Table 4.

Amyloid β and tau levels in interstitial fluid (ISF) in patients with traumatic brain injury-microdialysis (MD) studies.

Reference	Patients (N)	Type of injury	Catheter location	Catheter	Sample interval	Analyte	Analysis method	ISF levels (pg/ml)	ISF tau levels (pg/ml)	Major findings
Brody et al. (2008)	19	Severe TBI (n = 12); SAH (n = 6); unruptured aneurysm (n = 1)	Frontal in most patients	CMA70 (n = 6) CMA71 (n = 13)	Aβ1-x:1, every 2 h; Aβ 1–40 and Aβ 1–42, every 8 h	Aβ1-x Aβ 1–40 Aβ 1–42	ELISA	Not reported; estimated from Figures: Aβ42; most MD samples between 10 and 60 pg/ml Aβ1-x: median 1000 pg/ml	N/A	A positive correlation between changes in brain interstitial fluid Aβ concentration and neurological status was found
Marklund et al. (2009)	8	Severe TBI, focal/mixed (n = 5), DAI (n = 3)	Frontal (n = 6); peri-C (n = 2)	CMA71	Every 1 h	Aβ40, Aβ42, T-tau	ELISA	Aβ42 (median and range): 167 pg/ml (31–295)	T-tau: 2881 ± 1774 pg/ml (121–6500) Means ± SD and range	High levels of Aβ42 in ISF post-injury. Aβ42 levels were higher in DAI patients. Tau protein levels were higher in patients with focal/mixed disease
Magnoni et al. (2012)	16	DAI (n = 8), EML (n = 7), nEML (n = 1)	Frontal (n = 10); peri-C (n = 6)	CMA71	Every 1–2 h, every 4–6 h for most patients	Aβ1-x, T-tau, NF-L	ELISA	First 24 h (median and range): peri-C Aβ1-x: 270 pg/ml (83–417); non-C Aβ: 1023 pg/ml (778–1968)	First 24 h: peri-C T-tau: 15950 pg/ml (11390–27240); non-C T-tau: 3469 pg/ml (1684–8691)1	Patients in the pericontusional group had lower Aβ and higher tau levels compared to patients in the non-contusional group. Initial tau levels were inversely correlated with initial Aβ levels. In vitro recovery for αβ was 30 and 1–2% for tau

Since the normal, injured tau, and Aβ peptide levels in the injured human brain are unknown it is yet difficult to establish the magnitude of TBI-induced alterations. Both increased and decreased Aβ peptide levels have been suggested depending on injury site and catheter location. Aβ peptide levels may be increased due to their formation in injured axons and also be related to the level of consciousness and degree of neuronal activity. Interstitial tau levels may be higher in patients with a focal disease and be inversely correlated with Aβ peptide levels. It appears that MD is a useful tool for the study of Aβ and tau dynamics in the injured human brain following TBI.Aβ, beta amyloid; DAI, diffuse axonal injury; ELISA, enzyme-linked immunosorbent assay; EML, evacuated mass lesion; nEML, non-evacuated mass lesion, MD, microdialysis; N/A, not available; NF-L, neurofilament light chain; Non-C, non-contusional; Peri-C, pericontusional; SAH, subarachnoidal hemorrhage; TBI, traumatic brain injury; SD, standard deviations.