The amphiprotic character of azapropazone and its relevance to the gastric mucosa

A Collagen IV Matrix Is Required for Guinea Pig Gastric Epithelial Cell Monolayers to Provide an Optimal Model of the Stomach Surface for Biopharmaceutical Screening

The surface epithelial cells of the stomach represent a major component of the gastric barrier. Acell culturemodel of the gastric epithelial cell surface would prove useful for biopharmaceutical screening of new chemical entities and dosage forms. Primary cultures of guinea pig gastricmucous epithelial cellswere grown on filter inserts (Transwells®) for 3 days. Tight-junction formation, assessed by transepithelial electrical resistance (TEER) and permeability ofmannitol and fluorescein, was enhanced when collagen IV rather than collagen I was used to coat the polycarbonate filter. TEER for cells grown on collagen IV was close to that obtained with intact guinea pig gastric epithelium in vitro. Differentiation was assessed by incorporation of [3H]glucosamine into glycoprotein and by activity of NADPH oxidase, which produces superoxide. Both of these measures were greater for cells grown on filters coatedwith collagen I than for cells grown on plastic culture plates, but nomajor difference was found between cells grown on collagens I and IV. The proportion of cells, which stained positively for mucin with periodic acid Schiff reagent, was greater than 95% for all culture conditions. Monolayers grown on membranes coated with collagen IV exhibited apically polarized secretion of mucin and superoxide, and were resistant to acidification of the apical medium to pH 3.0 for 30 min. A screen of nonsteroidal anti-inflammatory drugs revealed a novel effect of diclofenac and niflumic acid in reversibly reducing permeability by the paracellular route. In conclusion, themucous cell preparation grown on collagen IV represents a good model of the gastric surface epithelium suitable for screening procedures.

Profile and mechanisms of gastrointestinal and other side effects of nonsteroidal anti-inflammatory drugs (NSAIDs)

The popular view that all nonsteroidal anti-inflammatory drugs (NSAIDs) act by inhibiting the production of prostaglandins has been challenged by the discovery that they also affect a wide variety of cellular processes that are important for their therapeutic actions and side effects. Although recognition of the differential activities of new and established NSAIDs on the activities of the cyclooxygenases (COXs) affecting production of inflammatory prostaglandins (from COX-2) and those that are physiologically important (from COX-1) may have significance for the prostaglandin components of the underlying inflammatory and physiologic processes, there are important features of their chemical structures that determine the various cellular and biochemical actions of these agents. Several established NSAIDs have low propensity to cause gastrointestinal (GI) ulceration and bleeding that may relate to these drugs having unique pharmacokinetic characteristics (pro-drugs, protein binding, etc). They also have weak effects on the production of GI mucosal prostaglandins and have specific physicochemical characteristics such that they cause minimal damage to mucosal membranes or effects on nonprostaglandin-related cellular mechanisms important in mucosal defenses. Some of the new COX-2-selective drugs with methyl or amino-sulfonyl moieties have relatively high pKa values and other properties that are similar to established NSAIDs with low GI ulcerogenicity. These physicochemical properties may contribute to the low irritancy of the new COX-2-selective drugs quite apart from their sparing of COX-1 in the GI mucosa. With concerns that some established NSAIDs may accelerate cartilage destruction in osteoarthritis (OA), interest is now focusing on whether the COX-2-selective drugs may have a lower potential for this adverse effect by avoiding the inhibitory effects on cartilage proteoglycan metabolism seen with such drugs as indomethacin and the salicylates. Meloxicam appears to be without inhibitory effects on proteoglycan metabolism, but it remains to be seen if this translates into any beneficial actions on the progression of joint changes in OA observed radiologically or from magnetic resonance imaging.

Effects of azapropazone on pain-related brain activity in human subjects

1. The dose-related effects of azapropazone on (i) event-related and spontaneous EEG-activity and (ii) the subjects' pain ratings were investigated using an experimental human pain model based on both chemo-somatosensory event-related potentials (CSSERP) and subjects' pain ratings. 2. Healthy subjects (n = 20) participated in a placebo-controlled, randomized, double-blind, four-way cross-over study. Single doses of azapropazone (300 mg, 600 mg and 1200 mg) and placebo were administered intravenously. Each experiment consisted of five sessions (before and 1, 2, 4 and 8 h after administration of the medication). Each session lasted for approximately 40 min. In the first 20 min, pain was induced by short CO2-stimuli presented to the right nostril (phasic pain; interstimulus interval 30 s) and EEG was recorded from five positions. CSSERPs were obtained in response to painful CO2-stimuli. In the following 20 min period, tonic pain was induced by a constant stream of dry air introduced in the left nostril. Subjects rated the intensity of both phasic and tonic pain by means of a visual analogue scale. Additionally, a frequency analysis of the spontaneous EEG was performed. 3. Azapropazone reduced the pain-related CSSERP-amplitudes at frontal and parietal recording positions. This topographical pattern was observed in previous studies with opioids, while NSAIDs such as flurbiprofen and ketoprofen exerted effects at frontal and central positions. In contrast to other NSAIDs, administration of azapropazone resulted in a reduction of the frequency bands alpha 1, delta and theta of the spontaneous EEG. At the subjective level, analgesic effects of azapropazone were observed in the ratings of tonic pain. 4. Analgesic properties of azapropazone were demonstrated in man. The topographical pattern of the changes in the CSSERPs and the effects on EEG background activity suggest a central component of the analgesic action of azapropazone.

Non-steroidal anti-inflammatory drugs and spinal nociceptive processing

Non-steroidal anti-inflammatory drugs have a direct action on spinal nociceptive processing in vivo with a relative order of potency which correlates with their capacity as inhibitors of cyclooxygenase activity. However, recent clinical surveys and new in vivo evidence strongly suggest that for some of these agents, centrally mediated analgesia may also be achieved by additional mechanisms, which are independent of prostaglandin synthesis inhibition. In this review we explore the likelihood for such mechanisms following an extensive survey of existing data. The implications of these mechanisms are discussed in the light of our current understanding of spinal nociceptive processing.

Dissociation between the antinociceptive and anti-inflammatory effects of the nonsteroidal anti-inflammatory drugs. A survey of their analgesic efficacy

The authors challenge the general view that the analgesic effect of the nonsteroidal anti-inflammatory drugs (NSAIDs) can be universally attributed to their inhibitory effects on the synthesis of peripherally formed prostaglandins. Analgesic activity by some of these compounds in the reduction of physiological pain elicited by a single noxious stimulus, or the treatment of acute pain which results from sudden trauma to otherwise healthy tissue, is better described as an antinociceptive effect. Single-dose studies in the dental pain model that have been conducted in double-blind conditions and included a placebo control group have been reviewed; those NSAIDs which are significantly superior to the reference compound aspirin 650mg and those which could represent real alternatives to the use of narcotics in certain situations for the management of acute pain have been identified. Azapropazone, diflunisal, naproxen, oxaprozin and tolmetin are all weak inhibitors of prostaglandin synthesis, yet they have been shown to be more effective than aspirin. In a model of joint pain, azapropazone 600mg has been shown to be as effective as pethidine (meperidine) 100mg despite being the weakest inhibitor of prostaglandin synthesis. Whether the antinociceptive effect of azapropazone acts at a peripheral or a central level, or both, is not clear; evidence for the effects of NSAIDs on the central nervous system (CNS) is discussed. Historically, the antinociceptive character of some NSAIDs is apparent in several studies in both animals and humans. More recently, experimental algesimetry models designed to distinguish the antinociceptive effects of NSAIDs include the use in humans of photoplethysmography and computer-supported infrared thermographic imaging.