The potential role for metformin in the prevention and treatment of tuberculosis

Metformin as adjuvant treatment in hepatitis C virus infections and associated complications

Hepatitis C virus is an important global cause of hepatitis and subsequently cirrhosis and hepatocellular carcinoma. These infections may also cause extrahepatic manifestations, including insulin resistance and type 2 diabetes mellitus. These two complications can potentially reduce sustained virologic responses (SVR) in some drug regimens for this infection. Metformin has important biochemical effects that can limit viral replication in cellular cultures and can improve the response to antiviral drug therapy based on ribavirin and interferon. Clinical studies comparing treatment regimens with interferon, ribavirin, metformin with these regimens without metformin have demonstrated that metformin increases viral clearance, establishes higher rates of SVRs, and increases insulin sensitivity. Metformin also reduces the frequency of hepatocellular carcinoma in patients who have had SVRs. Larger treatment trials are needed to determine metformin's short-term and long-term treatment effects in patients with diabetes using newer antiviral drugs. In particular, if metformin reduces the frequency of cirrhosis and hepatocellular carcinoma, this would significantly reduce the morbidity and mortality associated with this infection.

Metformin has immunomodulatory effects which support its potential use as adjunctive therapy in tuberculosis

Metformin is the preferred oral medication for patients with type 2 diabetes mellitus, and this blood glucose-lowering and insulin-sensitizing drug has immunomodulatory effects that could contribute to the management of patients with various other autoimmune and infectious diseases. Tuberculosis is one such infection, and it remains prevalent worldwide, largely due to the successful evasion of the host's immune responses by the infecting pathogen, Mycobacterium tuberculosis. This review focuses on the possible mechanisms relevant to metformin's modulation of innate and adaptive immune responses to Mycobacterium tuberculosis and its potential use as an adjunctive drug in the treatment of tuberculosis. Current data suggest that metformin increases autophagy, phagocytosis, and mitochondrial reactive oxygen species production, while limiting excess inflammation and tissue destruction. This multifaceted drug also augments cell-mediated immune responses by maintaining CD8+ T cell metabolic homeostasis and improving immunological memory. Several murine models have demonstrated that metformin can reduce tuberculosis severity and tissue pathology, and two in vitro human studies confirmed enhanced immune responses in metformin-treated cells. These studies provide convincing evidence supporting the use of metformin to augment immune responses in patients with tuberculosis.