The relationship of peritubular capillary density with glomerular volume and kidney function in living kidney donors

BACKGROUND

Peritubular capillary rarefaction plays an important role in the progression of chronic kidney disease. Little is known about the relation between peritubular capillary density, glomerular volume and filtration rate in the healthy kidney.

METHODS

In this single-center study, we included 69 living kidney donors who donated between 2005 and 2008 and had representative renal biopsies available. In all donors, glomerular filtration rate was measured using 125I-Iothalamate before donation and at five years after donation. Before donation, the increase in glomerular filtration rate after dopamine stimulation was measured. Glomerular volume and peritubular capillary density were determined in biopsies taken at the time of transplantation. Pearson's correlation coefficient and linear regression were used to assess relations between parameters.

RESULTS

Mean donor age was 52 ± 11 years and mean measured glomerular filtration rate was 119 ± 22 mL/min before donation and 82 ± 15 mL/min at five years after donation. While peritubular capillary density (measured by either number of peritubular capillaries/50,000 μm2 or number of peritubular capillaries/tubule) was not associated with measured glomerular filtration rate before or after donation, number of peritubular capillaries/tubule was associated with the increase in measured glomerular filtration rate after dopamine stimulation (St.β = 0.33, p = 0.004), and correlated positively with glomerular volume (R = 0.24, p = 0.047). Glomerular volume was associated with unstimulated measured glomerular filtration rate before donation (St.β = 0.31, p = 0.01) and at five years (St.β = 0.30, p = 0.01) after donation, independent of age.

CONCLUSIONS

In summary, peritubular capillary density was not related to unstimulated kidney function before or after kidney donation, in contrast to glomerular volume. However, number of peritubular capillaries/tubule correlated with the increase in glomerular filtration rate after dopamine stimulation in healthy kidneys, and with glomerular volume. These findings suggest that peritubular capillary density and glomerular volume differentially affect kidney function in healthy living kidney donors.

Micronutrient deficiencies and new-onset atrial fibrillation in a community-based cohort: data from PREVEND

Background

Impaired nutritional status has been linked to cardiovascular diseases. Both selenium and iron deficiency have been associated with impaired exercise tolerance and worse prognosis in patients with heart failure (HF) as well as mitochondrial dysfunction in human cardiomyocytes. With exception of magnesium, little is known about the role of micronutrients in the development of atrial fibrillation (AFib).

Purpose

To elucidate the association of micronutrient deficiencies with new-onset AFib.

Methods

Selenium, magnesium and iron parameters were measured in a well-characterized Dutch prospective cohort study (N=5452). Selenium deficiency was defined as selenium <70 μg/L, iron deficiency as ferritin <30 μg/L, and magnesium deficiency as magnesium <0.85 mmol/L. New-onset AFib was the primary outcome. All cases with suspected AFib as determined by electronic screening based on 12-lead ECG were manually reviewed and validated by 2 independent cardiologists. Competing-risk regression analyses were performed with death as a competing risk. Additionally, we tested for interaction between selenium deficiency and smoking status on the outcome because of the known lower serum selenium concentrations in smokers in various cohorts.

Results

The mean age was 53.3 (12.0) years and 2843 (52.1%) of all participants were women. During a mean follow-up of 6.2 years, 136 (2.5%) participants developed new-onset AFib. Of the participants who developed AFib, 25.7% had selenium deficiency, 5.1% had iron deficiency, and 75% had magnesium deficiency, compared to 21.1%, 14.9% and 65.8% of those who did not develop AFib, respectively. Smoking status significantly interacted with selenium deficiency on outcome (p=0.075). After multivariable adjustment for components of the CHARGE-AF model, selenium deficiency was associated with new-onset AFib in non-smokers (HR: 1.69, 95% CI: 1.08 to 2.66, p=0.022), but not in smokers (HR: 0.71, 95% CI: 0.27 to 1.90, p=0.494). There was no significant association between the new-onset AFib and magnesium deficiency (HR: 1.40, 95% CI: 0.93 to 2.12, p=0.108) or iron deficiency (HR: 0.59, 95% CI: 0.23–1.49, P=0.266). Participants with two or more deficiencies had higher risk to develop AFib compared to those without deficiencies (HR: 1.75, 95% CI: 1.00 to 3.06, p=0.050).

Conclusion

In a community-based cohort, selenium deficiency was associated with new-onset AFib in non-smoking participants. Interventional studies that investigate the effects of optimizing micronutrients status in a population at risk are needed to assess causality, especially in those with selenium deficiency.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): ENW-KLEIN grantthe Junior Scientific Masterclass-MD/PhD program of the UMCG

Fish and omega-3 fatty acid intake in relation to circulating fibroblast growth factor 23 levels in renal transplant recipients

BACKGROUND AND AIMS

A high circulating fibroblast growth factor 23 (FGF23) level is an independent risk factor for cardiovascular mortality in renal transplant recipients and the general population. N-3 fatty acids eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) may contribute to cardiovascular risk reduction. We investigated whether fish and EPA-DHA intake are related to FGF23 levels in renal transplant recipients.

METHODS AND RESULTS

We performed a cross-sectional analysis in 619 stable renal transplant recipients (mean age 53 years, 57% male, estimated glomerular filtration rate [eGFR] 53 ± 20 mL/min/1.73 m(2)). Dietary intake was assessed by a 177-item food frequency questionnaire. Serum intact FGF23 was measured by ELISA. We examined differences in FGF23 levels across categories of fish and EPA-DHA intake using analysis of variance models adjusted for age, sex, dietary and lifestyle factors and key determinants of FGF23. Patients consumed on average 15 g of fish and 139 mg EPA-DHA/day. Median FGF23 was 62 pg/mL (IQR 43-98 pg/mL). Higher dietary EPA-DHA and fish intake were associated with lower serum FGF23 levels. Subgroup analyses revealed that particularly in patients with reduced renal function (eGFR <60 mL/min/1.73 m(2)), adjusted FGF23 levels (114, 79, 75 pg/mL, P = 0.0001) were inversely associated with tertiles of EPA-DHA intake. Similarly, we observed an inverse association between fish consumption and serum FGF23 levels in adjusted analyses.

CONCLUSION

A higher intake of fish and dietary n-3 fatty acids (EPA-DHA) is related to lower circulating FGF23 levels in renal transplant recipients. Further research is needed to assess the causality of this association and the clinical implications.

Glomerular and tubular induction of the transcription factor c-Jun in human renal disease

The transcription factor c-Jun regulates the expression of genes involved in proliferation and inflammation in many cell types but its role in human renal disease is largely unclear. In the current study we investigated whether c-Jun activation is associated with human renal disease and if c-Jun activation regulates pro-inflammatory and pro-fibrotic genes in renal cells. Activation of c-Jun was quantified by scoring renal expression of phosphorylated c-Jun (pc-Jun) in control human renal tissue and in biopsies from patients with various renal diseases (diabetic nephropathy, focal glomerulosclerosis, hypertension, IgA nephropathy, membranous glomerulopathy, minimal change disease, membranoproliferative glomerulonephritis, systemic lupus erythematosus, acute rejection, and Wegener's granulomatosis); this was correlated with parameters of renal damage. Furthermore, we studied the functional role of c-Jun activation in human tubular epithelial cells (HK-2) stimulated with TGF-beta. Activated c-Jun was present in nuclei of glomerular and tubular cells in all human renal diseases, but only sporadically in controls. Across the diseases, the extent of pc-Jun expression correlated with the degree of focal glomerulosclerosis, interstitial fibrosis, cell proliferation, kidney injury molecule-1 (Kim-1) expression, macrophage accumulation, and impairment of renal function. In HK-2 cells, TGF-beta induced c-Jun activation after 1 h (+40%, p < 0.001) and 24 h (+160%, p < 0.001). The specific c-Jun N-terminal kinase (JNK) inhibitor SP600125 abolished c-Jun phosphorylation at all time points and blunted TGF-beta- or BSA-induced procollagen-1alpha 1 and MCP-1 gene expression in HK-2 cells. We conclude that in human renal disease, the transcription factor c-Jun is activated in glomerular and tubular cells. Activation of c-Jun may be involved in the regulation of inflammation and/or fibrosis in human renal disease.