Formation and excretion of branched-chain acylcarnitines and branched-chain hydroxy acids in the perfused rat kidney

Unraveling metabolism during kidney perfusion using tracer studies, a systematic review

BACKGROUND

Understanding kidney metabolism during perfusion is vital to further develop the technology as a preservation, viability assessment, and resuscitation platform. We reviewed the evidence on the use of labeled metabolites (tracers) to understand "on-pump" kidney behavior.

METHODS

PubMed, Embase, Web of Science, and Cochrane databases were systematically searched for studies evaluating metabolism of (non)radioactively labeled endogenous compounds during kidney perfusion.

RESULTS

Of 5899 articles, 30 were included. All were animal studies [rat (70%), dog (13%), pig (10%), rabbit (7%)] perfusing but not transplanting kidneys. Perfusion took place at hypothermic (4-12°C) (20%), normothermic (35-40°C) (77%), or undefined temperatures (3%). Hypothermic perfusion used albumin or a clinical kidney preservation solution, mostly in the presence of oxygen. Normothermic perfusion was mostly performed with oxygenated crystalloids often containing glucose and amino acids with unclear partial oxygen tensions. Active metabolism of carbohydrate, amino acid, lipids, and large molecules was shown in hypothermic and normothermic perfusion. Production of macromolecules, such as prostaglandin, thromboxane, and vitamin D, takes place during normothermic perfusion. No experiments compared differences in metabolic activity between hypothermic and normothermic perfusion. One conference abstract showed increased anaerobic metabolism in kidneys donated after circulatory death by adding labeled glucose to hypothermically perfused human kidneys.

CONCLUSIONS

Tracer studies during kidney perfusion contribute to unraveling kidney metabolic behavior in pre-clinical models. Whether findings are truly translational needs further investigation in large animal models of human kidneys. Furthermore, it is essential to better understand how ischemia changes this metabolic behavior.

The role of carnitine in normal and altered fatty acid metabolism

Carnitine is a low-molecular-weight compound obtained from the diet that also is biosynthesized from the essential amino acids lysine and methionine. Carnitine has been identified in a variety of mammalian tissues and has an obligate role in the mitochondrial oxidation of long-chain fatty acids through the action of specialized acyltransferases. Other roles for carnitine include buffering of the acyl coenzyme A (CoA)-CoA ratio, branched-chain amino acid metabolism, removal of excess acyl groups, and peroxisomal fatty acid oxidation. The growing body of evidence about carnitine function has led to increased understanding and identification of disorders associated with altered carnitine metabolism. Disorders of fatty acid oxidation and metabolism typically are associated with primary and secondary forms of carnitine deficiency. These disorders, which include increased lipolysis, increased lipid peroxidation, accumulation of acylcarnitines, and altered membrane permeability, have significant consequences for patients with myocardial diseases and kidney failure. Therapeutic administration of carnitine shows promise in treating selected groups of patients who have altered carnitine homeostasis, resulting in improved cardiac function, increased exercise capacity, reduced muscle cramps, and reduced intradialytic complications.

The hypolipidemic drug metabolites nafenopin-CoA and ciprofibroyl-CoA are competitive P2Y1 receptor antagonists

Coenzyme A (CoA-SH), endogenous and drug-derived CoA-derivatives were tested as putative antagonists of P2Y receptors expressed in Xenopus laevis oocytes, a method used to determine calcium-activated chloride current, an indicator of the activation of these receptors. CoA-SH antagonized reversibly and in a concentration-dependent manner the ATP-gated currents evoked by the human P2Y(1) but not the P2Y(2) receptor. Palmitoyl-CoA was four-fold more potent than CoA-SH as an antagonist while palmitoyl-carnitine was inactive, highlighting the role of the CoA-SH moiety in the antagonism. The CoA derivatives of nafenopin and ciprofibrate, two clinically relevant hypolipidemic drugs, increased 13 and three-fold the potency of CoA-SH, respectively. The K(B)s of nafenopin-CoA and ciprofibroyl-CoA were 58 and 148 nM, respectively; the slopes of the Schild plots were unitary. Neither 100 microM nafenopin nor ciprofibrate alone altered the P2Y(1) receptor activity. Neither CoA-SH nor ciprofibroyl-CoA antagonized the rat P2X(2) or the P2X(4) nucleotide receptors nor interacted with the 5-HT(2A/C) receptors. The bulky drug CoA-SH derivatives identify a hydrophobic pocket, which may serve as a potential target for novel selective P2Y(1) antagonists.

The effect of beta-hydroxy-beta-methylbutyrate on growth, mortality, and carcass qualities of broiler chickens

Experiments were conducted to determine whether the leucine catabolite beta-hydroxy-beta-methylbutyrate (HMB) could influence protein metabolism in broilers. In Experiment 1, HMB was fed at either .01 or .05% of the diet. beta-Hydroxy-beta-methylbutyrate did not improve feed conversion or BW gain; however, broilers fed HMB at .01% in a diet formulated to meet NRC (1984) recommendations had no mortality (P < .03) from 0 to 21 d of age. In Experiment 2, HMB fed at .003, .01, .03, and .09% of the diet had no significant affect on growth or carcass yield of the broilers when compared with control-fed broilers. In Experiment 3, HMB fed at .001, .003, and .01% of the diet had no effect on broiler growth. In Experiment 4, HMB was fed at .01% of the diet in combination with an antibiotic and coccidiostat (GP). Use of GP increased (P < .01) BW, feed conversion, and carcass yield when compared with the control broilers. In Experiment 5, HMB was fed at .1% of the diet, and effects of sex and GP were examined. beta-Hydroxy-beta-methylbutyrate decreased (P < .01) mortality by 72% in the male broilers. In a combined analysis, HMB fed at .01% of the diet (Experiments 1, 2, and 3) increased breast yield (P < .05) and reduced mortality by 56% (P < .04) from 0 to 21 d of age. In a combined analysis, HMB fed at .003% of the diet (Experiments 2 and 3) increased 42-d BW (P < .02) and hot (P < .04) and chilled (P < .05) carcass yields. In conclusion, across all HMB dosages mortality of male broilers was decreased from 6.37 to 4.39% (-31%, P < .04) by feeding HMB, with the pattern of death suggesting that HMB decreased the incidence of sudden death syndrome in these broilers.