Efficacy and safety of combination therapy with SGLT2 and DPP4 inhibitors in the treatment of type 2 diabetes: A systematic review and meta-analysis

BACKGROUND

This review evaluated the efficacy and safety of a combination therapy comprising a sodium-glucose cotransporter type 2 inhibitor (SGLT2i) and dipeptidyl peptidase-4 inhibitor (DPP4i) in type 2 diabetes.

METHODS

A literature search through to May 2017 was carried out of PubMed, Embase and the Cochrane Central Register of Controlled Trials. Studies were eligible if they were randomized controlled trials (RCTs) comparing SGLT2i plus DPP4i (SGLT2i/DPP4i) against DPP4i±placebo or SGLT2i±placebo and published in English. The primary outcome was change in HbA_1c from baseline.

RESULTS

Eight RCTs comparing SGLT2i/DPP4i and DPP4i, and five RCTs comparing SGLT2i/DPP4i and SGLT2i, with three RCTs involving both comparisons, were included in the present review. SGLT2i/DPP4i resulted in a greater mean HbA_1c reduction [weighted mean difference (WMD]): -0.62%] than did DPP4i alone, which was a much less marked reduction (WMD: -0.35%) than with SGLT2i alone. Also, significant differences in body weight loss from baseline were observed only with SGLT2i/DPP4i vs. DPP4i, but not vs. SGLT2i. The risk of hypoglycaemic events was low and similar between treatment groups. When subjects were stratified based on baseline HbA_1c, any reduction by SGLT2i/DPP4i in relation to DPP4i was proportional to baseline HbA_1c levels. However, compared with SGLT2i, HbA_1c reductions with SGLT2i/DPP4i were modest regardless of baseline HbA_1c.

CONCLUSION

Combination therapy with SGLT2i and DPP4i is both efficacious and safe. In particular, a marked additional glucose-lowering effect is evident when SGLT2i is combined with or added to DPP4i, and not vice versa. However, baseline HbA_1c determined the additional glucose-lowering effects of SGLT2i in combined treatment with DPP4i.

Chaperoning of closed syntaxin-3 through Lys46 and Glu59 in domain 1 of Munc18 proteins is indispensable for mast cell exocytosis

Understanding how Munc18 proteins govern exocytosis is crucial because mutations of this protein cause severe secretion deficits in neuronal and immune cells. Munc18-2 has indispensable roles in the degranulation of mast cell, partly by binding and chaperoning a subset of syntaxin isoforms. However, the key syntaxin that, crucially, participates in the degranulation – whose levels and intracellular localization are regulated by Munc18-2 – remains unknown. Here, we demonstrate that double knockdown of Munc18-1 and Munc-2 in mast cells results in greatly reduced degranulation accompanied with strikingly compromised expression levels and localization of syntaxin-3. This phenotype is fully rescued by wild-type Munc18 proteins but not by the K46E, E59K and K46E/E59K mutants of Munc-18 domain 1, each of which exhibits completely abolished binding to 'closed' syntaxin-3. Furthermore, knockdown of syntaxin-3 strongly impairs degranulation. Collectively, our data argue that residues Lys46 and Glu59 of Munc18 proteins are indispensable for mediating the interaction between Munc18 and closed syntaxin-3, which is essential for degranulation by chaperoning syntaxin-3. Our results also indicate that the functional contribution of these residues differs between immune cell degranulation and neuronal secretion.

A pivotal role for pro-335 in balancing the dual functions of Munc18-1 domain-3a in regulated exocytosis

Munc18-1 plays essential dual roles in exocytosis: (i) stabilizing and trafficking the central SNARE protein, syntaxin-1 (i.e. chaperoning function), by its domain-1; and (ii) priming/stimulating exocytosis by its domain-3a. Here, we examine whether or not domain-3a also plays a significant role in the chaperoning of syntaxin-1 and, if so, how these dual functions of domain-3a are regulated. We demonstrate that introduction of quintuple mutations (K332E/K333E/P335A/Q336A/Y337L) in domain-3a of Munc18-1 abolishes its ability to bind syntaxin-1 and fails to rescue the level and trafficking of syntaxin-1 as well as to restore exocytosis in Munc18-1/2 double knockdown cells. By contrast, a quadruple mutant (K332E/K333E/Q336A/Y337L) sparing the Pro-335 residue retains all of these capabilities. A single point mutant of P335A reduces the ability to bind syntaxin-1 and rescue syntaxin-1 levels. Nonetheless, it surprisingly outperforms the wild type in the rescue of exocytosis. However, when additional mutations in the neighboring residues are combined with P335A mutation (K332E/K333E/P335A, P335A/Q336A/Y337L), the ability of the Munc18-1 variants to chaperone syntaxin-1 and to rescue exocytosis is strongly impaired. Our results indicate that residues from Lys-332 to Tyr-337 of domain-3a are intimately tied to the chaperoning function of Munc18-1. We also propose that Pro-335 plays a pivotal role in regulating the balance between the dual functions of domain-3a. The hinged conformation of the α-helix containing Pro-335 promotes the syntaxin-1 chaperoning function, whereas the P335A mutation promotes its priming function by facilitating the α-helix to adopt an extended conformation.

The optimal morning:evening ratio in total dose of twice-daily biphasic insulin analogue in poorly controlled Type 2 diabetes: a 24-week multi-centre prospective, randomized controlled, open-labelled clinical study

AIMS

Biphasic insulin analogues are widely used in patients with Type 2 diabetes mellitus suboptimally controlled on oral anti-diabetic drugs. Several topics in this area remain controversial, including how to divide the daily dose of biphasic insulin analogue. We aimed to determine the optimal dosing ratio of twice-daily biphasic insulin analogue and to compare the glycaemic efficacy among groups of patients using different initial dosing ratios of biphasic insulin analogue.

METHODS

A total of 100 poorly controlled insulin-naive subjects with Type 2 diabetes [HbA1c ≥ 58 mmol/mol, (7.5%)] on oral anti-diabetic drugs were randomized into three groups according to initial morning:evening dosing ratio (group I, 50:50; group II, 55:45; group III, 60:40) of twice-daily biphasic insulin analogue (biphasic insulin aspart 70/30, biphasic insulin aspart 30). The primary outcome measure was the difference in pre-breakfast to pre-dinner dose ratio at the end of the study.

RESULTS

Twice-daily biphasic insulin analogue showed a significant improvement in glycaemic control [HbA1c from 70 mmol/mol (8.6%) to 60 mmol/mol (7.6%)] after 24 weeks regardless of the initial dose ratio given. Despite the similar efficacy and safety profiles among three groups, morning dose was significantly increased (from 50:50 to 55:45-60:40) in group I after 24 weeks. However, there was no significant change in splitting ratio in groups II and III (with higher morning dose) over the 24-week treatment period.

CONCLUSIONS

These results indicate that initiating twice-daily biphasic insulin analogue on regimens with a higher dose before breakfast than before dinner (i.e. ratio approximately 55:45 to 60:40) might be more appropriate in Korean subjects with Type 2 diabetes.

Clinical characteristics and insulin independence of Koreans with new-onset type 2 diabetes presenting with diabetic ketoacidosis

BACKGROUND

We evaluated the incidence, characteristics and insulin independence of Koreans with new-onset type 2 diabetes (T2D) initially presenting with diabetic ketoacidosis (DKA).

METHODS

We analysed clinical and biochemical data from diabetic patients presenting with DKA. They were classified into ketosis-prone diabetes (KPD) type 1A (KPD-T1A) (A+β-), type 1B (KPD-T1B) (A-β-), type 2A (KPD-T2A) (A+β+) or type 2B (KPD-T2B) (A-β+) according to the presence or absence of an autoantibody and β-cell reserve. Changes in therapy after insulin discontinuation were evaluated for up to 4 years. We also compared clinical and biochemical characteristics between newly diagnosed T2D patients presenting with DKA and previously diagnosed T2D patients presenting with DKA.

RESULTS

Among 60 newly diagnosed KPD patients, 18, 21 and 21 patients were classified as KPD-T1A, KPD-T1B and KPD-T2B, respectively. In the KPD-T2B group, both fasting and stimulated C-peptide were recovered over 6 months. After 4 years of DKA development, 75% of KPD-T2B subjects no longer required insulin. Compared with previously diagnosed T2D patients presenting with DKA, newly diagnosed KPD-T2B patients tended to be younger, more obese and showed better insulin secretory function after recovery from DKA.

CONCLUSIONS

New-onset T2D patients presenting with DKA was not uncommon among the Korean population. In contrast to previously diagnosed T2D patients presenting with DKA, who showed a progressive decrease in insulin secretory function, new-onset KPD-T2B patients recovered insulin secretory function over time, and insulin independence could be expected.

Calcium-dependent activator protein for secretion 1 (CAPS1) binds to syntaxin-1 in a distinct mode from Munc13-1

Calcium-dependent activator protein for secretion 1 (CAPS1) is a multidomain protein containing a Munc13 homology domain 1 (MHD1). Although CAPS1 and Munc13-1 play crucial roles in the priming stage of secretion, their functions are non-redundant. Similar to Munc13-1, CAPS1 binds to syntaxin-1, a key t-SNARE protein in neurosecretion. However, whether CAPS1 interacts with syntaxin-1 in a similar mode to Munc13-1 remains unclear. Here, using yeast two-hybrid assays followed by biochemical binding experiments, we show that the region in CAPS1 consisting of the C-terminal half of the MHD1 with the corresponding C-terminal region can bind to syntaxin-1. Importantly, the binding mode of CAPS1 to syntaxin-1 is distinct from that of Munc13-1; CAPS1 binds to the full-length of cytoplasmic syntaxin-1 with preference to its "open" conformation, whereas Munc13-1 binds to the first 80 N-terminal residues of syntaxin-1. Unexpectedly, the majority of the MHD1 of CAPS1 is dispensable, whereas the C-terminal 69 residues are crucial for the binding to syntaxin-1. Functionally, a C-terminal truncation of 69 or 134 residues in CAPS1 abolishes its ability to reconstitute secretion in permeabilized PC12 cells. Our results reveal a novel mode of binding between CAPS1 and syntaxin-1, which play a crucial role in neurosecretion. We suggest that the distinct binding modes between CAPS1 and Munc13-1 can account for their non-redundant functions in neurosecretion. We also propose that the preferential binding of CAPS1 to open syntaxin-1 can contribute to the stabilization of the open state of syntaxin-1 during its transition from "closed" state to the SNARE complex formation.

Assessment of the fatty liver index as an indicator of hepatic steatosis for predicting incident diabetes independently of insulin resistance in a Korean population

AIMS

Fatty liver disease, especially non-alcoholic fatty liver disease, is considered to be the hepatic manifestation of the metabolic syndrome, both closely associated with insulin resistance. Furthermore, fatty liver disease assessed by ultrasonography is known to be a predictor of the development of Type 2 diabetes mellitus. However, it remains unclear whether fatty liver disease plays a role in the pathogenesis of Type 2 diabetes independently of insulin resistance. In this study, we investigated whether fatty liver disease assessed by the fatty liver index can predict the development of Type 2 diabetes independently of systemic insulin resistance.

METHODS

We examined the clinical and laboratory data of 7860 subjects without diabetes who underwent general routine health evaluations at the Asan Medical Center in 2007 and had returned for follow-up examinations in 2011. Fatty liver index was calculated using an equation that considers serum triglyceride levels, γ-glutamyltransferase, waist circumference and BMI.

RESULTS

During a 4-year period, 457 incident diabetes cases (5.8%) were identified. The odds ratios for the development of Type 2 diabetes were significantly higher in the group with a fatty liver index ≥ 60 (fatty liver index-positive) than in the group with a fatty liver index < 20 (fatty liver index-negative) after adjusting for various confounding variables including homeostasis model assessment of insulin resistance. Odds ratios were significant regardless of the insulin resistance status at baseline.

CONCLUSIONS

Our results suggest that fatty liver index as a simple surrogate indicator of hepatic steatosis is valuable in identifying subjects at high risk for Type 2 diabetes. In addition, fatty liver disease itself contributes to the development of Type 2 diabetes independently of systemic insulin resistance.

Progression to insulin deficiency in Korean patients with Type 2 diabetes mellitus positive for anti-GAD antibody

AIMS

To investigate the rate of progression to insulin deficiency in Korean patients with Type 2 diabetes mellitus positive for anti-GAD antibody (GADA) and to determine the factors related to progression to insulin deficiency.

METHODS

We retrospectively analysed data on 87 GADA-positive and 87 age- and sex-matched GADA-negative patients with Type 2 diabetes. GADA-positive patients were further subclassified into high-titre (≥ 250 WHO units/ml) (n = 24) and low-titre (< 250 WHO units/ml) (n = 63) subgroups. Cox proportional hazard analysis was used to identify factors associated with progression to insulin deficiency.

RESULTS

Over a period of 6 years, two of 87 (2.3%) GADA-negative and 37 of 87 (42.5%) GADA-positive patients had progressed to insulin deficiency. The rate of progression to insulin deficiency was higher in the high-titre than in the low-titre subgroup (75.0 vs. 30.2%). Multivariate analysis in GADA-positive patients showed that high-titre GADA and low BMI at diagnosis were independent factors significantly related to progression to insulin deficiency.

CONCLUSIONS

The presence of GADA predicted the progression to insulin deficiency in Korean patients with Type 2 diabetes. In GADA-positive patients, high-titre GADA and low BMI were associated with this progression.

Delayed ascending aortic pseudoaneurysm in an adult onset Still's disease patient with previous mitral valve and aortic root replacement

A 59-year-old female patient with adult onset Still's disease (AOSD) presented with hemoptysis and pseudoaneurysm from an aortic root vent cannulation site that was created 4 years earlier for combined mitral and aortic valve surgery. The pseudoaneurysm was successfully repaired and the patient remained well during a follow-up period of 20 months.

Relationship between body composition and bone mineral density (BMD) in perimenopausal Korean women

OBJECTIVES

Osteoporosis is a disease that increases the fracture rates and it is the major cause of increased mortality and morbidity in the elderly people. To determine which component of body composition is most important to bone health, we analysed the relationship between elements of the body composition and bone mineral density (BMD) in Korean women.

DESIGN

Cross-sectional clinical study.

PATIENTS

Totally 1694 women (mean age 51 years) were selected from subjects who participated in a medical check-up program.

MEASUREMENTS

Body composition analysis was performed by segmental bioelectric impedance method and lean mass, fat mass and per cent body fat measured. Waist: hip ratio (WHR) was assessed as a marker for visceral fat. Lumbar spine (L-spine) BMD was measured by dual X-ray absorptiometry (DEXA). As menopausal status could not be confirmed in all subjects, we divided the subjects into two groups according to the age > 50 years and < 50 years.

RESULTS

Among the entire population, 599 subjects (35.4%) were osteopaenic and 229 subjects (13.5%) were osteoporotic. The bivariate correlation among the variables showed that weight had the highest correlation with fat mass. Mean lean mass was decreased and the WHR increased as the subjects progressed from normal to osteoporotic status; fat mass was the highest among the osteopaenic subjects. L-spine BMD showed a positive correlation with lean mass, and a negative correlation with WHR by bivariate correlation analysis. However, fat mass had a negative correlation with L-spine BMD only after adjustment for age and weight. Multiple regression analysis with L-spine BMD as the dependent variable showed that age, height, fasting insulin, lean mass and WHR were significant determinants of the L-spine BMD (R(2) = 0.170, P < 0.05).

CONCLUSION

In this Korean female population, L-spine BMD showed a consistently positive correlation with lean mass and a negative correlation with WHR. Fat mass failed to show any consistent correlation with L-spine BMD in this study population.

A comprehensive study on the laser decontamination of surfaces contaminated with Cs(+) ion

A Q-switched Nd:YAG laser with a 1064nm, 450mJ/pulse and 14ns pulse width was employed to study the decontamination characteristics of Type 304 stainless steel specimens contaminated with Cs(+) ions. The surrogate specimens were artificially contaminated with two kinds of premixed solutions. The laser was irradiated for 10, 20 and 100 shots. The results were investigated using a SEM, EPMA and XPS. For the surrogate specimen treated with the CsCl+KCl solution, more than 98% of the Cs(+) ions were removed during an irradiation of 100 shots. The specimen treated with the CsCl+KCl solution was easier to decontaminate. By comparing the ratio of the O(1s) intensity to the Fe(2p) intensity of the XPS spectra, it was found that the oxygen atoms that had evolved from the specimen treated with the CsNO(3)+KNO(3) solution had decreased the laser's decontamination performance.

Relationship between polymorphisms G395A in promoter and C1818T in exon 4 of the KLOTHO gene with glucose metabolism and cardiovascular risk factors in Korean women

BACKGROUND

Recently, klotho has been proposed as a link between cardiovascular diseases and premature aging, but the relationship between KLOTHO genes and cardiovascular risk factors, especially glucose metabolism, in humans is unclear.

OBJECTIVES

We investigate the relationship between polymorphisms G395A in promoter and C1818T in exon 4 of the KLOTHO gene with glucose metabolism and cardiovascular risk factors in Korean women.

MATERIAL AND METHODS

In 251 women (mean age 51.3+/-6.9 yr), body mass index (BMI), waist circumference, blood pressure, fasting plasma glucose, insulin and lipid profiles were measured. The genotyping of polymorphisms G395A in promoter and C1818T in exon 4 of the KLOTHO gene was performed by allelic discrimination using a 5' nuclease polymerase chain reaction assay.

RESULTS

Allele frequencies of G395A polymorphism was 0.829 for the G allele and 0.171 for the A allele and allele frequencies of C1818T polymorphism were 0.804 for the C allele and 0.196 for the T allele, both of which were in compliance with Hardy-Weinberg equilibrium and the two polymorphisms were in linkage disequilibrium (D'=0.43, p<0.01). Mean systolic blood pressure was significantly higher in A allele carriers of G395A polymorphism compared with non-carriers, and the significance was persistent even after adjustment for age and BMI. Mean fasting plasma glucose was significantly higher in T allele carriers of C1818T polymorphism compared with non-carriers, and the significance was persistent even after adjustment for age and BMI. Subjects without any minor allele from either single nucleotide polymorphisms (SNP) had significantly lower mean values for systolic, diastolic blood pressure and fasting plasma glucose levels compared with subjects with both minor allele from either SNP.

CONCLUSIONS

We observed that KLOTHO G395A polymorphism was associated with blood pressure and KLOTHO C1818T polymorphism was associated with glucose metabolism in Korean women. Further studies are needed to clarify this relationship.

Flow analysis of metals in a municipal solid waste management system

This study aimed to identify the metal flow in a municipal solid waste (MSW) management system. Outputs of a resource recovery facility, refuse derived fuel (RDF) production facility, carbonization facility, plastics liquefaction facility, composting facility, and bio-gasification facility were analyzed for metal content and leaching concentration. In terms of metal content, bulky and incombustible waste had the highest values. Char from a carbonization facility, which treats household waste, had a higher metal content than MSW incinerator bottom ash. A leaching test revealed that Cd and Pb in char and Pb in RDF production residue exceeded the Japanese regulatory criteria for landfilling, so special attention should be paid to final disposal of these substances. By multiplying metal content and the generation rate of outputs, the metal content of input waste to each facility was estimated. For most metals except Cr, the total contribution ratio of paper/textile/plastics, bulky waste, and incombustible waste was over 80%. Approximately 30% of Cr originated from plastic packaging. Finally, several MSW management scenarios showed that most metals are transferred to landfills and the leaching potential of metals to the environment is quite small.

Behavior of metals in ash melting and gasification-melting of municipal solid waste (MSW)

In this study, metal behavior in ash-melting and municipal solid waste (MSW) gasification-melting facilities were investigated. Eight ash-melting and three MSW gasification-melting facilities with a variety of melting processes and feedstocks were selected. From each facility, melting furnace fly ash (MFA) and molten slag were sampled, and feedstock of the ash-melting processes was also taken. For the ash melting process, the generation rate of MFA was well correlated with the ratio of incineration fly ash (IFA) in feedstock, and this was because MFA was formed mostly by mass transfer from IFA and a limited amount from bottom ash (BA). Distribution ratios of metal elements to MFA were generally determined by volatility of the metal element, but chlorine content in feedstock had a significant effect on Cu and a marginal effect on Pb. Distribution ratio of Zn to MFA was influenced by the oxidizing atmosphere in the furnace. High MFA generation and distribution ratio of non-volatile metals to MFA in gasification-melting facilities was probably caused by carry-over of fine particles to the air pollution control system due to large gas volume. Finally, dilution effect was shown to have a significant effect on metal concentration in MFA.

Metal distribution in incineration residues of municipal solid waste (MSW) in Japan

This study aimed to identify distribution of metals and the influential factors on metal concentrations in incineration residues. Bottom ash and fly ash were sampled from 19 stoker and seven fluidized bed incinerators, which were selected to have a variety of furnace capacity, furnace temperature, and input waste. In the results, shredded bulky waste in input waste increased the concentration of some metals, such as Cd and Pb, and the effect was confirmed by analysis of shredded bulky waste. During MSW incineration, lithophilic metals such as Fe, Cu, Cr, and Al remained mainly in the bottom ash while Cd volatilized from the furnace and condensed to the fly ash. About two thirds of Pb and Zn was found in the bottom ash despite their high volatility. Finally, based on the results obtained in this study, the amount of metal in incineration residues of MSW was calculated and the loss of metal was estimated in terms of mass and money. A considerable amount of metal was found to be lost as waste material by landfilling of incineration residues.

Material and heavy metal balance in a recycling facility for home electrical appliances

Collection and recycling of home electrical appliances was started in Japan in 2001 under a new recycling law. The law is aimed at promoting material recycling and at reducing the amount of waste to be landfilled. End of life products are processed by manual disassembly, shredding, and separation in 38 recycling facilities. The authors conducted a questionnaire survey and interviewed at some facilities to obtain information on process flow and material balance. By using the detailed records offered by one facility and by estimating the composition of recovered components, the material balance in the facilities was determined for four typical recycling processes. The heavy metal content of the recovered components was analyzed, then metal flow in the process was determined for each scenario. As a result, it was concluded that emissions to the environment of most heavy metals have been substantially reduced by the new recycling system, while a modest improvement in the rate of material recovery has been achieved.

The green tea polyphenol (-)-epigallocatechin gallate attenuates beta-amyloid-induced neurotoxicity in cultured hippocampal neurons

Previous evidence has indicated that the neuronal toxicity of amyloid beta (betaA) protein is mediated through oxygen free radicals and can be attenuated by antioxidants and free radical scavengers. Recent studies have shown that green tea polyphenols reduced free radical-induced lipid peroxidation. The purpose of this study was to investigate whether (-)-epigallocatechin gallate (EGCG) would prevent or reduce the death of cultured hippocampal neuronal cells exposed to betaA because EGCG has a potent antioxidant property as a green tea polyphenol. Following exposure of the hippocampal neuronal cells to betaA for 48 hours, a marked hippocampal neuronal injuries and increases in malondialdehyde (MDA) level and caspase activity were observed. Co-treatment of cells with EGCG to betaA exposure elevated the cell survival and decreased the levels of MDA and caspase activity. Proapoptotic (p53 and Bax), Bcl-XL and cyclooxygenase (COX) proteins have been implicated in betaA-induced neuronal death. However, in this study the protective effects of EGCG seem to be independent of the regulation of p53, Bax, Bcl-XL and COX proteins. Taken together, the results suggest that EGCG has protective effects against betaA-induced neuronal apoptosis through scavenging reactive oxygen species, which may be beneficial for the prevention of Alzheimer's disease.

Photoreaction of 2-halo-N-pyridinylbenzamide: intramolecular cyclization mechanism of phenyl radical assisted with n-complexation of chlorine radical

The photochemical behavior of 2-halo-N-pyridinylbenzamide (1-4 in Chart 1) was studied. The photoreaction of 2-chloro-N-pyridinylbenzamides 1a, 2a, 3a, and 4 afforded photocyclized products, benzo[c]naphthyridinones (6-9 and 16), in high yield, whereas the bromo analogues 1b, 2b, and 3b produced extensively photoreduced products, N-pyridinylbenzamides (1c, 10, and 11), with minor photocyclized product. Since the photocyclization reaction of 2-chloro-N-pyridinylbenzamide is retarded by the presence of oxygen and sensitized by the presence of a triplet sensitizer, acetone or acetophenone, a triplet state of the chloro analogue is involved in the reaction. Since several radical intermediates, particularly n-complexes of chlorine radical, are identified in the laser flash photolysis of 2-chloro-N-pyridinylbenzamide, an intramolecular cyclization mechanism of phenyl radical assisted with n-complexation of chlorine radical for the cyclization reaction is proposed: the triplet state (78 kcal/mol) of the chloro analogue (1a), which is populated by the excitation of 1a undergoes a homolytic cleavage of the C-Cl bond to give phenyl and chlorine radicals; while chlorine radical holds the neighbor pyridinyl ring with its n-complexation, the intramolecular arylation of the phenyl radical with the pyridinyl ring proceeds to produce a conjugated 2,3-dihydropyridinyl radical and then the conjugated radical aromatizes to afford a cyclized product, benzo[c]naphthyridinone by ejecting a hydrogen. The photoreduction product can be formed by hydrogen atom abstraction of the phenyl sigma radical from the environment.

Solid-phase extraction and liquid chromatographic quantitation of quinfamide in biological samples

This paper describes a high-performance liquid chromatographic method for the assay of quinfamide and its main metabolite, 1-(dichloroacetyl)-1,2,3,4,-tetrahydro-6-quinolinol, in plasma, urine and feces. It requires 1 ml of biological fluid, an extraction using Sep-Pack cartridges and acetonitrile for drug elution. Analysis was performed on a CN column (5 microm) using water-acetonitrile-methanol (40:50:10) as a mobile phase at 269 nm. Results showed that the assay was linear in the range between 0.08 and 2.0 microg/ml. The limit of quantitation was 0.08 microg/ml. Maximum assay coefficient of variation was 14%. Recovery obtained in plasma, urine and feces ranged from 82% to 98%.

D-ribose-5-phosphate isomerase from spinach: heterologous overexpression, purification, characterization, and site-directed mutagenesis of the recombinant enzyme

A cDNA encoding spinach chloroplastic ribose-5-phosphate isomerase (RPI) was cloned and overexpressed in Escherichia coli, and a purification scheme for the recombinant enzyme was developed. The purified recombinant RPI is a homodimer of 25-kDa subunits and shows kinetic properties similar to those of the homodimeric enzyme isolated from spinach leaves (A. C. Rutner, 1970, Biochemistry 9, 178-184). Phosphate, used as a buffer in previous studies, is a competitive inhibitor of RPI with a K(i) of 7.9 mM. D-Arabinose 5-phosphate is an effective inhibitor, while D-xylulose-5 phosphate is not, indicating that the configuration at carbon-3 contributes to substrate recognition. Although D-arabinose 5-phosphate binds to RPI, it is not isomerized, demonstrating that the configuration at carbon-2 is crucial for catalysis. Alignment of RPI sequences from diverse sources showed that only 11 charged amino acid residues of the 236-residue subunit are conserved. The possible function of four of these residues was examined by site-directed mutagenesis. D87A, K100A, and D90A mutants show greatly diminished k(cat) values (0. 0012, 0.074, and 0.38% of the wild type, respectively), while E91A retains substantial activity. Only insignificant or moderate changes in K(m) of D-ribose 5-phosphate are observed for D87A, K100A, and D90A, indicating a direct or indirect catalytic role of the targeted residues.

Spontaneous conversion of L-dehydroascorbic acid to L-ascorbic acid and L-erythroascorbic acid

Dehydroascorbic acid, an oxidation product of ascorbic acid (vitamin C), spontaneously decomposed at neutral and higher pH levels to form three products that could be quantitated by HPLC-electrochemical analysis. One of the products was ascorbic acid, suggesting that dehydroascorbic acid was reduced to ascorbic acid without adding an exogenous reductant. The major newly produced compound was almost identical to ascorbic acid by UV spectroscopy, which therefore potentially interfered in the study of ascorbic acid metabolism. The ascorbic acid-like compound was isolated by reversed-phase HPLC and identified as L-erythroascorbic acid by mass spectrometry. Fe(II) and Cu(I) increased, whereas desferrioxamine, a potent iron chelator, inhibited L-erythroascorbic acid production. Phosphate, used as buffer, and cyanide greatly enhanced dehydroascorbic acid conversion to L-erythroascorbic acid. The identification of L-erythroascorbic acid and its quantitation by an electrochemical method provides a useful tool for future study of dehydroascorbic acid metabolism.

Ascorbic acid is a stimulatory cofactor for mitochondrial glycerol-3-phosphate dehydrogenase

Mitochondrial glycerol 3-phosphate dehydrogenase (mGPDH) from control and scorbutic guinea pig brain, liver and skeletal muscle and from normal rat liver was stimulated several fold by l-ascorbic acid (AA). The amount of AA that gave half-maximal stimulation of guinea pig brain mGPDH was 7.1 microM. At concentrations of AA higher than 500 microM, mGPDH activity decreased to nearly the same activity as in the absence of AA. D-Ascorbic acid, erythorbic acid, was equally potent in the activation of washed mitochondrial mGPDH activity. The AA activation of mGPDH was completely inhibited by 50 microM EGTA, but could be fully restored by the sequential addition of 100 microM Ca2+. The AA activation of mGPDH was likewise completely inhibited by iron specific chelators, bathophenanthrolinedisulfonic acid, desferrioxamine, and 1,10-phenanthroline, but the activation could not be restored by the addition of excess Ca2+. In the absence of AA, mGPDH activity was not inhibited by either EGTA or the iron chelators and Ca2+ addition had no effect on the activity. The iron-sulfur protein, succinic dehydrogenase (complex II), was not significantly different in brain mitochondria from control or scorbutic guinea pigs, and was not activated by the subsequent addition of AA. In the presence of AA, succinic dehydrogenase activity was not affected by either bathophenanthrolinedisulfonic acid or EGTA. The results suggest that mGPDH is a probable site of action of AA in the related glucose-coupled insulin release from pancreatic islets.

S-glutathiolated hepatocyte proteins and insulin disulfides as substrates for reduction by glutaredoxin, thioredoxin, protein disulfide isomerase, and glutathione

The disulfide-reducing activities of glutaredoxin, thioredoxin, protein disulfide isomerase, glutathione, and cysteine were directly compared with a mixture of hepatocyte 35S-glutathiolated proteins as the substrate. Dethiolation of individual 35S-labeled protein bands from the mixture of hepatocyte proteins was analyzed by SDS-PAGE. All of the 35S-labeled protein bands could be completely dethiolated by glutaredoxin, thioredoxin, protein disulfide isomerase, glutathione, or cysteine. On a molar basis glutaredoxin was over 10 times more effective than either thioredoxin or protein disulfide isomerase. Dethiolation rates of individual proteins varied in minor ways. For example, glutaredoxin dethiolated the 15-, 30-, and 48-kDa protein bands 3 to 4 times faster than the 27-, 28-, and 77-kDa bands. Glutaredoxins from pig liver or from bovine heart had the same specificity and similar activity. The rate of dethiolation by glutathione alone was low compared to the glutaredoxin-catalyzed process, but all 35S-labeled protein bands could be reduced by glutathione, cysteine, or dithiothreitol. Glutathione was clearly more effective than cysteine when these two thiols were compared on the basis of the concentration of thiolate anion available at neutral pH. Therefore, glutathione is a more specific reductant of S-glutathiolated proteins than is cysteine but it is much less effective than glutaredoxin. Since glutaredoxin activity in cells is 10 times higher than the concentration used in these experiments, ample activity is available to account for substantial rates of dethiolation in vivo. Thioredoxin is quite inefficient as a reductant of S-glutathiolated proteins, but it was reasoned that it might first reduce glutaredoxin, which then could reduce the S-glutathiolated protein. A combination of thioredoxin and glutaredoxin was effective. It is proposed that glutaredoxin is the principal agent responsible for protein dethiolation in vivo. The effectiveness of glutaredoxin, thioredoxin, and protein disulfide isomerase as reductants for protein disulfide bonds was examined with insulin as the substrate. Protein disulfide isomerase was very effective and thioredoxin was nearly as effective. Human thioredoxin was similar to Escherichia coli thioredoxin in reactivity and specificity. Glutaredoxin did not facilitate insulin reduction at equal concentrations. Thus, protein disulfide isomerase and thioredoxin are more effective than glutaredoxin as reductants of insulin protein disulfides. The apparent reduction potential of pig liver glutaredoxin (-0.159 +/- 0.004 V) was determined by measuring the amount of reduced glutaredoxin in equilibrium with mixtures of glutathione and glutathione disulfide. Glutaredoxin was a weaker reductant than E. coli thioredoxin (-0.260 V) and was similar to protein disulfide isomerase (-0.11 to -0.19 V). The role of these proteins as disulfide reductants is not determined solely by thermodynamic considerations. A glutathione binding site at the dithiol region of glutaredoxin may be of primary importance for its function in protein dethiolation, while a different specific peptide binding site in thioredoxin may be more suited to certain protein disulfide structures.

Ascorbic acid is essential for the release of insulin from scorbutic guinea pig pancreatic islets

Pancreatic islets from young normal and scorbutic male guinea pigs were examined for their ability to release insulin when stimulated with elevated D-glucose. Islets from normal guinea pigs released insulin in a D-glucose-dependent manner showing a rapid initial secretion phase and three secondary secretion waves during a 120-min period. Islets from scorbutic guinea pigs failed to release insulin during the immediate period, and only delayed and decreased responses were observed over the 40-60 min after D-glucose elevation. Insulin release from scorbutic islets was greatly elevated if 5 mM L-ascorbic acid 2-phosphate was supplemented in the perifusion medium during the last 60 min of perifusion. When 5 mM L-ascorbic acid 2-phosphate was added to the perifusion medium concurrently with elevation of medium D-glucose, islets from scorbutic guinea pigs released insulin as rapidly as control guinea pig islets and to a somewhat greater extent. L-Ascorbic acid 2-phosphate without elevated D-glucose had no effect on insulin release by islets from normal or scorbutic guinea pigs. The pancreas from scorbutic guinea pigs contained 2.4 times more insulin than that from control guinea pigs, suggesting that the decreased insulin release from the scorbutic islets was not due to decreased insulin synthesis but due to abnormal insulin secretion.

The relationships of motor function, education, age and cognitive function to the physical activities of daily living

The physical activities of daily living are a final outcome of many functions and dependent on many factors. This study was aimed at exploring the relationships of motor function, dementia, education, age, and cognitive function to the physical activities of daily living in 67 elderly people residing in an institution in Taegu, Korea. Their mean ( +/- SD) age was 75.6 +/- 8.1 and 24 (35.8%) were men. Twenty-eight (41.8%) were classified as having definite cognitive impairment, 17 (25.4%) as having questionable impairment, and 22 (32.8%) as having no impairment by the Korean version of the mini-mental state examination. Of the aforementioned 5 variables, the Motoricity Index could account for 42% of the Barthel Activities of Daily Living variance. If the modified Blessed Dementia Rating Scale was included in the multiple regression, the accountable portion of the Activities variance increased by 4% only. Using the 2 variables, regression equation, y = 0.248 x chi 1-0.359 x chi 2-6.250 (y: Barthel Activities of Daily Living score, chi 1: Motoricity Index score, chi 2: modified Blessed Dementia Rating Scale score) could be produced. Conclusively, the physical activities of daily living of elderly people could be related mainly with motor function of the limbs and severity of dementia.

Multiple binding sites involved in the effect of choline esters on decarbamoylation of monomethylcarbamoyl- or dimethylcarbamoly-acetylcholinesterase

Multiple binding sites for inhibitory choline esters in spontaneous decarbamoylation of dimethylcarbamoyl-acetylcholinesterase (AChE) were suggested from a wide range of IC50 values, in contrast with a limited range of AC50 values (concentration giving 50% of maximal activation) at a peripheral activatory site. Association of choline esters containing a long acyl chain (C7-C12) with the hydrophobic zone in the active site could be deduced from a linear relationship between the size of the acyl group and the inhibitory potency in either spontaneous decarbamoylation or acetylthiocholine hydrolysis. Direct support for laurylcholine binding to the active site might come from the competitive inhibition (Ki 33 microM) of choline-catalysed decarbamoylation by laurylcholine. Moreover, its inhibitory action was greater for monomethylcarbamoyl-AChE than for dimethylcarbamoyl-AChE, where there is a greater steric hindrance at the active centre. In further support, the inhibition of pentanoylthiocholine-induced decarbamoylation by laurylcholine was suggested to be due to laurylcholine binding to a central site rather than a peripheral site, similar to the inhibition of spontaneous decarbamoylation by laurylcholine. Supportive data for acetylcholine binding to the active site are provided by the results that acetylcholine is a competitive inhibitor (Ki 7.6 mM) of choline-catalysed decarbamoylation, and its inhibitory action was greater for monomethylcarbamoyl-AChE than for dimethylcarbamoyl-AChE. Meanwhile, choline esters with an acyl group of an intermediate size (C4-C6), more subject to steric exclusion at the active centre, and less associable with the hydrophobic zone, appear to bind preferentially to a peripheral activity site. Thus the multiple effects of choline esters may be governed by hydrophobicity and/or a steric effect exerted by the acyl moiety at the binding sites.

Dementia among the elderly in a rural Korean community

The age-specific prevalence of dementia, its sex difference, and the relative prevalence of important types of dementia were studied in the elderly people in a Korean rural community. A two-stage approach was employed, involving screening and clinical assessment. The prevalence among individuals aged 65 and over was found to be 10.8%, with rates of 7.2% in men and 14.5% in women. The dementia was of the Alzheimer type in 60.0% of cases, multi-infarct dementia in 12.0%, mixed dementia of Alzheimer type and multi-infarct in 10.7%, alcoholic dementia in 8.0%, and others and unclassifiable in 9.3%. The prevalence of dementia of the Alzheimer type was significantly higher in women and rapidly increased with age in both sexes. The prevalence of multi-infarct dementia was not related to sex or age. Alcoholic dementia was identified only in men. These findings indicate that the prevalence of dementia in rural Korea is similar to that reported in Western countries and that the prevalence of dementia of the Alzheimer type in rural Korea is greater than that of multi-infarct dementia.

Potentiation effect of choline esters on choline-catalysed decarbamoylation of dimethylcarbamoyl-acetylcholinesterase

The choline esters potentiated the choline-catalysed decarbamoylation of dimethylcarbamoyl-acetylcholinesterase in proportion to the length of acyl group, although esters containing an acyl chain longer than the hexanoyl group exhibited a corresponding decrease in the potentiation. In structural requirement analysis it was found that both the quaternary ammonium moiety and the ester bond were important for the effective acceleration of choline-catalysed decarbamoylation. In general, the respective thiocholine ester was found to be more effective than the corresponding choline ester. Whereas the binding affinity (Ka) of choline in the decarbamoylation was not significantly altered, the maximum decarbamoylation rate (kr(max.)) of choline was greatly enhanced in the presence of choline esters or thiocholine esters. Along with the above observation, the isotope solvent effect, the effect of ionic strength and the antagonism studies demonstrate that the choline esters or thiocholine esters may interact with one of peripheral anionic sites, and thereby make the choline-catalysed decarbamoylation more favourable.

Identification of an abundant S-thiolated rat liver protein as carbonic anhydrase III; characterization of S-thiolation and dethiolation reactions

An S-thiolated 30-kDa protein has been purified from rat liver by two steps of ion-exchange chromatography. This monomeric protein has two "reactive" sulfhydryls that can be S-thiolated by glutathione (form a mixed disulfide with glutathione) in intact liver. The protein has been identified as carbonic anhydrase III by sequence analysis of tryptic peptides from the pure protein. The two "reactive" sulfhydryls on this protein can produce three different S-thiolated forms of the protein that can be separated by isoelectric focusing. Using this technique it was possible to study the S-thiolation and dethiolation reactions of the pure protein. The reduced form of this protein was S-thiolated both by thiol-disulfide exchange with glutathione disulfide and by oxyradical-initiated S-thiolation with reduced glutathione. The S-thiolation rate of this 30-kDa protein was somewhat slower than that of glycogen phosphorylase b by both S-thiolation mechanisms. The S-thiolated form of this protein was poorly dethiolated (i.e., reduced) by glutathione, cysteine, cysteamine, or coenzyme A alone. Enzymatic catalysis by two different enzymes (glutaredoxin and thioredoxin-like) greatly enhanced the dethiolation rate. These experiments suggest that carbonic anhydrase III is a major participant in the liver response to oxidative stress, and that the protein may be S-thiolated by two different non-enzymatic mechanisms and dethiolated by enzymatic reactions in intact cells. Thus, the S-thiolation/dethiolation of carbonic anhydrase III resembles glycogen phosphorylase and not creatine kinase.

Soybean lipoxygenase-catalyzed formation of lipoxin A and lipoxin B isomers from arachidonic acid via 5,15-dihydroperoxyeicosatetraenoic acid

Soybean lipoxygenase converted arachidonic acid to a group of polar products (lambda max, 300-301 nm), which were increasingly formed during the continued incubation at 20 degrees C after the initial incubation (2 hrs, at 4 degrees C). These products were identified as lipoxin A and B isomers, based on the chromatographic and spectrometric analyses. In further chromatographic analyses, the lipoxin A and B isomers were separated into at least three isomers, respectively. The exposure of 5,15-dihydroperoxyeicosatetraenoic acid to the soybean lipoxygenase produced the identical product profile of chromatography, substantiating the intermediacy of 5,15-dihydroperoxyeicosatetraenoic acid in the soybean lipoxygenase-catalyzed formation of lipoxins. Based on these results, it is proposed that the conversion of arachidonic acid into lipoxins by soybean lipoxygenase may bear a mechanistic resemblance to the formation of lipoxins in the human leukocytes.