Rapid determination of apolipoprotein E phenotypes from whole plasma by automated isoelectric focusing using PhastSystem and immunofixation

Arrayed isoelectric focusing using photopatterned multi-domain hydrogels

Isoelectric focusing (IEF) is a powerful separation method, useful for resolving subtle changes in the isoelectric point of unlabeled proteins. While microfluidic IEF has reduced the separation times from hours in traditional benchtop IEF to minutes, the enclosed devices hinder post-separation access to the sample for downstream analysis. The two-layer open IEF device presented here comprises a photopatterned hydrogel lid layer containing the chemistries required for IEF and a thin polyacrylamide bottom layer in which the analytes are separated. The open IEF device produces comparable minimum resolvable difference in isoelectric point and gradient stability to enclosed microfluidic devices while providing post-separation sample access by simple removal of the lid layer. Further, using simulations, we determine that the material properties and the length of the separation lanes are the primary factors that affect the electric field magnitude in the separation region. Finally, we demonstrate self-indexed photomasks for alignment-free fabrication of multi-domain hydrogels. We leverage this approach to generate arrayed pH gradients with a total of 80 concurrent separation lanes, which to our knowledge is the first demonstration of multiple IEF separations in series addressed by a single pair of electrodes.

Update on the laboratory investigation of dyslipidemias

The role of the clinical laboratory is evolving to provide more information to clinicians to assess cardiovascular disease (CVD) risk and target therapy more effectively. Current routine methods to measure LDL-cholesterol (LDL-C), the Friedewald calculation, ultracentrifugation, electrophoresis and homogeneous direct methods have established limitations. Studies suggest that LDL and HDL size or particle concentration are alternative methods to predict future CVD risk. At this time there is no consensus role for lipoprotein particle or subclasses in CVD risk assessment. LDL and HDL particle concentration are measured by several methods, namely gradient gel electrophoresis, ultracentrifugation-vertical auto profile, nuclear magnetic resonance and ion mobility. It has been suggested that HDL functional assays may be better predictors of CVD risk. To assess the issue of lipoprotein subclasses/particles and HDL function as potential CVD risk markers robust, simple, validated analytical methods are required. In patients with small dense LDL particles, even a perfect measure of LDL-C will not reflect LDL particle concentration. Non-HDL-C is an alternative measurement and includes VLDL and CM remnant cholesterol and LDL-C. However, apolipoprotein B measurement may more accurately reflect LDL particle numbers. Non-fasting lipid measurements have many practical advantages. Defining thresholds for treatment with new measurements of CVD risk remain a challenge. In families with genetic variants, ApoCIII and lipoprotein (a) may be additional risk factors. Recognition of familial causes of dyslipidemias and diagnosis in childhood will result in early treatment. This review discusses the limitations in current laboratory technologies to predict CVD risk and reviews the evidence for emergent approaches using newer biomarkers in clinical practice.

Apolipoprotein E genotyping using PCR-GoldMag lateral flow assay and its clinical applications

A polymerase chain reaction-gold magnetic nanoparticles lateral flow assay (PCR-GoldMag LFA) has been developed via integrating multiplex amplification refractory mutation system PCR (multi-ARMS-PCR) with GoldMag-based LFA for the visual detection of single-nucleotide polymorphisms (SNPs). This assay was applied to genotype Apolipoprotein E (ApoE). ApoE genotyping is important due to the predictive value for the development of coronary artery disease and Alzheimer's disease. The method requires two steps: i) Simultaneous amplifications of the two polymorphic codons (ApoE 158 and 112), performed in separated reactions using multi-ARMS-PCR; and ii) detection of the wild-type and mutant PCR products via dual immunoreactions, which can be performed in ~5 min. Within two LFAs, anti-digoxin antibody-conjugated GoldMag probes bind digoxin-labeled wild-type PCR products, and anti-fluorescein isothiocyanate (FITC) antibody-conjugated GoldMag probes bind FITC-labeled mutant PCR products. All PCR products are biotin labeled and are detected by streptavidin-coated regions on the LFA strip, resulting in a red color. The current approach is capable of detecting the SNPs of ApoE in ~1.5 h, with a broad detection range from 10–1,000 ng of genomic DNA. Thus, the present protocol may facilitate simple, fast and cost-effective screening for important SNPs, as demonstrated by the evaluation of the prevalence of ApoE variants in a Han Chinese cohort.

Pharmacogenetic aspects in familial hypercholesterolemia with the special focus on FHMarburg (FH p.W556R)

Objective

Familial hypercholesterolemia (FH) is an autosomal dominant inherited disorder caused by mutations in the low density lipoprotein receptor (LDLR) gene. FH is characterized by elevated plasma LDL cholesterol, premature atherosclerosis, and a high risk of premature myocardial infarction. In general, mutations within LDLR gene can cause five different classes of defects, namely: class I defect: no LDLR synthesis; class II defect: no LDLR transport; class III defect: no low density lipoprotein (LDL) to LDLR binding; class IV defect: no LDLR/LDL internalization; and class V defect: no LDLR recycling. One might expect that both the class of LDLR defect as well as the precise mutation influences the severity of hypercholesterolemia on one hand and the response on drug treatment on the other. To clarify this question we studied the effect of the LDLR mutation p.W556R in two heterozygote subjects.

Results

We found that two heterozygote FH patients with the LDLR mutation p.W556R causing a class II LDLR defect (transport defective LDLR) respond exceedingly well to the treatment with simvastatin 40 mg/ezetimibe 10 mg. There was a LDL cholesterol decrease of 55 and 64%, respectively. In contrast, two affected homozygote p.W556R FH patients, in the mean time undergoing LDL apheresis, had no response to statin but a 15% LDL cholesterol decrease on ezetimibe monotherapy.

Conclusions

The LDLR mutation p.W556R is a frequent and severe class II defect for FH. The affected homozygote FH patients have a total loss of the functional LDLR and—as expected—do not respond on statin therapy and require LDL apheresis. In contrast, heterozygote FH patients with the same LDLR defect respond exceedingly well to standard lipid-lowering therapy, illustrating that the knowledge of the primary LDLR defect enables us to foresee the expected drug effects.

Apolipoproteins: metabolic role and clinical biochemistry applications

Lipoprotein metabolism is dependent on apolipoproteins, multifunctional proteins that serve as templates for the assembly of lipoprotein particles, maintain their structure and direct their metabolism through binding to membrane receptors and regulation of enzyme activity. The three principal functions of lipoproteins are contribution to interorgan fuel (triglyceride) distribution (by means of the fuel transport pathway), to the maintenance of the extracellular cholesterol pool (by means of the overflow pathway) and reverse cholesterol transport. The most important clinical application of apolipoprotein measurements in the plasma is in the assessment of cardiovascular risk. Concentrations of apolipoprotein B and apolipoprotein AI (and their ratio) seem to be better markers of cardiovascular risk than conventional markers such as total cholesterol and LDL-cholesterol. Apolipoprotein measurements are also better standardized than the conventional tests. We suggest that measurements of apolipoprotein AI and apolipoprotein B are included as a part of the specialist lipid profile. We also suggest that lipoprotein (a) should be measured as part of the initial assessment of dyslipidaemias because of its consistent association with cardiovascular risk. Genotyping of apolipoprotein E isoforms remains useful in the investigation of mixed dyslipidaemias. Lastly, the role of postprandial metabolism is increasingly recognized in the context of atherogenesis, obesity and diabetes. This requires better markers of chylomicrons, very-low-density lipoproteins and remnant particles. Measurements of apolipoprotein B48 and remnant lipoprotein cholesterol are currently the key tests in this emerging field.

Genetics and kinetics of familial hypercholesterolemia, with the special focus on FH-(Marburg) p.W556R

OBJECTIVE

Familial hypercholesterolemia (FH) is an autosomal dominant inherited disorder, caused by mutations in the low density lipoprotein receptor (LDLR) gene. FH is characterized by elevated plasma LDL cholesterol, premature atherosclerosis and high risk of premature myocardial infarction. Extended work has been done to understand both, the primary genetic defect as well as the in vivo kinetic consequences of this disease. Both approaches, genetics and kinetics, are challenging but also fruitful approaches for a better understanding of this devastating disease. For this we reviewed the recent literature and used our in vitro and in vivo data on one of the most frequently occurring types of FH, the FH(Marburg) p.W556R.

METHODS

To identify the primary genetic defect of the FH(Marburg) we used denaturing gradient gel electrophoresis (DGGE) mutation analysis. In vivo kinetic studies were performed in a heterozygote FH(Marburg) subject and in 5 healthy control subjects utilizing a stable isotope tracer kinetic approach with 3D-leucine.

RESULTS

DGGE screening of the LDLR gene identified a tryptophan (W) to arginine (R) substitution at residue 556 (p.W556R) in the fifth conserved YWTD repeat of the LDLR-beta-propeller in FH(Marburg). In vivo kinetic studies in a heterozygote FH subject for FH(Marburg) and in 5 healthy control subjects demonstrated a severe decrease in LDL FCR and a mild increase of LDL PR in FH compared to healthy controls.

CONCLUSIONS

The LDLR mutation p.W556R is a frequent and severe defect for FH. This defect has a major influence on the in vivo lipoprotein kinetics and lipid levels. In a heterozygote FH patient we found a dual defect for the increase in LDL cholesterol, namely a decrease in the fractional catabolic rate (FCR) of LDL but also an increase in LDL production rate (PR). By this a well defined, single genetic defect may have a series of different in vivo metabolic consequences which could be used for potential therapeutic approaches to this disease.

Rapid and direct detection of apolipoprotein E genotypes using whole blood from humans

Polymerase chain reaction (PCR) is a powerful molecular biological tool in the field of toxicity testing and diagnostics. The use of PCR for large-scale genetic testing requires an effective method of sample processing. Unfortunately, isolation of PCR-quality DNA is time-consuming. PCR performed directly on whole blood is preferred because of time efficiency, cost of the procedure, and possible automation for large-scale toxicity evaluation and diagnosis. The apolipoprotein E (APOE) gene contains two single-nucleotide polymorphisms (SNP) located at codons 112 and 158, producing three APOE protein isoforms known to be associated with the risks of developing cardiovascular disease and susceptibility to Alzheimer's disease. In the present study, an attempt was made to use the AnyDirect solution for APOE genotyping by PCR using whole blood directly without DNA purification. Results for two PCR methods, (1) conventional PCR using purified DNA and conventional buffer and (2) direct PCR using whole blood and AnyDirect solution, were compared in four different PCR-based APOE genotyping methods including PCR restriction-fragment-length polymorphism (PCR-RFLP), allele-specific PCR, SNaPshot mini-sequencing, and multiplex tetra-primer amplification refractory mutation system (T-ARMS) PCR. There was complete concordance in the APOE genotypes between conventional PCR and direct PCR, in all four different PCR-based APOE genotyping methods. Data demonstrated that the four different PCR-based APOE genotyping methods are able to determine the APOE genotypes successfully using whole blood directly with the use of AnyDirect solution. The direct multiplex T-ARMS PCR using whole blood may be the most rapid, simple, and inexpensive method for detecting APOE genotypes among four different APOE genotyping methods.

Simple and effective determination of apolipoprotein E genotypes by positive/negative polymerase chain reaction products

Several protein and DNA-based methods have been previously described for the identification of apolipoprotein E isoforms or genotypes. However, all of them generate frequently false-positive results. The purpose of this study was to set up a new, simple, and effective method for the analysis of the apoE polymorphism. A total of 1,253 subjects previously examined for the apolipoprotein E polymorphism by restriction fragment length polymorphism were reanalyzed by our new method based on Taq DNA polymerase's inability to correctly initiate the replication in the presence of a mismatch at the 3' end of the primer. We conceived a combination of 4 specific primers in 3 different pairs sharing the same stringent polymerase chain reaction conditions to directly detect the presence/absence of polymerase chain reaction products, and thus reveal the 6 apolipoprotein E genotypes. We confirm our previous results in 1,171 subjects, whereas in 82 subjects out of 1,253 (about 6%), the results have been reinterpreted. The final analysis revealed a total of 12 homozygotic subjects for the e2 allele (1.0%), 874 homozygotes for the e3 allele (69.8 %), and 8 homozygotes for the e4 allele (0.6 %). The frequence of heterozygotes was 8.7% for the e2/e3 genotype (n=109), 1.4% for the e2/e4 genotype (n=17), and 0.6% for the e3/e4 genotype (n=8). Relative allele frequencies were e2=0.060, e3=0.834, and e4=0.106. We describe a new, simple, unequivocal, and nonexpensive method for the identification of the 6 apoE genotypes.

Apolipoprotein E genotyping in the Malay, Chinese and Indian ethnic groups in Malaysia-a study on the distribution of the different apoE alleles and genotypes

BACKGROUND

Apolipoprotein E (apoE) is encoded by a polymorphic gene located on chromosome 19. The three common apoE alleles are epsilon2, epsilon3 and epsilon4. We studied the frequencies of the apoE alleles and genotypes in the three ethnic groups-Malay, Chinese and Indian-in Malaysia using DNA amplification followed by agarose gel electrophoresis.

METHODS

EDTA blood was collected and DNA was extracted using proteinase K-SDS digestion and purified by phenol-chloroform extraction. The apoE gene sequence was amplified using the PCR and apoE genotyping was performed by restriction enzyme digestion with HhaI.

RESULTS

Genotyping of the apoE gene produces six genotypes-E2/E2, E2/E3, E3/E3, E2/E4, E3/E4 and E4/E4. The most common apoE genotype in the Malays, Chinese and Indians studied was E3/E3, thus the most common apoE allele was epsilon3. The three common apoE genotypes were E3/E3 followed by E3/E4 and E2/E3, except in the Indians where E2/E3 was not detected. The three apoE alleles were confirmed in the Malays, Chinese and Indians except for the epsilon2 allele which was absent in the Indians.

CONCLUSION

The combined frequency of the apoE alleles in the Malays, Chinese and Indians was 0.058, 0.829 and 0.114 for epsilon2, epsilon3 and epsilon4, respectively.

Apolipoprotein E polymorphism in patients with neuropsychiatric SLE

The aim of this study was to investigate a relationship between neuropsychiatric SLE (NPSLE), characterized by many different neurological and psychiatric disorders, and the polymorphism of apoE as a neurobiologically important molecule conferring increased risk and a worse prognosis of a variety of CNS diseases. One hundred and forty-six SLE patients and 93 healthy controls were studied. Out of the SLE cohort, 48 patients (32.8%) were diagnosed with NPSLE and further classified according to criteria of onset, extent, relapsing tendency and type of neuropsychiatric impairment. Apolipoprotein E (apoE) polymorphism was determined by PCR-RFLP and confirmed by isoelectrofocusing. The frequency of the epsilon4 allele was significantly higher in the NPSLE group than in the non-NPSLE group (17.7% vs. 3.1%, chi(2)=19.05, p<0.0001). Distribution of apoE genotypes was significantly different between NPSLE and non-NPSLE groups (chi(2)=80.95, p<0.0001). Both epsilon4 allele frequency (17.7% vs 8.6%, chi(2)=5.082, p<0.024) and genotype distribution (chi(2)=7.202, p<0.027) were significantly different between NPSLE group and the controls. The allele epsilon4 was also associated with earlier disease onset (Fisher's test, p<0.036) and peripheral nervous system involvement (chi(2)=8.242, p<0.0041), but not with relapse frequency ( p<0.37) or major/minor subtype of the disease ( p<0.90). The epsilon4 allele carriers did not develop significantly more neuropsychiatric syndromes than non- carriers (1.75+/-0.23 sy (mean +/- SD) in epsilon4 vs 1.85+/-0.19 sy (mean +/- SD) in non-epsilon4 carriers, Mann-Whitney test, p<0.78). In conclusion, the data suggest an association between apoE polymorphism and NPSLE.

Critical Role of Preconceptional Immunization for Protective and Nonpathological Specific Immunity in Murine Neonates

Expression of Th2 immunity against environmental Ags is the hallmark of the allergic phenotype and contrasts with the Th1-like pattern, which is stably expressed in healthy adults throughout life. Epidemiological studies indicate that the prenatal environment plays an important and decisive role in the development of allergy later in life. Since the underlying mechanisms were unclear, an animal model was developed to study the impact of maternal allergy on the development of an allergic immune response in early life. An allergic Th2 response was induced in pregnant mice by sensitization and aerosol allergen exposure. Both, IgG1 and IgG2a, but not IgE, Abs cross the placental barrier. Free allergen also crosses the placental area and was detected in serum and amniotic fluids of neonatal F(1) mice. These F(1) mice demonstrated a suppressed Th1 response, as reflected by lowered frequencies and reduced levels of IFN-gamma production. Development of an IgE response against the same allergen was completely prevented early in life. This effect was mediated by diaplacental transfer of allergen-specific IgG1 Abs. In contrast, allergic sensitization against a different allergen early in life was accelerated in these mice. This effect was mediated by maternal CD4 and OVA-specific Th2 cells induced by allergic sensitization during pregnancy. These data indicate a critical role for maternal T and B cell response in shaping pre- and postnatal maturation of specific immunity to allergens.

Detection of apolipoprotein E phenotype in unconcentrated cerebrospinal fluid

We developed a simple method to detect apolipoprotein E (Apo E) polymorphism distribution in approximately 20 microL of unconcentrated cerebrospinal fluid (CSF). A combination of isoelectric focusing in 3 M urea gel and immunoblotting was employed. Apo E phenotypes were identified in CSF samples from 45 patients with probable Alzheimer disease (AD), 15 with multiple sclerosis (MS), and 25 with other neurological diseases (OND). When the data were compared with a set of matched plasma samples, the results were identical. The method is useful for Apo E phenotyping from fresh or frozen unconcentrated CSF, when blood or plasma is not available.

Apolipoprotein E polymorphism: automated determination of apolipoprotein E2, E3, and E4 isoforms

Apolipoprotein E (apo E) plays an essential role in lipoprotein metabolism, where it is involved in the clearance of chylomicrons and very low density lipoproteins. Apart from some rare variants, apo E exists in three common isoforms (E2, E3, and E4). The different isoforms have not only been associated with different plasma lipid levels but have also been correlated with certain pathological conditions, such as lipid disorders (dysbetalipoproteinemia, hypercholesterolemia), cardiovascular diseases, and Alzheimer's disease. Here we describe a rapid, automated test for the determination of the most frequent polymorphisms (E2, E3, and E4). This polymerase chain reaction-based test allows the reliable discrimination of all six genotypes. The assay has been developed especially for the nonspecialized routine clinical laboratory by employing an analyzer and chemistry often present in this type of laboratory. Because of its low costs and easy handling, the assay can be performed on a daily basis.

Semi-automated rapid isoelectric focusing of apolipoproteins C from human plasma using Phastsystem and immunofixation

Apolipoproteins (apo) C-I, C-II, and C-III play crucial roles in intravascular lipid metabolism. Whereas apo C-II is an obligate cofactor for lipoprotein lipase, apo C-III was shown to inhibit its action. Apo C-I can be a potent cofactor of human lecithin:cholesterol acyltransferase. Structural mutants and deficiencies of apo C-II lead to hypertriglyceridemia. A similar phenotype is associated with apo C-III mutants and is inducible by overexpression of human apo C-III in transgenic animals. No structural variant has so far been reported for apo C-I. The present paper describes a rapid semi-automated procedure for isoelectric focusing analysis of these C-apolipoproteins from whole plasma or serum and their visualization by immunofixation and silver staining. The procedure allows detection of charged variants of C-apolipoproteins. As applied to 295 patients with coronary heart disease and 85 controls, it also serves to detect deficiency syndromes of these apolipoproteins. The procedure provides reliable, easy and quick analysis of C-apolipoproteins applicable as a routine or screening procedure not restricted to specialized laboratories.

Apo E structure determines VLDL clearance and atherosclerosis risk in mice

We have generated mice expressing the human apo E4 isoform in place of the endogenous murine apo E protein and have compared them with mice expressing the human apo E3 isoform. Plasma lipid and apolipoprotein levels in the mice expressing only the apo E4 isoform (4/4) did not differ significantly from those in mice with the apo E3 isoform (3/3) on chow and were equally elevated in response to increased lipid and cholesterol in their diet. However, on all diets tested, the 4/4 mice had approximately twice the amount of cholesterol, apo E, and apo B-48 in their VLDL as did 3/3 mice. The 4/4 VLDL competed with human LDL for binding to the human LDL receptor slightly better than 3/3 VLDL, but the VLDL clearance rate in 4/4 mice was half that in 3/3 mice. On an atherogenic diet, there was a trend toward greater atherosclerotic plaque size in 4/4 mice compared with 3/3 mice. These data, together with our earlier observations in wild-type and human APOE*2-replacement mice, demonstrate a direct and highly significant correlation between VLDL clearance rate and mean atherosclerotic plaque size. Therefore, differences solely in apo E protein structure are sufficient to cause alterations in VLDL residence time and atherosclerosis risk in mice.

[Laboratory diagnosis in preventive cardiology]

In recent years a large number of coronary artery disease risk factors were discovered. The knowledge of these factors improves the estimate of the coronary artery disease (CAD) risk--however it still remains to be only an "estimate". A perfect prediction of an upcoming CAD event is not possible, despite all high score laboratory technology. Therefore the use of specialized laboratory procedures should be applied carefully. Knowing the blood levels of cholesterol, triglycerides, HDL- and LDL-cholesterol and Lp(a) can be sufficient for many therapeutical decisions. Severe dyslipidemia, familial CAD and CAD without any obvious reasons demand a more specialized work-up, however, risk stratification factors such as family history, clinical history (CAD, hypertension, diabetes mellitus, smoker) and genetics are crucial, apart from the above mentioned laboratory values. Purely on the basis of the lipidologic baseline concentrations we can't give well based recommendations for the treatment of individual patients. Currently there are expert systems available which allow a risk estimate once important laboratory values (LDL cholesterol, HDL cholesterol, Triglycerides) as well as clinical data (blood pressure, family history, clinical history) are available. This system can be accessed by internet under "http:/(/)www.chd-taskforce.com".

Isoforms of murine and human serum amyloid P component

Isoelectric focusing (IEF) and immunofixation of murine serum amyloid P component (SAP), purified and in serum, showed a distinct and strain-dependent isoform pattern with up to seven bands (pI 5.1-5.7). Neuraminidase treatment caused a shift of the isoforms to more basic pI values, but did not affect their number. When the acute-phase response was analysed in three mouse strains, CBA/J and C3H/HeN initially showed seven SAP isoforms in serum and C57BL/6 J three or four. The responses in all three strains peaked at day 2 and were normalized within 14 days. On days 2 and 4, CBA/J and C3H/HeN mice showed one more acidic isoform and an increase in the concentration of the most basic isoform. C57BL/6 J mice exhibited two to three new isoforms during the acute-phase response. This appears to be the first demonstration of the physiological existence of SAP isoforms. In contrast, demonstration of isoforms of human SAP required the presence of urea and higher SAP concentrations. TEF and immunofixation of SAP monomers showed five to eight isoforms, ranging from pI 4.7-5.7. IEF of SAP in human serum resulted in a less distinct pattern and more acidic isoforms. As with murine SAP, neuraminidase treatment caused a shift of the isoforms, but no reduction in isoform number. Two-dimensional gel electrophoresis confirmed the existence of multiple isoforms of human SAP monomers.

Expression and conservation of apolipoprotein AIV in an avian species

In birds, intestinally derived lipoproteins are thought to be secreted directly into the portal vein rather than to enter the circulation via the lymphatic system as in mammals. Hepatic clearance of these so-called portomicrons must be rapid, but the protein(s) mediating their catabolism, presumably analogues of the 36-kDa mammalian apolipoprotein E, have not been identified. In searching for such a mediator(s), we have isolated a hitherto unknown 38-kDa protein from chicken serum, which we identified by microsequencing and molecular cloning as a counterpart to mammalian apolipoprotein AIV (apoAIV). Mature chicken apoAIV consists of 347 amino acids, lacks cysteine residues, and displays 57% sequence identity with human apoAIV and, to a significantly lesser extent, with apoAIVs of rodents. This first nonmammalian apoAIV characterized is the smallest homologue reported so far, because of the lack of repeated motifs at the carboxyl terminus with the consensus sequence Glu-Gln-Glu/Ala-Gln, a hallmark of mammalian apoAIVs. Chicken apoAIV (isoelectric point, 4.65) is also considerably more acidic than its human counterpart. Agarose gel electrophoresis revealed that unlike human apoAIV, which migrates to a pre-alpha-position, chicken apoAIV shows fast alpha migration. Functional characterization demonstrated that the avian protein is able to activate the enzyme lecithin:cholesterol acyltransferase. Roosters and hens express apoAIV predominantly in the gut, one-fifth as much in the liver, and no other sites of expression are identifiable by Northern blot analysis. Although pronounced intestinal synthesis is common to apoAIVs, the features of the avian protein support the notion that it represents a prototype of an apoprotein that evolved to acquire possibly distinct functions in mammals and birds.

Increased serum concentration of carbohydrate-deficient transferrin in patients with combined pancreas and kidney transplantation

Serum concentration of carbohydrate-deficient transferrin (cCDT) is used for laboratory diagnosis and follow-up of chronic alcohol abuse. In analyzing by CDTect-RIA (Pharmacia) sera from outpatients with combined pancreas and kidney transplantation and no excessive alcohol consumption, we found above-normal values for cCDT and CDT/transferrin ratios (CDT/Tf) in more than half of the samples. Isoelectric focusing of these samples showed distinct bands of carbohydrate-deficient isotransferrins, supporting the abnormal findings from the CDTect assay. In contrast, diabetics and outpatients who had received only kidney transplants showed normal values for cCDT, CDT/Tf, and isotransferrin patterns. Increased serum Tf, sialidase-producing microorganisms, and immunosuppressive medication were eliminated as causes of these abnormal cCDT and CDT/Tf results. Successful pancreas transplantation leads to hyperinsulinemia and normoglycemia, in contrast to hypoinsulinemia and hyperglycemia in the patients who receive kidney transplants alone. These factors may have pathogenic importance for CDT increase, yielding results falsely interpreted as positive with respect to alcohol abuse in patients with combined pancreas and kidney transplantation.

Clinical chemistry of common apolipoprotein E isoforms

Apolipoprotein E plays a central role in clearance of lipoprotein remnants by serving as a ligand for low-density lipoprotein and apolipoprotein E receptors. Three common alleles (apolipoprotein E(2), E(3) and E(4)) give rise to six phenotypes. Apolipoprotein E(3) is the ancestral form. Common apolipoprotein E isoforms derive from nucleotide substitutions in codons 112 and 158. Resulting cysteine-arginine substitutions cause differences in: affinities for low-density lipoprotein and apolipoprotein E receptors, low-density lipoprotein receptor activities, distribution of apolipoprotein E among lipoproteins, low-density lipoprotein formation rate, and cholesterol absorption. Accompanying changes in triglycerides, cholesterol and low-density lipoprotein may promote atherosclerosis development. Over 90% of patients with familial dysbetalipoproteinaemia have apolipoprotein E(2)/E(2). Apolipoprotein E(4) may promote atherosclerosis by its low-density lipoprotein raising effect. Establishment of apolipoprotein E isoforms may be important for patients with diabetes mellitus and several non-atherosclerotic diseases. Apolipoprotein E phenotyping exploits differences in isoelectric points. Isoelectric focusing uses gels that contain pH 4-7 ampholytes and urea. Serum is directly applied, or prepurified by delipidation, lipoprotein precipitation or dialysation. Isoelectric focusing is followed by immunofixation/protein staining. Another approach is electro- or diffusion blotting, followed by protein staining or immunological detection with anti-apolipoprotein E antibodies and an enzyme-conjugated second antibody. Apolipoprotein E genotyping demonstrates underlying point mutations. Analyses of polymerase chain reaction products are done by allele-specific oligonucleotide probes, restriction fragment length polymorphism, single-stranded conformational polymorphism, the primer-guided nucleotide incorporation assay, or denaturating gradient gel electrophoresis. Detection with primers that either or not initiate amplification is performed with the amplification refractory mutation system. Disparities between phenotyping and genotyping may derive from isoelectric focusing methods that do not adequately separate apolipoprotein E posttranslational variants, storage artifacts or faint isoelectric focusing bands.