Increased cell-free DNA in CSF and serum of hip fracture patients with delirium

Abstract

Delirium is a neuropsychiatric syndrome commonly presenting during acute illness. The pathophysiology of delirium is unknown, but neuroinflammation is suggested to play a role. In this cross-sectional study, we aimed to investigate whether cell-free DNA and markers of neutrophil extracellular traps in serum and CSF were associated with delirium and neuronal damage, assessed by neurofilament light chain. Hip fracture patients (n = 491) with a median (25, 75 percentiles) age of 83 (74, 88) years and 69% females were enrolled at Oslo University Hospital, Diakonhjemmet Hospital, Akershus University Hospital and Bærum Hospital. Delirium was assessed daily, pre- and postoperatively. Cognitively healthy adults (n = 32) with a median (25, 75 percentiles) age of 75 (70, 77) years and 53% females were included as controls. Cell-free DNA was measured by using the fluorescent nucleic acid stain Quant-iT PicoGreen® in serum and CSF. Myeloperoxidase-DNA and citrullinated histone H3 were analysed by enzyme-linked immunosorbent assay in serum. Hip fracture patients have significantly higher levels of cell-free DNA and neutrophil extracellular traps in blood than cognitively healthy controls. In hip fracture patients without dementia, cell-free DNA in CSF and serum was significantly higher in patients with (n = 68) versus without (n = 221) delirium after adjusting for age and sex (70 (59, 84) versus 62 (53, 77) ng/ml, P = 0.037) and 601 (504, 684) versus 508 (458, 572) ng/ml, P = 0.007, respectively). In the total hip fracture cohort, CSF levels of cell-free DNA and neurofilament light chain were significantly correlated after adjusting for age and sex (r = 0.441, P < 0.001). The correlation was stronger in those with delirium (r = 0.468, P < 0.001) and strongest in delirious patients without dementia (r = 0.765, P = 0.045). In delirious patients without dementia, significantly higher levels of cell-free DNA in CSF and serum were shown. The association between cell-free DNA and neurofilament light chain suggest simultaneous release of cell-free DNA and neuronal damage during delirium.

Keywords: cell-free DNA; delirium; neurofilament light chain; neuroinflammation; neutrophil extracellular traps.

Graphical Abstract

Figure 1

Correlation between cell-free DNA in CSF and serum of hip fracture patients (n = 135). Spearman's rho = 0.082, P = 0.343.

Figure 2

Distribution of cell-free DNA and NET markers of hip fracture patients without versus with delirium, stratified for dementia status. Median (bold dotted line) and 25 and 75 percentiles (dotted lines) are indicated in the figure. The Mann–Whitney U-test was used for group comparisons between the two groups ‘no delirium’ and ‘delirium’ in the no dementia and dementia group, separately. ^aAdjusted for age and sex in multivariate binary logistic regression analyses. Sample size in the different groups is shown in Supplementary Table 2.

Figure 3

Cell-free DNA and NET markers in CSF and serum of hip fracture patients without dementia according to delirium subgroups (n = 289). (A) Cell-free DNA in CSF, (B) cell-free DNA in serum, (C) MPO-DNA in serum and (D) CitH₃ in serum according to groups of delirium. Sub-syndromal delirium (SSD) (n = 26) is included in the no delirium group (total n = 221), prevalent delirium (n = 27) is defined as delirium diagnosed preoperatively, and incident delirium (n = 41) defined as delirium onset after CSF sampling. A one-way ANOVA is used in the between group comparisons of levels of cell-free DNA and NET markers for the delirium subgroups (p₁-values). Post hoc comparisons using the Tukey's Honestly Significant Difference test is applied for pairwise comparisons (p₂-values).

Figure 4

Associations between cell-free DNA and NfL in CSF of hip fracture patients (A) Hip fracture patients in general (n = 89): spearman's rho = 0.441, P < 0.001. (B) Hip fracture patients with delirium (n = 48): spearman's rho = 0.468, P < 0.001. (C) Hip fracture patients with delirium and without dementia (n = 9): spearman's rho = 0.765, P = 0.045. All adjusted for age and sex.