Physiologic, pharmacologic, and clinicalspects of proteinase inhibitors

Aprotinin and similar protease inhibitors as drugs against influenza

Efforts to develop new antiviral chemotherapeutic approaches are focusing on compounds that target either influenza virus replication itself or host factor(s) that are critical to influenza replication. Host protease mediated influenza hemagglutinin (HA) cleavage is critical for activation of virus infectivity and as such is a chemotherapeutic target. Influenza pathogenesis involves a "vicious cycle" in which host proteases activate progeny virus which in turn amplifies replication and stimulates further protease activities which may be detrimental to the infected host. Aprotinin, a 58 amino acid polypeptide purified from bovine lung that is one of a family of host-targeted antivirals that inhibit serine proteases responsible for influenza virus activation. This drug and similar agents, such as leupeptin and camostat, suppress virus HA cleavage and limit reproduction of human and avian influenza viruses with a single arginine in the HA cleavage site. Site-directed structural modifications of aprotinin are possible to increase its intracellular targeting of cleavage of highly virulent H5 and H7 hemagglutinins possessing multi-arginine/lysine cleavage site. An additional mechanism of action for serine protease inhibitors is to target a number of host mediators of inflammation and down regulate their levels in virus-infected hosts. Aprotinin is a generic drug approved for intravenous use in humans to treat pancreatitis and limit post-operative bleeding. As an antiinfluenzal compound, aprotinin might be delivered by two routes: (i) a small-particle aerosol has been approved in Russia for local respiratory application in mild-to-moderate influenza and (ii) a proposed intravenous administration for severe influenza to provide both an antiviral effect and a decrease in systemic pathology and inflammation.

Human leucocyte response to migration inhibitory activity from lymphocytes. Modification by aprotinin, Tranexamic acid and phenylmethyl sulfonylfluoride

Human lymphokines can elicit several effects associated with inflammation, e.g. leucocyte migration inhibition and fibrinolysis. These effects can be assessed in vitro by the leucocyte migration agarose technique (LMAT) and the leucocyte migration fibrinolysis technique (LMFT). The present study shows that preincubation of normal leucocytes with aprotinin, tranexamic acid and phenyl-methyl-sulfonylfluoride (PMSF) reduces or abolishes their migration inhibition response to leucocyte migration inhibition factor. The compounds exert this effect at non-toxic concentrations, which do not otherwise interfere with migration or fibrinolysis, and are non-toxic as estimated by PHA stimulation of lymphocytes. The LMFT is more sensitive to the modifying effect than the LMAT. The effect of aprotinin and tranexamic acid is reversible, the effect of PMSF is irreversible.

In vitro studies regarding the feasibility of bovine erythrocyte xenotransfusion

Pigs are considered the most likely source of organs and tissues should the barriers to xenotransplantation be overcome. The use of animal blood for transfusion, xenotransfusion, would have advantages over blood from random human donors with respect to supply and infection control. Large animals such as cows would be more suitable than pigs for blood donation because of easier venous access and large volume phlebotomy. Blood from 12 Holstein cows was typed and then tested for hemagglutination assay (HA), complement mediated lysis (CML), human IgM and IgG antibody binding, anti-human globulin augmented clinical cross-match and osmotic fragility with normal human serum. Results were compared with porcine erythrocytes (pRBC) and with human type O controls (hRBC). The frequency of ultra-low xenoantigen expressors was tested in a larger herd of various breeds using HA and CML. Median HA and CML titers were one of six (no HA-one of 64) and one of 26 (no CML-one of 64), respectively for bovine erythrocytes (bRBC). Hemagglutination titer was significantly higher for pRBC at one of 170 (one of four-one of 1024). HA and CML were lowest with bovine blood group J. Repeated HA and CML were negative with bRBC from one cow that also tested negative by anti-human globulin augmented cross-match with seven of nine random human sera representing the different blood groups. However, flow cytometry showed that bRBC from all cows bound human IgM and IgG. IgM mean channel fluorescence (MCF) was positively correlated with HA titer. The mean corpuscular fragility of pRBC, bRBC, and hRBC was 0.56, 0.48 and 0.41%, respectively. The frequency of HA-negative and CML-negative cows were 20 and 35%, respectively in herds of 49 animals. Bovine RBC elicit variable in vitro responses from human serum but these are uniformly much less than those seen with pRBC. Bovine RBC is more robust than pRBC. These characteristics including the potential ease and volume of blood collection make the cow a more suitable blood donor than the pig.

Effects of aprotinin on the kallikrein-kinin system in type I diabetes (insulitis)

Sub-diabetogenic doses of streptozotocin (STZ) produce insulitis, beta cell destruction and diabetes in mice. Since kinin have been proposed as an inflammatory mediator in several diseases, we decided to evaluate the role of the kallikrein-kinin system in the evolution of insulitis. Male C 57 BL/KsJ mdb mice were injected with STZ (40 mg/kg) for 5 consecutive d. Aprotinin (4000 KIU/d) was injected simultaneously with STZ during 10 d. Plasma and urine samples collected on day 15 were assayed for glucose concentration and proteins, nitrites and kallikrein. Diabetic mice showed hyperglycemia and increased diuresis, marked proteinuria, nitrites and kallikrein. Administration of aprotinin, a potent tissue kallikrein inhibitor, to STZ mice, reduced the hyperglycemia and the altered renal function of the diabetic mice to level no different from normal mice. The present studies are consistent with the hypothesis that the over-production of tissue kallikrein in insulitis could be controlled by the effect of aprotinin.

Further evidence of bradykinin involvement in septic shock: reduction of kinin production in vivo and improved survival in rats by use of polymer tailored SBTI with longer t1/2

Involvement of bradykinin in septic shock and its therapeutic endeavor using soybean trypsin inhibitor (SBTI, Kunitz type) were investigated in an in vivo model of septic shock induced by pseudomonal elastase. Pseudomonal elastase injection at 0.5 mg/kg i.v. to guinea pigs resulted in elevation level of bradykinin in the blood from < 1 ng/ml to 25 ng/ml which was accompanied by a drop of mean arterial blood pressure (MABP) (about 45 mmHg). When native soybean trypsin inhibitor (SBTI, Kunitz type, 20 kDa) was injected, into this model, induction of bradykinin generation and hypotension by the bacterial protease treatment was completely obliterated as judged by the both levels of bradykinin and MABP. Specifically, by the treatment with SBTI, bradykinin levels did not increase and the drop of the blood pressure was minimal (< 10 mmHg) in this time frame (< 30 min). We designed and prepared succinylated gelatin-conjugated SBTI (suc-gel SBTI) with enlarged molecular mass (M(r) approximately 110,000) and higher area under the curve of the plasma concentration, which exhibits about 6 times longer plasma half-life (t1/2) and about 4 times larger area under the curve of plasma concentration. Suc-gel-SBTI suppressed the pseudomonal protease-induced shock much more effectively than native SBTI, the conjugate exhibited its effect for more than 3 h, while the native SBTI showed the effect only within 2 h after i.v. injection.

Characteristics of DNA replication in isolated nuclei initiated by an aprotinin-binding protein

Isolated cell nuclei were used as the source of template DNA to investigate the role of a cytosolic aprotinin-binding protein (ADR) in the initiation of eukaryotic DNA replication. Computerized image cytometry demonstrated that the DNA content of individual nuclei increased significantly following incubation with ADR-containing preparations, and the extent of DNA synthesis is consistent with that allowed by the limiting concentration of dTTP. Thus, dTTP incorporation into isolated nuclei represents DNA synthesis and not parent strand repair. We found that dTTP incorporation into the isolated nuclei is dependent on DNA polymerase alpha (a principal polymerase in DNA replication) but that DNA polymerase beta (a principal polymerase in DNA repair processes) does not play a significant role in this system. Finally, neither aprotinin nor a previously described cytosolic ADR inhibitor can block the replication of nuclease-treated calf thymus DNA, while both strongly inhibit replication of DNA in isolated nuclei. This result, coupled with the relative ineffectiveness of nuclease-treated DNA compared with nuclear DNA to serve as a replicative template in this assay, argues against a significant contribution from repair or synthesis which initiates at a site of DNA damage. These data indicate that ADR-mediated incorporation of 3H-dTTP into isolated nuclei results from DNA replicative processes that are directly relevant to in vivo S phase events.

The urinary excretion of epidermal growth factor in the rat is reduced by aprotinin, a proteinase inhibitor

The present study on the rat shows that i.v. administration of the proteinase inhibitor aprotinin reduces the urinary output of immunoreactive epidermal growth factor (EGF) while the amount of immunoreactive EGF in the kidneys is increased. This indicates that the EGF-precursor in the rat kidney in vivo is processed by an aprotinin inhibitable proteinase. EGF is produced in the kidneys as a precursor with a molecular weight of approximately 130 kDa. In rat urine, nanomolar amounts of 6 kDa EGF are excreted per 24 h together with small amounts of high molecular weight forms of EGF. During i.v. administration of aprotinin the median urinary output of immunoreactive EGF is reduced to 15% of the excretion of control rats (23 pmol/2 h versus 157 pmol/2 h, P less than 0.001). Especially the excretion of 6 kDa EGF is reduced (median excretion 12 pmol/2 h versus 134 pmol/2 h, P less than 0.001). The amount of immunoreactive EGF in the kidney tissue is increased after aprotinin administration (median amount 0.11 pmol EGF/mg protein versus less than 0.04 pmol EGF/mg protein, P less than 0.001). Neither the creatinine clearance, the total urinary protein output, nor the volume of urine produced was affected by aprotinin.

Effect of aprotinin in adult respiratory distress syndrome

The possible beneficial effect of aprotinin, a broad protease inhibitor, on the incidence and outcome of ARDS was examined in two complementary studies. In the first study, the effect of aprotinin was assessed in 147 patients admitted with multiple trauma or shock. In the 57 patients who developed ARDS, mortality was significantly less in those who had previously received aprotinin (8/20, 40%) than in those who had not (26/37, 70%). Although both treatment groups were well matched, this was a retrospective study and a second prospective, randomised, controlled study was therefore carried out. In 78 patients at risk of ARDS, there was no significant difference between treated and control patients in the incidence, duration or severity of ARDS, or in mortality or other major complications. It is concluded that aprotinin is not effective in improving any aspect of ARDS or its outcome in seriously ill patients.

Synergic effects of kallikrein-kinin and prostaglandins on renin release on infusion of isolated hog kidney with aldosterone

The effects of infusion of a large amount of aldosterone into the renal artery of isolated perfused hog kidney on the release of renin, prostaglandins (PG) and kinin and the excretion of urinary kallikrein were investigated. Infusion of aldosterone at a rate of 100 ng/min (100 to 800 ng/ml of perfusate) resulted in significant releases of renin, PG (PGE2 , 6-0-PGF1 alpha), and kinin and increase in urinary kallikrein. Infusion of aldosterone and an inhibitor of kallikrein, aprotinin, decreased the releases of renin, PG and kinin and infusion of aldosterone with indomethacin decreased the release of PG but increased that of kinin and urinary kallikrein without significant change in renin releases. These findings suggest that the release of renin by aldosterone may result from synergic effects of renal PG and the kallikrein -kinin system.

Endotoxaemia in the horse

Endotoxins are non-protein fragments of the cell wall of Gram-negative bacteria. They must be absorbed into the circulation to produce disease and systemic effects are similar, regardless of bacterial source. Absorption of endotoxins occurs in obstructive bowel disease and may play a significant part in determining the severity of the disease. Many of the responses to experimentally administered endotoxin are identical to those of bowel diseases or the horse and include circulatory, haematological and metabolic alterations. Therapeutic approaches are indirect and include many drugs currently employed in equine practice. The agents are directed toward mediators of the disease rather than the endotoxins themselves and include fluids, corticosteroids, anti-inflammatory drugs, energy sources and vasoactive drugs. The rationale for use and dosages are discussed.

Progressive inhibition of human glandular (urinary) kallikrein by human serum and identification of the progressive antikallikrein as alpha 1-antitrypsin (alpha 1-protease inhibitor)

Human urinary kallikrein was inhibited by human alpha 1-antitrypsin (alpha 1-protease inhibitor) in a similar way as by equivalent amounts of human serum. The inhibitor present in the kallikrein-inhibitor complex formed was identified as alpha 1-antitrypsin by two-dimensional immunoelectrophoresis. Under the experimental conditions applied, 90 mIU (= 185 microgram) alpha 1-antitrypsin inhibits about 9 microgram of human urinary kallikrein in 24 h at 37 degrees C, 1 ml of human serum, containing 2-4 mg alpha 1-antitrypsin, inhibits about 70 microgram kallikrein. At an incubation temperature of 25 degrees C, the rate of inactivation is significantly lower than at 37 degrees C. No inhibition was observed at 0 degrees C or when alpha 1-antitrypsin was presaturated with trypsin.

Obstructive nephropathy in the rat: possible roles for the renin-angiotensin system, prostaglandins, and thromboxanes in postobstructive renal function

Relief of unilateral ureteral obstruction (UUO) of 24 h duration in rats is followed by severe renal vasoconstriction in the postobstructive kidney (POK). The present study examined possible roles of renal prostaglandins (PG) and thromboxanes (TX), as well as the renin-angiotensin system, in this vasoconstriction. Administration of the cyclooxygenase inhibitor indomethacin, which blocks both PG and TX production, failed to improve POK hemodynamics in UUO rats. To explore the possible role of the TX compounds, which include the potent vasoconstrictor thromboxane A2 (TXA2), UUO rats were infused with imidazole, an agent that blocks synthesis of TX, but not of PG. Imidiazole led to two- to threefold increases in the clearance of both inulin and rho-aminohippuric acid by the POK. This effect of imidazole was abolished by indomethacin, suggesting that the amelioration of POK vasoconstriction by imidazole was a result of inhibition of vasoconstrictor TX synthesis (e.g. TXA2), with PG vasodilators (e.g. PGE2 or PG12) still active. Urea, infused in a solution whose osmolality and volume were identical to the imidazole infusion, failed to improve hemodynamics in the POK, making it unlikely that nonspecific effects of volume expansion or osmotic diuresis mediated the beneficial effect of imidazole. Further studies examined the possible role of the renin-angiotensin systems in the vasoconstriction of the POK. UUO rats infused with the angiotensin II antagonist, Saralasin, exhibited no significant improvement in POK function, a finding that might be at least partly attributable to agonist/vasoconstrictor properties of Saralasin. In other experiments, treatment of UUO rats with the angiotensin-converting enzyme blocker SQ 14225 (Captopril), in order to inhibit angiotensin II formation, led to at least twofold increases in the clearance of both inulin and rho-aminohippuric acid in the POK. It is unlikely that Captopril exerted this beneficial effect by potentiating the vasodilator kinins, because the effect was not diminished by administration of either carboxypeptidase B (which destroys the kinins) or Trasylol (which blocks kinin synthesis). Thus, these results suggest that both angiotensin II, as well as metabolites of the PG-TX system, may be important determinants of postobstructive renal hemodynamics in the rat.

The effects of intravenously administered chlorophyll-A on naturally occurring serum protease inhibitors in rabbits

Effects of intravenously administered protease inhibitors on naturally occurring serum inhibitors were investigated in rabbits. Water-dispersed chlorophyll-a, trasylol and leupeptin were tested as exogenous protease inhibitors in the experiments. From the results of experiments, it was concluded that: 1) Pretreatment with chlorophyll-a infusion into rabbits, most effectively prevented the rapid consumption of naturally occurring serum protease inhibitors after successive trypsin infusion, and the duration of its action was observed longest when compared with other exogenous inhibitors, such as trasylol or leupeptin. 2) Final therapeutic effects of these exogenous protease inhibitors seem to have depended upon the disappearing way of the administered inhibitors from the blood in certain period of time, as well as upon biochemical potency of their inhibiting activity.

Interrelations of the renal kallikrein-kinin system and renal prostaglandins in the conscious rat. Influence of mineralocorticoids

To investigate possible relationships between mineralocorticoids, the renal kallikreinkinin system, and renal prostaglandins, we studied the effects of aldosterone and deoxycorticosterone acetate (DOCA) and of an inhibitor of kallikrein, aprotinin, on the urinary excretion of kallikrein and prostaglandin E-like substance (PGE) by the conscious rat. Aldosterone (0.25 mg/day, sc), injected into six rats for 14 consecutive days, increased PGE and kallikrein excretion from 52.3 +/- 8.7 (mean +/- SE) ng/day and 29.8 +/- 3.0 U/day to 141.5 +/- 30.7 ng/day (P less than 0.02) and 105.6 +/- 28.1 U/day (P less than 0.05), respectively. Similarly, injections of DOCA (5 mg/day) into 14 rats increased the excretion of PGE and kallikrein, measured before and after 10 days of treatment, from 41.6 +/- 3.9 ng/day and 39.4 +/-4.9 U/day to 194.3 +/- 20.7 ng/day (P less than 0.001) and 90.6 +/- 14.7 U/day (P less than 0.001), respectively. Injections of aprotinin for 4 days (50,000 KIU twice daily, sc) in conjunction with DOCA into eight rats pretreated with the steroid for 10 days decreased the urinary excretion of kallikrein and PGE, measured on the 4th day of aprotinin administration, by 61% (P less than 0.01) and 80% (P less than 0.001), respectively. Urinary potassium excretion decreased throughout the course of aprotinin treatment, whereas sodium excretion and urine volume decreased during the first 2 days but subsequently returned toward control values. This study demonstrates that mineralocorticoids enhance the urinary excretion of PGE, and this effect appears to be a consequence of activation of the renal kallikrein-kinin system by the steroids. Thus, changes in the intrarenal activity of the kallikrein-kinin system may modulate renal prostaglandin release.