Doxorubicin (DOX) is a topoisomerase II inhibitor commonly used in the treatment of several types of cancer. Despite its efficacy, DOX can potentially cause fatal adverse effects, like cardiotoxicity. This work aimed to assess the role of inflammation in DOX-treated infant and adult mice and its possible link to underlying cardiotoxicity. Two groups of CD-1 male mice of different ages (infants or adults) were subjected to biweekly DOX administrations, to reach a cumulative dose of 18.0 mg/kg, which corresponds approximately in humans to 100.6 mg/m² for infants and 108.9 mg/m² for adults a clinically relevant dose in humans. The classic plasmatic markers of cardiotoxicity increased, and that damage was confirmed by histopathological findings in both groups, although it was higher in adults. Moreover, in DOX-treated adults, an increase of cardiac fibrosis was observed, which was accompanied by an increase in specific inflammatory parameters, namely, macrophage M1 and nuclear factor kappa B (NF-κB) p65 subunit, with a trend toward increased levels of the tumor necrosis factor receptor 2 (TNFR2). On the other hand, the levels of myeloperoxidase (MPO) and interleukin (IL)-6 significantly decreased in DOX-treated adult animals. In infants, a significant increase in cardiac protein carbonylation and in the levels of nuclear factor erythroid-2 related factor 2 (Nrf2) was observed. In both groups, no differences were found in the levels of tumor necrosis factor (TNF-α), IL-1β, p38 mitogen-activated protein kinase (p38 MAPK) or NF-κB p52 subunit. In conclusion, using a clinically relevant dose of DOX, our study demonstrated that cardiac effects are associated not only with the intensity of the inflammatory response but also with redox response. Adult mice seemed to be more prone to DOX-induced cardiotoxicity by mechanisms related to inflammation, while infant mice seem to be protected from the damage caused by DOX, possibly by activating such antioxidant defenses as Nrf2.

Mandarin translation of Background and purpose: The relative contribution of distinct ecto‐nucleotidases to the modulation of purinergic signalling may depend on differential tissue distribution and substrate preference.Experimental approach: Extracellular ATP catabolism (assessed by high‐performance liquid chromatography) and its influence on [³H]acetylcholine ([³H]ACh) release were investigated in the myenteric plexus of rat ileumin vitro.Key results: ATP was primarily metabolized via ecto‐ATPDase (adenosine 5′‐triphosphate diphosphohydrolase) into AMP, which was then dephosphorylated into adenosine by ecto‐5′‐nucleotidase. Alternative conversion of ATP into ADP by ecto‐ATPase (adenosine 5′‐triphosphatase) was more relevant at high ATP concentrations. ATP transiently increased basal [³H]ACh outflow in a 2′,3′‐O‐(2,4,6‐trinitrophenyl)adenosine‐5′‐triphosphate (TNP‐ATP)‐dependent, tetrodotoxin‐independent manner. ATP and ATPγS (adenosine 5′‐[γ‐thio]triphosphate), but not α,β‐methyleneATP, decreased [³H]ACh release induced by electrical stimulation. ADP and ADPβS (adenosine 5′[β‐thio]diphosphate) only decreased evoked [³H]ACh release. Inhibition by ADPβS was prevented by MRS 2179 (2′‐deoxy‐N⁶‐methyl adenosine 3′,5′‐diphosphate diammonium salt, a selective P2Y₁antagonist); blockade of ADP inhibition required co‐application of MRS 2179 plus adenosine deaminase (which inactivates endogenous adenosine). Blockade of adenosine A₁receptors with 1,3‐dipropyl‐8‐cyclopentyl xanthine enhanced ADPβS inhibition, indicating that P2Y₁stimulation is cut short by tonic adenosine A₁receptor activation. MRS 2179 facilitated evoked [³H]ACh release, an effect reversed by the ecto‐ATPase inhibitor, ARL67156, which delayed ATP conversion into ADP without affecting adenosine levels.Conclusions and implications: ATP transiently facilitated [³H]ACh release from non‐stimulated nerve terminals via prejunctional P2X (probably P2X₂) receptors. Hydrolysis of ATP directly into AMP by ecto‐ATPDase and subsequent formation of adenosine by ecto‐5′‐nucleotidase reduced [³H]ACh release via inhibitory adenosine A₁receptors. Stimulation of inhibitory P2Y₁receptors by ADP generated alternatively via ecto‐ATPase might be relevant in restraining ACh exocytosis when ATP saturates ecto‐ATPDase activity.Mandarin translation of abstract