Rat model of familial combined hyperlipidemia as a result of comparative mapping

Research on Experimental Hypertension in Prague (1966-2009)

The study of ontogenetic aspects of water and electrolyte metabolism performed in the Institute of Physiology (Czechoslovak Academy of Sciences) led to the research on the increased susceptibility of immature rats to salt-dependent forms of hypertension since 1966. Hemodynamic studies in developing rats paved the way to the evaluation of hemodynamic mechanisms during the development of genetic hypertension in SHR. A particular attention was focused on altered renal function and kidney damage in both salt and genetic hypertension with a special respect to renin-angiotensin system. Renal damage associated with hypertension progression was in the center of interest of several research groups in Prague. The alterations in ion transport, cell calcium handling and membrane structure as well as their relationship to abnormal lipid metabolism were studied in a close cooperation with laboratories in Munich, Glasgow, Montreal and Paris. The role of NO and oxidative stress in various forms of hypertension was a subject of a joint research with our Slovak colleagues focused mainly on NO-deficient hypertension elicited by chronic L-NAME administration. Finally, we adopted a method enabling us to evaluate the balance of vasoconstrictor and vasodilator mechanisms in BP maintenance. Using this method we demonstrated sympathetic hyperactivity and relative NO deficiency in rats with either salt-dependent or genetic hypertension. At the end of the first decennium of this century we were ready to modify our traditional approach towards modern trends in the research of experimental hypertension. Keywords: Salt-dependent hypertension o Genetic hypertension o Body fluids o Hemodynamics o Ion transport o Cell membrane structure and function o Renal function o Renin-angiotensin systems.

Intestinal microbial circadian rhythms drive sex differences in host immunity and metabolism

Circadian rhythms dynamically regulate sex differences in metabolism and immunity, and circadian disruption increases the risk of metabolic disorders. We investigated the role of sex-specific intestinal microbial circadian rhythms in host metabolism using germ-free and conventionalized mice and manipulation of dietary-derived fat, fiber, and microbiota-accessible carbohydrates. Our findings demonstrate that sex differences in circadian rhythms of genes involved in immunity and metabolism depend on oscillations in microbiota, microbial metabolic functions, and microbial metabolites. Further, we show that consuming an obesogenic, high-fat, low-fiber diet produced sex-specific changes in circadian rhythms in microbiota, metabolites, and host gene expression, which were linked to sex differences in the severity of metabolic dysfunction. Our results reveal that microbial circadian rhythms contribute to sex differences in immunity and metabolism and that dietary factors can entrain new circadian rhythms and modify the magnitude of sex differences in host-microbe circadian dynamics.

Rat Models of Metabolic Syndrome

Metabolic syndrome is a complex disorder that comprises several other complex disorders, including obesity, hypertension, dyslipidemia, and diabetes. There are several rat models that encompass component features of MetS. Some models are inbred strains selected for one or more traits underlying MetS; others are population models with genetic risk for MetS traits, are induced by environmental stressors such as diet, are spontaneous monogenic mutant models, or are congenic strains derived from a combination of these models. Together they can be studied to identify the genetic and physiological underpinnings of MetS to identify candidate genes or mechanisms for study in human MetS subjects.

Acute Glycemic Changes in Brain and Subcutaneous Tissue Measured by Continuous Glucose Monitoring System in Hereditary Hypertriglyceridemic Rat

Parallel glucose measurements in blood and other different tissues give us knowledge about dynamics of glycemia changes, which depend on vascularization, distribution space and local utilization by tissues. Such information is important for the understanding of glucose homeostasis and regulation. The aim of our study was to determine the time-lag between blood, brain, and adipose tissue during rapid glucose changes in a male hHTG rat (n=15). The CGMS sensor Guardian RT (Minimed/Medtronic, USA) was inserted into the brain and into the abdominal subcutaneous tissue. Fixed insulin and variable rate of glucose infusion was used to maintain euglycemia during sensor calibration period. At 0 min, 0.5 g/kg of bolus of glucose was administered, and at 50 min, 5 IU/kg of bolus of insulin was administered. Further glucose and insulin infusion was stopped at this time. The experiment was finished at 130 min and animals were euthanized. The time-shift between glycemia changes in blood, brain, and subcutaneous tissue was calculated by identification of the ideal correlation function. Moreover, the time to achieve 90 % of the maximum glucose excursion after intervention (T90) was measured to compare our data with the literature. The time-lag blood vs. brain and blood vs. subcutaneous tissue was 10 (10; 15) min and 15 (15; 25) min, respectively. The difference was statistically significant (P=0.01). T90 after glucose bolus in brain and subcutaneous tissue was 10 min (8.75; 15) and 15 min (13.75; 21.25), respectively. T90 after insulin bolus in brain and subcutaneous tissue was 10 min (10; 15) and 20 min (20; 27.5), respectively. To the contrary, with literature, our results showed earlier glucose level changes in brain in comparison with subcutaneous tissue after glucose and insulin boluses. Our results suggest that glucose dynamics is different within monitored tissues under rapid changing glucose level and we can expect similar behavior in humans. Improved knowledge about glucose distribution and dynamics is important for avoiding hypoglycemia.

Genomic determinants of triglyceride and cholesterol distribution into lipoprotein fractions in the rat

The plasma profile of major lipoprotein classes and its subdivision into particular fractions plays a crucial role in the pathogenesis of atherosclerosis and is a major predictor of coronary artery disease. Our aim was to identify genomic determinants of triglyceride and cholesterol distribution into lipoprotein fractions and lipoprotein particle sizes in the recombinant inbred rat set PXO, in which alleles of two rat models of the metabolic syndrome (SHR and PD inbred strains) segregate together with those from Brown Norway rat strain. Adult male rats of 15 PXO strains (n = 8–13/strain) and two progenitor strains SHR-Lx (n = 13) and BXH2/Cub (n = 18) were subjected to one-week of high-sucrose diet feeding. We performed association analyses of triglyceride (TG) and cholesterol (C) concentrations in 20 lipoprotein fractions and the size of major classes of lipoprotein particles utilizing 704 polymorphic microsatellite markers, the genome-wide significance was validated by 2,000 permutations per trait. Subsequent in silico focusing of the identified quantitative trait loci was completed using a map of over 20,000 single nucleotide polymorphisms. In most of the phenotypes we identified substantial gradient among the strains (e.g. VLDL-TG from 5.6 to 66.7 mg/dl). We have identified 14 loci (encompassing 1 to 65 genes) on rat chromosomes 3, 4, 7, 8, 11 and 12 showing suggestive or significant association to one or more of the studied traits. PXO strains carrying the SHR allele displayed significantly higher values of the linked traits except for LDL-TG and adiposity index. Cholesterol concentrations in large, medium and very small LDL particles were significantly associated to a haplotype block spanning part of a single gene, low density lipoprotein receptor-related protein 1B (Lrp1b). Using genome-wide association we have identified new genetic determinants of triglyceride and cholesterol distribution into lipoprotein fractions in the recombinant inbred panel of rat model strains.

Obese locus in WNIN/obese rat maps on chromosome 5 upstream of leptin receptor

WNIN/Obese (WNIN/Ob) rat a new mutant model of metabolic syndrome was identified in 1996 from an inbred Wistar rat strain, WNIN. So far several papers are published on this model highlighting its physical, biochemical and metabolic traits. WNIN/Ob is leptin resistant with unaltered leptin or its receptor coding sequences - the two well-known candidate genes for obesity. Genotyping analysis of F₂ progeny (raised from WNIN/Ob × Fisher - 344) in the present study localized the mutation to a recombinant region of 14.15cM on chromosome 5. This was further corroborated by QTL analysis for body weight, which narrowed this region to 4.43 cM with flanking markers D5Rat256 & D5Wox37. Interval mapping of body weight QTL shows that the LOD score peak maps upstream of leptin receptor and shows an additive effect suggesting this as a novel mutation and signifying the model as a valuable resource for studies on obesity and metabolic syndrome.

Effect of green tea extract microencapsulation on hypertriglyceridemia and cardiovascular tissues in high fructose-fed rats

The application of polyphenols has attracted great interest in the field of functional foods and nutraceuticals due to their potential health benefits in humans. However, the effectiveness of polyphenols depends on their bioactivity and bioavailability. In the present study, the bioactive component from green tea extract (GTE) was administrated orally (50 mg/kg body weight/day) as free or in a microencapsulated form with maltodextrin in rats fed a high fructose diet. High fructose diet induced features of metabolic syndrome including hypertriglyceridemia, hyperuricemia, increased serum total cholesterol, and retroperitoneal obesity. In addition, myocardial fibrosis was increased. In rats receiving high fructose diet, the lowering of blood triglycerides, total cholesterol, non esterified fatty acid (NEFA) and uric acid, as well as the reduction in final body weight and retroperitoneal fat weight associated with the administration of GTE, led to a reversal of the features of metabolic syndrome (P < 0.05). In particular, the administration of microencapsulated GTE decreased myocardial fibrosis and increased liver catalase activity consistent with a further alleviation of serum NEFA, and hyperuricemia compared to administration of GTE. Taken together, our results suggest that microencapsulation of the bioactive components of GTE might have a protective effect on cardiovasucular system by attenuating the adverse features of myocardial fibrosis, decreasing uric acid levels and increasing hepatic catalase activity effectively by protecting their bioactivities.

Age and sex affect quantitative genetic parameters for dominance rank and aggression in free-living greylag geese

Knowledge of the genetic and environmental influences on a character is pivotal for understanding evolutionary changes in quantitative traits in natural populations. Dominance and aggression are ubiquitous traits that are selectively advantageous in many animal societies and have the potential to impact the evolutionary trajectory of animal populations. Here we provide age- and sex-specific estimates of additive genetic and environmental components of variance for dominance rank and aggression rate in a free-living, human-habituated bird population subject to natural selection. We use a long-term data set on individually marked greylag geese (Anser anser) and show that phenotypic variation in dominance-related behaviours contains significant additive genetic variance, parental effects and permanent environment effects. The relative importance of these variance components varied between age and sex classes, whereby the most pronounced differences concerned nongenetic components. In particular, parental effects were larger in juveniles of both sexes than in adults. In paired adults, the partner's identity had a larger influence on male dominance rank and aggression rate than in females. In sex- and age-specific estimates, heritabilities did not differ significantly between age and sex classes. Adult dominance rank was only weakly genetically correlated between the sexes, leading to considerably higher heritabilities in sex-specific estimates than across sexes. We discuss these patterns in relation to selection acting on dominance rank and aggression in different life history stages and sexes and suggest that different adaptive optima could be a mechanism for maintaining genetic variation in dominance-related traits in free-living animal populations.

Early endocrine and molecular changes in metabolic syndrome models

The twenty-first century arrived in the middle of a global epidemic of metabolic syndrome (MS) and type 2 diabetes mellitus (DM2). It is generally accepted that an excess of nutrients linked to a low physical activity triggers the problem. However, the molecular features that interact to develop the MS are not clear. In an effort to understand and control them, they have been extensively studied, but this goal has not been achieved yet. Nonhuman animal models have been used to explore diet and genetic factors in which experimental conditions are controlled. For example, only one factor in the diet, such as fats or carbohydrates can be modified to better understand a single change that would be impossible in humans. Most of the studies have been done in rodents. However, it is difficult to directly compare them, because experiments are different in more than one variable; genetic strains, amount, and the type of fat used in the diet and sex. Thus, the only possible criteria of comparison are the relevance of the observed changes. We review different animal models and add some original observations on short-term changes in metabolism and beta cells in our own model of adult Wistar rats that are not especially prone to get fat or develop DM2, treated with 20% sucrose in drinking water. One early change observed in pancreatic beta cells is the increase in GLUT2 expression that is located to the membrane of the cells. This change could partially explain the presence of insulin hypersecretion and hyperinsulinemia in these rats. Understanding early changes that lead to MS and in time to pancreatic islet exhaustion is an important biomedical problem that may contribute to learn how to prevent or even reverse MS, before developing DM2.

Gene-environment interactions in human disease: nuisance or opportunity?

Many environmental risk factors for common, complex human diseases have been revealed by epidemiologic studies, but how genotypes at specific loci modulate individual responses to environmental risk factors is largely unknown. Gene-environment interactions will be missed in genome-wide association studies and could account for some of the 'missing heritability' for these diseases. In this review, we focus on asthma as a model disease for studying gene-environment interactions because of relatively large numbers of candidate gene-environment interactions with asthma risk in the literature. Identifying these interactions using genome-wide approaches poses formidable methodological problems, and elucidating molecular mechanisms for these interactions has been challenging. We suggest that studying gene-environment interactions in animal models, although more tractable, might not be sufficient to shed light on the genetic architecture of human diseases. Lastly, we propose avenues for future studies to find gene-environment interactions.

Genome-wide association study of growth in crossbred beef cattle

Chromosomal regions harboring variation affecting cattle birth weight and BW gain to 1 yr of age were identified by marker association using the highly parallel BovineSNP50 BeadChip (50K) assay composed of 54,001 individual SNP. Genotypes were obtained from progeny (F(1); 590 steers) and 2-, 3-, and 4-breed cross grandprogeny (F(1)(2) = F(1) x F(1); 1,306 steers and 707 females) of 150 AI sires representing 7 breeds (22 sires per breed; Angus, Charolais, Gelbvieh, Hereford, Limousin, Red Angus, and Simmental). Genotypes and birth, weaning, and yearling BW records were used in whole-genome association analyses to estimate effects of individual SNP on growth. Traits analyzed included growth component traits: birth weight (BWT), 205-d adjusted birth to weaning BW gain (WG), 160-d adjusted postweaning BW gain (PWG); cumulative traits: 205-d adjusted weaning weight (WW = BWT + WG) and 365-d adjusted yearling weight (YW = BWT + WG + PWG); and indexes of relative differences between postnatal growth and birth weight. Modeled fixed effects included additive effects of calf and dam SNP genotype, year-sex-management contemporary groups, and covariates for calf and dam breed composition and heterosis. Direct and maternal additive polygenic effects and maternal permanent environment effects were random. Missing genotypes, including 50K genotypes of most dams, were approximated with a single-locus BLUP procedure from pedigree relationships and known 50K genotypes. Various association criteria were applied: stringent tests to account for multiple testing but with limited power to detect associations with small effects, and relaxed nominal P that may detect SNP associated with small effects but include excessive false positive associations. Genomic locations of the 231 SNP meeting stringent criteria generally coincided with described previously QTL affecting growth traits. The 12,425 SNP satisfying relaxed tests were located throughout the genome. Most SNP associated with BWT and postnatal growth affected components in the same direction, although detection of SNP associated with one component independent of others presents a possible opportunity for SNP-assisted selection to increase postnatal growth relative to BWT.

Association of SLC6A9 gene variants with human essential hypertension

AIM

We previously identified a quantitative trait locus (QTL) on rat chromosome 5 that appeared to be primarily controlled by the sympathetic nervous system. Because sympathetic overactivity is related to hypertension, solute carrier family 6, member 9 (SLC6A9) is a candidate gene for the connection of this QTL with blood pressure regulation. In the present study, we therefore explored the role of SLC6A9 genetic variations in human essential hypertension (EH).

METHODS

We evaluated three single nucleotide polymorphisms (SNPs) (rs2286245, rs3791124 and rs2486001) in 758 essential hypertension patients and 726 controls. Polymorphism-related genotypes were determined with TaqMan assays.

RESULTS

The allelic frequency of rs2286245 (C versus T, p=0.032) showed significant differences between EH and normotensive controls (NT) groups. The genotypic distribution of rs3791124 in its dominant model (AA+GA versus GG, p=0.027) also showed significant differences between EH and NT groups. The genotype and allele distributions of rs2486001 did not exhibit any significant differences.

CONCLUSION

We found an association between SLC6A9 gene polymorphisms and essential hypertension in a Japanese population, suggesting that SLC6A9 is a susceptibility locus for essential hypertension.

Genes on rat chromosomes 3, 5, 10, and 16 are linked with facets of metabolic syndrome

WOKW (Wistar Ottawa Karlsburg W) rats develop metabolic syndrome closely resembling human disorder. In crossing studies between disease-prone WOKW and disease-resistant DA (Dark Agouti) rats, several quantitative trait loci (QTLs) were mapped. To prove the in vivo relevance of QTLs, congenic DA.WOKW rats, briefly termed DA.3aW, DA.3bW, DA.5W, DA.10W, and DA.16W, were generated by transferring chromosomal regions of WOKW chromosomes 3, 5, 10, and 16 onto DA genetic background. Male (n=12) and female (n=12) rats of each congenic strain and their parental strain DA were characterized for adiposity index (AI), serum leptin, and serum insulin as well as serum cholesterol and serum triglycerides as single facets of metabolic syndrome at the age of 30 weeks. The data showed a significant higher AI for male and female DA.3aW and female DA.16W compared with DA. Serum leptin was significantly elevated in male and female DA.3aW, DA.10W, and DA.16W rats in comparison with DA. Rats of both sexes of DA.10W and female DA.16W showed significantly elevated serum insulin in comparison to DA. Female rats of all congenics had significantly higher serum cholesterol compared with DA, while males did not differ. Finally, triglycerides were only elevated in male DA.16W. The results demonstrate an involvement of WOKW chromosomes 3, 5, 10, and 16 in developing facets of the metabolic syndrome.

Investigating the effect of genetic background on proteinuria and renal injury using two hypertensive strains

An earlier linkage analysis conducted on a population derived from the Dahl salt-sensitive hypertensive (S) and the spontaneously hypertensive rat (SHR) identified 10 genomic regions linked to several renal and/or cardiovascular traits. In particular, loci on rat chromosomes (RNO) 8 and 13 were linked to proteinuria, albuminuria, and renal damage. At both loci, the S allele was associated with increased proteinuria and renal damage. The current study aimed to confirm the linkage analysis and to evaluate the effect of genetic background on the ability of each locus (either RNO8 or RNO13) to exert a phenotypic difference when placed on a genetic background either susceptible (S rat) or resistant (SHR) to the development of renal disease. Congenic strains developed to transfer genomic segments from either RNO8 or RNO13 from the SHR onto the S genetic background [S.SHR(8) or S.SHR(13)] demonstrated significantly reduced proteinuria and improved renal function. Both congenic strains demonstrated significantly reduced glomerular and tubular injury, with renal interstitial fibrosis as the predominant pathological difference compared with the S. In contrast, transfer of RNO8 or RNO13 genomic regions from the S onto the resistant SHR genetic background [SHR.S(8) or SHR.S(13)] yielded no significant difference in proteinuria or glomerular, tubular, or interstitial injury compared with SHR. These findings demonstrate that genetic context plays a significant and important role in the phenotypic expression of genes influencing proteinuria on RNO8 and RNO13.

Sex-specific genetic architecture of human disease

Sexual dimorphism in anatomical, physiological and behavioural traits are characteristics of many vertebrate species. In humans, sexual dimorphism is also observed in the prevalence, course and severity of many common diseases, including cardiovascular diseases, autoimmune diseases and asthma. Although sex differences in the endocrine and immune systems probably contribute to these observations, recent studies suggest that sex-specific genetic architecture also influences human phenotypes, including reproductive, physiological and disease traits. It is likely that an underlying mechanism is differential gene regulation in males and females, particularly in sex steroid-responsive genes. Genetic studies that ignore sex-specific effects in their design and interpretation could fail to identify a significant proportion of the genes that contribute to risk for complex diseases.

The metabolic syndrome

The "metabolic syndrome" (MetS) is a clustering of components that reflect overnutrition, sedentary lifestyles, and resultant excess adiposity. The MetS includes the clustering of abdominal obesity, insulin resistance, dyslipidemia, and elevated blood pressure and is associated with other comorbidities including the prothrombotic state, proinflammatory state, nonalcoholic fatty liver disease, and reproductive disorders. Because the MetS is a cluster of different conditions, and not a single disease, the development of multiple concurrent definitions has resulted. The prevalence of the MetS is increasing to epidemic proportions not only in the United States and the remainder of the urbanized world but also in developing nations. Most studies show that the MetS is associated with an approximate doubling of cardiovascular disease risk and a 5-fold increased risk for incident type 2 diabetes mellitus. Although it is unclear whether there is a unifying pathophysiological mechanism resulting in the MetS, abdominal adiposity and insulin resistance appear to be central to the MetS and its individual components. Lifestyle modification and weight loss should, therefore, be at the core of treating or preventing the MetS and its components. In addition, there is a general consensus that other cardiac risk factors should be aggressively managed in individuals with the MetS. Finally, in 2008 the MetS is an evolving concept that continues to be data driven and evidence based with revisions forthcoming.

Association between fatty acid binding protein 3 gene variants and essential hypertension in humans

BACKGROUND

We have earlier identified a quantitative trait locus (QTL) on rat chromosome 5 that appears to be primarily under the control of the sympathetic nervous system. Because sympathetic overactivity is related to both hypertension and insulin resistance, FABP3 is a candidate gene for the link between this QTL and blood pressure regulation. In this study, therefore, we explored the role of FABP3 genetic variations in essential hypertension (EH) in humans.

METHODS

We evaluated two single-nucleotide polymorphisms (SNPs) (rs2279885 and rs2271072) in 758 patients with EH and 726 controls. Polymorphism-related genotypes were determined using TaqMan assays, while haplotypes were estimated from the genotype data.

RESULTS

The frequencies of occurrence of the G allele of rs2279885 and the C allele of rs2271072 were significantly higher in subjects with EH than in normotensive (NT) subjects (P = 0.0339, P = 0.0209, respectively). However, the genotype distributions did not exhibit any significant differences.

CONCLUSION

We found an association between FABP3 gene polymorphisms and EH in a Japanese population, thereby suggesting that FABP3 is a susceptibility locus for EH.

Abnormal Igf2 gene in Prague hereditary hypertriglyceridemic rats: its relation to blood pressure and plasma lipids

Prague hypertriglyceridemic (HTG) rats represent a suitable model of metabolic syndrome. We have established the set of F(2) hybrids derived from HTG and Lewis progenitors to investigate the relationship between respective polymorphism(s) of Igf2 gene and blood pressure (BP) or other cardiovascular phenotypes. HTG rats had elevated systolic BP and plasma triglycerides but lower plasma cholesterol compared to Lewis rats of both genders. In males, there was higher mean arterial pressure, diastolic BP and relative heart weight in HTG than in Lewis rats. The results obtained in the total population of F(2) hybrids indicated strong segregation of Igf2 genotype with plasma triglycerides. There was no segregation of Igf2 genotype with any BP component except BP changes occurring after the blockade of either renin-angiotensin system (RAS) or NO synthase. When F(2) population was analyzed according to gender, male F(2) progeny homozygous for HTG Igf2 allele had significantly higher plasma triglycerides and greater BP changes after NO synthase blockade than those homozygous for Lewis allele. On the contrary, male F(2) progeny homozygous for HTG Igf2 allele had significantly lower plasma cholesterol and smaller BP changes after RAS blockade. PCR analysis of Igf2 gene by using of microsatelite D1Mgh22 has shown polymorphism between HTG and Lewis rats. Sequence analysis of cDNA revealed insertion of 14 nucleotides in HTG gene. In conclusion, polymorphism in Igf2 gene may be responsible for differences in lipid metabolism between HTG and Lewis rats. It remains to determine how these abnormalities could be involved in BP regulation by particular vasoactive systems.

Genetic determinants of emotionality and stress response in AcB/BcA recombinant congenic mice and in silico evidence of convergence with cardiovascular candidate genes

Genomic loci bearing stress-related phenotypes were dissected in recombinant congenic strains (RCS) of mice with C57BL/6J (B6) and A/J progenitors. Adult male mice from 14 A/J and 22 B6 background lines were evaluated for emotional reactivity in open-field (OF) and elevated plus-maze tests. Core temperature was monitored by radio telemetry during immobilization and on standard as well as salt-enriched diets. In addition, urinary electrolytes were measured. Genome-wide linkage analysis of the parameters revealed over 20 significant quantitative trait loci (QTL). The highest logarithm of odds (LOD) scores were within the previously-reported OF emotionality locus on Chr 1 (LOD = 4.6), in the dopa decarboxylase region on Chr 11 for the plus-maze (LOD = 4.7), and within a novel region of calmodulin 1 on Chr 12 for Ca++ excretion after a 24-h salt load (LOD = 4.6). RCS stress QTL overlapped with several candidate loci for cardiovascular (CV) disease. In silico evidence of functional polymorphisms by comparative sequence analysis of progenitor strains assisted to ascertain this convergence. The anxious BcA70 strain showed down regulation of Atp1a2 gene expression in the heart (P < 0.001) and brain (P < 0.05) compared with its parental B6 strain, compatible with the enhanced emotionality described in knock out animals for this gene, also involved in the salt-sensitive component of hypertension. Functional polymorphisms in regulatory elements of candidate genes of the CV/inflammatory/immune systems support the hypothesis of genetically-altered environmental susceptibility in CV disease development.

Drug discovery in the metabolic syndrome: context and some recent developments

The metabolic syndrome, encompassing the clinically distinct but related areas of dyslipidaemia, insulin resistance, obesity and vascular disease, offers a wide arena for drug discovery. There is substantial and growing unmet medical need, particularly as the worldwide epidemic of obesity continues to develop. There are also many targets and biological mechanisms that can be exploited. However, the context for clinical development is challenging because of the many ways in which the syndrome can be approached. As with most therapeutic areas, preclinical data provide only limited confidence in the potential of a novel target in humans. In this review, the author outlines the context for drug discovery in the metabolic syndrome, the clinical and biological scope and recent developments in preclinical models. Finally, existing examples of drug targets for a range of biological mechanisms are considered, outlining their biology and points relevant to lead identification and optimisation and clinical development.

A comprehensive view of sex-specific issues related to cardiovascular disease

Cardiovascular disease (CVD) is the leading cause of mortality in women. In fact, CVD is responsible for a third of all deaths of women worldwide and half of all deaths of women over 50 years of age in developing countries. The prevalence of CVD risk factor precursors is increasing in children. Retrospective analyses suggest that there are some clinically relevant differences between women and men in terms of prevalence, presentation, management and outcomes of the disease, but little is known about why CVD affects women and men differently. For instance, women with diabetes have a significantly higher CVD mortality rate than men with diabetes. Similarly, women with atrial fibrillation are at greater risk of stroke than men with atrial fibrillation. Historically, women have been underrepresented in clinical trials. The lack of good trial evidence concerning sex-specific outcomes has led to assumptions about CVD treatment in women, which in turn may have resulted in inadequate diagnoses and suboptimal management, greatly affecting outcomes. This knowledge gap may also explain why cardiovascular health in women is not improving as fast as that of men. Over the last decades, mortality rates in men have steadily declined, while those in women remained stable. It is also becoming increasingly evident that gender differences in cultural, behavioural, psychosocial and socioeconomic status are responsible, to various degrees, for the observed differences between women and men. However, the interaction between sex-and gender-related factors and CVD outcomes in women remains largely unknown.

Comprehensive QTL analysis of serum cholesterol levels before and after a high-cholesterol diet in SHRSP

The stroke-prone spontaneously hypertensive rat (SHRSP) showed an exaggerated response to a high-fat, high-cholesterol (HFC) diet, and the resulting reactive hypercholesterolemia was suggested to exacerbate the atherogenic process in this rat. We thus performed a quantitative trait locus (QTL) analysis on the serum cholesterol level of SHRSP before and after the HFC diet, with the final goal being the identification of the genetic mechanisms of its reactive hypercholesterolemia. Three hundred fifty-eight F2 rats between SHRSP and Wistar-Kyoto rat were employed in the study. The serum cholesterol and apoprotein E were measured before and after 2 wk of feeding with the HFC diet. Multiple QTLs for the basal cholesterol level were identified on chromosomes 1 and 5, whereas those for the postdietary cholesterol level were on chromosomes 7, 15, and 16. The cholesterol QTLs before and after HFC diet did not overlap with one another, implying that the involved metabolic processes were considerably different between the two conditions. Supporting this, VLDL and LDL cholesterol were the major components of the postdietary serum cholesterol, whereas the basal cholesterol level consisted mainly of HDL cholesterol. A substantial difference of the QTLs between males and females was observed, especially after the HFC diet. The QTL on chromosome 15 had an inverse effect on the cholesterol level, suggesting that the congenic substitution of the SHRSP fragment with that of Wistar-Kyoto rats could induce a greater cholesterol level in SHRSP. This observation is significant in establishing a new model for atherosclerosis with hypertension in rats.

DNA fingerprinting and phylogenetic analysis of WNIN rat strain and its obese mutants using microsatellite markers

Wistar is the oldest rat strain to be introduced in biomedical research, and various stocks of this strain are maintained in laboratories across the globe. The Wistar strain maintained in our facilities is 85 years old and is not typed genetically so far. Recently, two obese mutant rat strains evolved from this stock, one with euglycemia and the other with impaired glucose tolerance. These mutant rat strains, along with the parental Wistar stock and two other rat strains maintained in our facilities (WKY and F-344), were subjected to PCR-based DNA fingerprinting using microsatellite markers to evolve molecular signatures unique to them. Of the 96 markers screened, we identified a marker, leukosianin, that shows polymorphism between the strains tested and thus appears to be quite useful for rat strain identification. Also, the microsatellite data generated were subjected to hierarchical cluster analysis to generate a dendrogram and to estimate the phylogenetic closeness and distance between the rat strains tested. It was observed that the Wistar strain and its mutants maintained in our facility are genetically distinct and phylogenetically separate from the other two standard strains WKY and F-344.

Sex-specific genetic architecture of asthma-associated quantitative trait loci in a founder population

Identifying genes that influence susceptibility to asthma-related and atopy-related phenotypes has been challenging, owing to clinical heterogeneity and a complex underlying genetic architecture that includes both gene-gene and gene-environment interactions. In this article, we report the results of genome-wide linkage and association studies of eight asthma-associated quantitative traits in the Hutterites, a founder population of European descent. Our study revealed significant sex-specific genetic architecture for at least five of these traits, and identified 13 genome-wide significant quantitative trait loci (QTL) by linkage or association that are present in only one of the sexes (nine in males, four in females).

Novel double-congenic strain reveals effects of spontaneously hypertensive rat chromosome 2 on specific lipoprotein subfractions and adiposity

We have developed a new, double-congenic rat strain BN- Lx.SHR2, which carries two distinct segments of chromosome 2 introgressed from the spontaneously hypertensive rat strain (SHR) into the genetic background of congenic strain BN- Lx, which was previously shown to express variety of metabolic syndrome features. In 16-wk-old male rats of BN- Lx and BN- Lx.SHR2 strains, we compared their glucose tolerance and triacylglycerol and cholesterol concentrations in 20 lipoprotein subfractions and the lipoprotein particle sizes under conditions of feeding standard and high-sucrose diets. Introgression of two distinct SHR-derived chromosome 2 segments resulted in decreased adiposity together with aggravation of glucose intolerance in the double-congenic strain. The BN- Lx.SHR2 rats were more sensitive to sucrose-induced rise in triacylglycerolemia. Although the total cholesterol concentrations of the two strains were comparable after the standard diet and even lower in BN- Lx.SHR2 after sucrose feeding, detailed analysis revealed that under both dietary conditions, the double-congenic strain had significantly higher cholesterol concentrations in low-density lipoprotein fractions and lower high-density lipoprotein fractions. We established a new inbred model showing dyslipidemia and mild glucose intolerance without obesity, attributable to specific genomic regions. For the first time, the chromosome 2 segments of SHR origin are shown to influence other than blood pressure-related features of metabolic syndrome or to be involved in relevant nutrigenomic interactions.

Genetic relationship between placental and fetal weights and markers of the metabolic syndrome in rat recombinant inbred strains

Epidemiological studies have shown a clear link between fetal growth retardation and an increased propensity for later cardiovascular disease in adults. It has been hypothesized that such early fetal deprivation “programs” individuals toward a life-long metabolical “thrifty phenotype” that predisposes adults to such diseases. Here we test this hypothesis, and its possible genetic basis, in rat recombinant inbred (RI) strains that uniquely allow the longitudinal studies necessary for its testing. Placental and fetal weights were determined on day 20 of pregnancy in (at least) 6 litters from each of 25 available BXH/HXB RI strains and from their SHR and BN-Lx progenitors and were correlated with metabolic traits determined in adult rats from the same inbred lines. Quantitative trait loci (QTLs) associated with placental and fetal weights were identified by total genome scanning of RI strains using the Map Manager QTX program. Heritabilities of placental and fetal weights were 56% and 62%, respectively, and total genome scanning of RI strains revealed QTLs near the D1Rat266 marker on chromosome 1 and near the D15Rat101 marker on chromosome 15 that were significantly associated with fetal and placental weights respectively. Placental weights correlated with fetal weights ( r = 0.60, P = 0.001), while reduced fetal weights correlated with increased insulin concentrations during glucose tolerance test ( r = −0.71, P = 0.0001) and with increased serum triglycerides ( r = −0.54, P = 0.006) in adult rats. Our results suggest that predisposition toward a thrifty phenotype associated with decreased placental weight and restricted fetal growth is in part genetically determined.

High doses of bifendate elevate serum and hepatic triglyceride levels in rabbits and mice: animal models of acute hypertriglyceridemia

AIM

To investigate the effects of bifendate on serum and hepatic lipids level in rabbits and mice.

METHODS

Animals were administered bifendate [powdered pill suspended in 0.5% sodium carboxymethylcellulose (CMC)] at increasing doses (0.25-1 g/kg, ig). Blood lipid and apolipoprotein levels were measured using commercially available assay kits.

RESULTS

The treatment of rabbits with a single dose of bifendate (0.3 g/kg) caused a time-dependent and biphasic change in serum triglyceride (TG) levels, with the value reaching a maximum (3-fold increase compared to the baseline value) between 24 and 36 h post-dosing. When mice were orally treated with bifendate (0.25-1 g/kg), serum TG levels increased by 39%-76% and 14%-39% at 24 and 48 h post-dosing, respectively. When given at daily doses of 0.25 and 1 g/kg for 4 d, bifendate increased serum TG levels (56%-79%), with concomitant elevations in apolipoprotein A-I and apolipoprotein B levels at 24 h after the last dosing. TG levels were also increased (11%-43%) in liver samples of mice receiving single or multiple doses of bifendate. However, bifendate treatment caused slight reductions in serum and hepatic total cholesterol levels (9%-13%). The hypertriglyceridemia induced by bifendate was ameliorated by fenofibrate but not inositol nicotinate treatment in mice.

CONCLUSION

The findings suggest that bifendate treatment at high oral doses can cause an acute elevation in serum and hepatic TG levels.

A novel experimental model of acute hypertriglyceridemia induced by schisandrin B

Mice were intragastrically treated with single doses (0.05-0.8 g/kg) of schisandrin B (a dibenzocyclooctadiene derivative isolated from the fruit of Schisandra chinensis). Twenty-four hours after schisandrin B administration, the serum triglyceride level was increased by 10-235% in a dose-dependent manner. However, the serum low density lipoprotein cholesterol level was significantly decreased by 28% at a dose of 0.8 g/kg. When given once daily (0.01-0.2 g/kg) for 4 days, schisandrin B also dose-dependently elevated the serum triglyceride level (17-134%). Kinetics parameters estimated by Scott's plot analysis of schisandrin B-induced changes in serum and hepatic triglyceride levels were determined: serum-E(max) (maximal effect)=6 mmol/L (384% increase, P<0.001); K(D) (affinity)=0.59 mmol/kg; pD(2) (an index of affinity)=6.62; liver-E(max)=21 micromol/g (68% increase, P<0.001); K(D)=0.37 mmol/kg; pD(2)=6.83. The efficacy of schisandrin B in increasing the triglyceride level was 5.6-fold higher in serum than in liver tissue. Fenofibrate (0.2g/kg) treatment, when in combination with schisandrin B (0.2g/kg), for 4 days significantly reduced the schisandrin B-induced increase in serum triglyceride level (by 81%, P<0.001). Hepatic triglyceride level was also decreased (by 100%, P<0.001) by co-treatment with fenofibrate. Our results suggest that schisandrin B treatment can be used to establish a mouse model of acute hypertrigylceridemia.

The sex-specific genetic architecture of quantitative traits in humans

Mapping genetically complex traits remains one of the greatest challenges in human genetics today. In particular, gene-environment and gene-gene interactions, genetic heterogeneity and incomplete penetrance make thorough genetic dissection of complex traits difficult, if not impossible. Sex could be considered an environmental factor that can modify both penetrance and expressivity of a wide variety of traits. Sex is easily determined and has measurable effects on recognizable morphology; neurobiological circuits; susceptibility to autoimmune disease, diabetes, asthma, cardiovascular and psychiatric disease; and quantitative traits like blood pressure, obesity and lipid levels, among others. In this study, we evaluated sex-specific heritability and genome-wide linkages for 17 quantitative traits in the Hutterites. The results of this study could have important implications for mapping complex trait genes.

Quantitative founder-effect analysis of French Canadian families identifies specific loci contributing to metabolic phenotypes of hypertension

The Saguenay-Lac St-Jean population of Quebec is relatively isolated and has genealogical records dating to the 17th-century French founders. In 120 extended families with at least one sib pair affected with early-onset hypertension and/or dyslipidemia, we analyzed the genetic determinants of hypertension and related cardiovascular and metabolic conditions. Variance-components linkage analysis revealed 46 loci after 100,000 permutations. The most prominent clusters of overlapping quantitative-trait loci were on chromosomes 1 and 3, a finding supported by principal-components and bivariate analyses. These genetic determinants were further tested by classifying families by use of LOD score density analysis for each measured phenotype at every 5 cM. Our study showed the founder effect over several generations and classes of living individuals. This quantitative genealogical approach supports the notion of the ancestral causality of traits uniquely present and inherited in distinct family classes. With the founder effect, traits determined within population subsets are measurably and quantitatively transmitted through generational lineage, with a precise component contributing to phenotypic variance. These methods should accelerate the uncovering of causal haplotypes in complex diseases such as hypertension and metabolic syndrome.

Dynamic genetic architecture of metabolic syndrome attributes in the rat

The polydactylous rat strain (PD/Cub) is a highly inbred (F > 90) genetic model of metabolic syndrome. The aim of this study was to analyze the genetic architecture of the metabolic derangements found in the PD/Cub strain and to assess its dynamics in time and in response to diet and medication. We derived a PD/Cub × BN/Cub (Brown Norway) F2 intercross population of 149 male rats and performed metabolic profiling and genotyping and multiple levels of genetic linkage and statistical analyses at five different stages of ontogenesis and after high-sucrose diet feeding and dexamethasone administration challenges. The interval mapping analysis of 83 metabolic and morphometric traits revealed over 50 regions genomewide with significant or suggestive linkage to one or more of the traits in the segregating PD/Cub × BN/Cub population. The multiple interval mapping showed that, in addition to “single” quantitative train loci, there are more than 30 pairs of loci across the whole genome significantly influencing the variation of particular traits in an epistatic fashion. This study represents the first whole genome analysis of metabolic syndrome in the PD/Cub model and reveals several new loci previously not connected to the genetics of insulin resistance and dyslipidemia. In addition, it attempts to present the concept of “dynamic genetic architecture” of metabolic syndrome attributes, evidenced by shifts in the genetic determination of syndrome features during ontogenesis and during adaptation to the dietary and pharmacological influences.

Genetic studies in rat models: insights into cardiovascular disease

PURPOSE OF REVIEW

Limited to 2003-2004 publications, this review focuses on 'big picture' concepts learned from rat genetic studies of cardiovascular disease.

RECENT DEVELOPMENTS

Analysis reveals insights into pathogenic paradigms, as well as experimental perspectives into rat-based systems of analyses of complex cardiovascular disease. Key concepts are forwarded. Multiple susceptibility genes underlie several quantitative trait loci for blood pressure suggesting a 'quantitative trait loci cluster' concept; hypertension end-organ disease quantitative trait loci are distinct from blood pressure quantitative trait loci indicating differential susceptibility paradigms for hypertension and each complication (stroke, renal disease, cardiac hypertrophy); distinct blood pressure quantitative trait loci are found in males and females indicating gender-specific susceptibility; and genetic subtypes comprise polygenic hypertension in rat models suggesting a genetic basis for clinical heterogeneity of human essential hypertension. Gender specific genetic susceptibility plays a key role in coronary artery disease susceptibility; multiple distinct quantitative trait loci underlie hyperlipidemia and type-2 diabetes, indicating multiple susceptibilities in risk factors for cardiovascular disease. Studies in transgenic inbred rat-strain models demonstrate value for serial, complex, cardiovascular pathophysiological analyses within a genetic context.

SUMMARY

Cognizant of the limitations of animal model studies, observations from rat genetic studies provide insight into respective modeled human cardiovascular diseases and risk factor susceptibility, as well as systematically dissect the multifaceted complexities apparent in human complex cardiovascular disease. Given the recapitulation of many features of human cardiovascular disease, the value of rat model-based genetic studies for complex cardiovascular disease is unequivocal, thus mandating the expansion of resources for maximization of rat-based genetic studies.