Current Pharmaceutical Design - Volume 8, Issue 7, 2002

The constant increase of life expectancy is associated with major ageing of developed populations. This indicates that the new century will have one of most epidemic progressions of cardiovascular, cancer and inflammatory diseases. The high challenge for medical research is to compress such morbidity. In these conditions, invertebrates have demonstrated to be truly useful models in drug discovery for such ageing diseases. The last decade, drug discovery in leeches has opened the gate of new molecules to treat emphysema, coagulation, inflammation, dermitis and cancer. Also other invertebrates such as insects, which evolved from the annelids, harvest potential interesting molecules, such as serine protease inhibitors that can be exploited by the medical industry.

Serine proteases (SP), such as thrombin, factor Xa, elastase, trypsin are implicated in many clinical disorders such as emphysema, arthritis and cardiovascular diseases. These enzymes, in normal physiological conditions, are regulated by naturally occurring serine protease inhibitors, such as anti-thrombin III involved in thromb in inhibition. Primitive parasitic invertebrates have co-evolved highly specific mechanisms to communicate with their hosts for survival purposes, by blocking host processes such as blood coagulation. Thus a battery of new powerful molecules from blood-sucker animals acting at different points of the coagulation cascade such like factor Xa, thrombin, platelets aggregation inhibitors have been isolated and are now at a clinical level. In this review, we focus our attention on thrombin inhitors.

This review discusses the role of protease inhibition with emphasis on the effects of inflammation and vascular immune phenomena in non-immunocompromised hosts. A vast body of knowledge elucidating the role of protease inhibition and hemostasis has accumulated in recent years. The two subjects are intimately linked, but the focus of this review is limited to the anti-inflammatory effects of protease inhibitors. In light of the particular expertise of the present authors, this review will focus on human studies and often cite work related to open-heart surgery, since in recent years this is the area in which a large effort has been concentrated worldwide.

Since the initial description of a peptidase activity, namely pepsin, in the middle of the 19th century, our understanding of the molecular basis of peptidase function and activation has greatly improved. Further, by sequencing entire genomes, we have reached a stage whereby it is now possible to appreciate the tremendous diversity and unique specificities of peptidases. Because of their importance in most if not all vital processes of the cell including ultimately its death, their activities must be carefully localized and kept under tight control. In addition to endogenous inhibitors, control of enzymatic activity can be achieved through their synthesis and transport as inactive zymogens. This review article will focus on the characteristics as well as the role of the proregion contained within the peptidase zymogen structure. It will survey novel zymogen structures determined in the past 5 years as well as those of selected emerging peptidase families for which there exists as yet no or little structural data. These include members belonging to the caspase, ADAMS, TTSP, MMP, Aspartyl peptidases and convertase families.

During the last eight years a number of bioactive lipid mediators, the amides or esters of long chain fatty acids, have been discovered or re-discovered. These are: anandamide (N-arachidonoyl-ethanolamine, AEA) and 2-arachidonoylglycerol (2-AG), two endogenous agonists of cannabinoid receptors; oleamide (cis-9- octadecenoamide), a putative endogenous sleep-inducing factor; N-palmitoylethanol amine (PEA), a compound with promising anti-inflammatory and immune-modulatory activity. These compounds are all substrates for the same hydrolytic enzyme, fatty acid amide hydrolase (FAAH), whose molecular characterization was obtained in 1996. The molecular and enzymatic properties, tissue distribution, substrate recognition properties, physiological regulation and biological role of FAAH are discussed in this article, with special emphasis on the possible pharmacological manipulation of the activity of this enzyme with therapeutic purpose.

Following protein biosynthesis, some of the most important cellular mechanisms that generate biological diversity are the enzymatically driven post-translational modifications that ultimately lead to the formation of bioactive molecules. Within the secretory pathway, a multitude of precursor proteins are thus modified resulting in hormones, neuropeptides, growth factors, receptors and even enzymes. These modifications include cleavage at specific sites through endo- or exo-peptidase action, amidation, glycosylation and sulfation. In recent years, an important family of these processing enzymes was discovered and characterized. The so-called proprotein convertases are the products of seven distinct genes and function as endopeptidases that cleave protein precursors C-terminal to basic residue sites. They are structurally related to the bacterial subtilisin family of enzymes and are thus referred to as the subtilisin-like proprotein convertases (SPCs). Many studies have examined the inhibition of this family of enzymes, through the search of endogenous inhibitors or through the development of peptidyl, non-peptidyl or protein inhibitors. Some potent inhibitors have been discovered or engineered. While it is certain that potent inhibitors could serve as important tools to further elucidate the specific functions of each SPC, it has also been suggested that such inhibitors may be developed into lead compounds that could have important therapeutic applications. This review examines the progress made in regards to endogenous and engineered inhibitors and evidence for possible uses as molecular tools or in therapeutic applications. It is noted that although important inhibitory potencies have often been reported, there is generally insufficient evidence to demonstrate high levels of specificity. It is thus suggested that an important short-term challenge before the field will be a better understanding of the catalytic specificity of each SPC.