Ethnic differences in red blood cell sodium/lithium countertransport and metabolic correlates of hypertension: an international collaborative study

Baboons as a model to study genetics and epigenetics of human disease

A major challenge for understanding susceptibility to common human diseases is determining genetic and environmental factors that influence mechanisms underlying variation in disease-related traits. The most common diseases afflicting the US population are complex diseases that develop as a result of defects in multiple genetically controlled systems in response to environmental challenges. Unraveling the etiology of these diseases is exceedingly difficult because of the many genetic and environmental factors involved. Studies of complex disease genetics in humans are challenging because it is not possible to control pedigree structure and often not practical to control environmental conditions over an extended period of time. Furthermore, access to tissues relevant to many diseases from healthy individuals is quite limited. The baboon is a well-established research model for the study of a wide array of common complex diseases, including dyslipidemia, hypertension, obesity, and osteoporosis. It is possible to acquire tissues from healthy, genetically characterized baboons that have been exposed to defined environmental stimuli. In this review, we describe the genetic and physiologic similarity of baboons with humans, the ability and usefulness of controlling environment and breeding, and current genetic and genomic resources. We discuss studies on genetics of heart disease, obesity, diabetes, metabolic syndrome, hypertension, osteoporosis, osteoarthritis, and intrauterine growth restriction using the baboon as a model for human disease. We also summarize new studies and resources under development, providing examples of potential translational studies for targeted interventions and therapies for human disease.

Red blood cell dynamics: from cell deformation to ATP release

The mechanisms of red blood cell (RBC) deformation under both static and dynamic, i.e., flow, conditions have been studied extensively since the mid 1960s. Deformation-induced biochemical reactions and possible signaling in RBCs, however, were proposed only fifteen years ago. Therefore, the fundamental relationship between RBC deformation and cellular signaling dynamics i.e., mechanotransduction, remains incompletely understood. Quantitative understanding of the mechanotransductive pathways in RBCs requires integrative studies of physical models of RBC deformation and cellular biochemical reactions. In this article we review the physical models of RBC deformation, spanning from continuum membrane mechanics to cellular skeleton dynamics under both static and flow conditions, and elaborate the mechanistic links involved in deformation-induced ATP release.

Sodium-lithium countertransport activity in healthy, dyslipidemic, and hypertensive individuals

The aim of our study was to investigate the role of dyslipidemia on red blood cell sodium-lithium countertransport activity in healthy and hypertensive individuals. A total of 128 Caucasian individuals, aged 20 to 60 years old, were divided into 4 groups: dyslipidemic/ hypertensive, dyslipidemic/normotensive, normolipidemic/hypertensive, and normolipidemic/ normotensive (controls). Sodium-lithium countertransport activity was determined based on the Canessa et al method. Sodium-lithium countertransport activity was significantly higher in all patient groups compared with controls (P < .001) and similar in the 3 patient groups. Sodium-lithium countertransport activity was significantly and positively associated with triglyceride levels (P < .001), body mass index (P < .001), total cholesterol levels (P = .001), and systolic (P = .001) and diastolic blood pressure (P = .001). In multivariate regression analysis, triglycerides made the largest contribution to sodium-lithium countertransport variation among the variables tested (R(2) = 0.273). Our results suggest that dyslipidemia affects sodium-lithium countertransport activity independently of essential hypertension and even to a greater extent than hypertension.

Clinical characteristics of young-onset hypertension-implications for different genders

BACKGROUND

Hypertension may develop early, before the age of 40 years, in both genders, so-called young-onset hypertension. The clinical characteristics of young-onset hypertension have not been well defined.

METHODS

The personal history and clinical characteristics were evaluated in a series of patients with young-onset hypertension. With the individual-matching, case-controlled design, patients were initially matched for age, gender and residence with the first control (C1) group in either 2:1 or 1:1 fashion. They were then additionally matched for body mass index (BMI) with the second control (C2) group in 1:1 fashion. To elucidate the possible difference between genders, all the comparisons were conducted in males and females separately.

RESULTS

A total of 82 consecutive patients, 56 males and 26 females, with young-onset hypertension were included. Compared with the 148 subjects in C1 group, hypertensive patients were relatively highly educated and had less alcohol drinking in either gender. BMI (25.10+/-0.49 vs. 22.34+/-0.31 kg/m(2), P<0.001) and serum triglyceride level (153.35+/-10.71 vs. 98.76+/-5.12 mg/dl, P<0.001) were significantly increased in male patients, while serum uric acid (5.74+/-0.34 vs. 4.78+/-0.17 mg/dl, P=0.006) and triglyceride level (121.39+/-12.71 vs. 76.58+/-4.88 mg/dl, P=0.002) were increased in female ones. Compared to that in C2 group, serum triglyceride level was still increased in patients of either gender. Interestingly, serum cholesterol level in female patients was lower than that in either C1 or C2 group. Further, serum triglyceride level was significantly correlated to BMI, serum cholesterol and glucose level in male patients but only to serum uric acid level in female ones.

CONCLUSIONS

Clinical characteristics of young-onset hypertension were unique and different by gender. Though consistently increased in patients of either gender, serum triglyceride level was correlated to BMI, serum cholesterol and glucose level only in males, suggesting the gender-specific presence of metabolic syndrome in young-onset hypertension.

Ethnic subgroup differences in hypertension in Pakistan

OBJECTIVE

Cardiovascular risks are globally elevated in South Asians, but this masks important ethnic subgroup differences in risk factors, such as hypertension, which have not been fully explored. We conducted this study to explore the variations in hypertension within ethnic subgroups among South Asians.

DESIGN

Cross-sectional survey [National Health Survey of Pakistan (NHSP) (1990-1994)].

SETTING

Population based.

PARTICIPANTS

A total of 9442 individuals aged 15 years or over.

METHODS

Data on sociodemographic and clinical variables were collected. Distinct ethnic subgroups - Muhajir, Punjabi, Sindhi, Pashtun and Baluchi - were defined by mother tongue.

MAIN OUTCOME MEASURE

Hypertension defined as systolic blood pressure >or= 140 mmHg or diastolic blood pressure >or= 90 mmHg, or currently receiving antihypertensive therapy.

RESULTS

The age-standardized prevalence of hypertension was highest among Baluchis (25.3% in men and 41.4% in women), then Pashtuns (23.7% in men and 28.4% in women), Muhajirs (24.1% in men and 24.6% in women), and lowest among Punjabis (17.3% in men and 16.4% in women) and Sindhis (19.0% in men and 9.9% in women) (P = 0.001). While hypertension was more prevalent in urban (22.7%) versus rural dwellers (18.1%) [odds ratio (OR) 1.34; 95% confidence interval (CI), 1.20, 1.49], this difference was no longer significant after adjusting for body mass and waist circumference (OR 1.03; 95% CI, 0.91, 1.16). However, ethnic differences persisted after adjusting for major sociodemographic, dietary and clinical risk factors (unadjusted OR for Baluchi versus Sindhi, 2.92; 95% CI, 2.20-3.89; adjusted OR, 2.71; 95% CI, 1.97-3.75).

CONCLUSIONS

A threefold difference in prevalence of hypertension exists between people of South Asian descent, which, unlike the urban/rural difference, cannot be accounted for by measured risk factors. Further study would provide valuable etiological and therapeutic clues.

Sodium-lithium countertransport activity is linked to chromosome 5 in baboons

The genes involved in the regulation of cellular sodium transport characteristics, which are correlated with some forms of essential hypertension, have not yet been identified. We are studying the genes and environmental factors that affect red blood cell sodium-lithium countertransport (SLC) activity and intracellular sodium (ICNa) concentration in 634 baboons that comprise 11 pedigrees of 2 and 3 generations each. To detect and locate possible quantitative trait loci (QTLs) that affect SLC activity and ICNa concentration, we performed a genome screen by using a maximum likelihood-based variance-components linkage analysis program (SOLAR). SLC and ICNa phenotypes as well as genotypes on 281 microsatellite loci were available for all pedigreed animals. Both SLC and ICNa traits were highly heritable (residual heritability 0.593+/-0.083 [P<0.0001] and 0.739+/-0.082 [P<0.0001], respectively). We obtained evidence that a possible QTL for SLC activity is located on the baboon homologue of human chromosome 4 between D4S2456 and D4S2365 with a maximum multipoint lod score of 9.3 (P<10(-)(10)) near D4S1645. This QTL accounts for approximately two thirds of the total additive genetic variation in SLC activity in baboons. Although ICNa concentration was highly heritable, we found no evidence for linkage to a QTL with use of this methodology. Thus, we have evidence that a gene located on the baboon homologue of human chromosome 4 (baboon chromosome 5) affects cell sodium transport in baboons.