Abstract Body: Objective: Medial artery calcification (MAC) poses a significant obstacle to revascularization and is a risk factor for amputation in chronic limb-threatening ischemia (CLTI), particularly in patients with DM and CKD. Klotho is a pleiotropic renal and serum factor that is reduced in CKD, which may influence pathologic vascular osteogenic pathways promoting MAC. We hypothesize that serum Klotho (sKlotho) is inversely associated with MAC and with the severity of calcification of tibio-pedal arteries in patients with CLTI.
Methods: This is a single-center, prospective observational study of patients with CLTI and healthy controls. Serum was collected and banked at -80C, and patient data were gathered from medical records. sKlotho levels were analyzed by ELISA. Lower extremity arterial specimens were collected from CLTI patients undergoing amputation, fixed in formalin, and sectioned for histological analysis. Clinical calcification severity was quantified by applying the pedal MAC (pMAC) scoring system to radiographs of the foot.
Results: A total of 60 patients had sKlotho assays: 51 in the CLTI arm (9 with major amputation) and 9 in the control arm, with median age 71 years and 72% male. Comorbidities in the CLTI group included DM (80%), CKD stages 3-5 (47%), CAD (61%) and CHF (49%) (Table 1). In the CLTI arm, 46 (90%) had foot x-rays available for pMAC scoring [low in 21 (46%), high in 25 (54%)]. CKD 3-5 was independently associated with high pMAC (p=0.01).
Median sKlotho was 494 (341-615) pg/mL in the CLTI arm and 645 (555-727) pg/mL in controls (p=0.047). The CLTI group was stratified by pMAC severity, which was inversely associated with sKlotho, with median sKlotho levels of 590 (459-692) pg/mL in the low pMAC group and 415 (325-538) pg/mL in the high pMAC group (p=0.01; Figure 1). CKD 3-5 was also significantly associated with lower sKlotho levels (p=0.003).
Histologic examination of arteries harvested from amputation specimens demonstrated significant MAC and osteogenic transformation of the arterial wall, including luminal bone marrow formation, in specimens from low sKlotho patients. Conversely, high sKlotho specimens demonstrated no significant calcification or osteogenic features (Figure 2).
Conclusions: MAC in CLTI is strongly associated with DM and CKD and with revascularization failure and amputation. Our data suggests that circulating sKlotho may be an important biomarker/mediator relating these risk factors to MAC and vascular osteogenesis.