Cooking pinto beans in a pressure cooker
There doesn't seem to be much of a difference in nutrition between pressure cooking and boiling beans. Cooking at pressure cooker temperatures at 10, 20, or 40 minutes instead of boiling in a pot changed the nutrition/antinutrient content and digestibility by less than 5%.

Soaking prior to cooking was generally found to be advantageous. However, the results were not unanimous, and it didn't change very much in terms of nutrition. Soaking and discarding the water was found to: 


reduce the carbohydrate fraction and maintain/increase fiber content.
reduce mineral content, but increase bioavailability.
reduce the oligosaccarides that cause flatulence.


https://www.sciencedirect.com/science/article/pii/S0308814604004649

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2621.2010.02395.x