Vitamin D receptor activation by paricalcitol and insulin resistance in CKD.

BACKGROUND AND AIMS: The nature of the link (causal vs non-causal) between low 1,25-OH vitamin D and insulin resistance (IR) in patients with chronic kidney disease (CKD) remains elusive. We have now made a post hoc analysis of the effect of vitamin D receptor activation by paricalcitol on IR in the complete dataset of a double-blind, randomized, placebo controlled trial, the Paricalcitol and ENdothelial fuNction in chronic kidneY disease (PENNY). METHODS AND RESULTS: Eighty-eight patients with stage 3-4 CKD were randomized (1:1) to receive 2 µg/day paricalcitol or matching placebo for 12 weeks. IR was measured by five IR indices: the homeostasis model assessment of insulin resistance (HOMA-IR), the quantitative insulin sensitivity check index (QUICKI), the McAuley index, the HOMA corrected for adiponectin (HOMA-AD) and the Leptin-adiponectin ratio (LAR). As compared to placebo, paricalcitol produced the expected small rise in serum calcium (+0.07 mmol/L, P = 0.01) and phosphate (+0.08 mmol/L, P = 0.034) and the expected parathyroid hormone suppression (-96 pg/ml, P < 0.001). However, the drug largely failed to affect the five indices of IR which remained unchanged both in the active and the placebo arm (paricalcitol vs placebo, P ranging from 0.25 to 0.62) and no effect modification of paricalcitol on IR by vitamin D or other parameters was registered. CONCLUSION: Paricalcitol treatment for 12 weeks does not improve IR in patients with stage 3-4 CKD. Low vitamin D receptor activation is not a causal factor for IR in the CKD population.

Active vitamin D treatment in CKD patients raises serum sclerostin and this effect is modified by circulating pentosidine levels.

BACKGROUND AND AIMS: 1,25(OH)2Vitamin D increases the expression of the sclerostin gene. Whether vitamin D receptor activation (VDRA) influences serum sclerostin in CKD and whether compounds interfering with VDRA like Advanced Glycosylation End Products (AGEs) may alter the sclerostin response to VDRA is unknown. METHODS AND RESULTS: Eighty-eight stage G3-4 CKD patients randomly received 2 µg paricalcitol (PCT)/day (n = 44) or placebo (n = 44) for 12 weeks. Sclerostin, a major AGE compound like pentosidine, and bone mineral disorder biomarkers were measured at baseline, at 12 weeks and 2 weeks after stopping the treatments. At baseline, in the whole study population sclerostin correlated with male gender (P = 0.002), BMI (P < 0.001), waist circumference (P < 0.001), serum pentosidine (P = 0.002) and to a weaker extent, with diabetes (P = 0.04), 1,25(OH)2Vitamin D (r = 0.22, P = 0.04) and serum phosphate (r = -0.26, P = 0.01). Sclerostin increased during PCT treatment (average + 15.7 pg/ml, 95% CI: -3.0 to +34.3) but not during placebo (P = 0.03) and the PCT effect was abolished 2 weeks after stopping this drug. The increase in sclerostin levels induced by PCT was modified by prevailing pentosidine levels (P = 0.01) and was abolished by statistical adjustment for simultaneous changes in PTH but not by FGF23 changes. CONCLUSIONS: VDRA by paricalcitol causes a moderate increase in serum sclerostin in CKD patients. Such an effect is abolished by adjustment for PTH, suggesting that it may serve to counter PTH suppression. The sclerostin rise by PCT is attenuated by pentosidine, an observation in keeping with in vitro studies showing that AGEs alter the functioning of the VDRA.

Serum phosphate modifies the vascular response to vitamin D receptor activation in chronic kidney disease (CKD) patients.

BACKGROUND AND AIMS: Vitamin D receptor activation (VDRA) ameliorates endothelial dysfunction in CKD patients but also increases phosphate and FGF-23, which may attenuate the beneficial effect of VDRA on endothelial function. METHODS AND RESULTS: This is a pre-specified secondary analysis of the PENNY trial (NCT01680198) testing the effect of phosphate and FGF-23 on the flow mediated vasodilatory (FMD) response to paricalcitol (PCT, 2 µg/day) and placebo over a 12-weeks treatment period. Eighty-eight stage G3-4 CKD patients were randomized to PCT (n = 44) and Placebo (n = 44). Endothelial function was assessed by measuring endothelium dependent forearm blood flow (FBF) response to ischemia. The FMD response was by the 61% higher in PCT treated patients than in those on placebo (P = 0.01). Phosphate (+11%, P = 0.039), calcium (+3%, P = 0.01) and, particularly so, FGF23 (+164%, P < 0.001) increased in PCT treated patients. Changes in FMD by PCT associated inversely with phosphate (r = -0.37, P = 0.01) but were independent of FGF-23, calcium and PTH changes. The response to PCT was maximal in patients with no changes in phosphate (1st tertile), attenuated in those with mild-to-moderate rise in phosphate (2nd tertile) and abolished in those with the most pronounced phosphate increase (3rd tertile) (effect modification P = 0.009). No effect modification by FGF-23 and other variables was observed. CONCLUSIONS: The beneficial effect of PCT on endothelial function in CKD is maximal in patients with no or minimal changes in phosphate and it is abolished in patients with a pronounced phosphate rise. These findings generate the hypothesis that the endothelium protective effect by VDRA may be potentiated by phosphate lowering interventions.

Pro- and anti-inflammatory cytokine gene expression in subcutaneous and visceral fat in severe obesity.

BACKGROUND AND AIMS: Pro-inflammatory molecules produced by adipose tissue have been implicated in the risk of cardiovascular (CV) disease in obesity. We investigated the expression profile of 19 pro-inflammatory and seven anti-inflammatory genes in subcutaneous adipose tissue (SAT) and in visceral adipose tissue (VAT) in 44 severely obese individuals who underwent bariatric surgery. METHODS AND RESULTS: SAT and VAT expressed an identical series of pro-inflammatory genes. Among these genes, 12 were significantly more expressed in SAT than in VAT while just one (IL18) was more expressed in VAT. The remaining genes were equally expressed. Among pro-inflammatory cytokines, both IL6 and IL8 were about 20 times more intensively expressed in SAT than in VAT. The expression of nine genes was highly associated in SAT and VAT. Only for three pro-inflammatory cytokines (IL8, IL18, SAA1) in SAT the gene expression in adipose tissue associated with the circulating levels of the corresponding gene products while no such an association was found as for VAT. CONCLUSIONS: The expression of critical pro-inflammatory genes is substantially higher in SAT than in VAT in individuals with morbid obesity. The variability in circulating levels of pro-inflammatory cytokines is, in small part and just for three pro-inflammatory cytokines, explained by underlying gene expression in SAT but not in VAT. These results point to a compartment-specific adipose tissue contribution to inflammation in obesity and indicate that abdominal SAT contributes more than VAT to the pro-inflammatory milieu associated with severe obesity.

Circulating soluble receptor for advanced glycation end product (sRAGE) and left ventricular hypertrophy in patients with chronic kidney disease (CKD).

BACKGROUND AND AIM: A decoy receptor for advanced glycation end product (soluble RAGE or sRAGE) is involved in left ventricular hypertrophy (LVH), and cardiomyopathy myocardial damage in experimental models and observational studies in patients with heart failure support the hypothesis that sRAGE attenuates the progression of heart disease and prevents death. Since sRAGE accumulates in patients with chronic kidney disease (CKD) we studied the relationship between plasma sRAGE with LVH in CKD patients. METHODS AND RESULTS: We enrolled 142 patients with an average estimated glomerular filtration rate (eGFR) of 32 ml/min/1.73 m(2) and 49 healthy control individuals matched for age and gender. Plasma sRAGE was significantly higher in CKD patients than in healthy controls. Significant inverse relationships were found between sRAGE with left ventricular mass index (LVMI) and mean wall thickness (MWT) but no such associations were found in controls. A bootstrap re-sampling validation study confirmed the estimates of the link between sRAGE and these variables. On covariance analysis, the slopes of LVMI and MWT to sRAGE were significantly steeper in CKD patients than in the controls. On logistic regression analysis 1 log unit increase in sRAGE was associated with a 82% decrease in the odds for LVH in CKD patients. CONCLUSIONS: sRAGE is an inverse marker of LVH in CKD patients. This association generates the hypothesis that the RAGE pathway could be a causal risk factor for LVH in this population and that blockade of this pathway by the endogenous decoy receptor sRAGE could attenuate LVH in the same population.

Plasma cytokines, glomerular filtration rate and adipose tissue cytokines gene expression in chronic kidney disease (CKD) patients.

BACKGROUND AND AIM: Systemic inflammation is a hallmark of chronic kidney disease (CKD) and obesity represents a major risk factor for CKD. We investigated the relationship between plasma interleukin-6 (IL-6) and tumour necrosis factor-α (TNF-α) and the glomerular filtration rate (GFR) in 75 stage 2-5 CKD patients. METHODS AND RESULTS: We studied the steady-state relationship between plasma and subcutaneous adipose tissue (SAT) gene expression of the same cytokines in 19 patients and in 17 well-matched healthy subjects (HS) and compared SAT gene expression of these cytokines and of two additional cytokines (IL-1ß and IL-8) in CKD patients and in HS. Plasma IL-6 and TNF-α were higher in CKD patients than in HS (P < 0.001). IL-6 was similarly increased in patients with mild, moderate and severe CKD and largely independent of the GFR (r = -0.03, P = NS). TNF-α was inversely related to GFR, which was the first factor in rank (ß = -0.37, P = 0.001) explaining the variability in TNF-α in CKD. SAT messenger RNA (mRNA) levels of IL-6, TNF-α, IL- ß and IL-8 were similar in CKD patients and in HS. Plasma and SAT mRNA levels of IL-6 and TNF-α levels were largely unrelated. CONCLUSIONS: Plasma IL-6 rises early in CKD and does not show any further increase at more severe stages of CKD, whereas TNF-α is inversely associated with the GFR indicating a substantial difference in the dynamics of the relationship between these cytokines and renal function. Cytokines are not overexpressed in SAT in these patients, and circulating IL-6 and TNF-α are dissociated from the corresponding mRNA levels in SAT, both in CKD patients and in HS.

Waist circumference modifies the relationship between the adipose tissue cytokines leptin and adiponectin and all-cause and cardiovascular mortality in haemodialysis patients.

BACKGROUND: the relationships between the adipose tissue cytokines leptin and adiponectin (ADPN) and clinical outcomes have not been well studied in haemodialysis (HD) patients and remain highly controversial. As central obesity is an important modifier of the effect of various risk factors for clinical outcomes, we tested the hypothesis that waist circumference (WC) modifies the link between these cytokines and both overall and cardiovascular death in HD patients. METHODS: a total of 537 HD patients participated in a prospective cohort study. RESULTS: leptin and ADPN were inversely related to each other and robustly associated with WC (P < 0.001). During follow-up (average 29 months, range 1-47 months) 182 patients died, including 115 from cardiovascular causes. In analyses adjusting for potential confounders, there were strong interactions between leptin and WC in relationship to both all-cause (P < 0.001) and cardiovascular death (P = 0.002). Accordingly, a fixed excess of leptin signalled a gradually increasing risk for all-cause and cardiovascular mortality in patients with a large WC but an opposite effect in those with a relatively small WC. An interaction between ADPN and WC for all-cause (P = 0.01) and cardiovascular mortality (P = 0.01) emerged only in models excluding the leptin-WC interaction, suggesting that these adipokines share a common pathway leading to adverse clinical events in HD patients. CONCLUSIONS: the predictive value of leptin and ADPN for all-cause and cardiovascular death in HD patients appears to be critically dependent on WC. These findings support the hypothesis that disturbances in adipokine levels are involved in adverse clinical outcomes in HD patients with abdominal obesity.

Low triiodothyronine and survival in end-stage renal disease.

Plasma triiodothyronine (fT3) is a strong predictor of adverse clinical outcomes in various clinical conditions. Since fT3 in patients with end-stage renal diseases (ESRD) is frequently reduced and is associated with inflammation and cardiovascular damage, we prospectively tested the hypothesis that it predicts death in a cohort of 200 hemodialysis patients. Plasma fT3 was lower in ESRD patients (P<0.001) than in healthy subjects and in clinically euthyroid patients with normal renal function. During the follow-up 102 patients died. Patients who died had significantly lower plasma fT3 than those who survived (P<0.001) and in a Kaplan-Meyer analysis plasma fT3 was associated with death (P<0.001). On multivariate Cox's regression analyses, adjusting for a series of traditional and emerging risk factors including inflammation markers, patients with relatively higher plasma fT3 (hazard ratio (HR) (1 pg/ml increase in fT3)) had a 50% reduction in the risk of death (HR=0.50, 95% CI: 0.35-0.72) as compared to those having relatively lower fT3 levels. Of note, plasma fT3 captured most of the predictive power of interleukin-6 (IL-6) because this latter variable emerged as a significant predictor of death only in a model excluding fT3. Low fT3 is an independent predictor of death in hemodialysis patients. These data lend support to the hypothesis that thyroid dysfunction is implicated in the high risk of the ESRD population.

Urotensin II is an inverse predictor of incident cardiovascular events in end-stage renal disease.

Urotensin II (UTN) is a vasoactive substance that may induce vasoconstriction or vasodilatation. Although this peptide is seen as a vasculotoxic substance, to date there is no prospective study examining the relationship between UTN and hard end points like cardiovascular (CV) events. UTN is much increased in end-stage renal disease (ESRD) and this disease may represent a useful natural model to explore the relationship between UTN and CV outcomes. In this study, we analysed the relationship between plasma UTN and incident CV events (fatal and non-fatal) in a cohort of 191 haemodialysis patients followed up for an average time of 3.6 years (range 0.07-5.8 years). Plasma UTN in haemodialysis patients (median: 6.5 ng/ml) was twice higher than in healthy subjects (median: 3.3 ng/ml). During the follow-up period, 94 patients died and 88 had incident fatal and non-fatal CV events. UTN was significantly lower in patients with incident CV events (median: 5.3 ng/ml) than in events-free patients (median: 7.1 ng/ml), and in a Kaplan-Meier analysis, high UTN was strongly and inversely associated with incident CV events (P<0.001). Multivariate Cox's regression analysis fully confirmed plasma UTN as an inverse predictor of adverse CV outcomes, and in this analysis, UTN resulted to be the third factor in rank, after age and diabetes, explaining the incidence of CV events. UTN is an inverse predictor of CV outcomes in ESRD. Our data suggest that UTN should not be necessarily seen as a vasculotoxic peptide in haemodialysis patients.