Does intranasal dexmedetomidine provide adequate plasma concentrations for sedation in children: a pharmacokinetic study.

BACKGROUND: Atomised intranasal dexmedetomidine administration is an attractive option when sedation is required for paediatric diagnostic procedures, as vascular access is not required. The risk of haemodynamic instability caused by dexmedetomidine necessitates better understanding of its pharmacokinetics in young children. To date, intranasal dexmedetomidine pharmacokinetics has only been studied in adults. METHODS: Eighteen paediatric patients received dexmedetomidine 1 or 2 µg kg-1 intranasally or 1 µg kg-1 i.v. Plasma concentrations were determined by liquid chromatography/mass spectrometry. Non-compartmental analysis provided estimates of Cmax and Tmax. Volume of distribution, clearance, and bioavailability were estimated by simultaneous population PK analysis of data after intranasal and i.v. administration. Dexmedetomidine plasma concentration-time profiles were evaluated by simulation for intranasal and i.v. administration. RESULTS: An average peak plasma concentration of 199 pg ml-1 was achieved 46 min after 1 µg kg-1 dosing and 355 pg ml-1 was achieved 47 min after 2 µg kg-1 dosing. A two-compartment pharmacokinetic model, with allometrically scaled parameters, adequately described the data. Typical bioavailability was 83.8% (95% confidence interval 69.5-98.1%). CONCLUSION: Mean arterial plasma concentrations of dexmedetomidine in infants and toddlers approached 100 pg ml-1, the low end reported for sedative efficacy, within 20 min of an atomised intranasal administration of 1 µg kg-1. Doubling the dose to 2 µg kg-1 reached this plasma concentration within 10 min and achieved almost twice the peak concentration. Peak plasma concentrations with both doses were reached within 47 min of intranasal administration, with an overall bioavailability of 84%.

Catecholamine Concentrations: Changes in Plasma of Rats during Estrous Cycle and Pregnancy.

Concentrations of norepinephrine in plasma of rats during estrus and pregnancy were significantly lower than during diestrus. Epinephrlne concentrations in the plasma were significantly higher in both estrous and diestrous females than in males.

Do atmospheric pressure changes influence seizure occurrence in the epilepsy monitoring unit?

In a prior study of epilepsy and atmospheric pressure, we were able to show a small association between changes in atmospheric pressure and increased seizure frequency in consecutive patients with epilepsy undergoing video telemetry. In this study, we used a larger data set of similar patients undergoing telemetry at another Seattle institution, and examined the possible impact of atmospheric pressure (AP) changes on seizure onset in subtypes of seizures (focal, generalized, and nonepileptic). Comparisons were made between AP score at time of seizure onset and AP score at selected time ranges prior to the event (hour of seizure and 3, 6, and 24 hours prior) and a random sample of AP scores collected over similar time frames using nonparametric testing with correction for multiple comparisons. We could find no evidence to suggest atmospheric pressure changes made seizure occurrence more likely in any of the seizure groups across any of the time periods.

VLA-4 blockade suppresses endotoxin-induced uveitis: in vivo evidence for functional integrin up-regulation.

Leukocyte adhesion to the vascular wall is a critical early step in the pathogenesis of inflammatory diseases and is mediated in part by the leukocyte integrin, VLA-4, which binds to endothelial vascular cell adhesion molecule (VCAM) -1. Here, we investigate VLA-4's role in endotoxin-induced uveitis (EIU). At various time points (6-48 h) after EIU induction, the severity of the inflammation was evaluated by quantifying cell and protein content in the aqueous fluid, firm leukocyte adhesion in the retinal vessels, and the number of extravasated leukocytes into the vitreous. Functional activation of VLA-4 in vivo was investigated in our previously introduced autoperfused micro flow chamber assay. Firm adhesion of EIU leukocytes to immobilized VCAM-1 under physiological blood flow conditions was significantly increased compared with normal controls (P<0.05), suggesting an important role for VLA-4 in EIU. VLA-4 blockade in vivo significantly suppressed all uveitis-related inflammatory parameters studied, decreasing the clinical score by 45% (P<0.01), protein content in the aqueous fluid by 21% (P<0.01), retinal leukostasis by 68% (P<0.01), and leukocyte accumulation in the vitreous by 75% (P<0.01). Our data provide novel evidence for functional up-regulation of VLA-4 during EIU and suggest VLA-4 blockade as a promising therapeutic strategy for treatment of acute inflammatory eye diseases.

Activation of heat shock protein (hsp)70 and proto-oncogene expression by alpha1 adrenergic agonist in rat aorta with age.

Induction of heat shock proteins (hsp) most likely is a homeostatic mechanism in response to metabolic and environmental insults. We have investigated signal transduction mechanisms involved in alpha1, adrenergic receptor stimulation of hsp7O gene expression in isolated aortas with age. We found that alpha1 adrenergic agonists directly induced hsp70 mRNA in rat aorta in vitro; the alpha1, selective antagonist prazosin blocked this effect whereas chloroethylclonidine, an antagonist which has some selectivity for alpha1B receptors, was ineffective. This response was insensitive to pertussis toxin and was partially blocked by the protein kinase C inhibitor H7. Removal of extracellular calcium attenuated induction of hsp70 mRNA but not the induction of c-fos or c-myc. The induction of hsp70 mRNA by either norepinephrine or by phorbol dibutyrate was blunted in aortas from old (24-27 mo) rats whereas c-fos responses were not diminished in the older vessels. The hsp70 response to elevated temperature (42 degrees C) was not changed with age. Activation of hsp70 expression most likely involves a pertussis toxin insensitive G protein which activates protein kinase C, and requires extracellular calcium. With age, hsp70 gene expression induced by stimulation of alpha1 adrenergic receptors is markedly attenuated, which could modify responses to stress or vascular injury with aging.

Visualization of double-stranded RNAs from the myotonic dystrophy protein kinase gene and interactions with CUG-binding protein.

Myotonic dystrophy (DM) is associated with a (CTG) (n) triplet repeat expansion in the 3'-untranslated region of the myotonic dystrophy protein kinase (DMPK) gene. Using electron microscopy, we visualized large RNAs containing up to 130 CUG repeats and studied the binding of purified CUG-binding protein (CUG-BP) to these RNAs. Electron microscopic examination revealed perfect double-stranded (ds)RNA segments whose lengths were that expected for duplex RNA. The RNA dominant mutation model for DM pathogenesis predicts that the expansion mutation acts at the RNA level by forming long dsRNAs that sequester certain RNA-binding proteins. To test this model, we examined the subcellular distribution and RNA-binding properties of CUG-BP. While previous studies have demonstrated that mutant DMPK transcripts accumu-late in nuclear foci, the localization pattern of CUG-BP in both normal and DM cells was similar. Although CUG-BP in nuclear extracts preferentially photocrosslinked to DMPK transcripts, this binding was not proportional to (CUG) (n) repeat size. Moreover, CUG-BP localized to the base of the RNA hairpin and not along the stem, as visualized by electron micro-scopy. These results provide the first visual evidence that the DM expansion forms an RNA hairpin structure and suggest that CUG-BP is unlikely to be a sequestered factor.

Treadmill measures of ambulation rates in ovine models of spinal cord injury and neuropathic pain.

Our laboratories are developing treadmill-based gait analysis employing sheep to investigate potential efficacy of intra-dural spinal cord stimulation in the treatment of spinal cord injury and neuropathic pain. As part of efforts to establish the performance characteristics of the experimental arrangement, this study measured the treadmill speed via a tachometer, video belt-marker timing and ambulation-rate observations of the sheep. The data reveal a 0.1-0.3% residual drift in the baseline (unloaded) treadmill speed which increases with loading, but all three approaches agree on final speed to within 1.7%, at belt speeds of ≈ 4 km/h. Using the tachometer as the standard, the estimated upper limit on uncertainty in the video belt-marker approach is ± 0.18 km h(-1) and the measured uncertainty is ± 0.15 km h(-1). Employment of the latter method in determining timing differences between contralateral hoof strikes by the sheep suggests its utility in assessing severity of SCI and responses to therapeutic interventions.

Low erythrocyte folate, but not plasma vitamin B-12 or homocysteine,is associated with dementia in elderly Latinos.

The relationship between B vitamin status and cognitive function has been of interest for many years. There is evidence of relationships between intake and status of folate and vitamin B-12 with neurological, cognitive, and memory impairment, but results have been inconsistent. Plasma B-12, erythrocyte folate, methylmalonic acid,and homocysteine were evaluated as predictors of cognitive function in a large population based sample of Latino elderly living in the Sacramento, California region. The hypothesis tested was that low folate and/or B-12 status predicts cognitive function impairment and dementia. Logistic regression was used to examine the differences in B-vitamin status by cognitive function category. Erythrocyte folate was related to dementia after controlling for age, gender, education, income, diabetes diagnosis, serum creatinine, and depressive symptoms. The highest prevalence of low erythrocyte folate occurred in the Dementia group and was significantly higher than in the Normal group. Plasma B-12, MMA, Hcy, and prevalence of a normal values for these variables, were not significantly different among the cognitive function classes. We conclude that folate status is associated with dementia but that more research is needed on the relationship between vitaminB-12 status, Hcy and cognitive function to explore possible associations with these parameters.

Necrotic enlargement of cone photoreceptor cells and the release of high-mobility group box-1 in retinitis pigmentosa.

Retinitis pigmentosa (RP) refers to a group of inherited retinal degenerations resulting form rod and cone photoreceptor cell death. The rod cell death due to deleterious genetic mutations has been shown to occur mainly through apoptosis, whereas the mechanisms and features of the secondary cone cell death have not been fully elucidated. Our previous study showed that the cone cell death in rd10 mice, an animal model of RP, involves necrotic features and is partly mediated by the receptor interacting protein kinase. However, the relevancy of necrotic cone cell death in human RP patients remains unknown. In the present study, we showed that dying cone cells in rd10 mice exhibited cellular enlargement, along with necrotic changes such as cellular swelling and mitochondrial rupture. In human eyes, live imaging of cone cells by adaptive optics scanning laser ophthalmoscopy revealed significantly increased percentages of enlarged cone cells in the RP patients compared with the control subjects. The vitreous of the RP patients contained significantly higher levels of high-mobility group box-1, which is released extracellularly associated with necrotic cell death. These findings suggest that necrotic enlargement of cone cells is involved in the process of cone degeneration, and that necrosis may be a novel target to prevent or delay the loss of cone-mediated central vision in RP.

Membrane-bound and soluble Fas ligands have opposite functions in photoreceptor cell death following separation from the retinal pigment epithelium.

Fas ligand (FasL) triggers apoptosis of Fas-positive cells, and previous reports described FasL-induced cell death of Fas-positive photoreceptors following a retinal detachment. However, as FasL exists in membrane-bound (mFasL) and soluble (sFasL) forms, and is expressed on resident microglia and infiltrating monocyte/macrophages, the current study examined the relative contribution of mFasL and sFasL to photoreceptor cell death after induction of experimental retinal detachment in wild-type, knockout (FasL-/-), and mFasL-only knock-in (ΔCS) mice. Retinal detachment in FasL-/- mice resulted in a significant reduction of photoreceptor cell death. In contrast, ΔCS mice displayed significantly more apoptotic photoreceptor cell death. Photoreceptor loss in ΔCS mice was inhibited by a subretinal injection of recombinant sFasL. Thus, Fas/FasL-triggered cell death accounts for a significant amount of photoreceptor cell loss following the retinal detachment. The function of FasL was dependent upon the form of FasL expressed: mFasL triggered photoreceptor cell death, whereas sFasL protected the retina, indicating that enzyme-mediated cleavage of FasL determines, in part, the extent of vision loss following the retinal detachment. Moreover, it also indicates that treatment with sFasL could significantly reduce photoreceptor cell loss in patients with retinal detachment.

Macrophage- and RIP3-dependent inflammasome activation exacerbates retinal detachment-induced photoreceptor cell death.

Detachment of photoreceptors from the retinal pigment epithelium is seen in various retinal disorders, resulting in photoreceptor death and subsequent vision loss. Cell death results in the release of endogenous molecules that activate molecular platforms containing caspase-1, termed inflammasomes. Inflammasome activation in retinal diseases has been reported in some cases to be protective and in others to be detrimental, causing neuronal cell death. Moreover, the cellular source of inflammasomes in retinal disorders is not clear. Here, we demonstrate that patients with photoreceptor injury by retinal detachment (RD) have increased levels of cleaved IL-1ß, an end product of inflammasome activation. In an animal model of RD, photoreceptor cell death led to activation of endogenous inflammasomes, and this activation was diminished by Rip3 deletion. The major source of Il1b expression was found to be infiltrating macrophages in the subretinal space, rather than dying photoreceptors. Inflammasome inhibition attenuated photoreceptor death after RD. Our data implicate the infiltrating macrophages as a source of damaging inflammasomes after photoreceptor detachment in a RIP3-dependent manner and suggest a novel therapeutic target for treatment of retinal diseases.

Photosensitizer delivery for photodynamic therapy of choroidal neovascularization.

The present review examines the importance of improving photosensitizer delivery for choroidal neovascularization (CNV) in light of the clinical impact of photodynamic therapy (PDT) for CNV. An overview of the classes of available photosensitizers is provided and the properties governing photosensitizer uptake and circulation in serum are discussed. Current delivery systems, for example liposomal formulations as well as the use of the promising strategy of antibody targeted delivery as a strategy to improve PDT selectivity and efficiency for CNV treatment are described. A summary of the work using Verteporfin, tin ethyl purpurin and Lu-Tex--photosensitizers currently in clinical trials for CNV--is given.

Neuronal argyrophilia and phosphorylated neurofilament accumulation secondary to deafferentation.

This work tests the hypothesis that deafferentation caused by experimental brain lesions leads to the appearance of perikaryal argyrophilia and the accumulation of phosphorylated cytoskeletal proteins which are potential precursors for neurofibrillary tangle formation. Destructive lesions of the ventral tegmental area, the septum of the medial forebrain and the entorhinal cortex, when combined with systemic administration of a D-1 dopamine receptor antagonist, produced transsynaptic changes in neurons of the hippocampal formation in the midbrain. Abnormally phosphorylated neurofilament protein was demonstrated immunohistochemically in the cytoplasm of mesencephalic pyramidal neurons, particularly in the red nucleus. These same neurons also developed cytoplasmic argyrophilia in Bielschowsky histologic preparations. Although distinct neurofibrillary tangles were not produced with this paradigm, both the protein immunoreactivity and argyrophilia were arranged in cytoplasmic linear arrays. The structural changes induced in this experimental model may be an important preliminary stage for neurofibrillary tangle formation.

Orthostatic hypertension. Pathogenetic studies.

Among 1800 referred hypertensive patients, 181 had recumbent diastolic blood pressures (DBP) below 90 mm Hg and standing DBP above 90 mm Hg. Orthostatic increments in DBP were greater in these orthostatic hypertensive patients than in 181 persistently hypertensive patients and 134 normotensive subjects. In 12 patients with orthostatic hypertension, the orthostatic fall in cardiac output (27.3 +/- 2.9%, measured by a respiratory method) was double that in 8 normotensive subjects (13.3 +/- 3.7%, p less than 0.01). An inflated pressure suit over the pelvis and lower limbs prevented the excessive fall in cardiac output and significantly reduced (p less than 0.02) the excessive rise in standing DBP in orthostatic hypertensive patients. Gravitational pooling of blood in the legs and reduction of blood in the head was measured by external gamma counting of autologous erythrocytes labeled with sodium pertechnetate Tc 99m through ports in fixed positions over the leg and the temple. Orthostatic intravascular pooling was significantly greater (p less than 0.01) in orthostatic hypertensive subjects than in normotensive subjects, and the magnitudes of orthostatic pooling and orthostatic increases in DBP were closely correlated (r = +0.85). Plasma norepinephrine concentrations were similar in recumbency and after sustained handgrip exercise, but significantly greater (p less than 0.01) after 5 to 60 mins of standing in orthostatic hypertensive subjects than in normotensive subjects. Our results indicate that orthostatic hypertension is common and that its mechanism in representative patients involves excessive orthostatic blood pooling, which results in decreased venous return, decreased cardiac output, increased sympathetic stimulation (presumably through low-pressure cardiopulmonary receptors), and excessive arteriolar, but not venular, constriction.

Folate deficiency beyond megaloblastic anemia: hyperhomocysteinemia and other manifestations of dysfunctional folate status.

Folate plays a key role in nucleic acid synthesis. As a consequence, the most conspicuous complication of folate deficiency or of derangements of folate metabolism is megaloblastic macrocytic anemia caused by interdiction of normal proliferation of rapidly dividing bone marrow cells. Other rapidly dividing cells, including those in the gastrointestinal tract, may also be affected by the megaloblastic process. This may result in malabsorption. However, there is mounting evidence to indicate that there are other earlier manifestations of folate deficiency or of longstanding suboptimal folate nutrition. Chief among these manifestations of folate deficiency are an increased predisposition to occlusive vascular disease and thrombosis, which have been linked to increased levels of homocysteine found in folate deficiency and abnormal states of folate metabolism. In addition, folate deficiency, previously considered free of neurological consequences, is now known to be associated with disturbances of mood, and even spinal cord syndromes similar to those seen in vitamin B12 deficiency. Finally, there is both experimental and clinical evidence to suggest that folate deficiency may interfere with immunologic status and may be associated with an increased predisposition to neoplasia. Nutritional as well as genetic factors may contribute to these various nonhematological manifestations of folate insufficiency.

Oxidative damage caused by free radicals produced during catecholamine autoxidation: protective effects of O-methylation and melatonin.

Catecholamine autoxidation produces reactive oxygen species that have been implicated in the loss of dopaminergic neurons in the nigrostriatal region of the brain that occurs during normal aging and in Parkinson's disease. In the present study, the potential protective effects of catecholamine O-methylation and of melatonin against catecholamine autoxidation-induced protein damage were assessed in vitro using the oxygen radical absorbance capacity (ORAC) assay. The rate of oxidation of the fluorescent protein porphyridium cruentum beta-phycoerythrin (beta-PE) caused by the oxidizing agent CuSO4 was shown to be accelerated by addition of the catecholamines dopamine and L-dopa. Replacement of dopamine and L-dopa in the assay with their O-methylated metabolites 3-O-methyldopamine and 3-O-methyldopa significantly decreased the rate of beta-PE oxidation. When melatonin was added to the ORAC assay in combination with dopamine or L-dopa, the rate of beta-PE oxidation was decreased as well. These findings were consistent with the following interpretations: (1) O-methylated catecholamines are less susceptible to autoxidation than their nonmethylated precursors, and (2) melatonin, which has recently been shown to be a powerful antioxidant, is capable of scavenging free radicals produced during catecholamine autoxidation. These findings suggest that O-methylation and melatonin may be important components of the brain's antioxidant defenses against catecholamine autoxidation and may protect against consequent dopaminergic neurodegeneration.

The pathogenesis of homocysteinemia: interruption of the coordinate regulation by S-adenosylmethionine of the remethylation and transsulfuration of homocysteine.

A unified, biochemical hypothesis is proposed to explain the pathogenesis of homocysteinemia. This hypothesis is based on the existence of coordinate regulation by S-adenosylmethionine (SAM) of the partitioning of homocysteine between de novo methionine synthesis and catabolism through cystathionine synthesis. This coordination, which serves to modulate the cellular concentration of homocysteine based on the requirements for methionine, is impaired in homocysteinemia. This hypothesis is evaluated in the context of the conditions known to be associated with homocysteinemia, including enzymatic defects and vitamin deficiencies. The novelty of the hypothesis is the assertion that impairment of one homocysteine metabolic pathway must lead to the impairment of the other homocysteine metabolic pathway to cause homocysteinemia. This extends the simplistic view that a block of only one of the pathways is sufficient to cause homocysteinemia.

Nutritional factors in physical and cognitive functions of elderly people.

The quality of life of aging individuals depends profoundly on their capacity for physical mobility, mental alertness, and cognitive function. Independence and self-esteem are strongly determined by physical and mental capacities. Stimulated by reports of declining function with age, investigators have examined the relationships between lifestyle factors and maintenance of functional status. Growing evidence supports the view that continued physical activity and good nutritional status are important determinants of physical and cognitive function. It is possible that some of the decline in cognitive function associated with aging is preventable or reversible with improved vitamin nutriture, especially vitamin B-12, vitamin B-6, and folate. It might well be argued that the most practical outcome of research on the relationship of diet and nutrition to the aging process would be a better understanding of the ways in which our behavior can maintain a vigorous quality of life.

Vitamin B-6 deficiency vs folate deficiency: comparison of responses to methionine loading in rats.

The plasma homocysteine response to methionine loading was assessed in vitamin B-6- and folate-deficient rats. Rats fed vitamin B-6- or folate-deficient diets for 4 wk were administered a gastric gavage of methionine (100 mg/kg body wt). Subsequent plasma analyses revealed a peak post-methionine load increase in plasma homocysteine concentration of > 300 mumol/L in the vitamin B-6-deficient rats. Folate-deficient rats exhibited no significant changes in plasma homocysteine after the load. These disparate responses can be explained by the observed increase in hepatic S-adenosylmethionine (SAM) concentration because of the load. In vitamin B-6 deficiency, increased SAM inhibits homocysteine remethylation, which, in conjunction with the impaired homocysteine catabolism due to the deficiency and the increased synthesis of homocysteine due to the methionine load, leads to a large elevation of homocysteine in the blood. In folate deficiency, increased SAM activates homocysteine catabolism, which compensates for the increased synthesis of homocysteine due to the load and thus no change in blood homocysteine is observed. These results have significant bearing on the interpretation of both positive and negative responses to methionine loading in humans.