Cardiologists: Because of this, heart attacks in the morning are more dangerous

Cardiologists: Because of this, heart attacks in the morning are more dangerous

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Time of day with a significant influence on the risk of heart attack
Heart attacks are generally a life-threatening event. The chances of recovery from an infarct, however, depend largely on the time of day of the event, according to the results of a recent study by scientists from the Ludwig Maximillians University (LMU) in Munich. Heart attacks are particularly dangerous in the morning.

Heart attacks are one of the most common causes of death in modern industrialized nations. Previous epidemiological studies had already shown that myocardial infarctions (medical term for heart attacks) "occur more frequently in the morning and are associated with a poorer result in terms of mortality and recovery," reports the research team led by Prof. Sabine Steffens from the Institute for Epidemiology and prophylaxis of circulatory diseases at the LMU clinic. In their current study, the scientists have now examined the effect of the connection between the risk of heart attack and the time of day. The results of the study were published in the specialist magazine "EMBO Molecular Medicine".

Inflammatory response varies throughout the day
The researchers confirmed in their study on mice that after a heart attack it depends on the time of day how the inflammatory reaction proceeds in the affected heart muscle. They also found that "the strength of the immune response and thus the recruitment of neutrophil granulocytes to the site of inflammation fluctuates over the course of the day," the LMU said. The chemokine receptor CXCR2, the activity of which is influenced by the biorhythm, is crucial for this. Study leader Prof. Steffens and colleagues were able to demonstrate in the mouse model that the influx of neutrophils into the damaged heart muscle also depends on the biorhythm. The immune cells trigger an increased inflammation about an hour after the active phase begins than during the sleep phase or later in the day.

Neutrophil granulocytes crucial for the inflammatory response
When cardiac muscle cells die of a heart attack, cells of the immune system are alerted and sent to the damaged tissue. These so-called neutrophil granulocytes trigger an inflammatory reaction, in the course of which the dead tissue is broken down by immune cells. Prof. Steffens had already demonstrated the important role of neutrophils in the healing process in previous studies. However, this only applies as long as the immune response is in equilibrium and the neutrophils do not appear in excessive quantities.

Deciphered molecular mechanism
So far it has not been clear which molecular mechanism increases the risk of a heart attack in the early morning and the relationship between the time of day and the chances of recovery. In their current study, the LMU researchers were able to show that "more neutrophils are released from the bone marrow at the beginning of the active phase". For most people, this active phase is in the early morning, reports Prof. Steffens. "A heart attack at this time leads to an excessive inflammatory reaction from neutrophils," Steffens continues. As a result of the greater inflammation, according to the expert, more scars form in the tissue and the heart muscle expands more, which further weakens the heart.

New therapeutic options?
In their investigations, the scientists were also able to demonstrate that the chemokine receptor CXCR2, which is located on the cell surface of the neutrophils, works depending on the time. "It is most strongly expressed immediately after waking up," says the LMU. With drug suppression of the receptor, the inflammation and thus damage to the heart muscle had decreased significantly. "Our study shows that the time of day plays an important role in the treatment of a heart attack and that CXCR2 can be an interesting therapeutic target if too many neutrophils migrate into the damaged muscle tissue after a heart attack," emphasizes Prof. (fp)

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