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.

Effects of feeding lubabegron on gas emissions, growth performance, and carcass characteristics of beef cattle housed in small-pen environmentally monitored enclosures during the last 3 mo of the finishing period.

The development of technologies that promote environmental stewardship while maintaining or improving the efficiency of food animal production is essential to the sustainability of producing a food supply to meet the demands of a growing population. As such, Elanco (Greenfield, IN) pursued an environmental indication for a selective ß-modulator (lubabegron; LUB). LUB was recently approved by the United States Food and Drug Administration (FDA) to be fed to feedlot cattle during the last 14 to 91 d of the feeding period for reductions in gas emissions/kg of unshrunk final BW and HCW. A 4 × 2 factorial arrangement of treatments was used with the factors of dose (0.0, 1.38, 5.5, or 22.0 mg·kg-1 DM basis) and sex (steers or heifers). Three 91-d cycles were conducted (112 cattle/cycle) with each dose × sex combination being represented by a single cattle pen enclosure (CPE; 14 cattle/CPE) resulting in a total of 168 steers and 168 heifers (n = 6 replicates/dose). There were no interactions observed between dose and sex for any variable measured in the study (P ≥ 0.063). Five gases were evaluated for all pens based on CPE concentrations relative to ambient air: NH3, CH4, N2O, H2S, and CO2. Cumulative NH3 gas emissions were reduced by feeding cattle 5.5 and 22.0 mg·kg-1 LUB (P ≤ 0.023) and tended (P = 0.076) to be lower for the cattle fed 1.38 mg·kg-1 LUB compared with the negative controls (CON). The cumulative NH3 gas emission reductions of 960 to 1032 g, coupled with HCW increases (P ≤ 0.019) of 15 to 16 kg for all LUB doses vs. CON, led to reductions in NH3 gas emissions/kg HCW for all three LUB treatments (P ≤ 0.004). Similar to HCW, reductions in NH3 gas emissions/kg of unshrunk final BW were observed for all LUB doses (P ≤ 0.009) and were attributable to both decreases in NH3 gas emissions and numerical increases in BW. Dose had no effect on cumulative emissions or emissions standardized by BW or HCW for the other four gases (P ≥ 0.268). LUB is a novel tool to reduce emissions of NH3 gas per kilogram of unshrunk live BW and hot carcass weight.

Erratum to: Effects of various doses of lubabegron on calculated ammonia gas emissions, growth performance, and carcass characteristics of beef cattle during the last 56 days of the feeding period.

[This corrects the article DOI: 10.1093/tas/txab137.].

Effects of various doses of lubabegron on calculated ammonia gas emissions, growth performance, and carcass characteristics of beef cattle during the last 56 days of the feeding period.

Lubabegron (LUB; Experior, Elanco, Greenfield, IN, USA) was approved by the U.S. Food and Drug Administration in 2018 and is indicated for the reduction of ammonia (NH3) gas emissions·kg-1 body weight (BW) and hot carcass weight (HCW) when fed to feedlot cattle during the final 14 to 91 d of the finishing period. LUB demonstrates antagonistic behavior at the ß 1 and ß 2 receptor subtypes and agonistic behavior at the ß 3 receptor subtype in cattle and is classified by the Center for Veterinary Medicine as a "beta-adrenergic agonist/antagonist." This report describes a randomized complete block study that evaluated LUB dose (0, 1.5, 3.5, and 5.5 mg·kg-1 dry matter) during the last 56 d of the feeding period on calculated NH3 gas emissions, live weight, carcass weight, and associated ratios in beef feedlot cattle. Carcass characteristics, mobility, and health were also evaluated. All cattle received monensin and tylosin throughout the study. Ammonia gas emissions were calculated using the equation developed by Brown et al. (Brown, M. S., N. A. Cole, S. Gruber, J. Kube, and J. S. Teeter. 2019. Modeling and prediction accuracy of ammonia gas emissions from feedlot cattle. App. Anim. Sci. 35:347-356). The reduction in calculated cumulative NH3 gas emissions with LUB ranged from 1.3% to 11.0% (85 to 708 g/hd). When NH3 gas emissions were expressed on a live weight (unshrunk) and carcass weight basis, calculated NH3 gas emissions decreased by 3.0% to 12.8% and 3.8% to 14.6%, respectively. Daily dry matter intake was 2.3% greater (P trt < 0.05) for steers that received LUB. Average daily gain was 13.7% greater (P trt < 0.05; 1.68 vs. 1.91 kg), while gain efficiency was 10.8% greater (P trt < 0.05; 0.167 vs. 0.185) for steers fed LUB. Animal mobility was scored in the pen approximately 1 wk prior to harvest, when cattle were loaded on trucks scheduled for harvest, and at antemortem inspection during lairage. No treatment differences (P trt ≥ 0.170) were observed at any time for the percent of cattle receiving mobility scores of 1 or 2 (normal or minor stiffness but moving with the normal cattle, respectively). Cattle mobility scored as a 1 or 2 equaled or exceeded 92% at all times. Final BW and HCW increased (P trt < 0.05) 11.6 to 15.7 kg and 11.3 to 17.1 kg, respectively, in cattle receiving LUB compared to cattle receiving monensin plus tylosin alone.

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.

Effects of voluntary removal of ractopamine hydrochloride (Optaflexx) on live performance and carcass characteristics of beef steers.

There is a lack of consistency across the globe in how countries establish tissue ractopamine residue limits and which residue limits are applied to various tissues, particularly for edible noncarcass tissues. Therefore, some U.S. beef slaughter organizations have recommended a 48-h voluntary removal of ractopamine before slaughter to meet residue requirements of specific export countries and maintain international trade. Our objective was to assess the impact of voluntary removal of ractopamine hydrochloride (Optaflexx; Elanco, Greenfield, IN) up to 8 d before slaughter on growth performance and carcass characteristics. Crossbred beef steers (60 pens of 10 animals/pen) with an initial shrunk body weight (BW) of 611.8 ± 10 kg SEM were fed one of six treatments over 42 d. Treatments included a control that did not receive ractopamine, on-label use of ractopamine (0-d withdrawal), and 2, 4, 6, or 8 d of voluntary removal of ractopamine from feed before slaughter. The start of ractopamine feeding (30.1 mg/kg of diet dry matter for 32 d) was staggered, so that blocks could be slaughtered on the same day. Dry matter intake was decreased by 0.5 kg/d when ractopamine was fed with a 0-d withdrawal (P = 0.04) compared with the control, but was not altered (P = 0.56) as the duration of ractopamine removal increased from 0 to 8 d. Final BW, total BW gain, and average daily BW gain were increased by feeding ractopamine with a 0-d withdrawal (P = 0.09) compared with the control, but these variables decreased in a linear manner (P = 0.10) as the duration of removal increased from 0 to 8 d. Gain efficiency was improved by 15% (P < 0.01) by feeding ractopamine with a 0-d withdrawal compared with the control, and gain efficiency decreased linearly (P = 0.06) as the duration of ractopamine removal increased. Approximately 2/3 of the increase in gain efficiency remained after 8 d of removal. Hot carcass weight was increased by 6 kg (P = 0.02) by feeding ractopamine with a 0-d withdrawal compared to the control. Measured carcass characteristics were not altered by ractopamine feeding or by removal before slaughter (P ≥ 0.24). The consequences of voluntary removal of ractopamine up to 8 d before slaughter were a linear decrease in live BW gain (0.64 kg/d), poorer gain efficiency, and numerically lighter carcass weight.