Reciprocal regulation of cholesterol excretion in apolipoprotein E-null mice by angiotensin II type 1 and type 2 receptor deficiency

AIMS

The effects of AT(1) and AT(2) receptor deficiency on the intake and excretion of cholesterol were examined using atherosclerotic apolipoprotein E-null (ApoEKO) mice.

MAIN METHODS

ApoEKO, AT(1)a/ApoEKO and AT(2)/ApoEKO mice received a high-cholesterol diet (HCD: 1.25% cholesterol) for 10 days before sampling.

KEY FINDINGS

Plasma total cholesterol level was lower in AT(1)a/ApoEKO mice and higher in AT(2)/ApoEKO mice than in ApoEKO mice with a high cholesterol intake. In these mice, cholesterol content in feces was higher in AT(1)a/ApoEKO mice and lower in AT(2)/ApoEKO mice than in ApoEKO mice. Moreover, cholesterol content in bile tended to be higher in AT(1)a/ApoEKO mice and lower in AT(2)/ApoEKO mice than in ApoEKO mice, while a significant difference was observed only between AT(1)a/ApoEKO and AT(2)/ApoEKO mice. Cholesterol content and expression of HMG-CoA reductase and LDL receptor in liver were not different among the groups. Similar but weaker changes were also observed with a normal standard diet. Treatment with an AT(1) receptor blocker, irbesartan, increased cholesterol content in bile and tended to increase cholesterol excretion into feces in ApoEKO mice with HCD.

SIGNIFICANCE

These results suggest that AT(1) and AT(2) receptor stimulation was involved in the regulation of cholesterol excretion into bile and feces, and that the regulation acted reciprocally in a cholesterol overload condition with HCD.

Web-based standard-regimen selection (SRS) and cancer-care registry (CCR) systems of a nationwide network in Japan: An attempt to improve breast cancer treatment

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Background: Tokushukai group has a nation-wide network of 67 affiliated hospitals, and has started an “oncology project” to improve the quality of cancer care using web-based SRS and CCR systems. Methods: Every institution has been introduced the same electric-medical-record (EMR) to share the unified code to order chemotherapy regimens, and patient data could be collected on a database in the central office. 141 recommended regimens for 15 types of solid tumor have been approved in the cancer committee consisting of working-group and program-evaluation members. In breast cancer, 31 recommended regimens (7 for adjuvant and 24 for metastatic settings) were selected from the NCCN guidelines and approved by the committee. Not only recommended but also non-recommended regimens have their own specific codes in EMR, and the patterns of care in the selection of chemotherapy regimen were examined. Results: In 2011, 21 of 67 hospitals utilized these systems. 71.8% of 2,676 patients with cancer including 753 with colorectal, 317 with breast, 273 with gastric, 144 with non-small cell lung, 123 with pancreatic, and 73 patients with esophageal cancer had received 97 types of recommended therapies (11,022 cycles). In terms of breast cancer, 86% of 388 patients had been treated with recommended regimens (1,994 cycles). Among 71 patients received non-recommend therapies, only 6 patients (1.5%) had been treated with three regimens which were not regarded as standard regimens. Conclusions: The introduction of web-based SRS and CCR systems in a large medical group could facilitate standard chemotherapy regimen by an accurate examination of current treatment patterns.

Possible involvement of angiotensin-converting enzyme 2 and Mas activation in inhibitory effects of angiotensin II Type 1 receptor blockade on vascular remodeling

We explored the roles of angiotensin-converting enzyme 2 (ACE2), angiotensin-(1-7), and Mas activation in angiotensin II type 1 receptor blockade-mediated attenuation of vascular remodeling. Vascular injury was induced by polyethylene-cuff placement around the mouse femoral artery. After cuff placement, the mRNA level of both ACE2 and Mas was markedly decreased in wild-type mice, whereas ACE mRNA was not changed. Immunostaining of ACE2 and Mas was observed mainly in the media and was reduced in the injured artery. Administration of angiotensin-(1-7) decreased neointimal formation after cuff placement, whereas administration of [D-Ala(7)] angiotensin-(1-7), a Mas antagonist, increased it. Consistent with these results, we also demonstrated that neointimal formation induced by cuff placement was further increased in ACE2 knockout mice. In angiotensin II type 1a receptor knockout mice, mRNA expression and immunostaining of ACE2 and Mas in the injured artery were greater, with less neointimal formation than in wild-type mice. Increased ACE2 expression in the injured artery was also observed by treatment of wild-type mice with an angiotensin II type 1 receptor blocker, olmesartan. These results suggested that activation of the ACE2-angiotensin-(1-7)-Mas axis is at least partly involved in the beneficial effects of angiotensin II type 1 receptor blockade on vascular remodeling.

Deletion of the Angiotensin II Type 1a Receptor Prevents Atherosclerotic Plaque Rupture in Apolipoprotein E −/− Mice

Objective—

Angiotensin II is involved in the genesis of atherosclerosis. As the role of the angiotensin II type 1a (AT 1a ) receptor in plaque rupture is poorly understood, we assessed the hypothesis that the AT 1a receptor contributes to atherosclerotic plaque rupture.

Methods and Results—

Atherosclerotic plaque rupture was induced by carotid artery ligation for 4 weeks followed by polyethylene cuff placement around the carotid in apolipoprotein E (ApoE) −/− and ApoE −/− AT 1a −/− mice. The incidence of plaque rupture at 4 days after cuff placement was 72% in ApoE −/− mice compared with 24% in ApoE −/− AT 1a −/− mice ( P <0.01). Lipid accumulation, macrophage infiltration, expression of inflammatory cytokines, nicotinamide adenine dinucleotide phosphate-oxidase activity, and matrix metalloproteinase-9 activity in atherosclerotic plaque were markedly attenuated in ApoE −/− AT 1a −/− compared with ApoE −/− mice. Oxidized low-density lipoprotein inhibited macrophage migration in ApoE −/− macrophages. In contrast, oxidized low-density lipoprotein-induced macrophage trapping was abolished in ApoE −/− AT 1a −/− macrophages, and this was associated with decreased CD36 expression and focal adhesion kinase activity.

Conclusions—

Conclusion—

These results suggest that blocking the AT 1 receptor may reduce atherosclerotic plaque rupture and that AT 1a receptor-mediated macrophage trapping, inflammation, oxidative stress, and matrix metalloproteinase activation may play crucial roles in plaque vulnerability.

Abstract 528: Bone Marrow Angiotensin AT2 Receptor Deficiency Aggravates Atherosclerosis by Eliminating Macrophage Liver X Receptor-Mediated Antiatherogenic Actions

[BACKGROUND] The angiotensin II (Ang II) type 2 (AT2) receptor is crucially involved in atherogenesis; however, bone marrow (BM) AT2-mediated anti-atherogenic action remains undefined.

[METHOD AND RESULT] We generated BM chimera apoE-deficient (apoE-/-) mice whose BM cells were repopulated with AT2-deficient (Agtr2-/-) or wild type (Agtr2+/+) cells. Eight weeks after BM transplantation, all mice were fed a western diet for two months. Atherosclerotic lesion area was significantly increased in apoE-/-/BM-Agtr2 -/- mice compared with apoE-/-/BM-Agtr2+/+ mice (51%, P<0.05), accompanied by the enhanced accumulation of MOMA-2 positive cells (P<0.05). Hemodynamic data and lipid profile did not differ between the two groups. We first examined the expression levels of macrophage liver X receptors (LXRα and β), which have been reported to exert anti-atherogenic actions by reducing pro-inflammatory response and promoting cholesterol efflux and macrophage emigration. The mRNA expression of LXRβ, but not LXRα, was significantly decreased by 21% in Agtr2 -/- thioglycollate-induced peritoneal macrophages (TGPM) compared with Agtr2+/+ TGPM (P<0.01). Inversely, LXRβ mRNA expression was markedly increased by co-treatment of angiotensin II (100nM) with AT1 receptor blocker, Olmesartan (10μM) (47%, p<0.01). Treatment with LXR agonist (GW3965) significantly attenuated LPS-induced mRNA expressions of TNF-α and IL-1β in Agtr2+/+ TGPM (35%, 46%, respectively, P<0.01), however, anti-inflammatory effect of LXR agonist was markedly reduced in Agtr2 -/- TGPM (p<0.05). Furthermore, the expression levels of ATP-binding cassette transporter ABCA1 and CCR7, essentially implicated in cholesterol efflux and macrophage emigration, were much lower in Agtr2 -/- TGPM than Agtr2+/+ TGPM (34%, 53%, p<0.01). Flow cytometric analysis also showed a significantly lower expression of CCR7 in Agtr2 -/- TGPM (24%, p<0.05).

[CONCLUSION] Our findings demonstrate that BM-AT2 deficiency aggravates atherosclerosis, at least in part, by eliminating anti-atherogenic properties elicited by macrophage LXR activation, suggesting that AT2-mediated regulation of macrophage LXR activity could be a novel therapeutic target for the prevention of atherosclerosis.

Renin inhibitors inhibited the activity of recombinant human renin but not activity in healthy human plasma

BACKGROUND

Activity of renin substrate cleavage (renin-like activity) was measured in vitro in plasma samples obtained from healthy human volunteers.

METHODS

Renin-like activity was determined using FRET (Fluorescence Resonance Energy Transfer) human renin substrate. Recombinant human renin and human plasma showed dose-dependent cleavage activity of FRET human renin substrate.

RESULTS

Activity of recombinant human renin was completely inhibited by either a peptidergic or a non-peptidergic renin inhibitor. However, renin-like activity in human plasma was not inhibited by these renin inhibitors. In a mixture of recombinant renin and human plasma, renin inhibitors inhibited only that part of the activity caused by recombinant renin, while the activity in plasma still remained. Human plasma did not show cleavage activity of rat FRET renin substrate. Native human prorenin showed cleavage activity of human renin substrate. This activety was also completely inhibited by renin inhibitors. Immunoprecipitation with anti-renin or anti-prorenin antibodies did not reduce the activity in human plasma. Renin-like activity in human plasma was abolished by degeneration of protein when sample was heated to 95 degrees C. Activity of both recombinant renin and human plasma was significantly inhibited by a protease inhibitor cocktail.

CONCLUSIONS

These results suggest that the activity of renin substrate cleavage in human plasma is not mainly caused by the renin or prorenin molecule, but probably by other proteases.

Temporary treatment with AT1 receptor blocker, valsartan, from early stage of hypertension prevented vascular remodeling

BACKGROUND

The present study examined the inhibitory action of temporary treatment with an angiotensin type 1 (AT(1)) receptor blocker (ARB) on vascular remodeling using hypertensive mice with overexpression of the human renin (hRN) and angiotensinogen (hANG) genes.

METHODS

hRN/hANG transgenic mice (hRN/hANG-Tg) were treated with an ARB, valsartan, from 4 weeks of age. In some mice, valsartan treatment was stopped at 8 weeks of age (temporary treatment). Inflammatory vascular injury was induced by polyethylene-cuff placement around the femoral artery at the age of 10 weeks.

RESULTS

Compared with wild-type (WT) mice, hRN/hANG-Tg showed higher blood pressure (BP) and enhancement of oxidative stress and medial thickening even before cuff placement. Inflammatory vascular remodeling and oxidative stress after cuff placement were further enhanced in hRN/hANG-Tg. Temporary treatment with valsartan continuously lowered BP even after cessation of administration, and inhibited these changes. In contrast, administration of hydralazine lowered BP to a similar level to that with valsartan, but did not inhibit medial thickening and inflammatory vascular remodeling. In contrast to the valsartan treatment, BP immediately increased to the untreated level after cessation of hydralazine.

CONCLUSIONS

These results indicate that temporary ARB treatment leads to prolonged effect of BP lowering and prevents vascular remodeling in hypertensive mice induced by activation of the human renin-angiotensin system. The inhibitory action of valsartan is not due to the BP lowering but is at least in part due to a decrease in oxidative stress and inflammation.

Nifedipine, a calcium-channel blocker, attenuated glucose intolerance and white adipose tissue dysfunction in type 2 diabetic KK-A(y) mice

BACKGROUND

To explore the metabolic actions of nifedipine on diabetes, we examined glucose intolerance and white adipose tissue changes in type 2 diabetic KK-A(y) mice.

METHODS

Male KK-A(y) mice were treated with nifedipine (1.5 mg/kg/day in lab chow) for 5 weeks, which did not affect blood pressure or feeding of KK-A(y) mice.

RESULTS

After treatment with nifedipine, body weight tended to decrease and the weight of white adipose tissue was reduced. Without food restriction, nifedipine decreased plasma insulin level, while plasma glucose level tended to decrease. In oral glucose tolerance test, nifedipine suppressed the increase in glucose level after a glucose load without affecting plasma insulin concentration. Nifedipine also improved the result of insulin tolerance test. In white adipose tissue, nifedipine increased adipocyte number and the expression of peroxisome proliferator-activated receptor-γ (PPARγ) and adipocyte fatty acid-binding protein related to adipocyte differentiation. In addition, expression of adiponectin, insulin receptor, insulin receptor substrate-1, and glucose transporter type-4 was also increased by nifedipine. Nifedipine also increased the expression of NO synthase in white adipose tissue. Nifedipine did not affect expression of angiotensin II type 1 (AT₁) and type 2 (AT₂) receptors in white adipose tissue. Such changes in white adipose tissue were apparent in retroperitoneal adipose tissue. Nifedipine did not change the expression of angiotensin receptors, renin receptor, and angiotensinogen in white adipose tissue. Moreover, nifedipine attenuated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and increased superoxide dismutase (SOD) activity in white adipose tissue.

CONCLUSION

These results suggest that nifedipine can enhance insulin sensitivity and reduce white adipose tissue, possibly related to stimulation of adipocyte differentiation.

Bone Marrow AT 1 Augments Neointima Formation by Promoting Mobilization of Smooth Muscle Progenitors via Platelet-Derived SDF-1α

Objectives— Bone marrow (BM)-derived endothelial progenitor cells (EPCs) and vascular smooth muscle progenitor cells (VPCs) contribute to neointima formation, whereas the angiotensin II (Ang II) type 1 receptor (AT 1 )-mediated action on BM-derived progenitors remains undefined.

Methods and Results— A wire-induced vascular injury was performed in the femoral artery of BM-chimeric mice whose BM was repopulated with AT 1 -deficient (BM-Agtr1 −/− ) or wild-type (BM-Agtr1 +/+ ) cells. Neointima formation was profoundly reduced by 38% in BM-Agtr1 −/− mice. Although the number of circulating EPCs (Sca-1 + Flk-1 + ) and extent of reendothelialization did not differ between the 2 groups, the numbers of both circulating VPCs (c-Kit − Sca-1 + Lin − ) and tissue VPCs (Sca-1 + CD31 − ) incorporated into neointima were markedly decreased in BM-Agtr1 −/− mice. The accumulation of aggregated platelets and their content of stromal cell–derived factor-1α (SDF-1α) were significantly reduced in BM-Agtr1 −/− mice, accompanied by a decrease in the serum level of SDF-1α. Thrombin-induced platelets aggregation was dose-dependently inhibited (45% at 0.1 IU/mL, P <0.05) in Agtr1 −/− platelets compared with Agtr1 +/+ platelets, accompanied by the reduced expression and release of SDF-1α.

Conclusions— The BM-AT 1 receptor promotes neointima formation by regulating the mobilization and homing of BM-derived VPCs in a platelet-derived SDF-1α–dependent manner without affecting EPC-mediated reendothelialization.

The angiotensin II type 2 receptor in the brain

Recent clinical studies indicate that blockade of the renin-angiotensin system is important to prevent stroke, and accumulating results of basic research also indicate the possible involvement of the central renin-angiotensin system in ischaemic brain damage and cognition. When the angiotensin II type 1 receptor is blocked by an angiotensin type 1 receptor blocker, unbound angiotensin II acts preferentially on the angiotensin II type 2 (AT(2)) receptor. These results suggest the pathophysiological importance of the AT(2) receptor in the clinical use of angiotensin type 1 receptor blockers, which are widely used in patients with hypertension with the expectation of a decrease in the onset of cardiovascular and cerebrovascular disease. We review here the possible roles of AT(2) receptor activation in the brain, focusing on ischaemic stroke, cognitive function and neurogenesis, and potential effects of specific AT(2) receptor agonists.

Cognitive Deficit in Amyloid-β–Injected Mice Was Improved by Pretreatment With a Low Dose of Telmisartan Partly Because of Peroxisome Proliferator-Activated Receptor-γ Activation

The pathological hallmark of Alzheimer disease is deposition of amyloid-β protein (Aβ) in the brain. Telmisartan is a unique angiotensin II receptor blocker with peroxisome proliferator-activated receptor-γ (PPAR-γ)–stimulating activity. Activation of PPAR-γ is expected to prevent inflammation and Aβ accumulation in the brain. We investigated the possible preventive effect of telmisartan on cognitive decline in an Alzheimer disease mouse model via PPAR-γ activation. Here, male ddY mice underwent ICV injection of Aβ 1-40. Cognitive function was evaluated by the Morris water maze test. A low dose of telmisartan (0.35 mg/kg per day) was administered in drinking water with or without GW9662, a PPAR-γ antagonist. Cerebral blood flow was evaluated by laser speckle flowmetry. Inflammatory cytokine levels were measured by quantitative RT-PCR. Aβ 1-40 ICV injection significantly impaired cognitive function. Pretreatment with telmisartan improved this cognitive decline to a similar level to that in control mice. Cotreatment with GW9662, a PPAR-γ antagonist, attenuated this telmisartan-mediated improvement of cognition. Treatment with telmisartan enhanced cerebral blood flow and attenuated the Aβ-induced increase in expression of cytokines, such as tumor necrosis factor-α and inducible NO synthase in the brain. Interestingly, coadministration of GW9662 cancelled these beneficial effects of telmisartan. Aβ 1-40 concentration in the brain was significantly decreased by treatment with telmisartan, whereas administration of GW9662 attenuated the decrease in telmisartan-mediated Aβ 1-40 concentration. Taken together, our findings suggest that even a low dose of telmisartan had a preventive effect on cognitive decline in an Alzheimer disease mouse model, partly because of PPAR-γ activation.

Role of Angiotensin II Receptor Subtypes in Conjunctival Wound Healing

PURPOSE

To investigate the role of angiotensin II (Ang II) receptor subtypes in subconjunctival injury.

METHODS

A wound-healing model was developed by subconjunctival blunt dissection in male wild-type, AT1a receptor-deficient (AT1aKO) and AT2 receptor-deficient (AT2KO) mice. Collagen deposition and cell infiltration were evaluated histologically. Expression of collagen, matrix metalloproteinase (MMP), and tissue inhibitor of metalloproteinase-1 (TIMP-1) were determined by real-time PCR.

RESULTS

Subconjunctival injury increased the infiltration of inflammatory cells, collagen deposition in the subconjunctival space, and the expression of collagen type I and type III, TIMP-1 and MMP2. In AT1aKO mice, collagen deposition, cell infiltration, and expression of collagen and TIMP-1 were inhibited, but MMP2 expression was enhanced. In contrast, in AT2KO mice, the increase in collagen deposition, cell infiltration, and expression of collagen and TIMP-1 were further enhanced.

CONCLUSIONS

These results indicate that AT1a and AT2 receptor stimulation may in addition to other mechanisms be antagonistically involved in the wound-healing process after subconjunctival injury.