Methionine intolerance and plasma homocysteine after insulin infusion in type II diabetic patients

Background-To establish whether transsulfuration impairment (methionine intolerance) may influence total plasma homocysteine (Hcy) in response to insulin infusion in type II diabetic patients (DB).Materials and Methods- DB with normal (group A, n=13) and abnormal (hyperhomocysteinemia, HHcy)) (Group B, n=17) response to oral methionine load underwent a glucose/clamp study. At time 0, and 30, 60 and 120 minutes after hyperinsulinemia, Hcy and methionine (Met) plasma levels were assessed. All patients were assayed for fasting Homocysteine-Cysteine ratio (as marker of suspected heterozygosis for cystathionine--synthase deficit) and vitamin status [serum vitamin B6 (PLP), vitamin B12 and folate]. Results- After hyperinsulinemia, plasma methionine reduced (about –30% at 120 minutes vs. basal values) within both groups, whereas Hcy decreased in group A (up to –15.2  8.9 % at 120 minutes) and increased in group B (up to +30.6  10.9 % at 120 minutes). (see figure) PLP was higher in group A than in group B (94.2  42.6 vs. 54.6  32.4 nmol/L; p<0.01); group A showed a lower prevalence of suspected heterozygosis for cystathionine--synthase deficit (1/13 (7,7%) vs.13/17 (76.5%), p=0.000). Conclusions-Methionine intolerance may influence insulin effect on plasma Hcy. To prevent a possible acute HHcy due to insulin administration in case of transsulfuration impairment, it may be suggested to assess transsulfuration capacity in all patients due to be subjected to insulin therapy.