Circadian Dependence of the Acute Immune Response to Myocardial Infarction

Circadian rhythms influence the recruitment of immune cells and the onset of inflammation, which is pivotal in the response to ischemic cardiac injury after a myocardial infarction (MI). The hyperacute immune response that occurs within the first few hours after a MI has not yet been elucidated. Therefore, we characterized the immune response and myocardial damage 3 hours after a MI occurs over a full twenty-four-hour period to investigate the role of the circadian rhythms in this response. MI was induced at Zeitgeber Time (ZT) 2, 8, 14, and 20 by permanent ligation of the left anterior descending coronary artery. Three hours after surgery, animals were terminated and blood and hearts collected to assess the immunological status and cardiac damage. Blood leukocyte numbers varied throughout the day, peaking during the rest-phase (ZT2 and 8). Extravasation of leukocytes was more pronounced during the active-phase (ZT14 and 20) and was associated with greater chemokine release to the blood and expression of adhesion molecules in the heart. Damage to the heart, measured by Troponin-I plasma levels, was elevated during this time frame. Clock gene oscillations remained intact in both MI-induced and sham-operated mice hearts, which could explain the circadian influence of the hyperacute inflammatory response after a MI. These findings are in line with the clinical observation that patients who experience a MI early in the morning (i.e., early active phase) have worse clinical outcomes. This study provides further insight on the immune response occurring shortly after an MI, which may contribute to the development of novel and optimization of current therapeutic approaches.

Circadian dependence of the acute immune response to myocardial infarction

Aim

Circadian rhythms control many physiological processes, including numerous aspects of the immune system. Whether these immunological oscillations play a role in the pathophysiology after ischemic injury, such as myocardial infarction (MI), remains unclear. In this study, we aimed to characterize circadian rhythms during the acute inflammatory responses after MI.

Methods and results

Balb/c mice were operated at Zeitgeber Time (ZT) 2, 8, 14 and 20. Three hours after MI, animals were terminated and blood and hearts were collected to assess immunological status and damage. We observed diurnal fluctuation in leukocyte numbers in the blood, peaking during the rest-phase (ZT2 and 8) of the circadian cycle. Interestingly, the homing and infiltration of neutrophils to the injured myocardium was more pronounced during the active-phase of the mice (ZT14 and 20), at which time higher levels of Troponin-T were measured in the serum. Higher neutrophil extravasation during the active phase (especially the sleep-to-wake transition, ZT14) was also correlated to greater chemokine release in the blood and adhesion molecule expression in the heart.

Conclusion

The occurrence of a myocardial infarction during the early-morning hours leads to greater myocardial damage in patients. In the present study, we showed that the neutrophil response in the first hours after MI is stronger during the sleep-to-wake transition, thereby potentially playing a role in the worse clinical outcome observed during this time period.

Funding Acknowledgement

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): This research received funding from the EU's H2020 research and innovation programme under Marie S. Curie cofund RESCUE grant agreement No 801540.

Correlation between epicardial adipose tissue and body mass index in New Zealand ethnic populations

AIM

We aimed to investigate the correlation between epicardial adipose tissue (EAT) and body mass index (BMI) in different ethnic groups in New Zealand.

METHODS

The study included 205 individuals undergoing open heart surgery. Māori and Pacific groups were combined to increase statistical power. EAT was measured using 2D echocardiography.

RESULTS

There were 164 New Zealand Europeans (NZE) and 41 Māori/Pacific participants. The mean (SD) age of the study group was 67.9 (10.1) years, 69.1 (9.5) for NZE and 63.5 (11.4) for Māori/Pacific. BMI was 29.6 (5.5) kg/m2 for NZE and 31.8 (6.2) for Māori/Pacific. EAT thickness was 6.2 (2.2) mm and 6.0 (1.8) mm for NZE and Māori/Pacific, respectively. Using univariate linear regression, BMI showed moderate correlation with EAT in NZE (R2=0.26, p<0.001); however, there was no significant correlation between BMI and EAT in Māori/Pacific patients (R2=0.05, p=0.17). Using multivariate analysis, BMI remained a significant predictor of EAT thickness in NZE (R2 =0.27, p<0.001).

CONCLUSIONS

BMI was associated with EAT thickness in NZE patients, but not in Māori/Pacific patients. The same level of BMI can carry different connotations of risk in different ethnic groups, with BMI likely being an inconsistent measure of obesity in in Māori/Pacific patients.

Relationship between epicardial adipose tissue thickness and epicardial adipocyte size with increasing body mass index

Macroscopic deposition of epicardial adipose tissue (EAT) has been strongly associated with numerous indices of obesity and cardiovascular disease risk. In contrast, the morphology of EAT adipocytes has rarely been investigated. We aimed to determine whether obesity-driven adipocyte hypertrophy, which is characteristic of other visceral fat depots, is found within EAT adipocytes. EAT samples were collected from cardiac surgery patients (n = 49), stained with haematoxylin & eosin, and analysed for mean adipocyte size and non-adipocyte area. EAT thickness was measured using echocardiography. A significant positive relationship was found between EAT thickness and body mass index (BMI). When stratified into standardized BMI categories, EAT thickness was 58.7% greater (p = 0.003) in patients from the obese (7.3 ± 1.8 mm) compared to normal (4.6 ± 0.9 mm) category. BMI as a continuous variable significantly correlated with EAT thickness (r = 0.56, p < 0.0001). Conversely, no correlation was observed between adipocyte size and either BMI or EAT thickness. No difference in the non-adipocyte area was found between BMI groups. Our results suggest that the increased macroscopic EAT deposition associated with obesity is not caused by adipocyte hypertrophy. Rather, alternative remodelling via adipocyte proliferation might be responsible for the observed EAT expansion.