Background/Purpose: Exosomes, extracellular vesicles that are abundant in human urine and contain proteins from renal cells, are a potential source of biomarkers of renal disease in LN patients. We previously demonstrated that levels of Glycosphingolipids (GSL) glucosylceramide (GlcCer) and lactosylceramide (LacCer), and expression of a neuraminidase (NEU1) that mediates GSL catabolism, are elevated in the urine of human patients with nephritis compared to controls. Based on these results we hypothesized that lipids and proteins in the GSL catabolic pathway in urine exosomes could be used as biomarkers of therapeutic response and/or disease flare in LN patients.

Methods: Lipids and proteins were analyzed by mass spectrometry in exosome fractions isolated from urine in 1) a pilot study of lupus nephritis (LN) patients during quiescent disease (non-flare) and renal flare, and in non-nephritis lupus patients; and 2) LN patients that failed to respond or had a complete response to mycophenolate mofetil (MMF) treatment.

Results: In the LN flare versus non-flare versus non-nephritis pilot study, differences in GSL (GlcCers and LacCers) levels were observed among the three sets of samples. Differences in phospholipids were also observed. Proteomics results identified several abundant and known urine biomarkers for LN albumin and serotransferrin in the samples from LN patients. Additional known urine biomarkers in the LN samples included complement factors, anti-trypsin, and alpha-2-HS-glycoprotein/fetuin-A. Novel proteins that were differentially abundant (either higher or lower) in LN samples compared to non-nephritis lupus samples and/or in flare compared to non-flare samples also were identified and included lysosomal protective protein (cathepsin A), a co-factor for NEU1. In the treatment response study, significant differences in GlcCer levels in exosomes isolated from pooled urine samples collected at baseline (prior to MMF treatment) were observed between LN patients that responded compared to those that did not respond to therapy. These results are being validated in a cohort of MMF responder (30) and non-responder (30) LN patients using exosomes isolated from individual urine samples taken at baseline and at 3-, 6-, and 12-months post-treatment. Additional lipids and proteins that are differentially abundant in these urine exosome samples between responders and non-responders are being identified and validated.

Conclusion: Preliminary data suggest that lipid and protein molecules in urine exosomes may serve as early markers of disease flare and/or response to therapy in LN patients and may enhance the predictive power of current models of response to therapy.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/glycosphingolipids-and-proteins-in-urine-exosomes-potential-biomarkers-of-lupus-nephritis/