Long-term consequences of under-nutrition during suckling on glucose tolerance and lipoprotein profile in female and male rats

Litter expansion alters metabolic homeostasis in a sex specific manner

Nutritional manipulations early in life have been shown to influence growth rate and elicit long lasting effects which in turn has been found to impact lifespan. Therefore, we studied the long-term effects of pre-weaning dietary restriction implemented by litter expansion (4, 6, 8, 10, and 12 pups per dam: LS4, LS6, LS8, LS10, LS12) on male and female C57BL/6J mice. After weaning, these mice were fed ad libitum a commercial lab chow for the 15-month duration of the study. The male mice from large litter size (LS12) were significantly leaner and had reduced total fat mass compared to the normal size litters (LS 6) starting from weaning through to 15 months of age. Male LS10 & 12 mice also showed significant reduction in their fat depot masses at 15 months of age: gonadal, subcutaneous, and brown fat whereas the females did not mimic these findings. At 9 months of age, only male LS12 mice showed improved glucose tolerance and male LS12 mice also showed improved insulin tolerance starting at 5 months of age. In addition, we found that the male LS8, 10 & 12 mice at 15 months of age showed significantly reduced IGF-1 levels in the serum and various other organs (liver, gastrocnemius and brain cortex). Interestingly, the female LS8, 10, 12 mice showed a different pattern with reduced IGF-1 levels in serum, liver and gastrocnemius but not in the brain cortex. Similarly, the litter expanded mice showed sex specific response to levels of FGF21 and adiponectin with only the male mice showing increased FGF21 and adiponectin levels at 15 months of age. In summary, our data show that, litter expansion results in long-lasting metabolic changes that are age and sex dependent with the male mice showing an early and robust response compared to female mice.

Mismatch between obesogenic intrauterine environment and low-fat postnatal diet may confer offspring metabolic advantage

OBJECTIVE

Mismatch between a depleted intrauterine environment and a substrate-rich postnatal environment confers an increased risk of offspring obesity and metabolic syndrome. Maternal diet-induced obesity (MATOB) is associated with the same outcomes. These experiments tested the hypothesis that a mismatch between a nutrient-rich intrauterine environment and a low-fat postnatal environment would ameliorate offspring metabolic morbidity.

METHODS

C57BL6/J female mice were fed either a 60% high-fat diet (HFD) or a 10% fat control diet (CD) for 14-week pre-breeding and during pregnancy/lactation. Offspring were weaned to CD. Weight was evaluated weekly; body composition was determined using EchoMRI. Serum fasting lipids and glucose and insulin tolerance tests were performed. Metabolic rate, locomotor, and sleep behavior were evaluated with indirect calorimetry.

RESULTS

MATOB-exposed/CD-weaned offspring of both sexes had improved glucose tolerance and insulin sensitivity compared to controls. Males had improved fasting lipids. Females had significantly increased weight and body fat percentage in adulthood compared to sex-matched controls. Females also had significantly increased sleep duration and reduced locomotor activity compared to males.

CONCLUSIONS

Reduced-fat dietary switch following intrauterine and lactational exposure to MATOB was associated with improved glucose handling and lipid profiles in adult offspring, more pronounced in males. A mismatch between a high-fat prenatal and low-fat postnatal environment may confer a metabolic advantage. The amelioration of deleterious metabolic programming by strict offspring adherence to a low-fat diet may have translational potential.

Lactational programming of glucose homeostasis: a window of opportunity

The window of lactation is a critical period during which nutritional and environmental exposures impact lifelong metabolic disease risk. Significant organ and tissue development, organ expansion and maturation of cellular functions occur during the lactation period, making this a vulnerable time during which transient insults can have lasting effects. This review will cover current literature on factors influencing lactational programming such as milk composition, maternal health status and environmental endocrine disruptors. The underlying mechanisms that have the potential to contribute to lactational programming of glucose homeostasis will also be addressed, as well as potential interventions to reduce offspring metabolic disease risk.

Nutritional limitation in early postnatal life and its effect on aging and longevity in rodents

Nutrient limitation in the form of chronic dietary restriction (DR), or more specifically a life-long reduction of total daily nutritional intake, was first shown to extend longevity in rats more than eight decades ago and is one of the most robust anti-aging interventions known. More recently, it has become apparent that dietary restriction limited to only the first few weeks of life in rodents is also capable of significantly impacting aging and longevity. The imposition of nutrient limitation is often achieved via the manipulation of litter size or the modulation of maternal nutrient intake during the lactational period. Not surprisingly, nutrient limited pups are smaller at weaning, and remain so throughout their life, while exhibiting signs of slowed aging. In this review, we discuss potential mechanisms that account for the anti-aging effects of postnatal undernutrition with an emphasis on those pathways that parallel changes seen with chronic DR.

Metabolic programming in the immediate postnatal life

The metabolic programming effects of nutritional modifications in the immediate postnatal life are increasingly recognized to independently contribute to the development of metabolic syndrome in later life. Adjustment of litter size in rodents has been used to induce either under- or overnourishment in the immediate postnatal life of the offspring. While undernourishment led to growth retardation in the offspring, overnourishment produced increased body weight gains, hyperinsulinemia and hyperleptinemia. Overnourishment during the suckling period induced several adaptations in the energy circuitry in the hypothalamus of the offspring predisposing them for the onset of obesity later in life. Another approach for a nutritional modification in the immediate postnatal period is the artificial rearing of newborn rat pups on a high-carbohydrate (HC) milk formula without changes in the total calorie availability. Hyperinsulinemia, immediately evident in the HC pups, persisted in the post-weaning period even after withdrawal of the HC milk. Significant alterations in pancreatic islets supported chronic hyperinsulinemia in the HC rats. Alterations in the gene expression of hypothalamic neuropeptides predisposing to hyperphagia were evident during the period of the HC dietary modification. The persistence of these hypothalamic adaptations supported the obese phenotype in adult HC rats. A transgenerational effect gave rise to the development of chronic hyperinsulinemia and adult-onset obesity in the offspring of the HC female rats. Other studies have shown that lactation by a diabetic, obese or malnourished mother resulted in predisposition for the onset of metabolic disorders in the offspring. These observations from animal studies on the metabolic programming effects due to altered nutritional experiences in the immediate postnatal life strongly suggest that altered feeding practices for infants (formula feeding and early introduction of infant foods) could contribute to the rising incidence of overweight/obesity in children and adults.

Life-span extension in mice by preweaning food restriction and by methionine restriction in middle age

Life span can be extended in rodents by restricting food availability (caloric restriction [CR]) or by providing food low in methionine (Meth-R). Here, we show that a period of food restriction limited to the first 20 days of life, via a 50% enlargement of litter size, shows extended median and maximal life span relative to mice from normal sized litters and that a Meth-R diet initiated at 12 months of age also significantly increases longevity. Furthermore, mice exposed to a CR diet show changes in liver messenger RNA patterns, in phosphorylation of Erk, Jnk2, and p38 kinases, and in phosphorylation of mammalian target of rapamycin and its substrate 4EBP1, HE-binding protein 1 that are not observed in liver from age-matched Meth-R mice. These results introduce new protocols that can increase maximal life span and suggest that the spectrum of metabolic changes induced by low-calorie and low-methionine diets may differ in instructive ways.

Post-weaning protein malnutrition in the rat produces short and long term metabolic impairment, in contrast to earlier and later periods

Malnutrition during gestation and lactation modifies metabolic strategies and leads to metabolic disease in adult life. Studies in human populations suggest that malnutrition during infancy may also induce long term metabolic disorders.

The present study investigated if post-weaning and a late period of development might be sensitive for long term metabolic impairment. Hereto male Wistar rats were malnourished with a low protein diet (6%), during gestation and lactation (MGL), from weaning to 55 days (MPW) or during adulthood from 90 to 120 days (MA). Control rats (C) were fed with a regular diet (23% protein). We determine plasma concentrations of insulin, glucagon, triacylglycerols (TAG), free fatty acids (FFA), and liver glycogen after a Glucose Tolerance Test (GTT).

Independent of the age of onset, malnutrition induced low body weight. Early and post-weaning malnutrition produced impaired glucose tolerance and low values of TAG, also in MPW induced low values of insulin and glucagon. At 90 days, after balanced diet rehabilitation, the MGL group showed a similar glucose tolerance test as the controls but display low values of insulin, while the MPW group exhibited high levels of glucose and TAG, and low values of insulin, glucagon, FFA and hepatic glycogen. At 180 days, after balanced rehabilitation only MPW rats showed metabolic alterations. Malnutrition during adult life (MA) did not produce metabolic disturbances. Surprisingly the results uncover the post-weaning stage as a vulnerable period to malnutrition that induces long lasting metabolic alterations and deficiency in pancreatic function.

Metabolic programming in the pathogenesis of insulin resistance

This review focuses on different animal models of nutrient perturbations, inclusive of restrictive and excessive states mimicking human situations during pregnancy and lactation that cause aberrations in the offspring. These aberrations consist of diminished insulin sensitivity in the presence of defective insulin production. These phenotypic changes are due to altered peripheral tissue post-insulin receptor signaling mechanisms and pancreatic beta-islet insulin synthesis and secretion defects. While these changes during in utero or postnatal life serve as essential adaptations to overcome adverse conditions, they become maladaptive subsequently and set the stage for type 2 diabetes mellitus. Pregnancy leads to gestational diabetes with trans-generational propagation of the insulin resistant phenotype. This is in response to the metabolically aberrant maternal in utero environment, and tissue specific epigenetic perturbations that permanently alter expression of critical genes transmitted to future generations. These heritable aberrations consisting of altered DNA methylation and histone modifications remodel chromatin and affect transcription of key genes. Along with an altered in utero environment, these chromatin modifications contribute to the world-wide epidemic of type 2 diabetes mellitus, with nutrient excess dominating in developed and nutrient restriction in developing countries.