Document jmmRybkL68oV59d85pZ244aNk

y The Biochemistry of Lead: Review of the Body Distribution and Methods of Lead Determination ELEANOR BERMAN, Ph.D.* Lead is a cumulative poison. Though prevalent in man's environment, only a fraction of what is ingested is absorbed. Slow .acting and subtle, lead is powerful and produces a variety of symptoms with many body tissues vulnerable. T JLyEAD is prevalent in modern man's environ* ment, but its concentration varies from area to area. Soils of highly industrialized areas may contain up to several thousand parts per million, and soil in agricultural New Jersey show* a lead content of 13.9 to 95.7 ppm. Kehoe * found that an average adult's lead intake is from 0.1 mg. to 0.6 mg. daily. Routes of Lead Absorption The routes of lead absorption are governed by its chemical structure. Lead salts do not penetrate intact skin, but can be absorbed through abra sions. Significant amounts can also be absorbed from a byllet or shot wound, with lead shot conf sidered particularly dangerous because of its larger surface area permitting greater absorption. There have been reports of lead poisoning occurring within a month after a bullet wound. Organic lead compounds, such as tetraethyl lead in gasoline, rapidly penetrate the intact skin. Ab sorption into body tissues is more rapid with the organic than with the inorganic compounds, and also because of their higher lipid solubility, large amounts gain access to nerve tissue. Following absorption, lead is rapidly released in the body from organic combination. Vapors of organic lead compounds are also highly dangerous. One ol the two major routes of absorption of lead salts is the gastrointestinal tract. Most cases of lead intoxication in children result from lead As of May 1. i960. Toxicologist, Hektoen Insti tute of Cook County Hospital. Chicago, Illinois. CLINICAL PEDIATRICS May 1966 ingestion. Motor activity of the bowel is the only factor which significantly Influences lead absorp tion by this route. As the speed of evacuation decreases, lead absorption increases. The reverse is also true. The respiratory tract is the other major route of lead absorption. Most industrial cases and a few children's poisonings follow inhalation of lead dust or fumes. In 1925. Blumgart and Minot9- * demonstrated that lead can be ab sorbed from all portions of the respiratory tract in cluding tiie nasal passages. Absorption from these areas is actually much more rapid and complete than from the gastrointestinal tract. Goodman and Gilman* state that the mechanism of lead absorption from the respirators' tract may be in fluenced by two factors: (1) the high carbon di oxide tension present creates an acid medium, causing solution of the lead particles; and (2) it is also possible that particles may be phagocytized and, thus, gain access to the circulation. Tissue Distribution of Lead Following absorption, lead is distributed to various tissues, with highest soft tissue concen tration being in the liver and kidney. Lead quickly leaves soft tissue for deposition in bone as the relatively insoluble tri-lead- phosphate. Though the site of deposition is in controversy, it is generally believed to be the cancellous and compact tissue. Long bones contain more lead than flat bones. During the early period of lead deposition, especially in growing bone, concentration is highest in the epiphyseal portion. Skeletal lead is fairly inert, and the metal learn the skeleton only very slowly. Under certain metabolic con ditions, however, such as a slight acid-base dis turbance or an upper respiratory infection, lead may suddenly be mobilized from bones and an acute lead intoxication may be precipitated. E. M. Butt,* during his investigations of trace metal patterns in disease states, found that nor ma) control tissues held the following contents 287 I' i' i**2 i-".. I I / BERMAN Ta bl e 1. head Content of Fresh Tissuefrom 7't.v Children with Lead Tntoxicalion Tiuue bom (rib) Heart Liver Luna Lymph bode Spleen Thymu* Free* Kidney Brain Cave A (roii.,'100 Cm.) 3.84 0.133 O.OVJ J.US 0.024 0436 >. 0.371 2.27 Vot mbmiued Not rubmitted Cw b mu.lU0G:n.) Not fubmimd Nut Submitted Not Hjbmhied Not tubmitt+d Not tubmitted Not rubmitird 4.4 Not >ubmit led Not tubmhled 4.0 3.0 of load per 100 Cm. of dry tissue: liver, 0.79 mg.; kidney, 0.42 mg.; heart. 0.21 mg.; brain. 0.51 mg.; lung, 0.46 mg.; spleen, 0.51 mg.; pancreas, 0.57 mg.; and adrenal, 0.50 mg. In Comings'* compilation of reported lead levels in tissues of normal adult subjects deter* mined since 1940, brain was found to contain up to O.il mg./100 Gra. of fresh tissue; liver up to 0.5 mg.; kidney up to 2.2 mg. and rib up to 2.8 mg. Values for tissues from children with no history of lead exposure were not presented. It is expected that these would be much lower. Jn his compilation of reported lead levels in tissues in encephalopathies due to exposure to inorganic lead, brain was reported to contain up to 1.7 mg. per 100 Gm.; liver up to 26.1 mg.; kidney, up to 9.5 mg. Kehoe7 found normal liver to contain from 0.04 to 0.28 mg. of lead per 100 Cm. of fresh tis sue. Levels in bone from apparent normals varied from 0.67 to 3.59 mg. per 100 Cm. On the other hand, bone from those with lead intoxications held concentrations 20 to 30 times greater. Brain tissue taken from cases of encephalopathy con tained levels varying from 0.2 to 0.6 mg./lOO Cm. Ta bl e 2. Comparison of Blood Lead Lnels in Children Lead Level mcg.% Cases Not Considered as Lead Intoxicadon Clinically Cases Dignosed as Lead Intoxication 0-20 45 0 21-40 12 14 41-50 89 51-60 21 61-70 15 71-80 0 12 81-100 0 11 101-150 0 8 151-200 0 5 201-300 0 5 We had occasion to determine the lead content in tissues obtained at autopsy from two cases of lead intoxication. The findings are outlined in Table I. Case B was of special interest. This child was a two-year-old female admitted with signs of encephalopathy. She was afebrile. Previous history was nomontr.lbutory. Laboratory findings --blood, urine, spinal fluid--were not remarkable. The child expired in less than 24 hours following admission. .Autopsy findings were also lion-illumi nating. To determine tissue lead contents was an after-thought. Lead Excretion The excretion of lead is mediated in part by the gastro-imesrinal and urinary tram. Lead is also excreted in the sweat, the concentration here being similar to that in the urine. Balance studied show that all but 5 to 10 per cent of ingested lead is absorbed, but a portion of this is excreted back into the gastrointestinal tract and evacuated. An average adult excretes approximately 0.3 mg. lead into the feces and 0.03 mg. in die urine daily. Fecal lead mostly represents lead that was ingested, but not absorbed. Urinary lead indicates the degree of lead absorption, and concentrations above 15 mg./liter in adults and 0.08 mg./liier in children are considered dangerous. Blood Lead Levels Blood levels also indicate the dtgree of lead absorption, but these are of value only in acute cases since the blood is rapidly cleared of lead. Blood levels in chronic cases are not remarkable. What constitutes a'diagnostic blood lead level is a point of dispute. The older literature consid ered a blood lead level of 0.07 mg. per cent (70 mcg.%) as still within normal limits for an adult. We found that 100 adults admitted to Illinois Masonic Hospital for a variety of problems, but presenting neither history nor clinical evidence of lead exposure, had lead levels below 20 meg. per cent. Forty-five of 68 children seen at Cobk-County Hospital and considered not to be cases of clinical lead intoxication had levels of 20 meg. per cent or below. Twelve others in this group .showed lead -contents as high as 40 mrg. per cent. Ten had levels between 40 and 60 meg. per ce(nt. Only one had a level as high as 70 meg. per cent. Not one rase of another group of 70 children diag nosed as clinical lead intoxication had a level below 20 meg. per cent. Fourteen of these showed levels between 21 and 40 meg. per cent. Fifteen had lead levels between 41 and 70 meg. per cent and 41 of the group had higher levels. A com- 288 Vel. 5 No. 5 CLINICAL FEOIATHICS GLD35159 i i 1 BIOCHEMISTRY OF LEAD pamon of the distribution of lead levels in clinical lead intoxications and other ill children at Cool. County* Hospital is Illustrated in Table 2. On the basis of these figures we fee! that perhaps blood lead levels should now be interpreted as follows: 0-21 meg. per cent--negative 21-60 meg. per cent--evidence of increased lead exposure above 60_rotg. per cent--lead intoxication indi cated Since.Jead dears the blood stream fairly rap idly, a -blood lead level alone may not be suffi cient-to substantiate the diagnosis of lead intoxi cation. Urine lead content is also of value. Table 5 lists the comparison of Jead contents found m urine from a series of children. Care was taken to eliminate the possibility of contamination during the collection process. All with clinical symptoms of lead intoxica tion excreted-more than 80 mcg./L. of urine. Kehoe considers _ a urinary lead concentration above that level as dangerous in children. Blood values in many of the urinary 80-250 meg. group ranged between 20 and 40 meg. per cent. The protean" expressions of lead poisoning de velop as increasing concentrations gain access to the circulation. It was formerly believed that lead circulated as a salt (diphosphate, diphosphoglyccrate, citrate, or lead and calcium phosphate). It is now known, however, that over 90 per cent of the circulating lead is associated with the erythrocyte. Lead added to blood rapidly com bines with cells and is removed from plasma. Lead also injures the red cell surface and causes mild hemolysis. Lead also interrupts porphyrin metabolism and, no doubt, interferes with other metabolic path ways as well. Heavy metals are known to inactivate many enzyme systems and Wairach * reports de generation of cellular mitochondria in lead poison ing. Enzyme systems are now known to be con centrated in the mitochondria. Methods for Lead Analysts The literature is rich with descriptions of pro cedures for lead analysis. Various analytical tech nics applying spectrography, polarography, or colorimetry have been employed in industry for the determination of lead in blood, urine, and other materials.4 Each of these procedures leaves something to be desired under clinical pediatric conditions. A fairly large sized sample is usuallyrequired for analysis, and the time consumed in the analytical prcxedurc renders results so ot> tained of academic interest only. Ta b l e 3. Lrnd ConUnts Vrine of Cbildttn Content mcg./L 0-60 61-80 81-230 251-350 351-500 500-1,000 . Above 1.000 Cases N`ot Cases DugConsidered (.eat! nosed as I.ead Intoxicated Intoxicated 23 5 10 3 0 16 05 08 06 0 15 Some modification of a colorimetric technic in volving the formation of a colored complex of lead and dithizone is the most frequently em ployed technic in lead determinations in clinical laboratories. Though this method is sensitive, it lacks specificity. Approximately 17 heavy metals including thallium, cadmium, and mercury form colored complexes with dithizone. With the ex ception of thallium, all possible interfering ele ments are eliminated in the procedure prior to the formation of the colored complex. Even an experienced and careful chemist may upon oc casion mistake thallium for lead and vice versa, unless prewarned by an adequate description of physical findings. JPolarography, though fairly suitable in indus trial screening programs, lacks the sensitivity nec essary to make it a useful tool in a clinical lab oratory. An emission spectrograph is a sensitive but expensive instrument. Emission flame spec trometers which are used for routine sodium and potassium analyses do not possess the sensitivitynecessary for lead analyses in a clinical laboratory. ' In 1962,10 Willis in Australia reported on the application of atomic absorption flame spec trometry- to the determination of lead and other trace metals in urine. This instrumentation, pre viously used in analyses of copper in soils and calcium and magnesium among others in serum, has proved to have the sensitivity and specificity desired for clinical procedures. Adapting a previously established colorimetric method to the Perkin-Elmer Atomic Absorption Spectrometer model 214 enabled us to determine the lead content in blood. An analysis requires but one and one-half hours. For routine screening purposes a 5 ml. sample is adequate. During the acute phase when blood lead levels are markedly elevated, the determination can be done on a lesser quantity, at times even as little as 1 ml. Atomic absorption spectrometry possesses the sensitivity to detect less than 0.2 ppm. (20 mcg.%. 200 mcg./L.) lead in an aqueous solution. This CLINICAL PEDIATRICS May 1966 289 GLD35160 BERMAN Tic. 1. Perkins-Elmer Atomic Absorption Spectrome ter, model 2)4 used in determining lead content in the blood. implies that urine specimens with an abnormal content of lead can be detected by screening with a minimum of sample preparation. Since the other urinary constituents do not interfere with this determination, a centrifuged urine specimen is merely aspirated into the instrument. Lead analy ses can thus be completed in less than a minute. When excretory levels are less than 0.2 ppm. the lead present can be concentrated by Erst chelating the metal in the urine sample with am monium pyrollidine dithiocarbamate and then extracting a SO ml. aliquot into a 5 ml. volume of organic solvent. Tim takes less than SO min* utes.1 The instrument used in these analyses is shown in Figure J. We observed that the Jead verscnaie complex excreted during versenate therapy is not removed from the aqueous phase by this procedure. Thus, by applying atomic absorption spectrometry, we hoped to learn more about the nature of lead excreted during the phases of versenate therapy. Findings in specimens kindly sent to use from four cases treated at Michael Reese Hospital are shown in Table 4. Total lead was determined by direct aspiration. "Unbound lead'* is that quantity which was extractable into the organic phase. In-some instances coproporphyrin levels were also deter mined. All patients described in Table i presented his torical and clinical evidence of lead, intoxication. Blood levels were in an abnormal range of 41-82 meg. per cent. Initial urinary, lead concentrations, however, except in one case, were not remarkable. Following the initiation of BAL-versenate ther apy. total lead excretion increased three to ten fold and then gradually fell. Less than 2 per cent of the lead excreted during treatment was in the unbound state. The lead-versenate complex ap peared to be excreted slowly. Seven days after cessation of therapy. 75 per cent of the lead ex creted was still in the bound state. Patient R.M. F.. Q. K.T. j.R. Ta b l e 4. Lead end Copreporphyrin Excretion During Versenate Therapy Date 11/16 11/23 11/24 11/25 11/26 12/4 12/21 11/16 11/22 11/23 31/23 11/27 11/28 12/3 11/11 11/15 11/27 11/16 11/20 11/20 12/4 Blood Lead MR-ft Total Urine Lead .A Unbound Coproporphyrin Lead *>g./l. % Unbound % Bound jig./24hr. 58*.g.rj 60j*g./l. 313 Initiate therapy to 11/28 5,030 00 100 5.2 1.100 20 1.8 98.2 10.8 2.600 40 1.5 98.5 9.7 100 25 25 75 93 7 41 350 Kol done Initiate therapv to 11/27 1,050 00 100 2.3 1.400 23 1.6 98.4 11.7 300 33 11 89 4.8 200 50 25 75 -- 23 100 69 69 31 24 58 33 Initiate therapy to 11/20 198 43 22 329.3 78 82 56 initiate thcrapv to 11/25 2.300 30 30 250 60 1.3 24 76 556 12.4 150 290 Vel. S No. 5 CLINICAL PEDIATRICS GLD35161 BIOCHEMISTRY OF LEAD Urinary coproporphyria levels also decrease durii.g therapy, before treatment, levels excreted bythree subjects were SIS, 329, and 556 meg. per 24 hr. with the upper limit ol normal being ap proximately 120 >g. per 24 hr. During therapy, coproporphyrin levels dropped to 12 #ig. or less and then increased. In one instance the level rose to 150 *g. per 24 hr. ten days after cessation of the versenate. Preliminary data such as these, though admit tedly incomplete, suggest strongly that here a means of more adequately studying lead metabo lism in treated and'untreated patients. References 1, Berman, E.: Atomic Absorption Newsletter S: 111, 19&4 2. Blumgart, H. L.t J. Indust. Hyg. 6: 155. 192$. 5. Butt. . M. et el.: Metal Binding in Medicine. Philadelphia, j. B- Lippincott Co.. I960, pp. 45 ff. 4. Cholak, J.: Arch. Environ. Health 8: 222. 1964. 5. Comings, J. N.: Heavy Meuls and the Brain. Springfield, 111., Charles C Thomas, 1959, pp. 95 ff. 6. Goodman. E. S. and Gilman, A.: The Pharmaco logical Basis ol Therapeutics. New York, The Macmillan Co., 1955. ?. Kehoe, R.: Arch. Environ. Health 8: 252, 1964. 8. Minot, A. S.: J. Indust. Hyg. 6: 125, 1924. 9. Watrach, A. M.: J. UUrastnict Res. 10: 177, 1964. 10. Willis, J. B.: Anal. Chem. 34: 614,1962. READER'S CHECK UST (* >ntinued from page 275) land and Sweden. Pertinent to the newborn period there are discus sions dealing with physiology, re spiratory and circulatory adapta tions. hypoglycemia, respiratory dis tress, idiopathic hypoglycemia, and the late effects of obstetric hazards. There are excellent surveys also of contemporary knowledge of chro mosomal abnormalities, obesity, kwashiorkor, renal biopsy, disorders of growth, cancer, steroid treatment of asthma, hydrocephalus, and spina bifida cystica. x In short, here is a refresher course for the physician in practice, within the framework of the subjects cov ered. * Hematology Atlas of Haematology. G. A, Me. Do n a l d . T. C. Do d d s , and B. Cr u j c k s h an k . Baltimore, Williams and Wilkins, 1965. 163 pp. $10.50. An extensive and carefully se lected collection of magnificent blood ami bone marrow photo graphs. Though presented as being primarily for ''trainees'* in hematol ogy, this can serve as a useful ref erence for all who work in clinical laboratories. Many photographs of organ biopsies and of cell appear ances under phase contrast micros copy are included. Most of the sniMi* are stained with either Lcislv man's or the May-Grunwald-Giemsa method, but the appearances with these are not significantly different from what one sees with Wright's stain. Along with the text comes a separable poster-like colored chart showing the morphologic changes of the major cell series during matu ration. Referral Book American Pediatric Directory, 1965-1966. 12th td. Jo e T. Smit h . M.D., F.A.A.P., Editor and Pub lisher, 1SOO Magnolia Ave.. N.E.. Knoxville, Term. $12.00. "A Roster of Pediatricians of the United States and Canada, with Complete Professional Biography" (from the Preface). Therapy A:ew Drugs, Evaluated by the A.M.A. Council on Drugs, 1961. Chicago, 111,. American Medical Association. 5)6 pp. "The drugs that are discussed in detail are individual agents, gener ally available in the United States, that have been introduced within the past ten years. The statements on each of these drugs are based on an evaluation of the available lab oratory and clinical evidence by the Council and its consultants.'' Nearly 500 such drugs are arranged and discussed according to therapeutic purpose. Without question this is the most authoritative and all-in clusive reference of its type (or the practicing clinician, inasmuch as all statements made hare been ap proved by at least six independent consultants. Neuromuscular The Chemistry and Therapy of Disorders of Voluntary Muscles. E. C. Muawsv, M3., D.C.H., To ronto. Springfield, ID., Charles C Thomas, 1964. 123 pp. $6.50. An outline-like review p! "the main features" of die two facets mentioned in the title. Therapeutics Diets for Sick Children. D. J. W. Dix o n , Former Senior Dietitian. Hospital for Sick Children. Great Ormond Street, London. Oxford, Blackwood; Philadelphia. F. A, Davis Co., 1965. Ill pp. $2.50. A valuable paper-hack compen dium of diet lists and ancillary in structions for use in a wide variety of childhood illnesses. CUN1CAL PEDIATRICS Mo* 1966 291 GV.