IRS1 expression in hippocampus is age-dependent and is required for mature spine maintenance and neuritogenesis.

Insulin and insulin-like growth factor type I (IGF-1) play prominent roles in brain activity throughout the lifespan. Insulin/IGF1 signaling starts with the activation of the intracellular insulin receptor substrates (IRS). In this work, we performed a comparative study of IRS1 and IRS2, together with the IGF1 (IGF1R) and insulin (IR) receptor expression in the hippocampus and prefrontal cortex during development. We found that IRS1 and IRS2 expression is prominent during development and declines in the aged hippocampus, contrary to IR, which increases in adulthood and aging. In contrast, IGF1R expression is unaffected by age. Expression patterns are similar in the prefrontal cortex. Neurite development occurs postnatally in the rodent hippocampus and cortex, and it declines in the mature and aged brain and is influenced by trophic factors. In our previous work, we demonstrated that knockdown of IRS1 by shRNA impairs learning and reduces synaptic plasticity in a rat model, as measured by synaptophysin puncta in axons. In this study, we report that shIRS1 alters spine maturation in adult hilar hippocampal neurons. Lastly, to understand the role of IRS1 in neuronal neurite tree, we transfect shIRS1 into primary neuronal cultures and observed that shIRS1 reduced neurite branching and neurite length. Our results demonstrate that IRS1/2 and insulin/IGF1 receptors display different age-dependent expression profiles and that IRS1 is required for spine maturation, demonstrating a novel role for IRS1 in synaptic plasticity.

Differential role of interleukin-1ß in neuroinflammation-induced impairment of spatial and nonspatial memory in hyperammonemic rats.

Activated microglia and increased brain IL-1ß play a main role in cognitive impairment in much pathology. We studied the role of IL-1ß in neuroinflammation-induced impairment of the following different types of learning and memory: novel object recognition (NOR), novel object location (NOL), spatial learning, reference memory (RM), and working memory (WM). All these processes are impaired in hyperammonemic rats. We assessed which of these types of learning and memory are restored by blocking the IL-1 receptor in vivo in hyperammonemic rats and the possible mechanisms involved. Blocking the IL-1 receptor reversed microglial activation in the hippocampus, perirhinal cortex, and prefrontal cortex but not in the postrhinal cortex. This was associated with the restoration of NOR and WM but not of tasks involving a spatial component (NOL and RM). This suggests that IL-1ß would be involved in neuroinflammation-induced nonspatial memory impairment, whereas spatial memory impairment would be IL-1ß-independent and would be mediated by other proinflammatory factors.-Taoro-González, L., Cabrera-Pastor, A., Sancho-Alonso, M., Arenas, Y. M., Meseguer-Estornell, F., Balzano, T., ElMlili, N., Felipo, V. Differential role of interleukin-1ß in neuroinflammation-induced impairment of spatial and nonspatial memory in hyperammonemic rats.

Infliximab reduces peripheral inflammation, neuroinflammation, and extracellular GABA in the cerebellum and improves learning and motor coordination in rats with hepatic encephalopathy.

BACKGROUND: Peripheral inflammation contributes to the neurological alterations in hepatic encephalopathy (HE). Neuroinflammation and altered GABAergic neurotransmission mediate cognitive and motor alterations in rats with HE. It remains unclear (a) if neuroinflammation and neurological impairment in HE are a consequence of peripheral inflammation and (b) how neuroinflammation impairs GABAergic neurotransmission. The aims were to assess in rats with HE whether reducing peripheral inflammation with anti-TNF-α (1) prevents cognitive impairment and motor in-coordination, (2) normalizes neuroinflammation and extracellular GABA in the cerebellum and also (3) advances the understanding of mechanisms linking neuroinflammation and increased extracellular GABA. METHODS: Rats with HE due to portacaval shunt (PCS) were treated with infliximab. Astrocytes and microglia activation and TNF-α and IL-1ß were analyzed by immunohistochemistry. Membrane expression of the GABA transporters GAT-3 and GAT-1 was analyzed by cross-linking with BS3. Extracellular GABA was analyzed by microdialysis. Motor coordination was tested using the beam walking and learning ability using the Y maze task. RESULTS: PCS rats show peripheral inflammation, activated astrocytes, and microglia and increased levels of TNF-α and IL-1ß. Membrane expression of GAT-3 and extracellular GABA are increased, leading to impaired motor coordination and learning ability. Infliximab reduces peripheral inflammation, microglia, and astrocyte activation and neuroinflammation and normalizes GABAergic neurotransmission, motor coordination, and learning ability. CONCLUSIONS: Neuroinflammation is associated with altered GABAergic neurotransmission and increased GAT-3 membrane expression and extracellular GABA (a); peripheral inflammation is a main contributor to the impairment of motor coordination and of the ability to learn the Y maze task in PCS rats (b); and reducing peripheral inflammation using safe procedures could be a new therapeutic approach to improve cognitive and motor function in patients with HE

Septal projections to nucleus incertus in the rat: bidirectional pathways for modulation of hippocampal function.

Projections from the nucleus incertus (NI) to the septum have been implicated in the modulation of hippocampal theta rhythm. In this study we describe a previously uncharacterized projection from the septum to the NI, which may provide feedback modulation of the ascending circuitry. Fluorogold injections into the NI resulted in retrograde labeling in the septum that was concentrated in the horizontal diagonal band and areas of the posterior septum including the septofimbrial and triangular septal nuclei. Double-immunofluorescent staining indicated that the majority of NI-projecting septal neurons were calretinin-positive and some were parvalbumin-, calbindin-, or glutamic acid decarboxylase (GAD)-67-positive. Choline acetyltransferase-positive neurons were Fluorogold-negative. Injection of anterograde tracers into medial septum, or triangular septal and septofimbrial nuclei, revealed fibers descending to the supramammillary nucleus, median raphe, and the NI. These anterogradely labeled varicosities displayed synaptophysin immunoreactivity, indicating septal inputs form synapses on NI neurons. Anterograde tracer also colocalized with GAD-67-positive puncta in labeled fibers, which in some cases made close synaptic contact with GAD-67-labeled NI neurons. These data provide evidence for the existence of an inhibitory descending projection from medial and posterior septum to the NI that provides a "feedback loop" to modulate the comparatively more dense ascending NI projections to medial septum and hippocampus. Neural processes and associated behaviors activated or modulated by changes in hippocampal theta rhythm may depend on reciprocal connections between ascending and descending pathways rather than on unidirectional regulation via the medial septum.

Early biomarkers of acute kidney failure after heart angiography or heart surgery in patients with acute coronary syndrome or acute heart failure.

BACKGROUND: Acute kidney injury (AKI) is a common complication in cardiac surgery and coronary angiography, which worsens patients' prognosis. The diagnosis is based on the increase in serum creatinine, which is delayed. It is necessary to identify and validate new biomarkers that allow for early and effective interventions. AIMS: To assess the sensitivity and specificity of neutrophil gelatinase-associated lipocalin in urine (uNGAL), interleukin-18 (IL-18) in urine and cystatin C in serum for the early detection of AKI in patients with acute coronary syndrome or heart failure, and who underwent cardiac surgery or catheterization. METHODS: The study included 135 patients admitted to the intensive care unit for acute coronary syndrome or heart failure due to coronary or valvular pathology and who underwent coronary angiography or cardiac bypass surgery or valvular replacement. The biomarkers were determined 12 hours after surgery and serum creatinine was monitored during the next six days for the diagnosis of AKI. RESULTS: The area under the ROC curve (AUC) for NGAL was 0.983, and for cystatin C and IL-18 the AUCs were 0.869 and 0.727, respectively. At a cut-off of 31.9 ng/ml for uNGAL the sensitivity was 100% and the specificity was 91%. CONCLUSIONS: uNGAL is an early marker of AKI in patients with acute coronary syndrome or heart failure and undergoing cardiac surgery and coronary angiography, with a higher predictive value than cystatin C or IL-18.

3-nitro-tyrosine as a peripheral biomarker of minimal hepatic encephalopathy in patients with liver cirrhosis.

OBJECTIVES: Between 30 and 50% of the cirrhotic patients who do not show symptoms of clinical hepatic encephalopathy (HE) present minimal hepatic encephalopathy (MHE), with mild cognitive impairment. MHE impairs the quality of life, increases the risk of suffering accidents, predicts the appearance of clinical HE, and is associated with shortened lifespan. Early detection of MHE would be very useful. The "gold standard" for MHE diagnosis is the psychometric hepatic encephalopathy score (PHES). However, it is time consuming and needs adjusting for age and educational level. It would be very useful to have some blood biomarker reflecting the presence of MHE in cirrhotic patients. The aim of this work was to identify serum molecules useful as biomarkers for MHE. METHODS: We measured in 63 controls, 43 cirrhotic patients without MHE, and 44 patients with MHE, from Hospital Clinico de Valencia, serum levels of different amino acids, cyclic guanosine monophosphate (cGMP), nitrites+nitrates, and 3-nitrotyrosine. We analyzed for each parameter its diagnostic accuracy as an indicator of MHE, as assessed using the PHES. RESULTS: These studies supported that 3-nitro-tyrosine is a good marker for MHE. To validate its utility as a biomarker for MHE, we analyzed in a second cohort of 44 cirrhotic patients without MHE and 18 patients with MHE, from Hospital Arnau de Vilanova, serum levels of 3-nitro-tyrosine, methionine, and citrulline. Citrulline (173±17%), methionine (173±16%), and 3-nitro-tyrosine (857±92%) were increased in sera from patients with MHE when compared with those without MHE. The receiver operating characteristic (ROC) curve analysis of 3-nitro-tyrosine for the diagnosis of MHE in the first cohort showed an area under the curve (AUC) value of 0.96 (95% confidence interval 0.93-0.99). At the cutoff of 14 nM, the specificity was 93%, sensitivity 89%, and positive and negative predictive values were both 91%. When the same cutoff was applied to the second cohort, the specificity was 83% and sensitivity was 94%. The positive and negative predictive values were 70 and 97%, respectively. CONCLUSIONS: This pilot study, to be validated in a larger cohort, shows that determination of 3-nitro-tyrosine in serum, which is easy and not time consuming, is useful to identify patients with MHE, with good sensitivity, specificity, and positive and negative predictive values.

Cyclic GMP pathways in hepatic encephalopathy. Neurological and therapeutic implications.

Cyclic GMP (cGMP) modulates important cerebral processes including some forms of learning and memory. cGMP pathways are strongly altered in hyperammonemia and hepatic encephalopathy (HE). Patients with liver cirrhosis show reduced intracellular cGMP in lymphocytes, increased cGMP in plasma and increased activation of soluble guanylate cyclase by nitric oxide (NO) in lymphocytes, which correlates with minimal HE assessed by psychometric tests. Activation of soluble guanylate cyclase by NO is also increased in cerebral cortex, but reduced in cerebellum, from patients who died with HE. This opposite alteration is reproduced in vivo in rats with chronic hyperammonemia or HE. A main pathway modulating cGMP levels in brain is the glutamate-NO-cGMP pathway. The function of this pathway is impaired both in cerebellum and cortex of rats with hyperammonemia or HE. Impairment of this pathway is responsible for reduced ability to learn some types of tasks. Restoring the pathway and cGMP levels in brain restores learning ability. This may be achieved by administering phosphodiesterase inhibitors (zaprinast, sildenafil), cGMP, anti-inflammatories (ibuprofen) or antagonists of GABAA receptors (bicuculline). These data support that increasing cGMP by safe pharmacological means may be a new therapeutic approach to improve cognitive function in patients with minimal or clinical HE.

Chronic hyperammonemia induces tonic activation of NMDA receptors in cerebellum.

Reduced function of the glutamate--nitric oxide (NO)--cGMP pathway is responsible for some cognitive alterations in rats with hyperammonemia and hepatic encephalopathy. Hyperammonemia impairs the pathway in cerebellum by increasing neuronal nitric oxide synthase (nNOS) phosphorylation in Ser847 by calcium-calmodulin-dependent protein kinase II (CaMKII), reducing nNOS activity, and by reducing nNOS amount in synaptic membranes, which reduces its activation following NMDA receptors activation. The reason for increased CaMKII activity in hyperammonemia remains unknown. We hypothesized that it would be as a result of increased tonic activation of NMDA receptors. The aims of this work were to assess: (i) whether tonic NMDA activation receptors is increased in cerebellum in chronic hyperammonemia in vivo; and (ii) whether this tonic activation is responsible for increased CaMKII activity and reduced activity of nNOS and of the glutamate--NO--cGMP pathway. Blocking NMDA receptors with MK-801 increases cGMP and NO metabolites in cerebellum in vivo and in slices from hyperammonemic rats. This is because of reduced phosphorylation and activity of CaMKII, leading to normalization of nNOS phosphorylation and activity. MK-801 also increases nNOS in synaptic membranes and reduces it in cytosol. This indicates that hyperammonemia increases tonic activation of NMDA receptors leading to reduced activity of nNOS and of the glutamate--NO--cGMP pathway.

Role of NMDA receptors in acute liver failure and ammonia toxicity: therapeutical implications.

Acute liver failure (ALF) may lead to rapid death unless the patients receive a liver for transplantation. However, the number of livers available is not enough and a number of patients die before a suitable liver is available for transplantation. The liver has a high capacity for regeneration which may allow complete recovery even in patients with severe liver failure. It would be therefore very useful to have procedures to prevent or delay the mechanisms by which ALF leads to death. These mechanisms are no well understood. Progression of ALF leads to multi-organ failure, systemic inflammatory response, hepatic encephalopathy, cerebral oedema and increased intracranial pressure, which seem the most important immediate causes of mortality in patients with ALF. A main contributor to these events is hyperammonemia, due to impaired ammonia detoxification in the liver. Acute hyperammonemia per se leads to death, which is mediated by activation of the NMDA type of glutamate receptors in brain and may be prevented by antagonists blocking these receptors. Acute liver failure also leads to hyperammonemia and excessive activation of NMDA receptors in brain which contributes to ALF-induced death. Sustained blocking of NMDA receptors by continuous administration of the antagonists MK-801 or memantine increases about twice the survival time of rats with severe ALF due to injection of 2.5g/kg of galactosamine. In rats with milder ALF due to injection of 1.5g/kg of galactosamine, blocking NMDA receptors increases the percentage of surviving rats from 23% to 62% and increases about twice the survival time of the rats which die. These data strongly support that blocking NMDA receptors would improve survival of patients with ALF, either by allowing more time for liver regeneration or to get a liver suitable for transplantation.