Free fatty acids increase androgen precursors in vivo

CONTEXT

There is considerable evidence that metabolic factors such as insulin resistance may induce hyperandrogenemia in polycystic ovary syndrome. However, other metabolic factors such as free fatty acids (FFAs) may also contribute to androgen excess.

OBJECTIVE

The objective was to study effects of FFAs on adrenal production of androgen precursors in vivo.

DESIGN AND PARTICIPANTS

We investigated eight healthy young men, because male individuals produce the androgen precursors dehydroepiandrosterone (DHEA), DHEA sulfate, and androstenedione predominantly in the adrenal gland. A randomized controlled crossover trial was performed.

INTERVENTION

After a 10-h overnight fast, 20% lipid/heparin or saline/heparin infusion was given at a rate of 1.5 ml/min. Four hours after start of lipid infusion, a euglycemic hyperinsulinemic clamp was performed.

MAIN OUTCOME MEASURES

DHEA, androstenedione, 17-OH-progesterone, testosterone, estrone, LH, FSH, ACTH, and cortisol were measured.

RESULTS

The adrenal androgen precursors DHEA and androstenedione showed a circadian decline during saline/heparin infusion (P < 0.05 vs. baseline, respectively), whereas no significant changes were observed during lipid/heparin infusion (P = not significant vs. baseline, respectively). Correspondingly, DHEA and androstenedione values were significantly elevated during lipid compared with saline infusion (P < 0.05, respectively), and areas under curve of both androgen precursors were significantly increased with lipid compared with saline infusion. Notably, all changes were detected before induction of insulin resistance.

CONCLUSIONS

This study demonstrates that FFAs increase production of androgen precursors in vivo in men. These data tentatively suggest that hyperandrogenemia in polycystic ovary syndrome may be induced, at least in part, by elevated FFAs.

Increase in serum resistin during weight loss in overweight subjects is related to lipid metabolism

OBJECTIVE

Human resistin has been stated to influence preadipocyte cell numbers and to stimulate adipocyte triglyceride lipolysis in vivo and in vitro. However, its role in human obesity remains unclear.

DESIGN

Cross-sectional study for comparisons of lean and obese subjects, and subsequent longitudinal 4-month weight loss intervention study in obese subjects.

SUBJECTS

Healthy subjects, lean (n=20, BMI<25) and overweight (n=43, BMI>or=25).

MEASUREMENTS

Serum resistin, body weight, body fat, waist-to-hip ratio, as well as markers of insulin resistance and lipid metabolism at baseline and after 4 months of intervention.

RESULTS

Serum resistin was positively correlated to HOMA-IR (partial r=0.288; P=0.055), serum fructosamines (partial r=0.280; P=0.062), serum NEFA (partial r=0.276; P=0.066) and negatively to age (partial r=-0.349; P=0.019) and serum apolipoprotein A-1 (partial r=-0.363; P=0.014). During the intervention, serum resistin increased significantly (P<0.001). The increase was inversely related to changes in waist-to-hip ratio (P=0.025) and positively to serum apolipoprotein B (P=0.011). In males only, the increase in resistin during weight loss was predicted by total serum cholesterol at baseline (r=0.703, P=0.007). No relation was observed between changes in resistin and changes in HOMA-IR.

CONCLUSION

The present study indicates an association between serum resistin and markers of abdominal fat distribution as well as the regulation of lipid metabolism. However, human resistin is unlikely to play an independent role in the regulation of glucose metabolism.

Effects of marked weight loss on plasma levels of adiponectin, markers of chronic subclinical inflammation and insulin resistance in morbidly obese women

OBJECTIVE

Obesity is linked to the insulin resistance syndrome (IRS), type 2 diabetes (T2D) and cardiovascular disease. Markers of chronic subclinical inflammation such as high-sensitive C-reactive protein (hs-CRP) and interleukin 6 (IL-6) are closely related to insulin resistance and obesity. Recent evidence suggests that adiponectin, a protein whose circulating levels are decreased in obesity, has anti-inflammatory properties, and also appears to enhance potently insulin action and therefore appears to function as a signal produced by adipose tissue that influences whole-body glucose metabolism.

SUBJECTS AND METHODS

We investigated the cross-sectional and longitudinal association of adiponectin with CRP and IL-6 in 41 morbidly obese women with different stages of glucose tolerance before and 17 months after significant weight loss induced by gastric surgery. Adiponectin was measured by RIA. CRP and IL-6 were determined by commercially available ELISA systems.

RESULTS

Weight loss induced a significant shift from T2D (preoperatively 34% vs postoperatively 2%) to impaired glucose tolerance (IGT) (37% preoperatively vs 30% postoperatively) and normal glucose tolerance (NGT) (29% preoperatively vs 68% postoperatively). Preoperatively adiponectin levels were negatively correlated with CRP (r=-0.59, P<0.0006), IL-6 (r=-0.42, P<0.02) and leukocytes (r=-0.41, P<0.007). After gastroplasty, adiponectin concentrations increased significantly (15.4+/-8.2 vs 19.8+/-6.2 microg/ml, P<0.005) associated with changes of weight and body mass index (r=-0.45, P<0.007; r=-0.35, P<0.04). Furthermore, preoperative CRP was significantly associated with changes in adiponectin even after adjustment for sex, age, preoperative body mass index (BMI) impaired glucose metabolism and changes in BMI and changes in BMI (standardized beta 0.61, P=0.005).

CONCLUSION

Levels of adiponectin, which are associated with markers of chronic subclinical inflammation, could be significantly increased after weight loss in morbidly obese patients. This increase was more pronounced in patients with NGT compared to those with T2D and IGT. Preoperative levels of CRP are predictive for changes of adiponectin after weight loss.

In vivo activity of 11beta-hydroxysteroid dehydrogenase type 1 and free fatty acid-induced insulin resistance

INTRODUCTION

Free fatty acids (FFAs) induce hepatic insulin resistance and enhance hepatic gluconeogenesis. Glucocorticoids (GCs) also stimulate hepatic gluconeogenesis. The aim of this study was to investigate whether the FFA-induced hepatic insulin resistance is mediated by increased activity of hepatic 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), accompanied by elevated hepatic cortisol levels.

METHODS

Following a 10-h overnight fast, six healthy male volunteers were investigated. A euglycaemic hyperinsulinaemic clamp was performed during lipid or saline infusion. To assess hepatic 11beta-HSD1 activity, plasma cortisol levels were measured after oral administration of cortisone acetate during lipid or saline infusion. In addition, 11beta-HSD activities were determined in vivo by calculating the urinary ratios of GC metabolites.

RESULTS

Lipid infusion increased FFAs (5.41 +/- 1.00 vs. 0.48 +/- 0.20 mmol/l; P < 0.005) and significantly increased insulin resistance [glucose infusion rate (GIR) 6.02 +/- 2.60 vs. 4.08 +/- 2.15 mg/kg/min; P < 0.005]. After lipid and saline infusions no changes in 11beta-HSD1 activity were found, neither by changes in cortisone acetate to cortisol conversion nor by differences in urinary free cortisol (UFF) or cortisone (UFE), 5beta-tetrahydrocortisol (THF), 5alpha-THF, cortisone (THE), UFF/UFE and (5alpha-THF + THF)/THE ratios.

CONCLUSIONS

We found no change in hepatic and whole-body 11beta-HSD1 activity during acute FFA-induced insulin resistance. Further studies are necessary to clarify whether 11beta-HSD1 in muscle and adipose tissue is influenced by FFAs and whether 11beta-HSD1 is involved in other conditions of insulin resistance.

Glucagon inhibits ghrelin secretion in humans

OBJECTIVE

It is well known that i.m. glucagon administration stimulates GH and cortisol release in humans, although the mechanisms are unclear. These effects are similar to those described for ghrelin on somatotroph and corticotroph function. The aim of the present study was to investigate the role of ghrelin in mediating the stimulatory effects of glucagon and to evaluate the effect of glucagon on ghrelin secretion.

DESIGN AND METHODS

We studied the endocrine and metabolic response to i.m. glucagon administration in 24 subjects (14 men, 10 women; age 19-65 years; body mass index, 25.3 +/- 1 kg/m(2)), who were shown to have an intact anterior pituitary function as evaluated before enclosure.

RESULTS

Serum ghrelin concentrations fell significantly at 30, 60, 120 and 180 min after glucagon administration (means +/- s.e.m.; baseline, 377.9 +/- 34.5 pg/ml; nadir, 294.6 +/- 28.3 pg/ml (60 min); P < 0.01). Conversely, i.m. glucagon elicited an increase in GH (baseline, 1.5 +/- 0.4 microg/l; peak, 14.2 +/- 2.7 microg/l (180 min); P < 0.01) and cortisol concentrations (baseline, 452.6 +/- 35.2 nmol/l; peak, 622.1 +/- 44 nmol/l (180 min); P < 0.01). The changes in ghrelin concentration at both 120 and 180 min were still significant after correction for glucose and insulin (P < 0.05).

CONCLUSIONS

We show that i.m. glucagon decreases ghrelin significantly. Therefore, the already known stimulatory effects of i.m. glucagon on cortisol and GH are not mediated by a change in ghrelin concentrations. The mechanisms underlying the ghrelin suppression after i.m. glucagon are unlikely to include glucose or insulin variations and need to be further elucidated.

A dietary pattern protective against type 2 diabetes in the European Prospective Investigation into Cancer and Nutrition (EPIC)--Potsdam Study cohort

AIMS/HYPOTHESIS

The aim of this study was to identify a dietary pattern associated with diabetes-related biomarkers and to investigate whether this pattern is associated with the incidence of type 2 diabetes.

METHODS

A nested case-control study of 192 cases of incident type 2 diabetes and 382 control subjects matched for sex and age was conducted. All subjects were participants in the population-based European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam Study. Dietary pattern score was derived using intake data on 48 food groups as exposure variables and the biomarkers HbA1c, HDL cholesterol, C-reactive protein and adiponectin as response variables in reduced rank regression. The association of the score with diabetes risk was estimated by conditional logistic regression analysis.

RESULTS

A high score for the identified dietary pattern was characterised by a high intake of fresh fruit and a low intake of high-caloric soft drinks, beer, red meat, poultry, processed meat, legumes and bread (excluding wholegrain bread). Subjects with high scores had high plasma concentrations of HDL cholesterol and adiponectin and low plasma concentrations of HbA1c and C-reactive protein. After multivariate adjustment, the odds ratios for type 2 diabetes across increasing quintiles of the dietary pattern score were 1.0, 0.59, 0.51, 0.26 and 0.27, respectively (p = 0.0006 for trend).

CONCLUSIONS/INTERPRETATION

A high score for the identified dietary pattern is associated with a more favourable biomarker profile and a substantially reduced incidence of type 2 diabetes.

Arabinoxylan-enriched meal increases serum ghrelin levels in healthy humans

Soluble fibre like arabinoxylan (AX) is thought to have beneficial effects on metabolism. In this study, we investigated the effect of a breakfast enriched in AX fibre on glucose, insulin and ghrelin values. AX-enriched and control breakfasts were served to fifteen young volunteers (nine female, six male). Glucose, insulin and ghrelin responses were measured after the meal. To avoid effects from differences in glucose metabolism, further analysis was restricted to those subjects with known normal glucose regulation (seven female, four male). The AX fibre-enriched breakfast did not significantly change glucose levels for two hours after breakfast, but decreased insulin levels in the entire cohort (p = 0.035). Glucose response was also not significantly different in subjects with normal glucose regulation (p = 0.367), and the insulin responses after an AX-enriched breakfast showed only a tendency towards lower values (p = 0.065). Nevertheless, plasma ghrelin two hours after AX-enriched breakfast was higher than after the control meal (396.1 +/- 36.4 pg/ml vs. 328.3 +/- 32.6 pg/ml, p < 0.001). In subjects with normal glucose regulation, the AX-enriched breakfast increased ghrelin levels without any significant difference in glucose or insulin response. This effect is therefore unlikely to be mediated by insulin, but the underlying mechanism remains to be elucidated.

Bedeutung von Biomarkern des metabolischen Syndroms bei Gewichtsreduktion

INTRODUCTION

Obesity is a risk factor for type 2 diabetes, hypertension, dyslipidemia and cardiovascular disease. We aimed to analyse the changes of parameters of the metabolic syndrome and to investigate which markers are useful in the prediction of a successful weight loss. Preliminary data of an ongoing study are presented.

METHODS

18 obese individuals (15 female, 3 male, mean age 50.9 years, mean BMI 36.1) finished a 12 month weight loss program. This weight loss program was based on a hypocaloric diet (50 % carbohydrates, 30 % fat, 20 % protein) and at least 60 min physical activity per week. At baseline, 6 months and 12 months physical examination, indirect calorimetry, bioimpedance analysis were performed and blood was taken for routine laboratory. An oral glucose tolerance test and an euglycemic hyperinsulinemic clamp (n = 13) were carried out at baseline and after 6 months.

RESULTS

There was a decrease of the BMI (+/- SEM) from 36.1 +/- 1.3 to 33.4 +/- 1.2 after 6 months and 32.8 +/- 1.3 after 12 months. Waist circumference (-8.8 cm), fasting blood glucose (98.0 to 91.2 and 92.5 mg/dl) and HDL cholesterol (47.2 to 64.6 mg/dl after 12 months) improved significantly. Other parameters of the metabolic syndrome (blood pressure, lipids, insulin resistance) and adiponectin improved slightly, but changes failed to be significant. In a linear regression analysis age, insulin resistance (M-value) and adiponectin at baseline were significant and independent predictors of a successful weight loss.

CONCLUSION

In conclusion, most parameters of the metabolic syndrome improved after successful weight reduction, although changes of most parameters were modest and did not reach statistical significance.

Post-prandial decrease of human plasma ghrelin in the absence of insulin

Ghrelin is the most powerful orexigenic hormone in mammalian physiology. Ghrelin plasma concentrations increase prior to meal onset, but decrease post-prandially. We and others reported previously that insulin reduces circulating ghrelin levels and might therefore be a driving force for post-prandial suppression of ghrelin. To test the influence of insulin on post-prandial ghrelin regulation, a patient with Type I diabetes with complete insulin deficiency received a low glycemic index meal and subsequently an additional high glycemic index meal in the absence of insulin substitution. Subsequently, a sc injection of 0.08 IU Lispro insulin per kg body weight was given. Results were compared to those of a healthy control subject matched for sex, age and body mass index, which was undergoing the same test series (without Lispro bolus) in the presence of endogenous post-prandial insulin secretion. A substantial decrease of plasma ghrelin levels was observed in the insulin-deficient patient following low glycemic index carbohydrate load (27% plasma ghrelin decrease). The subsequent exposure to a high glycemic index meal resulted in a slight additional reduction of ghrelin levels (32% from baseline), while Lispro bolus did not induce further changes in circulating ghrelin (27% of baseline at termination). This post-prandial response was comparable to that of the healthy control subject (33% reduction after the first meal, 40% after the second meal). These data tentatively suggest that post-prandial secretion of ghrelin is not exclusively regulated by plasma insulin or plasma glucose but may depend on other metabolic factors yet to be identified.

Ca2+/calmodulin-dependent protein kinase II delta2 regulates gene expression of insulin in INS-1 rat insulinoma cells

Ca(2+)/calmodulin-dependent protein kinase II is a member of a broad family of ubiquitously expressed Ca(2+) sensing serine/threonine-kinases. Ca(2+)/calmodulin-dependent protein kinase II is highly expressed in insulin secreting cells and is associated with insulin secretory granules and has been proposed to play an important role in exocytosis or in insulin granule transport to release sites. To elucidate its function the antisense sequence of the major beta-cell subtype, Ca(2+)/calmodulin-dependent protein kinase II delta(2), was stably expressed in INS-1 rat insulinoma cells. This caused a loss of Ca(2+)/calmodulin-dependent protein kinase II delta(2) expression at the mRNA and protein level, while the expression of the 95% homologous Ca(2+)/calmodulin-dependent protein kinase II gamma and of beta-cell specific proteins such as the homeodomain factor pancreatic-duodenal homeobox factor-1 (PDX-1, also referred to as islet/duodenum homeobox-1, IDX-1, insulin promoter factor-1, IPF-1 and somatostatin transactivating factor-1, STF-1), the glucagon-like peptide-1 (GLP-1) receptor and K(ATP)-channels K(IR)6.2/SUR-1 (sulfonylurea receptor-1) was not altered. Unexpectedly, the cells showed a large reduction of insulin gene expression, which was due to reduced insulin gene transcription. Electrophoretic mobility shift assays of PDX-1 binding to the insulin promoter A1 and E2/A3A4 elements showed additional bands indicating alterations of PDX-1 complex formation. Stable over expression of Ca(2+)/calmodulin-dependent protein kinase II delta(2), by contrast, was associated with elevated expression of insulin mRNA. Therefore, we conclude that Ca(2+)/calmodulin-dependent protein kinase II delta(2) links fuel-dependent increases in intracellular Ca(2+) concentrations to transcriptional regulation of genes related to the metabolic control of insulin secretion.

Euglycemic hyperinsulinemia, but not lipid infusion, decreases circulating ghrelin levels in humans

The orexigenic and anabolic gastric hormone ghrelin is secreted in response to acute and chronic energy requirements. While pre-prandial increases and post-prandial decreases of plasma ghrelin levels in rodents and humans seem to indicate a role for the novel peptide hormone as an afferent meal initiator or "hunger hormone", the precise mechanisms which are suppressing ghrelin secretion in response to caloric intake remain largely unknown. We show here that human ghrelin levels decrease by almost 50% under hyperinsulinemic euglycemic clamp conditions (no.=4, p=0.001), revealing physiologically relevant increases of insulin levels as an independent determinant of circulating ghrelin levels. In a second study, 3-4-fold increased plasma free fatty acid levels, as another metabolic candidate for the modulation of circulating ghrelin concentrations, were generated by constant lipid infusion, but failed to change plasma ghrelin. Simultaneous elevation of free fatty acids and insulin again markedly decreased ghrelin concentration (no.=4, p=0.01). Insulin induced suppression of circulating ghrelin levels (or the lack thereof) could be a mechanism with relevance for the understanding of the (patho-) physiology of meal initiation and termination, the pathogenesis of the metabolic syndrome and for the development of respective therapeutic perspectives.

Insulin decreases human adiponectin plasma levels

Insulin resistance and hyperinsulinemia are known atherosclerosis risk factors. The association between adiponectin plasma levels and obesity, insulinemia, and atherosclerosis has been shown. Thus, adiponectin may be a link between hyperinsulinemia and vascular disease. In vitro data demonstrated a reduction of adiponectin expression by insulin. However, it is still unclear whether insulin regulates adiponectinemia in vivo in humans. Five healthy male volunteers were studied. Circulating adiponectin levels were determined before and during hyperinsulinemic euglycemic clamp. Adiponectin was measured by radioimmunoassay. Hyperinsulinemia (85.0 +/- 33.2 at baseline vs. 482.8 +/- 64.4 pmol/l during steady state; p < 0.01) was achieved using a euglycemic hyperinsulinemic clamp, keeping blood glucose levels basically unchanged during the intervention (4.6 +/- 0.14 vs. 4.37 +/- 0.15 mmol/l, respectively; ns). We found a significant decrease of adiponectin plasma levels during the steady state of hyperinsulinemic euglycemic clamp (26.7 +/- 3.5 micro g/ml) compared to baseline levels (30.4 +/- 5 micro g/ml; p < 0.05). Hyperinsulinemia caused a significant decrease of adiponectin plasma levels under euglycemic conditions. Considering existing data about adiponectin dependent effects, hypoadiponectinemia might at least partly be a link between hyperinsulinemia and vascular disease in metabolic syndrome.

Loss of the antiangiogenic pigment epithelium-derived factor in patients with angiogenic eye disease

Retinal neovascularization characterizes proliferative diabetic retinopathy (PDR). Pigment epithelium-derived factor (PEDF) has been shown to be a major antiangiogenic growth factor in the mammalian eye. PEDF expression is suppressed by hypoxia, and changes in PEDF have been correlated to the development of retinal neovascularization in animal models of hypoxic eye disease. However, whether this concept of a reduced angiogenesis inhibitor holds true in humans is as yet unclear. In this study, we analyzed the in vivo regulation of PEDF in patients with and without hypoxic eye disease. We used immunoblots to measure PEDF in ocular fluids obtained from 64 nondiabetic and diabetic patients. In addition, immunohistochemistry of PEDF was carried out in specimens of normal human retinas and retinas with various degrees of diabetic retinopathy. The PEDF concentrations in patients with PDR (P < 0.001) or extensive nondiabetic retinal neovascularization caused by retinal-vein occlusion (P < 0.001) were lower than in control patients. Levels of PEDF were replenished in PDR patients with previous retinal scatter photocoagulation compared with PDR patients without previous photocoagulation (P = 0.01). Immunohistochemistry revealed an interstitial staining pattern as expected for a secreted protein, with an intense staining in retinas of patients without proliferative eye disease. However, in patients with PDR, little or no staining was detectable. Our data strongly support the concept that retinal angiogenesis is induced by loss of the major angiogenesis inhibitor in the eye, PEDF, in combination with an increased expression of angiogenic growth factors such as vascular endothelial growth factor. Our findings suggest that substitution of angiogenesis inhibitors may be an effective approach in the treatment of PDR.

Retinal photocoagulation does not influence intraocular levels of IGF-I, IGF-II and IGF-BP3 in proliferative diabetic retinopathy-evidence for combined treatment of PDR with somatostatin analogues and retinal photocoagulation?

Retinal photocoagulation reduces the incidence of severe visual loss in proliferative diabetic retinopathy (PDR). Reduced levels of VEGF/VPF might result in an improved function of the blood-retina barrier and cause a decrease of blood derived intraocular growth factors such as IGF-I. This study investigates whether retinal photocoagulation is able to normalize the concentrations of IGF-I, IGF-II and IGF-BP3 in the vitreous humor of patients undergoing vitrectomy. Levels of IGFs and the permeability marker, albumin, were measured in serum and vitreous of 52 patients. Three groups were compared: controls without proliferating eye disease (n = 19) and patients with PDR with (PDR+; n = 25) and without (PDR-; n = 8) previous retinal photocoagulation. IGF-I, IGF-II, IGF-BP3 and albumin were determined by immunological methods and were confirmed to be increased in patients with PDR compared to controls. Retinal photocoagulation influenced neither the intraocular concentration of the permeability marker albumin (PDR+: 253.2 +/- 46 mg/dl; PDR-: 256.4 +/- 66.5 mg/dl) nor the levels of IGFs (PDR+: IGF-I: 1.2 +/- 0.1 ng/ml; p = 0.38; IGF-II: 34.8 +/- 2.2 ng/ml; p = 0.1; IGF-BP3: 75.7 +/- 9.7 ng/ml; p = 0.27; PDR-: IGF-I: 1.1 +/- 0.2ng/ml; IGF-II: 29.3 +/- 5.2 ng/ml; IGF-BP3: 61.5 +/- 18.3 ng/ml). Systemic levels of albumin and IGFs were not changed significantly by retinal photocoagulation. These results demonstrate that previous retinal photocoagulation in patients undergoing vitrectomy does not functionally reestablish the blood-retina barrier despite decreases in VEGF/VPF. The lack of influence on intraocular concentrations of the serum-derived growth factors, IGF-I, IGF-II and IGF-BP3, might in part explain the failure of previous photocoagulation in the investigated patients. These results suggest that a combined treatment with retinal photocoagulation and growth hormone-lowering drugs, such as somatostatin analogues, could be a useful treatment, which may prevent further loss of visual acuity in patients with PDR.

Effect of estradiol on insulin secreting INS-1 cells overexpressing estrogen receptors

BACKGROUND

Estrogen has been shown to have profound effects on insulin and glucose metabolism in vivo. Indeed, estrogens were recently shown to modulate ion channel and secretory activities in endocrine cells.

DESIGN AND METHODS

To investigate whether estrogenic influences are caused by direct effects on pancreatic beta-cells, we equipped INS-1 insulinoma cells with estrogen receptors and monitored insulin content and Ca(2+) fluxes as well as basal and stimulated insulin secretion upon different stimuli including glucose, the Ca(2+) ionophore ionomycin, the Ca(2+) channel agonist BayK8644, the protein kinase C activator TPA, and the adenylate cyclase activator forskolin.

RESULTS AND CONCLUSION

Our data reveal that estradiol has no significant direct effect on proliferation rate, insulin content, basal and stimulated insulin output as well as Ca(2+) fluxes of insulin secreting cells in vitro, indicating that in vivo responses to estrogen on insulin and glucose metabolism result from indirect betacytotropic effects.

Ca2+/calmodulin-dependent protein kinase II isoenzymes gamma and delta are both present in H+/K+-ATPase-containing rabbit gastric tubulovesicles

Ca2+/calmodulin-dependent protein kinase II is thought to participate in M3 muscarinic receptor-mediated acid secretion in gastric parietal cells. During acid secretion tubulovesicles carrying H+/K+-ATPase fuse with the apical membrane. We localized Ca2+/calmodulin-dependent protein kinase II from highly purified rabbit gastric tubulovesicles using Ca2+/calmodulin-dependent protein kinase II isoform-specific antibodies, in vitro phosphorylation and pharmacological inhibition of Ca2+/calmodulin-dependent protein kinase II activity by the potent Ca2+/calmodulin-dependent protein kinase II inhibitor KN-62. The presence of Ca2+/calmodulin-dependent protein kinase II in tubulovesicles was shown by immunoblot detection of both Ca2+/calmodulin-dependent protein kinase II-gamma (54 kDa) and Ca2+/calmodulin-dependent protein kinase II-delta (56.5 kDa). The immunoprecipitated Ca2+/calmodulin-dependent protein kinase II from tubulovesicles showed Ca2+/calmodulin-dependent protein kinase activity by phosphorylating autocamtide-II, a specific synthetic Ca2+/calmodulin-dependent protein kinase II substrate. KN-62 inhibited the in vitro autophosphorylation of tubulovesicle-associated Ca2+/calmodulin-dependent protein kinase II (IC50 = 11 nM). During the search for potential Ca2+/calmodulin-dependent protein kinase II substrates we identified different proteins associated with tubulovesicles, such as synaptophysin and beta-tubulin immunoreactivity, which were identified using specific antibodies. These targets are known to participate in intracellular membrane traffic. Ca2+/calmodulin-dependent protein kinase II is thought to play an important role in regulating tubulovesicular motor activity and therefore in acid secretion.

Insulin resistance and impaired insulin secretion due to phosphofructo-1-kinase-deficiency in humans

The etiology of non-insulin-dependent diabetes mellitus (NIDDM) is usually explained as a combination of peripheral insulin resistance and impaired beta-cell function. Phosphofructo-1-kinase (PFK1) is a rate limiting enzyme in glycolysis, and its muscle subtype (PFK1-M) deficiency leads to an autosomal recessively inherited disorder known as glycogenosis type VII or Tarui's disease. It was evaluated whether PFK1-M deficiency leads to NIDDM in humans. A core family of four was evaluated for PFK1-M deficiency by DNA- and enzyme-activity-analyses. All members underwent oral and intravenous glucose tolerance test (oGTT/ivgtt), as well as an insulin sensitivity test (IST) using octreotide.

RESULTS

Father (46 years, BMI 22.4 kg/m2) and older son (19 years, BMI 17.8 kg/m5) showed homozygous PFK1-M deficiency, while mother (47 years, BMI 28.4 kg/m5) and younger son (13 years, BMI 16.5 kg/m5) were shown to be heterozygously PFK1-M-deficient on enzyme activity levels. DNA analysis revealed an exon 5-missense-mutation at one allele of all four members, and an exon 22-frameshift-mutation at the other allele of the two homozygously affected individuals. By oGTT the father showed impaired glucose tolerance, and the mother clinical diabetes. By ivGTT both parents and the older son had a decreased first phase insulin secretion, and a diminished glucose disappearance rate. The IST showed marked insulin resistance in both parents and the older son, and moderate resistance in the younger son, previously not described.

CONCLUSION

PFK1-M-deficiency leads to a metabolic state typical for early NIDDM in homozygously affected humans, especially concerning insulin resistance and loss of first phase beta-cell insulin secretion, and may contribute to the manifestation of NIDDM in a subgroup of patients.

Purification and characterization of a Ca2+/calmodulin-dependent protein kinase II from hog gastric mucosa using a protein-protein affinity chromatographic technique

A peripheral member of the Ca2+/calmodulin-dependent protein kinase II (CaMkinase II) group has been purified from hog gastric mucosa with the use of a novel affinity-chromatographic step. For the well known neural isotypes of CaMkinase II, it is proposed that the subunits form holoenzymes through a specific domain at the C-terminus called the 'association domain'. We immobilized a bacterially expressed association domain from CaMkinase II-delta-2 and used it as an affinity column. This matrix was used as the last step in a sequential enzyme purification procedure from hog gastric mucosa and yielded a homogeneous CaMkinase II which showed the typical physical and enzymatic properties of CaMkinase II. The enzyme activity showed a dependence on Ca2+ and calmodulin (apparent K0.5 = 2.7 microM and K0.5 = 0.02 microM, respectively). We found a subunit molecular mass of 61 kDa. An apparent native molecular mass of 310 kDa was calculated. The Stokes radius and the sedimentation coefficient were 6.7 nm and 11.2 S, respectively. Moreover, the isolated CaMkinase II was very well inhibited by the CaMkinase-II-specific inhibitors KN-62 (Ki = 0.52 nM) and KT5926 (Ki = 0.79 nM). The phosphorylation of several substrates revealed its multifunctionality. The purified CaMkinase II had an apparent Km for Mg-ATP of 24.0 microM and for autocamtide-II of 0.62 microM. CaMkinase II is considered as a strong candidate for regulating vesicle released quanta such as acid, neurotransmitters or insulin.

Deficiency of phosphofructo-1-kinase/muscle subtype in humans impairs insulin secretion and causes insulin resistance

Non-insulin-dependent diabetes mellitus (NIDDM) is caused by peripheral insulin resistance and impaired beta cell function. Phosphofructo-1-kinase (PFK1) is a rate-limiting enzyme in glycolysis, and its muscle subtype (PFK1-M) deficiency leads to the autosomal recessively inherited glycogenosis type VII Tarui's disease. It was evaluated whether PFK1-M deficiency leads to alterations in insulin action or secretion in humans. A core family of four members was evaluated for PFK1-M deficiency by DNA and enzyme-activity analyses. All members underwent oral and intravenous glucose tolerance tests (oGTT and ivGTT) and an insulin-sensitivity test (IST) using octreotide. Enzyme activity determinations in red blood cells showed that the father (46 yr, body mass index [BMI] 22. 4 kg/m2) and older son (19 yr, BMI 17.8 kg/m2) had a homozygous, while the mother (47 yr, BMI 28.4 kg/m2) and younger son (13 yr, BMI 16.5 kg/m2) had a heterozygous PFK1-M deficiency. DNA analyses revealed an exon 5 missense mutation causing missplicing of one allele in all four family members, and an exon 22 frameshift mutation of the other allele of the two homozygously affected individuals. The father showed impaired glucose tolerance, and the mother showed NIDDM. By ivGTT, both parents and the older son had decreased first-phase insulin secretion and a diminished glucose disappearance rate. The IST showed marked insulin resistance in both parents and the older, homozygous son, and moderate resistance in the younger son. PFK1-M deficiency causes impaired insulin secretion in response to glucose, demonstrating its participation in islet glucose metabolism, and peripheral insulin resistance. These combined metabolic sequelae of PFK-1 deficiency identify it as a candidate gene predisposing to NIDDM.