Impact of Kallikrein Kinin System Components on Macrophages' Inflammatory Response under Normal and Hyperglycemic Conditions

Abstract

Background: Inflammation is greatly associated with the development of chronic diseases such as diabetes. Diabetes is the leading cause of death in the world since it can lead to many macrovascular and microvascular (nephropathy, retinopathy, and neuropathy) complications. The Kallikrein-kinin system (KKS) contributes to inflammation through generation of bradykinin and activation of bradykinin receptors and protease activated receptors (PARs). Components of the KKS has recently been implicated as a modulator of diabetic microvascular and macrovascular complications. Higher plasma kallikrein (PK) activity is associated with higher blood pressure and increased albumin excretion rate in type 1 diabetic subjects. Furthermore, circulating levels of plasma PK are associated with carotid intima-media thickness and its progression in subjects with type 1 diabetes. Collectively, these data suggest that KKS components may play a potential role as a risk marker of inflammation-induced tissue injury. Aims: In the present study we aimed to determine whether hyperglycemia will modulate the expression of KKS components in macrophages. Also, to detect the effect of the KKS components on macrophages inflammatory response under normal and high glucose concentrations.

Methods: THP-1 macrophages and mice bone marrow derived macrophages (BMDM) were exposed to normal glucose (5.5mM) and high glucose concentration (20mM) for 24 hours to assess their effects on the expression of KKS components and polarization of macrophages. In the second series of experiments we assessed the effects of KKS components on inflammation and polarization of macrophages under normal and hyperglycemic conditions. Gene expression profiles (bradykinin receptors, PARs, cytokines, and fibrotic factors) were measured by RT- qPCR and release of inflammatory cytokine (IL-6) was measured by ELISA. Results: Our preliminary results indicated that under normal glucose levels B2R, KNG-1 and TBXA2R genes expression were induced when THP-1 macrophages were stimulated with bradykinin (BK) and plasma kallikrein (PK). However, high glucose levels increased the expression of PAR2, PAR1 and B2R when stimulated with PK and BK. Moreover, kininogen and B1R levels elevated in response to BK under high glucose conditions. In addition, it was observed that high glucose promoted the release of interleukin 6 after stimulation of THP-1 with BK and PK. For bone marrow derived macrophages high glucose and stimulation with PK and BK showed an increase in B1R, B2R and PAR1 gene expression. Conclusion: These studies indicate that high glucose levels modulate the expression of KKS components in macrophages. Furthermore, these data demonstrate that components of the KKS can promote macrophages’ inflammatory response.