Does cooking in a pressure cooker destroy nutrients?
According to Eating Well who consulted a food scientist, yes, some heat sensitive nutrients are lost, but no more so than other forms of cooking:


  Pressure cooking can reduce heat-sensitive nutrients (e.g., vitamin C,
  folate) and bioactive phytonutrients, such as betacarotene,
  glucosinolates (helpful compounds found in cruciferous vegetables) and
  omega-3 fatty acids, that are beneficial for human health. But so do
  other cooking methods—and generally to more or less the same extent.


but in other cases, as in grains and legumes, the pressure-cooking is helpful:


  in the case of grains and legumes, although the vitamins and
  heat-sensitive vitamins and phytonutrients are vulnerable to
  deterioration, the net result of pressure-cooking is a positive
  nutritional gain—from the increased digestibility of the
  macronutrients (protein, fiber and starch) and the increased
  bioavailability of the essential minerals.