In past years, nonsurgical lipolysis has increased , and is the most economical use of subcutaneous injections to reduce local fat via chemical lipolysis . PPC injections using a variety of PPC formulations are popular as a treatment of local adiposities . However, no product intended for lipodissolution has yet been approved by the Food and Drug Administration, Medicines and Healthcare Products Regulatory Agency (MHRA), because of lack of data concerning safety and efficacy .
A PPC formulation generally used clinically consists of PPC and SD . It has been suggested that SD, the detergent in the PPC formulation, is the active lipodissolving substance, and not PPC . The main side effects of injection of PPC formulations are relatively minor, and include swelling, bruising, and sensitivity to touch under the skin in areas with the lipodissolution treatments . However, since injection of SD causes focal necrosis and inflammation in human lipomas , it is entirely conceivable that the aforementioned side effects of PPC formulations are due to SD, not to PPC itself. Presently, we confirmed that SD induces cell membrane lysis, resulting in necrosis. Interestingly, however, the results of the MTT assay clearly indicate that PPC alone without SD induced cell death of 3T3-L1 pre-adipocytes. The results also demonstrated that the effects of inducing 3T3-L1 cell death by PPC formulation did not depend only on SD. In addition, our flow cytometric experiments showed that Lipobean® treatment resulted in cell membrane lyses because of SD (data not shown). A large discrepancy in the extent of cell viability was presently evident between 0.5 mg/ml and 1 mg/ml Lipobean® (Figure 1C). These Lipobean® concentrations may be at the threshold for membrane stability.
In agreement with our study, PPC formulation and SD induce the lysis of various cell types including pre-adipocytes, normal human fibroblasts, endothelial cells, and skeletal muscle cells in a nonspecific manner . These results are very important because the injection of PPC formulation may cause tissue necrosis. However, in our study, PPC alone did not induce cell death of CCD-25Sk normal fibroblasts. It is very important that PPC reduced only adipocyte viability specifically, but did not decrease cell viability of other cell types such as fibroblasts. On the other hand, PPC formulation and SD induced cell death of both cell types. These results indicate that the SD constituent of PPC formulations initiates the cell lysis, leading to cell death. Clearly, more study is required to confirm this suggestion.
PPC induces apoptosis in cells such as colon cancer cells , vascular endothelial cells , and macrophages . Phosphorylation of stress-activated protein kinase pathways  and cleavage of caspases are main pathways of apoptosis . Especially, the death-receptor inducing activation of caspase-8 and mitochondrial pathways is the key point of apoptotic pathways . In the present study, PPC induced not only the activation of p38 and JNK, but also the cleavage of caspase-8, -9, -3, and PARP in 3T3-L1 pre-adipocytes (Figure 3). Specifically, PPC treatment unequivocably activated caspase-8 in both 3T3-L1 pre-adipocytes and differentiated 3T3-L1 cells (Figures 3B and 4C). The caspase-8 pathway is intimately involved in CD95-mediated apoptotic cell death [33, 34]. These results indicate that PPC-induced apoptosis may be due to increased death receptor activations. This possibility should be further examined to elucidate PPC-induced apoptotic pathways.
Furthermore, the increase of sub-G1 fraction is an indication of apoptosis that naturally occurs in cells , and the sub-G1 phase in the cell cycle is increased in apoptotic cell death . Therefore, to characterize apoptotic cells upon treatment of PPC, SD, and PPC formulation, flow cytometric analysis was presently performed. Treatment with 0.1 mg/ml PPC treatment increased sub-G1 phase in 3T3-L1 adipocytes. These results favor the view that PPC induces apoptosis of 3T3-L1 cells.