GABAergic system in β-cells: from autoimmunity target to regeneration tool

Targeting GABA signaling in type 1 diabetes and its complications- an update on the state of the art

Type 1 diabetes (T1D) is an autoimmune disease that leads to the progressive destruction of insulin-producing β cells, resulting in lifelong insulin dependence and a range of severe complications. Beyond conventional glycemic control, innovative therapeutic strategies are needed to address the underlying disease mechanisms. Recent research has highlighted gamma-aminobutyric acid (GABA) as a promising therapeutic target for T1D due to its dual role in modulating both β cell survival and immune response within pancreatic islets. GABA signaling supports β cell regeneration, inhibits α cell hyperactivity, and promotes α-to-β cell transdifferentiation, contributing to improved islet function. Moreover, GABA's influence extends to mitigating T1D complications, including nephropathy, neuropathy, and retinopathy, as well as regulating central nervous system pathways involved in glucose metabolism. This review consolidates the latest advances in GABA-related T1D therapies, covering animal preclinical and human clinical studies and examining the therapeutic potential of GABA receptor modulation, combination therapies, and dietary interventions. Emphasis is placed on the translational potential of GABA-based approaches to enhance β cell viability and counteract autoimmune processes in T1D. Our findings underscore the therapeutic promise of GABA signaling modulation as a novel approach for T1D treatment and encourage further investigation into this pathway's role in comprehensive diabetes management.

GABA and GLP-1 receptor agonist combination therapy modifies diabetes and Langerhans islet cytoarchitecture in a rat model of Wolfram syndrome

BACKGROUND AND AIM

Wolfram syndrome (WS) is a rare autosomal disorder caused by WFS1 gene mutations, currently lacking approved treatments. Preclinical and clinical reports suggest that diabetes medications, such as glucagon-like peptide-1 receptor agonist (GLP1-RA), slow WS-related diabetes and neurodegeneration, improving patient outcomes. Gamma-aminobutyric acid (GABA) has crucial role in pancreatic islet function and blood glucose regulation. However, its specific role in WS diabetic pathophysiology has never been explored. The aim of this study was to enhance the therapeutic efficacy of liraglutide in mitigating the progression of diabetes associated with WS through supplementation with GABA.

METHODS

In this study, 5-month-old glucose intolerant WS rats and their wild-type littermates where daily treated with GABA (1 g/kg/day), liraglutide (0.4 mg/kg/day), or a combination of both. During the four-month experimental period, the diabetic phenotype was closely monitored using intraperitoneal glucose tolerance tests (IPGTT) and corresponding hormone measurements via enzyme-linked immunoassay. Following the treatments, immunohistochemical staining was performed to examine the morphology, cellular distribution, and health of Langerhans islets.

RESULTS

Unlike in conventional diabetes models, GABA monotherapy alone had no significant effect on the diabetic phenotype in WS rats. In contrast, liraglutide monotherapy effectively delayed diabetes progression. Remarkably, the combined therapy of GABA and liraglutide reversed the diabetic phenotype, significantly enhancing glucose homeostasis, as well as insulin and C-peptide secretion. The combined treatment also increased β-cell mass and corrected the pancreatic Langerhans intra-islet ratio of α-, β-, and δ-cells. As a result, the overall morphology and cytoarchitecture of the pancreatic islets were fully restored, suggesting a potential role for these agents in preserving islet integrity. Additionally, both liraglutide and combination therapy increased the number of GAD (glutamic acid decarboxylase) 65/67-positive β-cells in WS rats, indicating an improvement in general β-cell health.

CONCLUSION

GABA monotherapy had no significant effect on the diabetic phenotype in WS rats, while liraglutide monotherapy effectively delayed diabetes progression. However, the combination therapy of GABA and liraglutide demonstrated a markedly superior effect, not only reversing the diabetic phenotype but also significantly enhancing glucose homeostasis, insulin and C-peptide secretion, and β-cell mass. This combined treatment led to a restoration of Langerhans islet architecture, correction of the endocrine cell proportions, and a notable increase in GAD65/67-positive β-cells, indicating improved β-cell health and function. These findings provide strong evidence supporting the evaluation of GABA and GLP-1 RAs as a combination therapy in clinical trials. Their synergistic effects may offer enhanced β-cell protection, promote functional recovery, and uncover novel therapeutic pathways for treating patients with WS.

The role of GABA in type 1 diabetes

Gamma aminobutyric acid (GABA) is synthesized from glutamate by glutamic decarboxylase (GAD). The entero-pancreatic biology of GABA, which is produced by pancreatic islets, GAD-expressing microbiota, enteric immune cells, or ingested through diet, supports an essential physiologic role of GABA in the health and disease. Outside the central nervous system (CNS), GABA is uniquely concentrated in pancreatic β-cells. They express GAD65, which is a type 1 diabetes (T1D) autoantigen. Glutamate constitutes 10% of the amino acids in dietary protein and is preeminently concentrated in human milk. GABA is enriched in many foods, such as tomato and fermented cheese, and is an over-the-counter supplement. Selected microbiota in the midgut have the enzymatic capacity to produce GABA. Intestinal microbiota interact with gut-associated lymphoid tissue to maintain host defenses and immune tolerance, which are implicated in autoimmune disease. Although GABA is a widely known inhibitory neurotransmitter, oral GABA does not cross the blood brain barrier. Three diabetes-related therapeutic actions are ascribed to GABA, namely, increasing pancreatic β-cell content, attenuating excess glucagon and tamping down T-cell immune destruction. These salutary actions have been observed in numerous rodent diabetes models that usually employed high or near-continuous GABA doses. Clinical studies, to date, have identified positive effects of oral GABA on peripheral blood mononuclear cell cytokine release and plasma glucagon. Going forward, it is reassuring that oral GABA therapy has been well-tolerated and devoid of serious adverse effects.

A critical review on diabetes mellitus type 1 and type 2 management approaches: from lifestyle modification to current and novel targets and therapeutic agents

Diabetes mellitus (DM) has emerged as an international health epidemic due to its rapid rise in prevalence. Consequently, scientists and or researchers will continue to find novel, safe, effective, and affordable anti-diabetic medications. The goal of this review is to provide a thorough overview of the role that lifestyle changes play in managing diabetes, as well as the standard medications that are currently being used to treat the condition and the most recent advancements in the development of novel medical treatments that may be used as future interventions for the disease. A literature search was conducted using research databases such as PubMed, Web of Science, Scopus, ScienceDirect, Wiley Online Library, Google Scholar, etc. Data were then abstracted from these publications using words or Phrases like "pathophysiology of diabetes", "Signe and symptoms of diabetes", "types of diabetes", "major risk factors and complication of diabetes", "diagnosis of diabetes", "lifestyle modification for diabetes", "current antidiabetic agents", and "novel drugs and targets for diabetes management" that were published in English and had a strong scientific foundation. Special emphasis was given to the importance of lifestyle modification, as well as current, novel, and emerging/promising drugs and targets helpful for the management of both T1DM and T2DM.

SARS-CoV-2-Vaccine-Related Endocrine Disorders: An Updated Narrative Review

The emergence of the COVID-19 pandemic has led to the rapid and worldwide development and investigation of multiple vaccines. While most side effects of these vaccines are mild and transient, potentially severe adverse events may occur and involve the endocrine system. This narrative review aimed to explore the current knowledge on potential adverse endocrine effects following COVID-19 vaccination, with thyroid disorders being the most common. Data about pituitary, adrenal, diabetes, and gonadal events are also reviewed. This review also provides a comprehensive understanding of the pathogenesis of endocrine disorders associated with SARS-CoV-2 vaccines. PubMed/MEDLINE, Embase database (Elsevier), and Google Scholar searches were performed. Case reports, case series, original studies, and reviews written in English and published online up to 31 August 2023 were selected and reviewed. Data on endocrine adverse events of SARS-CoV-2 vaccines are accumulating. However, their causal relationship with COVID-19 vaccines is not strong enough to make a definite conclusion, and further studies are needed to clarify the pathogenesis mechanisms of the endocrine disorders linked to COVID-19 vaccines.

Soy yoghurts produced with efficient GABA (γ-aminobutyric acid)-producing Lactiplantibacillus plantarum ameliorate hyperglycaemia and re-establish gut microbiota in streptozotocin (STZ)-induced diabetic mice

Soy yogurt has been gaining popularity as a vegan food produced simply by soymilk fermentation with proper microbial manipulation. It is well known that soy containing rich isoflavones is beneficial for ameliorating hyperglycaemic disorders. Soy fermentation can improve the bioavailability of these precious nutrients. Lactiplantibacillus plantarum is one of the most abundant and frequently isolated species in soymilk manufacturing. Soy yogurts produced with efficient GABA (γ-aminobutyric acid)-producing L. plantarum and the deglycosylating activity of L. plantarum were functionally assessed in a STZ-induced hyperglycaemic mouse model. Hyperglycaemic mice were assigned into groups and treated with daily gavage of either dH₂O, soymilk, soy yoghurts produced with high GABA-producing L. plantarum GA30 (LPGA30), low GABA-producing L. plantarum PV30 (LPPV30) or the soy yoghurts fortified with additional 30 mg g^-1 GABA counterparts (GA + GABA and PV + GABA groups). Except the dH₂O group, all soy yoghurt groups retained body weight with improved glucose homeostasis, glucose tolerance test results and renal tissue integrity, while the soymilk group shows partial benefits. Plasma GABA concentrations in the daily soy yoghurt-supplemented groups (LPGA30 and LPPV30) plateaued at 5 times higher than the average 0.5 μM in dH₂O and soymilk groups, and their GABA-fortified soy yoghurt counterparts (GA + GABA and PV + GABA) groups were accountable for the restored plasma insulin levels. Gut microbiome analysis revealed dysbiosis in STZ-induced hyperglycemic mice of the dH₂O group with breached out facultative anaerobic Proteobacteria over the normal phyla Firmicutes and Bacteroidetes. Restored gut microbiota with transitionally populated Actinobacteria was demonstrated in the LPGA30 group but not in the LPPV30 group. Soy yoghurts produced with efficient GABA-producing L. plantarum GA30 showed exceptional benefits in modulating gut microbiota with dominant genera of Enterococcus, Lactobacillus and Bifidobacterium, and the presence of some minor beneficial microbial communities including Akkermansia muciniphila, Butyricicoccus pullicaecorum, Corynebacterium spp. and Adlercreutzia spp. Efficient GABA-producing L. plantarum GA30 fermented soymilk to produce soy yoghurts that exhibit profound synergistic protections over rich soy isoflavones to restore pancreatic β-cell functions for insulin production in STZ-induced hyperglycaemic mice. Additionally, the probiotic role of GABA-producing L. plantarum in re-establishing healthy gut microbiota in hyperglycaemic mice implies a possible symbiotic relationship, awaiting further exploration.

Enhance Production of γ-Aminobutyric Acid (GABA) and Improve the Function of Fermented Quinoa by Cold Stress

Quinoa is an excellent source of γ-aminobutyric acid (GABA), which is a natural four-carbon non-protein amino acid with great health benefits. In this study, the quinoa was treated by cold stress before fermentation with Lactobacillus plantarum to enhance the amount of GABA. The best Lactobacillus plantarum for GABA production was selected from sixteen different strains based on the levels of GABA production and the activity of glutamic acid decarboxylase (GAD). Cold stress treatments at 4 °C and at -20 °C enhanced the amount of GABA in the fermented quinoa by a maximum of 1191% and 774%, respectively. The surface of the fermented quinoa flour treated by cold stress showed more pinholes, mucus, faults and cracks. A Fourier transform infrared spectrophotometer (FTIR) analysis revealed that cold stress had a violent breakage effect on the -OH bonds in quinoa and delayed the destruction of protein during fermentation. In addition, the results from the rapid visco analyzer (RVA) showed that the cold stress reduced the peak viscosity of quinoa flour. Overall, the cold stress treatment is a promising method for making fermented quinoa a functional food by enhancing the production of bioactive ingredients.

Persistent organic pollutants and β-cell toxicity: a comprehensive review

Persistent organic pollutants (POPs) are a diverse family of contaminants that show widespread global dispersion and bioaccumulation. Humans are continuously exposed to POPs through diet, air particles, and household and commercial products; POPs are consistently detected in human tissues, including the pancreas. Epidemiological studies show a modest but consistent correlation between exposure to POPs and increased diabetes risk. The goal of this review is to provide an overview of epidemiological evidence and an in-depth evaluation of the in vivo and in vitro evidence that POPs cause β-cell toxicity. We review evidence for six classes of POPs: dioxins, polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), organophosphate pesticides (OPPs), flame retardants, and per- and polyfluoroalkyl substances (PFAS). The available data provide convincing evidence implicating POPs as a contributing factor driving impaired glucose homeostasis, β-cell dysfunction, and altered metabolic and oxidative stress pathways in islets. These findings support epidemiological data showing that POPs increase diabetes risk and emphasize the need to consider the endocrine pancreas in toxicity assessments. Our review also highlights significant gaps in the literature assessing islet-specific endpoints after both in vivo and in vitro POP exposure. In addition, most rodent studies do not consider the impact of biological sex or secondary metabolic stressors in mediating the effects of POPs on glucose homeostasis and β-cell function. We discuss key gaps and limitations that should be assessed in future studies.

Cell Death Induction and Protection by Activation of Ubiquitously Expressed Anion/Cation Channels. Part 1: Roles of VSOR/VRAC in Cell Volume Regulation, Release of Double-Edged Signals and Apoptotic/Necrotic Cell Death

Cell volume regulation (CVR) is essential for survival and functions of animal cells. Actually, normotonic cell shrinkage and swelling are coupled to apoptotic and necrotic cell death and thus called the apoptotic volume decrease (AVD) and the necrotic volume increase (NVI), respectively. A number of ubiquitously expressed anion and cation channels are involved not only in CVD but also in cell death induction. This series of review articles address the question how cell death is induced or protected with using ubiquitously expressed ion channels such as swelling-activated anion channels, acid-activated anion channels and several types of TRP cation channels including TRPM2 and TRPM7. The Part 1 focuses on the roles of the volume-sensitive outwardly rectifying anion channels (VSOR), also called the volume-regulated anion channel (VRAC), which is activated by cell swelling or reactive oxygen species (ROS) in a manner dependent on intracellular ATP. First we describe phenotypical properties, the molecular identity, and physical pore dimensions of VSOR/VRAC. Second, we highlight the roles of VSOR/VRAC in the release of organic signaling molecules, such as glutamate, glutathione, ATP and cGAMP, that play roles as double-edged swords in cell survival. Third, we discuss how VSOR/VRAC is involved in CVR and cell volume dysregulation as well as in the induction of or protection from apoptosis, necrosis and regulated necrosis under pathophysiological conditions.

Metallothionein-3 as a multifunctional player in the control of cellular processes and diseases

Transition metals, such as iron, copper, and zinc, play a very important role in life as the regulators of various physiochemical reactions in cells. Abnormal distribution and concentration of these metals in the body are closely associated with various diseases including ischemic seizure, Alzheimer's disease, diabetes, and cancer. Iron and copper are known to be mainly involved in in vivo redox reaction. Zinc controls a variety of intracellular metabolism via binding to lots of proteins in cells and altering their structure and function. Metallothionein-3 (MT3) is a representative zinc binding protein predominant in the brain. Although the role of MT3 in other organs still needs to be elucidated, many reports have suggested critical roles for the protein in the control of a variety of cellular homeostasis. Here, we review various biological functions of MT3, focusing on different cellular molecules and diseases involving MT3 in the body.

Mechanism and effects of pulsatile GABA secretion from cytosolic pools in the human beta cell

Pancreatic beta cells synthesize and secrete the neurotransmitter γ-aminobutyric acid (GABA) as a paracrine and autocrine signal to help regulate hormone secretion and islet homeostasis. Islet GABA release has classically been described as a secretory vesicle-mediated event. Yet, a limitation of the hypothesized vesicular GABA release from islets is the lack of expression of a vesicular GABA transporter in beta cells. Consequentially, GABA accumulates in the cytosol. Here we provide evidence that the human beta cell effluxes GABA from a cytosolic pool in a pulsatile manner, imposing a synchronizing rhythm on pulsatile insulin secretion. The volume regulatory anion channel (VRAC), functionally encoded by LRRC8A or Swell1, is critical for pulsatile GABA secretion. GABA content in beta cells is depleted and secretion is disrupted in islets from type 1 and type 2 diabetic patients, suggesting that loss of GABA as a synchronizing signal for hormone output may correlate with diabetes pathogenesis.

Decreased Serum Level of Gamma-amino Butyric Acid in Egyptian Infertile Females with Polycystic Ovary Syndrome is Correlated with Dyslipidemia, Total Testosterone and 25(OH) Vitamin D Levels

Background

Polycystic ovary syndrome (PCOS) is one of the most common female endocrine disorders around the world. Increasing evidence suggests that neurotransmitter Gamma-aminobutyric acid (GABA) is involved in the pathogenesis of PCOS through its central role in the hypothalamus. However, the peripheral role of GABA in PCOS has not been sufficiently investigated in spite of its existence in peripheral organs. First, the aim of this study is to, investigate serum GABA level in Egyptian PCOS patients. Second, to explore the correlation between serum GABA level with Body Mass Index (BMI), dyslipidemia, totaltestosterone and 25 (OH) vitamin D.

Methods

Eighty PCOS patients and eighty age-matched healthy females were included in this study. All parameters were assessed colourimetrically or with ELISA.

Results

PCOS patients exhibited significantly decreased serum GABA level compared to controls (p < 0.001). There was a significant positive correlation between serum GABA and 25(OH) vitamin D levels (r = 0.26, p = 0.018), and a significant negative correlation with total testosterone (r = - 0.3, p = 0.02), total cholesterol (TC) (r = - 0.31, p = 0.01) and LDL-Cholesterol (LDL-C) (r = - 0.23, p = 0.045), respectively.

Conclusions

The findings of this study suggest that disrupted GABA level in the peripheral circulation is an additional contributing factor to PCOS manifestations. GABA deficiency was correlated with 25 (OH) vitamin D deficiency, dyslipidemia, and total testosterone. Further investigations for GABA adjustment might provide a promising means for better management of PCOS symptoms.

Regeneration of Pancreatic β-Islet Cells in a Type-II Diabetic

A case report is presented in which a type-II diabetic patient significantly improved his dysfunctional β-islet cells using a combination of a strenuous exercise program, cyclical ketogenic diet, and oral GABA/probiotic supplementation. The patient was diagnosed with type-II diabetes at the age of 41 which then progressed through a typical series of treatment changes over 14 years. Treatment periods consisted of metformin therapy alone for 4 years followed by a metformin/glyburide combination therapy for 6 years, and eventually an insulin/metformin combination therapy for 4 years. One year after the initiation of insulin, the patient increased the level of strenuous physical activity (hiking and weight lifting) and adopted a ketogenic diet. Oral GABA and probiotic supplementation were also initiated at the age of 52.7. By the age of 55, the patient no longer required any insulin and is currently being managed with metformin alone. C-peptide values indicate a functional improvement of the β-islet cells during the time of insulin/GABA/probiotic treatment.

GABA Regulates Release of Inflammatory Cytokines From Peripheral Blood Mononuclear Cells and CD4+ T Cells and Is Immunosuppressive in Type 1 Diabetes

The neurotransmitter γ-aminobutyric acid (GABA) is an extracellular signaling molecule in the brain and in pancreatic islets. Here, we demonstrate that GABA regulates cytokine secretion from human peripheral blood mononuclear cells (PBMCs) and CD4⁺ T cells. In anti-CD3 stimulated PBMCs, GABA (100 nM) inhibited release of 47 cytokines in cells from patients with type 1 diabetes (T1D), but only 16 cytokines in cells from nondiabetic (ND) individuals. CD4⁺ T cells from ND individuals were grouped into responder or non-responder T cells according to effects of GABA (100 nM, 500 nM) on the cell proliferation. In the responder T cells, GABA decreased proliferation, and inhibited secretion of 37 cytokines in a concentration-dependent manner. In the non-responder T cells, GABA modulated release of 8 cytokines. GABA concentrations in plasma from T1D patients and ND individuals were correlated with 10 cytokines where 7 were increased in plasma of T1D patients. GABA inhibited secretion of 5 of these cytokines from both T1D PBMCs and ND responder T cells. The results identify GABA as a potent regulator of both Th1- and Th2-type cytokine secretion from human PBMCs and CD4⁺ T cells where GABA generally decreases the secretion.

•

GABA regulates cytokine secretion in anti-CD3-stimulated peripheral blood mononuclear cells (PBMCs) and CD4⁺ T cells.

•

GABA inhibits secretion of 47 cytokines in PBMCs from type 1 diabetes patients.

•

GABA regulates secretion of pro- and anti-inflammatory cytokines in a concentration-dependent manner.

GABA is a signal molecule in the brain, blood and pancreatic islets where it is secreted by the insulin-producing β cells. GABA has many roles in human islets including optimizing function and survival of β cells. Bhandage et al. now show that GABA is a potent regulator of secretion of both pro- and anti-inflammatory cytokines in stimulated immune cells. In type 1 diabetes the β-cell mass is diminished and thus the protective effect of GABA in the islets although not in blood. Targeting GABA signaling in diabetes mellitus is likely to be a part of the solution when curing diabetes.

Functional Characterization of Native, High-Affinity GABAA Receptors in Human Pancreatic β Cells

In human pancreatic islets, the neurotransmitter γ-aminobutyric acid (GABA) is an extracellular signaling molecule synthesized by and released from the insulin-secreting β cells. The effective, physiological GABA concentration range within human islets is unknown. Here we use native GABA_A receptors in human islet β cells as biological sensors and reveal that 100–1000 nM GABA elicit the maximal opening frequency of the single-channels. In saturating GABA, the channels desensitized and stopped working. GABA modulated insulin exocytosis and glucose-stimulated insulin secretion. GABA_A receptor currents were enhanced by the benzodiazepine diazepam, the anesthetic propofol and the incretin glucagon-like peptide-1 (GLP-1) but not affected by the hypnotic zolpidem. In type 2 diabetes (T2D) islets, single-channel analysis revealed higher GABA affinity of the receptors. The findings reveal unique GABA_A receptors signaling in human islets β cells that is GABA concentration-dependent, differentially regulated by drugs, modulates insulin secretion and is altered in T2D.

•

In human islets GABA (≤μM) activates β cell-specific GABA_A receptors that become supersensitive to GABA in type 2 diabetes.

•

GABA_A receptors activity in β cells is enhanced by diazepam, anesthetics, the incretin GLP-1 but not the hypnotic zolpidem.

•

GABA modulates rate of insulin granule exocytosis and glucose-stimulated insulin secretion.

GABA is a signal molecule in the brain but is also secreted by the insulin-producing β cells in pancreatic islets. GABA has many roles in human islets that most aim at optimizing function and survival of β cells. In the report by Korol, Jin et al. the authors identify and characterize the molecular unit that GABA binds to in human β cells, the GABA_A receptors. These receptors normally sensitive become super-sensitive to GABA in type 2 diabetes. The GABA_A receptors regulate insulin secretion and can themselves be regulated by the anxiolytic diazepam, anesthetics, the incretin GLP-1 but not the hypnotic zolpidem. Targeting GABA signaling in human islets in diabetes mellitus is likely to be a part of the solution when curing diabetes.

Sleep Control, GPCRs, and Glucose Metabolism

Modern lifestyles prolong daily activities into the nighttime, disrupting circadian rhythms, which may cause sleep disturbances. Sleep disturbances have been implicated in the dysregulation of blood glucose levels and reported to increase the risk of type 2 diabetes (T2D) and diabetic complications. Sleep disorders are treated using anti-insomnia drugs that target ionotropic and G protein-coupled receptors (GPCRs), including γ-aminobutyric acid (GABA) agonists, melatonin agonists, and orexin receptor antagonists. A deeper understanding of the effects of these medications on glucose metabolism and their underlying mechanisms of action is crucial for the treatment of diabetic patients with sleep disorders. In this review we focus on the beneficial impact of sleep on glucose metabolism and suggest a possible strategy for therapeutic intervention against sleep-related metabolic disorders.

The role of metallothionein-3 in streptozotocin-induced beta-islet cell death and diabetes in mice

Metallothionein-3 (Mt3), a zinc (Zn)-regulatory protein mainly expressed in the central nervous system, may contribute to oxidative cell death. In the present study, we examined the possible role of Mt3 in streptozotocin (STZ)-induced islet cell death and consequent hyperglycemia. Quantitative real-time polymerase chain reaction (RT-PCR) confirmed that islet cells expressed Mt3 mRNA. In all cases, wild-type (WT) mice injected with STZ exhibited hyperglycemia 7-21 days later. In stark contrast, all Mt3-null mice remained normoglycemic following STZ injection. STZ treatment increased free Zn levels in islet cells and induced their death in WT mice, but failed to do so in Mt3-null mice. Consistent with this, cultured Mt3-null islet cells exhibited striking resistance to STZ toxicity. Notably, PDE3a (phosphodiesterase 3A) was downregulated in islets of Mt3-null mice compared to those of WT mice, and was not induced by STZ treatment. Moreover, the PDE3 inhibitor cilostazol reduced islet cell death, likely by increasing cAMP levels, further supporting a role for PDE3 in STZ-induced islet cell death. Collectively, these results demonstrate that Mt3 may act through PDE3a to play a key role in Zn dyshomeostasis and cell death in STZ-treated islets.

Interactions of γ-aminobutyric acid and whey proteins/caseins during fortified milk production

γ-aminobutyric acid mainly cross-links the β-lg fraction and adducts with α-la or α_s1-casein fractions, and tends to form its linear or membered ring structure oligomers.