C1q enables influenza hemagglutinin stem binding antibodies to block viral attachment and broadens the antibody escape repertoire

Antigenic drift, the gradual accumulation of amino acid substitutions in the influenza virus hemagglutinin (HA) receptor protein, enables viral immune evasion. Antibodies (Abs) specific for the drift-resistant HA stem region are a promising universal influenza vaccine target. Although anti-stem Abs are not believed to block viral attachment, here we show that complement component 1q (C1q), a 460-kilodalton protein with six Ab Fc-binding domains, confers attachment inhibition to anti-stem Abs and enhances their fusion and neuraminidase inhibition. As a result, virus neutralization activity in vitro is boosted up to 30-fold, and in vivo protection from influenza PR8 infection in mice is enhanced. These effects reflect increased steric hindrance and not increased Ab avidity. C1q greatly expands the anti-stem Ab viral escape repertoire to include residues throughout the HA, some of which cause antigenic alterations in the globular region or modulate HA receptor avidity. We also show that C1q enhances the neutralization activity of non-receptor binding domain anti-SARS-CoV-2 spike Abs, an effect dependent on spike density on the virion surface. These findings demonstrate that C1q can greatly expand Ab function and thereby contribute to viral evolution and immune escape.

Paradoxical imbalance between activated lymphocyte protein synthesis capacity and rapid division rate

Rapid lymphocyte cell division places enormous demands on the protein synthesis machinery. Flow cytometric measurement of puromycylated ribosome-associated nascent chains after treating cells or mice with translation initiation inhibitors reveals that ribosomes in resting lymphocytes in vitro and in vivo elongate at typical rates for mammalian cells. Intriguingly, elongation rates can be increased up to 30% by activation in vivo or fever temperature in vitro. Resting and activated lymphocytes possess abundant monosome populations, most of which actively translate in vivo, while in vitro, nearly all can be stalled prior to activation. Quantitating lymphocyte protein mass and ribosome count reveals a paradoxically high ratio of cellular protein to ribosomes insufficient to support their rapid in vivo division, suggesting that the activated lymphocyte proteome in vivo may be generated in an unusual manner. Our findings demonstrate the importance of a global understanding of protein synthesis in lymphocytes and other rapidly dividing immune cells.

Game of Omes: ribosome profiling expands the MHC-I immunopeptidome

Peptide ligands presented by cell-surface MHC class-I molecules enable T cells to eradicate intracellular pathogens and cancers. The presented peptide repertoire, the class-I immunopeptidome, is generated from each cell's translatome in a highly biased manner to avoid overrepresenting highly abundant translation products. The immunopeptidome can only be defined by mass spectrometry (MS). Here, we review recent advances in immunopeptidomics, focusing on using ribosome profiling as the optimal MS database to optimize the false- and failed-discovery rates and relate these findings to the contribution of defective ribosomal products and cellular quality control mechanisms to MHC class-I antigen processing and presentation.

Enhanced virulence and waning vaccine-elicited antibodies account for breakthrough infections caused by SARS-CoV-2 delta and beyond

Here we interrogate the factors responsible for SARS-CoV-2 breakthrough infections in a K18-hACE2 transgenic mouse model. We show that Delta and the closely related Kappa variant cause viral pneumonia and severe lung lesions in K18-hACE2 mice. Human COVID-19 mRNA post-vaccination sera after the 2nd dose are significantly less efficient in neutralizing Delta/Kappa than early 614G virus in vitro and in vivo. By 5 months post-vaccination, ≥50% of donors lack detectable neutralizing antibodies against Delta and Kappa and all mice receiving 5-month post-vaccination sera die after the lethal challenges. Although a 3rd vaccine dose can boost antibody neutralization against Delta in vitro and in vivo, the mean log neutralization titers against the latest Omicron subvariants are 1/3-1/2 of those against the original 614D virus. Our results suggest that enhanced virulence, greater immune evasion, and waning of vaccine-elicited protection account for SARS-CoV-2 variants caused breakthrough infections.

Cell surface SARS-CoV-2 nucleocapsid protein modulates innate and adaptive immunity

SARS-CoV-2 nucleocapsid protein (N) induces strong antibody (Ab) and T cell responses. Although considered to be localized in the cytosol, we readily detect N on the surface of live cells. N released by SARS-CoV-2-infected cells or N-expressing transfected cells binds to neighboring cells by electrostatic high-affinity binding to heparan sulfate and heparin, but not other sulfated glycosaminoglycans. N binds with high affinity to 11 human chemokines, including CXCL12β, whose chemotaxis of leukocytes is inhibited by N from SARS-CoV-2, SARS-CoV-1, and MERS-CoV. Anti-N Abs bound to the surface of N-expressing cells activate Fc receptor-expressing cells. Our findings indicate that cell surface N manipulates innate immunity by sequestering chemokines and can be targeted by Fc-expressing innate immune cells. This, in combination with its conserved antigenicity among human CoVs, advances its candidacy for vaccines that induce cross-reactive B and T cell immunity to SARS-CoV-2 variants and other human CoVs, including novel zoonotic strains.

Severe Acute Respiratory Syndrome Coronavirus 2 Seroassay Performance and Optimization in a Population With High Background Reactivity in Mali

BACKGROUND

False positivity may hinder the utility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serological tests in sub-Saharan Africa.

METHODS

From 312 Malian samples collected before 2020, we measured antibodies to the commonly tested SARS-CoV-2 antigens and 4 other betacoronaviruses by enzyme-linked immunosorbent assay (ELISA). In a subset of samples, we assessed antibodies to a panel of Plasmodium falciparum antigens by suspension bead array and functional antiviral activity by SARS-CoV-2 pseudovirus neutralization assay. We then evaluated the performance of an ELISA using SARS-CoV-2 spike protein and receptor-binding domain developed in the United States using Malian positive and negative control samples. To optimize test performance, we compared single- and 2-antigen approaches using existing assay cutoffs and population-specific cutoffs.

RESULTS

Background reactivity to SARS-CoV-2 antigens was common in prepandemic Malian samples. The SARS-CoV-2 reactivity varied between communities, increased with age, and correlated negligibly/weakly with other betacoronavirus and P falciparum antibodies. No prepandemic samples demonstrated functional activity. Regardless of the cutoffs applied, test specificity improved using a 2-antigen approach. Test performance was optimal using a 2-antigen assay with population-specific cutoffs (sensitivity, 73.9% [95% confidence interval {CI}, 51.6-89.8]; specificity, 99.4% [95% CI, 97.7-99.9]).

CONCLUSIONS

We have addressed the problem of SARS-CoV-2 seroassay performance in Africa by using a 2-antigen assay with cutoffs defined by performance in the target population.

Severe Acute Respiratory Syndrome Coronavirus 2 Seroassay Performance and Optimization in a Population With High Background Reactivity in Mali

BACKGROUND

False positivity may hinder the utility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serological tests in sub-Saharan Africa.

METHODS

From 312 Malian samples collected before 2020, we measured antibodies to the commonly tested SARS-CoV-2 antigens and 4 other betacoronaviruses by enzyme-linked immunosorbent assay (ELISA). In a subset of samples, we assessed antibodies to a panel of Plasmodium falciparum antigens by suspension bead array and functional antiviral activity by SARS-CoV-2 pseudovirus neutralization assay. We then evaluated the performance of an ELISA using SARS-CoV-2 spike protein and receptor-binding domain developed in the United States using Malian positive and negative control samples. To optimize test performance, we compared single- and 2-antigen approaches using existing assay cutoffs and population-specific cutoffs.

RESULTS

Background reactivity to SARS-CoV-2 antigens was common in prepandemic Malian samples. The SARS-CoV-2 reactivity varied between communities, increased with age, and correlated negligibly/weakly with other betacoronavirus and P falciparum antibodies. No prepandemic samples demonstrated functional activity. Regardless of the cutoffs applied, test specificity improved using a 2-antigen approach. Test performance was optimal using a 2-antigen assay with population-specific cutoffs (sensitivity, 73.9% [95% confidence interval {CI}, 51.6-89.8]; specificity, 99.4% [95% CI, 97.7-99.9]).

CONCLUSIONS

We have addressed the problem of SARS-CoV-2 seroassay performance in Africa by using a 2-antigen assay with cutoffs defined by performance in the target population.

Cell Surface SARS-CoV-2 Nucleocapsid Protein Modulates Innate and Adaptive Immunity

SARS-CoV-2 nucleocapsid protein (N) induces strong antibody and T cell responses. Although considered to be localized in the cytosol, we readily detect N on the surface of live cells. N released by SARS-CoV-2 infected cells or N-expressing transfected cells binds to neighboring cells by electrostatic high-affinity binding to heparan sulfate and heparin, but not other sulfated glycosaminoglycans. N binds with high affinity to 11 human chemokines, including CXCL12β, whose chemotaxis of leukocytes is inhibited by N from SARS-CoV-2, SARS-CoV-1, and MERS CoV. Anti-N Abs bound to the surface of N expressing cells activate Fc receptor-expressing cells. Our findings indicate that cell surface N manipulates innate immunity by sequestering chemokines and can be targeted by Fc expressing innate immune cells. This, in combination with its conserved antigenicity among human CoVs, advances its candidacy for vaccines that induce cross-reactive B and T cell immunity to SARS-CoV-2 variants and other human CoVs, including novel zoonotic strains.

Cell Surface SARS-CoV-2 Nucleocapsid Protein Modulates Innate and Adaptive Immunity

SARS-CoV-2 nucleocapsid protein (N) induces strong antibody and T cell responses. Although considered to be localized in the cytosol, we readily detect N on the surface of live cells. N released by SARS-CoV-2 infected cells or N-expressing transfected cells binds to neighboring cells by electrostatic high-affinity binding to heparan sulfate and heparin, but not other sulfated glycosaminoglycans. N binds with high affinity to 11 human chemokines, including CXCL12β, whose chemotaxis of leukocytes is inhibited by N from SARS-CoV-2, SARS-CoV-1, and MERS CoV. Anti-N Abs bound to the surface of N expressing cells activate Fc receptor-expressing cells. Our findings indicate that cell surface N manipulates innate immunity by sequestering chemokines and can be targeted by Fc expressing innate immune cells. This, in combination with its conserved antigenicity among human CoVs, advances its candidacy for vaccines that induce cross-reactive B and T cell immunity to SARS-CoV-2 variants and other human CoVs, including novel zoonotic strains.

SARS-CoV-2 seroassay optimization and performance in a population with high background reactivity in Mali

Serological tests are an indispensable tool to understand the epidemiology of the SARS-CoV-2 pandemic, particularly in areas where molecular diagnostics are limited. Poor assay performance may hinder the utility of these tests, including high rates of false-positivity previously reported in sub-Saharan Africa. From 312 Malian samples collected prior to 2020, we measured antibodies to the commonly tested SARS-CoV-2 antigens and four other betacoronaviruses by ELISA, and assessed functional cross-reactivity in a subset by SARS-CoV-2 pseudovirus neutralization assay. We then evaluated the performance of an ELISA developed in the US, using two-antigen SARS-CoV-2 spike protein and receptor-binding domain. To optimize test performance, we compared single and two-antigen approaches using existing assay cutoffs and population-specific cutoffs for Malian control samples (positive and negative). Background reactivity to SARS-CoV-2 antigens was common in pre-pandemic samples compared to US controls (43.4% (135/311) for spike protein, 22.8% (71/312) for RBD, and 33.9% (79/233) for nucleocapsid protein). SARS-CoV-2 reactivity correlated weakly with other betacoronavirus reactivity, varied between Malian communities, and increased with age. No pre-pandemic samples demonstrated functional activity. Regardless of the cutoffs applied, specificity improved using a two-antigen approach. Test performance was optimal using a two-antigen assay with population-specific cutoffs derived from ROC curve analysis [Sensitivity: 73.9% (51.6-89.8), Specificity: 99.4% (97.7-99.9)]. In the setting of high background reactivity, such as sub-Saharan Africa, SARS-CoV-2 serological assays need careful qualification is to characterize the epidemiology of disease, prevent unnecessary harm, and allocate resources for targeted control measures.

Genome-wide Screens Identify Lineage- and Tumor-Specific Genes Modulating MHC-I- and MHC-II-Restricted Immunosurveillance of Human Lymphomas

Tumors frequently subvert major histocompatibility complex class I (MHC-I) peptide presentation to evade CD8+ T cell immunosurveillance, though how this is accomplished is not always well defined. To identify the global regulatory networks controlling antigen presentation, we employed genome-wide screening in human diffuse large B cell lymphomas (DLBCLs). This approach revealed dozens of genes that positively and negatively modulate MHC-I cell surface expression. Validated genes clustered in multiple pathways including cytokine signaling, mRNA processing, endosomal trafficking, and protein metabolism. Genes can exhibit lymphoma subtype- or tumor-specific MHC-I regulation, and a majority of primary DLBCL tumors displayed genetic alterations in multiple regulators. We established SUGT1 as a major positive regulator of both MHC-I and MHC-II cell surface expression. Further, pharmacological inhibition of two negative regulators of antigen presentation, EZH2 and thymidylate synthase, enhanced DLBCL MHC-I presentation. These and other genes represent potential targets for manipulating MHC-I immunosurveillance in cancers, infectious diseases, and autoimmunity.

Severe intrauterine growth retardation and atypical diabetes associated with a translocation breakpoint disrupting regulation of the insulin-like growth factor 2 gene

CONTEXT

IGF-II is an imprinted gene (predominantly transcribed from the paternally inherited allele), which has an important role in fetal growth in mice. IGF2 gene expression is regulated by a complex system of enhancers and promoters that determine tissue-specific and development-specific transcription. In mice, enhancers of the IGF2 gene are located up to 260 kb telomeric to the gene. The role of IGF-II in humans is unclear.

OBJECTIVE

A woman of short adult stature (1.46 m, -3 sd score) born with severe intrauterine growth retardation (1.25 kg at term, -5.4 SD score) and atypical diabetes diagnosed at the age of 23 yr had a balanced chromosomal translocation t(1;11) (p36.22; p15.5). We hypothesized that her phenotype resulted from disruption of her paternally derived IGF2 gene because her daughter who inherited the identical translocation had normal birth weight.

DESIGN

Both chromosomal break points were identified using fluorescent in situ hybridization. Sequence, methylation, and expression of the IGF2 gene was examined. Hyperinsulinemic, euglycemic clamp with glucose tracers and magnetic resonance imaging of the thorax, abdomen, and pelvis were performed.

RESULTS

The 11p15.5 break point mapped 184 kb telomeric of the IGF2 gene. Microsatellite markers confirmed paternal origin of this chromosome. IGF2 gene sequence and methylation was normal. IGF2 gene expression was reduced in lymphoblasts. Clamp studies showed marked hepatic and total insulin resistance. Massive excess sc fat was seen on magnetic resonance imaging despite slim body mass index (21.1 kg/m2).

CONCLUSIONS

A break point 184 kb upstream of the paternally derived IGF2 gene, separating it from some telomeric enhancers, resulted in reduced expression in some mesoderm-derived adult tissues causing intrauterine growth retardation, short stature, lactation failure, and insulin resistance with altered fat distribution.

The impact of childhood body mass index on timing of puberty, adult stature and obesity: a follow-up study based on adolescent anthropometry recorded at Christ's Hospital (1936-1964)

OBJECTIVE

To examine the impact of childhood body mass index (BMI) on timing of puberty, adult stature and obesity.

DESIGN

A retrospective school-based cohort follow-up study.

SUBJECTS

A total of 1520 men born between 1927 and 1956 with serial height and weight measurements from the age of 9 to 18, followed up in adulthood at a mean age of 63 years.

MEASUREMENTS

Prepubertal (child) BMI; age at peak height velocity (APHV); adult leg length, waist and hip circumference (self-reported), and height and weight (measured).

RESULTS

Boys with a higher childhood BMI tended to have an earlier puberty (per s.d. increase in child BMI: -0.31 years, 95% confidence interval (CI): -0.23 to -0.39, P < 0.001). Childhood BMI correlated strongly and positively with adult adiposity, as measured by BMI (1.24 kg/m(2), 95% CI: 1.04-1.45, P < 0.001), waist (1.94 cm, 95% CI: 1.50-2.37, P < 0.001) and hip (1.91 cm, 95% CI: 1.55-2.28, P < 0.001). It correlated inversely with leg length (-0.40 cm, 95% CI: -0.68 to -0.12, P = 0.005), but not significantly with height or trunk length. Boys with a later puberty tended to be taller (per s.d. increase in APHV: 0.57 cm, 95% CI: 0.17-0.97, P = 0.006) and less adipose as adults (-0.55 kg/m(2), 95% CI: -0.33 to -0.77, P < 0.001).

CONCLUSION

The long-term consequences of childhood obesity into adulthood are well known, but the potential impact on early pubertal maturation is less well appreciated. The factors that contribute to the onset and persistence of childhood obesity require more public health focus.

An investigation of fetal, postnatal and childhood growth with insulin-like growth factor I and binding protein 3 in adulthood

OBJECTIVE

Weight at birth and adult height are positively associated with cancer risk. These patterns may be mediated by the insulin-like growth factor (IGF) axis. We have examined whether pre- and postnatal growth patterns have a long-term influence on adult IGF-I and IGFBP-3 levels.

DESIGN

A follow-up study of a randomized controlled trial of milk supplementation in pregnancy and childhood.

SUBJECTS

A total of 951 individuals took part in a study of diet and growth in South Wales between 1972 and 1974 followed up from birth until their mid-20s.

MEASUREMENTS

Anthopometric measures at birth, postnatally up to 5 years of age and in adulthood, and serum measures of IGF-I and IGF-I to IGFBP-3 ratio at mean age of 25 years.

RESULTS

A total of 63 subjects (70%) provided blood for analysis. We found no association between birth dimensions and adult IGF-I. Subjects who exhibited 'catch-down growth' had lower IGF-I levels (P-value for trend 0.02). Adult height was positively related to IGF-I, for every one standard deviation increase in adult height, IGF-I increased by 3.75 ng/dl (95% CI 0.46-7.08, P = 0.03). Adiposity was inversely associated with the IGF-I and IGF-I to IGFBP-3 ratio and positively associated with IGFBP-3. The strength of the associations increased with age. Downward centile crossing at any time in childhood was associated with lower IGF-I whilst the highest levels were observed in subjects who were tall throughout their early life course. Adult height remained a significant predictor of IGF-I even after adjustment for earlier growth.

CONCLUSIONS

Our results indicate that IGF-I levels in early adulthood are associated with patterns of childhood growth as well as adult stature and adiposity. These associations suggest the IGFs may contribute to anthropometric associations with cancer risk.

Association between insulin-like growth factor status and physical activity levels in rheumatoid arthritis

OBJECTIVE

To determine if the altered insulin-like growth factor (IGF) status in rheumatoid arthritis (RA) is due to inflammation, altered body composition, or lack of exercise.

METHODS

Subjects included 73 patients with RA, 54 patients with other rheumatic diseases, both inflammatory and noninflammatory, and 28 healthy, physically active controls. Serum levels of IGF-I, IGF-II, and IGF binding protein-3 (IGFBP-3) were measured by radioimmunoassay. Body composition was estimated by bioelectrical impedance analysis, and habitual exercise level approximated by questionnaire. Statistical analysis was performed by 2 and 3 way ANOVA and moderated hierarchical regression.

RESULTS

Serum IGF-I (p < 0.001), IGFBP-3 (p < 0.001), and the BP-3:total IGF molar ratio (p < 0.001) were depressed in both patient groups relative to controls. In contrast, IGF-II levels were depressed only in patients with RA (p < 0.01). Differences in the IGF proteins between patients and controls could not be attributed to inflammation. Habitual exercise level, but not body composition, was shown to be a significant predictor for IGF-I, IGFBP-3, and BP-3:total IGF molar ratio (p < 0.001).

CONCLUSION

Our results indicate that the reduction in circulating IGF proteins observed in our patients is more related to their sedentary lifestyle than to the inflammatory process. This conclusion is in agreement with reports that show that highly active individuals typically exhibit higher levels of systemic IGF proteins than age matched sedentary controls.

Growth hormone therapy in patients with cirrhosis: a pilot study of efficacy and safety

BACKGROUND & AIMS

The protein catabolic state of cirrhosis is associated with severe growth hormone (GH) resistance, with low levels of insulin-like growth factor (IGF)-I and its major binding protein (IGFBP)-3. The aim of this study was to conduct a randomized, double-blind, placebo-controlled pilot study of GH therapy in 20 cirrhotic patients to assess the reversibility of GH resistance and subsequent impact on protein economy and safety.

METHODS

Patients were treated with GH (0.25 IU/kg body wt) or placebo for 7 days. Serum levels of GH, IGF-I, IGFBP-3, and insulin were measured by radioimmunoassay and 24-hour urinary nitrogen by the Kjeldahl technique.

RESULTS

IGF-I levels increased only in the GH-treated group (mean, 69.2 +/- SE 7.0 to 170.6 +/- 48.8 ng/mL; P < 0.05) together with IGFBP-3 (1.65 +/- 0.3 to 2.94 +/- 0.6 mg/L; P < 0.005). Cumulative nitrogen balance similarly improved only in the GH group (2.87-24.16 g; P < 0.05). No significant side effects of GH were observed.

CONCLUSIONS

GH therapy can overcome the GH resistance of cirrhosis. The resulting improvement in nitrogen economy and possible influences on clinical outcomes will need to be confirmed in controlled studies of longer duration.

Relation between insulin-like growth factor-I, body mass index, and clinical status in cystic fibrosis

OBJECTIVES

Despite improved nutrition and intensive treatment, subjects with cystic fibrosis have difficulty in maintaining anabolism during intercurrent infections, which can result in reduced body mass index and impaired skeletal growth. Insulin-like growth factor-I (IGF-I) and its binding protein IGFBP3 are sensitive to changes in nutritional status. The aim of this study was to determine the relation between circulating concentrations of these peptides, body mass index, and clinical status in cystic fibrosis.

METHODS

Serum concentrations of IGF-I and IGFBP3 were measured in 197 subjects (108 males, 89 females; mean age 9.69 years, range 0.41-17.9 years) and these data were analysed with respect to body mass index, pubertal stage, and clinical status as assessed by Shwachman score and forced expiratory volume in one second (FEV1).

RESULTS

The mean height SD score of the children studied was -0.2 (SD 1.14) and the body mass index SD score -0.26 (1.4). The body mass index SD score declined with increasing age (r = -0.18) and paralleled changes in IGF-I concentrations, which also declined. The IGF-I SD score (calculated from control data) correlated with age (r = -0.53). The abnormalities were most obvious during late puberty, when IGF-I and IGFBP3 concentrations were significantly reduced compared with those in control subjects matched for pubertal stage. The IGF-I SD score correlated with height SD score (r = 0.14) and the decline in IGF-I concentrations with the fall in body mass index SD score (r = 0.42). IGF-I SD scores also correlated with the Shwachman score (r = 0.33) and FEV1 (r = 0.17).

CONCLUSIONS

The close relation between declining IGF-I and IGFBP3 concentrations and body mass index in patients with cystic fibrosis may simply reflect poor nutritional status and insulin hyposecretion. Nevertheless, IGF-I deficiency could also contribute towards the catabolism observed in these patients, and IGF-I SD scores correlated with other measures of clinical status such as the Shwachman score and FEV1.

Expression of IGF-I and IGF-binding protein genes in cirrhotic liver

The liver plays a central role in the IGF-I axis producing the majority of circulating hormone and some of its binding proteins (IGFBPs). Cirrhosis of the liver is characterised by changes in IGF-I and IGFBPs associated with liver fibrosis and regeneration. We have studied steady state levels of mRNA for the genes in the IGF-I axis in normal and cirrhotic human liver, localised the most highly expressed gene, IGFBP-1, and measured circulating IGFBP-3 by radioimmunoassay (RIA), IGFBP-2 and IGFBP-3 by Western ligand blot (WLB), and protease activity for IGFBP-3 in cirrhotic patients. Messenger RNA for IGF-I, IGFBP-1, IGFBP-2, and IGFBP-3 was detectable by Northern blotting in normal and cirrhotic liver although there was considerable variation in expression. IGFBP-2 and IGFBP-3 tended to be more highly expressed in cirrhotic liver and IGFBP-1 was more highly expressed in normal liver, although there were no significant differences. In normal liver, in situ hybridisation localised IGFBP-1 to hepatocytes. In cirrhotic liver the regenerating nodules showed expression of IGFBP-1 while there was none in fibrotic tissue. Circulating IGFBP-3 levels were low as measured by RIA and WLB but protease activity was only found in one patient. IGFBP-2 levels, assessed by WLB, were similar to the normal serum pool. Our data show that key mRNAs involved in the IGF-I axis continue to be expressed in cirrhotic liver despite end stage liver disease. The low levels of IGFBP-3 do not appear to be due to reduced gene transcription or increased protease activity.

Growth hormone, insulinlike growth factor-1, and insulinlike growth factor binding proteins 1 and 3 in chronic liver disease

The liver is the major source of circulating insulinlike growth factor-I (IGF-I) and has been suggested as a major source of at least two of the major binding proteins that modify its bioavailability. We aimed to assess the direct effects of liver dysfunction on serum levels of IGF-1 and its major binding proteins by measuring fasting levels of growth hormone, IGF-1, IGFBP-1, IGFBP-3, insulin, C peptide, and glucose in 35 patients with cirrhosis and during an oral glucose tolerance test in 16 of those patients. Serum levels of growth hormone (GH) were high in the patients: median, 12.0 mU/L (range, 1 to 87) compared with normals, 0.95 mU/L (0.1 to 20) (P < .0005) and serum IGF-1 levels were low: 81 ng/mL (38 to 153) versus 193 ng/mL (151 to 235) (P < .0001). Serum IGFBP-3 levels were low in the patients: 1.59 mg/L (0.46 to 4.43) compared with normals, 5.41 (4.34 to 6.11) (P < .0001), and there was a significant negative correlation between IGFBP-3 levels and Childs Pugh score (r = .63 P < .0001). Fasting IGFBP-1 levels were significantly higher in the patients 31 ng/mL (11 to 92) than normals, 14 (7 to 20) (P < .0001). There was no correlation between fasting insulin and IGFBP-1 levels despite high fasting insulin levels. A decrease in IGFBP-1 levels was seen during the glucose tolerance test (GTT) in all patients. In conclusion, there are significant changes in the levels of two of the major IGF-1 binding proteins that may further limit the bioavailability of already low circulating IGF-1 levels. Substrate availability appears to be a stronger influence on fasting IGFBP-1 levels than does insulin, and the close correlation of IGFBP-3 with liver function indicates a dominant regulatory role of the hepatocyte.

The effect of recombinant IGF-I on anterior pituitary function in healthy volunteers

OBJECTIVE

Insulin-like growth factor-I is the mediator of many of the actions of GH and is a potent metabolic regulator. Recombinant IGF-I (rhIGF-I) is of potential value in the treatment of syndromes associated with either GH or insulin resistance. This study was designed to assess the effects of subcutaneous (s.c.) rhIGF-I on anterior pituitary function.

DESIGN

Double-blind, placebo controlled, randomized cross-over study. The interval between investigations was 2 weeks.

SUBJECTS

Twelve normal volunteers received on one occasion a single s.c. dose of 40 micrograms/kg rhIGF-I and on the other, placebo.

MEASUREMENTS

Circulating levels were measured, over 24 hours, of GH, LH, FSH, PRL, TSH, cortisol, ACTH, glucose, IGF-I, IGF-II, insulin, C-peptides; IGF binding proteins by Western ligand blotting; total IGF bioactivity using FRTL-5 thyroid cells; and glucose by the glucose oxidase method.

RESULTS

Recombinant IGF-I increased AUC for plasma IGF-I, measured by radioimmunoassay (rhIGF-I mean 7065 +/- SEM 33 vs 3895 +/- 204 micrograms/l, P < 0.0001) and IGF bioactivity (22.5 +/- 3.4 vs 14.2 +/- 1.8 U/ml, P < 0.001) but plasma IGF-II fell (9308 +/- 403 vs 11052 +/- 451 micrograms/l, P < 0.0001). There was no biochemical or clinical evidence of hypoglycaemia and no difference in mean glucose levels. No difference existed in AUC for GH, LH, FSH, ACTH and cortisol between rhIGF-I and placebo; additionally, pulse number and amplitude for GH and LH were unaffected. TSH fell following rhIGF-I (33.0 +/- 3.36 vs 42.5 +/- 5.98 mU h/l, P = 0.01). Both mean plasma C-peptide (0.73 +/- 0.06 vs 0.91 +/- 0.05 nmol/l, P = 0.03), and insulin (10.81 +/- 1.02 vs 15.36 +/- 1.18 mU/l, P = 0.03) were lower following rhIGF-I. There was no change in IGFBPs.

CONCLUSION

A single injection of 40 micrograms/kg of subcutaneous rhIGF-I does not cause hypoglycaemia. IGF bioactivity was increased without inhibition of GH secretion. The only change observed in anterior pituitary function was a fall in plasma TSH.

Expression of IGFBP-1 in normal and cirrhotic human livers

Cirrhosis of the liver, a condition characterised by hepatocyte regeneration, is also associated with elevated insulin levels and insulin resistance. In animal models hepatic regeneration is associated with increased IGFBP-1 gene expression. Insulin is known to be an inhibitor of IGFBP-1 gene expression and circulating insulin levels in man demonstrate a negative correlation with IGFBP-1 levels. To further our understanding of the regulation of IGFBP-1 in cirrhosis we have studied steady state levels of IGFBP-1 mRNA in human liver from three groups of patients: Group 1, tissue obtained at the time of harvesting donor liver for orthotopic liver transplantation (n = 4); group 2, patients undergoing major liver resection with no histological evidence of chronic liver disease (n = 4); and group 3, patients undergoing orthotopic transplantation for chronic liver failure (n = 9). Simultaneous samples of serum were taken at the time of surgery in some patients and in these patients IGFBP-1 mRNA levels were related to circulating levels of IGFBP-1 and insulin. IGFBP-1 mRNA was detectable in all the human liver samples with the greatest levels seen from the normal livers of group 2 patients. Insulin levels were elevated in the cirrhotic group 3 patients compared to a normal range as were IGFBP-1 levels. There was no relationship between circulating levels of IGFBP-1 and IGFBP-1 gene expression. In conclusion, IGFBP-1 mRNA is present in human adult liver at the time of surgery and also in cirrhotic liver despite high levels of insulin suggesting that there are factors other than insulin regulating IGFBP-1 gene expression.

The effects of recombinant human insulin-like growth factor I on growth hormone secretion in adolescents with insulin dependent diabetes mellitus

OBJECTIVE

It has been proposed that low IGF-I levels and reduced IGF-I bioactivity may lead to elevated GH levels in adolescents with insulin dependent diabetes (IDDM). We have therefore studied the effects of human recombinant insulin-like growth factor I (rhIGF-I) administration on GH levels and GH secretion in adolescents with IDDM.

PATIENTS

Nine late pubertal adolescents (four male and five female) with IDDM.

DESIGN

A double-blind placebo controlled study of rhIGF-I administered subcutaneously in a dose of 40 micrograms/kg body weight at 1800 h.

MEASUREMENTS

IGF-I and GH concentrations were measured at regular intervals throughout the study. Twenty-two hour GH secretory rates were calculated by deconvolution analysis. Overnight GH profiles were analysed by distribution analysis, and Fourier transformations were performed on both overnight GH concentrations and GH secretory rates.

RESULTS

Mean IGF-I levels over the 22-hour study period were significantly elevated following rhIGF-I administration (350 +/- 26 vs 205 +/- 21 micrograms/l (mean +/- SEM), P < 0.01). Mean 22-hour GH levels were reduced following rhIGF-I administration (19.4 +/- 4.0 compared with 33.6 +/- 5.8 mU/l; P = 0.01). Distribution analysis demonstrated that the reduction in GH levels was due to changes in the proportion of values at both high and low concentrations. Deconvolution analysis also revealed a significant overall reduction in GH secretory rate following IGF-I administration (1.81 +/- 0.30 vs 2.98 +/- 0.47 mU/min, P = 0.01) which was still apparent during the final 5.5 hours of the study period (1.51 +/- 0.30 vs 2.76 +/- 0.61 mU/min, P = 0.02). The dominant periodicity of GH secretory episodes as determined by Fourier transformation was between 120 and 180 minutes after both IGF-I and placebo.

CONCLUSIONS

In late pubertal adolescents with IDDM the rise in IGF-I levels following rhIGF-I administration in a subcutaneous dose of 40 micrograms/kg body weight leads to a significant reduction in GH levels and GH secretory rate. The reduction in GH secretion is due to changes in pulse amplitude rather than frequency. A reduction in GH secretion was apparent at the beginning and also towards the end of the 22-hour study period.

The effects of recombinant insulin-like growth factor I administration on growth hormone levels and insulin requirements in adolescents with type 1 (insulin-dependent) diabetes mellitus

Type 1 (insulin-dependent) diabetes mellitus in adolescence is associated with reduced levels of insulin-like growth factor I, elevated growth hormone concentrations and insulin resistance. In order to determine whether restoring insulin-like growth factor I levels to normal might lead to a reduction in growth hormone levels and insulin requirements, we undertook a double-blind placebo controlled study of a single s.c. dose of recombinant insulin-like growth factor I (40 micrograms/kg body weight) in nine late pubertal subjects with Type 1 diabetes. After administration of placebo or insulin-like growth factor I at 18.00 hours, a variable rate insulin infusion was used to maintain euglycaemia overnight. Plasma insulin-like growth factor I, growth hormone, free insulin, and intermediate metabolite concentrations were monitored throughout the study. Recombinant insulin-like growth factor I led to a rise in plasma concentrations which reached a peak at 5.5 h (413.1 +/- 28.2 ng/ml, mean +/- SEM). Mean growth hormone levels between 20.00 and 08.00 hours were significantly reduced after recombinant insulin-like growth factor I (19.4 +/- 4.0 compared with 33.6 +/- 5.8 mU/l; p = 0.01), as were the insulin requirements for euglycaemia (0.25 +/- 0.02 compared with 0.31 +/- 0.04 mU.kg-1.min-1; p = 0.03). Plasma free insulin levels were lower after recombinant insulin-like growth factor I administration (31.9 +/- 2.7 compared with 67.9 +/- 16.0 mU/l; p = 0.001) but no significant differences in ketone or lactate levels were detected.(ABSTRACT TRUNCATED AT 250 WORDS)

IGFBP-1: a metabolic signal associated with exercise-induced amenorrhoea

Severe exercise in young females is a potent cause of menstrual irregularity, although the exact pathogenesis is currently unknown. We performed a cross-sectional endocrine and metabolic analysis of a group of elite athletes and dancers in order to establish which variable, if any, was specifically associated with changes in menstruation. By using a step-wise discriminant analysis, two independent predictors, elevated serum cortisol and insulin-like growth factor binding protein 1 (IGFBP-1) levels, were found to account for the majority (67%) of the variance. IGFBP-1 is a hepatic protein which is acutely and inversely regulated by insulin, and is thought to modulate the peripheral actions of IGF-1. While the change in serum cortisol may reflect activation of central stress pathways, these findings suggest for the first time that there is a second peripheral signal, IGFBP-1, which may relate the availability of metabolic fuels to the control of reproduction.

The Saccharomyces cerevisiae BAR1 gene encodes an exported protein with homology to pepsin

Saccharomyces cerevisiae a cells secrete an extracellular protein, called "barrier" activity, that acts as an antagonist of alpha factor, the peptide mating pheromone produced by mating-type alpha cells. We report here the DNA sequence of BAR1, the structural gene for barrier activity. The deduced primary translation product of 587 amino acids has a putative signal peptide, nine potential asparagine-linked glycosylation sites, and marked sequence similarity of the first two-thirds of the protein with pepsin-like proteases. Barrier activity was abolished by in vitro mutation of an aspartic acid predicted from this sequence homology to be in the active site. Therefore, barrier protein is probably a protease that cleaves alpha factor. The sequence similarity suggests that the first two-thirds of the barrier protein is organized into two distinct structural domains like those of the pepsin-like proteases. However, the BAR1 gene product has a third carboxyl-terminal domain of unknown function; deletion of at least 166 of the 191 amino acids of this region has no significant effect on barrier activity.

Action of centrally mediated autonomic stimulation on human upper gastrointestinal transit: a comparative study of two stimuli

Two well established experimental stressors, hand immersion in cold water, and mental stimulation with dichotomous listening, were applied to 37 normal subjects after the ingestion of a standard meal. Orocaecal transit was measured by serial exhaled breath hydrogen sampling. Cold water significantly delayed transit compared with warm water control (warm water 71.8 +/- 3.6 mins v cold water 93.2 +/- 5.7 mins p less than 0.01), with significant rises in blood pressure pulse rate perceived discomfort and plasma catecholamines. In contrast mental stimulation was unaccompanied by any change in transit (control; 67.4 +/- 4.7 v test 64.3 +/- 5.3 mins p greater than 0.1) despite a significant rise in pulse rate, skin conductance and plasma catecholamines. Repeated cold water immersion studies in eight individuals produced consistent orocaecal transit and autonomic responses, whereas mental stimulation showed reduced autonomic responses on repeat testing, suggesting that tolerance to the stimulus had occurred. The results of these studies show stimulus specific gastrointestinal response patterns to autonomic stimuli, and appear to have important implications for the design of future studies of human gastrointestinal autonomic physiology and for the investigation of patients with stress related gut dysfunction.

Multiple regulation of STE2, a mating-type-specific gene of Saccharomyces cerevisiae

The Saccharomyces cerevisiae STE2 gene, which is required for pheromone response and conjugation specifically in mating-type a cells, was cloned by complementation of the ste2 mutation. Transcription of STE2 is repressed by the MAT alpha 2 gene product, so that the 1.4-kilobase STE2 RNA is detected only in a or mat alpha 2 strains, not in alpha or a/alpha cells. However, STE2 RNA levels are also increased by the mating pheromone alpha-factor and decreased in strains bearing mutations in the nonspecific STE4 gene. Regulation of STE2 expression in a cells is therefore achieved by several mechanisms.