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Giorgio Minotti

Publications and source records attributed to Giorgio Minotti.

8 recordsLinked to original sources
PubMed2003

Anthracycline secondary alcohol metabolite formation in human or rabbit heart: biochemical aspects and pharmacologic implications.

Clinical use of the anticancer anthracyclines doxorubicin (DOX) and daunorubicin (DNR) is limited by development of cardiotoxicity upon chronic administration. Secondary alcohol metabolites, formed after two-equivalent reduction of a carbonyl group in the side chain of DOX or DNR, have been implicated as potential mediators of chronic cardiotoxicity. In the present study we characterized how human heart converted DOX or DNR to their alcohol metabolites DOXol or DNRol. Experiments were carried out using post-mortem myocardial samples obtained by ethically-acceptable procedures, and results showed that DOXol and DNRol were formed by flavin-independent cytoplasmic reductases which shared common features like pH-dependence and requirement for NADPH, but not NADH, as a source of reducing equivalents. However, studies performed with inhibitors exhibiting absolute or mixed specificity toward best known cytoplasmic reductases revealed that DOX and DNR were metabolized to DOXol or DNRol through the action of distinct enzymes. Whereas DOX was converted to DOXol by aldehyde-type reductase(s) belonging to the superfamily of aldo-keto reductases, DNR was converted to DNRol by carbonyl reductase(s) belonging to the superfamily of short-chain dehydrogenase/reductases. This pattern changed in cardiac cytosol derived from rabbit, a laboratory animal often exploited to reproduce cardiotoxicity induced by anthracyclines and to develop protectants for use in cancer patients. In fact, only carbonyl reductases were involved in metabolizing DOX and DNR in rabbit cardiac cytosol, although with different K(m) and V(max). Collectively, these results demonstrate that human myocardium convert DOX and DNR to DOXol or DNRol by virtue of different reductases, an information which may be of value to prevent alcohol metabolite formation during the course of anthracycline-based anticancer therapy. These results also raise caution on the preclinical value of animal models of anthracycline cardiotoxicity, as they demonstrate that the metabolic routes leading to DOXol in a laboratory animal may not be the same as those occurring in patients.

Alcohols↗
PubMed2003

Chronic cardiotoxicity of anticancer anthracyclines in the rat: role of secondary metabolites and reduced toxicity by a novel anthracycline with impaired metabolite formation and reactivity.

(1) The anticancer anthracycline doxorubicin (DOX) causes cardiomyopathy upon chronic administration. There is controversy about whether DOX acts directly or after conversion to its secondary alcohol metabolite DOXol. Here, the role of secondary alcohol metabolites was evaluated by treating rats with cumulative doses of DOX or analogues--like epirubicin (EPI) and the novel disaccharide anthracycline MEN 10755--which were previously shown to form less alcohol metabolites than DOX when assessed in vitro. (2) DOX induced electrocardiographic and haemodynamic alterations, like elongation of QalphaT or SalphaT intervals and suppression of isoprenaline-induced dP/dt increases, which developed in a time-dependent manner and were accompanied by cardiomegaly, histologic lesions and mortality. EPI caused less progressive or severe effects, whereas MEN 10755 caused essentially no effect. (3) DOX and EPI exhibited comparable levels of cardiac uptake, but EPI formed approximately 60% lower amounts of its alcohol metabolite EPIol at 4 and 13 weeks after treatment suspension (P<0.001 vs DOX). MEN 10755 exhibited the lowest levels of cardiac uptake; hence, it converted to its alcohol metabolite MEN 10755ol approximately 40% less efficiently than did EPI to EPIol at either 4 or 13 weeks. Cardiotoxicity did not correlate with myocardial levels of DOX or EPI or MEN 10755, but correlated with those of DOXol or EPIol or MEN 10755ol (P=0.008, 0.029 and 0.017, respectively). (4) DOX and EPI inactivated cytoplasmic aconitase, an enzyme containing an Fe-S cluster liable to disassembly induced by anthracycline secondary alcohol metabolites. DOX caused greater inactivation of aconitase than EPI, a finding consistent with the higher formation of DOXol vs EPIol. MEN 10755 did not inactivate aconitase, which was because of both reduced formation and impaired reactivity of MEN 10755ol toward the Fe-S cluster. Aconitase inactivation correlated (P<0.01) with the different levels of cardiotoxicity induced by DOX or EPI or MEN 10755. (5) These results show that (i) secondary alcohol metabolites are important determinants of anthracycline-induced cardiotoxicity, and (ii) MEN 10755 is less cardiotoxic than DOX or EPI, a behaviour attributable to impaired formation and reactivity of its alcohol metabolite.

Animals↗
PubMed2003

Cardiotoxic effects of anthracycline-taxane combinations.

The association of doxorubicin (DOX) and paclitaxel (PTX) is very active in breast cancer. Unfortunately, PTX may potentiate the cardiotoxic effects of anthracyclines: it causes nonlinear disposition of DOX and its metabolites, leading to persistant of elevated plasma concentrations of the anthracyclines. However, this pharmacokinetic interference is not sufficient to explain the enhanced cardiotoxicity of the combination. Recent data suggest that PTX stimulates the conversion of DOX to cardiotoxic metabolites (namely doxorubicinol) inside cardiomyocytes. Docetaxel (DTX) does not have a major influence on DOX plasma concentration because it does not interfere with its elimination. Clinical data suggest that DTX may not enhance anthracycline cardiotoxicity, but patients seldom received a total anthracycline dose compatible with increased risk. Furthermore, there are experimental data indicating that DTX can also stimulate the metabolism of DOX to toxic species in human heart.

Anthracyclines↗
PubMed2002

The iron regulatory proteins: targets and modulators of free radical reactions and oxidative damage.

Iron acquisition is a fundamental requirement for many aspects of life, but excess iron may result in formation of free radicals that damage cellular constituents. For this reason, the amount of iron within the cell is carefully regulated in order to provide an adequate level of a micronutrient while preventing its accumulation and toxicity. A major mechanism for the regulation of iron homeostasis relies on the post-transcriptional control of ferritin and transferrin receptor mRNAs, which are recognized by two cytoplasmic iron regulatory proteins (IRP-1 and IRP-2) that modulate their translation and stability, respectively. IRP-1 can function as a mRNA binding protein or as an aconitase, depending on whether it disassembles or assembles an iron-sulfur cluster in response to iron deficiency or abundancy, respectively. IRP-2 is structurally and functionally similar to IRP-1, but does not assemble a cluster nor exhibits aconitase activity. Here we briefly review the role of IRP in iron-mediated damage induced by oxygen radicals, nitrogen-centered reactive species, and xenobiotics of pharmacological and clinical interest.

Aconitate Hydratase↗
PubMed2002

Nitric oxide and peroxynitrite activate the iron regulatory protein-1 of J774A.1 macrophages by direct disassembly of the Fe-S cluster of cytoplasmic aconitase.

Posttranscriptional regulation of iron homeostasis involves, among other factors, a reversible conversion of the Fe-S enzyme cytoplasmic aconitase to a mRNA-binding iron regulatory protein (IRP-1) that lacks an Fe-S cluster. Previous studies have shown that aconitase/IRP-1 may be a target of *NO or peroxynitrite (ONOO(-)), formed after reaction of *NO with superoxide anion (O(2)(*-)); however, the mechanisms and consequences of such interactions have remained uncertain. In this study, recombinant aconitase/IRP-1 was exposed to SIN-1, whose thermal decomposition releases *NO and O(2)(*-). Results showed that SIN-1 was able to induce concomitant inactivation of aconitase and activation of IRP-1, attributable to cluster disassembly induced by ONOO(-). SIN-1 was used also in lysates of J774A.1 mouse macrophages grown under control conditions, or subjected to iron loading or starvation by treatment with hemin or desferrioxamine, respectively. Three lines of evidence confirmed that ONOO(-) activated IRP-1 by removing iron from the Fe-S cluster of cytoplasmic aconitase. First, IRP-1 activation was accompanied by iron release and loss of aconitase activity. Second, aconitase activity was recovered by reassembling Fe-S clusters with cysteine and ferrous ammonium sulfate. Third, iron release and IRP-1 activation were observed in lysates from control or iron-loaded macrophages, containing increasing levels of Fe-S clusters, but not in lysates from iron-starved macrophages, in which aconitase had already undergone cluster disassembly and switched to IRP-1. *NO was less efficient than ONOO(-) in attacking the Fe-S cluster of cytoplasmic aconitase; in fact, SIN-1-dependent iron release and IRP-1 activation were diminished by superoxide dismutase, which scavenged O(2)(*-) before it reacted with *NO to form ONOO(-). Under comparable conditions, however, both *NO and ONOO(-) inactivated an IRP-2 unable to assemble an Fe-S cluster. These results indicate that *NO and ONOO(-) may activate IRP-1 by attacking the Fe-S cluster of cytoplasmic aconitase, while also inactivating the cluster-deficient IRP-2. Such divergent actions offer clues to explain links between iron homeostasis and reactive nitrogen species in macrophages involved in inflammation or other pathophysiologic conditions.

Aconitate Hydratase↗
PubMed2002

Doxorubicin-dependent reduction of ferrylmyoglobin and inhibition of lipid peroxidation: implications for cardiotoxicity of anticancer anthracyclines.

Lipid peroxidation has been proposed to mediate cardiotoxicity induced by doxorubicin (DOX) and other anticancer anthracyclines; however, there have been reports showing that DOX can also inhibit lipid peroxidation. Here we characterized the effects of DOX on the oxo-ferryl moiety [Fe(IV)=O, Mb(IV)] of H(2)O(2)-activated myoglobin, a lipid oxidant likely formed in the heart during treatment with DOX. Mb(IV) was formed in vitro by reacting 100 microM H(2)O(2) with 50 microM horse heart metmyoglobin (Mb(III)). Spectral studies showed that DOX reduced Mb(IV) to Mb(III), half-maximal regeneration of Mb(III) occurring at approximately 18 microM DOX. Comparisons between DOX, its aglycone doxorubicinone, and other approved or investigational anthracyclines or model compounds (daunorubicin, idarubicin, aclarubicin, and naphthazarin), showed that DOX reduced Mb(IV) through the hydroquinone moiety of its tetracyclic ring. DOX inhibited Mb(IV)-dependent peroxidation of arachidonic acid, suppressing the formation of thiobarbituric acid-reactive substances with an IC(50) of approximately 18 microM. Lipid peroxidation was inhibited also by the hydroquinone-containing daunorubicin and idarubicin but not by the hydroquinone-deficient aclarubicin; moreover, neither simple hydroquinone nor other known Mb(IV) reductants (ascorbate, glutathione, and ergothioneine) reached measurable IC(50)s in a micromolar range. DOX-dependent inhibition of lipid peroxidation correlated with its ability to reduce Mb(IV) to Mb(III) in competition with arachidonic acid (r = 0.83, P = 0.029); it did not correlate with its ability to scavenge other free radical species [like e.g., peroxyl radicals generated through the thermal decomposition of 2,2'-azo-bis(2-amidinopropane)]. DOX reduced Mb(IV) and inhibited lipid peroxidation also when H(2)O(2), Mb(III) and arachidonic acid were reacted in cytosol of human myocardial biopsies, a model developed to predict the cardiotoxic mode of action of DOX in patients. These results illustrate "antioxidant" properties of DOX, mediated by reduction of Mb(IV) to Mb(III), and cast doubts on lipid peroxidation as a causative mechanism of anthracycline-induced cardiotoxicity.

Animals↗
PubMed2002

Anthracyclines.

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Animals↗