535 ISSN 1990-519X, Cell and Tissue Biology, 2024, Vol. 18, No. 5, pp. 535–548. © Pleiades Publishing, Ltd., 2024. The Protective Role of Caffeine against Histological and Ultrastructural Changes of Peripheral Nerve in Type 2 Diabetic Rats Manal A. Othman a, b, * (ORCID: 0000-0002-5967-1023), Bhagath Kumar Potu a (ORCID: 0000-0002-7945-5037), Aisha Rashid a (ORCID: 0000-0001-8910-214X), Ayesha Fatima a (ORCID: 0000-0002-2391-090X), and Wael Amin Nasr El-Din a, c (ORCID: 0000-0003-3673-990X) a Department of Anatomy, College of Medicine and Medical Sciences, Arabian Gulf University, Manama, Bahrain b Department of Histology and Cell Biology, Faculty of Medicine, Assiut University, Assiut, Egypt c Department of Human Anatomy and Embryology, Faculty of Medicine, Suez Canal University, Ismailia, Egypt *e-mail: manalamo@agu.edu.bh Received May 1, 2024; revised June 9, 2024; accepted June 17, 2024 Abstract—Type 2 diabetes mellitus (T2DM) is linked to injuries to many organs including the nervous system. Diabetic peripheral neuropathy (DPN) is a common complication of diabetes; it can result in disruption of Schwann cells (SCs) function, degeneration of nerve axons and demyelination. SCs provide trophic support to neurons and myelin formation and their role in nerve injury and regeneration is very crucial. Caffeine, a psychoactive beverage, was found to reduce the risk of many disorders including nervous system degenera- tion. The purpose of this study was to address the role of caffeine in peripheral nerve degeneration in a rat model of T2DM. Wistar rats were fed with a high caloric diet and injected with a single low dose of strepto- zotocin (STZ). Caffeine was administered to the rats orally for 5 weeks and was given one week before injec- tion of STZ. The rats were sacrificed, then sciatic nerves were harvested, and processed for histological and electron microscopic evaluations. Immunohistochemistry was also done using the primary antibodies: anti S-100 (Schwann cell marker), anti-MBP (myelin basic protein) and anti-VEGF-A (vascular endothelial growth factor A). Examination of the sciatic nerve of diabetic rats revealed degeneration of SCs and axons, myelin, and connective tissue coverings. There was decrease in immunostaining of S-100 and MBP and increase in VEGFA, in diabetic rats. Administration of caffeine to diabetic rats resulted in improvement of histological and ultrastructural changes and upregulation of S-100, MBP, and downregulation of VEGFA. There were degenerative changes of the sciatic nerve of diabetic rats that were ameliorated by the administra- tion of caffeine. Keywords: type 2 diabetes, peripheral nerve, myelin, schwann cell, VEGF, ultrastructure DOI: 10.1134/S1990519X24700500 INTRODUCTION Diabetic peripheral neuropathy (DPN) is one of the most common chronic complications of type 1 and type 2 diabetes mellitus (T2DM), which can affect half of the patients suffering from diabetes mellitus (Othman et al., 2018; Mizokami-Stout et al., 2020; Ding et al., 2023). Many patients may experience nerve degeneration 10–20 years after being diagnosed with diabetes (Srivastava et al., 2022). The exact mechanisms of the pathogenesis of DPN are not com- pletely discovered. It was reported that the main pathogenesis for DPN is related to hyperglycemia and insulin resistance (Kazamel et al., 2021). Additionally, microvascular impairment and injury to the endothe- lium of blood vessels may play major roles in DPN (Yorek, 2015). Schwann cells (SCs) are the glial cells of the peripheral nervous system, which are involved in the development and regeneration of peripheral nerves. They perform myelination and ensheathment of nerve axons and modulate axonal integrity and hence, neu- ronal function (Mizisin, 2014; Wang et al., 2020). Through the production of several neurotrophic sub- stances and extracellular matrix, SCs alter the endo- neurial milieu by enhancing sodium channels, insulat- ing the action potential velocity of axons, and encour- aging the regeneration of axons following nerve damage (Gonçalves et al., 2018; Hassen et al., 2019). Earlier studies reported that diabetic Schwannopathy is linked to peripheral nerve axonal demyelination and poor remyelination (Shi et al., 2013; Kim et al., 2020). Neuroaxonal dystrophy is thought to be the patholog- ical characteristic feature of neuropathy causing sig- nificant degenerative changes in SCs, which affect myelination of the peripheral nerves (Han et al., 2016). Further research has demonstrated that several