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J T Dunn

Publications and source records attributed to J T Dunn.

At least 37 records · Page 2Linked to original sources
PubMed1996

mRNA encoding human thyroglobulin's C-terminus is heterogeneous.

Thyroglobulin (Tg) provides the peptide backbone for synthesis for thyroid hormones. Because previous studies by various techniques have raised the possibility of heterogeneity in Tg's message and translated protein, we have applied a highly sensitive ribonuclease protection assay (RPA) to examine the mRNA species translating part of Tg's C-terminal region, an area containing three of Tg's hormonogenic sites. Tissue samples were obtained from 18 normal and diseased human thyroids at surgery. Three probes spanning part or all of the nucleotide segment containing bases 7808-8086 in the cDNA sequence, detected full-length mRNAs as the dominant transcripts but also showed the consistent presence of at least seven discrete smaller mRNA species in the thyroid samples. The amounts of these smaller mRNAs varied among tissue samples without a discernible relationship to the underlying clinical thyroid condition. We conclude that the mRNA for this region of Tg is quite heterogeneous and offers potential opportunities for translation of different peptide sequences that might affect hormonogenesis in the C-terminal region of the protein.

Adult↗
PubMed1996

The combined action of two thyroidal proteases releases T4 from the dominant hormone-forming site of thyroglobulin.

Thyroid hormones are synthesized within the thyroglobulin (Tg) molecule and must be released to reach the circulation and exert their metabolic effect. We have previously shown that three lysosomal endopeptidases, cathepsin B, D, and L, are active in the early stages of intrathyroidal degradation of Tg but do not themselves release free hormone. The current study examines the role of exopeptidases as the next step in thyroid hormone release. Human thyroidal cathepsin B and two partially purified exopeptidases, dipeptidyl peptidase II (DP-PII) and lysosomal dipeptidase I (LDPI), were used to digest the 20-kDa N-terminal peptide of rabbit Tg, which contains the dominant T4 site of Tg at residue 5. Cathepsin B acted as an endopeptidase initially, producing small T4-containing peptides. After more extended digestion, it also acted as an exopeptidase, producing the dipeptide T4-Gln, corresponding to residues 5 and 6 of Tg. Lysosomal dipeptidase I alone had no effect on 20 kDa but acted in combination with cathepsin B to release T4 from the T4-Gln dipeptide. Although addition of DPPII increased the release of hormone from 125I-Tg by an extract of DPPII-deficient lysosomes, it had no apparent effect on the degradation of the 20-kDa peptide, either alone or in combination with cathepsin B or LDPI. Thus DPPII may act in synergy with some other endopeptidase, or alternatively, may play a role in the release of hormone from other sites in Tg. We conclude that the N-terminus of Tg, which contains its major hormonogenic site, is particularly susceptible to hydrolysis by the endopeptidase cathepsin B and that cathepsin B additionally has an important exopeptidase action that allows it to release a T4 dipeptide that is then further degraded by LDPI to release free T4.

Amino Acid Sequence↗
PubMed1996

Seven deadly sins in confronting endemic iodine deficiency, and how to avoid them.

Iodine deficiency is a problem for almost all countries of the world. Goiter is its most obvious consequence, but others do more damage, particularly effects on the developing brain. In 1990, most countries and international agencies pledged the virtual elimination of iodine deficiency by the year 2000. The technology for the assessment and implementation is sufficient to attain this goal, but translating its potential into success requires careful planning. This article reviews seven major errors that frequently occur in iodine supplementation programs and offers suggestions for their avoidance. They are 1) unreliable assessment of iodine deficiency: the best indicators are urinary iodine concentration, thyroid size (preferably by ultrasound), blood spot thyroglobulin levels, and neonatal TSH determinations; the best group for surveys is schoolchildren; 2) poor iodine supplementation plan: iodized salt is the preferred supplement; its effective application frequently requires extensive changes in salt production and marketing, and poor handling of these changes will endanger the iodization program; other measures include iodized oil, iodized water, and iodine drops; all are occasionally useful, but the long range solution should generally be iodized salt; 3) exclusion of relevant stake-holders: the program should include not only health authorities but other arms of the government as well (education, commerce, agriculture, and standards), the salt industry, health professionals, and the iodine-deficient community itself; 4) inadequate education: an understanding of the effects of iodine deficiency and the means for its correction is essential at all levels, from government to affected population; 5) insufficient monitoring: the best instruments are urinary iodine levels, iodized salt use, and thyroid size, measured in representative groups at regular intervals with public reporting of results; 6) inattention to cost: the expense of iodization must be recognized and apportioned fairly; and 7) nonsustainability: for permanent success, an iodization program must be fair to all relevant parties and accompanied by a regular system of appropriate monitoring. Only with careful avoidance of these seven "deadly sins" can the goal of sustainable elimination of iodine deficiency be achieved.

Child↗
PubMed1995

Neurotoxic complaint base rates of personal injury claimants: implications for neuropsychological assessment.

This study reports base rate data for 113 family practice patients with no history of head trauma or toxic exposure, 68 family practice patients with a history of head trauma or toxic exposure, and 156 personal injury claimants with no history of toxic exposure or head trauma who presented for a psychological evaluation due to emotional distress. Personal injury claimants reported suffering from significantly more neurotoxic and neuropsychologic symptoms than subjects with a reported history of head trauma and/or toxic exposure. The authors urge that evaluating psychologists consider the base rate of these symptoms in litigating populations and use caution in relying on self-reported symptoms as evidence of injury when patients are in litigation.

Adult↗
PubMed1995

Thyroids from siblings with Pendred's syndrome contain thyroglobulin messenger ribonucleic acid variants.

We studied thyroid tissue from two siblings with Pendred's syndrome (familial goiter and congenital deafness), both with the Mondini-type inner ear malformation, goiter, and hypothyroidism. Iodine trapping and peroxidase levels were grossly normal. Thyroglobulin (Tg), the only iodoprotein found, had a normal monomer size (330 kilodaltons), but low content of hormone and iodine. Tg's expected N-terminal peptides of 26 and 18 kilodaltons, usually formed in association with iodination and thyroid hormone synthesis, were absent, but appeared after iodination in vitro. Reverse transcription of ribonucleic acid from Pendred thyroid tissue and amplification by polymerase chain reaction of specific regions encoding the most important hormonogenic sites of Tg revealed a normal complementary DNA sequence corresponding to the first 100 amino acid residues in Tg's N-terminus. However, 3 of 35 clones of the 3'-region corresponding to the Tg C-terminus exhibited a deletion of nucleotides 7860-7994; this deletion was not present in any of the 150 clones from 7 other thyroids we examined. Four Pendred clones had a 2-nucleotide deletion at positions 7870-7871, a change that would result in a premature stop codon and was found in thyroids from several other subjects as well. We conclude that the messenger ribonucleic acid encoding the 3'-region of Tg can be abnormal in Pendred's syndrome. Some, but not all, of these changes also occur in other human thyroids. Further work is necessary to show if and how these alterations relate to defective hormone synthesis and goiter.

Adult↗
PubMed1994

The ability of naive subjects to report symptoms of mild brain injury, post-traumatic stress disorder, major depression, and generalized anxiety disorder.

Diagnoses of major depression, post-traumatic stress disorder, generalized anxiety disorder, and mild brain injury are based in substantial part on the self-reported symptoms of patients. This study found that 96.9% of untrained subjects were able to endorse symptoms on checklists to meet the DSM-III-R self-report criteria for major depression, 96.9% for generalized anxiety disorder, and 86% for PTSD. For the non-DSM-III-R diagnosis of mild brain injury, 63.3% of subjects were able to correctly identify 5 or more of 10 symptoms associated with this condition. Forensic examiners are advised to exercise special care in utilizing evaluation procedures that are of a leading nature, such as symptom checklists in which examinees may exhibit response biases.

Adolescent↗
PubMed1994

Oral iodized oil for correcting iodine deficiency: optimal dosing and outcome indicator selection.

Oral iodized oil is the major alternative to iodized salt for correcting endemic iodine deficiency. This study responds to a need for better guidelines in its use. Schoolchildren, aged 6-11 yr, from a severely iodine-deficient area of Algeria received iodized poppy seed oil (Lipiodol) in a single oral dose containing 120, 240, 480, or 960 mg iodine (groups A-D) or in an im injection of 480 mg iodine (group E). Thyroid volume by ultrasonography had not changed 395 days after treatment in groups A, B, and C, had decreased in groups D and E. Urinary iodine concentration rose rapidly from an initial median of 0.21 mumol/L, but fell below 0.79 mumol/L (the currently accepted level for indicating iodine deficiency) by 150 days for groups A and B, and by 395 days for groups C and D. Median serum TSH and T4 levels were normal before and after treatment, whereas high initial serum thyroglobulin values decreased in all groups after iodized oil treatment. For correcting iodine deficiency in children, we recommend single oral doses of Lipiodol containing 240 mg iodine for 6-month coverage or 480 mg for 12 months. These doses may not completely sustain iodine sufficiency, but will prevent the worst of the iodine deficiency disorders. Additionally, we conclude that the urinary iodine concentration is the most useful epidemiological indicator for assessing current iodine status, and thyroid volume and serum thyroglobulin levels are the best markers for assessing chronic effects.

Algeria↗
PubMed1993

Iodine supplementation and the prevention of cretinism.

Normal development of the CNS requires adequate thyroid hormone exposure. Since iodine is an essential component of the thyroid hormone molecule, its deficiency during fetal development can cause hypothyroidism and irreversible mental retardation. The full-blown syndrome, called cretinism, includes deaf-mutism, short stature, spasticity, and profound mental retardation. The clinical spectrum can vary in degree and combination of these features. Screening programs in iodine-deficient countries show that up to 10% of neonates have elevated serum TSH levels, putting them at theoretical risk for permanent brain damage. About one billion people worldwide risk the consequences of iodine deficiency, all of which can be prevented by adequate maternal and infant iodine nutrition. Iodized salt is usually the preferred prophylactic vehicle, but iodized vegetable oil, iodized water, and iodine tablets are also occasionally used. The United Nations and the heads of state of most countries have pledged the virtual elimination of iodine deficiency by the year 2000. This goal is technically feasible if pursued with sufficient vigor and resources.

Central Nervous System↗
PubMed1993

Two simple methods for measuring iodine in urine.

Urinary iodine excretion is currently the most convenient laboratory marker of iodine deficiency. Accelerating international interest in correcting this condition demands rapid, simple methods for assessment and monitoring. We describe two adaptations of the Sandell-Kolthoff reaction, in which urine is first digested with chloric acid and iodine then determined from its catalytic reduction of ceric ammonium sulfate in the presence of arsenious acid. Both methods use gentle digestion by chloric acid in a heating block. Method A detects iodine in a colorimeter, method B by the indicator ferroin and a stopwatch. Results with 12 samples ranging from 1.8 to 19.0 micrograms/dL (0.14-1.48 mumol/L) differed from those in a reference laboratory by a mean of 9.1% for method A and 15.7% for method B. One technician can perform at least 150 tests per day at a total cost of less than $0.50 each. The speed, low cost, and simple instrumentation make these methods well suited to epidemiological assessment of iodine deficiency in developing countries.

Colorimetry↗
PubMed1993

Coordinated strategies for controlling micronutrient malnutrition: a technical workshop.

Participants in a November 1991 workshop concluded that coordinated strategies for controlling malnutrition due to iodine, iron, vitamin A and other micronutrients deficiencies are technically feasible and should be given consideration in planning control efforts. Coordinated surveys involving clinical, biochemical and dietary assessment of multiple micronutrients are feasible. Multiple fortification is also possible using such vehicles as salt, processed rice or sugar. Supplementation efforts can be integrated with existing health care programs. Food-based strategies are also effective. The best examples have been community-based and have included a strong nutrition and health education component designed to change food consumption patterns, improve food preservation and preparation practices, and link income-generating activities with food production activities. Successful coordinated efforts will require a strong political commitment and a supportive infrastructure. Specific recommendations include the formation of national coordinating bodies for micronutrient deficiency control, establishment of a micronutrient information network and expansion of technical exchange and training.

Developing Countries↗
PubMed1991

Thyroglobulin processing by thyroidal proteases. Major sites of cleavage by cathepsins B, D, and L.

The normal provision of thyroid hormones to the body requires their release from the prohormone, thyroglobulin (Tg). Previous work established the importance of cathepsins B, D, and L (formerly designated cysteine proteinase I) to this process but had not defined the points of proteolytic attack for each enzyme. In the present study we labeled rabbit Tg in vivo with sodium 125I and performed limited digestions with cathepsins B, D, and L, purified from human thyroids. The resultant peptide fragments were analyzed by amino-terminal sequencing and located within the Tg molecule by comparison with the cDNA-derived sequences from human Tg. We identified three cleavage points for cathepsin B, corresponding to P'1 residues 532, 795, and 2487; four cleavage points for cathepsin L, corresponding to P'1 residues 2389, 2452, 2490, and 2657; and four cleavage points for cathepsin D, corresponding to P'1 residues 551, 1835, 2468, and 2643. None of the cleavage points was near Tgs known hormonogenic sites, but these peptide fragments contained three of the four major hormonogenic sites in rabbit Tg, suggesting some preference for their early proteolytic processing. Cathespin B alone among the three endopeptidases had some exopeptidase activity toward Tg. The cleavage specificities for each of the endopeptidases resembled those described with other protein substrates. Thus, cathepsin D preferentially cleaved bonds between hydrophobic residues, and cathespin L cleaved bonds with hydrophobic residues at P2 and P3. Although cathepsin Bs specificity was less obvious, it produced a major cleavage between 2 leucine residues. The existence of three endopeptidases cleaving at different sites shows that Tg proteolysis is a complex process, suggests synergism among their enzyme activities, and provides a physiological mechanism for selective hormone release, including its regulation by TSH.

Alkylation↗
PubMed1991

Proteolytic processing of thyroglobulin by extracts of thyroid lysosomes.

The release of T4 and T3 from the prohormone thyroglobulin (Tg) occurs in thyroid lysosomes. To examine the role of cathepsin-B, -D, and -L, the three major endopeptidases in this process, we incubated rabbit [125I]Tg, labeled in vivo, with lysosomal extracts from human thyroids. Iodopeptide formation was evaluated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate after short term incubations (20-45 min), while iodoamino acid release was assessed by paper chromatography after long term incubations (8 and 24 h). Using pepstatin to inhibit cathepsin D, Z-Phe-Ala-CHN2 to inhibit both cathepsin B and L, and Z-Phe-Phe-CHN2 to selectively inhibit cathepsin L, we obtained the following results: 1) blocking of all three endopeptidases reduced both iodopeptide formation in short term experiments and iodoamino acid release in long term experiments by 80-90%; 2) iodopeptide formation was reduced by 85% with Z-Phe-Ala-CHN2, by 56% with Z-Phe-Phe-CHN2, and by 26% with pepstatin; 3) iodoamino acid release was reduced by 60-80% with Z-Phe-Ala-CHN2 and by 40-50% with either Z-Phe-Phe-CHN2 or pepstatin at 8 h, but by less than 20% at 24 h; pepstatin and Z-Phe-Phe-CHN2 together reduced iodoamino acid release by 80% and 60% at 8 and 24 h, respectively. Limited hydrolysis of Tg by lysosomal enzymes produced at least eight peptide fragments of less than 100,000 mol wt. Three of these, together representing 32% of the 125I released, resulted from cleavages in the C-terminal region of Tg corresponding to residues 2487, 2393, and 2390 of cDNA-derived human Tg. Several other peptides, together containing 38% of the 125I released, included the N-terminus of Tg. These C-terminal and N-terminal fragments contained three of Tg's four major hormonogenic sites, but none of the cleavage sites fell close to the hormone sites themselves. We conclude that 1) the formation of discrete iodopeptides precedes the release of iodothyronines and iodotyrosines from Tg; 2) the cysteine proteinases are more important than cathepsin D in this process; and 3) these endopeptidases selectively cleave Tg to favor the production of hormone-containing intermediates for subsequent processing by exopeptidases.

Chromatography, High Pressure Liquid↗