Role of secondary hyperparathyroidism in the genesis of hypertriglyceridemia and VLDL receptor deficiency in chronic renal failure

The vicious circle of chronic kidney disease and hypertriglyceridemia: What is first, the hen or the egg?

Chronic kidney disease (CKD) is documented to cause alterations in lipid metabolism, and this was considered a potent driver of increased cardiovascular risk. Among the diverse alteration of lipid traits in CKD, research endeavours have predominantly concentrated on low-density lipoproteins (LDL) in view of the potent pro-atherogenic role of these lipoprotein particles and the demonstration of protective cardiovascular effect of reducing LDL. However, few studies have focused on the metabolism of triglyceride-rich lipoproteins and even fewer on their role in causing kidney damage. Therefore, the comprehensive description of the impact of hypertriglyceridemia (HTG) in CKD pathophysiology remains largely undetermined. This reflects the difficulty of disentangling the independent role of triglycerides (TG) in the complex, bidirectional relationship between TG and kidney disease. Abnormal neutral lipid accumulation in the intrarenal vasculature and renal cells eventually due to HTG may also promote glomerular injury, throughout mechanisms including oxidative stress, mitochondrial dysfunction and proinflammatory responses. While epidemiological and experimental evidence suggests a potential role of TG in kidney damage, the causal mechanisms and their clinical relevance remain unclear, representing a significant area for future investigation. This review aims to highlight the intricate interplay between TG metabolism and kidney disease, shedding light on the mechanisms through which HTG may influence kidney functionality.

Reverse epidemiology for lipid disorders in hemodialysis-dependent patients: Role of dilutional hypolipidemia

Introduction:

Atherosclerotic cardiovascular disease is a major cause of mortality and morbidity in dialysis patients. Compared to general population, dialysis patients have lower lipid levels and higher vascular events. This paradox is popularly known as reverse epidemiology. Present study is an attempt to understand reasons for low lipids in dialysis patients.

Subjects and Methods:

This was a prospective observational multicentric study involving three stages across six dialysis units with Care Hospitals, Hyderabad. Maintenance hemodialysis patients were studied with fasting lipid profiles [TC, LDL-c, HDL-c, and TG], pre- and post-dialysis blood lipids and effluent water lipid profiles. Other parameters studied were use of statins, interdialytic weight gain, and ultrafiltration. All patients had uniform dialysis protocols regarding filter used and dialysis duration.

Results:

Of the 91 patients studied, we observed significant rise in post-dialysis TC, LDL, and HDL [P < 0.01] and lower lipids [P < 0.01] just before the next dialysis. Lipids were least filtered across the membrane except HDL, which was found in effluent water for more than 60% of patients. Single use of dialyser was associated with higher rise in post dialysis lipids as well as HDL getting filtered in effluent [P = 0.24]. Rosuvastatin was associated with lower lipid values [P = 0.08] and BMI [P = 0.19].

Conclusions:

Low lipid levels in dialysis patients are due to dilutional hypolipidemia and needs correction with an equation proposed in present study. Corrected lipids should be used for risk stratification and deploying treatment.

Lipoproteins in chronic kidney disease: from bench to bedside

Chronic kidney disease (CKD) is associated with high cardiovascular risk. CKD patients exhibit a specific lipoprotein pattern termed 'uraemic dyslipidaemia', which is characterized by rather normal low-density lipoprotein cholesterol, low high-density lipoprotein cholesterol, and high triglyceride plasma levels. All three lipoprotein classes are involved in the pathogenesis of CKD-associated cardiovascular diseases (CVDs). Uraemia leads to several modifications of the structure of lipoproteins such as changes of the proteome and the lipidome, post-translational protein modifications (e.g. carbamylation) and accumulation of small-molecular substances within the lipoprotein moieties, which affect their functionality. Lipoproteins from CKD patients interfere with lipid transport and promote inflammation, oxidative stress, endothelial dysfunction as well as other features of atherogenesis, thus contributing to the development of CKD-associated CVD. While, lipid-modifying therapies play an important role in the management of CKD patients, their efficacy is modulated by kidney function. Novel therapeutic agents to prevent the adverse remodelling of lipoproteins in CKD and to improve their functional properties are highly desirable and partially under development.

Lipoprotein Abnormalities in Chronic Kidney Disease and Renal Transplantation

Chronic kidney disease (CKD) is one of the most important risk factors for cardiovascular disease (CVD). Despite the kidney having no direct implications for lipoproteins metabolism, advanced CKD dyslipidemia is usually present in patients with CKD, and the frequent lipid and lipoprotein alterations occurring in these patients play a role of primary importance in the development of CVD. Although hypertriglyceridemia is the main disorder, a number of lipoprotein abnormalities occur in these patients. Different enzymes pathways and proteins involved in lipoprotein metabolism are impaired in CKD. In addition, treatment of uremia may modify the expression of lipoprotein pattern as well as determine acute changes. In renal transplantation recipients, the main lipid alteration is hypercholesterolemia, while hypertriglyceridemia is less pronounced. In this review we have analyzed lipid and lipoprotein disturbances in CKD and also their relationship with progression of renal disease. Hypolipidemic treatments may also change the natural history of CVD in CKD patients and may represent important strategies in the management of CKD patients.

Cholesterol Disturbances and the Role of Proper Nutrition in CKD Patients

Chronic kidney disease (CKD) is a widespread disease with increasing prevalence in the modern society. Lipid disturbances are common in this group of patients. In most patients with CKD atherogenic dyslipidemia is observed. Dyslipidemia in patients with renal diseases increases the risk of cardiovascular diseases and it accelerates the progression of chronic kidney disease to its end stage. The amelioration of dyslipidemia and the lowering of oxidative stress, inflammatory processes, insulin sensitivity and remnant lipoproteins levels may lead to the reduction in cardiovascular burden. Nutritional interventions can strengthen the beneficial effect of treatment and they play an important role in the preservation of overall well-being of the patients with CKD since the aim of appropriate diet is to reduce the risk of cardiovascular events, prevent malnutrition, and hamper the progression of kidney disease. The management of dyslipidemia, regardless of the presence of chronic kidney disease, should be initiated by the introduction of therapeutic lifestyle changes. The introduction of diet change was shown to exert beneficial effect on the lipid level lowering that reaches beyond pharmacological therapy. Currently available evidence give the impression that data on dietary interventions in CKD patients is not sufficient to make any clinical practice guidelines and is of low quality.

Lipid management in patients with chronic kidney disease

An increased risk of cardiovascular disease, independent of conventional risk factors, is present even at minor levels of renal impairment and is highest in patients with end-stage renal disease (ESRD) requiring dialysis. Renal dysfunction changes the level, composition and quality of blood lipids in favour of a more atherogenic profile. Patients with advanced chronic kidney disease (CKD) or ESRD have a characteristic lipid pattern of hypertriglyceridaemia and low HDL cholesterol levels but normal LDL cholesterol levels. In the general population, a clear relationship exists between LDL cholesterol and major atherosclerotic events. However, in patients with ESRD, LDL cholesterol shows a negative association with these outcomes at below average LDL cholesterol levels and a flat or weakly positive association with mortality at higher LDL cholesterol levels. Overall, the available data suggest that lowering of LDL cholesterol is beneficial for prevention of major atherosclerotic events in patients with CKD and in kidney transplant recipients but is not beneficial in patients requiring dialysis. The 2013 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline for Lipid Management in CKD provides simple recommendations for the management of dyslipidaemia in patients with CKD and ESRD. However, emerging data and novel lipid-lowering therapies warrant some reappraisal of these recommendations.

Hypolipidemic Therapy and Chronic Kidney Disease: Effects on Cardiovascular Risks and Renal Dysfunction

Steady increase in the prevalence of chronic kidney disease (CKD) is a serious public health problem, since CKD potentially leads to the development of end-stage renal disease (ESRD) that requires high-cost replacement therapy and is closely associated with increased risk of developing cardiovascular diseases (CVD), which are the cause of death in most patients. Progression of renal dysfunction and development of CVD are significantly affected by hyper- and dyslipidemia. This review contains results of studies evaluating the effect of hypolipidemic therapy on reduction of cardiovascular risk and slowdown of renal dysfunction in patients with CKD at pre-dialysis and dialysis stages of renal failure, as well as in patients with kidney transplant. In addition, recommendations on nutrition and new therapeutic approaches to lipid-lowering therapy in patients with CKD, as well as prospects for the usage of new hypolipidemic drugs are also presented.

Obesity and dyslipidemia

Obesity, a pandemic of the modern world, is intimately associated with dyslipidemia, which is mainly driven by the effects of insulin resistance and pro-inflammatory adipokines. However, recent evidence suggests that obesity-induced dyslipidemia is not a unique pathophysiological entity, but rather has distinct characteristics depending on many individual factors. In line with that, in a subgroup of metabolically healthy obese (MHO) individuals, dyslipidemia is less prominent or even absent. In this review, we will address the main characteristics of dyslipidemia and mechanisms that induce its development in obesity. The fields, which should be further investigated to expand our knowledge on obesity-related dyslipidemia and potentially yield new strategies for prevention and management of cardiometabolic risk, will be highlighted. Also, we will discuss recent findings on novel lipid biomarkers in obesity, in particular proprotein convertase subtilisin/kexin type 9 (PCSK9), as the key molecule that regulates metabolism of low-density lipoproteins (LDL), and sphingosine-1-phosphate (S1P), as one of the most important mediators of high-density lipoprotein (HDL) particles function. Special attention will be given to microRNAs and their potential use as biomarkers of obesity-associated dyslipidemia.

Association of Triglyceride-Related Genetic Variants With Mitral Annular Calcification

BACKGROUND

Mitral annular calcium (MAC), commonly identified by cardiac imaging, is associated with cardiovascular events and predisposes to the development of clinically important mitral valve regurgitation and mitral valve stenosis. However, its biological determinants remain largely unknown.

OBJECTIVES

The authors sought to evaluate whether a genetic predisposition to elevations in plasma lipids is associated with the presence of MAC.

METHODS

The authors used 3 separate Mendelian randomization techniques to evaluate the associations of lipid genetic risk scores (GRS) with MAC in 3 large patient cohorts: the Framingham Health Study, MESA (Multiethnic European Study of Atherosclerosis), and the AGE-RS (Age, Gene/Environment Susceptibility-Reykjavik Study). The authors provided cross-ethnicity replication in the MESA Hispanic-American participants.

RESULTS

MAC was present in 1,149 participants (20.4%). In pooled analyses across all 3 cohorts, a triglyceride GRS was significantly associated with the presence of MAC (odds ratio [OR] per triglyceride GRS unit: 1.73; 95% confidence interval [CI]: 1.24 to 2.41; p = 0.0013). Neither low- nor high-density lipoprotein cholesterol GRS was significantly associated with MAC. Results were consistent in cross-ethnicity analyses among the MESA Hispanic-Americans cohort (OR per triglyceride GRS unit: 2.04; 95% CI: 1.03 to 4.03; p = 0.04). In joint meta-analysis across all included cohorts, the triglyceride GRS was associated with MAC (OR per triglyceride GRS unit: 1.79; 95% CI: 1.32 to 2.41; p = 0.0001). The results were robust to several sensitivity analyses that limit both known and unknown forms of genetic pleiotropy.

CONCLUSIONS

Genetic predisposition to elevated triglyceride levels was associated with the presence of MAC, a risk factor for clinically significant mitral valve disease, suggesting a causal association. Whether reducing triglyceride levels can lower the incidence of clinically significant mitral valve disease requires further study.

Cholesterol Levels of Six Fractionated Serum Lipoproteins and its Relevance to Coronary Heart Disease Risk Scores

Aim: Evaluation of serum lipoprotein profiles including triglyceride (TG)-rich lipoprotein, that is, intermediate-density lipoprotein (IDL), very low-density lipoprotein (VLDL), and chylomicron (CM) remnant is important to manage coronary heart disease (CHD) risk. The purpose of this study was to investigate CHD or cardiovascular disease (CVD) risk scores with cholesterol levels of six fractionated lipoprotein classes {high-density lipoprotein [HDL], low-density lipoprotein [LDL], IDL, VLDL, CM including CM remnant, and lipoprotein (a) [Lp (a)]} in Japanese healthy men.

Methods: The present study enrolled 161 healthy men without any medications. Lipoprotein profiles (fractionated lipoprotein cholesterol levels) were measured by anion-exchange high-performance liquid chromatography (AEX-HPLC) method and were compared with age, estimated glomerular filtration rate (eGFR), and three risk scores, that is, NIPPON DATA, Hisayama risk predicting model, and Suita score.

Results: Levels of LDL-cholesterol (C), VLDL-C, and CM-C significantly differed with age, while values of HDL-C, IDL-C, and Lp(a)-C were not different. The eGFR inversely correlated with LDL-C, IDL-C, VLDL-C, and CM-C. In a stepwise multiple logistic regression analysis, VLDL-C only correlated independently with eGFR. Three risk scores significantly correlated with CM-C.

Conclusions: These results suggested that VLDL-C concentration contributes to an increased risk at early stages of renal dysfunction, and CM-C may serve as a marker for estimating CHD risk in Japanese healthy men.

Lipid disorders in patients with renal failure: Role in cardiovascular events and progression of chronic kidney disease

The spectrum of lipid disorders in chronic kidney disease (CKD) is usually characterized by high triglycerides and reduced high dense lipoprotein (HDL), associated with normal or slightly reduced low dense lipoprotein (LDL)-cholesterol. This dyslipidemia is associated with an increased risk for atherosclerotic cardiovascular disease. Keys for the cardiovascular risk reduction in these patients are lowering the number and modifying the composition of the cholesterol-carrying atherogenic lipoprotein particles. Statins have an important role in primary prevention of cardiovascular events and mortality in non-hemodialyzed CKD patients. The benefits in terms of progression of renal failure are contradictory. Patient education regarding dietary regimen should be part of the CKD clinical management.

The Effect of Omega-3 Supplement on Serum Lipid Profile in Patients Undergoing Hemodialysis: A Randomized Clinical Trial

BACKGROUND

Some recent suggestions could show omega-3 condition deficiency following prolonged hemodialysis; however, these claims and speculations have not been well demonstrated with sufficient evidences. Hence, we attempted to assess the beneficial effects of omega-3 on lipid profile in patients with end-stage renal disease (ESRD) undergoing hemodialysis.

METHODS

One hundred and seventeen ESRD patients who were on maintenance dialysis in Rasoul-e-Akram and Madaen Hospitals were enrolled in this randomized clinical trial. These patients were divided into two groups randomly using block randomization method (57 patients as the case group receiving omega-3 for 12 weeks and 60 as the control group). Blood sample was taken from all patients for measurement of lipid profile, serum hemoglobin, and C-reactive protein at baseline as well as after the completion of interventions (after 12 weeks).

RESULTS

The average change in the value of HDL-C was significantly more in the patients who received omega-3 than in the control group (MD, -7 mg/dL; 95% CI, -11 to 0 p = 0.000). Also, the reduction in serum creatinine level was more in the omega-3 group than in the control group (MD, 0.7 mg/dL; 95% CI, -0.4 to 2.1 p = 0.023). The change in other indices including serum triglyceride, total cholesterol, and serum hemoglobin levels was not different between the two groups. The multivariable linear regression analysis showed no difference in serum HDL level between the two groups adjusted for sex, age, and time of dialysis, while the level of serum HDL-C could be adversely predicted by duration time. Similar regression model showed a between-group difference in serum creatinine in the presence of potential confounders.

CONCLUSION

The change in serum HDL level following use of omega-3 supplement is influenced by time of dialysis, not by drug effect. However, consumption of omega-3 can significantly reduce serum creatinine.

Lipid abnormalities in kidney disease and management strategies

Patients with kidney diseases continue to experience significant cardiovascular disease (CVD) morbidity and mortality. Although there are many important risk factors playing a role in the pathogenesis of CVD in chronic kidney disease (CKD) patients, dyslipidemia (elevated triglycerides, elevated oxidized low-density lipoprotein and low/dysfunctional low high-density) represents one of the modifiable risk factors. Renal failure patients have unique lipid abnormalities which not only have complex role in pathogenesis of CVD but also cause relative resistance to usual interventions. Most of the randomized trials have been in hemodialysis population and data from CKD non-dialysis, peritoneal dialysis and renal transplant populations is extremely limited. Compared to general population, evidence of mortality benefit of lipid lowering medications in CKD population is scarce. Future research should be directed towards establishing long term benefits and side effects of lipid lowering medications, through randomized trials, in CKD population.

High-density lipoprotein: structural and functional changes under uremic conditions and the therapeutic consequences

High-density lipoprotein (HDL) has attracted interest as a therapeutic target in cardiovascular diseases in recent years. Although many functional mechanisms of the vascular protective effects of HDL have been identified, increasing the HDL plasma level has not been successful in all patient cohorts with increased cardiovascular risk. The composition of the HDL particle is very complex and includes diverse lipids and proteins that can be modified in disease conditions. In patients with chronic kidney disease (CKD), the accumulation of uremic toxins, high oxidative stress, and chronic micro-inflammatory conditions contribute to changes in the HDL composition and may also account for protein/lipid modifications. These conditions are associated with a decreased protective function of HDL. Therefore, the HDL quantity and the functional quality of the particle must be considered. This review summarizes the current knowledge of dyslipidemia in CKD patients, the effects of lipid-modulating therapy, and the structural modifications of HDL that are associated with dysfunction.

Treatment of dyslipidemia in chronic kidney disease: Effectiveness and safety of statins

Several cardiovascular (CV) risk factors may explain the high rate of CV death among patients with chronic kidney disease (CKD). Among them both traditional and uremia-related risk factors are implicated and, moreover, the presence of kidney disease represents "per se" a multiplier of CV risk. Plasma lipid and lipoprotein profiles are changed in quantitative, but above all in qualitative, structural, and functional ways, and lipoprotein metabolism is influenced by the progressive loss of renal function. Statin therapy significantly reduces cholesterol synthesis and both CV morbidity and mortality either directly, by reducing the lipid profile, or via pleiotropic effects; it is supposed to be able to reduce both the progression of CKD and also proteinuria. These observations derive from a post-hoc analysis of large trials conducted in the general population, but not in CKD patients. However, the recently published SHARP trial, including over 9200 patients, either on dialysis or pre-dialysis, showed that simvastatin plus ezetimibe, compared with placebo, was associated with a significant low-density lipoprotein cholesterol reduction and a 17% reduction in major atherosclerotic events. However, no benefit was observed in overall survival nor in preserving renal function in patients treated. These recent data reinforce the conviction among nephrologists to consider their patients at high CV risk and that lipid lowering drugs such as statins may represent an important tool in reducing atheromatous coronary disease which, however, represents only a third of CV deaths in patients with CKD. Therefore, statins have no protective effect among the remaining two-thirds of patients who suffer from sudden cardiac death due to arrhythmia or heart failure, prevalent among CKD patients. The safety of statins is demonstrated in CKD by several trials and recently confirmed by the largest SHARP trial, in terms of no increase in cancer incidence, muscle pain, creatine kinase levels, severe rhabdomyolysis, hepatitis, gallstones and pancreatitis; thus confirming the handiness of statins in CKD patients. Here we will review the latest data available concerning the effectiveness and safety of statin therapy in CKD patients.

Lipid abnormalities in patients with chronic kidney disease: implications for the pathophysiology of atherosclerosis

Cardiovascular disease is increased in patients with chronic kidney disease (CKD) and is the principle cause of morbidity and mortality in these patients. In patients with stage 5 CKD, structural changes in the myocardium have been implicated as the principle cardiovascular processes leading to this increase in morbidity and mortality, while atherosclerotic events including acute myocardial infarction and strokes are responsible for approximately 10-15% of cardiovascular deaths. Dyslipidemia is common in CKD patients and is usually not characterized by elevated cholesterol levels, except in patients with marked proteinuria. Increased triglyceride levels in conjunction with decreased high-density lipoprotein levels are the commonest qualitative abnormality. Characteristically, abnormalities in the metabolism of apolipoprotein (apo) B-containing lipoproteins have been described, including both gut derived (apoB-48) as well as those produced by hepatic synthesis (apoB-100). A decrease in enzymatic delipidation as well as reduced receptor removal of these lipoproteins both contribute to the increased levels of these apo-B-containing particles and their remnants (which are believed to be highly atherogenic). Abnormalities in the metabolism of apoA-containing lipoproteins are also present and these changes contribute to the lower levels of HDL seen. Qualitative abnormalities of these HDL particles may be associated with cellular oxidative injury and contribute to a pro-inflammatory, pro-thrombotic milieu that is frequently present in CKD patients.

Predicting hospital cost in CKD patients through blood chemistry values

Background

Controversy exists in predicting costly hospitalization in patients with chronic kidney disease and co-morbid conditions. We therefore tested associations between serum chemistry values and the occurrence of in-patient hospital costs over a thirteen month study period. Secondarily, we derived a linear combination of variables to estimate probability of such occurrences in any patient.

Method

We calculated parsimonious values for select variables associated with in-patient hospitalization and compared sensitivity and specificity of these models to ordinal staging of renal disease.

Data from 1104 de-identified patients which included 18 blood chemistry observations along with complete claims data for all medical expenses.

We employed multivariable logistic regression for serum chemistry values significantly associated with in-patient hospital costs exceeding $3,000 in any single month and contrasted those results to other models by ROC area curves.

Results

The linear combination of weighted Z scores for parathyroid hormone, phosphorus, and albumin correlated with in-patient hospital care at p < 0.005. ROC curves derived from weighted variables of age, eGFR, hemoglobin, albumin, creatinine, and alanine aminotransferase demonstrated significance over models based on non-weighted Z scores for those same variables or CKD stage alone. In contrast, the linear combination of weighted PTH, PO4 and albumin demonstrated better prediction, but not significance over non-weighted Z scores for PTH alone.

Conclusion

Further study is justified to explore indices that predict costly hospitalization. Such metrics could assist Accountable Care Organizations in evaluating risk adjusted compensation for providers.

Causes of dysregulation of lipid metabolism in chronic renal failure

End-stage renal disease (ESRD) is associated with accelerated atherosclerosis and premature death from cardiovascular disease. These events are driven by oxidative stress inflammation and lipid disorders. ESRD-induced lipid abnormalities primarily stem from dysregulation of high-density lipoprotein (HDL), triglyceride-rich lipoprotein metabolism, and oxidative modification of lipoproteins. In this context, production and plasma concentration of Apo-I and Apo-II are reduced, HDL maturation is impaired, HDL composition is altered, HDL antioxidant and anti-inflammatory functions are depressed, clearance of triglyceride-rich lipoproteins and their atherogenic remnants is impaired, their composition is altered, and their plasma concentration is elevated in ESRD. The associated defect in HDL maturation is largely caused by acquired lecithin-cholesterol acyltransferase deficiency while its triglyceride enrichment is due to hepatic lipase deficiency. Hypertriglyceridemia, abnormal composition, and impaired clearance of triglyceride-rich lipoproteins and their remnants are mediated by down-regulation of lipoprotein lipase, hepatic lipase, very low-density lipoprotein (VLDL) receptor, and LDL receptor-related protein, relative reduction in ApoC-II/ApoC-III ratio, up-regulation of acyl-CoA cholesterol acyltransferase, and elevated plasma level of cholesterol ester-poor prebeta HDL. Impaired clearance and accumulation of oxidation-prone VLDL and chylomicron remnants and abnormal LDL composition in the face of oxidative stress and inflammation favors their uptake by macrophages and resident cells in the artery wall. The effect of heightened influx of lipids is compounded by impaired HDL-mediated reverse cholesterol transport leading to foam cell formation which is the central event in atherosclerosis plaque formation and subsequent plaque rupture, thrombosis, and tissue damage.

Lipoprotein lipase disturbances induced by uremia and hemodialysis

Factors such as malnutrition, physical inactivity, uremic toxins, and inflammation are known to influence the activity of lipoprotein lipase (LPL), an important enzyme in metabolism of blood lipids. In patients with chronic kidney disease these factors are common and may result in a decreased LPL activity. This is particularly so in patients on hemodialysis. Further, during each dialysis treatment, the use of heparin (or low molecular weight heparin) induces a release of LPL from its normal binding sites at the plasma membrane of endothelial cells. This results in an increased degradation of the enzyme and a relative lack of LPL activity for up to 10 hours from the start of the dialysis. Thus, the use of conventional anticoagulation for hemodialysis, in addition to the consequences of the uremic state, may cause a severe functional deficiency of LPL. This in turn may have deleterious effects on energy metabolism and may contribute to the increased risk for cardiovascular disease in this vulnerable group of patients.

Survival after Parathyroidectomy in Patients with End-stage Renal Disease and Severe Hyperparathyroidism

BACKGROUND

Patients with end-stage renal disease (ESRD) and secondary hyperparathyroidism (SHPT) are at high risk of mortality. Whether an increased risk of death persists after a parathyroidectomy (PTX) is not clearly established.

SUBJECTS AND METHODS

The survival of 40 patients with ESRD and SHPT who underwent PTX was compared with that of 664 ESRD patients.

RESULTS

From first dialysis, a lower mortality rate was found in the group of patients who underwent PTX than in the nonoperated ESRD group (hazard ratio: 0.23; 95% CI: 0.14-0.37). The patients who underwent PTX were younger, had a longer time on dialysis, and had a higher prevalence of kidney transplantation. The mean number of comorbidities was lower (Charlson score 4.2 +/- 2.1 versus 6.4 +/- 2.9, p < 0.001). Then, we randomly selected two matched controls for each PTX case (80 controls, 40 PTX) who had at least an equivalent mean duration of dialysis between the first dialysis and PTX of the PTX group. In a univariate model, there was a trend for PTX being associated with prolonged survival. The mortality was higher both among those at an advanced age and those with a high Charlson score. Adjustments for these covariates made the effect of PTX no more significant.

CONCLUSIONS

The risk of death of patients with severe SHPT leading to PTX differed from that of nonoperated subjects. The apparent differences in survival may be related to the number and severity of associated comorbidities. ESRD patients who undergo PTX may represent a subset of healthier subjects.

Mechanisms of dyslipidemia of chronic renal failure

Chronic renal failure is associated with profound dysregulation of lipid metabolism and marked abnormalities of plasma lipid profile. This review is intended to provide an overview of the molecular basis of lipid disorders in chronic renal failure and explore their potential impact on cardiovascular disease and energy metabolism.

Skeletal muscle dysfunction in chronic renal failure: effects of exercise

A number of chronic illnesses such as renal failure (CRF), obstructive pulmonary disease, and congestive heart failure result in a significant decrease in exercise tolerance. There is an increasing awareness that prescribed exercise, designed to restore some level of physical performance and quality of life, can be beneficial in these conditions. In CRF patients, muscle function can be affected by a number of direct and indirect mechanisms caused by renal disease as well as various treatment modalities. The aims of this review are twofold: first, to briefly discuss the mechanisms by which CRF negatively impacts skeletal muscle and, therefore, exercise capacity, and, second, to discuss the available data on the effects of programmed exercise on muscle function, exercise capacity, and various other parameters in CRF.

Dyslipidemia of chronic renal failure: the nature, mechanisms, and potential consequences

Chronic renal failure (CRF) results in profound lipid disorders, which stem largely from dysregulation of high-density lipoprotein (HDL) and triglyceride-rich lipoprotein metabolism. Specifically, maturation of HDL is impaired and its composition is altered in CRF. In addition, clearance of triglyceride-rich lipoproteins and their atherogenic remnants is impaired, their composition is altered, and their plasma concentrations are elevated in CRF. Impaired maturation of HDL in CRF is primarily due to downregulation of lecithin-cholesterol acyltransferase (LCAT) and, to a lesser extent, increased plasma cholesteryl ester transfer protein (CETP). Triglyceride enrichment of HDL in CRF is primarily due to hepatic lipase deficiency and elevated CETP activity. The CRF-induced hypertriglyceridemia, abnormal composition, and impaired clearance of triglyceride-rich lipoproteins and their remnants are primarily due to downregulation of lipoprotein lipase, hepatic lipase, and the very-low-density lipoprotein receptor, as well as, upregulation of hepatic acyl-CoA cholesterol acyltransferase (ACAT). In addition, impaired HDL metabolism contributes to the disturbances of triglyceride-rich lipoprotein metabolism. These abnormalities are compounded by downregulation of apolipoproteins apoA-I, apoA-II, and apoC-II in CRF. Together, these abnormalities may contribute to the risk of arteriosclerotic cardiovascular disease and may adversely affect progression of renal disease and energy metabolism in CRF.

Pharmacological and clinical properties of calcimimetics: calcium receptor activators that afford an innovative approach to controlling hyperparathyroidism

Circulating levels of calcium ion (Ca2+) are maintained within a narrow physiological range mainly by the action of parathyroid hormone (PTH) secreted from parathyroid gland (PTG) cells. PTG cells can sense small fluctuations in plasma Ca2+ levels by virtue of a cell surface Ca2+ receptor (CaR) that belongs to the superfamily of G protein-coupled receptors (GPCR). Compounds that activate the CaR and inhibit PTH secretion are termed 'calcimimetics' because they mimic or potentiate the effects of extracellular Ca2+ on PTG cell function. Preclinical studies with NPS R-568, a first generation calcimimetic compound that acts as a positive allosteric modulator of the CaR, have demonstrated that oral administration decreases serum levels of PTH and calcium, with a leftward shift in the set-point for calcium-regulated PTH secretion in normal rats. NPS R-568 also suppresses the elevation of serum PTH levels and PTG hyperplasia and can improve bone mineral density (BMD) and strength in rats with chronic renal insufficiency (CRI). Clinical trials with cinacalcet hydrochloride (cinacalcet), a compound with an improved metabolic profile, have shown that long-term treatment continues to suppress the elevation of serum levels of calcium and PTH in patients with primary hyperparathyroidism (1HPT). Furthermore, clinical trials in patients with uncontrolled secondary hyperparathyroidism (2HPT) have demonstrated that cinacalcet not only lowers serum PTH levels, but also the serum phosphorus and calcium x phosphorus product; these are a hallmark of an increased risk of cardiovascular disease and mortality in dialysis patients with end-stage renal disease. Indeed, cinacalcet has already been approved for marketing in several countries. Calcimimetic compounds like cinacalcet have great potential as an innovative medical approach to manage 1HPT and 2HPT.

Down-regulation of hepatic LDL receptor-related protein (LRP) in chronic renal failure

BACKGROUND

Chronic renal failure (CRF) is associated with premature atherosclerosis, impaired high-density lipoprotein (HDL)-mediated reverse cholesterol transport, depressed clearance, and elevated plasma concentrations of very low-density lipoprotein (VLDL), chylomicrons, and their atherogenic remnants. LDL receptor-related protein (LRP) is a member of the LDL receptor gene family that is heavily expressed in the liver, and mediates removal of at least 30 different ligands, including VLDL remnants (IDL) and chylomicron remnants. This study was conducted to test the hypothesis that the well-known defect in clearance of IDL and chylomicron remnants in CRF may be indicative of diminished hepatic LRP abundance.

METHODS

Hepatic tissue LRP mRNA abundance [reverse transcription-polymerase chain reaction (RT-PCR)] and protein abundance (Western blot analysis) were determined in rats 8 weeks after 5/6 nephrectomy (CRF group) or sham operation (control group).

RESULTS

The CRF group exhibited hypertension, diminished creatinine clearance, increased plasma triglyceride concentration, and elevated total cholesterol-to-HDL cholesterol concentration ratio compared to the corresponding values found in the control group. This was associated with a significant down-regulation of hepatic LRP mRNA expression and immunodetectable LRP protein.

CONCLUSION

CRF results in down-regulation of hepatic LRP. This abnormality can, at least in part, account for the previously documented elevation of plasma concentration and depressed clearance of chylomicron remnants and IDL in CRF.

HMG-CoA reductase inhibition reverses LCAT and LDL receptor deficiencies and improves HDL in rats with chronic renal failure

Dyslipidemia is a prominent feature of chronic renal failure (CRF) and a major risk factor for atherosclerosis and the progression of renal disease. CRF-induced dyslipidemia is marked by hypertriglyceridemia and a shift in plasma cholesterol from HDL to the ApoB-containing lipoproteins. Several studies have demonstrated a favorable response to administration of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors (statins) in CRF. This study was intended to explore the effect of statin therapy on key enzymes and receptors involved in cholesterol metabolism. Accordingly, CRF ( nephrectomized) and sham-operated rats were randomized to untreated and statin-treated (rosuvastatin 20 mg·kg−1·day−1) groups and observed for 6 wk. The untreated CRF rats exhibited increased total cholesterol-to-HDL cholesterol ratio, diminished plasma lecithin:cholesterol acyltransferase (LCAT) and the hepatic LDL receptor, elevated hepatic acyl-CoA:cholesterol acyltransferase (ACAT), and no change in hepatic HMG-CoA reductase, cholesterol 7α-hydroxylase, or HDL receptor (SRB-1). Statin administration lowered HMG-CoA reductase activity, normalized plasma LCAT, total cholesterol-to-HDL cholesterol ratio, and hepatic LDL receptor but did not significantly change either plasma total cholesterol, hepatic cholesterol 7α-hydroxylase, total ACAT activity, or SRB-1 in the CRF animals. Statin administration to the normal control rats led to significant increases in plasma LCAT and hepatic LDL receptor, significant reductions of total cholesterol-to-HDL cholesterol ratio, hepatic HMG-CoA reductase activity, and cholesterol 7α-hydroxylase abundance with virtually no change in plasma cholesterol concentration. Thus administration of rosuvastatin reversed LCAT and LDL receptor deficiencies and promoted a shift in plasma cholesterol from ApoB-containing lipoproteins to HDL in CRF rats.

Cellular cholesterol enrichment impairs T cell activation and chemotaxis

Human aging is associated with an increase in immune cell cholesterol levels, independent of circulating cholesterol levels. The effects of such an increase in membrane cholesterol on lipid raft-associated immune cell function have not been investigated. We sought to examine the effects of in vitro cholesterol loading on two known lipid raft-associated pathways of T cells, namely T cell activation and chemokine stimulation. Using beta-cyclodextrin (BCD) as a vehicle, we were able to rapidly load cholesterol onto human T cell lines and primary peripheral blood T cells without inducing significant cell toxicity. Loading of cholesterol to four-fold that of normal levels induced significant inhibition of intracellular calcium mobilization by both alphaCD3 and SDF-1alpha. Cholesterol-loaded peripheral T cells were completely unresponsive to alphaCD3/alphaCD28 stimulation, demonstrating no increase in IL-2, GM1 expression or cell size. T cell polarization of lipid rafts to alphaCD3/alphaCD28 beads was also impaired. In addition, cholesterol loading potently inhibited SDF-1alpha-induced chemotaxis. We propose that excess membrane cholesterol could potentially disrupt raft-related cell functions downstream of receptor triggering and that the loss of cholesterol regulation of aging immune cells could contribute to immune cell senescence.

ACAT inhibition reverses LCAT deficiency and improves plasma HDL in chronic renal failure

Chronic renal failure (CRF) is associated with increased risk of arteriosclerotic cardiovascular disease and profound alteration of plasma lipid profile. Uremic dyslipidemia is marked by increased plasma concentration of ApoB-containing lipoproteins and impaired high-density lipoprotein (HDL)-mediated reverse cholesterol transport. These abnormalities are, in part, due to acquired LCAT deficiency and upregulation of hepatic acyl-CoA:cholesterol acyltransferase (ACAT). ACAT catalyzes intracellular esterification of cholesterol, thereby promoting hepatic production of ApoB-containing lipoproteins and constraining HDL-mediated cholesterol uptake in the peripheral tissues. In view of the above considerations, we tested the hypothesis that pharmacological inhibition of ACAT may ameliorate CRF-induced dyslipidemia. 5/6 Nephrectomized rats were treated with either ACAT inhibitor IC-976 (30 mg.kg(-1).day(-1)) or placebo for 6 wk. Sham-operated rats served as controls. Key cholesterol-regulating enzymes, plasma lipids, and creatinine clearance were measured. The untreated CRF rats exhibited increased plasma low-density lipoprotein (LDL) and very LDL (VLDL) cholesterol, unchanged plasma HDL cholesterol, elevated total cholesterol-to-HDL cholesterol ratio, reduced liver microsomal free cholesterol, and diminished creatinine clearance. This was accompanied by reduced plasma LCAT, increased hepatic ACAT-2 mRNA, ACAT-2 protein and ACAT activity, and unchanged hepatic HMG-CoA reductase and cholesterol 7alpha-hydroxylase. ACAT inhibitor raised plasma HDL cholesterol, lowered LDL and VLDL cholesterol, and normalized total cholesterol-to-HDL cholesterol ratio without changing total cholesterol concentration (hence, a shift from ApoB-containing lipoproteins to HDL). This was accompanied by normalizations of hepatic ACAT activity and plasma LCAT. In conclusion, inhibition of ACAT reversed LCAT deficiency and improved plasma HDL level in CRF rats. Future studies are needed to explore the efficacy of ACAT inhibition in humans with CRF.

Downregulation of hepatic acyl-CoA:diglycerol acyltransferase in chronic renal failure

Chronic renal failure (CRF) is associated with hypertriglyceridemia and elevated plasma VLDL and IDL concentrations. These events can be due to either increased production or depressed catabolism of triglyceride-rich lipoproteins. Several studies have documented downregulation of lipoprotein lipase, hepatic triglyceride lipase, and the VLDL receptor, leading to depressed clearance and elevated plasma concentration of triglyceride-rich lipoproteins and their remnants in CRF. However, the effect of CRF on the triglyceride biosynthetic pathway has not been explored. Diglycerol acyltransferase (DGAT) is a microsomal enzyme that joins acyl-CoA to 1,2 diacylglycerol and, as such, constitutes the final step in triglyceride biosynthesis. Two distinct forms of DGAT (DGAT-1 and -2) have thus far been identified. The present study was undertaken to examine the effect of CRF on DGAT gene expression and activity in the liver, which is the source of endogenous triglycerides in the circulation. Male Sprague-Dawley rats were studied 8 wk after 5/6 nephrectomy (CRF) or sham operation. DGAT-1 and DGAT-2 mRNA abundance and DGAT activity were quantified. The CRF group showed reduced creatinine clearance, elevated plasma triglycerides, and VLDL concentrations. This was accompanied by significant reductions in hepatic DGAT-2 mRNA abundance (P < 0.01) and total DGAT activity (P < 0.1), pointing to diminished hepatic triglyceride production capacity in CRF animals. In conclusion, CRF results in significant downregulation of hepatic DGAT gene expression and activity. Given the critical role of DGAT in triglyceride biosynthesis, the present study points to diminished, not increased, hepatic triglyceride synthetic capacity in CRF rats.

Beneficial effects of calcimimetics on progression of renal failure and cardiovascular risk factors

In renal failure, parathyroid hormone (PTH) is not only involved in the genesis of disturbed calcium/phosphate metabolism and ostitis fibrosa; it is also a permissive factor in the genesis of hypertension, cardiovascular damage, and dyslipidemia. The allosteric activator of the calcium sensing receptor NPSR-568 (R-568) has been shown to reduce the serum intact PTH (iPTH) concentration in uremic rats. It was the purpose of this study in subtotally nephrectomized (SNX) rats to compare pharmacologic abrogation of secondary hyperparathyroidism by R-568 with parathyroidectomy (PTX). The effects on progression of renal failure, BP, and lipid and structural parameters of kidney and heart were studied. Four groups of male SD-rats were studied: (1) sham-operated + vehicle-treated rats (controls); (2) SNX + vehicle-treated rats (SNX); (3) parathyroidectomized SNX + vehicle-treated rats (SNX+PTX); and (4) SNX + calcimimetic R-568-treated rats (SNX+R-568). R-568 (50 micro mol/kg per d) was administered by gavage. Eight weeks after SNX, serum creatinine concentration, urinary albumin excretion, BP, and serum LDL-cholesterol concentration were significantly lower in both R-568-treated and parathyroidectomized SNX compared with vehicle-treated SNX. In addition, structural abnormalities of the kidney (glomerulosclerosis, tubulointerstitial changes) and the heart (interstitial fibrosis, capillary length density, arteriolar wall thickness) were significantly less pronounced than in vehicle-treated SNX. It is concluded that in experimental renal failure abrogation of hyperparathyroidism by administration of a calcimimetic or PTX similarly attenuates progression of renal failure. Furthermore, it interferes with the development of cardiovascular risk factors and cardiac remodeling.

Upregulation of acyl-CoA: cholesterol acyltransferase in chronic renal failure

Chronic renal failure (CRF) is associated with profound abnormalities of lipid metabolism and accelerated arteriosclerotic cardiovascular disease. In a recent study, we found marked downregulation of hepatic lecithin-cholesterol acyltransferase, or LCAT, expression, which can account for impaired HDL maturation and depressed HDL cholesterol concentration in CRF. Here, we report on the effect of CRF on acyl-CoA:cholesterol acyltransferase (ACAT) expression. ACAT is an intracellular enzyme that catalyzes esterification of free cholesterol to cholesterol ester for storage or secretion. ACAT plays a major role in hepatic production and release of VLDL, intestinal absorption of cholesterol, foam cell formation, and atherogenesis. We examined hepatic expression of ACAT-1 and ACAT-2 mRNA (Northern blot) and protein (Western blot) abundance and total ACAT activity in male CRF rats (6 wk after 5/6 nephrectomy) and sham-operated controls. The CRF animals showed a significant reduction in creatinine clearance, marked hypertriglyceridemia, modest hypercholesterolemia, and significant upregulation of hepatic tissue ACAT-2 protein and mRNA abundance. In contrast, hepatic ACAT-1 mRNA and protein abundance were unaffected by CRF. Upregulation of ACAT-2 expression was accompanied by a significant increase in hepatic ACAT activity and a significant decrease in hepatic microsomal and whole liver free cholesterol concentration. Thus CRF results in significant upregulation of hepatic ACAT-2 (but not ACAT-1) expression and ACAT activity, which may, in part, contribute to the associated lipid disorders.

Down-regulation of lipoprotein lipase and VLDL receptor in rats with focal glomerulosclerosis

BACKGROUND

Patients and animals with nephrotic syndrome and those with chronic renal failure (CRF) often exhibit hypertriglyceridemia and impaired very low-density lipoprotein (VLDL) clearance. Imai rats that were originally derived from Sprague-Dawley rats develop spontaneous proteinuria, hyperlipidemia, progressive renal insufficiency and histologic changes of focal glomerulosclerosis (FGS), closely resembling human FGS. This study was undertaken to test the hypothesis that elevation of plasma triglyceride and VLDL concentrations in the Imai rats is associated with deficiency of lipoprotein lipase (LPL) and VLDL receptor which are the main pathways of triglyceride-rich lipoprotein clearance.

METHODS

Male Imai and Sprague-Dawley control rats were fed regular rat chow and studied at 10 and 34 weeks of age. Tissue LPL and VLDL-r protein abundance (Western analysis) and post-heparin lipolytic activity were determined.

RESULTS

At 10 weeks of age, Imai rats showed mild proteinuria, moderate hyperlipidemia, normal creatinine clearance and blood pressure. By 34 weeks of age, the study animal exhibited severe proteinuria, marked hyperlipidemia, significant renal insufficiency and hypertension. This was associated with a severe progressive reduction in skeletal muscle and adipose tissue LPL and VLDL-r protein abundance and depressed plasma post heparin, lipolytic activity.

CONCLUSION

Progressive hyperlipidemia in the Imai rats with spontaneous FGS is accompanied by severe combined LPL and VLDL-r deficiencies that can, in part, account for the associated hypertriglyceridemia and elevated plasma VLDL concentrations.

The effects of parathyroidectomy on nutritional and biochemical status of hemodialysis patients with severe secondary hyperparathyroidism

The nutritional and biochemical parameters of 15 chronic hemodialysis (HD) patients with severe secondary hyperparathyroidism who had undergone total parathyroidectomy (PTX), with a forearm implant, were retrospectively studied at 1, 3, 6, and 12 months pre- and post-PTX. The concentrations of serum calcium and phosphorous significantly decreased in the first 6 months post-PTX. The concentration of blood urea nitrogen significantly increased at 6 and 12 months post-PTX. In contrast with control chronic HD patients who had no weight gain after nonparathyroid surgery, there was a progressive weight gain leading to a significantly higher dry weight at 12 months post-PTX. There was no significant change in serum potassium, albumin, cholesterol, transferrin, bicarbonate, hematocrit, normalized protein catabolic rate (nPCR), or erythropoietin dose at any time point post-PTX. The biochemical parameters of the 8 patients who had more than 5% weight gain, during 12 months post-PTX, were not statistically different from the remaining 7 cases who had weight gain less than 5% (or had lost weight) in the same time period. The same was true for 4 patients with weight gain of more than 10% versus the latter group. In conclusion, HD patients with severe secondary hyperparathyroidism are prone to progressive weight gain post-PTX, which reaches significance by the twelfth month. In 53% of the patients, the weight gain is more than 5% above the baseline. The nutritional and biochemical parameters pre-PTX were not helpful in distinguishing those who developed significant weight gain post-PTX.

Antagonistic effects of vitamin D and parathyroid hormone on lipoprotein lipase in cultured adipocytes

The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) (calcitriol) and parathyroid hormone (PTH) on synthesis and secretion of lipoprotein lipase (LPL) were studied in 3T3-L1 adipocytes. Expression of the vitamin D receptor was demonstrated by saturation kinetics with radiolabeled calcitriol. Incubation with calcitriol (10(-8) M) for up to 4 d resulted in a time-dependent significant increase in heparin-releasable LPL activity (LPLa) accompanied by a significant increase in LPL mRNA. In contrast, incubation with intact (1-84) PTH (10(-6) to 10(-9) M) produced a time- and dose-dependent significant decrease in LPLa, but no change in LPL mRNA. The effect of PTH (24-h incubation, 10(-8) M) could be prevented by the calcium channel blocker verapamil. Coincubation with both calcitriol and PTH at equimolar concentration (10(-8) M) resulted in an increase in LPLa and LPL mRNA. These data indicate an antagonistic role for calcitriol and PTH in the regulation of LPL, possibly mediated by intracellular calcium, which may contribute to the alterations in lipoprotein metabolism occurring in uremia.

Parathyroid hormone, vitamin D, and cardiovascular disease in chronic renal failure

BACKGROUND

Parathyroid hormone and vitamin D have been shown to influence cardiac and vascular growth and function experimentally in human subjects with normal renal function. Because of the increased prevalence of hyperparathyroidism and altered vitamin D status in chronic renal failure, these alterations have been considered to contribute to the increased prevalence of cardiovascular disease and hypertension seen in this patient population. Methods and Results. In this article, we review experimental and clinical literature on the cardiovascular effects of parathyroid hormone and vitamin D and relate them to the development of cardiac and vascular dysfunction in uremia, such as: cardiomyopathy, myocardial hypertrophy, and fibrosis, as well as to myocardial ischemia; uremic glucose intolerance, dyslipidemia, and atherosclerosis; hypertension; and vascular and cardiac calcifications.

CONCLUSIONS

The hyperparathyroid state and altered vitamin D status found in uremia contribute to the cardiovascular pathology seen clinically in uremia and also to the excess mortality from cardiovascular causes found in this patient group. The therapeutic implications of these observations are also discussed.

Effect of increased afterload on cardiac lipoprotein lipase and VLDL receptor expression

Fatty acids are a major source of fuel for energy production by myocytes. Lipoprotein lipase (LPL) and very low density lipoprotein (VLDL) receptor are abundantly expressed by the heart and skeletal muscles. LPL and possibly VLDL receptor represent the primary route of access to fatty acids contained in circulating triglyceride-rich lipoproteins. Physical exercise and thyroid hormone, which promote energy consumption, upregulate LPL expression in skeletal muscles. This study tested the hypothesis that increased cardiac workload might modulate myocardial LPL and/or VLDL receptor expressions. Accordingly, cardiac tissue LPL activity, LPL and VLDL receptor proteins and mRNA abundance were studied in Sprague-Dawley rats 4 weeks after induction of severe thoracic aorta constriction or sham operation. Elevation of afterload with thoracic aortic constriction led to a significant cardiomegaly and a marked upregulation of cardiac LPL activity, LPL mRNA and LPL protein abundance, but did not modify VLDL receptor mRNA or protein abundance. Thus, increased cardiac workload in this model results in upregulation of myocardial LPL expression which can enhance fatty acid availability to accommodate the heart's increased energy requirement.