Distinct with mongo and node js

I am trying to get records using a rest service implemented with node js to populate a autocomplete of jquery. Here is the method

db.collection('publication', function(err, collection) {
        collection.distinct('title',{'$or':[{type:'an'},{type:'pub'}]}).toArray(function(err, items) {
                res.jsonp(items);
            });
        });
};

The query in mongo works ->

 db.publication.distinct('title',{'$or':[{type:'an'},{type:'pub'}]}) 

returns [ "Product", "Event" ] but the result is different when I use find, with find would be->

{ "_id" : ObjectId("51fbb2124e49d03810000000"), "title" : "Anuncio" }
{ "_id" : ObjectId("51fbb2ae4e49d03810000001"), "title" : "Evento" }

With the second way the autocomplete works, but with the first not

The error shown in node is: object is not a function.

Finally what I need is to return a json with the records to populate the autocomplete which is populated like this:

$('#search').autocomplete({
        source: function(req, res) {
            $.ajax({
                url: "http://www.example.com:3000/autocomplete/" + req.term ,
                dataType: "jsonp",
                type: "GET",
                data: {
                    term: req.term
                },
                success: function(data) {
                    res($.map(data, function(item) {
                        return {
                            label: item.title,
                            value: item.title
                        };
                    }));
                },
                error: function(xhr) {
                    alert(xhr.status + ' : ' + xhr.statusText);
                }
            });
        });