From the Journals

Proteins in urine may predict active lupus nephritis



A large-scale screen of urine proteins has identified molecules that may help to determine whether a patient has active lupus nephritis, according to a cross-sectional study published in Nature Communications. The proteins that best differentiate active lupus nephritis from inactive systemic lupus erythematosus (SLE) vary across ethnicities, the researchers wrote.

Dr. Chandra Mohan

“A longitudinal study is warranted to investigate how these molecules relate to disease pathology and progression over time,” said senior study author Chandra Mohan, MD, PhD, of the department of biomedical engineering at the University of Houston, and colleagues. In addition, researchers should investigate the roles of protein biomarkers ALCAM, PF-4, properdin, VCAM-1, and sE-selectin in mediating lupus nephritis.

Limitations of renal biopsy

About 60% of patients with SLE will develop lupus nephritis, and 10%-15% of patients who develop lupus nephritis progress to end-stage renal disease. Although renal biopsy is the gold standard for the diagnosis of renal involvement in SLE, biopsies are invasive, not serially repeatable, and may not represent the entire kidney, Dr. Mohan and colleagues wrote.

To identify potential urinary biomarkers of lupus nephritis using an unbiased, proteomic approach, the investigators screened urine samples from 23 participants – 7 with active lupus nephritis, 8 with inactive SLE, and 8 healthy controls. They used an aptamer-based screen to investigate more than 1,100 proteins. The researchers then validated biomarker candidates using enzyme-linked immunosorbent assays. Independent cross-sectional cohorts included 127 patients with inactive SLE, 107 patients with active lupus nephritis, 67 patients with active nonrenal lupus, and 74 healthy controls. The cohorts included patients who were African American, Caucasian, and Asian. The researchers excluded patients with renal failure and pediatric patients.

Of the 12 urine proteins studied, 10 outperformed traditional laboratory measures, such as C3/C4 and anti–double stranded DNA, in discriminating active lupus nephritis from inactive SLE, wrote Dr. Mohan and colleagues. A Lasso regression analysis found that the best predictive model included 8 of the 12 urine proteins as well as race. The model discriminated active lupus nephritis from inactive SLE with an area under the receiver operating characteristic curve (AUC) of 0.98.

Among African Americans, urine proteins that best distinguished active lupus nephritis from inactive disease included PF-4 (AUC, 0.88), VCAM-1 (AUC, 0.87), properdin (AUC, 0.85), and ALCAM (AUC, 0.84). Among Caucasians, they included sE-selectin (AUC, 0.87), VCAM-1 (AUC, 0.84), BFL-1 (AUC, 0.81), and hemopexin (AUC, 0.80). Among Asians, they included ALCAM (AUC, 0.93), VCAM-1 (AUC, 0.92), TFPI (AUC, 0.88), and PF-4 (AUC, 0.83).

The study is “unique in highlighting the importance of tailoring the biomarkers to patient ethnicity,” the researchers wrote.

Basing subgroups on race rather than phenotypic profiles

“This is an important study because it confirms the ability to predict active lupus nephritis from urine samples and utilized advanced technologies to find key markers for that,” said Joan T. Merrill, MD, of the Oklahoma Medical Research Foundation in Oklahoma City. “It is unfortunate that investigators with access to such advanced technology are still using an outdated and extremely questionable method for distinguishing subgroups of patients, that of race.”

Dr. Joan T. Merrill

Dr. Joan T. Merrill

Grouping patients by phenotypic profiles that reflect current disease states “would be a more accurate method for finding optimal urinary markers for active nephritis,” and is “likely to prove more accurate for individuals in all races,” Dr. Merrill said. Certain racial subgroups may be more likely to have particular disease phenotypes, “which are usually identified based on gene pathway coexpression patterns.” Still, “people who self-identify as a given race are not genetically identical,” Dr. Merrill added. “In fact, this is a very blunt instrument, compared to phenotypic profiling now available for lupus patients.”

SLE and lupus nephritis are “heavily influenced by genetics,” and African Americans are three times more likely than Caucasians to develop SLE and are more like to develop end-stage renal disease, Dr. Mohan and colleagues wrote. Nevertheless, “influence from environmental triggers or socioeconomic factors cannot be ruled out,” they added. “Although patient demographics are widely known to affect SLE disease manifestations and outcomes, there are virtually no studies investigating this phenomenon in the context of disease biomarkers; most SLE biomarkers studies focus on one demographic group or all ethnic groups combined, which yield results that may not be equally predictive in all demographic groups of SLE patients.”

Dr. Mohan is collaborating with a biotechnology company to study drugs that may block ALCAM, according to a University of Houston news release. ALCAM is involved in immune and inflammatory responses, the researchers noted. “When all SLE patients were combined, urine ALCAM levels had the strongest bearing on disease activity status, in an unsupervised Bayesian network analysis,” they wrote. “Urine ALCAM also emerged as one of the few proteins that distinguished active [lupus nephritis] from active nonrenal lupus.”

National Institutes of Health grants supported the research. The investigators had no competing interests.

SOURCE: Stanley S et al. Nat Commun. 2020 May 4. doi: 10.1038/s41467-020-15986-3.

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