An effective prediction model is necessary to prevent the hepatotoxicity associated with low-dose MTX. In real-world studies, the variables are not independent but are related nonlinearly. Multivariate analysis methods are challenging for capturing complex relationships. Therefore, we innovatively attempted to apply machine-learning methods that can capture nonlinear relationships between variables. Machine learning can explore risk factors and establish a prediction model for hepatotoxicity associated with low-dose MTX through data learning. Our retrospective study analyzed 15 risk factors for hepatoxicity. The BMI with missing data was imputed using the missForest method, which has been shown to successfully handle missing values, particularly in data sets that include different variables [35]. The results did not show significant differences between the processed and original data.
The eight machine learning methods were applied to establish a prediction model. The results showed that these machine algorithms performed well, especially the Random Forest. Random Forest uses bootstrap aggregation of multiple regression trees to reduce the risk of overfitting and combine the predictions of many trees to produce more accurate predictions [36]. The Random Forest showed that its AUC was 0.97. The accuracy and precision were 64.33% and 50.00%, respectively. Both the recall and the F1 scores were satisfactory. Random Forest outperformed other models selected to build the prediction model for hepatotoxicity associated with low-dose MTX.
Analysis of risk factors showed that all 15 variables helped predict low-dose MTX-related hepatotoxicity. Among risk factors, BMI was considered the most critical risk factor, which had a negative relationship with hepatotoxicity, demonstrating that patients with lower BMI were more likely to experience hepatotoxicity. Therefore, the dose of MTX should be individualized based on height and weight to avoid hepatotoxicity and a dose reduction of MTX is appropriate for patients with low BMI. Male gender was also identified as an important risk factor in our study. However, the causal relationship between gender and hepatotoxicity associated with low-dose MTX remains controversial [37, 38] and requires further research.
The importance of the number of drugs, the number of comorbidities, and the use of antibiotics was also confirmed. As the primary organ for drug metabolism, the liver is more vulnerable to damage by drugs, active metabolites, or drug interactions [39, 40]. Multiple drug treatments and comorbid diseases can increase the risks of polypharmacy, drug interactions, and even medication errors [41, 42], increasing the risk of hepatotoxicity. Antibiotics are the most common cause of liver damage [43]. However, the potential for liver injury caused by antibacterial drugs was underestimated [44]. Several real-world studies showed that antibiotic-induced liver injury ranged from 13.5–65% [45–47]. Therefore, to avoid hepatotoxicity during MTX therapy, simplifying treatment regimens should be an important measure for the benefit of patients.
Alcohol consumption is well known to harm the liver, particularly in excess [48]. The American College of Rheumatology and the British Society of Rheumatology recommend limiting alcohol intake for patients on MTX treatment [49, 50]. Similarly, we found a positive relationship between alcohol use and hepatotoxicity associated with low-dose MTX. Although the importance score for alcohol consumption was not high in this study due to the relatively small number of patients who drank alcohol, we still recommend limiting or avoiding alcohol intake.
Supplementation with folic or folinic acid during MTX treatment can ameliorate ADEs. Worldwide guidelines currently support the coadministration of folic acid with MTX. The recommended doses range from 0.5 to 2 mg per day or 5mg per week [50–52]. In our study, the incidence of liver injury in patients taking folic acid was 34.85%, while the liver injury rate in 59 patients who did not take folic acid was up to 45.76%. However, the results indicated that patients taking 15-35mg/week folic acid had a higher risk of liver injury than those taking 5-10mg/week folic acid. This result may be related to the higher proportion of patients who drank alcohol in the folic acid high dose group. Therefore, we also recommend supplementation with folic acid during MTX treatment.
Metabolic syndrome is a biochemical and clinical condition characterized by visceral obesity, dyslipidemia, hyperglycemia, and hypertension [53]. Disorders associated with metabolic syndrome can be significant risk factors for fibrosis and progression of liver damage. Type 2 diabetes contributed to the biological processes that drove the severity of nonalcoholic fatty liver disease, which was the leading cause of developing chronic liver diseases [54]. Several studies showed that nonalcoholic steatohepatitis and hyperlipidemia contributed to MTX hepatotoxicity in patients with psoriasis [37, 55]. These were consistent with our results that type 2 diabetes and hyperlipidemia were significant risk factors for hepatotoxicity associated with low-dose MTX.
Hepatitis B and hepatitis C can cause liver damage, increasing the risk of liver toxicity and even liver fibrosis and cirrhosis in patients taking MTX [56]. Infectious liver disease was one of the important risk factors for hepatotoxicity in this study, while its importance score was not high. The reason might be that patients with infectious liver disease were only 4.1% of the study sample. For health and safety reasons in China, many physicians choose other alternative treatments for patients with infectious liver disease instead of MTX. Similarly, only six patients had a history of kidney disease in this study. Therefore, the importance score for the history of kidney disease was low.
Our study has the following limitations 1) knowledge about specific risk factors is still lacking in this study. Although factors such as taking MTX for the first time, other immunosuppressive agents, age, and Chinese traditional medicines affected the occurrence of hepatotoxicity, the direction of influence of these factors was unclear. These factors could be influenced by other factors, such as drug regimens (the number of drugs and drug interactions), gender, and BMI; 2) the sample size was small. Future studies should include more patient data from different health care centers; 3) long-term studies are required to verify the association of these risk factors with liver fibrosis or cirrhosis; 4) it was difficult to obtain relatively complete medication and examination data of outpatients, so only patients during hospitalization were included, which could lead to selection bias.