Struck, Joachim

Abstract Background The assessment of kidney function and detection of acute kidney injury (AKI) remain cumbersome. On the one hand, because of limited accuracy of established tests: The most widely used methods are creatinine based, which lack in sensitivity, as creatinine is not purely filtrated by the kidney and rises relatively late after onset of AKI. On the other hand, because of labor-intensiveness: Gold standard inulin clearance and comparable methods involve intravenous compound infusion, blood sampling at several time points, and have error-sensitive determination methods. In recent years, several biomarkers have been put forward (e.g., NGAL, KIM-1, TIMP-2*IGFBP-7), but clinical implementation is limited up to now. Content Proenkephalin (PENK) represents a new candidate to determine kidney function. This peptide is cleaved from the precursor peptide preproenkephalin A alongside enkephalins (endogenous opioids) and is filtrated in the glomerulus. PENK plasma concentration appears to accurately represent glomerular filtration rate in patients diagnosed with sepsis or cardiac diseases. Moreover, increased PENK concentration is found to be associated with longer-term outcome concerning AKI and cardiac diseases. Lastly, the predominant receptor of enkephalins, the δ-opioid receptor, is expressed with the highest density in the kidney, suggesting that enkephalins could also exert a direct effect on kidney function. Summary In this review, we present an overview of enkephalins and the assessment of kidney function using this possible new functional biomarker PENK and compare it with established and novel biomarkers.

Context: Stress-mediated hypothalamic-pituitary-adrenal axis activation, regulated by arginine vasopressin (AVP), may have a role in the pathophysiology of metabolic syndrome (MetSyn). Objective: The objective of the study was to investigate whether plasma C-terminal provasopressin fragment (copeptin), a surrogate for circulating AVP, was associated with measures of insulin resistance and presence of MetSyn. Design, Setting, and Participants: This was a multicenter, community-based study, investigating novel biomarkers for vascular disease. Participants included 1293 African-Americans (AA) (64 ± 9 yr) and 1197 non-Hispanic whites (NHW) (59 ± 10 yr) belonging to hypertensive sibships. Main Outcome Measures: Plasma copeptin levels were measured by an immunoluminometric assay. MetSyn was defined per Adult Treatment Panel III criteria. Generalized estimating equations were used to assess whether plasma copeptin was associated with measures of insulin resistance and MetSyn. Results: The prevalence of MetSyn was 50% in AA and 49% in NHW. In each group, after adjustment for age and sex, plasma copeptin levels significantly correlated with body mass index, fasting plasma glucose and insulin, homeostasis model assessment of insulin resistance, triglycerides, and (inversely) high-density lipoprotein cholesterol (P < 0.05 for each variable). In multivariable logistic regression models that adjusted for age, sex, smoking, statin use, serum creatinine, education, physical activity, and diuretic use, plasma copeptin levels in the highest quartile were associated with an increased odds ratio of having MetSyn compared with bottom quartile: odds ratio (95% confidence interval) in AA, 2.07 (1.45–2.95); in NHW, 1.74 (1.21–2.5). Conclusions: Our findings indicate a novel cross-sectional association between plasma copeptin and measures of insulin resistance and MetSyn.