Myeloid cell ACE shapes cellular metabolism and function in PCSK-9 induced atherosclerosis

The pathogenesis of atherosclerosis is defined by impaired lipid handling by macrophages which increases intracellular lipid accumulation. This dysregulation of macrophages triggers the accumulation of apoptotic cells and chronic inflammation which contributes to disease progression. We previously reported that mice with increased macrophage-specific angiotensin-converting enzyme, termed ACE10/10 mice, resist atherosclerosis in an adeno-associated virus-proprotein convertase subtilisin/kexin type 9 (AAV-PCSK9)-induced model. This is due to increased lipid metabolism by macrophages which contributes to plaque resolution. However, the importance of ACE in peripheral blood monocytes, which are the primary precursors of lesional-infiltrating macrophages, is still unknown in atherosclerosis. Here, we show that the ACE-mediated metabolic phenotype is already triggered in peripheral blood circulating monocytes and that this functional modification is directly transferred to differentiated macrophages in ACE10/10 mice. We found that Ly-6Clo monocytes were increased in atherosclerotic ACE10/10 mice. The monocytes isolated from atherosclerotic ACE10/10 mice showed enhanced lipid metabolism, elevated mitochondrial activity, and increased adenosine triphosphate (ATP) levels which implies that ACE overexpression is already altered in atherosclerosis. Furthermore, we observed increased oxygen consumption (VO2), respiratory exchange ratio (RER), and spontaneous physical activity in ACE10/10 mice compared to WT mice in atherosclerotic conditions, indicating enhanced systemic energy consumption. Thus, ACE overexpression in myeloid lineage cells modifies the metabolic function of peripheral blood circulating monocytes which differentiate to macrophages and protect against atherosclerotic lesion progression due to better lipid metabolism.

Macrophage angiotensin-converting enzyme reduces atherosclerosis by increasing peroxisome proliferator-activated receptor α and fundamentally changing lipid metabolism

AIMS

The metabolic failure of macrophages to adequately process lipid is central to the aetiology of atherosclerosis. Here, we examine the role of macrophage angiotensin-converting enzyme (ACE) in a mouse model of PCSK9-induced atherosclerosis.

METHODS AND RESULTS

Atherosclerosis in mice was induced with AAV-PCSK9 and a high-fat diet. Animals with increased macrophage ACE (ACE 10/10 mice) have a marked reduction in atherosclerosis vs. WT mice. Macrophages from both the aorta and peritoneum of ACE 10/10 express increased PPARα and have a profoundly altered phenotype to process lipids characterized by higher levels of the surface scavenger receptor CD36, increased uptake of lipid, increased capacity to transport long chain fatty acids into mitochondria, higher oxidative metabolism and lipid β-oxidation as determined using 13C isotope tracing, increased cell ATP, increased capacity for efferocytosis, increased concentrations of the lipid transporters ABCA1 and ABCG1, and increased cholesterol efflux. These effects are mostly independent of angiotensin II. Human THP-1 cells, when modified to express more ACE, increase expression of PPARα, increase cell ATP and acetyl-CoA, and increase cell efferocytosis.

CONCLUSION

Increased macrophage ACE expression enhances macrophage lipid metabolism, cholesterol efflux, efferocytosis, and it reduces atherosclerosis. This has implications for the treatment of cardiovascular disease with angiotensin II receptor antagonists vs. ACE inhibitors.

Durable remission of thrombotic thrombocytopenic purpura in the setting of pembrolizumab therapy

BACKGROUND

There is a small but growing number of thrombotic thrombocytopenic purpura (TTP) cases attributed to immune checkpoint inhibitor therapy, with nivolumab and ipilimumab therapy being the most frequently described in the literature.

STUDY DESIGN AND METHODS

This report evaluates the course of a patient with a history of metastatic adenocarcinoma of the lung who developed TTP following treatment with the PD-1 inhibitor Pembrolizumab. The patient was treated with six sessions of therapeutic plasma exchange and appeared to be in remission. Exacerbation occurred 4 days later, and seven more sessions of plasma exchange were performed along with four total doses of Rituximab, and a steroid taper with monitoring of platelet counts and ADAMTS13 activity.

RESULTS

His platelet count recovered to a peak of 318,000 UL with an ADAMTS13 activity of 77% at the time of discharge. The patient has been following up regularly for outpatient testing with no TTP relapse as of the completion of this report.

DISCUSSION

This is one of a few cases of Pembrolizumab-associated TTP reported in the literature with successful complete remission following treatment. Plasma exchange in this setting may be an especially beneficial therapeutic intervention because of the removal of both the anti-ADAMTS13 antibody as well as the immune system upregulating anti-PDL1 monoclonal antibody with replacement of ADAMTS13 from donor plasma. Longer duration of plasma exchange and monitoring for normalization of ADAMTS13 levels in addition to platelet count before cessation of treatment may improve durable remission rates in this entity.

Tubular IL-1β Induces Salt Sensitivity in Diabetes by Activating Renal Macrophages

BACKGROUND

Chronic renal inflammation has been widely recognized as a major promoter of several forms of high blood pressure including salt-sensitive hypertension. In diabetes, IL (interleukin)-6 induces salt sensitivity through a dysregulation of the epithelial sodium channel. However, the origin of this inflammatory process and the molecular events that culminates with an abnormal regulation of epithelial sodium channel and salt sensitivity in diabetes are largely unknown.

METHODS

Both in vitro and in vivo approaches were used to investigate the molecular and cellular contributors to the renal inflammation associated with diabetic kidney disease and how these inflammatory components interact to develop salt sensitivity in db/db mice.

RESULTS

Thirty-four-week-old db/db mice display significantly higher levels of IL-1β in renal tubules compared with nondiabetic db/+ mice. Specific suppression of IL-1β in renal tubules prevented salt sensitivity in db/db mice. A primary culture of renal tubular epithelial cells from wild-type mice releases significant levels of IL-1β when exposed to a high glucose environment. Coculture of tubular epithelial cells and bone marrow-derived macrophages revealed that tubular epithelial cell-derived IL-1β promotes the polarization of macrophages towards a proinflammatory phenotype resulting in IL-6 secretion. To evaluate whether macrophages are the cellular target of IL-1β in vivo, diabetic db/db mice were transplanted with the bone marrow of IL-1R1 (IL-1 receptor type 1) knockout mice. db/db mice harboring an IL-1 receptor type 1 knockout bone marrow remained salt resistant, display lower renal inflammation and lower expression and activity of epithelial sodium channel compared with db/db transplanted with a wild-type bone marrow.

CONCLUSIONS

Renal tubular epithelial cell-derived IL-1β polarizes renal macrophages towards a proinflammatory phenotype that promotes salt sensitivity through the accumulation of renal IL-6. When tubular IL-1β synthesis is suppressed or in db/db mice in which immune cells lack the IL-1R1, macrophage polarization is blunted resulting in no salt-sensitive hypertension.

The non-cardiovascular actions of ACE

Angiotensin converting enzyme (ACE) is well known for its role producing the vasoconstrictor angiotensin II and ACE inhibitors are commonly used for treating hypertension and cardiovascular disease. However, ACE has many different substrates besides angiotensin I and plays a role in many different physiologic processes. Here, we discuss the role of ACE in the immune response. Several studies in mice indicate that increased expression of ACE by macrophages or neutrophils enhances the ability of these cells to respond to immune challenges such as infection, neoplasm, Alzheimer's disease, and atherosclerosis. Increased expression of ACE induces increased oxidative metabolism with an increase in cell content of ATP. In contrast, ACE inhibitors have the opposite effect, and in both humans and mice, administration of ACE inhibitors reduces the ability of neutrophils to kill bacteria. Understanding how ACE affects the immune response may provide a means to increase immunity in a variety of chronic conditions now not treated through immune manipulation.

RASAL3 Is a Putative RasGAP Modulating Inflammatory Response by Neutrophils

As first responder cells in host defense, neutrophils must be carefully regulated to prevent collateral tissue injury. However, the intracellular events that titrate the neutrophil’s response to inflammatory stimuli remain poorly understood. As a molecular switch, Ras activity is tightly regulated by Ras GTPase activating proteins (RasGAP) to maintain cellular active-inactive states. Here, we show that RASAL3, a RasGAP, is highly expressed in neutrophils and that its expression is upregulated by exogenous stimuli in neutrophils. RASAL3 deficiency triggers augmented neutrophil responses and enhanced immune activation in acute inflammatory conditions. Consequently, mice lacking RASAL3 (RASAL3-KO) demonstrate accelerated mortality in a septic shock model via induction of severe organ damage and hyperinflammatory response. The excessive neutrophilic hyperinflammation and increased mortality were recapitulated in a mouse model of sickle cell disease, which we found to have low neutrophil RASAL3 expression upon LPS activation. Thus, RASAL3 functions as a RasGAP that negatively regulates the cellular activity of neutrophils to modulate the inflammatory response. These results demonstrate that RASAL3 could serve as a therapeutic target to regulate excessive inflammation in sepsis and many inflammatory disease states.

Diagnosing heparin-induced thrombocytopenia in mechanical circulatory support device patients

BACKGROUND

Mechanical circulatory support device (MCSD) patients with positive heparin-induced thrombocytopenia (HIT) screening pose a unique challenge, as clinicians must make rapid decisions about their anticoagulation and whether they can safely undergo cardiopulmonary bypass. We identified screening practices at our institution and other institutions nationwide that differed from American Society of Hematology (ASH) guidelines. This discovery prompted a data review to confirm the applicability of guidelines to this unique population and to highlight complications of "gestalt" screening.

METHODS

Our study included MCSD patients with HIT testing from April 2014 to August 2020. We evaluated 510 PF4 IgG ELISA results.

RESULTS

HIT was confirmed in 4.2% of patients. There was an increased prevalence of HIT in patients with nondurable (5.3%) vs durable devices (2.9%) or those in the preimplantation setting (1.3%), however this difference was not statistically significant (p = 0.26). None of the patients with a low probability 4T Score had HIT. All patients with a high probability 4T Score and PF4 immunoassay OD >2.0 had HIT. False positive results occurred in 22% of assays ordered for patients with a low probability 4T Score. Twelve patients with a low probability 4T Score and a false positive immunoassay were switched to a direct thrombin inhibitor (DTI) while awaiting confirmatory results. Two patients experienced clinically significant bleeding after conversion to a DTI. An organ was refused in one patient with false positive HIT screening.

CONCLUSIONS

Our findings demonstrate that an opportunity exists to improve clinical outcomes by re-emphasizing the utility of established guidelines and highlighting their safe use in the MCSD patient population.

An ACE inhibitor reduces bactericidal activity of human neutrophils in vitro and impairs mouse neutrophil activity in vivo

Angiotensin-converting enzyme inhibitors (ACEIs) are used by millions of patients to treat hypertension, diabetic kidney disease, and heart failure. However, these patients are often at increased risk of infection. To evaluate the impact of ACEIs on immune responses to infection, we compared the effect of an ACEI versus an angiotensin receptor blocker (ARB) on neutrophil antibacterial activity. ACEI exposure reduced the ability of murine neutrophils to kill methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, and Klebsiella pneumoniae in vitro. In vivo, ACEI-treated mice infected with MRSA had increased bacteremia and tissue bacteria counts compared to mice treated with an ARB or with no drug. Similarly, ACEIs, but not ARBs, increased the incidence of MRSA-induced infective endocarditis in mice with aortic valve injury. Neutrophils from ACE knockout (KO) mice or mice treated with an ACEI produced less leukotriene B4 (LTB4) upon stimulation with MRSA or lipopolysaccharide, whereas neutrophils overexpressing ACE produced more LTB4 compared to wild-type neutrophils. As a result of reduced LTB4 production, ACE KO neutrophils showed decreased survival signaling and increased apoptosis. In contrast, neutrophils overexpressing ACE had an enhanced survival phenotype. Last, in a cohort of human volunteers receiving the ACEI ramipril for 1 week, ACEI administration reduced neutrophil superoxide and reactive oxygen species production and neutrophils isolated from volunteers during ramipril treatment had reduced bactericidal activity. Together, these data demonstrate that ACEI treatment, but not ARB treatment, can reduce the bacterial killing ability of neutrophils.

Potential Implications of a Type 1 Interferon Gene Signature on COVID-19 Severity and Chronic Inflammation in Sickle Cell Disease

At the onset of the corona virus disease 19 (COVID-19) pandemic, there were concerns that patients with sickle cell disease (SCD) might be especially vulnerable to severe sequelae of SARS-CoV-2 infection. While two reports support this conclusion, multiple studies have reported unexpectedly favorable outcomes in patients with SCD. However, mechanisms explaining these disparate conclusions are lacking. Here, we review recent studies indicating that the majority of patients with SCD express elevated levels of anti-viral type 1 interferons (IFNα/β) and interferon stimulated genes, independent of COVID-19, during their baseline state of health. We also present our data from the pre-COVID-19 era, illustrating elevated expression of a well-characterized interferon stimulated gene in a cohort of patients with SCD, compared to race-matched controls. These type 1 interferons and interferon stimulated genes have the potential to contribute to the variable progression of COVID-19 and other viral infections in patients with SCD. While the majority of evidence supports a protective role, the role of IFNα/β in COVID-19 severity in the general population remains an area of current investigation. We conclude that type 1 interferon responses in patients with SCD may contribute to the variable COVID-19 responses reported in prior studies. Additional studies investigating the mechanisms underlying IFNα/β production and other clinical consequences of IFNα/β-mediated inflammation in SCD disease are warranted.

Novel roles of the renal angiotensin-converting enzyme

The observation that all components of the renin angiotensin system (RAS) are expressed in the kidney and the fact that intratubular angiotensin (Ang) II levels greatly exceed the plasma concentration suggest that the synthesis of renal Ang II occurs independently of the circulating RAS. One of the main components of this so-called intrarenal RAS is angiotensin-converting enzyme (ACE). Although the role of ACE in renal disease is demonstrated by the therapeutic effectiveness of ACE inhibitors in treating several conditions, the exact contribution of intrarenal versus systemic ACE in renal disease remains unknown. Using genetically modified mouse models, our group demonstrated that renal ACE plays a key role in the development of several forms of hypertension. Specifically, although ACE is expressed in different cell types within the kidney, its expression in renal proximal tubular cells is essential for the development of high blood pressure. Besides hypertension, ACE is involved in several other renal diseases such as diabetic kidney disease, or acute kidney injury even when blood pressure is normal. In addition, studies suggest that ACE might mediate at least part of its effect through mechanisms that are independent of the Ang I conversion into Ang II and involve other substrates such as N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), Ang-(1-7), and bradykinin, among others. In this review, we summarize the recent advances in understanding the contribution of intrarenal ACE to different pathological conditions and provide insight into the many roles of ACE besides the well-known synthesis of Ang II.

Renal Inflammation Induces Salt Sensitivity in Male db/db Mice through Dysregulation of ENaC

BACKGROUND

Hypertension is considered a major risk factor for the progression of diabetic kidney disease. Type 2 diabetes is associated with increased renal sodium reabsorption and salt-sensitive hypertension. Clinical studies show that men have higher risk than premenopausal women for the development of diabetic kidney disease. However, the renal mechanisms that predispose to salt sensitivity during diabetes and whether sexual dimorphism is associated with these mechanisms remains unknown.

METHODS

Female and male db/db mice exposed to a high-salt diet were used to analyze the progression of diabetic kidney disease and the development of hypertension.

RESULTS

Male, 34-week-old, db/db mice display hypertension when exposed to a 4-week high-salt treatment, whereas equivalently treated female db/db mice remain normotensive. Salt-sensitive hypertension in male mice was associated with no suppression of the epithelial sodium channel (ENaC) in response to a high-salt diet, despite downregulation of several components of the intrarenal renin-angiotensin system. Male db/db mice show higher levels of proinflammatory cytokines and more immune-cell infiltration in the kidney than do female db/db mice. Blocking inflammation, with either mycophenolate mofetil or by reducing IL-6 levels with a neutralizing anti-IL-6 antibody, prevented the development of salt sensitivity in male db/db mice.

CONCLUSIONS

The inflammatory response observed in male, but not in female, db/db mice induces salt-sensitive hypertension by impairing ENaC downregulation in response to high salt. These data provide a mechanistic explanation for the sexual dimorphism associated with the development of diabetic kidney disease and salt sensitivity.

Tumors exploit CXCR4hiCD62Llo aged neutrophils to facilitate metastatic spread

Granulocytes are key players in cancer metastasis. While tumor-induced de novo expansion of immunosuppressive myeloid-derived suppressor cells (MDSCs) is well-described, the fate and contribution of terminally differentiated mature neutrophils to the metastatic process remain poorly understood. Here, we show that in experimental metastatic cancer models, CXCR4^hiCD62L^lo aged neutrophils accumulate via disruption of neutrophil circadian homeostasis and direct stimulation of neutrophil aging mediated by angiotensin II. Compared to CXCR4^loCD62L^hi naive neutrophils, aged neutrophils more robustly promote tumor migration and support metastasis through the increased release of several metastasis-promoting factors, including neutrophil extracellular traps (NETs), reactive oxygen species, vascular endothelial growth factors, and metalloproteinases (MMP-9). Adoptive transfer of aged neutrophils significantly enhanced metastasis of breast (4T1) and melanoma (B16LS9) cancer cells to the liver, and these effects were predominantly mediated by NETs. Our results highlight that in addition to modulating MDSC production, targeting aged neutrophil clearance and homeostasis may be effective in reducing cancer metastasis.

Abstract P008: Sex Differences In The Development Of Diabetic Kidney Disease And Salt Sensitivity In Db/db Mice

Introduction: Clinical studies show that men have higher risk than premenopausal women for the development of diabetic kidney disease. However, the mechanisms behind the sexual dimorphism associated with renal injury and salt sensitivity during diabetes remain unknown.

Methods: 7-month-old male and female diabetic (db/db) and non-diabetic (db/+) mice received either a high-salt (HS, 4% NaCl w/w) or a control (0.7% NaCl w/w) diet for 4 weeks (n=6). Mean arterial pressure (MAP) was measured by telemetry. A subgroup of male mice was exposed to HS and the anti-inflammatory drug mycophenolate mofetil (MMF, 30 mg/Kg/day, IP). At the end, mice were euthanized, and kidneys were preserved to assess renal sodium transporters and inflammation.

Results: Male db/db mice display hypertension when exposed to HS whereas female db/db mice remain normotensive during the whole treatment (MAP: 125±7 vs. 103±3 mmHg, P<0.05). Hypertension in male db/db mice was associated with an improper suppression of key sodium transporters: NKCC2 and ENaC. Renal angiotensin II and plasma aldosterone were suppressed after HS in all experimental groups negating a role of these hormones in sodium transporters dysregulation and salt sensitivity. Compared to females, male db/db mice show higher levels of proinflammatory cytokines (IL-1β: 2.3-fold, IL-6: 1.7-fold and TNFα: 2.3-fold, P<0.05 by ELISA) and more leucocyte infiltration (CD45+ cells: 1.6-fold, P<0.05 by flow cytometry) in the kidney. Blocking inflammation with MMF reduced NKCC2 and ENaC expression in response to HS and prevented salt sensitivity in male db/db mice (MAP: 105±10 mmHg).

Conclusion: Renal inflammation in male, but not in female, db/db mice induces salt-sensitive hypertension by preventing the suppression of key sodium transporters in response to HS. Thus, we provide a mechanistic explanation of the sexual dimorphism associated with the development of salt sensitivity during diabetes.

COVID-19 in cancer patients: risk, clinical features, and management

A novel coronavirus known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread across the world, prompting the World Health Organization to declare the coronavirus disease of 2019 (COVID-19) a public health emergency of international concern. Cancer patients are regarded as a highly vulnerable population to SARS-CoV-2 infection and development of more severe COVID-19 symptoms, which is possibly due to the systemic immunosuppressive state caused directly by tumor growth and indirectly by effects of anticancer treatment. Currently, much effort has been directed toward studying the pathogenesis and treatment of COVID-19, but the risk profiles, prognoses, and treatment outcomes in cancer patients remain unclear. Based on the current literature, we summarize the risk profiles, clinical and biochemical characteristics, and therapy outcomes of COVID-19 infections in cancer patients. The challenges in the clinical care of cancer patients with COVID-19 are discussed. The goal of this review is to stimulate research to better understand the biological impact and prognoses of COVID-19 infections in cancer patients, thus facilitating improvement of the clinical management of these patients.

Role of angiotensin-converting enzyme in myeloid cell immune responses

Angiotensin-converting enzyme (ACE), a dicarboxypeptidase, plays a major role in the regulation of blood pressure by cleaving angiotensin I into angiotensin II (Ang II), a potent vasoconstrictor. Because of its wide substrate specificity and tissue distribution, ACE affects many diverse biological processes. In inflammatory diseases, including granuloma, atherosclerosis, chronic kidney disease and bacterial infection, ACE expression gets upregulated in immune cells, especially in myeloid cells. With increasing evidences connecting ACE functions to the pathogenesis of these acquired diseases, it is suggested that ACE plays a vital role in immune functions. Recent studies with mouse models of bacterial infection and tumor suggest that ACE plays an important role in the immune responses of myeloid cells. Inhibition of ACE suppresses neutrophil immune response to bacterial infection. In contrast, ACE overexpression in myeloid cells strongly induced bacterial and tumor resistance in mice. A detailed biochemical understanding of how ACE activates myeloid cells and which ACE peptide(s) (substrate or product) mediate these effects could lead to the development of novel therapies for boosting immunity against a variety of stimuli, including bacterial infection and tumor.

ACE overexpression in myeloid cells increases oxidative metabolism and cellular ATP

Angiotensin-converting enzyme (ACE) affects blood pressure. In addition, ACE overexpression in myeloid cells increases their immune function. Using MS and chemical analysis, we identified marked changes of intermediate metabolites in ACE-overexpressing macrophages and neutrophils, with increased cellular ATP (1.7-3.0-fold) and Krebs cycle intermediates, including citrate, isocitrate, succinate, and malate (1.4-3.9-fold). Increased ATP is due to ACE C-domain catalytic activity; it is reversed by an ACE inhibitor but not by an angiotensin II AT1 receptor antagonist. In contrast, macrophages from ACE knockout (null) mice averaged only 28% of the ATP levels found in WT mice. ACE overexpression does not change cell or mitochondrial size or number. However, expression levels of the electron transport chain proteins NDUFB8 (complex I), ATP5A, and ATP5β (complex V) are significantly increased in macrophages and neutrophils, and COX1 and COX2 (complex IV) are increased in macrophages overexpressing ACE. Macrophages overexpressing ACE have increased mitochondrial membrane potential (24% higher), ATP production rates (29% higher), and maximal respiratory rates (37% higher) compared with WT cells. Increased cellular ATP underpins increased myeloid cell superoxide production and phagocytosis associated with increased ACE expression. Myeloid cells overexpressing ACE indicate the existence of a novel pathway in which myeloid cell function can be enhanced, with a key feature being increased cellular ATP.

Overexpression of ACE in Myeloid Cells Increases Immune Effectiveness and Leads to a New Way of Considering Inflammation in Acute and Chronic Diseases

PURPOSE OF REVIEW

To review recent studies exploring how myeloid cell overexpression of angiotensin-converting enzyme (ACE) affects the immune response and to formulate an approach for considering the effectiveness of inflammation in cardiovascular disease RECENT FINDINGS: While it is widely appreciated that the renin-angiotensin system affects aspects of inflammation through the action of angiotensin II, new studies reveal a previously unknown role of ACE in myeloid cell biology. This was apparent from analysis of two mouse lines genetically modified to overexpress ACE in monocytes/macrophages or neutrophils. Cells overexpressing ACE demonstrated an increased immune response. For example, mice with increased macrophage ACE expression have increased resistance to melanoma, methicillin-resistant Staphylococcus aureus, a mouse model of Alzheimer's disease, and ApoE-knockout-induced atherosclerosis. These data indicate the profound effect of increasing myeloid cell function. Further, they suggest that an appropriate way to evaluate inflammation in both acute and chronic diseases is to ask whether the inflammatory infiltrate is sufficient to eliminate the immune challenge. The expression of ACE by myeloid cells induces a heightened immune response by these cells. The overexpression of ACE is associated with immune function beyond that possible by wild type (WT) myeloid cells. A heightened immune response effectively resolves disease in a variety of acute and chronic models of disease including models of Alzheimer's disease and atherosclerosis.

Overexpression of myeloid angiotensin-converting enzyme (ACE) reduces atherosclerosis

BACKGROUND

Macrophages are ubiquitous in all stages of atherosclerosis, exerting tremendous impact on lesion progression and plaque stability. Because macrophages in atherosclerotic plaques express angiotensin-converting enzyme (ACE), current dogma posits that local myeloid-mediated effects worsen the disease. In contrast, we previously reported that myeloid ACE overexpression augments macrophage resistance to various immune challenges, including tumors, bacterial infection and Alzheimer's plaque deposition. Here, we sought to assess the impact of myeloid ACE on atherosclerosis.

METHODS

A mouse model in which ACE is overexpressed in myelomonocytic lineage cells, called ACE10, was generated and sequentially crossed with ApoE-deficient mice to create ACE^10/10ApoE^-/- (ACE10/ApoE). Control mice were ACE^WT/WTApoE^-/- (WT/ApoE). Atherosclerosis was induced using an atherogenic diet alone, or in combination with unilateral nephrectomy plus deoxycorticosterone acetate (DOCA) salt for eight weeks.

RESULTS

With an atherogenic diet alone or in combination with DOCA, the ACE10/ApoE mice showed significantly less atherosclerotic plaques compared to their WT/ApoE counterparts (p < 0.01). When recipient ApoE^-/- mice were reconstituted with ACE^10/10 bone marrow, these mice showed significantly reduced lesion areas compared to recipients reconstituted with wild type bone marrow. Furthermore, transfer of ACE-deficient bone marrow had no impact on lesion area.

CONCLUSION

Our data indicate that while myeloid ACE may not be required for atherosclerosis, enhanced ACE expression paradoxically reduced disease progression.

Abstract 714: Does the Sickle Trait Portend Increased Cardiovascular Risks?

Objectives: Despite the increased incidence and worse outcomes of cardiovascular diseases among African-Americans compared to the general population, the contribution of sickle cell trait (AS) to this racial disparity remains unknown. We aimed to delineate the impact of AS on the pathogenesis of cardiovascular diseases alone, and in the setting of other risk factors.

Methods: We compared multiple cardiovascular endpoints between AS and wild-type genotype (AA) using the humanized Townes sickle cell mouse model. To determine whether AS modifies a pre-existing cardiovascular risk factor, diabetes was induced in a cohort of mice using streptozotocin (STZ). Hind limb ischemia model was employed to evaluate collateral vessel formation, and perfusion recovery was characterized with LASER Doppler perfusion imaging (LDPI). The running wheel assay assessed spontaneous motor function after ischemia. Angiotensin II (Ang II) and L-NAME were used to evaluate hypertensive response. Experimental stroke was induced by unilateral common carotid artery ligation and daily 15 min exposure to 7.5% oxygen for 3 days, and the infarct size was quantified as the ratio of the infarcted area to the total area of the uninjured contralateral hemisphere. PCSK9 gain-of-function mutation in the setting of Ang II and high-fat diet was used to evaluate atherosclerosis development.

Results: 4 groups of mice were studied: AA, AS, AA-STZ and AS-STZ. The formation of collateral vessels was equivalent between the AA and AS (day 28, AA: 80 ± 6%, AS: 85 ± 5%, p=0.8), and in the setting of diabetes (39 ± 5% AA-STZ; 36 ± 4% AS-STZ). Systolic blood pressure at baseline (110 ± 4 mmHg vs 112 ± 5 mmHg), and in response to Ang II (148 ± 4 mmHg vs 142 ± 5 mmHg) and L-NAME (135 ± 3mmHg vs 138 ± 5 mmHg) were equivalent. Mortality from stroke was equivalent between AA and AS. After 1 month of PCKS9 gain-of-function mutation/high-fat diet, AA and AS demonstrated similar lipid profiles. Mortality and infarct volume after stroke induction were identical between AA and AS.

Conclusions: All major indices of cardiovascular outcomes were similar between AA and AS, even in the presence of diabetes. These various experimental models suggest that the sickle trait likely does not contribute significantly to the poor cardiovascular outcomes seen in the African-American population.

Abstract 028: Neutrophils Aged Under Oxidative Stress Impede Vascular Repair

Objectives: The link between chronic inflammation and poor cardiovascular outcomes has long been appreciated, but the regulation of immune cellular targets to improve cardiovascular health remains a challenge. Mounting evidence suggests that neutrophils, previously considered acute first responder cells, play critical role in chronic inflammation. Following systemic surveillance of tissues, patrolling neutrophils age in the circulation and traffic to the bone marrow, where they undergo macrophage-mediated clearance. Here, we assessed how chronic inflammation and oxidative stress modify neutrophil trafficking and function during ischemia.

Methods: Neutrophils from the Townes humanized sickle cell (SS) mice - surrogate for chronic inflammation and oxidative stress - were compared to neutrophils from MerTK deficient mice (MerKO), which age in the circulation owing to defective efferocytosis. Hind limb ischemia (HLI) was used as model of vascular injury. LASER Doppler perfusion imaging (LDPI) measured perfusion recovery after HLI.

Results: The proportion of CXCR4 Hi CD62L lo aged neutrophils in circulation was markedly elevated in the SS (34 ± 4%) and MerKO mice (38 ± 4%) when compared to wild-type mice (7 ± 1.2%). However, in contrast with MerKO neutrophils, aged neutrophils from SS showed impaired phagocytosis, increased capacity to produce reactive oxygen species, and pronounced release of extracellular traps (NETs). In response to HLI, neutrophils accumulated in the MerKO and SS mice, but perfusion recovery on LDPI was only impaired in the SS mice, suggesting differential role of neutrophils aged by oxidative stress. Importantly, the phenotype of SS mice was reversed by treatment with the anti-oxidant N-acetyl cysteine (NAC), which had no impact on perfusion recovery in MerKO mice.

Conclusion: Although SS and MerKO mice demonstrated elevated numbers of aged neutrophils, our data suggest that chronic inflammation and oxidative stress modifies the function of aged CXCR4 Hi CD62L lo neutrophils to impede vascular repair after ischemia. This specialized subset of neutrophils may be targeted to improve vascular health without compromising overall anti-microbial host defenses

Impaired Collateral Vessel Formation in Sickle Cell Disease

OBJECTIVE

The adaptive response to vascular injury is the formation of functional collateral vessels to maintain organ integrity. Many of the clinical complications associated with sickle cell disease can be attributed to repeated bouts of vascular insufficiency, yet the detailed mechanisms of collateral vessel formation after injury are largely unknown in sickle cell disease. Here, we characterize postischemic neovascularization in sickle cell disease and the role of neutrophils in the production of reactive oxygen species.

APPROACH AND RESULTS

We induced hindlimb ischemia by ligation of the femoral artery in Townes SS (sickle cell) mice compared with AA (wild type) mice. Perfusion recovery, ascertained using LASER (light amplification by stimulated emission of radiation) Doppler perfusion imaging, showed significant diminution in collateral vessel formation in SS mice after hindlimb ischemia (76±13% AA versus 34±10% in SS by day 28; P<0.001; n=10 per group). The incidence of amputation (25% versus 5%) and foot necrosis (80% versus 15%) after hindlimb ischemia was significantly increased in the SS mice. Motor function recovery evaluation by the running wheel assay was also impaired in SS mice (36% versus 97% at 28 days post-hindlimb ischemia; P<0.001). This phenotype was associated with persistent and excessive production of reactive oxygen species by neutrophils. Importantly, neutrophil depletion or treatment with the antioxidant N-acetylcysteine reduced oxidative stress and improved functional collateral formation in the SS mice.

CONCLUSIONS

Our data suggest dysfunctional collateral vessel formation in SS mice after vascular injury and provide a mechanistic basis for the multiple vascular complications of sickle cell disease.

Progesterone to improve neurocognitive outcomes following cranial irradiation

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Background: Neurocognitive functional decline is a common sequalae of cranial irradiation (CI) that significantly impacts quality of life. Preclinical studies and randomized clinical trials show that following traumatic brain injury and cerebrovascular accidents, premenopausal women demonstrate decreased mortality and improved neurocognitive function, with these benefits presumed to be derived from progesterone. We hypothesized that progesterone may serve similar role in neuroprotection following cranial irradiation. Methods: Adult non-tumor bearing wild type C57BL/6 male mice were treated with two separate fractionated radiation therapy regimen (9 Gy and 15 Gy) to the brain. Cohorts of these mice were administered progesterone (16mg/kg daily) as a pretreatment for 3 days and concurrent with the radiotherapy for a total of 14 days with tapering during the last two days. The animals were then tested using different behavioral measures for cognitive function including morris water maze (MWM) for assessing spatial and related forms of learning and memory, elevated plus maze (EPM), , and spontaneous locomotor activity (SLA) tests. Mice were tested for cognitive function on day 10 and after 30 days of treatment for short and long-term effects of (CI) on memory function. Results: All irradiated mice showed statistically significant decline in MWM, EPM, and SLA measures. There were no significant differences in the 9 Gy versus 15 Gy cohorts. Progesterone administration produced a statistically significant group effect (F (4, 25) = 8.553; P<0.001) in the improvement of long-term memory function over 5 days of learning process. Progesterone administration also demonstrated a significant group effect (F (4, 25) = 8.613; P<0.001) in the probe trial, and a significant beneficial effect (F (4, 25)= 7.993; P<0.001) in short-term memory functional latency to reach the platform. Conclusions: The preclinical data show that progesterone improves radiation-induced deficits in short-and long-term memory functions in adult mice. Further work is required to show if progesterone may show similar clinical benefit in neuroprotection for adults undergoing prophylactic CI or definitive CI for brain metastases or benign intracranial processes such as AVM.

Two heads better than one? Ipilimumab immunotherapy and radiation therapy for melanoma brain metastases

Melanoma is an aggressive malignancy with a deplorable penchant for spreading to the brain. While focal therapies such as surgery and stereotactic radiosurgery can help provide local control, the majority of patients still develop intracranial progression. Novel therapeutic combinations to improve outcomes for melanoma brain metastases (MBM) are clearly needed. Ipilimumab, the anticytotoxic T-lymphocyte-associated antigen 4 monoclonal antibody, has been shown to improve survival in patients with metastatic melanoma, but many of these trials either excluded or had very few patients with MBM. This article will review the efficacy and limitations of ipilimumab therapy for MBM, describe the current evidence for combining ipilimumab with radiation therapy, illustrate potential mechanisms for synergy, and discuss emerging clinical trials specifically investigating this combination in MBM.

Myeloid expression of angiotensin-converting enzyme facilitates myeloid maturation and inhibits the development of myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells which accumulate in cancer, infection and chronic inflammation. These cells suppress T-cell function and the immune response. Angiotensin-converting enzyme (ACE) is a peptidase that is now known to regulate aspects of myelopoiesis. Here, we show that ACE expression correlates with myeloid maturation in vitro. Forced ACE overexpression in monocytic cells reduces the generation of MDSCs. In vivo, mice with a genetic change resulting in myeloid cell ACE overexpression have reduced numbers of blood and splenic MDSCs in a tumor model and in a model of chronic inflammation induced by complete Freund's adjuvant. In contrast, ACE-null mice produce large numbers of MDSCs during chronic inflammation. Macrophages from mice with myeloid ACE overexpressing are more pro-inflammatory and have more tumor-killing activity than cells from wild-type mice. Thus, manipulating myeloid ACE activity can interfere with MDSC development and the maturation of myeloid cells.

Angiotensin-converting enzyme and the tumor microenvironment: mechanisms beyond angiogenesis

The renin angiotensin system (RAS) is a network of enzymes and peptides that coalesce primarily on the angiotensin II type 1 receptor (AT1R) to induce cell proliferation, angiogenesis, fibrosis, and blood pressure control. Angiotensin-converting enzyme (ACE), the key peptidase of the RAS, is promiscuous in that it cleaves other substrates such as substance P and bradykinin. Accumulating evidence implicates ACE in the pathophysiology of carcinogenesis. While the role of ACE and its peptide network in modulating angiogenesis via the AT1R is well documented, its involvement in shaping other aspects of the tumor microenvironment remains largely unknown. Here, we review the role of ACE in modulating the immune compartment of the tumor microenvironment, which encompasses the immunosuppressive, cancer-promoting myeloid-derived suppressor cells, alternatively activated tumor-associated macrophages, and T regulatory cells. We also discuss the potential roles of peptides that accumulate in the setting of chronic ACE inhibitor use, such as bradykinin, substance P, and N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), and how they may undercut the gains of anti-angiogenesis from ACE inhibition. These emerging mechanisms may harmonize the often-conflicting results on the role of ACE inhibitors and ACE polymorphisms in various cancers and call for further investigations into the potential benefit of ACE inhibitors in some neoplasms.

Patterns of failure in advanced-stage diffuse large B-cell lymphoma (DLBCL) patients treated with R-CHOP chemotherapy and the emerging role of consolidative radiotherapy

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Background: The role of consolidative radiotherapy (RT) after a complete response (CR) to R-CHOP for stage III-IV DLBCL patients is unclear. The goal of our study is to evaluate the Emory experience when consolidative RT is delivered to initial presenting nodal and extranodal sites or bulky sites in these patients. Methods: From 01/2000 to 05/2012, 211 histologically confirmed DLBCL patients with stage III-IV disease who received R-CHOP were identified at Emory University. Patterns of failure for patients who achieved CR to R-CHOP were analyzed. Local control (LC), distant control (DC), progression free survival (PFS) and overall survival (OS) were estimated using Kaplan-Meier method and compared between patients who received R-CHOP alone versus R-CHOP plus consolidative RT using Log-rank test. Multivariate analyses were also performed using Cox proportional hazards model. Results: 163 patients had detailed treatment records. After a median 6 cycles of R-CHOP, 110 patients (67.5%) achieved CR and were entered for analysis. Fourteen patients (12.7%) received consolidative RT to a median dose of 30.6 Gy as part of initial management. With a median follow up time of 32.9 months, 43.8% of patients who received R-CHOP alone failed at the initial presenting sites with or without distant recurrence (DR), whereas isolated DR only occurred in 3.2% of these patients. Consolidative RT was associated with significantly improved LC (91.7% vs 48.8%, p<0.0001), DC (92.9% vs 71.9%, p<0.0001), PFS (85.1% vs 44.2%, p<0.0001) and OS (92.3% vs 68.5%, p<0.0001) at 5-years when compared to patients with R-CHOP alone. In addition, the in-field control rate was 100% within irradiated sites for patients who received consolidative RT. On multivariate analysis, consolidative RT and non-bulky disease were predictive of increased LC and PFS, whereas bone marrow involvement was associated with increased risk of DR and worse OS. Conclusions: 44% of patients with advanced stage DLBCL failed at initial presenting sites despite achieving a CR to R-CHOP. Incorporation of consolidative RT as part of upfront treatment in these patients was associated with improved LC and PFS.

Obesity-driven inflammation and cancer risk: role of myeloid derived suppressor cells and alternately activated macrophages

During carcinogenesis, tumors induce dysfunctional development of hematopoietic cells. Myeloid lineage cells, in the form of myeloid derived suppressor cells (MDSCs) and alternatively polarized M2 macrophages, influence almost all types of cancers by regulating diverse facets of immunosuppression, angiogenesis, cell proliferation, growth and metastasis. One-third of Americans are obese, and accumulating evidence suggests that obesity is a risk factor for various cancers. However, the relationship between these immune players and obesity are not well-described. In this review, we evaluate potential mechanisms through which different aspects of obesity, namely insulin resistance, increased estrogen, adiposity and low grade chronic inflammation from adipose tissue macrophages, may coalesce to promote MDSC induction and M2 macrophage polarization, thereby facilitating cancer development. Detailed understanding of the interplay between obesity and myeloid mediated immunosuppression may provide novel avenues for therapeutic targeting, with the goal to reduce the challenge obesity presents towards gains made in cancer outcomes.

Increased angiotensin II-induced hypertension and inflammatory cytokines in mice lacking angiotensin-converting enzyme N domain activity

-Angiotensin-converting enzyme (ACE) is composed of the N- and C-terminal catalytic domains. To study the role of the ACE domains in the inflammatory response, N-knockout (KO) and C-KO mice, models lacking 1 of the 2 ACE domains, were analyzed during angiotensin II-induced hypertension. At 2 weeks, N-KO mice have systolic blood pressures that averaged 173±4.6 mm Hg, which is more than 25 mm Hg higher than the blood pressures observed in wild-type or C-KO mice (146±3.2 and 147±4.2 mm Hg). After 3 weeks, blood pressure differences between N-KO, C-KO, and wild-type were even more pronounced. Macrophages from N-KO mice have increased expression of tumor necrosis factor α after stimulation with either lipopolysaccharide (about 4-fold) or angiotensin II (about 2-fold), as compared with C-KO or wild-type mice. Inhibition of the enzyme prolyl oligopeptidase, responsible for the formation of acetyl-SerAspLysPro and other peptides, eliminated the blood pressure difference and the difference in tumor necrosis factor α expression between angiotensin II-treated N-KO and wild-type mice. However, this appears independent of acetyl-SerAspLysPro. These data establish significant differences in the inflammatory response as a function of ACE N- or C-domain catalytic activity. They also indicate a novel role of prolyl oligopeptidase in the cytokine regulation and in the blood pressure response to experimental hypertension.

Angiotensin-converting enzyme is required for normal myelopoiesis

Inhibition of angiotensin-converting enzyme (ACE) induces anemia in humans and mice, but it is unclear whether ACE is involved in other aspects of hematopoiesis. Here, we systemically evaluated ACE-knockout (KO) mice and found myelopoietic abnormalities characterized by increased bone marrow myeloblasts and myelocytes, as well as extramedullary myelopoiesis. Peritoneal macrophages from ACE-KO mice were deficient in the production of effector molecules, such as tumor necrosis factor-α, interleukin-12p40, and CD86 when stimulated with lipopolysaccharide and interferon-γ. ACE-KO mice were more susceptible to Staphylococcus aureus infection. Further studies using total or fractionated bone marrows revealed that ACE regulates myeloid proliferation, differentiation, and functional maturation via angiotensin II and substance P and through the angiotensin II receptor type 1 and substance P neurokinin 1 receptors. Angiotensin II was correlated with CCAAT-enhancer-binding protein-α up-regulation during myelopoiesis. Angiotensin II supplementation of ACE-KO mice rescued macrophage functional maturation. These results demonstrate a previous unrecognized significant role for ACE in myelopoiesis and imply new perspectives for manipulating myeloid cell expansion and maturation.

Different in vivo functions of the two catalytic domains of angiotensin-converting enzyme (ACE)

Angiotensin-converting enzyme (ACE) can cleave angiotensin I, bradykinin, neurotensin and many other peptide substrates in vitro. In part, this is due to the structure of ACE, a protein composed of two independent catalytic domains. Until very recently, little was known regarding the specific in vivo role of each ACE domain, and they were commonly regarded as equivalent. This is not true, as shown by mouse models with a genetic inactivation of either the ACE N- or C-domain. In vivo, most angiotensin II is produced by the ACE C-domain. Some peptides, such as the anti-fibrotic peptide AcSDKP, are substrates only of the ACE N-domain. Knowing the in vivo role of each ACE domain has great significance for developing ACE domain-specific inhibitors and for understanding the full effects of the anti-ACE pharmaceuticals in widespread clinical use.

Angiotensin-converting enzyme overexpression in mouse myelomonocytic cells augments resistance to Listeria and methicillin-resistant Staphylococcus aureus

Gene targeting in ES cells was used to substitute control of angiotensin converting enzyme (ACE) expression from the endogenous promoter to the mouse c-fms promoter. The result is an animal model called ACE 10/10 in which ACE is overexpressed by monocytes, macrophages, and other myelomonocytic lineage cells. To study the immune response of these mice to bacterial infection, we challenged them with Listeria monocytogenes or methicillin-resistant Staphylococcus aureus (MRSA). ACE 10/10 mice have a significantly enhanced immune response to both bacteria in vivo and in vitro. For example, 5 days after Listeria infection, the spleen and liver of ACE 10/10 mice had 8.0- and 5.2-fold less bacteria than wild type mice (WT). In a model of MRSA skin infection, ACE 10/10 mice had 50-fold less bacteria than WT mice. Histologic examination showed a prominent infiltrate of ACE-positive mononuclear cells in the skin lesions from ACE 10/10. Increased bacterial resistance in ACE 10/10 is directly due to overexpression of ACE, as it is eliminated by an ACE inhibitor. Critical to increased immunity in ACE 10/10 is the overexpression of iNOS and reactive nitrogen intermediates, as inhibition of iNOS by the inhibitor 1400W eliminated all in vitro and in vivo differences in innate bacterial resistance between ACE 10/10 and WT mice. Increased resistance to MRSA was transferable by bone marrow transplantation. The overexpression of ACE and iNOS by myelomonocytic cells substantially boosts innate immunity and may represent a new means to address serious bacterial infections.

New insights into the role of angiotensin-converting enzyme obtained from the analysis of genetically modified mice

Angiotensin-converting enzyme (ACE) has been well-recognized for its role in blood pressure regulation. ACE is made by many tissues, though it is most abundantly expressed on the luminal surface of vascular endothelium. ACE knockout mice show a profound phenotype with low blood pressure, but also with hemopoietic and developmental defects, which complicates understanding the biological functions of ACE in individual tissue types. Using a promoter-swapping strategy, several mouse lines with unique ACE tissue expression patterns were studied. These include mice with ACE expression in the liver (ACE 3/3), the heart (ACE 8/8), and macrophages (ACE 10/10). We also investigated mice with a selective inactivation of either the N- or C-terminal ACE catalytic domain. Our studies indicate that ACE plays a role in many other physiologic processes beyond simple blood pressure control.