Application of kinetic modeling to mineral metabolism management.

Patients with CKD face many consequences of renal failure, including disorders of bone and mineral metabolism. The current approach to management of these mineral metabolism issues lacks comprehensive quantitative assessment, so a kinetic modeling program has been designed to quantify intake and removal of phosphorus and calcium, as well as provide recommendations for treatment and prescriptions based on total mass balance and serum concentrations. This program is known as phosphorus kinetic modeling or PKM. The modeling program and associated graphical reports have been developed as a tool for clinicians in the management of mineral metabolism in CKD patients.

Sensitivity of NOS-dependent vascular relaxation pathway to mineralocorticoid receptor blockade in caveolin-1-deficient mice.

Endothelial caveolin-1 (cav-1) is an anchoring protein in plasma membrane caveolae where it binds endothelial nitric oxide synthase (eNOS) and limits its activation, particularly in animals fed a high salt (HS) diet. Cav-1 also interacts with steroid receptors such as the mineralocorticoid receptor (MR). To test the hypothesis that vascular reactivity is influenced by an interplay between MR and cav-1 during HS diet, we examined the effects of MR blockade on NOS-mediated vascular relaxation in normal and cav-1-deficient mice. Wild-type (WT) and cav-1 knockout mice (cav-1(-/-)) were fed for 14 days a HS (4% NaCl) diet with and without the MR antagonist eplerenone (Epl; 100 mg x kg(-1) x day(-1)). After systolic blood pressure (BP) was measured, the thoracic aorta was isolated for measurement of vascular reactivity, and the aorta and heart were used for measurement of eNOS and MR expression. BP was not different between WT + Epl and WT, but was higher in cav-1(-/-) + Epl than in cav-1(-/-) mice. Phenylephrine (Phe)-induced vascular contraction was less in cav-1(-/-) than WT, and significantly enhanced in cav-1(-/-) + Epl than in cav-1(-/-), but not in WT + Epl compared with WT. Endothelium removal and NOS blockade by N(omega)-nitro-l-arginine methyl ester (l-NAME) enhanced Phe contraction in cav-1(-/-), but not cav-1(-/-) + Epl. ACh-induced aortic relaxation was reduced in cav-1(-/-) + Epl versus cav-1(-/-), but not in WT + Epl compared with WT. Endothelium removal, l-NAME, and the guanylate cyclase inhibitor ODQ abolished the large ACh-induced relaxation in cav-1(-/-) and the remaining relaxation in the cav-1(-/-) + Epl but had similar inhibitory effect in WT and WT + Epl. Real-time RT-PCR indicated decreased eNOS mRNA expression in the aorta and heart, and Western blots revealed decreased total eNOS in the heart of cav-1(-/-) + Epl compared with cav-1(-/-). Vascular and cardiac MR expression was less in cav-1(-/-) than WT, but not in cav-1(-/-) + Epl compared with cav-1(-/-). Plasma aldosterone (Aldo) was not different between WT and cav-1(-/-) mice nontreated or treated with Epl. Thus in cav-1 deficiency states and HS diet MR blockade is associated with increased BP, enhanced vasoconstriction, and decreased NOS-mediated vascular relaxation and eNOS expression. The data suggest that, in the absence of cav-1, MR activation plays a beneficial role in regulating eNOS expression/activity and, consequently, the vascular function during HS diet.

Increased vascular angiotensin type 2 receptor expression and NOS-mediated mechanisms of vascular relaxation in pregnant rats.

Normal pregnancy is associated with reduced blood pressure (BP) and decreased pressor response to vasoconstrictors, even though the renin-angiotensin system is upregulated. Angiotensin II (ANG II) activates both angiotensin type 1 receptors (AT(1)Rs) and angiotensin type 2 receptors (AT(2)Rs). Although the role of the AT(1)R in vascular contraction is well documented, the role of the AT(2)R in vascular relaxation, particularly during pregnancy, is less clear. It was hypothesized that the decreased BP and vasoconstriction during pregnancy was, at least in part, due to changes in AT(2)R amount, distribution, and/or postreceptor mechanisms of vascular relaxation. To test this hypothesis, systolic BP was measured in virgin and pregnant (day 19) Sprague-Dawley rats. Isometric contraction/relaxation was measured in isolated aortic rings, and nitric oxide (NO) production was measured using 4-amino-5-methylamino-2',7'-difluorescein fluorescence. AT(1)R and AT(2)R mRNA expression and protein amount were measured in tissue homogenates using real-time RT-PCR and Western blots, and their local distribution was visualized in cryosections using immunohistochemistry and immunofluorescence. BP was lower in pregnant than virgin rats. Phenylephrine (Phe) caused concentration-dependent contraction that was reduced in the aorta of pregnant compared with virgin rats. Treatment with the AT(2)R antagonist PD-123319 caused greater enhancement of Phe contraction, and the AT(2)R agonist CGP-42112A caused greater relaxation of Phe contraction in the aorta of pregnant than virgin rats. ANG II plus the AT(1)R blocker losartan induced greater NO production in the aorta of pregnant than virgin rats. RT-PCR revealed increased mRNA expression of vascular endothelial NO synthase (eNOS), little change in AT(1)Rs, and increased AT(2)Rs in pregnant compared with virgin rats. Western blots revealed an increased protein amount of activated phospho-eNOS, little change in AT(1)Rs, and increased AT(2)Rs in pregnant compared with virgin rats. Immunohistochemistry and immunofluorescence analysis in aortic sections of virgin rats revealed abundant AT(1)R staining in tunica media that largely colocalized with actin in vascular smooth muscle and less AT(2)Rs mainly in the tunica intima and endothelium. In pregnant rats, AT(1)R staining in the smooth muscle layer and adventitia was reduced, and endothelial AT(2)R staining was enhanced. These data suggest an enhanced AT(2)R-mediated vascular relaxation pathway involving increased expression/activity of endothelial AT(2)Rs and increased postreceptor activated phospho-eNOS, which may contribute to the decreased BP during pregnancy.

Trans-sodium crocetinate and hemorrhagic shock.

Trans-sodium crocetinate (TSC) has been found to alleviate the symptoms of hemorrhagic shock in that, after the drug is given to hemorrhaged rats, blood pressure rises, elevated lactate levels are reduced, cellular damage in the liver and kidney is less, and survival is increased. The mechanism of action proposed for TSC is that it increases the diffusion of oxygen through blood plasma and into the tissue. The study reported here explores another proposed mechanism, the scavenging of free radicals. It is shown that TSC does scavenge radicals and may be more efficient than other free-radical scavengers. However, this may not be the mechanism of action for TSC during hemorrhagic shock. Not only are the TSC concentrations needed for radical scavenging greater than those which provide beneficial effects in hemorrhagic shock, but it is also shown that another radical scavenger, trolox, has no effect on oxygen consumption during shock. Trans-sodium crocetinate clearly holds promise as a useful treatment of hemorrhagic shock. Pharmacokinetics data are presented for different modes of administration. Initial studies suggest that instillation of TSC into the trachea or intramuscular injection may provide useful alternative treatment routes.

trans-Sodium crocetinate and diffusion enhancement.

trans-Sodium crocetinate (TSC) increases the diffusion coefficient of glucose through water by about 25-30%. This is the same percentage increase that TSC causes in the diffusivity of oxygen through water. TSC is also found to induce order in the surrounding water structure through increased hydrogen bonding of the water molecules, and molecular simulations suggest that the increase in diffusivity occurs only in these ordered regions.

Neurovascular mechanisms of hypertension in pregnancy.

Normal pregnancy is associated with significant changes in the neuronal and vascular control mechanisms of blood pressure (BP). Preeclampsia (PE) is a major complication of pregnancy characterized by proteinuria, and increased vascular resistance and BP. If untreated, PE leads to eclampsia with serious seizures and severe hypertension. However, the neurovascular mechanisms of hypertension in pregnancy and PE are unclear. Studies in animal models of hypertension in pregnancy suggest that inadequate cytotrophoblast invasion of uterine spiral arteries causes reduction in uteroplacental perfusion pressure leading to placental ischemia/hypoxia. Placental ischemia may promote the release of biologically active factors such as cytokines and reactive oxygen species. These circulating factors may increase the vascular permeability, cross the blood-brain barrier, and affect the sympathetic tone and the neuronal control mechanisms of BP. Placental factors could also cause endothelial cell dysfunction and inhibit nitric oxide (NO)-cyclic guanosine monophosphate (cGMP), prostacyclin (PGI(2))-cyclic adenosine monophosphate (cAMP), and hyperpolarizing factor vascular relaxation pathways. Additionally, placental factors may induce endothelium-derived contracting factors such as endothelin, thromboxane and angiotensin II, which stimulate Ca(2+)-dependent vascular smooth muscle (VSM) contraction or increase protein kinase C activity and enhance myofilament sensitivity to intracellular free calcium concentration ([Ca(2+)](i)). The increased sympathetic tone combined with systemic decrease in endothelium-dependent vascular relaxation and enhanced VSM contraction may contribute to the increased vascular resistance and BP associated with PE. The hypertensive state in severe PE may weaken the blood-brain barrier and precipitate convulsions and cerebral hemorrhage. Careful monitoring of maternal neuronal, endothelial, and VSM function during pregnancy should circumvent the life-threatening neurovascular complications of PE-eclampsia.

TSC for hemorrhagic shock: effects on cytokines and blood pressure.

Previous studies have shown that administering trans-sodium crocetinate (TSC) as a treatment of hemorrhagic shock leads to increased whole-body oxygen consumption and survival as well as protection of the liver and kidney. It has been suggested that TSC increases oxygen delivery by increasing the diffusivity of oxygen through plasma. However, as with any novel mechanism of action, there are always questions about whether the results could also be ascribed to other, previously described mechanisms of action. This study was designed to look at some aspects of that by examining the effect of different TSC dosing regimens on the blood pressure and the production of cytokines after hemorrhage because both responses have been reported with compounds that act via other mechanisms. In a constant-pressure rat model of hemorrhagic shock, it was seen that a singe bolus injection of TSC results in an immediate but transient increase in the arterial blood pressure. This is similar to the effect reported previously for using 100% oxygen. It was also found that if the TSC injections were repeated periodically over an hour, a sustained increase in the blood pressure would occur. Because inflammatory cytokines have been implicated in mortality and tissue damage, it has been suggested that TSC may affect the production of cytokines. Thus, the effect of TSC on the production of TNF-alpha and IL-10 was also examined. The data show that treatment with TSC results in lower concentrations of TNF-alpha in the liver and spleen as well as lower concentrations of IL-10 in the spleen. Again, similar effects on other cytokines have been seen with 100% oxygen. These results support the hypothesis that the effects of TSC on hemorrhagic shock are mediated via an effect on oxygen.