Malaria-specific metabolite hemozoin mediates the release of several potent endogenous pyrogens (TNF, MIP-1 alpha, and MIP-1 beta) in vitro, and altered thermoregulation in vivo.

A characteristic feature of malaria infection is the occurrence of periodic bouts of fever. Experimental and clinical studies have strongly implicated inflammatory cytokines, like tumour necrosis factor (TNF), in the induction of these intermittent fevers [Clark et al., Infect Immunol 32:1058-1066, 1981; Clark et al., Am J Pathol 129:192-199, 1987; Karunaweera et al., Proc Natl Acad Sci USA 89:3200-3203, 1992], but the malaria-specific metabolite(s) which induce the production of such endogenous pyrogens have not yet been fully characterized. It is well known that during the course of malaria infection, a unique schizont component, alternatively referred to as "malaria pigment" or hemozoin, is released along with merozoites as the host erythrocyte bursts [Urquhart, Clin Infect Dis 19:117-131, 1994]. We have recently determined that the core structure of hemozoin comprises a novel insoluble polymer of heme units linked by iron-carboxylate bonds [Slater et al., Proc Natl Acad Sci USA 88:325-329, 1991; Slater et al., Nature 355:167-169, 1992]. We now report that purified native, as well as chemically synthesized, hemozoin crystals potently induce the release of several pyrogenic cytokines, including TNF, MIP-1 alpha, and MIP-1 beta, from murine macrophages and human peripheral blood monocytes in vitro. Also, intravenous administration of chemically synthesized preparations of hemozoin to anaesthetized rats results in a marked drop in body temperature. A similar drop in body temperature is observed following the intravenous injection of other well-characterized pyrogenic cytokines (e.g., TNF) which are known to induce a fever response in awake animals, and is thought to reflect the inability of rats to appropriately regulate their body temperature while anaesthetized. As a consequence of its ability to induce pyrogenic cytokines in vitro, and thermal dysregulation in vivo, we propose that this unique parasite metabolite is an important pyrogen released by malaria parasites at schizogomy, which acts by eliciting the production of a group of potent endogenous pyrogens, which include MIP-1 alpha and MIP-1 beta, as well as TNF, in macrophages.

The effects on liver metastases of circadian patterned continuous hepatic artery infusion of FUDR.

Although continuous hepatic artery infusions (CHAI) of (FUDR) Floxuridine have been effective in reducing the size of colorectal hepatic metastases the toxicity of the infusions have been high with almost a quarter of the patients developing biliary sclerosis. Techniques to lower toxicity, yet continue the beneficial antitumor effects, are being investigated. One suggested strategy is to change the flow pattern of the continuous infusion from a constant rate to a day cycled pattern. In this infusion a continuous rate is given over a 24 hour period with 60% of the infusion delivered between 3 PM and 9 PM and the least amount of infusion delivered between 3 AM and 9 PM. Previous research has suggested that this day cycle pattern will lower the toxicity of the infusion. This experiment is a test of "day cycled" continuous hepatic artery infusions in rats bearing hepatic metastases from a colon adenocarcinoma. Previous research from our laboratory has shown a lowered toxicity when the constant infusion was replaced with the day cycled pattern. In the present study 10 rats with hepatic adenocarcinoma metastases were placed on constant CHAI of FUDR at 10mg/kg/day for 14 days. There was an 80% mortality from chemotherapy toxicity and a 90% objective response rate. Nine other rats were treated with "day cycled" CHAI of FUDR at 15mg/kg/d. There was no mortality in this group and the objective response rate was 90% as in the previous group. This study demonstrated that "day cycled" CHAI of FUDR was substantially less toxic and that the antitumor effect was identical to the constant infusion.

Improving responses in hepatomas with circadian-patterned hepatic artery infusions of recombinant interleukin-2.

Previous studies on continuous hepatic artery infusions of recombinant interleukin-2 (IL-2) have shown that in a nontumor-bearing animal a continuous infusion given in a circadian "day cycled" pattern was much less toxic and could be given with 10 times higher doses of IL-2 than if the constant pattern of infusion was used. In the present study, circadian-patterned continuous hepatic artery infusions of IL-2 were used in hepatoma-bearing rats. Doses of 10 mg/m2/day could be tolerated when IL-2 was given in a "day cycle" rhythm. Control animals were given 1 mg/m2/day of constant infusion IL-2, which was the highest hepatic artery infusion dose tolerated at a constant rate without mortality in nontumor-bearing animals. Animals treated with the constant infusions of IL-2 had a 37.5% mortality rate and a 25% objective response rate in measurable tumor size. Animals receiving the "day cycle" had no mortality and a 100% objective response rate. The conclusion was that "day cycled" circadian-patterned continuous hepatic artery infusions of IL-2 could be given with much lower toxicity and much improved tumor response rates than constant continuous infusions.

The effects on toxicity of circadian patterning of continuous hepatic artery infusion.

Long term continuous hepatic artery infusion of FUDR was carried out in 34 rats. In the animals who received a constant infusion schedule of 15 mg/kg/day all died of toxicity with a mean survival of 9.3 days. If the pattern of the continuous infusion was changed so that over 60% of the infusion was given during the hours of 3pm to 9pm than all of the animals survived the 14 day infusion. If the maximum dose of infusion was changed so that 60% of the infusion was given at night from 3am to 9am the infusion became more toxic and all the animals died in a mean of 5.5 days. Pathologic sectioning of all the livers reflected the above outcomes with the greatest amount of hepatic necrosis in the animals on the night cycles. This study underscores the recent advances in chronobiology demonstrating that for continuous hepatic arterial infusions the timing of delivery is crucial in determining the toxicity.