Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease, characterized by synovitis, systemic inflammation and generation of autoantibodies. In industrialized countries, up to 1.0% of the adult population is affected by RA and suffers from joint damage and loss of physical function [1]. Disease-modifying antirheumatic drugs (DMARDs) are used to treat RA. The most commonly used DMARD is methotrexate (MTX), which is the “anchor drug” for active RA and can be combined with a variety of other drugs. Biological agents can be used when arthritis is aggressive and/or not sufficiently controlled by chemical DMARDs [2]. However, the world wide use of biological agents is restricted by their high costs and risk of severe infections [3].

Tripterygium wilfordii Hook F (TwHF) is widely used in traditional Chinese medicine as a potent treatment for joint pain, fever, chills, edema and local inflammation [4, 5]. Extracts of TwHF have been analyzed and the three major diterpenoids, triptolide, tripdiolide and triptonide, are mainly responsible for its anti-inflammatory and immune regulatory activities [6–9]. TwHF has been approved to treat RA in China. Our clinical experiences from treating more than 30,000 patients with RA each year in Peking Union Medical College Hospital (PUMCH) also support the high cost effectiveness of TwHF or a combination of MTX + TwHF, with increases in daily therapeutic expense less than 1 US dollar [10]. Previously in three randomized controlled trials, extracts of TwHF have also been shown to have good efficacy in treating RA compared with placebo or sulfasalazine [11–13].

To further evaluate the role of TwHF in treating RA by comparing its effects to MTX, we recently conducted the “Comparison of Tripterygium wilfordii Hook F with methotrexate in the treatment of active rheumatoid arthritis” (TRIFRA) study [14]. In this open-label, multicenter randomized controlled trial, 207 DMARD-naïve patients were randomly allocated into three arms and treated with TwHF, MTX or TwHF+MTX. We evaluated the proportion of patients achieving an American College of Rheumatology (ACR) 50% response (ACR50) at week 24, together with other parameters to measure disease activities including ACR20, ACR70, European League Against Rheumatism (EULAR) good or moderate response, clinical Disease Activity Index (cDAI), 28-joint count Disease Activity Score (DAS28), Health Assessment Questionnaire (HAQ) and 36-item Short-Form Health Survey questionnaire (SF-36) scores. At week 24, ACR50 response was achieved in about half of the patients using MTX or TwHF alone, and in more than three quarters of the patients receiving combination therapy. Similar patterns were found for other parameters. Moreover, with TwHF monotherapy and the combination therapy there was no increased incidence of adverse events compared to MTX alone. Thus, we concluded that TwHF monotherapy was not inferior to, and MTX + TwHF was better than, MTX monotherapy in controlling disease activity safely in patients with RA [14].

Long-term control of disease activity and associated joint damage, with the preservation of physical function in a safe manner is the ultimate goal of RA management. Therefore, the evaluation of treatment efficacy from long-term trials is needed to determine long-range benefit. Aside from benefit in clinical measures such as ACR50, prevention of joint damage evident on radiography (radiographic joint damage) is an important outcome in determining the long-term treatment effects in clinical trials, and recommended as a surrogate marker for overall functional status in patients with RA [15]. Previous studies have shown that treatment with MTX or other DMARDs could slow the progression of radiographic damage [16, 17]. The TRIFRA study was designed to be a 24-week, multicenter, randomized controlled trial (RCT). After its termination, the patients continued to be followed, and disease activities were monitored in the real-world situation. Based on changes in perceived disease activity, treatment could be modified accordingly. In this observational report, we followed the participants from the TRIFRA trial for 2 years after the study initiation. Both functional measures and radiological images were collected at year 2 to determine whether the same efficacy patterns observed in the first 24 weeks were sustainable. Moreover, the long-term impact on radiographic progression and physical function was determined.

The TRIFRA study was designed as a 24-week, open-label, randomized study to evaluate the efficacy and safety of TwHF alone, MTX alone or the combination of TwHF + MTX in in the treatment of active RA. It was previously registered in ClinicalTrials.gov (NCT01613079). A detailed description of the study design was published previously [14]. After the end of the trial, subjects were followed by the investigators for 18 additional months and monitored using the same clinical outcome measures. In addition, radiographs of the hands and wrists were repeated to evaluate progressive joint damage.

Study protocol

The protocol was approved by Peking Union Medical College Hospital (PUMCH) ethical review board. Initially, enrolled participants were allocated into three arms by centralized randomization, as follows: oral TwHF pills 20 mg three times a day; MTX starting from 7.5 mg once a week and increasing to 12.5 mg once a week (0.20–0.25 mg/kg) within 4 weeks, with folic acid 10 mg on the day after each MTX administration; or TwHF plus MTX at the same dosage as aforementioned. In this study, the TwHF used was the same as that in the TRIFRA study, in which the concentration of triptolide (C20H24O5), the major immunosuppressive anti-inflammatory diterpenoid, was 1.2 μg/10 mg, and the concentration of wilforlide (C30H46O3), an anti-inflammatory triterpene, was 36.6 μg/10 mg. The patient’s DAS28 was evaluated at week 12, and monotherapy was continued only if their DAS28 reduced more than 30%; otherwise the patients switched to MTX + TwHF combination therapy. After 24 weeks, patients were followed up and their therapy would be modified based on the physician’s judgement. A detailed description of the study design was published previously and is also shown in Fig. 1.

The previous 24-week TRIFRA clinical trial is the first RCT that compared the efficacy of TwHF and MTX in treating DMARD-naïve patients with RA [14]. At week 24, TwHF was not inferior to MTX as measured by multiple parameters of disease activity, including ACR20, ACR50 and ACR70 response criteria, EULAR and cDAI good response criteria and DAS28 remission criteria and LDA rate. More importantly, patients with RA receiving MTX + TwHF combination therapy had better improvement in disease activity. Considering that RA is a chronic disease, we followed up the patients from the TRIFRA trial at year 2 and evaluated disease activity in the same way. Among 207 patients recruited in the TRIFRA trial, 109 of them returned for the 2-year follow up. Notably, the frequency of adhering to the initial protocol was comparable among the three groups. The disease activity at year 2 followed a similar pattern when comparing the MTX monotherapy and TwHF monotherapy groups (Table 1). The TwHF was not inferior to MTX in treating active RA. However, the combination therapy was not obviously more effective than MTX monotherapy at year 2. This may suggest that the combination therapy induces disease remission faster in the early stage of treatment, while the long-term efficacy was similar to that in the monotherapy groups. The limited sample size available is a concern at this stage and may have caused bias in the efficacy evaluation.

We did not attribute the two cancer deaths to the use of TwHF in this follow-up study. A number of clinical studies on TwHF have not found any association between cancer and TwHF, but rather with RA per se [12, 13, 27]. Notably, the TwHF + MTX combination group in this follow-up study also received the same dosage of TwHF, yet experienced no malignancies. Moreover, numerous pharmacological studies have suggested triptolide has an anti-tumor effect in various tumor models in vitro and in vivo [28, 29].

This study, as a long-term extension of a 24-week RCT, has several limitations. First, this follow-up study, together with the TRIFRA study, was designed as an open-label study. To increase the objectiveness of the results, blinded evaluators were employed. However, a randomized double-blinded trial is needed to provide more robust data and confirm our results. Second, a significant proportion of patients were lost to follow up or changed to other regimens for different reasons. This could bias the analysis, and, therefore, the power of the conclusion was weakened (Fig. 1). Furthermore, there might be significant bias in the analysis of adverse events. In this case, we performed both ITT and PP analysis of all the clinical measures to determine whether similar patterns were observed. Importantly, it was noted that the proportions of patients who withdrew or were lost to follow up were similar among the three groups. It was presumed that patients returned to “real-world” clinical practice and their treatments were monitored and optimized by their physicians’ judgement. Thus, we compared the rate of adherence to the original protocol and performed detailed cause analysis in the follow up, and showed that these were comparable among the three groups. Third, only the radiographic images of the hands and wrists were available for this analysis, and the feet were not included. Studies have shown that the joints of the feet are usually affected earlier than the joints of the hands, and therefore including the feet could help improve the sensitivity of joint damage assessment in early RA [30, 31]. In order to demonstrate the therapeutic efficacy, the patients recruited in the TRIFRA study were diagnosed with definite active RA and the mean disease duration was longer than 60 months. Moreover, considerable radiographic damage was noted in the hands and wrists, providing a reasonable baseline background to determine slowing of radiographic damage, even though the feet were not evaluated. The scores for the hands and wrists were representative of the disease activity at this stage, which was also indicated by its association with change in the DAS28. Ideally, the radiographic data should be obtained uniformly at baseline and the end of year 2. In this real-world follow-up study, we only successfully performed radiographic examination at the end of the 2 years in a proportion of subjects. To further maximize the power of our results, the analysis included all the patients who had at least two radiographic examinations with time intervals greater than 1 year. Notably, we calculated the estimated yearly radiographic progression based on these images. This might introduce additional bias to our results because this model presumed that radiographic progression was linear. Finally, the dose of MTX was limited to 12.5 mg per week and the dose of folic acid was 10 mg per week, which is very common in Asia. This point was discussed in our previous report on the TRIFRA study. As a follow up of the TRIFRA study, the same doses of MTX and folic acid were maintained. Although there has not yet been a direct comparison of the response rates to MTX in patients with RA from different ethnicities, we did notice that the clinical response in our TRIFRA trial was comparable to the data from patients with RA in Europe and North America receiving a higher dose of MTX [32]. We recognized that the response rate in RA may be further improved with more intensive combination treatment [33], although the frequency of adverse events may also increase as well. Most reviews and recommendations suggest a prescription of at least 5 mg folic acid (FA) per week [34]. So far, insufficient evidence has been collected on the optimal dose of FA. Studies have proven that low-dose FA (≤ 7 mg/week) was able to reduce MTX side effects significantly [35]. Doses larger than 5 mg did not lead to further amelioration of the MTX side effects and neither did they affect the efficacy of MTX therapy [36, 37]. Because of these considerations, we are less concerned that the therapeutic effects of MTX were compromised by our use of FA in our study.

This study confirmed the original finding that TwHF was not inferior to MTX in treating active RA in the long term, and that a further study with larger sample sizes should be performed to characterize the role of TwHF in RA therapy in greater detail.

Although this is a follow-up study with several limitations, including the relatively high rates of withdrawal and treatment strategy modifications, data from both the ITT and PP analyses indicate that TwHF monotherapy was not inferior to MTX monotherapy in controlling disease activity and retarding radiographic progression in patients with active RA. This is consistent with the previously published, randomized, controlled, parallel arm, active-comparator TRIFRA study.