The lysosome among targets of metformin: new anti-inflammatory uses for an old drug?
BACKGROUND
Rheumatoid arthritis and type-2 diabetes exhibit progressive co-morbidity. Chloroquine (CQ) reportedly improves both. CQ inhibits lysosomal function in cultured cells at supra-therapeutic concentration; however, this is doubted as target mechanism. Some anti-diabetic biguanides are metal-interactive lysosomal inhibitors; and all bind Zn(2+).


OBJECTIVE
i) To bioassay the potency of CQ using (3)H-leucine release from perfused myocardial tissue. ii) To determine whether metformin (MET) is CQ-mimetic, and interactive with Zn(2+).


RESULTS
Therapeutic CQ concentration (0.1 - 0.5 microM) clearly does cause lysosomal inhibition although delayed and submaximal. MET alone (10 microM) caused sub-maximal inhibition. Supra-physiological extracellular Zn(2+) (5 - 50 microM) alone increased tissue Zn(2+) content, and inhibited lysosomal proteolysis. Physiological equivalent Zn(2+) (approximately 1 microM) had no effect. MET (<or= 25 microM) and Zn(2+) (<or= 1 microM) exhibited astounding 10 - 100 fold anti-lysosomal synergy. Cathepsin B was 50% inhibited by 1 muM Zn(2+), and is reportedly inhibited by gold agents.


CONCLUSIONS
MET somehow increases the natural inhibitory action of action of Zn(2+) against cysteinyl proteases. TNF-alpha activates lysosomal function; and CatB is among post-receptor players. MET might decrease antigen processing in specialized cells, and lysosomal hyper-catabolism in other cells.


CONCLUSIONS
Trials of MET for new use as an anti-inflammatory agent are suggested. Guanidylguanidine is a practical pharmacophore for synthesis of future anti-lysosomal agents.
Lockwood
Thomas D
TD
Wright State University, School of Medicine, Department of Pharmacology and Toxicology, Dayton, Ohio 45435, USA. thomas.lockwood@wright.edu
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D066298:In Vitro Techniques; D008247:Lysosomes / Q000187:drug effects*; D008687:Metformin / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000893:Anti-Inflammatory Agents; D008687:Metformin