Dietary Resistant Starch Protects Against Diabetic Nephropathy by Inhibition of Complement

Abstract:

Aim To investigate immune mechanisms by which resistant starch (RS) supplementation may be protective against diabetic nephropathy.

Background Activation of complement occurs in diabetic nephropathy. C5a is a downstream complement component that activates the innate immune system contributing to inflammation. Dietary RS may be nephro-protective, however the effects of dietary RS on complement activation and the innate immune system have not been explored.

Methods Six week old non-diabetic mice (db/h), diabetic mice (db/db) and db/db mice on a regular chow diet supplemented with 25% RS (dbdb+RS) were maintained for ten weeks. 24-hour urine was collected for albumin and C5a measurement by ELISA. Kidneys were digested and enriched for leukocytes using Percoll gradient. Cells were stained with BV786-CD45, AF700-CD11b, PE-Cy7-CD11c, BV711-Siglec F, BV605-Ly6C, PE-CD86, FITC-C5aR antibodies and flow cytometry was performed.

Results Diabetes was associated with an increase in albuminuria (28.0±6.5 vs 411.3±275.8µg/24h, P<0.001, dbh vs dbdb), which was reduced in diabetic mice receiving RS supplementation (411.3±275.8 vs 125.6±37.3µg/24h, P<0.01, dbdb vs dbdb+RS). Urinary C5a excretion was increased by diabetes (92.6±17.6 vs 1324.0±429.7pg/24h, P<0.001, dbh vs dbdb) and decreased by RS (1324.0±429.7 vs 577.7±123.1pg/24h, P<0.05, dbdb vs dbdb+RS). In diabetes there was an increase in CD86 MFI (a marker of activation) on infiltrating macrophages (CD45+ CD11b+ CD11c- Siglec F- Ly6C hi), which was attenuated with RS (3.7±1.8 vs 1.5±1.0 fold change to dbh, P<0.05, dbdb vs dbdb+RS). Furthermore, infiltrating macrophages were more likely to be positive for C5aR with diabetes (4.8±3.9 vs 54.0±27.8%, P<0.001, dbh vs dbdb), which RS supplementation reduced (54.0±27.8 vs 11.7±4.2%, P<0.01, dbdb vs dbdb+RS).

Conclusions These studies support the notion that dietary RS is protective against renal disease via inhibition of complement.