In vitro and in vivo effects of probucol on hydrolysis of asymmetric dimethyl l-arginine and vasospasm in primates

Molecular dynamics study on micelle-small molecule interactions: developing a strategy for an extensive comparison

Theoretical predictions of the solubilizing capacity of micelles and vesicles present in intestinal fluid are important for the development of new delivery techniques and bioavailability improvement. A balance between accuracy and computational cost is a key factor for an extensive study of numerous compounds in diverse environments. In this study, we aimed to determine an optimal molecular dynamics (MD) protocol to evaluate small-molecule interactions with micelles composed of bile salts and phospholipids. MD simulations were used to produce free energy profiles for three drug molecules (danazol, probucol, and prednisolone) and one surfactant molecule (sodium caprate) as a function of the distance from the colloid center of mass. To address the challenges associated with such tasks, we compared different simulation setups, including freely assembled colloids versus pre-organized spherical micelles, full free energy profiles versus only a few points of interest, and a coarse-grained model versus an all-atom model. Our findings demonstrate that combining these techniques is advantageous for achieving optimal performance and accuracy when evaluating the solubilization capacity of micelles. All-atom (AA) and coarse-grained (CG) umbrella sampling (US) simulations and point-wise free energy (FE) calculations were compared to their efficiency to computationally analyze the solubilization of active pharmaceutical ingredients in intestinal fluid colloids.

Cerebral Vasospasm: A Review

Cerebral vasospasm is a prolonged but reversible narrowing of cerebral arteries beginning days after subarachnoid hemorrhage. Progression to cerebral ischemia is tied mostly to vasospasm severity, and its pathogenesis lies in artery encasement by blood clot, although the complex interactions between hematoma and surrounding structures are not fully understood. The delayed onset of vasospasm provides a potential opportunity for its prevention. It is disappointing that recent randomized, controlled trials did not demonstrate that the endothelin antagonist clazosentan, the cholesterol-lowering agent simvastatin, and the vasodilator magnesium sulfate improve patient outcome. Minimizing ischemia by avoiding inadequate blood volume and pressure, administering the calcium antagonist nimodipine, and intervention with balloon angioplasty, when necessary, constitutes current best management. Over the past two decades, our ability to manage vasospasm has led to a significant decline in patient morbidity and mortality from vasospasm, yet it still remains an important determinant of outcome after aneurysm rupture.

Dietary nitrate facilitates an acetazolamide-induced increase in cerebral blood flow during visual stimulation

The carbonic anhydrase (CA) inhibitor acetazolamide (AZ) is used routinely to estimate cerebrovascular reserve capacity in patients, as it reliably increases cerebral blood flow (CBF). However, the mechanism by which AZ accomplishes this CBF increase is not entirely understood. We recently discovered that CA can produce nitric oxide (NO) from nitrite, and that AZ enhances this NO production in vitro. In fact, this interaction between AZ and CA accounted for a large part of AZ's vasodilatory action, which fits well with the known vasodilatory potency of NO. The present study aimed to assess whether AZ acts similarly in vivo in the human cerebrovascular system. Hence, we increased or minimized the dietary intake of nitrate in 20 healthy male participants, showed them a full-field flickering dartboard, and measured their CBF response to this visual stimulus with arterial spin labeling. Doing so, we found a significant positive interaction between the dietary intake of nitrate and the CBF modulation afforded by AZ during visual stimulation. In addition, but contrary to studies conducted in elderly participants, we report no effect of nitrate intake on resting CBF in healthy human participants. The present study provides in vivo support for an enhancing effect of AZ on the NO production from nitrite catalyzed by CA in the cerebrovascular system. Furthermore, our results, in combination with the results of other groups, indicate that nitrate may have significant importance to vascular function when the cerebrovascular system is challenged by age or disease.

Inorganic nitrite therapy: historical perspective and future directions

Over the past several years, investigators studying nitric oxide (NO) biology and metabolism have come to learn that the one-electron oxidation product of NO, nitrite anion, serves as a unique player in modulating tissue NO bioavailability. Numerous studies have examined how this oxidized metabolite of NO can act as a salvage pathway for maintaining NO equivalents through multiple reduction mechanisms in permissive tissue environments. Moreover, it is now clear that nitrite anion production and distribution throughout the body can act in an endocrine manner to augment NO bioavailability, which is important for physiological and pathological processes. These discoveries have led to renewed hope and efforts for an effective NO-based therapeutic agent through the unique action of sodium nitrite as an NO prodrug. More recent studies also indicate that sodium nitrate may also increase plasma nitrite levels via the enterosalivary circulatory system resulting in nitrate reduction to nitrite by microorganisms found within the oral cavity. In this review, we discuss the importance of nitrite anion in several disease models along with an appraisal of sodium nitrite therapy in the clinic, potential caveats of such clinical uses, and future possibilities for nitrite-based therapies.

New regulatory, signaling pathways, and sources of nitric oxide

Discovered in 1980 by the late Robert F. Furchgott, endothelium-derived relaxing factor, nitric oxide (NO), has been in the forefront of vascular research for several decades. What was originally a narrow approach, has been significantly widened due to major advances in understanding the chemical and biological properties of NO as well as its signaling pathways and discovering new sources of this notorious free radical gas. In this review, recent discoveries regarding NO and their implications on therapy for delayed cerebral vasospasm are presented.

Nitric oxide synthase inhibitors and cerebral vasospasm

L-arginine is a source of nitric oxide (NO) that is cleaved from the terminal guanidino nitrogen atom by nitric oxide synthase (NOS). NO evokes, because of its free radical properties and affinity to heme, ferrous iron and cysteine, a wide spectrum of physiological and pathophysiological effects. For many years, different exogenous NOS inhibitors were used to elucidate the role of NOS and NO in health and disease. Later, endogenous NOS inhibitors, as asymmetric dimethylarginine (ADMA) were discovered. Endogenous inhibitors as ADMA are produced by post-translational methylation of L-arginine which is catalyzed by a family of protein N-methyltransferases (PRMT), using S-adenosylmethionine as a methyl group donor. ADMA is eliminated by dimethylarginine dimethylaminohydrolases (DDAH I or II). ADMA hydrolysis increases NOS activity and NO production. Furthermore, L-citrulline, a by-product of ADMA hydrolysis as well as of NO production by NOS, can in turn inhibit DDAH. Therefore, endogenous inhibition of NOS can be modified via different ways (1) changing the availability of L-arginine and/or of L-citrulline; (2) stimulating or inhibiting DDAH activity; (3) modifying methylation via regulating availability of adenosylmethionine; or (4) modifying PRMT activity. Research elucidating the role of NOS inhibitors in respect of delayed cerebral vasospasm after subarachnoid hemorrhage is summarized.

Modification of endothelial nitric oxide synthase through AMPK after experimental subarachnoid hemorrhage

Severe subarachnoid hemorrhage (SAH) induces dysfunction of endothelial nitric oxide synthase (eNOS), resulting in severe vasospasm. Clinically, however, some portions of cerebral arteries may show only mild vasospasm. Although severe vasospastic arteries after SAH have been intensively studied, activity of eNOS associated with the mild form of the disease has received less attention. The purpose of the present study was to clarify molecular mechanisms underlying the regulation of eNOS activity in mild vasospastic arteries after SAH. In a rat single-hemorrhage model, basilar arteries were obtained up to 7 days after SAH. Western blot analysis was used to study the temporal profiles of eNOS, phosphorylated (p)-eNOS at Ser(1177) or Thr(495), inducible NOS (iNOS), AMP-activated protein kinase alpha (AMPK alpha, p-AMPK alpha at Thr(172)Akt, p-Akt at Ser(473), cyclic AMP-dependent protein kinase (PKA), and p-PKA at Thr(197) in basilar arteries. Immunohistochemical studies were performed to examine the spatial expression patterns of p-eNOS at Ser(1177) and p-AMPK alpha at Thr(172). Western blot analysis showed eNOS to be significantly phosphorylated at Ser(1177) from 1 to 2 days after SAH, accompanied by upregulation of iNOS and AMPK, while activation states of Akt and PKA did not show significant change. Immunohistochemistry revealed phosphorylation of eNOS and AMPK alpha in endothelial cells of the basilar artery. SAH might thus induce temporary activation of AMPK alpha, which phosphorylates eNOS at Ser(1177) in endothelial cells of mild vasospastic basilar arteries. This signal transduction may play an important role in controlling cerebral blood flow after SAH.

Overexpression of Dimethylarginine Dimethylaminohydrolase Inhibits Asymmetric Dimethylarginine–Induced Endothelial Dysfunction in the Cerebral Circulation

Background and Purpose— Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthase (NOS). An elevation of plasma ADMA levels is associated with cardiovascular disease. ADMA is hydrolyzed by dimethylarginine dimethylaminohydrolases (DDAHs). The goal of this study was to determine whether overexpression of human DDAH-1 in transgenic (DDAH-1–Tg) mice inhibits the vascular effects of ADMA.

Methods— Using nontransgenic (non-Tg) and DDAH-1–Tg mice, we compared responses of the carotid artery and aorta (in vitro) and of the cerebral arterioles (in vivo) in the absence or presence of ADMA. DDAH-1 expression and plasma levels of ADMA were also measured.

Results— Western blotting indicated that vascular expression of DDAH-1 was increased markedly in DDAH-1–Tg mice. Plasma levels of ADMA were reduced by ≈50% in DDAH-1–Tg mice compared with non-Tg mice (0.19±0.02 vs 0.37±0.04 μmol/L, P <0.05). Contraction of the aorta to nitro- l -arginine methyl ester (an inhibitor of NOS), an index of basal production of NO, was increased in DDAH-1–Tg mice compared with controls (50±4% vs 34±4%, P <0.05). Relaxation of the carotid artery to acetylcholine (an endothelium-dependent agonist) was enhanced in DDAH-1–Tg animals compared with control mice (relaxation of 74±6% vs 59±5%, respectively, in response to 10 μmol/L acetylcholine, P <0.05). ADMA (100 μmol/L) impaired the vascular response to acetylcholine in both non-Tg and DDAH-1–Tg mice, but the relative difference between the 2 strains remained. Responses to the endothelium-independent NO donor nitroprusside were similar in all groups. In vivo, ADMA (10 μmol/L) reduced responses of the cerebral arterioles to acetylcholine by ≈70% in non-Tg mice ( P <0.05), and this inhibitory effect was largely absent in DDAH-1–Tg mice.

Conclusions— These findings provide the first evidence that overexpression of DDAH-1 increases basal levels of vascular NO and protects against ADMA-induced endothelial dysfunction in the cerebral circulation.

Lipid Peroxidation Scavengers Prevent the Carbonylation of Cytoskeletal Brain Proteins Induced by Glutathione Depletion

In this study, we investigated the possible link between lipid peroxidation (LPO) and the formation of protein carbonyls (PCOs) during depletion of brain glutathione (GSH). To this end, rat brain slices were incubated with the GSH depletor diethyl maleate (DEM) in the absence or presence of classical LPO scavengers: trolox, caffeic acid phenethyl ester (CAPE), and butylated hydroxytoluene (BHT). All three scavengers reduced DEM-induced lipid oxidation and protein carbonylation, suggesting that intermediates/products of the LPO pathway such as lipid hydroperoxides, 4-hydroxynonenal and/or malondialdehyde are involved in the process. Additional in vitro experiments revealed that, among these products, lipid hydroperoxides are most likely responsible for protein oxidation. Interestingly, BHT prevented the carbonylation of cytoskeletal proteins but not that of soluble proteins, suggesting the existence of different mechanisms of PCO formation during GSH depletion. In pull-down experiments, beta-actin and alpha/beta-tubulin were identified as major carbonylation targets during GSH depletion, although other cytoskeletal proteins such as neurofilament proteins and glial fibrillary acidic protein were also carbonylated. These findings may be important in the context of neurological disorders that exhibit decreased GSH levels and increased protein carbonylation such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis.

Determination of cerebrospinal fluid concentrations of arginine and dimethylarginines in patients with subarachnoid haemorrhage

Elevated cerebrospinal fluid (CSF) concentrations of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), are assumed to be related to delayed vasospasm after subarachnoid haemorrhage (SAH). However, data on CSF concentrations of L-arginine, ADMA and its structural isomer symmetric dimethylarginine (SDMA) are very sparse in humans. We here present a new hydrophilic interaction chromatography-tandem mass spectrometry (HILIC-MS-MS) method for the precise determination of these substances in CSF. The method requires only minimal sample preparation and features isotope labeled internal standards. First data of patients with SAH showed that on the day of admission CSF concentration values of L-arginine and ADMA were not significantly different from controls, but increased markedly during the course of the hospital stay. The decrease of the L-arginine to ADMA ratio points to a progressive impairment of the NO production rate in the brain after SAH which is confirmed by a simultaneous decrease in nitrate and nitrite concentrations in CSF.

Dysfunction of nitric oxide synthases as a cause and therapeutic target in delayed cerebral vasospasm after SAH

Nitric oxide (NO), also known as endothelium-derived relaxing factor, is produced by endothelial nitric oxide synthase (eNOS) in the intima and by neuronal nitric oxide synthase (nNOS) in the adventitia of cerebral vessels. It dilates the arteries in response to shear stress, metabolic demands, pterygopalatine ganglion stimulation and chemoregulation. Subarachnoid hemorrhage (SAH) interrupts this regulation of cerebral blood flow. Hemoglobin, gradually released from erythrocytes in the subarachnoid space, destroys nNOS-containing neurons in the conductive arteries. This deprives the arteries of NO, leading to initiation of delayed vasospasm. But such vessel narrowing increases shear stress, which stimulates eNOS. This mechanism normally would lead to increased production of NO and dilation of arteries. However, a transient eNOS dysfunction evoked by an increase in the endogenous competitive NOS inhibitor, asymmetric dimethylarginine (ADMA), prevents this vasodilation. eNOS dysfunction has been recently shown to be evoked by increased levels of ADMA in cerebrospinal fluid (CSF) in response to the presence of bilirubin-oxidized fragments (BOXes). A direct cause of the increased ADMA CSF level is most likely decreased ADMA elimination owing to disappearance of ADMA-hydrolyzing enzyme [dimethylarginine dimethylaminohydrolase II (DDAH II)] immunoreactivity in the arteries in spasm. This eNOS dysfunction sustains vasospasm. CSF ADMA levels are closely associated with the degree and time course of vasospasm; when CSF ADMA levels decrease, vasospasm resolves. Thus, exogenous delivery of NO, inhibiting the L-arginine-methylating enzyme or stimulating DDAH II, may provide new therapeutic modalities to prevent and treat vasospasm. This paper will present results of pre-clinical studies supporting the NO-based hypothesis of delayed cerebral vasospasm development and its prevention by increased NO availability.

Probucol Decreases Asymmetrical Dimethylarginine Level by Alternation of Protein Arginine Methyltransferase I and Dimethylarginine Dimethylaminohydrolase Activity

HYPOTHESIS

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor (NOS), may play an important role in endothelium dysfunction. Probucol, a potent antioxidant drug, may improve endothelium function via reduction of NOS inhibitor level. The present study examined whether the decreased level of ADMA by probucol is related to enhancement of protein arginine methyltransferase I (PRMT I) expression and reduction of dimethylarginine dimethylaminohydrolase (DDAH) activity.

METHODS

Endothelial cells were cultured and used for all these studies. ADMA concentration and DDAH activity were determined by HPLC. Expression of PRMT I and eNOS were characterized by western blot.

RESULTS

Pretreatment with oxidized-low density lipoprotein (ox-LDL) (10, 30 or 100 microg/ml) or lysophosphatidylcholine (LPC) (1.0, 2.5 or 5.0 microg/ml) for 12, 24 or 48 h markedly increased the activity of lactate dehydrogenase (LDH) in cultured endothelial cell. Incubation ofendothelial cells with ox-LDL (100 microg/ml) or LPC (5.0 microg/ml) for 48 h significantly increased the expression of PRMT I, and levels of MDA and ADMA, and decreased the concentration of nitrite/nitrate, the expression of eNOS and the activity of DDAH. Probucol significantly decreased the level of ADMA, concomitantly with reduction of PRMT I expression and elevation of DDAH activity and up-regulation of eNOS expression.

CONCLUSION

In summary, the present results suggest that the protective effect of probucol on endothelium is related to reduction of ADMA concentration by inhibition of PRMT I expression and enhancement of DDAH activity.