Food-derived hydrophilic antioxidant ergothioneine is distributed to the brain and exerts antidepressant effect in mice

Abstract

Background: Clinically used antidepressants suffer from various side effects. Therefore, we searched for a safe antidepressant with minimal side effects among food ingredients that are distributed to the brain. Here, we focused on ERGO (ergothioneine), which is a hydrophilic antioxidant and contained at high levels in edible golden oyster mushrooms. ERGO is a typical substrate of carnitine/organic cation transporter OCTN1/SLC22A4, which is expressed in the brain and neuronal stem cells, although little is known about its permeation through the BBB (blood-brain barrier) or its neurological activity.

Methods: To clarify the exposure of ERGO to brain and the possible antidepressant-like effect after oral ingestion, ERGO or GOME (golden oyster mushroom extract) which contains 1.2% (w/w) ERGO was mixed with feed and provided to mice for 2 weeks, and then ERGO concentration and antidepressant-like effect were evaluated by LC-MS/MS and FST (forced swimming test) or TST (tail suspension test), respectively.

Results: Diet containing ERGO or GOME greatly increased the ERGO concentrations in plasma and brain, and significantly decreased the immobility time in both FST and TST. The required amount of GOME (~37 mg/day) to show the antidepressant-like effect corresponds to at most 8 g/day in humans. In mice receiving GOME-containing diet, doublecortin-positive cells showed a significant increase from the basal level, suggesting promotion of neuronal differentiation.

Conclusion: Thus, orally ingested ERGO is transported across the BBB into the brain, where it may promote neuronal differentiation and alleviate symptoms of depression at plausibly achieved level of daily ingestion.

Keywords: Antidepressant effect; OCTN1; depression; disposition; ergothioneine; neuronal differentiation.

Figure 1

Schematic representation of experimental schedule. Each timeline shows experimental schedule for (A) Figs. 2, 5, (B) Figs. 3, 4, or (C) Fig. 6.

Figure 2

ERGO (Ergothioneine) concentrations in the body and pharmacokinetic parameters for ERGO in mice fed diet containing GOME. (A) ERGO concentrations in plasma and brain, and (B) those in blood, liver, and kidney were measured by LC‐MS/MS in mice given normal diet (white columns), or diet containing 0.1% (light gray columns), 0.3% (gray columns), 1% (dark gray columns), or 10% (black columns) GOME for 2 weeks. (C) CL _oral of ERGO was calculated from plasma concentration and daily intake of ERGO. (D) Kp in blood (open squares), brain (closed circles), liver (closed triangles), and kidney (closed diamonds) was calculated from the ERGO concentrations in plasma and each tissue. Each point and vertical bar represents the mean ± SEM. (n = 4). *P < 0.05, significant difference from the corresponding control value.

Figure 3

Behavioral test in mice given diet containing GOME, ERGO (ergothioneine), GBE (Ginkgo biloba extract), or AA. Mice were given normal diet (white columns), or diet containing 10% GOME (black columns), authentic ERGO (dark gray columns), GBE (dotted columns), or AA (diagonal columns) for 2 weeks. (A) Immobility time in 5 min of FST was measured in mice. Increase in immobility time was calculated from the values after each diet treatment and before the start of the treatment. Each value is the mean ± SEM. (Control: n = 11, GOME: n = 11, ERGO: n = 6, GBE: n = 6, AA: n = 6). (B) Locomotor activity of mice. Each mouse was placed in an individual cage, and locomotion was assessed for 5 min after habituation. Each value is shown as mean ± SEM. (n = 6). (C) Time spent in the center, middle, and outside zones was measured. Each mouse was placed in a novel chamber for 5 min. Each value is the mean ± SEM. (Control: n = 15, GOME: n = 15, ERGO: n = 6, GBE: n = 3, AA: n = 6). *P < 0.05, significant difference from the corresponding control value.

Figure 4

Comparison of ERGO (ergothioneine) concentrations in the body after oral ingestion of GOME or ERGO. (A) ERGO concentration in brain, and (B) those in blood, liver, and kidney were measured by HPLC in mice given normal diet (white columns), or diet containing 10% GOME (black columns), or authentic ERGO (dark gray columns) for 2 weeks. Each vertical bar represents the mean ± SEM. (n = 6). *P < 0.05, significant difference from the corresponding control value.

Figure 5

Dose‐dependent reduction in immobility time in TST after oral ingestion of GOME. Mice were given normal diet (white column, n = 15), or diet containing 0.1% (light gray column, n = 6), 0.3% (gray column, n = 6), 1% (dark gray column, n = 12), or 10% (black column, n = 15) GOME for 2 weeks and subjected to TST. Immobility time in 2 min was measured. Each value is the mean ± SEM. *P < 0.05, significant difference from the corresponding control value.

Figure 6

Bromodeoxyuridine incorporation or DCX expression in mice given diet containing GOME under a chronic stress condition. Mice were given normal diet ((A), (B) white symbols, (C), (D) upper left panels) or diet containing 10% GOME ((A), (B) diagonal symbols, (C), (D) upper right panels) under a normal condition, or normal diet ((A), (B) gray symbols, (C), (D) lower left panels), or diet containing 10% GOME ((A), (B) black symbols, (C), (D) lower right panels) under a chronic stress condition, for 21 days. Stress was imposed by forcing the animals into an immobilizer for 4 h/day. (A) Spleen weight was measured and normalized by body weight. Each value is shown as the mean ± SEM. (n = 3). (B) Change in body weight of each mouse was measured every week and normalized with that at the start of restraint stress. Each value is shown as the mean ± SEM. (n = 5). Typical phase‐contrast micrographs of (C) BrdU‐incorporating cells and (D) DCX‐expressing cells in each group are shown. The numbers of (E) BrdU‐incorporating cells and (F) DCX‐expressing cells were counted by using a cell image analyzer in at least two areas from four to eight individual mice in each group. Vertical bar represents the mean ± SEM. (Control: n = 8, GOME: n = 8, Control + Stress: n = 15, GOME + Stress: n = 14). *P < 0.05, significant difference from the corresponding control value.