DETERMINANTS OF THE KINETICS OF VERY LOW-DENSITY LIPOPROTEIN APOLIPOPROTEIN B-100 IN NON-OBESE MEN

1. Apolipoprotein B-100 (ApoB) is the principal structural and functional protein of the pro-atherogenic lipoproteins. Elevated plasma apoB is an independent risk factor for coronary artery disease. In the present study we aimed to assess the factors that determine the kinetics of apoB in the very low-density lipoprotein (VLDL) in healthy men. 2. We studied 17 non-obese men who were consuming an ad libitum diet and had the following characteristics: mean (± SD) age 45.5 ± 9.7 years, body mass index (BMI) 25.1 ± 1.4 kg/m², waist: hip ratio 0.91 ± 0.04, serum cholesterol 5.2 ± 0.6 mmol/L, triglycerides 1.08 ± 0.53 mmol/L and high-density lipoprotein-cholesterol 1.24 ± 0.31 mmol/L. Daily dietary intake was as follows: total fat 76 ± 26 g, carbohydrate 238 ± 67 g, protein 103 ± 33 g and alcohol 20 ± 16 g. 3. The kinetics of VLDL ApoB were studied using a primed, constant infusion (1 mg/kg per h) of l-[¹³C]-leucine over 8 h with measurement of isotopic enrichment of ApoB using gas chroma-tography/mass spectrometry. The fractional turnover rate of VLDL ApoB was estimated using a monoexponential function. The mean (± SD) absolute hepatic secretion rate (ASR) of ApoB was 8.5 ± 4.6 mg/kg per day and the fractional catabolic rate (FCR) was 7.9 ± 5.6 pools/day. The ASR was significantly correlated with the waist: hip ratio (r= 0.60; P= 0.04), but not with age, BMI, weight or nutrient intake. The FCR was significantly and inversely correlated with plasma triglycerides (r =—0.53; P= 0.03) and alcohol intake (r = -0.48; P= 0.05). 4. In conclusion, the hepatic secretion of VLDL ApoB in non-obese, healthy men is primarily determined by the waist: hip ratio, a measure of visceral fat. This is consistent with the hypothesis that the rate of lipid substrate supply to the liver regulates the output of ApoB. The fractional catabolism of VLDL ApoB may, however, be inversely related to alcohol intake and appears to determine the plasma concentration of triglycerides.     

Production of both IFN-gamma and IL-5 by Onchocerca volvulus S1 antigen- specific CD4+ T cells from putatively immune individuals

Protective immunity to the parasitic nematode Onchocerca volvulus (Ov) appears to be directed against molecules of invading L3 larvae. In this study, the cellular immune reaction to such an Ov L3 protein (S1) which is protective in an animal model was analyzed using peripheral blood mononuclear cells (PBMC) of individuals from a hyperendemic area in West Africa who were exposed to Ov but remained free from disease ('putatively immune individuals'). Despite seronegativity of these individuals against S1, proliferation of PBMC was inducible, allowing generation of an S1-specific T cell line which produced IFN-gamma upon stimulation with both Ov lysate and S1. However, S1 induced significantly more IL-5 than Ov lysate. S1-specific, DQ6 (DQA1*0103/DQB1*0603)-restricted T cell clones were generated which reacted against synthetic peptides comprising amino acids 99-111 of S1. These clones, which are the first generated against a recombinant fllarial antigen, produced both IFN-gamma and IL-5 as well as little IL- 4, suggestive of a Th0-like phenotype. In conclusion, in putative immunity, reactivity against a particular parasite protein can be detectable on the level of T but not B cells. Induction of both IFN- gamma and IL-5 by S1 suggests that it may trigger macrophage plus eosinophil dependent killing of L3 in vivo. The identification of a likely DQ6 (DQA1*0103/DQB1*0603)-restricted T cell epitope may be of more general relevance, given that allele combinations of DQ6, including DQA1*0103/DQB1*0603, are negatively associated with diabetes mellitus.      

Clinical studies of multiple endocrine neoplasia type 1 (MEN1) [published erratum appears in QJM 1996 Dec;89(12):957-8]

Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant disorder characterized by the combined occurrence of parathyroid, pancreatic islet and anterior pituitary tumours. To facilitate a screening programme for MEN1, we investigated 709 people (364 males and 345 females, age range 1-84 years) from 62 MEN1 families, and 36 non- familial MEN1 patients. Of those investigated, 220 (95 males and 125 females, age range 8-79 years) suffered from MEN1. Parathyroid, pancreatic and pituitary tumours occurred in 95%, 41% and 30% of the patients, respectively. Parathyroid tumours were the first manifestation of MEN1 in 87% of patients, and amongst the pituitary and pancreatic tumours, somatotrophinomas and gastrinomas were more common in patients above the age of 40 years, whilst insulinomas occurred more frequently in patients below the age of 40 years. Biochemical screening indicated that the penetrance of MEN1 by the ages of 20, 35 and 50 years was 43%, 85% and 94%, respectively, and that the development of MEN1 was confined to first-degree relatives in 91% of patients and to second-degree relatives in 9% of patients. These findings have helped to define a proposed screening programme for MEN1.      

Identical nucleotide sequences of the 3'A gamma globin gene enhancer elements from four different chromosomes

We have determined the nucleotide sequence of the 2,360-bp long EcoRI fragment from four chromosomes; this fragment is located 3' to the A gamma globin gene and is considered to contain the enhancer element identified by Bodine and Ley. The chromosomes were from an Arabian sickle cell anemia patient with high Hb F and a homozygosity for haplotype No 31 and from a black sickle cell anemia patient with low Hb F and a homozygosity for haplotype No 19. A third chromosome carried the determinant for a nondeletional hereditary persistence of fetal hemoglobin seen in a Chinese subject, and the fourth was a normal chromosome from a Yugoslavian subject. Twenty-one differences were observed when a comparison was made with the published sequence; no differences were seen between the sequences of the four different samples except for an additional mutation in the Chinese. These data make it unlikely that specific mutations within this sequence are associated with increases in G gamma and A gamma production.     

Production of F cells in sickle cell anemia: regulation by a genetic locus or loci separate from the beta-globin gene cluster

Levels of fetal hemoglobin (HbF) bearing reticulocytes (F reticulocytes) range from 2% to 50% in patients with sickle cell (SS) anemia. To learn whether any portion of such variation in F cell production is regulated by loci genetically separable from the beta- globin gene cluster, percentages of F reticulocytes were compared in 59 sib pairs composed solely of SS members, including 40 pairs from Jamaica and 19 from the United States. We reasoned that differences in F reticulocyte levels might arise (1) from any of several kinds of artifact, (2) via half-sib status, or (3) because one or more genes regulating F cell production segregate separately from beta S. We minimized the role of artifact by assay of fresh samples from 84 SS individuals, including both members of 38 sib pairs. In 78 of the 84 subjects, serial values for percent F reticulocytes fell within 99.9% confidence limits or were alike by t test (P greater than or equal to .05). This left 32 sib pairs for which F reticulocyte levels in each member were reproducible. When sib-sib comparisons were limited to these 32 pairs, percentages of F reticulocytes were grossly dissimilar within 12 Jamaican and 3 American sibships. Within them, the probability that sibs were alike was always less than or equal to .005 and usually less than or equal to 10(-4). We next minimized the contribution of half-sibs among Jamaicans by a combination of paternity testing and sib-sib comparison of beta-globin region DNA restriction fragment length polymorphisms, especially among discordant pairs. We thereafter concluded that at least seven to eight Jamaican pairs were composed of reproducibly discordant full sibs. There is thus little doubt that there are genes regulating between-patient differences in F cell production that are separate from the beta-globin gene cluster. Still unanswered is (1) whether or not these genes are actually linked to beta S, (2) why F reticulocyte levels in Americans tend to be lower than in Jamaicans, and (3) whether or not differences in F cell production among SS patients are regulated by several major loci or by only one.     

Possible interaction of genotypes at cystathionine β-synthase and methylenetetrahydrofolate reductase (MTHFR) in neural tube defects

Neural tube defects are a common, complex disorder with genetic and environmental components to risk. We investigated the previously reported interaction between homozygosity for the thermolabile variant at the methylenetetrahydrofolate reductase and heterozygosity for the 844ins68 allele at the cystathionine beta-synthase loci in cases with lumbosacral myelomeningocele and their parents. Using control allele frequencies from our sample pooled with those published in the literature, we confirm a marginally significant interaction at these two loci. This finding suggests that additional, larger studies are warranted to investigate this possible interaction in more detail.