Ashton Kutcher's Reaction About Demi Moore's Collapse !

Ashton Kutcher had no answer when asked if Demi Moore was okay following her nitrous oxide-induced medical emergency -- hopping wordlessly into a car beside a blonde mystery woman Tuesday night.

After Ashton leaving a nightclub in Sao Paulo, Brazil -- an agency photog asks, "Is Demi okay?" ... and Ashton keeps mum, piling into an idling vehicle with two acquaintances, one female.