ANTI-ULCEROGENIC EFFICACY AND MECHANISMS OF EDIBLE AND NATURAL INGREDIENTS IN NSAID-INDUCED ANIMAL MODELS

Efficacy

Although no data are available from human study, the antiulcerogenic benefits of edible, natural ingredients have been well demonstrated in animal models, as summarized in Table 2. Both aerial parts and fruits of trichosanthes cucumerina are edible, particularly in Asia. Study demonstrated that orally given 750 mg/kg body weight of trichosanthes cucumerina extract induced an 88% reduction in the numbers of haemorrhagic lesions caused by indomethacin in rats. The efficacy was comparable to that induced by conventional drug, cimetidine (100 mg/kg) (Arawwawala et al., 2010). Likewise, asparagus racemosus Willd is a common vegetable. In comparison to indomethacin alone, concurrently oral administrations of asparagus racemosus Willd extract at a daily dose of 100 mg/kg body weight with indomethacin for 15 days reduced ulcer index by over 80%, which was comparable to that induced by ranitidine at a daily dose of 30 mg/kg body weight (Bhatnagar and Sisodia., 2006). Moreover, Phyllanthus emblica fruit is commonly edible and available in Asia. Prior to induction of gastric ulcer with indomethacin, orally given Phyllanthus emblica fruit extract for 10 days caused a dose-dependent inhibition of ulcer index (Bandyopadhyay et al., 2000). Similarly, orally given pomegranate extract (500 mg/kg) 4 hours prior to aspirin administration induced an over 70% inhibition of ulcer index (Ajaikumar et al., 1997). Furthermore, edible natural ingredients also prevent the development of gastric ulcer in rats with diabetes, which is a risk factor for gastric ulcer (Masuda et al., 1976; Duggan et al., 1992). Pimple et al. showed that co-administrations of methanolic extract of Luffa acutangula fruits and aspirin could significantly lowered ulcer index in diabetes rats in comparison with aspirin alone (Pimple et al., 2012). Not all edible, natural ingredients display the preventive efficacy in a dose-dependent manner. It has been demonstrated that methanolic extract of Mouriri pusa at a dose of 250 mg/kg body weight lowered ulcer lesion index by 34% while 1000 mg/ kg body weight only induced a 7% inhibition of ulcer lesion index (Andreo et al., 2006). In addition, the inhibitory efficacy of Arctium lappa L.leaves is lower at the dose of 200 mg/kg body weight than at 50 mg/kg (de Almeida et al., 2012). Therefore, caution should be taken when determining what dose should be used because the efficacy of certain ingredients not always positively correlates with the dosage.

In addition to vegetables and fruits, certain edible oils also exhibit gastroprotective benefit. For instance, 1 hour prior to induction of ulcer by indomethacin orally given essential oil from Baccharis dracunculifolia at a single dose of 50 mg/kg body weight induced an 80 inhibition of ulcer index while oral cimetidine at a dose of 100 mg/kg body weight only caused 42% inhibition of ulcer index (Massignani et al., 2009). Evening primrose oil, another edible oil, can also dose-dependently prevent the development of gastric ulcer induced by either aspirin or indomethacin (al-Shabanah., 1997). Even the fish oil, one of the most common dietary supplements, displays antiulcerogenic benefit in aspirin- and indomethacin-induced gastric ulcer models of rats (al-Harbi et al., 1995). Moreover, soybean, a commonly consumed food, is a potent antiulcerogenic agent, too. Kumar et al. reported that once daily oral soybean paste 30 min prior to each aspirin administration for 7 days lowered gastric ulcer scores by over 40% in rats (Kumar et al., 2013). Furthermore, oral administration of extract from a mixture of Blumea balsamifera leaves, Curcuma domestica L. and Ammomum compactum S. pods almost completely prevented the development of aspirin-induced gastric ulcer (Mutmainah et al., 2014). Not only oral administration, but also intraperitoneal injection of food extract shows antiulcerogenic benefit. For example, morin is a flavonoid commonly found in almond, osage orange and fig. 30 min prior to induction of ulcer with indomethacin in rats, intraperitoneal injection of morin at a single dose of 50 mg/kg body weight reduced ulcer lesion index by over 80% (Singh et al., 2015).

It is worth noting that the preparation methods can affect the antiulcerogenic efficacy of certain edible ingredients. For instance, dichloromethane extract of Mouriri pusa leaves at a dose of 250mg/kg body weight induced a 51% inhibition of ulcer lesion index while the same dose of methanolic extract caused 34% inhibition (Andreo et al.,2006). Likewise, aqueous extract of Solanum nigrum at a dose of 4g/kg exhibited no preventive effect in an animal model of aspirin-induced gastric ulcer while the same dose of methanolic extract induced an over 20% inhibition of ulcer index (Akhtar and Munir., 1989). Similarly, methanolic extract of Luffa acutangula is more effective than its aqueous extract (Rozza et al., 2011). In contrast, aqueous extract of Brassica oleracea, but not methanolic extract, induced a 42% inhibition of ulcer index (Akhtar and Munir., 1989). However, both aqueous and methanolic extracts of Ocimum basilicum, exhibited a similar efficacy of antiulcerogenesis (Akhtar and Munir., 1989). Therefore, special attention should be paid to the preparation methods when using these ingredients.

Safety

In addition to soybean and common nutrient supplements such as fish oil and evening primrose oil, other edible, natural ingredients, also are generally safe. For instance, a single of 500 mg/kg body weight methanolic extract of Mouriri pusa could effectively lower ulcer lesion index (Andreo et al., 2006) while orally given a single dose of 5000 mg/kg body weight did not cause any signs or symptoms of acute toxicity during a 14-day follow-up period. No lesion or pathological changes occurred in internal organs of the mice (Andreo et al., 2006). Moreover, no adverse event was observed in rats 14 days after single oral administration of alcoholic extract of Brassica oleracea var. acephala DC leaves, a vegetable, at a dose of 2g/kg body weight (Lemos et al.,2011). The LD50 value for Petroselinum crispum (Mill.) extract is 13g/kg body weight in rats 3 days after a single intraperitoneal injection (Al-Howiriny et al.,2003). All these evidences indicate that edible, natural ingredients are safe for preventing the development of gastric ulcer.

Mechanisms

While NSAIDs can inhibit inflammation, they also induce the production of proinflammatory cytokines via activation of 5-lipoxygenase pathway (Sinha et al., 2013). NSAIDs can also inhibit prostaglandin E2 synthesis and induce oxidative stress (McAnulty et al., 2007; Sinha et al., 2013), eventually leading to the development of gastric ulcer (Sinha et al., 2013; Tandon et al., 2004). The mechanisms by which edible, natural ingredients display antiulcerogenic benefit include anti-inflammation, antioxidaion, stimulation of prostaglandin E2, and inhibition of acid secretion, etc. (Table 3).

a. Antioxidation

The role of oxidative stress in the pathogenesis of gastric ulcer is well recognized while NSAIDs can induce oxidative stress in various tissues including gastric mucosa (Adachi et al., 2007; Bhattacharyya et al. 2014; Ghosh et al., 2015; Hiraishi et al., 2000; Tandon et al., 2004). Accordingly, employment of antioxidants could benefit gastric ulcer. Studies have shown that the antioxidant property of certain natural ingredients can contribute to their preventive benefits in the development of gastric ulcer in various animal models (Alimi et al., 2010, 2011, 2013;

Nartey et al., 2012; Repetto et al., 2002). Bhatnagar et al. reported that oral administration of Asparagus racemosus extract at a daily dose of 100mg/kg body weight for 15 days did not only increase the activities of superoxide dismutase (SOD) and catalase (CAT), but also the content of ascorbic acid in both the stomach and liver to the levels comparable to ranitidine. In addition, the levels of malondialdehyde (MDA), a product of lipid peroxidation, were also significantly reduced in indomethacin-induced model of gastric ulcer (Bhatnagar et al., 2005). Orally given aqueous extract of Aegle marmelos fruits at a daily dose of 250 mg/kg body weight for 14 days significantly increased the content of reduced glutathione (GSH), and the activities of SOD and CAT in an animal model of aspirin-induced gastric ulcer (Das and Roy., 2012). Even only one hour prior to induction of gastric ulcer with aspirin, oral administration of extract of Punicagranatum L. fruits could dramatically increase the levels of SOD, CAT and glutathione peroxidase in the stomach in comparison with rats treated with aspirin alone (Ajaikumar et al., 2005). Extracts of both ginseng and Arctium lappa L. roots exhibit free-radical scavenging activity (Dos Santos et al., 2008; Jeong., 2002). Taken together, antiulcerogenic benefit of certain edible, natural ingredients could be attributed to their antioxidant property.

b. Inhibition of acid secretion

Increased acid secretion in part plays a role in the pathogenesis of gastric ulcer (Abdul-Aziz., 2011). Accordingly, sodium bicarbonate, a base, has been used to relieve the symptoms of gastric ulcer. Studies have shown that some edible natural ingredients prevent the development of gastric ulcer via inhibition of acid secretion in various animal models, including NSAID-induced gastric ulcer. Orally given Asparagus racemosus Willd. at a daily dose of 100 mg/kg body weight for 15 days markedly decreased the volume and acidity of gastric juice in a model of gastric ulcer induced by indomethacin (Bhatnagar et al., 2005). Likewise, oral administration of extract of Garcinia kola Heckel Seeds at a daily dose of 100 mg/kg body weight for 3 days induced an over 47% reduction in the volume of gastric juice and an over 45% increase in pH of the gastric juice (Olaleye and Farombi., 2006). There are several mechanisms involved in the inhibition of acid secretion induced by edible, natural ingredients. First, the enzyme H+, K+-ATPase in the gastric parietal cells is known to transports the H+ against a concentration gradient, leading to acid secretion [¹¹⁰]. Extracts of certain ingredients such as ginseng, Arctium lappa L. roots and Garcinia kola Heckel seeds are potent inhibitors of H+, K+-ATPase (Dos Santos et al., 2008; Onasanwo et al., 2011; Oyagi et al., 2010). For example, the IC50 of Arctium lappa L. root extract for H+, K+-ATPase is 53μg/ml (Dos Santos et al., 2008). IC50 of Garcinia kola Heckel seed extract is 43.8μg/ml while IC50 of omeprazole, a conventional inhibitor, is 32.3μg/ml (Onasanwo et al., 2011). Second, histamine stimulates acid secretion while NSAIDs enhance the effect of histamine on acid secretion (Schwartzel et al., 1984; Shamburek and Schubert., 1992). Studies have demonstrated that oral administration of the extract of Trichosanthes cucumerina (aerial parts) was more effective then chlorpheniramine in reduction of wheal size induced by subcutaneous injection of histamine, suggesting antihistamine effect (Arawwawala et al., 2010). In addition, pre-feed rats with oral Potentilla fulgens Wall. ex Hook extract for 7 days significantly lowered histamine levels in the stomach tissue in a model of gastric ulcer (Laloo et al., 2013). Third, prostaglandin E2 inhibits acid secretion, and to protect stomach from the damage induced by indomethacin (Befrits and Johansson., 1985; Robert et al., 1981; Takeuchi., 2014). But NSAIDs lower prostaglandin E2 levels (el-Bayar et al., 1985). Inhibition of acid secretion by some ingredients could be through stimulating prostaglandin E2 production. Yokota et al. demonstrated that pre-feed rat with Eriobotrya japonica seed extract for 14 days increased prostaglandin E2 levels by 95% in stomach tissue of indomethacin-induced ulcer (Yokota et al., 2011). Orally given 20 mg/kg body weight of Azadirachta indica seed extract is more potent than omeprazole (10mg/kg body weight) in elevation of prostaglandin E2 content in stomach tissue of aspirin-induced ulcer (Singh et al., 2015). Fourth, gastrin, a gastrointestinal hormone, can stimulate acid secretion independently or via histamine (Soll and Walsh., 1979). Treatment of rats with oral Solanum nigrum fruit extract dramatically lowered plasma levels of gastrin (Jainu and Devi., 2006). Additionally, serotonin can inhibit acid secretion (Bech., 1986). Treatment of rats with the extract of Aegle Marmelos fruits for 14 days could increase the serotonin content by 32% over aspirin treatment alone in an aspirin-induced gastric model (Singh et al., 2015). Collectively, edible, natural ingredients can inhibit H+, K+-ATPase activity, gastrin and histamine production while increase serotonin and prostaglandin E2 levels, leading to inhibition of acid secretion.

c. Inhibition of inflammation

Another feature of gastric ulcer is gastric inflammation, which is attributed in part to the NSAID-induced gastric ulcer (Sinha et al., 2013). Some ingredients that exert antiulcerogenic activity inhibit inflammation. In addition to an over 80% reduction in serum IL-1β levels, pre-feed rats with grape seed extract at a daily dose of 100mg/kg body weight for 6 days lowered serum TNFα to an undetectable level in indomethacin-induced gastric ulcer model (Kim et al., 2013). Likewise, co-administrations of ginger powder at a dose of 200 mg/kg body weight with aspirin for 4 hours induced an over 40% reduction in plasma TNFα and IL-1β levels in comparison with aspirin alone (Wang et al., 2011). Moreover, edible ingredients also inhibit inflammatory cell infiltration. 30 min prior to induction of gastric ulcer with indomethacin, pre-feed rats with extract of Bauhinia purpurea leaves provoked 100% inhibition of leukocytes infiltration into gastric wall (Hisam et al., 2012). Similarly, both eosinophil and mast cell infiltration into mucosal wall were inhibited by oral administration of extract of a mixture containing Blumea balsamifera leaves, Curcuma domestica L. and Ammomum compactum S. pods 10 min prior to induction of gastric ulcer with aspirin (Mutmainah et al., 2014). Consistent with anti-inflammation, oral mourin also reduced the expression levels of Intercellular adhesion molecule-1 in gastric mucosa in a model of aspirin-induced gastric ulcer (Sinha et al., 2015). Thus, inhibition of inflammation is another mechanism by which edible, natural ingredients prevent the development of NSAID-induced gastric ulcer.

This work was supported by Natural Science Foundation of China (81301360 and 81573075 for LH) and the Science Foundation of Tianjin Medical University (2013KY06 for Dr. LH).