Myocardial effects of VDR activators in renal failure

Phosphate and Coronary Artery Disease in Patients with Chronic Kidney Disease

Cardiovascular disease (CVD) is the leading cause of death in patients with chronic kidney disease (CKD). Both traditional and CKD-related factors are associated with CVD in CKD patients. Traditional factors that play an important role in the atherosclerotic process directly contribute to a higher risk of coronary artery disease in patients with early-stage CKD. Among CKD-related factors, CKD-mineral and bone disorder plays a critical role in the pathomechanism of nonatherosclerotic diseases, which increases the risk of cardiovascular morbidity and mortality in patients with advanced CKD. Higher serum phosphate levels were significantly associated with cardiovascular events and all-cause mortality in patients with or without CKD. An increased phosphate load, directly and indirectly, promotes arterial medial calcification and left ventricular hypertrophy, both of which predispose patients to coronary artery disease. Calciprotein particles that form in a hyperphosphatemic state promote the transformation of vascular smooth muscle cells (VSMCs) into osteoblastic cells, thereby providing a scaffold for medial calcification in the artery. Increases in fibroblast growth factor-23 and disturbed vitamin D metabolism induced by an excessive phosphate load play a significant role in the development of cardiomyocyte hypertrophy and cardiac fibrosis. Recently, hyperphosphatemia was reported to promote de novo cholesterol synthesis in VSMCs and macrophages, which is likely to contribute to statin resistance in patients with end-stage kidney disease. This review outlines the association between increased phosphate load and coronary artery disease in patients with CKD.

miRNAs in Uremic Cardiomyopathy: A Comprehensive Review

Uremic Cardiomyopathy (UCM) is an irreversible cardiovascular complication that is highly pervasive among chronic kidney disease (CKD) patients, particularly in End-Stage Kidney Disease (ESKD) individuals undergoing chronic dialysis. Features of UCM are an abnormal myocardial fibrosis, an asymmetric ventricular hypertrophy with subsequent diastolic dysfunction and a complex and multifactorial pathogenesis where underlying biological mechanisms remain partly undefined. In this paper, we reviewed the key evidence available on the biological and clinical significance of micro-RNAs (miRNAs) in UCM. miRNAs are short, noncoding RNA molecules with regulatory functions that play a pivotal role in myriad basic cellular processes, such as cell growth and differentiation. Deranged miRNAs expression has already been observed in various diseases, and their capacity to modulate cardiac remodeling and fibrosis under either physiological or pathological conditions is well acknowledged. In the context of UCM, robust experimental evidence confirms a close involvement of some miRNAs in the key pathways that are known to trigger or worsen ventricular hypertrophy or fibrosis. Moreover, very preliminary findings may set the stage for therapeutic interventions targeting specific miRNAs for ameliorating heart damage. Finally, scant but promising clinical evidence may suggest a potential future application of circulating miRNAs as diagnostic or prognostic biomarkers for improving risk stratification in UCM as well.

Direct and indirect effects of fibroblast growth factor 23 on the heart

Fibroblast growth factor (FGF)23 is a bone-derived phosphotropic hormone that regulates phosphate and mineral homeostasis. Recent studies have provided evidence that a high plasma concentration of FGF23 is associated with cardiac disease, including left ventricular hypertrophy (LVH), heart failure, atrial fibrillation, and cardiac death. Experimental studies have shown that FGF23 activates fibroblast growth factor receptor 4 (FGFR4)/phospholipase Cγ/calcineurin/nuclear factor of activated T-cells signaling in cardiomyocytes and induces cardiac hypertrophy in rodents. Activation of FGFR4 by FGF23 normally requires the co-receptor α-klotho, and klotho-independent signaling occurs only under conditions characterized by extremely high FGF23 concentrations. Recent studies have demonstrated that FGF23 activates the renin-angiotensin-aldosterone system (RAAS) and induces LVH, at least in part as a result of lower vitamin D activation. Moreover, crosstalk between FGF23 and RAAS results in the induction of cardiac hypertrophy and fibrosis. In this review, we summarize the results of studies regarding the relationships between FGF23 and cardiac events, and describe the potential direct and indirect mechanisms whereby FGF23 induces LVH.

Effects of calcitriol and paricalcitol on renal fibrosis in CKD

BACKGROUND

In chronic kidney disease, the activation of the renin-angiotensin-aldosterone system (RAAS) and renal inflammation stimulates renal fibrosis and the progression to end-stage renal disease. The low levels of vitamin D receptor (VDR) and its activators (VDRAs) contribute to worsen secondary hyperparathyroidism and renal fibrosis.

METHODS

The 7/8 nephrectomy model of experimental chronic renal failure (CRF) was used to examine the anti-fibrotic effects of treatment with two VDRAs, paricalcitol and calcitriol, at equivalent doses (3/1 dose ratio) during 4 weeks.

RESULTS

CRF increased the activation of the RAAS, renal inflammation and interstitial fibrosis. Paricalcitol treatment reduced renal collagen I and renal interstitial fibrosis by decreasing the activation of the RAAS through renal changes in renin, angiotensin receptor 1 (ATR1) and ATR2 mRNAs levels and renal inflammation by decreasing renal inflammatory leucocytes (CD45), a desintegrin and metaloproteinase mRNA, transforming growth factor beta mRNA and protein, and maintaining E-cadherin mRNA levels. Calcitriol showed similar trends without significant changes in most of these biomarkers.

CONCLUSIONS

Paricalcitol effectively attenuated the renal interstitial fibrosis induced by CRF through a combination of inhibitory actions on the RAAS, inflammation and epithelial/mesenchymal transition.

Active vitamin D is cardioprotective in experimental uraemia but not in children with CKD Stages 3-5

BACKGROUND

Uraemic cardiac remodelling is associated with vitamin D and Klotho deficiency, elevated fibroblast growth factor 23 (FGF23) and activation of the renin-angiotensin system (RAS). The cardioprotective properties of active vitamin D analogues in this setting are unclear.

METHODS

In rats with 5/6 nephrectomy (5/6Nx) treated with calcitriol, the cardiac phenotype and local RAS activation were investigated compared with controls. A nested case-control study was performed within the Cardiovascular Comorbidity in Children with Chronic Kidney Disease (4C) study, including children with chronic kidney disease (CKD) Stages 3-5 [estimated glomerular filtration rate (eGFR) 25 mL/min/1.73 m2] treated with and without active vitamin D. Echocardiograms, plasma FGF23 and soluble Klotho (sKlotho) were assessed at baseline and after 9 months.

RESULTS

In rats with 5/6Nx, left ventricular (LV) hypertrophy, LV fibrosis and upregulated cardiac RAS were dose-dependently attenuated by calcitriol. Calcitriol further stimulated FGF23 synthesis in bone but not in the heart, and normalized suppressed renal Klotho expression. In the 4C study cohort, treatment over a mean period of 9 months with active vitamin D was associated with increased FGF23 and phosphate and decreased sKlotho and eGFR compared with vitamin D naïve controls, whereas LV mass index did not differ between groups.

CONCLUSIONS

Active vitamin D ameliorates cardiac remodelling and normalizes renal Klotho expression in 5/6Nx rats but does not improve the cardiac phenotype in children with CKD Stages 3-5. This discrepancy may be due to further enhancement of circulating FGF23 and faster progression of CKD associated with reduced sKlotho and higher serum phosphate in vitamin D-treated patients.

Cardioprotective Effects of Paricalcitol Alone and in Combination With FGF23 Receptor Inhibition in Chronic Renal Failure: Experimental and Clinical Studies

BACKGROUND

In uremic animals, vitamin D receptor (VDR) agonists like paricalcitol (Pc) attenuate cardiac hypertrophy, but this effect has not been replicated consistently in humans with chronic kidney disease. Elevated fibroblast growth factor 23 (FGF23) levels cause cardiac hypertrophy with activation of the myocardial calcineurin/nuclear factor of activated T cell (NFAT) axis and may antagonize the cardioprotective effects of VDR agonist therapy. We hypothesized that the effectiveness of Pc may depend on the prevailing circulating levels of FGF23 and could be potentiated by the combined administration of a pan-FGF23 receptor (FGFR) blocker agent (PD173074).

METHODS

In rats with 5/6 nephrectomy treated with Pc or PD173074 or both agents concurrently, myocardial mRNA expression of renin-angiotensin system, VDR, FGFR4, and calcineurin/NFAT target genes was determined. In adolescents on hemodialysis, we analyzed sequential echocardiograms, blood pressures and serial FGF23 measurements, and their relations to the cumulative administered dose of parenteral Pc.

RESULTS

The ratio of Pc dose/plasma levels of FGF23 correlated inversely (P < 0.005) with the cardiac mass in uremic rats and in hemodialysis patients, independently of hypertension. Despite persistently elevated FGF23 levels and myocardial FGFR4 activation, Pc suppressed upregulated myocardial calcineurin/NFAT target genes, and the effects were amplified by coadministration of PD173074.

CONCLUSIONS

The beneficial effects of Pc on uremic cardiac hypertrophy are counterbalanced by the increased FGF23 levels. Blockade of FGF23-mediated signaling increased the Pc-induced suppression of the myocardial calcineurin/NFAT system. Higher doses of Pc should be considered in the treatment of patients with uremic cardiomyopathy.

Regulation of miR-29b and miR-30c by vitamin D receptor activators contributes to attenuate uraemia-induced cardiac fibrosis

Background

Uraemic cardiomyopathy, a process mainly associated with increased myocardial fibrosis, is the leading cause of death in chronic kidney disease patients and can be prevented by vitamin D receptor activators (VDRAs). Since some microRNAs (miRNAs) have emerged as regulators of the fibrotic process, we aimed to analyse the role of specific miRNAs in VDRA prevention of myocardial fibrosis as well as their potential use as biomarkers.

Methods

Wistar rats were nephrectomized and treated intraperitoneally with equivalent doses of two VDRAs: calcitriol and paricalcitol. Biochemical parameters, cardiac fibrosis, miRNA (miR-29b, miR-30c and miR-133b) levels in the heart and serum and expression of their target genes collagen I (COL1A1), matrix metalloproteinase 2 (MMP-2) and connective tissue growth factor (CTGF) in the heart were evaluated.

Results

Both VDRAs attenuated cardiac fibrosis, achieving a statistically significant difference in the paricalcitol-treated group. Increases in RNA and protein levels of COL1A1, MMP-2 and CTGF and reduced expression of miR-29b and miR-30c, known regulators of these pro-fibrotic genes, were observed in the heart of chronic renal failure (CRF) rats and were attenuated by both VDRAs. In serum, significant increases in miR-29b, miR-30c and miR-133b levels were observed in CRF rats, which were prevented by VDRA use. Moreover, vitamin D response elements were identified in the three miRNA promoters.

Conclusions

VDRAs, particularly paricalcitol, attenuated cardiac fibrosis acting on COL1A1, MMP-2 and CTGF expression, partly through regulation of miR-29b and miR-30c. These miRNAs and miR-133b could be useful serum biomarkers for cardiac fibrosis and also potential new therapeutic targets.

Paricalcitol and Peritoneal Protein Loss in Peritoneal Dialysis: A Double-Center Study

BACKGROUND/AIMS

Peritoneal protein loss (PPL) is associated with cardiovascular disease and mortality in peritoneal dialysis (PD). Controversial results have been published about the effect of paricalcitol in PPL among PD patients. This study intends to analyze the relationship between paricalcitol and PPL in PD.

METHODS

In a retrospective study, prevalent PD patients were divided into 2 groups: "with paricalcitol" and "without paricalcitol". X2-test, Student's t test, Pearson correlation coefficient and Logistic Regression analysis were applied.

RESULTS

Eighty-two patients were included. PPL was lower among patients medicated with paricalcitol (5.17 ± 1.71 vs. 6.79 ± 2.10 g/24 h, p = 0.0001). In multivariate analysis, paricalcitol and dialysate/plasma ratio of creatinine (D/P creatinine) were independently related to PPL (OR 4.270 [1.437-12.684], p = 0.009 and OR 0.205 [0.064-0.659], p = 0.008, respectively), adjusted for diabetes.

CONCLUSION

Paricalcitol and D/P creatinine were independently related to PPL. Paricalcitol may have an effect on PPL in PD patients.

Paricalcitol Attenuates Cardiac Fibrosis and Expression of Endothelial Cell Transition Markers in Isoproterenol-Induced Cardiomyopathic Rats

OBJECTIVES

Acute cardiomyopathy is a health problem worldwide. Few studies have shown an association between acute cardiomyopathy and low vitamin D status. Paricalcitol, a vitamin D receptor activator, clinically benefits patients with advanced kidney disease. The effect of paricalcitol supplement on cardiac remodeling in cardiomyopathic rats is unknown. This experimental study investigated the effect of paricalcitol in rats with cardiomyopathy induced by isoproterenol.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

Hospital-affiliated animal research institution.

SUBJECTS

Eight-week-old male Wistar-Kyoto rats.

INTERVENTIONS

Male Wistar-Kyoto rats were first injected intraperitoneally with isoproterenol to create a rat model of acute cardiomyopathy. Then paricalcitol was administered intraperitoneally to isoproterenol-injected rats at a dosage of 200 ng three times a week for 3 weeks. Relevant cardiomyopathy-related variables were measured regularly in three groups of rats, controls, isoproterenol, and isoproterenol plus paricalcitol. Rat hearts were obtained for evaluation of cardiac fibrosis using Masson trichrome staining and commercially available software, and evaluation of cell transition using immunofluorescence staining analysis.

MEASUREMENTS AND MAIN RESULTS

Isoproterenol infusions generated significant cardiac fibrosis (p < 0.001). Subsequent paricalcitol treatment attenuated the isoproterenol-induced cardiac fibrosis (p = 0.006). Fluorescence showed colocalization of endothelial and fibroblast cell markers (cluster differentiation 31 and α-smooth muscle actin, respectively) in the isoproterenol-treated hearts. Paricalcitol injections attenuated the isoproterenol-induced fluorescence intensity of two cell markers (p < 0.01).

CONCLUSIONS

Paricalcitol injections may ameliorate isoproterenol-induced cardiac fibrosis possibly through regulating cell transition.

Cardiac effect of vitamin D receptor modulators in uremic rats

Vitamin D receptor (VDR) modulators (VDRMs) are commonly used to control secondary hyperparathyroidism (SHPT) associated with chronic kidney disease, and are associated with beneficial outcomes in cardiovascular disease. In this study, we compared the cardiac effect of VS-105, a novel VDRM, with that of paricalcitol in 5/6 nephrectomized uremic rats. Male Sprague-Dawley rats were 5/6 nephrectomized, fed a standard diet for 4 weeks to establish uremia, and then treated (intraperitoneally, 3 times/week) with vehicle (propylene glycol), paricalcitol (0.025 and 0.15μg/kg), or VS-105 (0.05 and 0.3μg/kg) for 4 weeks. In uremic rats, neither VDRM (low and high doses) altered serum creatinine and phosphorus levels. Serum calcium was significantly higher with high dose paricalcitol compared to sham rats. PTH levels were significantly decreased with low dose paricalcitol and VS-105, and were further reduced in the high dose groups. Interestingly, serum FGF23 was significantly higher with high dose paricalcitol compared to sham rats, whereas VS-105 had no significant effect on FGF23 levels. Left ventricle (LV) weight and LV mass index determined by echocardiography were significantly suppressed in both high dose VDRM groups. This suppression was more evident with VS-105. Western blotting showed significant decreases in a fibrosis marker TGF-β1 in both high dose VDRM groups (vs. vehicle) and Masson trichrome staining showed significant decreases in cardiac fibrosis in these groups. These results suggest that VS-105 is less hypercalcemic than paricalcitol and has favorable effects on SHPT and cardiac parameters that are similar to those of paricalcitol in uremic rats. The cardioprotective effect is a noteworthy characteristic of VS-105.

A Genetic Biomarker of Oxidative Stress, the Paraoxonase-1 Q192R Gene Variant, Associates with Cardiomyopathy in CKD: A Longitudinal Study

Background. Oxidative stress is a hallmark of CKD and this alteration is strongly implicated in LV hypertrophy and in LV dysfunction. Methods and Patients. We resorted to the strongest genetic biomarker of paraoxonase-1 (PON1) activity, the Q192R variant in the PON1 gene, to unbiasedly assess (Mendelian randomization) the cross-sectional and longitudinal association of this gene-variant with LV mass and function in 206 CKD patients with a 3-year follow-up. Results. The R allele of Q192R polymorphism associated with oxidative stress as assessed by plasma 8-isoPGF2α (P = 0.03) and was dose-dependently related in a direct fashion to LVMI (QQ: 131.4 ± 42.6 g/m(2); RQ: 147.7 ± 51.1 g/m(2); RR: 167.3 ± 41.9 g/m(2); P = 0.001) and in an inverse fashion to systolic function (LV Ejection Fraction) (QQ: 79 ± 12%; RQ: 69 ± 9%; RR: 65 ± 10% P = 0.002). On longitudinal observation, this gene variant associated with the evolution of the same echocardiographic indicators [LVMI: 13.40 g/m(2) per risk allele, P = 0.005; LVEF: -2.96% per risk allele, P = 0.001]. Multivariate analyses did not modify these associations. Conclusion. In CKD patients, the R allele of the Q192R variant in the PON1 gene is dose-dependently related to the severity of LVH and LV dysfunction and associates with the longitudinal evolution of these cardiac alterations. These results are compatible with the hypothesis that oxidative stress is implicated in cardiomyopathy in CKD patients.

Arrhythmia and Sudden Death in Hemodialysis Patients: Protocol and Baseline Characteristics of the Monitoring in Dialysis Study

BACKGROUND

Dialysis patients have high rates of cardiovascular morbidity and mortality, but data on arrhythmia burden, arrhythmia type, arrhythmia triggers, and the identity of terminal arrhythmias have historically been limited by an inability to monitor heart rhythm for prolonged periods.

OBJECTIVES

To investigate arrhythmia and its association with sudden death in dialysis-dependent ESRD, describe the potential for implantable devices to advance study of dialysis physiology, review the ethical implications of using implantable devices in clinical studies, and report on the protocol and baseline results of the Monitoring in Dialysis Study (MiD).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this multicenter, interventional-observational, prospective cohort study, we placed implantable loop recorders in patients undergoing long-term hemodialysis. The proportion of patients experiencing clinically significant arrhythmias was the primary endpoint. For 6 months, we captured detailed data on the primary endpoint, symptomatic arrhythmias, other electrocardiographic variables, dialysis prescription, electrolytes, dialysis-related variables, and vital signs. We collected additional electrocardiographic data for up to 1 year.

RESULTS

Overall, 66 patients underwent implantation in sites in the United States and India. Diabetes was present in 63.6% of patients, 12.1% were age ≥70 years, 69.7% were men, and 53.0% were black. Primary and secondary endpoint data are expected in 2016.

CONCLUSIONS

Cardiac arrhythmia is an important contributor to cardiovascular morbidity and mortality in dialysis patients, but available technology has previously limited the ability to estimate its true burden and triggers and to define terminal rhythms in sudden death. Use of implantable technology in observational studies raises complex issues but may greatly expand understanding of dialysis physiology. The use of implantable loop recorders in MiD is among the first examples of such a trial, and the results are expected to provide novel insights into the nature of arrhythmia in hemodialysis patients.

Paricalcitol modulates ACE2 shedding and renal ADAM17 in NOD mice beyond proteinuria

Circulating and renal activity of angiotensin-converting enzyme 2 (ACE2) is increased in non-obese diabetic (NOD) mice. Because paricalcitol has been reported to protect against diabetic nephropathy, we investigated the role of paricalcitol in modulating ACE2 in these mice. In addition, renal ADAM17, a metalloprotease implied in ACE2 shedding, was assessed. NOD female and non-diabetic control mice were studied for 21 days after diabetes onset and divided into various treatment groups. Diabetic animals received either vehicle; 0.4 or 0.8 μg/kg paricalcitol, aliskiren, or a combination of paricalcitol and aliskiren. We then studied the effect of paricalcitol on ACE2 expression in proximal tubular epithelial cells. Paricalcitol alone or in combination with aliskiren resulted in significantly reduced circulating ACE2 activity in NOD mice but there were no changes in urinary albumin excretion. Serum renin activity was significantly decreased in mice that received aliskiren but no effect was found when paricalcitol was used alone. Renal content of ADAM17 was significantly decreased in animals that received a high dose of paricalcitol. Renal and circulating oxidative stress (quantified by plasma H2O2 levels and immunolocalization of nitrotyrosine) were reduced in high-dose paricalcitol-treated mice compared with non-treated diabetic mice. In culture, paricalcitol incubation resulted in a significant increase in ACE2 expression compared with nontreated cells. In NOD mice with type 1 diabetes, paricalcitol modulates ACE2 activity, ADAM17, and oxidative stress renal content independently from the glycemic profile and urinary albumin excretion. In tubular cells, paricalcitol may modulate ACE2 by blocking its shedding. In the early stage of diabetic nephropathy, paricalcitol treatment counterbalances the effect of diabetes on circulating ACE2 activity. Our results suggest that additional use of paricalcitol may be beneficial in treating patients with diabetes under standard therapeutic strategies.

The uses and abuses of Vitamin D compounds in chronic kidney disease-mineral bone disease (CKD-MBD)

Vitamin D is of paramount importance to skeletal development, integrity and health. Vitamin D homeostatis is typically deranged in a number of chronic conditions, of which chronic kidney disease is one of the most important. The use of vitamin D based therapy to target secondary hyperparathyroidism is now several decades old, and there is a large body of clinical practice, experience, guidelines and research to underpin this. However, there are many unknowns, of significant clinical relevance. Amongst which is what "species" of vitamin D we should be using, in what patient, and, under what conditions. Sadly, there has been a real dearth of randomised controlled trials, and trials with outputs of clinical relevance, which means our clinical practice has not developed and refined adequately ove the last 4 decades. This article will discuss the vexed but critical questions of which vitamin D therapies might suit which kidney patients, and will high-light the many important clinical questions which urgently require answering.

Differential expression and regulation of Klotho by paricalcitol in the kidney, parathyroid, and aorta of uremic rats

Klotho plays an important role in the pathogenesis of cardiovascular disease in chronic kidney disease (CKD). Klotho is highly expressed in the kidney and parathyroid glands, but its presence in the vasculature is debated. Renal Klotho is decreased in CKD, but the effect of uremia on Klotho in other tissues is not defined. The effect of vitamin D receptor activator therapy in CKD on expression of Klotho in various tissues is also in debate. In uremic rats (surgical 5/6^th nephrectomy model), we compared 3-months of treatment with and without paricalcitol on Klotho immunostaining in the kidney, parathyroid glands and aorta. With uremia, Klotho was unchanged in the parathyroid, significantly decreased in the kidney (66%) and the intimal-medial area of the aorta (69%), and significantly increased in the adventitial area of the aorta (67%) compared with controls. Paricalcitol prevented the decrease in Klotho in the kidney, increased expression in the parathyroid (31%), had no effect in the aortic media, but blunted the increase of Klotho in aortic adventitia. We propose that fibroblasts are responsible for expression of Klotho in the adventitia. In hyperplastic human parathyroid tissue from uremic patients, Klotho was higher in oxyphil compared with chief cells. Thus, under our conditions of moderate CKD and mild-to-moderate hyperphosphatemia in rats, the differential expression of Klotho and its regulation by paricalcitol in uremia is tissue-dependent.

Is left ventricular hypertrophy a modifiable risk factor in end-stage renal disease

PURPOSE OF REVIEW

Left ventricular hypertrophy (LVH) is common in end-stage renal disease (ESRD) and has been advocated as a therapeutic target. We review the considerations for targeting LVH as a modifiable risk factor in ESRD.

RECENT FINDINGS

Pathologic myocardial changes underlying LVH provide an ideal substrate for the spread of arrhythmia and may be key contributors to the occurrence of sudden death in ESRD. LVH is present in 68-89% of incident hemodialysis patients and is frequently progressive, although regression is observed in a minority of patients. Higher degrees of baseline LVH, as well as greater increases in left ventricular mass index over time, are associated with decreased survival, but whether these associations are causal remains uncertain. Several interventions, including angiotensin blockade and frequent dialysis, can reduce the left ventricular mass index, but whether this is associated with improved survival has not been definitively demonstrated.

SUMMARY

LVH is a highly prevalent and reversible risk factor, which holds promise as a novel therapeutic target in ESRD. Interventional trials are needed to provide additional evidence that LVH regression improves survival before prevention and reversal of LVH can be definitively adopted as a therapeutic paradigm in ESRD.

Cardiac and renal effects of atrasentan in combination with enalapril and paricalcitol in uremic rats

BACKGROUND/AIMS

The search for new therapies providing cardiorenal protection in chronic kidney disease (CKD) has led to treatments that combine conventional renin-angiotensin-aldosterone-system inhibitors with other drugs that exhibit potential in disease management.

METHODS

In rats made uremic by renal ablation, we examined the effects of addition of the endothelin-A receptor antagonist atrasentan to a previously examined combination of enalapril (angiotensin converting enzyme inhibitor) and paricalcitol (vitamin D receptor activator) on cardiac and renal parameters. The effects of the individual and combined drugs were examined after a 3-month treatment.

RESULTS

A decrease in systolic blood pressure, serum creatinine and proteinuria, and improvement of renal histology in uremic rats were attributed to enalapril and/or paricalcitol treatment; atrasentan alone had no effect. In heart tissue, individual treatment with the drugs blunted the increase in cardiomyocyte size, and combined treatment additively decreased cardiomyocyte size to normal levels. Perivascular fibrosis was blunted in uremic control rats with atrasentan or enalapril treatment.

CONCLUSIONS

We found distinct cardiac and renal effects of atrasentan. Combination treatment with atrasentan, enalapril and paricalcitol provided positive effects on cardiac remodeling in uremic rats, whereas combination treatment did not offer further protective effects on blood pressure, proteinuria or renal histology.

Paricalcitol downregulates myocardial renin-angiotensin and fibroblast growth factor expression and attenuates cardiac hypertrophy in uremic rats

BACKGROUND

Vitamin D attenuates uremic cardiac hypertrophy, possibly by suppressing the myocardial renin-angiotensin system (RAS) and fibroblast growth factors (FGFs). We compared the suppression of cardiac hypertrophy and myocardial expression of RAS and FGF receptor genes offered by the vitamin D analog paricalcitol (Pc) or the angiotensin-converting enzyme inhibitor enalapril (E) in experimental uremia.

METHODS

Rats with 5/6 nephrectomy received Pc or E for 8 weeks. Renal function, systolic blood pressure, and cardiac hypertrophy were evaluated. Myocardial expression of RAS genes, brain natriuretic peptide (BNP), and FGF receptor-1 (FGFR-1) were determined using quantitative reverse-transcription (pRT)-PCR.

RESULTS

Blood pressure, proteinuria, and serum creatinine were significantly higher in untreated uremic animals. Hypertension was significantly reduced by E but only modestly by Pc; however, cardiac hypertrophy in the untreated group was similarly attenuated by Pc or E. Upregulation of myocardial expressions of renin, angiotensinogen, FGFR-1, and BNP in untreated uremic animals was reduced similarly by Pc and E, while the angiotensin II type 1 receptor was downregulated only by E.

CONCLUSIONS

Uremic cardiac hypertrophy is associated with activation of the myocardial RAS and the FGFR-1. Downregulation of these genes induced by Pc and E results in similar amelioration of left ventricular hypertrophy despite the different antihypertensive effects of these drugs.

Vitamin D supplementation and lipid profile: what does the best available evidence show?

Vitamin D supplements have increasingly been used for the treatment and prevention of osteoporosis. Historically, effects of the vitamin on the cardiovascular (CV) system have been proposed and demonstrated in the literature, including benefits on serum lipids. Although observational studies support an association between increased serum vitamin D levels and a favorable lipid profile, interventional studies have shown no effects. This review presents and analyzes all the related randomized controlled trials (RCTs) identified in the literature from 1987 to present. A systematic literature search was conducted via MEDLINE, Cochrane Library and EMBASE and, out of 19 relevant RCTs identified, only one reported benefits of vitamin D supplementation on lipid profile parameters, while the rest showed no effects or even adverse outcomes, which are highlighted by the only meta-analysis in the field. Attempts to explain the paradox of beneficial findings of observational studies versus discouraging results of interventional studies have been made and the most popular suggests that high serum vitamin D concentrations may not be the cause of good health but its outcome instead, as healthy people are more likely to stay outdoors longer and have better eating habits. For definitive answers to be given, large, well-designed RCTs need to be conducted that will take into account and adjust for dietary consumption as well as serum calcium and parathyroid hormone levels, both of which have been shown to be associated with the CV system. Until then, recommendations for vitamin D supplementation should not change.

Speckle tracking echocardiography detects uremic cardiomyopathy early and predicts cardiovascular mortality in ESRD

Cardiovascular mortality is high in ESRD, partly driven by sudden cardiac death and recurrent heart failure due to uremic cardiomyopathy. We investigated whether speckle-tracking echocardiography is superior to routine echocardiography in early detection of uremic cardiomyopathy in animal models and whether it predicts cardiovascular mortality in patients undergoing dialysis. Using speckle-tracking echocardiography in two rat models of uremic cardiomyopathy soon (4-6 weeks) after induction of kidney disease, we observed that global radial and circumferential strain parameters decreased significantly in both models compared with controls, whereas standard echocardiographic readouts, including fractional shortening and cardiac output, remained unchanged. Furthermore, strain parameters showed better correlations with histologic hallmarks of uremic cardiomyopathy. We then assessed echocardiographic and clinical characteristics in 171 dialysis patients. During the 2.5-year follow-up period, ejection fraction and various strain parameters were significant risk factors for cardiovascular mortality (primary end point) in a multivariate Cox model (ejection fraction hazard ratio [HR], 0.97 [95% confidence interval (95% CI), 0.95 to 0.99; P=0.012]; peak global longitudinal strain HR, 1.17 [95% CI, 1.07 to 1.28; P<0.001]; peak systolic and late diastolic longitudinal strain rates HRs, 4.7 [95% CI, 1.23 to 17.64; P=0.023] and 0.25 [95% CI, 0.08 to 0.79; P=0.02], respectively). Multivariate Cox regression analysis revealed circumferential early diastolic strain rate, among others, as an independent risk factor for all-cause mortality (secondary end point; HR, 0.43; 95% CI, 0.25 to 0.74; P=0.002). Together, these data support speckle tracking as a postprocessing echocardiographic technique to detect uremic cardiomyopathy and predict cardiovascular mortality in ESRD.

Differential influence of vitamin D analogs on left ventricular mass index in maintenance hemodialysis patients

PURPOSE

Secondary hyperparathyroidism (SHPT) is a common feature in maintenance hemodialysis (MHD) patients. Inadequate treatment of SHPT has been associated with cardiovascular complications, and vitamin D therapy might influence the development of cardiovascular diseases. In the present study, we aimed to evaluate the effects of intravenous paricalcitol and calcitriol treatments on left ventricular mass index changes in MHD patients.

METHODS

We conducted an observational study with a 12-month follow-up duration to compare the outcomes of intravenous paricalcitol and calcitriol treatments in MHD patients. Eighty patients with moderate to severe SHPT were enrolled in the study. All the patients had normalized total serum Ca concentration <10.5 mg/dL, serum calcium-phosphorus product (Ca × P) <75, and parathyroid hormone level (PTH) level ≥300 pg/mL at the begining of the follow-up period.

RESULTS

The patients were divided into a paricalcitol group (n = 40) and a calcitriol group (n = 40). The demographic, clinical, and biochemical characteristics of the patients were similar at baseline. We observed significantly superior control of SHPT; lesser frequency of hypercalcemia and hyperphosphatemia, and Ca × P level elevations; and interruption of vitamin D treatment in the paricalcitol group. Moreover, we found no significant change in left ventricular mass index in the paricalcitol group, but found a significantly increased left ventricular mass index in the calcitriol group during the follow-up period (from 136.6 ± 35.2 g/m2 to 132.9 ± 40.4 g/m2 vs. from 137.2 ± 30.1 g/m2 to 149.4 ± 31.0 g/m2; p<0.044).

CONCLUSION

We observed that, compared with calcitriol therapy, paricalcitol therapy reduced the PTH concentrations more effectively without causing hypercalcemia and hyperphosphatemia and might have a substantial beneficial effect on the development of left ventricular hypertrophy.

Vitamin D and the cardiovascular system: an overview of the recent literature

Since the discovery that the enzyme catalyzing the synthesis of the most active natural vitamin D metabolite(calcitriol) and the vitamin D-specific receptor (VDR)were expressed in a wide range of tissues and organs, not only involved in the mineral metabolism (MM), there has been increasing interest on the putative ‘non classical’ roles of vitamin D metabolites, particularly on their possible effects on the cardiovascular (CV) system. These hypothetical CV effects of vitamin D gained particular interesting the nephrology field, given the high prevalence of CV disease in patients affected by either acute or chronic kidney diseases. However, notwithstanding a huge amount of experimental data suggesting a possible protective role of vitamin D on the CV system, the conclusions of two recent meta-analyses from the Cochrane group and a recent statement from the Institute of Medicine, based on a complete revision of the available data, concluded that there is no clear evidence for a role of vitamin D other than that strictly associated with bone health. However, a continuous and increasing flow of new studies still continues to add information on this topic. In the present review, we have tried to critically address the data added on this topicin the last 2 years, considering separately the experimental,observational, and intervention studies that have appeared in PubMed in the last 2 years, discussing the data providing proof, pro or contra, the involvement of vitamin D in CV disease, both in the absence or presence of kidney function impairment.

Pediatric cardiomyopathies: causes, epidemiology, clinical course, preventive strategies and therapies

Pediatric cardiomyopathies, which are rare but serious disorders of the muscles of the heart, affect at least one in every 100,000 children in the USA. Approximately 40% of children with symptomatic cardiomyopathy undergo heart transplantation or die from cardiac complications within 2 years. However, a significant number of children suffering from cardiomyopathy are surviving into adulthood, making it an important chronic illness for both pediatric and adult clinicians to understand. The natural history, risk factors, prevalence and incidence of this pediatric condition were not fully understood before the 1990s. Questions regarding optimal diagnostic, prognostic and treatment methods remain. Children require long-term follow-up into adulthood in order to identify the factors associated with best clinical practice including diagnostic approaches, as well as optimal treatment approaches. In this article, we comprehensively review current research on various presentations of this disease, along with current knowledge about their causes, treatments and clinical outcomes.

Vitamin D and the heart

Vitamin D receptors (VDR) are found in cells throughout the cardiovascular system. A variety of experimental studies indicate that the liganded VDR may play an important role in controlling cardiac hypertrophy and fibrosis, regulating blood pressure, and suppressing the development of atherosclerosis. Some, but not all, observational studies in humans provide support for these experimental findings, raising the possibility that vitamin D or its analogs might prove useful therapeutically in the prevention or treatment of cardiovascular disease.

Vitamin D receptor activation, left ventricular hypertrophy and myocardial fibrosis

BACKGROUND

Left ventricular hypertrophy (LVH), a common complication in chronic kidney disease (CKD), is associated with high cardiovascular mortality. The aim of this experimental study was to analyze the effect of different vitamin D receptor activators (VDRAs) on both LVH and myocardial fibrosis in chronic renal failure (CRF).

METHODS

Male Wistar rats with CRF, carried out by 7/8 nephrectomy, were treated intraperitoneally with equivalent doses of VDRAs (calcitriol, paricalcitol and alfacalcidol, 5 days per week) during 4 weeks. A placebo group (CRF + vehicle) and a Sham group with normal renal function served as controls. Biochemical, morphological, functional and molecular parameters associated with LVH were evaluated, as well as cardiac fibrosis, collagen I, transforming growth factor β1 (TGFβ1) and matrix metalloproteinase-1 (MMP1) expression.

RESULTS

All VDRAs treatment prevented LVH, with values of cardiomyocyte size, LV wall and septum thickness and heart-body weight ratio similar to those observed in the Sham group. At molecular levels, all VDRAs attenuated atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) expression compared with CRF + vehicle. The phosphorylation of ERK1/2, a signal for activating growth, was stimulated in the CRF + vehicle group; VDRAs use prevented this activation. Paricalcitol was the only VDRA used that maintained in the normal range all parameters associated with myocardial fibrosis (total collagen, collagen I, TGFβ1 and MMP1).

CONCLUSIONS

Our findings demonstrated that the three VDRAs used induced similar changes in bone metabolic parameters and LVH. In addition, paricalcitol was the only VDRA which showed a relevant beneficial effect in the reduction of myocardial fibrosis, a key factor in the myocardial dysfunction in CKD patients.

Vitamin D receptor activation and cardiovascular disease

Vitamin D has been recently associated with several renal, cardiovascular and inflammatory diseases, beyond mineral metabolism and bone health. This is due in part to widespread expression of vitamin D receptor (VDR) on tissues and cells such as heart, kidney, immune cells, brain and muscle. In chronic kidney disease (CKD) and other chronic disorders, vitamin D deficiency [serum 25(OH)D <20 ng/mL] is very common and is associated with adverse outcomes. Paricalcitol, a selective activator of VDR, has demonstrated in several experimental and clinical studies of diabetic and non-diabetic CKD a favourable profile compared to other VDR activators, alone or as add-on to standard therapy. These beneficial effects are mediated by different actions such as reduction of oxidative stress, inflammation, downregulation of cardiac and renal renin expression, downregulation of calcifying genes and direct vascular protective effects. Furthermore, paricalcitol beneficial effects may be independent of baseline serum parathyroid hormone (PTH), calcium and phosphate levels. These benefits should be confirmed in large and well-designed ongoing clinical trials.

Liganded vitamin D receptor displays anti-hypertrophic activity in the murine heart

Vitamin D and its analogs have been suggested to have palliative effects in the cardiovascular system. We have examined the effects of co-administration of the vitamin D receptor agonist, paricalcitol, on the hypertension, cardiac hypertrophy and interstitial fibrosis produced by chronic angiotensin II (AII) infusion. Administration of AII (800ng/kg/min) over a 14-day period resulted in increased blood pressure, myocyte hypertrophy, activation of the hypertrophic fetal gene program (atrial natriuretic peptide, B-type natriuretic peptide and alpha skeletal actin gene expression), increased expression of the pro-hypertrophic modulatory calcineurin inhibitor protein 1 (MCIP 1), and increased fibrosis with augmented procollagen 1 and 3 gene expression. In each case co-administration of paricalcitol (300ng/kg intraperitoneally every 48h) at least partially reversed the AII-dependent effect. These studies demonstrate that the liganded vitamin D receptor possesses potent anti-hypertrophic activity in this non-renin-dependent model of cardiac hypertrophy. The anti-hypertrophic activity appears to be at least partially intrinsic to the cardiac myocyte and may involve suppression of the MCIP 1 protein. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

Vitamin D and inflammation

Recent studies have provided evidence for an important role of vitamin D deficiency in the pathogenesis of cardiovascular disease (CVD) in the general population, and of an association with markers of inflammation. Vitamin D deficiency, defined by low serum levels of 25-hydroxyvitamin D, is especially prevalent in patients with chronic kidney disease (CKD). Chronic low-grade inflammation is a hallmark of CKD and has been disclosed as one important factor contributing to the progression of CKD and a high cardiovascular comorbidity. This review highlights clinical and experimental studies that could potentially explain a link between vitamin D and inflammation. Whether correction of vitamin D deficiency has beneficial effects on markers of inflammation and cardiovascular outcome should be investigated by controlled clinical trials.

The influence of selective vitamin D receptor activator paricalcitol on cardiovascular system and cardiorenal protection

The ubiquitous distribution of vitamin D receptors in the human body is responsible for the pleiotropic effects of vitamin D-receptor activation. We discuss the possible beneficial effects of a selective activator of vitamin D receptor, paricalcitol, on the cardiovascular system in chronic heart failure patients and chronic kidney patients, in light of new trials. Paricalcitol should provide additional clinical benefits over the standard treatment for chronic kidney and heart failure, especially in cases of cardiorenal syndrome.

Protective cardiovascular and renal actions of vitamin D and estrogen

Both basic science and clinical studies support the concept that vitamin D deficiency is involved in the pathogenesis of cardiovascular and renal diseases through its association with diabetes, obesity, and hypertension. Understanding the underlying mechanisms may provide a rationale for advocating adequate intake of vitamin D and calcium in all populations, thereby preventing many chronic diseases. This review explores the effect of vitamin D deficiency in the development of cardiovascular and renal diseases, and the role of vitamin D supplementation on cardiovascular outcomes. In addition, it highlights the importance of vitamin D intake for the prevention of adverse long-term health consequences, and in ways to facilitate the management of cardiovascular disease. This is particularly true for African American and postmenopausal women, who are at added risk for cardiovascular disease. We suggest that the negative cardiovascular effects of low vitamin D in postmenopausal women could be improved by a combined treatment of vitamin D and sex steroids acting through endothelium-dependent and/or -independent mechanisms, resulting in the generation of nitric oxide and calcitonin gene-related peptide (CGRP).

Fibroblast growth factor 23 and left ventricular hypertrophy in children on dialysis

BACKGROUND

Elevated fibroblast growth factor 23 (FGF-23) concentrations associate with left ventricular hypertrophy (LVH) and adverse outcomes in adult patients with chronic kidney disease. We hypothesized that similar associations are present in pediatric patients on maintenance hemodialysis.

METHODS

In this retrospective study of 26 young patients on chronic hemodialysis, aged 6-21 years, cardiac structure and geometry were measured by echocardiography, and circulating levels of FGF-23 and calciotropic hormones were obtained.

RESULTS

FGF-23 levels were uniformly elevated in all patients from three- to 835-fold above the upper limit of normal. The average LV mass index (LVMI) was 43 ± 13 g/m(2.7) and reflected LVH in 55 % of patients. Log-transformed FGF-23 concentrations correlated with LVMI (p = 0.03) and were independently associated with the interventricular septal thickness Z-score (p < 0.001). Concentric LVH was associated with the highest FGF-23 concentrations and the highest LVMI measurements (p < 0.001). Each 1 standard deviation increase in log-transformed FGF-23 levels was associated with a 17 % increase in LVMI.

CONCLUSIONS

FGF-23 levels are strongly associated with increased LVMI and with prevalent LVH in pediatric hemodialysis patients. Our cross-sectional findings provide observational evidence supporting the hypothesis linking FGF-23 to cardiac hypertrophy in patients with chronic kidney disease.

Randomized controlled trial of cholecalciferol supplementation in chronic kidney disease patients with hypovitaminosis D

BACKGROUND

Hypovitaminosis D is common in chronic kidney disease (CKD). Effects of 25-hydroxyvitamin D replenishment in CKD are not well described.

METHODS

An 8-week randomized, placebo-controlled, double-blind parallel intervention study was conducted in haemodialysis (HD) and non-HD CKD patients. Treatment consisted of 40,000 IU of cholecalciferol orally per week. Plasma 25-hydroxyvitamin D (25-OHD), plasma 1,25-dihydroxyvitamin D (1,25-diOHD), plasma parathyroid hormone (PTH), serum phosphate, ionized serum calcium and serum fibroblast growth factor 23 (FGF-23) were analysed. We also investigated biomarkers related to cardiovascular disease (plasma D-dimer, plasma fibrinogen, plasma von Willebrand factor antigen and activity, plasma interleukin 6, plasma C-reactive protein, blood pressure, aortic augmentation index, aortic pulse wave velocity and 24-h urinary protein loss). Objective and subjective health variables were assessed (muscle function tests, visual analogue scores and Health Assessment Questionnaire).

RESULTS

Fifty-two CKD patients with 25-OHD <50 nmol/L at screening were included. Cholecalciferol supplementation led to a significant increase to a median of 155 nmol/L 25-OHD (interquartile range 137-173 nmol/L) in treated patients (n = 25, P < 0.001). In non-HD patients, we saw a significant increase in 1,25-diOHD (n = 13, P < 0.01) and a lowering of PTH (n = 13, P < 0.001). This was not observed in HD patients. Cholecalciferol supplementation caused a significant increase in serum calcium and FGF-23.

CONCLUSIONS

25-OHD replenishment was effectively obtained with the employed cholecalciferol dosing. In non-HD patients, it had favourable effects on 1,25-diOHD and PTH. Vitamin D-supplemented patients must be monitored for hypercalcaemia. The present study could not identify significant pleiotropic effects of 25-OHD replenishment.

[Vitamin D hormone system and diabetes mellitus: lessons from selective activators of vitamin D receptor and diabetes mellitus]

The vitamin D hormone system has significant skeletal and extra-skeletal effects. Vitamin D receptor occurs in different tissues, and several cells other than renal cells are able to locally produce active vitamin D, which is responsible for transcriptional control of hundreds of genes related to its pleiotropic effects. There is increasing evidence relating vitamin D to development and course of type 1 and 2 diabetes mellitus. Specifically, influence of vitamin D on the renin-angiotensin-aldosterone system, inflammatory response, and urinary albumin excretion could explain the relevant impact of vitamin D status on diabetic nephropathy. Selective vitamin D receptor activators are molecules able to reproduce agonistic or antagonistic effects of active vitamin D depending on the tissue or even on the cell type. Specifically, paricalcitol has a beneficial profile because of its potency to reduce parathyroid hormone, with lower effects on serum calcium or phosphate levels. Moreover, in patients with diabetes and renal disease, paricalcitol decreases microalbuminuria, hospitalization rates, and cardiovascular mortality. Therefore, these molecules represent an attractive new option to improve prognosis of renal disease in patients with diabetes.

VS-105: a novel vitamin D receptor modulator with cardiovascular protective effects

BACKGROUND AND PURPOSE

Vitamin D receptor (VDR) modulators (VDRMs) such as calcitriol, paricalcitol and doxercalciferol are commonly used to manage hyperparathyroidism secondary to chronic kidney disease (CKD). CKD patients experience extremely high risks of cardiovascular morbidity and mortality. Clinical observations show that VDRM therapy may be associated with cardio-renal protective and survival benefits for CKD patients. However, hypercalcaemia remains a serious side effect for current VDRMs, which leads to the need for frequent dose titration and serum Ca (calcium) monitoring. Significant clinical benefits can be derived from a VDRM with cardiovascular protective effects without the hypercalcaemic liability.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were 5/6 nephrectomized and 6 weeks later, after they had established uraemia, elevated parathyroid hormone levels, endothelial dysfunction and left ventricular hypertrophy, the rats were treated with VS-105, a novel VDRM. The effects of VS-105 were also tested in cultured HL-60 cells.

KEY RESULTS

VS-105 induced HL-60 cell differentiation with an EC₅₀ value at 11.8 nM. Treatment (i.p., 3× a week over a period of 2 weeks) of the 5/6 nephrectomized rats by VS-105 (0.004-0.64 µg·kg⁻¹) effectively suppressed serum parathyroid hormone without raising serum Ca or phosphate levels. Furthermore, 2 weeks of treatment with VS-105 improved endothelium-dependent aortic relaxation and attenuated left ventricular abnormalities in a dose range that did not affect serum Ca levels. Similar results were obtained when VS-105 was administered i.p. or by oral gavage.

CONCLUSIONS AND IMPLICATIONS

VS-105 exhibits an overall therapeutic product profile that supports expanded use in CKD to realize the cardiovascular protective effects of VDR activation.

Cardiorenal syndrome and vitamin D receptor activation in chronic kidney disease

Cardiorenal syndrome (CRS) refers to a constellation of conditions whereby heart and kidney diseases are pathophysiologically connected. For clinical purposes, it would be more appropriate to emphasize the pathophysiological pathways to classify CRS into: (1) hemodynamic, (2) atherosclerotic, (3) uremic, (4) neurohumoral, (5) anemic–hematologic, (6) inflammatory–oxidative, (7) vitamin D receptor (VDR) and/or FGF23-, and (8) multifactorial CRS. In recent years, there have been a preponderance data indicating that vitamin D and VDR play an important role in the combination of renal and cardiac diseases. This review focuses on some important findings about VDR activation and its role in CRS, which exists frequently in chronic kidney disease patients and is a main cause of morbidity and mortality. Pathophysiological pathways related to suboptimal or defective VDR activation may play a role in causing or aggravating CRS. VDR activation using newer agents including vitamin D mimetics (such as paricalcitol and maxacalcitol) are promising agents, which may be related to their selectivity in activating VDR by means of attracting different post-D-complex cofactors. Some, but not all, studies have confirmed the survival advantages of D-mimetics as compared to non-selective VDR activators. Higher doses of D-mimetic per unit of parathyroid hormone (paricalcitol to parathyroid hormone ratio) is associated with greater survival, and the survival advantages of African American dialysis patients could be explained by higher doses of paricalcitol (>10 μg/week). More studies are needed to verify these data and to explore additional avenues for CRS management via modulating VDR pathway.

Vitamin D, disease and therapeutic opportunities

The discovery of the vitamin D endocrine system and a receptor for the hormonal form, 1α,25-dihydroxyvitamin D(3), has brought a new understanding of the relationship between vitamin D and metabolic bone diseases, and has also established the functions of vitamin D beyond the skeleton. This has ushered in many investigations into the possible roles of vitamin D in autoimmune diseases, cardiovascular disorders, infectious diseases, cancers and granuloma-forming diseases. This article presents an evaluation of the possible roles of vitamin D in these diseases. The potential of vitamin D-based therapies in treating diseases for which the evidence is most compelling is also discussed.

Vitamin D receptor agonist doxercalciferol modulates dietary fat-induced renal disease and renal lipid metabolism

Diet-induced obesity (DIO) and insulin resistance in mice are associated with proteinuria, renal mesangial expansion, accumulation of extracellular matrix proteins, and activation of oxidative stress, proinflammatory cytokines, profibrotic growth factors, and the sterol regulatory element binding proteins, SREBP-1 and SREBP-2, that mediate increases in fatty acid and cholesterol synthesis. The purpose of the present study was to determine whether treatment of DIO mice with the vitamin D receptor (VDR) agonist doxercalciferol (1α-hydroxyvitamin D2) prevents renal disease. Our results indicate that treatment of DIO mice with the VDR agonist decreases proteinuria, podocyte injury, mesangial expansion, and extracellular matrix protein accumulation. The VDR agonist also decreases macrophage infiltration, oxidative stress, proinflammatory cytokines, and profibrotic growth factors. Furthermore, the VDR agonist also prevents the activation of the renin-angiotensin-aldosterone system including the angiotensin II type 1 receptor and the mineralocorticoid receptor. An additional novel finding of our study is that activation of VDR results in decreased accumulation of neutral lipids (triglycerides and cholesterol) and expression of adipophilin in the kidney by decreasing SREBP-1 and SREBP-2 expression and target enzymes that mediate fatty acid and cholesterol synthesis and increasing expression of the farnesoid X receptor. This study therefore demonstrates multiple novel effects of VDR activation in the kidney which prevent renal manifestations of DIO in the kidney.

Diabetic microvascular complications: possible targets for improved macrovascular outcomes

The results of recent outcome trials challenge hypotheses that tight control of both glycohemoglobin and blood pressure diminishes macrovascular events and survival among type 2 diabetic patients. Relevant questions exist regarding the adequacy of glycohemoglobin alone as a measure of diabetes control. Are we ignoring mechanisms of vasculotoxicity (profibrosis, altered angiogenesis, hypertrophy, hyperplasia, and endothelial injury) inherent in current antihyperglycemic medications? Is the polypharmacy for lowering cholesterol, triglyceride, glucose, and systolic blood pressure producing drug interactions that are too complex to be clinically identified? We review angiotensin-aldosterone mechanisms of tissue injury that magnify microvascular damage caused by hyperglycemia and hypertension. Many studies describe interruption of these mechanisms, without hemodynamic consequence, in the preservation of function in type 1 diabetes. Possible interactions between the renin-angiotensin-aldosterone system and physiologic glycemic control (through pulsatile insulin release) suggest opportunities for further clinical investigation.