Thioredoxin-mimetic peptides (TXM) inhibit inflammatory pathways associated with high-glucose and oxidative stress.

Impaired insulin signaling and the associated insulin-resistance in liver, adipose tissue, and skeletal muscle, represents a hallmark of the pathogenesis of type 2-diabetes-mellitus. Here we show that in the liver of db/db mice, a murine model of obesity, type 2 diabetes, and dyslipidemia, the elevated activities of mitogen-activated protein kinases (MAPK; ERK1/2 and p38MAPK), and Akt/PKB are abolished by rosiglitazone-treatment, which normalizes blood glucose in db/db mice. This is unequivocal evidence of a functional link between the activation of the MAPK specific inflammatory-pathway and high-blood sugar. A similar reduction in ERK1/2, p38MAPK, and Akt activities but without affecting blood-glucose was observed in the liver of db/db mice treated with a molecule that mimics the action of thioredoxin, called thioredoxin-mimetic peptide (TXM). N-Acetyl-Cys-Pro-Cys-amide (TXM-CB3) is a free radical scavenger, a reducing and denitrosylating reagent that protects the cells from early death induced by inflammatory pathways. TXM-CB3 also lowered MAPK signaling activated by the disruption of the thioredoxin-reductase-thioredoxin (Trx-TrxR) redox-system and restored Akt activity in rat hepatoma FAO cells. Similarly, two other TXM-peptides, N-Acetyl-Cys-Met-Lys-Cys-amide (TXM-CB13; DY70), and N-Acetyl-Cys-γGlu-Cys-Cys-amide (TXM-CB16; DY71), lowered insulin- and oxidative stress-induced ERK1/2 activation, and rescued HepG2 cells from cell death. The potential impact of TXM-peptides on inhibiting inflammatory pathways associated with high-glucose could be effective in reversing low-grade inflammation. TXM-peptides might also have the potential to improve insulin resistance by protecting from posttranslational modifications like nitrosylation.

Thioredoxin-mimetic peptide CB3 lowers MAPKinase activity in the Zucker rat brain.

Diabetes is a high risk factor for dementia. High glucose may be a risk factor for dementia even among persons without diabetes, and in transgenic animals it has been shown to cause a potentiation of indices that are pre-symptomatic of Alzheimer's disease. To further elucidate the underlying mechanisms linking inflammatory events elicited in the brain during oxidative stress and diabetes, we monitored the activation of mitogen-activated kinsase (MAPKs), c-jun NH2-terminal kinase (JNK), p38 MAP kinases (p38(MAPK)), and extracellular activating kinsae1/2 (ERK1/2) and the anti-inflammatory effects of the thioredoxin mimetic (TxM) peptides, Ac-Cys-Pro-Cys-amide (CB3) and Ac-Cys-Gly-Pro-Cys-amide (CB4) in the brain of male leptin-receptor-deficient Zucker diabetic fatty (ZDF) rats and human neuroblastoma SH-SY5Y cells. Daily i.p. injection of CB3 to ZDF rats inhibited the phosphorylation of JNK and p38(MAPK), and prevented the expression of thioredoxin-interacting-protein (TXNIP/TBP-2) in ZDF rat brain. Although plasma glucose/insulin remained high, CB3 also increased the phosphorylation of AMP-ribose activating kinase (AMPK) and inhibited p70(S6K) kinase in the brain. Both CB3 and CB4 reversed apoptosis induced by inhibiting thioredoxin reductase as monitored by decreasing caspase 3 cleavage and PARP dissociation in SH-SY5Y cells. The decrease in JNK and p38(MAPK) activity in the absence of a change in plasma glucose implies a decrease in oxidative or neuroinflammatory stress in the ZDF rat brain. CB3 not only attenuated MAPK phosphorylation and activated AMPK in the brain, but it also diminished apoptotic markers, most likely acting via the MAPK-AMPK-mTOR pathway. These results were correlated with CB3 and CB4 inhibiting inflammation progression and protection from oxidative stress induced apoptosis in human neuronal cells. We suggest that by attenuating neuro-inflammatory processes in the brain Trx1 mimetic peptides could become beneficial for preventing neurological disorders associated with diabetes.

Thioredoxin-mimetic peptides (TXM) reverse auranofin induced apoptosis and restore insulin secretion in insulinoma cells.

The thioredoxin reductase/thioredoxin system (TrxR/Trx1) plays a major role in protecting cells from oxidative stress. Disruption of the TrxR-Trx1 system keeps Trx1 in the oxidized state leading to cell death through activation of the ASK1-Trx1 apoptotic pathway. The potential mechanism and ability of tri- and tetra-oligopeptides derived from the canonical -CxxC- motif of the Trx1-active site to mimic and enhance Trx1 cellular activity was examined. The Trx mimetics peptides (TXM) protected insulinoma INS 832/13 cells from oxidative stress induced by selectively inhibiting TrxR with auranofin (AuF). TXM reversed the AuF-effects preventing apoptosis, and increasing cell-viability. The TXM peptides were effective in inhibiting AuF-induced MAPK, JNK and p38(MAPK) phosphorylation, in correlation with preventing caspase-3 cleavage and thereby PARP-1 dissociation. The ability to form a disulfide-bridge-like conformation was estimated from molecular dynamics simulations. The TXM peptides restored insulin secretion and displayed Trx1 denitrosylase activity. Their potency was 10-100-fold higher than redox reagents like NAC, AD4, or ascorbic acid. Unable to reverse ERK1/2 phosphorylation, TXM-CB3 (NAc-Cys-Pro-Cys amide) appeared to function in part, through inhibiting ASK1-Trx dissociation. These highly effective anti-apoptotic effects of Trx1 mimetic peptides exhibited in INS 832/13 cells could become valuable in treating adverse oxidative-stress related disorders such as diabetes.