Using pro-vitamin A carotenoids as a therapeutic strategy to reduce the burden of obesity and atherosclerosis

Coronel Laica, Johana Alexandra

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https://hdl.handle.net/2142/117529 Copy

Description

Title

Using pro-vitamin A carotenoids as a therapeutic strategy to reduce the burden of obesity and atherosclerosis

Author(s)

Coronel Laica, Johana Alexandra

Issue Date

2022-09-13

Director of Research (if dissertation) or Advisor (if thesis)

Amengual Terrasa, Jaume

Doctoral Committee Chair(s)

Erdman, John W

Committee Member(s)

• Pepino de Guev, Maria Yanina
• Chen, Hong
• Siegel, Marcia H

Department of Study

Food Science & Human Nutrition

Discipline

Food Science & Human Nutrition

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Obesity
• gene therapy
• BCO1
• adeno associated virus
• retinoic acid, atherosclerosis, fat

Abstract

The prevalence of diseases caused by an excessive accumulation of lipids, such as obesity and atherosclerosis, is increasing rapidly. Obesity is a consequence of unbalanced energy intake to energy expenditure, leading to a positive energy balance in the organism. The hallmark of obesity is the excessive accumulation of triglyceride in the adipocytes, the main cellular component of the white adipose tissue. Conversely, atherosclerosis is the pathological consequence of the abnormal accumulation of cholesterol present in apolipoprotein B (apo B) lipoproteins within the arterial wall. The continuous accumulation of lipids, foam cells and extracellular materials generates atherosclerotic lesions, which can rupture and cause myocardial infarction or stroke. The anti-obesogenic and atheroprotective effects of carotenoids and carotenoid-derived products bring a novel perspective to therapeutic strategies to treat obesity and regress atherosclerosis. The bioactive properties of carotenoids are attributed to either (1) intact carotenoids or (2) carotenoid-cleavage products, named apocarotenoids, which include all vitamin A derivatives. Many animals accumulate carotenoids, but this accumulation varies between species. While humans accumulate large amounts of carotenoids in tissues, wild-type mice do not, even when fed pharmacological doses of these compounds. Therefore, these inters-specific differences limit the possibility of studying the effects of intact carotenoids in mice. Inter-specific differences in carotenoid accumulation can be attributed, at least in part, to the enzymatic activities of the carotenoid cleaving enzymes: β-carotene oxygenase 1 (BCO1) and BCO2. BCO1 primarily cleaves β-carotene to form retinal, the first vitamin A intermediate, while BCO2 cleaves several carotenoids, including β-cryptoxanthin and other oxygenated carotenoids. We focused our research on β-carotene and β-cryptoxanthin as two of the human diet's most relevant pro-vitamin A carotenoids. β-carotene contains two β-ionone rings that allow it to form two molecules of vitamin A. However, β-cryptoxanthin possesses a single β-ionone ring, although a hydroxyl group in its structure could favor its uptake in comparison to β-carotene. The feasibility of studying the effects of intact carotenoids in mice was overcome with the development of Bco1-/- and Bco2-/- mice, which accumulate β-carotene and β-cryptoxanthin, respectively, as humans do. These mouse strains are not commercially available, but our laboratory is fortunate to possess active colonies of Bco1-/- and Bco2-/- mice. While there are several mouse strains, we typically utilize mice in the C57BL/6J genetic background for our experiments in obesity and atherosclerosis. These mice are useful for studying metabolic diseases since they develop obesity when fed a high-fat diet. However, C57BL/6J mice do not develop atherosclerosis lesions, even when fed a Western diet (high fat, high cholesterol) for a prolonged period. An increasing number of experimental mouse models allow for studying atherosclerosis progression. One of the most used and well-known is the low-density lipoprotein receptor knockout (Ldlr-/-) mice, also in a C57Bl/6J genetic background. This thesis focused on studying atherosclerosis resolution (healing), a more clinically-relevant process. To this end, we utilized two distinct experimental approaches. First, we relied on a recent model in which we transiently depleted the expression of low-density lipoprotein receptor (LDLR) by performing weekly injections utilizing an antisense oligonucleotide (ASO). Our second model fed a Western diet to Ldlr-/- mice to develop atherosclerosis lesions; later, we performed a dietary switch to a Standard diet with or without β-carotene to promote atherosclerosis resolution. Our previous research suggests that β-carotene supplementation reduces adiposity in wild-type mice but not in Bco1-/- mice and that the cleavage of β-carotene to vitamin A delays atherosclerosis progression. However, whether the systemic or adipose tissue-derived β-carotene is responsible for the effect of dietary β-carotene in adiposity and whether β-carotene contributes to the resolution of atherosclerosis remains unknown. In the context of obesity (Chapter 2), we generated and optimized a novel adipose-tissue specific adeno-associated vector (AT-AAV) to over-express BCO1 locally in the adipose tissue in Bco1-/- mice fed a diet containing β-carotene. The overexpression of BCO1 in the adipose tissue reduced the adipose tissue size and the adipocyte area in female mice but not in male mice. These effects were mediated by increased retinoic acid in the adipocytes that occurred only in the female. Overall, our data reveal that β-carotene accumulated in the adipose tissue can serve as a precursor for retinoic acid formation to mitigate obesity. Next, in Chapter 3, we evaluated the potential of β-cryptoxanthin for the generation of vitamin A. Because β-cryptoxanthin can only form vitamin A upon its sequential cleavage by BCO2 and BCO1, we generated a second AT-AAV encoding for BCO2 (AT-AAV-BCO2). Our preliminary data show that the overexpression of BCO2 in combination with BCO1 in the adipose tissue of Bco1-/-/ Bco2-/- mice results in the cleavage of β-cryptoxanthin, presumably to form vitamin A derivatives including retinoic acid. In Chapters 4 and 5, we focused our attention on atherosclerosis. Our previous data show that β-carotene delays atherosclerosis progression in Ldlr-/- mice in a BCO1-dependent manner. These results were supported by our study in (Chapter 4), where we determine the impact of dietary β-carotene and the activity of BCO1 on circulating cholesterol concentration in preclinical and clinical studies. Both studies show that BCO1 activity reduces circulating cholesterol concentration, linking vitamin A formation with a reduced risk of atherosclerotic cardiovascular disease. Chapter 5 investigates the role of β-carotene in atherosclerosis resolution in two distinct mouse models. We found that the β-carotene supplementation during atherosclerosis resolution accelerates this healing process, a process driven by the expansion of anti-inflammatory regulatory T cells in the atherosclerotic lesion. The data presented in this thesis highlights the pivotal role of the BCOs in the positive health effects attributed to the pro-vitamin A carotenoid β-carotene and possibly β-cryptoxanthin. Based on these results, we propose pro-vitamin A carotenoids as potential therapeutic agents to prevent the development of obesity and atherosclerosis progression and to favor the resolution of atherosclerosis.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Johana Coronel

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