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Biomedical subjects

T Heinemann

Publications and source records attributed to T Heinemann.

33 records · Page 2Linked to original sources
PubMed1997

cis-4-Methylsphingosine decreases sphingolipid biosynthesis by specifically interfering with serine palmitoyltransferase activity in primary cultured neurons.

The effect of six different structurally modified sphingosine analogues on biosynthesis of sphingolipids was studied in primary cultured murine cerebellar neurons. Treatment of cells with cis-4-methylsphingosine at micromolar levels resulted in a markedly decreased sphingolipid biosynthesis, whereas the other compounds examined, trans-4-methylsphingosine, cis-5-methylsphingosine, trans-5-methylsphingosine, cis-sphingosine, and 1-deoxysphingosine, inhibited sphingolipid biosynthesis less efficiently. The inhibition of sphingolipid biosynthesis by the various compounds was paralleled by a decrease of serine palmitoyltransferase activity in situ. For cis-4-methylsphingosine the inhibitory effect on serine palmitoyltransferase activity was shown to be concentration- and time-dependent. Half-maximal reduction of enzyme activity occurred after 24 h of treatment with 10 microM of the compound. The activity of other enzymes of sphingolipid biosynthesis as well as phospholipid and protein biosynthesis was not affected. Analysis of the sphingoid moiety of cellular sphingolipids suggests that the sphingosine analogues listed above were subject to degradation rather than being utilized as precursors for sphingolipid biosynthesis by cultured neurons. Except of 1-deoxysphingosine, the other five sphingosine analogues were shown to be substrates for sphingosine kinase in vitro. After 24 h of treatment of primary cerebellar neurons with the various sphingosine analogues the relative percentage of the respective intracellular 1-phosphate derivatives paralleled exactly the inhibitory effect on serine palmitoyltransferase activity observed when cells were treated with the unphosphorylated compounds. In contrast to the respective 1-phosphate derivatives of the other methyl-branched sphingosine analogues examined, cis-4-methylsphingosine 1-phosphate showed an intracellular accumulation suggesting a delayed turnover rate in cultured murine neurons for this compound. These results suggest that the inhibitory effect of the sphingosine analogues on serine palmitoyltransferase is mediated by their respective 1-phosphate derivatives and that the pronounced effect of cis-4-methylsphingosine is caused by a high intracellular concentration of cis-4-methylsphingosine 1-phosphate. cis-4-Methylsphingosine, in addition, caused drastic changes in cell morphology of primary cerebellar neurons, which were not observed when these cells were treated with one of the other sphingosine analogues examined.

Acyltransferases↗
PubMed1997

Turnover of endogenous ceramide in cultured normal and Farber fibroblasts.

De novo synthesis and turnover of endogenous ceramide in cultured skin fibroblasts from patients affected with Farber lipogranulomatosis were studied by biosynthetical labeling of cellular sphingolipids with [14C]serine. The cellular uptake of [14C]serine and incorporation into de novo synthesized ceramide was similar in normal and Farber fibroblasts, with a half life of newly synthesized ceramide of 2.7 h in normal and diseased cells. Newly synthesized ceramide was found to be channeled directly into biosynthesis of complex sphingolipids rather than contributing to the pool of accumulated ceramide in Farber fibroblasts. The degradation of ceramide generated by the catabolism of complex sphingolipids in Farber cells was greatly delayed compared with control fibroblasts, with differences in the amount of radiolabeled cellular ceramide becoming evident after 6 h chase time. Individual Farber cell lines differed from each other in the amount of accumulated ceramide; however, no correlation was found between ceramide accumulation and residual acid ceramidase activity as determined in vitro. In addition, the amount of radiolabeled sphingomyelin was significantly increased in Farber fibroblasts suggesting a delayed degradation of this compound in this ceramide storage disorder. We propose biosynthetical labeling of endogenous ceramide with [14C]serine, in addition to other established methods, as a highly sensitive and reliable method for the diagnosis of Farber disease, allowing semiquantitative measurement of ceramide accumulation in cultured skin fibroblasts of patients affected with Farber lipogranulomatosis.

Acid Ceramidase↗
PubMed1994

Alternative polyadenylation of apolipoprotein B RNA is a major cause of B-48 protein formation in rat hepatoma cell lines transfected with human apoB-100 minigenes.

The human apoB gene encodes an mRNA of 14121 nucleotides. In liver the apoB gene products a full-length mature protein of 4,536 amino acids (B-100), whereas in the intestine this gene produces a truncated protein of 2,152 amino acids (B-48). B-48 results from RNA editing of nucleotide 6666 from C to U, thereby producing a stop codon at position 2153. Rat liver has been shown to contain apoB RNA editing capability resulting in production of both B-100 and B-48. To create an in vitro expression system for human B-100, a minigene with a wild type coding sequence for the entire B-100 protein (B-100/Gln) was stably transfected into rat hepatoma cells (McA-RH7777). Similarly, a minigene with mutation at nucleotide 6667 that allowed translation even after editing of nucleotide 6666 (B-100/Leu, nonstop mutant), a minigene with an additional nonsense mutation at nucleotide 7053 to produce B-50 (B-50/Leu), and a truncated wild type minigene with a stop signal at codon 3261 to produce B-74 and an mRNA of 10 kb (B-74/Gln) were also transfected. Very little full-length B-100 and B-74 was produced by any of the respective constructions, including the B-100/Leu with the nonstop mutation. Transfection with B-100/Gln, B-100/Leu and B-74/Gln constructions produced greater than 90% of apoB as B-48, whereas the B-50/Leu construction produced 76% B-50 and 24% B-48. The inability of the B-100/Leu construction to produce B-100 suggested an explanation for B-48 production other than RNA editing. Northern blot analysis showed that the RNA produced by all four transfectants was shortened to a size of about 7 kb. A 10-kb but no 7-kb RNA was observed in the B-74/Leu construction when transfected to Chinese hamster ovary cells suggesting cell type specificity in generation of a shortened RNA. The 3' end of apoB RNA from McA-RH7777 B-100/Leu transfectants was reverse transcribed, cloned, and sequenced. This revealed two species of RNA: one polyadenylated at or near nucleotide 6775 capable of coding for B-48, the other polyadenylated at nucleotide 7080 capable of coding for B-50. In 18% of the cDNA clones, nucleotide 6666 was edited from C to T. In 6 of 34 clones, addition of the poly(A) tail after nucleotide 6774 created a TAA stop codon, whereas no stop signals could be detected in the remaining clones.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Comparison of intestinal absorption of cholesterol with different plant sterols in man.

Intestinal absorption of cholesterol, campesterol, campestanol, stigmasterol and sitosterol were measured in 10 healthy subjects by an intestinal perfusion technique over a 50 cm segment of the upper jejunum using sitostanol as non-absorbable marker. Cholesterol absorption was highest and averaged 33%., whereas the absorption rate of sitosterol averaged 4.2% and of stigmasterol 4.8%. Higher absorption rates were found for campesterol (9.6%). Campestanol, the 5 alpha saturated derivative of campesterol, showed the highest absorption rate (12.5%) of all plant sterols. A positive correlation between the absorption rate of cholesterol and campesterol was established. In addition, there was a negative correlation between the ratio of sitosterol to cholesterol and the mass of cholesterol absorption. These results are in agreement with previous observations in animal studies, namely, that increasing the length of the side-chain of cholesterol decreases the absorbability of the sterol. Surprisingly, campestanol, the 5 alpha saturated derivate of campesterol, was shown to have higher absorbability compared with its unsaturated compound. This finding is in contrast to previous assumptions, that hydrogenisation of the nucleus double bond of a sterol causes a decrease of absorbability, as has been demonstrated for cholesterol/cholestanol and sitosterol/sitostanol.

Cholesterol↗
PubMed1991

Mechanisms of action of plant sterols on inhibition of cholesterol absorption. Comparison of sitosterol and sitostanol.

The effects of two different plant sterols on intestinal cholesterol absorption were compared in normal volunteers by an intestinal perfusion study during a control period followed by high dose infusion of sitosterol or sitostanol (3.6 mumol/min), to which subjects were allocated in a randomized manner. Cholesterol absorption during the control period was similar in the two groups, averaging 0.88 +/- 0.48 mumol/min (32 +/- 11%) for group I (sitosterol) and 0.68 +/- 0.33 mumol/min (29 +/- 9%) for group II (sitostanol). The infusion of a high dose of sitosterol resulted in a significant reduction of cholesterol absorption to 0.47 mumol/min (16%). Following the same dose of sitostanol, cholesterol absorption diminished significantly to 0.15 +/- 0.11 mumol/min (5.1 +/- 2.9%). Overall cholesterol absorption declined during sitosterol infusion by almost 50%, whereas sitostanol infusion caused a reduction of cholesterol absorption by almost 85%. These findings of a more effective inhibition of cholesterol absorption by sitostanol might confirm the observation recorded by others that an increase in hydrophobicity of a plant sterol results in a higher affinity but lower capacity to mixed micells. This may cause an effective displacement of cholesterol from micellar binding and therefore diminished cholesterol absorption.

Cholesterol↗
PubMed1986

Effect of low-dose sitostanol on serum cholesterol in patients with hypercholesterolemia.

Sitostanol (24-ethyl-5 alpha-cholestan-3 beta-ol), a hydrogenated derivative of sitosterol, was administered in a low dose (1.5 g/day) for 4 weeks to 6 patients with hypercholesterolemia. Total cholesterol was reduced significantly after 3 and 4 weeks by 10 and 15%, respectively. The reduction of total cholesterol was entirely due to a fall in LDL cholesterol. Total triglycerides and HDL cholesterol were not altered. Two weeks after cessation of sitostanol administration serum cholesterol returned to pretreatment levels. No significant amounts of sitostanol could be detected in plasma during therapy. These results suggest that low-dose sitostanol might be a useful hypolipidemic agent for the treatment of mild hypercholesterolemia.

Adult↗
PubMed1985

[Anesthesia in aortocoronary bypass surgery: comparison of effects on hemodynamics of recent technics of total intravenous anesthesia].

20 patients electively scheduled for operation were enrolled in the study and anaesthetized randomly with one of the two techniques etomidate + fentanyl (I) or flunitrazepam + fentanyl (II). Haemodynamics were assessed by continuously measuring blood pressure in the systemic and pulmonary circulations, as well as the heart rate, and intermittently determining the cardiac output. It could be shown that systemic arterial blood pressure, in spite of an initial drop after induction of anaesthesia, remained within an acceptable safety margin throughout the investigation period. Whereas heart rate remained almost constant in both groups, the rate-pressure product which may serve as a measure of myocardial oxygen consumption in the clinical setting, decreased considerably in both groups, although more appreciably under the influence of the anaesthetic technique flunitrazepam + fentanyl. Although the diastolic blood pressure as the most significant individual factor determining coronary blood flow was not changed appreciably in both groups, it remained at a higher level under the influence of the anaesthetic technique etomidate + fentanyl (I). We conclude that both anaesthetic regimes described here may be safely applied for the anaesthesia of patients with reduced coronary perfusion and cardio-haemodynamic reserve potential.

Adult↗