Feb 13, 2003 - C. Ruiz, A. Alegria, and R. Barbera, $elenium, zinc and copper in plasma of patierits with diabetesmel1itusdifferentmetaboliccontrolstates,].
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Levels of Zinc and MagnesIum in Senile and Diabetic Senile Cataractous Lenses GÜRAYGÜNDÜZ,IFiuz GÜNDÜZ, *,2
IcLAL YÜCEL,1
AND ÜMIT KEMAL SENTÜRK2
Departments of 1 Ophthalmology, 2Physiology, School of Medicine,
Akdeniz University, Antalya, Turkey Recejved November 20.2002; Revised February 13,2003; Accepted February 14.2003
ABSTRACT Zinc and magnesium in sentm, hali, and lens were determined in diabetic and nondiabenc patienis who have been operated because of senile catamet. Both trace elements were measured by atomic absorption spectrometry, after addic digestion of the lens and hali samples. Although there was no dillerence II\ senim, lens, and hali levels of magnesium between the two groups, the lens levels of zinc in diabetic patienis (0.56:1:0.05Jlmol! g dry weight) were significantly higher as compared with nondiabetic group (O.42:tO.O3 j.lJnollg dry weight). There was no statistically significant difference in serum and hair levels of zinc betweeri. the groups. The mcreased concentration of line in the lens of diabetic patienis suggests that zinc might play a role in developmentaI mechanism of the diabetie seni1e cataraet. Index Entrles: Diabetes; lens; cataract; zinc; magnesium.
INTRODUCTION Cataract is a common cause of blindness ardund the world. Numerolis factors have been impIicated in its etiology. These invoIve genetic facters, diabetes, smoking, nutrition, the cumulative effed of X-rays, ultraviolet irradiatlon, and alteranan in both endocrine and enzymatic equilibrium (1-4). on tl1eother hand, considerable evidence indicates that free radicals such as H20:2(1) could induce the formation of lens opacities and it has been observed that the actlvity of Na-K ATPase has diminished *Author to whom all correspondence and reprint requests should be addressed. Biolagical Trace Element Research
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with age and this effect increases membrane permeabiUty (3,5).The role of trace e1ements in the formatian process of cataract have alsa been studied by many authors. Because significant alteTaHongwere found in the concentrations of some trace elements such as Zn, Cu, K, Ca, and Mg in cataractous lenses (3-8), it is accepted that these elements participate in cataractogenesis. Experimental results have shown that the concentrations of Ca and Na in cataractous lenses increase and the K concentration decreases (6). on the other hand, it has been determined that especially Zn coneentrations in eataraetous lenses alsa merease (3,5,7,8).Therefore, inorganie ions may play a role in the mechanism of cataractogenesis. it is a fad that the appearanee of eataract in diabetic patients is more frequent and ea.rlier than the normal population (4). SeveraI studies have reported on the traee element status of paHents with diabetes mellihis. zn plays an important role m synthesis, starage, and release of instilin (9) and Mg, another essential trace element, is mvolved in glucose homeostasis (10) and the release of insulin. Hypomagnesemia and law serum zinc levels have been reported in diabetes mel1itus by various authors (9-12). However, we have less information abatlt the levels of zn and Mg in senile cataractous lenses of diabetic humans. Trace elements that play important role in glucose and instilin homeostasis such as zn and Mg may be responsible for the earlier formatian process of senile cataraci in diabetic patients. This study intends to evaluate this questiol1 by comparing the content of Zn and Mg in senile and diabetic senile cataractous lenses.
MATERIALS AND .METHODS Samples were obtamed from 29 diabetic senile cataractous (Bmen, 21 women) and 35 senile cataractous (18men, 17 women) patients. The group of diabetic patients was consistent of subjects who were not recelving instilin and were diabetic for at least 10 yi. The samples of serum and haIr were obtained before operation and lenses were extracted extracapsularly from patients. The venous bJood samples that were collected in the morning after an overnight fast were analyzed for glucose by glucose oxidase method. The lens samples were stored at -Booe until measurements. The haIc and lens samples were digested in nitric acid and the serum samples obiamed !rom patients were diluted with double-distilled water for measurement. All measurements were pertormed in a polarized Zeeman atarnk absarptian spectrophotometer (Hitachi, 2-8000).
Serum Zn and Mg Measurement Venous blood was collected in Zn- and Mg-free polypropylene tubes from all subjects at 8:00 A.M.after 12 h fast. All samples were centrifuged at 1500gfor 10 min to separate the serum for the estimation of Mg and Zn. The serum samples were diluted 1/5 (viv) for zinc and 1/50 (viv) for Mg Biologlcal Trace Elememt Researc:h
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Zn and Mg in Cataracts Table 1 Fasting Blood Glucose Levels and Clinical Characteristks of Senile and Diabetic Senile Cataractous Subjects Senile cataract 68.5:1: 1.23
Age (years)
Sex(MIF)
18/17
Fasting blood glucose (mg/di)
100.9:4.01
Diabetic senile camraet 65.2:1.45 8/21 177.1:t18.85*
i 6.6:t2.5]
Duration of diabetes (year) Nate: Va1ues are mca.ri :i::SD. .. p< 0.05, differelici:!
from
the pi:itients
with
senile
cataraci.
analysis with double-distilled water. The results were expressed in micromoles per dedliter and micromoles per gram dry weight. Hair Zn and Mg Measurement The hair samples were obtained from the occipital area and washed with a dear Bolution containing acetone, ether, and Tritan-X 10% (1/1/1). After Tinsingwith distilled water, the hair samples were dried at 150°C for 12 h. All samples were digested in nittic acid and were diluted 1/10 (viv) for Zn and 1/50 (viv) for Mg analysis with double-distilled water. The results were expressed as millimales per gram dry welght. Lens Zn and Mg Measurement The nucleus and cortex materials were dried at 100°Cfor 24 h to determine their water content and were digested in nitric acid. Each sample was diluted 1/10 (v/v) for zn and 1/50 (v/v) for Mg anaIysis with doiible-distilled water. The results were expressed as micromales per gram dry weight. Statistical
Analysis
EvaIuation of statistical difference between the graups was perfarmed by using the unpaired Student's i-test. Ap-value of < 0.05was taken as statisticaUysignificant.
RESULTS The fasting blood glucose levels and clinical characteristics af the subjects in both groiips are shown in TabIe 1. The cancentrations of Zn in serum, hair, and Iens are shown in Table 2. Thecataractous lenses obtained from diabetic patients had cihigher Zn content per dry weight than senile cataractous lenses and there were no significant differences in the serum Blologlcal
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Gündüz et al. Table 2 Serum (~ol/ dL), Hali (~mol! g Dry Weight), and Lens (~ol/ g Dry Weight) Zn Concentrations Senile tataraci Dlabetic senUe tataraet
Len! 0.42::0.03 0.56::1:0.05.
Serum i .30::0.03
Halr 2.37:1:0.11
1.32:tO.06
2. 17:!:0.12
Nole: Values are mean :i:SO. . p< 0.05, difference from the patients with senile cataract.
Table 3 serum (jJ.mol/dL), Hair ijLmol/g Dry Weight), and Lens (~mol/ g Dry Weight) Mg Concentrations uns Serum Senile cataraet 12.4:!:0.8 134.5=3.4 Diabetit seaUe tataraet
11.9:1:0.9
128.8:1:5.0
~
2.4:1:0.3 2.6:!:O.2
Note: Values are mean :!:SD.
and hali zn levels between two groups. The levels of Mg in serum, hair, and lens are shown in Table 3. The Mg concentranon in the serum, hair, and lens were similar in both groups and there were no sigiiificant differences between the two groups. There was no correlanon between zinc and magnesium concentranons in lenses of both groups. There were also no differences the zinc/ magnesium ratios in lenses (O.O47:1:0.056,O.034fO.038; diabetic senile and senile group, respectively), hair (0.834:tO.6,O.988:tO.37;diabenc senile and senI1e group, respectively), and serum (0.0103:1:0.012,0.0097:!:O.088; diabenc senile and senile group, respectively) between the two groups.
DiscaSSION The results of dur study suggest that the levels of Zn and Mg in serum and hali were similar in the diabetic and nondiabetic groups. The Zn levels in lenses of diabetic patients were significant1yhigher than those of the nondiabetic group, but the Mg levels did not exhibit any difference between the two groups. It's possible that the presence of elevated levels of Zn in the lens may facilHate cataractogenesis in diabetic patients. The transpareney of the lens is conditioned by protein structure and the constiwtion and the concentration of electrolytes. in sevefa! studies, it has been shown that the levels of zn in senilecataradous lenses were elevated (3,5,8).Therefore, it has been proposed that zn may play a role in developmental process of seni1ecataract. The elevanon of zn level may damage the 1e11sby different pathways. lts elevated leVelmay lead to damage the perBlological Trace Element Researen
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Zn and Mg in Calaracts
meability of the lens membrane via oxidation of sulfhydryl group S (8),leading to the formatian of the cataract. Because of a!tered membrane perrneability, the high-molecular-weight protein and sodium accumulation may occur in the lens and this process can participate in cataractogenesis. on the other hand, excess levels of Zn in the lens may induce the formatian of metallotmonein (8). in dur study, we observed that the concentranoI1Sof zn in diabetic senile cataractous lenses were significantly increased compared to senile cataradous lenses. There is no investigation on the zinc concentration in senile cataractous rens in diabenc hwnans. However, it has been shown that the concentrat:ions of zn in cataractous lenses were increased in the Sprague-Dawley rats that were injected with streptozotodn to induce a diabetic cataract (13).This finding is in agreement with dur results. it is well known that zinc Is absorbed in the jejuni.un and ileum and the presence of glucose in the intestinallumen assists Hsuptake 04). Thus, it may be possible that the elevated glucose concentrationIn aqueous humor may participate zinc entry into the lens in diabetic patients. We alsa assessed the Zn/Mg ratios in lenses, serum, and haIr of the two group s in our study. The Zn/Mg ranos were higher in the lenses and serum of diabetic senile patients compared to the senile group, whereas the hali Zn/Mg ratio was Icwer. Although these differences were not significant, the deereaged serum Mg level indiabetic patients as reported in other studies (10)may have a role in Zn accumulation in the lenses of these patients. Competition in transportation of divalent cation could be responsible for the observed higher Zn/Mg ratiD in lenses of diabetic patients, indicating a possible antagonistic relationship between zinc and magnesium in diabetic lenses that wou1d necessiti:itefurther research. in dur study, we did not detect my sigriificant difference either in the concentranons of magnesium in lens, hair, and serum or concentrations of zinc in hair and serum between the two groups. We measured the hali zn concentration as a marker of tissue Zn level because the disulfIde bonds in the cuticular proteins of hair are major sites for the deposition of metals (15). Severa! studies in diabetic patients have proposed that there was no change in serum zinc levels (16-19), a1thcmghsome others indkate that Mg and zn deficiency may occur in diabenc patients (9-12). in conclusion, we observed that thezinc concentrations in diabetic senile cataractous lenses were significantly increased compared to the senile cataractous lenses. The elevated zinc concentrations in diabetic cataractous lenses might be involved in the increase of diabetic cataractogenesis.
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