Differential restoration of functional hyperemia by antihypertensive drug classes in hypertension-related cerebral small vessel disease

Abstract

Dementia resulting from small vessel diseases (SVDs) of the brain is an emerging epidemic for which there is no treatment. Hypertension is the major risk factor for SVDs, but how hypertension damages the brain microcirculation is unclear. Here, we show that chronic hypertension in a mouse model progressively disrupts on-demand delivery of blood to metabolically active areas of the brain (functional hyperemia) through diminished activity of the capillary endothelial cell inward-rectifier potassium channel, Kir2.1. Despite similar efficacy in reducing blood pressure, amlodipine, a voltage-dependent calcium-channel blocker, prevented hypertension-related damage to functional hyperemia whereas losartan, an angiotensin II type 1 receptor blocker, did not. We attribute this drug class effect to losartan-induced aldosterone breakthrough, a phenomenon triggered by pharmacological interruption of the renin-angiotensin pathway leading to elevated plasma aldosterone levels. This hypothesis is supported by the finding that combining losartan with the aldosterone receptor antagonist eplerenone prevented the hypertension-related decline in functional hyperemia. Collectively, these data suggest Kir2.1 as a possible therapeutic target in vascular dementia and indicate that concurrent mineralocorticoid aldosterone receptor blockade may aid in protecting against late-life cognitive decline in hypertensive patients treated with angiotensin II type 1 receptor blockers.

Keywords: Hypertension; Microcirculation; Mouse models; Neuroscience; Vascular Biology.

Figure 1. Hypertension-related decline in functional hyperemia is prevented by amlodipine but not losartan.

(A) Experimental timelines. (B) Mean arterial pressure (MAP) in anesthetized male BPN and BPH mice at 1, 4, and 8 months of age, with and without treatment with amlodipine (BPH+A, ~10 mg/kg/d) or losartan (BPH+L, ~100 mg/kg/d) starting at 3 months of age. Data are presented as mean ± SEM (n = 5–9 mice/group). ^††P < 0.01 vs. BPN at corresponding ages; *P < 0.05, **P < 0.01 between groups; 1-way ANOVA followed by Tukey’s test. (C) Experimental scheme for measurement of whisker stimulation–induced functional hyperemia using laser-Doppler flowmetry (LDF). (D) Functional hyperemic responses, shown as CBF increases during whisker stimulation, in male BPN and BPH mice at 1, 4, and 8 months old, and 8-month-old BPH mice with antihypertensive treatment. (E) Age-dependent progression of functional hyperemia deficits in male BPH mice, with and without antihypertensive treatment. Data are presented as mean ± SEM (n = 5–9 mice/group). ^††P < 0.01 vs. BPN at corresponding ages; *P < 0.05 between groups; 1-way ANOVA followed by Tukey’s test. (F) Representative traces showing whisker stimulation–induced functional hyperemia before and after cortical superfusion of Ba²⁺. aCSF, artificial cerebrospinal fluid. (G) Summary data showing the Ba²⁺-sensitive component of whisker stimulation–induced functional hyperemia in male BPN and BPH mice, with and without antihypertensive treatment. Data are presented as mean ± SEM (n = 5–9 mice/group). ^††P < 0.01 vs. BPN at corresponding ages; **P < 0.01 between groups; 1-way ANOVA followed by Tukey’s test.

Figure 2. Capillary-to-arteriolar vasodilatory signaling is crippled in hypertension.

(A) Experimental scheme showing focal stimulation of a capillary in the ex vivo CaPA preparation by pressure ejection of a 10 mM K⁺ artificial cerebrospinal fluid solution via an approximately 5‑μm-tip glass micropipette and subsequent recording of dilation of the upstream parenchymal arteriole (green box). (B) Representative traces of upstream arteriolar dilatory response to 10 mM K⁺ stimulation of capillaries in CaPA preparations from 8-month-old BPN mice, BPH mice, and BPH mice treated with amlodipine (BPH+A) or losartan (BPH+L). (C) Age-dependent attenuation of arteriolar dilatory response to capillary stimulation with 10 mM K⁺ in BPH mice, with and without antihypertensive treatment. Data are presented as mean ± SEM (n = 4–9 mice/group). ^†P < 0.05, ^††P < 0.01 vs. BPN at corresponding ages; **P < 0.01 between groups; 1-way ANOVA followed by Tukey’s test. (D) Experimental scheme showing arteriolar dilatory response to application of 10 mM K⁺ directly onto the arteriole. (E) Representative traces of arteriolar dilation induced by application of 10 mM K⁺ onto the arteriole segment in CaPA preparations from 8-month-old BPN and BPH mice. (F) Hypertension-induced decrease in arteriolar dilatory response to direct stimulation of arterioles with 10 mM K⁺, with and without antihypertensive treatment. Data are presented as mean ± SEM (n = 4–9 mice/group). ^††P < 0.01 vs. BPN at corresponding ages by 1-way ANOVA followed by Tukey’s test.

Figure 3. Capillary EC Kir2.1 channel downregulation underlies deficits in capillary-to-arteriolar signaling, which is damaged by aldosterone.

(A) Patch-clamp electrophysiology in freshly isolated capillary ECs. Scale bar: 10 μm. (B) Representative traces of Kir2.1 currents in capillary ECs from 8-month-old BPN (black) and BPH (green) mice. (C) Summary data showing inward Kir2.1 currents (at –140 mV) in capillary ECs from 8-month-old BPN mice, BPH mice, and BPH mice treated with antihypertensives. Data are presented as mean ± SEM (n = 11–21 cells/group). *P < 0.05 between groups by 1-way ANOVA followed by Dunnett’s multiple comparisons test. (D) Plasma aldosterone concentrations in 8-month-old mice. Data are presented as mean ± SEM (n = 5–13 mice/group). *P < 0.05, **P < 0.01, ***P < 0.001 between groups by 1-way ANOVA followed by Tukey’s test. (E) Correlation between plasma aldosterone levels and whisker stimulation–induced increases in local CBF (n = 5–13 mice/group). (F) Representative traces showing whisker stimulation–induced CBF responses in mice treated with losartan (BPH+L) compared with those in mice treated with losartan and eplerenone (BPH+LE). (G and H) Restoration of total (G) and Ba²⁺-sensitive (H) functional hyperemia in BPH mice by combined treatment with losartan and eplerenone (BPH+LE), but not by treatment with losartan alone (BPH+L). Data are presented as mean ± SEM (n = 5–6 mice/group). **P < 0.01 between groups by unpaired t test.