Anand Vaidya

In Vivo Molecular Imaging of Acute and Subacute Thrombosis Using a Fibrin-Binding Magnetic Resonance Imaging Contrast Agent

Background—Plaque rupture with subsequent thrombosis is recognized as the underlying pathophysiology of most acute coronary syndromes and stroke. Thus, direct thrombus visualization may be beneficial for both diagnosis and guidance of therapy. We sought to test the feasibility of direct imaging of acute and subacute thrombosis using MRI together with a novel fibrin-binding gadolinium-labeled peptide, EP-1873, in an experimental animal model of plaque rupture and thrombosis. Methods and Results—Fifteen male New Zealand White rabbits (weight, ≈3.5 kg) were made atherosclerotic by feeding a high-cholesterol diet after endothelial aortic injury. Plaque rupture was then induced with the use of Russell’s viper venom (RVV) and histamine. Subsequently, MRI of the subrenal aorta was performed before RVV, after RVV, and after EP-1873. Histology was performed on regions suggested by MRI to contain thrombus. Nine rabbits (60%) developed plaque rupture and thrombus, including 25 thrombi visually apparent on MRI as “hot spots” after injection of EP-1873. Histological correlation confirmed all 25 thrombi (100%), with no thrombi seen in the other regions of the aorta. In the remaining 6 rabbits (control) without plaque rupture, no thrombus was observed on the MR images or on histology. Conclusions—We demonstrate the feasibility of in vivo “molecular” MRI for the detection of acute and subacute thrombosis using a novel fibrin-binding MRI contrast agent in an animal model of atherosclerosis and acute/subacute thrombosis. Potential clinical applications include thrombus detection in acute coronary syndromes and stroke.

Vitamin D and Hypertension. Current Evidence and Future Directions

The prevalence of vitamin D insufficiency, defined by a 25-hydroxyvitamin D (25[OH]D) level <30 ng/mL, in the United States was 77% in 2004.1 Although the use of vitamin D supplementation may be increasing since 2004, it is likely that the majority of US citizens continue to have inadequate vitamin D status.2 Observational studies suggest that low 25(OH)D levels are associated with a higher risk of hypertension. However, findings from randomized trials of vitamin D supplementation to lower blood pressure are inconsistent, possibly stemming from variability in study population, sample size, vitamin D dose, and duration. If vitamin D supplementation lowers blood pressure, its widespread use could have major public health benefits. In this review, we summarize the existing literature dealing with the vitamin D-hypertension link, including mechanistic studies, observational data, and clinical trials; we place special emphasis on recent findings. Biological mechanisms relating vitamin D with hypertension have been proposed for >25 years. Vitamin D has been implicated in the proximal regulation of the renin-angiotensin system (RAS) and in interacting with the RAS to determine the intracellular calcium milieu in vascular smooth muscle. ### Vitamin D and the RAS Dietary sodium and increased activity of the RAS are known to contribute to hypertension; salt restriction and inhibition of RAS activity reduce blood pressure.3–5 Li et al6 provided convincing support for vitamin D as a proximal inhibitor of the RAS when they described a phenotype of excess plasma renin activity and hypertension in mice lacking the vitamin D receptor, which normalized after treatment with RAS antagonists. These vitamin D receptor–null mice also displayed an increased susceptibility to obstructive renal injury that could be prevented with RAS antagonism.7 Mice with deficient 1α-hydroxylase activity were also found to have increased plasma renin activity and hypertension, and this unfavorable phenotype could be reversed with 1,25-dihydroxyvitamin …

Metal ion binding sites in a group II intron core

Group II introns are catalytic RNA molecules that require divalent metal ions for folding, substrate binding, and chemical catalysis. Metal ion binding sites in the group II core have now been elucidated by monitoring the site-specific RNA hydrolysis patterns of bound ions such as Tb3+ and Mg2+. Major sites are localized near active site elements such as domain 5 and its surrounding tertiary interaction partners. Numerous sites are also observed at intron substructures that are involved in binding and potentially activating the splice sites. These results highlight the locations of specific metal ions that are likely to play a role in ribozyme catalysis.

The relationship between vitamin D and the renin-angiotensin system in the pathophysiology of hypertension, kidney disease, and diabetes

Vitamin D has been implicated in the pathophysiology of extraskeletal conditions such as hypertension, kidney disease, and diabetes via its ability to negatively regulate the renin-angiotensin system (RAS). This article reviews the evidence supporting a link between vitamin D and the RAS in these conditions, with specific emphasis on translational observations and their limitations. A literature review of animal and human studies evaluating the role of vitamin D in hypertension, kidney disease, and diabetes was performed. Excess activity of the RAS has been implicated in the pathogenesis of hypertension, chronic kidney disease, decreased insulin secretion, and insulin resistance. Animal studies provide strong support for 1,25-dihydroxyvitamin D(3)-mediated downregulation of renin expression and RAS activity via its interaction with the vitamin D receptor. Furthermore, the activity of vitamin D metabolites in animals is associated with reductions in blood pressure, proteinuria and renal injury, and with improved β-cell function. Many observational, and a few interventional, studies in humans have supported these findings; however, there is a lack of well-designed prospective human interventional studies to definitively assess clinical outcomes. There is a need for more well-designed prospective interventional studies to validate this hypothesis in human clinical outcomes.

25-Hydroxyvitamin D is associated with plasma renin activity and the pressor response to dietary sodium intake in Caucasians

Introduction: Concentrations of 1,25-hydroxyvitamin D have been positively associated with dietary sodium and salt sensitivity (SS) of blood pressure (BP), and inversely with plasma renin activity (PRA). We investigated the association between PRA and 25-hydroxyvitamin D (25OHD), the most clinically relevant vitamin D metabolite, and whether 25OHD associates with SS of BP in renin phenotypes of hypertension. Methods: We performed cross-sectional analyses on 223 Caucasian subjects with hypertension maintained in high and low dietary sodium balance. Subjects were distinguished as having low-renin (LR) or normal-renin (NR) hypertension. Multivariable linear regression was used to evaluate adjusted relationships. Results: Increasing 25OHD concentrations were inversely associated with PRA (p < 0.05) on both salt diets. Furthermore, 25OHD was associated with SS of BP in LR hypertension (b = 0.62, p = 0.04), but not in NR hypertension (b = 0.06, p = 0.59). In an adjusted multivariable interaction model, renin status (LR vs. NR) was a significant effect modifier of the relationship between 25OHD and SS of BP (p = 0.04). Conclusions: Our findings suggest that 25OHD is inversely associated with PRA and positively associated with SS of BP in LR hypertension subjects. These results extend and support prior evidence indicating an interaction between dietary sodium, the RAS, and vitamin D that influences BP in hypertension.

Angiotensin Receptor Blockade With Candesartan Attenuates Atherosclerosis, Plaque Disruption, and Macrophage Accumulation Within the Plaque in a Rabbit Model

Background—Little is known about whether direct angiotensin receptor blockade can reduce atherosclerosis and plaque disruption. This study evaluated the effect of angiotensin receptor blockade on both the development of atherosclerosis and the disruption of plaque in a modified Constantinides animal model. Methods and Results—Twenty-eight New Zealand White rabbits underwent aortic balloon injury followed by a 1% cholesterol diet for 8 weeks. Thirteen rabbits received candesartan at 0.5 mg · kg−1 · d−1 beginning 2 days before aortic balloon injury and continued for the total 8 weeks of the cholesterol diet. The rabbits were then pharmacologically triggered and humanely killed, and their aortas were analyzed. The degree of atherosclerosis was determined by intima-media ratio of the infrarenal portion of the aorta. The frequency of intra-aortic thrombosis, a measure of plaque disruption, and the percentages of macrophage area and collagen-staining area of the plaque were determined. Candesartan-treated rabbits had less atherosclerosis (intima-media infrarenal aorta ratio of 1.18±0.08 versus 1.57±0.08 [mean±SEM] for the placebo group, P<0.001); fewer thrombi (3 of 13 versus 11 of 15; P<0.05); lower percentage area of macrophages to total plaque (18.8±2.7% versus 27±2.5%, P<0.05); and higher collagen to total plaque area (45±3% versus 35±2%, P<0.01). Conclusions—These results demonstrate that angiotensin receptor blockade attenuates the degree of atherosclerosis and reduces both plaque disruption and macrophage accumulation while increasing collagen deposition in the aortas of this animal model.

Human Interventions to Characterize Novel Relationships Between the Renin–Angiotensin–Aldosterone System and Parathyroid Hormone

Observational studies in primary hyperaldosteronism suggest a positive relationship between aldosterone and parathyroid hormone (PTH); however, interventions to better characterize the physiological relationship between the renin–angiotensin–aldosterone system (RAAS) and PTH are needed. We evaluated the effect of individual RAAS components on PTH using 4 interventions in humans without primary hyperaldosteronism. PTH was measured before and after study (1) low-dose angiotensin II (Ang II) infusion (1 ng/kg per minute) and captopril administration (25 mg×1); study (2) high-dose Ang II infusion (3 ng/kg per minute); study (3) blinded crossover randomization to aldosterone infusion (0.7 µg/kg per hour) and vehicle; and study (4) blinded randomization to spironolactone (50 mg/daily) or placebo for 6 weeks. Infusion of Ang II at 1 ng/kg per minute acutely increased aldosterone (+148%) and PTH (+10.3%), whereas Ang II at 3 ng/kg per minute induced larger incremental changes in aldosterone (+241%) and PTH (+36%; P<0.01). Captopril acutely decreased aldosterone (−12%) and PTH (−9.7%; P<0.01). In contrast, aldosterone infusion robustly raised serum aldosterone (+892%) without modifying PTH. However, spironolactone therapy during 6 weeks modestly lowered PTH when compared with placebo (P<0.05). In vitro studies revealed the presence of Ang II type I and mineralocorticoid receptor mRNA and protein expression in normal and adenomatous human parathyroid tissues. We observed novel pleiotropic relationships between RAAS components and the regulation of PTH in individuals without primary hyperaldosteronism: the acute modulation of PTH by the RAAS seems to be mediated by Ang II, whereas the long-term influence of the RAAS on PTH may involve aldosterone. Future studies to evaluate the impact of RAAS inhibitors in treating PTH-mediated disorders are warranted.

Vitamin D3 therapy corrects the tissue sensitivity to angiotensin ii akin to the action of a converting enzyme inhibitor in obese hypertensives: an interventional study.

CONTEXT Vitamin D deficiency and obesity are associated with increased tissue renin-angiotensin system (RAS) activity. OBJECTIVE The objective of the study was to evaluate whether vitamin D(3) therapy in obesity reduces tissue-RAS activity, as indicated by an increase in tissue sensitivity to angiotensin II (AngII). PARTICIPANTS Participants included obese subjects with hypertension and 25-hydroxyvitamin D less than 25 ng/ml. DESIGN Subjects were studied before and after 1 month of vitamin D(3) 15,000 IU/d, while in dietary sodium balance, and off all interfering medications. Fourteen subjects successfully completed all study procedures. SETTING The study was conducted at a clinical research center. OUTCOME MEASURES At each study visit, tissue sensitivity to AngII was assessed by measuring renal plasma flow (RPF), mean arterial pressure (MAP), and adrenal secretion of aldosterone during an infusion of AngII. Subjects were then given captopril, and a second AngII infusion to evaluate the effect of captopril on tissue-RAS activity. RESULTS Vitamin D(3) therapy increased 25-hydroxyvitamin D (18 to 52 ng/ml) and basal RPF (+5%) and lowered supine MAP (-3%) (all P < 0.01). There was a greater decline in RPF and higher stimulation of aldosterone with AngII infusion after vitamin D(3) therapy (both P < 0.05). As anticipated, captopril increased the renal-vascular, MAP, and adrenal sensitivity to AngII, but this effect was much smaller after vitamin D(3) therapy, indicating that vitamin D(3) therapy corrected the tissue sensitivity to AngII akin to captopril. CONCLUSIONS Vitamin D(3) therapy in obese hypertensives modified RPF, MAP, and tissue sensitivity to AngII similar to converting enzyme inhibition. Whether chronic vitamin D(3) therapy abrogates the development of diseases associated with excess RAS activity warrants investigation.

Association of ipilimumab therapy for advanced melanoma with secondary adrenal insufficiency: a case series.

OBJECTIVE To present a case series of ipilimumab-related secondary adrenal insufficiency. METHODS In this cases series, we review the presentation, evaluation, diagnosis, and management of patients with advanced melanoma who received ipilimumab and were referred to our endocrinology clinic for evaluation of hormonal abnormalities. RESULTS Seven patients presented with symptoms, signs, or biochemical evidence of adrenal insufficiency 6 to 12 weeks after starting ipilimumab therapy. Ipilimumab is a cytotoxic T-lymphocyte antigen 4 (CTLA-4) monoclonal antibody that is approved for the treatment of metastatic melanoma and has widespread use for this disease. All 7 patients had biochemical evidence of profound secondary adrenal insufficiency. Thyroid function abnormalities, central hypogonadism, and low insulinlike growth factor 1 levels were seen in a subset of patients. Only 2 patients had abnormal findings on pituitary magnetic resonance imaging. Posterior pituitary function remained normal. CONCLUSIONS Our findings suggest that the enhanced immune response associated with ipilimumab therapy may have a predilection for corticotroph and possibly thyrotroph cells. We recommend periodic hypothalamic-pituitary-adrenal axis monitoring for patients on this therapy.

VITAMIN D AND THE VASCULAR SENSITIVITY TO ANGIOTENSIN II IN OBESE CAUCASIANS WITH HYPERTENSION

Obesity and vitamin D deficiency have both been linked to augmented activity of the tissue renin–angiotensin system (RAS). We investigated whether obesity status influenced the relationship between 25-hydroxyvitamin D (25(OH)D) and vascular RAS activity. The levels of 25(OH)D were measured in hypertensive obese (n=39) and non-obese (n=58) Caucasian individuals. RAS activity was assessed by plasma renin activity, and evaluation of the vascular sensitivity to angiotensin II (AngII) using the mean arterial pressure (MAP) response to an infusion of AngII. Among obese subjects, 25(OH)D was an independent positive predictor of the MAP response to AngII (β=0.70, r=0.41, P<0.01); lower 25(OH)D concentrations were associated with a blunted MAP response to AngII. In contrast, 25(OH)D did not significantly predict the vascular sensitivity to AngII in non-obese subjects (β=0.10, r=0.07, P=0.62). A multivariable-adjusted interaction model confirmed that the positive relationship between 25(OH)D and the vascular sensitivity to AngII strengthened with obesity (P-interaction=0.03). These findings demonstrate a positive association between 25(OH)D and the vascular sensitivity to AngII in obese hypertensives, and further suggest that vascular RAS activity may progressively increase when 25(OH)D deficiency occurs in obesity. Future studies to evaluate the effect of vitamin D supplementation on vascular RAS activity in obesity are needed.