Insulin Sensitivity After Living Donor Nephrectomy

BACKGROUND

The kidney is essential for glucose and insulin metabolism. Living kidney donors (LKDs) experience a reduction in glomerular filtration rate of 25 to 30 mL/min after donor nephrectomy. Little is known about the effect of glomerular filtration rate decline on insulin sensitivity in LKDs.

METHODS

We conducted a prospective pilot study on 9 LKDs (N = 9) who underwent dynamic metabolic testing (mixed meal tolerance test) to measure proxies of insulin sensitivity (homeostatic model assessment of insulin resistance, the area under curve [AUC] for insulin/glucose ratio, and Matsuda insulin sensitivity index) before and 3 months after donor nephrectomy. The primary outcome was the change in insulin sensitivity indices (delta [post-nephrectomy - pre-nephrectomy]).

RESULTS

Four of the donors had a body mass index (BMI) between 32.0 and 36.7 predonation. Post-donor nephrectomy, compared with prenephrectomy values, median insulin AUC increased from 60.7 to 101.7 hr*mU/mL (delta median 33.3, P = .04) without significant change in median glucose AUC levels from 228.9 to 209.3 hr*mg/dL (delta median 3.2, P = .77). There was an increase in the median homeostatic model assessment of insulin resistance from 2 to 2.9 (delta median 0.8, P = .03) and the AUC insulin/glucose ratio from 30.9 to 62.1 pmol/mmol (delta median 17.5, P = .001), whereas the median Matsuda insulin sensitivity index decreased from 5.9 to 2.9 (delta median -2, P = .05). The changes were more pronounced in obese (BMI >32) donors.

CONCLUSION

LKDs appear to have a trend toward a decline in insulin sensitivity post-donor nephrectomy in the short term, especially in obese donors (BMI >32). Further investigation with a larger sample size and longer follow-up is needed.

Purification and characterization of the NAD-preferring glucose 6-phosphate dehydrogenase from Acetobacter hansenii (Acetobacter xylinum)

An NAD-preferring glucose 6-phosphate dehydrogenase of Acetobacter hansenii (formerly known as Acetobacter xylinum) has been purified to apparent homogeneity and kinetically characterized. The purified enzyme was stabilized by the use of glycerol, MgSO4, and 2-mercaptoethanol at pH 5.4. The molecular weight of the enzyme, determined by nondenaturing gel filtration, is 243,000. The subunit molecular weight is 60,140 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting that the native enzyme is a tetramer. At pH 5.4 the enzyme has Kms of 0.104 and 0.34 mM for NAD+ and NADP+, respectively; the Kms for glucose 6-phosphate are 0.071 and 0.089 mM, using NAD+ and NADP+, respectively; and the kcat values are 128,000 and 77,300 min-1 with NAD+ and NADP+, respectively. The Kms for NADP+ and glucose 6-phosphate are approximately 10 times higher than the corresponding Kms for the NADP-specific glucose 6-phosphate dehydrogenase in the same organism, but the kcat is also approximately 10-fold higher, so that the kcat/Km values for these two activities are nearly identical at pH 5.4. Both the NAD- and NADP-linked activities of the NAD-preferring enzyme are inhibited by ATP. The NADP-specific glucose 6-phosphate dehydrogenase is insensitive to ATP at pH 6.7 and 9.5, but at pH 5.4 ATP inhibits this enzyme. The possible roles of these two glucose 6-phosphate dehydrogenases in the metabolism of A. hansenii are discussed.