Discovering the therapeutic potential of hydrogen sulfide and carbon monoxide
Most of us think of hydrogen sulfide, known for its rotten egg smell, and carbon monoxide, often called the “silent killer,” as poisonous gases harmful to human health. While they can be lethal in large quantities, they are also part of a family of small molecules called gasotransmitters that are produced in our own bodies.
Lawson researchers Drs. Alp Sener and Gedas Cepinskas are using controlled doses of these molecules to pioneer new solutions to health care challenges.
Dr. Alp Sener found that hydrogen sulfide molecules can improve the preservation of kidneys before transplant to help make the kidneys last longer after transplantation.
The inspiration for Dr. Sener’s research on hydrogen sulfide and kidney transplantation came in part from a paper in the journal Science that his father showed him one day while he was an undergraduate student. The paper focused on the protective effects of hydrogen sulfide in hibernating animals. Hydrogen sulfide levels increase in animals when they hibernate and hibernation-like states can be induced in these animals by administering hydrogen sulfide.
Years later, during his postdoctoral training, he made a connection between the findings in the paper and the hibernation-like state that kidneys and other organs go into when they are being preserved in cold temperatures before transplant. He wondered what role hydrogen sulfide could play in improving this process.
Now a transplant surgeon in the Multi-Organ Transplant Program at London Health Sciences Centre (LHSC), Dr. Sener has investigated this question to address a major issue in kidney transplantation.
“Everywhere in the world there is a large discrepancy between the number of patients on the kidney transplant waiting list and the number of available organs,” says Dr. Sener. “Due to the lack of donor supply we often have to use ‘marginal’ deceased donor kidneys, which can be kidneys from older donors, donors with existing medical issues, and donors after circulatory death (loss of function of the heart and lungs). These kidneys often don’t work as long and are slower to recover after transplantation.”
After a kidney is taken from a donor, the typical process to prepare the organ for transplant can cause further injury to the cells and tissues. This process involves flushing the kidney with cold preservation solution and then putting it in cold storage for an average of 18-24 hours while it is being transported to the recipient.
Dr. Sener and his research team found that if hydrogen sulfide molecules are added to the preservation solution, organ storage can be prolonged without risk of tissue injury, dangerous inflammatory cells decrease, kidney function is recovered quicker after transplant, the kidneys have greater urine output, and recipient survival is improved.
“Our goal is to make these existing ‘marginal’ deceased donor kidneys work better, quicker and longer. Instead of a kidney lasting ten years, what if our treatment could make it last eleven? One year doesn’t seem like a lot but that means a patient doesn’t need to go on dialysis for another year, they can travel or continue to work. It means a lot for a patient’s quality of life, not to mention the significant economic impact that dialysis has on our health care system.”
Researchers in Dr. Alp Sener’s lab are able to create a transplantation-like environment for kidneys without actually transplanting the organ. They use this ex-vivo perfusion apparatus for experimental storage and perfusion of animal and unusable donated human kidneys. The machine enables them to control perfusion pressures and oxygenation, and to measure urine output and other physiological variables.
This method pioneered in Dr. Sener’s lab lends itself well to clinical translation. It involves the addition of a hydrogen sulfide molecule that is already approved for use in renal failure patients to existing organ preservation solutions. The drug does not have to be given to a recipient or a donor, only to the organ while it is in storage.
Their goal is to begin clinical trials once enough data is collected from their current studies that use discarded human grafts – kidneys from organ donors who have consented to research and whose organs were not candidates for transplant due to disease, injury or having no match on the transplant list. While he is now a leader in this growing field, Dr. Sener says it was hard convincing people at first that hydrogen sulfide, a smelly toxic molecule, could be used to improve kidney transplantation.
“When we started this research a lot of people said it was a crazy idea. We spent many years determining the correct dosage for therapeutic benefit to ensure there were no toxic effects. As this research becomes more mainstream, we hope it will eventually help improve outcomes of organ transplantation all over the world.”
Harnessing the silent killer
Dr. Gedas Cepinskas was the first to study carbon monoxide-releasing molecules as a potential treatment for systemic inflammation.
Carbon monoxide – a colourless, odourless gas produced by the burning of fuels – is widely known as the “silent killer.” While carbon monoxide can be lethal when inhaled at high concentrations, powdered carbon monoxide-releasing molecules (CORMs) have the potential to treat systemic inflammation.
Many conditions or illnesses can cause systemic inflammation, inflammation that simultaneously affects multiple organs. One of the most severe forms of systemic inflammation is sepsis, a lifethreatening complication of an infection. Sepsis is the leading cause of death in Intensive Care Units worldwide.
Apart from the use of antibiotics, treatments for systemic inflammation are limited. From his lab at LHSC’s Victoria Hospital, Dr. Cepinskas was the first to study the therapeutic potential of CORMs to treat systemic inflammation and is still one of very few researchers in the world working in this field.
Systemic inflammation occurs when many inflammatory molecules are released into the blood stream. These molecules activate cells in the blood vessel wall resulting in a loss of tight connections between these cells and creating microscopic gaps. Inflammatory molecules also activate white blood cells, which adhere to blood vessel walls and create more gaps. The gaps allow white blood cells and inflammatory molecules in the blood to escape from the blood vessels.
Normally, white blood cells protect our bodies by eliminating bacteria, but when inflammation is severe, too many white blood cells escape from the blood vessels into organs, including the brain and lungs, and cause serious tissue damage with their arsenal of biochemical “weapons” designed to kill bacteria.
Neutrophils, a type of white blood cell, release elastase and myeloperoxidase (MPO) enzymes, which kill bacteria, but at the same time contribute to the formation of gaps between cells in the blood vessel walls, further amplifying inflammation.
“We found that CORMs not only reduce the number of white blood cells entering inflamed tissue, but they also inhibit elastase and MPO activity,” says Dr. Cepinskas.
In addition, CORMs are “broad spectrum” inhibitors of several inflammation-associated signaling pathways, which are unique sequences of biochemical reactions that take place in the cells in response to interaction with a specific molecule. “Many drugs are designed to target a very specific signaling pathway. Unfortunately, all clinical trials using this approach to treat sepsis have failed because there are so many different inflammatory molecules produced during systemic inflammation, each with its own unique signaling pathway.
CORMs, on the other hand, simultaneously target many signaling pathways,” says Dr. Cepinskas. CORMs can be administered through an injection, which does not cause the toxic effects that occur when carbon monoxide gas is inhaled.
In addition to sepsis-focused research, Dr. Cepinskas has also studied the role CORMs can play in the treatment of other conditions that cause systemic inflammation, including limb compartment syndrome. This is a devastating complication of musculoskeletal trauma, such as a bone fracture or crushed muscle, characterized by severe swelling of the muscle. Currently, the only treatment is a surgical procedure to cut fascia (tissue that encapsulates muscle) to relieve tension and pressure in the limb.
Dr. Cepinskas and Dr. Abdel-Rahman Lawendy, a Lawson scientist and orthopaedic surgeon at LHSC, were the first to demonstrate that CORMs could minimize muscle damage caused by compartment syndrome.
Dr. Cepinskas is also collaborating with Dr.Sener and Dr. Patrick Luke, a Lawson scientist and co-director of the Multi-Organ Transplant Program at LHSC, to examine how CORMs could be used to improve organ transplantation. After an organ is transplanted, it is connected to the body’s blood vessels to restore blood flow. This causes inflammation throughout the body, which is very difficult to control.
Their research has shown that administering CORMS to kidneys before transplantation suppresses inflammation after the organ is transplanted and reduces the risk of transplant rejection.
“Now that carbon monoxide is accepted and recognized for its anti-inflammatory effects, there is huge potential for broader clinical applicability. We are proud that based on our findings, Lawson has become an internationally renowned research hub addressing the therapeutic applicability of gaseous molecules. Despite great advances, there is much that still needs to be understood and further tested before we can treat patients with these therapies,” says Dr. Cepinskas.
Dr. Alp Sener is a part of the Transplantation research program at Lawson. He is an associate professor in the Departments of Surgery and Microbiology and Immunology, Schulich School of Medicine & Dentistry at Western University.
Dr. Gedas Cepinskas leads the Critical Illness research program at Lawson. He is an associate professor in the Department of Medical Biophysics, Schulich School of Medicine & Dentistry at Western University.
Lawson Internal Research Fund
During the early stages of their research, both Dr. Sener and Dr. Cepinskas received funding from Lawson’s Internal Research Fund (IRF), which helped them to secure grants from large external funding agencies.
Lawson’s IRF is designed to allow Lawson scientists the opportunity to obtain start-up funds for new projects with potential to obtain larger funding, to be published in an important journal, or to provide a clinical benefit to patients.
The IRF is supported financially by the clinical departments at London Health Sciences Centre and St. Joseph’s Health Care London, as well as London Health Sciences Foundation and St. Joseph’s Health Care Foundation.