Elsevier

Journal of Functional Foods

Volume 35, August 2017, Pages 522-530
Journal of Functional Foods

Pomegranate peel extract ameliorates autoimmunity in animal models of multiple sclerosis and type 1 diabetes

https://doi.org/10.1016/j.jff.2017.06.021Get rights and content

Highlights

  • Pomegranate peel extract is rich in punicalin, punicalagin and ellagic acid.

  • Pomegranate peel extract ameliorates experimental autoimmune encephalomyelitis.

  • It prevents type 1 diabetes through inhibition of insulitis.

  • Pomegranate peel extract inhibits interleukin-17 production.

Abstract

Pomegranate peel extract (PPE) was obtained by aqueous-ethanol extraction and was abundant in punicalin, punicalagin and ellagic acid. As these compounds are known to act against inflammation and oxidative stress in synergistic fashion, effects of PPE were tested in vitro on immune cells and in animal models of multiple sclerosis and type 1 diabetes (T1D). In vitro, PPE inhibited interleukin-17 (IL-17) production from gut-associated lymphoid tissue (GALT) cells. PPE also reduced production of IL-17 in activated T cells isolated from animals with experimental autoimmune encephalomyelitis (EAE). It efficiently down-regulated clinical symptoms of EAE in DA rats and of streptozotocin-induced T1D in C57BL/6 mice. The effect of PPE in T1D was mediated by inhibition of immune cell infiltration into pancreatic islets and through interference with IL-17 and IFN-γ production in GALT. Our results suggest that PPE has the potential to be used as phytopharmaceutical for certain autoimmune and chronic inflammatory disorders.

Introduction

Type 1 diabetes (T1D) and multiple sclerosis are chronic inflammatory diseases that are characterized by autoimmune reactivity against pancreas and central nervous system, respectively. Autoreactive T helper cells (Th) that produce interferon (IFN)-γ (Th1) and those that produce interleukin (IL)-17 (Th17) have been shown crucial for initiation and propagation of autoimmune response in T1D and multiple sclerosis (Petermann and Korn, 2011, Walker and von Herrath, 2016). This autoimmunity ultimately leads to destruction of pancreatic beta cells, insulin hypo-production and hypoglycaemia in T1D and to demyelination and neurodegeneration in multiple sclerosis. Currently, insulin supplementation is the only available therapy for T1D, although there are numerous clinical trials with experimental drugs counteracting autoimmune reactivity and promoting regeneration of pancreatic beta cells (Ludvigsson, 2016). On the contrary, there are numerous disease-modifying drugs for multiple sclerosis that are currently in use (Straus Farber, Harel, & Lublin, 2016). Yet, in spite of this therapeutic plethora, multiple sclerosis, similar to T1D, still remains without the cure. Therefore, investigation of novel potential therapeutics, including plant-based agents is necessary for both diseases.

Pomegranate peel is characterized by the presence of different high molecular weight phenolics such as ellagitannins and proanthocyanidins, as well as flavonoids which were reported to exhibit anti-inflammatory and anti-oxidant effects, among other relevant biological activities (Dikmen et al., 2011, Ismail et al., 2012, Li et al., 2006, Prakash et al., 2013). The whole fruit is rich in phenolic compounds such as punicalagin isomers or ellagic acid derivatives, but biologically active phenolics, predominantly hydrolysable tannins are the most abundantly present in its peel. Punicalagin belongs to a family of ellagitannins and is unique to pomegranate. Its structure includes minor water soluble tannins i.e. punicalin and gallagic acid (Akhtar, Ismail, Fraternale, & Sestili, 2015). Ellagic and gallic acids, punicalagin and punicalin have been shown to act synergistically in achieving anti-inflammatory and anti-oxidant effects (Lee et al., 2010, Seeram and Heber, 2011). Pomegranate fruit is traditionally used in Mediterranean and Asian cuisine, while its peel and peel extract have a potential to be used as food additives and diet supplements (Akhtar et al., 2015).

In this study the effect of PPE on immune cells isolated from different lymphoid tissues of healthy animals or animals with experimental autoimmune encephalomyelitis (EAE) and T1D was examined. Also, impact on the course of EAE and T1D was investigated, followed by search for possible mechanisms of PPE action. It was shown that PPE efficiently restrained activity of immune cells and protected animals from EAE and T1D.

Section snippets

Plant material and extractions

Pomegranate fruits were collected at natural locality in village Do, Bosnia and Herzegovina during November 2015. Peels were separated from the fruit manually, air-dried at room temperature (4–6 days) and grounded with a laboratory mill. Pomegranate peel which was used for further extraction was characterized by 107.98 ± 2.04 mg GAE/g of total phenolics, 1.77 ± 0.23 mg catechin/g of total flavonoids, 6.52 ± 0.76% of total tannins and it contained 15.21 ± 0.12, 56.01 ± 0.43, 1.62 ± 0.02 and 5.45 ± 0.01 mg/g of

Chemical composition of pomegranate peel extract

The amounts of total phenolics, flavonoids and tannins in PPE were determined spectrophotometrically and results are presented in Table 1. HPLC-DAD technique was applied for characterization and quantification of individual phenolic compounds in pomegranate peel extract. Identification was carried out by comparing UV spectra and retention times with standard compounds and results are summarized in Table 2. We have identified four phenolic compounds: ellagic acid, gallic acid, punicalin and

Discussion

PPE exerts potent immunomodulatory effects that result in prevention or amelioration of EAE and streptozotocin-induced T1D. Although PPE was inefficient in modulating IL-17 production when given to healthy rats, when the cells became activated in vivo (either during EAE or T1D course), PPE effectively blocked IL-17 production in certain lymphoid tissues. Th17 blockade might be the common route of PPE-mediated interference with autoimmunity.

PPE has already been shown to possess anti-oxidant and

Conclusions

Our results demonstrate the ability of polyphenols rich aqueous-ethanol extract of pomegranate peel to interfere with autoimmune response and to prevent and/or reduce clinical expression of autoimmune disorders. Importantly, its effects are shown in T1D and EAE, i.e. autoimmune disorders that affect different target organs and that, although sharing basic mechanisms of autoreactivity, differ in many ways regarding etiopathogenesis. It seems that the inhibitory effects of the extract on Th17

Conflicts of interest

The authors declare that they have no conflicts of interest pertaining to this study.

Acknowledgements

This work was supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia (173013, 46013 and 173035).

References (42)

  • Y. Li et al.

    Evaluation of antioxidant properties of pomegranate peel extract in comparison with pomegranate pulp extract

    Food Chemistry

    (2006)
  • J. Li et al.

    Chemical fingerprint and quantitative analysis for quality control of polyphenols extracted from pomegranate peel by HPLC

    Food Chemistry

    (2015)
  • Zhongbing Lu et al.

    Structure–activity relationship analysis of antioxidant ability and neuroprotective effect of gallic acid derivatives

    Neurochemistry International

    (2006)
  • M. Marín et al.

    Intestinal anti-inflammatory activity of ellagic acid in the acute and chronic dextrane sulfate sodium models of mice colitis

    Journal of Ethnopharmacology

    (2013)
  • F. Petermann et al.

    Cytokines and effector T cell subsets causing autoimmune CNS disease

    FEBS Letters

    (2011)
  • M.A. Rosillo et al.

    Protective effect of ellagic acid, a natural polyphenolic compound, in a murine model of Crohn's disease

    Biochemical Pharmacology

    (2011)
  • R.C. van der Veen

    Nitric oxide and T helper cell immunity

    International Immunopharmacology

    (2001)
  • H. Wekerle et al.

    Remote control-triggering of brain autoimmune disease in the gut

    Current Opinion in Immunology

    (2013)
  • J. Zhishen et al.

    The determination of flavonoid contents in mulberry and their scavenging effects on superoxide radicals

    Food Chemistry

    (1999)
  • L.A. BenSaad et al.

    Anti-inflammatory potential of ellagic acid, gallic acid and punicalagin A&B isolated from Punica granatum

    BMC Complementary and Alternative Medicine

    (2017)
  • M.C. Deeds et al.

    Single dose streptozotocin-induced diabetes: Considerations for study design in islet transplantation models

    Laboratory Animals

    (2011)
  • Cited by (45)

    • Potential of phenolic compounds from pomegranate (Punica granatum L.) by-product with significant antioxidant and therapeutic effects: A narrative review

      2023, Saudi Journal of Biological Sciences
      Citation Excerpt :

      Adverse effects occur with an excess of free radicals when a phenomenon called oxidative stress occurs in the body (Sharma, 2014). Therefore, plant phenolic compounds as antioxidants are becoming increasingly popular practices to maintain optimal body function and can be called “the seventh major nutrient” (Hidekazu et al., 2012; Kurutas, 2016; Lv et al., 2021). Some authors claim that the metabolites of ellagitannin geranium, chlorogenic acid, and epigallocatechin gallate have stronger antioxidant activity than their respective parent compounds.

    • Inhibition of Escherichia coli ATP synthase and cell growth by dietary pomegranate phenolics

      2022, International Journal of Biological Macromolecules
      Citation Excerpt :

      However, its bioavailability and solubility are relatively low [65,66]. Punicalin, another abundant polyphenol in pomegranate, has been shown to have higher antioxidative properties and reduces the effects of cancer, diabetes, gastrointestinal distress, and inflammation [67,68]. Pomegranates found in Peru, South Africa, and Georgia have a higher content of punicalin [69].

    View all citing articles on Scopus
    View full text