Chemically evoked release of an angiotensin-like peptide from fetal rat brain cells in culture

Influence of loop diuretics on denosumab-induced hypocalcaemia in osteoporosis: a retrospective observational analysis

BACKGROUND

We examined whether denosumab-induced hypocalcaemia is evident in osteoporosis when given loop diuretics that promote urinary calcium excretion.

METHODS

Japanese Spontaneous Adverse Drug Event Reports was analyzed to examine signals for denosumab-induced hypocalcaemia co-administered loop diuretics. We retrospectively included osteoporotic patients to detect predictors for denosumab-induced hypocalcaemia (corrected calcium level < 8.5 mg/dL) using multivariate logistic regression analysis. We compared differences in corrected calcium levels (ΔCa = nadir-baseline).

RESULTS

A significant signal for hypocalcaemia was detected (Reporting odds ratio = 865.8, 95% confidence interval [95% CI]: 596.8 to 1255.9, p < 0.0001). Among 164 patients (hypocalcaemia, 12%), loop diuretics have a significant association with hypocalcaemia (odds ratio [OR] = 6.410, 95% CI: 1.005 to 40.90, p = 0.0494). However, hypocalcaemia was found to be lower in high corrected calcium levels at baseline (OR = 0.032, 95% CI: 0.005 to 0.209, p < 0.0001) and calcium and vitamin D supplementation (OR = 0.285, 95% CI: 0.094 to 0.868, p = 0.0270). In the non-hypocalcaemia, ΔCa decreased significantly in the denosumab plus loop diuretics than in the denosumab alone (-0.9 [-1.3 to -0.7] mg/dL vs. -0.5 [-0.8 to -0.3] mg/dL, p = 0.0156). However, ΔCa remained comparable in the hypocalcaemia despite loop diuretics co-administration (-1.0 [-1.2 to -0.8] mg/dL vs. -0.8 [-1.5 to -0.7] mg/dL, p = 0.7904).

CONCLUSIONS

Loop diuretics may predispose to developing denosumab-induced hypocalcaemia.

NHE3 in the thick ascending limb is required for sustained but not acute furosemide-induced urinary acidification

Na+/H+ exchanger isoform 3 (NHE3) facilitates Na+ reabsorption and H+ secretion by the kidneys. Despite stronger NHE3 abundance in the thick ascending limb (TAL) compared with the S1 and S2 segments of the proximal tubule, the role of NHE3 in the TAL is poorly understood. To investigate the role of NHE3 in the TAL, we generated and phenotyped TAL-specific NHE3 knockout (NHE3TAL-KO) mice. Compared with control mice, NHE3TAL-KO mice did not show significant differences in body weight, blood pH, or plasma Na+, K+, or Cl- levels. Fluid intake trended to be higher and urine osmolality was significantly lower in NHE3TAL-KO mice. Despite a similar glomerular filtration rate, NHE3TAL-KO mice had a greater urinary K+-to-creatinine ratio. One proposed role of NHE3 relates to furosemide-induced urinary acidification. Acute bolus treatment with furosemide under anesthesia did not result in differences in the dose dependence of urinary flow rate, Cl- excretion, or maximal urinary acidification between genotypes; however, in contrast with control mice, urinary pH returned immediately toward baseline levels in NHE3TAL-KO mice. Chronic furosemide treatment reduced urine osmolality similarly in both genotypes but metabolic alkalosis, hypokalemia, and calciuresis were absent in NHE3TAL-KO mice. Compared with vehicle, chronic furosemide treatment resulted in greater Na+-K+-2Cl- abundance regardless of genotype. Na+-phosphate cotransporter 2a abundance was also greater in furosemide-treated control mice compared with vehicle treatment, an effect that was absent in NHE3TAL-KO mice. In summary, NHE3 in the TAL plays a role in the sustained acidification effect of furosemide. Consistent with this, long-term treatment with furosemide did not result in metabolic alkalosis in NHE3TAL-KO mice.NEW & NOTEWORTHY Na+/H+ exchanger isoform 3 (NHE3) is very abundant in the thick ascending limb (TAL) compared with the proximal tubule. Much has been learned about the role of NHE3 in the proximal tubule; however, the function of NHE3 in the TAL remains elusive. A novel mouse model that lacks NHE3 selectively in the TAL not only shows a phenotype under baseline conditions but also identifies that NHE3 is required for sustained but not acute furosemide-induced urinary acidification.

Differences between perinatal angiotensin binding in the brains of SHR and WKY rats

A growing body of evidence suggests that angiotensin may have a functional role in growth and development, in addition to its classical role in the maintenance of body water homeostasis. Components of the renin-angiotensin system have been identified in the rat fetus. Because of the association between the renin-angiotensin system and hypertension, we quantified angiotensin receptor binding sites in the brains of spontaneously hypertensive rats (SHR) and Wistar Kyoto (WKY) rats during perinatal development. Using in vitro receptor autoradiography we identified specific 125I-Sar1,Ile8 AII binding in several areas of the brains of perinatal rats of both strains and observed significant differences in the concentration of binding sites, at different ages in several brain nuclei. With the knowledge that components of the renin-angiotensin system appear early in development and are known to have an association with cellular growth, it is possible that an irregularity in this system occurring during neurogenesis could contribute to developmental abnormalities, as well as subsequent hypertension.

Release of angiotensin in response to ionic stimulation: a possible role for calmodulin in the secretory event

Although the synthesis and distribution of the putative neurotransmitter angiotensin (ANG) has been well established, little is known about the mechanism for its release. In this study, we utilized dissociated cell cultures of fetal rat brain to examine the cellular and ionic properties of angiotensin release. Graded concentrations of 0-60 mM KCl in the presence of 5 mM CaCl2 were added to the cultured cells and the resulting angiotensin release was measured by radioimmunoassay and high-performance liquid chromatography. Levels of angiotensin release increased from 13.85 +/- 1.53 pg/mg protein to 172.64 +/- 17.49 pg/mg protein with increasing concentrations of K+. Cultures incubated with 60 mM KCl buffer that did not contain CaCl2 released 39.87 +/- 15.74 pg ANG/mg protein. To further show the link between ionic stimulation and angiotensin release and determine the potential role of extracellular sodium ions on angiotensin release, cultures were incubated with the Na(+)-channel blocker tetrodotoxin (300 nM TTX) prior to maximal stimulation with 60 mM KCl/5 mM CaCl2 in the presence of the channel antagonist. Release was attenuated following incubation with stimulating buffer containing TTX (300 nM) to 5.49 +/- 4.37 pg/mg protein. Finally, to determine the role of the calcium binding protein calmodulin in the release event, the cells were incubated with graded concentrations of W-7 (2.5-250 microM) and subsequently stimulated with 60 mM KCl/5 mM CaCl2 in the presence of the calmodulin antagonist. W-7, which displays specificity for inhibition of the Ca2+/calmodulin complex below 0.2 mM, decreased angiotensin release in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a high affinity, guanine nucleotide sensitive angiotensin receptor on differentiated neuroblastoma-glioma hybrid cells (NG108-15)

The binding characteristics of [125I]angiotensin II (ANG II) to membranes prepared from undifferentiated and differentiated neuroblastoma x glioma hybrid cells (NG108-15) were investigated. Scatchard analysis revealed the existence of high and low affinity sites in differentiated cells, but only a low affinity site in undifferentiated cells. Similarly, self-displacement studies revealed competition to a single low affinity site in undifferentiated cells, and to high and low affinity sites in differentiated cells. Angiotensin III (ANG III) displaced high affinity binding in differentiated cells but did not displace low affinity binding in either differentiated or undifferentiated cells. Furthermore, 5-guanyl imidodiphosphate (GPP(NH)P) inhibited [125I]ANG II binding to differentiated cells, in a dose-dependent fashion, but had no effect on binding to indifferentiated cells. These findings suggest that the high affinity site represents a G-protein linked receptor with approximately equal affinities for ANG II and ANG III. We hypothesize that the low affinity site represents a non-specific membrane-bound aminopeptidase.

The effect of Ca2+ channel antagonists (cadmium, omega-conotoxin GIVA, and nitrendipine) on the release of angiotensin II from fetal rat brain in vitro

We have shown previously that K+ stimulation of dissociated cell cultures of fetal rat brain results in a graded release of angiotensin II (ANG II) that is dependent on the availability of extracellular Ca2+. In this study, using dissociated cell cultures of fetal rat hypothalamus, thalamus, septum, and midbrain (HTSM), we further examined the role of calcium channels on ANG II release using specific channel blockers (cadmium, omega-conotoxin, and nitrendipine) and a calcium ionophore (A23187). Levels of ANG II release were quantitated by radioimmunoassay and HPLC. For control levels of ANG II release, cells were incubated in a stock buffer containing 89 mM choline chloride/58 mM KCl/2 mM CaCl2. Pretreatment of the cells with either 100 microM Cd2+ (to block N-, L-, and T-type calcium channels), 100 nM omega-conotoxin (to block N- and L-type calcium channels), or 500 nM nitrendipine (to block L-type calcium channels) decreased ANG II release by approximately 71%, 71% and 22%, respectively, when compared to control levels. In contrast, pretreatment of the cells with 1.6 microM A23187 (a calcium ionophore) increased ANG II release by approximately 90% over control levels. These findings suggest that angiotensin release is dependent on the intracellular entry of Ca2+ ions through primarily N-type channels, and to a lesser extent, L-type channels.

Angiotensinogen production by rat astroglial cells in vitro and in vivo

To investigate the production of angiotensinogen by the brain, primary cultures were prepared from the brains of one-day-old rats. Two to four weeks after plating, they were transferred to serum-free medium. The cultures, which contained approximately 15% neurons, 80% astroglia and 5% other types of cells, produced angiotensinogen at a steady rate for three to four days in serum-free medium. Cultures prepared from subcortical tissue produced more angiotensinogen than cultures prepared from cerebral cortical tissue. Angiotensinogen mRNA was also identified in those cultures. Forskolin treatment had no effect on angiotensinogen production. Astroglia-enriched cultures that contained no identifiable neurons also produced angiotensinogen and its mRNA. Astroglial cells from hypothalamus and thalamus produced more of both than astroglial cells from the cerebral cortex. In situ hybridization histochemistry on sections of the hypothalamus of adult male rats showed a diffuse distribution of cells containing angiotensinogen mRNA that was more consistent with a glial than a neuronal distribution. The data indicate that most if not all of the angiotensinogen in rat brain is produced by astrocytes.

Angiotensin II immunoreactivity in push-pull perfusates from the paraventricular nucleus

Push-pull perfusion of the hypothalamic paraventricular nucleus in sodium pentobarbital anesthetized Sprague-Dawley rats indicates the release of angiotensin II-immunoreactive material in this area. Attempts to demonstrate a neuronal origin of this material by chemical depolarization with perfusate containing either 40 or 120 mM K+ were unsuccessful. However, this material does appear to be of central origin since intravenous infusion of arginine-vasopressin, a similar sized peptide, did not result in the appearance of increased levels of this substrate in the perfusate, indicating that the integrity of the blood-brain barrier was not compromised by the perfusion.

Immunocytochemical localization of angiotensinogen in the rat brain

The distribution of angiotensinogen-like immunoreactivity in the rat brain was investigated using specific antisera against pure rat plasma angiotensinogen in conjunction with the sensitive streptavidin-biotin peroxidase method. Angiotensinogen antisera were shown by radioimmunoassay and Western blotting to recognize angiotensinogen from both rat plasma and cerebrospinal fluid, and to cross-react with des-AI-angiotensinogen (100%) but not with angiotensin I and II, tetradecapeptide, luteinizing hormone-releasing hormone, rat albumin and angiotensinogen from eight other species. Angiotensinogen-like immunoreactivity was detected throughout the rat brain in both neuroglia and neurons. The highest concentration of neuroglial angiotensinogen-like immunoreactivity was in the hypothalamus and preoptic areas, with moderate to heavy concentrations in the mesencephalon and myelencephalon. The cerebellum demonstrated neuroglial staining in the granular layer and fibre tracts. Very little neuroglial staining was noted in the cerebral cortex or olfactory bulbs. Neuronal immunostaining was observed throughout the globus pallidus and the caudate putamen, in various parts of the thalamus and the supraoptic nucleus of the hypothalamus. In the midbrain moderate immunostaining was observed in periaquaductal central gray, the deep mesencephalic nucleus, the inferior colliculus and in scattered cells in the anterior mesencephalon. In the medulla, neuronal staining was localized to the vestibular nuclei and to other cell bodies mainly in the dorsolateral regions. In the cerebellum, staining was noted mainly in the deeper cerebellar nuclei and in the Purkinje cells. Immunostaining in the cerebral cortex was localized to the cingulate cortex and the primary olfactory cortex. Light staining was present in the endopiriform cortex and in scattered neurons adjacent to the external capsule. In the olfactory bulbs light neuronal staining was mainly associated with the mitral cell layer. The widespread distribution of angiotensinogen-like immunoreactivity supports the view that it is synthesized in the central nervous system and forms part of a brain renin-angiotensin system. In addition, its presence at sites other than those normally associated with the control of blood pressure and fluid and electrolyte homeostasis suggests that its involvement may not be limited to these regulatory functions.

In vivo release of angiotensin II from the rat hypothalamus

Recent studies suggest that angiotensin II is released from neuronal tissue in vitro, but the occurrence of this phenomenon in the intact brain has not yet been demonstrated. To characterize the in vivo release of immunoreactive angiotensin II, push-pull cannulas were positioned in the anterior hypothalamus in 47 Sprague-Dawley rats (200-250 g) anesthetized with Inactin (100 mg/kg i.p.). Artificial cerebrospinal fluid was perfused at 20 microliters/min, and effluent samples were collected for 15-minute periods over 2 hours. Angiotensin II was detectable (greater than 2.5 pg/ml) in the push-pull cannula perfusate of the majority (76%) of the rats. Spontaneous release of immunoreactive angiotensin II was constant for 2 hours in 11 rats at values averaging from 4.4 +/- 1.5 to 8.2 +/- 2.2 pg/ml. In addition, bilateral nephrectomy performed 48 hours before did not affect the detection of angiotensin II (n = 3). Angiotensin immunoreactivity in the rat hypothalamus was further characterized by high performance liquid chromatography. The analysis showed that the perfusate contained authentic angiotensin II as well as other angiotensin metabolites. The effect of beta-adrenergic modulation on the release of angiotensin II was assessed in 20 rats by adding isoproterenol (10(-10), 10(-8), and 10(-6) M), propranolol (10(-6) M), or a combination of both. Neither activation nor inhibition of hypothalamic beta-receptors altered the spontaneous release of angiotensin II. These data demonstrate that angiotensin II and congener peptides are detectable in the microenvironment of the anterior hypothalamus of the anesthetized rat and that the release of angiotensin II immunoreactivity in the anterior hypothalamus is not modified by beta-adrenergic receptors.

The effects of substituting frusemide for a thiazide diuretic in the drug regimens of patients with essential hypertension

Eighteen patients with mild to moderate hypertension on a drug regimen which included a thiazide diuretic had the latter substituted by frusemide for twelve weeks after an initial two-week placebo wash-out period. Blood pressure and heart rate and a number of plasma and urinary biochemical indices were measured. Significant findings included a reduction in standing blood pressure and an elevation of plasma sodium, potassium, chloride, osmolarity, creatinine and alkaline phosphatase levels at the end of the twelve week frusemide phase relative to the values on the thiazide. However the means for all the biochemical indices remained within the normal laboratory reference limits. In the 24-hour urinary studies, no significant findings emerged, apart from an elevated calcium. The foregoing suggest that frusemide is an effective component of an anti-hypertensive drug regimen and that in a dose of 40 mg/day it produces no detectable perturbations of plasma electrolytes. The significance of the enhanced levels of urinary calcium excretion in conjunction with the augmented plasma alkaline phosphatase is unclear.