Bell peppers are a superfood because of Luteolin

      When asked about the health benefits of bell peppers, most people tend to think of their infamously high vitamin C content.

     Depending on the variety and the stage of ripeness (color), bell peppers can indeed offer very impressive amounts of vitamins C.

     According to the USDA’s nutrient database[1], yellow bell peppers contain about 183.5 mg of vitamin C per 100 grams and red bell peppers contain approximately 127.7 mg of vitamin C per 100 grams.

     This substantial difference of vitamin C content between yellow and red might prompt a person to focus primarily on consuming yellow peppers, although this would be a dietary mistake due to the various beneficial phytonutrient compounds that come along with that vibrant red color.

     In regards to overall antioxidant capacity, red peppers can actually offer a higher overall free radical scavenging ability than yellow peppers, in certain situations[2], despite their much lower vitamin C content. Mainly due to the potent colorful phytochemical compounds that develop during their later stages of maturity. Although, this antioxidant activity is likely to be more prominent in lipophilic environments due to the fat soluble nature of these polyphenols.

      The bright and vibrant colors of bell peppers are a product of a diverse blend of various polyphenols and carotenoids. Originally purposed with the task of protecting plant tissue from oxidation and environmental stressors, but also providing similar protective physiological benefits when consumed by humans as well. 

    One of the more outstanding examples of these compounds is luteolin; which is found in very high concentrations in the red colored bell peppers: with some studies reporting average concentrations of luteolin more than 4 times higher in red bell peppers than green bell peppers and almost double the amount commonly found in yellow peppers.[2]

     This flavonoid type of polyphenol has proven to offer some very promising physiological benefits in regards to neurological enhancement, cognitive health, endocrine function (reproductive vitality), and overall reduction in oxidative stress.

     While there are a few other  dietary options offering slightly higher concentrations of luteolin by weight, bell pepper offer one of the most practical solutions for consuming significant amounts of luteolin, without forcing large amounts of difficult to consume foods into your meals. 

Cognitive Benefits

     Interestingly, luteolin has proven to exhibit neuroprotective attributes[3] and it has shown to possess anti depressive properties amongst other cognitive benefits[4]

      It is theorized that these effect are partially due to luteolins modulation of various genetic transcription factors, and its protective effects on various neurotransmitter receptors in the brain, resulting in the optimization of certain neurotransmitter molecules(such as serotonin); directly perpetuating their activity and preventing their degradation[5].

      Luteolin has also demonstrated its ability to increase growth of new brain-cell connections[6]. a phenomenon called neurite outgrowth, which is enhance by luteolin through the modulation of genetic factor “micro-RNA-132” and the downregulation of PMAT(plasma membrane Monoamine Transporter), and the subsequent upgrading of brain derived neurotropic factor(BDNF) expression.

     Additionally, certain studies have shown luteolin exposure to modulate multiple cellular protein communication mechanisms such as TrkA[7], ERK1/2[8], Akt[9], and CREB[10]. Each of which have powerful implications in regards to physiological process of cellular healing and regeneration.

      Given the fact that Luteolin has shown to phosphorylate these various cellular signaling proteins (meaning that a phosphate group is added to them); luteolin exposure can ultimately trigger an increase in their activity by more than 2 to 3 fold. Which is crucial in regards to overall health and vitality because these particular signaling pathways are very important for the encouragement of cellular survival, cellular replication, cellular division, and cellular proliferation.

Hormonal Benefits

         As far as endocrine(hormone) function goes, luteolin has shown to display substantial aromatase inhibitor activity[11], by decreasing excess estrogen bio-synthesis, encouraging the degradation of aromatase, and decreasing the conversion of androgenic hormones into estrogenic hormones. 

    Which can ultimately be very beneficial for both men and women, especially in todays modern day high-pollution environment, where a wide variety of environmental and dietary contaminants(such as micro-plastics and phthalates) have been show to create hormonal imbalances and estrogen dominance[12] in large portions of the population

       Additionally, luteolin has shown to offer profound benefits regarding the protection of male reproductive health[13] systems as well. Most likely due to its epigenetic impacts on DNA signaling and gene expression 

      For example, luteolins fertility  protecting  properties can be seen in one interesting study published in the Journal of Toxicology Research, where researchers found that luteolin supplementation greatly improved diagnostic biomarkers in rodents who were  treated with fertility-reducing cancer drug treatments(compared to experimental control groups), showing that luteolin greatly encouraged the preservation of reproductive tissue structure/integrity and improved physiological activity of male reproductive organs; promoting considerably improved sperm quality and significantly increased testosterone levels in the test  subjects. 

Antioxidant Impact

     As far as luteolins overall antioxidant impacts go, luteolin offers a more profound approach to its prevention of free radical damage. Instead of simply scavenging active free radicals like many other antioxidant compounds do, luteolin actually takes preliminary action by preemptively inhibiting the generation of reactive oxygen species and free radicals by blocking activity of certain oxidase  enzymes[14] such as NADPH oxidase and xanthine oxidase. 

     Meaning that luteolin offers free radical mitigating actions both before and after the actual process of oxidation occurs, offering an especially well rounded and far-reaching antioxidant impact throughout the body. 

     Additionally, luteolin has proven to boost the activity and overall effectiveness of naturally occurring endogenous antioxidants enzymes as well., such as superoxide dismutase[15] and glutathione peroxidase[16], in order to help protect against oxidative stress. Which is partially due to the stimulation of transcription factors responsible for regulating the expression of these enzymes, such as Nrf2 (nuclear factor erythroid 2-related factor 2) and AP-1 (activator protein 1).

Final Thoughts

     Plus, for the record, luteolin is actually just one of the several powerful phytonutrients compounds found within bell-peppers! 

      There are several others beneficial phytochemicals which I plan to address in later additional blogs, although I definitely would recommend further exploration of this subject for anyone interested in valuable nutraceutical compounds, as peppers certainly have a treasure trove to offer and they can be quite fascinating. 

      So, if high vitamin C content isn’t a good enough reason for increasing  bell pepper consumption, there are plenty of other great reasons why it might be a wise dietary choice.   

References:

1.)USDA National Nutrient Database for Standard Reference Release 28. VitaminC-Content.pdf (nih.gov)

2.) T. Sun; Z. Xu; C.-T. Wu; M. Janes; W. Prinyawiwatkul; H. K. No (2007). Antioxidant Activities of Different Colored Sweet Bell Peppers “Capsicum annuum” . , 72(2), 0–0. doi:10.1111/j.1750-3841.2006.00245.x  Antioxidant Activities of Different Colored Sweet Bell Peppers (Capsicum annuum L.) – Sun – 2007 – Journal of Food Science – Wiley Online Library

3.) Rehfeldt SCH, Silva J, Alves C, et al. Neuroprotective Effect of Luteolin-7-O-Glucoside against 6-OHDA-Induced Damage in Undifferentiated and RA-Differentiated SH-SY5Y Cells. Int J Mol Sci. 2022;23(6):2914. Published 2022 Mar 8. doi:10.3390/ijms23062914 Neuroprotective Effect of Luteolin-7-O-Glucoside against 6-OHDA-Induced Damage in Undifferentiated and RA-Differentiated SH-SY5Y Cells – PMC (nih.gov)

4.) Ishisaka, M., Kakefuda, K., Yamauchi, M., Tsuruma, K., Shimazawa, M., Tsuruta, A., & Hara, H. (2011). Luteolin shows an antidepressant-like effect via suppressing endoplasmic reticulum stress. Biological & pharmaceutical bulletin, 34(9), 1481–1486. https://doi.org/10.1248/bpb.34.1481 Luteolin shows an antidepressant-like effect via suppressing endoplasmic reticulum stress – PubMed (nih.gov)

5.)) Shujie Zhu, Shaowei Lei, Sisi Zhou, Lisha Jin, Su Zeng, Huidi Jiang, Hui Zhou, Luteolin shows antidepressant-like effect by inhibiting and downregulating plasma membrane monoamine transporter (PMAT, Slc29a4), Journal of Functional Foods, Volume 54, 2019, Pages 440-448, ISSN 1756-4646, https://doi.org/10.1016/j.jff.2019.01.048.  Luteolin shows antidepressant-like effect by inhibiting and downregulating plasma membrane monoamine transporter (PMAT, Slc29a4) – ScienceDirect

6.) Lin LF, Chiu SP, Wu MJ, Chen PY, Yen JH. Luteolin induces microRNA-132 expression and modulates neurite outgrowth in PC12 cells. PLoS One. 2012;7(8):e43304. doi:10.1371/journal.pone.0043304 Luteolin Induces microRNA-132 Expression and Modulates Neurite Outgrowth in PC12 Cells – PMC (nih.gov)

7.) Xiong Gao, A., Xia, T. C., Shing-Hung Mak, M., Kin-Leung Kwan, K., Zhong-Yu Zheng, B., Xiao, J., Dong, T. T., & Tsim, K. W. (2021). Luteolin stimulates the NGF-induced neurite outgrowth in cultured PC12 cells through binding with NGF and potentiating its receptor signaling. Food & function, 12(22), 11515–11525. https://doi.org/10.1039/d1fo01096d Luteolin stimulates the NGF-induced neurite outgrowth in cultured PC12 cells through binding with NGF and potentiating its receptor signaling – PubMed (nih.gov)

8.) Park, E. J., Kim, Y. M., Kim, H. J., & Chang, K. C. (2018). Luteolin activates ERK1/2- and Ca2+-dependent HO-1 induction that reduces LPS-induced HMGB1, iNOS/NO, and COX-2 expression in RAW264.7 cells and mitigates acute lung injury of endotoxin mice. Inflammation research : official journal of the European Histamine Research Society … [et al.], 67(5), 445–453. https://doi.org/10.1007/s00011-018-1137-8 Luteolin activates ERK1/2- and Ca2+-dependent HO-1 induction that reduces LPS-induced HMGB1, iNOS/NO, and COX-2 expression in RAW264.7 cells and mitigates acute lung injury of endotoxin mice – PubMed (nih.gov)

9.) Ruiqi Baiyun, Siyu Li, Biying Liu, Jingjing Lu, Yueying Lv, Jianwen Xu, Jiahui Wu, Jiayi Li, Zhanjun Lv, Zhigang Zhang, Luteolin-mediated PI3K/AKT/Nrf2 signaling pathway ameliorates inorganic mercury-induced cardiac injury, Ecotoxicology and Environmental Safety, Volume 161, 2018, Pages 655-661, ISSN 0147-6513, https://doi.org/10.1016/j.ecoenv.2018.06.046. Luteolin-mediated PI3K/AKT/Nrf2 signaling pathway ameliorates inorganic mercury-induced cardiac injury – ScienceDirect

10.) Zhen, J. L., Chang, Y. N., Qu, Z. Z., Fu, T., Liu, J. Q., & Wang, W. P. (2016). Luteolin rescues pentylenetetrazole-induced cognitive impairment in epileptic rats by reducing oxidative stress and activating PKA/CREB/BDNF signaling. Epilepsy & behavior : E&B, 57(Pt A), 177–184. https://doi.org/10.1016/j.yebeh.2016.02.001

11.) Lu, D. F., Yang, L. J., Wang, F., & Zhang, G. L. (2012). Inhibitory effect of luteolin on estrogen biosynthesis in human ovarian granulosa cells by suppression of aromatase (CYP19). Journal of agricultural and food chemistry, 60(34), 8411–8418. https://doi.org/10.1021/jf3022817 Inhibitory effect of luteolin on estrogen biosynthesis in human ovarian granulosa cells by suppression of aromatase (CYP19) – PubMed (nih.gov)

12.) Harris CA, Henttu P, Parker MG, Sumpter JP. The estrogenic activity of phthalate esters in vitro. Environ Health Perspect. 1997;105(8):802-811. doi:10.1289/ehp.97105802 The estrogenic activity of phthalate esters in vitro. – PMC (nih.gov)

13.) Solomon E Owumi , Abigail O Ijadele, Uche O Arunsi , and Oyeronke A Odunola (2020) Luteolin abates reproductive toxicity mediated by the oxido-inflammatory response in Doxorubicin-treated rats, Journal of Toxicology Research and Application https://doi.org/10.1177/239784732097204 Luteolin abates reproductive toxicity mediated by the oxido-inflammatory response in Doxorubicin-treated rats – Solomon E Owumi, Abigail O Ijadele, Uche O Arunsi, Oyeronke A Odunola, 2020 (sagepub.com)

14.) Dong, Hao and Yang, Xiaocui and He, Jiapeng and Cai, Sheng and Xiao, Kaijun and Zhu, Liang”, “Enhanced antioxidant activity{,antibacterial activity and hypoglycemic effect of luteolin by complexation with manganese and its inhibition kinetics on xanthine oxidase”, Jounal of RSC Advances, 2017 http://dx.doi.org/10.1039/C7RA11036G Enhanced antioxidant activity, antibacterial activity and hypoglycemic effect of luteolin by complexation with manganese(ii) and its inhibition kinetics on xanthine oxidase – RSC Advances (RSC Publishing)

15.) Murugesan Madhesh, Manju Vaiyapuri, Effect of luteolin on lipid peroxidation and antioxidants in acute and chronic periods of isoproterenol induced myocardial infarction in rats, Journal of Acute Medicine, Volume 2, Issue 3, 2012, Pages 70-76, ISSN 2211-5587, https://doi.org/10.1016/j.jacme.2012.06.001 Effect of luteolin on lipid peroxidation and antioxidants in acute and chronic periods of isoproterenol induced myocardial infarction in rats – ScienceDirect

16.) Kang, K. A., Piao, M. J., Ryu, Y. S., Hyun, Y. J., Park, J. E., Shilnikova, K., Zhen, A. X., Kang, H. K., Koh, Y. S., Jeong, Y. J., & Hyun, J. W. (2017). Luteolin induces apoptotic cell death via antioxidant activity in human colon cancer cells. International journal of oncology, 51(4), 1169–1178. https://doi.org/10.3892/ijo.2017.4091 Luteolin induces apoptotic cell death via antioxidant activity in human colon cancer cells – PubMed (nih.gov)