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Original Paper |
Department of Internal Medicine "A", Internal Medicine "F" (N.C.), Assaf Harofeh Medical Center, Zerifin, affiliated with the Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, ISRAEL
Department of Nephrology (S.B., J.W.), Assaf Harofeh Medical Center, Zerifin, affiliated with the Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, ISRAEL
Address reprint requests to: Ahuva Golik, MD, Department of Internal Medicine "A", Assaf Harofeh Medical Center, 70300 Zerifin, ISRAEL.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONPATIENTS AND METHODSMETHODSRESULTSDISCUSSIONREFERENCES |
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Methods: Patients with newly diagnosed essential hypertension were randomly divided into two treatment groups: those treated with captopril only (n=16) and those treated with enalapril only (n=18). Ten healthy subjects served as controls. Prior to the start of treatment and again 6 months later, zinc was assessed in the serum, in urine collected over 24 hours, and in peripheral blood monocytes.
Results: Significant enhancement of 24-hour urinary zinc excretion (µg/24 hour) after 6 months of treatment was observed only in the captopril-treated group (p<0.01). However, intramonocytic zinc levels decreased significantly in both of the treated groups over the same period (p<0.01 and p<0.04 in the captopril- and enalapril-treated groups, respectively).
Conclusion: Treatment of hypertensive patients with captopril or enalapril may result in zinc deficiency.
Key words: ACE inhibitors, zinc metabolism, hypertension
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONPATIENTS AND METHODSMETHODSRESULTSDISCUSSIONREFERENCES |
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Captopril and enalapril are ACE inhibitors with different structures: captopril has a sulphydryl group (SH) while the enalapril is a carboxyalkyl peptide [2]. There is a possibility that the ability of the SH group of captopril to bind to bivalent metals induces a state of urinary zinc loss.
Zinc plays an important role in bone formation, cell-mediated immunity, host defense and tissue growth [3]. The multiplicity of functions in which zinc is involved is due to its participation in specific metal enzyme systems. Zinc has three functions in zinc-dependent enzymes: catalytic, co-catalytic and structural. Zinc may also be involved in regulating the amount of an enzyme that is synthesized [4]. It is now evident that zinc deficiency may occur in many clinical situations, including malabsorption syndromes, chronic renal disease, chronic liver diseases, sickle cell anemia [5,6], and as an effect of various drugs such as penicillamine [7], diuretics and ACE inhibitors [1,8,9]. However, clinical diagnosis of zinc deficiency in humans remains problematic, since plasma or serum zinc concentrations do not reflect the changes in zinc status brought about by different factors. It has been suggested that zinc in the leukocytes might give a more accurate reflection of tissue zinc content [10].
To the best of our knowledge, no prospective studies have investigated the effect of chronic treatment with ACE inhibitors on zinc metabolism. In this prospective study, we examined the hypothesis that ACE inhibitors may cause zinc deficiency by studying the effects of captopril and enalapril on zinc levels in the serum, monocytes, and urine of hypertensive patients.
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PATIENTS AND METHODS |
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TOPABSTRACTINTRODUCTIONPATIENTS AND METHODSMETHODSRESULTSDISCUSSIONREFERENCES |
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After randomization, 22 patients (12 males, 10 females) were treated with enalapril (Assia/Riesel, Israel) and 20 patients (10 males, 10 females) with captopril (Squibb, Pharmabest, Israel). Ten healthy subjects on the medical staff volunteered to serve as a control group. For each patient in the captopril-treated and enalapril-treated groups, the drug dose was determined by titration until normal blood pressure (systolic <140 mm Hg, diastolic <85 mm Hg) was achieved. In cases where the goal blood pressure was not reached after 2 months of treatment, the patient was excluded from the study.
Four patients on captopril dropped out during the study, two because of the need to add another antihypertensive drug, and two because of dizziness and cough. Two patients on enalapril did not complete the study, one because of headache and one because of uncontrolled hypertension. A total of 46 subjects (including the 10 healthy controls) completed the study.
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METHODS |
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TOPABSTRACTINTRODUCTIONPATIENTS AND METHODSMETHODSRESULTSDISCUSSIONREFERENCES |
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Aldosterone and plasma renin activity were assessed by radioimmunoassay. Electrolytes were measured by flame photometry.
Isolation of Human Monocytes from Peripheral Blood
Isolation of Peripheral Blood Mononuclear Cell (PBMC) Population.
Blood from a peripheral vein was withdrawn by vacutainer into Li Heparin precoated test tubes (Becton-Dickinson, England). Blood samples (20 ml) were transferred to 50-ml sterile polypropylene containers and diluted 1:1 with phosphate-buffered saline (PBS). The PBMC fraction was isolated by Ficoll-Hypaque (Pharmacia, Sweden) gradient centrifugation. Briefly, four 15-ml conical test tubes containing 2 ml of Ficoll-Hypaque solution were prepared for each blood sample. The diluted blood was carefully laid on the Ficoll layer (10 ml of diluted blood per tube) and the test tubes were centrifuged for 20 minutes at 1400 g. The PBMC layer was carefully collected, washed three times in PBS and resuspended in 1 ml of RPMI 1640 cell culture medium (Biological Industries, Israel). Cells were counted in a hemocytometer in 4% Turk solution. Viability was assessed by 0.1% eosin exclusion. Only those samples with viability of at least 90% were used for isolation of monocytes.
Isolation of the Monocyte Fraction from the PBMC Population.
PBMC were resuspended in 5 ml of RPMI 1640 and the test tubes were placed horizontally on ice on a rocking device. Under these conditions monocytes form large aggregates, a process unique to the monocyte fraction according to Mentzer et al [11]. After 30 minutes the test tubes were placed vertically on ice for 15 minutes, allowing the monocyte aggregates to sediment at unit gravity. For further purification, 3 ml of cold fetal calf serum (FCS) were added to the tubes, which were then left on ice for a further 15 minutes. The aggregates were resuspended in 10 ml of warm RPMI 1640 and incubated at 37°C for 30 minutes in a Petri dish. The medium was then discarded and replaced by a fresh portion of RPMI 1640, and the cells were washed twice and pipetted vigorously to disperse the remaining aggregates. The cell suspension, representing the purified monocyte population, as confirmed by routine cytological staining [12], was counted and checked for viability as described, and stored in 1 ml of PBS at -30°C.
Determination of Zinc in Monocytes
Monocyte zinc content was measured in all cell samples at the same time, using the same matrix and the same standard curve, by procedures described earlier for other mononuclear [11,12]. Cell populations monocyte number were the same throughout the study. The monocyte samples were defrosted, 1 ml of concentrated NaOH was added to each tube, and the samples were left at room temperature until the cells were completely digested. The samples were then diluted 10 times in distilled water, and zinc concentration was measured using an atomic absorption spectrophotometer (Spectra AA 800, Varian, Australia). The results were calculated as µg zinc per mg, per 1x106 cells or per protein content.
Statistics
Student’s t-test was used to compare pre- and post-treatment results in each group. Comparisons between the groups were performed using one-way analysis of variance.
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RESULTS |
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONPATIENTS AND METHODSMETHODSRESULTSDISCUSSIONREFERENCES |
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Captopril and enalapril are ACE inhibitors producing their action by having a prominant zinc binding moiety which binds to zinc in the active site of the ACE. In the captopril group, the binding site contains a sulphydryl group (SH) while in the enalapril, it is a carboxyalkyl dipeptide group. In addition to the direct binding of zinc to captopril and enalapril, the SH group of captopril may interact with intracellular sulfhydryl containing compounds (such as glutathione) thus changing the protein structure or function.
Current methods for clinical evaluation of zinc status may be inadequate. Zinc concentration in plasma or serum, the most common and readily available measure of zinc status, is subject to a wide variety of influences not necessarily related to zinc nutrition [13,14]. It has been suggested that zinc in the blood cells (leukocytes or erythrocytes) may give a more accurate indication of tissue zinc content [8,15]. Prasad and colleagues found that in elderly patients with mild zinc deficiency, plasma zinc was normal, but zinc levels in the granulocytes and lymphocytes were decreased. Other parameters for detecting zinc deficiency were decreased interleukin 2 production by peripheral blood mononuclear cells, decreased natural killer activity and alterations in T lymphocyte subpopulation [16].
In this study, however, we measured zinc levels in monocytes. In a study of zinc metabolism in Crohn’s disease [17], it was reported that zinc depletion in these patients is better reflected by intramonocytic zinc levels than by the levels in lymphocytes or polymorphonuclear cells.
In an earlier study, it was reported that continuous excessive loss of urinary zinc in patients on captopril therapy eventually results in a decrease in erythrocyte zinc content which may contribute to zinc depletion [1]. The results of the present study suggest that zinc deficiency can also be detected by monitoring zinc levels in monocytes.
The clinical significance of the present findings is not yet known. Abu-Hamdan et al [18] found that patients treated with captopril exhibited abnormalities of taste acuity, and suggested that this might be associated with lower zinc plasma levels and higher zinc excretion. Captopril and enalapril are widely used for treating hypertension and congestive heart failure and for preventing renal deterioration in diabetic patients. These medications are given on a chronic basis, so it is important to recognize their long-term effects and, if necessary, to take steps to remedy any induced zinc deficiency. The clinical manifestations of zinc deficiency include growth retardation, male hypogonadism, skin changes, poor appetite, mental lethargy, abnormal neurosensory changes, delay in wound healing, and susceptibility to infection [2,5,6]. It is possible that zinc deficiency might account for some of the side effects of ACE inhibitors, such as taste disturbances, paresthesias and poor appetite.
Received December 1, 1997. Accepted May 1, 1997.
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REFERENCES |
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This article has been cited by other articles:
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  C. Kojima, A. Kawakami, T. Takei, K. Nitta, and M. Yoshida Angiotensin-Converting Enzyme Inhibitor Attenuates Monocyte Adhesion to Vascular Endothelium through Modulation of Intracellular Zinc J. Pharmacol. Exp. Ther., December 1, 2007; 323(3): 855 - 860. [Abstract] [Full Text] [PDF]
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