Meta-analysis on the Efficacy of Platelet-rich Plasma in Patients with Androgenetic Alopecia

Abstract

Platelet-rich plasma (PRP) is an autologous platelet concentrate in plasma enriched with growth factors that may stimulate tissue regeneration, collagen formation, re-epithelization, and angiogenesis. PRP is widely used as an androgenetic alopecia treatment option. The present work aims to test the efficacy of various PRP methods, including those with single-spin and double-spin centrifugation. We performed a review of articles published from 2011 to 2021 in PubMed and ScienceDirect. The studies vary in the preparation procedure, dose, number, intervals between the procedures, and the injection technique because of low standardization of PRP preparation, complicating the evaluation of the clinical efficacy of the method. Based on the conducted statistical analysis, we came to the conclusion that the double-spin PRP preparation method was superior to the single-spin technique, which may be taken into account for AGA management.

INTRODUCTION

Androgenetic alopecia (AGA) is a multifactorial condition usually caused by genetic, hormonal, and environmental factors characterized by androgen-driven gradual thinning of terminal hair with the transformation into thin vellus hair eventually leading to its loss.[1,2] The hair follicle miniaturization is driven by 5-α-reductase-induced transformation of testosterone into dihydrotestosterone or by changes in the androgen receptor gene.[3]

Minoxidil and finasteride that are commonly used in AGA therapy show several side effects and disadvantages affecting patient adherence and satisfaction with the treatment. There is still a need for new therapeutic modalities with a good tolerance and efficacy profile.[4]

Platelet-rich plasma (PRP) is an autologous platelet concentrate in plasma enriched with growth factors that stimulate tissue regeneration, collagen formation, re-epithelization, and angiogenesis.[5,6] Moreover, the risk of side effects and infection is minimized owing to its autologous origin which makes PRP to be a safe treatment option for a number of skin disorders.[7]

To date, several PRP preparation methods have been proposed, but none of them is a standard for the AGA management, the optimal number of procedures and the intervals between them still being an open question. The basic preparation protocol includes blood collection, centrifugation for the platelet concentrate extracting, endogenous/exogenous platelet activation, and injection into the scalp. PRP is usually injected sub- or intra-epidermally in AGA patients.[8,9,10]

Growth factors and cytokines released by the degranulation of activated platelets play a central role in the supposed mechanism of action of PRP.[11] Activation of platelets is triggered by thrombin, calcium, and collagen.[12] The addition of calcium chloride or calcium gluconate solutions is believed to obtain a higher concentration of growth factors.[13,14] An alternative opinion is that natural activation is more efficient when occurring in the interaction with the endogenous collagen since the growth factors are released more slowly and longer.[9,12]

PRP administration with stromal vascular fraction (SVF) or dalteparin and protamine showed increased efficacy of therapy. SVF extracted from the adipose tissue is widely used due to the capability of multipotent cells to differentiate into different cell types and their expression of growth factors and cytokines.[8] In addition, SVF is believed to have a higher and prolonged anti-inflammatory and immunomodulatory activity than PRP.[15]

As mentioned above, a PRP activation step is crucial to a release growth factor and might be performed in two ways: an endogenous method by mechanical trauma or an exogenous method by chemicals.[9,16] The most commonly used exogenous platelet-activating agents are calcium chloride and calcium gluconate solutions.[13] Moreover, some findings have proved that activated PRP had a more significant effect than nonactivated PRP.[17]

MATERIALS AND METHODS

The aim of the present meta-analysis is to assess the efficacy of various PRP methods, including single- and double-spin centrifugation, and their potential usefulness in AGA treatment and to estimate whether using the activators (calcium gluconate/calcium chloride) is more effective or not. For this meta-analysis, we followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

The present meta-analysis was carried out in R v. 4.1. using metafor package.[18] A meta-regression assay was carried out, followed by an assessment of the influence of potential moderator variables (the study design, patients’ gender, the number of therapy sessions, the presence/absence of an activator, and the PRP preparation method) on the treatment outcomes. The DerSimonian and Laird approach was used for random effects meta-analysis. Hair density was utilized as a measure of PRP efficacy, and due to the high variability across the studies, standardized mean change using change score standardization (SMCC) was applied to estimate the effect size.[19,20] The risk of bias of all nine trials was graded by two reviewers [Figures 1 and 2].

Figure 1.

Summary of risk of bias in randomized and nonrandomized clinical trials

Figure 2.

The risk of bias evaluation of randomized and nonrandomized clinical trials

Search strategy

All authors individually carried out a search of the available literature through PubMed and ScienceDirect on PRP use in AGA from 2011 until March 19, 2022. The search was performed using the Boolean operators “OR” and “AND” with the following keywords: “androgenetic alopecia,” “PRP,” and “platelet-rich plasma” with no imposed language restrictions. Duplicate studies were subsequently removed. The exclusion criteria were sample size <10 patients, conference reports, and lack of data regarding hair density in extractable for the analysis format [Flowchart 1].

Flowchart 1.

Flowchart of the literature search and trial selection process

RESULTS

Ultimately, 257 patients from the 9 trials were the subjects for the primary overall analysis. The results showed a beneficial effect of the PRP intervention in all the trials, with the SMCC value being as high as 1.21 (95% confidence interval [CI]: 0.59–1.82), P < 0.01 [Figure 3].

Figure 3.

Forest plot showing the results of a primary overall analysis of the 9 included studies on PRP implementation in AGA therapy, with hair density as a measure of efficacy. PRP, platelet-rich plasma; AGA, androgenetic alopecia

At the same time, significant heterogeneity was observed: I² = 92.7%, Q = 109, P < 0.01. Thereby, we decided to carry out a subgroup analysis with the inclusion of potential moderators to find the sources of heterogeneity related to our study. The main source of heterogeneity proved to be the PRP preparation method [Table 1].

Table 1.

Results of univariate meta-regression testing with potential moderators

Potential confounder	Variance not explained by the predictor τ2	Remaining between-study heterogeneity I2, (%)	R 2	Test for residual heterogeneity, Q, P	Omnibus test, P
Study design: Randomized controlled trials versus others	0.93	93.4	0.0	<0.01	0.83
Male/female gender	0.89	92.9	0.0	<0.01	0.64
Presence of an activator	0.96	93.6	0.0	<0.01	0.67
Norwood-Hamilton stages 1-5 versus others	0.81	93.5	0.0	<0.01	0.42
Number of patients less than 24 (median) versus 24 patients and more	0.89	93.1	0.0	<0.01	0.11
Amount of treatment sessions	0.81	92.8	0.05	<0.01	0.39
Follow-up time	0.94	93.5	0.0	<0.01	0.54
PRP single-spin versus double-spin	0.03	29.7	96.7%	0.19	<0.01

PRP - Platelet-rich plasma

Thus, separate analyses for both single-spin and double-spin methods were performed.

For the trials used, the single-spin method SMCC was medium: 0.52 (95% CI: 0.27–0.77), P < 0.001 [Figure 4]. Heterogeneity was medium (I² = 46%), with q-test not being significant (Q [df = 5] = 9.26, P = 0.10).

Figure 4.

Forest plot showing the results of PRP single-spin subgroup analysis. PRP, platelet-rich plasma

The studies with double-spin PRP preparation technique showed high SMCC: 2.66 (95% CI: 2.28–3.04), P < 0.001 [Figure 5]. SMCC was robust, and heterogeneity was quite low: I² = 0%. q-test was not significant (Q [df = 2] = 0.7, P = 0.70). Thus, for both subgroups, a significant medium-to-strong effect was observed.

Figure 5.

Forest plot showing the results of PRP double-spin subgroup analysis. PRP, platelet-rich plasma

For the overall trial set [Figure 6] and for both subgroups [Figures 7 and 8 for single-spin and double-spin methods, respectively], funnel plots were drawn to assess potential publication bias.

Figure 6.

Funnel plot showing the distribution of all included study sets

Figure 7.

Funnel plot showing the distribution of single-spin study sets

Figure 8.

Funnel plot showing the distribution of double-spin study sets

The Egger test (with the standard error as a predictor) was implemented [Table 2].

Table 2.

Results of the Egger test (standard error used as a predictor)

Set of studies	β (95% CI)	Z	P
Overall trial set	−1.3 (−2.9-0.34)	3.08	<0.01
PRP single-spin subgroup	−0.17 (−1.8-1.51)	0.82	0.41
PRP double-spin subgroup	2.56 (1.04-4.09)	0.13	0.9

PRP - Platelet-rich plasma; CI - Confidence interval

Single-spin centrifugation method

Gkini et al. performed a prospective cohort study with 20 volunteers with AGA. The patients received three PRP procedures at 3-week intervals with a booster session within 6 months from the first visit. Therapy was evaluated with pull-test, dermatoscopic, and macroscopic photographs and patient questionnaires. The patients achieved the peak of hair density at 3 months. At 6 and 12 months, it was significantly increased compared to baseline (P < 0.001) [Table 3].[4]

Table 3.

Studies on the efficacy of platelet-rich plasma in androgenetic alopecia hair loss treatment

Author	Design of the study	Total amount of the patients (n)	Gender (n)	Norwood-Hamilton classification (I-VII)c Ludwig classification (I-III)d	PRP preparation	Activator	Increased platelet count	Treatment protocol	Efficacy measurement	Hair density before treatment	Hair density after treatment	Follow-up period (months)	Positive results (yes/no) P
Takikawa et al., 2011[27]	Prospective randomized controlled	26	n=16a n=10b	N/A	Double-spin method	No	N/A	Five treatment sessions with an interval of 2 weeks	Hair density	112±6 (PRP) 114±6 (PRP and D/P)	127±6 (PRP) 132±7 (PRP and D/P)	3	Yes P<0.001
Gkini et al., 2014[4]	Prospective cohort	20	n=18a n=2b	I-Vc I-IIId	Single-spin method	Calcium gluconate	×5.8	Three treatment sessions with an interval of 3 weeks A booster session at 6 months from the beginning of the treatment	Hair density	143.10±31.07	153.70±39.92	12	Yes P<0.001
Gentile et al., 2015[21]	Randomized placebo-controlled	23	n=23a	II-IVc	Single-spin method	Calcium gluconate	N/A	Three treatment sessions with an interval of 1 month	Hair density, hair diameter, anagen-to-telogen ratio, and vellus hair-to-terminal hair ratio (using TrichoScan and FotoFinder); Punch biopsy	161.2±41.9	207.1±56.3 (after 14 weeks)	24	Yes P<0.05
Alves et al., 2016[22]	Randomized placebo-controlled, double-blind	25	n=12a n=13b	II-Vc I-IIId	Single-spin method	Calcium chloride	×3	Three treatment sessions with an interval of 1 month	Hair count, hair density, terminal hair density, anagen (%), telogen (%), and the anagen/telogen ratio	167.1±55.61	179.9±62.71	6	Yes P<0.05
Ayatollahi et al., 2017[23]	Noncomparative	13	n=13a	III-VIc	Single-spin method	No	N/A	Five treatment sessions with an interval of 2 weeks	Hair density and diameter	149.62±49.56	168.46±43.703	3	No
Paththinige et al., 2019[25]	Randomized clinical	24	n=23a n=1b	II-VIIc IId	Double-spin method (kit	Calcium gluconate	N/A	Three treatment	Hair density	102.25±18.463	161.83±20.687	7	Yes P<0.001
Dr PRP)	sessions with an interval of 3 weeks, a booster session 2 months later
Butt et al., 2020[28]	Randomized controlled	22	n=17a n=5b	IIIc II-IIId	Single-spin method	No	N/A	Two treatment sessions with an interval of 1 month	Hair density, hair pull-test	52.44±9.66 (PRP) 37.66±7.43 (SVF-PRP)	63.72±11.68 (PRP) 57.11±7.73 (SVF-PRP)	6	Yes P<0.05
Pakhomova et al., 2020[26]	Comparative	69	n=69a	I-Vc	Double-spin method	Calcium chloride	N/A	Four treatment sessions with an interval of 1 month	Hair density and diameter, hair count, terminal to vellus hair ratio	408.4±43.6 (PRP + minoxidil) 381.5±45.4 (PRP)	539.6±52.1 (PRP + minoxidil) 426.1±50.1 (PRP)	4	Yes P<0.0001
Shapiro et al., 2020[24]	Randomized controlled	35	n=18a n=17b	III-Vc I-IId	Single-spin method	No	N/A	Three treatment sessions with an interval of 1 month	Hair density and diameter	151±39.82	170.96±37.14	3	Yes P<0.05

^aMales, ^bFemales, ^cNorwood-Hamilton classification (I-VII), ^dLudwig classification (I-III). N/A - Not available; PRP - Platelet-rich plasma; D/P - Dalteparin and protamine; SVF - Stromal vascular fraction

Gentile et al. enrolled 23 patients with AGA in a randomized placebo-controlled trial. The patients received three PRP sessions at 30-day intervals. The scalp was divided into frontal, parietal, occipital, and vertex areas. PRP was injected in the frontal areas only, and the physiological saline was injected in the control (parietal) area. In another group of patients, PRP was injected only in the parietal area, while placebo solution was injected in the vertex area. At the end of the treatment, patients showed an increase in total mean hair density of 45.9 hairs per cm² compared with baseline, whereas the control area showed a mean decrease of 3.8 hairs per cm² (control vs. treatment: P < 0.0001). Double-spin method of centrifugation was effective in men with AGA [Table 3].[21]

Alves and Grimalt conducted a randomized, double-blind, placebo-controlled trial. Twenty-five AGA patients were enrolled in the study. The scalp was conditionally divided into two parts treated with PRP or placebo. The course of the treatment included three procedures performed at 1-month intervals. Significant improvement was observed within 6 months in the PRP treatment area (an increase in hair density) compared to the control area. Thus, the authors concluded that PRP can be used as adjuvant therapy [Table 3].[22]

However, in another study, 13 men received 5 PRP procedures every 2 weeks. The effectiveness of the therapy was evaluated 3 months after the last PRP session by the means of trichograms (hair density and diameter) and photographs. Interestingly, there was no significant difference in the hair number that enabled the authors to consider the method as ineffective in men with AGA [Table 3].[23]

Shapiro et al. observed 35 patients with AGA. Two 7.6 cm × 7.6 cm squares were applied on a scalp with a resistant dye, and either PRP or a physiological solution was randomly injected into the area. The patients received 3 PRP sessions per month. Folliscope method showed that the density of hair in the PRP treated area was significantly higher compared to the initial level, but without significant difference with the control area [Table 3].[24]

Double-spin centrifugation method

Paththinige et al. treated 24 patients with AGA. The protocol included three PRP procedures with a 3-week interval and a booster session performed 2 months after the last injection. The results showed a significant improvement in hair density compared to baseline [Table 3].[25]

Pakhomova and Smirnova treated 69 patients with AGA. The participants were divided into three groups according to the treatment regimen. According to the group, each patient received PRP monotherapy, minoxidil monotherapy, or PRP injections combined with minoxidil. The mono-PRP group received four procedures with an interval of 4 weeks. Despite the fact that the best results were observed in patients who received combined PRP and minoxidil, PRP treatment can be considered an effective management option [Table 3].[26]

Platelet-rich plasma with stromal vascular fraction of adipose tissue and dalteparin in combination with protamine

Some researchers have successfully combined PRP therapy with other substances that enhance positive outcomes, such as SVF of adipose tissue and a low-molecular-weight heparin dalteparin combined with a coagulant protamine.

Takikawa et al. compared the efficacy of PRP and PRP combined with dalteparin and protamine (PRP and D/P). The latter is thought to have an advantageous effect owing to the extended release of growth factors in the injection sites. All participants received five procedures given 2–3 weeks apart. In spite of positive changes observed in both groups, administration of PRP and D/P provided better results than PRP alone [Table 3].[27]

Butt et al. aimed to study the efficacy of PRP and SVF-PRP therapy. Both groups comprised 11 participants and had two sessions with a 4-week interval. The authors concluded that both treatment options were effective; however, the efficacy of SVF−enriched PRP therapy was significantly higher compared to PRP alone [Table 3].[28]

DISCUSSION

Totally, 257 patients with AGA from 9 retrieved studies were included in the current meta-analysis. The results showed a beneficial impact of the PRP in AGA hair loss treatment, since the standardized mean change value equaled 1.21 (95% CI: 0.59–1.82), P < 0.01, comparing the hair density after PRP injections to the baseline. Similar findings of PRP efficacy were previously shown by Zhou et al. in a meta-analysis linked to female pattern hair loss (FPHL).[29] However, the observed efficacy of PRP in our work was higher than that reported by Gupta et al. in both 2017 standardized mean difference (SMD = 0.51, 95% CI: 0.14–0.88) and 2019 (SMD = 0.58, 95% CI: 0.35–0.80) years’ meta-analyses, which can be attributed mainly to differences in the study design.[30,31]

A previously published meta-analysis reported that the inclusion of an all-female study was not possible due to an introduction of high heterogeneity (measured I² = 89%).[31] Zhou et al. reported that the heterogeneity in their study on PRP in FPHL can be explained by the difference in female's nationalities and races, treatment regimen, PRP preparation methods, injection details, and PRP concentration.[29]

In the current analysis, significant heterogeneity was also demonstrated: I² = 92.7%, Q = 109, P < 0.01. The subgroup analysis with the inclusion of potential moderators showed that the PRP preparation method was mainly responsible for such an observation. Gender, study design, the disease stage, activator implementation, number of treatment sessions, and follow-up period did not influence significantly on the therapy result.

Gupta et al.[31] concluded that three sessions of PRP at 1-month intervals followed by a maintenance regimen were recommended and the use of an exogenous activator appeared the most connected to achieving desirable results (P = 0.08); however, we could not confirm both the findings statistically in our analysis, as mentioned above.

Oh et al. stated that the dual centrifugation method allows to achieve a higher platelet concentration compared to a single-spin one.[32]

Evans et al. in a PRP for AGA therapy meta-analysis supposed that until future research elucidates comparable results from optimized protocols, it is prudent for clinicians to utilize double spin protocols with added activators as a standard preparation.[33]

Mao et al. in a systematic review on PRP in AGA showed that the mean difference (MD) of hair density for single-spin centrifugation (n = 70, MD = 36.37, 95% CI: 14.80–57.59, P = 0.06, I² = 59%) was lower than that for double-spin centrifugation (n = 43, MD = 41.17, 95% CI: 3.09–79.24, P < 0.0001, I² = 94%).[34] Albeit, due to large statistical heterogeneity and the P value in the single-spin group, the authors concluded that the contrast was meaningless. Mao with colleagues did not find any difference between Ca²⁺-activated studies and no-activation studies (MD: 36.87 vs. 38.52) as well.

While having comparable findings on the activator benefit, due to the detected influence of the PRP preparation method on the observed heterogeneity, we performed a separate analysis for both the techniques and found that the double-spin PRP preparation technique showed SMCC of 2.66 (95% CI: 2.28–3.04, P < 0.001) compared with SMCC of 0.52 (95% CI: 0.27–0.77, P < 0.001). Furthermore, the heterogeneity was much lower between the double-spin studies (I² = 0%) than one between the works with single-spin (I² = 46%), indicating the considerable consistency of double-spin results. Thus, the double-spin centrifugation method may be associated with more pronounced beneficial clinical outcomes than the single-spin method based on our findings.

The potential publication bias was assessed with the Egger test for both all trials included and for single-spin and double-spin PRP techniques separately as well. The observed significance (P < 0.01) in overall set results was likely due to the moderator effect. Nevertheless, in both subgroups separately, there is no significance, which implies a low probability of publication bias.

CONCLUSIONS

PRP represents a promising method for AGA therapy with minimal observed side effects. However, despite the positive results of its use, the number of procedures, the interval between them, and the addition of an activator or other auxiliary substances varied significantly in PRP protocols.

Based on the conducted statistical analysis, we came to the conclusion that it is of clinical benefit to execute the double-spin PRP preparation method instead of the single-spin technique for AGA management.

Future comparative studies are needed, and they should be done in a blinded fashion manner to finally clarify the aspects of PRP efficacy in light of AGA therapy.

Financial support and sponsorship

Suvorov A. was financed by the Ministry of Science and Higher Education of the Russian Federation within the framework of state support for the creation and development of World-Class Research Centers “Digital biodesign and personalized healthcare” N 075-15-2020-926.

Conflicts of interest

There are no conflicts of interest.