New light on how aspirin works

The regulation of cyclin D1 degradation: roles in cancer development and the potential for therapeutic invention

Cyclin D1 is an important regulator of cell cycle progression and can function as a transcriptionl co-regulator. The overexpression of cyclin D1 has been linked to the development and progression of cancer. Deregulated cyclin D1 degradation appears to be responsible for the increased levels of cyclin D1 in several cancers. Recent findings have identified novel mechanisms involved in the regulation of cyclin D1 stability. A number of therapeutic agents have been shown to induce cyclin D1 degradation. The therapeutic ablation of cyclin D1 may be useful for the prevention and treatment of cancer. In this review, current knowledge on the regulation of cyclin D1 degradation is discussed. Novel insights into cyclin D1 degradation are also discussed in the context of ablative therapy. A number of unresolved questions regarding the regulation of cellular cyclin D1 levels are also addressed.

The effects of captopril (SQ 14,225) on bradykinin-induced bronchoconstriction in the anesthetized guinea pig

The effect of captopril (SQ 14,225) a potent inhibitor of angiotensin converting enzyme (ACE: kininase II) on the bronchoconstrictor response to bradykinin was studied in the anesthetized guinea pig. The i.v. administration of captopril caused a profound long lasting hypotension without affecting pulmonary resistance or dynamic compliance. Similarly, the i.v. administration of bradykinin caused small increases in pulmonary resistance and decreases in dynamic compliance which were not altered by the administration of captopril. However, after beta-receptor blockade with propranolol, bradykinin-induced changes in resistance and compliance were enhanced; additional captopril administration further potentiated the bradykinin effects. The prostaglandin synthetase inhibitor indomethacin antagonized the bradykinin-induced bronchoconstriction in beta-blocked animals and its potentiation by captopril. In the isolated perfused guinea pig lung, bradykinin caused a dose dependent release of a prostaglandin-like substance which was significantly increased by captopril and antagonized by indomethacin. These results suggest that bradykinin causes a prostaglandin-mediated bronchoconstriction. Captopril, a potent inhibitor of ACE, prevents the degradation of bradykinin thus potentiating the bradykinin-induced bronchoconstriction, an effect observed in intact animals only in the absence of pulmonary beta-receptor activation.

Role of platelets in aspirin-sensitive bronchoconstriction in the guinea-pig; interactions with salicylic acid

1 The bronchoconstriction caused in the guinea-pig by arachidonic acid (AA), bradykinin, adenosine diphosphate (ADP) and adenosine triphosphate (ATP) was correlated with effects on platelets. ATP and ADP produced a brief thrombocytopenia and AA a more prolonged one. Bradykinin had no effect on platelets.2 Aspirin inhibited bronchoconstriction and thrombocytopenia produced by AA and part of the bronchoconstriction produced by ATP, but had no effect against ADP. Thrombocytopenia produced by ADP and ATP was not affected by aspirin or indomethacin.3 Platelet depletion by antiserum prevented bronchoconstriction in response to ADP and to ATP, but not in response to bradykinin or to AA, showing that platelets are not involved in aspirin-sensitive bronchoconstriction. Infusions of ADP reduced bronchoconstriction and thrombocytopenia in response to ADP itself and to ATP, but not to AA. Bronchoconstriction by ADP or ATP involves an action on platelets. Only that due to ATP is partially dependent on the activity of prostaglandin synthetase.4 ATP induced aggregation in vitro in guinea-pig platelet-rich plasma (PRP). Rabbit PRP responded only when ATP was first incubated with guinea-pig plasma. The aggregating compound formed was probably ADP, since it was destroyed by apyrase. Its formation was not inhibited by aspirin or indomethacin, indicating that aspirin inhibits ATP-induced bronchoconstriction by a different mechanism.5 The aggregating effect of ATP on guinea-pig platelets was inhibited by concentrations of apyrase that block ADP-induced aggregation, and potentiated by lower concentrations of apyrase.6 Adenosine 5'-tetraphosphate did not aggregate platelets in vivo or in vitro. In vitro aggregation occurred when apyrase was added, suggesting transformation into ADP. Adenosine 5'-tetraphosphate and apyrase inhibited aggregation due to ADP, but failed to affect that due to AA. This suggests that aggregation involving products of prostaglandin synthesis does not require ADP.7 Salicylic acid did not interfere with bronchoconstriction or aggregation due to AA, but prevented inhibition by aspirin when the weight ratio, salicylic acid:aspirin was 4:1. Salicyclic acid may be useful in studies of potential inhibitors of thromboxane A2 synthesis and of thromboxane A2-dependent processes in vivo and in vitro.

Reduced symptoms of anaphylaxis in chickens by ACTH or heat

Exogenous ACTH, when administered intramuscularly in four equal doses of 2 I.U./100 gm. of body weight at 24, 23, 22, and 21 hours prior to challenge with BSA, reduced the severity of anaphylaxis in BSA sensitized juvenile chickens. Additionally, a single heat exposure (45 degrees C.) of 30 minutes at 24 hours prior to challenge consistently reduced the severity of anaphylaxis. Single heating exposures at 24 hours prior to sensitization or at 48 hours prior to challenge did not influence the anaphylactic response. In one of two experiments single heat exposures at one hour prior to challenge reduced the severity of anaphylaxis. The levels of anti-BSA antibody which existed immediately prior to challenge were not affected by the heat treatments. These data demonstrate clearly that exogenous ACTH and a single, non-lethal heating episode, when applied 24 hours prior to the induction of anaphylaxis, reduced the severity of the symptoms associated with this particular hypersensitive reaction in the domestic chicken.

Release of rabbit aorta contracting substance (RCS) and prostaglandins induced by chemical or mechanical stimulation of guinea-pig lungs

1. Rabbit aorta contracting substance (RCS) and prostaglandins were released from guinea-pig isolated perfused lungs by gentle massage and also by infusion of Prosparol.2. RCS and prostaglandins were also released by infusion into the pulmonary artery of bradykinin, arachidonic and dihomo-gamma-linolenic acids or shock perfusate (containing RCS-releasing factor).3. Arachidonic and dihomo-gamma-linolenic acids caused a prolonged release of RCS and prostaglandins whereas bradykinin and shock perfusate gave a short-lasting output.4. RCS and prostaglandins, together with histamine were released when superfused chopped lung tissue was agitated.5. Challenge of sensitized guinea-pigs in vivo led to the release of an RCS-like substance into the carotid arterial blood.6. Intravenous injection of bradykinin into guinea-pigs also released an RCS-like substance.7. The release of RCS and prostaglandins was inhibited by aspirin or indomethacin in all experiments.8. RCS contracted all vascular tissues investigated and also rat stomach strip.9. The half-life of RCS was estimated as 1-2 minutes.

Mode of action of antirheumatic drugs

The concentrations of free and protein-bound L-tryptophan were measured in sera from normal subjects, patients with rheumatoid arthritis, pregnant women, and patients with jaundice. In the patients with rheumatoid arthritis receiving treatment with one or more antirheumatic drugs the percentage of the amino-acid bound to the circulating proteins was significantly depressed and in one patient returned to normal when therapy was stopped. Pregnancy and jaundice were also associated with raised free tryptophan and decreased bound tryptophan concentrations and bilirubin displaced the amino-acid from its binding sites on human serum proteins in vitro. It is suggested the behaviour of tryptophan mimics that of certain peptides which protect susceptible tissues against chronic inflammatory insults.

The displacement of L-tryptophan and dipeptides from bovine albumin in vitro and from human plasma in vivo by antirheumatic drugs

l-Tryptophan occurs in a protein-bound and an unbound form in serum from normal subjects. The amino-acid is displaced from its binding sites in vitro by salicylate, phenylbutazone, indomethacin, prednisolone, chloroquine and gold salts and is virtually absent in serum obtained from patients with rheumatoid arthritis receiving therapy with antirheumatic drugs. Some dipeptides bind to bovine albumin in vitro and are displaced by salicylate. All the drugs displace l-phenylalanyl-l-phenylalanine from its binding to normal human serum in vitro.

A comparison of an effect of different anti-inflammatory drugs on human platelets

Different doses of aspirin, indomethacin, paracetamol, benorylate, and sodium salicylate were taken by four volunteers. The minimal dose that altered a platelet function test and the persistence of this alteration at different dose levels were studied. Minute doses of indomethacin (0.035 mg/kg) were effective but the effect of even a large single dose did not persist. A tenth of the therapeutic dose of aspirin (1 mg/kg) was effective, and higher doses altered the platelets' function for several days. Benorylate in a high therapeutic dose gave aspirin-like results. Paracetamol and sodium salicylate were relatively inactive. The persistence of the aspirin effect may be related to the acetyl group. These findings are surveyed in relation to a general theory of the action of anti-inflammatory drugs.

The effect of sodium salicylate on the release of acid phosphatase activity from rat liver lysosomes in vitro

Salicylate, in concentrations up to 10mM, does not inhibit the activity of the acid phosphatase liberated from rat liver lysosomes. The release of the enzyme from lysosomal preparations incubated with the drug depends on the pH of the incubation medium, the duration of incubation and the concentration of salicylate. It is concluded that salicylate does not influence lysosomal stability in vivo.