Activation of Human Salivary Aldehyde Dehydrogenase by Sulforaphane: Mechanism and Significance

Oral enzymatic detoxification system: Insights obtained from proteome analysis to understand its potential impact on aroma metabolization

The oral cavity is an entry path into the body, enabling the intake of nutrients but also leading to the ingestion of harmful substances. Thus, saliva and oral tissues contain enzyme systems that enable the early neutralization of xenobiotics as soon as they enter the body. Based on recently published oral proteomic data from several research groups, this review identifies and compiles the primary detoxification enzymes (also known as xenobiotic-metabolizing enzymes) present in saliva and the oral epithelium. The functions and the metabolic activity of these enzymes are presented. Then, the activity of these enzymes in saliva, which is an extracellular fluid, is discussed with regard to the salivary parameters. The next part of the review presents research evidencing oral metabolization of aroma compounds and the putative involved enzymes. The last part discusses the potential role of these enzymatic reactions on the perception of aroma compounds in light of recent pieces of evidence of in vivo oral metabolization of aroma compounds affecting their release in mouth and their perception. Thus, this review highlights different enzymes appearing as relevant to explain aroma metabolism in the oral cavity. It also points out that further works are needed to unravel the effect of the oral enzymatic detoxification system on the perception of food flavor in the context of the consumption of complex food matrices, while considering the impact of food oral processing. Thus, it constitutes a basis to explore these biochemical mechanisms and their impact on flavor perception.

Current View on the Mechanisms of Alcohol-Mediated Toxicity

Alcohol is a psychoactive substance that is widely used and, unfortunately, often abused. In addition to acute effects such as intoxication, it may cause many chronic pathological conditions. Some of the effects are very well described and explained, but there are still gaps in the explanation of empirically co-founded dysfunction in many alcohol-related conditions. This work focuses on reviewing actual knowledge about the toxic effects of ethanol and its degradation products.

Evaluation of spice and herb as phyto-derived selective modulators of human retinaldehyde dehydrogenases using a simple in vitro method

Selective modulation of retinaldehyde dehydrogenases (RALDHs)-the main aldehyde dehydrogenase (ALDH) enzymes converting retinal into retinoic acid (RA), is very important not only in the RA signaling pathway but also for the potential regulatory effects on RALDH isozyme-specific processes and RALDH-related cancers. However, very few selective modulators for RALDHs have been identified, partly due to variable overexpression protocols of RALDHs and insensitive activity assay that needs to be addressed. In the present study, deletion of the N-terminal disordered regions is found to enable simple preparation of all RALDHs and their closest paralog ALDH2 using a single protocol. Fluorescence-based activity assay was employed for enzymatic activity investigation and screening for RALDH-specific modulators from extracts of various spices and herbs that are well-known for containing many phyto-derived anti-cancer constituents. Under the established conditions, spice and herb extracts exhibited differential regulatory effects on RALDHs/ALDH2 with several extracts showing potential selective inhibition of the activity of RALDHs. In addition, the presence of magnesium ions was shown to significantly increase the activity for the natural substrate retinal of RALDH3 but not the others, while His-tag cleavage considerably increased the activity of ALDH2 for the non-specific substrate retinal. Altogether we propose a readily reproducible workflow to find selective modulators for RALDHs and suggest potential sources of selective modulators from spices and herbs.

Correlation between the Activity of Aldehyde Dehydrogenase and Oxidative Stress Markers in the Saliva of Diabetic Patients

BACKGROUND

Reactive aldehydes are involved in diseases associated with oxidative stress, including diabetes. Human salivary aldehyde dehydrogenase (hsALDH) presumably protects us from many toxic ingredient/contaminant aldehydes present in food.

OBJECTIVE

This study aimed to probe the activity of hsALDH in patients with diabetes and than to correlate it with various oxidative stress markers in the saliva.

METHODS

The saliva samples were collected from total 161 diabetic patients from Rajiv Gandhi Centre for Diabetes, Jawaharlal Nehru Medical College (JNMC), AMU, Aligarh, (India). HsALDH activity and markers of oxidative stress [8-hydroxydeoxyguanosine (8-OHDG), malondialdehyde (MDA) and advanced glycation end products (AGEs)] were measured in the saliva samples.

RESULTS

Patients with early stage of diabetes had higher activity of hsALDH when compared with the control group. As the history of diabetes increases, the activity of the enzyme decreases and also higher oxidative stress markers (8-OHDG, MDA and AGEs) are detected in the saliva samples. Negative significant correlation between hsALDH activity and oxidative stress markers were observed (p <0.0001).

CONCLUSION

The activity of hsALDH increases in early stages of diabetes most probably to counter the increased oxidative stress associated with diabetes. However, in later stages of diabetes, the activity of the enzyme decreases, possibly due to its inactivation resulting from glycation.

A mechanistic approach to prove the efficacy of combination therapy against New Delhi metallo-β-lactamases producing bacterial strain: a molecular and biochemical approach

BACKGROUND

NDM-1 is a novel broad-spectrum metallo-β-lactamase with the capability to grant resistance to almost all β-lactam antibiotics. Its widespread dissemination made treatment options a major challenge to combat, causing threat to public health worldwide. Due to antibiotic resistance problems, development of effective therapeutics for infections caused by NDM-1 producing strains is urgently required. Since combination therapies are proved to be effective in many cases, this study was initiated to put forward novel effective antibiotics combinations for fighting infections caused by NDM-1 producing strains.

METHODS

Streptomycin and amikacin combination and streptomycin and ciprofloxacin combination were tested by checkerboard assay. NDM-1 protein/enzyme was then expressed and purified to carry out enzyme kinetics study, CD and fluorescence spectroscopic studies.

RESULTS

Streptomycin and amikacin combination and streptomycin and ciprofloxacin combination showed synergistic effect towards NDM-1 producing bacterial strains as shown by FICI results. NDM-1 producing bacterial cells were expressed and purified to obtain protein as the source of enzyme. When NDM-1 enzyme was treated with streptomycin along with amikacin, the efficiency of enzyme was decreased by 49.37% and when the enzyme was treated with streptomycin along with ciprofloxacin, the efficiency of enzyme was decreased by 29.66% as revealed by enzyme kinetic studies. Due to binding of streptomycin and amikacin in combination and streptomycin and ciprofloxacin in combination, conformational changes in the secondary structure of NDM-1 enzyme were observed by CD spectroscopic studies. Antibiotics streptomycin and ciprofloxacin bind with NDM-1 through exothermic processes, whereas amikacin binds through an endothermic process. All three antibiotics bind spontaneously with an association constant of the order of 104 M-1 as revealed by fluorescence spectroscopic studies.

CONCLUSIONS

The therapeutic combination of streptomycin with amikacin and ciprofloxacin plays an important role in inhibiting NDM-1 producing bacterial strains. Therefore, these combinations can be used as effective future therapeutic candidates against NDM-1 producing bacterial cells.

Arsenic inhibits human salivary aldehyde dehydrogenase: Mechanism and a population-based study

Human salivary aldehyde dehydrogenase (hsALDH) is an important detoxifying enzyme and maintains oral health. Subjects with low hsALDH activity are at a risk of developing oral cancers. Arsenic (As) toxicity causes many health problems in humans. The objective of this population-based study was to correlate As contamination and hence low hsALDH activity with high incidence of cancer cases in Bareilly district of India. Here, it was observed that As inhibited hsALDH (IC₅₀ value: 33.5 ± 2.5 μM), and the mechanism of inhibition was mixed type (in between competitive and non-competitive). Binding of As to hsALDH changed the conformation of the enzyme. A static quenching mechanism was observed between the enzyme and As with a binding constant (K_b) of 9.77 × 10⁴ M^-1. There is one binding site for As on hsALDH molecule. Further, the activity of hsALDH in volunteers living in regions of higher As levels in drinking water (Bahroli and Mirganj village of Bareilly district, India), and those living in region having safe levels of As (Aligarh city, India) was determined. The As level in the saliva samples of the volunteers was determined by inductively coupled plasma mass spectroscopy (ICP-MS). Low hsALDH activity was found in volunteers living in the region of higher As levels. The activity of hsALDH and As concentration in the saliva was found to be negatively correlated (r = - 0.427, p < 0.0001). Therefore, we speculate that the high incidence of cancer cases reported in Bareilly district may be due to higher As contamination.

Lyophilized B. subtilis ZB183 Spores: 90-Day Repeat Dose Oral (Gavage) Toxicity Study in Wistar Rats

A 90-day repeated-dose oral toxicological evaluation was conducted according to GLP and OECD guidelines on lyophilized spores of the novel genetically modified strain B. subtilis ZB183. Lyophilized spores at doses of 10⁹, 10¹⁰, and 10¹¹ CFU/kg body weight/day were administered by oral gavage to Wistar rats for a period of 90 consecutive days. B. subtilis ZB183 had no effects on clinical signs, mortality, ophthalmological examinations, functional observational battery, body weights, body weight gains and food consumption in both sexes. There were no test item-related changes observed in haematology, coagulation, urinalysis, thyroid hormonal analysis, terminal fasting body weights, organ weights, gross pathology and histopathology. A minimal increase in the plasma albumin level was observed at 10¹⁰ and 10¹¹ CFU/kg/day doses without an increase in total protein in males or females and was considered a nonadverse effect. The “No Observed Adverse Effect Level (NOAEL)” is defined at the highest dose of 10¹¹ CFU/kg body weight/day for lyophilized B. subtilis ZB183 Spores under the test conditions employed.

Synergistic effect of doripenem in combination with cefoxitin and tetracycline in inhibiting NDM-1 producing bacteria

Aim: To propose newer combinations of antibiotics effective against NDM-1-producing bacterial strains. Materials & methods: Antibiotics combinations were tested by checkerboard assay. NDM-1 protein/enzyme was expressed and purified to perform enzyme kinetics, circular dichroism and fluorescence spectroscopic studies. Results: Doripenem-cefoxitin combination and doripenem-tetracycline combination showed synergistic effect toward NDM-1-producing strains. The catalytic efficiency of NDM-1 enzyme was decreased drastically by 96.6% upon doripenem-cefoxitin treatment and by 35.54% after doripenem-tetracycline treatment. Conformational changes were observed in NDM-1 upon combination treatment. Conclusion: NDM-1-producing bacterial strains show resistance to multiple antibiotics but the combination of doripenem-cefoxitin and doripenem-tetracycline are effective against them. The combination of a carbapenem and cephamycin antibiotic is proposed for future treatment options against bacteria-producing NDM-1.

Enhancement in the Catalytic Activity of Human Salivary Aldehyde Dehydrogenase by Alliin from Garlic: Implications in Aldehyde Toxicity and Oral Health

BACKGROUND

Lower human salivary aldehyde dehydrogenase (hsALDH) activity increases the risk of aldehyde mediated pathogenesis including oral cancer. Alliin, the bioactive compound of garlic, exhibits many beneficial health effects.

OBJECTIVE

To study the effect of alliin on hsALDH activity.

METHODS

Enzyme kinetics was performed to study the effect of alliin on the activity of hsALDH. Different biophysical techniques were employed for structural and binding studies. Docking analysis was done to predict the binding region and the type of binding forces.

RESULTS

Alliin enhanced the dehydrogenase activity of the enzyme. It slightly reduced the Km and significantly enhanced the Vmax value. At 1 µM alliin concentration, the initial reaction rate increased by about two times. Further, it enhanced the hsALDH esterase activity. Biophysical studies indicated a strong complex formation between the enzyme and alliin (binding constant, Kb: 2.35 ± 0.14 x 103 M-1). It changes the secondary structure of hsALDH. Molecular docking study indicated that alliin interacts to the enzyme near the substrate binding region involving some active site residues that are evolutionary conserved. There was a slight increase in the nucleophilicity of active site cysteine in the presence of alliin. Ligand efficiency metrics values indicate that alliin is an efficient ligand for the enzyme.

CONCLUSION

Alliin activates the catalytic activity of the enzyme. Hence, consumption of alliincontaining garlic preparations or alliin supplements and use of alliin in pure form may lower aldehyde related pathogenesis including oral carcinogenesis.

Significant role of Asn-247 and Arg-64 residues in close proximity of the active site in maintaining the catalytic function of CTX-M-15 type β-lactamase

Members of Enterobacteriaceae cause antibiotic-resistant infections worldwide. One such marker, CTX-M-15, expressed by Enterobacteriaceae produces β-lactamases, which hydrolyze the cephalosporin group of antibiotics, such as cefotaxime, used in the treatment of both Gram-positive and negative bacterial infections. Amino acid residues present in close proximity of the active site might also play a major role in the structure and function of CTX-M-15, hence the objective of this study was to investigate the significance of two amino acid residues, Asn-247 and Arg-64, present near to the active site in the hydrolysis of cefotaxime. bla_CTX-M-15, cloned from the E. cloacae strain, and using Polymerase Chain Reaction (PCR)-based site-directed mutagenesis, Asn247Val and Arg64Leu mutations were introduced. The minimum inhibitory concentrations of cefotaxime for the CTX-M-15 (N247V) and CTX-M-15 (R64L) mutants were reduced by 512 and 128 fold, respectively. Proteins/enzymes of wild-type CTX-M-15, CTX-M-15 (N247V) and CTX-M-15 (R64L) mutants were expressed and purified. Kinetic studies showed that the catalytic efficiencies of the N247V mutant and R64L mutant enzymes in the hydrolysis of cefotaxime were reduced by 89.66% and 71.11%, respectively. Circular dichroism spectroscopic studies showed considerable changes in the α-helical content of the mutant enzymes. A fluorescence study showed that N247V mutant-cefotaxime and R64L mutant-cefotaxime underwent complex formation with strong interactions. The study provides an understanding of the crucial role of the amino acid residues asparagine 247 and arginine 64 present in close proximity of the active site in the hydrolytic mechanism of CTX-M-15 type β-lactamases. Hence, Asn-247 and Arg-64 can be used as potential target sites for the design of inhibitory molecules against CTX-M-15-producing bacterial strains.

Mutations of amino acid residues present near active site decrease the catalytic efficiency of beta lactamase enzymes.

Hybrid pharmacophore approach for bio-relevant di-imines based homobimetallic complexes incorporating functionalized dicarboxylates as co-ligands: Synthesis, spectral and structural activity dependent biological insights (in-vitro DNA and HSA binding, antioxidant and cytotoxicity)

Synthesis of bio-efficient homobimetallic complexes, [Cu₂(L¹)₂(dipic)](NO₃)₂.3H₂O (1), [Zn₂(L¹)₂(dipic)](NO₃)₂.4H₂O (2), [Cu₂(L²)₂(oxa)](NO₃)₂.4H₂O (3) and [Zn₂(L²)₂(oxa)] (NO₃)₂.5H₂O (4) was carried out using Schiff bases [(N¹E,N²E)-N¹,N²-bis(5-chlorothiophen-2-ylmethylene)-4-chlorobenzene-1,2-diamine; L¹] and [(N¹E,N²E)-N¹,N²-bis(5-chlorofuran-2-ylmethylene)-4-chlorobenzene-1,2-diamine; L²] as main ligands and dicarboxylate moieties of 2,6-pyridine dicarboxylic acid (H₂-dipic) and oxalic acid (H₂-oxa) as co-ligands, respectively in order to apprehend their structure activity relationships on the basis of pharmacophore hybrid approach. The stoichiometry, geometry, thermal stability, morphology and crystallite size of the compounds were inferred by analytical, spectral (FT-IR, ¹H NMR and ¹³C NMR and Mass), thermal (TGA/DTA), SEM and XRD studies. In-vitro DNA and HSA binding profiles of complexes were analysed by different biophysical measurements. The absorption study divulged that the observed alterations in the physico-chemical properties of complexes upon binding with DNA connoted their intercalative binding mode while fluorescence quenching mechanism was quantified by using Stern Volmer constant (K_SV)_; 1.73×10⁴ (1), 1.47×10⁴ (2), 5.65×10³ (3) and 3.60×10³M^-1 (4) which discerned that hybrid pharmacophore active metal complexes (1 and 2) exhibited efficient quenching effect with Ct-DNA in comparison to complexes (3 and 4) due to greater planarity and extent of conjugation (π-π interactions). The intercalative binding mode of complexes is further supported by competitive displacement assay by using fluorogenic dyes (EtBr and Hoechst 33258). The results of HSA fluorescence study divulged static quenching of the complexes (1-4) with K_SV values of 7.24×10⁴ (1), 6.03×10⁴ (2), 5.06×10⁴ (3) and 2.85×10⁴ (4) while K_b values; 1.16×10⁵ (1), 2.01×10⁴ (2), 5.84×10³ (3) and 8.60×10² (4) suggested them potent avid binder of HSA. Additionally, comparative estimation of scavenging properties using DPPH, superoxide(O₂^.-), hydroxyl (OH^-) and ABTS method and in-vitro cytotoxicity against different cell lines (MCF-7, HeLa and Hep G2) brought out distinct biopotency of complexes due to diverse structural features and chelation effect.

Thymoquinone binds and activates human salivary aldehyde dehydrogenase: Potential therapy for the mitigation of aldehyde toxicity and maintenance of oral health

Human salivary aldehyde dehydrogenase (hsALDH) is a very important anti-oxidant enzyme present in the saliva. It is involved in the detoxification of toxic aldehydes and maintenance of oral health. Reduced level of hsALDH activity is a risk factor for oral cancer development. Thymoquinone (TQ) has many pharmacological activities and health benefits. This study aimed to examine the activation of hsALDH by TQ. The effect of TQ on the activity and kinetics of hsALDH was studied. The binding of TQ with the enzyme was examined by different biophysical methods and molecular docking analysis. TQ enhanced the dehydrogenase activity of crude and purified hsALDH by 3.2 and 2.9 fold, respectively. The K_m of the purified enzyme decreased and the V_max increased. The esterase activity also increased by 1.2 fold. No significant change in the nucleophilicity of the catalytic cysteine residue was observed. TQ forms a strong complex with hsALDH without altering the secondary structures of the enzyme. It fits in the active site of ALDH3A1 close to Cys 243 and the other highly conserved amino acid residues which lead to enhancement of substrate binding affinity and catalytic efficiency of the enzyme. TQ is expected to give better protection from toxic aldehydes in the oral cavity and to reduce the risk of oral cancer development through the activation of hsALDH. Therefore, the addition of TQ in the diet and other oral formulations is expected to be beneficial for health.

Monitoring thermal and chemical unfolding of Brugia malayi calreticulin using fluorescence and Circular Dichroism spectroscopy

Calreticulin of Brugia malayi (BmCRT) play very important role in host-parasite interaction. In previous study it was found that BmCRT is responsible for prevention of host classical complement pathway activation via its interaction with first component C1q of the human host. Therefore, BmCRT is an essential protein for parasite survival and an important drug target to fend filariasis. In the present study, we have carried out a systamatic biophysical characterization of BmCRT protein. Unfolding of BmCRT was found to be non-cooperative two-state process in the presence of both denaturant GdmCl and urea. The results also illustrated that protein lost its 50% activity at 1.5M GdmCl and 3M Urea. Partially unfolded and molten-globule like intermediate state was observed at 0.8 to 1.2M GdmCl while Urea unfolding showed intermediate state at 1.2 to 1.6M. Unfolding pathway monitored with the help of apolar quencher, favor above observations. All of these findings support the presence of detectable intermediate state during unfolding pathway of BmCRT. Furthermore, this study indicates that BmCRT is more stable toward temperature (Tm=65°C), pH and trypsin digestion. These differences in properties as compared to host can be fruitfully utilized for synthesis of compounds effective against the parasite.