Functional iron deficiency anemia was associated with higher mortality in chronic kidney disease patients: the NHANES III follow-up study.

Anemia, a common complication of chronic kidney disease (CKD), is associated with poor prognosis. However, it is not completely clear whether this association is caused by anemia per se or other comorbidities. Whether different types of iron deficiency anemia can predict the outcomes of CKD remains unclear. The dataset from NHANES III was analyzed and Cox multivariate regression models and propensity score matching (PSM) method were used to evaluate the effect of anemia on mortality. Of 4103 patients with CKD, 14.6% had anemia. Among those with anemia, 38.8% had absolute iron deficiency (AID), and 19.8% had functional iron deficiency (FID). During the median follow-up time of 13.8 years, 2964 deaths and 804 cardiovascular deaths were observed. Anemia was robustly associated with a high risk of all-cause mortality in CKD patients after adjusting covariates by two multivariate regression models (Model 1: HR = 1.485, 95%CI:1.340-1.647, p < 0.001; Model 2: HR = 1.391, 95%CI:1.250-1.546, p < 0.001). In the PSM cohort, anemia was still an independent risk factor for all-cause mortality (Model 1: HR = 1.443, 95%CI: 1.256-1.656, p < 0.001; Model 2: HR = 1.357, 95%CI:1.177-1.564, p < 0.001). In the CKD population, anemia patients with FID had the highest risk of mortality than the other anemia groups (p < 0.05), while AID had a mortality rate similar to those without anemia (p > 0.05). In conclusion, anemia was associated with a worse prognosis in patients with CKD, which may be attributed to the higher mortality risk of FID rather than AID. AID wasn't associated with a higher mortality rate compared with CKD patients without anemia.

The metabolites of de novo NAD+ synthesis are a valuable predictor of acute kidney injury.

Background: Acute kidney injury (AKI) is often iatrogenic and potentially preventable. Reduced renal nicotinamide adenine dinucleotide (NAD+) is reported to increase the susceptibility of AKI. The present study explored the predictive value of urinary de novo NAD+ synthetic metabolites for AKI using two independent cohorts. Methods: The expression of de novo NAD+ synthetic enzymes in human kidney was examined by immunohistochemistry and single-cell transcriptomes. Urine samples were collected from two independent cohorts: the methotrexate (MTX) cohort with high-dose MTX treatment for lymphoma (n = 189) and the liver transplantation cohort with orthotopic liver transplantation (n = 49). Urinary metabolomics study of NAD+ de novo synthesis was performed by liquid chromatography with mass spectrometry, screening for AKI predictive biomarkers. Nephroseq database and immunohistochemistry were used to analyze kidney de novo NAD+ synthetic enzymes expression in AKI-susceptible conditions. Results: Human proximal tubule was the main structure in the kidney that expressed the necessary enzymes for NAD+ de novo synthesis. In the MTX cohort, the urinary quinolinic acid (QA)/3-hydroxyanthranilic acid (3-OH AA) ratio before chemotherapy was significantly lower in those who developed AKI after chemotherapy compared with those who did not. This finding was consistent in the liver transplantation cohort. The area under the receiver-operating characteristic curve (AUC) of urinary QA/3-OH AA for AKI prediction was 0.749 and 0.729 in two cohorts, respectively. 3-Hydroxyanthranilic acid dioxygenase (HAAO), the enzyme catalyzing QA synthesis from 3-OH AA, decreased in AKI-susceptible diabetic kidneys. Conclusions: The human proximal tubules were important source of NAD+ from the de novo pathway. Reduced urinary QA/3-OH AA ratio, which possibly suggested decreased HAAO activity, could be a potential AKI predictive biomarker.