A Novel Rhein Derivative Modulates Bone Formation and Resorption and Ameliorates Estrogen-Dependent Bone Loss

Osteoporosis, an osteolytic disease that affects millions of people worldwide, features a bone remodeling imbalance between bone resorption by osteoclasts and bone formation by osteoblasts. Identifying dual target-directed agents that inhibit excessive bone resorption and increase bone formation is considered an efficient strategy for developing new osteoporosis treatments. Rhein, a natural anthraquinone, can be isolated from various Asian herbal medicines. Rhein and its derivatives have been reported to have various beneficial pharmacological effects, especially their bone-targeting ability and anti-osteoclastogenesis activity. Moreover, hydrogen sulfide (H₂ S) was reported to prevent ovariectomy- (OVX-) induced bone loss by enhancing bone formation, and sulfur replacement therapy has been considered a novel and plausible therapeutic option. Based on this information, we synthesized a rhein-derived thioamide (RT) and investigated its effects on bone resorption and bone formation in vitro and in vivo. It has been found that the RT-inhibited receptor activator of the nuclear factor-κB (NF-κB) ligand- (RANKL-) induced osteoclastogenesis and bone resorption in a dose-dependent manner. The expression of osteoclast marker genes was also suppressed by RT treatment. Furthermore, exploration of signal transduction pathways indicated that RT markedly blocked RANKL-induced osteoclastogenesis by attenuating MAPK pathways. However, RT treatment in an osteoblastic cell line, MC3TE-E1, indicated that RT led to an increase in the deposition of minerals and the expression of osteoblast marker genes, as demonstrated by Alizarin Red staining and alkaline phosphatase activity. Importantly, an OVX mouse model showed that RT could attenuate the bone loss in estrogen deficiency-induced osteoporosis in vivo with a smart H₂ S-releasing property and that there was a considerable improvement in the biomechanical properties of bone. Accordingly, our current work highlights the dual regulation of bone remodeling by the rhein-derived molecule RT. This may be a highly promising approach for a new type of anti-osteoporosis agent. © 2018 American Society for Bone and Mineral Research.

Possible involvement of peripheral TRP channels in the hydrogen sulfide-induced hyperalgesia in diabetic rats

BACKGROUND

Peripheral diabetic neuropathy can be painful and its symptoms include hyperalgesia, allodynia and spontaneous pain. Hydrogen sulfide (H2S) is involved in diabetes-induced hyperalgesia and allodynia. However, the molecular target through which H2S induces hyperalgesia in diabetic animals is unclear. The aim of this study was to determine the possible involvement of transient receptor potential (TRP) channels in H2S-induced hyperalgesia in diabetic rats.

RESULTS

Streptozotocin (STZ) injection produced hyperglycemia in rats. Intraplantar injection of NaHS (an exogenous donor of H2S, 3-100 µg/paw) induced hyperalgesia, in a time-dependent manner, in formalin-treated diabetic rats. NaHS-induced hyperalgesia was partially prevented by local intraplantar injection of capsazepine (0.3-3 µg/paw), HC-030031 (100-316 µg/paw) and SKF-96365 (10-30 µg/paw) blockers, at 21 days post-STZ injection. At the doses used, these blockers did not modify formalin-induced nociception. Moreover, capsazepine (0.3-30 µg/paw), HC-030031 (100-1000 µg/paw) and SKF-96365 (10-100 µg/paw) reduced formalin-induced nociception in diabetic rats. Contralateral injection of the highest doses used did not modify formalin-induced flinching behavior. Hyperglycemia, at 21 days, also increased protein expression of cystathionine-β-synthase enzyme (CBS) and TRPC6, but not TRPA1 nor TRPV1, channels in dorsal root ganglia (DRG). Repeated injection of NaHS enhanced CBS and TRPC6 expression, but hydroxylamine (HA) prevented the STZ-induced increase of CBS protein. In addition, daily administration of SKF-96365 diminished TRPC6 protein expression, whereas NaHS partially prevented the decrease of SKF-96365-induced TRPC6 expression. Concordantly, daily intraplantar injection of NaHS enhanced, and HA prevented STZ-induced intraepidermal fiber loss, respectively. CBS was expressed in small- and medium-sized cells of DRG and co-localized with TRPV1, TRPA1 and TRPC6 in IB4-positive neurons.

CONCLUSIONS

Our data suggest that H2S leads to hyperalgesia in diabetic rats through activation of TRPV1, TRPA1 and TRPC channels and, subsequent intraepidermal fibers loss. CBS enzyme inhibitors or TRP-channel blockers could be useful for treatment of painful diabetic neuropathy.

Mechanism of sodium hydrosulfide modulation of L-type calcium channels in rat colonic smooth muscle cells

Hydrogen sulfide (H₂S) can exert different effects on the gastrointestinal tract by modulating ion channels. Previously, we found that H₂S donor sodium hydrosulfide (NaHS) regulates colonic motility through L-type calcium channels, but the molecular mechanism remains unknown. The present study was designed to investigate possible mechanisms underlying the modulation of L-type calcium channels by NaHS in rat colonic smooth muscle cells. L-type calcium currents in colonic smooth muscle cells were recorded using the whole-cell patch-clamp technique. Spontaneous contractions of mid-colonic smooth muscle strips were measured in an organ bath system and a biological signal acquisition system. NaHS evoked a significant rightward shift in the steady-state activation curve of L-type calcium channels, changed the shape of the current-voltage (I-V) curve, and decreased the peak current density at 0mV, although it significantly increased with higher stimulatory voltage. The sulfhydryl-modifying reagent DL-dithiothreitol (DTT) enhanced the effects of NaHS on L-type calcium channels, while diamide (DM) and reduced L-glutathione (GSH) alleviated the effects of NaHS. Additionally, NaHS inhibited the spontaneous high-amplitude contractions of both longitudinal and circular smooth muscle strips in a dose-dependent manner. The inhibitory effects were reversible. DTT and GSH enhanced the effects of NaHS, while DM attenuated the effects of NaHS. In conclusion, NaHS modulates L-type calcium channels in rat colonic smooth muscle cells and regulates the contractile activity of colonic smooth muscle, potentially by modifying the free sulfhydryl groups of L-type calcium channels.

Inhibitory effect of estrogen receptor beta on P2X3 receptors during inflammation in rats

Estrogen receptor beta (ERβ) has been shown to play a therapeutic role in inflammatory bowel disease (IBD). However, the mechanism underlying how ERβ exerts therapeutic effects and its relationship with P2X3 receptors (P2X3R) in rats with inflammation is not known. In our study, animal behavior tests, visceromotor reflex recording, and Western blotting were used to determine whether the therapeutic effect of ERβ in rats with inflammation was related with P2X3R. In complete Freund adjuvant (CFA)-induced chronic inflammation in rats, paw withdrawal threshold was significantly decreased which were then reversed by systemic injection of ERβ agonists, DPN or ERB-041. In 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in rats, weight loss, higher DAI scores, increased visceromotor responses, and inflammatory responses were reversed by application of DPN or ERB-041. The higher expressions of P2X3R in dorsal root ganglia (DRG) of CFA-treated rats and those in rectocolon and DRG of TNBS-treated rats were all decreased by injection of DPN or ERB-041. DPN application also inhibited P2X3R-evoked inward currents in DRG neurons from TNBS rats. Mechanical hyperalgesia and increased P2X3 expression in ovariectomized (OVX) CFA-treated rats were reversed by estrogen replacements. Furthermore, the expressions of extracellular signal-regulated kinase (ERK) in DRG and spinal cord dorsal horn (SCDH) and c-fos in SCDH were significantly decreased after estrogen replacement compared with those of OVX rats. The ERK antagonist U0126 significantly reversed mechanical hyperalgesia in the OVX rats. These results suggest that estrogen may play an important therapeutic role in inflammation through down-regulation of P2X3R in peripheral tissues and the nervous system, probably via ERβ, suggesting a novel therapeutic strategy for clinical treatment of inflammation.

Colonic overexpression of the T-type calcium channel Cav 3.2 in a mouse model of visceral hypersensitivity and in irritable bowel syndrome patients

BACKGROUND

Among the different mechanisms involved in irritable bowel syndrome (IBS) physiopathology, visceral hypersensitivity seems to play a key role. It involves sensitization of the colonic primary afferent fibers, especially through an overexpression of ion channels. The aims of this translational study were to investigate the colonic expression of Ca_v 3.2 calcium channels and their involvement in an animal model of colonic hypersensitivity, and to assess their expression in the colonic mucosa of symptomatic IBS patients.

METHODS

This bench-to-bed study combined a preclinical experimental study on mice and a case-control clinical study. Preclinical studies were performed on wild-type and Ca_v 3.2-KO mice. Colonic sensitivity and Ca_v 3.2 expression were studied after a low-dose treatment of dextran sodium sulfate (DSS 0.5%). Regarding the clinical study, colonic biopsies were performed in 14 IBS patients and 16 controls during a colonoscopy to analyze the mucosal Ca_v 3.2 expression.

KEY RESULTS

Wild-type, but not Ca_v 3.2-KO, mice developed visceral hypersensitivity without colonic inflammation, after 0.5% DSS treatment. A significant increase of Ca_v 3.2 mRNA (p = 0.04) was found in the colon of low-dose DSS-treated wild-type (WT) mice compared to their controls. In human colonic biopsies, the Ca_v 3.2 mRNA level was significantly higher in the IBS group compared to the control group (p = 0.01). The immunofluorescence staining revealed their protein expression in colonic mucosa, particularly in nerve fibers.

CONCLUSIONS & INFERENCES

This translational study supports the involvement of the calcium channels Ca_v 3.2 in abdominal pain, as observed in IBS patients. It opens new therapeutic perspectives based on molecules specifically blocking these channels.

Exogenous hydrogen sulphide ameliorates diabetic cardiomyopathy in rats by reversing disordered calcium-handling system in sarcoplasmic reticulum

OBJECTIVES

Hydrogen sulphide (H2 S) has been found to be involved in cardiovascular diseases, but the exact mechanism has not been clarified. The purpose of this study was to investigate whether sodium hydrogen sulphide (NaHS), the donor of H2 S, can improve diabetic cardiomyopathy by reversing disordered calcium-handling system in sarcoplasmic reticulum (SR).

METHODS

Sprague Dawley rats were injected with streptozotocin (STZ, 60 mg/kg, i.p.) to build diabetic model. Treatment groups included: aminoguanidine group (AG, 100 mg/kg, p.o.) and NaHS group (5 mg/kg per day, s.c.).

KEY FINDINGS

Cardiac dysfunction and myocardial hypertrophy were found in diabetic model (DM) group, along with increased ROS levels and upregulated mRNA and protein expressions of NADPH p22(phox) , endothelin A receptor (ETA ) and protein kinase Cε (PKCε). Expressions of calcium-handling proteins in SR including FK506-binding proteins (FKBP12.6), sarcoplasmic reticulum Ca(2+) ATPase (SERCA2a) and calsequestrin 2 (CASQ2) were downregulated in DM group, accompanied by elevated concentration of diastolic free calcium in high glucose-incubated cardiomyocytes, indicating of calcium leak. After treated by NaHS, these abnormalities were attenuated significantly.

CONCLUSIONS

Exogenous H2 S played a protective role in diabetic cardiomyopathy by inhibiting abnormal calcium-handling system in SR and ET-NADPH oxidase-PKCε pathway.

Hydrogen sulfide attenuates IL-1β-induced inflammatory signaling and dysfunction of osteoarthritic chondrocytes

Inflammatory cytokines are crucial factors in the onset of osteoarthritis (OA). The pro-inflammatory cytokine, interleukin-1β (IL-1β), is capable of stimulating a few cartilage degradation mediators and is of importance to the pathogenesis of OA. It has been demonstrated that hydrogen sulfide (H2S) exerts an inhibitory effect on inflammation. Thus, in the present study, we aimed to investigate the therapeutic effects of H2S in OA. For this purpose, an in vitro model of cartilage inflammation was created. Human OA chondrocytes were cultured and pre-treated with H2S (0.06-1.5 mM) with or without IL-1β (10 ng/ml) and then Griess reagent was used to quantify the production of nitric oxide (NO). Using enzyme-linked immunosorbent assay, we quantified the production of prostaglandin E2 (PGE2) and matrix metalloproteinase-13 (MMP-13). In addition, we determined the gene expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and MMP-13 using reverse transcription-quantitative polymerase chain reaction and the expression of signaling molecules related to mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB) by western blot analysis. Our results revealed that H2S markedly reversed the effects of IL-1β on the gene expression of COX-2, MMP-13 and iNOS and on the production of MMP-13, PGE2 and NO. In addition, H2S inhibited the activation of the extracellular signal-regulated kinase (ERK)/IκBα/NF-κB pathway which was induced by IL-1β. On the whole, the results of the present study suggest that H2S exerts chondroprotective effects. Thus, H2S may have potential for use in the treatment of patients suffering from OA.