Jean-Pierre Clot

E1 pyruvate dehydrogenase deficiency in a child with motor neuropathy.

ABSTRACT: We report the case of a boy who developed a motor neuropathy during infectious episodes at 18 mo and 3 y of age. When he was 7 y old, he suffered persistent weakness and areflexia; his resting lactate and pyruvate values were 3.65 mM and 398 μM, respectively (controls: 1.1 ± 0.3 mM and 90 ± 22 μM), and an exercise test demonstrated a lactic acidosis (13.6 mM; controls: 6.4 ± 1.3 mM) with a high pyruvate level (537 μM; controls: 176 ± 15 μM) and a low lactate/pyruvate ratio (24.2; controls: 35 ± 2). The results of polarographic studies on muscle mitochondria suggested a defect in pyruvate oxidation (pyruvate 17 ng atom O/min/mg protein; controls: 115 ± 42), whereas glutamate, palmitoylcarnitine, and succinate were good respiratory substrates. The activity of total pyruvate dehydrogenase complex (PDHC) in muscle mitochondria and in fresh mononuclear cells was markedly decreased (9.7 and 0.054 nmol 14CO2/min/mg protein, respectively; controls: 123 ± 4.5 and 0.733 ± 0.03, respectively). Immunochemical analysis in muscle mitochondria demonstrated an absence of the α and β El PDHC subunits. After 2 y of treatment with 500 mg/d thiamine, the patient was clinically improved. A genetic study of the main regions of mutations (exon 10 and 11) in the X chromosome encoding for the El α subunit of PDHC did not show any mutation. These data indicate that, although genetically different, this case enters in a very rare category of patients with PDHC deficiency without cerebral dysfunction and improved by thiamine + L-carnitine therapy.

Evidence that growth hormone stimulates protein kinase C activity in isolated rat hepatocytes

The mechanism of action of growth hormone (GH) is not known, although indirect evidence suggests that protein kinase C (PKC) might play an important role in the insulin-like actions of GH. In this investigation, we directly examined the effects of GH relative to those of insulin on PKC activity in isolated rat hepatocytes. Human GH (10(-7) mol/L) significantly increased the activity of PKC in both cytosolic and particulate fractions. The effect was maximal at 1 minute, disappeared at 5 minutes, and then increased again at 30 minutes in both fractions. At 1 minute, maximal and half-maximal stimulation of PKC activity occurred at hGH concentrations of 10(-7) and 5 x 10(-9) mol/L, respectively. Insulin (10(-7) mol/L) also induced a significant and transient increase in enzyme activity at 2 minutes in cytosolic and particulate fractions; at 30 minutes, PKC activity was decreased in the soluble fraction (-17%) and increased in the particulate fraction (+65%). Measurement of specific [3H]-phorbol dibutyrate (PDBu) binding suggested translocation of PKC from the cytosol to the membrane fraction after 30 minutes of incubation, only after insulin treatment. The early effects of GH and insulin on PKC activity were additive in both the particulate and cytosolic fractions. Although the later effects of GH and insulin on PKC were quite different, both hormones rapidly activated PKC in isolated hepatocytes, suggesting that PKC might be involved in triggering the insulin-like actions of GH.

Effects of growth hormone on growth factors after renal transplantation

Abstract Growth retardation occurs frequently in renal transplanted children (RTx) and can be improved by growth hormone (GH) treatment. This study retrospectively examines the insulin-like growth factor-1 (IGF-1) and IGF binding protein (IGFBP) profile of ten growth-retarded children previously given renal allografts, after 1 year of GH treatment period. Ten prepubertal patients (nine boys and one girl) were investigated. They had a mean chronological age (CA) of 11.4±1.1 years and a mean bone age (BA) of 7.3±0.9 years. Mean height was –3.9±0.4 SD units below the mean for CA. The mean body mass index (BMI) was 16.9±0.6 and the mean inulin clearance was 36.5±4.9 ml/min/1.73 m2. Recombinant hGH was given at 4 IU/m2/day. Plasma GH, total and free IGF-1, IGFBP-2 and -3 were measured by specific radioimmunoassay (RIA). IGFBPs were characterized by SDS PAGE techniques and ligand and immunoblot analyses. Mean velocity was markedly increased (P<0.01) after 1 year of GH therapy, expressed as SD score for BA. The range of growth response was wide. The total and free plasma IGF-1 increased (P<0.01) by about 100% (mean values after GH therapy: 95.9± 2.1 nM and 165±29 pM, respectively). Plasma IGFBP-3 concentrations increased by about 40% (mean value: 148±18 pM, P<0.01), with a concomitant increase in both intact IGFBP-3 and its 30-kDa proteolytic fragment. There was no change in plasma IGFBP-2 concentration. Both mean values of inulin clearance and BMI were unchanged during the treatment. In view of the IGF-1/IGFBP concentration changes, there should have been an even better growth response to GH therapy in these patients. This strongly suggests IGF-1 insensitivity, probably as a result of corticosteroid therapy.

Degradation of Insulin and Glucagon in Isolated Liver Endosomes: Functional Relationships with ATP-Dependent Endosomal Acidification and Partial Characterization of Degradation Products

Upon interaction with liver cells, insulin is internalized along with its receptor into nonlysosomal endocytic structures termed endosomes (Bergeron et al, 1985; Sonne et al, 1989). At least three lines of evidence suggest that the degradation of internalized insulin occurs in endosomes rather than in lysosomes. First, little association of insulin with lysosomes is demonstrable in ultrastructural and cell fractionation studies (Bergeron et al, 1985). Secondly, the insulin which is recovered from endosomal fractions isolated at various stages of endocytosis undergoes a rapid loss in integrity (Duckworth et al, 1988; Sonne et al, 1989). On HPLC, two major degradation products with an intact A chain and three products with a cleaved B chain have been identified (Hamel etal, 1988). Third, a further loss of insulin integrity occurs when endosomal fractions containing internalized insulin are incubated at 37°C in isotonic medium (Pease et al, 1985).