Biomedical subjects

Bruno Claustrat

Publications and source records attributed to Bruno Claustrat.

At least 19 recordsLinked to original sources

PubMed2006

Circadian rhythm disorder in a rare disease: Smith-Magenis syndrome.

Smith-Magenis syndrome (SMS) is a clinically recognizable contiguous gene syndrome, caused by interstitial deletion of chromosome 17p11.2. The SMS phenotype include distinctive facial features, developmental delay and neurobehavioral abnormalities. The patients present major sleep disturbances ascribed to a phase shift of their circadian rhythm of melatonin with a paradoxical diurnal secretion of the hormone. Treatment with morning beta-blockers and evening melatonin reinstated a normally timed melatonin circadian rhythm, improved daytime behavior and restored normal sleep habits, resulting in a greatly improved quality of life for both SMS patients and their family. SMS is the demonstration of biological basis for sleep disorder in a genetic disease. Considering that clock genes mediate generation of circadian rhythms, we suggest that haploinsufficiency for a circadian system gene mapping to chromosome 17p11.2 may cause the inversion of circadian rhythm in SMS.

Child↗

PubMed2006

Melatonin concentrations in aqueous humor of glaucoma patients.

PURPOSE: To determine whether glaucoma patients exhibit an abnormal melatonin concentration in aqueous humor. DESIGN: Case-controlled study, laboratory investigation. METHODS: Aqueous humor and plasma samples of 28 patients with primary open-angle glaucoma and 31 nonglaucoma control patients were collected during surgery, and additional plasma samples were taken the night preceding surgery. Melatonin concentrations were determined using direct radioimmunoassay. RESULTS: This study shows detectable concentrations of melatonin in the aqueous humor of healthy humans (45% of subjects) and of glaucoma patients (36% of subjects) sampled in the morning, with similar levels of aqueous humor melatonin concentrations in both groups (6.4 +/- 9.3 standard deviation (SD) pg/ml and 3.6 +/- 1.9 pg/ml, respectively). We find no significant association between the severity of glaucoma and melatonin levels in aqueous humor or in plasma. CONCLUSIONS: Moderate and severe glaucoma does not appear to be associated with abnormal melatonin concentrations in aqueous humor, at least during the morning sampling period assayed in this study.

Aged↗

PubMed2006

Circadian expression of clock genes in purified hematopoietic stem cells is developmentally regulated in mouse bone marrow.

OBJECTIVE: Clock genes are known to mediate circadian rhythms in the central nervous system and peripheral organs. Although they are expressed in mouse hematopoietic progenitor and stem cells, it is unknown if they are related to circadian rhythms in these cells. We therefore investigated the 24-hour patterns in the activity of several clock genes in the bone marrow (BM) side population (SP) primitive stem cells, and compared these 24-hour patterns to clock gene variations in the whole BM and liver. METHODS: Cells were obtained from 84 B6D2F(1) mice in three replicate experiments on the second day after release into constant darkness from a standardizing light-dark schedule. mRNA expression of clock genes was measured with quantitative reverse transcriptase polymerase chain reaction. RESULTS: mPer2 displayed circadian rhythms in SP cells, whole BM, and liver cells. mPer1 and mRev-erb alpha showed a circadian rhythm in whole BM and liver, but not SP cells. mBmal1 was not expressed rhythmically in SP cells, nor in the whole BM, contrary to rhythms observed in the liver. CONCLUSIONS: With the exception of mPer2, most clock genes studied in primitive hematopoietic SP stem cells were not oscillating in a fully organized circadian manner, which is similar to immature cells in rapidly proliferating organs, such as the testis and thymus. These findings indicate that circadian clock gene expression variations in BM are developmentally regulated.

Animals↗

PubMed2006

Increased REM sleep associated with melatonin deficiency after pinealectomy: a case study.

The objectives of the investigation were to assess hypersomnia, which progressively appeared in a young patient after a pinealectomy, chemotherapy, and radiotherapy for a typical germinoma, as well as the potential benefit of melatonin administration in the absence of its endogenous secretion. 24 h ambulatory polysomnography and the Multiple Sleep Latency Test (MSLT) were performed; in addition, daily plasma melatonin, cortisol, growth hormone, prolactin, and rectal temperature profiles were determined before and during melatonin treatment (one 2 mg capsule given nightly at 21:00 h for 4 weeks). MSLT showed abnormal sleep latency and two REM sleep onsets. Nighttime total sleep duration was lengthened, mainly as a consequence of an increased REM sleep duration. These parameters were slightly modified by melatonin replacement. Plasma melatonin levels, which were constantly nil in the basal condition, were increased to supraphysiological values with melatonin treatment. The plasma cortisol profile showed nycthemeral variation within the normal range, and the growth hormone profile showed supplementary diurnal peaks. Melatonin treatment did not modify the secretion of either hormone. The plasma prolactin profile did not display a physiological nocturnal increase in the basal condition; however, it did during melatonin treatment, with the rise coinciding with the nocturnal peak of melatonin concentration. A 24 h temperature rhythm of normal amplitude was persistent, though the mean level was decreased and the rhythm was dampened during melatonin treatment. The role of radiotherapy on the studied parameters cannot be excluded; the findings of this case study suggest that the observed hypersomnia is not the result of melatonin deficiency alone. Overall, melatonin treatment was well tolerated, but the benefit on the sleep abnormality, especially on daytime REM sleep, was minor, requiring the re-introduction of modafinil treatment.

Adult↗

PubMed2006

Nocturnal sustained attention during sleep deprivation can be predicted by specific periods of subjective daytime alertness in normal young humans.

In our 24-h society, nocturnal sleep-related accidents are common. Because all individuals are not equal in their responses to sleep loss, it is very important to identify predictors of vulnerability to sleep deprivation in normal subjects. We investigated the performance of a cognitive test of sustained attention, electroencephalogram theta/alpha power, subjective sleepiness, and two circadian markers (core temperature and melatonin) in 18 healthy men (nine morning types and nine evening types, 21.4 +/- 1.9 years) during a 36-h sleep deprivation in a constant routine protocol. Sleep need (self-reported) and baseline sleep structure were also investigated. Nighttime performance impairment was defined as the difference between the mean nocturnal number of lapses (00:00-07:30 [corrected] hours) and the mean diurnal number of lapses (07:30-20:30 hours) expressed as a percentage. Feeling fully alert in the morning just after awakening and/or sleepy in early afternoon were the only two factors (Multiple R > 0.80, > 60% of explained variance) which better predicted the decrease in performances of nocturnal operational tasks requiring sustained attention.

Adult↗

PubMed2005

Atypical patterns of circadian clock gene expression in human peripheral blood mononuclear cells.

Circadian ( approximately 24 h) rhythms in physiology and behaviour are observed in all mammals, including humans. These rhythms are generated by circadian clocks located in the hypothalamus and also in most peripheral tissues. Clock genes are essential components of circadian clocks, and mutations or polymorphisms within several of them have been associated with circadian disorders in humans. However, information about human clock gene expression has remained very limited. Peripheral blood mononuclear cells (PBMCs) represent an ideal material to investigate non-invasively the human clock at the molecular level. In the present study, we analysed the expression of three key clock genes, PER2, BMAL1 and REV-ERBalpha in PBMCs from ten healthy humans over a 24-h cycle. PER2 and BMAL1 were found to oscillate throughout the light-dark cycle in all subjects. Interestingly, despite normal melatonin and cortisol secretion patterns, two groups of subjects could be distinguished with significantly different mean PER2 and BMAL1 acrophases. BMAL1 oscillated with approximately the same phase as PER2, instead of being anti-phasic as anticipated from data previously obtained in other peripheral tissues. Furthermore, this unusual phase relationship of PER2 and BMAL1 in human PBMCs was associated with a constant expression of REV-ERBalpha, a crucial regulator of BMAL1, which is highly rhythmic in many other systems. These results reveal the existence of different chronotypes of clock gene expression patterns and suggest specific regulatory mechanisms in human PBMCs.

ARNTL Transcription Factors↗

PubMed2005

Stable myocardial function and endocrine dysfunction during experimental brain death.

BACKGROUND: The origin of cardiac impairment during brain death (BD) is controversial. Using a pig experimental model we sought to assess hormonal changes during the first stage of brain death and how these changes contribute to hemodynamic alteration and myocardial dysfunction. METHODS: Twenty-two pigs were randomized into 2 groups: a control (C) group and a BD group. BD was induced by sub-dural inflation of a balloon catheter. Micromanometers and ultrasonic flow probes were placed on the myocardium to measure cardiovascular parameters. Blood samples and hemodynamic parameters were analyzed before and after induction of BD. RESULTS: A biphasic release of catecholamines was observed, with an initial peak occurring 1 minute after BD induction, followed by a second peak at 60 minutes. Similarly, a biphasic evolution of dP/dt(max) and systolic blood pressure (SBP) was observed at BD, in parallel with catecholamine evolution. In the BD group, both cortisol and aldosterone decreased progressively over time. Circulating triiodothyronine (T3), levothyroxine (T4), prolactin and melatonin concentrations were similar to those of the control group. The difference in arteriovenous (AV) lactate level in arterial and coronary sinus blood was not significantly different between the 2 groups, suggesting an absence of myocardial ischemia. Furthermore, myocardial contractility was not altered during the 3 hours of BD. CONCLUSIONS: During the initial period after induction of brain death, cerebral and thyroid hormones remained stable while cortico- and medullo-surrenal hormones varied significantly. We suggest that suprarenal gland impairment is among the first events occurring during brain death. Paradoxically, hemodynamic parameters and myocardial function were not found to be altered.

Animals↗

PubMed2005

The basic physiology and pathophysiology of melatonin.

Melatonin is a methoxyindole synthesized and secreted principally by the pineal gland at night under normal environmental conditions. The endogenous rhythm of secretion is generated by the suprachiasmatic nuclei and entrained to the light/dark cycle. Light is able to either suppress or synchronize melatonin production according to the light schedule. The nycthohemeral rhythm of this hormone can be determined by repeated measurement of plasma or saliva melatonin or urine sulfatoxymelatonin, the main hepatic metabolite. The primary physiological function of melatonin, whose secretion adjusts to night length, is to convey information concerning the daily cycle of light and darkness to body physiology. This information is used for the organisation of functions, which respond to changes in the photoperiod such as the seasonal rhythms. Seasonal rhythmicity of physiological functions in humans related to possible alteration of the melatonin message remains, however, of limited evidence in temperate areas in field conditions. Also, the daily melatonin secretion, which is a very robust biochemical signal of night, can be used for the organisation of circadian rhythms. Although functions of this hormone in humans are mainly based on correlative observations, there is some evidence that melatonin stabilises and strengthens coupling of circadian rhythms, especially of core temperature and sleep-wake rhythms. The circadian organisation of other physiological functions could depend on the melatonin signal, for instance immune, antioxidative defences, hemostasis and glucose regulation. Since the regulating system of melatonin secretion is complex, following central and autonomic pathways, there are many pathophysiological situations where the melatonin secretion can be disturbed. The resulting alteration could increase predisposition to disease, add to the severity of symptoms or modify the course and outcome of the disorder.

Adaptation, Physiological↗

PubMed2004

Effects of chronic jet lag on tumor progression in mice.

Frequent transmeridian flights or predominant work at night can increase cancer risk. Altered circadian rhythms also predict for poor survival in cancer patients, whereas physical destruction of the suprachiasmatic nuclei (SCN), the hypothalamic circadian pacemaker, accelerates tumor growth in mice. Here we tested the effect of functional disruption of circadian system on tumor progression in a novel experimental model of chronic jet lag. B6D2F(1) mice were synchronized with 12 hours of light and 12 hours of darkness or underwent repeat 8-hour advances of the light/dark cycle every 2 days before inoculation of Glasgow osteosarcoma. The 24-hour changes were assessed for plasma corticosterone, clock protein mPER1 expression in the SCN, and mRNA expression of clock genes mPer2 and mRev-erbalpha in liver and tumor. Time series were analyzed by spectral analysis and/or Cosinor. Differences were compared with analysis of variance (ANOVA). The 24-hour rest/activity cycle was ablated, and the rhythms of body temperature, serum corticosterone, and mPER1 protein expression in the SCN were markedly altered in jet-lagged mice as compared with controls (ANOVA, P < 0.001 for corticosterone and P = 0.01 for mPER1). Tumor grew faster in the jet-lagged animals as compared with controls (ANOVA, P < 0.001), whereas exposure to constant light or darkness had no effect (ANOVA, P = 0.66 and P = 0.8, respectively). The expression of mPer2 and mRev-erbalpha mRNAs in controls showed significant circadian rhythms in the liver (P = 0.006 and P = 0.003, respectively, Cosinor) and in the tumor (P = 0.04 and P < 0.001). Both rhythms were suppressed in the liver (P = 0.2 and P = 0.1, respectively, Cosinor) and in the tumor (P = 0.5) of jet-lagged mice. Altered environmental conditions can disrupt circadian clock molecular coordination in peripheral organs including tumors and play a significant role in malignant progression.

Animals↗

PubMed2004

Persistent twenty-four hour changes in liver and bone marrow despite suprachiasmatic nuclei ablation in mice.

Rest-activity or cortisol rhythms can be altered in cancer patients, a condition that may impair the benefits from a timed delivery of anticancer treatments. In rodents, the circadian pattern in rest-activity is suppressed by the destruction of the suprachiasmatic nuclei (SCN) in the hypothalamus. We sought whether such ablation would result in a similar alteration of cellular rhythms known to be relevant for anticancer drug chronopharmacology. The SCN of 77 B6D2F(1) mice synchronized with 12 h of light and 12 h of darkness were destroyed by electrocoagulation [SCN(-)], while 34 animals were sham operated. Activity and body temperature were recorded by telemetry. Blood and organs were sampled at one of six circadian times for determinations of serum corticosterone concentration, blood leukocyte count, reduced glutathione (GSH), and dihydropyrimidine dehydrogenase (DPD) mRNA expression in liver and cell cycle phase distribution of bone marrow cells. Sham-operated mice displayed significant 24-h rhythms in rest-activity and body temperature, whereas such rhythms were found in none and in 15% of the SCN(-) mice, respectively. SCN lesions markedly altered the rhythmic patterns in serum corticosterone and liver GSH, which became nonsinusoidal. Liver DPD mRNA expression and bone marrow cell cycle phase distribution displayed similar 24-h sinusoidal patterns in sham-operated and SCN(-) mice. These results support the existence of another light-dark entrainable pacemaker that can coordinate cellular functions in peripheral organs. They suggest that the delivery of anticancer treatments at an optimal time of day may still be beneficial, despite suppressed rest-activity or cortisol rhythms.

Anesthesia↗

PubMed2004

Temporal organization of the 24-h corticosterone rhythm in the diurnal murid rodent Arvicanthis ansorgei Thomas 1910.

Arvicanthis ansorgei is a diurnal murid rodent from sub-Saharan Africa. The present study reports on the temporal organization of one of the major hormonal rhythms, i.e. the adrenal steroid hormone corticosterone, in an attempt to characterize further the diurnal nature of this species. The data were obtained by means of two different physiological methods: blood sampling and intracerebral microdialysis. The results show a 12-h rhythm of corticosterone release with peak values close to the light-dark (ZT10) and dark-light transition (ZT22-24), which is clearly different from that in a nocturnal animal. Both corticosterone peaks are closely correlated with the occurrence of two major bouts of running wheel activity. As far as we are aware, this is the first demonstration of a hormonal rhythm with a clear crepuscular appearance (peak values around dusk and dawn). In conclusion, these data show that also in a rodent with a diurnal/crepuscular activity pattern, the tight association between the daily corticosterone peak and the onset of activity is maintained. In addition, intracerebral microdialysis is a suitable technique to measure hormonal rhythms when repeated blood sampling is not possible.

Animals↗

PubMed2004

Assessment of the role of 17beta-oestradiol in bone metabolism in men: does the assay technique matter? The MINOS study.

OBJECTIVE: 17Beta-oestradiol (17beta-E2), mainly its bioavailable fraction (bio-17beta-E2), is a determinant of bone mineral density (BMD) and bone remodelling in men. As direct measurement of bio-17beta-E2 is time-consuming, we compared the value of directly measured bio-17beta-E2 and of calculated bio-17beta-E2 and free 17beta-E2 by studying their association with BMD and markers of bone turnover in a cohort of men (MINOS). DESIGN: A cross-sectional study in which the association between BMD and bone markers, on the one hand, and serum levels of 17beta-E2, on the other, was analysed according to the levels of measured and calculated bio-17beta-E2 and free 17beta-E2 in a cohort of men. SUBJECTS: Men from the MINOS cohort including 87 men aged 19-45 to establish the reference control normal range of hormones and 637 men aged 50-85 (studied group). MEASUREMENTS: Total 17beta-E2, testosterone, SHBG and albumin were measured by standard methods. bio-17beta-E2 was directly measured after the precipitation of SHBG by ammonium sulfate. bio-17beta-E2 and free 17beta-E2 were calculated using serum SHBG and albumin levels as described by Sodegard et al. (J. Steroid Biochem., 16 (1982) 801). RESULTS: Calculated bio-17beta-E2 and free 17beta-E2 were correlated with measured bio-17beta-E2 and between themselves (r = 0.90-1.00, P < 0.0001). Calculated bio-17beta-E2 and free 17beta-E2 disclosed a similar association with BMD (difference between lowest and highest quartiles of 17beta-E2: 2.6-6.8%, P < 0.05-0.005) to that of measured bio-17beta-E2 (3.6-6.1%, P < 0.005-0.001). The association between bone markers levels and measured vs. calculated 17beta-E2 were also similar. Predictive accuracy for lowered BMD and elevated levels of biochemical bone markers (evaluated using receiver operating characteristics) was relatively low (area under curve -0.582 to 0.709) but similar for different forms of bioavailable and free 17beta-E2. CONCLUSIONS: In elderly men, the concentrations of bioavailable and free 17beta-E2, calculated using equations including either the measured albumin concentration or the constant albumin concentration of 43 g/l, can be used, at least in clinical studies, instead of the bio-17beta-E2 concentrations measured after ammonium sulfate precipitation.

Adolescent↗

PubMed2003

Hypersensitivity of the adrenal cortex to trophic and secretory effects of angiotensin II in Lyon genetically-hypertensive rats.

In Lyon hypertensive (LH) rats, a model of low-renin genetic hypertension, we investigated adrenal sensitivity to angiotensin II in terms of angiotensin II receptor (AT1 and AT2 receptors) regulation, morphological changes, and aldosterone and corticosterone secretion. Twelve-week-old LH rats, compared with normotensive LN and LL rats, were either untreated or treated for 4 weeks with AT1 receptor antagonist irbesartan (50 mg/kg/d), angiotensin-converting enzyme inhibitor perindopril (3 mg/kg/d), or perindopril (3 mg/kg/d) plus angiotensin II infusion (200 ng/kg/min). At 16 weeks, untreated LH rats had high systolic blood pressure (P<0.05), low aldosterone (P<0.05), and increased corticosterone (P<0.05) plasma levels. AT1-receptor binding density in the zona glomerulosa was similar in the three strains. In LH rats, angiotensin II infusion increased the relative adrenal weight from 10.5+/-0.3 to 16.7+/-0.7 mg/100g (P<0.05), whereas this change was very modest in normotensive rats. Zona glomerulosa enlarged and plasma aldosterone increased after angiotensin II infusion in the 3 strains, but more markedly in LH versus normotensive rats (2.4- versus 1.3- and 1.6-fold, respectively; 20- versus 10-fold in normotensive rats, P<0.05). Surprisingly, after angiotensin II infusion, despite the absence of angiotensin II receptors in the three strains, the zona fasciculata-reticularis enlarged 1.5-fold and plasma corticosterone increased 1.7-fold only in LH rats (P<0.05), suggesting an indirect control of this compartment by angiotensin II. The hypertrophy and hypersecretory activity of both zona glomerulosa and zona fasciculata-reticularis in LH rats in response to angiotensin II point to the adrenal cortex as a pivotal tissue in the pathophysiology of hypertension in LH rats.

Adrenal Cortex↗

PubMed2003

Radioimmunoassay of N-acetyl-N-formyl-5-methoxykynuramine (AFMK): a melatonin oxidative metabolite.

N-acetyl-N-formyl-5-methoxykynuramine (AFMK) is a melatonin metabolite identified in rat brain by Hirata et al. (The Journal of Biological Chemistry 249 (1974) 1311). Since no assay has been described for its routine measurement, we have developed and validated such a radioimmunoassay. We synthesized AFMK and N-acetyl-5-methoxykynuramine (AMK), in order to produce anti-AFMK antibodies and to standardize the assay. The tracer [3H]-AFMK was obtained from [3H]-melatonin. The assay was preceded by a chromatographic step on Celite microcolumn in order to increase its specificity. The assay was suitable for the measurement of AFMK levels ranging from 59 to 1894 pmol/L. The detection limit of the assay was routinely set at 65 pmol/L. The intra- and inter-assay coefficients of variation were 3.5% and 11% respectively. Investigation of the 24 h plasma pattern in healthy volunteers did not reveal any AFMK levels in plasma samples. In rats, plasma AFMK showed a peak after melatonin injection, which confirmed the in vivo AFMK production as a melatonin metabolite. This AFMK assay is suitable for studies on melatonin metabolism.

Animals↗

PubMed2003

Hormonal changes during 17 days of head-down bed-rest.

We investigated in six men the impact of 17 days of head-down bed rest (HDBR) on the daily rhythms of the hormones involved in hydroelectrolytic regulation. This HDBR study was designed to mimic a real space flight. Urine samples were collected at each voiding before, during and after HDBR. Urinary excretion of Growth Hormone (GH), Cortisol, 6 Sulfatoxymelatonin, Normetadrenaline (NMN) and Metadrenaline (NM) was determined. A decrease in urinary cortisol excretion during the night of HDBR was noted. For GH, a rhythm was found before and during HDBR. The rhythm of melatonin, evaluated with the urine excretion of 6 Sulfatoxymelatonin (aMT6S), the main hepatic metabolite, persisted throughout the experiment without any modification to the level of phase. A decrease during the night was noted for normetadrenaline urinary derivates, but only during the HDBR.

Adult↗

PubMed2003

Disruption of circadian coordination accelerates malignant growth in mice.

An animal model (mice B6D2F1) was developed to study the consequence of suprachiasmatic nuclei (SCN) destruction on tumor growth. SCN destruction abolished the rest-activity and body temperature rhythms and markedly altered the rhythms in serum corticosterone concentration and lymphocyte count. Tumor growth was faster in mice with lesioned SCN than in controls for both tumor models studied, Glasgow osteosarcoma (GOS) and pancreatic adenocarcinoma (P03). This shows that disruption of circadian coordination accelerates malignant growth in mice, suggesting that the host circadian clock controls tumor progression.

Adenocarcinoma↗

PubMed2003

Macroprolactinaemia associated with prolactin adenoma.

BACKGROUND: Macroprolactinaemia, defined as hyperprolactinaemia with a predominance of, or only, the big big prolactin (bbPRL) isoform, is considered idiopathic and poorly symptomatic. Since its association with a PRL adenoma is poorly documented, we examined a series of 13 patients with tumoral hyperprolactinaemia for the presence of macroprolactinaemia. METHODS: From a series of 36 patients with hyperprolactinaemia studied for PRL isoforms, we selected 13 with hyperprolactinaemia and a prolactinoma, and divided them into two groups on the basis of the predominant PRL isoform, the large PRL group (five patients), with a predominance of the big big PRL isoform, and the monomeric PRL (mPRL) group (eight patients), with a predominance of the mPRL isoform. Plasma PRL concentrations were measured by radioimmunoassay, while plasma PRL heterogeneity was studied by gel filtration chromatography. The plasma autoantibody-bound PRL and the histology of the tumours were also studied. RESULTS: Macroprolactinaemia was seen in five out of the 13 patients with a PRL adenoma. The clinical and biological characteristics of the groups with and without macroprolactinaemia were similar. In the large PRL group, no evidence for anti-PRL autoantibodies was found and the prolactinomas were either typical or exhibited unusual aggregates of immunoreactive PRL deposits, the latter suggesting the tumoral origin of these large forms. CONCLUSION: Our results suggest that PRL adenoma may be associated with macroprolactinaemia.

Adult↗

PubMed2003

A sensitive and practical competitive radioassay for plasma biotin.

BACKGROUND: Biotin is a water-soluble vitamin which plays an important biochemical role in a variety of carboxylase-mediated metabolic reactions. Determination of biotin status for the diagnosis of biotin deficiency is crucial. METHODS: We describe a solid-phase protein-binding assay involving [(125)I]iodostreptavidin as a tracer for the determination of biotin in plasma. The assay was conducted in one step by incubation of a fixed amount of [(125)I]iodostreptavidin as binding reagent with varying amounts of biotin, diluted in biotin-free plasma (standard curve) or unknown samples in tubes previously coated with biotin linked to goat antirabbit IgG. Increasing amounts of biotin in the standard or unknown samples in tubes previously coated with biotin occupy more sites on iodostreptavidin, resulting in fewer counts bound to tubes. The effects of the incubation time and temperature on the competitive binding of biotin with iodostreptavidin were tested. RESULTS: The detection limit of the plasma assay for biotin was 100 pmol/L. Only 100 microL of plasma were necessary for the assay, which was performed within 6 h. The dilutions of plasma and synthetic biotin gave a parallel response. Plasma biotin levels ranged from 0.49 to 1.33 nmol/L (mean 0.76 nmol/L) in healthy subjects. The intra and inter-assay coefficients of variation were 3.5% and 10%, respectively, at a concentration of 0.27 nmol/L. CONCLUSIONS: This assay was suitable for the direct measurement of biotin in human plasma and was robust and sensitive enough for screening for biotin deficiency.

Adult↗