Table 2 Overview of microcystin effects on the gastrointestinal tract and/or the (gut-associated) immune system

In vivo

Mouse (ICR, female)

Radionuclide recovery

3H-dihydro MC-LR, 70-µg/kg bw (i.p.); detection after 3–90 min

Stomach, small intestine, large intestine, gastrointestinal tract

Detection of exposure-linked radioactivity in the gastrointestinal tract (≈37.6% of the total administered dose), especially in small intestine (6.4%)

[5, 115]

Mouse (aged Balb/C, ICR)

Immunohistochemistry

MC-LR, 500-µg/kg bw (p.o.); 1–13 weeks

Stomach, small intestine, caecum

Especially small intestine (villi and lamina propria) stained highly immunopositive; erosion of small intestine

[89]

Mouse (Balb/C, s.p.f., 7-week-old female)

Histology, immunohistochemistry

75% of MC-LR LD50 (i.p.), 8–32 h

Small intestine

Apoptotic indices after 32-h exposure: 4.25 ± 0.125% (duodenum), 2.5 ± 0.125% (jejunum), 1.75 ± 0.125% (ileum)

[93]

Mouse (N:NIH-S, male)

Phosphatase inhibition assay

MC-LR, 50-µg/kg bw (p.o.) every 48 h, 30 days

Gut-associated lymphoid tissue

Decrease of intraepithelial lymphocytes by 28.7% ± 5.0%

[95]

Mouse (Swiss albino, female)

Comet assay (single-cell gel electrophoresis; DNA damage)

10 mL/kg bw (p.o. or i.p.), 3–24 h. oral doses: 2–4-mg MC-LR/kg bw; i.p. doses: 10–50 µg MC-LR/kg bw.

Blood, liver, kidney, small intestine (ileum), large intestine (colon)

DNA damage induced in intestinal tissues (ileum and colon) may contribute to increased cancer risk

[92]

Rat (Wistar)

Determination of MC-LR toxicokinetics by histopathology and LC–MS detection

MC-LR_equivalent, 80 µg/kg bw (i.v.); 1–24 h

Stomach

Detection of MC in different tissues upon intravenous gavage; 0.010–0.058-μg/g dry weight MC-LR_equivalent in the stomach

[116]

Fish (medaka)

Immunohistochemistry

5-µg/g MC-LR bw (p.o., direct administration to the fish stomach), 2 h

Gut-associated lymphoid tissue, intestine (submucosa)

MC-positive staining of submucosa (penetration through the epithelium); disrupted cellular cohesion; MC-positive stained macrophages

[108]

Human (fishermen)

Epidemiology, cohort study, risk assessment

MC-LR_equivalent

Whole organism

Estimated daily intake: 2.2–3.9 µg;

LOEL, tolerated daily intake: 0.28 µg/kg bw/day

[41, 94]

In vitro

Human (CaCo-2)

Apparent permeability of the pseudoepithelial cell layer to MC-LR

1–75 µM MC-LR; 0.5–24 h

Intestine (colon)

Apical-to-basolateral transport: 24–40% decrease in apical compartment/0.3–1.3% increase in basolateral compartment; low efflux from cellular to basolateral compartment. basolateral-to-apical transport: slow concentration decrease (basolateral, fast increase (apical); better efflux in basolateral-to-apical direction

[100]

Human (CaCo-2)

Immunolocalization (microcystin uptake)

1–50-µM MC-LR, -RR, 0.5–24 h

Intestine (colon)

Rapid uptake in less than 1 h of both variants (no difference in uptake profile); nuclear localization of MCs upon uptake; facilitated uptake (probably via OATPs) and active excretion

[103]

Human (CaCo-2)

Gene expression, transcriptomics

10–100 µM MC-LR, 4–24 h

Intestine (colon)

Major effects on oxidative stress, ERK/MAPK, and cell cycle pathways

[102]

Human (CaCo-2)

Bradford assay (cell number, protein content), neutral red uptake, MTS reduction (viability)

MC-LR, -RR, -YR; 50–200 µM, 24–48 h

Intestine (colon)

EC50: reduction of total protein content: 111.1 ± 3-µM MC-LR (24 h), ˃200 µM MC-RR (48 h); neutral red uptake: 57.3-µM MC-YR (48 h)

[97, 117]

Human (CaCo-2)

MTT assay, Comet assay

0.2–10.1 µM MC-LR, 4–48 h

Intestine (colon)

40% reduced cell viability upon 48-h exposure to 10-µM MC-LR (MTT assay), 19.6% damaged DNA after 4-h exposure to 0.2 µM MC-LR

[98]

Human (CaCo-2)

Lactate dehydrogenase (LDH) leakage (cytotoxicity), cell proliferation and morphology, protein phosphatase (PP) inhibition

1–50 µM MC-LR, -LF, LW, 22–48 h

Intestine (colon)

EC50: LDH leakage: 25% (50-µM MC-LR, control), 36% (MC-LW), 51% (MC-LF); PP inhibition: 3.0-nM MC-LF, 3.8-nM MC-LW, 1.0-nM MC-LR; apoptosis and morphological changes: membrane blebbing, cell shrinkage, chromatin condensation, cytoskeletal reorganization

[91]

Human (IEC-6)

CCK-8 (cell viability), apoptosis, trans-epithelial electric resistance (TEER), PP2A activity, western blot

0–50-µM MC-LR, 6–24 h

Intestine (colon)

LOEC/TEER: 50 µM (12 h), 12.5 µM (24 h); viability: 12.5 µM (24 h); apoptosis: 25 µM (24 h); western blot: 12.5 µM (24 h; occludin), 25 µM (24 h; ZO-1); PP2A activity: 12.5 µM (24 h)

[118]

Human (NCC)

Gene chip analysis, western blot, kinase activity assays, proliferation

0.1–1005-µM MC-LR, 28 d

Intestine (colon)

Neoplastic transformation; constitutive upregulation of signaling pathways (PI3K, APK2, Akt, cyclin D1 and D3), of Ras GTP/GDP proteins (IQGAP-2, RabGTPase, Rap1GAP, RasGAP, R-Ras, Krev-1, TC21) and Ras/MAPK pathway (A-Raf, B-Raf, PAK); decreased proliferation of MC-LR-transformed colorectal crypt cells

[77]

Human (DLD-1, HT29)

Western blot, RT-qPCR, gene knockdown by siRNA, cell migration

0.1–50-nM MC-LR, 24 h

Intestine (colon)

Motility acquired by epithelial-mesenchymal transition through exposure to 25-nM MC-LR (LOEC) in both colorectal cancer cell lines; MC-LR is likely to aggravate (colorectal) cancer development

[75]

Mouse (Balb/C, isolated peritoneal macrophages)

mRNA expression

1–1000-nM MC-LR + 100 µg/L LPS; 6 h

Innate immune system

Reduction/alleviation of LPS-induced inflammation

[112]

Mouse (RAW 264.7, blood macrophages)

Western blot, ELISA

1–1000 nM MC-LR, 0.5–24 h

Innate immune system

LOECs upon 24-h exposure to MC-LR for: MAPK (ERK1/2) activation (100 nM), NF-κB activation (1000 nM), TNF-α production (1 nM)

[69]

Human (predominantly)

Case study meta-analysis, review

Various

Various

References to human intoxication cases, relation between esophagus cancer and human contact with cyanotoxins through the food chain requires further investigation

[12]