Inhibition of angiotensin I–converting enzyme induces radioprotection by preserving murine hematopoietic short-term reconstituting cells

Ferroptosis, Inflammation, and Microbiome Alterations in the Intestine in the Göttingen Minipig Model of Hematopoietic-Acute Radiation Syndrome

Hematopoietic acute radiation syndrome (H-ARS) involves injury to multiple organ systems following total body irradiation (TBI). Our laboratory demonstrated that captopril, an angiotensin-converting enzyme inhibitor, mitigates H-ARS in Göttingen minipigs, with improved survival and hematopoietic recovery, as well as the suppression of acute inflammation. However, the effects of captopril on the gastrointestinal (GI) system after TBI are not well known. We used a Göttingen minipig H-ARS model to investigate captopril's effects on the GI following TBI (60Co 1.79 or 1.80 Gy, 0.42-0.48 Gy/min), with endpoints at 6 or 35 days. The vehicle or captopril (0.96 mg/kg) was administered orally twice daily for 12 days, starting 4 h post-irradiation. Ilea were harvested for histological, protein, and RNA analyses. TBI increased congestion and mucosa erosion and hemorrhage, which were modulated by captopril. GPX-4 and SLC7A11 were downregulated post-irradiation, consistent with ferroptosis at 6 and 35 days post-irradiation in all groups. Interestingly, p21/waf1 increased at 6 days in vehicle-treated but not captopril-treated animals. An RT-qPCR analysis showed that radiation increased the gene expression of inflammatory cytokines IL1B, TNFA, CCL2, IL18, and CXCL8, and the inflammasome component NLRP3. Captopril suppressed radiation-induced IL1B and TNFA. Rectal microbiome analysis showed that 1 day of captopril treatment with radiation decreased overall diversity, with increased Proteobacteria phyla and Escherichia genera. By 6 days, captopril increased the relative abundance of Enterococcus, previously associated with improved H-ARS survival in mice. Our data suggest that captopril mitigates senescence, some inflammation, and microbiome alterations, but not ferroptosis markers in the intestine following TBI.

Diverse biological functions of the renin-angiotensin system

The renin-angiotensin system (RAS) has been widely known as a circulating endocrine system involved in the control of blood pressure. However, components of RAS have been found to be localized in rather unexpected sites in the body including the kidneys, brain, bone marrow, immune cells, and reproductive system. These discoveries have led to steady, growing evidence of the existence of independent tissue RAS specific to several parts of the body. It is important to understand how RAS regulates these systems for a variety of reasons: It gives a better overall picture of human physiology, helps to understand and mitigate the unintended consequences of RAS-inhibiting or activating drugs, and sets the stage for potential new therapies for a variety of ailments. This review fulfills the need for an updated overview of knowledge about local tissue RAS in several bodily systems, including their components, functions, and medical implications.

Crosstalk between Oxidative Stress and Inflammation Induced by Ionizing Radiation in Healthy and Cancerous Cells

Radiotherapy (RT) is a unique modality in cancer treatment with no replacement in many cases and uses a tumoricidal dose of various ionizing radiation (IR) types to kill cancer cells. It causes oxidative stress through reactive oxygen species (ROS) production or the destruction of antioxidant systems. On the other hand, RT stimulates the immune system both directly and indirectly by releasing danger signals from stress-exposed and dying cells. Oxidative stress and inflammation are two reciprocal and closely related mechanisms, one induced and involved by the other. ROS regulates the intracellular signal transduction pathways, which participate in the activation and expression of pro-inflammatory genes. Reciprocally, inflammatory cells release ROS and immune system mediators during the inflammation process, which drive the induction of oxidative stress. Oxidative stress or inflammation-induced damages can result in cell death (CD) or survival mechanisms that may be destructive for normal cells or beneficial for cancerous cells. The present study has focused on the radioprotection of those agents with binary effects of antioxidant and anti-inflammatory mechanisms IR-induced CD.

Pocket ACEs: Discovering new function within an old player

Angiotensin-converting enzyme (ACE) is canonically known for its role in the renin-angiotensin system (RAS) where its conversion of angiotensin I (Ang I) to the bioactive peptide angiotensin II (Ang II) helps to regulate blood pressure, electrolyte, and volume homeostasis. Further studies on ACE have shown that its enzymatic activity is relatively non-specific and functions outside of the RAS axis. Of the multiple systems it has been implicated in, ACE has been found to play an important role in the development and modulation of hematopoiesis and the immune system, both through the RAS and independently of the RAS axis.

Gamma-Tocotrienol Modulates Total-Body Irradiation-Induced Hematopoietic Injury in a Nonhuman Primate Model

Radiation exposure causes acute damage to hematopoietic and immune cells. To date, there are no radioprotectors available to mitigate hematopoietic injury after radiation exposure. Gamma-tocotrienol (GT3) has demonstrated promising radioprotective efficacy in the mouse and nonhuman primate (NHP) models. We determined GT3-mediated hematopoietic recovery in total-body irradiated (TBI) NHPs. Sixteen rhesus macaques divided into two groups received either vehicle or GT3, 24 h prior to TBI. Four animals in each treatment group were exposed to either 4 or 5.8 Gy TBI. Flow cytometry was used to immunophenotype the bone marrow (BM) lymphoid cell populations, while clonogenic ability of hematopoietic stem cells (HSCs) was assessed by colony forming unit (CFU) assays on day 8 prior to irradiation and days 2, 7, 14, and 30 post-irradiation. Both radiation doses showed significant changes in the frequencies of B and T-cell subsets, including the self-renewable capacity of HSCs. Importantly, GT3 accelerated the recovery in CD34⁺ cells, increased HSC function as shown by improved recovery of CFU-granulocyte macrophages (CFU-GM) and burst-forming units erythroid (B-FUE), and aided the recovery of circulating neutrophils and platelets. These data elucidate the role of GT3 in hematopoietic recovery, which should be explored as a potential medical countermeasure to mitigate radiation-induced injury to the hematopoietic system.

Angiotensin converting enzyme (ACE) inhibitors as radiation countermeasures for long-duration space flights

Angiotensin converting enzyme (ACE) inhibitors are effective countermeasures to chronic radiation injuries in rodent models, and there is evidence for similar effects in humans. In rodent models ACE inhibitors are effective mitigators of radiation injury to kidney, lung, central nervous system (CNS) and skin, even when started weeks after irradiation. In humans, the best data for their efficacy as radiation countermeasures comes from retrospective studies of injuries in radiotherapy patients. We propose that ACE inhibitors, at doses approved for human use for other indications, could be used to reduce the risk of chronic radiation injuries from deep-space exploration. Because of the potential interaction of ACE inhibitors and microgravity (due to effects of ACE inhibitors on fluid balance) use might be restricted to post-exposure when/if radiation exposures reached a danger level. A major unresolved issue for this approach is the sparse evidence for the efficacy of ACE inhibitors after low-dose-rate exposure and/or for high-LET radiations (as would occur on long-duration space flights). A second issue is that the lack of a clear mechanism of action of the ACE inhibitors as mitigators makes obtaining an appropriate label under the Food and Drug Administration Animal Rule difficult.

High-throughput screening strategies for space-based radiation countermeasure discovery

As humanity begins to venture further into space, approaches to better protect astronauts from the hazards found in space need to be developed. One particular hazard of concern is the complex radiation that is ever present in deep space. Currently, it is unlikely enough spacecraft shielding could be launched that would provide adequate protection to astronauts during long-duration missions such as a journey to Mars and back. In an effort to identify other means of protection, prophylactic radioprotective drugs have been proposed as a potential means to reduce the biological damage caused by this radiation. Unfortunately, few radioprotectors have been approved by the FDA for usage and for those that have been developed, they protect normal cells/tissues from acute, high levels of radiation exposure such as that from oncology radiation treatments. To date, essentially no radioprotectors have been developed that specifically counteract the effects of chronic low-dose rate space radiation. This review highlights how high-throughput screening (HTS) methodologies could be implemented to identify such a radioprotective agent. Several potential target, pathway, and phenotypic assays are discussed along with potential challenges towards screening for radioprotectors. Utilizing HTS strategies such as the ones proposed here have the potential to identify new chemical scaffolds that can be developed into efficacious radioprotectors that are specifically designed to protect astronauts during deep space journeys. The overarching goal of this review is to elicit broader interest in applying drug discovery techniques, specifically HTS towards the identification of radiation countermeasures designed to be efficacious towards the biological insults likely to be encountered by astronauts on long duration voyages.

Myocardial Ischemia Related to Common Cancer Therapy-Prevention Insights

Modern antineoplastic therapy improves survival and quality of life in cancer patients, but its indisputable benefits are accompanied by multiple and major side effects, such as cardiovascular ones. Endothelial dysfunction, arterial spasm, intravascular thrombosis, and accelerated atherosclerosis affect the coronary arteries, leading to acute and chronic coronary syndromes that negatively interfere with the oncologic treatment. The cardiac toxicity of antineoplastic agents may be mitigated by using adequate prophylactic measures. In the absence of dedicated guidelines, our work provides the most comprehensive, systematized, structured, and up-to-date analyses of the available literature focusing on measures aiming to protect the coronary arteries from the toxicity of cancer therapy. Our work facilitates the implementation of these measures in daily practice. The ultimate goal is to offer clinicians the necessary data for a personalized therapeutic approach for cancer patients receiving evidence-based oncology treatments with potential cardiovascular toxicity.

Histopathological Evaluation of Protective Effect of Telmisartan against Radiation-Induced Bone Marrow Injury

BACKGROUND

Radiation-induced hematopoietic suppression and myelotoxicity can occur due to the nuclear accidents, occupational irradiation and therapeutic interventions. Bone marrow dysfunction has always been one of the most important causes of morbidity and mortality after ionizing irradiation.

OBJECTIVE

This study aims to investigate the protective effect of telmisartan against radiation-induced bone marrow injuries in a Balb/c mouse model.

MATERIAL AND METHODS

In this experimental study, male Balb/c mice were divided into four groups as follow: group 1: mice received phosphate buffered saline (PBS) without irradiation, group 2: mice received a solution of telmisartan in PBS without irradiation, group 3: mice received PBS with irradiation, and group 4: mice received a solution of telmisartan in PBS with irradiation. A solution of telmisartan was prepared and administered orally at 12 mg/kg body weight for seven consecutive days prior to whole body exposing to a single sub-lethal dose of 5 Gy X-rays. Protection of bone marrow against radiation induced damage was investigated by Hematoxylin-Eosin (HE) staining assay at 3, 9, 15 and 30 days after irradiation.

RESULTS

Histopathological analysis indicated that administration of telmisartan reduced X-radiation-induced damage and improved bone marrow histology. The number of different cell types in bone marrow, including polymorphonuclear /mononuclear cells and megakaryocytes significantly increased in telmisartan treated group compared to the only irradiated group at all-time points.

CONCLUSION

The results of the present study demonstrated an efficient radioprotective effect of telmisartan in mouse bone marrow against sub-lethal X-irradiation.

Radiomitigation by Melatonin in C57BL/6 Mice: Possible Implications as Adjuvant in Radiotherapy and Chemotherapy

BACKGROUND/AIM

Melatonin (N-acetyl-5-methoxytryptamine), a chief secretory molecule of the pineal gland, has multiple properties, and numerous clinical investigations regarding its actions are in progress. This study investigated the radiomitigative role of melatonin in C57BL/6 mice.

MATERIALS AND METHODS

Melatonin (100 mg/kg) was orally administered once daily starting at 1 h on day 1 and subsequently every 24 h until day 7 after whole-body irradiation (WBI) and survival was monitored for 30 days. The bone marrow, spleen, and intestine were studied to evaluate the mitigative potential of melatonin after radiation-induced damage.

RESULTS

Melatonin significantly improved the survival upto 60% and 90% after 9 Gy (lethal) and 7.5 Gy (sub-lethal) WBI, respectively. Melatonin alleviated WBI-induced myelosuppression and pancytopenia, and increased white blood cell, red blood cell, platelet, and lymphocyte (CD4⁺ and CD8⁺) counts in peripheral blood. Bone marrow and spleen cellularity were restored through enhanced haematopoiesis. Melatonin ameliorated the damage in the small intestine, and promoted recovery of villi length, crypts number, and goblet cell count.

CONCLUSION

Melatonin mitigates the radiation-induced injury in the gastrointestinal and haematopoietic systems. The observed radiomitigative properties of melatonin can also be useful in the context of adjuvant therapy for cancer and radiotherapy.

Effects of captopril against radiation injuries in the Göttingen minipig model of hematopoietic-acute radiation syndrome

Our laboratory has demonstrated that captopril, an angiotensin converting enzyme inhibitor, mitigates hematopoietic injury following total body irradiation in mice. Improved survival in mice is correlated with improved recovery of mature blood cells and bone marrow, reduction of radiation-induced inflammation, and suppression of radiation coagulopathy. Here we investigated the effects of captopril treatment against radiation injuries in the Göttingen mini pig model of Hematopoietic-Acute Radiation Syndrome (H-ARS). Minipigs were given captopril orally (0.96 mg/kg) twice daily for 12 days following total body irradiation (⁶⁰Co 1.79 Gy, 0.42–0.48 Gy/min). Blood was drawn over a time course following irradiation, and tissue samples were collected at euthanasia (32–35 days post-irradiation). We observed improved survival with captopril treatment, with survival rates of 62.5% in vehicle treated and 87.5% in captopril treated group. Additionally, captopril significantly improved recovery of peripheral blood mononuclear cells, and a trend toward improvement in recovery of red blood cells and platelets. Captopril significantly reduced radiation-induced expression of cytokines erythropoietin and granulocyte-macrophage colony-stimulating factor and suppressed radiation-induced acute-phase inflammatory response cytokine serum amyloid protein A. Using quantitative-RT-PCR to monitor bone marrow recovery, we observed significant suppression of radiation-induced expression of redox stress genes and improved hematopoietic cytokine expression. Our findings suggest that captopril activities in the Göttingen minipig model of hematopoietic-acute radiation syndrome reflect findings in the murine model.

Quercetin-3-rutinoside protects against gamma radiation inflicted hematopoietic dysfunction by regulating oxidative, inflammatory, and apoptotic mediators in mouse spleen and bone marrow

Radiation-induced hematopoietic dysfunction is one of the most common problems during unplanned radiation exposures and also in cancer patients receiving radiotherapy. Management of the hematopoietic system is necessary to promote survival against radiation. The present study was undertaken to demonstrate the protective potential of Quercetin 3 rutinoside (Q-3-R), against gamma radiation-induced hematopoietic injuries. C57BL/6 male mice exposed either to radiation or pretreated with Q-3-R (10 mg/kg body weight) were checked for hematopoietic protection using hematotoxicity indices, histopathological, and genotoxic evaluations. To elucidate the underlying mechanisms of Q-3-R mediated hematopoietic protection, oxidative/nitrosative stress, inflammatory and apoptotic markers as well as PCNA expression in spleen cross-sections were assessed. Studies revealed Q-3-R pretreatment inhibited radiation-induced ROS in spleen cells and better maintained the total antioxidant levels in serum that were otherwise altered post 7.5 Gy exposure. The NO levels and nitrotyrosine expression were also found inhibited by Q-3-R in the spleen. Differential regulations of Bcl2, Bax and NF-κB with reduced serum TNF-α level indicated anti-apoptotic and anti-inflammatory roles of Q-3-R. Q-3-R attenuated radiation mediated spleen damage by minimizing cell death and promoting proliferation. Restoration of abnormal histopathological changes in bone marrow following Q-3-R administration correlated to reduced apoptosis and altered cell cycle distributions. Chromosomal aberrations were also found reduced in Q-3-R pretreated bone marrow. Q-3-R restored the total leukocyte counts and serum IL-6 levels, further supporting its role in promoting hematopoiesis. These findings suggest that Q-3-R can potentially be used to minimize radiation inflicted hematopoietic toxicities during accidental as well as radiotherapy scenarios.

Repurposing Pharmaceuticals Previously Approved by Regulatory Agencies to Medically Counter Injuries Arising Either Early or Late Following Radiation Exposure

The increasing risks of radiological or nuclear attacks or associated accidents have served to renew interest in developing radiation medical countermeasures. The development of prospective countermeasures and the subsequent gain of Food and Drug Administration (FDA) approval are invariably time consuming and expensive processes, especially in terms of generating essential human data. Due to the limited resources for drug development and the need for expedited drug approval, drug developers have turned, in part, to the strategy of repurposing agents for which safety and clinical data are already available. Approval of drugs that are already in clinical use for one indication and are being repurposed for another indication is inherently faster and more cost effective than for new agents that lack regulatory approval of any sort. There are four known growth factors which have been repurposed in the recent past as radiomitigators following the FDA Animal Rule: Neupogen, Neulasta, Leukine, and Nplate. These four drugs were in clinic for several decades for other indications and were repurposed. A large number of additional agents approved by various regulatory authorities for given indications are currently under investigation for dual use for acute radiation syndrome or for delayed pathological effects of acute radiation exposure. The process of drug repurposing, however, is not without its own set of challenges and limitations.

Ilomastat contributes to the survival of mouse after irradiation via promoting the recovery of hematopoietic system

Ilomastat, a broad-spectrum inhibitor of matrix metalloproteinases (MMPs), has drawn attentions for its function in alleviating radiation damage. However, the detailed mechanisms of Ilomastat’s protection from animal model remain not fully clear. In this study, the C57BL/6 mice were pre-administrated with Ilomastat or vihicle for 2 h, and then total body of mice were exposed to 6 Gy of γ-rays. The protective effect of Ilomastat on the hematopoietic system in the irradiated mice were investigated. We found that pretreatment with Ilomastat significantly reduced the level of TGF-β1 and TNF-α, and elevated the number of bone marrow (BM) mononuclear cells in the irradiated mice. Ilomastat pretreatment also increased the fraction of BM hematopoietic progenitor cells (HPCs) and hematopoietic stem cells (HSCs) at day 30 after irradiation, and protected the spleen of mouse from irradiation. These results suggest that Ilomastat promotes the recovery of hematopoietic injury in the irradiated mice, and thus contributes to the survival of mouse after irradiation.

Radioprotection and Radiomitigation: From the Bench to Clinical Practice

The development of protective agents against harmful radiations has been a subject of investigation for decades. However, effective (ideal) radioprotectors and radiomitigators remain an unsolved problem. Because ionizing radiation-induced cellular damage is primarily attributed to free radicals, radical scavengers are promising as potential radioprotectors. Early development of such agents focused on thiol synthetic compounds, e.g., amifostine (2-(3-aminopropylamino) ethylsulfanylphosphonic acid), approved as a radioprotector by the Food and Drug Administration (FDA, USA) but for limited clinical indications and not for nonclinical uses. To date, no new chemical entity has been approved by the FDA as a radiation countermeasure for acute radiation syndrome (ARS). All FDA-approved radiation countermeasures (filgrastim, a recombinant DNA form of the naturally occurring granulocyte colony-stimulating factor, G-CSF; pegfilgrastim, a PEGylated form of the recombinant human G-CSF; sargramostim, a recombinant granulocyte macrophage colony-stimulating factor, GM-CSF) are classified as radiomitigators. No radioprotector that can be administered prior to exposure has been approved for ARS. This differentiates radioprotectors (reduce direct damage caused by radiation) and radiomitigators (minimize toxicity even after radiation has been delivered). Molecules under development with the aim of reaching clinical practice and other nonclinical applications are discussed. Assays to evaluate the biological effects of ionizing radiations are also analyzed.

Polydatin Attenuates 14.1 MeV Neutron-Induced Injuries via Regulating the Apoptosis and Antioxidative Pathways and Improving the Hematopoiesis of Mice

With more powerful penetrability and ionizing capability, high energetic neutron radiation (HENR) often poses greater threats than photon radiation, especially on such occasions as nuclear bomb exposure, nuclear accidents, aerospace conduction, and neutron-based radiotherapy. Therefore, there emerges an urgent unmet demand in exploring highly efficient radioprotectants against HENR. In the present study, high-throughput 14.1 MeV neutrons were generated by the high-intensity D-T fusion neutron generator (HINEG) and succeeded in establishing the acute radiation syndrome (ARS) mouse model induced by HENR. A series of preclinical studies, including morphopathological assessment, flow cytometry, peripheral complete blood, and bone marrow karyocyte counting, were applied showing much more serious detriments of HENR than the photon radiation. In specific, it was indicated that surviving fraction of polydatin- (PD-) treated mice could appreciably increase to up to 100% when they were exposed to HENR. Moreover, polydatin contributed much in alleviating the HENR-induced mouse body weight loss, spleen and testis indexes decrease, and the microstructure alterations of both the spleen and the bone marrow. Furthermore, we found that the HENR-damaged hematopoiesis was greatly prevented by PD treatment in such aspects as bone marrow hemocytogenesis, splenocytes balancing, or even the peripheral blood cellularity. The additional IHC investigations revealed that PD could exert potent hematopoiesis-promoting effects against HENR via suppressing apoptosis and promoting the antioxidative enzymes such as HO-1.

Radiogenomics Consortium Genome-Wide Association Study Meta-Analysis of Late Toxicity After Prostate Cancer Radiotherapy

BACKGROUND

A total of 10%-20% of patients develop long-term toxicity following radiotherapy for prostate cancer. Identification of common genetic variants associated with susceptibility to radiotoxicity might improve risk prediction and inform functional mechanistic studies.

METHODS

We conducted an individual patient data meta-analysis of six genome-wide association studies (n = 3871) in men of European ancestry who underwent radiotherapy for prostate cancer. Radiotoxicities (increased urinary frequency, decreased urinary stream, hematuria, rectal bleeding) were graded prospectively. We used grouped relative risk models to test associations with approximately 6 million genotyped or imputed variants (time to first grade 2 or higher toxicity event). Variants with two-sided Pmeta less than 5 × 10-8 were considered statistically significant. Bayesian false discovery probability provided an additional measure of confidence. Statistically significant variants were evaluated in three Japanese cohorts (n = 962). All statistical tests were two-sided.

RESULTS

Meta-analysis of the European ancestry cohorts identified three genomic signals: single nucleotide polymorphism rs17055178 with rectal bleeding (Pmeta = 6.2 × 10-10), rs10969913 with decreased urinary stream (Pmeta = 2.9 × 10-10), and rs11122573 with hematuria (Pmeta = 1.8 × 10-8). Fine-scale mapping of these three regions was used to identify another independent signal (rs147121532) associated with hematuria (Pconditional = 4.7 × 10-6). Credible causal variants at these four signals lie in gene-regulatory regions, some modulating expression of nearby genes. Previously identified variants showed consistent associations (rs17599026 with increased urinary frequency, rs7720298 with decreased urinary stream, rs1801516 with overall toxicity) in new cohorts. rs10969913 and rs17599026 had similar effects in the photon-treated Japanese cohorts.

CONCLUSIONS

This study increases the understanding of the architecture of common genetic variants affecting radiotoxicity, points to novel radio-pathogenic mechanisms, and develops risk models for testing in clinical studies. Further multinational radiogenomics studies in larger cohorts are worthwhile.

Delayed Captopril Administration Mitigates Hematopoietic Injury in a Murine Model of Total Body Irradiation

The increasing potential for accidental radiation exposure from either nuclear accidents or terrorist activities has escalated the need for radiation countermeasure development. We previously showed that a 30-day course of high-dose captopril, an ACE inhibitor, initiated 1–4 h after total body irradiation (TBI), improved Hematopoietic Acute Radiation Syndrome (H-ARS) and increased survival in mice. However, because of the time likely required for the deployment of a stockpiled radiation countermeasure to a radiation mass casualty site, there is a need for therapies that can be administered 24–48 hours after initial exposure. Using C57BL/6 mice exposed to an LD_50-80/30 of ⁶⁰Co TBI (7.75–7.9 Gy, 0.615 Gy/min), we show that low-dose captopril administration, initiated as late as 48 h post-TBI and continued for 14 days, significantly enhanced overall survival similarly to high-dose, rapid administration. Captopril treatment did not affect radiation-induced cell cycle arrest genes or the immediate loss of hematopoietic precursors. Reduced mortality was associated with the recovery of bone marrow cellularity and mature blood cell recovery at 21–30 days post-irradiation. Captopril reduced radiation-induced cytokines EPO, G-CSF, and SAA in the plasma. Finally, delayed captopril administration mitigated brain micro-hemorrhage at 21 days post-irradiation. These data indicate that low dose captopril administered as late as 48 h post-TBI for only two weeks improves survival that is associated with hematopoietic recovery and reduced inflammatory response. These data suggest that captopril may be an ideal countermeasure to mitigate H-ARS following accidental radiation exposure.

Captopril mitigates splenomegaly and myelofibrosis in the Gata1low murine model of myelofibrosis

Allogeneic stem cell transplantation is currently the only curative therapy for primary myelofibrosis (MF), while the JAK2 inhibitor, ruxolitinib. Has been approved only for palliation. Other therapies are desperately needed to reverse life-threatening MF. However, the cell(s) and cytokine(s) that promote MF remain unclear. Several reports have demonstrated that captopril, an inhibitor of angiotensin-converting enzyme that blocks the production of angiotensin II (Ang II), mitigates fibrosis in heart, lung, skin and kidney. Here, we show that captopril can mitigate the development of MF in the Gata1low mouse model of primary MF. Gata1low mice were treated with 79 mg/kg/d captopril in the drinking water from 10 to 12 months of age. At 13 months of age, bone marrows were examined for fibrosis, megakaryocytosis and collagen expression; spleens were examined for megakaryocytosis, splenomegaly and collagen expression. Treatment of Gata1low mice with captopril in the drinking water was associated with normalization of the bone marrow cellularity; reduced reticulin fibres, splenomegaly and megakaryocytosis; and decreased collagen expression. Our findings suggest that treating with the ACE inhibitors captopril has a significant benefit in overcoming pathological changes associated with MF.

Novel Indications for Commonly Used Medications as Radiation Protectants in Spaceflight

BACKGROUND

In the space environment, the traditional radioprotective principles of time, distance, and shielding become difficult to implement. Additionally, the complex radiation environment inherent in space, the chronic exposure timeframe, and the presence of numerous confounding variables complicate the process of creating appropriate risk models for astronaut exposure. Pharmaceutical options hold tremendous promise to attenuate acute and late effects of radiation exposure in the astronaut population. Pharmaceuticals currently approved for other indications may also offer radiation protection, modulation, or mitigation properties along with a well-established safety profile. Currently there are only three agents which have been clinically approved to be employed for radiation exposure, and these only for very narrow indications. This review identifies a number of agents currently approved by the U.S. Food and Drug Administration (FDA) which could warrant further investigation for use in astronauts. Specifically, we examine preclinical and clinical evidence for statins, nonsteroidal anti-inflammatory drugs (NSAIDs), angiotensin converting enzyme inhibitors (ACEIs), angiotensin II receptor blockers (ARBs), metformin, calcium channel blockers, β adrenergic receptor blockers, fingolimod, N-acetylcysteine, and pentoxifylline as potential radiation countermeasures.McLaughlin MF, Donoviel DB, Jones JA. Novel indications for commonly used medications as radiation protectants in spaceflight. Aerosp Med Hum Perform. 2017; 88(7):665-676.

A review of radiation countermeasures focusing on injury-specific medicinals and regulatory approval status: part III. Countermeasures under early stages of development along with 'standard of care' medicinal and procedures not requiring regulatory approval for use

PURPOSE

Terrorist attacks, with their intent to maximize psychological and economic damage as well as inflicting sickness and death on given targeted populations, are an ever-growing worldwide concern in government and public sectors as they become more frequent, violent, and sensational. If given the chance, it is likely that terrorists will use radiological or nuclear weapons. To thwart these sinister efforts, both physical and medical countermeasures against these weapons are currently being researched and developed so that they can be utilized by the first responders, military, and medical providers alike. This is the third article of a three-part series in which we have reviewed additional radiation countermeasures that are currently under early preclinical phases of development using largely animal models and have listed and discussed clinical support measures, including agents used for radiation-induced emesis, as well as countermeasures not requiring Food and Drug Administration approval.

CONCLUSIONS

Despite the significant progress that has been made in this area during the last several years, additional effort is needed in order to push promising new agents, currently under development, through the regulatory pipeline. This pipeline for new promising drugs appears to be unreasonably slow and cumbersome; possible reasons for this inefficiency are briefly discussed. Significant and continued effort needs to be afforded to this research and development area, as to date, there is no approved radioprotector that can be administered prior to high dose radiation exposure. This represents a very significant, unmet medical need and a significant security issue. A large number of agents with potential to interact with different biological targets are under development. In the next few years, several additional radiation countermeasures will likely receive Food and Drug Administration approval, increasing treatment options for victims exposed to unwanted ionizing irradiation.

Erythropoietin Regulation by Angiotensin II

The renin-angiotensin system (RAS) is a key regulator of blood pressure and blood volume homeostasis. The RAS is primarily comprised of the precursor protein angiotensinogen and the two proteases, renin and angiotensin-converting enzyme (ACE). Angiotensin I (Ang I) is derived from angiotensinogen by renin, but appears to have no biological activity. In contrast, angiotensin II (Ang II) that has a variety of biological functions in the cells is converted from Ang I through removal of two-C-terminal residues by ACE. The physiological effects of Ang II are due to Ang II signaling through specific receptor binding, resulting in muscle contraction leading to increased blood pressure and volume. To modulate RAS, three classes of drugs have been developed: (1) renin inhibitors to prevent angiotensinogen conversion to Ang I, (2) ACE inhibitors, to prevent Ang I processing to Ang II and (3) angiotensin receptor blockers, to inhibit Ang II signaling through its receptor. Studies using the RAS inhibitors and Ang II demonstrated that RAS signaling mediates actions of Ang II in the regulation of proliferation and differentiation of specific hematopoietic cell types, especially in the red blood cell lineage. Accumulating evidence indicates that RAS regulates EPO, an essential mediator of red cell production, for human anemia and erythropoiesis in vivo and in vitro. The regulation of EPO expression by Ang II may be responsible for maintaining red blood cell homeostasis. This review highlights the biological roles of RAS for blood cell and EPO homeostasis through Ang II signaling. The molecular mechanism for Ang II-induced EPO production of the cell or tissue type-specific expression is discussed.

Mitigation of radiation-induced hematopoietic injury by the polyphenolic acetate 7, 8-diacetoxy-4-methylthiocoumarin in mice

Protection of the hematopoietic system from radiation damage, and/or mitigation of hematopoietic injury are the two major strategies for developing medical countermeasure agents (MCM) to combat radiation-induced lethality. In the present study, we investigated the potential of 7, 8-diacetoxy-4-methylthiocoumarin (DAMTC) to ameliorate radiation-induced hematopoietic damage and the associated mortality following total body irradiation (TBI) in C57BL/6 mice. Administration of DAMTC 24 hours post TBI alleviated TBI-induced myelo-suppression and pancytopenia, by augmenting lymphocytes and WBCs in the peripheral blood of mice, while bone marrow (BM) cellularity was restored through enhanced proliferation of the stem cells. It stimulated multi-lineage expansion and differentiation of myeloid progenitors in the BM and induced proliferation of splenic progenitors thereby, facilitating hematopoietic re-population. DAMTC reduced the radiation-induced apoptotic and mitotic death in the hematopoietic compartment. Recruitment of pro-inflammatory M1 macrophages in spleen contributed to the immune-protection linked to the mitigation of hematopoietic injury. Recovery of the hematopoietic compartment correlated well with mitigation of mortality at a lethal dose of 9 Gy, leading to 80% animal survival. Present study establishes the potential of DAMTC to mitigate radiation-induced injury to the hematopoietic system by stimulating the re-population of stem cells from multiple lineages.

Protection against Radiotherapy-Induced Toxicity

Radiation therapy is a highly utilized therapy in the treatment of malignancies with up to 60% of cancer patients receiving radiation therapy as a part of their treatment regimen. Radiation therapy does, however, cause a wide range of adverse effects that can be severe and cause permanent damage to the patient. In an attempt to minimize these effects, a small number of compounds have been identified and are in use clinically for the prevention and treatment of radiation associated toxicities. Furthermore, there are a number of emerging therapies being developed for use as agents that protect against radiation-induced toxicities. The aim of this review was to evaluate and summarise the evidence that exists for both the known radioprotectant agents and the agents that show promise as future radioprotectant agents.

Enhanced Expression of the Local Haematopoietic Bone Marrow Renin-Angiotensin System in Polycythemia Rubra Vera

Local bone marrow (BM) renin-angiotensin system (RAS) affects physiological and pathological haematopoiesis, including erythropoiesis. In this study, quantitative expression of the messenger RNAs of the major RAS components – angiotensin-converting enzyme (CD143), renin and angiotensinogen – were measured in BM samples by quantitative real-time polymerase chain reaction, to evaluate the activity of local BM RAS in polycythemia rubra vera (PV) in comparison with normal erythropoiesis. The presence of CD143 was also investigated in the same BM samples by flow cytometry. Increased local synthesis of the major RAS components has been identified by demonstrating corresponding mRNAs in the BM of the patients with PV. Our findings indicate up-regulation of local BM RAS, together with down-regulation of the cell surface angiotensin-converting enzyme receptors, in the autonomous neoplastic clonal erythropoiesis of PV.

Radioprotective Agents: Strategies and Translational Advances

Radioprotectors are agents required to protect biological system exposed to radiation, either naturally or through radiation leakage, and they protect normal cells from radiation injury in cancer patients undergoing radiotherapy. It is imperative to study radioprotectors and their mechanism of action comprehensively, looking at their potential therapeutic applications. This review intimately chronicles the rich intellectual, pharmacological story of natural and synthetic radioprotectors. A continuous effort is going on by researchers to develop clinically promising radioprotective agents. In this article, for the first time we have discussed the impact of radioprotectors on different signaling pathways in cells, which will create a basis for scientific community working in this area to develop novel molecules with better therapeutic efficacy. The bright future of exceptionally noncytotoxic derivatives of bisbenzimidazoles is also described as radiomodulators. Amifostine, an effective radioprotectant, has been approved by the FDA for limited clinical use. However, due to its adverse side effects, it is not routinely used clinically. Recently, CBLB502 and several analog of a peptide are under clinical trial and showed high success against radiotherapy in cancer. This article reviews the different types of radioprotective agents with emphasis on the strategies for the development of novel radioprotectors for drug development. In addition, direction for future strategies relevant to the development of radioprotectors is also addressed.

Des-Aspartate-Angiotensin I Attenuates Mortality of Mice Exposed to Gamma Radiation via a Novel Mechanism of Action

ACE inhibitors and ARBs (angiotensin receptor blockers) have been shown to attenuate radiation injuries in animal models of lethal gamma irradiation. These two classes of drug act by curtailing the actions of angiotensin II-linked inflammatory pathways that are up-regulated during gamma radiation in organ systems such as the brain, lung, kidney, and bone marrow. ACE inhibitors inhibit ACE and attenuate the formation of angiotensin II from angiotensin I; ARBs block the angiotensin AT1 receptor and attenuate the actions of angiotensin II that are elicited through the receptor. DAA-I (des-aspartate-angiotensin I), an orally active angiotensin peptide, also attenuates the deleterious actions of angiotensin II. It acts as an agonist on the angiotensin AT1 receptor and elicits responses that oppose those of angiotensn II. Thus, DAA-I was investigated for its anticipated radioprotection in gamma irradiated mice. DAA-I administered orally at 800 nmole/kg/day for 30 days post exposure (6.4 Gy) attenuated the death of mice during the 30-day period. The attenuation was blocked by losartan (50 nmole/kg/day, i.p.) that was administered sequential to DAA-I administration. This shows that the radioprotection was mediated via the angiotensin AT1 receptor. Furthermore, the radioprotection correlated to an increase in circulating PGE2 of surviving animals, and this suggests that PGE2 is involved in the radioprotection in DAA-I-treated mice. At the hematopoietic level, DAA-I significantly improved two syndromes of myelosuppression (leucopenia and lymphocytopenia), and mice pre-treated with DAA-I prior to gamma irradiation showed significant improvement in the four myelodysplastic syndromes that were investigated, namely leucopenia, lymphocytopenia, monocytopenia and thrombocytopenia. Based on the known ability of PGE2 to attenuate the loss of functional hematopoietic stem and progenitor cells in radiation injury, we hypothesize that PGE2 mediated the action of DAA-I. DAA-I completely attenuated the increase in circulating level of two inflammatory cytokines, TNFα and IL-6, in irradiated mice; and this shows that DAA-I exerted additional anti-inflammatory actions, which could also have contributed to its radioprotection. These findings show that DAA-I acts via a novel mechanism of action on the angiotensin AT1 receptor to specifically release PGE2, which mediates radioprotection in the gamma irradiated mice.

New approaches to radiation protection

Radioprotectors are compounds that protect against radiation injury when given prior to radiation exposure. Mitigators can protect against radiation injury when given after exposure but before symptoms appear. Radioprotectors and mitigators can potentially improve the outcomes of radiotherapy for cancer treatment by allowing higher doses of radiation and/or reduced damage to normal tissues. Such compounds can also potentially counteract the effects of accidental exposure to radiation or deliberate exposure (e.g., nuclear reactor meltdown, dirty bomb, or nuclear bomb explosion); hence they are called radiation countermeasures. Here, we will review the general principles of radiation injury and protection and describe selected examples of radioprotectors/mitigators ranging from small-molecules to proteins to cell-based treatments. We will emphasize agents that are in more advanced stages of development.

Radiation countermeasure agents: an update (2011-2014)

INTRODUCTION

Despite significant scientific advances over the past 60 years towards the development of a safe, nontoxic and effective radiation countermeasure for the acute radiation syndrome (ARS), no drug has been approved by the US FDA. A radiation countermeasure to protect the population at large from the effects of lethal radiation exposure remains a significant unmet medical need of the US citizenry and, thus, has been recognized as a high priority area by the government.

AREA COVERED

This article reviews relevant publications and patents for recent developments and progress for potential ARS treatments in the area of radiation countermeasures. Emphasis is placed on the advanced development of existing agents since 2011 and new agents identified as radiation countermeasure for ARS during this period.

EXPERT OPINION

A number of promising radiation countermeasures are currently under development, seven of which have received US FDA investigational new drug status for clinical investigation. Four of these agents, CBLB502, Ex-RAD, HemaMax and OrbeShield, are progressing with large animal studies and clinical trials. G-CSF has high potential and well-documented therapeutic effects in countering myelosuppression and may receive full licensing approval by the US FDA in the future.

Enhanced hematopoietic protection from radiation by the combination of genistein and captopril

The hematopoietic system is sensitive to radiation injury, and mortality can occur due to blood cell deficiency and stem cell loss. Genistein and the angiotensin converting enzyme (ACE) inhibitor captopril are two agents shown to protect the hematopoietic system from radiation injury. In this study we examined the combination of genistein with captopril for reduction of radiation-induced mortality from hematopoietic damage and the mechanisms of radiation protection. C57BL/6J mice were exposed to 8.25Gy (60)Co total body irradiation (TBI) to evaluate the effects of genistein and captopril alone and in combination on survival, blood cell recovery, hematopoietic progenitor cell recovery, DNA damage, and erythropoietin production. 8.25Gy TBI resulted in 0% survival after 30days in untreated mice. A single subcutaneous injection of genistein administered 24h before TBI resulted in 72% survival. Administration of captopril in the drinking water, from 1h through 30days postirradiation, increased survival to 55%. Genistein plus captopril increased survival to 95%. Enhanced survival was reflected in a reduction of radiation-induced anemia, improved recovery of nucleated bone marrow cells, splenocytes and circulating red blood cells. The drug combination enhanced early recovery of marrow progenitors: erythroid (CFU-E and BFU-E), and myeloid (CFU-GEMM, CFU-GM and CFU-M). Genistein alone and genistein plus captopril protected hematopoietic progenitor cells from radiation-induced micronuclei, while captopril had no effect. Captopril alone and genistein plus captopril, but not genistein alone, suppressed radiation-induced erythropoietin production. These data suggest that genistein and captopril protect the hematopoietic system from radiation injury via independent mechanisms.

A modern understanding of the traditional and nontraditional biological functions of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc-dependent peptidase responsible for converting angiotensin I into the vasoconstrictor angiotensin II. However, ACE is a relatively nonspecific peptidase that is capable of cleaving a wide range of substrates. Because of this, ACE and its peptide substrates and products affect many physiologic processes, including blood pressure control, hematopoiesis, reproduction, renal development, renal function, and the immune response. The defining feature of ACE is that it is composed of two homologous and independently catalytic domains, the result of an ancient gene duplication, and ACE-like genes are widely distributed in nature. The two ACE catalytic domains contribute to the wide substrate diversity of ACE and, by extension, the physiologic impact of the enzyme. Several studies suggest that the two catalytic domains have different biologic functions. Recently, the X-ray crystal structure of ACE has elucidated some of the structural differences between the two ACE domains. This is important now that ACE domain-specific inhibitors have been synthesized and characterized. Once widely available, these reagents will undoubtedly be powerful tools for probing the physiologic actions of each ACE domain. In turn, this knowledge should allow clinicians to envision new therapies for diseases not currently treated with ACE inhibitors.

Accelerated hematopoietic recovery with angiotensin-(1-7) after total body radiation

PURPOSE

Angiotensin (1-7) [A(1-7)] is a component of the renin angiotensin system (RAS) that stimulates hematopoietic recovery after myelosuppression. In a Phase I/IIa clinical trial, thrombocytopenia after chemotherapy was reduced by A(1-7). In this study, the ability of A(1-7) to improve recovery after total body irradiation (TBI) is shown with specific attention to radiation-induced hematopoietic injury.

MATERIALS AND METHODS

Mice were exposed to TBI (doses of 2-7 Gray [Gy]) of cesium 137 gamma rays, followed by treatment with A(1-7), typical doses were 100-1000 μg/kg given once or once daily for a specified number of days depending on the study. Animals are injected subcutaneously via the nape of the neck with 0.1 ml drug in saline. The recovery of blood and bone marrow cells was determined. Effects of TBI and A(1-7) on survival and bleeding time was also evaluated.

RESULTS

Daily administration of A(1-7) after radiation exposure improved survival (from 60% to 92-97%) and reduced bleeding time at day 30 after TBI. Further, A(1-7) increased early mixed progenitors (3- to 5-fold), megakaryocyte (2- to 3-fold), myeloid (3- to 6-fold) and erythroid (2- to 5-fold) progenitors in the bone marrow and reduced radiation-induced thrombocytopenia (RIT) (up to 2-fold). Reduction in the number of treatments to 3 per week also improved bone marrow recovery and reduced RIT. As emergency responder and healthcare systems in case of nuclear accident or/and terrorist attack may be overwhelmed, the consequence of delayed initiation of treatment was ascertained. Treatment with A(1-7) can be delayed up to 5 days and still be effective in the reduction of RIT or acceleration of bone marrow recovery.

CONCLUSIONS

The data presented in this paper indicate that A(1-7) reduces the consequences of critical radiation exposure and can be initiated well after initial exposure with maximal effects on early responding hematopoietic progenitors when treatment is initiated 2 days after exposure and 5 days after exposure for the later responding progenitors and reduced thrombocytopenia. There was some effect of A(1-7) even when given days after radiation exposure.

The peptide network regulated by angiotensin converting enzyme (ACE) in hematopoiesis

The concept of a local bone marrow renin-angiotensin system (RAS) has been introduced and accumulating evidence suggests that the local RAS is actively involved in hematopoiesis. Angiotensin converting enzyme (ACE) is a key player in the RAS and makes the final effector angiotensin II. Besides angiotensin II, ACE also regulates a panel of bioactive peptides, such as substance P, Ac-SDKP and angiotensin 1-7. These peptides have also been individually reported in the regulation of pathways of hematopoiesis. In this setting, an ACE-regulated peptide network orchestrating hematopoiesis has emerged. Here, we focus on this peptide network and discuss the roles of ACE and its peptides in aspects of hematopoiesis. Special attention is given to the recent revelation that ACE is a bona fide marker of hematopoietic stem cells.

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.

Ramipril mitigates radiation-induced impairment of neurogenesis in the rat dentate gyrus

BACKGROUND

Sublethal doses of whole brain irradiation (WBI) are commonly administered therapeutically and frequently result in late delayed radiation injuries, manifesting as severe and irreversible cognitive impairment. Neural progenitors within the subgranular zone (SGZ) of the dentate gyrus are among the most radiosensitive cell types in the adult brain and are known to participate in hippocampal plasticity and normal cognitive function. These progenitors and the specialized SZG microenvironment required for neuronal differentiation are the source of neurogenic potential in the adult dentate gyrus, and provide a continuous supply of immature neurons which may then migrate into the adjacent granule cell layer to become mature granule cell neurons. The extreme radiosensitivity of these progenitors and the SGZ microenvironment suggests the hippocampus as a prime target for radiation-induced cognitive impairment. The brain renin-angiotensin system (RAS) has previously been implicated as a potent modulator of neurogenesis within the SGZ and selective RAS inhibitors have been implicated as mitigators of radiation brain injury. Here we investigate the angiotensin converting enzyme (ACE) inhibitor, ramipril, as a mitigator of radiation injury in this context.

METHODS

Adult male Fisher 344 rats received WBI at doses of 10 Gy and 15 Gy. Ramipril was administered beginning 24 hours post-WBI and maintained continuously for 12 weeks.

RESULTS

Ramipril produced small but significant reductions in the deleterious effects of radiation on progenitor proliferation and neuronal differentiation in the rat dentate gyrus following 10 Gy-WBI, but was not effective following 15 Gy-WBI. Ramipril also reduced the basal rate of neurogenesis within the SGZ in unirradiated control rats.

CONCLUSIONS

Our results indicate that chronic ACE inhibition with ramipril, initiated 24 hours post-irradiation, may reduce apoptosis among SGZ progenitors and/or inflammatory disruption of neurogenic signaling within SGZ microenvironment, and suggest that angiotensin II may participate in maintaining the basal rate of granule cell neurogenesis.

Timing of captopril administration determines radiation protection or radiation sensitization in a murine model of total body irradiation

OBJECTIVE

Angiotensin II (Ang II), a potent vasoconstrictor, affects the growth and development of hematopoietic cells. Mixed findings have been reported for the effects of angiotensin-converting enzyme (ACE) inhibitors on radiation-induced injury to the hematopoietic system. We investigated the consequences of different regimens of the ACE inhibitor captopril on radiation-induced hematopoietic injury.

MATERIALS AND METHODS

C57BL/6 mice were either sham-irradiated or exposed to (60)Co total body irradiation (0.6 Gy/min). Captopril was provided in the water for different time periods relative to irradiation.

RESULTS

In untreated mice, the survival rate from 7.5 Gy was 50% at 30 days postirradiation. Captopril treatment for 7 days prior to irradiation resulted in radiosensitization with 100% lethality and a rapid decline in mature blood cells. In contrast, captopril treatment beginning 1 hour postirradiation and continuing for 30 days resulted in 100% survival, with improved recovery of mature blood cells and multilineage hematopoietic progenitors. In nonirradiated control mice, captopril biphasically modulated Lin(-) marrow progenitor cell cycling. After 2 days, captopril suppressed G(0)-G(1) transition and a greater number of cells entered a quiescent state. However, after 7 days of captopril treatment Lin(-) progenitor cell cycling increased compared to untreated control mice.

CONCLUSION

These findings suggest that ACE inhibition affects hematopoietic recovery following radiation by modulating the hematopoietic progenitor cell cycle. The timing of captopril treatment relative to radiation exposure differentially affects the viability and repopulation capacity of spared hematopoietic stem cells and, therefore, can result in either radiation protection or radiation sensitization.

Expression of angiotensin-converting enzyme (CD143) identifies and regulates primitive hemangioblasts derived from human pluripotent stem cells

We report that angiotensin-converting enzyme (ACE), a critical physiologic regulator of blood pressure, angiogenesis, and inflammation, is a novel marker for identifying hemangioblasts differentiating from human embryonic stem cells (hESC). We demonstrate that ACE+CD45-CD34+/- hemangioblasts are common yolk sac (YS)-like progenitors for not only endothelium but also both primitive and definitive human lymphohematopoietic cells. Thrombopoietin and basic fibroblast growth factor are identified as critical factors for the proliferation of human hemangioblasts. The developmental sequence of human embryoid body hematopoiesis is remarkably congruent to the timeline of normal human YS development, which occurs during weeks 2 to 6 of human gestation. Furthermore, ACE and the renin-angiotensin system (RAS) directly regulate hemangioblast expansion and differentiation via signaling through the angiotensin II receptors AGTR1 and AGTR2. ACE enzymatic activity is required for hemangioblast expansion, and differentiation toward either endothelium or multipotent hematopoietic progenitors is dramatically augmented after manipulation of angiotensin II signaling with either AGTR1- or AGTR2-specific inhibitors. The RAS can therefore be exploited to direct the hematopoietic or endothelial fate of hESC-derived hemangioblasts, thus providing novel opportunities for human tissue engineering. Moreover, the initial events of human hematoendotheliogenesis can be delineated in a manner previously impossible because of inaccessibility to early human embryonic tissues.

The effect of losartan on hemoglobin concentration and renal outcome in diabetic nephropathy of type 2 diabetes

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers can decrease hemoglobin, causing anemia and this may be an independent risk factor for chronic kidney disease progression. We studied the relationship between a decline in hemoglobin and outcome in 1513 patients with type 2 diabetes and kidney disease by a post hoc analysis of the RENAAL Study (Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan) with an average follow-up of 3.4 years. The relationship between baseline and year-1 hemoglobin and treatment on end-stage renal disease (ESRD) and ESRD or death was evaluated using multivariate Cox models (covariates: baseline hemoglobin, proteinuria, serum albumin, serum creatinine, and year-1 hemoglobin). Compared with placebo, losartan treatment was associated with a significant decrease of hemoglobin, with the largest between-group difference at 1 year. After adjustment, there were significant relative risk reductions for losartan compared with placebo for ESRD and for ESRD or death regardless of the baseline hemoglobin even in those patients with a baseline hemoglobin below 120 g l(-1). Hence, the renoprotective properties of losartan were maintained despite a significant lowering of the hemoglobin concentration.

Over-expression of angiotensin-converting enzyme (CD 143) on leukemic blasts as a clue for the activated local bone marrow RAS in AML

Local bone marrow renin-angiotensin system (RAS) is an autocrine-paracrine system affecting hematopoiesis. Angiotensin II type 1a (AT1a) receptors are present on the CD34+ hematopoietic stem cells. Angiotensin II stimulates the proliferation of bone marrow and umbilical cord blood hematopoietic progenitors. There are preliminary data that local RAS might also be involved in leukemogenesis. ACE hyper-function may lead to the acceleration of negative hematopoietic regulator peptide, AcSDKP, metabolism, which in turn lowers its level in the bone marrow micro-environment, finally removing the anti-proliferative effect of AcSDKP on the hematopoietic cells and blasts. Renin expression could have a role on the leukemia development and angiotensin may act as an autocrine growth factor for acute myeloid leukemia (AML) cells. The aim of this study is to search ACE (CD 143) surface antigen by flow-cytometric analyses on the leukemic blast cells taken from the bone marrow of the patients with AML. Bone marrow aspiration materials and peripheral blood samples were obtained from 11 patients with AML (eight males, three females; aged 46 (range 26-67) years) and six patients with non-malignant hematological disorders (four males, two females; aged 56 (range 22-71) years). ACE (CD 143) surface antigen was shown to be over-expressed in leukemic myeloid blast cells. ACE is positively correlated with bone marrow blast count. Elucidation of the pathological activity of the local RAS-mediated regulation of the leukemogenesis is both pathobiologically and clinically important, since the angiotensin peptides represent a molecular target in the disease management.

The hematopoietic system: a new niche for the renin–angiotensin system

The role of the renin-angiotensin system was previously thought to be restricted to the cardiovascular system. It now appears that this system also has important functions in other tissues. Hematopoiesis can be affected by inhibitors of the renin system in patients and in various experimental models. The renin system, particularly angiotensin II, has a role in different stages of hematopoiesis, notably during the first wave in the chick embryo (primitive hematopoiesis) and in the human adult (definitive hematopoiesis). In addition, the renin-angiotensin system in mice is involved in reconstitutive hematopoiesis following experimental irradiation; inhibition of this system improved the hematopoietic recovery in this situation. The clinical relevance and therapeutic applications of these findings offer a new area of clinical research. In this article, we review the evidence for a role for the renin system in the control of hematopoiesis at its different stages.

Cytokine-based treatment of accidentally irradiated victims and new approaches

A major goal of medical management of acute radiation syndrome following accidental exposures to ionizing radiation (IR) is to mitigate the risks of infection and hemorrhage related to the period of bone marrow aplasia. This can be achieved by stimulating the proliferation and differentiation of residual hematopoietic stem and progenitor cells (HSPC) related to either their intrinsic radioresistance or the heterogeneity of dose distribution. This is the rationale for treatment with hematopoietic growth factors. In fact, apoptosis has recently been shown to play a major role in the death of the continuum of more or less radiosensitive HSPC, soon after irradiation. Therefore, administration of antiapoptotic cytokine combinations such as stem cell factor, Flt-3 ligand, thrombopoietin, and interleukin-3 (4F), may be important for multilineage recovery, particularly when these factors are administered early. Moreover, acute exposure to high doses of IR induces sequential, deleterious effects responsible for a delayed multiple organ dysfunction syndrome. These considerations strongly suggest that therapeutics could include tissue-specific cytokines, such as keratinocyte growth factor, and pleiotropic agents, such as erythropoietin, in addition to hematopoietic growth factors to ensure tissue damage repair and mitigate the inflammatory processes. Noncytokine drugs have also been proposed as an alternative to treat hematopoietic or nonhematopoietic radiation effects. To develop more effective treatments for radiation injuries, basic research is required, particularly to improve understanding of stem cell needs within their environment. In the context of radiological terrorism and radiation accidents, new growth promoting molecules need to be approved and available cytokines stockpiled.

Angiotensin II stimulates arachidonic acid release from bone marrow stromal cells

INTRODUCTION

Angiotensin II (Ang II) is recognised as a regulator of haematopoiesis, but its actions within the bone marrow are not fully understood. Support of haematopoiesis by bone marrow stromal cells (MSC) is dependent on factors that include arachidonic acid and macrophage colony stimulating factor (MCSF), both of which are increased by Ang II stimulation in other tissues. To further elucidate the mechanisms of Ang II-regulated haematopoiesis, we determined whether Ang II-stimulation alters arachidonic acid release and MCSF secretion from MSC.

METHODS

Cynomolgus monkey MSC isolated from bone marrow aspirates and the human HS-5 stromal cell line were studied for Ang II-mediated arachidonic acid (AA) release, while secretion of MCSF in response to Ang II was studied in HS-5 cells. Cells were labelled overnight with 3H-AA and the release of 3H-AA was measured in culture medium following 20 minutes stimulation with Ang II, alone or in combination with the AT1- or AT2-receptor antagonists, losartan and PD 123319, respectively. MCSF secretion into culture medium was measured using an enzyme immunoassay following 24 hours of treatment with Ang II alone or in combination with losartan or PD 123319. Phorbol-myristate-acetate, known to stimulate release of AA and MCSF, was used as a positive control in both experiments.

RESULTS

In response to Ang II, release of 3H-AA from monkey and human MSC was increased (p<0.05) to 147+/-4% and 124+/-3% of control, respectively. The AT1- and AT2-receptor antagonists, losartan and PD 123319, individually reduced Ang II-stimulated 3H-AA release. In contrast, Ang II had no effect on secretion of MCSF from HS-5 cells.

CONCLUSIONS

These results provide mechanistic evidence for Ang II-mediated haematopoiesis through AA release that may, in part, explain Ang II-facilitated recovery of haematopoiesis in experimental myelosuppression and the anaemias associated with Ang II receptor blockade.

Local umbilical cord blood renin?angiotensin system

Local bone marrow (BM) renin-angiotensin system (RAS) is an autocrine-paracrine system affecting normal and neoplastic hematopoiesis. Angiotensin II type 1a (AT1a) receptors are present on the CD34(+) hematopoietic stem cells (HSC). Angiotensin II stimulates the proliferation and differentiation of the HSC populations through the activation of AT1 receptors on HSC. Umbilical cord blood (UCB) is a rich source of HSC. The existence of a complete local UCB RAS has not been previously investigated. In this study, local synthesis of the major RAS components, namely, angiotensin-converting enzyme (ACE), renin, and angiotensinogen, was identified by demonstrating their corresponding mRNAs using quantitative reverse transcriptase polymerase chain reaction (RT-PCR) in human UCB. Local RAS could regulate cellular growth in a variety of tissues including the BM. Major RAS peptides can exert significant effects on primitive pluripotential HSC populations. Further studies should focus on the interactions between possible autocrine, paracrine, endocrine, and intracrine actions of the local UCB RAS and growth, engraftment, differentiation, and plasticity functions of HSC of UCB origin.