Space traveling and CVD risk: RACE to MACE

Lately, the space race has been the talk of the town and while it might seem that we are on the verge between science-fiction and reality, there is a long way to go before humans can overcome the health hazards associated with space travel and adapt to their new environment. Humans will likely be exposed to many health hazards emerging from the “space exposome” during their journey into space. Many of these health hazards can affect the cardiovascular (CV) system.

Astronauts are required to undergo an extensive training program including engineering and paramedic courses, intensive health check and various assessments to see how they can cope under stressful conditions. From the start, there is a specific selection process to identify the most ‘fit’ of people who can qualify for space travel. However, even the most ‘fit’ of people can’t escape the health hazards that are awaiting us when we leave mother Earth.

One of the most prominent health hazards associated with long distance space travel affecting the CV system is space radiation. Space radiation usually consists of solar radiation and, the more dangerous, cosmic radiation. Among the components of cosmic radiation, the HZE ions are the most hazardous to the human body because they are highly penetrating and can even generate secondary particles when they interact with shielding materials such as spacecraft or spacesuit. Space radiation damages DNA either directly by energy absorption leading to clustered DNA damage, mutations, chromosome exchanges, carcinogenesis and apoptotic cell death, or indirectly via the production of reactive oxygen species (ROS) from the radiolysis of water molecules.

Exposure to various types of radiation can lead to radiation-induced cardiovascular disease (RICVD) which is a known complication in patients undergoing radiation therapy to treat thoracic cancers and in Japanese atomic bomb survivors. RICVD following space radiation exposure can develop acutely in the form of pericarditis or chronically leading to myocardial remodeling and fibrosis, accelerated development of atherosclerosis, cardiomyopathies, valve abnormalities, arrhythmias and conduction disorders. RICVD can also develop 10-15 years following exposure.

The number of astronauts that have surpassed the low Earth Orbit, where the space radiation amount becomes significantly higher, were only from the Apollo mission which limits the amount of data available. Therefore, several studies to investigate RICVD have been done in animal models using different types of radiations to mimic, to a certain degree, RICVD in humans. These studies have shown that ⁵⁶Fe ions, the most prominent heavy ion found in cosmic radiation, lead to cardiac hypertrophy and myocardial remodeling. In addition, people that have been exposed to higher levels of radiation compared to the general population had increased risk of myocardial infarction due to atherosclerosis. Mouse models further showed that the effects of irradiation are rather local than systemic where atherosclerosis developed in the areas which were specifically subject to irradiation using ⁵⁶Fe ions. Plaques in these mice had a thickened intima (carotid), indicating a damage to the arterial wall, and a large necrotic core (aortic root) which increases the risk of instability and thrombogenic complications. The biological processes that have been suggested to induce RICVD include endothelial dysfunction leading to a pro-inflammatory and a pro-fibrogenic environment, apoptotic cell death of various cardiovascular cell types and alterations in DNA methylation.

To date, extensive research is going into improving the shielding methods to protect astronauts from the effects of space radiation. The administration of anti-oxidants such as N-acetyl cysteine (NAC), ascorbic acid (vitamin C), vitamin B, coenzyme Q10 and vitamin E can complement the vitamin deficiencies that humans are subject to during space travel and also remove the generated ROS limiting DNA damage and protecting from space radiation exposure. Some drugs such as angiotensin converting enzyme (ACE) inhibitors and statins have also shown to reduce radiation-induced cardiopulmonary complications and radiation induced atherosclerosis in animal models respectively but need further exploration. Of note, altered DNA methylation can serve as an early biomarker for space radiation exposure and might lead to personalized treatment based on the level of altered DNA methylation after exposure. Space radiation can also increase the risk of cancer and diseases of the central nervous system such as impaired motor function, neurobehavioral changes, Alzheimer’s disease or accelerated aging which can complicate an existing CVD.

Apart from space radiation, other health hazards are also associated with space traveling. Prolonged exposure to microgravity induces bone and muscle atrophy as well as cardiovascular deconditioning. This requires humans to exercise constantly to remain healthy which could be beneficial for CV outcomes. Being confined in a closed environment, disrupted circadian rhythms and the stress for being away from mother Earth also add another layer of psychological and mental challenges to be overcome when venturing into space.

 

References:

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