Inhaled nitric oxide protects cerebral autoregulation through prevention of impairment of ATP and calcium sensitive K channel mediated cerebrovasodilation after traumatic brain injury.

Hypotension and low cerebral perfusion pressure are associated with low cerebral blood flow, cerebral ischemia, and poor outcomes after traumatic brain injury (TBI). Cerebral autoregulation is impaired after TBI, contributing to poor outcome. In prior studies, ERK mitogen activated protein kinase (MAPK) and ET-1 had been observed to be upregulated and contribute to impairment of cerebral autoregulation and histopathology after fluid percussion brain injury (FPI). Activation of ATP and Calcium sensitive (Katp and Kca) channels produce cerebrovasodilation and contribute to autoregulation, both impaired after TBI. Upregulation of ERK MAPK and endothelin-1 (ET-1) produces K channel function impairment after CNS injury. Inhaled nitric oxide (iNO) has recently been observed to prevent impairment of cerebral autoregulation and hippocampal CA1 and CA3 neuronal cell necrosis after FPI via block of upregulation of ERK MAPK and ET-1. We presently investigated whether iNO prevented impairment of Katp and Kca-mediated cerebrovasodilation after FPI in pigs equipped with a closed cranial window. Results show that pial artery dilation in response to the Katp agonist cromakalim, the Kca agonist NS1619, PGE2 and the NO releaser sodium nitroprusside (SNP) were blocked by FPI, but such impairment was prevented by iNO administered at 2 h post injury. Protection lasted for at least 1 h after iNO administration was stopped. Using vasodilaton as an index of function, these data indicate that iNO prevents impairment of cerebral autoregulation and limits histopathology after TBI through protection of K channel function via blockade of ERK MAPK and ET-1.

Release of IL-6 After Stroke Contributes to Impaired Cerebral Autoregulation and Hippocampal Neuronal Necrosis Through NMDA Receptor Activation and Upregulation of ET-1 and JNK.

The sole FDA-approved drug treatment for ischemic stroke is tissue-type plasminogen activator (tPA). However, upregulation of JNK mitogen-activated protein kinase (MAPK) and endothelin 1 (ET-1) by tPA after stroke contributes to impaired cerebrovascular autoregulation. Wild-type (wt) tPA can bind to the lipoprotein-related receptor (LRP), which mediates vasodilation, or NMDA receptors (NMDA-Rs), exacerbating vasoconstriction. Elevations in IL-6, a marker of inflammation that accompanies stroke, are reported to be an adverse prognostic factor. We hypothesized that IL-6 released into CSF after stroke by wt-tPA through activation of NMDA-Rs and upregulation of ET-1 and JNK contribute to impairment of cerebrovascular autoregulation and increased histopathology. Results show that IL-6 was increased post stroke in pigs, which was increased further by wt-tPA. Co-administration of the IL-6 antagonist LMT-28 with wt-tPA prevented impairment of cerebrovascular autoregulation and necrosis of hippocampal cells. wt-tPA co-administered with the JNK inhibitor SP 600125 and the ET-1 antagonist BQ 123 blocked stroke-induced elevation of IL-6. Co-administration of LMT-28 with wt-tPA blocked the augmentation of JNK and ET-1 post stroke. In conclusion, IL-6 released after stroke, which is enhanced by wt-tPA through activation of NMDA-Rs and upregulation of ET-1 and JNK, impairs cerebrovascular autoregulation and increases histopathology. Strategies that promote fibrinolysis while limiting activation of NMDA-Rs and upregulation of IL-6 may improve the benefit/risk ratio compared to wt-tPA in treatment of stroke.

Inhaled Nitric Oxide Protects Cerebral Autoregulation and Reduces Hippocampal Necrosis After Traumatic Brain Injury Through Inhibition of ET-1, ERK MAPK and IL-6 Upregulation in Pigs.

OBJECTIVE: Traumatic brain injury (TBI) is an important contributor to morbidity and mortality. Cerebral autoregulation is impaired after TBI, contributing to poor outcome. Extracellular signal-related kinase (ERK) mitogen activated protein kinase (MAPK) and ET-1 are upregulated and contribute to impairment of cerebral autoregulation and histopathology after porcine fluid percussion brain injury (FPI). Recent studies show that inhaled nitric oxide (iNO) prevents impairment of cerebral autoregulation and histopathology after FPI in pigs. Unrelated studies indicated an association between ERK and increased IL-6 after FPI. However, the role of IL-6 in central nervous system (CNS) pathology is not well understood. We investigated whether iNO protects autoregulation and limits histopathology after FPI in pigs due to modulation of brain injury associated upregulation of ET-1, ERK MAPK, and IL-6. METHODS: Lateral FPI was produced in anesthetized pigs equipped with a closed cranial window and iNO administered at 30 min or 2 h post injury. RESULTS: CSF ET-1, ERK MAPK, and IL-6 were increased by FPI, but release was blocked by iNO administered at 30 min or 2 h after TBI. The IL-6 antagonist LMT-28 prevented impairment of cerebral autoregulation and hippocampal CA1 and CA3 neuronal necrosis after FPI. Papaverine induced dilation was unchanged by FPI and LMT-28. Protection lasted for at least 2 h after iNO administration was stopped. CONCLUSIONS: These data indicate that iNO protects cerebral autoregulation and reduces hippocampal necrosis after traumatic brain injury through inhibition of ET-1, ERK MAPK, and IL-6 upregulation in pigs.

Inhaled Nitric Oxide Protects Cerebral Autoregulation and Reduces Hippocampal Neuronal Cell Necrosis after Traumatic Brain Injury in Newborn and Juvenile Pigs.

Traumatic brain injury (TBI) contributes to morbidity in children, and boys are disproportionately represented. Cerebral blood flow (CBF) is reduced and autoregulation is impaired after TBI, contributing to poor outcome. Cerebral perfusion pressure (CPP) is often normalized by use of vasoactive agents to increase mean arterial pressure (MAP). In prior studies of male and female newborn and juvenile pigs, we observed that phenylephrine, norepinephrine, epinephrine, and dopamine demonstrated different sex- and age-dependent abilities to prevent impairment of cerebral autoregulation and limit histopathology after TBI, despite equivalent CPP values. This observation complicated treatment choice. Alternatively, administration of a cerebral vasodilator may improve cerebral hemodynamics after TBI by increasing CBF. In prior studies, intravenous sodium nitroprusside, a nitric oxide (NO) releaser, elevated CBF after TBI but failed to prevent impairment of cerebral autoregulation due to a confounding decrease in MAP, which lowered CPP. We presently test the hypothesis that inhaled NO (iNO) will protect cerebral autoregulation and prevent hippocampal histopathology after TBI. Results show that iNO administered at 30 min or 2 h after TBI protected cerebral autoregulation and prevented neuronal cell necrosis in CA1 and CA3 hippocampus equivalently in male and female newborn and juvenile pigs without change in MAP. Protection lasted for at least 2 h after iNO administration was stopped. Papaverine-induced dilation was unchanged by TBI and iNO. These data indicate that iNO offers the opportunity to have a single therapeutic that uniformly protects autoregulation and limits hippocampal neuronal cell necrosis across both ages and sexes.

Red blood cell-hitchhiking boosts delivery of nanocarriers to chosen organs by orders of magnitude.

Drug delivery by nanocarriers (NCs) has long been stymied by dominant liver uptake and limited target organ deposition, even when NCs are targeted using affinity moieties. Here we report a universal solution: red blood cell (RBC)-hitchhiking (RH), in which NCs adsorbed onto the RBCs transfer from RBCs to the first organ downstream of the intravascular injection. RH improves delivery for a wide range of NCs and even viral vectors. For example, RH injected intravenously increases liposome uptake in the first downstream organ, lungs, by ~40-fold compared with free NCs. Intra-carotid artery injection of RH NCs delivers >10% of the injected NC dose to the brain, ~10× higher than that achieved with affinity moieties. Further, RH works in mice, pigs, and ex vivo human lungs without causing RBC or end-organ toxicities. Thus, RH is a clinically translatable platform technology poised to augment drug delivery in acute lung disease, stroke, and several other diseases.

tPA variant tPA-A296-299 Prevents impairment of cerebral autoregulation and necrosis of hippocampal neurons after stroke by inhibiting upregulation of ET-1.

Tissue-type plasminogen activator (tPA) is neurotoxic and exacerbates uncoupling of cerebral blood flow (CBF) and metabolism after stroke, yet it remains the sole FDA-approved drug for treatment of ischemic stroke. Upregulation of c-Jun-terminal kinase (JNK) after stroke contributes to tPA-mediated impairment of autoregulation, but the role of endothelin-1 (ET-1) is unknown. Based on the Glasgow Coma Scale, impaired autoregulation is linked to adverse outcomes after TBI, but correlation with hippocampal histopathology after stroke has not been established. We propose that given after stroke, tPA activates N-Methyl-D-Aspartate receptors (NMDA-Rs) and upregulates ET-1 in a JNK dependent manner, imparing autoregulation and leading to histopathology. After stroke, CBF was reduced in the hippocampus and reduced further during hypotension, which did not occur in hypotensive sham pigs, indicating impairment of autoregulation. Autoregulation and necrosis of hippocampal CA1 and CA3 neurons were further impaired by tPA, but were preserved by the ET-1 antagonist BQ 123 and tPA-A,296-299 a variant that is fibrinolytic but does not bind to NMDA-Rs. Expression of ET-1 was increased by stroke and potentiated by tPA but returned to sham levels by tPA-A296-299 and the JNK antagonist SP600125. Results show that JNK releases ET-1 after stroke. Tissue-type plasminogen activator -A296-299 prevents impairment of cerebral autoregulation and histopathology after stroke by inhibiting upregulation of ET-1.

Dopamine protects cerebral autoregulation and prevents hippocampal necrosis after traumatic brain injury via block of ERK MAPK in juvenile pigs.

Traumatic brain injury (TBI) contributes to morbidity in children, and more boys experience TBI. Cerebral autoregulation is impaired after TBI, contributing to poor outcome. Cerebral Perfusion Pressure (CPP) is often normalized by use of vasoactive agents to increase mean arterial pressure (MAP). In prior studies of newborn and juvenile pigs, vasoactive agent choice influenced outcome after TBI as a function of age and sex, with none protecting cerebral autoregulation in both ages and sexes. Dopamine (DA) prevents impairment of cerebral autoregulation in male and female newborn pigs via inhibition of upregulation of ERK mitogen activated protein kinase (MAPK) after fluid percussion injury (FPI). We investigated whether DA protects autoregulation and limits histopathology after FPI in juvenile pigs and the role of ERK in that outcome. Results show that DA protects autoregulation in both male and female juvenile pigs after FPI. Papaverine induced dilation was unchanged by FPI and DA. DA blunted ERK MAPK and prevented loss of neurons in CA1 and CA3 hippocampus of males and females after FPI. These data indicate that DA protects autoregulation and limits hippocampal neuronal cell necrosis via block of ERK after FPI in male and female juvenile pigs. Of the vasoactive agents prior investigated, including norepinephrine, epinephrine, and phenylephrine, DA is the only one demonstrated to improve outcome after TBI in both sexes and ages. These data suggest that DA should be considered as a first line treatment to protect cerebral autoregulation and promote cerebral outcomes in pediatric TBI irrespective of age and sex.

Sex and age differences in phenylephrine mechanisms and outcomes after piglet brain injury.

BackgroundTraumatic brain injury (TBI) is the leading cause of injury-related death in children, with boys and children under 4 years of age having particularly poor outcomes. Cerebral autoregulation is often impaired after TBI, contributing to poor outcome. In prior studies on newborn pigs, phenylephrine (Phe) preferentially protected cerebral autoregulation in female but not in male subjects after TBI. We hypothesized that, in contrast to the newborn, Phe prevents impairment of autoregulation and tissue injury following TBI in both sexes of older pigs.MethodsCerebral autoregulation, cerebrospinal fluid (CSF) extracellular signal-related kinase (ERK) and endothelin, and histopathology were determined after moderate fluid percussion brain injury (FPI) in male and female juvenile pigs after Phe.ResultsAutoregulation was more impaired in male than in female subjects. Phe protects autoregulation in both sexes after FPI, blocks ERK and endothelin, and decreases the number of necrotic neurons in male and female subjects after FPI.ConclusionsThese data indicate that Phe protects autoregulation and limits neuronal necrosis via blockage of ERK and endothelin after FPI in male and female subjects. Together with prior observations in newborn pigs where Phe protected autoregulation in female but not in male subjects, these data suggest that use of Phe to improve outcomes after TBI is both sex- and age-dependent.

Noninvasive vagus nerve stimulation as treatment for trigeminal allodynia.

Implanted vagus nerve stimulation (VNS) has been used to treat seizures and depression. In this study, we explored the mechanism of action of noninvasive vagus nerve stimulation (nVNS) for the treatment of trigeminal allodynia. Rats were repeatedly infused with inflammatory mediators directly onto the dura, which led to chronic trigeminal allodynia. Administration of nVNS for 2 minutes decreased periorbital sensitivity in rats with periorbital trigeminal allodynia for up to 3.5 hours after stimulation. Using microdialysis, we quantified levels of extracellular neurotransmitters in the trigeminal nucleus caudalis (TNC). Allodynic rats showed a 7.7±0.9-fold increase in extracellular glutamate in the TNC after i.p. administration of the chemical headache trigger glyceryl trinitrate (GTN; 0.1 mg/kg). Allodynic rats that received nVNS had only a 2.3±0.4-fold increase in extracellular glutamate after GTN, similar to the response in control naive rats. When nVNS was delayed until 120 minutes after GTN treatment, the high levels of glutamate in the TNC were reversed after nVNS. The nVNS stimulation parameters used in this study did not produce significant changes in blood pressure or heart rate. These data suggest that nVNS may be used to treat trigeminal allodynia.