Protein concentration and mitochondrial content in the gastrocnemius predicts mortality rates in patients with peripheral arterial disease

Abstract

Objective: This study evaluated the hypothesis that protein concentration and mitochondrial content in gastrocnemius biopsies from patients with peripheral arterial disease (PAD) predict mortality rates.

Background: PAD patients experience advancing myopathy characterized by mitochondrial dysfunction, myofiber degradation, and fibrosis in their ischemic legs, along with increased mortality rates.

Methods: Samples from the gastrocnemius of PAD patients were used for all analyses. Protein concentration was normalized to muscle wet weight, and citrate synthase activity (standard measure of mitochondrial content in cells) was normalized to muscle wet weight and protein concentration. Protein and citrate synthase data were grouped into tertiles and 5-year, all-cause mortality for each tertile was determined with Kaplan-Meier curves and compared by the modified Peto-Peto test. A Cox-regression model for each variable controlled for the effects of clinical characteristics.

Results: Of the 187 study participants, 46 died during a mean follow-up of 23.0 months. Five-year mortality rate was highest for patients in the lowest tertile of protein concentration. Mortality was lowest for patients in the middle tertile of citrate synthase activity when normalized to either muscle wet weight or protein concentration. The mortality hazard ratios (HRs) from the Cox analysis were statistically significant for protein concentration normalized to muscle wet weight (lowest vs middle tertile; HR = 2.93; P = 0.008) and citrate synthase normalized to protein concentration (lowest vs middle tertile; HR = 4.68; P = 0.003; and lowest vs highest tertile; HR = 2.36; P = 0.027).

Conclusions: Survival analysis of a contemporaneous population of PAD patients identifies protein and mitochondrial content of their gastrocnemius as predictors of mortality rate.

Figure 1 –

Kaplan-Meier Curves for protein concentration in gastrocnemius biopsies from PAD patients. Protein concentration was determined as protein content (mg) per muscle wet weight (g). Patients in the lowest (dashed line) tertile of protein concentration in their gastrocnemius had the worst survival with 5-year mortality of 57.0%. Patients in either the middle (continuous line) or highest (squared dot line) tertile for protein concentrations in their gastrocnemius had the best survival with 5-year mortality of 34.8% and 37.5%, respectively.

Figure 2 –

Kaplan-Meier Curves for Citrate Synthase activity normalized to muscle wet weight in gastrocnemius biopsies from PAD patients. Citrate Synthase activity was normalized to muscle wet weight (g). Patients in the middle (continuous line) tertile had the best survival with a 5-year mortality of 33.3%. This was followed by the highest (squared dot line) tertile with a 5-year mortality rate of 44.2%. Mortality at 5 years was highest (50.1%) in those patients in the lowest (dashed line) tertile.

Figure 3 –

Kaplan-Meier Curves for Citrate Synthase activity normalized to protein content in muscle biopsies from PAD patients. Citrate Synthase activity was normalized to protein content (mg). Patients in the middle (continuous line) tertile had the best survival with a 5-year mortality of 23.2%. This was followed by the highest (squared dot line) tertile with a 5-year mortality rate of 44.2%. Mortality at 5 years was highest (64.0%) in those patients in the lowest (dashed line) tertile.