Oxidation of anthracyclines by peroxidase metabolites of salicylic Acid

A histopathological and stereological study of the effects of acetylsalicylic acid on doxorubicin-induced hepatotoxicity in mice

Doxorubicin (Dox) is an anthracycline antibiotic with antineoplastic activity. Acetylsalicylic acid (Asa) is recommended for use as a prophylactic for thromboembolism during treatment of cancers. We investigated liver toxicity due to combined use of Dox and Asa in chemotherapy regimens. We used 140 Swiss albino mice divided into four main groups: control, Dox, Asa, and Dox + Asa. Each group was subdivided into seven subgroups based on time of sacrifice, i.e., 6, 12, 24, 48 h and 7, 14, 21 days. Quantitative and histopathological changes in liver were assessed by light microscopy and stereology. The portal triad area of the Dox and Dox + Asa groups was increased significantly compared to controls at 6 h, whereas in the Asa group, the means were similar to controls. Assessment of histopathology indicated an increased time-dependent degeneration and necrosis of liver tissues in mice in the Dox and Dox + Asa groups. The protective effects of Asa were not evident in Dox + Asa group. When Dox and Asa were administered together, degenerative changes were greater than for in the group that was given Dox alone. We found that Asa and Dox combined therapy increased tissue damage.

The underlying factors that explain why nucleophilic reagents rarely co-elute with test chemicals in the ADRA

The Amino acid Derivative Reactivity Assay (ADRA) is an in chemico alternative to animal testing for skin sensitization potential that uses two different nucleophilic reagents and it is known that ADRA hardly exhibts co-elution compared with the Direct Peptide Reactivity Assay (DPRA) based on the same scientific principles. In this study, we have analyzed the factors underlying why co-elution, which is sometimes an issue during DPRA testing, virtually never occurs during ADRA testing. Chloramine T and dimethyl isophthalate both exhibited co-elution during DPRA testing, but when quantified at both DPRA's 220 nm and ADRA's 281 nm, we found that when the later detection wavelength was used, these test chemicals produced extremely small peaks that did not interfere with quantification of the peptides. And although both salicylic acid and penicillin G exhibited co-elution during DPRA testing, when tested at a concentration just 1% of that used in DPRA, the very broad peak produced at the higher concentration was reduced significantly. However, both these test chemicals exhibited very sharp peaks when the pH of the injection sample was adjusted to be acidic. Based on these results, we were able to clarify that the reasons why nucleophlic reagents hardly co-elute with test chemicals during ADRA testing are depend on the following three major reasons: (1)differences in the detection wavelength, (2)differences in test chemical concentrations in the injection sample, (3)differences in composition of the injection solvent.

Sulfosalicylic acid/Fe3+ based nanoscale coordination polymers for effective cancer therapy by the Fenton reaction: an inspiration for understanding the role of aspirin in the prevention of cancer

A new type of pH-responsive nanoscale coordination polymer for ROS-enhanced cancer therapy.

The electrochemistry of quinizarin revealed through its mediated reduction of oxygen

After 35 years the hunt for improved anthracycline antibiotics is unabated but has yet to achieve the levels of clinical success desired. Electrochemical techniques provide a large amount of kinetic and thermodynamic information, but the use of such procedures is hindered by issues of sensitivity and selectivity. This work demonstrates how by harnessing the mechanism of catalytic reduction of oxygen by the quinone functionality present within the anthracycline structure it is possible to study the reactive moiety in nanomolar concentration. This methodology allows electrochemical investigation of the intercalation of quinizarin into DNA and, in particular, the quinone oxidation and degradation mechanism. The reversible reduction of the quinizarin, which in the presence of oxygen leads to the formation of reactive oxygen species, is found to occur at -0.535 V (vs. SCE) pH 6.84 and the irreversible oxidation leading to the molecules degradation occurs at +0.386 V (vs. SCE) pH 6.84.

Doxorubicin inhibits oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) by a lactoperoxidase/H(2)O(2) system by reacting with ABTS-derived radical

The effect of doxorubicin on oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) by lactoperoxidase and hydrogen peroxide has been investigated. It was found that: (1) oxidation of ABTS to its radical cation (ABTS*(+)) is inhibited by doxorubicin as evidenced by its induction of a lag period, duration of which depends on doxorubicin concentration; (2) the inhibition is due to doxorubicin hydroquinone reducing the ABTS*(+) radical (stoichiometry 1: 1.8); (3) concomitant with the ABTS*(+) reduction is oxidation of doxorubicin; only when the doxorubicin concentration decreases to a near zero level, net oxidation of ABTS could be detected; (4) oxidation of doxorubicin leads to its degradation to 3-methoxysalicylic acid and 3-methoxyphthalic acid; (5) the efficacy of doxorubicin to quench ABTS*(+) is similar to the efficacy of p-hydroquinone, glutathione and Trolox C. These observations support the assertion that under certain conditions doxorubicin can function as an antioxidant. They also suggest that interaction of doxorubicin with oxidants may lead to its oxidative degradation.

Inactivation of anthracyclines by serum heme proteins

We have previously shown that the anticancer agent doxorubicin undergoes oxidation and inactivation when exposed to myeloperoxidase-containing human leukemia HL-60 cells, or to isolated myeloperoxidase, in the presence of hydrogen peroxide and nitrite. In the current study we report that commercial fetal bovine serum (FBS) alone oxidizes doxorubicin in the presence of hydrogen peroxide and that nitrite accelerates this oxidation. The efficacy of inactivation was dependent on the concentration of serum present; no reaction was observed when hydrogen peroxide or serum was omitted. Peroxidase activity assays, based on oxidation of 3,3',5,5'-tetramethylbenzidine, confirmed the presence of a peroxidase in the sera from several suppliers. The peroxidative activity was contained in the >10000 MW fraction. We also found that hemoglobin, a heme protein likely to be present in commercial FBS, is capable of oxidizing doxorubicin in the presence of hydrogen peroxide and that nitrite further stimulates the reaction. In contrast to intact doxorubicin, the serum + hydrogen peroxide + nitrite treated drug appeared to be nontoxic for PC3 human prostate cancer cells. Together, this study shows that (pseudo)peroxidases present in sera catalyze oxidation of doxorubicin by hydrogen peroxide and that this diminishes the tumoricidal activity of the anthracycline, at least in in vitro settings. Finally, this study also points out that addition of H2O2 to media containing FBS will stimulate peroxidase-type of reactions, which may affect cytotoxic properties of studied compounds.