David Mymin

Fatty infiltration of liver in hyperlipidemic patients

Hyperlipidemia is a known risk factor for fatty infiltration of the liver, a condition that can progress to cirrhosis and liver failure. The objectives of this study were to document the prevalence of fatty infiltration in the livers of hyperlipidemic patients and to identify the predictor variables associated with this condition. Over an 18-month recruitment period, clinical, biochemical, and radiologic assessments were performed in a cross-sectional manner in 95 adult patients referred to an urban hospital-based lipid clinic for evaluation and management of hyperlipidemia. The mean (±sd) age of the patients was 55 ± 13 years. Forty-eight (51%) were male. Fifty-two patients (55%) had hypercholesterolemia, 25 (26%) severe hypertriglyceridemia, 14 (15%) mixed hyperlipidemia, and 4 (4%) moderate hypertriglyceridemia. Obesity and diabetes were present in 36 (38%) and 12 (12%) of cases, respectively. A total of 61 (64%) patients had elevated liver enzyme tests. The most common enzyme abnormalities were an elevated serum ALT in 45 (47%) and GGT in 43 (45%) of patients. Ultrasound findings revealed diffuse fatty liver in 47 patients (50%), of which 21 cases (22%) were mild, 18 (19%) moderate, and 8 (9%) severe. The majority of patients with hypercholesterolemia [35/52 (67%)] had normal ultrasounds, whereas severe hypertriglyceridemia and mixed hyperlipidemia were frequently associated with radiologic evidence of fatty liver (odds ratios 5.9 and 5.1 respectively, P < 0.01). Independent predictors of fatty liver were; AST (P = 0.001), hyperglycemia (P = 0.02), and age (P = 0.04). In a model incorporating known risk factors for fatty liver, diabetes was the only risk factor other than hypertriglyceridemia that was significantly associated with fatty infiltration. No such effect was seen with age, gender, obesity, or alcohol consumption. In conclusions, the results of this study indicate that ultrasonographic evidence of fatty infiltration of the liver is evident in approximately 50% of patients with hyperlipidemia. Hypertriglyceridemia is the lipid profile most often associated with this condition. Serum AST values, hyperglycemia, and age independently predict the presence of fatty infiltration, while hypertriglyceridemia and diabetes are the only risk factors that significantly increase the risk of fatty infiltration in hyperlipidemic patients.

Lipids and atherosclerosis

Atherosclerosis is the leading cause of death in North America and within the next two decades will be the leading cause worldwide. Atherosclerosis is characterized by vascular obstruction from the deposits of plaque, resulting in reduced blood flow. Plaque rupture and the consequent thrombosis may lead to sudden blockage of the arteries and cause heart attack. High serum lipid levels, especially the elevated level of low-density lipoprotein (LDL), have been shown to be strongly related to the development of atherosclerosis. It is generally accepted that atherosclerotic lesions are initiated via an enhancement of LDL uptake by monocytes and macrophages. In the liver, uptake of plasma LDL is mediated via specific LDL receptors, but a scavenger receptor system is employed by macrophages. Plasma LDL must be modified prior to uptake by macrophages. Analysis of the lipid content in the oxidatively modified LDL from hyper lipidemic patients revealed that the level of lysophosphatidylcholine was greatly elevated, and the high level of the lysolipid was shown to impair the endothelium-dependent relaxation of the blood vessels. In a separate study, we showed that a high level of homocysteine caused the increase in cholesterol production and apolipoprotein B-100 secretion in hepatic cells. Statins have been used effectively to control the production of cholesterol in the liver, and recently, ezetimibe has been shown to supplement the efficacy of statins by inhibiting cholesterol absorption. The factor of elevated levels of triglyceride-rich lipoproteins in association with depressed high-density lipoproteins, usually in the context of insulin resistance, is an important contributor to atherosclerosis and can be effectively treated with fibric acid derivatives. In hyperhomocysteinemia, folic acid supplements may have a role in the control of cholesterol by reducing the plasma homocysteine level.

Serum lipids, plant sterols, and cholesterol kinetic responses to plant sterol supplementation in phytosterolemia heterozygotes and control individuals

BACKGROUND Plant sterol (PS) supplementation is increasingly accepted as a dietary strategy to lower plasma cholesterol concentrations. However, information is scarce about the effect of increased PS intake in potentially vulnerable groups, such as phytosterolemia heterozygotes (HET). OBJECTIVE This study assessed the responsiveness of circulating PS and lipid concentrations and cholesterol kinetics (absorption and synthesis) to daily PS supplementation in HET (ABCG8 S107X mutation) compared with a healthy control cohort. DESIGN A double-blind, randomized, crossover, placebo-controlled study was conducted in 10 HET and 15 control subjects. The participants had a mean (±SEM) age of 34 ± 2 y and a BMI (in kg/m²) of 29.9 ± 1.1 and consumed ∼1.6 g PS or placebo capsules daily with supper for 4 wk. Cholesterol absorption and synthesis were assessed by using [¹³C]cholesterol and deuterium oxide, respectively. RESULTS Plasma LDL-cholesterol concentrations decreased (P = 0.006) in both groups after PS supplementation (HET: 2.73 ± 0.19 mmol/L; control: 3.11 ± 0.19 mmol/L) compared with placebo (HET: 3.12 ± 0.20 mmol/L; control: 3.50 ± 0.21 mmol/L), whereas PS concentrations (campesterol+β-sitosterol) increased (P = 0.03) in both groups after PS supplementation (HET: 39.72 ± 6.05 μmol/L; control: 24.03 ± 1.65 μmol/L) compared with placebo (HET: 27.32 ± 3.80 μmol/L; control: 21.12 ± 2.05 μmol/L). Cholesterol absorption efficiency decreased (P = 0.010) by ∼22% and ∼17% and synthesis rates increased (P = 0.040) by ∼20% and ∼24% in the HET and control groups, respectively, in response to PS consumption compared with placebo. CONCLUSION These data suggest that heterozygosity for the ABCG8 S107X mutation does not influence the action of dietary PS on circulating cholesterol concentrations but may affect sterol absorption.

Atherosclerosis risk factors: the possible role of homocysteine

Atherosclerosis is the leading cause of death in North America. It is characterized by thickening of the coronary artery wall by the formation of plaques, resulting in reduced blood flow. Plaque rupture and the consequent thrombosis may lead to sudden blockage of arteries and causing stroke and heart attack. In the last several decades, more than 250 factors associated with the development of coronary artery disease have been identified. Recently, a relationship between atherosclerosis and elevated homocysteine level in the blood has been established. The mechanism for the production of atherosclerosis by homocysteine has been investigated. When human hepatoma cells (HepG2) were incubated with 4mM homocysteine, enhancements in the production of cholesterol and secretion of apolipoprotein B-100 were observed. The stimulatory effect on cholesterol synthesis was mediated via the enhancement of HMG-CoA reductase, which catalyzes the rate-limiting step in cholesterol biosynthesis. Cholesterol appears to play an important role in the regulation of apoB-100 secretion by hepatocytes. It is plausible that the increase in apoB secretion was caused by the elevated cholesterol level induced by homocysteine. The ability of homocysteine to produce a higher amount of cholesterol and promote the secretion of apoB would provide a plausible mechanism for the observed relationship between hyperhomocysteinemia and the development of atherogenesis and coronary artery disease.

Cyclooxygenase expression is elevated in retinoic acid-differentiated U937 cells

Cyclooxygenase (COX) is the rate-limiting enzyme for the biosynthesis of prostaglandins in monocytes/macrophages. The COX-1 is constitutively expressed in most tissues and may be involved in cellular homeostasis, whereas the COX-2 is an inducible enzyme that may play an important role in inflammation and mitogenesis. When U937 monocytic cells were incubated with retinoic acid (RA) for 48 h, cell differentiation took place with concomitant increases in prostaglandin E2 (PGE2) production and COX activity. In this study, the mechanism of RA (all-trans- or 9-cis-RA)-induced enhancement of PGE2 biosynthesis in U937 cells was examined. Treatment of cells with all-trans- or 9-cis-RA up to 48 h caused an increase in PGE2 production in a time- and dose-dependent manner. Both RA isomers caused the enhancement of PGE2 production and the up-regulation of COX-1 expression at the protein and mRNA levels. The increase in COX-1 mRNA was found to precede the increase in COX-1 protein expression. Interestingly, the COX-2 protein and COX-2 mRNA were not detected in U937 cells, and their levels remained undetectable during the entire course of RA treatment. We conclude that treatment of U937 cells by RA for 48 h caused the initiation of cell differentiation, which was found to be concomitant with a significant increase in PGE2 production mediated via the up-regulation of COX-1 mRNA and protein expression.

Effects of atorvastatin treatment on the oxidatively modified low density lipoprotein in hyperlipidemic patients

Atorvastatin is an established HMG-CoA reductase inhibitor which effectively reduces the plasma low density lipoprotein (LDL)-cholesterol level in hyperlipidemic patients. The present study was designed to investigate whether atorvastatin treatment can modify the biochemical content of oxidized LDL in hyperlipidemic patients and the ability of oxidized LDL to impair the endothelium-dependent relaxation of blood vessels. With atorvastatin (10 mg/day) treatment for 4 weeks in 19 type IIa hyperlipidemic patients, total cholesterol level was lowered by 23%, LDL-cholesterol was lowered by 32% and triacylglycerol was lowered by 19% as compared with dietary therapy alone. High density lipoprotein levels increased by approximatly 9%. The ability of oxidized LDL from hyperlipidemic patients after atorvastatin treatment to impair the endothelium-dependent relaxation was significantly reduced as compared with dietary intervention alone. Analysis of the biochemical contents of oxidized LDL from this group revealed that there was an 11% reduction in lysophosphatidylcholine (LPC) as compared with the group that received only dietary counseling. A decrease in the C16:0 moiety with a corresponding increase in the C18:0 moiety of LPC in the oxidized LDL was also observed in the atorvastatin treated group. We propose that the observed reduction and the change in composition of acyl groups in LPC in the oxidized LDL of the atorvastatin-treated group results from a combination of the continued dietary treatment as well as drug therapy. In view of an observation that both C16:0 and C18:0 LPC species are equally potent in the impairment of endothelium-dependent relaxation of the aortic rings, we feel that the reduced level of LPC in the oxidized LDL produced by atorvastatin treatment is partially responsible for the improvement in endothelium control of vascular tone.

Ezetimibe reduces plant sterol accumulation and favorably increases platelet count in sitosterolemia.

OBJECTIVE To assess if ezetimibe (EZE), a sterol-absorption inhibitor, improves platelet (PLT) count and size relative to its effect on plasma plant sterol (PS) in patients with sitosterolemia (STSL). STUDY DESIGN Patients with STSL (5 males, 3 females, 16-56 years of age) receiving EZE intervention as part of their routine care participated in this study. EZE was discontinued for 14 weeks (off) and then resumed for another 14 weeks (on). Hematology variables along with plasma and red blood cells (RBC) PS and total cholesterol (TC) levels were measured at the end of each phase. RESULTS EZE increased PLT count (23% ± 9%) and decreased mean PLT volume (MPV; 10% ± 3%, all P < .05). In patients off EZE, PLT counts inversely correlated (r = -0.96 and r = -0.91, all P < .01) with plasma and RBC PS to TC ratio (PS/TC), and MPV positively correlated (r = 0.91, P = .03 and r = 0.93, P = .02) with plasma and RBC PS/TC. EZE reduced plasma and RBC sitosterol (-35% ± 4% and -28% ± 3%), total PS (-37% ± 4% and -28% ± 3%, all P < .0001) levels, and PS/TC (-27% ± 4% and -28% ± 4%, P < .01). CONCLUSIONS EZE reduces plasma and RBC PS levels, while increasing PLT count and decreasing MPV, and thereby may reduce the risk for bleeding in STSL. Plasma PS levels and ABCG5/ABCG8 genes should be analyzed in patients with unexplained hematologic abnormalities.

The effect of fenofibrate treatment on endothelium-dependent relaxation induced by oxidative modified low density lipoprotein from hyperlipidemic patients

The objective of the research project was to investigate whether fenofibrate treatment may alter the biochemical content of the oxidized LDL and consequently its ability to impair the endothelium-dependent relaxation in hyperlipidemic patients. We hypothesized that fenofibrate treatment of hyperlipidemic patients may attenuate the ability of their oxidized LDL to impair the endothelium-dependent relaxation of the blood vessels as a consequence of fenofibrate-induced changes to the content and composition of lysoPC in the LDL molecule.Hyperlipidemic patients (Type IIb and Type IV) were recruited from the Lipid Clinic, HSC, Winnipeg, Canada, for this study. A blood sample was taken immediately after the recruitment, a second sample was taken after 6 weeks of dietary treatment, and a third sample was taken after 8 weeks of fenofibrate treatment. LDL was isolated from the plasma and oxidized by copper sulfate. Fenofibrate was shown to be highly effect in the reduction of total cholesterol, LDL cholesterol and triglycerides in these patients. Fenofibrate treatment also caused the attenuation of impairment of endothelium-dependent relaxation by the oxidized LDL from these patients. A slight reduction of lysophosphatidylcholine level was also found in the oxidized LDL of the fenofibrate treated patients, relative to LDL isolated after dietary treatment. In addition there were no changes in the fatty acid levels of the lysophosphatidylcholine isolated from LDL. Taken together, our results suggest that while the reduced lysophosphatidylcholine levels may contribute to the attenuated impairment of the endothelium-dependent relaxation of the aortic ring, other unidentified factors impacted by fenofibrate are likely to contribute to the attenuated effects.

Evaluation of a new apolipoprotein(a) isoform-independent assay for serum Lipoprotein(a).

The risk factor, Lipoprotein(a), [(Lp(a)], has been measured in numerous clinical studies by a variety of immunochemical assay methods. It is becoming apparent that for many of these assays antibody specificity towards the apolipoprotein(a) [apo(a)] repetitive component [the kringle 4 - type 2 repeats] and apo(a) size heterogeneity can significantly affect the accuracy of serum Lp(a) measurements. To address this issue, we investigated whether our current in house Lp(a) [Mercodia] assay showed such bias compared to a recently available assay [Apo-Tek], claiming to possess superior capability for isoform-independent measurement of Lp(a). Levels of Lipoprotein(a) by both Apo-Tek and Mercodia assays correlated inversely with apo(a) isoform sizes. No significant differences were observed between assays in ranges of Lp(a) concentration within each isoform group. The Mercodia assay exhibited similar isoform-independent behaviour to that of Apo-Tek for e quantitation of serum Lipoprotein(a). Essentially identical results were obtained by the two methods, suggesting that Mercodia assays capture monoclonal antibody also (as is the case for Apo-Tek) does not recognize the kringle 4-type 2 repetitive domain of apo(a). Correlation of Lp(a) concentrations in patient specimens between Apo-Tek and Mercodia assays showed good agreement, although an overall higher degree of imprecision and non-linearity was noted for the Apo-Tek procedure. A change-over to the Apo-Tek assay would therefore not improve on our current assessment of risk contribution from Lp(a) for atherosclerotic vascular disease in individuals with measurable levels of circulating Lipoprotein(a).

Thyroid Hormone Status in Sitosterolemia Is Modified by Ezetimibe

Objectives To assess the association between biomarkers of thyroid status and 5&agr;‐stanols in patients with sitosterolemia treated with ezetimibe (EZE). Study design Eight patients with sitosterolemia (16–56 years of age) were studied during 14 weeks off EZE therapy and 14 weeks on EZE (10 mg/day). Serum thyroid biomarkers (free triiodothyronine [FT3], free thyroxine [FT4], FT3/FT4 ratio, thyroid‐stimulating hormone), 5&agr;‐stanols (sitostanol and cholestanol), and cholestanol precursors (total cholesterol and its synthesis marker lathosterol, and 7&agr;‐hydroxy‐4‐cholesten‐3‐one cholestenol) were measured at baseline and during the 14 weeks off EZE and on EZE. Results EZE increased FT3/FT4 (10% ± 4%; P = .02). EZE reduced plasma and red blood cells sitostanol (−38% ± 6% and −20% ± 4%; all P < .05) and cholestanol (−18% ± 6% and −13% ± 3%; all P < .05). The change in plasma cholestanol level on EZE inversely correlated with the change in FT3/FT4 (r = −0.86; P = .01). EZE lowered total cholesterol (P < .0001) and did not affect 7&agr;‐hydroxy‐4‐cholesten‐3‐one cholestanol. EZE increased (P < .0001) lathosterol initially, but the level was not sustained, resulting in similar levels at week 14 off EZE and on EZE. Conclusion In patients with STSL, 5&agr;‐stanols levels might be associated with thyroid function. EZE reduces circulating 5&agr;‐stanols while increasing FT3/FT4, implying increased conversion of T4 to T3, thus possibly improving thyroid hormone status. Trial registration ClinicalTrials.gov NCT01584206.