Caffeine Intake, Plasma Caffeine Level, and Kidney Function: A Mendelian Randomization Study

Caffeine is a psychoactive substance widely consumed worldwide, mainly via sources such as coffee and tea. The effects of caffeine on kidney function remain unclear. We leveraged the genetic variants in the CYP1A2 and AHR genes via the two-sample Mendelian randomization (MR) framework to estimate the association of genetically predicted plasma caffeine and caffeine intake on kidney traits. Genetic association summary statistics on plasma caffeine levels and caffeine intake were taken from genome-wide association study (GWAS) meta-analyses of 9876 and of >47,000 European ancestry individuals, respectively. Genetically predicted plasma caffeine levels were associated with a decrease in estimated glomerular filtration rate (eGFR) measured using either creatinine or cystatin C. In contrast, genetically predicted caffeine intake was associated with an increase in eGFR and a low risk of chronic kidney disease. The discrepancy is likely attributable to faster metabolizers of caffeine consuming more caffeine-containing beverages to achieve the same pharmacological effect. Further research is needed to distinguish whether the observed effects on kidney function are driven by the harmful effects of higher plasma caffeine levels or the protective effects of greater intake of caffeine-containing beverages, particularly given the widespread use of drinks containing caffeine and the increasing burden of kidney disease.

Mitochondrial amidoxime-reducing component 1 p.Ala165Thr increases protein degradation mediated by the proteasome

OBJECTIVE

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a global health concern with no effective and specific drug treatment available. The rs2642438 minor allele in mitochondrial amidoxime-reducing component 1 (MARC1) results in an aminoacidic substitution (p.Ala165Thr) and associates with protection against MASLD. However, the mechanisms behind this protective effect are unknown. In this study, we examined the consequences of this aminoacidic substitution on protein stability and subcellular localization.

METHODS

We overexpressed the human MARC1 A165 (wild-type) or 165T (mutant) in vivo in mice and in vitro in human hepatoma cells (HepG2 and HuH-7), generated several mutants at position 165 by in situ mutagenesis and then examined protein levels. We also generated HepG2 cells stably overexpressing MARC1 A165 or 165T to test the effect of this substitution on MARC1 subcellular localization.

RESULTS

MARC1 165T overexpression resulted in lower protein levels than A165 both in vivo and in vitro. Similarly, any mutant at position 165 showed lower protein levels compared to the wild-type protein. We showed that the 165T mutant protein is polyubiquitinated and its degradation is accelerated through lysine-48 ubiquitin-mediated proteasomal degradation. We also showed that the 165T substitution does not affect the MARC1 subcellular localization.

CONCLUSIONS

This study shows that alanine at position 165 in MARC1 is crucial for protein stability, and the threonine substitution at this position leads to a hypomorphic protein variant due to lower protein levels. Our result supports the notion that lowering hepatic MARC1 protein level may be a successful therapeutic strategy for treating MASLD.

Is rheumatoid arthritis a risk factor for acute coronary syndrome also among individuals at elevated risk, such as individuals presenting with acute chest pain?

BACKGROUND

Patients with rheumatoid arthritis (RA) are, on average, at increased risk of acute coronary syndrome (ACS) compared to the general population, but it remains unknown whether RA remains an ACS risk factor also in settings where the ACS risk is already high elevated, such as among individuals presenting to the emergency department (ED) with chest pain.

METHODS AND RESULTS

We included 49 283 individuals (514 (1.0%) had RA) presenting with chest pain at the four hospital EDs in Stockholm, Sweden, 2013-2016 in a cohort study. Information on exposure (RA), outcome (ACS) and comorbidities was provided through national registers. The association between RA and ACS was assessed, overall and by levels of high-sensitivity cardiac troponin T (hs-cTnT) and number of ACS risk factors, using logistic regression models adjusted for age, sex, hospital, calendar year and cardiovascular risk factors. ACS was more common in patients with (8.2%) than without (4.6%) RA, adjusted OR =1.4, 95% CI 1.0 to 2.0. This association was particularly strong in individuals with initial hs-cTnT levels between 5 and 14 ng/L, or no additional ACS risk factors (adjusted ORs above 2), but no longer detectable in those with hs-cTnT >14 ng/L or with three or more additional ACS risk factors.

CONCLUSION

RA is a risk factor for ACS also among patients at the ED with chest pain. This association is not explained by traditional ACS risk factors, and most pronounced in patients with normal hs-cTnT and few other ACS risk factors, prompting particular ACS vigilance in this RA patient group.