Resveratrol has been used in humans, and previous data show that its toxicity is limited13. Since resveratrol ameliorated pathology and improved the function of MD animal models, we planned this study as a pilot study.
Resveratrol improved motor function and muscle power in the proximal muscles of participants. However, the distal muscles of patients were unaffected (Fig. 3c, Supplementary Fig. S1f). One patient with BMD (BMD 23 y) experienced relief from muscle pain during resveratrol administration, which may have contributed to the improvement in motor function. The observed increase in patients’ muscle strength following resveratrol treatment was consistent with findings in mdx mice10,12, in which approximately fivefold increases in slow-fibre-type myosin heavy chain and troponin gene transcripts were detected in the biceps femoris muscles10. Resveratrol binds the N-terminal region of the SIRT1 protein, resulting in the allosteric activation of SIRT1 activity7. SIRT1 deacetylates and activates peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), which switches muscle types from fast to slow fibres6,7,19. Indeed, transgenic mice overexpressing PGC-1α19 or SIRT18 show muscle type conversion from fast- to slow-twitch fibres. PGC-1α transgenic mice also show increased resistance to muscular fatigue19. Thus, the beneficial effects of resveratrol on the muscles of MD patients may involve PGC-1α activation by SIRT1. In mdx mice, serum CK levels were decreased by the overexpression of SIRT1 in the muscles8 and by the long-term administration of resveratrol12. Recently, we have shown that skeletal muscle-specific SIRT1-knockout mice have a fragile muscle cell plasma membrane and that SIRT1 is involved in membrane resealing after cell injury20. In the present study, mean CK levels were decreased by resveratrol, although the change was non-significant. We noted that patients with low serum CK levels, i.e., less than 2000 IU/L, showed little response to resveratrol treatment, which could be caused by the lack of sufficient muscle mass. Resveratrol administration at early disease stages may afford great benefits to MD patients.
Oxidative stress plays a key role in the development of MD pathology21. Resveratrol decreases ROS levels by inducing the expression levels of the antioxidant enzyme superoxide dismutase9, suppressing superoxide-generating NADPH oxidase10, and eliminating damaged mitochondria, a major cellular source of ROS22, via mitochondrial autophagy, known as mitophagy11,12,23,24. These antioxidative functions of resveratrol are mediated at least in part by the deacetylation and activation of Forkhead box O transcription factors and PGC-1α via SIRT1 activation6,7.
Cardiomyopathy and subsequent heart failure is a major cause of death in MD patients. Resveratrol suppresses cardiac hypertrophy and fibrosis in TO-2 hamsters9 and mdx mice25, which may be mediated by the deacetylation and ubiquitin-dependent degradation of transcriptional coactivator p300 via SIRT1 activation25. In the present study, we could not detect any improvement in echocardiographic parameters or levels of plasma brain natriuretic peptide (BNP), a marker of cardiomyopathy. This may be because all participants showed normal BNP levels (< 18.4 pg/ml), and only 2 patients had a reduced ejection fraction of less than 50% (Supplementary Table S1). Longer-term administration of resveratrol may be necessary to reveal the cardiac function of resveratrol in MD patients.
Resveratrol is rapidly absorbed and yields peak serum concentration at 1 h post dose13. In the present study, the levels of serum resveratrol concentration in MD patients (Fig. 5b–d) were consistent with those in healthy volunteers13. Six (54.5%) and three (27.3%) patients had diarrhoea and abdominal pain, respectively (Table 3). These symptoms were transient and tolerable in participants except for the female patient (FCMD 12 y), who suffered from severe diarrhoea at the dose of 1500 mg resveratrol. The weight of the patient was only 26.5 kg, and she could not continue the dose. Similar to our study, Brown et al. has reported mild to moderate gastrointestinal symptoms in healthy volunteers who ingested resveratrol at doses of 2500 and 5000 mg/day26. Two patients contracted transient grade 3 upper respiratory and lung infections, and one patient suffered from a grade 2 upper respiratory infection. We believe that these events were unrelated to resveratrol since all three patients had repeatedly suffered from respiratory infections before the clinical trial and recovered immediately while taking resveratrol.
We found that administration of resveratrol to mdx mice with the highest dose (4 g/kg food) is more effective in increasing myofibre cross-section area than lower doses of 0.4 g and 0.04 g/kg food12. However, a moderate dose of resveratrol (0.4 g/kg food) also decreases the number of fibres with central nuclei, the number of fine fibres, and serum creatine kinase levels. Additionally, it significantly improves motor function in mdx mice12. Resveratrol at 0.4 g/kg food was estimated to be approximately 50 mg/kg body weight/day10. The mean resveratrol level at 1000 mg/day was 36.9 ± 44.7 ng/mL (range, < 1.0–215.0 ng/mL) (Fig. 5a), which is consistent with the data of Almeida et al.27. The administration of resveratrol to healthy adult subjects at 150 mg six times/day for 13 doses resulted in a mean plasma concentration of 63.8 ng/mL and a half-life of resveratrol of 2–5 h27. Resveratrol at 36.9 ng/mL is equal to 160 nM. Because 160 nM resveratrol was 1/68 of the concentration needed for twofold activation of SIRT1 enzymatic activity in vitro28, the activation of SIRT1 by resveratrol in the present study did not seem strong. However, other studies show the physiological effects of resveratrol even in small amounts13,27. The administration of resveratrol at 150 mg/day for 30 days significantly decreased plasma glucose, insulin, triglycerides and leptin in healthy obese men29. Using muscular biopsy, Timmers et al. showed that resveratrol activates AMPK activity, increases SIRT1 and PGC1α levels, and promotes mitochondrial respiration activity in the muscle29. Based on these findings, we suggest that resveratrol at a dose of 25–50 mg/kg body weight/day is sufficient to treat MD patients. The dosing period required to detect an effect of resveratrol seems to be more than 4 months for MD patients.
Glucocorticoids have been shown to prolong the survival of patients with DMD5. In the present study, glucocorticoids were treated in only one patient with DMD (DMD 12 y), who showed increased muscle strength and motor function without any adverse effects during resveratrol administration. Recently, novel methods to treat DMD have been developed. Ataluren is a stop codon readthrough drug for DMD based on nonsense mutations3, and is currently being evaluated in a post-approval safety study in Europe. Eteplirsen is a morpholino antisense oligomer that induces the skipping of exon 51 of the dystrophin gene4, and accelerated approval for this drug was obtained from the U.S. Food and Drug Administration in 2016. The use of these kinds of therapies is expected to increase, although they have some limitations30,31. Given its unique mode of action and relatively mild adverse effects, resveratrol could combine with glucocorticoids or recent novel medicines such as ataluren and eteplirsen.
A limitation of the present study was that it was not a randomized, double-blind, placebo-controlled trial. We could not analyse an untreated group because the number of patients was limited, and three types of MD patients with various clinical conditions were recruited. In the case of rare diseases, phase I studies for cancer and phase IIa studies for other diseases have been executed without any control32,33,34,35,36. These trials were planned because of problems in recruiting patients, non-uniformity in patients’ disease conditions, the use of an investigational drug that has never been administered in humans, no prior information on dose levels, difficulty in preparing a control group or difficulty in obtaining the agreement of patients to use a placebo. Usually, if some possibility concerning effectiveness of the drug is found in a phase IIa study, a phase IIb clinical study is carried out to identify the effect and dose of the investigational drug by a randomized and double-blind study.
We repetitively measured the MFM and QMT scores of the participants. Some studies have reported that exercises increase the motor function and muscle strength of MD patients37. For example, the knee flexor maximum voluntary contraction torque of the limb-girdle in Becker and facioscapulohumeral MD patients increased by 13% after a 12-week resistance training programme38. However, two meta-analyses of exercise interventions on muscle strength in MD patients showed no evidence of improvement in muscle strength and in endurance39. Because the average time required for MFM has been reported to be 36 min (range 8–75 min)15, measuring MFM and QMT scores once every 8 weeks in the present study was unlikely to improve motor function of the patients. Since participants are aware of exercise interventions, the two meta-analyses39 also suggest that placebo effects of interventions are minimal on MD patients. Moreover, average muscle strength in DMD patients treated with placebo shows similar decline with that of untreated patients during administration for 6 months40. Because mean QMT scores of scapula elevation and shoulder abduction increased by twofold 24 weeks after resveratrol administration (Fig. 3a,b), it was less likely that the efficacy of resveratrol was a placebo effect.
As mentioned above, our study was a phase IIa study to investigate the possibility of the use of resveratrol in MD patients. To determine whether resveratrol could provide benefit for MD patients and be used as a symptomatic medication for MDs, a phase IIb study of resveratrol in a multi-centre trial with randomized, double-blind, and parallel-group comparison design will be necessary. An evaluation of the long-term effects of resveratrol on MD patients in a uniform cohort, such as age-matched young DMD patients, would be benefical.