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JLAR EFFECTS OF LEAD 

21 

R. A. Goyer and J. F. Moore 

Department of Pathology 

University of North Carolina at Chapel Hill 

The particular level of exposure to lead which results in an 

adverse healch effect is related to many factors including "critical organ content," route of administration and a number of metabolic and nutritional factors (Goyer and Mahaffey, 1972). Important considerations related to toxic manifestations of a heavy 

metal are its distribution among subcellular components and interaction with cellular function and whether it is complexed to a 

diffusible ligand or is bound to a non-diffusible complex. This 

paper is a review of available information regarding the subcellular distribution of lead, effects on cellular organelles and the 

relationship of these effects to symptoms of lead toxicity, and is 

modified from an earlier working paper submitted to a task group 

on metal accumulations (Goyer, 1972). 

SUBCELLULAR LOCALIZATION OF LEAD 

A number of techniques have been employed for measuring the 

subcellular distribution of lead. Uptake of radioactive lead isotopes at different time Intervals following intravenous administration provides a dynamic model whereby animals can be sacrified, 

and the subcellular distribution of labelled lead measured in 

cellular compartments following separation by differential centrifugation. Castellino and Aloj (1969) determined the distribution 

of lead in nuclei, mitochondria, microsomes and cell sap of liver 

and kidney of rats for 9 days after the intravenous injection of 

Lead entered the cells within one hour after injection. 

In the liver within the first 24 to 72 hours there was a decrease 

in radioactivity in the nuclear fraction and an increase in mitochondria; microsomes and soluble fractions remained stable. These 

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448 R. A. GOYER AND J. F. MOORE 

relative distributions remained constant for nine days. On the 

other hand, in the kidney relative increases of lead in both nuclear and mitochondrial fractions occurred during the first 24 

hours with a decrease in microsomes and little change in the soluble fraction. After 24 hours the distribution reached a steady 

state. Mitochondrial binding of lead was remarkably strong and 

resisted many washings. None of the rats had been pre-exposed to 

excessive amounts of lead. 

i -

A similar experiment was reported by Bar Itr ori and coworkers 

(1971). They measured the subcellular distribution of lead in 

heart, liver, kidney and spleen following intraperitoneal administration of 203pb. cells were fractionated into nuclear, mitochondrial-lysosomal, microsomal and soluble fractions between 2 hours 

and 14 days after administration of the isotope. Renal tissue was 

further separated Into lysosomal and mitochondrial fractions; 

most of the lead was in the mitochondrial fraction. However, pretreatment of the rats with lead diminished the in-vlvo uptake of 

radioactive lead by the mitochondria suggesting that lead binding 

sites on the mitochondrion may be saturated. However, isolated 

rat liver mitochondria incubated with lead form lead-containing 

granules in the inner compartment (Walton, 1973). Formation of 

these granules requires the presence of substrate and ATP and is 

reduced in the presence of metabolic inhibitors such as actlnomycin A or dinitrophenol suggesting that lead accumulation in mitochondria is an active, energy-dependent process. 

Direct measurement of lead content of subcellular components 

of the rat kidney has shown that the major fraction of the lead is 

present in the nucleus of both control and lead toxic rats but 

during excessive exposure to lead by far the greatest increment is 

in the nucleus (Goyer et al., 1970b). 

NUCLEAR INCLUSION BODIES 

A characteristic cellular reaction in lead Intoxication is 

the formation of discrete, dense staining, intranuclear Inclusion 

bodies. These were initially observed by Blackman (1936) some 37 

years ago in hepatic parenchymal cells and renal tubular lining 

cells of children dying of acute lead encephalopathy. More recently 

they have been reported in livers and renal tubular lining cells of 

•wine (Watrach and Vatter, 1962), dogs (Stowe et al, 1973), rabbits 

(Hass et al., 1964), fowls (Simpson et al., 1970) and ln kidneys 

only of rats (Goyer, 1968). 

The ultrastrueture of a typical inclusion body in the nucleus 

of a renal tubular lining cell of a lead-Intoxicated rat consists 

of a dense central core and an outer fibrillary zone. They are 

always independent of nucleoli. Inclusion bodies vary considerably 

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iOYER AND J. F. MOORE 

' days. On the 

ead in both nuthe first 24 

ange in the soleached a steady 

'bly strong and 

"\ pre-exposed to 

o and coworkers 

on of lead in 

rltoneal admininuclear, mitochonbetween 2 hours 

Renal tissue was 

•1 fractions; 

n. However, pre-

-vivo uptake of 

nat lead binding 

ever, Isolated 

ead-contalnlng 

Formation of 

and ATP and is 

:uch as actlnoumulatlon ln mlto-

.lular components 

on of the lead is 

oxic rats but 

icest increment is 

ntoxication is 

.uclear inclusion 

.n (1936) some 37 

tubular lining 

•chy. More recently 

ar lining cells of 

al, 1973), rabbits 

and in kidneys 

>dy in the nucleus 

ted rat consists 

one. They are 

vary considerably 

CELLULAR EFFECTS OF LEAD 449 

in siz e and in rati o of core to outer fibrils (Bracken et al. , 

1958; Beaver, 1961; Richter e t al. , 1968). Richter e t al. (1968) 

estimate the thickness of the fibrils to range from 100 £ to 130 £ , 

although the siz e of fibrils varie s with fixation and staining procedures. A fine structure to the fibrils (periodicity) has not 

been observed. The composition of lead-induced intranuclear inclusion bodies has been further studied by histochemistry, autoradiography and by direc t analysis after isolation. Histochemical 

studies have been summarized by Richter e t al. (1968). Inclusion 

bodies do not stain with the Feulgen reaction, although they are 

sometimes surrounded by Feulgen-positlve material; They do noc 

stain with fast green after treatment with trichloroaceti c acid, 

but do stain strongly with mercurial bromophenol blue and by basic 

fuchsin suggesting they contain protein, but probably not histones. 

The basis of the acid-fast reaction is uncertain; i t may simply be 

a physical phenomenon. Landing and Nakal (1959) showed that the 

inclusions contain at most small amounts of lipid and suggested 

the acid-fast properties of these bodies were related to the presence of sulfhydryl groups in the protein. 

The presence of lead in the inclusion bodies was suspected 

but unproved for many years. Finner and Calvery (1939) stained 

sections of kidneys from lead poisoned rats with hydrogen sulfide 

and found particle s of lead sulfide occurring In nucle i of tubular 

epithelia presumably corresponding to intranuclear inclusion bodies. 

Other attempts to identify the metal either histochemlcally or by 

x-ray diffraction have been unsuccessful (Watrach and Vatter, 1962). 

More recently, lead within the intranuclear Inclusion body has been 

positively demonstrated by autoradiography (Dallenbach, 1965) and 

electron-probe x-ray microanalysis (Carroll e t al. , 1970). 

The structure and composition of the inclusion bodies have 

been further studied after isolation by differentia l centrifugation 

and sonication (Goyer e t al. , 1970b). Treatment of Inclusions in 

tissue sections (Richter e t al. , 1968) or Isolated inclusion bodies 

(Goyer e t al. , 1970b) with proteolyti c enzymes results in partial 

digestion, but they are not altered by incubation with DNAase or 

RNAase. Direct chemical analysis of Isolated inclusion bodies confirms that they are composed of a lead-protein complex containing 

approximately 50 ug of lead per mg protein. Lead within the inclusion bodies is 60 to 100 times more concentrated than whole kidney 

lead (Goyer e t al. , 1970b; Horn, 1970). Amino acid composition and 

solubilit y characteristic s of the Inclusion body protein resemble 

those of the residual acidi c fraction of proteins in normal nucle i 

(Goyer et al. , 1971). 

The protein has high content of aspartic and glutamic acids, 

glycine , cystine , and tryptophan. The inclusion bodies are insoluble ln physiological media but may be dissolved in denaturants 

9m <*-m.'t3m&**rt^Ji i.dimiiaKij^wsi&tm't^^ 
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450 R. A. GOYER AND J. F. MOORE 

like 6 M urea and sodium deoxycholate. The lead is removable by 

incubation in-vitro with chelators like EDTA. In this circumstance 

the inclusion body loses its typical morphological structure and 

becomes an amorphous protein residue which continues to be insoluble (Moore et al., 1973). The inclusions also contain lesser 

amounts of other metals including calcium, iron, zinc, copper and 

cadmium in order of decreasing concentrations. 

A scheme has been proposed for the possible role of the intranuclear inclusion body In lead poisoning (Goyer, 1971). It ls 

suggested that the inclusion body serves as an adaptive or protective mechanism during transcellular transport of lead. In the 

course of excretion of lead from capillary to bile ln hepatic 

cells, or by transtubular flow in renal tubular lining cells, a portion of the lead enters the nucleus where It becomes bound into a 

lead-protein complex and ls no longer diffusible. This mechanism 

has the effect of maintaining a relatively low cytoplasmic concentration of lead and, therefore, reducing the toxic effects of lead 

on sensitive cellular functions, such as mitochondrial respiration 

and protein synthesis. 

Indirect support for this hypothesis is found in experimental 

studies of tbe relationship of the formation of intranuclear inclusion bodies and other renal effects of lead. When groups of rats 

are given different concentrations of lead in their drinking water, 

intranuclear inclusion bodies are observed at a lower dose than is 

any other renal effect of lead; in fact, at a lower dose of lead 

than that which produced signs and symptoms of lead toxicity. Inclusion bodies appear to be related to renal lead content and discernible in the rat models when kidney lead concentration is between 10 and 20 ug/g wet weight. 

The lead-induced nuclear Inclusion body may also facilitate 

urinary excretion of lead. They are found in the urine of children 

with acute lead poisoning (Landing and Nakai, 1959). In a recent 

study of renal biopsy material from five lead industry workers 

with varying times of exposure to lead from 16 weeks to more than 

20 years, typical lead-induced inclusions were only found in nuclei 

of workers employed for less than one year (Cramer et al., in press). 

Urinary excretion of lead was higher ln those workers with inclusion 

bodies than ln older workers without such complexes although other 

symptoms of lead toxicity were more marked ln the latter group. 

Whether the absence of Inclusion bodies in these workmen reflects 

repeated chelation therapy or implies an alternative cellular metabolism of lead is not known. 

A similar study of renal biopsies from 23 lead industry workers 

with varying periods of exposure to lead has been reported by Richet 

and coworkers (1964, 1966). Although some form of a nuclear body 

was found in 17 of the 23 renal biopsies, only one showed the 

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A. GOYER AND J. F. MOORE 

id Is removable by 

In this circumstance 

cal structure and 

. inues to be insolcontain lesser 

, zinc, copper and 

2 role of the intra-

. 1971). It Is 

idaptive or protec5 lead. In the 

lie in hepatic 

lining cells,a poroses bound into a 

This mechanism 

ytoplasmic concenic effects of lead 

ndrial respiration 

nd ln experimental 

intranuclear incluan groups of rats 

2ir drinking water, 

lower dose than is 

/er dose of lead 

;ad toxicity. In-

' content and dlantration is bealso facilitate 

urine of children 

9 ). In a recent 

jstry workers 

eks to more than 

ly found in nuclei 

- et al., in press), 

:ers with Inclusion 

>s although other 

latter group, 

orkmen reflects 

I've cellular meta-

•d industry workers 

reported by Richet 

a nuclear body 

showed the 

CELLULAR EFFECTS OF LEAD 451 

typical morphology of the characteristic lead-induced Inclusion 

body and this was the only individual in the group with a history 

of short (3 months) exposure to lead. Other nuclear bodies occurring in lead toxic workers resembled granular chromatin masses 

which occur in a number of pathological conditions characterized 

by cellular hyperactivity (Bouteille et al., 1967). 

Inclusion bodies occur in nuclei of osteoclasts of lead poisoned pigs (Hsu et al., 1973). Their formation is augmented by 

lowering dietary calcium,suggesting that lead is reabsorbed during 

osteolysis similarly to calcium. Lead becomea'bound into the nondlffuslble inclusion body. 

The lead-protein inclusion body phenomenon is not restricted 

to animal cell nuclei but also occurs in plant cells. Bryophytes 

(moss) are known to accumulate heavy metals in concentrations 

which are toxic for other groups of plants. It has recently been 

shown that moss cultivated in a greenhouse and watered dally with 

lead acetate solutions forms lead containing inclusion bodies in 

nuclei of leaf cells (Skaar et al., 1973). Similar inclusion 

bodies may occur in root cells of corn grown in soil with added 

lead (personal communication, Dr. D. E. Koeppe, University of Illinois, Urbana, Illinois). 

EFFECTS OF LEAD ON CELL DIVISION AND PROTEIN SYNTHESIS 

Although lead may be concentrated in nuclei in the form of a 

protein complex, the metabolic effect of lead localization on nuclear function, particularly cellular division, ls uncertain. The 

finding of granular chromatin bodies in biopsies of lead workers 

suggests Increased cell turnover time. Recent studies (Choie and 

Richter, 1972a) have shown that a single Intraperitoneal dose of 

lead will greatly enhance DNA synthesis and proliferation of renal 

tubular cells within 2 days and repeated injections given ln 2-day 

intervals will stimulate successive waves of nuclear DNA synthesis 

in tubular epithelial cells (Choie and Richter, 1972b). This finding 

is of particular interest since lead does have a carcinogenic 

effect in rats and mice after long-term Intoxication. On the other 

hand, a carcinogenic effect for lead has not been observed ln man 

or other species of animals. 

Excessive exposure to lead does produce structural alterations 

in the chromosomes of man and experimental animals. Nuclear polyploidy and abnormalities in mitosis have been noted in bone marrow 

cells by a number of authors (Waldron, 1966) but chromosomal aberrations in lead Intoxication have only recently been recognized. 

Chromosomes from leukocyte cultures from mice fed a diet containing 

IZ lead acetate show an increased number of gap-break type aberrations usually involving only single chromatids (Muro and Goyer, 

'•Z&AirZrri&J?-'-
£mf!!•! • 452 R. A. GOYER AND J. F. MOORE 

1969). Similar gap-break types were also found ln lead workers 

with blood lead levels ranging from 62 to 88 ug/100 g (Schwantltz 

et al., 1970). In addition, a variety of non-specific changes in 

chromosome morphology was also present such as adhesions and splralizing defects. Tetraplold mitosis and the mitotic index were 

also Increased in the workers. Moreover, the percentage of abnormal mitoses correlated very well with urinary d-ALA excretion. 

Similar studies have not been performed on acutely intoxicated 

children nor is the mechanism for this lead effect known. Lead, 

like other heavy metals, does have an affinity for nucleic acid 

binding but whether lead becomes biochemically bound to-chromosomes it» vivo ls not known. 

The effect of lead binding to nuclear proteins on cell division is also Incompletely understood. 

Lead is bound to insoluble nuclear proteins as discussed In 

the formation of nuclear inclusion bodies. Lead is also associated 

with NaOH soluble acidic proteins. Acidic nuclear proteins are 

Implicated in the regulation of DNA replication and influence DNAdependent RNA synthesis (Stein and Baserga, 1972). 

There ls some Information to suggest that lead may affect 

protein synthesis at the level of the ribosome. Waxman and Rablnovitz (1966) and Ulmer and Vallee (1969) observed that lead causes 

disaggregation of polyribosomes. The latter workers also reported 

inhibition by lead of leucine incorporation Into t-RNA in E. coli. 

Purified RNA is depolymerized by lead (Farkas, 1968). 

EFFECTS OF LEAD ON MITOCHONDRIA 

The affinity and relatively strong binding of lead to mitochondrial membranes suggests that this organelle is a particularly 

susceptible target of the subcellular effects of lead. 

Lead toxicity in humans and experimental animals is associated 

with alterations in ultrastrueture and function of mitochondria in 

hepatic parenchymal cells, renal proximal tubular lining cells and 

reticulocytes in the bone marrow. The principle clinical manifestations of lead toxicity involve these organs as well as the central 

nervous system. Although disturbances in mitochondrial structure 

and function are not the only subcellular effects of lead, it is 

suggested that the tn vivo effect of lead on these organelles contributes to the anemia of lead poisoning and impaired renal tubular 

function. The relationship of the mitochondrial effects of lead 

to other symptoms of lead toxicity are less well understood. 

Mitochondria in proximal .renal tubular lining cells of children, adults and experimental animals with lead poisoning show 

«j%»*a»ia6**4S»:«»a»K; 
\. GOYER AND J. F. MOORE 

in lead workers 

'100 g (Schwantitz 

•ecific changes in 

dhe8lons and spi-

'totic index were 

rcentage of abnorALA excretion. 

ly intoxicated 

ct known. Lead, 

or nucleic acid 

' ound to chromoins on cell divias discussed ln 

Is also associated 

r proceins are 

nd influence DNAad may affect 

'axman and Rablnothat lead causes 

ers also reported 

t-RNA In E. coli. 

•58). 

lead to mitoI Is a particularly 

I '-ead. 

-als Is associated 

c

 mitochondria in 

lining cells and 

linlcal manlfesell as the central 

Jdrial structure 

|of lead, it ls 

organelles conIrad renal tubular 

Iffects of lead 

fnderstood. 

cells of chillisoning show 

CELLULAR EFFECTS OF LEAD 453 

varying degrees of swelling with margination of cristae (Angevine 

et al., 1962; Cohen et al., 1960; and Goyer, 1968) probably secondary to increased membrane permeability. Such changes are similar 

to the non-specific swelling that occurs in the early stages of 

other forms of cellular Injury and is probably reversible. The 

fate of such mitochondria is uncertain but increased numbers of 

myelin figures and autophagocytosis suggest an Increased rate of 

turnover. Mitochondria ln cells of renal biopsy specimens from 

lead industry workers show evidence of budding and division. Lead 

induced granules or Inclusion bodies similar to those formed in 

nuclei may be produced .In vitro in isolated liver mitochondria 

(Walton, 1973) but these have not been noted in vivo. 

Other types of intramitochondrial inclusions have been observed but are probably not specific for lead poisoning. Watrach 

(1964) has described an intramitochondrial lamellar type crystalloid in liver parenchymal cells of lead poisoned swine. These are 

composed of an intersecting band of fine, loosely packed arrays 

that run parallel and perpendicular to form a lattice pattern. 

Such lamellar formations are characteristic of chronic cellular 

injury accompanying a number of metabolic abnormalities such as 

diabetes mellitus, alcohol intoxication and biliary obstruction 

as well as experimentally induced hypoxia (Shiraki and Neustein, 

1971). 

From the observed alterations in mitochondrial ultrastructurc 

some impairment of functional ability is suggested. Nevertheless, 

mitochondria from cells of subjects with chronic intoxication are 

expected to have some degree of respiratory ability since cellular 

necrosis or irreversible cellular injury is not a prominent morphologic feature. A decreased level of mitochondrial function is compatible with the concept of an altered functional steady state or 

lowered level of cellular activity. 

Measurement of respiratory activity of mitochondria from liver 

or kidney of lead-treated experimental animals confirms this concept. Teras and Kakhn (1967) found decreased respiratory rates in. 

mitochondria of rabbits treated with daily intraperitoneal injections of lead acetate (10 to 20 mg/kg body weight) for seven months. 

ADP stimulated respiration was lower for mitochondria from leadtreated rabbits in the presence of three different substrates: aketoglutarate, pyruvate and succinate. Phosphorylation was also 

decreased. The authors suggest respiratory impairment is most pronounced using pyruvate as substrate. 

Studies with mitochondria isolated from kidneys of lead poisoned rats show a specific Impairment in respiratory and phosphorylative abilities in pyruvate-dependent respiration %s evidenced by 

altered respiratory control (RCR) and ADP:0 ratios. Slightly 

higher State IV and State III rates of toxic mitochondria In the 
i ' 

1 > 

454 R. A. GOYER AND J. F. MOORE 

I i 

I* 

presence of pyruvate suggest partial uncoupling of phosphorylation. 

These functional parameters which are reflected by RCR and ADP:0 

are not different from the control mitochondria in succinate-dependent respiration (Goyer and Krall, 1969a). Since succinate oxidation and related electron transport by-pass the pyruvate-NAD reductase enzyme complex, i t Is suggested that the NAD reductase complex 

is more sensitiv e to lead. A more recent report indicates that 

magnesium restore s oxidative abilit y and dinitrophenol sensitivit y 

In lead toxic mitochondria for NAD coupled respiration, but It has 

no effec t on succinate-supported respiration (Krall and Dougherty, 

1971). Decreased oxygen uptake rate for both State III and IV in 

succinate-supported respiration in lead toxic mitochondria may be 

evidence of decreased succinoxldase enzyme which correlate s with 

decreased mitochondrial protein (Rhyne and Goyer, 1971). 

Ulmer and Vallee (1969) conclude that lead acts specificall y 

with dithio l bonds in the llpoamlde dehydrogenase ln the pyruvate 

dehydrogenase systent but this was validated by ln vitr o work only. 

This sit e ls sensitiv e to other metals such as mercury and cadmium 

but l t Is uncertain whether this sit e is accessibl e to lead in the 

in vivo system. 

The effec t of lead on mitochondria of bone marrow reticulo -

cyte s is of particular interest because of the resultant impairment 

in heme synthesis and subsequent clinica l anemia. It also serves 

as a fairly well defined example of a toxic change ln an Intramitochondrial enzyme system. 

At least three steps ln heme synthesis may be affected by 

lead. Inhibition of d-aminolevullnic acid dehydratase (AIA-D) is 

probably the enzyme in the heme pathway that is most sensitiv e to 

lead. Inhibition of this enzyme results in a block in utilizatio n 

of d-aminolevullnic acid (d-ALA) and subsequent decline in heme 

synthesis. Under the proposed scheme of negative feed-back control 

of heme synthesis as proposed by Granick and Levere (1964), d-ALA 

synthetase activit y is derepressed resulting In increased activit y 

and synthesis of d-ALA. This may be regarded as a second effec t 

of lead on heme synthesis. Since utilizatio n of d-ALA is blocked, 

urinary excretion is increased. Assay of urinary d-ALA serves as 

a sensitiv e index of a biochemical lead effec t and is widely used 

as an indication of lead toxicit y (Haeger-Aronsen, 1960). 

A third abnormality in heme synthesis described in lead intoxication is inhibition of the enzyme, ferrochelatase (heme synthetase) (Otrzonsek, 1967) which is located on the inner membrane 

of mitochondria (Jones and Jones, 1968). This effect Is particularly Interesting because of associated ultrastructural changes 

ln the mitochondrion. Ferrochelatase catalyzes the incorporation 

of the ferrous lon into the porphyrin ring structure. Bessls and 

Jensen (1965) have shown that iron In the form of apoferritln and 
P.10 

•.jsasEsHa&stt.' ::ij"LrnirFii'i: 

'ER AND J. F.MOORE 

ohosphorylation. 

ICR and ADP:0 

<:uccinate-depen-

-cinat e oxidarvate-NAD reduceductase complex 

•I icate s that 

| *^ol sensitivit y 

•on, but i t has 

and Dougherty, 

III and IV in 

'loadrla may be 

|"relate s with 

'71). 

specificall y 

l"» the pyruvate 

tro work only. 

•ry and cadmium 

to lead ln the 

•ow reticulo -

tant Impairment 

It als o serves 

•n an Intramitoffee ted by 

'se (ALA-D) ls 

sensitive to 

|ln utilization 

iine in heme 

Ied-back control 

(1964), d-ALA 

eased activit y 

econd effec t 

LA ls blocked, 

ALA serves as 

s widely used 

960). 

in lead inse (heme synnner membrane 

is partlcural changes 

Incorporation 

Bessis and 

?ferritin and 

CELLULAR EFFECTS OF LEAD 455 

ferruginous micelles accumulates in mitochondria of bone marrow 

reticulocytes from lead poisoned rats. 

Gibson and Goldberg (1970) recently reported no Inhibition of 

this enzyme (ferrochelatase) in homogenates prepared from liver of 

lead toxic rabbits, but when they added lead acetate to the homogenate ln concentrations similar to those present in the original 

unhomogenized tissues, a marked inhibition occurred. Lead associated with the enzyme in vivo may be so loosely bound as to be 

lost in the isolation procedure. Nevertheless, the experiment 

does show that ferrochelatase is readily inhibited by lead. 

Other steps in the biosynthetic pathway of heme may also be 

abnormal in lead toxicity but the evidence for these is incomplete. 

Increase in urinary excretion of coproporphyrin, the degradative 

product of coproporphyrinogen III, is a sensitive reflection of 

lead toxicity. Metabolism of porphobilinogen to coproporphyrinogen 

proceeds unimpaired. However, since ALA-D is an extra-mitochondrIal 

enzyme, and later steps in heme synthesis are intramitochondrial, 

coproporphyrinogen must re-enter the mitochondrion to be metabolized further. It has been suggested that transport of metabolites 

like coproporphyrinogen into the mitochondrial matrix might be impaired by altered inner membrane permeability, or decreased efficiency in oxidation and phosphorylation (Haeger-Aronsen et al., 

1968). Whether the increased urinary coproporphyrinogen occurring 

In lead poisoning ls a reflection of a non-specific alteration in 

mitochondrial membrane or reflects a more specific effect of lead 

on the intramitochondrial enzyme coproporphyrinogenase, is not 

known. 

The principal clinical manifestations of lead toxicity Involve 

three organ systems: the central nervous system, hematopoietic 

system and the kidney. A relationship between the mitochondrial 

effect of lead and the central nervous system pathology has not 

been demonstrated. However, functional impairment of mitochondria 

of reticulocytes is responsible, at least in part, for the anemia 

of lead poisoning, and lead toxic mitochondria of reticulocytes are 

responsible, at least in part, for the anemia of lead poisoning, 

and lead toxic mitochondria in proximal renal tubular lining cells 

must decrease the functional ability of these cells. Transport of 

a number of substances including sodium, potassium, phosphate 

ions and small organic molecules such as amino acids and glucose 

occurs in this portion of the renal tubule and is an active process 

dependent on ATP largely derived from mitochondrial oxidative phosphorylation. 

In acute lead poisoning, particularly in children, excessive 

excretion of amino acids, glucose and phosphate occurs (Chisolm, 

1962). Whether reduced reabsorption of these substances in lead 

ir 

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456 R. A. GOYER AND J. F. MOORE 

poisoning is entirely related to reduced energy production by 

lead toxic mitochondria or is also a consequence of a lead effect 

on other cellular membranes is uncertain. Most of the energy synthesized ln proximal tubular lining cells is required for sodium 

transport. It is interesting that Sandstead et al. (1970) have 

recently shown that men with chronic lead poisoning, following 

excessive industrial exposure to lead or ingestion of lead-contaminated Illicit moonshine, do have reduced sodium reabsorpclon. This 

defect, like the aminoaciduria, is reversible by treatment of the . 

lead poisoning with chelating agents (EDTA). 

r 

Respiratory rates of bone marrow reticulocytes from lead intoxicated rats are less than normal (Lessler et al., 1968), probably 

reflecting impaired mitochondrial respiration. Also some of the 

enzymes associated with heme synthesis are located either within 

the inner mitochondrial membrane of matrix or are in close association with this organelle and are dependent on intact mitochondrial 

respiration. Some impairment of heme enzyme function may follow 

the lead effect on respiration. 

The effect of lead on cellular content of other heme proteins 

such as cytochromes, catalase and peroxidases has received limited 

study. Prader and Vannotti In an attempt to compare effects of 

lead poisoning on hemoglobin and other cellular porphyrin moieties 

measured levels of hemoglobin and cytochrome c in rabbit liver. In 

contrast to decrease in the hemoglobin values cytochrome c level 

remained constant (Vannotti, 1955). However, measurement of the 

total cytochrome content of rat kidney mitochondria by difference 

spectra showed a selective decrease ln cytochrome 883 in lead poisoning (Rhyne and Goyer, 1971). Whether this decrease resulted from 

inhibition of mitochondrial protein synthesis which is reflected 

by decrease In cytochrome 883 or specific inhibition of the cytochrome 883 heme moiety has not been resolved. The protein moiety 

as well as the heme moiety differs for each class of cytochromes 

so inhibition of either fraction would result in a decrease of the 

cytochrome. 

LEAD AND LYSOSOMES 

The radioisotope studies of Barltrop and coworkers (1971) 

suggest that lead has less affinity for iysosomes than other subcellular organelles, particularly mitochondria and nuclei; nor 

does lead intoxication in the rat provoke any remarkable increase 

in lysosomal enzymes (Krigman et al., 1968). The origin of the 

lead-induced increase in urinary ^-glucuronidase noted by these 

workers is uncertain but may be derived from a lead effect on endoplasmic reticulum (Krigman et al., 1970). Autophagocytosis of lead 

containing mitochondria may result in lead containing secondary 

Iysosomes as suggested from observation of biopsy specimens from 

pi 

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50YER AND J. F. MOORE CELLULAR EFFECTS OF LEAD 457 

>roduction by 

'f a lead effec t 

the energy synred for sodium 

*• (1970) have 

g, following 

of lead-contamiabsorpcion. This 

reatment of the 

s from lead intoxi968), probably 

'so some of the 

either within 

in close associa-

~t mitochondrial 

'.on may follow 

•»r heme proteins 

-eceived limited 

-e effects of 

phyrin moieties 

-abblt liver. In 

hrome c level 

rement of the 

by difference 

-83 in lead polase resulted from 

• is reflected 

n of the cytoprotein moiety 

f cytochromes 

decrease of the 

Uers (1971) 

n an other subliuclei; nor 

|<able increase 

igin of the 

|->ted by these 

•ffect on endo-

|>cytosis of lead 

ig secondary 

hecimens from 

lead workers (Cramer et al., in press). Also, lead has been 

identified by x-ray microanalysis in dense cytoplasmic concretions 

in kidney cells of rats administered large doses of lead intraperitoneally (Murakami, 1971). Such concretions have not been found 

following oral administration of lead in rats and ln human biopsy9 

material. 

SUMMARY AND CONCLUSIONS 

1 • 

f 

The intracellular localization of lead has been best studied 

in liver and kidney, the two organs most concerned with transcellular transport and excretion of lead. Within the cell lead has the 

greatest affinity for mitochondrial membranes and nuclei. Nuclear 

lead binds with an acidic protein fraction and accumulates to form 

a discrete inclusion body which has a characteristic ultrastrueture. 

When the renal tubular cell is presented with even larger concentrations of lead intracytoplasmic concretions are formed. The 

relationship of these concretions to the lysosomal system has not 

been demonstrated but dense staining bodies do form ln secondary 

Iysosomes derived from degenerating lead toxic mitochondria. 

The effect of lead on membrane enzyme systems and biochemical 

activity of subcellular organelles is related to the pattern of 

intracellular partitioning. The lead effect on mitochondria decreases the ability of cells to form specific functions, e.g. transport functions in proximal renal tubular lining cells. Sensitivity 

of enzymes concerned with heme synthesis results ln anemia as well 

as increased urinary excretion of intermediate products of the heme 

synthesizing pathway. 

Measurable amounts of lead are present in most cells of persons 

ln the general population without apparent adverse effect. With an 

increase in lead burden the transition from no effect to toxicity 

is probably not sharply definable but reflects a spectrum of cellular 

events, some compensatory, some pathological. Knowledge of the 

intracellular distribution of lead and its effect on subcellular 

components should Improve the ability to discern between a tolerable 

and toxic lead burden. 

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-4fe*i-