Alphabetical definitions of specialist terms used throughout this wiki. Where a full concept page exists, the term links to it.
—-
AhR (aryl hydrocarbon receptor) — A ligand-activated transcription factor that senses microbial metabolites (especially indoles from tryptophan metabolism) and environmental pollutants, regulating immune responses, barrier integrity, and xenobiotic metabolism.
AMR (antimicrobial resistance) — The ability of microorganisms to withstand antimicrobial agents. In this wiki, AMR frequently arises through co selection, where metal resistance genes on mobile genetic elements carry antibiotic resistance genes alongside them. See antimicrobial resistance.
BCAA (branched-chain amino acids) — Leucine, isoleucine, and valine — essential amino acids whose circulating levels are elevated in metabolic syndrome, type 2 diabetes, and obesity, partly driven by gut microbial metabolism.
BBB (blood-brain barrier) — The selectively permeable endothelial barrier separating circulating blood from CNS extracellular fluid. Disrupted by heavy metals, inflammation, and neuroinflammation, permitting neurotoxic entry. See blood brain barrier.
BSH (bile salt hydrolase) — A microbial enzyme that deconjugates primary bile acids, initiating their transformation into secondary bile acids. Central to bile acid metabolism and the enterohepatic circulation.
CagA — The cytotoxin-associated gene A oncoprotein of helicobacter pylori, injected into gastric epithelial cells via the type IV secretion system. CagA hijacks host signaling (SHP-2, Grb2) to disrupt polarity and proliferation control, driving gastric cancer.
Calprotectin — A calcium- and zinc-binding protein (S100A8/S100A9 heterodimer) released by neutrophils. Fecal calprotectin is the gold-standard non-invasive biomarker for intestinal inflammation, distinguishing inflammatory bowel disease from ibs. See calprotectin.
Ceruloplasmin — The major copper-carrying protein in plasma (binds ~95% of circulating Cu). Also functions as a ferroxidase, oxidizing Fe2+ to Fe3+ for loading onto transferrin. Elevated as an acute phase reactant; the Cu/Zn ratio (driven partly by ceruloplasmin) is a pan-disease biomarker.
Co-selection — The process by which selection for one resistance trait (e.g., metal tolerance) simultaneously selects for linked traits (e.g., antibiotic resistance) when genes reside on the same mobile genetic element. See co selection.
CRP (C-reactive protein) — An acute-phase protein produced by the liver in response to IL-6. Elevated CRP is a systemic marker of inflammation used across many diseases in this wiki, from depression to cardiovascular disease.
Cuproptosis — A recently described form of regulated cell death triggered by excess intracellular copper binding to lipoylated TCA cycle proteins, causing proteotoxic stress. Relevant to copper toxicity and cancer therapeutics.
Dysbiosis — A disruption in the composition, diversity, or metabolic output of the gut microbiome associated with disease. Characterized by loss of beneficial taxa (e.g., butyrate producers) and expansion of pathobionts. See dysbiosis.
EDSS (Expanded Disability Status Scale) — The standard clinical scale for quantifying disability in multiple sclerosis, ranging from 0 (normal neurological exam) to 10 (death due to MS). Probiotic interventions in MS are often assessed by EDSS change.
Estrobolome — The aggregate of enteric bacterial genes capable of metabolizing estrogens, primarily through beta glucuronidase activity. Dysbiosis of the estrobolome alters circulating estrogen levels, linking the microbiome to breast cancer, endometriosis, and pcos. See estrobolome.
Exposome — The totality of environmental exposures an individual encounters from conception onward, including dietary metals, pollutants, microbiome composition, and lifestyle factors. See exposome.
Fenton reaction — The iron-catalyzed generation of hydroxyl radicals from hydrogen peroxide (Fe2+ + H2O2 -> Fe3+ + OH- + OH*). The primary mechanism linking iron excess to oxidative stress and DNA damage across neurodegeneration, cancer, and inflammatory disease.
Ferroptosis — An iron-dependent form of regulated cell death driven by lipid peroxidation, inhibited by GPX4 and glutathione. Central to pathology in parkinsons disease, alzheimers disease, chronic kidney disease, and cancer. See ferroptosis.
FMT (fecal microbiota transplantation) — The transfer of stool from a healthy donor to a recipient's GI tract to restore microbial diversity and function. Strongest evidence in ulcerative colitis and C. difficile infection. See fecal microbiota transplant.
GloI (glyoxalase I) — A metalloenzyme that detoxifies methylglyoxal, a reactive carbonyl compound. In some bacteria (e.g., klebsiella pneumoniae, helicobacter pylori), GloI is nickel-dependent rather than zinc-dependent. See glyoxalase.
GPX4 (glutathione peroxidase 4) — A selenium-dependent enzyme that reduces lipid hydroperoxides, serving as the primary defense against ferroptosis. Its activity depends on both selenium and glutathione availability.
Hepcidin — The master iron-regulatory hormone produced by hepatocytes. Hepcidin degrades ferroportin, blocking iron export from enterocytes and macrophages. Elevated by inflammation (IL-6), causing the anemia of chronic disease seen in inflammatory bowel disease, chronic kidney disease, and other conditions. See hepcidin.
HIF-1-alpha (hypoxia-inducible factor 1-alpha) — A transcription factor stabilized under low-oxygen conditions that activates genes for angiogenesis, glycolysis, and iron metabolism. Relevant to tumor hypoxia, inflammation, and the acidic microenvironment of the gut.
ICP-MS (inductively coupled plasma mass spectrometry) — The gold-standard analytical technique for measuring trace metal concentrations in biological samples. Used across metallomics studies to quantify metal levels in serum, tissue, hair, and stool.
IDO (indoleamine 2,3-dioxygenase) — An enzyme induced by IFN-gamma and TNF-alpha that diverts tryptophan from serotonin synthesis toward the kynurenine pathway. Central to tryptophan metabolism disruption in depression, schizophrenia, and other inflammatory conditions.
Irving-Williams series — The universal stability order of divalent transition metal complexes: Mn2+ < Fe2+ < Co2+ < Ni2+ < Cu2+ > Zn2+. Explains why copper can displace other metals from binding sites, driving mis metallation when metal homeostasis fails.
LPS (lipopolysaccharide) — A component of the outer membrane of Gram-negative bacteria. Translocated LPS activates TLR4-mediated inflammation and is a marker of intestinal permeability failure ("leaky gut") across multiple diseases.
MAIT cells (mucosal-associated invariant T cells) — Innate-like T cells enriched in mucosal tissues that recognize microbial riboflavin metabolites via MR1. Relevant to mucosal immunity in inflammatory bowel disease and multiple sclerosis.
Metallomics — The comprehensive study of the metallome — the full complement of metal and metalloid species in a biological system. Encompasses metal speciation, distribution, and functional roles. See metallomics.
Metalloestrogen — A metal that can activate estrogen receptors (especially ERalpha) independently of endogenous estrogens. Cadmium and nickel are the best-characterized metalloestrogens, linking metal exposure to breast cancer, endometriosis, and pcos. See metalloestrogens.
Metallophore — A small molecule secreted by microbes to scavenge metals from the environment. Broader than siderophores (iron-specific); includes nickelophores and zincophores. See siderophores metallophores.
Metalloproteome — The subset of a proteome consisting of metalloproteins — proteins that bind metal cofactors for structural or catalytic function. Estimated at 30-40% of all proteins; disrupted by mis metallation when metal ratios shift.
Metallostasis — The maintenance of optimal intracellular metal concentrations through coordinated import, export, storage, and trafficking systems. Disruption leads to dyshomeostasis, mis metallation, and disease.
Mis-metallation — The displacement of a native metal cofactor from a protein by a competing metal (typically one higher in the Irving-Williams series), resulting in loss of function or gain of toxic activity. See mis metallation.
MMP (matrix metalloprotease) — A family of zinc-dependent endopeptidases that degrade extracellular matrix components. Involved in tissue remodeling, inflammation, tumor invasion, and barrier breakdown. See matrix metalloproteases.
Nickelophore — A metallophore specific for nickel acquisition. Staphylopine (from staphylococcus aureus) and yersiniabactin (from escherichia coli, klebsiella pneumoniae) can scavenge Ni2+ in addition to other metals. See siderophores metallophores.
NF-kB (nuclear factor kappa-B) — A transcription factor family that is the master regulator of inflammatory gene expression. Activated by LPS, cytokines, and metal-induced oxidative stress; central to inflammation in virtually every disease in this wiki. See nf kappa b.
NLRP3 (NOD-like receptor protein 3) — An inflammasome sensor that assembles a caspase-1-activating platform in response to danger signals including ROS, LPS, and crystalline particles. NLRP3 activation drives IL-1beta and IL-18 release, linking oxidative stress and metal exposure to inflammation.
NRAMP1 (natural resistance-associated macrophage protein 1) — A divalent metal transporter on the phagolysosomal membrane that pumps Fe2+ and Mn2+ out of the phagosome, starving intracellular pathogens of metals. A key effector of nutritional immunity.
Nutritional immunity — The host strategy of sequestering essential metals (Fe, Zn, Mn) to starve invading pathogens. Mediated by calprotectin, lactoferrin, hepcidin, and lipocalin 2. See nutritional immunity.
Pathobiont — A commensal microorganism that can become pathogenic under conditions of dysbiosis, immune compromise, or altered metal availability. Examples include adherent-invasive escherichia coli in ulcerative colitis and ruminococcus gnavus in IBD flares.
Pharmacomicrobiomics — The study of how the gut microbiome influences drug metabolism, efficacy, and toxicity. Relevant to pharmacomicrobiomics interactions such as bacterial azoreductase activation of sulfasalazine and microbial beta-glucuronidase reactivation of drug metabolites.
PLS-DA (partial least squares discriminant analysis) — A multivariate statistical method used in metallomics and microbiome studies to classify disease vs. control groups based on multi-element or multi-taxa signatures. Often paired with VIP scores.
SCFA (short-chain fatty acids) — Microbial fermentation products (acetate, propionate, butyrate) that serve as colonocyte fuel, immune modulators, and barrier reinforcers. Depleted in dysbiosis across IBD, depression, and metabolic disease. See short chain fatty acids.
Siderophore — A small, high-affinity iron-chelating molecule secreted by microorganisms to scavenge Fe3+ from the environment. Examples include enterobactin (escherichia coli), pyoverdine (pseudomonas aeruginosa), and staphyloferrin (staphylococcus aureus). See siderophores metallophores.
SNAS (systemic nickel allergy syndrome) — A systemic allergic response to dietary nickel in nickel-sensitized individuals, manifesting as GI symptoms identical to ibs, plus extra-intestinal symptoms (headache, urticaria, fatigue). See nickel allergy.
TDI (tolerable daily intake) — The maximum amount of a substance that can be ingested daily over a lifetime without appreciable health risk. For metals, TDIs are set by EFSA and WHO; relevant to dietary nickel exposure, dietary cadmium exposure, and dietary lead exposure.
TLR4 (toll-like receptor 4) — The pattern recognition receptor that detects LPS and other microbial ligands. TLR4 activation triggers NF-kB-mediated inflammation and is a key sensor in the intestinal permeability-inflammation axis.
TMAO (trimethylamine N-oxide) — A microbiome-derived metabolite produced from dietary choline, carnitine, and betaine via microbial TMA lyases and hepatic FMO3 oxidation. Elevated TMAO promotes atherosclerosis and cardiovascular disease. See tmao.
Transferrin — The primary iron transport protein in plasma, binding two Fe3+ ions with high affinity. Transferrin saturation is a clinical marker of iron status; low saturation indicates deficiency, high saturation indicates overload risk. See transferrin.
Urease — A nickel-dependent metalloenzyme that hydrolyzes urea to ammonia and CO2. Critical for helicobacter pylori gastric acid neutralization, proteus mirabilis urinary stone formation, and klebsiella pneumoniae GI colonization. See urease.
VIP score (variable importance in projection) — A metric from PLS-DA models indicating which variables (metals, taxa) contribute most to group discrimination. VIP > 1.0 is conventionally considered important; used in metallomics and microbiome signature analyses.
Zonulin — A protein that modulates tight junction permeability in the intestinal epithelium. Elevated serum zonulin is a biomarker of increased intestinal permeability ("leaky gut") in inflammatory bowel disease, schizophrenia, type 1 diabetes, and other conditions.