Jimmy J. Romero

Interaction of Indomethacin and Naproxen with Gastric Surface-active Phospholipids: A Possible Mechanism for the Gastric Toxicity of Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

The possibility that the molecular mechanism underlying the topical gastric irritancy of nonsteroidal anti-inflammatory drugs (NSAIDs) may involve alterations in the surface-active properties of gastric phospholipids was investigated. Indomethacin and naproxen were intragastrically administered to rats and the hydrophobicity of the luminal surface of the stomach wall was assessed by contact angle analysis. Both NSAIDs have the ability to attenuate the phospholipid-related hydrophobic properties of the gastric mucosa by more than 80-85% in a dose-dependent fashion. Potential molecular interactions between both NSAIDs and surface-active phospholipids were analyzed using fluorescent probes. Indomethacin has the ability to displace, in a dose-dependent manner, ANS (1-anilino-8-naphthalene sulphonate), a fluorescent anionic probe previously bound to the head group of phosphatidylcholine molecules. Estimations of the resonance fluorescence transfer between naproxen and the surface probe ANS or the hydrophobic probe, pyrene, bound to dipalmitoylphosphatidylcholine (DPPC) vesicles revealed that naproxen diffuses within the phospholipid bilayers. The dynamic of the gastric lipid material extracted from the surface scraping material (SSM) of the mucosa was altered by the NSAID as shown by the increase in the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) (at 25 degrees, rSSM = 0.106+/-0.006, rssM + indomethacin = 0.137+/-0.005, and rSSM + naproxen = 0.133+/-0.007, P < 0.001). The thermodynamic behavior of a model bilayer containing DPPC was also perturbed by the NSAIDs tested. These results provide evidence that NSAIDs may reduce the ability of gastric surface-active phospholipids to form a hydrophobic protective layer.

Antibiotic properties of bovine lactoferrin on Helicobacter pylori.

To investigate a potential new treatment forgastric Helicobacter pylori infection, we have examinedthe use of the natural antibiotic lactoferrin, found inbovine milk, for activity against Helicobacter species both in vitro and in vivo. Lactoferrinwas bacteriostatic to H. pylori when cultured atconcentrations ≥0.5 mg/ml. Growth of H. pylori wasnot inhibited by another milk constituent, lysozyme, or by a metabolite of lactoferrin, lactoferricinB, but growth was inhibited by the iron chelatordeferoxamine mesylate. Lactoferrin inhibition of growthcould be reversed by addition of excess iron to the medium. Lactoferrin in retail dairy milk wasfound to be more stable intragastrically thanunbuffered, purified lactoferrin. Treatment of H.felis-infected mice with lactoferrin partially reversedmucosal disease manifestations. It is concluded thatbovine lactoferrin has significant antimicrobialactivity against Helicobacter species in vitro and invivo. Bovine lactoferrin should be further investigated for possible use in H. pylori infections inman.

Effect of bisphosphonates on surface hydrophobicity and phosphatidylcholine concentration of rodent gastric mucosa.

Bisphosphonates are a family of chemically related zwitterionic molecules that are used clinically to retard bone resorption in individuals with osteoporosis and associated skeletal diseases. Inflammation and ulceration of the upper gastrointestinal tract by a mechanism that relates to a topical irritant action is associated with the consumption of some bisphosphonates. In the present study, we investigated the effects of three bisphosphonate molecules, pamidronate, alendronate, and risedronate on the surface hydrophobicity and phosphatidylcholine (PC) concentration of the antral mucosa. We also examined how these surface changes related to mucosal injury in an established rat model, in which the test compounds were administered in combination with indomethacin. We initially determined that a combination of pamidronate (300 mg/kg) and indomethacin (40 mg/kg) induced a significant reduction in mucosal surface hydrophobicity and macroscopic lesion formation by 15 min and mucosal PC concentration by 30 min, with the magnitude of these changes increasing over the 4-hr study period. An equivalent dose of alendronate or risedronate in combination with indomethacin produced modest or no macroscopic injury, respectively, to the antral mucosa over the 4-hr study, although the bisphosphonates clearly induced surface injury and some glandular necrosis when examined at the light microscopic level. These bisphosphonates also induced modest decreases in antral surface hydrophobicity and mucosal PC concentration that appeared to be related to their injurious potential. In conclusion, the variable toxicity of bisphosphonates to the antral mucosa appears to be associated with their ability to compromise the surface hydrophobic phospholipid barrier of the tissue, with pamidronate >>> alendronate > risedronate. This bisphosphonate effect on the surface barrier may trigger the development of mucosal injury and possible ulceration.

Role of luminal ammonia in the development of gastropathy and hypergastrinemia in the rat

BACKGROUND/AIMS Chronic infection with Helicobacter pylori causes persistent elevations in gastric juice ammonia levels. Thus, we studied the effects of experimentally induced increases in gastric juice ammonia levels on gastric structure and function and gastrin homeostasis. METHODS Rats were fed either normal chow or the diet supplemented (20 g/dL) with ammonium or sodium acetate. RESULTS Long-term dietary ammonium loading for 2 weeks or longer resulted in a 1.5-2-fold increase in the weight and mucosal thickness of the stomach and proximal duodenum with evidence of mild gastritis and enterochromaffinlike cell hyperplasia. The ammonium-containing diet also induced a significant 2-3-fold increase in both circulating gastrin levels of fed rats and an increase in the postprandial gastrin responses over control values. Antral gastrin levels were also markedly elevated by long-term ingestion of the test diet, which was increased 3-4-fold over control values in fasted animals and less so after meal stimulation. Consistent with these findings, gastrin-specific messenger RNA was increased 2.5-3-fold in the antrum of ammonium fed rats, whereas actin-specific messenger RNA was not affected or decreased. Animals fed a diet supplemented with 20 g/dL sodium acetate sustained modest increases in mucosal thickness and serum and antral gastrin concentration, suggesting that nonspecific gastric injury and inflammation is also a factor that influences G-cell function. CONCLUSIONS Long-term exposure of the antral mucosa to elevated levels of ammonia in the gastric juice in the presence of gastritis, conditions similar to that occurring in subjects infected with H. pylori, seem to be causative factors in the development of G-cell hyperfunction.

Surface phospholipids in gastric injury and protection when a selective cyclooxygenase‐2 inhibitor (Coxib) is used in combination with aspirin

Clinical studies demonstrate that aspirin consumption reverses the gastrointestinal (GI) benefits of coxibs, by an undefined mechanism.

Attenuation of hydrophobic phospholipid barrier is an early event in Helicobacter felis-induced gastritis in mice

Helicobacter pylori infection has been linked tothe development of gastritis which can then progress toa number of disease entities including peptic ulcerdisease and gastric cancer. Since the pathogenic mechanism by which the bacteria causesgastritis is unresolved, we employed a model system, theH. felis-infected mouse to investigate the temporalrelationship between bacterially-induced alterations in the hydrophobic phospholipid barrier of thestomach and the development of gastritis. In the presentstudy, C57BL/6 mice were inoculated with 109CFU of H. felis and the changes in gastric wet weight, histology, surface hydrophobicity,phospholipid/phosphatidylcholine concentration,phospholipase A2 activity, and the pH ofcollected gastric juice were measured 0.5-2 monthspostinoculation. In related experiments, we investigated the effects oftreating H. felis infected mice with antibiotic/bismuththerapy on the above gastric properties. It wasdetermined that both gastric surface hydrophobicity and phospholipid composition were significantlyattenuated as early as 2-4 weeks postinfection,preceding signs of mucosal inflammation and glandularatrophy as indicated by increases in gastric wet weight, pH and a disappearance in parietal cells. Theseearly H. felis-induced changes in gastric surfacehydrophobicity and phospholipid concentration werereversed by antibiotic/bismuth therapy. Based on these results we conclude that H. felis infectioninduces an early transformation of the stomach from ahydrophobic to an acid-sensitive hydrophilic state thatmay trigger the subsequent development ofgastritis.

Recombinant human lactoferrin is effective in the treatment of Helicobacter felis-infected mice.

Recombinant human lactoferrin possesses in‐vitro antibiotic and anti‐inflammatory activity similar to the native form. It was tested for in‐vivo activity in mice infected with the gastritis‐inducing bacterium Helicobacter felis.

Lipopolysaccharide-induced gastrointestinal injury in rats: role of surface hydrophobicity and bile salts.

Sepsis of gastrointestinal origin can lead to life-threatening complications in vital organs due to bacterial overgrowth and/or translocation from the lumen into the blood. In a rat model of endotoxemia, changes in surface hydrophobicity (associated with barrier integrity) of the gastrointestinal mucosa were examined. Rats were treated with Escherichia coli lipopolysaccharide (LPS), and gastric and ileal tissue were collected for determination of surface hydrophobicity by contact angle analysis. A role for bile salts in hydrophobicity changes was tested by quantifying bile salts in the lumen of both the stomach and ileum after LPS and by the administration of LPS to bile duct-ligated rats. A single intraperitoneal dose of LPS induced a dose- and time-dependent reduction in hydrophobicity of both the stomach and ileum, with the stomach showing greater sensitivity at an earlier time than the ileum. LPS also induced gastric bleeding, reflux of bile acid into the gastric lumen, and decreased levels of bile salt in the ileum. The LPS-induced reductions in surface hydrophobicity of the stomach were prevented by prior bile duct ligation. We conclude that LPS disrupts gastrointestinal barrier integrity, in part by mechanisms involving bile constituents and an attenuation in the mucosas hydrophobic characteristics.

Gastrointestinal safety and therapeutic efficacy of parenterally administered phosphatidylcholine-associated indomethacin in rodent model systems

Background and purpose:  Indomethacin is a non‐steroidal anti‐inflammatory drug (NSAID) that is limited in its enteral or parenteral use by side effects of gastroduodenal bleeding and ulceration. We have investigated the ability of phosphatidylcholine associated with indomethacin to form a therapeutically effective drug (INDO‐PC) with reduced gastrointestinal (GI) toxicity for parenteral use.

Sterol-dependence of gastric protective activity of unsaturated phospholipids

The major aim of this study was to investigate the gastric protective effect of unsaturated phospholipids and to determine the ability of neutral lipids to enhance this activity. We found that although a liposomal suspension of unsaturated phosphatidylcholine (PC) administered intragastrically failed to protect rats from acid-induced gastric ulcer formation, addition of cholesterol to unsaturated PC induced a dose-dependent protective response with the maximally effective dose, reducing lesion score >70%. This effect also was seen with the plant sterol, β-sitosterol (reducing lesion score by 81.6±36%) but was blocked if cholesterol was esterified to fatty acids of varying chain length. Addition of sterols to liposomes of saturated dipalmitoylphosphatidylcholine, in contrast, attenuated the gastric protective action of the saturated PC. It appears that the protective mechanism elicited by sterols and unsaturated PC is not mediated by alterations in gastric emptying rate or protaglandin biosynthesis, although maintenance of surface hydrophobicity may be involved. These results suggest that the sterol may promote the packing of adjacent unsaturated phospholipid molecules of either the cell membrane or a putative extracellular hydrophobic lining of the gastric epithelium to provide the mucosa with protection against luminal acid.