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Platelet-rich plasma (PRP) was defined as a small volume of plasma containing platelet concentrations higher than those found in peripheral blood and was originally used as a transfusion product for the treatment of thrombocytopenia. To date, several growth factors and cytokines have been discovered that can accelerate wound healing and tissue regeneration, leading to a wider range of applications in medicine, such as sports medicine, regenerative medicine, and aesthetic medicine. Many studies have shown that PRP can be used effectively in the treatment of hair loss. Despite its widespread use, the exact mechanism of action of PRP is still not fully elucidated. In this article, we aim to review and update current information about the definition, classification, mechanism of action, clinical efficacy and side effects of PRP in hair regrowth.

Summary:Platelet-rich plasma (PRP) was defined as a small volume of plasma containing higher concentrations of platelets than those found in peripheral blood and was originally used as a transfusion product for the treatment of thrombocytopenia. To date, several growth factors and cytokines have been discovered that can accelerate wound healing and tissue regeneration, leading to a wider range of applications in medicine, such as sports medicine, regenerative medicine, and aesthetic medicine. Many studies have shown that PRP can be used effectively in the treatment of hair loss. Despite its widespread use, the exact mechanism of action of PRP is still not fully elucidated. In this article, we aim to review and update current information about the definition, classification, mechanism of action, clinical efficacy and side effects of PRP in hair regrowth.

Keywords:platelet-rich plasma, androgenetic alopecia, female pattern hair loss, alopecia areata, cicatricial alopecia, hair transplantation.

Platelet-rich plasma (PRP) was first defined in Hematology as a small volume of plasma containing higher platelet concentrations than that found in peripheral blood and was first used as a transfusion product for the treatment of thrombocytopenia since 1970. (1) Today, PRP has become a popular therapy. Since it contains various growth factors and cytokines that can accelerate wound healing and tissue restoration, it is used in sports medicine, (2) regenerative medicine, (2,3) aesthetic medicine (4) and hair loss treatment (5,6) and in many other fields. Both the device used to separate platelets and the subsequent use of the PRP product are regulated by the US Food and Drug Administration (FDA). (7) Any use of PRP other than blood transfusion, H
If done by a physician with the intention of planting, it is an “off-label use” that is not prohibited under FDA regulation. Despite its widespread application, the mechanism underlying the hair regrowth effects of PRP remains to be fully explored. We aim to review the efficacy of PRP as a hair loss treatment, including its definition, classification, mechanism of action, clinical efficacy in hair regrowth, and side effects.

Platelet-rich plasma (PRP), also known as platelet-rich growth factors or platelet concentrate, is a concentrate of platelet-rich plasma protein from whole blood centrifuged to remove red blood cells. In addition to the main component, which contains high concentrations of platelets, there are other components such as the presence or absence of leukocytes and platelet activating agents that are used to identify different types of PRP. The effectiveness of stimulating tissue regeneration depends on the concentration of platelets present in the plasma, several studies have shown that concentrations 4 to 6 times higher than the normal platelet count are required for optimal results.

Since there is no standard method for the preparation and application of PRP, there is a wide variety of preparation methods. However, the main principle is to prepare concentrated platelets from the patient's own blood. All PRP preparation protocols follow a general method that begins with collecting approximately 10 to 60 mL of venous blood from the patient and placing it in tubes containing an Anticoagulant, acid citrate dextrose or sodium citrate solution to prevent coagulation and premature secretion of alpha granules. Whole blood is then centrifuged and separated into 3 layers according to specific gravity, the lower layer contains leukocyte red blood cells (RBCs), the middle layer is PRP, and the upper layer is platelet-poor plasma (PPP). (9) There are various commercial PRP kits out there that simplify PRP preparation. These kits differ in platelet concentrations, presence of leukocytes and platelet activator, resulting in variation in growth factors concentration. All of these explain the variability in the clinical benefits of PRP reported in the literature. Some studies have induced growth factor secretion and degradation of alpha granules (activated PRP) by adding calcium gluconate, calcium chloride, or thrombin prior to administration. There is no consensus on whether to exogenously activate platelets or use host thrombin as the endogenous activator to maximize the therapeutic effect. (10 12) Platelet alpha granules secrete growth factors within 10 minutes after coagulation or activation, therefore 10 minutes of activation is prescribed for maximum benefit in PRP treatment. (13)

Classification of Platelet-Rich Plasma
There are many variations in PRP preparations, such as the type of collection tubes, power used, number of cycles and centrifugation time, PRP components, and an applied activation method. A standardized classification of PRP called DEPA was proposed by Magalon et al., based on four components: dose of platelets injected (baseline concentration of platelets at 200x10^9 /L), efficiency of the procedure (% platelet recovery rate), purity of PRP ( relative composition in platelets %) and activation process, (14) as shown in Table 1. From this classification, an "AAA" DEPA score refers to injection of high concentration platelets (>5 billion) with minimal red blood cell contamination and good condition and prepared by an appropriate method that results in a small loss of platelets from whole blood. The last category in the DEPA classification reports the presence or absence of any exogenous activator such as thrombin or calcium chloride.

PRP Effect Mechanism
Currently, many studies have shown that platelets not only affect the hemostatic system, but also affect the inflammatory system, angiogenesis, stem cell induction, and cell proliferation through the release of many different growth factors and cytokines.15–17 Platelets activated in PRP release a large number of growths. factors from alpha granules and cytokines (EGF), including platelet-derived endothelial growth factor (PDGF), transforming growth factor β (TGF β), fibroblast growth factor-2 (FGF-2), vascular endothelial growth factor (VEGF), epidermal growth factor, Insulin-like growth factor 1 (IGF-1), glial cell line-derived neurotrophic factor (GDNF), which plays an important role in stimulating hair growth through cell proliferation, differentiation and angiogenesis. 18–22 GDNF can stimulate cell proliferation and protect the hair follicle from premature catagen transition. . (23.24) VEGF plays an important role as a potent hair growth stimulator through an induction of angiogenesis.25,26 IGF-1 induces and prolongs the anagen phase of the hair growth cycle, while the survival of pro Cyclic Ki67+ basal keratinocytes. , PRP can induce proliferation of dermal papilla (DP) cells by activating extracellular signal-dependent kinase (ERK), fibroblast growth. factor 7 (FGF-7), beta-catenin and Akt signaling (an anti-apoptotic signaling molecule). There is also an increase in the expression of Bcl-2 protein (an anti-apoptotic protein) in human dermal papilla cells cultured with PRP in vitro. Thus, it has been clearly demonstrated that PRP can increase the survival of hair follicle cells through anti-apoptotic effects and stimulate hair growth by prolonging the anagen phase of the hair cycle. (30) This theory is further supported by microscopic examination results, which show an increase. in the number of follicular ridge cells, hair follicles, epidermal thickening, vascularization, and a higher number of Ki67+ basal keratinocytes in PRP-treated scalp tissue compared to placebo. (31)

Although PRP is a safe treatment with minimal side effects, there are some contraindications to consider. Absolute contraindications for PRP include critical thrombocytopenia, platelet dysfunction, hemodynamic instability, sepsis, local infection (regional PRP), and patient refusing to risk. Relative contraindications include NSAID use within 48 hours, glucocorticoid injection within one month, systemic glucocorticoid within 2 weeks, recent illness or fever, cancer, particularly bone or hematolymphoid, anemia (less than 10 grams per hemoglobin deciliter), thrombocytopenia (platelets). . less than 150,000 per microliter) and tobacco use. (32)

Use of Platelet-Rich Plasma in Hair Diseases
Androgenetic Alopecia

Androgenetic alopecia (AGA) is a non-marking alopecia characterized by a shortened anagen phase and progressive miniaturization of the terminal hairs to the vellus hairs.33 The condition is present in approximately 50% of Caucasian men by the age of 50 and in women up to 50% during their lifetime. 34 In men, baldness begins with anterior retraction and thinning of the hair on the crown (MPHL), while in women, hair loss is characterized by less hair density and smaller hair. shaft diameter on crown without anterior hairline indentations (FPHL). The FDA has approved oral finasteride (for men only) and topical minoxidil for the treatment of AGA.35 A meta-analysis of six studies (four studies randomized controlled trials, two retrospective studies) involving 177 patients, the number of hairs per cm2 after PRP injections compared to control. increase (mean difference (MD) 17.90, 95% CI 5.84–29.95, P=0.004) and an increasing trend in hair count and percentage hair thickness.36 Similar result, MD 38.75, 95% CI 22.22–55.28, P < 0.00001 and MD 30.35 were confirmed by two other meta-analysis studies showing a significant increase in hair count per cm2 after PRP injections in the treatment group compared to the control group with 95%. CI 1.77–58.93, P <0.00001, respectively.37.38 Compared with minoxidil, finasteride, and adult stem cell-based therapy, 84% of all studies reported a positive effect of PRP, 50%' while 34% showed a statistically significant improvement in hair density and hair thickness, although no P-value or statistical analysis was disclosed. There is no standard practice. Attempts have been made to standardize PRP therapy for AGA patients. A standardized PRP procedure was proposed by Stevens et al using a single spin centrifugation method to produce pure PRP with platelet enrichment 3 to 6 times the mean whole blood concentration and adding a platelet activator such as calcium chloride or calcium gluconate prior to administration. PRP as subcutaneous injections. Treatment intervals should be monthly for the first 3 months, then every 3 months for the first year. (27)
However, discussions on the standardization of PRP preparation continue in the literature. A prospective comparative clinical study of split scalp on 15 women with AGA was conducted with intradermal injection of double-turn prepared PRP into the right half of each patient's scalp and single-turn prepared PRP into the left half of the scalp for three treatment sessions. 3 weeks apart. While the results showed clinical improvement on both sides of the scalp, hair density measured by trichoscan revealed that the median terminal hair density of the right half of the scalp was significantly higher than the left half (P = 0.031), suggesting that the double-rotation method could yield better yields. showed. Results are better than the single rotation method.40 Additionally, a comparative study showed that patients treated with inactive PRP had greater increases in hair count and total hair density (19% ± 3% versus 31 ± 2%). P= 0.0029) more than patients treated with active-PRP, leading to the conclusion that PRP does not require activation prior to injection. (31) The important factor affecting the effectiveness of PRP is the platelet count. Higher platelet counts have a greater effect on hair density, follicle diameter, and terminal hair density than lower platelet counts. (41) In AGA, the effect of dihydrotestosterone on dermal papilla cells suppressed canonical WNT signaling, resulting in defective hair growth and delayed hair cycle. Promoting hair growth by activating WNT/β-Catenin signaling, PRP triggers the new hair cycle by causing proliferation and differentiation of hair follicle cells.42 Some studies have reported the ineffectiveness of PRP in the treatment of AGA, which may be caused by low platelet concentration, low volume. amount of PRP injected and insufficient frequency of treatment. (9) Treatment response to PRP in AGA patients can be estimated by measuring the proinflammatory cytokine IL-1α polymorphism from peripheral blood. One study reported that the C/C genotype of IL-1α was significantly higher in responders (66%) than non-responders (22%), with an odds ratio (OR) of 6.68, 95% CI 0.99–72, 95 (p<0.05) ). (43) Evidence from randomized controlled trials of PRP in AGA is summarized in Table 2.

Alopecia Areata
Alopecia areata (AA) is a common autoimmune disease that causes permanent hair loss in men and women of all ages. The estimated lifetime risk of AA is approximately 2% of the population, with no gender difference in incidence. Most patients have only one lesion of alopecia, and spontaneous hair growth may occur over months to years. However, there are many patients who can develop multiple lesions and develop into chronic hair loss. (58) It was discovered that PRP has a strong anti-inflammatory effect. It suppresses cytokine release and reduces local tissue inflammation, making PRP potentially useful in the treatment of inflammatory hair loss such as AA.59,60 PRP was initially tested in a randomized, double-blind, placebo-controlled, half-head study in patients with AA. . Forty-five patients with AA were randomized to receive intralesional injections of PRP or triamcinolone acetonide or placebo on one half of the scalp while the other half were untreated. The results showed that PRP significantly increased hair regrowth and Ki-67 level (a marker for cell proliferation) compared to injection of triamcinolone acetonide or placebo. (61) Collectively, several randomized controlled trials have shown that treatment with PRP can stimulate hair growth to the same extent as intralesional injection of triamcinolone acetonide in the treatment of AA. (62-65) Two recent studies have compared the therapeutic effect of intralesional PRP injections with triamcinolone acetonide in AA. One study found that the final alopecia severity mean (SALT) score showed significantly lower levels compared to baseline levels (P = 0.025 and P = 0.008) in both groups, with no significant difference between either treatment modality in terms of clinical improvement. areata symptom impact scale (AASIS) showed significant reduction in the PRP group (P = 0.006) but not in the triamcinolone group (P = 0.062). 62 Similar results were found in the other study, showing no statistically significant difference in SALT score. Scale of hair reduction and regrowth between these two groups. (63) Conversely, three randomized controlled clinical trials found differing results based on the Mac Donald Hull and Norris grading system, percentage of hair regrowth, and reduction in SALT score from baseline, showing that PRP was significantly less effective than intralesional steroid injection. , respectively. (66–68) All these results may explain that steroid is more potent than PRP in terms of having immunosuppressive and strong inhibitory effect on T lymphocyte activation. A beneficial effect of combination therapy with PRP was reported in a patient with prolonged AA treated with a combination of intralesional injection of triamcinolone acetonide and PRP on one half of the scalp, and in a patient with intralesional triamcinolone acetonide alone on the other half of the scalp. Half head treated with combined therapy showed greater hair regrowth and larger hair fiber diameter. (69) In addition, a prospective study on the efficacy of PRP treatment was conducted in 20 patients with chronic AA who did not respond to conventional treatment for 2 years, showing that all patients with chronic AA were successfully treated with PRP, and only one patient was successfully treated with PRP. recurrence after one year follow-up. (70) Successful treatment with PRP has also been reported in a patient with corticosteroid-resistant ophiiasis AA who experienced hair regrowth after PRP injections and in a patient suffering from alopecia areata barbae. (72) Therefore, PRP can be used as an alternative treatment for patients who do not respond to conventional treatment or who do not want steroid treatment, or as an adjuvant treatment for alopecia areata. Evidence from randomized controlled trials of PRP in AA is summarized in Table 4.

Cicatricial Alopecia
Cicatricial alopecia is a type of scarring alopecia caused by different inflammatory conditions, physical trauma, burns, or severe infections that lead to the destruction of hair follicles and subsequent scarring. The aim of treatment is to stop the progression of the disease and prevent further hair loss and scarring by using different anti-inflammatory drugs such as topical steroid, intralesional injection of triamcinolone acetonide and immunomodulatory agents. However, there is no effective treatment to promote hair regrowth in the fibrotic area. (73) Frontal fibrosing alopecia (FFA), a variant of lichen planopilaris, is currently the most common type of cicatricial alopecia and is characterized by perifollicular erythema and papules with progressive regression of the frontal and temporoparietal hairline. frontotemporal area. (74) Satisfactory treatment outcome with five consecutive PRP injections was reported in a 44-year-old female patient with FFA who did not respond to conventional intralesional steroid therapy. Just one month after treatment, perifollicular erythema, scaling, and lichenoid papules on the frontotemporal hairline had resolved and no hair loss was seen after 5 months. (75) Lichen planopilaris (LPP) is a chronic inflammatory, scarring alopecia characterized by follicular hyperkeratosis, perifollicular erythema, and loss of follicular orifices in the vertex and parietal region of the scalp. Bolanča et al. reported the efficacy of PRP treatment in a case of LPP that was first diagnosed by histopathology and did not respond to previous treatments. After 3 consecutive PRP treatments and followed for 6 months, complete regression of scalp pruritus and hair loss was seen, which was confirmed by perifollicular erythema and scaling undetected on trichoscopic examination. (76) Subsequently, two patients with central centrifugal cicatricial alopecia (CCCA) and one patient with LPP were reported on the success of PRP treatment, which resulted in a significant increase in hair density despite a previous history of unresponsiveness to conventional therapy. (77,78) Effective treatment of cicatricial alopecia with PRP is possible due to various cytokines and growth factors such as TGFβ, TGFβ1 found in platelet granules and have anti-inflammatory and proangiogenic effects. (79) Although there is evidence that PRP can be used as an effective treatment for some types of cicatricial alopecia, more clinical research is needed to generate further evidence.

Hair Transplant
The positive effect of using PRP together with hair transplantation has been proven by many studies. The first report was an experimental study of a group of 20 patients with male pattern baldness; showed 15% greater hair yield at follicular unit density in donor pre-treated areas with platelet plasma growth factors derived from the patient's autologous plasma compared to normal saline. (18.7 follicular units per cm2 vs 16.4 follicular units per cm2). (22) Similar results were found in two other studies, the first was a comparative study, showing that transplanted follicular unit grafts with platelet lysate (PL) or activated PRP (AA-PRP) continued to grow faster than normal saline after 4 months. operation, 99%, 75%, and 71% of follicle regeneration occurred in the areas of PL, AA-PRP, and saline treatment, respectively. hair density, graft removal, and hair thickness compared to normal salt water storage. (81) In addition, PRP can also be used as a combination therapy with follicular unit extraction (FUE) hair transplantation, as demonstrated in a single-blind, prospective randomized study in 40 FUE hair transplant patients. The patients were divided into two groups. In the PRP group, PRP was injected intraoperatively immediately after the slit was made in the recipient area, while normal saline was injected in the non-PRP group. It has been clearly seen that intraoperative PRP treatment is profitable in significantly increasing the density and quality of hair growth, reducing catagen loss of transplanted hair, early healing of the skin, and faster emergence of new anagen hair in FUE transplant patients.82 Thus, PRP is not only an effective hair loss treatment, It can also be used as an aid in hair transplantation.

Adverse Effects of Platelet-Rich Plasma
PRP is an autologous plasma preparation containing a high concentration of platelets. It is a relatively safe intervention with minimal side effects such as temporary and tolerable pain, mild headache, minimal itching, temporary erythema and edema in the treated area during treatment. Significant side effects such as scarring, infection, panniculitis, hematoma, or allergic reaction have not been documented following PRP treatment.39,83,84 After treatment, patients can return to their normal daily activities, with no antibiotics required to prevent infection. Most patients can return to work the next day.

PRP can be used as a monotherapy or conventional therapy for hair loss, including androgenetic alopecia and female pattern hair loss, or as a new therapeutic option as an adjunct to hair transplantation. PRP is also considered a safe, effective, steroid-saving and alternative treatment for alopecia areata. There was also evidence to suggest that PRP can improve clinical symptoms in some types of cicatricial alopecia. However, more studies are needed to determine the standard of PRP treatment preparation, treatment regimen including dosing protocols, injection technique, number and spacing of optimal treatment sessions to achieve maximum therapeutic efficacy.

Data Sharing Statement
Reader personally Dr. request access to data through Anon Paichitrojjana; Email:

The authors thank the Mae Fah Luang University School of Anti-Aging and Regenerative Medicine for their research facilities.

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