INTRODUCTION

Various treatments for hair loss include drug therapy, hair transplant surgery, low-level light therapy, platelet-rich plasma (PRP) therapy, microneedling, artificial hair implants, and others.[12345] Each of these treatment options has its own advantages and shortcomings, and thus there is always a search for new and alternative therapies. In recent times, the role of AT in the hair growth cycle has been explored. A number of recent publications have supported the hypothesis that AT, which is a complex and biologically active tissue, can be a source of stem cells and GFs that can influence and stimulate hair growth.

INTERACTIONS BETWEEN ADIPOSE CELLS AND NORMAL HAIR CYCLE

HFs are closely associated with subcutaneous fat in several ways. Usually, HFs encompassed by subcutaneous fat cells and the dermis shape an interfollicular dermal macro-environment, which is imperative for maintaining the best possible growth of bulge and follicle cells.[67] The AT appears to experience comparative changes in the HF cycle. Physiologically, fat tissue encompassing HFs have been found to increase from telogen to anagen.[7] Adipocytes emit BMP2 during the late anagen to the middle of the telogen stage, which supports the resting state of hair follicle stem cells (HFSCs) in the niche; however, the emission of BMP2 is lessened toward the late telogen stage, which bolsters the activation of HFSCs. Adipocytes, thus, have a critical role in extending the anagen stage.[8] Likewise, correspondence between fat tissue and the epithelium is continuous and vital. Transformations hindering the hair cycle have been found to restrain adipogenesis, which suggests that epithelial cells send signals actuating the expansion of the adipocytes.[9]

ADIPOSE-DERIVED STEM CELLS AND POSSIBLE ROLE IN HAIR GROWTH

The AT contains numerous cells, including adipocytes, adipose-derived stem cells (ADSCs), endothelial cells, fibroblasts, mural cells, and leukocytes [Figure 1].[10] The ADSCs have self-renewable capacity and display multi-lineage potential.[1112] The number of pluripotent cells contained in a cubic centimeter of AT is 100 to 1,000 times larger than the number of stem cells contained in the bone marrow.[13] Hence, ADSCs have shown potential in regenerative medicine.[14] The ADSCs also secrete various GFs that have been shown to promote hair growth. These GFs include vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), insulin-like growth factor-1 (IGF-1), platelet-derived growth factor (PDGF), keratinocyte growth factor (KGF), and fibroblast growth factor-1 and 2(FGF-1, FGF-2) [Table 1].[151617181920] The ADSCs-derived proteins improve hair growth and protect human dermal papilla cells against cytotoxic injury caused by androgen and reactive oxygen species. Moreover, the conditioned media of ADSC (ADSC-CM) induces the anagen phase and promotes hair growth in mice, and it enhances the elongation of hair shafts in ex vivo human hair organ cultures. The ADSC-CM promotes hair growth in vitro, ex vivo, and in vivo.[21]

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Figure 1

Flowchart showing composition of adipose tissue

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The various biomolecular GFs that have a role in hair growth and their actions are as follows[22]:

• HGF and HGF activators (discharged by dermal papilla cells (DPCs)) enhance the proliferation of follicular epithelial cells.

• Epidermal growth factor (EGF) improves the activity and growth of follicle outer-root sheath cells by activation of Wnt/β-catenin flagging.

• Basic-FGF improves the advancement of HFs.

• Interleukein-6 (IL-6) is involved in WIHN through STAT3 enactment.

• VEGF improves perifollicular angiogenesis.

• Transforming growth factor-β (TGF-β) stimulates the signaling pathways that manage the hair cycle.

• IGF-1 improves the migration, survival, and proliferation of HF cells.

• IGF binding protein-1 to -6 (IGFBP) manages the IGF-1 effect and its connection with extracellular matrix proteins at the HF level.

• BMP maintains the DPC phenotype (fundamental for stimulation of HFSCs).

• BMPR1a maintains the proper identity of the DPCs.

• Macrophage-colony stimulating factor (M-CSF) is involved in wound-induced hair growth.

• M-CSF receptor (M-CSFR) is involved in wound-induced hair growth.

• PDGF and PDGF receptor (PDGFR-β/-α64) upregulate the genes associated with HF separation, induction, and control of anagen. PDGF and its receptors are fundamental for follicular improvement.

• Wnt3a is involved in HF advancement through β-catenin flagging.

• PGE2 stimulates anagen in HF.

• PGF2α and analogs enhance change from telogen to anagen.

• PGE2 or hindrance of PGD2 or PGD2 receptor D2/GPR4477 enhances follicle regeneration.

STROMAL VASCULAR FRACTION

The stromal vascular fraction (SVF) is a heterogeneous population of stem/stromal cells isolated from the perivascular and extracellular matrix of adipose tissue complex (ATC). The SVF is suitable for use in regenerative surgery due to its lack of immunogenic properties, its simplicity of extraction, its multipotential characteristics, the simplicity of separating it into different cell lines, and its significant potential for angiogenesis. The SVF is commonly divided into cellular SVF (cSVF) and tissue SVF (tSVF). Cellular SVF is obtained from ATC by collagenase digestion, incubation/isolation, and pelletization by centrifugation. However, enzymatic disaggregation may alter the relevant biological characteristics of AT and hence in many countries, the isolation of cellular elements is most often limited to controlled clinical trials and subject to regulatory review. Several alternative, nonenzymatic methods of AT processing have been developed to obtain an autologous tSVF, which is easier, quicker, has minimal manipulation of cells, and, hence, bypasses regulatory approval and can be adopted in a clinical setting. These nonenzymatic methods use mechanical or physical forces to loosen the structural integrity of the AT extracellular matrix and periadventitial structures. Emulsification (nanofat), condensation, microfat, and mini-microfat are some examples of such mechanical processes. Commercial kits are also available for such extraction.[23]

Several recent scientific publications that are analyzed later have projected ADSCs as the next biological treatment, as the next PRP therapy. Several companies have marketed various products for purified fat preparations. Although this treatment is not as yet an established form of treatment, there are several reviews and early original articles that talk of its possible role in hair loss management.

ANALYSIS OF STUDIES ON ADIPOSE TISSUE AS A TREATMENT FOR HAIR REGENERATION [SUMMARIES ON TABLES 2 AND 3]

We searched Pub Med, Science Direct, Researchgate, Europe PMC, and Google Scholar for all articles with the following search terms: adipose tissue AND hair growth, fat grafting or nanofat AND alopecia, ADSC AND alopecia, SVF AND alopecia. The exclusion criteria were non-English language publications, animal studies, and those studies where AT was not used as a treatment for hair loss. This left us with 21 articles. We have analyzed these studies and presented their review.

Fat has been used in several ways for hair regeneration: AF transfer, nanofat, ADSCs, SVF, and micrografts of adipose tissue derived follicular stem cells. These have been tried not only in androgenetic alopecia (AGA), but also in other forms of alopecia such as alopecia areata (AA) and scarring alopecia. It has also been tried after the hair transplantation procedure. Each of these different aspects is dealt with in the analysis of the following studies.

STUDIES USING AUTOLOGOUS FAT

Fat transfer is an established treatment for atrophic scar, post-injury scars, scleroderma etc. Incidental hair growth has been observed on and around such scars, alopecic patches, and also AGA, treated with AF in various studies.

Nilforoushzadeh et al. reported a study including nine adults (five women, four men) with AGA who were injected with autologous AT in a single session. Hair regeneration was assessed via measurement of hair diameter and density using trichogram. Hair pull test was also done. There was a significant increase in hair diameter and density and a significant decrease in hair pull test in all patients at three and six months after the treatment.[24]

Nilforoushzadeh et al. also reported a case of scarring alopecia after trauma that responded to AF transfer, resulting in increased hair growth at the alopecic patch.[25]

Tedesco M published a case report on fat transfer in a 41-year-old female patient with 25 years of recurrent folliculitis decalvans not responding to conventional therapies. Two sessions were conducted at an interval of five months. Patient did not develop new folliculitis after treatment and were able to discontinue the antibiotic therapy. Hair regrowth was observed in the peripheral area affected by the disease.[26]

Dini M et al. reported a case of a 25-year-old woman with AA of the left eyebrow with atrophy caused by an intralesional steroid. After one session of autologous fat transplantation (AFT), not only was there an expected improvement in the area of atrophy but also hair regrowth was observed in the alopecic lesion three months after the fat transfer.[27]

Cho SB et al. reported a case of a 26-year-old woman with alopecia secondary to localized scleroderma that presented as an atrophic alopecic patch on the frontal scalp along with linear skin depression of the forehead. Two sessions of AFT at a three months interval was performed. In addition to improvement in the atrophy and depression, regrowth of terminal hairs was observed on the alopecic patch at three months, which had further grown thicker and longer after the second AFT.[28]

STUDIES USING NANOFAT

Nanofat is a form of mechanically emulsified SVF first described by Tonnard et al. in 2013.[29] Vestitia et al. described a study using nanofat for AGA in 12 male patients. The authors prepared nanofat using the Tonnard protocol, and a single session of nanofat injection was given. Each treated area showed an increase in the number and thickness of hairs.[30]

STUDIES USING MICROGRAFTS OF ADIPOSE TISSUE DERIVED FOLLICLE STEM CELLS

In a study reported by Pietro Gentile, 33 patients (23 males, 10 females) with AGA were injected with an autologous solution of micrografts from scalp tissue containing Human Intra- and Extra- Dermal Adipose Tissue-Derived Hair Follicle Stem Cells (HD-AFSCs). This solution was obtained from mechanical fragmentation and centrifugation of scalp biopsy using “Gentile protocol.” Three injections were administered at a 45 days interval. The author reported an improvement in hair density at 23 and 44 weeks after the last injections, with a mean increase of 33%±7.5% and 27%±3.5%, respectively, on photo-trichogram. On histological analysis of scalp biopsies done at 11 months from the last injections, there was expansion in the number of hair follicles per mm² compared with baseline (1.4 ± 0.27 vs 0.46 ± 0.15, respectively; P < 0.05).[31]

STUDIES USING ADIPOSE DERIVED STEM CELLS (ADSCs)

The ADSC has attracted a lot of attention and a number of studies about its role in hair loss have been published, which are discussed later.

Kuka et al. reported a clinical trial of 71 patients (17 females and 54 males) with AGA using adipose-derived regenerative cell (ADRC) enriched AF grafts. Lipoaspirate obtained from patients were processed in the Puregraft System to remove the impurities, and in the Kerastem Celution System to isolate and concentrate ADRCs. Patients were divided into four groups: 16 with Puregraft fat and 1.0 × 10⁶ ADRCs/cm² scalp (high-dose ADRC group), 22 with Puregraft fat and 0.5 × 10⁶ ADRCs/cm² scalp (low-dose ADRC group), 24 with Puregraft fat alone, and nine with saline control. Injection of purified fat with low-dose ADRC demonstrated superior results compared with other groups. The low-dose ADRC subgroup reported an increase in terminal hair count at all weeks (6, 12, 24, and 52 weeks), with maximum hair count seen at week 24. The group treated with fat and high-dose ADRC did not respond. At the 24-week evaluation of all patients, there were no statistical differences in terminal hair counts or width between any of the treatment groups.[32]

Tak et al. reported a clinical trial in 38 patients (29 men, nine women) with AGA treated with topical adipose-derived stem cell constituent extract [ADSC-CE; T-Stem Co. Ltd (Changwon-si, Republic of Korea)]. Patients were divided into two groups, an intervention group (IG), with twice-daily self-application of the ADSC-CE topical solution and a control group (CG). Patients were evaluated at week eight and 16. There was a significant increase in hair count and thickness in the IG compared with the CG at 16 weeks. The overall change in hair count was 28.1% in IG vs 7.1% in CG. Improvement of hair diameter was 14.2% in IG vs 6.3% in CG.[33]

In a report from Turkey, 20 patients (14 males, six females) with AGA were injected with SVF prepared by beautycell device (Bitorend company). Three months later, improvement was noted in hair density and diameter. Hair density in the temporoparietal region improved by 10–20% in 75% of patients, whereas there was no improvement in 25% of patients. In the vertex, there was a 10% increase in hair density in 75% of patients and a 20% increase in 25% of patients. In the temporoparietal region, hair thickness increased by 25% in all patients. In the vertex, there was no change in hair thickness in 50% of patients, whereas it increased by 10–30% in the remaining 50% of patients.[34]

Lee et al. studied the effect of topically administered ADSC-CM on AGA after nonablative fractional laser treatment in 30 patients (15 men, 15 women). They used commercially available ADSC-CM product SCM2-Black3 (Anterogen, Co. Ltd, Seoul, Korea). Assessment was done by phototrichograms and clinical digital photographs. The ADSC-CM group had significantly higher final hair densities compared with the placebo group. The authors concluded that the application of ADSC-CM after nonablative fractional laser treatment accelerated an increase in hair density and volume in patients with AGA.[35]

In a study done by Narita et al, 40 patients (21 men, 19 women) with AGA and female-PHL were treated with an intradermal injection of ADSC-CM every month for six months. They used advanced adipose-derived stem cell protein extract (AAPE), Prostemics Co, Ltd, Seoul, South Korea, which is a commercialized ADSC-CM product cultured under hypoxic conditions. Assessment via trichoscopy showed a significant increase in hair density and anagen hair rate.[36]

Butt et al. analyzed the efficacy of use of SVF in 11 patients with AGA. Patients were divided into two groups: PRP group (only PRP) and SVF-PRP group (mixture of SVF and PRP). Autologous AT was processed to obtain SVF in all patients. Patients were injected twice, four weeks apart, and evaluation was done at six months after the last injection. Mean hair density increased by 21.5% in the PRP group and by 51.6% in the SVF-PRP group. A reduction in pull test was seen in both groups, with a more significant reduction in the SVF-PRP group. There was also significant improvement in the physician and patient assessment scores in the SVF‐PRP group.[37]

Stevens et al. also reported a study evaluating the effect of SVF in combination with PRP [platelet-rich stroma (PRS)] in 10 male patients with AGA. All patients were treated with a single injection of autologous PRS. There was a significant increase in hair density at six weeks and 12 weeks posttreatment.[38] Since there was no control group in this study, the efficacy of SVF over PRP cannot be ascertained.

Shin et al. performed a retrospective observational study in 27 patients with female pattern hair loss (PHL) treated with ADSC-CM. They used commercial ADSC-CM product AAPE^TM (Prostemics Co, Ltd, Seoul, South Korea). AAPE^TM has been shown to contain numerous cytokines, including VEGF, HGF, basic FGF, KGF, and PDGF. After 12 weeks of treatment, the mean hair density increased by 16.4%; the mean hair thickness increased by 11.3%. These improvements were statistically significant.[39]

Fukuoka H et al. published three studies in which they evaluated the hair regenerative effects of AAPE in patients with male- and female-PHL.[404142]

In their first study conducted in 2012, Fukuoka et al. evaluated 25 patients (13 men and 12 women) with male- and female-PHL. In this study, AAPE injections were combined with buflomedyl, vitamin B1, vitamin B6, vitamin H, vitamin C, vitamin E, coenzyme Q10, and amino acids. This combined therapy was referred to as hair regenerative therapy (HARG) enhanced by hypoxic ADSC-CM. Mesotherapy techniques such as nappage and papule injections were used to administer the therapy. Patients received four treatment sessions every three to five weeks until hair regeneration was observed. Patients were followed up at a two to four months interval for at least one year after the final treatment session. Statistically significant improvements in physician-determined VAS scores were observed from the first treatment (P < 0.1). Patient-determined VAS scores also increased as the number of treatments increased.[40] However, this study lacked an objective and consistent means of evaluation.

In their next study conducted in 2015, Fukuoka et al. treated two groups of patients with ADSC-CM (AAPE®) with a somewhat complex design. In the first group, 22 patients (11 men and 11 women) with alopecia (type of alopecia not mentioned) were given intradermal injections of ADSC-CM. Finasteride was also administered to six out of 11 male patients. In the second group of 10 patients (eight men and two women), a half-side comparison study was performed. They received ADSC-CM treatment on the left side and placebo treatment (saline injection) on the right. Patients of both groups received treatment every three to five weeks for a total of six sessions and were examined with trichogram both before and after completing treatment. In the first group of 22 patients, the number of hairs increased significantly after treatment in both males and females. The mean increase in the number of hairs was 29 ± 4.1 in male patients and 15.6 ± 4.2 in female patients. Also in the first group, among six out of 11 male patients, the addition of finasteride made no significant difference in the number of hairs. In the half-side comparison group, the number of hairs increased significantly after treatment on both the left (ADSC-CM) and right (placebo) sides, but the increase was significantly higher on the ADSC-CM treated side than on the placebo side.[41]

In a third study conducted in 2017 by Fukuoka et al., 21 patients (16 males and five females) with male- and female-PHL were evaluated. Intradermal AAPE injections were given once a month and were repeated six to eight times. On evaluation by trichogram, the number of hairs at three months of treatment increased significantly in comparison to that before treatment (141.3±31.4 vs. 109.8±43.5, respectively; P < 0.01).[42]

Thus, these three studies by the same author suggested that ADSC-CM was effective in inducing hair growth. However, although the authors performed three studies over five years, they seem to have recruited different patients in each study, and hence the follow-up period was not long in any of the studies.

Perez-Meza et al. performed an observational study on nine patients (eight men, one women) with female- and male-PHL using a mixture of purified fat and SVF. Fat aspirated by liposuction was divided into two aliquots. Processing by Puregraft system^TM (Puregraft LLC, Solana Beach, CA, USA) was used to obtain a purified AF graft in the first aliquot, whereas Kerastem Celution System^TM was used to obtain a suspension of ADRCs (also known as SVF) in the second aliquot. Hair count, anagen percentage, telogen percentage, and cumulative thickness were calculated at six months. A mean increase of 31 hairs/cm² of scalp (23% relative percentage increase) was documented in five patients with proper follow-up. However, no statistically significant change was noted in cumulative thickness or percentage of hairs in the anagen or telogen phase.[43]

Besides male- and female-PHL, the use of ADSCs has been attempted in other pathological alopecias also, such as AA. In a retrospective study of 20 patients (11 men, nine women) with scalp AA, conducted by Anderi et al, autologous adipose-derived stromal vascular cells were injected in a single session treatment. After six months of treatment, the hair diameter increased significantly in 19 out of 20 patients (from 60.5 ± 1.8 μm to 80.8 ± 2.4 μm at 6 months). There was an average of 32% improvement in hair diameter, with greater improvement in females as compared with males.[44]

Treatment with ADSCs has been reported in patients undergoing hair transplantation as well. Zanzottera F et al. reported a case series of three patients who underwent hair restoration surgery along with the application of ADSCs and growth factors. The ADSC was obtained from the hypodermis and AT discarded from the donor strip of scalp, and it was processed using Rigenera system. Rigenera device is a standardized sample preparation system for the automated mechanical disaggregation of the cell population and it yields a cellular suspension composed of erythrocytes, epithelial cells, ADSCs, and immature adipocytes. The cell suspension was injected subcutaneously on the recipient area on the frontal region of the scalp. The patients were evaluated after five days, two weeks, and one month based on photographs and the patients’ impressions. The authors reported that there was continuous growth of the transplanted hair as early as two months after the procedure, with shortening of the dormant phase.[45] However, there was no comparative group and hence it was difficult to draw a definite conclusion.

Thus, a number of studies have been published on this topic, which indicate a potential benefit. Summaries of all these studies are given in Tables 2 and 3 including a description of treatment protocol, the method of evaluation of hair growth, treatment duration, and follow-up period.

DISCUSSION

The main goal of this review was to evaluate the logic and effectiveness of AT in hair regeneration. The review includes studies of male and female-PHL, AA, hair transplant surgery, folliculitis decalvans, traumatic alopecia, and localized scleroderma. All the studies showed improved outcomes with AT treatments. However, there was significant variation in the methods of preparation of ADSCs and fat from harvested AT. Till now, there is no universal protocol for fat grafting and the various methods of fat harvesting, processing, and reinjection can affect results, which leads to difficulty in comparing results from various studies. Most of these studies also had a small sample size, variable control groups, and different durations and outcome measures; lacked long-term data; and were either case reports, small case series, or pilot studies. Hence, the level of evidence is lower than randomized controlled trials (RCTs). However, such low-quality studies and lack of a higher level of evidence are true of all new treatment modalities.

Overall, based on above data, it can be said that AT and ADSCs may represent a new and promising therapy for hair regeneration and physicians need to be aware of developments in this field. However, the therapy is still in the experimental mode and as such cannot be a part of routine management of hair loss yet. The therapy needs further larger studies with high-quality large RCTs so that standardized and effective protocols can be made. In the future, as we gather more clinical evidence with new emerging trials, AT may be considered as a promising treatment option in the field of hair regeneration.