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Biomedical subjects

L S Phillips

Publications and source records attributed to L S Phillips.

At least 55 records · Page 3Linked to original sources
PubMed1995

Identification of novel promoter and repressor elements in the 5'-flanking regions of the rat insulin-like growth factor-I gene.

Although the major endocrine source of insulin-like growth factor-I (IGF-I) is the liver, little is known about IGF-I transcriptional mechanisms in this tissue. To evaluate the role of cis-regulatory elements, rat hepatocytes in primary culture were transfected with DNA constructs containing IGF-I 5'flanking sequences, fused to a luciferase reporter. We demonstrate the presence of a novel promoter approximately 0.5 kb upstream from exon 1 transcription initiation sites, together with a repressor element in this region, and a downstream repressor element which can modulate the activity of both endogenous and heterologous promoters.

Animals↗
PubMed1995

Glucocorticoid regulation of insulin-like growth factor-binding protein-3.

Short stature and decreased growth velocity are prominent features of endogenous and pharmacological glucocorticoid excess in children. Underlying processes may involve direct cellular effects or defective generation of insulin-like growth factors (IGFs) and/or IGF-binding proteins (IGFBPs), which modulate IGF-stimulated events and regulate growth. To evaluate potential mechanisms, we investigated the impact of dexamethasone (dex) on hepatic expression of IGFBP-3, the major carrier protein for IGFs. Using cocultured hepatic parenchymal and nonparenchymal cells, dex at 10(-8) and 10(-6) M decreased IGFBP-3 secretion by 67 +/- 9% and 73 +/- 9%, respectively (both P < 0.05 vs. no dex). In a separate experiment, IGFBP-3 messenger RNA (mRNA) expression was decreased by 84 +/- 2% and 75 +/- 2% (both P < 0.05 vs. no dex). In combined studies, levels of IGFBP-3 protein in conditioned medium were strongly correlated with the abundance of IGFBP-3 mRNA (r = 0.75; P < 0.01), consistent with regulation at a pretranslational level. After inhibition of transcription, levels of IGFBP-3 mRNA decreased 85% and 86% over 24 h in cells cultured in 10(-6) M and no dex, respectively; the t1/2 was 13.6 h at 10(-6) M and 12.6 h with no dex, indicating that dex had no effect on IGFBP-3 mRNA stability. To evaluate transcriptional effects, the rate of IGFBP-3 gene transcription was measured by incorporation of [alpha-32P]UTP into preinitiated message in isolated nuclei and fell 78% after the addition of 10(-6) M dex for 48 h (compared to cells cultured in 10(-9) M dex), an inhibition of a magnitude similar to the effects on protein release and mRNA abundance. We conclude that dex may reduce the production of IGFBP-3 by inhibiting IGFBP-3 gene transcription.

Animals↗
PubMed1995

Diabetic ketoacidosis in obese African-Americans.

Our preliminary data indicate that 15% of African-American patients presenting with diabetic ketoacidosis (DKA) are obese. To determine underlying mechanisms, we analyzed the clinical characteristics and indexes of insulin secretion and insulin sensitivity in 35 obese patients with DKA, 22 obese patients with hyperglycemia, 10 lean patients with DKA, and 10 obese nondiabetic subjects. Studies were performed 1 day after resolution of DKA and after 12 weeks of follow-up. At presentation, both obese DKA and obese hyperglycemic patients had no detectable insulin response to intravenous glucose, but they did respond to glucagon administration. The acute insulin response (AIR) to glucagon in obese DKA patients (0.9 +/- 0.1 ng/ml, P < 0.01), but significantly greater than in lean patients with DKA (0.1 +/- 0.1 ng/ml, P < 0.01). After 12 weeks of follow-up, the AIR to glucose improved in both groups of obese diabetic patients but remained significantly lower than in nondiabetic control subjects (both P < 0.01). In contrast, the AIR to glucagon was not significantly different from that in obese control subjects. Insulin sensitivity was decreased in both groups of obese diabetic patients at presentation and improved after follow-up to levels similar to those in obese nondiabetic control subjects. Reactivity with islet cell antibodies was not detected in any of the patients. During follow-up, 25 of 35 obese DKA and 16 of 22 hyperglycemic patients were able to discontinue insulin therapy, with continued good metabolic control. Our results indicate that in African-Americans, obese patients with DKA represent a subset of type II diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Diabetes in urban African-Americans. I. Cessation of insulin therapy is the major precipitating cause of diabetic ketoacidosis.

OBJECTIVE: To identify the causes of diabetic ketoacidosis (DKA) in a large urban hospital. RESEARCH DESIGN AND METHODS: Consecutive patients admitted during a 3-month period with a primary diagnosis of DKA and who had moderate-to-severe illness as shown by serum glucose > 13.9 mmol/l ( > 250 mg/dl), bicarbonate < 15 mmol/l, and pH < 7.35 were studied. Diabetes nurse educators interviewed patients and reviewed their medical records for the following: precipitating causes of DKA; content of previous diabetes education; frequency of blood glucose monitoring; recognition of symptoms of metabolic decompensation; and types of medical assistance obtained once patients were ill. RESULTS: There were 56 episodes of DKA, and 75% of the episodes were in patients with known diabetes. In the known diabetic patients, the most common cause of DKA was stopping insulin therapy, which occurred in 67% of episodes. Half of the patients (50%) stopped insulin because of reported lack of money to buy insulin from an outside pharmacy or get transportation to the hospital; 21% stopped insulin because of lack of appetite; 14% stopped insulin because of behavioral or psychological reasons; and 14% did so because they did not know how to manage diabetes on sick days. Of the known diabetic patients, > 80% recalled having been instructed as to blood glucose testing and acute and chronic complications, but fewer patients recalled having been instructed as to insulin dose adjustment (28%) or sick day management (35%). Symptoms of decompensated diabetes were recognized in 55% of the 42 episodes of DKA in patients with known diabetes. However, only 5% of patients contacted the Diabetes Unit when they became ill; the majority (95%) went directly to the emergency room. CONCLUSIONS: DKA occurred most often in patients with known diabetes who stopped insulin therapy because of reported lack of money for purchasing insulin or for transportation to the hospital and limited self-care skills in diabetes management. In urban African-American populations, up to two-thirds of the episodes of DKA may be preventable by improving patient education and access to care.

Adolescent↗
PubMed1995

Diabetes in urban African-Americans. II. High prevalence of microalbuminuria and nephropathy in African-Americans with diabetes.

OBJECTIVE: African-Americans with diabetes have an increased risk of endstage renal disease, but underlying mechanisms are poorly understood. We undertook this study to evaluate prevalence and risk factors for renal disease in an African-American population with diabetes. RESEARCH DESIGN AND METHODS: We measured urine albumin excretion in 578 consecutive patients presenting for the first time to the Grady Memorial Hospital Diabetes Unit in Atlanta, GA. The unit serves an urban population that is predominantly African-American; 85% of patients have non-insulin-dependent diabetes mellitus (NIDDM). Subjects provided 24-h and/or approximately 3-h urine collections for measurement of albumin and creatinine. RESULTS: Correlation of the albumin/creatinine ratio (micrograms/mg) with the 24-h albumin excretion rate was 0.89 (P < 0.001, n = 123). Although the median duration of diabetes was only 1 year, among all subjects, the estimated prevalence of microalbuminuria (30-300 mg albumin/24 h) was 25% and that of nephropathy ( > 300 mg albumin/24 h) was 11%. Among African-Americans with NIDDM (n = 466), the estimated prevalence of microalbuminuria was 24% and that of nephropathy was 12%; prevalence remained high (25 and 5%, respectively) among 219 patients with < 1 year known duration of diabetes. Metabolic control was not associated with disease. However, among all subjects with NIDDM, the odds ratio for nephropathy among subjects with disease duration > 5 years compared with those with disease duration < 1 year was 4.65 (95% confidence interval [CI] 2.24-9.79), and the odds ratio for nephropathy among subjects with hypertension compared with those without hypertension was 2.64 (CI 1.42-4.93). Odds ratios were comparable among African-Americans with NIDDM. Trends were similar but less significant for subjects with microalbuminuria. CONCLUSIONS: Albuminuria can be identified reliably and conveniently by the albumin/creatinine ratio in brief urine collections. In our patients, clinically significant albuminuria occurred in 36% of persons at first presentation. Since increased risk was associated with hypertension and control of hypertension can slow progression of renal disease, screening for albuminuria and treatment of hypertension should be aggressive in urban populations of African-Americans with diabetes.

Black or African American↗
PubMed1994

Coculture of primary rat hepatocytes and nonparenchymal cells permits expression of insulin-like growth factor binding protein-3 in vitro.

In biological fluids, the insulin-like growth factors (IGFs) are associated with binding proteins (IGFBPs), which modify IGF distribution and action. Circulating IGFs are bound predominantly to IGFBP-3, of apparent hepatic origin, but regulation of IGFBP-3 has been difficult to dissect because of the lack of systems suitable for examining hepatic production of IGFBP-3 in vitro. In the present studies, IGFBP-3 expression was identified primarily in hepatic nonparenchymal cells, particularly Kupffer and sinusoidal endothelial cells. Coculture with hepatocytes enhanced the stability of nonparenchymal cells to express IGFBP-3 in vitro. IGFBP-3 in conditioned medium had apparent mol wt of 150-300 kilodaltons, suggesting formation of a ternary complex with IGFs and the acid-labile subunit. Expression and secretion of IGFBP-3 were hormonally responsive and strongly correlated (r = 0.79; P < 0.001), with 2- to 3-fold stimulation by added insulin or IGF-I (both P < 0.05), but not by added GH alone. Our findings suggest that GH may act indirectly to promote IGFBP-3 generation in vivo via increasing both the secretion of insulin and the hepatic production of IGF-I; in patients with diabetes mellitus, reduced circulating levels of IGFBP-3 despite high levels of GH may result from both insulin deficiency and inadequate hepatic production of IGF-I. Coculture of hepatic nonparenchymal and parenchymal cells should be useful for further analysis of the mechanism of IGFBP-3 regulation.

Animals↗
PubMed1994

Preoperative localization of parathyroid tissue with technetium-99m sestamibi 123I subtraction scanning.

To evaluate the utility of technetium-99m (Tc-99m) sestamibi for visualization of functioning parathyroid tissue, 14 subjects underwent Tc-99m sestamibi 123I subtraction scanning as part of the preoperative evaluation for hyperparathyroidism. Informative scans were obtained in 13 subjects, including 7 patients with recurrent or persistent hyperparathyroidism, and correctly identified the location of the hyperfunctioning parathyroid tissue found at surgery. In all informative patients, hyperparathyroidism was due to adenomatous disease or hyperplasia secondary to renal failure. Successful scans were obtained with glands as small as 220 mg. In the lone patient in whom Tc-99m sestamibi scanning failed to localize hyperfunctioning parathyroid tissue, surgery revealed a 1700-mg hyperplastic parathyroid neoplasm in the neck. In no case did a Tc-99m sestamibi scan suggest parathyroid tissue where there was none. In 1 case, a patient presented with persistent hyperparathyroidism after 1 neck and a second combined neck and mediastinal exploration. Tc-99m sestamibi imaging revealed uptake in the periaortic region, and a 570-mg adenoma was found in the aortopulmonary window. Using only initial studies, prospective evaluation provided a sensitivity of 78.5% and a positive predictive value of 100%. After repeat studies in 5 patients, 2 of 3 patients with initially negative results and technically deficient scans became positive on restudy. Inclusion of these studies increased sensitivity to 93%. Tc-99m sestamibi 123I subtraction scanning appears to be a reliable noninvasive method for preoperative localization of hyperfunctioning parathyroid tissue.

Adult↗
PubMed1993

Differential regulation of IGF-1 and IGF-binding protein-1 by dietary composition in humans.

Although it is known that circulating levels of the insulin-like growth factors (IGFs) and the IGF-binding proteins (IGFBPs) fluctuate in response to changes in nutritional status, there is little information regarding either relative contributions from different dietary components or regulation by insulin in nondiabetic subjects. To define dietary contributions to IGF regulation, the authors examined the effects of fasting and hypocaloric diets of differing nutritional composition on serum IGF-1 and a IGFBP-1 in 16 healthy, obese adult women. Subjects received an isocaloric diet for 6 days, followed by 14 days of calorie restriction (fasting or a hypocaloric diet enriched in either protein, fat, or carbohydrate), and by 4 days refeeding. All diets produced 6-8% weight loss over 14 days with little difference between groups. The "protein-sparing" diet sustained nitrogen balance (+1.2 g/d, versus -4.5 g/d for the other three groups; p < 0.05). Serum IGF-1 levels decreased during calorie restriction with fasting or with diets high in fat or carbohydrates (CHO; combined mean 40 +/- 7%) but showed little change with the high protein regimen (3 +/- 16%; p < 0.05 compared to the other diets). In contrast, IGFBP-1 increased during calorie restriction in all four groups but significantly less with the high CHO diet (43 +/- 17% above baseline) than with the other diets (168 +/- 31%; p < 0.05). Levels of IGF-1 were correlated with nitrogen balance (r = 0.51; p < 0.05) but levels of IGFBP-1 were not. Although IGFBP-1 levels inversely correlated with measures of insulin secretion, IGF-1 levels did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Regulation of insulin-like growth factor-I (IGF-I) and IGF-binding protein 1 gene transcription by hormones and provision of amino acids in rat hepatocytes.

Synthesis of insulin-like growth factor-I (IGF-I) and IGF binding protein-1 (IGFBP-1) is altered in diabetes and malnutrition, but underlying processes are poorly understood. To study molecular mechanisms, we examined regulation of IGF-I and IGFBP-1 gene transcription in primary cultures of rat hepatocytes. Transcription of the IGF-I and IGFBP-1 genes was measured as incorporation of [alpha-32P]UTP into preinitiated message in isolated nuclei. IGFBP-1 gene transcription was not sensitive to reduction in amino acid concentration from 5x to 0.5x rat arterial plasma levels. However, IGF-I gene transcription fell 60-70% in response to reduced provision of amino acids. Culture with 10(-9) M insulin lowered IGFBP-1 gene transcription 50% below control levels (10-11 M) but did not affect IGF-I gene transcription; 10(-6) M insulin raised IGF-I gene transcription 2-fold. After an acute reduction in insulin concentration, IGFBP-1 transcription began to rise within 30 min, but IGF-I gene transcription was unchanged over 120 min. Similarly, 3-6 h were required for stimulation of IGF-I gene transcription by insulin, but a 40% decrease in IGFBP-1 gene transcription could be detected within 15 min after adding 10(-6) M insulin, and suppression of IGFBP-1 transcription by insulin was unaffected by the presence of cycloheximide. Effects of insulin on IGFBP-1 gene transcription were not mimicked or antagonized by phorbol ester.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1993

Value of technetium 99m sestamibi iodine 123 imaging in reoperative parathyroid surgery.

BACKGROUND: The purpose of this study was to assess the contribution of technetium 99m sestamibi iodine 123 (T/S) imaging to preoperative and intraoperative management of patients with persistent hyperparathyroidism. METHODS: During a period of 10 months, all patients being prepared for reoperative parathyroid surgery (n = 10), two patients deemed significant operative risks (one patient with severe chronic obstructive pulmonary disease and one patient with severe cervical spine ankylosing spondylitis), and two patients who had undergone prior thyroid operation were studied with T/S imaging. Six patients undergoing reoperative surgery had undergone one, three had undergone two, and one had undergone three prior procedures. RESULTS: T/S imaging correctly localized 14 of 16 parathyroid tumors. By comparison, only 1 of 6 thallium technetium and 3 of 12 computed tomography (CT) scans (in seven patients) were positive. T/S imaging guided the reoperative surgical approach accurately in 12 of 14 patients, including one case of an undescended left lower gland at the level of the mandible and identification of a third gland on the left in another case. Sternal split was required to remove three lesions localized by T/S imaging, two beneath the aortic arch and one nestled in the aortopulmonary window in a patient who had undergone two prior procedures including a sternal split. In these three cases T/S imaging was particularly useful, because CT scans, thallium technetium scans, magnetic resonance imaging, and arteriography were not diagnostic. The outcome after operation was favorable in all 14 cases, with correction of hypercalcemia and no permanent laryngeal nerve injuries or hypocalcemia. CONCLUSIONS: We concluded that T/S imaging is more accurate than thallium technetium and CT scans in evaluation of patients with persistent hyperparathyroidism.

Adult↗
PubMed1992

Expression of hepatic insulin-like growth factor-I and insulin-like growth factor-binding protein-1 genes is transcriptionally regulated in streptozotocin-diabetic rats.

Insulin-like growth factor-I (IGF-I) and IGF-binding protein-1 (BP-1) are critical cell regulators, with regulation and action in endocrine, paracrine, and autocrine modes. Although IGF-I and BP-1 are thought to be modulated mainly at the level of synthesis, underlying molecular mechanisms are poorly understood. To examine regulation by insulin, we used run-on assays to measure IGF-I and BP-1 gene transcription rates in nuclei isolated from the livers of normal and diabetic rats. Streptozotocin (STZ)-treated rats exhibited 20-25% weight loss, a 2.5- to 3-fold increase in serum glucose, and a 50-60% fall in circulating IGF-I levels (all P less than 0.001). Diabetic animals also had a 45% reduction in hepatic IGF-I mRNA and over 400% increases in BP-1 mRNA (both P less than 0.005); all parameters were restored toward normal after treatment with insulin. Metabolically responsive IGF-I gene transcription was evaluated effectively with a 3.2-kilobase BglII/EcoRI genomic probe located down-stream from all initiation sites in exon 1, while BP-1 gene transcription was studied with a cDNA probe. Animals treated with 144 mg/kg STZ exhibited 50-97% decreases in IGF-I gene transcription (P less than 0.05), while insulin treatment raised IGF-I gene transcription to control levels (P less than 0.02). IGF-I gene transcription appeared to be more sensitive to metabolic status than IGF-I mRNA levels, resulting in a modest correlation between transcription rates and mRNA levels (r = 0.68; P less than 0.001). In contrast, changes in BP-1 mRNA and gene transcription appeared to be exquisitely sensitive to metabolic status.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Nutrition and somatomedin XXIX. Molecular regulation of IGFBP-1 in hepatocyte primary culture.

The insulinlike growth factors (IGFs) circulate in association with insulinlike growth factor binding proteins (IGFBPs) that modulate IGF action, but mechanisms of IGFBP regulation are poorly understood. We investigated the regulation of IGFBPs in primary cultures of rat hepatocytes, measuring the appearance of export proteins by ligand blotting after separation via SDS/PAGE, and evaluating mRNA with cDNA probes. Northern blotting studies revealed that IGFBP-1 was expressed at high levels in cultured hepatocytes, in which sustained release of both insulinlike growth factor I and albumin marks preservation of differentiated status. In contrast, transcripts of IGFBP-3 and IGFBP-2 were not detected. Release of IGFBP-1 was unaffected by exposure to glucose (20-500 mg/dl) or to provision of amino acids (0.25-6.25 times normal rat arterial plasma levels). Hormonal studies revealed little effect of glucagon, inhibition by insulin, stimulation by dexamethasone, and blunting of dexamethasone effects by added insulin. Adding dexamethasone provided progressive stimulation: 5-, 11-, and 26-fold at 10(-9), 10(-8), and 10(-7) M, all P less than 0.01; increases in IGFBP-1 protein (ligand blot) and IGFBP-1 mRNA (Northern blot) were highly correlated (r = 0.62, P less than 0.001). In contrast, adding insulin resulted in progressive suppression of both IGFBP-1 protein and IGFBP-1 mRNA, 43% at 10(-10) M, 74% at 10(-9) M, and 83% (maximal) at 10(-8) M; ED50 of approximately 10(-10) M is within the physiological range of insulin concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1991

Extraction and nutritional/hormonal regulation of tissue insulin-like growth factor 1 activity.

Studies of insulin-like growth factor 1 (IGF-1) mRNA translation products suggest synthesis as a high Mr precursor, larger than circulating forms. To search for a precursor, we characterized IGF-1 immunoreactivity and IGF bioactivity in extracts from the liver and other body tissues. Sequential extraction with neutral followed by acid buffer was superior to extraction with acid/ethanol or acid alone in yield of immunoreactivity and specific activity. Extracts of normal rat liver exhibited both immuno- and bioactivity parallel to that of recombinant IGF-1 and serum IGFs over a 25-fold concentration range. Based on immunoreactivity, the liver of a 134-g rat appears to contain 1.2 micrograms of IGF-1 equivalents, 50% of the 2.45 micrograms in the circulation. Diaphragm, spleen, and kidney contained no significant IGF bioactivity and 8, 17, and 32% of the IGF-1 immunoreactivity of normal liver, respectively. Although serum IGFs were found at 7.5 kDa after size exclusion chromatography at pH 3, hepatic extracts contained a predominant peak of immuno- and bioactivity of apparent molecular mass of 30-35 kDa; both sizes were present in liver perfusates. Both immunoaffinity chromatography followed by Western blotting and IGF-binding protein affinity chromatography followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed two predominant species, at 18-19 and 12 kDa. The 18-19-kDa species is consistent with the apparent size of the glycosylated propeptide encoded by IGF-1A mRNA, while the 12-kDa species may be nonglycosylated propeptide. Extract activity was pituitary-dependent; the livers of hypophysectomized rats contained 15.4 and 48.8% of normal immuno- and bioactivity, respectively. During fasting and refeeding of rats, fluctuations in hepatic extract IGF-1 immunoreactivity generally paralleled changes in serum IGF-1 (r = 0.93, p less than 0.001). These studies demonstrate that the liver contains a pituitary- and nutrition-dependent, high Mr form of IGF-1 with immunological and biological properties similar to circulating IGF-1. Processing of this 18-19-kDa molecule through a 12-kDa intermediate may contribute IGF-1 to the circulation.

Animals↗
PubMed1991

Altered visceral yolk sac function produced by a low-molecular-weight somatomedin inhibitor.

A fraction from diabetic rat serum containing a low-molecular-weight (800-1000) somatomedin inhibitor (SI) alters growth and development in both neurulation and early limb bud staged mouse embryos in vitro. Previous studies suggested that an accumulation of serum proteins and morphological changes of the visceral yolk sac (VYS) were produced following exposure to the SI in early limb bud staged conceptuses. The morphological changes, characterized by the presence of large endosomes in the endodermal cells, suggested that the SI altered histiotrophic nutrition, whereby proteins are pinocytosed by the endodermal VYS cells and degraded to constituent amino acids. Therefore, the effects of the SI on pinocytosis and protein degradation by the VYS were evaluated using the whole embryo culture system. Results showed that the SI reduced fluid phase pinocytosis as determined by the uptake of [U-14C]sucrose, but that accumulation of [3H]leucine-labeled hemoglobin ([3H]Hb) by the VYS was greater following exposure to the SI than in controls. In contrast, the accumulation of 3H-labeled amino acids in the embryo (produced from the degradation of [3H]Hb by the VYS) was reduced by the SI. The extent of amino acid reduction in embryonic accumulation is dependent upon the concentration of SI in the culture medium and correlates with the incidence of malformations produced by the SI, i.e., high rates of malformations occur with large reductions in embryonic 3H-labeled amino acid accumulation. The apparent paradox of high [3H]Hb accumulation in the presence of decreased pinocytosis appears to be the result of altered processing of the [3H]Hb in the endodermal cells. The altered processing decreases the "elimination" of the proteins from the VYS and results in the decrease in 3H-labeled amino acid present in the embryo proper. Therefore, the SI appears to alter two processes of VYS histiotrophic function. (1) decreased pinocytosis and (2) altered protein processing, ultimately resulting in a decreased availability of substrates for the embryo. During the early stages of embryogenesis in the human, the trophoblast cells of the placenta are responsible for the transport of nutrients from the maternal to embryonic systems. Since these cells show high phagocytic and pinocytotic activities, the SI may also disrupt these processes in the chorioallantoic placenta and contribute to diabetes-induced embryopathies.

Animals↗