Role of cysteine proteases and protease inhibitors in gastric mucosal damage induced by ethanol or ammonia in the rat

A(a)LS: Ammonia-induced amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a dreadful, devastating and incurable motor neuron disease. Aetiologically, it is a multigenic, multifactorial and multiorgan disease. Despite intense research, ALS pathology remains unexplained. Following extensive literature review, this paper posits a new integrative explanation. This framework proposes that ammonia neurotoxicity is a main player in ALS pathogenesis. According to this explanation, a combination of impaired ammonia removal- mainly because of impaired hepatic urea cycle dysfunction-and increased ammoniagenesis- mainly because of impaired glycolytic metabolism in fast twitch skeletal muscle-causes chronic hyperammonia in ALS. In the absence of neuroprotective calcium binding proteins (calbindin, calreticulin and parvalbumin), elevated ammonia-a neurotoxin-damages motor neurons. Ammonia-induced motor neuron damage occurs through multiple mechanisms such as macroautophagy-endolysosomal impairment, endoplasmic reticulum (ER) stress, CDK5 activation, oxidative/nitrosative stress, neuronal hyperexcitability and neuroinflammation. Furthermore, the regional pattern of calcium binding proteins' loss, owing to either ER stress and/or impaired oxidative metabolism, determines clinical variability of ALS. Most importantly, this new framework can be generalised to explain other neurodegenerative disorders such as Huntington's disease and Parkinsonism.

The gastric ulcer protective and healing role of cysteine proteinases from Carica candamarcensis

Latex from Caricaceae contains proteolytic enzymes localized in the fruit, which are used ethnopharmacologically to treat digestive disorders. Some of these proteins display proliferative properties when probed with mammalian cells, suggesting a role in the reconstruction of wounded tissue. We tested the efficacy of a proteolytic fraction derived from Carica candamarcensis, designated as P1G10 in experimental rodent models, to protect and heal chemically induced gastric ulcers. The protective effect of oral administration of P1G10 fraction was analyzed in indomethacin-treated Wistar animals. The healing effect of P1G10 was studied following sub-serous injection of acetic acid in a Wistar rat model. The results show that P1G10 between 0.1 and 10 mg/kg protect indomethacin but not ethanol-induced gastric ulcers. The maximal protection attained was 67% with 10 mg/kg of P1G10. The healing rate by 10 mg/kg of P1G10 using the acetic acid ulcerogenic model is similar to that of omeprazole (10 mg/kg) or ranitidine (100 mg/kg). The effect of P1G10 at 10 mg/kg seems to be mediated by an increase in the mucus content by 25% and stimulation of angiogenesis by 64% in a manner similar to growth factors. These results confirm the protective and healing role of proteinases from C. candamarcensis.

Protein and non-protein sulfhydryls and disulfides in gastric mucosa and liver after gastrotoxic chemicals and sucralfate: Possible new targets of pharmacologic agents

AIM: To investigate the role of major non-protein and protein sulfhydryls and disulfides in chemically induced gastric hemorrhagic mucosal lesions (HML) and the mechanism of gastroprotective effect of sucralfate.

METHODS: Rats were given 1 mL of 75% ethanol, 25% NaCl, 0.6 mol/L HCl, 0.2 mol/L NaOH or 1% ammonia solutions intragastrically (i.g.) and sacrificed 1, 3, 6 or 12 min later. Total (reduced and oxidized) glutathione (GSH + GSSG), glutathione disulfide (GSSG), protein free sulfhydryls (PSH), protein-glutathione mixed disulfides (PSSG) and protein cystine disulfides (PSSP) were measured in gastric mucosa and liver.

RESULTS: Reduced glutathione (GSH) was depleted in the gastric mucosa after ethanol, HCl or NaCl exposure, while oxidized glutathione (GSSG) concentrations increased, except by HCl and NaOH exposure. Decreased levels of PSH after exposure to ethanol were observed, NaCl or NaOH while the total protein disulfides were increased. Ratios of reduced to oxidized glutathione or sulfhydrils to disulfides were decreased by all chemicals. No changes in thiol homeostasis were detected in the liver after i.g. abbreviation should be spelled out the first time here administration of ethanol. Sucralfate increased the concentrations of GSH and PSH and prevented the ethanol-induced changes in gastric mucosal thiol concentrations.

CONCLUSION: Our modified methods are now suitable for direct measurements of major protein and non-protein thiols/disulfides in the gastric mucosa or liver. A common element in the pathogenesis of chemically induced HML and in the mechanism of gastroprotective drugs seems to be the decreased ratios of reduced and oxidized glutathione as well as protein sulfhydryls and disulfides.

Metabolism of alcohol

Most tissues of the body contain enzymes capable of ethanol oxidation or nonoxidative metabolism, but significant activity occurs only in the liver and, to a lesser extent, in the stomach. Hence, medical consequences are predominant in these organs. In the liver, ethanol oxidation generates an excess of reducing equivalents, primarily as NADH, causing hepatotoxicity. An additional system, containing cytochromes P-450 inducible by chronic alcohol feeding, was demonstrated in liver microsomes and found to be a major cause of hepatotoxicity.

Regulation of cathepsin B and L expression in vitro in gastric cancer tissues by egg cystatin

BACKGROUND

Degradation of the basement membrane and surrounding extracellular matrix is likely to represent a key step in cancer invasion and metastasis. The purpose of this study was to determine whether gastric cancer tissues demonstrate higher cysteine proteases activities: cathepsins B and L during cancer progression in compression with non-cancerous tissues.

METHODS

We measured the expression of both cathepsins B and L in 30 patients with gastric cancer tissues and non-cancerous tissues activities by a fluorescence assay and immunohistochemical staining. We attempted to regulate cathepsin B and L expression using egg white cystatin.

RESULTS

The activities of cathepsins B and L were significantly higher in cancerous than in non-cancerous tissues (P </= 0.0001). Activities of these enzymes decreased 18-fold after treatment of tissue homogenates with 5 nM of purified egg white cystatin. Immunohistochemical staining was significant and positive expression of low molecular weight cystatin was observed on the tumor cell surface in gastric carcinoma. It was found that non-cancerous tissues (control) were not stained with anti-egg white antibody.

CONCLUSION

Our experiment demonstrated that the cysteine peptidases cathepsins B and L may be useful for the early detection of gastric cancer. The results suggest that addition of egg white cystatin reduces the activities of cathepsins B and L to that of non-cancerous values.

Gastrointestinal safety of nitric oxide-derived aspirin is related to inhibition of ICE-like cysteine proteases in rats

BACKGROUND & AIMS

Caspases, a class of cysteine proteases, modulate apoptosis. Nitric oxide (NO)-releasing nonsteroidal anti-inflammatory drugs (NSAIDs) are a new class of NSAID derivatives with reduced gastrointestinal toxicity. The aim of this study was to investigate whether cysteine endoproteases are involved in the pathogenesis of NSAID gastropathy and are target for NO-aspirin (NCX-4016).

METHODS

Rats were treated orally with aspirin or equimolar doses of NCX-4016. Caspase activities were measured by fluorometric assay. Apoptosis was quantified by an enzyme-linked immunosorbent assay for histone-associated DNA, DNA ladder on agarose gel, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay. A primary culture of gastric chief cells was used to investigate whether NCX-4016 modulates guanosine 3',5'-cyclic monophosphate (cGMP)-dependent pathways.

RESULTS

Short- and long-term (7 days) aspirin administration resulted in a time- and dose-dependent gastric injury that was associated with apoptosis and caspase up-regulation. Z-VAD.FMK, a pancaspase inhibitor, and NO donors protected from acute damage induced by aspirin. NCX-4016 spared the gastric mucosa and caused caspase inactivation by S-nitrosylation. Inhibition of tumor necrosis factor (TNF)-alpha release or activity by TAPI-2 or anti-TNF-alpha receptor monoclonal antibodies protected against mucosal damage and caspase activation. NCX-4016 protected gastric chief cells from toxicity induced by TNF-alpha by activating cGMP-dependent pathways.

CONCLUSIONS

Aspirin administration leads to a TNF-alpha-dependent activation of gastric caspases. NO-aspirin spares the gastric mucosa and inhibits caspase activity through cGMP-dependent and -independent pathways.

Nitric oxide-releasing NSAIDs inhibit interleukin-1beta converting enzyme-like cysteine proteases and protect endothelial cells from apoptosis induced by TNFalpha

BACKGROUND

Nitric oxide (NO)-releasing NSAIDs are a new class of NSAID derivatives with markedly reduced gastrointestinal toxicity. Although it has been demonstrated that NO-NSAIDs spare gastric mucosal blood flow, molecular determinants involved in this effect are unknown.

AIM

To investigate the effect of aspirin, naproxen and flurbiprofen, and their NO-derivatives, on gastric apoptosis and endothelial cell damage induced by tumour necrosis factor-alpha (TNFalpha). In other systems, TNFalpha-induced apoptosis is mediated by caspases, a growing family of cysteine proteases similar to the IL-1beta converting enzyme (ICE), and so we have investigated whether NO-NSAIDs modulate ICE-like endopeptidases.

METHODS

Rats were treated orally with aspirin, naproxen and flurbiprofen, or their NO-releasing derivatives in equimolar doses, and were killed 3 h later to assess mucosal damage and caspase activity. Endothelial cells (HUVECs) were obtained from human umbilical cord by enzymatic digestion. Caspase 1 and 3 activities were measured by a fluorimetric assay using selective peptides as substrates and inhibitors. Apoptosis was quantified by ELISA specific for histone-associated DNA fragments and by the terminal transferase nick-end translation method (TUNEL).

RESULTS

In vivo NSAID administration caused a time-dependent increase in gastric mucosal damage and caspase activity. NCX-4016, NO-naproxen and NO-flurbiprofen did not cause any mucosal damage and prevented cysteine protease activation. NSAIDs and NO-NSAIDs stimulated TNFalpha release. Exposure to TNFalpha resulted in a time- and concentration-dependent HUVEC apoptosis, an effect that was prevented by pretreating the cells with NCX-4016, NO-naproxen, NO-flurbiprofen, SNP or Z-VAD.FMK, a pan-caspase inhibitor. The activation of ICE-like cysteine proteases was required to mediate TNFalpha-induced apoptosis of HUVECs. Exogenous NO donors inhibited TNFalpha-induced cysteine protease activation. Inhibition of caspase activity was due to S-nitrosylation of ICE/CPP32-like proteases. NO-NSAIDs prevented IL-1beta release from endotoxin-stimulated macrophages.

CONCLUSIONS

NO-releasing NSAIDs are a new class of non-peptide caspase inhibitors. Inhibition of ICE-like cysteine proteases prevents endothelial cell damage induced by pro-inflammatory agents and might contribute to the gastro-protective effects of NO-NSAIDs.

Gastritis in the alcoholic: relationship to gastric alcohol metabolism and Helicobacter pylori

Chronic gastritis is common in the alcoholic. It is characterized by histological inflammation of the gastric mucosa and is associated with variable symptomatology. Its etiology is still the subject of debate. Recently, a new alcohol dehydrogenase isoenzyme, called sigma ADH, absent from the liver but predominant in the upper GI tract, has been fully characterized, its gene cloned, and it appears to play a major role in gastric ethanol metabolism. Indeed, it has now been established, both in vivo in experimental animals and in vitro in cultured human gastric cells, that alcohol is metabolized in the gastric mucosa, resulting in the production of acetaldehyde, a toxic metabolite. In addition, Helicobacter pylori infection is common in the alcoholic, resulting in the breakdown of urea to ammonia, another toxic product. A number of studies carried out over the last 40 years revealed that antibiotic treatment eradicates ammonia production and results in histological and symptomatic improvement in the majority of patients with alcoholic gastritis. Non-invasive tests for the detection of H. pylori are now available which will facilitate the large scale studies needed to confirm whether, in H. pylori -positive patients, antibiotics should become routine treatment for alcoholic gastritis.

Hans Selye and the development of the stress concept. Special reference to gastroduodenal ulcerogenesis

Hans Selye has a historic role in the development of the stress concept. Before his short article in Nature in 1936, the neuroendocrine response to nonspecific injury was thought to be restricted to the release of catecholamines, as recognized by Cannon. Selye was the first to appreciate the crucial role of the adrenal cortex/hypophysis axis in the stress response. He also insisted on the nonspecificity of this neuroendocrine response, and he named the stress-causing agent "stressors". His last major contribution was the distinction between negative, that is, distress, and positive, that is, eustress reactions. The "triad of stress" (adrenal hypertrophy, gastrointestinal ulcers, thymolymphatic atrophy) was also first described by Selye, who was fascinated by the fact that in stressed rodents only gastric and not duodenal ulcers would develop. It was not until the recognition of duodenal ulcerogenic properties of propionitrile and cysteamine as well as the subsequent quantitative structure-activity studies predicting the duodenal ulcerogenic action of complex molecules that pathogenetic investigations allowed a molecular and mechanistic approach for studying the etiology and pathogenesis of duodenal ulceration. Recent studies on the role of sulfhydryls, TRH, ET, and growth factors provide new insights into central and peripheral pre-ulcer pathways. We were surprised to learn that an organ-specific ET-1 release may play a role both in ulcer induction and healing, which seems to start with the expression of immediate early genes such as egr-1 and stimulation of the local synthesis of growth factors such as bFGF and PDGF. Thus, a historic review originating with Hans Selye and extending through the next 60 years allows a cellular and molecular approach to the better understanding of stress-related disorders such as gastroduodenal ulceration.

Gastric ethanol metabolism and gastritis: interactions with other drugs, Helicobacter pylori, and antibiotic therapy (1957-1997)--a review

The stomach provides some protection against the penetration of ethanol into the body by contributing to the metabolism of ethanol. The latter is attenuated by various drugs and, although the magnitude of this effect is still the subject of debate, patients should be warned of the corresponding possible increase in blood alcohol levels. Furthermore, oxidation of ethanol generates acetaldehyde, a toxic metabolite. In addition, chronic alcohol abuse seems to favor colonization by Helicobacter pylori, which produces ammonia that also contributes to the commonly associated chronic gastritis. Because antibiotics were shown over the last 4 decades to effectively eliminate gastric ammonia, they should be considered for the routine treatment of such chronic gastritis in the way they are now being used for ulcer therapy.