Low pH and ketoacids induce insulin receptor binding and postbinding alterations in cultured 3T3 adipocytes

The etiology of insulin resistance during diabetic ketoacidosis is still poorly understood. Changes in insulin receptor binding and the existence of postreceptor alterations have been proposed. In an attempt to clarify the role of low pH and ketone bodies in the insulin resistance, we examined the effectiveness of insulin during and after 48 h of exposure of cultured 3T3-L1 adipocytes to low pH and ketoacids. In the "acute" stage, lowering of physiologic pH (pH 7.4) to pH 6.9 induced a decrease in insulin binding (50%), which was due to a decrease in the rate of association. Concomitantly, the insulin sensitivity was decreased (ninefold). The basal hexose uptake and insulin responsiveness were only slightly decreased at low pH. Beta-hydroxybutyrate partially counteracted the effect of low pH on insulin binding and sensitivity in a dose-dependent fashion (ED50: 10 mM). The binding-enhancing effect of ketoacids was more pronounced at low pH than at physiologic pH and absent at optimum pH (pH 8.0). After 48 h of exposure of the cells to pH 6.9, insulin binding and insulin sensitivity (measured at physiologic pH) were similar as in cells cultured at pH 7.4. The insulin response, however, was substantially impaired (40%), due to an increase in basal hexose uptake as well as a decrease in maximal insulin-stimulated uptake. These postbinding alterations induced by low pH could be reversed by culturing the cells at physiologic pH for another 48 h. Prolonged exposure to ketoacids did not affect the insulin effectiveness.(ABSTRACT TRUNCATED AT 250 WORDS)     

Insulin-stimulated glucose transport and insulin internalization share a common postbinding step in adipocytes

We recently demonstrated that chymotrypsin substrate analogues inhibit receptor-mediated insulin internalization in isolated rat adipocytes. In this study, the effect on glucose transport of inhibiting insulin internalization with these agents was examined. Glucose transport was assayed by measuring [3H]-2-deoxyglucose uptake, and internalized insulin was measured after rapidly dissociating surface-bound insulin with an acidic buffer. The chymotrypsin substrate analogue N-acetyl-Tyr ethyl ester inhibited insulin internalization by 85% while increasing surface-bound insulin by 80-110%. Under these conditions, ATP levels were minimally altered, and basal glucose transport was unchanged; however, insulin-stimulated glucose transport was decreased by 86%. The inhibition of insulin-stimulated glucose transport was not overcome by supramaximal concentrations (400 ng/ml) of insulin. When insulin internalization and insulin-stimulated glucose transport were measured in the presence of increasing concentrations of N-acetyl-Tyr ethyl ester (0.1-1 mM), a strong and highly significant correlation (r = .97, P less than .001) was found between inhibition of insulin internalization and inhibition of insulin-stimulated glucose uptake. Fragments of N-acetyl-Tyr ethyl ester that do not inhibit insulin internalization were also without effect on insulin-stimulated glucose transport. In addition to N-acetyl-Tyr ethyl ester, four other chymotrypsin substrate analogues that are effective inhibitors of insulin internalization also markedly inhibited insulin-stimulated glucose transport. These results indicate that insulin internalization and insulin-stimulated glucose transport share a common postbinding step in adipocytes and that this step is inhibitable by chymotrypsin substrate analogues.     

Postbinding defects of insulin action in human adipocytes from uremic patients

It is now well established that longstanding human uremia is associated with impaired in vivo insulin action on glucose utilization of peripheral target tissues. In an attempt to define the cellular basis of the uremic insulin resistance we studied insulin action in adipocytes from eight patients with undialyzed chronic uremia and from eight matched healthy controls. (125I)-Insulin binding to fat cells from uremic patients was normal. In contrast (14C)-D-glucose transport exhibited decreased sensitivity to insulin. The concentrations of insulin that elicited half-maximal response was 422 +/- 95 pmoles/liter in uremic patients and 179 +/- 38 pmoles/liter in normal subjects (P less than 0.01). The noninsulin- and the maximal insulin-stimulated glucose transport of adipocytes from uremic patients with normal. (14C)-D-glucose conversion to total lipids was also measured in these cells in the absence and presence of various insulin concentrations. Similar to the findings in transport studies the lipogenesis of fat cells from uremic patients had depressed sensitivity to insulin (half-maximal stimulation at 38 +/- 8 pmoles/liter in uremic patients and at 11 +/- 3 pmoles/liter in normal subjects, P less than 0.01) with unchanged noninsulin and maximal insulin-stimulated lipogenesis. Taken together these results suggest that the insulin resistance of adipocytes from patients with chronic uremia may be accounted for primarily by postbinding defects localized to glucose transport and metabolism.     

Impaired glucose transport and insulin receptor tyrosine phosphorylation in skeletal muscle from obese women with gestational diabetes.

Women who develop gestational diabetes mellitus (GDM) have severe insulin resistance and markedly increased risk to develop subsequent type 2 diabetes. We investigated the effects of pregnancy and GDM on glucose transport activity and the expression and phosphorylation of the insulin receptor and insulin receptor substrate (IRS)-1 in human skeletal muscle fiber strips in vitro. Rectus abdominis muscle biopsies were obtained at the time of cesarean section from 11 pregnant women with normal glucose tolerance (pregnant control), 7 pregnant women with GDM, and 11 nonpregnant women undergoing elective surgery (nonpregnant control). Subjects were matched for age and similar degree of obesity. The rate of maximal insulin (10(-7) mol/l)-stimulated 2-deoxyglucose transport was reduced by 32% (P < 0.05) in muscle strips from the pregnant control group and even further in GDM subjects by 54% (P < 0.05 vs. pregnant control). The maximal effect of insulin on tyrosine phosphorylation of the insulin receptor was 37% lower (P < 0.05) in GDM subjects than in pregnant control subjects and was not related to changes in the abundance of the insulin receptor. Compared with nonpregnant control subjects, maximal insulin-stimulated IRS-1 tyrosine phosphorylation was significantly lower by 59 +/- 24% (mean +/- SD) (P < 0.05) and 62 +/- 28% (P < 0.05) in pregnant control and GDM subjects, respectively. This was reflected by a 23% (P < 0.05) and 44% (P < 0.002) reduction in IRS-1 protein levels in muscle from pregnant control and GDM subjects. Both pregnant control and GDM subjects exhibited a 1.5- to 2-fold increase in the levels of IRS-2 (P < 0.01) and p85alpha regulatory subunit of phosphatidylinositol (PI) 3-kinase (P < 0.05), despite reduced glucose transport activity. These data indicate that insulin resistance to glucose transport during pregnancy is uniquely associated with a decrease in IRS-1 tyrosine phosphorylation, primarily due to decreased expression of IRS-1 protein. However, in GDM subjects, a decrease in tyrosine phosphorylation of the insulin receptor beta-subunit is associated with further decreases in glucose transport activity. Thus, impaired insulin receptor autophosphorylation is an important early distinction underlying muscle insulin resistance in young women with GDM, and it may underlie future risk for the development of type 2 diabetes.     

Gliclazide therapy is associated with potentiation of postbinding insulin action in obese, non-insulin-dependent diabetic subjects

Six obese, non-insulin-dependent diabetic subjects were studied before and 3 mo after treatment with the sulfonylurea gliclazide, 40-80 mg b.i.d. Fasting plasma glucose fell significantly from 13.4 +/- 1.6 (SEM) to 8.6 +/- 1.2 mmol/L, accompanied by a significant reduction from 40.6 +/- 3.7 to 29.8 +/- 2.8 mM X h of the plasma glucose response to 75 g oral glucose. Fasting plasma insulin showed a nonsignificant increase from 24.8 +/- 2.0 to 31.3 +/- 2.3 mU/L. The percent specific binding of tracer 125I-insulin to erythrocytes and monocytes did not change significantly (from 9.8 +/- 1.7 to 8.5 +/- 0.7 for erythrocytes and 1.7 +/- 0.3 to 1.6 +/- 0.4 for monocytes). Glucose utilization was measured at three levels of insulin infusion (40, 100, and 300 mU/kg/h) by the euglycemic clamp technique. Overall there was a significant (P less than 0.05) increase in the disappearance rate (Rd) and metabolic clearance rate (MCRg) for glucose at the two higher insulin infusion rates (MCRg: 3.3 +/- 0.7 to 5.1 +/- 0.7 and 5.9 +/- 0.9 to 7.9 +/- 0.9 ml/kg/min), but not at the lowest infusion rate (MCRg: 3.6 +/- 0.8 to 3.3 +/- 0.6). Thus, the chronic hypoglycemic effect of gliclazide in obese diabetic subjects was associated with an improvement in insulin-mediated glucose utilization at high plasma insulin concentrations. This enhanced effect of insulin after gliclazide treatment was not accompanied by increased monocyte or erythrocyte insulin binding, which suggests that it was due to potentiation of postbinding insulin-sensitive pathways.     

In vitro studies of insulin resistance in patients with lipoatrophic diabetes. Evidence for heterogeneous postbinding defects

We studied the binding and action of insulin in cultured fibroblasts from six patients with lipoatrophic diabetes and marked in vivo insulin resistance and from seven control subjects. The binding of insulin was not altered, which corresponds well with studies with circulating erythrocytes. Similarly, the action of the hormone on amino acid uptake (estimated by active transport of aminoisobutyric acid) was comparable in patient and control cells. Conversely, studies concerning the effect of insulin on glucose transport (estimated by facilitated diffusion of 2-deoxyglucose) or glycogen synthesis (estimated by incorporation of glucose into cellular glycogen) revealed the presence of heterogeneous alterations among the different patient cell lines. However, although the nature of the defect(s) varied among the patients, alterations in glucose metabolism were present in all cases. These data suggest the presence of primary postbinding defects in glucose cellular pathways that give rise to insulin resistance in cells from lipoatrophic diabetic patients.     

Gestational urinary hyperthiosulfaturia protects hypercalciuric normal pregnant women from nephrolithiasis

Urinary calcium excretion increases by 1–2-fold during gestation in normal, uncomplicated pregnant women. Hypercalciuria occurs in all trimesters and elevates urine supersaturation with regards to calcium oxalate. However, crystalluria has not been a frequent clinical finding and stone formation is not a common complication of pregnancy. To elucidate this discrepancy we measured various chemical entities (i.e. calcium, oxalate, uric acid, phosphorous, magnesium, citrate, sulfate and thiosulfate) in urine at the end of each trimester of 25 pregnant women. Twenty-five healthy women served as controls. Our observations show that endogenous thiosulfate, a natural component of urine, increased considerably during pregnancy to approximately 36, 38 and 40 M/24 hour at the end of each three trimesters. One month after delivery, endogenous thiosulfaturia and hypercalciuria, in parallel, returned to initial normal values. Consequently, it seems that gestational hyperthiosulfaturia protects hypercalciuric normal pregnant women from the risk of nephrolithiasis.     

Antibody binding of insulin in diabetic ketoacidosis.

This study investigates the effects of insulin antibody binding on free insulin levels measured in patients with acute diabetic ketoacidosis receiving insulin by constant infusion. In spite of antibody binding ranging from 10 to 90 per cent of the total circulating insulin, the steady state concentrations of free insulin were similar to those observed in individuals on identical infusion rates but without insulin-binding antibodies. However, the levels of free insulin in two patients were substantially lower than expected for the rate of insulin infusion, even though levels of bound insulin were not greatly elevated. An infusion rate of at least 4 U. per hour produced satisfactory rate of fall of plasma glucose, whereas lower dose regimens (2 U. per hour)--producing steady state free insulin concentrations ranging from 28 to 49 mU. per liter in different subjects--were unreliable in controlling the metabolic abnormalities of diabetic ketoacidosis.     

Familial insulin resistance and acanthosis nigricans. Presence of a postbinding defect

Type A insulin resistance, associated with acanthosis nigricans and menstrual irregularity, has been ascribed to a decreased concentration of insulin receptors. We now report four affected females from one family, a mother and three daughters (including identical twins) who appear to have the type A syndrome. Two of the kindred had no apparent ovarian dysfunction, while the other two had hyperprolactinemia without other findings of polycystic ovary disease, suggesting a genetic disease with variable penetrance. All had normal erythrocyte and monocyte insulin binding. Insulin dose-response studies to assess glucose metabolism and insulin sensitivity were performed in the affected twins. The dose response to insulin was shifted to the right with a decrease in maximal response. These results are consistent with a postbinding defect in insulin action in these patients.     

Plasma protein binding of bupivacaine in pregnant women at term

The increased toxicity of bupivacaine in parturients is a well-known phenomenon. The reduced plasma protein binding of bupivacaine is one of the possible reasons. Therefore, we measured the free fraction of bupivacaine in plasma samples of parturients and non-pregnant volunteers. The free fraction was significantly higher in parturients (8.2% vs 5.4%) associated with a lower concentration of the alpha-1-acid glycoprotein (0.42 vs 1.01 g/l) and a higher concentration of progesterone (156 vs 0.4 ng/ml). The addition of progesterone to plasma samples of non-pregnant volunteers did not influence the free fraction of bupivacaine, whereas the addition of alpha-1-acid glycoprotein to the plasma of parturients decreased the free fraction significantly. Therefore, the lower concentration of this protein is the principal reason for the higher free fraction of bupivacaine in pregnancy and possibly one of the causes of the higher incidence of toxic side effects of bupivacaine in obstetric use.     

Effects of interrupted insulin treatment on fetal outcome of pregnant diabetic rats

Streptozocin-induced diabetic female rats became normoglycemic after subcutaneous insertion of insulin-releasing osmotic minipumps. These female rats were mated with normal males from the same Sprague-Dawley substrain. In this substrain, the offspring of diabetic rats show a markedly increased congenital malformation rate compared with fetuses of nondiabetic rats. The pregnant diabetic rats were subjected to removal and insertion of pumps at defined gestational days that marked the beginning or end of a 2- or 4-day period of insulin withdrawal. Evaluation of the offspring on day 20 of pregnancy included fetal/placental weights, estimated number of implants, resorptions, and morphological assessment of congenital malformations. Resorptions occurred in all interruption groups, but malformations were found only in animals with insulin withdrawal on gestational days 4-8, 6-8, 6-10, 8-10, and 8-12. The highest resorption (42%) and malformation (17%) rates were found in the rats subjected to insulin withdrawal during gestational days 6-10. Because manifestly diabetic rats with no insulin treatment showed similar resorption (39%) and malformation (17%) rates, this study suggests that a teratogenic period in diabetic rat pregnancy occurs during gestational days 6-10, a period corresponding to postconceptional wk 2-4 in human pregnancy. Interruption of insulin treatment induced similar maternal weight loss and similar maternal serum concentrations of D-glucose, cholesterol, urea, and creatinine in rats with and without malformed offspring.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of a high carbohydrate diet on insulin binding to adipocytes and on insulin action in vivo in man.

We studied the effects of short-term (5 days) and long-term (2 wk) high carbohydrate (75%) feedings on insulin binding to isolated adipocytes and insulin sensitivity in vivo in normal subjects. Ingestion of the high carbohydrate diet led to daylong hyperinsulinemia in both short- and long-term groups. Insulin binding to isolated adipocytes was decreased in both groups; in the short-term groups this decrease in insulin binding was caused by a decrease in the receptor affinity, whereas in the long-term group it was caused by a decrease in receptor number. On the other hand, despite this decrease in insulin binding, total in vivo insulin sensitivity was markedly improved in both groups. In conclusion, (1) the short-term adaptive response of the insulin receptor is a decrease in binding affinity whereas the long-term response is a decrease in receptor number, (2) sustained and chronic hyperinsulinemia can lead to a decrease in the number of cellular insulin receptors, (3) high carbohydrate diets lead to a general increase in insulin's ability to promote glucose removal from plasma, and (4) the paradox of enhanced insulin sensitivity in the face of decreased insulin binding can be explained if high carbohydrate diets also lead to an increase in the activity of steps in glucose metabolism distal to the insulin receptor.     

胰岛素生理盐水纱条用于糖尿病足换药效果观察

目的观察胰岛素生理盐水纱条用于糖尿病足换药的效果。方法将65例糖尿病足患者随机分为观察组(33例)和对照组(32例),对照组采用庆大霉素生理盐水纱条常规方法换药;观察组采用胰岛素生理盐水纱条换药,即每毫升生理盐水含胰岛素1.0~1.5 U配成换药液,将消毒纱条浸于此液中用于糖尿病足换药。结果两组治疗过程中均未出现任何不良反应;两组疗效和治愈时间比较,差异有统计学意义(均P<0.01)。结论糖尿病足采用胰岛素生理盐水纱条换药有较好的疗效,且安全、实用。     

糖代谢正常孕妇分娩巨大儿的相关因素分析

目的探讨糖代谢正常孕妇孕期体重增长速度及相关因素与分娩巨大儿的关系,以期早期警戒巨大儿的发生,减少巨大儿的出现,改善围产结局。方法回顾分析2014年11月1日至2015年12月1日于我院住院分娩的糖代谢正常且分娩新生儿体重≥4 000g的孕妇94例作为研究组,同期住院分娩新生儿体重4 000g孕妇90例作为对照组,比较两组孕妇年龄、孕产次、孕前体重指数、孕期体重增长速度、孕期体重增长总量及分娩孕周对妊娠结局的影响。结果研究组与对照组比较,平均年龄、身高、孕产次及妊娠并发症均无统计学差异(P0.05);研究组孕前体重指数显著高于对照组[(22.89±3.27)vs.(21.53±3.81)kg/m2],且研究组超重者比例(23.40%)显著高于对照组(6.67%)(P0.05);研究组孕期体重增加显著高于对照组[(17.49±5.13)vs.(15.30±4.58)kg](P0.05),尤其在孕第12~20周以及36周至分娩期两个时段,两组体重增加的差异尤为显著[分别为(4.93±2.21)vs.(3.73±1.66)kg、(2.18±1.56)vs.(1.65±1.29)kg](P0.05);研究组剖宫产率(56.38%)、产后出血率(20.21%)、胎儿窘迫发生率(14.89%)均显著高于对照组(分别为40.00%、6.67%、6.67%)(P0.05)。结论孕前体重超重及孕期增重过多是分娩巨大儿的高危因素,注意控制妊娠12~20周及36周至分娩前两个时段的体重增长,可以减少巨大儿的发生,改善母胎结局。     

Structure of the insulin receptor of rat adipocytes. The three interconvertible redox forms

Isolated intact rat adipocytes were photoaffinity labeled with radioactive and photoreactive N alpha B1-monoazidobenzoyl insulin (B1-MABI) or N epsilon B29-monoazidobenzoyl insulin (B29-MABI). Polyacrylamide gel electrophoresis of the labeled plasma membranes solubilized in sodium dodecyl sulfate revealed the specific labeling of three receptor species of 380 kDa, 300 kDa, and 230 kDa. Reduction of each species individually produced the subunits of 130 kDa, 90 kDa, and 40 kDa. Exposure of the adipocytes or plasma membranes after photolabeling to sulfhydryl alkylating agents such as N-ethylmaleimide or p-chloromercuriphenylsulfonate resulted in the appearance of the receptor quantitatively in the 380-kDa form. The effect of the sulfhydryl reagent was concentration dependent and in the case of p-chloromercuriphenylsulfonate the three receptor species reappeared when high concentrations of the reagent were used. Incubation of the adipocytes with low concentrations of dithiothreitol before photolabeling reduced these receptors to discrete lower-molecular-weight forms. In addition, an 85-kDa subunit was now photolabeled by B1-MABI. This subunit was demonstrated to be different from the 90-kDa subunit normally labeled by B29-MABI. We conclude that on the cell surface of the adipocyte, there is one molecular-weight form of insulin receptor of 380 kDa composed of one 130-kDa, one 90-kDa, one 85-kDa, and two 40-kDa subunits. The 300 kDa and 230 kDa are partially reduced forms of the 380-kDa species. We further postulate that a membrane factor or factors sensitive to sulfhydryl alkylating reagents may be involved in the partial reduction and oxidation of these three redox receptor species. The distribution of these redox receptor species may be related to the cellular or tissue sensitivity to insulin.     

Characterization of binding and phosphorylation defects of erythrocyte insulin receptors in the type A syndrome of insulin resistance

The type A syndrome of insulin resistance and acanthosis nigricans is characterized by severe insulin resistance due to a cellular defect in insulin action. To better understand the molecular nature of this defect, we have investigated insulin binding to circulating monocytes, erythrocytes, and the Triton X-100-solubilized erythrocyte receptor, and insulin-stimulated receptor autophosphorylation using cells and receptor from three type A patients. Insulin binding in both circulating cells and the soluble extract of erythrocytes indicated a heterogeneity of defects. Patients A1 and A2 both presented a major decrease in tracer insulin binding to intact cells and soluble insulin receptor. Determination of stoichiometric binding parameters using a cooperative model indicated that in patient A1 this was due to a reduction in the number of receptors, whereas in patient A2 the affinity constant for binding was decreased. Patient A3 presented near-normal insulin binding to erythrocytes and normal binding in intact monocytes, solubilized erythrocyte receptors, and cultured fibroblasts. Affinity labeling of erythrocyte receptor from this patient revealed a normal alpha-subunit and also a normal relative distribution of the higher-molecular-weight, nonreduced oligomeric forms of the receptor. Receptor autophosphorylation was measured using the solubilized insulin receptor from erythrocytes. The maximal stimulated phosphorylation was reduced by 79%, 76%, and 52% in patients A1, A2, and A3, respectively, relative to the simultaneous control. In all three patients, the autophosphorylation was stimulated only 1.0-3.5 times the basal level compared with controls, in which the stimulation was 5.7-fold +/- 1.2 (mean +/- 1 SD, P less than 0.005). In addition, in patients A1 and A2 a decrease in basal phosphorylation was observed and in patient A2 there was a rightward shift of the dose-response curve for insulin stimulation. These data and the correlation of coupling of receptor phosphorylation with the fractional occupancy of the receptor measured in the same extract suggest that these patients exhibit three types of defects. In patient A1, there is a loss in receptor number manifested by a parallel decrease in insulin binding and receptor phosphorylation. In patient A2, there is an additional decrease in the affinity constant leading to a decrease in both binding and receptor phosphorylation with an almost linear coupling between receptor occupancy and receptor phosphorylation.(ABSTRACT TRUNCATED AT 400 WORDS)