Soo-Kyung Lim

Cytokine response to burn injury : relationship with protein metabolism

Plasma levels of interleukin 1 beta (IL-1 beta), tumor necrosis factor alpha (TNF alpha), interleukin 6 (IL-6), and markers of protein metabolism were determined in 12 burn patients throughout the healing period (day 2 to 21 post-injury) to determine the pattern of variations in plasma cytokine concentration. To establish the relationship between cytokine production and the nutritional status a wide range of severity standpoints (burn surface area ranging from 9% to 82%) was chosen. Interleukin 6 levels were increased in all patients throughout the study period; maximum concentrations (615 +/- 198 pg/mL) were reached on day 4 and correlated (p < 0.01) with the extent of burn injury. Tumor necrosis factor alpha levels were also elevated; they were significantly higher on day 7 in the patients who developed sepsis than in the other patients (67 +/- 21 pg/mL vs. 20 +/- 7 pg/mL; p < 0.05) but did not correlate with the extent of burn injury. Interleukin 1 beta was rarely detected. Cortisolemia on day 7 was inversely correlated with levels of TNF alpha but not with those of IL-6. Interleukin 6 levels correlated positively with protein turnover (phenylalaninemia) and catabolism (3-methylhistidine/creatinine ratio) and negatively with levels of fibronectin and transthyretin. Our data indicate that the systemic cytokine response to burn injury is mainly represented by IL-6. These data also support the hypothesis that IL-6 is a key mediator of the variations in protein metabolism following burn injury.

Independent and combined actions of interleukin-1β, tumor necrosis factor α, and glucagon on amino acid metabolism in the isolated perfused rat liver

Conflicting reports concerning the hepatic effects of interleukin-1β (IL-1β) and tumor necrosis factor α (TNFα) in the metabolic response to injury led us to investigate the influence of physiological concentrations of these cytokines on amino acid metabolism in the isolated perfused rat liver. IL-1β was ineffective at a concentration of 1 ng/mL, whereas TNFα (0.7 ng/mL) reduced the uptake of some of the main gluconeogenic amino acids (alanine, −55.3 ± 4.9 v −72.9 ± 13.7 nmol·min−1·g−1 in controls, P < .05) without affecting urea synthesis. TNFα also increased glucose uptake by 237% and inhibited that of free fatty acids (−1.6 ± 1.4 v −9.9 ± 6.7 nmol·min−1·g−1 in controls, P < .05). IL-1β and TNFα potentiated glucagon-induced total amino acid uptake by 56% and 87%, respectively. They also affected glucagon-activated gluconeogenesis, leading to an initial potentiation of glucose release. Thereafter, IL-1β inhibited glucagon action, leading to an hepatic uptake of glucose. These results indicate that (1) in the conditions of the study, IL-1β has no direct effect on hepatic amino acid exchanges and utilization; (2) TNFα, which exerted an inhibitory effect on these parameters, could be involved in the reduced amino acid exchanges during the end stage of sepsis; (3) the TNFα-induced increase in glucose uptake could be related to an inhibition of gluconeogenesis and/or to the activation of glucose utilization by Kupffer cells; (4) IL-1β and TNFα both potentiate the action of glucagon on hepatic amino acid uptake and utilization; and (5) complex interactions between Kupffer cells and hepatocytes on the one hand and between cytokines and hormones on the other hand could account for the differences in hepatic metabolism according to the stage of the response to injury.

TNF-α and IL-6 synergistically inhibit ketogenesis from fatty acids and α-ketoisocaproate in isolated rat hepatocytes

BACKGROUND: During sepsis, lipid metabolism is shunted toward triacylglycerol synthesis and hepatic lipogenesis. A decrease in ketogenesis from free fatty acids also is observed, probably mediated by cytokines involved in host response to infection. Whether such an inhibition of ketogenesis occurs with other ketone body precursors such as ketoacids is not known. The aim of this study was to determine the effects of tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6) on hepatic ketone body production from octanoic acid, a medium-chain fatty acid, and from alpha-ketoisocaproate (KIC), the ketoanalogue of leucine. METHODS: The experiments were conducted in cultured hepatocytes isolated from 24-hour-fasted Sprague-Dawley rats. Hepatocyte monolayers were incubated for 6 hours, with either KIC or octanoic acid (1 mmol/L), in the presence of glucagon and TNF-alpha (25 micro/L) IL-6 (15 microg/L) and/or IL-6. Acetoacetate, beta-hydroxybutyrate, and free fatty acids were determined in culture medium by enzymatic methods and KIC was measured by high-performance liquid chromatography. RESULTS: KIC and octanoic acid uptake by hepatocytes was 79% and 92%, respectively, over 6 hours, and cytokines had no influence. However, TNF-alpha and IL-6 caused inhibition of ketogenesis from alpha-ketoisocaproate (5.6% +/- 2.3% and 4.4% +/- 3.0%, respectively), and from octanoic acid (7.9% +/- 2.9%, 5.7% +/- 3.2%, respectively). In addition, when the two cytokines were present together in the culture medium, the inhibition was enhanced (inhibition of ketogenesis from KIC: 14.0% +/- 4.8%; from octanoic acid: 11.6% +/- 3.4%). CONCLUSIONS: In our experimental conditions, cytokines mediate an inhibition of ketogenesis; this process could be explained by a direct effect of cytokines on metabolic pathways of octanoic acid and KIC oran indirect effect by modification of the mitochondrial redox state.

Kinetic nephelometric determination of albumin produced by rat hepatocytes in culture

A kinetic immunonephelometric method for the determination of albumin produced by rat hepatocytes in culture is described. This assay is simple, rapid and sensitive. The methodology allows detection of 0.7 mg/l albumin in 200 microliters of culture medium. Within-run precision CVs for three levels of concentrations were under 1.0% and between-day precision CVs were under 4.1%. The range of measurement obtained using appropriately diluted samples was 1.2 to 74 mg/l. The rabbit IgG fraction to rat albumin used in this method did not cross-react with albumin from cow, allowing the use of fetal calf serum in the medium. The method described can thus be used easily for the assessment of albumin synthesis in cellular studies using isolated hepatocytes.

Plasma Homocysteine Measurement with Ion Exchange Chromatography (Jeol Aminotac 500): A Comparison with the Abbott IMx Assay

Objective: We evaluated ion exchange chromatography (IEC) on the Jeol Aminotac 500 analyzer for total homocysteine (tHcy) determination and compared it with an immunoassay method using fluorescence polarization on an Abbott IMx analyzer. Methods: IEC method validation (linearity, limit of detection, precision, interference) was made according to the French Biology Society guidelines (Société Française de Biologie Clinique). Moreover, during a 2-month period, 55 plasma samples from patients scheduled for routine tHCy measurement were assayed by both methods for determining correlation. Results: The IEC method was found linear up to at least 190 µmol/l, and the limit of detection was 1.6 µmol/l. Precision was studied with 3 controls at 6, 15 and 30 µmol/l. Intra-assay coefficients of variation (n = 14) were 8.3, 3.1 and 2.3%, respectively, and inter-assay coefficients of variation (n = 15) were 9.6, 5.1 and 4.9%, respectively. No interference was found with other sulfur-containing amino acids (methionine, cysteine). An excellent agreement was found between IEC and fluorescence polarization (Deming regression; y = 0.99x – 1.23; r = 0.97; p < 0.001). Conclusion: The IEC method for tHcy measurement shows adequate precision and correlates highly with the IMx assay. The IEC method is more time-consuming but less expensive in reagent cost and allows simultaneous determination of plasma methionine concentration which may help to explain the underlying mechanism responsible for hyperhomocysteinemia.

Effect of recombinant human interleukin 1β (rhIL-1β) on amino acid flux in the isolated perfused rat liver

SummaryWe studied the effect of recombinant human IL-1β (rhIL-1β) on hepatic amino acid (AA) flux in the isolated perfused rat liver model. Two experimental groups were used — a control group (n = 5) and a rhIL-1β-treated group (n = 5). IL-1 was added to the perfusate in two successive boluses of 0.1µg and 0.9µg, respectively 35 min (final concentration 0.67 ng/ml) and 60 min (6 ng/ml) after beginning the perfusion. In the IL-1 treated group, a reduction in flux was observed for only three AA, alanine, phenylalanine and serine. Glucose and urea production in the IL-1-treated group was slightly but not-significantly lower than in the controls.rhIL-1β thus has only minor direct effects on AA flux and gluconeogenesis in the liver and cannot therefore be held responsible for the increase in hepatic amino acid uptake during stress.

Quantitative and qualitative changes in prescription of serum vitamin D assay

Consequence d’un regain d’interet lie a la richesse de la litterature qui a rapporte un grand nombre de donnees epidemiologiques demontrant la forte prevalence du deficit en vitamine D, le nombre des prescriptions de son dosage serique a cru de maniere exponentielle ces dernieres annees a l’origine d’un cout pour l’assurance-maladie qui a presque quintuple en quatre ans. L’analyse quantitative et qualitative des dosages realises de 2007 a 2011, au sein d’un hopital universitaire de court sejour pour adultes, montre des modifications de pratiques non seulement quantitatives mais aussi qualitatives. Elles se traduisent par une augmentation au cours du temps de la frequence des prescriptions chez des sujets plus jeunes, moins deficitaires et plus frequemment de sexe masculin. Cette evolution, qu’il est impossible de qualifier de derive en l’absence de referentiel, justifie la necessite urgente d’etablir, sur la base de faits demontres, des recommandations opposables de juste prescription et de bonne realisation du dosage de la vitamine D circulante.

[Changes in serum vitamin D assay usage and the need for evidence-based recommendations].

Consequence d’un regain d’interet lie a la richesse de la litterature qui a rapporte un grand nombre de donnees epidemiologiques demontrant la forte prevalence du deficit en vitamine D, le nombre des prescriptions de son dosage serique a cru de maniere exponentielle ces dernieres annees a l’origine d’un cout pour l’assurance-maladie qui a presque quintuple en quatre ans. L’analyse quantitative et qualitative des dosages realises de 2007 a 2011, au sein d’un hopital universitaire de court sejour pour adultes, montre des modifications de pratiques non seulement quantitatives mais aussi qualitatives. Elles se traduisent par une augmentation au cours du temps de la frequence des prescriptions chez des sujets plus jeunes, moins deficitaires et plus frequemment de sexe masculin. Cette evolution, qu’il est impossible de qualifier de derive en l’absence de referentiel, justifie la necessite urgente d’etablir, sur la base de faits demontres, des recommandations opposables de juste prescription et de bonne realisation du dosage de la vitamine D circulante.

Évolution des dosages sériques de vitamine D dans un hôpital d’adultesPlaidoyer pour l’élaboration de recommandations en vue d’une juste prescription

Consequence d’un regain d’interet lie a la richesse de la litterature qui a rapporte un grand nombre de donnees epidemiologiques demontrant la forte prevalence du deficit en vitamine D, le nombre des prescriptions de son dosage serique a cru de maniere exponentielle ces dernieres annees a l’origine d’un cout pour l’assurance-maladie qui a presque quintuple en quatre ans. L’analyse quantitative et qualitative des dosages realises de 2007 a 2011, au sein d’un hopital universitaire de court sejour pour adultes, montre des modifications de pratiques non seulement quantitatives mais aussi qualitatives. Elles se traduisent par une augmentation au cours du temps de la frequence des prescriptions chez des sujets plus jeunes, moins deficitaires et plus frequemment de sexe masculin. Cette evolution, qu’il est impossible de qualifier de derive en l’absence de referentiel, justifie la necessite urgente d’etablir, sur la base de faits demontres, des recommandations opposables de juste prescription et de bonne realisation du dosage de la vitamine D circulante.