Overview Topics |
Amyloid beta plays an important role in Alzheimer's disease. It has been shown to
induce oxidative stress in neurons, and to activate microglia. Yan et al [1]
studied a "receptor for advanced glycosylation end products" (RAGE) implicated
in the effect of beta amyloid on neurons and microglia.
The authors
showed a dose-dependent measure of cellular oxidative stress (as measured by
generation of thiobarbituric acid reactive substances TBARS) in response to
various doses of A-beta. They also showed how the binding of A-beta depends on
the concentration of A-beta supplied.
In their paper, Figure 1 b shows
levels of oxidative stress (TBARS) of rat cortical cells at various A-beta
concentrations in the range 0 - 1 micro M. Figure 1d shows specific binding of
A-beta at various A-beta concentration in the range 0-160 n M. From fig 1d we
see half-maximal binding occurring at approximately 40 nM A-beta.
The following data appears in Fig 1b of Yan et al [1], given as (A-Beta
concentration in nM, TBARS indicator of oxidative stress): [(0,1), (0.063, 3.5),
(0.125, 4), (0.25, 6), (1, 6)].
where X represents oxidative stress and
concentration is in nM.
We can fit an approximate Michaelis-Menten function of the form
where B is the
specific binding (appears to be total amount bound, not rate of binding) and
[A-beta] is concentration of Amyloid-beta in nM. According to Yan et al, there
were roughly molecules
bound per cell at saturation on mouse endothelial cells. They also cite an
equilibrium constant for binding:
.
(This is the ratio of reverse to forward rate constants for the binding :
.
Cultured rat cortical neurons, and cultured mouse brain microvascular endothelial cells, incubated with A-Beta(1-40) for TBARS experiments. For binding dose-response, I125-labled A beta was used, and cultures were incubated at 4 degrees C for 3 hrs.) Specific binding defined as total I125-A-beta binding in presence of 100-fold excess of unlabeled A-beta.
In Yan et al Fig 6 c is shown the binding of A-beta by micorglia. The authors found
for A-beta binding by these cells. A Michaelis Menten function to fit their
data (Fig 6c) would be
where B = amount A-beta bound in strange units (fmol per well)
and the [] conc is in nM units. The authors also measure the A-beta induced
secretion of TNF by microglia and found it to be in the range 0-200 pg/ml for
10^{6} cells incubated with 1 micro M A-beta for 4 hrs at 37C.
System
details: BV-2 cells are immortalized mouse microglia cells.