BLACKBERRIES AND RASPBERRIES FOR THE CONTROL OF GASTRIC INFLAMMATION
TANNINS AND DERIVATED COMPOUNDS
Plant tannins, one of the major groups of antioxidant polyphenols found in food and beverages, have attracted a lot of attention in recent years because of their multifunctional properties beneficial to human health.
A tannin is a polyphenolic compound that binds to and precipitates proteins and various other organic compounds including amino acids and alkaloids. The term "tannin" by extension is widely applied to any large polyphenolic compound containing sufficient hydroxyls and other suitable groups (such as carboxyls) to form strong complexes with various macromolecules.
Tannins may be classified chemically into three main groups:
- Complex tannins
- Condensed tannins: are formed through the condensation of flavan-3-ols (catechins) and are often referred to as proanthocyanidins.
- Hydrolyzable tannins: are derivatives of gallic acid which is esterified to a core polyoil groups. They can then be further divided in
Hydrolysable tannins as ellagitannins, which produce ellagic acid upon hydrolysis, constitute the largest group; the remaining group is gallotannins (galloylglucoses).
International Journal of Molecular Sciences ISSN 1422-0067 Review. Structural Features and Biological Properties of Ellagitannins in Some Plant Families of the Order Myrtales
RUBUS BERRIES AND ELLAGITANNIS
Rubus berries, raspberries and blackberries, are considered to be a rich source of dietary antioxidants due to their high content of phenolic compounds. They contain high levels of ellagitannins (ETs) and ellagic acid conjugates (EAC), a class of polyphenols relatively uncommon in fruit and vegetables in our diet, being found only in few fruits, such as strawberries, pomegranates, muscadine grapes, some nuts, raspberries (Rubus idaeus L.) and blackberries (Rubus fruticosus L.).
In Rubus berries, ETs and EAC are present in significant amounts (on average ca. 1.3 g/kg) both in raspberries and blackberries and represent the primary source of dietary ellagitannins.
- Blackberry Rubus fruticosus (fig. a)
- Raspberry Rubus idaeus (fig. b)
An increasing number of evidences support for the health beneficial effects of plant polyphenols, including ETs.
ELLAGITANNINS BIOLOGICAL ACTIVITY
ETs received great attention mainly as beneficial nutrients against cardiovascular disease and cancer and show relevant anti-inflammatory and anti-angiogenic effects. Furthermore, ETs from pomegranate can modulate the intestinal inflammatory response.
In this case the attention is focused on ETs present in Rubus berries raspberries and blackberries, to verify whether they are able to protect against gastric ulcer and how they interfere with the molecular cascade producing the inflammatory cell response at gastric level.
Ellagitannins from Rubus Berries for the Control of Gastric Inflammation: In Vitro and In Vivo Studies
ETIOLOGY AND ETIOPATOGENESIS
The pattern and distribution of gastritis strongly correlate with the risk of clinical duodenal or gastric ulcers, mucosal atrophy, gastric carcinoma or gastric lymphoma.
- H. Pylory:
The bacteria appear to trigger ulcers in the following way:
H. pylori's corkscrew shape enables them to penetrate the mucus layer of the stomach or duodenum so that they can attach themselves to the lining and it survive in the highly acidic environment by producing urease, an enzyme that generates ammonia to neutralize the acid.
H. pylori stimulate the increased release of gastrin. Higher gastrin levels promote increased acid secretion. The increased acid damages the intestinal lining, leading to ulcers in certain individuals.
H. pylori also alter certain immune factors that allow these bacteria to evade detection by the immune system and cause persistent inflammation.
Only around 10 - 15% of people who are infected with H. pylori develop peptic ulcer disease. H. pylori infections, particularly in older people, may not always lead to peptic ulcers. Other factors must also be present to actually trigger ulcers, including:
- Genetic Factors
- Immune Abnormalities
- Lifestyle Factors such as chronic stress, drinking coffee, and smoking.
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
Long-term use of NSAIDs is the second most common cause of ulcers. NSAIDs also increase the risk for gastrointestinal (GI) bleeding. Short courses of NSAIDs for temporary pain relief should not cause major problems, because the stomach has time to recover and repair any damage that has occurred.
- Other Causes
Certain drugs other than NSAIDs may aggravate ulcers. These include warfarin, oral corticosteroids, some chemotherapy drugs, spironolactone, and niacin.
Bevacizumab, a drug used to treat colorectal cancer, may increase the risk of GI perforation. Certain conditions may cause ulcers in the stomach or intestine, including:
It has been demonstrated that gastric epithelial cells, after H. pylori infection, show higher levels of cytokines including IL-1ß, TNF-a and IL-8, a potent neutrophil-activating chemokine that apparently plays a central role in gastric diseases.
H. Pylori strains carrying the Cag-PAI (Cag Pathogenicity Island) induce a far stronger IL-8 response than Cag-negative strains, and this response depends on the activation of NF-kB and the early-response transcription factor Activating Protein-1.
IL-21 is constitutively expressed in gastric mucosa as well, and is more abundant in biopsy from H. Pylori infected patients.
In response to pro-inflammatory stimuli gastric epithelial cells release several cytokines and induce the expression of NF-kB related genes, including metalloprotease-9. The integrity of the epithelial barrier is thus reduced, favouring pathogen infections.
NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) is a protein complex that controls transcription of DNA.
NF-κB is found in almost all animal cell types and is involved in cellular responses to stimuli such as stress, cytokines, free radicals, ultraviolet irradiation, oxidized LDL, and bacterial or viral antigens. NF-κB plays a key role in regulating the immune response to infection.
Incorrect regulation of NF-κB has been linked to cancer, inflammatory and autoimmune diseases, septic shock, viral infection, and improper immune development.
Nuclear factor kB (NF-kB) is a transcriptional regulator that plays a central part in responses to inflammatory signalling through Toll-like receptor, TNF receptors and the IL-1 receptor.
The inducers of NF-kB activation such as TNF-a and IL-1ß produce elevated reactive oxygen species (ROS) levels, suggesting that ROS act as common mediators of NF-kB activation that could be blocked by antioxidants or overexpression of antioxidant enzymes
- superoxide dismutase (SOD)
ROS including hydrogen peroxide (H2O2) are known to over-express IL-8 by activating oxidant-sensitive transcription factors such as NF-kB in gastric epithelial cells.
Patients with gastric ulcer have low levels of gastric antioxidants compared to normal mucosa. Oxidative stress is also involved in the gastric damage induced by various agents including ethanol.
Fruits and vegetables are suggested to confer protection for several pathologic conditions through their antioxidant effects.
ELLAGITANNINS FROM RUBUS BERRIES FOR THE CONTROL OF GASTRIC INFLAMMATION: IN VITRO AND IN VIVO STUDIES
At this aim, the efficacy of ETs was evaluated
- In vitro: ETs were assayed to investigate
- the inhibition of NF-kB translocation and driven transcription activity;
- the effect on IL-8 release in gastric epithelial cell line (AGS) stimulated with TNF-a, IL-1ß, H2O2, and ethanol
- In vivo: a rat model of ethanol-induced gastric ulcer
In vitro experiments with AGS gastric epithelial cells confirm and further characterize the molecular function of ETs. The activity ETs was tested in cells exposed to various inflammatory challengers known to activate NF-kB cell signalling: cytokines TNF-a and IL-1b, or the pro-oxidant agents ethanol and H2O2.
The results show that ETs interfere with the metabolic cascade deriving from the activation and translocation of NF-kB that in turn activates the transcription of targeted genes including that of
ETblack and ETrasp showed a high protective effect against ethanol injury,when given once a day for 10 consecutive days before the administration of 1 ml ethanol.
Both extracts significantly reduced gastric lesions by 88% and 75%, respectively.
EFFECT ON BIOCHEMICAL PARAMETERS EX VIVO
- In the gastric mucosa of rats treated with ethanol, the biochemical parameters relative to the oxidative state were modified with respect to control animals: Trolox equivalents, SOD and CAT activities were all reduced, indicating an unbalance of the steady state of the tissue versus an oxidant condition.
Both ETblack and ETrasp counteracted the oxidant effect of ethanol, ETblack being more efficient than ETrasp. In rats treated with ETblack, Trolox equivalents, SOD and CAT levels returned to the values found in control animals.
- The administration of ethanol caused a higher release of CINC-1 (the rat homologue of human IL-8).
In animals treated with ETblack and ETrasp the amount of CINC-1 was significantly lower with respect to ethanol.
The effect of ETs on CINC-1 was associated to a decrease of NF-kB translocation in ETblack and ETrasp animals in comparison with control and ethanol treated animals.
This study reports for the first time that ETs from blackberries and raspberries are able to protect the stomach against the gastric lesions caused by ethanol.
It is remarkable that the effect was obtained at a dose of ETs comparable with the amount consumed in a portion of berries of 125 g, corresponding to the weight of the content of the baskets distributed on the market. The anti-ulcer effect of blackberry, measured as UI, was higher than that of raspberry. Blackberry extract contained a higher amount of ETs (343 mg/100 g of fresh fruits) than raspberry (155 mg/100 g of fresh fruit); then, the difference in ETs content could account for the different response.
Gastroprotective properties of ETs has been proven for swimstress, ethanol, and ischemic/reperfusion-induced ulcers.
Its antiulcer effect is partially attributed to its inhibitory action on the gastric H+,K+-ATPase, in vivo antioxidant property and anti-H. pylori activity.
ETs, as demonstrated in different studies, is known to inhibit leukocyte recruitment and adherence to the endothelium through inhibition of reactive oxygen species (ROS) generation, cytokine- induced ROS generation, inflammation, and expression of adhesion molecules.
Ellagitannins from Rubus Berries for the Control of Gastric Inflammation: In Vitro and In Vivo Studies