Systemic leukotriene B4 receptor antagonism lowers arterial blood pressure and improves autonomic function in the spontaneously hypertensive rat

Abstract

Key points: Evidence indicates an association between hypertension and chronic systemic inflammation in both human hypertension and experimental animal models. Previous studies in the spontaneously hypertensive rat (SHR) support a role for leukotriene B₄ (LTB₄ ), a potent chemoattractant involved in the inflammatory response, but its mode of action is poorly understood. In the SHR, we observed an increase in T cells and macrophages in the brainstem; in addition, gene expression profiling data showed that LTB₄ production, degradation and downstream signalling in the brainstem of the SHR are dynamically regulated during hypertension. When LTB₄ receptor 1 (BLT1) receptors were blocked with CP-105,696, arterial pressure was reduced in the SHR compared to the normotensive control and this reduction was associated with a significant decrease in systolic blood pressure (BP) indicators. These data provide new evidence for the role of LTB₄ as an important neuro-immune pathway in the development of hypertension and therefore may serve as a novel therapeutic target for the treatment of neurogenic hypertension.

Abstract: Accumulating evidence indicates an association between hypertension and chronic systemic inflammation in both human hypertension and experimental animal models. Previous studies in the spontaneously hypertensive rat (SHR) support a role for leukotriene B₄ (LTB₄ ), a potent chemoattractant involved in the inflammatory response. However, the mechanism for LTB₄ -mediated inflammation in hypertension is poorly understood. Here we report in the SHR, increased brainstem infiltration of T cells and macrophages plus gene expression profiling data showing that LTB₄ production, degradation and downstream signalling in the brainstem of the SHR are dynamically regulated during hypertension. Chronic blockade of the LTB₄ receptor 1 (BLT1) receptor with CP-105,696, reduced arterial pressure in the SHR compared to the normotensive control and this reduction was associated with a significant decrease in low and high frequency spectra of systolic blood pressure, and an increase in spontaneous baroreceptor reflex gain (sBRG). These data provide new evidence for the role of LTB₄ as an important neuro-immune pathway in the development of hypertension and therefore may serve as a novel therapeutic target for the treatment of neurogenic hypertension.

Figure 1. Dynamic changes in expression of LTB₄ related genes over time during the development of hypertension

A, summary of genes measured as they relate to arachidonic acid metabolism. Evaluation of six genes affecting LTB₄ production (B and C, left panel), degradation (C, right panel) and signalling receptors (D) with reference to housekeeping gene Eif4e and WKY onset time point. ^* P < 0.05, ^#strain difference significant, two‐factor ANOVA, Tukey's post hoc, P < 0.05. Of note for strain significant difference: AloxAP, P value = 0.076; Lta4h, P value = 0.077. Und, undetermined expression, n = 3–4 per gene.

Figure 2. Increased lymphocyte brainstem infiltrates and increased expression circulating CD4⁺BLTR1 cells in the SHR

A, Gating Strategy for FACS Analysis B, percentage total CD45⁺ macrophages (HIS36) in the brainstem of SHR and Wistar rats C, representative flow cytometry cell scatter plot D, percentage total infiltrating CD45⁺CD3⁺ in the brainstem of SHR and Wistar E, representative flow cytometry cell scatter plot F, increased percentage of circulating lymphocytes expressing the LTB₄ receptor BLTR1 G, and corresponding representative flow cytometry cell scatter plot.

Figure 3. Increased circulating levels of CD11b⁺ cells in the SHR are reduced with CP‐105,696

Percentage total circulating CD11b⁺ cells in SHR and Wistar groups at baseline and following 5 days of CP‐105,696 (A), representative flow cytometry contour plot showing reduced circulating CD11b⁺ following CP‐105,696 (B), percentage total circulating CD44⁺ leukocytes before and after CP‐105‐696 (C) in SHR and Wistar groups; n = 5–6 per group; Data are presented as means ± SEM, ^* P < 0.05, ^# P < 0.05, baseline Wistar vs. baseline SHR.

Figure 4. Chronic administration of CP‐105,696 reduces blood pressure and heart rate in the SHR

Decreased change in systolic blood pressure (SBP) and heart rate from baseline in the SHR‐CP‐105,696 group with no change in SHR vehicle and Wistar CP‐105,696 and vehicle (A and C). Peak change in SBP and heart rate in SBP SHR‐CP‐105,696 (n = 5), SHR‐vehicle (n = 5) and WKY‐CP‐105,696 (n = 5) groups are shown in panels B and D. n = 5–6 per group; Data are presented as means ± SEM, ^* P < 0.05 overall main effect; post hoc analysis ^# P < 0.05 SHR‐vehicle vs. SHR‐CP‐105,696.

Figure 5. Improved autonomic function in the SHR following BLT1 receptor antagonism with CP‐105696

Increased change in spontaneous baroreceptor gain (sBRG) in the light phase of SHR‐CP‐105,696 vs. SHR‐vehicle groups (A), and peak changes in sBRG between groups (B), Decreased LF(SBP) and HF(SBP) in the light phase of the SHR‐CP‐105,696 and Wistar‐CP‐105,696 and ‐vehicle groups (C and E), and peak changes in LF(SBP) and HF(SBP) (D and F). n = 5–6 per group; Data are presented as means ± SEM, ^* P < 0.05; Wistar vs. SHR‐vehicle.