This review presents mechanisms of action and a review of the clinical applications of injections currently in development for localized fat reduction. After being received with initial enthusiasm earlier in the decade, mesotherapy and other injectable methods for fat loss (Lipodissolve, PC/DC, DC, injection lipolysis, adipolysis) have been subjects of critical scrutiny by the media and the US Food and Drug Administration. Several medications with novel detergent and lipolytic activity are in development and have demonstrated potential as minimally invasive fat reducing treatments.
Key points
- 1.
The US Food and Drug Administration (FDA) or any regulatory body worldwide has not approved injectable therapies to remove small quantities of fat.
- 2.
Lipodissolve and mesotherapy are unapproved combinations of unregulated compounded medication associated with adverse events and controversy.
- 3.
An adipolytic medication, sodium deoxycholate, is in registration trials for the reduction of submental fat.
- 4.
A lipolytic medication, a combination of a beta agonist (solmeterol xinafoate) and a steroid (fluticasone propionate), is in registration trials for the reduction of abdominal fat.
- 5.
The clinical applications of the (currently) unapproved medications presented in this review represent the authors experiences and a summary of the literature, not the outcome of clinical data generated through the ongoing pharmaceutical development of adipolytic or lipolytic formulations.
Since Rittes developed the procedure of injecting subcutaneous fat for localized reduction, a decade of erratic progress and setbacks in the use and understanding of injectable therapies for fat has passed. After being received with initial enthusiasm earlier in the decade, by 2007 mesotherapy and injectable methods for fat loss (termed most often as Lipodissolve, injection lipolysis, and injection adipolysis) were the subjects of critical scrutiny by the media and the US Food and Drug Administration. Despite the fact that the process of liposuction developed in much the same way (first tried on patients and then studied in the laboratory), the reputation of injectable fat loss therapies remains tarnished whereas, liposuction is the second most popular aesthetic procedure in the United States.
Liposuction removes fat by mechanical avulsion. The process has been enhanced by ultrasound, vibration, laser assistance, and radiofrequency heating. Nonsurgical fat reduction options include cryolipolysis, various types of external radiofrequency and ultrasound, low-level light therapy, and various injection methods. Although traditional mesotherapy remains unproven as a fat reducer, multiple researchers have confirmed the efficacy of injecting deoxycholate-based compounds, with recent focus on clarifying the exact mechanism of action as well as optimizing safety. The two most commonly used injectable formulas are phosphatidylcholine/deoxycholate (PC/DC) and deoxycholate (DC) alone. The use of additives or cocktail-type formulas, which defined traditional mesotherapy, has become less and less popular as proof of their lack of therapeutic efficacy and the presence of side effects has become well known. Therefore, the focus of this article rests primarily on injectable PC/DC and DC as methods to locally reduce fat.
Despite nonapproval by any regulatory body worldwide for the purpose of localized fat loss, practitioners have been using approved PC/DC combinations, such as Lipostabil (Aventis; Frankfurt, Germany) or Lipobean (Amipharm; Seoul, Korea), off-label for subcutaneous fat reduction in Europe and Korea, respectively. Clinicians using PC/DC combination or DC alone elsewhere, including the United States, obtain their medications from compounding pharmacies. Over the past decade, clinical practice has changed in that PC/DC or DC formulas have been replaced with more dilute solutions in an effort to increase safety and reduce side effects. Furthermore, although US users tend to treat small areas, such as the neck and jawline, lipomas, and bra rolls, other high-volume users, such as Korean physicians, treat larger areas, such as the abdomen, arms, and thighs. Low treatment costs and the availability of a standard, pharmaceutical-grade formula make injection lipolysis a popular fat reduction treatment in Korea, although the rest of the world has not seen a similar rise in popularity.
Mechanism of action
Membrane Disintegration
The mechanism of adipocyte lysis following injection of phosphatidylcholine or deoxycholate has been the subject of debate for many years. Several aspects of the controversy persist.
The mechanics of adipocyte lysis, the lytic agent, and the role of phosphatidylcholine, if any, are still conjecture to many practitioners, despite publication of scientifically proven illustrations of mechanism of action over a 5-year period. Speculation spoken as truth has led many clinicians to think and propagate the notion that rather than fat cell lysis caused by disintegration of cell membrane by detergent (DC), the scientifically proven mechanism, that adipocyte lysis following PC/DC or DC injections is induced by apoptosis, stimulation of hormone sensitive lipase, or the beta-adrenergic-stimulated egress of glycerol and fatty acids, all unsubstantiated theories.
The process of oncosis reveals the mechanism of action of detergent substrates on fatty tissue. Oncosis differs from the term necrosis as the method of cell death in that necrosis describes what happens to cells only after death. The process of oncosis, a term revived by cellular pathologists in 1995, was originally described by von Recklinghausen in 1910. The term oncosis is based on the Greek word for swelling, onkos . This process is usually seen after an anoxic event, which can be precipitated by an infarct or by a sudden cutoff of cellular oxygen. Clinically, the process is usually a regional one, localized to the affected tissue. It is characterized by sudden onset of profound cellular swelling and subsequent formation of blebs or mechanical insults in the cell wall, which cause an increase in membrane permeability. A sharp drop in regional pH is seen in the region caused by cellular oxygen deprivation. There is a subsequent shift to anaerobic glycogen metabolism. Glycolysis produces lactic acid, which in severely ischemic tissues is unable to be removed because of the lack of local circulation. If local circulation is restored at this point, cell death does not occur. If cellular respiration is not restored, lysosomes leak hydrolase into the favorable acid environment, causing further damage to the cell membrane. Irreversible cell destruction continues as the cell wall undergoes lysis. The detergent effect of sodium deoxycholate histologically creates the appearance of moth eaten holes in the adipocyte membranes immediately upon injection, perhaps promoting the lysosome hydrolase activity. Although the cells can repair small areas of membrane injury, larger areas of damage create an irreparable cascade of events leading to cell death.
Subsequent loss of mitochondria function, with subsequent insufficient adenosine triphosphate reduces cell functioning, sodium-potassium ion pump activity, and further regional swelling. Cellular and soft-tissue swelling reduce local circulation, with closing pressure of venules leading to the no-reflow phenomenon, as is seen in tissue affected by the sudden failure of venous circulation in a free flaps. Profound localized swelling creates an opportunity for extensive fat necrosis and even overlying skin loss is at risk (see later discussion).
Apoptosis
Claims of an apoptotic mechanism of cell death following PC/DC injections began with Peckitt in 2006, who describes a complex caspase cascade. Apoptosis is an important means of regulating cell populations and is characterized by noninflammatory cell shrinkage followed by phagocytosis. Studies performed in Regensburg tested tissue injected with a phosphatidylcholine/deoxycholate formula for apoptotic markers, which were found to be present. The process of apoptosis, characterized by noninflammatory shrinkage of affected cells, does not clinically or histologically correlate with the tissue reaction generated by deoxycholate injection. Furthermore, as of this writing (Bechara FG, unpublished data, 2011) there is unpublished experimental data to support a lytic, nonapoptotic mechanism of PC/DC-induced cell death.
Two types of cell death can be seen following a single subcutaneous injection of a toxic substance. Histologically, the region that stains pink under a hematoxylin and eosin (H&E) preparation indicates death by oncosis. Karyolytic nuclei are another oncotic marker. At the periphery of the region of coagulation necrosis, along the margin of live and dead cells, the occasional histologic presence of half moon nuclei marking apoptotic cell death is observed. These cells are few, and are only noted at the edge of the much larger region of oncotic tissue. If an apoptotic index (ratio of counted oncolytic dead cells vs apoptotic dead cells per hundred dead cells) is counted, the index is quite low (0 to 3 cells per 100) depending entirely on the region counted. Apoptosis is, by definition, a nonmassive reaction. The only current reproducible method of generating large regions of apoptosis is the repeated freezing and thawing of regional tissue, as is seen in cryolipolysis.
Although causative factors may vary, oncosis is generally induced by situations producing anoxia; whereas, apoptosis is either programmed because of cell signaling or by thermal shock. Histologic evaluation of detergent injected fat can clearly define both. Along with swelling, oncosis is accompanied by the presence of inflammation, specifically a neutrophilic infiltrate, and a later migration of macrophages in to the region.
Mechanism of action
Membrane Disintegration
The mechanism of adipocyte lysis following injection of phosphatidylcholine or deoxycholate has been the subject of debate for many years. Several aspects of the controversy persist.
The mechanics of adipocyte lysis, the lytic agent, and the role of phosphatidylcholine, if any, are still conjecture to many practitioners, despite publication of scientifically proven illustrations of mechanism of action over a 5-year period. Speculation spoken as truth has led many clinicians to think and propagate the notion that rather than fat cell lysis caused by disintegration of cell membrane by detergent (DC), the scientifically proven mechanism, that adipocyte lysis following PC/DC or DC injections is induced by apoptosis, stimulation of hormone sensitive lipase, or the beta-adrenergic-stimulated egress of glycerol and fatty acids, all unsubstantiated theories.
The process of oncosis reveals the mechanism of action of detergent substrates on fatty tissue. Oncosis differs from the term necrosis as the method of cell death in that necrosis describes what happens to cells only after death. The process of oncosis, a term revived by cellular pathologists in 1995, was originally described by von Recklinghausen in 1910. The term oncosis is based on the Greek word for swelling, onkos . This process is usually seen after an anoxic event, which can be precipitated by an infarct or by a sudden cutoff of cellular oxygen. Clinically, the process is usually a regional one, localized to the affected tissue. It is characterized by sudden onset of profound cellular swelling and subsequent formation of blebs or mechanical insults in the cell wall, which cause an increase in membrane permeability. A sharp drop in regional pH is seen in the region caused by cellular oxygen deprivation. There is a subsequent shift to anaerobic glycogen metabolism. Glycolysis produces lactic acid, which in severely ischemic tissues is unable to be removed because of the lack of local circulation. If local circulation is restored at this point, cell death does not occur. If cellular respiration is not restored, lysosomes leak hydrolase into the favorable acid environment, causing further damage to the cell membrane. Irreversible cell destruction continues as the cell wall undergoes lysis. The detergent effect of sodium deoxycholate histologically creates the appearance of moth eaten holes in the adipocyte membranes immediately upon injection, perhaps promoting the lysosome hydrolase activity. Although the cells can repair small areas of membrane injury, larger areas of damage create an irreparable cascade of events leading to cell death.
Subsequent loss of mitochondria function, with subsequent insufficient adenosine triphosphate reduces cell functioning, sodium-potassium ion pump activity, and further regional swelling. Cellular and soft-tissue swelling reduce local circulation, with closing pressure of venules leading to the no-reflow phenomenon, as is seen in tissue affected by the sudden failure of venous circulation in a free flaps. Profound localized swelling creates an opportunity for extensive fat necrosis and even overlying skin loss is at risk (see later discussion).
Apoptosis
Claims of an apoptotic mechanism of cell death following PC/DC injections began with Peckitt in 2006, who describes a complex caspase cascade. Apoptosis is an important means of regulating cell populations and is characterized by noninflammatory cell shrinkage followed by phagocytosis. Studies performed in Regensburg tested tissue injected with a phosphatidylcholine/deoxycholate formula for apoptotic markers, which were found to be present. The process of apoptosis, characterized by noninflammatory shrinkage of affected cells, does not clinically or histologically correlate with the tissue reaction generated by deoxycholate injection. Furthermore, as of this writing (Bechara FG, unpublished data, 2011) there is unpublished experimental data to support a lytic, nonapoptotic mechanism of PC/DC-induced cell death.
Two types of cell death can be seen following a single subcutaneous injection of a toxic substance. Histologically, the region that stains pink under a hematoxylin and eosin (H&E) preparation indicates death by oncosis. Karyolytic nuclei are another oncotic marker. At the periphery of the region of coagulation necrosis, along the margin of live and dead cells, the occasional histologic presence of half moon nuclei marking apoptotic cell death is observed. These cells are few, and are only noted at the edge of the much larger region of oncotic tissue. If an apoptotic index (ratio of counted oncolytic dead cells vs apoptotic dead cells per hundred dead cells) is counted, the index is quite low (0 to 3 cells per 100) depending entirely on the region counted. Apoptosis is, by definition, a nonmassive reaction. The only current reproducible method of generating large regions of apoptosis is the repeated freezing and thawing of regional tissue, as is seen in cryolipolysis.
Although causative factors may vary, oncosis is generally induced by situations producing anoxia; whereas, apoptosis is either programmed because of cell signaling or by thermal shock. Histologic evaluation of detergent injected fat can clearly define both. Along with swelling, oncosis is accompanied by the presence of inflammation, specifically a neutrophilic infiltrate, and a later migration of macrophages in to the region.
Identification of lytic agent
Deoxycholate was initially isolated from PC in 2004 and identified as the predominant lytic agent in the PC/DC formulation. Early literature supporting the role of DC as the lytic agent has been independently supported by a stem cell study performed by numerous studies. Occasionally, publications persist the notions that phosphatidylcholine is the active agent in PC/DC treatments. The difficulty in identifying the true lytic agent is that phosphatidylcholine is not significantly water soluble and therefore isolation of PC in water-based cell lysis experimental models have been technically difficult to reproduce. This problem was solved by identifying an inert solvent that was used to isolate PC as a single agent. The study performed at the McGowan research institute in Pittsburgh isolated PC, as well as other common constituents of Lipostabil and compounded PC/DC mixtures, to determine cytotoxicity and lipolytic activity of each constituent, using cultured adipocytes derived from stem cells. Cytotoxicity was calculated using lactate dehydrogenase and oil red O. Lipolytic activity (as opposed to cell lysis, lipolysis maintains cell integrity) was measured using a glycerol and triglyceride assay. The measure of permanent destruction of adipocytes is important, as many lipolytic agents only cause temporary egress of glycerol and triglyceride, and therefore only temporary results can be achieved. Table 1 shows the absence of any lytic activity by isolated PC and the results of the lysis assays. The only agent that causes adipolysis in a standard Lipostabil formula, or compounded PC/DC formulation, is sodium deoxycholate.
| Test Solution | Adipocyte Cell Lysis Obtained with this Solution |
|---|---|
| PC50/DC42 | ++ |
| Deoxycholate 1.0% | +++ |
| Deoxycholate 2.4% | +++ |
| Phosphatidylcholine 5.0% in mineral oil | 0 |
| Isuprel 0.08% injectable | 0 |
| Local anesthetic 5.0% | 0 |
| Saline 0.9% (control) | 0 |
| Benzyl alcohol | 0 |
Utility of DC alone versus PC/DC
Phosphatidylcholine, a phospholipid comprising a significant percentage of mammalian cell membranes, lacks detergent or adipolytic activity, as previously discussed; it would be counterintuitive to think that a substance that comprises most of the biphospholipid structure of a cell membrane could induce membrane disintegration.
There is great variation in the degree of tissue response, the dispersion of adipocyte lysis, and the onset of cell reaction between PC/DC and DC formulations. Previous studies have demonstrated that subcutaneous injection of deoxycholate and PC/DC both produce localized inflammatory reactions, with DC ( Fig. 1 ) appearing to produce more inflammation and cell lysis compared with PC/DC mixtures. Much if not all of these differences can be accounted for the fact that PC has an apparent buffering effect upon DC, thereby minimizing inflammation/tissue damage. This theory has been supported by recent experimental data, which demonstrates attenuation of DC LD 50 (the concentration of a substance at which 50% of cells die) by the addition of PC. Additional studies reveal that PC/DC combinations produce more dispersion ( Figs. 2, 3 ) relative to DC alone. As increasing concentrations of deoxycholate are introduced into PC/DC combinations, the onset of adipocyte lysis is hastened.
Isolated deoxycholate as well as PC/DC combinations reduce localized fat, and when injected with correct technique, are safe and efficacious. Clinical indications should direct which one of these compounds should be used for each condition. When a small, localized fatty deposit is present and near total removal is the desired outcome, DC alone (at 1% or less) would be indicated. The best illustration of this would be treatment of submental fat ( Fig. 4 ), bra strap fat, and lipomas. When a broader region is the target, some clinicians add PC thinking that it permits a more even dispersion of the solution. If a large, broad, or thick region of fat is the desired treatment region, some clinicians increase the PC/DC ratio to 1:<1 to minimize the PC-induced cholinergic side effects or significantly dilute PC/DC solutions.The thought that PC is inert, or perhaps even a buffer that inhibits the lytic activity of DC motivates most clinicians to consider using DC formula without PC, at low concentrations.
Tissue specificity of deoxycholate
In cell cultures, a significant, dose-dependent nonspecific toxic effect of deoxycholate, as well as formulas containing PC/DC, has been reported ( Fig. 5 ). Adipocytes, melanoma cells, skeletal muscle cells, keratinocytes, and fibroblasts are more or less uniformly destroyed with DC, although keratinocytes appear to be more susceptible to DC relative to the others.
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