Validation of variants in SLC28A3 and UGT1A6 as genetic markers predictive of anthracycline-induced cardiotoxicity in children

BACKGROUND

The use of anthracyclines as effective antineoplastic drugs is limited by the occurrence of cardiotoxicity. Multiple genetic variants predictive of anthracycline-induced cardiotoxicity (ACT) in children were recently identified. The current study was aimed to assess replication of these findings in an independent cohort of children.

PROCEDURE

. Twenty-three variants were tested for association with ACT in an independent cohort of 218 patients. Predictive models including genetic and clinical risk factors were constructed in the original cohort and assessed in the current replication cohort.

RESULTS

. We confirmed the association of rs17863783 in UGT1A6 and ACT in the replication cohort (P = 0.0062, odds ratio (OR) 7.98). Additional evidence for association of rs7853758 (P = 0.058, OR 0.46) and rs885004 (P = 0.058, OR 0.42) in SLC28A3 was found (combined P = 1.6 × 10(-5) and P = 3.0 × 10(-5), respectively). A previously constructed prediction model did not significantly improve risk prediction in the replication cohort over clinical factors alone. However, an improved prediction model constructed using replicated genetic variants as well as clinical factors discriminated significantly better between cases and controls than clinical factors alone in both original (AUC 0.77 vs. 0.68, P = 0.0031) and replication cohort (AUC 0.77 vs. 0.69, P = 0.060).

CONCLUSIONS

. We validated genetic variants in two genes predictive of ACT in an independent cohort. A prediction model combining replicated genetic variants as well as clinical risk factors might be able to identify high- and low-risk patients who could benefit from alternative treatment options.

Dipeptidylpeptidase inhibition is associated with improvement in blood pressure and diastolic function in insulin-resistant male Zucker obese rats

Diastolic dysfunction is a prognosticator for future cardiovascular events that demonstrates a strong correlation with obesity. Pharmacological inhibition of dipeptidylpeptidase-4 (DPP-4) to increase the bioavailability of glucagon-like peptide-1 is an emerging therapy for control of glycemia in type 2 diabetes patients. Accumulating evidence suggests that glucagon-like peptide-1 has insulin-independent actions in cardiovascular tissue. However, it is not known whether DPP-4 inhibition improves obesity-related diastolic dysfunction. Eight-week-old Zucker obese (ZO) and Zucker lean rats were fed normal chow diet or diet containing the DPP-4 inhibitor, linagliptin (LGT), for 8 weeks. Plasma DPP-4 activity was 3.3-fold higher in ZO compared with Zucker lean rats and was reduced by 95% with LGT treatment. LGT improved echocardiographic and pressure volume-derived indices of diastolic function that were impaired in ZO control rats, without altering food intake or body weight gain during the study period. LGT also blunted elevated blood pressure progression in ZO rats involving improved skeletal muscle arteriolar function, without reducing left ventricular hypertrophy, fibrosis, or oxidative stress in ZO hearts. Expression of phosphorylated- endothelial nitric oxide synthase (eNOS)(Ser1177), total eNOS, and sarcoplasmic reticulum calcium ATPase 2a protein was elevated in the LGT-treated ZO heart, suggesting improved Ca(2+) handling. The ZO myocardium had an abnormal mitochondrial sarcomeric arrangement and cristae structure that were normalized by LGT. These studies suggest that LGT reduces blood pressure and improves intracellular Cai(2+) mishandling and cardiomyocyte ultrastructure, which collectively result in improvements in diastolic function in the absence of reductions in left ventricular hypertrophy, fibrosis, or oxidative stress in insulin-resistant ZO rats.

Two novel mutations in apolipoprotein C3 underlie atheroprotective lipid profiles in families

Apolipoprotein C3 (APOC3) mutations carriers typically display high plasma high-density lipoprotein cholesterol (HDL-C) and low triglycerides (TGs). We set out to investigate the prevalence and clinical consequences of APOC3 mutations in individuals with hyperalphalipoproteinemia. Two novel mutations (c.-13-2A>G and c.55+1G>A) and one known mutation (c.127G>A;p.Ala43Thr) were found. Lipid profiles and apoCIII isoform distributions were measured. c.55+1G>A mutation carriers displayed higher HDL-C percentiles (35.6 ± 35.8 vs 99.0 ± 0, p = 0.002) and lower TGs (0.51 (0.37-0.61) vs 1.42 (1.12-1.81) mmol/l, p = 0.007) and apoCIII levels (4.24 ± 1.57 vs 7.33 ± 3.61 mg/dl, p = 0.18). c.-13-2A>G mutation carriers did not display significantly different HDL-C levels (84.0 ± 30.0 vs 63.7 ± 45.7, p = 0.50), a trend towards lower TGs [0.71 (0.54 to 0.78) vs 0.85 (0.85 to -) mmol/l, p = 0.06] and significantly lower apoCIII levels (3.09 ± 1.08 vs 11.45 ± 1.06 mg/dl, p = 0.003). p.Ala43Thr mutation carriers displayed a trend towards higher HDL-C percentiles (91.2 ± 31.8 vs 41.0 ± 29.7 mmol/l, p = 0.06) and significantly lower TGs [0.58 (0.36-0.63) vs 0.95 (0.71-1.20) mmol/l, p = 0.02] and apoCIII levels (4.92 ± 2.33 vs 6.60 ± 1.60, p = 0.25). Heterozygosity for APOC3 mutations results in high HDL-C and low TGs and apoCIII levels. This favourable lipid profile in patients with genetically low apoCIII levels holds promise for current studies investigating the potential of apoCIII inhibition as a novel therapeutic in cardiovascular disease prevention.

Renin inhibition and AT(1)R blockade improve metabolic signaling, oxidant stress and myocardial tissue remodeling

OBJECTIVE

Strategies that block angiotensin II actions on its angiotensin type 1 receptor or inhibit actions of aldosterone have been shown to reduce myocardial hypertrophy and interstitial fibrosis in states of insulin resistance. Thereby, we sought to determine if combination of direct renin inhibition with angiotensin type 1 receptor blockade in vivo, through greater reductions in systolic blood pressure (SBP) and aldosterone would attenuate left ventricular hypertrophy and interstitial fibrosis to a greater extent than either intervention alone.

MATERIALS/METHODS

We utilized the transgenic Ren2 rat which manifests increased tissue expression of murine renin which, in turn, results in increased renin-angiotensin system activity, aldosterone secretion and insulin resistance. Ren2 rats were treated with aliskiren, valsartan, the combination (aliskiren+valsartan), or vehicle for 21 days.

RESULTS

Compared to Sprague-Dawley controls, Ren2 rats displayed increased systolic blood pressure, elevated serum aldosterone levels, cardiac tissue hypertrophy, interstitial fibrosis and ultrastructural remodeling. These biochemical and functional alterations were accompanied by increases in the NADPH oxidase subunit Nox2 and 3-nitrotyrosine content along with increases in mammalian target of rapamycin and reductions in protein kinase B phosphorylation. Combination therapy contributed to greater reductions in systolic blood pressure and serum aldosterone but did not result in greater improvement in metabolic signaling or markers of oxidative stress, fibrosis or hypertrophy beyond either intervention alone.

CONCLUSIONS

Thereby, our data suggest that the greater impact of combination therapy on reductions in aldosterone does not translate into greater reductions in myocardial fibrosis or hypertrophy in this transgenic model of tissue renin overexpression.

Obesity-related alterations in cardiac lipid profile and nondipping blood pressure pattern during transition to diastolic dysfunction in male db/db mice

Obesity and a nondipping circadian blood pressure (BP) pattern are associated with diastolic dysfunction. Ectopic lipid accumulation is increasingly recognized as an important metabolic abnormality contributing to diastolic dysfunction. However, little is known about the contribution of different lipids and the composition of lipid analytes to diastolic dysfunction. We have performed functional and structural studies and analyzed cardiac lipid profile at two time points during progression to diastolic dysfunction in a genetic model of obesity. Serial cardiac magnetic resonance imaging and telemetric measures of BP between 12 and 15 wk of age in obese male db/db mice indicated a nondipping circadian BP pattern and normal diastolic function at 12 wk that progressed to a deteriorating nondipping pattern and onset of diastolic dysfunction at 15 wk of age. Lipidomic analysis demonstrated elevated fatty acids and ceramides in db/db at 12 wk, but their levels were decreased at 15 wk, and this was accompanied by persistent mitochondrial ultrastructural abnormalities in concert with evidence of increased fatty acid oxidation and enhanced production of reactive oxygen species. Triacylglyceride and diacylglyceride levels were elevated at both 12 and 15 wk, but their composition changed to consist of more saturated and less unsaturated fatty acyl at 15 wk. An increase in the lipid droplets was apparent at both time points, and this was associated with increases in phosphatidycholine. In conclusion, a distinct pattern of myocardial lipid remodeling, accompanied by oxidative stress, is associated with the onset of diastolic dysfunction in obese, insulin-resistant db/db mice.

Providing predictive testing for Huntington disease via telehealth: results of a pilot study in British Columbia, Canada

Predictive testing (PT) for Huntington disease (HD) usually requires several in-person appointments which acts as a barrier to testing for those from remote regions. This pilot study reports the use of telehealth PT to examine whether such telehealth testing improves access to HD PT while maintaining quality of care and support. Individuals underwent PT via the telehealth protocol or standard in-person protocol and were asked to complete surveys regarding their experience. Results reveal no significant differences between the in-person-tested and telehealth-tested groups with respect to quality of care, information, counselling and support. The majority of participants in both groups stated that pre-test counselling had provided them with sufficient knowledge about the advantages and disadvantages of undergoing testing, the opportunity to ask questions, and the ability to make an informed decision. The majority of participants in both groups were satisfied by the manner in which results were delivered and stated they had received sufficient information regarding the implications of these results. This study reveals that telehealth PT improves access while maintaining quality of care and support.

Abstract 321: Combination Dri With At1R Blockade Does Not Confer Additional Benefit to Improvement in Myocardial Tissue Hypertrophy and Fibrosis

Data support the notion that direct renin inhibition and angiotensin type 1 receptor (AT 1 R) blockade improve myocardial hypertrophy and fibrosis. Even with contemporary use of AT 1 R blockade and renin inhibition, the burden of heart failure remains high. Thereby, we sought to determine if combination of direct renin inhibition with AT 1 R blockade in vivo , through greater reductions in systolic blood pressure (SBP) and aldosterone would attenuate left ventricular (LV) hypertrophy and interstitial fibrosis to a greater extent than either intervention alone. We utilized the transgenic Ren2 rat which manifests increased expression of murine renin which, in turn, results in increased tissue RAS activity, aldosterone secretion and elevated SBP. Ren2 rats were treated with renin inhibition (aliskiren), AT 1 R blockade (valsartan), the combination (aliskiren+valsartan), or vehicle for 21 days. Compared to Sprague-Dawley controls, Ren2 rats displayed increased SBP, serum aldosterone levels, LV and cardiomyocyte hypertrophy, interstitial fibrosis and ultrastructural remodeling. These biochemical and functional alterations were accompanied by increases in LV tissue NADPH oxidase subunit Nox2 and 3-nitrotyrosine (3-NT) content along with increases in mammalian target of rapamycin (mTOR) and reductions in protein kinase B phosphorylation. Combination therapy contributed to greater reductions in SBP and serum aldosterone but did not result in greater improvement in metabolic signaling or markers of oxidative stress, fibrosis or hypertrophy beyond either intervention alone. Thereby, our data suggest that the greater impact of combination therapy on reductions in aldosterone does not translate into greater reductions in myocardial fibrosis or hypertrophy in this transgenic model of tissue renin overexpression.

Abstract 458: Obesity-related Alterations in Cardiac Lipid Profile During the Transition to Diastolic Dysfunction

Myocardial accumulation of fatty acids and lipid intermediates may contribute to cardiac dysfunction, but the interrelationship between different lipid species to diastolic dysfunction is not clearly understood. Herein, we examined changes in levels and composition of different lipid species during the progression to diastolic dysfunction in a clinically relevant model of obese insulin-resistant db/db mice at 12 and 15 wks of age. Obese db/db mice manifested loss of circadian BP dipping and diastolic dysfunction at 15 wks. Myocardial lipidomic analysis demonstrated elevated ceramides and fatty acids in db/db at 12 wks, but their levels were decreased at 15 wk and this was accompanied by increased fatty acid oxidation and enhanced production of reactive oxygen species. Triacylglyceride and diacylglyceride levels remained elevated at both 12 and 15 wk, but their composition changed to consist of more saturated and less unsaturated fatty acyl at 15 wks of age compared to 12 wk. Dysregulation of phospholipid metabolism persisted at 15 wk in db/db. Changes in triacylglyceride and diacylglyceride composition, phospholipid metabolism, β-oxidation, and oxidative stress that are temporally related to non-dipping of BP and diastolic dysfunction suggest a switch in metabolism of lipid intermediates contributes to the development of diastolic dysfunction in over-nutrition.

"Grasping the grey": patient understanding and interpretation of an intermediate allele predictive test result for Huntington disease

Since the discovery of the genetic mutation underlying Huntington disease (HD) and the development of predictive testing, the genetics of HD has generally been described as straightforward; an individual receives either mutation-positive or negative predictive test results. However, in actuality, the genetics of HD is complex and a small proportion of individuals receive an unusual predictive test result called an intermediate allele (IA). Unlike mutation-positive or negative results, IAs confer uncertain clinical implications. While individuals with an IA will usually not develop HD, there remains an unknown risk for their children and future generations to develop the disorder. The purpose of this study was to explore how individuals understood and interpreted their IA result. Interviews were conducted with 29 individuals who received an IA result and 8 medical genetics service providers. Interviews were analyzed using the constant comparative method and the coding procedures of grounded theory. Many participants had difficulty "Grasping the Grey" (i.e. understanding and interpreting their IA results) and their family experience, beliefs, expectations, and genetic counseling influenced the degree of this struggle. The theoretical model developed informs clinical practice regarding IAs, ensuring that this unique subset of patients received appropriate education, support, and counseling.

Human Mendelian pain disorders: a key to discovery and validation of novel analgesics

We have utilized a novel application of human genetics, illuminating the important role that rare genetic disorders can play in the development of novel drugs that may be of relevance for the treatment of both rare and common diseases. By studying a very rare Mendelian disorder of absent pain perception, congenital indifference to pain, we have defined Nav1.7 (endocded by SCN9A) as a critical and novel target for analgesic development. Strong human validation has emerged with SCN9A gain-of-function mutations causing inherited erythromelalgia (IEM) and paroxysmal extreme pain disorder, both Mendelian disorder of spontaneous or easily evoked pain. Furthermore, variations in the Nav1.7 channel also modulate pain perception in healthy subjects as well as in painful conditions such as osteoarthritis and Parkinson disease. On the basis of this, we have developed a novel compound (XEN402) that exhibits potent, voltage-dependent block of Nav1.7. In a small pilot study, we showed that XEN402 blocks Nav1.7 mediated pain associated with IEM thereby demonstrating the use of rare genetic disorders with mutant target channels as a novel approach to rapid proof-of-concept. Our approach underscores the critical role that human genetics can play by illuminating novel and critical pathways pertinent for drug discovery.

Combination of direct renin inhibition with angiotensin type 1 receptor blockade improves aldosterone but does not improve kidney injury in the transgenic Ren2 rat

Enhanced renin-angiotensin-aldosterone system (RAAS) activation contributes to proteinuria and chronic kidney disease by increasing glomerular and tubulointerstitial oxidative stress, promotion of fibrosis. Renin activation is the rate limiting step in angiotensin (Ang II) and aldosterone generation, and recent work suggests direct renin inhibition improves proteinuria comparable to that seen with Ang type 1 receptor (AT(1)R) blockade. This is important as, even with contemporary use of AT(1)R blockade, the burden of kidney disease remains high. Thereby, we sought to determine if combination of direct renin inhibition with AT(1)R blockade in vivo, via greater attenuation of kidney oxidative stress, would attenuate glomerular and proximal tubule injury to a greater extent than either intervention alone. We utilized the transgenic Ren2 rat with increased tissue RAS activity and higher serum levels of aldosterone, which manifests hypertension and proteinuria. Ren2 rats were treated with renin inhibition (aliskiren), AT(1)R blockade (valsartan), the combination (aliskiren+valsartan), or vehicle for 21days. Compared to Sprague-Dawley controls, Ren2 rats displayed increased systolic pressure (SBP), circulating aldosterone, proteinuria and greater urine levels of the proximal tubule protein excretory marker beta-N-acetylglucosaminidase (β-NAG). These functional and biochemical alterations were accompanied by increases in kidney tissue NADPH oxidase subunit Rac1 and 3-nitrotyrosine (3-NT) content as well as fibronectin and collagen type III. These findings occurred in conjunction with reductions in the podocyte-specific protein podocin as well as the proximal tubule-specific megalin. Further, in transgenic animals there was increased tubulointerstitial fibrosis on light microscopy as well as ultrastructural findings of glomerular podocyte foot-process effacement and reduced tubular apical endosomal/lysosomal activity. Combination therapy led to greater reductions in SBP and serum aldosterone, but did not result in greater improvement in markers of glomerular and tubular injury (i.e. β-NAG) compared to either intervention alone. Further, combination therapy did not improve markers of oxidative stress and podocyte and proximal tubule integrity in this transgenic model of RAAS-mediated kidney damage despite greater reductions in serum aldosterone and BP levels.

Overweight female rats selectively breed for low aerobic capacity exhibit increased myocardial fibrosis and diastolic dysfunction

The statistical association between endurance exercise capacity and cardiovascular disease suggests that impaired aerobic metabolism underlies the cardiovascular disease risk in men and women. To explore this connection, we applied divergent artificial selection in rats to develop low-capacity runner (LCR) and high-capacity runner (HCR) rats and found that disease risks segregated strongly with low running capacity. Here, we tested if inborn low aerobic capacity promotes differential sex-related cardiovascular effects. Compared with HCR males (HCR-M), LCR males (LCR-M) were overweight by 34% and had heavier retroperitoneal, epididymal, and omental fat pads; LCR females (LCR-F) were 20% heavier than HCR females (HCR-F), and their retroperitoneal, but not perireproductive or omental, fat pads were heavier as well. Unlike HCR-M, blood pressure was elevated in LCR-M, and this was accompanied by left ventricular (LV) hypertrophy. Like HCR-F, LCR-F exhibited normal blood pressure and LV weight as well as increased spontaneous cage activity compared with males. Despite normal blood pressures, LCR-F exhibited increased myocardial interstitial fibrosis and diastolic dysfunction, as indicated by increased LV stiffness, a decrease in the initial filling rate, and an increase in diastolic relaxation time. Although females exhibited increased arterial stiffness, ejection fraction was normal. Increased interstitial fibrosis and diastolic dysfunction in LCR-F was accompanied by the lowest protein levels of phosphorylated AMP-actived protein kinase [phospho-AMPK (Thr(172))] and silent information regulator 1. Thus, the combination of risk factors, including female sex, intrinsic low aerobic capacity, and overweightness, promote myocardial stiffness/fibrosis sufficient to induce diastolic dysfunction in the absence of hypertension and LV hypertrophy.

CAG repeat expansion in Huntington disease determines age at onset in a fully dominant fashion

OBJECTIVE

Age at onset of diagnostic motor manifestations in Huntington disease (HD) is strongly correlated with an expanded CAG trinucleotide repeat. The length of the normal CAG repeat allele has been reported also to influence age at onset, in interaction with the expanded allele. Due to profound implications for disease mechanism and modification, we tested whether the normal allele, interaction between the expanded and normal alleles, or presence of a second expanded allele affects age at onset of HD motor signs.

METHODS

We modeled natural log-transformed age at onset as a function of CAG repeat lengths of expanded and normal alleles and their interaction by linear regression.

RESULTS

An apparently significant effect of interaction on age at motor onset among 4,068 subjects was dependent on a single outlier data point. A rigorous statistical analysis with a well-behaved dataset that conformed to the fundamental assumptions of linear regression (e.g., constant variance and normally distributed error) revealed significance only for the expanded CAG repeat, with no effect of the normal CAG repeat. Ten subjects with 2 expanded alleles showed an age at motor onset consistent with the length of the larger expanded allele.

CONCLUSIONS

Normal allele CAG length, interaction between expanded and normal alleles, and presence of a second expanded allele do not influence age at onset of motor manifestations, indicating that the rate of HD pathogenesis leading to motor diagnosis is determined by a completely dominant action of the longest expanded allele and as yet unidentified genetic or environmental factors.

Ultrastructure Study of Transgenic Ren2 Rat Aorta - Part 1: Endothelium and Intima

BACKGROUND: The renin-angiotensin-aldosterone system plays an important role in the development and progression of hypertension and accelerated atherosclerosis (atheroscleropathy) associated with the cardiorenal metabolic syndrome and type 2 diabetes mellitus. Additionally, the renin-angiotensin-aldosterone system plays an important role in vascular-endothelial-intimal cellular and extracellular remodeling. METHODS: Thoracic aortas of young male transgenic heterozygous (mRen2)27 (Ren2) rats were utilized for this ultrastructural study. This lean model of hypertension, insulin resistance and oxidative stress harbors the mouse renin gene with increased local tissue (aortic) levels of angiotensin II and angiotensin type 1 receptors and elevated plasma aldosterone levels. RESULTS: The ultrastructural observations included marked endothelial cell retraction, separation, terminal nuclear lifting, adjacent duplication, apoptosis and a suggestion of endothelial progenitor cell attachment. The endothelium demonstrated increased caveolae, microparticles, depletion of Weibel-Palade bodies, loss of cell-cell and basal adhesion hemidesmosome-like structures, platelet adhesion and genesis of subendothelial neointima. CONCLUSION: These observational ultrastructural studies of the transgenic Ren2 vasculature provide an in-depth evaluation of early abnormal remodeling changes within conduit-elastic arteries under conditions of increased local levels of angiotensin II, oxidative stress, insulin resistance and hypertension.

Mineralocorticoid receptor-dependent proximal tubule injury is mediated by a redox-sensitive mTOR/S6K1 pathway

BACKGROUND/AIMS

The mammalian target of rapamycin (mTOR) is a serine kinase that regulates phosphorylation (p) of its target ribosomal S6 kinase (S6K1), whose activation can lead to glomerular and proximal tubular cell (PTC) injury and associated proteinuria. Increased mTOR/S6K1 signaling regulates signaling pathways that target fibrosis through adherens junctions. Recent data indicate aldosterone signaling through the mineralocorticoid receptor (MR) can activate the mTOR pathway. Further, antagonism of the MR has beneficial effects on proteinuria that occur independent of hemodynamics.

METHODS

Accordingly, hypertensive transgenic TG(mRen2)27 (Ren2) rats, with elevated serum aldosterone and proteinuria, and age-matched Sprague-Dawley rats were treated with either a low dose (1 mg/kg/day) or a conventional dose (30 mg/kg/day) of spironolactone (MR antagonist) or placebo for 3 weeks.

RESULTS

Ren2 rats displayed increases in urine levels of the PTC brush border lysosomal enzyme N-acetyl-β-aminoglycosidase (β-NAG) in conjunction with reductions in PTC megalin, the apical membrane adherens protein T-cadherin and basolateral α-(E)-catenin, and fibrosis. In concert with these abnormalities, Ren2 renal cortical tissue also displayed increased Ser2448 (p)/activation of mTOR and Thr389 (p)-S6K1 and increased 3-nitrotyrosine (3-NT) content, a marker for peroxynitrite. Low-dose spironolactone had no effect on blood pressure but decreased proteinuria and β-NAG comparable to a conventional dose of this MR antagonist. Both doses of spironolactone attenuated ultrastructural maladaptive alterations and led to comparable reductions in (p)-mTOR/(p)-S6K1, 3-NT, fibrosis, and increased expression of α-(E)-catenin, T- and N-cadherin.

CONCLUSIONS

Thereby, MR antagonism improves proximal tubule integrity by targeting mTOR/S6K1 signaling and redox status independent of changes in blood pressure.

Nebivolol improves insulin sensitivity in the TGR(Ren2)27 rat

Hypertension is often associated with increased oxidative stress and systemic insulin resistance. Use of β-adrenergic receptor blockers in hypertension is limited because of potential negative influence on insulin sensitivity and glucose homeostasis. We sought to determine the impact of nebivolol, a selective vasodilatory β₁-adrenergic blocker, on whole-body insulin sensitivity, skeletal muscle oxidative stress, insulin signaling, and glucose transport in the transgenic TG(mRen2)27 rat (Ren2). This rodent model manifests increased tissue renin angiotensin expression, excess oxidative stress, and whole-body insulin resistance. Young (age, 6-9 weeks) Ren2 and age-matched Sprague-Dawley control rats were treated with nebivolol 10 mg/(kg d) or placebo for 21 days. Basal measurements were obtained for glucose and insulin to calculate the homeostasis model assessment. In addition, insulin metabolic signaling, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, reactive oxygen species, and ultrastructural changes as evaluated by transmission electron microscopy were examined ex vivo in skeletal muscle tissue. The Ren2 rat demonstrated systemic insulin resistance as examined by the homeostasis model assessment, along with impaired insulin metabolic signaling in skeletal muscle. This was associated with increased oxidative stress and mitochondrial remodeling. Treatment with nebivolol was associated with improvement in insulin resistance and decreased NADPH oxidase activity/levels of reactive oxygen species in skeletal muscle tissue. Nebivolol treatment for 3 weeks reduces NADPH oxidase activity and improves systemic insulin resistance in concert with reduced oxidative stress in skeletal muscle in a young rodent model of hypertension, insulin resistance, and enhanced tissue RAS expression.

Phosphate Metabolism in Cardiorenal Metabolic Disease

Hyperphosphatemia is a major risk factor for cardiovascular disease, abnormalities of mineral metabolism and bone disease, and the progression of renal insufficiency in patients with chronic renal disease. In early renal disease, serum phosphate levels are maintained within the 'normal laboratory range' by compensatory increases in phosphaturic hormones such as fibroblast growth factor-23 (FGF-23). An important co-factor for FGF-23 is Klotho; a deficiency in Klotho plays an important role in the pathogenesis of hyperphosphatemia, renal tubulointerstitial disease, and parathyroid and bone abnormalities. Clinical hyperphosphatemia occurs when these phosphaturic mechanisms cannot counterbalance nephron loss. Hyperphosphatemia is associated with calcific uremic arteriolopathy and uremic cardiomyopathy, which may explain, in part, the epidemiologic connections between phosphate excess and cardiovascular disease. However, no clinical trials have been conducted to establish a causal relationship, and large, randomized trials with hard endpoints are urgently needed to prove or disprove the benefits and risks of therapy. In summary, hyperphosphatemia accelerates renal tubulointerstitial disease, renal osteodystrophy, as well as cardiovascular disease, and it is an important mortality risk factor in patients with chronic kidney disease.

Prenatal Programming and Epigenetics in the Genesis of the Cardiorenal Syndrome

The presence of a group of interacting maladaptive factors, including hypertension, insulin resistance, metabolic dyslipidemia, obesity, and microalbuminuria and/or reduced renal function, collectively constitutes the cardiorenal metabolic syndrome (CRS). Nutritional and other environmental cues during fetal development can permanently affect the composition, homeostatic systems, and functions of multiple organs and systems; this process has been referred to as 'programming'. Since the original formulation of the notion that low birth weight is a proxy for 'prenatal programming' of adult hypertension and cardiovascular disease, evidence has also emerged for programming of kidney disease, insulin resistance, obesity, metabolic dyslipidemia, and other chronic diseases. The programming concept was initially predicated on the notion that in utero growth restriction due to famine was responsible for increased hypertension, and cardiovascular and renal diseases. On the other hand, we are now more commonly exposed to increasing rates of maternal obesity. The current review will discuss the overarching role of maternal overnutrition, as well as fetal undernutrition, in epigenetic programming in relation to the pathogenesis of the CRS in children and adults.

Novel mutations in scavenger receptor BI associated with high HDL cholesterol in humans

The scavenger receptor class B, member 1 (SR-BI), is a key cellular receptor for high-density lipoprotein (HDL) in mice, but its relevance to human physiology has not been well established. Recently a family was reported with a mutation in the gene encoding SR-BI and high HDL cholesterol (HDL-C). Here we report two additional individuals with extremely high HDL-C (greater than the 90th percentile for age and gender) with rare mutations in the gene encoding SR-BI. These mutations segregate with high HDL-C in family members of each proband and are associated with a 37% increase in plasma HDL-C in heterozygous individuals carrying them. Both mutations occur at highly conserved positions in the large extracellular loop region of SR-BI and are predicted to impair the function of the SR-BI protein. Our findings, combined with the prior report of a single mutation in the gene encoding SR-BI, further validate that mutations in SR-BI are a rare but recurring cause of elevated HDL-C in humans.

Possible Mechanisms of Local Tissue Renin-Angiotensin System Activation in the Cardiorenal Metabolic Syndrome and Type 2 Diabetes Mellitus

The role of local tissue renin-angiotensin system (tRAS) activation in the cardiorenal metabolic syndrome (CRS) and type 2 diabetes mellitus (T2DM) is not well understood. To this point, we posit that early redox stress-mediated injury to tissues and organs via accumulation of excessive reactive oxygen species (ROS) and associated wound healing responses might serve as a paradigm to better understand how tRAS is involved. There are at least five common categories responsible for generating ROS that may result in a positive feedback ROS-tRAS axis. These mechanisms include metabolic substrate excess, hormonal excess, hypoxia-ischemia/reperfusion, trauma, and inflammation. Because ROS are toxic to proteins, lipids, and nucleic acids they may be the primary instigator, serving as the injury nidus to initiate the wound healing process. Insulin resistance is central to the development of the CRS and T2DM, and there are now thought to be four major organ systems important in their development. In states of overnutrition and tRAS activation, adipose tissue, skeletal muscle (SkM), islet tissues, and liver (the quadrumvirate) are individually and synergistically related to the development of insulin resistance, CRS, and T2DM. The obesity epidemic is thought to be the driving force behind the CRS and T2DM, which results in the impairment of multiple end-organs, including the cardiovascular system, pancreas, kidney, retina, liver, adipose tissue, SkM, and nervous system. A better understanding of the complex mechanisms leading to local tRAS activation and increases in tissue ROS may lead to new therapies emphasizing global risk reduction of ROS resulting in decreased morbidity and mortality.

Angiotensin II activation of mTOR results in tubulointerstitial fibrosis through loss of N-cadherin

BACKGROUND/AIMS

Angiotensin (Ang) II contributes to tubulointerstitial fibrosis. Recent data highlight mammalian target of rapamycin (mTOR)/S6 kinase 1 (S6K1) signaling in tubulointerstitial fibrosis; however, the mechanisms remain unclear. Thereby, we investigated the role of Ang II on mTOR/S6K1-dependent proximal tubule (PT) injury, remodeling, and fibrosis.

METHODS

We utilized young transgenic Ren2 rats (R2-T) and Sprague-Dawley rats (SD-T) treated with the Ang type 1 receptor (AT(1)R) blocker telmisartan (2 mg · kg(-1) · day(-1)) or vehicle (R2-C; SD-C) for 3 weeks to examine PT structure and function.

RESULTS

Ren2 rats displayed increased systolic blood pressure, proteinuria and increased PT oxidant stress and remodeling. There were parallel increases in kidney injury molecule-1 and reductions in neprilysin and megalin with associated ultrastructural findings of decreased clathrin-coated pits, endosomes, and vacuoles. Ren2 rats displayed increased Serine(2448) phosphorylation of mTOR and downstream S6K1, in concert with ultrastructural basement membrane thickening, tubulointerstitial fibrosis and loss of the adhesion molecule N-cadherin. Telmisartan treatment attenuated proteinuria as well as the biochemical and tubulointerstitial structural abnormalities seen in the Ren2 rats.

CONCLUSIONS

Our observations suggest that Ang II activation of the AT(1)R contributes to PT brush border injury and remodeling, in part, due to enhanced mTOR/S6K1 signaling which promotes tubulointerstitial fibrosis through loss of N-cadherin.

Childhood-Adolescent Obesity in the Cardiorenal Syndrome: Lessons from Animal Models

BACKGROUND/AIMS

Childhood-adolescent overweight and obesity have grown to pandemic proportions during the past decade. The onset of obesity in younger adults will likely be manifested as earlier onset of myocardial and renal end-organ disease in younger adults. For the first time, it is estimated that the current generation may not live to be as old as their parents. Thus, it is important to develop animal models of childhood obesity to understand fundamental pathological organ changes.

METHODS

In this regard, we utilize transmission electron microscopy evaluation to evaluate early remodeling changes of two adolescent rodent obesity models: the Zucker obese (fa/fa) rat and the db/db mouse models of obesity. We have concentrated on the initial ultrastructural remodeling (obese adipose tissue, skeletal muscle, and islet remodeling) and the associated changes in target end organs (including the myocardium and kidney) in young rodent models of obesity and insulin resistance, collectively manifesting as the cardiorenal metabolic syndrome (CRS).

RESULTS

Briefly, tissues revealed the following ultrastructural remodeling abnormalities: inflammation, hypertrophy, and early fibrosis in adipose tissue; loss of mitochondria in skeletal muscles, hyperplasia, fibrosis, and depletion of insulin-secretory granules in pancreatic islets; increased intramyocardial lipid accumulation, fibrosis, and mitochondrial deposition in the myocardium, and obesity-related glomerulopathy and tubulopathy in the kidney.

CONCLUSION

Based on the current knowledge and ultrastructural observations of organ pathology, we propose mechanisms whereby obesity appears to be the driving force behind the development of the CRS.