Endocrine Care 145
Authors
W. Smith, R. Schutte, H. W. Huisman, J. M. Van Rooyen, L. J. Ware, C. M. T. Fourie, C. M. C. Mels, R. Kruger, N. McCarthy, A. E. Schutte
Affiliation
Hypertension in Africa Research Team (HART), North-West University, Potchefstroom, South Africa
Key words ▶ African ethnicity ● ▶ hypertension ● ▶ leptin ● ▶ low BMI ●
Abstract
▼
Severe underweight may be a risk factor for hypertension in developing countries, although the manner whereby this occurs is unknown. Leptin is known to exert both beneficial and detrimental vascular effects, and is predictive of poor cardiovascular outcome at high levels, but also at low levels. We explored the relationship between blood pressure and leptin in black men from South Africa with a body mass index (BMI) in the underweight to normal range. We included 113 African men (BMI ≤ 25 kg/m2) and took anthropometric, biochemical and cardiovascular measures. The blood pressure-leptin relationship was then investigated along quintiles of leptin and within BMI stratified median split (20 kg/m2) groups. Blood pressure increased across leptin quintiles 1–3 (p for trend ≤ 0.040), whereas no
relationship was observed along quintiles 3 to 5 (p for trend ≥ 0.14) (adjusted for age and waist circumference). Blood pressure was similar in the two BMI median split groups (p ≥ 0.083). In the low BMI group only, blood pressure associated positively with leptin following unadjusted, partial, and full adjustment (systolic blood pressure and diastolic blood pressure: R2 = 0.20–0.27, β = 0.32– 0.34, p ≤ 0.009). Decreasing leptin levels are not likely to contribute to hypertension prevalence in the underweight. Rather, in African men with a BMI ≤ 20 kg/m2, low leptin levels are positively and independently associated with elevated blood pressure, which is not seen at higher BMI (20–25 kg/m2). Our findings suggest a differential concentration dependent vascular effect of leptin in underweight and normal weight African men. Supporting Information for this article is available online at http://www.thieme-connect.de/products
received 13.03.2014 accepted 20.08.2014 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1389926 Published online: October 8, 2014 Horm Metab Res 2015; 47: 145–151 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0018-5043 Correspondence Dr. W. Smith Hypertension in Africa Research Team (HART) North-West University Potchefstroom Campus Private Bag X6001 Potchefstroom 2520 South Africa Tel.: + 27/18/299 2053 Fax: + 27/18/299 1053 [email protected]
Introduction
▼
Sub-Saharan Africa is facing a hypertension epidemic, with the estimated 74.7 million hypertensive adults projected to increase by 68 % from 2008 to 2025 [1]. Excess body weight has long been recognized as a risk factor for hypertension [2]. However, recent data from Ethiopia suggests that there may be a U-shaped relationship between body mass index (BMI) and hypertension status in men, with extremely low BMI also presenting an increased risk for hypertension [3]. The biological determinants of this underweight related hypertension are unclear. Leptin is an adipokine that is predominantly released from white subcutaneous adipose tissue [4] at concentrations reflecting the degree of adiposity [5]. Besides the ability of leptin to regulate food intake and energy expenditure [6], the last 2 decades have seen the emergence of leptin’s role in regulating a range of both beneficial and detri-
mental vascular effects [7, 8]. Of particular importance to the vasculature, studies have shown opposing direct or indirect vascular actions of leptin, whereby it may contribute to both arterial vasodilation [9, 10] and vasoconstriction [11]. The previously mentioned pressor actions of leptin are thought to involve increased sympathetic activation [12, 13]. Whereas the adverse clinical impact of high leptin levels have been demonstrated in terms of incident hypertension [14] and cardiovascular outcomes [15], less information is available in those with low leptin levels. However, in patients with stable coronary artery disease, low circulating levels of leptin have been shown to predict cardiovascular mortality [16]. The authors speculated that their findings might in part be attributable to an inability of leptin to exert its beneficial vascular actions in a state of relative leptin deficiency.
Smith W et al. Leptin and Blood Pressure in Low BMI African Men … Horm Metab Res 2015; 47: 145–151
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Leptin is Positively Associated with Blood Pressure in African Men with a Low Body Mass Index: The SAfrEIC Study
Our aim is therefore to explore whether decreasing leptin levels are associated with an increase in blood pressure (BP) in a group consisting of both underweight and normal weight African men.
Subjects and Methods
▼
Study design
The present study was part of the larger South African study on the influence of Sex, Age, and Ethnicity on Insulin sensitivity and Cardiovascular function (SAfrEIC), a cross-sectional study that included 756 black (hereafter referred to as African) and white men and women (20–70 years of age) from the North West province of South Africa. The data collection took place between March and July 2007. The present sub-study included African men with BMI values below 25.0 kg/m2 (16 men with BMI values over 25.0 kg/m2 were excluded). Participants were excluded if they were missing data for the main dependent (BP) and independent variables (leptin) (n = 10) or had unmeasurable leptin levels (n = 47). The final group of African men (n = 113; aged 20–67 years) were first studied along quintiles of serum leptin, and then by stratification via a BMI median split, forming low (BMI ≤ 20 kg/m2; range: 15.35–19.98 kg/m2; n = 56) and normal BMI (BMI > 20 kg/ m2; range: 20.01–24.72 kg/m2; n = 57) groups. Supplementary Table 1S compares the various characteristics of the 47 participants with unmeasurable leptin levels, with the rest of the study population. Participants with unmeasurable leptin levels had a lower BMI, waist circumference (WC), insulin, Homeostasis Model Assessment for Insulin Resistance (HOMAIR), estimated creatinine clearance (eCcr), diastolic BP (DBP), and mean arterial pressure (MAP) than participants in our study population. These excluded participants furthermore smoked more than the study population.
Study procedures
Participants arrived at the North-West University’s Metabolic Unit facility at approximately 07:00 AM following an overnight fast (requested period of 10 h). Participants were provided with information regarding the study protocol and questions were answered in the participants’ home language. Participation was voluntary and all participants signed an informed consent form. The SAfrEIC study was approved by the Ethics Committee of the North-West University and conducted in accordance with the Declaration of Helsinki (2008).
Anthropometric measurements
Body height (Invicta, IP 1465, Leicester, UK, with accuracy of measurement of 0.1 cm), WC (Lufkin nonextensible, flexible steel tape (W606PM), calibrated in centimetres with millimetre gradations) and body weight (Precision Health Scale, A & D Company, Japan, measured to the nearest 0.1 kg) were measured using procedures described by Marfell-Jones et al. [17]. BMI was subsequently calculated as kg/m2.
Biochemical measurements
Blood was collected from participants and serum was prepared according to standard procedures and stored at − 80 °C. Serum glucose and lipids [total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C)], gamma-glutamyl transferase (GGT), high-sensitivity C-reactive protein (CRP), and creatinine were determined with the Konelab auto-analyzer (Thermo
Fisher Scientific, Oy, Vantaa, Finland). Serum cotinine (a marker of tobacco use) was assessed using the IMMULITE 2000 Nicotine Metabolite assay (Siemens Medical Solutions Diagnostics Ltd., Los Angeles, CA, USA; Catalogue number: L2KNM6). Insulin (ST AIA-PACK IRI, Catalogue number: 025260) was determined using a 2-cite immunoenzymometric assay on the TOSOH AIA System analyzers (San Francisco, CA, USA). Serum leptin levels were analyzed using an enzyme-linked immunosorbant kit (Diagnostic Systems Laboratories, Inc., Webster, TX, USA, Catalogue number: DSL-10–23100i). To test for the presence of the human immunodeficiency virus (HIV), rapid tests were performed directly after blood collection in accordance with protocols set out by the South African National Department of Health. These included the First Response Test (PMC Medical, Daman, India) followed by the Pareeshak Test (BHAT Bio-tech, Bangalore, India) to confirm the result. The HOMA-IR was calculated using the following formula: [fasting glucose (mmol/l) × fasting insulin (μU/ml)]/22.5 [18]. The eCcr was calculated using the Cockcroft-Gault formula [19].
Cardiovascular measurements
After blood samples were drawn, participants were given time to rest before cardiovascular measurements were taken. As both leptin and BP variables follow a circadian rhythm [20, 21], this protocol prevented the confounding influence of leptin and BP circadian rhythms from influencing the findings of the study. Brachial systolic BP (SBP), diastolic BP (DBP), and heart rate were determined using an OMRON HEM-757 apparatus (Omron Healthcare, Kyoto, Japan). Briefly, participants were allowed to rest in a seated position for 10 min after which they were fitted with the appropriately sized cuff on the upper left arm. BP measurements were then taken in duplicate with a 5-min resting period in-between measurements. The second BP measurement was then used in subsequent analysis. MAP was calculated using the formula: DBP + [(SBP-DBP)/3]. Carotid radialis pulse wave velocity (c-r PWV) was determined on the left side of the body while in the supine position with the Complior SP Acquisition system (Artech-Medical, Pantin, France). Spontaneous baroreflex sensitivity (BRS) was determined by the validated crosscorrelation BRS method [22], derived from the continuous BP measurement (Finometer aparatus, FMS, Finapres Medical Systems, Amsterdam, the Netherlands). BRS computes the correlation between beat-to-beat SBP and R-R interval, resampled at 1 Hz, over 10-s sliding windows, a timespan sufficient to accommodate fully a 10-s variability in rhythm, or several cycles at ventilatory frequencies [22]. It has been suggested that this method be used in clinical and experimental settings because of its lower within-patient variance than other BRS methods. During the measurement of BRS, participants rested in the semiFowler’s position.
Questionnaires
Socio-demographic, health, and lifestyle questionnaires were completed by participants. In this manner, information regarding participant income and use of medication was obtained. The Baecke Physical Activity Questionnaire was also completed [23].
Statistical analysis
Statistical analyses were performed using Statistica version 11 (Statsoft, Inc., Tulsa, OK, USA, 2012) and SAS software, version 9.3 (SAS Institute Inc., Cary, NC). Normally distributed variables were presented as arithmetic mean and standard deviations.
Smith W et al. Leptin and Blood Pressure in Low BMI African Men … Horm Metab Res 2015; 47: 145–151
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
146 Endocrine Care
Endocrine Care 147 Results
▼
Characteristics of the participants
The characteristics of the men and the comparisons between the low BMI and normal BMI groups (BMI median split of 20 kg/m2) are provided in ● ▶ Table 1. In general, 74 % and 86 % of participants reported using tobacco and alcohol products respectively. The majority of the participants (90 %) received less than R2000 per month (1R was approximately $0.14 in 2007, i. e., less than $ 280). Participants from the low and normal BMI groups were of a comparable age. Fifty four percent (n = 30) of the low BMI group were underweight (BMI
Authors
W. Smith, R. Schutte, H. W. Huisman, J. M. Van Rooyen, L. J. Ware, C. M. T. Fourie, C. M. C. Mels, R. Kruger, N. McCarthy, A. E. Schutte
Affiliation
Hypertension in Africa Research Team (HART), North-West University, Potchefstroom, South Africa
Key words ▶ African ethnicity ● ▶ hypertension ● ▶ leptin ● ▶ low BMI ●
Abstract
▼
Severe underweight may be a risk factor for hypertension in developing countries, although the manner whereby this occurs is unknown. Leptin is known to exert both beneficial and detrimental vascular effects, and is predictive of poor cardiovascular outcome at high levels, but also at low levels. We explored the relationship between blood pressure and leptin in black men from South Africa with a body mass index (BMI) in the underweight to normal range. We included 113 African men (BMI ≤ 25 kg/m2) and took anthropometric, biochemical and cardiovascular measures. The blood pressure-leptin relationship was then investigated along quintiles of leptin and within BMI stratified median split (20 kg/m2) groups. Blood pressure increased across leptin quintiles 1–3 (p for trend ≤ 0.040), whereas no
relationship was observed along quintiles 3 to 5 (p for trend ≥ 0.14) (adjusted for age and waist circumference). Blood pressure was similar in the two BMI median split groups (p ≥ 0.083). In the low BMI group only, blood pressure associated positively with leptin following unadjusted, partial, and full adjustment (systolic blood pressure and diastolic blood pressure: R2 = 0.20–0.27, β = 0.32– 0.34, p ≤ 0.009). Decreasing leptin levels are not likely to contribute to hypertension prevalence in the underweight. Rather, in African men with a BMI ≤ 20 kg/m2, low leptin levels are positively and independently associated with elevated blood pressure, which is not seen at higher BMI (20–25 kg/m2). Our findings suggest a differential concentration dependent vascular effect of leptin in underweight and normal weight African men. Supporting Information for this article is available online at http://www.thieme-connect.de/products
received 13.03.2014 accepted 20.08.2014 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1389926 Published online: October 8, 2014 Horm Metab Res 2015; 47: 145–151 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0018-5043 Correspondence Dr. W. Smith Hypertension in Africa Research Team (HART) North-West University Potchefstroom Campus Private Bag X6001 Potchefstroom 2520 South Africa Tel.: + 27/18/299 2053 Fax: + 27/18/299 1053 [email protected]
Introduction
▼
Sub-Saharan Africa is facing a hypertension epidemic, with the estimated 74.7 million hypertensive adults projected to increase by 68 % from 2008 to 2025 [1]. Excess body weight has long been recognized as a risk factor for hypertension [2]. However, recent data from Ethiopia suggests that there may be a U-shaped relationship between body mass index (BMI) and hypertension status in men, with extremely low BMI also presenting an increased risk for hypertension [3]. The biological determinants of this underweight related hypertension are unclear. Leptin is an adipokine that is predominantly released from white subcutaneous adipose tissue [4] at concentrations reflecting the degree of adiposity [5]. Besides the ability of leptin to regulate food intake and energy expenditure [6], the last 2 decades have seen the emergence of leptin’s role in regulating a range of both beneficial and detri-
mental vascular effects [7, 8]. Of particular importance to the vasculature, studies have shown opposing direct or indirect vascular actions of leptin, whereby it may contribute to both arterial vasodilation [9, 10] and vasoconstriction [11]. The previously mentioned pressor actions of leptin are thought to involve increased sympathetic activation [12, 13]. Whereas the adverse clinical impact of high leptin levels have been demonstrated in terms of incident hypertension [14] and cardiovascular outcomes [15], less information is available in those with low leptin levels. However, in patients with stable coronary artery disease, low circulating levels of leptin have been shown to predict cardiovascular mortality [16]. The authors speculated that their findings might in part be attributable to an inability of leptin to exert its beneficial vascular actions in a state of relative leptin deficiency.
Smith W et al. Leptin and Blood Pressure in Low BMI African Men … Horm Metab Res 2015; 47: 145–151
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Leptin is Positively Associated with Blood Pressure in African Men with a Low Body Mass Index: The SAfrEIC Study
Our aim is therefore to explore whether decreasing leptin levels are associated with an increase in blood pressure (BP) in a group consisting of both underweight and normal weight African men.
Subjects and Methods
▼
Study design
The present study was part of the larger South African study on the influence of Sex, Age, and Ethnicity on Insulin sensitivity and Cardiovascular function (SAfrEIC), a cross-sectional study that included 756 black (hereafter referred to as African) and white men and women (20–70 years of age) from the North West province of South Africa. The data collection took place between March and July 2007. The present sub-study included African men with BMI values below 25.0 kg/m2 (16 men with BMI values over 25.0 kg/m2 were excluded). Participants were excluded if they were missing data for the main dependent (BP) and independent variables (leptin) (n = 10) or had unmeasurable leptin levels (n = 47). The final group of African men (n = 113; aged 20–67 years) were first studied along quintiles of serum leptin, and then by stratification via a BMI median split, forming low (BMI ≤ 20 kg/m2; range: 15.35–19.98 kg/m2; n = 56) and normal BMI (BMI > 20 kg/ m2; range: 20.01–24.72 kg/m2; n = 57) groups. Supplementary Table 1S compares the various characteristics of the 47 participants with unmeasurable leptin levels, with the rest of the study population. Participants with unmeasurable leptin levels had a lower BMI, waist circumference (WC), insulin, Homeostasis Model Assessment for Insulin Resistance (HOMAIR), estimated creatinine clearance (eCcr), diastolic BP (DBP), and mean arterial pressure (MAP) than participants in our study population. These excluded participants furthermore smoked more than the study population.
Study procedures
Participants arrived at the North-West University’s Metabolic Unit facility at approximately 07:00 AM following an overnight fast (requested period of 10 h). Participants were provided with information regarding the study protocol and questions were answered in the participants’ home language. Participation was voluntary and all participants signed an informed consent form. The SAfrEIC study was approved by the Ethics Committee of the North-West University and conducted in accordance with the Declaration of Helsinki (2008).
Anthropometric measurements
Body height (Invicta, IP 1465, Leicester, UK, with accuracy of measurement of 0.1 cm), WC (Lufkin nonextensible, flexible steel tape (W606PM), calibrated in centimetres with millimetre gradations) and body weight (Precision Health Scale, A & D Company, Japan, measured to the nearest 0.1 kg) were measured using procedures described by Marfell-Jones et al. [17]. BMI was subsequently calculated as kg/m2.
Biochemical measurements
Blood was collected from participants and serum was prepared according to standard procedures and stored at − 80 °C. Serum glucose and lipids [total cholesterol (TC) and high-density lipoprotein cholesterol (HDL-C)], gamma-glutamyl transferase (GGT), high-sensitivity C-reactive protein (CRP), and creatinine were determined with the Konelab auto-analyzer (Thermo
Fisher Scientific, Oy, Vantaa, Finland). Serum cotinine (a marker of tobacco use) was assessed using the IMMULITE 2000 Nicotine Metabolite assay (Siemens Medical Solutions Diagnostics Ltd., Los Angeles, CA, USA; Catalogue number: L2KNM6). Insulin (ST AIA-PACK IRI, Catalogue number: 025260) was determined using a 2-cite immunoenzymometric assay on the TOSOH AIA System analyzers (San Francisco, CA, USA). Serum leptin levels were analyzed using an enzyme-linked immunosorbant kit (Diagnostic Systems Laboratories, Inc., Webster, TX, USA, Catalogue number: DSL-10–23100i). To test for the presence of the human immunodeficiency virus (HIV), rapid tests were performed directly after blood collection in accordance with protocols set out by the South African National Department of Health. These included the First Response Test (PMC Medical, Daman, India) followed by the Pareeshak Test (BHAT Bio-tech, Bangalore, India) to confirm the result. The HOMA-IR was calculated using the following formula: [fasting glucose (mmol/l) × fasting insulin (μU/ml)]/22.5 [18]. The eCcr was calculated using the Cockcroft-Gault formula [19].
Cardiovascular measurements
After blood samples were drawn, participants were given time to rest before cardiovascular measurements were taken. As both leptin and BP variables follow a circadian rhythm [20, 21], this protocol prevented the confounding influence of leptin and BP circadian rhythms from influencing the findings of the study. Brachial systolic BP (SBP), diastolic BP (DBP), and heart rate were determined using an OMRON HEM-757 apparatus (Omron Healthcare, Kyoto, Japan). Briefly, participants were allowed to rest in a seated position for 10 min after which they were fitted with the appropriately sized cuff on the upper left arm. BP measurements were then taken in duplicate with a 5-min resting period in-between measurements. The second BP measurement was then used in subsequent analysis. MAP was calculated using the formula: DBP + [(SBP-DBP)/3]. Carotid radialis pulse wave velocity (c-r PWV) was determined on the left side of the body while in the supine position with the Complior SP Acquisition system (Artech-Medical, Pantin, France). Spontaneous baroreflex sensitivity (BRS) was determined by the validated crosscorrelation BRS method [22], derived from the continuous BP measurement (Finometer aparatus, FMS, Finapres Medical Systems, Amsterdam, the Netherlands). BRS computes the correlation between beat-to-beat SBP and R-R interval, resampled at 1 Hz, over 10-s sliding windows, a timespan sufficient to accommodate fully a 10-s variability in rhythm, or several cycles at ventilatory frequencies [22]. It has been suggested that this method be used in clinical and experimental settings because of its lower within-patient variance than other BRS methods. During the measurement of BRS, participants rested in the semiFowler’s position.
Questionnaires
Socio-demographic, health, and lifestyle questionnaires were completed by participants. In this manner, information regarding participant income and use of medication was obtained. The Baecke Physical Activity Questionnaire was also completed [23].
Statistical analysis
Statistical analyses were performed using Statistica version 11 (Statsoft, Inc., Tulsa, OK, USA, 2012) and SAS software, version 9.3 (SAS Institute Inc., Cary, NC). Normally distributed variables were presented as arithmetic mean and standard deviations.
Smith W et al. Leptin and Blood Pressure in Low BMI African Men … Horm Metab Res 2015; 47: 145–151
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
146 Endocrine Care
Endocrine Care 147 Results
▼
Characteristics of the participants
The characteristics of the men and the comparisons between the low BMI and normal BMI groups (BMI median split of 20 kg/m2) are provided in ● ▶ Table 1. In general, 74 % and 86 % of participants reported using tobacco and alcohol products respectively. The majority of the participants (90 %) received less than R2000 per month (1R was approximately $0.14 in 2007, i. e., less than $ 280). Participants from the low and normal BMI groups were of a comparable age. Fifty four percent (n = 30) of the low BMI group were underweight (BMI
