Cerebral microvascular inflammation in DOCA salt-induced hypertension: role of angiotensin II and mitochondrial superoxide

Abstract

Angiotensin II-mediated hypertension (HTN) is accompanied by a pro-inflammatory and pro-thrombotic state in the cerebral microvasculature. Whether comparable phenotypic changes are elicited in other models of HTN remains unclear. Using wild-type mice with deoxycorticosterone acetate (DOCA) salt-induced HTN and intravital microscopy, we observed significant increases in the adhesion of both leukocytes and platelets in cerebral venules, compared with uninephrectomized control mice, without an accompanying increase in blood-brain barrier permeability. The cell-cell interactions in hypertensive mice were more pronounced after ischemic stroke, but no difference in infarct size was detected. The blood cell recruitment was largely prevented in the following groups of DOCA salt mice: losartan (angiotensin II AT1 receptor blocker) treated, AT1 receptor knockout mice, tempol (a membrane-permeable oxygen radical scavenger) treated, and mito-TEMPO (a mitochondria-targeted antioxidant) treated. A similar pattern of protection was noted in mice subjected to ischemic stroke. The blunted cell recruitment responses were not accompanied by reductions in blood pressure (BP). These findings implicate mitochondria-derived oxygen radicals and angiotensin II in the cerebral inflammation associated with DOCA salt HTN and suggests that BP per se is not a critical determinant of the phenotypic changes that accompany HTN, even after ischemic stroke.

Figure 1

Systolic blood pressures measured in control (Uni, n=9), deoxycorticosterone acetate (DOCA) salt (n=11), DOCA salt mice treated with losartan (n=12), AT1R knockout (−/−) mice+DOCA salt (n=8), DOCA salt mice treated with tempol (n=12), and DOCA salt mice treated with mito-TEMPO (n=6). ^**P<0.01 and ^***P<0.001 relative to the control group.

Figure 2

Effects of losartan, tempol, mito-TEMPO, and AT1R deficiency on the leukocyte (A) and platelet (B) adhesion responses to deoxycorticosterone acetate (DOCA) salt hypertension. Uninephrectomized (Uni) controls (n=8), DOCA salt (n=9), DOCA salt+losartan (n=8), AT1R knockout (−/−) mice+DOCA salt (n=7), DOCA salt+tempol (n=7), and DOCA salt+mito-TEMPO (n=6) were tested. ^*P<0.05 and ^***P<0.001 versus Uni, ^#P<0.05, ^##P<0.01 and ^###P<0.001 versus DOCA salt.

Figure 3

Effects of deoxycorticosterone acetate (DOCA) salt hypertension on blood–brain barrier (BBB) permeability (Evans blue (EB) extravasation) (A) and brain water content (B). Uninephrectomized (Uni) controls (n=5) and DOCA salt (n=5). No significant differences were noted between groups.

Figure 4

Effects of losartan and mito-TEMPO on the leukocyte (A) and platelet (B) adhesion responses during deoxycorticosterone acetate (DOCA) salt hypertension and after 20 minutes of cerebral ischemia and 4 hours reperfusion (I/R). In the sham group, the middle cerebral artery was visualized but not occluded. The following groups were tested: wild type, sham (WT) (n=10), wild type, I/R (WT) (n=7), DOCA salt, I/R (n=5), DOCA salt+losartan, I/R (n=4), and DOCA salt+mito-TEMPO, I/R (n=4). ^*P<0.05 and ^***P<0.001 versus WT, sham, ^#P<0.05 and ^###P<0.001 versus WT, I/R, ^&P<0.05 and ^&&P<0.01 versus DOCA salt, I/R.

Figure 5

Representative picture (A) and graph (B) of the infarct area obtained in wild-type and deoxycorticosterone acetate (DOCA) salt hypertensive mice exposed to 20 minutes ischemia and 4 hours reperfusion. Wild type (WT) (n=7) and DOCA salt (n=6) were used. No significant differences were noted between groups.