scholarly journals Restoration in vitro of normal rates of very-low-density lipoprotein triacylglycerol and apoprotein B secretion in hepatocyte cultures from diabetic rats

1993 ◽  
Vol 294 (1) ◽  
pp. 167-171 ◽  
Author(s):  
J M Duerden ◽  
G F Gibbons
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Basal Medium ◽  
Inhibitory Response ◽  
Diabetic Rats ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Culture Dish ◽  
Apoprotein B

Hepatocytes derived from diabetic rats were cultured in serum-free Waymouth's medium containing various supplements, after an initial 4 h period during which the cells were allowed to attach to the culture dish in the presence of foetal-bovine serum (10%). After removal of serum, these cells secreted much less very-low-density lipoprotein (VLDL) apoprotein B (apoB) and triacylglycerol than those derived from normal rats when cultured for 24 h in the basal medium. Inclusion of oleate (0.75 mM) in the medium initially increased the output of apoB and triacylglycerol, but the rates remained lower than those observed in normal hepatocytes and declined to zero after 72 h. This time-dependent decline in VLDL output was prevented by addition of dexamethasone to the oleate-containing medium. Levels of apoB and triacylglycerol output characteristic of normal hepatocytes could only be completely restored, however, by further addition of a mixture of lipogenic substrates (lactate plus pyruvate) to the medium. Restoration of normal levels of VLDL secretion in diabetic hepatocytes in vitro by this means was accompanied by a normal inhibitory response of apoB and triacylglycerol output to short-term (24 h) treatment with insulin or glucagon. Exposure of the cells to insulin for 72 h enhanced the secretion of VLDL, whereas treatment with glucagon for the same period potentiated the original inhibitory effect. The defective secretion of VLDL apoB observed when diabetic hepatocytes were cultured in the basal medium for 24 h could also be rectified by inclusion of a mixture of oleate (0.75 mM), lactate (10 mM), pyruvate (1 mM), dexamethasone (1 microM) and insulin (78 nM) in the medium during the 4 h attachment period in the presence of serum. Under these conditions, the increase in the secretory response of triacylglycerol was not so pronounced.

scholarly journals Low density lipoprotein and very low density lipoprotein are selectively bound by aggregated C-reactive protein.

1982 ◽  
Vol 156 (1) ◽  
pp. 230-242 ◽  
Author(s):  
F C de Beer ◽  
A K Soutar ◽  
M L Baltz ◽  
I M Trayner ◽  
A Feinstein ◽  
...  
Keyword(s):  
Acute Phase ◽  
Solid Phase ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
C Reactive Protein ◽  
Calcium Dependent ◽  
Reactive Protein

C-reactive protein (CRP), the classical acute-phase protein, can bind phospholipids by virtue of its specific, calcium-dependent reactivity with phosphorylcholine residues. However, analysis of acute-phase serum by gel filtration and by density gradient ultracentrifugation showed that the CRP was in a free, uncomplexed form, despite the coexistent presence of the various classes of serum lipoproteins, all of which contain phospholipids. In contrast, when isolated CRP was aggregated by immobilization at a sufficient density on a solid phase and then exposed to normal human serum, it selectively bound low density lipoprotein (LDL) and traces of very low density lipoprotein. The reaction was calcium dependent and reversible by free phosphorylcholine but not by heparin. LDL isolated from normal plasma was also bound by aggregated CRP. CRP reacts in vitro with a wide variety of different ligands both of extrinsic and of autogenous origin, e.g., microbial products and damaged cell membranes, respectively. If CRP aggregated in vivo by complexing with these ligands than acquires the capacity to selectively bind LDL, the phenomenon may have significant implications for the function of CRP and for the metabolism, clearance, and deposition of LDL.

scholarly journals Regulation of very-low-density-lipoprotein lipid secretion in hepatocyte cultures derived from diabetic animals

1989 ◽  
Vol 262 (1) ◽  
pp. 313-319 ◽  
Author(s):  
J M Duerden ◽  
S M Bartlett ◽  
G F Gibbons
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Inhibitory Effect ◽  
Diabetic Rats ◽  
Whole Body ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Short Period ◽  
Streptozotocin Diabetic Rats ◽  
Cholesterol Secretion

Hepatocytes were derived from 2-3-day streptozotocin-diabetic rats and maintained in culture for up to 3 days. Compared with similar cultures from normal animals, these hepatocytes secreted less very-low-density-lipoprotein (VLDL) triacylglycerol, but the decrease in the secretion of VLDL non-esterified and esterified cholesterol was not so pronounced. This resulted in the secretion of relatively cholesterol-rich VLDL particles by the diabetic hepatocytes. Addition of insulin for a relatively short period (24 h) further decreased the low rates of VLDL triacylglycerol secretion from the diabetic hepatocytes. The secretion of VLDL esterified and non-esterified cholesterol also declined. These changes occurred irrespective of whether or not exogenous fatty acids were present in the culture medium. Little or no inhibitory effect of insulin was observed after longer-term (24-48 h) exposure to the hormone. Both dexamethasone and a mixture of lipogenic precursors (lactate plus pyruvate) stimulated VLDL triacylglycerol and cholesterol secretion, but not to the levels observed in hepatocytes from normal animals. The low rate of hepatic VLDL secretion in diabetes contrasts with the increase in whole-body VLDL production rate. This suggests that the intestine is a major source of plasma VLDL in insulin-deficient diabetes.

scholarly journals The preferential uptake of very-low-density lipoprotein cholesteryl ester by rat liver in vivo

1990 ◽  
Vol 272 (3) ◽  
pp. 735-741 ◽  
Author(s):  
J C Holder ◽  
V A Zammit ◽  
D S Robinson
Keyword(s):  
Fatty Acid ◽  
Cholesteryl Ester ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Apoprotein B ◽  
Preferential Uptake ◽  
Triacylglycerol Fraction

The removal from the blood and the uptake by the liver of injected very-low-density lipoprotein (VLDL) preparations that had been radiolabelled in their apoprotein and cholesteryl ester moieties was studied in lactating rats. Radiolabelled cholesteryl ester was removed from the blood and taken up by the liver more rapidly than sucrose-radiolabelled apoprotein. Near-maximum cholesteryl ester uptake by the liver occurred within 5 min of the injection of the VLDL. At this time, apoprotein B uptake by the liver was only about 25% of the maximum. Maximum uptake of the injected VLDL apoprotein B label was not achieved until at least 15 min after injection, by which time the total uptakes of cholesteryl ester and apoprotein B label were very similar. The results suggest that preferential uptake of the lipoprotein cholesteryl ester by the liver occurred before endocytosis of the entire lipoprotein complex. The fate of the injected VLDL cholesteryl ester after its uptake by the liver was also monitored. Radiolabel associated with the hepatic cholesteryl ester fraction fell steadily from its early maximum level, the rate of fall being faster and more extensive when the fatty acid, rather than the cholesterol, moiety of the ester was labelled. By 30 min after the injection of VLDL containing [3H]cholesteryl ester, over one-third of the injected label was already present as [3H]cholesterol in the liver. When VLDL containing cholesteryl [14C]oleate was injected, a substantial proportion (about 25%) of the injected radiolabelled fatty acid appeared in the hepatic triacylglycerol fraction within 60 min: very little was present in the plasma triacylglycerol fraction at this time.

scholarly journals Chronic exogenous hyperinsulinaemia does not modify the acute inhibitory effect of insulin on the secretion of very-low-density lipoprotein triacylglycerol and apolipoprotein B in primary cultures of rat hepatocytes

1996 ◽  
Vol 314 (1) ◽  
pp. 103-108 ◽  
Author(s):  
Catherine S. BOURGEOIS ◽  
David WIGGINS ◽  
Geoffrey F. GIBBONS
Keyword(s):  
Apolipoprotein B ◽  
Low Density Lipoprotein ◽  
Primary Cultures ◽  
Density Lipoprotein ◽  
Inhibitory Effect ◽  
Cell Protein ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Plasma Insulin Concentration

Male Wistar rats were fitted with subcutaneous osmotic minipumps that delivered insulin at a constant rate of 0.20 i.u./h for 7 days. This treatment raised the plasma insulin concentration from 31±4 to 201±64 μ-i.u./ml. Hepatocytes prepared from the hyperinsulinaemic animals secreted very-low-density lipoprotein (VLDL) triacylglycerol (TAG) at a higher rate (172±21 μg per 24 h per mg cell protein) than did those from sham-operated controls (109±12 μg per 24 h per mg) (P < 0.05). However, chronic exogenous hyperinsulinaemia had no stimulatory effect on the secretion of VLDL apolipoprotein B (apoB) in derived hepatocytes compared with those from the sham-operated controls (2.32±0.38 compared with 3.09±0.40 μg per 24 h per mg). Hepatocytes from the hyperinsulinaemic rats thus secreted larger VLDL particles as evidenced by the increased TAG:apoB ratio (78.4±13.1 compared with 38.4±7.6; P < 0.05). In hepatocytes from the hyperinsulinaemic rats a larger proportion of the newly synthesized TAG was secreted as VLDL. Hepatocytes from the hyperinsulinaemic and the sham-operated control animals were equally sensitive to the inhibitory effect of insulin added in vitro on the secretion of VLDL TAG. Insulin added in vitro to the culture medium of hepatocytes from hyperinsulinaemic animals significantly decreased the TAG:apoB ratio of the secreted VLDL. This change did not occur in hepatocytes from sham-operated rats. These results suggest that, in vivo, chronic hyperinsulinaemia is not in itself sufficient to desensitize the liver to the acute inhibitory effect of insulin on the secretion of VLDL.

scholarly journals Long-term maintenance of high rates of very-low-density-lipoprotein secretion in hepatocyte cultures. A model for studying the direct effects of insulin and insulin deficiency in vitro

1989 ◽  
Vol 263 (3) ◽  
pp. 937-943 ◽  
Author(s):  
J M Duerden ◽  
S M Bartlett ◽  
G F Gibbons
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Secretory Process ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Triacylglycerol Synthesis ◽  
Vldl Secretion ◽  
Pre Treatment

High rates of hepatic cellular triacylglycerol synthesis and very-low-density-lipoprotein (VLDL) triacylglycerol output were maintained in vitro for at least 3 days when hepatocytes were cultured in a medium lacking insulin but supplemented with 1 microM-dexamethasone, 10 mM-lactate, 1 mM-pyruvate and 0.75 mM-oleate (supplemented medium). Under these conditions VLDL output remained constant, whereas cell triacyglycerol content increased 10-fold over 3 days, suggesting that the secretory process was saturated. Insulin, present during the first 24 h period, enhanced the storage of cellular triacylglycerol by inhibiting the secretion of VLDL. This stored triacyglycerol was subsequently released into the medium as VLDL if insulin was removed. With the supplemented medium the increased rate of VLDL secretion after insulin removal exceeded that observed under ‘saturating’ conditions, suggesting that pre-treatment with insulin enhanced the capacity for VLDL secretion. In contrast with the short-term (24 h) effects of insulin, longer-term exposure (greater than 48 h) to insulin enhanced the secretion of VLDL compared with insulin-untreated cultures. Under these conditions, insulin increased the net rates of triacylglycerol synthesis. The results suggest that insulin affects the secretion of VLDL triacylglycerol by two distinct and opposing mechanisms: first, by direct inhibition of secretion; second by increasing triacylglycerol synthesis, which stimulates secretion. The net effect at any time depends upon the relative importance of each of these processes.

The Passage of Apoproteins from Plasma Lipoproteins into the Lipoproteins of Peripheral Lymph in Man

1977 ◽  
Vol 53 (3) ◽  
pp. 221-226
Author(s):  
D. Reichl ◽  
N. B. Myant ◽  
J. J. Pflug ◽  
D. N. Rudra
Keyword(s):  
Intravenous Injection ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Plasma Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Intermediate Density Lipoprotein ◽  
Peripheral Lymph ◽  
Apoprotein B ◽  
Intermediate Density

1. The transport of apoprotein B from the lipoproteins of plasma into the lipoproteins of lymph draining the foot has been studied in four men with type III hyperlipoproteinaemia. 2. Three subjects were given autologous 125I-labelled very-low-density lipoprotein (VLDL) and 131I-labelled low-density lipoprotein (LDL) by intravenous injection; the fourth was given autologous 125I-labelled VLDL and 131I-labelled intermediate-density lipoprotein (IDL) plus LDL. 3. The 125I/131I ratios in serum and lymph apoprotein B, and the 125I and 131I specific radioactivities of apoprotein B in VLDL, IDL and LDL from serum and lymph, indicate that apoprotein B in the circulating VLDL can reach peripheral lymph without the intermediacy of circulating LDL.

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