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Biomedical subjects

S A Roberts

Publications and source records attributed to S A Roberts.

At least 73 records · Page 4Linked to original sources
PubMed2000

Endoscopic ultrasound guided biopsy of sub-carinal lymph nodes.

AIM/METHODS: Endoscopic ultrasound (EUS) guided biopsy is not widely available in the U.K., and sub-carinal nodes can be difficult to biopsy percutaneously. Tissue obtained from these nodes can influence patient management. We describe our initial experience with EUS guided transoesophageal biopsy of sub-carinal nodes using a Pentax FG-34 EUS probe and a 22 G Hancke-Villman or Echotip needle in 20 patients. RESULTS: Malignant cells were obtained from the nodes in 13 patients, and in another patient in whom the node biopsy was negative, small cell carcinoma cells were obtained from a lesion in the liver. There were no complications. CONCLUSIONS: Mediastinoscopy to obtain tissue, or the blind treatment of presumed malignancy was avoided in all the patients in whom a positive biopsy was obtained. In many of these patients, more conventional methods to obtain a tissue diagnosis had already failed. The problem solving capability of this safe, well-tolerated technique is discussed.Roberts, S. A. Clinical Radiology55, 832-836.

Adult↗
PubMed2000

Effects of deficiency in p53 or bcl-2 on the sensitivity of clonogenic cells in the small intestine to low dose-rate irradiation.

PURPOSE: To study the role of p53 and bcl-2 in the response of the small intestine to irradiation delivered at low dose-rate. MATERIALS AND METHODS: Mice homozygous for p53 or bcl-2 deletion (-/-), their respective heterozygotes (+/-), and their wild-type littermates (+/+) including a previously used hybrid strain (B6D2F1), were irradiated to the whole-body using 60Co gamma-rays at 1 Gy h(-1). Crypt survival levels in the small intestine were measured at day 3 after the end of irradiation. RESULTS: Crypt survival levels were higher in p53 -/- mice than in the other p53 genotypes after 25-30 Gy, but not after lower or higher doses. Similar experiments with the three genotypes for bcl-2 status showed lower crypt survival after all doses used in the -/- mice, compared with the +/- and +/+ mice, which were similar in response. The marked degree of curvature in the survival curve observed for the p53 genotypes was also observed in B6D2F1 hybrid mice, was particularly striking in the p53 -/- mice, but was not seen to the same extent in the bcl-2 genotypes. The heterozygotes for p53 or for bcl-2 were nearer in response to their respective +/+ genotypes rather than the -/- genotypes. CONCLUSION: The increased crypt survival levels at some radiation dose levels in the p53 nulls contrasts with the lack of change reported previously using irradiation at high dose-rate. The decreased survival in the bcl-2 nulls is consistent with the known 'survival' function of bcl-2, although bcl-2 expression has not been detected immunohistochemically in this intestinal site. The marked degree of curvature in the dose-response curve at high dose levels for some genotypes was unexpected at this low dose-rate.

Animals↗
PubMed2000

The use of cryopreserved lymphocytes in assessing inter-individual radiosensitivity with the micronucleus assay.

PURPOSE: The feasibility of using cryopreserved lymphocytes to detect inter-individual differences in chromosomal radiosensitivity was investigated. Typically, such studies are conducted with fresh blood samples but, in a clinical setting, when availability of samples is unpredictable, this is not always convenient. The sensitivity of 23 normal healthy donors, 11 breast cancer patients who had shown severe acute skin reactions to radiotherapy and seven ataxia telangiectasia (A-T) heterozygotes was determined. MATERIALS AND METHODS: Thawed lymphocytes were exposed to high (HDR) or low dose rate (LDR) gamma irradiation (3.5 Gy) in Go, stimulated with PHA, treated with cytochalasin-B 24 h later and then harvested at 90 h for the determination of micronucleus (MN) yields in binucleate cells. RESULTS: Each normal donor was tested one to three times. Mean MN yields were 76.1 +/- 9.3/100 cells at HDR and 44.5 +/- 5.3 at LDR, giving an LDR sparing effect of 39.6 +/- 9.3%. A relatively high proportion of tests failed to yield sufficient binucleate cells for analysis. Inter-experimental variability was also high and it was not possible to demonstrate inter-individual differences in sensitivity in spite of the use of an internal control sample from a single normal donor in each experiment. There was a small but significant increase in radiation-induced MN in the breast cancer patients compared with the normals at LDR (but not at HDR), but a complete overlap with the normal range. There was no increase in sensitivity in the A-T heterozygotes at HDR. The LDR samples failed because the LDR protocol reduced proliferation rates, and radiation-induced mitotic inhibition in this group was higher than in normals. CONCLUSIONS: In comparison with previous experience with fresh blood samples, the use of frozen lymphocytes is not as satisfactory because: (1) experimental failures are higher; (2) inter-experiment variability is higher: (3) dose-rate sparing is lower, suggesting poorer repair; and (4) the ability to discriminate between breast cancer cases and normals is probably lower.

Adult↗
PubMed2000

Heritability of chromosomal radiosensitivity in breast cancer patients: a pilot study with the lymphocyte micronucleus assay.

Of breast cancer patients, 30% are sensitive in a lymphocyte assay of radiation-induced chromosome damage (micronucleus induction) compared with 10% of healthy controls. Twenty-two first-degree relatives of 11 sensitive patients had an average micronucleus yield significantly higher than that of 68 controls. This suggests that radiosensitivity in this assay may be an inherited characteristic associated with predisposition to breast cancer.

Breast Neoplasms↗
PubMed2000

The New York High-Risk Project: comorbidity for axis I disorders is preceded by childhood behavioral disturbance.

The relationship between childhood behavioral disturbance and comorbidity for adult psychiatric disorders has not been sufficiently investigated. Subjects of this report (N = 185) were offspring of parents with schizophrenia or affective disorder and of normal parents from the New York High-Risk Project. Data on childhood behavior at the mean age of 9.5 years were obtained in a parent interview at initial assessment in 1971-72. Adulthood outcomes were assessed through standardized interviews, and lifetime axis I diagnoses were based on Research Diagnostic Criteria. Subjects with comorbidity for axis I disorders exhibited significantly more behavioral problems as children, compared with those who developed either one or no psychiatric disorder in adulthood. This association was not biased by gender or parental diagnosis of psychiatric disorder. The findings emphasize that psychiatric comorbidity can be traced back to childhood and underline the importance of longitudinal observations in psychiatric research.

Adult↗
PubMed2000

Immunohistochemical performance of antibodies on previously frozen tissue.

Immunohistochemical stains are occasionally performed on paraffin-embedded, fixed material that was previously frozen, most frequently for an intraoperative frozen section diagnosis. A retrospective study comparing immunohistochemistry on previously frozen then fixed tissue with freshly fixed tissue was designed. Of 43 cases identified during the period 1994-1996 in which immunohistochemistry was performed on frozen section blocks, 19 met criteria for inclusion. Immunohistochemistry using antibodies to S-100, HMB-45, synaptophysin, chromogranin, neuron-specific enolase (NSE), neurofilament, glial fibrillary acidic protein, vimentin, and carcinoembryonic antigen (CEA) was compared. Staining for cytokeratins was unchanged. Staining for S-100, HMB-45, synaptophysin, and NSE were negative in frozen/fixed tissue and positive in comparable fresh/fixed tissue in at least one case each. Chromogranin and CEA exhibited a significant decrease in the frozen/ fixed tissue. We conclude that caution must be exercised in interpreting immunohistochemical results using tissue that was frozen for intraoperative consultation before formalin fixation and paraffin embedding.

Antigens, Neoplasm↗
PubMed2000

Attention, memory, and motor skills as childhood predictors of schizophrenia-related psychoses: the New York High-Risk Project.

OBJECTIVE: Childhood neurobehavioral deficits in offspring of schizophrenic, affectively ill, and psychiatrically normal parents were evaluated as predictors of schizophrenia-related psychoses in adulthood. METHOD: The offspring were tested with neurobehavioral measures at 7-12 years of age and assessed in mid-adulthood for axis I diagnoses. The relationships of childhood deficits in attention, verbal memory, and gross motor skills to adulthood schizophrenia-related psychoses were examined in separate path analyses by using logistic regression equations. Sensitivity and specificity were determined for each of the childhood dysfunctions. RESULTS: For the offspring of schizophrenic parents, childhood deficits in verbal memory, gross motor skills, and attention identified 83%, 75%, and 58%, respectively, of the subjects with schizophrenia-related psychoses; 50% were identified by all three variables combined. False positive rates in subjects who did not develop schizophrenia-related psychoses ranged from 18% for those with deficits in attention during childhood to 28% for those with deficits in memory. The three variables had low deficit rates in the offspring of the other two parental groups and were not associated with other psychiatric disorders in any group. CONCLUSIONS: Schizophrenia-related psychoses in adulthood are distinguished in subjects at risk for schizophrenia by childhood deficits in verbal memory, gross motor skills, and attention. The findings suggest that deficits in these variables are relatively specific to schizophrenia risk and may be indicators of the genetic liability to schizophrenia.

Adolescent↗
PubMed2000

Detection of individual differences in radiation-induced apoptosis of peripheral blood lymphocytes in normal individuals, ataxia telangiectasia homozygotes and heterozygotes, and breast cancer patients after radiotherapy.

Quantification of radiation-induced apoptosis in peripheral blood lymphocytes (PBLs) has been proposed as a possible screening test for cancer-prone individuals and also for the prediction of normal tissue responses after radiotherapy. We have used the TUNEL assay (terminal transferase nick-end labeling) 24 h after irradiation with 4 Gy at high dose rate to assess interindividual differences in radiation-induced apoptosis between (1) a panel of normal individuals, (2) ataxia telangiectasia (AT) homozygotes and heterozygotes, and (3) breast cancer patients who had received radiotherapy 8-13 years ago, including a number of patients who had suffered adverse responses to radiation. With this protocol, we show clear differences in radiation-induced apoptosis between individuals, and good reproducibility in the assay. In agreement with previous reports using EBV-transformed lymphoblasts, we show a very poor induction of apoptosis in AT homozygotes and a reduced level in AT heterozygotes compared to normal individuals. A similar reduced level compared to normal individuals was seen in the breast cancer patients. Despite a wide range of values in the breast cancer patients and good reproducibility on repeat samples, there was no correlation of rates of apoptosis with the severity of breast fibrosis, retraction or telangiectasia. The reduced rate of apoptosis observed in the breast cancer cases may be associated with genetic predisposition to breast cancer; however, we conclude that assays of lymphocyte apoptosis are unlikely to be of use in predicting normal tissue tolerance to radiotherapy.

Adult↗
PubMed2000

Undesirable cytokeratin immunoreactivity of native nonepithelial cells in sentinel lymph nodes from patients with breast carcinoma.

CONTEXT: Use of cytokeratin immunohistochemistry on histologically negative sentinel lymph nodes (SLNs) in patients with breast carcinoma has been shown to be efficient in detecting false-negative nodes. Several recent studies have shown that micrometastases detected by immunohistochemistry constitute an independent predictor of disease-free period and overall survival for breast cancer patients. It has been demonstrated that the fibroblastic type of reticulum cells in lymph nodes also express cytokeratin, and unawareness of such cytokeratin reactivity in SLNs could result in difficulty in the interpretation of the results of immunohistochemistry. OBJECTIVES: To study the incidence of undesirable cytokeratin reactivity in reticulum cells and other native nonepithelial cells of SLNs and to compare the immunoreactivity of 3 commonly used cytokeratin antibodies (AE1/AE3, pancytokeratin [pan-CK], and CAM5.2). DESIGN: Immunohistochemistry with pan-CK, AE1/AE3, and CAM5.2 antibodies was performed on paraffin sections of SLNs from patients with breast cancer. Correlation of undesirable cytokeratin reactivity with size and metastatic status of the SLNs was also analyzed. PATIENT MATERIAL: Paraffin sections of 84 SLNs from 38 consecutive patients with breast cancer in our tertiary-care, teaching hospital. RESULTS: Cytokeratin reactivity was found in reticulum cells and plasma cells in 29 (35%) and 9 (10%) of the 84 SLNs, respectively, with pan-CK and CAM5.2 but not with AE1/AE3 (P <.001). The presence of cytokeratin-positive reticulum cells did not correlate with the size and metastatic involvement of the SLNs. CONCLUSIONS: The incidence of undesirable keratin reactivity in SLNs from breast cancer patients could be limited by using an AE1/AE3 antibody cocktail. The AE1/AE3 antibody cocktail is a sensitive epithelial marker and appears to be more specific in recognizing epithelial cells in SLNs.

Antibody Specificity↗
PubMed1999

Time factors in larynx tumor radiotherapy: lag times and intertumor heterogeneity in clinical datasets from four centers.

PURPOSE: To use the time-dependent linear-quadratic model, both in the standard form and in a form modified to incorporate intertumor heterogeneity, in a reanalysis of 4 datasets for larynx tumor control, to provide more representative and direct estimates of the lag period, the time factor (lambda/alpha), and the clonogen population inactivation dose ([lnk]/alpha). METHODS AND MATERIALS: The data comprised 2,225 patients treated in Edinburgh (UK), Glasgow (UK), Manchester (UK), or Toronto (Canada), with tumor control assessed after at least 2 years. Heterogeneity in each series was taken into account using the coefficient of variation (CV) of the clonogen radiosensitivity (alpha). Maximum likelihood techniques were used to provide best estimates of the parameters, and also direct estimation of the more stable parameter ratios of interest. RESULTS: The use of different heterogeneity factors for the different series allowed common dose/time parameters to be fitted across all four series in a way not possible using the standard model, enabling the inherent effect of heterogeneity in flattening dose-response curves and in reducing time factors to be separated from the underlying more-representative values. Radiosensitivity CVs were calculated to be 30% (Edinburgh), 36% (Glasgow), 40% (Manchester), and 71% (Toronto). The lag phase was 32 days (95% CL 20-38 days) which was longer than the value of 23 days (11-36 days) deduced using the standard model without the heterogeneity parameter. The time factor was 1.2 (0.8-2.2) Gy/day, again greater than the value of 0.80 (0.54-1.41) Gy/day derived using the standard model. Similar larger time factors and longer lag periods could be reproduced using the standard model either by using a parameterization based on parameter ratios, or by omitting the discordant Toronto data and refitting just the data from the three UK centers. CONCLUSION: It was concluded that the heterogeneity model provides a better representation of the time factor for tumor control when data are analyzed comprising different stages of disease treated at different centers. The model allows different amounts of heterogeneity in different series, which tend to flatten dose-responses curves and reduce time factors, to be taken in to account. Also, direct maximum likelihood estimates can be made of the lag period, the time factor (lambda/alpha), and the fractionation sensitivity (beta/alpha), as well as the clonogen population inactivation dose (lnk)/alpha. Values of these parameter ratios are more robust and stable than the individual parameter values. The results of the present analysis using a total of 2,225 patients from four centers indicate that the average lag period may be somewhat longer and the average time factor somewhat greater (and the 95% confidence limits of the time factor exclude previous estimates), than the values deduced previously using simpler models and more diverse multi-center datasets.

Dose-Response Relationship, Radiation↗
PubMed1999

Utility of immunohistochemistry in the evaluation of necrotic thyroid tumors.

We have previously shown that necrotic tumors retain their immunoreactivity for a range of cytokeratin antibodies. Some thyroid tumors undergo extensive necrosis after fine-needle aspiration (FNA) procedures. We evaluated the sensitivity of antibodies on necrotic thyroid tumors by examining a series of thyroid tumors consisting of 10 Hurthle cell neoplasms, 8 carcinomas, and 2 follicular adenomas (12 with post-FNA necrosis). These were stained with antibodies to AE1/3, PANCK, thyroglobulin and S100. Four of the cases of papillary carcinoma were also stained with antibodies to CK19. As a control for the specificity of thyroglobulin immunoreactivity in necrotic tissue, we also stained 11 nonthyroid tumors with extensive necrosis (7 carcinomas, 1 lymphoma, 2 melanomas, 1 sarcoma) for thyroglobulin. Six of 8 thyroid carcinomas were positive for AE1/3 and PANCK; AE1/3 reactivity was retained in necrotic areas of 4 of 6. AE 1/3 was positive in necrotic portions of 5 of 10 Hurthle cell lesions, whereas PANCKwas negative in all but 1. Thyroglobulin reactivity was present in 18 of 20 cases, and was preserved in necrotic portions of 5 of 6 carcinomas, as well as 8 of 10 Hurthle cell neoplasms. S100 cytoplasmic reactivity was present in 4 Hurthle cell neoplasms and 1 papillary carcinoma; this staining was lost in necrotic areas. No staining by thyroglobulin was observed in the viable or necrotic areas of nonthyroid neoplasms. The preservation of cytokeratin reactivity, measured by AE1/3, in thyroid neoplasms is a diagnostically useful feature in spontaneous and post-FNA infarction. PANCK is not a well-preserved marker in necrotic thyroid tissue. This difference may be due to detection of keratin 19 by AE1/3. Thyroglobulin is preserved in some necrotic thyroid carcinomas and in Hurthle cell lesions. Preservation of thyroglobulin reactivity in necrotic tissue is specific in that no staining was observed in nonthyroid neoplasms. These results suggest that thyroglobulin is useful in demonstrating thyroid lineage of both primary and metastatic necrotic tumor masses.

Adenoma↗
PubMed1999

Radiation-induced G1 arrest is not defective in fibroblasts from Li-Fraumeni families without TP53 mutations.

Radiation-induced G1 arrest was studied in four classes of early passage skin fibroblasts comprising 12 normals, 12 heterozygous (mut/wt) TP53 mutation-carriers, two homozygous (mut/-) TP53 mutation-carriers and 16 strains from nine Li-Fraumeni syndrome or Li-Fraumeni-like families in which no TP53 mutation has been found, despite sequencing of all exons, exon-intron boundaries, 3' and 5' untranslated regions and promoter regions. In an assay of p53 allelic expression in yeast, cDNAs from these non-mutation strains behaved as wild-type p53. Using two different assays, we found G1 arrest was reduced in heterozygous strains with mis-sense mutations and one truncation mutation, when compared to the range established for the normal cells. Heterozygous strains with mutations at splice sites behaved like normal cells, whilst homozygous (mut/-) strains showed either extremely reduced, or no, arrest. Strains from all nine non-mutation families gave responses within the normal range. Exceptions to the previously reported inverse correlation between G1 arrest and clonogenic radiation resistance were observed, indicating that these phenotypes are not strictly interdependent.

Alleles↗
PubMed1999

Tumour vascularity is a significant prognostic factor for cervix carcinoma treated with radiotherapy: independence from tumour radiosensitivity.

The aim of the study was to investigate the relationship between intrinsic radiosensitivity and vascularity in carcinoma of the cervix given radiotherapy, and assess whether more refined prognostic information can be gained by combining the two parameters. A retrospective study was carried out on 74 patients with locally advanced carcinoma of the cervix. Formalin-fixed, paraffin-embedded tumour biopsies were stained with anti-factor VIII using immunohistochemistry. Vascularity was scored using the intra-tumour microvessel density (IMD), or 'hot-spot', technique. For the same patients, the measurement of intrinsic radiosensitivity (SF2) had been made previously on the same pretherapy samples. Patients were stratified by the median IMD and SF2 scores. Women with radioresistant and highly vascular tumours had poorer 5-year survival (P = 0.0005, P = 0.035 respectively) and local control (P = 0.012, P = 0.077 respectively) than those with radiosensitive and poorly vascular tumours. No significant correlation was seen between IMD and SF2. Multivariate analysis (including tumour stage and patient age) showed that only SF2 and IMD were significant prognostic factors for survival. Patients with both a radioresistant and highly vascular tumour had a 5-year survival level of 18% compared to 77% for those patients with a radiosensitive and poorly vascularized tumour. Tumour angiogenesis and cellular radiosensitivity are independent prognostic factors for cervix carcinoma treated with radiotherapy. Allowing for tumour radiosensitivity increases the prognostic significance of vascularity measurements in cervix tumours.

Adult↗
PubMed1999

Endosonographic staging of 100 consecutive patients with esophageal carcinoma: introduction of the 8-mm esophagoprobe.

Endoscopic ultrasound of esophageal carcinoma is conventionally performed using the 13-mm fiberoptic/ultrasound echoendoscope. However, the large diameter results in an inability to negotiate the primary tumor in 25% of patients. The aim of this study was first to determine whether use of the 8-mm esophagoprobe would overcome this problem and second to evaluate the accuracy of the smaller diameter instrument. One hundred consecutive patients with esophageal cancer underwent initial gastroscopy. Based upon the degree of luminal stenosis, patients were staged with either the conventional echoendoscope (luminal diameter > or = 15 mm) or the esophagoprobe (luminal diameter < 15 mm). The primary tumor was successfully negotiated in all subjects (echoendoscope 30, esophagoprobe 70) so that T- and N-staging was accomplished in every patient. Esophageal dilatation was performed in 12 patients (12%). The procedure was well tolerated and there were no complications, in particular no patient suffered esophageal perforation. The accuracy of the esophagoprobe for T-staging was 90% (19 out of 20) and that for N-staging was 75% (15 out of 20). This was similar to the accuracy of staging with the conventional echoendoscope, 90% (9 out of 10) for T-stage and 90% (9 out of 10) for N-stage. The esophagoprobe can safely and accurately stage patients with esophageal carcinoma, including those with high-grade stenoses.

Adult↗
PubMed1999

Increased chromosomal radiosensitivity in breast cancer patients: a comparison of two assays.

PURPOSE: It has been shown previously that sensitivity to the induction of chromosome damage by ionizing radiation is, on average, higher in G2 or G0 lymphocytes of breast cancer patients than of normal healthy controls. The authors suggested that elevated chromosomal radiosensitivity may be a marker for breast cancer predisposition. To investigate whether the G0 micronucleus assay is a true surrogate for the more demanding G2 metaphase assay, both tests have now been performed on the same blood samples from 80 patients. METHODS: For the G0 micronucleus assay, cells were exposed to 3.5 Gy 137Cs gamma-rays 6 h before mitogenic stimulation, treated with cytochalasin B at 24 h post-stimulation and harvested at 90 h. For the G2 assay, at 72 h after stimulation cells were given 0.5 Gy X-rays and harvested 90 min later. RESULTS: Previous observations were confirmed, now with much larger numbers of donors, in that approximately 40% of breast cancer patients showed elevated sensitivity in the G2 assay (135 patients, 105 normals) and 25% in the G0 assay (130 patients, 68 normals). However, there was no correlation between G2 and G0 sensitivity for the 80 patients tested (r = -0.001, p = 0.99). Most of the sensitive patients were either G2 or G0 sensitive, with only 4% sensitive in both assays. CONCLUSIONS: The results suggest that different mechanisms of chromosomal radiosensitivity operate in G2 and G0 cells and that, in general, each chromosomally radiosensitive patient is defective in only one such mechanism, possibly via mutation (or polymorphism) of a single gene. Such mutations may confer cancer predisposition, of low penetrance, in a substantial proportion of patients.

Adult↗
PubMed1999

Heritability of cellular radiosensitivity: a marker of low-penetrance predisposition genes in breast cancer?

Many inherited cancer-prone conditions show an elevated sensitivity to the induction of chromosome damage in cells exposed to ionizing radiation, indicative of defects in the processing of DNA damage. We earlier found that 40% of patients with breast cancer and 5%-10% of controls showed evidence of enhanced chromosomal radiosensitivity and that this sensitivity was not age related. We suggested that this could be a marker of cancer-predisposing genes of low penetrance. To further test this hypothesis, we have studied the heritability of radiosensitivity in families of patients with breast cancer. Of 37 first-degree relatives of 16 sensitive patients, 23 (62%) were themselves sensitive, compared with 1 (7%) of 15 first-degree relatives of four patients with normal responses. The distribution of radiosensitivities among the family members showed a trimodal distribution, suggesting the presence of a limited number of major genes determining radiosensitivity. Segregation analysis of 95 family members showed clear evidence of heritability of radiosensitivity, with a single major gene accounting for 82% of the variance between family members. The two alleles combine in an additive (codominant) manner, giving complete heterozygote expression. A better fit was obtained to a model that includes a second, rarer gene with a similar, additive effect on radiosensitivity, but the data are clearly consistent with a range of models. Novel genes involved in predisposition to breast cancer can now be sought through linkage studies using this quantitative trait.

Alleles↗
PubMed1999

Prior protein intake may affect phenylalanine kinetics measured in healthy adult volunteers consuming 1 g protein. kg-1. d-1.

Study of the amino acid metabolism of vulnerable groups, such as pregnant women, children and patients, is needed. Our existing protocol is preceded by 2 d of adaptation to a low 13C formula diet at a protein intake of 1 g. kg-1. d-1 to minimize variations in breath 13CO2 enrichment and protein metabolism. To expand on our potential study populations, a less invasive protocol needs to be developed. We have already established that a stable background 13CO2 enrichment can be achieved on the study day without prior adaptation to the low 13C formula. Therefore, this study investigates phenylalanine kinetics in response to variations in prior protein intake. Healthy adult subjects were each fed nutritionally adequate mixed diets containing 0.8, 1.4 and 2.0 g protein. kg-1. d-1 for 2 d. On d 3, subjects consumed an amino acid-based formula diet containing the equivalent of 1 g protein. kg-1. d-1 hourly for 10 h and primed hourly oral doses of L-[1-13C]phenylalanine for the final 6 h. Phenylalanine kinetics were calculated from plasma-free phenylalanine enrichment and breath 13CO2 excretion. A significant quadratic response of prior protein intake on phenylalanine flux (P = 0.012) and oxidation (P = 0.009) was identified, such that both variables were lower following adaptation to a protein intake of 1.4 g. kg-1. d-1. We conclude that variations in protein intake, between 0.8 and 2.0 g. kg-1. d-1, prior to the study day may affect amino acid kinetics and; therefore, it is prudent to continue to control protein intake prior to an amino acid kinetics study.

Adult↗