Lubabegron fumarate acts as a ß-adrenergic receptor antagonist in cultured bovine intramuscular and subcutaneous adipocytes.

We hypothesized that lubabegron fumarate (LUB) (Experior, Elanco Animal Health, Greenfield, IN) would act as an antagonist to ß-adrenergic receptor (ß-AR) subtypes in primary bovine subcutaneous (s.c.) and intramuscular (i.m.) adipocytes differentiated in culture. This study employed LUB, dobutamine (DOB, a selective ß1-agonist), salbutamol (SAL, a selective ß2-agonist), and propranolol (PRO, a non-selective ß-AR antagonist). Preadipocytes were isolated by standard techniques from bovine longissimus muscle and overlying s.c. adipose tissue and differentiated to adipocytes for 14 d. The adipocyte source x stage of differentiation interaction was significant for ß-adrenergic receptors-1 (ADRB1) (P = 0.001) and ADRB2 (P = 0.01) in that expression of ADRB1 and ADRB2 was greater in s.c. adipocytes than in s.c. preadipocytes; expression of the ADRB1-3 did not change after differentiation of i.m. adipocytes. CCATT/enhancer-binding protein alpha (CEBPA) expression increased upon differentiation in both s.c. and i.m. adipocytes (P = 0.006). The source x stage of differentiation interaction was significant for peroxisome proliferator-activated receptor gamma (PPARG) (P ≤ 0.001) and fatty acid binding protein-4 (FABP4) (P = 0.004). Expression of PPARG increased after differentiation of s.c. preadipocytes to adipocytes, but PPARG expression did not change with differentiation of i.m. preadipocytes to adipocytes. FABP4 expression increased after differentiation of both s.c. and i.m. adipocytes, but FABP4 expression increased to a greater extent in s.c. adipocytes. In s.c. adipocytes, DOB elevated cAMP and glycerol production and protein kinase A (PKA) activity, and SAL increased PKA activity; these effects were abolished by LUB and PRO (P < 0.001). Incubation of i.m. adipocytes with SAL increased cAMP production and PKA activity, which was attenuated by LUB and PRO (P ≤ 0.006). In s.c. adipocytes, SAL, LUB + SAL, and LUB + DOB upregulated hormone sensitive lipase (HSL) (P < 0.001) and perilipin (P = 0.002) gene expression. In i.m. adipocytes, DOB and LUB + DOB increased HSL gene expression (P = 0.001) and LUB + SAL depressed adipose triglyceride lipase expression below control levels (P = 0.001). These results demonstrate that LUB is a ß-AR antagonist at the ß1-AR and ß2-AR subtypes in s.c. adipocytes, and that s.c. and i.m. exhibit different responses to ß-AA and LUB.

We hypothesized that lubabegron fumarate (Experior, Elanco, Greenfield, IN) would act as an antagonist to ß-adrenergic receptor subtypes in primary bovine backfat (subcutaneous) and marbling (intramuscular) adipocytes differentiated in culture. Fat cells were isolated from marbling of longissimus muscle and overlying backfat. In backfat cells, lubabegron fumarate downregulated genes associated with turnover of stored lipid, and lubabegron fumarate reversed the increase in cyclic AMP and protein kinase A caused by the ß1-adrenergic receptor agonist, dobutamine, and the ß2-adrenergic agonist, salbutamol. Increasing cyclic AMP amount and protein kinase A activity would lead to a decrease in backfat lipid stores (reducing backfat thickness), and this would be effectively blocked by lubabegron fumarate. Salbutamol but not dobutamine increased cyclic AMP amount and protein kinase A activity in marbling fat cells, and this effect was blocked by lubabegron fumarate. Taken together, the results of this study indicate that lubabegron fumarate antagonizes the effects of hormones that promote lipid loss from backfat and marbling. However, marbling fat cells are not as responsive as backfat fat cells to ß-adrenergic agonists, so ß-adrenergic agonists such as Zilmax and OptiFlex should have less effect on marbling scores than on backfat thickness.

Characterization of ß-adrenergic receptors in bovine intramuscular and subcutaneous adipose tissue: comparison of lubabegron fumarate with ß-adrenergic receptor agonists and antagonists.

Chinese hamster ovary cell constructs expressing either the ß 1-, ß 2- or ß 3-adrenergic receptor (AR) were used to determine whether a novel ß-AR modulator, lubabegron fumarate (LUB; Experior, Elanco Animal Health) might exert greater potency for a specific ß-AR subtype. EC50 values calculated based on cAMP accumulation in dose response curves indicate that LUB is highly selective for the ß 3-AR subtype, with an EC50 of 6 × 10-9 M, with no detectible agonistic activity at the ß 2-AR. We hypothesized that the accumulation of lipolytic markers would reflect the agonist activity at each of the ß-receptor subtypes of the specific ligand; additionally, there would be differences in receptor subtype expression in subcutaneous (s.c.) and intrmuscular (i.m.) adipose tissues. Total RNA was extracted from adipose tissue samples and relative mRNA levels for ß 1-, ß2-, and ß 3-AR were measured using real-time quantitative polymerase chain reaction. Fresh s.c. and i.m. adipose tissue explants were incubated with isoproterenol hydrochloride (ISO; ß-AR pan-agonist), dobutamine hydrochloride (DOB; specific ß 1-AA), salbutamol sulfate (SAL; specific ß 2-AA), ractopamine hydrochloride (RAC), zilpaterol hydrochloride (ZIL), BRL-37344 (specific ß 3-agonist), or LUB for 30 min following preincubation with theophylline (inhibitor of phosphodiesterase). Relative mRNA amounts for ß 1-, ß 2-, and ß 3-AR were greater (P < 0.05) in s.c. than in i.m. adipose tissue. The most abundant ß-AR mRNA in both adipose tissues was the ß 2-AR (P < 0.05), with the ß 1- and ß 3-AR subtypes being minimally expressed in i.m. adipose tissue. ISO, RH, and ZH stimulated the release of glycerol and nonesterified fatty acid (NEFA) from s.c. adipose tissue, but these ß-AR ligands did not alter concentrations of these lipolytic markers in i.m. adipose tissue. LUB did not affect glycerol or NEFA concentrations in s.c. or i.m. adipose tissue, but attenuated (P < 0.05) the accumulation of cAMP mediated by the ß 1- and ß 2-AR ligands DOB and SAL in s.c. adipose tissue. Collectively, these data indicate that bovine i.m. adipose tissue is less responsive than s.c. adipose tissue to ß-adrenergic ligands, especially those that are agonists at the ß 1- and ß3-receptor subtypes. The minimal mRNA expression of the ß 1- and ß 3 subtypes in i.m. adipose tissue likely limits the response potential to agonists for these ß-AR subtypes.