Hypolipidemia associated with inactivation of TM6SF2 is due to decreased VLDL-lipids secretion

Background

A missense variant in Transmembrane 6 Superfamily Member 2 [TM6SF2 (E167K)] is associated with reduced plasma lipid levels and protection from coronary atherosclerosis. The substitution of lysine for glutamate at residue 167 is associated with a marked decrease in TM6SF2 protein expression, consistent with a loss-of-function mutation. However the biological role of TM6SF2 is not known, and the mechanism(s) responsible for the hypolipidemia associated with mutation gene has not been fully defined. To elucidate the pathological mechanism for the hypolipidemia associated with TM6SF2 deficiency, we inactivated Tm6sf2 in mice and rats.

Methods

Tm6sf2−/− mice were generated as described previously. Two lines of Tm6sf2−/− rats with different frameshift mutations in exon 1 were generated using CRISPR/Cas9 technology. Primary hepatocytes were isolated from WT and Tm6sf2−/− mice for microscopy. Rats were fasted 16 or 4 hours and tissues were collected on ice for cell fractionation, and in liquid nitrogen for biochemical analyses. Frozen samples were stored at −80°C for subsequent analyses.

Result

In both mice and rats, inactivation of Tm6sf2 recapitulated the phenotype of humans with the E167K substitution: steatosis, reduced plasma lipid levels, and transaminitis. The phenotype was readily apparent in animals fed chow diets. Both species had reduced secretion of VLDL-TG, as determined by TRITON WR1399 injection, with no decrease in secretion of ApoB. Experiments in isolated perfused livers from WT and Tm6sf2−/− mice confirmed that the decreased TG secretion observed in intact animals reflected reduced TG secretion from the liver. Lipidomic analysis of the liver perfusates by by LC-MS indicated that secretion of cholesteryl esters, and phospholipids was also decreased in the KO animals. Taken together, these findings are consistent with a role for TM6SF2 in lipidation of ApoB-containing lipoproteins. To further elucidate the function of TM6SF2, we used fluorescence microscopy and cell fractionation to determine the subcellular localization of the protein. Microscopic analysis showed that TM6SF2 co-localized with ER and Golgi markers, but cell fractionation studies indicated that the protein is located primarily in the smooth ER. The ratio of TG to ApoB was lower in Golgi fractions from TM6sf2−/− rats than in corresponding fractions from WT animals.

Conclusions

Since the sequela of TM6SF2 inactivation are already apparent in the Golgi, we speculate that TM6SF2 promotes lipidation of VLDL in a pre-Golgi compartment. We are currently performing additional studies to further define the specific mechanism whereby TM6SF2 promotes lipidation of ApoB-containing lipoproteins.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): National Institutes of Health

Using human genetics to discover new therapeutic targets for plasma lipids

Genetic variation arises through multiple different alleles that vary in frequency and severity of effect. Mutations that give rise to Mendelian disorders, such as the LDL receptor (LDLR) mutations that result in familial hypercholesterolaemia, are efficiently winnowed from the population by purifying selection and are almost inevitably rare. Conversely, alleles that are common in the population (such that homozygotes for the minor allele are present even in modest sample sizes) typically have very modest phenotypic effects. Mutations in the gene for proprotein convertase subtilisin/kexin type 9 (PCSK9) represent an unusual but informative exception in that they are relatively common but have large effects on phenotype. Loss-of-function mutations in PCSK9 occur in ~2.5% of African Americans and are associated with large reductions in coronary heart disease (CHD) risk. The development of agents to inhibit PCSK9 demonstrates the utility of translating genetics into clinical therapeutics. Attempts to identify genes responsible for hypercholesterolaemia have used traditional linkage analysis, which requires samples collected from multiple families with defects in the same gene, or genome-wide association, which requires thousands of samples from the population. More recently, whole-exome sequencing studies have revealed loss-of-function mutations in ANGPTL3 associated with pan-hypolipidemia, and in APOC3 that confer protection against CHD. The application of whole-exome sequencing to large populations or to carefully selected patients can streamline the discovery of causal genetic mutations.

Diclofenac plus B vitamins versus diclofenac monotherapy in lumbago: the DOLOR study

OBJECTIVES

To assess the influence of vitamins B1, B6 and B12 on the analgesia success achieved by diclofenac in subjects with acute lumbago.

RESEARCH DESIGN AND METHODS

A randomised, double blind controlled clinical study in parallel groups, in which subjects received twice-daily oral administration of either the combination therapy, Group DB (50 mg diclofenac plus 50 mg thiamine, 50 mg pyridoxine and 1 mg cyanocobalamin) or diclofenac monotherapy, Group D (50mg diclofenac). The study period lasted a maximum of 7 days. If sufficient pain reduction was achieved (defined as Visual Analogue Scale <20 mm and patient's satisfaction), subjects could withdraw from the treatment after 3 or 5 days. All subjects gave written informed consent to participate in the study.

MAIN OUTCOME MEASURES

The primary confirmatory study objective was to determine the number of patients with sufficient pain reduction after 3 days of treatment.

RESULTS

Three hundred and seventy-two subjects were allocated at random to either treatment group: Group DB - 187 subjects and Group D - 185 subjects. After 3 days of treatment, a statistically significant higher proportion of subjects in Group DB (n = 87; 46.5%) than in Group D (n = 55; 29%) terminated the study due to treatment success (chi(2): 12.06; p = 0.0005). Furthermore, the combination therapy yielded superior results in pain reduction, improvement of mobility and functionality. Drug safety monitoring profile throughout the trial was within the expected safety profile of diclofenac.

CONCLUSIONS

The combination of diclofenac with B vitamins was superior to diclofenac monotherapy in lumbago relief after 3 days of treatment. As a study drawback, daily VAS measurements were only recorded until subject withdrawal from treatment, whether after 3, 5, or 7 days. There were no differences in safety profile between the two study groups.

Comparison of closed chamber and open chamber evaporimetry

BACKGROUND

Recently it has been asserted that a closed chamber evaporimeter, the VapoMeter, offers advantages over standard open chamber devices in measuring transepidermal water loss (TEWL). Purported improvements include the ability to take measurements at any angle, short reading times and insensitivity to external air currents. These claims are compelling, considering that measuring TEWL at diverse skin sites can be tedious, especially with children. The primary aim of this study was to compare the performance of closed and open chamber instruments when they were held at various angles and, secondly to evaluate the ability of the devices to discriminate between test conditions.

METHODS

The performance of closed chamber (VapoMeter) and open chamber (DermaLab) evaporimeters were compared by measuring water vapor emitted from IMS Vitro-skin that had been hydrated to a predetermined level. Measurements were taken at three angles from vertical - 0 degrees, 45 degrees, and 90 degrees. Vitro-skin samples were weighed periodically throughout the experimental phase to verify water loss rates.

RESULTS

Both the VapoMeter and the DermaLab yielded significantly lower water loss values when held at angles that varied from the vertical (0 degrees) position, indicating that the closed chamber device is no more capable of accurately measuring TEWL at any angle than an open chamber instrument. The DermaLab provided better discrimination than the VapoMeter when the instruments were held vertically, as is the only prescribed testing position for open-chamber instruments. The VapoMeter was easier to use than the DermaLab; however, there was evidence that the sealed chamber could become saturated under high water loss conditions.

CONCLUSIONS

Previous assertions that the VapoMeter closed chamber evaporimeter is capable of measuring TEWL regardless of angle were not validated. Each device appeared capable of accurately estimating water loss rates only in the vertical position. Although the VapoMeter was easier to use than the open chamber device, its tendency to become saturated under high water loss conditions could be a disadvantage when assessing dynamic TEWL.

Tackling corruption in the pharmaceutical systems worldwide with courage and conviction

Poor drug access continues to be one of the main global health problems. Global inequalities in access to pharmaceuticals are caused by a number of variables including poverty, high drug prices, poor health infrastructure, and fraud and corruption--the latter being the subject of this article. There is growing recognition among policy makers that corruption in the pharmaceutical system can waste valuable resources allocated to pharmaceutical products and services. This, in turn, denies those most in need from life-saving or life-enhancing medicines. As a result, international organizations, including the World Health Organization and the World Bank are beginning to address the issue of corruption in the health sector broadly and the pharmaceutical system specifically. This is encouraging news for improving drug access for the global poor who are most harmed by corruption as they tend to purchase less expensive drugs from unqualified or illegal drug sellers selling counterfeit or sub-standard drugs. In our paper, we illuminate what are the core issues that relate to corruption in the pharmaceutical sector. We argue that corruption in the pharmaceutical system can be detrimental to a country's ability to improve the health of its population. Moreover, unless policy makers deal with the issue of corruption, funding allocated to the pharmaceutical system to treat health conditions may simply be wasted and the inequality between rich and poor in access to health and pharmaceutical products will be aggravated.

TRIPS, the Doha Declaration and increasing access to medicines: policy options for Ghana

There are acute disparities in pharmaceutical access between developing and industrialized countries. Developing countries make up approximately 80% of the world's population but only represent approximately 20% of global pharmaceutical consumption. Among the many barriers to drug access are the potential consequences of the Trade Related Aspects of Intellectual Property Rights (TRIPS) Agreement. Many developing countries have recently modified their patent laws to conform to the TRIPS standards, given the 2005 deadline for developing countries. Safeguards to protect public health have been incorporated into the TRIPS Agreement; however, in practice governments may be reluctant to exercise such rights given concern about the international trade and political ramifications. The Doha Declaration and the recent Decision on the Implementation of Paragraph 6 of the Doha Declaration on the TRIPS Agreement and Public Health may provide more freedom for developing countries in using these safeguards. This paper focuses on Ghana, a developing country that recently changed its patent laws to conform to TRIPS standards. We examine Ghana's patent law changes in the context of the Doha Declaration and assess their meaning for access to drugs of its population. We discuss new and existing barriers, as well as possible solutions, to provide policy-makers with lessons learned from the Ghanaian experience.

An apolipoprotein influencing triglycerides in humans and mice revealed by comparative sequencing

Comparison of genomic DNA sequences from human and mouse revealed a new apolipoprotein (APO) gene (APOAV) located proximal to the well-characterized APOAI/CIII/AIV gene cluster on human 11q23. Mice expressing a human APOAV transgene showed a decrease in plasma triglyceride concentrations to one-third of those in control mice; conversely, knockout mice lacking Apoav had four times as much plasma triglycerides as controls. In humans, single nucleotide polymorphisms (SNPs) across the APOAV locus were found to be significantly associated with plasma triglyceride levels in two independent studies. These findings indicate that APOAV is an important determinant of plasma triglyceride levels, a major risk factor for coronary artery disease.

Mutations in ATP-cassette binding proteins G5 (ABCG5) and G8 (ABCG8) causing sitosterolemia

Sitosterolemia is an autosomal recessive disorder caused by mutations in two adjacent genes encoding coordinately regulated ATP binding cassette (ABC) half transporters (ABCG5 and ABCG8). In this paper we describe three novel mutations causing sitosterolemia: 1) a frameshift mutation (c.336-337insA) in ABCG5 that results in premature termination of the protein at amino acid 197; 2) a missense mutation that changes a conserved residue c.1311C>G; N437K) in ABCG5 and 3) a splice site mutation in ABCG8 (IVS1-2A>G). This study expands the spectrum of the ABCG5 and ABCG8 mutations that cause sitosterolemia. Nine nonsynonymous polymorphisms are also reported: I523V, C600Y, Q604E, and M622V in ABCG5; and D19H, Y54C, T400K, A632V, and Y641F in ABCG8.

Molecular characterization of L-CPT I deficiency in six patients: insights into function of the native enzyme

Carnitine palmitoyltransferase I (CPT I) catalyzes the formation of acylcarnitine, the first step in the oxidation of long-chain fatty acids in mitochondria. The enzyme exists as liver (L-CPT I) and muscle (M-CPT I) isoforms that are encoded by separate genes. Genetic deficiency of L-CPT I, which has been reported in 16 patients from 13 families, is characterized by episodes of hypoketotic hypoglycemia beginning in early childhood and is usually associated with fasting or illness. To date, only two mutations associated with L-CPT I deficiency have been reported. In the present study we have identified and characterized the mutations underlying L-CPT I deficiency in six patients: five with classic symptoms of L-CPT I deficiency and one with symptoms that have not previously been associated with this disorder (muscle cramps and pain). Transfection of the mutant L-CPT I cDNAs in COS cells resulted in L-CPT I mRNA levels that were comparable to those expressed from the wild-type construct. Western blotting revealed lower levels of each of the mutant proteins, indicating that the low enzyme activity associated with these mutations was due, at least in part, to protein instability. The patient with atypical symptoms had approximately 20% of normal L-CPT I activity and was homozygous for a mutation (c.1436C-->T) that substituted leucine for proline at codon 479. Assays performed with his cultured skin fibroblasts indicated that this mutation confers partial resistance to the inhibitory effects of malonyl-CoA. The demonstration of L-CPT I deficiency in this patient suggests that the spectrum of clinical sequelae associated with loss or alteration of L-CPT I function may be broader than was previously recognized.

Impaired mitochondrial fatty acid oxidative flux in fibroblasts from a patient with malonyl-CoA decarboxylase deficiency

Malonyl-CoA decarboxylase deficiency is a rare inborn error of metabolism. It has been suggested but never demonstrated that many of the clinical features arise due to inhibition of mitochondrial fatty acid oxidation by accumulated malonyl-CoA. We studied the oxidation of fatty acids in cultured skin fibroblasts from a recently described patient with malonyl-CoA decarboxylase deficiency. There was a marked reduction in the oxidation of palmitic and myristic acids both under baseline conditions and when the cells were cultured in the presence of high concentrations of acetate, a malonyl-CoA precursor. These results suggest that there is inhibition of fatty acid oxidation in malonyl-CoA decarboxylase deficiency and that this inhibition may be related to some of the clinical phenotypes.

Sequence diversity in genes of lipid metabolism

Elevated plasma lipoprotein levels play a crucial role in the development of coronary artery disease. Genetic factors strongly influence the levels of plasma lipoproteins, but the genes and sequence variations contributing to the most common forms of dyslipidemias are not known. We used GeneChip probe arrays to resequence the coding regions of 10 key genes of lipid metabolism. The sequences of these genes were analyzed in 80 dyslipidemic individuals. Fourteen nonsynonymous and twenty-two synonymous single nucleotide changes were identified that could be confirmed by conventional sequencing. Seven of the fourteen nonsynonymous sequence variants were polymorphisms with allele frequency >1% in the general population. The remaining seven were not found in normolipidemic controls (25 Caucasians and 25 African-Americans). The relationship between nonsynonymous sequence variations and various dyslipidemias was explored in association and family studies. No evidence was found for coding sequence variations in any of the 10 genes contributing to dyslipidemia. Only a single sequence variation, a missense mutation in the low density lipoprotein receptor gene, co-segregated with hyperlipidemia in the proband's family. This study illustrates some of the difficulties associated with identifying sequence variations contributing to complex traits.

Autosomal recessive hypercholesterolemia caused by mutations in a putative LDL receptor adaptor protein

Atherogenic low density lipoproteins are cleared from the circulation by hepatic low density lipoprotein receptors (LDLR). Two inherited forms of hypercholesterolemia result from loss of LDLR activity: autosomal dominant familial hypercholesterolemia (FH), caused by mutations in the LDLR gene, and autosomal recessive hypercholesterolemia (ARH), of unknown etiology. Here we map the ARH locus to an approximately 1-centimorgan interval on chromosome 1p35 and identify six mutations in a gene encoding a putative adaptor protein (ARH). ARH contains a phosphotyrosine binding (PTB) domain, which in other proteins binds NPXY motifs in the cytoplasmic tails of cell-surface receptors, including the LDLR. ARH appears to have a tissue-specific role in LDLR function, as it is required in liver but not in fibroblasts.

Gene transfer into the fetal primate: evidence for the secretion of transgene product

In utero adenoviral-mediated transfer of genes via the amniotic fluid results in sustained high-efficiency expression in rodent lung and intestine. Rhesus macaque (Macaca mulatta) fetuses were injected with adenovirus vectors encoding reporter genes at different gestational ages to evaluate feasibility and timing in primates. The fetuses developed normally following gene transfer and no maternal adverse affects were noted. Highly efficient viral uptake and transgene protein expression occurred in the target organs. The lungs exhibited no immune response and transgenic protein was observed up to 30 days postinfection. Unexpectedly, large amounts of reporter gene protein were released, apparently from the lung, into the circulation and accumulated in the renal proximal tubules and bladder. PCR detection for adenovirus DNA was consistently negative in tissues not in contact with the amniotic fluid, such as kidneys, liver, gonads, and eyes. Treatment of primate fetuses at 110 days gestation with an adenovirus expressing the cystic fibrosis transmembrane conductance regulator (cftr) gene resulted in accelerated differentiation of the lung. These studies demonstrate the efficacy of in utero gene therapy in primates and its potential application to genetic diseases.

Cystic fibrosis revisited

Cystic fibrosis is a pleiotropic disease whose primary defect is thought to be abnormal chloride conductance. Despite intensive study, the role of the protein in the airway and the mechanism for its direct participation in the disease pathology remain unclear. This paper reviews CFTR's cell regulatory functions and data supporting the role of CFTR in secretory epithelial cell development. A hypothesis for CF pathophysiology based on secretory cell differentiation is proposed.

CFTR modulates lung secretory cell proliferation and differentiation

We have permanently reversed the lethal phenotype in the cystic fibrosis (CF) transmembrane conductance regulator (CFTR)-deficient (knockout) mouse after in utero gene therapy with an adenovirus containing the cftr gene. The gene transfer targeted somatic stem cells in the developing lung and intestine, and these epithelial surfaces demonstrated permanent developmental changes after treatment. The survival statistics from the progeny of heterozygote-heterozygote matings after in utero cftr gene treatment demonstrated an increased mortality in the homozygous normal pups, indicating that overexpression during development was detrimental. The lungs of these pups revealed accelerated secretory cell proliferation and differentiation. The extent of proliferation and differentiation in the secretory cells of the lung parenchyma after in utero transfer of the cftr gene was evaluated with morphometric and biochemical analyses. These studies provide further support of the regulatory role of the cftr gene in the development of the secretory epithelium.

Premature cardiovascular disease is common in relatives of patients with premature peripheral atherosclerosis

BACKGROUND

Numerous clinical conditions have been proposed to explain the premature onset of symptomatic peripheral vascular disease (PVD) in young adults, but the role of genetic factors has not been defined. This study was performed to determine the prevalence of cardiovascular disease among family members of patients with premature PVD.

METHODS

The prevalence of early cardiovascular events occurring in first-degree relatives of 90 subjects with premature PVD (onset < or =49 years) was determined. The prevalence of occult atherosclerosis was determined by duplex ultrasonography in a cohort of 20 asymptomatic siblings. Reference groups included first-degree relatives of 80 subjects with premature coronary artery disease (CAD) and first-degree relatives of 48 healthy subjects.

RESULTS

Cardiovascular events occurred at age 55 years or younger in 28% of the parents of PVD subjects, in 23% of parents of CAD subjects, and in 7% of the parents of healthy controls (P<.001). Cardiovascular events occurred in 24% of siblings of PVD subjects, in 14% of siblings of CAD subjects, and in 7% of siblings of healthy controls (P<.001). Duplex ultrasonography detected early plaques in the lower extremity circulation of 10 (50%) of the asymptomatic siblings of PVD subjects.

CONCLUSIONS

Early, symptomatic cardiovascular disease is more common in first-degree relatives of individuals with premature PVD than in relatives of healthy individuals or of probands with premature CAD. Occult vascular disease in the lower extremity is prevalent among asymptomatic siblings of probands with premature PVD. These observations indicate that susceptibility to premature PVD has a familial basis.

Under which conditions do the skin and probe decouple during sinusoidal vibrations?

Previous experiments performed on monkey and human fingertips suggested that the skin surface and stimulus probe decouple for sinusoidal displacements applied perpendicularly to the skin surface. From these observations, it was concluded that sinusoidal vibration may not be a suitable stimulus for understanding and modeling the tactile system. We repeated these experiments on human observers using stimulus frequencies ranging from 0.5 to 240 Hz and with displacement amplitudes up to 1 mm peak-to-peak (p-p). The skin and probe movements were measured in the steady-state using stroboscopic illumination and video microscopy. Contrary to previous conclusions, we found that decoupling did not occur for amplitudes less then 0.25 mm p-p, regardless of stimulus frequency. Decoupling was only observed for stimulus amplitudes greater than 0.25 mm over the stimulus-frequency range investigated. To further investigate this effect, a modified stimulus contactor was used, which permitted the measurement of the skin's movement using reflected light. Measurements were made on both the index fingertip and the thenar eminence. Regardless of body site, no decoupling between the skin and stimulus probe was observed for frequencies ranging from 20 to 100 Hz up to displacements of 0.25 mm p-p. These levels are well within the range used in most human psychophysical experiments performed on these parts of the body. We conclude that sinusoidal vibration can be used reliably to stimulate the tactile system and is an appropriate stimulus for developing models of touch.

Hepatic lipase (LIPC) promoter polymorphism in men with coronary artery disease. Allele frequency and effects on hepatic lipase activity and plasma HDL-C concentrations

Hepatic lipase is an important determinant of plasma HDL concentration and LDL subclass distribution and may therefore influence susceptibility to coronary artery disease (CAD). To assess the effect of genetic variation in hepatic lipase activity on CAD susceptibility, we determined the frequency of the -514T allele of hepatic lipase in white men with CAD and in controls who did not have CAD. In men with CAD, postheparin plasma hepatic lipase activity was 15% to 20% lower in heterozygotes and 30% lower in homozygotes for the -514T allele. Allele frequencies were similar in cases and controls, however, and were consistent with Hardy-Weinberg expectation in both groups. This finding was confirmed in a second group comprising cases with premature symptomatic CAD and controls who were free of disease. These data indicate that a primary decrease in hepatic lipase activity of as much as 30% does not influence susceptibility to CAD in white men.

Contribution of cholesterol 7alpha-hydroxylase to the regulation of lipoprotein metabolism

Clinical studies have clearly established a relationship between bile acid synthesis and plasma LDL-cholesterol concentrations. Interruption of the enterohepatic circulation of bile acids leads to increased bile acid synthesis and a reduction in plasma LDL-cholesterol concentrations. New studies indicate that genetic variation in cholesterol 7alpha-hydroxylase activity accounts for a significant fraction of the inter-individual variation in plasma LDL-cholesterol concentrations in the general population, and a specific CYP7A1 allele associated with increased plasma LDL-cholesterol concentrations has been identified. Studies in which cholesterol 7alpha-hydroxylase was transiently overexpressed in hamsters and mice indicate that direct manipulation of cholesterol 7alpha-hydroxylase leads to changes in plasma LDL-cholesterol concentrations. Interestingly, targeted inactivation of the gene encoding cholesterol 7alpha-hydroxylase does not lead to increased plasma LDL-cholesterol concentrations in mice.

Hepatic lipase: new insights from genetic and metabolic studies

Hepatic lipase catalyses the hydrolysis of triglycerides and phospholipids in all major classes of lipoproteins. Genetic deficiency of this enzyme is associated with a unique plasma lipoprotein profile, characterized by hypertriglyceridemia and elevated concentrations of intermediate density lipoproteins and HDL. Recent studies have identified common polymorphisms in the hepatic lipase gene that are associated with low hepatic lipase activity and increased concentrations of large HDL. Association studies using these polymorphisms are elucidating the effects of variation in hepatic lipase activity on plasma lipoprotein concentrations and susceptibility to coronary atherosclerosis.

Testing for linkage under robust genetic models

Robust genetic models are used to assess linkage between a quantitative trait and genetic variation at a specific locus using allele-sharing data. Little is known about the relative performance of different possible significance tests under these models. Under the robust variance components model approach there are several alternatives: standard Wald and likelihood ratio tests, a quasilikelihood Wald test, and a Monte Carlo test. This paper reports on the relative performance (significance level and power) of the robust sibling pair test and the different alternatives under the robust variance components model. Simulations show that (1) for a fixed sample size of nuclear families, the variance components model approach is more powerful than the robust sibling pair approach; (2) when the number of nuclear families is at least approximately 100 and heritability at the trait locus is moderate to high (>0.20) all tests based on the variance components model are equally effective; (3) when the number of nuclear families is less than approximately 100 or heritability at the trait locus is low (<0. 20), on balance, the Monte Carlo test provides the best power and is the most valid. The different testing procedures are applied to determine which are able to detect the known association between low density lipoprotein cholesterol and the common genotypes at the locus encoding apolipoprotein E. Results from this application show that the robust sibling pair method may be more effective in practice than that indicated by simulations.

Hepatic lipase activity influences high density lipoprotein subclass distribution in normotriglyceridemic men. Genetic and pharmacological evidence

Several studies have reported an inverse relationship between hepatic lipase activity and plasma high density lipoprotein (HDL) cholesterol concentrations. The purpose of the present study was to determine whether genetic and pharmacological variation in hepatic lipase activity alters the distribution of HDL subclasses. Two independent analytical methods (nuclear magnetic resonance and gradient gel electrophoresis) were used to compare HDL subclass distributions in 11 homozygotes for the -514C allele of hepatic lipase and in 6 homozygotes for the -514T allele. Mean hepatic lipase activity was 45 +/- 15 mmol. l(-1). hr(-1) in -514C homozygotes and 20 +/- 7 mmol. l(-1). hr(-1) in -514T homozygotes. Both analytical methods indicated that HDL(2b) was significantly higher and HDL(3a) was significantly lower in -514T homozygotes than in -514C homozygotes. No differences were noted in the other HDL fractions (HDL(2a), HDL(3b), and HDL(3c)). To determine the effects of increased hepatic lipase activity, 20 men were given the synthetic anabolic steroid, stanozolol. Stanozolol treatment increased hepatic lipase activity more than two-fold (38 +/- 18 to 85 +/- 25 mmol. l(-1). hr(-1) ), and markedly reduced the plasma concentrations of the larger HDL subclasses (HDL(2b) and HDL(2a)). The plasma concentrations of the smallest HDL subclasses (HDL(3b) and HDL(3c)) were unchanged by stanozolol treatment. Taken together, these genetic and pharmacological data indicate that variation in hepatic lipase activity has highly specific effects on the distribution of HDL subclasses in the circulation.-Grundy, S. M., G. L. Vega, J. D. Otvos, D. L. Rainwater, and J. C. Cohen. Hepatic lipase activity influences high density lipoprotein subclass distribution in normotriglyceridemic men: genetic and pharmacological evidence.

Cloning and mutational analysis of human malonyl-coenzyme A decarboxylase

Malonyl coenzyme A (CoA) decarboxylase (E.C.4. 1.1.9) catalyzes the conversion of malonyl CoA to acetyl CoA. The metabolic role of malonyl CoA decarboxylase has not been fully defined, but deficiency of the enzyme has been associated with mild mental retardation, seizures, hypotonia, cardiomyopathy, vomiting, hypoglycemia, metabolic acidosis, and malonic aciduria. Here we report the isolation and sequencing of the human gene encoding malonyl CoA decarboxylase, and the identification of a mutation causing malonyl CoA decarboxylase deficiency. Human malonyl CoA decarboxylase cDNA sequences were identified by homology to the goose gene, and the intron/exon boundaries were determined by direct sequencing of a PAC clone containing the entire human gene. The 1479 basepair human cDNA is 70 percent identical to the goose sequence, and the intron/exon boundaries are completely conserved between the two species. The genetic mutation underlying malonyl CoA decarboxylase deficiency was determined in a patient with clinical features of this defect, malonic aciduria, and markedly reduced malonyl CoA decarboxylase activity.

Plasma platelet-activating factor acetylhydrolase activity is not associated with premature coronary atherosclerosis

Platelet-activating factor acetylhydrolase activity in plasma was compared between 72 subjects with angiographically normal coronary arteries and matched controls with clinically significant obstruction. No difference was seen, and we conclude that variation in plasma platelet-activating factor acetylhydrolase activity is not a risk factor for coronary artery disease.

Modification of development by the CFTR gene in utero

The in utero infection of rats at 16-17 days gestation with a recombinant adenovirus carrying the human cystic fibrosis transmembrane conductance regulator (cftr) gene resulted in altered lung development and morphology. These structural alterations prompted an evaluation of concurrent functional changes in the cftr-treated lung. CFTR protein could be detected in treated lungs for up to 30 days postinfection, although it was not detected in the intestines at this time. Increased levels of secreted glycoconjugates and lipids were found in lungs treated in utero with human cftr and large vacuoles containing glycoconjugates were detected within cells of the intestines. The scope and durability of these changes suggested that in utero cftr treatment influenced the activity of secretory cells in the developing lung. Altered secretory products in the lungs of cystic fibrosis patients are thought to be associated with increased susceptibility to Pseudomonas aeruginosa infection. We challenged 3-month-old rats (treated in utero with the human cftr gene) with a lethal, intratrachial dose of this bacteria. Rats treated with cftr exhibited enhanced resistance to Pseudomonas infection when compared to controls. These animals displayed little or no associated inflammatory response. No evidence of the adenovirus transgene was detectable at the time of P. aeruginosa inoculation, indicating that continuous ectopic expression of hcftr was not required for enhanced protection. These data demonstrate that in utero, cftr expression influenced the development and function of cells involved in the primary host defense against bacterial infection in the lung.

Three polymorphisms associated with low hepatic lipase activity are common in African Americans

We have shown previously that a hepatic lipase allele (designated -514T) is common among African Americans and contributes to low hepatic lipase activity in this population. To identify other hepatic lipase alleles associated with low hepatic lipase activity in this population, the coding region and intron-exon boundaries of the hepatic lipase gene were sequenced in 20 African American men with low hepatic lipase activity. Two polymorphisms (N193S and L334F) were associated with low post-heparin plasma hepatic lipase activity and were much more common in African Americans than in whites. This finding, together with our previous data on the -514T allele, indicates that at least three different hepatic lipase polymorphisms associated with low hepatic lipase activity are common among African Americans. Analysis of hepatic lipase haplotypes revealed that 97% of African Americans have at least one hepatic lipase allele that is associated with low hepatic lipase activity.

The -514 polymorphism in the hepatic lipase gene (LIPC) does not influence androgen-mediated stimulation of hepatic lipase activity

The -514T allele of hepatic lipase is associated with increased high density lipoprotein-cholesterol levels in men, but not in women. This observation suggests that the -514C to T polymorphism may diminish the response of hepatic lipase to androgens. To test this hypothesis, five -514T and five -514C homozygous men were treated with the anabolic steroid stanozolol for 6 days. The mean increase in hepatic lipase activity was similar in the two groups (45+/-10 vs. 51+/-10 mmol x hr(-1) x l(-1), P = 0.5). To evaluate the association between the -514 polymorphism and hepatic lipase activity at different physiological androgen concentrations, hepatic lipase genotypes and activities were measured in 44 men and 40 premenopausal women. The effect of the -514T allele on hepatic lipase activity was significant and quantitatively similar in both sexes. These data indicate that the -514 polymorphism does not influence the response of hepatic lipase activity to androgens, and that the effects of this polymorphism on hepatic lipase activity are independent of androgen action.

Molecular pathophysiology of cystic fibrosis based on the rescued knockout mouse model

Cystic fibrosis transmembrane conductance regulator (cftr) gene mutations are thought to result in cystic fibrosis due to an absence of the protein's chloride channel. Recently, the lethal intestinal blockage in the cftr knockout mouse was reversed by a single in utero dose of a recombinant adenovirus containing the human cftr gene. The rescue of these animals did not require continuous expression of the gene and the cAMP-dependent chloride channel was not permanently restored. These data suggested that cftr was required for normal development of the intestine but not for normal function of the adult organ. Phenotypic changes in the intestines and lungs of in utero cftr-treated knockout and heterozygous mice revealed that altered development was induced. The intestines of the untreated knockout mice were shown to be deficient in both intracellular calcium and UTP receptors. Both of these deficiencies were partially corrected in the rescued knockout mice, whereas treatment of heterozygous animals disrupted the normal pattern of these markers. Examination of the lungs of knockout cftr (-/-) mice with lectins showed an increase in secreted glycoconjugates containing alpha(2,6)-sialic acid and fucose as compared with control heterozygotes. The in utero-treated knockouts showed an increase in this material as well, but it was contained in intracellular vesicles. Electron microscopy of these tissues confirmed the developmental alteration of secretory cell differentiation in the lungs. These data show that cftr is required in both the lung and intestines for normal differentiation of a secretory cell population and that in its absence these cells fail to develop properly.

Body mass index and hepatic lipase gene (LIPC) polymorphism jointly influence postheparin plasma hepatic lipase activity

The -514 polymorphism in the hepatic lipase gene (LIPC) is associated with decreased hepatic lipase activity. In the present study, the interaction between body mass index (BMI), the -514 polymorphism, and hepatic lipase activity was examined in 118 white men and in 51 African American men. BMI was significantly positively correlated with hepatic lipase activity in both populations. BMI was similar in men with genetic differences in hepatic lipase activity, indicating that high hepatic lipase activity did not cause increased BMI. The data therefore suggest that high BMI leads to increased hepatic lipase activity. The actions of BMI and the -514 polymorphism on hepatic lipase activity appear to be additive and independent, rather than synergistic. This finding indicates that hepatic lipase activity is a multifactorial trait, determined in part by polymorphism within the LIPC gene as well as by factors that influence BMI.

Linkage between cholesterol 7alpha-hydroxylase and high plasma low-density lipoprotein cholesterol concentrations

Interindividual differences in plasma low-density lipoprotein cholesterol (LDL-C) levels reflect both environmental variation and genetic polymorphism, but the specific genes involved and their relative contributions to the variance in LDL-C are not known. In this study we investigated the relationship between plasma LDL-C concentrations and three genes with pivotal roles in LDL metabolism: the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and cholesterol 7alpha-hydroxylase (CYP7). Analysis of 150 nuclear families indicated statistically significant linkage between plasma LDL-C concentrations and CYP7, but not LDLR or APOB. Further sibling pair analyses using individuals with high plasma LDL-C concentrations as probands indicated that the CYP7 locus was linked to high plasma LDL-C, but not to low plasma LDL-C concentrations. This finding was replicated in an independent sample. DNA sequencing revealed two linked polymorphisms in the 5' flanking region of CYP7. The allele defined by these polymorphisms was associated with increased plasma LDL-C concentrations, both in sibling pairs and in unrelated individuals. Taken together, these findings indicate that polymorphism in CYP7 contributes to heritable variation in plasma LDL-C concentrations. Common polymorphisms in LDLR and APOB account for little of the heritable variation in plasma LDL-C concentrations in the general population.

Hepatic lipase activity is lower in African American men than in white American men: effects of 5' flanking polymorphism in the hepatic lipase gene (LIPC)

Plasma high density lipoprotein cholesterol (HDL-C) concentrations are higher in African American men than in white men, but the mechanism(s) responsible for this ethnic difference has not been elucidated. This study examined the relationship between hepatic lipase activity, plasma HDL-C concentrations, and a hepatic lipase polymorphism (-514T) in African American and white American men. Consistent with previous reports, plasma HDL-C concentrations were significantly higher in African American men than in white American men. Mean post-heparin plasma hepatic lipase activity was significantly lower in African American than in white American men (27 +/- 12 vs. 44 +/- 17 mmol x h(-1) x l(-1), P < 0.001). The -514T hepatic lipase allele was associated with low hepatic lipase activity in both populations, and was 3-fold more common among African Americans than white Americans. Taken together, these data suggest that genetic differences in hepatic lipase activity contribute to the differences in plasma HDL-C concentrations between African American men and white American men.

Determinants of plasma platelet-activating factor acetylhydrolase: heritability and relationship to plasma lipoproteins

Plasma platelet-activating factor acetylhydrolase (PAF-AH) is the enzyme that inactivates PAF (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine). We determined the relative contributions of genetic and environmental factors to variation in plasma PAF-AH activity in 240 individuals from 60 nuclear families. Regression of mean-offspring PAF-AH activity on the mid-parent value indicated that 62% of the variation in plasma PAF-AH activity was heritable. Spousal values were weakly negatively correlated, indicating that familial aggregation of PAF-AH activity is due to genetic rather than to environmental factors. Among normolipidemic individuals, plasma PAF-AH activity was strongly correlated with the plasma concentration of low density lipoprotein cholesterol (LDL-C), and treatment with lovastatin resulted in proportional decreases in plasma PAF-AH activity and LDL-C concentrations. To further elucidate the relationship between PAF-AH and plasma concentrations of LDL, plasma PAF-AH activity was measured in families with well-defined, monogenic disorders of LDL metabolism. Plasma PAF-AH activity cosegregated with plasma LDL-C concentrations in familial hypercholesterolemia, but not in familial hypobetalipoproteinemia. We speculate that the rate of removal of LDL from the circulation may determine the clearance rate of PAF-AH, thereby modulating the activity of PAF-AH in blood.

Extension of the Haseman-Elston method to multiple alleles and multiple loci: theory and practice for candidate genes

The Haseman & Elston (1972) sibling-pair regression method has been used to detect and estimate the variance contribution to observed values of a quantitative trait by allelic variation in specific candidate genes. The procedure was developed under a model with a single biallelic trait locus. This assumption does not hold for several known systems. In this paper we prove that for candidate gene analysis the Haseman-Elston procedure extends to the case of multiple trait loci, each possibly having more than two alleles. Simulation experiments comparing single-locus to two-locus models show that fitting the extended regression equations maintains nominal significance levels, but the power to detect linkage to trait variation is not improved by including additional loci. These results indicate that the original proposal is statistically robust to violations of the underlying genetic model. Practical issues associated with quantifying the relative variance contribution by individual loci are also discussed. Applications of the extended regression equations to lipoprotein(a) and high density lipoprotein cholesterol are given for illustration.

A hepatic lipase (LIPC) allele associated with high plasma concentrations of high density lipoprotein cholesterol

Genetic factors strongly influence interindividual variation in plasma high density lipoprotein cholesterol (HDL-C) levels, but the specific genetic polymorphisms that confer heritable variation in HDL-C levels have not been identified. In this study we examined the relationship between polymorphism in LIPC, the gene encoding hepatic lipase, and plasma HDL-C concentrations using a sequential approach comprising linkage analysis, DNA sequencing, and association studies. Linkage studies in 1465 American white subjects from 218 nuclear families indicated that allelic variation at, or closely linked to, the hepatic lipase gene accounts for a significant fraction ( approximately 25%) of the variation in plasma HDL-C concentrations. The hepatic lipase gene was then sequenced in selected individuals, and four novel polymorphisms were identified in the 5' flanking region of the gene. These polymorphisms were in complete linkage disequilibrium and thus identified a single novel allele. Association studies indicated that heterozygosity for the rare allele was associated with modestly increased concentrations of plasma HDL-C (41 +/- 11 vs. 37 +/- 10 mg/dl, P < 0.05) and apolipoprotein AI in men (131 +/- 23 vs. 122 +/- 21 mg/dl, P < 0.05) but not in women. Homozygosity for the rare allele was associated with markedly higher plasma HDL-C (63 +/- 3 mg/dl) and apolipoprotein AI (153 +/- 9 mg/dl) concentrations in men. The results of the association study were replicated in a second, independently ascertained sample. Taken together, the results of the linkage and association studies provide strong evidence that genetic variation in hepatic lipase activity is a major determinant of plasma HDL-C levels.

Allelic variation in the gene encoding the cholesteryl ester transfer protein is associated with variation in the plasma concentrations of cholesteryl ester transfer protein

The cholesteryl ester transfer protein (CETP) mediates the transfer of cholesteryl esters from high density lipoproteins (HDL) to triglyceride-rich lipoproteins. Mutations that abolish CETP function are associated with very high levels of HDL cholesterol, but the effect of more common allelic variation at this locus is less clear. In this study, we have measured plasma CETP concentration and plasma HDL cholesterol concentrations in 694 individuals from 106 nuclear families. Robust sibling-pair methods indicated linkage between the CETP locus and inter-individual variation in plasma CETP concentrations. Allelic variation at the CETP locus accounted for 20% of the variation in plasma CETP concentration. No relation between allelic variation at the CETP locus and plasma HDL cholesterol levels was detected. These data indicate that polymorphism in the CETP gene confers variation in plasma CETP concentration. However, this degree of variation in CETP function is not systematically associated with variation in plasma HDL-C concentrations.

Assessment of vibrotactile sensitivity in patients with carpal tunnel syndrome

The effectiveness of using vibrotactile threshold measures to aid in the diagnosis of carpal tunnel syndrome (CTS) was evaluated. Thresholds for detecting 1-, 10-, and 300-Hz vibratory stimuli were measured on the fingertips of 24 CTS patients and 20 healthy control subjects. There were no significant differences in threshold for 1- and 300-Hz between the two groups. Although there were significant differences for 10-Hz stimuli, the mean patient threshold was within 1 standard deviation of the mean threshold for the control group. These results indicate that threshold testing is not a suitable diagnostic tool for CTS. Additionally, we examined whether thresholds were elevated in the presence of pain. Seven patients reported experiences of pain and no pain sessions. No significant differences in threshold were found between the two pain conditions, indicating that the presence of pain related to CTS does not affect threshold.

Evolving therapies for peptic ulcer disease: Helicobacter pylori treatment

In the era of Helicobacter pylori, our concepts about peptic ulcer disease have undergone a major paradigm shift. New ways of thinking about the etiology of ulcers are leading to new treatment modalities. Treating peptic ulcers with antibiotics is an idea that would have been laughed at a mere decade ago, yet it has become the standard of care for H. pylori-associated disease. Our current state of knowledge, and where we seem to be heading, is the subject of this review.

Safety, immunogenicity, and efficacy of a recombinantly produced Plasmodium falciparum circumsporozoite protein-hepatitis B surface antigen subunit vaccine

Twenty malaria-naive volunteers received a recombinant Plasmodium falciparum malaria vaccine (RTS,S) containing 19 NANP repeats and the carboxy terminus (amino acids 210-398) of the circumsporozoite (CS) antigen coexpressed in yeast with hepatitis B surface antigen. Ten received vaccine adjuvanted with alum, and 10 received vaccine adjuvanted with alum plus 3-deacylated monophosphoryl lipid A (MPL). Both formulations were well tolerated and immunogenic. MPL enhanced CS antibody levels (measured by ELISA, immunofluorescence, and inhibition of sporozoite invasion assays). After sporozoite challenge, 6 of 6 in the alum group and 6 of 8 in the alum-MPL group developed patent malaria. Protected subjects had higher levels of CS antibody titers on day of challenge than did nonprotected subjects. After immunization, 1 protected subject had increased cytotoxic T lymphocyte activity against CS and recall of memory T cell responses to RTS,S and selected CS.

Variation at the hepatic lipase and apolipoprotein AI/CIII/AIV loci is a major cause of genetically determined variation in plasma HDL cholesterol levels

Genetic factors have been shown to play an important role in determining interindividual variation in plasma HDL-C levels, but the specific genetic determinants of HDL cholesterol (HDL-C) levels have not been elucidated. In this study, the effects of variation in the genomic regions encoding hepatic lipase, apolipoprotein AI/CIII/AIV, and the cholesteryl ester transfer protein on plasma HDL-C levels were examined in 73 normotriglyceridemic, Caucasian nuclear families. Genetic factors accounted for 56.5 +/- 13% of the interindividual variation in plasma HDL-C levels. For each candidate gene, adjusted plasma HDL-C levels of sibling pairs who shared zero, one, or two parental alleles identical-by-descent were compared using sibling-pair linkage analysis. Allelic variation in the genes encoding hepatic lipase and apolipoprotein AI/CIII/AIV accounted for 25 and 22%, respectively, of the total interindividual variation in plasma HDL-C levels. In contrast, none of the variation in plasma HDL-C levels could be accounted for by allelic variation in the cholesteryl ester transfer protein. These findings indicate that a major fraction of the genetically determined variation in plasma HDL-C levels is conferred by allelic variation at the hepatic lipase and the apolipoprotein AI/CIII/AIV gene loci.

Genetic analysis of a polymorphism in the human apolipoprotein A-I gene promoter: effect on plasma HDL-cholesterol levels

Previous studies have indicated that a G to A substitution at position -76 in the gene encoding apolipoprotein A-I (apoA-I) confers increased plasma high density lipoprotein cholesterol (HDL-C). Increased HDL-C may be a direct consequence of the A allele, or may reflect the action of a locus in linkage disequilibrium with the A allele. To elucidate this question, we examined the effect of this polymorphism in a large sample (n = 409) of unrelated Caucasians and their nuclear families (n = 22). To eliminate the confounding effects of hypertriglyceridemia, individuals with triglyceride levels greater than 150 mg/dl were excluded from the study. ApoA-I genotype was determined by polymerase chain reaction (PCR) amplification of genomic DNA and restriction digestion with Msp I. Individuals were grouped by genotype (GG, GA or AA) and mean adjusted HDL levels of the three groups were compared by one-way analysis of variance. Our analysis indicates that HDL-C levels do not vary by genotype, and no gene dosage effect is apparent in men or in women. Analysis of 22 informative Caucasian nuclear families showed no significant difference between individuals with the A allele and their GG siblings. These data suggest that polymorphism at -76 in the apoA-I gene does not directly affect HDL levels. Therefore, the increased HDL-C levels reported in other populations must reflect linkage disequilibrium between the A allele and a putative HDL-raising allele. As we find no evidence for association between the A allele and high HDL levels, this putative allele must occur at a low frequency in the population sampled in this study.

Comparative analysis of the apo(a) gene, apo(a) glycoprotein, and plasma concentrations of Lp(a) in three ethnic groups. Evidence for no common "null" allele at the apo(a) locus

Distributions of plasma lipoprotein(a) (Lp[a]) concentrations exhibit marked interracial differences. Apolipoprotein(a) (apo[a]), the unique constituent of Lp(a), is highly polymorphic in length due to allelic variations in the number of kringle 4(K-4)-encoding sequences. Plasma Lp(a) concentrations are inversely related to the number of K-4 repeats in the apo(a) alleles. To determine the contribution of this length variation to the interracial variation in plasma Lp(a) levels, we compared apo(a) allele size, glycoprotein size, and plasma Lp(a) concentrations in Caucasians, Chinese, and African Americans. Caucasians and African Americans had very different distributions of plasma Lp(a) concentrations yet there was no significant difference in the overall frequency distributions of their apo(a) alleles. Over the entire size spectrum of apo(a) alleles, the plasma Lp(a) levels were higher in African Americans than in Caucasians. Conversely, Caucasians and Chinese had similar plasma Lp(a) concentrations but significantly different apo(a) allele size distributions. Therefore, interracial differences in the plasma concentrations of Lp(a) are not due to differences in the frequency distributions of apo(a) alleles. We also examined the relationship between apo(a) allele size and the presence of detectable plasma apo(a) protein in plasma. Apo(a) alleles associated with no detectable plasma protein were not of uniformly large size, as had been expected, but were distributed over the entire size spectrum. From this analysis, we conclude that there is no common "null" allele at the apo(a) locus.