Animal experiment:

DM is induced via a single intraperitoneal (i.p) injection of nicotinamide (110 mg/kg/body weight) dissolved in normal saline 15 min prior to streptozotocin (STZ) (55 mg/kg/body weight) injection, which is dissolved in a freshly prepared 0.1mol/Lcitrate buffer (pH 4.5). These injections are given following an overnight fast. Control rats (n=6) are injected with the same amount of solvent. In order to prevent hypoglycemia in the first 24 h following STZ injection, rats are allowed to have free access to water with 5% dextrose (D5W). Three days after STZ-nicotinamide injection, rats with FBG levels greater than 7.0 mM are considered as diabetic.

IC50: N/A

Nicotinamide is an inhibitor of poly(ADP-ribose) polymerase (PARP-1) enzymes. Poly(ADP-ribose) polymerase-1 (PARP-1) is found as a DNA repair enzyme. The excessive activation of PARP-1, such as ischemia and trauma, can deplete cellular nicotinamide adenine dinucleotide as a substrate and leads to brain cell death eventually.

In vitro: Previous findings suggested that nicotinamide had a protective effect against PARP-1-induced astrocyte death. The transporter-mediated uptake of nicotinamide, which was extracellular pH-sensitive and common to N-methylnicotinamide, was found to be critical for prevention of PARP-1-triggered cell death [1].

In vivo: Type 2 diabetes was induced in Wistar rats by streptozotocin followed by nicotinamide. Test compounds and standard treatment were continued for 15 days. Results showed that there was significant normalisation of liver antioxidant enzymes compared to diabetic rats, suggesting all the tested compounds were beneficial in reducing oxidative stress [2].

Clinical trial: Previous clinical trials showed nicotinamide was well tolerated. Phase 1 showed a dose-response relation for proportional change in frataxin protein concentration. Phases 2 and 3 showed daily dosing resulted in a sustained and significant upregulation of frataxin expression [3].

References:
[1] Suzuki E,Okuda H,Nishida K,Fujimoto S,Nagasawa K. Protective effect of nicotinamide against poly(ADP-ribose) polymerase-1-mediated astrocyte death depends on its transporter-mediated uptake. Life Sci.2010 Apr 24;86(17-18):676-82.
[2] Yogendra Nayak, Venkatachalam Hillemane,Vijay Kumar Daroji,B. S. Jayashree,andM. K. Unnikrishnan. Antidiabetic Activity of Benzopyrone Analogues in Nicotinamide-Streptozotocin Induced Type 2 Diabetes in Rats. Scientific World Journal. 2014; 2014: 854267.
[3] Libri V,Yandim C,Athanasopoulos S,Loyse N,Natisvili T,Law PP,Chan PK,Mohammad T,Mauri M,Tam KT,Leiper J,Piper S,Ramesh A,Parkinson MH,Huson L,Giunti P,Festenstein R. Epigenetic and neurological effects and safety of high-dose nicotinamide in patients with Friedreich's ataxia: an exploratory, open-label, dose-escalation study. Lancet.2014 Aug 9;384(9942):504-13.