Naringenin and β-carotene convert human white adipocytes to a beige phenotype and elevate hormone- stimulated lipolysis

Frontiers in Endocrinology · 9 authors, 7 centres

AI SUMMARY

FIDELITY 100%

POPULATIONPrimary human adipocyte cultures derived from adipose stem cells of overweight and obese female donors (BMI 27–36 kg/m²)

INTERVENTIONTreatment with 8 µM naringenin + 2 µM β-carotene (NRBC) for seven days in culture

COMPARISONUntreated (vehicle control) adipocytes, or treatment with naringenin alone or β-carotene alone

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TL;DR

This study demonstrates that the combination of naringenin (a citrus flavonoid) and β-carotene synergistically converts human white adipocytes into beige, thermogenic cells by upregulating UCP1, GLUT4, adiponectin, and multiple non-UCP1 energy-expenditure pathways. The treatment also elevates hormone-stimulated lipolysis and increases expression of receptors for exercise- and cold-related signals, including β1-adrenergic and parathyroid hormone receptors. These findings suggest NRBC has therapeutic potential as a safe, peripherally-acting treatment for obesity and type 2 diabetes.

Full summary

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**Background:** Adipose tissue contains white adipocytes that store triglycerides and beige/brown adipocytes that express uncoupling protein 1 (UCP1) to dissipate energy as heat. Increasing beige adipocyte density is associated with elevated energy expenditure and resistance to obesity and type 2 diabetes. Naringenin (NR), a citrus polyphenol, activates PPARα and PPARγ and has been shown to upregulate UCP1 and oxygen consumption in human adipocytes. Carotenoids like β-carotene (BC) are metabolized into retinoid ligands for retinoic-X-receptors (RXRs), which heterodimerize with PPARs. This study tested whether BC could amplify NR's effects on converting white adipocytes to a beige phenotype.

**Methods:** Human adipose-derived stem cells from overweight/obese female donors were differentiated into adipocytes and treated for seven days with 8 µM NR and/or 2 µM BC (NRBC). Gene expression was measured by qRT-PCR and whole transcriptome sequencing (RNA-seq). Protein levels were assessed by Western blotting. PPARγ immunoprecipitation was used to detect RXR isoform binding. Lipolysis was measured by glycerol release after 4-hour exposure to receptor agonists (PTH, isoproterenol, dobutamine, ANP, and others). Statistical analysis used linear mixed effect models with significance at p < 0.05.

**Key Results:** BC and lutein (pro-vitamin A carotenoids) synergistically boosted UCP1 mRNA with NR (p < 0.001), while lycopene (non-pro-vitamin A) did not. NRBC synergistically increased mRNA for UCP1 (p < 0.005), GLUT4 (p < 0.02), ATGL (p < 0.04), and adiponectin (p < 0.05) compared to NR or BC alone. Protein levels of PPARα, PPARγ, PGC-1α, and NAMPT increased 3- to 6-fold (p < 0.001) without corresponding mRNA increases, suggesting post-translational stabilization. RNA-seq identified 3881 differentially expressed genes (adjusted p < 0.05). NRBC induced non-UCP1 thermogenic pathways: PM20D1 (15.7-fold), creatine kinases CKMT1A (5.1-fold), CKMT1B (3.9-fold), CKMT2 (3.8-fold), and triglyceride cycling genes (PDK4 4.2-fold, GK 2.4-fold, PCK1 3.8-fold). RXRγ was induced 10-fold. Eight receptors were significantly upregulated (Padj < 0.002), including β1AR, PTHR, TGR5, TRPM8, ADORA1, NPR1, GPER1, and GHR. PTH-stimulated lipolysis was the highest among all agonists tested and increased significantly in NRBC-treated cells (p ≤ 0.02). Isoproterenol and dobutamine-stimulated lipolysis were also significantly elevated. RXRγ was detected in PPARγ immunoprecipitates from both untreated and NRBC-treated cells, indicating constitutive binding.

**Clinical Implications:** NRBC reprograms human white adipocytes toward a beige phenotype by upregulating multiple thermogenic pathways (UCP1, creatine cycling, PM20D1/NAA uncoupling, triglyceride cycling), beneficial secreted factors (adiponectin, ANGPTL4, FNDC4, GDF11), and receptors for exercise- and cold-related hormones (β1AR, PTHR, NPR1). The increased lipolytic capacity and receptor sensitivity suggest NRBC could enhance energy expenditure in response to physiological stimuli. NR and BC have established safety profiles in humans, and this peripherally-acting combination avoids CNS side effects common to many obesity drugs. A randomized, double-blind placebo-controlled clinical trial is needed to determine whether these in vitro effects translate to weight loss and improved insulin sensitivity in humans.

PICO

PPOPULATION

Primary human adipocyte cultures derived from adipose stem cells of overweight and obese female donors (BMI 27–36 kg/m²)

IINTERVENTION

Treatment with 8 µM naringenin + 2 µM β-carotene (NRBC) for seven days in culture

OOUTCOME

mRNA and protein levels of thermogenesis and glucose metabolism genes (UCP1, GLUT4, ATGL, adiponectin, PPARα, PPARγ, PGC-1α, NAMPT); whole transcriptome changes; agonist-stimulated glycerol release (lipolysis); RXRγ binding to PPARγ complexes

STUDY TYPE

other

SPECIALTY

endocrinology

SUMMARISED BY

AI pipeline

FIDELITY CHECK

100% · A

ORIGINAL PAPER

PMC10153092

Naringenin and β-carotene convert human white adipocytes to a beige phenotype and elevate hormone- stimulated lipolysis

Frontiers in Endocrinology

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ABSTRACT

Abstract Introduction Naringenin, a peroxisome proliferator-activated receptor (PPAR) activator found in citrus fruits, upregulates markers of thermogenesis and insulin sensitivity in human adipose tissue. Our pharmacokinetics clinical trial demonstrated that naringenin is safe and bioavailable, and our case report showed that naringenin causes weight loss and improves insulin sensitivity. PPARs form heterodimers with retinoic-X-receptors (RXRs) at promoter elements of target genes. Retinoic acid is an RXR ligand metabolized from dietary carotenoids. The carotenoid β-carotene reduces adiposity and insulin resistance in clinical trials. Our goal was to examine if carotenoids strengthen the beneficial effects of naringenin on human adipocyte metabolism. Methods Human preadipocytes from donors with obesity were differentiated in culture and treated with 8µM naringenin + 2µM β-carotene (NRBC) for seven days. Candidate genes involved in thermogenesis and glucose metabolism were measured as well as hormone-stimulated lipolysis. Results We found that β-carotene acts synergistically with naringenin to boost UCP1 and glucose metabolism genes including GLUT4 and adiponectin, compared to naringenin alone. Protein levels of PPARα, PPARγ and PPARγ-coactivator-1α, key modulators of thermogenesis and insulin sensitivity, were also upregulated after treatment with NRBC. Transcriptome sequencing was conducted and the bioinformatics analyses of the data revealed that NRBC induced enzymes for several non-UCP1 pathways for energy expenditure including triglyceride cycling, creatine kinases, and Peptidase M20 Domain Containing 1 (PM20D1). A comprehensive analysis of changes in receptor expression showed that NRBC upregulated eight receptors that have been linked to lipolysis or thermogenesis including the β1-adrenergic receptor and the parathyroid hormone receptor. NRBC increased levels of triglyceride lipases and agonist-stimulated lipolysis in adipocytes. We observed that expression of RXRγ, an isoform of unknown function, was induced ten-fold after treatment with NRBC. We show that RXRγ is a coactivator bound to the immunoprecipitated PPARγ protein complex from white and beige human adipocytes. Discussion There is a need for obesity treatments that can be administered long-term without side effects. NRBC increases the abundance and lipolytic response of multiple receptors for hormones released after exercise and cold exposure. Lipolysis provides the fuel for thermogenesis, and these observations suggest that NRBC has therapeutic potential. Keywords: UCP1, naringenin, carotenoid, PPARγ, RXRγ, PPARα, adiponectin, lipolysis

CITATION EXPORT

Ann A Coulter, Frank L Greenway, Dachuan Zhang et al.. Naringenin and β-carotene convert human white adipocytes to a beige phenotype and elevate hormone- stimulated lipolysis. Frontiers in Endocrinology. (2023). https://doi.org/10.3389/fendo.2023.1148954

AUTHORS

9 · 7 CENTRES

Ann A Coulter, Frank L Greenway, Dachuan Zhang, Sujoy Ghosh, Cathryn R Coulter, Sarah L James, Yanlin He, Luke A Cusimano, Candida J Rebello

1 Computational Biology, Pennington Biomedical Research Center, Baton Rouge, LA, United States
2 Clinical Trials, Pennington Biomedical Research Center, Baton Rouge, LA, United States
3 Biostatistics, Pennington Biomedical Research Center, Baton Rouge, LA, United States
4 Adjunct Faculty, Pennington Biomedical Research Center, Baton Rouge, LA, United States
5 Brain Glycemic and Metabolism Control, Pennington Biomedical Research Center, Baton Rouge, LA, United States
6 Cusimano Plastic and Reconstructive Surgery, Baton Rouge, LA, United States
7 Nutrition and Chronic Disease, Pennington Biomedical Research Center, Baton Rouge, LA, United States