(DESH), which is characteristic of iNPH, show that L-PGDS levels are reduced in iNPH [24]. Our study showed a trend of increasing L-PGDS levels in the “Improved Cognitive group,” but no increase in the “Poor Cognitive group” (Table 4). Cystatin C is also involved in the metabolism of Aβ protein and is chiefly secreted from the choroid plexus [35]. In iNPH pathology, where the circulation of CSF is chronically impaired, fluid secretion from the choroid plexus into the CSF is also reduced [25,34], including cystatin C. In patients with iNPH, cystatin C levels were low, but increased after LPS treatment. Choi et al. reported that Aβ polymerization (formation of Aβ oligomers) was promoted by delaying the flow of interstitial fluids in a culture experiment [2]. The results of animal experiments suggest that 10–15% of Aβ is metabolized by interstitial fluids [31]. The extent to which the pathology of iNPH accounts for the reduced turnover of CSF and the metabolism of Aβ is unclear.It is possible that the reduction in enzymes related to Aβ metabolism such as L-PGDS and cystatin C in iNPH creates an environment where Aβ aggregation is increased, forming highly neurotoxic Aβ oligomers. After CSF shunt treatment, turnover of CSF appears to increase, thereby increasing the production of CSF, inducing cystatin C secretion from the CSF choroid plexus, and L-PDGS from the arachnoid membrane of the brain, spinal cord, and oligodendrocytes, thus promoting the metabolism of Aβ.
5. Conclusions
P-tau levels and the Aβ1–38/Aβ1–42 and Aβ1–42/p-tau ratios in preoperative CSF may serve as biomarkers for the prognosis of cognitive function after shunt surgery in iNPH. However,in the age ≥80 operated group,functional prognosis of cognition remains confined,especially on MMSE values. We suggest improved CSF circulation in iNPH after LPS increases the amount of cystatin C and L-PGDS, possibly contributing to Aβ elimination and improvement of arange of symptoms. The switch in Aβ-variant synthesis from Aβ1–42 to Aβ1–38 also resulted in the improvementof functional prognosis.
Conflicts of interest
The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication.
Acknowledgments
This research was supported by the Grant-in-Aid for Scientific Research Grant Number (B #26293326 and C #26462217) from the Japan Society for the Promotion of Science.