The time course of myosin light-chain phosphorylation in blood-induced vasospasm

Highly sensitive myosin phosphorylation analysis in the renal afferent arteriole

The regulation of smooth muscle contraction and relaxation involves phosphorylation and dephosphorylation of regulatory proteins, particularly myosin. To elucidate the regulatory mechanisms, analyzing the phosphorylation signal transduction is crucial. Although a pharmacological approach with selective inhibitors is sensitive and a useful technique, it leads to speculation regarding a signaling pathway but does not provide direct evidence of changes at a molecular level. We developed a highly sensitive biochemical technique to analyze phosphorylation by adapting Phos-tag SDS-PAGE. With this technique, we successfully analyzed myosin light chain (LC₂₀) phosphorylation in tiny renal afferent arterioles. In the rat afferent arterioles, endothelin-1 (ET-1) induced diphosphorylation of LC₂₀ at Ser19 and Thr18 as well as monophosphorylation at Ser19 via ET_B receptor activation. Considering that LC₂₀ diphosphorylation can decrease the rate of dephosphorylation and thus relaxation, we concluded that LC₂₀ diphosphorylation contributes, at least in part, to the prolonged contraction induced by ET-1 in the renal afferent arteriole.

Involvement of myosin regulatory light chain diphosphorylation in sustained vasoconstriction under pathophysiological conditions

Smooth muscle contraction is activated primarily by phosphorylation at Ser19 of the regulatory light chain subunits (LC₂₀) of myosin II, catalysed by Ca²⁺/calmodulin-dependent myosin light chain kinase. Ca²⁺-independent contraction can be induced by inhibition of myosin light chain phosphatase, which correlates with diphosphorylation of LC₂₀ at Ser19 and Thr18, catalysed by integrin-linked kinase (ILK) and zipper-interacting protein kinase (ZIPK). LC₂₀ diphosphorylation at Ser19 and Thr18 has been detected in mammalian vascular smooth muscle tissues in response to specific contractile stimuli (e.g. endothelin-1 stimulation of rat renal afferent arterioles) and in pathophysiological situations associated with hypercontractility (e.g. cerebral vasospasm following subarachnoid hemorrhage). Comparison of the effects of LC₂₀ monophosphorylation at Ser19 and diphosphorylation at Ser19 and Thr18 on contraction and relaxation of Triton-skinned rat caudal arterial smooth muscle revealed that phosphorylation at Thr18 has no effect on steady-state force induced by Ser19 phosphorylation. On the other hand, the rates of dephosphorylation and relaxation are significantly slower following diphosphorylation at Thr18 and Ser19 compared to monophosphorylation at Ser19. We propose that this diphosphorylation mechanism underlies the prolonged contractile response of particular vascular smooth muscle tissues to specific stimuli, e.g. endothelin-1 stimulation of renal afferent arterioles, and the vasospastic behavior observed in pathological conditions such as cerebral vasospasm following subarachnoid hemorrhage and coronary arterial vasospasm. ILK and ZIPK may, therefore, be useful therapeutic targets for the treatment of such conditions.

Endothelin-1, but not angiotensin II, induces afferent arteriolar myosin diphosphorylation as a potential contributor to prolonged vasoconstriction

Bolus administration of endothelin-1 elicits long-lasting renal afferent arteriolar vasoconstriction, in contrast to transient constriction induced by angiotensin II. Vasoconstriction is generally evoked by myosin regulatory light chain (LC20) phosphorylation at Ser19 by myosin light chain kinase (MLCK), which is enhanced by Rho-associated kinase (ROCK)-mediated inhibition of myosin light chain phosphatase (MLCP). LC20 can be diphosphorylated at Ser19 and Thr18, resulting in reduced rates of dephosphorylation and relaxation. Here we tested whether LC20 diphosphorylation contributes to sustained endothelin-1 but not transient angiotensin II-induced vasoconstriction. Endothelin-1 treatment of isolated arterioles elicited a concentration- and time-dependent increase in LC20 diphosphorylation at Thr18 and Ser19. Inhibition of MLCK or ROCK reduced endothelin-1-evoked LC20 mono- and diphosphorylation. Pretreatment with an ETB but not an ETA receptor antagonist abolished LC20 diphosphorylation, and an ETB receptor agonist induced LC20 diphosphorylation. In contrast, angiotensin II caused phosphorylation exclusively at Ser19. Thus, endothelin-1 and angiotensin II induce afferent arteriolar constriction via LC20 phosphorylation at Ser19 due to calcium activation of MLCK and ROCK-mediated inhibition of MLCP. Endothelin-1, but not angiotensin II, induces phosphorylation of LC20 at Thr18. This could contribute to the prolonged vasoconstrictor response to endothelin-1.

Myosin regulatory light chain diphosphorylation slows relaxation of arterial smooth muscle

The principal signal to activate smooth muscle contraction is phosphorylation of the regulatory light chains of myosin (LC(20)) at Ser(19) by Ca(2+)/calmodulin-dependent myosin light chain kinase. Inhibition of myosin light chain phosphatase leads to Ca(2+)-independent phosphorylation at both Ser(19) and Thr(18) by integrin-linked kinase and/or zipper-interacting protein kinase. The functional effects of phosphorylation at Thr(18) on steady-state isometric force and relaxation rate were investigated in Triton-skinned rat caudal arterial smooth muscle strips. Sequential phosphorylation at Ser(19) and Thr(18) was achieved by treatment with adenosine 5'-O-(3-thiotriphosphate) in the presence of Ca(2+), which induced stoichiometric thiophosphorylation at Ser(19), followed by microcystin (phosphatase inhibitor) in the absence of Ca(2+), which induced phosphorylation at Thr(18). Phosphorylation at Thr(18) had no effect on steady-state force induced by Ser(19) thiophosphorylation. However, phosphorylation of Ser(19) or both Ser(19) and Thr(18) to comparable stoichiometries (0.5 mol of P(i)/mol of LC(20)) and similar levels of isometric force revealed differences in the rates of dephosphorylation and relaxation following removal of the stimulus: t(½) values for dephosphorylation were 83.3 and 560 s, and for relaxation were 560 and 1293 s, for monophosphorylated (Ser(19)) and diphosphorylated LC(20), respectively. We conclude that phosphorylation at Thr(18) decreases the rates of LC(20) dephosphorylation and smooth muscle relaxation compared with LC(20) phosphorylated exclusively at Ser(19). These effects of LC(20) diphosphorylation, combined with increased Ser(19) phosphorylation (Ca(2+)-independent), may underlie the hypercontractility that is observed in response to certain physiological contractile stimuli, and under pathological conditions such as cerebral and coronary arterial vasospasm, intimal hyperplasia, and hypertension.

Vascular smooth muscle myosin light chain diphosphorylation: mechanism, function, and pathological implications

Smooth muscle contraction is activated primarily by phosphorylation at S19 of the 20-kDa regulatory light chain subunits of myosin II (LC(20) ) catalyzed by Ca(2+) /calmodulin-dependent myosin light chain kinase. Other kinases, for example, integrin-linked kinase (ILK), Rho-associated kinase (ROCK), and zipper-interacting protein kinase (ZIPK), can phosphorylate T18 in addition to S19, which increases the actin-activated myosin MgATPase activity at subsaturating actin concentrations ∼3-fold. These phosphorylatable residues and the amino acid sequence surrounding them are highly conserved throughout the animal kingdom; they are also found in an LC(20) homolog within the genome of Monosiga brevicollis, the closest living relative of metazoans. LC(20) diphosphorylation has been detected in mammalian vascular smooth muscle tissues in response to specific contractile stimuli and in pathophysiological situations associated with hypercontractility. LC(20) diphosphorylation has also been observed frequently in cultured cells where it activates force generation. Kinases such as ILK, ROCK, and ZIPK, therefore, are potential therapeutic targets in the treatment of, for example, cerebral vasospasm following subarachnoid hemorrhage and atherosclerosis.

Enhanced contractility and myosin phosphorylation induced by Ca(2+)-independent MLCK activity in hypertensive rats

AIMS

The role of Ca(2+) sensitization induced by a Ca(2+)-independent myosin light chain kinase (MLCK) in hypertension has not been determined. The aim of this study was to clarify the role of possible Ca(2+)-independent MLCK activity in hypertension.

METHODS AND RESULTS

We compared increases in contractile force and phosphorylation of myosin light chain (MLC) evoked by calyculin A, a phosphatase inhibitor, in β-escin-permeabilized mesenteric arteries at pCa 9.0 between spontaneously hypertensive rat (SHR) and Wistar Kyoto rat (WKY). We found that there was no detectable phosphorylation of MLC at pCa 9.0, but that the administration of 1 μM calyculin A gradually increased force and mono- and di-phosphorylation of MLC. This contraction was inhibited by staurosporine but not by wortmannin, Y-27632, or calphostin-C. The calyculin A-induced contraction was significantly greater in the SHR than in the WKY and was associated with an increase in mono- and di-phosphorylation of MLC. SM-1, a zipper-interacting protein kinase (ZIPK)-inhibiting peptide, significantly inhibited the amplitude of the calyculin A-induced contraction and di-phosphorylation. Total ZIPK expression (54 + 32 kDa) was greater in the SHR than in the WKY. Phosphorylation of myosin phosphatase target subunit at Thr(697), but not at Thr(855), was consistently stronger in the SHR than in the WKY in calyculin A-treated tissues at pCa 9.0.

CONCLUSIONS

Our results suggest that Ca(2+)-independent MLCK activity is enhanced in the SHR, and that ZIPK plays, at least in part, an important role as a candidate for this kinase in rat mesenteric arteries.

Key role of the RhoA/Rho kinase system in pulmonary hypertension

Pulmonary hypertension (PH) is a general term comprising a spectrum of pulmonary hypertensive disorders which have in common an elevation of mean pulmonary arterial pressure (mPAP). The prototypical form of the disease, termed pulmonary arterial hypertension (PAH), is a rare but lethal syndrome with a complex aetiology characterised by increased pulmonary vascular resistance (PVR) and progressive elevation of mPAP; patients generally die from heart failure. Current therapies are inadequate and median survival is less than three years. PH due to chronic hypoxia (CH) is a condition separate from PAH and is strongly associated with chronic obstructive pulmonary disease (COPD). An early event in the pathogenesis of this form of PH is hypoxic pulmonary vasoconstriction (HPV), an acute homeostatic process that maintains the ventilation-perfusion ratio during alveolar hypoxia. The mechanisms underlying HPV remain controversial, but RhoA/Rho kinase (ROK)-mediated Ca²+-sensitisation is considered important. Increasing evidence also implicates RhoA/ROK in PASMC proliferation, inflammatory cell recruitment and the regulation of cell motility, all of which are involved in the pulmonary vascular remodelling occurring in all forms of PH. ROK is therefore a potential therapeutic target in treating PH of various aetiologies. Here, we examine current concepts regarding the aetiology of PAH and also PH due to CH, focusing on the contribution that RhoA/ROK-mediated processes may make to their development and on ROK inhibitors as potential therapies.

Biomarkers and vasospasm after aneurysmal subarachnoid hemorrhage

Subarachnoid hemorrhage from the rupture of a saccular aneurysm is a devastating neurological disease that has a high morbidity and mortality not only from the initial hemorrhage, but also from the delayed complications, such as cerebral vasospasm. Cerebral vasospasm can lead to delayed ischemic injury 1 to 2 weeks after the initial hemorrhage. Although the pathophysiology of vasospasm has been described for decades, the molecular basis remains poorly understood. With the many advances in the past decade in the development of sensitive molecular biological techniques, imaging, biochemical purification, and protein identification, new insights are beginning to reveal the etiology of vasospasm. These findings will not only help to identify markers of vasospasm and prognostic outcome, but will also yield potential therapeutic targets for the treatment of this disease. This review focuses on the methods available for the identification of biological markers of vasospasm and their limitations, the current understanding as to the utility and prognostic significance of identified biomarkers, the utility of these biomarkers in predicting vasospasm and outcome, and future directions of research in this field.

Opportunities to Target Specific Contractile Abnormalities with Smooth Muscle Protein Kinase Inhibitors

Smooth muscle is a major component of most hollow organ systems (e.g., airways, vasculature, bladder and gut/gastrointestine); therefore, the coordinated regulation of contraction is a key property of smooth muscle. When smooth muscle functions normally, it contributes to general health and wellness, but its dysfunction is associated with morbidity and mortality. Rho-associated protein kinase (ROCK) is central to calcium-independent, actomyosin-mediated contractile force generation in the vasculature, thereby playing a role in smooth muscle contraction, cell motility and adhesion. Recent evidence supports an important role for ROCK in the increased vasoconstriction and remodeling observed in various models of hypertension. This review will provide a commentary on the development of specific ROCK inhibitors and their clinical application. Fasudil will be discussed as an example of bench-to-bedside development of a clinical therapeutic that is used to treat conditions of vascular hypercontractility. Due to the wide spectrum of biological processes regulated by ROCK, many additional clinical indications might also benefit from ROCK inhibition. Apart from the importance of ROCK in smooth muscle contraction, a variety of other protein kinases are known to play similar roles in regulating contractile force. The zipper-interacting protein kinase (ZIPK) and integrin-linked kinase (ILK) are two well-described regulators of contraction. The relative contribution of each kinase to contraction depends on the muscle bed as well as hormonal and neuronal stimulation. Unfortunately, specific inhibitors for ZIPK and ILK are still in the development phase, but the success of fasudil suggests that inhibitors for these other kinases may also have valuable clinical applications. Notably, the directed inhibition of ZIPK with a pseudosubstrate molecule shows unexpected effects on the contractility of gastrointestinal smooth muscle.

Pathogenesis of cerebral vasospasm following aneurysmal subarachnoid hemorrhage: putative mechanisms and novel approaches

Cerebral vasospasm is a potentially incapacitating or lethal complication in patients with aneurysmal subarachnoid hemorrhage (SAH). The development of effective preventative and therapeutic interventions has been largely hindered by the fact that the underlying pathogenic mechanisms of cerebral vasospasm remain poorly understood. However, intensive research during the last 3 decades has identified certain mechanisms that possibly play a role in its development. Experimental data suggest that calcium-dependent and -independent vasoconstriction is taking place during vasospasm. It appears that the breakdown products of blood in the subarachnoid space are involved, through direct and/or indirect pathways, in the development of vasospasm after SAH. Free radicals reactions, an imbalance between vasoconstrictor and vasodilator substances (endothelium derived substances, e.g., nitric oxide, endothelin; arachidonic acid metabolites, e.g., prostaglandins, prostacyclin), inflammatory processes, an upheaval of neuronal mechanisms that regulate vascular tone, endothelial proliferation, and apoptosis have all been put forward as causative and/or pathogenic factors. Translational research in the field of vasospasm has traditionally aimed to identify agents/interventions in order to block the cascades initiated after SAH. The combination of novel approaches such as cerebral microdialysis, magnetic resonance spectroscopy, proteomics, and lipidomics could serve a dual purpose: elucidating the complex pathobiochemistry of vasospasm and providing clinicians with tools for early detection of this feared complication. The purpose of this Mini-Review is to provide an overview of the pathogenesis of cerebral vasospasm and of novel approaches used in basic and translational research.

The relaxant effect of okadaic acid on canine basilar artery involves activation of PKCalpha and phosphorylation of the myosin light chain at Thr-9

Vasodilator responses induced by okadaic acid were investigated in canine basilar artery precontracted with 80 mM KCl. Okadaic acid (1 microM) relaxed the artery and this relaxant effect was partially inhibited by Gö6976, a conventional protein kinase C inhibitor, and calphostin C, an inhibitor of conventional and novel PKCs. Rottlerin, a specific inhibitor of PKCdelta, did not influence okadaic acid's effect. KCl increased phosphorylation of 20,000-Dalton myosin light chain (MLC(20)) at Ser-19. Okadaic acid additionally increased MLC(20) phosphorylation at Thr-18 and Thr-9, resulting in triphosphorylation of MLC(20). This phosphorylation was inhibited by Gö6976. Okadaic acid stimulated phosphorylation of PKCalpha and 17,000-Dalton PKC-potentiated inhibitory phosphoprotein (CPI-17), and Gö6976 inhibited these phosphorylations. These results suggest that okadaic acid's relaxant effect involves MLC(20) triphosphorylation through a direct phosphorylation by PKCalpha and an indirect phosphorylation by inhibition of myosin light chain phosphatase through PKCalpha-mediated CPI-17 phosphorylation.

Staurosporine inhibition of zipper-interacting protein kinase contractile effects in gastrointestinal smooth muscle

Zipper-interacting protein kinase (ZIPK) is a serine–threonine kinase that has been implicated in Ca2+-independent myosin II phosphorylation and contractile force generation in vascular smooth muscle. However, relatively little is known about the contribution of this kinase to gastrointestinal smooth muscle contraction. The addition of a recombinant version of ZIPK that lacked the leucine zipper domain to permeabilized ileal strips evoked a Ca2+-independent contraction and resulted in myosin regulatory light chain diphosphorylation at Ser19and Thr18. Neither Ca2+-independent force development nor myosin regulatory light chain phosphorylation was elicited by the addition of kinase-dead ZIPK to the ileal strips. The sensitivity of ZIPK-induced contraction to various kinase inhibitors was similar to the in vitro sensitivity of purified ZIPK to these inhibitors. Staurosporine was the most effective ZIPK inhibitor, with a Kivalue calculated to be 2.6 ± 0.3 µmol/L. Through the use of specific kinase inhibitors, we determined that Rho-associated protein kinase and Ca2+/phospholipid-dependent protein kinase (protein kinase C) do not mitigate ZIPK-induced contraction in ileum. Our findings support a role for ZIPK in Ca2+-independent contractile force generation in gastrointestinal smooth muscle.

Integrin-linked kinase is responsible for Ca2+-independent myosin diphosphorylation and contraction of vascular smooth muscle

Smooth muscle contraction is activated by phosphorylation at Ser-19 of LC20 (the 20 kDa light chains of myosin II) by Ca2+/calmodulin-dependent MLCK (myosin light-chain kinase). Diphosphorylation of LC20 at Ser-19 and Thr-18 is observed in smooth muscle tissues and cultured cells in response to various contractile stimuli, and in pathological circumstances associated with hypercontractility. MLCP (myosin light-chain phosphatase) inhibition can lead to LC20 diphosphorylation and Ca2+-independent contraction, which is not attributable to MLCK. Two kinases have emerged as candidates for Ca2+-independent LC20 diphosphorylation: ILK (integrin-linked kinase) and ZIPK (zipper-interacting protein kinase). Triton X-100-skinned rat caudal arterial smooth muscle was used to investigate the relative importance of ILK and ZIPK in Ca2+-independent, microcystin (phosphatase inhibitor)-induced LC20 diphosphorylation and contraction. Western blotting and in-gel kinase assays revealed that both kinases were retained in this preparation. Ca2+-independent contraction of calmodulin-depleted tissue in response to microcystin was resistant to MLCK inhibitors [AV25 (a 25-amino-acid peptide derived from the autoinhibitory domain of MLCK), ML-7, ML-9 and wortmannin], protein kinase C inhibitor (GF109203X) and Rho-associated kinase inhibitors (Y-27632 and H-1152), but blocked by the non-selective kinase inhibitor staurosporine. ZIPK was inhibited by AV25 (IC50 0.63+/-0.05 microM), whereas ILK was insensitive to AV25 (at concentrations as high as 100 microM). AV25 had no effect on Ca2+-independent, microcystin-induced LC20 mono- or di-phosphorylation, with a modest effect on force. We conclude that direct inhibition of MLCP in the absence of Ca2+ unmasks ILK activity, which phosphorylates LC20 at Ser-19 and Thr-18 to induce contraction. ILK is probably the kinase responsible for myosin diphosphorylation in vascular smooth muscle cells and tissues.

Signal transduction pathways in cerebral vasospasm

Cerebral vasospasm is a deadly complication following the rupture of intracranial aneurysms. The time course of cerebral vasospasm is unique in that it is slow developing, usually takes 4-7 days to peak, but lasts up to 2-3 weeks, and is resistant to most known vasodilators. These special features make cerebral vasospasm the most important determinant in the outcome of patients suffering subarachnoid hemorrhage. The available treatment strategies include mechanical dilation of spastic cerebral arteries (angioplasty) and non-selective vasodilatation such as by Ca(2+) channel blockers. One new development in the experimental treatment of cerebral vasospasm is the looming target of signaling pathways. Understanding vasospastic signals in cerebral arteries might offer a new avenue for selective treatment of cerebral vasospasm in the future.

Sustained arterial narrowing after prolonged exposure to perivascular endothelin

OBJECTIVE

The vasoconstrictor peptide endothelin-1 (ET-1) produces narrowing of cerebral arteries and has been implicated in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage. Little is known, however, regarding the physiological consequences of prolonged exposure of arterial wall to ET-1.

METHODS

In 30 rats, normal saline or 10(-8) mol/h of ET-1 was continuously applied for 3 or 5 days to the adventitial surface of the femoral artery in a Silastic cuff via an osmotic infusion pump. Vessels were examined for histopathological changes and luminal narrowing during ET-1 infusion (3 or 5 d) or at intervals from 2 to 9 days after infusion was stopped.

RESULTS

Marked arterial constriction (30-40% arterial diameter reduction) was present during continuous ET-1 infusion for 3 or 5 days. For both 3- and 5-day ET-1 infusions, significant reduction in arterial cross sectional area persisted up to 4 days after cessation of infusion, after which normal caliber returned. In arteries with persistent luminal narrowing after cessation of ET-1 infusion, light microscopic findings revealed morphological changes in the vessel wall similar to those observed in cerebral vasospasm after subarachnoid hemorrhage, with apparent increased collagen deposition in media and adventitia.

CONCLUSION

Continuous infusion of ET-1 produces reversible arterial narrowing that persists beyond the usual interval of physiological effect for this agent. Prolonged arterial constriction may produce physiological changes in arterial wall that act to maintain a narrowed lumen.

Expression of endothelial nitric oxide synthase after exposure to perivascular blood

OBJECTIVE

Although nitric oxide (NO) has been implicated in the development of vasospasm after subarachnoid hemorrhage, little is known regarding the time course of NO synthesis in vessel wall after exposure to perivascular blood. This study measures temporal characteristics of changes in vessel wall NO synthesis.

METHODS

Rat femoral arteries exposed to perivascular blood for 3, 5, or 7 days were assayed for the endothelial isoform of NO synthase (eNOS) by Western blot testing. Additionally, rat femoral arteries exposed to perivascular blood for intervals from 3 to 14 days were analyzed by means of immunohistochemistry for eNOS.

RESULTS

Semiquantitative densitometry of femoral artery Western blots demonstrated a biphasic pattern of eNOS expression after exposure to perivascular blood. Compared with control arteries, eNOS expression increased at 3 days (53 +/- 36%), normalized at 5 days (-6 +/- 7%), and decreased by 7 days (-39 +/- 15%). Immunohistochemistry confirmed the changes in expression of immunoreactive eNOS in femoral endothelium during the first week after chronic perivascular blood exposure and apparent reduced eNOS immunostaining, which persisted up to 14 days after application of blood.

CONCLUSION

The expression of endothelial-derived NO in rat femoral artery exposed to perivascular whole blood does not directly correlate with changes in vessel caliber during this interval. The biphasic expression of eNOS observed in these experiments highlights the complexity of processes occurring in the vicinity of the vessel wall during vasospasm and may be related to several mechanisms that modulate vessel tone and response to injury.

Upregulation of rho A and rho kinase messenger RNAs in the basilar artery of a rat model of subarachnoid hemorrhage

OBJECT

Rho A, a small guanosine triphosphate-binding protein, and rho kinases have been suggested to play an important role in the agonist-induced myofilament Ca++ sensitization and cytoskeletal organization of smooth-muscle cells. To discover their possible roles in the prolonged contraction seen in cerebral vasospasm, the authors investigated the messenger (m)RNA expressions of rho A and rho-associated kinases alpha and beta in the basilar artery (BA) of a rat double cisternal blood-injection model.

METHODS

An experimental subarachnoid hemorrhage (SAH) was achieved in rats by twice injecting autologous arterial blood into the cisterna magna of each animal. The mRNAs for rho A and rho-associated kinases alpha and beta of the rat BA were analyzed using reverse transcription-polymerase chain reaction (RT-PCR). The cisternal blood injection induced a marked corrugation of elastic lamina and contraction of smooth-muscle cells observed with the aid of light and transmission electron microscopy in the rat BA on Days 3, 5, and 7. Results of the RT-PCR revealed that mRNAs for rho A and rho kinases alpha and beta were expressed in the rat BA and that they were significantly upregulated and reached their peaks on Day 5.

CONCLUSIONS

The mRNA upregulation of these proteins indicates that activation of rho A/rho kinase-related signal transduction pathways is involved in the development of long-lasting contraction of cerebral arteries after SAH.

The presence of an extractable substance in the CSF of humans with cerebral vasospasm after subarachnoid haemorrhage that correlates with phosphatase inhibition

The cellular events leading to cerebral vasospasm after subarachnoid haemorrhage are poorly understood, although an increase in smooth muscle myosin light chain phosphorylation has been observed. This study set out to determine if phosphatase inhibition may be involved in the pathological maintenance of tension observed during vasospasm. We found that 1 nM okadaic acid, a type 2A protein phosphatase inhibitor, elicited an increase in rate of O(2) consumption in the porcine carotid artery similar to that by cerebrospinal fluid (CSF) from vasospastic patients (CSF(V), n=5) (control 0.23+/-0.03, CSF(V) 0.84+/-0.16 and okadaic acid 0.85+/-0.02 micromol min(-1) g dwt(-1)). It was also observed that phosphatase inhibition with 1 nM okadaic acid significantly slowed relaxation after a stretch in a similar fashion to CSF(V) haemorrhage. CSF from vasospastic subarachnoid haemorrhage patients, but not from those without vasospasm, contains an extractable substance which modulates myosin light chain phosphorylation in vitro. A phosphatase preparation obtained from the porcine carotid artery dephosphorylated 63+/-2% of the phosphorylated (MLC(20)) substrate in vitro, and non-vasospastic CSF treated enzyme dephosphorylated 60+/-2.6%. Okadaic acid inhibited phosphatase dephosphorylated only 7.5+/-1% of the substrate where CSF(V) treated enzyme dephosphorylated 22+/-2.8% of the substrate. We conclude that inhibition of smooth muscle phosphatase may be involved in the mechanisms associated with cerebral vasospasm after subarachnoid haemorrhage.

Plasma endothelin concentrations after aneurysmal subarachnoid hemorrhage

OBJECT

The pathogenesis of cerebral vasospasm and delayed ischemia after subarachnoid hemorrhage (SAH) seems to be complex. An important mediator of chronic vasospasm may be endothelin (ET), with its powerful and long-lasting vasoconstricting activity. In this study the author investigated the correlation between serial plasma concentrations of ET and ischemic symptoms, angiographically demonstrated evidence of vasospasm, and computerized tomography (CT) findings after aneurysmal SAH.

METHODS

Endothelin-1 immunoreactivity in plasma was studied in 70 patients with aneurysmal SAH and in 25 healthy volunteers by using a double-antibody sandwich-enzyme immunoassay (immunometric) technique. On the whole, mean plasma ET concentrations in patients with SAH (mean +/- standard error of mean, 2.1 +/- 0.1 pg/ml) did not differ from those of healthy volunteers (1.9 +/- 0.2 pg/ml). Endothelin concentrations were significantly higher (p < 0.05) in patients who experienced delayed cerebral ischemia with fixed neurological deficits compared with those in other patients (post-SAH Days 0-5, 3.1 +/- 0.8 pg/ml compared with 2.1 +/- 0.2 pg/ml; post-SAH Days 6-14, 2.5 +/- 0.4 pg/ml compared with 1.9 +/- 0.2 pg/ml). Patients with angiographic evidence of severe vasospasm also had significantly (p < 0.05) elevated ET concentrations (post-SAH Days 0-5, 3.2 +/- 0.8 pg/ml; post-SAH Days 6-14, 2.7 +/- 0.5 pg/ml) as did those with a cerebral infarction larger than a lacuna on the follow-up CT scan (post-SAH Days 0-5, 3.1 +/- 0.8 pg/ml; post-SAH Days 6-14, 2.5 +/- 0.4 pg/ml) compared with other patients. Patients in whom angiography revealed diffuse moderate-to-severe vasospasm had significantly (p < 0.05) higher ET levels than other patients within 24 hours before or after angiography (2.6 +/- 0.3 compared with 1.9 +/- 0.2 pg/ml). In addition, patients with a history of hypertension or cigarette smoking experienced cerebral infarctions significantly more often than other patients, although angiography did not demonstrate severe or diffuse vasospasm more often in these patients than in others.

CONCLUSIONS

Endothelin concentrations seem to correlate with delayed cerebral ischemia and vasospasm after SAH. The highest levels of ET are predictive of the symptoms of cerebral ischemia and vasospasm, and ET may also worsen ischemia in patients with a history of hypertension. Thus, ET may be an important causal or contributing factor to vasospasm, but its significance in the pathogenesis of vasospasm remains unknown.

Glutathione monoethyl ester and inhibition of the oxyhemoglobin-induced increase in cytosolic calcium in cultured smooth-muscle cells

OBJECT

The mechanism of arterial vasoconstriction caused by oxyhemoglobin production after subarachnoid hemorrhage was investigated.

METHODS

Using a fluorescent Ca++ indicator (fura-2 acetoxymethyl ester), the change in the cytosolic intracellular Ca++ concentration, [Ca++]i. was measured in cultured rat vascular smooth-muscle cells exposed to oxyhemoglobin and other substances. Oxyhemoglobin induced transient elevation of smooth-muscle cell [Ca++]i in either the presence or absence of ethyleneglycol-bis (beta-aminoethylether)-N,N'-tetraacetic acid, indicating that Ca++ released by oxyhemoglobin was derived from [Ca++]i stores. In contrast, methemoglobin had no effect on the smooth-muscle cells. Exposure of the cells to reactive oxygen species generated by xanthine plus xanthine oxidase yielded the same results as with oxyhemoglobin, that is, transient elevation of smooth-muscle cell [Ca++]i. Procaine (a Ca++ channel blocker) failed to inhibit the oxyhemoglobin-induced elevation of [Ca++]i. Ryanodine (a Ca++ channel opener) plus oxyhemoglobin caused markedly greater elevation of [Ca++]i than ryanodine alone, whereas thapsigargin (an adenosine triphosphate [ATP]-dependent Ca++ pump inhibitor) plus oxyhemoglobin had no additional effect when compared with thapsigargin alone. The oxyhemoglobin-induced elevation of [Ca++]i could be blocked by an Fe++ chelator (ferene), but not by an Fe chelator (deferoxamine mesylate). Treatment with either dithiothreitol or glutathione monoethyl ester markedly inhibited the oxyhemoglobin-induced elevation of [Ca++]i.

CONCLUSIONS

These results indicate that Fe++-catalyzed hydroxyl radicals generated from oxyhemoglobin-derived free radicals induce the elevation of [Ca++]i by inhibiting the ATP-dependent Ca++ pump rather than the Ca++ channels in the sarcoplasmic reticulum and that thiols may prevent Ca++ pump inactivation by inhibiting the oxidation of membrane sulfhydryl groups.

Myosin light chain phosphorylation and contractile proteins in a canine two-hemorrhage model of subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Subarachnoid hemorrhage (SAH) impairs both contraction and relaxation response in cerebral arteries. We tested the hypothesis that cerebral vasospasm might be ATP-independent contraction, such as latch state, and protein synthesis might be substantially downregulated due to ATP consumption after long-lasting contraction.

METHODS

Chronic cerebral vasospasm was induced in the canine 2-hemorrhage model of SAH. The normal and spastic basilar arteries were stabilized in Krebs-Henseleit solution, and contraction was induced by 30 micromol/L prostaglandin F2alpha (PGF2alpha) in vitro and in vivo. Before and at 15 minutes and 1 hour after the treatment with PGF2alpha, the levels of phosphorylated 20-kDa myosin light chain (MLC20) were measured. The time course of expression of contraction proteins actin and MLC20, and contraction-inhibiting proteins h-caldesmon and calponin was determined by immunoblotting techniques.

RESULTS

A significant vasospasm occurred in the basilar artery during days 4 to 21, most prominently on days 7 and 14. There were no significant differences in the baseline levels of phosphorylated MLC20 between normal and spastic basilar arteries. The increase in MLC20 phosphorylation by PGF2alpha was significantly attenuated in the spastic basilar artery in vitro and in vivo (P<0.05). The immunoreactivity for actin, h-caldesmon, and calponin in the spastic basilar arteries was progressively decreased until day 14 and returned to the normal level on day 21. In contrast, protein levels of MLC20 did not significantly change during days 0 to 21.

CONCLUSIONS

Chronic cerebral vasospasm closely resembles the latch state, and temporary deficiencies of contractile proteins may result from increased destruction and inhibition of protein synthesis.

Comparison of balloon angioplasty and papaverine infusion for the treatment of vasospasm following aneurysmal subarachnoid hemorrhage

OBJECT

The purpose of this study was to test the hypothesis that balloon angioplasty is superior to papaverine infusion for the treatment of proximal anterior circulation arterial vasospasm following subarachnoid hemorrhage (SAH). Between 1989 and 1995, 125 vasospastic distal internal carotid artery or proximal middle cerebral artery vessel segments were treated in 52 patients.

METHODS

Blood flow velocities of the involved vessels were assessed by using transcranial Doppler (TCD) monitoring in relation to the day of treatment with balloon angioplasty or papaverine infusion. Balloon angioplasty and papaverine infusion cohorts were compared based on mean pre- and posttreatment velocity at 24 and 48 hours using the one-tailed, paired-samples t-test. Balloon angioplasty alone was performed in 101 vessel segments (81%) in 39 patients (75%), whereas papaverine infusion alone was used in 24 vessel segments (19%) in 13 patients (25%). Although repeated treatment after balloon angioplasty was needed in only one vessel segment, repeated treatment following papaverine infusion was required in 10 vessel segments (42%) in six patients because of recurrent vasospasm (p < 0.001). Seven vessel segments (29%) with recurrent spasm following papaverine infusion were treated with balloon angioplasty. Although vessel segments treated with papaverine demonstrated a 20% mean decrease in blood flow velocity (p < 0.009) on posttreatment Day 1, velocities were not significantly lower than pretreatment levels by posttreatment Day 2 (p = 0.133). Balloon angioplasty resulted in a 45% mean decrease in velocity to a normal level following treatment (p < 0.001), a decrease that was sustained.

CONCLUSIONS

Balloon angioplasty is superior to papaverine infusion for the permanent treatment of proximal anterior circulation vasospasm following aneurysmal SAH.

Inhibition of experimental vasospasm with anti-intercellular adhesion molecule-1 monoclonal antibody in rats

BACKGROUND AND PURPOSE

Inflammation may play a role in delayed chronic vasospasm after aneurysmal subarachnoid hemorrhage. We investigated the role of intercellular adhesion molecule-1 (ICAM-1) and macrophage/granulocyte infiltration in the rat femoral artery model of vasospasm using systemic administration of a murine anti-ICAM-1 monoclonal antibody (MAb).

METHODS

The femoral arteries (n = 72) in Sprague-Dawley rats (n = 36) were enclosed in latex pouches bilaterally. Autologous blood was injected into the pouch on one side, and saline was injected on the contralateral side. Chronic vessel narrowing was evaluated with the use of 29 rats, which were randomized into one of three groups for intraperitoneal injections: (1) anti-ICAM-1 MAb (2 mg/kg per dose, n = 10), (2) isotype-matched MAb (2 mg/kg per dose, n = 9), or (3) saline (n = 10), given at 3 hours and 3, 6, and 9 days after blood exposure. These rats were killed 12 days after blood exposure, and femoral artery lumen cross-sectional areas were determined by computerized image analysis. Saturation of ICAM-1 binding sites with this dosing schedule was evaluated by fluorescence-activated cell sorter (FACS) analysis of splenocytes. Immunohistochemical studies with objective cell counts were performed to evaluate macrophage/granulocyte infiltration at 24 hours in 7 rats, comparing anti-ICAM-1 MAb treatment (n = 4) with isotype-matched control MAb (n = 3).

RESULTS

Animals treated with anti-ICAM-1 MAb showed a significant inhibition of arterial narrowing at 12 days (P = .0081), with lumen patency of 96.5 +/- 5.3% (mean +/- SEM), compared with 77.3 +/- 5.6% for isotype-matched MAb and 72.2 +/- 5.3% for saline-treated controls. FACS analysis of splenocytes from animals treated with anti-ICAM-1 MAb confirmed saturation of ICAM-1 binding sites. Vessels treated with anti-ICAM-1 MAb showed a significant decrease in inflammatory cell infiltrates, with objective macrophage/granulocyte counts of 31.3 +/- 26.6 (mean +/- SEM) per high-powered field, compared with 171.4 +/- 30.7 for isotype-matched control MAb (P = .0027).

CONCLUSIONS

Anti-ICAM-1 MAb administered systemically starting 3 hours after blood exposure results in significant inhibition of chronic vasospasm in the rat femoral artery model and is correlated with a reduction in the number of infiltrating macrophages and granulocytes in the periadventitial region of blood-exposed arteries. We conclude that inflammatory changes associated with ICAM-1-mediated macrophage and granulocyte migration play an important role in the development of posthemorrhagic chronic vasospasm in this model.

Protein kinase C has two different major roles in lattice compaction enhanced by cerebrospinal fluid from patients with subarachnoid hemorrhage

BACKGROUND AND PURPOSE

Compaction of extracellular matrix (ECM) lattices by cultured fibroblasts was accelerated by cerebrospinal fluid (CSF) from patients with subarachnoid hemorrhage (SAH). The rate of acceleration was significantly related to the clinical grade of vasospasm. However, the mechanism remains unclear. Evidence exists for an important role in cerebral vasospasm for protein kinase C (PKC). The purpose of this study was to help clarify whether PKC has a role in contraction of the ECM.

METHODS

We studied the effects of a myristoylated PKC peptide inhibitor (Myr-Arg-Phe-Ala-Arg-Lys-Gly-Ala-Leu-Arg-Gln-Lys-Asn-Val) (PKC peptide inhibitor), (5-isoquinolinesulfonyl)-homopiperazine (HA-1077) (inhibitor of protein kinase A, myosin light-chain kinase, and protein kinase G), 7-deacetyl-6-(N-ace-tylglycyl)-forskolin (forskolin) (adenyl cyclase activator), and diacylglycerol-lactone (DAG-lactone) (PKC activator) on fibroblast-populated collagen lattice compaction with or without CSF from SAH patients. Four sets of fibroblasts were used: three explanted from skin and one from cerebral artery.

RESULTS

Moderate and high concentrations of PKC peptide inhibitor inhibited lattice compaction with or without acceleration by CSF. Low concentration of PKC peptide inhibitor enhanced acceleration by CSF but had no effects without CSF. HA-1077 could not inhibit lattice compaction. Forskolin inhibited compaction. DAG-lactone accelerated compaction in early phases.

CONCLUSIONS

In the mechanism of acceleration of contraction of ECM under the influence of CSF, PKC seems to have two different roles. Protein kinase A and myosin light-chain kinase apparently play more minor roles than PKC in the mechanism, but no evidence was found of a role for protein kinase G activation in matrix compaction.

Papaverine-sensitive vasospasm and arterial contractility and compliance after subarachnoid hemorrhage in dogs

This study examined the relationship between papaverine-sensitive and -insensitive components of vasospasm, arterial contractility and compliance, and time after subarachnoid hemorrhage (SAH) in dogs. Eighteen dogs underwent angiography and then two intracisternal injections of blood. Angiography was repeated 4 (n = 5), 7 (n = 4), 10 (n = 4), or 14 (n = 5) days later. Papaverine, 100 to 200 mg, was infused into the basilar artery, and angiography was repeated. Four additional dogs had cerebral angiography only and served as controls. The basilar arteries were removed and studied pharmacologically. Significant vasospasm of the basilar artery was observed each time after SAH. Papaverine significantly reversed vasospasm at 4 and 7 days (88 +/- 6% and 63 +/- 11% of vasospasm reversed; analysis of variance, P < 0.05). The papaverine-insensitive component of vasospasm increased significantly with increasing time after SAH and with increasing severity of vasospasm. Arterial contractility and compliance decreased significantly with increasing time after SAH and were significantly related to the degree of papaverine-insensitive vasospasm but not to the severity of vasospasm. In conclusion, the majority of vasospasm early after SAH in dogs was caused by reversible vasoconstriction. The ability of papaverine to reverse vasospasm depended on the time after SAH and on the severity of vasospasm, a finding that may be important to the use of papaverine in humans. The pathological and biochemical basis for the association between papaverine-insensitive vasospasm and reduced arterial wall contractility and compliance remains to be determined.