In vitro Studies on Metabolism of Salvinorin A

Microbial transformation of natural products is a well established model for mammalian metabolism. Salvinorin A, a diterpenoid isolated from the hallucinogenic mint Salvia divinorum Epling & Játiva-M (Lamiaceae), is a potent non-nitrogenous κ-opioid receptor agonist. The metabolism of salvinorin A has still not yet been well established. Thirty fungal species were screened for the ability to metabolize salvinorin A. We observed that salvinorin A undergoes fast hydrolysis of the acetate group at carbon atom C2, resulting in formation of the pharmacologically inactive product, salvinorin B. Ex vivo experiments were also performed using organelle fractions isolated from rat liver and brain. Crude tissue homogenate and individual organelles show that the primary route of salvinorin A metabolism is hydrolysis to salvinorin B. No metabolic transformation of salvinorin B was observed in these studies

Vitamin D serum level predicts stroke clinical severity, functional independence, and disability—A retrospective cohort study

BackgroundStroke is a leading cause of mortality and disability and one of the most common neurological conditions globally. Many studies focused on vitamin D as a stroke risk factor, but only a few focused on its serum level as a predictor of stroke initial clinical severity and recovery with inconsistent results. The purpose of this study was to assess the relationship between serum vitamin D levels and stroke clinical severity at admission and functional independence and disability at discharge in Saudi Arabia.MethodologyA retrospective cohort study of adult ischemic stroke patients who had their vitamin D tested and admitted within 7 days of exhibiting stroke symptoms at King Abdulaziz Medical City (KAMC) Jeddah, Saudi Arabia. Based on vitamin D level, the patients were categorized into normal [25(OH)D serum level ≥ 75 nmol/L], insufficient [25(OH)D serum level is 50–75 nmol/L], and deficient [25(OH)D serum level ≤ 50 nmol/L]. The primary outcome was to assess the vitamin D serum level of ischemic stroke patients’ clinical severity at admission and functional independence at discharge. The National Institute of Health Stroke Scale (NIHSS) was used to assess the clinical severity, whereas the modified Rankin scale (mRS) was used to assess functional independence and disability.ResultsThe study included 294 stroke patients, out of 774, who were selected based on the inclusion and exclusion criteria. The mean age of the participants was 68.2 ± 13.4 years, and 49.3% were male. The patients’ distribution among the three groups based on their vitamin D levels is: normal (n = 35, 11.9%), insufficient (n = 66, 22.5%), and deficient (n = 196, 65.6%). After adjusting for potential covariates, regression analysis found a significant inverse relationship of NIHSS based on 25(OH)D serum level (beta coefficient: −0.04, SE: 0.01, p = 0.003). Patients with deficient serum vitamin D level also had significantly higher odds of worse functional independence in mRS score [OR: 2.41, 95%CI: (1.13–5.16), p = 0.023] when compared to participants with normal vitamin D level.ConclusionLow vitamin D levels were associated with higher severity of stroke at admission and poor functional independence and disability at discharge in patients with acute ischemic stroke. Further randomized clinical and interventional studies are required to confirm our findings

Animal models of BMAA neurotoxicity: a critical review

Of all the molecules reported to have toxicological effects, BMAA (beta-methylamino alanine) stands out as having the most checkered past. In the late 1960\u27s it was reported to be a toxic component of the cycad flour consumed by Chamorros on Guam which caused the high incidence of amyotrophic lateral sclerosis (ALS) in Guam, that was associated with a Parkinson\u27s disease-like dementia complex (ALS-PDC). However, because ALS-PDC is a slow onset disease, manifesting itself as long as 30 years following exposure to the putative neurotoxin, and only acute toxic effects of BMAA were observed in animal studies, interest in BMAA waned. A seminal study by Spencer et al., in 1987 showing neurological impairments with long-term BMAA-fed monkeys revived the hypothesis that BMAA could cause ALS-PDC. However, the amounts of BMAA used in that study were viewed as being the equivalent of a person consuming their body weight of cycad flour every day. Again, the BMAA hypothesis was discarded. Recently a third iteration of the BMAA hypothesis has been proposed. It is based on the discovery of a novel dietary source of BMAA via biomagnification of BMAA in flying foxes, once consumed in great amounts by Chamorros. Also, reports that BMAA can be incorporated into plant and animal proteins, a heretofore unrecognized dietary source of BMAA, further solidified this new hypothesis. However, once again this hypothesis has its detractors and it remains controversial. This manuscript critically evaluates in vivo studies directed at establishing an animal model of BMAA-induced ALS-PDC and their implications for this hypothesis

Enzymatic pathways of the brain renin-angiotensin system: unsolved problems and continuing challenges

The brain renin-angiotensin system continues to be enigmatic more than 40 years after the brain was first recognized to be a site of action of angiotensin II. This review focuses on the enzymatic pathways for the formation and degradation of the growing number of active angiotensins in the brain. A brief description and nomenclature of the peptidases involved in the processing of angiotensin peptides in the brain is given. Of primary interest is the array of enzymes that degrade radiolabeled angiotensins in receptor binding assays. This poses major challenges to studies of brain angiotensin receptors and it is debatable whether an accurate determination of brain angiotensin receptor binding kinetics has yet been made. The quandary facing the investigator of brain angiotensin receptors is the need to protect the radioligand from metabolic alteration while maintaining the characteristics of the receptors in situ. It is the tenet of this review that we have yet to fully understand the binding characteristics of brain angiotensin receptors and the extent of their distribution in the brain because of our inability to fully protect the angiotensins from metabolic alteration until equilibrium binding conditions can be attained

The significance of brain aminopeptidases in the regulation of the actions of angiotensin peptides in the brain

From the outset, the concept of a brain renin-angiotensin system (RAS) has been controversial and this controversy continues to this day. In addition to the unresolved questions as to the means by which, and location(s) where brain Ang II is synthesized, and the uncertainties regarding the functionality of the different subtypes of Ang II receptors in the brain, a new controversy has arisen with respect to the identity of the angiotensin peptide(s) that activate brain AT(1) receptors. While it has been known for some time that Ang III can activate Ang II receptors with equivalent or near-equivalent efficacy to Ang II, it has been proposed that in the brain, only Ang III is active. This proposal, which we have named The Angiotensin III Hypothesis states that Ang II must be converted to Ang III in order to activate brain AT(1) receptors. This review examines several aspects of the controversies regarding the brain RAS with a special focus on brain aminopeptidases, studies that either support or refute The Angiotensin III Hypothesis, and the implications of The Angiotensin III Hypothesis for the activity of the brain RAS. It also addresses the need for further research that can test The Angiotensin III Hypothesis and definitively identify the angiotensin peptide(s) that activate brain AT(1) receptor-mediated effects

Identification of a novel non-AT1, non-AT2 angiotensin binding site in the rat brain

Efforts to protect radiolabeled angiotensins from metabolism during receptor binding assays date back more than 30 years. However, this continues to be a problem. This study focused on the effects of a protease inhibitor, p-chloromercuribenzoate (PCMB), on the binding of (125)I-Ang II to rat brain membranes. Addition of PCMB to the incubation medium revealed a high affinity binding site for (125)I-Ang II in brain membranes (K(d)=1-4 nM) with a greater amount of binding than revealed in previous studies of brain Ang II receptors. Further characterization of this binding, revealed it to be insensitive to inhibition by losartan (an AT(1) receptor antagonist) and PD123319 (an AT(2) receptor antagonist). This non-AT1, non-AT2 binding site was not present in liver or adrenal membranes. It was activated by a limited range of concentrations of PCMB, with maximal activation at 0.3-1 mM. This binding site was equally abundant in cerebral cortex (a brain region with few Ang II receptors) and the hypothalamus (a brain region with abundant Ang II receptors). The binding site was also present in mouse brain, but not mouse liver. The binding site shows high affinity for Ang I, Ang II and Ang III (K(i) approximately 40-100 nM), but lesser affinity for smaller angiotensin fragments and other neuropeptides. This binding site shares some characteristics with the liver cytosolic Ang II binding proteins, later identified as endopeptidases EC 3.4.24.15 and/or EC 3.4.24.16. However, some unique characteristics of this non-AT1, non-AT2 binding site suggest that it may be a novel angiotensin binding substance

Brain angiotensin receptors and binding proteins

This review addresses classical and novel aspects of the brain angiotensin system. The brain contains both the AT1 and AT2 angiotensin II (Ang II) receptor subtypes which are well-characterized guanine nucleotide binding protein (G protein)-coupled receptors (GPCRs). Like other GPCRs, novel signal transduction pathways and protein interactions are being described for Ang II receptors. For brain AT1 receptors, there is a controversy regarding the identity of the active angiotensin peptide in the brain which is addressed in this review. This review also summarizes a recent discovery of a novel, membrane-bound, non-AT1, non-AT2 binding site for angiotensin peptides that appears to be brain-specific. This binding site is unmasked by a limited concentration range of the organometallic sulfhydryl-reactive agent p-chloromercuribenzoic acid (PCMB) suggesting that functional expression of this binding site may depend on the redox state of the milieu of the brain. While this binding site has similarities to a previously described soluble angiotensin-binding protein found in liver that is unmasked by PCMB, it has many different characteristics. The possible functional significance of this novel non-AT1, non-AT2 binding site for angiotensin peptides as a mediator of non-traditional actions of Ang II in the brain, e.g., stimulation of dopamine release from the striatum, as a peptidase, or as a clearance receptor, and the importance of the state of the internal environment of the brain to its function is reviewed

Distribution of the non-AT1, non-AT2 angiotensin-binding site in the rat brain: preliminary characterization

The discovery of a novel, non-AT1, non-AT2 binding site for angiotensin II (Ang II) in the brain adds a new dimension to the brain angiotensin system. The distribution of the non-AT1, non-AT2 binding site in the rat brain was determined using radioligand-binding assays and in vitro receptor autoradiography. There is a marked rostral to caudal gradient of the density of this binding site from the olfactory bulbs to the cervical spinal cord, with a consistent binding affinity, K(d) approximately 1-3 nM. Binding is widespread throughout the brain, however, areas of very intense binding are present in a large number of brain regions. The olfactory nerve layer of the olfactory bulb has the highest binding site density. Very high binding site density is also seen in the cerebral cortex with highest binding density in pyriform, insular and entorhinal cortex. Very high binding occurs in brain regions associated with dopaminergic reward (nucleus accumbens, ventral tegmental area) and motor (substantia nigra, caudate/putamen) systems. Very high to high binding also occurs in brain regions associated with the development of Alzheimer\u27s disease (nucleus basalis of Meynert, substantia innominata). Very high to high binding is also seen in brain regions associated with cardiovascular regulation (subfornical organ, median, medial and anteroventral preoptic nucleus, paraventricular nucleus of the hypothalamus, solitary tract nucleus), areas that harbor high densities of the AT1 Ang II receptor subtype. High non-AT1, non-AT2 binding site density is present in brain regions containing high levels of the AT2 Ang II receptor subtype (amygdala, several thalamic nuclei, superior colliculus). Very high binding is also present in the choroid plexus, peri-third ventricular ependyma, and the subcommissural organ. The widespread, yet discrete distribution of high levels of this binding site suggests that it could function as a component of the blood-brain barrier, as a highly specific angiotensinase, or as a receptor for Ang II that mediates known and novel functions of this peptide, or that it serves as a clearance receptor for Ang II

Angiotensin II type 1 receptor antagonists in the treatment of hypertension in elderly patients: focus on patient outcomes

Artavazd Tadevosyan1, Eric J MacLaughlin2, Vardan T Karamyan31Departments of Medicine, Montreal Heart Institute and Université de Montréal, Montreal, QC, Canada; 2Department of Pharmacy Practice, 3Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, TX, USAAbstract: Hypertension in the elderly is one of the main risk factors of cardiovascular and cerebrovascular diseases. Knowledge regarding the mechanisms of hypertension and specific considerations in managing hypertensive elderly through pharmacological intervention(s) is fundamental to improving clinical outcomes. Recent clinical studies in the elderly have provided evidence that angiotensin II type 1 (AT1) receptor antagonists can improve clinical outcomes to a similar or, in certain populations, an even greater extent than other classical arterial blood pressure-lowering agents. This newer class of antihypertensive agents presents several benefits, including potential for improved adherence, excellent tolerability profile with minimal first-dose hypotension, and a low incidence of adverse effects. Thus, AT1 receptor antagonists represent an appropriate option for many elderly patients with hypertension, type 2 diabetes, heart failure, and/or left ventricular dysfunction.Keywords: angiotensin II, ARB, cardiovascular disease, antihypertensive therapy, elderl