A chelate theory for the mechanism of action of aspirin-like drugs

The Puzzle of Aspirin and Iron Deficiency: The Vital Missing Link of the Iron-Chelating Metabolites

Acetylsalicylic acid or aspirin is the most commonly used drug in the world and is taken daily by millions of people. There is increasing evidence that chronic administration of low-dose aspirin of about 75-100 mg/day can cause iron deficiency anaemia (IDA) in the absence of major gastric bleeding; this is found in a large number of about 20% otherwise healthy elderly (>65 years) individuals. The mechanisms of the cause of IDA in this category of individuals are still largely unknown. Evidence is presented suggesting that a likely cause of IDA in this category of aspirin users is the chelation activity and increased excretion of iron caused by aspirin chelating metabolites (ACMs). It is estimated that 90% of oral aspirin is metabolized into about 70% of the ACMs salicyluric acid, salicylic acid, 2,5-dihydroxybenzoic acid, and 2,3-dihydroxybenzoic acid. All ACMs have a high affinity for binding iron and ability to mobilize iron from different iron pools, causing an overall net increase in iron excretion and altering iron balance. Interestingly, 2,3-dihydroxybenzoic acid has been previously tested in iron-loaded thalassaemia patients, leading to substantial increases in iron excretion. The daily administration of low-dose aspirin for long-term periods is likely to enhance the overall iron excretion in small increments each time due to the combined iron mobilization effect of the ACM. In particular, IDA is likely to occur mainly in populations such as elderly vegetarian adults with meals low in iron content. Furthermore, IDA may be exacerbated by the combinations of ACM with other dietary components, which can prevent iron absorption and enhance iron excretion. Overall, aspirin is acting as a chelating pro-drug similar to dexrazoxane, and the ACM as combination chelation therapy. Iron balance, pharmacological, and other studies on the interaction of iron and aspirin, as well as ACM, are likely to shed more light on the mechanism of IDA. Similar mechanisms of iron chelation through ACM may also be implicated in patient improvements observed in cancer, neurodegenerative, and other disease categories when treated long-term with daily aspirin. In particular, the role of aspirin and ACM in iron metabolism and free radical pathology includes ferroptosis, and may identify other missing links in the therapeutic effects of aspirin in many more diseases. It is suggested that aspirin is the first non-chelating drug described to cause IDA through its ACM metabolites. The therapeutic, pharmacological, toxicological and other implications of aspirin are incomplete without taking into consideration the iron binding and other effects of the ACM.

Synthesis, Characterization, Antimicrobial, Density Functional Theory, and Molecular Docking Studies of Novel Mn(II), Fe(III), and Cr(III) Complexes Incorporating 4-(2-Hydroxyphenyl azo)-1-naphthol (Az)

This work synthesized three new CrAz₂, MnAz₂, and FeAz₂ complexes and investigated them using IR, mass, UV spectroscopy, elemental analysis, conductivity and magnetic tests, and thermogravimetric analysis. The azo-ligand, 4-(2-hydroxyphenylAzo)-1-naphthol (Az), couples with metal ions via its nitrogen (in -N=N- bonds) and oxygen (in hydroxyl group) atoms, according to the IR spectra of these complexes. Through thermal examination (TG/TGA), the number and location of water in the complexes were also determined. Density functional theory (DFT) theory is applied to ameliorate the structures of the ligand (Az) and metal complexes and analyze the quantum chemical characteristics of these complexes. The antifungal and antibacterial activity of the ligand and its complexes opposed to several hazardous bacteria and fungi was investigated in vitro. Metal complexes were discovered to have a higher inhibitory impact on some organisms than the free ligand. The MnAz₂ complex exhibited the best activity among the studied materials, whereas the CrAz₂ complex had the lowest. The compounds' binding affinity to the E. coli (PDB ID: 1hnj) structure was predicted using molecular docking. Binding energies were calculated by analyzing protein-substrate interactions. These encouraging findings imply that these chemicals may have physiological effects and may be valuable for a variety of medical uses in the future.

Nitric oxide, afferent sensory nerves, and antioxidative enzymes in the mechanism of protection mediated by tricarbonyldichlororuthenium(II) dimer and sodium hydrosulfide against aspirin-induced gastric damage

BACKGROUND

Aspirin exerts side effects within the gastrointestinal tract. Hydrogen sulfide (H₂S) and carbon monoxide (CO) have been implicated in gastroprotection but the mechanism of beneficial action of these gaseous mediators against aspirin-induced damage has not been fully studied. We determined the involvement of afferent sensory neurons, calcitonin-gene-related peptide (CGRP), lipid peroxidation, and nitric oxide (NO) biosynthesis in gastroprotection of H₂S-releasing NaHS and CO-releasing tricarbonyldichlororuthenium(II) dimer (CORM-2) against aspirin-induced injury.

METHODS

Wistar rats with or without capsaicin-induced denervation of sensory neurons were pretreated with vehicle, CORM-2 (5 mg/kg intragastrically), or NaHS (5 mg/kg intragastrically) with or without capsazepine (5 mg/kg intragastrically) or N ^G-nitro-L-arginine (L-NNA, 20 mg/kg intraperitoneally). The areas of aspirin-induced lesions and gastric blood flow (GBF) were assessed by planimetry and laser flowmetry respectively. Gastric mucosal messenger RNA and/or protein expression of CGRP, heme oxygenase 1, inducible nitric oxide synthase, cyclooxygenase 2, interleukin-1β, glutathione peroxidase 1 (GPx-1), and superoxide dismutase was determined by real-time PCR or Western blot. Malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) content was determined by colorimetric assay.

RESULTS

Aspirin caused gastric lesions, decreased GBF, and raised MDA content, but pretreatment with NaHS and CORM-2 reduced these effects. Capsaicin-induced denervation or co-treatment with capsazepine reversed the gastroprotective and vasodilatory effects of NaHS but not those of CORM-2. L-NNA reversed NaHS-induced gastroprotection and partly reduced CORM-2-induced gastroprotection. NaHS and CORM-2 decreased MDA and 4-HNE content, restoring GPx-1 protein expression.

CONCLUSIONS

We conclude that H₂S- but not CO-mediated gastroprotection against aspirin-induced injury involves afferent sensory nerves and partly NO activity. NaHS and CORM-2 prevented aspirin-induced gastric mucosal lipid peroxidation via restoration of microcirculation and antioxidative GPx-1 protein expression.

Physicochemical studies on Ciclopirox olamine complexes with divalent metal ions

Ciclopirox olamine (CPO) metal complexes have been prepared and characterized using elemental analysis, infra red (IR), melting point and differential scanning calorimetry (DSC). Spectroscopic titration using molar ratio method indicated the occurrence of 1:1 complexes for CPO with almost all the examined metals. Physicochemical properties were also studied including aqueous solubility and apparent partition coefficient. Results showed that generally complex formation dramatically decreased the solubility and increased apparent partition coefficient. However, some metal complexes exhibited opposite effect. It could be concluded that complex formation can modify the solubility and apparent partition coefficient, which may suggest the use of complexes to manipulate the physicochemical properties of the drug.

Inhibition of the gravitropic bending response of flowering shoots by salicylic acid

The upward gravitropic bending of cut snapdragon, lupinus and anemone flowering shoots was inhibited by salicylic acid (SA) applied at 0.5 mM and above. This effect was probably not due to acidification of the cytoplasm, since other weak acids did not inhibit bending of snapdragon shoots. In order to study its mode of inhibitory action, we have examined in cut snapdragon shoots the effect of SA on three processes of the gravity-signaling pathway, including: amyloplast sedimentation, formation of ethylene gradient across the stem, and differential growth response. The results show that 1 mM SA inhibited differential ethylene production rates across the horizontal stem and the gravity-induced growth, without significantly inhibiting vertical growth or amyloplast sedimentation following horizontal placement. However, 5 mM SA inhibited all three gravity-induced processes, as well as the growth of vertical shoots, while increasing flower wilting. It may, therefore, be concluded that SA inhibits bending of various cut flowering shoots in a concentration-dependent manner. Thus, at a low concentration SA exerts its effect in snapdragon shoots by inhibiting processes operating downstream to stimulus sensing exerted by amyloplast sedimentation. At a higher concentration SA inhibits bending probably by exerting general negative effects on various cellular processes.

Desferrioxamine treatment increases the genomic stability of Ataxia-telangiectasia cells

Ataxia-telangiectasia (AT) is an autosomal recessive disorder characterized by genomic instability, chronic oxidative damage, and increased cancer incidence. Compared to normal cells, AT cells exhibit unusual sensitivity to exogenous oxidants, including t-butyl hydroperoxide (t-BOOH). Since ferritin releases labile iron under oxidative stress (which is chronic in AT) and labile iron mediates the toxic effects of t-butyl hydroperoxide, we hypothesized that chelation of intracellular labile iron would increase the genomic stability of AT cells, with and without exogenous oxidative stress. Here we report that desferrioxamine treatment increases the plating efficiency of AT, but not normal cells, in the colony forming-efficiency assay (a method often used to measure genomic stability). Additionally, desferrioxamine increases AT, but not normal cell resistance, to t-butyl hydroperoxide in this assay. Last, AT cells exhibit increased sensitivity to the toxic effects of FeCl(2) in the colony forming-efficiency assay and fail to demonstrate a FeCl(2)-induced G(2) checkpoint response when compared to normal cells. Our data indicates that: (1) chelation of labile iron increases genomic stability in AT cells, but not normal cells; and (2) AT cells exhibit deficits in their responses to iron toxicity. While preliminary, our findings suggest that AT might be, in part, a disorder of iron metabolism and treatment of individuals with AT with desferrioxamine might have clinical efficacy.

Effects of known and potential antioxidants on animal models of pathological processes (diabetes, gastric lesions, allergic bronchospasm)

Highly reactive oxygen-free radicals are implicated in the pathogenic process of various diseases. Using an animal model of diabetes (alloxan-induced hyperglycaemia in mice), a model of gastric ulcer (indomethacin-induced gastric lesion in rats), and a model of bronchial asthma (ovalbumin-induced allergic bronchospasm in guinea pigs), a potential therapeutic effect was tested in known antioxidant drugs (alpha-tocopherol, ubiquinone), the thio-compound mesna, and drugs with a possible antioxidant effect (substances derived from the ergoline structure: 6-hydroxynicotinic acid and 4-hydroxypyridine). The pre-treatment with ubiquinone and 6-hydroxynicotinic acid almost completely prevented alloxan-induced hyperglycaemia (94 and 93% inhibition of hyperglycaemia, respectively). A weaker effect was shown by alpha-tocopherol and 4-hydroxypyridine (31 and 27% inhibition of hyperglycaemia, respectively). Mesna negligibly increased hyperglycaemia. 32% and 21% inhibitions of the number of gastric lesions were shown after administration of 6-hydroxynicotinic acid and alpha-tocopherol, respectively. Other drugs, most markedly mesna, aggravated gastric lesions. The most marked protective effect on ovalbumin-induced bronchospasm was exerted by 6-hydroxynicotinic acid (the pulmonary ventilation was increased by 84% in comparison with control group), while mesna and (alpha-tocopherol had a weaker effect (amelioration by 50 and 51 %, respectively). Ubiquinone and 4-hydroxypyridine aggravated pulmonary ventilation. The most marked protective effect in the animal models used was shown by 6-hydroxynicotinic acid.

[Pharmacology of aspirin]

Aspirin (acetylsalicylic acid) is the best-known salicylate and belongs to the non steroid anti-inflammatory drug class. Despite wide use being made since more than 100 years, knowledge about mechanism of action and therapeutic issues continually evolves. The main mechanism of action is prostaglandin synthesis inhibition. This is achieved through inhibition of prostaglandin endoperoxide synthase (PGHS) or cyclooxygenase (COX) synthesis. Most of the therapeutic uses of aspirin are explained by this mechanism. Nevertheless aspirin uses change as time goes by: if the main one during the first fifty years was an analgesic, anti-pyretic and anti-inflammatory one, the last fifty years saw aspirin being used mainly as an anti-thrombotic agent, in primary and secondary thrombo-embolic prevention. Better knowledge of mechanism of action points today at, on one hand, more selective and therefore better tolerated molecules, and, on the other hand, at new therapeutic applications, such as anti-cancer and neurodegenerative diseases prevention.

A theory for the mechanism of homocysteine-induced vascular pathogenesis

An attempt is made to reveal the mechanism of homocysteine-induced vascular pathogenesis and a theory is developed on the basis of an analysis of available data. In the blood, homocysteine molecules, which possess the capacity of forming chelate complexes with metallic cations including calcium ions, interact with the calcium ions of the calcium-dependent cell adhesions/junctions of the vascular endothelium. Such an action results in the departure of calcium ions from some cell adhesions/junctions, causing the latter structures to dissociate and the vascular endothelium to be injured. While such factors as high levels of plasma calcium ion tend to restore the disrupted cell adhesions/junctions, other factors including blood pressure, bloodstream shearing force and high cholesterol/phospholipid ratio in the membranes are unfavorable to the repair. The injuries to the vascular endothelium may initiate inflammatory reactions. Over a long time, as such endothelial injuries occur repeatedly and, additionally, a small number of unrepaired cell adhesion/junction disruptions exacerbate slowly but progressively, inflammation may be constantly present. As the inflammation becomes excessive or uncontrollable, irreversible vascular pathogenesis takes place. Added to the condition is thrombosis caused by excessive coagulation activities triggered by the vascular endothelium injuries. In addition to the interference due to decreased membrane fluidity to the restoration of interrupted cell adhesions/junctions, cholesterol may further promote vascular pathogenesis (induced by either homocysteine or other factors) by impeding the detachment and departure of the foam cells from the vascular lesions. Such impediment is presumably related to an inhibitory effect on cell shape change and cell movement by the formation of a stable and rigid cytoskeleton-membrane network characterized by reduced membrane malleability and enhanced cytoskeleton-membrane association.

A theory for the mechanism of action of the alpha-hydroxy acids applied to the skin

A theory for the mechanism of action of alpha-hydroxy acids topically applied to the skin is proposed on the basis of an analysis with the experimental and clinical data. The alpha-hydroxy acids reduce the calcium ion concentration in the epidermis and remove calcium ions from the cell adhesions by chelation. This causes a loss of calcium ions from the cadherins of the desmosomes and adherens junctions, from the tight junctions, and possibly also from other divalent metallic cation-dependent cell adhesion molecules. The cell adhesions are thereby disrupted, resulting in desquamation. Desquamation is enhanced by cleavage of the endogenous stratum corneum chymotryptic enzyme on the cadherins, which are otherwise protected from proteolysis by conjugation with calcium ions. The decrease of calcium ion level so brought about in the epidermis also tends to promote cell growth and retard cell differentiation, giving rise to a younger-looking skin. This property of alpha-hydroxy acids suggests that caution should be taken with excessive and chronic use of these compounds and studies in this regard are warranted. Alpha-hydroxy acids may also possess anti-inflammatory capacities.

Aspirin-like drugs cause gastrointestinal injuries by metallic cation chelation

Aspirin-like (nonsteroidal anti-inflammatory) drugs may cause injuries including ulcers to the gastrointestinal tract by chelation of the divalent and/or multivalent metallic cations in the gastrointestinal mucus and mucosa, as suggested by the chemical properties of these drugs and supported by experimental and clinical data.