Ruttkay-Nedecky et al. 2013 — The role of metallothionein in oxidative stress

Ruttkay-Nedecky and colleagues at the Central European Institute of Technology and Mendel University in Brno, with co-authors from Masaryk University, Charles University, and University Hospital Motol in Prague, review the published literature on metallothionein (MT) as a small cysteine-rich heavy-metal-binding protein that participates in cellular protective responses against oxidative stress. The review compiles evidence from mammalian cell-line, transgenic mouse, and Drosophila knockout systems on MT’s structure, its role as a zinc reservoir and cysteine-thiol-mediated radical scavenger, its induction by oxidative and nitrosative stimuli, and its relevance to cancer and apoptosis. The paper reports no primary chemical or toxicological measurements; its value to the wiki is mechanistic — it organises the vocabulary used by the underlying cadmium-toxicology and zinc-homeostasis literature on which subsequent occurrence and exposure papers depend.

Why this matters

• The review summarises the structural basis for MT’s heavy-metal binding (two cysteine-cluster domains, α and β; 20 cysteine residues in mammalian MT-1; covalent thiolate binding of divalent metals) and identifies the three-binding-site β-domain and four-binding-site α-domain as the canonical mammalian MT fold (source p. 6046).
• It catalogues genetic evidence for MT-mediated cadmium protection: transgenic MT-overexpressing mice are protected from cadmium lethality and hepatotoxicity (refs 25, 26), and MT-1/MT-2 double-knockout mice are sensitised to cadmium toxicity. This is the load-bearing mechanism the cadmium page draws on when explaining biological detoxification.
• It positions MT as an inducible oxidative-stress response: hepatic MT-Zn content rises 5-fold and MT protein content rises 15-fold by 18 h after whole-body X-irradiation in rats (Shiraishi et al. ref 160), and liver MT rises 200–800 % above baseline after Cd, Mn, or Zn injection (Matsubara et al. refs 163, 164). These are the dose-response anchors for any future synthesis page that frames MT as an exposure biomarker.
• It introduces the MT redox cycle (Figure 4) — Zn-MT releases Zn under oxidising conditions (ROS, GSSG), forming MT-disulfide; reduction by GSH or selenium-dependent catalysis restores Zn-MT. This thiol-disulfide interchange is the chemical mechanism cited by the broader literature on MT-mediated heavy-metal sequestration and is repeated almost verbatim in the review-derived secondary literature.

Key concepts and structure

The review is organised into an introduction (Section 1), seven topical sections (Section 2 Metallothioneins; Section 3 Zinc as Signaling Compound and Antioxidant; Section 4 Zinc and MT; Section 5 The Role of MT in Cancer and Apoptosis; Section 6 Antioxidant Function of MT), and a brief conclusions section (Section 7). It cites 173 references spanning 1957 (Margoshes and Vallee’s founding cadmium-binding paper) to 2013.

Reactive oxygen and nitrogen species (source Section 1, Table 1, p. 6045)

The introduction summarises the ROS/RNS taxonomy underpinning oxidative stress (source Table 1 reproduced):

The review then frames the harmful effects of free radicals as balanced by antioxidant enzymes and non-enzymatic antioxidants, with oxidative damage to DNA, proteins, and lipids cited as a driver of cancer, atherosclerosis, arthritis, and neurodegenerative disease.

Metallothionein structure and isoforms (source Section 2, p. 6045–6047)

Mammalian MTs contain 61–68 amino acids of which 20 are cysteines. MTs bind zinc preferentially under physiological conditions but Zn is readily displaced by excess Cu²⁺ or Cd²⁺ (refs 21, 22). Four mammalian MT isoforms (MT-1, MT-2, MT-3, MT-4) and 13 MT-like human proteins are identified. Tissue expression patterns: MT-1 and MT-2 are present in almost all soft tissues; MT-3 is brain-dominant with additional expression in heart, kidneys, and reproductive organs; MT-4 is expressed in stratified squamous epithelia (oral epithelia, esophagus, upper stomach, tail, footpads, neonatal skin). In humans, the MT gene cluster on chromosome 16 contains 16 identified genes, of which five are pseudogenes. The active MT-I subset comprises MT-IA, -IB, -IE, -IF, -IG, -IH, -IM, and -IX; MT-1C, -1D, -1I, -1J, and 1L are pseudogenes not expressed in humans.

The mammalian MT three-dimensional structure (source Figure 1) is composed of two binding domains. The N-terminal β-domain has three binding sites for divalent ions; the C-terminal α-domain has the ability to bind four divalent metal ions. The Brno group’s reference sequence for human MT (reproduced in Figure 1) is MDPNCSCATDGSCSCAGSCKCKQCKCTSCKKSCCSCCPVGCAKCSQGCLCKEASDKCSCCA, with residues 1–29 in the β-domain and 30–61 in the α-domain.

Zinc as signalling compound and antioxidant (source Section 3, p. 6047–6049)

Zinc itself has no redox capacity but is described as a potent antioxidant agent operating through induction of MT expression and glutathione (GSH) synthesis, regulation of oxidant production, and association with cysteines (refs 45, 58–61). Metal-regulatory transcription factor 1 (MTF-1), a 753-amino-acid transcription factor, responds directly to free Zn²⁺ and initiates MT transcription by binding the metal-responsive element of the MT gene. The MTF-1 → MT autoregulatory loop is the principal Zn-homeostasis mechanism the review discusses. Zinc(II) supplementation protects primary rat endothelial cells from H₂O₂-induced cell death via increased transcription of glutamate-cysteine ligase (GCLC) and elevated GSH concentrations; conversely, zinc depletion decreases GCLC expression and GSH levels (ref 65). Zinc(II) is an integral component of up to 10 % of all human proteins (ref 67), including zinc-finger domains; Zn exchange between MT and zinc-finger transcription factors (refs 17, 71–77) is the proposed mechanism by which MT modulates DNA binding by estrogen receptor, SP1, TFIIIA, Gal4, and tramtrack zinc fingers.

Zinc and MT (source Section 4, p. 6048–6050)

MT functions as a zinc chaperone for metalloproteins and metal-dependent transcription factors. Thermodynamically, Zn–MT binding is stable, making MT an ideal in vivo Zn reservoir; how MT releases Zn to other molecules is the open mechanistic question the review surveys. Maret et al. (ref 76) demonstrated fast Zn exchange between MT isoforms 1 and 2 and between MT2 and the Zn cluster in the Gal4 transcription factor. Jacob et al. (ref 80) showed Zn transfer between MT and the apo-forms of E. coli alkaline phosphatase and bovine carboxypeptidase A. The GSH/GSSG ratio modulates the rate and number of Zn atoms transferred (refs 79, 81, 82): GSH inhibits Zn release in the absence of GSSG, indicating MT is stabilised at high cellular GSH concentrations; GSSG triggers Zn release. Under stress conditions, Zn release from MT occurs when nitric oxide or reactive oxygen species levels increase (refs 83–86). Treatment of lung fibroblasts with the NO donor S-nitrosocysteine increases intracellular labile Zn in wild-type but not MT-null fibroblasts (ref 84); sheep pulmonary artery endothelial cells show MT-mediated NO-induced changes in intracellular Zn(II) (ref 84); cultured pulmonary artery endothelial cells expressing a MT-GFP FRET sensor undergo conformational changes consistent with metal release from MT thiolate clusters in the presence of NO (refs 87–90).

MT in cancer and apoptosis (source Section 5, p. 6050–6052)

The review reports increased MT expression in human tumours of the breast, colon, kidney, liver, lung, nasopharynx, ovary, prostate, salivary gland, testes, thyroid, and urinary bladder (ref 91). MT expression in tumour tissues correlates mainly with proliferative capacity (ref 101). Exceptional cases: MT-I and MT-II are downregulated in hepatocellular carcinoma (ref 102) with concurrent intracellular Zn reduction, granulocyte increase, and lymphocyte decrease; MT1M is identified as a tumour suppressor in hepatocellular carcinoma with its promoter methylated in the majority of HCC tumours examined (Mao et al. ref 104); MT1F downregulation by loss of heterozygosity occurs in colon cancer tissue, and exogenous MT1F expression in colon cancer cell line RKO increases apoptosis and inhibits migration/invasion/adhesion (Yan et al. ref 105); DNA methylation of MT1E in malignant melanoma suggests MT1E is also a potential tumour suppressor (Faller et al. ref 106).

On apoptosis: MT plays a dual role, regulating intracellular Zn concentration and interacting with apoptosis-relevant proteins. Zn addition prevents DNA fragmentation and inhibits caspases and calcium-magnesium-dependent proteases (ref 116). Cellular Zn is described as an inhibitor of apoptosis; Zn depletion activates caspases-3, -8, and -9 (ref 119). Zn is required for structural stabilisation of p53 (refs 121–123); recombinant thionein (apo-MT) removes Zn from p53 in vitro and abrogates its DNA binding, an effect reversed by equimolar Zn supplementation. MT also regulates NF-κB: MT-1 and MT-2 regulate NF-κB level, activity, and cellular location (refs 133–136); MT interacts with the p50 subunit of NF-κB to increase NF-κB transactivation (ref 135), and MT overexpression upregulates NF-κB DNA binding (ref 137), implicated in the antiapoptotic effect of MT in some tumours.

Antioxidant function of MT (source Section 6, p. 6052–6056)

The principal claim is that MT functions as a free radical scavenger via its 20 cysteine sulfur atoms. The rate constant for the reaction of hydroxyl radical with MT is reported as approximately 340-fold higher than that with GSH (Thornalley and Vasak ref 138, using rabbit liver MT-1 against •OH and O₂⁻• produced by the xanthine/xanthine oxidase reaction; assayed in a cell-free system).

Specific cell-line and animal-model evidence:

• HL-60 human promyelocytic leukaemia cells induced with ZnCl₂ for 24 h require a 1.65:1 ratio of H₂O₂ concentrations to reduce cell survival by 50 % in Zn-MT-induced cells compared with normal cells; Zn-MT-induced cells are more resistant to oxidative stress caused by H₂O₂ (Quesada et al. ref 148).
• V79 Chinese hamster cells with zinc-induced MT and concomitant GSH increase are more resistant to DNA-strand scission by H₂O₂ than parental cells (Chubatsu et al. ref 149).
• NIH 3T3 cells transfected with mouse metallothionein-I gene (NIH3T3/MT) show a four-fold increase in intracellular MT and six-fold greater resistance than antisense-transfected (NIH3T3/TM) cells to tert-butyl hydroperoxide cytotoxicity; NIH3T3/MT homogenates more effectively scavenge in vitro phenoxyl radicals by electron spin resonance (Schwarz et al. ref 142).
• In rats, Zn pre-injection increases renal cortex MT content and ameliorates gentamicin-induced proximal tubular necrosis and acute renal failure; malondialdehyde and hydroxyl radical production in PT of Zn-preinjected rats is significantly lower than in normal and saline-pre-injected rats (Du et al. ref 143).
• In rats, subcutaneous paraquat (PQ) increases MT-I concentration linearly with dose in lung at 24 h post-injection; liver MT-I plateaus at 30 mg/kg body weight; kidney MT-I does not increase even at high PQ doses; Zn is the principal metal bound to MT in liver (Sato et al. ref 158).
• Whole-body X-irradiation increases hepatic MT-Zn content five-fold and MT protein content 15-fold by 18 h post-irradiation in rats (Shiraishi et al. ref 160).
• In mice with MT-I transgene (56 copies) and elevated tissue MT, no protection against gamma-radiation toxic effects is observed (Liu et al. ref 165), indicating MT-mediated radioprotection is dose- and context-dependent.
• Pretreatment of mice with cadmium, manganese, or zinc to induce hepatic MT raises liver MT levels approximately 200–800 % above baseline (Matsubara et al. refs 163, 164). Mouse normal liver MT level is reported as 20 µg/g tissue; this increases to up to 70 µg/g tissue at 6.3 Gy irradiation.

Transgenic mouse evidence for MT antioxidant action: cardiac-specific MT-overexpressing transgenic mice are protected against doxorubicin chronic cardiotoxicity (Sun et al. ref 166), ischemia/reperfusion-induced myocardial apoptosis (Kang et al. ref 167), streptozotocin-induced diabetic cardiomyopathy with associated superoxide generation and 3-nitrotyrosine formation suppressed only in transgenic mice (Cai et al. ref 168), alcohol-induced cardiac hypertrophy and fibrosis where MT-null mice are sensitised (Wang et al. ref 169), and angiotensin II-induced apoptosis/nitrosative damage/membrane translocation of NOX subunit p47phox (Zhou et al. ref 171).

A Drosophila melanogaster MT family knockout (MtnA/MtnB/MtnC/MtnD; Egli et al. ref 172) produces viable flies highly sensitive to copper, cadmium, and to a lesser extent zinc load during development; MT expression is particularly important for male viability, with adult males lacking MTs showing severely reduced lifespan attributable to Cu-mediated oxidative stress.

Methods (brief)

The paper is a narrative review with no original experimental work, no primary chemical or biological measurements, and no analytical methods of its own. The reference list contains 173 entries spanning 1957 (Margoshes and Vallee’s founding cadmium-binding paper) to 2013. The review does not declare a formal search strategy, inclusion/exclusion criteria, PRISMA flow, or risk-of-bias assessment — it is a narrative review.

The journal (International Journal of Molecular Sciences, MDPI) is open-access; the article is published under CC BY 3.0. Funding: GA CR P301/10/0356, DOC CEITEC.02/2012, CEITEC CZ.1.05/1.1.00/02.0068, and project for conceptual development of research organisation 00064203. Conflicts of interest: the authors declare none. Received 14 January 2013; revised 14 February 2013; accepted 20 February 2013; published 15 March 2013.

Implications

• Certification: The review contributes no occurrence data and no exposure data, so it does not move any HMTc threshold-setting work. It is mechanistic background for any future mitigation chapter and for the cadmium-toxicology section of the cadmium page.
• App: No routing to ingredient or product pages. This source contributes background reading for cadmium specifically — MT-mediated biological detoxification, MT induction by Cd exposure, and the MT redox cycle — but does not feed any contamination-occurrence or exposure-assessment downstream.
• Courses: Useful as a single-source orientation to MT redox biology and the MT–zinc–oxidative-stress axis for an educator-audience module on heavy-metal cellular handling. Should not be cited as the authority for any specific quantitative claim; trace claims to their primary references first.
• Microbiome: Marginal. The review does not engage the gut microbiome or the heavy-metal-microbiome axis. WikiBiome federation is unlikely to draw on this source.

Limitations

This is a narrative review with no declared search strategy, no inclusion or exclusion criteria, no PRISMA flow, and no risk-of-bias assessment. Quantitative claims (the 340-fold hydroxyl-radical reaction rate constant versus GSH, the four-fold MT increase and six-fold cytotoxicity resistance in NIH3T3/MT cells, the 200–800 % liver MT elevation after Cd/Mn/Zn pretreatment, the 5-fold hepatic MT-Zn and 15-fold MT protein increase 18 h post-X-irradiation, the 1.65:1 H₂O₂-concentration ratio in HL-60 Zn-MT cells) are reported with attribution to single primary references but without consistent context (assay conditions, replicate counts, dose-response framing) and should be traced to the underlying primary papers before propagation to downstream synthesis pages. Coverage of arsenic, mercury, lead, nickel, and chromium is essentially absent: the review focuses on cadmium as the canonical MT substrate, with copper and zinc treated as physiological-essential context. Speciation (iAs vs tAs; MeHg vs tHg; Cr-III vs Cr-VI) is not addressed. The review’s claims about MT as a tumour biomarker and its role in chemotherapy resistance are consistent with the wider 2013 oncology literature but represent the authors’ interpretation of heterogeneous primary studies rather than a meta-analytic synthesis.

Wiki pages this source may touch

• cadmium
• remediation-evidence

Verification notes

Existing-page check. DOI grep (10.3390/ijms14036044), raw_handle grep (MFK_11-the-role-of-metallothionein-in-oxidative-stress), and cite-key glob (ruttkay-nedecky2013-*) over wiki/sources/ on 2026-06-08 returned no hits. This is a NEW source page — no prior version to merge-enhance. The novelty CSV at data/evidence/june8-kimi-novelty-2026-06-08.csv confirms this PDF as novel with no near-duplicate, and lists an identical-content PDF at Kimi_Agent_Heavy Metal Peptide PDFs/heavy_metals_peptides/11_The_Role_of_Metallothionein_in_Oxidative_Stress.pdf (same sha256) flagged duplicate_in_folder; that sibling will be skipped by the manual-fetch tracker.

Evidence tier. B (secondary narrative review). The paper reports no primary measurements and declares no systematic search strategy. A-tier is reserved for primary peer-reviewed studies and authoritative agency monographs; this is neither. The review is published in a Scopus/Web of Science-indexed open-access journal (Int. J. Mol. Sci., MDPI) and is highly cited in the MT mechanistic literature, supporting B over C.

Metals frontmatter. The review explicitly discusses Cd as the canonical MT-binding heavy metal (Sections 2, 5, 6) — cadmium is named in the founding 1957 Margoshes-Vallee paper, in transgenic MT protection experiments (refs 25, 26), and in the MT-Mn-Zn induction comparison (refs 163, 164). Cu and Zn are extensively discussed as physiological essential ions and are not on the HMTc 10-analyte list. Pb, iAs, tAs, MeHg, tHg, Ni, Cr-VI, Al, Sn are not addressed substantively in this review (Mn appears in the Matsubara induction series but is also not on the HMTc list). From the HMTc 10-analyte priority list, only Cd is recorded in the metals: frontmatter.

Ingredients, products, matrices, jurisdictions frontmatter. All empty. The source measures nothing in any food, beverage, personal-care, or environmental sampling matrix; it reviews MT biology and oxidative-stress mechanism. No ingredients: slug applies (the experimental systems are cell lines, transgenic mice, and Drosophila, none of which is a food ingredient). No products: slug applies. No matrices: slug applies (the only “matrix” framing is liver/kidney/lung tissue in rodent toxicology models, which is exposure-route framing rather than HMI food-matrix sampling). No jurisdiction applies (the literature scope is international; authors are based in the Czech Republic but no national regulatory framework is applied).

Sample size. Null. This is a review with no sampling frame of its own.

Brand firewall (Part 12). No brand names appear in the source. Cell line names (HL-60, NIH 3T3, V79, HeLa, Hep3B, RKO, PC12, MeWo, Meth-A, MCF-7, etc.) and reagent names (S-nitrosocysteine, tert-butyl hydroperoxide, paraquat, doxorubicin, streptozotocin, 5-fluorouracil, dexamethasone, ZnCl₂) are scientific-method materials per the Exception 2 carve-out and are preserved. No firewall action required.

HMTc firewall (Part 2). The review contains no HMTc-threshold language, no “consistent with the literature consensus” framing in either direction, and no consumer-audience risk advisories. The cancer/apoptosis sections are presented as basic-science mechanism, not as cadmium-exposure risk-assessment claims that could move HMTc thresholds. No firewall action required.

Scope fit. This paper is in scope per the 2026-06-02 commit 3f47f95 — scope: mitigation/remediation is in-scope, not a skip. The “Black Market Peptide Metal Survey” folder context is Karen’s peptide-metal literature harvest. This source is mechanistic background for cadmium biological handling and the MT-as-scavenger thesis; it does not address peptide-product contamination but does inform the broader metals-and-peptides programme.

Date arithmetic. Received 14 January 2013, revised 14 February 2013, accepted 20 February 2013, published 15 March 2013 — all consistent with the year frontmatter (2013) and the citation. Article DOI 10.3390/ijms14036044 resolves to Int. J. Mol. Sci. 2013, Vol 14, pp. 6044–6066.

Audit subagent (2026-06-08) verdict: REVISE. Five checks (numerical fidelity, slug vocabulary, speciation/methods, brand firewall, HMTc firewall) returned ✅✅✅✅✅ at the body level with three ⚠️ findings and no ❌. (1) The Why-this-matters bullet compressed Shiraishi et al.’s two distinct endpoints (5-fold MT-Zn content; 15-fold MT protein content) into a single ambiguous “5–15-fold” range; verified against PDF p. 6054 (“the hepatic MT-Zn content increased five-fold, and MT protein content increased 15-fold by 18 h following irradiation”) — the body section already had the two-endpoint phrasing; the bullet has been rewritten to mirror it. (2) The MT-redox-cycle bullet contained a self-referential wikilink [[ruttkay-nedecky2013-metallothionein-oxidative-stress]]-derived secondary literature that was a copy-paste template artifact; removed, replaced with “review-derived secondary literature”. (3) The auditor flagged [[mitigation/remediation-evidence]] as outside the taxonomy snapshot’s vocabulary; verified against wiki/mitigation/remediation-evidence.md (which exists) — finding is a false positive because the taxonomy snapshot scopes ingredients/products/metals/regulations as the auditor’s drafting vocabulary, not the full wiki section index; the mitigation/ subtree is a legitimate routing destination (same wikilink form is used in the sibling yang2024-metallothionein-comprehensive-review page). No change applied on finding (3).

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.