The moose, purine degradation, and environmental adaptation

Weiqi Zhang 0 1 Philip Stott 0 1 Minghai Zhang 0 1 0 P. Stott School of Animal and Veterinary Sciences, The University of Adelaide , Roseworthy, SA 5371, Australia 1 Communicated by C. Gortzar 2 ) College of Wildlife Resources, Northeast Forestry University , 26 Hexing Road, Harbin, Heilongjiang 150040, People's Republic of China It is accepted that allantoin is the end-product of purine degradation in mammals, except that uricase activity has been lost during the evolution of humans in which uric acid protects the brain from oxidative damage. However, we have found that the moose Alces americanus excretes extremely low urinary concentrations of allantoin and high concentrations of uric acid very similar to those of humans. Exposure to extreme cold is known to cause oxidative damage, and we suggest that the retention of uric acid by the moose represents an adaptation enabling the species to survive at high latitudes. - It is generally accepted that low concentrations of plasma uric acid occur in non-primate mammalian species (Cutler 1984). However, in 1959 it was pointed out that the conclusion that all mammals other than primates have uricase capability is based on studies of a limited number of species (Keilin 1959). The seminal data for concentrations of purine derivatives in ungulate urine was provided by Hunter and Givens (1914), who examined the major domestic ungulates, and found that purine derivatives were mostly to almost always excreted as allantoin. Since then, all published studies of mammals other than primates have confirmed the primacy of allantoin as the end-product of purine degradation, including additional studies in ruminants such as sheep (Bristow et al. 1992; Surra et al. 1997), goats (Belenguer et al. 2002; Bristow et al. 1992), cattle (Bristow et al. 1992), water buffalo (Chen et al. 1996), yak (Long et al. 1999), camel (Mohamed 2006; Guerouali et al. 2004), llama (Bakker et al. 1996), red deer (Vagnoni et al. 1996; Garrott et al. 1996; Christianson and Creel 2010; Zhang and Zhang 2012), and white-tailed deer (DelGiudice et al. 2000; Cabanac et al. 2005). Nevertheless, only a small portion of ruminant species have been investigated, and many environments to which ruminants have adapted do not have a representative species. We undertook a study intended to determine whether the nutritional status of moose Alces americanus in northeast China was influencing winter survival. We used analyses of purine derivatives in urine, which have been used as indices for evaluation of nutritional condition in various species of domestic (Moorby et al. 2006) and free-ranging (White et al. 1997) ruminants. In the course of that study, we failed to find allantoin in the urine of any Chinese moose. We obtained confirmation of our finding through samples collected on our behalf from North American moose and sent directly to an independent North American metabolomics laboratory for analysis. The aim of this paper is to report that all non-primate mammals are committed to extending the process of purine degradation to the conversion of uric acid to allantoin, and to suggest that the loss of uricase capability by the moose is adaptive. During January in the winters of 20062010, we collected 106 frozen urine samples from the surface of the snow at Erkehe Forest, Heilongjiang Province, China (48 39 3048 48 21 N; 127 59 05128 15 19 E). January wind chill (WC) ranged from 15.8 to 50.9 C, and mean snow depth from 174 to 413 mm. We searched for moose bedding sites, and then followed hoof prints until we found urine deposits. We used hoof-print locations and trajectories to ensure that individual moose were represented no more than once each year. We collected samples into containers, added sulphuric acid to maintain pH below 3, and stored them at 20 C. For comparison with well-fed moose free of cold stress, during 2012, we arranged for urine from ten well-fed captive moose in Alaska (mean WC on the day of collection 4.1 C) and one in Colorado (WC 15.5 C) to be sent directly to the Metabolomics Laboratory, University of California Davis (UC Davis) Genome Center, for analysis. We used HPLC to detect hypoxanthine, xanthine, urate, and allantoin in urine following George et al. (2006). Creatinine was used to standardize against dilution effects. Separation was performed at 25 C on a Thermo-Fisher Scientific C18 reversed-phase column (2504.60 mm, 0.5 m particle size). The mobile phase was a 0.01 mol/L potassium dihydrogen phosphate solution. Standard samples were used to identify PD. Peak areas were calculated using Waters Corporation Empower software. Calibration curves were calculated ranging from 1.0 to 200.0 g/ml for the four PD. Analysis at the Metabolomics Laboratory, UC Davis, of the urine of captive moose was undertaken using liquid chromatographic and gas chromatographic mass spectroscopy following Robertson et al. (2011). All data were converted to molar values to facilitate comparison. No allantoin wa (...truncated)