of MAGL-selective inhibitors as candidate analgesics for acute inflammatory pain. SIGNIFICANCE STATEMENT: This study characterized a spectrum of endocannabinoid catabolic enzyme inhibitors ranging in selectivity from monoacylglycerol lipase-selective to fatty acid amide hydrolase-selective in a battery of pain-stimulated, pain-depressed, and pain-independent behaviors previously pharmacologically characterized in a companion paper. This battery provides a method for prioritizing candidate analgesics by effectiveness to alleviate pain-related behaviors at doses that do not alter pain-independent behaviors, with inclusion of pain-depressed behaviors increasing translational validity and decreasing susceptibility to motor-depressant false positives.

Apparent CB1 Receptor Rimonabant Affinity Estimates: Combination with THC and Synthetic Cannabinoids in the Mouse In Vivo Triad Model

Synthetic cannabinoids (SCs) represent an emerging class of abused drugs associated with psychiatric complications and other substantial health risks. These ligands are largely sold over the internet for human consumption, presumably because of their high cannabinoid 1 receptor (CB₁R) affinity and their potency in eliciting pharmacological effects similar to Δ⁹-tetrahydrocannabinol (THC), as well as circumventing laws illegalizing this plant. Factors potentially contributing to the increased prevalence of SC abuse and related hospitalizations, such as increased CB₁R efficacy and non-CB₁R targets, highlight the need for quantitative pharmacological analyses to determine receptor mediation of the pharmacological effects of cannabinoids. Accordingly, the present study used pA₂ and pK_B analyses for quantitative determination of CB₁R mediation in which we utilized the CB₁R-selective inverse agonist/antagonist rimonabant to elicit rightward shifts in the dose-response curves of five SCs (i.e., A-834,735D; WIN55,212-2; CP55,950; JWH-073; and CP47,497) and THC in producing common cannabimimetic effects (i.e., catalepsy, antinociception, and hypothermia). The results revealed overall similarity of pA₂ and pK_B values for these compounds and suggest that CB₁Rs, and not other pharmacological targets, largely mediated the central pharmacological effects of SCs. More generally, affinity estimation offers a powerful pharmacological approach to assess potential receptor heterogeneity subserving in vivo pharmacological effects of SCs.

Stratification of Cannabinoid 1 Receptor (CB1R) Agonist Efficacy: Manipulation of CB1R Density through Use of Transgenic Mice Reveals Congruence between In Vivo and In Vitro Assays

Synthetic cannabinoids (SCs) are an emerging class of abused drugs that differ from each other and the phytocannabinoid ∆⁹-tetrahydrocannabinol (THC) in their safety and cannabinoid-1 receptor (CB₁R) pharmacology. As efficacy represents a critical parameter to understanding drug action, the present study investigated this metric by assessing in vivo and in vitro actions of THC, two well-characterized SCs (WIN55,212-2 and CP55,940), and three abused SCs (JWH-073, CP47,497, and A-834,735-D) in CB₁ (+/+), (+/-), and (-/-) mice. All drugs produced maximal cannabimimetic in vivo effects (catalepsy, hypothermia, antinociception) in CB₁ (+/+) mice, but these actions were essentially eliminated in CB₁ (-/-) mice, indicating a CB₁R mechanism of action. CB₁R efficacy was inferred by comparing potencies between CB₁ (+/+) and (+/-) mice [+/+ ED₅₀ /+/- ED₅₀], the latter of which has a 50% reduction of CB₁Rs (i.e., decreased receptor reserve). Notably, CB₁ (+/-) mice displayed profound rightward and downward shifts in the antinociception and hypothermia dose-response curves of low-efficacy compared with high-efficacy cannabinoids. In vitro efficacy, quantified using agonist-stimulated [³⁵S]GTPγS binding in spinal cord tissue, significantly correlated with the relative efficacies of antinociception (r = 0.87) and hypothermia (r = 0.94) in CB₁ (+/-) mice relative to CB₁ (+/+) mice. Conversely, drug potencies for cataleptic effects did not differ between these genotypes and did not correlate with the in vitro efficacy measure. These results suggest that evaluation of antinociception and hypothermia in CB₁ transgenic mice offers a useful in vivo approach to determine CB₁R selectivity and efficacy of emerging SCs, which shows strong congruence with in vitro efficacy.

Diacylglycerol lipase β inhibition reverses nociceptive behaviour in mouse models of inflammatory and neuropathic pain

BACKGROUND AND PURPOSE

Inhibition of diacylglycerol lipase (DGL)β prevents LPS-induced pro-inflammatory responses in mouse peritoneal macrophages. Thus, the present study tested whether DGLβ inhibition reverses allodynic responses of mice in the LPS model of inflammatory pain, as well as in neuropathic pain models.

EXPERIMENTAL APPROACH

Initial experiments examined the cellular expression of DGLβ and inflammatory mediators within the LPS-injected paw pad. DAGL-β (-/-) mice or wild-type mice treated with the DGLβ inhibitor KT109 were assessed in the LPS model of inflammatory pain. Additional studies examined the locus of action for KT109-induced antinociception, its efficacy in chronic constrictive injury (CCI) of sciatic nerve and chemotherapy-induced neuropathic pain (CINP) models.

KEY RESULTS

Intraplantar LPS evoked mechanical allodynia that was associated with increased expression of DGLβ, which was co-localized with increased TNF-α and prostaglandins in paws. DAGL-β (-/-) mice or KT109-treated wild-type mice displayed reductions in LPS-induced allodynia. Repeated KT109 administration prevented the expression of LPS-induced allodynia, without evidence of tolerance. Intraplantar injection of KT109 into the LPS-treated paw, but not the contralateral paw, reversed the allodynic responses. However, i.c.v. or i.t. administration of KT109 did not alter LPS-induced allodynia. Finally, KT109 also reversed allodynia in the CCI and CINP models and lacked discernible side effects (e.g. gross motor deficits, anxiogenic behaviour or gastric ulcers).

CONCLUSIONS AND IMPLICATIONS

These findings suggest that local inhibition of DGLβ at the site of inflammation represents a novel avenue to treat pathological pain, with no apparent untoward side effects.

Inhibition of monoacylglycerol lipase reduces nicotine withdrawal

BACKGROUND AND PURPOSE

Abrupt discontinuation of nicotine, the main psychoactive component in tobacco, induces a withdrawal syndrome in nicotine-dependent animals, consisting of somatic and affective signs, avoidance of which contributes to drug maintenance. While blockade of fatty acid amide hydrolase, the primary catabolic enzyme of the endocannabinoid arachidonoylethanolamine (anandamide), exacerbates withdrawal responses in nicotine-dependent mice, the role of monoacylglycerol lipase (MAGL), the main hydrolytic enzyme of a second endocannabinoid 2-arachidonylglycerol (2-AG), in nicotine withdrawal remains unexplored.

EXPERIMENTAL APPROACH

To evaluate the role of MAGL enzyme inhibition in nicotine withdrawal, we initially performed a genetic correlation approach using the BXD recombinant inbred mouse panel. We then assessed nicotine withdrawal intensity in the mouse after treatment with the selective MAGL inhibitor, JZL184, and after genetic deletion of the enzyme. Lastly, we assessed the association between genotypes and smoking withdrawal phenotypes in two human data sets.

KEY RESULTS

BXD mice displayed significant positive correlations between basal MAGL mRNA expression and nicotine withdrawal responses, consistent with the idea that increased 2-AG brain levels may attenuate withdrawal responses. Strikingly, the MAGL inhibitor, JZL184, dose-dependently reduced somatic and aversive withdrawal signs, which was blocked by rimonabant, indicating a CB1 receptor-dependent mechanism. MAGL-knockout mice also showed attenuated nicotine withdrawal. Lastly, genetic analyses in humans revealed associations of the MAGL gene with smoking withdrawal in humans.

CONCLUSIONS AND IMPLICATIONS

Overall, our findings suggest that MAGL inhibition maybe a promising target for treatment of nicotine dependence.

In vivo characterization of the highly selective monoacylglycerol lipase inhibitor KML29: antinociceptive activity without cannabimimetic side effects

BACKGROUND AND PURPOSE

Since monoacylglycerol lipase (MAGL) has been firmly established as the predominant catabolic enzyme of the endocannabinoid 2-arachidonoylglycerol (2-AG), a great need has emerged for the development of highly selective MAGL inhibitors. Here, we tested the in vivo effects of one such compound, KML29 (1,1,1,3,3,3-hexafluoropropan-2-yl 4-(bis(benzo[d][1,3]dioxol-5-yl)(hydroxy)methyl)piperidine-1-carboxylate).

EXPERIMENTAL APPROACH

In the present study, we tested KML29 in murine inflammatory (i.e. carrageenan) and sciatic nerve injury pain models, as well as the diclofenac-induced gastric haemorrhage model. KML29 was also evaluated for cannabimimetic effects, including measurements of locomotor activity, body temperature, catalepsy, and cannabinoid interoceptive effects in the drug discrimination paradigm.

KEY RESULTS

KML29 attenuated carrageenan-induced paw oedema and completely reversed carrageenan-induced mechanical allodynia. These effects underwent tolerance after repeated administration of high-dose KML29, which were accompanied by cannabinoid receptor 1 (CB1 ) receptor desensitization. Acute or repeated KML29 administration increased 2-AG levels and concomitantly reduced arachidonic acid levels, but without elevating anandamide (AEA) levels in the whole brain. Furthermore, KML29 partially reversed allodynia in the sciatic nerve injury model and completely prevented diclofenac-induced gastric haemorrhages. CB1 and CB2 receptors played differential roles in these pharmacological effects of KML29. In contrast, KML29 did not elicit cannabimimetic effects, including catalepsy, hypothermia and hypomotility. Although KML29 did not substitute for Δ(9) -tetrahydrocannabinol (THC) in C57BL/6J mice, it fully and dose-dependantly substituted for AEA in fatty acid amide hydrolase (FAAH) (-/-) mice, consistent with previous work showing that dual FAAH and MAGL inhibition produces THC-like subjective effects.

CONCLUSIONS AND IMPLICATIONS

These results indicate that KML29, a highly selective MAGL inhibitor, reduces inflammatory and neuropathic nociceptive behaviour without occurrence of cannabimimetic side effects.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Mouse models of atherosclerosis

Genetically altered mice carrying mutations of genes encoding crucial components of the immune system and lipid metabolism have been widely used to study the role of immune responses and inflammation in atherosclerosis. These mice are often fed a diet, with a high content of cholesterol and saturated fat in order to induce hypercholesterolemia and arterial lesions. We review the different mouse models of atherosclerosis, type of diets, and techniques to measure lipid deposition and lesion size in the arterial walls. Moreover, the methods used to determine the presence of the immune cells in atherosclerotic lesions are also described here.

Blockade of endocannabinoid-degrading enzymes attenuates neuropathic pain

Direct-acting cannabinoid receptor agonists are well known to reduce hyperalgesic responses and allodynia after nerve injury, although their psychoactive side effects have damped enthusiasm for their therapeutic development. Alternatively, inhibiting fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), the principal enzymes responsible for the degradation of the respective endogenous cannabinoids, anandamide (AEA) and 2-arachydonylglycerol (2-AG), reduce nociception in a variety of nociceptive assays, with no or minimal behavioral effects. In the present study we tested whether inhibition of these enzymes attenuates mechanical allodynia, and acetone-induced cold allodynia in mice subjected to chronic constriction injury of the sciatic nerve. Acute administration of the irreversible FAAH inhibitor, cyclohexylcarbamic acid 3'-carbamoylbiphenyl-3-yl ester (URB597), or the reversible FAAH inhibitor, 1-oxo-1-[5-(2-pyridyl)-2-yl]-7-phenylheptane (OL-135), decreased allodynia in both tests. This attenuation was completely blocked by pretreatment with either CB(1) or CB(2) receptor antagonists, but not by the TRPV1 receptor antagonist, capsazepine, or the opioid receptor antagonist, naltrexone. The novel MAGL inhibitor, 4-nitrophenyl 4-(dibenzo[d][1,3]dioxol-5-yl(hydroxy)methyl)piperidine-1-carboxylate (JZL184) also attenuated mechanical and cold allodynia via a CB(1), but not a CB(2), receptor mechanism of action. Whereas URB597 did not elicit antiallodynic effects in FAAH(-/-) mice, the effects of JZL184 were FAAH-independent. Finally, URB597 increased brain and spinal cord AEA levels, whereas JZL184 increased 2-AG levels in these tissues, but no differences in either endo-cannabinoid were found between nerve-injured and control mice. These data indicate that inhibition of FAAH and MAGL reduces neuropathic pain through distinct receptor mechanisms of action and present viable targets for the development of analgesic therapeutics.

The endogenous cannabinoid system modulates nicotine reward and dependence

A growing body of evidence suggests that the endogenous cannabinoid system modulates the addictive properties of nicotine, the main component of tobacco that produces rewarding effects. In our study, complementary transgenic and pharmacological approaches were used to test the hypothesis that the endocannabinoid system modulates nicotine reward and dependence. An acute injection of nicotine elicited normal analgesic and hypothermic effects in cannabinoid receptor (CB)(1) knockout (KO) mice and mice treated with the CB(1) antagonist rimonabant. However, disruption of CB(1) receptor signaling blocked nicotine reward, as assessed in the conditioned place preference (CPP) paradigm. In contrast, genetic deletion, or pharmacological inhibition of fatty acid amide hydrolase (FAAH), the enzyme responsible for catabolism of the endocannabinoid anandamide, enhanced the expression of nicotine CPP. Although the expression of spontaneous nicotine withdrawal (14 days, 24 mg/kg/day nicotine) was unaffected in CB(1) KO mice, acute administration of rimonabant (3 mg/kg) ameliorated somatic withdrawal signs in wild-type mice. Increasing endogenous levels of anandamide through genetic or pharmacological approaches exacerbated the physical somatic signs of spontaneous nicotine withdrawal in a milder withdrawal model (7 days, 24 mg/kg/day nicotine). Moreover, FAAH-compromised mice displayed increased conditioned place aversion in a mecamylamine-precipitated model of nicotine withdrawal. These findings indicate that endocannabinoids play a role in the rewarding properties of nicotine as well as nicotine dependence liability. Specifically, increasing endogenous cannabinoid levels magnifies, although disrupting CB(1) receptor signaling, attenuates nicotine reward and withdrawal. Taken together, these results support the hypothesis that cannabinoid receptor antagonists may offer therapeutic advantages to treat tobacco dependence.

The psychoactive plant cannabinoid, Delta9-tetrahydrocannabinol, is antagonized by Delta8- and Delta9-tetrahydrocannabivarin in mice in vivo

BACKGROUND AND PURPOSE

To follow up in vitro evidence that Delta(9)-tetrahydrocannabivarin extracted from cannabis (eDelta(9)-THCV) is a CB(1) receptor antagonist by establishing whether synthetic Delta(9)-tetrahydrocannabivarin (O-4394) and Delta(8)-tetrahydrocannabivarin (O-4395) behave as CB(1) antagonists in vivo.

EXPERIMENTAL APPROACH

O-4394 and O-4395 were compared with eDelta(9)-THCV as displacers of [(3)H]-CP55940 from specific CB(1) binding sites on mouse brain membranes and as antagonists of CP55940 in [(35)S]GTPgammaS binding assays performed with mouse brain membranes and of R-(+)-WIN55212 in mouse isolated vasa deferentia. Their ability to antagonize in vivo effects of 3 or 10 mg kg(-1) (i.v.) Delta(9)-tetrahydrocannabinol in mice was then investigated.

KEY RESULTS

O-4394 and O-4395 exhibited similar potencies to eDelta(9)-THCV as displacers of [(3)H]-CP55940 (K (i)=46.6 and 64.4 nM, respectively) and as antagonists of CP55940 in the [(35)S]GTPgammaS binding assay (apparent K (B)=82.1 and 125.9 nM, respectively) and R-(+)-WIN55212 in the vas deferens (apparent K (B)=4.8 and 3.9 nM respectively). At i.v. doses of 0.1, 0.3, 1.0 and/or 3 mg kg(-1) O-4394 and O-4395 attenuated Delta(9)-tetrahydrocannabinol-induced anti-nociception (tail-flick test) and hypothermia (rectal temperature). O-4395 but not O-4394 also antagonized Delta(9)-tetrahydrocannabinol-induced ring immobility. By themselves, O-4395 and O-4394 induced ring immobility at 3 or 10 mg kg(-1) (i.v.) and antinociception at doses above 10 mg kg(-1) (i.v.). O-4395 also induced hypothermia at 3 mg kg(-1) (i.v.) and above.

CONCLUSIONS AND IMPLICATIONS

O-4394 and O-4395 exhibit similar in vitro potencies to eDelta(9)-THCV as CB(1) receptor ligands and as antagonists of cannabinoid receptor agonists and can antagonize Delta(9)-tetrahydrocannabinol in vivo.

Interactions between THC and cannabidiol in mouse models of cannabinoid activity

RATIONALE

Interest persists in characterizing potential interactions between Delta(9)-tetrahydocannabinol (THC) and other marijuana constituents such as cannabidiol (CBD). Such interactions may have important implications for understanding the long-term health consequences of chronic marijuana use as well as for attempts to develop therapeutic uses for THC and other CB(1) agonists.

OBJECTIVES

We investigated whether CBD may modulate the pharmacological effects of intravenously administered THC or inhaled marijuana smoke on hypoactivity, antinociception, catalepsy, and hypothermia, the well characterized models of cannabinoid activity.

RESULTS

Intravenously administered CBD possessed very little activity on its own and, at a dose equal to a maximally effective dose of THC (3 mg/kg), failed to alter THC's effects on any measure. However, higher doses of CBD (ED(50)=7.4 mg/kg) dose-dependently potentiated the antinociceptive effects of a low dose of THC (0.3 mg/kg). Pretreatment with 30 mg/kg CBD, but not 3 mg/kg, significantly elevated THC blood and brain levels. No interactions between THC and CBD were observed in several variations of a marijuana smoke exposure model. Either quantities of CBD were applied directly to marijuana, CBD and THC were both applied to placebo plant material, or mice were pretreated intravenously with 30 mg/kg CBD before being exposed to marijuana smoke.

CONCLUSIONS

As the amount of CBD found in most marijuana strains in the US is considerably less than that of THC, these results suggest that CBD concentrations relevant to what is normally found in marijuana exert very little, if any, modulatory effects on CB(1)-receptor-mediated pharmacological effects of marijuana smoke.

Cannabinoid tolerance and dependence

The use of marijuana for recreational and medicinal purposes has resulted in a large prevalence of chronic marijuana users. Consequences of chronic cannabinoid administration include profound behavioral tolerance and withdrawal symptoms upon drug cessation. A marijuana withdrawal syndrome is only recently gaining acceptance as being clinically significant. Similarly, laboratory animals exhibit both tolerance and dependence following chronic administration of cannabinoids. These animal models are being used to evaluate the high degree of plasticity that occurs at the molecular level in various brain regions following chronic cannabinoid exposure. In this review, we describe recent advances that have increased our understanding of the impact of chronic cannabinoid administration on cannabinoid receptors and their signal transduction pathways. Additionally, we discuss several potential pharmacotherapies that have been examined to treat marijuana dependence.

Disruption of CB(1) receptor signaling impairs extinction of spatial memory in mice

RATIONALE

A growing body of in vitro and in vivo evidence indicates that a central endocannabinoid system, consisting of CB(1) receptors and endogenous cannabinoids, modulates specific aspects of mnemonic processes. Previous research has demonstrated that either permanent or drug-induced disruption of CB(1) receptor signaling interferes with the extinction of a conditioned fear response.

OBJECTIVES

In the present study, we evaluated whether the endocannabinoid system also plays a role in extinguishing learned escape behavior in a Morris water maze task.

METHODS

CB(1) (-/-) mice and mice repeatedly treated with 3 mg/kg of the CB(1) receptor antagonist SR 141716 (Rimonabant) were trained to locate a hidden platform in the Morris water maze. Following acquisition, the platform was removed and subjects were assigned to either a massed (i.e., five consecutive sessions consisting of four 2-min trials/session) or a spaced (a single, 1-min trial every 2-4 weeks) extinction protocol.

RESULTS

Strikingly, both 3 mg/kg SR 141716-treated mice and CB(1) (-/-) mice continued to return to the target location across all five trials in the spaced extinction procedure, while the control mice underwent extinction by the third or fourth trial. In contrast, both the 3-mg/kg SR 141716-treated and CB(1) (-/-) mice exhibited extinction in the massed extinction trial procedure.

CONCLUSIONS

These findings indicate that disruption of CB(1) receptor signaling impairs extinction processes in the Morris water maze, thus lending further support to the hypothesis that the endocannabinoid system plays an integral role in the suppression of non-reinforced learned behaviors.

Delta9-tetrahydrocannbinol accounts for the antinociceptive, hypothermic, and cataleptic effects of marijuana in mice

Although it is widely accepted that delta9-tetrahydrocannabinol (delta9-THC) is the primary psychoactive constituent of marijuana, questions persist as to whether other components contribute to marijuana's pharmacological activity. The present experiments assessed the cannabinoid activity of marijuana smoke exposure in mice and tested the hypothesis that delta9-THC mediates these effects through a CB1 receptor mechanism of action. First, the effects of delta9-THC on analgesia, hypothermia, and catalepsy were compared with those of a marijuana extract with equated delta9-THC content after either i.v. administration or inhalation exposure. Second, mice were exposed to smoke of an ethanol-extracted placebo plant material or low-grade marijuana (with minimal delta9-THC but similar levels of other cannabinoids) that were impregnated with varying quantities of delta9-THC. To assess doses, delta9-THC levels in the blood and brains of drug-exposed mice were determined following both i.v. and inhalation routes of administration. Both marijuana and delta9-THC produced comparable levels of antinociception, hypothermia, and catalepsy regardless of the route of administration, and these effects were blocked by pretreatment with the CB1 antagonist SR141716 [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide HCl]. Importantly, the blood and brain levels of delta9-THC were similar in mice exhibiting similar pharmacological effects, regardless of the presence of non-delta9-THC marijuana constituents. The present experiments provide evidence that the acute cannabinoid effects of marijuana smoke exposure on analgesia, hypothermia, and catalepsy in mice result from delta9-THC content acting at CB1 receptors and that the non-delta9-THC constituents of marijuana (at concentrations relevant to those typically consumed) influence these effects only minimally, if at all.

Delta(9)-THC-induced cognitive deficits in mice are reversed by the GABA(A) antagonist bicuculline

RATIONALE

The results of recent in vitro studies have underscored the important role that activation of CB(1) receptors has on GABAergic activity in brain areas associated with memory.

OBJECTIVES

The primary purpose of this study was to test the hypothesis that the memory disruptive effects of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) in vivo are mediated through GABAergic systems. Conversely, we also evaluated whether blocking CB(1) receptor signaling would alter memory deficits elicited by GABA agonists.

METHODS

The GABA(A) antagonist bicuculline and GABA(B) antagonist CGP 36742 were evaluated for their ability to ameliorate Delta(9)-THC-induced deficits in a mouse working memory Morris water maze task. Mice were also assessed in a T-maze task, as well as non-cognitive behavioral assays. Additionally, the effects of GABA(A) and GABA(B) agonists were assessed in either CB(1) (-/-) mice or wild type mice treated with the CB(1) antagonist SR 141716.

RESULTS

Memory deficits resulting from 10 mg/kg Delta(9)-THC in the Morris water maze were completely reversed by bicuculline, though unaffected by CGP 36742. Bicuculline also blocked the disruptive effects of Delta(9)-THC in the T-maze, but failed to alter non-mnemonic effects of Delta(9)-THC. Although CB(1) (-/-) mice exhibited supersensitivity to muscimol-induced water maze deficits compared with wild type control mice, muscimol elicited virtually identical effects in SR 141716-treated and vehicle-treated wild type mice.

CONCLUSIONS

This is the first demonstration of which we are aware showing that GABA(A) receptors may play a necessary role in Delta(9)-THC-induced memory impairment in whole animals.

NEUROSCIENCE: Stout Guards of the Central Nervous System

Endocannabinoids have paradoxical effects on the mammalian nervous system: Sometimes they block neuronal excitability and other times they augment it. In their Perspective, Mechoulam and Lichtman discuss new work (Marsicano et al.) showing that activation of the cannabinoid receptor CB1 by the endocannabinoid anandamide protects against excitotoxic damage in a mouse model of kainic acid-induced epilepsy.

Endocannabinoids in cognition and dependence

Cannabis use is associated with a wide range of pharmacological effects, some of which have potential therapeutic benefit while others result in negative outcomes. Acute cannabinoid intoxication has been well documented to produce deficits in cognitive functioning with concomitant changes in glutamatergic, GABAergic, and cholinergic neurochemical systems in the hippocampus, each of which has been implicated in memory. Additionally, cannabis-dependent individuals abstaining from this drug can undergo a constellation of mild withdrawal effects. The use of the CB(1) cannabinoid receptor antagonist SR141716A and transgenic mice lacking the CB(1) receptor are critical tools for investigating the role of the endocannabinoid system in cognition, drug dependence, and other physiological processes. Converging evidence in which performance in a variety of memory tasks is enhanced following either SR141716A treatment or in CB(1) receptor knockout mice indicates that this system may play an important role in modulating cognition. There are also indications that this system may function to modulate opioid dependence. The purpose of this review is to describe recent advances that have furthered our understanding of the roles that the endocannabinoid system play on both cognition and drug dependence.

Acetylcodeine, an impurity of illicitly manufactured heroin, elicits convulsions, antinociception, and locomotor stimulation in mice

Acetylcodeine is one of the major impurities present in illicitly manufactured heroin (diacetylmorphine). Data on its pharmacology and toxicology are limited and its ability to alter the toxic effects of diacetylmorphine is not known. The first objective of the present study was to compare the acute pharmacological and toxicological effects of acetylcodeine to those of codeine and diacetylmorphine in mice by assessing nociception in the tail-flick test, locomotor stimulation, and convulsive behavior. The second goal of this study was to determine whether acetylcodeine would alter the convulsant effects of diacetylmorphine. The antinociceptive potencies of acetylcodeine and codeine were similar, as reflected by their ED50 (95% confidence limits) values of 35 (29-44) and 51 (40-65) micromol/kg, respectively. Acetylcodeine was somewhat less potent than codeine in stimulating locomotor behavior, with ED50 values of 28 (22-37) and 12 (6-24) micromol/kg, respectively. Diacetylmorphine was considerably more potent than the other two drugs, producing antinociception and locomotor stimulation at ED50 values of 2.4 (1.4-4.1) and 0.65 (0.36-1.2) micromol/kg, respectively. On the other hand, the convulsant effects of acetylcodeine (ED50=138 (121-157) micromol/kg) and diacetylmorphine (ED50=115 (81-163) micromol/kg) were similar in potency and both were more potent than codeine (ED50=231 (188-283) micromol/kg). Finally, a subthreshold dose of acetylcodeine (72 micromol/kg) decreased the convulsant ED50 dose of diacetylmorphine to 40 (32-49). These findings suggest that the convulsant effects of acetylcodeine are more potent than predicted by its effects on locomotor activity and antinociception. The observation that acetylcodeine potentiated the convulsant effects of diacetylmorphine suggests a mechanism for some of the heroin-related deaths reported in human addicts.

IL-12, STAT4-dependent up-regulation of CD4(+) T cell core 2 beta-1,6-n-acetylglucosaminyltransferase, an enzyme essential for biosynthesis of P-selectin ligands

TCR activation of naive T cells in the presence of IL-12 drives polarization toward a Th1 phenotype and synthesis of P- and E-selectin ligands. Fucosyltransferase VII (Fuc-T VII) and core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT) are critical for biosynthesis of selectin ligands. P-selectin glycoprotein ligand-1 is the best characterized ligand for P-selectin and also binds E-selectin. The contributions of TCR and cytokine signaling pathways to up-regulate Fuc-T VII and C2GnT during biosynthesis of E- and P-selectin ligands, such as P-selectin glycoprotein ligand 1, are unknown. IL-12 signals via the STAT4 pathway. Here, naive DO11.10 TCR transgenic and STAT4(-/-) TCR transgenic CD4(+) T cells were stimulated with Ag and IL-12 (Th1 condition), IL-4 (Th2), or neutralizing anti-IL-4 mAb only (Th0). The levels of Fuc-T VII and C2GnT mRNA in these cells were compared with their adhesive interactions with P- and E-selectin in vitro under flow. The data show IL-12/STAT4 signaling is necessary for induction of C2GnT, but not Fuc-TVII mRNA, and that STAT4(-/-) Th1 cells do not traffic normally to sites of inflammation in vivo, do not interact with P-selectin, and exhibit a partial reduction of E-selectin interactions under shear stress in vitro. Ag-specific TCR activation in CD4(+) T cells was sufficient to trigger induction of Fuc-TVII, but not C2GnT, mRNA and expression of E-selectin, but not P-selectin, ligands. Thus, Fuc-T VII and C2GnT are regulated by different signals during Th cell differentiation, and both cytokine and TCR signals are necessary for the expression of E- and P-selectin ligands.

Opioid and cannabinoid modulation of precipitated withdrawal in delta(9)-tetrahydrocannabinol and morphine-dependent mice

The goal of the present study was to elucidate the relationship between cannabinoid and opioid systems in drug dependence. The CB(1) cannabinoid receptor antagonist SR 141716A precipitated both paw tremors and head shakes in four different mouse strains that were treated repeatedly with Delta(9)-tetrahydrocannabinol (Delta(9)-THC). SR 141716A-precipitated Delta(9)-THC withdrawal was ameliorated in mu-opioid receptor knockout mice compared with the wild-type control animals and failed to occur in mice devoid of CB(1) cannabinoid receptors. An acute injection of morphine in Delta(9)-THC-dependent mice undergoing SR 1417161A-precipitated withdrawal dose dependently decreased both paw tremors, antagonist dose 50 (AD(50)) (95% CL) = 0.035 (0.03--0.04), and head shakes, AD(50) (95% CL) = 0.07 (0.04--0.12). In morphine-dependent mice, the opioid antagonist naloxone precipitated head shakes, paw tremors, diarrhea, and jumping. As previously reported, naloxone-precipitated morphine withdrawal failed to occur in mu-opioid knockout mice and was significantly decreased in CB(1) cannabinoid receptor knockout mice. Acute treatment of Delta(9)-THC in morphine-dependent mice undergoing naloxone-precipitated withdrawal blocked paw tremors, AD(50) (95% CL) = 0.5 (0.3--1.0), and head shakes AD(50) (95% CL) = 0.6 (0.57--0.74) in dose-dependent manners, but failed to diminish the occurrence of diarrhea or jumping. Finally, naloxone and SR 141716A failed to elicit any overt effects in Delta(9)-THC-dependent and morphine-dependent mice, respectively. These findings taken together indicate that the mu-opioid receptor plays a modulatory role in cannabinoid dependence, thus implicating a reciprocal relationship between the cannabinoid and opioid systems in dependence.

Differential effects of delta 9-THC on spatial reference and working memory in mice

RATIONALE

Marijuana remains the most widely used illicit drug in the U.S., and recent attention has been given to putative therapeutic uses of marijuana and cannabinoid derivatives. Thus, developing a better understanding of delta9-THC (tetrahydrocannabinol)-induced mnemonic deficits is of critical importance.

OBJECTIVES

These experiments were conducted to determine whether delta9-THC has differential effects on spatial reference and working memory tasks, to investigate its receptor mechanism of action, and to compare these effects with those produced by two other compounds--scopolamine and phencyclidine--known to produce mnemonic deficits. In addition, the potency of delta9-THC in these memory tasks was compared with its potency in other pharmacological effects traditionally associated with cannabinoid activity.

METHODS

Two different versions of the Morris water maze were employed: a working memory task and a reference memory task. Other effects of delta9-THC were assessed using standard tests of hypomotility, antinociception, catalepsy, and hypothermia.

RESULTS

delta9-THC disrupted performance of the working memory task (3.0 mg/kg) at doses lower than those required to disrupt performance of the reference memory task (100 mg/kg), or elicit hypomotility, antinociception, catalepsy, and hypothermia. These performance deficits were reversed by SR 141716A. The effects of delta9-THC resembled those of scopolamine, which also selectively disrupted the working maze task. Conversely, phencyclidine disrupted both tasks only at a dose that also produced motor deficits.

CONCLUSIONS

These data indicate that delta9-THC selectively impairs performance of a working memory task through a CB, receptor mechanism of action and that these memory disruptions are more sensitive than other pharmacological effects of delta9-THC.

Supersensitivity to anandamide and enhanced endogenous cannabinoid signaling in mice lacking fatty acid amide hydrolase

The medicinal properties of marijuana have been recognized for centuries, but clinical and societal acceptance of this drug of abuse as a potential therapeutic agent remains fiercely debated. An attractive alternative to marijuana-based therapeutics would be to target the molecular pathways that mediate the effects of this drug. To date, these neural signaling pathways have been shown to comprise a cannabinoid receptor (CB(1)) that binds the active constituent of marijuana, tetrahydrocannabinol (THC), and a postulated endogenous CB(1) ligand anandamide. Although anandamide binds and activates the CB(1) receptor in vitro, this compound induces only weak and transient cannabinoid behavioral effects in vivo, possibly a result of its rapid catabolism. Here we show that mice lacking the enzyme fatty acid amide hydrolase (FAAH(-/-)) are severely impaired in their ability to degrade anandamide and when treated with this compound, exhibit an array of intense CB(1)-dependent behavioral responses, including hypomotility, analgesia, catalepsy, and hypothermia. FAAH(-/-)-mice possess 15-fold augmented endogenous brain levels of anandamide and display reduced pain sensation that is reversed by the CB(1) antagonist SR141716A. Collectively, these results indicate that FAAH is a key regulator of anandamide signaling in vivo, setting an endogenous cannabinoid tone that modulates pain perception. FAAH may therefore represent an attractive pharmaceutical target for the treatment of pain and neuropsychiatric disorders.

The pharmacological activity of inhalation exposure to marijuana smoke in mice

Although the majority of cannabinoid users smoke marijuana, the preponderance of laboratory animal research is based on administration of Delta9-tetrahydrocannabinol (Delta9-THC) or other cannabinoid agents via injection. The aim of the present study was to evaluate the impact of inhaling marijuana, or ethanol-extracted placebo smoke in the mouse model of cannabinoid activity by assessing inhibition of spontaneous activity, antinociception, catalepsy, and body temperature. In order to determine dosimetry, blood levels of Delta9-THC were obtained following either marijuana exposure or intravenous injection of Delta(9)-THC. Inhalation exposure to marijuana produced dose-related increases in antinociception and catalepsy, with estimated ED50 doses of Delta9-THC of 2.4 and 3.8 mg/kg, respectively. However, hypothermia and locomotor depression occurred in both the placebo- and marijuana-exposed mice. The CB1 receptor antagonist, SR 141716A antagonized the antinociceptive effects of marijuana (AD50 = 0.6 mg/kg), but only slightly decreased marijuana-induced catalepsy, and failed to alter either the hypothermic or locomotor depressive effects. In contrast, SR 141716A antagonized the antinociceptive, cataleptic, and hypothermic effects of intravenously administered Delta9-THC in mice that were exposed to air alone, though all subjects exhibited locomotor depression, possibly related to the restraint. In accordance with reports of others, these data suggest that exposure to smoke alone has pharmacological consequences. Our findings also indicate that marijuana-induced antinociception is mediated through a CB1-receptor mechanism of action and are consistent with the notion that Delta9-THC is mainly responsible for this effect.

Precipitated cannabinoid withdrawal is reversed by Delta(9)-tetrahydrocannabinol or clonidine

The availability of the cannabinoid antagonist, SR 141716A, to precipitate withdrawal following repeated cannabinoid administration provides a model to investigate the mechanisms underlying cannabinoid dependence as well as potential treatments to alleviate withdrawal symptoms. The goal of the present study was to determine whether SR 141716A-precipitated withdrawal symptoms in Delta(9)-tetrahydrocannabinol (Delta(9)-THC)-tolerant mice could be alleviated by either readministration of Delta(9)-THC or clonidine, an alpha(2)-receptor agonist. SR 141716A elicited paw tremors in Delta(9)-THC-tolerant mice, but produced a significant increase in head shakes independently of repeated Delta(9)-THC treatment. Readministration of Delta(9)-THC, following SR 141716A-precipitated withdrawal, reversed paw tremors (ED(50)=9.9 mg/kg), but failed to reduce head shaking behavior. Clonidine reversed SR 141716A-precipitated paw tremors (ED(50)=0.18 mg/kg) and blocked head shakes at all doses tested. The reversal effects did not appear to be the result of motor impairment because neither decreases in spontaneous locomotor activity nor motor incoordination, as assessed in the inverted screen test, could account for the effects. These findings suggest that SR 141716A precipitates paw tremors in mice by competing with Delta(9)-THC at the CB(1) receptor, though it also produced head shaking in nondependent animals. Finally, the observation that clonidine alleviated SR 141716A-precipitated paw tremors suggests its potential as a treatment for cannabinoid dependence.

CD8+ T cell subsets TC1 and TC2 cause different histopathologic forms of murine cardiac allograft rejection

BACKGROUND

CD4+ T cell effector function is sufficient to mediate allograft rejection, and it is suggested that CD8+ T cell-mediated effects are dependent on CD4+ T cell help. CD8+ T cells can be classified into at least two functional subsets: Tc1, producing high amounts of interferon (IFN)-gamma and Tc2, producing interleukin (IL)-4, -5, -10, and -13 and low levels of IFN-gamma. Because these subsets express different chemokine receptors, they may have different capabilities of migrating into grafts. Once in the graft, each subset may perform different effector functions dependent on the cytokines it produces. We asked whether allospecific CD8+ T cells, in the absence of CD4+ T cells, are capable of mediating rejection of a primarily vascularized allograft, and if Tcl and Tc2 cells differ in their ability to mediate rejection.

METHODS

Hearts from H-2d mice were transplanted into H-2b RAG 1-/- recipients. Without manipulation, these fully mismatched allografts would survive indefinitely due to the absence of mature T and B cells. We adoptively transferred allo-(H-2d)-reactive Tcl or Tc2 cells from H-2b mice into each recipient. Grafts were harvested and analyzed on predefined timepoints, rejection was graded on a modified ISHLT scale.

RESULTS

On day 7, grafts from Tc1- or Tc2-injected animals showed grade 1-2 parenchymal rejection with stable phenotype and comparable distribution of graft infiltrating CD8+ T cells. Adoptive transfer of IFN-gammahigh Tc1, but not of IFN-gammalow Tc2 cells was followed by the development of graft vasculitis, as well as graft arteriopathy. Adoptive transfer of IL-4high IL-5high Tc2, but not of IL-4low IL-5low Tc1 cells lead to extensive infiltration of eosinophils and formation of giant cells.

CONCLUSIONS

Both Tc1 and Tc2 cells can mediate murine cardiac allograft rejection in the absence of CD4+ T cell help, although each subset elicits a different type of inflammatory response. In this model, cytokine secretion of either functional CD8+ T effector cell subset is an important effector mechanism in the process of allograft rejection: IFN-gammahigh Tc1 cells are important in early graft vasculitis, although IL-4high IL-5high Tc2 cells promote recruitment of secondary effectors like eosinophils.

SR 141716A enhances spatial memory as assessed in a radial-arm maze task in rats

A tonically active endogenous cannabinoid system has been proposed to modulate learning and memory. The purpose of the present study was to determine whether administration of the cannabinoid CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide HCl (SR 141716A) would enhance memory as assessed in an eight-arm radial maze task. Because the high degree of choice accuracy in the standard radial-arm maze procedure precludes the possibility of detecting memory enhancement, the difficulty of the task was increased by imposing a delay of varying durations between a two-phase procedure consisting of acquisition and test phases. Significantly fewer errors were committed during the test phase following an injection of SR 141716A than the vehicle treatment. These results provide additional evidence supporting the hypothesis that endogenous cannabinoid systems play a role in memory processes.

Integration of TCR and IL-4 signals through STAT6 and the regulation of IL-4 gene expression

Signals generated by both antigen and cytokines binding to CD4(+) T cells synergize to promote helper T cell subset differentiation. For Th2 cell commitment neither IL-4 nor T cell receptor (TCR) stimulation are sufficient to drive differentiation. Th2 differentiation requires IL-4-receptor mediated signal transducers and activators of transcription 6 (STAT6) activation, but the possibility that IL-4 can directly enhance IL-4 production by T cells has remained unclear. In this report, IL-4 is shown to increase anti-CD3 or ionomycin induced IL-4 mRNA in differentiated murine Th2 cells. Anti-CD3 or ionomycin also enhances IL-4 induction of STAT6 activation, assayed by gel shift analysis of nuclear lysates. Surprisingly, cyclosporin A (CsA) also enhances STAT6 induction. Both ionomycin and CsA also enhance IL-4-induced transcriptional activity of a STAT6-linked promoter-reporter construct. In vitro calcineurin activity reduces STAT6 interactions with DNA, and CsA or FK506 can block this effect of calcineurin. These results indicate that IL-4 and TCR-generated calcium signals interact to maximize IL-4 gene expression and STAT6 activity. Calcineurin-mediated serine dephosphorylation of STAT6 and STAT6 serine phosphorylation may counter-regulate transcriptional activity of STAT6.

Pharmacological evaluation of aerosolized cannabinoids in mice

The reemergence on the debate of the use of marijuana for medicinal purposes has been the impetus for developing an acceptable delivery form of aerosolized cannabinoids. The goals of the present study were to: (1) develop and characterize the physical properties of an aerosolized form of Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the major psychoactive constituent present in marijuana; and (2) assess the pharmacological effects of cannabinoid inhalation in mice. A Small Particle Aerosol Generator (SPAG) nebulizer, used to generate the aerosol, had an output of approximately 0.154 mg/l of aerosolized Delta(9)-THC with a 2.0 microm mass median aerodynamic diameter and a 2.2 geometric standard deviation (GSD). Virtually all the particles were less than 5.0 microm in diameter suggesting that they were sufficiently small to penetrate deeply into the lungs. Inhalation exposure to aerosolized Delta(9)-THC in mice elicited antinociceptive effects that were dependent on concentration and exposure time with an estimated Delta(9)-THC dose of 1.8 mg/kg. On the other hand, inhalation exposure to Delta(9)-THC failed to produce two other indices indicative of cannabinoid activity, hypothermia and decreases in spontaneous locomotor activity. The antinociceptive effects occurred within 5 min of exposure and lasted approximately 40 min in duration. The cannabinoid receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide HCl (SR 141716A), but not naloxone, blocked these antinociceptive effects (AD(50)=0.09 mg/kg) indicating a cannabinoid receptor mechanism of action. Similarly, inhalation exposure to a water soluble cannabinoid analog, 3-(5'-cyano-1', 1'dimethylheptyl)-1-(4-N-morpholinobutyrloxy)-Delta(8)-te trahydrocann abinol (O-1057), produced antinociception that was blocked by SR 141716A. These results demonstrate that the development of an aerosolized form of cannabinoids for human medicinal use is feasible.

Alpha4beta1-integrin activation is necessary for high-efficiency T-cell subset interactions with VCAM-1 under flow

OBJECTIVE

The purpose of this study was to examine the relationship between alpha4beta1-integrin state of activation on CD4+ T-cell subsets and their adhesive interaction to VCAM-1 under flow.

METHODS

Human CD4+ memory and naive T-cells were freshly isolated and effector-helper T-cell subsets. Th1 and Th2 cells, were differentiated in vitro from CD4+ naive T-cells. The expression of activation/ligand induced epitopes on beta1-integrins of each T-cell subset was assessed using mAb HUTS21 and mAb 15/7. T-cell subsets attachment and rolling on VCAM-1 was determined under defined flow conditions and the rates of attachment (ka), accumulation, and instantaneous rolling velocities were correlated to their beta1-integrin activation epitope expression.

RESULTS

A subset of memory T-cells constitutively express activation/ligand induced epitopes on beta1-integrins recognized by mAb HUTS21 and 15/7, whereas expression levels on naive T-cells is low or not detectable. Consistent with an activated phenotype, memory T-cells exhibit significantly higher rates of attachment and accumulation on VCAM-1 under flow as compared to naive T-cells. Interestingly, the expression of activation/ligand induced epitopes on beta1-integrins on Th2 cells and the ability of these cells to interact with VCAM-1 are comparable to memory T-cells. In contrast, Th1 cells did not interact as efficiently with VCAM-1, which correlated with lower expression of activation/ligand induced epitopes on these cells. VCAM-1 interactions are inhibited completely by pretreatment of the T-cells with blocking mAb to alpha4-integrins or beta1-integrins, indicating that alpha4beta1 is the predominant T-cell integrin involved.

CONCLUSIONS

Memory T-cells express constitutively active alpha4beta1-integrins, as compared to naive T-cells, which mediate high rates of initial attachment and sustained high-affinity adhesive interactions with VCAM-1 under flow conditions in vitro. Similarly, in vitro differentiated Th2 cells but not Th1 cells, which also express elevated levels of activated alpha4beta1-integrins, are capable of sustaining high-affinity adhesive interactions with VCAM-1. The differences observed in beta1-integrin activation on T-cell subsets may underlie selective recruitment patterns of T-cell subsets in vivo.

Cutting edge: heat shock protein (HSP) 60 activates the innate immune response: CD14 is an essential receptor for HSP60 activation of mononuclear cells

Heat shock proteins (HSP), highly conserved across species, are generally viewed as intracellular proteins thought to serve protective functions against infection and cellular stress. Recently, we have reported the surprising finding that human and chlamydial HSP60, both present in human atheroma, can activate vascular cells and macrophages. However, the transmembrane signaling pathways by which extracellular HSP60 may activate cells remains unclear. CD14, the monocyte receptor for LPS, binds numerous microbial products and can mediate activation of monocytes/macrophages and endothelial cells, thus promoting the innate immune response. We show here that human HSP60 activates human PBMC and monocyte-derived macrophages through CD14 signaling and p38 mitogen-activated protein kinase, sharing this pathway with bacterial LPS. These findings provide further insight into the molecular mechanisms by which extracellular HSP may participate in atherosclerosis and other inflammatory disorders by activating the innate immune system.

Hyperlipidemia and atherosclerotic lesion development in LDL receptor-deficient mice fed defined semipurified diets with and without cholate

Past studies of atherosclerosis in mice have used chow-based diets supplemented with cholesterol, lipid, and sodium cholate to overcome species resistance to lesion formation. Similar diets have been routinely used in studies with LDL receptor-deficient (LDLR(-/-)) mice. The nonphysiological nature and potential toxicity of cholate-containing diets have led to speculation that atherogenesis in these mice may not accurately reflect the human disease process. We have designed a semipurified AIN-76A-based diet that can be fed in powdered, pelleted, or liquid form and manipulated for the precise evaluation of diet-genetic interactions in murine atherosclerosis. LDLR(-/-) mice were randomly assigned among 4 diets (n=6/diet) as follows: 1, control, 10% kcal lipid; 2, high fat (40% kcal), moderate cholesterol (0.5% by weight); 3, high fat, high cholesterol (1.25% by weight); and 4, high fat, high cholesterol, and 0.5% (wt/wt) sodium cholate. Fasting serum cholesterol was increased in all cholesterol-supplemented mice compared with controls after 6 or 12 weeks of feeding (P<0.01). The total area of oil red O-stained atherosclerotic lesions was determined from digitally scanned photographs. In contrast to the control group, all mice in cholesterol-supplemented dietary groups 2 to 4 had lesions involving 7.01% to 12.79% area of the thoracic and abdominal aorta at 12 weeks (P<0.002, for each group versus control). The distribution pattern of atherosclerotic lesions was highly reproducible and comparable. The histological features of lesions in mice fed cholate-free or cholate-containing diets were similar. This study shows that sodium cholate is not necessary for the formation of atherosclerosis in LDLR(-/-) mice and that precisely defined semipurified diets are a valuable tool for the examination of diet-gene interactions.

Leukocyte adhesion molecules in atherogenesis

Functions of mononuclear leukocytes and endothelial cell leukocyte adhesion molecules in the formation of early atherosclerotic lesions is discussed. The main transgenic mouse models developed to study cholesterol metabolism and atherosclerotic lesion formation, including apolipoprotein E knockout and low density lipoprotein receptor knockout (LDLR-/-) mice, are reviewed. Differences in their dependence on dietary cholesterol supplementation is emphasized and a new semi-purified, cholate-free mouse diet for LDLR-/- mice is described. This diet is highly reproducible, versatile (pellet, powder or liquid formulations), inexpensive and promotes hypercholesterolemia and atherosclerotic lesion development despite absence of sodium cholate. We describe the expression patterns of leukocyte adhesion molecules in rabbit and mouse models of atherosclerosis and compare them to humans. Finally, ongoing studies are summarized which utilize transgenic mice to assess the roles of individual adhesion molecules in atherosclerotic lesion formation.

Acquisition of selectin binding and peripheral homing properties by CD4(+) and CD8(+) T cells

Different T cell subsets exhibit distinct capacities to migrate into peripheral sites of inflammation, and this may in part reflect differential expression of homing receptors and chemokine receptors. Using an adoptive transfer approach, we examined the ability of functionally distinct subsets of T cells to home to a peripheral inflammatory site. The data directly demonstrate the inability of naive T cells and the ability of effector cells to home to inflamed peritoneum. Furthermore, interleukin (IL)-12 directs the differentiation of either CD4(+) or CD8(+) T cells into effector populations that expresses functional E- and P-selectin ligand and that are preferentially recruited into the inflamed peritoneum compared with T cells differentiated in the presence of IL-4. Recruitment can be blocked by anti-E- and -P-selectin antibodies. The presence of antigen in the peritoneum promotes local proliferation of recruited T cells, and significantly amplifies the Th1 polarization of the lymphocytic infiltrate. Preferential recruitment of Th1 cells into the peritoneum is also seen when cytokine response gene 2 (CRG-2)/interferon gamma-inducible protein 10 (IP-10) is used as the sole inflammatory stimulus. We have also found that P-selectin binds only to antigen-specific T cells in draining lymph nodes after immunization, implying that both antigen- and cytokine-mediated signals are required for expression of functional selectin-ligand.

Costimulation reverses the defect in IL-2 but not effector cytokine production by T cells with impaired IkappaBalpha degradation

Although the transcriptional basis for states of unresponsiveness in primary T cells is unclear, tolerant B lymphocytes exhibit inhibition of both c-Jun N-terminal kinase induction and IkappaBalpha (inhibitor of NF-kappaBalpha) degradation, leading to lower levels of both nuclear AP-1 and NF-kappaB. Expression of an IkappaBalpha mutant resistant to signal-induced degradation in transgenic T cells caused markedly deficient effector cytokine (IL-4, IFN-gamma) production after primary TCR stimulation despite a detectable level of nuclear NF-kappaB. A TCR response element from the IFN-gamma promoter, despite lacking detectable NF-kappaB/Rel sites, was also unresponsive to TCR ligation. Nuclear induction of AP-1 proteins in response to T cell activation was diminished in transgenic T cells. Costimulation induced by anti-CD28 mAb increased IL-2 production, but failed to reverse the defects in effector cytokine production. Taken together, these data indicate that impaired NF-kappaB/Rel signaling in T cells interferes with the signal transduction pathways required for efficient induction of effector cytokine production.

Expression of functional selectin ligands on Th cells is differentially regulated by IL-12 and IL-4

Immune responses may be qualitatively distinct depending on whether Th1 or Th2 cells predominate at the site of Ag exposure. T cell subset-specific expression of ligands for vascular selectins may underlie the distinct patterns of recruitment of Th1 or Th2 cells to peripheral inflammatory sites. Here we examine the regulation of selectin ligand expression during murine T helper cell differentiation. Large numbers of Th1 cells interacted with E- and P-selectin under defined flow conditions, while few Th2 and no naive T cells interacted. Th1 cells also expressed more fucosyltransferase VII mRNA than naive or Th2 cells. IL-12 induced expression of P-selectin ligands on Ag-activated naive T cells, even in the presence of IL-4, and on established Th2 cells restimulated in the presence of IL-12 and IFN-gamma. In contrast, Ag stimulation alone induced only E-selectin ligand. Interestingly, restimulation of established Th2 cells in the presence of IL-12 and IFN-gamma induced expression of P-selectin ligands but not E-selectin ligands; IFN-gamma alone did not enhance expression of either selectin ligand. In summary, functional P- and E-selectin ligands are expressed on most Th1 cells, few Th2 cells, but not naive T cells. Furthermore, selectin ligand expression is regulated by the cytokine milieu during T cell differentiation. IL-12 induces P-selectin ligand, while IL-4 plays a dominant role in down-regulating E-selectin ligand.

Chlamydial and human heat shock protein 60s activate human vascular endothelium, smooth muscle cells, and macrophages

Both chlamydial and human heat shock protein 60s (HSP 60), which colocalize in human atheroma, may contribute to inflammation during atherogenesis. We tested the hypothesis that chlamydial or human HSP 60 activates human endothelial cells (ECs), smooth muscle cells (SMCs), and monocyte-derived macrophages. We examined the expression of adhesion molecules such as endothelial-leukocyte adhesion molecule-1 (E-selectin), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1), and the production of the proinflammatory cytokine interleukin-6 (IL-6). We also tested whether either HSP 60 induces nuclear factor-kappaB (NF-kappaB), which contributes to the gene expression of these molecules. Either chlamydial or human HSP 60 induced E-selectin, ICAM-1, and VCAM-1 expression on ECs similar to levels induced by Escherichia coli lipopolysaccharide (LPS). Each HSP 60 also significantly induced IL-6 production by ECs, SMCs, and macrophages to an extent similar to that induced by E. coli LPS, as assessed by enzyme-linked immunosorbent assay (ELISA). In ECs, either HSP 60 triggered activation of NF-kappaB complexes containing p65 and p50 Rel proteins. Heat treatment abolished all these effects, but did not alter the ability of E. coli LPS to induce these functions. Chlamydial and human HSP 60s therefore activate human vascular cell functions relevant to atherogenesis and lesional complications. These findings help to elucidate the mechanisms by which a chronic asymptomatic chlamydial infection might contribute to the pathophysiology of atheroma.

Pharmacological effects of methamphetamine and other stimulants via inhalation exposure

The effects of methamphetamine-HCl, methcathinone-HCl, cocaine and ephedrine on locomotor stimulation were compared between inhalation exposure and i.v. injection in mice. Methamphetamine-HCl was readily volatilized upon heating at 300 degrees C in a glass pipe with only trace amounts of amphetamine being produced. The ED50 dose (9.4 and 6.5 mumol/kg for inhalation exposure and i.v. injections, respectively) and biodisposition of methamphetamine-HCl were similar for both routes of administration. Methcathinone-HCl and cocaine were readily volatilized. Their dose response profiles also appeared similar for both routes of administration. Ephedrine did not appear to be easily volatilized and was only effective in stimulating locomotor activity after i.v. administration. These findings indicate that inhalation exposure to methamphetamine-HCl, cocaine and methcathinone possess similar pharmacological characteristics as the i.v. route of administration. In particular, this model may have implications in predicting the pharmacological activity of various stimulants via the inhalation route of administration.

IL-4 enhances IL-10 gene expression in murine Th2 cells in the absence of TCR engagement

Both IL-4 and IL-10 are regulatory cytokines produced by Th2 cells that can down-regulate cell-mediated immune responses. The studies reported here examine the influence of various cytokines in the regulation of T cell IL-10 production. The results indicate that IL-10 gene expression by TCR transgenic Th2 cells is significantly up-regulated by IL-4 in the absence of TCR signals. IL-4 enhances both IL-10 mRNA levels and secreted protein, and this effect is not related to enhanced mRNA stability. TCR-mediated IL-10 gene expression is inhibited by cyclosporin A, but IL-4-mediated IL-10 expression is not. IL-4 also enhances IL-13 mRNA levels, to a lesser extent than IL-10, but does not significantly effect the expression of other cytokine mRNAs. Furthermore, IL-4 does not significantly enhance IL-10 expression in Th1 cells. IL-2 also enhances effector cytokine production in the absence of TCR signals, but in a subset nonspecific manner, increasing both Th2 IL-4 mRNA and Th1 IFN-gamma mRNA. These data suggest that Th2 IL-4 production may contribute to the down-regulation of immune responses by directly enhancing Th2 IL-10 production. In addition, the data clearly demonstrate that exogenous cytokines can significantly influence effector cytokine production by effector T cells without the requirement for TCR signals.

IL-4 Enhances IL-10 Gene Expression in Murine Th2 Cells in the Absence of TCR Engagement

Both IL-4 and IL-10 are regulatory cytokines produced by Th2 cells that can down-regulate cell-mediated immune responses. The studies reported here examine the influence of various cytokines in the regulation of T cell IL-10 production. The results indicate that IL-10 gene expression by TCR transgenic Th2 cells is significantly up-regulated by IL-4 in the absence of TCR signals. IL-4 enhances both IL-10 mRNA levels and secreted protein, and this effect is not related to enhanced mRNA stability. TCR-mediated IL-10 gene expression is inhibited by cyclosporin A, but IL-4-mediated IL-10 expression is not. IL-4 also enhances IL-13 mRNA levels, to a lesser extent than IL-10, but does not significantly effect the expression of other cytokine mRNAs. Furthermore, IL-4 does not significantly enhance IL-10 expression in Th1 cells. IL-2 also enhances effector cytokine production in the absence of TCR signals, but in a subset nonspecific manner, increasing both Th2 IL-4 mRNA and Th1 IFN-γ mRNA. These data suggest that Th2 IL-4 production may contribute to the down-regulation of immune responses by directly enhancing Th2 IL-10 production. In addition, the data clearly demonstrate that exogenous cytokines can significantly influence effector cytokine production by effector T cells without the requirement for TCR signals.

Cannabinoid transmission and pain perception

The use of cannabis for the management of a wide range of painful disorders has been well documented in case reports throughout history. However, clinical evaluations of cannabis and its psychoactive constituent THC have not led to a consensus regarding their analgesic effectiveness. On the other hand, THC and its synthetic derivatives have been shown to be effective in most animal models of pain. These antinociceptive effects are mediated through cannabinoid receptors in the brain that in turn appear to interact with noradrenergic and kappa opioid systems in the spinal cord to modulate the perception of painful stimuli. The endogenous ligand, anandamide, is also an effective antinociceptive agent. The extent to which the endogenous cannabinoid system is involved in the modulation of pain is currently unknown.

Endothelial antigen presentation: stimulation of previously activated but not naïve TCR-transgenic mouse T cells

In vitro experiments have shown that endothelial cells can function as antigen-presenting cells to CD4(+) T lymphocytes. The studies presented here address the question of whether naïve versus previously activated CD4(+) helper T cells differ in their responses to endothelial antigen presentation. TCR-transgenic mice were used as a source of naive T cells of defined antigen specificity. These cells were stimulated in vitro with antigen and splenic antigen-presenting cells to generate populations of T lymphocytes with a previously activated/memory phenotype. Two different types of mouse endothelial cells were used as antigen-presenting cells, including the SVEC4-10 line derived from lymph node endothelium and primary murine pulmonary microvascular endothelium. Monolayer cultures of both types of endothelium were capable of antigen-dependent stimulation of previously activated TCR-transgenic CD4(+) cells. In contrast, neither endothelial type could activate naïve CD4(+) T cells. When costimulatory signals were provided in trans by the addition of MHC-mismatched mouse spleen cells, activation of naïve T cells by endothelial antigen presentation could be demonstrated. The expression of ICAM-1 or VCAM-1 on the endothelial cells was not sufficient to activate naïve T cells. Furthermore, the mouse lung endothelium constitutively expresses B7-1, and therefore, the inability of endothelium to stimulate naïve T cells could not be attributed to a lack of CD28-ligands. These studies suggest that the potential role of endothelial antigen presentation in immune responses is restricted to promoting responses by T cells which have previously encountered antigen presented by other antigen-presenting cells.

Interactions between T lymphocytes and endothelial cells in allograft rejection

Vascular endothelial cells participate in the process of allograft rejection by promoting both the recruitment and the activation of alloreactive T cells. There have been three major recent advances in the field of interactions between T cells and endothelial cells that are of direct relevance to the process of cell-mediated responses to allografts: first, endothelial cells mediate selective recruitment of CD4+ T cell subsets, including naive and memory T cells and T cell subsets of the Th1 and Th2 phenotypes; second, endothelial cells co-stimulate the production of effector cytokines by helper T cells; and third, endothelial cells regulate T cell apoptosis.

Effects of SR 141716A after acute or chronic cannabinoid administration in dogs

The effects of N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-met hyl-1H-pyrazole-3-carboxamide HCl (SR 141716A), a specific cannabinoid receptor antagonist, were assessed in the dog static ataxia test after either acute treatment with two cannabinoid receptor agonists, delta9-tetrahydrocannabinol and arachidonylethanolamide (anandamide), or chronic treatment with delta9-tetrahydrocannabinol. As previously reported, acute intravenous (i.v.) injected delta9-tetrahydrocannabinol produced dose-dependent cannabinoid effects, including marked static ataxia, prancing, loss of muscle tone, and incoordination. The behavioral profile of anandamide was distinctly different in that it produced a loss of muscle tone and considerable sedation with little static ataxia, prancing, or incoordination. Despite these qualitative differences between the two agonists, SR 141716A blocked the acute behavioral effects of both drugs indicating a cannabinoid receptor mechanism of action. Interestingly, SR 141716A was able to precipitate a withdrawal syndrome in delta9-tetrahydrocannabinol-tolerant dogs, but failed to produce any observable effects in dogs receiving chronic vehicle injections. Acute toxicity caused by anandamide, which was not blocked by SR 141716A, precluded conducting dependence studies with this drug. The delta9-tetrahydrocannabinol precipitated withdrawal syndrome included diarrhea, vomiting, excessive salivation, decreases in social behavior, and increases in restless behavior and trembling. This is the first demonstration of a precipitated withdrawal syndrome in a non-rodent species.

The up-and-down method substantially reduces the number of animals required to determine antinociceptive ED50 values

As a consequence of an awareness of animal welfare concerns, one of the goals in biomedical research is to reduce, whenever possible, the number of laboratory animals used for experimentation. The up-and-down method is a procedure that has been confirmed to reduce the number of animals needed to determine LD50 values without compromising reliability. The purpose of the present study was to evaluate whether the up-and-down method could be applied to reduce the number of animals required to obtain the ED50 values of various antinociceptive agents. The ED50 values of morphine, heroin, fentanyl, codeine, meperidine, delta9-THC, CP 55,940, nicotine, and epibatidine for mice in the tail-flick test did not differ between the up-and-down method and a traditional dose-response procedure. Whereas a mean of 28 mice/drug were used in the dose-response procedure, only eight mice/drug were used in the up-and-down method. Moreover, the ED50 values calculated by both methods were highly correlated with each other (r = 0.99). Similarly, intracerebroventricular administration of either delta9-THC or CP 55,940 to rats resulted in nearly identical ED50 values for both methods. These results support the use of the up-and-down method as an effective procedure to reduce substantially the number of animals needed to determine ED50 values of a variety of antinociceptive drugs.

Chlamydial heat shock protein 60 localizes in human atheroma and regulates macrophage tumor necrosis factor-alpha and matrix metalloproteinase expression

BACKGROUND

Recent evidence has implicated Chlamydia pneumoniae in the aggravation of atherosclerosis. However, the mechanisms by which this agent affects atherogenesis remain poorly understood. Chlamydiae produce large amounts of heat shock protein 60 (HSP 60) during chronic, persistent infections, and C pneumoniae localizes predominantly within plaque macrophages. Several studies have furnished evidence that endogenous (human) HSP 60 may play a role in atherogenesis. We tested here the hypothesis that atheroma contains chlamydial HSP 60 and that this bacterial product might stimulate macrophage functions considered relevant to atherosclerosis and its complications, such as production of proinflammatory cytokines as tissue necrosis factor-alpha (TNF-alpha) and matrix-degrading metalloproteinases (MMPs).

METHODS AND RESULTS

Surgical specimens of human carotid atherosclerotic arteries (n = 19) and normal arterial wall samples (n=7, 2 carotid arteries and 5 aortas) were tested immunohistochemically for the presence of chlamydial HSP 60 and human HSP 60. Macrophage localization of these antigens was assessed by double immunostaining. Murine peritoneal macrophages, maintained in serum-free conditions for 48 hours after harvesting, were incubated with C pneumoniae, chlamydial HSP 60, human HSP 60, or Escherichia coli lipopolysaccharide (LPS). Culture supernatants, collected at 24 hours for concentration-dependence experiments and at up to 72 hours for time-dependence experiments, were analyzed for TNF-alpha by ELISA and for MMP by gelatin zymography. Atherosclerotic lesions showed immunoreactive chlamydial HSP 60 in 47% (9 of 19) of the cases and human HSP 60 in 89% (17 of 19) of the cases. Chlamydial HSP 60 colocalized with human HSP 60 within plaque macrophages in 77% (7 of 9) of the cases. Nonatherosclerotic samples contained neither HSP. Both C pneumoniae and recombinant chlamydial HSP 60 induced TNF-alpha production by mouse macrophages in a concentration- and time-dependent fashion. E coli LPS and human HSP 60 produced similar effects. Similarly, C pneumoniae and HSPs induced MMPs in a concentration- and time-dependent manner. Heat treatment abolished the effect of C pneumoniae and HSPs on both TNF-alpha and MMP production, but it did not alter the ability of E coli LPS to induce these functions.

CONCLUSIONS

Chlamydial HSP 60 frequently colocalizes with human HSP 60 in plaque macrophages in human atherosclerotic lesions. Chlamydial and human HSP 60 induce TNF-alpha and MMP production by macrophages. Chlamydial HSP 60 might mediate the induction of these effects by C pneumoniae. Induction of such macrophage functions provides potential mechanisms by which chlamydial infections may promote atherogenesis and precipitate acute ischemic events.

Down-regulation of IL-4 gene transcription and control of Th2 cell differentiation by a mechanism involving NFAT1

Transcription factors of the NFAT family play a critical role in the immune response by activating the expression of cytokines and other inducible genes in antigen-stimulated cells. Here we show that a member of this family, NFAT1, is involved in down-regulating the late phase of IL-4 gene transcription, thus inhibiting T helper 2 responses. Whereas stimulated T cells from wild-type mice show a transient increase and then a rapid decline in the steady-state levels of IL-4 mRNA in vitro, the levels of IL-4 gene transcripts in NFAT1-deficient T cells are maintained at high levels under the same conditions. Consistent with this observation, NFAT1-/- mice are more susceptible to infection with Leishmania major. This report provides evidence that NFAT proteins regulate not only the initiation but also the termination of gene transcription.

Human endothelial cell costimulation of T cell IFN-gamma production

In this report, we show that human endothelial cells (EC) provide costimulatory signals to mitogen-activated CD4+ T cells to augment IFN-gamma production. We also show that EC can enhance responsiveness of the T cells to IL-12. While IL-12 has no effect on IFN-gamma production by cultured CD4+ T cells in the absence of EC, addition of IL-12 to T cell-EC cocultures augments IFN-gamma production by as much as fivefold. Separation of T cells from EC by a semipermeable membrane inhibits the effect of EC and IL-12 on IFN-gamma production. Anti-LFA-3 Abs, in the absence or presence of IL-12, inhibit EC costimulation of IFN-gamma production by up to 50%, while Abs to intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), LFA-1, and very late antigen-4 (VLA-4) have relatively little effect. Pretreatment of T cells with conditioned medium from T cell-EC cocultures, or with IL-2 or IL-1 alpha similarly primes CD4+ T cells for the costimulatory effect of IL-12 on IFN-gamma production. EC costimulation of IFN-gamma production is inhibited by cyclosporine. However, in the presence of IL-12 there is a marked resistance to this inhibitory effect, suggesting that the IL-12-induced costimulatory pathway is distinct from the costimulatory pathway activated by endothelium alone. Our data are consistent with the hypothesis that, as a consequence of interactions with endothelium, T cells that migrate into an inflammatory site are primed to have enhanced responses to Ag and cytokine(s), such as IL-12, that influence T cell-cytokine production.