Paradoxical Increase in Body Mass Induced by Beta-Guanidinopropionic Acid in Juvenile Spontaneously Hypertensive Rats

Background

The adenosine triphosphate (ATP) regenerating enzyme creatine kinase (CK) is intimately involved in blood pressure generation. Consequently, the creatine transporter and CK inhibitor beta-guanidinopropionic acid (GPA) successfully reduced blood pressure in 16-week-old spontaneously hypertensive rats (SHR), but GPA may cause growth retardation in juvenile mammals. This report considers a serendipity observation of paradoxical growth increase after using GPA to prevent hypertension in three-week-old SHR.

Methods

Implementing the “Animal Research: Reporting of In Vivo Experiments” (ARRIVE) guideline, male, three-week-old spontaneously hypertensive rats (N=22) were randomly assigned to standard soy-based (creatine-free) chow with GPA 0.1% vs control chow during four weeks (primary, t=4w) or six weeks of treatment (t=6w). Blood pressure measured by the tail-cuff method was the main outcome. Other outcomes included body mass and contractility characteristics of isolated arteries.

Results 

Body mass at baseline was 28.4 (SE 0.71) g (n=22). With similar food intake/100 gram animal in both groups, GPA-treated rats (n=11) developed a strikingly larger body size and mass: t=4w, GPA 110.4 g (3.7) vs controls (n=11) 65.0 g (4.8) (+69.8%; p<0.001); t=6w, GPA 154.3 (4.7) vs controls 68.0 (4.7) g. There were no significant differences in cardiovascular parameters including blood pressure.

Discussion

An unexpected increase in body mass and size without concurrent blood pressure increase was observed in juvenile SHR on GPA vs control soy-based chow. It is speculated that the partial creatine agonist activity of GPA contributed to these effects. Further studies are needed to confirm these findings and better understand the impact of modulating energy metabolism in juvenile hypertension-prone mammals.

Signaling Pathways Governing the Caspofungin Paradoxical Effect in Aspergillus fumigatus

Aspergillus fumigatus is responsible for a wide range of diseases affecting several million people worldwide. Currently, a few families of antifungals are available to fight aspergillosis, and we are facing a worrisome increase in resistance to azoles, the drugs used for both first-line treatment and prophylaxis of invasive aspergillosis. In this context, some of the latest antifungals, i.e., echinocandins, have gained attention. Even though acquired resistance to echinocandins is yet uncommon in A. fumigatus clinical isolates, some strains exhibit another characteristic that relies on their capacity to grow at suprainhibitory echinocandin concentrations in vitro.

Aspergillus fumigatus is responsible for a wide range of diseases affecting several million people worldwide. Currently, a few families of antifungals are available to fight aspergillosis, and we are facing a worrisome increase in resistance to azoles, the drugs used for both first-line treatment and prophylaxis of invasive aspergillosis. In this context, some of the latest antifungals, i.e., echinocandins, have gained attention. Even though acquired resistance to echinocandins is yet uncommon in A. fumigatus clinical isolates, some strains exhibit another characteristic that relies on their capacity to grow at suprainhibitory echinocandin concentrations in vitro. This intriguing phenomenon, especially observed with caspofungin and now referred to as the caspofungin paradoxical effect (CPE), relies on molecular mechanisms that were hitherto little understood. Here, we discuss the recent key findings of Valero and colleagues published in mBio (C. Valero, A. C. Colabardini, J. Chiaratto, L. Pardeshi, et al., mBio 11:e00816-20, 2020, https://doi.org/10.1128/mBio.00816-20) that will allow a better understanding of the complex regulatory pathway involved in governing the response of A. fumigatus to caspofungin.

Relative Frequency of Paradoxical Growth and Trailing Effect with Caspofungin, Micafungin, Anidulafungin, and the Novel Echinocandin Rezafungin against Candida Species

Rezafungin is a next-generation echinocandin that has favorable pharmacokinetic properties. We compared the occurrence of paradoxical growth (PG) and trailing effect (TE) characteristics to echinocadins with rezafungin, caspofungin, micafungin and anidulafungin using 365 clinical Candida isolates belonging to 13 species. MICs were determined by BMD method according to CLSI (M27 Ed4). Disconnected growth (PG plus TE) was most frequent with caspofungin (49.6%), followed by anidulafungin (33.7%), micafungin (25.7%), while it was least frequent with rezafungin (16.9%). PG was relatively common in the case of caspofungin (30.1%) but was rare in the case of rezafungin (3.0%). C. tropicalis, C. albicans, C. orthopsilosis and C. inconspicua exhibited PG most frequently with caspofungin, micafungin or anidulafungin. PG never occurred in the case of C. krusei isolates. Against C. tropicalis and C. albicans, echinocandins frequently showed PG after 24 h followed by TE after 48 h. All four echinocandins exhibited TE for the majority of C. auris and C. dubliniensis isolates. Disconnected growth was common among Candida species and was echinocandin- and species-dependent. In contrast to earlier echinocandins, PG was infrequently found with rezafungin.

Recent Insights into the Paradoxical Effect of Echinocandins

Echinocandin antifungals represent one of the most important drug classes for the treatment of invasive fungal infections. The mode of action of the echinocandins relies on inhibition of the β-1,3-glucan synthase, an enzyme essentially required for the synthesis of the major fungal cell wall carbohydrate β-1,3-glucan. Depending on the species, echinocandins may exert fungicidal or fungistatic activity. Apparently independent of this differential activity, a surprising in vitro phenomenon called the “paradoxical effect” can be observed. The paradoxical effect is characterized by the ability of certain fungal isolates to reconstitute growth in the presence of higher echinocandin concentrations, while being fully susceptible at lower concentrations. The nature of the paradoxical effect is not fully understood and has been the focus of multiple studies in the last two decades. Here we concisely review the current literature and propose an updated model for the paradoxical effect, taking into account recent advances in the field.

Role of Virulence Determinants in Candida albicans' Resistance to Novel 2-bromo-2-chloro-2-(4-chlorophenylsulfonyl)-1-phenylethanone

We investigated the role of KEX2, SAP4-6, EFG1, and CPH1 in the virulence of Candida under a novel compound 2-bromo-2-chloro-2-(4-chlorophenylsulfonyl)-1-phenylethanone (Compound 4). We examined whether the exposure of C. albicans cells to Compound 4, non-cytotoxic to mammalian cells, reduces their adhesion to the human epithelium. We next assessed whether the exposure of C. albicans cells to Compound 4 modulates the anti-inflammatory response (IL-10) and induces human macrophages to respond to the Candida cells. There was a marked reduction in the growth of the sap4Δsap5Δsap6Δ mutant cells when incubated with Compound 4. Under Compound 4 (minimal fungicidal concentration MFC = 0.5–16 µg/mL): (1) wild type strain SC5314 showed a resistant phenotype with down-regulation of the KEX2 expression; (2) the following mutants of C.albicans: sap4Δ, sap5Δ, sap6Δ, and cph1Δ displayed decreased susceptibility with the paradoxical effect and up-regulation of the KEX2 expression compared to SC5314; (3) the immune recognition of C. albicans by macrophages and (4) the stimulation of IL-10 were not blocked ex vivo. The effect of deleting KEX2 in C. albicans had a minor impact on the direct activation of Compound 4’s antifungal activity. The adhesion of kex2Δ is lower than that of the wild parental strain SC5314, and tends to decrease if grown in the presence of a sub-endpoint concentration of Compound 4. Our results provide evidence that SAP4–6 play a role as regulators of the anti-Candida resistance to Compound 4. Compound 4 constitutes a suitable core to be further exploited for lead optimization to develop potent antimycotics.

Antifungal Effect of Novel 2-Bromo-2-Chloro-2-(4-Chlorophenylsulfonyl)-1-Phenylethanone against Candida Strains

We investigated the antifungal activity of novel a 2-bromo-2-chloro-2-(4-chlorophenylsulfonyl)-1-phenylethanone (compound 4). The synthesis of compound 4 was commenced from sodium 4-chlorobenzene sulfinate and the final product was obtained by treatment of α-chloro-β-keto-sulfone with sodium hypobromite. The sensitivity of 63 clinical isolates belonging to the most relevant Candida species toward compound 4 using the method M27-A3 was evaluated. We observed among most of the clinical strains of C. albicans MIC ranging from 0.00195 to 0.0078 μg/mL. Compound 4 at 32 μg/mL exhibited fungicidal activity against nine Candida strains tested using the MFC assay. Compound 4 displayed anti-Candida activity (with clear endpoint) against 22% of clinical strains of Candida. Under compound 4, Candida susceptibility and tolerance, namely paradoxical effect (PG), was found for only two clinical isolates (C. glabrata and C. parapsilosis) and reference strain 14053 using both M27-A3 and MFC method. We found that compound 4 does not induce toxicity in vivo against larvae of Galleria mellonella (≥97% survival) and it displays reduced toxicity on mammalian cells in vitro (< CC₂₀ at 64 μg/mL). Furthermore, XTT assay denoted clear metabolic activity of sessile cells in the presence of compound 4. Thus, the effect of compound 4 on formed C. albicans biofilms was minimal. Moreover, strain 90028 exhibited no defects in hyphal growth on Caco-2 monolayer under compound 4 influence at MIC = 16 μg/mL. The MIC values of compound 4 against C. albicans 90028, in medium with sorbitol did not suggest that compound 4 acts by inhibiting fungal cell wall synthesis. Our findings with compound 4 suggest a general strategy for antifungal agent development that might be useful in limiting the emergence of resistance in Candida strains.