Regional variations in total and nonprotein sulfhydryl compounds in the human gastric mucosa and effects of ethanol

Oral peptide delivery: Are there remarkable effects on drugs through sulfhydryl conjugation?

In oral peptide delivery, the gap between convenient administration and low blood concentration has to be minimized. We found that oral peptide drugs have not only to pass the various commonly known barriers encountered with the gastrointestinal tract but that these drugs, under certain conditions, have also to be seen as redox partners for thiol bearing substrates. The interaction of glutathione (GSH) with peptides via thiol-disulfide exchange reactions was investigated for three peptides, vasotocin, oxytocin and octreotide. The extent of thiol-disulfide exchange reactions was investigated by liquid chromatography (LC) and further confirmed by hyphenation to electrospray ionization (ESI) and MALDI-TOF mass spectrometry (MS). We found that the presence of aromatic amino acid residues in the neighbourhood of the disulfide bond minimizes the thiol-disulfide interaction: oxytocin was degraded more than 80% with 1% reduced glutathione at pH 3.0 and vasotocin more than 40% under the same conditions. In the case of octreotide no interaction with GSH was observed. The obtained results revealed that thiol-disulfide exchange reactions have an important impact on the alteration of peptide drugs and proteins in the gastrointestinal tract.

Erythrocyte glutathione depletion impairs resistance to haemolysis in women consuming alcohol

Alcohol abuse is known to cause an array of ethanol induced abnormalities in men but very few reports are available on the effect of alcohol in women. None of them discuss the effect of ethanol consumption on erythrocyte membrane. In the present study, erythrocytes in women who consume alcohol showed significant decrease in their ability to resist haemolysis with HPLC studies. Erythrocyte membrane indicates decreased phospholipid (p<0.05) levels, which increased the cholesterol/phospholipid ratio significantly (p<0.01) in women who consume alcohol. This can decrease the fluidity of membrane, which appears to be related to the effect of ethanol on erythrocyte membrane. Also the protection against exogenous and endogenous peroxides in the erythrocytes of alcoholic women is considerably affected due to decreased (p<0.05) activity of catalase, glucose-6-phosphate dehydrogenase, protein-SH group and glutathione (GSH). Enhanced free radical generation induced oxidation of oxyHb to metHb in alcoholics. Increased methemoglobin leads to significant reduction in membrane GSH, which may cause protein thiol oxidation. Thus peroxidative damage to membrane lipids and oxidation of membrane protein thiols potentially harmful to membrane fluidity and flexibility is responsible for decreased resistance to haemolysis as demonstrated in women who consume alcohol.

Topographical variation in metabolic signatures of human gastrointestinal biopsies revealed by high-resolution magic-angle spinning 1H NMR spectroscopy

Individual and topographical variation in the metabolic profiles of multiple human gastrointestinal tract (GIT) biopsies have been characterized using high-resolution magic-angle spinning (HRMAS) 1H NMR spectroscopy and pattern recognition. Samples from antrum, duodenum, jejunum, ileum, and transverse colon were obtained from 8 male and 8 female participants. Each gut region generated a highly characteristic metabolic profile consistent with the varying structural and functional properties of the tissue at different longitudinal levels of the gut. The antral (stomach) mucosa contained higher levels of choline, glycogen, phosphorylethanolamine, and taurine than other gut regions. The spatially close regions of the duodenum and jejunum were equivalent in terms of their gross biochemical composition with high levels of choline, glutathione, glycerophosphocholine (GPC), and lipids relative to other gut regions. The ileal mucosa showed poor discrimination from the duodenum and jejunum tissues and generated strong amino acids signatures but had relative low GPC signals. The colon (large intestine) was high in acetate, glutamate, inositols, and lactate and low in creatine, GPC, and taurine compared to the small intestine. These longitudinal metabolic variations in the human GIT could be attributed to functional variations in energy metabolism, osmoregulation, gut microbial activity, and oxidative protection. This work indicates that 1H HRMAS NMR studies may be of value in analyzing local metabolic variation due to pathological processes in gut biopsies.

Aqueous suspension of anise “Pimpinella anisum” protects rats against chemically induced gastric ulcers

AIM: To substantiate the claims of Unani and Arabian traditional medicine practitioners on the gastroprotective potential effect of a popular spice anise, “Pimpinella anisum L.” on experimentally-induced gastric ulceration and secretion in rats.

METHODS: Acute gastric ulceration in rats was produced by various noxious chemicals including 80% ethanol, 0.2 mol/L NaOH, 25% NaCl and indomethacin. Anti-secretory studies were undertaken using pylorus-ligated Shay rat technique. Levels of gastric non-protein sulfhydryls (NP-SH) and wall mucus were estimated and gastric tissue was also examined histologically. Anise aqueous suspension was used in two doses (250 and 500 mg/kg body weight) in all experiments.

RESULTS: Anise significantly inhibited gastric mu-cosal damage induced by necrotizing agents and indomethacin. The anti-ulcer effect was further confirmed histologically. In pylorus-ligated Shay rats, anise suspension significantly reduced the basal gastric acid secretion, acidity and completely inhibited the rumenal ulceration. On the other hand, the suspension significantly replenished ethanol-induced depleted levels of gastric mucosal NP-SH and gastric wall mucus concentration.

CONCLUSION: Anise aqueous suspension possesses significant cytoprotective and anti-ulcer activities against experimentally-induced gastric lesions. The anti-ulcer effect of anise is possibly prostaglandin-mediated and/or through its anti-secretory and antioxidative properties.

Characterisation of the thiol–disulphide chemistry of desmopressin by LC, μ-LC, LC-ESI-MS and Maldi-Tof

To date, the majority of therapeutic peptides and proteins have to be administered via parenteral routes, which are painful and inconvenient. In order to gain sufficient high blood concentrations after oral application, various barriers in the gastrointestinal tract have to be overcome. Apart from a poor membrane uptake and intense enzymatic degradation, this study will demonstrate that thiol-disulphide reactions are an underestimated essential part of the presystemic metabolism. Glutathione, integrative part of the antioxidant defence system in the gastrointestinal tract, may play an important role in the inactivation of orally given peptides and proteins. In order to verify this hypothesis, desmopressin which bears a single disulphide bond was used as model peptide drug. Desmopressin was incubated with GSH in various concentrations, and the extent of thiol/disulphide exchange reactions between the peptide drug and GSH was investigated in dependence on pH and ratio of reactants determined as a function of time via HPLC, LC-MS and Maldi-Tof-MS analyses. Results showed that desmopressin is degraded by 1% reduced glutathione at pH 4 and pH 5.5. In presence of 0.01%, 0.1% and 1% of reduced glutathione 6.1%, 19.4% and 52.1% of desmopressin, respectively, were degraded. The masses of the conjugates after deconvolution measured by liquid chromatography and electrospray ionisation mass spectrometric detection were m/z 1069.67, m/z 1376.50, m/z 1683.40 and m/z 2138. These molecular masses, confirmed by Maldi-Tof-MS analysis, correspond with the masses of conjugates expected in theory. Under defined conditions, these results reveal that thiol-disulphide exchange reactions have a considerable impact on the alteration of peptide drugs and proteins.

Mechanisms of gastroprotection by lansoprazole pretreatment against experimentally induced injury in rats: role of mucosal oxidative damage and sulfhydryl compounds

This study investigated the mechanisms involved in the protective actions exerted by lansoprazole against experimental gastric injury. Following the intraluminal injection of ethanol-HCl, the histomorphometric analysis of rat gastric sections demonstrated a pattern of mucosal lesions associated with a significant increase in the mucosal contents of malondialdehyde and 8-iso-prostaglandin F(2alpha) (indices of lipid peroxidation), as well as a decrease in the levels of mucosal sulfhydryl compounds, assayed as reduced glutathione (GSH). Pretreatment with lansoprazole 90 micromol/kg, given intraduodenally as single dose or once daily by intragastric route for 8 days, significantly prevented ethanol-HCl-induced gastric damage. The concomitant changes in the mucosal levels of malondialdehyde, 8-iso-prostaglandin F(2alpha) and GSH elicited by ethanol-HCl were also counteracted by lansoprazole. In separate experiments, performed on animals undergoing 2-h pylorus ligation, lansoprazole did not enhance the concentration of prostaglandin E(2), bicyclo-prostaglandin E(2), or nitric oxide (NO) metabolites into gastric juice. Western blot analysis revealed the expression of both type 1 and 2 cyclooxygenase (COX) isoforms in the gastric mucosa of pylorus-ligated rats. These expression patterns were not significantly modified by single-dose or repeated treatment with lansoprazole. Lansoprazole also exhibited direct antioxidant properties by reducing 8-iso-prostaglandin F(2alpha) generation in an in vitro system where human native low-density lipoproteins were subjected to oxidation upon exposure to CuSO(4). The present results suggest that the protective effects of lansoprazole can be ascribed to a reduction of gastric oxidative injury, resulting in an increased bioavailability of mucosal sulfhydryl compounds. It is also proposed that lansoprazole does not exert modulator effects on the gastric expression of COX isoforms as well as on the activity of NO pathways.

The ingestion of inorganic nitrate increases gastric S-nitrosothiol levels and inhibits platelet function in humans

Platelets play an important role in the development of vascular disease, while vegetarian diets, which are rich in inorganic nitrate, protect against it. This study was performed to assess the effect of potassium nitrate (KNO(3)) ingestion on platelet function in humans. Oral KNO(3) (2 mmol) was given to healthy volunteers and its effect on platelet function assessed by measuring the aggregant effect of collagen. Blood samples were taken for measurement of plasma S-nitrosothiols (RSNO) and platelet cyclic GMP and nitrotyrosine levels. Gastric juice samples were taken for measurement of RSNO. In a separate study, the effect of oral KNO(3) on portal RSNO levels in patients with intrahepatic porto-systemic shunts was assessed. KNO(3) caused a significant increase in gastric RSNO levels, from 0.46 +/- 0.06 to 3.62 +/- 2.82 microM (t(max) 45 min; P < 0.001), and significantly inhibited platelet function (t(max) 60 min; P < 0.001). There was no effect on systemic or portal RSNO, platelet cGMP or platelet nitrotyrosine levels. Oral KNO(3) inhibits platelet aggregation. The time course suggests that gastric RSNO production may be involved in this effect. The protection against vascular events associated with a high intake of vegetables may be due to their high nitrate content.

Low levels of gastric mucosal glutathione during upper gastric bleeding associated with the use of nonsteroidal anti-inflammatory drugs

OBJECTIVES

To investigate the glutathione concentrations in gastric mucosa from patients with acute gastric bleeding related to nonsteroidal anti-inflammatory drugs (NSAIDs), and to test the influence of nutritional status on mucosal glutathione. Glutathione protects the gastrointestinal mucosa against reactive oxygen species, and glutathione content in various tissues may be depleted during malnutrition.

METHODS

Endoscopic biopsies were obtained from 39 patients. Eighteen of these (9 well-nourished, 9 malnourished) presented with gastric bleeding ulcers related to NSAIDs. Twenty-one other patients (12 well-nourished, 9 malnourished) underwent normal routine diagnostic endoscopy and served as controls. Malnutrition was defined as a loss of over 10% of normal body weight and/or plasma albumin levels below 30 g/l. Gastric biopsies were taken from the fundus and antrum (controls) and from the region of the ulcer (patients with acute bleeding) and frozen quickly until glutathione analysis by high-performance liquid chromatography (HPLC) coulometric detection. Results were expressed as nmol/mg wet tissue.

RESULTS

Gastric mucosal glutathione levels were significantly (P < 0.05) lower in both the antrum (0.81 +/- 0.34 v. 1.41 +/- 0.88 nmol/mg tissue) and the fundus (1.04 +/- 0.54 v. 1.43 +/- 0.92 nmol/mg tissue, P < 0.05) in malnourished than in well-nourished control patients. Glutathione mucosal concentrations were decreased significantly in patients with NSAID-induced gastric bleeding compared with control patients (0.38 +/- 0.36 v. 1.12 +/- 0.56 nmol/mg tissue, P < 0.001), and the lowest glutathione levels were observed in malnourished patients (0.28 +/- 0.20 v. 0.48 +/- 0.15 nmol/mg tissue in well-nourished patients, not significant).

CONCLUSION

Malnutrition is associated with low levels of gastric glutathione. This may contribute to the severity and the onset of haemorrhage in NSAID-induced gastric ulcers.

Evidence for protective and antioxidant properties of rutin, a natural flavone, against ethanol induced gastric lesions

This study was designed to determine the ulcer-protecting effects of rutin, a natural flavone, against gastric lesions induced by 50% ethanol, the experimental model related to lesion pathogenesis with production of reactive species. The possible involvement of sulphydryl compounds (SH), neutrophil infiltration, and the capacity of this flavone to restrain the oxidative process produced in the gastric tissue were also investigated. The levels of thiobarbituric acid (TBA, as index of lipid peroxidation), the myeloperoxidase activity (MPO, as a marker of neutrophil infiltration), the content of mucosal sulphydryls (SH) groups and the activity of glutathione peroxidase (GSH-Px, an important antioxidant enzyme) were determined. Pretreatment with the highest dose of rutin (200 mg/kg), 120 min before 50% ethanol, resulted in the most effective necrosis prevention. TBA reactive substances in the gastric mucosa, were increased by ethanol injury, and this increase was inhibited by the administration of 200 mg/kg of rutin. However, the flavonoid was not able to modify the ethanol-induced neutrophil infiltrate expressed as myeloperoxidase activity. Exposure of the gastric mucosa to 50% ethanol induced a significant diminution in gastric non-protein SH content; this parameter also was not modified by the treatment with rutin. GSH-Px activity decreased in the gastric mucosa after ethanol-treatment. In contrast, rutin at all tested doses induced a significant increase in this enzymatic activity, higher than in control group. These results suggest that the gastroprotective effect of rutin in this experimental model appears through an anti-lipoperoxidant effect, and also by enhancement of the anti-oxidant enzymatic (GSH-Px) activity.

Transport of ascorbic acid in gastric epithelial cells in vitro

The normal human stomach contains high concentrations of ascorbic acid in both the mucosa and gastric juice, but the mechanism of ascorbic acid transport in the stomach is unknown. To understand more, ascorbic acid accumulation in gastric epithelial cell lines was investigated. Ascorbic acid was transported into gastric epithelial cells (Kato III and AGS cell lines) and accumulated up to eight-fold against a concentration gradient, as measured by high-performance liquid chromatography with electrochemical detection. Kinetic analysis using both non-radioactive and radioactive sources of ascorbic acid showed that ascorbic acid accumulation was mediated by one saturable concentration-dependent transport system with a Km of 3-11 micromol/l and Vmax of 0.8-0.9 nmol/10(8) cells/min. These data suggest that ascorbic acid uptake in gastric mucosal cells may be facilitated by a high-affinity saturable transport activity. Loss of intracellular ascorbic acid from Kato III and AGS cells was slower than seen in vivo which may limit the usefulness of these cell lines as a physiological model for the secretion of mucosal ascorbic acid into gastric juice.

Ethanol-induced gastrointestinal damage. Influence of endogenous antioxidant components and gender

This study compared the effects of undiluted and 8% ethanol administered orally on gastrointestinal antioxidant components of male and female rats. Eight percent ethanol increased the activities of duodenal glutathione peroxide (29% in males, 14% in females) and superoxide dismutase in female gastric (24%) and male duodenal (15%) mucosa. This dose of ethanol also increased the glutathione content of gastric mucosa (12% in males, 13% in females). Undiluted ethanol decreased glutathione levels in gastric mucosa (22% in males, 11% in females) and increased glutathione peroxide activity in gastric mucosa (14% in males, 9% in females). Undiluted alcohol also produced decreases in the activity of glutathione reductase in stomach (14% in males, 9% in females) and duodenum (16% in males, 12% in females). Undiluted ethanol caused mucosal damage in the body of the stomach in both genders, accompanied by an increase in luminal pH and fluid accumulation in the stomach; these changes were absent in rats given 8% ethanol. The increase in gastrointestinal antioxidant capacity associated with the administration of 8% ethanol may be a factor in the reported cytoprotective effect of lower doses of ethanol.

The role of gastric mucosal sulphydryls in the ulcer-protecting effects of cisapride

The present study was designed to examine the role of endogenous sulphydryls (SHs) in the gastro-protection induced by cisapride (CIS) (10, 25 and 50 mg kg-1 i.p.), a potent benzamide stimulating gastrointestinal motility in mucosal injury induced by 50% v/v ethanol. Results were compared with those of 5-hydroxytryptamine (5-HT) (10mg kg-1). Ethanol mucosal damage was significantly reduced by treatment with CIS and 5-HT. On the contrary, administration of n-ethylmaleimide (NEM) (10 mg kg-1) an SH alkylator, markedly worsened lesion formation and counteracted the protective effect of CIS. Rats pretreated with CIS significantly increased the total sulphydryls as reflected in the non-protein and protein fractions however, 5-HT treatment showed a fall in the non-protein level. The present results suggest that 5-HT-ergic dependent mechanisms have no relation to the gastro-protection afforded by CIS in this experimental model. It is possible that mucosal SHs could be involved.

Glutathione prevents ethanol induced gastric mucosal damage and depletion of sulfhydryl compounds in humans

Whether parenteral administration of reduced glutathione prevented ethanol induced damage to and depletion of sulfhydryl compounds in the human gastric mucosa was investigated. Ten healthy volunteers underwent endoscopy on three separate occasions. Gastric mucosal damage was induced by spraying 80% ethanol on to the gastric mucosa through the biopsy channel of the endoscope. The gastric mucosal score, total sulfhydryls, glutathione, and cysteine were evaluated in basal conditions and after ethanol administration with and without pretreatment with parenteral glutathione. Glutathione significantly decreased the extent of ethanol induced macroscopic injury to the mucosa of the gastric body and antrum. Glutathione's protective effect is associated with appreciable inhibition of ethanol induced depletion of gastric sulfhydryl compounds. This is the first report of protection against ethanol induced gastric mucosal damage by a sulfhydryl containing agent in humans.