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Modified glucocorticoid stabilizes dysferlin-deficient muscle cell membrane in experimental models

August 27, 2018

Sen Chandra Sreetama and Jyoti K Jaiswal

Limb girdle muscular dystrophy type 2B (LGMD2B) – a disease so rare that researchers aren’t even sure how many people it affects – is characterized by chronic muscle inflammation and progressively weakened muscles in the pelvis and shoulder girdle. It can affect able-bodied people during their childbearing years and makes it difficult to tiptoe, walk, run or rise unaided from a squat. Ultimately, many with the muscle-wasting condition require wheelchair assistance. There is no therapy approved by the Food and Drug Administration for this condition.

In a head-to-head trial between the conventional glucocorticoid, prednisolone, and a modified glucocorticoid, vamorolone, in experimental models of LGMD2B, vamorolone improved dysferlin-deficient muscle cell membrane stability and repair. This correlated with increased muscle strength and decreased muscle degeneration, according to a Children’s-led study published online Aug. 27, 2018, in Molecular Therapy. By contrast, prednisolone worsened muscle weakness, impaired muscle repair and increased myofiber atrophy.

“These two steroids differ by only two chemical groups,” says Jyoti K. Jaiswal, MSC, Ph.D., a principal investigator at Children’s National Health System and senior study author. “One made muscle repair better. The other made muscle repair worse or about the same as untreated experimental models. This matches experience in the clinic as patients with LGMD2B experienced increased muscle weakness after being prescribed conventional glucocorticoids, such as prednisolone.”

Healthy muscle cells rely on the protein dysferlin to properly repair the sarcolemmal membrane, a cell membrane specialized for muscle cells that serves a vital role in ensuring that muscle fibers are strong enough and have the necessary resources to contract. Mutations in the DYSF gene that produces this essential protein causes LGMD2B.

Jaiswal likens the plasma membrane to a balloon that sits atop the myofiber, a long cell that when healthy can flex and contract. If, in the process of myofiber contraction, the plasma membrane experiences anything out of sync or overly stressful, it develops a tear that needs to be quickly sealed. An intact balloon keeps air inside; tear it, and air escapes. When the plasma membrane tears, calcium from the outside leaks in, causing the muscle cell to collapse into a ball and die. The body contends with the dead cell by breaking it up into fragments and sending in inflammatory cells to clear the debris.

Lack of dysferlin is associated with increased lipid mobility in the LGMD2B cell membrane

Lack of dysferlin is associated with increased lipid mobility in the limb girdle muscular dystrophy type 2B (LGMD2B) cell membrane, which is further increased by injury and prednisolone treatment, causing failure of these cells to undergo repair. By contrast, vamorolone treatment stabilizes the LGMD2B muscle cell membrane to near healthy cell level, enabling repair of injured cells.

The study team got the idea for the current research project during a previous study of the experimental treatment vamorolone for a different type of muscular dystrophy. “In Duchenne muscular dystrophy (DMD), treatment with vamorolone not only reduced inflammation, but the membranes of muscle fibers were stabilized. That was the team’s ah-hah moment,” he says.

Three different doses of vamorolone were tested on cells derived from patients with LGMD2B with higher cell membrane repair efficacy seen with rising treatment dose. The dysferlinopathic experimental models were treated for three months with daily doses of cherry syrup laced with either 30 mg/kg of vamorolone or prednisolone or cherry syrup alone as the placebo arm.

“Right now there are zero treatments,” he says. People with LGMD2B turn to rehabilitative therapies and movement aids to cope with loss of mobility. Doctors are cautioned not to prescribe steroids. Jaiswal says many patients with LGMD2B grew up doing strenuous exercise, former athletes whose first indication of a problem was muscle cramping and pain. How this progresses to muscle weakness and loss is an area of active research in Jaiswal’s lab. “While additional research is needed, our findings here suggest that modified steroids such as vamorlone may be an option for some patients,” Jaiswal says.

“There is a nuance here: In addition to genomic effects, steroids also have physical effects on the cell membrane which may make some of the approved steroids ‘good’ steroids for dysferlinopathy that could selectively be used for this disease,” adds Sen Chandra Sreetama, lead study author. Further research could indicate whether vamorolone, which is in Phase II human clinical trials for DMD, or any off-the-shelf drug could slow decline in muscle function for patients with LGMD2B.

Additional Children’s study authors include Goutam Chandra; Jack H. Van der Meulen; Mohammad Mahad Ahmad; Peter Suzuki; Shivaprasad Bhuvanendran; and Kanneboyina Nagaraju and Eric P. Hoffman, both of ReveraGen BioPharma.

Research reported in this news release was supported by the Clark Charitable Foundation; Muscular Dystrophy Association, under award number MDA277389; National Institute of Arthritis and Musculoskeletal and Skin Diseases, under award number R01AR055686; National Institutes of Health (NIH), under award numbers K26OD011171 and R24HD050846; and the District of Columbia Intellectual and Developmental Disabilities Research Center under NIH award number 1U54HD090257.

Long-term glucocorticoids help patients with DMD

December 4, 2017

Glucocorticoids, a class of steroid hormone medications, have definite long-term benefits for patients with Duchenne muscular dystrophy, including extending muscle strength and function over years and decreasing the risk of death.

There is currently no cure for the devastating, progressive neuromuscular disease known as Duchenne muscular dystrophy (DMD). But clinics that treat patients with this disease have long relied on a class of steroid hormone medications, known as glucocorticoids, to ease its symptoms. Over weeks and months, these drugs help preserve muscle strength and function. Though these short-term benefits have been clear, some physicians have balked at using these medications over the long term – their benefits over years was unknown, making their potential side effects not worth the risk.

Now, a study published online Nov. 22, 2017 in The Lancet suggests that these medicines have definite long-term benefits, including extending muscle strength and function over years and even decreasing the risk of death. These findings support what has become the standard prescribing practice at many clinics and could help sway parents who are on the fence about their children receiving these therapies.

DMD is characterized by loss of muscle function and progressive muscle weakness that begins in the lower limbs and typically affects males due to the location of its causative genetic mutation. Patients with this devastating neuromuscular disease often receive glucocorticoids at some point as the disease progresses. Studies since the late 1980s have confirmed short-term benefits of treating with these drugs, including delaying the loss of muscle strength and function.

However, no prospective study had followed long-term glucocorticoid use in these patients, explains Heather Gordish-Dressman, Ph.D., a statistician at the Center for Genetic Medicine Research at Children’s National Health System and study senior author. The lack of long-term data led some physicians to delay treatment with these drugs since their use can lead to significant side effects, including weight gain, delayed growth and immunosuppression.

“Everyone had the idea that long-term use could be beneficial, but nobody had really rigorously tested that,” Gordish-Dressman says.

Craig McDonald, M.D., a University of California, Davis, professor and lead author of the study adds: “This long-term, follow-up study provides the most definitive evidence that the benefits of glucocorticoid steroid therapy in DMD extend over the entire lifespan. Most importantly, patients with Duchenne using glucocorticoids experienced an overall reduction in risk of death by more than 50 percent.”

To determine whether the short-term benefits of these drugs extend in the long term, Gordish-Dressman and researchers scattered across the country tapped data from the Cooperative International Neuromuscular Research Group’s Duchenne Natural History Study, the largest study to follow patients with DMD over time. They gathered data for 440 males with DMD aged 2 to 8 years old. About 22 percent had never taken glucocorticoids or had taken these medications for less than one year. The remainder had taken them for at least one year or longer.

By analyzing data for up to 10 years for these patients, the long-term benefits became clear, Gordish-Dressman adds. Glucocorticoid treatment for patients who received it for more than one year delayed loss of mobility milestones that affected the lower limbs by 2.1 to 4.4 years, such as going from supine to standing, climbing four stairs, and walking or running 10 meters, compared with boys who received the medications for less than one year. Long-term glucocorticoid therapy also delayed the loss of mobility milestones in upper limbs, such as hand function, performing a full overhead reach and raising the hands to the mouth.

Long-term use of these drugs also was associated with a decreased risk of death over the length of the study. Furthermore, deflazacort – a glucocorticoid recently approved by the Food and Drug Administration specifically for DMD – delayed loss of the ability to move from supine position to standing, walking and hand-to-mouth function significantly better than prednisone, the most popular glucocorticoid prescribed for DMD in the United States.

Gordish-Dressman says that glucocorticoids are currently a standard part of care for most patients with DMD, with some clinics prescribing these medications as soon as patients are diagnosed. However, because long-term data supporting their use was lacking, some physicians hesitate to prescribe glucocorticoids until the disease had progressed, when patients already had lost significant function.

Future studies will examine which medicines in this class of drugs and which regimens might offer the most benefits as well as how benefits differ with longer-term medication use.

Research reported in this news release was supported by the U.S. Department of Education/NIDRR, H133B031118 and H133B090001; the U.S. Department of Defense, W81XWH-12-1-0417; National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under award number R01AR061875; and Parent Project Muscular Dystrophy.

Antioxidants could thwart muscle repair

September 6, 2017

Science Signaling features a Research Article that describes the pathway by which mitochondria transduce the increase in cytosolic Ca2+ caused by plasma membrane injury into a ROS-dependent repair response. The image shows ROS production and actin polymerization as detected by fluorescent reporters near a plasma membrane injury site in a skeletal myofiber in an intact bicep of an experimental model. Credit: Adam Horn and Jyoti Jaiswal, M.S.C., Ph.D. Children’s National Health System and The George Washington University School of Medicine and Health Sciences

Reactive oxygen species (ROS) are a biological double-edged sword. These atoms, molecules or molecular fragments containing oxygen that is poised for chemical reactions, are a key part of the immune response, used by immune cells to kill potentially dangerous invaders such as bacteria. However, too much ROS – which also are produced as a normal part of cellular metabolism – can cause extreme damage to normal, healthy cells.

Because oxidative damage has been linked with cancer, many people make a concerted effort to consume antioxidants in food and as concentrated supplements. These compounds can neutralize ROS, stemming cellular damage. Taking antioxidants also has been thought to stem the muscle soreness from exercise since ROS are produced in excess during hard physical activity.

However, a new study led by researchers from Children’s National Health System finds that taking antioxidants could thwart the processes that repair muscle fibers. According to the study published Sept. 5, 2017 in Science Signaling and featured on the journal’s cover, oxidative species are crucial signals that start the process of repairing muscle fibers.

Cellular powerhouses known as mitochondria help injured muscle cells (myofibers) repair by soaking up calcium that enters from the site of injury and using it to trigger increased production of reactive oxygen species. Loading up mitochondria with excess antioxidants inhibits this signaling process, blocking muscle repair, exacerbating myofiber damage and diminishing muscle strength.

“Our results suggest a physiological role for mitochondria in plasma membrane repair in injured muscle cells, a role that highlights a beneficial effect of reactive oxygen species,” says Jyoti K. Jaiswal, M.S.C., Ph.D., principal investigator in the Center for Genetic Medicine Research at Children’s National Health System, associate professor of genomics and precision medicine at The George Washington University School of Medicine and Health Sciences and senior study author. “Our work highlights the need to take a nuanced view of the role of reactive oxygen species, as they are necessary when they are present at the right place and right time. Indiscriminate use of antioxidants actually could harm an adult with healthy muscles as well as a child with diseased muscle.”

Antioxidants are widely used by Baby Boomers with muscles that ache from a grueling workout or newborns diagnosed with muscular dystrophy. Jaiswal and Children’s National colleagues understand that their results buck conventional wisdom that antioxidants generally benefit muscle recovery.

“It is still a common belief within the fitness community that taking antioxidant supplements after a workout will help your muscles recover better. That’s what people think; that’s what I thought,” says Adam Horn, lead study author, a graduate student at The George Washington University who works with Jaiswal at Children’s National. “What we’ve done is figure out that mitochondria need to produce a very specific oxidative signal in response to muscle damage in order to help injured muscles repair.” Jyoti Jaiswal and Adam Horn

The oxidative signals produced by mitochondria are delicately balanced by the antioxidant defenses in healthy cells. This balance can be disrupted in diseases such as Duchenne muscular dystrophy, which is caused by the lack of a muscle-specific protein, dystrophin. Lack of dystrophin makes the muscle cell plasma membrane more vulnerable to injury. In an experimental model of Duchenne muscular dystrophy, the muscles at birth are seemingly normal but, within weeks, show obvious muscle damage and progressive weakness.

“What changes? One of the things that changes in the third and fourth week of life of this experimental model is mitochondrial functionality,” Jaiswal adds. “They end up with many dysfunctional mitochondria, which compromise repair of injured myofibers. This permits chronic and excessive oxidation of the myofibers and disruption of the proper oxidant-antioxidant balance.”

In this case, a dose of antioxidants may restore that proper balance and help to reverse muscle damage and progressive weakness.

As a next step, the research team is examining oxidation in healthy and diseased muscle to understand how the oxidant-antioxidant balance is disrupted and how it could be restored efficiently by using existing supplements. In one such study funded by the National Institutes of Health, the team is looking at the potential benefit of vitamin E supplements for patients with muscular dystrophy.

“Antioxidant supplements are made from extracts of bark, sap, chocolate and other compounds so they’re all different,” Jaiswal says. “Knowing which ones can restore balance under a specific circumstance has the potential to help the body maintain proper cellular signaling ability, which will keep muscles healthy and working properly.”

The response of actin protein following injury to a pair of muscle fibers in an intact biceps muscle.