Natural variation in light sensitivity of Arabidopsis

Because plants depend on light for growth, their development and physiology must suit the particular light environment. Plants native to different environments show heritable, apparently adaptive, changes in their response to light. As a first step in unraveling the genetic and molecular basis of these naturally occurring differences, we have characterized intraspecific variation in a light-dependent developmental process-seedling emergence. We examined 141 Arabidopsis thaliana accessions for their response to four light conditions, two hormone conditions and darkness. There was significant variation in all conditions, confirming that Arabidopsis is a rich source of natural genetic diversity. Hierarchical clustering revealed that some accessions had response patterns similar to known photoreceptor mutants, suggesting changes in specific signaling pathways. We found that the unusual far-red response of the Lm-2 accession is due to a single amino-acid change in the phytochrome A (PHYA) protein. This change stabilizes the light-labile PHYA protein in light and causes a 100-fold shift in the threshold for far-red light sensitivity. Purified recombinant Lm-2 PHYA also shows subtle photochemical differences and has a reduced capacity for autophosphorylation. These biochemical changes contrast with previously characterized natural alleles in loci controlling plant development, which result in altered gene expression or loss of gene function.

A specific brassinosteroid biosynthesis inhibitor, Brz2001: evaluation of its effects on Arabidopsis, cress, tobacco, and rice

Brassinazole is the only known specific brassinosteroid (BR)-biosynthesis inhibitor, and it has been shown to be useful for elucidating the function of BRs. In the course of a structure-activity relationship study of brassinazole, we found a more specific BR-biosynthesis inhibitor, Brz2001. This new inhibitor induced similar morphological changes to those seen in brassinazole-treated plants, including Arabidopsis thaliana (L.) Heynh., Nicotiana tabacum L., and Lepidium sativum L. These changes included dwarfism with altered leaf morphology, including downward curling and dark-green color, and the changes were reversed by brassinolide. Although the structure of Brz2001 is similar to that of uniconazole, a gibberellin-biosynthesis inhibitor, Brz2001-treated plants showed almost no recovery with the addition of gibberellic acid (GA3). Comparison of the responses of both brassinazole- and Brz2001-treated cress to brassinolide and GA3 suggested that Brz2001 is a more specific BR-biosynthesis inhibitor than brassinazole. Unlike the results just described, Brz2001-treated rice did not show any morphological changes. This suggests that the roles of BRs in rice may be different from those in the dicotyledonous plants examined in this study. Brz2001 can be used to clarify the function of BRs in dicots as a complement to BR-deficient mutants, and to elucidate the different roles of BRs in monocots and dicots.

Brassinazole, an inhibitor of brassinosteroid biosynthesis, inhibits development of secondary xylem in cress plants (Lepidium sativum)

Brassinazole (Brz) is a specific brassinosteroid biosynthesis inhibitor. Cress plants (Lepidium sativum) grown in medium containing Brz exhibited a slight predominance of phloem differentiation at the expense of xylem differentiation and remarkable inhibition of the development of secondary xylem. This result indicates that brassinosteroids function in xylem development in vivo.

Effects of thyroid hormone deficiency on electrocardiogram findings of congenitally hypothyroid neonates

Hypothyroid status is believed to cause various metabolic changes in infants. However, it is interesting that even severely hypothyroid neonates, detected during mass neonatal screening, rarely show bradycardia, hypothermia, or inactivity. To study cardiac functions of screen-detected neonates with congenital hypothyroidism (CH), we recorded the electrocardiograms (ECG) of 53 screen-detected CH neonates before levothyroxine (LT4) replacement therapy, and 15 age-matched normal neonates for controls. The 53 CH neonates were divided into two groups according to initial serum thyroid hormone levels: a mildly hypothyroid group (n = 37), serum thyroid-stimulating hormone (TSH) less than 100 microIU/mL and free thyroxine (FT4) 0.6 ng/dl or more; and a severely hypothyroid group (n = 16), TSH 100 microIU/mL or more and FT4 less than 0.6 ng/dL. TSH, FT4, and other blood chemicals were measured on an autoanalyzer (Hitachi 7170). After blood sampling, the ECG was recorded during induced sleep by oral administration of triclofos sodium syrup. ECG parameters, including HR, PR, QRS, QT time and corrected QT time (QTc) were automatically obtained, using an auto-ECG analyzing system. The following results were obtained. No CH patients showed abnormal ECG findings. There was no significant difference of the mean heart rates (HRs) between the mildly hypothyroid (147.5 +/- 16.3 beats per minute) and the control group (148.3 +/- 12.1 beats per minute). The mean HR in the severely hypothyroid group (134.0 +/- 17.9 beats per minute, p = 0.007) was significantly low compared with the normal control group. However, all values were within normal ranges. QTc in the severely hypothyroid group (0.414 +/- 0.015, p = 0.033) was significantly shorter than in the control group (0.440 +/- 0.052). No statistical differences of PR, QRS, and QT time were noted among the three groups. All ECG parameters were within normal ranges. HR positively correlated with FT4 and log (FT4), and negatively with TSH and log (TSH). From these results we conclude that the deficiency of thyroid hormones does not affect ECG findings of congenitally hypothyroid neonates. This may be consistent with the unexpectedly mild signs and symptoms of screen-detected hypothyroid neonates.

Selective interaction of triazole derivatives with DWF4, a cytochrome P450 monooxygenase of the brassinosteroid biosynthetic pathway, correlates with brassinosteroid deficiency in planta

Brassinazole, a synthetic chemical developed in our laboratory, is a triazole-type brassinosteroid biosynthesis inhibitor that induces dwarfism in various plant species. The target sites of brassinazole were investigated by chemical analyses of endogenous brassinosteroids (BRs) in brassinazole-treated Catharanthus roseus cells. The levels of castasterone and brassinolide in brassinazole-treated plant cells were less than 6% of the levels in untreated cells. In contrast, campestanol and 6-oxocampestanol levels were increased, and levels of BR intermediates with hydroxy groups on the side chains were reduced, suggesting that brassinazole treatment reduced BR levels by inhibiting the hydroxylation of the C-22 position. DWF4, which is an Arabidopsis thaliana cytochrome P450 isolated as a putative steroid 22-hydroxylase, was expressed in Escherichia coli, and the binding affinity of brassinazole and its derivatives to the recombinant DWF4 were analyzed. Among several triazole derivatives, brassinazole had both the highest binding affinity to DWF4 and the highest growth inhibitory activity. The binding affinity and the activity for inhibiting hypocotyl growth were well correlated among the derivatives. In brassinazole-treated A. thaliana, the CPD gene involved in BR biosynthesis was induced within 3 h, most likely because of feedback activation caused by the reduced levels of active BRs. These results indicate that brassinazole inhibits the hydroxylation of the C-22 position of the side chain in BRs by direct binding to DWF4 and that DWF4 catalyzes this hydroxylation reaction.

Obtusifoliol 14alpha-demethylase (CYP51) antisense Arabidopsis shows slow growth and long life

Obtusifoliol 14alpha-demethylase is a plant orthologue of sterol 14alpha-demethylase (CYP51) essential in sterol biosynthesis. We have prepared CYP51 antisense Arabidopsis in order to shed light on the sterol and steroid hormone biosynthesis in plants. Arabidopsis putative CYP51 cDNA (AtCYP51) was obtained from Arabidopsis expressed sequence tag (EST) library and its function was examined in a yeast lanosterol 14alpha-demethylase (Erg11) deficient mutant. A recombinant AtCYP51 protein fused with a yeast Erg11 signal-anchor peptide was able to complement the erg11 mutation, which confirmed AtCYP51 to be a functional sterol 14alpha-demethylase. AtCYP51 was then used to generate transgenic Arabidopsis by transforming with pBI vector harboring AtCYP51 in the antisense direction under CaMV35S promoter. The resulting transgenic plants were decreased in accumulation of AtCYP51 mRNA and increased in the amount of endogenous obtusifoliol. They showed a semidwarf phenotype in the early growth stage and a longer life span than control plants. This newly found phenotype is different from previously characterized brassinosteroid (BR)-deficient campesterol biosynthesis mutants.

Cytokinin-induced gene expression in cultured green cells of Nicotiana tabacum identified by fluorescent differential display

The cell growth and plastid development of cultured green tobacco cells were maintained by the phytohormone cytokinin. After subculture into cytokinin-free medium, when cytokinin treatment was resumed, physiological changes induced by cytokinin were analyzed. Changes in chlorophyll biosynthesis and photosynthetic gene expression were observed 1 week after cytokinin induction, and changes in cell growth were observed 2 weeks after cytokinin induction. Two cytokinin-induced genes (cig) were isolated from these cells using the fluorescent differential display technique. Northern analysis confirmed that expression of these cig was induced by both natural and synthetic cytokinins. The expression of cig1 was also induced by abscisic acid, and its cDNA sequence was similar to the proline dehydrogenase gene. The expression of cig2 is specific to cytokinin and is not induced by other phytohormones. The amino acid sequence encoded by cig2 is similar to the GDP/GTP exchange factor eIF2B, which regulates translation initiation. The expression of these cig suggests a complex induction system involving cytokinin and other phytohormones.

Biological evaluation of 5-substituted pyrimidine derivatives as inhibitors of brassinosteroid biosynthesis

A series of 5-substituted pyrimidine derivatives was synthesized, and their ability to inhibit brassinosteroid biosynthesis was tested. The biological activity of these compounds was evaluated by the cress stem elongation method. Among the synthesized compounds, alpha-(4-chlorophenyl)-alpha-phenyl-5-pyrimidinemethanol (DPPM 4) exhibited potent inhibitory activity for retarding cress stem elongation in the light. This inhibition was reversed by the application of 10 nM brassinolide, but not by 1 microM GA3. DPPM 4 also affected Arabidopsis growth in the dark. DPPM 4-treated Arabidopsis had phenotypes like those of brassinosteroid-deficient mutants, with short hypocotyls and open cotyledons, in the dark. These biological changes were restored by the co-application of 10 nM brassinolide, but not by 1 microM GA3, suggesting that the primary site of action of DPPM 4 was the brassinosteroid biosynthetic pathway.

Vitreoretinal traction maculopathy caused by retinal diseases

PURPOSE

To study the morphological findings of vitreoretinal traction maculopathy caused by retinal vascular diseases and their changes after vitrectomy.

METHODS

Optical coherence tomographic images of 13 eyes of 12 cases were evaluated before and after vitrectomy.

RESULTS

The tractional force appeared to be mainly tangential with a possible anterior vector in 11 eyes, and mainly in the anterior direction in 2 eyes. After surgery, the increased foveal thickness decreased markedly in all eyes, and visual acuity improved in 8 eyes.

CONCLUSION

Preoperative optical coherence tomographic examination can reveal the fine structure of vitreoretinal separations and adherences caused by retinal vascular diseases. These observations permitted better surgical planning and results.

Plasma free fatty acids in neonates with congenital hypothyroidism

Since the introduction of neonatal mass screening for congenital hypothyroidism (CH), numerous cases have been detected. It is of interest that even severely hypothyroid neonates rarely exhibit bradycardia, hypothermia, or inactivity, which have been recognized as typical signs of CH. Regarding neonates and young infants, few reported data are available on the effects of thyroid hormones on energy expenditure. Plasma free fatty acids (FFAs), markers for lipolysis, play essential roles in maintaining physiologic homeostasis. To study fuel utilization in CH neonates, we measured heart rates, plasma FFA, and thyroid hormones before and after levothryoxine (LT4) replacement therapy. Fifty-five screen-detected CH neonates and 29 age-matched normal neonates for controls were enrolled. The CH neonates were divided into two groups according to serum thyroid hormone levels: a mildly hypothyroid group (n = 37), serum thyrotropin (TSH) less than 100 microIU/mL and free thyroxine (FT4) 0.6 ng/dL or more; and a severely hypothyroid group (n = 18), TSH 100 microIU/mL or more and FT4 less than 0.6 ng/dL. Twenty-four of the 55 patients had their heart rates measured by electrocardiography. Fasting blood samples were taken from the subjects during physical movements. Serum levels of TSH, FT4, FFA, and other blood chemicals, measured on an autoanalyzer system in our hospital, were compared before and after LT4 substitution therapy. The following results were obtained. The mean plasma FFA values before LT4 replacement were 208.5 +/- 89.4 microEq/L in the mildly hypothyroid group, 228.5 +/- 114.7 microEq/L in the severely hypothyroid group, and 213.9 +/- 97.7 microEq/L in controls. No statistical differences were noted among the three values. Two months after LT4 replacement therapy, at the age of 3 months, plasma FFA concentrations significantly increased in both groups compared with those before the therapy. Control infants also showed a significant increase in plasma FFA concentrations from 1 to 3 months of age. There were no significant differences in plasma FFA concentrations among the three groups at the age of 3 months. No significant correlations were found between plasma FFA and serum thyroid hormones. From these results it is suggested that in neonates and young infants, thyroid hormones do not play major roles in mobilization of fats through the adrenergic regulation of lipolysis for energy supply. This may be one of the reasons for the unexpectedly mild signs and symptoms in the screen-detected hypothyroid neonates.

Elevated serum creatinine levels in infants with congenital hypothyroidism: reflection of decreased renal function?

The effects of hypothyroid status on renal function have been poorly studied in children. We assessed the renal function of hypothyroid infants detected during neonatal mass screening for congenital hypothyroidism (CH). Eighty hypothyroid infants and 20 age-matched normal infants for controls were enrolled. The 80 patients, aged 1 mo, were divided into two groups based on the initial thyroid stimulating hormone (TSH) and free thyroxine (FT4) values: a mild-moderately hypothyroid (MHT) group (n = 64, 31M and 33F) and a severely hypothyroid (SHT) group (n = 16, 3M and 13F). Serum creatinine (SCr), TSH, FT4 and other chemicals were compared before and 2 mo after L-thyroxine (LT4) substitution therapy. The following results were obtained: SCr levels were significantly higher in the SHT group (33.2+/-10.0 micromol/L, p < 0.001) compared with the MHT group (20.6+/-6.4 micromol/L) and normal control group (21.0+/-4.4 micromol/L). Two months after the LT4 replacement therapy, the elevated SCr levels in the SHT group decreased by 41.3% to the level (19.5+/-6.0 micromol/L) very close to that in the MHT group (18.8+/-5.1 micromol/L). No significant differences were noted among BUN levels in the three groups. Although serum creatinine kinase levels were significantly higher in the SHT group (230.3+/-102.3 U/L, p < 0.001) than in the MHT group (121.1+/-60.8 U/L), rhabdomyolysis was not considered to be responsible for the impaired renal function.

CONCLUSION

From these results we conclude that serum creatinine levels are elevated in congenitally hypothyroid infants. This is a reversible change with thyroid hormone replacement therapy. The possibility of impaired renal functions should be kept in mind when treating hypothyroid infants.

Treatment of dark-grown Arabidopsis thaliana with a brassinosteroid-biosynthesis inhibitor, brassinazole, induces some characteristics of light-grown plants

When a brassinosteroid biosynthesis inhibitor, brassinazole (Brz), was applied at concentrations ranging from 0.1 to 2 microM. Arabidopsis thaliana (L.) Heynh seedlings grown in the dark exhibited morphological features of light-grown plants, i.e. short hypocotyls, expanded cotyledons, and true leaves, in a dose-dependent manner. Control (non Brz-treated) seedlings grown in the dark for 40 d did not develop leaf primordia. However, treatment with the lowest concentration of Brz induced the development of leaf buds, although it hardly induced any short hypocotyls, and treatment with the highest concentration of Brz induced both short hypocotyls and leaves. Labeling experiments with the thymidine analogue 5-bromo-2'-deoxyuridine revealed that amplification of cell nuclei and organellar nucleoids is activated in the shoot apical meristems of dark-grown Brz-treated seedlings. These results suggest that Brz-treatment induces development of true leaves. Furthermore, condensation and scattering of plastid nucleoids, which is known to occur during the differentiation of etioplasts into chloroplasts, was observed in the plastids of dark-grown Brz-treated cotyledons. In addition, high levels of ribulose-1,5-bisphosphate carboxylase-oxygenase proteins accumulated in the plastids of the cotyledons. Electron microscopy showed that the plastids were etioplasts with a prolamellar body and few thylakoid membranes. These results suggest that Brz treatment in the dark induces the initial steps of plastid differentiation, which occur prior to the development of thylakoid membranes. This is a novel presumed function of brassinosteroids. These cytological changes seen in Brz-treated Arabidopsis were exactly the same as those seen in a brassinosteroid-biosynthesis-deficient mutant, det2, supporting the hypothesis that Brz has no side-effects except inhibiting brassinosteroid biosynthesis, and should prove a useful tool in clarifying the role of brassinosteroids.

Plasma cholesteryl ester transfer protein activity is high in infants and is not affected by thyroid hormones

We investigated the effects of thyroid dysfunction on cholesteryl ester transfer protein (CETP) by studying plasma CETP activity in hypothyroid infants before and after they were rendered euthyroid by L-thyroxine (LT4) replacement therapy. To exclude environmental factors possibly affecting plasma CETP activity, we selected hypothyroid infants to study plasma CETP activity. Plasma CETP activity was measured as the rate of radiolabeled cholesteryl ester transfer from high-density lipoprotein (HDL) to serum apolipoprotein B (apo B)-containing lipoproteins in plasma from 14 hypothyroid infants before and 2 months after LT4 replacement, 23 normal infants, and 61 normal adults. Relationships between CETP and thyroid hormones were examined separately in the 14 hypothyroid infants and 32 euthyroid infants, including the 14 above-described hypothyroid infants and an additional 18 treated hypothyroid infants. Serum levels of thyrotropin (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) were also determined on an autoanalyzer system in our hospital. In contrast to previous reports, we found no differences in plasma CETP activity between hypothyroid infants and age-matched normal infants. LT4 substitution did not cause any changes in plasma CETP activity after therapy. Plasma CETP activity showed no correlation with serum TSH, FT4, and FT3 levels. Both hypothyroid and normal infants were found to have significantly higher plasma CETP activity than normal adults. From these results, we conclude that in infants thyroid hormones do not affect plasma CETP activity, and normal infants have high plasma CETP activity, compared with normal adults.

Synthesis and biological activity of 4'-methoxy derivatives of abscisic acid

Replacing the 4'-carbonyl group of abscisic acid with a methoxy group does not affect the abscisic acid (ABA)-like activities of the product in barley aleurone protoplasts, although the reduction of ABA to 4'-hydroxyl derivatives significantly reduces the ABA-like activity of the products. This suggests that methoxy derivatives of abscisic acid might be used to produce probes for ABA binding proteins.

Relationship between serum leptin and thyroid hormones in children

BACKGROUND

Because leptin decreases food intake and increases energy expenditure, the possible influence of thyroid status on the leptin system has been investigated mainly in adults and animals. However, the data available at present are very confusing. The aim of the present study was to assess the possible interaction of thyroid hormones with the leptin system.

METHODS

Serum free thyroxine (FT4), a biologically active thyroid hormone, and thyroid stimulating hormone (TSH), a sensitive and reliable index of thyroid status, were examined in 51 children (19 males, 32 females) with mass screening-detected congenital hypothyroidism on continuous L-thyroxine (L-T4) substitution therapy. The subjects were divided into younger (n = 35, aged 1 month-5 years) and older (n = 16, 6 years-11 years) children groups. Serum levels of leptin and thyroid hormones were measured in the subjects. Body mass index (BMI) was estimated by the formula bodyweight (kg)/height x height (m2), which is known as the Kaup index in younger children and BMI in older children and adults.

RESULTS

In the younger children group, serum leptin levels showed no correlation with serum TSH, FT4 or T4. In the older children group, serum leptin concentrations significantly correlated with T4 (r = 0.510, P < 0.05) and BMI (n = 16, r = 0.647, P < 0.01), but not with TSH or FT4.

CONCLUSION

The role of thyroid hormones in modulating leptin synthesis and secretion seems to have little, if any, clinical or biological relevance.

Characterization of brassinazole, a triazole-type brassinosteroid biosynthesis inhibitor

Screening for brassinosteroid (BR) biosynthesis inhibitors was performed to find chemicals that induce dwarfism in Arabidopsis, mutants that resembled BR biosynthesis mutants that can be rescued by BR. Through this screening experiment, the compound brassinazole was selected as the most potent chemical. In dark-grown Arabidopsis, brassinazole-induced morphological changes were nearly restored to those of wild type by treatment with brassinolide. The structure of brassinazole is similar to pacrobutrazol, a gibberellin biosynthesis inhibitor. However, in assays with cress (Lepidium sativum) plants, brassinazole-treated plants did not show recovery after the addition of gibberellin but showed good recovery after the addition of brassinolide. These data demonstrate that brassinazole is a specific BR biosynthesis inhibitor. Brassinazole-treated cress also showed dwarfism, with altered leaf morphology, including the downward curling and dark green color typical of Arabidopsis BR-deficient mutants, and this dwarfism was reversed by the application of 10 nM brassinolide. This result suggests that BRs are essential for plant growth, and that brassinazole can be used to clarify the function of BRs in plants as a complement to BR-deficient mutants. The brassinazole action site was also investigated by feeding BR biosynthesis intermediates to cress grown in the light.

An evaluation of neurobehavioural problems as perceived by family members and levels of family stress 1-3 years following traumatic brain injury in Japan

OBJECTIVE

To ascertain the proportion of patients with traumatic brain injury (TBI) admitted to a Japanese district hospital and to evaluate the levels of stress and anxiety in fami ies living with those TBI patients.

DESIGN

A retrospective study of patients admitted to hospital from April 1995 to March 1997 and a questionnaire study of family members of survivors.

SETTING AND SUBJECTS

All patients referred or transferred to the Emergency Department at the Saga Medical School Hospital, Japan with a primary diagnosis of TBI were studied. Family members living with TBI patients were sent questionnaires.

MAIN OUTCOME MEASURES

The Barthel Index, the Patient Competency Rating Scale, the modified Caregiver Strain Index and the Hospital Anxiety and Depression Scale.

RESULTS

There were 34 patients who required hospitalization for care relating to TBI. Of these, nine family members took part in the questionnaire study. Three carers reported fairly high levels of stress and another three carers were considered to be at risk of anxiety and depression. There was a tendency for family members who reported that patients had difficulties in performing behavioural tasks to have higher levels of stress themselves.

CONCLUSION

These preliminary results showed that family members experienced certain levels of stress and were also at risk of anxiety and depression. The impact of TBI on families as well as patients should receive more attention.

Purification from conditioned medium and chemical identification of a factor that inhibits somatic embryogenesis in carrot

Somatic embryogenesis is strongly inhibited in cultures of carrot (Daucus carota L.) cells when the cell density is high. The inhibition is caused by factors that are released by cells into the medium of such cultures. In this study, we purified and identified one of the inhibitory factors found in the medium of high-cell-density cultures of carrot cells. The inhibitory factor with the strongest apparent activity was purified by fractionation with ethylacetate, chromatography on an octadecylsilyl (ODS) silica gel-column and HPLC. The inhibitory factor had a single peak of absorbance at 280 nm and was identified as 4-hydroxybenzyl alcohol by mass spectrometry and 1H- and 13C-NMR spectroscopy. Authentic 4-hydroxybenzyl alcohol strongly inhibited the formation of somatic embryos at a concentration equal to that in high-cell-density cultures. These results suggest that 4-hydroxybenzyl alcohol is a major factor that accumulates in high-cell-density cultures of carrot cells and inhibits somatic embryogenesis.

Isolation and initial characterization of 13(2)-hydroxychlorophyll a induced by cyclohexanedione derivatives in tobacco cell suspension cultures

This paper reports that a new photobleaching compound, 2-(2-chloro-5-propoxycarbonylphenyl)aminomethylidene-5-5-dim ethyl- cyclohexane-1,3-dione (RWH-21), stimulates accumulation of 13(2)-hydroxychlorophyll a in cultured tobacco cells. This was shown based on isolation of 13(2)-hydroxychlorophyll a from pigment extracts of cultured tobacco cells by diode-array HPLC and subsequent fast atom bombardment mass spectrometry analysis. 13(2)-Hydroxychlorophyll a rapidly accumulates in tobacco cells both in the light and dark in the presence of RWH-21 (50 microM). Analysis of 13(2)-hydroxychlorophyll a formation in tobacco cells indicates that 13(2)-hydroxychlorophyll a is rapidly accumulated within 20 h incubation time both in the dark and light. Although the amount of 13(2)-hydroxychlorophyll a is continuously increased in the dark, the amount of 13(2)-hydroxychlorophyll a decreased remarkably in the light after 20 h incubation. Analysis of 13(2)-hydroxychlorophyll a formation and lipid peroxidation by determination malondialdehyde in tobacco cells suggests that RWH-21-induced 13(2)-hydroxychlorophyll a has the potential to cause a photodynamic action in cultured tobacco cells.

Changes in serum apolipoprotein concentrations after L-thyroxine therapy in infants with congenital hypothyroidism

To further characterize the impact of thyroid hormones on the serum lipid profile, we studied serum apolipoproteins in infants with congenital hypothyroidism before and after L-thyroxine (L-T4) replacement therapy. Serum high-density lipoprotein cholesterol (HDLC) decreased after L-T4 therapy. Total cholesterol (TC) and low-density lipoprotein cholesterol (LDLC) levels did not change significantly after therapy. Two months after L-T4 replacement therapy, serum apolipoprotein A-I (apo A-I), C-III, and E declined and apo B increased significantly. No significant changes were observed for serum concentrations of apo A-II and C-II after L-T4 substitution. We conclude that in infants, thyroid hormone reduces serum levels of apo A-I, the principal protein component of HDLC, and this may contribute to the decline of serum HDLC concentrations after L-T4 replacement therapy.

Brassinosteroid biosynthesis inhibitors

Recent work on the physiological responses of brassinosteroid-deficient mutants has led to the designation of brassinosteroids as a new class of phytohormone. However, information on other possible roles of brassinosteroids is limited because the mutant analysis has been confined to a relatively small number of plant species. In this context, specific inhibitors of brassinosteroid biosynthesis would be valuable for investigating the roles of brassinosteroids at various stages of plant development, such as germination, leaf expansion and flowering. Data on the oxidative processes involved in brassinosteroid biosynthesis have permitted the rational design of biosynthesis inhibitors. The development of such inhibitors has confirmed the importance of brassinosteroids in broad aspects of plant growth and development, with drastic morphological changes in inhibitor-treated plants, almost identical to those found in brassinosteroid-deficient mutants. The normal phenotype of inhibitor-treated plants can be recovered by the addition of brassinolide, revealing that inhibitors can be used to complement brassinosteroid-deficient mutants in clarifying the functions of brassinosteroids.

Endogenous neurotrophin-3 is retrogradely transported in the rat sciatic nerve

To address the active transport of neurotrophins, nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 in the peripheral nerves, we examined the levels of proteins and messenger RNAs in the sciatic nerve of adult rats following transection, using enzyme immunoassays and reverse transcription polymerase chain reaction method, respectively. Neurotrophin-3 protein increased one day after transection only in the distal segment next to the transection site and returned to the original level two days later. This was considered to reflect accumulation of neurotrophin-3 transported from the periphery toward the neuronal cell bodies, because the neurotrophin-3 messenger RNA level was not changed in any sciatic segments during this experimental period. An increase in brain-derived neurotrophic factor protein was observed simultaneously in both the distal and proximal stumps three days after transection. Brain-derived neurotrophic factor messenger RNA was elevated in the same stumps two days after transection, suggesting that brain-derived neurotrophic factor was produced within the transected stumps. These observations demonstrate that neurotrophin-3, like nerve growth factor, is retrogradely transported in the sciatic nerve but that brain-derived neurotrophic factor is not. This suggests that neurotrophin-3 plays a role in the conveyance of trophic signals from target organs to neurons.

Thyroxine inversely regulates serum intermediate density lipoprotein levels in children with congenital hypothyroidism

BACKGROUND

Although there have been numerous studies on the effects of thyroid hormones on serum lipid profiles, the effects of thyroxine on intermediate how density lipoprotein (IDL) remain uncertain. In an attempt to clarify, this issue, under conditions with very little influence exerted by sex hormones on serum lipid profiles, we studied the relationship between serum thyroid hormone levels and the proportion of serum IDL fractions in children.

METHODS

Nineteen children with congenital hypothyroidism and 13 children with non-thyroid diseases were enrolled in this study. Blood samples were taken to measure serum thyroid stimulating hormone, triiodothyronine, free thyroxine (FT4), total cholesterol, high density lipoprotein (HDL) cholesterol, triglyceride and apolipoprotein levels. Lipoprotein fractions, including very low density lipoprotein (VLDL), IDL, low density lipoprotein (LDL) and HDL, were determined by their electrophoretic mobility in a non-denaturing polyacrylamide gel.

RESULTS

The proportion of IDL fractions showed a significant inverse correlation with serum FT4 levels and a significant correlation with serum total cholesterol and apolipoprotein B and C-II levels. Serum VLDL, LDL and HDL fractions did not correlate with serum thyroid hormone levels.

CONCLUSION

From these results and other studies, we suggest that thyroxine promotes the conversion of IDL into LDL, possibly by its stimulatory effects on hepatic lipase activity.

Serum lipoproteins and apolipoprotein E in infants with congenital hypothyroidism

BACKGROUND

Hypothyroid adults have a high risk of atherosclerosis, secondary to increased levels of various cholesterol fractions, particularly low-density lipoprotein cholesterol (LDL-C). We investigated the existence of a correlation between thyroid hormone deficiency and serum lipoproteins and a possible effect of different apolipoprotein E (apoE) phenotypes on lipoprotein levels in 75 infants with hypothyroidism.

METHODS

Seventy-three of the 75 infants had congenital hypothyroidism. At the age of one month, prior to the initiation of thyroid hormone substitution therapy, thyroid-stimulating hormone (TSH), thyroid hormones and lipid profile parameters were determined. Subsequently, apoE phenotyping in all patients was performed by isoelectric focusing followed by immunoblotting.

RESULTS

Significant negative correlations were identified between triiodothyronine (T3) and LDL-C and total cholesterol (TC) levels and between thyroxine (T4) and TC levels. There were no correlations between TSH and free (F)T4 and lipid profile parameters. Although infants carrying at least one E4 allele had higher LDL-C (as well as TC and triglyceride) levels than those carrying at least one E2 allele, these differences were not statistically significant. No significant differences in thyroid hormones were noted in E4 allele carriers in comparison with other patients.

CONCLUSIONS

The observed lack of a significant correlation between thyroid hormones (except T3), apoE phenotypes and lipoprotein levels suggests that, early in infancy, other factors may play a more important role in determining lipoprotein levels.