The thing is "amico mio" as such is correct Italian, it just sounds fake. You'd probably just say "amico", which is what I hear Italians say every so often.
The problem with Lou is not so much spoken, but written language though. Whereas "my friend" can be quite casual in written English (you're not necessarily talking to someone you know good enough to call him your friend), it's not so casual in written Italian. It makes no sense to put in a phrase like that unless you're a retarded freak.