IntroductionPlasmin and its precursor, plasminogen, are detectable in urine from patients with glomerular disease. Urinary plasmin(ogen) levels correlate with blood pressure (BP) and may contribute to renal Na+ retention by activating the epithelial Na+ channel (ENaC). In a longitudinal nested-cohort study, we asked whether urinary plasmin(ogen) levels predict subsequent increase in BP, incident hypertension, or mortality in subjects with type I diabetes, who often develop proteinuria.MethodsThe Pittsburgh Epidemiology of Diabetes Complications (EDC) study followed up type I diabetic subjects for 25 years. Urine specimens from 70 subjects with a spectrum of baseline urinary albumin levels were examined. Outcomes included increased BP after 2 years (≥1 SD over baseline systolic or diastolic BP, examined via logistic regression), 25-year incident hypertension (≥140/90 mm Hg or initiating BP-lowering medications), and all-cause or cardiovascular mortality, examined using Cox regression.ResultsSubjects experiencing a 2-year increase in BP had higher baseline urinary plasmin(ogen)/creatinine levels (uPl/Cr) than other subjects (P = 0.04); the difference in baseline urinary albumin/creatinine levels (uAlb/Cr) was similar (P = 0.07). Baseline uPl/Cr was associated with increased 25-year hypertension incidence (hazard ratio = 2.05, P = 0.001), all-cause mortality (HR = 2.05, P = 0.01) and cardiovascular mortality (HR = 3.30, P = 0.005), although not independent of uAlb/Cr.ConclusionThis is the first long-term prospective study addressing clinical outcomes associated with increased urinary plasmin(ogen). Findings are consistent with a role for plasmin(ogen) in promoting increased BP, but also demonstrate the difficulty in distinguishing effects due to plasmin(ogen) from those of albuminuria.
Introduction Renal Na+ retention and extracellular fluid volume expansion are hallmarks of nephrotic syndrome, which occurs even in the absence of activation of hormones that stimulate renal Na+ transporters. Plasmin-dependent activation of the epithelial Na+ channel (ENaC) has been proposed to have a role in renal Na+ retention in the setting of nephrotic syndrome. We hypothesized that the ENaC inhibitor amiloride would be an effective therapeutic agent in inducing a natriuresis and lowering blood pressure in individuals with macroscopic proteinuria. Methods We conducted a pilot double-blind randomized cross-over study comparing the effects of daily administration of either oral amiloride or hydrochlorothiazide (HCTZ) to patients with type 2 diabetes and macroscopic proteinuria. Safety and efficacy were assessed by monitoring systolic blood pressure (SBP), kidney function, adherence, weight, urinary Na+ excretion and serum electrolytes. Nine subjects were enrolled in the trial. Results No significant difference in SBP or weight was seen between HCTZ and amiloride (p≥0.15). Amiloride induced differences in serum K+ (p<0.001), with a 0.88±0.30 mmol/L greater acute increase observed. Two subjects developed acute kidney injury and hyperkalemia when treated with amiloride. Four subjects had readily detectable levels of urinary plasminogen plus plasmin (uPl), and five did not. Changes in SBP in response to amiloride did not differ between individuals with vs. those without detectable uPl. Conclusion In summary, among patients with type 2 diabetes, normal renal function and proteinuria, there were reductions in SBP in groups treated with HCTZ or amiloride. Acute kidney injury and severe hyperkalemia were safety concerns with amiloride.
mTORC2 is a kinase complex that targets predominantly Akt, SGK1, and PKC, and has well characterized roles in mediating hormone and growth factor effects on a wide array of cellular processes. Recent evidence suggests that mTORC2 is also directly stimulated in renal tubule cells by increased extracellular potassium (K+) concentration, leading to activation of the Na+ channel, ENaC, and increasing the electrical driving force for K+ secretion. We identify here a signaling mechanism for this local effect of K+. We show that an increase in extracellular [K+] leads to a rise in intracellular chloride (Cl-), which stimulates a previously unknown scaffolding activity of With No Lysine-1 (WNK1) kinase. WNK1 interacts selectively with SGK1 and recruits it to mTORC2 resulting in enhanced SGK1 phosphorylation, and SGK1-dependent activation of ENaC. This scaffolding effect of WNK1 is independent of its own kinase activity and does not cause a generalized stimulation of mTORC2 kinase activity. These findings establish a novel WNK1- dependent regulatory mechanism, which harnesses mTORC2 kinase activity selectively toward SGK1 to control epithelial ion transport and electrolyte homeostasis.
Well-designed research, with CVD as primary outcome, is needed to help bridge the gap in our knowledge on this topic. In the meantime, caution should be applied to avoid overdiagnosis and overtreatment of vitamin D deficiency.
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