Carmen Montiel

Predictive Value of Nuclear Factor κB Activity and Plasma Cytokine Levels in Patients with Sepsis

ABSTRACT The relationship between fluctuating cytokine concentrations in plasma and the outcome of sepsis is complex. We postulated that early measurement of the activation of nuclear factor κB (NF-κB), a transcriptional regulatory protein involved in proinflammatory cytokine expression, may help to predict the outcome of sepsis. We determined NF-κB activation in peripheral blood mononuclear cells of 34 patients with severe sepsis (23 survivors and 11 nonsurvivors) and serial concentrations of inflammatory cytokines (interleukin-6, interleukin-1, and tumor necrosis factor) and various endogenous antagonists in plasma. NF-κB activity was significantly higher in nonsurvivors and correlated strongly with the severity of illness (APACHE II score), although neither was related to the cytokine levels. Apart from NF-κB activity, the interleukin-1 receptor antagonist was the only cytokine tested whose level in plasma was of value in predicting mortality by logistic regression analysis. These results underscore the prognostic value of early measurement of NF-κB activity in patients with severe sepsis.

Relationship of Plasma Leptin to Plasma Cytokines and Human Survival in Sepsis and Septic Shock

Leptin production is increased in rodents by administration of endotoxin or cytokines. To investigate whether circulating leptin is related to cytokine release and survival in human sepsis, plasma concentrations of leptin, interleukin (IL)-6, IL-1beta, tumor necrosis factor (TNF)-alpha, soluble TNF receptor type I, IL-1 receptor antagonist (IL-1ra), and the inflammatory modulator IL-10 were measured as soon as severe sepsis (n=28) or septic shock (n=14) developed and every 6 h for 24 h. Patients with sepsis or septic shock had leptin concentrations 2.3- and 4.2-fold greater, respectively, than the control group. There was an independent association for leptin with IL-1ra and IL-10 in both patient groups. By discriminant analysis, leptin and IL-6 were independent predictors of death. These findings suggest that increases in leptin levels may be a host defense mechanism during sepsis.

Changes in the intracellular homocysteine and glutathione content associated with aging.

Since moderate hyperhomocysteinemia is an independent risk factor for vascular disease by mean of its oxidant effect and glutathione plays a main role as intracellular redox-regulating agent, we have studied for the first time the total intracellular content of homocysteine in aging. Plasma homocysteine concentration, total intracellular and plasma glutathione, and other related thiol compounds such as cysteine and the glutathione catabolite cysteinglycine were also studied. Forty three healthy elderly subjects and twenty seven healthy young ones were studied. The total intracellular peripheral blood mononuclear cell content was higher for homocysteine, cysteine and cysteinglycine, whereas that of the total glutathione was greatly decreased in elderly people with respect to young ones. Elderly subjects showed significantly higher levels than young ones of total plasma homocysteine and cysteinglycine, but not cysteine, whereas total plasma glutathione levels were increased. In addition, elderly subjects showed significantly decreased plasma vitamin E levels and increased concentrations of serum lipid peroxides measured as TBARS (reaction product of malondialdehyde with thiobarbituric acid). The intracellular glutathione content presented significantly negative correlation with serum TBARS, and intracellular and plasma homocysteine levels. These findings show an increase of homocysteine synthesis associated with aging, which in turn can produce an augmented oxidant effect on endothelium, and an impaired intracellular antioxidant capacity leading to an enhanced lipid peroxidation and decreased total intracellular glutathione content.

The novel Na+/Ca2+ exchange inhibitor KB‐R7943 also blocks native and expressed neuronal nicotinic receptors

We studied the effects of the novel Na+/Ca2+ exchange inhibitor KB‐R7943, 2‐[2‐[4‐(4‐nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulphonate, on the native nicotinic receptors present at the bovine adrenal chromaffin cells, as well as on rat brain α3β4 and α7 nicotinic acetylcholine receptors (AChRs) expressed in Xenopus oocytes. As expected, KB‐R7943 blocked the Na+‐gradient dependent 45Ca2+ uptake into chromaffin cells (IC50 of 5.5 μM); but in addition, the compound also inhibited the 45Ca2+ entry and the increase of cytosolic Ca2+ concentration, [Ca2+]c, stimulated by 5 s pulses of ACh (IC50 of 6.5 and 1.7 μM, respectively). In oocytes expressing α3β4 and α7 nicotinic AChRs, voltage‐clamped at −60 mV, inward currents elicited by 1 s pulses of 100 μM ACh (IACh) were blocked by KB‐R7943 with an IC50 of 0.4 μM and a Hill coefficient of 0.9. Blockade of α3β4 currents by KB‐R7943 was noncompetitive; moreover, the blocker (0.3 μM) became more active as the ACh concentration increased (34 versus 66% blockade at 30 μM and 1 mM ACh, respectively). Inhibition of α3β4 currents by 0.3 μM KB‐R7943 was more pronounced at hyperpolarized potentials. If given within the ACh pulse (10 μM), the inhibition amounted to 33, 64 and 80% in oocytes voltage‐clamped at −40, −60 and −100 mV, respectively. The onset of blockade was faster and the recovery slower at −100 mV; the reverse was true at −40 mV. In conclusion, KB‐R7943 is a potent blocker of nicotinic AChRs; moreover, it displays many features of an open‐channel blocker at the rat brain α3β4 AChR. These results should be considered when KB‐R7943 is to be used to study Ca2+ homeostasis in cells expressing nicotinic AChRs and the Na+/Ca2+ exchanger.

Interleukin-1β Enhances GABAA Receptor Cell-surface Expression by a Phosphatidylinositol 3-Kinase/Akt Pathway RELEVANCE TO SEPSIS-ASSOCIATED ENCEPHALOPATHY

Sepsis-associated encephalopathy (SAE) is a frequent but poorly understood neurological complication in sepsis that negatively influences survival. Here we present clinical and experimental evidence that this brain dysfunction may be related to altered neurotransmission produced by inflammatory mediators. Compared with septic patients, SAE patients had higher interleukin-1β (IL-1β) plasma levels; interestingly, these levels decreased once the encephalopathy was resolved. A putative IL-1β effect on type A γ-aminobutyric acid receptors (GABAARs), which mediate fast synaptic transmission in most cerebral inhibitory synapses in mammals, was investigated in cultured hippocampal neurons and in Xenopus oocytes expressing native or foreign rat brain GABAARs, respectively. Confocal images in both cell types revealed that IL-1β increases recruitment of GABAARs to the cell surface. Moreover, brief applications of IL-1β to voltage-clamped oocytes yielded a delayed potentiation of the GABA-elicited chloride currents (IGABA); this effect was suppressed by IL-1ra, the natural IL-1 receptor (IL-1RI) antagonist. Western blot analysis combined with IGABA recording and confocal images of GABAA Rs in oocytes showed that IL-1β stimulates the IL-1RI-dependent phosphatidylinositol 3-kinase activation and the consequent facilitation of phospho-Akt-mediated insertion of GABAARs into the cell surface. The interruption of this signaling pathway by specific phosphatidylinositol 3-kinase or Akt inhibitors suppresses the cytokine-mediated effects on GABAAR, whereas activation of the conditionally active form of Akt1 (myr-Akt1.ER*) with 4-hydroxytamoxifen reproduces the effects. These findings point to a previously unrecognized signaling pathway that connects IL-1β with increased “GABAergic tone.” We propose that through this mechanism IL-1β might alter synaptic strength at central GABAergic synapses and so contribute to the cognitive dysfunction observed in SAE.

Function of partially duplicated human α77 nicotinic receptor subunit CHRFAM7A gene: potential implications for the cholinergic anti-inflammatory response.

The neuronal α7 nicotinic receptor subunit gene (CHRNA7) is partially duplicated in the human genome forming a hybrid gene (CHRFAM7A) with the novel FAM7A gene. The hybrid gene transcript, dupα7, has been identified in brain, immune cells, and the HL-60 cell line, although its translation and function are still unknown. In this study, dupα7 cDNA has been cloned and expressed in GH4C1 cells and Xenopus oocytes to study the pattern and functional role of the expressed protein. Our results reveal that dupα7 transcript was natively translated in HL-60 cells and heterologously expressed in GH4C1 cells and oocytes. Injection of dupα7 mRNA into oocytes failed to generate functional receptors, but when co-injected with α7 mRNA at α7/dupα7 ratios of 5:1, 2:1, 1:1, 1:5, and 1:10, it reduced the nicotine-elicited α7 current generated in control oocytes (α7 alone) by 26, 53, 75, 93, and 94%, respectively. This effect is mainly due to a reduction in the number of functional α7 receptors reaching the oocyte membrane, as deduced from α-bungarotoxin binding and fluorescent confocal assays. Two additional findings open the possibility that the dominant negative effect of dupα7 on α7 receptor activity observed in vitro could be extrapolated to in vivo situations. (i) Compared with α7 mRNA, basal dupα7 mRNA levels are substantial in human cerebral cortex and higher in macrophages. (ii) dupα7 mRNA levels in macrophages are down-regulated by IL-1β, LPS, and nicotine. Thus, dupα7 could modulate α7 receptor-mediated synaptic transmission and cholinergic anti-inflammatory response.The neuronal α7 nicotinic receptor subunit gene (CHRNA7) is partially duplicated in the human genome forming a hybrid gene (CHRFAM7A) with the novel FAM7A gene. The hybrid gene transcript, dupα7, has been identified in brain, immune cells, and the HL-60 cell line, although its translation and function are still unknown. In this study, dupα7 cDNA has been cloned and expressed in GH4C1 cells and Xenopus oocytes to study the pattern and functional role of the expressed protein. Our results reveal that dupα7 transcript was natively translated in HL-60 cells and heterologously expressed in GH4C1 cells and oocytes. Injection of dupα7 mRNA into oocytes failed to generate functional receptors, but when co-injected with α7 mRNA at α7/dupα7 ratios of 5:1, 2:1, 1:1, 1:5, and 1:10, it reduced the nicotine-elicited α7 current generated in control oocytes (α7 alone) by 26, 53, 75, 93, and 94%, respectively. This effect is mainly due to a reduction in the number of functional α7 receptors reaching the oocyte membrane, as deduced from α-bungarotoxin binding and fluorescent confocal assays. Two additional findings open the possibility that the dominant negative effect of dupα7 on α7 receptor activity observed in vitro could be extrapolated to in vivo situations. (i) Compared with α7 mRNA, basal dupα7 mRNA levels are substantial in human cerebral cortex and higher in macrophages. (ii) dupα7 mRNA levels in macrophages are down-regulated by IL-1β, LPS, and nicotine. Thus, dupα7 could modulate α7 receptor-mediated synaptic transmission and cholinergic anti-inflammatory response.

A dopaminergic receptor modulates catecholamine release from the cat adrenal gland.

Nicotine evokes the release of catecholamines from perfused cat adrenal glands in a concentration‐dependent manner, the median effective concentration for nicotine being 5 microM. Two 2 min pulses of 5 microM‐nicotine, 40 min apart (S1 and S2) gave net catecholamine outputs of 7.64 and 3.55 micrograms/8 min, respectively. The ratio S2/S1 in control glands was 0.5. Increasing concentrations of apomorphine (1‐10 microM) markedly inhibited catecholamine release during the second nicotine pulse (S2). At 1 microM‐apomorphine, the release during S2 was significantly reduced to 16% of S1; with 10 microM‐apomorphine, the secretory response was reduced further to only 3% of S1, the ratio S2/S1 being 0.03. The presence of haloperidol, sulpiride or picobenzide (each 0.5 microM) during S2, completely reversed the inhibition of catecholamine release produced by apomorphine. Haloperidol itself increased the nicotinic secretory response during S2; so, while the ratio S2/S1 was 0.5 in control conditions, this ratio increased significantly to 0.95 if haloperidol (0.5 microM) was present during S2, suggesting that the presence of this dopaminergic antagonist removed a negative feed‐back mechanism that inhibits nicotine‐evoked catecholamine release. If present during S2, dopamine (1 microM) also markedly inhibited catecholamine release evoked by nicotine; this inhibition was again reversed by 0.5 microM‐haloperidol. Neither the opiate antagonist naloxone nor the alpha‐adrenoceptor blocking agent phentolamine (at concentrations of 0.5‐5 microM) affected the inhibition by apomorphine of the secretory response to nicotine. These data strongly suggest that the cat adrenal medulla chromaffin cell membrane contains a dopaminergic receptor which modulates the catecholamine secretory process triggered by stimulation of the nicotinic cholinoceptor. The fact that dopamine is released in measurable amounts, together with adrenaline and noradrenaline, from perfused cat adrenal glands in response to nicotinic stimulation (V. Ceña, unpublished results), favours a role for this dopaminergic receptor in modulating catecholamine release from the chromaffin cell.

Effects of collagenase on the release of [3H]‐noradrenaline from bovine cultured adrenal chromaffin cells

1 Bovine isolated adrenal chromaffin cells maintained in culture at 37°C for 1–7 days become polygonal and bipolar, with typical varicosity‐like extensions. Catecholamine levels and dopamine β‐hydroxylase activity decreased after 24–48 h of culture, but recovered to normal levels 3–7 days later. 2 Incubation of 1–7 day‐old cells in the presence of increasing concentrations of [3H]‐noradrenaline (3.91 to 125 nm) resulted in the retention by the cells of amounts of radioactivity directly proportional to the amine present in the media. One day‐old cells took up and retained only one third of the radioactivity found in 2–7 day‐old cells. 3 The addition of collagenase to cultured cells caused a decrease in the uptake of tritium. However, the enzyme treatment did not affect the amine taken up by the cell before collagenase treatment. 4 Release of tritium from cultured cells evoked by nicotine, acetylcholine (ACh) or 59 mm K+ was very poor in 24 h‐old cells; the secretory response to nicotine, ACh or K+ was dramatically increased after 2–7 days of culture. Bethanecol did not cause any secretory response. 5 When treated with collagenase, cultured cells which had recovered fully their secretory response, lost again the ability to release tritium evoked by ACh or nicotine. However, the responses to high K+, veratridine or ionophore X537A were not affected. The nicotinic response was recovered two days after collagenase treatmen. 6 The data suggest that the use of collagenase to disperse the adrenomedullary tissue during the isolation procedure might be responsible for the lost secretory response of young cultured chromaffin cells. Since collagenase specifically impairs the nicotinic cholinoceptor‐mediated catecholamine release, it seems likely that the enzyme is exerting its action on the ACh receptor complex. It is unlikely that either voltage‐sensitive Na+ or Ca2+ channels are affected by collagenase as the responses induced by high K+ or veratridine were unaffected by this enzyme.

Greater diversity than previously thought of chromaffin cell Ca2+ channels, derived from mRNA identification studies

Using reverse transcription followed by PCR amplification (RT‐PCR), we have identified multiple messenger RNAs encoding for the neuronal pore‐forming Ca2+ channel subunits α1A (P/Q channel), α1B (N channel), α1D (neuronal/endocrine L channel), α1E (R channel), α1G‐H (T channel) and α1S (skeletal muscle L channel) in bovine chromaffin cells. mRNAs for the auxiliary β2, β3, β4, α2/δ and γ2 subunits were also identified. In agreement with these molecular data, perforated patch‐clamp recordings of whole‐cell Ca2+ currents reveal the existence of functional R‐type Ca2+ channels in these cells that were previously undetected with other techniques. Our results provide a molecular frame for a much wider functional diversity of Ca2+ channels in chromaffin cells than that previously established using pharmacological and electrophysiological approaches.

A perforated patch-clamp study of calcium currents and exocytosis in chromaffin cells of wild-type and α1A knockout mice

Simultaneous recordings of inward whole‐cell Ca2+ channel currents (ICa) and increments of capacitance as an indication of exocytosis (ΔCm), were performed in voltage‐clamped single adrenal chromaffin cells from wild‐type and α1A subunit deficient mice, using the perforated‐patch configuration of the patch‐clamp technique. Using protocol #1 (one single Ca2+ channel blocker per cell), to dissect the components of ICa, L channels contributed 43%, N channels 35% and P/Q channels 30% to the total ICa of wild‐type cells. Using protocol #2 (cumulative sequential addition of 3 µm nifedipine, 1 µmω‐conotoxin GVIA, and 1 µmω‐agatoxin IVA), L, N and P/Q channels contributed 40%, 34% and 14%, respectively, to ICa; an R component of around 11% remained. In wild‐type mice the changes of ΔCm paralleled those of ICa. In α1A deficient mice the L component of ICa rose to 53% while the P/Q disappeared; the N and R components were similar. In these mice, ΔCm associated to N and R channels did not vary; however, the P/Q component was abolished while the L component increased by 20%. In conclusion, exocytosis was proportional to the relative density of each Ca2+ channel subtype, L, N, P/Q, R. Ablation of the α1A gene led to a loss of P/Q channel current and to a compensatory increase of L channel‐associated secretion; however, this compensation was not sufficient to maintain the overall exocytotic response, that was diminished by 35% in α1A‐deficient mice. This may be due to altered Ca2+ homeostasis in these mice, as compared to wild mouse chromaffin cells.