Teik Chye Ooi

Adipocytes Produce Aldosterone Through Calcineurin-Dependent Signaling Pathways: Implications in Diabetes Mellitus–Associated Obesity and Vascular Dysfunction

We reported aldosterone as a novel adipocyte-derived factor that regulates vascular function. We aimed to investigate molecular mechanisms, signaling pathways, and functional significance of adipocyte-derived aldosterone and to test whether adipocyte-derived aldosterone is increased in diabetes mellitus–associated obesity, which contributes to vascular dysfunction. Studies were performed in the 3T3-L1 adipocyte cell line and mature adipocytes isolated from human and mouse (C57BL/6J) adipose tissue. Mesenteric arteries with and without perivascular fat and mature adipocytes were obtained from obese diabetic db/db and control db/+ mice. Aldosterone synthase (CYP11B2; mRNA and protein) was detected in 3T3-L1 and mature adipocytes, which secrete aldosterone basally and in response to angiotensin II (Ang II). In 3T3-L1 adipocytes, Ang II stimulation increased aldosterone secretion and CYP11B2 expression. Ang II effects were blunted by an Ang II type 1 receptor antagonist (candesartan) and inhibitors of calcineurin (cyclosporine A and FK506) and nuclear factor of activated T-cells (VIVIT). FAD286 (aldosterone synthase inhibitor) blunted adipocyte differentiation. In candesartan-treated db/db mice (1 mg/kg per day, 4 weeks) increased plasma aldosterone, CYP11B2 expression, and aldosterone secretion were reduced. Acetylcholine-induced relaxation in db/db mesenteric arteries containing perivascular fat was improved by eplerenone (mineralocorticoid receptor antagonist) without effect in db/+ mice. Adipocytes possess aldosterone synthase and produce aldosterone in an Ang II/Ang II type 1 receptor/calcineurin/nuclear factor of activated T-cells–dependent manner. Functionally adipocyte-derived aldosterone regulates adipocyte differentiation and vascular function in an autocrine and paracrine manner, respectively. These novel findings identify adipocytes as a putative link between aldosterone and vascular dysfunction in diabetes mellitus–associated obesity.

Novel Loss-of-Function PCSK9 Variant Is Associated with Low Plasma LDL Cholesterol in a French-Canadian Family and with Impaired Processing and Secretion in Cell Culture

BACKGROUND PCSK9 (proprotein convertase subtilisin/kexin type 9) is a polymorphic gene whose protein product regulates plasma LDL cholesterol (LDLC) concentrations by shuttling liver LDL receptors (LDLRs) for degradation. PCSK9 variants that cause a gain or loss of PCSK9 function are associated with hyper- or hypocholesterolemia, which increases or reduces the risk of cardiovascular disease, respectively. We studied the clinical and molecular characteristics of a novel PCSK9 loss-of-function sequence variant in a white French-Canadian family. METHODS In vivo plasma and ex vivo secreted PCSK9 concentrations were measured with a commercial ELISA. We sequenced the PCSK9 exons for 15 members of a family, the proband of which exhibited very low plasma PCSK9 and LDLC concentrations. We then conducted a structure/function analysis of the novel PCSK9 variant in cell culture to identify its phenotypic basis. RESULTS We identified a PCSK9 sequence variant in the French-Canadian family that produced the PCSK9 Q152H substitution. Family members carrying this variant had mean decreases in circulating PCSK9 and LDLC concentrations of 79% and 48%, respectively, compared with unrelated noncarriers (n=210). In cell culture, the proPCSK9-Q152H variant did not undergo efficient autocatalytic cleavage and was not secreted. Cells transiently transfected with PCSK9-Q152H cDNA had LDLR concentrations that were significantly higher than those of cells overproducing wild-type PCSK9 (PCSK9-WT). Cotransfection of PCSK9-Q152H and PCSK9-WT cDNAs produced a 78% decrease in the secreted PCSK9-WT protein compared with control cells. CONCLUSIONS Collectively, our results demonstrate that the PCSK9-Q152H variant markedly lowers plasma PCSK9 and LDLC concentrations in heterozygous carriers via decreased autocatalytic processing and secretion, and hence, inactivity on the LDLR.

Efficacy and Safety of a New Hydroxymethylglutaryl-Coenzyme A Reductase Inhibitor, Atorvastatin, in Patients with Combined Hyperlipidemia: Comparison with Fenofibrate

This 24-week, randomized, open-label multicenter study evaluated the efficacy and safety of atorvastatin compared with fenofibrate in the treatment of patients with combined hyperlipidemia (CHL). Following a 6-week baseline period, 84 patients with CHL were randomly assigned to either atorvastatin treatment, 10 mg QD for 12 weeks increasing to 20 mg QD for 12 weeks, or fenofibrate treatment, 100 mg TID for 24 weeks. Changes from baseline in lipid parameters were evaluated at weeks 12 and 24. At both 10- and 20-mg doses, atorvastatin treatment resulted in significantly greater reductions in LDL cholesterol, apolipoprotein (apo) B, total cholesterol, LDL-apoB, and lipoprotein-B compared to 300-mg fenofibrate treatment (P < .05). While atorvastatin also resulted in clinically significant reductions in triglyceride, VLDL cholesterol, apoB in VLDL, triglyceride in VLDL, and apoC-III and significant increases in HDL cholesterol and apoA-I levels, fenofibrate was more effective than atorvastatin in altering all these parameters. However, by significantly affecting both the cholesterol-rich and triglyceride-rich particles, atorvastatin holds promise as a lipid-regulator able to adequately treat a broad range of patients that includes those with CHL.

Effect of gemfibrozil and lovastatin on postprandial lipoprotein clearance in the hypoalphalipoproteinemia and hypertriglyceridemia syndrome

Eleven men with hypoalphalipoproteinemia (HPAL; fasting plasma high density lipoprotein (HDL) cholesterol level of < 0.9 mmol/l), mild hypertriglyceridemia (HTG; triglycerides (TG) level of 1.75-7.5 mmol/l) and a normal calculated LDL cholesterol level (< 3.7 mmol/l) participated in a randomized, double-blind, double-placebo, crossover trial to compare the effect of two drugs, lovastatin (40 mg once daily) and gemfibrozil (600 mg twice daily), on clearance of postprandial lipoproteins. A 2-week washout period separated drug treatment periods of 6 weeks each. Ten subjects completed each treatment period. After ingestion of a vitamin A fat load, plasma, chylomicron and non-chylomicron retinyl palmitate (RP) and TG responses (areas under curves) were reduced in all subjects on gemfibrozil therapy and in 7 on lovastatin therapy. There was close correlation between change in fasting TG (but not fasting HDL-cholesterol) and change in postprandial RP areas on gemfibrozil but not lovastatin therapy. Postheparin lipoprotein lipase (LPL) and hepatic lipase (HL) activities were increased by gemfibrozil therapy while only a mild elevation in LPL activity alone was seen on lovastatin therapy. These data indicate that improvement in HTG is the main feature associated with improvement in postprandial lipemia and this is likely due to LPL-mediated enhancement of lipolytic hydrolysis. Gemfibrozil is more effective than lovastatin in attenuating postprandial lipemia in the HPAL/HTG syndrome.

Differential effects of PCSK9 loss of function variants on serum lipid and PCSK9 levels in Caucasian and African Canadian populations

ObjectivesVariants of the secreted glycoprotein, proprotein convertase subtilisin/kexin 9 (PCSK9), associate with both hypo- and hyper-cholesterolemic phenotypes. Herein, we carried out full exonic sequencing of PCSK9 documenting the frequency of single and multiple PCSK9 variations and their effects on serum lipoprotein and PCSK9 levels in Caucasian Canadians.MethodsThe 12 exons of PCSK9 were sequenced in 207 unrelated Caucasian Canadians. Minor allele frequencies of PCSK9 variants were compared amongst LDL cholesterol (LDLC) quintiles. Serum PCSK9 levels were measured by ELISA and lipoproteins by enzymatic methods. Comparisons were made with a Caucasian family cohort (n = 51) and first generation African Canadians (n = 31).ResultsIn Caucasians, but not African Canadians, the c.61_63insCTG (denoted L10Ins) and A53V PCSK9 variations were linked and their frequency was significantly higher among Caucasian Canadians with LDLC levels in the <25th percentile. In both the unrelated and family Caucasian cohorts those carrying the L10A53V PCSK9 variant had significantly lower LDLC without reduction in plasma PCSK9. The I474V PCSK9 variant associated with significantly lower serum PCSK9 and LDLC. A novel PCSK9 variant was identified; E206K. We found that the frequency of multiple PCSK9 variations was higher in first generation African Canadians.ConclusionsWe showed that the L10A53V and I474V PCSK9 variants were significantly associated with lower LDLC levels in Caucasian Canadians but differed in their effect on serum PCSK9 concentrations, illuminating differences in their mechanism of inaction and indicating that that PCSK9 measurement alone may not always be a good indicator of PCSK9 function.Full exonic sequencing of PCSK9 pointed to factors that may contribute to L10Ins PCSK9 variant loss of function in Canadians of Caucasian but not those of African descent. These included; (1) its tight linkage with the A53V variant in Caucasians and/or (2) for both the L10 and I474V, the combined (and negating) effect of multiple, differing phenotypic PCSK9 variants within individuals of African ancestry for which combinations of PCSK9 variations and their overall frequency was higher. No population studies, to our knowledge, have addressed or accessed the effect of multiple PCSK9 variants on cholesterol profiles. Our results indicate that this should be considered.

Delayed clearance of postprandial chylomicrons and their remnants in the hypoalphalipoproteinemia and mild hypertriglyceridemia syndrome.

Hypoalphalipoproteinemia (HPAL) with mild hypertriglyceridemia (HTG) is associated with increased coronary artery disease (CAD) risk. The aim of this study was to examine the metabolism of postprandial lipoproteins in HPAL/HTG subjects (n = 21). They had a fasting plasma high density lipoprotein (HDL) cholesterol level < 0.9 mmol/l, a triglycerides (TG) level of 2.0-7.1 mmol/l, and a normal low density lipoprotein (LDL) cholesterol level (< 3.7 mmol/l). They were either homozygous for apoprotein E3 (n = 13) or heterozygous for apoprotein E4 (n = 5) or E2 (n = 3). After ingestion of a vitamin A fat load, plasma and chylomicron (CM) retinyl palmitate (RP) response (areas under curves) was three times and non-CM RP response 2.5 times greater than in normolipidemic control subjects (n = 13). There was close correlation between fasting plasma TG level and postprandial RP response in HPAL/HTG subjects (plasma, r = 0.87; CM, r = 0.89; and non-CM, r = 0.84). In control subjects this correlation was present for plasma RP (r = 0.80) and CM RP (r = 0.61) but not for non-CM RP (r = 0.53). In contrast, postprandial RP response was not correlated with fasting plasma HDL cholesterol levels for both groups. There was also no correlation between fasting TG and fasting HDL cholesterol. Postheparin lipoprotein lipase and hepatic lipase activities were slightly higher in HPAL/HTG subjects. The pattern of postprandial change in HDL composition was similar to that in control subjects. These data indicate enhanced postprandial lipemia in the HPAL/HTG syndrome, and this may account for their increased CAD risk.(ABSTRACT TRUNCATED AT 250 WORDS)

Transition of Patients with Type 2 Diabetes from Specialist to Primary Care: A Survey of Primary Care Physicians on the Usefulness of Tools for Transition

Transition from specialty to primary care for patients with type 2 diabetes has not been well studied. Stable patients may be retained in specialty clinics due to concern over the maintenance of diabetes care post-discharge, thus limiting access to specialists for new referrals. Understanding primary care physicians’ perceptions of barriers to diabetes care and the helpfulness of existing tools used in the transition back to primary care is important for facilitating the transition process. Objectives were 1) to determine the perceived helpfulness of preselected tools that could be used in the transition of patients from specialist to primary care; 2) to identify the barriers to implementation of evidence-based diabetes care from the primary care perspective; and 3) to identify the tools used currently by primary care physicians during the transition process.

Chronic kidney disease on hemodialysis is associated with decreased serum PCSK9 levels

OBJECTIVES Serum low density lipoprotein-cholesterol (LDL-C) correlates positively with serum PCSK9 in the general population, consistent with PCSK9 being a determinant of LDL-C levels. Patients with chronic kidney disease (CKD) on hemodialysis (HD) have lower total cholesterol (TC) and LDL-C compared to the general population. Serum PCSK9 and its relationship with serum lipids have not been reported in CKD patients on HD (CKD-HD). METHODS We measured serum PCSK9 by ELISA and lipid levels in 66 CKD-HD patients and compared them to 178 non-CKD subjects. Since statins increase serum PCSK9 levels, CKD-HD patients were separated into those not on statin therapy (HD-NS, n = 32) and those taking statins (HD-S, n = 34). No control subjects were on statin therapy. RESULTS Serum PCSK9, TC, LDL-C and HDL-C levels were significantly lower in the CKD-HD group (n = 66) compared to the control group. HD-NS patients showed lower PCSK9, TC and LDL-C levels than control subjects and PCSK9 levels correlated with TC and LDL-C levels (r = 0.35, p = 0.050; r = 0.423, p = 0.0158 respectively) as well as TG levels (r = 0.413, p = 0.0188). In HD-S patients, PCSK9 levels were not significantly different from the non-CKD group. There was no correlation between PCSK9 levels and TC and LDL-C levels in the HD-S group. CONCLUSION Our data are the first quantitative analysis of serum PCSK9 levels in CKD-HD patients. We show that serum PCSK9 in HD-NS patients is decreased and it retains a positive correlation with LDL-C, suggesting that PCSK9 may remain a significant determinant of LDL-C in CKD-HD subjects. We also show that statin therapy disrupts the correlation between LDL-C and PCSK9 in CKD-HD patients. These data suggest that the regulation of LDL-C by PCSK9 remains intact in CKD-HD patients. PCSK9 may also play a role in the metabolism of triglyceride-rich lipoproteins in CKD-HD patients.

Paradoxically Decreased HDL-Cholesterol Levels Associated with Rosiglitazone Therapy

Objective: To report 2 cases of very low high-density lipoprotein cholesterol (HDL-C) levels associated with rosiglitazone therapy. Case Summary: Two patients with type 2 diabetes taking rosiglitazone for glycemic control developed paradoxically low HDL-C levels during rosiglitazone therapy. In the first patient, the HDL-C level decreased from 33 to 11.6 mg/dL after 8 months of therapy. The second patients HDL-C level decreased from the baseline level of 44.8 mg/dL to 19.7 mg/dL after 4 months of rosiglitazone use. These abnormalities resolved on discontinuation of rosiglitazone and were not observed when the patients were treated with pioglitazone. The patients had no changes to other drug therapy or medical conditions known to affect lipid metabolism during treatment with rosiglitazone. Discussion: Thiazolidinediones, insulin sensitizers widely used in the treatment of type 2 diabetes, have been reported to have beneficial effects on lipids, such as triglyceride lowering and HDL-C elevation, in addition to their glucose-lowering effects. It has been suggested that rosiglitazone and pioglitazone, the 2 currently available thiazolidinediones, may differ in their effects on lipids. As of July 2006, a total of 8 cases of paradoxical lowering of plasma HDL-C associated with rosiglitazone have now been reported. Based on use of the Naranjo probability scale, the 2 cases presented here were probably associated with rosiglitazone. The duration of therapy may be important in this paradoxical effect. Conclusions: Rosiglitazone is associated with a paradoxical decrease in HDL-C levels in patients with type 2 diabetes. In patients receiving rosiglitazone, a baseline lipid panel should be performed and lipid values should be monitored during the course of therapy.

Resistance exercise but not aerobic exercise lowers remnant-like lipoprotein particle cholesterol in type 2 diabetes: A randomized controlled trial ☆

The comparative effects of aerobic and resistance exercise on triglyceride-rich lipoproteins including remnant lipoproteins are controversial. This study examined exercise effect on remnant-like lipoprotein particle cholesterol (RLP-C) in type 2 diabetes. Participants were randomized to control (Control), aerobic (Aerobic), resistance (Resistance), or both (Combined) exercise groups. Baseline and 6-month fasting RLP-C and apolipoprotein B48 concentrations were measured. Data analysis was on an intention-to-treat basis. At 6 months, RLP-C was lower in all groups; ΔRLP-C mg/dl, (95% confidence interval), Control -3.91, (-6.21 to -1.6), p=0.001; Aerobic -3.89, (-6.41 to -1.36), p=0.003, Resistance -7.52, (-9.89 to -5.15), p=0.0001, Combined -7.50, (-9.87 to -5.13), p=0.0001. Total triglycerides were significantly lower in Resistance and Combined groups only; -17.7mg/dl (-32.8 to -2.7), p=0.02 and -27.5 (-42.5 to -11.5), p=0.001, respectively. Inter-group comparisons showed no difference in RLP-C change between Aerobic and Control and a significant difference in RLP-C change only where groups incorporating resistance exercise were compared with those without. There was no significant difference in RLP-C change between Resistance and Combined. Inter-group comparisons of total triglycerides change were significant only between Combined and Control. Changes in apolipoprotein B48 were not significant in inter-group comparisons. In conclusion, our data indicate that resistance exercise training, not aerobic, lowers RLP-C in type 2 diabetes. This effect was not revealed by changes in total triglycerides and apolipoprotein B48. The discordance between changes in RLP-C and apolipoprotein B48 in response to resistance exercise may indicate (a) a decrease in VLDL remnant and not chylomicron remnant particle number and/or (b) a depletion of cholesterol in chylomicron and/or VLDL remnants.