Original Article Drug/Regimen Diabetes Metab J 2020;44:542-554 https://doi.org/10.4093/dmj.2019.0099 pISSN 2233-6079 · eISSN 2233-6087 DIABETES & METABOLISM JOURNAL γ-Linolenic Acid versus α-Lipoic Acid for Treating Painful Diabetic Neuropathy in Adults: A 12-Week, Double-Placebo, Randomized, Noninferiority Trial Jong Chul Won1, Hyuk-Sang Kwon2, Seong-Su Moon3, Sung Wan Chun4, Chong Hwa Kim5, Ie Byung Park6, In Joo Kim7, Jihyun Lee8, Bong Yun Cha9, Tae Sun Park10 1 Division of Endocrinology and Metabolism, Department of Internal Medicine, Cardiovascular and Metabolic Disease Center, Inje University Sanggye Paik Hospital, Inje University College of Medicine, Seoul, 2 Division of Endocrinology and Metabolism, Department of Internal Medicine, Yeouido St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, 3Department of Internal Medicine, Dongguk University College of Medicine, Gyeongju, 4 Division of Endocrinology and Metabolism, Department of Internal Medicine, Soonchunhyang University Cheonan Hospital, Soonchunhyang University College of Medicine, Cheonan, 5Division of Endocrinology and Metabolism, Department of Internal Medicine, Sejong General Hospital, Bucheon, 6 Division of Endocrinology and Metabolism, Department of Internal Medicien, Gachon University Gil Medical Center, Gachon University College of Medicine, Incheon, 7 Division of Endocrinology and Metabolism, Department of Internal Medicine, Pusan National University Hospital, Pusan National University School of Medicine, Busan, 8Department of Internal Medicine, Daegu Catholic University School of Medicine, Daegu, 9Division of Endocrinology and Metabolism, Department of Internal Medicine, College of Medicine, The Catholic University of Korea, Seoul, 10Division of Endocrinology and Metabolism, Department of Internal Medicine, Chonbuk National University Medical School, Jeonju, Korea Background: This study was a multicenter, parallel-group, double-blind, double-dummy, randomized, noninferiority trial to evaluate the efficacy and safety of γ-linolenic acid (GLA) relative to α-lipoic acid (ALA) over a 12-week treatment period in type 2 diabetes mellitus (T2DM) patients with painful diabetic peripheral neuropathy (DPN). Methods: This study included 100 T2DM patients between 20 and 75 years of age who had painful DPN and received either GLA (320 mg/day) and placebo or ALA (600 mg/day) and placebo for 12 weeks. The primary outcome measures were mean changes in pain intensities as measured by the visual analogue scale (VAS) and the total symptom scores (TSS). Results: Of the 100 subjects who initially participated in the study, 73 completed the 12-week treatment period. Per-protocol analyses revealed significant decreases in the mean VAS and TSS scores compared to baseline in both groups, but there were no significant differences between the groups. The treatment difference for the VAS (95% confidence interval [CI]) between the two groups was −0.65 (−1.526 to 0.213) and the upper bound of the 95% CI did not exceed the predefined noninferiority margin (δ1 =0.51). For the TSS, the treatment difference was −0.05 (−1.211 to 1.101) but the upper bound of the 95% CI crossed the non- inferiority margin (δ2 =0.054). There were no serious adverse events associated with the treatments. Conclusion: GLA treatment in patients with painful DPN was noninferior to ALA in terms of reducing pain intensity measured by the VAS over 12 weeks. Keywords: Diabetic neuropathies; Gamma-linolenic acid; Thioctic acid Corresponding author: Tae Sun Park https://orcid.org/0000-0001-7216-8468 This is an Open Access article distributed under the terms of the Creative Commons Division of Endocrinology and Metabolism, Department of Internal Medicine, Chonbuk Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) National University Medical School, 20 Geonji-ro, Deokjin-gu, Jeonju 54907, Korea which permits unrestricted non-commercial use, distribution, and reproduction in any E-mail: [email protected] medium, provided the original work is properly cited. Received: May 22, 2019; Accepted: Aug. 13, 2019 Copyright © 2020 Korean Diabetes Association https://e-dmj.org γ-Linolenic acid in painful DPN INTRODUCTION trials [18,19], the efficacy of GLA for improving the symptoms of patients with painful DPN has yet to be determined. The occurrence of type 2 diabetes mellitus (T2DM) is increas- Thus, the primary aim of the present study was to investigate ing worldwide [1], and in Korea, one in every seven adults the noninferiority of the efficacy of GLA (Evoprim; Dalim Bio- aged 30 years or older has diabetes [2]. Diabetic sensorimotor tech, Seoul, Korea) relative to ALA (Lipo-A HR; Dalim Bio- distal symmetric polyneuropathy, or diabetic peripheral neu- tech) as an active comparator. GLA was orally administered for ropathy (DPN), is the most common neuropathy associated 12 weeks as a treatment for the neuropathic symptoms of with diabetes as well as the most common complication in dia- T2DM patients with painful DPN. betes patients. Approximately one in every three T2DM pa- tients in Korea has DPN [3], and 42.3% of those with DPN ex- METHODS perience painful symptoms or are taking medication(s) for their current pain [4]. Although many available guidelines rec- Study population ommend anticonvulsants and antidepressants as first-line Subjects were eligible for the present study if they agreed to treatments for painful DPN, there are unmet needs in terms of participate, were between 20 and 75 years of age, had T2DM efficacy and tolerability, and these treatment modalities modu- with glycosylated hemoglobin (HbA1c) levels ≤11.0% at the late the pain rather than favorably influencing the underlying time of screening, had an average visual analogue scale (VAS) neuropathic processes [5]. Additionally, the painful symptoms score ≥4.0 for the 24-hour average pain score (0 to 10 numeri- of DPN may vary with the course of nerve damage, the pres- cal rating scale), and a diagnosis of DPN after a thorough eval- ence of comorbidities, and/or ethnic and cultural differences uation for other causes of neuropathy at the screening. The ex- [6], which creates therapeutic challenges regarding the man- clusion criteria consisted of the following: a confounding neu- agement of painful symptoms [5]. rological disease or neuropathy caused by progressive or de- A novel treatment option, γ-linolenic acid (GLA), is an n-6 generative disorders that may have interfered with the assess- polyunsaturated fatty acid that is converted from dietary lino- ment of DPN severity; uncontrolled hypertension (systolic or lenic acid (primrose oil), and as an essential component of diastolic blood pressure levels ≥160 or ≤100 mm Hg or ≥95 structural phospholipids in neural cell membranes, is neces- or ≤60 mm Hg, respectively); an amputated foot or leg; a clini- sary for the maintenance of normal nerve membrane structure cally significant cardiac, pulmonary, gastrointestinal, hemato- and function [7]. For example, decreases in the production and logical, or other endocrinological disease (e.g., abnormal thy- increases in the destruction of GLA are associated with im- roid function test even though taking medication); organ paired nerve conduction in patients with T2DM [8,9]. Thus, transplants; aspartate aminotransferase or alanine aminotrans- based on the pathogenetic mechanisms of DPN, GLA has been ferase levels >3 times normal levels; serum creatinine levels developed as a potential disease-modifying therapeutic drug >2.0 mg/dL; drug or alcohol abuse within the last year; use of [10,11], along with other potential treatment modalities such an investigational drug within the last 6 months; severe or ana- as α-lipoic acid (ALA) [12,13], aldose reductase inhibitors phylactic reactions; pregnant or lactating women; and/or cor- [14], vascular endothelial growth factors [15], and protein ki- ticosteroid or local anesthetic therapies within the last 2 nase C-β inhibitors [16]. These treatment options were de- months. Subjects were enrolled at 11 sites in the Republic of signed to favorably influence the underlying pathophysiology Korea and the study was carried out from January 26, 2016 to of DPN rather than merely provide symptomatic relief for July 25, 2018 (ClinicalTrials.gov number, #NCT03914404). All DPN patients. GLA treatment corrects impaired nerve func- study procedures were conducted in accordance with the Dec- tion in animal models of diabetes [17] and is beneficial for laration of Helsinki and ICH Good Clinical Practice, and were neurophysiological parameters, thermal thresholds, and clini- approved by Institutional Review Board at all sites (IRB No.: cal sensory symptoms in patients with T2DM [8]. A previous CUH 2015-06-001, XC15MSMV0063K, 1528, GAIRB2015- study of 934 Korean patients with painful DPN found that 237, XC15MSMV0063S, D-1506-022-041, CR-15-069-L, 40.2% (n=396) were prescribed ALA and 17.2% (n=169) were 110757-201507-HR-01, SCHCA 2015-06-021-007, 4-2015- prescribed GLA [3]. Although the efficacies of oral and intra- 0628, SGPAIK 2017-08-01). Written informed consent was venous ALA have been established by meta-analyses of clinical obtained from all patients. https://e-dmj.org Diabetes Metab J 2020;44:542-554 543 Won JC, et al. Study design and medication defined as the intake of at least 80% of the trial medications. Study design No other agents for the treatment of DPN were allowed, but all The present study was a multicenter, double-blind, double- subjects were advised to continue