Methods for determining total body skeletal muscle mass

Abstract

The present invention is based on the finding that enrichment of D3-creatinine in a urine sample following oral administration of a single defined dose of D3-creatine can be used to calculate total-body creatine pool size and total body skeletal muscle mass in a subject. The invention further encompasses methods for detecting creatinine and D3-creatinine in a single sample. The methods of the invention find use, inter alia, in diagnosing disorders related to skeletal muscle mass, and in screening potential therapeutic agents to determine their effects on muscle mass.

1 . A method of determining the concentration of creatinine in a biological sample from a subject, said method comprising the steps of:
 (a) obtaining a biological sample from the subject;   (b) analyzing the biological sample to determine the peak area of the creatinine M+2 isotope peak for the biological sample;   (c) comparing the peak area determined in step (b) to a calibration curve generated using D3-creatinine to determine the concentration of the creatinine M+2 isotope in the biological sample;   (d) dividing the concentration obtained in step (c) by a dilution factor, where the dilution factor is the ratio of the concentration of creatinine M+2 to the concentration of creatinine M+0 in the biological sample.   
     
     
         2 . The method of  claim 1 , wherein said biological sample is a urine sample. 
     
     
         3 . The method of  claim 1 , wherein said biological sample is a blood sample. 
     
     
         4 . The method of  claim 1 , wherein said subject is human. 
     
     
         5 . The method of  claim 1 , where the peak area of the creatinine M+2 isotope peak is determined using liquid chromatography/mass spectroscopy (LC/MS/MS). 
     
     
         6 . The method of  claim 1 , wherein the dilution factor is 0.0002142±0.0000214. 
     
     
         7 . The method of  claim 1  wherein the dilution factor is 0.0002142±0.00001. 
     
     
         8 . The method of  claim 1  wherein the dilution factor is 0.0002142±0.000005. 
     
     
         9 . The method of  claim 1  wherein D3-creatine has been administered to the subject and wherein the method further comprises the step of analyzing the biological sample to determine the peak area of D3-creatinine in the biological sample. 
     
     
         10 . A method of determining the total body skeletal muscle mass in a human subject, comprising the steps of:
 (a) orally administering 10-200 mg D3-creatine or a salt or hydrate thereof to the subject;   (b) allowing at least 24 hours to elapse after the administration of the D3-creatine;   (c) obtaining a biological sample from the subject,   (d) determining the concentration of creatinine in said sample according to the method of  claim 1 ;   (e) determining the concentration of D3-creatinine in said biological sample; and   (f) using the creatinine and D3-creatinine concentrations determined in steps (d) and (e) to calculate the total body skeletal muscle mass of the subject.   
     
     
         11 . The method of  claim 9  wherein said subject is female and 20-40 mg of D3-creatine are administered. 
     
     
         12 . The method of  claim 9  wherein said subject is male and 50-70 mg of D3-creatine are administered. 
     
     
         13 . The method of  claim 9 , wherein D3-creatine monohydrate is administered to the subject.