Amyloid-β peptide (Aβ) is eliminated from the brain across the blood–brain barrier (BBB) by an insulin-sensitive process. To investigate the involvement of insulin-degrading enzyme (IDE) in this process, the present study was implemented to clarify the effect of a novel IDE-specific inhibitor, Ii1, on the elimination of [¹²⁵I]Aβ(1-40) from rat brain via the brain efflux index method. The results showed that such elimination was significantly inhibited by the co-administration of Ii1. The maximum inhibitory effect of Ii1 and IC₅₀ were 69.4% and 9.96 µM, respectively. Insulin alone inhibited the elimination of [¹²⁵I]Aβ(1-40), but the inhibitory effect of co-administering insulin and Ii1 was not significantly different from that of Ii1 alone. Meanwhile, thiorphan, an inhibitor of neprilysin, showed an additive inhibitory effect with Ii1. Aβ(1-13) and Aβ(1-14), which are major fragments produced by the degradation of Aβ(1-40) by IDE, and inhibitors of receptor for advanced glycation end products (RAGE) did not significantly inhibit the [¹²⁵I]Aβ(1-40) elimination. These results suggest that IDE is involved in the insulin-sensitive process of [¹²⁵I]Aβ(1-40) elimination across the BBB, to which neprilysin and RAGE make minor contributions. These findings suggest that impairment of IDE may be involved in the onset of sporadic Alzheimer’s disease.

This study investigated the protective effects of metformin against combined high glucose (HG)- and UVA-induced cytotoxicity in fetal rat skin keratinocytes (FRSK cells), a model of diabetic photoaging. HG combined with UVA caused a synergistic loss of cell viability accompanied by marked increases in phosphorylation of AMP-activated protein kinase (p-AMPK), reactive oxygen species (ROS) generation, senescence-associated β-galactosidase (SA-β-Gal) activity, and Sirtuin 1 (SIRT1) expression. HG alone induced moderate cytotoxicity and senescence, whereas UVA alone under normal glucose conditions (NG + UVA) produced negligible ROS and minimal viability loss. Metformin improved cell viability under dual stress conditions in a dose-dependent manner, with maximal protection observed at 8 mM. In UVA-free cultures, metformin increased p-AMPK in both NG and HG, peaking at 8 mM. Under HG + UVA, p-AMPK was higher than in NG + UVA and HG alone, with no additional increase following metformin treatment. ROS accumulation occurred only under HG + UVA and was strongly suppressed by metformin, nearly to baseline at 8 mM. The HG + UVA-induced increases in SA-β-Gal activity and SIRT1 expression were reduced in parallel with ROS suppression. These findings suggest that metformin’s cytoprotective effect in this model is primarily mediated by attenuation of ROS rather than by further AMPK activation, indicating an AMPK-independent antioxidant mechanism.

“Antibody engineering” is a promising strategy for generating high-affinity antibodies required for developing sensitive immunoassays. Therein, the variable domains (V_H and V_L) of the parental antibody are genetically randomized and combined to produce diverse single-chain Fv fragment (scFv) molecules. Subsequently, high-affinity scFv mutants are selectively isolated. In the randomization process, mutations have conventionally been targeted to the complementarity-determining regions (CDRs) in the variable domains, which often interact directly with antigens. However, we previously discovered that, pinpoint insertion of only a single amino acid (leucine, asparagine, aspartic acid, proline, glutamine, arginine, or histidine) between positions 6 and 7 in the framework region 1 (FR1) of the V_H, which is unlikely to interact with antigens, enhanced the affinity of an anti-cortisol scFv (original K_a, 3.6 × 10⁸ M⁻¹) up to 17–61-fold. These findings prompted us to conduct a comprehensive study of this affinity-enhancement phenomenon involving the remaining amino acids. Thus, we generated the necessary 13 scFv mutants and compared their K_a values. Remarkably, all mutants showed enhanced affinities, similar to those of the previous 7 mutants. Among the 20 mutants, the leucine-inserted scFv showed the largest K_a (2.2 × 10¹⁰ M⁻¹) and consequently enabled a 75-fold more sensitive enzyme-linked immunosorbent assay (midpoint, 9.86 pg/assay) compared to the assay using the parental scFv (midpoint, 744 pg/assay). In silico modeling suggested that, regardless of the amino acid inserted, elongated FR1 can alter the conformation of the CDR3 in V_H to facilitate a favorable interaction with cortisol.

It is known that the daily feeding cycle affects the dosing time-dependent changes in the pharmacodynamics and pharmacokinetics of many drugs. Our previous study demonstrated that administration of empagliflozin (EMPA), sodium-glucose cotransporter 2 (SGLT2) inhibitor, at the beginning of daily feeding cycle (active phase) effectively prevents the development of neuropathic pain in streptozotocin (STZ)-induced diabetic mice. Although the blood glucose levels are closely related to feeding, the relationship between the daily feeding cycle and the optimal dosing time of EMPA remains unclear. In this study, we used STZ-induced diabetic mice and implemented a daily time-restricted feeding (TRF) regimen to investigate whether the dosing time-dependent preventive effect of EMPA on the diabetic neuropathy is modulated by TRF. Animals were housed under a 12-h light/dark cycle, and were assigned to either light-phase TRF (feeding during the light phase) or dark-phase TRF (feeding during the dark phase). The hypoglycemic effect of EMPA was enhanced when the drug was administrated at the beginning of both TRF conditions. A similar influence of the daily feeding cycle on the dosing time-dependent hypoglycemic effect of EMPA was also observed in its preventive effect on the development of diabetic neuropathic pain. Further analysis revealed that dosing time-dependent variations in both the hypoglycemic effect of EMPA and its preventive effect on diabetes-induced pain hypersensitivity were attributable to corresponding changes in urinary glucose excretion. Our results support the notion that the administration of EMPA at the onset of daily feeding cycle effectively suppresses the development of diabetic peripheral neuropathy.

Metabolic enzymes are occasionally downregulated in in vitro induction studies. Recently, HepaRG cells have been used for CYP induction assays instead of human hepatocytes in the early drug discovery stage; however, there is limited information on CYP downregulation by drug stimulation. In this study, we evaluated the effect of hypoxia-inducible factor-prolyl hydroxylase (HIF-PH) inhibitors, which downregulate CYP in human hepatocytes, on CYP gene expression in HepaRG cells. Microarray analysis to determine the expression levels of pharmacokinetics-related enzymes and RT-PCR to determine the expression levels of CYP3A4, CYP2B6, CYP1A2, and their nuclear receptor mRNA were conducted in HepaRG cells treated with HIF-PH inhibitors. Treatment of HepaRG cells with HIF-PH inhibitors decreased the expression of several pharmacokinetics-related metabolic enzymes, whereas Erythropoietin (EPO) and Pyruvate Dehydrogenase Kinase1 (PDK1) genes were induced. The expression of CYP3A4 and CYP2B6 in HepaRG cells showed concentration- and time-dependent downregulation following treatment with the HIF-PH inhibitor. The downregulation of these enzymes was correlated with the decrease of PXR/RXRα and CAR/RXRα, respectively. CYP1A2 decreased transiently, but recovered with continued HIF-PH inhibitor treatment. CYP3A4 and CYP2B6 were downregulated by HIF-PH inhibitors in HepaRG cells and human hepatocytes. In contrast, CYP1A2 in HepaRG cells responded differently to HIF-PH inhibitors than in human hepatocytes. Since CYP downregulation is commonly observed with HIF-PH inhibitors, along with the induction of EPO and PDK1 genes, stabilizing HIF may be one of the factors involved in CYP downregulation.