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C G de Haas

Publications and source records attributed to C G de Haas.

10 recordsLinked to original sources
PubMed1997

Relationships between phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin metabolism in cultured oligodendrocytes.

In most cell types the major pathway of sphingomyelin synthesis is the direct transfer of the phosphocholine head group from phosphatidylcholine to ceramide catalyzed by the enzyme L-acylsphingosine:phosphatidylcholine phosphocholinetransferase (SM synthase; EC 2.7.8.-). Although this pathway has been demonstrated in brain tissue, its quantitative importance has been questioned. An alternative biosynthetic pathway for sphingomyelin synthesis in brain tissue has been proposed, viz., the direct transfer of phosphoethanolamine from phosphatidylethanolamine to ceramide, followed by methylation of the ethanolamine moiety to a choline group. We have evaluated various possible biosynthetic pathways of sphingomyelin synthesis in rat spinal cord oligodendrocytes, the myelin-forming cells of the CNS, by labeling cells in culture with radiolabeled choline, ethanolamine, or serine. Our results indicate that, in oligodendrocytes, most of the phosphocholine for the biosynthesis of sphingomyelin is provided by phosphatidylcholine, which is predominantly derived from de novo synthesis. No evidence was found for the operation of the alternative pathway via ceramide-phosphoethanolamine. Furthermore, our results indicate that a small pool of phosphatidylcholine is provided by methylation of phosphatidylethanolamine, which in turn is formed preferentially by decarboxylation of phosphatidylserine.

Animals↗
PubMed1990

Acute effects of interleukin 1 alpha and 6 on intermediary metabolism in freshly isolated rat hepatocytes.

Using hepatocytes in suspension, freshly isolated from adult male fed rats, we studied the acute influence of recombinant human interleukins 1 alpha, 2 and 6 on glycogen and fatty acid metabolism. By far the largest effects were observed with interleukin-1 alpha: short incubations (up to 60 min) sufficed to depress glycogen synthesis in a dose-dependent manner, while the rates of glycogenolysis and glycolysis were increased as indicated by the release of glucose and lactate. Interleukin-6 acted similarly, though being much less effective on a molar basis, whereas interleukin-2 only caused a small increase in lactate production. In hepatocytes from 24h-starved rats interleukin-1 alpha caused a minor stimulation of gluconeogenesis. Although neither fatty acid synthesis nor oxidation of fatty acids in quiescent hepatocytes from fed rats was significantly affected by interleukins, interleukin-1 alpha was able to cause appreciable inhibition of fatty acid synthesis in hepatocytes from regenerating liver (isolated 22h after partial hepatectomy). It is concluded (i) that interleukins, in particular interleukin-1 alpha, acutely promote hepatic glucose release, and (ii) that transition of adult hepatocytes from a quiescent into a proliferatory state allows the occurrence of rapid effects of interleukin-1 alpha on fatty acid metabolism.

Animals↗
PubMed1987

Stimulation by a tumor-promoting phorbol ester of acetyl-CoA carboxylase activity in isolated rat hepatocytes.

Acetyl-CoA carboxylase (EC 6.4.1.2) in hepatocytes from meal-fed rats was activated by phorbol myristate acetate (PMA) in a time- and concentration-dependent fashion. This activation can account for the PMA-induced stimulation of de novo fatty acid synthesis. Purified rat-liver acetyl-CoA carboxylase was found to be phosphorylated and activated by protein kinase C, thus providing a possible mechanism for the metabolic action of PMA in intact hepatocytes.

Acetyl-CoA Carboxylase↗
PubMed1986

Phorbol esters, but not epidermal growth factor or insulin, rapidly decrease soluble protein kinase C activity in rat hepatocytes.

Exposure of freshly isolated rat hepatocytes to tumor-promoting phorbol esters like phorbol 12-myristate 13-acetate resulted in a time- and concentration-dependent translocation of protein kinase C from the soluble to the particulate fraction of the cells. No such disappearance of soluble protein kinase C activity was observed with either epidermal growth factor or insulin, indicating that activation of protein kinase C is not necessarily involved in the short-term metabolic action of physiological growth factors on rat hepatocytes.

Animals↗
PubMed1985

Differential short-term effects of growth factors on fatty acid synthesis in isolated rat-liver cells.

Hepatocytes in suspension, freshly isolated from meal-fed rats, were used to study the acute influence of growth factors on the rate of de novo fatty acid synthesis. Nerve growth factor (2.5 S) and epidermal growth factor caused a substantial increase in the rate of fatty acid synthesis, whereas fibroblast growth factor was inhibitory. Little effect was observed with nerve growth factor (7 S), bombesin or substance P. Transferrin did not affect hepatic fatty acid synthesis. The results are discussed in relation to the effects of insulin and tumor-promoting phorbol esters.

Animals↗
PubMed1985

Acute effects of tumor-promoting phorbol esters on hepatic intermediary metabolism.

In hepatocytes isolated from meal-fed rats, phorbol 12-myristate 13-acetate as well as phorbol 12,13-didecanoate stimulated de novo fatty acid synthesis in a dose-dependent manner. Moreover, phorbol 12-myristate 13-acetate inhibited ketogenesis from exogenous oleate, but slightly enhanced oleate esterification. The stimulation of esterification was more pronounced with endogenously synthesized fatty acids. In hepatocytes from 24h-starved rats a moderate stimulation of gluconeogenesis and ureogenesis was observed with glutamine as substrate. It is concluded that tumor-promoting phorbol esters mimic the short-term effects of insulin on hepatic fatty acid metabolism.

Animals↗
PubMed1981

Regulation of triacylglycerol synthesis in the liver: a decrease in diacylglycerol acyltransferase activity after treatment of isolated rat hepatocytes with glucagon.

Isolated rat hepatocytes were used to investigate the possibility of a short-term effect of glucagon on the synthesis of triacylglycerols in the liver. Incubation of hepatocytes in the presence of glucagon, followed by homogenization in a buffer containing F- (50 mM) and EDTA (2.5 mM), resulted in a 53% decrease in activity of microsomal diacylglycerol acyltransferase (EC 2.3.1.20), the only enzyme that is exclusively involved in the synthesis of triacylglycerols. The activity of cholinephosphotransferase (EC 2.7.8.2), which also uses diacylglycerols as substrate, was not decreased after exposure of the hepatocytes to glucagon. This may imply that triacylglycerol synthesis can be regulated independently of phosphatidylcholine synthesis. The activity of diacylglycerol acyltransferase in microsomes isolated from a homogenate of whole liver could be reduced by preincubating the microsomes with Mg2+ (5 mM), ATP (1 mM) and 105 000 X g supernatant. The enzyme could be reactivated by incubation of the washed microsomes with a 105 000 X g supernatant in the presence of dithiothreitol (5 mM). Fluoride (50 mM) inhibited this reactivation. It is concluded that the activity of diacylglycerol acyltransferase is subject to hormonal short-term control, possibly via a phosphorylation-dephosphorylation mechanism.

Acyltransferases↗
PubMed1977

Urinary hydroxyproline as a measure in fracture healing.

The determination of any pattern in urinary total OH-proline following bone fractures has been the purpose of this investigation. This was carried out in a group of 11 patients with major fractures, a group of 8 patients with minor fractures and a control group of 10 healthy laboratory technicians. Indeed, some patterns could be detected. In patients with major fractures a considerable elevation of urinary total OH-proline was found which was correlated to the size and number of fractures and the healing tendency of the fracture. Normal to only slightly elevated urinary total OH-proline values during the course of the healing process of major fractures could perhaps indicate delayed union, or even malunion. Since fracture healing is usually assessed by X-ray examination and clinical experience, this study could provide a more accurate measure of the healing process of fractures.

Fractures, Bone↗