Gail Mick

Hypothalamic-Pituitary Dysfunction after Radiation for Brain Tumors

Background Patients with brain tumors who are treated with radiation frequently have growth hormone deficiency, but other neuroendocrine abnormalities are presumed to be uncommon. Methods We studied endocrine function in 32 patients (age, 6 to 65 years) 2 to 13 years after they had received cranial radiotherapy for brain tumors. The doses of radiation to the hypothalamic-pituitary region ranged from 3960 to 7020 rad (39.6 to 70.2 Gy). Nine patients also received 1800 to 3960 rad (18.0 to 39.6 Gy) to the craniospinal axis. Serum concentrations of thyroid, gonadal, and pituitary hormones were measured at base line and after stimulation. Results Nine patients (28 percent) had symptoms of thyroid deficiency, and 20 patients (62 percent) had low serum total or free thyroxine or total triiodothyronine concentrations. Of the 23 patients treated only with cranial radiation, 15 (65 percent) had hypothalamic or pituitary hypothyroidism. Of the nine patients who also received spinal (and thus direct thyroid) radiati...

Neonatal Cord Blood Leptin: Its Relationship to Birth Weight, Body Mass Index, Maternal Diabetes, and Steroids

Leptin is a 16-kD protein encoded by the ob/ob (obesity) gene. In rodents it plays a role in obesity, diabetes, fertility, and neuroendocrine function. In humans serum concentrations of leptin correlate with total body fat in both adults and children. We measured cord blood leptin in 186 neonates that included 82 appropriate for gestational age (AGA), 47 large for gestational age (LGA), 20 infants of diabetic mothers, 52 preterm infants, and 15 intrauterine growth-retarded (IUGR) infants. There were 16 pairs of twins. The mothers of 17 preterm infants were treated with steroids before delivery. Leptin (mean ± SD) concentration in term, AGA infants (39.4 ± 1.1 wk) with birth weight (BW) of 3.2 ± 0.3 kg, body mass index (BMI) of 12.6 ± 1.1 was 4.01 ± 3.5 ng/mL. BW correlated with cord leptin (p = 0.002) in a multivariate analysis controlling for potential confounders. Both LGA infants and infants of diabetic mothers had higher cord leptin concentration 7.3 ± 3.8 and 6.1 ± 4.8 ng/mL, respectively, compared with AGA infants (p < 0.05). Preterm infants had a mean leptin level of 1.8 ± 0.97 ng/mL and a 3-fold elevation was seen if mothers received steroids antenatally (p = 0.006). IUGR infants had increased leptin (6.5 ± 3.9 ng/mL, p= 0.03). Concerning the twin pairs, the smaller had a higher leptin level compared with larger twin (4.1 ± 9.51 versus 2.8 ± 5.14, p = NS). Neonatal cord leptin concentrations correlate well with BW and BMI. No gender differences were found in cord blood leptin. Maternal obesity had no effect on cord leptin, whereas exogenous maternal steroids increased neonatal leptin concentrations.

Evidence That the 11 β-Hydroxysteroid Dehydrogenase (11 β-HSD1) Is Regulated by Pentose Pathway Flux STUDIES IN RAT ADIPOCYTES AND MICROSOMES

11 β-hydroxysteroid dehydrogenase type 1 (11 β-HSD1) catalyzes the interconversion of biologically inactive 11 keto derivatives (cortisone, 11-dehydrocorticosterone) to active glucocorticoids (cortisol, corticosterone) in fat, liver, and other tissues. It is located in the intraluminal compartment of the endoplasmic reticulum. Inasmuch as an oxo-reductase requires NADPH, we reasoned that 11 β-HSD1 would be metabolically interconnected with the cytosolic pentose pathway because this pathway is the primary producer of reduced cellular pyridine nucleotides. To test this theory, 11 β-HSD1 activity and pentose pathway were simultaneously measured in isolated intact rodent adipocytes. Established inhibitors of NAPDH production via the pentose pathway (dehydroandrostenedione or norepinephrine) inhibited 11 β-HSD1 oxo-reductase while decreasing cellular NADPH content. Conversely these compounds slightly augmented the reverse, or dehydrogenase, reaction of 11 β-HSD1. Importantly, using isolated intact microsomes, the inhibitors did not directly alter the tandem microsomal 11 β-HSD1 and hexose-6-phosphate dehydrogenase enzyme unit. Metabolites of 11 β-HSD1 (corticosterone or 11-dehydrocorticosterone) inhibited or increased pentose flux, respectively, demonstrating metabolic interconnectivity. Using isolated intact liver or fat microsomes, glucose-6 phosphate stimulated 11 β-HSD1 oxo-reductase, and this effect was blocked by selective inhibitors of glucose-6-phosphate transport. In summary, we have demonstrated a metabolic interconnection between pentose pathway and 11 β-HSD1 oxo-reductase activities that is dependent on cytosolic NADPH production. These observations link cytosolic carbohydrate flux with paracrine glucocorticoid formation. The clinical relevance of these findings may be germane to the regulation of paracrine glucocorticoid formation in disturbed nutritional states such as obesity.

Prevalence of hypovitaminosis D in early infantile hypocalcemia

AIM To further define the pathogenesis of infantile hypocalcemia, the prevailing vitamin D status, and treatment outcomes. METHODS AND RESULTS Of the 23 infants admitted with infantile hypocalcemia, 21 had biochemical evidence of hypocalcemia and hyperphosphatemia and the other two had isolated hypocalcemia. The majority of these infants had relatively low serum intact parathyroid hormone responses against the backdrop of hypocalcemia. Thirteen (56.5%) of these infants had low 25-hydroxyvitamin D (25-OHD) levels, of whom 69% were Hispanic and 23% were African American. Infantile serum vitamin D status reflected that of the mother in all the 16 instances in which it was measured. Treatment with calcitriol hastened recovery from hypocalcemia in our series. CONCLUSIONS Relative hypoparathyroidism is the etiology in the majority of cases of late onset and early infantile hypocalcemia. We identified vitamin D deficiency in a significant percentage of infants with hypocalcemia, especially Hispanics and African Americans. Maternal 25-OHD concentrations should be ascertained if the infant has low 25-OHD levels.

Modification of microsomal 11β-HSD1 activity by cytosolic compounds: Glutathione and hexose phosphoesters

11beta-Hydroxysteroid dehydrogenase1(11beta-HSD1) can serve either as an oxo-reductase or dehydrogenase determined by the redox state in the endoplasmic reticulum (ER). This bidirectional enzyme governs paracrine glucocorticoid production. Recent in vitro studies have underscored the key role of cytoplasmic glucose-6-phosphate (G6P) in controlling the flux direction of 11betaHSD-1 by altering the intraluminal ER NADPH/NADP ratio. The hypothesis that other hexose phosphoesters or the plentiful cellular oxidative protector glutathione could also regulate microsomal 11betaHSD-1 activity was tested. Fructose-6-phosphate increased the activity of 11beta-HSD1 reductase in isolated rat and porcine liver microsomes but not porcine fat microsomes. Moreover, oxidized glutathione (GSSG) attenuated 11beta-HSD1 reductase activity by 40% while reduced glutathione (GSH) activated the reductase in liver. Fat microsomes were unaffected because they lack glutathione reductase. Nonetheless, another oxidizing agent, hydrogen peroxide (0.5mM), inhibited both fat and liver 11beta-HSD1 reductase. Consistent with the major role of the redox state, 2.5mM GSSG and hydrogen peroxide augmented the 11beta-HSD1 dehydrogenase, antithetical to the reductase, by 20-30% in liver microsomes. Given the key role of reactive oxygen species and hexose phosphate accumulation in the pathoetiology of obesity and diabetes, these compounds might also modify 11beta-HSD1 in these conditions.

Manifold effects of palmitoylcarnitine on endoplasmic reticulum metabolism: 11β-hydroxysteroid dehydrogenase 1, flux through hexose-6-phosphate dehydrogenase and NADPH concentration.

With the exception of the oxidation of G6P (glucose 6-phosphate) by H6PDH (hexose-6-phosphate dehydrogenase), scant information is available about other endogenous substrates affecting the redox state or the regulation of key enzymes which govern the ratio of the pyridine nucleotide NADPH/NADP. In isolated rat liver microsomes, NADPH production was increased, as anticipated, by G6P; however, this was strikingly amplified by palmitoylcarnitine. Subsequent experiments revealed that the latter compound, well within its physiological concentration range, inhibited 11β-HSD1 (11β-hydroxysteroid dehydrogenase 1), the bidirectional enzyme which interconnects inactive 11-oxo steroids and their active 11-hydroxy derivatives. Notably, palmitoylcarnitine also stimulated the antithetical direction of 11β-HSD1 reductase, namely dehydrogenase. This stimulation of H6PDH may have likewise contributed to the NADPH accretion. All told, the result of these enzyme modifications is, in a conjoint fashion, a sharp amplification of microsomal NADPH production. Neither the purified 11β-HSD1 nor that obtained following microsomal sonification were sensitive to palmitoylcarnitine inhibition. This suggests that the long-chain amphipathic acylcarnitines, given their favourable partitioning into the membrane lipid bilayer, disrupt the proficient kinetic and physical interplay between 11β-HSD1 and H6PDH. Finally, although IDH (isocitrate dehydrogenase) and malic enzyme are present in microsomes and increase NADPH concentration akin to that of G6P, neither had an effect on 11β-HSD1 reductase, evidence that the NADPH pool in the endoplasmic reticulum shared by the H6PDH/11β-HSD1 alliance is uncoupled from that governed by IDH and malic enzyme.

Leptin in Children with Newly Diagnosed Type 1 Diabetes: Effect of Insulin Therapy

Leptin, the gene product of adipose tissue that signals caloric plentitude via central nervous system receptors, may also have diverse peripheral metabolic actions. Of paramount interest has been the potential interaction(s) between leptin and insulin. Insofar as insulin alters leptin secretion/action (or vice versa), dysregulation of this system could contribute to disease states such as diabetes. The purpose of this study was to examine the effect of exogenous insulin on serum leptin in children with newly-diagnosed Type 1 diabetes. Since these patients are hypoinsulinemic (insulindeplet. ed) at diagnosis, they present an ideal opportunity to examine the effect of insulin repletion on serum leptin. Seventeen patients were enrolled. At baseline (prior to insulin therapy), leptin levels were 4.3 ± 1.1ng/ml; they were not statistically related to the baseline serum insulin or illness severity. There was no significant change in serum leptin before, shortly (1–6 days) or several weeks (3–26 weeks) after insulin treatment even when the data was corrected for changes in BMI, hemoglobin A1C, and daily insulin dose. Since repletion of the insulin deficiency that is present in non-acidotic, ambulatory patients with new onset Type 1 diabetes did not alter serum leptin, these results argue against an effect of insulin on serum leptin in the absence of the acute diabetic ketoacidosis. Because as the recuperative months following the diagnosis of new onset Type 1 diabetes are marked by weight gain, the absence of a rise in serum leptin might also indicate either an adaptive (weight permissive) or pathologic (impaired secretory) deficit.

Cord blood and postnatal serum leptin and its relationship to steroid use and growth in sick preterm infants.

OBJECTIVE To study the effect of prenatal and postnatal glucocorticoids use on serum leptin and weight gain in sick preterm infants and its correlation with caloric intake. METHODS Serum leptin was measured in 24 neonates at day 1 (cord), 14 and 28 by radioimmunoassay. Total caloric intake (enteral and parenteral) and weight were measured on days 14 and 28 of life. RESULTS Mean birth weight and gestational age of study infants were 864 +/- 273 g (mean +/- SD) (range 520-1755 g), and 26.6 +/- 2.4 weeks (23-32 weeks) respectively. Cord blood leptin was greater in infants whose mothers received antenatal steroids (1.98 +/- 1.05 ng/ml vs 0.94 +/- 0.39 ng/ml, p=0.004). Serum leptin increased postnatally from 1.52 +/- 1.0 ng/ml at birth to 2.2 +/- 1.3 ng/ml on day 28 of life (p=0.03). Mean serum leptin had an inverse exponential relationship with postnatal weight gain by day 28 of life (R2=0.56). Total caloric intake on days 14 and 28 of life did not correlate with postnatal weight gain. CONCLUSIONS Increased serum concentration of leptin following glucocorticoids may be associated with poor weight gain in sick preterm infants.

Diminished in Situ Glucose-6-Phosphate Flux in Permeabilized Adipocytes From Streptozocin-Induced Diabetic Rats

With metabolically active, saponin-permeabilized adipocytes, in situ pathway metabolism, which was distal to glucose transport, was examined in acute streptozocin-induced diabetic (STZ-D) rats. Metabolic reactions were initiated with selectively radiolabeled glucose-6-phosphate (G6P), an otherwise inert substrate with intact cells. Thus, the membrane pores permitted a direct comparison of cellular flux between control and STZ-D adipocytes at identical initial substrate concentrations. Three metabolic pathways were studied: 1) proximal glycolysis through the triosephosphates ([3-3H]G6P to 3H2O), 2) glycolysis-Krebs ([6-14C]G6P) oxidation, and 3) lipogenesis ([6-14C]G6P incorporation into triglyceride). The extent of membrane porosity was assessed by both propidium iodide staining and lactate dehydrogenase leakage to assure that porosity was comparable between the cell groups. Porous adipocytes from STZ-D rats had markedly attenuated rates of G6P metabolism compared with controls. At enzyme-saturating concentrations of G6P (4 mM), this deficit ranged from 44% for glycolysis-Krebs oxidation to 88% for lipogenesis. The reduction in glycolysis-Krebs oxidation was also evident between 0.5 and 6 mM G6P. These porous-cell data were compared with parallel studies of glucose metabolism and clearance in intact adipocytes. Finally, several glycolytic enzymes and acetyl-CoA carboxylase were measured in cell-free (sonicated) extracts with traditional in vitro methods under Vmax conditions. Overall, the in situ porous-cell flux measurements uncovered larger deficits in posttransport cellular metabolism than were apparent in the cell-free, in vitro assays. We conclude that, in actively metabolizing porous rat adipocytes, there exists a striking and unequivocal transport-independent defect in intermediary metabolism after acute STZ-D.

Effect of diabetes on enzymes involved in rat hepatic corticosterone production

Background:  Numerous studies have explored the etiologic or permissive role of 11β‐hydroxysteroid dehydrogenase (11β‐HSD1) in obesity and Type 2 diabetes, biochemical conditions often with concurrent hyperinsulinism. In contrast, there are limited data on the effect of insulin deficiency (i.e. Type 1 diabetes) on 11β‐HSD1 or endoplasmic reticulum enzymes that generate the reduced pyridine cofactor NADPH. Thus, the aim of the present study was to examine the effect of insulin‐deficient, streptozotozin diabetes on key microsomal enzymes involved in rat hepatic corticosterone production.