Higher serum concentrations of tyrosine and glutamate in schizophrenia patients treated with clozapine, compared to in those treated with conventional antipsychotics.

RATIONALE: The effect of long-term treatment with the atypical antipsychotic clozapine on the serum amino acid profile in schizophrenia patients has not previously been studied. OBJECTIVES: The aim of this study was to compare serum amino acid patterns in patients on long-term clozapine treatment with long-term conventional antipsychotic treatment, and their relationships to insulin resistance and antipsychotic serum concentrations. METHODS: Thirty-three patients with schizophrenia or schizoaffective disorder on long-term treatment (mean 8.3 years) with clozapine (n=20) or conventional antipsychotics (n=13) were studied. Amino acids were quantified in fasting serum samples by ion exchange chromatography and markers of insulin resistance and antipsychotic drug concentrations were determined by standard methods. RESULTS: Several amino acids, most notably tyrosine and glutamic acid, were elevated above the reference range in several patients receiving clozapine. Additionally, significantly higher mean values of tyrosine (1.5-fold, p=0.001), glutamic acid (2-fold, p=0.0005) and six other amino acids were observed in the clozapine group than in the conventional antipsychotic group. Several amino acids were related to insulin resistance in both treatment groups. CONCLUSIONS: In this study, we show that serum tyrosine and glutamic acid concentrations are markedly elevated in patients on long-term clozapine treatment, compared to patients on long-term conventional antipsychotic treatment. These findings are of importance since these two amino acids have been implicated in the pathophysiology of schizophrenia.

The Insulin-Like Growth Factor System in Obesity, Insulin Resistance and Type 2 Diabetes Mellitus.

The insulin-like growth factor (IGF) system, acting in concert with other hormone axes, is important in normal metabolism. In obesity, the hyperinsulinaemia that accompanies peripheral insulin resistance leads to reduced growth hormone (GH) secretion, while total IGF-I levels are relatively unchanged due to increased hepatic GH sensitivity. IGF-binding protein (IGFBP)-1 levels are suppressed in relation to the increase in insulin levels in obesity and low levels predict the development of type 2 diabetes several years later. Visceral adiposity and hepatic steatosis, along with a chronic inflammation, contribute to the IGF system phenotype in individuals with metabolic syndrome and type 2 diabetes mellitus, including changes in the normal inverse relationship between IGFBP-1 and insulin, with IGFBP-1 concentrations that are inappropriately normal or elevated. The IGF system is implicated in the vascular and other complications of these disorders and is therefore a potential therapeutic target.

Neonatal IGF-1/IGFBP-1 axis and retinopathy of prematurity are associated with increased blood pressure in preterm children.

AIM: Preterm children are at risk of developing increased blood pressure (BP). We evaluated possible associations between BP, early insulin-like growth factor-1 (IGF-1) and IGF-binding protein-1 (IGFBP-1) levels and retinopathy of prematurity (ROP) in preterm children. METHODS: The study included 32 infants: median gestational age 28.1 weeks (range 24.6-31.3) and birthweight standard deviation scores (SDS) (±SD) 1.0 ± 2.7. IGF-1 and IGFBP-1 at postnatal weeks 32.6-34.6 and ROP stages were established after birth. BP was measured at the age of 4 years. The ratio (IGF-1)(2)/IGFBP-1 was created to investigate the influence of both IGF-1 and IGFBP-1 to later BP. RESULTS: Diastolic BP correlated with IGFBP-1, inversely correlated with IGF-1 and IGF-1(2)/IGFBP-1 (r = -0.71, p < 0.0001) and positively correlated with catch-up growth velocity from lowest weight SDS to age 36.5 weeks (r = 0.48, p < 0.01), independent of gestational age. Children with moderate-to-severe ROP as neonates had higher mean arterial BP [78 (±95%CI 74-83) vs 71 (±95%CI 68-75) mm Hg, p < 0.05] adjusted for gestational age and birthweight SDS compared to children diagnosed with no to mild ROP. CONCLUSION: Low neonatal IGF-1(2)/IGFBP-1 and severe ROP were associated with higher BP in 4-year-old children born very preterm and may thus predict future cardiovascular morbidity.

Leptin may enhance hepatic insulin sensitivity in children and women born small for gestational age.

OBJECTIVE: Children born small for gestational age (SGA) are at risk for developing type 2 diabetes. Lipodystrophy leads to early type 2 diabetes and leptin reverses the metabolic consequences of the disease. Low IGF-binding protein 1 (IGFBP1) can predict the development of type 2 diabetes. The aim of this study was to determine leptin, insulin, and IGFBP1 in children and adult women born preterm or SGA to evaluate the role of leptin as a compensatory mechanism in insulin resistance development. METHODS: Seventy-six children (8.5-10 years, 41 girls and 35 boys) and 45 women (23-30 years) were studied. The children comprised subjects born appropriate for gestational age (<30 gestational weeks) (n=22), born SGA at term (n=23), and full-term normal-weight controls (n=31). Among the women, the corresponding figures were, n=10, n=18, and n=17 respectively. Fasting levels of IGFBP1, leptin, insulin, and IGF1 were determined and total adiponectin only in women. RESULTS: In girls and women, term SGA subjects had higher leptin levels in relation to BMI SDS (P=0.042 and P=0.03 respectively). More than half of IGFBP1 variability was explained by leptin and insulin in children. In term SGA women, IGFBP1 level was lower compared with controls (P=0.012) and the regression line of IGFBP1 on insulin was suppressed below -1 s.d. of a reference material. CONCLUSION: Leptin levels were elevated in term SGA girls and women, in particular in adult women, but not found in preterm girls and women. IGFBP1 was lower in term SGA women. In children, leptin and insulin were strong suppressors of IGFBP1. We speculate that higher leptin levels could be a protective event to enhance hepatic insulin sensitivity.

Pubertal stage and measures of adiposity in British schoolchildren.

BACKGROUND: Puberty is a critical period in the development of obesity. Body mass index (BMI), waist circumference and skin-fold thickness are used generally as estimates of body fat in children and adults. AIM: To identify a marker of adiposity that is independent of pubertal status and determine its relationship to physical fitness in adolescence. SUBJECTS AND METHODS: Girls (n = 147) and boys (n = 100) from year 8 in three Welsh schools self-reported Tanner stages. Anthropometric measurements of adiposity were made and aerobic fitness estimated with a 20-metre shuttle-run test. RESULTS: Children in early and late puberty were of similar chronological age. BMI strongly correlated with height in early puberty in girls (r = 0.366, p < 0.001) and boys (r = 0.594, p < 0.001), but not in late puberty. Waist-to-height ratio adjusted for the effect of height on waist measurements; and correlated with percentage fat mass in early and late puberty in girls (r = 0.865 and r = 0.772, both p < 0.001) and boys (r = 0.868 and r = 0.877, both p < 0.001). Physical fitness score was inversely related to waist-to-height ratio, with similar regression lines in early and late puberty, in girls (r = - 0.545, p < 0.001 and r = - 0.362, p = 0.005) and boys (r = - 0.490, p < 0.001 and r = - 0.400, p = 0.003). CONCLUSION: Pubertal status should be taken into account in adjusting weight for height in adolescents. Waist-to-height ratio is a convenient and appropriate measure of adiposity during puberty.

Differences in insulin resistance markers between children born small for gestational age or born preterm appropriate for gestational age.

AIM: To evaluate the impact of prenatal or postnatal compromised environment on glucose homoeostasis in children born preterm and appropriate for gestational age or small for gestational age (SGA) at term. METHOD: Seventy-seven children (median 9.9 years, range 8.5-10) born at Karolinska Hospital were allocated to three groups: 21 subjects born before 30 weeks of gestational age (preterm), 26 SGA at term and 30 at term with appropriate birth weight (control). Anthropometric measurements were taken, and fasting blood samples for haemoglobin A1c, glucose, insulin, IGFBP-1, IGF-1 and lipid profile were taken. Glucose, insulin and IGFBP-1 samples were taken at 0, 30 and 120 min during an oral glucose tolerance test (OGTT). RESULTS: Subjects born preterm or SGA were shorter and thinner compared with Controls. After adjustment for body mass index (BMI), the SGA group had higher basal insulin levels (p = 0.029), higher homoeostasis model assessment-insulin resistance (p = 0.012) and lower whole-body insulin sensitivity index (p = 0.007) than Controls. IGFBP-1 decrease during OGTT was attenuated in the Preterm group compared with the Control (p = 0.045) and SGA groups (p = 0.007). CONCLUSION: The higher fasting insulin level in the SGA children, adjusted for BMI, could indicate peripheral insulin resistance. Preterm born children had reduced suppression of IGFBP-1 during OGTT, suggesting hepatic insulin resistance.

Insulin sensitivity and lipid profile in prolactinoma patients before and after normalization of prolactin by dopamine agonist therapy.

Hyperprolactinemia has been associated with impaired metabolism, including insulin resistance. However, the metabolic effects of elevated prolactin (PRL) levels are not completely clarified. The aim of this study was to obtain more insights of metabolic consequences in hyperprolactinemia patients. Fourteen consecutive patients, eight women and six men, aged 39.7 (±13.7) years with prolactinomas (median PRL 72 [49-131] µg/L in women and 1,260 [123-9,600] µg/L in men) were included. Anthropometric data and metabolic values were studied before and after 2 and 6 months on DA agonists (Bromocriptine [5.7 (±3.9) mg/day, n = 13] or Cabergoline [0.5 mg/week, n = 1]). Euglycemic hyperinsulinemic clamps were studied in six patients before and after 6 months of treatment. PRL normalized in all patients. Anthropometric data changed only in males with a significant decrease of median body weight (95.6 [80.7-110.1] to 83.4 [77.8-99.1] kg, P = 0.046), waist circumference and fat percentage after 6 months. LDL cholesterol was positively correlated to PRL at diagnosis (r = 0.62, P = 0.025) and decreased within 2 months (3.4 [±0.9] to 2.9 [±0.6] mmol/L, P = 0.003). Insulin, IGFBP-1 and total adiponectin levels did not change. Insulin sensitivity tended to improve after 6 months; M-value from 5.7 (±1.8) to 7.8 (±2.6) mg/kg/min, P = 0.083 and per cent improvement in M-value was correlated to per cent reduction in PRL levels (r = -0.85, P = 0.034). In conclusion, beneficial metabolic changes were seen in prolactinoma patients after treatment with DA agonists, underscoring the importance of an active treatment approach and to consider the metabolic profile in the clinical management of hyperprolactinemia patients.

Associations between amino acids and bone mineral density in men with idiopathic osteoporosis.

Idiopathic osteoporosis in middle-aged men is characterized by low-level bone formation. Inhibited anabolism may be involved in the pathogenesis of the disease and amino acids may be of importance. In the present study fasting amino acid profiles in plasma and erythrocytes were determined in 22 male idiopathic osteoporosis (MIO) patients and in 20 age-matched healthy men and associated with bone mineral density, bone histomorphometry and hormones. The osteoporotic patients had normal plasma essential amino acids but increased non-essential amino acids (p=0.001), particularly glutamine and glycine. The ratio essential/non-essential amino acids, an index of protein nutritional status, was decreased in the MIO patients (0.59 (0.04) µmol/l, mean (SD)), compared to controls (0.66 (0.05), p=0.001). In the MIO patients, the ratio essential/non-essential plasma amino acids (r=0.60, p=0.003) was positively correlated with lumbar spine bone mineral density. The erythrocyte amino acids represent a large proportion of the free amino acids in blood. A novel finding was the lower levels of erythrocyte tryptophan in MIO (12 (2) µmol/l) compared to controls (16 (3), p=0.001) and decreased erythrocyte/plasma ratio (0.28 (0.07) vs. 0.33, (0.06), p<0.01), suggesting an altered amino acid transport of tryptophan between plasma and erythrocytes. In the combined group of MIO and control men (n=42), bone mineral density was positively correlated with erythrocyte tryptophan in both the lumbar spine (r=0.45, p=0.003) and femoral neck (r=0.56, p<0.001). The bone histomorphometric variables wall thickness, trabecular thickness and mineral apposition rate were all positively associated with erythrocyte tryptophan levels in the MIO patients. In the combined group of MIO and controls, a multiple regression analysis showed that erythrocyte tryptophan could explain 22% of the variation of lumbar spine and 30% of the variation in femoral neck bone mineral density. We conclude that men with idiopathic osteoporosis have changes in free amino acid profiles which indicate their altered utilization. The correlations between tryptophan and bone mineral density and bone histomorphometry suggest a link between tryptophan and osteoblast function which may be important for bone health.

IGF-binding protein 1 and abdominal obesity in the development of type 2 diabetes in women.

OBJECTIVE: Low levels of IGF-binding protein 1 (IGFBP1) are associated with metabolic syndrome and predict diabetes development in men. The aim of this study was to determine the levels of IGFBP1 in women who later develop diabetes, in relation to abdominal obesity, and to compare these levels with those of men. METHODS: IGFBP1 levels were determined at baseline and after 8 years in a case-control, prospective study of Swedish women aged 35-56 years. Individuals with normal oral glucose tolerance test (OGTT) who developed abnormal glucose regulation (n=240) were pair matched to controls for age and family history of diabetes and also compared to men of the same age (n=355). RESULTS: Low fasting IGFBP1 and increased waist measurement predicted development of diabetes in women (n=60; odds ratio (OR) 70, 95% confidence interval (CI) 8-661, lowest tertile and OR 27, 95% CI 5-141, highest tertile). In women developing diabetes, baseline IGFBP1 levels were lower than expected for fasting insulin values, were associated with impaired suppression after OGTT and increased during 8 years despite an increase in fasting insulin. All individuals in the highest tertile for waist and with

IGFBP-1 protease activity and IGFBP-1 fragments in a patient with multiple myeloma.

OBJECTIVE: Cleavage of IGFBPs by proteases results in IGFBP fragments that have altered IGF-binding affinity, and IGF-independent roles. We have previously purified a specific IGFBP-1 protease activity from the urine of an individual with multiple myeloma and dermatitis. The aim of this study was to determine whether IGFBP-1 protease activity and/or IGFBP-1 fragments were present in the circulation of this patient. METHODS: The size of immunoreactive IGFBP-1 in serum samples was determined after Superose 12 chromatography. Intact IGFBP-1 and IGFBP-1 fragments were characterized in four RIAs and after SDS-PAGE. RESULTS: Specific proteolysis of IGFBP-1 generated an N-terminal fragment (IGFBP-1(1-130)) with a predicted molecular mass of 13kDa but an apparent mass of 21kDa on SDS-PAGE. A C-terminal fragment (IGFBP-1(131-234)) produced in vitro migrated at 11.4kDa, close to its predicted size. However a C-terminal fragment of cleaved IGFBP-1 (IGFBP-1(142-234)) migrated at 14kDa on SDS-PAGE. Serum from the patient inhibited IGFBP-1 protease activity. Immunoreactive IGFBP-1 in patient serum was present at molecular masses consistent with IGFBP-1 fragments, in addition to intact IGFBP-1. CONCLUSIONS: Specific cleavage of IGFBP-1 occurs at the tissue level and not in the circulation in a patient with multiple myeloma and dermatitis. The fragments that are generated may have endocrine roles.

Insulin-like growth factor binding protein 1 as a novel specific marker of hepatic insulin sensitivity.

BACKGROUND AND AIMS: The liver is the main source and insulin the main regulator of IGF binding protein 1 (IGFBP-1) in humans. Here we examined how serum IGFBP-1 concentrations are related to directly measured hepatic insulin sensitivity and liver fat content in humans. METHODS: We measured fasting serum (fS) IGFBP-1 concentrations and liver fat content by proton magnetic resonance spectroscopy in 113 nondiabetic subjects. In addition, hepatic insulin sensitivity was measured using the euglycemic hyperinsulinemic clamp (insulin 0.3 mU/kg.min) technique in combination with the infusion of [3-(3)H]glucose in 78 subjects. RESULTS: fS-IGFBP-1 concentrations were inversely related to liver fat content (r = -0.38, P < 0.0001). Of circulating parameters, fS-IGFBP-1 was better correlated to hepatic insulin sensitivity (r = 0.48, P < 0.0001) than fS-insulin (r = -0.42, P = 0.0001), fS-C-peptide (r = -0.41, P = 0.0002), fS-triglyceride (r = -0.33, P = 0.003), or fS-high-density lipoprotein cholesterol (r = 0.30, P = 0.007). In multiple linear regression analyses, body mass index (P < 0.0001) and fS-IGFBP-1 (P = 0.008), but neither age nor gender, were independently associated with hepatic insulin sensitivity (P < 0.0001 for ANOVA). Neither fS-insulin nor fS-C-peptide were independent determinants of hepatic insulin sensitivity after adjusting for age, gender, and body mass index. CONCLUSIONS: fS-IGFBP-1 is inversely correlated with liver fat and is an obesity-independent and liver-specific circulating marker of hepatic insulin sensitivity.

Altered response of insulin-like growth factor-binding protein 1 to nutritional deprivation in type 2 diabetes mellitus.

Circulating insulin-like growth factor-binding protein 1 (IGFBP-1) normally has a close inverse relationship to insulin secretion, which results in a characteristic diurnal variation. However, in type 2 diabetes the correlation with insulin may be lost and IGFBP-1 concentrations relatively increased. The aim of this study was to determine the effect of nutritional deprivation on the diurnal patterns of IGFBP-1 regulation in type 2 diabetes mellitus. After a baseline assessment period, food intake was reduced over 48 hours to 627.6 kJ/d (150 kcal/d) for 72 hours and increased again over 24 hours to baseline (refeeding). Blood samples were taken at 2-hour intervals, for 24 hours in the baseline period, 48 hours during nutritional deprivation, and 24 hours during refeeding. Six individuals with type 2 diabetes were compared with 2 groups that were selected for normal fasting glucose and insulin levels and comprised 6 obese and 6 lean subjects. During energy (caloric) restriction, fasting insulin levels decreased to a similar extent in each study group. At baseline, IGFBP-1 concentrations were similar in each of the study groups and at the end of the period of energy (caloric) restriction the 6:00 AM fasting levels had increased by 144% in the obese control group and by 245% in the lean individuals (each P < .001). In the patients with type 2 diabetes there was a blunted increase in IGFBP-1 concentrations with nutritional deprivation by 33% compared with baseline. During refeeding after nutritional deprivation the IGFBP-1 response to insulin was restored in the individuals with diabetes. In conclusion, patients with type 2 diabetes mellitus have altered IGFBP-1 regulation, relating to impaired hepatic insulin sensitivity, which improves after a period of energy (caloric) restriction.

Troglitazone stimulates IGF-binding protein-1 by a PPAR gamma-independent mechanism.

IGFBP-1 modulates IGF availability for glucose homeostasis and it may also play a paracrine role in hepatocyte survival. IGFBP-1 is inhibited transcriptionally by insulin and is also regulated by a number of pathways that influence hepatic insulin sensitivity. The effect of the thiazolidinedione troglitazone on IGFBP-1 production was studied in HepG2 human hepatoma cells, which were found to express PPAR alpha, PPAR gamma, and PXR. Troglitazone stimulated IGFBP-1 mRNA expression 2-fold within 3h of exposure (P<0.001) and stimulated secretion up to 3-fold over a narrow dose range within 24h (P<0.001). This effect was mimicked by the PXR ligands clotrimazole and phenobarbital, but not by Wy14,643 or rosiglitazone, which are ligands for PPAR alpha and -gamma, respectively. We conclude that the effect of troglitazone on IGFBP-1 production by HepG2 cells is independent of PPAR and may involve PXR.

Glucagon and GLP-1 stimulate IGFBP-1 secretion in Hep G2 cells without effect on IGFBP-1 mRNA.

Glucagon has previously been reported to increase serum levels of insulin-like growth factor binding protein-1 (IGFBP-1) in humans. The in vitro effect of glucagon and glucagon-like peptide-1 (7-36) amide (GLP-1) was investigated in Hep G2 human hepatoma cells. The expression of IGFBP-1 mRNA was determined by solution hybridization assay and IGFBP-1 secretion was measured by radioimmunoassay. In contrast to forskolin the peptides glucagon and GLP-1 had no effect on IGFBP-1 mRNA at 3, 6 and 24 h incubation or any detectable effect on the apparent half-life of IGFBP-1 mRNA. However, the exposure to glucagon (10 microg/mL, 2.87 microM) and GLP-1 (1 microM) caused a two-fold stimulation in protein levels of IGFBP-1 after 6 h incubation, declining to control levels after 24 h. This transient effect was dose dependent, remained when transcription was inhibited and required protein synthesis. The regulation of IGFBP-1 secretion by glucagon and GLP-1 appeared to be cAMP independent. In conclusion, glucagon and GPL-1 were shown to have a post-transcriptional stimulatory effect on IGFBP-1 release.

Altered expression of low affinity insulin-like growth factor binding protein related proteins in hepatoblastoma.

Hepatoblastoma is a poorly understood rare pediatric liver tumour. We have previously shown that the IGF-axis is seriously disrupted in this tumour type. With the recent discovery that several other proteins also have the potential to bind to IGFs called insulin-like growth factor binding protein related proteins (IGFBP-rPs), we undertook an examination of several such genes in a series of hepatoblastomas with matched normal liver tissue. The expression profiles obtained reveal that the expression of these genes are also disturbed in these tumours, and may have implications for our understanding of the IGF-axis and its importance in this disease.

Hormonal evaluation in schizophrenic patients treated with neuroleptics.

The aim of this study was to hormonally evaluate schizophrenic patients on long-term treatment with neuroleptics. Twenty-eight patients (14 men and 14 women) on long-term therapy with different neuroleptics were investigated. Blood samples for prolactin (PRL), growth hormone (GH) and insulin-like growth factor I (IGF-I) were measured, as well as gonadotropins and testosterone in the males. In addition, clinical signs and symptoms of the neuroleptic side effects were evaluated. Seven out of 14 women had elevated PRL and five of the six fertile women in this group had menstrual disturbances. Twelve of the l4 men had normal PRL levels, whereas two had slightly elevated PRL without related symptoms. Four patients had low IGF-I levels, which in one case was combined with elevated PRL. We conclude that PRL levels in schizophrenic patients on long-term therapy with neuroleptics are elevated in about 50% of the women and in 10-20% of the men. Furthermore, irrespective of PRL levels or other hormonal disturbances, some patients on long-term neuroleptic therapy show low IGF-I levels, pointing at a possible interference with neuroleptics on the hypothalamic-pituitary regulation of GH-dependent IGF-I secretion.