Neerupma Silswal

FGF23 directly impairs endothelium-dependent vasorelaxation by increasing superoxide levels and reducing nitric oxide bioavailability

Fibroblast growth factor 23 (FGF23) is secreted primarily by osteocytes and regulates phosphate and vitamin D metabolism. Elevated levels of FGF23 are clinically associated with endothelial dysfunction and arterial stiffness in chronic kidney disease (CKD) patients; however, the direct effects of FGF23 on endothelial function are unknown. We hypothesized that FGF23 directly impairs endothelial vasorelaxation by hindering nitric oxide (NO) bioavailability. We detected expression of all four subtypes of FGF receptors (Fgfr1-4) in male mouse aortas. Exogenous FGF23 (90-9,000 pg/ml) did not induce contraction of aortic rings and did not relax rings precontracted with PGF2α. However, preincubation with FGF23 (9,000 pg/ml) caused a ∼36% inhibition of endothelium-dependent relaxation elicited by acetylcholine (ACh) in precontracted aortic rings, which was prevented by the FGFR antagonist PD166866 (50 nM). Furthermore, in FGF23-pretreated (9,000 pg/ml) aortic rings, we found reductions in NO levels. We also investigated an animal model of CKD (Col4a3(-/-) mice) that displays highly elevated serum FGF23 levels and found they had impaired endothelium-dependent vascular relaxation and reduced nitrate production compared with age-matched wild types. To elucidate a mechanism for the FGF23-induced impairment, we measured superoxide levels in endothelial cells and aortic rings and found that they were increased following FGF23 treatment. Crucially, treatment with the superoxide scavenger tiron reduced superoxide levels and also restored aortic relaxation to ACh. Therefore, our data suggest that FGF23 increases superoxide, inhibits NO bioavailability, and causes endothelial dysfunction in mouse aorta. Together, these data provide evidence that high levels of FGF23 contribute to cardiovascular dysfunction.

Phosphatidylinositol 3,5-bisphosphate increases intracellular free Ca2+ in arterial smooth muscle cells and elicits vasocontraction.

Phosphoinositide (3,5)-bisphosphate [PI(3,5)P(2)] is a newly identified phosphoinositide that modulates intracellular Ca(2+) by activating ryanodine receptors (RyRs). Since the contractile state of arterial smooth muscle depends on the concentration of intracellular Ca(2+), we hypothesized that by mobilizing sarcoplasmic reticulum (SR) Ca(2+) stores PI(3,5)P(2) would increase intracellular Ca(2+) in arterial smooth muscle cells and cause vasocontraction. Using immunohistochemistry, we found that PI(3,5)P(2) was present in the mouse aorta and that exogenously applied PI(3,5)P(2) readily entered aortic smooth muscle cells. In isolated aortic smooth muscle cells, exogenous PI(3,5)P(2) elevated intracellular Ca(2+), and it also contracted aortic rings. Both the rise in intracellular Ca(2+) and the contraction caused by PI(3,5)P(2) were prevented by antagonizing RyRs, while the majority of the PI(3,5)P(2) response was intact after blockade of inositol (1,4,5)-trisphosphate receptors. Depletion of SR Ca(2+) stores with thapsigargin or caffeine and/or ryanodine blunted the Ca(2+) response and greatly attenuated the contraction elicited by PI(3,5)P(2). The removal of extracellular Ca(2+) or addition of verapamil to inhibit voltage-dependent Ca(2+) channels reduced but did not eliminate the Ca(2+) or contractile responses to PI(3,5)P(2). We also found that PI(3,5)P(2) depolarized aortic smooth muscle cells and that LaCl(3) inhibited those aspects of the PI(3,5)P(2) response attributable to extracellular Ca(2+). Thus, full and sustained aortic contractions to PI(3,5)P(2) required the release of SR Ca(2+), probably via the activation of RyR, and also extracellular Ca(2+) entry via voltage-dependent Ca(2+) channels.

FGF23/FGFR4-mediated left ventricular hypertrophy is reversible

Fibroblast growth factor (FGF) 23 is a phosphaturic hormone that directly targets cardiac myocytes via FGF receptor (FGFR) 4 thereby inducing hypertrophic myocyte growth and the development of left ventricular hypertrophy (LVH) in rodents. Serum FGF23 levels are highly elevated in patients with chronic kidney disease (CKD), and it is likely that FGF23 directly contributes to the high rates of LVH and cardiac death in CKD. It is currently unknown if the cardiac effects of FGF23 are solely pathological, or if they potentially can be reversed. Here, we report that FGF23-induced cardiac hypertrophy is reversible in vitro and in vivo upon removal of the hypertrophic stimulus. Specific blockade of FGFR4 attenuates established LVH in the 5/6 nephrectomy rat model of CKD. Since CKD mimics a form of accelerated cardiovascular aging, we also studied age-related cardiac remodeling. We show that aging mice lacking FGFR4 are protected from LVH. Finally, FGF23 increases cardiac contractility via FGFR4, while known effects of FGF23 on aortic relaxation do not require FGFR4. Taken together, our data highlight a role of FGF23/FGFR4 signaling in the regulation of cardiac remodeling and function, and indicate that pharmacological interference with cardiac FGF23/FGFR4 signaling might protect from CKD- and age-related LVH.

Skeletal Muscle, but not Cardiovascular Function, Is Altered in a Mouse Model of Autosomal Recessive Hypophosphatemic Rickets

Autosomal recessive hypophosphatemic rickets (ARHR) is a heritable disorder characterized by hypophosphatemia, osteomalacia, and poor bone development. ARHR results from inactivating mutations in the DMP1 gene with the human phenotype being recapitulated in the Dmp1 null mouse model which displays elevated plasma fibroblast growth factor 23. While the bone phenotype has been well-characterized, it is not known what effects ARHR may also have on skeletal, cardiac, or vascular smooth muscle function, which is critical to understand in order to treat patients suffering from this condition. In this study, the extensor digitorum longus (EDL-fast-twitch muscle), soleus (SOL–slow-twitch muscle), heart, and aorta were removed from Dmp1 null mice and ex-vivo functional tests were simultaneously performed in collaboration by three different laboratories. Dmp1 null EDL and SOL muscles produced less force than wildtype muscles after normalization for physiological cross sectional area of the muscles. Both EDL and SOL muscles from Dmp1 null mice also produced less force after the addition of caffeine (which releases calcium from the sarcoplasmic reticulum) which may indicate problems in excitation contraction coupling in these mice. While the body weights of the Dmp1 null were smaller than wildtype, the heart weight to body weight ratio was higher. However, there were no differences in pathological hypertrophic gene expression compared to wildtype and maximal force of contraction was not different indicating that there may not be cardiac pathology under the tested conditions. We did observe a decrease in the rate of force development generated by cardiac muscle in the Dmp1 null which may be related to some of the deficits observed in skeletal muscle. There were no differences observed in aortic contractions induced by PGF2α or 5-HT or in endothelium-mediated acetylcholine-induced relaxations or endothelium-independent sodium nitroprusside-induced relaxations. In summary, these results indicate that there are deficiencies in both fast twitch and slow twitch muscle fiber type contractions in this model of ARHR, while there was less of a phenotype observed in cardiac muscle, and no differences observed in aortic function. These results may help explain skeletal muscle weakness reported by some patients with osteomalacia and need to be further investigated.

PPARα-Independent Arterial Smooth Muscle Relaxant Effects of PPARα Agonists

We sought to determine direct vascular effects of peroxisome proliferator-activated receptor alpha (PPARα) agonists using isolated mouse aortas and middle cerebral arteries (MCAs). The PPARα agonists GW7647, WY14643, and gemfibrozil acutely relaxed aortas held under isometric tension and dilated pressurized MCAs with the following order of potency: GW7647≫WY14643>gemfibrozil. Responses were endothelium-independent, and the use of PPARα deficient mice demonstrated that responses were also PPARα-independent. Pretreating arteries with high extracellular K+ attenuated PPARα agonist-mediated relaxations in the aorta, but not in the MCA. In the aorta, the ATP sensitive potassium (KATP) channel blocker glibenclamide also impaired relaxations whereas the other K+ channel inhibitors, 4-aminopyridine and Iberiotoxin, had no effect. In aortas, GW7647 and WY14643 elevated cGMP levels by stimulating soluble guanylyl cyclase (sGC), and inhibition of sGC with ODQ blunted relaxations to PPARα agonists. In the MCA, dilations were inhibited by the protein kinase C (PKC) activator, phorbol 12,13-dibutyrate, and also by ODQ. Our results demonstrated acute, nonreceptor-mediated relaxant effects of PPARα agonists on smooth muscle of mouse arteries. Responses to PPARα agonists in the aorta involved KATP channels and sGC, whereas in the MCA the PKC and sGC pathways also appeared to contribute to the response.

Pharmacokinetics and Bioavailability of Annatto ô-tocotrienol in Healthy Fed Subjects

Background: Although, α-tocopherol is the most bioavailable form of vitamin E, but several animal and clinical studies have demonstrated tocotrienol bioavailability to various tissues. There are few reports on bioavailability of tocotrienols in humans. Most studies were carried out with mixtures of tocotrienols + tocopherols rather than pure tocotrienols. Moreover, dietary α-tocopherol interferes with the bioavailability of tocotrienols, and prevents absorption and delivery to organs and tissues. Aim: Pharmacokinetics and bioavailability of annatto-based δ-tocotrienol, plasma levels of α-, β-, γ-, δ-tocotrienol and tocopherols were quantified. In addition, several cytokines and microRNAs were examined. Study design: An open-label, randomized study evaluated pharmacokinetics and bioavailability of δ-tocotrienol in 33 healthy fed subjects. All subjects (11/dose) were randomly assigned to doses of 125, 250, or 500 mg/d. Plasma samples collected at 0, 1, 2, 3, 4, 6, 8, 10 h intervals were estimated by HPLC for tocols (tocotrienols and tocopherols). Results: The present study describes the effects of δ-tocotrienol on pharmacokinetic parameters of all eight tocol isomers. Supplementation of 125, 250 and 500 mg/d doses resulted in dose- dependent increases of (a) area under concentration-time curve (AUCt0 - t10 ng/ml) 2464, 5412, 14986; (b) maximum concentration (Cmax, ng/ml) 829, 1920, 3278 (P<0.001); (c) time to achieve maximum peak (Tmax; h) 3, 3, 6; (d) elimination of half-life (t1/2 h) 1.74, 1.39, 2.54; (e) time of clearance (Cl-T, h-1) 0.049, 0.045, 0.030; (f) volume of distribution (Vd/f, mg/h) 0.119, 0.114, 0.113; and (g) elimination rate constant (Ke; h-1) 0.412, 0.401, 0.265. Similar results were reported for the other tocols. Maximum plasma levels of δ-tocotrienol were observed at 3 h with doses of 125 and 250 mg/d, and 6 h with 500 mg/d. γ-tocotrienol, β-tocotrienol, α-tocotrienol, δ-tocopherol, γ-tocopherol β-tocopherol and α-tocopherol were appeared in the plasma after 2 h. Moreover, δ-tocotrienol treatment resulted in down-regulation of eight cytokines and upregulation of adiponectin, TGF-β1, and leptin. The expression of miR-34a (increased in bipolar disorder) was down-regulated, but expression of miR-107, miR-122a, and miR-132 (decreased in Alzheimer’s disease) was upregulated by δ-tocotrienol treatment. Conclusion: This is the first study describing the effect of δ-tocotrienol on pharmacokinetics and bioavailability of all eight tocol isomers. When tocotrienols are supplemented in absence of tocopherols, δ-tocotrienol has better bioavailability, and δ-tocotrienol is converted stepwise to other tocotrienols/tocopherols. These results support that tocotrienol, particularly δ-tocotrienol, as a dietary supplement might be useful in the prevention of age-related and chronic ailments.

Restoration of Endothelial Function in Pparα−/− Mice by Tempol

Peroxisome proliferator activated receptor alpha (PPARα) is one of the PPAR isoforms belonging to the nuclear hormone receptor superfamily that regulates genes involved in lipid and lipoprotein metabolism. PPARα is present in the vascular wall and is thought to be involved in protection against vascular disease. To determine if PPARα contributes to endothelial function, conduit and cerebral resistance arteries were studied in Pparα −/− mice using isometric and isobaric tension myography, respectively. Aortic contractions to PGF2α and constriction of middle cerebral arteries to phenylephrine were not different between wild type (WT) and Pparα −/−; however, relaxation/dilation to acetylcholine (ACh) was impaired. There was no difference in relaxation between WT and Pparα −/− aorta to treatment with a nitric oxide (NO) surrogate indicating impairment in endothelial function. Endothelial NO levels as well as NO synthase expression were reduced in Pparα −/− aortas, while superoxide levels were elevated. Two-week feeding with the reactive oxygen species (ROS) scavenger, tempol, normalized ROS levels and rescued the impaired endothelium-mediated relaxation in Pparα −/− mice. These results suggest that Pparα −/− mice have impaired endothelial function caused by decreased NO bioavailability. Therefore, activation of PPARα receptors may be a therapeutic target for maintaining endothelial function and protection against cardiovascular disease.

Comparative Evaluation of NS-5 Mixture and its Components on Superoxide Production in HUVEC, and Inflammatory Biomarkers in Humans

Background: Inhibitory effects of NS-5 mixture of resveratrol, quercetin, δ-tocotrienol, nicotinic acid on several inflammatory and cardiovascular risk factors have been reported in normal cholesterolemic and hypercholesterolemic humans. The hypothesis was that combination of cholesterol-lowering and inflammatory-reducing properties of NS-5 mixture would be more effective than its individual components in reducing the serum levels of several biomarkers of cardiovascular disease in humans. However, effects of NS-5 mixture and its components did not report effects on cytokines, gene expression, and microRNAs were not reported in previous publication. As this area is gaining importance in the understanding of various transcriptional factors and signal pathways, which regulate several biomarkers in various diseases. Aims: Modulation of NS-5 mixture, and its components were evaluated on superoxide production in HUVEC in vitro, and on serum levels of total cholesterol, NO, CRP, TAS, plasma cytokines, gene expression, miRNAs in vivo in normal cholesterolemic and hypercholesterolemic humans. Study design: Study was carried out as double-blind randomized, trial of NS-5 mixture, resveratrol, quercetin, and δ-tocotrienol in free-living healthy and hypercholesterolemic humans. Results: The NS-5 mixture, resveratrol, quercetin, δ-tocotrienol, or nicotinic acid treatments caused reduction in superoxide production (11% to 24%; P<0.01) in HUVEC. These reductions were more pronounced with LPSstimulated HUVEC (26% to 40%; P<0.01) compared to predose values. These findings were further supported by decreases (P<0.01) in serum total cholesterol levels of NS-5 treated group (24%) versus resveratrol (18%), quercetin (20%), and δ-tocotrienol (22%) in hypercholesterolemic humans, followed by reduction of NO, CRP and increases in TAS in normal cholesterolemic and hypercholesterolemic humans. There was significant (P<0.001) down-regulation in pro-inflammatory cytokines and gene expression of resistin, IL-2α, IL-6, IL-12, IL-18, TNF-α, and others, that are normally involved in pathogenesis of atherosclerosis, diabetes, and aging processes. The plasma inflammatory miRNAs (miR-101a, miR-125a, miR-155, miR-223) were down-regulated as compared to predose values. The elevated levels of miRNA-146a during senescence were down-regulated after treatment with these compounds. Conclusions: This is the first report that describes the effects of NS-5 mixture, its components on proteomics, gene expression and levels of miRNAs in normal cholesterolemic and hypercholesterolemic humans. Results suggest that NS-5 mixture and its components are potent agents in the reduction of superoxide production, cardiovascular risk factors and inflammatory biomarkers, which are modulated by NF-κB. Maximum inhibition in superoxide production and other risk factors was observed with NS-5 mixture as compared with its individual components, thus supporting our hypothesis.

Statins impact primary embryonic mouse neural stem cell survival, cell death, and fate through distinct mechanisms

Statins inhibit HMG-CoA reductase, the rate-limiting enzyme in the cholesterol biosynthesis pathway (CBP), and are used for the prevention of cardiovascular disease. The anti-inflammatory effects of statins may also provide therapeutic benefits and have led to their use in clinical trials for preeclampsia, a pregnancy-associated inflammatory condition, despite their current classification as category X (i.e. contraindicated during pregnancy). In the developing neocortex, products of the CBP play essential roles in proliferation and differentiation of neural stem-progenitor cells (NSPCs). To understand how statins could impact the developing brain, we studied effects of pravastatin and simvastatin on primary embryonic NSPC survival, proliferation, global transcription, and cell fate in vitro. We found that statins dose dependently decrease NSPC expansion by promoting cell death and autophagy of NSPCs progressing through the G1 phase of the cell cycle. Genome-wide transcriptome analysis demonstrates an increase in expression of CBP genes following pravastatin treatment, through activation of the SREBP2 transcription factor. Co-treatment with farnesyl pyrophosphate (FPP), a CBP metabolite downstream of HMG-CoA reductase, reduces SREBP2 activation and pravastatin-induced PARP cleavage. Finally, pravastatin and simvastatin differentially alter NSPC cell fate and mRNA expression during differentiation, through a non-CBP dependent pathway.

Of Mice and Men: Proteasome's Role in Lps-induced Inflammation and Tolerance.

ABSTRACT The molecular basis responsible for tolerance following inflammatory response to lipopolysaccharide (LPS) is not well understood. We hypothesized that inflammation/tolerance in monocytes/ macrophages is dependent on the proteases of proteasome. To test our hypothesis, first, we examined the expression of different proteasome subunits in different human and mouse monocytes/macrophages. Secondly, we investigated the effect of proteasome subunits/ proteases on LPS-induced expression of tumor necrosis factor-&agr; (TNF-&agr;) and nitric oxide (NO) during inflammation and tolerance using mouse RAW 264.7 macrophages, THP1 cells, and cluster of differentiation 14 positive (CD14+) human monocytes. We found that RAW 264.7 cells (XYZ), mouse peritoneal resident, thioglycollate-elicited macrophages, primed RAW 264.7 (XYZ, LMP), and human monocytes (LMP) expressed different types of proteasome subunits/activities. Cells containing predominantly either LMP subunits (such as THP-1 and human monocytes), or only X, Y, Z subunits (RAW 264.7 cells not primed) could only induce TNF-&agr;, but not NO, while cells containing all five to six subunits (XYZ, LMP) of the proteasome could induce both mediators in response to LPS. Distinct states of inflammation/tolerance in LPS treated cells, strongly correlated with an upregulation or downregulation of proteasomes subunits (proteases), respectively. Moreover, interferon-&ggr; treatment of tolerant cells caused robust induction of proteasomes subunit expression in mouse macrophages and human monocytes, and cells regained their ability to respond to LPS. These studies are vital for understanding function of proteasomes subunits during inflammation/tolerance in mouse and human cells, and for design of therapeutic strategies for all diseases based on inflammation.