Effect of age, stress and protein supply on plasma amino acids during continuous enteral nutrition; a pragmatic study in rats.

BACKGROUND & AIMS: As life expectancy increases, an increasing older population may require surgery with perioperative nutritional management. While little is known about the combined effect of age and stress on amino acid metabolism during enteral nutrition, we hypothesized that blood amino acid bioavailability may be influenced not only by the characteristics of the ingested protein but also by intestinal ageing and splanchnic sequestration of amino acids. Plasma amino acid kinetics were thus evaluated in aged and adult rats receiving continuous enteral nutrition before and after standardized surgical stress. METHODS: Sixteen 5-month-old and sixteen 21-month-old male rats were used. After a gastrostomy, the insertion of a jugular vein catheter and a one-week recovery, the animals were enterally fed with commercially available formulas containing whole milk proteins or a whey hydrolysate for 24 h before (healthy state) and 18 h after a standardized laparotomy (surgical stress). Data were analyzed by 3-factor ANOVA. RESULTS: In all rats, enteral nutrition was associated with a marked increase in plasma alanine, threonine, lysine and proline (+50 to +150 µmol/L; p < 0.001), and a decrease in glycine (≈-80 µmol/L; p < 0.01). For most amino acids, their availability depended first on the amino acid composition of each protein and second on surgical stress. Aging was only associated with higher tyrosine and threonine availability (p < 0.001). There was only limited statistical interaction between age and surgical stress. CONCLUSION: In rats, plasma amino acid availability during continuous enteral nutrition is determined by the nature of the protein source and the occurrence of stress. The effects of aging on plasma amino acid availability seem very limited. Commonly used formulas therefore appear to be as suitable for elderly patients as for adult patients.

Effect of aging on the availability of amino acids from an immune-enhancing diet (IED) after a surgical stress in rats.

BACKGROUND & AIMS: Dietary amino acid (AA) requirements increase after a surgical stress while the systemic AA availability from the diet decreases with age, due to splanchnic sequestration. While immune-enhancing diets (IEDs) have been recommended for the nutritional management of surgical patients, the systemic bioavailability of their AA supply has not been evaluated in elderly surgical patients. This was determined in surgically-stressed IED-fed aged rats. METHODS: Thirty-four 5-month- or 21-month-old male Sprague-Dawley rats were used. After a gastrostomy and placement of a jugular vein catheter and a one-week recovery period, the animals underwent two 24 h-enteral feedings with an arginine-enriched IED (Impact®, Nestlé Health Science) before (healthy state) and 18 h after a standardized laparotomy, used as a model of surgical stress. During enteral nutrition, blood samples were repeatedly collected to measure plasma AA bioavailability (incremental areas under the curve) at 2, 5 and 24 h. Surgical stress was evaluated from urinary catecholamines and plasma protein profile. RESULTS: Whatever the age or stress situation, IED feeding was associated with decreased plasma glycine and increased alanine, proline and arginine. Aging was mainly associated with a delayed plasma AA accumulation in the first hours after the initiation of enteral nutrition. Stress was associated with higher plasma arginine increase and lower histidine, methionine, phenylalanine and tyrosine accumulation. Age and stress interactions seem limited. CONCLUSIONS: AA bioavailability from an arginine-enriched IED seems to be maintained whatever age and stress situation. Aging appears to be mainly associated with a delay in plasma AA accumulation probably related to age-associated splanchnic sequestration of AAs. Additional effects of surgical stress per se seem limited.

Estimation of glomerular filtration rate in cancer patients with abnormal body composition and relation with carboplatin toxicity.

PURPOSE: Carboplatin clearance is correlated with glomerular filtration rate (GFR) and usually estimated with creatinine clearance using Cockcroft-Gault (CG) formula. Because plasma creatinine level is highly correlated with muscle mass, we hypothesized that an abnormal body composition with a low lean body mass (LBM) percentage [(LBM/weight) × 100] may result in inadequate carboplatin dosing. Serum cystatin C is an alternative marker of GFR, not affected by muscle mass. We aimed to investigate the influence of total LBM and LBM percentage on GFR calculation, using creatinine (CrCl) or cystatin C (GFRcysC-creat) in cancer patients. METHODS: Pretreatment serum creatinine and cystatin C were prospectively measured in consecutive patients. CrCl (CG formula), GFRcysC-creat (CKD-EPI creatinine-cystatin equation), and LBM (CT scan) were calculated. Severe thrombocytopenia post-carboplatin were analyzed. RESULTS: In 131 patients without renal insufficiency, LBM was correlated with creatinine (r = 0.30, p < 0.005) but not with cystatin C (r = -0.07, p = 0.43). In patients with the lowest LBM percentage, the CrCl was significantly higher than GFRcysC-creat indicating an overestimation of GFR with creatinine (p = 0.0004). In 24 patients treated with carboplatin AUC 5 (mg/ml min) ± paclitaxel, the risk of severe thrombocytopenia was associated with lower LBM percentage (p = 0.0002) and higher CrCl/GFRcysC-creat ratio (p = 0.006). By ROC analysis, the CrCl/GFRcysC-creat ratio threshold predicting severe thrombocytopenia was 1.23. CONCLUSIONS: A low LBM percentage increases the risk of inadequate GFR calculation by CG formula, and carboplatin overdosage with severe thrombocytopenia. High CrCl/GFRcysC-creat ratio allows the identification of these patients.

Effect of piracetam on polyphosphoinositide metabolism, cytosolic calcium release, and oxidative burst in human polymorphonuclear cells: interaction with fMLP-induced stimulation.

We investigated the action of piracetam on human polymorphonuclear leukocyte (PMN) responsiveness in vitro. We first studied phosphoinositide metabolism and calcium release with and without fMLP (formyl-methionyl-leucyl-phenylalanine) stimulation. Piracetam at concentrations from 10(-4) to 10(-2) M induced a slight increase in inositol 1,4,5-trisphosphate (IP3) release and phosphatidylinositol 4,5-bisphosphate (PIP2) breakdown. At concentrations above 10(-3) M, piracetam sensitized PMNs to subsequent stimulation by fMLP used at subliminal concentrations (10(-9) and 10(-8) M), inducing a significant increase in IP3 release and PIP2 breakdown similar to that obtained with cells stimulated by the highest effective concentrations of fMLP (10(-7) and 10(-6) M). In the same way, piracetam greatly enhanced calcium release induced by weak concentrations of fMLP. However, piracetam had no effect on oxidative metabolism. We then studied the binding of (3H)fMLP to the PMN membrane in the presence of various concentrations of piracetam. We were not able to demonstrate an obvious action of piracetam either on receptor recruitment or on receptor affinity to fMLP. The difference between the actions of piracetam on phosphoinositide metabolism and calcium release on the one hand and oxidative burst on the other could be explained by an uncoupling of the triggering and activating effects of piracetam on PMNs. The enhancement by piracetam of intracellular cyclic AMP levels rapidly induced termination of the PMN response and accounted for the lack of effect on superoxide production. Thus, piracetam was able to modulate human PMN reactivity and in particular to exert a "priming effect" (rather due to structural modifications of the membrane), which might be of importance in infectious episodes given the absence of deleterious actions such as oxygen free radical production leading to tissue injury.

Dermaseptin, a peptide antibiotic, stimulates microbicidal activities of polymorphonuclear leukocytes.

Dermaseptin (DRs S1), a 34-amino acid residue cationic antimicrobial peptide was studied for its effects on the production of reactive oxygen species (respiratory burst) and exocytosis of polymorphonuclear leukocytes (PMN). Treatment of PMN with DRs S1 (10-100 nM) stimulated significant production of reactive oxygen species (approximately a 2-fold increase relative to control) and release of myeloperoxidase. In addition, low DRs S1 concentrations (1-10 nM) primed the stimulation of respiratory burst induced by zymosan particles. In contrast to the native peptide, a dermaseptin fragment without either the COOH-terminal (DRs 1-10) or NH2 terminal (DRs 16-34) portion was inactive. The DRs S1-induced respiratory burst was inhibited by a selective protein kinase C inhibitor, GF 109203X, and was associated with early signalling events such as a rapid and transient elevation of cytosolic-free calcium concentration and phospholipase D activity. These data provide the first evidence of stimulating and priming properties of a peptide antibiotic on microbicidal activities of neutrophils, suggesting a potential role of dermaseptin in modulating host-defense mechanisms.

Liver metastases: safety and efficacy of detection with superparamagnetic iron oxide in MR imaging.

PURPOSE: To evaluate the clinical and biologic safety of superparamagnetic iron oxide (SPIO) as a contrast agent in magnetic resonance (MR) imaging and to assess its efficacy in the detection of liver metastases. MATERIALS AND METHODS: Twenty adults with liver metastases underwent MR imaging at 1.5 T before and 1 hour after infusion of SPIO. Four spin-echo (SE) sequences and one gradient-echo (GRE) sequence were used. RESULTS: There were no adverse reactions. Alterations in serum protein, serum iron, transferrin, and ferritin levels and transferrin saturation coefficient were statistically significant. The mean tumor-to-liver contrast-to-noise ratio (C/N) increased markedly with all sequences. The best postcontrast tumor-to-liver contrast was obtained with the GRE sequence (repetition time msec/echo time msec = 300/15). The mean number of apparent lesions detected after administration of SPIO increased by 12 with the proton-density-weighted SE sequences (800/30 and 2,500/30), four with the T2-weighted SE sequence (2,500/90), and seven with the GRE sequence (300/15). CONCLUSION: SPIO is safe, increases tumor-to-liver C/Ns with some sequences, and improves the detection of liver metastases.

[Surgery of primary hyperparathyroidism. Contribution of the peroperative assay of urinary cyclic AMP]. / Chirurgie de l'hyperparathyroïdie primaire. Apport du dosage peropératoire de l'AMP cyclique urinaire.

The increase of nephrogenic cyclic AMP is an excellent index of parathyroid hypersecretion. A successful treatment of primary hyperparathyroidism results in a rapid fall in nephrogenic cAMP. In a series of 24 patients with proven primary hyperparathyroidism (hyperplasia 3, adenoma 21) and 2 patients with suspected hyperparathyroidism, the success of surgical excision was evaluated by measuring the urinary cAMP/urinary creatinine ratio (R), which in the absence of renal impairment, is proportional to the level of nephrogenic cAMP. Sequential assays of urinary cAMP and creatinine were performed during surgery; laboratory results were available within less than one hour. Among 22 patients with elevated baseline value or R, R became normal in 18 and decreased by more than 50% in 3; these findings suggested that the operation would be successful. In 1 case, R was not measured as the patient had impaired renal function. In another patient with normal baseline value of R, R did not significantly decrease after excision. Surgery failed in 1 patient, although the high value of R at the end of the operation should have prompted us to continue. Finally, in 2 patients the diagnosis was erroneous since R was lower than 0.5 as in controls. Surgeons, therefore, now have a reliable biochemical method at their disposal, but its use will be limited by its cost and complexity.

Action of a polysaccharide fraction of Haemophilus influenzae lipopolysaccharide on macrophage: implication of receptor for mannosyl-polysaccharides.

A polysaccharide fraction (PS) was separated by mild hydrolysis from Haemophilus influenzae lipopolysaccharide. This preparation contained glycosyl-galactosyl, rhamnosyl, glucosaminyl and mannosyl residues (molar ratio: 4-1-1-2-2). It was nontoxic and immunogenic and consisted of at least one stable molecular group (fraction A; MW approximately equal to 10(6)) and an association of aggregated units (fraction B;MW approximately equal to 10(4)). This study evaluated the capacity of phagocytosis and quantitative nitroblue-tetrazolium reduction of mouse macrophages in presence of these polysaccharide fractions. After a 24-h incubation period, PS and fraction A, at 1 mg/ml, increased both phagocytosis and reduction potential of mouse peritoneal macrophages by 100%. In contrast, 1-h incubation with PS or fraction A induced a decrease of 50% in phagocytosis but no modification of NBT reduction. An identical incubation with various sugars showed that only mannosyl polymers could significantly decrease this phagocytic process. As in the case of toxic lipopolysaccharides, macrophages responded to a nontoxic preparation obtained from an endotoxin. We confirmed the role of mannosyl residues in recognition of macrophage binding receptors. Moreover, we suggest that this mannose binding ability was dependent on dose, aggregation state and molecular weight of the preparation.U

[A colorimetric method for the evaluation of phagocytosis by mouse peritoneal macrophages (author's transl)]. / Technique colorimétrique d'évaluation de l'activité phagocytaire des macrophages péritonéaux de souris.

In this study, a technique for the evaluation of circulating leukocyte phagocytosis has been adapted to mouse peritoneal macrophages. This quantitative determination was performed by the spectrophotometric measurement of the reduced nitroblue tetrazolium (NBT) fixed on bacteria or latex spherules. Capacity of phagocytosis was thus correlated with the intensity of the NBT intracellular reduction by macrophages. This method is technically simple and requires no expensive materials. The phagocytosis of latex did not significantly differ, neither in the presence of autologous or heterologous serum (X +/- G = 0.100 +/- 0.014/2.5 X 10(6) cells) nor in the absence of serum (X +/- G = 0.088 +/- 0.007/2.5 X 10(6) cells). The use of macrophages suspended in the culture medium highly decreased the phagocytic activity (X +/- G = 0.021 +/- 0.002/2.5 X 10(6) cells) and confirmed thus the role played by the support in endocytosis. A specific antiserum weakly enhanced the phagocytic process for Escherichia coli. The mean values with and without serum were 0.065 +/- 0.005/2.5 X 10(6) cells and 0.050 +/- 0.005, respectively. Heating of the serum (56 degrees C, 30 min) and inhibition of both complement activation pathways by EDTA showed that complement plays the major role in this weak enhancement of bacterial phagocytosis by peritoneal mouse macrophages. Bacterial phagocytic stimulation of macrophages was not induced by addition of CA+++ or Mg++ into the culture medium.