Endotoxin stimulation of liver parenchymal cell phosphofructokinase activity requires nonparenchymal cells

Abstract

The rate of carbohydrate flux through phosphofructokinase (measured as the rate of [3-3H]glucose detritiation) was increased fourfold in rat liver parenchymal cells incubated with conditioned mediuni from lipopolysaccharide-stimulated adherent liver non-parenchymal cells. The rate was not affected in parenchymal cells incubated either with lipopolysaccharide directly or with conditioned medium from non-stimulated non-parenchymal cells. The stimulation of carbohydrate flux through phosphofructokinase by conditioned medium was not duplicated by peptide cytokines known to be released by lipopolysaccharide-activated liver non-parenchymal cells (interleukin-1, interleukin-6, tumor necrosis factor-a, and transforming growth factor-p) or platelet activating factor. Furthermore, formation of the active conditioned medium was not prevented by inclusion of cycloheximide or dexamethasone to inhibit cytokine synthesis, or indomethacin or BW7SSc to inhibit arachidonic acid metabolism, during lipopolysaccharide-stimulation of the non-parenchymal cells. The results indicate that intercellular communication between lipopolysaccharide-stimulated liver non-parenchymal cells and parenchymal cells by soluble mediators is responsible for thc stimulation of liver phosphofructokinase activity during endotoxin-induced shock. Studies to isolate and identify the factor(s) in the conditioned medium are currently in progress.Septic shock, which results from the host response to bacterial endotoxin (i. e. lipopolysaccharide, LPS), is characterized by profound alterations in glucose homeostatis. In vivo, LPS administration results in transient hyperglycemia followed by progressive and frequently fatal hypoglycemia Abbrcviarions. BW75Sc, 3-amino-I -[3-(trifluoromcthyl)-phenyl]-2-pyrazoline; Fru(2,6)P2, fructose 2,6-bisphosphate; hrTL-I, human recombinant interleukin-I ; hrIL-6, human recombinant interleukin-6 ; hTGF-b, human transforming growth factor-/?; hrTNF-a, human recombinant tumor necrosis factor-cc; LPS, lipopolysaccharide; PAF, platelet activating factor.Enzymes. Phosphofructokinase (EC 2.7.1.1 1); phosphoenolpyruvate carboxykinase (EC 4.1 .I .32); pyruvate kinase (EC 2.7.1.40); pyruvate carboxylase (EC 6.4.1.1); glucokinase (EC 2.7.1.2); collagenasc (EC 3.4.24.3); cyclooxygenase (EC 1.13.11.-); 5-lipoxygenase (EC 1.13.11.34).enolpyruvate carboxykinase, pyruvate kinase, pyruvate carboxylase or glucokinase. We recently demonstrated that endotoxin administration to fasted rats results in a 2 -3-fold elevation in the level of fructose 2,6-bisphosphate [Fru(2,6)P2] in liver within 3 h and that the level remains elevated for at least 24 h [8]. Fru(2,6)P2 is a potent activator of phosphofructokinase and its concentration is considered to be the primary factor regulating carbohydrate flux through phosphofructokinase in liver [9]. The activities of phosphoenolpyruvate carboxykinase or pyruvate kinase were not significantly altered when assayed in liver homogenates prepared up to 12 h after LPS administration [8].The apparent specific increas...

Inhibition of hepatic gluconeogenesis by nitric oxide: a comparison with endotoxic shock

“…In contrast with previous studies [6,8], the work of Miller et al [13] has suggested that the increase in PFK-1 flux following endotoxin treatment and the inhibition of gluconeogenesis can be dissociated, with the stimulation of PFK-1 flux being independent of both cytokine action and lowered glucose synthesis.…”

“…Gram-negative bacterial infection or treatment of animals with bacterial endotoxin is characterized by profound alterations in glucose homoeostasis, typically an initial transient hyperglycaemia followed by a prolonged and frequently fatal hypoglycaemic phase [1][2][3][4][5][6][7][8][9]. During the initial phase there is a pronounced mobilization of hepatic glycogen [10-12] and increased flux through 6-phosphofructo-1 -kinase [8,13], whereas in the latter phase hepatic glucose synthesis from lactate, pyruvate and a number of other substrates is decreased [1][2][3][4][5][6][7][8][9]. We have suggested that the inhibition of gluconeogenesis results primarily from a lowered substrate flux through phosphoenolpyruvate carboxykinase, with the increase in 6-phosphofructo-1-kinase activity being of secondary importance [8,9].…”

“…We have suggested that the inhibition of gluconeogenesis results primarily from a lowered substrate flux through phosphoenolpyruvate carboxykinase, with the increase in 6-phosphofructo-1-kinase activity being of secondary importance [8,9]. Evidence suggests that the effects of endotoxin on carbohydrate metabolism are not the result of a direct effect of the lipopolysaccharide at the level of the hepatic parenchymal cell [1,5], but the result of an interaction of the bacterial endotoxin with the Kupffer cells in the liver [10][11][12][13]. The hyperglycaemic phase has been attributed to the release of prostaglandins by the Kupffer cells [10][11][12], although the rapid stimulation of 6-phosphofructo-1-kinase has been proposed to be independent of any changes in either prostaglandins or cytokines [13].…”

“…The mechanism underlying the inhibition of gluconeogenesis remains to be established [13]; however, recent studies into the mechanisms of hepatocellular dysfunction during sepsis suggest that the longer-term responses involve the release of cytokines from the Kupffer cells which interact with the hepatocytes to induce NO synthase with concomitant NO production [14][15][16][17]. The time of induction of the Ca2+-independent NO synthase within the liver parenchymal cells both in vivo and in vitro correlates with the inhibition of glucose synthesis [16,18] and is comparable with that of endotoxin treatment of the rat with lactate plus pyruvate as the substrate.…”

Bacterial lipopolysaccharide (LPS) and interleukin 1 (IL-1) exert multiple physiological effects in the tilapia Oreochromis mossambicus (Teleostei)

“…For mammals, emphasis is laid on the role of sessile or tissue macrophages as intermediates in the bidirectional communication between the immune and endocrine systems. This is illustrated by the mechanism of action of LPS on liver metabolism (Miller et al 1992), on pituitary hormone release (Spangelo and MacLeod 1990) and on gonadal function (Sun et al 1993). Fish are particularly insensitive to the toxic effects of LPS (Wedemeyer el al.…”