Biomedical subjects
A Kahn
Publications and source records attributed to A Kahn.
Guanine nucleotide--an intracellular traffic cop.
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Medicine era 1985.
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[Study of hereditary fructose intolerance by methods of molecular biology].
Fructose intolerance is caused by a deficit of the liver aldolase B enzyme. Its molecular mechanisms were studied at different sites: The protein was studied by a method combining electrophoresis, transfer and immunology. It was present in the 15 cases examined. The genetic variability was demonstrated by the quantitative differences of the immunoreactive proteins. Aldolase messenger RNA was prepared and used to direct in vitro synthesis of human aldolase. Cloning complementary DNA of human aldolase was achieved by using the messenger RNA. Two clones were prepared. The aldolase B gene was then analysed using restriction enzymes in 60 control subjects and 11 patients. An abnormality of the DNA was demonstrated in one of the patients and in her father.
Aseptic loosening in metal-backed acetabular components for total hip replacement. A minimum five-year follow-up.
We reviewed the cases of thirty-six patients who had forty cemented total hip replacements with the Harris metal-backed acetabular component. The operations were done between 1972 and 1977, and the duration of follow-up averaged 7.6 years (range, five to 10.8 years). The average age of the patients was forty-four years (range, sixteen to sixty-two years). Aseptic loosening of the acetabular component occurred in three hips (7.5 per cent), and three more sockets were revised for other reasons. Two of the three sockets with aseptic loosening were in the fifteen patients (seventeen hips) who were forty-five years old or younger. The remaining loose cup was in one of the twenty-one patients (twenty-three hips) who were forty-six years old or older. The reduction in the rate of aseptic loosening of the socket in our series, compared with the higher rates reported in similar long-term studies in which other acetabular components were used, supports the conclusion that there is enhanced longevity of acetabular fixation when a metal-backed acetabular component is used in cemented total hip arthroplasty.
Phenothiazine-induced sleep apneas in normal infants.
A relationship between sudden infant death syndrome and the use of phenothiazine-containing medications is suspected. In order to investigate the influence of phenothiazines upon cardiorespiratory and sleep characteristics, four normal infants (mean age 15.8 weeks) had polygraphic recordings made for one night. The recordings were repeated three nights later, after the daily administration of a usual therapeutic dose of a standard phenothiazine syrup (promethazine, 1 mg/kg of body weight per day). The infants were monitored for six days after the first treatment. Findings from the first polygraphic recordings were normal for each infant. The second recordings disclosed an increase in sleep time, a reduction in the number and duration of awakenings, an increase in non-rapid eye movement (NREM) III sleep state, and a reduction in body movements. During the second night, each infant showed an increase in the number of central apneas, and each infant also had several episodes of obstructive apneas (median duration four seconds). It is concluded that promethazine depresses the arousal and respiratory mechanisms in normal infants during sleep. This observation reinforces the opinion that CNS depressants should be avoided in infants less than 1 year of age; CNS depressants could result in sudden death in apnea-prone infants.
[Sleep in school-age children].
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Insomnia and cow's milk allergy in infants.
A group of eight infants (six boys and two girls, 7 to 46 weeks of age) is reported, in whom a causal relationship between cow's milk allergy and chronic sleeplessness was suspected. They were referred because of waking and crying episodes that had occurred since the early days of life during sleep hours. During an average night, they slept about 4.5 hours and woke their parents about five times. They cried a lot during the day and were described as fussy. Two infants had been treated with phenothiazine without improvement. No cause for chronic insomnia was found during a standard medical and psychologic workup. An all-night polygraphic recording confirmed the disrupted sleep pattern of these infants, as compared with that of normal infants, and excluded further causes of arousals. Due to a clinical suspicion of atopy, the infants were further subjected to a series of allergy tests. IgE levels were shown to be elevated in each child, and radioallergosorbent tests were positive for cow's milk protein. The infants were than fed exclusively with a hydrolyzed milk protein mixture for 4 weeks. Sleep normalized within 2 weeks in every infant: night sleep increased to a median of 10 hours, and the awakenings only occurred occasionally. In four infants less than 6 months of age, cow's milk was reintroduced in the diet, and within 1 week all four became severely sleepless. Cow's milk was again excluded from the diet and the babies' sleep behaviors were again normalized. It is concluded that, when no evident cause for sleeplessness can be found in an infant, the possibility of milk allergy should be given serious consideration.
Cyclic AMP as a transcriptional inhibitor of upper eukaryotic gene transcription.
Recently, glucagon and its second messenger, cyclic AMP, have been shown to stimulate the transcription rate of several upper eukaryotic genes (1-5). We show here that glucagon can also block gene transcription. Both glucagon and cyclic AMP were found to inhibit the transcription of the genes encoding three liver glycolytic enzymes, including L-type pyruvate kinase and aldolase B. Thus, cyclic AMP proves to be not only an activator but also an inhibitor of gene transcription in eukaryotes.
Immunological screening of standard cDNA libraries in pBR322 vectors: detection of human fibrinogen and prothrombin cDNA clones.
The in situ immunological detection of antigens encoded by cDNA inserted into the PstI site of pBR322 plasmids was optimized. It was found that sensitivity of the detection was dramatically increased by in situ amplification of the recombinant plasmids on chloramphenicol-containing medium followed by a brief incubation without chloramphenicol during which protein synthesis resumes. In addition, several modifications of the previously described methods which permit total suppression of background and false positives are described. These techniques allowed easy detection of cDNA clones for human B beta- and gamma-fibrinogen and -prothrombin using a human liver double-stranded cDNA recombinant plasmid library in pBR322 vectors.
Tuberculosis management in Soweto.
Despite the availability of highly effective therapy, tuberculosis (TB) remains a major problem in South Africa, even in urban centres such as Soweto which is relatively well provided with health services. We therefore assessed two aspects of TB management in Soweto: (i) the proportion of known tuberculous patients adequately treated; (ii) whether case finding through investigation of home contacts of notified patients was effective. In 1978 patients with TB were required to take chemotherapy for at least a year. Only 28% of newly notified patients attended the clinics frequently enough and/or were hospitalized long enough to obtain 80% or more of the treatment they required during that first year. A major part of this problem of non-compliance was infrequent attendance; these patients received therapy of an adequate duration, but at an inadequate dosage. At least 17% of patients over 10 years of age had tubercle bacilli in their sputa on microscopy more than 4 months after therapy was started. About two-thirds of known home contacts were investigated by the health services in accordance with their stated policy, and 5% of contacts were subsequently notified. Home-contact tracing therefore seems worthwhile.
In vivo hormonal control of L-type pyruvate kinase gene expression. Effects of glucagon, cyclic AMP, insulin, cortisone, and thyroid hormones on the dietary induction of mRNAs in the liver.
Using a cDNA probe complementary to rat L-type pyruvate kinase mRNAs, we studied the respective roles of glucocorticoids, thyroid hormones, glucagon, and insulin in the induction of specific mRNAs in the liver of animals refed either a maltose-rich or a fructose-rich diet. Neither adrenalectomized nor thyroidectomized nor diabetic animals could express L-type pyruvate kinase mRNAs in their liver when refed the carbohydrate-rich diets. When the animals were given the missing hormone, the level of hybridizable mRNAs returned to normal values but administration of the hormone alone failed to induce mRNA synthesis in fasted animals. Both glucagon and cyclic AMP abolished the induction of L-type pyruvate kinase mRNAs in refed animals. Exogenous insulin, whatever the dose, could not reverse the inhibitory action of glucagon. Insulin has usually been regarded as the main regulator of L-type pyruvate kinase gene expression. It appears now that glucagon, beside regulating the enzyme activity by phosphorylation mechanisms, may also modulate L-type pyruvate kinase synthesis at a pre-translational level. Consequently, our results show that three conditions are required for the synthesis of liver L-type pyruvate kinase mRNAs: (i) the presence of dietary carbohydrates, (ii) the cessation of glucagon release, and (iii) the presence of permissive hormones, including insulin.
Expression of the transferrin gene during development of non-hepatic tissues: high level of transferrin mRNA in fetal muscle and adult brain.
Using a cloned rat transferrin cDNA probe, we looked for transferrin mRNA in the various rat tissues during development. In all the cases the mRNA detected seemed to be the same and to be product of a single gene. The transferrin gene is early expressed at a high level during liver differentiation. In the muscle and other non-hepatic and non-nervous tissues, the gene expression is maximal just before birth (19-20th day of gestational age), then markedly decreases during the postnatal development, the mRNA level being very low in the adult tissues. In brain, by contrast, transferrin mRNA level is very low before birth, then gradually increases during the postnatal development and reaches a plateau in the adult. Maximal mRNA concentration in fetal muscle (2 days before birth) and adult brain is about 1:7 to 1:10 of that obtained in adult liver. These results are analyzed in the light of the evidence that transferrin is not only an iron-binding protein, but also a factor involved in cell proliferation and differentiation, and particularly in nerve control of muscle differentiation.
Analysis of fibrinogen genes in patients with congenital afibrinogenemia.
Several cDNA clones coding for A alpha, B beta and gamma chains of fibrinogen have been isolated from a human liver cDNA library. They were selected by differential hybridization with probes raised against fractionated liver mRNA (positive probes) and muscle and albumin mRNA (negative probes), then firmly identified by positive hybridization selection. Three of these clones, encoding A alpha, B beta and gamma fibrinogen chain sequences, were further characterized by restriction mapping and used as probes to characterize fibrinogen mRNAs from adult and fetal liver and fibrinogen genes in normal individuals and two afibrinogenemic patients. The results indicate that there is a single copy of the fibrinogen genes which are present and grossly intact in afibrinogenemic DNA.
Molecular cloning and sequence analysis of cDNA for human transferrin.
A cDNA clone for human transferrin was identified from a human liver cDNA library by pre-screening with different ss-cDNA probes against length-fractionated liver mRNAs, positive hybridization-selection and nucleotide sequence analysis. The insert was of 1 kb, encoding human transferrin from aminoacid 403 through the COOH terminus, with a 3' non coding region of 166 nucleotides. This insert hybridized with a single major mRNA species of about 2.4 kb and several genomic DNA restriction fragments. Hybridization of the Southern blots with different parts of the transferrin insert and at different stringences suggest that the various bands observed correspond to splice sites inside one gene rather than to hybridization to several related genes. Finally, a single or a low number of transferrin gene copies seem to exist in the human genome.
Treatment of congenital osteopetrosis with high-dose calcitriol.
We administered high doses of calcitriol (up to 32 micrograms per day) to an infant with malignant osteopetrosis, in an attempt to stimulate bone resorption. The patient was placed on a low-calcium diet to prevent hypercalcemia. Measures of bone turnover increased during calcitriol therapy; hydroxyproline excretion rose from 140 to 1358 micrograms per milligram of creatinine per 24 hours, with parallel increases in the ratio of calcium to creatinine in the urine, urinary gamma-carboxyglutamic acid, serum osteocalcin, and serum alkaline phosphatase. A pretreatment bone-biopsy specimen contained no osteoclasts with ruffled borders, a feature of active osteoclasts. After 11 days of calcitriol, ruffled borders were noted. After three months, numerous osteoclasts with ruffled borders and associated bony disruption were evident. Before therapy, the patient's monocytes were incapable of in vitro bone resorption, but after calcitriol, their resorptive capacity was increased to 3.3 times control levels. These data demonstrate that calcitriol increased bone mineral and matrix turnover in our patient. However, during the three months of calcitriol therapy there was only slight clinical improvement in her severe disease. Early and sustained treatment with calcitriol may be useful in osteopetrosis.
Dietary control of aldolase B and L-type pyruvate kinase mRNAs in rat. Study of translational activity and hybridization with cloned cDNA probes.
Liver L-type pyruvate kinase and aldolase B mRNAs are the two species whose translational activity increases the most after feeding starved rats a high carbohydrate diet (Simon, M. P., Besmond, C., Cottreau, D., Weber, A., Chaumet-Riffaud, P., Dreyfus, J. C., Sala Trépat, J., Marie, J., and Kahn, A. (1984) J. Biol. Chem., in press). We therefore compared the pattern of this induction in three tissues synthesizing these enzymes, e.g. the liver, small intestine, and kidney. Influence of high lipid and protein diets on liver L-type pyruvate kinase and aldolase B mRNAs was also investigated. In the starved rat livers, L-type pyruvate kinase mRNA was practically undetectable. Carbohydrate diet induced an increase of both mRNA concentrations, with a maximum at the 12-18th h; at this time, mRNA concentration was increased about 4-8 times for aldolase B and 40-100 times for L-type pyruvate kinase, translational activities representing about 1% of the total mRNA activity for both enzymes. After the 24th h of carbohydrate diet, mRNA concentrations decreased slightly, then remained in plateau. In animals refed the high carbohydrate diet, starvation as well as high lipid and protein diets provoked a rapid decrease of both mRNA concentrations and translational activities. In the kidney, aldolase B mRNA synthesis was high in starved rats and was only slightly stimulated by carbohydrates (1.5-2.5 times). L-type pyruvate kinase mRNA concentration was increased 6-15-fold after feeding a high carbohydrate diet. In the small intestine, in contrast, the extent of aldolase B mRNA induction by a carbohydrate diet was similar to that in the liver, while L-type pyruvate kinase mRNA concentration was practically similar in starved and refed rats (about 1:10 of the concentration observed in refed rat liver). These results seem to indicate that the mechanisms responsible for carbohydrate induction of L-type pyruvate kinase and aldolase B are different. In addition, dietary control of each enzyme is also different in the various tissues which synthesize them.