Dorothy H. Wood, Ph.D.

Dissertation research performed under the guidence of Dr. Richard R. Tidwell

ABSTRACT
    The aromatic diamidine 1,5-bis(4-amidinophenoxy)pentane (pentamidine) has been used for decades for the treatment of Pneumocystis carinii pneumonia.  Its clinical use is restricted, however, because of severe toxicity, which includes acute hypoglycemia.  As an alternative to pentamidine, we have designed and synthesized over 800 dicationic compounds, many with amidine and imidazoline moieties, as potential antimicrobial agents, striving for increased efficacy and fewer side effects.  We have shown that pentamidine has an affinity for the imidazoline I2 receptor comparable to the most potent known ligands (Ki = 1.4 ± 0.2 nM).  The molecules are able to differentiate between the I1 and I2 imidazoline receptors and a2-adrenoceptors.  Radioligand binding studies with these novel compounds provide a valuable tool to characterize the imidazoline receptors.
    Compounds with an imidazoline moiety can stimulate insulin secretion from pancreatic b-cells.  Evidence suggests this is via closure of an ATP-dependent K+ (KATP) channel following interaction with the I3 imidazoline receptor.  Our studies demonstrate that pentamidine can initiate and potentiate insulin secretion in HIT-T15 cells.  Moreover, it can overcome the inhibition of insulin secretion by diazoxide, which exerts its mechanism of action by opening the KATP channel.  This action is rapid, within 5 minutes of pentamidine addition, and in a dose-responsive manner.  Cell viability studies confirm the cells are intact following experimentation.  This is highly suggestive of a stimulus-secretion coupling rather than a non-specific leaking from cells, damaged subsequent to pentamidine exposure, as previously speculated.  Stimulation of insulin release by novel compounds does not correlate with affinity for I1 or I2 receptors.  Occasionally insulin-dependent diabetes mellitus develops in patients receiving long-term pentamidine treatment. Studies with healthy rats reveal little difference between the islets of saline and pentamidine-treated rats.  However, a comparison of the pancreata in healthy rats to saline and pentamidine-treated immunosuppressed rats reveals striking differences in the morphology of the islets of Langerhans.  This would seem indicative that development of diabetes is not solely a result of exposure to pentamidine, but rather that many underlying factors related to the condition of the patient play a significant role in contributing to the disease.