Secondary metabolites have been found to have interesting applications over and above their well-known medical uses, e.g., as antimicrobials, etc. These alternative applications include antitumor,
cholesterol-lowering,
immunosuppressant, antiprotozoal, antihelminth,
antiviral and anti-ageing activities. Polyene
antibiotics, such as
amphotericin B, are of use as antiprion
agents, antitumor drugs and against
leishmaniasis. Other microbial natural products that show
antibiotic activity are used against
cancer e.g.,
doxorubicin,
neomycin, β-
lactams,
bleomycin and
rapamycin.
Macrolide antibiotics, such as
erythromycin,
clarithromycin and
azithromycin, improve pulmonary function in patients suffering from panbioncholitis. Pigments like
prodigiosin and
shikonin have antitumor activity, while
violacein has anti-
ulcer and antitumor activity and also acts as an antiprotozoal agent.
Statins, in addition to lowering
cholesterol and
LDL levels, also decrease elevated
C-reactive protein (CRP) levels independent of their
cholesterol effects.
Immunosuppressants have many alternative effects: (i)
Cyclosporin is proving useful in treatment of inflammatory disease such as
asthma and
muscular dystrophy. (ii)
Rapamycin is extremely useful in preventing restenosis of
stents grafted in balloon angioplasty. (iii)
Tacrolimus and
ascomycin help in treating inflammatory
skin disease such as
allergic contact dermatitis and
psoriasis.
Artemisinin, an
antimalarial agent, is also showing antitumor activity. Other natural products, including those from plants (
betulinic acid and
shikonin), animals (
bryostatins) and microbes (
squalestatin and sophorolipids) have a multiplicity of potentially useful actions. Unexpected functions of known secondary metabolites are continuously being unraveled, and are fulfilling some of the needs of present day medicine and show great promise for the future.