1. The Role of VFAs in Lipid and Carbohydrate Metabolism Barry J. Bradford 1 and Michael S. Allen 2 1 Kansas State University, 2 Michigan State University 1 Contact information: Barry Bradford, Associate Professor 135 Call Hallbbradfor@ksu.edu Manhattan, KS 665061-785-532-7974

2. Metabolism of VFA: substrate effects The concept of bioactive nutrients Direct signals Endocrine effects Neuronal effects Conclusions Topics

3. Different VFAs play different roles Cellulose (primarily) Acetate Fatty acids + ATP Starch (more) Propionate Glucose Microbial metabolism Host animal metabolism Butyrate: Unique role as the preferred energy source for ruminal epithelium.

4. Minor VFA play a major role in physiology Acetate comprises 50 – 75% of total VFA produced in the rumen, propionate 15 – 45%, butyrate 1 – 12%. (Sutton et al., 2003) Propionate and butyrate often have more dramatic effects on metabolic physiology Ash et al., 1964

5. Uptake of VFA is tissue-specific Ash and Baird, 1973, Biochem. J. 136:311

6. Bioactive Nutrients Nutrients that influence physiology independent of substrate effects. This typically occurs through activation of cell membrane receptors or nuclear receptors resulting in: – Altered cellular function – Release of endocrine factors – Stimulation of neuronal signals

7. Substrate vs. receptor-mediated nutrient effects Substrate effects Impact limited to tissues utilizing the nutrient Interactions with other nutrients key Responses in different metabolic state or life stages dependent on metabolism of nutrient Receptor-mediated effects Impact dependent on distribution of receptor Interactions with hormones may be critical Responses in different metabolic states or life stages dependent on expression of receptor

8. GPR81 GPR41 GPR43 AcetatePropionate Butyrate Lactate Intracellular Signal Transduction G-protein coupled receptors can mediate effects of short-chain fatty acids

9. Acetate and propionate promote adipogenesis in cultured pre-adipocytes Hong et al., 2005 Red = Oil red O lipid stain

10. Acetate and propionate suppress lipolysis through GPR43 in mice Ge et al., 2008

11. Importance in cattle? GPR41 and GPR43 were not detected in adipose tissue of cattle (Wang et al., 2009) Propionate increased leptin secretion in mice, but not in cattle (Bradford et al., 2006) Role in liver metabolism??

12. VFA can stimulate expression of gluconeogenic genes in pre-ruminant calves Donkin et al., 2009

13. Importance in cattle? In most experiments evaluating signaling effects of VFA, obvious effects are seen only in fasted animals or pre-ruminant calves. Basal concentrations of VFA in fed ruminants may be adequate to activate these receptors constitutively.

14. Endocrine effects of VFA VFA can also impact metabolism by altering secretion of metabolic hormones

15. Propionate potently stimulates insulin secretion Bradford et al., 2006

16. Propionate flux to the liver increases dramatically at meals Feeding Benson et al., 2002 J. Dairy Sci. 85:1804

17. Diurnal variation in plasma insulin and metabolites for mid-lactation cows offered feed ad libitum Allen et al., 2005 Annu. Rev. Nutr. 25:523

18. Propionate depresses feed intake compared to acetate Infusion of propionate into the mesenteric vein of steers decreased feed intake but infusion of acetate at similar rates did not (Elliot et al., 1985) Hepatic extraction of propionate > 70% of total supply (Reynolds et al., 2003) Ruminant hepatocytes have high activity of propionyl CoA synthetase but not acetyl CoA synthetase (Ricks and Cook, 1981; Demigne et al., 1986)

19. Propionate vs. acetate 0 5 10 15 20 25 30 35 03367100 Oba and Allen, 2003 J. Nutr. 133:1094 % propionate NE L intake, Mcal/12 h Infusion of mixtures of propionate and acetate at 25 mmol/min from 2 h before feeding until 12 h after feeding NE L intake intake = feed + VFA Linear effect P < 0.0001

20. Is hypophagia from propionate insulin-dependent? Propionate has depressed DMI without altering plasma insulin (Farningham and Whyte, 1993; Frobish and Davis, 1977) Insulin’s putative effects on DMI are through receptors in the CNS, yet hepatic vagotomy eliminated response to propionate infusion Hyperinsulinemic-euglycemic clamps generally do not depress energy intake (Mackle et al. 1999; Griinari et al. 1997; McGuire et al. 1995)

21. Propionate’s effects on intake are nerve-mediated *** Anil and Forbes, 1988

22. Connection from the liver to the brain: hepatic vagus Satiety Hunger ATP

23. Fuels oxidized in ruminant liver Fatty acids Diet Adipose Amino acids Lactate Glycerol Propionate Glucose Acetate NOT:

24. Model by which propionate may stimulate satiety (+) insulin (-) (+) NEFA acetyl CoA satiety center (+) (-) feed intake propionate flux to liver (+) increased diet fermentability oxidation ketones glucose

25. Hypophagic effects of propionic acid increased with hepatic acetyl CoA concentation TRT*Acetyl CoA Interaction, P = 0.07 Stocks and Allen, 2011

26. Propionate is a primary end-product of ruminal starch digestion Ruminal production rates vary greatly between diets, primarily because of differences in starch fermentability Can be produced and absorbed at very high rates; rapidly taken up by the liver Once propionate is absorbed it is metabolized almost exclusively by the liver Hypophagic effects of propionate are eliminated by hepatic vagotomy Propionate regulation of feed intake by hepatic oxidation?

27. Take-home points VFA can influence ruminant metabolism through substrate-level effects, by directly altering cellular function, by altering hormone secretion, or by activating neural signals. As we learn more about functional roles of VFA, these concepts will be used to improve diet formulation to support health and productivity.

28. Thank you! Sweet ride.