Use adapter for catalog metadata?

Is there a way to use an adapter for getting catalog metadata from indexed object? I know plone.indexer can be used for indexes, but I want to just have the value provided by adapter added to metadata (stuff in catalog brain), so no need for index.

Not sure what you mean.
The indexer adapter will be used for the all of the indexing operation, so if you simply add a catalog metadata for foo then provide a right plone.indexer adapter for foo you can control what to be idexed (and stored in the metadata).
The presence of a foo index is not required I think.

Thanks, I thought it was not possible to use plone.indexer that way.

You could make an adapter ofcourse, which would do a catalog search on the uid of your current object's UID.
But I don't see what the added value of that would be? You already have your object 'in hand'