Tubular Damage Is Present In Patients With MGUS and Asymptomatic Multiple Myeloma Even In The Absence Of Impaired Estimated Glomerular Filtration Rate; Alterations Of Neutrophil Gelatinase-Associated Lipocalin and Cystatin-C In Myeloma Patients Post IMiD- and Bortezomib-Based Regimens
Authors: Terpos Evangelos , Christoulas Dimitrios , Kastritis Efstathios , Papassotiriou Gerasimos-Petros , Apostolakou Filia , Margeli Alexandra , Kanellias Nikolaos , Eleutherakis-Papaiakovou Evangelos , Papassotiriou Ioannis , Dimopoulos Meletios A. 
Published: October 2019

Abstract
Neutrophil gelatinase-associated lipocalin (NGAL) is a 25 kDa protein, which is produced by the injured tubule epithelium. In contrast to serum creatinine (sCr), NGAL is specifically induced in the damaged nephron and then released into blood and urine; thus it is considered as an early marker of renal tubular injury. Our group has recently shown that urinary and serum NGAL were elevated in the vast majority (90% and 70%, respectively) of newly diagnosed patients with multiple myeloma (MM), while serum cystatin-C (CysC), an accurate marker of GFR, was elevated in 70% of them. However, there is no information for the value of these markers in patients with MGUS, asymptomatic MM (AMM), as well as in symptomatic MM post treatment.
Thus, we measured urinary and serum NGAL and serum CysC in 40 patients with MGUS (23M/17F, median age 72 years), 36 with AMM (16M/20F, 60 years) and 120 healthy controls. Furthermore, we measured serum NGAL and CysC in 39 newly diagnosed symptomatic MM patients (24M/15F, 70 years) before and after frontline therapy with novel agents. Serum and urinary NGAL was measured using an ELISA method (BioPorto Diagnostics A/S, Gentofte, Denmark), while CysC was measured using a latex particle-enhanced nephelometric immunoassay (Dade Behring-Siemens Healthcare Diagnostics, Liederbach, Germany). The estimated GFR (eGFR) was calculated using the CKD-EPI equation. Patients were divided into the 5 CKD stages of the KDIGO classification, according to eGFR (stage 1: eGFR >90 ml/min/1.73m2; stage 2: 60-89 ml/min/1.73m2; stage 3: 30-59 ml/min/1.73m2; stage 4: 15-29 ml/min/1.73m2; stage 5: <15 ml/min/1.73m2or on dialysis).
Only two (5%) patients with MGUS and two (5.5%) with AMM had sCr above the upper normal limit, but none had sCr >2 mg/dl. Regarding eGFR, 34 (85%) patients with MGUS and 31 (86%) with AMM had CKD stage 1/2, while 6 (15%) MGUS and 5 (14%) AMM patients had CKD stage 3. Urinary NGAL was elevated in patients with MGUS (median: 14 ng/ml, range 0.5-31 ng/ml) and AMM (22.3 ng/ml, 0.9-78 ng/ml) compared to controls (5.3 ng/ml, 0.7-9.8 ng/ml, p<0.001 for both comparisons). Similarly, serum NGAL was elevated in patients with MGUS (106 ng/ml, 74.9-205.5 ng/ml) and AMM (94.2 ng/ml, 29.5-306.4 ng/ml) compared to controls (63ng/ml, 37-106 ng/ml; p<0.01). There was no difference between MGUS and controls or MGUS and AMM regarding CysC serum values, indicating that traditional indices of renal function could not detect early renal damage. However, 22 (55%) patients with MGUS and 24 (66%) with AMM had higher urinary NGAL values than the higher value of the controls. Similarly, 9 (22.5%) MGUS and 11 (30%) AMM patients had higher levels of serum NGAL than the higher value in the control group.
Twelve (31%) patients with symptomatic MM had sCr >2 mg/dl, while 41% had CKD stages 1/2, 28% had CKD stage 3 and 31% CKD stages 4/5. As expected, patients with symptomatic MM had elevated serum NGAL and CysC (p<0.001). NGAL strongly correlated with CysC (r=0.675, p<0.001) and CKD stage (mean±SD values for stages 1/2, stage 3 and stages 4/5 were: 97±57 ng/ml, 144±79 ng/ml and 205±124 ng/ml, respectively; ANOVA p=0.014). CysC also correlated with CKD stage (0.96±0.29 mg/l, 1.54±0.32 mg/l and 2.51±1.00 mg/l respectively, ANOVA p<0.001). Seven patients received bortezomib-based regimens and 32 patients received IMiD-based regimens as frontline therapy: 9 patients achieved sCR, 13 VGPR, 12 PR, while 3 had stable disease and 2 progressed. Among patients with eGFR <50 ml/min at baseline (n=22), 4/4 who received bortezomib-based regimens and 5/18 who received IMiD-based regimens achieved at least minor renal response. After 4 cycles of therapy, serum NGAL increased in patients who received IMiD-based therapy compared to baseline (255±264 ng/ml vs. 147±104ng/ml, p=0.021), but not in patients who received bortezomib (119±68 ng/ml vs. 159±111 ng/ml p=0.520), regardless of myeloma response to treatment.
We conclude that the high levels of urinary and serum NGAL in MGUS and AMM indicate the presence of subclinical renal damage in these patients early in the course of their disease, when other markers of renal function, such as sCr or even the more sensitive CysC indicate that renal function is preserved. Thus, NGAL may be useful as an early marker that predicts the development of renal damage and the progression of the disease in these patients. NGAL seems also to increase in patients with renal impairment who receive IMiD-based regimens.

Disclosures:
No relevant conflicts of interest to declare.