Membrane fluidity and sodium transport by renal membranes from dogs with spontaneous idiopathic Fanconi syndrome

[Acquired transient Fanconi syndrome after feeding jerky treats in dogs - A case series]

Between April 2018 and August 2019, 6 dogs with laboratory diagnostic evidence of Fanconi syndrome were presented to the Tierklinik Hofheim. The presumptive diagnosis was confirmed via urine amino acid analysis in all dogs. In 5 of the 6 dogs an alimentary origin was suspected, in 3 dogs the course of the disease could be followed. Supportive therapeutic measures and elimination of jerky treats from the dogs' diet improved the clinical symptoms in all dogs with known follow-up. This is the first case series of dogs with alimentary acquired Fanconi syndrome in Germany. The frequency of occurrence of the disease in that short period of time in only one small animal clinic suggests a significantly higher incidence than currently assumed.

Fanconi syndrome in four non-basenji dogs exposed to chicken jerky treats

Four small-breed dogs were diagnosed with acquired Fanconi syndrome. All dogs ate varying amounts of chicken jerky treats. All dogs were examined for similar clinical signs that included, but were not limited to, lethargy, vomiting, anorexia, diarrhea, and altered thirst and urination. The quantity of chicken jerky consumed could not be determined; however, based on the histories obtained, the chicken jerky treats were a significant part of the diet and were consumed daily by all dogs. Extensive diagnostic testing eliminated other causes of the observed clinical signs, such as urinary tract infection and rickettsial disease. Glucosuria in the face of euglycemia or hypoglycemia, aminoaciduria, and metabolic acidosis confirmed the diagnosis of Fanconi syndrome. All dogs received supportive care, including IV fluids, antibiotics, gastroprotectants, and oral nutritional supplements. Three dogs exhibited complete resolution of glucosuria, proteinuria, and the associated azotemia; however, one dog remained azotemic, resulting in a diagnosis of chronic kidney disease.

Megalin knockout mice as an animal model of low molecular weight proteinuria

Megalin is an endocytic receptor expressed on the luminal surface of the renal proximal tubules. The receptor is believed to play an important role in the tubular uptake of macromolecules filtered through the glomerulus. To elucidate the role of megalin in vivo and to identify its endogenous ligands, we analyzed the proximal tubular function in mice genetically deficient for the receptor. We demonstrate that megalin-deficient mice exhibit a tubular resorption deficiency and excrete low molecular weight plasma proteins in the urine (low molecular weight proteinuria). Proteins excreted include small plasma proteins that carry lipophilic compounds including vitamin D-binding protein, retinol-binding protein, alpha(1)-microglobulin and odorant-binding protein. Megalin binds these proteins and mediates their cellular uptake. Urinary loss of carrier proteins in megalin-deficient mice results in concomitant loss of lipophilic vitamins bound to the carriers. Similar to megalin knockout mice, patients with low molecular weight proteinuria as in Fanconi syndrome are also shown to excrete vitamin/carrier complexes. Thus, these results identify a crucial role of the proximal tubule in retrieval of filtered vitamin/carrier complexes and the central role played by megalin in this process.

Renal brush border membrane lipid composition in Basenji dogs with spontaneous idiopathic Fanconi syndrome

To comprehend the renal defect underlying idiopathic Fanconi syndrome in the Basenji dog, we have focused on delineating the lipid profiles of renal brush border membranes isolated from affected and normal Basenji dogs to establish any physical or compositional changes underlying previously observed transport and membrane-fluidity changes. The lipid composition was studied with respect to total lipid, cholesterol, and phospholipid content, cholesterol to phospholipid ratio, distribution of the major phospholipid classes, and fatty acid composition. Total phospholipid of the isolated renal brush border membranes from Fanconi syndrome dogs analyzed by 31P nuclear magnetic resonance showed no difference compared with that of normal dogs. Examination of total fatty acids in both membranes using gas-liquid chromatography analysis of fatty acid methyl esters showed no difference in the mole percents of the major fatty acids. Our data suggest that changes in bulk membrane fluidity of the Fanconi syndrome dog renal brush border as measured by 1,6-diphenyl-1,3,5-hexatriene cannot be attributed to phospholipid and fatty acid compositional change. In the membranes isolated from affected dog kidney, the cholesterol content determined by gas-liquid chromatography analysis was 66 mol% higher than in membranes isolated from normal dog kidney. This correlates with the higher cholesterol to phospholipid molar ratio of 0.82 +/- 0.08 in the affected animal as compared with 0.58 +/- 0.04 in the normal. Cholesterol content and its microdomain in the membrane bilayer may be important in modulating transport functions. Increased membrane cholesterol content may affect the conformational motility of membrane transport proteins and thus affect their function.