Dissertation
Unraveling the interplay between GPx4 genotype, carbonyl stress and cardiovascular diseases: harnessing the therapeutic potential of carnosine
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2023
DOI: 10.25820/etd.006984
Abstract
Lipid peroxidation (LPO) is increasingly recognized as a pathological factor in cardiovascular disease (CVD), through interconnected oxidative-inflammatory pathways. Recent studies have shown that LPO products are predictive markers for CVD and are significantly elevated in specific cardiovascular events, indicating their significance in this context. Notably, Glutathione peroxidase 4 (GPx4), a LPO inhibiting enzyme, was found to be significantly lower in the myocardium of patients who have diabetes and correlates with the severity of diabetes nephropathy. Moreover, several GPX4 gene variants were found to be associated with CVD occurrence and to affect GPx4 enzyme level/activity. Importantly, the two most common risk factors for CVD, namely diabetes and obesity, are characterized by heightened LPO and systemic inflammation. Cardiac fibrosis is a hallmark of the myocardial tissue of diabetics and obese patients and contributes significantly to the pathogenesis of heart failure and arrhythmias. Carnosine, a naturally occurring histidine dipeptide, is a pleiotropic molecule that has been proven to be an effective quencher of various LP products. Additionally, ample preclinical and clinical evidence indicate that carnosine has a role in the prevention and treatment of the cardiometabolic complications associated with obesity and type 2 diabetes. Based on this evidence, this thesis tests two main hypotheses: 1) We hypothesize that single nucleotide polymorphism (SNP) in the GPX4 gene is associated with increased risk of poly unsaturated fatty acid (POAF) in humans and are associated with GPx4 enzyme content/activity. 2)We hypothesize that carnosine supplementation can mitigate cardiac fibrosis associated with diet-induced obesity in a model of enhanced LPO of GPx4-deficient mouse model (GPx4+/-).
To test the first hypothesis, a comprehensive sequencing analysis was conducted on the coding region of GPX4 located on chromosome 19, involving a cohort of 189 patients who underwent elective coronary artery bypass graft surgery. Concurrently, GPx4 enzyme content and activity were assessed in the corresponding atrial myocardium samples from these patients. We identified five GPX4 gene variants associated with increased risk of POAF (permutated p-value of ≤ 0.05), while eight variants were associated with alterations in myocardial GPx4 content/activity (p-value of < 0.05). Notably, one of these variants (rs713041) is a known modifier of CVD risk.
To test the carnosine effectiveness in mitigating cardiac fibrosis, wild-type (WT) and GPx4+/− male mice were fed on either standard chow (CNTL) or high fat high sucrose diet (HFHS) for 16 weeks. Seven weeks after starting the diet two groups of the HFHS - WT and GPx4+/− were started on 80 mM carnosine treatment, added to their drinking water throughout the entire study period. We observed a moderate glycemic control enhancement with carnosine treatment in both genotypes with HFHS diet, while we didn’t observe changes in insulin sensitivity. Remarkably, despite our finding that carnosine therapy has no significant impact on overall gene expression as it was revealed by the transcriptomic analysis, it was noteworthy carnosine substantially increased the expression of cardiac GPx4 in both WT and GPx4+/− mice following the HFHS diet. Interestingly, carnosine demonstrated a significant reduction in protein carbonyls and iron levels in both genotypes on the HFHS diet. Notably, our study revealed a strong antifibrotic effect of carnosine treatment on the hearts of obese mice, accompanied by a significant anti-collagen cross-linking effect.
Collectively, this thesis accentuated the importance of GPx4 variants as potential modifiers for POAF risk and demonstrated a GPx4 enzyme genotype-phenotype associations. Additionally, this thesis highlighted the potential of carnosine in mitigating cardiac fibrosis associated with obesity under GPx4 deficiency and emphasized the importance of key mechanisms involved in its activity. These results may offer a novel perspective on the treatment of cardiac fibrosis in obesity.
Details
- Title: Subtitle
- Unraveling the interplay between GPx4 genotype, carbonyl stress and cardiovascular diseases: harnessing the therapeutic potential of carnosine
- Creators
- Islam A. Berdaweel
- Contributors
- Ethan J Anderson (Advisor)Jonathan Doorn (Committee Member)Marie Gaine (Committee Member)Michael Duffel (Committee Member)Nicole Brogden (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Pharmacy
- Date degree season
- Autumn 2023
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.006984
- Number of pages
- xv, 103 pages
- Copyright
- Copyright 2023 Islam A. Berdaweel
- Language
- English
- Date submitted
- 09/15/2023
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 83-103).
- Public Abstract (ETD)
Diseases affecting the heart and blood vessels are a primary cause of death worldwide. One significant factor contributing to these diseases is oxidative stress, which occurs when there is an imbalance between the production of reactive oxygen species (highly reactive molecules that contain oxygen) and the body's ability to detoxify them, which results in disturbing the normal body physiology. One important consequence of high oxidative stress is damaging the lipid molecule and producing toxic molecules that can contribute to a number of heart diareses such as irregular heartbeats or cardiac fibrosis. Having cardiac fibrosis means that certain areas of the heart are damaged and scarred which makes the heart weaker. In healthy individuals, an enzyme called glutathione peroxidase 4 (GPx4) plays a crucial role in clearing these toxic molecules from the body. Research have shown that in certain disease conditions, the level or the functionality of the GPx4 may be reduced. Researchers think that these abnormalities in GPx4 could be partly due to changes in the GPx4 gene.
The aim of my research project is to study the status of the GPx4 gene and enzyme in hearts samples obtained from patients who have undergone open heart surgery. We also aim to determine whether their gene or enzyme status is associated with an increased risk of developing arrhythmia (irregular heartbeats) after the surgery. Results show that some changes in the GPx4 gene can increase the patient’s risk of having arrythmia after cardiac surgery. We also found some changes in the GPx4 gene that were associated with the myocardial GPx4 abundance or activity.
Another purpose of this project is to evaluate the effectiveness of carnosine, a naturally occurring molecule and over-the-counter supplement, in preventing cardiac fibrosis in mice with GPx4 deficiency. We also fed these mice on a diet that is rich in fat and sugar, creating a condition that mimics diabetes. carnosine has previously shown potential in binding and clearing the toxic molecules produced by oxidative stress, thereby potentially preventing cardiac fibrosis. Our results show that carnosine was able to control blood sugar in the GPx4 deficient obese mice. Additionally, carnosine was able to prevent cardiac fibrosis in these mice. Finding an effective treatment for cardiac fibrosis is important because it significantly raises the risk of death and negatively impact the patient’s quality of life. It is also important to mention that there are currently limited drug options for cardiac fibrosis. By understanding the role of GPx4 and investigating the potential therapeutic benefits of carnosine, this research aims to contribute to the development of a novel treatment strategy for cardiac fibrosis.
- Academic Unit
- Pharmacy
- Record Identifier
- 9984546750802771
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