A new study found that patients who had heart attacks during the day had higher neutrophil counts and greater heart damage, suggesting that immune cells themselves could play a role in worsening the damage.
For decades, cardiologists have observed that heart attacks cause more damage when they occur during the day than when they happen at night.
There are many theories about why daytime heart attacks are more harmful. Some point to daily fluctuations in stress hormones and blood pressure as possible culprits. However, the role of the immune system has remained less clear.
Previous investigations have shown that immune cells called neutrophilswhich act as first responders in the event of injury, cause more inflammation and collateral tissue damage at injured sites during the day. At night, they are relatively calmer.
In a new study last week at Journal of Experimental Medicinescientists were able to connect the dots between daytime heart attacks and aggressive neutrophils.
As detailed by , when analyzing clinical records of more than 2,000 people who had had heart attacks, the team discovered that patients admitted during the day had higher neutrophil counts and greater heart damage, suggesting that the patients themselves neutrophils could play a role in worsening the injury.
The same pattern was later confirmed in experiments with mice.
The researchers divided the laboratory mice into two groups: one with normal neutrophil levels and another whose neutrophil levels were reduced through antibody treatment. They then induced heart attacks in the rats at different times of the day and night.
In the first set of rats, they observed a pronounced rhythm of greater cardiac damage in the morning than in the evening, similar to that seen in the human data. However, in mice with low neutrophil counts, this rhythm disappeared and heart attacks caused less damage overall.
Next, the researchers genetically disabled a gene that helps control the circadian clock, a regulator of the body’s 24-hour cycles. As they expected, the rhythm disappeared again and overall heart damage was reduced in these modified mice.
The researchers also discovered an interesting pattern behind the action of neutrophils: in both skin wounds and heart tissue, neutrophils daytime neutrophils tend to spread to neighboring uninjured areasenlarging the area of the lesion. The calmer neutrophils at night, on the other hand, remain confined to the center of the damaged area – the leader of the investigation explained to Live Science, Andres Hidalgo.
As the same magazine writes, the study’s conclusions suggest that there may be Ways to tune neutrophils and reduce their aggressiveness without, however, compromising its defense capacity.
