Estrogen prevents neuroprotection by caffeine in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease

Abstract

Epidemiological studies have strongly linked caffeine consumption with a reduced risk of developing Parkinson's disease (PD) in men. Interestingly, in women, this inverse association is present only in those who have not taken postmenopausal estrogens, suggesting an interaction between the influences of estrogen and caffeine use on the risk of PD. To explore a possible biological basis for this interaction, we systematically investigated how the neuroprotective effect of caffeine is influenced by gender, ovariectomy (OVX), and then exogenous estrogen in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD. (1) Caffeine treatment produced a dose-dependent attenuation of MPTP-induced striatal dopamine loss in both young and retired breeder (RB) male, but not female, mice. (2) In female mice (both young and RB), caffeine was less potent or altogether ineffective as a neuroprotectant after sham surgery compared to OVX or after OVX plus estrogen replacement compared to OVX plus placebo treatment. (3) Estrogen treatment also prevented the protection of caffeine against dopamine loss in young male mice. (4) Consistent with the putative protective effect of estrogen, female and OVX plus estrogen mice were relatively resistant to MPTP toxicity compared to male and OVX plus placebo mice, respectively. (5) There was no overall difference in brain levels of caffeine and its metabolites between OVX plus placebo and OVX plus estrogen mice. Together, these results suggest that estrogen can occlude and thereby prevent the neuroprotective effect of caffeine in a model of PD neurodegeneration, supporting a biological basis for the interaction between estrogen and caffeine in modifying the risk of PD.

Figure 1.

Caffeine dose-dependently attenuates MPTP-induced dopamine depletion in male but not female C57BL/6 mice, either young (∼10 weeks old; A) or retired breeder (6–9 months old; B). Caffeine (5–40 mg/kg, i.p.) or saline was administered 10 min before a single dose of MPTP (40 mg/kg, i.p.; n = 4–12) or saline (n = 3–6). One week later, striatal dopamine content was determined. The bars represent striatal dopamine levels (mean ± SEM) calculated as a percentage of their respective controls (i.e., S+S group). The dopamine concentrations (in picomoles per milligram of tissue) of these controls are 71.8 ± 2.4 and 70.6 ± 2.6 (A) and 80 ± 9 and 92 ± 9.8 (B) for males and females, respectively. Data were analyzed by two-way ANOVA, followed by Fisher's LSD test. A, *p < 0.05, **p < 0.01, and ***p < 0.001 compared with the respective S+M group; ^#p < 0.05 compared with the respective C5+M group; ⁺p < 0.05 compared with S+M in male mice; ^@p < 0.01 compared with C40+Min male mice.B, *p<0.05 and **p<0.01 compared with the respective S+M group; ^#p<0.05 compared with the respective C10+M group; ^@p<0.05 compared with C40+M in male mice. S, Saline; M, MPTP; C5–40, caffeine at 5–40 mg/kg.

Figure 2.

A low dose of caffeine attenuates MPTP-induced dopamine depletion in OVX but not sham-operated young female mice. Ten days after ovariectomy or sham operation, mice received caffeine (5 or 20 mg/kg, i.p.) or saline administration 10 min before a single dose of MPTP (40 mg/kg, i.p.; n = 8) or saline (n = 5–7). One week later, striatal dopamine content was determined. The bars represent striatal dopamine levels (mean ± SEM) calculated as a percentage of their respective controls (i.e., S+S group). The dopamine concentrations of these controls are 61 ± 3.7 and 67 ± 2.7 pmol/mg of tissue for OVX and sham mice, respectively. Data were analyzed by two-way ANOVA, followed by Fisher's LSD test. **p < 0.01 and ***p < 0.001 compared with the respective S+M group; ^#p < 0.001 compared with the respective C5+M group; ^@p < 0.01 compared with C5+M in OVX mice. S, Saline; M, MPTP; C5 or C20, caffeine at 5 or 20 mg/kg.

Figure 3.

Caffeine attenuates MPTP-induced dopamine depletion in OVX female mice receiving placebo (OVX+P) but not estrogen (OVX+E) replacement (A, young mice; B, retired breeders). Ten days after ovariectomy, mice were implanted with placebo or estrogen pellets (17β-estradiol, 0.1 mg per pellet, 21 d release) subcutaneously. Ten days later, caffeine (5–40 mg/kg, i.p.) or saline was administered 10 min before a single dose of MPTP (40 mg/kg, i.p.; n = 6–15) or saline (n = 3–6). Striatal dopamine content was determined 1 week after MPTP. The bars represent striatal dopamine levels (mean ± SEM) calculated as a percentage of their respective controls (i.e., S+S group). The dopamine concentrations (in picomoles per milligram of tissue) of these controls are 72 ± 4 and 78 ± 4.7 (A) and 78.9 ± 7.3 and 73.9 ± 7.7 (B) for males and females, respectively. Data were analyzed by two-way ANOVA, followed by Fisher's LSD test. A, **p < 0.01 and ***p < 0.001 compared with the respective S+M group; ^#p < 0.05 compared with the respective C5+M and C10+M groups; ⁺p < 0.05 compared with the respective S+M or C5+M in OVX+P mice. B, *p < 0.05, **p < 0.01, and ***p < 0.001 compared with the respective S+M group; ^#p < 0.001 compared with the respective C5+M, C10+M, or C20+M group; ^@p < 0.05 compared with C40+M in OVX+P mice. S, Saline; M, MPTP; C5–40, caffeine at 5–40 mg/kg.

Figure 4.

Caffeine attenuates MPTP-induced dopamine depletion in young male mice receiving placebo but not estrogen treatment. Mice were implanted with placebo or estrogen pellets. Ten days later, caffeine (10–40 mg/kg, i.p.) or saline was administered 10 min before a single dose of MPTP (40 mg/kg, i.p.; n = 8–9) or saline (n = 3). Striatal dopamine content was determined 1 week after MPTP. The bars represent striatal dopamine levels (mean ± SEM) calculated as a percentage of their respective controls (i.e., S+S group). The dopamine concentrations of these controls are 79 ± 10.6 and 80.6 ± 4.2 pmol/mg of tissue for placebo- and estrogen-treated mice, respectively. Data were analyzed by two-way ANOVA, followed by Fisher's LSD test. *p < 0.05 and **p < 0.01 compared with the respective S+M group. S, Saline; M, MPTP; C10–40, caffeine at 10–40 mg/kg.

Figure 5.

Caffeine metabolism is not changed by estrogen replacement in OVX retired breeder female mice. Ten days after ovariectomy, mice were implanted with placebo or estrogen pellets. Caffeine (5 or 40 mg/kg, i.p.) was administered 10 d after pellet implantation. Brain concentrations of caffeine and its metabolites were measured at 10, 30, 60, 120, 180, 240, or 360 min after injection (n = 5 for each time point). A, Brain caffeine concentration after intraperitoneal 5 mg/kg caffeine. The levels of metabolites are below the detection limit. B, Brain concentrations of caffeine, paraxanthine, theophylline, and theobromine, respectively, after intraperitoneal 40 mg/kg caffeine. Data were analyzed by two-way ANOVA, followed by Fisher's LSD test. *p < 0.05 and **p < 0.01 compared with the respective estrogen-treated group.