Metabolic adaptation to experimentally increased glucose demand in ruminants

In vitro addition of epinephrine, norepinephrine, and carnitine alters palmitate oxidation and esterification in isolated ovine hepatocytes

Hepatocytes from 4 wethers were used to study the effects of carnitine and increasing concentrations of epinephrine and norepinephrine on palmitate oxidation and esterification. Liver cells were isolated from the wethers and incubated in Krebs-Ringer bicarbonate buffer with 1 mM [¹⁴C]-palmitate. Radiolabel incorporation was measured in CO₂, acid-soluble products, and esterified products, including triglyceride, diglyceride, and cholesterol esters. Carnitine increased production of CO₂ and acid-soluble products from palmitate by 41% and 216%, respectively, but had no effect on conversion of palmitate to esterified products. Epinephrine had a quadratic-increasing effect on palmitate oxidation to CO₂, but norepinephrine did not increase palmitate oxidation to CO₂. Neither epinephrine nor norepinephrine affected the production of acid-soluble products from palmitate. Increasing concentrations of norepinephrine and epinephrine linearly increased rates of triglyceride formation from palmitate. Increasing norepinephrine concentrations linearly increased diglyceride and cholesterol ester formation from palmitate in the presence of carnitine; epinephrine did not affect diglyceride or cholesterol ester formation. In general, catecholamine treatment had the greatest effect on the formation of esterified products from palmitate, and effects of norepinephrine were more pronounced than epinephrine. Conditions that result in catecholamine release might lead to fat accumulation in liver.

Effects of in vivo phlorizin treatment and in vitro addition of carnitine, propionate, acetate, and 5-tetradecyloxy-2-furoic acid on palmitate metabolism in ovine hepatocytes

Modulatory effects of l-carnitine, acetate, propionate, and 5-tetradecyloxy-2-furoic acid (TOFA; an inhibitor of acetyl-CoA carboxylase) on oxidation and esterification of [1-¹⁴C]-palmitate were studied in hepatocytes isolated from phlorizin-treated and control wethers. Our hypotheses were that (1) palmitate oxidation would be greater in hepatocytes from sheep injected with phlorizin; (2) l-carnitine would increase palmitate oxidation more in hepatocytes from sheep injected with phlorizin; and (3) acetate and propionate would decrease oxidation in sheep hepatocytes partly through action of acetyl-CoA carboxylase. Palmitate metabolism did not differ between cells from control and those from phlorizin-treated wethers. Carnitine increased oxidation of palmitate to CO₂ and acid-soluble products (ASP; mainly ketone bodies) and decreased esterification of palmitate in isolated hepatocytes from both groups of wethers, but the increase in oxidation to ASP was greater in cells from phlorizin-treated wethers. Propionate increased palmitate oxidation to CO₂ in phlorizin-treated wethers. Propionate increased oxidation of palmitate to ASP in control wethers but decreased oxidation to ASP in phlorizin-treated wethers. Propionate increased esterification of palmitate to total esterified products and triglyceride, and the effect was larger in phlorizin-treated wethers. Acetate decreased palmitate esterification to total esterified products in control wethers, but the effect was blunted in phlorizin-treated wethers. Acetate did not affect palmitate oxidation. Addition of TOFA increased production of triglyceride from palmitate in the presence of propionate. The lack of interaction between TOFA and propionate indicates that propionate does not inhibit carnitine palmitoyltransferase I via cytosolic generation of methylmalonyl-CoA by acetyl-CoA carboxylase. In conclusion, although in vivo phlorizin treatment did not affect in vitro metabolism of palmitate by isolated ovine hepatocytes, phlorizin increased the stimulatory effect of carnitine on oxidation of palmitate to ASP and the inhibitory effect of propionate on oxidation of palmitate to ASP. Metabolism of acetate and propionate by acetyl-CoA carboxylase did not affect palmitate oxidation or esterification. Results provide additional insight into control of fatty acid metabolism in hepatocytes.

Sodium-Glucose Cotransporter-2 Inhibitors: Lack of a Complete History Delays Diagnosis

On 15 May 2015, the U.S. Food and Drug Administration (FDA) warned that administration of sodium-glucose cotransporter-2 (SGLT2) inhibitors could lead to ketoacidosis in patients with diabetes mellitus. This announcement came more than 2 years after the FDA's first approval of an SGLT2 inhibitor, although the phenomenon had been known for more than 125 years. Luminaries of diabetes research (including Josef von Mering, Frederick Allen, I. Arthur Mirsky, and George Cahill) had described ketosis and ketoacidosis induced by administration of the phytochemical phlorizin, the prototypical SGLT inhibitor, as well as in patients with familial renal glucosuria, a condition that is considered a natural model of SGLT2 inhibition. Neither government regulators nor manufacturers of SGLT2 inhibitors evinced an awareness of this extensive historical record. The absence of historical inquiry delayed notice of ketoacidosis as an adverse reaction, which could have reduced the burden of illness from these drugs.

SGLT-2 inhibition and glucagon: Cause for alarm?

Recent studies raised the alarm that the inhibition of sodium-coupled glucose transporter type-2 in humans increases endogenous glucose production rates by an unclear mechanism. Surprisingly, a potential explanation may be linked directly to the alpha-cell. Is this a mechanistic spoiler or an added benefit?

Integrative analyses of hepatic differentially expressed genes and blood biomarkers during the peripartal period between dairy cows overfed or restricted-fed energy prepartum

Using published dairy cattle liver transcriptomics dataset along with novel blood biomarkers of liver function, metabolism, and inflammation we have attempted an integrative systems biology approach applying the classical functional enrichment analysis using DAVID, a newly-developed Dynamic Impact Approach (DIA), and an upstream gene network analysis using Ingenuity Pathway Analysis (IPA). Transcriptome data was generated from experiments evaluating the impact of prepartal plane of energy intake [overfed (OF) or restricted (RE)] on liver of dairy cows during the peripartal period. Blood biomarkers uncovered that RE vs. OF led to greater prepartal liver distress accompanied by a low-grade inflammation and larger proteolysis (i.e., higher haptoglobin, bilirubin, and creatinine). Post-partum the greater bilirubinaemia and lipid accumulation in OF vs. RE indicated a large degree of liver distress. The re-analysis of microarray data revealed that expression of >4,000 genes was affected by diet × time. The bioinformatics analysis indicated that RE vs. OF cows had a liver with a greater lipid and amino acid catabolic capacity both pre- and post-partum while OF vs. RE cows had a greater activation of pathways/functions related to triglyceride synthesis. Furthermore, RE vs. OF cows had a larger (or higher capacity to cope with) ER stress likely associated with greater protein synthesis/processing, and a higher activation of inflammatory-related functions. Liver in OF vs. RE cows had a larger cell proliferation and cell-to-cell communication likely as a response to the greater lipid accumulation. Analysis of upstream regulators indicated a pivotal role of several lipid-related transcription factors (e.g., PPARs, SREBPs, and NFE2L2) in priming the liver of RE cows to better face the early postpartal metabolic and inflammatory challenges. An all-encompassing dynamic model was proposed based on the findings.

Phlorizin Induces Lipolysis and Alters Meal Patterns in Both Early-and Late-Lactation Dairy Cows

Phlorizin is known to increase whole-body glucose demand, but it has also stimulated lipolysis in past studies in ruminants. Increased lipolysis complicates studies of dry matter intake (DMI) regulation by hepatic oxidation by providing the liver with additional oxidative substrate. Therefore, to assess whether increased glucose demand selectively increases DMI for cows in negative energy balance, phlorizin was administered to early- and late-lactation cows. Six Holstein cows in early lactation (19 +/- 6 DIM, 50.0 +/- 1.8 kg/d of milk, mean +/- SD) and 6 Holstein cows in late lactation (228 +/- 18 DIM, 30.6 +/- 1.9 kg/d of milk) were randomly assigned to treatment sequence in a crossover design. Periods were 14 d with 7-d adaptation periods and 7 d of treatment. Phlorizin (4 g/d) and propylene glycol (carrier and control) were administered subcutaneously every 6 h throughout the treatment periods. Feeding behavior and DMI data were collected for the final 4 d of each treatment period; blood samples and total urine output were collected on d 4 of each treatment period. Phlorizin caused urinary loss of glucose at 333 g/d in early-lactation cows and 532 g/d in late-lactation cows. Phlorizin increased plasma nonesterified fatty acid concentrations similarly in early- and late-lactation cows, but did not significantly alter plasma insulin concentrations. Treatment with phlorizin tended to decrease meal size, but also decreased intermeal interval, resulting in no effect on DMI. The effects of phlorizin on lipolysis, feeding behavior, and DMI are not dependent on relative energy balance.