E5 doesn't seem to be causing any problems, I'd doubt E10 would. I wonder if Nissan thought you were asking about fuel with higher ethanol content such as E40 / E85 (85% ethanol)?
Engines see all sorts of acids which build up in oil.
Too much ethanol could damage any rubber seals in the fuel system etc. Beyond a certain percentage of ethanol content the engine management system wouldn't be able to adapt properly to the ethanol content so even regardless of seals failing etc the engine would have trouble running properly anyway... but still I doubt the engine itself would suffer hard part damage beyond minor parts such as seals. There won't be many changes to an engine itself to run even E85, changes mostly involve removing replacing rubber seals in the fuel system and breather pipes and making changes to the engine management system to allow it to cope with the different stochiometric ratios of ethanol versus petrol and different ignition timing.
Here's an example: Before ethanol was added to petrol late 1990's and early 2000's BMW V8s were fitted with rubber breather pipes at the rear end of cam covers, these breather always seemed in good condition. As soon as ethanol was used in petrol it started to turn these breather pipes into mush. Later spec / replacement BMW breather pipes seem ethanol proof, at least good enough for E5 and I would expect E10. I wouldn't know if they're OK for E85, the engine management system certainly wouldn't be able to run E85 because the engine isn't designated a flexfuel design... But I'm pretty sure that the metal bits in the engine won't be hurt by E85.
A simple way to avoid running on ethanol is to convert to LPG