Overexpression of histamine H4 receptors in the kidney of diabetic rat

Renal histaminergic system and acute effects of histamine receptor 2 blockade on renal damage in the Dahl salt-sensitive rat

Histamine is involved in the regulation of immune response, vasodilation, neurotransmission, and gastric acid secretion. Although elevated histamine levels and increased expression of histamine metabolizing enzymes have been reported in renal disease, there is a gap in knowledge regarding the mechanisms of histamine-related pathways in the kidney. We report here that all four histamine receptors as well as enzymes responsible for the metabolism of histamine are expressed in human and rat kidney tissues. In this study, we hypothesized that the histaminergic system plays a role in salt-induced kidney damage in the Dahl salt-sensitive (DSS) rat, a model characterized with inflammation-driven renal lesions. To induce renal damage related to salt sensitivity, DSS rats were challenged with 21 days of a high-salt diet (4% NaCl); normal-salt diet (0.4% NaCl)-fed rats were used as a control. We observed lower histamine decarboxylase and higher histamine N-methyltransferase levels in high-salt diet-fed rats, indicative of a shift in histaminergic tone; metabolomics showed higher histamine and histidine levels in the kidneys of high-salt diet-fed rats, whereas plasma levels for both compounds were lower. Acute systemic inhibition of histamine receptor 2 in the DSS rat revealed that it lowered vasopressin receptor 2 in the kidney. In summary, we established here the existence of the local histaminergic system, revealed a shift in the renal histamine balance during salt-induced kidney damage, and provided evidence that blockage of histamine receptor 2 in the DSS rat affects water balance and urine concentrating mechanisms.NEW & NOTEWORTHY Histamine is a nitrogenous compound crucial for the inflammatory response. The knowledge regarding the renal effects of histamine is very limited. We showed that renal epithelia exhibit expression of the components of the histaminergic system. Furthermore, we revealed that there was a shift in the histaminergic tone in salt-sensitive rats when they were challenged with a high-salt diet. These data support the notion that histamine plays a role in renal epithelial physiological and pathophysiological functions.

Functional role of histamine receptors in the renal cortical collecting duct cells

Histamine is an important immunomodulator, as well as a regulator of allergic inflammation, gastric acid secretion, and neurotransmission. Although substantial histamine level has been reported in the kidney, renal pathological and physiological effects of this compound have not been clearly defined. The goal of this study was to provide insight into the role of histamine-related pathways in the kidney, with emphasis on the collecting duct (CD), a distal part of the nephron important for the regulation of blood pressure. We report that all four histamine receptors (HRs) as well as enzymes responsible for histamine metabolism and synthesis are expressed in cultured mouse mpkCCD_cl4 cells, and histamine evokes a dose-dependent transient increase in intracellular Ca²⁺ in these cells. Furthermore, we observed a dose-dependent increase in cAMP in the CD cells in response to histamine. Short-circuit current studies aimed at measuring Na⁺ reabsorption via ENaC (epithelial Na⁺ channel) demonstrated inhibition of ENaC-mediated currents by histamine after a 4-hr incubation, and single-channel patch-clamp analysis revealed similar ENaC open probability before and after acute histamine application. The long-term (4 hr) effect on ENaC was corroborated in immunocytochemistry and qPCR, which showed a decrease in protein and gene expression for αENaC upon histamine treatment. In summary, our data highlight the functional importance of HRs in the CD cells and suggest potential implications of histamine in inflammation-related renal conditions. Further research is required to discern the molecular pathways downstream of HRs and assess the role of specific receptors in renal pathophysiology.

The Interplay between Histamine H4 Receptor and the Kidney Function: The Lesson from H4 Receptor Knockout Mice

Previous studies implicated the histamine H₄ receptor in renal pathophysiology. The aim here is to elucidate the role of this receptor on renal function using H₄ receptor knockout mice (H₄R^-/-). Healthy and diabetic H₄R^-/- mice compared to their C57BL/6J wild-type counterpart for renal function and the expression of crucial tubular proteins. H₄R^-/- and wild-type mice, matched for ages, showed comparable weight gain curves reaching similar median weight at the end of the study. However, H₄R^-/- mice displayed a higher basal glycemia. H₄R^-/- mice showed a lower urine 24 h outflow, and albumin-to-creatinine ratio (ACR) compared to wild-type mice. Consistently, H₄R^-/- mice presented a higher expression of megalin and a lower basal expression of the sodium-hydrogen exchanger (NHE)3 and aquaporin (AQP)2. According to these basal differences, diabetic H₄R^-/- mice developed more severe hyperglycemia and a higher 24 h urine volume, but a lower increase in ACR and decrease in urine pH were observed. These events were paralleled by a reduced NHE3 over-expression and megalin loss in diabetic H₄R^-/- mice. The AQP1 and AQP7 patterns were also different between H₄R^-/- and wild-type diabetic mice. The collected results highlight the role of the histamine H₄ receptor in the control of renal reabsorption processes, particularly albumin uptake.

The implications of histamine metabolism and signaling in renal function

Inflammation is an essential part of the immune response; it has been found to be central to the disruption of kidney function in acute kidney injury, diabetic nephropathy, hypertension, and other renal conditions. One of the well‐known mediators of the inflammatory response is histamine. Histamine receptors are expressed throughout different tissues, including the kidney, and their inhibition has proven to be a viable strategy for the treatment of many inflammation‐associated diseases. Here, we provide an overview of the current knowledge regarding the role of histamine and its metabolism in the kidney. Establishing the importance of histamine signaling for kidney function will enable new approaches for the treatment of kidney diseases associated with inflammation.

Enigmatic Histamine Receptor H4 for Potential Treatment of Multiple Inflammatory, Autoimmune, and Related Diseases

The histamine H4 receptor, belonging to the family of G-protein coupled receptors, is an increasingly attractive drug target. It plays an indispensable role in many cellular pathways, and numerous H4R ligands are being studied for the treatment of several inflammatory, allergic, and autoimmune disorders, including pulmonary fibrosis. Activation of H4R is involved in cytokine production and mediates mast cell activation and eosinophil chemotaxis. The importance of this receptor has also been shown in inflammatory models: peritonitis, respiratory tract inflammation, colitis, osteoarthritis, and rheumatoid arthritis. Recent studies suggest that H4R acts as a modulator in cancer, neuropathic pain, vestibular disorders, and type-2 diabetes, however, its role is still not fully understood.

Histamine in the kidneys: what is its role in renal pathophysiology?

Starting with a role for histamine role in renal haemodynamics, evidence has accumulated, over time, suggesting a wider range of actions on renal function and this has renewed interest in the pathophysiological role of histamine in the kidney. Here we provide an up-to-date review of this topic. As the kidney expresses enzymes that synthesize and metabolise histamine, along with its receptors, all the components for histaminergic transmission are present in this tissue. The distribution of histamine receptors matches a wide range of effects. We address the questions of the redundancy of H1 and H2 receptors in renal haemodynamics, the complementary role of H1 and H4 receptors in renal filtration and reabsorption, and the dichotomy between local and neuronal H1 and H3 receptors. Experimental models of renal disease raise the possibility of new therapeutic approaches based on histamine. The effects of histamine on renal function are not yet fully understood and their elucidation is still ongoing. LINKED ARTICLES: This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

Effect of Bilastine on Diabetic Nephropathy in DBA2/J Mice

Diabetic nephropathy is an unmet therapeutic need, and the search for new therapeutic strategies is warranted. Previous data point to histamine H₁ receptor as a possible target for glomerular dysfunction associated with long term hyperglycaemia. Therefore, this study investigated the effects of the H₁ receptor antagonist bilastine on renal morphology and function in a murine model of streptozotocin-induced diabetes. Diabetes was induced in DBA2/J male mice and, from diabetes onset (glycaemia ≥200 mg/dL), mice received bilastine (1–30 mg/kg/day) by oral gavage for 14 consecutive weeks. At the end of the experimental protocol, diabetic mice showed polyuria (+195.5%), increase in Albumin-to-Creatine Ratio (ACR, +284.7%), and a significant drop in creatinine clearance (p < 0.05). Bilastine prevented ACR increase and restored creatinine clearance in a dose-dependent manner, suggesting a positive effect on glomerular filtration. The ultrastructural analysis showed a preserved junctional integrity. Preservation of the basal nephrin, P-cadherin, and synaptopodin expression could explain this effect. In conclusion, the H₁ receptor could contribute to the glomerular damage occurring in diabetic nephropathy. Bilastine preserved the glomerular junctional integrity, leading to the hypothesis of anti-H₁ antihistamines as a possible add-on therapy for diabetic nephropathy.

AXL targeting reduces fibrosis development in experimental unilateral ureteral obstruction

The AXL receptor tyrosine kinase (RTK) is involved in partial epithelial-to-mesenchymal transition (EMT) and inflammation - both main promoters of renal fibrosis development. The study aim was to investigate the role of AXL inhibition in kidney fibrosis due to unilateral ureteral obstruction (UUO). Eight weeks old male C57BL/6 mice underwent UUO and were treated with oral AXL inhibitor bemcentinib (n = 22), Angiotensin-converting enzyme inhibitor (ACEI, n = 10), ACEI and bemcentinib (n = 10) or vehicle alone (n = 22). Mice were sacrificed after 7 or 15 days and kidney tissues were analyzed by immunohistochemistry (IHC), western blot, ELISA, Sirius Red (SR) staining, and hydroxyproline (Hyp) quantification. RNA was extracted from frozen kidney tissues and sequenced on an Illumina HiSeq4000 platform. After 15 days the ligated bemcentinib-treated kidneys showed less fibrosis compared to the ligated vehicle-treated kidneys in SR analyses and Hyp quantification. Reduced IHC staining for Vimentin (VIM) and alpha smooth muscle actin (αSMA), as well as reduced mRNA abundance of key regulators of fibrosis such as transforming growth factor (Tgfβ), matrix metalloproteinase 2 (Mmp2), Smad2, Smad4, myofibroblast activation (Aldh1a2, Crlf1), and EMT (Snai1,2, Twist), in ligated bemcentinib-treated kidneys was compatible with reduced (partial) EMT induction. Furthermore, less F4/80 positive cells, less activity of pathways related to the immune system and lower abundance of MCP1, MCP3, MCP5, and TARC in ligated bemcentinib-treated kidneys was compatible with reduction in inflammatory infiltrates by bemcentinib treatment. The AXL RTK pathway represents a promising target for pharmacologic therapy of kidney fibrosis.

Histamine and diabetic nephropathy: an up-to-date overview

The classification of diabetic nephropathy (DN) as a vascular complication of diabetes makes the possible involvement of histamine, an endogenous amine that is well known for its vasoactive properties, an interesting topic for study. The aim of the present review is to provide an extensive overview of the possible involvement of histamine in the onset and progression of DN. The evidence collected on the role of histamine in kidney function together with its well-known pleiotropic action suggest that this amine may act simultaneously on glomerular hyperfiltration, tubular inflammation, fibrosis development and tubular hypertrophy.

Differential cardiac sympatho-inhibitory responses produced by the agonists B-HT 933, quinpirole and immepip in normoglycaemic and diabetic pithed rats

This study compared the cardiac sympatho-inhibitory responses produced by agonists at α₂ -adrenergic (B-HT 933), dopamine D₂ -like (quinpirole) and histamine H₃ /H₄ (immepip) receptors between normoglycaemic and streptozotocin-pretreated (diabetic) pithed rats. Intravenous (i.v.) continuous infusions of B-HT 933, quinpirole or immepip were used in normoglycaemic and diabetic pithed rats to analyse their sympatho-inhibitory effects on the electrically-stimulated cardioaccelerator sympathetic outflow. Both in normoglycaemic and diabetic animals, B-HT 933 (until 100 μg/kg per minute) and quinpirole (until 10 μg/kg per minute) inhibited the tachycardic responses to electrical sympathetic stimulation, but not those to i.v. bolus of exogenous noradrenaline. These sympatho-inhibitory responses were more pronounced in diabetic than in normoglycaemic animals. Accordingly, the areas under the curve for 100 μg/kg per minute B-HT 933 and 10 μg/kg per minute quinpirole in diabetic rats (1065 ± 70 and 920 ± 35, respectively) were significantly smaller (P < .05) than those in normoglycaemic rats (1220 ± 45 and 1360 ± 42, respectively). In contrast, immepip infusions produced cardiac sympatho-inhibition in normoglycaemic (until 10 μg/kg per minute), but not in diabetic (until 100 μg/kg per minute) animals. Our results suggest that in diabetic pithed rats: (i) the more pronounced cardiac sympatho-inhibition to B-HT 933 and quinpirole may be probably due to up-regulation of α₂ -adrenergic and dopamine D₂ -like receptors, respectively; (ii) the histamine H₃ /H₄ receptors do not seem to play a sympatho-inhibitory role; and (iii) there is a differential participation of α₂ -adrenergic and dopamine D₂ -like receptors, which may certainly represent therapeutic targets for the treatment of diabetic complications such as cardiovascular autonomic neuropathy.

Histamine H4 receptor antagonism prevents the progression of diabetic nephropathy in male DBA2/J mice

Due to the incidence of diabetes and the related morbidity of diabetic nephropathy, identification of new therapeutic strategies represents a priority. In the last few decades new and growing evidence on the possible role of histamine in diabetes has been provided. In particular, the histamine receptor H₄R is emerging as a new promising pharmacological target for diabetic nephropathy. The aim of this study was to evaluate the efficacy of selective H₄R antagonism by JNJ39758979 on the prevention of diabetic nephropathy progression in a murine model of diabetes induced by streptozotocin injection. JNJ39758979 (25, 50, 100 mg/kg/day p.o.) was administered for 15 weeks starting from the onset of diabetes. Functional parameters were monitored throughout the experimental period. JNJ39758979 did not significantly affect glycaemic status or body weight. The urine analysis indicated a dose-dependent inhibitory effect of JNJ39758979 on Albumin-Creatinine-Ratio, the Creatinine Clearance, the 24 h urine volume, and pH urine acidification (P < 0.05). The beneficial effects of JNJ39758979 on renal function paralleled comparable effects on renal morphological integrity. These effects were sustained by a significant immune infiltration and fibrosis reduction. Notably, megalin and sodium-hydrogen-exchanger 3 expression levels were preserved. Our data suggest that the H₄R participates in diabetic nephropathy progression through both a direct effect on tubular reabsorption and an indirect action on renal tissue architecture via inflammatory cell recruitment. Therefore, H₄R antagonism emerges as a possible new multi-mechanism therapeutic approach to counteract development of diabetic nephropathy development.

International Union of Basic and Clinical Pharmacology. XCVIII. Histamine Receptors

Histamine is a developmentally highly conserved autacoid found in most vertebrate tissues. Its physiological functions are mediated by four 7-transmembrane G protein-coupled receptors (H1R, H2R, H3R, H4R) that are all targets of pharmacological intervention. The receptors display molecular heterogeneity and constitutive activity. H1R antagonists are long known antiallergic and sedating drugs, whereas the H2R was identified in the 1970s and led to the development of H2R-antagonists that revolutionized stomach ulcer treatment. The crystal structure of ligand-bound H1R has rendered it possible to design new ligands with novel properties. The H3R is an autoreceptor and heteroreceptor providing negative feedback on histaminergic and inhibition on other neurons. A block of these actions promotes waking. The H4R occurs on immuncompetent cells and the development of anti-inflammatory drugs is anticipated.

Histamine receptor expression in human renal tubules: a comparative pharmacological evaluation

OBJECTIVE AND DESIGN

The aim of this study is to evaluate the expression of the histamine receptors, particularly focusing on the H4R in human renal tubules.

MATERIAL

The ex vivo evaluation was carried on specimens from human renal cortex. Primary and immortalized tubular epithelial cells (TECs) and the HK-2 cell line were used as in vitro models.

TREATMENT

Cells were pretreated for 10 min with chlorpheniramine maleate 10 μM (H1R antagonist), ranitidine 10 µM (H2R antagonist), GSK189254 1 µM (H3R antagonist) or JNJ7777120 10 µM (H4R antagonist), and then exposed to histamine (3 pM-10 nM) for 30 min.

METHODS

The ex vivo evaluation on specimens from human renal cortex was performed by immunohistochemistry. The expression of histamine receptors on primary and immortalized TECs and the HK-2 cell line was evaluated at both gene (RT-PCR) and protein (immunocytofluorescence) levels. The pharmacological analysis was performed by TR-FRET measurements of second messenger (IP3 and cAMP) production induced by histamine with or without the selective antagonists.

RESULTS

Our data revealed the presence of all histamine receptors in human tubules; however, only TECs expressed all the receptors. Indeed, histamine elicited a sigmoid dose-response curve for IP3 production, shifted to the right by chlorpheniramine maleate, and elicited a double bell-shaped curve for cAMP production, partially suppressed by the selective H2R, H3R and H4R antagonists when each added alone, and completely ablated when combined together.

CONCLUSIONS

Herein, we report the identification of all four histamine receptors in human renal tubules.

The therapeutic potential of histamine receptor ligands in inflammatory bowel disease

In the intestine of patients suffering from inflammatory bowel disease concentrations of histamine are increased compared to healthy controls. Genetic ablation of histamine production in mice ameliorates the course of experimentally induced colitis. These observations and first pharmacological studies indicate a function of histamine in the pathogenesis of inflammatory bowel disease. However, a closer examination reveals that available data are highly heterogeneous, limiting the rational design of strategies addressing specific histamine receptor subtypes as possible target for pharmacological interaction. However, very recently first clinical data indicate that antagonism at the histamine receptor subtype H4 provides a beneficial effect in at least the skin. Here, we discuss the available data on histamine effects and histamine receptor subtype functions in inflammatory bowel disease with a special emphasis on the histamine H4-receptor.