Amyloid-beta (Ab) is the hallmark peptide deposited in amyloid plaques found in Alzheimer's disease. Ab is primarily and continuously produced by astroglia with nano-molar concentrations in the cerebro-spinal fluid (CSF). However, after head trauma, an Ab increase in the CSF into the micro-molar range was observed. The effect of such increased concentrations of Ab on the cerebral micro-vasculature is not known.
Methods
Rat cerebral penetrating arterioles were cannulated, pressurized to 60 mmHg and observed at 37C in vitro. After development of spontaneous tone and viability testing, freshly dissolved amyloid-beta40 (Ab40) was added (1 nM to 1 uM) and the vessel diameter change measured. Dose response to Adenosine tri-phosphate (ATP, 1pM to 10 uM) before and after Ab40 (100 nM) was observed. In cell cultures of rat cerebral microvascular endothelial (RCMEC) and smooth muscle cells (RCMSMC), we measured oxygen radical production with MitoTracker red.
Results
Ab40 dose-dependently constricted penetrating arterioles by ∼25%, decreased dilation to low concentrations of ATP and enhanced transient ATP-induced constriction. Ab40 dose dependently increased fluorescence in RCMEC and RCMSMC, which was dose-dependently inhibited by MnTBAP (O2- and peroxynitrite scavenger), but not by superoxide dismutase or catalase.
Conclusion
Acute Ab40 directly affects cerebral arterioles. Increased Ab40 after head trauma may lead to arteriolar constriction and reduced dilatory response to ATP, contributing to local hypoperfusion. Production of oxygen radical, O2- and/or peroxynitrite, may be one mechanism involved in the Ab40 effects observed.
Footnotes
Acknowledgements
Supported by NIH RO1 NS30555, NIH P50 AG05681 and ADRC Washington University.