Like Gd, Mn is toxic, but unlike Gd, Mn is naturally present in the body (and also in pineapples) which means that long-term accumulation is less likely. The main difficulty is the lack of strong enough complexing agents because of the tendency for zinc (naturally present at relatively high concentrations in the body) to steal the ligand from Mn, a problem currently being studied:

https://onlinelibrary.wiley.com/doi/full/10.1002/ange.202115...