Name: CARMEN CASTARDELI
Publication date: 26/03/2024
Examining board:
Name |
Role |
|---|---|
| ANA PAULA COUTO DAVEL | Examinador Externo |
| ANDRE SOARES LEOPOLDO | Examinador Interno |
| CARMEM LUIZA SARTORIO | Examinador Externo |
| MAICON LANDIM VIEIRA | Examinador Externo |
Summary: ntroduction: Myocardial infarction (MI) is a severe clinical condition involving
inflammatory processes and oxidative stress, potentially leading to heart failure and
death. Following MI, underlying mechanisms can lead to increased production of
reactive oxygen species (ROS), generating oxidative stress, which in turn may
stimulate further ROS production through other enzymes, termed ROS-induced ROS
release. This mechanism can cause vascular dysfunction and, consequently,
contribute to the development of heart failure. In this context, MitoQ, a mitochondriaspecific
antioxidant, emerges as a promising strategy to reduce oxidative stress and
preserve vascular function post-MI. Objective: To evaluate the involvement of
mitochondrial oxidative stress, the COX pathway, and the NADPH oxidase pathway in
the reactivity of rat thoracic aorta rings, 7 days after MI. Methods: Wistar rats were
randomly divided into four groups: Myocardial Infarction (MI), Myocardial Infarction
Mitoquinone (MI MitoQ), Sham, and Sham Mitoquinone (Sham MitoQ). The animals
were treated for seven days with 100 M Mitoquinone (MitoQ), administered in drinking
water. MI was surgically induced by occlusion of the left anterior descending coronary
artery. Seven days after MI induction, hemodynamic evaluations, weight gain
analyses, and sample collection for protein expression analyses by Western Blot, nitric
oxide (NO) production by DAF, oxidative stress by DHE (cytoplasmic), and Mitosox
(mitochondrial) were performed. Vascular reactivity was subsequently assessed in
isolated thoracic aorta rings, which were stimulated with increasing concentrations of
phenylephrine. Statistical analysis of the results was performed using t-tests, two-way
analysis of variance, and analyses of repeated or completely randomized measures,
considering p<0,05 as statistically significant.
Results: MitoQ treatment did not alter infarct area (MI: 46.56±0.47 vs. MI MitoQ:
43.64±0.53 %) but prevented weight gain reduction in the MI group. Additionally, MitoQ
prevented the increase in left ventricular end-diastolic pressure (LVEDP, mmHg) and
attenuated left ventricular (LV) relaxation dysfunction (dP/dtmin, mmHg/s), although it
did not demonstrate efficacy in improving dP/dtmax (mmHg/s). The increase in
pulmonary weight relative to body weight in the MI group was prevented by MitoQ
treatment, and lung water content was similar among all groups. LV mass was similar
in all experimental groups. MitoQ treatment prevented right ventricular (RV)
hypertrophy. Reactivity to phenylephrine increased in the MI group (Rmax Sham:
97.7±2 vs. MI: 125±3* % KCl 75 mM; p<0,05). MitoQ treatment prevented the increase
in vascular reactivity in the MI group (Rmax MI: 125±3 vs. MI MitoQ: 103±2* % KCl 75
mM; p<0,05). The lack of responsiveness to L-NAME in the MI group (Sham + LNAME:
141±4; MI + L-NAME: 138±5 % KCl 75 mM; p>0,05) was prevented with MitoQ
treatment (MI MitoQ + L-NAME: 154±16 % KCl 75 mM; p<0,05). Endothelial removal
promoted an increase in phenylephrine response in the Sham, Sham MitoQ, and MI
MitoQ groups, but not in the MI group (MI E+: 119.8±1.5 vs. MI E-: 114.8±1.4 % KCl
75 mM; p>0,05). There was a reduction in NO production and an elevation in ROS
generation in the MI group compared to the Sham group. Supplementation with
indomethacin reduced phenylephrine reactivity in the MI group (MI: 138±11 vs. MI +
Indo: 106.1±7.2 % KCl 75 mM; p<0,05), which was normalized in the MI MitoQ group
(MI MitoQ: 98.4±3.3 vs. MI MitoQ + Indo: 92.3±5 % KCl 75 mM; p>0,05). Reactivity
was reduced in the MI group with superfusion with the specific NOX inhibitor, ML 171-
5 M (MI: 124±1.8 vs. MI + ML 171: 107±2.4 % KCl 75 mM; p<0,05), which was
prevented with MitoQ treatment (MI MitoQ: 103±1.9 vs. MI MitoQ + ML 171: 99±1.9 %
KCl 75 mM; p>0,05), suggesting the involvement of the NOX pathway. Consistent with
these results, we found increased protein expressions of COX1 and NOX4. MitoQ
treatment reduced protein expressions of COX1, NOX1, and NOX4. There were no
changes in protein expressions of superoxide dismutase and catalase enzymes.
Conclusion: The increase in vascular reactivity to phenylephrine, seven days after MI,
was accompanied by a reduction in NO production and an elevation in ROS
generation. MitoQ treatment was able to prevent these alterations, suggesting the
importance of the mitochondrial ROS production pathway. A reduction in COX and
NOX protein expressions was observed in treated animals, consequently resulting in
ROS reduction. Therefore, our data suggest a positive feedback mechanism between
mitochondrial ROS, the COX and the NADPH oxidase pathway, playing a significant
role in vascular dysfunction seven days after MI in rats.
