Amir Tirosh Lab
Long-term metabolic effects of
non-nutritive sweeteners
Excessive consumption of added sugars has been linked to the rise in obesity and associated metabolic abnormalities. Non-nutritive sweeteners (NNSs) offer a potential solution to reduce sugar intake, yet their metabolic safety remains debated. This study aimed to systematically assess the long-term metabolic effects of commonly used NNSs under both normal and obesogenic conditions.
To ensure consistent sweetness level and controlling for the acceptable daily intake (ADI), eight weeks old C57BL/6 male mice were administered with acesulfame K (ace K, 535.25 mg/L), aspartame (411.75 mg/L), sucralose (179.5 mg/L), saccharin (80 mg/L), or steviol glycoside (Reb M, 536.25 mg/L) in the drinking water, on the background of either regular or high-fat diets (in high fat diet 60% of calories from fat). Water or fructose-sweetened water (82.3.gr/L), were used as controls. Anthropometric and metabolic parameters, as well as microbiome composition, were analyzed following 20-weeks of exposure.
Under a regular chow diet, chronic NNS consumption did not significantly affect body weight, fat mass, or glucose metabolism as compared to water consumption, with aspartame demonstrating decreased glucose tolerance. In diet-induced obesity, NNS exposure did not increase body weight or alter food intake. Exposure to sucralose and Reb M led to improved insulin sensitivity and decreased weight gain. Reb M specifically was associated with increased prevalence of colonic Lachnospiracea bacteria.
Long-term consumption of commonly used NNSs does not induce adverse metabolic effects, with Reb M demonstrating a mild improvement in metabolic abnormalities. These findings provide valuable insights into the metabolic impact of different NNSs, aiding in the development of strategies to combat obesity and related metabolic disorders.
Rathaus, M., Azem, L., Livne, R., Ron, S., Ron, I., Hadar, R., Efroni, G., Amir, A., Braun, T., Haberman, Y., Tirosh, A., Long-term metabolic effects of non-nutritive sweeteners., Molecular Metabolism, (2024), 101985. https://doi.org/10.1016/j.molmet.2024.101985.
Adipose tissue-derived FABP4 mediates glucagon-stimulated hepatic glucose production in gestational diabetes
One of the most common complications of pregnancy is gestational diabetes mellitus (GDM), which may result in significant health threats of the mother, fetus and the newborn. Fatty acid-binding protein 4 (FABP4) is an adipokine that regulates glucose homeostasis by promoting glucose production and liver insulin resistance in mouse models. FABP4 levels are increased in GDM and correlates with maternal indices of insulin resistance, with a rapid decline post-partum. We therefore aimed to determine the tissue origin of elevated circulating FABP4 levels in GDM and to assess its potential contribution in promoting glucagon-induced hepatic glucose production.
FABP4 protein and gene expression was determined in biopsies from placenta, subcutaneous (sWAT) and visceral (vWAT) white adipose tissues from GDM and normoglycaemic pregnant women. FABP4 differential contribution in glucagon-stimulated hepatic glucose production was tested in conditioned media before and after its immune clearance.
We showed that FABP4 is expressed in placenta, sWAT and vWAT of pregnant women at term, with a significant increase in its secretion from vWAT of women with GDM compared with normoglycaemic pregnant women. Neutralizing FABP4 from both normoglycaemic pregnant women and GDM vWAT secretome, resulted in a decrease in glucagon-stimulated hepatic glucose production.
This study provides new insights into the role of adipose tissue-derived FABP4 in GDM, highlighting this adipokine, as a potential co-activator of glucagon-stimulated hepatic glucose production during pregnancy.
Ron, I., Mdah, R., Zemet, R., Ulman, R.Y., Rathaus, M., Brandt, B., Mazaki-Tovi, S., Hemi, R., Barhod, E., Tirosh, A., Adipose tissue-derived FABP4 mediates glucagon-stimulated hepatic glucose production in gestational diabetes., Diabetes, Obesity & Metabolism, 25 (11) (2023), 3192–3201. https://doi.org/10.1111/dom.15214.
Fatty acid-binding protein 4: a key regulator of ketoacidosis in new-onset type 1 diabetes
Fatty acid-binding protein 4 (FABP4) is an adipokine with a key regulatory role in glucose and lipid metabolism. We prospectively evaluated the role of FABP4 in the pathophysiology of diabetic ketoacidosis (DKA) in new-onset type 1 diabetes.
Clinical and laboratory data were prospectively collected from consecutive children presenting with new-onset type 1 diabetes. In addition to blood chemistry and gases, insulin, C-peptide, serum FABP4 and NEFA were collected upon presentation and 48 h after initiation of insulin treatment. In a mouse model of type 1 diabetes, glucose, insulin, β-hydroxybutyrate and weight were compared between FABP4 knockout
(Fabp4−/−) and wild-type (WT) mice.
Included were 33 children (mean age 9.3 ± 3.5 years, 52% male), of whom 14 (42%) presented with DKA. FABP4 levels were higher in the DKA group compared with the non-DKA group (median [IQR] 10.1 [7.9–14.2] ng/ml vs 6.3 [3.9–7] ng/ml, respectively; p = 0.005). The FABP4 level was positively correlated with HbA1c at presentation and inversely correlated with venous blood pH and bicarbonate levels (p < 0.05 for all). Following initiation of insulin therapy, a marked reduction in FABP4 was observed in all children. An FABP4 level of 7.22 ng/ml had a sensitivity of 86% and a specificity of 78% for the diagnosis of DKA, with an area under the receiver operating characteristic curve of 0.78 (95% CI 0.6, 0.95; p = 0.008). In a streptozotocin-induced diabetes mouse model, Fabp4−/− mice exhibited marked hypoinsulinaemia and hyperglycaemia similar to WT mice but displayed no significant increase in β-hydroxybutyrate and were protected from ketoacidosis.
FABP4 is suggested to be a necessary regulator of ketogenesis in insulin-deficient states.
Gruber, N., Rathaus, M., Ron, I., Livne, R., Sheinvald, S., Barhod, E., Hemi, R., Tirosh, A., Pinhas-Hamiel, O., Tirosh, A., Fatty acid-binding protein 4: a key regulator of ketoacidosis in new-onset type 1 diabetes., Diabetologia, 65 (2) (2022), 366–374. https://doi.org/10.1007/s00125-021-05606-0.
The adipokine FABP4 is a key regulator of neonatal glucose homeostasis
During pregnancy, fetal glucose production is suppressed, with rapid activation immediately postpartum. Fatty acid–binding protein 4 (FABP4) was recently demonstrated as a regulator of hepatic glucose production and systemic metabolism in animal models. Here, we studied the role of FABP4 in regulating neonatal glucose hemostasis. Serum samples were collected from pregnant women with normoglycemia or gestational diabetes at term, from the umbilical circulation, and from the newborns within 6 hours of life. The level of FABP4 was higher in the fetal versus maternal circulation, with a further rise in neonates after birth of approximately 3-fold. Neonatal FABP4 inversely correlated with blood glucose, with an approximately 10-fold increase of FABP4 in hypoglycemic neonates. When studied in mice, blood glucose of 12-hour-old WT, Fabp4 , and Fabp4 littermate mice was 59 ± 13 mg/dL, 50 ± 11 mg/dL, and 43 ± 11 mg/dL, respectively. Similar to our observations in humans, FABP4 levels in WT mouse neonates were approximately 8-fold higher compared with those in adult mice. RNA sequencing of the neonatal liver suggested altered expression of multiple glucagon-regulated pathways in Fabp4 mice. Indeed, Fabp4 liver glycogen was inappropriately intact, despite a marked hypoglycemia, with rapid restoration of normoglycemia upon injection of recombinant FABP4. Our data suggest an important biological role for the adipokine FABP4 in the orchestrated regulation of postnatal glucose metabolism.
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Ron, I., Lerner, R.K., Rathaus, M., Livne, R., Ron, S., Barhod, E., Hemi, R., Tirosh, A., Strauss, T., Ofir, K., Goldstein, I., Pessach, I.M., Tirosh, A., The adipokine FABP4 is a key regulator of neonatal glucose homeostasis., Journal of Clinical Investigation Insight, 6 (20) (2021),. https://doi.org/10.1172/jci.insight.138288.
Intercellular Transmission of Hepatic
ER Stress in Obesity Disrupts Systemic Metabolism
Endoplasmic reticulum stress (ERS) has a pathophysiological role in obesity-associated insulin resistance. Yet, the coordinated tissue response to ERS remains unclear. Increased connexin 43 (Cx43)-mediated intercellular communication has been implicated in tissue-adaptive and -maladaptive response to various chronic stresses. Here, we demonstrate that in hepatocytes, ERS results in increased Cx43 expression and cell-cell coupling. Co-culture of ER-stressed “donor” cells resulted in intercellular transmission of ERS and dysfunction to ERS-naive “recipient” cells (“bystander response”), which could be prevented by genetic or pharmacologic suppression of Cx43. Hepatocytes from obese mice were able to transmit ERS to hepatocytes from lean mice, and mice lacking liver Cx43 were protected from diet-induced ERS, insulin resistance, and hepatosteatosis. Taken together, our results indicate that in obesity, the increased Cx43-mediated cell-cell coupling allows intercellular propagation of ERS. This novel maladaptive response to over-nutrition exacerbates the tissue ERS burden, promoting hepatosteatosis and impairing whole-body glucose metabolism.
Tirosh, A., Tuncman, G., Calay, E.S., Rathaus, M., Ron, I., Tirosh, A., Yalcin, A., Lee, Y.G., Livne, R., Ron, S., Minsky, N., Arruda, A.P., Hotamisligil, G.S., Intercellular transmission of hepatic ER stress in obesity disrupts systemic metabolism., Cell Metabolism, 33 (2) (2021), 319-333.e6. https://doi.org/10.1016/j.cmet.2020.11.009.
The short-chain fatty acid propionate increases glucagon and FABP4 production, impairing insulin action in mice and humans
The short-chain fatty acid propionate is a potent inhibitor of molds that is widely used as a food preservative and endogenously produced by gut microbiota. Although generally recognized as safe by the U.S. Food and Drug Administration, the metabolic effects of propionate consumption in humans are unclear. Here, we report that propionate stimulates glycogenolysis and hyperglycemia in mice by increasing plasma concentrations of glucagon and fatty acid–binding protein 4 (FABP4). Fabp4-deficient mice and mice lacking liver glucagon receptor were protected from the effects of propionate. Although propionate did not directly promote glucagon or FABP4 secretion in ex vivo rodent pancreatic islets and adipose tissue models, respectively, it activated the sympathetic nervous system in mice, leading to secretion of these hormones in vivo. This effect could be blocked by the pharmacological inhibition of norepinephrine, which prevented propionate-induced hyperglycemia in mice. In a randomized, double-blind, placebo-controlled study in humans, consumption of a propionate-containing mixed meal resulted in a postprandial increase in plasma glucagon, FABP4, and norepinephrine, leading to insulin resistance and compensatory hyperinsulinemia. Chronic exposure of mice to a propionate dose equivalent to that used for food preservation resulted in gradual weight gain. In humans, plasma propionate decreased with weight loss in the Dietary Intervention Randomized Controlled Trial (DIRECT) and served as an independent predictor of improved insulin sensitivity. Thus, propionate may activate a catecholamine-mediated increase in insulin counter-regulatory signals, leading to insulin resistance and hyperinsulinemia, which, over time, may promote adiposity and metabolic abnormalities. Further evaluation of the metabolic consequences of propionate consumption is warranted.
Tirosh, A., Calay, E.S., Tuncman, G., Claiborn, K.C., Inouye, K.E., Eguchi, K., Alcala, M., Rathaus, M., Hollander, K.S., Ron, I., Livne, R., Heianza, Y., Qi, L., Shai, I., Garg, R., Hotamisligil, G.S., The short-chain fatty acid propionate increases glucagon and FABP4 production, impairing insulin action in mice and humans., Science Translational Medicine, 11 (489) (2019),. https://doi.org/10.1126/scitranslmed.aav0120.