Age-associated changes in amyloid-ß and formaldehyde concentrations in cerebrospinal fluid of rhesus monkeys.

Rhesus monkeys ( Macaca mulatta) are valuable experimental animals for studies on neurodegenerative diseases due to their evolutionarily close relationship to humans (Zhang et al., 2014). Rhesus monkeys also display similar hallmarks of aging and neurodegeneration as humans, including formation of senile plaques in the brain (Beckman et al., 2019; Paspalas et al., 2018). However, changes in formaldehyde (FA) levels in the cerebrospinal fluid (CSF) of rhesus monkeys with aging have not been reported. Additionally, whether changes in CSF FA are correlated with changes in amyloid-ß (Aß) concentrations have not yet been explored. Here, the CSF levels of Aß 40, Aß 42, and FA were measured in 56 rhesus monkeys of different ages, ranging from 4 to 26 years old. Results revealed significant declines in Aß 40 and Aß 42, and an increase in FA with age. Interestingly, the increase in FA levels was negatively correlated with Aß 40 and Aß 42 concentrations in aged rhesus monkeys but not in young and middle-aged monkeys. These results appear to parallel changes seen within human aging, i.e., decreased levels of CSF Aß and increased levels of FA in normal aged adults and Alzheimer's disease (AD) patients. These findings further indicate that rhesus monkeys are a reliable model for studying age-related neurological disorders such as AD and suggest that FA is an important factor in AD development and may be used as a diagnostic indicator of such disease.

Evidence for Conversion of Methanol to Formaldehyde in Nonhuman Primate Brain.

Many studies have reported that methanol toxicity to primates is mainly associated with its metabolites, formaldehyde (FA) and formic acid. While methanol metabolism and toxicology have been best studied in peripheral organs, little study has focused on the brain and no study has reported experimental evidence that demonstrates transformation of methanol into FA in the primate brain. In this study, three rhesus macaques were given a single intracerebroventricular injection of methanol to investigate whether a metabolic process of methanol to FA occurs in nonhuman primate brain. Levels of FA in cerebrospinal fluid (CSF) were then assessed at different time points. A significant increase of FA levels was found at the 18th hour following a methanol injection. Moreover, the FA level returned to a normal physiological level at the 30th hour after the injection. These findings provide direct evidence that methanol is oxidized to FA in nonhuman primate brain and that a portion of the FA generated is released out of the brain cells. This study suggests that FA is produced from methanol metabolic processes in the nonhuman primate brain and that FA may play a significant role in methanol neurotoxicology.

Formaldehyde up-regulates TRPV1 through MAPK and PI3K signaling pathways in a rat model of bone cancer pain.

OBJECTIVE: Our previous study showed that tumor tissue-derived formaldehyde at low concentrations plays an important role in bone cancer pain through activating transient receptor potential vanilloid subfamily member 1 (TRPV1). The present study further explored whether this tumor tissue-derived endogenous formaldehyde regulates TRPV1 expression in a rat model of bone cancer pain, and if so, what the possible signal pathways are during the development of this type of pain. METHODS: A rat model of bone cancer pain was established by injecting living MRMT-1 tumor cells into the tibia. The formaldehyde levels were determined by high performance liquid chromatography, and the expression of TRPV1 was examined with Western blot and RT-PCR. In primary cultured dorsal root ganglion (DRG) neurons, the expression of TRPV1 was assessed after treatment with 100 µmol/L formaldehyde with or without pre-addition of PD98059 [an inhibitor for extracellular signal-regulated kinase], SB203580 (a p38 inhibitor), SP600125 [an inhibitor for c-Jun N-terminal kinase], BIM [a protein kinase C (PKC) inhibitor] or LY294002 [a phosphatidylinositol 3-kinase (PI3K) inhibitor]. RESULTS: In the rat model of bone cancer pain, formaldehyde concentration increased in blood plasma, bone marrow and the spinal cord. TRPV1 protein expression was also increased in the DRG. In primary cultured DRG neurons, 100 µmol/L formaldehyde significantly increased the TRPV1 expression level. Pre-incubation with PD98059, SB203580, SP600125 or LY294002, but not BIM, inhibited the formaldehyde-induced increase of TRPV1 expression. CONCLUSION: Formaldehyde at a very low concentration up-regulates TRPV1 expression through mitogen-activated protein kinase and PI3K, but not PKC, signaling pathways. These results further support our previous finding that TRPV1 in peripheral afferents plays a role in bone cancer pain.