Obesity, a complex medical condition stemming from an imbalance between calorie intake and expenditure, affects a staggering number of individuals globally . In 2016, the World Health Organization (WHO) reported that over 1.9 billion adults were overweight, and more than 650 million were classified as obese . Recognized as a disease due to its association with various health issues, including hypertension, cardiovascular diseases, diabetes, musculoskeletal disorders, osteoarthritis, and cancer, obesity necessitates effective treatment strategies .
Current treatments often involve lifestyle modifications, pharmacotherapy, or surgical interventions, each carrying its own set of challenges and limitations . Amidst these challenges, the exploration of natural products (NPs) and bioactive compounds derived from them has gained traction, aiming to counteract obesity with minimal side effects .
Citrus-Derived Polymethoxyflavones (PMFs) as Potential Anti-Obesity Agents
A promising avenue in the quest for natural anti-obesity agents lies in polymethoxyflavones (PMFs) derived from citrus fruits [6,7,8]. Citrus peels, rich in PMFs such as hesperidin, naringin, nobiletin, and tangeretin, exhibit various health benefits, including anti-inflammatory, antioxidant, and anti-cancer properties [9,10,11,12,13]. Studies on cell and animal models have shown that these PMFs play a crucial role in preventing obesity, type 2 diabetes, and other metabolic disorders .
Mechanisms involving the inhibition of apoB secretion, regulation of lipid synthesis, and suppression of adipogenesis highlight the potential of citrus-derived PMFs in managing obesity [15,16,17]. Specifically, PMFs from Citrus aurantium L. have demonstrated the ability to prevent high-fat-diet-induced obesity in mice through the promotion of adaptive thermogenesis in adipose tissues .
The molecular mechanisms involve the upregulation of protein kinase A (PKA) signaling, including phosphorylation of protein kinase A catalytic subunit α (PKACα), adenosine monophosphate-activated protein kinase (AMPK), and acetyl-CoA carboxylase (ACC) . Additionally, the suppression of adipogenesis is linked to the inhibition of serine phosphorylation of protein kinase B (AKT) .
Citrus sphaerocarpa (Kabosu) and its Potential in Obesity Management
Citrus sphaerocarpa, commonly known as Kabosu, is a sour citrus extensively used in Japan for various culinary purposes . While essential oils derived from citrus peels are widely utilized in the food, beverage, pharmaceutical, and cosmetic industries, the anti-obesity effects of C. sphaerocarpa supplementation have been scarcely reported.
Recent research has shed light on the anti-obesity potential of the hexane extract of C. sphaerocarpa (CSHE) . In vitro studies using differentiated 3T3-L1 adipocytes demonstrated that CSHE suppressed lipid accumulation, with RNA sequencing analysis suggesting an association with the activation of β-oxidation through the PI3K/AKT and PKA/AMPK signaling pathways.
Exploring Anti-Obesity Effects In Vivo
To further investigate the preventive and therapeutic potential of CSHE against obesity, in vivo experiments were conducted using zebrafish and mice models. Zebrafish (Danio rerio), a well-established model organism for human disease studies, has been utilized to develop obesity models [22,23]. Previous work has identified various natural products with anti-obesity properties using zebrafish [26,27,28].
In this study, the anti-obesity effects of CSHE were evaluated in both zebrafish and mice models. Changes in genes and proteins associated with lipid metabolism were assessed in the liver and epididymal white adipose tissue (eWAT) of mice to elucidate the molecular mechanisms underlying the observed effects. Additionally, findings from in vivo experiments were validated using differentiated 3T3-L1 adipocytes.
Figure . The proposed model of the signaling pathway induced by the CSHE treatment. CSHE: hexane extract of Citrus sphaerocarpa; eWAT: epididymal white adipose tissue; pAKT: phosphorylated protein kinase B; pAMPK: phosphorylated adenosine monophosphate-activated protein kinase; pFoxO1: phosphorylated forkhead box protein O1; pACC: phosphorylated acetyl-CoA carboxylase; PPARα: peroxisome proliferator-activated receptor alpha; ACOX1: acyl-coenzyme A oxidase 1 and palmitoyl; FoxO1: forkhead box protein O1; FASN: fatty acid synthase; Acetyl-CoA: acetyl coenzyme A; Malonyl-CoA: Malonyl coenzyme A. The red and blue arrows indicate the up- and down-regulation of protein and lipid metabolism, respectively. The dotted arrows represent the model estimated from the results obtained in this study.
Adipocyte Differentiation and Lipid Accumulation
The association between obesity and adipocyte differentiation and lipid accumulation is well-established, making adipocytes promising targets for anti-obesity interventions . The hexane extract of Citrus sphaerocarpa (CSHE) demonstrated its potential in suppressing lipid accumulation in 3T3-L1 adipocytes . In this study, the anti-obesity effects of CSHE were explored in juvenile obese zebrafish and mice models. The significant suppression of visceral lipid accumulation in zebrafish juveniles after one-day exposure to a higher dose of CSHE (20 μg/mL) highlighted its efficacy, suggesting its potential as a preventive agent. Additionally, the findings were mirrored in the mammalian mouse model, providing a new candidate for anti-obesity drug discovery.
Lipogenesis Regulation and Molecular Targets
Lipogenesis, the synthesis of fatty acids and triglycerides, plays a pivotal role in fat accumulation, and several key regulators influence this process . In this study, CSHE exhibited a multi-faceted impact on lipogenesis-related factors. It downregulated the expression of Fasn in the epididymal white adipose tissue (eWAT) of obese mice, indicating a reduction in de novo lipogenesis. Furthermore, the upregulation of Cebpa and Cebpb in eWAT suggested that CSHE might promote adipocyte differentiation and regulate fatty acid uptake, contributing to the suppression of fat accumulation. Interestingly, the upregulation of Fasn in the livers of CSHE-treated mice hinted at enhanced fatty acid synthesis, suggesting a complex interplay of mechanisms contributing to the observed effects.
Lipolysis and Fatty Acid Metabolism:
The balance between lipogenesis and lipolysis is crucial for metabolic homeostasis, and the dysregulation of this balance is implicated in obesity . CSHE demonstrated a significant elevation in the mRNA levels of Ppara and Acox1 in the liver of obese mice, indicating an enhancement of fatty acid β-oxidation. The increased expression of Ppargc1a in eWAT suggested activated β-oxidation in this tissue. These findings align with the idea that CSHE may suppress hepatic lipid accumulation by promoting fatty acid β-oxidation and reducing lipogenesis in eWAT.
Exploring Upstream Factors and Signaling Pathways
The study delved into the upstream factors and signaling pathways influenced by CSHE, focusing on the protein expression and phosphorylation of the PI3K/AKT and AMPK pathways. The proposed model suggested that CSHE treatment activates phosphorylation of AKT and AMPK, enhancing PPARα and ACOX1 expression, leading to increased lipolysis and reduced lipid accumulation in the liver. In eWAT, CSHE was hypothesized to suppress lipogenesis by increasing phosphorylation of FoxO1, resulting in decreased FASN expression. The upregulation of ACC phosphorylation was proposed to lower malonyl-CoA, contributing to decreased lipogenesis. Future studies should analyze acetyl-CoA levels to corroborate this hypothesis.
Consideration of PMFs and Synergistic Effects
The study acknowledged the presence of polymethoxyflavones (PMFs) in CSHE, known for their role in suppressing lipid accumulation through the PKA/AMPK/ACC signaling pathway. The proposed model integrated these known pathways but recognized the potential influence of other components present in CSHE. The extract’s ability to reduce lipid droplet accumulation in HepG2 cells, akin to its effects in zebrafish and mice, suggested a comprehensive impact on lipid metabolism.
Potential Impact on Ectopic Lipid Accumulation
Ectopic lipid accumulation, often associated with fatty liver disease, was considered in the discussion. CSHE treatment triggered the phosphorylation of AKT and AMPK in the liver, potentially initiating a signaling cascade leading to lipolysis. The study postulated that various components of CSHE may hinder factors facilitating ectopic lipid accumulation, supported by observations in HepG2 cells.
Implications for Preventive Medicine and Pharmacology
In conclusion, the findings underscored the potential of CSHE as a multifaceted anti-obesity agent, impacting adipocyte differentiation, lipid metabolism, and signaling pathways. The complexity of its effects, involving both known and potentially novel mechanisms, emphasizes the need for further research to fully elucidate its therapeutic potential. Comprehensive knowledge of CSHE’s functional components can provide insights for preventive medicine and pharmacology, opening avenues for future research and drug discovery in the fight against obesity.
reference link: https://www.mdpi.com/1420-3049/28/24/8026