Reduced pancreatic β-cell mass is associated with decreased FoxO1 and Erk1/2 protein phosphorylation in low-protein malnourished rats

Association between protein undernutrition and diabetes: Molecular implications in the reduction of insulin secretion

Undernutrition is still a recurring nutritional problem in low and middle-income countries. It is directly associated with the social and economic sphere, but it can also negatively impact the health of the population. In this sense, it is believed that undernourished individuals may be more susceptible to the development of non-communicable diseases, such as diabetes mellitus, throughout life. This hypothesis was postulated and confirmed until today by several studies that demonstrate that experimental models submitted to protein undernutrition present alterations in glycemic homeostasis linked, in part, to the reduction of insulin secretion. Therefore, understanding the changes that lead to a reduction in the secretion of this hormone is essential to prevent the development of diabetes in undernourished individuals. This narrative review aims to describe the main molecular changes already characterized in pancreatic β cells that will contribute to the reduction of insulin secretion in protein undernutrition. So, it will provide new perspectives and targets for postulation and action of therapeutic strategies to improve glycemic homeostasis during this nutritional deficiency.

Geriatric nutritional risk index is correlated with islet function but not insulin resistance in elderly patients with type 2 diabetes: A retrospective study

The geriatric nutritional risk index (GNRI) is a simple nutritional assessment tool that can predict poor prognosis in elderly subjects. The aim of this study was to evaluate the association between GNRI and both islet function and insulin sensitivity in patients with type 2 diabetes mellitus. This research carries significant implications for the integrated treatment and nutritional management of this patient population. A total of 173 patients with type 2 diabetes mellitus, aged 60 years or older, who were hospitalized in the Endocrinology Department at Hebei General Hospital from February 2018 to June 2021, were selected as the research subjects. These subjects were divided into 4 groups according to the quartile of their GNRI values: T1 (GNRI < 99.4, n = 43), T2 (99.4 ≤ GNRI < 103, n = 43), T3 (103 ≤ GNRI < 106.3, n = 43), and T4 (GNRI ≥ 106.3, n = 44). Glucose, insulin, and C-peptide concentrations were tested at 0, 30, 60, 120, and 180 minutes during a 75 g oral glucose tolerance test. The homeostasis model assessment for insulin resistance and the homeostasis model assessment for β cell function index were calculated. As the GNRI value increased, the levels of total protein, albumin, hemoglobin, alanine transaminase, aspartate aminotransferase, and 25-hydroxyvitamin D increased significantly. The area under the curve for blood glucose decreased significantly across the 4 groups, while the AUCs for insulin and C-peptide showed an overall increasing trend. β Cell function index increased significantly with the increase of GNRI; meanwhile, both the early-phase insulin secretion index and the late-phase insulin secretion index increased significantly. Although there was an increasing trend, homeostasis model assessment for insulin resistance did not change significantly among the 4 groups. This study indicates that elderly type 2 diabetes patients with higher nutritional risk have worse islet function, while insulin sensitivity is not associated with nutritional risk.

IGF Signaling in Intervertebral Disc Health and Disease

Low back pain (LBP) is a common musculoskeletal symptom, which brings a lot of pain and economic loss to patients. One of the most common causes of LBP is intervertebral disc degeneration (IVDD). However, pathogenesis is still debated, and therapeutic options are limited. Insulin-like growth factor (IGF) signaling pathways play an important role in regulating different cell processes, including proliferation, differentiation, migration, or cell death, which are critical to the homeostasis of tissues and organs. The IGF signaling is crucial in the occurrence and progression of IVDD. The activation of IGF signaling retards IVDD by increasing cell proliferation, promoting extracellular matrix (ECM) synthesis, inhibiting ECM decomposition, and preventing apoptosis and senescence of disc cells. However, abnormal activation of IGF signaling may promote the process of IVDD. IGF signaling is currently considered to have a promising treatment prospect for IVDD. An in-depth understanding of the role of IGF signaling in IVDD may help find a novel approach for IVDD treatment.

Impact of the exposome on the development and function of pancreatic β-cells

The development and plasticity of the endocrine pancreas responds to both the intrauterine and postnatal exposome in a constant attempt to predict and respond to alterations in nutritional availability and metabolic requirements. Both under- and over-nutrition in utero, or exposure to adverse environmental pollutants or maternal behaviors, can each lead to altered β-cell or function at birth, and a subsequent mismatch in pancreatic hormonal demands and secretory capacity postnatally. This can be further exacerbated by metabolic stress postnatally such as from obesity or pregnancy, resulting in an increased risk of gestational diabetes, type 2 diabetes, and even type 1 diabetes. This review will discuss evidence identifying the cellular pathways in early life whereby the plasticity of the endocrine pancreatic can become pathologically limited. By necessity, much of this evidence has been gained from animal models, although extrapolation to human fetal development is possible from the fetal growth trajectory and study of the newborn. Cellular limitations to plasticity include the balance between β-cell proliferation and apoptosis, the appearance of β-cell oxidative stress, impaired glucose-stimulated insulin secretion, and sensitivity to circulating cytokines and responsiveness to programmed death receptor-1. Evidence suggests that many of the cellular pathways responsible for limiting β-cell plasticity are related to paracrine interactions within the islets of Langerhans.

Amino acid restriction alters survival mechanisms in pancreatic beta cells: possible role of the PI3K/Akt pathway

Background and aims

Malnutrition in the early stages of life may lead to changes in the glycemic metabolism during adulthood, such as pancreatic beta cells dysfunction and failure. Therefore, this study aimed to evaluate the effects of an in vitro amino acid restriction model on the function and viability of pancreatic beta cells.

Methods

Insulin-producing cells (INS-1E) were maintained in control or amino acid restricted culture medium containing 1 × or 0.25 × of amino acids, respectively, for 48 h.

Results

Amino acid restricted group showed lower insulin secretion and insulin gene expression, reduced mitochondrial oxygen consumption rate and reactive oxygen species production. Besides, amino acid restricted group also showed higher levels of endoplasmic reticulum stress and apoptosis markers and enhanced Akt phosphorylation. However, even with higher levels of apoptosis markers, amino acid restricted group did not show higher levels of cell death unless the PI3K/Akt pathway was inhibited.

Conclusion

Amino acid restricted beta cell viability seems to be dependent on the PI3K/Akt pathway.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00394-021-02568-2.

Reduced glucose-induced insulin secretion in low-protein-fed rats is associated with altered pancreatic islets redox status

In the present study, we investigated the relationship between early life protein malnutrition-induced redox imbalance, and reduced glucose-stimulated insulin secretion. After weaning, male Wistar rats were submitted to a normal-protein-diet (17%-protein, NP) or to a low-protein-diet (6%-protein, LP) for 60 days. Pancreatic islets were isolated and hydrogen peroxide (H₂ O₂ ), oxidized (GSSG) and reduced (GSH) glutathione content, CuZn-superoxide dismutase (SOD1), glutathione peroxidase (GPx1) and catalase (CAT) gene expression, as well as enzymatic antioxidant activities were quantified. Islets that were pre-incubated with H₂ O₂ and/or N-acetylcysteine, were subsequently incubated with glucose for insulin secretion measurement. Protein malnutrition increased CAT mRNA content by 100%. LP group SOD1 and CAT activities were 50% increased and reduced, respectively. H₂ O₂ production was more than 50% increased whereas GSH/GSSG ratio was near 60% lower in LP group. Insulin secretion was, in most conditions, approximately 50% lower in LP rat islets. When islets were pre-incubated with H₂ O₂ (100 μM), and incubated with glucose (33 mM), LP rats showed significant decrease of insulin secretion. This effect was attenuated when LP islets were exposed to N-acetylcysteine.

Reduced insulin clearance and lower insulin-degrading enzyme expression in the liver might contribute to the thrifty phenotype of protein-restricted mice

Nutrient restriction during the early stages of life usually leads to alterations in glucose homeostasis, mainly insulin secretion and sensitivity, increasing the risk of metabolic disorders in adulthood. Despite growing evidence regarding the importance of insulin clearance during glucose homeostasis in health and disease, no information exists about this process in malnourished animals. Thus, in the present study, we aimed to determine the effect of a nutrient-restricted diet on insulin clearance using a model in which 30-d-old C57BL/6 mice were exposed to a protein-restricted diet for 14 weeks. After this period, we evaluated many metabolic variables and extracted pancreatic islet, liver, gastrocnemius muscle (GCK) and white adipose tissue samples from the control (normal-protein diet) and restricted (low-protein diet, LP) mice. Insulin concentrations were determined using RIA and protein expression and phosphorylation by Western blot analysis. The LP mice exhibited lower body weight, glycaemia, and insulinaemia, increased glucose tolerance and altered insulin dynamics after the glucose challenge. The improved glucose tolerance could partially be explained by an increase in insulin sensitivity through the phosphorylation of the insulin receptor/protein kinase B and AMP-activated protein kinase/acetyl-CoA carboxylase in the liver, whereas the changes in insulin dynamics could be attributed to reduced insulin secretion coupled with reduced insulin clearance and lower insulin-degrading enzyme (IDE) expression in the liver and GCK. In summary, protein-restricted mice not only produce and secrete less insulin, but also remove and degrade less insulin. This phenomenon has the double benefit of sparing insulin while prolonging and potentiating its effects, probably due to the lower expression of IDE in the liver, possibly with long-term consequences.

Global variability in diabetes mellitus and its association with body weight and primary healthcare support in 49 low- and middle-income developing countries

AIMS

In the absence of any previous global comparison, we examined the variability in prevalence of diabetes mellitus across 49 developing countries, and the associations of diabetes with body weight and primary healthcare support using data from the World Health Survey.

METHODS

Diabetes mellitus was defined by individuals' self-report of a physician diagnosis of diabetes. BMI is the weight (kg)/the square of the height (m). Healthcare support was assessed using clinical treatment status and whether patients with diabetes followed prescribed behaviour changes to control diabetes. Associations of diabetes with BMI and diabetes treatment status were analysed cross-sectionally.

RESULTS

A total of 215898 participants were included in the analysis. Age-adjusted prevalence of diabetes ranged from 0.27% (Mali) to 15.54% (Mauritius). Participants who were underweight (BMI <18.5 kg/m(2) ), overweight (BMI 25-29.9 kg/m(2) ) and obese (BMI ≥ 30 kg/m(2) ) were significantly associated with odds of having diabetes as compared with those who were of normal weight (BMI 18.5-24.9 k/m(2) ), with corresponding values of multivariate adjusted odds ratios (95% CI) of 1.15 (1.07-1.24), 1.56 (1.44-1.68) and 2.35 (2.17-2.61), respectively. The overall untreated rate of those with diabetes mellitus was 9.6% in the total sample. Patients with underweight had the highest diabetes untreated rate, followed by those with normal weight, overweight and obesity.

CONCLUSION

There are significant variations in prevalence of diabetes and primary healthcare support for diabetes across low- and middle-income countries. Aggressively preventing abnormal body weight and improving healthcare support may play a pivotal role in ameliorating the unfavourable epidemic of diabetes in developing countries.

Functional and structural adaptations in the pancreatic α-cell and changes in glucagon signaling during protein malnutrition

Chronic malnutrition leads to multiple changes in β-cell function and peripheral insulin actions to adapt glucose homeostasis to these restricted conditions. However, despite glucose homeostasis also depends on glucagon effects, the role of α-cells in malnutrition is largely unknown. Here, we studied α-cell function and hepatic glucagon signaling in mice fed with low-protein (LP) or normal-protein diet for 8 wk after weaning. Using confocal microscopy, we found that inhibition of Ca²⁺ signaling by glucose was impaired in α-cells of LP mice. Consistent with these findings, the ability of glucose to inhibit glucagon release in isolated islets was also diminished in LP mice. This altered secretion was not related with changes in either glucagon gene expression or glucagon content. A morphometric analysis showed that α-cell mass was significantly increased in malnourished animals, aspect that was probably related with their enhanced plasma glucagon levels. When we analyzed the hepatic function, we observed that the phosphorylation of protein kinase A and cAMP response-binding element protein in response to fasting or exogenous glucagon was impaired in LP mice. Additionally, the up-regulated gene expression in response to fasting observed in the hepatic glucagon receptor as well as several key hepatic enzymes, such as peroxisome proliferator-activated receptor γ, glucose-6-phosphatase, and phosphoenolpyruvate carboxykinase, was altered in malnourished animals. Finally, liver glycogen mobilization in response to fasting and the ability of exogenous glucagon to raise plasma glucose levels were lower in LP mice. Therefore, chronic protein malnutrition leads to several alterations in both the α-cell function and hepatic glucagon signaling.

Reduced insulin secretion in protein malnourished mice is associated with multiple changes in the beta-cell stimulus-secretion coupling

The mechanism by which protein malnutrition impairs glucose-stimulated insulin secretion in the pancreatic beta-cell is not completely known but may be related to alterations in the signaling events involved in insulin release. Here, we aimed to study the stimulus-secretion coupling of beta-cells from mice fed with low-protein (LP) diet or normal-protein (NP) diet for 8 wk after weaning. Patch-clamp measurements in isolated cells showed that beta-cells from LP mice had a resting membrane potential that was more hyperpolarized than controls. Additionally, depolarization and generation of action potentials in response to stimulatory glucose concentrations were also impaired in beta-cells of LP mice. All these alterations in the LP group were most likely attributed to higher ATP-dependent K(+) (K(ATP)) channel activity in resting conditions and lower efficiency of glucose to induce the closure of these channels. Moreover, a Western blot analysis revealed higher protein levels of the sulphonylurea receptor of the K(ATP) channel in islets of LP mice. Because beta-cell Ca(2+) signals depend on electrical activity, intracellular Ca(2+) oscillations were measured by fluorescence microscopy in intact islets, indicating a lower response to glucose in the LP group. Finally, cell-to-cell synchrony of Ca(2+) signals was analyzed by confocal microscopy. Islets from LP mice exhibited a decreased level of coupling among beta-cells, which was probably due to the low expression levels of connexin 36. Therefore, low-protein diet leads to several alterations in the stimulus-secretion coupling of pancreatic beta-cells that might explain the diminished insulin secretion in response to glucose in this malnutrition state.