Enhancement in gastric mucosal EGF and PDGF receptor expression with ulcer healing by sulglycotide

Effect of sulglycotide on the apoptotic processes associated with indomethacin-induced gastric mucosal injury

AIMS

In this study we investigated the effect of the antiulcer agent, sulglycotide, on the activity of a key pro-apoptotic protease, caspase-3, and the expression of inducible nitric oxide synthase (NOS-2) associated with gastric epithelial cell apoptosis triggered by the enhancement in tumour necrosis factor-alpha (TNF-alpha) during indomethacin-induced gastric mucosal injury.

METHODS

The experiments were conducted with rats pretreated intragastrically with sulglycotide (200 mg/kg) or vehicle, followed 30 min later by an intragastric dose of indomethacin (60 mg/kg). The animals were killed 2 h later and their mucosal tissue used for macroscopic assessment, assays of epithelial cell apoptosis and TNF-alpha, and the measurement of caspase-3 and NOS-2 activities.

RESULTS

In the absence of sulglycotide, indomethacin caused multiple haemorrhagic lesions accompanied by a 20-fold enhancement in gastric epithelial cell apoptosis and a 47% increase in mucosal expression of TNF-alpha, while NOS-2 showed an 11.9-fold induction and the activity of caspase-3 increased 3.9-fold. Pretreatment with sulglycotide produced a 51.2% reduction in the extent of mucosal damage caused by indomethacin, a 43.9% decrease in the epithelial cell apoptosis and a 39.7% reduction in TNF-alpha, while the activity of caspase-3 decreased by 58.8% and that of NOS-2 showed a 47.3% decline.

CONCLUSIONS

Our findings implicate the enhanced expression of caspase-3 and NOS-2 in the process of death signalling cascade associated with indomethacin-induced gastric mucosal injury, and show that sulglycotide is capable of suppressing the pathway of apoptotic events propagated by TNF-alpha, NOS-2 and caspase-3.

Role of growth factors and their receptors in gastric ulcer healing

The repair of gastric ulcers requires the reconstitution of epithelial structures and the underlying connective tissue, including vessels and muscle layers. Several growth factors have been implicated in this process, since they are able to regulate important cell functions, such as cell proliferation, migration, differentiation, secretion, and degradation of extracellular matrix, all of which are essential during tissue healing. Epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), hepatocyte growth factor (HGF), and trefoil factors (TFFs) are mainly involved in the reconstitution of the epithelial structures. Platelet derived growth factor (PDGF), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and transforming growth factor-beta (TGF-beta) play a major role in the reconstitution of connective tissue, including vessels and smooth muscle cells, and provide the extracellular matrix substrate for cell migration and differentiation. The expression of these growth factors and their receptors is increased during ulcer healing and, in some cases, intracellular signaling related to receptor binding and transduction has been demonstrated. EGF, TGF-alpha and TFFs are normally present either in the gastric juice or in the mucosa, and may exert their effects immediately after damage, before newly synthesized EGF and TFFs are released from the ulcer margin. The inhibition of their effects by neutralizing antibodies may result in delayed ulcer healing, while the administration of recombinant or natural analogues may improve ulcer repair. In this review, we will summarize the basic molecular characteristics of some of these growth factors, and will discuss available evidence supporting their role in the ulcer repair process.

Suppression of gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide by sulglycotide

The effect of the antiulcer agent sulglycotide on gastric epithelial cell apoptosis and the expression of tumor necrosis factor-alpha (TNF-alpha) and interleukin-4 (IL-4) during Helicobacter pylori lipopolysaccharide-induced acute gastritis was investigated. Rats, pretreated twice daily for 3 consecutive days with sulglycotide at 200 mg/kg or vehicle, were subjected to surface epithelial application of H. pylori lipopolysaccharide (50 microg/animal), and, after 4 additional days on the drug or vehicle regimen, their mucosal tissue was used for histologic assessment, quantitation of TNF-alpha and IL-4, and the assay of epithelial cell apoptosis. In the absence of sulglycotide, H. pylori lipopolysaccharide caused acute mucosal responses manifested by the inflammatory infiltration of the lamina propria with lymphocytes and plasma cells, edema, hyperemia, and epithelial hemorrhage. These responses were accompanied by an 11-fold increase in epithelial cell apoptosis and a 9-fold enhancement of the mucosal expression of proinflammatory cytokine TNF-alpha. However, the mucosal expression of regulatory cytokine IL-4 decreased by 15%. Treatment with sulglycotide produced significant (56.6%) reduction in the extent of acute mucosal inflammatory changes caused by H. pylori lipopolysaccharide. Moreover, the effect of sulglycotide was manifested in an 88.3% reduction in the epithelial cell apoptosis and a 69.1% decrease in the mucosal expression of TNF-alpha, whereas the expression of IL-4 showed only marginal (6%) enhancement. The results suggest that the cytoprotective agent sulglycotide suppresses the inflammatory and apoptotic events elicited in gastric mucosa by H. pylori lipopolysaccharide through stimulation of TNF-alpha expression.

Gastric mucosal cell cycle regulation with ulcer healing by sulglycotide

BACKGROUND

The progression of the events associated with gastric mucosal repair is controlled in an orderly manner by a plethora of the extracellular cues exerting their effect on the cell cycle regulatory proteins, cyclins, and cyclin-dependent kinases, the expression of which varies through the cycle stages. The purpose of this study was to evaluate the expression of cyclin-dependent kinase (Cdk2) and proliferating cell nuclear antigen (PCNA) during chronic ulcer healing with sulglycotide.

METHODS

Rats with experimentally induced gastric ulcers were treated twice daily for 14 days either with sulglycotide at 200 mg/kg or vehicle, and at different stages of the treatment their stomachs were used for macroscopic damage assessment and quantitation of gastric mucosal Cdk2 and PCNA expression.

RESULTS

The assays showed that the ulcer healing was accompanied by an increase in mucosal expression of Cdk2 and PCNA. The maximum increase in Cdk2 (2.3-fold) occurred by the 4th day of healing. An accelerated ulcer healing (10 days) with sulglycotide treatment was reflected in a marked enhancement in Cdk2 expression attained a maximum 2.1-fold increase by the 6th day of treatment and remained substantially increased for up to 10 days.

CONCLUSIONS

The findings show a complex interplay between the extracellular cues and cell cycle regulatory proteins, an orderly progression that drives the mucosal repair process. We also show that the gastroprotective agent sulglycotide is capable of affecting the expression of the cell cycle regulatory proteins that control cell cycle progression through G1 and into S phase.

Cell cycle progression during gastric ulcer healing by ebrotidine and sucralfate

1. The effect of antiulcer agents, ebrotidine and sucralfate, on the expression of gastric mucosal proliferating cell nuclear antigen (PCNA) and cyclin-dependent kinase (p34Cdk2) during chronic ulcer healing was examined. 2. Rats with experimentally induced gastric ulcers were treated twice daily for 14 days with either ebrotidine at 100 mg/kg, sucralfate at 100 mg/kg or vehicle, and at different stages of treatment their stomachs were used for quantitization of gastric mucosal PCNA and Cdk2 expression. 3. The assays revealed that the ulcer healing was accompanied by a marked elevation in mucosal expression of PCNA and Cdk2. The maximum increase in PCNA (4.7-fold) occurred by the second day of healing, and the expression of Cdk2 reached a maximum increase (2.3-fold) by the fourth day. 4. Accelerated ulcer healing with ebrotidine (7 days) and sucralfate (8 days) treatments was reflected in a significant enhancement of PCNA and Cdk2 expression. By the second day of treatment, ebrotidine evoked a 15-fold increase in PCNA expression, and sucralfate produced an 11.8-fold enhancement. The mucosal expression of Cdk2 attained a maximum of 4.3-fold increase over that of the controls by the sixth day of healing with ebrotidine, and a fivefold increase in Cdk2 expression occurred by the fourth day of ulcer treatment with sucralfate. 5. The findings implicate cell cycle regulatory proteins in the processes to leading to mucosal repair and suggest that the two drugs exert a similar effect on the expression of proteins that control cell cycle progression.