ARG2 and obesity due to melanocortin 4 receptor deficiency: Consistent with an increase in nitrogen levels in obesity-associated PDA, we found a significant accumulation of 15N-ammonia in tumors of the obese, the levels of which tended to further increase upon ARG2 knockdown (P ≤ 0.05, one-way ANOVA followed by Tukey test, Fig. 4e).