Effect of calcitonin-gene-related peptide on postoperative neurological deficits after subarachnoid haemorrhage

Myocardial perfusion recovery induced by an α-calcitonin gene-related peptide analogue

BACKGROUND

Endogenous calcitonin gene-related peptide (CGRP) induces cardioprotective effects through coronary vasodilation. However, the systemic administration of CGRP induces peripheral vasodilation and positive chronotropic and inotropic effects. This study aims to examine the net effect on coronary perfusion of the systemically administered α-calcitonin gene-related peptide analogue, SAX, in rats during myocardial infarction.

METHODS

Forty Sprague-Dawley rats underwent myocardial infarction. Following left anterior descending artery occlusion, [99mTc]Tc-sestamibi was administered to determine the myocardial perfusion before treatment. Twenty minutes, 24 and 48 h after [99mTc]Tc-sestamibi injection, the rats were treated with either SAX or placebo. Final infarct size was determined three weeks later by [99mTc]Tc-sestamibi SPECT/CT scan.

RESULTS

Thirty-one rats survived the surgery and 20 completed the follow-up SPECT/CT scan (SAX n = 12; Placebo n = 8). At baseline, there was no difference in size of perfusion defect between the groups (P = .88), but at follow-up the SAX group had improved myocardial recovery compared to the placebo group (P = .04), corresponding to a relative perfusion recovery of 55% in SAX-treated rats.

CONCLUSION

The CGRP analogue, SAX, has a cardioprotective effect in this rat model of myocardial infarction, improving myocardial perfusion recovery after chronic occlusion of the coronary artery.

Drug Safety in Episodic Migraine Management in Adults. Part 2: Preventive Treatments

PURPOSE OF REVIEW

The aim of this review is to aid in decision-making when choosing safe and effective options for preventive migraine medications.

RECENT FINDINGS

In Part 2, we have compiled clinically relevant safety considerations for commonly used migraine prophylactic treatments. Preventive treatment of episodic migraine includes nonspecific and migraine-specific drugs. While medications from several pharmacological classes-such as anticonvulsants, beta-blockers, and antidepressants-have an established efficacy in migraine prevention, they are associated with a number of side effects. The safety of migraine-specific treatments such as anti-CGRP monoclonal antibodies and gepants are also discussed. This review highlights safety concerns of commonly used migraine prophylactic agents and offers suggestions on how to mitigate those risks.

Trigeminal Nerve Stimulation Improves Cerebral Macrocirculation and Microcirculation After Subarachnoid Hemorrhage: An Exploratory Study

BACKGROUND

Delayed cerebral ischemia (DCI) is the most consequential secondary insult after aneurysmal subarachnoid hemorrhage (SAH). It is a multifactorial process caused by a combination of large artery vasospasm and microcirculatory dysregulation. Despite numerous efforts, no effective therapeutic strategies are available to prevent DCI. The trigeminal nerve richly innervates cerebral blood vessels and releases a host of vasoactive agents upon stimulation. As such, electrical trigeminal nerve stimulation (TNS) has the capability of enhancing cerebral circulation.

OBJECTIVE

To determine whether TNS can restore impaired cerebral macrocirculation and microcirculation in an experimental rat model of SAH.

METHODS

The animals were randomly assigned to sham-operated, SAH-control, and SAH-TNS groups. SAH was induced by endovascular perforation on Day 0, followed by KCl-induced cortical spreading depolarization on day 1, and sample collection on day 2. TNS was delivered on day 1. Multiple end points were assessed including cerebral vasospasm, microvascular spasm, microthrombosis, calcitonin gene-related peptide and intercellular adhesion molecule-1 concentrations, degree of cerebral ischemia and apoptosis, and neurobehavioral outcomes.

RESULTS

SAH resulted in significant vasoconstriction in both major cerebral vessels and cortical pial arterioles. Compared with the SAH-control group, TNS increased lumen diameters of the internal carotid artery, middle cerebral artery, and anterior cerebral artery, and decreased pial arteriolar wall thickness. Additionally, TNS increased cerebrospinal fluid calcitonin gene-related peptide levels, and decreased cortical intercellular adhesion molecule-1 expression, parenchymal microthrombi formation, ischemia-induced hypoxic injury, cellular apoptosis, and neurobehavioral deficits.

CONCLUSION

Our results suggest that TNS can enhance cerebral circulation at multiple levels, lessen the impact of cerebral ischemia, and ameliorate the consequences of DCI after SAH.

Endogenous calcitonin gene-related peptide in cerebrospinal fluid and early quality of life and mental health after good-grade spontaneous subarachnoid hemorrhage-a feasibility series

The vasodilatory calcitonin gene-related peptide (CGRP) is excessively released after spontaneous subarachnoid hemorrhage (sSAH) and modulates psycho-behavioral function. In this pilot study, we prospectively analyzed the treatment-specific differences in the secretion of endogenous CGRP into cerebrospinal fluid (CSF) during the acute stage after good-grade sSAH and its impact on self-reported health-related quality of life (hrQoL). Twenty-six consecutive patients (f:m = 13:8; mean age 50.6 years) with good-grade sSAH were enrolled (drop out 19% (n = 5)): 35% (n = 9) underwent endovascular aneurysm occlusion, 23% (n = 6) microsurgery, and 23% (n = 6) of the patients with perimesencephalic SAH received standardized intensive medical care. An external ventricular drain was inserted within 72 h after the onset of bleeding. CSF was drawn daily from day 1–10. CGRP levels were determined via competitive enzyme immunoassay and calculated as “area under the curve” (AUC). All patients underwent a hrQoL self-report assessment (36-Item Short Form Health Survey (SF-36), ICD-10-Symptom-Rating questionnaire (ISR)) after the onset of sSAH (t₁: day 11–35) and at the 6-month follow-up (t₂). AUC CGRP (total mean ± SD, 5.7 ± 1.8 ng/ml/24 h) was excessively released into CSF after sSAH. AUC CGRP levels did not differ significantly when dichotomizing the aSAH (5.63 ± 1.77) and pSAH group (5.68 ± 2.08). aSAH patients revealed a higher symptom burden in the ISR supplementary item score (p = 0.021). Multiple logistic regression analyses corroborated increased mean levels of AUC CGRP in CSF at t₁ as an independent prognostic factor for a significantly higher symptom burden in most ISR scores (compulsive-obsessive syndrome (OR 5.741, p = 0.018), anxiety (OR 7.748, p = 0.021), depression (OR 2.740, p = 0.005), the supplementary items (OR 2.392, p = 0.004)) and for a poorer performance in the SF-36 physical component summary score (OR 0.177, p = 0.001). In contrast, at t₂, CSF AUC CGRP concentrations no longer correlated with hrQoL. To the best of our knowledge, this study is the first to correlate the levels of endogenous CSF CGRP with hrQoL outcome in good-grade sSAH patients. Excessive CGRP release into CSF may have a negative short-term impact on hrQoL and emotional health like anxiety and depression. While subacutely after sSAH, higher CSF levels of the vasodilator CGRP are supposed to be protective against vasospasm-associated cerebral ischemia, from a psychopathological point of view, our results suggest an involvement of CSF CGRP in the dysregulation of higher integrated behavior.

Vascular pathology of large cerebral arteries in experimental subarachnoid hemorrhage: Vasoconstriction, functional CGRP depletion and maintained CGRP sensitivity

Subarachnoid hemorrhage (SAH) is associated with increased cerebral artery sensitivity to vasoconstrictors and release of the perivascular sensory vasodilator CGRP. In the current study the constrictive phenotype and the vasodilatory effects of exogenous and endogenous perivascular CGRP were characterized in detail applying myograph technology to cerebral artery segments isolated from experimental SAH and sham-operated rats. Following experimental SAH, cerebral arteries exhibited increased vasoconstriction to endothelin-1, 5-hydroxytryptamine and U46419. In addition, depolarization-induced vasoconstriction (60 mM potassium) was significantly increased, supporting a general SAH-associated vasoconstrictive phenotype. Using exogenous CGRP, we demonstrated that sensitivity of the arteries to CGRP-induced vasodilation was unchanged after SAH. However, vasodilation in response to capsaicin (100 nM), a sensory nerve activator used to release perivascular CGRP, was significantly reduced by SAH (P = 0.0079). Because CGRP-mediated dilation is an important counterbalance to increased arterial contractility, a reduction in CGRP release after SAH would exacerbate the vasospasms that occur after SAH. A similar finding was obtained with artery culture (24 h), an in vitro model of SAH-induced vascular dysfunction. The arterial segments maintained sensitivity to exogenous CGRP but showed reduced capsaicin-induced vasodilation. To test whether a metabolically stable CGRP analogue could be used to supplement the loss of perivascular CGRP release in SAH, SAX was systemically administered in our in vivo SAH model. SAX treatment, however, induced CGRP-desensitization and did not prevent the development of vasoconstriction in cerebral arteries after SAH.

Cerebral artery myogenic reactivity: The next frontier in developing effective interventions for subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is a devastating cerebral event that kills or debilitates the majority of those afflicted. The blood that spills into the subarachnoid space stimulates profound cerebral artery vasoconstriction and consequently, cerebral ischemia. Thus, once the initial bleeding in SAH is appropriately managed, the clinical focus shifts to maintaining/improving cerebral perfusion. However, current therapeutic interventions largely fail to improve clinical outcome, because they do not effectively restore normal cerebral artery function. This review discusses emerging evidence that perturbed cerebrovascular "myogenic reactivity," a crucial microvascular process that potently dictates cerebral perfusion, is the critical element underlying cerebral ischemia in SAH. In fact, the myogenic mechanism could be the reason why many therapeutic interventions, including "Triple H" therapy, fail to deliver benefit to patients. Understanding the molecular basis for myogenic reactivity changes in SAH holds the key to develop more effective therapeutic interventions; indeed, promising recent advancements fuel optimism that vascular dysfunction in SAH can be corrected to improve outcome.

Alpha Calcitonin Gene-Related Peptide Increases Cerebral Vessel Diameter in Animal Models of Subarachnoid Hemorrhage: A Systematic Review and Meta-analysis

Delayed cerebral ischemia (DCI) is a life-threatening complication after subarachnoid hemorrhage. There is a strong association between cerebral vessel narrowing and DCI. Alpha calcitonin gene-related peptide (αCGRP) is a potent vasodilator, which may be effective at reducing cerebral vessel narrowing after subarachnoid hemorrhage (SAH). Here, we report a meta-analysis of data from nine in vivo animal studies identified in a systematic review in which αCGRP was administered in SAH models. Our primary outcome was change in cerebral vessel diameter and the secondary outcome was change in neurobehavioral scores. There was a 40.8 ± 8.2% increase in cerebral vessel diameter in those animals treated with αCGRP compared with controls (p < 0.0005, 95% CI 23.7–57.9). Neurobehavioral scores were reported in four publications and showed a standardized mean difference of 1.31 in favor of αCGRP (CI −0.49 to 3.12). We conclude that αCGRP reduces cerebral vessel narrowing seen after SAH in animal studies but note that there is insufficient evidence to determine its effect on functional outcomes.

Role of calcitonin gene-related peptide in cerebral vasospasm, and as a therapeutic approach to subarachnoid hemorrhage

Calcitonin gene-related peptide (CGRP) is one of the most potent microvascular vasodilators identified to date. Vascular relaxation and vasodilation is mediated via activation of the CGRP receptor. This atypical receptor is made up of a G protein-coupled receptor called calcitonin receptor-like receptor (CLR), a single transmembrane protein called receptor activity-modifying protein (RAMP), and an additional protein that is required for Ga(s) coupling, known as receptor component protein (RCP). Several mechanisms involved in CGRP-mediated relaxation have been identified. These include nitric oxide (NO)-dependent endothelium-dependent mechanisms or cAMP-mediated endothelium-independent pathways; the latter being more common. Subarachnoid hemorrhage (SAH) is associated with cerebral vasoconstriction that occurs several days after the hemorrhage and is often fatal. The vasospasm occurs in 30-40% of patients and is the major cause of death from this condition. The vasoconstriction is associated with a decrease in CGRP levels in nerves and an increase in CGRP levels in draining blood, suggesting that CGRP is released from nerves to oppose the vasoconstriction. This evidence has led to the concept that exogenous CGRP may be beneficial in a condition that has proven hard to treat. The present article reviews: (a) the pathophysiology of delayed ischemic neurologic deficit after SAH (b) the basics of the CGRP receptor structure, signal transduction, and vasodilatation mechanisms and (c) the studies that have been conducted so far using CGRP in both animals and humans with SAH.

Pathophysiology and therapeutic possibilities of calcitonin gene-related peptide in hypertension

Calcitonin gene related peptide (CGRP), a 37 amino acid neuropeptide, is the most potent vasodilator known. Participation of CGRP in hypertension and related diseases, such as preeclampsia or vasospasm after subarachnoid haemorrage, is one of the most studied topics. In this review we summarize the published roles of CGRP in pathophysiology of hypertension in humans and in experimental models. We also discuss the effects of direct administration of CGRP in the treatment of hypertension and of anti-hypertensive drugs that enhance the release or response of endogenous calcitonin gene-related peptide: angiotensin converting enzyme inhibitors, selective antagonists for the angiotensin II receptor, beta-blockers, magnesium sulphate for preeclampsia and rutaecarpine, as well as the possibilities using CGRP in gene therapy for prevention of vasospasm after subarachnoid haemorrage.

BIBN4096BS Antagonizes Human α-calcitonin Gene Related Peptide–induced Headache and Extracerebral Artery Dilatation*

BACKGROUND AND OBJECTIVE

Calcitonin gene-related peptide (CGRP) plays a pivotal role in migraine pathogenesis. BIBN4096BS is the first CGRP receptor antagonist available for human studies, and its efficacy in the acute treatment of migraine has been demonstrated. We investigated the ability of BIBN4096BS to inhibit human alphaCGRP (h-alphaCGRP)-induced headache and cerebral hemodynamic changes in healthy volunteers.

METHODS

Ten healthy volunteers completed this double-blind, placebo-controlled crossover study with 2.5 mg BIBN4096BS and placebo as pretreatments before a 20-minute intravenous infusion of h-alphaCGRP (1.5 microg/min). Transcranial Doppler ultrasonography was used to measure blood flow velocity in the middle cerebral artery (MCA); regional and global cerebral blood flow (CBF) was measured by xenon 133 inhalation single-photon emission computed tomography. The temporal and radial artery diameter was measured by high-frequency ultrasound. Systemic hemodynamics, end-tidal partial pressure of carbon dioxide (PETCO(2)), and headache were monitored.

RESULTS

Of the 10 volunteers, 6 had a CGRP-induced headache during the in-hospital phase after placebo pretreatment but none after BIBN4096BS (P = .031). BIBN4096BS did not affect changes in the diameter of the MCA or changes in CBF induced by h-alphaCGRP. Vasodilatation of the extracranial arteries was, however, significantly inhibited (P < .001 for temporal artery and P = .001 for radial artery).

CONCLUSIONS

These results show that BIBN4096BS effectively prevents CGRP-induced headache and extracerebral vasodilatation but does not significantly affect the induced cerebral hemodynamic changes.

Gene therapy for cerebral vascular disease: update 2003

Gene therapy is a promising strategy for cerebrovascular diseases. Several genes that encode vasoactive products have been transferred via cerebrospinal fluid for the prevention of vasospasm after subarachnoid hemorrhage. Transfer of neuroprotective genes, including targeting of proinflammatory mediators, is a current strategy of gene therapy for ischemic stroke. Stimulation of growth of collateral vessels, stabilization of atherosclerotic plaques, inhibition of thrombosis, and prevention of restenosis are important objectives of gene therapy for coronary and limb arteries, but application of these approaches to carotid and intracranial arteries has received little attention. Several fundamental advances, including development of safer vectors, are needed before gene therapy achieves an important role in the treatment of cerebrovascular disease and stroke.

Gene transfer of calcitonin gene-related peptide prevents vasoconstriction after subarachnoid hemorrhage

We sought to determine whether adenovirus-mediated gene transfer in vivo of calcitonin gene-related peptide (CGRP), a potent vasodilator, ameliorates cerebral vasoconstriction after experimental subarachnoid hemorrhage (SAH). Arterial blood was injected into the cisterna magna of rabbits to mimic SAH 5 days after injection of AdRSVCGRP (8x10(8) pfu), AdRSVbetagal (control virus), or vehicle. After injection of AdRSVCGRP, there was a 400-fold increase in CGRP in cerebrospinal fluid. Contraction of the basilar artery to serotonin in vitro was greater in rabbits after SAH than after injection of artificial cerebrospinal fluid (P<0.001). Contraction to serotonin was less in rabbits with SAH after AdRSVCGRP than after AdRSVbetagal or vehicle (P:<0.02). Basal diameter of the basilar artery before SAH (measured with digital subtraction angiogram) was 13% greater in rabbits treated with AdRSVCGRP than in rabbits treated with vehicle or AdRSVbetagal (P:<0.005). In rabbits treated with vehicle or AdRSVbetagal, arterial diameter after SAH was 25+/-3% smaller than before SAH (P<0.0005). In rabbits treated with AdRSVCGRP, arterial diameter was similar before and after SAH and was reduced by 19+/-3% (P<0.01) after intracisternal injection of CGRP-(8-37) (0.5 nmol/kg), a CGRP(1) receptor antagonist. To determine whether gene transfer of CGRP after SAH may prevent cerebral vasoconstriction, we constructed a virus with a cytomegalovirus (CMV) promoter, which results in rapid expression of the transgene product. Treatment of rabbits with AdCMVCGRP after experimental SAH prevented constriction of the basilar artery 2 days after SAH. Thus, gene transfer of CGRP prevents cerebral vasoconstriction in vivo after experimental SAH.

Neuropeptides in drug research

Neuropeptides have been a subject of considerable interest in the pharmaceutical industry over the last 20 years or more. Many drug discovery teams have contributed to our understanding of neuropeptide biology but no significant drugs that act selectively upon neuropeptide receptors have yet emerged from the clinic. There are, however, a plethora of clinically useful drugs that act at other classes of neurotransmitter and neuromodulator receptors, many of them discovered over the last 20 years. Nevertheless, we think that the future for the discovery of novel drugs acting at neuropeptide receptors looks bright for two reasons: (1) there has been a substantial increase in our understanding of the function of neuropeptides; and (2) high-throughput screening (HTS) against neuropeptide receptors has now begun to yield many interesting drug-like molecules, rather than peptides, that have the potential to become clinically useful drugs. The objective of this review is to summarise our current understanding of specific areas of neuropeptide biology and pharmacology in the CNS as well as the PNS. We will also speculate on where we think the new generation of neuropeptide agonists and antagonists could emerge from the clinic.

Gene transfer of calcitonin gene-related peptide to cerebral arteries

Overexpression of calcitonin gene-related peptide (CGRP), an extremely potent vasodilator, to blood vessels is a possible strategy for prevention of vasospasm. We constructed an adenoviral vector that encodes prepro-CGRP (Adprepro-CGRP) and examined the effects of gene transfer on cultured cells and cerebral arteries. Transfection of Adprepro-CGRP to Cos-7 and NIH-3T3 cells increased CGRP-like immunoreactivity in media and produced an increase in cAMP in recipient cells. Five days after injection of Adprepro-CGRP into the cisterna magna of rabbits, the concentration of CGRP-like immunoreactivity increased by 93-fold in cerebrospinal fluid. In basilar artery, cAMP increased by 2.3-fold after Adprepro-CGRP compared with a control adenovirus. After transfection of Adprepro-CGRP, contraction of basilar artery in vitro to histamine and serotonin was attenuated, and relaxation to an inhibitor of cyclic nucleotide phosphodiesterase 3-isobutyl-1-methylxanthine was augmented compared with nontransduced arteries or arteries transfected with a control gene. Altered vascular responses were restored to normal by pretreatment with a CGRP(1) receptor antagonist CGRP-(8-37). Thus gene transfer of prepro-CGRP in vivo overexpresses CGRP in cerebrospinal fluid and perivascular tissues and modulates vascular tone. We speculate that this approach may be useful in prevention of vasospasm after subarachnoid hemorrhage.

Neuroanatomical localization, pharmacological characterization and functions of CGRP, related peptides and their receptors

Calcitonin generelated peptide (CGRP) is a neuropeptide discovered by a molecular approach over 10 years ago. More recently, islet amyloid polypeptide or amylin, and adrenomedullin were isolated from human insulinoma and pheochromocytoma respectively, and revealed between 25 and 50% sequence homology with CGRP. This review discusses findings on the anatomical distributions of CGRP mRNA, CGRP-like immunoreactivity and receptors in the central nervous system, as well as the potential physiological roles for CGRP. The anatomical distribution and biological activities of amylin and adrenomedullin are also presented. Based upon the differential biological activity of various CGRP analogs, the CGRP receptors have been classified in two major classes, namely the CGRP1 and CGRP2 subtypes. A third subtype has also been proposed (e.g. in the nucleus accumbens) as it does not share the pharmacological properties of the other two classes. The anatomical distribution and the pharmacological characteristics of amylin binding sites in the rat brain are different from those reported for CGRP but share several similarities with the salmon calcitonin receptors. The receptors identified thus far for CGRP and related peptides belong to the G protein-coupled receptor superfamily. Indeed, modulation of adenylate cyclase activity following receptor activation has been reported for CGRP, amylin and adrenomedullin. Furthermore, the binding affinity of CGRP and related peptides is modulated by nucleotides such as GTP. The cloning of various calcitonin and most recently of CGRP1 and adrenomedullin receptors was reported and revealed structural similarities but also significant differences to other members of the G protein-coupled receptors. They may thus form a new subfamily. The cloning of the amylin receptor(s) as well as of the other putative CGRP receptor subtype(s) are still awaited. Finally, a broad variety of biological activities has been described for CGRP-like peptides. These include vasodilation, nociception, glucose uptake and the stimulation of glycolysis in skeletal muscles. These effects may thus suggest their potential role and therapeutic applications in migraine, subarachnoid haemorrhage, diabetes and pain-related mechanisms, among other disorders.

Prevention of cerebral vasospasm by calcitonin gene-related peptide slow-release tablet after subarachnoid hemorrhage in monkeys

OBJECTIVE

The goal of this work was to investigate the efficacy of a calcitonin gene-related peptide (CGRP) slow-release tablet (CGRP tablet) for the prevention of cerebral vasospasm after subarachnoid hemorrhage (SAH).

METHODS

Experimental SAH was produced in 10 cynomolgus monkeys by placing a clot around the internal carotid artery bifurcation (Day 0). In five animals, CGRP tablets (1200 micrograms of CGRP) were then placed in the cerebrospinal fluid space (CGRP group). In two animals, placebo tablets were similarly placed (placebo group). The remaining three animals were treated with no tablets after SAH (SAH group). A series of angiographic analyses were performed, before SAH and on Days 7 and 14, to examine changes in the diameters of the ipsilateral internal carotid artery, middle cerebral artery, and anterior cerebral artery. The CGRP concentration in the cerebrospinal fluid taken before each angiogram was also determined.

RESULTS

In the SAH and placebo groups, cerebral vasospasm developed on Day 7 (54.8% of the pre-SAH value at the internal carotid artery, 62.3% at the middle cerebral artery, 51.3% at the anterior cerebral artery, and 56.1% as an average of the three arteries). In the CGRP group, vasospasm was significantly ameliorated at the middle cerebral artery, at the anterior cerebral artery, and on average (81.7, 81.1, and 75.7%, P < 0.05, 0.03, and 0.02, respectively). The CGRP concentration was positive only on Day 7 for the CGRP group (6.5 nmol/L).

CONCLUSION

The CGRP tablet prevented cerebral vasospasm after SAH and may have significant potential for the treatment of patients with SAH.

Development of calcitonin gene-related peptide slow-release tablet implanted in CSF space for prevention of cerebral vasospasm after experimental subarachnoid haemorrhage

The calcitonin gene-related peptide (CGRP), a known potent intrinsic cerebral vasodilator, is contained in the sensory nerves from trigeminal ganglia that inervate the cerebral arteries. We previously reported that human alpha CGRP (hCGRP) dilates spastic cerebral arteries after experimental subarachnoid haemorrhage (SAH) in rabbits. In the present study, we investigated the prophylactic potential of a sustained higher cerebrospinal fluid level of hCGRP against experimental cerebral vasospasm. An hCGRP slow-release tablet (hCGRP s-r tablet) was developed for cisternal implantation. Experimental SAH was induced by percutaneous cisternal injection of autologous arterial blood. Angiography was initiated on day 1 (before SAH) and performed everyday. The hCGRP s-r tablet was implanted into the cisterna magna on day 2 in the treated groups. The spastic response of the basilar artery was maximized on day 4 in the non-treated (80.7% of day 1) and the placebo-treated (79.3%) groups. In contrast, the arterial diameters on day 4 were 96.1% and 90.5% of day 1 in the groups implanted with hCGRP 24 micrograms and 153 micrograms s-r tablets, respectively. We also measured the concentration of hCGRP in the cerebrospinal fluid (CSF) following implantation of the hCGRP 24 micrograms s-r tablet in the cisterna magna. The hCGRP concentration before implantation was below the dectable level. Following implantation, the hCGRP level in the CSF was 23.12 nmol/L on the second day and remained at elevated levels until the fifth day. These experiments suggest that the intrathecal single implantation of the hCGRP s-r tablet could produce an elevated concentration of hCGRP in the CSF over five days and have prevented the cerebral vasospasm after SAH in the rabbit. The hCGRP s-r tablet may be clinically applicable in the treatment of patients with SAH against cerebral vasospasm.

Calcitonin gene-related peptide inhibits human platelet aggregation

Calcitonin gene-related peptide (CGRP) is a potent vasodilator in humans. CGRP receptors have also been found in various tissues other than blood vessels, such as the central nervous system, kidney, and heart. However, little is known about the effects of CGRP on human platelets. We investigated the effect of CGRP (human alpha type) on platelet aggregation in 21 healthy subjects (9 men and 12 women, mean age 54.6 years). CGRP inhibited platelet aggregation in vitro in 19 of the subjects (90.5%) in a dose-dependent manner with 50% inhibitory doses of 1.6 mumol/L and 1.1 mumol/L for aggregation induced by epinephrine and collagen, respectively. 125I-labeled CGRP bound specifically to intact platelets. The dissociation constant (Kd) was 61.9 +/- 17.7 pmol and the maximum number of binding sites (Bmax) was 5.4 +/- 3.9 pmol/10(9) platelets. The CGRP analogue (8-37)CGRP, but not calcitonin, inhibited the binding of 125I-CGRP to platelets. CGRP (5 mumol/L), but not (8-37)CGRP or calcitonin, increased the platelet cyclic AMP (cAMP) concentration by 31.7 +/- 3.6%. Thus, CGRP inhibits platelet aggregation via a specific receptor and by increasing the platelet cAMP concentration. CGRP may play a role in the modulation of platelet function in humans.

Effect of calcitonin gene-related peptide on delayed cerebral vasospasm after experimental subarachnoid hemorrhage in rabbits

BACKGROUND

Calcitonin gene-related peptide (CGRP) is an intrinsic vasodilatory substance contained in perivascular nerve fibers of intracranial arteries. It is suggested that CGRP plays a role in cerebral vasospasm after subarachnoid hemorrhage (SAH).

METHOD

An experimental SAH was produced by intracisternal injection of arterial blood in rabbits. The animals were treated with intrathecal administration of CGRP solution 3 days after SAH. The degree of vasospasm and the effect of CGRP were evaluated angiographically by measuring the basilar artery diameter.

RESULTS

The basilar artery constricted to 73.0% of the pre-SAH values 3 days after SAH. Fifteen minutes after injection of 10(-10) mol/kg CGRP, the basilar artery dilated to 117.1% (n = 8), which was significantly larger than 67.1% in the vehicle group (n = 8) (p < 0.01). The significant vasodilatory effect of CGRP, compared with the vehicle group, lasted for 6 hours.

CONCLUSIONS

Intrathecal administration of CGRP has therapeutic potential for treating cerebral vasospasm.

Calcitonin gene-related peptide (human alpha-CGRP) counteracts vasoconstriction in human subarachnoid haemorrhage

Calcitonin gene-related peptide (CGRP) is a neuropeptide co-stored with tachykinins (substance P, neurokinin A) in cerebrovascular sensory fibers in the trigeminal ganglion. Preceding studies on subarachnoid hemorrhage (SAH) revealed that an enhanced release of CGRP resulted in the selective loss of perivascular CGRP. Therefore, the present study was designed to evaluate the effects of intravenous administration of human alpha-CGRP on cerebral vasoconstriction in the postoperative course after SAH in 5 patients (8 infusions). Cerebral vasoconstriction was evaluated with transcranial Doppler sonography. The increase in the relationship between middle cerebral artery (MCA) velocity and internal carotid artery (ICA) velocity (the hemodynamic index) was used as an indicator of vasoconstriction and compared to the contralateral side. A significant reduction was found in the hemodynamic index during the CGRP infusion (4.3 +/- 0.5, P < 0.05) as to compared to before infusion (6.2 +/- 0.5). There was no measurable change in the hemodynamic index on the contralateral side. No significant change was observed in pulsatility index, blood pressure or consciousness during the peptide infusion. A significant increase in heart rate was observed during the infusion as compared to before and after infusion (90 +/- 4 vs. 76 +/- 5). Cardiac ultrasound data indicated a mean cardiac output increase of 1.9 liter/min, and a mean decrease in total peripheral resistance of 538 dynes s/cm5. The results obtained show that infusion of human alpha-CGRP may induce normalisation of cerebrovascular tone in SAH.

Calcitonin gene-related peptide in treatment of severe peripheral vascular insufficiency in Raynaud's phenomenon

Calcitonin gene-related peptide (CGRP) is a potent vasodilator that may be involved in the regulation of the peripheral circulation and in its response to cold. There is evidence that CGRP in digital cutaneous perivascular nerves is deficient in Raynaud's phenomenon. Our pilot study of intravenous CGRP suggested that this substance is beneficial in patients with Raynaud's phenomenon; here we have extended our studies. Ten patients with severe Raynaud's phenomenon secondary to connective tissue disease were randomly assigned to groups receiving intravenous CGRP (0.6 micrograms/min for 3 h per day on 5 days) or saline. Hand and digital blood flow and skin temperature were measured by thermocouple and laser doppler flowmetry. Blood flow was significantly (p < 0.05) increased by CGRP in both hands (median blood flow after infusion as percentage of baseline reading 179 [range 100-355]%) and fingers (149 [100-161]%); saline had no effect (hands 102 [84-123]%, fingers 96 [81-113]%). Hand temperature was increased more by CGRP than by saline (2.8 [1.5-4.0] vs 1.0 [-1.0 to 2.5] degrees C, p < 0.05). Digital temperature increased after CGRP but the difference between the treatment groups in temperature rise was not significant, perhaps because saline caused increases in some patients. All ulcers healed in four of five CGRP-treated patients but in no saline-treated patients. Thus intravenous CGRP effectively dilates the compromised digital cutaneous vasculature in severe Raynaud's phenomenon.

Vigabatrin

OBJECTIVE

To introduce the reader to the use of a new agent, vigabatrin, in the treatment of refractory complex partial seizures. Clinical trials and pharmacokinetic data are reviewed, as well as neuropathology, adverse effects, drug interactions, and dosage guidelines.

DATA SOURCES

A MEDLINE search through March 1992 was used to identify pertinent English-language literature, including clinical trials, reviews, abstracts, and conference proceedings. Indexing terms included vigabatrin and anticonvulsants.

STUDY SELECTIONS

All clinical trials (total of 21) were reviewed, as were all pharmacokinetic studies (total of 8). Selected studies highlighting chemistry, pharmacology, neuropathology, and adverse effects were also reviewed.

DATA EXTRACTION

Performed subjectively by the author. Trials were assessed by design, sample size, types of seizures of the subjects, and clinical response.

DATA SYNTHESIS

Vigabatrin represents the first of a new class of antiepileptic drugs (AEDs)--the gamma-aminobutyric acid transaminase (GABA-T) inhibitors. Vigabatrin works by selective, irreversible inhibition of GABA-T, thus preventing the breakdown of GABA. It has been shown to produce dose-dependent increases in cerebrospinal fluid GABA concentrations, and decreases in GABA-T activity. Vigabatrin may also cause a decrease in excitation-related amino acids. It is well absorbed, is not protein bound, and is eliminated by glomerular filtration. However, even with a short half-life (5-7 h), vigabatrin may be given once or twice daily because of its mechanism of action. Few drug interactions have been reported with this agent, although decreases in phenytoin concentration may reach clinical significance. Concern over neuropathologic findings (microvacuolization of white matter) in animals caused trials of vigabatrin to be halted in 1983, but trials have now resumed as there is no evidence of toxicity in humans. Clinical efficacy of vigabatrin has been evaluated in controlled trials and appears to be most effective in complex partial seizures, producing a 50 percent or greater reduction in seizure frequency in approximately 50 percent of the adult patients studied. Efficacy in children with partial seizures also appears promising, and one uncontrolled study suggests that further study of vigabatrin in infantile spasms may be warranted.

CONCLUSIONS

Vigabatrin appears to be effective in treating refractory complex partial seizures in adults and refractory partial seizures in children. Its relatively benign adverse-effect profile and few known drug interactions may given this agent an advantage over existing anticonvulsants. However, definitive conclusions about the role of vigabatrin in epilepsy treatment should await the completion of ongoing Phase II and Phase III trials.

Cerebrovascular changes following administration of gammaglobulins against substance P or calcitonin gene related peptide in monkey with subarachnoid haemorrhage

Cerebrovascular changes after intrathecal (ith) administration of gammaglobulins against substance P (SP) or calcitonin gene-related peptide (CGRP) were investigated before and following a simulated subarachnoid haemorrhage (SAH) in the squirrel monkey. The SAH was produced by injection of homologous blood into the interpeduncular fossa and the cisterna magna. The gammaglobulins were given both prior to the blood injections and daily in 5 days post-SAH. The effect of the gammaglobulins was examined by angiography pre-SAH and at 10 min and at 6 days post-SAH, i.e. the time points for maximal acute and late spasm in the present model. Cerebral blood flow (CBF) was measured under general anesthesia at day 6 post-SAH with an autoradiographic technique. Five of nine animals treated with CGRP antigammaglobulin died from respiratory failure. Four animals received SP antigammaglobulin and two control animals received normal globulin. SP antigammaglobulin per se had no effect on baseline arterial diameter, while CGRP antigammaglobulin significantly reduced the diameter of the arteries. SP antigammaglobulin prevented the occurrence of acute spasm and significantly reduced the degree of late spasm. Moreover, the reduction in CBF noted in the control SAH animals was significantly reduced. In contrast, CGRP antigammaglobulin treatment had no effect on the degree of spasm and did not cause any change in CBF as compared to controls. The finding that CGRP but not SP antigammaglobulin significantly reduces the arterial diameter in conjunction with our previous demonstration that a post-, but not preganglionic trigeminal lesion reduces the baseline arterial diameter, indicates that CGRP could be the transmitter involved in a peripheral axon reflex. The function of SP might be as a neurotransmitter conveying information to the brainstem. The transmitter role is supported by the effect of SP antigammaglobulin impairing SP containing neurons and, in that way, mimicking a bilateral trigeminal rhizotomy.

Accumulation of calcitonin-gene related peptide-like immunoreactivity after hypoxic-ischaemic brain injury in the infant rat

Unilateral carotid ligation in immature rats, followed by either 15 min (moderate group) or 90 min (severe group) of hypoxia were used to assess the effects of hypoxia-ischaemia (HI) on the accumulation of the neuropeptide calcitonin-gene related peptide (CGRP). Severe, but not moderate, HI produced a massive time-dependent increase in CGRP-like immunoreactivity throughout the damaged regions of the brain (neocortex, caudate-putamen, hippocampus) beginning at 24 h and maximal at 3-5 days after HI. By 11 days after HI levels appeared to have returned to baseline. The increased immunoreactivity was largely localized to presumed axon terminals contacting neurons, blood vessels and non-nerve cells. Scattered neurons in the cingulate cortex, piriform cortex and striatum also showed increased immunoreactivity in their soma. These results raise the possibility that CGRP may be involved in neuronal repair after HI in the infant brain.

Effect of intracisternal and intravenous calcitonin gene-related peptide on experimental cerebral vasospasm in rabbits

We investigated the vasodilatory effect of intracisternal (i.c.) and intravenous (i.v.) administration of calcitonin gene-related peptide (CGRP) on arterial narrowing after experimental subarachnoid hemorrhage (SAH). Forty-one rabbits were divided into five groups: control (normal animals); SAH plus i.c. infusion of vehicle; SAH plus i.c. infusion of CGRP; SAH plus i.v. infusion of vehicle; SAH plus i.v. infusion of CGRP. In all but the control group, either CGRP (100 ng/kg/min) or vehicle solution was infused for two hours immediately prior to sacrifice by perfusion-fixation. A morphometric technique was employed to measure the luminal diameter of rabbit basilar arteries two days after SAH. The diameter of the basilar arteries in either the i.c. or i.v. CGRP groups was significantly greater than that of the respective vehicle group (i.c., p < 0.001; i.v., p < 0.01). Although there was no significant difference in systemic arterial blood pressure after infusion between the i.c. vehicle and i.c. CGRP groups, i.v. CGRP caused significant hypotension. Our results suggest that exogenous CGRP has some therapeutic potential for arterial narrowing after SAH not only by intrathecal application, but also by systemic use.

The role of neuroeffector mechanisms in cerebral hyperperfusion syndromes

Cerebral hyperperfusion, a state in which blood flow exceeds the metabolic needs of brain, may complicate a number of neurological and neurosurgical conditions. It may account for the propensity with which hemorrhage, cerebral edema, or seizures follow embolic stroke, carotid endarterectomy, or the excision of large arteriovenous malformations, and for some of the morbidity that accompanies acute severe head injury, prolonged seizures, and acute severe hypertension. Hyperperfusion syndromes have in common acute increases in blood pressure, vasodilatation, breakdown of the blood-brain barrier, and the development of cerebral edema. These common features suggest the possibility that they share the same pathogenic mechanisms. It was believed until recently that reactive hyperemia was caused primarily by the generation of vasoactive metabolites, which induced vasodilatation through relaxation of vascular smooth muscle. However, the authors have recently established that the release of vasoactive neuropeptides from perivascular sensory nerves via axon reflex-like mechanisms has a significant bearing upon a number of hyperperfusion syndromes. In this article, the authors summarize their data and discuss possible therapeutic implications for blockade of these nerves or their constituent neuropeptides.

Cerebral vasospasm following subarachnoid hemorrhage: effect of calcitonin gene-related peptide on middle cerebral artery velocities using transcranial Doppler sonography

The case of a middle cerebral artery vasospasm following subarachnoid hemorrhage is discussed. The effectiveness of treating the vasospasm with calcitonin gene-related peptide is illustrated.

Regional haemodynamic effects of prolonged infusions of human alpha-calcitonin gene-related peptide in conscious, Long Evans rats

1. Haemodynamic measurements were made in conscious, Long Evans rats chronically instrumented for the assessment of changes in regional blood flows (renal, mesenteric and hindquarters, or internal and common carotid) and systemic arterial blood pressure and heart rate, before, during and after 3 day infusions of vehicle or human alpha-calcitonin gene-related peptide (CGRP) (1.5 or 15 nmol kg-1 h-1). 2. In animals with renal, mesenteric and hindquarters flow probes (n = 8), during the first day of infusion of human alpha-CGRP (1.5 nmol kg-1 h-1) there was sustained tachycardia and hypotension, a sustained reduction in renal flow, a transient reduction in mesenteric flow and a relatively well-maintained increase in hindquarters flow. All these effects were significantly different from the changes seen in vehicle-infused rats (n = 8), but calculation of vascular conductances showed only the late mesenteric vasodilatation and the sustained hindquarters vasodilatation were different from the changes in vehicle-infused rats. However, by the second day of infusion and thereafter cardiovascular variables in the animals receiving vehicle and those receiving human alpha-CGRP were not different. 3. Nine animals instrumented with probes to monitor changes in internal and common carotid haemodynamics initially received human alpha-CGRP infused at a rate of 1.5 nmol kg-1 h-1. Three of these animals still showed some response to the human alpha-CGRP (tachycardia, hypotension, hyperaemic vasodilatation) throughout the second day of infusion and hence were taken through the 3 day infusion protocol. When the infusion was stopped on the fourth day all these animals showed reversal of the effects of human alpha-CGRP. 4. The results indicate substantial inter-individual variation in the haemodynamic effects of prolonged infusions of human alpha-CGRP in conscious, Long Evans rats. However, since increasing the dose of human alpha-CGRP overcame the desensitization, it is feasible that, in the clinical setting, maintained increases in internal carotid blood flow could be achieved by individually-adjusted infusions of human alpha-CGRP.