Protein tyrosine kinase and mitogen-activated protein kinase activation contribute to K(ATP) and K(ca) channel impairment after brain injury

Regulation of the Cerebral Circulation During Development

The cerebral microcirculation undergoes dynamic changes in parallel with the development of neurons, glia, and their energy metabolism throughout gestation and postnatally. Cerebral blood flow (CBF), oxygen consumption, and glucose consumption are as low as 20% of adult levels in humans born prematurely but eventually exceed adult levels at ages 3 to 11 years, which coincide with the period of continued brain growth, synapse formation, synapse pruning, and myelination. Neurovascular coupling to sensory activation is present but attenuated at birth. By 2 postnatal months, the increase in CBF often is disproportionately smaller than the increase in oxygen consumption, in contrast to the relative hyperemia seen in adults. Vascular smooth muscle myogenic tone increases in parallel with developmental increases in arterial pressure. CBF autoregulatory response to increased arterial pressure is intact at birth but has a more limited range with arterial hypotension. Hypoxia-induced vasodilation in preterm fetal sheep with low oxygen consumption does not sustain cerebral oxygen transport, but the response becomes better developed for sustaining oxygen transport by term. Nitric oxide tonically inhibits vasomotor tone, and glutamate receptor activation can evoke its release in lambs and piglets. In piglets, astrocyte-derived carbon monoxide plays a central role in vasodilation evoked by glutamate, ADP, and seizures, and prostanoids play a large role in endothelial-dependent and hypercapnic vasodilation. Overall, homeostatic mechanisms of CBF regulation in response to arterial pressure, neuronal activity, carbon dioxide, and oxygenation are present at birth but continue to develop postnatally as neurovascular signaling pathways are dynamically altered and integrated. © 2021 American Physiological Society. Compr Physiol 11:1-62, 2021.

The role of endothelin and endothelin antagonists in traumatic brain injury: a review of the literature

OBJECTIVES

To date, there is increasing evidence for the role of endothelins in the pathophysiological development of cerebral vasospasms associated with a variety of neurological diseases, e.g., stroke and subarachnoid hemorrhage. In contrast, only little is known regarding the role of endothelins in impaired cerebral hemodynamics after traumatic brain injury. Therapeutic work in blocking the endothelin system has led to the discovery of a number of antagonists potentially useful in restoring cerebral blood flow after traumatic brain injury, potentially reducing the detrimental effects of secondary brain injury. Therefore, the present work provides an overview of background topics such as structures and biosynthesis of endothelins, different types as well as potential mechanisms and sites of action. In addition, the role of age for the effects of endothelins on cerebral hemodynamics after traumatic brain injury is discussed.

RESULTS

Description of data supporting the role of the endothelins play in a host of neurological deficits.

CONCLUSIONS

Endothelin antagonists may be effective as novel treatments for various neuropathologies.

Nociceptin/orphanin phenylalanine glutamine (FQ) receptor and cardiovascular disease

Nociceptin/Orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ receptor. N/OFQ acts directly on blood vessels to elicit vasodilation. This review will describe the peripheral cardiovascular effects of N/OFQ observed in studies conducted in vitro and in vivo, along with those designed to characterize systemic cardiovascular effects resulting from direct injection into brain tissue. Emphasis is placed on the cerebrovascular action of N/OFQ and its function considered in the setting of central nervous system (CNS) pathology. Although N/OFQ is unlikely to cross the blood-brain barrier because of its size, use of N/OFQ antagonists to alleviate the potentially deleterious action of centrally released N/OFQ may be of therapeutic importance in treatment of cerebral ischemia of diverse origin, such as stroke and traumatic brain injury. Targeting N/OFQ may also be of therapeutic importance in alleviating the hyperemia and pain associated with joint inflammation.

Hyperthermia-induced vasoconstriction of the carotid artery and the role of potassium channels

Clinical experience and experimental studies have shown that hyperthermia can cause cerebral ischaemia and brain damage. By in vitro experiments with heating, we previously were able to induce carotid artery constriction. The objective of the present study was to clarify the mechanism of this thermal response. Isometric tension was recorded in rabbit carotid artery specimens using organ baths during stepwise temperature elevation. The heating responses were investigated at basal tone, in precontracted vessels, after blocking of adrenergic responses and administration of potassium (K)-channel activators and inhibitors. Stepwise heating of carotid artery strips from 37 degrees C to 47 degrees C induced reproducible graded contraction. The hyperthermic responses were not due to adrenergic stimulation, which were reduced and resistant to neurogenic blockade by tetrodotoxin. Heating-induced contractions were potentiated by the K-channel inhibitors tetraethylammonium, BaCl2, charybdotoxin, and the Na+/K+ ATPase inhibitor ouabain. Levcromakalim (BRL), a K+-channel activator, reduced heating induced contractions. Heating of carotid artery preparations induced reversible graded vasoconstriction proportional to temperature. The heating-induced contractions were not mediated by an adrenergenic process, but rather were due to inhibition of K+ channels, which increases Ca2+ entry. In vivo, this reaction may lead to a disturbance of autoregulation of cerebral blood flow and ischemia with brain damage.

Autonomic Regulation of Voltage-Gated Cardiac Ion Channels

Altering voltage-gated ion channel currents, by changing channel number or voltage-dependent kinetics, regulates the propagation of action potentials along the plasma membrane of individual cells and from one cell to its neighbors. Functional increases in the number of cardiac sodium channels (Na(V)1.5) at the myocardial sarcolemma are accomplished by the regulation of caveolae by beta adrenergically stimulated G-proteins. We demonstrate that Na(V)1.5, Ca(V)1.2a, and K(V)1.5 channels specifically localize to isolated caveolar membranes, and to punctate regions of the sarcolemma labeled with caveolin-3. In addition, we show that Na(V)1.5, Ca(V)1.2a, and K(V)1.5 channel antibodies label the same subpopulation of isolated caveolae. Plasma membrane sheet assays demonstrate that Na(V)1.5, Ca(V)1.2a, and K(V)1.5 cluster with caveolin-3. This may have interesting implications for the way in which adrenergic pathways alter the cardiac action potential morphology and the velocity of the excitatory wave.

Soy isoflavones and cognitive function

There is growing interest in the physiological functions of soy isoflavones, especially in whether they affect cognitive function and have beneficial effects on neurodegenerative diseases. Here we review the recent evidence from clinical and experimental studies supporting a role for soy isoflavones in cognitive function. Soy isoflavones may mimic the actions and functions of estrogens on brain, and they have been shown to have positive effects on the cognitive function in females; however, studies on their effects on spatial memory have not provided consistent results in males. Although data from humans, cultures, and animal models are currently insufficient for elucidating the metabolism of soy isoflavone actions on cognitive function and the nervous system, we suggest two putative pathways; (1) an estrogen receptor-mediated pathway and (2) via the inhibition of tyrosine kinase, in particular by genistein, which is one of the soy isoflavones. Although soy isoflavones appear to have a positive effect on brain function, further research is needed to determine not only the efficacy but also the safety of soy isoflavones on the nervous system and cognitive function.

NOC/oFQ activates ERK and JNK but not p38 MAPK to impair prostaglandin cerebrovasodilation after brain injury

Fluid percussion brain injury (FPI) elevates the CSF concentration of the opioid nociceptin/orphanin FQ (NOC/oFQ), which contributes to impairment of pial artery dilation to the prostaglandins (PG) PGE2 and PGI2. This study investigated the role of the ERK, p38, and JNK isoforms of mitogen-activated protein kinase (MAPK) in impaired PG cerebrovasodilation after FPI, and the relationship of brain injury induced release of NOC/oFQ to MAPK in such vascular impairment in newborn pigs equipped with a closed cranial window. FPI blunted PGE2 pial artery dilation, but U 0126 and SP 600125 (10(-6) M) (ERK and JNK MAPK inhibitors, respectively) partially prevented such impairment (7 +/- 1, 12 +/- 1, and 17 +/- 1 vs. 2 +/- 1, 3 +/- 1, and 5 +/- 1 vs. 4 +/- 1, 7 +/- 1, and 12 +/- 1% for 1, 10, and 100 ng/ml PGE2 in control, FPI, and FPI + U 0126 pretreated animals, respectively). In contrast, administration of SB 203580 (10(-5) M) (p38 MAPK inhibitor) did not prevent FPI impairment of PGE2 dilation. Co-administration of NOC/oFQ at the dose of 10(-10) M, the cerebrospinal fluid concentration observed after FPI, with PGE2 under non-brain injury conditions blunted PG dilation, but U 0126 or SP 600125 partially prevented such impairment (7 +/- 1, 11 +/- 1, and 16 +/- 2 vs. 0 +/- 1, 1 +/- 1, and 2 +/- 1, vs. 5 +/- 1, 9 +/- 1, and 13 +/- 2 for responses to PGE2 in control, NOC/oFQ, and NOC/oFQ + U 0126 treated animals, respectively). Administration of SB 203580 did not prevent impairment of PG pial artery dilation by NOC/oFQ. These data show that activation of ERK and JNK but not p38 MAPK contributes to impairment of PG cerebrovasodilation after FPI. These data suggest that NOC/oFQ induced ERK and JNK but not p38 MAPK activation contributes to impaired cerebrovasodilation to PG after FPI.

Age and cerebral circulation

Cerebral blood flow, and its control, vary as a function of age. This review focuses on the perinatal period and compares/contrasts this age period to that of the juvenile/adult. Additionally, this review describes mechanisms important in the control of the cerebral circulation as a function of age during physiologic and pathologic conditions. Two topics of pathophysiology are considered: cerebral hypoxia ischemia, often seen in perinates due to problems with delivery or respiratory management post delivery, and traumatic brain injury, described as the shaken impact syndrome, an example of child abuse. Clinically, it is important to understand the pathophysiology of the cerebral circulation in order to optimize mechanistically appropriate therapeutic modalities.

Altered NO function contributes to impairment of uPA and tPA cerebrovasodilation after brain injury

Urokinase (uPA) and tissue plasminogen activator (tPA) are serine proteases implicated in fibrinolysis, but their role in the regulation of the cerebrovascular response to brain trauma has not been investigated. This study was designed to (1) characterize the cerebrovascular activity of uPA and tPA, (2) investigate the role of nitric oxide (NO) in uPA and tPA vascular activity, and (3) characterize the effect of fluid percussion brain injury (FPI) on vascular responses to uPA and tPA. The closed cranial window technique in chloralose anesthetized newborn pigs was used to measure pial artery diameter and collect CSF for radioimmunoassay (RIA) of cGMP concentration. Topical uPA (10(-9), 10(-7) M) elicited pial artery dilation that was blunted by the NO synthase inhibitor, L-NNA (10(-6) M) (8 +/- 1% and 13 +/- 1 vs. 3 +/- 1% and 7 +/- 2%, respectively). Vasodilation in response to uPA was associated with an increase in CSF cGMP concentration (645 +/- 20, 865 +/- 39 and 1088 +/- 33 fmol/mL cGMP for control, uPA 10(-9), 10(-7) M, respectively). Similar data were obtained for tPA. Pial artery dilation to uPA was blunted following FPI (7 +/- 1% and 12 +/- 1% vs. 3 +/- 1% and 6 +/- 1%, respectively), while uPA-associated release of cGMP was blocked (677 +/- 45, 909 +/- 53, and 1110 +/- 55 vs. 283 +/- 10, 316 +/- 18, and 333 +/- 26 fmol/mL for control, uPA 10(-9), 10(-7) M before and after FPI, respectively). Similar data were obtained for tPA. These data show that uPA and tPA produce pial artery dilation in an NO-dependent manner. FPI blunted uPA and tPA induced pial artery dilation as well as the associated release of cGMP. These data suggest therefore that altered NO function contributes to the impairment of uPA and tPA cerebrovasodilation after brain injury.

Inhibitory effect of high concentration of glucose on relaxations to activation of ATP-sensitive K+ channels in human omental artery

OBJECTIVE

The present study was designed to examine in the human omental artery whether high concentrations of D-glucose inhibit the activity of ATP-sensitive K+ channels in the vascular smooth muscle and whether this inhibitory effect is mediated by the production of superoxide.

METHODS AND RESULTS

Human omental arteries without endothelium were suspended for isometric force recording. Changes in membrane potentials were recorded and production of superoxide was evaluated. Glibenclamide abolished vasorelaxation and hyperpolarization in response to levcromakalim. D-glucose (10 to 20 mmol/L) but not l-glucose (20 mmol/L) reduced these vasorelaxation and hyperpolarization. Tiron and diphenyleneiodonium, but not catalase, restored vasorelaxation and hyperpolarization in response to levcromakalim in arteries treated with D-glucose. Calphostin C and Gö6976 simultaneously recovered these vasorelaxation and hyperpolarization in arteries treated with D-glucose. Phorbol 12-myristate 13 acetate (PMA) inhibited the vasorelaxation and hyperpolarization, which are recovered by calphostin C as well as Gö6976. D-glucose and PMA, but not l-glucose, significantly increased superoxide production from the arteries, whereas such increased production was reversed by Tiron.

CONCLUSIONS

These results suggest that in the human visceral artery, acute hyperglycemia modulates vasodilation mediated by ATP-sensitive K+ channels via the production of superoxide possibly mediated by the activation of protein kinase C.

Nociceptin/orphanin FQ alters prostaglandin cerebrovascular action following brain injury

Previous studies have observed that fluid percussion brain injury (FPI) elevated the CSF concentration of the opioid nociceptin/orphanin FQ (NOC/oFQ). In separate studies, FPI impaired pial artery dilation to the prostaglandins PGI2 and PGE2. This study was designed to investigate the following: (1) role of NOC/oFQ in impaired dilation to PGI2 and PGE2, (2) the effects of FPI on vasoconstriction to the TXA2 mimic U46619 and PGF2alpha, and (3) the role of NOC/oFQ in such FPI induced effects on U46619 and PGF(2alpha). Lateral FPI was induced in newborn pigs equipped with a closed cranial window. PGI2 (1, 10, 100 ng/ml) vasodilation was blunted by FPI and fully restored by the NOC/oFQ antagonist, [F/G] NOC/oFQ (1-13) NH2 (10(-6)M) (9 +/- 1, 13 +/- 1, and 19 +/- 1 vs. 2 +/- 1, 4 +/- 1, and 5 + 1 vs 7 +/- 1, 12 +/- 2, and 17 +/- 3% for control, FPI, and FPI + [F/G] NOC/oFQ (1-13) NH2, respectively). Similar effects were observed for PGE2. In contrast, U46619 (1, 10 ng/ml) induced vasoconstriction was potentiated by FPI but returned to the response observed prior to FPI by [F/G] NOC/oFQ (1-13) NH2 ( -8 +/- 1 and -14 +/- 1 vs. -15 +/- 1 and -25 +/- 1 vs. -7 +/- 1 and -12 +/- 2% for control, FPI, and FPI + [F/G] NOC/oFQ (1-13) NH2, respectively). Similar effects were observed for PGF(2alpha). Coadministration of NOC/oFQ (10(-10)M), the CSF concentration observed after FPI, with agonists under nonbrain injury conditions blunted PGI2 and PGE2 vasodilation, but potentiated U46619 and PGF2alpha vasoconstriction similarly to that observed after FPI. These data show that FPI blunted PGI2 and PGE2 vasodilation but potentiated U46619 and PGF2alpha vasoconstriction. Additionally, these data show that administration of a NOC/oFQ receptor antagonist prevented such FPI associated events. NOC/oFQ administrated in a concentration observed after FPI produced blunted dilator prostaglandin and potentiated vasoconstriction prostaglandin vascular responses under nonbrain injury conditions. Finally, these data suggest that NOC/oFQ alters prostaglandin cerebrovascular action following brain injury.

Differential role of PTK and ERK MAPK in superoxide impairment of K(ATP) and K(Ca) channel cerebrovasodilation

Previously, superoxide (O2 -) has been observed to impair pial artery dilation (PAD) to activators of the ATP-sensitive (KATP) and calcium-sensitive (KCa) K+ channels. This study tested the hypothesis that activation of protein tyrosine kinase (PTK) and the ERK isoform of MAPK by O2 - contribute to impairment of KATP and KCa channel PAD. Exposure of the cerebral cortex to a xanthine oxidase O2 --generating system (OX) blunted PAD to cromakalim, a KATP agonist, but preadministration of genistein, a PTK antagonist, or U-0126, an ERK MAPK inhibitor, almost completely prevented such impairment (11 +/- 1 and 22 +/- 1 vs. 3 +/- 1 and 7 +/- 1 vs. 10 +/- 1 and 16 +/- 2% for cromakalim with 10-8 and 10-6 M PAD during control, OX, and OX + genistein conditions). In contrast, neither genistein nor U-0126 robustly protected PAD to NS-1619, a KCa agonist, after OX exposure (11 +/- 1 and 18 +/- 2 vs. 1 +/- 1 and 2 +/- 1 vs. 4 +/- 1 and 6 +/- 1% for 10-8 and 10-6 M NS-1619 during control, OX, and OX + genistein conditions). These data show that PTK and ERK MAPK activation contribute to O2 --induced KATP and KCa channel PAD impairment and suggest a differential greater role for PTK and ERK MAPK in KATP vs. KCa channel PAD impairment.

PTK, MAPK, and NOC/oFQ impair hypercapnic cerebrovasodilation after hypoxia/ischemia

This study characterized the contributions of protein tyrosine kinase (PTK) and mitogen-activated protein kinase (MAPK) in nociceptin/orphanin FQ (NOC/oFQ)-induced impairment of hypercapnic pial artery dilation (PAD) after hypoxia/ischemia (H/I) in piglets equipped with a closed cranial window. NOC/oFQ (10(-10) M cerebrospinal fluid H/I concentration) impaired hypercapnic PAD (21 +/- 2% vs. 13 +/- 1%). Coadministration of either of the PTK inhibitors genistein or tyrphostin A23 or the MAPK inhibitors U-0126 or PD-98059 with NOC/oFQ (10(-10) M) partially prevented the inhibition of hypercapnic PAD compared with that observed in their absence (21 +/- 2% vs. 17 +/- 1% for genistein). After exposure to H/I, PAD in response to hypercapnia was impaired, but pretreatment with either genistein, tyrphostin A23, U-0126, or PD-98059 partially protected such impairment (17 +/- 1% vs. 4 +/- 1% vs. 9 +/- 1% for sham control, H/I, and H/I + genistein pretreatment, respectively). These data show that PTK and MAPK activation contribute to NOC/oFQ-induced impairment of hypercapnic PAD. These data suggest that activation of PTK and MAPK is also involved in the mechanism by which NOC/oFQ impairs hypercapnic PAD after H/I.