Comparison of Protein N-Homocysteinylation in Rat Plasma under Elevated Homocysteine Using a Specific Chemical Labeling Method

Homocysteinylation and Sulfhydration in Diseases

Homocysteine (Hcy) is an important intermediate in methionine metabolism and generation of one-carbon units, and its dysfunction is associated with many pathological states. Although Hcy is a non-protein amino acid, many studies have demonstrated protein-related homocysteine metabolism and possible mechanisms underlying homocysteinylation. Homocysteinylated proteins lose their original biological function and have a negative effect on the various disease phenotypes. Hydrogen sulfide (H₂S) has been recognized as an important gaseous signaling molecule with mounting physiological properties. H₂S modifies small molecules and proteins via sulfhydration, which is supposed to be essential in the regulation of biological functions and signal transduction in human health and disorders. This review briefly introduces Hcy and H₂S, further discusses pathophysiological consequences of homocysteine modification and sulfhydryl modification, and ultimately makes a prediction that H₂S might exert a protective effect on the toxicity of homocysteinylation of target protein via sulfhydration. The highlighted information here yields new insights into the role of protein modification by Hcy and H₂S in diseases.

Role of hydrogen sulfide in endothelial dysfunction: Pathophysiology and therapeutic approaches

BACKGROUND

The vascular endothelium represents a fundamental mechanical and biological barrier for the maintenance of vascular homeostasis along the entire vascular tree. Changes in its integrity are associated to several cardiovascular diseases, including hypertension, atherosclerosis, hyperhomocysteinemia, diabetes, all linked to the peculiar condition named endothelial dysfunction, which is referred to the loss of endothelial physiological functions, comprehending the regulation of vascular relaxation and/or cell redox balance, the inhibition of leukocyte infiltration and the production of NO. Among the endothelium-released vasoactive factors, in the last years hydrogen sulfide has been viewed as one of the main characters involved in the regulation of endothelium functionality, and many studies demonstrated that H2S behaves as a vasoprotective gasotransmitter in those cardiovascular diseases where endothelial dysfunction seems to be the central issue.

AIM

The role of hydrogen sulfide in endothelial dysfunction-related cardiovascular diseases is discussed in this review.

KEY SCIENTIFIC CONCEPTS

Possible therapeutic approaches using molecules able to release H2S.

Elevated homocysteine and differential risks of the renal function decline in hypertensive patients

IMPORTANCE

In several studies, homocysteine (hcy) is a documented risk for predicting renal function decline. The differential effects between various levels of hcy have yet to be quantified.

METHODS

In this retrospective cohort study, data was obtained from patients admitted to our hospital from Jan. 2015 to Apr. 2019. Hyperhomocysteinemia is defined as serum hcy concentration >15 μmol/L. Study population eligible subjects included those who had a diagnostic hypertension. The endpoint event was defined as a fall in eGFR between the follow-up and baseline. Logistic regression models were used to examine the related ratio risk results. Cox models were performed to explore the effect of study groups on survival. The significant level was set at a P value of <0.05.

RESULTS

A total of 7,240 patients presented over 3,564 person-years and were retrospectively enrolled in this study. Overall, 1,145 patients had a hypertension grade 1 [15.8%], 2,455 hypertension grade 2 [33.9%], and 3,640 hypertension grade 3 [50.27%]. Among patients who developed hyperhomocysteinemia (3,604 patients), their renal function had a higher long-term rate of decline (P= .005, hazard ratio (HR) = 1.097, 95% confidence interval (CI) [1.028, 1.171]), compared to patients who didn't developed hyperhomocysteinemia (3,636 patients). After adjusting for covariables, patients' (hcy > 15 μmol/L group) eGFR decreasing had a more hazard ratio (P = .002, aHR= 1.112; 95%CI [1.039, 1.190]). Compared with the serum hcy ≤ 10 μmol/L patients, their renal function decline ratio was higher in the 10 μmol/L < hcy ≤ 15 μmol/L group (P = .008, HR= 1.195, 95% CI [1.048,1.364]), 15 μmol/L < hcy ≤ 20 μmol/L group (P = .000, HR= 1.400, 95%CI [1.227,1.597]), and hcy > 20 μmol/L group (P = .000, HR = 1.475, 95%CI [1.305,1.667]).

CONCLUSION

Elevated hcy concentration increases the risk of renal function decline in hypertensive patients. Hcy concentration might also be considered as an important factor in risk stratification of the renal function for hypertensive patients.

A chemoselective reaction between protein N-homocysteinylation and azides catalyzed by heme(ii)

Herein, we present a serendipitously discovered chemoselective labelling of protein N-homocysteinylation with bioorthogonal azide probes. The reaction proceeds rapidly under alkaline and heating conditions. Our experiments suggest that azides can be converted to aldehydes in situ catalyzed by heme(ii), followed by a condensation with protein N-homocysteinylation to afford stable 1,3-thiazines.

Therapeutic Cocktail Approach for Treatment of Hyperhomocysteinemia in Alzheimer's Disease

In the United States, Alzheimer's disease (AD) is the most common cause of dementia, accompanied by substantial economic and emotional costs. During 2015, more than 15 million family members who provided care to AD patients had an estimated total cost of 221 billion dollars. Recent studies have shown that elevated total plasma levels of homocysteine (tHcy), a condition known as hyperhomocysteinemia (HHcy), is a risk factor for AD. HHcy is associated with cognitive decline, brain atrophy, and dementia; enhances the vulnerability of neurons to oxidative injury; and damages the blood-brain barrier. Many therapeutic supplements containing vitamin B12 and folate have been studied to help decrease tHcy to a certain degree. However, a therapeutic cocktail approach with 5-methyltetrahydrofolate, methyl B12, betaine, and N-acetylcysteine (NAC) have not been studied. This novel approach may help target multiple pathways simultaneously to decrease tHcy and its toxicity substantially.