1. Department of Endocrinology St Vincent’s Hospital, Sydney
Bile acids more closely align with insulin resistance and visceral and hepatic adiposity than total body fat in adult humans
Ramy Bishay
Department of Endocrinology
St Vincent’s Hospital, Sydney

2. Bile Acid Physiology
7a-hydroxylase (CYP7A1)
Produced exclusively in the liver as end-products of cholesterol catabolism
Facilitate hepatobiliary secretion (endogenous metabolites, xenobiotics)
Intestinal absorption lipophilic nutrients (ADEK)
Energy expenditure
Glucose metabolism
7a)
Classical pathway (90% contribution) vs alternative (acidic pathway)
7a hydroxylase – first and most important, rate-limiting step in primary BA synthesis
CA vs CDCA dictated by enzymatic reaction of sterol 12α-hydroxylase (CYB8B1) -> controls the synthesis of cholic acid and as such is under tight transcriptional control
CDCA (45%), CA (31%)
Diab Care 32(2): 2009; J of Lipids, Vol 2012, Article ID ; Pharmacol Rev 66:948–983, Oct 2014; Michael W King, 1996–2016 themedicalbiochemistrypage.org; J of Lipids, Vol 2012, Article ID

3. Bile Acid Physiology Homeostasis self-governed
Modulated by multiple receptors at different tissues
FXR, TGR5, RXR, LXR
50% cholesterol turnover
Prevent crystallisation and gallstones by solubilising cholesterol
BA are physiological ligands for FXR

4. Study Aims
1. To determine if bile acid levels are increased in humans with diabetes
In vitro:
Hyperglycaemia stimulates 7a-hydroxylation (increased bile acid synthesis)
Mouse models (Type 1 and Type 2 diabetes):
Hyperglycaemia increased bile acid synthesis
Larger bile acid pool size in db/db mice (Cholic, Deoxycholic acids)
Humans: Bile acid sequestration improves hyperglycaemia
(HbA1c -0.5%), insulin sensitivity (via GLP-1)
JCEM 98, E708-E712; Cell Metab, 10, ; Biochem Biophys Res Commun, 329, ; Sci Rep 2, 430; Nature, vol. 439, no. 7075, pp. 484–489, 2006; Eur J Endocrinol Aug;171(2):R47-65; Ann Intern Med 1994;121:416–422; Curr. Opin. Lipidol. 23, 43-55; Trends Endocinol Metab 2014, Vol. 25, No. 5 ; Hepatology 52, 1455–1464; Diabetes 62, ; Diabetes Care Vol 32, supp 2, 2009.

5. Study Aims
2. To determine if bile acid levels are associated with obesity
Higher fasting bile acids (cholic acid) in obese vs non-obese
Weight loss
Bile acid sequestration
Activation of TGR5 (increased E expenditure)
Promote GLP-1 (certain bile acids, via TGR5)
Insulin reduced serum bile acid but affect blunted in obese subjects
Roux-en-Y gastric bypass (but not lap-banding) result in elevated circulating bile acids
3. To determine if bile acid levels are increased in obese humans
independent of insulin resistance?
???
TGR5 - GPCR expressed in intestine, BAT, WAT, gall bladder less so in liver, muscle
BA activation of TGR5 - In brown adipose tissue -> induces D2, FA oxidation genes transcription
J Clin Endocrinol Metab 101: 1935–1944, 2016; Trends Endocinol Metab 2014, Vol. 25, No. 5; Hepatology 52, 1455–1464; Diabetes 62, ; Diabetes Care Vol 32, supp 2, 2009.

6. Methods 71 adult volunteers
4 groups based on BMI, homeostatic model assessment of insulin resistance (HOMA-IR) and a 75-g OGTT:
1. Lean insulin-sensitive (BMI≤25 kg/m2, HOMA-IR<2.0, n=19)
2. Overweight/obese insulin-sensitive non-diabetic (Obsen, BMI>25 kg/m2, HOMA-IR<1.5, n=11)
3. Overweight/obese insulin-resistant (Obres, BMI>25 kg/m2, HOMA-IR>3.0, n=20)
4. Type 2 diabetes mellitus (T2DM, n=21).
Insulin sensitivity measured by hyperinsulinaemic (80 mUm−2min−1)–euglycaemic (5 mmol/l) clamp
Body composition and central abdominal fat by DXA
Visceral fat area by CT
Fasting insulin, adiponectin, FGF21
BA (baseline and during clamp)
Primary – CA, CDCA,
Secondary – DCA
Conjugated

7. Baseline Characteristics

8. Results: Total Bile Acids

9. Chenodeoxycholic Acid
Results: 1° Bile Acids
Cholic Acid
Chenodeoxycholic Acid

10. Results: 2° & Conjugated Bile Acids
Deoxycholic Acid
Conjugated BA

11. - + Correlations Cholic (1° BA) Chenodeoxycholic Deoxycholic (2° BA)
Conjugated BA
Waist Circumference
BMI
Central fat (% or kg)
Visceral fat (cm2)
P = 0.06 +
Liver fat
Insulin
P = 0.051
GDR/FFM
P = 0.054 -
FFM
FGF 21
Adiponectin + -

12. Summary
Bile acids are lower in insulin sensitive individuals, independent of adiposity
Obsens have significantly lower:
Total and conjugated bile acids vs T2D
Total bile acids and chenodeoxycholic acid (1° BA) vs Obres
Lean have lower Deoxycholic acid (2° BA) compared with T2D
Bile acid levels are suppressed with insulin
Bile acids are associated with metabolic risk factors
Cholic acid (1°): central/visceral adiposity, hepatic fat and insulin resistance
Deoxycholic acid (2°): type 2 diabetes, central/visceral fat, adiponectin, elevated fasting insulin

13. Conclusions Bile acids are complex signalling molecules
Align closely to insulin resistance
May have a pathophysiological role in the development of insulin resistance, obesity and hepatic adiposity
Supports previous positive studies on therapeutic role of bile acid sequestration and signalling blockade on glycaemic control (mixed results)

14. Thank you Acknowledgements
Garvan Institute of Medical Research & St Vincent’s Hospital, Dept Endocrinology
Dr Katherine Tonks
A/Prof Jerry Greenfield
Prof Don Chisholm
Dr Dorit Samocha-Bonet
The Charles Perkins Centre, University of Sydney
Prof David E James
Storr Liver Centre, Westmead Millennium Institute and Westmead Hospital
Prof Jacob George