The effect of bradykinin on the pro-inflammatory response of human adipocytes.

The proper functioning of adipose tissue is one of the factors in maintaining energy homeostasis. Adipocytes not only store lipids but also produce active molecules such as adipokines and adipocytokines, which are involved in many functions of adipose tissue, including the secretion of hormones that regulate energy and lipid metabolism. Inflammation has been shown to underlie the deregulation of adipose tissue function. Bradykinin belongs to a family of pro-inflammatory kinin peptides that are abundant in most tissues and biological fluids. This study aimed to determine the ability to produce kinin peptides and characterize the effect of bradykinin on pro-inflammatory responses in adipocytes. The Chub-S7 human preadipocyte line was differentiated to show specific properties for adipose tissue cells. The differentiated cells expressed genes that encode proteins such as kininogen, kallikrein, and prolylcarboxypeptidase that are involved in the production of kinins and also showed the expression of kinin receptors. The response of adipocytes to bradykinin was examined in relation to kinin concentration and the presence of kininase inhibitors. The high concentration of bradykinin induced a moderate increase in lipid accumulation, increased release of pro-inflammatory cytokines, and altered gene expression of molecules involved in adipocyte function, such as adiponectin, lipoprotein lipase, and other transcription factors. This study suggests an important role for kinin peptides in inducing inflammatory responses in adipocytes, which can modify the function of adipose tissue and ultimately lead to diseases related to disturbance of energy homeostasis. The results obtained may enrich our understanding of the mechanisms underlying obesity-related disorders.

Influence of bradykinin B2 receptor and dopamine D2 receptor on the oxidative stress, inflammatory response, and apoptotic process in human endothelial cells.

Endothelial dysfunction is a hallmark of a wide range of cardiovascular diseases and is often linked to oxidative stress and inflammation. Our earlier study reported the formation of a functional heterodimer between bradykinin receptor 2 (B2R) and dopamine receptor 2 (D2R) that may modulate cell responses, dependent on intracellular signaling. Here, for the first time, we showed a cooperative effect of these receptors on the modulation of processes involved in oxidative stress, inflammation, and apoptosis in endothelial cells. Sumanirole, a specific D2R agonist, was shown to diminish the excessive production of reactive oxygen species induced by bradykinin, a proinflammatory B2R-activating peptide. This effect was accompanied by modified activities of antioxidant enzymes and increased phosphorylation of endothelial nitric oxide synthase, leading to enhance NO production. In turn, endothelial cell co-stimulation with B2R and D2R agonists inhibited the release of interleukin-6 and endothelin-1 and modulated the expression of apoptosis markers, such as Bcl-2, Bcl-xL, Bax, and caspase 3/7 activity. All these observations argue that the D2R agonist counteracts the pro-oxidative, pro-inflammatory, and pro-apoptotic effects induced through B2R, finally markedly improving endothelial functions.

Bradykinin B2 receptor and dopamine D2 receptor cooperatively contribute to the regulation of neutrophil adhesion to endothelial cells.

Leukocyte adhesion to the vascular endothelium contributes to many immunological and inflammatory disorders. These processes have been shown to be mediated by bradykinin receptor type 2 (B2R) and dopamine receptor type 2 (D2R). In a previous study, we reported the formation of a B2R-D2R heterodimer, possibly altering cellular functions. Hence, in the present study, we examined the effect of co-activation of endothelial cells with B2R and D2R agonists on the interaction of these cells with neutrophils. Bradykinin, the main B2R agonist, significantly increased cell adhesion, and this effect was reversed when the endothelial cells were additionally co-treated with a selective D2R agonist, sumanirole. These results were dependent on the incubation time, showing an opposite tendency after prolonged stimulation. Significant changes in the expression of adhesion proteins, such as E-selectin and intercellular adhesion molecule 1 in endothelial cells were observed. Additionally, the cells preincubated with tumor necrosis factor-α showed decreased cell adhesion and IL-8 release after long incubation with both agonists. The modulation of cell adhesion by D2R and B2R seem to be mediated via STAT3 phosphorylation. In summary, this study demonstrated a protective role of D2R in neutrophil-endothelial cell adhesion induced by bradykinin, especially in cytokine-stimulated endothelial cells.

Bradykinin B2 and dopamine D2 receptors form a functional dimer.

In recent years a wide range of studies have shown that G protein-coupled receptors modulate a variety of cell functions through the formation of dimers. For instance, there is growing evidence for the dimerization of bradykinin or dopamine receptors, both as homodimers and heterodimers. A discovery of direct interactions of angiotensin II receptors with bradykinin 2 receptor (B2R) or dopamine D2 (D2R) receptor has led to a hypothesis on a potential dimerization between two latter receptors. In this study, we have demonstrated a constitutive colocalization of receptors on the membranes of HEK293 cells transiently transfected with plasmid vectors encoding B2R and D2R, fused with fluorescent proteins. The receptor colocalization was significantly enhanced by specific agonists of B2R or D2R after 5min following the addition, whereas simultaneous stimulation with these agonists did not influence the B2R/D2R colocalization level. In addition, B2R-D2R heterodimerization was confirmed with FLIM-FRET technique. The most characteristic signaling pathways for B2R and D2R, dependent on intracellular Ca2+ and cAMP concentration, respectively, were analyzed in cells presenting similar endogenous expression of B2R and D2R. Significant changes in receptors' signaling were observed after simultaneous stimulation with agonists, suggesting transformations in proteins' conformation after dimerization. The evidence of B2R-D2R dimerization may open new perspectives in the modulation of diverse cellular functions which depend on their activation.

Kinin Peptides Enhance Inflammatory and Oxidative Responses Promoting Apoptosis in a Parkinson's Disease Cellular Model.

Kinin peptides ubiquitously occur in nervous tissue and participate in inflammatory processes associated with distinct neurological disorders. These substances have also been demonstrated to promote the oxidative stress. On the other hand, the importance of oxidative stress and inflammation has been emphasized in disorders that involve the neurodegenerative processes such as Parkinson's disease (PD). A growing number of reports have demonstrated the increased expression of kinin receptors in neurodegenerative diseases. In this study, the effect of bradykinin and des-Arg10-kallidin, two representative kinin peptides, was analyzed with respect to inflammatory response and induction of oxidative stress in a PD cellular model, obtained after stimulation of differentiated SK-N-SH cells with a neurotoxin, 1-methyl-4-phenylpyridinium. Kinin peptides caused an increased cytokine release and enhanced production of reactive oxygen species and NO by cells. These changes were accompanied by a loss of cell viability and a greater activation of caspases involved in apoptosis progression. Moreover, the neurotoxin and kinin peptides altered the dopamine receptor 2 expression. Kinin receptor expression was also changed by the neurotoxin. These results suggest a mediatory role of kinin peptides in the development of neurodegeneration and may offer new possibilities for its regulation by using specific antagonists of kinin receptors.

Hypothetical orchestrated cooperation between dopaminergic and kinin receptors for the regulation of common functions.

The G protein-coupled receptors (GPCRs), one of the largest protein families, are essential components of the most commonly used signal-transduction systems in cells. These receptors, often using common pathways, may cooperate in the regulation of signal transmission to the cell nucleus. Recent scientific interests increasingly focus on the cooperation between these receptors, particularly in a context of their oligomerization, e.g. the formation of dimers that are able to change characteristic signaling of each receptor. Numerous studies on kinin and dopamine receptors which belong to this family of receptors have shown new facts demonstrating their direct interactions with other GPCRs. In this review, current knowledge on signaling pathways and oligomerization of these receptors has been summarized. Owing to the fact that kinin and dopamine receptors are widely expressed in cell membranes where they act as mediators of numerous common physiological processes, the information presented here sheds new light on a putative crosstalk of these receptors and provides more comprehensive understanding of possible direct interactions that may change their functions. The determination of such interactions may be useful for the development of new targeted therapeutic strategies against many disorders in which kinin and dopamine receptors are involved.

The effect of differentiation agents on inflammatory and oxidative responses of the human neuroblastoma cell line SK-N-SH.

Obtaining a suitable experimental cellular model is a major problem for neuroscience studies. Neuroblastoma cell lines have been often applied in studies related to pathological disorders of nervous system. However, in the search for an ideal model, these cells must be differentiated to cancel their tumor character. The subsequent reactions that are caused by differentiation are not always indifferent to the same model. We evaluated the effect of two well known substances, used for SH-N-SK cell line differentiation, retinoic acid (RA) and phorbol-12-myristate-13-acetate (PMA), on the induction of pro-inflammatory and pro-oxidative reactions in these cells. Cells differentiated with PMA were able to produce significantly higher amounts of pro-inflammatory cytokines whereas the release of nitric oxide radicals was similar to that in undifferentiated cells. On the contrary, in RA-differentiated cells no significant changes in cytokine production were observed and the nitric oxide release was decreased. Additionally, the RA-differentiated neuronal model was more sensible to lipopolysaccharide stimulation, producing pro-inflammatory cytokines abundantly. These results suggest that RA-differentiated SH-N-SK cells provide a more suitable experimental model for the study of molecular and cellular mechanisms of the inflammation and oxidative stress in neuronal cells.