Pathogenesis and Physiologic Mechanisms of Neonatal Pulmonary Hypertension: Preclinical Studies

Neonatal pulmonary hypertension (PH) is a devastating disorder of the pulmonary vasculature characterized by elevated pulmonary vascular resistance and mean pulmonary arterial pressure. Occurring predominantly because of maldevelopment or maladaptation of the pulmonary vasculature, PH in neonates is associated with suboptimal short-term and long-term outcomes because its pathobiology is unclear in most circumstances, and it responds poorly to conventional pulmonary vasodilators. Understanding the pathogenesis and pathophysiology of neonatal PH can lead to novel strategies and precise therapies. The review is designed to achieve this goal by summarizing pulmonary vascular development and the pathogenesis and pathophysiology of PH associated with maladaptation, bronchopulmonary dysplasia, and congenital diaphragmatic hernia based on evidence predominantly from preclinical studies. We also discuss the pros and cons of and provide future directions for preclinical studies in neonatal PH.

c-Myc Drives inflammation of the maternal-fetal interface, and neonatal lung remodeling induced by intra-amniotic inflammation

Background: Intra-amniotic inflammation (IAI) is associated with increased risk of preterm birth and bronchopulmonary dysplasia (BPD), but the mechanisms by which IAI leads to preterm birth and BPD are poorly understood, and there are no effective therapies for preterm birth and BPD. The transcription factor c-Myc regulates various biological processes like cell growth, apoptosis, and inflammation. We hypothesized that c-Myc modulates inflammation at the maternal-fetal interface, and neonatal lung remodeling. The objectives of our study were 1) to determine the kinetics of c-Myc in the placenta, fetal membranes and neonatal lungs exposed to IAI, and 2) to determine the role of c-Myc in modulating inflammation at the maternal-fetal interface, and neonatal lung remodeling induced by IAI. Methods: Pregnant Sprague-Dawley rats were randomized into three groups: 1) Intra-amniotic saline injections only (control), 2) Intra-amniotic lipopolysaccharide (LPS) injections only, and 3) Intra-amniotic LPS injections with c-Myc inhibitor 10058-F4. c-Myc expression, markers of inflammation, angiogenesis, immunohistochemistry, and transcriptomic analyses were performed on placenta and fetal membranes, and neonatal lungs to determine kinetics of c-Myc expression in response to IAI, and effects of prenatal systemic c-Myc inhibition on lung remodeling at postnatal day 14. Results: c-Myc was upregulated in the placenta, fetal membranes, and neonatal lungs exposed to IAI. IAI caused neutrophil infiltration and neutrophil extracellular trap (NET) formation in the placenta and fetal membranes, and neonatal lung remodeling with pulmonary hypertension consistent with a BPD phenotype. Prenatal inhibition of c-Myc with 10058-F4 in IAI decreased neutrophil infiltration and NET formation, and improved neonatal lung remodeling induced by LPS, with improved alveolarization, increased angiogenesis, and decreased pulmonary vascular remodeling. Discussion: In a rat model of IAI, c-Myc regulates neutrophil recruitment and NET formation in the placenta and fetal membranes. c-Myc also participates in neonatal lung remodeling induced by IAI. Further studies are needed to investigate c-Myc as a potential therapeutic target for IAI and IAI-associated BPD.

Tokyo-1 Mutation: Hereditary Spherocytosis in a Hispanic Newborn Presenting as Early Onset Severe Hyperbilirubinemia

BACKGROUND

Hereditary spherocytosis in the Hispanic population does not often present with severe hyperbilirubinemia. Spectrin and band 3 mutations are most frequent in this population.

CASE REPORT

We present a Hispanic full-term female newborn with early onset significant hyperbilirubinemia without a history of familial hemolytic disorders. She was diagnosed with hereditary spherocytosis based on laboratory findings, including presence of spherocytes on a peripheral smear, and was later found by next-generation sequencing to have Tokyo-1 mutation, an ANK1 gene mutation, that was previously only reported in Japanese population.

CONCLUSION

Our report adds to the currently limited literature of the genetic spectrum and characteristics of hereditary spherocytosis in the Hispanic population. The absence of a positive family history does not preclude hereditary spherocytosis as a differential for pathologic neonatal hyperbilirubinemia.

Scrotal pyoderma gangrenosum associated with Crohn's disease

Scrotal pyoderma gangrenosum is uncommon. We present a 17-year-old Chinese male patient with newly diagnosed Crohn's disease presenting with scrotal pyoderma gangrenosum. Biopsy and other investigations were done to diagnose and look for associated diseases of pyoderma gangrenosum. Treatment with high-dose prednisolone failed. Subsequent treatment with oral cyclosporine was successful.

Enhanced expression of interferon-inducible protein-10 correlates with disease activity and clinical manifestations in systemic lupus erythematosus

Our objective was to investigate the serum levels of interferon-inducible protein-10 (IP-10) in systemic lupus erythematosus (SLE) and their correlation with disease activity and organ manifestations. Serum IP-10 levels were assessed in 464 SLE patients and 50 healthy donors. Disease activity was assessed by the revised SLE Activity Measure, and the concomitant active organ manifestations, anti-ds DNA antibody titres, complement levels and erythrocyte sedimentation rates recorded. Peripheral blood mononuclear cell (PBMC) synthesis of IP-10 in SLE patients and controls was determined by in vitro cultures stimulated with mitogen or lipopolysaccharide. Elevated serum IP-10 levels were observed in SLE patients, which were significantly higher in the presence of active haematological and mucocutaneous manifestations. SLE PBMCs exhibited enhanced spontaneous IP-10 production in vitro. Serial IP-10 levels correlated with longitudinal change in SLE activity, even at low levels where anti-dsDNA antibody and complement levels remain unchanged. These data demonstrate that IP-10 levels are increased in SLE and serum IP-10 may represent a more sensitive marker for monitoring disease activity than standard serological tests.

Ocular manifestations and complications of Stevens-Johnson syndrome and toxic epidermal necrolysis: an Asian series

BACKGROUND

To describe the acute and late ocular manifestations and complications in toxic epidermal necrosis (TEN) and Stevens-Johnson syndrome (SJS), and identify predictors for development of late complications.

METHODS

Cases of TEN and SJS during a 9-year period were included. Patients with ocular involvement were reviewed for acute ocular complications. Patients with a minimum 6 months follow-up were reviewed for late complications. Records were reviewed for their demographics, etiology, and severity of ocular involvement.

RESULTS

There were 117 patients with a mean age of 52.2 +/- 18.6 years. Eighty-one of these (69%) had acute ocular involvement. This was mild in 40%, moderate in 25% and severe in 4%. Adverse drug reactions were the predominant cause. Patients with thrombocytopenia had more severe acute ocular involvement. Forty-four patients had a minimum 6 months of follow-up and half developed late complications. Severe dry eyes and trichiatic lashes were the commonest late complications. Patients treated with topical antibiotic were more likely to have late complications, particularly dry eyes. There was no difference in the severity of acute eye involvement or late complications when SJS and TEN patients were compared. The severity of the acute ocular disease and abnormal laboratory tests were not found to be the significant risk factors of late complications.

CONCLUSIONS

Ocular involvement is common in SJS and TEN and can be severe and blinding. The severity of acute ocular complications does not predict late complications. The diagnosis of TEN does not imply a more severe ocular involvement or increased frequency of late ocular complications compared with SJS. Care should be taken even in mild cases. Appropriate intervention during acute ocular disease may prevent late complications.

High-dose intravenous immunoglobulin in the treatment of toxic epidermal necrolysis: a study of ocular benefits

PURPOSE

To compare acute ocular complications of toxic epidermal necrolysis (TEN) following treatment with high-dose human intravenous immunoglobulin (IVIG) with a historical cohort not treated with IVIG.

METHODS

Retrospective, historically controlled study. In all, 10 consecutive patients with TEN (treatment cohort) presenting between 1 July 2001 and 30 June 2002. Totally, 18 consecutive patients with TEN (historical cohort). SettingTan Tock Seng Hospital, Singapore. The treatment cohort received high-dose IVIG (2 g/kg body weight over 2 days). Patients' records were retrospectively reviewed for their demographic characteristics, causative drug, treatment, ocular involvement (if any, as assessed by an ophthamologist), and its severity. The historical cohort comprised patients coded with a diagnosis of TEN (ICD Code 695.1) between 1 July 1995 and 30 June 2001.

RESULTS

Nine (90%) of 10 patients treated with IVIG had ocular involvement. Phenytoin was the implicated drug in three (37.5%) patients. Of the nine patients, 1 died of septic shock. Of the eight survivors, IVIG was initiated immediately upon onset of TEN as all the patients were hospitalized by the time of onset of an exanthema. Acute ocular complications were mild in two (25%) (lid oedema or mild conjunctival injection), moderate in four (50%) (pseudomembranes) and severe in two (25%) (nonhealing epithelial defect with visual loss and symblepharon). In total, 10 (55.6%) of 18 patients in the historical cohort with TEN had acute ocular involvement. Two patients died. Ocular involvement in survivors was mild in five (62.5%) cases and moderate in three (37.5%), with no severe cases.

CONCLUSIONS

IVIG did not appear to reduce the severity of visually significant ocular complications. Larger studies are needed to confirm this finding.

A case of nephrogenic fibrosing dermopathy

INTRODUCTION

Nephrogenic fibrosing dermopathy is a recently recognised fibrosing disorder originally identified as a scleromyxoedema-like cutaneous disease in patients with renal disease.

CLINICAL PICTURE

A 45-year-old lady with systemic lupus erythematosus presented with well-defined erythematous, non-tender, indurated plaques on both legs 4 months after haemodialysis for rapidly progressive glomerulonephritis and acute renal failure. Skin biopsy showed dermal fibrosis with increased proliferation of dermal fibroblasts and collagen bundles separated by clefts. There were increased dermal deposits of mucin and an increase in elastic fibres.

TREATMENT AND OUTCOME

Haemodialysis was instituted for 2 weeks followed by monthly intravenous cyclophosphamide. Skin lesions remained unchanged 8 months later despite normalisation of renal function.

CONCLUSION

Nephrogenic fibrosing dermopathy appears to be a definite new entity in patients with underlying renal insufficiency. Further multi-centre collaborative study is necessary to identify the prevalence, cause, treatment and prognosis of this disorder.

Assessment of hypercholesterolemia control in a managed care organization

To determine the extent of achievement of goal low-density lipoprotein cholesterol (LDL) as defined by National Cholesterol Education Program-Adult Treatment Panel II (NCEP-ATP 11) and American Diabetes Association (ADA) 2000 guidelines, we conducted a retrospective study by integrating data from medical, laboratory, and pharmacy claims databases. Subjects were selected from a 232,000-member staff-model managed care organization consisting of 19 clinics in the Minneapolis-St. Paul, Minnesota, metropolitan area. A total of 124,971 members aged 18 years and older, who had been continuously enrolled from July 1, 1996-June 6, 1998, were included. Outcome measures were the extent of achievement of goal LDL as defined by NCEP-ATP II and the use of antihyperlipidemic drugs for patients with and without diabetes at various levels of risk for coronary heart disease (CHD). Of 124,971 subjects, 6538 had a history of CHD, 1523 of whom met their LDL goal. Of the population with CHD who did not achieve goal, 1141 (43%) missed by over 30 mg/dl; 621 (54%) of these patients were not receiving drug therapy A total of 17,267 had no history of CHD but had two or more risk factors; 3,298 of these achieved their LDL goal. Of those who did not achieve goal, 1,136 (35%) missed by over 30 mg/dl; 897 (79%) of these were not receiving drug therapy A total of 6,586 had a history of diabetes; 1,004 and 2,340 reached an LDL of 100 mg/dl or lower and less than 130 mg/dl, respectively Of those with diabetes who had an LDL greater than 100 mg/dl, 1,276 (49%) missed their goal by over 30 mg/dl; 898 (70%) of these were not receiving drug therapy. Inadequate use of pharmacologic agents plays a significant role in failure to achieve goal LDL for patients with CHD, without CHD, and with diabetes. Analysis of the data based on the new ADA guidelines for LDL demonstrates the need for continued vigilance. Finally, the successful merging of medical, laboratory, and pharmacy claims databases provides a benchmark for other institutions.

Quantitation of peripheral blood cytomegalovirus DNA for monitoring recurrent cytomegalovirus retinitis in pediatric solid organ transplant recipients

Cytomegalovirus (CMV) infection is a major concern following solid organ transplantation, especially in the pediatric population who remain at high risk of primary infection. CMV disease leads not only to increased patient and graft morbidity, but also to increased health care costs. This study describes the usefulness of a quantitative CMV polymerase chain reaction (PCR) technique for monitoring peripheral blood CMV DNA in pediatric recipients of kidney and liver allografts who had recurrent CMV retinitis. The incidence of CMV disease in 28 pediatric transplant recipients was 28.6%, one-half of whom developed retinitis. Two of these patients had recurrent retinitis on cessation of anti-viral treatment. A peripheral blood CMV DNA copy number of > or =500/microg of DNA was associated with recrudescence of the retinitis in these patients. We conclude that the measurement of peripheral blood CMV DNA by PCR is a useful tool for the surveillance of disease resolution and recurrence. This is particularly important in patients with CMV retinitis, who may remain asymptomatic for a period of time, despite recurrences.

Obesity, fitness, willingness to communicate and health care costs

BACKGROUND

Obesity and low levels of physical fitness are independently associated with a variety of diseases and disorders. These conditions are modifiable and affect health care utilization. The degree to which these health risks are modifiable is directly related to the readiness of individuals to change the underlying behaviors. This study analyzes the relationship between health care costs, obesity, physical fitness, and willingness to communicate. In addition, we tested the hypothesis that willingness to communicate is directly associated with an individual's readiness to change behavior.

METHODS

Multiple regression was used to estimate the relationship between adverse behavioral health outcomes, willingness to communicate, and annualized health care costs incurred over a period of 33 months before the completion of a health risk assessment survey in an employed population enrolled in a Midwestern managed care organization (N = 8822).

RESULTS

High body mass index (BMI), low physical fitness (predicted VO2max), and greater willingness to communicate were directly and significantly (P < 0.05) associated with higher health care costs. Relative to low-risk, annualized health care costs for each of the high-risk factors were 8% higher for BMI (rate ratio, 1.08; 95% confidence interval, 1.01-1.15), 10% higher for low predicted VO2max (rate ratio 1.10, 95% confidence interval, 1.02-1.18), and 22% higher for willingness to communicate (rate ratio, 1.22, 95% confidence interval, 1.14-1.30). The association between these health risks and health care costs was independent of age, sex, age-sex interaction, role-mental and role-physical limitations, and nine chronic conditions. Furthermore, willingness to communicate was directly related to a greater readiness to change behavior.

CONCLUSIONS

The prevalence of obesity and low physical fitness is high, and these health risks are directly related to health care costs. Willingness of health plan members to communicate around health improvement opportunities appears greatest among those who incur higher costs, and these patients also have more favorable readiness to change profiles. Effective, proactive population-based health improvement efforts appear to have significant potential for positive economic impact.

Does professional advice influence aspirin use to prevent heart disease in an HMO population?

OBJECTIVE

Aspirin use seems to reduce coronary artery disease events in some groups of patients. Factors associated with use of aspirin to prevent heart disease in an HMO population were examined.

DESIGN

A population-based survey.

SETTING

A large HMO in the midwestern United States.

PARTICIPANTS

8000 health plan members 40 years of age and older.

MAIN OUTCOME MEASURES

The survey assessed use of aspirin, professional advice to use aspirin, and coronary heart disease risk factors and status. The sample was stratified by whether members had none, one, or more than one of the following chronic conditions: diabetes, hypertension, lipid disorder, or heart disease. The mailed survey had a corrected response rate of 82.4%.

RESULTS

Overall, 38% of respondents reported using aspirin at least three times a week to prevent heart disease. Aspirin use did not vary in owned versus contracted clinics. Aspirin use was 71.3% in patients with and 27.7% in patients without diagnosed coronary heart disease (P < 0.001). In logistic regression models, professional advice to take aspirin was strongly associated with self-reported use of aspirin (odds ratio, 13.86) (P < 0.001) after adjustment for age, sex, level of education, and chronic disease status.

CONCLUSIONS

Aspirin is widely used by HMO members with coronary artery disease to prevent subsequent coronary artery disease events. Professional advice to use aspirin seems to be strongly related to aspirin use.

In vivo phosphorylation of liver glycogen synthase. Effect of glucose and glucagon treatment of liver cells on the distribution of the [32P]phosphate

Glycogen synthase was phosphorylated in vivo by perfusing rat liver or incubating liver cells with [32P]phosphate. It was then isolated by immunoprecipitation and subjected to exhaustive tryptic proteolysis. The trypsin-derived [32P]phosphopeptides were separated by high pressure liquid chromatography (HPLC). Incubation of in vivo phosphorylated synthase with endogenous synthase phosphatase to convert synthase D to synthase R resulted in removal of phosphate from all of the labeled phosphopeptides. In prelabeled liver cells treated with glucagon or glucose, the activities of synthase and phosphorylase changed in the direction expected. The total labeling in the immunoprecipitated synthase was found to be increased to 126% and decreased to 67% of the control with glucagon and glucose treatment, respectively. When the HPLC [32P]phosphopeptide profile of synthase from glucagon-treated animals was compared with that of controls, there were only minor differences in the two profiles. All the peaks were present and the proportion of labeling in each remained similar. There also was only a modest change in the [32P]phosphopeptide profile with glucose treatment when compared with that of controls. These results indicate that regulation of synthase activity in the hepatocyte involves changes in phosphorylation at multiple sites. Indeed, in 32P-labeled liver cells, all of the labeled sites appeared to be involved.

The primary structure of rat liver glycogen synthase deduced by cDNA cloning. Absence of phosphorylation sites 1a and 1b

The cDNA for rat liver glycogen synthase was isolated by screening a rat liver cDNA library constructed in lambda gt11. The cDNA was 2.4 kilobases in length and encoded a protein of 703 amino acid residues with a molecular mass of 80.5 kDa. Comparison of the rat liver and the human muscle sequences show that the amino- and carboxyl-terminal regions are quite divergent as compared to the internal sequences which show an 80% identity. The rat liver carboxyl-terminal region is truncated by 33 residues and has only 46% identity with the muscle sequence but retains the common feature of a low content of hydrophobic amino acids (13%). Phosphorylation sites 1a and 1b, which are the primary targets for phosphorylation by cAMP-dependent protein kinase, are absent in the liver sequence. The presence of these divergent, structurally anomalous carboxyl-terminal regions in liver and muscle glycogen synthase suggests the absence of the requirement that they possess a tertiary structure that is integral to that of the protein core. A model is proposed in which this region interacts with a catalytic core to maintain the I state, and in which phosphorylation serves to uncouple this interaction.

Regulation of glycogen synthesis in the liver

The glycogen synthase-mediated reaction is rate-limiting for glycogen synthesis in the liver. Glycogen synthase has been purified essentially to homogeneity and has been shown to be a dimer composed of identical subunits. It is regulated by a phosphorylation-dephosphorylation mechanism, catalyzed by kinases and a phosphatase. The subunits of synthase D, the most phosphorylated form, each contain approximately 17 phosphates. The subunits of synthase I, the least phosphorylated form, each contain 14 phosphates. Thus, during the transition between these two forms, a net of three phosphoryl groups is added or removed. In synthase D, six of the phosphates are alkali-labile. In synthase I, three of the phosphates are alkali-labile. Therefore, all of the phosphorylation sites important in the interconversion of these two forms are alkali-labile (attached to serine or threonine residues). In short-term experiments using isolated hepatocytes, [32P]phosphate was only incorporated into the alkali-labile sites and the phosphate in these sites was shown to turn over rapidly. Glucose addition, which is known to reduce the proportion of synthase in the D form when assayed kinetically, also reduced the [32P]phosphate content. Glucagon addition, which increases the proportion of synthase in the D form, increased it. These changes do not appear to be site-specific. Ingestion or administration of fructose, or galactose, as well as glucose, result in a shift in synthase equilibrium in favor of the less phosphorylated forms. Possible mechanisms by which synthase phosphatase activity may be increased after ingestion of glucose or fructose, and thus shift the equilibrium in favor of the less phosphorylated forms, are discussed. The mechanism by which galactose may stimulate the phosphatase reaction is completely unknown.

L-type glycogen synthase. Tissue distribution and electrophoretic mobility

We previously reported (Kaslow, H.R., and Lesikar, D.D.FEBS Lett. (1984) 172, 294-298) the generation of antisera against rat skeletal muscle glycogen synthase. Using immunoblot analysis, the antisera recognized the enzyme in crude extracts from rat skeletal muscle, heart, fat, kidney, and brain, but not liver. These results suggested that there are at least two isozymes of glycogen synthase, and that most tissues contain a form similar or identical to the skeletal muscle type, referred to as "M-type" glycogen synthase. We have now used an antiserum specific for the enzyme from liver, termed "L-type" glycogen synthase, to study its distribution and electrophoretic mobility. Immunoblot analysis using this antiserum indicates that L-type glycogen synthase is found in liver, but not skeletal muscle, heart, fat, kidney, or brain. In sodium dodecyl sulfate-polyacrylamide gels of crude liver extracts prepared with protease inhibitors, rat L-type synthase was detected with electrophoretic mobility Mapp = 85,000. In contrast, the M-type enzyme in crude skeletal muscle extracts with protease inhibitors was detected with Mapp = 86,000 and 89,000. During purification of L-type synthase, apparent proteolysis can generate forms with increased electrophoretic mobility (Mapp = 75,000), still recognized by the antiserum. These M-type and L-type antisera did not recognize a protein with Mapp greater than phosphorylase. The anti-rat L-type antisera recognized glycogen synthase in blots of crude extracts of rabbit liver, but with Mapp = 88,000, a value 3,000 greater than that found for the rat liver enzyme. The anti-rat M-type antisera failed to recognize the enzyme in blots of crude extracts of rabbit muscle. Thus, in both muscle and liver, the corresponding rat and rabbit enzymes are structurally different. Because the differences described above persist after resolving these proteins by denaturing sodium dodecyl sulfate electrophoresis, these differences reside in the structure of the proteins themselves, not in some factor bound to the protein in crude extracts.

In vivo phosphorylation of liver glycogen synthase. Isolation of the 32P-labeled enzyme and studies on the nature of the bound [32P]phosphates

Our previous study (Tan, A. W. H., and Nuttall, F. Q. (1983) J. Biol. Chem. 258, 9624-9630) indicated that liver synthase D contained a large number of endogenous phosphates, 12 of which were stable and 6 labile to alkali treatment. We wished to investigate the nature of the phosphates on synthase which became isotopically labeled when inorganic [32P]phosphate was given either to intact rats or to isolated liver cells. An antibody against liver synthase D was used for the isolation of synthase. The antibody recognized both the phosphorylated and dephosphorylated form of the enzyme, native as well as partially cleaved species. A large enzyme form, with Mr of 90,000 as well as one with Mr of 73,000 was observed. A 61% decrease in [32P]phosphate was found in synthase when prelabeled liver cells were treated with glucose, whereas a 25% increase was seen in cells treated with glucagon. After [32P]synthase D was converted to synthase I by synthase phosphatase, 95% of the [32P]phosphate was lost. All of the bound [32P]phosphates were found to be labile to alkali. Thus, under the in vivo conditions used, the [32P]phosphates incorporated into synthase were characterized by their fast turnover rate, alkali lability and susceptibility to the action of synthase phosphatase, both in vivo and in vitro. These criteria serve to distinguish them from the slower turning-over, alkali-stable phosphates found previously in both synthases D and I.

Endogenous phosphates on liver glycogen synthase D and synthase I. Studies on the number and location

Synthase D and synthase I of high specific activity have been isolated from rabbit liver, with subunit Mr = 78,000 and 85,000, respectively. Minor bands of Mr = 78,000 and 71,000 were also observed, and these were shown to be proteolytic products containing synthase activity. Incubation with trypsin resulted in no activity changes, but there was a conversion of synthase I to the Mr = 78,000 species. Incubation with chymotrypsin produced no change in total synthase activity, but both enzymes were converted to the Mr = 71,000 species. Synthase I, after chymotrypsin treatment, became dependent on glucose-6-P for activity. Kinetic studies indicated that the chymotrypsin-treated synthase D and synthase I were not the same species. Synthase D contained 5.7 mol of alkali-labile phosphate/subunit and synthase I, 2.9 mol/subunit. With trypsin treatment there was little loss of phosphate from synthase. With chymotrypsin treatment, there was a loss of 3.1 and 1.5 mol of phosphate/subunit from synthase D and I, respectively. Some conversion to synthase I still occurred when chymotrypsin-treated synthase D was incubated with crude extract, suggesting that the phosphates which remained were still removable by synthase phosphatase. The presence of additional alkali-stable phosphates was indicated when the synthase samples were ashed. The total phosphates were 17.3 mol/subunit for synthase D and 13.4 mol/subunit for synthase I. Our results indicate that the liver synthase enzymes are highly phosphorylated and extremely susceptible to endogenous and exogenous proteolysis. The alkali-labile phosphates are distributed in chymotrypsin-sensitive as well as chymotrypsin-insensitive sites. Both sites are involved in the conversion of synthase D to synthase I.

Liver phosphorylase kinase: characterization of two interconvertible forms and partial purification of phosphorylase kinase a

The presence of two interconvertible forms of phosphorylase kinase has been confirmed in rat liver extracts. The pH optimum of the nonactivated form (PhK b) was lower than the pH optimum of the activated form (PhK a) as reported by others (2). In the absence of calcium the Km of PhK b for phosphorylase b was 53 +/- 10 U/ml with a Vm of 17 +/- 1 U/gm of tissue. The Km of PhK a for phosphorylase b was 20 +/- 2 U/ml with a Vm of 65 U/gm. Calcium stimulated both forms of phosphorylase kinase (A0.5 approximately 0.03 micro). In the presence of 0.1 microM calcium the Km for phosphorylase b of both forms of the enzyme was reduced. In addition, calcium increased the Vm of both forms, but the effect was greater for PhK b than for PhK a. The Km of both forms of phosphorylase kinase for ATP was 0.05 mM and was unaffected by calcium. All of these studies were done using liver phosphorylase b as substrate. Conditions for assaying PhK a activity virtually independent of PhK b activity also are indicated. This will enable the monitoring of interconversion reactions in tissue extracts. Phosphorylase kinase a was purified to near homogeneity using DEAE-cellulose, Sepharose 4B gel filtration and ATP affinity chromatography. The molecular weight was approximately 1 x 10(6). The pH profile, calcium requirements and kinetic constants were the same as those for PhK a in the crude extract.

Glycogen synthase R in livers of starved rats and starved rats given glucose

We reported that when synthase D was converted to synthase I in a rat liver extract, it progressed through a synthase form with activity characteristics which could not be explained by a mixture of synthase D and synthase I (Tan, A. W. H. (1981) Biochem. J. 200, 169-172). In this study we will borrow the "R" nomenclature to describe this "non-D" and "non-I" activity. Using activities measured at five different conditions and simultaneous equations, the amount of the three synthase forms in liver extracts can be estimated. During incubation of the liver extract, the amount of synthase R was found to increase with time and then to decrease as synthase I was generated, a profile typical of an enzyme intermediate. We investigated for the presence of synthase R in rat liver under different in vivo conditions. In contrast to the liver of fed rats which had very little synthase R, the liver of fasted rats was found to have 30% of its synthase in the R form. This synthase R was increased 2-fold when glucose was given and decreased to a very low level when glucagon was given. Synthase I was not detected, even in the livers of starved rats given glucose. Using conditions which were closer to those of the cell, synthase R was found to have relatively high activity, up to 70% that of synthase I. Based on these results, synthase R is proposed to be an active enzyme form responsible for glycogen synthesis in rat liver.

Presence of an intermediate synthase form during the conversion of glycogen synthase D into synthase I in rat liver extract

When synthase D was converted into synthase I in a liver extract, it progressed through a synthase form with activity characteristics that could not be explained by a mixture of the original synthase D and the final product, synthase I. This form was distinguished by an affinity for UDP-glucose, in the absence of glucose 6-phosphate, which was intermediate between those of the two known forms.

Effect of starvation and insulin treatment on glycogen synthase D and synthase D phosphatase activity in rat heart

We have previously shown that synthase phosphatase activity was decreased in starved animals and was rapidly restored by insulin administration (1). In order to determine whether the decreased phosphatase activity was due to a decrease in phosphatase enzyme per se or to a change in the substrate, synthase D, phosphatase activity has been determined using purified synthase D substrate. Using purified heart or liver synthase D, phosphatase activity was lower in extracts from starved animals than in fed animals. Insulin administration rapidly increased phosphatase activity in extracts from the starved animals. The total amount of endogenous synthase D which was convertible to synthase I was lower in extracts from starved animals, but this was rapidly increased within 15 minutes following insulin administration. These data suggest that starvation and insulin have a direct effect on the phosphatase enzyme activity per se and probably on the substrate suitability of synthase D as well.

Characterization of the glycogen synthase D found in liver of the adrenalectomized fasted rats

We have previously shown that the synthase D (UDPglucose:glycogen 4-alpha-D-glucosyltransferase, EC 1.4.1.11) present in the liver of the adrenalectomized fasted rat was not converted to synthase I by synthase phosphatase from normal animals, suggesting the presence of a non-substrate form of synthase D (Tan, A.W.H. and Nuttall, F.Q. (1976) Biochim. Biophys. Acta 445, 118--130). The enzymatic properties of this synthase D have now been examined. Using optimal assay conditions, the total amount of synthase D activity in the adrenalectomized fasted rats was similar to that of normal fed rats when 1% glycogen was included in the homogenizing buffer. However, the two enzymes appeared to have different affinities for the substrate, UDPglucose and the modifier, glucose-6-P. The changes in kinetic properties were not due to differences in glycogen or to a dialyzable modifier in the extracts. Synthase D from adrenalectomized fasted and from normal fed rats was partially purified. After DEAE-cellulose chromatography, modification appeared to have occurred such that the enzyme from the adrenalectomized fasted rat had properties similar to that of the normal fed rat. The enzymes were cold-labile, had different properties from enzymes in the crude extract and they were both converted to synthase I by synthase phosphatase. We conclude from these studies that the phosphorylation site in the synthase is in a flexible region of the protein. Changes in the ability of the synthase D to interact and be dephosphorylated by synthase phosphatase can occur readily in vivo and in vitro. The molecular basis for the modification remains unknown.

Growth hormone effects on creatine uptake by muscle in the hypophysectomized rat

Specific radioactive enzyme assays were developed to measure the effect of growth hormone on kidney transamidinase and liver methyltransferase in the hypophysectomized rat. In contrast to minimal changes (20%) in liver methyltransferase, kidney transamidinase was decreased threefold in the hypophysectomized rat. Enzyme activities were equal to normal values in those rats receiving growth hormone for three days. The formation of creatine from radioactive precursors and the uptake of 14C-creatine in muscle was examined under these conditions. After injection of 14C-arginine in the hypophysectomized rat, the 14C-creatine content of muscle was greatly decreased compared to sham operated controls and the 14C-creatine content was normal after growth hormone administration. After injection of 14C-guanidoacetate and of 14-creatine, the 14C-creatine content of muscle was decreased in the hypophysectomized rat, but was equal to sham control values in rats receiving growth hormone. These studies indicate that the uptake of newly synthesized creatine by muscle is impaired in the hypophysectomized rat and that growth hormone can have a role in controlling the rate of creatine uptake by muscle in addition to its effect on kidney transamidinase and to other factors involved in creatine metabolism.

Glycogen synthase, synthase phosphatase, and phosphorylase response to glucose in somatostatin-pretreated intact rats

The response of the glycogen synthase and phosphorylase systems of the liver to intravenous glucose in the presence and absence of short-term somatostatin blockade of insulin secretion was determined in fed and 20-h fasted rats. These enzyme systems regulate glycogen synthesis and degradation, respectively. In the presence of somatostatin, intravenous glucose (1.0 g/kg), promptly (5 min) increased the proportion of synthase in the I (active) form, and the increase was similar to that in animals that had not received somatostatin. In the same animals, phosphorylase a also was decreased, and the decrease was similar in all groups. When a smaller dose of glucose (250 mg/kg) was used that only modestly increased plasma glucose (139 mg/dl) and produced a less than maximal synthase response, insulin (1 U/kg) did not potentiate glucose activation of synthase either in the presence or absence of somatostatin. Phosphorylase a did not change significantly in any group.

Glucose, in both the presence and absence of somatostatin, also rapidly (2 min) converted synthase phosphatase from a form inhibited by EDTA to a form not inhibited by EDTA.

These data indicate that the synthase and phosphorylase systems in vivo respond primarily to a rise in plasma glucose and not to a simultaneous elevation in plasma insulin. Thus, glucose is regulating its own storage as glycogen in the liver. The effect of glucose on the synthase may be mediated through a conversion of the synthase phosphatase to a form that is not dependent on divalent cation for activity. This form presumably is more active in vivo.

A simplified method for the preparation of pure UDP[14C] glucose

A two-step enzymatic synthesis of UDP[14C] glucose was described which resulted in high yield. Separation of product from labelled intermediates and other contaminants was achieved by a simple ion exchange chromatography method.

Evidence for the non-identity of proteins having synthase phosphatase, phosphorylase phosphatase and histone phosphatase activity in rat liver

Synthase phosphatase, phosphorylase phosphatase and histone phosphatase in rat liver were measured using as substrates purified liver synthase D, phosphorylase alpha and 32P-labelled phosphorylated f1 histone, respectively. The three phosphatase enzymes had different sedimentation characteristics. Both synthase phosphatase and phosphorylase phosphatase were found to sediment with the microsomal fraction under our experimental conditions. Only 10% of histone phosphatase was in this fraction; the majority was in the cytosol. No change in histone phosphatase was observed in the adrenalectomized fasted rat whereas synthase phosphatase and phosphorylase phosphatase activities were decreased 5-10 fold. Fractionation of liver extract with ethanol produced a dissociation of the three phosphatase activities. When a partially purified fraction was put on a DEAE-cellulose column, synthase phosphatase and phosphorylase phosphatase both exhibited broad elution profiles but their activity peaks did not coincide. Histone phosphatase eluted as a single discrete peak. When the supernatant of CaCl2-treated microsomal fraction was put on a Sepharose 4B column, the majority of synthase phosphatase was found to elute with the larger molecular weight proteins whereas the majority of phosphorylase phosphatase eluted with the smaller species. Histone phosphatase migrated as a single peak and was of intermediate size. Synthase phosphorylase phosphatase by synthase D (Ki approximately 2 units/ml). The inhibition of synthase phosphatase by phosphorylase alpha was kinetically non-competitive with substrate. Histone phosphatase activity was not inhibited by synthase D or by phosphorylase alpha. The above results suggest that different proteins are involved in the dephosphorylation of synthase D, phosphorylase alpha and histone in the cell.

Regulation of synthase phosphatase and phosphorylase phosphatase in rat liver

Using substrates purified from liver, the apparent Km values of synthase phosphatase ([UDPglucose--glycogen glucosyltransferase-D]phosphohydrolase, EC 3.1.3.42) and phosphorylase phosphatase (phosphorylase a phosphohydrolase, EC 3.1.3.17) were found to be 0.7 and 60 units/ml respectively. The maximal velocity of phosphorylase phosphatase was more than a 100 times that of synthase phosphatase. In adrenalectomized, fasted animals there was a complete loss of synthase phosphatase but only a slight decrease in phosphorylase phosphatase when activity was measured using endogenous substrates in a concentrated liver extract. When assayed under optimal conditions with purified substrates, both activities were present but had decreased to very low levels. Mixing experiments indicated that synthase D present in the extract of adrenalectomized fasted animals was altered such that it was no longer a substrate for synthase phosphatase from normal rats. Phosphorylase a substrate on the other hand was unaltered and readily converted. When glucose was given in vivo, no change in percent of synthase in the I form was seen in adrenalectomized rats but the percent of phosphorylase in the a form was reduced. Precipitation of protein from an extract of normal fed rats with ethanol produced a large activation of phosphorylase phosphatase activity with no corresponding increase in synthase phosphatase activity. Despite the low phosphorylase phosphatase present in extracts of adrenalectomized fasted animals, ethanol precipitation increased activity to the same high level as obtained in the normal fed rats. Synthase phosphatase and phosphorylase phosphatase activities were also decreased in normal fasted, diabetic fed and fasted, and adrenalectomized fed rats. Both enzymes recovered in the same manner temporally after oral glucose administration to adrenalectomized, fasted rats. These results suggest an integrated regulatory mechanism for the two phosphatase.

Characteristics of the dephosphorylated form of phosphorylase purified from rat liver and measurement of its activity in crude liver preparations

The phosphorylated form of liver glycogen phosphorylase (alpha-1,4-glucan : orthophosphate alpha-glucosyl-transferase, EC 2.4.1.1) (phosphorylase a) is active and easily measured while the dephosphorylated form (phosphorylase b), in contrast to the muscle enzyme, has been reported to be essentially inactive even in the presence of AMP. We have purified both forms of phosphorylase from rat liver and studied the characteristics of each. Phosphorylase b activity can be measured with our assay conditions. The phosphorylase b we obtained was stimulated by high concentrations of sulfate, and was a substrate for muscle phosphorylase kinase whereas phosphorylase a was inhibited by sulfate, and was a substrate for liver phosphorylase phosphatase. Substrate binding to phosphorylase b was poor (KM glycogen = 2.5 mM, glucose-1-P = 250 mM) compared to phosphorylase a (KM glycogen = 1.8 mM, KM glucose-1-P = 0.7 mM). Liver phosphorylase b was active in the absence of AMP. However, AMP lowered the KM for glucose-1-P to 80 mM for purified phosphorylase b and to 60 mM for the enzyme in crude extract (Ka = 0.5 mM). Using appropriate substrate, buffer and AMP concentrations, assay conditions have been developed which allow determination of phosphorylase a and 90% of the phosphorylase b activity in liver extracts. Interconversion of the two forms can be demonstrated in vivo (under acute stimulation) and in vitro with little change in total activity. A decrease in total phosphorylase activity has been observed after prolonged starvation and in diabetes.