Mineral metabolism abnormalities and vitamin D receptor activation in cardiorenal syndromes

Cardiorenal Syndrome in the Hospital

The cardiorenal syndrome refers to a group of complex, bidirectional pathophysiological pathways involving dysfunction in both the heart and kidney. Upward of 60% of patients admitted for acute decompensated heart failure have CKD, as defined by an eGFR of <60 ml/min per 1.73 m2. CKD, in turn, is one of the strongest risk factors for mortality and cardiovascular events in acute decompensated heart failure. Although not well understood, the mechanisms in the cardiorenal syndrome include venous congestion, arterial underfilling, neurohormonal activation, inflammation, and endothelial dysfunction. Arterial underfilling may lead to activation of the renin-angiotensin-aldosterone system and sympathetic nervous system, leading to sodium reabsorption and vasoconstriction. Venous congestion likely also mediates and perpetuates these maladaptive pathways. To rule out intrinsic kidney disease that is distinct from the cardiorenal syndrome, one should obtain a careful history, review longitudinal eGFR trends, assess albuminuria and proteinuria, and review the urine sediment and kidney imaging. The hallmark of the cardiorenal syndrome is intense sodium avidity and diuretic resistance, often requiring a combination of diuretics with varying pharmacological targets, and monitoring of urinary response to guide escalations in therapy. Invasive means of decongestion may be required including ultrafiltration or kidney RRT such as peritoneal dialysis, which is often better tolerated from a hemodynamic perspective than intermittent hemodialysis. Strategies for increasing forward perfusion in states of low cardiac output and cardiogenic shock may include afterload reduction and inotropes and, in the most severe cases, mechanical circulatory support devices, many of which have kidney-specific considerations.

Non-classical Vitamin D Actions for Renal Protection

Chronic Kidney Disease (CKD), a disorder that affects 11% of the world's population, is characterized by an acceleration in skeletal, immune, renal, and cardiovascular aging that increases the risk of cardiovascular mortality by 10- to 20-fold, compared to that in individuals with normal renal function. For more than two decades, the progressive impairment in renal capacity to maintain normal circulating levels of the hormonal form of vitamin D (1,25-dihydroxyvitamin D or calcitriol) was considered the main contributor to the reduced survival of CKD patients. Accordingly, calcitriol administration was the treatment of choice to attenuate the progression of secondary hyperparathyroidism (SHPT) and its adverse impact on bone health and vascular calcification. The development of calcitriol analogs, designed to mitigate the resistance to calcitriol suppression of PTH associated with CKD progression, demonstrated survival benefits unrelated to the control of SHPT or skeletal health. The exhaustive search for the pathophysiology behind survival benefits associated with active vitamin D analogs has identified novel anti-inflammatory, anti-hypertensive, anti-aging actions of the vitamin D endocrine system. A major paradigm shift regarding the use of calcitriol or active vitamin D analogs to improve survival in CKD patients emerged upon demonstration of a high prevalence of vitamin D (not calcitriol) deficiency at all stages of CKD and, more significantly, that maintaining serum levels of the calcitriol precursor, 25(OH)vitamin D, above 23 ng/ml delayed CKD progression. The cause of vitamin D deficiency in CKD, however, is unclear since vitamin D bioactivation to 25(OH)D occurs mostly at the liver. Importantly, neither calcitriol nor its analogs can correct vitamin D deficiency. The goals of this chapter are to present our current understanding of the pathogenesis of vitamin D deficiency in CKD and of the causal link between defective vitamin D bioactivation to calcitriol and the onset of molecular pathways that promote CKD progression independently of the degree of SHPT. An understanding of these mechanisms will highlight the need for identification of novel sensitive biomarkers to assess the efficacy of interventions with vitamin D and/or calcitriol(analogs) to ameliorate CKD progression in a PTH-independent manner.

The Kidney-Heart Connection in Obesity

There is a strong relationship between the kidney and the heart, where if one of these organs fails, so does the other, in the so-called cardiorenal syndrome (CRS). Besides, there are also interactions with the rest of the body leading to a metabolic state that establishes a feedback loop that is perpetuated. The CRS is characterized by hemodynamic changes, activation of neuro-humoral systems, natriuretic peptides, and changes in mineral metabolism. In this scenario, the kidney and heart, connected by a dysfunctional endothelium, inevitably fail. In obesity, this syndrome is exacerbated due to the complications of adipose tissue dysfunction, in the so-called cardiorenal metabolic syndrome (CRMetS). Obesity promotes adipose tissue dysfunction because it exceeds lipid storage capacity and leads to a lipotoxic state, characterized by inflammation, hypertension, insulin resistance and dyslipidemia, oxidative stress, and hyperuricemia, among others, that affect different organs other than the adipose tissue. In addition, the pro-inflammatory gut microbiota present in obese patients releases uremic toxins, contributing to oxidative stress and inflammation, perpetuating and accelerating the progression of this pathology. In this article, we describe the contribution of obesity, the factors and mechanisms implicated in the development of the CRMetS. Despite the great knowledge about the CRS, more research is needed to characterize the CRMetS given the global obesity epidemic.

Neurohormonal, Endocrine, and Immune Dysregulation and Inflammation in Cardiorenal Syndrome

“Organ crosstalk” is the complex physiological communication between different body systems, and it is necessary for the optimal equilibrium and functioning of the organism. In particular, heart and kidney function is tightly connected, and interplay between these two organs occurs through a vast array of dynamic and bidirectional mechanisms. The term cardiorenal syndrome (CRS) indicates an interaction between the heart and kidneys in acute and chronic disease settings. In all types of CRS, multiple pathophysiological processes are implicated in the initiation and progression of organ injury. In addition to hemodynamic parameters, endothelial injury, immunological imbalance, cell death, inflammatory cascades, oxidative stress, neutrophil migration, leukocyte trafficking, caspase-mediated apoptosis, extracellular vesicles, small noncoding RNAs, and epigenetics play pivotal roles in the development of CRS. In this review, we will focus on neurohormonal, endocrine, and immune dysregulation and inflammation as mechanisms involved in the pathogenesis of CRS.

Working Toward an Improved Understanding of Chronic Cardiorenal Syndrome Type 4

Chronic diseases of the heart and of the kidneys commonly coexist in individuals. Certainly combined and persistent heart and kidney failure can arise from a common pathologic insult, for example, as a consequence of poorly controlled hypertension or of severe diffuse arterial disease. However, strong evidence is emerging to suggest that cross talk exists between the heart and the kidney. Independent processes are set in motion when kidney function is chronically diminished, and these processes can have distinct adverse effects on the heart. The complex chronic heart condition that results from chronic kidney disease (CKD) has been termed cardiorenal syndrome type 4. This review will include an updated description of the cardiac morphology in patients who have CKD, an overview of the most likely CKD-sourced culprits for these cardiac changes, and the potential therapeutic strategies to limit cardiac complications in patients who have CKD.

Cardiorenal Syndrome and the Role of the Bone-Mineral Axis and Anemia

The association between chronic kidney disease (CKD) and cardiovascular disease (CVD) is well established, and there is mounting evidence of interorgan cross talk that may accelerate pathologic processes and the progression of organ dysfunction in both systems. This process, termed cardiorenal syndrome (CRS) by the Acute Dialysis Quality Initiative, is considered a major health problem: patients with CKD and CVD are at much higher risk of mortality than patients with either condition alone. To date, the majority of CRS research has focused on neurohormonal mechanisms and hemodynamic alterations. However, mounting evidence suggests that abnormalities in the normal pathophysiology of the bone-mineral axis, iron, and erythropoietin play a role in accelerating CKD and CVD. The goal of this article is to review the role and interrelated effects of the bone-mineral axis and anemia in the pathogenesis of chronic CRS.

Vitamin D metabolites and fibroblast growth factor-23 in patients with left ventricular assist device implants: association with stroke and mortality risk

PURPOSE

Stroke and mortality risk in patients with left ventricular assist device (LVAD) implants continue to be high. Whether nonclassical cardiovascular risk markers such as vitamin D metabolites and fibroblast growth factor (FGF)-23 contribute to this risk remains to be studied, and this was the objective of our work.

METHODS

In 154 LVAD patients (91 HeartWare and 63 HeartMate II implants), we measured circulating 25-hydroxyvitamin D (25OHD), 1,25-dihydroxyvitamin D3 (1,25[OH]2D3), parathyroid hormone (PTH) and FGF-23 shortly before LVAD implantation and investigated their association with stroke and mortality risk during 1-year follow-up.

RESULTS

Of the study cohort, 34.4 and 92.2%, respectively, had deficient 25OHD (<25 nmol/l) and 1,25(OH)2D3 (<41 pmol/l) values, whereas 42.6 and 98.7%, respectively, had elevated PTH levels (>6.7 pmol/l) and FGF-23 values above the reference range (100 RU/ml). One-year freedom from stroke was 80.9 %, and 1-year survival was 64.3%. The multivariable-adjusted hazard ratio of stroke was 2.44 (95% CI: 1.09-5.45; P = 0.03) for the subgroup of 25OHD levels <25 nmol/l (reference group: 25OHD levels ≥25 nmol/l). The multivariable-adjusted hazard ratio of 1-year mortality was 2.78 (95% CI: 1.52-5.09; P = 0.001) for patients with 25OHD levels <25 nmol/l compared with patients with 25OHD levels ≥25 nmol/l. PTH, FGF-23 and 1,25(OH)2D3 were not associated with stroke or mortality risk.

CONCLUSIONS

In LVAD patients, deficient 25OHD levels are independently associated with high stroke and mortality risk. If confirmed in randomized controlled trials, preoperative correction of deficient vitamin D status could be a promising measure to reduce stroke and mortality risk in LVAD patients.

Effect of VDRA on survival in incident hemodialysis patients: results of the FARO-2 observational study

BACKGROUND

Mortality rate among patients with stage five chronic kidney disease (CKD) maintained on hemodialysis (HD) is high. Although evidence suggests that use of Vitamin D Receptor Activators (VDRA) in CKD patients increases survival, few studies have examined the effect of VDRA in incident HD patients. The FARO-2 study evaluated the clinical outcome of VDRA therapy on mortality in incident HD patients.

METHODS

FARO-2 was a longitudinal epidemiological study performed on 568 incident HD patients followed prospectively from 26 dialysis centers over a 3-year period. Data were collected every 6 months using a questionnaire, obtaining clinical, biochemical and therapeutic parameters. Kaplan-Meier curves and Cox proportional hazard regression models were used to determine cumulative probability of time-to-death and adjusted hazard ratios.

RESULTS

568 patients (68% male) with an average age of 65.5 years were followed up. Mean dialysis duration at study entry was 3 months. VDRA use increased from 46% at 6 months to 54.7% at 36 months of follow-up (p = 0.08). No difference was observed in the presence of comorbid diseases at baseline in patients with and without VDRA therapy. Cumulative probability of survival at 24 months was 74.5% (95% CI: 70.2-78.3). Patients receiving VDRA therapy showed a significant increase in survival at 24 months (80.7%; 95% CI: 75.7-84.8) compared to those without (63.3%; 95% CI: 54.8-70.7, p <0.01). The presence of vascular disease, decreased hemoglobin, increased P and lack of VDRA treatment were significantly associated with an increased risk of mortality. Lack of VDRA treatment still remained significant as a predictor of mortality after adjusting for levels of PTH, P and Ca (HR = 2.16, 95% CI: 1.09-4.30, p = 0.03).

CONCLUSIONS

Findings from FARO-2 indicate that in incident HD patients VDRA therapy was associated with increased survival.

Achievement of NKF/K-DOQI recommended target values for bone and mineral metabolism in incident hemodialysis patients: results of the FARO-2 cohort

BACKGROUND

Mineral Bone Disorders (MBD) is prevalent in hemodialysis (HD) patients and associated with increased cardiovascular mortality. The FARO-2 study evaluated the achievement of the NKF/K-DOQI guidelines on recommended target values for serum calcium (Ca), phosphorous (P) and intact parathyroid hormone (PTH) levels on survival in incident HD patients.

METHODS

Data were collected by questionnaire from 568 incident HD patients followed prospectively over a 3-year period from 26 Italian dialysis units. The cumulative probability of time-to-death for CKD-MBD treatment characteristics was determined by the Kaplan-Meier curves.

RESULTS

Serum PTH levels (median values at 6 months vs. 36 months; 225 vs. 254 pg/ml), Ca (8.8 vs. 8.9 g/dl) and P (5.1 vs. 4.8 mg/dl) were not significantly different at 6 months versus follow-up. The majority of incident HD patients (60-70%) who were followed up for 36 months did not achieve the NKF/K-DOQI recommended target values. Survival rates were higher in patients on target for three parameters versus patients off target (survival at 24 months: at target 95.7% (95% CI: 84.0-98.9) versus not on target 71.1% (95% CI: 66.3-75.4, p < 0.01)). The 30.1% of patients on target for three MBD parameters at least once during the follow-up period had better survival rates compared to those not reaching these targets (survival at 24 months: at least once 88.0% (95% CI: 81.9-92.1); 67.7% (95% CI: 61.9-72.8, p < 0.01)).

CONCLUSION

Our findings indicate that incident HD patients who achieved target levels (for three MBD parameters) for at least one visit have a lower risk of mortality.

Advances in pathogenesis and current therapeutic strategies for cardiorenal syndrome

Cardiorenal syndrome (CRS) is characterized as a syndrome involving both the cardiovascular system and kidneys. Due to its complexity and high mortality, it has becoming a significant burden and a universal clinical challenge to society worldwide. The mechanisms underlying CRS are potentially multifactorial, including hemodynamic alterations, neurohormonal activation, inflammation, oxidative stress, iron disorders, anemia, and mineral metabolic derangements. Despite the understanding and awareness of CRS gaining attention, appropriate approaches to manage CRS remain deficient. Loop diuretic and thiazides, inhibition of the renin-angiotensin system, vitamin D receptor activation and dopamine and natriuretic peptides could potentially be helpful to improve the prognosis of CRS. Ultrafiltration might be an alternative therapeutic strategy for the loss of liquid. However, adenosine receptor antagonists do not appear to be superior to furosemide in CRS treatment. novel therapeutic approaches should be explored.

Management of cardiorenal metabolic syndrome in diabetes mellitus: a phytotherapeutic perspective

Cardiorenal syndrome (CRS) is a complex disease in which the heart and kidney are simultaneously affected and their deleterious declining functions are reinforced in a feedback cycle, with an accelerated progression. Although the coexistence of kidney and heart failure in the same individual carries an extremely bad prognosis, the exact cause of deterioration and the pathophysiological mechanisms underlying the initiation and maintenance of the interaction are complex, multifactorial in nature, and poorly understood. Current therapy includes diuretics, natriuretic hormones, aquaretics (arginine vasopressin antagonists), vasodilators, and inotropes. However, large numbers of patients still develop intractable disease. Moreover, the development of resistance to many standard therapies, such as diuretics and inotropes, has led to an increasing movement toward utilization and development of novel therapies. Herbal and traditional natural medicines may complement or provide an alternative to prevent or delay the progression of CRS. This review provides an analysis of the possible mechanisms and the therapeutic potential of phytotherapeutic medicines for the amelioration of the progression of CRS.

The puzzle of kidney dysfunction in heart failure: an introduction

Heart failure and kidney disease often coexist, and each of the two conditions may lead to progression of the other. Kidney dysfunction is an independent prognostic factor in patients with either acute or chronic heart failure. Worsening renal function may be related with poorer outcomes as well. Multiple mechanisms are involved in the cardio-renal interaction, including hemodynamic abnormalities, neurohormonal and inflammatory activation, oxidative stress, anemia, and abnormalities in mineral and vitamin D metabolism. Serum creatinine has limitations for the assessment of kidney function in patients with heart failure as its short-term changes are dependent on hemodynamic changes and fluid status. New biomarkers of glomerular and tubular function might allow an earlier and more accurate detection of worsening renal function.

Cardio-renal cachexia syndromes (CRCS): pathophysiological foundations of a vicious pathological circle

Cardio-renal syndromes (CRS) are defined as disorders of the heart and kidney whereby acute or chronic dysfunction in one organ may induce acute or chronic dysfunction of the other. CRS have been classified into five categories, where types 2 and 4 represent respectively chronic cardio-renal and chronic reno-cardiac syndromes. In these conditions, the chronic disorder of either the heart or kidney has been shown to induce some degree of cachexia. At the same time, cachexia has been proposed as a possible mechanism contributing to the worsening of such pathological organ cross talk. Common pathogenetic mechanisms underlie body wasting in cachectic states of different chronic heart and kidney diseases. In these circumstances, a vicious circle could arise, in which cachexia associated with either heart failure or chronic kidney disease may contribute to further damage of the other organ. In chronic CRS, activation of the immune and neuroendocrine systems contributes to the genesis of cachexia, which in turn can negatively affect the heart and kidney function. In patients with cardiac sustained activation of the immune and neuroendocrine systems and oxidative stress, renal vascular resistance can increase and therefore impair renal perfusion, leading to worsening kidney function. Similarly, in renal cachexia, increased levels of pro-inflammatory cytokines can cause progressive left ventricular systolic dysfunction, myocardial cell death, endothelial dysfunction and increased myocardial fibrosis, with consequent impairment of the chronic reno-cardiac syndrome type 4. Thus, we speculate that the occurrence of different types of chronic CRS could represent a fundamental step in the genesis of cachexia, being renal and cardiac dysfunction closely related to the occurrence of systemic disorders leading to a final common pathway. Therefore, the heart and kidney and cachexia represent a triad causing a vicious circle that increases mortality and morbidity: In such circumstances, we may plausibly talk about cardio-renal cachexia syndrome. Complex interrelations may explain the transition from CRS to cachexia and from cachexia to CRS. Identification of the exact mechanisms occurring in these conditions could potentially help in preventing and treating this deadly combination.