Primary human hepatocytes and NPCs from three different donors were cultured as spheroid microtissues together with pathophysiological levels of free fatty acids (FFAs), glucose and insulin in order to emulate liver steatosis, oxidative stress and insulin resistance associated with obesity and NAFLD (Supplementary Table 12; donor 1)33,34. Here, INS is linked to obesity due to melanocortin 4 receptor deficiency.