Vagal nerve stimulation in prevention and management of coronary heart disease

Coronary heart disease (CHD) that is due to atherosclerosis is associated with low-grade systemic inflammation. Congestive cardiac failure and arrhythmias that are responsible for mortality in CHD can be suppressed by appropriate vagal stimulation that is anti-inflammatory in nature. Acetylcholine, the principal vagal neurotransmitter, is a potent anti-inflammatory molecule. Polyunsaturated fatty acids (PUFAs) augment acetylcholine release, while acetylcholine can enhance the formation of prostacyclin, lipoxins, resolvins, protectins and maresins from PUFAs, which are anti-inflammatory and anti-arrhythmic molecules. Furthermore, plasma and tissue levels of PUFAs are low in those with CHD and atherosclerosis. Hence, vagal nerve stimulation is beneficial in the prevention of CHD and cardiac arrhythmias. Thus, measurement of catecholamines, acetylcholine, various PUFAs, and their products lipoxins, resolvins, protectins and maresins in the plasma and peripheral leukocytes, and vagal tone by heart rate variation could be useful in the prediction, prevention and management of CHD and cardiac arrhythmias.     

Profiling in resolving inflammatory exudates identifies novel anti‐inflammatory and pro‐resolving mediators and signals for termination

Abstract. Norling LV, Serhan CN (Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA). Profiling in resolving inflammatory exudates identifies novel anti‐inflammatory and pro‐resolving mediators and signals for termination (Review). J Intern Med 2010; 268 :15–24. A highly orchestrated inflammatory response and its completion, termed resolution, are essential for ongoing health. Thus, complete understanding of the cellular and molecular events that govern natural resolution is vital. Using an unbiased systems approach to profile self‐limited inflammatory exudates, we identified a novel genus of specialized pro‐resolving lipid mediators (SPMs) comprised of three new families coined the resolvins, protectins and most recently the maresins biosynthesized from ω‐3 fatty acids. These join the lipoxin‐ and aspirin‐triggered lipoxins as anti‐inflammatory and pro‐resolving lipid mediators formed from arachidonic acid with the genus. SPMs have proven stereoselective, and control both the duration and magnitude of inflammation. Mapping these endogenous resolution circuits provides new avenues to probe the molecular basis of many widely occurring diseases where uncontrolled inflammation is characteristic. The focus of this JIM review is to depict recent advances from studies by the authors and colleagues on the biosynthesis and actions of these novel anti‐inflammatory, pro‐resolving and protective lipid mediators. Together these findings indicate that defective mechanisms and pathways in resolution may underlie our current appreciation of the inflammatory phenotype(s) that characterize some prevalent human diseases.     

Novel lipid mediators promote resolution of acute inflammation: impact of aspirin and statins

The resolution of acute inflammation is a process that allows for inflamed tissues to return to homeostasis. Resolution was held to be a passive process, a concept now overturned with new evidence demonstrating that resolution is actively orchestrated by distinct cellular events and endogenous chemical mediators. Among these, lipid mediators, such as the lipoxins, resolvins, protectins, and newly identified maresins, have emerged as a novel genus of potent and stereoselective players that counter-regulate excessive acute inflammation and stimulate molecular and cellular events that define resolution. Given that uncontrolled, chronic inflammation is associated with many cardiovascular pathologies, an appreciation of the endogenous pathways and mediators that control timely resolution can open new terrain for therapeutic approaches targeted at stimulating resolution of local inflammation, as well as correcting the impact of chronic inflammation in cardiovascular disorders. Here, we overview and update the biosynthesis and actions of proresolving lipid mediators, highlighting their diverse protective roles relevant to vascular systems and their relation to aspirin and statin therapies.     

Novel mediators and mechanisms in the resolution of infectious inflammation: evidence for vagus regulation

Excessive chronic inflammation is linked to many diseases and considered a stress factor in humans (Robbins Pathologic Basis of Disease. Philadelphia: W.B. Saunders Co., 1999, Proc Natl Acad Sci USA, 2008, 105: 17949, Immunity, 44, 2016, 44: 463, N Engl J Med, 2011, 364: 656). Today, the resolution of inflammation is widely recognized as a cellular biochemically active process involving biosynthesis of a novel superfamily of endogenous chemical signals coined specialized pro‐resolving mediators (SPMs; Nature, 2014, 510:92). Herein, we review recent evidence, indicating a role for the vagus nerve and vagotomy in the regulation of lipid mediators. Vagotomy reduces pro‐resolving mediators, including the lipoxins, resolvins, protectins and maresins, delaying resolution in mouse peritonitis. Vagotomy also delays resolution of Escherichia coli infection in mice. Specifically, right vagus regulates peritoneal Group 3 innate lymphoid cell (ILC‐3) number and peritoneal macrophage responses with lipid mediator profile signatures with elevated pro‐inflammatory eicosanoids and reduced resolvins, including the novel protective immunoresolvent agonist protectin conjugate in tissue regeneration1 (PCTR1). Acetylcholine upregulates PCTR biosynthesis, and administration of PCTR1 to vagotomized mice restores tissue resolution and host responses to E. coli infections. Results obtained with human vagus ex vivo indicate that vagus can produce both pro‐inflammatory eicosanoids, such as prostaglandins and leukotrienes, as well as the SPM. Electrical stimulation of human vagus in vitro reduces both prostaglandins and leukotrienes and enhances resolvins and the other SPM. These results elucidate a host protective mechanism mediated by vagus stimulation of SPM that includes resolvins and PCTR1 to regulate myeloid antimicrobial functions and resolution of infection. Moreover, they define a new pro‐resolution of inflammation reflex operative in mice and human tissue that involves a vagus SPM circuit.     

New endogenous anti-inflammatory and proresolving lipid mediators: implications for rheumatic diseases

Prostaglandins and leukotrienes are lipid mediators that carry out pivotal roles in host defense and acute inflammation. Failure to completely resolve an acute inflammatory response can lead to chronic inflammation, scarring, and eventual loss of tissue function. Until recently, it was thought that tissue resolution of acute inflammation was a passive event. However, it is now known than lipoxins, which--like prostaglandins and leukotrienes--are also derived from arachidonic acid, are active anti-inflammatory and proresolution mediators, acting in part by reducing neutrophil entry to the inflammation site and stimulating the uptake of apoptotic polymorphonuclear leukocytes by macrophages. Novel families of locally acting and locally generated mediators derived from omega-3 polyunsaturated fatty acids have also been identified as biosynthetically active components in the resolution phase of inflammation. The new families of chemical mediators are termed 'resolvins' and 'protectins' because individual members of each family are stereospecific in controlling the duration and magnitude of inflammation in animal models. Possible deficiencies in the biosynthesis of lipoxins, resolvins, and protectins, and/or their signal transduction, might underlie some aspects of pathogenesis in chronic inflammatory diseases.     

A Scanning Electron Microscopic Investigation of Effects of Prostacyclin on Platelet Retention in Glass Bead Columns

As whole blood passes through a column of glass beads, platelets are activated and all 3 basic platelet properties (adhesion, release reaction and aggregation) displayed, an aspect similar to platelets being involved in a hemostatic process. For this reason, we chose the platelet retention test as the tool to study the effect of synthetic prostacyclin (PGI₂) on platelet function and behavior. PGI₂ inhibited platelet retention with its major impact on platelet aggregation. The extent of inhibition was not proportional to the concentration of PGI₂. It appears that 2 levels of platelet aggregation take place inside the column. One, triggered by a weak stimulus, is readily inhibitable by low concentrations of PGI². The other, brought about by a strong stimulus, requires higher concentrations of PGI₂ to achieve complete inhibition. Even with as much as 100 ng PGI₂/ml blood, a 15% retention remained which probably represented platelet adhesion to glass beads. Scanning electron microscopic examination of glass beads showed massive platelet aggregation and adhesion in control blood samples. No platelet aggregate was observed on beads filtered with blood containing 20 ng/ml or more PGI₂. Individual platelets were found on glass beads filtered with samples containing any concentration of PGI₂; these platelets exhibited extensive morphologic changes.     

Contribution of cyclooxygenase-1 to thromboxane formation, platelet-vessel wall interactions and atherosclerosis in the ApoE null mouse

ObjectiveProstaglandin and thromboxane (TXA₂) generation is increased in atherosclerosis. Studies with selective inhibitors attribute the enhanced prostacyclin (PGI₂) generation to both cyclooxygenase-1 (COX-1) and COX-2 whereas the increased TXA₂ generation reflects platelet COX-1 expression. However, TXA₂ formation remains elevated in patients with cardiovascular disease on doses of aspirin that fully suppress platelet COX-1, suggesting other tissue sources for TXA₂ formation. Disruption of the thromboxane receptor gene suppresses the development of atherosclerosis. Notwithstanding this, the role of COX-1 in atherosclerosis is unclear, as it is widely distributed and contributes to a number of products, including those that potentially contribute to the resolution of inflammation.Methods and resultsWe examined the role of COX-1 on prostaglandin generation, development of atherosclerosis and platelet–vessel wall interactions in the apoE^?/? murine model by disrupting the COX-1 gene. ApoE^?/?/COX-1^+/+, ApoE^?/?/COX-1^+/? and ApoE^?/?/COX-1^?/?, were administered a 1% cholesterol diet for 8 weeks. Stable urinary metabolites of PGI₂ and TXA₂, which were markedly increased in the ApoE^?/?/COX-1^+/+ were reduced by disruption of COX-1. Deletion of one or both copies of the COX-1 gene suppressed lesion formation. Assessment of platelet–vessel wall interactions by intravital microscopy showed a significant decrease in firm adhesion of platelets in the apoE/COX-1 double knockout (DKO).ConclusionCOX-1 contributes to the enhanced formation of both PGI₂ and TXA₂ in atherosclerosis, and to the development of the disease. Non-platelet sources of COX-1 and TXA₂ that are inaccessible to standard doses of aspirin may contribute to the development of atherosclerosis.     

Prostaglandins,other eicosanoids and endothelial cells

Summary Endothelial cells are an important source of eicosanoid formation in the cardiovascular systems. All major pathways of eicosanoid production have been demonstrated in endothelial cells, yielding significant amounts of prostacyclin (PGI₂), PGE₂, PGF₂, thromboxane A₂, leukotrienes and a number of hydroxy fatty acids. The regulation of eicosanoid formation by endothelial cells is poorly understood. There is evidence that precursors, such as arachidonic acid or prostaglandin endoperoxides, may also be provided by other cell types. Endothelial cell-derived eicosanoids are involved in the regulation of local vessel tone, intravascular platelet activation, cell locomotion and, eventually, cell proliferation. Most of the available information considers PGI₂. This compound is the quantitatively dominating eicosanoid in endothelial cells. Major actions of PGI₂ include inhibition of platelet activation and aggregation, relaxation of arterial vessels and inhibition of growth-factor release. There is probably a tight interaction with other biologically active mediators which needs further evaluation. This also applies to the clinical significance of eicosanoid-related pathways for the mechanism of action of cardiovascular drugs, such as organic nitrates or acetylsalicylic acid. The unique property of the cicosanoid system to become activated only in response to stimulation, the local nature of this reaction, the multiplicity of products formed and the short half-time of most of them are currently the most significant obstacles to define the role of endothelial cell-derived eicosanoids in clinical practice.     

Effect of insulin treatment on prostacyclin in experimental diabetes

Summary Diabetic patients have a high susceptibility to microvascular complications, atherosclerosis and thrombosis. Platelet hyperreactivity possibly related to an imbalance in arachidonic acid metabolism may be involved. Aortic rings or renal cortex produced a potent inhibitor of platelet aggregation, identified as prostacyclin (PGI₂). Release of PGI₂ by tissues from streptozotocin — diabetic rats (aorta: 0.07±0.1 ng/ mg wet weight; renal cortex 0.004±0.001 ng/mg wet weight) was significantly depressed when compared with controls (aorta: 0.26±0.07 ng/mg wet weight; renal cortex: 0.009±0.001 ng/mg wet weight). Treatment of diabetic animals with insulin for 8 days restored PGI₂ production to normal. The finding that PGI₂ is depressed in the aorta and in the kidney, tissues which develop angiopathy, and that this is normalised by insulin, suggests that impaired PGI₂ production, perhaps associated with platelet hyperreactivity may play a role in the vascular complications of diabetes.Department for antiserum to prostacyclin and to Mrs. T. E. Robinson, Mr. M. J. A. Arnstein, Mrs. S. Jones and Miss S. Bowden for technical assistance.     

Metabolic syndrome X: An inflammatory condition?

Obesity, atherosclerosis, insulin resistance and hyperinsulinemia, hyperlipidemia, essential hypertension, type 2 diabetes mellitus, and coronary heart disease (CHD) are the components of metabolic syndrome X and are associated with elevated plasma levels of C-reactive protein, interleukin-6, and tumor necrosis factor-α, which are markers of inflammation. This suggests that metabolic syndrome X is a low-grade, systemic, inflammatory condition. Hence, instituting anti-inflammatory measures might be beneficial in preventing or halting the progress of metabolic syndrome X in high-risk populations.     

Synthesis of prostaglandins by cultured rat hearts myocytes and cardiac mesenchymal cells

Ischemia, trauma and hormonal stimulation elicit the release of prostaglandins (PGs) from the heart. Although PGI₂ is synthesized by coronary arteries, the capacities for PG synthesis of individual types of cells comprising the heart have not been elucidated. Accordingly, synthesis of prostaglandins by cultured rat cardiac myocytes and mesenchymal cells was evaluated by radiochromatography of products obtained by incubating cells with [1-¹⁴C]arachidonate, and verified by assessing the effects of cell incubation medium on platelet aggregation. Cultured mesenchymal cells synthesized PGs E₂, F_2α and 6-keto-F_1α, a metabolite of PGI₂ (2076 ± 183, 1284 ± 158 and 1194 ± 152 dpm/mg protein/30 min, respectively). Medium from mesenchymal cells inhibited platelet aggregation, an effect abolished by preincubating the cells with indomethacin, further indicating that these cells synthesized PGI₂. Cardiac myocytes synthesized PGE₂ and PGF_2α (952 ± 227 and 287 ± 104 dpm/mg protein/30 mins, respectively), but no PGI₂. Medium from myocytes did not inhibit platelet aggregation. Prostaglandins D₂, A₂ and thromboxane were not synthesized by either type of cell. Thus, PGI₂ is synthesized by cardiac mesenchymal cells and the hitherto uncharacterized sources of PGE₂ and PGF_2α found in coronary sinus effluent may include cardiac myocytes as well as mesenchymal cells.     

Mechanisms of Disease: leukotrienes and lipoxins in scleroderma lung disease--insights and potential therapeutic implications

Scleroderma interstitial lung disease (SLD) is a leading cause of morbidity and mortality in patients with systemic sclerosis. Although the pathogenesis of SLD is not clear, excessive fibrosis and inflammatory cell infiltration are the main histologic features of this disorder. Leukotrienes and lipoxins are two functionally different classes of lipoxygenase-derived eicosanoids. Leukotrienes are potent proinflammatory mediators and directly and indirectly stimulate fibroblast chemotaxis, proliferation, and collagen synthesis. Lipoxins counter-regulate the proinflammatory actions of leukotrienes and activate resolution of the inflammatory response. In addition, lipoxins inhibit growth-factor-induced fibroblast proliferation and collagen synthesis. Studies using bronchoalveolar lavage have revealed that there is an overproduction of proinflammatory and profibrotic leukotrienes in the lungs of patients with SLD, and that leukotriene levels correlate with inflammatory indices within the lungs. Moreover, the increased levels of leukotrienes in these patients are not balanced by an upregulation of anti-inflammatory and antifibrotic lipoxins. Unopposed actions of leukotrienes might, therefore, induce chronic inflammation and fibrosis in the lungs of SLD patients. Accordingly, pharmacologic correction of a leukotriene-lipoxin imbalance using leukotriene inhibitors or lipoxin analogs might be a new approach to the treatment of SLD.     

The Inhibitory Effect of Aspirin on Platelet and Vascular Prostaglandins in Rats cannot be Completely Dissociated

Summary . Blood platelets and vascular endothelium generate prostaglandin derivatives with opposing effects: cyclic endoperoxides and thromboxane A₂ (TXA₂) aggregate platelets, whereas prostaglandin I₂ (PGI₂, prostacyclin) inhibits aggregation. Since aspirin inhibits the synthesis and effects of all these metabolites of arachidonic acid, the rationale for clinical use of this drug in thrombosis prevention trials is questionable. Treatment schedules would have to be calibrated to inhibit proaggregating platelet prostaglandins and TXA₂ without affecting protective vascular prostaglandins (PGI₂). This important clinical information cannot easily be obtained from studies in man. The present study indicates that normal rat platelets are more sensitive to aspirin (ID₅₀=3.6 mg/kg) than arterial tissues (ID₅₀=25.0 mg/kg) and are almost as sensitive as venous tissues (ID₅₀=2.3 mg/kg). Platelet prostaglandin production was monitored through the measurement of malondialdehyde (MDA) output under standard stimulation with thrombin. PGI₂-like activity released from the abdominal aorta and inferior vena cava was determined as platelet aggregation inhibitory potency and characterized by standard criteria. The inhibitory effect of aspirin (at doses of 10 and 50 mg/kg) on platelet MDA production lasted much longer in platelets (96–120 h) than in venous (24–72 h) or arterial tissue (less than 24 h). The findings suggest that in rats the (potentially antithrombotic) effect of aspirin on platelet prostaglandin and TXA₂ generation may be distinguished, though not completely, from the (potentially prothrombotic) effect on vascular PGI₂ on the basis of duration of inhibition more than on the sensitivity of the target cells to the drug. The different capacities of anucleated platelets and of nucleated vascular endothelial cells to overcome aspirin inhibition could be exploited for more rational clinical use of this drug.     

Physiology and pharmacology of prostaglandins

Prostaglandins (PGs) are products of polyunsaturated acid metabolism, particularly arachidonic acid (AA) released from membrane phospholipids by the action of phospholipase A₂ in response to a variety of physical, chemical, and neurohormonal factors. AA is rapidly metabolized to oxygenated products by two distinct enzymatic pathways: cyclooxygenase and lipoxygenase. The intermediate cyclooxygenase products are converted to primary PGs, while the lipoxygenase products are converted to leukotrienes. The generation of various cyclooxygenase products varies from tissue to tissue. Aspirin and related antiinflammatory drugs reduce tissue biosynthesis of all cyclooxygenase products; their therapeutic effects and side effects parallel the inhibition of cyclooxygenase. Exogenous PGs exhibit a broad spectrum of effects. PGs of the E series and PGI₂ are generated by the endothelium and the vessel wall to maintain the microcirculation and to counteract the vasoconstrictive and proaggregatory actions of thromboxane A₂ (TXA₂). Exogenous PGs of the E and I series are potent vasodilators in various vascular beds, and result in decreased systemic blood pressure and reflex stimulation of heart rate. PGEs and PGI₂ increase renal blood flow and provoke diuresis and natriuresis, partly by modulating the renin-angiotensin-aldosterone system. PGFs contract the bronchial and gut muscle, while PGEs and PGI₂ have opposite effects. PGEs and PGFs, but not PGI₂, cause a strong contraction of the uterine muscle, hence their undesirable uterotonic effects. PGEs relax bronchial muscle, whereas PGFs cause bronchoconstriction; their imbalance may contribute to the high bronchial tone in bronchial asthma. PGs of the E and I series and TXA₂ are generated by the gastrointestinal mucosa and released into the lumen upon neural or hormonal stimulation; they probably participate in the maintenance of mucosal integrity and microcirculation. Exogenous PGs of the E and I series inhibit gastric acid secretion and stimulate alkaline secretion while increasing mucosal blood flow. All PGs, including those noninhibitory for acid secretion, are cytoprotective against various ulcerogens and necrotizing agents. The classic PGs constitute only a small fraction of biologically active products of AA metabolism, and recent studies on the lipoxygenase products emphasize their biological activity and involvement in a variety of pathological conditions.     

Obesity and its relationship to coronary heart disease.

There is reasonable evidence to believe that obesity and itsassociated conditions such as hypertension, dyslipidemia, type2 diabetes mellitus, atherosclerosis, and coronary heart diseaseare low-grade systemic inflammatory conditions.^1,2 Althoughadipose tissue distribution is dependent on genetic, environmental,and hormonal factors, there are distinct functional differencesamong adipose cells depending on their location. For instance,gluteal–femoral fat cells in females have     

Compartmentalisation of cAMP-dependent signalling in blood platelets: The role of lipid rafts and actin polymerisation

Abstract

Prostacyclin (PGI₂) inhibits blood platelets through the activation of membrane adenylyl cyclases (ACs) and cyclic adenosine 3',5'-monophosphate (cAMP)-mediated signalling. However, the molecular mechanism controlling cAMP signalling in blood platelet remains unclear, and in particular how individual isoforms of AC and protein kinase A (PKA) are coordinated to target distinct substrates in order to modulate platelet activation. In this study, we demonstrate that lipid rafts and the actin cytoskeleton may play a key role in regulating platelet responses to cAMP downstream of PGI₂. Disruption of lipid rafts with methyl-beta-cyclodextrin (MβCD) increased platelet sensitivity to PGI₂ and forskolin, a direct AC cyclase activator, resulting in greater inhibition of collagen-stimulated platelet aggregation. In contrast, platelet inhibition by the direct activator of PKA, 8-CPT-6-Phe-cAMP was unaffected by MβCD treatment. Consistent with the functional data, lipid raft disruption increased PGI₂-stimulated cAMP formation and proximal PKA-mediated signalling events. Platelet inhibition, cAMP formation and phosphorylation of PKA substrates in response to PGI₂ were also increased in the presence of cytochalasin D, indicating a role for actin cytoskeleton in signalling in response to PGI₂. A potential role for lipid rafts in cAMP signalling is strengthened by our finding that a pool of ACV/VI and PKA was partitioned into lipid rafts. Our data demonstrate partial compartmentalisation of cAMP signalling machinery in platelets, where lipid rafts and the actin cytoskeleton regulate the inhibitory effects induced by PGI_2. The increased platelet sensitivity to cAMP-elevating agents signalling upon raft and cytoskeleton disruption suggests that these compartments act to restrain basal cAMP signalling.     

Role of hepatocyte growth factor in endothelial regulation: prevention of high D-glucose-induced endothelial cell death by prostaglandins and phosphodiesterase type 3 inhibitor

Summary Injury of endothelial cells (EC) has been postulated as the initial trigger of the progression of atherosclerosis in patients with diabetes mellitus. We previously reported that decrease in a novel endothelium-specific growth factor, hepatocyte growth factor (HGF), by high d-glucose might be a trigger of endothelial injury. However, the physiological role of the local vascular HGF system has not yet been clarified. To investigate the role of HGF in endothelial injury, we initially examined the effects of HGF on endothelial injury induced by serum deprivation. Decrease in EC number by serum deprivation was significantly attenuated by addition of HGF as well as recombinant basic fibroblast growth factor, whereas vascular endothelial growth factor showed no effect. Apoptotic changes in EC induced by serum deprivation were also significantly attenuated by addition of HGF (p < 0.01). Given the protective action of HGF, we next studied the physiological role of local HGF production in endothelial regulation. We focused on the protective actions of prostaglandin (PG) I₂, PGE and a phosphodiesterase type 3 inhibitor (cilostazol) on endothelial injury by high glucose, since these agents are widely used in the treatment of peripheral arterial disease which is frequently observed in diabetic patients. Treatment of human aortic EC with PGE₁, PGE₂, and a PGI₂ analogue (beraprost sodium) as well as cilostazol stimulated EC growth. HGF concentration in conditioned medium from EC treated with PGE₁, PGE₂ or PGI₂ analogue as well as cilostazol was significantly higher than that with vehicle (p < 0.01). Interestingly, treatment with PGI₂ analogue or cilostazol attenuated high d-glucose-induced EC death, which was abolished by neutralizing anti-HGF antibody. Moreover, decreased local HGF production by high d-glucose was also significantly attenuated by PGI₂ analogue or cilostazol. Finally, we tested the effects of PGE, PGI₂ analogue and cilostazol on local HGF production in human aortic vascular smooth muscle cells (VSMC). Although high d-glucose treatment resulted in a significant increase in VSMC number, PGI₂ analogue and/or cilostazol treatment had no effects on VSMC growth. However, the decrease in local HGF production by high d-glucose was significantly attenuated by addition of PGI₂ analogue or cilostazol. Overall, this study demonstrated that treatment with PGE, PGI₂ analogue or cilostazol prevented aortic EC death induced by high d-glucose, probably through the activation of local HGF production. Increased local vascular HGF production by prostaglandins and cilostazol may prevent endothelial injury, potentially resulting in the improvement of peripheral arterial disease. [Diabetologia (1997) 40: 1053–1061] Received: 17 February 1997 and in revised form: 7 May 1997     

Berberine inhibits the expression of TNFα, MCP-1, and IL-6 in AcLDL-stimulated macrophages through PPARγ pathway

Macrophages are the main source of cytokines in atherosclerotic plaques. Modified low-density lipoproteins may stimulate macrophages to produce large quantities of proinflammatory cytokines that promote atherosclerosis. Berberine is the main component of the traditional Chinese medicine umbellatine, which has a widespread effect and was used to treat many diseases clinically. Our previous study found that berberine could increase adipophilin expression in macrophages, which is a target gene of PPARγ. PPARγ agonist could decrease proinflammatory cytokines in macrophage. In this study, we investigated the effects and the mechanism of action of berberine on the expression and secretion of TNFα, MCP-1, and IL-6 in vitro to identify new pharmacological actions of berberine. The results of RT-PCR and ELISA shows that berberine may inhibit the expression and secretion of the tumor necrosis factor α (TNFα), monocyte chemoattractant protein 1 (MCP-1), and interleukin-6 (IL-6) in macrophages stimulated by acetylated low-density lipoprotein (AcLDL), whereas the peroxisome proliferator-activated receptor γ (PPARγ) inhibitor GW9662 could attenuate this effect of berberine. This study demonstrates that berberine may inhibit the expression and production of TNF-α, MCP-1, and IL-6 in AcLDL-stimulated macrophages. This effect might be partially mediated through PPARγ activity.     

Current concepts for a drug-induced inhibition of formation and action of thromboxane A2

Summary Urinary and plasma metabolites of thromboxane A₂ (TxA₂) indicate an increased TxA₂ synthesis in a number of diseases, whereby TxA₂ is assumed to contribute to the underlying pathomechanisms by its profound effects on platelet aggregation and smooth muscle contraction. In some clinical situations the increment in TxA₂ biosynthesis is accompanied by an increased formation of prostacyclin (PGI₂) which is one of the most potent inhibitors of platelet activation and smooth muscle contraction. Therefore, drugs are being developed which suppress the formation or action of TxA₂ without interfering with its functional antagonist PGI₂.Low doses of acetylsalicylic acid (ASA) preferentially inhibit cyclooxygenase activity in platelets and the synthesis of TxA₂ in vivo. However, neither low doses (approximately 300 mg/day) nor very low doses spare the formation of PGI₂ completely. Despite its limited selectivity, very low dose ASA (approximately 40 mg/day) provides an attractive perspective in TxA₂ pharmacology.Although thromboxane synthase inhibitors selectively suppress TxA₂ biosynthesis PGH₂ can accumulate instead of TxA₂ and substitute for TxA₂ at their common TxA₂/PGH₂ receptors. Thromboxane synthase inhibitors can only exert platelet-inhibiting and vasodilating effects if PGH₂ rapidly isomerizes to functional antagonists like PGI₂ that can be formed from platelet-derived PGH₂ by the vessel wall.TxA₂/PGH₂ receptor antagonists provide a specific and effective approach for inhibition of TxA₂. These inhibitors do not interfere with the synthesis of PGI₂ and other prostanoids but prevent TxA₂ and PGH₂ from activating platelets and inducing smooth muscle contractions. Most of the available TxA₂/PGH₂ receptor antagonists produce a competitive antagonism that can be overcome by high agonist concentrations. Since in certain disease states very high local TxA₂ concentrations are to be antagonized, non-competitive receptor antagonists may be of particular interest. Some recent TxA₂/PGH₂ receptor antagonists produce such a non-competitive type of inhibition due to their low dissociation rate constant. As a consequence, agonists like TxA₂ or PGH₂ only reach a hemiequilibrium state at their receptors, previously occupied by those antagonists.A combination of a thromboxane synthase inhibitor with a TxA₂/PGH₂ receptor antagonist presents a very high inhibitory potential that utilizes the dual activities of the synthase inhibitor to increase PGI₂ formation and of the receptor antagonist to antagonize PGH₂ and TxA₂. Such combinations or dual inhibitors, combining both moieties in one compound, prolong the skin bleeding time to a greater extent than thromboxane synthase inhibitors and even more than low dose ASA or TxA₂/PGH₂ receptor antagonists.