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Abstract Background The role of glycemic control and its variability on the rate of kidney function decline after the onset of diabetic kidney disease (DKD) remains unclear. Methods The association between baseline glycated hemoglobin (HbA1c) and rates of estimated glomerular filtration rate (eGFR) loss during follow-up was examined by mixed-effects linear regression in 530 individuals with type 1 diabetes and early-to-moderate DKD from the Preventing Early Renal Loss (PERL) trial and 2378 individuals with type 2 diabetes and established DKD from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial. The benefit of intensive vs standard glycemic control in slowing eGFR decline was examined in ACCORD. The associations between continuous glucose monitoring-derived short-term glycemic variability indices and rate of eGFR decline were also evaluated in PERL. Results A higher baseline HbA1c was associated with a more negative eGFR slope in both PERL and ACCORD (−0.87 and −0.27 mL/min/1.73 m2/year per Hba1c unit increment, P < .0001 and P = .0002, respectively). In both studies, the strength of this association progressively increased with increasing levels of albuminuria (P for interaction <.05). Consistent with this, the benefit of intensive glycemic control on eGFR decline was greater in ACCORD participants with severe rather than moderate albuminuria (+1.13 vs + 0.26 mL/min/1.73 m2/year, P = .01). No independent associations were found in PERL between short-term glycemic variability indices and rate of eGFR decline. Conclusion In both type 1 and type 2 diabetes, poor glycemic control is associated with a more rapid rate of glomerular filtration rate decline after DKD onset, especially in persons with severe albuminuria.

Many clinical outcomes have improved over the past two decades for people living with diabetes. 1 However, relatively little progress has been made in the treatment of diabetic kidney disease. Among adults with diabetes in the United States, the prevalence of diabetic kidney disease has remained steady, near 26%, 2 and, depending on the data source, rates of end-stage renal disease (ESRD) have either remained stable or decreased only slightly. 1 Why has diabetic kidney disease proved so difficult to prevent and treat? In part, the successes of preventing atherosclerotic complications and prolonging life mean that people with diabetes are exposed to longer . . .

Vitamin D and parathyroid hormone (PTH) may affect cardiovascular health in patients with kidney disease and in the general population. The aim of this study was to investigate associations of serum 25-hydroxyvitamin D (25(OH)D) and PTH concentrations with a comprehensive set of biochemical, electrocardiographic, and echocardiographic measurements of cardiac structure and function in the Cardiovascular Health Study. A total of 2,312 subjects who were free of cardiovascular disease at baseline were studied. Serum 25(OH)D and intact PTH concentrations were measured using mass spectrometry and a 2-site immunoassay. Outcomes were N-terminal pro-B-type natriuretic peptide, cardiac troponin T, electrocardiographic measures of conduction, and echocardiographic measures of left ventricular mass and diastolic dysfunction. At baseline, subjects had a mean age of 73.9 ± 4.9 years, 69.7% were women, and 21% had chronic kidney disease (glomerular filtration rate <60 ml/min). Mean 25(OH)D was 25.2 ± 10.2 ng/ml, and median PTH was 51 pg/ml (range 39 to 65). After adjustment, 25(OH)D was not associated with any of the biochemical, conduction, or echocardiographic outcomes. Serum PTH levels ≥65 pg/ml were associated with greater N-terminal pro-B-type natriuretic peptide, cardiac troponin T, and left ventricular mass in patients with chronic kidney disease. The regression coefficients were: 120 pg/ml (95% confidence interval 36.1 to 204), 5.2 pg/ml (95% confidence interval 3.0 to 7.4), and 17 g (95% confidence interval 6.2 to 27.8) (p <0.001). In subjects with normal kidney function, PTH was not associated with the outcomes. In conclusion, in older adults with chronic kidney disease, PTH excess is associated with higher N-terminal pro-B-type natriuretic peptide, cardiac troponin T, and left ventricular mass. These findings suggest a role for PTH in cardiovascular health and the prevention of cardiac diseases.

We studied the incidence and progression of coronary artery calcification in people with early chronic kidney disease. We used a cohort of 562 adult patients with chronic kidney disease who had an estimated glomerular filtration rate of <60ml/min/1.73m2, in a community-based study of people without clinical cardiovascular disease, the Multi-Ethnic Study of Atherosclerosis. The majority had stage 3 disease. Coronary artery calcification was measured at baseline and again approximately 1.6 or 3.2 years later. The prevalence of coronary artery calcification at baseline was 66%, and its adjusted prevalence was 24% lower in African Americans as compared to Caucasians. The incidence of coronary artery calcification was 6.1% per year in women and 14.8% in men. Coronary artery calcification progressed in approximately 17% of subjects per year across all subgroups, and diabetes was associated with a 65% greater adjusted risk of progression. Male gender and diabetes were the only factors associated with adjusted coronary artery calcification incidence and progression, respectively. Our study shows that coronary artery calcification is common in people with stage 3 disease, progresses rapidly, and may contribute to cardiovascular risk.

Abstract Context A comprehensive characterization of racial/ethnic variations in vitamin D metabolism markers may improve our understanding of differences in bone and mineral homeostasis and the risk of vitamin D–related diseases. Objective Describe racial/ethnic differences in vitamin D metabolism markers and their associations with genetic ancestry. Design, Setting, Participants In a cross-sectional study within the Multi-Ethnic Study of Atherosclerosis (MESA), we compared a comprehensive panel of vitamin D metabolism markers across self-reported racial/ethnic groups of Black (N = 1759), White (N = 2507), Chinese (N = 788), and Hispanic (N = 1411). We evaluated associations of proportion African and European ancestry with this panel of markers in Black and Hispanic participants using ancestry informative markers. Latent class analysis evaluated associations between patterns of vitamin D measurements with race/ethnicity. Results Compared with Black participants, White participants had significantly higher serum concentrations of 25-hydroxyvitamin D and fibroblast growth factor-23; lower concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D; circulating vitamin D metabolite ratios suggesting lower CYP27B1 and higher CYP24A1 activity; higher urinary concentrations of calcium and phosphorus with higher urinary fractional excretion of phosphorus; and differences in vitamin D binding globulin haplotypes. Higher percent European ancestry was associated with higher 25-hydroxyvitamin D and lower parathyroid hormone concentrations among Black and Hispanic participants. Latent classes defined by vitamin D measurements reflected these patterns and differed significantly by race/ethnicity and ancestry. Conclusions Markers of vitamin D metabolism vary significantly by race/ethnicity, may serve to maintain bone and mineral homeostasis across ranges of 25-hydroxyvitamin D production, and be attributable, at least partly, to genetic ancestry.

Diabetic kidney disease (DKD) can lead to end-stage kidney disease (ESKD) and mortality; however, few mechanistic biomarkers are available for high-risk patients, especially those without macroalbuminuria. Urine from participants with diabetes from the Chronic Renal Insufficiency Cohort (CRIC) study, the Singapore Study of Macro-angiopathy and Micro-vascular Reactivity in Type 2 Diabetes (SMART2D), and the American Indian Study determined whether urine adenine/creatinine ratio (UAdCR) could be a mechanistic biomarker for ESKD. ESKD and mortality were associated with the highest UAdCR tertile in the CRIC study and SMART2D. ESKD was associated with the highest UAdCR tertile in patients without macroalbuminuria in the CRIC study, SMART2D, and the American Indian study. Empagliflozin lowered UAdCR in nonmacroalbuminuric participants. Spatial metabolomics localized adenine to kidney pathology, and single-cell transcriptomics identified ribonucleoprotein biogenesis as a top pathway in proximal tubules of patients without macroalbuminuria, implicating mTOR. Adenine stimulated matrix in tubular cells via mTOR and stimulated mTOR in mouse kidneys. A specific inhibitor of adenine production was found to reduce kidney hypertrophy and kidney injury in diabetic mice. We propose that endogenous adenine may be a causative factor in DKD.

Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that controls blood phosphate levels by increasing renal phosphate excretion and reducing 1,25-dihydroxyvitamin D3 [1,25(OH)2D] production. Disorders of FGF23 homeostasis are associated with significant morbidity and mortality, but a fundamental understanding of what regulates FGF23 production is lacking. Because the kidney is the major end organ of FGF23 action, we hypothesized that it releases a factor that regulates FGF23 synthesis. Using aptamer-based proteomics and liquid chromatography-mass spectrometry-based (LC-MS-based) metabolomics, we profiled more than 1600 molecules in renal venous plasma obtained from human subjects. Renal vein glycerol-3-phosphate (G-3-P) had the strongest correlation with circulating FGF23. In mice, exogenous G-3-P stimulated bone and bone marrow FGF23 production through local G-3-P acyltransferase-mediated (GPAT-mediated) lysophosphatidic acid (LPA) synthesis. Further, the stimulatory effect of G-3-P and LPA on FGF23 required LPA receptor 1 (LPAR1). Acute kidney injury (AKI), which increases FGF23 levels, rapidly increased circulating G-3-P in humans and mice, and the effect of AKI on FGF23 was abrogated by GPAT inhibition or Lpar1 deletion. Together, our findings establish a role for kidney-derived G-3-P in mineral metabolism and outline potential targets to modulate FGF23 production during kidney injury.

​ObjectiveCompared with hemoglobin A1c (HbA1c), continuous glucose monitoring (CGM) may better capture risk of diabetes complications in patients with chronic kidney disease (CKD), including diabetic peripheral neuropathy (DPN). We hypothesized that glucose time in range (TIR), measured by CGM, is associated with DPN symptoms among participants with type 2 diabetes mellitus (type 2 DM) and moderate-to-severe CKD.​Research design and methodsWe enrolled 105 people with type 2 DM treated with insulin or sulfonylurea, 81 participants with CKD (estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2) and 24 matched control participants with eGFR ≥60 mL/min/1.73 m2. Each participant wore a CGM for two 6-day periods. Calculated glycemic measures included TIR (glucose 70–180 mg/dL) and glucose management indicator (GMI). DPN symptoms were assessed using the Michigan Neuropathy Screening Instrument (MNSI) questionnaire, with a positive MNSI score defined as ≥2 symptoms.​ResultsParticipants with CKD had a mean age of 68 years, diabetes duration 20 years, eGFR 38 mL/min/1.73 m2 and HbA1c 7.8%, 61 mmol/mol. Sixty-two participants reported ≥2 DPN symptoms, 51 (63%) with CKD and 11 (46%) controls. Less TIR and higher GMI were associated with higher risk of MNSI questionnaire score ≥2 (OR 1.25 (95% CI 1.02 to 1.52) per 10% lower TIR, and OR 1.79 (95% CI 1.05 to 3.04) per 1% higher GMI, adjusting for age, gender and race). Similar results were observed when analyses were restricted to participants with CKD. In contrast, there was no significant association of HbA1c with DPN symptoms.​ConclusionsSymptoms of DPN were common among participants with long-standing type 2 DM and CKD. Lower TIR and higher GMI were associated with DPN symptoms.

The prevalence of chronic kidney disease (CKD) is increasing, leading to significant morbidity and mortality. Kidney biopsy remains the gold standard for diagnosing the underlying etiology of CKD, but the procedure carries complication risks. The aim of this study was to identify novel noninvasive biomarkers correlating with kidney function and histopathology in biopsy-proven CKD patients. We profiled 2402 urinary microRNAs (miRNAs) to identify and confirm differentially expressed miRNAs associated with kidney function and histopathology in patients with diabetic nephropathy (n = 58) or lupus nephritis (n = 89), important etiologies of CKD, compared with healthy controls (n = 93 and 119, respectively). Top performing miRNAs were then measured in 2 independent multi-institutional cohorts of patients with diabetes mellitus with (n = 74) or without nephropathy (n = 71) and systemic lupus erythematosus with (n = 86) or without (n = 37) nephritis. In patients with diabetic nephropathy, miR-2861, miR-1915-3p, and miR-4532 were down-regulated (>10-fold, < 0.0001) and were associated with estimated glomerular filtration rate ( < 0.01) and interstitial fibrosis/tubular atrophy ( < 0.05). The -statistics for miR-2861, miR-1915-3p, and miR-4532 were 0.91, 0.86, and 0.85, respectively. In lupus nephritis patients, miR-3201 and miR-1273e were down-regulated (>3-fold, < 0.0001) and associated with endocapillary glomerular inflammation ( < 0.01), with -statistics of 0.97 and 0.91, respectively. We have identified novel miRNAs that correlate with histopathological lesions and functional markers of kidney damage to facilitate sensitive, specific, and noninvasive detection of diabetic nephropathy and lupus nephritis.

Aims/hypothesisInterventions that reduce inflammation may delay progression of microvascular and macrovascular complications in diabetes. We examined the effects of vitamin D3 and/or n-3 fatty acid supplementation vs placebo on 5 year changes in serum inflammatory and cardiac biomarkers in adults with type 2 diabetes.MethodsThis study reports pre-specified secondary outcomes of the Vitamin D and Omega-3 Trial to Prevent and Treat Diabetic Kidney Disease, in which 1312 US adults with type 2 diabetes and without known cardiovascular disease, malignancy, or end-stage kidney disease were randomised using computer-generated random numbers in blocks of eight to vitamin D3 (2000 IU/day) vs placebo and n-3 fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]; 1 g/day) vs placebo in a 2 × 2 factorial design. Participants, examiners, and researchers assessing outcomes were blinded to intervention assignment. We measured serum IL-6, high-sensitivity C-reactive protein (hsCRP) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) at baseline and after 2 and 5 years.ResultsA total of 333 participants were randomised to vitamin D3 and placebo n-3 fatty acids, 289 to n-3 fatty acids and placebo vitamin D3, 370 to vitamin D3 and n-3 fatty acids, and 320 to 2 placebos; 989 (75%) and 934 (71%) participants returned blood samples at 2 and 5 years, respectively. Participants had a mean age of 67.6 years (46% women). Overall, baseline geometric means of IL-6, hsCRP and NT-proBNP were 1.2 pg/ml, 1.9 mg/l and 262 ng/l, respectively. After 5 years, mean IL-6 and hsCRP remained within 6% of their baseline values while mean NT-proBNP increased by 55% overall. Compared with placebo, participants assigned to vitamin D3 had a 1.24-fold greater increase in NT-proBNP over 5 years (95% CI 1.09, 1.41; p = 0.003), while IL-6 and hsCRP did not have a significant difference in change. Comparing n-3 fatty acids with placebo, there was no significant difference in change in IL-6, hsCRP or NT-proBNP. No heterogeneity was observed in subgroup analyses accounting for baseline eGFR, urine albumin to creatinine ratio, initial biomarker concentration, 25-hydroxyvitamin D level or EPA+DHA index.Conclusions/interpretationAmong adults with type 2 diabetes, supplementation with vitamin D3 or n-3 fatty acids did not reduce IL-6, hsCRP or NT-proBNP over 5 years.Trial registrationClinicalTrials.gov NCT01684722FundingThe study was funded by grant R01DK088762 from the National Institute of Diabetes and Digestive and Kidney Diseases.