Antiproliferative mechanism of a cannabinoid agonist by cell cycle arrest in human gastric cancer cells

For gastric cancers, the antineoplastic activity of cannabinoids has been investigated in only a few reports and knowledge regarding the mechanisms involved is limited. We have reported previously that treatment of gastric cancer cells with a cannabinoid agonist significantly decreased cell proliferation and induced apoptosis. Here, we evaluated the effects of cannabinoids on various cellular mediators involved in cell cycle arrest in gastric cancer cells. AGS and MKN-1 cell lines were used as human gastric cancer cells and WIN 55,212-2 as a cannabinoid agonist. Cell cycles were analyzed by flow cytometry and western blotting. Treatment with WIN 55,212-2 arrested the cell cycle in the G0/G1 phase. WIN 55,212-2 also upregulated phospho-ERK1/2, induced Kip1/p27 and Cip1/WAF1/p21 expression, decreased cyclin D1 and cyclin E expression, decreased Cdk 2, Cdk 4, and Cdk 6 expression levels, and decreased phospho-Rb and E2F-1 expression. ERK inhibitor decreased the proportion of G0/G1 phase which was induced by WIN 55,212-2. Inhibition of pAKT led to cell cycle arrest in gastric cancer cells. Cell cycle arrest preceded apoptotic response. Thus, this cannabinoid agonist can reduce gastric cancer cell proliferation via G1 phase cell cycle arrest, which is mediated via activation of the MAPK pathway and inhibition of pAKT.     

Role of receptor internalization in the agonist-induced desensitization of cannabinoid type 1 receptors

Agonist-induced internalization of G protein-coupled receptors (GPCRs) is an important mechanism for regulating signaling transduction of functional receptors at the plasma membrane. We demonstrate here that both caveolae/lipid-rafts- and clathrin-coated-pits-mediated pathways were involved in agonist-induced endocytosis of the cannabinoid type 1 receptor (CB1R) in stably transfected human embryonic kidney (HEK) 293 cells and that the internalized receptors were predominantly sorted into recycling pathway for reactivation. The treatment of CB1 receptors with the low endocytotic agonist Δ⁹-THC induced a faster receptor desensitization and slower resensitization than the high endocytotic agonist WIN 55,212-2. In addition, the blockade of receptor endocytosis or recycling pathway markedly enhanced agonist-induced CB1 receptor desensitization. Furthermore, co-expression of phospholipase D2, an enhancer of receptor endocytosis, reduced CB1 receptor desensitization, whereas co-expression of a phospholipase D2 negative mutant significantly increased the desensitization after WIN 55,212-2 treatment. These findings provide evidences for the importance of receptor endocytosis in counteracting CB1 receptor desensitization by facilitating receptor reactivation. Moreover, in primary cultured neurons, the low endocytotic agonist Δ⁹-THC or anandamide exhibited a greater desensitization of endogenous CB1 receptors than the high endocytotic agonist WIN 55,212-2, CP 55940 or 2-arachidonoyl glycerol, indicating that cannabinoids with high endocytotic efficacy might cause reduced development of cannabinoid tolerance to some kind cannabinoid-mediated effects.     

Modulation of cannabinoid agonist binding by 5-HT in the rat cerebellum

Cross-talk between cannabinoid CB1 and serotonin 5-HT receptors in rat cerebellar membranes was investigated using radioligand binding. In competition against the CB1 antagonist, [3 H]SR141716A, the agonist, WIN 55,212-2 yielded a biphasic isotherm. The majority of binding was to a high-affinity state that was significantly reduced by the GTP analogue, Gpp(NH)p. Interestingly, 5-HT enhanced the high-affinity binding constant of WIN 55,212-2 while attenuating the proportion of high-affinity binding. 5-HT also significantly reduced the proportion of high-affinity binding of the cannabinoid agonist, HU 210, but had no effect on the agonist, CP 55,940. The effect of 5-HT on WIN 55,212-2 binding was inhibited by the 5-HT2 receptor antagonist ritanserin as well as Gpp(NH)p, suggesting a dependence on the 5-HT2 receptor and on G protein-receptor interactions, respectively. Subsequent [3 H]WIN 55,212-2 dissociation kinetic experiments revealed that 5-HT promoted a slower-dissociating species of radiolabelled agonist-receptor complex. Our findings support a membrane-delimited cross-talk between two G protein-coupled receptors that are co-localized in certain cells of the central nervous system. Intriguingly, the cannabinoid agonist dependence of the 5-HT modulatory effect suggests that agonist-specific conformations of the CB1 receptor may also be important in determining the extent of this cross-talk.     

Cannabinoids Inhibit Acid-Sensing Ion Channel Currents in Rat Dorsal Root Ganglion Neurons

Local acidosis has been found in various pain-generating conditions such as inflammation and tissue injury. Cannabinoids exert a powerful inhibitory control over pain initiation via peripheral cognate receptors. However, the peripheral molecular targets responsible for the antinociceptive effects of cannabinoids are still poorly understood. Here, we have found that WIN55,212-2, a cannabinoid receptor agonist, inhibits the activity of native acid-sensing ion channels (ASICs) in rat dorsal root ganglion (DRG) neurons. WIN55,212-2 dose-dependently inhibited proton-gated currents mediated by ASICs. WIN55,212-2 shifted the proton concentration–response curve downwards, with an decrease of 48.6±3.7% in the maximum current response but with no significant change in the EC₅₀ value. The inhibition of proton-gated current induced by WIN55,212-2 was almost completely blocked by the selective CB1 receptor antagonist AM 281, but not by the CB2 receptor antagonist AM630. Pretreatment of forskolin, an AC activator, and the addition of cAMP also reversed the inhibition of WIN55,212-2. Moreover, WIN55,212-2 altered acid-evoked excitability of rat DRG neurons and decreased the number of action potentials induced by acid stimuli. Finally, WIN55,212-2 attenuated nociceptive responses to injection of acetic acid in rats. These results suggest that WIN55,212-2 inhibits the activity of ASICs via CB1 receptor and cAMP dependent pathway in rat primary sensory neurons. Thus, cannabinoids can exert their analgesic action by interaction with ASICs in the primary afferent neurons, which was novel analgesic mechanism of cannabinoids.     

Potentiated Interaction between Ineffective Doses of Budesonide and Formoterol to Control the Inhaled Cadmium-Induced Up-Regulation of Metalloproteinases and Acute Pulmonary Inflammation in Rats

The anti-inflammatory properties of glucocorticoids are well known but their protective effects exerted with a low potency against heavy metals-induced pulmonary inflammation remain unclear. In this study, a model of acute pulmonary inflammation induced by a single inhalation of cadmium in male Sprague-Dawley rats was used to investigate whether formoterol can improve the anti-inflammatory effects of budesonide. The cadmium-related inflammatory responses, including matrix metalloproteinase-9 (MMP-9) activity, were evaluated. Compared to the values obtained in rats exposed to cadmium, pretreatment of inhaled budesonide (0.5 mg/15 ml) elicited a significant decrease in total cell and neutrophil counts in bronchoalveolar lavage fluid (BALF) associated with a significant reduction of MMP-9 activity which was highly correlated with the number of inflammatory cells in BALF. Additionally, cadmium-induced lung injuries characterized by inflammatory cell infiltration within alveoli and the interstitium were attenuated by the pre-treatment of budesonide. Though the low concentration of budesonide (0.25 mg/15 ml) exerted a very limited inhibitory effects in the present rat model, its combination with an inefficient concentration of formoterol (0.5 mg/30 ml) showed an enhanced inhibitory effect on neutrophil and total cell counts as well as on the histological lung injuries associated with a potentiation of inhibition on the MMP-9 activity. In conclusion, high concentration of budesonide alone could partially protect the lungs against cadmium exposure induced-acute neutrophilic pulmonary inflammation via the inhibition of MMP-9 activity. The combination with formoterol could enhance the protective effects of both drugs, suggesting a new therapeutic strategy for the treatment of heavy metals-induced lung diseases.     

Parecoxib and its metabolite valdecoxib directly interact with cannabinoid binding sites in CB1-expressing HEK 293 cells and rat brain tissue

Cyclooxygenase 2 inhibitors (COX 2) such as parecoxib (par) and valdecoxib (val) are used in the treatment of neuropathic pain. Using the radioligand binding assay it was demonstrated that both the prodrug par as well as its active metabolite val have a specific affinity to the cannabinoid (CB) receptor measured in CB1-expressing HEK 293 cells and rat brain tissue. Agonist activity was detected by GTPγS assays, cAMP formation experiments and ex vivo modulation of glutamate and GABA release of the rat brain tissue. In comparison to the specific cannabinoid agonist, WIN 55,212-2, the two COX 2 inhibitors are about 2 orders of magnitude less potent. The data suggest that the analgesic effects of par and its metabolite val in Wistar rats may be at least partially mediated by a direct interaction with the CB1 receptors. The COX 2 inhibitors appear to be a hypothetically useful tool for add-on therapy of neuropathic pain.     

Cannabinoid receptor stimulation of guanosine-5′-O-(3-[35S]thio)triphosphate binding in rat brain membranes

Cannabinoid receptors belong to the class of G-protein-coupled receptors which inhibit adenylyl cyclase. Coupling of receptors to G-proteins can be assessed by the ability of agonists to stimulate guanosine-5′-O-(3-[³⁵S]thio)triphosphate ([³⁵S]GTPγS) binding in the presence of excess GDP. The present study examined the effect of cannabinoid agonists on [³⁵S]GTPγS binding in rat brain membranes. Assays were conducted with 0.05 nM [³⁵S]GTPγS, incubated with rat cerebellar membranes, 1–30 μM GDP and the cannabinoid agonist WIN 55212-2. Results showed that the ability of WIN 55212-2 to stimulate [³⁵S]GTPγS binding increased with increasing concentrations of GDP, with 10–30 μM GDP providing approximately 150–200% stimulation by the cannabinoid agonist. The pharmacology of cannabinoid agonist stimulation of [³⁵S]GTPγS binding paralleled that of previously reported receptor binding and adenylyl cyclase assays, and agonist stimulation of [³⁵S]GTPγS binding was blocked by the cannabinoid antagonist SR141716A. Brain regional studies revealed widespread stimulation of [³⁵S]GTPγS binding by WIN 55212-2 in a number of brain areas, consistent with in vitro [³⁵S]GTPγS autoradiography. These results demonstrate that [³⁵S]GTPγS binding in the presence of excess GDP is an effective measure of cannabinoid receptor coupling to G-proteins in brain membranes.     

Inhibition of autophagy and enhancement of endoplasmic reticulum stress increase sensitivity of osteosarcoma Saos‐2 cells to cannabinoid receptor agonist WIN55,212‐2

WIN55,212‐2, a cannabinoid receptor agonist, can activate cannabinoid receptors, which has proven anti‐tumour effects in several tumour types. Studies showed that WIN can inhibit tumour cell proliferation and induce apoptosis in diverse cancers. However, the role and mechanism of WIN in osteosarcoma are still unclear. In this study, we examined the effect of WIN55,212‐2 on osteosarcoma cell line Saos‐2 in terms of cell viability and apoptosis. Meanwhile, we further explored the role of endoplasmic reticulum stress and autophagy in apoptosis induced by WIN55,212‐2. Our results showed that the cell proliferation of Saos‐2 was inhibited by WIN55,212‐2 in a dose‐dependent and time‐dependent manner. WIN55,212‐2‐induced Saos‐2 apoptosis through mitochondrial apoptosis pathway. Meanwhile, WIN55,212‐2 can induce endoplasmic reticulum stress and autophagy in Saos‐2 cells. Inhibition of autophagy and enhancement of endoplasmic reticulum stress increased apoptosis induced by WIN55,212‐2 in Saos‐2 cells. These findings indicated that WIN55,212‐2 in combination with autophagic inhibitor or endoplasmic reticulum stress activator may shed new light on osteosarcoma treatment. Copyright © 2016 John Wiley & Sons, Ltd.     

Analogues and homologues of N-palmitoylethanolamide, a putative endogenous CB(2) cannabinoid, as potential ligands for the cannabinoid receptors.

The presence of CB(2) receptors was reported in the rat basophilic cell line RBL-2H3 and N-palmitoylethanolamide was proposed as an endogenous, potent agonist of this receptor. We synthesized a series of 10 N-palmitoylethanolamide homologues and analogues, varying by the elongation of the fatty acid chain from caproyl to stearoyl and by the nature of the amide substituent, respectively, and evaluated the affinity of these compounds to cannabinoid receptors in the rat spleen, RBL-2H3 cells and CHO-CB(1) and CHO-CB(2) receptor-transfected cells. In rat spleen slices, CB(2) receptors were the predominant form of the cannabinoid receptors. No binding of [(3)H]SR141716A was observed. [(3)H]CP-55,940 binding was displaced by WIN 55,212-2 and anandamide. No displacement of [(3)H]CP-55,940 or [(3)H]WIN 55,212-2 by palmitoylethanolamide derivatives was observed in rat spleen slices. In RBL-2H3 cells, no binding of [(3)H]CP-55,940 or [(3)H]WIN 55,212-2 could be observed and conversely, no inhibitory activity of N-palmitoylethanolamide derivatives and analogues was measurable. These compounds do not recognize the human CB(1) and CB(2) receptors expressed in CHO cells. In conclusion, N-palmitoylethanolamide was, in our preparations, a weak ligand while its synthesized homologues or analogues were essentially inactive. Therefore, it seems unlikely that N-palmitoylethanolamide is an endogenous agonist of the CB(2) receptors but it may be a compound with potential therapeutic applications since it may act via other mechanisms than cannabinoid CB(1)-CB(2) receptor interactions.     

Cellular localization of cannabinoid receptors and activated G-proteins in rat anterior cingulate cortex

Cannabinoid receptors are found in moderate density throughout the cerebral cortex. The anterior cingulate cortex (ACC) is of particular interest due its high level of cannabinoid receptors and role in behaviors known to be modulated by cannabinoids. These studies were conducted to determine the cellular localization of cannabinoid receptors and to compare the level of cannabinoid receptor binding with receptor-mediated G-protein activity in the rat ACC. Either ibotenic acid or undercut lesions were made in ACC, and brains were processed for [3H]WIN 55,212-2 and WIN 55,212-2-stimulated [35S]GTPgammaS autoradiography. Both cannabinoid receptors and receptor-activated G-proteins were highest in laminae I and VI of ACC in control tissue. Although similar levels of receptor binding were found in these laminae, significantly higher levels of receptor-activated G-proteins were found in lamina VI. Ibotenic acid lesions that destroyed ACC neurons decreased [3H]WIN 55,212-2 binding by 60-70% and eliminated WIN 55,212-2-stimulated [35S]GTPgammaS binding. In contrast, deafferentation of the ACC with undercut lesions had no significant effect on cannabinoid receptor binding or G-protein activation. These results indicate that cannabinoid receptors in laminae I and VI of the ACC are located on somatodendritic elements or axons intrinsic to the ACC. In addition, differences in the relative levels of cannabinoid binding sites and activated G-proteins between cortical laminae indicate that the efficiency of cannabinoid receptors for G-protein activation may vary within a specific brain region.     

Involvement of PAR-4 in Cannabinoid-Dependent Sensitization of Osteosarcoma Cells to TRAIL-Induced Apoptosis

The synthetic cannabinoid WIN 55,212-2 is a potent cannabinoid receptor agonist with anticancer potential. Experiments were performed to determine the effects of WIN on proliferation, cell cycle distribution, and programmed cell death in human osteosarcoma MG63 and Saos-2 cells. Results show that WIN induced G2/M cell cycle arrest, which was associated with the induction of the main markers of ER stress (GRP78, CHOP and TRB3). In treated cells we also observed the conversion of the cytosolic form of the autophagosome marker LC3-I into LC3-II (the lipidated form located on the autophagosome membrane) and the enhanced incorporation of monodansylcadaverine and acridine orange, two markers of the autophagic compartments such as autolysosomes. WIN also induced morphological effects in MG63 cells consisting in an increase in cell size and a marked cytoplasmic vacuolization. However, WIN effects were not associated with a canonical apoptotic pathway, as demonstrated by the absence of specific features, and only the addition of TRAIL to WIN-treated cells led to apoptotic death probably mediated by up-regulation of the tumor suppressor factor PAR-4, whose levels increased after WIN treatment, and by the translocation of GRP78 on cell surface.     

大麻素抑制大鼠三叉神经节神经元ATP激活电流

本文在培养的大鼠三叉神经节(trigeminal ganglion,TG)神经元上采用全细胞膜片钳技术,探讨大麻素对大鼠TG神经元ATP激活电流(ATP-activated currents,IATP)的影响.结果显示(1)胞外给予ATP,大部分受检细胞(67/75,89.33%)可记录到一个内向电流,且具有剂量依赖性.该电流可被P2X嘌呤受体特异性拮抗剂PPADS所阻断.(2)预加WIN55212-2[大麻素受体1(cannabinoid receptor 1,CB1受体)激动剂]可对IATP产生抑制作用,此作用呈剂量依赖性,并可被CB1受体特异性拮抗剂AM281阻断.预加不同浓度的WIN55212-2(1x10-13、1x10-12、1x10-11、1x10-10、1x10-9和1x10-8mol/L)对IATP(1x10-4mol/L ATP)的抑制作用分别为(8.14±3.14)%、(20.11±2.72)%、(46.62±3.51)%、(72.16±5.64)%、(80.21±2.80)%和(80.59±3.55)%.(3)预加WIN55212-2后IATP的浓度-反应曲线明显下移;最大反应浓度时的IATP幅值减小了(58.02±4.21)%,而阈值基本不变;预加WIN55212.2前后曲线的EC50值非常接近(1.15x10-4mol/L vs 1.27x10-4 mol/L).(4)预加forskolin[腺苷酸环化酶(adenylyl cyclase,AC)激动剂]或8-Br-cAMP可以逆转WIN55212-2对IATP的抑制作用.以上结果表明,大麻素可能作用于CB1受体,通过抑制AC-cAMP-PKA途径发挥对IATP的抑制作用.     

PPARγ mediates the effects of WIN55,212-2, an synthetic cannabinoid, on the proliferation and apoptosis of the BEL-7402 hepatocarcinoma cells

Cannabis sativa has long been used as a traditional medicine in China. Among its effective compounds are cannabinoids. This study determined the effect of WIN55,212-2 (WIN), a synthetic cannabinoid, on the BEL-7402 human hepatocellular carcinoma (HCC) cell line. The results showed that WIN could decrease the proliferation of BEL-7402 cells. Moreover, WIN could cause apoptosis of the cells via up-regulation of Bax expression, down-regulation of Bcl-2 expression, induction of the mitochondrial membrane potential, increase of caspase-3, -8 and -9 activities, and induction of the cleavage of caspase-3 and poly-ADP-ribose polymerase (PARP). The WIN-induced apoptosis was accompanied by the up-regulation of PPARγ expression, the activation of PPARγ DNA binding activity, and a down-regulation of PPARγ target oncogene c-myc. Conversely, the effects of WIN could be attenuated by PPARγ antagonist GW9662, and the WIN induced PPARγ expression was partially attenuated by AM630, a cannabinoid receptor-2 antagonist, whereas the WIN-induced reduction of c-myc expression was partially restored by GW9662. Collectively, our results suggest that WIN can decrease the proliferation and cause apoptosis of the BEL-7402 cells via a mitochondrial-caspase pathway and mediated by PPARγ. These results may provide a basis for the application of WIN in HCC treatment.     

Cannabinoids reduce markers of inflammation and fibrosis in pancreatic stellate cells

Background

While cannabinoids have been shown to ameliorate liver fibrosis, their effects in chronic pancreatitis and on pancreatic stellate cells (PSC) are unknown.

Methodology/Principal Findings

The activity of the endocannabinoid system was evaluated in human chronic pancreatitis (CP) tissues. In vitro, effects of blockade and activation of cannabinoid receptors on pancreatic stellate cells were characterized. In CP, cannabinoid receptors were detected predominantly in areas with inflammatory changes, stellate cells and nerves. Levels of endocannabinoids were decreased compared with normal pancreas. Cannabinoid-receptor-1 antagonism effectuated a small PSC phenotype and a trend toward increased invasiveness. Activation of cannabinoid receptors, however, induced de-activation of PSC and dose-dependently inhibited growth and decreased IL-6 and MCP-1 secretion as well as fibronectin, collagen1 and alphaSMA levels. De-activation of PSC was partially reversible using a combination of cannabinoid-receptor-1 and -2 antagonists. Concomitantly, cannabinoid receptor activation specifically decreased invasiveness of PSC, MMP-2 secretion and led to changes in PSC phenotype accompanied by a reduction of intracellular stress fibres.

Conclusions/Significance

Augmentation of the endocannabinoid system via exogenously administered cannabinoid receptor agonists specifically induces a functionally and metabolically quiescent pancreatic stellate cell phenotype and may thus constitute an option to treat inflammation and fibrosis in chronic pancreatitis.     

Internalization and Recycling of the CB1 Cannabinoid Receptor

Tolerance develops rapidly to cannabis, cannabinoids, and related drugs acting at the CB1 cannabinoid receptor. However, little is known about what happens to the receptor as tolerance is developing. In this study, we have found that CB1 receptors are rapidly internalized following agonist binding and receptor activation. Efficacious cannabinoid agonists (WIN 55,212-2, CP 55,940, and HU 210) caused rapid internalization. Methanandamide (an analogue of an endogenous cannabinoid, anandamide) was less effective, causing internalization only at high concentration, whereas delta9-tetrahydrocannabinol caused little internalization, even at 3 microM. CB1 internalized via clathrin-coated pits as sequestration was inhibited by hypertonic sucrose. Internalization did not require activated G protein alpha(i), alpha(o), or alpha(s) subunits. A region of the extreme carboxy terminus of the receptor was necessary for internalization, as a mutant CB1 receptor lacking the last 14 residues did not internalize, whereas a mutant lacking the last 10 residues did. Steps involved in the recycling of sequestered receptor were also investigated. Recovery of CB1 to the cell surface after short (20 min) but not long (90 min) agonist treatment was independent of new protein synthesis. Recycling also required endosomal acidification and dephosphorylation. These results show that CB1 receptor trafficking is dynamically regulated by cannabimimetic drugs.     

Matrix metalloproteinase-8 deficiency promotes granulocytic allergen-induced airway inflammation

Matrix metalloproteinases (MMPs) are involved in inflammatory reaction, including asthma-related airway inflammation. MMP-8, mainly produced by neutrophils, has recently been reported to be increased in the bronchoalveolar lavage fluid (BALF) from asthmatic patients. To evaluate the role of MMP-8 in asthma, we measured MMP-8 expression in lung tissue in an OVA-sensitized mouse model of asthma and addressed the effect of MMP-8 deletion on allergen-induced bronchial inflammation. MMP-8 production was increased in lungs from C57BL/6 mice exposed to allergens. After allergen exposure, MMP-8(-/-) mice developed an airway inflammation characterized by an increased neutrophilic inflammation in BALF and an increased neutrophilic and eosinophilic infiltration in the airway walls. MMP-8 deficiency was associated with increased levels of IL-4 and anti-OVA IgE and IgG1 in BALF and serum, respectively. Although allergen exposure induced an enhancement of LPS-induced CXC chemokine, KC, and MIP-2 levels in BALF and lung parenchyma, no difference was observed between the two genotypes. Inflammatory cell apoptosis was reduced in the lungs from MMP-8(-/-) mice. For the first time, our study evidences an important role of MMP-8 in the control of neutrophilic and eosinophilic infiltration during allergen-induced lung inflammation, and demonstrates that the anti-inflammatory effect of MMP-8 is partly due to a regulation of inflammatory cell apoptosis.     

Effect of a synthetic cannabinoid agonist on the proliferation and invasion of gastric cancer cells

Although cannabinoids are associated with antineoplastic activity in a number of cancer cell types, the effect in gastric cancer cells has not been clarified. In the present study, we investigated the effects of a cannabinoid agonist on gastric cancer cell proliferation and invasion. The cannabinoid agonist WIN 55,212‐2 inhibited the proliferation of human gastric cancer cells in a dose‐dependent manner and that this effect was mediated partially by the CB₁ receptor. We also found that WIN 55,212‐2 induced apoptosis and down‐regulation of the phospho‐AKT expression in human gastric cancer cells. Furthermore, WIN 55,212‐2 treatment inhibited the invasion of gastric cancer cells, and down‐regulated the expression of MMP‐2 and VEGF‐A through the cannabinoid receptors. Our results open the possibilities in using cannabinoids as a new gastric cancer therapy. J. Cell. Biochem. 110: 321–332, 2010. © 2010 Wiley‐Liss, Inc.     

Chronic delta9-tetrahydrocannabinol treatment produces a time-dependent loss of cannabinoid receptors and cannabinoid receptor-activated G proteins in rat brain

Chronic treatment of rats with delta9-tetrahydrocannabinol (delta9-THC) results in tolerance to its acute behavioral effects. In a previous study, 21-day delta9-THC treatment in rats decreased cannabinoid activation of G proteins in brain, as measured by in vitro autoradiography of guanosine-5'-O-(3-[35S]thiotriphosphate) ([35S]GTPgammaS) binding. The present study investigated the time course of changes in cannabinoid-stimulated [35S]GTPgammaS binding and cannabinoid receptor binding in both brain sections and membranes, following daily delta9-THC treatments for 3, 7, 14, and 21 days. Autoradiographic results showed time-dependent decreases in WIN 55212-2-stimulated [35S]GTPgammaS and [3H]WIN 55212-2 binding in cerebellum, hippocampus, caudate-putamen, and globus pallidus, with regional differences in the rate and magnitude of down-regulation and desensitization. Membrane binding assays in these regions showed qualitatively similar decreases in WIN 55212-2-stimulated [35S]GTPgammaS binding and cannabinoid receptor binding (using [3H]SR141716A), and demonstrated that decreases in ligand binding were due to decreases in maximal binding values, and not ligand affinities. These results demonstrated that chronic exposure to delta9-THC produced time-dependent and region-specific down-regulation and desensitization of brain cannabinoid receptors, which may represent underlying biochemical mechanisms of tolerance to cannabinoids.     

Unopposed matrix metalloproteinase-9 expression in human tuberculous granuloma and the role of TNF-alpha-dependent monocyte networks

Tuberculosis is characterized by granuloma formation and caseous necrosis, but the factors causing tissue destruction are poorly understood. Matrix metalloproteinase (MMP)-9 (92-kDa gelatinase) secretion from monocytes is stimulated by Mycobacterium tuberculosis (M. tb) and associated with local tissue injury in tuberculosis patients. We demonstrate strong immunohistochemical MMP-9 staining in monocytic cells at the center of granuloma and adjacent to caseous necrosis in M. tb-infected patient lymph nodes. Minimal tissue inhibitor of MMPs-1 staining indicated that MMP-9 activity is unopposed. Because granulomas characteristically contain few mycobacteria, we investigated whether monocyte-monocyte cytokine networks amplify MMP-9 secretion. Conditioned medium from M. tb-infected primary human monocytes or THP-1 cells (CoMTB) stimulated MMP-9 gene expression and a >10-fold increase in MMP-9 secretion by monocytes at 3-4 days (p < 0.009, vs controls). Although CoMTB stimulated dose-dependent MMP-9 secretion, MMP-1 (52-kDa collagenase) was not induced. Anti-TNF-alpha Ab but not IL-1R antagonist pretreatment decreased CoMTB-induced MMP-9 secretion by 50% (p = 0.0001). Anti-TNF-alpha Ab also inhibited MMP-9 secretion from monocytic cells by 50%, 24 h after direct M. tb infection (p = 0.0002). Conversely, TNF-alpha directly stimulated dose-dependent MMP-9 secretion. Pertussis toxin inhibited CoMTB-induced MMP-9 secretion and enhanced the inhibitory effect of anti-TNF-alpha Ab (p = 0.05). Although chemokines bind to G protein-linked receptors, CXCL8, CXCL10, CCL2, and CCL5 did not stimulate monocyte MMP-9 secretion. However, the response to cholera toxin confirmed that G protein signaling pathways were intact. In summary, MMP-9 within tuberculous granuloma is associated with tissue destruction, and TNF-alpha, critical for antimycobacterial granuloma formation, is a key autocrine and paracrine regulator of MMP-9 secretion.