Measurement of Plasma Glucagon Levels Using Mass Spectrometry in Patients with Type 2 Diabetes on Maintenance Hemodialysis

BACKGROUND

Recently, attention has been focused on the effect of glucagon on blood glucose variability. The dynamics of glucagon have attracted attention as a new target in the treatment of diabetes patients. However, the dynamics of glucagon in hemodialysis (HD) patients with type 2 diabetes mellitus (T2DM) remain unclear.

OBJECTIVES

The aim of this study was to assess the dynamics of glucagon in HD patients with T2DM.

MATERIALS AND METHODS

We measured plasma glucagon in HD patients with T2DM by liquid chromatography-high-resolution mass spectrometry (LC-HRMS), sandwich enzyme-linked immunosorbent assay (ELISA), and radioimmunoassay (RIA). The glucagon levels measured by each method were compared. We used the glucagon levels determined by our developed LC-HRMS method as the standard in this study.

RESULTS

Plasma glucagon levels measured by LC-HRMS before HD were significantly higher than those measured after HD. Plasma glucagon levels measured using sandwich ELISA had a significantly higher correlation with those measured using LC-HRMS compared with RIA.

CONCLUSIONS

This was the first study to assess glucagon levels in HD patients with T2DM using LC-HRMS, which is considered a highly accurate method. Sandwich ELISA was shown to measure glucagon levels accurately as well.

Pseudo-hyperglucagonemia was observed in pancreatectomized patients when measured by glucagon sandwich enzyme-linked immunosorbent assay

Glucagon is detected in plasma even after total pancreatectomy, and it is debated whether this glucagon is derived from the gastrointestinal tract. Here, we applied sandwich enzyme-linked immunosorbent assay (ELISA) and liquid chromatography-high-resolution mass spectrometry to measure plasma glucagon levels in one patient after partial pancreatectomy (one-seventh of the pancreas remaining) and three patients after total pancreatectomy. Sandwich ELISA detected higher glucagon levels in pancreatectomy patients than in healthy individuals. In contrast, liquid chromatography-high-resolution mass spectrometry showed that plasma glucagon levels in pancreatectomy patients were below the lower limit of quantification. Plasma glucagon measured by sandwich ELISA showed a striking correlation with plasma glicentin, suggesting cross-reaction with this gastrointestinal glucagon-related peptide. These results indicated that pancreatectomized patients falsely showed pseudo-hyperglucagonemia when measured by glucagon sandwich ELISA.

Effects of anagliptin on plasma glucagon levels and gastric emptying in patients with type 2 diabetes: An exploratory randomized controlled trial versus metformin

AIMS

Glucagon has an important role in glucose homeostasis. Recently, a new plasma glucagon assay based on liquid chromatography-high resolution mass spectrometry was developed. We evaluated the influence of a dipeptidyl peptidase-4 inhibitor (anagliptin) on plasma glucagon levels in Japanese patients with type 2 diabetes by using this new assay.

METHODS

Twenty-four patients with type 2 diabetes were enrolled in a prospective, single-center, randomized, open-label study and were randomly allocated to 4 weeks of treatment with metformin (1000 mg/day) or anagliptin (200 mg/day). A liquid test meal labeled with sodium [¹³C] acetate was ingested before and after the treatment period. Samples of blood and expired air were collected over 3 h. Plasma levels of glucose, glucagon, C-peptide, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) were measured, and gastric emptying was also evaluated.

RESULTS

Twenty-two patients completed the study (metformin group: n = 10; anagliptin group: n = 12). Glycemic control showed similar improvement in both groups. In the anagliptin group, there was a slight decrease of the incremental area under the plasma concentration versus time curve for glucagon after the test meal (P = 0.048). In addition, the plasma level of active GLP-1 and GIP was increased, and plasma C-peptide was also increased versus baseline. Neither anagliptin nor metformin delayed gastric emptying.

CONCLUSIONS

In patients with type 2 diabetes maintained endogenous insulin secretion, anagliptin increased the plasma level of active GLP-1 and GIP in association with a slight stimulation of insulin secretion and slight inhibition of glucagon secretion, but did not delay gastric emptying. Clinical Trial Registry: University hospital Medical Information Network UMIN000028293.

Postprandial Plasma Glucagon Kinetics in Type 2 Diabetes Mellitus: Comparison of Immunoassay and Mass Spectrometry

CONTEXT

Accurate glucagon level measurements are necessary for investigation of mechanisms for postprandial hyperglycemia in type 2 diabetes.

OBJECTIVE

To evaluate the accuracy of postprandial glucagon level measurements using a sandwich ELISA vs a recently established liquid chromatography-high resolution mass spectrometry (LC-HRMS) method in type 2 diabetes mellitus.

DESIGN AND PARTICIPANTS

Twenty patients with type 2 diabetes treated with insulin underwent a meal test before and after administration of the dipeptidyl peptidase-4 inhibitor anagliptin for 4 weeks. Blood samples were taken serially after the meal, and glucagon levels were measured using both ELISA and LC-HRMS. We compared the change from baseline to 4 weeks (Δ0-4W) using the area under the curve for plasma glucagon during the meal test [area under the curve (AUC)0-3h] measured using ELISA and LC-HRMS.

RESULTS

ELISA-based glucagon AUC0-3h was higher than LC-HRMS-based AUC0-3h at baseline and 4 weeks. However, differences in Δ0-4W-AUC0-3h measured using ELISA and LC-HRMS were not statistically significant. Additionally, Δ0-4W-AUC0-3h measured using ELISA and LC-HRMS were strongly correlated (r = 0.87, P < 0.001).

CONCLUSIONS

Plasma glucagon levels during a meal test in patients with type 2 diabetes measured using ELISA were consistently higher than those measured using LC-HRMS. However, given that the changes in glucagon levels measured using ELISA before and after dipeptidyl peptidase-4 inhibitor therapy were similar to those based on LC-HRMS, this ELISA seems to be useful for evaluating the effect of the drug interventions on postprandial glucagon levels.

A highly sensitive assay for xanthine oxidoreductase activity using a combination of [(13) C2 ,(15) N2 ]xanthine and liquid chromatography/triple quadrupole mass spectrometry

In this study, we developed a highly sensitive assay for xanthine oxidoreductase (XOR) activity utilizing a combination of [(13) C2 ,(15) N2 ]xanthine and liquid chromatography (LC)/triple quadrupole mass spectrometry (TQMS). In this assay, the amount of [(13) C2 ,(15) N2 ]uric acid (UA) produced by XOR was determined by using LC/TQMS. For this assay, we synthesized [(13) C2 ,(15) N2 ]xanthine as a substrate, [(13) C2 ,(15) N2 ]UA as an analytical standard, and [(13) C3 ,(15) N3 ]UA as an internal standard. The [(13) C2 ,(15) N2 ]UA calibration curve obtained using LC/TQMS under the selected reaction monitoring mode was evaluated, and the results indicated good linearity (R(2)  = 0.998, weighting of 1/x(2) ) in the range of 20 to 4000 nM. As a model reaction of less active samples, the XOR activity of serial-diluted mouse plasma was measured. Thereby, the XOR activity of the 1024-fold-diluted mouse plasma was 4.49 ± 0.44 pmol/100 μL/h (mean ± standard deviation, n = 3). This value is comparable to the predicted XOR activity value of healthy human plasma. Hence, this combination method may be used to obtain high-sensitivity measurements required for XOR activity analysis on various organs or human plasma.

Microbial degradation of physiologically active peptides by strain B-9

The reaction of some physiologically active peptides with bacterial strain B-9 has been investigated. Bradykinin, β-endorphin, and [Leu(5)]enkephalin were quickly degraded, with half-lives of <5 min. Somatostatin, substance P, and angiotensin I were degraded relatively smoothly, with half-lives of 10 min to 1 h, whereas oxytocin and insulin were slowly degraded, with half-lives of 1 and 4 days, respectively. Vasopressin was barely degraded, with a half-life of >7 days. Linearized vasopressin, prepared by the reductive cleavage of the disulfide bond followed by alkylation with iodoacetamide, was degraded significantly faster than intact vasopressin, with a half-life of 2.5 h. A loop formed by disulfide bond formation was regarded as one of the degradation-resistant factors. Hydrolysis of the peptides in this study took place through cleavage of various peptide bonds, and the strain B-9 may bear similarities to the neutral endopeptidase in terms of its broad selectivity.

Discovery, optimization, and pharmacological characterization of novel heteroaroylphenylureas antagonists of C-C chemokine ligand 2 function

Through the application of TRAP (target-related affinity profiling), we identified a novel class of heteroaroylphenylureas that inhibit human CCL2-induced chemotaxis of monocytes/macrophages both in vitro and in vivo. This inhibition was concentration-dependent and selective with regard to other chemokines. The compounds, however, did not antagonize the binding of (125)I-labeled CCL2 to the CCR2 receptor nor did they block CCR2-mediated signal transduction responses such as calcium mobilization. Optimization of early leads for potency and pharmacokinetic parameters resulted in the identification of 17, a potent inhibitor of chemotaxis (IC(50) = 80 nM) with excellent oral bioavailability in rats (F = 60%). Compound 17 reduced swelling and joint destruction in two rat models of rheumatoid arthritis and delayed disease onset and produced near complete resolution of symptoms in a mouse model of multiple sclerosis.

Toxicokinetics of bisphenol A in rats, monkeys and chimpanzees by the LC–MS/MS method

We examined the toxicokinetics of bisphenol A (BPA) in F344 rats, cynomolgus monkeys and chimpanzees. Serum BPA levels were quantified using the LC-MS/MS method. After oral administration at 10 mg/kg, the maximum concentration in the serum (C(max)) and the area under the serum concentration curve (AUC) of BPA in cynomolgus monkeys and chimpanzees were greater than in rats. After oral administration at 100 mg/kg, AUC during the first 4h (AUC(0-->4h)) in cynomolgus monkeys was greater than in rats. In rats, the serum BPA levels were increased again 6h or later after oral administration at each dose, which suggested the enterohepatic circulation of BPA in rats. After subcutaneous administration at 10 mg/kg, the AUCs were ranked in the following order: cynomolgus monkeys>chimpanzees>rats, and C(max) in cynomolgus monkeys was greater than in rats and chimpanzees. After subcutaneous administration at 100 mg/kg to cynomolgus monkeys and rats, both the C(max) and AUCs in cynomolgus monkeys were greater than in rats. In all species, the oral administration of BPA resulted in much lower C(max) and AUCs than subcutaneous administration at the corresponding doses, indicating the low bioavailability of oral administration. This result suggests that BPA undergoes an extensive first-pass metabolism in these animal species. AUCs of subcutaneous administration and the AUC (0-->4h) of oral administration in the two primates were greater than that in rats. Because the systemic clearance for BPA is assumed to be dependent on the hepatic blood flow-rate, the high AUCs in primates are considered to be due to the lower systemic clearance by a lower hepatic blood flow-rate in primates than in rats. In addition, the toxicokinetics of the metabolites of BPA were examined. After the oral administration of 10 mg/kg BPA, both C(max) and AUCs of BPA metabolites were ranked in the following order: cynomolgus monkeys>chimpanzees>rats, and the terminal elimination half-life (T(1/2)) in rats was greater than that in cynomolgus monkeys and chimpanzees, suggesting the enterohepatic circulation of BPA in rats. From these results, the systemic clearance of BPA in primates is considered to be close to that in humans due to the similarity of the hepatic blood flow-rate. Furthermore, the major elimination route of BPA metabolites in primates is assumed to be renal excretion, as in humans, because the enterohepatic circulation that was observed in rats was not observed. In conclusion, primates are thought to be served as a valuable surrogate model for the toxicokinetics of BPA in humans.

Non-steroidal anti-inflammatory drug, nabumetone, prevents indometacin-induced gastric damage via inhibition of neutrophil functions

Nabumetone is a non-steroidal anti-inflammatory drug (NSAID). It works as a prodrug and is extensively metabolized to an active metabolite, 6-methoxy-2-naphthylacetic acid (6MNA). It is well known that neutrophil infiltration and activation are critical in the pathogenesis of NSAID-induced gastric injury, and nabumetone shows less incidence of gastrointestinal irritancy. We examined the effects of nabumetone on neutrophil activation and on indometacin-induced gastric damage. In the indometacin-induced gastric mucosal injury, rats were treated with indometacin and then nabumetone or 6MNA was orally administered. Nabumetone prevented gastric damage accompanied by the reduction of neutrophil infiltration into gastric mucosa, but such an effect was not observed with 6MNA. Nabumetone reduced the formyl methionyl leucyl phenylalanine (fMLP)-induced respiratory burst of human neutrophils to 30% of the control level in-vitro, but 6MNA did not. In addition, nabumetone prevented the fMLP-induced migration of neutrophils. Nabumetone did not inhibit O2- generation in the xanthine-xanthine oxidase system. These results suggest that nabumetone prevents gastric damage induced by the active metabolite, 6MNA, via the suppression of neutrophil activation in gastric mucosa.

Constitutive c-fos expression in osteoblastic MC3T3-E1 cells stimulates osteoclast maturation and osteoclastic bone resorption

The effect of culture supernatants of c-fos-transfected MC3T3-E1 osteoblastic cells on osteoclastic bone resorption was studied. Human c-fos cDNA was integrated in the expression vector pH8, and the cells were transfected using the calcium phosphate precipitation technique. Osteoclastic bone resorption was quantified by the pit formation assay, and the osteoclast maturation from precursor was assessed by the generation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells (MNC). The culture supernatants of MC3T3-E1 transfectants constitutively expressing c-fos gene enhanced osteoclast-like MNC formation from haematopoietic blast cells compared with those of control transfectants (P < 0.01). The culture supernatants also promoted osteoclastic bone resorption: the pit number, 118.7 +/- 38.5, was significantly higher than 19.0 +/- 10.1 of the control (P < 0.05). The absorption area, 12,394 +/- 3145 mm2, was significantly larger than 1646 +/- 314 mm2 of the control (P < 0.05). The culture supernatants also promoted bone resorption by purified chick osteoclasts (P < 0.05). The results show that constitutive expression of c-fos gene in osteoblastic MC3T3-E1 cells stimulates osteoclast maturation and osteoclastic bone resorption by releasing humoral mediator(s).

[Clinical study of anti-phospholipid antibody in patients with sarcoidosis]

Serum antibodies against five types of phospholipids were measured by enzyme-linked immunosorbent assay (ELISA) in 55 patients with sarcoidosis. In 21 cases (38%), either IgG antibodies or IgM antibodies were detected. These antibodies were thought to mainly be infective type. This positive rate was significantly higher than that (7%) of the control group (70 cases) (p < 0.01). As to the immunoglobulin classes, 5 cases had IgG antibodies only, 11 cases had IgM antibodies only, and 5 cases had both IgG and IgM antibodies. No correlation was observed between the occurrence of anti-phospholipid antibodies (APL-Ab) and disease activity of sarcoidosis. Significant correlations were found between the occurrence of APL-Ab and skin lesions, many extrathoracic organ lesions and the persistence of abnormal chest X-ray findings for over 2 years and 5 years. From these data, it is suggested that the presence of APL-Ab is associated with prolonged disease activity of sarcoidosis.

[Interleukin-2 receptor expression in pulmonary granulomatous diseases]

Interleukin-2 receptor expression (IL-2R) on monocytes and alveolar macrophages (AM) was determined in patients with sarcoidosis and pulmonary tuberculosis. In sarcoidosis and tuberculosis, IL-2R on monocytes was detectable, while it was undetectable in healthy controls. IL-2R on AM in sarcoidosis and tuberculosis was significantly increased as compared to healthy controls. IFN-gamma, which has been shown to be increased in sarcoidosis and tuberculosis as compared to healthy controls, induced IL-2R on monocytes in healthy controls, suggesting that IFN-gamma is at least in part responsible for the induction or enhancement of IL-2R on monocytes or AM in sarcoidosis and tuberculosis. Phorbol myristate acetate which is known to be protein kinase C (PKC) activator induced IL-2R on monocytes, and PKC inhibitor, H7, inhibited IFN-gamma-induced IL-2R on monocytes in healthy controls. Calcium ionophore, A23187, induced IL-2R on monocytes and calmodulin antagonist, W7, inhibited IFN-gamma-induced IL-2R on monocytes. Based on these results, it seems that not only the PKC pathway but also the calcium-calmodulin pathway is involved in IFN-gamma-induced IL-2R.

[Serum soluble IL-2 receptor level in patients with sarcoidosis]

Serum levels of soluble IL-2 receptors (sIL-2R) by an ELISA method in 28 patients with sarcoidosis and 16 healthy controls were studied, and the source of sIL-2R was further examined. sIL-2R in serum was significantly higher in sarcoidosis than in controls. In sarcoidosis sIL-2R in serum significantly correlated with serum ACE level, and was significantly higher in stage II or III patients than in stage O patients. sIL-2R in supernatants of cultured monocytes (Mo) and alveolar macrophages (AM) was significantly higher in sarcoidosis than in controls. sIL-2R in supernatants of cultured T lymphocytes obtained from peripheral blood or BALF was barely detectable in sarcoidosis, while it was undetectable in controls. Furthermore, sIL-2R in serum was significantly correlated with sIL-2R in supernatants of cultured Mo and AM. These results indicate that sIL-2R in serum is an useful index of the disease activity of sarcoidosis, and may be mainly derived from IL-2R on Mo and AM.

Antigen-presenting capacity in patients with sarcoidosis

Antigen-presenting capacity by monocytes and AMs was determined in 13 patients with sarcoidosis and nine healthy control subjects, using PPD as the antigen. The patients and healthy control subjects all had positive PPD skin tests. Monocytes from both the control subjects and the patients with sarcoidosis exhibited antigen-presenting capacity to autologous peripheral T-lymphocytes, without any significant difference between the two groups. The AMs from patients, but not control subjects, demonstrated antigen-presenting capacity to autologous peripheral T-lymphocytes. Antigen-presenting capacity by monocytes and AMs to lung T-lymphocytes was lower than to peripheral T-lymphocytes, but not significantly. Antigen-presenting capacity was not significantly different between patients with sarcoidosis who had positive and negative PPD skin tests. The mechanism of enhanced antigen-presenting capacity by AMs in sarcoidosis is uncertain at present, but no significant difference was observed in DR antigen expression on AMs between controls and patients with sarcoidosis, and the addition of exogenous IL-1 or IFN-gamma did not induce antigen-presenting capacity by AMs in controls, suggesting that neither increased DR antigen expression on AMs nor increased release of IL-1 or IFN-gamma from AMs is responsible. Thus, these results suggest that T-lymphocyte activation in sarcoidosis may in part be attributable to an enhanced antigen-presenting capacity by AMs.

[A case of miliary tuberculosis with prolonged high fever for more than 2 months under antituberculous therapy]

A 28 year-old male was admitted to our hospital with persistent cough and high fever. He was diagnosed to have miliary tuberculosis by the transbronchial lung biopsy specimen and tuberculous choroidal lesions in the ocular fundus. Antituberculosis therapy was immediately started. In spite of the fact that the bacilli were sensitive to the antituberculosis drugs used and he had no other complications, high fever persisted and lasted for more than 2 months. When tuberculosis is suspected, and antituberculosis treatment is tried to observe its clinical response, the presence of similar cases mentioned above should be taken into consideration.

[A case of pigeon breeder's disease]

A 73-year-old woman developed dry cough and exertional dyspnea. She had been breeding pigeons for thirty years. Her serum showed positive precipitin reaction against pigeon serum. Furthermore the lymphocyte stimulation test against pigeon serum was positive. An X-ray film of the chest showed diffuse ground glass infiltrate, fine nodular shadows and reticular shadows. Histopathology revealed diffuse interstitial infiltration with mononuclear cells and occasional giant cell formation as well as granuloma formation in the bronchiole. The symptoms subsided after admission. From these results, this case was diagnosed as pigeon breeder's disease. She had the subacute form probably because of her old age and smoking. It could be that exacerbation of pneumonitis was caused by cessation of smoking in an attempt to alleviate the symptoms. This is the fifth case reported in Japan.

[Antigen presentation in pulmonary tuberculosis]

Antigen presenting capacity (APCC) by monocytes (Mono) and alveolar macrophages (AM), using PPD as the antigen, was determined in 15 patients with pulmonary tuberculosis and 9 healthy controls who all showed positive PPD skin tests. Results were as follows: 1) Mono from both healthy controls and tuberculosis showed APCC to autologous peripheral T lymphocytes, and no significant difference was observed between the two groups. 2) AM from tuberculosis showed APCC to autologous peripheral T lymphocytes, however AM from healthy controls did not. 3) APCC by autologous Mono or AM to lung T-lymphocytes was lower than that to peripheral T-lymphocytes, but the difference was not significant. 4) In tuberculosis, APCC, observed before chemotherapy, was remarkably weakened during the first two months of therapy, and almost recovered to the previous level thereafter. 5) The mechanism which enhances APCC by AM in tuberculosis is uncertain. But neither increased DR antigen expression on AM nor release of IL-1 from AM suggested to be be responsible for the enhanced APCC in tuberculosis.