Taurine supplementation to a low protein diet during foetal and early postnatal life restores a normal proliferation and apoptosis of rat pancreatic islets

Maternal taurine supplementation in rats partially prevents the adverse effects of early-life protein deprivation on β-cell function and insulin sensitivity

Dietary protein restriction during pregnancy and lactation in rats impairs β-cell function and mass in neonates and leads to glucose intolerance in adult offspring. Maternal taurine (Tau) supplementation during pregnancy in rats restores β-cell function and mass in neonates, but its long-term effects are unclear. The prevention of postnatal catch-up growth has been suggested to improve glucose tolerance in adult offspring of low-protein (LP)-fed mothers. The objective of this study was to examine the relative contribution of β-cell dysfunction and insulin resistance to impaired glucose tolerance in 130-day-old rat offspring of LP-fed mothers and the effects of maternal Tau supplementation on β-cell function and insulin resistance in these offspring. Pregnant rats were fed i) control, ii) LP, and iii) LP+Tau diets during gestation and lactation. Offspring were given a control diet following weaning. A fourth group consisting of offspring of LP-fed mothers, maintained on a LP diet following weaning, was also studied (LP-all life). Insulin sensitivity in the offspring of LP-fed mothers was reduced in females but not in males. In both genders, LP exposure decreased β-cell function. Tau supplementation improved insulin sensitivity in females and β-cell function in males. The LP-all life diet improved β-cell function in males. We conclude that i) maternal Tau supplementation has persistent effects on improving glucose metabolism (β-cell function and insulin sensitivity) in adult rat offspring of LP-fed mothers and ii) increasing the amount of protein in the diet of offspring adapted to a LP diet after weaning may impair glucose metabolism (β-cell function) in a gender-specific manner.

Increased amino acid supply potentiates glucose-stimulated insulin secretion but does not increase β-cell mass in fetal sheep

Amino acids and glucose acutely stimulate fetal insulin secretion. In isolated adult pancreatic islets, amino acids potentiate glucose-stimulated insulin secretion (GSIS), but whether amino acids have this same effect in the fetus is unknown. Therefore, we tested the effects of increased fetal amino acid supply on GSIS and morphology of the pancreas. We hypothesized that increasing fetal amino acid supply would potentiate GSIS. Singleton fetal sheep received a direct intravenous infusion of an amino acid mixture (AA) or saline (CON) for 10-14 days during late gestation to target a 25-50% increase in fetal branched-chain amino acids (BCAA). Early-phase GSIS increased 150% in the AA group (P < 0.01), and this difference was sustained for the duration of the hyperglycemic clamp (105 min) (P < 0.05). Glucose-potentiated arginine-stimulated insulin secretion (ASIS), pancreatic insulin content, and pancreatic glucagon content were similar between groups. β-Cell mass and area were unchanged between groups. Baseline and arginine-stimulated glucagon concentrations were increased in the AA group (P < 0.05). Pancreatic α-cell mass and area were unchanged. Fetal and pancreatic weights were similar. We conclude that a sustained increase of amino acid supply to the normally growing late-gestation fetus potentiated fetal GSIS but did not affect the morphology or insulin content of the pancreas. We speculate that increased β-cell responsiveness (insulin secretion) following increased amino acid supply may be due to increased generation of secondary messengers in the β-cell. This may be enhanced by the paracrine action of glucagon on the β-cell.

Epigenetic basis for fetal origins of age-related disease

The current concept of fetal origins of adult diseases describes in utero programming, or adaptation to a spectrum of adverse environmental conditions that ultimately leads to increased susceptibility to age-related diseases (e.g., type 2 diabetes and cardiovascular disease) later in life. Although the precise mechanism of this biological memory remains unclear, mounting evidence suggests an epigenetic basis. The increased susceptibility to chronic disease and involvement of multiple organ systems that is observed is analogous to the decline in resistance to disease that is typical of normal aging. Although the cumulative environment over the course of a lifetime can induce increasing epigenetic dysregulation, we propose that adverse events that occur during early development can induce significant additional dysregulation of the epigenome. Here, we describe the current evidence for fetal origins of adult disease and the associated role of epigenetic dysregulation. In addition, we present a new perspective on the induction of epigenetic alterations in utero, which subsequently lead to an aging phenotype marked by increased susceptibility to age-related diseases.

From Mice to Men: research models of developmental programming

Developmental programming can be defined as a response to a specific challenge to the mammalian organism during a critical developmental time window that alters the trajectory of development with persistent effects on offspring phenotype and predisposition to future illness. We focus on the need for studies in relevant, well-characterized animal models in the context of recent research discoveries on the challenges, mechanisms and outcomes of developmental programming. We discuss commonalities and differences in general principles of developmental programming as they apply to several species, including humans. The consequences of these differences are discussed. Obesity, metabolic disorders and cardiovascular diseases are associated with the highest percentage of morbidity and mortality worldwide. Although many of the causes are associated with lifestyle, high-energy diets and lack of physical activity, recent evidence has linked developmental programming to the epidemic of metabolic diseases. A better understanding of comparative systems physiology of mother, fetus and neonate using information provided by rapid advances in molecular biology has the potential to improve the lifetime health of future generations by providing better women's health, diagnostic tools and preventative and therapeutic interventions in individuals exposed during their development to programming influences.

Perinatal taurine imbalance alters the interplay of renin-angiotensin system and estrogen on glucose-insulin regulation in adult female rats

Perinatal taurine depletion followed by high sugar intake (postweaning) alters the renin-angiotensin system (RAS) and glucose regulation in adult female rats. This study tests the hypothesis that in adult female rats, RAS and estrogen contribute to insulin resistance resulting from perinatal taurine imbalance. Female Sprague-Dawley rats were fed normal rat chow with 3% β-alanine (taurine depletion, TD), 3% taurine (taurine supplementation, TS), or water alone (control, C) from conception to weaning. Their female offspring were fed normal rat chow with 5% glucose in water (TDG, TSG, CG) or water alone (TDW, TSW, CW) throughout the experiment. At 7-8 weeks of age, animals were studied with or without captopril inhibition of the RAS and with or without estrogen receptor inhibition by tamoxifen. Compared to CW and CG groups, perinatal taurine depletion but not supplementation slightly increased plasma insulin levels. High sugar intake slightly increased plasma insulin only in TSG. Captopril treatment significantly increased plasma insulin in all groups except CG (the greatest increase was in TDG). Changes in insulin resistance and insulin secretion paralleled the changes in plasma insulin levels. In contrast, tamoxifen treatment increased insulin resistance and decreased insulin secretion only in TDG and this group displayed hyperglycemia and glucose intolerance. These data indicate that perinatal taurine imbalance alters the interplay of RAS and estrogen on glucose-insulin regulation in adult female rats.

Perinatal taurine exposure affects adult arterial pressure control

Taurine is an abundant, free amino acid found in mammalian cells that contributes to many physiologic functions from that of a simple cell osmolyte to a programmer of adult health and disease. Taurine's contribution extends from conception throughout life, but its most critical exposure period is during perinatal life. In adults, taurine supplementation prevents or alleviates cardiovascular disease and related complications. In contrast, low taurine consumption coincides with increased risk of cardiovascular disease, obesity and type II diabetes. This review focuses on the effects that altered perinatal taurine exposure has on long-term mechanisms that control adult arterial blood pressure and could thereby contribute to arterial hypertension through its ability to program these cardiovascular regulatory mechanisms very early in life. The modifications of these mechanisms can last a lifetime and transfer to the next generation, suggesting that epigenetic mechanisms underlie the changes. The ability of perinatal taurine exposure to influence arterial pressure control mechanisms and hypertension in adult life appears to involve the regulation of growth and development, the central and autonomic nervous system, the renin-angiotensin system, glucose-insulin interaction and changes to heart, blood vessels and kidney function.

Strategies for reversing the effects of metabolic disorders induced as a consequence of developmental programming

Obesity and the metabolic syndrome have reached epidemic proportions worldwide with far-reaching health care and economic implications. The rapid increase in the prevalence of these disorders suggests that environmental and behavioral influences, rather than genetic causes, are fueling the epidemic. The developmental origins of health and disease hypothesis has highlighted the link between the periconceptual, fetal, and early infant phases of life and the subsequent development of metabolic disorders in later life. In particular, the impact of poor maternal nutrition on susceptibility to later life metabolic disease in offspring is now well documented. Several studies have now shown, at least in experimental animal models, that some components of the metabolic syndrome, induced as a consequence of developmental programming, are potentially reversible by nutritional or targeted therapeutic interventions during windows of developmental plasticity. This review will focus on critical windows of development and possible therapeutic avenues that may reduce metabolic and obesogenic risk following an adverse early life environment.

Developmental origins of adult diseases

There is considerable evidence for the fact that early life environment in human beings are associated with future development of various metabolic diseases. Fetal programming and perinatal events appear to exert effects on later life that are independent of environmental risk factors in adults. Our understanding of the underlying mechanisms are limited and remains unclear. However several animal models and epidemiological studies have shown this association, and it is assumed secondary to the penalties of developmental plasticity. In this review, we amalgamate facts from several disciplines to support this hypothesis.

Methionine, homocysteine, one carbon metabolism and fetal growth

Methionine and folate are the key components of one carbon metabolism, providing the methyl groups for numerous methyl transferase reactions via the ubiquitous methyl donor, s-adenosyl methionine. Methionine metabolism is responsive to nutrient intake, is regulated by several hormones and requires a number of vitamins (B12, pyridoxine, riboflavin) as co-factors. The critical relationship between perturbations in the mother's methionine metabolism and its impact on fetal growth and development is now becoming evident. The relation of folate intake to fetal teratogenesis has been known for some time. Studies in human pregnancy show a continuous decrease in plasma homocysteine, and an increase in plasma choline concentrations with advancing gestation. A higher rate of transsulfuration of methionine in early gestation and of transmethylation in the 3rd trimester was seen in healthy pregnant women. How these processes are impacted by nutritional, hormonal and other influences in human pregnancy and their effect on fetal growth has not been examined. Isocaloric protein restriction in pregnant rats, resulted in fetal growth restriction and metabolic reprogramming. Isocaloric protein restriction in the non-pregnant rat, resulted in differential expression of a number of genes in the liver, a 50% increase in whole body serine biosynthesis and high rate of transmethylation, suggesting high methylation demands. These responses were associated with a significant decrease in intracellular taurine levels in the liver suggesting a role of cellular osmolarity in the observed metabolic responses. These unique changes in methionine and one carbon metabolism in response to physiological, nutritional and hormonal influences make these processes critical for cellular and organ function and growth.

Taurine attenuates maternal and embryonic oxidative stress in a streptozotocin-diabetic rat model

Oxidative stress mechanisms have been implicated in congenital anomalies and morbidity/mortality of fetus/newborn in diabetic pregnancy. Numerous antioxidant treatments have shown varied beneficial effects in improving both maternal and fetal outcomes. The present study examined the propensity of taurine to attenuate the degree of embryopathy and oxidative stress among pregnant diabetic rats. Adult rats (CFT-Wistar) were rendered diabetic with an acute dose of streptozotocin (STZ; 45 mg/kg bodyweight) on gestation day (GD) 4. Both Diabetic and non-diabetic dams were given oral supplements of taurine (0.5 and 1g/kg bodyweight/day) from GD 5 to GD 12. Maternal diet intake, bodyweight gain and urine output were monitored and dams were killed on GD 13. Markers of oxidative stress were determined in embryos and maternal livers. STZ treatment induced marked embryopathy (32%) and taurine supplements markedly reduced the degree of embryopathy (54% protection). The STZ-induced higher oxidative stress was significantly attenuated in rats given taurine supplements (P<0.05) and a similar effect was seen in embryos (P<0.05). These data suggest that dietary taurine during pregnancy provides significant protection against diabetes-induced oxidative stress in both the mother and the embryos and thus may serve as a therapeutic supplement during diabetic pregnancy. Diabetes during pregnancy affects >5% of all pregnancies, causing reproductive abnormalities that enhance spontaneous abortion - congenital anomalies, morbidity and mortality of both mother and fetus/newborn. One of the major mechanisms is increased oxidative stress caused by hyperglycaemia and the most prominent anti-teratogenic effect was achieved using antioxidative agents. Management of oxidative stress is considered, along with tight glycaemic control, to be beneficial both before conception and during pregnancy. Taurine, a ubiquitous amino acid found in almost all mammalian tissues, constitutes more than 50% of free amino acids. The aim of the study was to determine whether oral taurine supplementation given to pregnant diabetic rats during the post-implantation period could reduce embryo lethality and protect the developing embryos against maternal hyperglycaemia-induced oxidative stress. Adult rats were rendered diabetic with an acute dose of streptozotocin on gestation day (GD) 4. Both diabetic and non-diabetic dams were administered oral taurine for a period of 8 days (GD 5-13). Maternal diet intake, bodyweight gain and urine output were monitored and dams were killed on GD 13. Markers of oxidative stress and antioxidant defences were studied in embryos and maternal livers. STZ induced marked embryopathy (32%) and taurine supplementation offered significant protection (54%). Taurine significantly offset diabetes-associated oxidative stress in the embryos of diabetic rats. These data suggest that dietary taurine supplementation during pregnancy provides significant protection against diabetes-induced oxidative stress both in mother and embryos and thus may serve as a therapeutic supplement under diabetic pregnancy.

Developmental origins of type 2 diabetes in aboriginal youth in Canada: it is more than diet and exercise

Type 2 diabetes mellitus (T2DM) is classically viewed as a disease of adults caused by poor nutrition, physical inactivity, and obesity. However, with increasing awareness of the heterogeneity of T2DM, new risk factors are being identified that add complexity. Some of these new risk factors have been identified in Canadian people with Aboriginal Oji-Cree heritage, a group that demonstrates one of the highest rates of T2DM in the world. This high prevalence may be due to the rapid change, over the past 50 years, away from their traditional way of life on the land. Another environmental change is the increased rate of pregnancies complicated by obesity, gestational diabetes, or T2DM, resulting in more children being exposed to an abnormal intrauterine environment. Furthermore, the Oji-Cree of central Canada possesses the unique HNF-1α G319S polymorphism associated with reduced insulin secretion. We propose that intrauterine exposure to maternal obesity and T2DM, associated with the HNF-1α G319S polymorphism, results in fetal programming that accelerates the progression of early-onset T2DM. This paper describes the evolution of T2DM in children with a focus on the Oji-Cree people over the past 25 years and the unique prenatal and postnatal gene-environment interaction causing early-onset T2DM.

Endocrine pancreas development: effects of metabolic and intergenerational programming caused by a protein-restricted diet

Experimental studies have demonstrated an association between low birth weight and the later development of type 2 diabetes. This association could be a result of the programming process that affects pancreatic beta-cell development due to poor fetal nutrition. This mechanism may not be limited to the first generation. In rodents, endocrine cells of the pancreas are derived from cells of the endodermal dorsal and ventral anlage that migrate and gather in clusters in a process termed isletogenesis. Islet development occurs relatively late in gestation, and islets undergo substantial remodeling immediately after birth under the regulation of a transcription factor network. Furthermore, the offspring of mice fed a protein-restricted diet exhibit a reduced pancreatic beta-cell mass at birth, lower vascularization, increased apoptosis rate, and changes in glucose metabolism in later life. Although the mechanisms underlying these relationships are unclear, it has been hypothesized that in utero nutritional conditions affect epigenetic patterns of gene transcription that persist throughout life and subsequent generations. We aimed to review the process of the formation of the endocrine pancreas in rodents, the consequences of a protein-restricted diet on offspring, and the transgenerational effects of this insult on the incidence of type 2 diabetes.

Maternal malnutrition programs the endocrine pancreas in progeny

Type 2 diabetes arises when the endocrine pancreas fails to secrete sufficient insulin to cope with metabolic demands resulting from β cell secretory dysfunction, decreased β cell mass, or both. Epidemiologic studies have shown strong relations between poor fetal and early postnatal nutrition and susceptibility to diabetes later in life. Animal models have been established, and studies have shown that a reduction in the availability of nutrients during fetal development programs the endocrine pancreas and insulin-sensitive tissues. We investigated several modes of early malnutrition in rats. Regardless of the type of diet investigated, whether there was a deficit in calories or protein in food or even in the presence of a high-fat diet, malnourished pups were born with a defect in their β cell population, with fewer β cells that did not secrete enough insulin and that were more vulnerable to oxidative stress; such populations of β cells will never completely recover. Despite the similar endpoint, the cellular and physiologic mechanisms that contribute to alterations in β cell mass differ depending on the nature of the nutritional insult. Hormones that are operative during fetal life, such as insulin, insulin-like growth factors, and glucocorticoids; specific molecules, such as taurine; and islet vascularization have been implicated as possible factors in amplifying this defect. The molecular mechanisms responsible for intrauterine programming of β cells are still elusive, but among them the programming of mitochondria may be a strong central candidate.

Impairment of rat fetal beta-cell development by maternal exposure to dexamethasone during different time-windows

Aim

Glucocorticoids (GCs) take part in the direct control of cell lineage during the late phase of pancreas development when endocrine and exocrine cell differentiation occurs. However, other tissues such as the vasculature exert a critical role before that phase. This study aims to investigate the consequences of overexposure to exogenous glucocorticoids during different time-windows of gestation for the development of the fetal endocrine pancreas.

Methods

Pregnant Wistar rats received dexamethasone acetate in their drinking water (1 µg/ml) during the last week or throughout gestation. Fetuses and their pancreases were analyzed at day 15 and 21 of gestation. Morphometrical analysis was performed on pancreatic sections after immunohistochemistry techniques and insulin secretion was evaluated on fetal islets collected in vitro.

Results

Dexamethasone given the last week or throughout gestation reduced the beta-cell mass in 21-day-old fetuses by respectively 18% or 62%. This was accompanied by a defect in insulin secretion. The alpha-cell mass was reduced similarly. Neither islet vascularization nor beta-cell proliferation was affected when dexamethasone was administered during the last week, which was however the case when given throughout gestation. When given from the beginning of gestation, dexamethasone reduced the number of cells expressing the early marker of endocrine lineage neurogenin-3 when analyzed at 15 days of fetal age.

Conclusions

GCs reduce the beta- and alpha-cell mass by different mechanisms according to the stage of development during which the treatment was applied. In fetuses exposed to glucocorticoids the last week of gestation only, beta-cell mass is reduced due to impairment of beta-cell commitment, whereas in fetuses exposed throughout gestation, islet vascularization and lower beta-cell proliferation are involved as well, amplifying the reduction of the endocrine mass.

Alteration of mitochondrial function in adult rat offspring of malnourished dams

Under-nutrition as well as over-nutrition during pregnancy has been associated with the development of adult diseases such as diabetes and obesity. Both epigenetic modifications and programming of the mitochondrial function have been recently proposed to explain how altered intrauterine metabolic environment may produce such a phenotype. This review aims to report data reported in several animal models of fetal malnutrition due to maternal low protein or low calorie diet, high fat diet as well as reduction in placental blood flow. We focus our overview on the β cell. We highlight that, notwithstanding early nutritional events, mitochondrial dysfunctions resulting from different alteration by diet or gender are programmed. This may explain the higher propensity to develop obesity and diabetes in later life.

Nutritional programming of pancreatic β-cell plasticity

Nutritional insufficiency during pregnancy has been shown to alter the metabolism of the offspring and can increase the risk of type 2 diabetes. The phenotype in the offspring involves changes to the morphology and functional capacity of the endocrine pancreas, and in the supporting islet microvasculature. Pancreatic β-cells possess a plastic potential and can partially recover from catastrophic loss. This is partly due to the existence of progenitors within the islets and the ability to generate new islets by neogenesis from the pancreatic ducts. This regenerative capacity is induced by bone marrow-derived stem cells, including endothelial cell progenitors and is associated with increased angiogenesis within the islets. Nutritional insults in early life, such as feeding a low protein diet to the mother, impair the regenerative capacity of the β-cells. The mechanisms underlying this include a reduced ability of β-cells to differentiate from the progenitor population, changes in the inductive signals from the microvasculature and an altered presence of endothelial progenitors. Statin treatment within animal models was associated with angiogenesis in the islet microvasculature, improved vascular function and an increase in β-cell mass. This demonstrates that reversal of the impaired β-cell phenotype observed following nutritional insult in early life is potentially possible.

Effects of periconceptional undernutrition on maternal taurine concentrations in sheep

Taurine has an important role in numerous physiological processes, including many aspects of fetal development such as development of the pancreas and brain, and requirements increase during pregnancy. Periconceptional undernutrition has long-term effects on pancreas and brain function of the offspring, but the effects on maternal taurine economy are unknown. We, therefore, studied the effects of different periods of periconceptional undernutrition on maternal plasma and urine taurine concentrations before and during pregnancy. Four groups of singleton-bearing ewes were studied (n10–11): controls fedad libitum, and groups undernourished from 60 d before until mating (PreC), from 2 d before mating until 30 d after mating (PostC) or from 60 d before until 30 d after mating (Pre+PostC). In PreC ewes, plasma taurine concentrations remained at control levels for the first 30 d, and then decreased through the remainder of undernutrition, but recovered by 30 d after mating; urinary taurine excretion was low at mating, but recovered similarly. In PostC ewes, plasma taurine concentrations recovered after 2 weeks despite ongoing undernutrition; urinary taurine excretion had recovered by 30 d after mating. Pre+PostC ewes followed the same pattern as PreC for the first 60 d, but plasma taurine concentrations and urinary excretion recovered slowly, and did not reach the control levels until 97 d. These data suggest that different periods of mild periconceptional undernutrition in sheep have different but substantial effects on maternal taurine homoeostasis. These effects may be one mechanism by which maternal periconceptional undernutrition alters development of the offspring with implications for adult health.

Developmental origins of health and disease: experimental and human evidence of fetal programming for metabolic syndrome

The concept of developmental origins of health and disease has been defined as the process through which the environment encountered before birth, or in infancy, shapes the long-term control of tissue physiology and homeostasis. The evidence for programming derives from a large number of experimental and epidemiological observations. Several nutritional interventions during diverse phases of pregnancy and lactation in rodents are associated with fetal and neonatal programming for metabolic syndrome. In this paper, recent experimental models and human epidemiological studies providing evidence for the fetal programming associated with the development of metabolic syndrome and related diseases are revisited.

Taurine supplementation restored the changes in pancreatic islet mitochondria in the fetal protein-malnourished rat

Intra-uterine growth retardation has been linked to the development of type 2 diabetes in later life. Mitochondrial changes have been suggested as a link between fetal malnutrition and adult insulin resistance. Taurine has been implicated in this process. We investigated whether protein malnutrition in early life alters mitochondria of the pancreatic islets in adulthood, and whether taurine supplementation restores these changes. Male offspring of rats fed a control diet, a low-protein diet or a low-protein diet supplemented with taurine during pregnancy and lactation were weaned onto the control diet. In each group, at 20 weeks of age, intravenous glucose tolerance tests, euglycaemic–hyperinsulinaemic clamp studies, morphometric analysis of the pancreatic islets and ultra-structural analysis of the mitochondria of the β-cells were performed. The expressions of cytochrome c oxidase (COX) I and mitochondrial respiratory chain complex II were also measured. Fetal protein-malnourished rats showed decreased pancreatic islet mass and reduced insulin-secretory responses to a glucose load. These rats also showed reduced mitochondrial DNA-encoded COX I gene expression in the islets. Electron microscopic examination showed abnormal mitochondrial shapes in the β-cells of fetal protein-malnourished rats. Taurine supplementation to the low-protein diet restored all these changes. Our findings indicate that a maternal protein-restriction diet causes long-lasting mitochondrial changes that may contribute to the development of type 2 diabetes later in life. The lack of taurine may be a key causative factor for these dysfunctional mitochondrial changes.

Maternal amino acid supplementation for intrauterine growth restriction

Maternal dietary protein supplementation to improve fetal growth has been considered as an option to prevent or treat intrauterine growth restriction. However, in contrast to balanced dietary supplementation, adverse perinatal outcomes in pregnant women who received high amounts of dietary protein supplementation have been observed. The responsible mechanisms for these adverse outcomes are unknown. This review will discuss relevant human and animal data to provide the background necessary for the development of explanatory hypotheses and ultimately for the development therapeutic interventions during pregnancy to improve fetal growth. Relevant aspects of fetal amino acid metabolism during normal pregnancy and those pregnancies affected by IUGR will be discussed. In addition, data from animal experiments which have attempted to determine mechanisms to explain the adverse responses identified in the human trials will be presented. Finally, we will suggest new avenues for investigation into how amino acid supplementation might be used safely to treat and/or prevent IUGR.

Epigenetics and maternal nutrition: nature v. nurture

Under- and over-nutrition during pregnancy has been linked to the later development of diseases such as diabetes and obesity. Epigenetic modifications may be one mechanism by which exposure to an altered intrauterine milieu or metabolic perturbation may influence the phenotype of the organism much later in life. Epigenetic modifications of the genome provide a mechanism that allows the stable propagation of gene expression from one generation of cells to the next. This review highlights our current knowledge of epigenetic gene regulation and the evidence that chromatin remodelling and histone modifications play key roles in adipogenesis and the development of obesity. Epigenetic modifications affecting processes important to glucose regulation and insulin secretion have been described in the pancreatic β-cells and muscle of the intrauterine growth-retarded offspring, characteristics essential to the pathophysiology of type-2 diabetes. Epigenetic regulation of gene expression contributes to both adipocyte determination and differentiation in in vitro models. The contributions of histone acetylation, histone methylation and DNA methylation to the process of adipogenesis in vivo remain to be evaluated.

A maternal low protein diet has pronounced effects on mitochondrial gene expression in offspring liver and skeletal muscle; protective effect of taurine

Background

Low birth weight is associated with an increased risk of developing impaired glucose tolerance, and eventually type 2 diabetes in adult life. Gestational protein restriction in rodents gives rise to a low birth weight phenotype in the offspring.

Results

We examined gene expression changes in liver and skeletal muscle of mice subjected to gestational protein restriction (LP) or not (NP), with or without taurine supplementation in the drinking water. LP offspring had a 40% lower birth weight than NP offspring, with taurine preventing half the decrease. Microarray gene expression analysis of newborn mice revealed significant changes in 2012 genes in liver and 967 genes in skeletal muscle of LP offspring. Taurine prevented 30% and 46% of these expression changes, respectively. Mitochondrial genes, especially those involved with oxidative phosphorylation, were more abundantly changed than other genes. The mitochondrial genes were mainly upregulated in liver, but downregulated in skeletal muscle, despite no change in citrate synthase activity in either tissue. Taurine preferentially rescued genes concerned with fatty acid metabolism in liver and with oxidative phosphorylation and TCA cycle in skeletal muscle. A mitochondrial signature was seen in the liver of NP offspring with taurine supplementation, as gene sets for mitochondrial ribosome as well as lipid metabolism were over represented in 4-week-old offspring subjected to gestational taurine supplementation. Likewise, 11 mitochondrial genes were significantly upregulated by gestational taurine supplementation in 4-week-old NP offspring.

Conclusions

Gestational protein restriction resulted in lower birth weight associated with significant gene expression changes, which was different in liver and muscle of offspring. However, a major part of the birth weight decrease and the expression changes were prevented by maternal taurine supplementation, implying taurine is a key factor in determining expression patterns during development and in that respect also an important component in metabolic fetal programming.

Consequences of a compromised intrauterine environment on islet function

Low birth weight is an important risk factor for impaired glucose tolerance and diabetes later in life. One hypothesis is that fetal beta-cells inherit a persistent defect as a developmental response to fetal malnutrition, a primary cause of intrauterine growth restriction (IUGR). Our understanding of fetal programing events in the human endocrine pancreas is limited, but several animal models of IUGR extend our knowledge of developmental programing in beta-cells. Pathological outcomes such as beta-cell dysfunction, impaired glucose tolerance, and diabetes are often observed in adult offspring from these animal models, similar to the associations of low birth weight and metabolic diseases in humans. However, the identified mechanisms underlying beta-cell dysfunction across models and species are varied, likely resulting from the different methodologies used to induce experimental IUGR, as well as from intraspecies differences in pancreas development. In this review, we first present the evidence for human beta-cell dysfunction being associated with low birth weight or IUGR. We then evaluate relevant animal models of IUGR, focusing on the strengths of each, in order to define critical periods and types of nutrient deficiencies that can lead to impaired beta-cell function. These findings frame our current knowledge of beta-cell developmental programing and highlight future research directions to clarify the mechanisms of beta-cell dysfunction for human IUGR.

The developmental origins, mechanisms, and implications of metabolic syndrome

Metabolic syndrome (MetS) represents a combination of cardio-metabolic risk determinants, including central obesity, insulin resistance, glucose intolerance, dyslipidemia, hypertension, hyperinsulinemia, and microalbuminuria. The prevalence of MetS is rapidly increasing worldwide, largely as a consequence of the ongoing obesity epidemic. Environmental factors during periods early in development have been shown to influence the susceptibility to develop disease in later life. In particular, there is a wealth of evidence from both epidemiological and animal studies for greater incidence of features of MetS as a result of unbalanced maternal nutrition. The mechanisms by which nutritional insults during a period of developmental plasticity result in a MetS phenotype are now beginning to receive considerable scientific interest. This review focuses on recent data regarding these mechanisms, in particular the epigenetic and transcriptional regulation of key metabolic genes in response to nutritional stimuli that mediate persistent changes and an adult MetS phenotype. A continued and greater understanding of these mechanisms will eventually allow specific interventions, with a favorable impact on the global incidence of cardiovascular disease and type 2 diabetes in the future.

Gestational protein restriction in mice has pronounced effects on gene expression in newborn offspring's liver and skeletal muscle; protective effect of taurine

We examined gene expression changes in liver and skeletal muscle of newborn mice subjected to a maternal low protein (LP) or normal protein (NP) diet during pregnancy, with or without taurine supplementation in the drinking water. LP offspring had a 40% lower birthweight than NP offspring, whereas it was reduced by only 20% with taurine supplementation. Microarray gene expression analysis revealed significant changes in 2012 genes in liver and 967 genes in skeletal muscle of LP offspring. By unknown mechanisms, taurine partially or fully prevented 30 and 46% of these expression changes, respectively. Mitochondrial genes, in particular genes associated with oxidative phosphorylation, were more abundantly changed in LP offspring, with primarily up-regulation in liver but down-regulation in skeletal muscle. In both tissues, citrate synthase activity remained unchanged. Taurine preferentially rescued changes in genes concerned with fatty acid metabolism in liver and with oxidative phoshorylation and tri carboxylic acid (TCA) cycle in skeletal muscle.

ABBREVIATIONS

Gestational protein restriction resulted in lower birthweight associated with significant gene expression changes, which was different in liver and muscle of offspring. However, a major part of the birthweight decrease and the expression changes were prevented by maternal taurine supplementation, implying taurine is a key component in metabolic fetal programming.

The timing of "catch-up growth" affects metabolism and appetite regulation in male rats born with intrauterine growth restriction

Epidemiological studies demonstrated a relationship between low birth weight mainly caused by intrauterine growth restriction (IUGR) and adult metabolic disorders. The concept of metabolic programming centers on the idea that nutritional and hormonal status during the key period of development determines the long-term control of energy balance by programming future feeding behavior and energy expenditure. The present study examined the consequence of early or late "catch-up growth" after IUGR on feeding behavior and metabolic cues of male offspring of rat dams exposed to protein restriction during gestation and/or lactation. Our results suggest that early catch-up growth may be favorable for fasting metabolic parameters at weaning, as no differences were observed on plasma leptin, triglyceride, glucose, and insulin levels compared with controls. In contrast, if pups remained malnourished until weaning, low insulin concentration was detected and was accompanied by hyperphagia associated with a large increase in hypothalamic NPY and AgRP mRNA expression. At adult age, on a regular chow diet, only the meal structure was modified by fetal programming. The two IUGR groups demonstrated a reduced meal duration that enhanced the speed of food ingestion and consequently increased the rest period associated to the satiety state without changes in the hypothalamic expression of appetite neuropeptides. Our findings demonstrate that in IUGR, regardless of postnatal growth magnitude, metabolic programming occurred in utero and was responsible for both feeding behavior alteration and postprandial higher insulin level in adults. Additionally, catch-up growth immediately after early malnutrition could be a key point for the programming of postprandial hyperleptinemia.

Impact of maternal undernutrition on diabetes and cardiovascular disease risk in adult offspring

Epidemiological, clinical, and experimental observations have led to the hypothesis that the risk of developing chronic diseases in adulthood is influenced not only by genetic and adult lifestyle factors, but also by environmental factors during early life. Low birth weight, a marker of intrauterine stress, has been linked to predisposition to cardiovascular disease (CVD) and diabetes. The compelling animal evidence and significant human data to support this conclusion are reviewed. Specifically, the review discusses the role of maternal nutrition before and during pregnancy, placental insufficiencies and epigenetic changes in the increased predisposition to diabetes and CVD in adult life. The impact of low birth weight and catch-up growth as they pertain to risk of disease in adult life is also discussed. In addition, adult disease risk in the overnourished fetus is also mentioned. Reference is made to some of the mechanisms of the induction of diabetes and CVD phenotype. It is proposed that fetal nutrition, growth and development through efficient maternal nutrition before and during pregnancy could constitute the basis for nutritional strategies for the primary prevention of diabetes and CVD.

Early low protein diet aggravates unbalance between antioxidant enzymes leading to islet dysfunction

BACKGROUND

Islets from adult rat possess weak antioxidant defense leading to unbalance between superoxide dismutase (SOD) and hydrogen peroxide-inactivating enzymatic activities, catalase (CAT) and glutathione peroxidase (GPX) rending them susceptible to oxidative stress. We have shown that this vulnerability is influenced by maternal diet during gestation and lactation.

METHODOLOGY/PRINCIPAL FINDINGS

The present study investigated if low antioxidant activity in islets is already observed at birth and if maternal protein restriction influences the development of islet antioxidant defenses. Rats were fed a control diet (C group) or a low protein diet during gestation (LP) or until weaning (LPT), after which offspring received the control diet. We found that antioxidant enzymatic activities varied with age. At birth and after weaning, normal islets possessed an efficient GPX activity. However, the antioxidant capacity decreased thereafter increasing the potential vulnerability to oxidative stress. Maternal protein malnutrition changed the antioxidant enzymatic activities in islets of the progeny. At 3 months, SOD activity was increased in LP and LPT islets with no concomitant activation of CAT and GPX. This unbalance could lead to higher hydrogen peroxide production, which may concur to oxidative stress causing defective insulin gene expression due to modification of critical factors that modulate the insulin promoter. We found indeed that insulin mRNA level was reduced in both groups of malnourished offspring compared to controls. Analyzing the expression of such critical factors, we found that c-Myc expression was strongly increased in islets from both protein-restricted groups compared to controls.

CONCLUSION AND SIGNIFICANCE

Modification in antioxidant activity by maternal low protein diet could predispose to pancreatic islet dysfunction later in life and provide new insights to define a molecular mechanism responsible for intrauterine programming of endocrine pancreas.

Effects of taurine supplementation on bone mineral density in ovariectomized rats fed calcium deficient diet

Taurine supplementation has been shown to have a beneficial effect on femur bone mineral content in ovariectomized rats. It therefore seemed desirable to find out whether the beneficial effect of taurine on ovariectomized rats fed calcium deficient diet could also be reproduced. Forty female Sprague-Dawley rats were divided into two groups. One group was OVX and the other group received sham operation (SHAM), and received either control diet or a taurine supplemented diet for 6 weeks. All rats were fed on calcium deficient diet (AIN-93: 50% level of calcium) and deionized water. Bone mineral density (BMD) and bone mineral content (BMC) were measured in spine and femur. The serum and urine concentrations of calcium and phosphorus were determined. Bone formation was measured by serum osteocalcin and alkaline phosphatase (ALP) concentrations. Bone resorption rate was measured by deoxypyridinoline (DPD) crosslinks immunoassay and corrected for creatinine. Urinary calcium and phosphorus excretion, osteocalcin in blood and cross link value were not significantly different among the groups. Within the OVX group, the taurine supplemented group had not higher femur bone mineral content than the control group. This study established the need for a study on the taurine effect on bone with different calcium levels.

Developmental origins of adult disease

Intrauterine growth retardation (IUGR) has been linked to development of type 2 diabetes in adulthood. Using a rat model, we tested the hypothesis that uteroplacental insufficiency disrupts the function of the electron transport chain in the fetal beta-cell and leads to a debilitating cascade of events. The net result is progressive loss of beta-cell function and eventual development of type 2 diabetes in the adult. Studies in the IUGR rat demonstrate that an abnormal intrauterine environment induces epigenetic modifications of key genes regulating beta-cell development; experiments directly link chromatin remodeling with suppression of transcription. Future research will be directed at elucidating the mechanisms underlying epigenetic modifications in offspring.

Taurine supplementation enhances nutrient-induced insulin secretion in pancreatic mice islets

BACKGROUND

Taurine (TAU), a naturally occurring sulfur-containing amino acid, is found at high concentrations in plasma and mammalian tissues and regulates osmolarity, ion channel activity, and glucose homeostasis. Several reports have shown that physiological plasma TAU levels seem to be important for adequate beta (beta)-cell function and insulin action, since low concentrations of TAU in the plasma have been reported in the pre-diabetic and diabetic states.

METHODS

Glucose tolerance and insulin sensitivity were investigated in mice supplemented with 2% (w/v) TAU in their drinking water for 30 days, as well as the insulin secretion from isolated islets stimulated by glucose or L-leucine.

RESULTS

TAU-supplemented mice demonstrated improved glucose tolerance and higher insulin sensitivity, compared to controls (CTL). In addition, their islets secreted more insulin in response to high concentrations of glucose and L-leucine. L-[U-(14)C]leucine oxidation was higher in TAU than in CTL islets, whereas D-[U-(14)C]glucose oxidation, ATP levels, glucose transporter (GLUT) 2 and glucokinase (GCK) protein expressions were similar in both types of islets. The L-type beta(2) subunit voltage-sensitive Ca(2+) channel protein, as well as (45)Ca uptake, were significantly higher in TAU-supplemented than CTL islets. In addition, islets from TAU-supplemented mice secreted more glucagon than CTL islets at low glucose.

CONCLUSIONS

TAU supplementation improves glucose tolerance and insulin sensitivity in mice, as well as insulin secretion from isolated islets. The latter effect seems to be, at least in part, dependent on a better Ca(2+) handling by the islets.

3T3-L1 adipocytes and rat adipose tissue have a high capacity for taurine synthesis by the cysteine dioxygenase/cysteinesulfinate decarboxylase and cysteamine dioxygenase pathways

Taurine is the most abundant free amino acid in the body and is synthesized in mammals by 2 pathways. Taurine is synthesized either from the oxidation of cysteine via cysteine dioxygenase (CDO), which generates cysteinesulfinate that is decarboxylated by cysteinesulfinic acid decarboxylase (CSAD), or from the oxidation of cysteamine by cysteamine (2-aminoethanethiol) dioxygenase (ADO). Both pathways generate hypotaurine, which is oxidized to taurine. To determine whether these pathways for taurine synthesis are present in the adipocyte, we studied 3T3-L1 cells during their adipogenic conversion and fat from rats fed diets with varied sulfur-amino acid content. CDO, CSAD, and ADO protein levels increased during adipogenic differentiation of 3T3-L1 cells and all of these enzymes were significantly increased when cells achieved a mature adipocyte phenotype. Furthermore, these changes were accompanied by an increased hypotaurine and taurine production, particularly when cells were treated with cysteine or cysteamine. CDO mRNA levels also responded robustly to cysteine or cysteamine treatment in adipocytes but not in undifferentiated 3T3-L1 cells. Furthermore, CDO protein and activity were greater in adipose tissue from rats fed a high protein or cystine-supplemented low protein (LP) diet than in adipose tissue from rats fed a LP diet. Overall, our results demonstrate that CDO is regulated at both the level of enzyme abundance and the level of mRNA in mature adipocytes.

Are nutrition-induced epigenetic changes the link between socioeconomic pathology and cardiovascular diseases?

The prevalence of cardiovascular diseases (CVD) and diabetes mellitus type 2 (DM 2) is decreasing in developed countries despite the increase in the percentage of subjects with obesity and other well-recognized cardiovascular risk factors. In contrast, the recent transition of the economic model experienced by developing countries, characterized by the adoption of a Western lifestyle, that we have named "socioeconomic pathology," has led to an increase in the burden of CVD. It has been demonstrated that conventional cardiovascular risk factors in developed and developing countries are the same. Why then does the population of developing countries currently have a higher incidence of CVD than that of developed countries if they share the same risk factors? We have proposed the existence of a higher susceptibility to the development of systemic inflammation at low levels of abdominal obesity in the population of developing countries and the consequent endothelial dysfunction, insulin resistance, DM 2, and CVD. In contrast, an important percentage of obese people living in developed countries have a healthy phenotype and low risk of developing CVD and DM 2. Human epidemiologic studies and experimental dietary interventions in animal models have provided considerable evidence to suggest that nutritional imbalance and metabolic disturbances early in life may later have a persistent effect on an adult's health that may even be transmitted to the next generations. Epigenetic changes dependent on nutrition could be key in this evolutionary health behavior, acting as a buffering system, permitting the adaptation to environmental conditions by silencing or increasing the expression of certain genes.

The intrauterine metabolic environment modulates the gene expression pattern in fetal rat islets: prevention by maternal taurine supplementation

AIMS/HYPOTHESIS

Events during fetal life may in critical time windows programme tissue development leading to organ dysfunction with potentially harmful consequences in adulthood such as diabetes. In rats, the beta cell mass of progeny from dams fed with a low-protein (LP) diet during gestation is decreased at birth and metabolic perturbation lasts through adulthood even though a normal diet is given after birth or after weaning. Maternal and fetal plasma taurine levels are suboptimal. Maternal taurine supplementation prevents these induced abnormalities. In this study, we aimed to reveal changes in gene expression in fetal islets affected by the LP diet and how taurine may prevent these changes.

METHODS

Pregnant Wistar rats were fed an LP diet (8% [wt/wt] protein) supplemented or not with taurine in the drinking water or a control diet (20% [wt/wt] protein). At 21.5 days of gestation, fetal pancreases were removed, digested and cultured for 7 days. Neoformed islets were collected and transcriptome analysis was performed.

RESULTS

Maternal LP diet significantly changed the expression of more than 10% of the genes. Tricarboxylic acid cycle and ATP production were highly targeted, but so too were cell proliferation and defence. Maternal taurine supplementation normalised the expression of all altered genes.

CONCLUSIONS/INTERPRETATION

Development of the beta cells and particularly their respiration is modulated by the intrauterine environment, which may epigenetically modify expression of the genome and programme the beta cell towards a pre-diabetic phenotype. This mis-programming by maternal LP diet was prevented by early taurine intervention.

Epigenetic regulation and fetal programming

Fetal programming encompasses the role of developmental plasticity in response to environmental and nutritional signals during early life and its potential adverse consequences (risk of cardiovascular, metabolic and behavioural diseases) in later life. The first studies in this field highlighted an association between poor fetal growth and chronic adult diseases. However, environmental signals during early life may lead to adverse long-term effects independently of obvious effects on fetal growth. Adverse long-term effects reflect a mismatch between early (fetal and neonatal) environmental conditions and the conditions that the individual will confront later in life. The mechanisms underlying this risk remain unclear. However, experimental data in rodents and recent observations in humans suggest that epigenetic changes in regulatory genes and growth-related genes play a significant role in fetal programming. Improvements in our understanding of the biochemical and molecular mechanisms at play in fetal programming would make it possible to identify biomarkers for detecting infants at high risk of adult-onset diseases. Such improvements should also lead to the development of preventive and therapeutic strategies.

Different mechanisms operating during different critical time-windows reduce rat fetal beta cell mass due to a maternal low-protein or low-energy diet

AIMS/HYPOTHESIS

Adverse events during intra-uterine life may programme organ growth and favour disease later in life. In animals, protein or energy restriction during gestation alters the development of the endocrine pancreas, even though the duration of malnutrition is different. Here, we evaluate the specific effects of both diets during different periods of gestation and the mechanisms underlying the decreased beta cell mass.

METHODS

Pregnant Wistar rats were fed either a low-protein or a low-energy diet during the last week of gestation or throughout gestation. Fetuses and their pancreases were analysed at days 15 and 21 of gestation.

RESULTS

The low-energy diet reduced the beta cell mass from 21-day-old fetuses by 33 or 56% when administered during the last week or throughout gestation, respectively. Fetal corticosterone levels were increased. At 15 days of fetal age, the number of cells producing neurogenin 3 (NEUROG3) or pancreatic and duodenal homeobox gene 1 (PDX-1) was reduced. Neither islet vascularisation nor beta cell proliferation was affected. The low-protein diet, in contrast, was more efficient in decreasing the fetal beta cell mass when given during the last week of gestation (-53%) rather than throughout gestation (-33%). Beta cell proliferation was decreased by 50% by the low-protein diet, independently of its duration, and islet vascularisation was reduced. This diet did not affect NEUROG3- or PDX-1-positive cell numbers.

CONCLUSION/INTERPRETATION

Although both diets reduced the fetal beta cell mass, the cellular mechanisms and the sensitivity windows were different. Early alteration of neogenesis due to elevated corticosterone levels is likely to be responsible for the decreased beta cell mass in low-energy fetuses, whereas impaired beta cell proliferation and islet vascularisation at later stages are implicated in low-protein fetuses.

Intrauterine programming of the endocrine pancreas

Epidemiological studies have revealed strong relationships between poor foetal growth and subsequent development of the metabolic syndrome. Persisting effects of early malnutrition become translated into pathology, thereby determine chronic risk for developing glucose intolerance and diabetes. These epidemiological observations identify the phenomena of foetal programming without explaining the underlying mechanisms that establish the causal link. Animal models have been established and studies have demonstrated that reduction in the availability of nutrients during foetal development programs the endocrine pancreas and insulin-sensitive tissues. Whatever the type of foetal malnutrition, whether there are not enough calories or protein in food or after placental deficiency, malnourished pups are born with a defect in their beta-cell population that will never completely recover, and insulin-sensitive tissues will be definitively altered. Despite the similar endpoint, different cellular and physiological mechanisms are proposed. Hormones operative during foetal life like insulin itself, insulin-like growth factors and glucocorticoids, as well as specific molecules like taurine, or islet vascularization were implicated as possible factors amplifying the defect. The molecular mechanisms responsible for intrauterine programming of the beta cells are still elusive, but two hypotheses recently emerged: the first one implies programming of mitochondria and the second, epigenetic regulation.

Protective effects of taurine on endothelial cells impaired by high glucose and oxidized low density lipoproteins

BACKGROUND

Endothelial dysfunction, common to diabetes and cardiovascular diseases, is an early step in the development of atherosclerosis and diabetic angiopathies. Deficiencies of taurine have been related to diabetes and cardiovascular diseases.

AIMS OF THE STUDY

We investigated whether taurine provides protective action against endothelial dysfunction induced by hyperglycemia and/or oxidized low density lipoproteins (oxLDL).

METHODS

Quiescent human umbilical cord venous endothelial cells were exposed for 20 h to high glucose (35 mM) and/or oxLDL (60 microg/ml) alone and in presence of taurine (0.5-2.5 mg/ml). Apoptosis, caspase-3 activity, soluble(s) and cell surface expressions of vascular cellular (VCAM-1) and intercellular (ICAM-1) adhesion molecules were determined. Results are given as a percentage of the low glucose medium control. Apoptosis, VCAM-1 and ICAM-1 expressions were related to cell number.

RESULTS

Hyperglycemia increased apoptosis to 162.5 +/- 19.2%, caspase-3 activity to 153.2 +/- 10.3%, cell-surface expression of VCAM-1 to 125.1 +/- 5.8%, the expression of ICAM-1 to 123.7 +/- 2.8% and sICAM-1 to 146.5 +/- 7.9%. Taurine (0.5-2.5 mg/ml) restored apoptosis, caspase-3 activity and expressions of VCAM-1 and ICAM-1. OxLDL (60 microg/ml) increased apoptosis to 114.8 +/- 3.1%; taurine (2.5 mg/ml) reduced this apoptosis to 40.5 +/- 4.1%. The combination of hyperglycemia and oxLDL increased apoptosis to 211.7 +/- 11.6%. This increase was normalized by taurine (2.5 mg/ml) to 97.9 +/- 12.8%.

CONCLUSION

Taurine protects HUVECs from endothelial dysfunction induced by hyperglycemia through down-regulation of apoptosis and adhesion molecules. Counteracting the combination of oxLDL and hyperglycemia requires pharmacological concentrations of taurine.

Neonatal taurine administration modifies metabolic programming in male mice

The semi-essential amino-acid taurine is involved in glucose homeostasis either in adults or in parental life. Taurine is currently used in neonatal life because it is added to milk formula for babies, and to parental solution for prematures. Here, it has been examined whether taurine administration in lactation modifies adult glucose metabolism. Neonatally taurine-treated mice (50 mg/kg body weight/day, for the first 21 days of life) as adults have lower basal glucose and iAUC after glucose loading curves in comparison with vehicle-treated mice, whereas iAUC following insulin loading curves, plasma lipids and malondialdehyde (MDA), an index of lipid peroxidation were not significantly changed. Thus, in rodents, neonatally administered taurine produces enduring effects in a way that could be advantageous for the control of glucose homoeostasis.

Maternal-fetal deprivation and the cardiometabolic syndrome

Epidemiologic studies suggest a relationship between low birth weight and adverse cardiovascular outcomes. Risk factors such as obesity, insulin resistance, diabetes mellitus, and hypertension--the cardiometabolic syndrome--are similarly affected. These observations are now supported by numerous animal studies. The mechanisms linking low birth weight and the cardiometabolic syndrome later in life appear to be multifactorial and involve alterations in the normal cellular and physiologic systems associated with growth in an unfavorable environment. Such "fetal programming," an adaptation to a shortage of nutrients, may bring about maladaptation upon postnatal exposure to an abundance of nutrients. This review briefly summarizes the adaptive responses in various models used to induce an intrauterine growth restriction, and discusses insights into the mechanisms mediating the fetal programming of the cardiometabolic syndrome.

Enzymes of the taurine biosynthetic pathway are expressed in rat mammary gland

Taurine is the most abundant free amino acid in the body and is present at high concentrations during development and in the early milk. It is synthesized from cysteine via oxidation of cysteine to cysteinesulfinate by the enzyme cysteine dioxygenase (CDO), followed by the decarboxylation of cysteinesulfinate to hypotaurine, catalyzed by cysteine sulfinic acid decarboxylase (CSAD). To determine whether the taurine biosynthetic pathway is present in mammary gland and whether it is differentially expressed during pregnancy and lactation, and also to further explore the possible regulation of hepatic taurine synthesis during pregnancy and lactation, we measured mammary and hepatic CDO and CSAD mRNA and protein concentrations and tissue, plasma and milk taurine concentrations. CDO and CSAD mRNA and protein were expressed in mammary gland and liver regardless of physiological state. Immunohistochemistry demonstrated the expression of CDO in ductal cells of pregnant rats, but not in other mammary epithelial cells or in ductal cells of nonpregnant rats. CDO was also present in stromal adipocytes in mammary glands of both pregnant and nonpregnant rats. Our findings support an upregulation of taurine synthetic capacity in the mammary gland of pregnant rats, based on mammary taurine and hypotaurine concentrations and the intense immunohistochemical staining for CDO in ductal cells of pregnant rats. Hepatic taurine synthetic capacity, particularly CSAD, and taurine concentrations were highest in rats during the early stages of lactation, suggesting the liver may also play a role in the synthesis of taurine to support lactation or repletion of maternal reserves.

Role of metabolic programming in the pathogenesis of beta-cell failure in postnatal life

Intrauterine growth retardation (IUGR) has been linked to later development of type 2 diabetes in adulthood. Human studies indicate that individuals who were growth retarded at birth have impaired insulin secretion and insulin resistance. Multiple animal models of IUGR demonstrate impaired beta-cell function and development. We have developed a model of IUGR in the rat that leads to diabetes in adulthood with the salient features of most forms of type 2 diabetes in the human: progressive defects in insulin secretion and insulin action prior to the onset of overt hyperglycemia. Decreased beta-cell proliferation leads to a progressive decline in beta-cell mass. Using this model, we have tested the hypothesis that uteroplacental insufficiency disrupts the function of the electron transport chain in the fetal beta-cell and leads to a debilitating cascade of events: increased production of reactive oxygen species, which in turn damage mitochondrial (mt) mtDNA and causes further production of reactive oxygen species (ROS). The net result is progressive loss of beta-cell function and eventual development of type 2 diabetes in the adult. Studies in the IUGR rat also demonstrate that an abnormal intrauterine environment induces epigenetic modifications of key genes regulating beta-cell development; experiments directly link chromatin remodeling with suppression of transcription. Future research will be directed at elucidating the mechanisms underlying epigenetic modifications in offspring.

Experimental IUGR and later diabetes

It is widely accepted that an association exists between the intrauterine environment in which a fetus grows and develops and the subsequent development of type 2 diabetes. Any disturbance in maternal ability to provide nutrients and oxygen to the fetus can lead to fetal intrauterine growth restriction (IUGR). Here we will review IUGR in rodent models, in which maternal metabolism has been experimentally manipulated to investigate the molecular basis of the relationship between IUGR and development of type 2 diabetes in later life, and the identification of the molecular derangements in specific metabolically - sensitive organs/tissues.