Glutathione as a Biomarker in Parkinson’s Disease: Associations with Aging and Disease Severity

Objectives. Oxidative stress contributes to Parkinson’s disease (PD) pathophysiology and progression. The objective was to describe central and peripheral metabolites of redox metabolism and to describe correlations between glutathione (Glu) status, age, and disease severity. Methods. 58 otherwise healthy individuals with PD were examined during a single study visit. Descriptive statistics and scatterplots were used to evaluate normality and distribution of this cross-sectional sample. Blood tests and magnetic resonance spectroscopy (MRS) were used to collect biologic data. Spearman’s rank-order correlation coefficients were used to evaluate the strength and direction of the association. The Unified PD Rating Scale (UPDRS) and the Patient-Reported Outcomes in PD (PRO-PD) were used to rate disease severity using regression analysis. Results. Blood measures of Glu decreased with age, although there was no age-related decline in MRS Glu. The lower the blood Glu concentration, the more severe the UPDRS (P=0.02, 95% CI: −13.96, −1.14) and the PRO-PD (P=0.01, 95% CI: −0.83, −0.11) scores. Discussion. These data suggest whole blood Glu may have utility as a biomarker in PD. Future studies should evaluate whether it is a modifiable risk factor for PD progression and whether Glu fortification improves PD outcomes

Influence of Enterohepatic Recycling on the Time Course of Brain-to-Blood Partitioning of Valproic Acid in Rats

A widely used metric of substrate exposure in brain is the brain-to-serum partition coefficient (K(p,brain); C(brain)/C(serum)), most appropriately determined at distribution equilibrium between brain tissue and serum. In some cases, C(brain)/C(serum) can peak and then decrease, as opposed to monotonically increasing to a plateau, precluding accurate estimation of partitioning. This “overshoot” has been observed with compounds that undergo enterohepatic recycling (ER), such as valproic acid (VPA). Previous simulation experiments identified a relationship between overshoot in the C(brain)/C(serum) versus time profile and distribution into a peripheral “compartment” (e.g., the ER loop). This study was conducted to evaluate model predictions of that relationship. Initial experiments tested the ability of activated charcoal, antibiotics, or Mrp2 deficiency to impair VPA ER in rats, thereby limiting the apparent volume of distribution associated with ER. Mrp2 deficiency (significantly) and antibiotics (moderately) interrupted VPA ER. Subsequently, brain partitioning was evaluated in the presence versus absence of ER modulation. Although overshoot was not eliminated completely, deconvolution revealed that overshoot was reduced in Mrp2-deficient and antibiotic-treated rats. Consistent with model predictions, overshoot was higher after antibiotic treatment (moderate ER interruption) than in Mrp2 deficiency (substantial ER interruption). Steady-state K(p,brain) was unaffected by experimental manipulation, also consistent with model predictions. These data support the hypothesis that C(brain)/C(serum) may overshoot K(p,brain) based on the extent of peripheral sequestration. Consideration of this information, particularly for compounds that undergo significant extravascular distribution, may be necessary to avoid erroneous estimation of K(p,brain)

Glutathione as a Biomarker in Parkinson's Disease: Associations with Aging and Disease Severity

Objectives. Oxidative stress contributes to Parkinson's disease (PD) pathophysiology and progression. The objective was to describe central and peripheral metabolites of redox metabolism and to describe correlations between glutathione (Glu) status, age, and disease severity. Methods. 58 otherwise healthy individuals with PD were examined during a single study visit. Descriptive statistics and scatterplots were used to evaluate normality and distribution of this cross-sectional sample. Blood tests and magnetic resonance spectroscopy (MRS) were used to collect biologic data. Spearman's rank-order correlation coefficients were used to evaluate the strength and direction of the association. The Unified PD Rating Scale (UPDRS) and the Patient-Reported Outcomes in PD (PRO-PD) were used to rate disease severity using regression analysis. Results. Blood measures of Glu decreased with age, although there was no age-related decline in MRS Glu. The lower the blood Glu concentration, the more severe the UPDRS ( = 0.02, 95% CI: −13.96, −1.14) and the PRO-PD ( = 0.01, 95% CI: −0.83, −0.11) scores. Discussion. These data suggest whole blood Glu may have utility as a biomarker in PD. Future studies should evaluate whether it is a modifiable risk factor for PD progression and whether Glu fortification improves PD outcomes