Factors affecting the regulation of apo B secretion by liver cells

Lipid profile as a novel prognostic predictor for patients with acute myeloid leukemia

Purpose

This study investigated the relationship between serum lipid levels and clinical outcomes in acute myeloid leukemia (AML) by establishing a predictive risk classification model.

Method

A total of 214 AML patients who were pathologically diagnosed and treated with standard induction chemotherapy at Sun Yat-Sen University Cancer Center were included. The patients were randomly divided into the training (n = 107) and validation (n=107) cohorts. Univariate and multivariate Cox analyses were used to assess the value of triglyceride (TG), Apolipoprotein B (Apo B), Apo Apolipoprotein A-I (Apo A-I), cholesterol (CHO), and high-density lipoprotein (HDL) as prognostic factors for AML.

Results

After a series of data analyses, a five-factor model was established to divide the patients into high- and low-risk groups. Kaplan-Meier survival analysis showed that the high-risk group had a poor prognosis (P<0.05). The area under the curve of the novel model for five-year OS was 0.737. A nomogram was constructed to integrate the model with age and the 2017 ELN cytogenetic classification, with the merged model showing improved accuracy with an area under the curve of 0.987 for five-year OS.

Conclusion

A novel model was constructed using a combination of the serum lipid profile and clinical characteristics of AML patients to enhance the predictive accuracy of clinical outcomes. The nomogram used the lipid profile which is routinely tested in clinical blood biochemistry and showed both specific prognostic and therapeutic potential.

New dimension of statin action on ApoB atherogenicity

Newer, more effective statins are powerful agents for reducing elevated levels of low-density lipoprotein (LDL) cholesterol and thereby lowering the risk of coronary heart disease (CHD) and related adverse events. Although LDL remains the primary target of therapy for reducing CHD risk, increased interest is focusing on apolipoprotein B (apoB)-containing lipoprotein subfractions--particularly very-low-density lipoprotein (VLDL). VLDL remnants, and intermediate-density lipoproteins (IDL)--as secondary targets of therapy. Elevated apoB is known to be an important risk factor for CHD, and dysregulation of the metabolism of apoB-containing lipoproteins is involved in the progression of atherosclerosis. Statins reduce circulating concentrations of atherogenic apoB-containing lipoproteins by decreasing the production of VLDL in the liver and, thus, the production of VLDL remnants and LDL. Statins also increase the clearance of these particles through upregulation of LDL receptors in the liver. Efforts to develop statins with enhanced lipid-modifying properties are ongoing. The optimal statin would offer a high degree of inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, a prolonged duration of action, hepatic selectivity for maximal upregulation of LDL receptors, and a low potential for drug-drug interactions. Recent studies have shown that rosuvastatin, a new agent in this class, demonstrates these qualities. Rosuvastatin is a highly effective inhibitor of HMG-CoA reductase, is relatively nonlipophilic, has a half-life of approximately 20 h, exhibits hepatic selectivity, has little systemic availability, and has a low potential for drug-drug interactions because of its limited degree of metabolism by the cytochrome P450 system. A recent double-blind, crossover study revealed that treatment with rosuvastatin resulted in marked reductions in apoB-containing lipoproteins in patients with type IIa or IIb dyslipidemia. By reducing the number of atherogenic lipoprotein particles, rosuvastatin decreases the atherosclerotic burden in hyperlipidemic patients at high risk for CHD and related adverse outcomes.

Suppression of VLDL associated triacylglycerol secretion by both alpha- and beta-adrenoceptor agonists in isolated rat hepatocytes

The signal transduction pathways of intracellular calcium and adenosin 3',5'-cyclic monophosphate (cAMP) participate in the regulation of intrahepatic metabolism of very low density lipoproteins (VLDL). The adrenoceptors are linked to calcium and cAMP signal transduction pathways so it is proposed that they may be involved in the regulation of VLDL secretion. The current study is designed to test the effects of alpha- and beta-adrenoceptor agonists and antagonists on triacylglycerol secretion in freshly isolated rat hepatocytes. The inhibitory effect of epinephrine appeared at concentrations of more than 1 microM and reached a plateau at 100 microM. Epinephrine concentration for the half of the maximal bio-effect (EC(50)) was about 10 microM. Epinephrine at a concentration of 10 microM suppressed the secretion of triacylglycerol by 33% (P<or=0.01) and increased cellular content of triacylglycerol (18%, P<or=0.05) and total phospholipids (20%, P<or=0.05). Time course experiments for triacylglycerol secretion exhibited a linear relationship with a slope of 8.2+/-0.6 mug triacylglycerol/3 h mg cell protein. In the presence of epinephrine, cellular triacylglycerol and total phospholipids were slightly but significantly higher than the respective control at all points of time examined. The inhibitory effect elicited by epinephrine (10 microM) was abolished by the inclusion of the general alpha-adrenoceptor antagonist phentolamine (10 microM) and the specific alpha(1)-antagonist prazosin (1 microM) but not with the nonselective beta-antagonist propranolol (10 microM). Trifluoperazine an alpha-adrenoceptor antagonist and anticalmodulin agent, concealed the inhibitory effect of epinephrine in a concentration dependent manner, whereas theobromine a cAMP-phosphodiestrase inhibitor did not have any significant effect. The secretion of triacylglycerol was decreased not only by the alpha-adrenoceptor agonist phenylephrine (10 microM) but also by the beta-agonist isoproterenol (10 microM). Dibutyryl-cAMP (0.1 mM) also inhibited the secretion of triacylglycerol by 30% (P<or=0.01). The results suggest that epinephrine inhibits the secretion of triacylglycerol from rat hepatocytes via the alpha(1)-adrenoceptor while stimulation of beta- as well as alpha-adrenoceptors can also exert a similar effect.

A common apolipoprotein B signal peptide polymorphism modifies the relation between plasma non-esterified fatty acids and triglyceride concentration in men

Insulin and non-esterified fatty acids (NEFA) are important regulators of triglyceride metabolism. The relations between these compounds and the effect of a common 3 amino acid deletion in the apolipoprotein B (ApoB) signal peptide (SP) following an oral glucose challenge have been investigated. The frequency of the shorter SP-24 allele was 32% (95% C.I. 29.5-36.5) in 725 subjects undergoing an oral glucose tolerance test (OGTT). Fasting plasma triglyceride concentration was positively correlated with fasting plasma insulin concentration and negatively with the degree of plasma NEFA suppression following the glucose challenge. Linear regression analysis showed the relation between triglyceride concentration and NEFA suppression, but not the relation between triglyceride concentration and fasting insulin, to be altered by the SP polymorphism in men but not in women. The strength of the association was dependent on the number of SP-24 alleles, with SP-24 homozygotes showing the greatest dependence (men P=0.031, women P=0. 914). It was proposed that the complex regulation of very low density lipoprotein (VLDL) output by NEFA and by insulin may explain, at least in part, the conflicting reports concerning the presence of the ApoB SP polymorphism, fasting serum lipids and ischaemic heart disease (IHD).

Stearoyl-CoA desaturase 1 coding sequences and antisense RNA affect lipid secretion in transfected chicken LMH hepatoma cells

Hepatic stearoyl CoA desaturase (SCD) activity in chickens from a fat line is higher than that of chickens from a lean line and correlates with plasma triacylglycerol concentrations. Furthermore, in these lines, the hepatic SCD1 mRNA level is positively correlated with the adipose tissue weight. To analyze the contribution of the SCD1 gene in the regulation of adiposity in the early stages of triacylglycerol secretion, SCD1 coding sequence and antisense RNA expression vectors were transfected in LMH cells. After selection, these cells were analyzed with regard to SCD1 expression and lipid secretion. The amounts of secreted triacylglycerols and phospholipids were shown to be higher in LMH cells transfected with the SCD1 gene, but reduced in those transfected with the SCD1 antisense sequences when compared to cells transfected with the vector alone (without SCD1 sequences). These results provide direct evidence that the expression of the SCD1 gene plays a major role in the triacylglycerol and phospholipid secretion process.

Impaired secretion of very low density lipoprotein-triglycerides by apolipoprotein E- deficient mouse hepatocytes

To explore mechanisms underlying triglyceride (TG) accumulation in livers of chow-fed apo E-deficient mice (Kuipers, F., J.M. van Ree, M.H. Hofker, H. Wolters, G. In't Veld, R.J. Vonk, H.M.G. Princen, and L.M. Havekes. 1996. Hepatology. 24:241-247), we investigated the effects of apo E deficiency on secretion of VLDL-associated TG (a) in vivo in mice, (b) in isolated perfused mouse livers, and (c) in cultured mouse hepatocytes. (a) Hepatic VLDL-TG production rate in vivo, determined after Triton WR1339 injection, was reduced by 46% in apo E-deficient mice compared with controls. To eliminate the possibility that impaired VLDL secretion is caused by aspecific changes in hepatic function due to hypercholesterolemia, VLDL-TG production rates were also measured in apo E-deficient mice after transplantation of wild-type mouse bone marrow. Bone marrow- transplanted apo E-deficient mice, which do not express apo E in hepatocytes, showed normalized plasma cholesterol levels, but VLDL-TG production was reduced by 59%. (b) VLDL-TG production by isolated perfused livers from apo E-deficient mice was 50% lower than production by livers from control mice. Lipid composition of nascent VLDL particles isolated from the perfusate was similar for both groups. (c) Mass VLDL-TG secretion by cultured apo E-deficient hepatocytes was reduced by 23% compared with control values in serum-free medium, and by 61% in the presence of oleate in medium (0. 75 mM) to stimulate lipogenesis. Electron microscopic evaluation revealed a smaller average size for VLDL particles produced by apo E-deficient cells compared with control cells in the presence of oleate (38 and 49 nm, respectively). In short-term labeling studies, apo E-deficient and control cells showed a similar time-dependent accumulation of [3H]TG formed from [3H]glycerol, yet secretion of newly synthesized VLDL-associated [3H]TG by apo E-deficient cells was reduced by 60 and 73% in the absence and presence of oleate, respectively. We conclude that apo E, in addition to its role in lipoprotein clearance, has a physiological function in the VLDL assembly-secretion cascade.