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Biomedical subjects

R F Labbé

Publications and source records attributed to R F Labbé.

24 records · Page 2Linked to original sources
PubMed1977

History and background of protoporphyrin testing.

Lead intoxication was first associated with increased coproporphyrin excretion almost 100 years ago; but not until the 1930's were abnormalities in blood protoporphyrin detected. These later findings have been interpreted as an inhibition by lead of iron incorporation into protoporphyrin during heme synthesis. The testing and application of this hypothesis had to await three more decades of research during which prophyrin/heme biosynthesis was elucidated, control of the pathway was intensively studied, and methodology was greatly improved. The heme biosynthetic pathway is uniquely affected by lead at several sites. These toxic effects can be manifested as increased coproporphyrin and delta-aminolevulinate excretion, decreased erythrocyte delta-aminolaevulinate dehydratase activity, and increased erythrocyte protoporphyrin concentration, all of which have been used and promoted as diagnostic tests for lead intoxication. Among these, the last appears to be becoming the test of choice. The historical background of this development is discussed from a biochemical viewpoint.

Erythrocytes↗
PubMed1976

Erythrocyte uroporphyrinogen I synthase activity in diagnosis of acute intermittent porphyria.

Measurement of the activity of uroporphyrinogen I synthase provides an excellent laboratory aid in the diagnosis of acute intermittent porphyria, particularly in those patients who are asymptomatic or in whom the disease is not biochemically manifested by porphyrin precursor excretion. We describe here a simplified fluorometric method for measuring the activity of this enzyme in whole blood. The assay is based upon a coupled-enzyme procedure in which added delta-aminolevulinic acid and the dehydratase that is present in erythrocytes are used to generate porphobilinogen as substrate for uroporphyrinogen synthase. After appropriate incubation the protein is removed we sensitivity, specificity, and precision of the assay compare well with previously described procedures. Activity in nonporphyric male subjects was 31 (SD, 6.0) nmol of porphyrin formed per milliliter of erythrocytes per hour at 37 degrees C. Application of the method for identifying gene carriers of acute intermittent porphyria is demonstrated in three generations of an affected family.

Acute Disease↗
PubMedDate not supplied

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.

Adult↗