Introduction
Micronutrient deficiency is an underestimated problem in the westernized population with unclear effects on the manifestation of acute or chronic disease. Westernized lifestyle instigates disrupted gut-microbial crosstalk and chronic low-grade inflammation1. Tryptophan (Trp) is an essential amino acid used for de novo synthesis of cellular nicotinamide adenine dinucleotide (NAD). We have previously shown increased Trp degradation in several chronic inflammatory disorders, including IBD2,3. Whether Trp deficiency is a widespread phenomenon in the western population is unknown. Here, we tested the hypothesis that Trp deficiency is frequent in the western population and associates with increased overall disease severity in internal-medicine and especially gastrointestinal (GI) diseases.
Aims & Methods
To screen the micronutrient status of the healthy population, we assessed quantitative amino acid levels in n=15.188 healthy controls (HC) with a commercially available home-care dry blood spot test for targeted metabolomics (cohort 1). Self-reported symptoms were assessed with a digital questionnaire. To validate Trp deficiency (defined as the lowest Trp quartile) in acute internal-medicine diseases (cohort 2), we measured serum Trp by HPLC in HC (n=291) and patients presenting in the emergency ward of the University Hospital Schleswig-Holstein, Kiel (n=4349, categorized by ICD10; thereof GI diseases n=516 (K00-K93: diseases of the digestive system); 10/2023-09/2024). Next to laboratory and clinical assessment at presentation, disease courses were followed up digitally for at least 6 months. Statistical analyses were performed with linear mixed models (LMM) and logistic regression correcting for age and sex at birth; predictive performance was evaluated via area under the receiver-operating-characteristic (AUROC; R version 4.4.1).
Results
In cohort 1, 39.3% of HC presented with Trp deficiency. Trp deficiency significantly inversely correlated with the amount of self-reported symptoms, such as e.g. GI symptoms. Validating these findings in internal-medicine and a subgroup of GI diseases in cohort 2, we found significantly reduced serum Trp compared to HC (mean Trp 56.58±10.84µM vs. 45.06±16.65 (all disease groups), 45.21±20.69 (GI diseases)), especially when the serum inflammation marker C-reactive protein was not elevated (<5 mg/l). Here, Trp deficiency was observed in 1.4% of HC, while it was strongly increased in all disease groups (26.6%) and GI diseases (30.2%). Using LMM, we found that patients that were hospitalized, admitted to the ICU or died within the follow-up period had a significantly lower Trp compared to patients with favourable outcomes (outpatient/no ICU/alive). Patients with Trp at the lowest compared to the highest quartile underwent longer hospitalisation and ICU treatment (all diseases: 3.17/0.37 days (d) longer; GI diseases: 3.91/0.48d longer) as well as a higher number of in-hospital procedures (all diseases: 1.47 more; GI diseases: 3.3 more). The predictive value of Trp for complicated outcomes (hospitalisation, hospitalisation >7d, ICU treatment, death) as assessed by AUROC was low-moderate (all diseases: AUC 0.69, 0.67, 0.61, 0.72; GI diseases: AUC 0.61, 0.6, 0.54 and 0.62, respectively).
Conclusion
We report that Trp deficiency is frequent in the westernized population and associates with more severe disease courses. Our data suggests Trp degradation along the de novo NAD synthesis pathway as an overarching metabolic hallmark of chronic low-grade inflammation and a risk factor for severe disease courses of internal-medicine and GI diseases.
References
1. Christ, A. & Latz, E. The Western lifestyle has lasting effects on metaflammation. Nature Reviews Immunology vol. 19 267–268 Preprint at https://doi.org/10.1038/s41577-019-0156-1 (2019).
2. Harris, D. M. M. et al. Tryptophan degradation as a systems phenomenon in inflammation – an analysis across 13 chronic inflammatory diseases. EBioMedicine 102, 105056 (2024).
3. Nikolaus, S. et al. Increased Tryptophan Metabolism Is Associated With Activity of Inflammatory Bowel Diseases. Gastroenterology 153, (2017).