Effects of D-3-hydroxybutyrate and acetoacetate on lactate removal in isolated perfused livers from starved and fed rats

Impact of dietary walnuts, a nutraceutical option, on circulating markers of metabolic dysregulation in a rodent cachectic tumor model

Background:

Nutraceutical foods, like walnuts which are rich in immunonutrients, can have medicinal benefits. Dietary walnuts have been shown to slow or prevent tumor growth in mice genetically programmed to grow breast or prostate tumors. This study investigated whether walnuts could exert the same preventable effect in a transplantable carcinoma rat model.

Methods:

Eighteen rats were randomly fed a diet containing walnuts (10% of food by weight), and 36 were fed a diet without walnuts (control) for 21 days. On day 22, 18 control diet rats were switched to the walnut diet. All other animals remained on their same diet. Within each diet group, 6 rats were implanted with the Ward colon carcinoma (TB), and 12 were sham-operated. Five days later, 6 sham-operated animals were weight-matched to a TB and then pair-fed for the remainder of the study. The remaining 6 sham-operated, or non-tumor-bearing rats, were ad-lib fed.

Results:

The tissue of the walnut-eating rats showed higher omega-3 fatty acid (immunonutrient) content which did not slow or prevent tumor growth or the loss of lean and fat mass typical of this TB model. In addition, blood glucose, insulin, IGF-1, and adiponectin levels were significantly lower in the TB, demonstrating metabolic dysregulation. Again, these changes were unaltered by consuming walnuts. Plasma proteomics identified six proteins elevated in the TB, but none could be connected with the observed metabolic dysregulation.

Conclusion:

Although walnuts’ rich immunonutrient content prevented tumor growth in genetically programmed mice models, there was no effect in this model.

Further observations on the uptake and effects of phosphonates in perfused rat liver studied by (31)P-NMR

We examined the route of uptake of 2-aminoethylphosphonate (NEthPo) and of phenylphosphonate (PhePo; 10 mM each) in perfused liver by (31)P-NMR. Uptake of NEthPo was concentrative. The rate of uptake was reduced to 21 +/- 2% (n = 3; all percentages refer to control rates) by substituting choline for Na(+), and to 21 +/- 4% (n = 3), 32 +/- 6% (n = 5) and 70 +/- 5% (n = 3) by replacing Cl(-) by gluconate, SO(4)(2-) or NO(3)(-), respectively. Taurine (20 mM) reduced NEthPo uptake to 38 +/- 6% (n = 3). The data are consistent with uptake of NEthPo by the Na(+)-coupled Cl(-)-dependent beta-amino acid transporter. A small fraction of NEthPo was incorporated into phospholipid. PhePo uptake evolved over 1 h towards levels of the membrane-permeant volume marker dimethyl methylphosphonate. Uptake depended on H(+), and was inhibited by 4, 4'-diisothiocyanato-stilbene-2,2'-disulphonic acid (100 microM), bumetanide and furosemide (1 mM each) and alpha-cyano-4-OH-cinnamic acid (5 mM) to 31 +/- 4% (n = 4), 28 +/- 4% (n = 4), 27 +/- 5% (n = 6) and 40 +/- 7% (n = 4), respectively. These characteristics of PhePo uptake are reminiscent of H(+)-coupled monocarboxylate transport. The monocarboxylates, lactate and acetate (20 mM), and the substrate analogue, phenylalanine (20 mM), were not inhibitory, while benzoic acid (20 mM) slightly inhibited (to 82 +/- 5%; n = 4) PhePo uptake. The tested phosphonates (10 mM) did not significantly affect hepatic extraction of [(3)H]-cholate or [(3)H]-taurocholate (25 microM each; 1:3 bile salt:albumin). The monocarboxylate analogue, PhePo (10 mM), did not significantly interfere with disposal of lactate (0.3-5 mM).

Carrier-mediated lactate entry into isolated hepatocytes from fed and starved rats: zonal distribution and temperature dependence

We examined the possibility of quantitative differences in lactate entry into periportal and perivenous hepatocytes under different nutritional states. The rate of 14C-L(+)-lactate uptake was determined after 15-second incubations with freshly isolated zonally separated hepatocytes using a centrifuge stop technique at 37 degrees C and 4 degrees C, in the presence or absence of either differing amounts of unlabelled lactate or of a hepatocyte lactate transport inhibitor, alpha-cyano-3-hydroxycinnamate. Total entry as well as carrier mediated entry of 14C-L(+)-lactate into the isolated cell populations was found to be similar in periportal and perivenous hepatocytes, irrespective of the nutritional state of the animal. Periportal and perivenous hepatocytes showed a greater tendency to transport lactate when isolated from starved animals, in agreement with previously reported data from non-zonally separated isolated hepatocytes. The activity of the hepatocyte plasma-membrane lactate transporter was diminished between fourfold and eightfold in transport studies conducted at 4 degrees C; similar results were obtained in unseparated and zonally separated suspensions. Temperature dependence of the hepatocyte transporter is markedly less than that reported for the erythrocyte transporter.

Effect of insulin and glucose load on bile lactate secretion by the isolated rat liver. Role of hepatic parenchyma heterogeneity

Parenchymal heterogeneity in lactate disposal by perivenous and periportal hepatocytes is believed to be an important factor affecting the overall lactate metabolism by the liver. The aim of this work was to investigate the possibility of the existence of a different role of both acinar zones 1 and 3 in lactate secretion into bile. The effect of insulin and glucose load was also studied using isolated in situ rat liver preparations. Perfusions with erythrocyte-free Krebs-Henseleit solutions were carried out in intact livers and after restricted damage of zone 1 or zone 3 by digitonin administration as a bolus through the portal or the hepatic vein, respectively. In intact livers lactate concentrations in bile were similar to those found in the perfusate. In both compartments lactate concentrations were observed to increase over 90 min of perfusion. During this time, bile lactate output increased from 5 to 8 nmol/min per g liver with no significant effect on bile flow. Replacement of perfusate by a fresh lactate-free one at 60 min failed to induce any reduction in lactate concentration in bile samples collected during the following 30 min which suggests the absence of easy equilibration of biliary lactate with the sinusoidal compartment. Insulin administration (bolus: 100 mU/100 g body weight, plus portal infusion: 5 mU/min per 100 g body weight) was found to markedly enhance bile lactate concentrations (+110%) and output (+139%). On the contrary, glucose load was found to have no effect on lactate output into bile. No significant difference in the increase in bile lactate output was observed during 90 min perfusion with either 0, 5, 10, 15, 25 or 35 mM initial glucose concentrations. After restricted damage of acinar zone 1 or 3, insulin-induced bile lactate secretion was significantly reduced. This effect was not different regardless the damaged acinar zone. In summary these results suggest that insulin plays an important role in the control of the output of lactate into bile and that the existence of acinar heterogeneity in this function seems unlikely. Moreover the quantitative contribution of bile lactate to overall lactate handling by the liver and to bile formation seems very low.