Volume Retention, Metabolism, and Cellular Composition of Human Fat Xenografts

BACKGROUND: To optimize the take of transferred fat, better understanding of fat graft morphology and growth properties in vivo is critical. We aim to evaluate survival, volume retention, metabolism, and cellular composition of various aliquots of human fat xenografts. METHODS: Twenty athymic nude mice were injected subcutaneously in opposing flanks with 0.1 ml (small) and 1.0 ml (large) aliquots of human fat graft. Volume (ultrasound) of fat aliquots was measured at baseline, 1, 3, and 12 weeks after implantation. Tissue metabolism ((18)F-FDG), Hematoxylin and Eosin, special stains, and immunohistochemical analysis were performed at 3 and 12 weeks to determine graft viability, cell origin, and proliferative activity. RESULTS: Only 1 of 10 small grafts were detected after 12 weeks by ultrasound and 5 of 10 were found at necropsy. Volume of large grafts decreased significantly from baseline at 3 (827 ± 195 mm(3) versus 953 ± 122 mm(3); P = 0.004) and 12 weeks (515 ± 163 mm(3) versus 953 ± 122 mm(3); P = 0.0001). Metabolism increased with time in small (0.6 ± 0.4%ID/g versus 2.0 ± 1.1%ID/g, P = 0.01) and large grafts (0.4 ± 0.3%ID/g versus 1.4 ± 0.9 %ID/g; P = 0.005). Large grafts viability decreased between 3 and 12 weeks (72 ± 20% versus 31 ± 30%; P = 0.012) although small graft viability remained unchanged. Viable and proliferating human and mouse adipocytes and chimeric blood vessels were seen within grafts at both time points. CONCLUSIONS: Larger graft aliquot was associated with better volume retention by ultrasound but lower viability by histology. Graft metabolism increased with time irrespective of aliquot size potentially due to regenerative processes of both donor and recipient origin.