Effects of Ginkgo biloba extract on diabetic retinopathy: a meta-analysis and systematic review

Wenxin Wang,Dan Zhang,Shuang Han,Jiaxing He,Shuang Tang,Chuanxin Liu＊,Jianmei Huang＊

1 School of Chinese Materia Medica, Beijing University of Chinese Medicine, Liangxiang Town,Fangshan District,Beijing 102488,China.

Abstract

Keywords:Ginkgo biloba extract,Diabetic retinopathy,Randomized controlled trial,Meta analysis

Introduction

Diabetic retinopathy (DR) is one of the most common microvascular complications of diabetes.According to the World Health Organization (WHO) [1], there are approximately 346 million people with diabetes in the world, about 10% of whom have severe visual impairment, and DR is already one of the main causes of vision loss and blindness in adults, therefore, the early diagnosis and treatment of DR has urgently clinical significance.

At present, the conventional treatment of DR is mainly based on strict control of blood glucose,retinal laser photocoagulation and anti-vascular endothelial growth factor (VEGF) drug treatment (such as Ziv-aflibercept, Bevacizumab and so on), hormone therapy (Triamcinolone Acetonide, dexamethasone)and surgical treatment.However, these therapies have ineluctable adverse reactions.For example, visual field defects, contrast sensitivity decreased and the production of central dark spots or paracentral dark spots caused by laser treatment [2] ;intravitreal injection of anti-VEGF drugs can induce vasoconstriction of fibers, associated with traction retinal detachment [3];intravitreal injection of Triamcinolone Acetonide accelerated cataract formation, followed by risk of glaucoma,endophthalmitis,retinal detachment[4].

Doctors of traditional Chinese medicine against DR mainly use therapeutic principle and method, such as activating blood, clearing away heat, tonifying qi and nourishing yin etc.[5].At present, Ginkgo biloba extract is widely used in clinical practice.Its main active ingredients are flavonoids and azlactones,which have dilated blood vessels,regulate blood lipids,antagonize platelet activating factor, protect against ischemic injury,anti-inflammatory and anti-tumor,etc.[6].At the same time, Huang et al.[7] found that Ginkgo biloba extract has the ability to improve blood viscosity and viscoelasticity, is conducive to blood perfusion, and effectively improves the retinal capillary blood flow velocity in patients with type 2 DR.In addition,it has been proven that Ginkgo biloba extract had a tendency to improve clinical symptoms on early stage of DR in 29 diabetic patients through a 6-month double-blind trial[8].

There are no conclusions of large sample,multicenter and random double-blind controlled trials,and there is no systematic evaluation about Ginkgo biloba extract combined with western medicine treatment DR.Therefore, a comprehensive meta-analysis of Ginkgo biloba extract combined with conventional therapy for DR has been conducted to provide evidence for clinical decision-making and further research.

Methods

Search strategy

Six databases were used to conduct a computerized search for relevant available articles published up to June 2019: Chinese Journal Full-text Database(CNKI), VIP Information Chinese Journal Service Platform (VIP), Wanfang Journal Database, , China Biomedical Literature Service System (SinoMed),PubMed, Cochrane Library Database.In addition, the references of related literature were searched manually.An example of the retrieval strategy using PubMed was listed as follows:

#1:“Diabetic retinopathy”[Mesh]

#2: “ Diabetic retinopathy* ” [Title/Abstract] OR“ Retinopathies, Diabetic ” [Title/Abstract] OR“Retinopathy,Diabetic”[Title/Abstract]

#3:#1OR#2

#4:“Ginkgo biloba extract”[Mesh]

#5: “ Ginkgo biloba extract* ” [Title/Abstract] OR“ginaton”[Title/Abstract] OR “extract of Ginkgo biloba”[Title/Abstract] OR “Ginkgo leaves extract”[Title/Abstract] OR “ GBE ” [Title/Abstract] OR“ EGB ” [Title/Abstract] “ Ginkgo leaf extract ”[Title/Abstract] OR “ Rokan ” [Title/Abstract] OR“ Tanakan ” [Title/Abstract] OR “ GBE 761 ”[Title/Abstract] OR “ Ginkgo biloba extract 761 ”[Title/Abstract] OR “GBE-761”[Title/Abstract] OR“ Tebofortran ” [Title/Abstract] OR “ Tebokan ”[Title/Abstract] OR “Tebonin”[Title/Abstract] OR“EGb 761”[Title/Abstract] OR “GBE 761 ONC”[Title/Abstract] OR “EGb-761”[Title/Abstract] OR“EGb761”[Title/Abstract]

#6:#4OR#5

#7: “randomized controlled trial”[Publication Type]OR “randomized”[Title/Abstract] OR “randomly”[Title/Abstract]

#8:#3 AND#6 AND#7

Studies that meet the following criteria were included:

1)The type of study was RCT.

2) The types of participants were diagnosed with DR[9], DR staging referred to DR variable classification standard formulated by fundus diseases group of Chinese Medical Association in 2014[10].

3) The control group was treated with Western medicine routinely; the experimental group was combined with Ginkgo biloba extract on the basis of the control group.

4) Outcome measures include total effective rate,vision level and average visual field defect.

The exclusion criteria were as follows:

1)Case reports, animal experiments, literature review,re-listed and published literature, and medical review and retrospective studies and so on.

2) Patients with other retinopathy (such as uvea, optic neuritis,glaucoma,etc.

3) Outcomes: RCTs did not report the total effective rate, visual acuity level and average visual field defect.

蘇軾《守歲》詩說：“兒童強不睡，相守夜歡嘩。”[28]128 舊時守歲要有火。 屋內(nèi)爐火越旺越好，以辟邪除惡，也預示來年紅火興旺。 民國《晉祠志》記錄除夕時“廟祝潔除內(nèi)外，更貼楹聯(lián)。 至夕陳設(shè)祭品，燒炬以待五鼓迎神，閭巷亦然。”[29]38 山西煤炭資源豐富，有架火塔、壘旺火的習俗。 午夜時鞭炮齊鳴，家長將旺火點燃，頓時火勢熊熊，“旺氣沖天”。 男女老少齊來觀賞，兒童雀躍，歡歡喜喜。 陜北神木等地的旺火也很出名。

Data Extraction and Quality Assessment

The two researchers independently read the topics and abstracts according to the inclusion and exclusion criteria for preliminary screening.Data extraction of standards-compliant literature includes the following topics: title, author, publication time, interventions,and observation indicators.Subsequently, the two subjects independently evaluated the quality assessment of each RCT according to the Revised Cochrane risk-of-bias tool for randomized trials (RoB 2)[11], Each aspect had three levels: “High”, “some concerns”, and “Low”.“High” means that the outcomes may be influenced by the information.“Low” means that the outcomes were less affected by the information.“Unclear” means that there was inadequate information to assess bias.

Statistical Analyses

Meta-analysis was performed using Review Manager 5.3.The heterogeneity test was first carried out on the included literature.The between-study heterogeneity was tested using the chi-square test I2statistic.IfP≥0.1 and I2≤ 50%, it can be considered that there is homogeneity among multiple similar studies, and the fixed effect model was used for analysis; A random effects model was used on the condition ofP< 0.1 or I2> 50%.The dichotomous uses the odds ratio (OR)value, and the continuous variable is expressed by the weighted mean difference (MD), and both were calculated with 95% confidence intervals (CI).Sensitivity analyses were also conducted, by which the influence of a single study on the pooled effect was examined by removing one study at a time.Forest plots were displayed to summary weighted estimates and the funnel plots could be used to assess the publication bias.

Results

Search results

According to the search strategy, 99 relevant Chinese documents were initially retrieved.After further reading the abstracts and the full text,according to the inclusion and exclusion criteria, a total of 9 RCTs were finally included 798 patients.The literature screening process and results were shown in Figure 1.

Figure 1.Flow chart of literature search

Characteristics of the included studies

A total of 9 studies with 798 patients were included ultimately.Among them, 408 cases were in the experimental group and 390 cases were in the control group.Table 1 summarized the basic characteristics of the study.

Methodological Quality of Included Studies

For randomization process domain, 1 RCT was divided into groups by random number table, and the selection bias was remarked as “l(fā)ow risk”.4 RCTs grouped according to the admission time and the principle of voluntariness, so the selection bias was appraised as “high risk”.The other 4 RCTs did not explain the specific method of random sequence generation, “ Some concerns ” .The specific risk assessment results were shown in the Figure 2.

Table1.Basic Characteristics of Inclusion Documentation

Figure 2.Risk of bias summary

Meta-Analysis Results

Total effective rate

Nine studies included in the study literature reported total effective rate, and the homogeneity test showed[Chi2=4.89,df=8(P=0.77);I2=0%],and the fixed effect model was used.The results of the meta-analysis showed that there was a statistically significant difference in the total effective rate between the experimental group and the control group[OR=0.33,CI=(0.23,0.46),P<0.00001],the combined application of Ginkgo biloba extract on the basis of conventional treatment can improve total effective rate.(Figure 3)(Total effective rate =(Number of markedly effective cases + Number of effective cases)/Total number of cases×100%)

Visual acuity level

Observing the change of visual acuity level, a total of 3 studies were included.The heterogeneity test results were [Chi2= 2.04, df = 2(P= 0.36);I2= 2%],therefore, the fixed effect model was used.The meta-analysis displayed that there was a statistically obvious difference in visual acuity between the experimental group and the control group[OR=-0.11,95% CI = (-0.14, -0.07),P< 0.00001], the combined application of Ginkgo biloba extract on the basis of conventional treatment can improve the visual acuity of the patients with DR.

Visual field average defect

Observing the change of the average visual field defect level, a total of 3 studies were included.The heterogeneity test results were [Chi2= 1.43, df = 2(P= 0.49); I2 = 0%]and the fixed effect model was applied.The results of the meta-analysis showed that there was a statistically significant difference in the mean visual field defects between the experimental group and the control group [OR = 0.59, 95% CI =(0.53, 0.65),P< 0.00001], the combined application of Ginkgo biloba extract on the basis of conventional treatment can enhance the average visual field defect level of patients with DR.(Table 2)

Figure 3.Meta-analysis of total effective rate

Table 2.Analysis of the effect of Ginkgo biloba extract combined with routine treatment on fundus index

Sensitivity Analysis and Publication Bias

The inverted funnel plot showed asymmetry in the included literature,indicating the potential presence of publication bias, as shown in Figure 4.For the total combined effect of clinical total effective outcome indicators, the sensitivity analysis was performed by using the elimination method one by one, the operation process was to exclude one study at a time,and the remaining studies were analyzed to judge the stability of the results.The results showed that there was no qualitative change in the combined effect,indicating that the results of this study were stable, as shown in Figure 5.

Figure 4.Funnel plot of the clinical total effective rate

Figure 5.Sensitivity analysis of total effective rate

Discussion

DR is a serious blinding fundus lesion, mainly manifested by retinal capillary basement membrane thickening and increased vascular permeability,resulting in the destruction of blood retinal barrier.Oxygen free radicals are involved in its pathological process [21].On the one hand, when DR patients are hyperglycemic, plasma viscosity increases, red blood cell concentration increases, and erythrocyte deformability decreases, Erythrocyte agglutination and platelet aggregation function hyperfunction, all of which increase the viscosity of whole blood, slow down the blood flow of retina, reduce the blood flow of retina by [22-23], on the other hand, the basement membrane of capillaries is thickened, erythrocyte deformability is reduced, and oxygen dispersion is blocked, resulting in retinal ischemia and anoxia.[24-25].DR is mainly divided into non proliferative diabetic retinopathy(NPDR)and proliferative diabetic retinopathy (PDR).NPDR often occurs in the early stage of DR, and its main characteristics are retinal hemorrhage, microaneurysm, retinal microvascular abnormalities, etc[26].According to the severity of these symptoms, they can be divided into stage I,stage II and stage III.Stage I refers to mydriatic fundus examination with only micro aneurysms or small bleeding spots.In stage II, there are not only micro aneurysms, but also yellowish white "soft exudation"or bleeding spots.In stage III,on this basis,the retina appears white "soft exudation" or accompanied with bleeding spots.PDR is another type of retinopathy, which has the risk of other structural complications [27].According to the severity of PDR,PDR can be divided into stage IV, stage V and stage VI.There were neovascularization or vitreous hemorrhage in stage Ⅳ, neovascularization and fibroplasia in stage Ⅴ, and neovascularization and fibroplasia in fundus in stage Ⅵ, and retinal detachment occurred in stage Ⅵ [28].Compared with NPDR, PDR is more harmful to vision, which can lead to severe visual loss or even complete blindness[29].

The traditional Chinese medicine doctor, believes that DR is a category of “diabetes and eye diseases”,“sight seeing faint” and “sudden blindness”.It is due to the thirst for diabetes, which leads to deficiency of liver and kidney, phlegm dampness and stagnation of the eyes and blood stasis.The treatment is based on the principle of nourishing yin and replenishing qi and promoting blood circulation to dissipate blood stasis.At present, the main treatment is currently treated mainly by supplementing qi, activating blood circulation, nourishing liver and kidney, promoting blood circulation to dissipate blood stasis, removing dampness, removing phlegm, dredging collaterals and improving eyesight [30].However, it has been proved by practice that controlling blood sugar simply is not very effective in delaying the occurrence and development of diabetic angiopathy, and the traditional Chinese medicine for promoting blood circulation and removing blood stasis is attracting more and more attention in preventing and treating diabetic vascular diseases [31].Ginkgo biloba extract is a kind of vascular protective agent.It has a good effect in treating DR.For example, Wang Zhizhong[32] found that Ginkgo Dispersible Tablets lactone has the effect of dilating blood vessels, which can obviously improve the microcirculation and increase the blood flow of microcirculation.According to the study of Lou Jixian [33], a certain concentration of Ginkgo biloba extract can reduce the damage of retinal cells caused by high glucose.Wang Yu Fang[34] found that Ginkgo biloba extract not only can protect HBCEC in high sugar environment, but also can reduce the expression of MMP2 and NF- kappa Bp65, which is widely used in the prevention and treatment of Ginkgo biloba leaves.There are many kinds of chemical constituents, but most of them are medicinal value components terpenoid lactone and ginkgo flavonoid [35].Pharmacological studies have proved that ginkgo flavonoid glycosides have antioxidant effect and inhibit free radical production.It also removes the free radicals produced and protects the cell membrane from lipid peroxidation.Ginkgo flavone glycosides can protect the cell membrane structure and function [36], and protect the retinal structure and function caused by ischemia reperfusion,photo toxicity and inflammation [37-38].Ginkgolide has a highly specific natural PAF receptor antagonist,of which ginkgolide B has the strongest effect.By targeting receptors on target cell membrane, platelet aggregation and thromboxane increase were inhibited[39].To sum up, Ginkgo biloba extract can promote absorption of bleeding and reduce exudation, improve microcirculation, reduce retinal edema, improve retinal function and improve eyesight [40-41].In addition, Ginkgo biloba extract can also reduce blood lipids, blood viscosity, improve hemorheology,increase red blood cell oxygen carrying capacity, and improve blood glucose metabolism and hyperinsulinemia effect[42-44,46].

In this study, meta analysis was used to analyze the clinical efficacy of Ginkgo biloba extract in the treatment of DR.The results showed that Ginkgo biloba extract combined with Ginkgo biloba extract has certain adjuvant therapeutic effect on diabetic retinopathy on the basis of routine treatment in western medicine.The results are as follows:conventional therapy combined with Ginkgo biloba extract can not only improve the total clinical efficiency, it also improved the visual acuity and visual field average defect of the patients.The difference between the treatment group and the control group was statistically significant.As for the safety of the Ginkgo biloba extract, the adverse reactions of Ginkgo biloba extract were not reported in the literature.On the one hand, this study not only compiled the RCT literature on DR treatment of Ginkgo biloba extract, but also carried out meta analysis.It made up for the shortage of Ginkgo biloba extract in treating evidence-based medicine in DR,and provided data support for other related research.On the other hand, it is suggested that the rational medication plan should be made according to the patient's constitution, gender and medical history in order to avoid adverse reactions.Meanwhile, regular follow-up should be paid attention to during the treatment process to monitor the long-term treatment effect of the drug.In addition, in clinical work, we found that if the blood glucose level of patients was well controlled or the operation was successful, there might be of ischemic optic neuropathy or macular edema [45].How to do better to protect and improve the eyesight of patients is a problem that the majority of ophthalmologists are actively exploring [47].Based on clinical data,this study explained scientifically that the application of Ginkgo biloba extract on the basis of conventional treatment can improve the vision level and visual field defect of the patients,thus providing a theoretical support for the safe and effective use of Ginkgo biloba extract.

At the same time, there are limitations in this study,which are mainly reflected in the following aspects:(1)6 of the 9 articles included in the systematic reviews mentioned specific random methods,and the rest were not explained; at the same time, 9 papers did not mention allocation concealment and blind methods.These factors may lead to bias in selection, bias in implementation and measurement bias, all of which reduced the reliability of the conclusions of the study in varying degrees.It is doubtful for the authenticity of the study.(2) The inverted funnel plot of clinical total efficiency is asymmetrical, suggesting that there is a possibility of publication bias in the literature,that is,there are some negative results or not yet published.(3) The results show only short-term clinical efficacy,there is a lack of relevant safety indicators such as follow up and survival rate.(4) In this study, we selected DR patients with stage I and VI and non value-added DR patients as research subjects.Future research can choose single stage DR patients to make more accurate conclusions.(5) This study included Extract of Ginkgo Biloba Leaves Tablets, ginkgo leaf dropping pills and ginkgo leaf tincture formulations.In this respect, the clinical heterogeneity of the study was not well avoided.(6) Although this study is the treatment plan of Ginkgo biloba extract, different courses and doses of RCTs may produce different effects.Overview, this study suggests that clinical trials should focus on improving methodological quality and standardizing clinical RCTs reporting.More well-designed and larger scale multicenter RCTs studies are needed to provide better evidence-based medical evidence for Ginkgo biloba extract in the treatment of DR.

Conclusions

In summary, this study revealed that the combination of Ginkgo biloba extract and conventional medicine had a better effect on treating DR.However,due to the limitations of the current meta-analysis, the strength of evidence was needed to be promoted by rigorously designed, multicentered, large-sample randomized double-blind controlled trials.

Contributors:Wenxin wang and Dan Zhang conceived the idea of the study.Dan Zhang and Cuanxin Liu performed the screening of journals, the extraction of data,and the statistical analysis.The first draft of the manuscript was performed by Wenxin wang, with inputs from Dan Zhang.Wenxin wang is the guarantor of the manuscript’s data.Shuang Han,Jiaxing He, and Shuang Tang reviewed and provided valuable information, insight and edition to the manuscript.All authors have agreed on the final version of the manuscript.