Altered transcriptional regulation of phosphoenolpyruvate carboxykinase in rats following endotoxin treatment

Lipopolysaccharide regulation of lipoprotein lipase expression in murine macrophages

The enzyme lipoprotein lipase is expressed in a number of cell types and plays a central role in lipid metabolism. Multiple factors regulate its expression in a tissue-specific manner. In murine macrophages, lipopolysaccharide inhibits lipoprotein lipase enzyme activity. The current work examines this process in the established J774 macrophage line and primary peritoneal macrophages from endotoxin-sensitive (C3HeB/Fej) and endotoxin-resistant (C3H/Hej) murine strains. Lipopolysaccharide inhibition of macrophage lipoprotein lipase occurred at the enzyme and mRNA levels in a time- and concentration-dependent manner. Cells from endotoxin-resistant animals maintained their expression of lipoprotein lipase following treatment with lipopolysaccharide. Results of gel retention assays showed that lipopolysaccharide treatment of the J774 macrophages altered the level of nuclear proteins recognizing and binding the lipoprotein lipase promoter DNA. Nuclear extracts from resting J774 cells contained proteins which bound specifically to the octamer motif and to the CAAT box within the lipoprotein lipase promoter. Exposure of the J774 cells to lipopolysaccharide for 16 h increased the level of protein-octamer DNA complexes. Similar responses were obtained in endotoxin-sensitive, but not endotoxin-resistant, primary macrophages following in vitro treatment with lipopolysaccharide. This finding suggests that transcriptional events may contribute to the lipopolysaccharide regulation of macrophage lipoprotein lipase expression.

Alterations in carbohydrate metabolism during stress: a review of the literature

Patients with sepsis, burn, or trauma commonly enter a hypermetabolic stress state that is associated with a number of alterations in carbohydrate metabolism. These alterations include enhanced peripheral glucose uptake and utilization, hyperlactatemia, increased glucose production, depressed glycogenesis, glucose intolerance, and insulin resistance. The hypermetabolic state is induced by the area of infection or injury as well as by organs involved in the immunologic response to stress; it generates a glycemic milieu that is directed toward satisfying an obligatory requirement for glucose as an energy substrate. This article reviews experimental and clinical data that indicate potential mechanisms for these alterations and emphasizes aspects that have relevance for the clinician.

Inhibition by recombinant human interleukin-6 of the glucagon-dependent induction of phosphoenolpyruvate carboxykinase and of the insulin-dependent induction of glucokinase gene expression in cultured rat hepatocytes: regulation of gene transcription and messenger RNA degradation

The influence of recombinant human interleukin-6, the major mediator of the inflammatory response in liver, on the glucagon- and insulin-dependent induction of the phosphoenolpyruvate carboxykinase and glucokinase gene, respectively, was monitored on the level of gene transcription, mRNA abundance and enzyme activity in cultured rat hepatocytes. As control markers of the interleukin-6-induced acute-phase response the mRNA levels of the acute phase proteins alpha 2-macroglobulin and beta-fibrinogen were determined. In cultured rat hepatocytes, recombinant human interleukin-6, added simultaneously with glucagon and insulin, lowered the maximal increase in glucagon-induced phosphoenolpyruvate carboxykinase mRNA levels after 2 hr and the maximal increase in glucokinase mRNA levels after 3 hr to about 30%, respectively. It inhibited the glucagon-induced increase in phosphoenolpyruvate carboxykinase gene transcription and phosphoenolpyruvate carboxykinase enzyme activity, as well as the insulin-induced increases in glucokinase gene transcription and glucokinase enzyme activity. Recombinant human interleukin-6 increased the mRNA levels of the acute-phase proteins alpha 2-macroglobulin and beta-fibrinogen gradually over 4 to 6 hr. Recombinant human interleukin-6, added 2 hr after glucagon or 3 hr after insulin at the maximum of the hormone-induced enzyme mRNA levels, almost doubled the decay rate of phosphoenolpyruvate carboxykinase mRNA and glucokinase mRNA. The results show that interleukin-6 induced the expression of inflammatory proteins and simultaneously inhibited the hormone-induced expression of enzymes of intermediary metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of high-dose endotoxin on glucose production and utilization

The purpose of the present study was to determine how a high dose of endotoxin (lipopolysaccharide [LPS]), which produces hypoglycemia, alters in vivo glucose uptake by individual tissues. Catheterized conscious fasted rats were injected intravenously (i.v.) with either saline, LPS (1 mg/100 g body weight [BW], lethal dose [LD] 100), or 3-mercaptopicolinic acid (3-MP), an inhibitor of gluconeogenesis. In the latter two groups, blood glucose levels were clamped at either 6 mmol/L (euglycemia) or 3 mmol/L (hypoglycemia). In the first series of experiments, whole-body glucose flux was determined using [3-3H]glucose, and in the second study in vivo glucose uptake (Rg) by individual tissues was estimated by the tracer [U-14C]-2-deoxyglucose technique. The relative contribution of hypoglycemia per se to the LPS effect was determined by comparing the values from LPS- versus 3-MP-treated animals. There was no difference in the rate of whole-body glucose utilization (Rd) between saline-infused control rats and LPS-treated animals that were hypoglycemic. However, Rg by diaphragm, spleen, liver, and lung was increased in hypoglycemic LPS-treated rats. The increased Rg in these tissues was not observed in 3-MP-treated rats with a comparable hypoglycemia. Only the gastrocnemius muscle showed a reduction in Rg under hypoglycemic conditions, and the decrease was similar in both LPS- and 3-MP-treated animals. When sufficient glucose was infused into LPS-injected rats to maintain euglycemia, whole-body glucose Rd was increased compared with that in hypoglycemic LPS-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of treatment of the rat with bacterial endotoxin on gluconeogenesis and pyruvate metabolism in subsequently isolated hepatocytes

The effect of treatment of rats with bacterial endotoxin on gluconeogenesis and the flux through pyruvate kinase, phosphoenolpyruvate carboxykinase (PEPCK), pyruvate carboxylase and pyruvate dehydrogenase (PDH) was measured in isolated hepatocytes, prepared from animals starved for 18 h, incubated in the presence of 1 mM pyruvate. The lipopolysaccharide reduced gluconeogenesis by 50% and lowered the flux through pyruvate kinase, PEPCK and pyruvate carboxylase by comparable amounts. There was no effect of endotoxaemia on PDH flux, indicating that the lowered rate of gluconeogenesis is not the result of a redistribution of pyruvate metabolism between oxidation and carboxylation. The results confirm that a stimulation of pyruvate kinase activity following treatment with lipopolysaccharide is not involved in the inhibition of gluconeogenesis, but that the effect resides at the level of phosphoenolpyruvate formation. The most favoured mechanism for the inhibition of glucose synthesis is via an inhibition of PEPCK and subsequent feedback inhibition of pyruvate carboxylase, although a secondary effect at the level of the mitochondria and pyruvate carboxylase cannot be excluded.

Identification of tumor necrosis factor as a transcriptional regulator of the phosphoenolpyruvate carboxykinase gene following endotoxin treatment of mice

The decreased synthesis of hepatic phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting enzyme of gluconeogenesis, that occurs during endotoxemia was shown previously in rats to occur at the transcriptional level. In the current study, the exogenous administration of human recombinant tumor necrosis factor (TNF), a proximal mediator of endotoxic shock, reduced the PEPCK transcription rate, mRNAPEPCK levels, and PEPCK enzyme activity in a time- and dose-dependent manner in CD-1 mice. Comparable amounts of circulating TNF were measured in mice 2 h after injection of human recombinant TNF (10(5) U) or a 50% lethal dose of Escherichia coli endotoxin (20 mg/kg). Direct action of TNF to decrease the PEPCK transcription rate was confirmed in vitro with H-4-II-E Reuber hepatoma cells, in which a dose-dependent inhibition of PEPCK transcription was observed with 1 to 100 U of TNF per ml. A role for TNF-elicited changes in PEPCK gene expression during endotoxemia was confirmed by the protective effect of rabbit polyclonal antibodies to recombinant murine TNF. C57BL/6 mice passively immunized with anti-TNF 4 h prior to endotoxin challenge exhibited normal PEPCK enzyme activity. Neutralization of circulating TNF with anti-TNF failed, however, to prevent the hypoglycemia commonly observed during endotoxemia, suggesting the participation of other mediators. Anti-TNF treatment reduced circulating interleukins 1 and 6 at 3 and 6 h after endotoxin treatment, respectively. These results suggest that during endotoxemia, the development of hypoglycemia is multifaceted and that several cytokines are most likely involved. The findings from the Reuber hepatoma cell model afford an opportunity in future work to map putative cytokine response elements in the PEPCK promoter responsible for perturbed hormonal regulation of the gene during endotoxemia.

Experimental and clinical applications of molecular cell biology in nutrition and metabolism

Rapid advances in molecular biology have yielded important new techniques for understanding the cellular mechanisms of normal homeostasis and disease. In particular, molecular laboratory methodologies have become important investigative tools for nutritional studies. Detection techniques for specific DNAs, RNAs, and proteins allow direct examination of cellular regulation of protein expression in health and illness. Construction of transgeneic models by recent techniques of inserting foreign genes into experimental animals has provided novel models for studies of cellular metabolism. In addition, molecular biology has had impact on clinical nutrition and therapy. Molecular techniques not only allow for early diagnosis of many inborn genetic errors of metabolism, recombinant technology has also provided for large-scale production of proteins and hormones of potential therapeutic value. The possibility for direct gene therapies is also nearing reality. Hence, understanding the language of molecular biology and the recent developments in this field is not only of research interest, but is also of clinical relevance.