VLDL-activated cell signaling pathways that stimulate adrenal cell aldosterone production

Discovery of RXFP2 genetic association in resistant hypertensive men and RXFP2 antagonists for the treatment of resistant hypertension

Hypertension remains a leading cause of cardiovascular and kidney diseases. Failure to control blood pressure with ≥ 3 medications or control requiring ≥ 4 medications is classified as resistant hypertension (rHTN) and new therapies are needed to reduce the resulting increased risk of morbidity and mortality. Here, we report genetic evidence that relaxin family peptide receptor 2 (RXFP2) is associated with rHTN in men, but not in women. This study shows that adrenal gland gene expression of RXFP2 is increased in men with hypertension and the RXFP2 natural ligand, INSL3, increases adrenal steroidogenesis and corticosteroid secretion in human adrenal cells. To address the hypothesis that RXFP2 activation is an important mechanism in rHTN, we discovered and characterized small molecule and monoclonal antibody (mAb) blockers of RXFP2. The novel chemical entities and mAbs show potent, selective inhibition of RXFP2 and reduce aldosterone and cortisol synthesis and release. The RXFP2 mAbs have suitable rat pharmacokinetic profiles to evaluate the role of RXFP2 in the development and maintenance of rHTN. Overall, we identified RXFP2 activity as a potential new mechanism in rHTN and discovered RXFP2 antagonists for the future interrogation of RXFP2 in cardiovascular and renal diseases.

Fatty acids as a direct regulator of aldosterone hypersecretion

Primary hyperaldosteronism is a major cause of secondary hypertension and carries additional cardiovascular risks beyond that of the elevated blood pressure. Primary hyperaldosteronism is more prevalent in obese people, and weight loss reduces aldosterone levels. It needs to be determined whether obesity related factors directly contribute to the pathogenesis of primary hyperaldosteronism. Here we show that the non-esterified fatty acids (NEFA) palmitic acid, and to a lesser extent, linoleic acid significantly stimulated aldosterone production and steroid enzyme induction in adrenocortical HAC15 cells of human origin. Palmitic acid, linoleic acid, and to a much lesser extent, oleic acid induced the expression of aldosterone synthase. Induction of the Steroidogenic Acute Regulatory Protein (StAR) was modest. Increased aldosterone secretion was independent of fatty acid beta-oxidation in the mitochondria but may involve free fatty acid receptor 1 (FFAR1/GPR40) and endoplasmic reticulum (ER) stress. Palmitic acid and linoleic acid induced the expression of C/EBP Homologous Protein (CHOP), a marker of ER stress, correlating with their ability to induce aldosterone synthase gene expression. Palmitic acid, but not linoleic acid decreased mitochondrial potentials and induced uncoupling protein 2 (UCP2). Palmitic acid enhanced, while docosahexaenoic acid (DHA) suppressed aldosterone response to angiotensin II (Ang-II). Our study provides evidence that NEFAs modulate aldosterone production, and further suggests that hyperaldosteronism shares similar pathogenesis with other obesity-related disorders such as metabolic syndrome.

Emerging Evidence of Pathological Roles of Very-Low-Density Lipoprotein (VLDL)

Embraced with apolipoproteins (Apo) B and Apo E, triglyceride-enriched very-low-density lipoprotein (VLDL) is secreted by the liver into circulation, mainly during post-meal hours. Here, we present a brief review of the physiological role of VLDL and a systemic review of the emerging evidence supporting its pathological roles. VLDL promotes atherosclerosis in metabolic syndrome (MetS). VLDL isolated from subjects with MetS exhibits cytotoxicity to atrial myocytes, induces atrial myopathy, and promotes vulnerability to atrial fibrillation. VLDL levels are affected by a number of endocrinological disorders and can be increased by therapeutic supplementation with cortisol, growth hormone, progesterone, and estrogen. VLDL promotes aldosterone secretion, which contributes to hypertension. VLDL induces neuroinflammation, leading to cognitive dysfunction. VLDL levels are also correlated with chronic kidney disease, autoimmune disorders, and some dermatological diseases. The extra-hepatic secretion of VLDL derived from intestinal dysbiosis is suggested to be harmful. Emerging evidence suggests disturbed VLDL metabolism in sleep disorders and in cancer development and progression. In addition to VLDL, the VLDL receptor (VLDLR) may affect both VLDL metabolism and carcinogenesis. Overall, emerging evidence supports the pathological roles of VLDL in multi-organ diseases. To better understand the fundamental mechanisms of how VLDL promotes disease development, elucidation of the quality control of VLDL and of the regulation and signaling of VLDLR should be indispensable. With this, successful VLDL-targeted therapies can be discovered in the future.

The role of lipid second messengers in aldosterone synthesis and secretion

Second messengers are small rapidly diffusing molecules or ions that relay signals between receptors and effector proteins to produce a physiological effect. Lipid messengers constitute one of the four major classes of second messengers. The hydrolysis of two main classes of lipids, glycerophospholipids and sphingolipids, generate parallel profiles of lipid second messengers: phosphatidic acid (PA), diacylglycerol (DAG), and lysophosphatidic acid versus ceramide, ceramide-1-phosphate, sphingosine, and sphingosine-1-phosphate, respectively. In this review, we examine the mechanisms by which these lipid second messengers modulate aldosterone production at multiple levels. Aldosterone is a mineralocorticoid hormone responsible for maintaining fluid volume, electrolyte balance, and blood pressure homeostasis. Primary aldosteronism is a frequent endocrine cause of secondary hypertension. A thorough understanding of the signaling events regulating aldosterone biosynthesis may lead to the identification of novel therapeutic targets. The cumulative evidence in this literature emphasizes the critical roles of PA, DAG, and sphingolipid metabolites in aldosterone synthesis and secretion. However, it also highlights the gaps in our knowledge, such as the preference for phospholipase D-generated PA or DAG, as well as the need for further investigation to elucidate the precise mechanisms by which these lipid second messengers regulate optimal aldosterone production.

The fatty acid elongase ELOVL6 regulates bortezomib resistance in multiple myeloma

Resistance to the proteasome inhibitor bortezomib (BTZ) represents a major obstacle in the treatment of multiple myeloma (MM). The contribution of lipid metabolism in the resistance of MM cells to BTZ is mostly unknown. Here we report that levels of fatty acid elongase 6 (ELOVL6) were lower in MM cells from BTZ-nonresponsive vs BTZ-responsive patients and in cultured MM cells selected for BTZ resistance compared with parental counterparts. Accordingly, depletion of ELOVL6 in parental MM cells suppressed BTZ-induced endoplasmic reticulum (ER) stress and cytotoxicity, whereas restoration of ELOVL6 levels in BTZ-resistant MM cells sensitized them to BTZ in tissue culture settings and, as xenografts, in a plasmacytoma mouse model. Furthermore, for the first time, we identified changes in the BTZ-induced lipidome between parental and BTZ-resistant MM cell lines underlying a functional difference in their response to BTZ. We demonstrated that restoration of ELOVL6 levels in BTZ-resistant MM cells resensitized them to BTZ largely via upregulation of ELOVL6-dependent ceramide species, which was a prerequisite for BTZ-induced ER stress and cell death in these cells. Our data characterize ELOVL6 as a major clinically relevant regulator of MM cell resistance to BTZ, which can emerge from the impaired ability of these cells to alter ceramide composition in response to BTZ.

Lipid profile and left ventricular geometry pattern in obese children

Background

Left ventricular hypertrophy (LVH) is an important risk factor for cardiovascular and all-cause mortality. Previous studies reported conflicting results concerning the relationship between serum lipid levels and left ventricular geometry pattern. We sought to explore the relationship between standard serum lipid profile measures with left ventricular geometry pattern in obese children.

Patients and methods

In this cross-sectional study, a total of 70 obese children were examined. Fasting blood samples were taken to measure total cholesterol, low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), triglycerides (TGs), glucose, and insulin. Based on these values TG/HDL ratio, BMI and HOMA index were calculated. We also measured the average 24-h ambulatory systolic blood pressure (SBP) and two-dimensional (2/D) transthoracic echocardiography was performed to determine left ventricular mass index (LVMI) and relative wall thickness (RWT). Multiple regression analyses were conducted to explore relationships between study variables and the LVMI or RWT as outcome variables. The final model with LVMI included TG/HDL ratio, BMI, 24 h-average SBP, age and sex, while for the RWT we included BMI, insulin, age and sex.

Results

Our study included 70 children (65.71% boys and 34.29% girls) median age (14 years, IQR = 12–16)." We demonstrated independent and positive association of TG/HDL ratio, BMI and 24 h-average SBP with LVMI (effect = 3.65, SE = 1.32, p < 0.01; effect = 34.90, SE = 6.84, p < 0.01; effect = 0.32, SE = 0.12, p < 0.01, respectively). On the other hand, in model with RWT as outcome variable, only BMI and insulin were significantly linked (BMI: effect = 13.07, SE = 5.02, p = 0.01 Insulin: effect = 2.80, SE = 0.97).

Conclusion

Increased TG/HDL ratio in obese children is associated with the development of eccentric left ventricular hypertrophy while increased BMI and insulin were associated with concentric left ventricular hypertophy.

Lipoproteins modulate growth and P-glycoprotein expression in drug-resistant HER2-overexpressed breast cancer cells

Background

Drug resistance remains as a challenge in the treatment of HER2-overexpressed breast cancer. Emerging evidence from clinical studies show relation of oxidized low density lipoprotein (LDL) and very low density lipoprotein (VLDL) level with drug resistance. However, the underlying molecular mechanisms for this effect remain unclear. Therefore, the aim of this study was to determine the effects of oxidized-LDL and VLDL in drug-resistant HER2-overexpressed breast cancer cells.

Methods

An in vitro cell model for tamoxifen-resistant HER2 overexpressed UACC732 cells was created using the pulse method. Cells were exposed to oxidized LDL (oxLDL) and very low density lipoprotein (VLDL) separately. Effects on cell morphology was studied using phase contrast microscopic changes. Percentage of cell viability was measured using proliferation assay kit. Development of tamoxifen resistance was determined based on P-gp expression with flow cytometry. Further analysis includedcell death measurement with flow cytometry method.

Results

UACC732 cells exposed to VLDL exhibited fibroblast-like morphology. This was further supported by proliferation assay, where the percentage of cell viability achieved more than 100% with 100 μg/ml of VLDL exposure, indicating cell proliferation. Findings also showed that VLDL caused reduction in expression of Pgp in resistant cells compared to resistant cells alone (p = 0.02).

Conclusion

Results of this study suggest that VLDL may play a role in growth of drug-resistant HER2-overexpressing cells. Lower expression of P-gp in presence of VLDL need to be investigated further.

Very low-density lipoprotein (VLDL)-induced signals mediating aldosterone production

Aldosterone, secreted by the adrenal zona glomerulosa, enhances sodium retention, thus increasing blood volume and pressure. Excessive production of aldosterone results in high blood pressure and contributes to cardiovascular and renal disease, stroke and visual loss. Hypertension is also associated with obesity, which is correlated with other serious health risks as well. Although weight gain is associated with increased blood pressure, the mechanism by which excess fat deposits increase blood pressure remains unclear. Several studies have suggested that aldosterone levels are elevated with obesity and may represent a link between obesity and hypertension. In addition to hypertension, obese patients typically have dyslipidemia, including elevated serum levels of very low-density lipoprotein (VLDL). VLDL, which functions to transport triglycerides from the liver to peripheral tissues, has been demonstrated to stimulate aldosterone production. Recent studies suggest that the signaling pathways activated by VLDL are similar to those utilized by AngII. Thus, VLDL increases cytosolic calcium levels and stimulates phospholipase D (PLD) activity to result in the induction of steroidogenic acute regulatory (StAR) protein and aldosterone synthase (CYP11B2) expression. These effects seem to be mediated by the ability of VLDL to increase the phosphorylation (activation) of their regulatory transcription factors, such as the cAMP response element-binding (CREB) protein family of transcription factors. Thus, research into the pathways by which VLDL stimulates aldosterone production may identify novel targets for the development of therapies for the treatment of hypertension, particularly those associated with obesity, and other aldosterone-modulated pathologies.