Synthesis, Biological Evaluation, and Binding Mode of a New Class of Oncogenic K-Ras4b Inhibitors.

Ras proteins are implicated in some of the most common life-threatening cancers. Despite intense research during the past three decades, progress towards small-molecule inhibitors of mutant Ras proteins still has been limited. Only recently has significant progress been made, in particular with ligands for binding sites located in the switch II and between the switch I and switch II region of K-Ras4B. However, the structural diversity of inhibitors identified for those sites to date is narrow. Herein, we show that hydrazones and oxime ethers of specific bis(het)aryl ketones represent structurally variable chemotypes for new GDP/GTP-exchange inhibitors with significant cellular activity.

Design, expression, purification and characterization of a YFP-tagged 2019-nCoV spike receptor-binding domain construct

2019-nCoV is the causative agent of the serious, still ongoing, worldwide COVID-19 pandemic. High quality recombinant virus proteins are required for research related to the development of vaccines and improved assays, and to the general understanding of virus action. The receptor-binding domain (RBD) of the 2019-nCoV spike (S) protein contains disulfide bonds and N-linked glycosylations, therefore, it is typically produced by secretion. Here, we describe a construct and protocol for the expression and purification of yellow fluorescent protein (YFP) labeled 2019-nCoV spike RBD. The fusion protein, in the vector pcDNA 4/TO, comprises an N-terminal interferon alpha 2 (IFN2) signal peptide, an eYFP, a FLAG-tag, a human rhinovirus 3C protease cleavage site, the RBD of the 2019-nCoV spike protein and a C-terminal 8x His-tag. We stably transfected HEK 293 cells. Following expansion of the cells, the fusion protein was secreted from adherent cells into serum-free medium. Ni-NTA IMAC purification resulted in very high protein purity, based on analysis by SDS-PAGE. The fusion protein was soluble and monodisperse, as confirmed by size-exclusion chromatography (SEC) and negative staining electron microscopy. Deglycosylation experiments confirmed the presence of N-linked glycosylations in the secreted protein. Complex formation with the peptidase domain of human angiotensin-converting enzyme 2 (ACE2), the receptor for the 2019-nCoV spike RBD, was confirmed by SEC, both for the YFP-fused spike RBD and for spike RBD alone, after removal of YFP by proteolytic cleavage. Possible applications for the fusion protein include binding studies on cells or in vitro, fluorescent labeling of potential virus-binding sites on cells, the use as an antigen for immunization studies or as a tool for the development of novel virus- or antibody-detection assays.

A continuum theory for multicomponent chromatography modeling.

A continuum theory is proposed for modeling multicomponent chromatographic systems under linear conditions. The model is based on the description of complex mixtures, possibly involving tens or hundreds of solutes, by a continuum. The present approach is shown to be very efficient when dealing with a large number of similar components presenting close elution behaviors and whose individual analytical characterization is impossible. Moreover, approximating complex mixtures by continuous distributions of solutes reduces the required number of model parameters to the few ones specific to the characterization of the selected continuous distributions. Therefore, in the frame of the continuum theory, the simulation of large multicomponent systems gets simplified and the computational effectiveness of the chromatographic model is thus dramatically improved.

Normal insulin-like peptide-3 levels despite low testosterone in adult males with Prader-Willi syndrome: variations in Leydig cell function from infancy through adulthood.

BACKGROUND: Cryptorchidism, incomplete pubertal development, and low testosterone are manifestations of hypogonadism in Prader-Willi syndrome (PWS). Insulin-like peptide-3 (INSL3) facilitates testicular descent in the fetus and reflects Leydig cell number in adults. INSL3 levels in PWS have not been previously reported. OBJECTIVES: The objectives of the study were to characterize the age-related changes in INSL3 in PWS males and correlate INSL3 with unilateral vs. bilateral cryptorchidism, body mass index, gonadotropins, testosterone, anti-mullerian hormone (AMH), and inhibin B. STUDY DESIGN AND PARTICIPANTS: We measured INSL3, LH, FSH, testosterone, AMH, and inhibin B in 40 PWS males (23 deletion, 17 uniparental disomy) aged 2 months to 36 yr. Control samples for INSL3 were obtained from 365 normal males, aged 1 d to 36 yr. RESULTS: INSL3 levels (mean and range) for PWS age groups younger than 6 months, 0.5-10.0 yr, 10.1-19.0 yr, and older than 19.0 yr were 217 (68-380), 42 (16-112), 390 (16-1028), and 642 (290-964) pg/ml, respectively, and did not differ significantly from values for normal males. In seven of 14 boys aged 10.1-19 yr, INSL3, testosterone, and LH were low (37.4 ± 19.4 pg/ml, 1.44 ± 0.46 nmol/liter, 0.3 ± 0.6 IU/liter). The other seven with higher INSL3, testosterone, and LH (693.1 ± 305.8 pg/ml, 5.91 ± 2.77 nmol/liter, 2.7 ±1.9 IU/liter) had more advanced pubertal development. INSL3 was normal in seven of nine males aged older than 19 yr, despite low testosterone in six. After controlling for age, INSL3 correlated with LH (P = 0.005) and testosterone (P < 0.001) but not with FSH, AMH, or inhibin B. CONCLUSIONS: Most PWS males have normal INSL3 levels. By contrast, testosterone levels after infancy are low. These findings suggest a specific defect in Leydig cell function.

Clinical and hormonal status of infants with nonmosaic XXY karyotype.

AIM: To compare our recent findings in a cohort of 77 nonmosaic XXY infants <2 years of age with clinical and biological features already reported. RESULTS: The majority of reported XXY neonates had normal external genitalia. Only undescended testes and/or micropenis were identified reasons for referral. Delayed ambulation and speech skills were also indications for postnatally karyotyping. All subjects from our cohort (73 prenatally detected subjects, five postnatal diagnoses) had height and weight within the normal range, and were not dysmorphic. Insulin-like-peptide-3 and testosterone secretion by Leydig cells appeared normally sensitive to luteinizing hormone. In reported studies, inhibin B levels were within normal range, anti-Mullerian hormone levels were normal or high and follicle-stimulating hormone (FSH) levels were significantly higher than control values, data consistent with a relative resistance to FSH. CONCLUSION: Early detection of Klinefelter syndrome is desirable for prospectively monitoring the apparition of developmental problems and the progressive decline in the tubular function of the testis, with the hope of designing future conservative interventions before germ cell degeneration is completed.

Assessment of Leydig and Sertoli cell functions in infants with nonmosaic Klinefelter syndrome: insulin-like peptide 3 levels are normal and positively correlated with LH levels.

CONTEXT: Klinefelter syndrome (KS) is the most common sex chromosome disorder and a major cause of male infertility. In adult patients, serum inhibin B and anti-Mullerian-hormone (AMH) are undetectable, testosterone secretion is often impaired, and the tubules are depleted of germ cells. Before puberty, inhibin B, AMH, and testosterone levels are within the normal range. OBJECTIVE: Sertoli and Leydig cell secretions, including insulin-like peptide-3 (INSL3), were evaluated in infants with nonmosaic XXY karyotype to assess testicular function soon after birth. DESIGN: The study was conducted in four University Pediatric Departments from the United States and France. SUBJECTS: Sixty-eight prenatally diagnosed infants aged 2-750 d were enrolled. MAIN OUTCOME MEASURES: Serum FSH, LH, inhibin B, AMH, and INSL3 were measured by immunoassay, and testosterone was measured by tandem mass-spectrometry. RESULTS: In infants with KS, INSL3 levels transiently increased at 2-3 months of age and were significantly correlated with testosterone (Spearman r = 0.57) and LH (Spearman r = 0.73) levels. They did not differ from controls. Testosterone levels were within the normal range, but most of them were below the median of controls. Inhibin B and AMH levels were also within normal range. Inhibin B was correlated with FSH (Spearman r = 0.49). AMH was not correlated with FSH or testosterone. FSH levels were above normal in 25% of patients, despite normal inhibin B levels. CONCLUSIONS: In infants with KS, Leydig cells are normally sensitive to the LH proliferative effect. In contrast, the Sertoli cell sensitivity to FSH is questionable, which may be prophetic of the postpubertal Sertoli cell resistance to FSH.

The x-ray crystal structure of the first RNA recognition motif and site-directed mutagenesis suggest a possible HuR redox sensing mechanism.

Hu-antigen R (HuR) is a ubiquitous RNA-binding protein that comprises three RNA recognition motifs (RRMs). The first two tandem RRMs are known to bind to AU-rich elements (AREs) in the 3'-untranslated region of many mRNAs. The third RRM is connected to the second RRM through a basic hinge region that contains a localization signal termed HuR nucleocytoplasmic shuttling. Binding of HuR to the ARE in the 3'-untranslated region of mRNA leads to nuclear export, stabilization, and/or translational de-repression of the mRNA, resulting in upregulation of the encoded protein. Among the various ARE binding proteins known to date, HuR is still the only known ubiquitous antagonist of posttranscriptional gene silencing by AREs. Given the wide repertoire of known and suspected targets of HuR, it is considered to be a central node in the ARE pathway. Here, the x-ray crystal structure of the first RRM of HuR (amino acids 18-99) at 2.0 A resolution is presented. The overall fold consists of two alpha-helices and a four-stranded beta-sheet, with a beta1-alpha1-beta2-beta3-alpha2-beta4 topology and a beta-hairpin between alpha2 and beta4. The asymmetric unit consists of four chains. The large crystal contact interfaces observed between chains A/B and C/D contain hydrophobic residues located at the alpha-helix side of the fold, opposite to the RNA-binding interface. This hydrophobic region structurally resembles the protein-protein interaction site of RRM domains of other proteins. Because the nature of the assumed HuR homodimerization is mechanistically not well understood to date, we used site-directed mutagenesis, analytical size-exclusion chromatography and multiangle light scattering to investigate HuR interactions via the RRM hydrophobic region. Our data indicate that in vitro, HuR RRM1 and RRM1,2 homodimerization involves a disulfide bond at cysteine 13. This homodimerization mode may have a functional significance in redox modulation of HuR activity in response to oxidative stress. Because HuR is involved in many diseases (e.g., cancer, cachexia, and inflammatory bowel disease), the presented structure may provide a basis for rational drug design.

Impact level of dihydrotestosterone on the hypothalamic-pituitary-leydig cell axis in men.

Dihydrotestosterone (DHT) the physiologically most potent androgen cannot be aromatised into oestrogen. DHT is used as a treatment for idiopathic gynaecomastia. In order to investigate the different sites of action of DHT on the hypothalamic-pituitary-testicular axis, two groups of adult men were studied. Group I included 10 gonadotropin-releasing hormone (GnRH)-deficient men who were evaluated before and during a pulsatile infusion of GnRH alone for 2 weeks and then in association with DHT given transdermally at doses used in the treatment of gynaecomastia for further two weeks. Luteinizing hormone (LH) pulsatility was assessed at the end of each step of the study. Plasma LH levels were measured every 15 min. Plasma testosterone (T), DHT, oestradiol (E2), free alpha-subunit (FAS) of glycoproteic hormones and LH bioactivity were measured on pooled plasma samples. Group II included 12 healthy men in whom plasma T, DHT and E2 were measured before and then 24, 48 and 72 h after the injection of 5000 IU hCG alone or in combination with either DHT or the pure anti-androgen nilutamide. Two weeks separated each of the 3 hCG testing. In group I, except for bioactive/immunoreactive (B/I) LH ratio which was unchanged, GnRH treatment induced significant rises (p < 0.01) in all plasma hormone levels, LH pulse amplitude and frequency. During treatment with GnRH+DHT, plasma DHT levels increased up to 16.8 +/- 2.5 nm, while plasma hormone levels, B/I LH ratio, LH pulse amplitude and frequency were similar to those obtained with GnRH alone. In group II, the peak of hCG-induced T rise was not modified by either DHT or nilutamide. In contrast, DHT reduced by 50% (p < 0.01) the E2 peak in response to hCG. These data show that DHT exerts no direct action on the pituitary to retroregulate LH secretion and to modify either B/I LH ratio or FAS secretion. Its reducing effect on LH secretion is likely mediated at the hypothalamic level. DHT does not appear to have a physiological influence on Leydig cells steroidogenesis. Administered at therapeutic doses, DHT directly reduces testicular aromatase activity that combined with its antigonadotropic effect leads to the gain in the symptomatic treatment of gynaecomastia.

Terminal adenosyl transferase activity of posttranscriptional regulator HuR revealed by confocal on-bead screening.

Posttranscriptional regulation and RNA metabolism have become central topics in the understanding of mammalian gene expression and cell signalling, with the 3' untranslated region emerging as the coordinating unit. The 3' untranslated region trans-acting factor Hu protein R (HuR) forms a central posttranscriptional pathway node bridging between AU-rich element-mediated processes and microRNA regulation. While (m)RNA control by HuR has been extensively characterized, the molecular mode of action still remains elusive. Here we describe the identification of the first RRM3 (RNA recognition motif 3) targeted low molecular weight HuR inhibitors from a one-bead-one-compound library screen using confocal nanoscanning. A further compound characterization revealed the presence of an ATP-binding pocket within HuR RRM3, associated with enzymatic activity. Centered around a metal-ion-coordinating DxD motif, the catalytic site mediates 3'-terminal adenosyl modification of non-polyadenylated RNA substrates by HuR. These findings suggest that HuR actively contributes to RNA modification and maturation and thereby shed an entirely new light on the role of HuR in RNA metabolism.

Activating mutations in the luteinizing hormone receptor gene: a human model of non-follicle-stimulating hormone-dependent inhibin production and germ cell maturation.

CONTEXT: Familial male-limited precocious puberty is a dominant autosomal genetic disease caused by activating LH receptor gene mutations, clinically expressed only in males. In preliminary studies, in addition to the expected testosterone increase, we found high inhibin B levels before the age of normal puberty. OBJECTIVES: The objective of the study was to assess the cellular origin of serum inhibin thanks to testis section immunostaining. MAIN OUTCOME MEASURES: Serum testosterone, gonadotropin, inhibin B, pan-alphaC-inhibin, and anti-Mullerian hormone levels were measured. Immunostaining was performed using specific anti-alpha- and anti-beta-subunit antibodies. SUBJECTS AND METHODS: Five boys from three families (mutation M398T or I542L) were investigated at onset (2-6 yr), on ketoconazole treatment, and at adolescence. Testis biopsies were performed in three subjects before the disease was fully characterized. RESULTS: The high testosterone levels were suppressed by ketoconazole. Anti-Mullerian hormone levels were inversely related to testosterone: low at diagnosis, elevated after testosterone suppression. Despite FSH suppression, inhibin B and pan-alphaC-inhibin levels were high from clinical onset to adolescence. Biopsy specimens showed normal Sertoli cell complement and germ cell maturation until the spermatocyte II stage. Sertoli and Leydig cells displayed positive inhibin alpha-subunit immunostaining. Only Leydig cells and spermatogonia stained positively for the inhibin betaB-subunit. CONCLUSIONS: Familial male-limited precocious puberty is a unique model of inhibin B secretion, demonstrating that Leydig cells can produce significant amounts of the dimeric molecule. Our results also suggest that the pubertal FSH rise is not required for full expression of the two inhibin B genes and for the initiation of germ cell maturation.

Screening for Down syndrome using first-trimester combined screening followed by second-trimester ultrasound examination in an unselected population.

OBJECTIVE: Recent studies have reported the efficacy of first-trimester combined screening for Down syndrome based on maternal age, serum markers (human chorionic gonadotropin, pregnancy-associated plasma protein A), and ultrasound measurement of fetal nuchal translucency. However, those do not incorporate the value of the widely accepted routine 20-22 weeks' anomaly scan. STUDY DESIGN: We carried out a multicenter, interventional study in the unselected population of a single health authority in order to assess the performance of first-trimester combined screening, followed by routine second trimester ultrasound examination and/or screening by maternal serum markers (free beta-hCG and alpha-fetoprotein measurement or total hCG, alpha-fetoprotein, and unconjugated estriol measurement) when incidentally performed. Detection and screen positive rates were estimated using a correction method for nonverified issues. A cost analysis was also performed. RESULTS: During the study period, 14,934 women were included. Fifty-one cases of Down syndrome were observed, giving a prevalence of 3.4 per 1000 pregnancies. Of these, 46 were diagnosed through first (n = 41) or second (n = 5) trimester screening. Among the 5 screen-negative Down syndrome cases, all were diagnosed postnatally after an uneventful pregnancy. Detection and screen positive rates of first-trimester combined screening were 79.6% and 2.7%, respectively. These features reached 89.7%, and 4.2%, respectively, when combined with second-trimester ultrasound screening. The average cost of the full screening procedure was 108 euros (120 dollars) per woman and the cost per diagnosed Down syndrome pregnancy was 7,118 euros (7909 dollars). CONCLUSION: Our findings suggest that 1 pragmatic interventional 2-step approach using first-trimester combined screening followed by second-trimester detailed ultrasound examination is a suitable and acceptable option for Down syndrome screening in pregnancy.

Adult height after ketoconazole treatment in patients with familial male-limited precocious puberty.

Familial male-limited precocious puberty is a rare cause of precocious puberty due to activating mutations of the LH receptor, leading to early onset virilization and short stature. Two therapeutic approaches have been proposed: the P450 cytochrome inhibitor ketoconazole or combined treatment with spironolactone and testolactone. Results on adult heights have not been reported to date after these two treatments, and in this study we present results from five patients treated with ketoconazole at a median dose of 16.2 mg/kg.d for a median of 6.2 yr. Adult height was 173 cm (median; interquartile range, 14), similar to target height (175 cm; interquartile range, 9) and significantly higher than pretreatment predicted height (165 cm; interquartile range, 12; P < 0.01). During treatment, 39 of 58 (68%) testosterone measurements were less than 0.5 ng/ml (1.7 nmol/liter), nine of 58 (15%) were between 0.5 and 1 ng/ml (3.5 nmol/liter), and 10 of 58 (17%) were above 1 ng/ml. We observed a physiological increase in GnRH-stimulated LH levels after the age of 10 yr, and none of the patients had early activation of the gonadotropic axis. Liver tolerance was excellent, and only one patient had a transient and modest increase in serum transaminases. We conclude that ketoconazole is an efficient and well tolerated long-term treatment of familial male-limited precocious puberty that should be proposed as a first line therapy.

Inhibin B in pubertal development and pubertal disorders.

The inhibin B pubertal surge is a prominent signal of gonadal maturation in females as well as in males. In boys, it denotes the final functional maturation of Sertoli cells, which is accompanied by a progressive suppression of antimüllerian hormone production. In girls it reflects the initial recruitment of preantral follicles and their evolution to the antral stage. In both the prepubertal quiescent phase and the active peripubertal phase there is a striking sexual dimorphism, inhibin B levels being significantly higher in boys than in girls, in contrast to follicle-stimulating hormone (FSH) levels. Determining inhibin B levels together with FSH levels is of considerable help for diagnosing disorders of pubertal development. In girls with central precocious precocity, inhibin B levels are in accordance with the clinical stage of maturation, by contrast to normal or low levels in the McCune-Albright syndrome. In boys with delayed puberty, inhibin B levels are very low in congenital defects of the gonadotropin-releasing hormone-FSH-testis axis, but they are normal or intermediate in constitutional delayed puberty. Together with antimüllerian hormone, inhibin B is a useful marker of the presence of Sertoli cells in bilateral cryptorchidism and in the androgen insensitivity syndrome. In addition, inhibin B measurement, together with that of inhibin A, is helpful for the diagnosis and follow-up of inhibin-secreting tumors: granulosa cell tumors in girls and Sertoli cell tumors of the Peutz-Jeghers syndrome in boys. In conclusion, inhibin determination is an essential tool in the assessment of physiological development as well as in the management of pubertal disorders.

Precocious puberty and statural growth.

Precocious puberty results mostly from the precocious activation of the gonadotropic axis. Although the age limits have recently been discussed, most physicians consider that onset of pubertal development before the age of 8 years in a girl or 9 years in a boy warrants at least a clinical and bone age evaluation by a paediatric endocrinologist. The major concern in precocious puberty is the underlying condition, and central nervous system or gonadal neoplasm have to be formally excluded as a first step in the diagnosis. A secondary concern is height, since precocious puberty leads to accelerated growth, accelerated bone maturation and ultimately reduced stature. Precocious puberty is heterogeneous and strict criteria should be used to define it, both in terms of age and in terms of potential for progression. Depot forms of GnRH agonists are now the standard treatment for progressive central precocious puberty and aim at alleviating the clinical symptoms of early pubertal development, their psychological consequences and the effects on growth. Here, we review the consequences of both central and gonadotropin-independent precocious puberty on adult stature and the information available on outcomes using the therapeutic regimens currently available. In girls with progressive precocious puberty, all published evidence indicates a gain of adult height over height predicted before treatment or over untreated historical controls. However, the apparent height gain (derived from the comparison of predicted and actual heights) is very variable, in large part due to the inaccuracy of height prediction methods. In girls with onset of puberty at the lower half of the normal age (8-10 years) distribution, trials using GnRH agonists have given negative results (no benefit of treatment). In boys, precocious puberty is rare and fewer results are available but point in the same direction. The most appropriate time for interrupting the treatment is still controversial. In conclusion, GnRH agonists restore adult height in children when it is compromised by precocious puberty.

[Investigation, treatment and surveillance of late-onset hypogonadism in males: the official guidelines of the International Society for the Study of the Aging Male (ISSAM) with comments]. / Diagnostic, traitement et surveillance de l'hypogonadisme de survenue tardive chez l'homme : recommandations officielles de l'International Society for the Study of the Aging Male (ISSAM) et commentaires.

There is growing interest in the hormonal changes of the ageing male, particularly in view of the expected growth of the population of males over the age of 50. Current research topics essentially concern androgen decline in the aging male (ADAM), or partial androgen deficiency of the aging male (PADAM), commonly called "andropause" in France. Although progress has been made in our knowledge concerning androgen deficiency of the aging male, it is still incomplete, sometimes confused, and some aspects of androgen replacement therapy remain controversial. The International Society for the Study of the Aging Male (ISSAM) therefore considered it appropriate to propose a series of practical and official guidelines concerning the investigation, treatment and surveillance of late-onset hypogonadism in males. The French translation of these recent international guidelines is presented and discussed in this article.

Inhibin B and anti-Müllerian hormone, but not testosterone levels, are normal in infants with nonmosaic Klinefelter syndrome.

Klinefelter syndrome is a major cause of infertility in the male. Nevertheless, pregnancies were recently obtained by intracytoplasmic injection of sperm retrieved by surgery or ejaculation, underscoring the need to understand the role of Sertoli and Leydig cell secretions during development. In 18 infants with prenatally diagnosed homogenous 47,XXY karyotype, blood samples were taken from birth to 3 yr of age. Inhibin B (INHB), anti-Müllerian hormone (AMH), testosterone, FSH, and LH levels were compared with those in six adolescents with XXY karyotype and reference values established in 215 control infants. In XXY infants FSH, LH, INHB, and AMH did not differ from controls. Testosterone levels during the first trimester exhibited a physiological increase but were lower than in controls (P = 0.0001). Significant correlations were found between testosterone and LH (P < 0001), between INHB and FSH (P = 0.0011), and between AMH and INHB (P = 0.025). In XXY adolescents, AMH and INHB were undetectable. Our findings demonstrate that testosterone secretion is impaired in infants with Klinefelter syndrome. By contrast, INHB and AMH secretions were not altered, which raises the question of the mechanism(s) governing the decline of Sertoli cell function after puberty.

Both relative insulin resistance and defective islet beta-cell processing of proinsulin are responsible for transient hyperglycemia in extremely preterm infants.

OBJECTIVE: Many extremely preterm infants develop hyperglycemia in the first week of life during continuous glucose infusion. The objective of this study was to determine whether defective insulin secretion or resistance to insulin was the primary factor involved in transient hyperglycemia of extremely preterm infants. METHODS: A prospective comparative study was conducted in appropriate-for-gestational-age preterm infants <30 weeks of gestational age with the aim specifically to evaluate the serum levels of proinsulin, insulin, and C-peptide secreted during transient hyperglycemia by specific immunoassays. Three groups of infants were investigated hyperglycemic (n = 15) and normoglycemic preterm neonates (n = 12) and normal, term neonates (n = 21). In addition, the changes in beta-cell peptide levels were analyzed during and after intravenous insulin infusion in the hyperglycemic group. Data were analyzed using analysis of variance and analysis of variance for repeated measures. RESULTS: At inclusion, insulin and C-peptide levels did not differ in hyperglycemic subjects and in preterm controls. Proinsulin concentration was significantly higher in the hyperglycemic group (36.5 +/- 3.9 vs 23.2 +/- 0.9 pmol/L). Compared with term neonates, proinsulin and C-peptide levels were higher in normoglycemic preterm infants (23.2 +/- 0.9 vs 18.9 +/- 2.71 pmol/L and 1.67 +/- 0.3 vs 0.62 +/- 0.12 nmol/L, respectively). During and after insulin infusion in hyperglycemic neonates, plasma glucose concentration fell and proinsulin and C-peptide levels were lowered (18.4 +/- 7.6 and 20.7 +/- 4.5 pmol/L, respectively). CONCLUSION: These data suggest that 1) preterm neonates are sensitive to changes in plasma glucose concentration, but proinsulin processing to insulin is partially defective in hyperglycemic preterm neonates; 2) hyperglycemic neonates are relatively resistant to insulin because higher insulin levels are needed to achieve euglycemia in this group compared with normoglycemic neonates. These results also show that insulin infusion is beneficial in extremely preterm infants with transient hyperglycemia.