Studies on the mechanism of action of salicylates. IV. Effect of salicylates on oxidative phosphorylation

Adenosine and adenosine receptors in the pathogenesis and treatment of rheumatic diseases

Adenosine, a nucleoside derived primarily from the extracellular hydrolysis of adenine nucleotides, is a potent regulator of inflammation. Adenosine mediates its effects on inflammatory cells by engaging one or more cell-surface receptors. The expression and function of adenosine receptors on different cell types change during the course of rheumatic diseases, such as rheumatoid arthritis (RA). Targeting adenosine receptors directly for the treatment of rheumatic diseases is currently under study; however, indirect targeting of adenosine receptors by enhancing adenosine levels at inflamed sites accounts for most of the anti-inflammatory effects of methotrexate, the anchor drug for the treatment of RA. In this Review, we discuss the regulation of extracellular adenosine levels and the role of adenosine in regulating the inflammatory and immune responses in rheumatic diseases such as RA, psoriasis and other types of inflammatory arthritis. In addition, adenosine and its receptors are involved in promoting fibrous matrix production in the skin and other organs, and the role of adenosine in fibrosis and fibrosing diseases is also discussed.

Management of gastroduodenal ulcers caused by non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) are a major cause of morbidity and mortality, probably resulting in the death of 1200 patients per annum in the UK. The main mechanism of toxicity involves an inhibition of prostaglandin synthesis that results in mucosal erosion as a result of the abrogation of defence mechanisms. However, acid peptic attack can deepen this initial injury. Thus, logical treatments include prostaglandin analogues as 'replacement therapy', acid suppression, enteric coating to avoid topical effects and the use of safer NSAIDs, including those that have little or no effect on gastric mucosal prostaglandin synthesis. There is less logic to the strategy of Helicobacter pylori (H. pylori) eradication, and the status of this approach is controversial. Overall, proton pump inhibitors have the best profile of efficacy and side-effects for the healing and prevention of NSAID-associated ulcers. Misoprostol is also effective and appears to be superior to proton pump inhibitors for superficial erosive injury. Early indications are that selective inhibitors of the inducible cyclooxygenase-2 enzyme have little or no effect in causing ulcers. Growing experience with these agents will probably revolutionize the management of patients with arthritic conditions. However, the increasing use of low-dose aspirin for cardiovascular prophylaxis means that gastroenterologists will have to continue to grapple with the problems of NSAID-associated ulcers for some time to come.

Parenteral aspirin and sodium salicylate are equally injurious to the rat gastric mucosa

The effects of parenteral aspirin (ASA) or sodium salicylate (SA) on the gastric mucosa were investigated in anesthetized pylorus-ligated rats 3 h after a bolus intravenous injection of ASA or SA, 150 mg/kg, or NaCl (control). Aspirin or SA produced similar extensive gross mucosal hemorrhagic lesions and similar microscopic damage in the presence of luminal acid (luminal pH 1.3 +/- 0.05). Neither ASA nor SA produced gastric mucosal injury with intragastric instillation of saline (luminal pH 3.7 +/- 0.5). Pretreatment for 1 h with luminal or subcutaneous 16,16-dimethyl prostaglandin E2 completely prevented the formation of red streaks in ASA-treated rats but not in SA-treated rats, although prostaglandin E2 pretreatment significantly reduced the gross lesion area in SA-treated rats (p less than 0.05). We conclude the following: (a) Intravenous SA is as damaging as intravenous ASA as long as luminal acid is present. (b) 16,16-Dimethyl prostaglandin E2 completely protected the gastric mucosa from injury by intravenous ASA, and to a lesser extent by intravenous SA. (c) In view of the damaging effects of SA on the gastric mucosa and the rapid conversion of ASA to SA, the mechanism of the gastric mucosal injury by intravenous ASA is much more complex than simple inhibition of endogenous prostaglandin synthesis.

Effect of simulated systemic administration of aspirin, salicylate, and indomethacin on amphibian gastric mucosa

The effects of 20 mM aspirin (ASA), 20 mM sodium salicylate (SA), or 10(-4) M indomethacin placed in the nutrient solution (N) to stimulate systemic administration were investigated at pHN 7.3 in Ussing-chambered amphibian gastric mucosae. In histamine-stimulated tissues, the initial rise and subsequent rapid fall in potential difference, rise in resistance, and inhibition of hydrogen ion (H+) secretion induced by SAN did not occur with ASAN unless hydrolysis of ASAN produced a SAN of greater than 3 mM. In metiamide-treated tissues, 20 mM SAN caused an immediate fall in potential difference and an increase in resistance; 2 mM SAN and 20 mM ASA produced similar qualitative electrical changes, but only those induced by ASA were reversible. IndomethacinN caused no significant changes in potential difference, resistance, or H+ secretion in histamine- or metiamide-treated tissues. Despite producing highly significant reductions in generation of prostaglandin E2, and prostaglanndin F2 alpha and 6-keto prostaglandin F1 alpha, ASAN and indomethacin caused no surface ulceration. Sodium salicylate placed in the nutrient solution caused only a small reduction in prostaglandin F2 alpha, without change in the other prostaglandins, and produced extensive edema in the lamina propria, histologically. We conclude the following: (a) The inhibition of H+ secretion and electrical changes caused by SAN in histamine-treated gastric fundus are not observed with ASAN unless there is hydrolysis to [SAN] greater than 3 mM. (b) Our data strongly implicate the SAN in ASAN-containing solutions as being responsible for the electrical effects and inhibition of H+ secretion. (c) There is no correlation in vitro between inhibition of prostaglandin synthesis and the electrical or morphologic changes produced by nutrient exposure to ASA, SA, or indomethacin.

Effects of different doses of acetylsalicylic acid on renal oxygen consumption

The aim of the present study was to examine the acute effect of acetylsalicylic acid (ASA) on renal oxygen consumption (Qo2) and renal sodium excretion (UNaV) in anaesthetized dogs. With plasma salicylic acid (SA) concentrations ranging from 200-400 microgram/ml, Qo2 increased 36% (P less than 0.05) in spite of a 16% decrease in renal blood flow. At plasma SA concentrations of 80-200 microgram/ml Qo2 was significantly increased 45 min after the onset of ASA infusion. UNaV decreased from 97.7 to 21. 5 mumol/min (P less than 0.05). Glomerular filtration rate and absolute tubular reabsorption of sodium (RNa) was unchanged. The ratio RNa/Qo2 decreased from 31.0 to 21.3 (P less than 0.05). Renal lactate uptake increased. The results are most consistent with an uncoupling affect of ASA on oxidative phosphorylation in the kidney.

Salicylate- and aspirin-induced uncoupling of oxidative phosphorylation in mitochondria isolated from the mucosal membrane of the stomach

The hypothesis that the damaging effect on the stomach mucosa of salicylic acid and its derivatives is ascribable to an uncoupling of oxidative phosphorylation has been investigated by testing of mitochondria isolated from the corpus gland area of mini-pig gastric mucosa. Mitochondria, influenced by salicylate or acetylsalicylate (0.7-5.6 mmol/l), demonstrated increased respiration rate, decreased respiratory control ratio, and decreased P/O ratio when tested in vitro. Uncoupling of oxidative phosphorylation occurred at a salicylate concentration between 3.5 and 5.6 mmol/l.

Direct effects of salicylate on renal function in the dog

Sodium salicylate was administered to anesthetized dogs in doses sufficient to produce concentrations in plasma comparable to those common in human salicylate toxicity. Salicylate administration increased the rates of excretion of water, sodium, and chloride in the urine. Salicylate administration also increased the rate of excretion of potassium so that its clearance often exceeded that of creatinine. This enhancement of potassium excretion was dissociated from the alkalosis that accompanies salicyate toxicity. Administration of 5% CO(2) in inspired gas did not attenuate the excretion of potassium; injection of salicylate into one renal artery caused a unilateral kaliuresis. Phosphate excretion increased progressively after administration of salicylate. On several occasions the clearance of phosphate equalled that of creatinine. Salicylate reduced renal tubular glucose reabsorption. When salicylate was injected into a renal artery, a glycosuria occurred ipsilaterally at filtered loads of glucose far below the reabsorptive capacity of the dog kidney. Salicylate administration also was associated with early elevation of glucose, phosphate, and potassium concentration in plasma. Salicylate administration reduced the content of adenosine triphosphate in the renal medulla. Salicylate was concentrated within the medulla between 1.5 and 3 times that of the cortex, a gradient equal to that for chloride.