Serum luteinizing hormone concentrations, as measured by a sensitive immunoradiometric assay, in children with normal, precocious or delayed pubertal development.

To determine the diagnostic potential of a highly sensitive immunoradiometric assay (IRMA) for LH in children with normal puberty or altered tempo of sexual maturation, we compared serum LH levels by IRMA (LH IRMA) and standard RIA (LH RIA) in children with idiopathic precocious thelarche (IPT; n = 6), idiopathic premature adrenarche (IPA; n = 14), central precocious puberty (CPP; n = 15), and constitutional delay of puberty (DP; n = 15), and 160 control children (79 males and 81 females). Subjects in the latter group were staged, according to their genital or breast development, as early prepubertal (P1E; age, less than 8 yr), late prepubertal (P1L; 8-12 yr), or stage II-V (P2-P5; n = 22-34 for each subgroup). Serum LH IRMA levels in P1E, IPT, and IPA children were either undetectable (95% of subjects less than 0.25 IU/L) or barely detectable (5% of subjects, less than or equal to 0.5 IU/L). Serum LH IRMA levels were greater than 0.5 IU/L in 38% of P1L (mean +/- SD for the group, 1.0 +/- 1.3 IU/L) and 57% of P2 (1.4 +/- 1.3 IU/L); they were greater than 1.0 IU/L in 100% of P3 (2.6 +/- 1.3 IU/L), P4 (3.9 +/- 2 IU/L), and P5 (8.6 +/- 4 IU/L) children. Comparison of serum LH levels between contiguous pubertal stages showed significantly higher LH IRMA concentrations in P3 vs. P1E, P4 vs. P2, P5 vs. P4 (all P less than 0.001), and P3 vs. P1L (P less than 0.05). In contrast, LH RIA values were not significantly different in P1E (2.0 +/- 0.6 IU/L), P1L (2.3 +/- 0.6 IU/L), P2 (2.7 +/- 0.9 IU/L), P3 (3.2 +/- 1.3 IU/L), and P4 (3.7 +/- 2.2 IU/L), although they were higher in P5 (6.8 +/- 4 IU/L) than in P4 (P less than 0.001). From P1E to P5 LH IRMA levels increased 38-fold in females and 21-fold in males, while LH RIA increased 4- and 2.1-fold, respectively. Serum LH IRMA correlated significantly with serum testosterone levels in boys from P1L to P5 (r = 0.76; P less than 0.001), while LH RIA levels did not (r = 0.18). Serum LH IRMA concentrations were above the prepubertal range (greater than 0.5 IU/L) in 67% of children with CPP (group average, 1.8 +/- 1.4 IU/L) and 87% of children with DP (1.6 +/- 1.4 IU/L).(ABSTRACT TRUNCATED AT 400 WORDS)

Toxic heme in sickle cells: an explanation for death of malaria parasites.

In an effort to elucidate a mechanism of genetic resistance to malaria, we asked whether a toxic form of heme is included in the excess of ferriprotoporphyrin IX (FP) which has been reported to accumulate as hemichromes in sickle cells. When FP is bound to certain erythrocytic elements, such as native hemoglobin, it is inaccessible to bind chloroquine with high affinity and is nontoxic. However, when FP is accessible to bind chloroquine with high affinity, it has been demonstrated to be sufficiently free to have membrane toxicity and, under certain conditions, to lyse Plasmodium falciparum parasites. [14C]-chloroquine was used, therefore, as a reporter molecule to evaluate the quantity, accessibility, and potential toxicity of FP released from hemoglobin. Intact erythrocytes from subjects with sickle cell anemia bound approximately 71 mumoles of chloroquine per kg with an apparent Kd of 10(-6) M. Erythrocytes from normal subjects or subjects with sickle trait bound little or no chloroquine with high affinity. Since the oxidant stress introduced by malaria parasites would increase the tendency for denaturation of hemoglobin S with additional release of FP, we suggest that FP toxicity accounts for the death of malaria parasites in sickle cells.

Ferriprotoporphyrin IX: a mediator of the antimalarial action of oxidants and 4-aminoquinoline drugs.

Ferriprotoporphyrin IX (FP) is released from hemoglobin by oxidative denaturation or by proteolytic degradation. FP added exogenously to cells or released intracellularly is a lytic toxin. Chloroquine enhances the accumulation of exogenous FP in cellular membranes and potentiates its lytic effect. Menadione is an example of an oxidant drug that denatures hemoglobin, releases FP intracellularly, and thereby lyses cells. Chloroquine increases the accumulation of FP in the membranes of menadione-treated erythrocytes and enhances the hemolysis induced by menadione. Intraerythrocytic malaria parasites release FP from hemoglobin by proteolytic degradation, but they ordinarily survive the exposure either because FP interacts with a soluble intracellular substance, which renders it nontoxic, or because FP is sequestered in an innocuous, insoluble form in malaria pigment. Chloroquine binds tightly to FP, diverts it away from the soluble detoxifying substance in malaria parasites, and delays its sequestration into malarial pigment. Malaria parasites exposed to chloroquine while degrading hemoglobin accumulate a chloroquine-FP complex, which is sufficiently toxic to kill them. FP has a detergent-like effect on biological membranes which may account for its lytic toxicity.

Intracellular ferriprotoporphyrin IX is a lytic agent.

Human erythrocytes were treated with menadione to oxidatively denature hemoglobin and release ferriprotoporphyrin IX (ferriheme, FP) intracellularly. The high affinity of FP for chloroquine was used to detect its release. After incubation for 1 hr at 37 degrees C and pH 7.4 with 0.5 mM menadione, erythrocytes bound 14C-chloroquine with an apparent dissociation constant of 10(-6)M. Untreated erythrocytes did not bind chloroquine with high affinity. At a chloroquine concentration in the medium of 2 microM, for example, menadione-treated erythrocytes bound 70 mumole chloroquine/kg and untreated erythrocytes bound 13.4 mumole/kg. The intracellular location of FP released by menadione was verified by finding that Tween 80 did not prevent chloroquine binding. By contrast, Tween 80 inhibited the binding of chloroquine to erythrocytes treated with extracellular FP. The hemolytic response to menadione was characteristic of the hemolytic response to FP. Thus, 5 microM chloroquine caused hemolysis to increase to 60% from baseline values of 5% in experiments using erythrocytes treated either with 0.5 mM menadione or with 5 microM FP; and, in both cases, the potentiating effect of chloroquine was inhibited by 1 microM mefloquine or 10 microM quinine. Higher concentrations of menadione caused hemolysis in the absence of chloroquine. We conclude that FP released by menadione exists intracellularly in a form that is accessible to bind chloroquine and to express its lytic activity.

Lysis of Plasmodium falciparum by ferriprotoporphyrin IX and a chloroquine-ferriprotoporphyrin IX complex.

Ferriprotoporphyrin IX (FP) and a chloroquine-FP complex lysed isolated Plasmodium falciparum parasites as judged by decreases in the turbidity of parasite suspensions and by ultrastructural changes. Exposure of parasite suspensions to 50 microM FP or to a complex formed from 50 microM FP and 20 MicroM chloroquine reduced the number of identifiable parasites and caused swelling and loss of internal detail in those that were identifiable. The amount of lysis was dose-dependent over the range of 10 to 50 microM FP. Formation of a chloroquine-FP complex reduced, but did not eliminate, the toxicity of FP. Since there is evidence indicating that a chloroquine-FP complex forms when chloroquine-susceptible parasites are exposed to chloroquine, we suggest that accumulation of this complex may account for the chemotherapeutic effect of chloroquine against P. falciparum.

The antimalarial drug mefloquine binds to membrane phospholipids.

The new antimalarial drug mefloquine bound with high affinity (Kd approximately 3 X 10-7 M) to membrane lipids of normal mouse erythrocytes and of erythrocytes infected either with chloroquine-susceptible or chloroquine-resistant Plasmodium berghei. Approximately 80 nmol of mefloquine was bound per mg of total lipid. Mefloquine also bound to purified phospholipids with high affinity (Kd approximately 3 X 10-7 M). Phosphatidylinositol and phosphatidylserine bound 300 to 400 nmol of mefloquine per mg. Phosphatidylcholine and phosphatidylethanolamine bound approximately 100 nmol of mefloquine per mg. Mefloquine did not bind to hemoglobin with high affinity, but it bound to free ferriprotoporphyrin IX with a Kd of approximately 3 X 10-7 M. In comparison with mefloquine, chloroquine did not bind effectively to purified phospholipids, although it is known to bind with high affinity to free ferriprotoporphyrin IX. Greater binding to phospholipids may account for the superiority of mefloquine in the treatment of chloroquine-resistant malaria.

Hemin lyses malaria parasites.

Malaria parasites isolated from mouse erythrocytes are lysed by ferriprotoporphyrin IX chloride (hemin) or by a chloroquine-hemin complex in amounts that could be produced by release of less than 0.1 percent of the heme in erythrocytic hemoglobin. This effect of hemin may explain the protection against malaria provided by thalassemia and other conditions causing intracellular denaturation of hemoglobin. The toxicity of the chloroquine-hemin complex may explain the selective antimalarial action of chloroquine.

Biochemical and ultrastructural changes in skeletal muscle induced by a creatine antagonist.

To evaluate the essentiality of creatine and phosphocreatine for the maintenance of the ultrastructure of skeletal muscle, chicks were fed a creatine antagonist, beta-guanidinobutyric acid (beta-GBA), as 2% of a Chow diet. Chicks fed beta-GBA exhibited growth retardation and weakness, and they accumulated large amounts of a monosubstituted guanidino compound, presumably beta-GBA, in their skeletal muscles. After 2 wk, there was a 74% decrease in the uptake of [14C]-1-creatine into pectoralis muscles of chicks fed beta-GBA. After 2 wk there as a significant decrease in phosphocreatine concentrations in pectoralis muscles from 20.1 +/- 2.8 mumoles per g wet weight (mean +/- S.D.) for 8 control chicks to 16.5 +/- 2.5 for 7 chicks fed beta-GBA. Selected fibers of the pectoralis and gastrocnemius muscles of chicks fed beta-GBA exhibited ultrastructural abnormalities including loss of thick and thin filaments, disruption of the Z band, dilated mitochondria, and dilated and displaced sarcoplasmic reticulum. The pectoralis muscles of chicks given 6% creatine in addition to 2% beta-GBA in the diet accumulated little beta-GBA, maintained normal phosphocreatine concentrations, and exhibited no significant ultrastructural abnormalities. These findings are the first experimental evidence that high concentrations of phosphocreatine are essential for the maintenance of the ultrastructural integrity of skeletal muscle.

Sequestration of the chloroquine receptor in cell-free preparations of erythrocytes infected with Plasmodium berghei.

When mouse erythrocytes infected with Plasmodium berghei were preincubated with [14C]chloroquine and then lysed by hypotonic shock, chloroquine remained bound to the resulting cell-free preparation. In an isotonic medium at pH 7.4 and 25 degrees C, chloroquine was bound to the cell-free preparation with an apparent dissociation constant of 1.8 x 10(-7) M. The bound [14C]chloroquine could be displaced by nonradioactive chloroquine, amodiaquine, quinacrine, and mefloquine, as would be predicted from knowledge of the specificity of ferriprotoporphyrin IX for antimalarial drugs. Also, as predicted, primaquine did not displace the [14C]chloroquine. The ability of these cell-free preparations to bind chloroquine with high affinity decreased rapidly with incubation at 37 degrees C and became undetectable within 1 h; at 4 degrees C the decrease occurred more slowly. This behavior of the endogenous receptor-chloroquine complex was duplicated by an exogenous ferriprotoporphyrin IX-chloroquine complex loaded into cell-free preparations of erythrocytes infected with P. berghei. These findings support the hypothesis that ferriprotoporphyrin IX is the endogenous chloroquine receptor of P. berghei and indicate that it can be sequestered rapidly in a form that is inaccessible to chloroquine.

Phosphocreatine does not inhibit rabbit muscle phosphofructokinase or pyruvate kinase.

Certain phosphocreatine preparations contain a contaminant that inhibits phosphofructokinase and pyruvate kinase assays. The contaminant can be separated from phosphocreatine by anion exchange chromatography. After appropriate purification, phosphocreatine has no effect on phosphofructokinase or pyruvate kinase; thus, there is no evidence that it serves muscle as a regulator of these enzymes. Although the inhibitory preparations of phosphocreatine contain inorganic phosphate and trace amounts of more negatively charged phosphorylated contaminants, the inhibitor is not inorganic phosphate or pyrophosphate. The nature of the inhibitor remains to be determined.

Chloroquine resistance in malaria: accessibility of drug receptors to mefloquine.

The process of mefloquine accumulation was studied in mouse erythrocytes infected with either Plasmodium berghei CS (chloroquine susceptible) or P. berghei CR (chloroquine resistant). In both cases, mefloquine was accumulated by a saturable process with an apparent dissociation constant of 2.5 x 10(-6) M and an apparent maximal capacity of 700 mumol per kg of erythrocyte pellet; uninfected mouse erythrocytes accumulated more than half as much mefloquine as infected erythrocytes. The process of accumulation was not stimulated by providing glucose as a substrate, and it was not inhibited in infected erythrocytes by azide, iodoacetate, or incubation at 2 degrees C. Although mefloquine was accumulated more effectively than chloroquine by uninfected erythrocytes and by erythrocytes infected with P. berghei CR, competition between chloroquine and mefloquine was observed, raising the possibility that the same process of accumulation serves both drugs. Chloroquine competitively inhibits mefloquine accumulation, with an apparent inhibitor constant of 1.7 x 10(-3) M, and mefloquine competitively inhibits chloroquine accumulation, with an apparent inhibitor constant of 2 x 10(-6) M. The same process of accumulation and the same group of receptors could serve both drugs if mefloquine has greater access than chloroquine to the receptors. Regardless of whether the same process serves both drugs, undiminished accumulation by erythrocytes infected with P. berghei CR provides an explanation for the superiority of mefloquine in treating chloroquine-resistant malaria.

Erythrocyte surface: novel determinant of drug susceptibility in rodent malaria.

To study the role of the erythrocyte membrane in the process of chloroquine accumulation, surface polypeptides were digested with a nonspecific protease from Streptomyces griseus. This treatment activated a saturable process of chloroquine accumulation with an affinity and a specificity similar to those of mouse erythrocytes infected with Plasmodium berghei CS (chloroquine susceptible). Studies of competitive inhibitors of chloroquine accumulation yielded the following approximate values for K(i): amodiaquine, 2 x 10(-7) M; quinacrine, 5 x 10(-7) M; quinine, 2 x 10(-6) M; and mefloquine, 2 x 10(-5) M. Lack of a substrate requirement distinguished this process from the one used by P. berghei and permitted the protease to be used in studies of infected erythrocytes. Protease treatment of erythrocytes infected with P. berghei CR (chloroquine resistant) produced a dramatic transformation. Instead of describing a sigmoid curve, the process of chloroquine accumulation became saturable and substrate dependent, with a K(diss) of approximately 10(-8) M; i.e., protease-treated erythrocytes infected with P. berghei CR now behaved similarly to those infected with P. berghei CS. Coating the erythrocyte surface with albumin completely inhibited the protease-activated process of chloroquine accumulation. These findings are presented as evidence that erythrocyte surface components determine the affinity with which chloroquine is accumulated and thereby determine whether or not the malaria parasite will be susceptible to the drug.

Chloroquine resistance in malaria: variations of substrate-stimulated chloroquine accumulation.

The response of [14C]chloroquine accumulation to the provision of substrate was evaluated using washed erythrocytes infected with Plasmodium berghei CS (chloroquine-susceptible), with P. berghei CR (chloroquine-resistant), with Plasmodium vinckei CS, with P. vinckei CR, or with a strain of P. berghei spontaneously resistant to chloroquine, Plasmodium berghei yoelii 17X. Erythrocytes infected with chloroquine-resistant parasites had a blunted response, particularly to low glucose concentrations. In the presence of 0.5 mM glucose in one set of experiments, for example, chloroquine accumulation increased by a factor of 8 in erythrocytes infected with P. berghei CS whereas there was no increase in erythrocytes infected with P. berghei CR or with P. berghei yoelii 17X; the difference between P. vinckei CS and P. vinckei CR was less dramatic. In every case except for P. berghei CR, the process of chloroquine accumulation in the presence of 5 mM glucose exhibited a component which became saturated at low concentrations of chloroquine in the medium. For P. berghei CR, plotting steady-state accumulation of chloroquine as a function of the concentration of chloroquine in the medium yielded a sigmoid curve, revealing that higher concentrations of chloroquine (above 100 mM) somehow relieve the blunted response to glucose and suggesting that the variation is in the process of accumulation rather than in substrate utilization.

Amodiaquin accumulation by mouse erythrocytes infected with Plasmodium berghei.

[14C]amodiaquin accumulation by washed erythrocyte preparations was characterized to permit comparisons with chloroquine accumulation. Erythrocytes infected with Plasmodium berghei CS (chloroquine-susceptible) accumulate amodiaquin by a saturable process that has an apparent dissociation constant for amodiaquin of 7.6 X 10(-8) M and is competitively inhibited by chloroquine, quinine and quinacrine, as is the process of chloroquine accumulation. Within experimental error, the K1 of 8 X 10(-7) M estimated for chloroquine is the same regardless of whether the drug being accumulated is [14C]amodiaquin or [14C]chloroquine. Likewise, the K1 for amodiaquin is the same regardless of which drug is being accumulated. In addition, glucose stimulates and hydrogen ion, cold or interruption of glycolysis inhibits amodiaquin as well as chloroquine accumulation. These findings are evidence that a single process serves to accumulate both drugs. In the absence of substrate, erythrocytes infected with P. berghei CR (chloroquine-resistant) accumulate twice as much amodiaquin as chloroquine, and they accumulate more amodiaquin than do erythrocytes infected with P. berghei CS. These differences occur because P. berghei CR infects polychromatophilic erythrocytes possessing a high-affinity, substrate-independent process of accumulation to which amodiaquin has greater access than chloroquine. In the presence of glucose, amodiaquin accumulation by erythrocytes infected with P. berghei CR, when plotted as a function of amodiaquin concentration in the medium, describes a sigmoid curve.