Insulin signaling and antioxidant proteins in adipose tissue explants from dairy cows challenged with hydrogen peroxide are altered by supplementation of arginine or arginine plus methionine

Arginine (Arg) and methionine (Met) can elicit anti-inflammatory and antioxidant effects in animals. Unlike Met, however, it is unknown if the supply of Arg can impact key aspects of adipose tissue (AT) function in dairy cows. Since Met and Arg metabolism are linked through the synthesis of polyamines, it is also possible that they have a complementary effect on aspects of AT function during a stress challenge. In this experiment, subcutaneous AT was harvested from four lactating multiparous Holstein cows (~27.0 kg milk per day, body condition score 3.38 ± 0.23) and used for incubations (4 h) with the following: control medium with an "ideal" profile of essential amino acids (IPAA; CTR; Lys:Met 2.9:1), IPAA plus 100 μM H2O2 (HP), H2O2 plus greater Arg supply (HPARG; Lys:Arg 1:1), or H2O2 plus greater Arg and methionine (Met) supply (HPARGMET; Lys:Met 2.5:1 and Lys:Arg 1:1). Western blotting was used to measure abundance of 18 protein targets associated with insulin and AA signaling, nutrient transport, inflammation, and antioxidant response. Reverse transcription polymerase chain reaction (RT-PCR) was used to assess effects on genes associated with Arg metabolism. Among the protein targets measured, although abundance of phosphorylated (p) AKT serine/threonine kinase (P = 0.05) and p-mechanistic target of rapamycin (P = 0.04) were lowest in HP explants, this effect was attenuated in HPARG and especially HPARGMET compared with CTR. Compared with HP, incubation with HPARG led to upregulation of the AA transporter solute carrier family 1 member 3 (L-glutamate transporter; P = 0.03), the reactive oxygen species detoxification-related enzyme glutathione S-transferase mu 1 (GSTM1; P = 0.03), and fatty acid synthase (P = 0.05). Those effects were accompanied by greater abundance of solute carrier family 2 member 4 (insulin-induced glucose transporter) in explants incubated with HPARG and also HPARGMET (P = 0.04). In addition, compared with other treatments, the peak response in abundance of the intracellular energy sensor 5'-prime-AMP-activated protein kinase was detected with HPARGMET (P = 0.003). There was no effect of Arg or Arg plus Met on the mRNA abundance of genes associated with Arg metabolism (ARG1, NOS2, AMD1, SMS, and SRM). Overall, supplementation of Arg alone or with Met partially alleviated the negative effects induced by H2O2. More systematic studies need to be conducted to explore the function of Arg supply with or without Met on AT function.