We extend our gratitude to Dr. Komori and Dr. Nishad for their insightful editorials on our recent study evaluating HK-660S as a treatment option for primary sclerosing cholangitis (PSC) [1]. Their editorials highlight key points and provide constructive criticism on various aspects, from trial design to potential clinical implications, that will enhance the scope and direction of future research [2,3]. Here, we aim to clarify our study’s rationale and address the valuable points they raised.

HK-660S introduces an innovative approach to PSC treatment by targeting NAD+ levels to activate sirtuin family proteins, specifically Sirt1 and Sirt3, which may alleviate mitochondrial dysfunction and bile acid (BA) toxicity in PSC [4]. Although our study was exploratory with limited sample size and duration, it demonstrated a mean reduction of 15.2% in alkaline phosphatase (ALP) levels in the HK-660S group, suggesting a promising therapeutic potential. As Dr. Komori highlighted, further research to elucidate the broad metabolic interactions of HK-660S is crucial. Specifically, we plan to explore the role of NAD+-sirtuin interactions in BA synthesis and inflammation, aligning with emerging evidence on FXR signaling and mitochondrial resilience [5].

Both editorials commend the inclusion of the modified Anali (mAnali) score alongside conventional biomarkers as endpoints, noting its relevance for assessing PSC’s structural and biochemical changes [6]. We acknowledge the limitations of using mAnali due to inter-observer variability and subjectivity [7]. To mitigate these issues, we utilized a dual-radiologist assessment protocol with an independent adjudicator to standardize imaging evaluations. As Dr. Nishad has suggested, quantitative MRCP metrics, such as MRCP+™, and artificial intelligence-guided analysis will be integral to our future trials to improve endpoint fidelity and reduce variability in imaging-based assessments [8].

Moreover, Dr. Nishad pointed out that age and baseline characteristics may have influenced the results. Even though our randomization process aimed to ensure balanced baseline demographics, we recognize the potential impact of these factors on PSC severity and trial outcomes. Future trials will include stratification by disease severity and comorbidities to better assess the effects of HK-660S across diverse patient subsets.

As highlighted in both editorials, PSC is a heterogeneous disease, with variations such as small-duct and large-duct PSC, as well as an association with inflammatory bowel disease (IBD) [9,10]. Dr. Nishad emphasized the importance of recruiting diverse patient groups and differentiating analysis based on the PSC subtype. Indeed, some patients in our study with bile duct stricture improvements demonstrated an apparent rapid response, which may reflect the anti-inflammatory properties of HK-660S. In future studies, we will incorporate stratified analyses based on PSC subtype, IBD status, and baseline ALP levels to improve understanding of the HK-660S efficacy across distinct PSC phenotypes, and to optimize recruitment to reflect the heterogeneous nature of PSC.

Among the ten patients with IBD in this study, nine had ulcerative colitis and one had Crohn’s disease. Eight patients were assigned to the experimental group, and two to the control group. Five patients were receiving mesalazine; one was on steroids; and one was taking a combination of mesalazine and azathioprine; while three patients were not receiving any treatment for IBD. None of the participants had severe IBD, and their conditions were well-managed with medication.

Both editorials stress the importance of assessing safety, especially given the gastrointestinal-related adverse drug reactions (ADRs) observed only in the HK-660S group. Even though most ADRs observed were mild to moderate, we acknowledge that gastrointestinal symptoms may have potentially led to unblinding. Although we followed established blinding protocols, our team recognizes this as a potential limitation. In future studies, we will implement additional measures to improve the management of ADRs while preserving the integrity of the blinding.

One serious adverse event occurred in a female patient in her 50s from the experimental group. Two weeks into taking medication, she developed a fever and was hospitalized for 11 days. She was treated with antibiotics for acute cholangitis and bacteremia and recovered without sequelae. The event was determined to be unrelated to the study medication.

Dr. Nishad suggested that the inclusion of the NQO1 genotype as a stratification factor could be clarified. NQO1 has been implicated in NAD+ metabolism and sirtuin activation, which may influence the efficacy of HK-660S. We plan to expand the analysis of NQO1 genotypes in future studies to explore potential pharmacogenetic interactions with HK-660S and its therapeutic impact on PSC.

The editorials accurately identify the limited sample size and 12-week duration as constraints that affected statistical power. We selected this timeframe to establish initial safety and feasibility; however, we concur that a prolonged duration and a large sample size are essential for thoroughly evaluating the effects of HK-660S on PSC progression. We aim to perform follow-up trials with a treatment period of at least 24 weeks, employing a conventional 5% significance level, and to explore additional markers of disease progression, such as Pro-C3 and ELF scores.

We thank Dr. Komori and Dr. Nishad for their detailed reviews and for underscoring the importance of addressing the complexities of PSC through innovative trial designs and robust endpoints. By expanding our methodological approach and refining trial protocols based on their recommendations, we hope to contribute to the development of a safe and effective treatment for PSC. We remain committed to advancing HK-660S research, confident that future studies can substantiate its potential as a promising therapeutic option.