New mechanisms of phenytoin in calcium homeostasis: competitive inhibition of CD38 in hippocampal cells

The role of nuclear receptor 4A1 (NR4A1) in drug-induced gingival overgrowth

Drug-induced gingival overgrowth (DIGO) is a side effect of cyclosporine A (CsA), nifedipine (NIF), and phenytoin (PHT). Nuclear receptor 4A1 (NR4A1) plays a role in fibrosis in multiple organs. However, the relationship between NR4A1 and DIGO remains unclear. We herein investigated the involvement of NR4A1 in DIGO. In the DIGO mouse model, CsA inhibited the up-regulation of Nr4a1 expression induced by periodontal disease (PD) in gingival tissue, but not that of Col1a1 and Pai1. We detected gingival overgrowth (GO) in Nr4a1 knock out (KO) mice with PD. A NR4A1 agonist inhibited the development of GO in DIGO model mice. TGF-β increased Col1a1 and Pai1 expression levels in KO mouse gingival fibroblasts (mGF) than in wild-type mice, while the overexpression of NR4A1 in KO mGF suppressed the levels. NR4A1 expression levels in gingival tissue were significantly lower in DIGO patients than in PD patients. We also investigated the relationship between nuclear factor of activated T cells (NFAT) and NR4A1. NFATc3 siRNA suppressed the TGF-β-induced up-regulation of NR4A1 mRNA expression in human gingival fibroblasts (hGF). CsA suppressed the TGF-β-induced translocation of NFATc3 into the nuclei of hGF. Furthermore, NIF and PHT also decreased NR4A1 mRNA expression levels and suppressed the translocation of NFATc3 in hGF. We confirmed that CsA, NIF, and PHT reduced cytosolic calcium levels increased by TGF-β, while CaCl₂ enhanced the TGF-β-up-regulated NR4A1 expression. We propose that the suppression of the calcium-NFATc3-NR4A1 cascade by these three drugs plays a role in the development of DIGO.

The inefficacy of donepezil on glycated-AChE inhibition: Binding affinity, complex stability and mechanism

Donepezil (DPZ) is a well-known drug for Alzheimer's disease that inhibits acetylcholinesterase activity (AChE). In the present study, the inhibitory effect of DPZ on non-enzymatic glycated-AChE (GLY-AChE) was studied by different experimental and simulation techniques. The initial investigation revealed that glycation process could reduce AChE activity approximately 60% in the pure enzyme and 38% in the extracted crude AChE from neural cells cultured in the presence of high glucose (HG) concentration. It is suggested that glycation of lysine residues on the structure of AChE could change the conformation of the active site (Trp-86 and His-447) in a way that the orientation of acetylcholine interrupted. The further studies indicated that DPZ is although a strong inhibitor for the native enzyme, it is not able to affect the GLY-AChE activity. The K_D values of AChE-DPZ and GLY-AChE-DPZ complexes were estimated to be 1.88 × 10^-9 and 2.10 × 10^-6, respectively. The stability assessment showed that AChE-DPZ complex is more stable than the glycated complex. Our results indicate that, glycation process could impact on the conformation of the residues involved in the DPZ binding cavity on α-helix domain. Therefore, DPZ is not able to bind its specific cavity to induce its inhibitory effects on GLY-AChE.

Phenytoin - An anti-seizure drug: Overview of its chemistry, pharmacology and toxicology

Phenytoin is a long-standing, anti-seizure drug widely used in clinical practice. It has also been evaluated in the context of many other illnesses in addition to its original epilepsy indication. The narrow therapeutic index of phenytoin and its ubiquitous daily use pose a high risk of poisoning. This review article focuses on the chemistry, pharmacokinetics, and toxicology of phenytoin, with a special focus on its mutagenicity, carcinogenicity, and teratogenicity. The side effects on human health associated with phenytoin use are thoroughly described. In particular, DRESS syndrome and cerebellar atrophy are addressed. This review will help in further understanding the benefits phenytoin use in the treatment of epilepsy.

Pseudo-ginsengenin DQ ameliorated aconitine-induced arrhythmias by influencing Ca2+ and K+ currents in ventricular myocytes

Pseudo-ginsengenin DQ (PDQ) is the product of the oxidative cyclization of protopanaxadiol. PDQ exhibits various bioactivities, including reversal of multidrug resistance in cancer, renal protective effects against acute nephrotoxicity and attenuating myocardial ischemia injury induced by isoproterenol or ligation of coronary arterials, but its effect on arrhythmias has not been clear until now. Because of the complicated effects of ginseng on the cardiovascular system, it is necessary to investigate whether PDQ affects arrhythmias, which are always concomitant with other cardiac diseases. Aconitine was used to induce arrhythmia in vivo. To understand its electrophysiological fundamental, whole-cell patch-clamp was used to record the L-type calcium current (I_Ca,L) and potassium currents (I_K and I_K1) in the ventricular myocytes in rats. Oral administration of PDQ exerted obvious antiarrhythmic effects, as indicated by the decreased incidence rate, lower number of occurrences, and shorter duration time of ventricular tachycardia and ventricular tachycardia, decreased mortality rate and increased survival time. I_Ca,L and I_K were inhibited by PDQ treatment while I_K1 was not affected. To conclude, PDQ may have an anti-arrhythmia effect through inhibiting I_Ca,L and I_K.

Pseudo-ginsengenin DQ (PDQ) is the product of the oxidative cyclization of protopanaxadiol. PDQ could ameliorate aconitine-induced arrhythmias by influencing Ca²⁺ and K⁺ currents in ventricular myocytes.