Using aspirin to prevent and treat cancer.

This review will discuss evidence that aspirin possesses anticancer activity. Long-term observational retrospective studies on nurses and health professionals demonstrated that regular aspirin users had a significantly lower incidence of colorectal cancer (RCT). Prospective studies on patients with a high risk of developing colorectal polyps/cancer confirmed that aspirin use significantly lowered colorectal dysplasia. Numerous observational studies focused on the use of aspirin in a broad range of cancers demonstrating a consistent 20-30% preventive effect on cancer incidence and mortality. Random Controlled Trials provided conflicting results on the benefit of aspirin in preventing CRC. Based on the age, weight/body size of the subjects for reasons still being explored. Studies on rats/mice further demonstrated that treatment of animals with aspirin where colon cancer was induced chemically or genetically (APCMin mice) reduced colonic dysplasia and polyp formation. Aspirin treatment was also effective at reducing the growth of cancer cells transplanted into normal/immunocompromised mice, suggesting that aspirin may be effective in treating different cancers. This possibility is also supported in clinical studies that aspirin use pre- and postcancer diagnosis significantly reduced the metastatic spread of cancer and increased patient survival. Lastly, the importance of the antiplatelet actions of aspirin in the drug's anticancer activity and specifically cancer metastatic spread is discussed and the current controversy related to the conflicting recommendations of the USPSTF over the past five years on the use of aspirin to prevent CRC.

A closer look at endothelial injury-induced platelet hyperactivity and the use of aspirin in the treatment of COVID infection.

In this commentary, we make a case that the mechanism of COVID pathogenesis is related to virus-induced endothelial injury resulting in platelet activation and the formation of microthrombi both systemically and in cardiac and pulmnonary circulation which result in major causes of COVID morbidity and mortality. Aspirin by virtue of its irreversible inhibition of platelet COX-1, should reverse these platelet-induced pathogenic changes associated with COVID infection for the 6-9 day lifetime of the platelet. We also cite recent findings of a retrospective analysis that supports the use of low-dose (81 mg) aspirin to treat the symptoms associated with the early stages of COVID infection.

Sulindac plus a phospholipid is effective for polyp reduction and safer than sulindac alone in a mouse model of colorectal cancer development.

BACKGROUND: Non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin and sulindac are effective for colorectal cancer prevention in humans and some animal models, but concerns over gastro-intestinal (GI) ulceration and bleeding limit their potential for chemopreventive use in broader populations. Recently, the combination of aspirin with a phospholipid, packaged as PL-ASA, was shown to reduce GI toxicity in a small clinical trial. However, these studies were done for relatively short periods of time. Since prolonged, regular use is needed for chemopreventive benefit, it is important to know whether GI safety is maintained over longer use periods and whether cancer prevention efficacy is preserved when an NSAID is combined with a phospholipid. METHODS: As a first step to answering these questions, we treated seven to eight-week-old, male and female C57B/6 Apcmin/+ mice with the NSAID sulindac, with and without phosphatidylcholine (PC) for 3-weeks. At the end of the treatment period, we evaluated polyp burden, gastric toxicity, urinary prostaglandins (as a marker of sulindac target engagement), and blood chemistries. RESULTS: Both sulindac and sulindac-PC treatments resulted in significantly reduced polyp burden, and decreased urinary prostaglandins, but sulindac-PC treatment also resulted in the reduction of gastric lesions compared to sulindac alone. CONCLUSIONS: Together these data provide pre-clinical support for combining NSAIDs with a phospholipid, such as phosphatidylcholine to reduce GI toxicity while maintaining chemopreventive efficacy.

Beyond COX-1: the effects of aspirin on platelet biology and potential mechanisms of chemoprevention.

After more than a century, aspirin remains one of the most commonly used drugs in western medicine. Although mainly used for its anti-thrombotic, anti-pyretic, and analgesic properties, a multitude of clinical studies have provided convincing evidence that regular, low-dose aspirin use dramatically lowers the risk of cancer. These observations coincide with recent studies showing a functional relationship between platelets and tumors, suggesting that aspirin's chemopreventive properties may result, in part, from direct modulation of platelet biology and biochemistry. Here, we present a review of the biochemistry and pharmacology of aspirin with particular emphasis on its cyclooxygenase-dependent and cyclooxygenase-independent effects in platelets. We also correlate the results of proteomic-based studies of aspirin acetylation in eukaryotic cells with recent developments in platelet proteomics to identify non-cyclooxygenase targets of aspirin-mediated acetylation in platelets that may play a role in its chemopreventive mechanism.

In vitro evidence that phosphatidylcholine protects against indomethacin/bile acid-induced injury to cells.

Indomethacin is a powerful analgesic nonsteroidal anti-inflammatory drug (NSAID), but is limited in use by its primary side effect to cause gastrointestinal bleeding and serious injury. One factor important for exacerbating NSAID injury is the presence of bile acids, which may interact with indomethacin to form toxic mixed micelles in the gut. The development of a safer gastrointestinal formulation of indomethacin that is chemically complexed with phosphatidylcholine (PC-indomethacin) may offer an improved therapeutic agent, particularly in the presence of bile acid, but its potential protective mechanism is incompletely understood. Intestinal epithelial cells (IEC-6) were tested for injury with indomethacin (alone and plus various bile acids) compared with PC-indomethacin (alone and plus bile acids). To explore a role for bile acid uptake into cells as a requirement for NSAID injury, studies were performed using Madin-Darby canine kidney cells transfected with the apical sodium-dependent bile acid transporter (ASBT). Indomethacin, but not PC-indomethacin, was directly and dose-dependently injurious to IEC-6 cells. Similarly, the combination of any bile acid plus indomethacin, but not PC-indomethacin, induced cell injury. The expression of ASBT had a modest effect on the acute cytotoxicity of indomethacin in the presence of some conjugated bile acids. Complexing PC with indomethacin protected against the acute intestinal epithelial injury caused by indomethacin regardless of the presence of bile acids. The presence of luminal bile acid, but not its carrier-mediated uptake into the enterocyte, is required for acute indomethacin-induced cell injury. It is likely that initial cell damage induced by indomethacin occurs at or near the cell membrane, an effect exacerbated by bile acids and attenuated by PC.

Suppression of contractile activity in the small intestine by indomethacin and omeprazole.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are widely used to treat a number of conditions, and proton pump inhibitors (PPIs) are often used to prevent NSAID-induced gastric mucosal damage; however, the effects of NSAIDs on intestinal motility are poorly understood. The purpose of the present study is to determine the effects of a prototypical NSAID, indomethacin, either alone or in conjunction with the PPI omeprazole, on intestinal motility. Rats were randomly divided into four groups treated with vehicle, omeprazole, indomethacin, or a combination of indomethacin and omeprazole. Intestinal motility and transit were measured along with inflammatory mediators in the intestinal smooth muscle, markers of mucosal damage, and bacterial counts in the intestinal wall. Indomethacin, but not omeprazole, caused mucosal injury indicated by lower gut bleeding; however, both omeprazole and indomethacin suppressed contractile activity and frequency in the distal part of the small intestine. Cotreatment with omeprazole did not reduce indomethacin-induced intestinal bleeding. Furthermore, although indomethacin caused increased inflammation as indicated by increased edema development and inflammatory mediators, cotreatment with omeprazole did not reduce inflammation in the intestinal smooth muscle or prevent the increased bacterial count in the intestinal wall induced by indomethacin. We conclude that both NSAID and PPI treatment suppressed contractile activity in the distal regions of the small intestine. The suppression of intestinal contractility was associated with increased inflammation in both cases; however, indomethacin and omeprazole appear to affect intestinal motility by different mechanisms.

Bile acids modulate signaling by functional perturbation of plasma membrane domains.

Eukaryotic cell membranes are organized into functional lipid and protein domains, the most widely studied being membrane rafts. Although rafts have been associated with numerous plasma membrane functions, the mechanisms by which these domains themselves are regulated remain undefined. Bile acids (BAs), whose primary function is the solubilization of dietary lipids for digestion and absorption, can affect cells by interacting directly with membranes. To investigate whether these interactions affected domain organization in biological membranes, we assayed the effects of BAs on biomimetic synthetic liposomes, isolated plasma membranes, and live cells. At cytotoxic concentrations, BAs dissolved synthetic and cell-derived membranes and disrupted live cell plasma membranes, implicating plasma membrane damage as the mechanism for BA cellular toxicity. At subtoxic concentrations, BAs dramatically stabilized domain separation in Giant Plasma Membrane Vesicles without affecting protein partitioning between coexisting domains. Domain stabilization was the result of BA binding to and disordering the nonraft domain, thus promoting separation by enhancing domain immiscibility. Consistent with the physical changes observed in synthetic and isolated biological membranes, BAs reorganized intact cell membranes, as evaluated by the spatial distribution of membrane-anchored Ras isoforms. Nanoclustering of K-Ras, related to nonraft membrane domains, was enhanced in intact plasma membranes, whereas the organization of H-Ras was unaffected. BA-induced changes in Ras lateral segregation potentiated EGF-induced signaling through MAPK, confirming the ability of BAs to influence cell signal transduction by altering the physical properties of the plasma membrane. These observations suggest general, membrane-mediated mechanisms by which biological amphiphiles can produce their cellular effects.

Aggregation behavior of ibuprofen, cholic acid and dodecylphosphocholine micelles.

Non-steroidal anti-inflammatory drugs (NSAIDs) are frequently used to treat chronic pain and inflammation. However, prolonged use of NSAIDs has been known to result in Gastrointestinal (GI) ulceration/bleeding, with a bile-mediated mechanism underlying their toxicity to the lower gut. Bile acids (BAs) and phosphatidylcholines (PCs), the major components of bile, form mixed micelles to reduce the membrane disruptive actions of monomeric BAs and simple BA micelles. NSAIDs are suspected to alter the BA/PC balance in the bile, but the molecular interactions of NSAID-BA or NSAID-BA-PC remain undetermined. In this work, we used a series of all-atom molecular dynamics simulations of cholic acid (CA), ibuprofen (IBU) and dodecylphosphocholine (DPC) mixtures to study the spontaneous aggregation of CA and IBU as well as their adsorption on a DPC micelle. We found that the size of CA-IBU mixed micelles varies with their molar ratio in a non-linear manner, and that micelles of different sizes adopt similar shapes but differ in composition and internal interactions. These observations are supported by NMR chemical shift changes, NMR ROESY crosspeaks between IBU and CA, and dynamic light scattering experiments. Smaller CA-IBU aggregates were formed in the presence of a DPC micelle due to the segregation of CA and IBU away from each other by the DPC micelle. While the larger CA-IBU aggregates arising from higher IBU concentrations might be responsible for NSAID-induced intestinal toxicity, the absence of larger CA-IBU aggregates in the presence of DPC micelles may explain the observed attenuation of NSAID toxicity by PCs.

Insight into NSAID-induced membrane alterations, pathogenesis and therapeutics: characterization of interaction of NSAIDs with phosphatidylcholine.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most widely consumed pharmaceuticals, yet both the mechanisms involved in their therapeutic actions and side-effects, notably gastrointestinal (GI) ulceration/bleeding, have not been clearly defined. In this study, we have used a number of biochemical, structural, computational and biological systems including; Fourier Transform InfraRed (FTIR). Nuclear Magnetic Resonance (NMR) and Surface Plasmon Resonance (SPR) spectroscopy, and cell culture using a specific fluorescent membrane probe, to demonstrate that NSAIDs have a strong affinity to form ionic and hydrophobic associations with zwitterionic phospholipids, and specifically phosphatidylcholine (PC), that are reversible and non-covalent in nature. We propose that the pH-dependent partition of these potent anti-inflammatory drugs into the phospholipid bilayer, and possibly extracellular mono/multilayers present on the luminal interface of the mucus gel layer, may result in profound changes in the hydrophobicity, fluidity, permeability, biomechanical properties and stability of these membranes and barriers. These changes may not only provide an explanation of how NSAIDs induce surface injury to the GI mucosa as a component in the pathogenic mechanism leading to peptic ulceration and bleeding, but potentially an explanation for a number of (COX-independent) biological actions of this family of pharmaceuticals. This insight also has proven useful in the design and development of a novel class of PC-associated NSAIDs that have reduced GI toxicity while maintaining their essential therapeutic efficacy to inhibit pain and inflammation.

Cellular and organismal toxicity of the anti-cancer small molecule, tolfenamic acid: a pre-clinical evaluation.

BACKGROUND/AIMS: The small molecule, Tolfenamic acid (TA) has shown anti-cancer activity in pre-clinical models and is currently in Phase I clinical trials at MD Anderson Cancer Center Orlando. Since specificity and toxicity are major concerns for investigational agents, we tested the effect of TA on specific targets, and assessed the cellular and organismal toxicity representing pre-clinical studies in cancer. METHODS: Panc1, L3.6pl, and MiaPaCa-2 (pancreatic cancer), hTERT-HPNE(normal), and differentiated/un-differentiated SH-SY5Y (neuroblastoma) cells were treated with increasing concentrations of TA. Cell viability and effect on specific molecular targets, Sp1 and survivin were determined. Athymic nude mice were treated with vehicle or TA (50mg/kg, 3times/week for 6 weeks) and alterations in the growth pattern, hematocrit, and histopathology of gut, liver, and stomach were monitored. RESULTS: TA treatment decreased cell proliferation and inhibited the expression of Sp1 and survivin in cancer cells while only subtle response was observed in normal (hTERT-HPNE) and differentiated SH-SY5Y cells. Mice studies revealed no effect on body weight and hematocrit. Furthermore, TA regimen did not cause signs of internal-bleeding or damage to vital tissues in mice. CONCLUSION: These results demonstrate that TA selectively inhibits malignant cell growth acting on specific targets and its chronic treatment did not cause apparent toxicity in nude mice.

Endotoxin-induced changes in phospholipid dynamics of the stomach.

BACKGROUND: The gastric mucosa is protected in part by a hydrophobic layer of phosphatidylcholine (PC) that overlies the mucus gel on the stomach. Endotoxin treatment (i.e., lipopolysaccharide [LPS]) results in an apparent disruption of this layer, as evidenced by a reduction in surface hydrophobicity and an increase in transmural permeability. The current studies compared PC and lyso-PC levels in mucus and gastric mucosa before and after LPS treatment, and examined potential mechanisms for surface phospholipid changes. METHODS: Rats were administered LPS (5 mg//kg, intraperitoneally) and samples were collected after 5 h for analysis of PC and its primary degradant, lyso-PC, in the loosely and firmly adherent mucus layers and the mucosa. The dependence of LPS-induced effects on gastric alkalinization, PC synthetic activity, and intestinal reflux material was assessed. RESULTS: The gastric contents after LPS, which also contained duodenal reflux material, had greatly increased amounts of PC and lyso-PC. The firmly adherent mucus layer was unchanged. The gastric mucosa after LPS revealed significant reductions of PC levels and no change in lyso-PC content. These phospholipid changes were not caused by alkalinization of the stomach or altered PC synthesis. Prevention of duodenogastric reflux by pylorus ligation blocked the LPS-induced increase in luminal lyso-PC and the reduction in mucosal PC. CONCLUSIONS: LPS appears to induce a release of PC from gastric mucosa into the lumen, along with degradation of PC to lyso-PC, without an effect on PC synthesis. Component(s) of intestinal reflux material appear to be required for these effects. The lowered PC levels in gastric mucosa after LPS may contribute to reduced barrier properties of this tissue.

Development of the PC-NSAID technology: From contact angle to Vazalore®.

We describe strategies in drug development to reduce the gastrointestinal (GI) toxicity of nonsteroidal anti-inflammatory drugs (NSAIDs). We then provide an overview of the experiments that led to the development of PC-NSAIDs, a novel family of NSAIDs associated with phosphatidylcholine (PC) that have reduced GI toxicity and full therapeutic activity. Furthermore, we describe the evidence showing: that the stomach possesses hydrophobic properties that are attributable to phospholipids lining the mucus gel layer; and that NSAIDs chemically associate with intrinsic PC, thereby attenuating the tissue's hydrophobic properties. Further, pre-associating NSAIDs with PC reduces the GI toxicity of these drugs, both in rodent ulcer models and in human subjects, without affecting the drugs' therapeutic activity. Finally, we discuss the commercialization and launch of Aspirin-PC, an over-the-counter (OTC) drug with the brand name Vazalore®.

In vitro and in vivo protection against indomethacin-induced small intestinal injury by proton pump inhibitors, acid pump antagonists, or indomethacin-phosphatidylcholine.

BACKGROUND/AIMS: Proton pump inhibitors (PPIs) are widely used to prevent nonsteroidal anti-inflammatory drug (NSAID)-induced peptic ulcers. NSAIDs produce small intestinal injury and some PPIs have been reported to protect against NSAID-induced small bowel injury in rats. The aim of this study was to compare PPIs, revaprazan, and phosphatidylcholine-associated indomethacin (Indo-PC) for protection against indomethacin (Indo)-induced small bowel injury. METHODS: Rat intestinal epithelial cells (IEC-6) were pretreated with omeprazole, lansoprazole, or revaprazan prior to exposure to Indo or Indo-PC. Cell viability was assessed by methyl thiazolyl tetrazolium assay. Omeprazole, lansoprazole, or revaprazan was administered orally to rats prior to the vehicle or Indo. Indo-PC was administered alone. After 24 h, small intestinal erosions were counted; intestinal bleeding was assessed as the hemoglobin concentration of small intestinal fluid. RESULTS: Omeprazole, lansoprazole, and revaprazan did not protect against Indo-induced IEC-6 cell injury. Indo-PC was less damaging in vitro than Indo alone. In vivo, neither omeprazole nor lansoprazole protected against Indo-induced small bowel injury; however, revaprazan pretreatment and Indo-PC resulted in significantly fewer erosions (>50% reduction) or bleeding (>80% reduction). CONCLUSION: PPIs showed no small bowel protective effect in vitro or in vivo. Revaprazan showed a small bowel protective effect in vivo, whereas Indo-PC was protective both in vitro and in vivo.

The anti-inflammatory drug indomethacin alters nanoclustering in synthetic and cell plasma membranes.

The nonsteroidal anti-inflammatory drug indomethacin exhibits diverse biological effects, many of which have no clear molecular mechanism. Membrane-bound receptors and enzymes are sensitive to their phospholipid microenvironment. Amphipathic indomethacin could therefore potentially modulate cell signaling by changing membrane properties. Here we examined the effect of indomethacin on membrane lateral heterogeneity. Fluorescence lifetime imaging of cells expressing lipid-anchored probes revealed that treatment of BHK cells with therapeutic levels of indomethacin enhances cholesterol-dependent nanoclustering, but not cholesterol-independent nanoclustering. Immuno-electron microscopy and quantitative spatial mapping of intact plasma membrane sheets similarly showed a selective effect of indomethacin on promoting cholesterol-dependent, but not cholesterol-independent, nanoclustering. To further evaluate the biophysical effects of indomethacin, we measured fluorescence polarization of the phase-sensitive probe Laurdan and FRET between phase-partitioning probes in model bilayers. Therapeutic levels of indomethacin enhanced phase separation in DPPC/DOPC/Chol (1:1:1) and DPPC/Chol membranes in a temperature-dependent manner, but had minimal effect on the phase behavior of pure DOPC at any temperature. Taken together, the imaging results on intact epithelial cells and the biophysical assays of model membranes suggest that indomethacin can enhance phase separation and stabilize cholesterol-dependent nanoclusters in biological membranes. These effects on membrane lateral heterogeneity may have significant consequences for cell signaling cascades that are assembled on the plasma membrane.

Low-dose aspirin-induced ulceration is attenuated by aspirin-phosphatidylcholine: a randomized clinical trial.

OBJECTIVES: Relative contributions of local and systemic mechanisms of upper gastrointestinal (GI) injury following aspirin are unknown. Studies suggest that aspirin's GI risk is age related and that gastroprotection may be needed at therapy initiation. We determined acute gastroduodenal erosion and ulceration following low-dose aspirin and aspirin-phosphatidylcholine complex (PL2200) in subjects at risk of aspirin ulcers. METHODS: In a randomized, single blind, multicenter active-controlled study, we compared upper GI damage of aspirin and PL2200 in healthy subjects (n=204, ages 50-74 years) following 7 days of oral 325 mg once daily, immediate release aspirin or PL2200. RESULTS: Overall, 42.2% of aspirin-treated subjects developed multiple erosions and/or ulcers, whereas 22.2% treated with PL2200 developed such damage (P=0.0027). Gastroduodenal ulcers were observed in 17.6% of aspirin-treated compared with 5.1% of subjects treated with PL2200 (P=0.0069). CONCLUSIONS: Low-dose aspirin induced a surprisingly high incidence of acute gastroduodenal ulcers in at risk subjects, highlighting that aspirin's upper GI risk begins early and may require gastroprotection. Local mechanisms of GI protection are important as aspirin's preassociation with surface-active phospholipids significantly reduced mucosal damage. PL2200 may be an attractive alternative or complement to proton pump inhibitors in older patients who are at risk of aspirin-induced ulceration. Longer-term studies assessing clinical GI events are desirable to confirm the clinical GI safety profile of PL2200.

Is COVID-19-Induced Platelet Activation a Cause of Concern for Patients with Cancer?

Patients with cancer are more susceptible to be infected by SARS-CoV-2 and develop severe outcomes including ICU admittance, mechanical ventilator support, and a high rate of mortality. Like mid-to late-stage cancer, SARS-CoV-2 infection is associated with platelet hyperactivity, systemic inflammation, thrombotic complications, and coagulopathy. Platelets also promote cancer cell growth, survival in circulation, and angiogenesis at sites of metastases. In this article, we will discuss the potential for platelets in the development of systemic inflammation and thrombosis in SARS-CoV-2-infected patients with cancer, with the concern that the platelet-induced pathogenic events are likely magnified in cancer patients with COVID-19.

The role of membrane cholesterol in determining bile acid cytotoxicity and cytoprotection of ursodeoxycholic acid.

In cholestatic liver diseases, the ability of hydrophobic bile acids to damage membranes of hepatocytes/ductal cells contributes to their cytotoxicity. However, ursodeoxycholic acid (UDC), a hydrophilic bile acid, is used to treat cholestasis because it protects membranes. It has been well established that bile acids associate with and solubilize free cholesterol (CHOL) contained within the lumen of the gallbladder because of their structural similarities. However, there is a lack of understanding of how membrane CHOL, which is a well-established membrane stabilizing agent, is involved in cytotoxicity of hydrophobic bile acids and the cytoprotective effect of UDC. We utilized phospholipid liposomes to examine the ability of membrane CHOL to influence toxicity of individual bile acids, such as UDC and the highly toxic sodium deoxycholate (SDC), as well as the cytoprotective mechanism of UDC against SDC-induced cytotoxicity by measuring membrane permeation and intramembrane dipole potential. The kinetics of bile acid solubilization of phosphatidylcholine liposomes containing various levels of CHOL was also characterized. It was found that the presence of CHOL in membranes significantly reduced the ability of bile acids to damage synthetic membranes. UDC effectively prevented damaging effects of SDC on synthetic membranes only in the presence of membrane CHOL, while UDC enhances the damaging effects of SDC in the absence of CHOL. This further demonstrates that the cytoprotective effects of UDC depend upon the level of CHOL in the lipid membrane. Thus, changes in cell membrane composition, such as CHOL content, potentially influence the efficacy of UDC as the primary drug used to treat cholestasis.

Bile acids improve the antimicrobial effect of rifaximin.

Diarrhea is one of the most common infirmities affecting international travelers, occurring in 20 to 50% of persons from industrialized countries visiting developing regions. Enterotoxigenic Escherichia coli (ETEC) is the most common causative agent and is isolated from approximately half of the cases of traveler's diarrhea. Rifaximin, a largely water-insoluble, nonabsorbable (<0.4%) antibiotic that inhibits bacterial RNA synthesis, is approved for use for the treatment of traveler's diarrhea caused by diarrheagenic E. coli. However, the drug has minimal effect on the bacterial flora or the infecting E. coli strain in the aqueous environment of the colon. The purpose of the present study was to evaluate the antimicrobial effect and bioavailability of rifaximin in aqueous solution in the presence and absence of physiologic concentrations of bile acids. The methods used included growth measurement of ETEC (strain H10407), rifaximin solubility measurements, total bacterial protein determination, and assessment of the functional activity of rifaximin by monitoring inhibition of bacterial beta-galactosidase expression. Solubility studies showed rifaximin to be 70- to 120-fold more soluble in bile acids (approximately 30% in 4 mM bile acids) than in aqueous solution. Addition of both purified bile acids and human bile to rifaximin at subinhibitory and inhibitory concentrations significantly improved the drug's anti-ETEC effect by 71% and 73%, respectively, after 4 h. This observation was confirmed by showing a decrease in the overall amount of total bacterial protein expressed during incubation of rifaximin plus bile acids. Rifaximin-treated samples containing bile acids inhibited the expression of ETEC beta-galactosidase at a higher magnitude than samples that did not contain bile acids. The study provides data showing that bile acids solubilize rifaximin on a dose-response basis, increasing the drug's bioavailability and antimicrobial effect. These observations suggest that rifaximin may be more effective in the treatment of infections in the small intestine, due to the higher concentration of bile in this region of the gastrointestinal tract than in the colon. The water insolubility of rifaximin is the likely explanation for the drug's minimal effects on colonic flora and fecal pathogens, despite in vitro susceptibility.

Effect of indomethacin on bile acid-phospholipid interactions: implication for small intestinal injury induced by nonsteroidal anti-inflammatory drugs.

The injurious effect of nonsteroidal anti-inflammatory drugs (NSAIDs) in the small intestine was not appreciated until the widespread use of capsule endoscopy. Animal studies found that NSAID-induced small intestinal injury depends on the ability of these drugs to be secreted into the bile. Because the individual toxicity of amphiphilic bile acids and NSAIDs directly correlates with their interactions with phospholipid membranes, we propose that the presence of both NSAIDs and bile acids alters their individual physicochemical properties and enhances the disruptive effect on cell membranes and overall cytotoxicity. We utilized in vitro gastric AGS and intestinal IEC-6 cells and found that combinations of bile acid, deoxycholic acid (DC), taurodeoxycholic acid, glycodeoxycholic acid, and the NSAID indomethacin (Indo) significantly increased cell plasma membrane permeability and became more cytotoxic than these agents alone. We confirmed this finding by measuring liposome permeability and intramembrane packing in synthetic model membranes exposed to DC, Indo, or combinations of both agents. By measuring physicochemical parameters, such as fluorescence resonance energy transfer and membrane surface charge, we found that Indo associated with phosphatidylcholine and promoted the molecular aggregation of DC and potential formation of larger and isolated bile acid complexes within either biomembranes or bile acid-lipid mixed micelles, which leads to membrane disruption. In this study, we demonstrated increased cytotoxicity of combinations of bile acid and NSAID and provided a molecular mechanism for the observed toxicity. This mechanism potentially contributes to the NSAID-induced injury in the small bowel.