An investigation of the correlation between the S-glutathionylated GAPDH levels in blood and Alzheimer's disease progression

Abstract

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by two aggregates, namely, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) of hyperphosphorylated tau protein (tau-p), which are released into the blood in a very small amount and cannot be easily detected. An increasing number of recent studies have suggested that S-glutathionylated glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is highly correlated with Aβ in patients with AD and that S-glutathionylated GAPDH plays a role as a proapoptotic factor in AD. We found that S-glutathionylated GAPDH is abundant in the blood of AD patients, which is unusual because S-glutathionylated GAPDH cannot exist in the blood under normal conditions. The aim of this study was to further explore the correlation between the S-glutathionylated GAPDH levels in blood plasma and AD progression. As controls, we recruited 191 people without AD, which included 111 healthy individuals and 37 patients with depression and insomnia, in the psychosomatic clinic. Moreover, 47 patients with AD (aged 40-89 years) were recruited at the neurology clinic. The blood S-glutathionylated GAPDH levels in the AD patients were significantly (p < 0.001) higher (752.7 ± 301.7 ng/dL) than those in the controls (59.92 ± 122.4 ng/dL), irrespective of gender and age. For AD diagnosis, the criterion blood S-glutathionylated GAPDH level > 251.62 ng/dL exhibited 95.74% sensitivity and 92.67% specificity. In fact, the individuals aged 70-89 years, namely, 37 patients from the psychosomatic clinic and 42 healthy individuals, showed significant blood S-glutathionylated GAPDH levels (230.5 ± 79.3 and 8.05 ± 20.51 ng/dL, respectively). This finding might indicate neurodegenerative AD progression in psychosomatic patients and suggests that the degree of neuronal apoptosis during AD progression might be sensitively evaluated based on the level of S-glutathionylated GAPDH in blood.

Fig 1. At different ages, the blood S-glutathionylated GAPDH levels of the patients with AD were higher than those of the controls.

(A) The controls were separated into the age ranges of 20–29 (n = 18), 30–39 (n = 3), 40–49 (n = 13), 50–59 (n = 32), 60–69 (n = 46), 70–79 (n = 56), and 80–89 years (n = 23), for comparison with the patients with AD aged 40–69 (n = 8), 70–79 (n = 18), and 80–89 years (n = 21). ^{a, b}Different letters indicate significant differences, as determined by one-way ANOVA (p < 0.001). (B) The comparison between the total set of controls aged 20–79 years (n = 191) and the total set of patients with AD aged 40–89 years (n = 47) showed significant differences (***p < 0.001).

Fig 2. Receiver Operating Characteristic (ROC) curve used to identify the criterion based on the blood S-glutathionylated GAPDH levels for AD diagnosis.

(A) The criterion was a blood S-glutathionylated GAPDH level > 251.62 ng/dL. The sensitivity was 95.74%, and the specificity was 92.67%. The numbers 0 and 1 represent the controls and patients with AD, respectively. (B) The area under the ROC curve (AUC) was 0.983 ± 0.0.00691, which indicated a high accuracy for AD diagnosis with a 95% CI of 0.957–0.995 (z statistic 69.814, p < 0.0001).

Fig 3. The blood S-glutathionylated GAPDH levels of the healthy controls from the community (1) are markedly lower than those of the controls from the outpatient psychosomatic clinic (2) and the patients with AD.

^{a, b, c} Different letters indicate significant differences, as determined by one-way ANOVA (p < 0.001).

Fig 4. Novel pathway through which the release of blood S-glutathionylated GAPDH from apoptotic neurons reflects the extent of neuronal apoptosis in AD brains.