The consequences of sudden fluid shifts on body composition in critically ill patients.

INTRODUCTION: Estimation of body composition as fat-free mass (FFM) is subjected to many variations caused by injury and stress conditions in the intensive care unit (ICU). Body cell mass (BCM), the metabolically active part of FFM, is reported to be more specifically correlated to changes in nutritional status. Bedside estimation of BCM could help to provide more valuable markers of nutritional status and may promote understanding of metabolic consequences of energy deficit in the ICU patients. We aimed to quantify BCM, water compartments and FFM by methods usable at the bedside for evaluating the impact of sudden and massive fluid shifts on body composition in ICU patients. METHODS: We conducted a prospective experimental study over an 6 month-period in a 18-bed ICU. Body composition of 31 consecutive hemodynamically stable patients requiring acute renal replacement therapy for fluid overload (ultrafiltration ≥5% body weight) was investigated before and after the hemodialysis session. Intra-(ICW) and extracellular (ECW) water volumes were calculated from the raw values of the low- and high-frequency resistances measured by multi-frequency bioelectrical impedance. BCM was assessed by a calculated method recently developed for ICU patients. FFM was derived from BCM and ECW. RESULTS: Intradialytic weight loss was 3.8 ± 0.8 kg. Percentage changes of ECW (-7.99 ± 4.60%) and of ICW (-7.63 ± 5.11%) were similar, resulting ECW/ICW ratio constant (1.26 ± 0.20). The fall of FFM (-2.24 ± 1.56 kg, -4.43 ± 2.65%) was less pronounced than the decrease of ECW (P < 0.001) or ICW (P < 0.001). Intradialytic variation of BCM was clinically negligible (-0.38 ± 0.93 kg, -1.56 ± 3.94%) and was significantly less than FFM (P < 0.001). CONCLUSIONS: BCM estimation is less driven by sudden massive fluid shifts than FMM. Assessment of BCM should be preferred to FFM when severe hydration disturbances are present in ICU patients.

Assessment of body cell mass at bedside in critically ill patients.

Critical illness affects body composition profoundly, especially body cell mass (BCM). BCM loss reflects lean tissue wasting and could be a nutritional marker in critically ill patients. However, BCM assessment with usual isotopic or tracer methods is impractical in intensive care units (ICUs). We aimed to modelize the BCM of critically ill patients using variables available at bedside. Fat-free mass (FFM), bone mineral (Mo), and extracellular water (ECW) of 49 critically ill patients were measured prospectively by dual-energy X-ray absorptiometry and multifrequency bioimpedance. BCM was estimated according to the four-compartment cellular level: BCM = FFM - (ECW/0.98) - (0.73 × Mo). Variables that might influence the BCM were assessed, and multivariable analysis using fractional polynomials was conducted to determine the relations between BCM and these data. Bootstrap resampling was then used to estimate the most stable model predicting BCM. BCM was 22.7 ± 5.4 kg. The most frequent model included height (cm), leg circumference (cm), weight shift (Δ) between ICU admission and body composition assessment (kg), and trunk length (cm) as a linear function: BCM (kg) = 0.266 × height + 0.287 × leg circumference + 0.305 × Δweight - 0.406 × trunk length - 13.52. The fraction of variance explained by this model (adjusted r(2)) was 46%. Including bioelectrical impedance analysis variables in the model did not improve BCM prediction. In summary, our results suggest that BCM can be estimated at bedside, with an error lower than ±20% in 90% subjects, on the basis of static (height, trunk length), less stable (leg circumference), and dynamic biometric variables (Δweight) for critically ill patients.

Early ICU energy deficit is a risk factor for Staphylococcus aureus ventilator-associated pneumonia.

BACKGROUND: Caloric insufficiency during the first week of ICU stay has been associated with increased infection rates. The connection between specific pathogens and host nutritional status in the ICU is not well known. This study was undertaken to determine the impact of patients' early in-ICU energy balance on the pathogens responsible for ventilator-associated pneumonia (VAP). METHODS: In this prospective, observational, cohort study conducted in a teaching hospital ICU, energy balance (energy delivered - calculated resting energy expenditure) was compared according to the microbiologic results of the fiber-optic BAL cultures of 76 consecutive patients receiving acute prolonged (≥ 96 h) mechanical ventilation who developed VAP during their ICU stay. RESULTS: Among the 76 BAL cultures, 22 contained significant Staphylococcus aureus concentrations. The cumulated energy deficit of patients with S aureus VAP was greater than those with VAP caused by other pathogens (-10,275 ± 4,211 kcal vs -7,376 ± 4,013 kcal from ICU admission to day of BAL, P < .01). ICU admission, nutritional status, and conditions potentially limiting feeding did not differ significantly between the two groups. Patients with S aureus VAP had lower prescribed and delivered energy, causing higher energy deficits. Multivariate analysis identified energy deficit as being independently associated with S aureus VAP. More-severe energy deficit and higher rate of S aureus-positive BAL cultures (P = .01 comparing quartiles) were observed. CONCLUSIONS: Early ICU energy deficit is an independent determinant for acquiring S aureus VAP in patients on acute prolonged mechanical ventilation.

Alpha-synuclein overexpression in PC12 and chromaffin cells impairs catecholamine release by interfering with a late step in exocytosis.

Alpha-synuclein (alpha-syn), a protein implicated in Parkinson's disease pathogenesis, is a presynaptic protein suggested to regulate transmitter release. We explored how alpha-syn overexpression in PC12 and chromaffin cells, which exhibit low endogenous alpha-syn levels relative to neurons, affects catecholamine release. Overexpression of wild-type or A30P mutant alpha-syn in PC12 cell lines inhibited evoked catecholamine release without altering calcium threshold or cooperativity of release. Electron micrographs revealed that vesicular pools were not reduced but that, on the contrary, a marked accumulation of morphologically "docked" vesicles was apparent in the alpha-syn-overexpressing lines. We used amperometric recordings from chromaffin cells derived from mice that overexpress A30P or wild-type (WT) alpha-syn, as well as chromaffin cells from control and alpha-syn null mice, to determine whether the filling of vesicles with the transmitter was altered. The quantal size and shape characteristics of amperometric events were identical for all mouse lines, suggesting that overexpression of WT or mutant alpha-syn did not affect vesicular transmitter accumulation or the kinetics of vesicle fusion. The frequency and number of exocytotic events per stimulus, however, was lower for both WT and A30P alpha-syn-overexpressing cells. The alpha-syn-overexpressing cells exhibited reduced depression of evoked release in response to repeated stimuli, consistent with a smaller population of readily releasable vesicles. We conclude that alpha-syn overexpression inhibits a vesicle "priming" step, after secretory vesicle trafficking to "docking" sites but before calcium-dependent vesicle membrane fusion.

Dopaminergic neurons in rat ventral midbrain cultures undergo selective apoptosis and form inclusions, but do not up-regulate iHSP70, following proteasomal inhibition.

Dysfunction of the ubiquitin-dependent protein degradation system, either at the level of the proteasome itself, or at the level of ubiquitination, may play a role in the pathogenesis of Parkinson's disease (PD) and other related neurodegenerative disorders. We have employed a cellular model of this dysfunction in which lactacystin or epoxomicin, selective pharmacological inhibitors of the proteasome, are applied to primary cultures of embryonic rat ventral midbrain. Proteasomal inhibition with either agent led to apoptotic death specifically within phenotypically defined tyrosine hydroxylase (TH)-positive dopaminergic neurons, with little or no apoptotic death induced in GABAergic neurons. Inhibition of the proteasome also led to the formation of ubiquitin and alpha-synuclein-positive cytoplasmic inclusions in TH-positive and TH-negative neurons. Inclusions were observed in viable as well as apoptotic neurons, and required new or ongoing transcription. Tyrosine hydroxylase immunolabeling was often present within the inclusions. Such mislocalization may lead to dysfunction of dopamine biosynthesis. Interestingly, dopaminergic neurons, unlike other neurons within these cultures or cultured cortical neurons, failed to induce the chaperone Hsp70 in response to proteasomal inhibition. This failure may explain in part the increased sensitivity of these neurons to proteasomal inhibitors.

Regulation of alpha-synuclein by bFGF in cultured ventral midbrain dopaminergic neurons.

Alpha-synuclein is a neuronal protein that is implicated in the control of synaptic vesicle function and in Parkinson's disease (PD). Consequently, alterations of alpha-synuclein levels may play a role in neurotransmission and in PD pathogenesis. However, the factors that regulate alpha-synuclein levels are unknown. Growth factors mediate neurotrophic and plasticity effects in CNS neurons, and may play a role in disease states. Here we examine the regulation of alpha-synuclein levels in primary CNS neurons, with particular emphasis on dopaminergic neurons. E18 rat cortical neurons and dopaminergic neurons of E14 rat ventral midbrain showed an induction of alpha-synuclein protein levels with maturation in culture. Application of basic Fibroblast growth factor (bFGF) promoted alpha-synuclein expression selectively within dopaminergic, and not GABAergic or cortical neurons. This induction was blocked by actinomycin D, but not by inhibition of bFGF-induced glial proliferation. alpha-Synuclein levels were not altered by glial-derived neurotrophic factor (GDNF), or by apoptotic stimuli. We conclude that bFGF promotes alpha-synuclein expression in cultured ventral midbrain dopaminergic neurons through a direct transcriptional effect. These results suggest that distinct growth factors may thus mediate plasticity responses or influence disease states in ventral midbrain dopaminergic neurons.