The researchers, led by Professor Ravi Acharya from the University of Bath and Professor Ed Sturrock from the Institute of Infectious Disease and Molecular Medicine at the University of Cape Town, have demonstrated that ciprofloxacin interacts with ACE in an unconventional manner. Unlike existing drugs that target the zinc-containing catalytic pocket within ACE, ciprofloxacin binds to an allosteric site located on the C-domain of the enzyme. This allosteric site is spatially distinct from the active site, and the binding of ciprofloxacin here effectively blocks the conversion of angiotensin I to angiotensin II without compromising the enzyme’s other physiological functions.

ACE plays a pivotal role in the renin-angiotensin system by elevating blood pressure through the conversion of angiotensin I, an inactive precursor, into angiotensin II, a potent vasoconstrictor responsible for narrowing blood vessels. While ACE inhibitors have been the cornerstone of antihypertensive therapy for decades, their mechanism of action involves binding to the active site of ACE, which also contributes to off-target effects. These effects manifest clinically as troublesome side effects, including a persistent dry cough and angioedema, limiting patient compliance and therapeutic efficacy.

The dual-domain architecture of ACE, encapsulating both the N-terminal and C-terminal domains with distinct active sites, has long posed challenges for the design of selective inhibitors. Current medications indiscriminately inhibit both domains, inadvertently influencing non-blood-pressure-related physiological processes such as renal function, reproductive health, and immune responses. The promiscuity of ACE inhibitors has thus been a significant hurdle in pharmaceutical development, motivating the search for selective modulators that can fine-tune enzyme activity more precisely.

In this study, published in ACS Bio & Med Chem Au, the team employed advanced X-ray crystallography techniques to resolve the three-dimensional structure of ACE in complex with ciprofloxacin. Their structural data reveal that ciprofloxacin docks into a previously uncharacterized allosteric exosite located on the C-domain. This binding event induces a conformational change that occludes the substrate angiotensin I from accessing the active site, effectively suppressing ACE activity related to blood pressure without interfering with the enzyme’s multifaceted physiological roles.

The allosteric inhibition mechanism identified here represents a paradigm shift in ACE drug design. By targeting an exosite remote from the catalytic zinc ion, allosteric inhibitors like ciprofloxacin analogues could offer significant therapeutic advantages. These include increased selectivity, reduced adverse effects, and the preservation of ACE functions outside blood pressure regulation. This discovery opens avenues for the development of tailor-made ACE inhibitors that maintain cardiovascular efficacy while minimizing systemic toxicity and patient discomfort associated with current treatments.

Although ciprofloxacin itself binds relatively weakly to the ACE allosteric site and is unlikely to function as a standalone antihypertensive medication, its chemical scaffold provides a valuable template for medicinal chemistry efforts. The research team envisions that optimizing ciprofloxacin derivatives could enhance binding affinity and specificity, culminating in a new class of ACE inhibitors engineered to exploit the allosteric mechanism. Such drugs would not only improve patient outcomes but also expand the pharmacological toolkit available to clinicians managing hypertension and related cardiovascular conditions.

The collaborative nature of this research, supported by UKRI-BBSRC and involving a confluence of expertise in enzymology, structural biology, and pharmacology, underscores the importance of interdisciplinary approaches in addressing complex biomedical challenges. Dr. Vinasha Ramasamy and Professor Ed Sturrock contributed essential enzymatic kinetics analyses, while Dr. Kyle Gregory and Professor Ravi Acharya’s team meticulously determined the ACE-ciprofloxacin complex structure. Their combined efforts have illuminated a novel path for antihypertensive drug discovery that merges structural insight with functional biochemistry.

Looking forward, the team is poised to screen and synthesize various chemical analogues of ciprofloxacin to refine their interaction with ACE’s allosteric site. By leveraging structure-guided drug design and high-throughput screening, future compounds can be tailored to maximize therapeutic efficacy while minimizing side effects. This approach holds promise for addressing the global burden of hypertension, which affects approximately one in three adults in the UK, and for whom ACE inhibitors remain a critical component of treatment despite their limitations.

Beyond potential pharmaceutical applications, the findings have broader implications for understanding enzyme regulation via allosteric modulation. The ability to selectively inhibit a multi-functional enzyme like ACE through distal binding sites exemplifies an elegant biological control mechanism and inspires analogous strategies in drug discovery targeting other clinically relevant enzymes. This work exemplifies how repurposing known drugs can reveal latent activities, thereby accelerating the path from bench to bedside.

In conclusion, this seminal study reframes our understanding of ACE inhibition by unveiling ciprofloxacin’s unexpected capacity to engage an allosteric exosite on the ACE C-domain, impeding angiotensin I conversion without wholesale enzymatic blockade. Such insights herald a transformative approach in the design of future antihypertensive agents that combine precision, safety, and efficacy. As the global incidence of hypertension escalates, innovations like this are indispensable in refining therapeutic regimens and improving patient quality of life.

Subject of Research: Not applicable

Article Title: Ciprofloxacin Inhibits Angiotensin I-Converting Enzyme (ACE) Activity by Binding at the Exosite, Distal to the Catalytic Pocket

News Publication Date: 9-Jun-2025

Web References:
https://pubs.acs.org/doi/10.1021/acsbiomedchemau.5c00089

References:
Acharya, R. et al. (2025) ‘Ciprofloxacin Inhibits Angiotensin I-Converting Enzyme (ACE) Activity by Binding at the Exosite, Distal to the Catalytic Pocket’, ACS Bio & Med Chem Au, DOI: 10.1021/acsbiomedchemau.5c00089.

Image Credits: Professor Ravi Acharya, University of Bath

Keywords:
Drug discovery, Drug design, Drug targets, Drug candidates, Enzymatic activity, Enzyme inhibitors, Structural biology, Biomolecular structure, Tertiary structure, Activation loops, Binding pockets, Antihypertensive activity, Vasopressors

For years, the renin-angiotensin system has been primarily studied within the contexts of renal and cardiovascular physiology, where its role in regulating blood pressure and fluid balance is well established. However, the skin has increasingly been recognized not merely as a passive barrier but as an active endocrine organ capable of synthesizing and responding to various bioactive molecules. The current study by Taguchi et al. pushes the boundaries of this understanding by showing that skin-specific molecular disturbances can profoundly influence systemic hypertensive processes, potentially unveiling new therapeutic avenues.

At the molecular core of this phenomenon is ATRAP, a known modulator of angiotensin II receptor type 1 (AT1R) signaling. The AT1R mediates many of the hypertensive and pathological effects of angiotensin II, a peptide hormone critical to cardiovascular regulation. ATRAP serves as a negative regulator, attenuating the receptor’s signaling activity, and thus its deficiency results in the heightened activation of angiotensin II pathways. In keratinocytes, the absence of ATRAP appeared to unleash unchecked AT1R signaling, exacerbating hypertension in response to angiotensin II.

Intricately, the investigators employed sophisticated genetic manipulation to create mouse models in which ATRAP was selectively knocked out in keratinocytes, leaving other tissues unaffected. This cell-specific targeting allowed for precise dissection of physiological consequences attributable solely to skin ATRAP deficiency. What emerged was a striking increase in systemic blood pressure when these mice were infused with angiotensin II, underscoring the pathological contribution of skin-derived RAS activation.

Digging deeper into the mechanistic pathways, the research revealed that keratinocyte ATRAP deficiency amplified not only local angiotensin II signaling but also the expression of renin and angiotensinogen—key components involved in the generation of angiotensin II—within the skin milieu. This suggests the existence of an autonomous or semi-autonomous skin RAS loop capable of exacerbating systemic hypertensive states when dysregulated.

The translational implications of this study are profound. Current anti-hypertensive therapies primarily target systemic RAS components such as angiotensin-converting enzyme inhibitors or AT1R blockers. However, these drugs might inadequately address local tissue-specific regulatory circuits like the one emerging from the skin. Conceivably, this discovery could pave the way for the development of novel topical or targeted interventions aimed at restoring ATRAP function or dampening skin RAS hyperactivity, thus complementing conventional systemic therapies.

Furthermore, the study challenges the long-held dogma that the skin’s involvement in systemic blood pressure is negligible. By revealing that keratinocytes can modulate cardiovascular function through molecular signaling networks, it expands the understanding of skin biology far beyond its classical roles in protection and thermoregulation. This underscores the skin’s complex endocrine and paracrine capacities and invites attention to other potentially unexplored pathways within this organ that may impact systemic health.

From a methodological standpoint, the investigators utilized state-of-the-art in vivo blood pressure monitoring, molecular biology assays, and histological examinations to characterize the hypertensive phenotype and molecular changes induced by keratinocyte ATRAP deletion. Their integrative approach allowed for both macroscopic physiological insights and detailed cellular mechanistic delineation, rendering the findings robust and highly convincing.

Moreover, the skin RAS activation was linked to increased oxidative stress and inflammatory signaling pathways, which are well-known contributors to vascular dysfunction and hypertension. The interplay between angiotensin II signaling, reactive oxygen species generation, and inflammatory cytokine production within keratinocytes likely forms a vicious cycle potentiating hypertensive pathology.

Intriguingly, this new evidence opens fresh questions about the role of environmental factors that affect the skin, such as ultraviolet radiation, allergens, or microbial imbalances, in modulating local RAS activity and subsequent systemic effects. Could chronic skin insults synergize with genetic factors like ATRAP deficiency to elevate hypertension risk? Further research will be essential to unravel these complex interactions.

Another noteworthy aspect is the potential clinical relevance of the skin RAS in human hypertensive patients. The study prompts a reevaluation of skin biopsies and biomarker profiling in hypertensive individuals, which might reveal hitherto unrecognized predictive or diagnostic indicators. Future clinical investigations could explore whether topical modulation of skin RAS has tangible benefits for blood pressure control in human populations.

Perhaps equally fascinating is the insight this research provides into the cross-talk between different organ systems. It reinforces the systemic integration of cardiovascular regulation, showing that components once thought peripheral can exert meaningful control over core physiological parameters. This knowledge could stimulate holistic therapeutic strategies aimed at multiple tissues rather than the isolated targeting of systemic blood pressure mechanisms.

In summary, this seminal work by Taguchi and colleagues illuminates a previously underappreciated axis in hypertension pathogenesis involving keratinocyte-specific ATRAP deficiency and resultant hyperactivation of the skin renin-angiotensin system. The conceptual leap from skin barrier function to a dynamic regulator of systemic vascular tone marks a turning point in cardiovascular and dermatological research alike, inviting new investigations and innovative treatment paradigms.

As hypertension continues to pose formidable challenges globally, insights such as these remind us that the answers may lie in unexpected places—even at the very surface of our bodies. Bridging dermatology and cardiovascular science could unlock novel strategies to combat one of the most pervasive health conditions worldwide, potentially transforming millions of lives through targeted, tissue-specific therapies.

Further studies expanding on this discovery will likely explore the molecular intricacies of ATRAP regulation, its interaction partners within keratinocytes, and the downstream effects on vascular smooth muscle and endothelial function. The elucidation of such pathways holds promise for new drug targets capable of fine-tuning hypertensive responses with greater precision and fewer side effects.

Ultimately, this research underscores the remarkable plasticity and complexity of physiological systems and highlights the skin’s emerging status as a crucial player in systemic homeostasis. It challenges researchers and clinicians alike to reconsider the traditional compartmentalization of organ systems and to embrace a more integrative approach to understanding and managing human disease.

Subject of Research: Keratinocyte-specific angiotensin II receptor-associated protein deficiency exacerbates angiotensin II-dependent hypertension via activation of the skin renin-angiotensin system.

Article Title: Keratinocyte-specific angiotensin II receptor-associated protein deficiency exacerbates angiotensin II-dependent hypertension via activation of the skin renin-angiotensin system.

Article References:
Taguchi, S., Azushima, K., Kitada, K. et al. Keratinocyte-specific angiotensin II receptor-associated protein deficiency exacerbates angiotensin II-dependent hypertension via activation of the skin renin-angiotensin system. Nat Commun 16, 4789 (2025). https://doi.org/10.1038/s41467-025-60041-8

Image Credits: AI Generated