Endoplasmic Reticulum Stress and Renin-Angiotensin System Crosstalk in Endothelial Dysfunction

BACKGROUND

Vascular endothelial dysfunction (VED) significantly results in catastrophic cardiovascular diseases with multiple aetiologies. Variations in vasoactive peptides, including angiotensin II and endothelin 1, and metabolic perturbations like hyperglycaemia, altered insulin signalling, and homocysteine levels result in pathogenic signalling cascades, which ultimately lead to VED. Endoplasmic reticulum (ER) stress reduces nitric oxide availability, causes aberrant angiogenesis, and enhances oxidative stress pathways, consequently promoting endothelial dysfunction. Moreover, the renin-angiotensin system (RAS) has widely been acknowledged to impact angiogenesis, endothelial repair and inflammation. Interestingly, experimental studies at the preclinical level indicate a possible pathological link between the two pathways in the development of VED. Furthermore, pharmacological modulation of ER stress ameliorates angiotensin-II mediated VED as well as RAS intervention either through inhibition of the pressor arm or enhancement of the depressor arm of RAS, mitigating ER stress-induced endothelial dysfunction and thus emphasizing a vital crosstalk.

CONCLUSION

Deciphering the pathway overlap between RAS and ER stress may open potential therapeutic avenues to combat endothelial dysfunction and associated diseases. Several studies suggest that alteration in a component of RAS may induce ER stress or induction of ER stress may modulate the RAS components. In this review, we intend to elaborate on the crosstalk of ER stress and RAS in the pathophysiology of VED.

Rational syntheses of porphyrins bearing up to four different meso substituents

Porphyrins bearing specific patterns of substituents are crucial building blocks in biomimetic and materials chemistry. We have developed methodology that avoids statistical reactions, employs minimal chromatography, and affords up to gram quantities of regioisomerically pure porphyrins bearing predesignated patterns of up to four different meso substituents. The methodology is based upon the availability of multigram quantities of dipyrromethanes. A procedure for the diacylation of dipyrromethanes using EtMgBr and an acid chloride has been refined. A new procedure for the preparation of unsymmetrical diacyl dipyrromethanes has been developed that involves (1) monoacylation with EtMgBr and a pyridyl benzothioate followed by (2) introduction of the second acyl unit upon reaction with EtMgBr and an acid chloride. The scope of these acylation methods has been examined by preparing multigram quantities of diacyl dipyrromethanes bearing a variety of substituents. Reduction of the diacyl dipyrromethane to the corresponding dipyrromethane-dicarbinol is achieved with NaBH(4) in methanolic THF. Porphyrin formation involves the acid-catalyzed condensation of a dipyrromethane-dicarbinol and a dipyrromethane followed by oxidation with DDQ. Optimal conditions for the condensation were identified after examining various reaction parameters (solvent, temperature, acid, concentration, time). The conditions identified (2.5 mM reactants in acetonitrile containing 30 mM TFA at room temperature for <7 min) provided reaction without detectable scrambling (LD-MS) for aryl-substituted dipyrromethanes, and trace scrambling for alkyl-substituted dipyrromethanes. The desired porphyrins were obtained in 14-40% yield. The synthesis is compatible with diverse functionalities: amide, aldehyde, carboxylic acid, ester, nitrile, ether, bromo, iodo, ethyne, TMS-ethyne, TIPS-ethyne, perfluoroarene. In total 30 porphyrins of the types A(3)B, trans-A(2)B(2), trans-AB(2)C, cis-A(2)B(2), cis-A(2)BC, and ABCD were prepared, including >1-g quantities of three porphyrins.

Efficient synthesis of monoacyl dipyrromethanes and their use in the preparation of sterically unhindered trans-porphyrins

The condensation of an aldehyde with a dipyrromethane bearing a sterically unhindered aryl substituent at the 5-position typically results in low yield and a mixture of porphyrin products derived from acidolytic scrambling. We have developed a concise nonscrambling synthesis of such trans-porphyrins that takes advantage of the availability of multigram quantities of dipyrromethanes. This route involves the selective monoacylation of the dipyrromethanes with a pyridyl thioester, reduction of the monoacyl dipyrromethane to the corresponding carbinol, and self-condensation of the carbinol to form the porphyrin. The monoacylation procedure has wide scope as demonstrated by the preparation of a set of 15 diverse monoacyl dipyrromethanes in good yield at the multigram scale. The dipyrromethanecarbinol self-condensation reaction is extremely rapid (<3 min) under mild room-temperature conditions and affords the trans-porphyrin in 16-28% yield. Analysis by laser-desorption mass spectrometry (LD-MS) of samples from the crude reaction mixture revealed no scrambling within the limit of detection (1 part in 100). The self-condensation is compatible with a range of electron-withdrawing or -releasing substituents as well as substituents for building block applications (TMS-ethyne, ethyne, iodo, ester). The absence of any detectable scrambling in the self-condensation enables a simple purification. The synthesis readily affords gram quantities of pure, sterically unhindered trans-porphyrins in a process involving minimal chromatography.

Growth hormone-releasing hormone immunoreactivity in the brain, pituitary, and pineal of the goldfish, Carassius auratus

Using antisera directed against carp growth hormone-releasing hormone (cGHRH), the distribution of immunoreactive (ir) structures in the brain, pituitary, and pineal of the goldfish, Carassius auratus, was investigated. The antisera were produced in rabbits by administration of cGHRH(1-44)-NH(2) followed by cGHRH(1-45)-OH for different periods of time, both coupled to human alpha-globulins via bisdiazotized benzidine as immunogen. Immunoreactive perikarya were visualized in the nucleus preopticus periventricularis (NPP), nucleus lateralis tuberis (NLT), nucleus of the lateral lemniscus (NLL), and the pineal. The preoptic area and area ventralis telencephali seemed to receive innervation from the NPP cells. The fibers of the NLT cell bodies extended caudally along the infundibular floor and innervated the hypophysis. The processes of the NLL perikarya extended rostrally along the lateral lemniscus, curved ventrally along the outer margin of the glomerular nuclear complex, and extended to the dorsal area of the lateral recess, while issuing fascicles that branched off and fanned out to innervate extensively the nucleus diffusus of the hypothalamic inferior lobes and the nucleus lateralis tori; several fiber bundles branched off and extended toward the lateral areas of the paraventricular organ area and even into the rostral region of the hypothalamic inferior lobes. A small percentage of the corticotrophs of the rostral pars distalis, a few cells in the central area of the pars intermedia (PI), and neurohypophysial fibers in the peripheral area of the PI of the pituitary gland had colocalization of GHRH-ir; GHRH-ir fibers in the rostral and proximal pars distalis were sparse. It is suggested that the GHRH-ir perikarya of the diencephalon may stimulate growth hormone release either by modulating the activity of somatotrophs or of other hypothalamic neurosecretory neurons. The innervation of the hypothalamic inferior lobe by GHRH-ir perikarya of the NLL suggests some influence on feeding processes. Presence of GHRH in the pineal implies involvement in some daily cyclic activity.

Sexual dimorphism of galanin-like immunoreactivity in the brain and pituitary of goldfish, Carassius auratus

A sexually dimorphic distribution of galanin (GAL)-like immunoreactive (ir) neurons and fibers was found in the brain and pituitary of goldfish. The rostralmost GAL-ir perikarya were found in the area ventralis telencephali pars supracommissuralis dorsal to the anterior commissure. In the diencephalon, there was several GAL-ir perikarya in the nucleus preopticus periventricularis (NPP). Males had many GAL-ir perikarya in the nucleus preopticus pars parvocellularis (NPOpp) and isolated GAL-ir perikarya in the NPO pars magnocellularis, and lateral to the NPO; in females GAL-ir perikarya were not found in these sites. A large GAL-ir neuronal aggregation was observed in the nucleus lateralis tuberis pars posterioris (NLTp). Several ir perikarya were present in the nucleus posterioris tuberis; however, unlike in other regions the males revealed fewer neurons than females. Besides the established innervation of the pituitary gland by the NPP, NPO and NLT, the present study revealed GAL-ir perikarya of these nuclei apparently also innervating the telencephalon, thalamus, optic tectum, tegmentum and even some areas of the rhombencephalon. Isolated perikarya were found in the nucleus posterioris periventricularis, the dorsal vicinities of the nucleus recessus lateralis (NRL), nucleus recessus posterioris, and nucleus saccus vasculosus, and in the medulla oblongata ventral to the vagal lobes. In the pituitary gland, GAL-ir fibers ramify and terminate among the pars distalis cells. A small percentage of growth hormone-secreting cells colocalize GAL. In males, most GAL-ir cells of the proximal pars distalis (PPD) showed granular ir product in the entire cell, and some had one or two large granules; in females the ir PPD cells showed clusters of a few fine ir granules of uniform size in each. Sexual dimorphism was also found in the olfactory bulb, telencephalon, infundibulum, mesencephalic tegmentum, optic tectum and medulla oblongata, the males having a more extensive GAL-ir fiber system than the females. Galanin may play a role in both hypophysiotropic and motor functions.

Differential actions of a mammalian gonadotropin-releasing hormone antagonist on gonadotropin-II and growth hormone release in goldfish, Carassius auratus

In goldfish the two native forms of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH-II (cGnRH-II), stimulate both gonadotropin-II (GTH-II) and growth hormone (GH) release. Modifications of GnRH structure at positions 1, 2, 3, and 6 often result in an antagonist in goldfish, an observation well documented in mammalian studies. In a preliminary study in goldfish, a mammalian GnRH antagonist, [Ac-D(2)Nal1, 4Cl-D-Phe2, D(3)-Pal3,6, Arg5, D-Ala10]-mGnRH (analog L) weakly stimulated GTH-II release, and strongly inhibited GH release. The objectives of the present study were to study the dose-related actions of analog L on GTH-II and GH release in the goldfish, the specificity of inhibition of native GnRH actions, and to test whether analog L can act directly on goldfish pituitary cells. In a goldfish pituitary fragments perifusion system, analog L at different concentrations, given as 2-min pulses or as 30-min prolonged treatments, stimulated GTH-II and inhibited GH release in a dose-dependent manner. Analog L at 2 microM concentration (45 min) significantly suppressed sGnRH- and cGnRH-II-stimulated GTH-II as well as GH release. Analog L specifically inhibited GnRH-stimulated GH release, without having any significant effects on the GH release induced by either SKF38393, a dopamine D1 receptor agonist, or thyrotropin-releasing hormone. The GTH-II stimulatory and GH-inhibitory actions of analog L were significantly suppressed by a 'true' GnRH antagonist (Ac-delta 3-Pro1, 4FD-Phe2, D-Trp3,6)-mGnRH. Further, analog L stimulated GTH-II release and suppressed GH release from the enzymatically dispersed goldfish pituitary cells, indicating the direct actions of analog L at the pituitary cell level. Analog L also displaced 125I-(D-Arg6, Pro9 NHEt)-sGnRH bound to crude goldfish pituitary membrane preparations in a dose-related manner. In conclusion, contrary to its action as a potent GnRH antagonist in mammals, analog L has GTH-II stimulatory action in goldfish. Analog L by acting via GnRH receptors at the pituitary cell level differentially acts on GTH-II and GH release, suggesting functional differences in the properties of the GnRH receptors on GTH and GH cells. Analog L also specifically inhibits sGnRH and cGnRH-II actions on GTH-II and GH release.

Regeneration of supraspinal projection neurons in the adult goldfish

Regeneration of descending supraspinal projections were identified in adult goldfish following administration of HRP to different levels of the spinal cord. While in the untreated normal fish 17 nuclei were shown to project into the spinal cord, only 11 of them seem to have participated in the process of regeneration. The nuclei whose axons regenerated include the nucleus ventromedialis (NVMD), nucleus of the median longitudinal fasciculus (NMLF), nucleus reticularis superior (NRS), nucleus reticularis medialis (NRM), nucleus reticularis inferior (NRI), anterior octaval nucleus (AON), magnocellular octaval nucleus (MON), descending octaval nucleus (DON) and certain neurons of the facial lobe. The neurons of the magnocellular preoptic nucleus (NPO), raphe nucleus (NR), Mauthner cell (MC), posterior octaval nucleus (PON) and somata located adjacent to the descending trigeminal tract were not labeled. The nuclei that apparently participated in the regeneration process were significantly larger in size than the corresponding cell bodies in the untreated normal fish.

Topographic organization of descending projection neurons to the spinal cord of the goldfish, Carassius auratus

Several neurons from different nuclei give rise to descending spinal tracts and project to various levels in the spinal cord of goldfish, Carassius auratus. These were visualized by retrograde transport of horseradish peroxidase (HRP) administered to the bilaterally transected spinal cord at 6 levels, corresponding to 1st, 5th, 10th, 15th, 20th and 25th segments of the vertebral column. As many as 16 brain nuclei or neuronal aggregations and the Mauthner cells project posteriorly up to the 20th spinal segment. Restricted neurons of the dorsolateral area in the nucleus preopticus magnocellularis and those of the ventromedial nucleus of the thalamus projected up to the 20th and 25th segments respectively. In the mesencephalon, the nucleus ruber and the nucleus of the medial longitudinal fasciculus revealed retrogradely labeled somata; the former extended up to the 20th segment, while the latter projected up to the 25th segment. The remaining descending projection neurons of the brain belonged to the rhombencephalon. The nucleus of the lateral lemniscus; anterior, magnocellular, descending and posterior divisions of the octaval nucleus; raphe nucleus; Mauthner cell and the neurons located adjacent to the trigeminal tract and those in the vicinity of the secondary gustatory tract sent their processes up to 20th segmental level. However, somata of the superior, medial and inferior divisions of the reticular nucleus and restricted neurons of the facial lobe extended up to 25th segmental level. The pattern of neuronal projections into the spinal cord suggests a topographic organization.

Distribution of corticotropin-releasing factor immunoreactive neurons in the brain of the tigerfrog, Rana tigrina

The distribution of immunoreactive (ir) neurons containing corticotropin-releasing factor (CRF) is described in the brain of the tigerfrog, Rana tigrina. The olfactory bulb, medial pallium, nucleus of the diagonal band of Broca and medial area of the amygdala of the telencephalon showed ir-CRF perikarya. The anterior and ventromedial thalamic nuclei, and the magnocellular nucleus preopticus (NPO) revealed several ir cells; a few NPO neurons were cerebrospinal fluid contacting in nature. The nucleus hypothalamicus ventromedialis contained a few cells, but the nucleus infundibularis ventralis of the infundibulum revealed several diffusely distributed perikarya. Individual ir-CRF perikarya were visualized in the optic tectum and interpeduncular nucleus. Extensive fiber terminals were present in the median eminence, but no fibers were discerned either in the neural lobe or in the pituitary gland.

Hypophysiotropic neurons in the hypothalamus of the catfish Clarias batrachus: a cobaltous lysine and HRP study

Seven hypothalamic nuclei and several isolated perikarya that send projections to the pituitary gland were identified following administration of cobaltous lysine or horseradish peroxidase (HRP) to severed hypophysial stalks of previously hypophysectomized catfish, Clarias batrachus. Retrogradely labelled neurons were identified in the nucleus preopticus periventricularis, suprachiasmatic nucleus, paraventricular and supraoptic divisions of the magnocellular nucleus preopticus (NPO) and nucleus lateralis tuberis. A few neurons in the paraventricular subdivision of the NPO, however, remained unfilled; these may project to extrahypophysial sites. Three other nuclei contributing to the innervation of the pituitary gland include the paraventricular organ, nucleus recessus lateralis (NRL) and nucleus recessus posterioris (NRP), all of which contain cerebrospinal fluid-contacting aminergic neurons. These three neuronal aggregations were retrogradely labelled with cobaltous lysine but not with HRP. Isolated neurons displaying hypophysial connections were identified in the organon vasculosum laminae terminalis area, in the nucleus hypothalamicus ventromedialis, and in the vicinity of the NRL and NRP. Thus the present study reveals that hypothalamic projections to the pituitary gland of catfish have their origin in several peptidergic and aminergic nuclei and perikarya hitherto unreported.

Retinal projections in the catfish, Mystus vittatus (Bloch) as revealed by tracer studies with horseradish peroxidase

The retinal efferents of the catfish, Mystus vittatus, were investigated with the use of the horseradish peroxidase (HRP) technique. Most retinal fibres extended contralateral to the eye that had received HRP label, while a few fascicles projected to the ipsilateral side without decussation in the optic chiasma. The contralateral fibres projected to the suprachiasmatic nucleus, the nucleus opticus dorsolateralis, the nucleus of the posterior commissure, the nucleus geniculatus lateralis, pretectal nuclear complex, and to two layers of the optic tectum, i.e., stratum fibrosum et griseum superficiale and stratum griseum centrale. The accessory optic tract arose from the inner area of the optic tract and extended ventromedially to the accessory optic nucleus. The ipsilateral fascicles projected to almost all the above mentioned nuclei, but these projections were comparatively sparse. The ipsilateral retinal projection was restricted to the rostral tectum.

Identification of the cell types in the rostral pars distalis of the pituitary gland of the catfish, Clarias batrachus (Linn)

The cells in the rostral pars distalis (RPD) of the hypophysis of the catfish, Clarias batrachus were distinguished into 2 types by tinctorial affinities, and their functional significance was ascertained experimentally. The lead haematoxylin (PbH)-positive cells of the RPD, herein referred to as the cell type 1, are in the form of a 3-8 cell layer thick palisade along the border between the neurohypophysis (NH) and the RPD. Administration of metopirone caused significant stimulatory changes in these cells, whereas injection of ACTH, hydrocortisone or dexamethasone resulted in marked regression suggesting their ACTH-secreting nature. The type 2 cells constitute a major part of the RPD and are erythrosinophilic in nature. They showed regressive changes after immersion of the catfish in sodium chloride solution and distilled water, and a similar change was observed after injection of prolactin which indicates their prolactin-secreting nature.

Cytoarchitectonic pattern of the hypothalamus in the cobra, Naja naja

The distribution and cytoarchitectonic pattern of the magno- and parvocellular hypothalamic nuclei of the cobra. Naja naja, are described at the light-microscopic level. With respect to their tinctorial affinity to paraldehyde fuchsin (AF) as a representative of the Gomori-type of stains, the magnocellular neurons belong to the "AF-positive" and the parvocellular neurons to the "AF-negative" elements. In addition to the supraoptic and paraventricular nuclei proper, two accessory aggregations of magnocellular neurons, the nucleus retrochiasmaticus and nucleus circularis, can be identified. Although in a peculiar location, they may be regarded as subunits of the supraoptico-paraventricular neurosecretory complex. As many as 22 "AF-negative" nuclear areas are identified in the hypothalamus of the cobra. The nucleus periventricularis hypothalami of earlier authors is subdivided into several circumscribed neuronal complexes. The nucleus arcuatus, nucleus hypothalamicus lateralis and nucleus lateralis recessus infundibuli are well developed. An attempt is made to interpret the significance of these nuclei on a comparative and phylogenetic basis.

Effect of electrical stimulation of the optic nerve on the nucleus preopticus and nucleus lateralis tuberis of the catfish, Clarias batrachus (Linn.)

The changes in the nucleus preopticus (NPO) and nucleus lateralis tuberis (NLT) of the catfish, Clarias batrachus, were studied after electrical stimulation of the optic nerve. The aldehyde fuchsin (AF)-positive neurosecretory material from the entire NPO was depleted after a 10-min stimulation as revealed from the bulk-stained preparations and tissue sections. However, a 3-min stimulation was sufficient to cause significant hypertrophic changes in the neuronal nuclei (p less than 0.005 in the ventral neurons; p less than 0.01 in the dorsal neurons). In order to evoke significant stimulatory changes in the cell nuclei of the NLT, a longer period of stimulation than that for the NPO was essential. Similarly, stimulations of different durations were required to induce significant hypertrophic changes in the pars anterior and pars posterior of the NLT. Based on these observations, the possible existence of an afferent pathway from the optic nerve to the hypothalamic neurosecretory nuclei is suggested.

Congestive heart failure in two patients of lepromatous leprosy

Two cases of lepromatous leprosy are presented with heart disease, one with cardiomegaly and the other with ischaemic heart disease. It is very difficult to say whether heart disease was due to any other cause associated with leprosy or due to leprous affection of myocardium. As there are no references in the literature regarding these, two cases are presented as problem cases.