1. Introduction
The development of peptic ulcers is a result of an imbalance between endogenous mucosal mechanisms—mucus, bicarbonate, prostaglandins, nitric oxide (NO) and sulfhydryl compounds—and the presence of endogenous aggressive factors such hydrochloric acid and pepsin. Exogenous factors such as
Helicobacter pylori, use of steroidal anti-inflammatory drugs (corticosteroids) and non-steroids (NSAIDs), alcohol abuse and stress [
1,
2]. Peptic ulcers may develop in any region of the gastrointestinal tract, being more frequent in the stomach and duodenum. Gastric ulcers are usually related to weakening of the mucosal defense mechanisms and the presence of aggressive factors, whereas the development of duodenal ulcers is often associated with the hypersecretion of hydrochloric acid and pepsin, and in this situation even when the defense mechanisms are normal, they are not able to avoid aggression [
3].
Ethanol attacks the gastric mucosa directly inducing lesions in the mucosa, because this acts to promote destruction of the mucosa’s protective layer due to depletion of mucus and bicarbonate, resulting in cellular necrosis. Cellular necrosis results from a cascade of events that involve the release of reactive oxygen species (ROS), infiltration of inflammatory cells that produce chemical markers, and leading to vasoconstriction, edema, hemorrhage and compromised blood flow with consequent ischemia and death of the gastric cells [
4,
5].
Indomethacin is a representative of the NSAID family and causes gastric lesions through inhibition of the enzyme cyclooxygenase-1 (COX-1) resulting in decreased production of endogenous prostaglandins, thereby rendering gastric mucosa susceptible to endogenous and exogenous attacks/aggression; in addition, this NSAID acts as a pro-oxidant catalyst initiating lipoperoxidation, producing ROS and, thus, interfering with the endogenous antioxidant systems of the mucosal cells, as well as inducing recruitment of leukocytes and boosting the inflammatory response [
6,
7].
Brazil holds the largest share of biodiversity, around 15–20% of the world total; among the elements that compose it, plants are a raw material for manufacturing herbal medicines and other medicines [
8]. The World Health Organization (WHO) has expressed its position on the need to value the use of medicinal plants in health since the Declaration of Alma-Ata in 1978, considering that 80% of the world population uses these plants or preparations thereof with regard to Primary Health Care. Alongside this, the participation of the developing countries in this process stands out, since they have 67% of the vegetal species in the world [
9].
Kalanchoe brasiliensis Cambess and
Kalanchoe pinnata (Lamarck) Persoon, from the Crassulaceae family, both popularly known as “coirama” and “saião” are popularly used in treating peptic ulcers. The described method of use is the leaf juice of the fresh leaves [
10]. Added to all of this, it is worth mentioning that the presence of the species
K. pinnata is in the National Relation of Species of Interest of Health Unic System (RENISUS).
In this context, the present study was carried out to establish the action mechanism involved in gastroprotective activity of K. brasiliensis and K. pinnata leaf juices against gastric lesions induced by ethanol and by indomethacin in rats.
3. Discussion
In the present study, we observed that the pre-treatment with K. brasileinsis and K. pinnata leaf juice protects the mucosa of rats against the gastric damage of indomethacin and ethanol-induced gastric lesions, suggesting that they exhibit a significant gastroprotective effect. In addition, pre-treatment with leaf juices of both species significantly reduced damage by improving parameters related to oxidative stress and inflammation on mucosal structures.
Several mechanisms are associated with the production of gastric mucosal lesions. Ethanol and indomethacin cause intense damage to the gastric mucosa in the form of ulcerative lesions. Ethanol attacks the gastric mucosa directly inducing mucosal injury, since it acts to reduce secretion of bicarbonate and the generation of mucus, in addition to the excessive production of ROS, disturbances in gastric microcirculation and lesion of the epithelial cells, causing rupture of mucous cell membranes and cytotoxic effects, along with consequent propagation of the inflammatory cascade [
5]. On the other hand, indomethacin causes gastric lesions due to the weakening of the gastric mucosa caused by synthesis inhibition of prostaglandins by COX-1; in addition, NSAID also acts as a pro-oxidant catalyst and initiates the lipoperoxidation producing ROS and, thus, interfering with the antioxidant systems endogenous cells of the mucosa, and inducing the leukocyte recruitment and boosting the inflammatory response [
6,
7].
The administration of ethanol on the gastric mucosa causes lipid peroxidation, which together with the increase of free radicals generates oxidative stress, resulting in cell death [
15,
16]. Oxidative stress may play a major role in the induction and pathogenesis of stomach ulcers. Decreased GSH levels are observed in both the ethanol-induced acute gastric lesions induction model and indomethacin, making the gastric mucosa more susceptible to injury [
17]. In addition to reducing GSH levels, ethanol and indomethacin affect the properties of gastric tissue by raising lipid peroxidation [
18], with MDA being the main indicator of lipid peroxidation. Thus, MDA acts as a marker of ROS, mediated by the development of gastric lesions [
15]. On the other hand,
K. brasiliensis and
K. pinnata leaf juice and ranitidine (50 mg/kg) had significant antioxidant activity, observed by reducing MDA levels (
Figure 4C,D) and increasing the GSH levels (
Figure 4A,B) in response to oxidative stress due to treatment with ethanol and indomethacin.
Gastric lesions caused by ethanol result in high neutrophil infiltration, releasing ROS that are extremely cytotoxic and promote the development of tissue lesions [
19]. The MPO is the main constituent of the azurophilic granules of neutrophils, being readily released after activation, and contributing to innate immune defense [
20]. Our results revealed the protection of the gastric mucosa and the inhibition of leukocyte infiltration in gastric tissue in rats pre-treated with leaf juices and with ranitidine (50 mg/kg) (
Figure 4E,F). The activation and infiltration of neutrophils seems to be involved in the initial processes that form these lesions. Salga et al. [
21] demonstrated that reducing neutrophil infiltration in ulcerated gastric tissues helped prevent gastric lesions in rats [
21].
The involvement of proinflammatory cytokines such as IL-1β and TNF-α in the gastric lesion is remarkable [
22,
23]. TNF-α is one of the most aggressive factors in the inflammation, injury and carcinogenesis processes in various tissues, including the development of gastric mucosal ulcers [
24]. IL-1β contributes to the development of lesions in the gastric mucosa after ethanol administration, because this cytokine acts by inducing accumulation of neutrophils, which leads to the release of inflammatory mediators [
15]. TNF-α reduces gastric microcirculation around the ulcer and delays healing due to its ability to potentiate the inflammatory response [
25]. Ethanol-induced gastric lesions and gastric epithelial cells undergo apoptosis triggered by locally increased TNF-α [
26]. In the same context, NF-κB-p65 is a transcription factor that mediates crucial inflammatory events in gastric lesions induced by ethanol, including the expression of several proinflammatory targets such as TNF-α, chemokines and adhesion molecules [
27,
28,
29]. In the inactive state, NF-κB-p65 (a heterodimer located in the cytosol of cells) is maintained inactive by binding to the inhibitory protein IκBα. Following exposure to stress signals such as ROS and inflammatory cytokines, IκBα undergoes phosphorylation and subsequent proteasomal degradation. In the present study, pre-treatment with leaf juice and ranitidine (50 mg/kg) was able to reduce levels of IL-1β (
Figure 5A,B) and TNF-α (
Figure 5C,D) and expression of NF-κB-p65 (
Figure 10A,B) in both the ethanol and indomethacin induced acute gastric lesion induction model.
Histological results indicated that ethanol and indomethacin caused the appearance of severe to very serious gastric lesions in the gastric mucosa with the presence of extensive edema and infiltration of leukocytes in the submucosa layer. It was possible to observe that pre-treatment with the leaf juices of both species at a dose of 500 mg/kg exert a cytoprotective effect on the gastric mucosa (
Figure 6 and
Figure 7). Exposure to gastric lesions such as ethanol and NSAIDs results in a decrease of the protective mucus gel and the phospholipid layer, leading to acid diffusion and mucosal injury [
30]. The results of our study showed intense staining of glycoprotein secretions of gastric wall mucosal glands in rats pre-treated with
K. brasiliensis and
K. pinnata leaf juice at a dose of 500 mg/kg and ranitidine (50 mg/kg) (
Figure 8A,B). Mucus secretion is one of the important mechanisms of gastric mucosal defense against necrotizing agents [
21,
27,
31], playing a significant role in the process of gastric lesion inhibition because the mucus/bicarbonate layer protects newly formed cells from acid and peptic lesions [
32,
33].
Previous studies have suggested that TNF-α and other proinflammatory cytokines activate NF-κβ, leading to the activation of transcription of several inflammatory genes, including iNOS. NO is described as the second major defense mechanism in the GI tract, so that it acts on the regulation of gastric mucosal integrity and acidity together with prostaglandin E2 (PGE2), as well as being involved in the inhibition of neutrophil aggregation and increased blood flow [
34,
35]. The inducible NOS-derived NO (iNOS) is produced in high amounts giving rise to inflammatory responses that will favor the formation of gastric lesions through the generation of ROS [
36]. Pre-treatment with
K. brasiliensis and
K. pinnata leaf juices at a dose of 500 mg/kg and ranitidine (50 mg/kg) was able to reduce the expression of the iNOS enzyme in the gastric mucosa of rats, both in the ethanol and indomethacin induction models (
Figure 9A,B).
Zo-1 is a trans-membrane protein that preserves the integrity of the tight junctions which are the indicators of epithelial integrity of the mucosa [
37]. Immunohistochemical analysis showed that pre-treatment with
K. brasiliensis and
K. pinnata leaf juices at a dose of 500 mg/kg and ranitidine (50 mg/kg) was able to increase ZO-1 expression in the gastric mucosa of rats, both in the ethanol and indomethacin induction models (
Figure 11A,B).
When we associate the results of the UHPLC-MS phytochemical analysis with the pharmacological results, it can be suggested that the flavonoids identified in the leaf juices of the two plant species can contribute, at least in part, in the reduction of the inflammatory process generated in the gastric mucosa. Flavonoids of different classes are known to have various biological activities and medicinal value. Most have anti-inflammatory properties and can suppress the expression and transcription of inflammatory cytokines [
38]. In a study by Jabeen et al. [
39] which used a rheumatoid arthritis induction model, it was observed that treatment with patuletin was able to decrease ROS; therefore, a decrease in nitric oxide concentration and an increase in glutathione levels were also observed. In addition, there was inhibition of TNF-α, IL-1β expression and decreased T-cell proliferation, thereby suppressing the inflammation.
Our results show preclinical evidence of the effect of these extracts as gastroprotectors. Previous studies reported in literature (using different extraction method) have demonstrated that the
K. pinnata species presents gastroprotective activity [
40,
41,
42,
43,
44] as well as only one study reported the gastroprotective activity of
K. brasiliensis [
45]. It is worth noting that when comparing our study with others described previously, we used an extraction method to obtain the leaf juices according to popular medicine without the use of toxic solvent. Beside, our work showed an investigation more detailed about the gastroprotective action mechanism added to chemical characterization of extracts, often not presented in the previous works.
Flavonoids were detected in both extracts according to the UHPLC-MS analysis. These secondary metabolites may be involved with the gastroprotective effect of the extract, since it has been reported that quercetin, a strong antioxidant, may protect gastric epithelial cells from oxidative damage by decreasing ROS production in acute gastric mucosa lesion [
46]. In vivo studies have shown a gastroprotective effect of quercetin against gastric lesions induced by ethanol. Studies have shown that eupafolin has anti-inflammatory [
47,
48] and antioxidant properties [
49]. Eupafolin was able to inhibit NO release in LPS stimulated macrophages [
50]. This flavonoid also reduced iNOS and cyclooxygenase-2 (COX-2) in these cells [
51]. In addition, eupafolin inhibited the adhesion of leukocytes to the endothelium by inhibition of intercellular adhesion molecule 1 (ICAM-1) expression [
52]. Kaempferol has antioxidant and anti-inflammatory activity [
53]. Regarding the anti-inflammatory activity of kaempferol, it has been described that this flavonoid presents mechanisms of inhibiting iNOS and COX-2 levels in a dose-dependent way [
54].
In the literature, flavonoids are described as possessing both cytoprotective and antisecretion properties. In mammals, they exert a gastroprotective effect by increasing the levels of endogenous prostaglandin, decreasing histamine secretion, eliminating ROS and inhibiting
H. pylori bacteria [
55,
56]. Flavonoids such as naringin, quercetin, silymarin, anthocyanosides, soforadine and rutin have been reported to have antiulcerogenic properties [
57]. For this, future studies with the isolated flavonoids that have been identified in
K. brasileinsis and
K. pinnata leaf juices can be performed to investigate the role of these compounds in gastroprotective activity.
The current data revealed that pre-treatment with K. brasiliensis and K. pinnata leaf juices did not alter the evaluated acid secretion parameters (pH, total acidity and volume). In contrast, pre-treatment with ranitidine (50 mg/kg) reduced total acidity and increased the pH. Thus, we can suggest that K. brasiliensis and K. pinnata leaf juices did not show antisecretion activity.
In conclusion, the pre-treatment with K. brasiliensis and K. pinnata leaf juices increased the antioxidant defense system and glutathione (GSH), whereas malondialdehyde, myeloperoxidase, IL-1β and TNF-α levels were significantly decreased. In addition, the pre-treatment led to the upregulation of ZO-1 and the downregulation of iNOS and NF-κB-p65, while also showing a cytoprotective effect and maintaining mucus production. These findings show that the leaf juices of the two species have gastroprotective effects on ethanol and gastric indomethacin injury which were a consequence of gastric inflammation suppression, antioxidant activity and the maintenance of cytoprotective defenses and mucosal structure architecture.