science explains why they are ‘less deadly’

The key lies in neutrophils, a type of white blood cell that plays a fundamental role in the immune response. These cells are part of the body’s defense system against infections and have an activity modulated by the circadian rhythm. As humans are a predominantly diurnal species and are more exposed to pathogens during the day, the immune system increases its activity during this period.

However, this increased defensive activity can also be detrimental in certain circumstances. The team led by Andrés Hidalgo, from the National Center for Cardiovascular Research (CNIC), discovered that neutrophils have an “internal clock” that regulates their behavior throughout the day and determines their ability to damage heart tissue after a heart attack.

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The role of neutrophils in cardiac damage

Previous research has shown that about half of the damage to the heart after a heart attack is due to the neutrophil-mediated inflammatory response. This response is not constant, but fluctuates throughout the day, which testifies to the existence of circadian mechanisms capable of limiting its destructive effect.

To explore this hypothesis further, the CNIC team analyzed data from thousands of patients at the 12 de Octubre University Hospital, in Madrid, in collaboration with the multidisciplinary translational cardiovascular research group led by Héctor Bueno. The analysis confirmed that lower neutrophil activity at night is associated with less severe heart attacks during this time. The results of the study were published in the Journal of Experimental Medicine.

As the first author of the work, Alejandra Aroca-Crevillén, explains, during the night, neutrophils move more precisely towards the damaged area, thus preserving the surrounding healthy tissue. On the other hand, during the day they lose this directionality, which increases inflammatory damage in areas not directly affected by the infarction.

Therapeutic implications

Based on these results, the researchers developed an experimental pharmacological strategy aimed at blocking the molecular clock of neutrophils. In the models studied, this intervention reduced heart damage associated with a heart attack. Furthermore, the study highlights that this circadian blockade not only protects the heart, but can also improve the response to certain microorganisms and reduce complications such as embolisms associated with sickle cell anemia.

These results describe the existence of a circadian “checkpoint” at the level of neutrophils, a control mechanism that limits excessive inflammation and which could be activated for therapeutic purposes without compromising the body’s natural defenses.

The authors emphasize that these advances pave the way for the development of new therapies based on the biology of time, an approach that seeks to adapt treatments to the circadian rhythm to maximize their effectiveness and minimize adverse effects.

Factors that influence the severity of a heart attack

Although the time of day is a relevant factor, experts point out that the severity and prognosis of a heart attack depend on several variables. Among the most important are:

• The location of damage in the myocardial tissue.
• The extent of the area affected by the lack of blood supply.
• The speed and quality of first medical aid.
• Care received after the acute phase.
• The treatment established.
• The age and sex of the patient.
• The presence of previous or chronic illnesses.
• The emergence of complications, such as arrhythmias.

The study reinforces the idea that understanding the body’s biological rhythms can be fundamental to improving the prevention and treatment of cardiovascular disease.