Intramuscular Nanofat Injection Promotes Inflammation-Induced Gastrocnemius Regeneration in Syngeneic Rat Sciatic Nerve Injury Model

Abstract

Background: Mechanical emulsification of adipose tissue to concentrate protein and stromal cell components (ie, nanofat) has gained considerable interest in clinical practice. Although the regenerative potential of nanofat has largely been used in aesthetic applications, these effects have considerable potential in reconstruction as well. Here, the authors investigated the therapeutic properties of nanofat injected directly into the denervated gastrocnemius after a sciatic nerve injury in Lewis rats. Methods: Muscle denervation was induced by transecting and immediately repairing the sciatic nerve. Inguinal and subcutaneous adipose was harvested from donor rodents, processed into nanofat, and then injected intramuscularly into the gastrocnemius. Gait analysis was performed weekly. Rodents were euthanized at 9 and 12 weeks, after which tetanic contraction force was measured, and gene expression, histology, and cytokine multiplexing were performed. Results: Intramuscular injection of nanofat significantly increased maximum tetanic force generation at 9 and 12 weeks. The forces of the nanofat-injected gastrocnemii were better correlated to their contralateral gastrocnemii relative to controls. Muscle repair-associated inflammatory gene expressions were significantly up-regulated in nanofat-injected gastrocnemii. Cytokines interleukin (IL)-1β, IL-18, vascular endothelial growth factor, granulocyte-macrophage colony-stimulating factor, and tissue inhibitor of metalloproteinase-1 were significantly higher in nanofat-injected gastrocnemii relative to control gastrocnemii, and the tetanic force was linearly and significantly correlated to IL-1β and IL-18 and their interacting effects. Conclusions: Intramuscular injection of emulsified adipose tissue (nanofat) significantly increased gastrocnemii contraction force after sciatic nerve injury, with prolonged reconstructive inflammation by means of CD68, inducible nitric oxide synthase, IL-1β, and IL-18 all being potential mechanisms for this recovery. This application could potentially increase the therapeutic breadth of nanofat to include muscular recovery after nerve injury. Clinical Relevance Statement: The authors’ study investigates a clinically translatable therapy to mitigate muscle atrophy after nerve injury.

Evaluation of Postoperative Nerve Regeneration in Murine Experimental Models Subjected to Nerve Transection

“…In this study, eight articles [16,[19][20][21][22]25,26,31] utilized the "Sciatic Functional Index" (SFI) for evaluating nerve function. Based on Medicaneli et al (1982) [43], the method is reliable for assessing muscle strength index and tissue electrophysiology, thus evaluating the performance of nerve function in the injured lower limb.…”

“…Regarding the Muscle Weight Ratio (MWR), nine articles used this method [17,19,[21][22][23]25,26,29,31]. This parameter appears to be used due to the ease of its application in studies, often being the only type of functional evaluation performed [23,29].…”

Short-term cryoprotectant-free cryopreservation at −20°C does not affect the viability and regenerative capacity of nanofat

“…Nanofat is generated by mechanical emulsification and filtration of adipose tissue and has been evaluated in various experimental and clinical settings to prove its beneficial regenerative properties ( Menkes et al, 2020 ; Qi et al, 2021 ; Rageh et al, 2021 ; Han et al, 2022 ; Schilling et al, 2023 ; Tran et al, 2023 ). This fat derivative contains high quantities of growth factors, mesenchymal stem cells and microvascular fragments, which stimulate blood vessel and tissue formation ( Jeyaraman et al, 2021 ).…”