Are there cards which turn life gain into damage instead?
Yes, there's Rain of Gore.


  If a spell or ability would cause its controller to gain life, that player loses that much life instead


As well as False Cure.


  Until end of turn, whenever a player gains life, that player loses 2 life for each 1 life he or she gained.


There's also Sanguine Bond.


  Whenever you gain life, target opponent loses that much life.