Overview Topics

Beta-Amyloid binding and neurotoxicity.

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.

Oxidative stress:

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.


 

A-beta Binding to neuronal cells:

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 :

.

 

System details:

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.

Microglia and 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.

 

Parameter values obtained from this paper:

 

 

Bibliography: