Neuroprotection by caffeine: time course and role of its metabolites in the MPTP model of Parkinson's disease

Abstract

Epidemiological studies have raised the possibility of caffeine serving as a neuroprotective agent in Parkinson's disease (PD). This possibility has gained support from findings that dopaminergic neuron toxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or other neurotoxins is attenuated by co-administration of caffeine in mice. Here we examined the time window of caffeine's neuroprotection as well as the effects of caffeine's metabolites (theophylline and paraxanthine) in the MPTP mouse model of PD. In the first experiment, caffeine pre-treatment (30 mg/kg ip) significantly attenuated MPTP-induced striatal dopamine depletion when it was given 10 min, 30 min, 1 h, or 2 h but not 6 h before MPTP (40 mg/kg ip) treatment. Meanwhile, caffeine post-treatment also significantly attenuated striatal dopamine loss when it was given 10 min, 30 min, 1 h or 2 h but not 4 h, 8 h or 24 h after MPTP injection. In the second experiment, both theophylline (10 or 20 mg/kg) and paraxanthine (10 or 30 mg/kg) administration (10 min before MPTP) significantly attenuated MPTP-induced dopamine depletion in mice, as did caffeine (10 mg/kg) treatment. Thus the metabolites of caffeine also provide neuroprotective effects in this mouse model of PD. The data suggest that if caffeine protects against putative toxin-induced dopaminergic neuron injury in humans, then precise temporal pairing between caffeine and toxin exposures may not be critical because the duration of neuroprotection by caffeine may be extended by protective effects of its major metabolites.

Figure 1

Figure 1A. Caffeine pre-treatment significantly attenuate MPTP-induced dopaminergic toxicity. C57Bl/6 male mice received saline or caffeine (30mg/kg ip) at different time points before MPTP (40mg/kg, n=7–9) or saline (n=3–4) ip treatment. Striatal dopamine content was determined one week later. Bars represent striatal dopamine levels (mean ± SEM) calculated as percentage of their control (i.e., saline 10min before saline treatment group, in which dopamine content is 65±2.1 pmol/mg tissue). Data were analyzed with one-way ANOVA followed by Fisher’s LSD test. **-p<0.01, ***-p<0.001 when compared with saline 10min before MPTP treatment group. Figure 1B. Caffeine post-treatment significantly attenuate MPTP-induced dopaminergic toxicity. C57Bl/6 male mice received saline or caffeine (30mg/kg ip) at different time points after MPTP (40mg/kg, n=7–20) or saline (n=5–6) ip treatment. Striatal dopamine content was determined one week after MPTP. Bars represent striatal dopamine levels (mean ± SEM) calculated as percentage of their control (i.e., saline 10min post saline treatment group in which dopamine content is 42±4.8 pmol/mg tissue). Data were analyzed with one-way ANOVA followed by Fisher’s LSD test. **-p<0.01, ***-p<0.001 when compared with Saline 10min post MPTP treatment group.

Figure 1

Figure 1A. Caffeine pre-treatment significantly attenuate MPTP-induced dopaminergic toxicity. C57Bl/6 male mice received saline or caffeine (30mg/kg ip) at different time points before MPTP (40mg/kg, n=7–9) or saline (n=3–4) ip treatment. Striatal dopamine content was determined one week later. Bars represent striatal dopamine levels (mean ± SEM) calculated as percentage of their control (i.e., saline 10min before saline treatment group, in which dopamine content is 65±2.1 pmol/mg tissue). Data were analyzed with one-way ANOVA followed by Fisher’s LSD test. **-p<0.01, ***-p<0.001 when compared with saline 10min before MPTP treatment group. Figure 1B. Caffeine post-treatment significantly attenuate MPTP-induced dopaminergic toxicity. C57Bl/6 male mice received saline or caffeine (30mg/kg ip) at different time points after MPTP (40mg/kg, n=7–20) or saline (n=5–6) ip treatment. Striatal dopamine content was determined one week after MPTP. Bars represent striatal dopamine levels (mean ± SEM) calculated as percentage of their control (i.e., saline 10min post saline treatment group in which dopamine content is 42±4.8 pmol/mg tissue). Data were analyzed with one-way ANOVA followed by Fisher’s LSD test. **-p<0.01, ***-p<0.001 when compared with Saline 10min post MPTP treatment group.

Figure 2. Caffeine’fs metabolites significantly attenuate MPTP-induced dopaminergic toxicity

C57Bl/6 male mice received ip injection of caffeine (10mg/kg), theophylline (10 or 20 mg/kg), paraxanthine (10 or 30 mg/kg) or saline 10 min before MPTP (40mg/kg, n=7–20) or saline (n=3–7) ip treatment. Striatal dopamine content was determined one week later. Bars represent striatal dopamine levels (mean ± SEM) calculated as percentage of their control (i.e., saline 10min before saline treatment group in which dopamine content is 58±3.5 pmol/mg tissue). P10 or P30, paraxanthine 10 or 30 mg/kg, respectively; T10 or T20, theophylline 10 or 20 mg/kg, respectively. Data were analyzed with one-way ANOVA followed by Fisher’s LSD test. *-p<0.05, ***-p<0.01when compared with saline 10min before MPTP treatment group.

Figure 3. Serum and brain levels of caffeine and its metabolites after caffeine injection

C57bl/6 male mice were treated with caffeine (10 or 30 mg/kg ip) and killed at 5, 10, 20, 30, 60, 120, 360min or 24hr (n=6 for each time point) after injection. Serum and brain concentrations of caffeine and its metabolites (paraxanthine, theophylline and theobromine) were determined.

Figure 3. Serum and brain levels of caffeine and its metabolites after caffeine injection

C57bl/6 male mice were treated with caffeine (10 or 30 mg/kg ip) and killed at 5, 10, 20, 30, 60, 120, 360min or 24hr (n=6 for each time point) after injection. Serum and brain concentrations of caffeine and its metabolites (paraxanthine, theophylline and theobromine) were determined.