Abstract
Felids have a high incidence of chronic kidney disease (CKD), for which the most common renal lesion is chronic interstitial nephritis (CIN). CIN can be induced by tissue oxidative stress, which is determined by the cellular balance of pro- and anti-oxidant metabolites. Fish-flavoured foods are more often fed to cats than dogs, and such foods tend to have higher arsenic content. Arsenic is a pro-oxidant metallic element. We propose that renal accumulation of pro-oxidant elements such as arsenic and depletion of anti-oxidant elements such as zinc, underpin the high incidence of CIN in domestic cats. Total arsenic and other redox-reactive metal elements were measured in kidneys (after acid-digestion) and urine (both by inductively-coupled plasma-mass spectrometry) of domestic cats (kidneys, n = 56; urine, n = 21), domestic dogs (kidneys, n = 54; urine, n = 28) and non-domesticated Scottish Wildcats (kidneys, n = 17). Renal lesions were graded by severity of CIN. In our randomly sampled population, CIN was more prevalent in domestic cat versus domestic dog (51%, n = 32 of 62 cats; 15%, 11 of 70 dogs were positive for CIN, respectively). CIN was absent from all Scottish wildcats. Tissue and urinary (corrected for creatinine) arsenic content was higher in domestic cats, relative to domestic dogs and wildcats. Urine arsenic was higher in domestic cats and dogs with CIN. Arsenobetaine, an organic and relatively harmless species of arsenic, was the primary form of arsenic found in pet foods. In summary, the kidneys of domestic cats appear to have greater levels of pro-oxidant trace elements, as compared to dogs and wildcats. Since there was no difference in renal arsenic levels in cats with or without CIN, renal arsenic accumulation does not appear a primary driver of excess CIN in cats. Given clear differences in renal handling of pro vs. anti-oxidant minerals between cats and dogs, further in vivo balance studies are warranted. These may then inform species-specific guidelines for trace element incorporation into commercial diets.
Highlights
Felids have a high incidence of chronic kidney disease (CKD), for which the most common renal lesion is chronic interstitial nephritis (CIN)
From our sample collected over an 1.5-2 year period from the UoN-VPS, based on the interstitial inflammation, the incidence of CIN per se was greater in domestic cats (77% [48 of 62 examined]) versus dogs (51% [36/70]; P < 0.01 by χ2 test)
Similar to the amount of interstitial inflammation, moderate-to-severe fibrosis was identified in a greater proportion of domestic cat than dog kidneys (Cat, 90%; 9/10; Dog, 40%; 6/15)
Summary
Felids have a high incidence of chronic kidney disease (CKD), for which the most common renal lesion is chronic interstitial nephritis (CIN). Cellular redox-balance is determined by many factors including the relative proportions of pro- and anti-oxidant mineral elements Arsenic is one such pro-oxidant, metallic element often found at high concentration in fish-flavoured foods which are more often fed to cats than dogs. We describe for the first time that domestic cat kidneys (cf canine kidneys) have an elemental profile considered to be ‘pro-oxidant’; that is, relative bioaccumulation of pro-oxidant elements coupled with lower levels of elements that support anti-oxidant functions For one such pro-oxidant element – arsenic – we further characterised the specific species (e.g. organic vs inorganic) found in four cat foods, selected as having a relatively high arsenic content. We propose that in the long-term, such an elemental microenvironment in the feline kidney may underpin the domestic cat’s propensity to CKD
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