I have not seen any open letter supporting FIDE Champion Topalov published on ChessBase.Com until today, there are two open letters on Topalov side , one from the " famous Bulgarian grandmasters" the other one is from the President of Bulgaria

first read what the ChessBase.com try to defend that their position was neutral.
from Chessbase.com:
"...We did not leave a single letter written by grandmaster or title chess player in support of Topalov unpublished. Below, incidentally, is the first we found-and it took some trouble locating it"

from "famous Bulgarian grandmasters" open letter called "Hand off from the World Champion!"
.....the high point of this dirty aggression was reached with the open letter of Russian grandmasters Peter Svidler and Evgeny Bareev. What a moral position do they represent, since they are demonstrably part of the Challenger's staff? of what do you, dear sirs, accuse Topalov ? That he fights and does it openly and honestly?
from the President of Bulgaria:
"... It is no secret the representatives of the match organizing nation often have certain advantages, I firmly stand the idea that political games must not influence situation on the board...."