Correlation between Treatment Outcomes and Serum Vitamin D Levels As Well As Infliximab Trough Concentration among Chinese Patients with Crohn's Disease

Background The relationship between vitamin D (vit-D) levels and the effectiveness of infliximab (IFX) in patients with Crohn's disease (CD) remains controversial. Objective To evaluate the interaction between vit-D levels and the response to IFX therapy in patients with CD. Methods This was a retrospective cohort study. Serum vit-D and IFX trough concentrations (TC) were measured in 84 patients, and statistical analyses were performed. Results The total vit-D deficiency rate at enrollment, at week 14 and week 38, was 64.3%, 41.67%, and 37.5%, respectively (P < 0.001). CD activity index (CDAI) (120, range, 93–142.75) and simplified endoscopic activity score for CD (SES-CD) (2, range, 0–4) at week 14 were lower than that of enrollment (CDAI, 136.5, range, 101.25–196; SES-CD 13, range, 5–23) (P < 0.001). The biochemical remission (BR), clinical remission (CR), endoscopic remission (ER), and response (ERe) rates of week 38 were 76.1%, 88.5%, 22.4%, and 67.2%, respectively. vit-D levels at enrollment were positively correlated with CDAI at week 38 (P = 0.024). IFX serum TC was related to BR (P = 0.036), CR (P = 0.032) at week 14, and ERe (P = 0.009) at week 38. Conclusion Among Chinese patients with CD, vit-D levels prior to IFX therapy are related to CDAI scores, and IFX serum TC is associated with BR, CR, and ERe.


Introduction
Inflammatory bowel disease (IBD) is a chronic inflammatory disease of the intestine that encompasses ulcerative colitis (UC) and Crohn's disease (CD).Clinical symptoms include chronic or subacute abdominal pain, diarrhea, bloody stool, fever, oral ulcers, crissum abscess or fistula, arthritis, and skin rashes.Recurrent disease can cause anemia, weight loss, and malnutrition, which seriously affect patients' quality of life and impose an economic burden and psychological pressure [1,2].According to the reported global incidence of IBD [3], the highest incidence of UC is 5.05/1000, and that of CD is 3.22/1000.In China, the total number of IBD cases from 2005 to 2014 was approximately 350,000, and it is expected to reach 1.5 million by 2025 [4].In genetically susceptible individuals, a dysregulated immune response to intestinal flora and environmental factors has been proposed as the pathogenic mechanism in the incidence and progression of IBD [5].
Anti-tumour necrosis factor-α (anti-TNFα) biological therapies have dramatically reduced surgery and hospitalization rates while simultaneously improving the quality of life in patients with IBD [6].Although TNFα inhibitors are highly effective, nearly 30% of patients lose their therapeutic response, partly due to antidrug antibody production and inadequate drug concentrations [7,8].Vitamin D (vit-D) is a nutrient that plays an important role in the pathogenesis of IBD [9,10].Recent research has shown that serum vit-D levels impact anti-TNFα therapy.A study in pediatric patients with IBD found that vit-D insufficiency before anti-TNFα treatment resulted in a poor response to induction therapy [11].Zator et al. demonstrated an association with earlier cessation of anti-TNFα therapy in patients with IBD who had insufficient vit-D levels before initiation of therapy, suggesting that vit-D may be an important auxiliary treatment to anti-TNFα therapy [12].However, this remains controversial.Reich et al. demonstrated that patients with low serum vit-D before initiating therapy reached a higher proportion of clinical remission (CR) after induction doses of infliximab (IFX) [13].
The current study is aimed at establishing the association of clinical outcomes with serum vit-D and a possible correlation with IFX serum trough concentration (TC) and anti-TNFα antibody (ATI) levels, or the lack thereof.

Materials and Methods
This retrospective cohort study was conducted at Chongqing General Hospital.The study involved 38 weeks of follow-up and was conducted from January 2019 to May 2021.Written informed consent was obtained from all patients, and the study was approved by the ethics committee of the Chongqing General Hospital (ethics review number: KY-S2022-023-01).

Study Design.
Patients with available data at enrollment were included and followed up at the week 14 IFX treatment and the week 38 IFX treatment.Demographic and clinical characteristics were collected at enrollment, and nutritional indices (including vit-D levels) and biochemical parameters were collected at all three-time points.Additionally, data on clinical outcomes, including biochemical remission (BR) and CR, were collected at week 14 and week 38, and endoscopic response and endoscopic remission were collected at week 38.In addition, serum IFX concentrations were collected at week 14.Correlation analysis was carried out among vit-D levels, serum IFX concentrations at week 14, and clinical outcomes (Figure 1).

Patient Population.
Inclusion criteria were confirmed with CD according to the Chinese consensus on the diagnosis and treatment of IBD (2018, Beijing) [14] and according to the guidelines for the management of IBD in adults [15].The diagnosis of CD was based on standard criteria, including the combination of clinical symptoms, endoscopy, radiology, pathology, and surgical history.The main treatment plan was IFX therapy, without vit-D supplementation, with complete blood biochemical parameters and nutritional indices, as well as week 14 biological agent serum concentration monitoring (IFX-TC and IFX-ATI) and week 38 endoscopic assessment.Patients with vit-D supplementation and incomplete multiple blood biochemical parameters or incomplete endoscopic evaluation were excluded.The final CD cohort consisted of 84 patients.

Vit-D Assessments.
Vit-D data prior to IFX therapy was available for 84 patients.The cut-off concentration for vit-D deficiency was based on the Endocrine Society Clinical Practice Guideline 2011 [16]; patients with vit-D levels < 20 ng/mL were considered vit-D deficient, those with >30 ng/mL were classified as vit-D sufficient, and those with 20-30 ng/mL were classified as vit-D insufficient.Peripheral blood vit-D was detected using chemiluminescence in the laboratory of Chongqing General Hospital.

Classification and Definition.
The extent of the disease was defined using the Montreal classification [18].BR was defined as C-reactive protein (CRP) < 5 mg/L and erythrocyte sedimentation rate (ESR) < 20 mm/h [19].CR was defined as a CD activity index (CDAI) < 150 [20].Endoscopic assessment was performed at the clinical endpoint (38 weeks), with endoscopic remission defined as a simplified endoscopic activity score for CD (SES-CD) < 4 and endoscopic response as a 50% reduction in the SES-CD score from baseline [21].
2.6.Statistical Analyses.All statistical tests were performed using SPSS software version 25.0 (SPSS, Chicago, IL, USA) and GraphPad Prism version 5 (GraphPad Software, San Diego, CA).For quantitative variables, data are shown as the mean ± standard deviation, or as the median and interquartile range (IQR), according to the presence or absence of a normal distribution, respectively.Categorical variables are expressed as percentages.Student's t-test and the Mann-Whitney U test were used to compare independent continuous variables, whereas the paired t-test and the Wilcoxon signed-rank test were used to compare dependent continuous variables.Categorical variables were compared using the chi-square test and rank-sum test.Linear regression was used to determine the independent factors associated with the CDAI outcomes.All P values < 0.05 in the final multivariate model were considered statistically significant.

Discussion
The correlation between vit-D levels and IFX-TC has not yet been extensively explored.This study analyzed the relationship between vit-D nutritional status, serum IFX concentration, and clinical outcomes to determine the long-term treatment outcomes in patients with CD.We found that vit-D deficiency is common in patients with CD.Low vit-D levels prior to IFX treatment are negatively correlated with   Vit-D deficiency in patients with IBD is currently considered detrimental, and several studies have hypothesized that vit-D is related to IBD outcomes.A meta-analysis has previously demonstrated that vit-D levels are inversely related to CD and UC [22].Furthermore, vit-D normalization is associated with a reduced risk of relapse [23][24][25].In our study, the total vit-D deficiency rate was 64.3%.Additionally, the advancement of CD treatment with IFX gradually improves vit-D levels.We also observed that lower baseline vit-D levels led to higher CDAI, despite IFX treatment.However, vit-D levels did not impact clinical outcomes, including BR, CR, endoscopic remission, and endoscopic response rates.The lack of effect on clinical out-comes may be attributable to the small sample size or the insufficient degree of change in CDAI to influence disease activity and the remission period.At present, we are expanding the sample size and conducting multicenter studies to clarify the relationship between vit-D and clinical outcomes.
As the most classic biological agent for CD treatment, IFX has maximal therapeutic effects and maintains high CR and endoscopic remission rates, which are essential for clinical treatment.Monitoring anti-TNFα levels helps control serum drug levels, predict long-term clinical outcomes, optimize treatment, and decrease the economic burden on patients.Several studies have independently demonstrated a correlation between IFX-TC and IBD disease status [26,27].In this study, we monitored the concentration of IFX and evaluated its relationship with CR, endoscopic remission, and

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Gastroenterology Research and Practice endoscopic response.Patients with sufficient serum concentrations had a higher BR, CR, and endoscopic response rate.Our findings are consistent with those of a systematic review and meta-analysis that revealed a significant difference between serum IFX levels in patients with IBD in remission and those patients who relapsed with a trough threshold of >2 μg/mL during maintenance associated with a greater probability of CR and mucosal healing.In addition, IFX-ATI did not influence CR, endoscopic remission, or endoscopic response.
There are some limitations to the study.First, the sample size was small.Second, we could not measure the disease activity of all patients by endoscopy or radiological examination.Third, the lack of dietary intake monitoring could affect the nutritional status assessments.Finally, there may be a need for a more extensive follow-up time to accurately determine clinical outcomes.

Conclusions
Vit-D levels prior to IFX therapy are related to CD activity index scores, and IFX-TCs are associated with the outcomes of patients with CD.

Table 2 :
Biochemical parameters, nutritional indices, and clinical assessment at three follow-up time points.

Table 3 :
The influence of vitamin D levels at three-time points on Crohn's disease activity index at the week 38 IFX treatment in Crohn's disease patients (linear regression, enter) (n = 84).

Table 4 :
The influence of vitamin D level at enrollment on clinical outcomes at the week 14 and week 38 IFX treatment in Crohn's disease patients.

Table 5 :
The influence of infliximab trough concentration on clinical outcomes at the week 14 and week 38 treatment in Crohn's disease patients.