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Low dose gossypol for male contraception

Zhi-Ping GU1, Bai-Yong MAO1, Yi-Xin WANG2, Ren-An ZHANG3, Yong-Zhi TAN4,  Zheng-Xing CHEN2, Lin CAO1, Gen-Di YOU1, S.J. Segal5

1Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai  200031, China
2Ren Ji Hospital, Shanghai Second Medical University, Shanghai  200001, China
3Zhong Shan Hospital, Medical Centre of Fudan University, Shanghai 200032, China
4Jing An District Central Hospital, Shanghai  200040, China
5Population Division, Rockefeller Foundation, New York, USA

Asian J Androl  2000 Dec; 2:  283-287

Keywords: gossypol; male contraceptive agents; LH; FSH; testosterone;  serum potassium
Abstract
Aim: To ascertain whether the side effects of gossypol, hypokalemia and irreversibility, could be avoided on dose reduction. Methods: Seventy-seven male volunteers were divided into 3 groups: control (22 cases), 10 mg gossypol (29 cases) and 12.5 mg (26 cases). Serum levels of testosterone, FSH and LH were measured by RIA and potassium by flame photometry.  Sperm counts and motility were examined before and regularly after treatment for the evaluation of contraceptive efficacy. Results: The average sperm density and motility started to decrease significantly by the end of month 2 of medication and gradually reached the infertility levels  (<4 million /mL) in both treated groups. After that the 10 mg group was asked to take the same dose every other day for up to a total observation period of 16-18 months for the maintenance of infertility. Subjects in the 12.5 mg group did not  take gossypol any more so as to observe the length of the loading dose required, but in a few, a maintenance dose of 12.5 mg every other day was instituted for a few more months. In both treated groups, none of the spouses was pregnant during the maintenance dose period. Serum levels of potassium, FSH, LH and testosterone were not significantly changed and not a single volunteer complained of myoasthenia. After cessation of drug administratioin, the semen data returned to pretreatment levels. Conclusion: A regimen with 10 or 12.5 mg of gossypol as the daily loading dose and 35 or 43.75 mg as the weekly maintenance dose could induce infertility in male volunteers without developing hypokalemia or irreversibility.
1 Introduction
Gossypol, a yellow polyphenolic compound isolated from the seed of the cotton plant (family Malvaceae), has been reported to induce infertility by  suppressing spermatogenesis[1].  In a multicentre study carried out in China, 8086 male volunteers from 14 provinces, were treated with gossypol for contraceptive purposes.  Results showed that the effective rate of contraception was 98.5% at anoral dose of  20 mg  per  day  for  75 days as the initial dose, followed by a maintenance dose of 40-50 mg  per week[2]. Gossypol was thus considered by some as a potential male contraceptive[3].  However, hypokalemia and irreversibility, side effects occurring in a few subjects, caused hesitations and doubts for its clinical use.  The average incidence of hypokalemia was found to be 0.75% and that of irreversibility, 9.90%[2]. So far, preventive measures for these side effects have not been available in the literature. The present study was an attempt to explore an optimal dose that might induce contraception without developing hypokalemia and irreversibility.
2 Materials and methods

2.1 Treatment

Seventy-seven male volunteers with normal fertility and renal function were divided into 3 groups: (1) Control: 22 cases, (2) 10 mg group: 29 cases, and (3) 12.5 mg group: 26 cases. In the treatment groups, subjects were given gossypol at a daily oral dose of 10 or 12.5 mg until their sperm counts decreased to the generally accepted infertile level (<4 million/mL). After that volunteers in the 10 mg group were asked to take the same dose every other day to see whether the dose regime could maintain the contraceptive efficacy, up to a total observation period of 16-18 months. Subjects in the 12.5 mg group did not take gossypol any more as the purpose of this group was to observe the length of the loading dose required, but a number of subjects were advised to take a maintenance dose of 12.5 mg every other day for a few more months. All the subjects were asked to follow the dose regime strictly. During the trial, condoms, but no other contraceptive measures, were used until the sperm counts reached the infertile level to avoid unwanted pregnancy. For the controls, condoms were used during the whole observation period.

2.2 Semen examination

Sperm counts and motility were measured before medication, and  monthly after the commencement of medication. Semen specimens were obtained after 2-4 days of sexual abstinence.

2.3 Serum potassium and hormones

Blood samples were collected between  08:00  and 10:00  on the day before medication and at monthly intervals after the commencement of treatment. Serum levels of testosterone, FSH and LH were measured by RIA and potassium by flame photometry.

2.4 Statistical analysis

Data were represented as meanSD. Statistical analyses were made using t-test and significance was inferred when P<0.05.

3 Results

3.1 Spouse pregnancy

None of the spouses of the two treatment groups conceived during the period of maintenance dose, when condom was no longer used.

3.2 Duration of gossypol administration (Table 1) 

In the 10 mg group, 8 cases stopped medication by the end of month 9 and 18 cases, by the end of month 12. In the 12.5 mg group 11 subjects stopped to take gossypol by the end of month  8 and 15 cases continued to take the maintenance dose for two more months and 4 cases for 4 more months.

Table 1.   Duration of gossypol administration (No. of cases).

Month

0

4

6

8

9

10

12

16-18

10 mg

29

29

27

 

21

 

9

11

12.5 mg

26

26 

26

15

 4

 

 

3.3 Length of the loading phase

Table 2 shows the distribution of subjects by length of the loading phase. At the end of 6 month medication, in 69% of subjects in the 10 mg group and 73% of subjects in the 12.5 mg group, semen data reached the infertile levels. In the 12.5 mg group, the sperm count in one case decreased to less than 4 million/mL by the end of month 2  and in 9 cases, by the end of month 3 of treatment. By the end of month 4, the semen data of 12 cases in the 12.5 mg group and 13 case in the 10 mg group reached infertile level; these values were not significantly different.

Table 2.    Distribution of subjects according to the duration of the loading phase.     

Group

Loading phase
(month)

No. of cases

Sperm count<4 million/mL

Motile sperm<5%

10 mg
(n=29)

2

0

3

4

13

11

6

7

9

 

Total 20

23

12.5 mg
(n=26)

2

1

6

4

11

11

6

7

3

 

Total 19

20

3.4 Semen examination

As shown in Tables 3 and 4, in both treated groups the average sperm density and motility started to decrease significantly by the end of month 2 of medication and gradually reached infertile levels. Figures 1 and 2 show the pharmacodynamic profiles of sperm density and percentage of the mobile sperm in both groups.

Table 3.  Sperm density, motility and serum potas 10 mg  gossypol group means (n). bP<0.05, cP<0.01, as compared with the control or admission level.

 

 

Admission

Month of medication

2

4

6

9

12

16-18

Sperm density106/mL

Control

76.581.4(22)

93.46.6(13)

70.417.7(22)

64.447.1(20)

51.126.3(13)

82.817.0(5)

70.427(9)

Treatment

86.157.7(42)

41.432.3b(29)

10.613.8c(29)

5.38.6c(27)

1.23.7c(21)

2.56.3c(9)

3.05.9c(11)

Motility:(%)

Control

6220
(22)

807
(13)

7419
(22)

5636
(20)

4636
(13)

6918
(5)

766
(9)

Treatment

7013
(42)

3530b(29)

1621c
(29)

815c
(27)

28c
(21)

49c
(9)

1017c(11)

Serum K+: (mEq/L)

Control

4.20.3(22)

4.00.3(13)

3.90.3(22)

4.20.4(20)

4.10.3(13)

4.10.2(5)

3.90.2(9)

Treatment

4.30.3(42)

4.20.4(29)

3.90.3(29)

4.20.3(27)

4.20.3(21)

4.30.5(9)

3.80.3(11)

Table  4.    Sperm density, motility and serum potassium  in 12.5 mg gossypol group means (n). bP<0.05, cP<0.01,as compared with the admission level.

 

Admission

Month of medication

1

2

3

4

5

6

7

8

9

10

Sperm density:(106/mL)

6639
(26)

4817(16)

3015b(16)

2119b(26)

1419b(25)

918c(20)

48c
(14)

1317b(15)

78c(15)

43c
(5)

115b(4)

Motility:(%)

6610
(26)

3016(16)

1414c(16)

1214c(26)

1016c(25)

611c(20)

610c(14)

916c(15)

813c(15)

45c
(5)

21c
(4)

Serum K+(mEq/L)

4.50.5(11)

4.30.4(10)

4.20.2(6)

4.10.1(11)

3.90.4(9)

3.80.4(8)

3.60.1b(3)

3.50.4b(10)

4.20.2(6)

3.80.2(5)

4.40.2(4)

Figure 1.    Average Sperm density (meanSD) of subjects in control and treated groups.  
Figure 2.    Average Percent of motile sperm (meanSD) of subjects in control and treated groups. 

3.5 Hormone profiles

Table 5 shows serum levels of FSH, LH and testosterone in the 10 mg group. They were not significantly different from the levels at admission.

Table  5. Serum concentration of LH, FSH and testostero in 10 mg gossypol medication means (n).     

 

Admission

Month of medication

2

4

6

8

12

16-18

FSH (IU/L)

4.02.0(20)

2.71.1(19)

2.91.4(24)

4.95.1(22)

4.63.6(15)

3.01.5(9)

4.14.0(11)

LH (IU/L)

8.86.8(9)

6.22.8(6)

6.82.7(8)

8.54.8(7)

7.02.6(6)

6.94.3(7)

6.53.6(7)

Testosterone (nmol/L)

18.13.6(9)

15.73.2(6)

17.64.7(8)

19.44.9(7)

20.95.3(6)

16.63.2(7)

16.23.1(7)

3.6 Serum potassium

The serum potassium levels of subjects in treated groups are presented in Table 3 and 4. In the 12.5 mg group (Table 6), the serum K levels in 7 cases were occassionally lower than 3.5 mEq/L during the whole observation period. However, it would spontaneously return to the normal level during the next follow up even when the subject continued to take gossypol. None of them complained of hypokalemic myoasthenia. Figure 3 shows the profile of blood K+ during the whole year in the 10 mg group and control group. Lower serum K+ was seen in the summer season both in the control and treated groups. The K+ values in control subjects in August of 1987 and 1988 was 3.900.25 and 3.900.22 mEq/L respectively, while in treated group they were 3.860.30 and 3.750.28 mEq/L respectively. There were no significant differences between the data of the two groups.

Table 6. Subjects in whom serum potassium levels appeared below 3.5 mEq/L in 12.5 mg group.

Name

Serum  K+(mEq/L)

Admission

Date of sample collection

89.6

90.1

89.12

90.3

90.4

90.5

90.6

90.7

90.8

90.10

Li

5.6

 

4.6

4.2

4.1

4.2

3.7

3.1

3.9

4.3

Meng

4.6

 

4.4

4.3

4.3

4.0

3.6

3.1

4.0

4.3

Hua

4.1

 

4.2

4.0

 

4.3

 

3.2

3.8

4.2

Da

3.7

 

4.3

3.9

 

4.3

3.5

3.1

3.5

4.2

Wang

5.2

 

 

4.5

4.3

4.2

 

3.4

3.7

4.7

Qin

 

4.4

 

4.2

4.0

4.1

3.5

3.4

3.9

4.3

Shen

 

4.2

 

3.7

3.9

3.7

3.2

 

3.4

4.1

Figure 3. The profile of blood  potassium during a year in 10 mg group and control.

4 Discussion

Results of the present study indicated that the low dose gossypol regimen (10 or 12.5 mg) could induce infertility in the majority of subjects. The requirement for a longer loading phase, however, was the principal disadvantage of this regimen. No demonstrable alterations were found in the hormone profiles. Our previous study provided evidence that FSH might be the only hormone stepping up significantly at the early stage of the maintenance phase in subjects exhibiting irreversibility and hence, we concluded that  monitoring of serum FSH levels could be used as a diagnostic tool for identifying these kind of subjects during gossypol treatment[4]. In the present low dose trial, normal FSH levels during medication might indicate that there would not be much risk for the development of irreversibility.

Hypokalemic myoasthenia is a major concern of gossypol treatment[2].  It was not observed in the present low dose regimen. Though low K+ concentration occasionally occurred in some in the 12.5 mg group, those low values were found in summer seasons and would return to normal value even when the subjects continued to take gossypol. Lower K was also observed in the controls in summer seasons. Obviously, Chinese living in Shanghai showed the lowest serum potassium in summer when compare to the levels in other seasons. This data as well as the data published previously suggests that people living in Shanghai, China may be predisposed to hypokalemia by a combination of factors which include territorial difference[5], living conditions[6], seasons etc. Results presented in this paper indicated that gossypol at a low dose level of 10 mg or 12.5 mg could induce infertility in men without producing hypokalemia and irreversibility.

References

[1] National Coordinating Group on Male Antifertility Agents. Gossypol -- a new antifertility agent for males.  Chin Med J (New series) 1978; 58, 455-60.
[2] National Coordinating Team on the clinical study of gossypol as Male Antifertility Drug. The clinical study of gossypol in 8806 men. Reprod Contraception (in Chinese) 1985; 5 (4), 5-11.
[3] Segal SJ, editor. Gossypol: A potential contraceptive for men. Plenum, New York; 1985. p 271-4.
[4] Gu ZP, Wan YX, Sang GW, Wang WC, Chen ZX, Zhao XJ, et al. Relationship between hormone profiles and the testoration of spermatogenesis in men treated with gossypol. Int J Androl 1990; 13: 253.
[5] Reidenberg MM, Gu ZP, Lorenzo B, Coutinho E, Athayde C, Frick J, et al.  Difference in serum potassium concentration in normal men in different geographic locations.  J Clin Chem 1993; 39: 72-5.
[6] Gu ZP, Reidenberg MM, Segal S. Serum potassium value in normal man in Shanghai vs those in men from Shanghai living abroad. Clin Chem 1994; 10: 340.
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Correspondence to: Prof. Zhi-Ping GU, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 294 Taiyuan Road, Shanghai 200031, China.
Tel: +86-21-6431 1833 Ext 310    Fax: +86-21-6437 0269
e-mail: zpgu@mail.shcnc.ac.cn
Received 2000-08-22     Accepted 2000-11-08