Robert F. Labbe

Heme biosynthesis on the incorporation of iron into protoporphyrin

The enzyme(s) responsible for converting protoporphyrin and iron to heme has been studied using rat-liver prepations and 59Fe as a tracer. The enzyme is located in the mitochondrial fraction. It has optimum activity at pH 7.4 and is stimulated significantly by GSH and DPN or DPNH. Less stimulation is shown by TPN, TPNH, FAD, histidine and homocysteine. Preincubation of the enzyme with protoporphyrin and DPN indicates that the formation of an intermediate occurs before iron is chelated.

Preparation and properties of the iron-protoporphyrin chelating enzyme.

Abstract Further studies are reported on the iron-protoporphyrin chelating enzyme. The enzyme was prepared in soluble form from rat-liver mitochondria and was assayed spectrophotometrically. These procedures and numerous properties of IPCE are described. The enzyme is quite stabe, has maximum activity at pH 8.2 and the only established cofactor requirement is a reducing agent such as glutathione. It exhibits numerous properties of an enzyme requiring a sulfhydryl group for activity.

Zinc Protoporphyrin/Heme Ratio for Diagnosis of Preanemic Iron Deficiency

Objective. Iron deficiency anemia is known to impair cognitive and psychomotor development. The zinc protoporphyrin/heme (ZPP/H) ratio is a simple, accurate, and sensitive laboratory screening test that detects early iron depletion before the onset of anemia. The objective of this work was to evaluate this test in a primary pediatric practice setting. Methods. The iron status of a cohort of 361 children was screened during routine examinations at a community pediatric practice. Whole blood hemoglobin concentration, hematocrit ratio, serum transferrin saturation, ferritin concentration, and the ZPP/H ratio were measured. The ZPP/H ratio then was evaluated as a single indicator of iron status by comparing it with other tests for detecting the onset of iron deficiency and for monitoring recovery after iron supplementation. Results. Significant age- and sex-related differences in the ZPP/H ratio were found. In this cohort, serum ferritin concentration and the ZPP/H ratio independently identified the same fraction of iron-deficient patients (3%–4%), and both tests were more specific than was either hemoglobin or hematocrit. A concordance of three iron status parameters changed the prediction of iron deficiency to ≤1%. Children <3 years of age and adolescent girls had significantly higher ZPP/H results. Conclusion. The prevalence of iron deficiency anemia in the typical healthy American pediatric population is low, but iron deficiency without anemia remains relatively common at some stages of development. Increase in the ZPP/H ratio is demonstrated to be a sensitive, specific, and cost-effective test for identifying preanemic iron deficiency in a community pediatric practice. anemia, nutrition, development.

Coarse facies, calvarial thickening and hyperphosphatasia associated with long-term anticonvulsant therapy.

GROSS enlargement of the lips and nose and a generalized thickening of subcutaneous tissues of the face and scalp in several residents in a state institution for the mentally retarded prompted a re...

Metal specificity of the iron-protoporphyrin chelating enzyme from rat liver☆

Abstract The metal specificity of the iron-protoporphyrin chelating enzyme from rat liver was studied. The conversion of protoporphyrin plus Fe 2+ to heme was demonstrated spectrophotometrically. At high concentrations Fe 2+ inhibited, probably through reaction with the sulfhydryl groups. Co 2+ behaved very similar to Fe 2+ , and isotope dilution experiments indicated that Co 2+ was utilized via the same enzymic mechanism as was Fe 2+ , 54 Mn 2+ in low concentrations was incorporated into protoporphyrin in trace amounts, even though Mn 2+ was an inhibitor of the enzyme. Mn 2+ apparently did not attack the sulfhydryl groups but did inhibit non-competitively with respect to Fe 2+ . Sn 2+ was neither utilized by the enzyme nor inhibitory, while all other metals tested (Mg 2+ , Ca 2+ , Ni 2+ , Cd 2+ , Pb 2+ , Cu 2+ , Mn 2+ , Zn 2+ , Hg 2+ ) were inhibitory.

Erythrocyte Zinc Protoporphyrin Is Elevated With Prematurity and Fetal Hypoxemia

Objective. To examine the utility of red blood cell (RBC) zinc protoporphyrin/heme ratio (ZnPP/H) as an indicator of fetal iron status, because unfavorable neurodevelopmental outcomes have been associated with poor iron status at birth, as indicated by low serum ferritin, and because few reliable indicators of fetal and early neonatal iron status exist. Methods. Consecutively studied preterm and term fetuses at delivery included the following groups: (1) control nonhypoxic, (2) fetuses with intrauterine growth retardation (IUGR), and (3) fetuses of insulin-treated mothers (FDM). We hypothesized (1) that rapid growth velocity associated with an accelerated erythropoiesis among normal fetuses will lead to reduced iron delivery to a rapidly expanding RBC mass and higher umbilical cord blood RBC ZnPP/H and (2) that fetuses that are exposed to pathologic hypoxemia will experience an additional increase in erythropoiesis and higher cord ZnPP/H. ZnPP/H was determined on saline-washed cord blood erythrocytes by hematofluorometry and was examined for its relationship with clinical factors and cord blood laboratory measurements indicative of tissue oxygenation (plasma erythropoietin [EPO] and reticulocyte count) and iron status (plasma ferritin and erythrocyte indices). Statistical testing included 1-way analysis of variance, 2-way analysis of variance with covariates, simple linear regression, and multiple regression analysis. Results. Among control group subjects, gestational age at birth was inversely correlated with RBC ZnPP/H and reticulocyte count and positively correlated with ferritin and EPO. Relative to control subjects, IUGR and FDM fetuses at specified gestational age groupings had higher ZnPP/H, lower plasma ferritin, and higher plasma EPO. Statistical modeling of the relationship between ZnPP/H and plasma ferritin among all study groups demonstrated significant impacts of gestational age, plasma EPO, maternal hypertension, and maternal smoking. Conclusions. The inverse association of fetal ZnPP/H with gestational age at birth among control subjects is attributable to erythropoietic stimulation likely as a result of increasing growth velocity at the earliest gestational ages. The relatively higher ZnPP/H observed among fetuses in the IUGR and FDM groups likely is attributable to increased erythropoietic activity secondary to pathologic hypoxemia. Decreased placental iron transfer may also have limited iron availability and contributed to elevated ZnPP/H in the IUGR group. These data support the concept that increased erythropoietic activity and/or limited iron transport may place infants of diabetic mothers and infants with growth retardation at risk for developing systemic iron deficiency later in infancy and in early childhood.

Agreement between laboratory tests and self-reports of alcohol, tobacco, caffeine, marijuana and other drug use in post-partum women

The agreement between self-reported consumption of several drugs and laboratory tests used to detect their use is examined. Post-partum women (N = 108) enrolled in a research study participated in a detailed interview covering alcohol and caffeine ingestion, tobacco smoking and use of marijuana and other psychoactive drugs. They also kept a 4-day record of their use of these substances. Blood and urine samples were taken and a physical exam done at the close of the record period. Laboratory tests to detect use of alcohol, tobacco, caffeine, marijuana and other drugs were carried out and the results compared to self-reported drug use in the interview and the record. The degree of agreement depended on the drug taken, the test used and the pattern of drug use in the sample. Sporadic or infrequent consumption related poorly to laboratory tests, especially those that were designed as screening tools. Regular consumption could be identified with greater accuracy. However, the group associations evident between self-reports of drug use and laboratory results were not sufficient to guarantee that subjects were correctly classified. Error in both self-report and the decision made from laboratory values must be taken into account in determining the confidence that should be placed in the data and the conclusions drawn from it.

Relation of barbiturate structure to DPNH oxidase inhibition

Abstract A series of barbiturates, carbamides, and miscellaneous compounds were examined in order to elucidate the structural requirements for an Amytal-like inhibition of DPNH oxidase. It was found that the essential molecular structure consisted of a nonspecific hydrocarbon group attached to an amide, carbamide, or barbituric acid, these compounds having in common the CONH group. None of the compounds inhibited the oxidation of succinate by succinic oxidase. Similarity was noted between the structural requirements for DPNH oxidase inhibition and for experimental porphyria induction.

Zinc Protoporphyrin Past, Present, and Future

The course of zinc protoporphyrin research has progressed at an increasingly rapid pace on several fronts. A variety of biochemical and clinical evidence viewed in toto now suggests that ferrochelatase catalyzes zinc protoporphyrin formation in states of relative iron-deficient erythropoiesis and in lead-inhibited iron metabolism. Furthermore, a redefinition of the relationship of zinc protoporphyrin to certain other parameters of iron status has been made based upon changes during the earliest states of iron depletion. These clinical studies show that the zinc protoporphyrin level and the ferritin level vary in concert but that changes in the percent transferrin saturation and in the hematocrit results are less consistent. Thus zinc protoporphyrin and ferritin are closely linked metabolically such that iron-deficient erythropoiesis becomes an initial manifestation of iron depletion. The measurement and expression of results as mumoles zinc protoporphyrin/mole heme have improved the quality of results, partly by the elimination of the assumed hematocrit designed into existing instruments. Other refinements in hematofluorometry technology have permitted exploration of the potentially extensive applications of zinc protoporphyrin measurements for lead surveillance and diagnosis, blood banking, pediatrics, obstetrics, sports medicine, and other clinical situations where a very sensitive, cost-effective indication of iron status is required.

Ascorbic Acid Clearance in Diabetic Nephropathy

The incidence of cardiovascular disease is increased in diabetic nephropathy. Increased oxidative stress in diabetes is believed to play an important role in the pathogenesis of atherosclerosis in diabetes. Since antioxidant vitamins, such as ascorbic acid, often are reduced in diabetes, we hypothesized that the renal clearance of ascorbic acid is increased in patients with diabetic nephropathy. Thirty-seven subjects with diabetic nephropathy were studies: 18 had microalbuminuria (30-300 mg/day albuminuria); the remainder had clinical nephropathy (> 300 mg/day albuminuria). Indices of glycemic control (glucose, hemoglobin A1C) and renal function (albuminuria and creatinine clearance) were measured in addition to serum and urinary ascorbic acid levels. Results showed that subjects with clinical nephropathy had lower mean plasma ascorbic acid (p=0.0009) and higher renal clearance of ascorbic acid (p=0.005) than those with microalbuminuria. Bivariate analysis revealed an inverse correlation between creatinine clearance and AA clearance (r=-0.42, p=0.009). There was a significant linear association between the quantity of albuminuria and ascorbic acid clearance (r=0.49, p=0.002). Thus, patients with diabetic nephropathy have reduced ascorbic acid levels due to increased ascorbic acid clearance. The decrease in antioxidant defense that arises from the low levels of vitamin C may contribute to the increased cardiovascular morbidity and mortality observed in this population.