A common apolipoprotein B signal peptide polymorphism modifies the relation between plasma non-esterified fatty acids and triglyceride concentration in men

Sex hormones and macronutrient metabolism

The biological differences between males and females are determined by a different set of genes and by a different reactivity to environmental stimuli, including the diet, in general. These differences are further emphasized and driven by the exposure to a different hormone flux throughout the life.

These differences have not been taken into appropriate consideration by the scientific community. Nutritional sciences are not immune from this “bias” and when nutritional needs are concerned, females are considered only when pregnant, lactating or when their hormonal profile is returning back to “normal,” i.e., to the male-like profile.

The authors highlight some of the most evident differences in aspects of biology that are associated with nutrition.

This review presents and describes available data addressing differences and similarities of the “reference man” vs. the “reference woman” in term of metabolic activity and nutritional needs. According to this assumption, available evidences of sex-associated differences of specific biochemical pathways involved in substrate metabolism are reported and discussed. The modulation by sexual hormones affecting glucose, amino acid and protein metabolism and the metabolization of nutritional fats and the distribution of fat depots, is considered targeting a tentative starting up background for a gender concerned nutritional science.

The APOB insertion/deletion polymorphism (rs17240441) influences postprandial lipaemia in healthy adults

Background

Apolipoprotein (apo)B is the structural apoprotein of intestinally- and liver- derived lipoproteins and plays an important role in the transport of triacylglycerol (TAG) and cholesterol. Previous studies have examined the association between the APOB insertion/deletion (ins/del) polymorphism (rs17240441) and postprandial lipaemia in response to a single meal; however the findings have been inconsistent with studies often underpowered to detect genotype-lipaemia associations, focused mainly on men, or with limited postprandial characterisation of participants. In the present study, using a novel sequential test meal protocol which more closely mimics habitual eating patterns, we investigated the impact of APOB ins/del polymorphism on postprandial TAG, non-esterified fatty acids, glucose and insulin levels in healthy adults.

Findings

Healthy participants (n = 147) consumed a standard test breakfast (0 min; 49 g fat) and lunch (330 min; 29 g fat), with blood samples collected before (fasting) and on 11 subsequent occasions until 480 min after the test breakfast. The ins/ins homozygotes had higher fasting total cholesterol, LDL-cholesterol, TAG, insulin and HOMA-IR and lower HDL-cholesterol than del/del homozygotes (P < 0.017). A higher area under the time response curve (AUC) was evident for the postprandial TAG (P < 0.001) and insulin (P = 0.032) responses in the ins/ins homozygotes relative to the del/del homozygotes, where the genotype explained 35% and 7% of the variation in the TAG and insulin AUCs, respectively.

Conclusions

In summary, our findings indicate that the APOB ins/del polymorphism is likely to be an important genetic determinant of the large inter-individual variability in the postprandial TAG and insulin responses to dietary fat intake.

Trans-11–18: 1 is effectively δ9-desaturated compared withTrans-12–18: 1 in humans

The aim of this human intervention study was to evaluate the Δ9-desaturation oftrans-11–18:1 (trans-vaccenic acid;tVA) tocis-9,trans-11–18:2 (c9,t11 conjugated linoleic acid; CLA) and oftrans-12–18:1 (t12) tocis-9,trans-12–18:2 after a short-term (7d) and a long-term (42d) supplementation period. The conversion rates of bothtrans-18:1 isomers were estimated by lipid analysis of serum and red blood cell membranes (RBCM). Subjects started with a 2-week adaptation period without supplements. During the 42d intervention period, the diet of the test group was supplemented with 3g/d oftVA and 3g/d oft12. The diet of the control group was supplemented with a control oil. SerumtVA andt12 levels in the test group increased by fivefold and ninefold after 7d, respectively, and by eight- and 12-fold after 42d, respectively, when compared with the adaptation period (p≤0·002). The serumc9,t11CLA levels increased by 1·7- and 2·0-fold after 7d and 42d, respectively (p≤0·001). After 42d, the test group's RBCMc9,t11CLA content was elevated by 20% (p=0·021), whereas in the control group it was decreased by 50% (p=0·002). The conversion rate oftVA was estimated at 24% by serum and 19% by RBCM. No increase inc9,t12–18:2 was observed in the serum and RBCM, and thus no conversion oft12 could be determined. In conclusion, the endogenous conversion of dietarytVA toc9,t11CLA contributes approximately one quarter to the human CLA pool and should be considered when determining the CLA supply.

Sexual dimorphism in human lipid metabolism

The existing work demonstrates that striking differences exist between men and women in lipid kinetics. These differences cannot be explained simply by the presence and action of sex hormones and are not always due to secondary, phenotypic traits that characterize men and women (e.g., body-composition, regional fat distribution). In fact, some of these secondary traits may even be the result of sexual dimorphism in metabolism, and being of female or male genotype also determines intermediary metabolism. This review provides an overview of the currently available information regarding sexual dimorphism in human lipid metabolism but does not provide an in-depth account of current knowledge (due to limited space); it will be a broad introduction to those interested in the field and will, hopefully, stimulate further efforts to unravel the secrets of male and female metabolism. What has been discovered so far regarding differences in lipid metabolism between men and women is likely only the tip of the iceberg; clearly, more work is necessary to fully understand human substrate metabolism and the implications the presence of sexual dimorphism in the control of substrate kinetics has on the prevention and treatment of disease.

PPARGC1A genotype (Gly482Ser) predicts exceptional endurance capacity in European men

Animal and human data indicate a role for the peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PPARGC1A) gene product in the development of maximal oxygen uptake (V(O2 max)), a determinant of endurance capacity, diabetes, and early death. We tested the hypothesis that the frequency of the minor Ser482 allele at the PPARGC1A locus is lower in World-class Spanish male endurance athletes (cases) [n = 104; mean (SD) age: 26.8 (3.8) yr] than in unfit United Kingdom (UK) Caucasian male controls [n = 100; mean (SD) age: 49.3 (8.1) yr]. In cases and controls, the Gly482Ser genotype met Hardy-Weinberg expectations (P > 0.05 in both groups tested separately). Cases had significantly higher V(O2 max) [73.4 (5.7) vs. 29.4 ml x kg(-1) x min(-1) (3.8); P < 0.0001] and were leaner [body mass index: 20.6 (1.5) vs. 27.6 kg/m2 (3.9); P < 0.0001] than controls. In unadjusted chi2 analyses, the frequency of the minor Ser482 allele was significantly lower in cases than in controls (29.1 vs. 40.0%; P = 0.01). To assess the possibility that genetic stratification could confound these observations, we also compared Gly482Ser genotype frequencies in Spanish (n = 164) and UK Caucasian men (n = 381) who were unselected for their level of fitness. In these analyses, Ser482 allele frequencies were very similar (36.9% in Spanish vs. 37.5% in UK Caucasians, P = 0.83), suggesting that confounding by genetic stratification is unlikely to explain the association between Gly482Ser genotype and endurance capacity. In summary, our data indicate a role for the Gly482Ser genotype in determining aerobic fitness. This finding has relevance from the perspective of physical performance, but it may also be informative for the targeted prevention of diseases associated with low fitness such as Type 2 diabetes.

PGC-1alpha genotype modifies the association of volitional energy expenditure with [OV0312]O2max

Sedentary lifestyles are increasingly common and result in low cardiorespiratory fitness ([OV0312]O2max), a well-established predictor of early mortality and coronary heart disease (CHD). Adaptation in [OV0312]O2max after exercise training varies considerably between people. Because there are hereditary components to fitness, it is likely that genetic factors explain some of this variability. PPARGC1 (PGC-1alpha) coactivates genes involved in energy transduction and mitochondrial biogenesis. Transgenic mouse data demonstrate that overexpression of PGC-1alpha mRNA increases endurance capacity by transformation of nonoxidative to oxidative skeletal muscle tissue. Other murine studies demonstrate that exercise increases PGC-1alpha mRNA expression.

PURPOSE

To explore whether a candidate polymorphism in the PGC-1alpha gene modifies the association between physical activity energy expenditure (PAEE) and predicted [OV0312]O2max ([OV0312]O2max.pred).

METHOD

We examined whether the Gly482Ser polymorphism of PGC-1alpha modified the relationship between objectively measured PAEE and [OV0312]O2max.pred in a population-based sample of 599 healthy middle-aged people. PAEE was assessed using individual calibration with 4 d of heart rate monitoring. [OV0312]O2max.pred was measured during a submaximal exercise stress test on a bicycle ergometer.

RESULTS

Homozygosity at the Ser482 allele was found in 12.7% of the cohort, whereas 38.9% and 48.4% carried the Gly482Gly and Gly482Ser genotypes, respectively. The association between PAEE and [OV0312]O2max.pred (mL x kg(-1) x min(-1)) was strongest in people homozygous for the Ser482 allele (beta = 12.03; P < 0.00001) compared with carriers of the Gly allele (beta = 5.61; P < 0.00001). In a recessive model for the Ser482 allele, the interaction between PAEE and genotype on [OV0312]O2max.pred (L x min(-1)) was highly significant (P = 0.009).

CONCLUSION

Our results indicate that Ser482 homozygotes may be most capable of improving cardiorespiratory fitness when physically active, and that Gly482Ser may explain some of the between-person variance previously reported in cardiorespiratory adaptation after exercise training.

Uncoupling protein 3 genetic variants in human obesity: the c-55t promoter polymorphism is negatively correlated with body mass index in a UK Caucasian population

OBJECTIVE

To investigate whether genetic variation at the UCP3 locus contributes to human obesity.

SUBJECTS

Ninety-one obese children (BMI>4 standard deviations from age related mean) and 419 Caucasian adults from the Isle of Ely Study.

DESIGN

Single strand conformation polymorphism (SSCP) analysis was used to scan the coding region of the UCP3 gene in 91 severely obese children. A common polymorphism identified in this gene (c-55t) has been shown to associate with lower UCP3 mRNA expression. Polymerase chain reaction-based forced restriction digestion was used to detect this allele in Caucasian adults. Multiple regression analysis was used to determine associations between the c-55t genotype and anthropometric, energetic and biochemical indices relevant to obesity.

MEASUREMENTS

For the obese children, SSCP analysis and sequencing of variants were carried out. For the Isle of Ely Study, c-55t genotype and anthropometric (body mass index, waist-hip ratio, percentage body fat), energetic (dietary fat intake, physical activity index, adjusted metabolic rate, maximum oxygen consumption) and biochemical indices (pre- and post-glucose challenge plasma triglycerides, non-esterified fatty acids, insulin and glucose) were determined.

RESULTS

A previously reported missense mutation (V102I) was detected in a single obese Afro-Carribean child. Twenty-one percent of the genes examined in the Isle of Ely study carried the c-55t promoter variant. Age-adjusted body mass index (BMI) was significantly (P=0.0037) lower in carriers of this variant.

CONCLUSION

Mutations in the coding sequence of UCP3 are unlikely to be a common monogenic cause of severe human obesity. In a Caucasian population the UCP3 c-55t polymorphism is negatively associated with BMI.