Low blood selenium: A probable factor in essential hypertension

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1 African Journal of Bioechnology Vol. 6 (14), pp , 18 July 2007 Available online a hp:// ISSN Academic Journals Full Lengh Research Paper Low blood selenium: A probable facor in essenial hyperension Babalola O. O. 1 *, Aneor J. I 2 and Adeniyi F. A. A. 2 1 Deparmen of Biochemisry, Faculy of Science, Obafemi Awolowo Universiy, Ile Ife, Nigeria. 2 Deparmen of Chemical Pahology, College of Medicine, Universiy of Ibadan, Nigeria. Acceped 16 April, 2007 The possible associaion beween selenium and essenial hyperension was invesigaed in his sudy. Blood selenium (BSe) and plasma gluahione peroxidase (plgsh-px) aciviy were measured as biochemical markers of selenium saus of 103 hyperensive paiens (44 males and 59 females) and 88 apparenly healhy subjecs (40 males and 48 females). The hyperensive paiens were classified ino hree groups based on he severiy of he disease namely: mild (Group 1), moderae (Group 2) and severe (Group 3). The healhy and he hyperensive subjecs were recruied from Abeokua and Ibadan (Souh-Wesern Nigeria). The mean age of he hyperensive paiens was 41.9 ± 10.3 (range 21 68) years, while he mean age of he healhy subjecs was 37.8 ± 8.6 (range 18 52) years. The weigh, heigh, blood pressure and pulse raes of all subjecs were measured and heir body mass indices (BMI) compued. BSe was deermined by aomic absorpion specrophoomery (AAS) while plgsh-px aciviy was measured by specrophoomeric mehod. The mean BSe concenraion was significanly lower in he hyperensive paiens (0.136 ± mg/l) han in he healhy group (0.188 ± mg/l) (P < 0.001). However wih respec o plgsh-px aciviy, here was no saisically significan difference beween he hyperensive paiens (0.126 ± U/mL) and he healhy group (0.127 ± U/mL). Blood Selenium concenraion was found o decrease wih he severiy of he disease. The difference in BSe concenraion of Group 1 and Group 2 paiens was no significan. However, here were significan differences in he BSe levels of Group 2 and Group 3 paiens (P < 0.05) and Group 1 and Group 3 paiens (P < 0.05). The observed low BSe in hyperensive subjecs implies ha low BSe is probably a predisposing facor o essenial hyperension or a consequence of he disease. The severiy of he disease was also observed o be inversely relaed o he level of BSe, suggesing ha BSe level may have a role in he prognosis of he disease. Aleraion in BSe saus appears o confirm he elemenal basis of he aeiopahogenesis of cerain diseases. Despie he reducion in BSe level in he hyperensive paiens, i was sill adequae o mainain plgsh-px aciviy a a level comparable o hose of he healhy group. This suggess ha BSe may exis in anoher funcional form, which plays a role in he pahogenesis or prognosis of he disease. Key words: Selenium, essenial hyperension, biochemical markers, disease, paiens, aeiopahogenesis. INTRODUCTION The role of selenium in hear disease has been inensely debaed since an inverse correlaion was repored beween moraliy from areriosclerosis and hyperensive hear disease and he selenium conen of crops and waer in counries such as Finland and New Zealand (Samb- *Corresponding auhor. docorbablo@yahoo.com. Tel.: erger e al., 1978). In he USA, an inverse correla-ion was repored beween he plasma selenium level and he severiy of coronary areriosclerosis (Moore e al., 1984). Earlier, Wesermark (1977) found ha blood selenium level in paiens wih acue myocardial infarcion were lower han hose of healhy aduls bu here were no differences in he hear and liver selenium level of paiens who died from myocardial infarcion and hose who died from oher diseases.

2 1698 Afr. J. Bioechnol. Table 1. Classificaion of he hyperensive paiens. *Group No. of Subjecs Average of Blood Pressure(mmHg) Group 1 (Mild Hyperension) 35 DBP or SBP Group 2 (Moderae Hyperension) 42 DBP or SBP Group 3 (Severe Hyperension) 26 DBP 110 or SBP 180 *Afer WHO-ISH, DBP = Diasolic blood pressure; and SBP = Sysolic blood pressure. Aemps were also made by a number of invesigaors o conrol for poenial confounding facors by using conrols mach for five major coronary hear disease risk facors namely age, sex, serum choleserol, smoking hisory and hisory of angina pecoris and in women of menopausal saus. Also, aemps o correlae blood selenium and GSH-Px aciviy wih acceped risk facors for cardiovascular disease, has shown diverse resuls. (Lockich, 1989). Abou 40 years afer he discovery of he imporance of selenium, here is sill conroversy over he cause and effec of selenium deficiency in a variey of clinical saes. This scienific work herefore focuses on he possible involvemen of selenium in one human disease of muliple aeiopahogenesis, hyperension. There is increased incidence of his disease in his environmen. Babalola e al. (2003) had earlier deermined he selenium levels in blood of apparen healhy aduls in Souh Wesern Nigeria and observed ha here is no selenium deficiency in our environmen. The presen sudy is designed o compare he levels of blood selenium and plasma gluahione peroxidase of he hyperensive wih hose of he apparen healhy subjecs. This is expeced o advance our undersanding of he pahogenesis of he disease, and probably, come up wih new approaches o is diagnosis, managemen and reamen. MATERIALS AND METHODS Selecion of hyperensive paiens One hundred and hree adul Nigerians of boh sexes aged beween 21 and 68 years wih essenial hyperension were seleced for he sudy. All paiens were examined by he consulan physiccians and heir complee medical hisory and physical examinaion were documened. The diagnosis of essenial hyperension was based on a leas wo separae blood pressure readings wihin a minimum of wo weeks inervals and laboraory examinaions. The paiens were considered o be hyperensive as defined by an average of wo or more diasolic blood pressure in he range of mmhg and/or he average of muliple sysolic blood pressure in he range of mmhg in he siing posiion, on wo of more subsequen visis o he clinic. The paiens were divided ino hree groups based on he severiy of he disease namely: mild (Group 1), moderae (Group 2) and severe (Group 3) hyperension. Table I shows he hree groups and he crieria for he classificaion. They were recruied from Abi Memorial Hospial, Abeokua, Federal Medical Cener (F. M. C), Abeokua, and Universiy College Hospial (U. C. H.), Ibadan. These comprised of newly diagnosed paiens and hose ha were previously on anihyperensive agens such as Propanolol and Modureic. The blood pressure (in mmhg) and pulse rae (per min) were again aken a he ime of sample collecion using Omron Auomaic Digial Blood Pressure Monior HEM - 713C (Omron Healhcare Inc. Vernon Hill Illinois 60061). The mean of hree reading was calculaed for each paien. The following exclusion crieria were employed in his sudy: (i) All cases of hyperension secondary o oher diseases were excluded from he sudy. (ii) Paiens wih hisory of alcoholism, cigaree smoking, drug abuse or any form of menal disorder. (iii) Paiens wih angina pecoris. (iv) Female paiens were neiher pregnan nor lacaing mohers nor on any oral conracepives a he ime of he sudy. (v) All obese paiens (BMI of paiens no 27 Kg/m 2 ) (vi) Paiens wih diabees mellius. (vii) Paiens wih evidence of renal disease. The following Inclusion Crieria was also adoped: Paricipaion in he sudy was purely volunary. Informed consens were obained from paiens afer hey were properly educaed abou he benefi of he sudy. Selecion of healhy subjecs group (Conrols) These consis of eighy-eigh apparenly healhy subjecs of boh sexes, aged beween 18 and 52 years. The subjecs were all apparenly healhy wih heir blood pressure in he normal range. They were all non-smokers and non-alcoholics and were mainly sudens, office workers and raders. They were no aking any medicaion during he period of he sudy. The conrol group was seleced as much as possible o mach he hyperensive group in age, sex and BMI. Their blood pressure and pulse raes were similarly measured a he ime of sample collecion. Also, none of he apparenly healhy subjecs was obese. They were also classified ino male and female subgroup. Inform consens were obained from all paricipans afer being educaed on he benefi of he sudy. Anhropomeric indices The curren ages of he subjec were noed. Also he curren body weigh was measured wih minimal clohing using a balance beam scale. Heighs were also measured barefooed, using a meer rule. Heigh (m) and Weigh (Kg) were used o calculae he body mass index (BMI) (kg/m 2 ). Collecion of blood Abou 10 ml of venous blood was obained from he anecubial fossa vein using disposable pyrogen-free needle and syringes abou 3 ml of blood was dispensed ino heparinized ubes conaining lihium heparin his was frozen as heparinized whole blood sam-

3 Babalola e al Table 2. Age, weigh, heigh and body mass index (BMI) of healhy and hyperensive subjecs. Parameer Healhy Subjecs (n = 88) Hyperensive Subjecs (n = 103) P Age (years) 37.8 ± 8.6 (18 52) 41.9 ± 10.3 (21 68) 2.99 P<0.01 Weigh (kg) 62.2 ±9.3 (42 78) 64.3 ± 10.7 (56 78) 1.45 NS Heigh (meres) 1.66 ± 0.09 ( ) 1.65 ± 0.07 ( ) 0.85 NS Body Mass Index (BMI; kg/m 2 ) ± 2.74 ( ) ± 3.84 ( ) 1.07 NS Values are in mean ± SD; n = No. of subjecs; BMI = Body Mass Index; SD = Sandard Deviaion; and NS = no significan difference. Table 3. Age, weigh, heigh and BMI in he hree groups of hyperensive paiens. Subjec/Group Age (years) Weigh (Kg) Heigh (m) BMI (Kg/m 2 ) Group 1 ( n = 35) 41.7 ± ± ± ± 2.03 Group 2 ( n = 42) 41.2 ± ± ± ± 1.77 Group 3 ( n = 26) 42.0 ± ± ± ± a,ns 0.35 b,ns 0.12 c,ns 3.89 a,** 0.89 b,ns 2.62 c,* 3.99 a,** 1.21 b,ns 1.65 c,ns 5.58 a,** 1.25 b,ns 4.35 c, ** Values are in mean ± SD; Group 1 = Mild Hyperension; Group 2 = Moderae Hyperension; Group 3 = Severe Hyperension; BMI = Body Mass Index; n = No. of subjecs; SD = Sandard deviaion; a = Comparison of Group 1 and Group 2; b = Comparison of Group 2 and Group 3; c = Comparison of Group 1 and Group 3; NS = No significan; * = P < 0.01; and ** = P < Table 4. Blood pressure and pulse raes of healhy and hyperensive subjecs. Parameer Healhy Subjecs (n = 88) Hyperensive Subjecs (n = 103) P Diasolic BP (mmhg) 81.6 ± ± <0.001 Sysolic BP (mmhg) ± ± <0.001 Pulse rae (/min) 73.1 ± ± <0.05 Values are in mean ± SD; BP = Blood pressure; and n = No. of Subjecs. sample; he remaining blood sample was dispensed ino plain vacuainer ube conaining EDTA. The sample was cenrifuged a 450 g in IEC cenrifuge for abou 5 min o obain plasma, which was ransferred wih a pipee ino plain vacuainer ubes and hen frozen. Samples were kep frozen a -70 o C unil analysed. Deerminaion of plasma gluahione peroxidase (EC ) GSH-Px aciviy was assayed by a modificaion of he couple mehod of Paglia and Valenine (1967) using hydrogen peroxide as subsrae and monioring he oxidaion of NADPH a 340 nm. One uni of enzyme aciviy is defined as 1 µmole NADPH oxidized/min. and he resul is expressed as uni/ml of plasma. Deerminaion of blood selenium Selenium in blood was deermined wih aomic absorpion specrophoomeer (AAS) by he mehod of Pleban e al. (1982) Aomic absorpion specrophoomeric measuremens of blood selenium concenraion were performed on a Perkin Elmer model 703 (Perkin Elmer Oak Brown, Illinois, USA). Saisical analysis Resuls were expressed as mean ± sandard deviaion (SD). Suden -es was used o deermine significance beween means. The 5% (p < 0.05) level of significance using he wo-ailed able was used o compare he calculaed and criical value from he able and hus saisical significance. RESULTS AND DISCUSSION Tables 2 and 3 show he resuls of he anhropomerics indices of he healhy and he hyperensive subjecs. Tables 4 and 5, he resuls of he blood pressure and pulse rae of he healhy and he hyperensive subjecs while Tables 6 and 7 show he resuls of heir BSe and plgsh-px aciviy. In he presen sudy we assessed he selenium saus of hyperensive paiens (specifically paiens wih essenial hyperension) classified ino hree major groups based on he severiy of he disease. Earlier, we had esabli-

4 1700 Afr. J. Bioechnol. Table 5. Blood pressure and pulse raes of he hree groups of hyperensive paiens. Parameer Group 1 (n = 35) Group 2 (n = 42) Group 3 (n = 26) Diasolic BP (mmhg) 95.5 ± ± ± 7.5 Sysolic BP (mmhg) ± ± ± 20.4 Pulse rae (/mins) 74.2 ± ± ± 4.7 Values are in mean ± SD; BP = Blood pressure; and n = No. of Subjecs. Table 6. BSe and plgsh-px aciviy in healhy and hyperensive subjecs. Parameer Healhy subjecs (n = 88) Hyperensive subjecs (n = 103) P Bse (mg/l) ± ± <0.001 PlGSH-Px (U/ml) ± ± NS Values are in mean ± SD; BSe = Blood selenium; plgsh-px = plasma gluahione aciviy; NS = No significan difference; and n = No of subjecs. Table 7. BSe and plgsh-px in he 3 groups of hyperensive paiens. Parameer BSe (mg/l) PlGSH-Px U/mL) Group 1 Vs Group 2 P value Group 2 Vs Group 3 P value Group 1 Vs Group3 P value ± ± NS ± ± P< ± ± P< ± ± NS ± ± p< ± ± NS Values are in mean ± SD; Group 1 = Mild hyperension; Group 2 = Moderae hyperension; Group 3 = Severe hyperension; BSe = Blood Selenium; plgsh-px = Plasma gluahione peroxidase; and NS = No significan. shed ha he values of blood selenium and plasma gluahione peroxidase aciviies for healhy aduls in his environmen is comparable wih hose from oher areas of he world where selenium concenraion in soil and crops are said o be adequae (Babalola e al., 2003). Our ineres is based on he fac ha selenium is an inegral componen of he ubiquious anioxidan enzyme, GSH-Px (Zagrodzki e al., 2000) and issues ha are highly vulnerable o oxidan damage are hose wih susained meabolic aciviies, such as he hear (Diplock, 1974) and he blood vessels. Indeed oher workers had observed ha increased oxidaive damage in paiens wih essenial hyperension, migh caused a decrease in he aciviy of gluahione peroxidase in response o increased producion of reacive oxygen species in hyperensive subjecs (Lockich, 1989). Furhermore, he fac ha epidemiological sudies have relaed low dieary selenium wih increased incidence of cardiovascular moraliy in low selenium areas of he world (Shamberger e al., 1975) suggess ha selenium probably have a role in he pahogenesis of cardiovascular disease. For he sudy, he selenium saus of hyperensive paiens was compared wih hose of healhy aduls, so as o esablish any possible associaion beween selen-ium and he disease. The cases and he conrols were comparable for mos of he confounding facors. The differences in heir mean weighs, heighs and BMIs were no significan, here was a sligh differen in heir mean ages (P<0.01), hese however fall ino he middle age bracke. From our resuls, here was significanly lower BSe in hyperensive paiens compared wih he healhy subjecs (P < 0.001). Though he mean plgsh-px aciviy was slighly reduced in hyperensive paiens compared wih he healhy group; he difference was no saisically significan. Also here was a negaive correlaion beween BSe and blood pressure and beween plasma GSH-Px and blood pressure in hyperensive paiens (r = , P<0.005 and r = , P<0.05, respecively). No such correlaions in hese parameers were found in healhy group. This aleraion in BSe level appears o confirm he elemenal basis of he aeiopahogenesis of cerain disease. The observed low BSe in hyperensive paiens also implies ha low BSe is probably a facor in essenial hyperension, eiher a predisposing facor or a consequence of he disease. This also appears o jusify he hypohesis ha selenium deficiency may render he hear suscepible o injury (Shamberger, 1978), if cenral role of selenium in GSH-Px anioxidan aciviy is considered.

5 Babalola e al However, despie he significan reducion of BSe levels, plgsh-px aciviies were no significanly differen in healhy subjecs and hyperensive paiens. There are many possible explanaions for hese discrepancies. Since he recogniion of he essenialiy of selenium, decreese dieary supplies have been associaed wih a large number of clinical condiions. Also since he discovery of GSH-Px and he recogniion of he imporance of selenium in he enzyme, aemps were made o explain he role of selenium in prevenion of many diseases as a consequence of is anioxidan effec hrough GSH-Px. Wih he discovery and characerizaion of several oher selenoproeins, i is probable ha he mechanism by which selenium exers is role on disease may no only be hrough is anioxidan acion. Secondly from earlier sudies, i was observed ha here was an excellen correlaion beween human whole blood selenium concenraion and GSH-Px aciviy only a concenraion below 0.1 mg/l (Thomson e al., 1977). However above his concenraion, he aciviy of he enzyme is no noiceably increased, which suggess eiher ha his concenraion is opimal and ha an inake ha mainained his concenraion is adequae for funcion as measured by GSH-Px aciviy, or, ha above his concenraion, oher facors may play a greaer role in influencing GSH-Px aciviy. I is probable ha since he whole blood selenium concenraion in hypenensive subjecs was above 0.1 mg/l, he blood selenium level was sill adequae o mainain he aciviy of he GSH-Px in he blood of hyperensive subjecs a level comparable o hose of he healhy conrol group. Thirdly, only abou 10% of he oal selenium in human blood is associaed wih gluahione peroxidase (Behne and Wolers, 1979). This means ha he non gluahione peroxidase selenium accouns for abou 90% of he oal selenium in human blood. Thus, he role of selenium in gluahione peroxidase may no be he only funcion of he elemen. I is probable ha he whole blood selenium fully represens oher funcional forms of he elemen, which may be associaed wih he disease. In addiion, mos selenium compounds were known o be very efficienly absorbed from he duodenum (Levander, 1984), absorbed selenium is readily aken up by he liver, eryhrocye (Griffihs e al., 1976) and many oher issues. The disribuion of selenium in human organs varies from one organ o anoher (Schroeder e al., 1970). GSH-Px represens he only funcional selenium in issue, no selenium ha has been non-specifically incorporaed ino proein or hose ha have formed biologically inacive complexes wih heavy meals (Hoeksra, 1975). Thompson e al. (1976) suggesed ha he reason for high blood selenium levels bu low blood GSH-Px aciviies in some species could perhaps be relaed o an increased level of hese non funcional selenium in he blood such as selenomehionine ha has been non specifically incorporaed ino proein as a subsiue for mehionine. Thus i is probable ha selenium inake mus be markedly low before GSH-Px aciviy can be alered significanly. Consequenly i is probable ha here may be oher funcional forms of selenium, associaed wih his disease, since he pahophysiological consequence of low BSe was no inexricably linked o change in GSH- Px aciviy. This observaion suggess ha here were "non-gluahione peroxidase" funcion of selenium. A number of physiological mechanisms are involved in he mainenance of normal blood pressure and heir derangemen may play a par in he developmen of essenial hyperension. I is probable ha here are very many inerrelaed facors ha conribue o a raised blood pressure in hyperensive paiens and heir relaive roles may differ beween individuals. Among he facors ha have been inensively sudied are sal inake, obesiy and insulin resisance, he renin-angioensin aldoserone sysem and he sympaheic nervous sysem. The pahophysiologic facors ha have been implicaed in he genesis of essenial hyperension include increase sympaheic nervous sysem aciviy, overproducion of an unidenified sodium-reaining hormone, chronic high sal inake, inadequae dieary inakes of poassium, calcium, and magnesium, increase or "inappropriae" renin secreion, deficiencies of various vasodialaory subsances such as prosaglandins and congenial abnormaliies of he resisance vessels. I is probable from he resuls obained from his sudy ha low BSe is a facor ha conribue o raised blood pressure in hyperensive paiens. There are numerous pahophysiological feaures of essenial hyperension, many of which undoubedly represen compensaory mechanism ha offse primary abnormaliy. Unlike animal model however where experimenal deficiencies of a single nurien can be produced, low blood selenium in man is only one facor in a complex se of oher variables ha may predispose o or proec agains disease. Moreover essenial hyperension is said o be a geneically based disease wih underlined inheried biochemical abnormaliies, consequenly he possible involvemen of selenium in his disorder sill need o be fully clarified. The hyperensive paiens were also classified ino hree groups based on he severiy of he disease in accordance wih WHO-ISH 1999 guidelines for classifycaion of hyperensive paiens; his is o ascerain he relaionship beween selenium and he severiy of he disease. The mean ages of he hree groups were similar. BSe concenraions were however found o decrease wih he severiy of he disease suggesing ha selenium probably have a cenral role in he pahogenesis of he disease. The mean BSe concenraion of Group 1 paiens was higher han ha of Group 2 paiens, he difference was however no saisically significan. The mean BSe concenraion in Group 2 paiens was significanly higher han ha of Group 3 paiens, also BSe level in Group 1 paiens was significanly higher han ha of Group 3 paiens. A negaive correlaion was also obser-

6 1702 Afr. J. Bioechnol. ved beween BSe concenraion and blood pressure in hyperensive paiens, his again appears o corrobo-rae he view ha selenium has a pivoed role in he pahogenesis of hyperension. Unlike BSe, however, he plgsh-px aciviies in he hree groups of hyper-ensive paiens were similar. These various observaions appear o confirm ha he severiy of hyperension is inversely relaed o he level of BSe, suggesing ha apar from he possible role of selenium in he pahogenesis of he disease, BSe may also have a role in he prognosis of he disease. REFERENCES Babalola OO, Aneor JI, Adeniyi FAA (2003) Assessmen of selenium saus of healhy adul in Souh-wesern Nigeria. ASSET Serial A 3(4) Behne D, Wolers W (1979) Selenium conen and gluahione peroxidase aciviy in he plasma and eryhrocyes of pregnan women. J. Clin. Chem. Clin. Biochem. 17, 133. Diplock AT (1974). The nuriional and meabolic roles of selenium and viamin E. Proc. Nur. Soc. 33, 315. Griffihs WM, Sewar RDH, Robinson MF (1976). The meabolism of ( 75 Se) selenomehionine in four women Bri. J. Nur. 35, 372. Schroeder HA, Fros DV, Balassa JJ (1970). Essenial race meals in man: selenium. J. Chron. Dis. 23: Hoeksra WG (1975b) Gluahione peroxidase aciviy of animal issues as an index of selenium saus. In: Hemphill, D.D. ed. Trace subsances in environmenal healh. IX, Columbia, Missouri, Universiy of Missouri Press, pp Levander OA (1984). Imporance of selenium in oal parenaral nuriion Ann. Of N. Y. Acad. Sci. 60, 144. Lockich G (1989). Selenium, Clinical significance and analyical conceps Cri. Rev. Chin. Lab. Sci. 27, 483. Moore JA, Noiva R, Wells IC (1984). Selenium concenraions in plasma of paiens wih areriographically defined coronary arherosclerosis. Clin. Chem. 30(7): Paglia D, Valenine WN (1967). Sudy on he quaniaive and qualiaive characerizaion of eryhrocye gluahione peroxides J. Lab. Clin Med Pleban PA, Munyani A, Beachum J (1982). Deerminaion of selenium concenraion and gluahione peroxidase aciviy in plasma and eryhrocyes. Clin. Chem. 28: Shamberger RJ, Tyko SA, Willis CE (1975). Selenium and hear disease. In Hemphill, D.D ed. Trace Subsances in environmenal healh IX, Columbia, Missouri, Universiy of Missouri Press pp Shamberger RJ, Gunsch MS, Willis CE, McCormack LJ (1978). Selenium in hear disease II. Selenium and oher race meal inake and hear disease in 25 counries,in Trace subsances in Environmenal Healh, Vol. 12, Hemphill D. D. Ed. Universiy of Missouri Press, Columbia, 48 Thomson CD, Rea HM, Doesburg VM, Robinson MF (1977) Selenium concenraion and gluahione peroxidase aciviies in whole blood of New Zealand residens Br. J. Nur Wesermark T, Raunu P, Kirjarina M, Lappalainen L (1977) Selenium conen of whole blood and serum in aduls and children of differen ages from differen pars of Finland. Aca pharmacol. oxicol. 40: World Healh Organizaion (1999). Inernaional Sociey of Hyperension guidelines for he Managemen of hyperension. Guidelines Subcommiee J. Hyperens 17: Zagrodzki AD, Szmigiel H, Raajczak R, Szybinski Z, Zachwieja Z (2000). The role of selenium in iodine meabolism in children wih goier. Environmenal Healh Perspecives 108, 1