The inhibitory effect of salicylate on the acetylation of human albumin by acetylsalicylic acid

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.

Some aspect of the interactions of adriamycin with human serum albumin

The interaction of adriamycin with human serum albumin (HSA) has been studied by absorption, CD, fluorescence spectroscopy, and quantitative precipitating HSA-antibody test. Our results demonstrate that adriamycin react with HSA and the binding to the protein molecule has a very distinct influence on the stability of ADR in aqueous solutions. The drug molecule binds protein as a monomer. The structural studies have shown the conformational change of HSA modified by adriamycin. The binding of ADR lowers the helicity of the native protein of ca. 15% and ca. 10% in the case of acHSA. The quantitative precipitating test supports distinct changes in the conformation upon ADR binding that decreases the ability of HSA to precipitate with its antibody.

Protein binding investigation by difference circular dichroism: native and acetylated human serum albumins

A modified albumin was prepared by selective reaction of Lys199 with acetyl salicylic acid. Protein binding investigation was carried out on native and modified proteins by difference circular dichroism (delta CD). Acetylation of Lys199 reduces significantly the effects of the interaction between drugs in the stereoselective HSA binding at specific binding areas.

Characterization of the binding sites for dicarboxylic acids on bovine serum albumin

Dicarboxylic acids are prominent features of several diseases, including Reye's syndrome and inborn errors of mitochondrial and peroxisomal fatty acid oxidation. Moreover, dicarboxylic acids are potentially toxic to cellular processes. Previous studies [Tonsgard, Mendelson & Meredith (1988) J. Clin. Invest. 82, 1567-1573] demonstrated that long-chain dicarboxylic acids have a single high-affinity binding site and between one and three lower-affinity sites on albumin. Medium-chain-length dicarboxylic acids have a single low-affinity site. We further characterized dicarboxylic acid binding to albumin in order to understand the potential effects of drugs and other ligands on dicarboxylic acid binding and toxicity. Progesterone and oleate competitively inhibit octadecanedioic acid binding to the single high-affinity site. Octanoate inhibits binding to the low-affinity sites. Dansylated probes for subdomain 2AB inhibit dodecanedioic acid binding whereas probes for subdomain 3AB do not. In contrast, low concentrations of octadecanedioic acid inhibit the binding of dansylated probes to subdomain 3AB and 2AB. L-Tryptophan, which binds in subdomain 3AB, inhibits hexadecanedioic acid binding but has no effect on dodecanedioic acid. Bilirubin and acetylsalicylic acid, which bind in subdomain 2AB, inhibit the binding of medium-chain and long-chain dicarboxylic acids. Our results suggest that long-chain dicarboxylic acids bind in subdomains 2C, 3AB and 2AB. The single low-affinity binding site for medium-chain dicarboxylic acids is in subdomain 2AB. These studies suggest that dicarboxylic acids are likely to be unbound in disease states and may be potentially toxic.

Conformational changes of human serum albumin in vivo induced by free fatty acids as studied by Fourier transform infrared spectroscopy

Binding of free fatty acids (FFA) to human serum albumin (HSA) was studied by Fourier transform infrared (FT-IR) spectroscopy. Six volunteers ran a marathon race in order to induce changes in their basal plasma FFA levels. Three volunteers were well-trained and three untrained. The non-deconvolved HSA spectra show two types of spectra: the first one includes the untrained runners, who, after the run, display noticeable changes in the absorbance intensity of the amide I band, which also shifts to higher frequencies. The second one includes the well-trained subjects who exhibit few changes after the race. Examination of the deconvolved spectra of HSA shows two types of spectra, as well: the first class displays important decreases in the absorbance of the component assigned to alpha-helix after the race, together with a gradual growth of the two components that can be assigned to turns. The second class, which includes the well-trained subjects, exhibits few changes after the run. These data are interpreted in terms of conformational changes due to a less ordered alpha-helix state of HSA after FFA binding, while the emergence of components assigned to turns may reflect the exposure of several histidine residues to the solvent (which are buried in HSA when FFA/HSA less than 4). Our data are consistent with the Karush model of FFA to HSA binding.

Influence of aspirin and iron(III) tetrasulfonated phthalocyanine on bilirubin binding by human serum albumin

The interaction of bilirubin with aspirin-modified human serum albumin (HSA) and the influence of iron tetrasulfonated phthalocyanine on bilirubin binding by the native protein has been studied by difference spectroscopy and circular dichroism measurements. Spectroscopic studies of the systems containing bilirubin and aspirin-modified HSA compared to the analogous systems with the native protein have shown that selective acetylation of albumin at lysine 199 inhibits bilirubin binding by this protein. In both cases, interaction between bilirubin and albumin leads to complex formation at a molar ratio of ligand to protein of 2:1. The studies of the reaction of bilirubin with fragments of albumin produced by reaction with CNBr have demonstrated that one of the strong bilirubin binding sites is located in the M fragment and is close to the high-affinity binding site of aspirin. The other one was found in fragment C. Acetylation of albumin brings about marked conformational change in the protein, which probably accounts for the decrease in its ability to react with anti-HSA antibody. Bilirubin does not change the secondary structure of albumin but, like aspirin, lowers its antigenicity. It has been suggested that the decrease in antigenic properties in this case results from cooperation of the closely neighboring antigenic and bilirubin-binding sites. The studies of the influence of iron(III) tetrasulfonated phthalocyanine on bilirubin binding by HSA suggest that there is no competition between strong sites for iron(III) tetrasulfonated phthalocyanine and bilirubin, but these compounds compete for some of the weaker sites.

Comparative analgesic and anti-inflammatory properties of sodium salicylate and acetylsalicylic acid (aspirin) in rheumatoid arthritis

1. Enteric coated sodium salicylate 4.8 g daily was compared with the same dose of enteric coated aspirin in 18 patients with rheumatoid arthritis. 2. After an initial washout period lasting 3 days, patients were randomly allocated to treatment with sodium salicylate or aspirin. After 2 weeks the two treatments were crossed over. 3. Pain relief, reduction in articular index of joint tenderness, increase in grip strength, decrease in digital joint circumference and patients' assessment showed significant improvement with both treatments compared with the washout period. No significant differences were found between the two therapies. 4. No correlation was found in the degree of improvement in any of the clinical outcomes and the salicylate concentrations at steady state.

Interaction of salicylates and other non-steroidal anti-inflammatory agents in rats as shown by gastro-ulcerogenic and anti-inflammatory activities, and plasma concentrations

The interaction of salicylates and other non-steroidal anti-inflammatory drugs was studied in rats. Concurrent oral administration of sodium salicylate (SS) or salicylic acid (SA) and indomethacin (IND) significantly reduced the gastro-ulcerogenicity and the plasma concentrations of IND. Acetylsalicylic acid (ASA) failed to do so. IND had no significant influence on plasma concentrations of SA. Simultaneous administration of SS and IND intraperitoneally or subcutaneously showed the same pattern of interaction as for oral administration. Concurrent oral administration of SS and IND exerted similar anti-inflammatory activity as the single drugs. SS significantly antagonized the ulcerogenicity of ibuprofen and tended to antagonize the ulcerogenic activity of ASA, phenylbutazone, tolfenamic acid and naproxen. The results suggest that in rats SS and SA (but not ASA) interact with IND concerning both gastro-ulcerogenicity and plasma concentrations of IND (but not of SA) and that the interaction is systemic in nature. We propose that the ulcerogenic interaction might be explained partly by the reduced IND plasma concentrations and partly by a weaker inhibition by SS of the prostaglandin system in the rat stomach.

Modification of human serum albumin with N-(2,5-dinitro-4-fluorophenyl)-4-amino-2,2,6,6-tetramethyl-piperidinooxy radical

Human serum albumin has been treated with the spin-labeling reagent indicated in the title. Ultraviolet spectral studies of the protein so modified suggest that reaction takes place at lysine and tyrosine sidechains; kinetic experiments indicate that there are two especially reactive amino groups of the protein which are preferentially modified. Evidence is presented that these groups include the one acetylated by aspirin (Lys-199) or those arylated by 2.6-dinitro-4-trifluoromethylbenzenesulfonate. Esr experiments show that bound spin labels have about the same correlation time expected for overall tumbling of the protein; ESR observations indicate that molecular freedom near the spin labels is not increased when the protein is transferred to 8 M urea.

Reactions of 2,6-dinitro-4-trifluoromethylbenzenesulfonate with human serum albumin

The reaction of the title compound with human serum albumin has been examined at various concentrations of the sulfonate. Kinetic data suggest that there are two highly reactive lysine amino groups on the protein, five lysine residues which are less reactive and an undetermined number of additional nucleophilic groups that react very slowly with the reagent at pH 7.5. One of the rapidly reacting lysines is tentatively identified as lysine-199 in the protein sequence. Fluorine NMR experiments indicate the presence of tight binding sites on the protein for the sulfonate which are not near reactive functional groups.

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.

Functional modification of indole binding site with indomethacin congeners

Indomethacin and four congeners were shown by equilibrium dialysis to interfere with the binding of L-tryptophan at the primary indole binding site on defatted human serum albumin. Incubation of albumin with 1-(p-bromoacetamidobenzovl)- and 1-(m-bromoacetamidobenzoyl)-5-methoxy-2-methyl-3-indolylacetic acid functionally modified this site, decreasing the availability of the site for the binding of L-tryptophan. Incubation in the presence of a large excess of L-tryptophan resulted in the partial protection of the site from modification by 1-(m-bromoacetamidobenzoyl)-5-methoxy-2-methyl-3-indolylacetic acid.