The LPL gene in individuals with familial combined hyperlipidemia and decreased LPL activity

Maternal High Fat Diet and its Expressions in the Heart and Liver in the Mice Embryogenesis

BACKGROUND

The developmental biology for the nonalcoholic fatty liver disease and coronary heart disease are known but elaborative ideas of triglycerides phenomenon in the embryo-genesis of the liver and the heart are still not clear.

OBJECTIVE

The aim of the study was to relate different triglycerides like LXRα, LPL, LDL R, PPARG-, SREBP-1C expression in the high fat fed mice with the normal fed diet mice in the process of developmental and embryo-genesis biology.

METHODS

Tissue preparation was done by ripalysis. Different protein content was obtained via western blot for the 6 samples namely a-17.5 days mice embryo heart; b- 0th day or the birthday mice infant heart; c-1 week mice infant heart; d-2 weeks mice infant heart; e-3 weeks mice infant heart; f-Adult mice heart. Protein lysates from the heart tissues of the mice was obtained via homegenization and centrifugation. Hematoxylin and Eosin (H and E) was done to see the fat droplets in the liver tissues at the different developmental stages.

RESULT

LXRα,SREBP-1C expression in 17.5 days mice embryo heart and 0th day or the birthday mice infant heart is highly expressed in the high fat diet. LDL-R in the high fat diet mice is increased in 2 weeks mice infant heart but in17.5 days mice embryo heart and in 0th day or the birthday mice infant heart it is low expression but from 1week mice infant heart to the adult mice heart the expression is in decreasing trend. Similarly LPL is highly expressed in17.5 days mice embryo heart and 1 week mice infant heart and thus low expression in decreasing order until adult mice heart.Thus, these results collectively shows that maternal HF diet increases expression of proteins such as LPL, LDLr in the embryo phase and thus getting normal expressions in the adult phase that facilitate Triglycerides (TAG) hydrolysis across the liver and the heart. Also,maternal high fat diet increases the SREBP1c expression, leading to stimulation of LPL Expression.

CONCLUSION

In summary, using a pregnant mice model, we found that maternal high fat diet increases the fetal fat accumulation. Elevated placental LPL activity and expression of genes that facilitate placental lipid transport suggest that enhanced placental lipid transport may play a key role in maternal nutrition and obesity-induced fetal fat accumulation.

Approach to patients with hypertriglyceridemia

Elevated triglyceride levels increase the risk of arteriosclerotic cardiovascular disease (ASCVD) and severely elevated triglyceride levels also increase the risk of triglyceride-induced pancreatitis. Although substantially reducing triglyceride levels will prevent pancreatitis, whether lowering triglycerides per se will reduce CVD risk is unclear. In this review, we outline several principles that will help in deciding who and how to treat patients with elevated triglyceride levels in order to prevent both ASCVD and pancreatitis. Using these principles will help in making decisions regarding the treatment of elevated triglyceride levels.

An automated method for measuring lipoprotein lipase and hepatic triglyceride lipase activities in post-heparin plasma

BACKGROUND

Lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL) play a central role in triglyceride-rich lipoprotein metabolism by catalyzing the hydrolysis of triglycerides. Quantification of LPL and HTGL activity is useful for diagnosing lipid disorders, but there has been no automated method for measuring these lipase activities.

METHODS

The automated kinetic colorimetric method was used for assaying LPL and HTGL activity in the post-heparin plasma using the natural long-chain fatty acid 2-diglyceride as a substrate. LPL activity was determined with apoCII and HTGL activity was determined without apoCII with 2 channel of auto-analyzer.

RESULTS

The calibration curve for dilution tests of the LPL and HTGL activity assay ranged from 0.0 to 500 U/L. Within-run CV was obtained within a range of 5%. No interference was observed in the testing of specimens containing potentially interfering substances. The measurement range of LPL activity in the post-heparin plasma was 30-153 U/L, while HTGL activity was 135-431 U/L in normal controls.

CONCLUSIONS

The L PL and HTGL activity assays are applicable to quantitating the LPL and HTGL activity in the post-heparin plasma. This assay is more convenient and faster than radiochemical assay and highly suitable for the detection of lipid disorders.

Deficiency of Lipoprotein Lipase in Neurons Decreases AMPA Receptor Phosphorylation and Leads to Neurobehavioral Abnormalities in Mice

Alterations in lipid metabolism have been found in several neurodegenerative disorders, including Alzheimer’s disease. Lipoprotein lipase (LPL) hydrolyzes triacylglycerides in lipoproteins and regulates lipid metabolism in multiple organs and tissues, including the central nervous system (CNS). Though many brain regions express LPL, the functions of this lipase in the CNS remain largely unknown. We developed mice with neuron-specific LPL deficiency that became obese on chow by 16 wks in homozygous mutant mice (NEXLPL-/-) and 10 mo in heterozygous mice (NEXLPL+/-). In the present study, we show that 21 mo NEXLPL+/- mice display substantial cognitive function decline including poorer learning and memory, and increased anxiety with no difference in general motor activities and exploratory behavior. These neurobehavioral abnormalities are associated with a reduction in the 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid (AMPA) receptor subunit GluA1 and its phosphorylation, without any alterations in amyloid β accumulation. Importantly, a marked deficit in omega-3 and omega-6 polyunsaturated fatty acids (PUFA) in the hippocampus precedes the development of the neurobehavioral phenotype of NEXLPL+/- mice. And, a diet supplemented with n-3 PUFA can improve the learning and memory of NEXLPL+/- mice at both 10 mo and 21 mo of age. We interpret these findings to indicate that LPL regulates the availability of PUFA in the CNS and, this in turn, impacts the strength of synaptic plasticity in the brain of aging mice through the modification of AMPA receptor and its phosphorylation.

Severe/Extreme Hypertriglyceridemia and LDL Apheretic Treatment: Review of the Literature, Original Findings

Hypertriglyceridemia (HTG) is a feature of numerous metabolic disorders including dyslipidemias, metabolic syndrome, and diabetes mellitus type 2 and can increase the risk of premature coronary artery disease. HTG may also be due to genetic factors (called primary HTG) and particularly the severe/extreme HTG (SEHTG), which is a usually rare genetic disorder. Even rarer are secondary cases of SEHTG caused by autoimmune disease. This review considers the causes of SEHTG, and their management including treatment with low density lipoprotein apheresis and analyzes the original findings.

Recent advances in pharmacotherapy for hypertriglyceridemia

Elevated plasma triglyceride (TG) concentrations are associated with an increased risk of atherosclerotic cardiovascular disease (CVD), hepatic steatosis and pancreatitis. Existing pharmacotherapies, such as fibrates, n-3 polyunsaturated fatty acids (PUFAs) and niacin, are partially efficacious in correcting elevated plasma TG. However, several new TG-lowering agents are in development that can regulate the transport of triglyceride-rich lipoproteins (TRLs) by modulating key enzymes, receptors or ligands involved in their metabolism. Balanced dual peroxisome proliferator-activated receptor (PPAR) α/γ agonists, inhibitors of microsomal triglyceride transfer protein (MTTP) and acyl-CoA:diacylglycerol acyltransferase-1 (DGAT-1), incretin mimetics, and apolipoprotein (apo) B-targeted antisense oligonucleotides (ASOs) can all decrease the production and secretion of TRLs; inhibitors of cholesteryl ester transfer protein (CETP) and angiopoietin-like proteins (ANGPTLs) 3 and 4, monoclonal antibodies (Mabs) against proprotein convertase subtilisin/kexin type 9 (PCSK9), apoC-III-targeted ASOs, selective peroxisome proliferator-activated receptor modulators (SPPARMs), and lipoprotein lipase (LPL) gene replacement therapy (alipogene tiparvovec) enhance the catabolism and clearance of TRLs; dual PPAR-α/δ agonists and n-3 polyunsaturated fatty acids can lower plasma TG by regulating both TRL secretion and catabolism. Varying degrees of TG reduction have been reported with the use of these therapies, and for some agents such as CETP inhibitors and PCSK9 Mabs findings have not been consistent. Whether they reduce CVD events has not been established. Trials investigating the effect of CETP inhibitors (anacetrapib and evacetrapib) and PCSK9 Mabs (AMG-145 and REGN727/SAR236553) on CVD outcomes are currently in progress, although these agents also regulate LDL metabolism and, in the case of CETP inhibitors, HDL metabolism. Further to CVD risk reduction, these new treatments might also have a potential role in the management of diabetes and non-alcoholic fatty liver disease owing to their insulin-sensitizing action (PPAR-α/γ agonists) and potential capacity to decrease hepatic TG accumulation (PPAR-α/δ agonists and DGAT-1 inhibitors), but this needs to be tested in future trials. We summarize the clinical trial findings regarding the efficacy and safety of these novel therapies for hypertriglyceridemia.

Making, baking, and breaking: the synthesis, storage, and hydrolysis of neutral lipids

The esterification of amphiphilic alcohols with fatty acids is a ubiquitous strategy implemented by eukaryotes and some prokaryotes to conserve energy and membrane progenitors and simultaneously detoxify fatty acids and other lipids. This key reaction is performed by at least four evolutionarily unrelated multigene families. The synthesis of this "neutral lipid" leads to the formation of a lipid droplet, which despite the clear selective advantage it confers is also a harbinger of cellular and organismal malaise. Neutral lipid deposition as a cytoplasmic lipid droplet may be thermodynamically favored but nevertheless is elaborately regulated. Optimal utilization of these resources by lipolysis is similarly multigenic in determination and regulation. We present here a perspective on these processes that originates from studies in model organisms, and we include our thoughts on interventions that target reductions in neutral lipids as therapeutics for human diseases such as obesity and diabetes.

The genetics of familial combined hyperlipidaemia

Almost 40 years after the first description of familial combined hyperlipidaemia (FCHL) as a discrete entity, the genetic and metabolic basis of this prevalent disease has yet to be fully unveiled. In general, two strategies have been applied to elucidate its complex genetic background, the candidate-gene and the linkage approach, which have yielded an extensive list of genes associated with FCHL or its related traits, with a variable degree of scientific evidence. Some genes influence the FCHL phenotype in many pedigrees, whereas others are responsible for the affected state in only one kindred, thereby adding to the genetic and phenotypic heterogeneity of FCHL. This Review outlines the individual genes that have been described in FCHL and how these genes can be incorporated into the current concept of metabolic pathways resulting in FCHL: adipose tissue dysfunction, hepatic fat accumulation and overproduction, disturbed metabolism and delayed clearance of apolipoprotein-B-containing particles. Genes that affect metabolism and clearance of plasma lipoprotein particles have been most thoroughly studied. The adoption of new traits, in addition to the classic plasma lipid traits, could aid in the identification of new genes implicated in other pathways in FCHL. Moreover, systems genetic analysis, which integrates genetic polymorphisms with data on gene expression levels, lipidomics or metabolomics, will attribute functions to genetic variants in addition to revealing new genes.

Investigation of variants identified in caucasian genome-wide association studies for plasma high-density lipoprotein cholesterol and triglycerides levels in Mexican dyslipidemic study samples

BACKGROUND

Although epidemiological studies have demonstrated an increased predisposition to low high-density lipoprotein cholesterol and high triglyceride levels in the Mexican population, Mexicans have not been included in any of the previously reported genome-wide association studies for lipids.

METHODS AND RESULTS

We investigated 6 single-nucleotide polymorphisms associated with triglycerides, 7 with high-density lipoprotein cholesterol, and 1 with both triglycerides and high-density lipoprotein cholesterol in recent Caucasian genome-wide association studies in Mexican familial combined hyperlipidemia families and hypertriglyceridemia case-control study samples. These variants were within or near the genes ABCA1, ANGPTL3, APOA5, APOB, CETP, GALNT2, GCKR, LCAT, LIPC, LPL (2), MMAB-MVK, TRIB1, and XKR6-AMAC1L2. We performed a combined analysis of the family-based and case-control studies (n=2298) using the Z method to combine statistics. Ten of the single-nucleotide polymorphisms were nominally significant and 5 were significant after Bonferroni correction (P=2.20 x 10(-3) to 2.6 x 10(-11)) for the number of tests performed (APOA5, CETP, GCKR, and GALNT2). Interestingly, our strongest signal was obtained for triglycerides with the minor allele of rs964184 (P=2.6 x 10(-11)) in the APOA1/C3/A4/A5 gene cluster region that is significantly more common in Mexicans (27%) than in whites (12%).

CONCLUSIONS

It is important to confirm whether known loci have a consistent effect across ethnic groups. We show replication of 5 Caucasian genome-wide association studies lipid associations in Mexicans. The remaining loci will require a comprehensive investigation to exclude or verify their significance in Mexicans. We also demonstrate that rs964184 has a large effect (odds ratio, 1.74) and is more frequent in the Mexican population, and thus it may contribute to the high predisposition to dyslipidemias in Mexicans.

Lipoprotein lipase: from gene to obesity

Lipoprotein lipase (LPL) is a multifunctional enzyme produced by many tissues, including adipose tissue, cardiac and skeletal muscle, islets, and macrophages. LPL is the rate-limiting enzyme for the hydrolysis of the triglyceride (TG) core of circulating TG-rich lipoproteins, chylomicrons, and very low-density lipoproteins (VLDL). LPL-catalyzed reaction products, fatty acids, and monoacylglycerol are in part taken up by the tissues locally and processed differentially; e.g., they are stored as neutral lipids in adipose tissue, oxidized, or stored in skeletal and cardiac muscle or as cholesteryl ester and TG in macrophages. LPL is regulated at transcriptional, posttranscriptional, and posttranslational levels in a tissue-specific manner. Nutrient states and hormonal levels all have divergent effects on the regulation of LPL, and a variety of proteins that interact with LPL to regulate its tissue-specific activity have also been identified. To examine this divergent regulation further, transgenic and knockout murine models of tissue-specific LPL expression have been developed. Mice with overexpression of LPL in skeletal muscle accumulate TG in muscle, develop insulin resistance, are protected from excessive weight gain, and increase their metabolic rate in the cold. Mice with LPL deletion in skeletal muscle have reduced TG accumulation and increased insulin action on glucose transport in muscle. Ultimately, this leads to increased lipid partitioning to other tissues, insulin resistance, and obesity. Mice with LPL deletion in the heart develop hypertriglyceridemia and cardiac dysfunction. The fact that the heart depends increasingly on glucose implies that free fatty acids are not a sufficient fuel for optimal cardiac function. Overall, LPL is a fascinating enzyme that contributes in a pronounced way to normal lipoprotein metabolism, tissue-specific substrate delivery and utilization, and the many aspects of obesity and other metabolic disorders that relate to energy balance, insulin action, and body weight regulation.

Small and dense LDL in familial combined hyperlipidemia and N291S polymorphism of the lipoprotein lipase gene

There is a predominance of small and dense LDL cholesterol particles in familial combined hyperlipidemia (FCH). The lipoprotein lipase gene could exert an influence in these circumstances.

To study the relationship of pattern B LDL and lipids with N291S polymorphism of lipoprotein lipase (LPL) in FCH patients.

Lipid profile, apolipoproteins, diameter of LDL and N291S polymorphism were determined in 93 patients with FCH and 286 individuals from the general population.

FCH patients with N291S polymorphism showed a lower mean diameter of LDL. FCH patients with pattern B LDL showed higher concentrations of triglycerides, VLDLc, non-HDLc and apo B100 and lower levels of HDLc than those with pattern A. Of FCH patients with polymorphism 87.5% presented pattern B and 12.5% pattern A, while patients without polymorphism presented pattern A in 69.2% cases and pattern B in 30.8% cases, with differences being statistically significant (p < 0.004). The prevalence of this mutation in our FCH patients was 9.7%.

The prevalence of N291S mutation in our FCH patients was similar to the 9.3% described in Dutch FCHL patients but clearly higher than the 2–5% described for other Caucasian populations. No polymorphism was found in our general population sample. FCH patients with phenotype B of LDL possessed an atherogenic lipid profile. The relationship between small and dense LDL and the presence of the N291S mutation may identify patients with high cardiovascular risk.

The lipoprotein lipase gene in combined hyperlipidemia: evidence of a protective allele depletion

Background

Lipoprotein Lipase (LPL), a key enzyme in lipid metabolism, catalyzes the hydrolysis of triglycerides (TG) from TG-rich lipoproteins, and serves a bridging function that enhances the cellular uptake of lipoproteins. Abnormalities in LPL function are associated with pathophysiological conditions, including familial combined hyperlipidemia (FCH). Whereas two LPL susceptibility alleles were found to co-segregate in a few FCH kindred, a role for common, protective alleles remains unexplored. The LPL Ser447Stop (S447X) allele is associated with anti-atherogenic lipid profiles and a modest reduction in risk for coronary disease. We hypothesize that significant depletion of the 447X allele exists in combined hyperlipidemia cases versus controls. A case-control design was employed. The polymorphism was assessed by restriction assay in 212 cases and 161 controls. Genotypic, allelic, and phenotypic associations were examined.

Results

We found evidence of significant allelic (447X_control: 0.130 vs. 447X_case: 0.031, χ² = 29.085; 1df; p < 0.001) and genotypic association (SS: 0.745 vs. 0.939, and SX+XX: 0.255 vs. 0.061) in controls and cases, respectively (χ² = 26.09; 1df; p < 0.001). In cases, depletion of the 447X allele is associated with a significant elevation in very-low-density lipoprotein cholesterol (VLDL-C, p = 0.045). Consonant with previous studies of this polymorphism, regression models predict that carriers of the 447X allele displayed significantly lower TG, low-density lipoprotein cholesterol (LDL-C) and TG/high-density lipoprotein cholesterol (HDL-C) ratio.

Conclusion

These findings suggest a role for the S447X polymorphism in combined hyperlipidemia and demonstrate the importance of evaluating both susceptibility and protective genetic risk factors.

Two novel mutations in the beta-myosin heavy chain gene associated with dilated cardiomyopathy

BACKGROUND

Dilated cardiomyopathy (DCM) is familial in approximately 20-35% of cases of idiopathic DCM. Several mutations in the different sarcomere protein genes have been reported to cause DCM.

AIMS

We wanted to investigate the role of sarcomere protein gene variants in Finnish DCM patients.

METHODS AND RESULTS

We screened all coding exons of five sarcomere protein genes (beta-myosin heavy chain, alpha-tropomyosin, troponin C, troponin I and troponin T) in a well-characterized population of 52 DCM patients in Eastern Finland by the PCR-SSCP and sequencing method. Two novel mutations, Arg1053Gln and Arg1500Trp, in the beta-myosin heavy chain gene in two index patients were detected. The proband with the Arg1053Gln mutation had a dilated left ventricle and impaired systolic function, but other family members carrying this mutation presented with septal hypertrophy. It thus seems that the Arg1053Gln mutation is primarily a HCM mutation, which can also lead to DCM. The other mutation, Arg1500Trp, was associated with a typical DCM phenotype. The Arg1500Trp mutation carrier had only one family member alive, but she did not carry the mutation and, therefore, cosegregation of the mutation and the disease in this family could not be reliably verified. No disease-causing mutations were found in the other sarcomere protein genes.

CONCLUSIONS

Two novel mutations in the beta-myosin heavy chain gene were detected in patients with DCM. Overall, mutations in the beta-myosin heavy chain gene seem to be relatively uncommon in Finnish DCM patients.

A novel substitution at the translation initiator codon (ATG→ATC) of the lipoprotein lipase gene is mainly responsible for lipoprotein lipase deficiency in a patient with severe hypertriglyceridemia and recurrent pancreatitis

A patient with severe hypertriglyceridemia and recurrent pancreatitis was found to have significantly decreased lipoprotein lipase (LPL) activity and normal apolipoprotein C-II concentration in post-heparin plasma. DNA analysis of the LPL gene revealed two mutations, one of which was a novel homozygous G-->C substitution, resulting in the conversion of a translation initiation codon methionine to isoleucine (LPL-1). The second was the previously reported heterozygous substitution of glutamic acid at residue 242 with lysine (LPL-242). In vitro expression of both mutations separately or in combination demonstrated that LPL-1 had approximately 3% protein mass and 2% activity, whereas LPL-242 had undetectable activity but normal mass. The combined mutation LPL-1-242 exhibited similar changes as for LPL-1, with markedly reduced mass, and for LPL-242, with undetectable activity. These results suggest that the homozygous initiator codon mutation rather than the heterozygous LPL-242 alteration was mainly responsible for the patient phenotypes.

Unraveling the complex genetics of familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) constitutes a substantial risk factor for atherosclerosis since it is observed in about 20% of coronary heart disease (CHD) patients under 60 years. FCHL, characterized by elevated levels of total cholesterol (TC) and triglycerides (TGs), or both, is also one of the most common familial hyperlipidemias with a prevalence of 1%-6% in Western populations. Numerous studies have been performed to identify genes contributing to FCHL. The recent linkage and association studies and their replications are beginning to elucidate the genetic variations underlying the susceptibility to FCHL. Three chromosomal regions on 1q21-23, 11p and 16q22-24.1 have been replicated in different study samples, offering targets for gene hunting. In addition, several candidate gene studies have replicated the influence of the lipoprotein lipase (LPL) gene and apolipoprotein A1/C3/A4/A5 (APOA1/C3/A4/A5) gene cluster in FCHL. Recently, the linked region on chromosome 1q21 was successfully fine-mapped and the upstream transcription factor 1 (USF1) gene identified as the underlying gene for FCHL. This finding has now been replicated in independent FCHL samples. However, the total number of variants, the risk related to each variant and their relative contributions to the disease susceptibility are not known yet.

Missense mutation W86R in exon 3 of the lipoprotein lipase gene in a boy with chylomicronemia

BACKGROUND

Familial LPL deficiency is a rare inborn error of metabolism caused by mutational change within the LPL gene, which leads to massive hypertriglyceridemia.

METHODS

The underlying molecular defect in a boy of Croatian descent was studied by SSCP analysis, DNA sequencing and finally confirmed by RFLP.

RESULTS

DNA analysis showed the child to be a homozygote and his parents heterozygotes for TGG-->CGG change in codon 86 of the LPL gene, which leads to W86R amino acid substitution. DNA sequence analysis also showed a silent mutation in the third exon of father's DNA, V108V. Determination of some LPL gene polymorphisms showed the child and his parents to have HindIII/H+H+ and both S447 wild-type alleles, whereas for PvuII the parents had P(+)P- and the child P(+)P+ genotype.

CONCLUSIONS

In this case, W86R mutation was the reason for the production of nonfunctional enzyme and consequently triacylglycerol (TG) exceeding 15 mmol/l. This implies the risk of frequent episodes of acute pancreatitis. Decreased LPL activity leads to elevated triacylglycerol levels and reduced HDL-cholesterol, both risk factors for the development of coronary artery disease. LPL genotyping especially of young patients with hypertriglyceridemia is therefore necessary and justifiable.

A novel mutation, Arg71Thr, in the delta-sarcoglycan gene is associated with dilated cardiomyopathy

Approximately 20-35% of cases of idiopathic dilated cardiomyopathy are familial. DCM-associated mutations have been reported in 13 genes including the desmin, delta-sarcoglycan, and metavinculin genes. This study screened for variants in these genes in Finnish patients with DCM. All coding regions of the desmin and delta-sarcoglycan genes and the metavinculin-specific exon of the vinculin gene were screened in 52 DCM patients from eastern Finland by PCR-SSCP. We detected a novel mutation, Arg71Thr, in the delta-sarcoglycan gene in two members of a small DCM family. One of the mutation carriers fulfills diagnostic criteria for DCM and is also symptomatic. The other mutation carrier has slightly dilated left ventricle and well preserved systolic function. Therefore carriers of the Arg71Thr mutation had a relatively mild phenotype and a late onset of the disease. Disease-associated mutations were not found in the desmin gene or the metavinculin-specific exon of the vinculin gene. We conclude that the desmin and delta-sarcoglycan genes are not predominant disease-causing genes in patients with DCM in eastern Finland.

Impaired expression of peroxisome proliferator-activated receptor gamma in ulcerative colitis

BACKGROUND & AIMS

The peroxisome proliferator-activated receptor gamma (PPAR gamma) has been proposed as a key inhibitor of colitis through attenuation of nuclear factor kappa B (NF-kappa B) activity. In inflammatory bowel disease, activators of NF-kappa B, including the bacterial receptor toll-like receptor (TLR)4, are elevated. We aimed to determine the role of bacteria and their signaling effects on PPAR gamma regulation during inflammatory bowel disease (IBD).

METHODS

TLR4-transfected Caco-2 cells, germ-free mice, and mice devoid of functional TLR4 (Lps(d)/Lps(d) mice) were assessed for their expression of PPAR gamma in colonic tissues in the presence or absence of bacteria. This nuclear receptor expression and the polymorphisms of gene also were assessed in patients with Crohn's disease (CD) and ulcerative colitis (UC), 2 inflammatory bowel diseases resulting from an abnormal immune response to bacterial antigens.

RESULTS

TLR4-transfected Caco-2 cells showed that the TLR4 signaling pathway elevated PPAR gamma expression and a PPAR gamma-dependent reporter in an I kappa kappa beta dependent fashion. Murine and human intestinal flora induced PPAR gamma expression in colonic epithelial cells of control mice. PPAR gamma expression was significantly higher in the colon of control compared with Lps(d)/Lps(d) mice. Although PPAR gamma levels appeared normal in patients with CD and controls, UC patients displayed a reduced expression of PPAR gamma confined to colonic epithelial cells, without any mutation in the PPAR gamma gene.

CONCLUSIONS

These data showed that the commensal intestinal flora affects the expression of PPAR gamma and that PPAR gamma expression is considerably impaired in patients with UC.

Clinical relevance of the biochemical, metabolic, and genetic factors that influence low-density lipoprotein heterogeneity

Traditional risk factors for coronary artery disease (CAD) predict about 50% of the risk of developing CAD. The Adult Treatment Panel (ATP) III has defined emerging risk factors for CAD, including small, dense low-density lipoprotein (LDL). Small, dense LDL is often accompanied by increased triglycerides (TGs) and low high-density lipoprotein (HDL). An increased number of small, dense LDL particles is often missed when the LDL cholesterol level is normal or borderline elevated. Small, dense LDL particles are present in families with premature CAD and hyperapobetalipoproteinemia, familial combined hyperlipidemia, LDL subclass pattern B, familial dyslipidemic hypertension, and syndrome X. The metabolic syndrome, as defined by ATP III, incorporates a number of the components of these syndromes, including insulin resistance and intra-abdominal fat. Subclinical inflammation and elevated procoagulants also appear to be part of this atherogenic syndrome. Overproduction of very low-density lipoproteins (VLDLs) by the liver and increased secretion of large, apolipoprotein (apo) B-100-containing VLDL is the primary metabolic characteristic of most of these patients. The TG in VLDL is hydrolyzed by lipoprotein lipase (LPL) which produces intermediate-density lipoprotein. The TG in intermediate-density lipoprotein is hydrolyzed further, resulting in the generation of LDL. The cholesterol esters in LDL are exchanged for TG in VLDL by the cholesterol ester tranfer proteins, followed by hydrolysis of TG in LDL by hepatic lipase which produces small, dense LDL. Cholesterol ester transfer protein mediates a similar lipid exchange between VLDL and HDL, producing a cholesterol ester-poor HDL. In adipocytes, reduced fatty acid trapping and retention by adipose tissue may result from a primary defect in the incorporation of free fatty acids into TGs. Alternatively, insulin resistance may promote reduced retention of free fatty acids by adipocytes. Both these abnormalities lead to increased levels of free fatty acids in plasma, increased flux of free fatty acids back to the liver, enhanced production of TGs, decreased proteolysis of apo B-100, and increased VLDL production. Decreased removal of postprandial TGs often accompanies these metabolic abnormalities. Genes regulating the expression of the major players in this metabolic cascade, such as LPL, cholesterol ester transfer protein, and hepatic lipase, can modulate the expression of small, dense LDL but these are not the major defects. New candidates for major gene effects have been identified on chromosome 1. Regardless of their fundamental causes, small, dense LDL (compared with normal LDL) particles have a prolonged residence time in plasma, are more susceptible to oxidation because of decreased interaction with the LDL receptor, and enter the arterial wall more easily, where they are retained more readily. Small, dense LDL promotes endothelial dysfunction and enhanced production of procoagulants by endothelial cells. Both in animal models of atherosclerosis and in most human epidemiologic studies and clinical trials, small, dense LDL (particularly when present in increased numbers) appears more atherogenic than normal LDL. Treatment of patients with small, dense LDL particles (particularly when accompanied by low HDL and hypertriglyceridemia) often requires the use of combined lipid-altering drugs to decrease the number of particles and to convert them to larger, more buoyant LDL. The next critical step in further reduction of CAD will be the correct diagnosis and treatment of patients with small, dense LDL and the dyslipidemia that accompanies it.

Genetics of lipoprotein abnormalities associated with coronary artery disease susceptibility

Coronary heart disease is a complex genetic disease with many genes involved, environmental influences, and important gene-environment interactions. This review discusses the genetic basis of the principal lipoprotein abnormalities associated with coronary heart disease susceptibility in the general population. Individual sections discuss genes regulating LDL cholesterol, HDL cholesterol, and triglyceride levels. A section is included on the effects of the common apo E genetic variation on lipoprotein levels, as well as sections on the genetic regulation of lipoprotein(a) levels, genes regulating the inverse relationship between triglyceride-rich lipoproteins and HDL cholesterol levels, and our current understanding of the genetic basis of familial combined hyperlipidemia. It is clear that the field has progressed, with early studies focused mainly on the association of candidate gene RFLPs with phenotypes, later studies of candidate genes in both parametric and nonparametric linkage studies, and now more and more studies combining linkage analysis with genome scans to identify new loci that influence lipoprotein phenotypes. The future should provide us with the capability to perform reasonable genetic profiling for lipoprotein abnormalities associated with coronary heart disease susceptibility.

Common mutations of the lipoprotein lipase gene and their clinical significance

The accumulation of triglyceride-rich lipoproteins is an independent factor for an increased risk for premature arteriosclerosis. Common mutations in the lipoprotein lipase (LPL) gene are at least in part inherited susceptibility factors involved in the age- and sex-dependent phenotypic expression of hypertriglyceridemia. It can be estimated that about 20% of patients with hypertriglyceridemia are carriers of common LPL gene mutations (Asp9Asn, Asn291Ser, Trp86Arg, Gly188Glu, Pro207Leu, Asp250Asn) associated with the HLP. Genotyping of these LPL gene mutations is recommended especially in patients with high risk for premature arteriosclerosis. A comparably high number of individuals are carriers of common mutations (Ser447X) or silent mutations (Thr361) associated with low favorable lipids.

Genetics of familial combined hyperlipidemia

Complex disorders are caused by several environmental factors that interact with multiple genes. These diseases are common at the population level and constitute a major health problem in Western societies. Familial combined hyperlipidemia (FCHL) is characterized by elevated levels of serum total cholesterol, triglycerides, or both. This disorder is estimated to be common in Western populations with a prevalence of 1% to 2%. In addition, 14% of patients with premature coronary heart disease (CHD) have FCHL, making this disorder one of the most common genetic dyslipidemias underlying premature CHD. Both genetic and environmental factors are suggested to affect the complex FCHL phenotype, but no specific susceptibility genes to FCHL have been identified. It is hoped that further analysis of the first FCHL locus and other new loci obtained in genome-wide scans will guide us to genes predisposing to this complex disorder.

No linkage of the lipoprotein lipase locus to hypertension in Caucasians

OBJECTIVE

A previous study has shown significant linkage of five markers near the lipoprotein lipase locus to systolic blood pressure, but not to diastolic blood pressure, in nondiabetic members of 48 Taiwanese families selected for noninsulin-dependent diabetes. However, lipoprotein lipase markers did not appear strongly linked to systolic blood pressure in a study of Mexican-Americans using a variety of selection schemes. The objective of the current study was to test whether markers near the lipoprotein lipase gene were linked to hypertension in Caucasians.

DESIGN

To test for linkage of genetic markers in or near the lipoprotein lipase gene to hypertension in Caucasians, two sets of Caucasian hypertensive sibships were genotyped. The samples included 261 sibships (431 effective sibpairs) from four field centers of the National Heart, Lung and Blood Institute Family Heart Study and 211 sibships (282 effective sibpairs) from the Health Family Tree database in Utah.

RESULTS

Two highly polymorphic markers in or near the lipoprotein lipase gene showed no evidence of excess allele sharing in either set of hypertensive sibships. Combining the two datasets resulted in 653 and 713 effective sibpairs for the two markers, sharing 0.495 +/- 0.30 and 0.486 +/- 0.28 alleles identical by descent compared to an expected sharing of 0.50. Multipoint analysis of the two loci also did not show linkage (P = 0.95).

CONCLUSIONS

We conclude that the lipoprotein lipase locus and nearby regions do not appear to be linked to hypertension in Caucasians.

The cardiac beta-myosin heavy chain gene is not the predominant gene for hypertrophic cardiomyopathy in the Finnish population

OBJECTIVES

The aim of the study was to screen 36 unrelated patients with hypertrophic cardiomyopathy (HCM; 16 familial and 20 sporadic cases) from a genetically homogeneous area in eastern Finland for variants in the cardiac beta-myosin heavy chain (beta-MHC) and alpha-tropomyosin (alpha-TM) genes.

BACKGROUND

Mutations in the beta-MHC and alpha-TM genes have been reported to be responsible for 30% to 40% and less than 5% of familial HCM cases, respectively. However, most genetic studies have included patients from tertiary care centers and are subject to referral bias.

METHODS

Exons 3-26 and 40 of the beta-MHC gene and the nine exons of the alpha-TM gene were screened with the PCR-SSCP (polymerase chain reaction-single strand conformation polymorphism) method. Linkage analyses between familial HCM locus and two intragenic polymorphic markers (MYO I and MYO II) of the beta-MHC gene were performed in 16 familial HCM kindreds.

RESULTS

A previously reported Arg719Trp (arginine converted to tryptophan in codon 719) mutation of the beta-MHC gene was found in one proband and two relatives. In addition, a novel Asn696Ser (asparagine converted to serine in codon 696) substitution was found in one HCM patient. No linkage between familial HCM and the beta-MHC gene was observed in 16 familial kindreds. A previously reported Aspl75Asn (aspartic acid converted to asparagine in codon 175) mutation of the alpha-TM gene was found in four probands and 16 relatives. Mutations in the beta-MHC and alpha-TM genes accounted for 6% and 25% familial HCM cases and 3% and 11% of all cases, respectively.

CONCLUSIONS

Our results indicate that the beta-MHC gene is not the predominant gene for HCM in the Finnish population, whereas HCM caused by the Aspl75Asn mutation of the a-TM gene is more common than previously reported.

A Pro12Ala substitution in PPARgamma2 associated with decreased receptor activity, lower body mass index and improved insulin sensitivity

The peroxisome proliferator-activated receptor-gamma (PPARgamma) is a transcription factor that has a pivotal role in adipocyte differentiation and expression of adipocyte-specific genes. The PPARgamma1 and gamma2 isoforms result from alternative splicing and have ligand-dependent and -independent activation domains. PPARgamma2 has an additional 28 amino acids at its amino terminus that renders its ligand-independent activation domain 5-10-fold more effective than that of PPARgamma1. Insulin stimulates the ligand-independent activation of PPARgamma1 and gamma2 (ref. 5), however, obesity and nutritional factors only influence the expression of PPARgamma2 in human adipocytes. Here, we report that a relatively common Pro12Ala substitution in PPARgamma2 is associated with lower body mass index (BMI; P=0.027; 0.015) and improved insulin sensitivity among middle-aged and elderly Finns. A significant odds ratio (4.35, P=0.028) for the association of the Pro/Pro genotype with type 2 diabetes was observed among Japanese Americans. The PPARgamma2 Ala allele showed decreased binding affinity to the cognate promoter element and reduced ability to transactivate responsive promoters. These findings suggest that the PPARgamma2 Pro12Ala variant may contribute to the observed variability in BMI and insulin sensitivity in the general population.

Different regulation of free fatty acid levels and glucose oxidation by the Trp64Arg polymorphism of the beta3-adrenergic receptor gene and the promoter variant (A-3826G) of the uncoupling protein 1 gene in familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) is characterized by variable expression of dyslipidemias and insulin resistance. Because the genetic background for FCHL is unknown, we investigated the effect of the Trp64Arg polymorphism of the beta3-adrenergic receptor (beta3-AR) gene and the promoter variant A --> G (-3826) of the uncoupling protein 1 (UCP1) gene on glucose and lipid metabolism in FCHL families. Both polymorphisms were screened in 228 members from 27 families with FCHL and in 82 control men from a random population sample. The frequency of the polymorphisms of the beta3-AR and UCP1 genes did not differ between patients with FCHL and controls. Although the rate of insulin-stimulated whole-body glucose uptake evaluated by the euglycemic clamp in family members of patients with FCHL was unaffected by both polymorphisms, subjects with the Trp64Arg genotype of the beta3-AR gene had higher rates of glucose oxidation (17.6+/-4.5 v 15.8+/-4.1 micromol/kg/min, P=.017) and lower levels of free fatty acids (FFAs) in the fasting state (0.56+/-0.27 v 0.61+/-0.28 mmol/L, P=.027) and during the euglycemic clamp (0.12+/-0.10 v 0.21+/-0.15 mmol/L, P=.041) than subjects with the Trp64Trp genotype. We conclude that in FCHL families, codon 64 polymorphism of the beta3-AR gene may influence the rate of glucose oxidation via FFA levels.

Defects of lipoprotein metabolism in familial combined hyperlipidaemia

Familial combined hyperlipidaemia is the most common inherited hyperlipidaemia and is found in up to 10% of patients with premature myocardial infarction. The genetic and metabolic bases of the disorder have not yet been defined. This review discusses the important advances in the past year in our understanding of the different metabolic pathways contributing to the pathogenesis of familial combined hyperlipidaemia.

Gender-related association between the -93T-->G/D9N haplotype of the lipoprotein lipase gene and elevated lipid levels in familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) is a frequent cause of premature coronary artery disease. Affected family members are characterized by different combinations of elevated cholesterol and/or triglyceride levels. A reduction in lipoprotein lipase (LPL) activity has been observed in a subgroup of FCHL patients. Recently, we have demonstrated an increased frequency of mutations in the LPL gene in Dutch FCHL patients compared to normolipidemic controls. In the present study, we have applied a pedigree-based maximum likelihood method to study the effect of LPL mutations on the phenotypic expression of FCHL in families. In 40 FCHL probandi, three different previously reported mutations in the LPL gene were identified resulting in amino acid changes, D9N, N291S, and S447X. The D9N mutation in exon 2 appeared to be in strong linkage disequilibrium with a T-->G substitution at position -93 in the promoter region of the LPL gene. We present data that the -93T-->G/D9N haplotype is associated with significantly higher levels of LDL and VLDL cholesterol, and VLDL triglycerides. Interestingly, the effect was only observed in male carriers. In line with our previous observations, these results further sustain that the LPL gene is a susceptibility gene for dyslipidemia which explains part of the variability in the phenotype observed among FCHL family members.

Common variation in the lipoprotein lipase gene: effects on plasma lipids and risk of atherosclerosis

The importance of the enzyme lipoprotein lipase (LPL) in the development of dyslipidaemia and atherosclerosis is increasingly recognised. Variations in the LPL gene which are common in the general population have been shown to be associated with alterations in plasma lipids. D9N and N291S both occur at carrier frequencies of up to about 5% and have been associated with increased plasma triacylglycerol and decreased high density lipoprotein cholesterol concentrations, effects which seem to be magnified in more obese individuals. S447X carrier frequency is approximately 20%, but unlike carriers of N9 or S291, X447 carriers appear to have a more favourable lipid profile. A transition within the LPL promoter at position-93 may lead to increased LPL activity and have a beneficial effect on plasma lipids. Greater knowledge of the underlying mechanisms of these variations within the LPL gene may be of considerable importance in understanding genetic predisposition to atherosclerosis and heart disease.

New variants in the glycogen synthase gene (Gln71His, Met416Val) in patients with NIDDM from eastern Finland

Impaired glycogen synthesis after insulin stimulation accounts for most of the insulin resistance in patients with non-insulin-dependent diabetes mellitus (NIDDM). The glycogen synthase gene (GYS1), which encodes the rate-limiting enzyme for glycogen synthesis, is a promising candidate gene for NIDDM. Therefore, we screened all 16 exons of this gene by single-strand conformation polymorphism analysis in 40 patients with NIDDM (age 67 +/- 2 years, body mass index 28.2 +/- 0.6 kg/m2) from Taipalsaari, eastern Finland. The Gly464Ser variant (exon 11) and a silent polymorphism TTC342TTT (exon 7) have been reported previously. In addition, we found a new variant Gln71His (exon 2) and a new amino acid polymorphism Met416Val (exon 10). An additional sample of 65 patients with NIDDM and 82 normoglycaemic men (age 54 +/- 1 years, body mass index 26.3 +/- 1.4 kg/m2) were screened. The allele frequency of the TTC342TTT silent substitution was 0.29 in both NIDDM and normoglycaemic subjects. The Gln71His and Gly464Ser variants were found in 1 (1%) and 3 (3%) subjects, respectively, of the 105 NIDDM patients and in none of the 82 normoglycaemic men. The Met416Val polymorphism was found in 16 (15%) of the 105 NIDDM patients and in 14 (17%) of the 82 control subjects (all heterozygous). The Met416Val polymorphism was not associated with insulin resistance in two groups of normoglycaemic subjects. In conclusion, the new Gln71His and Met416Val substitutions and other variants of the glycogen synthase gene are unlikely to make a major contribution to insulin resistance and NIDDM in diabetic patients from eastern Finland.

The acylation stimulating protein pathway: clinical implications

OBJECTIVES

The present review will focus particularly on acylation stimulating protein (ASP) and its role in adipose tissue. Two issues will be addressed (1) in vitro biochemical characterization of ASP in cell culture studies, and (2) in vivo clinical relevance for normal physiology and in pathological conditions.

CONCLUSIONS

Fat is In! There can be no question that in recent years fat tissue has become recognized as more than just a passive storage site. It is a metabolically active tissue that, under normal conditions, allows the efficient clearance of triglyceride and glucose for storage as energy. Under abnormal conditions, adipose tissue dysfunction is associated with obesity, diabetes and coronary heart disease. Adipose tissue function may be controlled by many factors.

Complex genetic contribution of the Apo AI-CIII-AIV gene cluster to familial combined hyperlipidemia. Identification of different susceptibility haplotypes

Familial combined hyperlipidemia (FCH) is a common genetic lipid disorder in Western societies. In a recent report (Dallinga-Thie, G.M., X.D. Bu, M. van Linde-Sibenius Trip, J.I. Rotter, A.J. Lusis, and T.W.A. de Bruin. J. Lipid Res., 1996, 36:136-147) we have studied three restriction enzyme polymorphisms: XmnI, and MspI sites 5' of the apo AI gene and SstI site in the 3' untranslated region of exon 4 of the apo CIII gene in 18 FCH pedigrees, including 18 probands, 178 hyperlipidemic relatives, 210 normolipidemic relatives, and 176 spouses. DNA variations in the apo AI-CIII-AIV gene cluster had a modifying effect on plasma triglycerides, LDL cholesterol, and apolipoprotein CIII levels. In this study, combinations of haplotypes were analyzed to further characterize their interactions and effect on the expression of severe hyperlipidemia in FCH subjects. A specific combination of haplotypes with one chromosome carrying the X1M1S2 (1-1-2) haplotype and the other the X2M2S1 haplotype (2-2-1) was significantly more frequent in hyperlipidemic relatives (6%) than in normolipidemic relatives (3%) and spouses (0.5%). Associated with this combination of haplotypes were significantly elevated plasma cholesterol (P < 0.0001), triglycerides (P < 0.0001), and apo CIII (P < 0.001) levels when compared to the wild type combination of haplotypes 1-1-1/1-1-1. The only spouse with this specific combination of haplotypes showed a severe hyperlipidemic phenotype, similar to FCH. Furthermore, nonparametric sibpair linkage analysis revealed significant linkage between these markers in the gene cluster and the FCH phenotype (MspI P = 0.0088, SstI P = 0.044, and XMS haplotype P = 0.037). The present findings confirm that the apo AI-CIII-IV gene cluster contributes to the FCH phenotype, but this contribution is genetically complex. An epistatic interaction between different haplotypes of the gene cluster was demonstrated. The S2 allele on one haplotype was synergistic to the X2M2 allele on the other haplotype in its hyperlipidemic effect. Therefore, two different susceptibility loci exist in the gene cluster, demonstrating the paradigm of complex genetic contribution to FCH.

Lipoprotein lipase gene variants and risk of coronary disease: a quantitative analysis of population-based studies

The purpose of this study is to quantify the magnitude of the association between common variants in the lipoprotein lipase gene and coronary disease, based on published population-based studies. Fourteen studies, representing 15,708 subjects, report allelic distribution for lipoprotein lipase gene variants among coronary disease patients and control subjects. Patient outcomes included clinical coronary disease events and documented coronary disease based on angiography. Allele frequencies are estimated for disease and non-disease groups within each study. A 2 x 2 contingency table is used to compute individual study odds ratios and 95% confidence intervals, relating the presence of the rare allele to disease status. Mantel-Haenszel-stratified analysis of each allelic variant results in a summary odds ratio and 95% confidence interval for the association between each rare allele in the lipoprotein lipase gene and coronary disease. The lipoprotein lipase D9N allele has a summary odds ratio of 1.59 (95% confidence interval 1.03-2.55), indicating a 59% increase in risk of coronary disease for carriers with this allelic variant. The lipoprotein lipase N291S allele showed no association with coronary disease (summary odds ratio 0.93, 95% confidence interval 0.73-1.19). The summary odds ratio for lipoprotein lipase S447Ter allele is 0.81 (95% confidence interval 0.65-1.0), indicating a marginal negative association between this variant and coronary disease. The common lipoprotein lipase Pvu II polymorphism shows no relation to coronary disease (summary odds ratio 0.90, 95% confidence interval 0.80-1.01). The rare allele of the lipoprotein lipase HindIII polymorphism is negatively associated with coronary disease (summary odds ratio 0.84, 95% confidence interval 0.73-0.96). The lipoprotein lipase D9N allele is associated with high levels of triglyceride and low levels of high-density lipoprotein. Similar atherogenic lipid levels are observed in subjects with structural mutations lipoprotein lipase C188E and P207L. Carriers of the S447Ter allele have low levels of triglyceride. The lipoprotein, lipase gene variants which decrease lipoprotein lipase catalytic activity are associated with familial combined hyperlipidemia, but not the elevation of apolipoprotein B seen in this disorder. In conclusion, allelic variants in the lipoprotein lipase gene are associated with altered lipid levels and differential coronary disease risk.

Effect of apolipoprotein E and insulin resistance on VLDL particles in combined hyperlipidemic patients

Apolipoprotein (apo) E2 and high insulin levels are associated with the severity of hypertriglyceridemia in patients with combined hyperlipidemia. To study how these determinants affect very low-density lipoprotein (VLDL) in combined hyperlipidemic patients, we characterized VLDL particles in 106 unrelated patients with combined hyperlipidemia. The study was performed after 9 weeks of standardized dietary intake and after an overnight fast. Patients heterozygous for apoE2 had significantly higher mean levels of VLDL cholesterol by 0.71 mmol/l (95% CI, 0.30 to 1.12 mmol/l, P < 0.005) and VLDL triglycerides by 0.88 mmol/l, (95% CI, 0.30 to 1.47 mmol/l, P < 0.005) compared to patients without apoE2. The VLDL triglyceride content per particle and the calculated diameter of the VLDL particles were similar in both groups, which indicate a higher number of circulating VLDL particles in heterozygous apoE2 carriers. Patients with high fasting insulin levels (> or = 80 pmol/l) had a higher mean serum VLDL triglyceride level by 0.56 mmol/l (95% CI, 0.04 to 1.07 mmol/l, P < 0.05). The calculated VLDL diameter was larger by 3.7 nm (95% CI, 1.2 to 6.2 nm, P < 0.005) and the particles contained more triglycerides by 2.7 weight percent (95% CI, 0.3 to 5.1 weight percent, P < 0.05). These insulin-dependent changes in VLDL particles were only present in the absence of apoE2. In conclusion, patients heterozygous for apoE2 have higher numbers of circulating VLDL particles, whereas patients with high fasting insulin levels have larger, triglyceride enriched VLDL particles.

Lipoprotein lipase gene mutations D9N and N291S in four pedigrees with familial combined hyperlipidaemia

The role of the lipoprotein lipase (LPL) gene in familial combined hyperlipidaemia (FCH) is unclear at present. We screened a group of 28 probands with familial combined hyperlipidaemia and a group of 91 population controls for two LPL gene mutations, D9N and N291S. LPL-D9N was found in two probands and one normolipidaemic population control. LPL-N291S was found in four probands and four population controls. Subsequently, two pedigrees from probands with the D9N mutation and two pedigrees from probands with the N291S mutation were studied, representing a total of 24 subjects. Both LPL gene mutations were associated with a significant effect on plasma lipids and apolipoproteins. Presence of the D9N mutation (n = 7) was associated with hypertriglyceridaemia [2.69 +/- 1.43 (SD) mmol L-1] and reduced plasma high-density lipoprotein cholesterol (HDL-C) concentrations (0.92 +/- 0.21 mmol L-1) compared with 11 non-carriers (triglyceride 1.75 +/- 0.64 mmol L-1; HDL-C 1.23 +/- 0.30 mmol L-1, P = 0.03 and P = 0.025 respectively). LPL-D9N carriers had higher diastolic blood pressures than non-carriers. LPL-N291S carriers (n = 6) showed significantly higher (26%) apo B plasma concentrations (174 +/- 26 mg dL-1) than non-carriers (138 +/- 26 mg dL-1; P = 0.023), with normal post-heparin plasma LPL activities. Linkage analysis revealed no significant relationship between the D9N or N291S LPL gene mutations and the FCH phenotype (hypertriglyceridaemia, hypercholesterolaemia or increased apo B concentrations). It is concluded that the LPL gene did not represent the major single gene causing familial combined hyperlipidaemia in the four pedigrees studied, but that the LPL-D9N and LPL-N291S mutations had significant additional effects on lipid and apolipoprotein phenotype.

In vitro lipolysis of human VLDL: effect of different VLDL compositions in normolipidemia, familial combined hyperlipidemia and familial hypertriglyceridemia

Suboptimal lipolysis of very low density lipoproteins (VLDL) due to reduced substrate affinity for lipoprotein lipase (LPL) may contribute to the accumulation of apolipoprotein (apo) B in familial combined hyperlipidemia (FCH) or the characteristic increase in triglyceride-rich lipoproteins in familial hypertriglyceridemia (FHTG). To investigate this hypothesis in detail, the VLDL composition and substrate affinity for lipoprotein lipase was determined in 22 normolipidemic controls, 16 FCH probands, and 12 FHTG subjects. VLDL from FCH subjects were enriched in cholesterol and phospholipid. VLDL from FHTG subjects were enriched in triglycerides, cholesterol and phospholipid. Potential apolipoprotein regulators of LPL activity including apo C-II, apo C-III and apo E were not significantly different between FCH and controls when expressed per VLDL apo B. High apo C-III concentrations were present in FHTG-VLDL, and the apo C-III/E-ratio was significantly higher than in FCH- and control-VLDL. An increase of C-III-0, the desialylated isoform, was observed in FHTG-VLDL. The kinetic indicators for in vitro triglyceride hydrolysis by LPL, KM and VMAX, were not significantly different between the groups. KM values measured in vitro were remarkably and consistently high (1.54 mmol VLDL-TG/I), predicting saturation of LPL when VLDL-TG levels exceed 5.5 mmol/l (2 times KM + 2S.D.). In conclusion, VLDL from individuals with FCH or FHTG are normal substrate for lipoprotein lipase in spite of significant differences in lipid and apolipoprotein composition. The high apo C-III content of FHTG-VLDL supports a role in the expression of hypertriglyceridemia.

The lipoprotein lipase (Asn291-->Ser) mutation is associated with elevated lipid levels in families with familial combined hyperlipidaemia

Familial combined hyperlipidaemia (FCHL) is one of the major genetic causes of coronary heart disease (CHD) and is characterised by elevated levels of plasma cholesterol and/or triglycerides in individuals within a single family. Decreased lipoprotein lipase (LPL) activity has been found in some cases of FCHL. A recent study revealed a common mutation in the LPL gene, LPL(Asn291-->Ser), with a frequency of 9.3% in Dutch FCHL patients (Reymer et al,. Circulation, 90 (1994) I-998). This mutation was found in 3 out of 17 FCHL families. Extensive family studies were subsequently performed to determine the effect of this mutation on the phenotypic expression of FCHL. Using a pedigree-based maximum likelihood estimate, we demonstrated that the LPL(Asn291-->Ser) mutation significantly affects the levels of plasma and very low density lipoprotein (VLDL) triglycerides (2.03 +/- 0.21 vs. 1.14 +/- 0.13 and 1.21 +/- 0.16 vs. 0.62 +/- 0.09 mmol/l, carriers and non-carriers, respectively) and VLDL- and high density lipoprotein (HDL) cholesterol (0.83 +/- 0.10 vs. 0.38 +/- 0.06 and 1.02 +/- 0.08 vs. 1.29 +/- 0.05 mmol l, carriers and non-carriers, respectively), but not those of plasma and low density lipoprotein (LDL) cholesterol. These findings indicate that the LPL(Asn291-->Ser) mutation is associated with elevated lipid levels, indicating it may be one of the genetic factors predisposing to FCHL in the families studied.

Family study of lipoprotein lipase gene polymorphisms and plasma triglyceride levels

To better characterize the role of the lipoprotein lipase (LPL) gene in the determination of triglyceride levels in healthy subjects, a study was performed in 193 nuclear families (384 parents, means age = 42.0 +/- 5.2 years; 399 offspring, mean age = 14.6 +/- 4.3 years) volunteering to have a free health checkup examination. The pattern of familial resemblance was compatible with a zero correlation between spouses, a weak father-offspring correlation (0.099 +/- 0.054; P < 0.07), and significant mother-offspring (0.235 +/- 0.053; P < 10(-4)) and sib-sib (0.294 +/- 0.064; P < 10(-4)) correlations. Associations of triglyceride levels with the LPL HindIII and PvuII polymorphisms were investigated by a familial measured genotype analysis, specifying sex- and age-dependent polymorphism effects. The effects associated with both polymorphisms were significant only in fathers, the H+ and P+ alleles being associated with raised triglyceride levels. The HindIII and PvuII polymorphisms explained 3.5% and 3%, respectively, of the variability of triglycerides in fathers. The relationship was weakened after prior adjustment on body mass index, but remained significant for PvuII. Because of the lack of effect in mothers and offspring, the polymorphisms did not contribute to the covariance of triglyceride levels in relatives. In conclusion, this family study showed a weak relationship of the HindIII and PvuII polymorphisms to plasma triglyceride levels in young healthy male subjects. The effects detectable only in fathers suggest a possible modulation of the LPL expression by hormonal or lifestyle factors.

Two novel apolipoprotein A-IV variants in individuals with familial combined hyperlipidemia and diminished levels of lipoprotein lipase activity

It has been suggested that apo A-IV may play a role in modulating the activation of lipoprotein lipase (LPL) by apo C-II (Goldberg et al., 1990). Therefore, the role of genetic variation at the apolipoprotein A-IV locus in familial combined hyperlipidemia (FCHL) was investigated. A subset of FCHL patients with half the level of plasma LPL activity was screened by single-strand conformation polymorphism (SSCP) for variants in the apolipoprotein A-IV gene. Two of 20 such individuals were found to be heterozygous carriers of previously undescribed amino acid substitutions: S158L and R 244Q substitutions, designated A-IV-Seattle-1 and A-IV-Seattle-2, respectively. These substitutions were not detected among 20 other FCHL patients with normal LPL levels and among 97 unselected medical students. The finding of these two alleles among only the 20 patients with FCHL with reduced levels of LPL suggests an association with this phenotype. It is hypothesized that these two alleles may contribute, along with alleles of other genes or environmental factors, to the development of FCHL. A third previously undescribed variant (A141S) was observed in four (two homozygotes and two heterozygotes) of the 97 medical students.

Molecular pathobiology of the human lipoprotein lipase gene

Lipoprotein lipase (LPL; E.C. 3.1.1.34) is a key enzyme in the metabolism of lipids. Many diseases, including obesity, coronary heart disease, chylomicronemia (pancreatitis), and atherosclerosis, appear to be directly or indirectly related to abnormalities in LPL function. Human LPL is a member of a superfamily of lipases that includes hepatic lipase and pancreatic lipase. These lipases are characterized by extensive homology, both at the level of the gene and the mature protein, suggesting that they have a common evolutionary origin. A large number of natural mutations have been discovered in the human LPL gene, which are located at different sites in the gene and affect different functions of the mature protein. There is a high prevalence of two of these mutations (207 and 188) in the Province of Québec, and one of them (207) is almost exclusive to the French-Canadian population. A study of these and other naturally occurring mutant LPL molecules, as well as those created in vitro by site-directed mutagenesis, indicate that the sequence of LPL is organized into multiple structural and functional units that act in concert in the normal enzyme. In this review, we discuss the interrelationships of LPL structure and its function, the molecular etiology of abnormal LPL in humans, and the clinical and therapeutic aspects of LPL deficiency.

Severe hypertriglyceridemia, reduced high density lipoprotein, and neonatal death in lipoprotein lipase knockout mice. Mild hypertriglyceridemia with impaired very low density lipoprotein clearance in heterozygotes

Lipoprotein lipase (LPL)-deficient mice have been created by gene targeting in embryonic stem cells. At birth, homozygous knockout pups have threefold higher triglycerides and sevenfold higher VLDL cholesterol levels than controls. When permitted to suckle, LPL-deficient mice become pale, then cyanotic, and finally die at approximately 18 h of age. Before death, triglyceride levels are severely elevated (15,087 +/- 3,805 vs 188 +/- 71 mg/dl in controls). Capillaries in tissues of homozygous knockout mice are engorged with chylomicrons. This is especially significant in the lung where marginated chylomicrons prevent red cell contact with the endothelium, a phenomenon which is presumably the cause of cyanosis and death in these mice. Homozygous knockout mice also have diminished adipose tissue stores as well as decreased intracellular fat droplets. By crossbreeding with transgenic mice expressing human LPL driven by a muscle-specific promoter, mouse lines were generated that express LPL exclusively in muscle but not in any other tissue. This tissue-specific LPL expression rescued the LPL knockout mice and normalized their lipoprotein pattern. This supports the contention that hypertriglyceridemia caused the death of these mice and that LPL expression in a single tissue was sufficient for rescue. Heterozygous LPL knockout mice survive to adulthood and have mild hypertriglyceridemia, with 1.5-2-fold elevated triglyceride levels compared with controls in both the fed and fasted states on chow, Western-type, or 10% sucrose diets. In vivo turnover studies revealed that heterozygous knockout mice had impaired VLDL clearance (fractional catabolic rate) but no increase in transport rate. In summary, total LPL deficiency in the mouse prevents triglyceride removal from plasma, causing death in the neonatal period, and expression of LPL in a single tissue alleviates this problem. Furthermore, half-normal levels of LPL cause a decrease in VLDL fractional catabolic rate and mild hypertriglyceridemia, implying that partial LPL deficiency has physiological consequences.

The genetic determinants of plasma cholesterol and response to diet

In general, risk factors for multifactorial disorders such as atherosclerosis and hyperlipidaemia show a continuous distribution in the population, and this is the result of both interaction between genetic variation at genetic loci, and genetic and environmental interaction. Therefore, the investigation of the genetics of intermediate phenotypes such as levels of plasma lipid traits is likely to be particularly informative. Once the genes involved in determining the levels of these phenotypes have been identified, it should be possible to use the information to obtain a better understanding of the way these genetic variations determine the clinical end points. In the population it will be possible to identify a number of polygenes that are having a small effect on determining the trait, but for a particular individual, or the relatives of that individual, only a subset of all these polygenes will determine the level of the trait and therefore the risk of developing the disorder. In general, mutations with a large effect on the trait are rare in the population, By contrast, polymorphisms with a small effect on the trait may be common, such as is found with the effect of the apoE alleles and variation at the apoB gene locus on lipid levels. In the field of hyperlipidaemia and atherosclerosis research, molecular techniques have already given a great deal of information on how specific sequence variations in some of the candidate genes are involved in determining levels of plasma apoproteins, lipoproteins and lipids. As more mutations and sequence variations are identified, this will not only aid our understanding of the underlying pathology, but should be useful for identifying individuals who are at risk of developing atherosclerosis because of their particular genotype or combination of genotypes.

A mutation in the promoter of the lipoprotein lipase (LPL) gene in a patient with familial combined hyperlipidemia and low LPL activity

We have identified a naturally occurring mutation in the promoter of the lipoprotein lipase (LPL) gene. One of 20 patients with familial combined hyperlipidemia (FCHL) and reduced levels of postheparin plasma LPL activity was found to be a heterozygote carrier of this mutation. The mutation, a T-->C substitution at nt -39, occurred in the binding site of the transcription factor Oct-1. As a result, the transcriptional activity of the mutant promoter was < 15% of wild type, as determined by transfection studies in the human macrophage-like cell line THP-1. This decrease in promoter activity was observed in undifferentiated as well as in phorbol ester-differentiated THP-1 cells. Furthermore, the inductive effect of elevating the levels of intracellular cAMP was equally reduced. This mutation was not present among 20 FCHL patients with normal plasma LPL levels nor has it been reported among individuals with familial LPL deficiency. Thus, heterozygosity for LPL promoter mutations may be one of several factors that contribute to the etiology of FCHL.

Polymorphisms of the human hexokinase II gene: lack of association with NIDDM and insulin resistance

Skeletal muscle and adipose tissue hexokinase II is a promising candidate gene for non-insulin-dependent diabetes mellitus (NIDDM) and insulin resistance. Therefore, we investigated the association of alleles at four polymorphic loci in this gene with NIDDM and insulin resistance in 110 Finnish diabetic patients with NIDDM and in 97 Finnish control subjects with normal glucose tolerance and a negative family history of diabetes. The four polymorphic nucleotide substitutions (silent) in the coding region of the hexokinase II gene were: GAC 251 GAT (exon 7), AAC 692 AAT and CCG 736 CCC (exon 15), and CTG 766 CTA (exon 16). Allele frequencies of each of these polymorphisms did not differ between patients with NIDDM and control subjects. In addition, subjects who were homozygous for the less frequent allele of each of the four polymorphisms had a similar degree of insulin resistance, as determined by the euglycaemic clamp technique, as did the subjects who were homozygous for the common allele in both control subjects and in patients with NIDDM. In conclusion, polymorphisms in the hexokinase II gene are not associated with the risk of NIDDM or insulin resistance in the Finnish population.