Lipid droplets in felid kidneys: prevalence and composition by lipidomics

Key results

1. 01

   ShownFelid kidneys (domestic cat and Scottish wildcat) showed similar Oil Red O-positive (ORO+ve) cortical lipid, both well above dog. Cats exceeded dogs at every available age, and lipid declined rather than accumulated with age in both species.

   Median [IQR] ORO+ve area: domestic cat 18.48% [9.069%, 25.66%] (n=21), Scottish wildcat 14.09% [6.756%, 22.90%] (n=8), dog 1.002% [0.0917%, 13.63%] (n=22); P = 0.018 (NP-ANOVA). Cat vs dog regression intercepts differed (P <0.001); adipose positive control 54.76%. · Histological evaluation and quantification of…; Oil-Red-O staining of kidney tissue; Figure legends

2. 02

   ShownDomestic cat extracts nearly always had an unidentified high-performance thin-layer chromatography (HPTLC) band (UB) less polar than triacylglycerol (TAG), regardless of CIN status; it was absent in dogs and captive wildcats, sporadic in Scottish wildcats, and partly substituted for TAG with age.

   UB in 23 of 24 domestic cats, including all adult healthy (n=12) and CIN (n=12) cats, and in none of 12 dogs or 3 captive wildcats (2 snow leopards, 1 tiger); Rf 0.9 to 1.0. Semi-quantitative TAG:UB: cat kittens 22.6:20.0% vs adults 6.4:25.3%; Scottish wildcat kittens 24.1:14.0% vs adults 7.8:21.2%. · High Performance Thin Layer Chromatography…; Felid kidneys have an unusually common presence…; Age and sex of the animal

3. 03

   SuggestedIn felids, TAG dominated total kidney extracts; domestic cat TGs were rich in short-chain monounsaturated species, while Scottish wildcat profiles leaned to longer chains. Dog extracts held less TAG, more phospholipid and fewer TG species, built mainly from palmitic, oleic and linoleic chains.

   LC-MS annotated 2353 lipids across n=19 kidneys. TAG share: domestic cat 71.6% (n=9), Scottish wildcat 71.8% (n=6), dog 39.4% (n=4); phospholipid 16.7% and 12.2% vs 31.5% in dog. Top cat species TG(14:1_14:1_16:1) and TG(14:1_16:1_16:1) were undetectable in dog, whose TGs were dominated by 50:2, 50:3 and 50:1. · Liquid Chromatography Mass Spectrometry of total…; Felid kidneys have an unusually common presence…; Figure legends

4. 04

   SuggestedUB-positive extracts had more TAG, wax esters and named ether-linked species than UB-negative ones, though lower overall alkyl-acyl and fatty ether shares; MADAG annotations occurred in all UB-positive and no UB-negative extracts. UB FAMEs featured lauric (C12:0) and myristic (C14:0) acids.

   LC-MS/MS of UB+ve (n=5) vs UB-ve (n=6) extracts: straight-chain fatty acids 44.65% vs 66.43% [62.84-75.74%], alkyl-acyl lipids 1.70% vs ~6.00%, fatty ethers 1.16% vs 2.18%; ether species [O-31:2_23:2], [O-38:7], [O-4:0_22:6] enriched in UB+ve; MADAG calls rest on m/z and formula matches (Table S1). · Fatty acid methyl esters (FAMEs) in the UB; LC-MS/MS evaluation of the unidentified band; Figure legends

5. 05

   SuggestedCryo-OrbiSIMS of frozen cortex sections found a set of peaks specific to domestic cat. Their annotations included branched-chain fatty acids, monoalkylglycerols and ether-linked glycerolipids, which supports MADAG-like lipids being present in the tissue itself.

   Of 2212 peaks, 733 were unique to domestic cat relative to Scottish wildcat and dog; LIPID MAPS gave 347 lipid assignments, and n=19 matched accurate masses previously identified as MADAGs. One section per individual; isobaric ambiguity noted (m/z 757.539 as PA 39:2;O or PG O-36:3). · In situ lipidomics of frozen kidney sections…; LC-MS/MS evaluation of the unidentified band; Felid kidneys have an unusually common presence…