In both sickle cell disease (SCD) and thalassemias, known collectively as hemoglobinopathies, the bone marrow produces red blood cells that contain mutated hemoglobin. The consequences of this mutation can be severe. In SCD, for example, several biological processes are impaired, and damage occurs to almost every organ system. Given the complex pathology of hemoglobinopathies, the NHLBI recognized the need for a multidisciplinary approach to researching these conditions and created the Excellence in Hemoglobinopathies Research Award (EHRA) program to support such broad-based studies. The EHRA program has awarded grants to eight multidisciplinary research centers, each with distinct research aims. Together, these centers are working to translate discoveries about disease processes into improved clinical care. Below we describe each center’s research—and what can be gained if the research succeeds.
Reactivating the Gamma Globin Gene in SCD
Two Centers: Boston Children’s Hospital and a center composed of the University of Michigan, University of Illinois, Cleveland Clinic, and Case Western Reserve University
The promise of reversing SCD symptoms by reactivating a suppressed gene has attracted the interest of two EHRA-funded centers. Although they are taking different approaches, each center has the same goal: stimulating red blood cells in the bone marrow to produce fetal hemoglobin, a non-mutant form of hemoglobin that the body normally stops producing shortly after birth. Although patients with SCD have a mutant gene for a component of adult hemoglobin, their gene for gamma globin, the novel subunit of fetal hemoglobin, is not mutated. Thus, these patients have within their genome the genetic pieces their red blood cells need to produce functioning fetal hemoglobin. Researchers in these two centers are exploring ways to successfully reactivate the gamma globin gene. More information on this promising research, which could also be used to treat beta thalassemias, can be found here.
Understanding Kidney and Heart Problems in SCD
Cincinnati Children’s Hospital Medical Center
SCD can harm proper kidney and heart functioning, but little is known about the precise mechanisms that drive these dysfunctions. This research center will investigate exactly how SCD leads to stiffened heart muscle and scarred, impaired kidney tissue. The investigators in Cincinnati Children’s Hospital Medical Center also plan to conduct a clinical trial that will test novel cardiac imaging techniques. With improved imaging procedures, doctors would be able to more effectively monitor heart health in patients with SCD and potentially intervene before significant damage is done.
Monitoring Blood Flow in SCD
Children’s Hospital of Los Angeles
In SCD, the sickle-shaped blood cells have a tendency to obstruct the smallest vessels in the body, impairing blood flow, which leads to tissue damage and pain. Despite the importance of blood flow rate in SCD, doctors presently do not have any way of non-invasively measuring it. To meet this clinical need, researchers at the Children’s Hospital of Los Angeles are developing and refining ways to non-invasively assess blood flow. Once the researchers validate a reliable approach, doctors will be able to use it to gauge the effectiveness of new treatments, particularly those designed to promote normal blood flow in patients.
Inhibiting the Coagulation Cascade in SCD
University of North Carolina at Chapel Hill
For reasons that are not completely clear, the blood of patients with SCD is more prone to activation of coagulation, or blood clotting. Although blood clotting can be healthy in the right context, inappropriate coagulation puts patients with SCD at increased risk for stroke and dangerous blood clots in the lungs. To better understand this “hypercoagulability” in patients with SCD and its contribution to disease pathology, researchers at the University of North Carolina at Chapel Hill are studying proteins that drive coagulation and testing the effects of compounds that inhibit these proteins. Their studies in mice indicate that inhibiting coagulation-promoting proteins not only limits coagulation but also dampens inflammation. The researchers plan to test whether interfering with these proteins also improves symptoms in patients with SCD.
Blocking Endothelin-1 to Improve SCD Symptoms
Georgia Regents University, Rutgers University, and University of Alabama at Birmingham
Research in mice has shown that increased levels of the protein endothelin-1 play a role in kidney damage, lung injuries, and chronic pain. This center has assembled a multidisciplinary team of researchers with expertise in kidney disease, the mouse model of SCD, molecular biology, and pain research with the hope of making further discoveries about the wide-ranging effects of endothelin-1.
These researchers will study how endothelin-1 contributes to disease manifestations and test whether a drug can reduce the protein’s negative effects in mice. The drug being tested binds to one of the cellular receptors for endothelin-1, thereby preventing endothelin-1 from docking in that receptor and initiating unwanted cellular changes. In preliminary research by the team, this endothelin-1 “blockade” has improved symptoms in SCD mice, including returning their heightened sensitivity to pain to normal levels. In addition to testing the therapy in animal models, toward the end of the five-year research project, the investigators will assess whether inhibition of endothelin-1 in humans ameliorates SCD symptoms. The researchers may also study how endothelin-1 contributes to disease in thalassemias.
Understanding Pain Pathways, Measuring Pain, and Treating Pain in SCD
University of Minnesota
Many patients with SCD live with recurrent pain crises their entire lives, starting in infancy. However, few SCD researchers have focused on pain. This center hopes to make up for the dearth of SCD pain research by exclusively studying pain—its molecular pathways, how to measure it, and how to treat it more effectively. More information about the pain signaling pathways this center has already uncovered and the readily available therapeutic the center will be testing can be found here.
Unraveling and Preventing the Causes of Acute Chest Syndrome in SCD
University of Pittsburgh, Emory University, and Vanderbilt University
Acute chest syndrome (ACS) is the leading cause of death in SCD. In addition to being potentially fatal, ACS is very painful and, if it occurs repeatedly, is a risk factor for chronic lung disease. Given the serious threat ACS poses to health and quality of life in patients with SCD, this center is conducting studies to better understand the molecular underpinnings of how this condition develops. In particular, researchers will be testing their hypothesis that hemin, a component of hemoglobin, causes ACS through interaction with another protein, TLR4. Hemin is more abundant in the bloodstream of patients with SCD because their red blood cells are more prone to rupturing, which results in the release of hemin. The center is studying at least two potential approaches to preventing the pathological interaction between hemin and TLR4: inhibiting TLR4 and injecting hemopexin, a natural blood component that is readily available and that in effect mops up the free hemin.
In addition to funding research, the EHRA program requires centers to mentor and train new investigators in hemoglobinopathy translational research. Supported by EHRA funds, some centers are also providing summer research opportunities to high school students. This training component of the program has the potential to create a pipeline of researchers for future hemoglobinopathy research.
“Training new researchers and funding transformative research is the core of our mission at the NHLBI,” said Harvey Luksenburg, M.D., SCD Project Director for the NHLBI. “The EHRA program is the latest phase in our efforts to reinvigorate research into hemoglobinopathies. And with this group of centers, I’m confident that we stand to make significant progress in improving treatment for SCD and thalassemias.”
The seed for this center’s research was planted several years ago during a scientific conference. Dr. Kalpna Gupta, a cancer biologist, was attending a sickle cell disease meeting to learn about blood vessel development research relevant to her study of cancer. While there, she heard a 10-year-old with SCD describe the frequent pain he experienced that caused him to miss school days. When Dr. Gupta later asked sickle cell disease researchers what they were doing to study pain, she discovered that few, if any, studies were devoted to pain in SCD.
And with that, Dr. Gupta shifted her research focus from cancer biology to pain in sickle cell disease. Now, she is the principal investigator for an EHRA center focused on understanding the molecular and cellular pathways that govern severe pain in patients with SCD.
As the center works to uncover these pathways, they will simultaneously study and test alternatives to opioids, the conventional treatment for pain in patients with SCD. As the standard treatment, opioids have several disadvantages. For example, although they can dampen pain, they can also activate pain pathways. Specifically, in mice, opioids activate mast cells, and these cells in turn activate peripheral nerve cells, causing more pain.
Another problem with treating SCD pain with opioids is that doctors must often prescribe them for long periods, which creates the risk that the patient’s body will develop a tolerance for the drug, reducing the drug’s effectiveness. Doctors who fear this outcome or worry about the patient developing an addiction may undertreat the patient, resulting in the patient enduring more pain than needed. Overtreatment of pain is also a risk and can cause death from overdose. Thus, opioids as the standard of care for treating SCD pain have several drawbacks.
Dr. Gupta’s center is exploring alternative pain medicines, including compounds that would inhibit mast cells and thereby block one pain activation pathway. However, Dr. Gupta pointed out it that may take 10 years to receive regulatory approval for use of newer compounds. Thus, in the meantime, Dr. Gupta and her colleagues are also studying the potential pain-reduction value of a readily available, relatively inexpensive compound: vaporized Cannabis.
Dr. Gupta pointed out that Cannabis doesn’t have many of the liabilities associated with opioids, such as respiratory depression and constipation. In addition, “the fear of addiction is far less with Cannabis than with opioids,” she noted. “So, from every point of view, Cannabis seems like a very convenient alternative for the time being.”
The center will soon begin a clinical trial testing the effectiveness of Cannabis in patients with SCD.
In addition to researching pain pathways and improved pain treatments, the center is refining neuroimaging and electroencephalogram techniques that will allow doctors to objectively quantify a patient’s degree of pain. Currently, a patient has to subjectively describe his or her level of pain, which is often difficult to do with precision or consistency. Once the center validates a new means of measuring pain, researchers will be able to deploy the technique to fine tune treatment plans.
All of these refinements in understanding and treating SCD pain are ones that might not have come about if Dr. Gupta hadn’t been moved by a young patient’s plight. Reflecting on the scientific conference that changed the direction of her career, Dr. Gupta reaffirmed the importance of studying pain in SCD and her optimism about the research.
“I said, ‘Somebody’s got to do it.’ And so it was a huge risk I took to divert my career into a different direction, but I think every day that we make progress in little baby steps, it’s very rewarding to see it’s going toward the right direction. And now we are able to do a trial, so I am very optimistic. Should it show something positive, it would at least bring a little light to the table, and I see light at the end of the tunnel at least.”
Altering the Epigenetics of Red Blood Cells to Treat Hemoglobinopathies
Two centers: Boston Children’s Hospital and a center composed of the University of Michigan, University of Illinois, Cleveland Clinic, and Case Western Reserve University)
In recent years, research has increasingly revealed the health importance of epigenetic changes—that is, changes in gene expression (i.e., production of a protein from a gene) without any change in the gene sequence itself. For example, cancer may arise if a particular gene, despite lacking a mutation, stops producing a needed protein product. Although SCD results from a mutated globin gene, a suppressed non-mutant globin gene remains in the genome, available for epigenetic activation. If turned on, this gene would enable the production of fetal hemoglobin and healthy red blood cells.
Fetal hemoglobin is a form of hemoglobin produced by fetuses that is better able to bind oxygen than adult hemoglobin. The superior affinity of fetal hemoglobin for oxygen is necessary because fetal hemoglobin must pull oxygen molecules from the adult hemoglobin in maternal red blood cells. Shortly after birth, newborns switch from producing fetal hemoglobin to adult hemoglobin.
Two EHRA centers hope to reverse that change. To do so, they are building on basic research that has revealed a new picture of the molecular mechanisms governing the switch. This research shows that several proteins can form complexes that repress expression of the fetal globin gene: gamma globin. (Gamma globin proteins, along with alpha globins, make up fetal hemoglobin, whereas adult hemoglobin consists of alpha globins combined with beta globins.)
The proteins that combine to repress gamma globin gene expression represent targets that these EHRA researchers are trying to inhibit. So far, the researchers have found that several compounds successfully inhibit the repressors, thereby restoring gamma globin expression (and fetal hemoglobin production) in mice. In addition, the effect has been pancellular—that is, it has worked in all red blood cells rather than in only a fraction of cells.
Achieving a pancellular effect is critical because any treatment that allows a certain percentage of cells to remain sickled will be somewhat ineffective. In fact, one of the reasons that hydroxyurea, a current treatment for SCD, is not completely effective is that, although it increases fetal hemoglobin production, its effect is heterocellular—that is, some cells do not produce fetal hemoglobin and still develop the sickle shape.
Researchers from the center made up of the University of Illinois at Chicago, the University of Michigan, Cleveland Clinic, and Case Western Reserve University are also working on another important aspect of any therapeutic: precise targeting. Whatever compounds prove effective must be targeted at developing red blood cells and avoid entering other cell types where they might have undesired effects. To achieve this targeting, researchers at this EHRA center are linking the therapeutic compounds to a protein that only binds to receptors on developing red blood cells.
Dr. Doug Engel, from the University of Michigan, said that he hopes the center’s research ultimately leads to a pill that can be taken regularly to fix red blood cells, which are continuously generated by bone marrow. Such a pill would not only benefit U.S. patients but also patients outside the country, who make up the vast majority of the hemoglobinopathy patient population. For these patients, many of whom live in developing countries in Africa and Southeast Asia, a simple pill would be a more viable alternative than expensive and risky bone marrow stem cell transplants.
Any therapeutics that the centers develop also have the potential to treat beta thalassemia, a condition that involves problems in the production of beta globins, leading to defective adult hemoglobin. Because the epigenetic treatment the researchers are developing would turn off beta globin production and turn on gamma globin production, patients’ cells could construct viable hemoglobin molecules made of alpha and gamma globins.
In addition, the benefits of these two centers’ research extend beyond hemoglobinopathies. Dr. Raffaele Renella, a physician researcher at Boston Children’s Hospital, pointed out that in their efforts to develop a therapy, they are making a lot of discoveries about fundamental molecular and cellular processes, including how genes are expressed; how proteins are formed; and how cells develop, divide, and maintain a healthy state.
Envisioning the possibilities, Dr. Engel is optimistic about an epigenetic approach to treating SCD and beta thalassemias.
“There’s a good reason to be excited about the possibilities,” he said. “I think we’re much closer now with targeted drug delivery because we know many of the players. We know specifically what we’re going for. So, we’re targeting specific molecules now and not just trying everything off the shelf.”