Effect of oxygen-glucose deprivation on degranulation and histamine release of mast cells

Mast cells: a novel therapeutic avenue for cardiovascular diseases?

Mast cells are tissue-resident immune cells strategically located in different compartments of the normal human heart (the myocardium, pericardium, aortic valve, and close to nerves) as well as in atherosclerotic plaques. Cardiac mast cells produce a broad spectrum of vasoactive and proinflammatory mediators, which have potential roles in inflammation, angiogenesis, lymphangiogenesis, tissue remodelling, and fibrosis. Mast cells release preformed mediators (e.g. histamine, tryptase, and chymase) and de novo synthesized mediators (e.g. cysteinyl leukotriene C4 and prostaglandin D2), as well as cytokines and chemokines, which can activate different resident immune cells (e.g. macrophages) and structural cells (e.g. fibroblasts and endothelial cells) in the human heart and aorta. The transcriptional profiles of various mast cell populations highlight their potential heterogeneity and distinct gene and proteome expression. Mast cell plasticity and heterogeneity enable these cells the potential for performing different, even opposite, functions in response to changing tissue contexts. Human cardiac mast cells display significant differences compared with mast cells isolated from other organs. These characteristics make cardiac mast cells intriguing, given their dichotomous potential roles of inducing or protecting against cardiovascular diseases. Identification of cardiac mast cell subpopulations represents a prerequisite for understanding their potential multifaceted roles in health and disease. Several new drugs specifically targeting human mast cell activation are under development or in clinical trials. Mast cells and/or their subpopulations can potentially represent novel therapeutic targets for cardiovascular disorders.

An Update of Palmitoylethanolamide and Luteolin Effects in Preclinical and Clinical Studies of Neuroinflammatory Events

The inflammation process represents of a dynamic series of phenomena that manifest themselves with an intense vascular reaction. Neuroinflammation is a reply from the central nervous system (CNS) and the peripheral nervous system (PNS) to a changed homeostasis. There are two cell systems that mediate this process: the glia of the CNS and the lymphocites, monocytes, and macrophages of the hematopoietic system. In both the peripheral and central nervous systems, neuroinflammation plays an important role in the pathogenesis of neurodegenerative diseases, such as Parkinson’s and Alzheimer’s diseases, and in neuropsychiatric illnesses, such as depression and autism spectrum disorders. The resolution of neuroinflammation is a process that allows for inflamed tissues to return to homeostasis. In this process the important players are represented by lipid mediators. Among the naturally occurring lipid signaling molecules, a prominent role is played by the N-acylethanolamines, namely N-arachidonoylethanolamine and its congener N-palmitoylethanolamine, which is also named palmitoylethanolamide or PEA. PEA possesses a powerful neuroprotective and anti-inflammatory power but has no antioxidant effects per se. For this reason, its co-ultramicronization with the flavonoid luteolin is more efficacious than either molecule alone. Inhibiting or modulating the enzymatic breakdown of PEA represents a complementary therapeutic approach to treating neuroinflammation. The aim of this review is to discuss the role of ultramicronized PEA and co-ultramicronized PEA with luteolin in several neurological diseases using preclinical and clinical approaches.

Future Needs in Mast Cell Biology

The pathophysiological roles of mast cells are still not fully understood, over 140 years since their description by Paul Ehrlich in 1878. Initial studies have attempted to identify distinct "subpopulations" of mast cells based on a relatively small number of biochemical characteristics. More recently, "subtypes" of mast cells have been described based on the analysis of transcriptomes of anatomically distinct mouse mast cell populations. Although mast cells can potently alter homeostasis, in certain circumstances, these cells can also contribute to the restoration of homeostasis. Both solid and hematologic tumors are associated with the accumulation of peritumoral and/or intratumoral mast cells, suggesting that these cells can help to promote and/or limit tumorigenesis. We suggest that at least two major subsets of mast cells, MC1 (meaning anti-tumorigenic) and MC2 (meaning pro-tumorigenic), and/or different mast cell mediators derived from otherwise similar cells, could play distinct or even opposite roles in tumorigenesis. Mast cells are also strategically located in the human myocardium, in atherosclerotic plaques, in close proximity to nerves and in the aortic valve. Recent studies have revealed evidence that cardiac mast cells can participate both in physiological and pathological processes in the heart. It seems likely that different subsets of mast cells, like those of cardiac macrophages, can exert distinct, even opposite, effects in different pathophysiological processes in the heart. In this chapter, we have commented on possible future needs of the ongoing efforts to identify the diverse functions of mast cells in health and disease.

The Role of Mast Cells in Stroke

Mast cells (MCs) are densely granulated perivascular resident cells of hematopoietic origin. Through the release of preformed mediators stored in their granules and newly synthesized molecules, they are able to initiate, modulate, and prolong the immune response upon activation. Their presence in the central nervous system (CNS) has been documented for more than a century. Over the years, MCs have been associated with various neuroinflammatory conditions of CNS, including stroke. They can exacerbate CNS damage in models of ischemic and hemorrhagic stroke by amplifying the inflammatory responses and promoting brain–blood barrier disruption, brain edema, extravasation, and hemorrhage. Here, we review the role of these peculiar cells in the pathophysiology of stroke, in both immature and adult brain. Further, we discuss the role of MCs as potential targets for the treatment of stroke and the compounds potentially active as MCs modulators.

PEA and luteolin synergistically reduce mast cell-mediated toxicity and elicit neuroprotection in cell-based models of brain ischemia

The combination of palmitoylethanolamide (PEA), an endogenous fatty acid amide belonging to the family of the N-acylethanolamines, and the flavonoid luteolin has been found to exert neuroprotective activities in a variety of mouse models of neurological disorders, including brain ischemia. Indirect findings suggest that the two molecules can reduce the activation of mastocytes in brain ischemia, thus modulating crucial cells that trigger the inflammatory cascade. Though, no evidence exists about a direct effect of PEA and luteolin on mast cells in experimental models of brain ischemia, either used separately or in combination. In order to fill this gap, we developed a novel cell-based model of severe brain ischemia consisting of primary mouse cortical neurons and cloned mast cells derived from mouse fetal liver (MC/9 cells) subjected to oxygen and glucose deprivation (OGD). OGD exposure promoted both mast cell degranulation and the release of lactate dehydrogenase (LDH) in a time-dependent fashion. MC/9 cells exacerbated neuronal damage in neuron-mast cells co-cultures exposed to OGD. Likewise, the conditioned medium derived from OGD-exposed MC/9 cells induced significant neurotoxicity in control primary neurons. PEA and luteolin pre-treatment synergistically prevented the OGD-induced degranulation of mast cells and reduced the neurotoxic potential of MC/9 cells conditioned medium. Finally, the association of the two drugs promoted a direct synergistic neuroprotection even in pure cortical neurons exposed to OGD. In summary, our results indicate that mast cells release neurotoxic factors upon OGD-induced activation. The association PEA-luteolin actively reduces mast cell-mediated neurotoxicity as well as pure neurons susceptibility to OGD.

Effect of oxygen and glucose deprivation on VEGF and its receptors in microvascular endothelial cells co-cultured with mast cells

The aim of this study was to determine the correlation between angiogenesis and the differential expression of vascular endothelial growth factor (VEGF) and its receptors in myocardial microvascular endothelial cells (MMVECs) co-cultured with mast cells (MCs) or mast cell granules (MCGs) under oxygen and glucose deprivation (OGD). MMVECs and MCs were isolated from Wistar rats. MCs spontaneously degranulated in OGD. The expression of VEGF peaked at 8 h and decreased from 16 h in OGD. However, the expression of its receptor, fms-like tyrosine kinase-1 (Flt-1), and fetal liver kinase-1 (Flk-1), decreased significantly, and angiogenic potential of MMVECs decreased in OGD. Expression of VEGF, Flt-1, and Flk-1 increased significantly when MMVECs were co-cultured with MCGs or active MCs, but MCs had only a limited ability to induce angiogenesis in OGD. The angiogenic potential of MMVECs cultured in OGD (even with MCGs) was inferior to that of MMVECs cultured under normoxic conditions. OGD have a profound effect on angiogenesis, which is more pronounced than the effect of MCs on angiogenesis.

Mast cells promote blood brain barrier breakdown and neutrophil infiltration in a mouse model of focal cerebral ischemia

Blood brain barrier (BBB) breakdown and neuroinflammation are key events in ischemic stroke morbidity and mortality. The present study investigated the effects of mast cell deficiency and stabilization on BBB breakdown and neutrophil infiltration in mice after transient middle cerebral artery occlusion (tMCAo). Adult male C57BL6/J wild type (WT) and mast cell-deficient (C57BL6/J Kit(Wsh/Wsh) (Wsh)) mice underwent tMCAo and BBB breakdown, brain edema and neutrophil infiltration were examined after 4 hours of reperfusion. Blood brain barrier breakdown, brain edema, and neutrophil infiltration were significantly reduced in Wsh versus WT mice (P<0.05). These results were reproduced pharmacologically using mast cell stabilizer, cromoglycate. Wild-type mice administered cromoglycate intraventricularly exhibited reduced BBB breakdown, brain edema, and neutrophil infiltration versus vehicle (P<0.05). There was no effect of cromoglycate versus vehicle in Wsh mice, validating specificity of cromoglycate on brain mast cells. Proteomic analysis in Wsh versus WT indicated that effects may be via expression of endoglin, endothelin-1, and matrix metalloproteinase-9. Using an in vivo model of mast cell deficiency, this is the first study showing that mast cells promote BBB breakdown in focal ischemia in mice, and opens up future opportunities for using mice to identify specific mechanisms of mast cell-related BBB injury.

Chymase inhibition prevents myocardial fibrosis through the attenuation of NOX4-associated oxidative stress in diabetic hamsters

Aims/Introduction:  Diabetic cardiomyopathy entails the cardiac injury induced by diabetes, independent of vascular disease or hypertension. Despite numerous experimental studies and clinical trials, the pathogenesis of diabetic cardiomyopathy remains elusive. Here, we report that chymase, an immediate angiotensin II (AngII)-forming enzyme in humans and hamsters, and NOX4-induced oxidative stress have pathogenic roles in myocardial fibrosis in diabetic hamsters.

MATERIALS AND METHODS

  Expression of chymase was evaluated in the hearts of streptozotocin (STZ)-induced diabetic hamsters. The impact of chymase-specific inhibitors, TEI-E00548 and TEI-F00806, on myocardial fibrosis, and increased levels of intracardiac AngII, accumulation of 8-hydroxy-2'-deoxyguanosine (an oxidative stress marker in urine and heart tissue) and expression of heart NOX4 in diabetic hamsters were investigated.

RESULTS

  Myocardial chymase expression was markedly upregulated in STZ hamsters in a glucose-dependent manner. A total of 8 weeks after STZ administration, the diabetic hamsters showed enhanced oxidative stress and NOX4 expression in the heart, in parallel with increased myocardial AngII production. Oral administration of chymase-specific inhibitors, TEI-F00806 and TEI-E00548, normalized heart AngII levels, and completely reversed NOX4-induced oxidative stress and myocardial fibrosis in STZ-induced diabetic hamsters, although they did not affect the activity of the systemic renin-angiotensin system or systolic blood pressure.

CONCLUSIONS

  Chymase inhibition might prevent oxidative stress and diabetic cardiomyopathy at an early stage by reducing local AngII production. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2012.00202.x, 2012).

Antipruritic activity of extracts of Humulus scandens, the combinations of bioactive flavonoids

The antipruritic effects of the ethanol fractions of Humulus scandens on the 4-AP (4-aminopyridine)-induced and chloroquine-induced scratching in ICR mice were examined. The 40% ethanol fractions of H. scandens suppressed both the 4-AP- and chloroquine-induced scratching behavior, which significantly inhibited degranulation of rat peritoneal mast cell and antigen-stimulated histamine release. Further studies proved that the 40% ethanol fractions of H. scandens decreased the content of IL4 in serum of chloroquine-induced scratching ICR mice. The results suggest that the 40% ethanol fractions of H. scandens has antipruritic effects on both antihistamine-resistant and -sensitive pruritus.

An emerging role of mast cells in cerebral ischemia and hemorrhage

Mast cells (MCs) are perivascularly located resident cells of hematopoietic origin, recognized as effectors in inflammation and immunity. Their subendothelial location at the boundary between the intravascular and extravascular milieus, and their ability to rapidly respond to blood- and tissue-borne stimuli via release of potent vasodilatatory, proteolytic, fibrinolytic, and proinflammatory mediators, render MCs with a unique status to act in the first-line defense in various pathologies. We review experimental evidence suggesting a role for MCs in the pathophysiology of brain ischemia and hemorrhage. In new-born rats, MCs contributed to brain damage in hypoxic-ischemic insults. In experimental cerebral ischemia/reperfusion, MCs regulated permeability of the blood-brain barrier, brain edema formation, and the intensity of local neutrophil infiltration. MCs were reported to play a role in the tissue plasminogen activator-mediated cerebral hemorrhages after experimental ischemic stroke, and to be involved in the expansion of hematoma and edema following intracerebral hemorrhage. Importantly, the MC-stabilizing drug cromoglycate inhibited MC-mediated adverse effects on brain pathology and improved survival of experimental animals. This brings us to a position to consider MC stabilization as a novel initial adjuvant therapy in the prevention of brain injuries in hypoxia-ischemia in new-borns, as well as in ischemic stroke and intracerebral hemorrhage in adults.

Carnosine attenuates mast cell degranulation and histamine release induced by oxygen-glucose deprivation

Carnosine (beta-alanyl-histidine) is a naturally occurring dipeptide that has been characterized as a putative hydrophilic antioxidant. The protective function of carnosine has been demonstrated in neuronal cells under ischemic injury. The purpose of this study was to investigate the effects of carnosine on oxygen-glucose deprivation (OGD)-induced degranulation and histamine release from mast cells. Cultured mast cells were exposed to OGD for 4 h, and then the degranulation was observed immediately by microscopy. Histamine release was analyzed by high-performance liquid chromatography (HPLC). OGD caused degranulation of mast cells, and increased histamine and lactate dehydrogenase (LDH) release. Carnosine (at a concentration of 5 mM) alone did not produce any appreciable effect on degranulation, histamine, and LDH release from mast cells under normal condition, but significantly inhibited the degranulation, histamine, and LDH release of mast cells induced by OGD. These results indicate that carnosine can protect mast cells from degranulation and histamine release and it may be an endogenous mast cell stabilizer in the pathological processes induced by ischemia.

Mast cell stabilization limits hypoxic-ischemic brain damage in the immature rat

Perinatal hypoxic-ischemic (HI) brain damage is a major cause of mortality and neurological morbidity in infants and children. Using an established model of unilateral hypoxia-ischemia in neonatal rats, the present study focused on mast cells (MCs), important regulators of inflammatory processes, as potential contributors to HI damage. MCs are present in the pia of the neonatal rat, entering the central nervous system (CNS) during cerebral development along penetrating blood vessels. Following hypoxia-ischemia, MC numbers increased dramatically in the ipsilateral (ischemic) hemisphere (p < 0.01). In animals exposed to hypoxia only, the numbers of MCs were elevated in both hemispheres to an extent equal to that observed in the contralateral hemisphere of HI animals (p < 0.05 vs. control). Within damaged areas (ipsilateral only), MCs were observed in regions of activated microglia and astroglia that characterize the ischemic hemisphere. Using a triple-label paradigm, MCs were observed along elongating blood vessels, some of which express the GLUT1 isoform of the glucose transporter protein, indicative of blood-brain barrier vessels. To determine whether MC activation has a role in HI brain damage, rat pups were treated with the MCs stabilizer, disodium cromoglycate (cromolyn), prior to and/or following hypoxia-ischemia. The cromolyn treatment inhibited MC migration into the CNS (p < 0.05) and limited brain damage more than 50% (p < 0.01) vs. saline controls. These data support the hypothesis that MCs are key contributors to the extent of brain damage due to hypoxia-ischemia in the immature animal.

Mast cell-derived mediators protect against oxygen-glucose deprivation-induced injury in PC12 cells and neurons

Recent reports and our previous study suggest that mast cells play a crucial role in the pathological processes that follow cerebral ischemia. In this study, the effect of mast cells on neuron injury after cerebral ischemia was determined by adding in vitro ischemia-induced supernatant from mast cells to neurons and PC12 cells under the same conditions (oxygen-glucose deprivation, OGD). The degree of cell injury was evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5-dipheny-ltetrazolium bromide (MTT) assay. Mast cell-derived supernatant protected against OGD-induced injury of PC12 cells and neurons, and this protection was reversed by a histamine H1 antagonist and by anti-histamine serum, but not by an H2 antagonist. However, histamine and nerve growth factor (NGF) added separately or together did not have protective effects against OGD-induced injury. These results indicate that mast cell-derived protection during in vitro ischemia is histamine-dependent, and involves cooperation with other mediators, but not NGF.