Implications for the offspring of circulating factors involved in beta cell adaptation in pregnancy

The Role of Fatty Acid Signaling in Islet Beta-Cell Adaptation to Normal Pregnancy

BACKGROUND

Maintenance of a normal fetal nutrient supply requires major adaptations in maternal metabolic physiology, including of the islet beta-cell. The role of lipid signaling processes in the mechanisms of islet beta-cell adaptation to pregnancy has been minimally investigated.

OBJECTIVE

To determine the effects of pregnancy on islet fatty acid (FA) metabolic partitioning and FA augmentation of glucose-stimulated insulin secretion (GSIS).

METHODS

Age matched virgin, early pregnant (gestational day-11, G11) and late pregnant (G19) Sprague-Dawley rats were studied. Fasted and fed state biochemistry, oral glucose tolerance tests (OGTT), and fasted and post-OGTT liver glycogen, were determined to assess in vivo metabolic characteristics. In isolated islets, FA (BSA-bound palmitate 0.25 mmol/l) augmentation of GSIS, FA partitioning into esterification and oxidation processes using metabolic tracer techniques, lipolysis by glycerol release, triacylglycerols (TG) content, and the expression of key beta-cell genes were determined.

RESULTS

Plasma glucose in pregnancy was lower, including during the OGTT (glucose area under the curve 0-120 min (AUC_0-120); 655±24 versus 849±13 mmol.l^-1.min; G19 vs virgin; P<0.0001), with plasma insulin concentrations equivalent to those of virgin rats (insulin AUC_0-120; 97±7 versus 83±7 ng.ml^-1.min; G19 vs virgin; not significant). Liver glycogen was depleted in fasted G19 rats with full recovery after oral glucose. Serum TG increased during pregnancy (4.4±0.4, 6.7±0.5; 17.1±1.5 mmol/l; virgin, G11, G19, P<0.0001), and islet TG content decreased (147±42, 172±27, 73±13 ng/µg protein; virgin, G11, G19; P<0.01). GSIS in isolated islets was increased in G19 compared to virgin rats, and this effect was augmented in the presence of FA. FA esterification into phospholipids, monoacylglycerols and TG were increased, whereas FA oxidation was reduced, in islets of pregnant compared to virgin rats, with variable effects on lipolysis dependent on gestational age. Expression of Ppargc1a, a key regulator of mitochondrial metabolism, was reduced by 51% in G11 and 64% in G19 pregnant rat islets compared to virgin rat islets (P<0.001).

CONCLUSION

A lowered set-point for islet and hepatic glucose homeostasis in the pregnant rat has been confirmed. Islet adaptation to pregnancy includes increased FA esterification, reduced FA oxidation, and enhanced FA augmentation of glucose-stimulated insulin secretion.

Possible mechanisms involved in improved beta cell function in pregnant women with type 1 diabetes

Pregnancy is known to be associated with an increased demand for insulin that is normally compensated by an increased beta cell mass and insulin secretion. Recent studies have suggested enhanced beta cell function during pregnancy in women with type 1 diabetes (T1D). To explore the possible mechanisms behind enhanced beta cell function during pregnancy in women with T1D we investigated the impact of circulating factors in serum from nine women from each group of pregnant women with and without T1D, after pregnancy and non-diabetic non-pregnant women on rat islet cell proliferation and apoptosis, and on T-lymphocyte activation. In addition, circulating levels of pancreatic hormones and selected cytokines and adipokines were measured. Rat islet cell proliferation was higher in serum from pregnant women with T1D (p < 0.05) compared to T1D women after pregnancy. Apoptosis in INS-1E cell was lower (p < 0.05) in serum from pregnant women with T1D compared to T1D women after pregnancy. T-lymphocyte cell (Jurkat) proliferation was reduced by serum from pregnant women without T1D only (p < 0.05). Higher C-peptide levels and lower levels of ghrelin, IL-6, MCP-1, IL-8 and adipsin were observed in pregnant women with T1D compared to T1D women after pregnancy. In conclusion, the improved beta cell function in women with T1D during pregnancy may be due to lower levels of proinflammatory cytokines and/or higher levels of pregnancy-associated growth factors.

Placental Lactogen as a Marker of Maternal Obesity, Diabetes, and Fetal Growth Abnormalities: Current Knowledge and Clinical Perspectives

Placental lactogen (PL) is a peptide hormone secreted throughout pregnancy by both animal and human specialized endocrine cells. PL plays an important role in the regulation of insulin secretion in pancreatic β-cells, stimulating their proliferation and promoting the expression of anti-apoptotic proteins. Cases of pregnancy affected by metabolic conditions, including obesity and diabetes, are related to alterations in the PL secretion pattern. Whereas obesity is most often associated with lower PL serum concentrations, diabetes results in increased PL blood levels. Disruptions in PL secretion are thought to be associated with an increased prevalence of gestational complications, such as placental dysfunction, diabetic retinopathy, and abnormalities in fetal growth. PL is believed to be positively correlated with birth weight. The impaired regulation of PL secretion could contribute to an increased incidence of both growth retardation and fetal macrosomia. Moreover, the dysregulation of PL production during the intrauterine period could affect the metabolic status in adulthood. PL concentration measurement could be useful in the prediction of fetal macrosomia in women with normal oral glucose tolerance test (OGTT) results or in evaluating the risk of fetal growth restriction, but its application in standard clinical practice seems to be limited in the era of ultrasonography.

Evaluation of Circulating Determinants of Beta-Cell Function in Women With and Without Gestational Diabetes

CONTEXT

Gestational diabetes (GDM) arises in women in whom there is insufficient β-cell compensation for the insulin resistance of late pregnancy. The mechanisms underlying both normal antepartum β-cell adaptation and its aberrancy in GDM are unclear. Preclinical studies have suggested that the hormones prolactin and human placental lactogen (HPL) may stimulate β-cell mass, whereas the furan fatty acid metabolite 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) has recently emerged as a potential negative regulator of β-cell function. However, there has been limited study of these factors in humans.

OBJECTIVE

Our objective was to systematically evaluate HPL, prolactin, and CMPF in relation to glucose homeostasis and β-cell function in women with and without GDM.

DESIGN/SETTING/PARTICIPANTS

Three-hundred-and-ninety-five women underwent an oral glucose tolerance test in late pregnancy, enabling assessment of GDM status, glycemia (area-under-the-glucose-curve on oral glucose tolerance test [AUCglucose]), β-cell function (Insulin Secretion-Sensitivity Index-2, insulinogenic index/homeostatic model assessment of insulin resistance [HOMA-IR]), insulin sensitivity/resistance (Matsuda index, HOMA-IR), and circulating HPL, prolactin, and CMPF.

RESULTS

Serum concentrations of HPL, prolactin, and CMPF were similar between women with GDM (n = 105) and women without GDM (n = 290). However, on multiple linear regression analyses, CMPF emerged as a significant predictor of AUCglucose in women with GDM (t = 4.75, P < .0001) but not in their peers (P = .60). Furthermore, CMPF independently predicted lower Insulin Secretion-Sensitivity Index-2 (t = -2.28, P = .02) and lower insulinogenic index/HOMA-IR (t = -2.22, P = .03) in women with GDM but not in the non-GDM group (both P = .93). Neither HPL nor prolactin was significantly associated with AUCglucose, β-cell function, or insulin sensitivity.

CONCLUSION

CMPF is a potential circulating determinant of β-cell dysfunction and hyperglycemia in women with GDM.

Beta cell adaptation in pregnancy: a tribute to Claes Hellerström

Pregnancy is associated with a compensatory increase in beta cell mass. It is well established that somatolactogenic hormones contribute to the expansion both indirectly by their insulin antagonistic effects and directly by their mitogenic effects on the beta cells via receptors for prolactin and growth hormone expressed in rodent beta cells. However, the beta cell expansion in human pregnancy seems to occur by neogenesis of beta cells from putative progenitor cells rather than by proliferation of existing beta cells. Claes Hellerström has pioneered the research on beta cell growth for decades, but the mechanisms involved are still not clarified. In this review the information obtained in previous studies is recapitulated together with some of the current attempts to resolve the controversy in the field: identification of the putative progenitor cells, identification of the factors involved in the expansion of the beta cell mass in human pregnancy, and the relative roles of endocrine factors and nutrients.