Peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor with key roles in adipocyte differentiation and glucose homeostasis. G3335 is a cell-permeable dipeptide that potently antagonizes PPARγ (Kd = 8.34 μM). It reversibly and competitively blocks activation of PPARγ by rosiglitazone (IC50 = 8-32 μM). G3335 is active in vivo, abolishing the protective effects of rosiglitazone in experimental spinal cord injury in rats. G3335 has also been used to evaluate the role of PPARγ in neurotoxicity studies.