Dick J. De Wildt

ACE inhibitor-induced angioedema. Incidence, prevention and management.

SummaryAvailable information from 1980 to 1997 on angiotensin converting enzyme (ACE) inhibitor-induced angioedema and its underlying mechanisms are summarised and discussed. The incidence of angioedema is low (0.1 to 0.2%) but can be considered as a potentially life-threatening adverse effect of ACE inhibitor therapy. This adverse effect of ACE inhibitors, irrespective of the chemical structure, can occur early in treatment as well as after prolonged exposure for up to several years. The estimated incidence is quite underestimated. The actual incidence can be far higher because of poorly recognised presentation of angioedema as a consequence of its late onset in combination with usually long term therapy. Also, a spontaneous reporting bias can contribute to an actual higher incidence of this phenomenon. The incidence can be even higher (up to 3-fold) in certain risk groups, for instance Black Americans. Treatment includes immediate withdrawal of the ACE inhibitor and acute symptomatic supportive therapy followed by immediate (and long term) alternative therapy with other classes of drugs to manage hypertension and/or heart failure.Preclinical and clinical studies for the elucidation of the underlying mechanism(s) of ACE inhibitor-associated angioedema have not generated definite conclusions. It is suggested that immunological processes and several mediator systems (bradykinin, histamine, substance P and prostaglandins) are involved in the pathogenesis of angioedema. A great part of all reviewed reports suggest a relationship between ACE inhibitor-induced angioedema and increased levels of (tissue) bradykinin. However, no conclusive evidence of the role of bradykinin in angioedema has been found and an exclusive role of bradykinin seems unlikely. So far, no clear-cut evidence for an immune-mediated pathogenesis has been found. In addition, ACE gene polymorphism and some enzyme deficiencies are proposed to be involved in ACE inhibitor-induced angioedema. Progress in pharmacogenetic and molecular biological research should throw more light on a possible genetic component in the pathogenesis of ACE inhibitor-associated angioedema.

Melanocortins and cardiovascular regulation.

The melanocortins form a family of pro-opiomelanocortin-derived peptides that have the melanocyte-stimulating hormone (MSH) core sequence, His-Phe-Arg-Trp, in common. Melanocortins have been described as having a variety of cardiovascular effects. We review here what is known about the sites and mechanisms of action of the melanocortins with respect to their effects on cardiovascular function, with special attention to the effects of the gamma-melanocyte-stimulating hormones (gamma-MSHs). This is done in the context of present knowledge about agonist selectivity and localisation of the five melanocortin receptor subtypes cloned so far. gamma2-MSH, its des-Gly12 analog (= gamma1-MSH) and Lys-gamma2-MSH are 5-10 times more potent than adrenocorticotropic hormone-(4-10)(ACTH-(4-10)) to induce a pressor and tachycardiac effect following intravenous administration. The Arg-Phe sequence near the C-terminal seems to be important for full in vivo intrinsic activity. Related peptides with a C-terminal extension with (gamma3-MSH) or without the Arg-Phe sequence (alpha-MSH, as well as the potent alpha-MSH analog, [Nle4,D-Phe7]alpha-MSH), are, however, devoid of these effects. In contrast, ACTH-(1-24) has a depressor effect combined with a tachycardiac effect, effects which are not dependent on the presence of the adrenals. Although the melanocortin MC3 receptor is the only melanocortin receptor subtype for which gamma2-MSH is selective, in vivo and in vitro structure-activity data indicate that it is not via this receptor that this peptide and related peptides exert either their pressor and tachycardiac effects or their extra- and intracranial blood flow increasing effect. We review evidence that the pressor and tachycardiac effects of the gamma-MSHs are due to an increase of sympathetic outflow to the vasculature and the heart, secondary to activation of centrally located receptors. These receptors are most likely localised in the anteroventral third ventricle (AV3V) region, a brain region situated outside the blood-brain barrier, and to which circulating peptides have access. These receptors might be melanocortin receptors of a subtype yet to be identified. Alternatively, they might be related to other receptors for which peptides with a C-terminal Arg-Phe sequence have affinity, such as the neuropeptide FF receptor and the recently discovered FMRFamide receptor. Melanocortin MC4 receptors and still unidentified receptors are part of the circuitry in the medulla oblongata which is involved in the depressor and bradycardiac effect of the melanocortins, probably via interference with autonomic outflow. Regarding the effects of the gamma-MSHs on cortical cerebral blood flow, it is not yet clear whether they involve activation of the sympathetic nervous system or activation of melanocortin receptors located on the cerebral vasculature. The depressor effect observed following intravenous administration of ACTH-(1-24) is thought to be due to activation of melanocortin MC2 receptors whose location may be within the peripheral vasculature. Melanocortins have been observed to improve cardiovascular function and survival time in experimental hemorrhagic shock in various species. Though ACTH-(1-24) is the most potent melanocortin in this model, alpha-MSH and [Nle4,D-Phe7]alpha-MSH and ACTH-(4-10) are quite effective as well. As ACTH-(4-10) is a rather weak agonist of all melanocortin receptors, it is difficult to determine via which of the melanocortin receptors the melanocortins bring about this effect. Research into the nature of the receptors involved in the various cardiovascular effects of the melanocortins would greatly benefit from the availability of selective melanocortin receptor antagonists.

Delayed Antibiotic-Induced Lysis of Escherichia coli in vitro is Correlated with Enhancement of LPS Release

A kinetic turbidimetric Limulus amebocyte lysate (LAL) assay was used to study the effects of gentamicin, amoxycillin and ciprofloxacin (16 x MIC) upon release of lipopolysaccharide at different stages of a growing Escherichia coli 055:B5:H culture in vitro. In this model a linear correlation was present between the logarithms of colony counts and free LAL activities. Untreated E. coli grew from log values of 4.9 +/- 0.15 (low inoculum) and 6.8 +/- 0.08 cfu/ml (high inoculum) at t = 0 to 8.9 +/- 0.05 and 9.1 +/- 0.13 cfu/ml at t = 6 h, respectively. The log values of basal free LAL activities at low and high inoculum sizes were 1.9 +/- 0.07 and 3.3 +/- 0.14 endotoxin units/ml, increasing 2100- and 69-fold, respectively during a 6-h growth. Amoxycillin-induced lysis was not significantly associated with an increase in free LAL activity. Efficacy of bacterial killing by gentamicin was high, but free LAL activity increased only 3.2- and 7.7-fold at the low and high inoculum experiments, respectively. Ciprofloxacin induced cell filamentation during the experiments. At low and high inoculum conditions exposure to ciprofloxacin induced a 43- and 68-fold increase in free LAL activities, respectively. Our data indicate that (a) LPS is released as long as E. coli remain structurally intact; (b) LPS release is enhanced when bacterial biomass increases; and (c) are taken as evidence against the concept of lysis-correlated LPS release.

The hemodynamic effects of γ2-melanocyte-stimulating hormone and related melanotropins depend on the arousal potential of the rat

In conscious rats, i.v. administered adrenocorticotropic hormone (ACTH-(4-10)) and gamma 2-melanocyte-stimulating hormone (gamma 2-MSH) induced a dose-dependent increase in blood pressure (BP), heart rate (HR) and pulse pressure (PP). No circadian influence on these effects was observed. The structurally related peptide, alpha-melanocyte-stimulating hormone (alpha-MSH), only caused an increase in HR, which was not dose-dependent, whereas the stable ACTH-(4-9) analog, Org 2766, was without effect on these hemodynamic parameters. In rats under light urethane-induced anesthesia, which is known to maintain reflexes and sufficient sympathetic tone, gamma 2-MSH caused hemodynamic responses similar to those observed in conscious rats. In contrast, gamma 2-MSH had an opposite effect in rats under deep pentobarbital-induced anesthesia: a depressor effect combined with a slight bradycardia. A comparative study with rats of a more arousable Wistar rat substrain (Riv:TOX) and of a less excitable rat substrain (U:WU) showed that the dose-pressor response curves for ACTH-(4-10) and gamma 2-MSH were shifted to the left in the more excitable rats as compared to the in the less excitable rats. We conclude that a restricted amino acid sequence in the N-terminal part of the pro-opiomelanocortin (POMC)-molecule (gamma 2-MSH/ACTH-(4-10)-like) is responsible for the stimulating effects on the cardiovascular system and that those effects are strongly dependent on the state of arousal, i.e. sympathetic tone, of the rat. These stimulatory effects override a depressor phenomenon which can only be detected during central depression.

Cardiovascular effects of γ-MSH/ACTH-like peptides: structure-activity relationship

Intravenous administration of γ2-melanocyte-stimulating hormone (γ2-MSH) to conscious rats causes a dose-dependent increase in blood pressure and heart rate, while the structurally related peptide adrenocorticotropic hormone-(4–10) (ACTH-(4–10)) is 5–10 times less potent in this respect. This prompted us to investigate which amino acid sequence is determinant for the cardiovascular selectivity of peptides of the γ-MSH family. Lys-γ2-MSH, most likely the endogenously occurring γ-MSH analog, was as potent as γ2-MSH in inducing increases in blood pressure and heart rate. Removal of C-terminal amino acids resulted in γ-MSH-fragments which were devoid of cardiovascular activities. Removal of amino acids from the N-terminal side of γ2-MSH resulted in fragments which were less potent, but had an intrinsic activity not different from that of γ-MSH. Surprisingly, γ-MSH-(6–12) was more potent than γ2-MSH. The shortest fragment which displayed pressor and tachycardiac responses was the MSH ‘core’, His-Phe-Arg-Trp (= γ-MSH-(5–8)), which is identical to ACTH-(6–9). This was corroborated by testing fragments of ACTH-(4–10). We conclude that the message essential for cardiovascular effects resides in the γ-MSH-(5–8)/ACTH-(6–9) sequence. Proper C-terminal elongation is required for full expression of cardiovascular activity of γ2-MSH, as the sequence of Asp9-Arg10-Phe11 appears to play an important role in establishing intrinsic activity. The amino acids N-terminal to the MSH ‘core’ sequence appear to be essential for the potency of the peptides.

Middle cerebral artery occlusion in Wistar and Fischer-344 rats : functional and morphological assessment of the model

Cerebral infarction volume after occlusion of a short proximal segment of the middle cerebral artery (MCA) is reported to be different in Wistar compared to Fischer-344 (F344) rats, in both size and variability. Knowledge about the cause of these differences might enable us to explain and perhaps reduce the variation in infarct volume and create a reproducible model of focal cerebral ischemia in the rat. We investigated in Wistar and F344 rats both the effect of occlusion of a long proximal MCA segment on cerebral infarction volume, visualized by magnetic resonance imaging and histology, and the morphology of the major cerebral arteries. Occlusion of a long proximal MCA segment resulted in a striatal and a small cortical infarction in Wistar and a striatal and sizable cortical infarction in F344 rats (as is the case after occlusion of a short proximal MCA segment). In Wistar rats, however, occlusion of a long proximal MCA segment strongly reduced the variability in infarction volume in comparison to occlusion of a small proximal MCA segment. Analysis of the morphology of the major cerebral arteries showed a significantly higher number of proximal side branches of the long proximal MCA segment in Wistar rats than in F344 rats. We conclude that after short-segment proximal MCA occlusion, extreme variability in cerebral infarction volume in Wistar rats compared to F344 rats may be attributable to a significantly greater number of proximal MCA side branches in Wistar rats than F344 rats.

Effect of gamma 2-melanocyte-stimulating hormone on cerebral blood flow in rats.

The effects of the proopiomelanocortin-(POMC)-derived peptide gamma 2-melanocyte-stimulating hormone (gamma 2-MSH) on mean arterial blood pressure (BP: MAP), heart rate (HR), internal and total carotid blood flow (BF) (CFint and CFtot, respectively), and regional cerebrocortical blood flow (CBF) were measured in urethane-anesthetized rats after intravenous (i.v.) and intracarotid (i.car.) administration of the peptide. gamma 2-MSH (1.5-100 nmol/kg) administered i.v. and i.car. caused a dose-dependent increase in MAP and HR. Injection of the peptide i.car. in the middose range resulted in a more pronounced pressor effect. Furthermore, the earlier onset of the hemodynamic effects after i.car. injection suggests that forebrain structures play a role in these effects. In addition to the pressor response, gamma 2-MSH produced a strong increase in CFint, CFtot, and CBF after both routes of administration, suggesting an increased intracerebral BF. Whereas the effects of the higher doses of gamma 2-MSH on MAP and CFtot were quantitatively comparable after either the intravenous or intracarotid administration, the effect on regional CBF and CFint was about twice as high after i.car. infusion, indicating a centrally mediated phenomenon underlying this effect on CBF. The increase in CFint cannot in itself be ascribed to a gamma 2-MSH-mediated higher perfusion pressure (i.e., BP), since an equipressor dose of norepinephrine (NE) caused a significant decrease in CFint. The significant and more than twofold higher increase in CBF after intracarotid administration of gamma 2-MSH in comparison with administration of NE by the same route also suggests a central origin for the enhancement of microcirculatory flow due to the peptide.

Distribution of Lys-γ2-melanocyte-stimulating hormone- (Lys-γ2-MSH)-like immunoreactivity in neuronal elements in the brain and peripheral tissues of the rat

Abstract Using an antiserum raised against Lys-γ 2 -melanocyte-stimulating hormone (Lys-γ 2 -MSH), with a high specificity for this peptide and its des-Lys derivative, γ 2 -MSH, we found Lys-γ 2 -MSH-like immunoreactivity to have a widespread distribution in the rat brain. In colchicine-treated rats, groups of immunopositive cell bodies were found in the intermediate and anterior lobes of the pituitary gland, in the hypothalamic arcuate nucleus and in the commissural part of the nucleus of the solitary tract (NTS). Immunopositive fibers were found to originate from the latter two cell body regions. The distribution of these fibers was similar to that of the pro-opiomelanocortin-containing cell bodies and projections as it has been described previously. Immunopositive terminals were found in brain regions containing neurons which have been shown to express mRNA for melanocortin receptors, though the distribution of Lys-γ 2 -MSH-like immunoreactivity is considerably more widespread than that of mRNA for the ‘γ-MSH receptor’ (the melanocortin MC 3 receptor), which has been reported to be mainly expressed in the hypothalamus. In the periphery Lys-γ 2 -MSH immunoreactivity was localized in the adrenal medulla and in neuronal fibers and varicosities in the heart. The vascular system, the bronchi and kidney were immunonegative. The occurrence of Lys-γ 2 -MSH immunoreactivity in many of the brain regions which are involved in cardiovascular regulation offers leads for further studies on the putative role of γ-MSHs in cardiovascular control. The occurrence in the rat heart of Lys-γ 2 -MSH-containing fibers suggests a role of the γ-MSHs in cardiac function.

Effects of nimodipine on sciatic nerve blood flow and vasa nervorum responsiveness in the diabetic rat

Evidence is accumulating that impairment of nerve blood flow is a key factor in the pathogenesis of diabetic neuropathy. Nimodipine, a 1,4-dihydropyridine type Ca2+ channel antagonist, has been shown to ameliorate an existing neuropathy in the streptozotocin-induced diabetic rat. In the present study the effect of diabetes mellitus itself and the effect of chronic nimodipine treatment on the sciatic nerve blood flow of streptozotocin-induced diabetic rats were investigated. Nerve blood flow was assessed using laser-Doppler flowmetry. Nerve blood flow gradually decreased during the first 10 weeks of diabetes mellitus and remained relatively stable thereafter. Intervention with nimodipine significantly improved the flow deficit observed in the diabetic rats. Vasa nervorum adrenergic responsiveness was also investigated. Diabetic rats showed a postsynaptic adrenergic hyporesponsiveness. Treatment with nimodipine restored the reduced presynaptic responsiveness independent of the postsynaptic adrenergic hyporesponsiveness. It was concluded that, in addition to direct neuroprotective effects, nimodipine exerts beneficial effects on disturbed nerve blood flow and on reduced presynaptic adrenergic responsiveness of the vasa nervorum in experimental diabetic neuropathy.

Different cardiovascular profiles of three melanocortins in conscious rats; evidence for antagonism between γ2-MSH and ACTH-(1–24)

We investigated the effects of [Nle4,d‐Phe7]α‐melanocyte‐stimulating hormone (NDP‐MSH), adrenocorticotropin‐(124) (ACTH‐(124)) and γ2‐MSH, three melanocortins with different agonist selectivity for the five cloned melanocortin receptors, on blood pressure and heart rate in conscious, freely moving rats following intravenous administration. As was previously found by other investigators as well as by us, γ2‐MSH, a peptide suggested to be an agonist with selectivity for the melanocortin MC3 receptor, caused a dose‐dependent, short lasting pressor response in combination with a tachycardia. Despite the fact that NDP‐MSH is a potent agonist of various melanocortin receptor subtypes, among which the melanocortin MC3 receptor, it did not affect blood pressure or heart rate, when administered i.v. in doses of up to 1000 nmol kg−1. ACTH‐(124) caused a dose‐dependent decrease in blood pressure in combination with a dose‐dependent increase in heart rate in a dose‐range from 15 to 500 nmol kg−1. The cardiovascular effects of ACTH‐(124) were independent of the presence of the adrenals. Pretreatment with ACTH‐(124) caused a pronounced, dose‐dependent parallel shift to the right of the dose‐response curve for the pressor and tachycardiac effects of γ2‐MSH. The antagonistic effect of ACTH‐(124) was already apparent following a dose of this peptide as low as 10 nmol kg−1, which when given alone had no intrinsic hypotensive activity. These results form further support for the notion that it is not via activation of one of the as yet cloned melanocortin receptors that γ‐MSH‐like peptides increase blood pressure and heart rate. The cardiovascular effects of ACTH‐(124) seem not to be mediated by the adrenal melanocortin MC2 receptors, for which ACTH‐(124) is a selective agonist, or by adrenal catecholamines. There appears to be a functional antagonism between ACTH‐(124) and γ2‐MSH, two melanocortins derived from a common precursor, with respect to their effect on blood pressure and heart rate. Whether this antagonism plays a (patho)physiological role remains to be shown.