Dietary Saturated Fat Promotes Arrhythmia by Activating NADPH Oxidase 2 (NOX2)

In the first study mice were fed a diet with 60% fat 20/20% Protein and Carbs. Fat used was Palm oil, which is pretty high is palmitic acid 44% of it, the rest is Oleic acid a MUFA.

Second study always done with mice, again using Palm oil but this time cal from fat were 45%.

I will dig a bit more, to understand if there is another study showing same results but this time with another type of saturated fat. I do not think there is another SFA out there that contains so much Palmitic acid like Palm oil does. Both study shows that palmitic acid may be dangerous when burned for energy (betaoxidation)

Thoughts?

as always, link to the full study at the end.

Abstract
Background -
Obesity and diets high in saturated fat increase the risk of arrhythmias and sudden cardiac death. However, the molecular mechanisms are not well understood. We hypothesized that an increase in dietary saturated fat could lead to abnormalities of calcium homeostasis and heart rhythm by a NADPH oxidase 2 (NOX2)-dependent mechanism.

Methods -
We investigated this hypothesis by feeding mice high fat diets. In vivo heart rhythm telemetry, optical mapping, and isolated cardiac myocyte imaging was used to quantify arrhythmias, repolarization, calcium transients, and intracellular calcium sparks.

Results -
We found that saturated fat activates NOX, whereas polyunsaturated fat does not. The high saturated fat diet increased repolarization heterogeneity and ventricular tachycardia (VT) inducibility in perfused hearts. Pharmacologic inhibition or genetic deletion of NOX2 prevented arrhythmogenic abnormalities in vivo during high statured fat diet and resulted in less inducible VT. High saturated fat diet activates Ca2+/calmodulin-dependent protein kinase (CaMK) in the heart, which contributes to abnormal calcium handling, promoting arrhythmia.

Conclusions -
We conclude that NOX2 deletion or pharmacologic inhibition prevents the arrhythmogenic effects of a high saturated fat diet, in part mediated by activation of CaMK. This work reveals a molecular mechanism linking cardiac metabolism to arrhythmia, and suggests that NOX2 inhibitors could be a novel therapy for heart rhythm abnormalities caused by cardiac lipid overload.


[www.ahajournals.org]



Edited 1 time(s). Last edit at 08/21/2023 11:15PM by Marco.

Inhibition of NAPDH Oxidase 2 (NOX2) Prevents Oxidative Stress and Mitochondrial Abnormalities Caused by Saturated Fat in Cardiomyocytes



Abstract
Obesity and high saturated fat intake increase the risk of heart failure and arrhythmias. The molecular mechanisms are poorly understood. We hypothesized that physiologic levels of saturated fat could increase mitochondrial reactive oxygen species (ROS) in cardiomyocytes, leading to abnormalities of calcium homeostasis and mitochondrial function. We investigated the effect of saturated fat on mitochondrial function and calcium homeostasis in isolated ventricular myocytes. The saturated fatty acid palmitate causes a decrease in mitochondrial respiration in cardiomyocytes. Palmitate, but not the monounsaturated fatty acid oleate, causes an increase in both total cellular ROS and mitochondrial ROS. Palmitate depolarizes the mitochondrial inner membrane and causes mitochondrial calcium overload by increasing sarcoplasmic reticulum calcium leak. Inhibitors of PKC or NOX2 prevent mitochondrial dysfunction and the increase in ROS, demonstrating that PKC-NOX2 activation is also required for amplification of palmitate induced-ROS. Cardiomyocytes from mice with genetic deletion of NOX2 do not have palmitate-induced ROS or mitochondrial dysfunction. We conclude that palmitate induces mitochondrial ROS that is amplified by NOX2, causing greater mitochondrial ROS generation and partial depolarization of the mitochondrial inner membrane. The abnormal sarcoplasmic reticulum calcium leak caused by palmitate could promote arrhythmia and heart failure. NOX2 inhibition is a potential therapy for heart disease caused by diabetes or obesity.



[journals.plos.org]


from the full study, interesting part is bold, but read all of it.


PKC, NOX, and ROS
It is possible that palmitate can cause low-level activation of PKC directly, which leads to NOX2 activation. However, the experiments with etomoxir, shown in Fig 4, indicate that full activation of PKC requires palmitate to enter the mitochondria. We postulate that palmitate initially causes a small amount of mitochondrial ROS. This activates NOX2 via PKC, generating more ROS, which causes more mitochondrial dysfunction in a feed-forward cycle. In vascular tissue, there is cross talk between mitochondrial ROS and NOX, such that the one can amplify the other [38]. ROS-induced ROS release (RIRR) has been shown to occur in cardiomyocytes using stimulation such as photo-induced oxidation [46] and in Langendorff preparations perfused with H2O2 [39]. The molecular pathways responsible for RIRR in the heart have not been identified. We demonstrate that is critical for amplifying mitochondrial ROS in cardiomyocytes, and thus NOX2 is a critical component of RIRR in this model system. The role of NOX enzymes in cardiac pathology is complex [47]. Low-level NOX activity may be beneficial and generate ROS as signaling intermediates. However, NOX activity is increased in human heart failure [48] and NOX2 is activated in the atria of patients with atrial fibrillation and large animal models of atrial fibrillation [49, 50]. Chronic activation of NOX2 by saturated fat could promote heart failure and arrhythmia.

We also show that NOX2 is required for ROS generation caused by PKC activation in cardiomyocytes. Further, we show that activating endogenous PKC in cardiomyocytes is sufficient to trigger NOX2-mediated ROS generation that in turn causes an increase in mitochondrial ROS. Our experiments identify NOX2 as the major mediator of PKC induced ROS in cardiomyocytes. Activation of conventional PKC isoforms has been implicated as a major factor in heart failure pathophysiology [51]. Additional work will be necessary to determine if of PKC’s harmful effects are mediated by NOX2-generated ROS in other disease states.

Abnormal calcium homeostasis
The observation that saturated fat increases calcium sparks is novel. The interaction between NOX2 and RyR2 has been described previously, and accounts for increased sarcoplasmic reticulum release with myocytes stretch [52]. This interaction was not previously known to have a role in mitochondrial metabolic abnormalities. Our findings indicate that palmitate causes mitochondrial calcium overload due to increased sarcoplasmic reticulum leak from RyR channels. Since cardiac mitochondria are physically connected to the sarcoplasmic reticulum, and mitochondria take up calcium released from the sarcoplasmic reticulum [53], it is plausible that abnormal calcium release induced by palmitate could initiate mitochondrial dysfunction in cardiomyocytes. Inhibition of RyR calcium release prevents ROS production by preventing mitochondrial calcium overload and dysfunction. Our experiments with cresol demonstrate that increased sarcoplasmic reticulum leak is sufficient to trigger mitochondrial ROS. These results give us mechanistic insight into the cardiac biology that connects lipid overload to abnormal calcium homeostasis and mitochondrial function.

We conclude that, in adult cardiomyocytes, palmitate induces ROS by a mechanism that requires mitochondrial uptake and beta-oxidation of palmitate, and the mitochondrial ROS is amplified by PKC-NOX2 activation. Activating this pathway results in increased sarcoplasmic reticulum calcium leak, mitochondrial calcium overload, and mitochondrial dysfunction. Pharmacologic NOX2 inhibition prevents the abnormalities caused by saturated fat. The mechanisms revealed by this work may have therapeutic implication for heart disease caused by diabetes and obesity. Although clinical trials of antioxidants for cardiovascular disease have been disappointing, for the most part, there is some clinical evidence supporting beneficial effects on heart rhythm [54–56]. It may be that antioxidants are only beneficial in certain forms of cardiovascular disease, where increased ROS has a central role in the pathophysiology. Pharmacotherapy that specifically targets the source of ROS could be more effective. NOX2 inhibition may be a potential therapy for heart rhythm abnormalities in obese and diabetic patients. In addition, since increased RyR calcium leak is an important mechanism in heart failure [57], it is possible that NOX2 inhibition could be used as a treatment for heart failure.

To note.

If I remember well, when are overweight but especially obese, our liver will start producing palmitic acid from excess carbohydrates. That is why in the studies they mentioned more than once obesity and diabetes, as our body will overproduce Palmitic acid in these two conditions. A possible connection.

In general mice don't do well on high fat diets. Here is a Nature article on the topic.

Plant oils with high concentrations of linoleic acid are death. I don't blame the mice for their verdict.

Quote
GeorgeN
In general mice don't do well on high fat diets. Here is a Nature article on the topic.

thanks for the article. However, in the first study I linked, mice were still fed a high fat diet but when Olive Oil was used, there was no reported NOX2 activation. Below a quote from the study. Of course, in mice not humans.

"These findings indicate that a HSFD can cause the same arrhythmogenic abnormalities as diet-induced obesity without substantial weight gain, and that a high fat diet does not cause cardiac abnormalities if it is composed of olive oil."

Quote
gloaming
Plant oils with high concentrations of linoleic acid are death. I don't blame the mice for their verdict.

Palm oil has about 10% linolenic acid, perhaps enough to cause the trouble at 45/60% of tot calories

as right now, I couldn't find any meaningful evidence supporting this in humans, beside this study below. But unless someone is type 2 diabetic or possibly gargling Palm oil, there should not be an issue with intracellular Ca activation and other SFA's



Oxidative stress and calcium dysregulation by palmitate in type 2 diabetes


Abstract
Free fatty acids (FFAs) are important substrates for mitochondrial oxidative metabolism and ATP synthesis but also cause serious stress to various tissues, contributing to the development of metabolic diseases. CD36 is a major mediator of cellular FFA uptake. Inside the cell, saturated FFAs are able to induce the production of cytosolic and mitochondrial reactive oxygen species (ROS), which can be prevented by co-exposure to unsaturated FFAs. There are close connections between oxidative stress and organellar Ca2+ homeostasis. Highly oxidative conditions induced by palmitate trigger aberrant endoplasmic reticulum (ER) Ca2+ release and thereby deplete ER Ca2+ stores. The resulting ER Ca2+ deficiency impairs chaperones of the protein folding machinery, leading to the accumulation of misfolded proteins. This ER stress may further aggravate oxidative stress by augmenting ER ROS production. Secondary to ER Ca2+ release, cytosolic and mitochondrial matrix Ca2+ concentrations can also be altered. In addition, plasmalemmal ion channels operated by ER Ca2+ depletion mediate persistent Ca2+ influx, further impairing cytosolic and mitochondrial Ca2+ homeostasis. Mitochondrial Ca2+ overload causes superoxide production and functional impairment, culminating in apoptosis. This vicious cycle of lipotoxicity occurs in multiple tissues, resulting in β-cell failure and insulin resistance in target tissues, and further aggravates diabetic complications.


[www.nature.com]

I may conclude my research about SFA effecting Afib with this study.

My conclusion is that excess Palmitic acid is associated with increased incidence of Afib, we have a rat interventional study using Palm Oil which is high in Palmitic Acid, and two human studies pointing out the issue with Palmitic acid and Afib as well.

However, excess Palmitic acid in the blood is obtained by constantly overeating carbohydrates and drinking alcohol. Being type 2 diabetic or obese will definitely have someone liver to produce excess Palmitic acid. Other than that, other SFA actually are associated with a reduction in the incidence of Afib




Plasma Phospholipid Saturated Fatty Acids and Incident Atrial
Fibrillation: The Cardiovascular Health Study

In conclusion, the results of this analysis suggest that
among older adults, higher levels of circulating 16:0 are
associated with a higher risk of AF, whereas higher levels of
circulating 18:0, 20:0, 22:0, and 24:0 are associated with
lower risk. This study adds to the growing body of evidence
suggesting potential differences in the health effects and/or
underlying metabolic determinants of different types of
circulating SFAs. These novel findings highlight the need for
further observational and mechanistic investigation to
better understand how circulating SFAs may influence risk
of AF.