Citation: Cabello-Olmo, M.; Oneca, M.; Urtasun, R.; Pajares, M.J.; Goñi, S.; Riezu-Boj, J.I.; Milagro, F.I.; Ayo, J.; Encio, I.J.; Barajas, M.; et al. Pediococcus acidilactici pA1c ® Improves the Beneficial Effects of Metformin Treatment in Type 2 Diabetes by Controlling Glycaemia and Modulating Intestinal Microbiota. Pharmaceutics 2023, 15, 1203. https://doi.org/10.3390/ pharmaceutics15041203 Academic Editor: Barbara R. Conway Received: 17 February 2023 Revised: 21 March 2023 Accepted: 4 April 2023 Published: 10 April 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). pharmaceutics Article Pediococcus acidilactici pA1c ® Improves the Beneficial Effects of Metformin Treatment in Type 2 Diabetes by Controlling Glycaemia and Modulating Intestinal Microbiota Miriam Cabello-Olmo 1 , María Oneca 2 , Raquel Urtasun 1 , María J. Pajares 1,3 , Saioa Goñi 1 , José I. Riezu-Boj 3,4 , Fermín I. Milagro 3,4,5 , Josune Ayo 2 , Ignacio J. Encio 1 , Miguel Barajas 1, * ,† and Miriam Araña 1, * ,† 1 Biochemistry Area, Department of Health Science, Public University of Navarre, 31008 Pamplona, Spain 2 Genbioma Aplicaciones S.L. Polígono Industrial Noain-Esquíroz, Calle S, Nave 4, 31191 Esquíroz, Spain 3 IDISNA Navarra’s Health Research Institute, 31008 Pamplona, Spain 4 Center for Nutrition Research, Department of Nutrition, Food Science and Physiology, University of Navarra, 31008 Pamplona, Spain 5 Centro de Investigación Biomédica en Red de la Fisiopatología de la Obesidad y Nutrición (CIBERobn), Instituto de Salud Carlos III, 28029 Madrid, Spain * Correspondence: miguel.barajas@unavarra.es (M.B.); miriam.arana@unavarra.es (M.A.); Tel.: +34-9-4816-6141 (M.A.) † These authors contributed equally to this work. Abstract: Type 2 diabetes (T2D) is a complex metabolic disease, which involves maintained hyper- glycemia, mainly due to the development of an insulin resistance process. Metformin administration is the most prescribed treatment for diabetic patients. In a previously published study, we demon- strated that Pediococcus acidilactici pA1c ® (pA1c) protects from insulin resistance and body weight gain in HFD-induced diabetic mice. The present work aimed to evaluate the possible beneficial impact of a 16-week administration of pA1c, metformin, or the combination of pA1c and metformin in a T2D HFD-induced mice model. We found that the simultaneous administration of both prod- ucts attenuated hyperglycemia, increased high-intensity insulin-positive areas in the pancreas and HOMA-β, decreased HOMA-IR and also provided more beneficial effects than metformin treat- ment (regarding HOMA-IR, serum C-peptide level, liver steatosis or hepatic Fasn expression), and pA1c treatment (regarding body weight or hepatic G6pase expression). The three treatments had a significant impact on fecal microbiota and led to differential composition of commensal bacterial populations. In conclusion, our findings suggest that P. acidilactici pA1c ® administration improved metformin beneficial effects as a T2D treatment, and it would be a valuable therapeutic strategy to treat T2D. Keywords: Pediococcus acidilactici; probiotic; metformin; high-fat diet; diabetes; glycaemia; intestinal microbiota 1. Introduction Type 2 diabetes mellitus (T2D) is a chronic metabolic disease, mainly characterized by an increased blood glucose concentration produced by deficient insulin secretion by pancreatic islet β cells in the context of impaired insulin sensitivity [1,2]. Type 2 diabetes accounts for more than 90% of patients with diabetes, and the incidence and prevalence of the disease continue to rise globally, becoming one of the leading causes of death world- wide [3]. Moreover, although T2D is mainly linked to adults, lately, the prevalence of this disease has dramatically increased in adolescents and young adults. Genetic predisposition partially explains the individual susceptibility to developing T2D, but an unhealthy diet and a sedentary lifestyle are determinant factors of the current global epidemic [4]. Pharmaceutics 2023, 15, 1203. https://doi.org/10.3390/pharmaceutics15041203 https://www.mdpi.com/journal/pharmaceutics